Bisphosphine monoxides with o-phenylene backbones in Pt, Pd and Fe complexes

A new route to aromatic bisphosphine monoxides has been explored through ortholithiation of triphenylphosphine oxide and subsequent reaction of the lithiated intermediate with a range of alkyl and aryl phosphine chlorides. Routes to the known bisphosphine monoxide (BMPO) (o-C6H4){P(O)Ph-2}PPh2 (2aO) and a range of new BPMOs of the type Ph2P(O)(o-C6H4)PR2 where R-2 = Pr-i(2), Cy-2, Et-2 are described. Reaction of 2aO with MCl2(cod) (M = Pd, PC: cod = cyclooctadiene) gives products of the form [MCl(kappa(1)-P-2aO)( kappa(2)-P,O-2aO)](+) Cl- and MCl2(kappa(2)-P,O-2aO): the former exhibits fluxional behaviour which has been analysed by Pt-195 NMR and (31)p variable-temperature NMR spectroscopy. The bidentate complex is not fluxional for either the Pd or the PC example; the PC Complex PtCl2(kappa(2)-P,O-2aO) has been characterised by X-ray crystallography. By comparison of the product distribution seen by P-31 NMR spectroscopy and ESI-MS it was established that the different coordination modes of 2aO result in quite different behaviour of the complexes when Studied by ESI-MS: when the O is formally coordinated to the metal its ionisation efficiency is very low. Synthesis of Fe(CO)(4)(2aO) confirmed the ability of the 2aO ligand to render a neutral complex with no alternative pathways for ionisation to be readily detected by ESI-MS. (C) 2009 Elsevier Ltd. All rights reserved.