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Stereochemical Analysis of Cobalt( III ) Complexes with Tridentate Imino‐ and Amino‐Oxime Ligands
Author(s) -
Calligaris Mario,
Randaccio Lucio
Publication year - 2002
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/1099-0682(200211)2002:11<2920::aid-ejic2920>3.0.co;2-4
Subject(s) - chemistry , oxime , diastereomer , stereochemistry , bond length , chirality (physics) , cobalt , crystallography , molecular geometry , medicinal chemistry , crystal structure , molecule , inorganic chemistry , organic chemistry , nambu–jona lasinio model , chiral symmetry breaking , physics , quantum mechanics , quark
The stereochemistry of a new class of models of the vitamin B 12 system, containing tridentate pyridyl‐imino‐oxime [C 6 H 5 N(CH 2 ) n NC(CH 3 )C(CH 3 )NO − ; n = 1, L 1 ; n = 2, L 2 ] and pyridyl‐amino‐oxime [C 6 H 5 N(CH 2 ) n NHCH(CH 3 )C(CH 3 )NO − ; n = 1, L 3 ; n = 2, L 4 ] ligands, has been investigated through molecular mechanics calculations based on a specific force field. It is shown that, among all the possible diastereomers of the imino complexes [Co(L 1,2 ) 2 ] + , the minimum strain energy is exhibited in a mer configuration. For the amino complexes [Co(L 3,4 )(HL 3,4 )] 2+ , the minimum is exhibited in a fac configuration, with the amino nitrogen atoms all having the same chirality, opposite to that of the adjacent carbon atoms. Furthermore, comparison of the effect of five‐ (L 1 , L 3 ) or six‐membered (L 2 , L 4 ) chelate rings on the complexes indicates that the strain energy decreases upon passing from L 1 to L 2 complexes, while it increases upon passing from L 3 to L 4 complexes. The effect of rotation around the axial pyridyl Co−N bond on the coordination geometry has also been studied through a conformational analysis of the methyl (R = Me) and adamantyl (R = Adam) organocobalt derivatives [RCo(L 4 )(HL 4 )] + . The most important result is that the rotation is rather hindered in the case of the bulky Adam group, while in the Me case the pyridyl group can rotate across a wide angular range. In both cases, the rotation causes a significant change in the Co−N bond length, while the Co−C distance is almost unaffected. It is also shown that the aromatic base is oriented with respect to the equatorial ligand in a fashion quite different from other B 12 models. (© Wiley‐VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)