Mixed-Metal Cluster Chemistry. 16.1 Syntheses of Oligourethanes Containing Clusters in the Backbone

Bis(hydroxyalkylcyclopentadienyl)-containing mixed molybdenum−iridium clusters Mo2Ir2(CO)10{η-C5H4(CH2)xOH}2 [x = 2 (1), 10] react with alkyl or aryl 1,ω-diisocyanates OCNRNCO [R = (CH2)y (y = 4, 6, 12), trans-1,4-cyclohexyl, or 4-C6H4CH2-4-C6H4] to form oligourethanes with transition metal clusters in the oligomer backbone. Characterization of the cluster-containing oligourethanes is aided by spectral comparison with model cluster diurethanes Mo2Ir2(CO)10{η-C5H4(CH2)2OC(O)NHRH}2 [R = (CH2)y [y = 4 (6), 6, 12], trans-1,4-cyclohexyl] prepared from reaction between the cluster diol 1 and alkyl isocyanates HRNCO. The precursor diol cluster 1 and cluster diurethane 6 have been characterized by single-crystal X-ray diffraction studies. The extent of polymerization has been assessed by gel permeation chromatography, with little dependence on diisocyanate precursor linker R but strong dependence on alkylcyclopentadienyl linker length (CH2)x, suggesting that the steric influence of the bulky dimolybdenum−diiridiu...