Core Expansion Reactions of Cyanamido/Carbodiimido-Bridged Polynuclear Iridium Complexes

Core expansion reactions of di- and tetrairidium complexes [Cp*Ir(μ2-NCN-N,N)]2 (1; Cp* = η5-C5Me5), [Cp*Ir(μ3-NCN-N,N,N)]4 (2), and phosphine derivatives of 1 have been investigated, and it has been revealed that cyanamido ligands in these complexes can change their coordination modes flexibly on reactions with a second transition metal complex. Treatment of diiridium complex 1 with [Cp*IrCl2]2 gives the tetrairidium complex [(Cp*Ir)2(μ3-NCN-N,N,N′)2(IrCp*Cl2)2] (6) with μ3-κN,κN,κN′ cyanoimido(2-) ligands. On the other hand, the reaction of 1 with [PdCl(η3-C3H5)]2 affords the NCN-bridged Ir2Pd4 hexanuclear complex [(Cp*IrCl)2(μ4-NCN-N,N,N′,N′)2{Pd2(μ-Cl)(η3-C3H5)2}2] (7) and Ir4Pd4 octanuclear complex [(Cp*Ir)4(μ4-NCN-N,N,N,N′)4{PdCl(η3-C3H5)}4] (8). The NCN-bridges in 7 provide the first example of the crystallographically determined μ4-κN,κN,κN′,κN′ carbodiimido(2-) ligand. Complex 8 with μ4-κN,κN,κN,κN′ cyanoimido(2-) ligands can also be synthesized selectively by the reaction of the parent cubane complex 2 with [PdCl(η3-C3H5)]2. Diphosphine derivative of 1, [{Cp*Ir(μ2-NCN)}2(μ-dppm)] (4; dppm = Ph2PCH2PPh2), behaves differently on reactions with [PdCl(η3-C3H5)]2 and [MCl(cod)]2 (cod = cycloocta-1,5-diene) to form the NCN-bridged Ir2M2 (M = Pd, Rh, Ir) tetranuclear complexes [(Cp*Ir)2(μ3-NCN-N,N,N′)2{PdCl(η3-C3H5)}2(μ-dppm)] (9) and [(Cp*Ir)2(μ3-NCN-N,N,N′)2{MCl(cod)}2(μ-dppm)] (11a, M = Rh; 11b, M = Ir), respectively. The molecular structures for 6, 7, 8, 11a, and 11b have been determined by single-crystal X-ray analyses.