Chiral metal complexes 36. Stereoselectivity enhanced by N,N′-dimethylation of a chiral N4 tetradentate, including the crystal structure of Δ-α12-{[(N,N′-dimethyl-3R-methyl-1,6-di(2-pyridyl)-2,5-diazahexane)(S-alaninato)]-cobalt(III)} perchlorate

Ronald R. Fenton, Frederick S. Stephens, Robert S. Vagg*, Peter A. Williams

*Corresponding author for this work

Research output: Contribution to journalArticle

13 Citations (Scopus)

Abstract

N,N′-dimethylation of the N4 linear tetradentate R-picpn (3R-methyl-1,6-di(2-pyridyl)-2,5-diazahexane) in DMF in the presence of excess formaldehyde and sodium cyanoborohydride produces, in high yield, R-picpnMe2 (N,N′- dimethyl-3R-methyl-1,6-di(2-pyridyl)-2,5-diazahexane). Reaction of this ligand with cobalt(III) in the presence of excess chloride ion under non-aqueous conditions produces stereospecifically the Δ-cis-α dichloro complex in high yield. The chloride donor atoms undergo replacement by water, nitrite, oxalate or S-alaninate with retention of this stereochemistry. The alaninato complex crystallises in the orthorhombic space group P212121, with a=10.502(3), b=13.623(7), c=18.655(7) Å and Z=4. The structure was refined by least-squares methods to R=0.048 for 2085 diffractometer data collected at -130 °C.The cobalt atom has octahedral coordination with the N4 tetradentate adopting Δ-α topology and with the aminoacidate completing the coordination sphere. The S-ala CoN and CoO bond distances are 1.965(7) and 1.887(6) Å and the CoN(py) and CoN(tert-amine) distances average 1.95(1) and 1.990(7) Å, respectively. This latter bond distance is significantly longer than CoN(sec-amine) distances observed for analogous complexes with cis-β topology. The two geometric isomers which are possible for this asymmetric complex form, defined herein as cis-α1 and cis-α2, are observed to co-crystallise. In the crystal structure the cation shows positional disorder for the methyl substituent on the central link of the tetradentate, and the indicated 2:1 ratio for these isomers is consistent with NMR data.

Original languageEnglish
Pages (from-to)157-164
Number of pages8
JournalInorganica Chimica Acta
Volume201
Issue number2
DOIs
Publication statusPublished - 15 Nov 1992

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