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 reactivityBased on the presentation given at Dalton Discussion No. 4, 10–13th January 2002, Kloster Banz, Germany.

The iridium phosphine complexes Ir(CO)Cl(L)(2) [L = PPh3, PMe3, AsPh3 and PPh2Cl, and L-2 = (PPh2Cl)(PPh3)] add H-2 to form the corresponding dihydrides IrH2(CO)Cl(L)(2). These products are detected at enhanced levels of sensitivity through the H-1 NMR signatures of their hydride resonances via para-hydrogen (p-H-2) 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)Cl-2(AsPh3), are also formed in a thermal reaction. When IrH2(CO)Cl(L)(2) is warmed or photolysed with H-2 and CO, the corresponding products are produced for L = PPh3 and PMe3. However after photolysis with H-2 alone Ir(H)(3)(CO)(L)(2) is the favoured product. Additional products detected during the photochemical studies include Ir(H)(2)(PPh3)(PPh2C5H4CO), an unusual orthometallation product containing an eta(2)-acyl ligand, and the binuclear products H(Cl)Ir(PMe3)(2)(mu-H)(mu-Cl)Ir(PMe3)(CO) and (H)(2)Ir(PMe3)(2)(mu-Cl)(2)Ir(PMe3)(CO).