Construction of iridium and rhodium cyclometalated macrocycles based on p-carborane and N,N′-donor bridging ligands

Abstract

Six tetranuclear half-sandwich iridium and rhodium complexes bridged by neutral N,N′-donor pyridyl-imine ligands and 1,12-dicarbadodecaborane(12)-1,12-dicarboxylate (p-CDC) were controllably synthesized and fully characterized. The results revealed that the precursors, binuclear complexes [(Cp*M)₂{1,4-bis(2-pyridylmethyleneamino)benzene}Cl₂][OTf]₂ (Cp* = η⁵-pentamethylcyclopentadienyl, M = Ir (2a), Rh (2b)), have different preferential configurations, and tetranuclear complexes [(Cp*M)₄{1,4-bis(2-pyridylmethyleneamino)benzene}₂(p-CDC)₂][OTf]₄ (M = Ir (3a), Rh (3b)), which were prepared using monodentate p-carborane dicarboxylate and 2a or 2b, showed highly twisted backbones. Likewise, homologous regular rectangular compounds [(Cp*M)₄{1,4-{(2-C₅H₄N)HCN}₂-2,3,5,6-Me₄C₆}₂(p-CDC)₂][OTf]₄ (M = Ir (4a), Rh (4b)) and [(Cp*M)₄{1,4-{(2-C₅H₄N)HCN}₂-1,5-naphthalene}₂(p-CDC)₂][OTf]₄ (M = Ir (5a), Rh (5b)) were obtained following a similar synthetic route. X-ray determination confirmed that 4b and 5b have stacking channels as well.