有机氟化合物量子化学研究 I: 二氟乙炔分子中化学键特性的从头计算

实验发现, F-C≡C-F与H-C≡C-H相比, 其C≡C三重键的离解能要小250.8kJ/mol,而该键的键长却比C~2H~2的短。这与"键越短键就越强"的传统看法不一致。我们通过从头计算研究, 发现主要原因是C~2F~2分子中F原子的孤对电子对C≡C三重键起反键作用, 从而削弱了C≡C三重键的强度; F原子的吸电子性又使C的原子轨道收缩效应增强,而使得C≡C三重键变短。     

有机氟化合物量子化学研究 Ⅰ.二氟乙炔分子中化学键特性的从头计算

实验发现,F—C≡C—F与H—C≡C—H相比,其C≡C三重键的离解能要小250.8kJ/mol,而该键的键长却比C_2H_2的短。这与“键越短键就越强”的传统看法不一致。我们通过从头计算研究,发现主要原因是C_2F_2分子中F原子的孤对电子对C≡C三重键起反键作用,从而削弱了G≡C三重键的强度;F原子的吸电子性又使C的原子轨道收缩效应增强,而使得C≡C三重键变短。     

多重键的研究进展

多重键是化学键的一个基本概念。元素周期表中的主族元素最多能形成三重键,主族元素轻原子如C、N和O等能形成稳定的二重键和三重键,而主族元素重原子由于Pauli排斥作用很难形成多重键。后来合成了含有p区重元素同原子或杂原子双键化合物。p区重主族元素形成三重键更加困难,因为其活性太高。最近合成、分离和表征了一个稳定的含有Si≡Si三重键的二硅炔化合物。对过渡金属-过渡金属的相互作用实验和理论研究发现了四重键、五重键甚至是六重键,主要是因为d轨道和f轨道参加了成键。锕系元素同原子间最高能形成六重键。     

为什么N_2分子和C_2H_2分子里的三键活动性截然两样?

N_2分子的电子结构可简单地写为:N≡N:即两个 N 原子之间有一个σ键,二个π键。同时,每个 N原子还有一对“孤对电子”。乙炔分子的电子结构可简单地写为:H—C≡C—H即两个 C 原子之间有一个σ键,二个π键。另外,每个 C 原子与一个 H 原子间有一个σ键。对比 N_2分子与 C_2H_2的电子结构,可以看出在 N_2     

钯催化的Grignard型反应

对钯催化的Grignard类型反应作了论述.总结了钯催化的有机卤化物或炔烃与C=O键或C≡N键的二组分反应和有机卤化物、烯烃或炔烃与C=O键或C≡N键的三组分反应.在这些反应中的C-Pd键是通过C-X键与Pd(0)的氧化加成或通过碳碳双键或叁键的碳/亲核钯反应生成,C-Pd键与C=O键或C≡N键之间的反应一般为分子内反应.当然,人们也观察到了通过芳香C-H键活化产生的芳基碳钯键与腈基的分子间反应.在这些反应中催化剂的再生是关键.本工作对反应的机理也作了一些探讨.     

铍的夹心和半夹心化合物中铍原子的共价

用DV-XαSCC方法和自然键轨道法研究了CpBeH和Cp_2Be的电子结构和成键情况,进而根据作者之一提出的共价定义研究了CpBeX(X=H,Cl,Br,CH_3,C≡CH,……)和Cp_2Be等化合物中铍原子的共价.结果表明,在这些化合物中,铍原子的共价均为6.     

固氮酶底物配位活化的量子化学模拟

用EHMO法就Roussin红盐, MoFeS4(NO)2^2^-, Roussin黑盐及网兜状模型对C2H2,N2, NNH^+和NCH等固氮酶底物的配位活化进行了量子化学模拟. 综合考虑体系总能量与底物多重键的Mulliken键级的变化, 得知乙炔与二核簇相距1.2埃时为最佳活化构型;在Roussin黑盐及网兜状模型以“架炮"方式与乙炔组成的配位体系中, C≡C键呈5度仰角时为最佳活化构型. 铁比钼更有利于削弱C≡C键. 在N2, NNH^+NCH以“投网"方式与网兜模型组成的配位体系中, 底物的多重键受到较大的削弱. “投网"配位方式使兜口外氮原子上的电荷密度增加, 容易受亲电子试剂的进攻, H^+沿N-N轴线方向攻击N2对活化N≡N键最有利.     

1. 5-环辛二烯-3, 7-二炔(C~8H~4)结构和光谱性质的理论研究

采用量子化学从头算方法研究了1,5-环辛二烯-3,7-二炔(C~8H~4)的结构和光谱性质,根据等键反应分析和自然键轨道方法研究了它的稳定性、成键情况和共轭性。结果表明1,5-环辛二烯-3,7-二炔(C~8H~4)分子为平面刚性结构,可能稳定存在。分子中C≡C键与C=C键存在一定程度的共轭,可能具有芳香性。     

孤对键弱化效应研究

在H_2O_2、N_2H_4、F_2分子中,O—O、N—N、F—F键的键长分别是0.148、0.148、0.144nm,虽比C_2H_6分子中的C—C键(0.154nm)短,但其σ键键能分别是146、160、155kJ/mol,却比C—C键能(365 kJ/mol)小约2.5倍,通常称这类原子的单键键能的反常现象为“孤对键弱化效应”。传统观点认为,半径很小的N、O、F等在化合时必须相当接近才能键合,孤对电子的排斥作用阻止了其相互接近,削弱了键能,降低了键的稳定性。显然,将这种削弱效应考虑为原子间效应是不合理的。本文用键参数图解法对“孤对键弱化效应”提出了合理的解释。     

具有三重Mo—Mo键的配合物Mo_2Cl_6[SC(NH_2)_2]_3·2H_2O合成、晶体结构和电子构型

分别通过Mo≡Mo→Mo≡Mo的双电子氧化还原反应及由单核Mo(Ⅲ)配合物经硫脲[SC(NH_2)_2]桥联的方法合成具有三重Mo—Mo键的配合物Mo_2Cl_5[SC(NH_2)_2]_3·2H_O.该配合物晶体的结晶学参数为:三斜晶系,PI空间群,.晶胞中2个结晶学独立的分子中Mo—Mo键长分别为2.439(1)A和2.443(1)A.配合物的S-C键削弱了桥S原子参与d-p相互作用的程度,有利于形成较强的Mo≡Mo键,其d-d分子轨道的电子构型是ν~2(π+δ)~4.     

The nature of the chemical bond revisited: an energy-partitioning analysis of nonpolar bonds

The nature of the chemical bond in nonpolar molecules has been investigated by energy-partitioning analysis (EPA) of the ADF program using DFT calculations. The EPA divides the bonding interactions into three major components, that is, the repulsive Pauli term, quasiclassical electrostatic interactions, and orbital interactions. The electrostatic and orbital terms are used to define the nature of the chemical bond. It is shown that nonpolar bonds between main-group elements of the first and higher octal rows of the periodic system, which are prototypical covalent bonds, have large attractive contributions from classical electrostatic interactions, which may even be stronger than the attractive orbital interactions. Fragments of molecules with totally symmetrical electron-density distributions, like the nitrogen atoms in N(2), may strongly attract each other through classical electrostatic forces, which constitute 30.0 % of the total attractive interactions. The electrostatic attraction can be enhanced by anisotropic charge distribution of the valence electrons of the atoms that have local areas of (negative) charge concentration. It is shown that the use of atomic partial charges in the analysis of the nature of the interatomic interactions may be misleading because they do not reveal the topography of the electronic charge distribution. Besides dinitrogen, four groups of molecules have been studied. The attractive binding interactions in H(n)E-EH(n) (E=Li to F; n=0-3) have between 20.7 (E=F) and 58.4 % (E=Be) electrostatic character. The substitution of hydrogen by fluorine does not lead to significant changes in the nature of the binding interactions in F(n)E-EF(n) (E=Be to O). The electrostatic contributions to the attractive interactions in F(n)E-EF(n) are between 29.8 (E=O) and 55.3 % (E=Be). The fluorine substituents have a significant effect on the Pauli repulsion in the nitrogen and oxygen compounds. This explains why F(2)N-NF(2) has a much weaker bond than H(2)N-NH(2), whereas the interaction energy in FO-OF is much stronger than in HO-OH. The orbital interactions make larger contributions to the double bonds in HB=BH, H(2)C=CH(2), and HN=NH (between 59.9 % in B(2)H(2) and 65.4 % in N(2)H(2)) than to the corresponding single bonds in H(n)E-EH(n). The orbital term Delta E(orb) (72.4 %) makes an even greater contribution to the HC triple bond CH triple bond. The contribution of Delta E(orb) to the H(n)E=EH(n) bond increases and the relative contribution of the pi bonding decreases as E becomes more electronegative. The pi-bonding interactions in HC triple bond CH amount to 44.4 % of the total orbital interactions. The interaction energy in H(3)E-EH(3) (E=C to Pb) decreases monotonically as the element E becomes heavier. The electrostatic contributions to the E-E bond increases from E=C (41.4 %) to E=Sn (55.1 %) but then decreases when E=Pb (51.7 %). A true understanding of the strength and trends of the chemical bonds can only be achieved when the Pauli repulsion is considered. In an absolute sense the repulsive Delta E(Pauli) term is in most cases the largest term in the EPA.     

Regioselective coupling of pentafluorophenyl substituted alkynes: mechanistic insight into the zirconocene coupling of alkynes and a facile route to conjugated polymers bearing electron-withdrawing pentafluorophenyl substituents

The reaction of Cp(2)ZrCl(2) with 2 equiv of BuLi at -78 degrees C, followed by the addition of an unsymmetrical tetra- or pentafluorophenyl substituted alkyne R(1)C[triple bond]CAr(f) (R(1), Ar(f) = (CH(2))(4)Me, p-C(6)F(4)H; Me, p-C(6)F(4)H; Ph, C(6)F(5)), resulted in regioselective couplings of these alkynes to zirconacyclopentadienes in which the Ar(f) substituents preferentially adopt the 3,4-positions (beta beta) of the zirconacyclopentadiene ring. With Cp(2)Zr(py)(Me(3)SiC[triple bond]CSiMe(3)) as the zirconocene reagent, the couplings could be carried out at room temperature; however, at higher temperatures significant quantities of the 2,4-fluoroaryl substituted (alpha beta) isomers were also formed. None of the conditions employed produced the 2,5-fluoroaryl substituted (alpha alpha) isomers. These fluoroaryl-substituted zirconacyclopentadienes were readily converted to butadienes via reactions with acids. The zirconacyclopentadiene Cp(2)ZrC(4)-2,5-Ph(2)-3,4-(C(6)F(5))(2), which resulted from the coupling of PhC[triple bond]C(C(6)F(5)), was converted to the corresponding thiophene by reaction with S(2)Cl(2), and to an arene by reaction with MeO(2)CC[triple bond]CCO(2)Me/CuCl. Mechanistic studies on zirconocene couplings of (p-CF(3)C(6)H(4))C[triple bond]C(p-MeC(6)H(4)) indicate that the observed regioselectivities are determined by an electronic factor that controls the orientation of at least one of the two alkynes as they are coupled. Additionally, these studies suggest an unsymmetrical transition state for the zirconocene coupling of alkynes, and this is supported by DFT calculations. The reaction of [(C(6)F(5))C[triple bond]CCH(2)](2)CH(2) with Cp(2)Zr(py)(Me(3)SiC[triple bond]CSiMe(3)) resulted in a zirconacyclopentadiene in which the pentafluorophenyl substituents have been forced into the 2,5-positions (alpha alpha). Zirconocene coupling of the diyne (C(6)F(5))C[triple bond]C-1,4-C(6)H(4)-C[triple bond]C(C(6)F(5)) provided a route to conjugated polymers bearing electron-withdrawing pentafluorophenyl groups.     

Electronic structure and chain-length effects in diplatinum polyynediyl complexes trans,trans-[(X)(R3P)2Pt(C triple bond C)(n)Pt(PR3)2(X)]: a computational investigation

Structure and bonding in the title complexes are studied using model compounds trans,trans-[(C6H5)(H3P)2Pt(C triple bond C)(n)Pt(PH3)2(C6H5)] (PtCxPt; x = 2n = 4-26) at the B3LYP/LACVP* level of density functional theory. Conformations in which the platinum square planes are parallel are very slightly more stable than those in which they are perpendicular (DeltaE = 0.12 kcal mol(-1) for PtC8Pt). As the carbon-chain length increases, progressively longer C triple bond C triple bonds and shorter triple bond C-C triple bond single bonds are found. Whereas the triple bonds in HCxH become longer (and the single bonds shorter) as the interior of the chain is approached, the PtC triple bond C triple bonds in PtCxPt are longer than the neighboring triple bond. Also, the Pt-C bonds are shorter at longer chain lengths, but not the H-C bonds. Accordingly, natural bond orbital charge distributions show that the platinum atoms become more positively charged, and the carbon chain more negatively charged, as the chain is lengthened. Furthermore, the negative charge is localized at the two terminal C triple bond C atoms, elongating this triple bond. Charge decomposition analyses show no significant d-pi* backbonding. The HOMOs of PtCxPt can be viewed as antibonding combinations of the highest occupied pi orbital of the sp-carbon chain and filled in-plane platinum d orbitals. The platinum character is roughly proportional to the Pt/Cx/Pt composition (e.g., x = 4, 31 %; x = 20, 6 %). The HOMO and LUMO energies monotonically decrease with chain length, the latter somewhat more rapidly so that the HOMO-LUMO gap also decreases. In contrast, the HOMO energies of HCxH increase with chain length; the origin of this dichotomy is analyzed. The electronic spectra of PtC4Pt to PtC10Pt are simulated. These consist of two pi-pi* bands that redshift with increasing chain length and are closely paralleled by real systems. A finite HOMO-LUMO gap is predicted for PtCinfinityPt. The structures of PtCxPt are not strictly linear (average bond angles 179.7 degrees -178.8 degrees ), and the carbon chains give low-frequency fundamental vibrations (x = 4, 146 cm(-1); x = 26, 4 cm(-1)). When the bond angles in PtC12Pt are constrained to 174 degrees in a bow conformation, similar to a crystal structure, the energy increase is only 2 kcal mol(-1). The above conclusions should extrapolate to (C triple bond C)(n) systems with other metal endgroups.     

Synthetic and structural studies on C-ethynyl- and C-bromo-carboranes

A high-yield preparation of the C-monoethynyl para-carborane, 1-Me(3)SiC[triple bond]C-1,12-C2B10H11, from C-monocopper para-carborane and 1-bromo-2-(trimethylsilyl)ethyne, BrC[triple bond]CSiMe(3) is reported. The low-yield preparation of 1,12-(Me3SiC[triple bond]C)2-1,12-C2B10H10 from the C,C'-dicopper para-carborane derivative with 1-bromo-2-(trimethylsilyl)ethyne, BrC[triple bond]CSiMe3, has been re-investigated and other products were identified including the C-monoethynyl-carborane 1-Me3SiC[triple bond]C-1,12-C2B10H11 and two-cage assemblies generated from cage-cage couplings. The contrast in the yields of the monoethynyl and diethynyl products is due to the highly unfavourable coupling process between 1-RC[triple bond]C-12-Cu-1,12-C2B10H10 and the bromoalkyne. The ethynyl group at the cage carbon C(1) strongly influences the chemical reactivity of the cage carbon at C(12)-the first example of the "antipodal effect" affecting the syntheses of para-carborane derivatives. New two-step preparations of 1-ethynyl- and 1,12-bis(ethynyl)-para-carboranes have been developed using a more readily prepared bromoethyne, 1-bromo-3-methyl-1-butyn-3-ol, BrC[triple bond]CCMe2OH. The molecular structures of the two C-monoethynyl-carboranes, 1-RC[triple bond]C-1,12-C2B10H11 (R = H and Me3Si), were experimentally determined using gas-phase electron diffraction (GED). For R = H (R(G) = 0.053) a model with C(5v) symmetry refined to give a C[triple bond]C bond distance of 1.233(5) A. For R = Me3Si (R(G) = 0.048) a model with C(s) symmetry refined to give a C[triple bond]C bond distance of 1.227(5) A. Molecular structures of 1,12-Br2-1,12-C2B10H10, 1-HC[triple bond]C-12-Br-1,12-C2B10H10 and 1,12-(Me(3)SiC[triple bond]C)2-1,12-C2B10H10 were determined by X-ray crystallography. Substituents at the cage carbon atoms on the C2B10 cage skeleton in 1-X-12-Y-1,12-C2B10H10 derivatives invariably lengthen the cage C-B bonds. However, the subtle substituent effects on the tropical B-B bond lengths in these compounds are more complex. The molecular structures of the ethynyl-ortho-carborane, 1-HC[triple bond]C-1,2-C2B10H11 and the ethene, trans-Me3SiBrC=CSiMe3Br are also reported.     

Synthesis of [F3S(triple bond)NXeF][AsF6] and structural study by multi-NMR and Raman spectroscopy, electronic structure calculations, and X-ray crystallography

The salt, [F3S(triple bond)NXeF][AsF6], has been synthesized by the reaction of [XeF][AsF6] with liquid N(triple bond)SF3 at -20 degrees C. The Xe-N bonded cation provides a rare example of xenon bound to an inorganic nitrogen base in which nitrogen is formally sp-hybridized. The F3S(triple bond)NXeF+ cation was characterized by Raman spectroscopy at -150 degrees C and by 129Xe, 19F, and 14N NMR spectroscopy in HF solution at -20 degrees C and in BrF5 solution at -60 degrees C. Colorless [F3S(triple bond)NXeF][AsF6] was crystallized from HF solvent at -45 degrees C, and its low-temperature X-ray crystal structure was determined. The Xe-N bond is among the longest Xe-N bonds known (2.236(4) A), whereas the Xe-F bond length (1.938(3) A) is significantly shorter than that of XeF2 but longer than in XeF+ salts. The Xe-F and Xe-N bond lengths are similar to those of HC(triple bond)NXeF+, placing it among the most ionic Xe-N bonds known. The nonlinear Xe-N-S angle (142.6(3)o) contrasts with the linear angle predicted by electronic structure calculations and is attributed to close N...F contacts within the crystallographic unit cell. Electronic structure calculations at the MP2 and DFT levels of theory were used to calculate the gas-phase geometries, charges, bond orders, and valencies of F3S(triple bond)NXeF+ and to assign vibrational frequencies. The calculated small energy difference (7.9 kJ mol-1) between bent and linear Xe-N-S angles also indicates that the bent geometry is likely the result of crystal packing. The structural studies, natural bond orbital analyses, and calculated gas-phase dissociation enthalpies reveal that F3S(triple bond)NXeF+ is among the weakest donor-acceptor adducts of XeF+ with an Xe-N donor-acceptor interaction that is very similar to that of HC(triple bond)NXeF+, but considerably stronger than that of F3S(triple bond)NAsF5. Despite the low dissociation enthalpy of the donor-acceptor bond in F3S(triple bond)NXeF+, 129Xe, 19F, and 14N NMR studies reveal that the F3S(triple bond)NXeF+ cation is nonlabile at low temperatures in HF and BrF5 solvents.     

Effects of fluorine on the structures and energetics of the propynyl and propargyl radicals and their anions

[reaction: see text] The adiabatic electron affinity (EA(ad)) of the CH(3)-C[triple bond]C(*) radical [experiment = 2.718 +/- 0.008 eV] and the gas-phase basicity of the CH(3)-C[triple bond]C:(-) anion [experiment = 373.4 +/- 2 kcal/mol] have been compared with those of their fluorine derivatives. The latter are studied using theoretical methods. It is found that there are large effects on the electron affinities and gas-phase basicities as the H atoms of the alpha-CH(3) group in the propynyl system are substituted by F atoms. The predicted electron affinities are 3.31 eV (FCH(2)-C[triple bond]C(*)), 3.86 eV (F(2)CH-C[triple bond]C(*)), and 4.24 eV (F(3)C-C[triple bond]C(*)), and the predicted gas-phase basicities of the fluorocarbanion derivatives are 366.4 kcal/mol (FCH(2)-C[triple bond]C:(-)), 356.6 kcal/mol (F(2)CH-C[triple bond]C:(-)), and 349.8 kcal/mol (F(3)C-C[triple bond]C:(-)). It is concluded that the electron affinities of fluoropropynyl radicals increase and the gas-phase basicities decrease as F atoms sequentially replace H atoms of the alpha-CH(3) in the propynyl system. The propargyl radicals, lower in energy than the isomeric propynyl radicals, are also examined and their electron affinities are predicted to be 0.98 eV ((*)CH(2)-C[triple bond]CH), 1.18 eV ((*)CFH-C[triple bond]CH), 1.32 eV ((*)CF(2)-C[triple bond] CH), 1.71 eV ((*)CH(2)-C[triple bond]CF), 2.05 eV ((*)CFH-C[triple bond]CF), and 2.23 eV ((*)CF(2)-C[triple bond]CF).     

Probing ruthenium-acetylide bonding interactions: synthesis, electrochemistry, and spectroscopic studies of acetylide-ruthenium complexes supported by tetradentate macrocyclic amine and diphosphine ligands

The synthesis and spectroscopic properties of trans-[RuL4(C[triple bond]CAr)2] (L4 = two 1,2-bis(dimethylphosphino)ethane, (dmpe)2; 1,5,9,13-tetramethyl-1,5,9,13-tetraazacyclohexadecane, 16-TMC; 1,12-dimethyl-3,4:9,10-dibenzo-1,12-diaza-5,8-dioxacyclopentadecane, N2O2) are described. Investigations into the effects of varying the [RuL4] core, acetylide ligands, and acetylide chain length for the [(-)C[triple bond]C(C6H4C[triple bond]C)(n-1)Ph] and [(-)C[triple bond]C(C6H4)(n-1)Ph] (n = 1-3) series upon the electronic and electrochemical characteristics of trans-[RuL4(C[triple bond]CAr)2](0/+) are presented. DFT and TD-DFT calculations have been performed on trans-[Ru(L')4(C[triple bond]CAr)2](0/+) (L' = PH3 and NH3) to examine the metal-acetylide pi-interaction and the nature of the associated electronic transition(s). It was observed that (1) the relationship between the transition energy and 1/n for trans-[Ru(dmpe)2{C[triple bond]C(C6H4C[triple bond]C)(n-1)Ph}2] (n = 1-3) is linear, and (2) the sum of the d(pi)(Ru(II)) --> pi*(C[triple bond]CAr) MLCT energy for trans-[Ru(16-TMC or N2O2)(C[triple bond]CAr)2] and the pi(C[triple bond]CAr) --> d(pi)(Ru(III)) LMCT energy for trans-[Ru(16-TMC or N2O2)(C[triple bond]CAr)2]+ corresponds to the intraligand pi pi* absorption energy for trans-[Ru(16-TMC or N2O2)(C[triple bond]CAr)2]. The crystal structure of trans-[Ru(dmpe)2{C[triple bond]C(C6H4C[triple bond]C)2Ph}2] shows that the two edges of the molecule are separated by 41.7 A. The electrochemical and spectroscopic properties of these complexes can be systematically tuned by modifying L4 and Ar to give E(1/2) values for oxidation of trans-[RuL4(C[triple bond]CAr)2] that span over 870 mV and lambda(max) values of trans-[RuL4(C[triple bond]CAr)2] that range from 19,230 to 31,750 cm(-1). The overall experimental findings suggest that the pi-back-bonding interaction in trans-[RuL4(C[triple bond]CAr)2] is weak and the [RuL4] moiety in these molecules may be considered to be playing a "dopant" role in a linear rigid pi-conjugated rod.     

Synthesis and characterization of mono- and binuclear platinum complexes containing terminal and bridging diynyldiphenylphosphine ligands

A series of mononuclear platinum complexes containing diynyldiphenylphosphine ligands [cis-Pt(C(6)F(5))(2)(PPh(2)C[triple bond]CC(6)H(4)C[triple bond]CR)L](n)(n= 0, L = tht, R = Ph 2a, Bu(t)2b; L = PPh(2)C[triple bond]CC(6)H(4)C[triple bond]CR, 4a, 4b; n=-1, L = CN(-), 3a, 3b) has been synthesized and the X-ray crystal structures of 4a and 4b have been determined. In order to compare the eta2-bonding capability of the inner and outer alkyne units, the reactivity of towards [cis-Pt(C(6)F(5))(2)(thf)(2)] or [Pt(eta2)-C(2)H(4))(PPh(3))(2)] has been examined. Complexes coordinate the fragment "cis-Pt(C(6)F(5))(2)" using the inner alkynyl fragment and the sulfur of the tht ligand giving rise the binuclear derivatives [(C(6)F(5))(2)Pt(mu-tht)(mu-1kappaP:2eta2-C(alpha),C(beta)-PPh(2)C[triple bond]CC(6)H(4)C[triple bond]CR)Pt(C(6)F(5))(2)](R = Ph 5a, Bu(t)5b). The phenyldiynylphosphine complexes 2a, 3a and 4a react with [Pt(eta2)-C(2)H(4))(PPh(3))(2)] to give the mixed-valence Pt(II)-Pt(0) complexes [((C(6)F(5))(2)LPt(mu-1kappaP:2eta2)-C(5),C(6)-PPh(2)C[triple bond]CC(6)H(4)C[triple bond]CPh))Pt(PPh(3))(2)](n)(L = tht 6a, CN 8a and PPh(2)C[triple bond]CC(6)H(4)C[triple bond]CPh 9a) in which the Pt(0) fragment is eta2-complexed by the outer fragment. Complex 6a isomerizes in solution to a final complex [((C(6)F(5))(2)(tht)Pt(mu-1kappaP:2eta2)-C(alpha),C(beta)-PPh(2)C[triple bond]CC(6)H(4)C[triple bond]CPh))Pt(PPh(3))(2)]7a having the Pt(0) fragment coordinated to the inner alkyne function. In contrast, the tert-butyldiynylphosphine complexes 2b and 3b coordinate the Pt(0) unit through the phosphorus substituted inner acetylenic entity yielding 7b and 8b. By using 4a and 2 equiv. of [Pt(eta2)-C(2)H(4))(PPh(3))(2)] as precursors, the synthesis of the trinuclear complex [cis-((C(6)F(5))(2)Pt(mu-1kappaP:2eta2)-C(5),C(6)-PPh(2)C[triple bond]CC(6)H(4)C[triple bond]CPh)(2))(Pt(PPh(3))(2))(2)]10a, bearing two Pt(0)(PPh(3))(2)eta2)-coordinated to the outer alkyne functions is achieved. The structure of 7a has been confirmed by single-crystal X-ray diffraction.     

A microwave spectroscopic and quantum chemical study of 3-butyne-1-selenol (HSeCH2CH2C[triple bond]CH)

The microwave spectrum of 3-butyne-1-selenol has been studied by means of Stark-modulation microwave spectroscopy and quantum chemical calculations employing the B3LYP/aug-cc-pVTZ and MP2/6-311++G(3df,3pd) methods. Rotational transitions attributable to the H80SeCH2CH2C[triple bond]CH and H78SeCH2CH2C[triple bond]CH isotopologues of two conformers of this molecule were assigned. One of these conformers possesses an antiperiplanar arrangement for the atoms Se-C-C-C, while the other is synclinal and seems to be stabilized by the formation of a weak intramolecular hydrogen bond between the hydrogen atom of the selenol group and the pi electrons of the CC triple bond. The energy difference between these conformers was determined to be 0.2(5) kJ/mol by relative intensity measurements, and the hydrogen-bonded form was slightly lower in energy.     

Unusual collision-induced dissociation of fluorated and non-fluorated alpha-nitrotoluene analogs in a gas chromatograph triple-stage quadrupole mass spectrometer under electron-capturing negative-ion chemical ionization conditions

Unusual collision-induced dissociation (CID) of perfluorated and non-perfluorated alpha-nitrotoluene analogs in a gas chromatograph triple-stage quadrupole (TSQ) mass spectrometer (GC-QqQ-MS) under electron-capturing negative-ion chemical ionization conditions is reported. CID of [M - 1]- of alpha-nitro-2,3,4,5,6-pentafluorotoluene (C6F5CH2-NO2) and alpha-nitro-2,5-difluorotoluene (C6H3F2CH2-NO2) produced an intense ion with m/z 66. By using 15N- or 18O-labelled C6F5CH2-NO2 analogs, we found that this anion has the formula C3NO. By contrast, CID of [M - 1]- of alpha-nitrotoluene (C6H5CH2-NO2) and alpha-nitro-3,5-difluorotoluene (C6H3F2CH2-NO2) produced an anion with m/z 86 with the formula C3H4NO2. The expected CID of the C-N-bond of all alpha-nitrotoluene analogs to form the nitrite anion (NO2-, m/z 46) did not occur. We propose mechanisms for the formation of the anions C3NO and C3H4NO2 in the collision chamber of the TSQ mass spectrometer. The most likely structures for the anion C3NO are :C=C=C=N--O and N triple bond C-C triple bond C--O-. The unique CID behavior of C6F5CH2--NO2 can be utilized to unequivocally identify and accurately quantify nitrite in biological fluids by GC-tandem MS.