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

Abstract

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 (L CH; the superscript specifies the position of the tautomerizable H atom in the imidazole ring) with HBF4·Et2O to give the imidazolium salt [HL CH]+[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)­{L NH-κ3 N imine,N Py,C NHC}]+[BF4]− (3 +[BF4]−). Substitution of MeCN in 3 +[BF4]− by treatment with triiso­propyl­phosphine gave the analogue [Ir­(H)­(Cl)­P­(i-Pr)3{L NH-κ3 N imine,N Py,C NHC}]+[BF4]− (4 +[BF4]−). Chloride abstraction from 3 +[BF4]− by AgBF4 gave [Ir­(H)­(NCMe)2{L NH-κ3 N imine,N Py,C NHC}]2+[BF4 –]2 (5 2+[BF4 –]2). The centro­symmetric dinuclear Ir­(III) complex [Ir­(H)­(NCMe)­{μ-(L CH−H)-κ3 N imine,N Py,C2,κN3}]2 2+[B­(C6F5)3F–]2 (6 2+[B­(C6F5)3F–]2) was obtained after deprotonation of 5 2+[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, 5 2+[BF4 –]2·2CH2Cl2, and 6 2+[B­(C6F5)3F–]2·4CH2Cl2 have been determined by X-ray diffraction.

Modulating the σ-Accepting Properties of an Antimony Z-type Ligand via Anion Abstraction: Remote-Controlled Reactivity of the Coordinated Platinum Atom

“…The lower J Pt–P coupling constants measured for [ 5 ] + and [ 6 ] + are consistent with a decrease in electron density at the platinum center. Abstraction of a fluoride anion was confirmed by the appearance of new signals in the 19 F NMR spectrum at −134.7, −161.7, and −166.1 ppm and a broad singlet −191.4 ppm corresponding to the [BF­(C 6 F 5 ) 3 ] − anion . However, no signals corresponding to the antimony-bound fluoride ligands could be observed even at −50 °C in CDCl 3 .…”

Complexes Bearing Protic N-Heterocyclic Carbene Ligands

“…In the absence of electrophilic reagents, the nucleophilic azolyl (or anionic NHC) complexes generated by deprotonation of pNHC ligands often dimerize to complexes of type 216 by replacement of one coligand, , as exemplified in Scheme …”

“…During their studies on the chelate-assisted tautomerization of imidazole 81 bearing an imine–pyridine anchor, Danopoulos and Braunstein found that reaction of 81 with the iridium­(I) complex [IrCl­(cod)] 2 yields either the N-metalated iridium­(I)–imidazole complex 82 or the cyclometalated iridium­(III) complex 83 , depending on the ratio of metal precursor to 81 (Scheme ). If the imidazole moiety in 81 is protonated to give 84 , N-coordination of this group is suppressed, and oxidative addition to give the pincer-type pNHC iridium­(III) complex 85 was observed.…”

Functionalised N‐Heterocyclic Carbene Ligands in Bimetallic Architectures

“…Different synthetic methodology led to the formation of the desired pincer ligand bound to Ir (25), and deprotonation of the NÀHt hen led to the homobimetallic Ir complex 26,d escribed as containing bridging imidazolide donors. [33] Ad ifferent synthetic methodr elied on the reactiono f2lithio-1-methylimidazole with au ranyl b-diketiminato chloride complex that led to ah eterobimetallic imidazolide complex with the Ca toms bound to Ua nd aL ic ation bridging between the Na toms (Scheme 5, 27). Upon reaction with CoCl 2 and FeCl 2 ,r earrangement was observed with the carbene C atom binding to the transition metal (TM, 28).…”