Agostic interaction in the methylidene metal dihydride complexes H2MCH2 (M=Y, Zr, Nb, Mo, Ru, Th, or U)

Multiconfigurational quantum chemical methods (complete active space self-consistent field (CASSCF)/second-order perturbation theory (CASPT2)) have been used to study the agostic interaction between the metal atom and H(C) in the methylidene metal dihydride complexes H2MCH2, where M is a second row transition metal or the actinide atoms Th or U. The geometry of some of these complexes is highly irregular due to the formation of a three center bond CH...M, where the electrons in the CH bond are delocalized onto empty or half empty orbitals of d- or f-type on the metal. No agostic interaction is expected when M=Y, where only a single bond with methylene can be formed, or when M=Ru, because of the lack of empty electron accepting metal valence orbitals. The largest agostic interaction is found in the Zr and U complexes.     

过渡金属M (M=Cu,Ag, Au)对X…Cl (X = F,Cl, Br)卤键相互作用强度的影响

采用量子化学方法,通过MCH2X…ClF(M=Cu,Ag,Au;X=F,Cl,Br)和CH3X…ClF两类复合物的对比,探讨了过渡金属对卤键相互作用强度的影响.CH3X…ClF复合物只有卤键相互作用,而优化MCH2X…ClF复合物除了得到一种只含有卤键相互作用的构型外,还得到一种含有过渡金属和Cl原子相互作用的稳定构型.含有过渡金属的复合物稳定性明显增加,Ag取代的复合物稳定性增加最为明显,Cu次之,Au最不明显.X原子最负分子表面静电势(MEP)减小是复合物稳定性增加的根本原因.利用自然键轨道(NBO)及分子中原子(AIM)分析进一步对体系的分子间相互作用进行了探讨.二阶稳定化能与键鞍点处拓扑性质的计算结果与相互作用能符合得很好.     

Ab Initio Studies on MCH2(OH) and CH3OM(M=H, -, Li, Na)

IntroductionThe greatsynthetic utility of organolithium reagents has been extended by the introduc-tion ofα-lithium-etherreagents[1— 4] .Those reagentsareeasily prepared,and they can be usedas anionic resources to synthesize a large variety of compounds stereo-selectively[5— 8] .Fur-thermore,such reagents can react with nucleophiles like RLi,only a typical reaction of car-benoid[9,1 0 ] .Though the ambidentnature isof greatinterest,only a little work has been doneon model molecule Li CH2 …     

硼氢二茂铁铵盐的结构化学研究——Ⅲ.十二硼十二氢双(二茂铁甲基二甲基)铵晶体结构

标题的化合物晶体属斜方晶系,空间群为Pcnb,晶胞参数为:a=12.975(26),b=16.342(28),c=17.582(48),Z=4。晶体结构用直接法,三维Patterson函数和差值Fourier方法解出,经全矩阵最小二乘法修正,对1674个独立衍射点[I≥3σ(I)],最后偏离因子R=0.054。 该化合物属于离子型,阴离子和阳离子分别以六面体和四面体配位。     

Metathesis of nitrogen atoms within triple bonds involving carbon, tungsten, and molybdenum

(ButO)3Mo triple bond N and W2(OBut)6(M triple bond M) react in hydrocarbons to form Mo2(OBut)6(M triple bond M) and (ButO)3W triple bond N via the reactive intermediate MoW(OBut)6(M triple bond M). (ButO)3W triple bond N and CH3C triple bond N15 react in tetrahydrofuran (THF) at room temperature to give an equilibrium mixture involving (ButO)3W triple bond N15 and CH3C triple bond N. The (ButO)3W triple bond N compound is similarly shown to act as a catalyst for N15-atom scrambling between MeC13 triple bond N15 and PhC triple bond N to give a mixture of MeC13 triple bond N and PhC triple bond N15. From studies of degenerate scrambling of N atoms involving (ButO)3W triple bond N and MeC13 triple bond N in THF-d8 by 13C(1H) NMR spectroscopy, the reaction was found to be first order in acetonitrile and the activation parameters were estimated to be DeltaH = 13.4(7) kcal/mol and DeltaS = -32(2) eu. A similar reaction is observed for (ButO)3Mo triple bond N and CH3C triple bond N15 upon heating in THF-d8. The reaction is suppressed in pyridine solutions and not observed for the dimeric [(ButMe2SiO)3W triple bond N]2. The reaction pathway has been investigated by calculations employing density functional theory on the model compounds (MeO)3M triple bond N and CH3C triple bond N where M = Mo and W. The transition state was found to involve a product of the 2 + 2 cycloaddition of M triple bond N and C triple bond N, a planar metalladiazacyclobutadiene. This resembles the pathway calculated for alkyne metathesis involving (MeO)3W triple bond CMe, which modeled the metathesis of (ButO)3W triple bond CBut. The calculations also predict that the energy of the transition state is notably higher for M = Mo relative to M = W.     

CRYSTAL STRUCTURE OF Ce(ClO_4)_3 COMPLEX WITH 3,3-R,R''''-16-C-5(R=CH_3;R''''=CH_3O(CH_2)_2OCH~-_2)

<正> The title compound C18H37O20NCeCl3, Mr = 834. 25, orthorhom-bic, P212121, a = 11.836(4), b = 13.899(6), c= 19. 401(6) A ; V=3192(2)A3; Z = 4; Dc=1. 74gcm-3, F (000) = 1684,μ= 17. 8cm-1 (MoKa). The final R = 0. 080, Rw = 0. 081. The Ce(Ⅲ) ion is coordinated to one O atom of one C1O4- ion, a CH3CN molecule, a water molecule and seven O atoms from a crown ether molecule. The other two C1O4- ions are not coordinated to the metal. The bond lengths of Ce-N(CH3CN), Ce -O(ClO4-), Ce -O(H2O) and Ce-O(crown) are 2. 61,2. 82,2. 53, and 2. 56A, respectively.     

Synthesis, structure, and reactivity of Group 4 metallacycles incorporating a Me2C-linked cyclopentadienyl-carboranyl ligand

Group 4 metallacycles [eta5:sigma-Me2C(C5H4)(C2B10H10)]Ti[eta2-N(Me)CH2CH2N(Me)] (1a), [eta5:sigma-Me2C(C5H4)(C2B10H10)]Zr[eta2-N(Me)CH2CH2N(Me)](HNMe2) (1b) and [eta5:sigma-Me2C(C5H4)(C2B10H10)]M[eta2-N(Me)CH2CH2CH2N(Me)] (M = Ti (2a), Zr (2b), Hf (2c)) were synthesized by reaction of [eta5:sigma-Me2C(C5H4)(C2B10H10)]M(NMe2)(2) (M = Ti, Zr, Hf) with MeNH(CH2)(n)NHMe (n = 2, 3). These metal complexes reacted with unsaturated molecules such as 2,6-Me2C6H3NC, PhNCO and PhCN to give exclusively M-N bond insertion products. The M-C(cage) bond remained intact. Such a preference of M-N over M-C(cage) insertion is suggested to most likely be governed by steric factors, and the mobility of the migratory groups plays no obvious role in the reactions. This work also shows that the insertion of unsaturated molecules into the metallacycles is a useful and effective method for the construction of very large ring systems.     

硼氢二茂铁季铵盐的结构化学研究——Ⅰ、十硼十氢双(二茂铁甲基三甲基)铵晶体结构

本文报告了(C_5H_5FeC_5H_4CH_2N(CH_3)_3)_2B_(10)H_(10)晶体的结构。该晶体属三斜晶系、空间群为P_1~-。晶胞参数为:a=10.043(2),b=10.513(7),C=15.094(10),a=85.01(6),β=97.58(3),Υ=94.87(3)°,V=1625.7~3,Z=2。晶体在室温下用CAD-4四圆衍射仪收集衍射强度数据(MoKa),用重原子法解出铁原子坐标,综合应用E图、Fourief合成和差Fourier合成解出其他非氢原子坐标,按SDP加氢程序等求解阳离子中40个氢原子位置。各原子坐标及热振动参数经全矩阵最小二乘方修正,对于2258个独立衍射点(I≥3σI)],偏离因子R=0.043。 结构分析表明,B_(10)H_(10)~(2+)阴离子和C_5H_5FeC_5H_4CH_2N(CH_3)_3~+阳离子分别按畸变的八面体和畸变的三角形配位。两个二茂铁季铵阳离子中,两对戊二稀环平面间距为3.271(5)。阳离子中主要键长平均值为:Fe-C=2.026,C—C(环)=1.401,C—N=1.503。B_(10)H_(10)~(2+)阴离子为四方(三角)十六面体笼状结构,主要键长平均值为:B—B(顶点到正方形平面原子)1.706A,B—B(其它原子间)=1.830。     

Thermodynamics, kinetics, and mechanism of (silox)3M(olefin) to (silox)3M(alkylidene) rearrangements (silox = tBu3SiO; M = Nb, Ta)

Olefin complexes (silox)(3)M(ole) (silox = (t)Bu(3)SiO; M = Nb (1-ole), Ta (2-ole); ole = C(2)H(4), C(2)H(3)Me, C(2)H(3)Et, C(2)H(3)C(6)H(4)-p-X (X = OMe, H, CF(3)), C(2)H(3)(t)Bu, (c)C(5)H(8), (c)C(6)H(10), (c)C(7)H(10) (norbornene)) rearrange to alkylidene isomers (silox)(3)M(alk) (M = Nb (1=alk), Ta (2=alk); alk = CHMe, CHEt, CH(n)Pr, CHCH(2)C(6)H(4)-p-X (X = OMe, H, CF(3) (Ta only)), CHCH(2)(t)Bu, (c)C(5)H(8), (c)C(6)H(10), (c)C(7)H(10) (norbornylidene)). Kinetics and labeling experiments suggest that the rearrangement proceeds via a delta-abstraction on a silox CH bond by the beta-olefin carbon to give (silox)(2)RM(kappa(2)-O,C-OSi(t)Bu(2)CMe(2)CH(2)) (M = Nb (4-R), Ta (6-R); R = Me, Et, (n)Pr, (n)Bu, CH(2)CH(2)C(6)H(4)-p-X (X = OMe, H, CF(3) (Ta only)), CH(2)CH(2)(t)Bu, (c)C(5)H(9), (c)C(6)H(11), (c)C(7)H(11) (norbornyl)). A subsequent alpha-abstraction by the cylometalated "arm" of the intermediate on an alpha-CH bond of R generates the alkylidene 1=alk or 2=alk. Equilibrations of 1-ole with ole' to give 1-ole' and ole, and relevant calculations on 1-ole and 2-ole, permit interpretation of all relative ground and transition state energies for the complexes of either metal.     

Organotin and organogermanium linkers for simple, direct functionalization of polyoxotungstates

Fifteen Keggin-anion-derived polytungstates [TW11O39[MCH2CH2X]]n- (T = Si, Ge, Ga; M = Sn, Ge; X = COOH, COOCH3, CONH2, CN; n = 5, 6) were prepared in aqueous or aqueous-organic solution from the corresponding lacunary polytungstates and trichlorotin and -germanium precursors, and were isolated as caesium salts. The derivatized polytungstates were characterized by elemental analysis, multinuclear NMR spectroscopy, and cyclic voltammetry; they are stable in aqueous solution to pH 6-7. NMR spectroscopy revealed the presence of a second (beta1 or beta3) isomer in the tungstogallate derivatives. Acid hydrolysis of the ester and nitrile derivatives could be achieved without decomposition of the polytungstate moieties, and esterification and amidation of the carboxylate functions was straightforward using standard coupling techniques, e.g. the formation, isolation and characterization of [SiW11O39[Ge(CH2)2CONHCH2COOCH3]]5- from glycine methyl ester. Since the Cl3MCH2CH2X precursors are readily accessible by hydrostannation/germanation reactions with the corresponding alkenes, novel coupled polytungstates, such as [(SiW11O39GeCH2CH2COOCH2)4C]20- from pentaerythritol tetraacrylate, can also be prepared.     

Preparation and Crystal Structure of a Charge-transfer Complex between an Organic Substrate and Molybdosilicic Acid [(CH_3)_2NH(CH_2)C_6H_5]_4SiMo_(12)O_(40)·2CH_3CN·H_2O

1 INTRODUCTION Photochromism of intermolecular complexes based on polyoxometalates has received increasing attention due to their potential applications in ma- terial science[1～3]. However, most studies of photo- chromism have been made in solution[4～7], and those in solid state are relatively less and only a few with photosenstivity properties have been studied crystal- lographically. The title compound has a light yellow color in the darkness and turns greenish when exposed to sunligh…     

硼氢二茂铁季铵盐的结构化学研究——Ⅱ.三硼八氢N—二茂铁甲基三甲基铵的晶体构结

本文报道了C_5H_5FeC_5H4CH_4N(CH_3)_3B_3_H_8的晶体结构。晶体属正交晶系,空间群为Pnam,晶胞参数:a=13.707(6),b=13.365(4),c=9,339(9),Z=4用三维Patterson函数等方法解出全部非氢原子的坐标和B_3H_8~-中“氢桥”的2个H原子坐标,对817个独立衍射点[I≥3σ(I)]计算偏离因子,最终偏离因子R=0.071 C_5H_5FeC_5H_4CH_2N(CH_3)_3B_3H_8为离子型化合物,B_3H_8~-阴离子和C_5H_5~-FeC_5H_4CH_2N(CH_3)_3~+阳离子按四面体配位,配位数为4。二个戊二烯环平面相互平行,相距3.31,且属完全遮盖型的。二个戊二烯环平面之间夹角φ)=1.7°。平均键长:Fe—C=2.057,C—C(Cp环)=1.438,C—N=1.513。B_3H_8阴离子中“氢桥”的2个H原子和3个B原子共面。B—B(氢桥连结)=1.734;B—B(非氢桥连结)=1.779。“氢桥”是非对称的,B—H(氢桥)分别为1.460和1.209。     

Structural and spectral characteristics of the electrogenerated tetracyanoethylene dianion

Structural and spectral characteristics of the electrogenerated tetracyanoethylene dianion (TCNE2-) were experimentally and theoretically examined. Spectroelectrochemistry of TCNE gives the spectra of TCNE2- in CH3CN at 220 nm, and in CH2Cl2 at 300 nm. These spectral characteristics are well explained by CIS/6-31G(d) and semiempirical CNDO/S-CI calculations. The bands in CH3CN and in CH2Cl2 are assigned to the degenerate 1E<--1A1 transition at the D2d structure and the 1B2u<--1Ag transition at the D2h structure, respectively. The rotation barrier of the C=C bond in TCNE2- is estimated by Hartree-Fock (HF), second-order M?ller-Plesset perturbation (MP2) and fourth-order MP (MP4) calculations with 6-31G(d), 6-31+G(d) and 6-311+G(d) basis sets as 42-51 kJ mol(-1). The D2d structure is most stable, and the D2h structure represents the transition state of the internal rotation. The calculations reveal that the two-electron addition to the antibonding LUMO of TCNE causes an easy rotation around the C=C bond of TCNE2- characterized by the formal single bond. These results show that TCNE2- preferentially adopts D2d and D2h structures in solvents depending upon the solvent nature by virtue of the easy rotation around the C=C bond.     

Intramolecular cyclization of ruthenium vinylidene complexes with a tethering vinyl group: facile cleavage and reconstruction of the C-C double bond

Protonation of ruthenium acetylide complexes [M]-*C*CCPh2CH2CH=CH2 (2a, [M] = (eta5-C5H5)(P(OPh)3)(PPh3)Ru; 2a', [M] = (eta5-C5H5)(dppp)Ru; *C = 13C-labeled carbon atom) with HBF4 in ether produces [[M]=*C=CHCH2CPh2*CH=CH2][BF4] (4, 4') exclusively via a metathesis process of the terminal vinyl group with the *C=*C of the resulting vinylidene group. For 4 in methanol, bond reconstruction of the two labeled *C atoms readily takes place via a retro-metathesis process followed by a cyclization of the resulting vinylidene ligand giving the cyclic carbene complex 5, which is fully characterized by single-crystal X-ray diffraction analysis. The protonation of 2a in MeOH is followed by a cyclization, also giving 5. Deuterium-labeling study indicates that the C-C bond formation of this cyclization proceeds simultaneously with the formation of 4 consistent with facile cleavage and reconstruction of C=C bonds. For comparison, complex 4 in alcohol yields, besides 5, the corresponding alkoxycyclohexene 6. Formation of 6 from 4 also involves a skeletal rearrangement with reconstruction of the C=C bond. Interestingly, [[Ru']=*C=C(Me)CH2CPh2*CH=CH2][BF4] (8') originally from a complex with two connected labeled carbon atoms also undergoes reestablishment of the *C=*C bond yielding the cyclic allenyl complex 9'. 13C-labeling studies clearly reveal the reestablishment of two C=C double bonds in the transformation of both 4 to 5 and 8' to 9'. The proposed mechanism implicates a cyclobutylidene intermediate formed either via a regiospecific [2+2] cycloaddition of two double bonds in the ruthenium vinylidene 4 or via a cyclization of 4 giving a nonclassical ion intermediate followed by a 1,2-alkyl shift.     

Aluminacyclopropene: syntheses, characterization, and reactivity toward terminal alkynes

Reactions of LAl with ethyne, mono- and disubstituted alkynes, and diyne to aluminacyclopropene LAl[eta2-C2(R1)(R2)] ((L = HC[(CMe)(NAr)]2, Ar = 2,6-iPr2C6H3); R1 = R2 = H, (1); R1 = H, R2 = Ph, (2); R1 = R2 = Me, (3); R1 = SiMe3, R2 = C[triple bond]CSiMe3, (4)) are reported. Compounds 1 and 2 were obtained in equimolar quantities of the starting materials at low temperature. The amount of C2H2 was controlled by removing an excess of C2H2 in the range from -78 to -50 degrees C. Compound 4 can be alternatively prepared by the substitution reaction of LAl[eta2-C2(SiMe3)2] with Me3SiC[triple bond]CC[triple bond]CSiMe3 or by the reductive coupling reaction of LAlI2 with potassium in the presence of Me3SiC[triple bond]CC[triple bond]CSiMe3. The reaction of LAl with excess C2H2 and PhC[triple bond]CH (<1:2) afforded the respective alkenylalkynylaluminum compounds LAl(CH=CH2)(C[triple bond]CH) (5) and LAl(CH=CHPh)(C[triple bond]CPh) (6). The reaction of LAl(eta2-C2Ph2) with C2H2 and PhC[triple bond]CH yielded LAl(CPh=CHPh)(C[triple bond]CH) (7) and LAl(CPh=CHPh)(C[triple bond]CPh) (8), respectively. Rationally, the formation of 5 (or 6) may proceed through the corresponding precursor 1 (or 2). The theoretical studies based on DFT calculations show that an interaction between the Al(I) center and the C[triple bond]C unit needs almost no activation energy. Within the AlC2 ring the computational Al-C bond order of ca. 1 suggests an Al-C sigma bond and therefore less pi electron delocalization over the AlC2 ring. The computed Al-eta2-C2 bond dissociation energies (155-82.6 kJ/mol) indicate a remarkable reactivity of aluminacyclopropene species. Finally, the 1H NMR spectroscopy monitored reaction of LAl(eta2-C2Ph2) and PhC[triple bond]CH in toluene-d8 may reveal an acetylenic hydrogen migration process.     

C7 and C9 carbon-rich bridges in diruthenium systems: synthesis, spectroscopic, and theoretical investigations of different oxidation States

Two methodologies of C-C bond formation to achieve organometallic complexes with 7 or 9 conjugated carbon atoms are described. A C7 annelated trans-[Cl(dppe)2Ru=C=C=C-CH=C(CH2)-C[triple bond]C-Ru(dppe)2Cl][X] (X = PF6, OTf) complex is obtained from the diyne trans-[Cl(dppe)2Ru-(C[triple bond]C)2-R] (R = H, SiMe3) in the presence of [FeCp2][PF6] or HOTf, and C7 or C9 complexes trans-[Cl(dppe)2Ru-(C[triple bond]C)n-C(CH3)=C(R1)-C(R2)=C=C=Ru(dppe)2Cl][X] (n = 1, 2; R1 = Me, Ph, R2 = H, Me; X = BF4, OTf) are formed in the presence of a polyyne trans-[Cl(dppe)2Ru-(C[triple bond]C)n-R] (n = 2, 3; R = H, SiMe3) with a ruthenium allenylidene trans-[Cl(dppe)2Ru=C=C=C(CH2R1)R2][X]. These reactions proceed under mild conditions and involve cumulenic intermediates [M+]=(C=)nCHR (n = 3, 5), including a hexapentaenylidene. A combination of chemical, electrochemical, spectroscopic (UV-vis, IR, NIR, EPR), and theoretical (DFT) techniques is used to show the influence of the nature and conformation of the bridge on the properties of the complexes and to give a picture of the electron delocalization in the reduced and oxidized states. These studies demonstrate that the C7 bridging ligand spanning the metal centers by almost 12 angstroms is implicated in both redox processes and serves as a molecular wire to convey the unpaired electron with no tendency for spin localization on one of the halves of the molecules. The reactivity of the C7 complexes toward protonation and deprotonation led to original bis(acetylides), vinylidene-allenylidene, or carbyne-vinylidene species such as trans-[Cl(dppe)2Ru[triple bond]C-CH=C(CH3)-CH=C(CH3)-HC=C=Ru(dppe)2Cl][BF4]3.     

On the nature of metal-carbon bonding: AIM and ELF analyses of MCH(n) (n = 1-3) compounds containing early transition metals

Ab initio and DFT calculations have been performed on a series of organometallic compounds, according to the formula MCH(n), where M = K, Ca, Sc, Ti, V, Cr, or Mn and n = 1-3. Various theoretical methods are compared, the B3LYP level yielding the same agreement with the experimental geometries available as the correlated MP2 and CISD methods, with the 6-311++G(3df,2p) basis set for C and H and Wachter's (15s11p6d3f1g)/[10s7p4d3f1g] basis set for transition metals. The main geometric and electronic features of the molecules studied are described, analyzing the M-C bonding characteristics in terms of the atoms in molecules theory (AIM) and the electron localization function (ELF). Although multiple bonding is expected from the Lewis bonding scheme, the results indicate an almost pure ionic bond for all of the systems studied. The net charge transfer from the metal to the carbon atom ranges from 0.5 to 1 e(-), and the electronic structure of the CH(n)(-) moiety is unaltered after the interaction with the metal cation, showing little or no effect on the shape of the electron pairing. The bond paths corresponding to a possible alpha-agostic bond for these systems are not present.     

Synthesis,spectroscopy, and catalytic properties of cationic organozirconium adsorbates on "super acidic" sulfated alumina. "Single-site" heterogeneous catalysts with virtually 100 active sites

Sulfated alumina (AlS), a highly Br?nsted acidic sulfated metal oxide, is prepared by the impregnation of gamma-alumina with 1.6 M H(2)SO(4), followed by calcination at 550 degrees C for 3 h. (13)C CPMAS NMR spectroscopy of the chemisorbed (13)C(alpha)-enriched organozirconium hydrocarbyl Cp'(2)Zr((13)CH(3))(2) (2)/AlS (Cp' = eta(5)-(CH(3))(5)C(5)) reveals that the chemisorption process involves M[bond]C sigma-bond protonolysis at the strong surface Br?nsted acid surface sites to yield a "cation-like" highly reactive zirconocenium electrophile, Cp'(2)Zr(13)CH(3)(+). In contrast, chemisorption of 2 on dehydroxylated alumina (DA) yields a similar cation via methide transfer to surface Lewis acid sites, while chemisorption onto dehydroxylated silica yields a mu-oxo Cp'(2)Zr((13)CH(3))-OSi[triple bond] species. Two complementary active site kinetic assays for benzene hydrogenation show that, unlike typical heterogeneous and supported organometallic catalysts, 97 +/- 2% of all Cp'ZrMe(3) (3)/AlS sites are catalytically significant, demonstrating that the species identified by (13)C CPMAS NMR is indeed the active species. 3/AlS mediates benzene hydrogenation with a turnover frequency of 360 h(-1) at 25 degrees C/1.0 atm H(2). Active site assays were also conducted for ethylene polymerization and reveal that 87 +/- 3% of 3/AlS sites are catalytically active, again demonstrating that nearly all zirconium sites are catalytically significant. Relative rates of ethylene homopolymerization mediated by the catalysts prepared via Cp(2)Zr(CH(3))(2) (1), Cp'(2)Zr(CH(3))(2) (2), Cp'Zr(CH(3))(3) (3), Zr(CH(2)TMS)(4) (4), and Zr(CH(2)Ph)(4) (5) (Cp = eta(5)-C(5)H(5)) chemisorption on AlS are 5/AlS > or = 4/AlS > or = 3/AlS > 2/AlS > or = 1/AlS for ethylene homopolymerization at 150 psi C(2)H(4), 60 degrees C. Under identical conditions, the polymerization rate for 3/DA is approximately 1/10th that for 3/AlS.     

Composés propargyliques et alléniques du Si,Ge, Sn chiraux possédant en α un carbone asymétrique mise en évidence des diastéréoisomères

The propargylic R¹R²R³MCH(CH₃)CCH and allenic R¹R²R³MCHCCHCH₃ compounds (M = Si, Ge, Sn) with two neighbouring asymmetric centres exist in two diastereotopic erythro and threo forms observable in NMR.     

Carbon-to-carbon identity proton transfer from allene, ketene, ketenimine, and thioketene to their respective conjugate anions in the gas phase. An ab initio study.

Gas-phase acidities of CH2=C=X (X = CH2, NH, O, and S) and barriers for the identity proton transfers (X=C=CH2 + HC triple bond C-X- right harpoon over left harpoon -X-C triple bond CH + CH2=C=X) as well as geometries and charge distributions of CH2=C=X, HC triple bond C-X- and the transition states of the proton transfer were determined by ab initio methods at the MP2/6-311+G(d,p)//MP2/6-311+G(d,p) and B3LYP/6-311+G(d,p) levels of theory. The acidities were also calculated at the CCSD(T)/6-311+G(2df,p) level. A major objective of this study was to examine how the enhanced unsaturation of CH2=C=X compared to that of CH3CH=X may affect acidities, transition state imbalances, and intrinsic barriers of the identity proton transfer. The results show that the acidities are all higher while the barriers are lower than for the corresponding CH3CH=X series. The transition states are all imbalanced but less so than for the reactions of CH3CH=X.