Mixed-Metal Cluster Chemistry. 11.¹Reactions of Tungsten−Iridium Clusters with Terminal Alkynes and Tungsten Acetylides:  X-ray Crystal Structures of Cp₂W₂Ir₂(μ₄-η²-HC₂Ph)(μ-CO)₄(CO)₄and Cp₂W₂Ir₃(μ₄-η²-C₂C₆H₄Me-4)(μ-CO)(CO)₉

Abstract

Reactions of Cp 2 W 2 Ir 2 (CO) 10 ( 1 ) with terminal arylalkynes HC⋮CR afford the complexes Cp 2 W 2 Ir 2 (μ 4 -η 2 -HC 2 R)(μ-CO) 4 (CO) 4 [R = Ph ( 3 ), C 6 H 4 Me-4 ( 4 ), C 6 H 4 NO 2 -4 ( 5 )] in excellent yields (56−70%). The analogous adduct with the terminal alkylalkyne HC⋮CBu t is obtained in much lower yield (20%). An X-ray structural study of 3 reveals that the alkynes have formally inserted into the W−W bond of 1, affording clusters with a pseudooctahedral geometry. The site of reactivity in 1 is consistent with the lack of reactivity towards terminal alkynes of the isostructural and isolobally related CpWIr 3 (CO) 11 ( 2 ). Reaction of 1 with the buta-1,3-diynyl complex CpW(CO) 3 (C⋮CC⋮CH) ( 8 ) affords the analogous adduct Cp 2 W 2 Ir 2 {μ 4 -η 2 -HC 2 C⋮CW(CO) 3 Cp)(μ-CO) 4 (CO) 4 ( 9 ), shown spectroscopically to be attached via the C⋮CH unit rather than the WC⋮C group. Attempts at condensing the pendant CpW(CO) 3 C⋮C unit with the W 2 Ir 2 core in 9 have proven unsuccessful. Reactions of CpWIr 3 (CO) 11 ( 2 ) with equimolar amounts of the tungsten acetylides CpW(CO) 3 (C⋮CR) (R = Ph, C 6 H 4 Me-4, C 6 H 4 NO 2 -4, C⋮CPh) afford the products Cp 2 W 2 Ir 3 (μ 4 -η 2 -C 2 R)(μ-CO)(CO) 9 [R = Ph ( 11 ), C 6 H 4 Me-4 ( 12 ), C 6 H 4 NO 2 -4 ( 13 ), C⋮CPh ( 14 )] in fair yields (23−45%). Product 12 has been structurally characterized, with the structural study revealing an edge-bridged tetrahedral metal core geometry and an unusual μ 4 -η 2 (3σ + π)-coordinated alkynyl ligand. The reaction corresponds to formal insertion of the alkynyltungsten reagent into an Ir−Ir linkage of 2 . Reactions of 1 with these tungsten acetylides were not successful under the experimental conditions attempted, a result ascribed to steric constraints.