The hydrolysis of monochlorophosphine and monochloroarsine complexes of platinum(II): bridging phosphinato- and arsinato-groups

The hydrolysis of complexes of the type cis-[PtX2(MR2Cl)(M′R′3)](I)(X = Cl, Br, or I; M = P or As; M′= P or As; R and R′= alkyl or phenyl group) is described. The first hydrolysis products are cis-[PtX2(MR2OH)(M′R′3)](II) which exist as strongly hydrogen-bonded dimers especially when M = P. These readily lose HCl by further hydrolysis to form binuclear phosphinato- or arsinato-bridged complexes [(M′R′3)XPt(R2MO)2PtX(M′R′3)](III). The arsinato-bridged compound can be hydrolysed no further, but the phosphinato-bridged complexes hydrolyse readily to give two isomeric hydroxides α- and β-[(M′R′3)(OH)Pt(R2PO)2Pt(OH)(M′R′3)](IV). By treatment with concentrated hydrohalic acid, the phosphinato-bridged complexes revert to (II; M = P) and the arsinato-bridged compounds to (I; M = As). (III) and (IV) react with NaSEt to form thio-bridged complexes with terminal [R2MO]– groups. The structures were determined by 1H n.m.r. and infrared spectra, and the P–O stretching frequency was correlated with its position in the complex; ν(P–OH)terminalca. 880, ν(P–O)bridgeca. 1010, and ν(P–O)terminalca. 1103 cm.–1. The phosphinato-bridged platinum(II) system is stronger than the iodidobridge, but weaker than the ethylthio-bridge.It is shown that diphenylhydroxyphosphine exists in equilibrium with diphenylphosphine oxide in sufficient concentration to react in the hydroxy-form with [Pt2Cl4(PEt3)2], to form (II; M = M′= P; R = Ph, R′= Et].The Pt(R2PO)2Pt ring behaves as if both oxygen and phosphorus have an equal and high trans-influence, similar to that of the diphenylphosphido-bridge, suggesting considerable conjugation around the ring. This would be in accord with the peculiar stability of the dihydroxide (IV). The only other proven example of a hydroxyplatinum(II) complex, trans-[Pt(OH)(GePh3)(PEt3)2], also has a group of high trans-influence trans to hydroxide.