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(d(t)bpx)(dba)] [d(t)bpx = 1,2-(CH2PBu2t)(2)C6H4; dba = trans, trans-(PhCH=CH)(2)CO], 1, into [Pd(d(t)bpx)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(t)bpx)(eta(2)-O-2)], 3, [Pd(d(t)bpx)(eta(2)-BQ)] (BQ = benzoquinone), 4, [Pd(dcpx)(dbaH)](+) [dcpx = 1,2-(CH2PCy2)(2)C6H4], 7, and [Pd(d(t)bpx)(eta(2)-MeSO3)](+), 9b.