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

A series of luminescent alkyl complexes of formula IrR(CO)L(2)(mnt), where mnt = maleonitriledithiolate, R = Me, Et, Pr, and CH2CN, and L is a triarylphosphine, have been synthesized and characterized. The complexes possess octahedral coordination geometries with the phosphine ligands 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)degrees, V = 1919.9 A(3); Z = 2, 6298 reflections (h, +/-k, +/-l, 4 degrees < 2 theta < 45 degrees), R(1) = 0.020, R(2) = 0.028, and GOF = 1.09. The Ir-S distances of 2,442(1) and 2.371(1) Angstrom reflect the structural influence of the trans ligands (Me and CO, respectively). The alkyl complexes luminesce in fluid solution with an emission energy in the range of 695-780 nm and a band shape that suggests vibronic structure characteristic of other mnt complexes. Photolysis of IrMe-(CO)(PPh(3))(2)(mnt) in the presence of H-atom sources and radical traps leads to products consistent with Ir-alkyl bond homolysis. Further photochemical studies in the presence of (CO)-C-13 suggest that Ir-Me bond homolysis is favored strongly over CO photodissociation. Photochemistry of IrR(CO) (PPh(3))(2)(mnt), where R contains beta-hydrogens, produces 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 phosphine, CO, or different radical trapping agents. The quantum yield for photochemical beta-elimination of 0.30 is much greater than that determined for photochemical disappearance of IrMe(CO)L(2)(mnt) and is consistent with an efficient H-atom transfer from R* to *Ir(CO)L(2)(mnt) within the radical pair generated by photolysis.