Organometallic macrocycles and cages based on bis(amidinate) ligands

Abstract

Abstract A series of half-sandwich iridium-based complexes bearing 1,4-benzenebis (N,N′-dicyclohexylamidine) (H2L1) or 4,4′-bisphenylbis(N,N′-dicyclohexylamidine) (H2L2) has been synthesized and characterized. Treatment of [Cp*IrCl2]2 (Cp* = η5-pentamethyl-cyclo pentadienyl) with deprotonated H2L1 or H2L2 at low temperature resulted in formation of binuclear complexes [Cp*IrCl]2 (L1) and [Cp*IrCl]2(L2). They were chosen as precursors to construct macrocycles and cages. Tetranuclear metallamacrocycles [(Cp*Ir)4(L1)2 (pyrazine)2][OTf]4 and [(Cp*Ir)4(L2)2(pyrazine)2][OTf]4 were assembled by the reaction of complex [Cp*IrCl]2 (L1) or [Cp*IrCl]2(L2) with pyrazine after the removal of chloride from the iridium centers with silver salt AgOTf (OTf = O2SCF3). When 2,4,6-tri(4-pyridyl)-1,3,5-triazine (tpt) is used instead of pyrazine under the same conditions, hexanuclear metallacages [(Cp*Ir)6(L1)3(tpt)2][OTf]6 and [(Cp*Ir)6(L2)3(tpt)2][OTf]6 were formed. Single-crystal X-ray analysis indicated that the cation of complex [(Cp*Ir)4(L1)2 (pyrazine)2][OTf]4 is a rectangular structure, while the cation of complex [(Cp*Ir)4(L2)2(pyrazine)2][OTf]4 is seriously distorted, nearly to a tetrahedral state. Moreover, complexes [(Cp*Ir)6(L1)3(tpt)2][OTf]6 and [(Cp*Ir)6(L2)3(tpt)2][OTf]6 are prism-like cages with large cavity size, which can be prepared in very high yield in the absence of templates. Surprisingly, solutions of multinuclear complexes are very sensitive to carbon monoxide, in which the frameworks were destroyed, giving the binuclear complexes [(Cp*Ir)2(CO)2(L1)][OTf]2 and [(Cp*Ir)2(CO)2(L2)][OTf]2.