PHOTOCHEMISTRY OF THE LUMINESCENT ALKYL COMPLEXES (TRIARYLPHOSPHINE)(MALEONITRILEDITHIOLATO)IRIDIUM, IRR(CO)(PAR3)(2)(MNT)

A series of luminescent alkyl complexes of formula IrR(CO)L(2)(mnt), w here mnt = maleonitriledithiolate, R = Me, Et, Pr, and CH2CN, and L is a triarylphosphine, have been synthesized and characterized. The comp lexes possess octahedral coordination geometries with the phosphine li gands in mutually trans positions, as confirmed by a crystal structure determination of the methyl derivative. Crystal data for IrMe(CO)(PPh (3))(2)(mnt): IrS2P2ON2C42H33, triclinic space group P (1) over bar, a = 13.178(4) Angstrom, b = 13.670(4) Angstrom, c = 12.592(2) Angstrom, alpha = 105.03(2)degrees, beta = 115.42(2)degrees, gamma = 95.72(2)de grees, V = 1919.9 A(3); Z = 2, 6298 reflections (h, +/-k, +/-l, 4 degr ees < 2 theta < 45 degrees), R(1) = 0.020, R(2) = 0.028, and GOF = 1.0 9. The Ir-S distances of 2,442(1) and 2.371(1) Angstrom reflect the st ructural influence of the trans ligands (Me and CO, respectively). The alkyl complexes luminesce in fluid solution with an emission energy i n the range of 695-780 nm and a band shape that suggests vibronic stru cture characteristic of other mnt complexes. Photolysis of IrMe-(CO)(P Ph(3))(2)(mnt) in the presence of H-atom sources and radical traps lea ds to products consistent with Ir-alkyl bond homolysis. Further photoc hemical studies in the presence of (CO)-C-13 suggest that Ir-Me bond h omolysis is favored strongly over CO photodissociation. Photochemistry of IrR(CO) (PPh(3))(2)(mnt), where R contains beta-hydrogens, produce s only the beta-elimination products of olefin and the hydride complex IrH(CO)(PPh(3))(2)(mnt) even in the presence of large excesses of pho sphine, CO, or different radical trapping agents. The quantum yield fo r photochemical beta-elimination of 0.30 is much greater than that det ermined for photochemical disappearance of IrMe(CO)L(2)(mnt) and is co nsistent with an efficient H-atom transfer from R to *Ir(CO)L(2)(mnt) within the radical pair generated by photolysis.