Phosphoraneiminato tungsten alkylidyne complexes as highly efficient alkyne metathesis catalysts

The tungsten neopentylidyne complexes [Me3CCtriple bond; length of mdashW(NPR3){OCMe(CF3)2}2] (3a, R = Cy; 3b, R = iPr) were prepared in excellent yields by the reaction of the solvate complex [Me3CCtriple bond; length of mdashW{OCMe(CF3)2}3(DME)] (DME = 1,2-dimethoxyethane) with equimolar amounts of the corresponding phosphoraneiminato lithium species R3PNLi (R = Cy, iPr) at room temperature. The products were characterized by 1H, 13C{1H}, 19F{1H} and 31P{1H} NMR spectroscopy and elemental analysis. Single crystals of both complexes were obtained from diethyl ether solutions at −35 °C, and the molecular structures were determined by X-ray diffraction analysis. Complexes 3a and 3b are able to efficiently catalyse alkyne cross-metathesis (ACM) of 3-pentynyl benzyl ether (4) and ring-closing alkyne metathesis (RCAM) of bis(3-pentynyl)adipate (6) at room temperature and with low catalyst loadings (1 or 2 mol%) to afford the diether 5 and the cyclic diester 7 in virtually quantitative yields. The reactions were carried out in the presence of molecular sieve 5 Å to adsorb 2-butyne during the metathesis.