A series of diplatinum dications [Pt2(~-H)2(L-L)2][BF,11, [L-L = (C6H1 1)2P(CH2),P(C6Hl 1 ) 2 , Bu',P(CH,),PBu',, M = 2 or 31 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 [PtH,(L-L)] with an excess of HBF,-OMe,. The complexes have been characterized by multinuclear ('H, 31P and 195Pt) NMR spectroscopy 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(p-H)2(Bu'2P(CH2)3PBu12}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(p-H)2{ B U ' ~P ( C H ~) ~P B U ' , ) , ] ~+, 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.
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