Activation of H2 by halocarbonyl bis-phosphine and bis-arsine iridium(I) complexes. The use of parahydrogen induced polarisation to detect species present at low concentration and investigate their reactivity

Article abstract of DOI:10.1039/b107444j

The iridium phosphine complexes Ir(CO)Cl(L)₂ [L = PPh₃, PMe₃, AsPh₃ and PPh₂Cl, and L₂ = (PPh₂Cl)(PPh₃)] add H₂ to form the corresponding dihydrides IrH₂(CO)Cl(L)₂. These products are detected at enhanced levels of sensitivity through the ¹H NMR signatures of their hydride resonances via para-hydrogen (p-H₂) based spin state synthesis. Products corresponding to addition across both the Cl-Ir-CO and L-Ir-L axes are detected. For L = PPh₃, there is a 100 fold preference for the former pathway at 295 K, while for L = AsPh₃ the second product is favoured by a factor of 2.85. At elevated temperatures a third product corresponding to addition over the Cl-Ir-L axis is detected for L = AsPh₃ and PPh₂Cl. Under these conditions, the CO and HCl transfer products Ir(H)₃(CO)₂(AsPh₃), and IrH(CO)Cl₂(AsPh₃)₂ are also formed in a thermal reaction. When IrH₂(CO)Cl(L)₂ is warmed or photolysed with H₂ and CO, the corresponding products are produced for L = PPh₃ and PMe₃. However after photolysis with H₂ alone Ir(H)₃(CO)(L)₂ is the favoured product. Additional products detected during the photochemical studies include Ir(H)₂(PPh)₃(PPh₂C₅H₄ CO), an unusual orthometallation product containing an η²-acyl ligand, and the binuclear products H(Cl)Ir(PMe₃)₂(μ-H)(μ-Cl)Ir(PMe₃)(CO) and (H)₂Ir(PMe₃)₂(μ-Cl)₂Ir(PMe) ₃(CO).