Coordination chemistry of the soft chiral Lewis acid [Cp*Ir(TsDPEN)] +

Article abstract of DOI:10.1021/ic200160q

The paper surveys the binding of anions to the unsaturated 16e Lewis acid [Cp*Ir(TsDPEN)]⁺ ([1H]⁺), where TsDPEN is racemic H₂NCHPhCHPhNTs^-. The derivatives Cp*IrX(TsDPEN) were characterized crystallographically for X^- = CN^-, Me(C=NH)S^-, NO₂^-, 2-pyridonate, and 0.5 MoS₄^2-. [(1H)₂(μ-CN)]⁺ forms from [1H]⁺ and 1H(CN). Aside from 2-pyridone, amides generally add reversibly and bind to Ir through N. Thioacetamide binds irreversibly through sulfur. Compounds of the type Cp*IrX(TsDPEN) generally form diastereoselectively, although diastereomeric products were observed for the strong ligands (X = CN^-, H^- (introduced via BH ₄^-), or Me(C=NH)S^-). Related experiments on the reaction (p-cymene)Ru(TsDPEN-H) + BH₄^- gave two diastereomers of (p-cymene)RuH(TsDPEN), the known hydrogenation catalyst and a second isomer that hydrogenated acetophenone more slowly. These experiment provide new insights into the enantioselectivity of these catalysts. Diastereomerization in all cases was first order in metal with modest solvent effects. The diphenyl groups are generally diequatorial for the stable diastereomers. For the 2-pyridonate adduct, axial phenyl groups are stabilized in the solid state by puckering of the IrN₂C₂ ring induced by intramolecular hydrogen-bonding. Crystallographic analysis of [Cp*Ir(TsDPEN)]₂(MoS₄) revealed a unique example of a κ¹,κ¹-tetrathiometallate ligand. Cp*Ir(SC(NH)Me)TsDPEN) is the first example of a κ¹-S- thioamidato complex.