Synthesis and characterization of cationic dinuclear complexes of platinum with bridging hydrides; Crystal structures of [Pt-2(mu-H)(2){Bu(2)(t)P(CH2)(3)-PBu(2)(t)}(2)][BF4](2) and [Pt-2(mu-H)(2){(C6H11)(2)P(CH2)(3)P(C6H11)(2)}(2)][BF4](2)

A series of diplatinum dications [Pt-2(mu-H)(2)(L-L)(2)][BF4](2) [L-L = (C6H11)(2)P(CH2)(n)P(C6H11)(2), Bu(2)(t)P(CH2)(n)PBu(2)(t), n = 2 or 2] with two chelating diphosphine and two bridging hydride ligands has been n or wt 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 . OMe(2). The complexes have been characterized by multinuclear (H-1, P-31 and Pt-195) NMR spectroscopy and for [Pt-2(mu-H)(2){Bu(2)(t)P(CH2)(3)PBu(2)(t)}(2)][BF4](2) and [Pt-2(mu-H)(2){(C6H11)(2)P(CH2)(3)P(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 tn Path other by 36.6 degrees The twisting in [Pt-2(mu-H)(2){Bu(2)(t)P(CH2)(3)PBu(2)(t)}(2)][BF4](2) 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, which has the most sterically particularly when L-L is large. Thus [Pt-2(mu-H)(2){Bu(2)(t)P(CH2)(3)PBu(2)(t)}(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.