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

The sequence of reaction steps and the role of each reactant, required for the transformation of the Pd(0) precursor [Pd(dtbpx)(dba)] [dtbpx = 1,2-(CH2PBut2)2C6H4; dba = trans,trans-(PhCHCH)2CO], 1, into [Pd(dtbpx)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(dtbpx)(η2-O2)], 3, [Pd(dtbpx)(η2-BQ)] (BQ = benzoquinone), 4, [Pd(dcpx)(dbaH)]+ [dcpx = 1,2-(CH2PCy2)2C6H4], 7, and [Pd(dtbpx)(η2-MeSO3)]+, 9b.