Bis(alkyl) scandium and yttrium complexes coordinated by an amidopyridinate ligand: synthesis, characterization and catalytic performance in isoprene polymerization, hydroelementation and carbon dioxide hydrosilylation

摘要

New neutral bis(alkyl) Sc and Y complexes [N,N-py,N-]Ln(CH2SiMe3)(2)(THF)(n) [n = 0, Ln = Sc (1(Sc)), Y (1(Y)); n = 1, Ln = Y (1(Y)(THF))] stabilized by a tridentate monoanionic amidopyridinate ligand were straightforwardly prepared by alkane elimination, upon mixing ligand [N,N-py,N-]H and metal precursor Ln(CH2SiMe3)(3)(THF)(2) in toluene at 0 degrees C. Depending on the work-up conditions, yttrium bis(alkyl)s were isolated as either a pentacoordinate Lewis base free complex [N,N-py,N-]Y(CH2SiMe3)(2) (1(Y)) or as a hexacoordinate THF adduct [N,N-py,N-]Y(CH2SiMe3)(2)THF (1(Y)(THF)). For the smaller Sc ion the only solvent-free complex [N,N-py,N-]Y(CH2SiMe3)(2) (1(Sc)) was isolated as a pentacoordinate species irrespective of the reaction/work-up/crystallization conditions applied. Complexes 1(Ln) (Ln = Y, Sc) and 1(Y)(THF) were scrutinized as pre-catalysts in ternary catalytic systems Ln/borate/(AlBu3)-Bu-i (borate = [HNMe2Ph][B(C6F5)(4)] or [Ph3C][B(C6F5)(4)]), applied to isoprene (IP) polymerization, providing moderate activity albeit high selectivity with predominant formation of 1,4-cis polyisoprene (up to 99%). The same complexes proved to be effcient catalysts also for the intermolecular hydrolelementation of styrene with various EH sustrates (pyrrolidine, morpholine, Ph2PH, PhPH2, PhSH) affording linear anti-Markovnikov addition products exclusively. After a preliminary activation by B(C6F5)(3), selected bis(alkyl) complexes from this series have been finally used as valuable pre-catalysts for the CO2 hydrosylilation to CH4 in the presence of organosilanes as reducing agents (PhMe2SiH, PhSiH3, Et2MeSiH).