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The 1 : 2 reaction of the imidazole‐based dithiolate (2) with GeCl2 • dioxane in THF/TMEDA gives 3, a TMEDA‐complexed dithiolene‐based germylene. Compound 3 is converted to monothiolate‐complexed (5) and N‐heterocyclic carbene‐complexed (7) germanium(II) dithiolene complexes via Lewis base ligand exchange. A bis‐dithiolene‐based germylene (8), involving a 3c–4e S‐Ge‐S bond, has also been synthesized through controlled hydrolysis of 7. The bonding nature of 3, 5, and 8 was investigated by both experimental and theoretical methods. [ABSTRACT FROM AUTHOR]

Synthesis and applications of fluoroalkyl and fluoroalkenyliodonium salts are summarized in this account article, focusing preferably to the reagents designed in our laboratory in the last decade. Among these reagents trifluoroethyl(aryl)iodonium salts have been used most frequently to build carbon‐carbon and carbon‐heteroatom bonds in simple nucleophilic substitutions and through transition metal catalyzed coupling reactions. Iodonium salts equipped with unsaturated fluorinated function showed diverse reactivity due to their electron deficient character, and these molecular motifs enable cycloadditions and nucleophilic additions to prepare fluorinated carbo‐ and heterocyclic molecules. Beyond the overview of existing transformations, with the presented collection, we aim to inspire future developments of iodonium reagents and their application in organic synthesis. [ABSTRACT FROM AUTHOR]

This paper investigates four of the constitutional isomers of Si2H2+, namely the butterfly, vinylidene‐like, monobridged, and trans structures. These isomer geometries were all studied using the CCSD(T) method with basis sets as large as cc‐pV5Z. Higher level methods CCSDT and CCSDT(Q) were used for final energetics. It is found that the butterfly isomer has the lowest energy, followed by vinylidene‐like and monobridged structures; the trans structure has the highest energy of the four. All structures were compared with their neutral counterparts. Partial charges are computed and it is found that all isomers share the positive charge between the silicon atoms. NBO analysis shows that the cation Si−Si bond order is reduced by 0.5 relative to the neutral versions of the same isomer in the case of the butterfly, vinylidene‐like, and monobridged; and reduced by 0.6 for the trans isomer. Vibrational frequencies, infrared intensities, and dipole moments are predicted to encourage the spectroscopic identification of Si2H2+. [ABSTRACT FROM AUTHOR]

Many binuclear nickel complexes have NiNi distances suggesting NiNi covalent bonds, including lantern‐type complexes with bridging bidentate ligands. This DFT study treats tetragonal, trigonal, and digonal lantern‐type complexes with the formamidinate, guanidinate, and formate ligands, besides some others. Formal bond orders (ranging from zero to two) are assigned to all the NiNi bonds on the basis of MO occupancy considerations. A VB‐based electron counting approach assigns plausible resonance structures to the dinickel cores. Model tetragonal complexes with the dimethylformamidinate and the dithioformate ligands have singlet ground states whose non‐covalently bonded NiNi distances are close to those in their experimentally known counterparts. Trigonal dinickel complexes are unknown, but are predicted to have quartet ground states with NiNi bonds of order 0.5. The model digonal complexes are predicted to have triplet ground states, but the predicted NiNi bond lengths are longer than those found in their experimentally known counterparts. This could owe to inadequate treatment of electron correlation by DFT in these short NiNi bonds with their multiconfigurational character. All the NiNi bond distances here are categorized into ranges according to the NiNi bond orders of 0, 0.5, 1, 1.5, and 2, no NiNi bonds of order higher than two being identified. The NiNi bonds of given order in these lantern‐type complexes are consistently shorter than the corresponding NiNi bonds in dinickel complexes having carbonyl ligands, attributable to the metalmetal bond lengthening effect of CO ligands. [ABSTRACT FROM AUTHOR]

Binuclear alkyne manganese carbonyls of the type (RC≡CR')Mn2(CO)n (R and R'=methyl or dimethylamino; n=8, 7, 6) and their isomers related to the experimentally known (MeC2NEt2)Mn2(CO)n (n=8, 7) structures have been investigated by density functional theory. The alkyne ligand remains intact in the only low energy (Me2N)2C2Mn2(CO)8 isomer, which has a central Mn2C2 tetrahedrane unit and is otherwise analogous to the well‐known (alkyne)Co2(CO)6 derivatives except for one more CO group per metal atom. The low‐energy structures of the unsaturated (Me2N)2C2Mn2(CO)n (n=7, 6) systems include isomers in which the nitrogen atom of one of the dimethylamino groups as well as the C≡C triple bond of the alkyne is coordinated to the central Mn2 unit. In other low‐energy (Me2N)2C2Mn2(CO)n (n=7, 6) isomers the alkyne C≡C triple bond has broken completely to form two separate bridging dimethylaminocarbyne Me2NC ligands analogous to the experimentally known iron carbonyl complex (Et2NC)2Fe2(CO)6. The (alkyne)Mn2(CO)n (n=8, 7, 6) systems of the alkynes MeC≡CMe and Me2NC≡CMe with methyl substituents have significantly more complicated potential surfaces. In these systems the lowest energy isomers have bridging ligands derived from the alkyne in which one or two hydrogen atoms have migrated from a methyl group to one or both of the alkyne carbon atoms. These bridging ligands include allene, manganallyl, and vinylcarbene ligands, the first two of which have been realized experimentally in research by Adams and coworkers. Theoretical studies suggest that the mechanism for the conversion of the simple alkyne octacarbonyl (MeC2NMe2)Mn2(CO)8 to the dimethylaminomanganaallyl complex Mn2(CO)7[μ‐η4‐C3H3Me2] involves decarbonylation to the heptacarbonyl and the hexacarbonyl complexes. Subsequent hydrogen migrations then occur through intermediates with C−H−Mn agostic interactions to give the final product. Eight transition states for this mechanistic sequence have been identified with activation energies of ∼20 kcal/mol for the first hydrogen migration and ∼14 kcal/mol for the second hydrogen migration. [ABSTRACT FROM AUTHOR]

Aluminyl anions are low‐valent, anionic, and carbenoid aluminum species commonly found stabilized with potassium cations from the reaction of Al‐halogen precursors and alkali compounds. These systems are very reactive toward the activation of σ‐bonds and in reactions with electrophiles. Various research groups have detected that the potassium atoms play a stabilization role via electrostatic and cation⋯π interactions with nearby (aromatic)‐carbocyclic rings from both the ligand and from the reaction with unsaturated substrates. Since stabilizing K⋯H bonds are witnessed in the activation of this class of molecules, we aim to unveil the role of these metals in the activation of the smaller and less polarizable H2 molecule, together with a comprehensive characterization of the reaction mechanism. In this work, the activation of H2 utilizing a NON‐xanthene‐Al dimer, [K{Al(NON)}]2 (D) and monomeric, [Al(NON)]− (M) complexes are studied using density functional theory and high‐level coupled‐cluster theory to reveal the potential role of K+ atoms during the activation of this gas. Furthermore, we aim to reveal whether D is more reactive than M (or vice versa), or if complicity between the two monomer units exits within the D complex toward the activation of H2. The results suggest that activation energies using the dimeric and monomeric complexes were found to be very close (around 33 kcal mol−1). However, a partition of activation energies unveiled that the nature of the energy barriers for the monomeric and dimeric complexes are inherently different. The former is dominated by a more substantial distortion of the reactants (and increased interaction energies between them). Interestingly, during the oxidative addition, the distortion of the Al complex is minimal, while H2 distorts the most, usually over 0.77 ΔEdist≠. Overall, it is found here that electrostatic and induction energies between the complexes and H2 are the main stabilizing components up to the respective transition states. The results suggest that the K+ atoms act as stabilizers of the dimeric structure, and their cooperative role on the reaction mechanism may be negligible, acting as mere spectators in the activation of H2. Cooperation between the two monomers in D is lacking, and therefore the subsequent activation of H2 is wholly disengaged. [ABSTRACT FROM AUTHOR]

Pnictinidenes are an increasingly relevant species in main group chemistry and generally exhibit proclivity for the triplet electronic ground state. However, the elusive singlet electronic states are often desired for chemical applications. We predict the singlet‐triplet energy differences (ΔEST=ESinglet−ETriplet) of simple group 15 and 16 substituted pnictinidenes (Pn−R; Pn=P, As, Sb, or Bi) with highly reliable focal‐point analyses targeting the CCSDTQ/CBS level of theory. The only cases we predict to have favorable singlet states are P−PH2 (−3.2 kcal mol−1) and P−NH2 (−0.2 kcal mol−1). ΔEST trends are discussed in light of the geometric predictions as well as qualitative natural bond order analysis to elucidate some of the important electronic structure features. Our work provides a rigorous benchmark for the ΔEST of fundamental Pn−R moieties and provides a firm foundation for the continued study of heavier pnictinidenes. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Keywords: Aromatische elektrophile Substitutionen; Dichtefunktionalrechnungen; Nitrierungen; Reaktionsmechanismen EN Aromatische elektrophile Substitutionen Dichtefunktionalrechnungen Nitrierungen Reaktionsmechanismen 8062 8062 1 05/13/20 20200518 NES 200518 In dieser Zuschrift stellten die Autoren eine theoretische Studie zum Mechanismus der Benzolnitrierung mit einer Säuremischung vor. Namentlich wurde die UV-Absorption bei 320 nm (in den fast sofort nach dem Mischen der Reaktanten aufgenommene Spektren; Abbildung 3 der Originalzuschrift) fälschlich einem frühen Reaktionskomplex zugeordnet. Die Autoren danken Professor Svetlana Simova, Institute of Organic Chemistry with Centre of Phytochemistry, Bulgarian Academy of Sciences, für die Aufnahme und Analyse der NMR-Spektren. [Extracted from the article]

Oxiranes are a class of cyclic ethers formed in abundance during low‐temperature combustion of hydrocarbons and biofuels, either via chain‐propagating steps that occur from unimolecular decomposition of β‐hydroperoxyalkyl radicals (β‐̇QOOH) or from reactions of HȮO with alkenes. The cis‐ and trans‐isomers of 2,3‐dimethyloxirane are intermediates of n‐butane oxidation, and while rate coefficients for β‐̇QOOH → 2,3‐dimethyloxirane + ̇OH are reported extensively, subsequent reaction mechanisms of the cyclic ethers are not. As a result, chemical kinetics mechanisms commonly adopt simplified chemistry to describe the consumption of 2,3‐dimethyloxirane by convoluting several elementary reactions into a single step, which may introduce mechanism truncation error—uncertainty derived from missing or incomplete chemistry. The present research examines the isomer dependence of 2,3‐dimethyloxirane reaction mechanisms in support of ongoing efforts to minimize mechanism truncation error. Reaction mechanisms are inferred via the detection of products from Cl‐initiated oxidation of both cis‐2,3‐dimethyloxirane and trans‐2,3‐dimethyloxirane using multiplexed photoionization mass spectrometry (MPIMS). The experiments were conducted at 10 Torr and temperatures of 650 K and 800 K. To complement the experiments, the enthalpies of stationary points on the ̇R + O2 surfaces were computed at the ccCA‐PS3 level of theory. In total, 28 barrier heights were computed on the 2,3‐dimethyloxiranylperoxy surfaces. Two notable aspects are low‐lying pathways that form resonance‐stabilized ketohydroperoxide‐type radicals caused by ̇QOOH ring‐opening when the unpaired electron is localized adjacent to the ether group, and cis‐trans isomerization of ̇R and ̇QOOH radicals, via inversion, which enable reaction pathways otherwise restricted by stereochemistry. Several species were identified in the MPIMS experiments from ring opening of 2,3‐dimethyloxiranyl radicals. Neither of the two conjugate alkene isomers prototypical of ̇R + O2 reactions were detected. Products were also identified from decomposition of ketohydroperoxide‐type radicals. The present work provides the first analysis of 2,3‐dimethyloxirane oxidation chemistry and reveals that consumption pathways are complex and require the expansion of submechanisms in chemical kinetics mechanisms. [ABSTRACT FROM AUTHOR]

Oxiranes are a class of cyclic ethers formed in abundance during low‐temperature combustion of hydrocarbons and biofuels, either via chain‐propagating steps that occur from unimolecular decomposition of β‐hydroperoxyalkyl radicals (β‐̇QOOH) or from reactions of HOȮ with alkenes. Ethyloxirane is one of four alkyl‐substituted cyclic ether isomers produced as an intermediate from n‐butane oxidation. While rate coefficients for β‐̇QOOH → ethyloxirane + ȮH are reported extensively, subsequent reaction mechanisms of the cyclic ether are not. As a result, chemical kinetics mechanisms commonly adopt simplified chemistry to describe ethyloxirane consumption by convoluting several elementary reactions into a single step, which may introduce mechanism truncation error—uncertainty derived from missing or incomplete chemistry. The present work provides fundamental insight on reaction mechanisms of ethyloxirane in support of ongoing efforts to minimize mechanism truncation error. Reaction mechanisms are inferred from the detection of products during chlorine atom‐initiated oxidation experiments using multiplexed photoionization mass spectrometry conducted at 10 Torr and temperatures of 650 K and 800 K. To complement the experiments, calculations of stationary point energies were conducted using the ccCA‐PS3 composite method on ̇R + O2 potential energy surfaces for the four ethyloxiranyl radical isomers, which produced barrier heights for 24 reaction pathways. In addition to products from ̇QOOH → cyclic ether + ȮH and ̇R + O2 → conjugate alkene + HOȮ, both of which were significant pathways and are prototypical to alkane oxidation, other species were identified from ring‐opening of both ethyloxiranyl and ̇QOOH radicals. The latter occurs when the unpaired electron is localized on the ether group, causing the initial ̇QOOH structure to ring‐open and form a resonance‐stabilized ketohydroperoxide‐type radical. The present work provides the first analysis of ethyloxirane oxidation chemistry, which reveals that consumption pathways are complex and may require an expansion of submechanisms to increase the fidelity of chemical kinetics mechanisms. [ABSTRACT FROM AUTHOR]

The first‐row transition metal 1‐norbornyl derivatives CpM(nor) Cp = η5‐C5H5; nor = 1‐norbornyl; M = Ti to Cu), including the experimentally known CpNi(nor) reported by Lehmkuhl and Dimitrov, have been examined by density functional theory and benchmarked by the more accurate DLPNO‐CCSD(T) method. The lowest energy CpM(nor) structures for the later first row transition metals from manganese to copper are found to be high‐spin state structures in which the 1‐norbornyl ligand is bonded to the metal only through the M–C σ‐bond to the bridgehead carbon atom. The favored spin states range from doublet for CpCu(nor) to sextet for CpMn(nor). The pattern of favorable structure types changes for the CpM(nor) derivatives of the earlier first row transition metals to the left of manganese since all of their low energy structures have singly or doubly agostic 1‐norbornyl groups. The agostic C–H–M interactions in the CpM(nor) derivatives are characterized by their reduced density gradients and low ν(C–H) frequencies. [ABSTRACT FROM AUTHOR]

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 E2H2 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 E2H2 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. [ABSTRACT FROM AUTHOR]

The structures and energetics of the bis(butadiene) complexes of the second row transition metals (C4H6)2M) M=Zr to Pd) have been investigated by density functional theory. The energetically accessible (C4H6)2M structures (M=Zr to Rh) are found to have only tetrahapto η4‐C4H6 ligands. The second row transition metals energetically prefer low spin states in their bis(butadiene) derivatives (C4H6)2M reflecting their increased ligand field strength relative to the first row transition metals. Thus the energies of the singlet and doublet spin states for (C4H6)2Ru and (C4H6)2Tc, respectively, are lower than their triplet and quartet spin state isomers in contrast to the corresponding iron and manganese systems, respectively. Furthermore, the staggered maximum spin (C4H6)2M structures with χ ≈ 90° having tetrahedral coordination of the central metal to the four C=C double bonds of the two butadiene ligands found as lowest energy structures for the first row transition metals are not found for the second row transition metals from Mo to Pd. Instead the lowest energy (C4H6)2M structures for the second row transition metals have an eclipsed confirmation with χ ≈ 0° implying square planar coordination of the central metal. The lowest energy structure of the palladium complex (C4H6)2Pd is anomalous since only one of the two butadienes is a tetrahapto ligand whereas the second butadiene is only a dihapto ligand leaving one uncomplexed C=C double bond. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Ionized water clusters, H2On+, have been of remarkable interest owing to their crucial roles in many chemical and biological processes. Small cationic water clusters H2On+, n = 2 to 6 serve as reasonable models for understanding the nature of the ionized water. In this study, employing high‐level ab initio quantum chemical methods, such as the density‐fitted orbital‐optimized linearized coupled‐cluster doubles (DF‐OLCCD), coupled‐cluster singles and doubles (CCSD), and coupled‐cluster singles and doubles with perturbative triples [CCSD(T)], a high‐accuracy study of structures and energetics for cationic water clusters [H2On+, n = 2‐6] is presented. In this study, 2 dimer, 8 trimer, 18 tetramer, 23 pentamer, and 25 hexamer clusters are reported. Most of the structures considered are reported for the first time. Relative, binding, and vertical attachment energies (VAEs), for the first time, are presented at the complete basis set (CBS) limit, extrapolating energies of the aug‐cc‐pVTZ and aug‐cc‐pVQZ basis sets, to provide the most accurate energetics to date. Our results demonstrate that as cluster size increases, the VAE value decreases, which indicates that large‐size clusters better compensate for the electron deficiency compared with small‐size clusters. The VAE values for pentamer and hexamer clusters are 118.5 to 165.5 and 121.9 to 153.7 kcal mol−1, respectively. Further, our binding energy results, at the CCSD(T)/CBS level, indicate strong bindings in cationic clusters due to hydrogen bond interactions. The average binding energy per water molecule varies from −16.6 to −21.8 kcal mol−1 for the clusters considered. Hence, we present the most extensive and accurate study on ionized water clusters to date. Further, our results indicate that the DF‐OLCCD method is very promising for ionic molecular clusters, and its accuracy approaches the CCSD(T) quality. The inexpensive analytic gradients of DF‐OLCCD, compared with CCSD(T), make it very helpful for high‐accuracy studies of molecular geometries. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Abstract: The potential energy surfaces for the SN2 reactions of allyl and propyl chlorides with 21 anionic and neutral nucleophiles was studied by using ωB97X‐D/6‐311++G(3df,2pd) computations. The “allylic effect” on SN2 barriers was observed for all reactions, and compared with propyl substrates, the energy barriers differed by −0.2 to −4.5 kcal mol−1 in the gas phase. Strong correlations of the SN2 net activation barriers with cation affinities, proton affinities, and electrostatic potentials at nuclei demonstrated the powerful influence of electrostatic interactions on these reactions. For the reactions of anionic (but not neutral) nucleophiles with allyl chloride, some of the incoming negative charge (0.2–18 %) migrated into the carbon chains, which would provide secondary stabilization of the SN2 transition states. Activation strain analysis provided additional insight into the allylic effect by showing that the energy of geometric distortion for the reactants to reach the SN2 transition state was smaller for each allylic reaction than for its propyl analogue. In many cases, the interaction energies between the substrate and nucleophile in this analysis were more favorable for propyl chloride reactions, but this compensation did not overcome the predominant strain energy effect. [ABSTRACT FROM AUTHOR]

Abstract: Whereas low‐temperature (−78 °C) reaction of the lithium dithiolene radical 1. with boron bromide gives the dibromoboron dithiolene radical 2., the parallel reaction of 1. with (C6H11)2BCl (0 °C) affords the dicyclohexylboron dithiolene radical 3.. Radicals 2. and 3. were characterized by single‐crystal X‐ray diffraction, UV/Vis, and EPR spectroscopy. The nature of these radicals was also probed computationally. Under mild conditions, 3. undergoes unexpected thiourea‐mediated B−C bond activation to give zwitterion 4, which may be regarded as an anionic dithiolene‐modified carbene complex of the sulfenyl cation RS+ (R=cyclohexyl). [ABSTRACT FROM AUTHOR]

The conformational structures and properties of the anticancer drug docetaxel (DTX) are studied theoretically. A total of 3888 trial structures were initially generated by all combinations of internal single‐bond rotamers and screened with the B3LYP/3‐21G* method. A total of 31 unique conformers were further optimized at the B3LYP/6‐311G* method. Their relative energies, dipole moments, rotational constants, and harmonic vibrational frequencies were predicted. Single‐point relative energies were then determined at the M06‐L/6‐311G(2df,p) level. The UV spectrum of the lowest‐lying DTX conformer in methanol was investigated with the TD‐CAM‐B3LYP/6‐311 + G(2df,p) method. The 31 unique DTX structures are mainly docked at three different sites within β‐tubulin. Based on the results of molecular docking and double‐float MD simulations, the lowest‐lying DTX conformer consistently exhibits good docking performance with β‐tubulin. We identified the residues LYS299, ARG215, GLN294, LEU275, THR216, GLU290, PRO274, and THR276 on β‐tubulin as active sites forming a binding pocket responsible for locking DTX within β‐tubulin to make the combination more stable. The RMSD values show that the predicted complexes are favorable, and the SASA analysis shows that the hydrophilic properties of DTX are better than paclitaxel. © 2018 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Density functional theory computations with the B3LYP/6‐311++G(2df,2p) method and IR spectroscopy are employed in investigating the properties of twenty π‐hydrogen bonded complexes between substituted phenols and hexamethylbenzene. All complexes possess T‐shaped structures. The methyl hyperconjugative effects on interactions energies and OH stretching frequencies are estimated via comparisons with previously reported theoretical and experimental results for analogous phenol complexes with benzene. The theoretical computations provide excellent quantitative predictions of the OH stretching frequency shifts (ΔνOH) resulting from the hydrogen bonding. The ΔνOH shifts in the hexamethylbenzene complexes are approximately twice as large as the corresponding shifts for the benzene complexes. Hirshfeld charges, electrostatic potential at nuclei values, and molecular electrostatic potential maps are employed in gaining insights into the mechanisms of methyl hyperconjugative effects on complex formation. © 2017 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Perfluorination of one η5-C5H5 ring in the MC10H10 system (M = Ni, Pd, Pt) to give an MC10H5F5 system greatly destabilizes structures containing a perfluorinated pentahapto η5-C5F5 ring. As a result, the metallapentafluorobenzene structures (η5-C5H5)(MC5F5) are the lowest-energy structures for all three metals, with energy differences of 1.4, 6.2, and 16.2 kcal/mol for nickel, palladium, and platinum, respectively. In addition, palladium and platinum isomeric metallatetrafluorocyclopentadiene structures, with a complexed fluorobenzene ring; that is, (C6H5F)(MC4F4) (M = Pd, Pt), are lower-energy structures than the lowest-energy metallocene structures. Furthermore, for palladium and platinum, the lowest-energy metallocene structures are slipped metallocenes with a trihapto, rather than a pentahapto, pentafluorocyclopentadienyl ring. These theoretical results suggest the pentafluorocyclopentadienyl anion as a reagent for synthesizing metallapentafluorobenzene derivatives by reactions with (η5-C5R5)M(CO)X, (η5-C5R5)2M2(µ-CO)2, or (η5-C5R5)2Ni (R = H, Me; M = Ni, Pt). [ABSTRACT FROM AUTHOR]

Density functional theory has been used to examine the dimetallocene-like dicycloheptatrienyl dimetal compounds of the second-row transition metals (C7H7)2M2 (M5Ru, Tc, Mo, Nb, Zr). The lowest energy (C7H7)2Mo2 structure is a coaxial structure with terminal η7-C7H7 rings, whereas the lowest energy (C7H7)2M2 structures (M5Ru, Tc, Nb, Zr) are perpendicular structures with bridging η4,η4-7H7 rings except for the perpendicular (η4,η3-C7H7)2Ru2 structure. The metal- metal bond orders in the (C7H7)2M2 structures (M5Ru, Tc, Mo, Nb), as determined by analysis of their frontier molecular orbitals, suggest preferred 16- rather than 18-electron configurations for the central metal atoms. Thus, in the coaxial (57-C7H7)2M2 structures the formal bond orders are two for M = Tc and three for M = Mo. For the perpendicular structures both (η4,η3-C7H7)2Ru2 and (η4,η4-C7H7)2Tc2 have 16-electron configurations with metal-metal single bonds owing to the different modes of bonding of the bridging C7H7 rings in the two structures. For the (C7H7)2Zr2 system the perpendicular structure has a formal Zr=Zr double bond and the coaxial structure has a very long (~3.5 Å) Zr-Zr bond indicating only 12- to 14-electron configurations for the zirconium atoms. [ABSTRACT FROM AUTHOR]

The 2014 synthesis of the remarkable dimagnesium compound Mg2[C4(CH3)2(Si(CH3)3)2](C3H7)2(C4H8O)2 may point the way to a new chapter in alkaline earth organometallic chemistry. Accordingly, we have studied the known Mg compound and the analogous Be, Ca, Sr, and Ba structures. Although most of our theoretical predictions come from density functional methods, the latter have been benchmarked using coupled cluster theory including single, double, and perturbative triplet excitations, CCSD(T) using cc-pVTZ basis sets. Among our most important predictions are the energies for dissociation to the butadiene plus the RM−MR [R=(C3H7)2(C4H8O)2; M=Be, Mg, Ca, Si, and Ba] entities. The most reliable predictions for the dissociation energies are 99-104 (Be), 85-93 (Mg), 90-99 (Ca), 83-92 (Sr), and 83-94 (Ba) kcal mol−1. Thus, there is reason to anticipate that the four unknown compounds should be achievable synthetically. The predicted metal-metal distances (not single bonds) are 2.89 Å (Mg⋅⋅⋅Mg), 3.46 Å (Ca⋅⋅⋅Ca), 3.75 Å (Sr⋅⋅⋅Sr), and 4.04 Å (Ba⋅⋅⋅Ba). The separated RM−MR compounds have longer M−M distances but genuine metal-metal single bonds. This perhaps counter intuitive result is due to the presence of the bridging carbons in the alkaline earth butadiene compounds. All five compounds incorporate metal-carbon ionic interactions. [ABSTRACT FROM AUTHOR]

Enantiomers of chiral molecules commonly exhibit differing pharmacokinetics and toxicities, which can introduce significant uncertainty when evaluating biological and environmental fates and potential risks to humans and the environment. However, (the irreversible transformation of one enantiomer into the racemic mixture) and enantiomerization (the reversible conversion of one enantiomer into the other) are poorly understood. To better understand these processes, we investigated the chiral fungicide, triadimefon, which undergoes in soils, water, and organic solvents. (NMR) and / (GC/MS) techniques were used to measure the rates of enantiomerization and , deuterium isotope effects, and activation energies for triadimefon in H2O and D2O. From these results we were able to determine that: 1) the alpha-carbonyl carbon of triadimefon is the reaction site; 2) cleavage of the C-H (C-D) bond is the rate-determining step; 3) the reaction is base-catalyzed; and 4) the reaction likely involves a symmetrical . The B3LYP/6-311 + G** level of theory was used to compute optimized geometries, harmonic vibrational frequencies, nature population analysis, and intrinsic reaction coordinates for triadimefon in water and three pathways were hypothesized. This work provides an initial step in developing predictive, structure-based models that are needed to identify compounds of concern that may undergo . Chirality 28:633-641, 2016. © 2016 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

The entrance complex, transition state, and exit complex for the bromine atom plus water dimer reaction Br + (H2O)2 → HBr + (H2O)OH and its reverse reaction have been investigated using the CCSD(T) method with correlation consistent basis sets up to cc-pVQZ-PP. Based on the CCSD(T)/cc-pVQZ-PP results, the reaction is endothermic by 31.7 kcal/mol. The entrance complex Br⋯(H2O)2 is found to lie 6.5 kcal/mol below the separated reactants. The classical barrier lies 28.3 kcal/mol above the reactants. The exit complex HBr⋯(H2O)OH is bound by 6.0 kcal/mol relative to the separated products. Compared with the corresponding water monomer reaction Br + H2O → HBr + OH, the second water molecule lowers the relative energies of the entrance complex, transition state, and exit complex by 3.0, 3.8, and 3.7 kcal/mol, respectively. Both zero-point vibrational energies and spin-orbit coupling effects make significant changes to the above classical energetics. Including both effects, the predicted energies relation to separated Br + (H2O)2 are −3.0 kcal/mol [Br···(H2O)2], 28.2 kcal/mol [transition state], 26.4 kcal/mol [HBr···(H2O)OH], and 30.5 kcal/mol [separated HBr + (H2O)OH]. The potential energy surface for the Br + (H2O)2 reaction is related to that for the valence isoelectronic Cl + (H2O)2 system but radically different from the F + (H2O)2 system. © 2015 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

The opposed and parallel structures for the binuclear bis(azulene) 'submarine' sandwiches (C10H8)2M2 (M = Ti, V, Cr, Mn, Fe, Co, Ni) have been optimized using density functional theory. The lowest energy (C10H8)2M2 structures of the early transition metals Ti, V, Cr, and Mn have the azulene units functioning as bis(pentahapto) ligands to each metal atom similar to the azulene ligand in the long-known molybdenum carbonyl complex (η5,η5-C10H8)Mo2(CO)6. The metal-metal bonds in these early transition metal structures have distances and Wiberg bond indices consistent with the formal bond orders required to give each metal atom an 18-electron configuration for the singlet structures and a 17-electron configuration for the triplet structures. For the later transition metals Fe, Co, and Ni, the lowest energy (C10H8)2M2 structures contain pentahapto-trihapto azulene ligands with an uncomplexed CC double bond, similar to that in the long-known iron carbonyl complex (η5,η3-C10H8)Fe2(CO)5. The parallel (η5,η3-C10H8)2M2 (M = Fe, Co, Ni) structures contain metallocene subunits with their metal atoms at long nonbonding distances of 3.5-3.9 Å from the other metal atom, which is located between the azulene C7 rings. Higher energy opposed (C10H8)2Fe2 structures contain an unprecedented distorted η6,η4-azulene ligand using six carbon atoms for bonding to one iron atom as a hexahapto fulvene ligand and the remaining four carbon atoms for bonding to the other iron atom as a tetrahapto diene ligand. © 2015 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Molecular mechanics (MM4) studies have been carried out on the catenane (C13H26)2, specifically 13-13D2. The structure obtained is in general agreement with second-order perturbation theory. More importantly, the MM4 structure allows a breakdown of the energy of the molecule into its component classical parts. This allows an understanding of why the structure is so distorted, in terms of CC bonding and nonbonding interactions, van der Waals repulsion, CCC and CCH angle bending, torsional energies, stretch-bend, torsion-stretch, and bend-torsion-bend interactions. Clearly, the hole in 113-membered ring is too small for the other ring to fit through comfortably. There are too many atoms trying to fit into the limited space at the same time, leading to large van der Waals repulsions. The rings distort in such a way as to enlarge this available space, and lower the total energy of the molecule. While the distortions are spread around the rings, one of the nominally tetrahedral CCC bond angles in each ring is opened to 147.9° by MM4 (146.8° by MP2). The stability of the compound is discussed in terms of the strain energy. © 2015 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Self-assembling building blocks like the 4-pyridone can exhibit extraordinary H-bond-aromaticity coupling effects. Computed dissected nucleus independent chemical shifts (NICS(1) zz), natural bond orbital (NBO) charges, and energy decomposition analyses (EDA) for a series of hydrogen (H-) bonded 4-pyridone chains (4-py)n (n = 2 to 8) reveal that H-bonding interactions can polarize the 4-pyridone exocyclic C=O bonds and increase 4n+2 π-electron delocalization in the six-membered ring. The resulting H-bonded 4-pyridone units display enhanced π-aromatic character (both magnetically and energetically) and their corresponding NH···OC interactions are strengthened. These π-electron polarization effects do not depend on the relative orientations (co-planar or perpendicular) of the neighboring 4-pyridone units, but increase with the number of H-bonded units. © 2015 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Experimental evidence is reported for the first intermediate in the classic SEAr reaction of benzene nitration with mixed acid. The UV/Vis spectroscopic investigation of the reaction showed an intense absorption at 320 nm (appearing as a band shoulder) arising from a reaction intermediate. Our theoretical modeling shows that the interaction between the two principal reactants with solvent (H2SO4) molecules significantly affects the structure of the initial complex. In this complex, a larger distance between the aromatic ring and nitronium ion precludes the possibility for electronic charge transfer from the benzene π-system to the electrophile. The computational modeling of the potential energy surface reveals that the reaction favors a stepwise mechanism with intermediate formation of π- and σ- (arenium ion) complexes. [ABSTRACT FROM AUTHOR]

The potential energy profile for the F+(H2O)3→HF+(H2O)2OH reaction has been investigated using the 'gold standard' CCSD(T) method with correlation-consistent basis sets up to cc-pVQZ. Four different reaction pathways have been found and these are related, both geometrically and energetically. The entrance complexes F⋅⋅⋅(H2O)3 for all four reaction pathways are found lying ca. 7 kcal mol−1 below the separated reactants F+(H2O)3. The four reaction barriers on their respective reaction coordinates lie ca. 4 kcal mol−1 below the reactants. There are also corresponding exit complexes HF⋅⋅⋅(H2O)2OH, lying about 13 kcal mol−1 below the separated products HF+(H2O)2OH. Compared with analogous F+(H2O)2 and F+H2O reactions, the F+(H2O)3 reaction is somewhat similar to the former but qualitatively different from the latter. It may be reasonable to predict that the reactions between atomic fluorine and water tetramer (or even larger water clusters) may be similar to the F+(H2O)3 reaction. [ABSTRACT FROM AUTHOR]

Reaction of carbene-stabilized disilicon ( 1) with Fe(CO)5 gives the 1:1 adduct L:SiSi[Fe(CO)4]:L (L:=C{N(2,6-Pr i2C6H3)CH}2) ( 2) at room temperature. At raised temperature, however, 2 may react with another equivalent of Fe(CO)5 to give L:Si[μ-Fe2(CO)6](μ-CO)Si:L ( 3) through insertion of both CO and Fe2(CO)6 into the Si2 core, which represents the first experimental realization of transition metal-carbonyl-mediated cleavage of a SiSi double bond. The structures and bonding of both 2 and 3 have been investigated by spectroscopic, crystallographic, and computational methods. [ABSTRACT FROM AUTHOR]