A New Route to Coordination Complexes of Nitroxyl (HNO) via Insertion Reactions of Nitrosonium Triflate with Transition-Metal Hydrides

Nitrosonium triflate reacts with cold methylene chloride solutions of mer,trans-ReH(CO)3(PPh3)2 (1) with 1,1-insertion of NO+ into the Re−H bond to give the orange nitroxyl complex [mer,trans-Re(NHO)(CO)3(PPh3)2][SO3CF3] (3) in 86% isolated yield. Use of [NO][PF6] or [NO][BF4] gives analogous insertion products at low temperature, which decompose on warning to ambient temperature to the fluoride complex mer,trans-ReF(CO)3(PPh3)2 (4). A related 1,1-insertion is observed in the reaction of 1 with [PhN2][PF6] in acetone that affords the yellow-orange phenyldiazene salt [mer,trans-Re(NHNPh)(CO)3(PPh3)2][PF6] (2), which has been characterized by X-ray crystallographic methods. The methyl derivative mer,trans-Re(CH3)(CO)3(PPh3)2 (5) also undergoes a 1,1-insertion reaction with [NO][SO3CF3] to give the nitrosomethane adduct [mer,trans-Re{N(CH3)O}(CO)3(PPh3)2][SO3CF3] (6) as red crystals in 75% yield. The nitroxyl complex [cis,trans-OsBr(NHO)(CO)2(PPh3)2][SO3CF3] (8) can be similarly prepared as orange crystals in 52% yield by reaction of cis,trans-OsHBr(CO)2(PPh3)2 (7) with [NO][SO3CF3] in cold methylene chloride solution.