Selectivity of the OsHCl(CO)(O2)(PCy3)2 catalyzed hydrogenation of nitrile-butadiene rubber

Abstract

A new homogeneous catalyst precursor has been discovered for the hydrogenation of carbon–carbon unsaturation resident within acrylonitrile–butadiene copolymers. The hydrido‐phosphine complex OsHCl(CO)(O2)(PCy3)2 (1) selectively and quantitatively saturates olefin, leaving the copolymer's nitrile functionality intact. However, the process suffers from an undesirable crosslinking reaction that is not demonstrated by the established rhodium technology. The extent of this crosslinking is dependent on the process conditions and can be minimized by operating with a low catalyst concentration and high H2 pressure. Kinetic studies have identified a previously unknown unexpected influence of olefin on the polymer crosslinking process. In light of this new information, the prevailing mechanism for this class of reactions has been reconsidered. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1618–1626, 2001

Hydrogenation of cis‐1,4‐poly(isoprene) catalyzed by OsHCl(CO)(O2)(PCy3)2

“…Figures 9(a), 9(b), and 9(c) illustrate the effect of catalyst concentration, carbon–carbon double‐bond concentration, and hydrogen pressure on the relative viscosity of HCPIP, respectively. This figure also shows results for OsHCl(CO)(O 2 )(PCy 3 ) 2 on CPIP hydrogenation, as compared with the results of hydrogenation of NBR 23. The relative viscosity of HCPIP is constant with increasing the concentration of catalyst, carbon–carbon double bond, and hydrogen pressure.…”

“…This figure also shows results for OsHCl(CO)(O 2 )(PCy 3 ) 2 on CPIP hydrogenation, as compared with the results of hydrogenation of NBR. 23 The relative viscosity of HCPIP is constant with increasing the concentration of catalyst, carbon-carbon double bond, and hydrogen pressure.…”

Ruthenium and Osmium

“…The styrene that is produced cannot be hydrogenated until this compound is consumed, after which the hydrogenation to ethylbenzene is rapid [117]. The catalyst precursor OsHCl (CO)(g 2 -O 2 )(PCy 3 ) 2 is effective, and more active than RhCl(PPh 3 ) 3 , for the selective hydrogenation of the disubstituted C=C bonds instead of the C:N triple bonds of nitrile-butadiene rubbers at 5-40 bar H 2 , 130 8C in monochlorobenzene [124].…”

Homogeneous Catalytic Hydrogenation of Polymers

“…However, this catalyst is not as effective as Wilkinson's catalyst in suppressing the polymer crosslinking problem, which tends to occur during the later stages of hydrogenation. Although a Michael-type addition mechanism (see Scheme 19.3) was speculated to account for this problem, and there were some signs to support this mechanism (e.g., the hydrogenation of NBR catalyzed by ruthenium-based catalysts in the presence of an amine helped to suppress crosslinking [12]), this mechanism has not been substantiated by definitive experimental results [71]. Because of the high efficiency of the ruthenium catalyst, the catalyst required to realize the hydrogenation is used at a very low level.…”

“…Because of the high efficiency of the ruthenium catalyst, the catalyst required to realize the hydrogenation is used at a very low level. When the amount of each metal is identical, the catalytic activity of the bimetallic complex catalyst system was similar to that of the single rhodium-complex catalyst, containing Scheme 19.3 Michael-type addition mechanism for nitrile butadiene rubber (NBR) crosslinking [71]. Ruthenium-based catalysts have also been used for the hydrogenation of NBR [6-12, 15, 68], polyisoprene [68,69] and PB [68,70].…”