Synthesis and reaction chemistry of the heterobimetallic FeIr complexes (CO)3(PPh3)Fe(μ-PCy2)Ir(PPh3)(CO)2 and (CO)4Fe(μ-PCy2)Ir(1,5-COD)

Reactions of Li[Fe(CO)4(PCy2)] with trans-IrCl(CO)(PPh3)2 and [IrCl(1,5-COD)]2 (COD = cyclooctadiene) results in the formation of the μ-PCy2 bridged complexes (CO)3(PPh3)Fe(μ-PCy2)Ir(PPh3)(CO)2, 1, and (CO)4Fe(μ-PCy2)Ir(1,5-COD), 2, respectively. 1 is coordinatively saturated with an FeIr dative bond and does not form an adduct with CO or undergo oxidative addition with H2, HCl, or CH3I. The protonation of 1 with HBF4 gives the Ir hydride compound [(CO)3(PPh3)Fe(μ-PCy2)Ir(H)(PPh3)(CO)][BF4]. 1 undergoes phosphine substitution reactions in which PPh3 is replaced by PR3. Substitution is at Ir for PEt3, PnBu3, PiPr3, PBz3, and PCy3, at Fe for PMe2Ph, and at both metal centers for PPh2Me. The substitution pattern is selective and appears to be sterically controlled. There is also evidence for cooperativity between metal centers in the formation of the PPh2Me adduct since only the disubstituted product can be detected. Coordinative unsaturation was generated at the Ir centre by thermally induced CO loss from (CO)3(PPh3)Fe(μ-PCy2)Ir(PCy3)(CO)2 to give (CO)3(PPh3)Fe(μ-PCy2)Ir(PCy3)(CO). The reaction of 2 with excess CO(g) resulted in the formation of the carbonyl species (CO)4Fe(μ-PCy2)Ir(CO)3. 2 also reacts with 2 PEt3 or DPPE (DPPE = 1,2-bis(diphenylphosphino)ethane) under CO(g) to give the disubstituted products (CO)3(PEt3)Fe(μ-PCy2)Ir(PEt3)(CO)2 and (CO)3Fe(μ-PCy2)(μ-DPPE)Ir(CO)2 with loss of 1,5-COD. Keywords: heterobimetallic FeIr complexes, cooperativity, phosphido-bridge.