Synthesis, Structure, and Ion Pair Dynamics of β-Diketiminato-Supported Organoscandium Contact Ion Pairs

A rare family of base-free organoscandium alkyl cations stabilized by β-diketiminato ligands (Ar)NC(R)CHC(R)N(Ar) (Ar = 2,6- i Pr-C 6 H 3; R = CH 3 (L Me ), R = t Bu (L t Bu )) has been prepared by reaction of LScR 2 with perfluorinated boranes B(C 6 F 5 ) 3 and (C 12 F 8 )B(C 6 F 5 ). While the L Me ancillary lacked sufficient steric bulk to prevent C 6 F 5 transfer to the metal center, the L t Bu derivatives were quite robust in solution. Although these species were subject to thermal decomposition via metalation of an isopropyl group and loss of RH (Δ S ⧧ = −7.0(7) eu and Δ Η ⧧ = 21.5(2) kcal mol - 1 ), the process was not sufficiently rapid to hinder the development of their rich organometallic chemistry. The solution and solid state structures were studied in detail, revealing the presence of both exo - and endo -MeB(Ar F ) 3 isomers if the metal alkyl was small. Detailed NMR studies (low-temperature EXSY) allowed for observation of both inter- and intramolecular ion pair reorganization processes, whose mechanism is discussed in terms of the involvement of “solvent separated ion pairs”. This is the first such study involving non-metallocenium group 3 metal based ion pairs.