Well-defined imidotitanium alkyl cations: agostic interactions, migratory insertion vs.[2+2] cycloaddition, and the first structurally authenticated AlMe3 adduct of any transition metal alkyl cation

The imidotitanium alkyl cations [Ti(NtBu)(Me3[9]aneN3)R]+(R = Me (3+) or CH2SiMe3(4+)) possess either a very weak (alpha)-agostic or (beta)-Si–C agostic interactions, respectively, according to 13C and 29Si NMR and DFT studies; reaction of 4+ with iPrNCNiPr gives totally selective insertion into the Ti–alkyl bond; reaction of 3+ with AlMe3 gives the first structurally characterised AlMe3 adduct of a transition metal alkyl cation (Me3[9]aneN3= 1,4,7trimethyltriazacyclononane).