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Comparison of the potential energy surface including the ZPVE corrections of the highly exothermic hydrogen abstraction reaction H2Te + OH with the H2Se + OH, H2S + OH, and H2O + OH reactions at the CCSD(T)/5Z level.

A series of reactions between Lewis bases and an imidazole-based dithione dimer (1) has been investigated. Both cyclic(alkyl)(amino)carbene (CAAC) (2) and N-heterocyclic carbene (NHC) (4), in addition to N-heterocyclic silylene (NHSi) (6), demonstrate the capability to cleave the sulphur-sulphur bonds in 1, giving carbene-stabilized dithiolene (L0 ) zwitterions (3 and 5) and a spirocyclic silicon-dithiolene compound (7), respectively. The bonding nature of 3, 5, and 7 are probed by both experimental and theoretical methods.

A low-dropout linear regulator (LDO) without external capacitors is designed, combining ultra-low power consumption and ultra-fast transient response. The common support voltage of the LDO is 2.5 V to 3.6 V with a stable output voltage of 1.2 V and an output current dynamic range of 10 μA to 20 mA to supply power to other circuit modules. A Rail-to-Rail Input-Output (RRIO) Class AB push-pull output amplifier and a dynamic bias circuit are also designed. Meanwhile, a dynamic bias circuit which can regulate the operating current of error amplifier is proposed by monitoring output voltage variation in order to provide a larger compensation current to the operational amplifier when the load current changes are at high frequency and maintain ultra-low operating current at low clock frequency. The LDO is designed without resistors, and the deep well NMOS is applied in the output stage in order to reduce the difficulty of loop compensation. Designed in a 180 nm CMOS process, the post-simulation results show that under the condition of 40 °C and 3 V input voltage, the static power consumption is 31.7 nA with a settling time (±5%) of less than 35 ns.

The Br + (H2O)3→ HBr + (H2O)2OH reaction has been investigated using the CCSD(T) method with the basis sets as large as cc-pVQZ(-PP). The Br + (H2O)3reaction is also compared with related Br + H2O/(H2O)2and F/Cl + (H2O)3reactions.

In 2019, Diaz-Urrutia and Ott developed a high-yield method for direct conversion of methane to methanesulfonic acid and proposed a cationic chain reaction mechanism. However, Roytman and Singleton questioned this mechanism, and they favored a free-radical mechanism. In the present paper, we studied both the cationic chain and radical mechanisms and found the radical mechanism is more favorable, since it has a much lower energy barrier. However, the radical mechanism has not considered the effect of ions for the reaction taking place in oleum. Thus, we studied a simple model of a protonated radical mechanism, which further lowers the energy barrier. Although the true mechanism for the CH4 + SO3 reaction could be more complicated in electrolyte solutions, this model should be helpful for the further study of the mechanism of this reaction.

A carbene-stabilized dithiolene zwitterion (

Important recent experimental studies have allowed the isomer-selective identification of the 2-, 3-, and 4-picolyl radicals. The picolyl radicals and their valence isoelectronic P, As, Sb, and Bi congeners are investigated here. For the three observed parent radicals, the theoretical ionization potentials agree with experiment to within 0.02 eV. Two rules are proposed for predicting vertical ionization potentials (EVIE) and relative energies. The EVIE values for these radicals will be higher when large percentages of the SOMO orbitals are distributed on the atoms with greater electronegativities. The cations of these systems were also studied along with the closed-shell methylpyridines and their P, As, Sb, and Bi analogs. The energies for the cationic species will lie lower when high percentages of π natural localized molecular orbitals occur on the more electronegative atoms. The structures of the 2- and 4-isomers strongly depend upon the heteroatoms, with the C-C linkages adopting a single-double alternating bond manner when the heteroatoms become heavier. The 3-isomers adopt roughly equal C-C bond distances with small changes from N to Bi.

The geometries and energies of mononuclear and binuclear octafluorocyclohexadiene iron carbonyl derivatives have been studied using density functional theory. The lowest energy C6F8Fe(CO)3 tricarbo...

Four different reaction pathways are initially located for the reaction of Cl atom plus water trimer Cl + (H2O)3 → HCl + (H2O)2OH using a standard DFT method. As found for the analogous fluorine reaction, the geometrical and energetic results for the four chlorine pathways are closely related. However, the energetics for the Cl reaction are very different from those for fluorine. In the present paper, we investigate the lowest-energy chlorine pathway using the “gold standard” CCSD(T) method in conjunction with correlation-consistent basis sets up to cc-pVQZ. Structurally, the stationary points for the water trimer reaction Cl + (H2O)3 may be compared to those for the water monomer reaction Cl + H2O and water dimer reaction Cl + (H2O)2. Based on the CCSD(T) energies, the title reaction is endothermic by 19.3 kcal mol−1, with a classical barrier height of 16.7 kcal mol−1 between the reactants and the exit complex. There is no barrier for the reverse reaction. The Cl⋯(H2O)3 entrance complex lies 5.3 kcal mol−1 below the separated reactants. The HCl⋯(H2O)2OH exit complex is bound by 8.6 kcal mol−1 relative to the separated products. The Cl + (H2O)3 reaction is somewhat similar to the analogous Cl + (H2O)2 reaction, but qualitatively different from the Cl + H2O reaction. It is reasonable to expect that the reactions between the chlorine atom and larger water clusters may be similar to the Cl + (H2O)3 reaction. The potential energy profile for the Cl + (H2O)3 reaction is radically different from that for the valence isoelectronic F + (H2O)3 system, which may be related to the different bond energies between HCl and HF.

While the 1 : 1 reaction of 3 with an N-heterocyclic carbene ({(Me)CN(i-Pr)}2C:) in THF resulted in ligand-substituted product 4, the corresponding 1 : 2 reaction (in the presence of H2O) gives the first structurally characterized germanium tris(dithiolene)dianion 5 as the major product and the "naked" dithiolene radical 6˙ as a minor by-product. The structure and bonding of 4 and 5 were probed by experimental and theoretical methods. Our study suggests that carbene-mediated partial hydrolysis may represent a new method to access tris(dithiolene) complexes of main-group elements.

Reaction of the lithium dithiolene radical 2(•) with the imidazolium salt [{(Me)CN(i-Pr)}(2)CH](+)[Cl](−) (in a 1:1 molar ratio) gives the first stable naked anionic dithiolene radical 3(•), which, when coupled with hexasulfide, [{(Me)CN(i-Pr)}(2)CH](+)(2)[S(6)](2−) (4), and N-heterocyclic silylene 5, unexpectedly results in synergic THF ring-opening via a radical mechanism.

This research reports a search for peculiar monobridged structures of the E2H2 molecules (E = Be, Mg, Ca, Sr, Ba). For Be2H2 and Mg2H2, the monobridged geometry is not an equilibrium but rather a t...

Lithiation of an imidazole-based monothiolate, 2, by excess n-butyllithium gives a white powder containing both a lithiated product and an nBuLi contaminant (in a ca. 1:1 molar ratio). This white p...

A new molecular system for nitrogen reduction, involving a 2,3'-bipyridine-anchored, end-on-bridging dinitrogen complex of the Me2B-BMe2 intermediate (4), has been explored by theoretical methods. The 2,3'-bipyridine-mediated cleavage of the Bsp3-Bsp3 bond in 4 may lead to transient electron-rich sp3-hybridized boron species and subsequent activation of the strong N≡N triple bond of the complexed N2. Through a boryl transfer sequence, a catalytic cycle may be achieved for the reductive addition of diboranes to a dinitrogen molecule with an energy span of 23 kcal/mol. In addition, the reaction is exothermic by 80.5 kcal/mol, providing a substantive chemical driving force.

All important stationary points on the potential energy surface (PES) for the reaction OH + (H2O)3 → (H2O)2OH + H2O have been fully optimized using the “gold standard” CCSD(T) method with the large Dunning correlation-consistent cc-pVQZ basis sets. Three types of pathways were found. For the pathway without hydrogen abstraction, the barrier height of the transition state (TS1) is predicted to lie 5.9 kcal mol−1 below the reactants. The two major complexes (H2O)3⋯OH (CP1 and CP2a) are found to lie 6.3 and 11.0 kcal mol−1, respectively, below the reactants [OH + (H2O)3]. For one of the H-abstraction pathways the lowest classical barrier height is predicted to be much higher, 6.1 kcal mol−1 (TS2a) above the reactants. For the other H-abstraction pathway the barrier height is even higher, 15.0 (TS3) kcal mol−1. Vibrational frequencies and the zero-point vibrational energies connected to the PES are also reported. The energy barriers for the H-abstraction pathways are compared with those for the OH + (H2O)2 and OH + H2O reactions, and the effects of the third water on the energetics are usually minor (0.2 kcal mol−1).

This mechanistic study demonstrates that an unusual η1 -coordinated alkyne complex is critical for the 1-pentyne 1,1-diboration reaction. The comparative studies suggest the "pull-push" antagonistic effect arising from Lewis acidity and steric congestion as the reason for the existence of η1 -coordinated alkyne complexes. Analogous η1 -coordinated alkene complexes are also predicted and seem to be promising for their application to the important olefin polymerization reaction.

Lithium-containing molecules, such as C2H2Li2, C6Li6, and several lithium halides, have been studied in the present paper, and the nature of lithium bonds in these structures is investigated. In co...

Four different reaction pathways are initially located for the reaction of Cl atom plus water trimer Cl + (H

A series of imidazolium-based synthetic routes to imidazolium cyclopentadienides are reported. The 2:1 reaction of imidazolium (1) with [Cp2TiIIICl]2 gives [NHCDippH]+[Cp2TiIIICl2]− (NHCDipp = 2,6-diisopropylphenyl-substituted N-heterocyclic carbene) (2). The “inverse sandwich” imidazolium cyclopentadienide (3) is obtained as a crystalline solid via reaction of 1 with both [Cp2TiIIICl]2 and cyclopentadienyllithium (CpLi) (in a molar ratio of 2:1:1) in THF/toluene at elevated temperature. Notably, the 1:1 reaction of 1 with CpLi leads to the isolation of “multidecker” 4 in the solid state, while the corresponding 1:2 reaction of 1 with CpLi gives the crystals of CpLi-bound cyclopentadienyl-imidazolium complex 5. While compounds 3, 4, and 5 have been structurally characterized using single-crystal X-ray diffraction, in solution these complexes dissociate due to the conversion of [NHCDippH]+[Cp]− to both cyclopentadiene and NHCDipp through intramolecular proton transfer. The equilibrium of the acid–base conv...

The structures and energetics of the binuclear phospholyl chromium carbonyl derivatives (C4H4P)2Cr2(CO)n (n = 6, 5, 4, 3) have been investigated by density functional theory. The lowest energy (C4H4P)2Cr2(CO)n (n = 6, 4, 3) structures are completely analogous to their Cp2Cr2(CO)n analogues with two terminal pentahapto phospholyl rings. However, for the pentacarbonyl (C4H4P)2Cr2(CO)5 the lowest energy structure has a bridging seven-electron donor η5,η1-C4H4P ligand using the phosphorus lone pair in addition to the π-system of the phospholyl ligand as well as a Cr-Cr single bond. Thus, except for the pentacarbonyl the phosphorus lone pair of the phospholyl ligand is seen to play a minor role in the energetically preferred structures of the binuclear phospholyl chromium carbonyl derivatives.

The (C4H4BH)2Co2(CO)n (n = 4, 3, 2, 1) systems have been examined by density functional theory for comparison with the analogous (C4H4BCH3)2Co2(CO)n systems. For the tetracarbonyl (C4H4BH)2Co2(CO)4 a higher energy unbridged structure is found at ∼7 kcal/mol above the lowest energy doubly bridged structure similar to (C4H4BCH3)2Co2(CO)4. The lowest energy structures for the unsaturated derivatives (C4H4BH)2Co2(CO)n (n = 3, 2, 1) have bridging borole ligands with agostic hydrogen atoms from their B–H groups to a cobalt atom. Structures without agostic hydrogens analogous to the low-energy structures for the corresponding methylborole derivatives (C4H4BCH3)2Co2(CO)n are higher energy (C4H4BH)2Co2(CO)n structures.

The mechanism for the reaction of hydrogen selenide (H2Se) with the OH radical is examined using the "gold standard" CCSD(T) method along with the correlation consistent basis sets up to aug-cc-pV5Z. For the Se atom, the corresponding basis sets are combined with the core relativistic pseudopotential, designated as aug-cc-pVnZ-PP (n = D, T, Q, and 5). The predicted geometries and vibrational frequencies for reactants and products agree well with the available experimental results. For the entrance complex, the two-center three-electron hemibonded H2Se···OH structure (RC-B) is predicted to be the lowest. This structure lies 5.1 kcal/mol below the separated reactants H2Se + OH without zero-point energy correction. For the analogous H2S and H2O reactions, the entrance complexes lie 3.3 and 5.7 kcal/mol, respectively, below the reactants. The relative energies of the transition states are -1.7 (H2Se), +0.1 (H2S), and +9.5 (H2O) kcal/mol with respect to the appropriate reactants. The three reaction exoergicities are 40.8 (H2Se), 29.5 (H2S), and 0.0 (H2O) kcal/mol. Compared to the separated products XH + H2O (X = O, S, and Se), the exit well depths are 2.1 (Se), 2.9 (S), and 5.7 (O) kcal/mol. Intrinsic reaction coordinate analysis indicates that all stationary points were correctly identified. Several other stationary points were identified and analyzed. Finally, 29 density functional theory methods were tested systematically to explore their ability in describing the potential energy surface of the H2Se + OH reaction. The hemibonded H2Se···OH entrance complex should be observable, initially via matrix isolation spectroscopy.

Density functional theory studies show that the lowest energy C4F8Fe(CO)4 structure is not the very stable experimentally known ferracyclopentane isomer (CF2CF2CF2CF2)Fe(CO)4 obtained from Fe(CO)12 and tetrafluoroethylene. Instead isomeric (perfluoroolefin)Fe(CO)4 structures derived from perfluoro-2-butene, perfluoro-1-butene, and perfluoro-2-methylpropene are significantly lower energy structures by up to ∼17 kcal mol−1. However, the activation energies for the required fluorine shifts from one carbon to an adjacent carbon atom to form these (perfluoroolefin)Fe(CO)4 complexes from tetrafluoroethylene are very high (e.g., ∼70 kcal mol−1). Therefore the ferracyclopentane isomer (CF2CF2CF2CF2)Fe(CO)4, which does not require a fluorine shift to form from Fe3(CO)12 and tetrafluoroethylene, is the kinetically favored product. The lowest energy structures of the binuclear (C4F8)2Fe2(CO)n (n = 7, 6) derivatives have bridging perfluorocarbene ligands and terminal perfluoroolefin ligands.

The RSSH + H2S → RSH + HSSH reaction has been suggested by numerous labs to be important in H2S-mediated biological processes. Seven different mechanisms for this reaction (R = CH3, as a model) have been studied using the DFT methods (M06-2X and ωB97X-D) with the Dunning aug-cc-pV(T+d)Z basis sets. The reaction of CH3SSH with gas phase H2S has a very high energy barrier (>45 kcal mol−1), consistent with the available experimental observations. A series of substitution reactions R1–S–S–H + −S–R2 (R1 = Me, tBu, Ad, R2 = H, S–Me, S–tBu, S–Ad) have been studied. The regioselectivity is largely affected by the steric bulkiness of R1, but is much less sensitive to R2. Thus, when R1 is Me, all −S–R2 favorably attack the internal S atom, leading to R1–S–S–R2. While for R1 = tBu, Ad, all −S–R2 significantly prefer to attack the external S atom to form −S–S–R2. These results are in good agreement with the experimental observations.

The redox chemistry of the first stable anionic dithiolene radical 1˙ was investigated by both reactivity and cyclic voltammetry studies. While one-electron reduction of 1˙ by Cp2Co or KC8 affords the corresponding dithiolate dimers 2 and 3, respectively, one-electron oxidation of 1˙ by Ph3C+BF4- (or O2) conveniently gives 4, the neutral dithiolene dimer.

The known sandwich compound [η5-(CH2)3N2(BPh)2CMe]2Fe in which adjacent C2 units are replaced by isoelectronic BN units can be considered as a boraza analogues of ferrocene similar to borazine, B3N3H6, considered as a boraza analogue of benzene. In this connection, the related bis(1,2,3,5-tetramethyl-1,2-diaza-3,5-diborolyl) derivatives (Me4B2N2CH)2M (M = Ti, V, Cr, Mn, Fe, Co, Ni) for all of the first row transition metals have been optimized using density functional theory for comparison with the isoelectronic tetramethylcyclopentadienyl derivatives (Me4C5H)2M. Low-energy sandwich structures having parallel B2N2C rings in a trans orientation are found for all seven metals. The 1,2-diaza-3,5-diborolyl ligand appears to be a weaker field ligand than the isoelectronic cyclopentadienyl ligand as indicated by higher spin ground states for some (η5-Me4B2N2CH)2M sandwich compounds relative to the corresponding metallocenes (η5-Me4C5H)2M. Thus (η5-Me4B2N2CH)2Cr has a quintet ground state in contrast to the triplet ground state of (η5-Me4C5H)2Cr. Similarly, the sextet ground state of (η5-Me4B2N2CH)2Mn lies ∼18 kcal mol−1 below the quartet state in contrast to the doublet ground state of the isoelectronic (Me4C5H)2Mn. These sandwich compounds are potentially accessible by reaction of 1,2-diaza-3,5-diborolide anions with metal halides analogous to the synthesis of [η5-(CH2)3N2(BPh)2CMe]2Fe.

Borinium, a two-coordinated boron cation, is a strong Lewis acid that was thought difficult to prepare due to a lower number of coordinating ligands and susceptibility toward nucleophilic reactions. Recently a dimesityl borinium cation (Mes2B+) with high thermal stability has been synthesized and characterized by Shoji and co-workers. These findings suggest that, despite being extremely electron-demanding, borinium cations might be stabilized with certain substituted function groups. In the present study, we have studied a series of the borinium cations [X–B–X]+ with different substituted groups using the NBO and the BLW methods. Our computations revealed that both π-conjugation and hyperconjugation effects can effectively stabilize substituted borinium cations [X–B–X]+. Substituents such as X = C═CH2 stabilize the borinium center through highly delocalized π-bonding, involving the formally “empty” boron px and py orbitals. We suggest the borinium cations [X–B–X]+ with X = cyc-N(CH)2 and especially X = C═...

The structures and energetics of the binuclear phospholyl vanadium carbonyls (C4H4P)2V2(CO)n (n = 7, 6, 5, 4, 3, 2, 1) have been investigated using density functional theory. The lowest energy heptacarbonyl (C4H4P)2V2(CO)7 structures resemble those of the dimanganese pentacarbonyl (C4H4P)2Mn2(CO)5 with one seven-electron donor bridging η5,η1-C4H4P ring and no direct vanadium–vanadium bond. Similarly, the lowest energy hexacarbonyl (C4H4P)2V2(CO)6 structure resembles that of the dimanganese tetracarbonyl (C4H4P)2Mn2(CO)4 with two seven-electron donor bridging η5,η1-C4H4P rings and no direct vanadium–vanadium bond. The lowest energy pentacarbonyl (C4H4P)2V2(CO)5 structure has terminal η5-C4H4P phospholyl rings and a formal V≡V triple bond of length ~ 2.45 A similar to the experimentally known and structurally characterized cyclopentadienyl analogue (η5-C5H5)2V2(CO)5. Various combinations of V=V double bonds or V≡V triple bonds, four-electron donor bridging carbonyl groups and seven-electron donor bridging η5,η1-C4H4P rings are found in the more highly unsaturated derivatives (C4H4P)2V2(CO)n (n = 4, 3, 2) to give 17- and 18-electron vanadium configurations for triplet- and singlet-state structures, respectively. Formal V≣V quadruple bonds are found only in the highly unsaturated lowest energy singlet (C4H4P)2V2(CO)n (n = 2, 1) structures, which, however, lie at somewhat higher energies than isomeric triplet structures.

This research reports a search for peculiar monobridged structures of the E

Taxanes (paclitaxel, docetaxel, cabazitaxel) are anticancer drugs as microtubule inhibitors. Following our previous studies on paclitaxel and docetaxel, in this work, we examine cabazitaxel and compare these three taxenes. The binding interaction of three taxanes with various β-tubulin isotypes is studied by homology modeling, molecular docking, and molecular dynamics simulations. The results show that the effects of docetaxel on βI-tubulin (- 29.5 kcal/mol) and of paclitaxel on βIIa-tubulin (- 25.5 kcal/mol) are much stronger than their effects on βIII-tubulin (- 17.8 kcal/mol and - 8.6 kcal/mol, respectively). However, the effect of cabazitaxel on βIII-tubulin (- 23.0 kcal/mol) is comparable with that on βI-tubulin (- 24.0 kcal/mol) and βIIa-tubulin (- 25.9 kcal/mol), consistent with the fact that overexpression of βIII-tubulin increases the drug resistance to paclitaxel and docetaxel, but has little influence for cabazitaxel. This theoretical research supports the use of cabazitaxel for patients who are resistant to the action of paclitaxel and docetaxel.

There is considerable interest, from both experimental and theoretical perspectives, in molecules incorporating multiple bonds between main group elements. Herein, we not only consider the parent molecules HE=EH (E=As, Sb, Bi), but also a number of their isomers. For each E2 H2 molecule, a number of different structures were optimized with four different DFT methods. Final structures were determined with the coupled cluster method CCSD(T) using large basis sets, namely cc-pVQZ-PP, incorporating relativistic psuedopotentials. All feasible dissociation pathways are examined. For all three E2 H2 molecules the trans isomer lies lowest in energy, with the cis isomer higher by 2.7 (As), 2.1 (Sb), and 1.8 (Bi) kcal mol-1 , respectively. However, both cis and trans structures should be observable, as large barriers (27.7, 20.5, and 17.7 kcal mol-1 ) separate them. For both the cis and trans structures, in the infrared the strong E-H stretching frequencies should also be observable. Only the cis structures have dipole moments (0.62, 0.01, and 0.83 debye, respectively), and their observation by microwave spectroscopy would be stunning. Also considered were the higher energy vinylidene-like, pyramidal, monobridged, and linear structures. We conclude that molecules such as HSb=SbH-Fe(CO)4 , HBi=BiH-Fe(CO)4 , and related systems, should be feasible synthetic targets.

Fluorocarbons have been shown experimentally by Baker and coworkers to combine with the cyclopentadienylcobalt (CpCo) moiety to form fluoroolefin and fluorocarbene complexes as well as fluorinated cobaltacyclic rings. In this connection density functional theory (DFT) studies on the cyclopentadienylcobalt fluorocarbon complexes CpCo(L)(CnF2n) (L = CO, PMe3; n = 3 and 4) indicate structures with perfluoroolefin ligands to be the lowest energy structures followed by perfluorometallacycle structures and finally by structures with perfluorocarbene ligands. Thus, for the CpCo(L)(C3F6) (L = CO, PMe3) complexes, the perfluoropropene structure has the lowest energy, followed by the perfluorocobaltacyclobutane structure and the perfluoroisopropylidene structure less stable by 8 to 11 kcal mol−1, and the highest energy perfluoropropylidene structure less stable by more than 12 kcal mol−1. For the two metal carbene structures Cp(L)CoC(CF3)2 and Cp(L)CoCF(C2F5), the former is more stable than the latter, even though the latter has Fischer carbene character. For the CpCo(L)(C4F8) (L = CO, PMe3) complexes, the perfluoroolefin complex structures have the lowest energies, followed by the perfluorometallacycle structures at 10 to 20 kcal mol−1, and the structures with perfluorocarbene ligands at yet higher energies more than 20 kcal mol−1 above the lowest energy structure. This is consistent with the experimentally observed isomerization of the perfluorinated cobaltacyclobutane complexes CpCo(PPh2Me)(–CFR–CF2–CF2–) (R = F, CF3) to the perfluoroolefin complexes CpCo(PPh2Me)(RCFCF2) in the presence of catalytic quantities of HN(SO2CF3)2. Further refinement of the relative energies by the state-of-the-art DLPNO-CCSD(T) method gives results essentially consistent with the DFT results summarized above.

The structures and energetics of the binuclear cyclobutadiene titanium carbonyl derivatives (C4H4)2Ti2(CO)n (n = 8, 7, 6, 5, 4, 3) have been investigated by density functional theory. The lowest energy (C4H4)2Ti2(CO)8 structure is found to have a central prolate Ti2C4 octahedron with Ti(CO)5 and (η4-C4H4)Ti(CO)3 moieties in polar positions. Similar central Ti2C4 prolate octahedra are found in an only slightly higher energy triplet (C4H4)2Ti2(CO)8 structure as well as in the lowest energy triplet (C4H4)2Ti2(CO)7 structure. An only slightly higher energy (C4H4)2Ti2(CO)8 isomer has a totally different type of structure which can be dissected into the complex (η4-C4H4)Ti(CO)5 with an 18-electron titanium configuration functioning as a Lewis base to a coordinatively unsaturated (η4-C4H4)Ti(CO)3 fragment through an O → Ti bond from one of its carbonyl groups. The low-energy structures of the more highly unsaturated (C4H4)2Ti2(CO)n (n = 6, 5, 4, 3) species have various combinations of four-electron donor bridging η2-µ-CO groups and six-electron donor bridging η4,η1-C4H4 cyclobutadiene ligands with agostic C H Ti interactions bridging a central formal Ti Ti double bond.

Reaction of carbene-stabilized disilicon (1) with the lithium-based dithiolene radical (2. ) affords the first dianionic silicon tris(dithiolene) complex (3). Notably, the formation of 3 represents the unprecedented utilization of carbene-stabilized disilicon (1) as a silicon-transfer agent. The nature of 3 was probed by multinuclear NMR spectroscopy, single-crystal X-ray diffraction, and DFT computations.

Decarbonylation of the experimentally known CpRu(CO)2(η1-C5H5), CpMo(CO)2(η3-C7H7), and CpNb(CO)2(η4-C8H8) (Cp = η5-C5H5), each with uncomplexed 1,3-butadiene units in the CnHn ring, as well as the related CpTc(CO)2(η2-C6H6), to give the corresponding carbonyl-free derivatives CpM(ηn-CnHn) derivatives has been studied by density functional theory. For ruthenium, technetium, and molybdenum the coordinated CnHn ring of the intermediate monocarbonyl CpM(CO)(ηn–2-CnHn) contains an uncomplexed C═C double bond and each decarbonylation step proceeds with a significant energy barrier represented by a higher energy transition state. However, decarbonylation of CpNb(CO)2(η4-C8H8) to the monocarbonyl proceeds without an energy barrier, preserving the tetrahapto coordination of the C8H8 ring to give CpNb(CO)(η4-C8H8) in which the niobium atom has only a 16-electron configuration. All of the monocarbonyl derivatives CpM(CO)(CnHn) are predicted to be strongly energetically disfavored with respect to disproportionation ...

A substituted divinylborinium cation was synthesized recently and characterized crystallographically as a gauche structure with a 153° C1-C2-C3-C4 dihedral angle. A full theoretical geometrical optimization of the bis(2-mesityl-1,2-diphenylvinyl)-borane cation shows excellent agreement with the crystal structure. However, for the parent unsubstituted divinylborinium cation, we predict a nearly 90° C1-C2-C3-C4 dihedral angle using the CCSD(T)/cc-pVTZ coupled cluster method. The cis and trans planar geometries (0° and 180° for the C1-C2-C3-C4 dihedral angle) proved to be transition states with energy barriers of 2.8 and 2.3 kcal/mol, respectively, with respect to unimolecular conversion to the gauche equilibrium. The structures of the heavier boron group cations (Al, Ga, In, and Tl) have also been investigated here, finding even lower energy barriers (0.3-0.7 kcal/mol). After the ZPVE corrections, the barriers are further decreased. The torsional angles for the unknown Al, Ga, In, and Tl dimesityl substituted compounds should be somewhat less than 153°. Many of these findings may be understood in terms of qualitative electronic structure theory. The torsional folding of borane complex, including cationic divinylborinium and elementary vinylborane (C

The structures and energetics of the cyclopentadienyliron carbonyl boronyls Cp2Fe2(BO)2(CO)n (n = 3, 2, 1, 0) have been examined by density functional theory. The lowest energy Cp2Fe2(BO)2(CO)n (n = 2, 0) structures are found to have bridging dioxodiborene (µ-B2O2) ligands that can exist as cis or trans stereoisomers. Either µ-B2O2 stereoisomer functions as a net three-electron donor to each iron atom in such binuclear complexes. The lowest energy Cp2Fe2(BO)2(CO)n (n = 3, 1) structures resemble their isoelectronic Cp2Mn2(CO)n+2 analogues. Thus the lowest energy Cp2Fe2(BO)2(CO)3 structure consists of two CpFe(BO)(CO) units joined by an Fe–Fe bond bridged by a CO group. The lowest energy Cp2Fe2(BO)2(CO) structure is a singlet triply bridged structure with a short ∼2.17 A Fe Fe distance suggesting a formal triple bond. This latter structure is very similar to the experimental structure of the isoelectronic Cp*2Mn2(µ-CO)3, synthesized by Hermann and coworkers and shown by X-ray crystallography to be a triply bridged structure with a ∼2.17 A Mn Mn distance.

The lowest energy structures for the unsaturated Mn2(BO)2(CO)n (n = 8, 7) are very different from those of the isoelectronic Cr2(CO)n+2 owing to the greater basicity of the oxygen atoms in BO groups relative to CO groups. Thus the lowest energy Mn2(BO)2(CO)n (n = 8, 7) structures have two bridging three-electron donor η2 µ BO groups bonded to the manganese atoms through both their boron and oxygen atoms. The long Mn⋯Mn distances in these structures indicate the lack of metal–metal bonding. These Mn2(BO)2(CO)n (n = 8, 7) structures thus differ from their Cr2(CO)n+2 analogues, which have normal two-electron donor CO groups and Cr Cr bonds. The only example of manganese-manganese multiple bonding in the Mn2(BO)2(CO)n systems occurs in a high-energy triply bridged Mn2(BO)2(CO)7 structure with a short ∼2.3 A Mn Mn distance suggesting a formal triple bond. This structure is completely analogous to the lowest energy Cr2(CO)9 structure.

Theoretical methods show that the lowest energy bis(butadiene)metal structures (C4H6)2M (M = Ti to Ni) have a perpendicular relative orientation of the two butadiene ligands corresponding to a tetrahedral coordination of the central metal atom to the four CC double bonds of the butadiene ligands. Distribution of the metal d electrons in the resulting tetrahedral ligand field rationalizes the predicted spin states increasing monotonically from singlet to quartet from nickel to manganese and back from quartet to singlet from manganese to titanium.