85318-49-6Relevant academic research and scientific papers
Carbon-carbon bond-forming reductive elimination from arylpalladium complexes containing functionalized alkyl groups. Influence of ligand steric and electronic properties on structure, stability, and reactivity
Culkin, Darcy A.,Hartwig, John F.
, p. 3398 - 3416 (2008/10/09)
A series of arylpalladium alkyl complexes of the formula [(DPPBz)Pd(Ar)(R)] (DPPBz = 1,2-bis(diphenylphosphino)benzene; R = methyl, benzyl, enolate, cyanoalkyl, trifluoroalkyl, or malonate) has been prepared to reveal the influence of steric and electronic parameters on structure, stability, and reactivity. Arylpalladium enolate and cyanoalkyl complexes ligated by EtPh 22P, 1,1-bis(diisopropylphosphino)ferrocene (D iPrPF), and BINAP were prepared to evaluate the effect of the ancillary ligand. The coordination modes of the enolate and cyanoalkyl complexes were determined by spectroscopic methods, in combination with X-ray crystallography. In the absence of steric effects, the C-bound isomer was favored electronically if the enolate or cyanoalkyl group was located trans to a phosphine, and the O-bound isomer was favored if the enolate was located trans to an aryl group. The thermodynamic stability of the enolate and cyanoalkyl complexes was controlled by the steric properties of the enolate or cyanoalkyl group, and complexes with more substitution at the α-carbon were less stable. Arylpalladium methyl, benzyl, enolate, cyanoalkyl, and trifluoroethyl complexes underwent carbon-carbon bond-forming reductive elimination upon heating. Reductive elimination was faster from complexes with electron-withdrawing substituents on the palladium-bound aryl group and with sterically hindered alkyl groups. The electronic properties of the alkyl group had the largest impact on the rate of reductive elimination: electron-withdrawing groups on the α-carbon retarded the rate of reductive elimination. The rates of reductive elimination correlated with the Taft polar substituent constants of the groups on the carbon alpha to the metal.
Carbon-sulfur bond-forming reductive elimination involving sp-, sp2-, and sp3-hybridized carbon. Mechanism, steric effects, and electronic effects on sulfide formation
Mann, Grace,Baranano, David,Hartwig, John F.,Rheingold, Arnold L.,Guzei, Ilia A.
, p. 9205 - 9219 (2007/10/03)
Palladium thiolato complexes [(L)Pd(R)(SR')], within which L is a chelating ligand such as DPPE, DPPP, DPPBz, DPPF, or TRANSPHOS, R is a methyl, alkenyl, aryl, or alkynyl ligand, and R' is an aryl or alkyl group, were synthesized by substitution or proton-transfer reactions. All of these thiolato complexes were found to undergo carbon-sulfur bond-forming inductive elimination in high yields to form dialkyl sulfides, diaryl sulfides, alkyl aryl sulfides, alkyl alkenyl sulfides, and alkyl alkynyl sulfides. Reductive eliminations forming alkenyl alkyl sulfides and aryl alkyl sulfides were the fastest. Eliminations of alkynyl alkyl sulfides were slower, and elimination of dialkyl sulfide was the slowest. Thus the relative rates for sulfide elimination as a function of the hybridization of the palladium-bound carbon follow the trend sp2 > sp >> sp3. Rates of reductive elimination were faster for cis-chelating phosphine ligands with larger bite angles. Kinetic studies, along with results from radical trapping reactions, analysis of solvent effects; and analysis of complexes with chelating phosphines of varying rigidity, were conducted with [Pd(L)(S-tert-butyl)(Ar)] and [Pd(L)(S- tert-butyl)(Me)]. Carbon-sulfur bond-forming reductive eliminations involving both saturated and unsaturated hydrocarbyl groups proceed by an intramolecular, concerted mechanism. Systematic changes in the electronic properties of the thiolate and aryl groups showed that reductive elimination is the fastest for electron deficient aryl groups and electron rich arenethiolates, suggesting that the reaction follows a mechanism in which the thiolate acts as a nucleophile and the aryl group an electrophile. Studies with thiolate ligands and hydrocarbyl ligands of varying steric demands favor a migration mechanism involving coordination of the hydrocarbyl ligand in the transition state.
Reactions of (phosphine)palladium(0) complexes with thiocarbonyl selenide and the x-ray crystal structure of [1,2-C6H4(CH2PPh2) 2]Pd(η2-CSSe)
Werner,Ebner,Bertleff,Schubert
, p. 891 - 895 (2008/10/08)
The reactions of Pd(P-i-Pr3)n (n = 2 or 3) and Pd(PPh3)4 with CSSe yield the compounds (PR3)2Pd-(η2-CSSe) (1,2) for which a η2-bonding mode via C and Se is indicated by infrared data. (PPh3)2Pd(η2-CSSe) (2) reacts with the diphosphines 1,2-C2H4(PPh2)2 (diphos) and 1,2-C6H4(CH2PPh2)2 (dpmb) by displacement of the PPh3 ligands to form the chelate complexes (diphos)Pd(η2-CSSe) (3) and (dpmb)Pd(η2-CSSe) (4). From 2 and 1,2-C6H4(Ph2)2 (dppb), the compound Pd(dppb)2 (5) is obtained. The molecular structure of 4 has been determined by X-ray investigation. 4 crystallizes in the space group P21/c with a = 958.5 (13) pm, b = 1502 (2) pm, c = 2150 (5) pm, and β = 103.1 (2)°. The four atoms linked to palladium are approximately in one plane. The thiocarbonyl selenide unit is coordinated via C and Se with a S-C-Se angle of 141 (1)°. The C-Se and C-S distances are 180 (2) and 162 (2) pm; i.e., they are longer than in free CSSe. The Pd-P bond lengths (228.3 (5) pm trans to Se and 236.6 (5) pm trans to C) differ significantly reflecting the characteristic trans-lengthening effect of the CSSe carbon atom.
