Pentamethylcyclopentadienyl halo- and alkyl-alkoxo tantalum(V) complexes. Crystal structure of taCp*(CH2SiMe3) 2{η2-O(2-CH2-6-MeC6H3)}

Article abstract of DOI:10.1016/0022-328X(95)06004-G

Reaction of TaCp*Cl₄ with MOR (M = Li, Na) in different molar ratios gives halo alkoxides TaCp*Cl_n(OR)_4-n (n = 3: R = ^tBu 1; SiPh₃ 2; 2,6-Me₂C₆H₃ 3; n = 2: R = ^tBu 4; SiPh₃ 5; 2,6-Me₂C₆H₃ 6; n = 1: R = SiMe₃ 7) in good yields. The alkylidene complex TaCp*(CH₂SiMe₃)₂(CHSiMe₃) is hydrolyzed in the presence of traces of water to give the oxo dialkyl derivative [TaCp*(CH₂SiMe₃)₂O]_n 8, and reacts with 1 equivalent of 2,6-Me₂C₆H₃NC affording a new η²-iminoacyl compound TaCp*(CH₂SiMe₃)(CHSiMe₃){η²-C(CH₂SiMe₃)=N(2,6-Me₂C₆H₃)} 9. Reactions of TaCp*(CH₂SiMe₃)₂(CHSiMe₃) with 1 equivalent of C₆H₅OH and 4-MeC₆H₃(OH)₂ result in the formation of the alkyl phenoxo TaCp*(CH₂SiMe₃)₃(OC₆H₅) 10 and 4-methyl pyrocatecholate TaCp*(CH₂SiMe₃)₂(O₂C₆H₃Me) 11, whereas the related reaction with 2,6-Me₂C₆H₃OH leads to the cyclic alkyl-alkoxo compound TaCp*(CH₂SiMe₃)₂{η²-O(2-CH₂-6-MeC₆H₃)} 12. All the complexes were characterized by IR and NMR (¹H and ¹³C) spectroscopy. The crystal and molecular structure of 12 has been determined. Crystals of 12 are triclinic, space group P1 with Z = 2 in a unit cell of dimensions a = 9.151(5) A, b = 11.835(5) A, c = 14.045(4) A, α = 89.35(3)°, β = 72.34(3)° and γ = 88.51(4)°, V = 1449(1) A³. Final values of R = 0.025 and Rw = 0.0655 were obtained from 5547 reflections measured (5070, > 2σ(I)).