Synthesis and structural characterization of iridium(I) complexes of 20-membered macrocyclic rings bearing chelating bis(N-heterocyclic carbene) ligands.

Abstract

The reactivities of two 20-membered macrocyclic ligands, each containing two N-heterocyclic carbene (NHC) and two amine groups, towards [IrCl(COD)]2 (COD is cycloocta-1,5-diene) were investigated. Macrocycles containing imidazolin-2-ylidene groups formed the monometallic complex [(1,2,5,6-η)-cycloocta-1,5-diene](5,16-dibenzyl-1,5,9,12,16,20-hexaazatricyclo[18.2.1.19,12]tetracosa-10,21-dien-21,22-diylidene)iridium(I) bromide dichloromethane monosolvate, [Ir(C8H12)(C32H42N6)]Br·CH2Cl2, 2a. The structure of iridium complex 2a at 100 K has triclinic P-1 symmetry. The ligand in 2a coordinates to the Ir center through the NHC moieties in a cis fashion. Additionally, the ligand adopts an umbrella-like structure that appears to envelope the Ir center. The structure displays C-H...Br interactions. Macrocycles containing benzimidazolin-2-ylidene groups formed the bimetallic complex [μ-5,20-dibenzyl-1,5,9,16,20,24-hexaazapentacyclo[22.6.1.19,16.010,15.025,30]dotriaconta-10(15),11,13,25(30),26,28-hexaene-31,32-diylidene]bis{bromido[(1,2,5,6-η)-cycloocta-1,5-diene]iridium(I)}, [Ir2Br2(C8H12)2(C40H46N6)], 2b. The structure of complex 2b at 100 K has orthorhombic Pbca symmetry. Each NHC moiety in 2b coordinates in a monodentate fashion to an Ir(COD) fragment. The structure exhibits disorder of the main molecule. This disorder is found in the portion of the macrocycle containing an amine group. This structure also displays C-H...Br interactions. Finally, the structure of the hexafluorophosphate salt of the imidazolin-2-ylidene-containing macrocycle, namely 5,16-dibenzyl-1λ5,5,9,12λ5,16,20-hexaazatricyclo[18.2.1.19,12]tetracosa-1(23),10,12(24),21-tetraene-1,12-diium bis(hexafluorophosphate), C32H44N62+·2PF6-, 1c, was determined. The structure of macrocycle 1c at 100 K has triclinic P-1 symmetry and was found to contain C-H...F interactions.