TY - JOUR
T1 - Exploring the Alcohol Stability of Bis(phosphine) Cobalt Dialkyl Precatalysts in Asymmetric Alkene Hydrogenation
AU - Zhong, Hongyu
AU - Friedfeld, Max R.
AU - Camacho-Bunquin, Jeffrey
AU - Sohn, Hyuntae
AU - Yang, Ce
AU - Delferro, Massimiliano
AU - Chirik, Paul J.
N1 - Publisher Copyright:
© 2018 American Chemical Society.
PY - 2019/1/14
Y1 - 2019/1/14
N2 - Cobalt complexes bearing enantiopure, bidentate bis(phosphine) ligands exhibit extraordinary activity and stereoselectivity for the hydrogenation of enamides. Optimal performance was observed in polar protic solvents such as methanol, an industrially preferred green solvent but a medium that is often a poison for reduced Earth abundant metals. The interaction of the low-spin cobalt(II) dialkyl complex, (R,R)-( i Pr-DuPhos)Co(CH 2 SiMe 3 ) 2 , with alcohols including 4-methoxyphenol, pinacol, and CH 3 OH was studied. With the alcohols lacking β-hydrogens, cobalt bis(alkoxide) complexes were isolated and structurally characterized. With methanol, protonolysis of the alkyl ligands was again observed followed by dehydrogenation of the alcohol and [(R,R)-( i Pr-DuPhos)Co] 2 (μ-CO) 2 was isolated. Both solid-state and solution EXAFS studies were conducted to establish the spectroscopic signatures of bis(phosphine) cobalt(II) and cobalt(0) complexes relevant to catalytic hydrogenation and also to probe the role of phosphine dissociation in methanol.
AB - Cobalt complexes bearing enantiopure, bidentate bis(phosphine) ligands exhibit extraordinary activity and stereoselectivity for the hydrogenation of enamides. Optimal performance was observed in polar protic solvents such as methanol, an industrially preferred green solvent but a medium that is often a poison for reduced Earth abundant metals. The interaction of the low-spin cobalt(II) dialkyl complex, (R,R)-( i Pr-DuPhos)Co(CH 2 SiMe 3 ) 2 , with alcohols including 4-methoxyphenol, pinacol, and CH 3 OH was studied. With the alcohols lacking β-hydrogens, cobalt bis(alkoxide) complexes were isolated and structurally characterized. With methanol, protonolysis of the alkyl ligands was again observed followed by dehydrogenation of the alcohol and [(R,R)-( i Pr-DuPhos)Co] 2 (μ-CO) 2 was isolated. Both solid-state and solution EXAFS studies were conducted to establish the spectroscopic signatures of bis(phosphine) cobalt(II) and cobalt(0) complexes relevant to catalytic hydrogenation and also to probe the role of phosphine dissociation in methanol.
UR - http://www.scopus.com/inward/record.url?scp=85059907947&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85059907947&partnerID=8YFLogxK
U2 - 10.1021/acs.organomet.8b00516
DO - 10.1021/acs.organomet.8b00516
M3 - Article
AN - SCOPUS:85059907947
SN - 0276-7333
VL - 38
SP - 149
EP - 156
JO - Organometallics
JF - Organometallics
IS - 1
ER -