Mixed-Metal Cluster Chemistry. 16. Syntheses of Oligourethanes Containing Clusters in the Backbone

Bis(hydroxyalkylcyclopentadienyl)-containing mixed molybdenum−iridium clusters Mo 2 Ir 2 (CO) 10 { η -C 5 H 4 (CH 2 ) x OH} 2 [ x = 2 ( 1 ), 10] react with alkyl or aryl 1, ω -diisocyanates OCNRNCO [R = (CH 2 ) y ( y = 4, 6, 12), trans- 1,4-cyclohexyl, or 4-C 6 H 4 CH 2 -4-C 6 H 4 ] 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 Mo 2 Ir 2 (CO) 10 { η -C 5 H 4 (CH 2 ) 2 OC(O)NHRH} 2 [R = (CH 2 ) 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 (CH 2 ) x, suggesting that the steric influence of the bulky dimolybdenum−diiridium cluster core and co-ligands is the most important factor governing extent of polymerization. Supporting this assessment, the considerably more sterically hindered precursor 2-butyn-1,4-diol-substituted cluster Mo 2 Ir 2 { μ 4 - η 2 -C 2 (CH 2 OH) 2 }(CO) 8 ( η -C 5 H 5 ) 2 fails to react to any significant extent with 1,6-diisocyanatohexane.