Generation and reactivity of Cp*W(NO)(CH2SiMe3)H, a 16-valence-electron alkyl hydride complex

Article abstract of DOI:10.1021/om00005a061

Treatment of solutions of Cp*W(NO)(CH₂SiMe₃)₂ with H₂ generates in situ the reactive 16-valence-electron alkyl hydride Cp*W(NO)(CH₂SiMe₃)H, formed by hydrogenolysis of one of the W-C σ-bonds of the dialkyl reactant. The Lewis-acidic hydride complex has not yet been isolated, but its existence has been inferred on the basis of the varied chemical reactions that it undergoes when generated in the presence of reactive substrates. PPh₃ affords the orthometalated complex Cp*W(NO)(H)(PPh₂C₆H₄) as a yellow crystalline solid probably via the 18-electron adduct Cp*W(NO)(CH₂SiMe₃)(PPh₃)H. Consistently, the same reaction effected with PPh₃-d₁₅ results in complete deuteration of the hydride position in the product. Acyclic, conjugated dienes such as butadiene or 2,3-dimethyl-1,3-butadiene afford Cp*W-(NO)(η⁴-trans-diene) complexes. The characteristic chemistry of Cp*W(NO)(CH₂SiMe₃)H is, however, dominated by the ability of its W-H link to insert unsaturated linkages, the regioselectivity of the insertions indicating that the hydride ligand is hydridic in nature. For instance, insertion of acetonitrile affords the ethylideneamido complex Cp*W(NO)(CH₂SiMe₃)(N=CHMe), which is isolable as a diastereomeric pair. Similarly, insertions of organic reagents containing carbonyl (O=C) or imine (HN=C) functional groups produce the corresponding alkyl alkoxide or alkyl amide products, respectively, in virtually quantitative yields. Phenylacetylene affords the novel alkyl alkenyl compound Cp*W(NO)(CH₂SiMe₃)(CPh=CH₂), which is thermally unstable and isolable in only low yields. Insertions into the W-H bond by other olefinic substrates are successful only if the unsaturated hydrocarbon also contains a Lewis-base functional group. Thus, propargylamine and allylamine produce the related metallacyclic complexes Cp*W(NO)(CH₂SiMe₃)(NH₂CH₂CHCH) and Cp*W(NO)(CH₂SiMe₃)(NH₂CH ₂CH₂CH₂), respectively. Treatment of Cp*W(NO)(CH₂SiMe₃)₂ with H₂ in the presence of allyl alcohol does not produce an oxometallacycle, but rather affords the allylalkoxo complex resulting from the alcohol simply functioning as a protonic acid toward the dialkyl reactant. The solid-state molecular structures of Cp*W(NO)(CH₂SiMe₃)(N=CHMe) and Cp*W(NO)(CH₂SiMe₃)(NH₂CH ₂CH₂CH₂) have been established by single-crystal X-ray crystallographic analyses. Crystals of Cp*W(NO)(CH₂SiMe₃)(N=CHMe) are monoclinic of space group P2₁/n: a = 9.515(2) A?; b = 21.946(3) A?; c = 9.552(2) A?; Z = 4; V = 1946.8 A?³; T = 200 K; R_f = 0.029 for 2035 data (I_o ≥ 2.5σ(I_o)) and 106 variables. Crystals of Cp*W(NO)(CH₂SiMe₃)(NH₂CH ₂CH₂CH₂) are orthorhombic of space group P2₁2₁2₁: a = 11.417(4) A?; b = 13.178(2) A?; c = 13.804(4) A?; Z = 4; V = 2076.9 A?³; T = 200 K; R_f = 0.020 for 2420 data (I_o ≥ 2.5σ(I_o)) and 208 variables.