ANIONIC MU-IMIDO COMPLEXES OF IRIDIUM(I) - SYNTHESIS AND SPECTROSCOPIC CHARACTERIZATION

The bridging amido ligands in Ir-2[mu-NH(p-tolyl)](2)(CO)4, 1, undergo deprotonation by 'BuLi in a stepwise manner. The first deprotonation product is a monoanionic mu-amido/mu-imido complex of formula LiIr2[mu -NH(p-tolyl)][mu-N(p-tolyl)](CO)(4).2THF, 2, which shows three CO band s in the IR, similar to the pattern observed for 1. However, the bands are shifted to lower energy by an average of similar to 50 cm(-1). Th e second deprotonation step produces a dianionic bis(mu-imido) complex , Li2Ir2[mu-N(p-tolyl)](2)(CO)4.3THF, 3, in which the CO bands are shi fted by another 25 cm(-1)(average). The high solubility of the ionic c omplexes in hydrocarbon solvents, coupled with the number of THF molec ules available for each lithium ion, suggests strong cation-anion inte raction, most likely at the imido nitrogens. Variable-temperature NMR studies have detected the formation of aggregates in solution for 2. C omplex 3 possesses two inequivalent lithium ions that produce separate Li-7 signals at temperatures below 0 degrees C but produce an average signal around room temperature. The THF molecules in 2 and 3 can be d isplaced by 12-Crown-4 to give complexes 2.Crown and 3.Crown, in which the lithium ions are encapsulated by the crown ether. The reaction of 3 with (PPh(3))AuCl generates a tetranuclear complex, [(CO)(2)Ir(mu-N (p-tolyl))Au(PPh(3))](2), 4.