Syntheses of Heteroleptic Amidinate Strontium Complexes Using a Superbulky Ligand

Strontium complexes are presented with two different bulky amidinate ligands (Am): <i>t</i>BuC­(N<i>-</i>DIPP)<sub>2</sub> (DIPP = 2,6-diisopropylphenyl), abbreviated here as <i>t</i>BuAm<sup>DIPP</sup>, and (<i>p</i>-tolyl)­C­(N-Ar<sup>‡</sup>)<sub>2</sub> (Ar<sup>‡</sup> = 2,6-Ph<sub>2</sub>CH-4-<i>i</i>Pr-phenyl) abbreviated here as <i>p</i>TolAm<sup>Ar‡</sup>. The amidine <i>t</i>BuAm<sup>DIPP</sup>-H was deprotonated by Sr­[N­(SiMe<sub>3</sub>)<sub>2</sub>]<sub>2</sub> in benzene at 60 °C. Although the product, <i>t</i>BuAm<sup>DIPP</sup>SrN­(SiMe<sub>3</sub>)<sub>2</sub>, could be characterized by NMR, attempts to isolate it led to ligand scrambling via a Schlenk equilibrium. Reaction of in situ prepared <i>t</i>BuAm<sup>DIPP</sup>SrN­(SiMe<sub>3</sub>)<sub>2</sub> with PhSiH<sub>3</sub> gave PhH<sub>2</sub>SiN­(SiMe<sub>3</sub>)<sub>2</sub> and presumably the intermediate <i>t</i>BuAm<sup>DIPP</sup>SrH, but the latter is not stable and the homoleptic complex (<i>t</i>BuAm<sup>DIPP</sup>)<sub>2</sub>Sr was isolated and structurally characterized. Deprotonation of the bulkier amidine <i>p</i>TolAm<sup>Ar‡</sup>-H with Sr­[N­(SiMe<sub>3</sub>)<sub>2</sub>]<sub>2</sub> needed forcing conditions, inevitably giving rise to deprotonation of the Ph<sub>2</sub>CH substituent as well. Reaction of <i>p</i>TolAm<sup>Ar‡</sup>-H with the less bulky and less basic Sr­[N­(SiHMe<sub>2</sub>)<sub>2</sub>]<sub>2</sub>, however, gave the heteroleptic product <i>p</i>TolAm<sup>Ar‡</sup>SrN­(SiHMe<sub>2</sub>)<sub>2</sub>, which has been structurally characterized. The latter was also at 60 °C stable toward ligand scrambling. Reaction with PhSiH<sub>3</sub> did give hydride exchange, but the product <i>p</i>TolAm<sup>Ar‡</sup>SrH decomposed even at −30 °C. Instead, an amidinate complex with a deprotonated Ph<sub>2</sub>CH substituent was isolated and structurally characterized (<b>7</b>). The latter catalyzed the intramolecular alkene hydroamination.