Characterization and Dynamics of [Pd(L−L)H(solv)]<sup>+</sup>, [Pd(L−L)(CH<sub>2</sub>CH<sub>3</sub>)]<sup>+</sup>, and [Pd(L−L)(C(O)Et)(THF)]<sup>+</sup> (L−L = 1,2-(CH<sub>2</sub>PBu<sup>t</sup><sub>2</sub>)<sub>2</sub>C<sub>6</sub>H<sub>4</sub>): Key Intermediates in the Catalytic Methoxycarbonylation of Ethene to Methylpropanoate
作者:William Clegg、Graham R. Eastham、Mark R. J. Elsegood、Brian T. Heaton、Jonathan A. Iggo、Robert P. Tooze、Robin Whyman、Stefano Zacchini
DOI:10.1021/om010938g
日期:2002.4.29
A detailed spectroscopic study has allowed the solution structure and dynamic properties of all the intermediates in the Pd-catalyzed methoxycarbonylation of ethene to be established. [Pd(L-L)H(solv)](-) 1 (L-L = 1,2-(CH2PBu2t)(2)C6H4; solv = MeOH, 1a; (PrOH)-O-n, 1b; THF, 1c; EtCN, 1d) is static, and the two inequivalent P atoms do not become equivalent through solvent exchange over all the temperatures studied. [Pd(L-L)(CH2CH3)](+), 2, contains a strong beta-agostic C-H interaction which is remarkably stable and is not displaced even in strongly coordinating solvents such as EtCN. C-alpha and C-beta Of the ethyl group in 2 become equivalent via a stereospecific interchange involving [Pd(L-L)H(eta(2)-C2H4)](+) without making the two P atoms equivalent; at higher temperatures these two inequivalent P atoms do become equivalent probably via a T-shaped intermediate. For [Pd(L-L)(C(O)Et)(solv)](+), 6, there is no beta-agostic C-H interaction and multiple C-13-labeling of the C(O)Et group shows that the inequivalent P atoms become equivalent via movement of the intact C(O)Et group. The crystal structure of the related complex [Pd(L-L)(C(O)Et)Cl] cocrystallized with dibenzylacetone has been determined.