34664-50-1Relevant articles and documents
Homogeneous Hydrogenation with a Cobalt/Tetraphosphine Catalyst: A Superior Hydride Donor for Polar Double Bonds and N-Heteroarenes
Duan, Ya-Nan,Du, Xiaoyong,Cui, Zhikai,Zeng, Yiqun,Liu, Yufeng,Yang, Tilong,Wen, Jialin,Zhang, Xumu
supporting information, p. 20424 - 20433 (2019/12/27)
The development of catalysts based on earth abundant metals in place of noble metals is becoming a central topic of catalysis. We herein report a cobalt/tetraphosphine complex-catalyzed homogeneous hydrogenation of polar unsaturated compounds using an air- and moisture-stable and scalable precatalyst. By activation with potassium hydroxide, this cobalt system shows both high efficiency (up to 24 000 TON and 12 000 h-1 TOF) and excellent chemoselectivities with various aldehydes, ketones, imines, and even N-heteroarenes. The preference for 1,2-reduction over 1,4-reduction makes this method an efficient way to prepare allylic alcohols and amines. Meanwhile, efficient hydrogenation of the challenging N-heteroarenes is also furnished with excellent functional group tolerance. Mechanistic studies and control experiments demonstrated that a CoIH complex functions as a strong hydride donor in the catalytic cycle. Each cobalt intermediate on the catalytic cycle was characterized, and a plausible outer-sphere mechanism was proposed. Noteworthy, external inorganic base plays multiple roles in this reaction and functions in almost every step of the catalytic cycle.
Synthesis and electrochemical studies of cobalt(III) monohydride complexes containing pendant amines
Wiedner, Eric S.,Roberts, John A. S.,Dougherty, William G.,Kassel, W. Scott,Dubois, Daniel L.,Bullock, R. Morris
, p. 9975 - 9988 (2013/09/23)
Two new tetraphosphine ligands, P nC-PPh2 2N Ph2 (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 [Co II(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 [HCo III(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-Co 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 [Co I(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.
