71265-76-4Relevant academic research and scientific papers
New sandwich complexes containing 6,6-dimethylcyclohexadienyl (dmCh): (dmCh)2M (M = Ti, V, Cr, Fe) and (dmCh)2M-CO (M = Ti, V)
DiMauro, Peter T.,Wolczanski, Peter T.
, p. 1947 - 1954 (1987)
Deprotonation of 5,5-dimethylcyclohexadiene ((dmCh)H) with KO-t-Bu/n-BuLi afforded potassium 6,6-dimethylcyclohexadienyl (K(dmCh)). Treatment of MCln(THF)m with n equiv of K(dmCh) afforded the new sandwich complexes (dmCh)2M (M = Ti (1), V (2), Cr (3), Fe (5)) in moderate yield (35-68%). The Ti and Fe complexes are diamagnetic, while 2 and 3 possess one and two unpaired electrons. When exposed to CO, 1 and 2 formed the monocarbonyl adducts (dmCh)2M-CO (M = Ti (6), V (7)); EPR spectra of thermally unstable (dmCh)2V-PMe3 (8) and (dmCh)2V-PF3 (10) and NMR evidence for (dmCh)2Ti-PF3 (9) were also obtained. While Ch2Fe (11, Ch = η5-C6H7) could be prepared from FeCl2 and LiCh, generated via LDA and 1,4-C6H8 (-78°C), this procedure was not general. The isomerization of 11 to (η6-C6H6)-Fe(η4-1,3-C 6H8) (12), concomitant with Fe0, was also noted. The expected C2v symmetry of 6 was confirmed via an X-ray crystallographic investigation. Crystal data: monoclinic, P21./n, a = 7.372 (1) A?, b = 9.900 (1) A?, c = 22.101 (3) A?, β = 105.100 (8)°, Z = 4, T = 25°C. Standard refinement procedures yielded an R of 0.074 and Rw = 0.076 from 1356 reflections where |Fo| ≥ 3σ(Fo). The structures, bonding, and stability of 1-10 are discussed in relation to Cp and pentadienyl analogues.
