Synthesis of a new oxo-bridged osmium porphyrin carbene complex and its structural characterization

An oxo-bridged osmium porphyrin carbene complex, {[(OEP)Os(CPh2)]2(μ-O)} 1, was prepared from a 1:1 molar ratio of [(OEP)Os(CO)] and Ph2CN2 in refluxing CH2Cl2 or in heating toluene at 50 °C in air. The molecular structure of 1 was confirmed in solution by the 1H NMR spectrum as well as in crystalline state by X-ray diffraction. Under the similar preparative conditions with [(TTP)Os(CO)] gave a mixture of {[(TTP)Os(CPh2)]2(μ-O)} 2 and bis(carbene) complex [(TTP)Os(CPh2)2] 3, but isolation of 3 has been unsuccessful due to its gradual decomposition into 2. The OEP analog of the bis(carbene) complex 3 has not been afforded even by increasing the amount of Ph2CN2 as a carbene source. In 1, the 1H NMR spectrum without any paramagnetic shifted signals and the shorter Os–O bond length [1.8925(3) Å] would imply delocalization of the electrons along the Os–O–Os bonds and the stronger double-bonding character than that in 2, affected by the less steric repulsion between the OEP rings. In 1, the sum of the axial Osdouble bond; length as m-dashC and Os–O bond lengths [3.823(8) Å] is very close to the average value of Os(IV) porphyrins [3.84 Å].