Methyl- and phenyl-bis(tertiary phosphine) hydroxo complexes of platinum(II): Reactions with weak acids and hydration of nitriles catalysed by hydroxo and N-bonded carboxamido complexes of platinum(II)

Abstract

Methyl- and phenyl-hydroxo complexes of platinum(II), Pt(OH)RL 2 (R = Ph, L = Pcy 3, P-t-Bu 2Me, P-t-BuMe 2, PEt 3, PMePh 2, PMe 2Ph; R = Me, L = P-t-Bu 2Me, P-i-Pr 3) have been prepared by the action of KOH on cationic acetone complexes [PtR(OCMe 2)L 2] + generated in situ. All have mutually trans-phosphine ligands, except for Pt(OH)Ph(PMe 2Ph) 2, which was isolated in an impure state as a cis-trans mixture. The hydroxo complexes behave as strong bases and react with nitromethane, acetone or p-cresol to give, respectively, C-bonded nitromethyl-(CH 2NO 2), C-bonded acetonyl-(CH 2COMe) and O-bonded p-cresolato-( p-MeC 6H 4O) platinum(II) complexes. Complexes in the first two of these classes can also be obtained in lower yield by reaction of PtClRL 2 with nitromethane or acetone in the presence of silver oxide. Methyl cyanoacetate, NCCH 2CO 2Me, reacts with Pt(OH)PhL 2 (L = PEt 3, P-t-Bu 2Me) to give N-bonded methoxycarbonyl-keteniminato complexes Pt(NCCHCO 2Me)PhL 2, but with Pt(OH)Me(dppp) the product is the C-bonded cyano(methoxycarbonyl)methyl complex Pt[CH(CN)(CO 2Me)]Me(dppp). Both hydroxo complexes and N-bonded acetamido complexes Pt(NHCOMe)RL 2 catalyse hydration of acetonitrile to acetamide at 80°C, but are less efficient than trialkylphosphine platinum(0) complexes. The order of activity for R = Ph is L = PEt 3 > P-t-BuMe 2 > PPh 3 ∼ PMe 2Ph > P-t-Bu 2Me >> Pcy 3, while for a given tertiary phosphine the order of activity is R =, Ph > Me. Hydration of acrylonitrile under similar conditions generally gives a mixture of acrylamide, β-cyanoethanol and ββ-dicyanoethyl ether, the last two products arising in irreproducible amounts by addition of water to the olefinic double bond. The mechanisms of these reactions are discussed in the light of the observed trends.