Neutral Adducts Research Articles

Neutral Adducts of Molybdenum Hexafluoride: Structure and Bonding in MoF6(NC5H5) and MoF6(NC5H5)2.

The first Lewis acid base adducts of MoF6 and an organic base have been synthesized, i. e., MoF6(NC5H5) and MoF6(NC5H5)2. These adducts are structurally characterized with X-ray crystallography, showing that both adducts adopt capped trigonal prismatic structures. The MoF6(NC5H5) and MoF6(NC5H5)2 adducts are fluxional on the NMR time scale at room temperature. Two different fluorine environments could be resolved by 19F NMR spectroscopy at -80 °C for the 1 : 2 adduct, MoF6(NC5H5)2, whereas MoF6(NC5H5) remains fluxional at that temperature. Density functional theory (DFT) calculations aide the assignment of the infrared and Raman spectra. Natural Bond Order and Molecular Electrostatic Potential analyses elucidate the structures and properties of the MoF6 pyridine adducts. Regions of significantly higher molecular electrostatic potential, i. e., σ-holes, in trigonal prismatic compared to octahedral MoF6 rationalize the capped trigonal prismatic geometry of the adducts. Whereas MoF6(NC5H5) is stable at room temperature under exclusion of moisture, MoF6(NC5H5)2 decomposes at 60 °C in pyridine solvent, and the solid slowly decomposes at room temperature after 24 h.

Characterization of Electrospray Ionization Complexity in Untargeted Metabolomic Studies.

The annotation of metabolites detected in LC-MS-based untargeted metabolomics studies routinely applies accurate m/z of the intact metabolite (MS1) as well as chromatographic retention time and MS/MS data. Electrospray ionization and transfer of ions through the mass spectrometer can result in the generation of multiple "features" derived from the same metabolite with different m/z values but the same retention time. The complexity of the different charged and neutral adducts, in-source fragments, and charge states has not been previously and deeply characterized. In this paper, we report the first large-scale characterization using publicly available data sets derived from different research groups, instrument manufacturers, LC assays, sample types, and ion modes. 271 m/z differences relating to different metabolite feature pairs were reported, and 209 were annotated. The results show a wide range of different features being observed with only a core 32 m/z differences reported in >50% of the data sets investigated. There were no patterns reporting specific m/z differences that were observed in relation to ion mode, instrument manufacturer, LC assay type, and mammalian sample type, although some m/z differences were related to study group (mammal, microbe, plant) and mobile phase composition. The results provide the metabolomics community with recommendations of adducts, in-source fragments, and charge states to apply in metabolite annotation workflows.

Introducing Weakly Ligated Tris(trifluoromethyl)copper(III)

AbstractTris(trifluoromethyl)copper(III), Cu(CF3)3, was prepared for the first time and fully characterized in the form of weakly coordinated highly reactive solvent neutral adducts (DMF)2Cu(CF3)3 and (MeCN)Cu(CF3)3. Free Cu(CF3)3 is an elusive molecule of distorted T‐shaped geometry with Lewis acid properties, which is stabilized by solvation. Substitution of solvent molecules with monoanionic ligands in mild conditions afforded the first Cu(III)(CF3)3 carboxylates [Cu(CF3)3(OAc)]− and [Cu(CF3)3(OBz)]− and Cu(III) nitrito complex [Cu(CF3)3(ONO)]−. An improved synthesis of valuable Grushin's trifluoromethylation reagents via the intermediacy of (MeCN)Cu(CF3)3 was developed. (DMF)2Cu(CF3)3 demonstrated promising properties in photoinduced radical C‐H trifluoromethylation. Oxidation state theoretical studies showed the Cu(CF3)3 compounds to be borderline between classical Cu(III) and inverted ligand field Cu(I) assignment.

N-Iodophthalimide as a halogen bond donor, a comparison with N-iodosuccinimide and N-iodosaccharin

The halogen bond (HaB) donor ability of N-iodophthalimide (NIPht) is evaluated in its crystal structure, in its neutral adducts with different pyridines, and in its anionic symmetric complex with the phthalimidate anion.

Low coordinate Zn(II) organocations bearing extremely bulky NHC ligands: structural features, air-/water-tolerance and use in hydrosilylation and hydrogenation catalysis.

This work details the synthesis and characterization of low-coordinate Zn(II)-based organocations [(NHC)Zn(R)]+ incorporating extremely bulky NHCs [ITr] and [IAd] ([ITr] = ([ITr] = [(HCNCPh3)2C:]; [IAd] = [(HCNAd)2C:], Ad = adamantyl)). Their structural features and particularities are thoroughly assessed as well as their air and water tolerance. Neutral ITr and IAd adducts [(ITr)Zn(R)2] (1, R = Me; 2, R = Et) and [(IAd)Zn(R)2] (3, R = Me; 4, R = Et) were synthesized by reaction of carbene [ITr] or [IAd] with a stoichiometric amount of [ZnR2] and isolated in good yields. Despite the steric bulk of [ITr] and [IAd], neutral compounds 1-4 are robust and the solid state structure of adduct 3 was established through X-ray crystallographic studies as a trigonal monomer Zn(II) species. Adducts 1-4 may readily be ionized by [Ph3C][B(C6F5)4] to afford two-coordinate Zn(II) alkyl cations [(ITr)Zn(Me)]+ ([5]+) and [(ITr)Zn(Et)]+ ([6]+), [(IAd)Zn(Me)]+ ([7]+) and [(IAd)Zn(Me)]+ ([8]+), all isolated in high yields (>80%) as [B(C6F5)4]- salts, which were fully characterized. Remarkably, cation [(ITr)Zn(C6F5)]+ ([9]+), prepared by reaction of [5][B(C6F5)4] with [B(C6F5)3], features π-arene interactions with the electrophilic Zn(II), as deduced from solid state data and further completed by DFT-estimated non-covalent interactions (NCI), indicating that [ITr] may provide substantial steric and electrostatic stabilization. The latter certainly explains the remarkable stability of [(ITr)Zn(C6F5)]+ ([9]+) towards hydrolysis at RT, as it only coordinates H2O to afford an unprecedented stable Zn-OH2 organocation [10]+. Also noteworthy, H2O coordination is reversible allowing recovery of [(ITr)Zn(C6F5)]+ cation, even after prolonged air exposure. Yet, controlled hydrolysis of [(ITr)Zn(C6F5)]+ may occur upon heating with selective protonolysis of the Zn-C6F5 bond to afford structurally characterized dication [(ITr)Zn(OH)]22+ [11]2+. Interestingly, despite steric hindrance, the air-/water-tolerant cation [(ITr)Zn(C6F5)]+ is an effective CO2 hydrosilylation catalyst, and was also shown to mediate imine hydrogenation catalysis.

Enthalpy of Formation of the Nitrogen-Rich Salt Guanidinium 5,5′-Azotetrazolate (GZT) and a Simple Approach for Estimating the Enthalpy of Formation of Energetic C, H, N, O Salts

The discrepancy between the calculated (CBS-4M/Jenkins) and experimentally determined enthalpies of formation recently reported for the 2:1 salt TKX-50 raised the important question of whether the enthalpies of formation of other 2:1 C, H, N, O salts calculated using the CBS-4M/Jenkins method are reliable values. The standard (p° = 0.1 MPa) enthalpy of formation of crystalline guanidinium 5,5′-azotetrazolate (GZT) (453.6 ± 3.2 kJ/mol) was determined experimentally using static-bomb combustion calorimetry and was found to be in good agreement with the literature’s values. However, using the CBS-4M/Jenkins method, the calculated enthalpy of formation of GZT was again in poor agreement with the experimentally determined value. The method we used recently to calculate the enthalpy of formation of TKX-50, based on the calculation of the heat of formation of the salt and of the corresponding neutral adduct, was then applied to GZT and provided excellent agreement with the experimentally determined value. Finally, in order to validate the findings, this method was also applied to predict the enthalpy of formation of a range of 1:1 and 2:1 salts (M+X− and (M+)2X2− salts, respectively), and the values obtained were comparable to experimentally determined values. The agreement using this approach was generally very good for both 1:1 and 2:1 salts; therefore, this approach provides a simple and reliable method which can be applied to calculate the enthalpy of formation of energetic C, H, N, O salts with much greater accuracy than the current, commonly used method.

Halogen-Bonding-Mediated Radical Reactions: The Unexpected Behavior of Piperazine-Based Dithiooxamide Ligands in the Presence of Diiodine.

N,N'-Dialkylpiperazine-2,3-dithiones (R2pipdt) were recognized as a class of hexa-atomic cyclic dithiooxamide ligands with peculiar charge-transfer donor properties toward soft electron-acceptors such as noble metal cations and diiodine. The latter interaction is nowadays better described as halogen bonding. In the reaction with diiodine, R2pipdt unexpectedly provides the corresponding triiodide salts, differently from the other dithiooxamides, which instead typically achieve ligand·nI2 halogen-bonded adducts. In this paper, we report a combined experimental and theoretical study that allows elucidation of the nature of the cited products and the reasons behind the unpredictable behavior of these ligands. Specifically, low-temperature single-crystal X-ray diffraction measurements on a series of synthetically obtained R2pipdt (R = Me, iPr, Bz)/I3 salts, complemented by neutron diffraction experiments, were able to experimentally highlight the formation of [R2pipdtH]+ cations with a -S-H bond on the dithionic moiety. Differently, with R = Ph, a benzothiazolylium cation, resulting from an intramolecular condensation reaction of the ligand, is obtained. Based on density functional theory (DFT) calculations, a reasonable reaction mechanism where diiodine plays the fundamental role of promoting a halogen-bonding-mediated radical reaction has been proposed. In addition, the comparison of combined experimental and computational results with the corresponding reactions of N,N'-dialkylperhydrodiazepine-2,3-dithione (R2dazdt, a hepta-atomic cyclic dithiooxamide), which provide neutral halogen-bonded adducts, pointed out that the difference in the torsion angle of the free ligands represents the structural key factor in determining the different reactivities of the two systems.

Ionization of Cp2 ZrMe2 and Lewis Bases by Methylaluminoxane: Computational Insights.

The interactions of the Lewis bases CO, octamethyltrisiloxane (OMTS) and 2,2'-bipyridine (bipy) with a sheet model for the principal activator (MeAlO)16 (Me3 Al)6 (16,6) in hydrolytic methylaluminoxane (MAO) were investigated by DFT. These studies reveal that OMTS and bipy form adducts with Me3 Al prior to methide abstraction by 16,6 to form the ion-pairs [Me2 Al(κ2 -L)][16,6] (5: L=OMTS, 6: L=bipy, [16,6]- =[(MeAlO)16 (Me3 Al)6 Me]- ) while CO simply binds to a reactive edge site without ionization. The binding and activation of Cp2 ZrMe2 with 16,6 to form both neutral adducts 1 Cp2 ZrMe2 ⋅16,6 and contact ion-pairs 4 and 7, both with formula [Cp2 ZrMe][μ-Me(MeAlO)16 (Me3 Al)6 ], featuring terminal and chelated MAO-anions, respectively was studied by DFT. The displacement of the anion with either excess Cp2 ZrMe2 or Me3 Al was also studied, forming outer-sphere ion-pairs [(Cp2 ZrMe)2 μ-Me][16,6] (2) and [Cp2 Zr(μ-Me)2 AlMe2 ][16,6] (3). The theoretical NMR spectra of these species were compared to experimental spectra of MAO and Cp2 ZrMe2 and found to be in good agreement with the reported data and assignments. These studies confirm that 16,6 is a very suitable model for the activators present in MAO but highlight the difficulty in accurately calculating thermodynamic quantities for molecules in this size regime.

Fluoro-Germanium (IV) Cations with Neutral Co-Ligands—Synthesis, Properties and Comparison with Neutral GeF4 Adducts

The reaction of [GeF4L2], L = dmso (Me2SO), dmf (Me2NCHO), py (pyridine), pyNO (pyridine-N-oxide), OPPh3, OPMe3, with Me3SiO3SCF3 (TMSOTf) and monodentate ligands, L, in a 1:1:1 molar ratio in anhydrous CH2Cl2 formed the monocations [GeF3L3][OTf]. These rare trifluoro-germanium (IV) cations were characterised by microanalysis, IR, 1H, 19F{1H} and, where appropriate, 31P{1H} NMR spectroscopy. The 19F{1H} NMR data show that in CH3NO2 solution the complexes exist as a mixture of mer and fac isomers, with the mer isomer invariably having the higher abundance. The X-ray structure of mer-[GeF3(OPPh3)3][OTf] is also reported. The attempts to remove a second fluoride using a further equivalent of TMSOTf and L were mostly unsuccessful, although a mixture of [GeF2(OAsPh3)4][OTf]2 and [GeF3(OAsPh3)3][OTf] was obtained using excess TMSOTf and OAsPh3. The reaction of [GeF4(MeCN)2] with TMSOTf in CH2Cl2 solution, followed by the addition of 2,2′:6′,2”-terpyridine (terpy) formed mer-[GeF3(terpy)][OTf], whilst a similar reaction with 1,4,7-trimethyl-1,4,7-triazacyclononane (Me3-tacn) in MeCN solution produced fac-[GeF3(Me3-tacn)][OTf]. Dicationic complexes bearing the GeF22+ fragment were isolated using the tetra-aza macrocycles, 1,4,7,10-tetramethyl-1,4,7,10-tetra-azacyclododecane (Me4-cyclen) and 1,4,8,11-tetramethyl-1,4,8,11-tetra-azacyclotetradecane (Me4-cyclam), which reacted with [GeF4(MeCN)2] and two equivalents of TMSOTf to cleanly form the dicationic difluoride salts, cis-[GeF2(Me4-cyclen)][OTf]2 and trans-[GeF2(Me4-cyclam)][OTf]2. The 19F{1H} NMR spectroscopy shows that in CH3NO2 solution there are four stereoisomers present for trans-[GeF2(Me4-cyclam)][OTf]2, whereas the smaller ring-size of Me4-cyclen accounts for the formation of only cis-[GeF2(Me4-cyclen)][OTf], and is confirmed crystallographically. New spectroscopic data are also reported for [GeF4(L)2] (L = dmso, dmf and pyNO). Density functional theory calculations were used to probe the effect on the bonding as fluoride ligands were sequentially removed from the germanium centre in the OPMe3 complexes.

Cooperative redox and spin activity from three redox congeners of sulfur-bridged iron nitrosyl and nickel dithiolene complexes

The synthesis of sulfur-bridged Fe-Ni heterobimetallics was inspired by Nature's strategies to "trick" abundant first row transition metals into enabling 2-electron processes: redox-active ligands (including pendant iron-sulfur clusters) and proximal metals. Our design to have redox-active ligands on each metal, NO on iron and dithiolene on nickel, resulted in the observation of unexpectedly intricate physical properties. The metallodithiolate, (NO)Fe(N2S2), reacts with a labile ligand derivative of [NiII(S2C2Ph2)]0, NiDT, yielding the expected S-bridged neutral adduct, FeNi, containing a doublet {Fe(NO)}7. Good reversibility of two redox events of FeNi led to isolation of reduced and oxidized congeners. Characterization by various spectroscopies and single-crystal X-ray diffraction concluded that reduction of the FeNi parent yielded [FeNi]-, a rare example of a high-spin {Fe(NO)}8, described as linear FeII(NO-). Mössbauer data is diagnostic for the redox change at the {Fe(NO)}7/8 site. Oxidation of FeNi generated the 2[FeNi]+⇌[Fe2Ni2]2+ equilibrium in solution; crystallization yields only the [Fe2Ni2]2+ dimer, isolated as PF6- and BArF- salts. The monomer is a spin-coupled diradical between {Fe(NO)}7 and NiDT+, while dimerization couples the two NiDT+ via a Ni2S2 rhomb. Magnetic susceptibility studies on the dimer found a singlet ground state with a thermally accessible triplet excited state responsible for the magnetism at 300 K (χMT = 0.67 emu·K·mol-1, µeff = 2.31 µB), and detectable by parallel-mode EPR spectroscopy at 20 to 50 K. A theoretical model built on an H4 chain explains this unexpected low energy triplet state arising from a combination of anti- and ferromagnetic coupling of a four-radical molecular conglomerate.

Adsorption and catalytic study of cyclopentyl methyl ether formation: structure-activity interplay in medium-pore zeolites

Symmetrical and asymmetrical ethers produced from renewable feedstock play a key role in numerous green chemistry technologies. The aim of our contribution is to understand how textural properties and the location of active sites affect the mechanism of cross-etherification of cyclopentanol with methanol, which yields the asymmetric product cyclopentyl methyl ether. For this purpose, commercial MFI, nanosponge MFI, and nanolayered MFI zeolites with similar concentrations of acid sites, as well as medium-pore TUN and IMF zeolites with internal voids, slightly larger than those of MFI, were investigated by combining catalytic tests with infrared adsorption studies. Detailed FTIR analysis revealed three adsorption adducts, whose fractions varied with the alcohol loading and with the type of zeolite: i) a neutral single H-bonded adduct, ii) a bulky ionic H-bonded adduct, and iii) a neutral cyclopentoxy group. MFI zeolite is the most efficient catalyst in cyclopentanol cross-etherification, reaching 70% cyclopentyl methyl ether yield. Both hierarchical (48%-42%) and medium-pore (48%-58%) zeolites exhibited significantly reduced cyclopentyl methyl ether yields due to their larger internal voids and high number of strong Lewis acid sites, which presumably catalyze the undesired reaction of cyclopentanol dehydration to cyclopentene.

Synthesis and characterization of a tertiary amine:boric acid (1:1) co-crystal and a neutral zwitterionic diamine pentaboron adduct

The syntheses of the 4,4′-trimethylenebis(N-methylpiperidine):boric acid (1:1) co-crystal, 4,4′-(1-MeNC5H9)2(CH2)3.B(OH)3 (1), and a zwitterionic tetrahydroxidohexaoxidopentaboron adduct, [B5O6(OH)4(κN-NH2CH2CH2NHEt2).H2O (2), (NH2CH2CH2NEt2 = deen) from appropriate combinatorial libraries primed with B(OH)3, are reported together with their spectroscopic (NMR, IR) and single-crystal XRD characterization data. Solid-state H-bond interactions are the likely strong drivers for their formation, and these are described in detail. H-bond networks present in co-crystal 1 include C22(16), R22(8), and R66(36) whilst zwitterionic pentaboron derivative 2 has three R22(8) intermolecular H-bond interactions and the Et2NH- group is involved in a S(7) intramolecular H-bond. Thermal (TGA/DSC) data are also reported for 1 which thermally decomposes to B2O3, in a multistage process: dehydration (60–70 °C) and oxidation and further dehydration (90–700 °C).

A Combined Experimental and Theoretical Investigation of Arene-Supported Actinide and Ytterbium Tetraphenolate Complexes.

Modular tetraphenolate ligands tethered with a protective arene platform (para-phenyl or para-terphenyl) are used to support mononuclear An(IV) (An = Th, U) complexes with an exceptionally large and open axial coordination site at the metal. The base-free complexes and a series of neutral donor adducts were synthesized and characterized by spectroscopies and single-crystal X-ray diffraction. Anionic Th(IV) -ate complexes with an additional axial aryloxide ligand were also synthesized and characterized. The para-phenyl-tethered mononuclear complexes exhibit rare An(IV)-arene interactions, and the An(IV)-arene distance broadly increases with axial donor strength. The para-terphenyl-tethered complexes have almost no interaction with the arene base, isolating the central metal cation. Computational analysis of the mononuclear complexes and their reduced analogues, and Yb(III) congeners, as well as the effect of additional donor ligand binding, seek to elucidate the electronic structure of the metal-arene interactions and establish whether they, or their reduced or oxidized counterparts, could function as molecular qubits.

Azidoborolate anions and azidoborole adducts: isolable forms of an unstable borole azide.

Boroles are well known to undergo ring expansion reactions with organic azides to yield 1,2-azaborinines. A synthon featuring both azide and borole moieties within the same molecule, 1-azido-2,3,4,5-tetraphenylborole, was found to be much less stable than the related, previously-reported azidoborafluorene and decomposed to intractable mixtures well below room temperature. It could, however, be trapped at -75 °C through the formation of Lewis base adducts, even in the form of the "azide-stabilized azidoborole" complex anion diazidoborolate. DFT calculations provide a rationale for the low stability of the azidoborole under study.

Rh Complexes with Pincer Carbene CNC Lutidine-Based Ligands: Reactivity Studies toward H2Addition

Lutidine-based NHCs pincer precursors CNCMe and CNCMes were combined with [Rh(acac)(nbd)] (acac = acetylacetonate; nbd = 2,5-norbornadiene) in the presence of Cs2CO3 to yield complexes [(CNC)MeRh(nbd)]PF6 (3) and [(CNC)MesRh(NCMe)]PF6 (4), respectively. While in 3, the nbd diolefin remains coordinated, in 4, the voluminous mesityl ligands induce nbd decoordination, so acetonitrile stabilizes Rh(I) adduct 4, which in turn undergoes substitution reactions with a number of neutral ligands to produce cationic complexes [(CNC)MesRh(L)]PF6 (L = CO (5), PMe2Ph (6), PEt3 (7), C2H4 (8)). These complexes have been studied through VT NMR measurements and the molecular structures by X-ray crystallography in the case of adducts 4–7. Deprotonation reactions on cationic complexes 3–6 with hard bases yielded the corresponding neutral complexes [(CNC)*MeRh(nbd)] (9) and mesityl derivatives [(CNC)*MesRh(L)] (L = NCCH3 (10), CO (11), PMe2Ph (12)), all of which are dearomatized complexes due to the deprotonation of one of the methylene arms, a situation confirmed by the X-ray molecular structure of carbonyl adduct 5. We studied the reactivity toward dihydrogen with neutral adducts 11 and 12. The electron rich phosphane 12 adds H2 through oxidative addition, affording the bis(hydrido) Rh(III) complex [(CNC)*MesRh(PMe2Ph)H2] (14). However, the carbonyl adduct 11 reacts with H2 in a different way, so that the central pyridinic ring becomes hydrogenated, breaking the aromaticity and leading to complex [(CNC-H2)*MesRh(CO)] (13), isolated as a mixture of two isomers. DFT studies were carried out in order to establish the mechanisms followed on these hydrogenations, finding that, while the phosphane adduct reacts following an oxidative addition mechanism, the carbonyl complex follows a more complex base-induced profile due to the instability of hydride carbonyl species.

On the Origin of E-Selectivity in the Ring-Opening Metathesis Polymerization with Molybdenum Imido Alkylidene N-Heterocyclic Carbene Complexes.

The understanding and control of stereoselectivity is a central aspect in ring-opening metathesis polymerization (ROMP). Herein, we report detailed quantum chemical studies on the reaction mechanism of E-selective ROMP of norborn-2-ene (NBE) with Mo(N-2,6-Me2-C6H3)(CHCMe3)(IMes)(OTf)2 (1, IMes = 1,3-dimesitylimidazol-2-ylidene) as a first step to stereoselective polymerization. Four different reaction pathways based on an enesyn or eneanti approach of NBE to either the syn- or anti-isomer of the neutral precatalyst have been studied. In contrast to the recently established associative mechanism with a terminal alkene, where a neutral olefin adduct is formed, NBE reacts directly with the catalyst via [2 + 2] cycloaddition to form molybdacyclobutane with a reaction barrier about 30 kJ mol–1 lower in free energy than via the formation of a catalyst–monomer adduct. However, the direct cycloaddition of NBE was only found for one out of four stereoisomers. Our findings strongly suggest that this stereoselective approach is responsible for E-selectivity and point toward a substrate-specific reaction mechanism in olefin metathesis with neutral Mo imido alkylidene N-heterocyclic carbene bistriflate complexes.

Synthesis, Characterization, and Density Functional Theory Studies of Three-Dimensional Inorganic Analogues of 9,10-Diboraanthracene-A New Class of Lewis Superacids.

The three-dimensional inorganic analogues of 9,10-diboraanthracene, B2X2(C2B10H10)2 (X = Cl, 1; X = Br, 2), were attained by salt elimination of Li2C2B10H10 and trihaloboranes. The methyl- and phenyl-substituted compounds B2Me2(C2B10H10)2 (3) and B2Ph2(C2B10H10)2 (4) were obtained by treating 1 or 2 with the corresponding Grignard reagents. These compounds were fully characterized by NMR, cyclic voltammetry (CV), IR, and single-crystal X-ray diffraction analyses. Experimental (CV and Gutmann-Beckett method) and computational (fluoride ion affinity, hydride ion affinity and LUMO energy) results suggest that the order of Lewis acidity is 2 > 1 > 4 > 3 > SbF5. Treatment of 1 or 2 with HSiEt3 gave a rare neutral borane-silane adduct, (Et3SiH)2B2H2(C2B10H10)2 (5). The equilibrium of 5 in solution was thoroughly investigated by spectroscopy and quantum calculations.

NHCs as Neutral Donors towards Polyphosphorus Complexes.

The first adducts of NHCs (=N‐heterocyclic carbenes) with aromatic polyphosphorus complexes are reported. The reactions of [Cp*Fe(η5‐P5)] (1) (Cp*=pentamethyl‐cyclopentadienyl) with IMe (=1,3,4,5‐tetramethylimidazolin‐2‐ylidene), IMes (=1,3‐bis(2,4,6‐trimethylphenyl)‐imidazolin‐2‐ylidene) and IDipp (=1,3‐bis(2,6‐diisopropylphenyl)‐imidazolin‐2‐ylidene) led to the corresponding neutral adducts which can be isolated in the solid state. However, in solution, they quickly undergo a dissociative equilibrium between the adduct and 1 including the corresponding NHC. The equilibrium is influenced by the bulkiness of the NHC. [Cp′′Ta(CO)2(η4‐P4)] (Cp′′=1,3‐di‐tert‐butylcyclopentadienyl) reacts with IMe under P atom abstraction to give an unprecedented cyclo‐P3‐containing anionic tantalum complex. DFT calculations shed light onto the energetics of the reaction pathways.

Quadruple bonding of bare group-13 atoms in transition metal complexes.

Density functional theory calculations at the M06-D3/def2-TZVPPD level of the group-13 anion complexes EFe(CO)3- (E = B-Tl) and the isoelectronic neutral and charged boron adducts BTM(CO)3q (TMq = Fe-, Ru-, Os-, Co, Rh, Ir, Ni+, Pd+, Pt+) give tetrahedral (C3v) geometries in the 1A1 electronic ground state as equilibrium structures. The analysis of the bonding situation with the energy decomposition analysis in combination with natural orbital for chemical valence method suggests that the E-TM(CO)3q bonds possess four bonding components: (a) one strong electron-sharing σ bond E-TM(CO)3q; (b) two π backdonations E⇇TM(CO)3q and (c) one weak σ donation E→TM(CO)3q. The relative strength of the four bonding components depends on the charge of the system, the transition metal TM and the group-13 atom E. The σ donation E→TM(CO)3q is in all systems rather weak while the associated charge migration is not negligible. A similar situation of the bonding of terminal group-13 atoms Ga and In is found in Ga-TM(GaCp)4+ and E-Pt(PMe3)3+ (TM = Ni, Pd, Pt; E = Ga, In), which are model compounds for the stable complexes GaTM(GaCp*)4+ (TM = Ni, Pt) and InPt(PPh3)3+. The quadruple bonds E→TML2 are hybrids of electron-sharing and dative bonds.

Intermolecular Non-Covalent Carbon-Bonding Interactions with Methyl Groups: A CSD, PDB and DFT Study.

A systematic evaluation of the CSD and the PDB in conjunction with DFT calculations reveal that non-covalent Carbon-bonding interactions with X–CH3 can be weakly directional in the solid state (P ≤ 1.5) when X = N or O. This is comparable to very weak CH hydrogen bonding interactions and is in line with the weak interaction energies calculated (≤ –1.5 kcal·mol−1) of typical charge neutral adducts such as [Me3N-CH3···OH2] (2a). The interaction energy is enhanced to ≤–5 kcal·mol−1 when X is more electron withdrawing such as in [O2N-CH3··O=Cdme] (20b) and to ≤18 kcal·mol−1 in cationic species like [Me3O+-CH3···OH2]+ (8a).