Experimental and theoretical study of the kinetic and thermodynamic sites of protonation in (CO)Pt(mu-PBu2t)(2)Pt((PBu2H)-H-t)

The (PtPt1)-Pt-1 monocarbonyl derivative ((Bu2HP)-H-t)Pt(mu-PBu2t)(2)Pt(CO) (5), with a planar, asymmetrically substituted Pt-2(mu-PBu2t)(2) core, rea cts with CF3SO3H to give the new pt(II)pt(II) carbonyl hydride [((Bu2HP)-H- t)Pt(mu-PBu2t)(2)Pt(Co)(H)]CF3SO3 (6a). Complex 6a, in which the proton is terminally attached to the Pt atom bearing the carbonyl ligand, is formed u nder kinetic control and is stable in well-dried nonbasic solvents. This is omer is converted quantitatively by an external weak base into the thermody namically favored form, [((PBu2H)-H-t)(H)Pt(mu-PBu2t)(2)Pt(CO)]CF3SO3 (6b), in which the proton is terminally attached to the Pt atom bearing the phos phine group. In the presence of an excess of triflic acid, 6a is further pr otonated to give [Pt-2(mu-PBu2t)(mu-H)(CO)((PBu2H)-H-t)(eta(2)-(PBu2H)-H-t) ](CF3SO3)(2) (7) by the formation of a P-H bond between the hydride and the adjacent phosphido ligand induced by metal protonation. Complex 7 was char acterized by multinuclear NMR spectroscopy, which strongly suggests a Pt-H- P agostic interaction. Like 6a, complex 7 is stable in nonbasic media, but yields 6b rapidly and quantitatively in the presence of a base. Experimenta l data compare well with the results of ab initio calculations on model com pounds corresponding to 5, 6a(+), and 6b(+), whose structures have been opt imized in the gas phase.