Carbene Adducts Research Articles

Silylium–Arene Adducts: An Experimental and Theoretical Study

The solvent-coordinated [Me(3)Si·arene][B(C(6)F(5))(4)] salts (arene = benzene, toluene, ethylbenzene, n-propylbenzene, isopropylbenzene, o-xylene, m-xylene, p-xylene, 1,2,3-trimethylbenzene, 1,2,4-trimethylbenzene, 1,3,5-trimethylbenzene) are prepared and fully characterized. As an interesting decomposition product the formation of bissilylated fluoronium ion [Me(3)Si-F-SiMe(3)](+) was observed and even cocrystallized with [Me(3)Si·arene][B(C(6)F(5))(4)] (arene = benzene and toluene). Investigation of the degradation of [Me(3)Si·arene][B(C(6)F(5))(4)] reveals the formation of fluoronium salt [Me(3)Si-F-SiMe(3)][B(C(6)F(5))(4)], B(C(6)F(5))(3), and a reactive "C(6)F(4)" species which could be trapped with CS(2). Upon addition of CS(2), the formation of a formal S-heterocyclic carbene adduct, C(6)F(4)CS(2)-B(C(6)F(5))(3), was observed. The structure and bonding of substituted [Me(3)Si·arene][B(C(6)F(5))(4)] with arene = R(n)C(6)H(6-n) (R = H, Me, Et, Pr, and Bu; n = 0-6) is discussed on the basis of experimental and theoretical data. X-ray data of [Me(3)Si·arene][B(C(6)F(5))(4)] salts reveal nonplanar arene species with significant cation···anion interactions. As shown by different theoretical approaches (charge transfer, partial charges, trimethylsilyl affinity values) stabilizing inductive effects occur; however, the magnitude of such effects differs depending on the degree of substitution and the substitution pattern.

Pyrazolium-sulfonates. Mesomeric betaines possessing iminium-sulfonate partial structures

Pyrazolium-3-sulfonates and pyrazolium-4-sulfonates possessing the iminiomethanesulfonate and the 3-iminio-pro-1-ene-2-sulfonate partial structure are prepared. Formally, they represent sulfur analogs of cross-conjugated (CCMB) and pseudo-cross-conjugated heterocyclic mesomeric betaines (PCCMB) and sulfur trioxide adducts of abnormal N-heterocyclic carbenes (aNHC) and N-heterocyclic carbenes (NHC), respectively. The theoretical as well as experimental vibrational spectra of these two classes are compared. Results of calculations of HOMO/LUMO profiles and an X-ray single crystal structure analysis are presented.

Carbene adduct of cyclopalladated ferrocenylimine catalyzed α-arylation of ketones with aryl chlorides or bromides

Carbene adduct of cyclopalladated ferrocenylimine exhibited highly catalytic activity for the α-arylation of ketones with aryl halides. The corresponding products were obtained in moderate to excellent yields. Such protocol was applied to various ketones and a broad scope of aryl halides including aryl chlorides, bromides as well as unactivated and sterically hindered aryl halides.

Carbon–Silicon and Carbon–Carbon Bond Formation by Elimination Reactions at Metal N-Heterocyclic Carbene Complexes

Two functional groups can be delivered at once to organo-rare earth complexes, (L)MR(2) and (L)(2)MR (M = Sc, Y; L = ({1-C(NDippCH(2)CH(2)N)}CH(2)CMe(2)O), Dipp = 2,6-(i)Pr(2)-C(6)H(3); R = CH(2)SiMe(3), CH(2)CMe(3)), via the addition of E-X across the metal-carbene bond to form a zwitterionic imidazolinium-metal complex, (L(E))MR(2)X, where L(E) = {1-EC(NDippCH(2)CH(2)N)}CH(2)CMe(2)O, E is a p-block functional group such as SiR(3), PR(2), or SnR(3), and X is a halide. The "ate" complex (L(Li))ScR(3) is readily accessible and is best described as a Li carbene adduct, ({1-Li(THF)C(NDippCH(2)CH(2)N)}CH(2)CMe(2)O)Sc(CH(2)SiMe(3))(3), since structural characterization shows the alkoxide ligand bridging the two metals and the carbene Li-bound with the shortest yet recorded Li-C bond distance. This can be converted via lithium halide-eliminating salt metathesis reactions to alkylated or silylated imidazolinium derivatives, (L(E))ScR(3) (E = SiMe(3) or CPh(3)). All the E-functionalized imidazolinium complexes spontaneously eliminate functionalized hydrocarbyl compounds upon warming to room temperature or slightly above, forming new organic products ER, i.e., forming C-Si, C-P, and C-Sn bonds, and re-forming the inorganic metal carbene (L)MR(X) or (L)(2)MX complex, respectively. Warming the tris(alkyl) complexes (L(E))MR(3) forms organic products arising from C-C or C-Si bond formation, which appears to proceed via the same elimination route. Treatment of (L)(2)Sc(CH(2)SiMe(3)) with iodopentafluorobenzene results in the "reverse sense" addition, which upon thermolysis forms the metal aryl complex (L)(2)Sc(C(6)F(5)) and releases the iodoalkane Me(3)SiCH(2)I, again facilitated by the reversible functionalization of the N-heterocyclic carbene group in these tethered systems.

Synthesis and Structural Characterization of the First Thermally Stable, Neutral, and Electrophilic Phosphinidene Complexes of Vanadium

The first thermally stable, neutral, electrophilic phosphinidene complexes of vanadium, [CpV(CO)3{η1-P(NR2)}] (R = iPr (3a), Cy (3b)), have been prepared by the reaction of [Na]2[CpV(CO)3] with Cl2PNR2. The molecules 3a and 3b have been characterized by microanalysis, IR, and 1H and 31P{1H} NMR spectroscopy, and for 3a also by single-crystal X-ray diffraction. The structure of 3a exhibits a piano stool geometry closely related to that of CpV(CO)4 with an η1-phosphinidene ligand replacing CO in one of the basal coordination sites of the vanadium atom (V(1)−P(1) = 2.300(2) A). The reactivity of 3a toward a variety of unsaturated substrates: PhC≡CPh, di-tBu-imidazol-2-ydene, PhN3, and Ph2C═N═N has been examined to probe the electrophilic (or nucleophilic) character of the low-coordinate P(I) site. In all cases reactions occur exclusively at the phosphinidene phosphorus atom, without CO displacement, affording examples of P-coordinated phosphirene [CpV(CO)3{P(NiPr2)CPh═CPh}] (7), abnormal NCN carbene adduct [...

Amino-Substituted Butatrienes: Unusual η1 Ligands Formed by an Unusual Reaction

The reaction of the bis(amino)allenylidene complex [(CO)5W═C═C═C(NMe2)2] with diethyldiazomethane yields two products, a cyclic carbene complex (2) by 1,2-addition of Et2C−N2 to the Cα−Cβ bond of the allenylidene ligand and the η1-butatriene complex [(CO)5W{C[C(NMe2)2]═C═CEt2}] (3). Complex 2 slowly eliminates N2 and rearranges into 3. In contrast, only η1-butatriene complexes, [(CO)5M{C[C(NMe2)XR]═C═C(R′)2}], are isolated from the reaction of diazoalkanes (R′)2C−N2 (R′ = Me, Et, nPr) with alkoxy(amino)allenylidene complexes [(CO)5M═C═C═C(NMe2)OR] (M = Cr, W; R = Me, Et, (−)-menthyl) or with the (alkylthio)(amino)allenylidene complex [(CO)5W═C═C═C(NMe2)SnPr]. These new η1-butatriene complexes are related to Cα phosphine adducts of allenylidene complexes such as [(CO)5W{C(PMe3)═C═C(NMe2)Ph}] (17) and might be regarded as Cα carbene adducts. However, the PMe3 substituent in 17 is not replaced when 17 is treated with an N-heterocyclic carbene. Vice versa, the “carbene” substituent “C(NMe2)OEt” in the η1-butatriene complex [(CO)5Cr{C[C(NMe2)OEt]═C═CEt2}] is not replaceable by PMe3. Free N-heterocyclic carbenes do not add to the Cα atom of the allenylidene complex [(CO)5W═C═C═C(C6H4NMe2-p)2] but instead to the Cγ atom, giving the dipolar neutral alkynyl complexes [(CO)5W−C≡CC(C6H4NMe2-p)2L] (L = SIMe, SIMes). DFT calculations on the reaction mechanism indicate that a cyclic carbene complex and two isomeric η2-butatriene complexes are intermediates in the reaction pathway to form η1-butatriene complexes. The structure of two representative examples of η1-butatriene complexes and of one Cγ carbene adduct has been established by X-ray structure analyses.

Sc2C2@C80 Rather than Sc2@C82: Templated Formation of Unexpected C2v(5)-C80 and Temperature-Dependent Dynamic Motion of Internal Sc2C2 Cluster

Unambiguous X-ray crystallographic results of the carbene adduct of Sc(2)C(82) reveal a new carbide cluster metallofullerene with the unexpected C(2v)(5)-C(80) cage, that is, Sc(2)C(2)@C(2v)(5)-C(80). More interestingly, DFT calculations and NMR results disclose that the dynamic motion of the internal Sc(2)C(2) cluster depends strongly on temperature. At 293 K, the cluster is fixed inside the cage with two nonequivalent Sc atoms on the mirror plane, thereby leading to C(s) symmetry of the whole molecule. However, when the temperature increases to 413 K, the (13)C and (45)Sc NMR spectra show that the cluster rotates rapidly inside the C(2v)(5)-C(80) cage, featuring two equivalent Sc atoms and weaker metal-cage interactions.

Synthesis and Crystal Structures of Two N-Heterocyclic Carbene Adducts of CrCl2

The reactions of CrCl2 with two N-heterocyclic carbenes (NHC) have afforded the complexes, trans-[CrCl2(NHC)2] (NHC = :C{N(C6H3Pr 2 i -2,6)C(H)}2 1 or :C{N(Pri)C(Me)}2 2). The cell parameters of the compounds are 1: P212121, a = 12.9445(4), b = 20.7364(5), c = 21.2841(6); 2: Pca21, a = 21.7583(14), b = 9.9465(8), c = 11.4414(9). The crystal structures of the complexes are the first for NHC adducts of CrCl2, and both exhibit square planar chromium centers. The synthesis and crystal structures of two N-heterocyclic carbene adducts of CrCl2, trans-[CrCl2(NHC)2] (NHC = :C{N(C6H3Pr 2 i -2,6)C(H)}2 or :C{N(Pri)C(Me)}2) are reported.

Structure and bonding in three-coordinate N-heterocyclic carbene adducts of iron(ii) bis(trimethylsilyl)amide

The molecular structures, chemical bonding and magnetochemistry of the three-coordinate iron(II) NHC complexes [(NHC)Fe{N(SiMe(3))(2)}(2)] (NHC = IPr, 2; NHC = IMes, 3) are reported.

ChemInform Abstract: Study on the Heck Reaction Promoted by Carbene Adduct of Cyclopalladated Ferrocenylimine and the Related Reaction Mechanism.

Abstract Carbene adduct of cyclopalladated ferrocenylimine has been successfully applied to Heck reaction of various aryl bromides with olefins. On the basis of kinetic studies, in situ 13C NMR spectra investigations and Hg poisoning experiments, it was proposed that the Heck reaction catalyzed by carbene adduct of cyclopalladated ferrocenylimine proceeded through a classical Pd(0)/Pd(II) cycle and such palladacycle was only a reservoir of the catalytically active Pd(0) species.

ChemInform Abstract: Reaction of Dichlorocarbene with Substituted 3,4-Dihydroisoquinolines and 1-Methylene-1,2,3,4-tetrahydroisoquinolines.

Reaction of dichlorocarbene with 3,3-dialkyl-3,4-dihydroisoquinolines results in the formation of gemdichloroazirino[2,1-a]isoquinolines, which are in turn converted to 3-benzazepinones upon hydrolysis. Reaction of dichlorocarbene with the ethyl ester or amide of (3,3-dimethyl-1,2,3,4-tetrahydroisoquinolin-1-ylidene)acetic acid is accompanied by rearrangement of the intermediate carbene adducts at the enamine C=C bond and results in the formation of a 1-azadiene, 3-(3,3-dimethyl-3,4-dihydroisoquinolin-1-yl)-3-chloroacrylic acid ethyl ester, and a spirolactam, 3,3-dimethyl-3-chlorospiro[1,2,3,4-tetrahydroisoquinoline-1,2′-pyrrole]-5′(2′H)-one, respectively.

ChemInform Abstract: Efficient Synthesis of Biaryls Through the Kumada Reaction Catalyzed by Carbene Adducts of Cyclopalladated Ferrocenylimine.

AbstractThe novel ferrocene‐Pd‐carbene catalyst allows the preparation of a variety of biaryls and polyarylalkenes in high yields from aryl bromides and chlorides.

Synthesis and Structures of Fused N-Heterocylic Carbenes and Their Rhodium Complexes

New procedures for the synthesis of N-heterocyclic carbenes with multiple fused rings have been developed utilizing a key ring-closing metathesis step. Rhodium complexes were obtained via the pentafluorophenyl carbene adducts. Solid-state structural behaviors of the new carbene ligands were analyzed via X-ray crystallography.

Deboronation and Deprotonation of ortho‐Carborane with N‐Heterocyclic Carbenes

It is a matter of size: N-Heterocyclic carbenes can remove a proton from ortho-carborane to form a two-cage anion or attack the electropositive boron of ortho-carborane to yield a stable 1:2 carborane–carbene adduct. Which end product is formed depends on the steric bulk of the alkyl groups attached to the nitrogen atoms of the carbene.

Synthesis of a stable adduct of dialane(4) (Al2H4) via hydrogenation of a magnesium(I) dimer

The desorption of dihydrogen from magnesium(II) hydride, MgH2 (containing 7.6 wt% H), is reversible. MgH2 therefore holds promise as a hydrogen storage material in devices powered by fuel cells. We believed that dimeric magnesium(I) dimers (LMgMgL, L=β-diketiminate) could find use as soluble models to aid the study of the mechanisms and/or kinetics of the hydrogenation of magnesium and its alloys. Here, we show that LMgMgL can be readily hydrogenated to yield LMg(µ-H)2MgL by treatment with aluminium(III) hydride complexes. In one case, hydrogenation was reversed by treating LMg(µ-H)2MgL with potassium metal. The hydrogenation by-products are the first thermally stable, neutral aluminium(II) hydride complexes to be produced, one of which, [{(IPr)(H)2Al}2] (IPr=:C[{(C6H3-i-Pr(2)-2,6)NCH}2]), is an N-heterocyclic carbene adduct of the elusive parent dialane4 (Al2H4). A computational analysis of this compound is presented.

Synthesis of 4- and 4,5-functionalized imidazol-2-ylidenes from a single 4,5-unsubstituted imidazol-2-ylidene.

Using the nucleophilicity of NHCs and aNHCs, as well as the leaving group ability of the former, the carbon-carbon double bond of imidazol-2-ylidenes can be readily mono- and difunctionalized. These results provide also a new light on the formation of abnormal carbene adducts from classical unsaturated NHCs.

Study on the Heck reaction promoted by carbene adduct of cyclopalladated ferrocenylimine and the related reaction mechanism

Carbene adduct of cyclopalladated ferrocenylimine has been successfully applied to Heck reaction of various aryl bromides with olefins. On the basis of kinetic studies, in situ 13C NMR spectra investigations and Hg poisoning experiments, it was proposed that the Heck reaction catalyzed by carbene adduct of cyclopalladated ferrocenylimine proceeded through a classical Pd(0)/Pd(II) cycle and such palladacycle was only a reservoir of the catalytically active Pd(0) species.

Efficient Synthesis of Biaryls through the Kumada Reaction Catalyzed by Carbene Adducts of Cyclopalladated Ferrocenylimine

AbstractA series of carbene adducts of cyclopalladated ferrocenylimine were prepared and evaluated in the cross‐coupling reaction of aryl halides with Grignard reagents (the Kumada reaction). Complex d exhibited high catalytic activity for the coupling of aryl chlorides with sterically hindered Grignard reagents and the reaction tolerated various functional groups. A wide range of biaryls were efficiently obtained in good to excellent yields in the presence of 0.5 mol‐% catalyst under mild reaction conditions.

Stable N‐Heterocyclic Carbene Adducts of Arylchlorosilylenes and Their Germanium Homologues

The first N-heterocyclic carbene adducts of arylchlorosilylenes are reported and compared with the homologous germanium compounds. The arylsilicon(II) chlorides SiArCl(Im-Me(4)) [Ar=C(6)H(3)-2,6-Mes(2) (Mes=C(6)H(2)-2,4,6-Me(3)), C(6)H(3)-2,6-Trip(2) (Trip=C(6)H(2)-2,4,6-iPr(3))] were obtained selectively on dehydrochlorination of the arylchlorosilanes SiArHCl(2) with 1,3,4,5-tetramethylimidazol-2-ylidene (Im-Me(4)). The analogous arylgermanium(II) chlorides GeArCl(Im-Me(4)) were prepared by metathetical exchange of GeCl(2)(Im-Me(4)) with LiC(6)H(3)-2,6-Mes(2) or addition of Im-Me(4) to GeCl(C(6)H(3)-2,6-Trip(2)). All compounds were fully characterized. Density functional calculations on ECl(C(6)H(3)-2,6-Trip(2))(Im-Me(4)), where E=Si, Ge, at different levels of theory show very good agreement between calculated and experimental bonding parameters, and NBO analyses reveal similar electronic structures of the two aryltetrel(II) chlorides. The low gas-phase Gibbs free energy of bond dissociation of SiCl(C(6)H(3)-2,6-Trip(2))(Im-Me(4)) (Delta(calcd) degrees=28.1 kJ mol(-1)) suggests that the carbene adducts SiArCl(Im-Me(4)) may be valuable transfer reagents of the arylsilicon(II) chlorides SiArCl.

Different electronic structure of phosphonyl radical adducts of N-heterocyclic carbenes, silylenes and germylenes: EPR spectroscopic study and DFT calculations

Stable N-heterocyclic carbenes and germylenes were allowed to react with a phosphonyl radical, (i-PrO)2(O)P˙ (7), generated by photolysis of [(i-PrO)2(O)P]2Hg. The products were identified by EPR spectroscopy. An unsaturated carbene (1) and germylene (3) react with 7 at the divalent atom to give unstable radical products (τ½ = 0.2 s). A benzo-annulated carbene (4) and a saturated germylene (6) react with 7 to give more active radicals. An unsaturated (2) and a saturated silylene (5) undergo rapid reaction (in the dark) with [(i-PrO)2(O)P]2Hg to yield unusual silyl phosphites. In these cases only secondary radicals were observed. DFT (PBE0/TZVP//B3LYP/6-31+G(d)) calculations of the radical adducts of the different (C, Si, Ge) unsaturated N-heterocyclic divalent species with the phosphonyl radical show that the unpaired electron is delocalized over the five-membered ring; the spin density on the central atoms decreases in the order C, 39% > Si, 14% > Ge, 2%. These trends can be understood in terms of a zwitterionic structure of the radical adducts. The calculations of the radical adducts of 4, 5 and 6 with 7 indicate larger spin density on the central atom, 47%, 58% and 42% on C, Si, Ge, respectively.