Photochemistry of the luminescent alkyl complexes alkyl(carbonyl)bis(triarylphosphine)(maleonitrile-dithiolato)iridium, IrR(CO)(PAr3)2(mnt)

Article abstract of DOI:10.1021/ja00086a019

A series of luminescent alkyl complexes of formula IrR(CO)L₂(mnt), where mnt = maleonitriledithiolate, R = Me, Et, Pr, and CH₂CN, and L is a triarylphosphine, have been synthesized and characterized. The complexes posses 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)(PPh₃)₂(mnt): IrS₂P₂ON₂C₄₂H₃₃, triclinic space group P1, a = 13.178(4) A, b = 13.670(4) A, c = 12.592(2) A, a = 105.03(2)°, β = 115.42(2)°, γ = 95.72(2)°, V = 1919.9 A³; Z = 2, 6298 reflections (h, ±k, ±l, 4° < 26 < 45°), R₁ = 0.020, R₂ = 0.028, and GOF = 1.09. The Ir-S distances of 2.442(1) and 2.371(1) A 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) (PPh₃)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 ¹³CO suggest that Ir-Me bond homolysis is favored strongly over CO photodissociation. Photochemistry of IrR(CO)(PPh₃)₂(mnt), where R contains β-hydrogens, produces only the β-elimination products of olefin and the hydride complex IrH(CO)(PPh₃)₂(mnt) even in the presence of large excesses of phosphine, CO, or different radical trapping agents. The quantum yield for photochemical β-elimination of 0.30 is much greater than that determined for photochemical disappearance of IrMe(CO)L₂(mnt) and is consistent with an efficient H-atom transfer from R to Ir(CO)L₂(mnt) within the radical pair generated by photolysis.