CHIRAL CHLOROBISMUTHINES STABILIZED BY THE INTRAMOLECULAR COORDINATION OF AN N,N-DIMETHYLAMINO GROUP - X-RAY STRUCTURE-ANALYSIS, ASYMMETRICINDUCTION AT THE BISMUTH CENTER, AND DYNAMIC BEHAVIOR IN SOLUTION
H. Suzuki et al., CHIRAL CHLOROBISMUTHINES STABILIZED BY THE INTRAMOLECULAR COORDINATION OF AN N,N-DIMETHYLAMINO GROUP - X-RAY STRUCTURE-ANALYSIS, ASYMMETRICINDUCTION AT THE BISMUTH CENTER, AND DYNAMIC BEHAVIOR IN SOLUTION, Journal of the Chemical Society. Perkin transactions. I, (23), 1993, pp. 2969-2973
Chiral chlorobismuthines 3 stabilized by intramolecular coordination o
f an NN-dimethylamino group have been synthesized by the selective flu
orodearylation of the bismuthines 1 with boron trifluoride-diethyl eth
er, followed by halogen exchange of the resulting fluorobismuthines 2
with brine. An X-ray crystallographic structure analysis of 3b reveale
d that the bismuth centre has a distorted pseudotrigonal bipyramidal s
tructure through the formation of a hypervalent 3-centre 4-electron bo
nd with the chlorine and nitrogen atoms at apical positions. H-1 NMR s
pectra of compounds 3 in CDCl3 at room temperature reflected their fix
ed conformation in the solid state. Chiral chlorobismuthines 7a and 7b
were obtained in a similar manner starting from optically pure (R)-N,
N-dimethyl-1-phenylethylamine as a mixture of two diastereoisomers (77
:23 and 78:22, respectively), the isomeric ratios of which were not in
fluenced by the equatorial aryl groups present. Variable-temperature d
ynamic H-1 NMR spectra of the diastereoisomeric mixture of 7a provided
important information about its behaviour in solution; in [H-2(8)]tol
uene dynamic but reversible dissociation of intramolecular Bi-N coordi
nation was observed only at elevated temperatures, while in [H-2(6)]-D
MSO it occurred quite easily below room temperature, leading to the in
version of configuration at the chiral bismuth centre.