The crystal structure of [Ni(dmf)6][NiCl4] and comments on the hydrolysis of coordinated amides and peptides in metal complexes

Robert W. Hay*, Sabine Albedyhl, Philip Lightfoot

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

14 Citations (Scopus)

Abstract

Solutions of nickel(II) chloride in N,N-dimethylformamide (DMF) in the presence of Et2O slowly give blue-green crystals of [Ni(dmf)6][NiCl4] whose structure has been confirmed by X-ray crystallography. The complex crystallises with three crystallographically distinct [Ni(dmf)6]2+ cations in the asymmetric unit, Ni(1) on a general position and Ni(2) and Ni(3) on centres of symmetry. There are also two unique [NiCl4]2- anions, both on general positions. N,N-Dimethylformamide is O-bonded to nickel as coordination via nitrogen would cause the loss of the resonance energy of the amide group. All Ni-O bond lengths are within the expected range for such complexes [2.029(4)-2.084(4) Å]. The C=O bond lengths, which range from 1.219(7) to 1.259(7) Å, are not significantly different from those for uncomplexed dmf (1.232 ± 0.004 Å), suggesting that there is very little polarisation of the C=O bond by nickel(II). Oxygen-bonded dmf undergoes rapid hydrolysis in metal complexes, for example the base hydrolysis of [Co(NH3)5dmf]3+ to give the formato complex is some 104-fold faster than that of the free ligand. Copper(II)-catalysed amide and peptide bond hydrolysis is subject to ca. 106-fold rate enhancements. The origin of these rate enhancements, which appear to be due to transition state effects rather than ground state effects, is discussed in detail.

Original languageEnglish
Pages (from-to)257-260
Number of pages4
JournalTransition Metal Chemistry
Volume23
Issue number3
DOIs
Publication statusPublished - 1 Jan 1998

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