An ovel metal-free synthesis of 3,3-disubstituted benzofuran-2-(3H)-ones through reacting a-aryl-a-diazoacetates with triarylboranes is presented. Initially,t riarylboranes were successfully investigated in a-arylations of a-diazoacetates,h owever in the presence of ah eteroatom in the ortho position, the boron enolate intermediate undergoes an intramolecular rearrangement to form aq uaternary center.T he intermediate cyclizes to affordv aluable 3,3-disubstituted benzofuranones in good yields.

Nickel(II) fluorido complexes bearing NNN-pincer ligands were found to be catalysts in the hydrodefluorination of geminal difluorocyclopropanes which undergo ring-opening to form the corresponding monofluoroalkenes in good yield and high Z-selectivities. Evidence for a radical based mechanism involving nickel(I) and nickel hydrido complexes as key intermediates was obtained in the corresponding stoichiometric reactions.

Homolytic C-X bond cleavage of organohalides by the T-shaped nickel(I) complexes [LigNi(I)] 1 bearing the iso-PyrrMeBox ligand had been found previously to be the crucial activation step in the asymmetric hydrodehalogenation of geminal dihalides. Here, this mechanistic investigation is extended to aryl halides, which allowed a systematic study of the activation process by a combination of experimental data and density functional theory modeling. While the activation of both aryl chlorides and geminal dichlorides appears to proceed via an analogous transition state, the generation of a highly stabile nickel(II)aryl species in the reaction of the aryl chlorides for the former represents a major difference in the reactive behavior. This difference was found to have a crucial impact on the activity of these nickel pincer systems as catalysts in the dehalogenation of aryl chlorides compared to geminal dichlorides and highlights the importance of the regulatory pathways controlling the nickel(I) concentration throughout the catalysis. These results along with the identification and characterization of novel nickel(II)aryl species are presented.

Bench-stable nickel fluoride complexes bearing NNN pincer ligands have been employed as precursors for the regioselective hydrosilylation of epoxides at room temperature. A nickel hydride assisted epoxide opening is followed by the cleavage of the newly formed nickel oxygen bond by σ-bond metathesis with a silane.

A new class of chiral C-symmetric N-donor pincer ligands, 2,5-bis(2-oxazolinyldimethylmethyl)pyrroles (PdmBox)H, was synthesized starting from the readily available ethyl 2,2-dimethyl-3-oxobutanoate (1). The synthesis of the ligand backbone was achieved by oxidative enole coupling with CuC1 followed by Paal-Knorr-type pyrrole synthesis. The corresponding protioligands (PdmBox)H (R = iPr: 5a; Ph: 5b) were obtained by condensation with amino alcohols and subsequent zinc-catalyzed cyclization. Reaction of the lithiated ligands with [NiCl(dme)] yielded the corresponding square-planar nickel(II) complexes [(PdmBox)NiCl] (6a/b). Salt metathesis of 6a with the corresponding alkali or cesium salts in acetone led to the formation of air- and moisture-stable [(PdmBox)NiX] (X = F (7), X = Br (8), X = I (9), X = N (10), X = OAc (11). Furthermore, the conversion of [(PdmBox)NiF] (7) with hydride transfer reagents such as PhSiH led to the stable hydrido species [(PdmBox)NiH] (27), the stoichiometric transformations of which were studied. Treatment of 6a with organometallic reagents such as ZnEt, PhLi, PhC≡CLi, NsLi, or (Bn)Mg(THF) gave the corresponding alkyl, alkynyl, or aryl complexes. The availability of the new nonisomerizable PdmBox pincer ligands allowed the comparative study of their ligation to square-planar complexes as helically twisted spectator ligands as opposed to the enforced planar rigidity of their iso-PmBox analogues and the way this influences the reactivity of the Ni complexes.

The employment of lithium hexamethyldisilazide for the deprotonation of methylene-bridged bis­(imidazolium) salts led to the formation of lithium carbene adducts. Depending on the crystallization method and the substituents of the ligands, monomeric, dimeric, or polymeric solid-state structures were obtained. These lithium carbene complexes represent the first examples of lithium complexes bearing neutral bis­(N-heterocyclic carbene) ligands.

Abstract:The coordination chemistry of PdmBOX [2,5-bis(2-oxazolinyldimethylmethyl) (5)

We developed a series of new conjugated cruciform fluorophores (XF) featuring imine groups. The condensation of an XF containing aldehyde functionalities and selected primary amines leads to several XF-imine derivatives. Upon addition of Cu(2+) or Zn(2+) ions to solutions of the imine XFs in different solvents, a red-shifted emission is detected, resulting in an altered emission color. The imine acts as a simple modular metallo-reactive fluorophore.