Studies of the Synthesis and Thermochemistry of Coordinatively Unsaturated Chelate Complexes (η5-C5Me5)IrL2 (L2 = TsNCH2CH2NTs, TsNCH2CO2, CO2CO2)

A comparative synthetic, structural, and thermochemical study on a series of chelate complexes containing the fragment (η5-C5Me5)Ir [(η5-C5Me5)Ir(TsNCH2CH2NTs) (1), (η5-C5Me5)Ir(TsNCH2CO2) (2), (η5-C5Me5)Ir(CO2CO2) (3)] was performed to clarify the roles of carboxylato and sulfonamido ligands. Whereas 1 and 2 are monomeric in solution and in the solid state, 3 appears to exist as an oligomer or polymer, (3)n, which can be broken up by addition of a ligand L such as a phosphine, CO, or 2-methoxypyridine to form (η5-C5Me5)Ir(L)(CO2CO2) (6). The synthesis of (3)n from [(η5-C5Me5)IrCl(μ-Cl)]2 required the use of silver oxalate in CH3CN, but if other solvents were used, the bridging oxalato complex (η5-C5Me5)IrCl(μ-η22-C2O4)ClIr(η5-C5Me5) (7) was obtained and identified by X-ray diffraction. Enthalpies for reaction of THF-soluble monomers 1 and 2 with PMe3 were determined to be −28.7(0.5) and −28.5(0.4) kcal mol-1, respectively. The oligomerization behavior of 3 may be a result of reduced σ- or π-donation of carboxylato ligands compared to N-tosylamido ligands, because the values for νCO in oxalato and bissulfonamido complexes 6−CO and (η5-C5Me5)Ir(CO)(TsNCH2CH2NTs) (4−CO) were 2064 and 2042 cm-1, respectively.