Isocyanate Insertion into a La-P Phosphide Bond: A Versatile Route to Phosphaureate-Bridged Heterobimetallic Lanthanide-Coinage-Metal Complexes.

A new route to heterobimetallic lanthanide-coinage-metal complexes is disclosed. The selective insertion of organic substrates such as phenyl iso(thio)cyanate into the La-P bond of the primary phosphido complex (PN)2La(PHMes) (1) (with PN- = (N-(2-(diisopropylphosphanyl)-4-methylphenyl)-2,4,6-trimethylanilide) yields the phospha(thio)ureate complexes (PN)2La(OC(NPh)(PHMes)) (2) and (PN)2La(SC(NPh)(PHMes)) (3) with retention of the PH protons. Subsequent deprotonation of the phosphaureate complex 2 with potassium hexamethyldisilazide (KHMDS, K[N(SiMe3)2]) leads to the polymeric complex [K{(PN)2La(OC(NPh)(PMes))}]n (4). Complex 4 was found to be an excellent precursor for salt metathesis reactions with copper(I) and gold(I) chlorides supported by an N-heterocyclic carbene (NHC, 5 and 6) or a cyclic alkyl amino carbene (CAAC, 7 and 8). This resulted in the unprecedented formation of heterobimetallic lanthanum-coinage-metal complexes, containing the first example of a µ,κ2(O,N):κ1(P)-phosphaureate bridging ligand. For an alternative route to complex 8 a direct protonolysis protocol between a new basic gold(I) precursor, namely (MeCAAC)Au(HMDS), and 2 was also investigated. The complexes have been characterized by multinuclear NMR spectroscopy, IR spectroscopy, and X-ray crystallography (except for 8).

A mesoionic carbene complex of manganese in five oxidation states.

Reaction between a carbazole-based mesoionic carbene ligand and manganese(II) iodide results in the formation of a rare air-stable manganese(IV) complex after aerobic workup. Cyclic voltammetry reveals the complex to be stable in five oxidation states. The electronic structure of all five oxidation states is elucidated chemically, spectroscopically (NMR, high-frequency EPR, UV-Vis, MCD), magnetically, and computationally (DFT, CASSCF).

Coupling of CO2 and epoxides catalysed by novel N-fused mesoionic carbene complexes of nickel(II).

We report the syntheses of two rigid mesoionic carbene (MIC) ligands with a carbazole backbone via an intramolecular Finkelstein-cyclisation cascade and investigate their coordination behavior towards nickel(II) acetate. Despite the nickel(II) carbene complexes 4a,b showing only minor differences in their chemical composition, they display curious differences in their chemical properties, e.g. solubility. Furthermore, the potential of these novel MIC complexes in the coupling of carbon dioxide and epoxides as well as the differences in reactivity compared to classical NHC-derived complexes are evaluated.

Bright luminescent lithium and magnesium carbene complexes.

We report on the convenient synthesis of a CNC pincer ligand composed of carbazole and two mesoionic carbenes, as well as the corresponding lithium- and magnesium complexes. Mono-deprotonation affords a rare "naked" amide anion. In contrast to the proligand and its mono-deprotonated form, tri-deprotonated s-block complexes show bright luminescence, and their photophysical properties were therefore investigated by absorption- and luminescence spectroscopy. They reveal a quantum yield of 16% in solution at ambient temperature. Detailed quantum-chemical calculations assist in rationalizing the emissive properties based on an Intra-Ligand-Charge-Transfer (ILCT) between the carbazolido- and mesoionic carbene ligands. (Earth-)alkali metals prevent the distortion of the ligand following excitation and, thus, by avoiding non-radiative deactivation support bright luminescence.