Papers by Cezar Comanescu
Crystals, May 27, 2023
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Journal of Nanoparticle Research, Feb 22, 2014
ABSTRACT Novel metal nanoporous TM (transition metal) oxides MxOy (Co3O4, CuO) have been synthesi... more ABSTRACT Novel metal nanoporous TM (transition metal) oxides MxOy (Co3O4, CuO) have been synthesized by thermal decomposition of inorganic salts precursors (acetates, nitrates) impregnated into hexagonal mesoporous silica (OMS, ordered mesoporous silica) of SBA-15 type (prepared in-house) at different precursor loadings, the mesocomposites thus obtained being monitored after each impregnation-calcination step by small and wide angle powder XRD. The pore size for the ordered silica host range from 5.08 to 7.06 nm. Retention of the hexagonal silica framework has been observed in spite of the temperatures up to 500°C. Mesoporous Co3O4 has been obtained by leaching the silica through overnight HF dissolution, which partially preserved the small-range ordering found in the parent Co3O4@OMS composite prior to leaching. Both Co3O4 (meso) and Co3O4@SBA-15 have been tested in methane oxidation and were found to be superior to the bulk Co3O4 performance, with mesoporous Co3O4 being able to fully oxidize methane to CO2 and H2O at 350°C, while Co3O4@OMS exhibits a lower activity with 20% conversion at 350°C. CuO@OMS shows the lowest activity, with only ~13% conversion at 500°C.
International Journal of Molecular Sciences, Dec 21, 2022
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Energies, Jun 5, 2023
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Materials, Mar 19, 2022
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Hyperfine Interactions, Nov 25, 2021
Fe oxide magnetic nanoparticles (MNPs) in general and cobalt ferrite nanoparticles in particular ... more Fe oxide magnetic nanoparticles (MNPs) in general and cobalt ferrite nanoparticles in particular have immense potential for applications in catalysis, medicine, information and energy storage, etc. MNPs feature interesting physical and chemical properties, different to those of corresponding bulk materials. The magnetic anisotropy constant of almost spherical CoFe 2 O 4 MNPs is much higher than that of magnetite (Fe 3 O 4 ) MNPs of similar geometrical parameters due to the magnetocrystalline contribution. CoFe 2 O 4 shows significant magnetization at saturation, high coercive field and Curie temperature, and good chemical and magnetic stability, being therefore preferable to the most usual Fe 3 O 4 MNPs. A surfactant-assisted synthetic route was employed to synthesize Fe oxide and in particular cobalt ferrite MNPs over a wide pH range (3–13), endeavor which allowed analysis of transient and parasitic phase identified in acidic reaction conditions.
Angewandte Chemie, Jan 11, 2019
o-Alkenyl-N-triflylanilides undergo Rh(III)-catalyzed oxidative annulations with alkynes to produ... more o-Alkenyl-N-triflylanilides undergo Rh(III)-catalyzed oxidative annulations with alkynes to produce different types of naphthylamides, in a process which involves the cleavage of two C-H bonds. Remarkably, in addition to formal dehydrogenative (4C+2C) cycloadducts, the reaction also produces variable amounts of isomeric naphthylamides whose formation requires a formal migration of the alkenyl moiety from the ortho to the meta position of the anilide. Also interestingly, the annulation reaction can be efficiently carried out in the absence of external oxidants, such as Cu(OAc)2. European Research Council (Advanced Grant No. 340055). R. G.-F. thanks Spanish Government MINECO for the Ramon y Cajal (RYC-RYC-2016-20335) contract. The orfeo-cinqa network CTQ2016-81797-REDC is kindly acknowledged. All calculations were carried out at Centro de Supercomputación de Galicia (CESGA).
Organic Letters, Mar 27, 2017
Reactions were conducted in dry solvents under Argon atmosphere unless otherwise stated. Dry solv... more Reactions were conducted in dry solvents under Argon atmosphere unless otherwise stated. Dry solvents were Aldrich and used without further purification. Dried acetonitrile was also from Aldrich and dried with a solvent system (MBraun, SPS 800 manual), Pd(OAc) 2 (98%) [3375-31-3]. All other chemicals were purchased in Aldrich and used without further purification. The abbreviation "rt" refers to reactions carried out at a temperature between 21-25 ºC. Reaction mixtures were stirred using Teflon-coated magnetic stir bars. High reaction temperatures were maintained using Thermowatch-controlled heating blocks. Thin-layer chromatography (TLC) was performed on silica gel plates and components were visualized by observation under UV light, and / or by treating the plates with p-anisaldehyde or cerium nitrate solutions, followed by heating. Flash chromatography was carried out on silica gel. Dryings were performed with anhydrous Na 2 SO 4. Concentration refers to the removal of volatile solvents via distillation using a Büchi rotary evaporator followed by high vacuum. All Palladium-catalyzed reactions were carried out without particular precautions to extrude moisture or oxygen. 1 H-NMR (300MHz) spectra were recorded at room temperature on a Varian 300MHz or 500 MHz spectrometer in CDCl 3 * [using CDCl 3 (for 1H, δ = 7.26) as internal standard]. 13 C NMR (75 MHz) spectra on a Varian spectrometer in CDCl 3 [using CDCl 3 (for 13 C, δ = 77.160) as internal standard]. The following abbreviations were used to explain the multiplicities: s = singlet, d = doublet, t = triplet, q = quartet, m = multiplet, brs = broad singlet. Carbon types and structure assignments were determined from DEPT-NMR and two dimensional experiments (HMQC and HMBC, COSY and NOESY). NMR spectra were analyzed using MestReNova© NMR data processing software (www.mestrelab.com). Mass spectra were acquired using electronic impact (EI) and were recorded at the CACTUS facility of the University of Santiago de Compostela or Amazon SL Bruker using ESI (ion plarity negative and positive). Allene 2g (3-methylbuta-1,2-dien-1-yl)benzene) was prepared according to the procedure reported in
International Journal of Molecular Sciences, Jun 26, 2022
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Chemistry, Aug 27, 2022
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Materials, Jan 2, 2023
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Organometallics, Oct 7, 2014
ABSTRACT Two formal palladium carbene complexes, [PC(sp2)P]Pd(PR3) ([PC(sp3)HP] = bis[2-(di-isopr... more ABSTRACT Two formal palladium carbene complexes, [PC(sp2)P]Pd(PR3) ([PC(sp3)HP] = bis[2-(di-isopropylphosphino)-phenyl]methyl, iPr2P-C6H4-CHC6H4-PiPr2, 3: R = Me; 4: R = Ph), were isolated and characterized. Structural studies and DFT calculations indicate that the interaction between palladium and carbon is best described as a single bond, associated with nucleophilic character at that carbon atom. The characteristics of 3were probed by reactions with electrophiles (MeI), acids (MeOH and HCl), and para-toluidine.
Organometallics, Jun 26, 2018
A series of palladium pincer complexes supported by (i Pr 2 P-C 6 H 4) 2 CH 2 (PC(sp 3)H 2 P = bi... more A series of palladium pincer complexes supported by (i Pr 2 P-C 6 H 4) 2 CH 2 (PC(sp 3)H 2 P = bis(2-(diisopropylphosphanyl)phenyl)methane) was isolated and characterized. Different modes of C−H activation were observed for [{PC(sp 3)H 2 P}PdX 2 ] (X = Cl, OTf, Me, OAc). The thermal treatment of [{PC(sp 3)H 2 P}PdX 2 ] (X = Cl, OTf) induced a backbone C−H bond activation to generate the respective [{PC(sp 3)HP}PdX] complex, while under similar reaction conditions [{PC(sp 3)H 2 P}PdMe 2 ] underwent a C−C reductive elimination that led to the formation of a Pd(0) dimer, [{PC(sp 3)H 2 P}Pd] 2. For the analogous diacetate complex [{PC(sp 3)H 2 P}Pd(OAc) 2 ], the C−H activation occurred at the phosphine isopropyl methine group to generate a palladacycle.
Inorganic Chemistry, Aug 7, 2014
CH 2 CH 2) was investigated to determine the preference for cis/trans coordination to palladium(0... more CH 2 CH 2) was investigated to determine the preference for cis/trans coordination to palladium(0), palladium(II), and rhodium(I). Increasing the length of the bridging alkyl backbone from one to two carbons changes the geometry of the resulting palladium(II) complexes, with L 1 coordinating preferentially cis, while L 2 coordinates in a trans fashion. Coordination to Pd(0) leads to L 1 Pd(dba) and L 2 Pd(dba), in which both ligands accommodate a P−M−P angle close to 120°. L 2 was found to coordinate cis in a rhodium(I) complex ([L 2 Rh(nbd)][BF 4 ], where nbd = norbornadiene).
Polyhedron, Mar 1, 2018
E-H bond cleavage by [{PC(sp 2)P}Pd(PMe 3)] (1, PC(sp 2)P = i Pr 2 P-C 6 H 4-CC 6 H 4-P i Pr 2) o... more E-H bond cleavage by [{PC(sp 2)P}Pd(PMe 3)] (1, PC(sp 2)P = i Pr 2 P-C 6 H 4-CC 6 H 4-P i Pr 2) of alcohols led to a series of new square-planar tridentate palladium alkoxides, [{PC(sp 3)HP}Pd(O i Pr)] (3), [{PC(sp 3)HP}Pd(O t Bu)] (4), and [{PC(sp 3)HP}Pd(OPh)] (5, PC(sp 3)HP = bis[2-(di-iso-propylphosphino)phenyl]methyl). The analogous reaction with amines led to the formation of [{PC(sp 3)HP}Pd(NPh 2)] (6) and [{PC(sp 3)HP}Pd(NHMes)] (7). The molecular structure of 7 was further probed by a CO 2 insertion reaction into the Pd-N bond, yielding the corresponding carbamate 8. The molecular structures of 3-8 were determined by single-crystal X-ray diffraction and conform to the corresponding solution structures as determined by NMR spectroscopy. The reactivity of carbene 1 towards alcohols and amines is dictated by the nucleophilic/basic character at the carbene backbone carbon atom, the pKa and bond dissociation energy of the E-H bond (E =N, O), and the steric properties of the organic substrates used.
Chemical Communications, 2016
The polarity of the Pd–C bond can be tuned by the phosphine substituents of palladium carbene com... more The polarity of the Pd–C bond can be tuned by the phosphine substituents of palladium carbene complexes as shown by the reactions of these compounds with silanes.
Polyhedron, 2019
The reactivity of a nucleophilic palladium carbene, [{PC(sp 2)P} H Pd(PMe3)] (1, [PC(sp 2)P] = bi... more The reactivity of a nucleophilic palladium carbene, [{PC(sp 2)P} H Pd(PMe3)] (1, [PC(sp 2)P] = bis[2-(di-iso-propylphosphino)phenyl]methylene), towards 2,6-dimesitylphenyldiazomethane ((dmp)CHN2) and 2,6-dimesitylphenylazide ((dmp)N3) was explored. When treated with (dmp)CHN2, the carbene complex was fully consumed to generate a 3-coordinate Pd(0) complex [{PC(=N-N=CH(dmp))P} H Pd(PMe3)] (2), with a newly formed double bond between the backbone carbon and the terminal nitrogen of the diazo compound. Similar reactivity occurred between [{PC(sp 2)P} H Pd(PMe3)] and (dmp)N3 to yield [{PC(=N-N=N(dmp))P} H Pd(PMe3)] (3); in this instance, there is an interaction between the newly formed C=N moiety and the Pd(0) metal center, resulting in a 4-coordinate distorted tetrahedral complex.
Chemistry: A European Journal, Nov 6, 2017
A series of chalcogen analogues encompassing a ketone and chalcogenoketones [{PC(=E)P}Pd(PMe3)] (... more A series of chalcogen analogues encompassing a ketone and chalcogenoketones [{PC(=E)P}Pd(PMe3)] (E=O, S, Se, Te) was generated from a nucleophilic palladium carbene compound, [{PC(sp2)P}Pd(PMe3)] ([PC(sp3)HP]=bis[2‐(diisopropylphosphino)‐phenyl]methyl, iPr2P‐C6H4‐CH‐C6H4‐PiPr2). The thio‐, seleno‐, and telluroketone were all synthesized by means of an atom transfer from the respective chalcogens. The ketone analogue, however, required the use of nitrobenzene or nitrosobenzene as the oxygen‐atom transfer agent.
Chemical Communications, 2015
Organometallics, Jul 9, 2015
The reactivity of a nucleophilic palladium carbene, [PC(sp 2)P]Pd(PMe 3) (1; [PC(sp 2)P] = bis[2-... more The reactivity of a nucleophilic palladium carbene, [PC(sp 2)P]Pd(PMe 3) (1; [PC(sp 2)P] = bis[2-(diisopropylphosphino)phenyl]methylene), toward the C−H bonds of CH 3 COCH 3 , CH 3 CN, Ph−CCH, fluorene, and 9,10dihydroanthracene was investigated. All surveyed substrates reacted with 1. However, there was no detectable reaction of 1 with Ph 2 CH 2. It is proposed that the pK a values of the studied C−H bonds govern their reactivity toward 1: our results show that substrates with a pK a higher than 29, such as Ph 2 CH 2 (pK a = 32.2), do not react even with prolonged heating.
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Papers by Cezar Comanescu