C6 H3 Research Articles

Univalent Gallium Complexes of Simple and ansa-Arene Ligands: Effects on the Polymerization of Isobutylene.

Using [Ga(C6 H5 F)2 ]+ [Al(ORF )4 ]- (1) (RF =C(CF3 )3 ) as starting material, we isolated bis- and tris-η6 -coordinated gallium(I) arene complex salts of p-xylene (1,4-Me2 C6 H4 ), hexamethylbenzene (C6 Me6 ), diphenylethane (PhC2 H4 Ph), and m-terphenyl (1,3-Ph2 C6 H4 ): [Ga(1,4-Me2 C6 H4 )2.5 ]+ (2+ ), [Ga(C6 Me6 )2 ]+ (3+ ), [Ga(PhC2 H4 Ph)]+ (4+ ) and [(C6 H5 F)Ga(μ-1,3-Ph2 C6 H4 )2 Ga(C6 H5 F)]2+ (52+ ). 4+ is the first structurally characterized ansa-like bent sandwich chelate of univalent gallium and 52+ the first binuclear gallium(I) complex without a GaGa bond. Beyond confirming the structural findings by multinuclear NMR spectroscopic investigations and density functional calculations (RI-BP86/SV(P) level), [Ga(PhC2 H4 Ph)]+ [Al(ORF )4 ]- (4) and [(C6 H5 F)Ga(μ-1,3-Ph2 C6 H4 )2 Ga(C6 H5 F)]2+ {[Al(ORF )4 ] - }2 (5), featuring ansa-arene ligands, were tested as catalysts for the synthesis of highly reactive polyisobutylene (HR-PIB). In comparison to the recently published 1 and the [Ga(1,3,5-Me3 C6 H3 )2 ]+ [Al(ORF )4 ]- salt (6) (1,3,5-Me3 C6 H3 =mesitylene), 4 and 5 gave slightly reduced reactivities. This allowed for favorably increased polymerization temperatures of up to +15 °C, while yielding HR-PIB with high contents of terminal olefinic double bonds (α-contents=84-93 %), low molecular weights (Mn =1000-3000 g mol-1 ) and good monomer conversions (up to 83 % in two hours). While the chelate complexes delivered more favorable results than 1 and 6, the reaction kinetics resembled and thus concurred with the recently proposed coordinative polymerization mechanism.

Experimental and computational studies of the molybdenum-flanking arene interaction in quadruply bonded dimolybdenum complexes with terphenyl ligands.

To clarify the nature of the Mo-Carene interaction in terphenyl complexes with quadruple Mo-Mo bonds, ether adducts of composition [Mo2 (Ar')(I)(O2 CR)2 (OEt2)] have been prepared and characterized (Ar'=Ar(Xyl) 2 , R=Me; Ar'=ArMes2, R=Me; Ar'=Ar(Xyl2), R=CF3) (Mes=mesityl; Xyl=2,6-Me2 C6 H3, from now on xylyl) and their reactivity toward different neutral Lewis bases investigated. PMe3 , P(OMe)3 and PiPr3 were chosen as P-donors and the reactivity studies complemented with the use of the C-donors CNXyl and CN2 C2 Me4 (1,3,4,5-tetramethylimidazol-2-ylidene). New compounds of general formula [Mo2 (Ar')(I)(O2 CR)2 (L)] were obtained, except for the imidazol-2-ylidene ligand that yielded a salt-like compound of composition [Mo2 (Ar(Xyl2))(O2 CMe)2 (CN2 C2 Me4)2]I. The Mo-Carene interaction in these complexes has been analyzed with the aid of X-ray data and computational studies. This interaction compensates the coordinative and electronic unsaturation of one of the Mo atoms in the above complexes, but it seems to be weak in terms of sharing of electron density between the Mo and Carene atoms and appears to have no appreciable effect in the length of the Mo-Mo, Mo-X, and Mo-L bonds present in these molecules.

Geminally diaurated aryls bridged by semirigid phosphine pillars: syntheses and electronic structure.

Geminally diaurated μ2 -aryl complexes have been prepared where gold(I) centers were bridged by the semirigid diphosphine ligands bis(2-diphenylphosphinophenyl)ether (DPEphos) and 4,6-bis(diphenylphosphanyl)dibenzo[b,d]furan (DBFphos). Diaurated complexes were synthesized in ligand redistribution reactions of the corresponding di-gold dichlorides with di-gold diaryls (six of them new) and silver(I) salts. Diaurated complexes were isolated as salts of the minimally coordinating anions SbF6 (-) and ReO4 (-). Efforts to prepare salts of the tetraarylborate [B(3,5-(CF3)2 C6 H3)4](-) led to transmetalation from boron, with crystallization of the fluorinated aryl complex. The new complexes were characterized by multinuclear NMR, absorption and emission spectroscopies, 77 K emission lifetimes, and by combustion analysis; three are crystallographically characterized. Structures of geminally diaurated aryl ligands are compared to those of mono-aurated analogues. Both crystal structures and density-functional theory calculations indicate slight but observable disruptions of aryl ligand aromaticity by geminal di-gold binding. An intermolecular aurophilic interaction in one structurally authenticated complex was examined computationally.

Podand-based dimeric chromium(III)-salen complex for asymmetric Henry reaction: cooperative catalysis promoted by complexation of alkali metal ions.

A new kind of podand-based dimeric salen ligand was synthesized, and its association with potassium cations was investigated by (1) H NMR spectroscopy. The corresponding Cr(III) -salen dimer was assembled by a supramolecular host-guest self-assembly process and was then used as a catalyst in highly efficient and enantioselective asymmetric Henry reactions. Regulation by KBArF (BArF =[3,5-(CF3 )2 C6 H3 ]4 B) led to remarkable improvements in yield (by up to 58 %) and enantioselectivity (for example, from 80 % ee to 96 % ee).

Expanded-ring N-heterocyclic carbenes for the stabilization of highly electrophilic gold(I) cations.

Strategies for the synthesis of highly electrophilic Au(I) complexes from either hydride- or chloride-containing precursors have been investigated by employing sterically encumbered Dipp-substituted expanded-ring NHCs (Dipp=2,6-iPr2 C6 H3 ). Thus, complexes of the type (NHC)AuH have been synthesised (for NHC=6-Dipp or 7-Dipp) and shown to feature significantly more electron-rich hydrides than those based on ancillary imidazolylidene donors. This finding is consistent with the stronger σ-donor character of these NHCs, and allows for protonation of the hydride ligand. Such chemistry leads to the loss of dihydrogen and to the trapping of the [(NHC)Au](+) fragment within a dinuclear gold cation containing a bridging hydride. Activation of the hydride ligand in (NHC)AuH by B(C6 F5 )3 , by contrast, generates a species (at low temperatures) featuring a [HB(C6 F5 )3 ](-) fragment with spectroscopic signatures similar to the "free" borate anion. Subsequent rearrangement involves BC bond cleavage and aryl transfer to the carbophilic metal centre. Under halide abstraction conditions utilizing Na[BAr(f) 4 ] (Ar(f) =C6 H3 (CF3 )2 -3,5), systems of the type [(NHC)AuCl] (NHC=6-Dipp or 7-Dipp) generate dinuclear complexes [{(NHC)Au}2 (μ-Cl)](+) that are still electrophilic enough at gold to induce aryl abstraction from the [BAr(f) 4 ](-) counterion.

Small molecule activation by POC(sp3)OP-nickel complexes.

This contribution describes the reactivities of CO2 , CO, O2 , and ArNC with the pincer-type complexes [(κ(P) ,κ(C) ,κ(P') -POC sp 3OP)NiX] (POC sp 3OP=(R2 POCH2 )2 CH; R=iPr; X=OSiMe3 , NArH; Ar=2,6-iPr2 C6 H3 ). Reaction of the amido derivative with CO2 and CO leads to a simple insertion into the NiN bond to give stable carbamate and carbamoyl derivatives, respectively, the pincer ligand backbone remaining intact in both cases. In contrast, the analogous reactions with the siloxide derivative produced kinetically labile insertion products that either revert to the starting material (in the case of CO2 ) or react further to give the mixed-valent, dinickel species [(POC sp 3OP)Ni(II) {μ,κ(O) ,κ(P) ,κ(P') -OCOCH(CH2 CH2 OPR2 )2 }Ni(0) (CO)2 ]. The zero-valent center in the latter compound is ligated by a new ligand arising from transformation of the POC sp 3OP ligand backbone. The carbonylation and carboxylation of the siloxido derivative also produced minor quantities of a side-product identified as the trinickel species, [{(η(3) -allyl)Ni(μ(O) ,κ(P) -R2 PO)2 }2 Ni], arising from total dismantling of the POC sp 3OP ligand. Similar reactivities were observed with isonitrile, ArNC: reaction with the siloxido derivative resulted in a complex sequence of steps involving initial insertion, a 1,3-hydrogen shift, and an Arbuzov rearrangement to give [Ni(CNAr)4 ] and a methacrylamide based on fragments of the POC sp 3OP ligand. Oxygenation of the amido and siloxido derivatives led to the phosphinate derivative, [(POC sp 3OP)Ni(OP(O)R2 )], arising from oxidative transformation of the original ligand frame; the reaction with the Ni-NHAr derivative also gave ArHNP(O)R2 through a complex NP bond-forming reaction.

2-chloro-azaborolyl anion: a source of 1,2-azaborole isosteric to cyclopentadienylidene.

Azaborolyl anions, the five-membered BN heterocycles, have attracted a considerable attention due to their aromaticity and isoelectronic relationship with ubiquitous cyclopentadienyl ligands. Besides their syntheses and applications in the preparation of metal complexes, the other aspects of their chemistry have been virtually unexplored. Reduction of the azabutadienyl chelate boron dichloride [ArNC(R)CHC(R)]BCl2 (2, Ar=2,6-Me2 C6 H3 , R=tBu) with two equivalents of potassium yielded the novel 2-chloro-azaborolyl anion [ArNC(R)CHC(R)BCl]K(thf) (3) as a stable product in good yield. Reaction of 3 with 1,3,4,5-tetramethylimidazol-2-ylidene (NHC) yielded the first NHC-azaborole adduct with the elimination of KCl. The salt elimination reaction was also observed in the reactions with H2 O and the organic azide ArN3 , leading to the formation of an oxo-bridged 3H-1,2-diazaborole and an intramolecular donor-stabilized iminoborane, demonstrating that 3 is a source of the unexplored 1,2-azaborole isosteric to cyclopentadienylidene.

Synthesis and structure of bis(m-terphenyl)zinc (2,6-Mes2 C6 H3)2 Zn

AbstractThe title compound bis(

XeF2/Fluoride Acceptors as Versatile One‐Electron Oxidants

No phlogiston but xenon is released when XeF2 /F(-) acceptors act as new one-electron oxidants. F(-) acceptors are Lewis acids BF3 , B(C6 F5 )3 , and Al{OC(CF3 )3 }3 , and silyl derivatives TfOSiMe3 , Tf2 NSiMe3 , Me3 Si(+) B(C6 F5 )4 (-) , and Me3 Si(+) CHB11 Cl11 (-) . The anions BF4 (-) , TfO(-) , Tf2 N(-) , FB(C6 F5 )3 (-) , FAl{OC(CF3 )3 }3 (-) , B(C6 F5 )4 (-) , or CHB11 Cl11 (-) can be introduced into oxidation products of R2 E2 (E=S, Se, Te), [FeCp2 ], [(FeCpS)4 ], tetrathiafulvalene, thianthrene, and (2,4-Br2 C6 H3 )3 N.

The Role of 2,6‐Diaminopyridine Ligands in the Isolation of an Unprecedented, Low‐Valent Tin Complex

Stabilization of the central atom in an oxidation state of zero through coordination of neutral ligands is a common bonding motif in transition-metal chemistry. However, the stabilization of main-group elements in an oxidation state of zero by neutral ligands is rare. Herein, we report that the transamination reaction of the DAMPY ligand system (DAMPY=2,6-[ArNH-CH2 ]2 (NC5 H3 ) (Ar=C6 H3 -2,6-iPr2 )) with Sn[N(SiMe3 )2 ]2 produces the DIMPYSn complex (DIMPY=(2,6-[ArNCH]2 (NC5 H3 )) with the Sn atom in a formal oxidation state of zero. This is the first example of a tin compound stabilized in a formal oxidation state of zero by only one donor molecule. Furthermore, three related low-valent Sn(II) complexes, including a [DIMPYSn(II) Cl](+) [SnCl3 ](-) ion pair, a bisstannylene DAMPY{Sn(II) [N(SiMe3 )2 ]2 }2 , and the enamine complex MeDIMPYSn(II) , were isolated. Experimental results and the conclusions drawn are also supported by theoretical studies at the density functional level of theory and (119) Sn Mössbauer spectroscopy.

An Extensive n, π, σ‐Electron Delocalized Si4 Ring

The tetrasilacyclobutadiene [LSi(μ-SiL')2 SiL] (L=PhC(NtBu)2 , L'=2,6-iPr2 C6 H3 NSiMe3 ) consists of an aromatic silicon-containing four-membered ring in which two π, two σ, and two lone-pair electrons are cyclically delocalized. The electron delocalization was illustrated by theoretical studies and reactivity with elemental sulfur to form the allylic zwitterionic cyclic compound [(LSi)2 (μ-SiL')(μ-Si(S)L')] with 2π-electron delocalization along the Si3 skeleton.

Zwitterionic Base‐Stabilized Digermadistannacyclobutadiene and Tetragermacyclobutadiene

The syntheses of a zwitterionic base-stabilized digermadistannacyclobutadiene and tetragermacyclobutadiene supported by amidinates and low-valent germanium amidinate substituents are described. The reaction of the amidinate Ge(I) dimer, [LGe:]2 (1, L=PhC(NtBu)2 ), with two equivalents of the amidinate tin(II) chloride, [LSnCl] (2), and KC8 in tetrahydrofuran (THF) at room temperature afforded a mixture of the zwitterionic base-stabilized digermadistannacyclobutadiene, [L2 Ge2 Sn2 L'2 ] (3; L'=LGe:), and the bis(amidinate) tin(II) compound, [L2 Sn:] (4). Compound 3 can also be prepared by the reaction of 1 with [L(Ar) SnCl] (5, L(Ar) =tBuC(NAr)2 , Ar=2,6-iPr2 C6 H3 ) in THF at room temperature. Moreover, the reaction of 1 with the "onio-substituent transfer" reagent [4-NMe2 -C5 H4 NSiMe3 ]OTf (8) in THF and 4-(N,N-dimethylamino)pyridine (DMAP) at room temperature afforded a mixture of the zwitterionic base-stabilized tetragermacyclobutadiene, [L4 Ge6 ] (9), the amidinium triflate, [PhC(NHtBu)2 ]OTf (10), and Me3 SiSiMe3 (11). X-ray structural data and theoretical studies show conclusively that compounds 3 and 9 have a planar and rhombic charge-separated structure. They are also nonaromatic.

Turning a Transition State into a Minimum-The Nature of the Bonding in Diplumbylene Compounds RPbPbR (R=H, Ar).

Quantum-chemical calculations at the B3LYP level show that the bulky ligands Ar*=2,6-Ph2 C6 H3 in Ar*PbPbAr* yield the trans-bent equilibrium structure shown as the lowest lying energy minimum form. There is no Pb-Pb π bond in Ar*PbPbAr*. The parent compounds PhPbPbPh and HPbPbH have doubly bridged energy minima structures.

Stable, Monomeric Imides of Aluminum and Gallium: Synthesis and Characterization of [{HC(MeCDippN)2 }MN-2,6-Trip2 C6 H3 ] (M=Al or Ga; Dipp=2,6-iPr2 C6 H3 ; Trip=2,4,6-iPr3 C6 H2 ).

A short Ga-N bond with double-bond character is displayed by the first monomeric imide of gallium, which was obtained by the reaction of [{HC(MeCDippN)2 }M:] (Dipp=2,6-iPr2 C6 H3 , M=Ga; see picture) with N3 -2,6-Trip2 C6 H3 (Trip=2,4,6-iPr3 C6 H2 ). The analogous aluminum (M=Al) compound is also readily available.

A Route to a Germanium-Carbon Triple Bond: First Chemical Evidence for a Germyne.

Photolysis of a diazogermylene generates a germylene-carbene species, a resonance form of a germyne. Support for the intermediacy of the triply bonded form in the trapping reaction with an alcohol is provided by the fact that the diazo precursor does not behave as a germylene and that its photolysis product does not react with carbene traps such as 2,3-dimethylbutadiene. Hence, this is the first chemical evidence for a germyne. Ar=2,6-(iPr2 NCH2 )2 C6 H3 ; R=Me, tBu.

Synthesis and Structure of a Monomeric Aluminum(I) Compound [{HC(CMeNAr)2 }Al] (Ar=2,6-iPr2 C6 H3 ): A Stable Aluminum Analogue of a Carbene.

A monovalent aluminum monomer [{HC(CMeNAr)2}Al] was obtained by reduction of the corresponding aluminum(III) diiodide. The molecular structure shows a unique two-coordinate aluminum center and a planar heterocyclic Al-N-C-C-C-N six-membered ring system (see picture). A nonbonded lone pair of electrons on the Al atom indicates the Lewis base character of the aluminum center. Ar=2,6-iPr2C6H3.

Thermally Stable Heterobinuclear Bivalent Group 14 Metal Complexes Ar2 M-Sn[1,8-(NR)2 C10 H6 ] (M=Ge, Sn; Ar=2,6-(Me2 N)2 C6 H3 ; R=CH2 tBu).

The first thermally robust Ge(II) -Sn(II) compound 1 and the structurally characterized Sn(II) -Sn(II) analogue 2, which maintain their structural integrity in solution, were obtained by treating MAr2 (M=Ge, Sn; Ar=2,6-(Me2 N)2 C6 H3 ) with Sn[1,8-(NR2 )2 C10 H6 ] (R=CH2 tBu). On the basis of structural and spectroscopic data, the M-Sn bond is regarded as the interaction of a MAr2 donor with an Sn[1,8-(NR2 )2 C10 H6 ] acceptor.

{MeAl(μ2 -F)}2 N(2,6-iPr2 C6 H3 )]4 - A Molecular Al-F-N Cage Compound.

In a two-step elimination reaction the molecular Al-F-N cage compound 1 is synthesized from (2,6-iPr2 C6 H3 )NH2 (ArNH2 ) and Me2 AlF under methane evolution. Compound 1 was characterized by means of X-ray structure analysis and can be regarded as a precursor for ternary Al-F-N systems.

Reaction of RGeBr3 (R=iPr2 C6 H3 NSiMe3 ) with Ammonia To Give (RGe)2 (NH2 )4 (NH): A Compound Containing Terminal NH2 Groups.

The surprisingly facile preparation of (RGe)2 (NH2 )4 (NH) (1; R=iPr2 C6 H3 NSiMe3 ), which contains one NH and four NH2 groups, is achieved by the introduction of gaseous ammonia into a solution of iPr2 C6 H3 NSiMe3 GeBr3 in diethyl ether.

Organometallic Triskelia: Novel Tris(vinylideneruthenium(II)), Tris(alkynylruthenium(II)), and Triruthenium-Triferrocenyl Complexes.

Incorporation of a redox-passive bridge affords three identical redox systems in the triskelion-shaped, carbon-rich, polyvinylidenemetal complex 1. The complex was isolated from the activation of the tripodal polyyne 1,3,5-(HC≡CC6 H4 C≡C)3 C6 H3 with [RuCl2 ({(Ph2 P)2 C2 H4 }2 ] and further converted into polyynylmetal complexes and a triple ferrocenyl-substituted ruthenium complex.