Synthèse et réactivité de complexes manganèse-propynylidène dérivés du méthylcymantrène

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

A Stable Anionic N-Heterocyclic Carbene and Its Zwitterionic Complexes

International audiencePyrimidinium betaïnes (1), readily accessible via a straightforward modular synthesis from a formamidine and a monosubstituted malonic acid, are readily deprotonated by nBuLi (or KHMDS) to give the stable carbene species [2]Li+ (abbreviated as maloNHC). The latter represents the archetype of a subgroup of N-heterocyclic carbenes incorporating a malonate as remote anionic functional group within their heterocyclic backbone. While playing the dual role of monodentate 2 e− L type donor and noncoordinating charge carrier X, such ligands are seen to provide a rational route to zwitterionic complexes, as illustrated here by three examples (Rh, Fe, Ag). In particular, the reaction of [2]Li+ with [RhCl(1,5-COD)]2 produces the neutral 14 e− complex Rh(maloNHC)(COD) (3) in which coordinative unsaturation at the metal is relieved in the solid state by an uncommon labile bonding interaction between the Cipso of one of the mesityl arms and the Rh center

Electronic Tuning of a Carbene Center via Remote Chemical Induction, and Relevant Effects in Catalysis

International audienceThe present report develops the idea that an N-heterocyclic carbene incorporating a remote anionic functionality—here, a malonate group—as a backbone component of its heterocyclic framework, can be “post-functionalized” directly from its transition-metal complexes, upon simple addition of a variety of electrophiles interacting directly with the malonate group in the outer coordination sphere. From a palette of selected electrophilic reagents, it was thus possible to modulate the electronic donor properties of the carbene center over a rather broad range. Both the zwitterionic complex [Rh{malo-NHC}(cod)] and the cationic derivatives [Rh{malo-NHCE}(cod)]+ (where “malo-NHCE” represents the ligand modified by a selected electrophile “E”) were used as pre-catalysts in two types of catalytic reactions, namely, the polymerization of phenylacetylene and the hydroboration of styrene. The results indicate that, in both cases, the zwitterionic species is by far the best catalyst, whereas a decrease in the ligand donicity induced by the added electrophile results in a concomitant reduction of catalytic activity. Apparent deviations to such a trend in the case of the hydroboration of styrene were rationalized in terms of an interaction between the reactive catecholborane substrate and the remote functionality of the N-heterocyclic carbene leading to an in situ modification of the nature of the active species. These observations serve as a useful basis to define the scope and limitations of the present conceptual approach in catalysis

Reprogramming of a Malonic N‐Heterocyclic Carbene: A Simple Backbone Modification with Dramatic Consequences on the Ligand's Donor Properties

International audienceReaction of N,N′-dimesitylformamidine with dimethylmalonyl dichloride in dichloromethane in the presence of an excess of triethylamine gives the 2-chloro-4,5-dioxohexahydropyrimidine 1. The corresponding diamidocarbene 3 is generated in situ by further deprotonation with KHMDS at –40 °C and identified by trapping with S8 to give the fully characterized (including X-ray structure) sulfur adduct 4. It also reacts with [RhCl(cod)]2 to yield the NHC complex [RhCl(3)(cod)] (5) (characterized also by X-ray structure). The donor properties of 3 were evaluated against the established IR [ν(CO)] scale from [RhCl(3)(CO)2] (6). The average value of ν(CO) = 2045 cm–1 indicates that the diamidocarbene 3 is much less nucleophilic than structurally relevant six-membered NHCs including the anionic diaminocarbenes previously reported in our group

Binuclear Cu(I) and Mn(0) Complexes with a Tridentate Pyridine-NHC-Phosphane Ligand in a µ-κ 2 Ĉ,N -M;κ 1 P -M Coordination Mode

International audienceThe reaction of a non-symmetrical pyridine-NHC-phosphane (NĈP) ligand – generated in situ upon the deprotonation of the corresponding imidazolium salt – with equimolar amount of [Cu(NCMe)4](BF4) or Mn2(CO)10 leads to the formation of bimetallic complexes [Cu2(NĈP)2(NCMe)](BF4)2 and [Mn2(CO)7(NĈP)], respectively, in which the tridentate ligand exhibits an unusual µ-κ2Ĉ,N-M;κ1P-M coordination mode. According to NMR spectroscopy and mass spectrometry, the binuclear copper complex is in equilibrium in MeCN solution with two mononuclear species, namely [Cu(κ2Ĉ,P-NĈP)2](BF4) and [Cu(κ3-N,Ĉ,P-NĈP)(NCMe)](BF4)

Snapshot of a Chelation-Assisted C-H/Alkyne Coupling: A Ruthenium Complex Caught in the Act of C-C Bond Formation

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An Ambidentate Janus-Type Ligand System Based on Fused Carbene and Imidato Functionalities

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