Protonation of Fischer-type alkylidyne carbonyltungsten complexes.: Structural comparison of alkylidyne and alkylidene metal complexes, including a neutron diffraction study of [W(CHCH3)Cl2(CO)(PMe3)2]

Protonation of alkylidyne tungsten complexes of the types [W(CR)Cl(CO)(PMe3)(3)] or [W(CR)Cl(CO)(py)(PMe3)(2)] with HCl affords the eta(2)-alkylidene tungsten complexes [W(CHR)Cl-2(CO)(PMe3)(2)] (7) (R=Me, Et, Ph, p-Tol). Protonation of the complexes [W(CR)X(CO) (CNR') (PMe3)(2)] with HOSO2CF3 or HBF4 gives the alkylidene complexes [W(CHR)X(CO) (CNR') (PMe3)(2)] [Y] (8) (R=Me, R'=CMe3, X=Cl, Y=CF3SO3. R=Ph, X=Cl; R'=CMe3, Y=CF3SO3, BF4; R'=C6H11, Y=BF4; R'=C6H3Me2-2,6, Y = CF3SO3. R = Ph, R' = CMe3, X = I, Y = CF3SO3, BF4). 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) (CNCMe3) (PMe3)(2)] (5b), [W(CHMe)Cl-2-(CO) (PMe3)(2)] (7a), [W(CHPh)Cl-2(CO) (PMe3)(2)] (7c), and [W(CHPh)Cl(CO) (CNCMe3) (PMe3)(2)] [ BF4] (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 eta(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) Angstrom, respectively, in the case of 7a. The length of the alkylidene C-H bond in 7a is 1.185(7) Angstrom. 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 Angstrom and the W-C-Ph angle to bend by about 15 degrees. The major induced structural change, however, may be described as a lateral shift of the CPh group by about 0.6 Angstrom away from the coordination axis defined by the extension of the Cl-W vector. (C) 1998 Elsevier Science S.A. All rights reserved.