Synthesis of [alkenyl(dimethylamino)carbene]tungsten complexes using the peterson reaction: X-ray crystal structure of (EHCO)₅W[C(NMe₂)CH=CH(η-C₅H₄)Fe(η-C₅H₅)]

Treatment of (CO)₅W[C(NMe₂)CH₃] (1) with n-BuLi followed by Me₃SiCl produced (CO)₅W[C-(NMe₂)CH₂SiMe₃] (2) in 90% yield. (CO)₅W[C(NMe₂)CHSiMe₃]Li, which was formed in the reaction between 2 and n-BuLi, reacted with several nonenolizable aldehydes or ketones to afford moderate yields (45-61%) of the desired (alkenylaminocarbene)tungsten complexes (CO)₅W[C(NMe₂)CH—CR¹R²] (3a-f) (a, R¹ = R² = H; b, R¹ = H, R² = Ph; c, R¹ = H, R² = 2-furyl; d, R¹ = H, R² - trans-CH=CHPh; e, R¹ = H, R² = (η-C₅H₄)Fe(η-C₅H₅); f, R¹ = R² = Ph). For compounds 3b-e, exclusive formation of the E isomer occurred. Treatment of 2 with n-BuLi followed by either CF₃S0₃CH₃ or CH₂==CHCH₂Br afforded complexes 4a and 4b (70-90%), (CO)₅W[C(NMe₂)CH(R)SiMe₃] (4a, R = CH₃; 4b, R = CH₂CH=CH₂), respectively. Complexes 4a or 4b could not be obtained by reacting the corresponding complexes 5a or 5b, (CO)₅W-[C(NMe₂)CH₂R] (5a, R = CH₃; 5b, R = CH₂CH=CH₂), with n-BuLi followed by Me₃SiCl. Furthermore, the lithium anions (CO)₅W[C(NMe₂)C(R)SiMe₃]Li (R = CH₃, CH₂CH—CH₂) from 4a or 4b did not react with aldehydes or ketones to afford the desired a-substituted (alkenylaminocarbene)tungsten complexes. One example of such a complex, (CO)₅W[C(NMe₂)C(CH₃)=CH₂] (7), could, however, be prepared in 75-80% yield by treating (CO)₆W[C(OCH₃)C(CH₃)=CH₂] (6) with HNMe₂ in ether. (CO)₅W[C(NMe₂)CHSiMe₃]Li was made to react with PhCOCl to yield the enol silyl ether derivative (CO)₅W[C(NMe₂)CH=C(OSiMe₃)Ph] (8) (26%) along with a trace of an air-sensitive complex (C0)₅W[C(NMe₂)CH₂C(0)Ph) (9). (2S)-(CO)₆W-[C(NMe₂)CH=CH(η-C₅H₄)Fe(η-C₅H₅)] (3e) was further characterized by single-crystal X-ray diffraction methods. Complex 3e crystallizes in the monoclinic space group P2₁/c with (at 20 °C) a = 12.022 (4) Å, b = 12.857 (8) Å, c = 13.826 (8) Å, β= 102.19 (4)°, and D_calcd = 1.88 g cm⁻³ for Z = 4. Least-squares refinement based on 2604 independent observed [F₀≥5σ(F₀)] reflections led to a final conventional R value of 0.044.