C. Elschenbroich et al., Metal complexes of heteroarenes. 11. eta(6)-coordination of arsenine to titanium, vanadium, and chromium, ORGANOMETAL, 18(8), 1999, pp. 1495-1503
By means of metal-ligand vapor co-condensation techniques the homoleptic ar
senine sandwich complexes (eta(6)-C5H5As)(2)Ti (2), (eta(6)-C5H5As)(2)V (3)
, and (eta(6)-C5H5As)(2)Cr (4) have been prepared. 2 is the first example o
f an unsubstituted group 15 heteroarene sandwich complex which yielded to f
ull structural characterization by X-ray diffraction. The most remarkable f
eature of the structure of 2 in the crystal is the synperiplanar conformati
on and the short intramolecular interannular As As distances which imply se
condary bonding. The latter may also contribute to the packing since intera
nnular As As distances, which fall short of the sum of the van der Waals ra
dii, are detected. The result of a competition experiment, in which benzene
and arsenine are offered as ligands to chromium, illustrate the pronounced
preference of chromium for arsenine as an eta(6) ligand. The mixed-ligand
complexes (eta(6)-C5H5As)(eta(6)-C6H6)Cr (6) and (eta(6)-C5H5As)Cr(CO)(3) (
8) have also been prepared and studied spectroscopically in order to underp
in the notion that arsenine, compared to benzene, is the superior eta(6) li
gand. The study is rounded off by an investigation of the redox behavior of
2, 3, 4, and 6 (cyclic voltammetry) and by EPR measurements on 3(.) and 4(
.+). The latter confirm the pronounced pi-acceptor character of eta(6)-arse
nince. This conclusion is based on the increase of the hyperfine coupling c
onstant a(V-51) upon going from bis(benzene)vanadium to the arsenine counte
rpart which is thought to reflect V(d(z)2) orbital contraction in 3(.), cau
sed by a slight increase of positive partial charge on vanadium.