Mixed-Metal Cluster Chemistry. 21. Synthesis and Crystallographic and Electrochemical Studies of Alkyne-Coordinated Group 6−Iridium Clusters Linked by Phenylenevinylene Groups

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Abstract

The pseudooctahedral monocluster compounds M2Ir2(μ4-η2-R1C2R2)(μ-CO)4(CO)4(η5-C5H4Me)2 (M = Mo, R2 = Ph, R1 = H (12), Ph (13), Me (14); M = W, R2 = Ph, R1 = Me (15); M = Mo, R1 = n-hexyl, R2 = C6H4-4-CHO (16), C6H4-4-CH2P(O)(OEt)2 (17)) have been prepared from reactions between the tetrahedral cluster compounds M2Ir2(CO)10(η5-C5H4Me)2 and the alkynes R1C2R2. Similar reactions between tetrahedral cluster precursors and di- or triynes have afforded the related compounds [M2Ir2(μ-CO)4(CO)4(η5-C5H4R)2]2(μ8-η4-R1C2BC2R1) (R = H, R1 = H, B = 4-C6H4-(E)-CHCH-4-C6H4, M = Mo (18); R = Me, R1 = n-hexyl, B = 4-C6H4, M = Mo (19), W (20); R = Me, R1 = n-hexyl, B = 4-C6H4-(E)-CHCH-4-C6H4, M = Mo (22), W (23); R = Me, R1 = n-hexyl, B = 4-C6H4-(E)-CHCH-4-C6H4-(E)-CHCH-4-C6H4, M = Mo (24); R = Me, R1 = H, B = (CH2)2, M = W (27)), [Mo2Ir2(μ-CO)4(CO)4(η5-C5H4Me)2]3{μ12-η6-1,3,5-C6H3[(E)-CHCHC6H4-4‘-C2(CH2)5Me]3} (25), and W2Ir2(μ4-η2-R1C2R2)(μ-CO)4(CO)4(η5-C5H4Me)2 (R1 = n-hexyl, R2 = 4-C6H4C⋮C(CH2)5Me (21); R1 = H, R2 = (CH2)2C⋮CH (26)). Compounds 18−20 and 22−25 contain two or three cluster units linked by unsaturated bridges, while 27 contains two cluster units linked by a saturated bridge. Compound 22 was prepared in lower yield by coupling 16 and 17 under Emmons−Horner conditions. Structural studies of examples of mono- (15), di- (22), and tricluster (25) compounds have been undertaken. Cyclic voltammetric scans for 12−15, 19, 20, 22−24, 27 and the related cluster W2Ir2(μ4-η2-PhC2Ph)(μ-CO)4(CO)4(η5-C5H4Me)2 (4) have been collected. All compounds show a reversible/partially reversible oxidation, followed by an irreversible oxidation process; potentials for the former increase on replacement of tungsten by molybdenum and alkyne substituent variation Me < H < Ph. UV−vis−near-IR spectroelectrochemical studies of the first oxidation process for 12, 15, and 20 show similar spectral progressions for these mono- and dicluster compounds. The reductive cyclic voltammetric scans for 4, 12−15, 22−24, and 27 all show one irreversible reduction process; compounds 19 and 20, distinguished by possessing the shortest unsaturated bridge, show two reduction processes.

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