Trifunctional pNHC, Imine, Pyridine Pincer-Type Iridium(III) Complexes: Synthetic, Structural, and Reactivity Studies

Iridium­(III) complexes with a trifunctional
pincer ligand containing
protic N-heterocyclic carbene (pNHC), pyridine, and imine donor groups
were obtained in two sequential steps: (i) protonation of 2-(1-(2,6-diiso­propyl­phenyl­imino)­ethyl)-6-(1-imidazolyl)­pyridine
(LCH; the superscript specifies the position
of the tautomerizable H atom in the imidazole ring) with HBF4·Et2O to give the imidazolium salt [HLCH]+[BF4]− (protonation
always occurs at the imidazole N atom) and (ii) metalation of the
latter with [Ir­(cod)­(μ-Cl)]2 to give the hydrido
pincer complex [Ir­(H)­(Cl)­(NCMe)­{LNH-κ3Nimine,NPy,CNHC}]+[BF4]− (3+[BF4]−). Substitution of MeCN in 3+[BF4]− by treatment with triiso­propyl­phosphine
gave the analogue [Ir­(H)­(Cl)­P­(i-Pr)3{LNH-κ3Nimine,NPy,CNHC}]+[BF4]− (4+[BF4]−). Chloride abstraction
from 3+[BF4]− by AgBF4 gave [Ir­(H)­(NCMe)2{LNH-κ3Nimine,NPy,CNHC}]2+[BF4–]2 (52+[BF4–]2). The centro­symmetric dinuclear Ir­(III) complex [Ir­(H)­(NCMe)­{μ-(LCH−H)-κ3Nimine,NPy,C2,κN3}]22+[B­(C6F5)3F–]2 (62+[B­(C6F5)3F–]2) was obtained after deprotonation of 52+[BF4–]2 with KO-t-Bu, followed by addition of B­(C6F5)3. It contains two Ir pincer moieties, each
with a Nimine,NPy,C2 donor set, which are connected
by the Ir–N bonds involving the imidazolide rings, leading
to a μ-C,N bridging mode for the latter. Remarkably, all of
the donor atoms in the tetradentate bridging chelating ligands are
chemically different. The molecular structures of 3+[BF4]−·CH2Cl2, 4+[BF4]−·CH2Cl2, 52+[BF4–]2·2CH2Cl2, and 62+[B­(C6F5)3F–]2·4CH2Cl2 have been determined by X-ray diffraction.