Efficient catalytic alkyne metathesis with a fluoroalkoxy-supported ditungsten(III) complex

The molybdenum and tungsten complexes M(2)(OR)(6) (Mo2F6, M = Mo, R = C(CF(3))(2)Me; W2F3, M = W, R = OC(CF(3))Me(2)) were synthesized as bimetallic congeners of the highly active alkyne metathesis catalysts [MesC≡M{OC(CF(3))(n)Me(3−)(n)}] (MoF6, M = Mo, n = 2; WF3, M = W, n = 1; Mes = 2,4,6-trimethylphenyl). The corresponding benzylidyne complex [PhC≡W{OC(CF(3))Me(2)}] (W(Ph)F3) was prepared by cleaving the W≡W bond in W2F3 with 1-phenyl-1-propyne. The catalytic alkyne metathesis activity of these metal complexes was determined in the self-metathesis, ring-closing alkyne metathesis and cross-metathesis of internal and terminal alkynes, revealing an almost equally high metathesis activity for the bimetallic tungsten complex W2F3 and the alkylidyne complex W(Ph)F3. In contrast, Mo2F6 displayed no significant activity in alkyne metathesis.