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

Synthesis and Characterization of Amine-Bridged Bis(phenolate) Yttrium Guanidinates and Their Application in the Ring-Opening Polymerization of 1,4-Dioxan-2-one

A series of neutral yttrium guanidinates supported by an amine-bridged bis­(phenolate) ligand were synthesized, and their catalytic behaviors for the ring-opening polymerization of 1,4-dioxan-2-one (<i>p</i>-dioxanone, PDO) were explored. Metathesis reactions of amine-bridged bis­(phenolate) yttrium chlorides LLnCl­(THF) [L = Me₂NCH₂CH₂N­{CH₂-(2-OC₆H₂-<i>t</i>Bu₂-3,5)}₂] with corresponding lithium guanidinates generated in situ in a 1:1 molar ratio in THF gave the neutral yttrium guanidinates LY­[R₂NC­(NR¹)₂] [R¹ = −Cy, R₂N = −N­(TMS)₂ (<b>1</b>), −N<i>i</i>Pr₂ (<b>2</b>), −N­(CH₂)₅ (<b>3</b>); R¹ = −<i>i</i>Pr, R₂N = −N<i>i</i>Pr₂ (<b>4</b>) −NPh₂ (<b>5</b>))]. These complexes were well characterized by elemental analyses, IR, and NMR spectroscopy. The definitive molecular structures of these complexes were determined by single-crystal X-ray analysis. It was found that these complexes can efficiently initiate the ring-opening polymerization (ROP) of PDO, and the catalytic activity is affected by the nature of the guanidinate groups with the active sequence of <b>1</b> > <b>2</b> ≈ <b>3</b> ≈ <b>4</b> > <b>5</b>. The influences of reaction conditions such as polymerization time, polymerization temperature, and molar ratio of monomer to initiator on the polymerization were also investigated. The polymerization kinetics of PDO catalyzed by complex <b>1</b> is first-order with respect to monomer concentration, and the apparent activation energy amounts to 30.8 kJ mol^–1. The mechanistic investigations showed that the ROP of PDO proceeded through a coordination–insertion mechanism with a rupture of the acyl–oxygen bond of the monomer. MALDI-TOF mass spectrum analysis of the oligomer revealed that there are two kinds of polymer chains in this catalytic system, e.g., the linear chains H–[OCH₂CH₂OCH₂CO]_<i>n</i>–OH and the PPDO macrocycles