Recent studies in our laboratory have shown the ability of the monocyclopentadienyl (Cp) monoamidinate (Am) ligand combination to stabilize early transition metal alkyl complexes. The group 4 complexes are shown to be usually stable toward b-hydride elimination, opening up possibilities for probing the mechanistic pathways of selective ethylene oligomerization. The addition of two equivalents of n-butyllithium or n-hexyllithium to (h⁵-C₅Me₅)Zr[N(ⁱPr)C(Me)N(ⁱPr)](Cl₂) (1) affords the bis-alkyl complexes. (h⁵-C₅Me₅)Zr[N(ⁱPr)C(Me)N(ⁱPr)](R₂), R=n-butyl (2a), n-hexyl (2b), thermolyzes slowly at 40ºC to the h⁴-butadiene complexes (h⁵-C₅Me₅)Zr[N(ⁱPr)C(Me)N(ⁱPr)](h⁴-C₄H₅R), R=H (3a), ethyl (3b). However, addition of two equivalents of n-butyllithium to (h⁵-C₅Me₅)Ti[N(ⁱPr)C(Me)N(ⁱPr)](Cl₂) (4) results in the paramagnetic Ti(III) mono-alkyl complex, (h⁵-C₅Me₅)Ti[N(ⁱPr)C(Me)N(ⁱPr)](n-butyl) (5), as determined by ¹H NMR and single-crystal X-ray analysis (Figure 1). This talk will focus on the results of studies aimed at elucidating the stabilities and chemical reactivities of these and other group 4 CpAm n-alkyl complexes and their possible relation to the mechanism of selective ethylene oligomerization.

Figure 1. Molecular structure of (30% thermal ellipsoids) 5.