Protonation of Fischer-type alkylidyne carbonyltungsten complexes. Structural comparison of alkylidyne and alkylidene metal complexes, including a neutron diffraction study of [W(CHCH 3)Cl 2(CO)(PMe 3) 2

Abstract

Protonation of alkylidyne tungsten complexes of the types [W(CR)Cl(CO)(PMe 3) 3] or [W(CR)Cl(CO)(py)(PMe 3) 2] with HCl affords the η 2-alkylidene tungsten complexes [W(CHR)Cl 2(CO)(PMe 3) 2] ( 7) (R = Me, Et, Ph, p-Tol). Protonation of the complexes [W(CR)X(CO)(CNR′)(PMe 3) 2] with HOSO 2CF 3 or HBF 4 gives the alkylidene complexes [W(CHR)X(CO)(CNR′)(PMe 3) 2][Y] ( 8) (R = Me, R′ = CMe 3, X = Cl, Y = CF 3SO 3, R = Ph, X = Cl; R′ = CMe 3, Y = CF 3SO 3, BF 4; R′ = C 6H 11, Y = BF 4; R′ = C 6H 3Me 2-2,6, Y = CF 3SO 3, R = Ph, R′ = CMe 3, X = I, Y = CF 3SO 3, BF 4). The CH bonds of the alkylidene ligands are easily deprotonated with bases such as pyrrolidinocyclopentene or triethylamine. The solid state structures of [W(CPh)Cl(CO)(CNCMe 3)(PMe 3) 2] ( 5b), [W(CHMe)Cl 2(CO)(PMe 3) 2] ( 7a). [W(CHPh)Cl 2(CO)(PMe 3) 2] ( 7c), and [W(CHPh)Cl(CO)(CNCMe 3)(PMe 3) 2][BF 4] ( 8c) were determined by X-ray crystallography. The structure of 7a was also determined by neutron diffraction. Based on the neutron diffraction data of 7a, and closely matching results from the X-ray diffraction studies, it is found that the η 2-coordination mode of the alkylidene ligands gives rise to almost equal WC(R) and WH bond distances, 1.857(4) and 1.922(6) Å, respectively, in the case of 7a. The length of the alkylidene CH bond in 7a is 1.185(7) Å. The structural comparison of 5b and 8c reveals that the protonation of the alkylidyne ligand causes the WCPh bond to lengthen by less than 0.1 Å and the WCPh angle to bend by about 15°. The major induced structural change, however, may be described as a lateral shift of the CPh group by about 0.6 Å away from the coordination axis defined by the extension of the ClW vector.