Radical anions of 1,1-azoliumdithiocarboxylates.

The 1,1-azoliumdithiocarboxylate cAAC-CS (1a) was prepared and its redox chemistry was evaluated and compared to NHC based dithiocarboxylates IDipp-CS (1b) and IMes-CS (1c). Radical anions [carbene-CS]˙ were prepared by metallic reduction as the potassium or magnesium ion complexes [K(18-crown-6)(cAAC-CS)] (2a), [K(18-crown-6)(NHC-CS)] (NHC = IDipp: 2b, IMes: 2c), and [Mg(NacNac)(cAAC-CS)] (3) and extensively characterized (SC-XRD, EPR, UV/VIS/NIR, DFT). These complexes represent the first examples of isolated radical anions of 1,1-dithiolenes.

NHC aluminum chemistry on the rise.

This perspective highlights recent developments of the use of -heterocyclic carbenes (NHCs) and cyclic (alkyl)(amino)carbenes (cAACs) in alane and aluminum organyl chemistry. Especially in the last few years this flourishing research field led to some remarkable discoveries including various substitution patterns at the central aluminum atom, different oxidation states, neutral and charged compounds with varying coordination numbers and unique reactivities. Thereby NHCs play a vital role in the stabilization of these otherwise highly reactive compounds, which would not be realizable without the use of this intriguing class of ligands.

Construction of a Boron Chain on a Single Metal by Dehydrocoupling of Borane Ligands.

Borane coordination, B-H borane bond activation, and borane catenation via metal-mediated dehydrocoupling to form electron-precise B-B bonds are reported. The reaction of -[M(IMes)Cl] (M = W, Mo) (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene) with borates Li[BHR] (R = Mes, Dur; Mes = 2,4,6-MeCH and Dur = 2,3,5,6-MeCH) afforded the complexes [M(IMes)(η-HBR)(η-HBR)] (M = W: R = Mes , R = Dur ; M = Mo: R = Mes , R = Dur ). Three borane ligands are coordinated in to the group 6 metal atom via five (σ-B-H) bonds.

The tetracyanoborate anion as a building block for the heterocubane cluster cage [Cr{B(CN)}].

The tetracyanoborate anion [B(CN)] (TCB) was utilized as a building block for the synthesis of polynuclear chromium carbonyl compounds upon photolytic reaction with [Cr(CO)]. Up to four κN-coordinated cyano groups of TCB can be involved in binding to chromium, giving mixtures of [B(CN){CN-Cr(CO)}] ( = 1-4; 1-4) and [{Cr(CO)(B(CN))}] (5). The reaction of [B(CN)] with -[Cr(CO)(MeCN)] led to isolation of salts of the tetraanionic heterocubane cage [{Cr(CO)(B(CN))}].

Fluoride Abstraction Induced by Tris(pentafluoroethyl)difluorophosphorane: A Convenient Way to Synthesize Cationic -Heterocyclic Carbene- and Cyclic (Alkyl)(amino)carbene-Ligated Copper Alkyne and Arene Complexes.

We herein report the convenient synthesis of different -heterocyclic carbene (NHC)- and cyclic (alkyl)(amino)carbene (cAAC)-ligated copper cations using the weakly coordinating tris(pentafluoroethyl)trifluorophosphate counterion ( anion, [(CF)PF]). The reaction of the fluorido complexes [(carbene)CuF] (carbene = NHC, cAAC) - and the tris(pentafluoroethyl)difluorophosphorane (CF)PF in the presence of alkynes or arenes led to fluoride transfer from Cu to the phosphorane with formation of the cationic transition metal complexes [(carbene)Cu()] and the weakly coordinating counteranion [(CF)PF] (). Using this method, the complexes [(IDipp)Cu()] (IDipp = 1,3-bis(2,6-di--propylphenyl)-imidazolin-2-ylidene; = PhC≡CPh, ; PhC≡CMe, ), [(cAAC)Cu()] (cAAC = 1-(2,6-di--propylphenyl)-3,3,5,5-tetramethyl-pyrrolidin-2-ylidene; PhC≡CPh, ; PhC≡CMe, ), [(SIDipp)Cu(CMe)] (), (SIDipp = 1,3-bis(2,6-di--propylphenyl)-imidazolidine-2-ylidene), and [(cAAC)Cu(CMe)] () have been synthesized and characterized.

Phosphine-Catalyzed 1,2-cis-Diboration of 1,3-Butadiynes.

Trialkyl phosphines PMe and PEt catalyze the 1,2-cis-diboration of 1,3-butadiynes to give 1,2-diboryl enynes. The products were utilized to synthesize 1,1,2,4-tetraaryl enynes using a Suzuki-Miyaura protocol and can readily undergo proto-deborylation.

Applications of Transition Metal-Catalyzed -Fluorine-Directed C-H Functionalization of (Poly)fluoroarenes in Organic Synthesis.

The synthesis of organic compounds efficiently via fewer steps but in higher yields is desirable as this reduces energy and reagent use, waste production, and thus environmental impact as well as cost. The reactivity of C-H bonds to fluorine substituents in (poly)fluoroarenes with metal centers is enhanced relative to and positions. Thus, direct C-H functionalization of (poly)fluoroarenes without prefunctionalization is becoming a significant area of research in organic chemistry.

NHC-ligated indenyl- and fluorenyl-substituted Alanes and Gallanes: synthons towards indenyl- and fluorenyl-bridged (AlC)-heterocycles ( = 2,3).

Indenyl-(Ind) and fluorenyl-(Fl) substituted NHC-stabilized alanes and gallanes (NHC)·EHR 1-12 (NHC = IiPr, IiPr, IMe; E = Al, Ga; R = Ind, Fl) were prepared reaction of the corresponding NHC-iodoalanes and -gallanes with LiInd and LiFl, respectively. Analogously, the alane adducts with two Ind/Fl substituents (NHC)·AlHR13-18 (NHC = IiPr, IiPr, IMe; R = Ind, Fl) were obtained by using two equivalents of LiInd/LiFl. Elimination of indene and fluorene was induced thermally affording unusual dimeric and trimeric NHC-alane adducts {(NHC)·AlH}-μ-Fl 19-20 and {(NHC)·AlH-μ-R}21-23 (R = Ind, Fl; = 2, 3) with bridging indenyl and fluorenyl ligands.

How to Decarbonize N-Heterocyclic Carbenes (NHCs): The simple Alane Adducts (NHC) ⋅ AlR (R=H, Me, Et).

The reaction of the amine-stabilized alane (NMe) ⋅ AlH 1 with the backbone-saturated N-heterocyclic carbene (NHC) SIDipp (SIDipp=1,3-bis-{2,6-di-iso-propyl-phenyl}-imidazolidin-2-ylidene) at 0 °C yielded the NHC alane adduct (SIDipp) ⋅ AlH 2. Reaction at elevated temperatures or prolonged reaction at room temperature gave the product of a ring expansion reaction (RER) of the NHC, (NMe) ⋅ AlH(RER-SIDippH) 3 ⋅ (NMe). Subsequent reaction of the latter with sterically less hindered NHCs (IMe {=1,3,4,5-tetramethyl-imidazolin-2-ylidene}, IiPr {=1,3-di-iso-propyl-4,5-dimethyl-imidazolin-2-ylidene}, and IiPr {=1,3-di-iso-propyl-imidazolin-2-ylidene}) afforded the NHC-stabilized RER-products (NHC) ⋅ AlH(RER-SIDippH) 3 ⋅ (NHC) (NHC=IMe, IiPr, IiPr), while no reaction was observed with the sterically more demanding NHCs IDipp (=1,3-bis-{2,6-di-iso-propyl-phenyl}-imidazolin-2-ylidene), SIDipp and ItBu (=1,3-di-tert-butyl-imidazolin-2-ylidene).

NHC-ligated nickel(II) cyanoborate complexes and salts.

A comprehensive study on the synthesis and characterization of NHC-ligated nickel(II) cyanoborates (CBs) is presented (NHC = N-heterocyclic carbene). Nickel(II) cyanoborates Ni[BH(CN)]·HO (Ib·HO), Ni[BH(CN)]·0.5HO (Ic·0.

Pd-Catalyzed Oxidative C-H Arylation of (Poly)fluoroarenes with Aryl Pinacol Boronates and Experimental and Theoretical Studies of its Reaction Mechanism.

We report the synergistic combination of Pd(OAc) and AgO for the oxidative C-H arylation of (poly)fluoroarenes with aryl pinacol boronates (Ar-Bpin) in DMF as the solvent. This procedure can be conducted easily in air, and without using additional ligands, to afford the fluorinated unsymmetrical biaryl products in up to 98 % yield. Experimental studies suggest that the formation of [PdL(CF)] in DMF as coordinating solvent does not take place under the reaction conditions as it is stable to reductive elimination and thus would deactivate the catalyst.

Nickel(II) Cyanoborates and Cyanoborate-Ligated Nickel(II) Complexes.

Nickel(II) cyanoborates Ni[BH(CN)]·HO (·HO), Ni[BH(CN)]·0.5HO (·0.5HO), and Ni[B(CN)]·0.

Aluminum(III) Cations [(NHC) ⋅ AlMes ] : Synthesis, Characterization, and Application in FLP-Chemistry.

The three-coordinate aluminum cations ligated by N-heterocyclic carbenes (NHCs) [(NHC) ⋅ AlMes ] [B(C F ) ] (NHC=IMe 4, IiPr 5, IiPr 6, Mes=2,4,6-trimethylphenyl) were prepared via hydride abstraction of the alanes (NHC) ⋅ AlHMes (NHC=IMe 1, IiPr 2, IiPr 3) using [Ph C] [B(C F ) ] in toluene as hydride acceptor. If this reaction was performed in diethyl ether, the corresponding four-coordinate aluminum etherate cations [(NHC) ⋅ AlMes (OEt )] [B(C F ) ] 7-9 (NHC=IMe 7, IiPr 8, IiPr 9) were isolated. According to a theoretical and experimental assessment of the Lewis-acidity of the [(IMe ) ⋅ AlMes ] cation is the acidity larger than that of B(C F ) and of similar magnitude as reported for Al(C F ) .

NHC-Stabilized Dialanes(4) of Al Mes.

The synthesis and characterization of novel N-heterocyclic carbene (NHC) stabilized dialanes Al Mes as well as first investigations concerning the reactivity of these compounds are reported. The synthesis of these compounds proceeds via the mesityl-substituted alanes (NHC)⋅AlHMes (NHC=IMe {=1,3,4,5-tetramethyl-imidazolin-2-ylidene}, IiPr {=1,3-di-iso-propyl-4,5-dimethylimidazolin-2-ylidene}) and iodo-alanes (NHC)⋅AlIMes (NHC=IMe , IiPr ). Metallic reduction of (NHC)⋅AlIMes afforded the new NHC-stabilized dialanes (NHC) ⋅Al Mes (NHC=IMe , IiPr ).

N-Heterocyclic carbene and cyclic (alkyl)(amino)carbene ligated half-sandwich complexes of chromium(II) and chromium(I).

The synthesis and characterization of a series of Cr(II) N-Heterocyclic Carbene (NHC) complexes of the type [{Cr(NHC)Cl(μ-Cl)}] and [(Cyp)Cr(NHC)X] (Cyp = η-CH, cyclopentadienyl; η-CMe, pentamethylcyclopentadienyl; X = Cl, η-CH; NHC = IMe, IiPr, IMes, IDipp) as well as the cyclic (alkyl)(amino)carbene cAAC ligated complexes [(η-CH)Cr(cAAC)X] (X = Cl, NPh), [(η-CH)Cr(cAAC)Cl] (CH = Ind, indenyl) and [(η-CH)Cr(cAAC)Cl] (CH = Fl, fluorenyl) are reported. The reduction of [(η-CMe)Cr(IMe)Cl] with KC in the presence of CO afforded the NHC ligated Cr(I) metallo-radical [(η-CMe)Cr(IMe)(CO)]. Quantum chemical calculations performed on [(η-CMe)Cr(IMe)(CO)] confirm for this complex a predominantly chromium centered radical.

On the Reactivity of a NHC Nickel Bis-Boryl Complex: Reductive Elimination and Formation of Mono-Boryl Complexes.

The synthesis of the first terminal mono-boryl complexes of nickel, which are not stabilized by a pincer ligand, is reported. The reaction of the nickel bis-boryl complex cis-[Ni( Pr Im ) (Bcat) ] 1 (cat=1,2-O C H ) with the small donor ligand PMe led to a complete ligand exchange at nickel with reductive elimination of B cat and formation of the bis-NHC adduct [B cat  ⋅ ( Pr Im ) ] 3 and [Ni(PMe ) ] 2 as the metal-containing species. Electrophilic attack of MeI on complex 1 or ligand dismutation of 1 with trans-[Ni( Pr Im ) Br ] led to loss of only one boryl ligand of 1 and afforded the nickel mono-boryl complexes trans-[Ni( Pr Im ) (Bcat)Br] 4 a and trans-[Ni( Pr Im ) (Bcat)I] 4 b.

Anionic N-heterocyclic carbenes featuring weakly coordinating perfluoroalkylphosphorane moieties.

The anionic 1-methyl-3-(tris(pentafluoroethyl)difluorophosphorane)imidazoline-2-ylidenate 3 and the 1,3-bis(tris(pentafluoroethyl)difluorophosphorane)imidazoline-2-ylidenate dianion 4 were obtained in high yield by deprotonation of {(CF)PF}-methylimidazole 1 and the {(CF)PF}-imidazolate anion 2. Carbenes 3 and 4 are first examples for a novel class of NHCs carrying weakly coordinating anions (WCA-NHCs). First reactions of these new ligands with elemental selenium and chloro(phosphine)gold(I) complexes to result in an anionic selenium adduct (5) and WCA-NHC gold complexes (6 and 7) have been undertaken.

Solution and solid-state studies of hydrogen and halogen bonding with N-heterocyclic carbene supported nickel(II) fluoride complexes.

Nickel fluoride complexes of the type [Ni(F)(L)(Ar)] (L = phosphine, Ar = fluorinated arene) are well-known to form strong halogen and hydrogen bonds in solution and in the solid state. A comprehensive study of such non-covalent interactions using bis(carbene) complexes as acceptors and suitable halogen and hydrogen bond donors is presented. In solution, the complex [Ni(F)(iPrIm)(CF)] forms halogen and hydrogen bonds with iodopentafluorobenzene and indole, respectively, which have formation constants () an order of magnitude greater than those of structurally related phosphine supported nickel fluorides.

Subvalent group 13 molecules by carbene-induced hydrogen abstraction.

The -Heterocyclic Carbene (NHC) alane and gallane adducts (NHC)·Cp*AlH (NHC = MeIm5, iPrIm6, DippIm 7) and (NHC)·Cp*GaH (NHC = MeIm8, iPrIm9, DippIm 10; RIm = 1,3-di-organyl-imidazolin-2-ylidene; Dipp = 2,6 diisopropylphenyl; MeIm = 1,3,4,5-tetra-methyl-imidazolin-2-ylidene; Cp* = CMe) were prepared either the reaction of (AlHCp*)1 with the NHC or by the treatment of (NHC)·GaHI (NHC = MeIm2, iPrIm3, DippIm 4) with KCp*. The reaction of (AlHCp*)1 with the backbone saturated NHC DippIm led to NHC ring expansion instead with the formation of (RER-DippImH)AlCp* 12. Heating solutions of the gallium compounds 8-10 triggered reductive elimination of Cp*H and afforded Cp*Ga16.

An easy-to-perform evaluation of steric properties of Lewis acids.

Steric and electronic effects play a very important role in chemistry, as these effects influence the shape and reactivity of molecules. Herein, an easy-to-perform approach to assess and quantify steric properties of Lewis acids with differently substituted Lewis acidic centers is reported. This model applies the concept of the percent buried volume (% ) to fluoride adducts of Lewis acids, as many fluoride adducts are crystallographically characterized and are frequently calculated to judge fluoride ion affinities (FIAs).

Nickel boryl complexes and nickel-catalyzed alkyne borylation.

The first nickel bis-boryl complexes -[Ni( PrIm)(Bcat)], -[Ni( PrIm)(Bpin)] and -[Ni( PrIm)(Beg)] are reported, which were prepared the reaction of a source of [Ni( PrIm)] with the diboron(4) compounds Bcat, Bpin and Beg ( PrIm = 1,3-di-iso-propyl-4,5-dimethylimidazolin-2-ylidene; Bcat = bis(catecholato)diboron; Bpin = bis(pinacolato)diboron; Beg = bis(ethylene glycolato)diboron). X-ray diffraction and DFT calculations strongly suggest that a delocalized, multicenter bonding scheme dictates the bonding situation of the NiB moiety in these square planar complexes, reminiscent of the bonding situation of "non-classical" H complexes. [Ni( PrIm)] also efficiently catalyzes the diboration of alkynes using Bcat as the boron source under mild conditions.

Boranes Paving the Way to Anionic Cyclic (Alkyl)(amino)carbenes (Ani-cAACs).

First examples of anionic cyclic (alkyl)(amino)carbenes (Ani-cAACs) that contain borane substituents have been synthesized. The nature of the borane substituents allows a modulation of the σ-donor or π-acceptor abilities compared to their neutral analogues. A B(CN) -substituted Ani-cAAC has been generated and used in situ.

N-heterocyclic carbene and cyclic (alkyl)(amino)carbene complexes of molybdenum(IV) and tungsten(IV).

The synthesis and characterization of N-heterocyclic carbene (NHC) and cyclic (alkyl)(amino)carbene (cAAC) complexes of molybdenum(IV) and tungsten(IV) chloride is reported. Reaction of two equivalents of the NHCs IMes (1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene), IDipp (1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene) and IiPr (1,3-diisopropyl-4,5-dimethylimidazolin-2-ylidene) with [MCl(SEt)] (M = Mo, W) in toluene afforded the bis-NHC complexes [MCl(NHC)] (M = Mo: NHC = IMes 1, NHC = IMes 2; M = W: NHC = IMes 3, NHC = IDipp 4, NHC = IiPr5). Mono-carbene complexes [MCl(NHC)(SEt)] 6-9 (M = Mo: NHC = IMes 6, NHC = IMes 7; M = W: NHC = IMes 8, NHC = IDipp 9) are available ligand dismutation of 1-4 with [MCl(SEt)].

Activation of Ge-H and Sn-H Bonds with N-Heterocyclic Carbenes and a Cyclic (Alkyl)(amino)carbene.

A study of the reactivity of several N-heterocyclic carbenes (NHCs) and the cyclic (alkyl)(amino)carbene 1-(2,6-di-iso-propylphenyl)-3,3,5,5-tetramethyl-pyrrolidin-2-ylidene (cAAC ) with the group 14 hydrides GeH Mes and SnH Me (Me=CH , Mes=1,3,5-(CH ) C H ) is presented. The reaction of GeH Mes with cAAC led to the insertion of cAAC into one Ge-H bond to give cAAC H-GeHMes (1). If 1,3,4,5-tetramethyl-imidazolin-2-ylidene (Me Im ) was used as the carbene, NHC-mediated dehydrogenative coupling occurred, which led to the NHC-stabilized germylene Me Im ⋅GeMes (2).

-heterocyclic carbene and cyclic (alkyl)(amino)carbene adducts of plumbanes and plumbylenes.

-acid/base adducts of -heterocyclic carbenes (NHCs) and the cyclic (alkyl)(amino)carbene cAAC (1-(2,6-di-iso-propylphenyl)-3,3,5,5-tetramethyl-pyrrolidin-2-ylidene) with selected lead(II) and lead(IV) compounds are presented. The reaction of the NHCs MeIm (1,3,4,5-tetramethyl-imidazolin-2-ylidene), iPrIm (1,3-di-isopropyl-4,5-dimethyl-imidazolin-2-ylidene), DippIm (1,3-bis-(2,6-di-isopropylphenyl)-imidazolin-2-ylidene) and cAAC (1-(2,6-di-iso-propylphenyl)-3,3,5,5-tetramethyl-pyrrolidin-2-ylidene) with PbI yielded the NHC-containing plumbylenes NHC·PbI (NHC = MeIm (1), iPrIm (2), DippIm (3) and cAAC·PbI (4)). Using the Pb(IV) compound PbClPh, the plumbane adducts NHC·PbClPh (NHC = MeIm (5), iPrIm (6), DippIm (7)) and cAAC·PbClPh (8)) were isolated in high yields.