Ligand exchange processes of OsHCl(CO)(L)(PR 3) 2 (L=vacant, H 2, R′CN, O 2; R=Cy, i-Pr)

Abstract

The reactivity of complexes formed by the addition of O 2, H 2 and R′CN to OsHCl(CO)(PR 3) 2 ( 1a:R=Cy; 1b:R= i-Pr) has been examined. Under 24 bar H 2 and 65°C, the dioxygen ligand of OsHCl(CO)(O 2)(PR 3) 2 ( 2a, b) is displaced to yield the trans-hydridodihydrogen complexes OsHCl( η 2-H 2)(CO)(PR 3) 2 ( 3a, b). Measurements of the equilibrium constant, K H 2 =[ 3a]/[ 1a][H 2], for the direct addition of H 2 to 1a yield Δ H°=−49.1±2.4 kJ/mol and Δ S°=−95.7±7.9 J/mol K. 1a, b react reversibly with aryl and alkyl nitriles to produce the isolable complexes, OsHCl(CO)(R′CN)(PR 3) 2 ( 4a, b). The phosphine ligands of 1a, b and 3a, b exchange with unbound, bulky alkyl phosphines at a rate that is slow relative to the NMR timescale. In the presence of excess PCy 3, complex 3b yields the exchange products OsHCl( η 2-H 2)(CO)(P i-Pr 3)(PCy 3) and 3a. While a tris-phosphine complex cannot be detected, limited kinetic data characterize the exchange as associative process.