Phenoxyacetylcobalt Tetracarbonyl as Catalyst for Copolymerization of Imines and CO to Produce Polypeptides†

doi:10.7503/cjcu20130435

Abstract

Abstract:

A new phenoxyacetylcobalt tetracarbonyl catalyst was synthesis and used to catalyze alternating copolymerization of imines and CO. ¹H NMR study indicated that this catalyst existed in the form of an equilebium between the aklycobalt and acylcobalt complexes under 1×10⁵ Pa of CO atmosphere. The results obtained using the catalyst in imines and CO copolymerization demonstrates that this catalyst had good performance, producing polypeptides of high molecular weights, with phenoxyacetyl groups at the starting ends of the polymer chains, and of narrow molecular weight distributions. The structures of polypeptide obtained were characterized by ¹H NMR and ¹³C NMR, IR as well as MALDI-TOF MS methods. It is revealed that at the terminal ends of the polymer chains there exist end groups of amide structures in addition to those observed previously. Possible mechanism for the formation of the amide end groups was provided.

Key words: Acylcobalt, Alkylcobalt, Catalyst, Imine, Polypeptide

CLC Number:

O627.8

TrendMD:

ZHANG Yongpo, SUN Huailin. Phenoxyacetylcobalt Tetracarbonyl as Catalyst for Copolymerization of Imines and CO to Produce Polypeptides^†[J]. Chem. J. Chinese Universities, 2014, 35(1): 54.

Figures/Tables 7

Scheme 1 Synthesis of compound 1

Fig.1 1H NMR spectrum of compound 1 under CO

Scheme 2 Copolymerization of imines and CO catalyzed by compound 1

Table 1 Results of copolymerization of imines and CO catalyzed by compound 1

Entry	Imine	n(M)/n(C)^a	Time/h	Yield(%)	Polypeptide	$M n b$	PDI^c
1	(2)	50∶1	24	100	(4)	8701	1.24
2	(2)	100∶1	36	100	(4)	18032	1.25
3	(3)	50∶1	24	100	(5)	8409	1.17
4	(3)	100∶1	48	100	(5)	18856	1.26

Table 1 Results of copolymerization of imines and CO catalyzed by compound 1

Entry	Imine	n(M)/n(C)^a	Time/h	Yield(%)	Polypeptide	$M n b$	PDI^c
1	(2)	50∶1	24	100	(4)	8701	1.24
2	(2)	100∶1	36	100	(4)	18032	1.25
3	(3)	50∶1	24	100	(5)	8409	1.17
4	(3)	100∶1	48	100	(5)	18856	1.26

Fig.2 1H NMR spectra of polypeptide 4 from Entry 1 in Table 1

Fig.3 MALDI-TOF MS spectra of polypeptide sample 5 obtained from Entry 3 in Table 1 and structures A and B(A) Full spectrum; (B) an expansion of the m/z region from 4430 to 4460; (C) structure of A; (D) structure of B. The m/z difference between peaks of the same type of ions with contiguous n values is 141[e.g. the difference between peaks of (B+K+) with n=29 and n=30, Δm/z=4437.5-4296.4=141.1], which just equals the mass of the repeating unit of the polypeptides.

Scheme 3 Possible mechanism for the formation of amide end groups at the terminal ends of the polypeptide chains

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