Complexes of rhodium and iridium with the β-ketophosphines PBut2-(CH2COR)(R = Ph or But)

Abstract

The bulky β-ketophosphines PBu^t₂(CH₂COPh)(Q) and PBu^t₂(CH₂COBu^t)(Q′) are shown to behave towards rhodium or iridium either as unidentate ligands (through phosphorus), as bidentate ligands through phosphorus and the keto-group, or as bidentate enolate ions. Treatment of [Rh₂Cl₂(CO)₄] with Q or Q′ gives trans-[RhCl(CO)Q₂] or trans-[RhCl(CO)Q′₂] These react with sodium methoxide to give complexes of type [[graphic ommitted])R}{PBu^t₂(CH₂COR)}](R = Ph or Bu^t) which with hydrogen chloride give back trans-[RhCl(CO){PBu^t₂(CH₂COR)}₂]. The salt RhCl₃·3H₂O with PBu^t₂(CH₂COPh) gives [[graphic ommitted]Ph}-{PBu^t₂(CH₂COPh);(4a) in which both phosphines are bidentate and which the keto-group is strongly co-ordinated, not being displaced by vigorous treatment with carbon monoxide. The six-co-ordinate rhodium(III) complex with sodium methoxide rapidly gives what appears to be an intensely blue rhodium(II) complex [graphic ommitted]. Iridium trichloride with PBu^t₂(CH₂COR) similarly gives the six-co-ordinate [graphic ommitted] [R = Ph (4b) or Bu^t(4c)]. These with sodium ethoxide give purple five-co-ordinate square-pyramidal hydrides [graphic ommitted] (7a) and (7b) which are quite stable to prolonged exposure to air and show ¹H(hydride) shifts to exceptionally high field. They both take up carbon monoxide to give colourless hydridocarbonyls [graphic ommitted] (9a) and (9b) which lose carbon monoxide on heating to give back the five-co-ordinate hydrides. Carbonylation of Na₂[IrCl₆] followed by addition of PBu^t₂(CH₂COPh) gives [[graphic ommitted]{PBu^t₂(CH₂COPh)}](11a) with an unco-ordinated keto-group. With base (NaOEt) this gives a mixture of (9a) and trans-[IrCl(CO){PBu^t₂(CH₂COPh)}₂](unidentate phosphines). Similar addition of PBu^t₂(CH₂COBu^t) to a carbonylated solution of Na₂[IrCl₆] gives a [IrHCl₂(CO){PBu^t₂CH₂COBu^t}₂](10a) contaminated with about 10% of [[graphic ommitted])Bu^t}-{PBu^t₂(CH₂COBu^t)}](11b). When this mixture is heated in chloroform it gives almost pure (11b) contaminated by ca. 2–3% of (10a). Proton and ³¹P n.m.r. and i.r. data are given and discussed.