Synthesis and characterization of cationic dinuclear complexes of platinum with bridging hydrides; crystal structures of [Pt2(µ-H)2{But2P(CH2)3PBut2}2][BF4]2and [Pt2(µ-H)2{(C6H11)2P(CH2)3P(C6H11)2}2][BF4]2

Abstract

A series of diplatinum dications [Pt2(µ-H)2(L–L)2][BF4]2[L–L =(C6H11)2P(CH2)nP(C6H11)2, But2P(CH2)nPBut2, n= 2 or 3] with two chelating diphosphine and two bridging hydride ligands has been prepared by the elimination of ethene from the agostic alkyl complexes [PtEt(L–L)]+ or alkene–hydride complexes [PtH(C2H4)(L–L)]+, or by the reaction of the dihydride complexes [PtH2(L–L)] with an excess of HBF4·OMe2. The complexes have been characterized by multinuclear (1H, 31P and 195Pt) NMR spectroscopy and for [Pt2(µ-H)2{But2P(CH2)3PBut2}2][BF4]2 and [Pt2(µ-H)2{(C6H11)2P(CH2)3P(C6H11)2}2][BF4]2 by single-crystal X-ray crystallography. The latter complex has a structure in which the platinum and phosphorus atoms are coplanar whereas in the former the co-ordination planes of the platinum atoms are twisted with respect to each other by 36.6°. The twisting in [Pt2(µ-H)2{But2P(CH2)3PBut2}2][BF4]2 is ascribed to the steric pressure of the large diphosphine which destabilises the planar geometry. Significantly this complex is fluxional on the NMR time-scale at 290 K whereas the others are static and there is a shift in colour from yellow to red for the strained complex. The dinuclear species are useful synthetic precursors of the [PtH(L–L)]+ fragment, particularly when L–L is large. Thus [Pt2(µ-H)2{But2P(CH2)3PBut2}2]2+, which has the most sterically demanding diphosphine, reacts with alkenes [e.g. ethene (reversibly) or norbornene] to form mononuclear alkyl complexes with a three-centre, two-electron (agostic) bond.