Mixed-metal cluster chemistry.: 11.: Reactions of tungsten-iridium clusters with terminal alkynes and tungsten acetylides:: X-ray crystal structures of Cp2W2Ir2(μ4-η2-HC2Ph)(μ-CO)4(CO)4 and CP2W2Ir3(μ4-η2-C2C6H4Me-4)(μ-CO)(CO)9

Reactions of Cp2W2Ir2(CO)(10) (1) with terminal arylalkynes HC=CR afford the complexes Cp2W2Ir2(mu(4)-eta(2)-HC2R)(mu-CO)(4)(CO)(4) [R = Ph (3), C6H4Me-4 (4), C6H4NO2-4 (5)] in excellent yields (56-70%). The analogous adduct with the terminal alkylalkyne HC=CBut 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 CpWIr3(CO)(11) (2). Reaction of 1 with the buta-1,3-diynyl complex CpW(CO)(3)(C=CC=CH) (8) affords the analogous adduct Cp2W2Ir2{mu(4)-eta(2)-HC2C=CW(CO)(3)CP)(mu-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 W2Ir2 core in 9 have proven unsuccessful. Reactions of CpWIr3(CO)(11) (2) with equimolar amounts of the tungsten acetylides CpW(CO)(3)(C=CR) (R =Ph, C6H4Me-4, C6H4NO2-4, C=CPh) afford the products Cp2W2Ir3(mu(4)-eta(2)-C2R)(mu-CO)(CO)(9) [R = Ph (11), C6H4Me-4, (12), C6H4NO2-4 (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 mu(4)-eta(2) (3 sigma + pi)-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.