Reversible formation of Pt2(.mu.-H)2H(PEt3)4+ and Pt2(.mu.-H)H2(PEt3)4+ from the cis and trans isomers of dihydrobis(triethylphosphine)platinum(II)

Abstract

Irradiation of Pt(C/sub 2/O/sub 4/)L/sub 2/, where L = P(C/sub 2/H/sub 5/)/sub 3/, in Ch/sub 3/Cn solvent under a hydrogen atmosphere produces (Pt/sub 2/(..mu..-H)/sub 2/HL/sub 4/)(O/sub 2/CH), 1(O/sub 2/CH), and CO/sub 2/. Dimer 1 can also be prepared by the condensation reaction between PtH/sub 2/L/sub 2/ (a 90:10 trans:cis equilibrium mixture) and PtH(S)L/sub 2//sup +/, where S = a solvent such as acetone. When PtD/sub 2/L/sub 2/ is used in the reaction, deuterium is only incorporated into the bridging positions. Analyses of the spin and isotopic distribution patterns in the /sup 31/P, /sup 1/H, and /sup 195/Pt NMR spectra establish a solution geometry for 1 based on a cis-PtH/sub 2/L/sub 2/ molecule bound to the PtHL/sub 2//sup +/ fragment. The solution chemistry of 1 depends dramatically on the counterion. Basic anions X = I/sup -/, OCH/sub 3//sup -/, and O/sub 2/CH/sup -/ generate small equilibrium concentrations of PtH/sub 2/L/sub 2/, PtHXL/sub 2/, and (PtH(S)L/sub 2/)X. For example, 1(O/sub 2/CH) reacts completely in the presence of C/sub 2/H/sub 4/ to yield Pt(C/sub 2/H/sub 4/)L/sub 2/ whereas 1(B(C/sub 6/H/sub 5/)/sub 4/) exhibits no such reactivity. Complex 1 efficiently catalyzes the decomposition of formic acid at 25/sup 0/C; however, formate ion must bemore » added in excess to promote the reaction. Monomers appear to be the active catalysts. The species 1(OH) formed by the addition of H/sub 2/O to PtH/sub 2/L/sub 2/ also catalyzes the hydration of acetonitrile to acetamide. A symmetrical isomer, Pt/sub 2/(..mu..-H)H/sub 2/L/sub 4//sup +/ (2), of dimer 1 can be generated by the UV photolysis of Pt(C/sub 2/O/sub 4/)L/sub 2/ in methanol. It appears that the initially formed trans-PtH(OCH/sub 3/)L/sub 2/ complex undergoes ..beta..-hydride abstraction to stereoselectively yield trans-PtH/sub 2/L/sub 2/. This species is trapped by trans-PtH(OCH/sub 3/)L/sub 2/ or (trans-PtH(S)L/sub 2/)(CH/sub 3/O) to form 2 before isomerization to cis-PtH/sub 2/L/sub 2/ (and thereby 1) takes place. Dimer 2 is thermodynamically unstable with respect to 1, and bases such as pyridine or I/sup -/ catalyze the isomerization.« less