OXYGEN-ATOM TRANSFER BETWEEN CIS-COORDINATED NITRITE AND NITROSYL LIGANDS - THE CASE OF THE CPCR(NO)2(NO2) CPCR(NO)2(ONO) LINKAGE ISOMERS/

CpCr(NO)2(NO2) exists as a mixture of the nitro and nitrito linkage is omers, with the nitrito isomer predominating in both solution and the solid state (Cp = eta5-C5H5). The Cr-NO2 reversible Cr-ONO equilibrium is markedly solvent and temperature dependent: in CDCl3, DELTAH(eq) = 1.8(3) kcal/mol and DELTAS(eq) = 9.3(9) eu. The treatment of CPCr(NO) 2(NO2) with (NaNO2)-N-15 in MeOH leads to the exchange of free and bou nd NO2-, eventually giving a statistical distribution of the N-15 labe l in the NO and NO2 ligands and free NO2- at equilibrium. The linkage isomers of the labeled (CpCr(NO)2(NO2))-N-15 complex convert to a stat istical mixture of the (CpCr(NO)(NO)(NO2))-N-15 and (CpCr(NO)(NO)(ONO) )-N-15 isotopomers in solution and in the solid state. The initial dis appearance rate of the (CpCr(NO)2(NO2))-N-15 isotopomer is first-order , leading to DELTAH(double dagger) = 11.3(6) kcal/mol and DELTAS(doubl e dagger) = 10(2) eu in MeOH and DELTAH(double dagger) = 14(l) kcal/mo l and DELTAS(double dagger) = 20(l) eu in toluene. This behavior, toge ther with the fact that (CpCr(NO)2(NO2))-N-15 equilibrates to (CpCr(NO )(NO)(NO2))-N-15 in the solid state, supports an intramolecular O atom transfer process between cis-coordinated NO and NO2 ligands.