34664-50-1Relevant academic research and scientific papers
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 Reactivity of Tris(Hydroxymethyl)Phosphine-Mimicking Nonsymmetrical Diphosphine Ligands
Nijland, Aike,Van Zutphen, Steven,Carmichael, Duncan
, p. 720 - 724 (2016/01/15)
As part of a study to obtain well-defined tris(hydroxymethyl)phosphine (THP)-inspired ligands, a new nonsymmetrical diphosphine featuring two hydroxymethyl functional groups on one phosphine terminus has been synthesized. A double formylation reaction was employed to effect the hydroxymethylation of the primary phosphine function in Ph2P(CH2)2PH2 and furnish the target bis(hydroxymethyl)phosphanylethyldiphenylphosphine. Initially, this methodology afforded complex product mixtures whose composition varied according to the reaction solvent, and these are assumed to result from acetalization of excess formaldehyde by the hydroxymethyl groups of the anticipated phosphine. The desired target could be obtained via a borane protection - deprotection pathway or by repeatedly treating the product mixture with H2O, thereby probably shifting a hemiacetal equilibrium of the phosphine with formaldehyde towards the free hydroxymethyl functionalities.
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
supporting information, 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.
Allosteric effects in asymmetric hydrogenation catalysis? Asymmetric induction as a function of the substrate and the backbone flexibility of C 1-symmetric diphosphines in rhodium-catalysed hydrogenations
Baber, Angharad,De Vries, Johannes G.,Orpen, A. Guy,Pringle, Paul G.,Von Der Luehe, Karl
, p. 4821 - 4828 (2007/10/03)
The new unsymmetrical, optically active ligands 1,2-C2H 4(PPh2)(2′R,5′R-2′,5′- dimethylphospholanyl) (La) and 1,3-C3H 6(PPh2)(2′R,5′R-2′,5′- dimethylphospholanyl) (Lb) form complexes of the type [Rh(L)(cyclooctadiene)][BF4] where L = La (1a) or L b (1b), [PtCl2(L)] where L = La (2a) or L b (2b) and [PdCl2(L)] where L = La (3a) or Lb (3b). The crystal structures of 2a and 2b show the chelate ligand backbones adopt δ-twist and flattened chair conformations respectively. Asymmetric hydrogenation of enamides and dehydroaminoesters using 1a and 1b as catalysts show that the ethylene-backboned diphosphine La gives a more efficient catalyst in terms of asymmetric induction than the propylene-backboned analogue Lb. The greatest enantioselectivities were obtained with 1a and enamide substrates with ees up to 91%. Substrate-induced conformational changes in the Rh-diphosphine chelates are proposed to explain some of the ees observed in the hydrogenation of enamides. The Royal Society of Chemistry 2006.
