Studies of the synthesis and thermochemistry of coordinatively unsaturated chelate complexes (η5-C5Me5)IrL2 (L2 = TsNCH2CH2NTS, TsNCH2CO2, CO2CO2)

Article abstract of DOI:10.1021/ic990870l

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-η²-η²-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 v(CO) in oxalato and bissulfonamido complexes 6-CO and (η⁵-C₅Me₅)Ir(CO)(TsNCH₂CH₂NTs) (4-CO) were 2064 and 2042 cm^-1, respectively.