Synthesis and reactivity of palladium hydrido-solvento complexes, including a key intermediate in the catalytic methoxycarbonylation of ethene to methyl propanoate

Abstract

The sequence of reaction steps and the role of each reactant, required for the transformation of the Pd(0) precursor [Pd(d^tbpx)(dba)] [d^tbpx = 1,2-(CH₂PBu^t₂)₂C₆H₄; dba = trans,trans-(PhCHCH)₂CO], 1, into [Pd(d^tbpx)H(MeOH)]⁺, 2a, the active Pd(II)-hydride catalyst for the methoxycarbonylation of ethene to methylpropanoate, have been delineated using a combination of spectroscopic and crystallographic methods. The preparation and characterisation of a variety of related complexes are described including some unusual examples involving bidentate sulfonate complexes and mono-cationic and neutral palladium hydride complexes. X-Ray crystal structures have been determined for [Pd(d^tbpx)(η²-O₂)], 3, [Pd(d^tbpx)(η²-BQ)] (BQ = benzoquinone), 4, [Pd(dcpx)(dbaH)]⁺ [dcpx = 1,2-(CH₂PCy₂)₂C₆H₄], 7, and [Pd(d^tbpx)(η²-MeSO₃)]⁺, 9b.