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 η²-alkylidene tungsten complexes [W(CHR)Cl₂(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)Cl₂-(CO)(PMe₃)₂] (7a), [W(CHPh)Cl₂(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 η²-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.