Unusual Si–H Bond Activation and Formation of Cationic Scandium Amide Complexes from a Mono(amidinate)-Ligated Scandium Bis(silylamide) Complex and Their Performance in Isoprene Polymerization

Amine elimination of scandium tris­(silylamide) complex Sc­[N­(SiHMe₂)₂]₃(THF) with 1 equiv of the amidine [PhC­(N-2,6-^<i>i</i>Pr₂C₆H₃)₂]H in toluene afforded the neutral mono­(amidinate) scandium bis­(silylamide) complex [PhC­(N-2,6-^<i>i</i>Pr₂C₆H₃)₂]­Sc­[N­(SiHMe₂)₂]₂ (<b>1</b>) in 93% isolated yield. When <b>1</b> was activated with 1 equiv of [Ph₃C]­[B­(C₆F₅)₄] in the presence of THF, the unexpected cationic amidinate scandium amide complex [{PhC­(N-2,6-^<i>i</i>Pr₂C₆H₃)₂}­ScN­{SiHMe₂}­{SiMe₂N­(SiHMe₂)₂}­(THF)₂]­[B­(C₆F₅)₄] (<b>2</b>) was generated. Treatment of <b>1</b> with excess AlMe₃ gave the Sc/Al heterometallic methyl complex [PhC­(N-2,6-^<i>i</i>Pr₂C₆H₃)₂]­Sc­[(μ-Me)₂AlMe₂]₂ (<b>3</b>). All these complexes were well-characterized by elemental analysis, NMR spectroscopy, and X-ray crystallography. The combination <b>1</b>/[Ph₃C]­[B­(C₆F₅)₄] in toluene showed activity toward isoprene polymerization. Addition of excess AlMe₃ to the <b>1</b>/[Ph₃C]­[B­(C₆F₅)₄] catalyst system switched the regioselectivity of isoprene polymerization from 3,4-specific to cis-1,4-selective

Unusual Si–H Bond Activation and Formation of Cationic Scandium Amide Complexes from a Mono(amidinate)-Ligated Scandium Bis(silylamide) Complex and Their Performance in Isoprene Polymerization

Amine elimination of scandium tris­(silylamide) complex Sc­[N­(SiHMe₂)₂]₃(THF) with 1 equiv of the amidine [PhC­(N-2,6-^<i>i</i>Pr₂C₆H₃)₂]H in toluene afforded the neutral mono­(amidinate) scandium bis­(silylamide) complex [PhC­(N-2,6-^<i>i</i>Pr₂C₆H₃)₂]­Sc­[N­(SiHMe₂)₂]₂ (<b>1</b>) in 93% isolated yield. When <b>1</b> was activated with 1 equiv of [Ph₃C]­[B­(C₆F₅)₄] in the presence of THF, the unexpected cationic amidinate scandium amide complex [{PhC­(N-2,6-^<i>i</i>Pr₂C₆H₃)₂}­ScN­{SiHMe₂}­{SiMe₂N­(SiHMe₂)₂}­(THF)₂]­[B­(C₆F₅)₄] (<b>2</b>) was generated. Treatment of <b>1</b> with excess AlMe₃ gave the Sc/Al heterometallic methyl complex [PhC­(N-2,6-^<i>i</i>Pr₂C₆H₃)₂]­Sc­[(μ-Me)₂AlMe₂]₂ (<b>3</b>). All these complexes were well-characterized by elemental analysis, NMR spectroscopy, and X-ray crystallography. The combination <b>1</b>/[Ph₃C]­[B­(C₆F₅)₄] in toluene showed activity toward isoprene polymerization. Addition of excess AlMe₃ to the <b>1</b>/[Ph₃C]­[B­(C₆F₅)₄] catalyst system switched the regioselectivity of isoprene polymerization from 3,4-specific to cis-1,4-selective