Conformational analysis of coordination compounds. XII. N- and C-Substituted five-membered diamine chelate rings

Abstract

An analysis of the 3JH,H coupling constants for the CH2CH2 segment in the chelate rings formed by N-methylethane-1,2-diamine, and a crystal structure analysis of [Co(NH3)4{(±)-pn}] (S2O6)1.5,H2 (pn, propane-1,2-diamine) have shown that in cobalt(III) five-membered diamine chelate rings the NCCN torsional angle is approximately 51°. For platinum(II) complexes of N-methylethane-1,2- diamine, the 3JH,H technique yielded a value of 52.5° for the NCCN torsional angle. Problems involved with the refinement of the structure prevented the determination of a reliable value of this torsional angle in the crystal structure analysis of [Co(NH3),{(-)-dmbn}] (NO3)3,1.5H2O where dmbn is 3,3-dimethylbutane-1,2-diamine. However, this analysis showed that (-)-dmbn has the (R)-absolute configuration. The 3J H,H values for the CH2CH segment in complexes of dmbn show that the NCCN torsional angle for the dmbn chelates in solution is significantly greater than for the other diamines. The conformer populations for the N-methylethane-1,2-diamine complexes were also determined by the 3JH,H technique. For the tetraamminecobalt(III) and tetracyanocobaltate(III) complexes the mole fractions of the conformer with the methyl group equatorial were found to be 0.92 and 0.78, respectively. For the bipyridineplatinum(II) complex, one conformation was found to be populated exclusively. This was assumed to be the axial conformer because of the unfavourable interaction of the equatorial N-methyl group with the proton on C6 of the 2,2'-bipyridine group. The Jpt, H values for an equatorial C-H proton in square-planar platinum(II) complexes of dmbn show that the t-butyl group is restricted to the equatorial orientation even in this stereochemistry. The conformational-energy minimization technique was applied to the two complexes studied by crystal structure analysis.

Efficient stereochemical regulation of octahedral cobalt(III) complexes by a chiral bidentate ligand. Part 2. Remarkable effect of the chelate-ring size in the stereoselective formation of sym-cis-(ethylenediamine-N,N′-diacetato)(pentane-2,4-diamine)cobalt(III)

“…~~' ~, ' * It has been reported that protons in the CHCH,CH fragment of the 2R,4R-ptn chelate are observed as a A,B2 pattern even for the case in which the contribution of the skew-boat conformation is dominant, although an AA'BB' pattern is expected for this conformation. 18 The present complexes also show an A,B, pattern for these protons. The JAB value is 8.3 Hz for l b and 6.4 Hz for la, respectively.…”

Induction of Chirotopicity in the Self-Assembly Process of Heterocuprates: Structural and Stereochemical Aspects of Neutral CuLi2BrAryl2 Aggregates

“…A Karplus analysis , of the vicinal proton−proton coupling constants within the NCH 2 CH 2 N‘ multiplets of 1 indicates that N,N‘-chelate binding to Li results in a five-membered chelate ring with predominantly (94.2%) λ-conformation (Figure ). The calculated torsion angle (ω) is 58.2°.…”

Molecular mechanics study of the ruffling of metalloporphyrins

“…Several approximations for complexes of transition-metal ions, predominantly in "bonded" MM models that include electron distribution effects, are accordingly found; these range from setting the M-L dipoles to zero and excluding charges to arbitrary choices of parameters. 52,[56][57][58][59]61,[64][65][66][67][68]86 Electrostatic parameters for metalligand interactions will obviously be more critical in the "nonbonded" approach,62 and a recent strategy, in which dynamic adjustment of charge distribution in the M-L bonds during conformational optimization is effected, has improved the reliability of calculations for metal ions in proteins.62 However, it is interesting to note that in several instances there are only minor differences in the results, arising from small variations in, or the neglect of, electrostatic parameters.87-89…”