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Flexibility and lability of a phenyl ligand in hetero-organometallic 3d metal-Sn(IV) compounds and their catalytic activity in Baeyer–Villiger oxidation of cyclohexanone

Abstract

The single compartmental Schiff base N,N-ethylenebis(salicylaldimine) (H2L) and [SnPh2Cl2] were utilized to synthesize heterobimetallic 3d-Sn complexes, the CoIIISnIV compound [{SnPhCl2}(1O2N2,2O2--L)(-OMe){CoPh}] (1), the NiIISnIV compound [{SnPh2Cl2}(1O2N2,2O2--L)Ni] (2) and the CuIISnIV compound [{SnPh2Cl2}(1O2N2,2O2--L)Cu] (3). Attempting to prepare the ethoxido bridged compound analogous to 1 (in ethanol) gives the phenylcobalt(III) complex [Co(O2N2)Ph(H2O)] (1A). Single crystal X-ray structure analyses reveal that 1 is derived from an intermetallic (Sn to Co) phenyl shift and that 1A is a transmetallated product; in compounds 2 and 3, the phenyl groups remain coordinated to SnIV but one of them  interacts with the 3d-metal. Thus, while systems 1 and 1A show the lability of the phenyl ligand, 2 and 3 reveal its flexible nature. Theoretical DFT calculations demonstrate that the Ph group shift conceivable occurs in the oxidized CoIII intermediate [{SnIVPh2Cl2}(O2N2--L){CoIII(MeO)}] (5) rather than in the corresponding CoII species [{SnIVPh2Cl2}(O2N2--L){CoII(MeOH)}] (4). Their catalytic studies in Baeyer–Villiger oxidation of cyclohexanone into ɛ-caprolactone with two different oxidants reveals that the sacrificial aldehyde method (with dioxygen/benzaldehyde) is better than that with aqueous H2O2 (30%). The effects of various reaction parameters such as solvent, catalyst amount, temperature, time and heating method were studied allowing to achieve yields up to 83 % with 89 % selectivity.

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Publication details

The article was received on 12 Jul 2017, accepted on 03 Aug 2017 and first published on 03 Aug 2017


Article type: Paper
DOI: 10.1039/C7DT02534C
Citation: Dalton Trans., 2017, Accepted Manuscript
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    Flexibility and lability of a phenyl ligand in hetero-organometallic 3d metal-Sn(IV) compounds and their catalytic activity in Baeyer–Villiger oxidation of cyclohexanone

    S. Hazra, N. M. R. Martins, M. L. Kuznetsov, M. F. C. Guedes da Silva and A. J. L. Pombeiro, Dalton Trans., 2017, Accepted Manuscript , DOI: 10.1039/C7DT02534C

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