Starting from
CpVCl2(PMe3)2 (1)
the paramagnetic mono- and bis(phenylethynyl)
complexes
CpVCl2
-
n
(C⋮CPh)
n
(PMe3)2
[n = 1 (2), 2 (3)] have been
synthesized. Both compounds were
characterized by X-ray diffraction and were found to be thermally more
stable than other
CpVIII hydrocarbyl complexes. The CpVIII
bis(phenyl) complex
CpVPh2(PMe3)2 (5)
decomposes
at ambient temperature through β-hydrogen abstraction to give the
first isolated vanadium
benzyne complex,
CpV(η2-C6H4)(PMe3)2
(6). The molecular structure of 6 indicates
that this
compound can best be described as a high-spin d2
vanadium(III) benzometallacyclopropene.
The cyclopropene character is expressed in the reactivity of
6, showing insertion of
unsaturated substrates. Insertion of diphenylacetylene gives
CpV(η2-PhCCPhC6H4)(PMe3)2
(7), with a planar vanadaindene structure, whereas terminal
alkenes CH2CRR‘ (R = H,
Me; R‘ = H, Me) insert regioselectively to give β-substituted
metallaindanes
CpV(η2-CH2CRR‘C6H4)PMe3 (R and R‘ = H,
8a; R = H, R‘ = Me, 8b; R and R‘ = Me,
8c), which show a
low thermal stability in case one of the β-substituents is a
hydrogen. With t-BuCN double
insertion followed by rearrangement of the intermediate
diazametallacycle gives the
isoindolenine-substituted vanadium(III) imido complex
CpV[NC(t-Bu)N=C(t-Bu)C6H4](PMe3)2
(9). The benzyne complex 6 reacts with
dihydrogen to form the known triple-decker
CpV(C6H6)VCp through partial hydrogenation
of the benzyne ligand.
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