Scandium Bis(<i>o</i>-aminobenzyl) Complexes Coordinated by 5-Methyl-5,6-dihydroindeno[2,1-<i>b</i>]indolyl Ligands: Synthesis, Structures, and Catalytic Activity in Isoprene Polymerization and Olefin Hydrophosphination

Deprotonation of 5-methyl-5,6-dihydroindeno[2,1-b]indole (L1H) or 2-(tert-butyl)-5-methyl-5,6-dihydroindeno[2,1-b]indole (L2H) with an equimolar amount of n-BuLi in Et2O affords the 5,6-dihydroindeno[2,1-b]indolyl derivatives L1Li(Et2O)2 (1) and [L2Li(Et2O)]6 (2) in 67 and 73% yields. Complex 1 proved to be monomeric in the crystalline state, whereas 2 adopts a cyclic hexameric structure. The protonation of Sc(CH2C6H4-o-NMe2)3 by an equimolar amount of [HNEt3][BPh4] allows for the synthesis of a cationic scandium bis(o-aminobenzyl) complex [Sc(CH2C6H4-o-NMe2)2(THF)2][BPh4] (3) which was successfully employed as a precursor for the preparation of bis(o-aminobenzyl) 5,6-dihydroindeno[2,1-b]indolyl species. The salt metathesis reactions of lithium derivatives 1 and 2 with 3 (THF, 20 °C) afford complexes L1Sc(CH2C6H4-o-NMe2)2 (4) and L2Sc(CH2C6H4-o-NMe2)2 (5) in 69 and 73% yields. Complexes 4 and 5 are monomeric and Lewis-base free. Complexes 4 and 5 as part of binary (4, 5/[Ph3C][B(C6F5)4], 4, 5/[PhNHMe][B(C6F5)4]) and ternary (4, 5/([Ph3C][B(C6F5)4], [PhNHMe][B(C6F5)4])/AliBu3 (1:1:10)) catalytic systems are efficient initiators for isoprene polymerization which enable quantitative conversion of monomers in 30 min ([IP]/[Ln] = 1000) even at −30 °C. The resulting polymers have a predominantly cis-1,4 structure (up to 80.9%; Mn = 58.8–2315.9 × 103; Mw/Mn = 1.35–3.12). Complexes 4 and 5 catalyze the intermolecular hydrophosphination of styrene, α-methylstyrene, and phenylacetylene with Ph2PH and PhPH2 under mild conditions.