Mixed-metal cluster chemistry. 37. Syntheses, structural, spectroscopic, electrochemical, and optical power limiting studies of tetranuclear molybdenum-iridium clusters
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Tetrahedral Mo2Ir2(μ3-CO)(μ-CO)5(CO)4(η5-C5H5)2 (1) reacted with P(C6H4Me-4)3, P(C6H2Me2-3,5-OMe-4)3, and AsPh3 to afford the substitution products Mo2Ir2(μ-CO)3(CO)6(L)(η5-C5H5)2 [L = P(C6H4Me-4)3 (3), P(C6H2Me2-3,5-OMe-4)3 (4), AsPh3 (5)] in fair to good yields, while reaction of 1 with HC≡CSiPri3 proceeded by insertion into the Mo–Mo bond to give the pseudo-octahedral Mo2Ir2(μ4-η2-HC2SiPri3)(μ-CO)4(CO)4(η5-C5H5)2 (6) in fair yield. While MoIr3(μ-CO)3(CO)7(η5-C5H5) reacted with HC≡CSiMe3 to give a complex mixture of thus-far-uncharacterized products, its phosphine substitution product MoIr3(μ-CO)3(CO)5(PPh3)2(η5-C5H5) reacted with the same alkyne via insertion into a Mo–Ir bond to afford the pseudo-octahedral MoIr3(μ4-η2-HC2SiMe3)(μ-CO)3(CO)4(PPh3)2(η5-C5H5) (8) in good yield. Clusters 4, 5 (two isomers), 6 and 8 have been characterized by single-crystal X-ray diffraction studies. Cyclic voltammetric studies of Mo2Ir2(μ-CO)3(CO)6(PPh3)(η5-C5H5)2 (2), 3–6 and 8 confirmed the tuning of redox potentials upon phosphines/arsine introduction and alkyne modification. IR spectroelectrochemical studies of 2, 6, and 8 suggest decreasing proclivity for bridging carbonyl ligands following oxidation. Variable temperature 31P NMR studies of 3 and 4 revealed interconverting isomers in solution, the structures of which are assigned as analogues of the X-ray diffraction-confirmed isomers of 5. Studies of 2–5 using ns pulses and the open-aperture Z-scan technique revealed that all are optical limiters at wavelengths in the visible region.
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