Mechanistic studies of the copolymerization reaction of aziridines and carbon monoxide to produce poly-beta-peptoids.
The coupling of carbon monoxide and aziridines has been shown to be selective for comonomer-alternating enchainment in the presence of PhCH2C(O)Co(CO)4 to afford poly-beta-peptoids. In this article, we have investigated the mechanistic aspects of the reaction of CO and N-butylaziridine by means of in situ infrared spectroscopy employing CH3C(O)Co(CO)3L (L = PPh3 (1) and P(o-tolyl)3 (2)) as precatalysts. Precatalyst 1 exists in solution under catalytic conditions as an equilibrium mixture of 1 and CH3C(O)Co(CO)4, and affords both poly-beta-butylalanoid and the corresponding lactam. By way of contrast, precatalyst 2 which possesses the sterically bulky and labile P(o-tolyl)3 ligand, affords only the acyl cobalt tetracarbonyl species in solution during catalysis with concomitant selective production of the copolymer. Kinetic studies conducted with precatalyst 2 showed the coupling reaction to have a first order dependence on catalyst, a first order dependence on N-butylaziridine, and only a slight dependence on the concentration of CO over the pressure range 17-69 bar. The working mechanistic model for the copolymerization reaction involves first aziridine insertion into the cobalt-acyl bond, rate determining ring opening by the cobaltate species, followed by the migratory CO insertion.
Darensbourg
Donald J
DJ
Department of Chemistry, Texas A&M University, College Station, Texas 77843, USA. djdarens@mail.chem.tamu.edu
Phelps
Andrea L
AL
Gall
Nathalie Le
NL
Jia
Li
L
D001388:Aziridines / Q000737:chemistry*; D040761:Biomimetic Materials / Q000138:chemical synthesis / Q000737:chemistry; D002248:Carbon Monoxide / Q000737:chemistry*; D002384:Catalysis; D003035:Cobalt / Q000737:chemistry; D018360:Crystallography, X-Ray; D007700:Kinetics; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry; D034444:Peptoids / Q000138:chemical synthesis* / Q000737:chemistry; D013055:Spectrophotometry, Infrared
D001388:Aziridines; D009942:Organometallic Compounds; D034444:Peptoids; D003035:Cobalt; D002248:Carbon Monoxide