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

Deprotonation of 5-methyl-5,6-dihydroindeno[2,1-<i>b</i>]indole (<b>L</b><sup><b>1</b></sup><b>H</b>) or\n2-(<i>tert</i>-butyl)-5-methyl-5,6-dihydroindeno[2,1-<i>b</i>]indole (<b>L</b><sup><b>2</b></sup><b>H</b>) with an equimolar amount of <i>n-</i>BuLi in Et<sub>2</sub>O affords the 5,6-dihydroindeno[2,1-<i>b</i>]indolyl derivatives <b>L</b><sup><b>1</b></sup>Li(Et<sub>2</sub>O)<sub>2</sub> (<b>1</b>) and [<b>L</b><sup><b>2</b></sup>Li(Et<sub>2</sub>O)]<sub>6</sub> (<b>2</b>) in 67 and 73% yields. Complex <b>1</b> proved to be monomeric in the crystalline state, whereas <b>2</b> adopts a cyclic hexameric structure. The protonation of\nSc(CH<sub>2</sub>C<sub>6</sub>H<sub>4</sub>-<i>o</i>-NMe<sub>2</sub>)<sub>3</sub> by an equimolar amount of [HNEt<sub>3</sub>][BPh<sub>4</sub>] allows for the synthesis of a cationic scandium bis(<i>o</i>-aminobenzyl) complex [Sc(CH<sub>2</sub>C<sub>6</sub>H<sub>4</sub>-<i>o</i>-NMe<sub>2</sub>)<sub>2</sub>(THF)<sub>2</sub>][BPh<sub>4</sub>] (<b>3</b>) which was successfully\nemployed as a precursor for the preparation of bis(<i>o</i>-aminobenzyl) 5,6-dihydroindeno[2,1-<i>b</i>]indolyl species.\nThe salt metathesis reactions of lithium derivatives <b>1</b> and <b>2</b> with <b>3</b> (THF, 20 °C) afford\ncomplexes <b>L</b><sup><b>1</b></sup>Sc(CH<sub>2</sub>C<sub>6</sub>H<sub>4</sub>-<i>o</i>-NMe<sub>2</sub>)<sub>2</sub> (<b>4</b>) and <b>L</b><sup><b>2</b></sup>Sc(CH<sub>2</sub>C<sub>6</sub>H<sub>4</sub>-<i>o</i>-NMe<sub>2</sub>)<sub>2</sub> (<b>5</b>) in 69 and 73% yields. Complexes <b>4</b> and <b>5</b> are monomeric and Lewis-base free. Complexes <b>4</b> and <b>5</b> as part of binary (<b>4</b>, <b>5</b>/[Ph<sub>3</sub>C][B(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub>], <b>4</b>, <b>5</b>/[PhNHMe][B(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub>]) and ternary (<b>4</b>, <b>5/</b>([Ph<sub>3</sub>C][B(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub>], [PhNHMe][B(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub>])/AliBu<sub>3</sub> (1:1:10)) catalytic\nsystems are efficient initiators for isoprene polymerization which\nenable quantitative conversion of monomers in 30 min ([IP]/[Ln] =\n1000) even at −30 °C. The resulting polymers have a predominantly <i>cis</i>-1,4 structure (up to 80.9%; <i>M</i><sub>n</sub> = 58.8–2315.9 × 10<sup>3</sup>; <i>M</i><sub>w</sub>/<i>M</i><sub>n</sub> = 1.35–3.12). Complexes <b>4</b> and <b>5</b> catalyze the intermolecular hydrophosphination\nof styrene, α-methylstyrene, and phenylacetylene with Ph<sub>2</sub>PH and PhPH<sub>2</sub> under mild conditions.