TIME-RESOLVED TRANSIENT DIFFERENCE ABSORPTION-SPECTRA OF IRIDIUM-SILICON BONDED COMPLEXES - EVIDENCE FOR A SOLVATED INTERMEDIATE FORMED VIA IRIDIUM-SILICON BOND-CLEAVAGE

The transient time-resolved difference absorption spectra (100-4000 ns) of two fac-Ir [(6-isopropyl-8 quinolyl) diorganosilyl], complexes (diorgano = dimethyl or phenylmethyl) in nitrogen-saturated toluene have been measured. The spectra indicate that the initial excitation by a pulsed nitrogen laser (10 ns, 337 nm) gives rise to a broad visible absorption characteristic of a quinoyl radical anion as well as bleaching of the ground-state absorption bands due to a-bond-to-ligand charge transfer. Regeneration of the bleaching occurs on the same time scale as the disappearance of transient absorption of the quinolyl radical anion following pulsed excitation of the dimethyl derivative; however, residual bleaching persists for several microseconds following the disappearance of the quinolyl radical anion subsequent to pulsed excitation of the phenylmethyl derivative. The results indicate transient formation of a solvated intermediate due to Ir-Si bond cleavage prior to eventual re-formation of the starting complex in the latter instance.