Accelerated Ligand Metalation in a β-Diketiminato Scandium Dimethyl Complex Activated with Bis(pentafluorophenyl)borane

Equimolar reactions of LScMe2 (L = (Ar)NC(tBu)CHC(tBu)N(Ar); Ar = 2,6-iPr2-C6H3) and
HB(C6F5)2 proceed through an isolable ion pair 2 to a metalated scandium borate 3 with loss of methane.
Multinuclear NMR experiments confirm the proposed structure, which was also verified by synthesis via
alternative routes and derivatization. Deuterium labeling studies offer insight into the mechanism of
methane loss, which occurs through C−H activation of an abstracted methide rather than the direct
intramolecular metalation commonly observed for β-diketiminato scandium alkyl complexes. A large
primary kinetic isotope effect of kH/kD = 8.7(6) was observed for the decomposition of 2, which
corroborates the proposed mechanism while also implicating a highly reactive four-membered scandocycle
intermediate, LSc((H)CH2B(C6F5)2). Reaction of 2 equiv of HB(C6F5)2 with LScR2 yields μ2-hydridoborate
complexes [LScCH3][(μ-H)2B(C6F5)2] (5), while 4 equiv of borane react to afford the bis-μ2-hydridoborate
complex [LSc][(μ-H)2B(C6F5)2]2, 6.