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Yves Jean

Publications and source records attributed to Yves Jean.

9 recordsLinked to original sources
PubMed2007

2,2'-Biphosphinines and 2,2'-bipyridines in homoleptic dianionic Group 4 complexes and neutral 2,2'-biphosphinine Group 6 d(6) metal complexes: octahedral versus trigonal-prismatic geometries.

The geometric and electronic structure of formally d(6) tris-biphosphinine [M(bp)(3)](q) and tris-bipyridine [M(bpy)(3)](q) complexes were studied by means of DFT calculations with the B3LYP functional. In agreement with the available experimental data, Group 4 dianionic [M(bp)(3)](2-) complexes (1P-3P for M=Ti, Zr, and Hf, respectively) adopt a trigonal-prismatic (TP) structure, whereas the geometry of their nitrogen analogues [M(bpy)(3)](2-) (1N-3N) is nearly octahedral (OC), although a secondary minimum was found for the TP structures (1N'-3N'). The electronic factors at work in these systems are discussed by means of an MO analysis of the minima, MO correlation diagrams, and thermodynamic cycles connecting the octahedral and trigonal-prismatic limits. In all these complexes, pronounced electron transfer from the metal center to the lowest lying pi* ligand orbitals makes the d(6) electron count purely formal. However, it is shown that the bp and bpy ligands accommodate the release of electron density from the metal in different ways because of a change in the localization of the HOMO, which is a mainly metal-centered orbital in bp complexes and a pure pi* ligand orbital in bpy complexes. The energetic evolution of the HOMO allows a simple rationalization of the progressive change from the TP to the OC structure on successive oxidation of the [Zr(bp)(3)](2-) complex, a trend in agreement with the experimental structure of the monoanionic complex. The geometry of Group 6 neutral complexes [M(bp)(3)] (4P and 5P for M=Mo and W, respectively) is found to be intermediate between the TP and OC limits, as previously shown experimentally for the tungsten complex. The electron transfer from the metal center to the lowest lying pi* ligand orbitals is found to be significantly smaller than for the Group 4 dianionic analogues. The geometrical change between [Zr(bp)(3)](2-) and [W(bp)(3)] is analyzed by means of a thermodynamic cycle and it is shown that a larger ligand-ligand repulsion plays an important role in favoring the distortion of the tungsten complex away from the TP structure.

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PubMed2006

DFT study on the palladium-catalyzed allylation of primary amines by allylic alcohol.

The palladium-catalyzed allylation of primary amines has been investigated by DFT calculations (B3PW91, PCM method), and two potential mechanisms were studied. The first mechanism relies on the formation of cationic hydridopalladium complexes. Their formation involves a metal-assisted formal (1,3) shift of a proton from the nitrogen atom of an ammonium to the Cbeta carbon atom. The second part of the cycle relies on a ligand exchange through a pentacoordinated 18VE hydridopalladium complex. The last step likely proceeds through a bimolecular pathway and formally consists of a proton transfer from the allylammonium to the alcohol group of the complex. The second mechanism, which is closer to that currently admitted for nucleophilic allylic substitutions, relies on the decomplexation of the coordinated allylammonium and appears to be favored. This catalytic cycle was recomputed on model complexes varying the ligands, and a charge decomposition analysis was carried out to assess the influence of the electronic properties of the ligands. To compare our results with competitive experiments, CDA calculations were also performed on real ligands. In agreement with experimental observations, this process was found to be strongly ligand dependent, decomplexation being favored by strong pi-acceptor ligands. These calculations led us to show experimentally that complex [Pd(P(OPh)(3))(2)(eta(3)-C(3)H(5))][OTf] is an efficient catalyst for this allylation. Finally, this catalytic process proved to be sensitive to the nature of the amine, with poorly basic amines favoring the re-formation of the catalytic precursor.

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PubMed2005

A theoretical study of the formation of the parent phosphinine C5H5P from the flash vacuum thermolysis of diallylvinylphosphine.

The gas-phase decomposition of diallylvinylphosphine 1 into C5H5P 12 is studied by DFT/6-311+G(d,p) calculations with the B3LYP functional, followed by single-point energy-only calculations at the CCSD(T)/6-311+G(d,p) level. According to these calculations, the first step involves a retro-ene elimination that yields 3-phosphahexatrienes 2Z and 2E. Both compounds equilibrate through the formation of 1,2- and 3,4-dihydrophosphetes 3 and 4, and it is shown that the formation of 2Z is favored by the exothermic formation of the 3,4-dihydrophosphinine 5 through a 6pi-electrocyclization. Though 5 can easily isomerize into 2,3- (6) and 1,2-diyhydrophosphinines (7) by successive 1,5-hydrogen shifts, the formation of 12 from 5, 6, or 7 through an elimination of H2 is found to be a high energy process. It is also shown that the elimination of H2 from lambda5-phosphinine 8 following a C2v pathway is a symmetry-forbidden process. Finally, 1,4-dihydrophosphinine 9, which can be formed through a 1,4-hydrogen shift from lambda5-phosphinine 8, is found to be a convenient precursor of 12 through a 1,4-elimination of H2. The formation of 9 from 5 involves the intermediary formation of 3-phosphabicyclo[3.1.0]hex-2-ene 10. The mechanism eventually proposed for the formation of 12 from 2Z is given in Scheme 16 at the CCSD(T) level.

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PubMed2003

Why [CpW(CO)3]+ reduces H2 to dihydride.

The [CpW(CO)3]+ complex, with three pi acceptor ligands and a positive charge, is shown to have an unexpected reducing ability towards H2 because of a low lying triplet state energy.

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PubMed1996

Theoretical Evaluation of Steric Effects in [ReH(5)(PR(3))(2)(SiR(3))(2)] Complexes with the IMOMM Method.

A theoretical study including full geometry optimizations is carried out at the IMOMM(MP2:MM3) (IMOMM = integrated molecular orbital molecular mechanics) computational level on the [ReH(5)(PPh(i)()Pr(2))(2)(SiHPh(2))(2)] and [ReH(5)(PCyp(3))(2)(SiH(2)Ph)(2)] systems, the results being compared with available experimental diffraction data, as well as with MP2 results on the model system [ReH(5)(PH(3))(2)(SiH(3))(2)]. A simple scheme for the analysis of the relative weight of different contributions to the "steric" distortion is also proposed and applied to the same [ReH(5)(PPh(i)()Pr(2))(2)(SiHPh(2))(2)] and [ReH(5)(PCyp(3))(2)(SiH(2)Ph)(2)] species.

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PubMed1996

Trans or (Unusual) Cis Geometry in d(2) Octahedral Dioxo Complexes. A DFT Study.

Geometry optimization of the cis and the trans isomers of several octahedral dioxo complexes of d(2) electronic configuration are performed using the gradient-corrected density functional theory (B3LYP and, for some key structures, BP86). With only monodentate sigma donor ligands (ReO(2)(NH(3))(4)(+), 7), the usual energy order is found (i.e., the trans isomer is the most stable). Complexes with a chelating bidentate ligand, OsO(2)(OCH(2)CH(2)O)(NH(3))(2) (10) and ReO(2)(HN=CHCH=NH)(NH(3))(2)(+) (11), are used as models for the experimental complexes 5 and 2 in which the arrangement of the O=M=O unit is trans and cis, respectively. Our calculations actually show an inversion of the relative energy of the two isomers in going from 10 to 11: while the trans isomer is found to be the most stable in 10, the unusual cis diamagnetic isomer is favored by about 29 kcal mol(-)(1) in 11. This result is traced to the geometric and electronic properties of the bidentate ligand, in particular an acute bite angle and good pi acceptor character. In complex 14 with a bipyridine chelating ligand (weaker pi acceptor than diaza-1,4-butadiene in 11), this energy difference is, however, reduced to 7.5 kcal mol(-)(1) (partial geometry optimization).

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