The non-heteroatom-substituted manganese alkynyl carbene complexes (eta5-MeC5H4)(CO)2Mn=C(R)C[tri... more The non-heteroatom-substituted manganese alkynyl carbene complexes (eta5-MeC5H4)(CO)2Mn=C(R)C[triple bond]CR'(3; 3a: R = R'= Ph, 3b: R = Ph, R'= Tol, 3c: R = Tol, R'= Ph) have been synthesised in high yields upon treatment of the corresponding carbyne complexes [eta5-MeC5H4)(CO)2Mn[triple bond]CR][BPh4]([2][BPh4]) with the appropriate alkynyllithium reagents LiC[triple bond]CR' (R'= Ph, Tol). The use of tetraphenylborate as counter anion associated with the cationic carbyne complexes has been decisive. The X-ray structures of (eta5-MeC5H4)(CO)2Mn=C(Tol)C[triple bond]CPh (3c), and its precursor [(eta5-MeC5H4)(CO)2Mn=CTol][BPh4]([2b](BPh4]) are reported. The reactivity of complexes toward phosphines has been investigated. In the presence of PPh3, complexes act as a Michael acceptor to afford the zwitterionic sigma-allenylphosphonium complexes (eta5-MeC5H4)(CO)2MnC(R)=C=C(PPh3)R' (5) resulting from nucleophilic attack by the phosphine on the remote alkynyl carbon atom. Complexes 5 exhibit a dynamic process in solution, which has been rationalized in terms of a fast [NMR time-scale] rotation of the allene substituents around the allene axis; metrical features within the X-ray structure of (eta5-MeC5H4)(CO)2MnC(Ph)=C=C(PPh3)Tol (5b) support the proposal. In the presence of PMe3, complexes undergo a nucleophilic attack on the carbene carbon atom to give zwitterionic sigma-propargylphosphonium complexes (eta5-MeC5H4)(CO)2MnC(R)(PMe3)C[triple bond]CR' (6). Complexes 6 readily isomerise in solution to give the sigma-allenylphosphonium complexes (eta5-MeC5H4)(CO)2MnC(R')=C=C(PMe3)R (7) through a 1,3 shift of the [(eta5-MeC5H4)(CO)2Mn] fragment. The nucleophilic attack of PPh2Me on 3 is not selective and leads to a mixture of the sigma-propargylphosphonium complexes (eta5-MeC5H4)(CO)2MnC(R)(PPh(2)Me)C[triple bond]CR' (9) and the sigma-allenylphosphonium complexes (eta5-MeC5H4)(CO)2MnC(R)=C=C(PPh(2)Me)R' (10). Like complexes 6, complexes 9 readily isomerize to give the sigma-allenylphosphonium complexes (eta5-MeC5H4)(CO)2MnC(R')=C=C(PPh2Me)R'). Upon gentle heating, complexes 7, and mixtures of 10 and 10' cyclise to give the sigma-dihydrophospholium complexes (eta5-MeC5H4)(CO)2MnC=C(R')PMe2CH2CH(R)(8), and mixtures of complexes (eta5-MeC5H4)(CO)2MnC=C(Ph)PPh2CH2CH(Tol)(11) and (eta5-MeC5H4)(CO)2MnC=C(Tol)PMe2CH2CH(Ph)(11'), respectively. The reactions of complexes 3 with secondary phosphines HPR(1)(2)(R1= Ph, Cy) give a mixture of the eta2-allene complexes (eta5-MeC5H4)(CO)2Mn[eta2-{R(1)(2)PC(R)=C=C(R')H}](12), and the regioisomeric eta4-vinylketene complexes [eta5-MeC5H4)(CO)Mn[eta4-{R(1)(2)PC(R)=CHC(R')=C=O}](13) and (eta5-MeC5H4)(CO)Mn[eta4-{R(1)(2)PC(R')=CHC(R)=C=O}](13'). The solid-state structure of (eta5-MeC5H4)(CO)2Mn[eta2-{Ph2PC(Ph)=C=C(Tol)H}](12b) and (eta5-MeC5H4)(CO)Mn[eta4-{Cy2PC(Ph)=CHC(Ph)=C=O}](13d) are reported. Finally, a mechanism that may account for the formation of the species 12, 13, and 13' is proposed.
... Yannick Ortin, Yannick Coppel, Noël Lugan*, René Mathieu and Michael J. McGlinchey‡. Laborato... more ... Yannick Ortin, Yannick Coppel, Noël Lugan*, René Mathieu and Michael J. McGlinchey‡. Laboratoire de Chimie de Coordination du CNRS, 205 route de Narbonne, 31077 ... On sabbatical leave from: Department of Chemistry, McMaster University, Hamilton, Ont., Canada L8S ...
ABSTRACT The non-heteroatom-substituted alkynyl carbene Cp′(CO) 2MnC(Tol)CCPh ( 1, Cp′ ≡ (η 5-MeC... more ABSTRACT The non-heteroatom-substituted alkynyl carbene Cp′(CO) 2MnC(Tol)CCPh ( 1, Cp′ ≡ (η 5-MeC 5H 4)) is first shown to react at low temperature with lithium diorganophosphide LiPR 2 (R = Ph, Cy) to form an anionic species. Subsequent treatment with CF 3SO 3H affords the η 4-vinylketene complex Cp′(CO) 2Mn[η 4-{R 2P(Ph)CCHC(Tol)CO}] ( 2; 2a: R = Ph (70% yield), 2b: R = Cy (55% yield)) as the major compound, along with trace amounts of the η 2-allene complex syn-Cp′(CO) 2Mn[η 2-{Ph 2P(Tol)CCC(Ph)H}] ( syn- 3a) for R = Ph, or along with the η 2-allene complex Cp′(CO) 2Mn[η 2-{H(Tol)CCC(Ph)PCy 2}] ( 4b, 26% yield, 1:2 mixture of syn/ anti isomers) for R = Cy. On the other hand, subsequent treatment with NH 4Cl aq affords only η 2-allene complexes, obtained either as a ca. 1:9 mixture of syn- 3a and Cp′(CO) 2Mn[η 2-{H(Tol)CCC(Ph)PPh 2}] ( 4a) (75% yield) for R = Ph or as a 1:2 mixture of syn- and anti- 4b for R = Cy (74% yield). Combined NMR and single-crystal X-ray diffraction studies (for 2a, anti- 4b, and syn- 4b) revealed that both type 2 and type 4 species result from a nucleophilic attack of the diorganophosphide onto the remote alkynyl carbon atom in 1 (C γ), whereas type 3 species results from a nucleophilic attack of the carbene carbon atom (C α). Complexes 3a and 4a, b are prone to undergo a thermal rearrangement to give the η 1-phosphinoallene complexes Cp′(CO) 2Mn[η 1-{Ph 2P(Tol)CCC(Ph)H}] ( 5a) and Cp′(CO) 2Mn[η 1-{R 2P(Ph)CCC(Tol)H}] ( 6; 6a: R = Ph, 6b: R = Cy), respectively. Reaction of 1 with p-toluenethiol in the presence of NEt 3 (20%) affords a 1.8:1 mixture of Cp′(CO) 2Mn[η 2-{TolS(Tol)CCC(Ph)H}] ( syn- 11), resulting from a nucleophilic attack at C α in 1, and Cp′(CO) 2Mn[η 2-{H(Tol)CCC(Ph)STol}] ( 12), resulting from a nucleophilic attack at C γ, whereas treatment of 1 with lithium p-toluenethiolate at –80 °C followed by protonation with NH 4Cl aq gave the same syn- 11 and 12 complexes now in a 1:2.3 ratio. Finally, 1 was found to react with cyclohexanone lithium enolate to afford, upon protonation, the η 2-allene complex Cp′(CO) 2Mn[η 2-{H(Tol)CCC(Ph)CH(CH 2) 4C(O)}] ( syn- 13), resulting from a nucleophilic attack at C γ in 1. The solid-state structures of syn- 11 and syn- 13 are also reported.
Non-heme iron(II) oxidases (NHIOs) catalyse a diverse array of oxidative chemistry in Nature. As ... more Non-heme iron(II) oxidases (NHIOs) catalyse a diverse array of oxidative chemistry in Nature. As part of ongoing efforts to realize biomimetic, iron-mediated C-H activation, we report the synthesis of a new 'three-amine-one-carboxylate' ligand designed to complex with iron(II) and mimic the NHIO active site. The tetradentate ligand has been prepared as a single enantiomer in nine synthetic steps from N-Cbz-L-alanine, pyridine-2,6-dimethanol and diphenylamine, using Seebach oxazolidinone chemistry to control the stereochemistry. X-Ray crystal structures are reported for two important intermediates, along with variable temperature NMR experiments to probe the hindered interconversion of conformational isomers of several key intermediates, 2,6-disubstituted pyridine derivatives. The target ligand and an N-Cbz-protected precursor were each then complexed with iron(II) and tested for their ability to promote alkene dihydroxylation, using hydrogen peroxide as the oxidant.
The non-heteroatom-substituted manganese alkynyl carbene complexes (eta5-MeC5H4)(CO)2Mn=C(R)C[tri... more The non-heteroatom-substituted manganese alkynyl carbene complexes (eta5-MeC5H4)(CO)2Mn=C(R)C[triple bond]CR'(3; 3a: R = R'= Ph, 3b: R = Ph, R'= Tol, 3c: R = Tol, R'= Ph) have been synthesised in high yields upon treatment of the corresponding carbyne complexes [eta5-MeC5H4)(CO)2Mn[triple bond]CR][BPh4]([2][BPh4]) with the appropriate alkynyllithium reagents LiC[triple bond]CR' (R'= Ph, Tol). The use of tetraphenylborate as counter anion associated with the cationic carbyne complexes has been decisive. The X-ray structures of (eta5-MeC5H4)(CO)2Mn=C(Tol)C[triple bond]CPh (3c), and its precursor [(eta5-MeC5H4)(CO)2Mn=CTol][BPh4]([2b](BPh4]) are reported. The reactivity of complexes toward phosphines has been investigated. In the presence of PPh3, complexes act as a Michael acceptor to afford the zwitterionic sigma-allenylphosphonium complexes (eta5-MeC5H4)(CO)2MnC(R)=C=C(PPh3)R' (5) resulting from nucleophilic attack by the phosphine on the remote alkynyl carbon atom. Complexes 5 exhibit a dynamic process in solution, which has been rationalized in terms of a fast [NMR time-scale] rotation of the allene substituents around the allene axis; metrical features within the X-ray structure of (eta5-MeC5H4)(CO)2MnC(Ph)=C=C(PPh3)Tol (5b) support the proposal. In the presence of PMe3, complexes undergo a nucleophilic attack on the carbene carbon atom to give zwitterionic sigma-propargylphosphonium complexes (eta5-MeC5H4)(CO)2MnC(R)(PMe3)C[triple bond]CR' (6). Complexes 6 readily isomerise in solution to give the sigma-allenylphosphonium complexes (eta5-MeC5H4)(CO)2MnC(R')=C=C(PMe3)R (7) through a 1,3 shift of the [(eta5-MeC5H4)(CO)2Mn] fragment. The nucleophilic attack of PPh2Me on 3 is not selective and leads to a mixture of the sigma-propargylphosphonium complexes (eta5-MeC5H4)(CO)2MnC(R)(PPh(2)Me)C[triple bond]CR' (9) and the sigma-allenylphosphonium complexes (eta5-MeC5H4)(CO)2MnC(R)=C=C(PPh(2)Me)R' (10). Like complexes 6, complexes 9 readily isomerize to give the sigma-allenylphosphonium complexes (eta5-MeC5H4)(CO)2MnC(R')=C=C(PPh2Me)R'). Upon gentle heating, complexes 7, and mixtures of 10 and 10' cyclise to give the sigma-dihydrophospholium complexes (eta5-MeC5H4)(CO)2MnC=C(R')PMe2CH2CH(R)(8), and mixtures of complexes (eta5-MeC5H4)(CO)2MnC=C(Ph)PPh2CH2CH(Tol)(11) and (eta5-MeC5H4)(CO)2MnC=C(Tol)PMe2CH2CH(Ph)(11'), respectively. The reactions of complexes 3 with secondary phosphines HPR(1)(2)(R1= Ph, Cy) give a mixture of the eta2-allene complexes (eta5-MeC5H4)(CO)2Mn[eta2-{R(1)(2)PC(R)=C=C(R')H}](12), and the regioisomeric eta4-vinylketene complexes [eta5-MeC5H4)(CO)Mn[eta4-{R(1)(2)PC(R)=CHC(R')=C=O}](13) and (eta5-MeC5H4)(CO)Mn[eta4-{R(1)(2)PC(R')=CHC(R)=C=O}](13'). The solid-state structure of (eta5-MeC5H4)(CO)2Mn[eta2-{Ph2PC(Ph)=C=C(Tol)H}](12b) and (eta5-MeC5H4)(CO)Mn[eta4-{Cy2PC(Ph)=CHC(Ph)=C=O}](13d) are reported. Finally, a mechanism that may account for the formation of the species 12, 13, and 13' is proposed.
Upon controlled potential electrolysis (-1.30 V vs. SCE), the alkynylcarbene complexes MeCp(CO)2M... more Upon controlled potential electrolysis (-1.30 V vs. SCE), the alkynylcarbene complexes MeCp(CO)2Mn=C(R)C [triple bond]CR' are seen to undergo an electrocatalytic dimerisation by coupling of the remote alkynyl carbon atoms to afford the ene-diyne dimanganese complexes [MeCp(CO)2Mn]2[eta 4-(E)-RC [triple bond] C(R')C=C(R')C [triple bond] CR].
Journal of the American Chemical Society, Nov 1, 2010
The syntheses, X-ray crystal structures, and molecular dynamics of 9-ferrocenylanthracene, 3, 9,1... more The syntheses, X-ray crystal structures, and molecular dynamics of 9-ferrocenylanthracene, 3, 9,10-diferrocenylanthracene, 4, 9-ferrocenyltriptycene, 7, and 9,10-diferrocenyltriptycene, 8, are reported. At 193 K, 3 exhibits C(s) symmetry via oscillation of the ferrocenyl only about the anthracene plane; at higher temperatures, complete rotation about the C(9)-ferrocenyl linkage becomes evident with a barrier of 10.6 kcal mol(-1). At 193 K, the ferrocenyls in 4 give rise to syn (C(2v)) and anti (C(2h)) rotamers that also interconvert at room temperature. In the corresponding triptycyl systems, 7 and 8, these rotational barriers increase to 17 kcal mol(-1); 9,10-diferrocenyltriptycene exists as slowly interconverting meso and racemic rotamers, in which the ferrocenyl moieties are, respectively, eclipsed (C(2v)) or staggered (C2). 2D-EXSY NMR data recorded with different mixing times indicate clearly that these interconversions proceed in a stepwise manner, for example, rac→meso→rac, thus behaving as a set of molecular dials.
In [eta(6)-2-(9-triptycyl)-indene]tricarbonylchromium (2a), the indenyl-chromium moiety is linked... more In [eta(6)-2-(9-triptycyl)-indene]tricarbonylchromium (2a), the indenyl-chromium moiety is linked directly to the axis of the three-bladed triptycene paddlewheel. However, the molecular structure of 2a reveals that there is no steric interaction between these components, and the paddlewheel is free to rotate. Accordingly, its NMR spectrum indicates the full equivalence of the blades of the triptycene. Deprotonation of the indene induces a haptotropic shift of the organometallic fragment from the six-membered to the five-membered ring of the indene and, in the sodium [eta(5)-2-(9-triptycyl)-indenyl]tricarbonylchromium salt (3a), so formed, rotation of the three-bladed molecular paddlewheel is now blocked by the bulky tripod. NMR data for 3a, and also for the isostructural eta(5)-Mn(CO)(3) and eta(5)-Re(CO)(3) complexes, 3b and 3c, respectively, reveal a 2:1 splitting of the blades of the triptycyl moiety, thus breaking its original threefold symmetry. The X-ray crystal structures of the chromium complex, 2a, and of the manganese and rhenium complexes, 3b and 3c, provide pictures of the system in both its "ON" and "OFF" states, whereby the M(CO)(3) tripod has moved about 2 A towards the triptycene, thus blocking its rotation. Comparison of the rotational barriers in 2-(9-triptycyl)indene (1) and its complexes 2 and 3, suggests that rotation of the paddlewheel can be slowed by a factor of approximately 10(8).
A topological analysis of the electron density in the ketene complex (eta(5)-MeC(5)H(4))(CO)(2)Mn... more A topological analysis of the electron density in the ketene complex (eta(5)-MeC(5)H(4))(CO)(2)Mn[eta(2)-O=C=C((mu-eta(2)-CCPh)Co(2)(CO)(6))Ph] indicates a predisposition for the carbene component of the ketene ligand to bind the neighboring C atom of the adjacent CO ligand.
Dyad (g 4 -C 4 Ph 4 )Co(g 5 -C 5 H 4 CH@CHFc) (2) containing isolobal iron and cobalt metallocene... more Dyad (g 4 -C 4 Ph 4 )Co(g 5 -C 5 H 4 CH@CHFc) (2) containing isolobal iron and cobalt metallocene fragments has been prepared and its structure and spectroelectrochemical properties examined. Both the E and Z isomers have been characterised and their X-ray structures determined. B3LYP/6-31G * calculations for 2 show that the HOMO has more electron density on the Fc than on the CbCo(g 5 -C 5 H 4 ) fragment whereas the reverse is the case for the LUMO. Both isomers undergo chemically reversible oxidations at the Fc (0.49 and 0.53 V) and CbCo redox centres (0.96 V) but the [2Z] 2+ cation isomerises to [2E] 2+ concomitant with the second oxidation process. A NIR band at 1290 nm for the [2E] + cation is assigned to a CbCo(g 5 -C 5 H 4 ) ! Fc + charge-transfer.
The tetraethyl- and tetramethyl-cyclobutadiene complexes [(η4-C4R4)Co(η5-C5H4CHO)] R = Et, 5, R =... more The tetraethyl- and tetramethyl-cyclobutadiene complexes [(η4-C4R4)Co(η5-C5H4CHO)] R = Et, 5, R = Me, 7, and [(η4-C4R4)Co(η5-C5H4CO2Me)] R = Et, 6, R = Me, 8, are conveniently prepared by photolysis of the corresponding isocobaltocenium cations [(η4-C4R4)Co(η6-C6H5Me)]+ in acetonitrile, and subsequent treatment with Na[C5H4CHO] or Na[C5H4CO2Me]. The aldehydes 5 and 7 undergo Wittig and Knoevenagel reactions with [FcCH2PPh3]I and CH2(CN)2, to form [(η4-C4R4)Co(η5-C5H4CH=CHFc)] and [(η4-C4R4)Co(η5-C5H4CH=C(CN)2], 11 and 15, respectively. The Horner-Wittig reaction of [(η4-C4R4)Co(η5-C5H4CH2P([(Formylcyclopentadienyl)(tetraalkylcyclobutadiene)cobalt] complexes, 5 and 7, undergo a range of Wittig and aldol reactions to incorporate ferrocenyl and other metal sandwich moieties. The unexpected formation of [(η5-cyclopentadienyl)(η4-3,4,5,6-tetraethyl-α-pyrone)cobalt], 18, was also observed, and a mechanistic rationale is proposed.
Journal of the American Chemical Society, Jan 19, 2014
Rates and energy barriers of degenerate halide substitution on tetracoordinate halophosphonium ca... more Rates and energy barriers of degenerate halide substitution on tetracoordinate halophosphonium cations have been measured by NMR techniques (VT and EXSY) using a novel experimental design whereby a chiral substituent ((s)Bu) lifts the degeneracy of the resultant salts. Concomitantly, a viable computational approach to the system was developed to gain mechanistic insights into the structure and relative stabilities of the species involved. Both approaches strongly suggest a two-step mechanism of formation of a pentacoordinate dihalophosphorane via backside attack followed by dissociation, resulting in inversion of configuration at phosphorus. The experimentally determined barriers range from <9 kcal mol(-1) to nearly 20 kcal mol(-1), ruling out a mechansm via Berry pseudorotation involving equatorial halides. In all cases studied, epimerization of chlorophosphonium chlorides has a lower energy barrier (by 2 kcal mol(-1)) than the analogous bromo salts. Calculations determined that...
The indenyltriptycenes, and , where the 3- or 2-indenyl, respectively, is attached at the 9-posit... more The indenyltriptycenes, and , where the 3- or 2-indenyl, respectively, is attached at the 9-position of the triptycene, are attractive prototypes of molecular gearing systems that can also incorporate a brake. These molecules have been prepared from their respective indenylanthracenes, and , by the [4 + 2] cycloaddition of benzyne to the anthracene fragment, and the rotational barriers about the indenyl-triptycenyl single bonds in (12 kcal mol(-1)) and (<9 kcal mol(-1)) have been measured. The precursor anthracenes, and , were prepared by using palladium-catalysed coupling reactions. Unexpectedly, the Heck-type reaction of 9-bromoanthracene, , with indene leads to the formation of 3-indenylanthracene ; moreover, this process is accompanied by a novel palladium-catalysed carbocyclisation reaction leading to the indenophenanthrylene . The addition of benzyne to 9-(3-indenyl)anthracene, , yields the corresponding indenyltriptycene, , and, surprisingly, the anthracenyl methano-bridge...
Eleven new mononuclear manganese(III) complexes prepared from two hexadentate ligands, L1 and L2,... more Eleven new mononuclear manganese(III) complexes prepared from two hexadentate ligands, L1 and L2, with different degrees of steric bulk in the substituents are reported. L1 and L2 are Schiff bases resulting from condensation of N,N&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;-bis(3-aminopropyl)ethylenediamine with 3-methoxy-2-hydroxybenzaldehyde and 3-ethoxy-2-hydroxybenzaldehyde respectively, and are members of a ligand series we have abbreviated as R-Sal2323 to indicate the 323 alkyl connectivity in the starting tetraamine and the substitution (R) on the phenolate ring. L1 hosts a methoxy substituent on both phenolate rings, while L2 bears a larger ethoxy group in the same position. Structural and magnetic properties are reported in comparison with those of a previously reported analogue with L1, namely, [MnL1]NO3, (1e). The BPh4(-) and PF6(-) complexes [MnL1]BPh4, (1a), [MnL2]BPh4, (2a), [MnL1]PF6, (1b&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;), and [MnL2]PF6, (2b), with both ligands L1 and L2, remain high-spin (HS) over the measured temperature range. However, the monohydrate of (1b&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;) [MnL1]PF6·H2O, (1b), shows gradual spin-crossover (SCO), as do the ClO4(-), BF4(-), and NO3(-) complexes [MnL1]ClO4·H2O, (1c), [MnL2]ClO4, (2c), [MnL1]BF4·H2O, (1d), [MnL2]BF4·0.4H2O, (2d), [MnL1]NO3, (1e), and [MnL2]NO3·EtOH, (2e). The three complexes formed with ethoxy-substituted ligand L2 all show a higher T1/2 than the analogous complexes with methoxy-substituted ligand L1. Analysis of distortion parameters shows that complexes formed with the bulkier ligand L2 exhibit more deformation from perfect octahedral geometry, leading to a higher T1/2 in the SCO examples, where T1/2 is the temperature where the spin state is 50% high spin and 50% low spin. Spin state assignment in the solid state is shown to be solvate-dependent for complexes (1b) and (2e), and room temperature UV-visible and NMR spectra indicate a solution-state spin assignment intermediate between fully HS and fully low spin in 10 complexes, (1a)-(1e) and (2a)-(2e).
Chemical communications (Cambridge, England), Jan 21, 2015
P-Hydroxytetraorganophosphorane, the long-postulated intermediate in phosphonium salt and ylide h... more P-Hydroxytetraorganophosphorane, the long-postulated intermediate in phosphonium salt and ylide hydrolysis, has been observed and characterised by low temperature NMR, finally definitively establishing its involvement in these reactions. The results require modification of the previously accepted mechanism for ylide hydrolysis: P-hydroxytetraorganophosphorane is generated directly by 4-centre reaction of ylide with water.
The non-heteroatom-substituted manganese alkynyl carbene complexes (eta5-MeC5H4)(CO)2Mn=C(R)C[tri... more The non-heteroatom-substituted manganese alkynyl carbene complexes (eta5-MeC5H4)(CO)2Mn=C(R)C[triple bond]CR&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;(3; 3a: R = R&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;= Ph, 3b: R = Ph, R&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;= Tol, 3c: R = Tol, R&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;= Ph) have been synthesised in high yields upon treatment of the corresponding carbyne complexes [eta5-MeC5H4)(CO)2Mn[triple bond]CR][BPh4]([2][BPh4]) with the appropriate alkynyllithium reagents LiC[triple bond]CR&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39; (R&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;= Ph, Tol). The use of tetraphenylborate as counter anion associated with the cationic carbyne complexes has been decisive. The X-ray structures of (eta5-MeC5H4)(CO)2Mn=C(Tol)C[triple bond]CPh (3c), and its precursor [(eta5-MeC5H4)(CO)2Mn=CTol][BPh4]([2b](BPh4]) are reported. The reactivity of complexes toward phosphines has been investigated. In the presence of PPh3, complexes act as a Michael acceptor to afford the zwitterionic sigma-allenylphosphonium complexes (eta5-MeC5H4)(CO)2MnC(R)=C=C(PPh3)R&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39; (5) resulting from nucleophilic attack by the phosphine on the remote alkynyl carbon atom. Complexes 5 exhibit a dynamic process in solution, which has been rationalized in terms of a fast [NMR time-scale] rotation of the allene substituents around the allene axis; metrical features within the X-ray structure of (eta5-MeC5H4)(CO)2MnC(Ph)=C=C(PPh3)Tol (5b) support the proposal. In the presence of PMe3, complexes undergo a nucleophilic attack on the carbene carbon atom to give zwitterionic sigma-propargylphosphonium complexes (eta5-MeC5H4)(CO)2MnC(R)(PMe3)C[triple bond]CR&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39; (6). Complexes 6 readily isomerise in solution to give the sigma-allenylphosphonium complexes (eta5-MeC5H4)(CO)2MnC(R&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;)=C=C(PMe3)R (7) through a 1,3 shift of the [(eta5-MeC5H4)(CO)2Mn] fragment. The nucleophilic attack of PPh2Me on 3 is not selective and leads to a mixture of the sigma-propargylphosphonium complexes (eta5-MeC5H4)(CO)2MnC(R)(PPh(2)Me)C[triple bond]CR&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39; (9) and the sigma-allenylphosphonium complexes (eta5-MeC5H4)(CO)2MnC(R)=C=C(PPh(2)Me)R&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39; (10). Like complexes 6, complexes 9 readily isomerize to give the sigma-allenylphosphonium complexes (eta5-MeC5H4)(CO)2MnC(R&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;)=C=C(PPh2Me)R&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;). Upon gentle heating, complexes 7, and mixtures of 10 and 10&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39; cyclise to give the sigma-dihydrophospholium complexes (eta5-MeC5H4)(CO)2MnC=C(R&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;)PMe2CH2CH(R)(8), and mixtures of complexes (eta5-MeC5H4)(CO)2MnC=C(Ph)PPh2CH2CH(Tol)(11) and (eta5-MeC5H4)(CO)2MnC=C(Tol)PMe2CH2CH(Ph)(11&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;), respectively. The reactions of complexes 3 with secondary phosphines HPR(1)(2)(R1= Ph, Cy) give a mixture of the eta2-allene complexes (eta5-MeC5H4)(CO)2Mn[eta2-{R(1)(2)PC(R)=C=C(R&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;)H}](12), and the regioisomeric eta4-vinylketene complexes [eta5-MeC5H4)(CO)Mn[eta4-{R(1)(2)PC(R)=CHC(R&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;)=C=O}](13) and (eta5-MeC5H4)(CO)Mn[eta4-{R(1)(2)PC(R&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;)=CHC(R)=C=O}](13&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;). The solid-state structure of (eta5-MeC5H4)(CO)2Mn[eta2-{Ph2PC(Ph)=C=C(Tol)H}](12b) and (eta5-MeC5H4)(CO)Mn[eta4-{Cy2PC(Ph)=CHC(Ph)=C=O}](13d) are reported. Finally, a mechanism that may account for the formation of the species 12, 13, and 13&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39; is proposed.
... Yannick Ortin, Yannick Coppel, Noël Lugan*, René Mathieu and Michael J. McGlinchey‡. Laborato... more ... Yannick Ortin, Yannick Coppel, Noël Lugan*, René Mathieu and Michael J. McGlinchey‡. Laboratoire de Chimie de Coordination du CNRS, 205 route de Narbonne, 31077 ... On sabbatical leave from: Department of Chemistry, McMaster University, Hamilton, Ont., Canada L8S ...
ABSTRACT The non-heteroatom-substituted alkynyl carbene Cp′(CO) 2MnC(Tol)CCPh ( 1, Cp′ ≡ (η 5-MeC... more ABSTRACT The non-heteroatom-substituted alkynyl carbene Cp′(CO) 2MnC(Tol)CCPh ( 1, Cp′ ≡ (η 5-MeC 5H 4)) is first shown to react at low temperature with lithium diorganophosphide LiPR 2 (R = Ph, Cy) to form an anionic species. Subsequent treatment with CF 3SO 3H affords the η 4-vinylketene complex Cp′(CO) 2Mn[η 4-{R 2P(Ph)CCHC(Tol)CO}] ( 2; 2a: R = Ph (70% yield), 2b: R = Cy (55% yield)) as the major compound, along with trace amounts of the η 2-allene complex syn-Cp′(CO) 2Mn[η 2-{Ph 2P(Tol)CCC(Ph)H}] ( syn- 3a) for R = Ph, or along with the η 2-allene complex Cp′(CO) 2Mn[η 2-{H(Tol)CCC(Ph)PCy 2}] ( 4b, 26% yield, 1:2 mixture of syn/ anti isomers) for R = Cy. On the other hand, subsequent treatment with NH 4Cl aq affords only η 2-allene complexes, obtained either as a ca. 1:9 mixture of syn- 3a and Cp′(CO) 2Mn[η 2-{H(Tol)CCC(Ph)PPh 2}] ( 4a) (75% yield) for R = Ph or as a 1:2 mixture of syn- and anti- 4b for R = Cy (74% yield). Combined NMR and single-crystal X-ray diffraction studies (for 2a, anti- 4b, and syn- 4b) revealed that both type 2 and type 4 species result from a nucleophilic attack of the diorganophosphide onto the remote alkynyl carbon atom in 1 (C γ), whereas type 3 species results from a nucleophilic attack of the carbene carbon atom (C α). Complexes 3a and 4a, b are prone to undergo a thermal rearrangement to give the η 1-phosphinoallene complexes Cp′(CO) 2Mn[η 1-{Ph 2P(Tol)CCC(Ph)H}] ( 5a) and Cp′(CO) 2Mn[η 1-{R 2P(Ph)CCC(Tol)H}] ( 6; 6a: R = Ph, 6b: R = Cy), respectively. Reaction of 1 with p-toluenethiol in the presence of NEt 3 (20%) affords a 1.8:1 mixture of Cp′(CO) 2Mn[η 2-{TolS(Tol)CCC(Ph)H}] ( syn- 11), resulting from a nucleophilic attack at C α in 1, and Cp′(CO) 2Mn[η 2-{H(Tol)CCC(Ph)STol}] ( 12), resulting from a nucleophilic attack at C γ, whereas treatment of 1 with lithium p-toluenethiolate at –80 °C followed by protonation with NH 4Cl aq gave the same syn- 11 and 12 complexes now in a 1:2.3 ratio. Finally, 1 was found to react with cyclohexanone lithium enolate to afford, upon protonation, the η 2-allene complex Cp′(CO) 2Mn[η 2-{H(Tol)CCC(Ph)CH(CH 2) 4C(O)}] ( syn- 13), resulting from a nucleophilic attack at C γ in 1. The solid-state structures of syn- 11 and syn- 13 are also reported.
Non-heme iron(II) oxidases (NHIOs) catalyse a diverse array of oxidative chemistry in Nature. As ... more Non-heme iron(II) oxidases (NHIOs) catalyse a diverse array of oxidative chemistry in Nature. As part of ongoing efforts to realize biomimetic, iron-mediated C-H activation, we report the synthesis of a new &amp;amp;amp;amp;amp;amp;#39;three-amine-one-carboxylate&amp;amp;amp;amp;amp;amp;#39; ligand designed to complex with iron(II) and mimic the NHIO active site. The tetradentate ligand has been prepared as a single enantiomer in nine synthetic steps from N-Cbz-L-alanine, pyridine-2,6-dimethanol and diphenylamine, using Seebach oxazolidinone chemistry to control the stereochemistry. X-Ray crystal structures are reported for two important intermediates, along with variable temperature NMR experiments to probe the hindered interconversion of conformational isomers of several key intermediates, 2,6-disubstituted pyridine derivatives. The target ligand and an N-Cbz-protected precursor were each then complexed with iron(II) and tested for their ability to promote alkene dihydroxylation, using hydrogen peroxide as the oxidant.
The non-heteroatom-substituted manganese alkynyl carbene complexes (eta5-MeC5H4)(CO)2Mn=C(R)C[tri... more The non-heteroatom-substituted manganese alkynyl carbene complexes (eta5-MeC5H4)(CO)2Mn=C(R)C[triple bond]CR&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;(3; 3a: R = R&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;= Ph, 3b: R = Ph, R&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;= Tol, 3c: R = Tol, R&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;= Ph) have been synthesised in high yields upon treatment of the corresponding carbyne complexes [eta5-MeC5H4)(CO)2Mn[triple bond]CR][BPh4]([2][BPh4]) with the appropriate alkynyllithium reagents LiC[triple bond]CR&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39; (R&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;= Ph, Tol). The use of tetraphenylborate as counter anion associated with the cationic carbyne complexes has been decisive. The X-ray structures of (eta5-MeC5H4)(CO)2Mn=C(Tol)C[triple bond]CPh (3c), and its precursor [(eta5-MeC5H4)(CO)2Mn=CTol][BPh4]([2b](BPh4]) are reported. The reactivity of complexes toward phosphines has been investigated. In the presence of PPh3, complexes act as a Michael acceptor to afford the zwitterionic sigma-allenylphosphonium complexes (eta5-MeC5H4)(CO)2MnC(R)=C=C(PPh3)R&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39; (5) resulting from nucleophilic attack by the phosphine on the remote alkynyl carbon atom. Complexes 5 exhibit a dynamic process in solution, which has been rationalized in terms of a fast [NMR time-scale] rotation of the allene substituents around the allene axis; metrical features within the X-ray structure of (eta5-MeC5H4)(CO)2MnC(Ph)=C=C(PPh3)Tol (5b) support the proposal. In the presence of PMe3, complexes undergo a nucleophilic attack on the carbene carbon atom to give zwitterionic sigma-propargylphosphonium complexes (eta5-MeC5H4)(CO)2MnC(R)(PMe3)C[triple bond]CR&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39; (6). Complexes 6 readily isomerise in solution to give the sigma-allenylphosphonium complexes (eta5-MeC5H4)(CO)2MnC(R&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;)=C=C(PMe3)R (7) through a 1,3 shift of the [(eta5-MeC5H4)(CO)2Mn] fragment. The nucleophilic attack of PPh2Me on 3 is not selective and leads to a mixture of the sigma-propargylphosphonium complexes (eta5-MeC5H4)(CO)2MnC(R)(PPh(2)Me)C[triple bond]CR&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39; (9) and the sigma-allenylphosphonium complexes (eta5-MeC5H4)(CO)2MnC(R)=C=C(PPh(2)Me)R&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39; (10). Like complexes 6, complexes 9 readily isomerize to give the sigma-allenylphosphonium complexes (eta5-MeC5H4)(CO)2MnC(R&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;)=C=C(PPh2Me)R&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;). Upon gentle heating, complexes 7, and mixtures of 10 and 10&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39; cyclise to give the sigma-dihydrophospholium complexes (eta5-MeC5H4)(CO)2MnC=C(R&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;)PMe2CH2CH(R)(8), and mixtures of complexes (eta5-MeC5H4)(CO)2MnC=C(Ph)PPh2CH2CH(Tol)(11) and (eta5-MeC5H4)(CO)2MnC=C(Tol)PMe2CH2CH(Ph)(11&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;), respectively. The reactions of complexes 3 with secondary phosphines HPR(1)(2)(R1= Ph, Cy) give a mixture of the eta2-allene complexes (eta5-MeC5H4)(CO)2Mn[eta2-{R(1)(2)PC(R)=C=C(R&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;)H}](12), and the regioisomeric eta4-vinylketene complexes [eta5-MeC5H4)(CO)Mn[eta4-{R(1)(2)PC(R)=CHC(R&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;)=C=O}](13) and (eta5-MeC5H4)(CO)Mn[eta4-{R(1)(2)PC(R&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;)=CHC(R)=C=O}](13&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;). The solid-state structure of (eta5-MeC5H4)(CO)2Mn[eta2-{Ph2PC(Ph)=C=C(Tol)H}](12b) and (eta5-MeC5H4)(CO)Mn[eta4-{Cy2PC(Ph)=CHC(Ph)=C=O}](13d) are reported. Finally, a mechanism that may account for the formation of the species 12, 13, and 13&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39; is proposed.
Upon controlled potential electrolysis (-1.30 V vs. SCE), the alkynylcarbene complexes MeCp(CO)2M... more Upon controlled potential electrolysis (-1.30 V vs. SCE), the alkynylcarbene complexes MeCp(CO)2Mn=C(R)C [triple bond]CR&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39; are seen to undergo an electrocatalytic dimerisation by coupling of the remote alkynyl carbon atoms to afford the ene-diyne dimanganese complexes [MeCp(CO)2Mn]2[eta 4-(E)-RC [triple bond] C(R&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;)C=C(R&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;)C [triple bond] CR].
Journal of the American Chemical Society, Nov 1, 2010
The syntheses, X-ray crystal structures, and molecular dynamics of 9-ferrocenylanthracene, 3, 9,1... more The syntheses, X-ray crystal structures, and molecular dynamics of 9-ferrocenylanthracene, 3, 9,10-diferrocenylanthracene, 4, 9-ferrocenyltriptycene, 7, and 9,10-diferrocenyltriptycene, 8, are reported. At 193 K, 3 exhibits C(s) symmetry via oscillation of the ferrocenyl only about the anthracene plane; at higher temperatures, complete rotation about the C(9)-ferrocenyl linkage becomes evident with a barrier of 10.6 kcal mol(-1). At 193 K, the ferrocenyls in 4 give rise to syn (C(2v)) and anti (C(2h)) rotamers that also interconvert at room temperature. In the corresponding triptycyl systems, 7 and 8, these rotational barriers increase to 17 kcal mol(-1); 9,10-diferrocenyltriptycene exists as slowly interconverting meso and racemic rotamers, in which the ferrocenyl moieties are, respectively, eclipsed (C(2v)) or staggered (C2). 2D-EXSY NMR data recorded with different mixing times indicate clearly that these interconversions proceed in a stepwise manner, for example, rac→meso→rac, thus behaving as a set of molecular dials.
In [eta(6)-2-(9-triptycyl)-indene]tricarbonylchromium (2a), the indenyl-chromium moiety is linked... more In [eta(6)-2-(9-triptycyl)-indene]tricarbonylchromium (2a), the indenyl-chromium moiety is linked directly to the axis of the three-bladed triptycene paddlewheel. However, the molecular structure of 2a reveals that there is no steric interaction between these components, and the paddlewheel is free to rotate. Accordingly, its NMR spectrum indicates the full equivalence of the blades of the triptycene. Deprotonation of the indene induces a haptotropic shift of the organometallic fragment from the six-membered to the five-membered ring of the indene and, in the sodium [eta(5)-2-(9-triptycyl)-indenyl]tricarbonylchromium salt (3a), so formed, rotation of the three-bladed molecular paddlewheel is now blocked by the bulky tripod. NMR data for 3a, and also for the isostructural eta(5)-Mn(CO)(3) and eta(5)-Re(CO)(3) complexes, 3b and 3c, respectively, reveal a 2:1 splitting of the blades of the triptycyl moiety, thus breaking its original threefold symmetry. The X-ray crystal structures of the chromium complex, 2a, and of the manganese and rhenium complexes, 3b and 3c, provide pictures of the system in both its &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot;ON&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot; and &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot;OFF&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot; states, whereby the M(CO)(3) tripod has moved about 2 A towards the triptycene, thus blocking its rotation. Comparison of the rotational barriers in 2-(9-triptycyl)indene (1) and its complexes 2 and 3, suggests that rotation of the paddlewheel can be slowed by a factor of approximately 10(8).
A topological analysis of the electron density in the ketene complex (eta(5)-MeC(5)H(4))(CO)(2)Mn... more A topological analysis of the electron density in the ketene complex (eta(5)-MeC(5)H(4))(CO)(2)Mn[eta(2)-O=C=C((mu-eta(2)-CCPh)Co(2)(CO)(6))Ph] indicates a predisposition for the carbene component of the ketene ligand to bind the neighboring C atom of the adjacent CO ligand.
Dyad (g 4 -C 4 Ph 4 )Co(g 5 -C 5 H 4 CH@CHFc) (2) containing isolobal iron and cobalt metallocene... more Dyad (g 4 -C 4 Ph 4 )Co(g 5 -C 5 H 4 CH@CHFc) (2) containing isolobal iron and cobalt metallocene fragments has been prepared and its structure and spectroelectrochemical properties examined. Both the E and Z isomers have been characterised and their X-ray structures determined. B3LYP/6-31G * calculations for 2 show that the HOMO has more electron density on the Fc than on the CbCo(g 5 -C 5 H 4 ) fragment whereas the reverse is the case for the LUMO. Both isomers undergo chemically reversible oxidations at the Fc (0.49 and 0.53 V) and CbCo redox centres (0.96 V) but the [2Z] 2+ cation isomerises to [2E] 2+ concomitant with the second oxidation process. A NIR band at 1290 nm for the [2E] + cation is assigned to a CbCo(g 5 -C 5 H 4 ) ! Fc + charge-transfer.
The tetraethyl- and tetramethyl-cyclobutadiene complexes [(η4-C4R4)Co(η5-C5H4CHO)] R = Et, 5, R =... more The tetraethyl- and tetramethyl-cyclobutadiene complexes [(η4-C4R4)Co(η5-C5H4CHO)] R = Et, 5, R = Me, 7, and [(η4-C4R4)Co(η5-C5H4CO2Me)] R = Et, 6, R = Me, 8, are conveniently prepared by photolysis of the corresponding isocobaltocenium cations [(η4-C4R4)Co(η6-C6H5Me)]+ in acetonitrile, and subsequent treatment with Na[C5H4CHO] or Na[C5H4CO2Me]. The aldehydes 5 and 7 undergo Wittig and Knoevenagel reactions with [FcCH2PPh3]I and CH2(CN)2, to form [(η4-C4R4)Co(η5-C5H4CH=CHFc)] and [(η4-C4R4)Co(η5-C5H4CH=C(CN)2], 11 and 15, respectively. The Horner-Wittig reaction of [(η4-C4R4)Co(η5-C5H4CH2P([(Formylcyclopentadienyl)(tetraalkylcyclobutadiene)cobalt] complexes, 5 and 7, undergo a range of Wittig and aldol reactions to incorporate ferrocenyl and other metal sandwich moieties. The unexpected formation of [(η5-cyclopentadienyl)(η4-3,4,5,6-tetraethyl-α-pyrone)cobalt], 18, was also observed, and a mechanistic rationale is proposed.
Journal of the American Chemical Society, Jan 19, 2014
Rates and energy barriers of degenerate halide substitution on tetracoordinate halophosphonium ca... more Rates and energy barriers of degenerate halide substitution on tetracoordinate halophosphonium cations have been measured by NMR techniques (VT and EXSY) using a novel experimental design whereby a chiral substituent ((s)Bu) lifts the degeneracy of the resultant salts. Concomitantly, a viable computational approach to the system was developed to gain mechanistic insights into the structure and relative stabilities of the species involved. Both approaches strongly suggest a two-step mechanism of formation of a pentacoordinate dihalophosphorane via backside attack followed by dissociation, resulting in inversion of configuration at phosphorus. The experimentally determined barriers range from <9 kcal mol(-1) to nearly 20 kcal mol(-1), ruling out a mechansm via Berry pseudorotation involving equatorial halides. In all cases studied, epimerization of chlorophosphonium chlorides has a lower energy barrier (by 2 kcal mol(-1)) than the analogous bromo salts. Calculations determined that...
The indenyltriptycenes, and , where the 3- or 2-indenyl, respectively, is attached at the 9-posit... more The indenyltriptycenes, and , where the 3- or 2-indenyl, respectively, is attached at the 9-position of the triptycene, are attractive prototypes of molecular gearing systems that can also incorporate a brake. These molecules have been prepared from their respective indenylanthracenes, and , by the [4 + 2] cycloaddition of benzyne to the anthracene fragment, and the rotational barriers about the indenyl-triptycenyl single bonds in (12 kcal mol(-1)) and (<9 kcal mol(-1)) have been measured. The precursor anthracenes, and , were prepared by using palladium-catalysed coupling reactions. Unexpectedly, the Heck-type reaction of 9-bromoanthracene, , with indene leads to the formation of 3-indenylanthracene ; moreover, this process is accompanied by a novel palladium-catalysed carbocyclisation reaction leading to the indenophenanthrylene . The addition of benzyne to 9-(3-indenyl)anthracene, , yields the corresponding indenyltriptycene, , and, surprisingly, the anthracenyl methano-bridge...
Eleven new mononuclear manganese(III) complexes prepared from two hexadentate ligands, L1 and L2,... more Eleven new mononuclear manganese(III) complexes prepared from two hexadentate ligands, L1 and L2, with different degrees of steric bulk in the substituents are reported. L1 and L2 are Schiff bases resulting from condensation of N,N&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;-bis(3-aminopropyl)ethylenediamine with 3-methoxy-2-hydroxybenzaldehyde and 3-ethoxy-2-hydroxybenzaldehyde respectively, and are members of a ligand series we have abbreviated as R-Sal2323 to indicate the 323 alkyl connectivity in the starting tetraamine and the substitution (R) on the phenolate ring. L1 hosts a methoxy substituent on both phenolate rings, while L2 bears a larger ethoxy group in the same position. Structural and magnetic properties are reported in comparison with those of a previously reported analogue with L1, namely, [MnL1]NO3, (1e). The BPh4(-) and PF6(-) complexes [MnL1]BPh4, (1a), [MnL2]BPh4, (2a), [MnL1]PF6, (1b&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;), and [MnL2]PF6, (2b), with both ligands L1 and L2, remain high-spin (HS) over the measured temperature range. However, the monohydrate of (1b&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;) [MnL1]PF6·H2O, (1b), shows gradual spin-crossover (SCO), as do the ClO4(-), BF4(-), and NO3(-) complexes [MnL1]ClO4·H2O, (1c), [MnL2]ClO4, (2c), [MnL1]BF4·H2O, (1d), [MnL2]BF4·0.4H2O, (2d), [MnL1]NO3, (1e), and [MnL2]NO3·EtOH, (2e). The three complexes formed with ethoxy-substituted ligand L2 all show a higher T1/2 than the analogous complexes with methoxy-substituted ligand L1. Analysis of distortion parameters shows that complexes formed with the bulkier ligand L2 exhibit more deformation from perfect octahedral geometry, leading to a higher T1/2 in the SCO examples, where T1/2 is the temperature where the spin state is 50% high spin and 50% low spin. Spin state assignment in the solid state is shown to be solvate-dependent for complexes (1b) and (2e), and room temperature UV-visible and NMR spectra indicate a solution-state spin assignment intermediate between fully HS and fully low spin in 10 complexes, (1a)-(1e) and (2a)-(2e).
Chemical communications (Cambridge, England), Jan 21, 2015
P-Hydroxytetraorganophosphorane, the long-postulated intermediate in phosphonium salt and ylide h... more P-Hydroxytetraorganophosphorane, the long-postulated intermediate in phosphonium salt and ylide hydrolysis, has been observed and characterised by low temperature NMR, finally definitively establishing its involvement in these reactions. The results require modification of the previously accepted mechanism for ylide hydrolysis: P-hydroxytetraorganophosphorane is generated directly by 4-centre reaction of ylide with water.
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Papers by Yannick Ortin