Reactivity of the Bicyclic Amido-Substituted Silicon(I) Ring Compound Si4{N(SiMe3)Mes}4 with FLP-Type Character

The bicyclic amido-substituted silicon(I) ring compound Si₄{N(SiMe₃)Mes}₄ 2 (Mes=Mesityl=2,4,6-Me₃C₆H₂) features enhanced zwitterionic character and different reactivity from the analogous compound Si₄{N(SiMe₃)Dipp}₄ 1 (Dipp=2,6-ⁱPr₂C₆H₃) due to the smaller mesityl substituents. In a reaction with the N-heterocyclic carbene NHC (1,3,4,5-tetramethyl-imidazol-2-ylidene), we observe adduct formation to give Si₄{N(SiMe₃)Mes}₄ ⋅ NHC ( 3 ). This adduct reacts further with the Lewis acid BH₃ to yield the Lewis acid–base complex Si₄{N(SiMe₃)Mes}₄ ⋅ NHC ⋅ BH₃ ( 4 ). Coordination of AlBr₃ to 2 leads to the adduct 5 . Calculated proton affinities and fluoride ion affinities reveal highly Lewis basic and very weak Lewis acidic character of the low-valent silicon atoms in 1 and 2 . This is confirmed by protonation of 1 and 2 with Brookharts acid yielding 6 and 7 . Reaction with diphenylacetylene only occurs at 111 °C with 2 in toluene and is accompanied by fragmentation of 2 to afford the silacyclopropene 8 and the trisilanorbornadiene species 9 .     

A Flexible Approach to Strained Sandwich Compounds: Chiral [1]Ferrocenophanes with Boron,Gallium, Silicon,and Tin in Bridging Positions

The enantiomerically pure dibromoferrocene 3 [(S_p,S_p)‐1,1′‐dibromo‐2,2′‐di(isopropyl)ferrocene], equipped with two iPr groups in α positions, was prepared using known “Ugi amine” chemistry. Species 3 was targeted in order to gain access to new [1]ferrocenophanes ([1]FCPs) to be used as monomers for ring‐opening polymerization. The iPr groups on the sandwich unit were introduced to stabilize bridging moieties, as well as to increase solubilities of targeted metallopolymers. The planar chiral dibromide 3 can quantitatively be lithiated at 0 °C [2 equiv nBuLi, hexanes/thf (9:1), 30 min]. Salt‐metathesis reactions with respective element dichloride species gave chiral [1]FCPs with a variety of bridging moieties [ER_x=Ga[2‐(Me₂NCH₂)C₆H₄] ( 4 a ), SiMe₂ ( 4 b ), SntBu₂ ( 4 c ), BNiPr₂ ( 4 d )]. The new [1]FCPs were fully characterized including single‐crystal X‐ray analysis. The stabilizing iPr groups on the Cp rings increase the thermal stabilities of 4 b – d compared to known [1]FCPs, equipped with the same bridging moieties. All three compounds 4 b – d are volatile and could be isolated by vacuum sublimation. Our new approach to [1]FCPs has the potential to overcome many of the existing difficulties in ferrocenophane chemistry, such as limited stability of starting monomers and low solubilities of resulting polyferrocenes.     

ChemInform Abstract: Cryogenic Reactions of Gallium with Molecular Hydrogen and Methane

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.     

Stable Radical Cation and Dication of an N‐Heterocyclic Carbene Stabilized Digallene: Synthesis,Characterization and Reactivity

One‐ and two‐electron oxidation of a digallene stabilized by an N‐heterocyclic carbene afforded the first stable gallium‐based radical cation and dication salts, respectively. Structural analysis and theoretical calculations reveal that the oxidation occurs at the Ga=Ga double bond, leading to removal of π electrons of the double bond and a decrease of the bond order. The spin density of the radical cation mainly locates at the two gallium centers as demonstrated by EPR spectroscopy and theoretical calculations. Moreover, the reactivity of the radical cation salt toward nBu₃SnH and cyclo‐S₈ was studied; a digallium–hydride cation salt containing a Ga?Ga single bond and a gallium sulfide cluster bearing an unprecedented ladder‐like Ga₄S₄ core structure were obtained, respectively.     

Ruthenium Olefin Metathesis Catalysts Featuring N-Heterocyclic Carbene Ligands Tagged with Isonicotinic and 4-(Dimethylamino)benzoic Acid Rests: Evaluation of a Modular Synthetic Strategy

A modular and flexible strategy towards the synthesis of N-heterocyclic carbene (NHC) ligands bearing Brønsted base tags has been proposed and then adopted in the preparation of two tagged NHC ligands bearing rests of isonicotinic and 4-(dimethylamino)benzoic acids. Such tagged NHC ligands represent an attractive starting point for the synthesis of olefin metathesis ruthenium catalysts tagged in non-dissociating ligands. The influence of the Brønsted basic tags on the activity of such obtained olefin metathesis catalysts has been studied.     

Reactivity of a Dihydrodiborene with CO: Coordination,Insertion, Cleavage,and Spontaneous Formation of a Cyclic Alkyne

Under a CO atmosphere, the dihydrodiborene [(cAAC)HB=BH(cAAC)] underwent coordination of CO concomitant with reversible hydrogen migration from boron to the carbene carbon atom, as well as reversible CO insertion into the B=B bond. Heating the CO adduct resulted in two unusual cAAC ring‐expansion products, one presenting a B=C bond to a six‐membered 1,2‐azaborinane‐3‐ylidene, the other an unprecedented nine‐membered cyclic alkyne resulting from reductive cleavage of CO and spontaneous formation of a C≡C bond.     

Mixture of Azolium Tetraphenylborate with Isopropylthioxanthone: A New Class of N-Heterocyclic Carbene (NHC) Photogenerator for Polyurethane,Polyester, and ROMP Polymers Synthesis

In the search of smarter routes to control the conditions of N-heterocyclic carbene (NHCs) formation, a two-component air-stable NHC photogenerating system is reported. It relies on the irradiation at 365 nm of a mixture of 2-isopropylthioxanthone (ITX) with 1,3-bis(mesityl)imidazoli(ni)um tetraphenylborate. The photoinduced liberation of NHC is evidenced by reaction with a mesitoyl radical to form an NHC-radical adduct detectable by electron spin resonance spectroscopy. The NHC yield can be determined by ¹H NMR spectroscopy through the formation of a soluble and stable NHC–carbodiimide adduct. To deprotonate the azolium salt and liberate the NHC, a mechanism is proposed in which the role of base is played by ITX radical anion formed in situ by a primary photoinduced electron-transfer reaction between electronically excited ITX (oxidant) and BPh₄⁻ (reductant). An NHC yield as high as 70 % is achieved upon starting with a stoichiometric ratio of ITX and azolium salt. Three different photoNHC-mediated polymerizations are described: synthesis of polyurethane and polyester by organocatalyzed step-growth polymerization and ring-opening copolymerization, respectively, and generation of polynorbornene by ring-opening metathesis polymerization using an NHC-coordinated Ru catalyst formed in situ.     

Tetrahydrofuran Ring Opening with Acyl Chlorides or Anhydrides Catalyzed by Gallium Triiodides: A Novel and Facile Method for the Preparation of Iodo Esters

Recently gallium and its compounds are gradually attracting attention as useful reagentsin organic synthesis'-'. Gallium enolate-mediated intermolecular aldol reaction andaddition reaction of Q -bromoketone with imine, a straightforward and versatilepreparation of propargylic alcohols from l-alkynes and aldehydes via Gal, and aminehave been documented3. Kobayashi reported that gallium reagents could efficientlypromote the glycosidation of glycopyranosyl fluorides'. The reaction of alkyne with…     

Adduct Formation,B−H Activation and Ring Expansion at Room Temperature from Reactions of HBcat with NHCs

We report the reactions of catecholborane (HBcat; 1 ) with unsaturated and saturated NHCs as well as CAAC^Me. Mono‐NHC adducts of the type HBcat?NHC (NHC=nPr₂Im, iPr₂Im, iPr₂Im^Me, and Dipp₂Im) were obtained by stoichiometric reactions of HBcat with the unsaturated NHCs. The reaction of CAAC^Me with HBcat yielded the B?H activated product CAAC^Me(H)Bcat via insertion of the carbine‐carbon atom into the B?H bond. The saturated NHC Dipp₂SIm reacted in a 2:2 ratio yielding an NHC ring‐expanded product at room temperature forming a six‐membered ?B?C=N?C=C?N? ring via C?N bond cleavage and further migration of the hydrides from two HBcat molecules to the former carbene‐carbon atom.     

Stable ‐ESiMe3 Complexes of CuI and AgI (E=S,Se) with NHCs: Synthons in Ternary Nanocluster Assembly

As a part of efforts to prepare new “metallachalcogenolate” precursors and develop their chemistry for the formation of ternary mixed‐metal chalcogenide nanoclusters, two sets of thermally stable, N‐heterocyclic carbene metal–chalcogenolate complexes of the general formula [(IPr)Ag?ESiMe₃] (IPr=1,3‐bis(2,6‐diisopropylphenyl)imidazolin‐2‐ylidene; E=S, 1 ; Se, 2 ) and [(iPr₂‐bimy)Cu?ESiMe₃]₂ (iPr₂‐bimy=1,3‐diisopropylbenzimidazolin‐2‐ylidene; E=S, 4 ; Se, 5 ) are reported. These are prepared from the reaction between the corresponding carbene metal acetate, [(IPr)AgOAc] and [(iPr‐bimy)CuOAc] respectively, and E(SiMe₃)₂ at low temperature. The reaction of [(IPr)Ag?ESiMe₃] 1 with mercury(II) acetate affords the heterometallic complex [{(IPr)AgS}₂Hg] 3 containing two (IPr)Ag?S^? fragments bonded to a central Hg^II, representing a mixed mercury–silver sulfide complex. The reaction of [(iPr₂‐bimy)Cu‐SSiMe₃]₂, which contains a smaller N‐heterocyclic‐carbene, with mercuric(II) acetate affords the high nuclearity cluster, [(iPr₂‐bimy)₆Cu₁₀S₈Hg₃] 6 . The new N‐heterocyclic carbene metal–chalcogenolate complexes 1 , 2 , 4 , 5 and the ternary mixed‐metal chalcogenolate complex 3 and cluster 6 have been characterized by multinuclear NMR spectroscopy (¹H and ¹³C), elemental analysis and single‐crystal X‐ray diffraction.     

一种新型2，6-吡啶二甲酸镓(Ⅲ)配合物的合成、结构及抑菌活性研究(英)

A novel coordination polymer [NaGa(dipic)₂(H₂O)₂]_n was synthesized by the reaction of gallium(Ⅲ) trichloride with Na-salt of 2,6-pyridinedicarboxylic acid and its crystal structure was determined by X-ray diffraction method. The crystal belongs to monoclinic, space group Cc; the unit cell parameters are a=1.502 9(3), b=1.228 1(3) and c=0.872 38(17) nm, β=92.85(3)°, and Z=4, V=1.608 2(6) nm³, F(000)=920. Infrared, electronic absorption, ¹H NMR spectra, as well as the thermal behavior are reported. The antibacterial activity of the gallium(Ⅲ) complex has been studied against Escherichia coli, Bacillus subtilis and Staphylococcus aureus in order to check its potential for chemotherapy agent. The activity is notable and higher than that of the H₂L. CCDC: 240619.     

Heterometallic Coii-Lii carboxylate complexes with N-heterocyclic carbene,triphenylphosphine and pyridine: a comparative study of magnetic properties

Heterometallic Coii-Lii compounds with N-heterocyclic carbene 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes), tri phenylphosphine (Ph3P) and pyridine (py), [Co2Li2(Piv)6(IMes)2] (Piv is the anion of pivalic acid), [Co2Li2(Piv)6(Ph3P)2] and [Co2Li2(Fur)6(py)2] (Fur is the anion of 2-furoic acid), respectively, have been prepared and structurally characterized by X-ray crystallography. Easy-plane magnetic anisotropy in Coii complexes with pseudo-tetrahedral cores CoO3X (X = C, P and N) was revealed by measuring the magnetic properties together with quantum-chemical calculations using the SA-CASSCF/NEVPT2 approach. The field-induced slow magnetic relaxation of the complexes was mainly attributed to the Raman and direct processes.     

Bench‐Stable Stock Solutions of Silicon Grignard Reagents: Application to Iron‐ and Cobalt‐Catalyzed Radical C(sp3)–Si Cross‐Coupling Reactions

A robust method for the preparation of silicon‐based magnesium reagents is reported. The MgBr₂ used in the lithium‐to‐magnesium transmetalation step is generated in situ from 1,2‐dibromoethane and elemental magnesium in hot THF. No precipitation of MgBr₂ occurs in the heat, and transmetalation at elevated temperature leads to homogeneous stock solutions of the silicon Grignard reagents that are stable and storable in the fridge. This method avoids the preparation of silicon pronucleophiles such as Si?Si and Si?B reagents. The new Grignard reagents were applied to unprecedented iron‐ and cobalt‐catalyzed cross‐coupling reactions of unactivated alkyl bromides. The functional‐group tolerance of these magnesium reagents is excellent.     

Theoretical Study of Nucleophilic Identity Substitution Reactions at Nitrogen,Silicon and Phosphorus versus Carbon: Reaction Pathways,Energy Barrier,Inversion and Retention Mechanisms

Gas‐phase identity S_N2(N), S_N2(Si) and S_N2(P) versus S_N2(C) reactions with Cl^? are investigated by the ab initio method. Front‐side attack identity S_N2 reactions considered have all double‐well potential energy surfaces (PES), and back‐side attack identity S_N2(C) and S_N2(N) reactions have also double‐well PES, while back‐side attack identity S_N2(Si) and S_N2(P) have single‐well PES. In addition, the geometrical transformations, potential energy profiles of front‐side and back‐side attack identity S_N2(N), S_N2(Si) and S_N2(P) versus S_N2(C) reactions based on the IRC calculations are described, the differences between them for the front‐side or back‐side attack reactions have been demonstrated.