The addition of PH, to formaldehyde to give P(CH,OH), is catalysed by a range of platinum-(iv), -(II) and2 and [Pt{P(CH,OH),},]~H,O 3. A large ratio of P(CH,OH), to Pt is present under the conditions in which the catalysis is operated and the hypothesis that a common platinum-P(CH,OH), complex is present under these conditions has been tested. It is shown that Na,[PtC16] is reduced by 3 equivalents of P(CH,OH), to give [PtCI,{P(CH,OH),},] 2, the same species that is formed upon addition of 2 equivalents of P(CH,OH), t o K,[PtCI,]. Addition of 1 equivalent of P(CH,OH), t o 2 gives [PtCI{P(CH,OH),}],CI 4a while addition of 2 equivalents of P(CH,OH), to 2 gives an unstable species, tentatively assigned the five-co-ordinate structure [PtCI{P(CH,OH),},]CI 5a. In the presence of further P(CH,OH),, 5a decomposes smoothly t o give a mixture of [PtH{P(CH,OH),},]CI 3b, [P(CH,OH),]CI and the unusual bis(che1ate) salts trans-and cis-[Pt{(HOCH,),PCH,0P(CH20H),},]CI,6a and 6b. A mechanism rationalising this reaction is presented. The pH of the reaction medium during the catalysis is ca. 9-10 and it is therefore concluded that [Pt{P(CH,OH),},] 3a is the main platinum-containing species present during all the platinum catalysed reactions. It is shown that [Ni{P(CH,OH),},] 18 and [Pd{P(CH,OH),},] 19 are also catalysts for the hydrophosphination of formaldehyde and a general mechanism is suggested.
