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-iPr-C6H3; R = CH3 (LMe), R = tBu (LtBu)) has been prepared
by reaction of LScR2 with perfluorinated boranes B(C6F5)3 and (C12F8)B(C6F5). While the
LMe ancillary lacked sufficient steric bulk to prevent C6F5 transfer to the metal center, the
LtBu derivatives were quite robust in solution. Although these species were subject to thermal
decomposition via metalation of an isopropyl group and loss of RH (ΔS⧧ = −7.0(7) eu and
ΔΗ⧧ = 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(ArF)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.