Oxidative addition of H-R (H - Ph and H2) to trans-Ir( - Ph)(CO)(PPh3)2 (2) gives the initial products, cis, cis-Ir(H)( - Ph)2(CO)(PPh3)2 (3a) and cis, cis-Ir(H)2( - Ph)(CO)(PPh3)2 (3b), respectively. Both cis-bis(PPh3) complexes, 3a and 3b undergo isomerization to give the trans-bis(PPh3) complexes, trans, trans-Ir(H)( - Ph)2(CO)(PPh3)2 (4a) and cis, trans-Ir(H)2( - Ph)(CO)(PPh3)2 (4b). The isomerization, 3b→4b is first order with respect to 3b with k1=6.37×10-4 s-1 at 25°C under N2 in CDCl3. The reaction rate (k1) seems independent of the concentration of H2. A large negative entropy of activation (ΔS≠=-24.9±5.7 cal deg-1 mol-1) and a relatively small enthalpy of activation (ΔH≠=14.5±3.3 kcal mol-1) were obtained in the temperature range 15~35°C for the isomerization, 3b→4b under 1 atm of H2.
Bibliographical noteFunding Information:
We wish to thank the Korea Science and Engineering Foundation (Grant No. 97-05-01-05-01-3) and the Korean Ministry of Education (Grant No. BSRI-97-3412) for their financial supports of this study.
All Science Journal Classification (ASJC) codes
- Physical and Theoretical Chemistry
- Inorganic Chemistry
- Materials Chemistry