Synthesis and stereochemistry of mono- and di-olefin derivatives of tetrairidium carbonyl clusters

Abstract

The reactions of NEt 4[Ir 4(CO) 11Br] (I) with ethylene, cyclopropene, 5,6-dimethylidene-7-oxabicyclo[2.2.1]hept-2-ene and bicyclo[2.2.1]hept-2-ene in the presence of AgBF 4 gave high yields of Ir 4(CO) 11(olefin) (II-V), in which the olefin is bonded in an axial position on a basal Ir atom. The mono-olefin in II-V is quantitatively displaced by CO giving Ir 4(CO) 12 or by SO 2 giving Ir 4(CO) 11(SO 2). The reaction of I with bicyclo[2.2.1]hepta-2,5-diene, cycloocta-1,5-diene or cyclooctatetraene in the presence of AgBF 4 gave Ir 4(CO) 10(η 4-polyolefin), the first substitution taking place preferentially at an axial site giving Ir 4(CO) 11(η 2-polyolefin), followed by chelation on a radial site of the same metal center. All the above clusters are fluxional at room temperature.