Synthesis and Electrochemical Studies of Cobalt(III) Monohydride Complexes Containing Pendant Amines

详细信息    查看全文

• 作者：Eric S. Wiedner ; John A. S. Roberts ; William G. Dougherty ; W. Scott Kassel ; Daniel L. DuBois ; R. Morris Bullock
• 刊名：Inorganic Chemistry
• 出版年：2013
• 出版时间：September 3, 2013
• 年：2013
• 卷：52
• 期：17
• 页码：9975-9988
• 全文大小：545K
• 年卷期：v.52,no.17(September 3, 2013)
• ISSN：1520-510X

文摘

Two new tetraphosphine ligands, PnC-PPh22NPh2 (1,5-diphenyl-3,7-bis((diphenylphosphino)alkyl)-1,5-diaza-3,7-diphosphacyclooctane; alkyl = (CH2)2, n = 2 (L2); (CH2)3, n = 3 (L3)), have been synthesized. Coordination of these ligands to cobalt affords the complexes [CoII(L2)(CH3CN)]2+ and [CoII(L3)(CH3CN)]2+, which are reduced by KC8 to afford [CoI(L2)(CH3CN)]+ and [CoI(L3)(CH3CN)]+. Protonation of the CoI complexes affords [HCoIII(L2)(CH3CN)]2+ and [HCoIII(L3)(CH3CN)]2+. The cyclic voltammetry of [HCoIII(L2)(CH3CN)]2+, analyzed using digital simulation, is consistent with an ErCrEr reduction mechanism involving reversible acetonitrile dissociation from [HCoII(L2)(CH3CN)]+ and resulting in formation of HCoI(L2). Reduction of HCoIII also results in cleavage of the H鈥揅o bond from HCoII or HCoI, leading to formation of the CoI complex [CoI(L2)(CH3CN)]+. Under voltammetric conditions, the reduced cobalt hydride reacts with a protic solvent impurity to generate H2 in a monometallic process involving two electrons per cobalt. In contrast, under bulk electrolysis conditions, H2 formation requires only one reducing equivalent per [HCoIII(L2)(CH3CN)]2+, indicating a bimetallic route wherein two cobalt hydride complexes react to form 2 equiv of [CoI(L2)(CH3CN)]+ and 1 equiv of H2. These results indicate that both HCoII and HCoI can be formed under electrocatalytic conditions and should be considered as potential catalytic intermediates.