The IX (X=O,N,C) Double Bond in Hypervalent Iodine Compounds: Is it Real?

I? X (X=O, N, C) bonding was analyzed in the related hypervalent iodine compounds based on the adaptive natural density partitioning (AdNDP) approach. The results confirm the presence of a I→X σ dative bond, as opposed to the widely used I?X notation. A clear formulation of the electronic structure of these hypervalent iodine compounds would be useful in establishing reaction mechanisms and electronic structures in bioinorganic problems of general applicability.     

Electronic structure of cations X ?OH (XC,N,O)

RHF(UHF)+MP2 and CASSCF calculations of potential energy surfaces' sections of cations X  OH (XC,N,O) and corresponding neutral particles are performed. It is shown that all cations should be relatively stable both with respect to X  O bond breaking and intramolecular rearrangements. Reactions of electron capture by these cations are also studied. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 77: 580–588, 2000     

Hypervalent Intramolecular X←N (X = C,Si, Ge) Coordination in Atranes: Quantum-Chemical Study

The structure and pentacoordination effect in atranes containig Group IVa element were studied ab initio [MP2(full)/6-31G**] and in terms of the density functional theory [B3LYP/6-311+G**]. Stabiliza- tion of these compounds is determined mainly by the secondary hypervalent (R)XN bond (X = C, Si, Ge), whose strength increases in the series X = C, Si, Ge. Attractive (R)XN interaction originates from donation of unshared electron pair on the nitrogen atom to the antibonding ^* _XR orbital.     

Ruthenium Catalyzed Intramolecular C−X (X=C,N, O,S) Bond Formation via C−H Functionalization: An Overview

Ruthenium catalyzed C−H activation is well known for its high tolerance towards the functional group and broad applicability in organic synthesis and molecular sciences, with significant applications in pharmaceutical industries, material sciences, and polymer industry. In the last few decades, enormous progress has been observed with ruthenium-catalyzed C−H activation chemistry. Notably, the vast majority of the C−H functionalization known in the literature are intermolecular, although the intramolecular variant provides fascinating new structural facet starting from the simple molecular scaffolds. Intramolecular C−H functionalization is atom economical and step efficient, results in less formation of undesired products which is easy to purify. This has created a lot of interest in organic chemistry in developing new synthetic strategies for such functionalization. The focus of this review is to present the relatively unexplored intramolecular functionalization of C−H bonds into C−X (X=C, N, O, S) bonds utilizing versatile ruthenium catalysts, their scope, and brief mechanistic discussion.     

Amide‐Based Nonheme Cobalt(III) Olefin Epoxidation Catalyst: Partition of Multiple Active Oxidants CoVO,CoIVO,and CoIII?OO(O)CR

A mononuclear nonheme cobalt(III) complex of a tetradentate ligand containing two deprotonated amide moieties, [Co(bpc)Cl₂][Et₄N] ( 1 ; H₂bpc=4,5‐dichloro‐1,2‐bis(2‐pyridine‐2‐carboxamido)benzene), was prepared and then characterized by elemental analysis, IR, UV/Vis, and EPR spectroscopy, and X‐ray crystallography. This nonheme Co^III complex catalyzes olefin epoxidation upon treatment with meta‐chloroperbenzoic acid. It is proposed that complex 1 shows partitioning between the heterolytic and homolytic cleavage of an O? O bond to afford Co^V?O ( 3 ) and Co^IV?O ( 4 ) intermediates, proposed to be responsible for the stereospecific olefin epoxidation and radical‐type oxidations, respectively. Moreover, under extreme conditions, in which the concentration of an active substrate is very high, the Co? OOC(O)R ( 2 ) species is a possible reactive species for epoxidation. Furthermore, partitioning between heterolysis and homolysis of the O? O bond of the intermediate 2 might be very sensitive to the nature of the solvent, and the O? O bond of the Co? OOC(O)R species might proceed predominantly by heterolytic cleavage, even in the presence of small amounts of protic solvent, to produce a discrete Co^V?O intermediate as the dominant reactive species. Evidence for these multiple active oxidants was derived from product analysis, the use of peroxyphenylacetic acid as the peracid, and EPR measurements. The results suggest that a less accessible Co^V?O moiety can form in a system in which the supporting chelate ligand comprises a mixture of neutral and anionic nitrogen donors.     

N-alkyl-C-polyfluoroalkyl-C-chlorosulfinimides RFC(Cl)SN?R

The N-alkyl-C-polyfluoroalkyl-C-chlorosulfinimides R_FC(Cl)SN R have been investigated. Some aspects of their thermal stability and their [3 + 2] and [3 + 1] cycloaddition reactions have been examined.     

Chalkogenid-Disilicate der Lanthanoide vom Typ M4X3[Si2O7] (M  Ce?Er; X  S,Se)

M₄X₃[Si₂O₇]-Type Lanthanide Chalcogenide Disilicates (M ? Ce? Er; X ? S, Se) Attempts to produce single crystals of MSe₂ (or MSe^2?X) by vapour phase transport with iodine or the oxidation of MCl₂ (or MClH) with sulfur in the presence of NaCl in sealed evacuated quartz containers often yielded well-grown single crystals with the composition M₄X₃[Si₂O₇] (M ? pr, Sm, Gd, X ? Se, and M ? Nd, Er, X ? S) as by-products. The crystal structures (tetragonal, 14₁/amd (no. 141)), Z = 8, contain two crystallographically independent M₃₊ Cations that are interconnected by chalcogenide (X_2?) and disilicate anions ([Si₂O₇]^6?). (M1)³⁺ is surrounded by eight (five X^2? and three terminal O_2? of the disilicate group), (M2)³⁺ by nine (three X^2? and six terminal O^2? of the [Si₂O₇]_6? anion) chalcogenide anions. The disilicate anion itself exhibits the eclipsed conformation with non-linear Si? O? Si bridges (angles: 128 – 133°).     

NbX(X=C,N,O)的能带结构研究

本文采用EHT近似下的紧束缚能带方法,计算了NbX(X=C,N,O)的能带结构。结果表明,它们的能带结构相近,Nb—X间存在较强的成键作用,传导电子主要具有Nb的4d特征,Nb—Nb键与超导电性相关,从C到N,Nb—Nb键共价性削弱,Tc提高。尽管计算所得NbO中Nb—Nb键强度介于NbC和NbN之间,但其实际Tc却比NbC和NbN的都低,这是NbO的空位效应所致,这一结果可从我们对有序缺陷的Nb_(0.75)O_(0.75)晶体能带结构的计算得到验证。     

Homolytic S?S Bond Dissociation of 11 Bis(thiocarbonyl)disulfides R‐C(S)?S?S?C(S)R and Prediction of A Novel Rubber Vulcanization Accelerator

The structures and energetics of eight substituted bis(thiocarbonyl)disulfides (RCS₂)₂, their associated radicals RCS₂^., and their coordination compounds with a lithium cation have been studied at the G3X(MP2) level of theory for R=H, Me, F, Cl, OMe, SMe, NMe₂, and PMe₂. The effects of substituents on the dissociation of (RCS₂)₂ to RCS₂^. were analyzed using isodesmic stabilization reactions. Electron‐donating groups with an unshared pair of electrons have a pronounced stabilization effect on both (RCS₂)₂ and RCS₂^.. The S? S bond dissociation enthalpy of tetramethylthiuram disulfide (TMTD, R=NMe₂) is the lowest in the above series (155 kJ mol^?1), attributed to the particular stability of the formed Me₂NCS₂^. radical. Both (RCS₂)₂ and the fragmented radicals RCS₂^. form stable chelate complexes with a Li⁺ cation. The S? S homolytic bond cleavage in (RCS₂)₂ is facilitated by the reaction [Li(RCS₂)₂]⁺+Li⁺→2 [Li(RCS₂)]^.+. Three other substituted bis(thiocarbonyl) disulfides with the unconventional substituents R=OSF₅, Gu¹, and Gu² have been explored to find suitable alternative rubber vulcanization accelerators. Bis(thiocarbonyl)disulfide with a guanidine‐type substituent, (Gu¹CS₂)₂, is predicted to be an effective accelerator in sulfur vulcanization of rubber. Compared to TMTD, (Gu¹CS₂)₂ is calculated to have a lower bond dissociation enthalpy and smaller associated barrier for the S? S homolysis.     

Fluorsulfonylmethylidene sulfur difluoride oxide,FSO2?CH  SF2  O

SO₃ adds across the CS double bond of H₂C  SF₄ with formation of 2-tetrafluoro-4-dioxo-1,2,4-oxadithietane, which rearranges to fluorsulfonylmethylidene sulfur difluoride oxide, F SO₂ CH  SF₂  O in the presence of CsF. © John Wiley & Sons, Inc.     

Theoretical prediction regarding structural and thermodynamical characteristics of stable CH3PO2 isomers and unimolecular decomposition mechanisms of species CH3P(O)2, CH3O?PO,and CH2P(O)OH

The detailed isomerization and dissociation reaction potential energy profile of the CH₃PO₂ system was established at the UCCSD(T)/6‐311++G(3df,2p)//UB3LYP/6‐311++G(d,p) level of theory. Seventy minimum isomers were located and connected by 93 optimized interconversion transition states. Furthermore, 32 isomers with high kinetic stability were predicted to be possible candidates for further experimental detection. The bonding nature of the suggested stable isomers was analyzed while their molecular properties including heats of formation, adiabatic ionization potentials, and adiabatic electronic affinities were calculated at the G2, G2(MP2), G3, and CBS‐Q levels. Based on the isomerization and dissociation potential energy surface, possible unimolecular decomposition mechanisms and pathways of the low‐lying molecules CH₃P(?O)₂, CH₃O? P?O, and CH₂?P(?O)OH were discussed. Furthermore, the transition state theory rate constants of the primary unimolecular dissociation channels were also calculated. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2009     

PuX~ (X=H,O,N,C)的结构与势能函数

用密度泛函B3LYP方法对PuX＋(X=H,O,N,C)分子离子体系进行了理论研究.结果表明,这些分子离子的基态电子状态分别是X 7Σ－(PuH＋)、X 6Σ－(PuO＋)、X 5Σ＋(PuN＋)和X 8Σ－(PuC＋);势能函数为Murrell-Sorbie势函数.并得到了相应的几何性质、力学性质和光谱数据.     

Attempted 1,3-trimethylsilyl migration in Me3Si?PSN?R system

A dimer of thioxo-N-t-butylimino(trimethylsiloxy)-phosphorane 5 has been prepared by reaction of tris(trimethylsilyl) phosphine with N-sulfinyl-N-tert-butylamine. The structure of 5 has been confimed by X-ray analysis data. 1-Aza-2-thia-3-phosphaallene 1 , thiaphosphaziridine 3 , iminophosphine P-sulfide 4 are postulated as intermediates of the reaction studied.     

Efficient Olefin Epoxidation by Robust Re4 Cluster‐Supported MnIII Complexes with Peracids: Evidence of Simultaneous Operation of Multiple Active Oxidant Species,MnVO,MnIVO,and MnIII?OOC(O)R

Two new tetranuclear chalcocyanide cluster complexes, [{Mn(saloph)H₂O}₄Re₄Q₄(CN)₁₂]?4 CH₃OH? 8 H₂O (saloph=N,N′‐o‐phenylenebis(salicylidenaminato), Q=Se ( 1 ‐Se), Te ( 2 ‐Te)), have been synthesized by the diffusion of a methanolic solution of [PPh₄]₄[Re₄Q₄(CN)₁₂] into a methanolic solution of [Mn(saloph)]⁺. The structure of 2 ‐Te has been determined by X‐ray crystallography. These rhenium cluster‐supported [Mn^III(saloph)] complexes have been found to efficiently catalyze a wide range of olefin epoxidations under mild experimental conditions in the presence of meta‐chloroperbenzoic acid (mCPBA). Olefin epoxidation by these catalysts is proposed to involve the multiple active oxidants Mn^V?O, Mn^IV?O, and Mn^III? OOC(O)R. Evidence in support of this interpretation has been derived from reactivity and Hammett studies, H₂¹⁸O‐exchange experiments, and the use of peroxyphenylacetic acid as a mechanistic probe. Moreover, it has been observed that the participation of Mn^V?O, Mn^IV?O, and Mn^III? OOC(O)R can be controlled by changing the substrate concentration. This mechanism provides the greatest congruity with related oxidation reactions that employ certain Mn complexes as catalysts.     

PuX＋(X=H,O,N,C)的结构与势能函数

用密度泛函B3LYP方法对PuX＋(X=H,O,N,C)分子离子体系进行了理论研究.结果表 明,这些分子离子的基态电子状态分别是X 7Σ-(PuH＋)、X 6Σ-(PuO＋)、X 5Σ＋(P uN＋)和X 8Σ-(PuC＋);势能函数为Murrell-Sorbie势函数.并得到了相应的几何性质、 力学性质和光谱数据.     

Niobium Bis- and Mono(Pentafulvene) Complexes: E−H Bond Cleavage and Insertion Reactions (E=C,N, O)

Bis(η⁵:η¹-(di-para-tolyl)pentafulvene)niobium chloride ( 1 ) reacts with methyl lithium via salt metathesis to the methylated bis(pentafulvene)niobium complex 2 , and with lithium 2,6-diisopropylanilide addition and subsequent N−H bond activation to the imido mono(pentafulvene)niobium complex 3 . Avoiding the competing protonation of the chloride, bis(pentafulvene)niobium complex 2 reacts with primary aromatic and aliphatic amines to form terminal niobocene imido complexes, and with water to form the analog terminal oxo complex. Secondary methyl amines undergo a simultaneous N−H and C−H activation to form niobaaziridines under mild conditions. In contrast to other reported examples, 3 can be employed to investigate the uncontested reactivity of mono(pentafulvene)niobium complexes. Reaction with 4-tert-butylphenol selectively yields a niobocene phenolate complex. Unprecedented for mono(pentafulvene)niobium complexes, treating 3 with multiple-bond-containing substrates (nitriles, isocyanates) smoothly results the insertion into the Nb-C_exo σ-bond, forming the corresponding alkylidene amido and imidato complexes.     

Characterization of the N?H···ON and N?H···NO H‐bonds in nitrosamine dimers

Ab initio molecular orbital and DFT calculations have been carried out for three most stable dimers of parent nitrosamine (NA) in order to elucidate the structures and energetics of the dimers. The structures were optimized using HF, B3LYP, and MP2 methods with 6‐311+G(d,p) and 6‐311++G(2d,2p) basis sets. At the optimized geometries obtained at MP2/6‐311++G(2d,2p) level of theory, the energies were evaluated at QCISD/aug‐cc‐pVDZ and CCSD/aug‐cc‐pVDZ levels. The most stable dimer has two N? H···O?N hydrogen bonds and the least stable dimer has two N? H···N?O hydrogen bonds. The natural bond orbital analysis showed that the lpO(N) → BD*(N? N) and lpO(N) → BD*(N? H_b) interactions play a decisive role in the stabilization of the NH···O(N) hydrogen bonds in dimers. The atoms in molecules results reveal that the intermolecular N? H···O(N) H‐bonds in dimers have electrostatic character. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008