Chiral Sulfur Functional Groups as Definers of the Chirality at the Metal in Ir and Rh Half‐Sandwich Complexes: A Combined CD/X‐ray Study

Abstract

Mesoionic carbenes (MICs) derived from triazolium salts that contain chiral sulfoxide or sulfoximine functional groups were used to construct enantiopure chiral-at-metal Ir and Rh half-sandwich complexes through the synthetic sequence of MIC complexation/C-H aromatic activation. The process was efficient and diastereoselective for the formation of enantiopure five-membered metallacycles. The use of the enantiomers of the chiral sulfur groups allowed us to prepare complexes that had opposite configurations at the metal center. Complete retention of the configuration at the metal center was observed during the formation of cationic Ir complexes and upon insertion of alkynes into the Ir -C bond, as demonstrated by a combined circular dichroism/X-ray study. These results point to a vicinal-assisted S 1-like mechanism.

Chiral‐at‐Metal BODIPY‐Based Iridium(III) Complexes: Synthesis and Luminescence Properties

“…This strong negative Cotton absorption is maintained (287.0 nm) for the Ir(III) complex 7c. [19] In previous studies, [10] this negative Cotton absorption was assigned to an absolute configuration R at the metallic center. Since absolute configuration R at the Ir(III) for 7b has been unambiguously established by X-ray analysis (absolute structure factor x = 0.013 7), we can conclude that the absolute configuration at the metallic center for complexes 7a and 7c may be R as well.…”

“…During our work in the synthesis of transition metal complexes having 1,2,3-triazolylidene (MIC) ligands with enantiopure sulfoxide and sulfoxiimine moieties, [8] we have reported the role of the chiral mesoionic carbene ligand (MIC) in defining the catalytic reactivity of their Au(I) derivatives, [9] preparing enantiopure chiral-at-metal complexes, [10] and enantiopure complexes having chiral-at-metal and chiral planar metallocene moieties. [11] On the other hand, our work in push-pull systems containing a Cr(0) and W(0) Fischer metal carbene moiety, I, clearly demonstrated that the system geometry is reflected in the deactivation of the fluorescence.…”

“…The absolute configuration of complexes 7 was determined by a combination of circular dichroism and X-ray diffraction as previously established by us for similar piano-stool MIC. [10] Figure 3 compiles the CD spectra of compounds 5a, 6a and 7a as representative examples of the compounds studied in this work (see the SI for the comparative CD spectra of the remaining compounds). Triazole 5a and triazolium salt 6a are less absorptive than the iridium complex 7a.…”

Central (S) to Central (M=Ir, Rh) to Planar (Metallocene, M=Fe, Ru) Chirality Transfer Using Sulfoxide‐Substituted Mesoionic Carbene Ligands: Synthesis of Bimetallic Planar Chiral Metallocenes

“…Continuing our work on the use of 1,2,3‐triazolylidene mesoionic carbenes (MICs) containing enantiopure sulfoxide moieties, we reported for the first time the use of these MICs for the preparation of enantiopure cyclometalated Ir III and Rh III half‐sandwich complexes . The process takes place through the sequence MIC coordination/enantioselective C−H activation (Scheme ).…”

“…The process takes place through the sequence MIC coordination/enantioselective C−H activation (Scheme ). Metalation to form five‐membered metallacycles produces enantiomerically pure complexes, whereas the formation of the six‐membered analogues is not totally diastereoselective …”