Phosphoraneiminato tungsten alkylidyne complexes as highly efficient alkyne metathesis catalysts

Abstract

The tungsten neopentylidyne complexes [Me 3CC W(NPR 3){OCMe(CF 3) 2} 2] ( 3a, R = Cy; 3b, R = iPr) were prepared in excellent yields by the reaction of the solvate complex [Me 3CC W{OCMe(CF 3) 2} 3(DME)] (DME = 1,2-dimethoxyethane) with equimolar amounts of the corresponding phosphoraneiminato lithium species R 3PNLi (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.