HALIDE AND TERTIARY PHOSPHINE DERIVATIVES OF THE TUNGSTEN(IV) ETA(2)-ACETYL COMPLEX CPW(NCME)(3)(ETA(2)-COME)(2- REVERSIBLE AG+-ASSISTED OPENING OF AN ETA(2)-ACETYL GROUP() )
V. Skagestad et al., HALIDE AND TERTIARY PHOSPHINE DERIVATIVES OF THE TUNGSTEN(IV) ETA(2)-ACETYL COMPLEX CPW(NCME)(3)(ETA(2)-COME)(2- REVERSIBLE AG+-ASSISTED OPENING OF AN ETA(2)-ACETYL GROUP() ), Inorganic chemistry, 34(12), 1995, pp. 3194-3202
The dicationic W(TV) eta(2)-acetyl complex CpW(NCMe)(3)(eta(2)-COMe)(2
+) (1) serves as the precursor for new tungsten(IV) eta(2)-acetyl deri
vatives, Treatment of 1 with halides provided trans-CpW(NCMe)(2)(X)(et
a(2)-COMe)(+) (X = Cl, Br, I) in high yields. The reaction between CpW
(NCMe)(2)(Br)(eta(2)-COMe)(+) and dppe yielded the 5-ring chelate CpW(
eta(2)-dppe)(Br)(eta(2)-COMe)(+), while reactions with monodentate ter
tiary phosphines led to trans-CpW(PR(3))(2)(Br) (eta(2)-COMe)(+) via t
he intermediate CpW(NCMe)(PR(3))(Br) (eta(2)-COMe)(+) (PR(3) = PMePh(2
), PPh(3)). Addition of acetonitrile to a nitromethane solution of CpW
(PPh(3))(2)(Br)(eta(2)-COMe)(+) set up an equilibrium between the subs
trate and CpW(NCMe)(PPh(3))(Br)(eta(2)-COMe)(+). When AgBF4 was added,
this ligand substitution reaction was accelerated. Reversible attachm
ent of Ag+ at the 1 eta(2)-acetyl oxygen, ring opening, and reversible
BF4- binding at the resulting vacant coordination site at W in trans-
CpW(PMePh(2))(2)(Br)(eta(2)-COMe)(+) is suggested on the basis of H-1
and F-19 NMR spectroscopic observations. Similar steps are thought to
be involved in the Ag+-catalyzed ligand substitution reaction. A singl
e-crystal X-ray structure determination of CpW(NCMe)(2)(Br)(eta(2)-COM
e)(+) revealed a four-legged piano stool structure in which the Br and
eta(2)-acetyl ligands are located in a trans relationship and the C-O
bond vector points away from the Cp ligand. Crystal data for 4(BF4-):
space group P (1) over bar, a = 7.782(2) Angstrom, b = 12.277(3) Angs
trom, c = 16.173(4) Angstrom, alpha = 89.48(2)degrees, beta = 88.81(2)
degrees, and gamma = 88.74(2)degrees. Least-squares refinement based o
n 4849 reflections converged to R = 0.056 and R(W) = 0.054.