Reductive Elimination of Organic Molecules from Palladium−Diphosphine Complexes

Abstract

The effects governing the rate of reductive elimination of dimethyl ether, acetonitrile, vinyl cyanide, and methyl ethanoate from palladium diphosphine complexes were studied by means of a density functional theory method. Energy barriers, computed as the difference in energy between the reactant and the corresponding transition state using H2P(CH2)2PH2 as model for diphosphine ligands, varied from 38 kcal mol-1 (dimethyl ether) to barrierless elimination of methyl ethanoate, in good agreement with experimental results. MO analysis reveals striking differences that are related to the donor/acceptor capabilities of the reacting moieties. For the elimination of acetonitrile, the bite angle effect on the reaction rate, observed by Moloy when different diphosphine ligands were used, was studied in depth. We considered (R2PXPR2)Pd(CH3)(CN) complexes for a number of different ligand backbones (X = (CH2) n , n = 1−4; X = cis-, trans-but-2-ene) which span a large bite angle range and for a number of different phosphine substituents (R = H, Me, Ph). With the use of QM/MM strategies, steric and electronic effects were separated and evaluated, and the results indicate that the rate enhancement is electronic in nature, steric effects being negligible. The analysis reveals that wide bite angle ligands destabilize the reactant and stabilize the transition state, thus accelerating the reaction.

Phosphine Ligands in the Palladium‐Catalysed Methoxycarbonylation of Ethene: Insights into the Catalytic Cycle through an HP NMR Spectroscopic Study

“…There have been many experimental [11][12] and theoretical studies of the reaction. [50][51][52] Initially, it was concluded that monodentate phosphines favour hydroesterification of ethene to give methyl propanoate, whereas bidentate phosphines lead to polyketones. [9] Subsequently, van Leeuwen showed that the chemoselectivity of the reaction can be…”

Binaphthol‐Based Diphosphite Ligands in Asymmetric Nickel‐Catalyzed Hydrocyanation of Styrene and 1,3‐Cyclohexadiene: Influence of Steric Properties

“…[17][18][19] We believe that the steric bulk not only prevents the formation of bis-chelates with ligands L3-L5 but also has an effect on either the rate of reductive elimination or on the rate of deactivation. This would explain the fact that these systems become more efficient in the hydrocyanation of styrene (in conversion and enantioselectivity) with increasing steric bulk.…”

Room‐Temperature Palladium‐Catalyzed Negishi‐Type Coupling: A Combined Experimental and Theoretical Study

“…[7] A simplified, traditional mechanism involves three steps: 1) the oxidative addition of the halogeno-arene (OA, Scheme 1), [8] 2) the transmetalation with the organozinc derivative, (TM, Scheme 1), [9] and 3) the reductive elimination that forms the biaryl product and regenerates the active Pd 0 species (RE, Scheme 1). [10] To date, only few computational studies have addressed the full catalytic cycle. [11] Most recently, we have incorporated the phosphabarrel-A C H T U N G T R E N N U N G ene ligand 1 (= L in Scheme 1 and 2), in various catalytic processes, such as the Pt-catalyzed hydrosilylation of alkynes, or the Pd-catalyzed Suzuki-Miyaura cross-coupling [a] of chloroarenes at room temperature.…”