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

The pseudooctahedral monocluster compounds M 2 Ir 2 (μ 4 -η 2 -R 1 C 2 R 2 )(μ-CO) 4 (CO) 4 (η 5 -C 5 H 4 Me) 2 (M = Mo, R 2 = Ph, R 1 = H ( 12 ), Ph ( 13 ), Me ( 14 ); M = W, R 2 = Ph, R 1 = Me ( 15 ); M = Mo, R 1 = n -hexyl, R 2 = C 6 H 4 -4-CHO ( 16 ), C 6 H 4 -4-CH 2 P(O)(OEt) 2 ( 17 )) have been prepared from reactions between the tetrahedral cluster compounds M 2 Ir 2 (CO) 10 (η 5 -C 5 H 4 Me) 2 and the alkynes R 1 C 2 R 2 . Similar reactions between tetrahedral cluster precursors and di- or triynes have afforded the related compounds [M 2 Ir 2 (μ-CO) 4 (CO) 4 (η 5 -C 5 H 4 R) 2 ] 2 (μ 8 -η 4 -R 1 C 2 BC 2 R 1 ) (R = H, R 1 = H, B = 4-C 6 H 4 -( E )-CH CH-4-C 6 H 4, M = Mo ( 18 ); R = Me, R 1 = n -hexyl, B = 4-C 6 H 4, M = Mo ( 19 ), W ( 20 ); R = Me, R 1 = n -hexyl, B = 4-C 6 H 4 -( E )-CH CH-4-C 6 H 4, M = Mo ( 22 ), W ( 23 ); R = Me, R 1 = n -hexyl, B = 4-C 6 H 4 -( E )-CH CH-4-C 6 H 4 -( E )-CH CH-4-C 6 H 4, M = Mo ( 24 ); R = Me, R 1 = H, B = (CH 2 ) 2, M = W ( 27 )), [Mo 2 Ir 2 (μ-CO) 4 (CO) 4 (η 5 -C 5 H 4 Me) 2 ] 3 {μ 12 -η 6 -1,3,5-C 6 H 3 [( E )-CH CHC 6 H 4 -4‘-C 2 (CH 2 ) 5 Me] 3 } ( 25 ), and W 2 Ir 2 (μ 4 -η 2 -R 1 C 2 R 2 )(μ-CO) 4 (CO) 4 (η 5 -C 5 H 4 Me) 2 (R 1 = n -hexyl, R 2 = 4-C 6 H 4 C⋮C(CH 2 ) 5 Me ( 21 ); R 1 = H, R 2 = (CH 2 ) 2 C⋮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 W 2 Ir 2 (μ 4 -η 2 -PhC 2 Ph)(μ-CO) 4 (CO) 4 (η 5 -C 5 H 4 Me) 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.