Halocarbonyltungsten(II) Complexes Containing Tripodal Tris(pyrazolyl)borate Ligands
dataset
posted on 1998-02-24, 00:00 authored by Charles G. Young, Simon Thomas, Robert W. GableThe halo tricarbonyl complexes LWX(CO)3 (X = I,
Br, Cl) are formed when
NEt4[LW(CO)3] is reacted with
I2,
N-bromosuccinimide, and N-chlorosuccinimide (or
PhICl2), respectively, while reaction of
NEt4[LPrW(CO)3] and
I2 yields LPrWI(CO)3 [L
= hydrotris(3,5-dimethylpyrazol-1-yl)borate,
LPr =
hydrotris(3-isopropylpyrazol-1-yl)borate]. Reaction of
NEt4[LW(CO)3] with Br2
yields mixtures of LWBr(CO)3 and
LBrWBr(CO)3 [LBr =
hydrotris(4-bromo-3,5-dimethylpyrazol-1-yl)borate] as a result of
competitive bromination of both tungsten and ligand L.
The complexes generally exhibit three ν(CO) bands, one at
ca. 2025 cm-1 and two between 1930 and 1900
cm-1,
and NMR spectra consistent with fluxional carbonyl-capped octahedral
(Cs) structures. Crystals of
LPrWI(CO)3·MeOH are orthorhombic, space group Pbca, with a
= 11.779(2) Å, b = 15.975(4) Å, c
= 29.476(3) Å, and V
= 5547(2) Å3 for Z = 8. The
seven-coordinate complex exhibits a 3:3:1 carbonyl-capped octahedral
structure.
In hot acetonitrile or tetrahydrofuran, the tricarbonyl complexes
are converted into brown, paramagnetic (μeff
ca.
1.15 μB) dicarbonyl species, LWX(CO)2 and
LBrWBr(CO)2, which exhibit two
ν(CO) bands (ca. 1930 and 1840
cm-1) and isotropically shifted NMR spectra
consistent with a mononuclear structure with
Cs symmetry.
Further
decarbonylation of LBrWBr(CO)2 in
refluxing acetonitrile results in the formation of
LBrWBr(MeCN-κ2N,C)(CO), which crystallizes in monoclinic space group
C2/c, with a = 22.245(4) Å,
b = 19.077(4) Å, c =
15.639(3)
Å, β = 128.61(2)°, and V = 5286(2)
Å3 for Z = 8. The seven-coordinate
complex features a “side-on” bonded,
four-electron-donor acetonitrile ligand and a completely 4-brominated
LBr ligand.
