HIGH-PRESSURE NMR INVESTIGATION OF THE INTERMEDIATES OF PLATINUM-PHOSPHINE HYDROFORMYLATION CATALYSTS

The reactions of square-planar alkylplatinum-diphosphine complexes, Pt (Me)(Cl)(bdpp) (1) and Pt(Me)(SnCl3)(bdpp) (2), as well as Pt{CH(COOEt )CH3}(Cl)(dppp) (3) (where bdpp=(2S,4S)-2,4-bis(diphenylphosphino)pent ane, dppp=1,3-bis(diphenylphosphino)propane) with carbon monoxide and carbon monoxide/hydrogen mixture have been studied by high pressure NM R. Carrying out the pressurization at 273 K and the measurement of a s ample containing 2 at 173 K, a methylplatinum-hydride was detected und er 50 bar CO/H-2=1/1 pressure in CD2Cl2 which was transferred to [Pt(C H3)(CO)(bdpp]+SnCl3- (2a) and [Pt(COCH3)(CO)(bdpp]+SnCl3- (2b) at room temperature. The platinum complex containing an alkyl stable to beta- hydride elimination Pt{CH(COOEt)CH3}(Cl)(dppp) (3) was reacted with ca rbon monoxide resulting mainly in Pt(dppp)Cl-2 and an ionic intermedia te analogous to 2a, [Pt{CH(COOEt)CH3}(CO)(dppp)]Cl-+(-) (3a). However, the same reaction with the in situ formed SnCl2-inserted product, Pt{ CH(COOEt)CH3}(SnCl3)(dppp) yielded [Pt(CH3)(CO)(dppp)]+SnCl3- (4a) as a minor component besides PtCl2(dppp) and the decomposition product Pt (Me)(Cl)(dppp) (1'). (C) 1997 Elsevier Science S.A.