Mechanistic Studies of the Copolymerization Reaction of Aziridines and Carbon Monoxide to Produce Poly-β-peptoids

Abstract

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.

Cobalt‐Catalyzed Carbonylation of N‐Alkylbenzaldimines to ‘N‐Alkylphthalimidines’ (= 2,3‐Dihydro‐1H‐isoindol‐1‐ones) via Tandem CH Activation and Cyclocarbonylation

“…Analogous to that proposed by Jia and co-workers [16], the initial step of the reaction is likely to be nucleophilic attack of the benzaldimine on the Co-acyl functionality to generate a cobaltate species. In the case of Jia's copolymerization of N-alkylaziridines with CO, ring opening of N-alkylaziridine relieves steric strain and leads to a new Co-alkyl species and eventual copolymer formation (see Scheme 3 above).…”

“…(D 8 )-1,4-Dioxane (Aldrich) and C 6 A C H T U N G T R E N N U N G D 6 (Aldrich) were dried over molecular sieves (Aldrich) [30]. The complex [Co( 13 CH 3 C(O))(CO) 3 A C H T U N G T R E N N U N G (P(o-tol) 3 )] 1 ) was synthesized from [NaCo(CO) 4 ], tris(o-tolyl)-phosphine (P(o-tol) 3 ; Strem), and 13 CH 3 I (Aldrich) according to literature procedures [16]. The aldimines were synthesized according to published procedures [31] by condensation of the appropriate aldehydes and amines, dried over CaH 2 (Acros) and purified by solvent removal (when necessary), followed by distillation.…”

Cobalt‐Catalyzed Carbonylative Copolymerization of N‐Alkylazetidines and Tetrahydrofuran

“…The synthesis of catalyst 1 was previously reported. [6] THF was refluxed over Na/benzophenone and freshly distilled.…”

“…The formation of g-LA did not annihilate the living character of the polymerization. Therefore, we tentatively attribute the formation of g-LA to a process intrinsically coupled to the polymerization, most likely "backbiting" [6] as opposed to catalyst decomposition.…”

Synthesis and Structural Characterization of Bis(aziridine) Cobalt(II), Zinc(II) and Palladium(II) Complexes

“…The reactive nature of aziridine compounds is mainly due to Baeyer [7] and Pitzer ring strain which results in ring opening reactions if protonation of the amino group or any nucleophilic attack on the ring occurs. Therefore, aziridines offer a great variety of synthetic applications in organic chemistry, for example, as synthons in natural product synthesis [8,9], monomers in macromolecular chemistry [10,11], or biologically important target molecules [12 -14].…”