HYDROPHOSPHINATION OF FORMALDEHYDE CATALYZED BY TRIS-(HYDROXYMETHYL)PHOSPHINE COMPLEXES OF PLATINUM, PALLADIUM OR NICKEL

The addition of PH3 to formaldehyde to give P(CH2OH)3 is catalysed by a range of platinum-(IV), -(II) and -(0) compounds including Na2[PtCl6], K2[PtCl4], [PtCl2{P(CH2OH)3}2] 2 and [Pt{P(CHOH)3}4].H2O 3. A large ratio of P(CH2OH)3 to Pt is present under the conditions in which the catalysis is operated and the hypothesis that a common platinum-P(CH2OH)3 complex is present under these conditions has been tested. It is shown that Na2[PtCl6] is reduced by 3 equivalents of P(CH2OH)3 to give [PtCl2{P(CH2OH)3}2] 2, the same species that is formed upon addition of 2 equivalents of P(CH2OH)3 to K2[PtCl4]. Addition of 1 equivalent of P(CH2OH)3 to 2 gives [PtCl{P(CH2OH)3}]3Cl 4a while addition of 2 equivalents of P(CH2OH)3 to 2 gives an unstable species, tentatively assigned the five-co-ordinate structure [PtCl{P(CH2OH)3}4]Cl 5a. In the presence of further P(CH2OH)3, 5a decomposes smoothly to give a mixture of [PtH{P(CH2OH)3}4]Cl 3b, [P(CH2OH)4]Cl and the unusual bis(chelate) salts trans- and cis-[Pt{(HOCH2)2PCH2OP(CH2OH)2}2]Cl2 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(CH2OH)3}4] 3a is the main platinum-containing species present during all the platinum catalysed reactions. It is shown that [Ni{P(CH2OH)3}4] 18 and [Pd{P(CH2OH)3}4] 19 are also catalysts for the hydrophosphination of formaldehyde and a general mechanism is suggested.