Organometallic chemistry of fluorinated allenes

Reaction of 1,1-difluoroallene and tetrafluoroallene with a series of transition metal complex fragments yields the mononuclear allene complexes [CpMn(CO)(2)(allene)] (1), [(CO)(4)Fe(allene)] (2), [(Ph(3)P)(2)Pt(C(3)H(2)F(2))] (4), [Ir(PPh(3))(2)(C(3)H(2)F(2))(2)Cl] (5), and the dinuclear complexes [mu-eta(1)-eta(3)-C(3)H(2)F(2))Fe(2)(CO)(7)] (3), [Ir(PPh(3))(C(3)H(2)F(2))(2)Cl](2) (6), and [mu-eta(2)-eta(2)-C(3)H(2)F(2))(CpMo(CO)(2))(2)] (9), respectively. In attempts to synthesize cationic complexes of fluorinated allenes [CpFe(CO)(2)(C(CF(3))=CH(2))] (7a), [CpFe(CO)(2)(C(CF(3))=CF(2))] (7b) and [mu-I-(CpFe(CO)(2))(2)][B(C(6)H(3)-3,5-(CF(3))(2))(4)] were isolated. The spectroscopic and structural data of these complexes revealed that the 1,1-difluoroallene ligand is coordinated exclusively with the double bond containing the hydrogen-substituted carbon atom. 1,1-Difluoroallene and tetrafluoroallene proved to be powerful pi acceptor ligands.     

Carboranes and baskets from reaction of B4H10 with allene

The reaction of the boron hydride B4H10 with allene was studied at the CCSD(T)/6-311+G(d)//MP2/6-31G(d) level. The mechanism is surprisingly complex with 44 transition states and several branching points located. The four carboranes and one basket that have been observed experimentally are all connected by pathways that have very similar free energies of activation. In addition, two new structures, a basket (2,4-(CH2CH2CH2)B4H8, 5a) and a "classical" structure (1,4-(Me2C)bisdiborane, 7), which might be obtained from the B4H10 + C3H4 reaction under the right conditions (hot/cold, quenched, etc.) have been identified. The first branch point in the reaction is the competition between H2 elimination from B4H10 (DeltaG(298 K) = 32.2 kcal/mol) and the hydroboration of allene by B4H10 (DeltaG(298 K) = 31.3 kcal/mol). The next branch point in the hydroboration mechanism controls the formation of 2,4-(MeCHCH2)B4H8 (1) (DeltaG(298 K) = 31.5 kcal/mol) and arachno-1,2/arachno-1,3-Me2-1-CB4H7 (8 and 8a) (DeltaG(298 K) = 34.3 kcal/mol). Another branch point in the H2-elimination mechanism controls the formation of 1-Me-2,5-micro-CH2-1-CB4H7 (29) (DeltaG(298 K) = 0.1 kcal/mol) and 2,5-micro-CHMe-1-CB4H7 (25/26) (DeltaG(298 K) = 7.3 kcal/mol). Formation of 2-Me-2,3-C2B4H7, a carborane observed in the reaction of methylacetylene with B4H10, is calculated to be blocked by a high barrier for H2 elimination. All free energies are relative to B4H10 + allene. An interesting reaction step discovered is the "reverse hydroboration step" in which a hydrogen atom is transferred from carbon back to boron, which allows a CH hydrogen to shuttle between the terminal and central carbon of allene.     

“D和L-丙氨酸宇称破缺能差正负”的争论

在宇宙开始大爆炸的时候，电荷变号与镜象反射共轭（CP）是对称的.但现在我们的宇宙绝大部分是正物质核子和电子等组成的，所以我们的宇宙是不对称的. D和L-丙氨酸通常称为对映体（enantiomer），实际上它们并不是由正、反粒子组成的真正的对映体，而是空间反演的，即x→－x, y→－y, z→－z 的非对映异构体（diastereoisomer），所以D-和L-丙氨酸是不对称的，两者间有能量的差别.自然界的力只有弱力是宇称不守恒的.在分子物理中，电弱力宇称不守恒是导致D-和L-丙氨酸能差的根源.所有以前的研究都认为L型丙氨酸比D型稳定.但是，最近以 Quack和 Schwerdtfeger为首的理论物理学家计算了L-丙氨酸在气相和溶液两种状态下,宇称破缺能差与分子构象的关系，提出“D-和L-丙氨酸究竟哪一个稳定”的质疑.由于气相和液相中两面角较难测定，我们用X射线四圆单晶衍射法，测定了270 K和250 K 时D-和L-丙氨酸的O(1)O(2)C(1)C(2)H(4)的原子坐标，算出了二面角，按照 Quack的MC-LR方法，D-和L-丙氨酸宇称破缺能差为1.2×10－19 Hartree, 相当于3.3× 10－18 eV/分子或3.2×10－16 kJ•mol－1，从而得出D-丙氨酸能态高于L-丙氨酸的结论.     

On the measurement of the parity violating energy difference between enantiomers

An experiment is outlined for measuring the small energy difference between two enantiomers due to the parity-violating weak neutral current perturbation. The method is based on the violation of the selection rules for the time evolution of states of well defined initial parity in isolated molecules. It could confirm or reject recent quantitative theoretical estimates of parity-violating energy differences.     

Crossed molecular beam studies of the reactions of allyl radicals, C3H5(X2A2), with methylacetylene (CH3CCH(X1A1)), allene (H2CCCH2(X1A1)), and their isotopomers

The chemical dynamics of the reaction of allyl radicals, C(3)H(5)(X(2)A(2)), with two C(3)H(4) isomers, methylacetylene (CH(3)CCH(X(1)A(1))) and allene (H(2)CCCH(2)(X(1)A(1))) together with their (partially) deuterated counterparts, were unraveled under single-collision conditions at collision energies of about 125 kJ mol(-1) utilizing a crossed molecular beam setup. The experiments indicate that the reactions are indirect via complex formation and proceed via an addition of the allyl radical with its terminal carbon atom to the terminal carbon atom of the allene and of methylacetylene (alpha-carbon atom) to form the intermediates H(2)CCHCH(2)CH(2)CCH(2) and H(2)CCHCH(2)CHCCH(3), respectively. The lifetimes of these intermediates are similar to their rotational periods but too short for a complete energy randomization to occur. Experiments with D4-allene and D4-methylacetylene verify explicitly that the allyl group stays intact: no hydrogen emission was observed but only the release of deuterium atoms from the perdeuterated reactants. Further isotopic substitution experiments with D3-methylacetylene combined with the nonstatistical nature of the reaction suggest that the intermediates decompose via hydrogen atom elimination to 1,3,5-hexatriene, H(2)CCHCH(2)CHCCH(2), and 1-hexen-4-yne, H(2)CCHCH(2)CCCH(3), respectively, via tight exit transition states located about 10-15 kJ mol(-1) above the separated products. The overall reactions were found to be endoergic by 98 +/- 4 kJ mol(-1) and have characteristic threshold energies to reaction between 105 and 110 kJ mol(-1). Implications of these findings to combustion and interstellar chemistry are discussed.     

The protonation of allene and some heteroallenes, a computational study

Protonation of allene and seven heteroallenes, X = Y = Z, at the terminal and central positions has been studied computationally at the MP2/6-311+G**, B3LYP/6-31+G**, and G3 levels. In all but one case protonation at a terminal position is preferred thermodynamically. The exception is allene, where protonation at C2 giving allyl cation prevails by about 10 kcal/mol over end-protonation, which gives the 2-propenyl cation. In the heteroallenes, protonation at a terminal carbon is strongly favored, activated by electron donation from the other terminal atom. Transition states for identity proton-transfer reactions were found for 10 of the "end-to-end" proton transfers. When the transfer termini are heteroatoms these processes are barrier free. We found no first-order saddle point structures for "center-to-center" proton transfers. An estimate of DeltaH++ for an identity center-to-center proton transfer could be made only for the reaction between the allyl cation and allene; it is approximately 22 kcal/mol higher than DeltaH++ for the end-to-end proton transfer between the 2-propenyl cation and allene. First-order saddle points for the proton transfer from H3S+ to both C1 and C2 of allene were found. The difference in activation enthalpies is 9.9 kcal/mol favoring protonation at C1 in spite of the thermodynamic disadvantage. We infer that protonation of X = Y = Z at central atoms passes through transition states much like primary carbenium (nitrenium, oxenium) cations, poorly conjugated with the attached vinylic or heterovinylic group. Several other processes following upon center protonation were studied and are discussed in the text, special attention being given to comparison of open and cyclic isomers.     

Perturbational calculations of parity-violating effects in nuclear-magnetic-resonance parameters

We investigate the effects of the parity-violating electroweak interaction in the spectral parameters of nuclear magnetic resonance. Perturbational theory of parity-violating effects in the nuclear magnetic shielding is presented to the order of G(F)alpha, and in the indirect spin-spin coupling, to the order of G(F)alpha3. These leading-order parity-violating corrections are evaluated using analytical linear-response theory methods based on Hartree-Fock and density-functional theory reference states. Parity-violating contributions to spin-spin couplings are evaluated for the first time at the first-principles level. Calculations are carried out for two chiral halomethanes, bromochlorofluoromethane and bromofluoroiodomethane.     

1,2-Bis(diphenylphosphino)carborane as a dual mode ligand for both the Sonogashira coupling and hydride-transfer steps in palladium-catalyzed one-pot synthesis of allenes from aryl iodides

[reaction: see text] One-pot allene synthesis from aryl iodides 1 and propargyldicyclohexylamine 2 proceeded in the presence of Pd(2)(dba)(3).CHCl(3) catalyst (2.5 mol %), 1,2-bis(diphenylphosphino)carborane 5 (10 mol %), CuI (15 mol %), and Et(3)N (150 mol %) to give the corresponding allenes 4 in good to high yields. Electron-deficient bidentate phosphines, such as 1,2-bis(diphenylphosphino)carborane 5 and (C(6)F(5))(2)PC(2)H(4)P(C(6)F(5))(2), play the role of a dual mode ligand for both the Sonogashira coupling and hydride-transfer reactions.     

Reaction dynamics of phenyl radicals (C6H5, X2A') with methylacetylene (CH3CCH(X1A1)), allene (H2CCCH2(X1A1)), and their D4-isotopomers

Crossed molecular beam experiments were utilized to untangle the reaction dynamics to form 1-phenylmethylacetylene [CH(3)CCC(6)H(5)] and 1-phenylallene [C(6)H(5)HCCCH(2)] in the reactions of phenyl radicals with methylacetylene and allene, respectively, over a range of collision energies from 91.4 to 161.1 kJ mol(-1). Both reactions proceed via indirect scattering dynamics and are initiated by an addition of the phenyl radical to the terminal carbon atom of the methylacetylene and allene reactants to form short-lived doublet C(9)H(9) collision complexes CH(3)CCHC(6)H(5) and C(6)H(5)H(2)CCCH(2). Studies with isotopically labeled reactants and the information on the energetics of the reactions depict that the energy randomization in the decomposing intermediates is incomplete. The collision complexes undergo atomic hydrogen losses via tight exit transition states leading to 1-phenylmethylacetylene [CH(3)CCC(6)H(5)] and 1-phenylallene [C(6)H(5)HCCCH(2)]. The possible role of both C(9)H(8) isomers as precursors to PAHs in combustion flames and in the chemistry of circumstellar envelopes of dying carbon stars is discussed.     

Carbene chemistry. Part 13 [1]. Preparation of sole fluoroallenes by a carbene route,and the reaction of allenes with halogenocarbenes

Fluoroallene and 1, 3-difluoroallene are prepared in good overall yield by the addition of dichlorocarbene to vinyl fluoride and 1, 2-difluoroethylene respectively, followed by pyrolysis of the dichlorocyclopropanes and treatment of the resulting dichloropropenes with zinc. Pyrolysis of 1, 1-dichloro-2-fluorocyclopropane over zinc gives fluoroallene directly.The reaction of allene with 2, 2, 3-trifluoro-3-trifluoro- methyloxiran at 180°C as a source of difluorocarbene gives both 1, 1-difluoro-2-methylenecyclopropane and its rearrangement product 1-(difluoromethylene)cyclopropane, the latter reacting more readily with a second difluorocarbene to give 2, 2, 3, 3- tetrafluorospiropentane. In an analogous way, fluoroallene reacts with dichlorocarbene, generated from trifluoro(trichloromethyl) silane at 140°C, to give $\text{E}$- and $\text{Z}$-1, 1-dichloro-2- (fluoromethylene)cyclopropane, 1-(dichloromethylene)-2-fluorocyclopropane, and 2, 2, 3, 3-tetrachloro-4-fluorospiropentane.     

Structures and dynamic solution behavior of cationic, two-coordinate gold(I)-π-allene complexes

A family of seven cationic gold complexes that contain both an alkyl substituted π-allene ligand and an electron-rich, sterically hindered supporting ligand was isolated in >90% yield and characterized by spectroscopy and, in three cases, by X-ray crystallography. Solution-phase and solid-state analysis of these complexes established preferential binding of gold to the less substituted C=C bond of the allene and to the allene π face trans to the substituent on the uncomplexed allenyl C=C bond. Kinetic analysis of intermolecular allene exchange established two-term rate laws of the form rate=k(1)[complex]+k(2)[complex][allene] consistent with allene-independent and allene-dependent exchange pathways with energy barriers of ΔG(≠)(1)=17.4-18.8 and ΔG(≠)(2)=15.2-17.6 kcal mol(-1), respectively. Variable temperature (VT) NMR analysis revealed fluxional behavior consistent with facile (ΔG(≠)=8.9-11.4 kcal mol(-1)) intramolecular exchange of the allene π faces through η(1)-allene transition states and/or intermediates that retain a staggered arrangement of the allene substituents. VT NMR/spin saturation transfer analysis of [{P(tBu)(2)o-binaphthyl}Au(η(2)-4,5-nonadiene)](+)SbF(6)(-) (5), which contains elements of chirality in both the phosphine and allene ligands, revealed no epimerization of the allene ligand below the threshold for intermolecular allene exchange (ΔG(≠)(298K)=17.4 kcal mol(-1)), which ruled out the participation of a η(1)-allylic cation species in the low-energy π-face exchange process for this complex.     

Bimolecular kinetic studies with high-temperature gas-phase 19F NMR: cycloaddition reactions of fluoroolefins

A gas-phase NMR kinetic technique has been used for the first time to obtain accurate measurements of rate constants of some bimolecular, second-order cycloaddition reactions. As a test of the potential use of this technique for the study of second-order reactions, the rate constants and the activation parameters for the cyclodimerization reactions of chlorotrifluoroethylene (CTFE) and tetrafluoroethylene (TFE) were determined in the temperature range 240-340 degrees C, using a commercial high-temperature NMR probe. Obtaining excellent agreement of the results with published data, the technique was then applied to the reaction of 1,1-difluoroallene with 1,3-butadiene, the results of which indicate that the use of gas-phase NMR for reaction kinetics is particularly valuable when a reagent is available only in small amounts and in cases where there are several competing processes occurring simultaneously. The major processes observed in this reaction are regioselective [2+2] and [2+4] cycloadditions, whose rates and activation parameters were determined [k2 = 9.3 x 10(6) exp(-20.1 kcal x mol(-1)/RT) L/mol(-1) x s(-1) and k3 = 1.2 x 10(6) exp(-18.4 kcal x mol(-1)/RT) L/mol(-1) x s(-)(1), respectively] in the temperature range 130-210 degrees C.     

Synthesis of chiral 1-substituted tetrahydroisoquinolines by the intramolecular 1,3-chirality transfer reaction catalyzed by Bi(OTf)3

The intramolecular 1,3-chirality transfer reaction of chiral amino alcohols 1 with 99% ee was developed to construct chiral 1-substituted tetrahydroisoquinoline 2. Bi(OTf)(3) (10 mol %)-catalyzed cyclization of 1 (R = H) afforded (S)-1-(E)-propenyl tetrahydroisoquinoline 2 (R = H) in 83% yield with a ratio of 98:2. The stereochemistry at the newly formed chiral center was produced by a syn S(N)2'-type process. In this reaction, the substituent on the benzene ring of 1 significantly affected the reactivities and selectivities. A plausible reaction mechanism was proposed.     

B(C6F5)3- vs Al(C6F5)3-derived metallocenium ion pairs. Structural, thermochemical, and structural dynamic divergences

The thermodynamic and structural characteristics of Al(C6F(5)3-derived vs B(C6F5)3-derived group 4 metallocenium ion pairs are quantified. Reaction of 1.0 equiv of B(C6F5)3 or 1.0 or 2.0 equiv of Al(C6F5)3 with rac-C2H4(eta5-Ind)2Zr(CH3)2 (rac-(EBI)Zr(CH3)2) yields rac-(EBI)Zr(CH3)(+)H3CB(C6)F5)(3)(-) (1a), rac-(EBI)Zr(CH3)+H3CAl(C6F5)(3)(-) (1b), and rac-(EBI)Zr2+[H3CAl(C6F5)3](-)(2) (1c), respectively. X-ray crystallographic analysis of 1b indicates the H3CAl(C6F5)(3)(-) anion coordinates to the metal center via a bridging methyl in a manner similar to B(C6F5)3-derived metallocenium ion pairs. However, the Zr-(CH3)(bridging) and Al-(CH3)(bridging) bond lengths of 1b (2.505(4) A and 2.026(4) A, respectively) indicate the methyl group is less completely abstracted in 1b than in typical B(C6F5)3-derived ion pairs. Ion pair formation enthalpies (DeltaH(ipf)) determined by isoperibol solution calorimetry in toluene from the neutral precursors are -21.9(6) kcal mol(-1) (1a), -14.0(15) kcal mol(-1) (1b), and -2.1(1) kcal mol(-1) (1b-->1c), indicating Al(C6F5)3 to have significantly less methide affinity than B(C6F5)3. Analogous experiments with Me2Si(eta5-Me4C5)(t-BuN)Ti(CH3)2 indicate a similar trend. Furthermore, kinetic parameters for ion pair epimerization by cocatalyst exchange (ce) and anion exchange (ae), determined by line-broadening in VT NMR spectra over the range 25-75 degrees C, are DeltaH++(ce) = 22(1) kcal mol(-1), DeltaS++(ce) = 8.2(4) eu, DeltaH++(ae) = 14(2) kcal mol(-1), and DeltaS++(ae) = -15(2) eu for 1a. Line broadening for 1b is not detectable until just below the temperature where decomposition becomes significant ( approximately 75-80 degrees C), but estimation of the activation parameters at 72 degrees C gives DeltaH++(ce) approximately 22 kcal mol(-1)and DeltaH++(ae) approximately 16 kcal mol(-1), consistent with the bridging methide being more strongly bound to the zirconocenium center than in 1a.     

Synthesis and Crystal Structure of N,N′-Bis-[3-chloro-5-S-(l-menthyloxy)-2(5H)-4-furanon-yl]-propane-1,3-diamine

The title compound,N,N′-bis-[3-chloro-5-S-(l-menthyloxy)-2(5H)-4-furanon-yl]-propane-1,3-diamine(C31H48Cl2N2O6,Mr = 615.61),has been synthesized and characterized by IR,1H NMR,MS,elemental analysis and single-crystal X-ray diffraction.The crystal crystallizes in the monoclinic system,space group C2 with a = 16.1091(4),b = 11.1880(3),c = 19.2854(5) ,β = 106.297(2)°,V = 3336.12(15) 3,Z = 4,Dc = 1.226 mg/m3,μ = 0.237 mm-1,F(000) = 1320,the final R = 0.0531 and wR = 0.0700 for 2760 observed reflections(I > 2σ(I)).X-ray analysis reveals that the title compound possesses four rings:two chiral five-membered furanone rings and two six-membered cyclohexane rings with chair conformation,containing eight chiral centers:C2(S),C3(R),C5(R),C10(S),C18(S),C21(R),C22(S) and C25(R).The structure is stabilized by N-H…O hydrogen bonding interaction.     

Fenton chemistry of 1,3-dimethyluracil

Hydroxyl radicals were generated in the Fenton reaction at pH 4 (Fe(2+) + H(2)O(2) --> Fe(3+) + .OH + OH-, k approximately equal to 60 L mol(-1) s(-1)) and by pulse radiolysis (for the determination of kinetic data). They react rapidly with 1,3-dimethyluracil, 1,3-DMU (k = 6 x 10(9) L mol(-1) s(-1)). With H(2)O(2) in excess and in the absence of O(2), 1,3-DMU consumption is 3.3 mol per mol Fe(2+). 1,3-DMUglycol is the major product (2.95 mol per mol Fe(2+)). Dimers, prominent products of .OH-induced reactions in the absence of Fe(2+)/Fe(3+) (Al-Sheikhly, M.; von Sonntag, C. Z. Naturforsch. 1983, 31b, 1622) are not formed. Addition of .OH to the C(5)-C(6) double bond of 1,3-DMU yields reducing C(6)-yl 1 and oxidizing C(5)-yl radicals 2 in a 4:1 ratio. The yield of reducing radicals was determined with tetranitromethane by following the buildup of nitroform anion. Reaction of 1 with Fe(3+) that builds up during the reaction or with H(2)O(2) gives rise to a short-chain reaction that is terminated by the reaction of Fe(2+) with 2, which re-forms 1,3-DMU. In the presence of O(2), 1.1 mol of 1,3-DMU and 0.6 mol of O(2) are consumed per mol Fe(2+) while 0.16 mol of 1,3-DMU-glycol and 0.17 mol of organic hydroperoxides (besides further unidentified products) are formed. In the presence of O(2), 1 and 2 are rapidly converted into the corresponding peroxyl radicals (k = 9.1 x 10(8) L mol(-1) s(-1)). Their bimolecular decay (2k = 1.1 x 10(9) L mol(-1) s(-1)) yields approximately 22% HO(2)./O(2).(-) in the course of fragmentation reactions involving the C(5)-C(6) bond. Reduction of Fe(3+) by O(2).(-) leads to an increase in .OH production that is partially offset by a consumption of Fe(2+) in its reaction with the peroxyl radicals (formation of organic hydroperoxides, k approximately 3 x 10(5) L mol(-1) s(-1); value derived by computer simulation).     

A crossed molecular beam study on the formation of hexenediynyl radicals (H(2)CCCCCCH; C(6)H(3) (X(2)A')) via reactions of tricarbon molecules, C(3)(X(1)Sigma(g)(+)), with allene (H(2)CCCH(2); X(1)A(1)) and methylacetylene (CH(3)CCH; X(1)A(1))

Crossed molecular beams experiments have been utilized to investigate the reaction dynamics between two closed shell species, i.e. the reactions of tricarbon molecules, C(3)(X(1)Sigma(g)(+)), with allene (H(2)CCCH(2); X(1)A(1)), and with methylacetylene (CH(3)CCH; X(1)A(1)). Our investigations indicated that both these reactions featured characteristic threshold energies of 40-50 kJ mol(-1). The reaction dynamics are indirect and suggested the reactions proceeded via an initial addition of the tricarbon molecule to the unsaturated hydrocarbon molecules forming initially cyclic reaction intermediates of the generic formula C(6)H(4). The cyclic intermediates isomerize to yield eventually the acyclic isomers CH(3)CCCCCH (methylacetylene reaction) and H(2)CCCCCCH(2) (allene reaction). Both structures decompose via atomic hydrogen elimination to form the 1-hexene-3,4-diynyl-2 radical (C(6)H(3); H(2)CCCCCCH). Future flame studies utilizing the Advanced Light Source should therefore investigate the existence of 1-hexene-3,4-diynyl-2 radicals in high temperature methylacetylene and allene flames. Since the corresponding C(3)H(3), C(4)H(3), and C(5)H(3) radicals have been identified via their ionization potentials in combustion flames, the existence of the C(6)H(3) isomer 1-hexene-3,4-diynyl-2 can be predicted as well.     

Thermochemistry of key soot formation intermediates: C3H3 isomers

Accurate standard enthalpies of formation for allene, propyne, and four C3H3 isomers involved in soot formation mechanisms have been determined through systematic focal point extrapolations of ab initio energies. Auxiliary corrections have been applied for anharmonic zero-point vibrational energy, core electron correlation, the diagonal Born-Oppenheimer correction (DBOC), and scalar relativistic effects. Electron correlation has been accounted for via second-order Z-averaged perturbation theory (ZAPT2) and primarily through coupled-cluster theory, including single, double, and triple excitations, as well as a perturbative treatment of connected quadruple excitations [ROCCSD, ROCCSD(T), ROCCSDT, and UCCSDT(Q)]. The correlation-consistent hierarchy of basis sets, cc-pVXZ (X = D, T, Q, 5, 6), was employed. The CCSDT(Q) corrections do not exceed 0.12 kcal mol(-)1 for the relative energies of the systems considered here, indicating a high degree of electron correlation convergence in the present results. Our recommended values for the enthalpies of formation are as follows: Delta(f)H(o)(0)(propargyl) = 84.76, Delta(f)H(o)(0) (1-propynyl) = 126.60, Delta(f)H(o)(0) (cycloprop-1-enyl) = 126.28, Delta(f)H(o)(0)(cycloprop-2-enyl) = 117.36, Delta(f)H(o)(0)(allene) = 47.41, and Delta(f)H(o)(0)(propyne) = 46.33 kcal mol(-1), with estimated errors no larger than 0.3 kcal mol(-1). The corresponding C3H3 isomerization energies are about 1 kcal mol(-1) larger than previous coupled-cluster results and several kcal mol(-1) below those previously obtained using density functional theory.     

Dehydrophenylnitrenes: quartet versus doublet states

The geometries and energies of 4-, 3-, and 2-dehydrophenylnitrenes (3, 4, and 5) are investigated using complete active space self-consistent field (CASSCF), multiconfiguration quasi-degenerate second-order perturbation (MCQDPT), and internally contracted multiconfiguration-reference configuration interaction (MRCI) theories in conjunction with a correlation consistent triple-zeta basis set. 4-Dehydrophenylnitrene 3 has a quartet ground state ((4)A(2)). The adiabatic excitation energies to the (2)A(2), (2)B(2), (2)A(1), and (2)B(1) states are 5, 21, 34, and 62 kcal mol(-1), respectively. The (2)B(2) state has pronounced closed-shell carbene/iminyl radical character, while the lowest-energy (2)B(1) state is a combination of a planar allene and a 2-iminylpropa-1,3-diyl. The MCQDPT treatment overestimates the excitation energy to (2)B(2) significantly as compared to CASSCF and MRCI+Q. Among quartet states, (4)A(2)-3 is the most stable one, while those of 4 and 5 (both (4)A') are 3 and 1 kcal mol(-1) higher in energy. 5 also has a quartet ground state and a (2)A' ' state 7 kcal mol(-1) higher in energy. On the other hand, the doublet-quartet energy splitting is -6 kcal mol(-1) for 4 in favor of the doublet state ((2)A'). Hence, (2)A'-4 is the most stable dehydrophenylnitrene, 3.5 kcal mol(-1) below (4)A(2) of 3. The geometry of (2)A'-4 shows the characteristic features of through-bond interaction between the in-plane molecular orbitals at N and at C3. The (2)A' state of 4 resembles the (2)A(1) state of 3 and lies 32 kcal mol(-1) above (4)A'-4. The lowest-energy (2)A' state of 5, on the other hand, resembles the (2)B(2) state of 3 and lies 22 kcal mol(-1) above (4)A'-5.     

A bipyridyl thorium metallocene: synthesis, structure and reactivity

The synthesis, structure and reactivity of a new bipy thorium metallocene have been studied. The reduction of the thorium chloride metallocene [η(5)-1,3-(Me(3)C)(2)C(5)H(3)](2)ThCl(2) (1) with potassium graphite in the presence of 2,2'-bipyridine gives the purple bipy metallocene [η(5)-1,3-(Me(3)C)(2)C(5)H(3)](2)Th(bipy) (2) in good yield. Complex 2 has been fully characterized by various spectroscopic techniques, elemental analysis and X-ray diffraction analysis. Complex 2 reacts cleanly with trityl chloride, silver halides and diphenyl diselenide, leading to the halide metallocenes [η(5)-1,3-(Me(3)C)(2)C(5)H(3)](2)ThX(2) (X = Cl (1), Br (3), I (4)) and [η(5)-1,3-(Me(3)C)(2)C(5)H(3)](2)Th(F)(μ-F)(3)Th[η(5)-1,3-(Me(3)C)(2)C(5)H(3)](F)(bipy) (5), and selenido metallocene [η(5)-1,3-(Me(3)C)(2)C(5)H(3)](2)Th(SePh)(2) (6), in good conversions. In addition, 2 cleaves the C[double bond, length as m-dash]S bond of CS(2) to give the sulfido complex, [η(5)-1,3-(Me(3)C)(2)C(5)H(3)](2)ThS (7), which further undergoes an irreversible dimerization or nucleophilic addition with CS(2), leading to the dimeric sulfido complex {[η(5)-1,3-(Me(3)C)(2)C(5)H(3)](2)Th}(μ-S)(2) (8) and dimeric trithiocarbonate complex {[η(5)-1,3-(Me(3)C)(2)C(5)H(3)](2)Th}(μ-CS(3))(2) (10) in good yields, respectively.