Multifaceted coordination of naphthyridine−functionalized N-heterocyclic carbene: a novel “Ir^III(C^∧N)(C^∧C)” compound and its evaluation as transfer hydrogenation catalyst

Abstract

The 1,8-naphthyridine−functionalized N-heterocyclic carbene 1-benzyl-3-(5,7-dimethyl-1,8-naphthyrid-2-yl)imidazol-2-ylidene (BIN) has been successfully coordinated to Pd(II), W(0), Rh(I), and Ir(III), exhibiting its diverse binding modes. Reaction of BIN·HBr with Ag₂O, followed by transmetalation with PdCl₂(COD)₂ provides a cis complex PdCl₂(κC₂-BIN)₂ (1). Treatment of BIN·HBr with W(CO)₄(piperidine)₂ in acetonitrile affords a chelate complex W(CO)₄(κ²C2, N₁′-BIN) (2). Reaction of {RhCl(COD)}₂ with KO^tBu and subsequent treatment with BIN·HBr in 1:2 and 1:1 ratio results in the mono and dinuclear complexes [Rh(COD)Br(κC₂-BIN)] (3) and [{Rh(COD)Br}₂(κN₈′:κC₂-BIN)] (4), respectively. In complex 3, the “Rh(COD)Br” unit is coordinated to the carbene center, whereas an additional “Rh(COD)Br” unit is attached to naphthyridine nitrogen in complex 4 in an anti arrangement. Under identical reaction condition, a novel Ir(III) complex [Ir(κ²C₂,N₁′-BIN)(κ²C₃′,C₂-BIN)(H₂O)Br]Br (5) has been synthesized. Complex 5 is proved to be catalytically active in hydrogen transfer reaction from ⁱPrOH. All complexes have been characterized by spectroscopic methods and X-ray crystallography.