Preparation of a Compound with a SiII -SiIV -SiII Bonding Arrangement.

Herein, we report the synthesis of a rare bis-silylene, 1, in which two SiII atoms are bridged by a SiIV atom. Compound 1 contains an unusual SiII -SiIV -SiII bonding arrangement with SiII -SiIV bond distances of 2.4212(8) and 2.4157(7) Å. Treatment of 1 with Fe(CO)5 afforded a dinuclear Fe0 complex 2 with two unusually long Si-Si bonds (2.4515(8) and 2.4488(10) Å). We have also carried out a detailed computational study to understand the nature of the Si-Si bonds in these compounds. Natural bond orbital (NBO) and energy decomposition analysis-natural orbital for chemical valence (EDA-NOCV) analyses reveal that the Si-Si bonds in 1 and 2 are of an electron-sharing nature.

Stability and bonding of carbon(0)-iron-N2 complexes relevant to nitrogenase co-factor: EDA-NOCV analyses.

The factors/structural features which are responsible for the binding, activation and reduction of N2 to NH3 by FeMoco of nitrogenase have not been completely understood well. Several relevant model complexes by Holland et al. and Peters et al. have been synthesized, characterized and studied by theoretical calculations. For a matter of fact, those complexes are much different than real active N2 -binding Fe-sites of FeMoco, which possesses a central C(4-) ion having an eight valence electrons as an µ6 -bridge. Here, a series of [(S3 C(0))Fe(II/I/0)-N2 ]n- complexes in different charged/spin states containing a coordinated σ- and π-donor C(0)-atom which possesses eight outer shell electrons [carbone, (Ph3 P)2 C(0); Ph3 P→C(0)←PPh3 ] and three S-donor sites (i.e. - S-Ar), have been studied by DFT, QTAIM, and EDA-NOCV calculations. The effect of the weak field ligand on Fe-centres and the subsequent N2 -binding has been studied by EDA-NOCV analysis. The role of the oxidation state of Fe and N2 -binding in different charged and spin states of the complex have been investigated by EDA-NOCV analyses. The intrinsic interaction energies of the Fe-N2 bond are in the range from -42/-35 to -67 kcal/mol in their corresponding ground states. The S3 C(0) donor set is argued here to be closer to the actual coordination environment of one of the six Fe-centres of nitrogenase. In comparison, the captivating model complexes reported by Holland et al. and Peter et al. possess a stronger π-acceptor C-ring (S2 Cring donor, π-C donor) and stronger donor set like CP3 (σ-C donor) ligands, respectively.

Uncovering the hidden reactivity of benzyne/aryne precursors utilized under milder condition: Bonding and stability studies by EDA-NOCV analyses.

Arenes [C6 H3 R(TMS)(OTf); also called benzyne/aryne precursors] containing inter-related leaving groups Me3 Si (TMS) and CF3 SO3 (OTf) on the adjacent positions (1,2-position) are generally converted to their corresponding aryne-intermediates via the addition of fluoride anion (F- ) and subsequent elimination of TMS and OTf groups. This reaction is believed to proceed via the formation of an anionic intermediate [C6 H4 (TMS-F)(OTf)]- . The EDA-NOCV analysis (EDA-NOCV = energy decomposition analysis-natural orbital for chemical valence) of over 35 such precursors of varied types have been reported to reveal bonding and stability of CAr Si and COTf bonds. EDA-NOCV showed that the nature of the CAr Si bond of C6 H3 R(TMS)(OTf) can be expressed as both dative and electron sharing [CAr Si, CAr →Si]. The CAr OTf bond, on the other hand, can be described explicitly as dative [CAr ←OTf]. The nature of CAr Si bond of [C6 H4 (TMS-F)(OTf)]- exclusively changes to covalent dative σ-bond CAr →S(Me)3F on the attachment of F- to the TMS group of C6 H4 (TMS)(OTf). Introduction of σ-electron withdrawing group (like OMe, NMe2 , and NO2 ) to the ortho-position of the TMS group of functionalized arynes C6 H3 R(TMS)(OTf) prefer to have a covalent dative σ-bond (CAr →Si) over an electron-sharing covalent σ-bond (CAr Si). If this σ-electron withdrawing group is shifted from ortho-position to meta- and para-positions, then the preference for a dative bond decreases significantly, implying that the electronic effect on the nature of chemical bonds affects through bond paths. This effect dies with distance, similar to the well-known inductive effect.

EDA-NOCV analysis of carbene-borylene bonded dinitrogen complexes for deeper bonding insight: A fair comparison with a metal-dinitrogen system.

Binding of dinitrogen (N2 ) to a transition metal center (M) and followed by its activation under milder conditions is no longer impossible; rather, it is routinely studied in laboratories by transition metal complexes. In contrast, binding of N2 by main group elements has been a challenge for decades, until very recently, an exotic cAAC-borylene (cAAC = cyclic alkyl(amino) carbene) species showed similar binding affinity to kinetically inert and non-polar dinitrogen (N2 ) gas under ambient conditions. Since then, N2 binding by short lived borylene species has made a captivating news in different journals for its unusual features and future prospects. Herein, we carried out different types of DFT calculations, including EDA-NOCV analysis of the relevant cAAC-boron-dinitrogen complexes and their precursors, to shed light on the deeper insight of the bonding secret (EDA-NOCV = energy decomposition analysis coupled with natural orbital for chemical valence). The hidden bonding aspects have been uncovered and are presented in details. Additionally, similar calculations have been carried out in comparison with a selected stable dinitrogen bridged-diiron(I) complex. Singlet cAAC ligand is known to be an exotic stable species which, combined with the BAr group, produces an intermediate singlet electron-deficient (cAAC)(BAr) species possessing a high lying HOMO suitable for overlapping with the high lying π*-orbital of N2 via effective π-backdonation. The BN2 interaction energy has been compared with that of the FeN2 bond. Our thorough bonding analysis might answer the unasked questions of experimental chemists about how boron compounds could mimic the transition metal of dinitrogen binding and activation, uncovering hidden bonding aspects. Importantly, Pauling repulsion energy also plays a crucial role and decides the binding efficiency in terms of intrinsic interaction energy between the boron-center and the N2 ligand.

Stabilization of Interstellar CSi2 Species by Donor Base Ligands: L-CSi2-L; L = cAACMe, NHCMe, and PMe3.

The donor ligand bonded singlet (L)2Si2C containing a bent Si2C unit in the middle has been studied by theoretical quantum mechanical calculations (NBO, QTAIM, EDA-NOCV analyses) [L = cAAC, NHC, Me3P]. EDA-NOCV analysis suggests that this Si2C is possible to stabilize by a pair of donor base ligands. The bond dissociation energy of the Si2C fragment is endothermic (85-45 kcal/mol) with a sufficiently high intrinsic interaction energy (ΔEint = -89 to -48 kcal/mol). Fifty percent of the total stabilization energy arises from electrostatic interactions, and nearly 45% is contributed by covalent orbital interaction between Si2C and (L)2 fragments in their singlet states. 75-80% of the orbital interaction energy is contributed by two sets of σ-donation L → SiCSi ← L. The π-back-donation is only 15-10%. The dispersion energy is not negligible (3-5%). The interaction energy is highest for 1 (L = cAAC) among three compounds. Additionally, (cAAC)2Si2C-Ni(CO)3 (4) has been studied. The interaction energy between 1 and Ni(CO)3 is nearly 61 kcal/mol with the major contribution coming from donation of electron cloud from electron rich Si2C backbone to empty hybrid orbital of Ni(CO)3 fragment. A sufficiently strong π-back-donation from (OC)3Ni to Si2C has also been identified.

Stabilization of group 14 elements E = C, Si, Ge by hetero-bileptic ligands cAAC, MCOn with push-pull mechanism.

The stability and bonding of a series of hetero-diatomic molecules with general formula (cAAC)EM(CO)n , where cAAC = cyclic alkyl(amino) carbene; E = group 14 elements (C, Si, and Ge); M = transition metal (Ni, Fe, and Cr) have been studied by quantum chemical calculations using density functional theory (DFT) and energy decomposition analysis-natural orbital chemical valence (EDA-NOCV). The equilibrium geometries were calculated at the BP86/def2-TZVPP level of theory. The tri-coordinated group 14 complex (1a, 4a, and 7a) in which one of the CO groups is migrated to the central group 14 element from adjacent metal is theoretically found to be more stable when the central atom (E) is carbon. On the other hand, the two-coordinate group 14 element containing metal-complexes (2, 5, 8, 3, 6, and 9) are found to be more stable with their corresponding heavier analogues. The electronic structures of all the molecules have been analyzed by molecular orbital, topological analysis of electron density and natural bond orbital (NBO) analysis at the M06/def2-TZVPP//BP86/def2-TZVPP level of theory. The nature of the cAACE and EM bonds has been studied by EDA-NOCV calculations at BP86-D3(BJ)/TZ2P level of theory. The EDA analysis suggests that the bonding of cAACC(CO) can be best represented by electron sharing σ and π interactions, whereas, C(CO)M(CO)n-1 by dative σ and π interactions. On the other hand, EDA-NOCV calculations suggests both dative σ and π interactions for cAACE and EM(CO)n bonds of the corresponding Si and Ge analogues having stronger σ- and relatively weaker π-bonds. The topological analysis of electron density supports the closed-shell interaction for the Si and Ge complexes and open-shell interaction for the carbon complexes. The calculated proton affinity and hydride affinity values corroborated well with the present bonding description. This class of complexes might act as efficient future catalysts for different organic transformations due to the presence of electron rich group 14 element and metal carbonyl.

Chemical Bonding in Homoleptic Carbonyl Cations [M{Fe(CO)5 }2 ]+ (M=Cu, Ag, Au).

Syntheses of the copper and gold complexes [Cu{Fe(CO)5 }2 ][SbF6 ] and [Au{Fe(CO)5 }2 ][HOB{3,5-(CF3 )2 C6 H3 }3 ] containing the homoleptic carbonyl cations [M{Fe(CO)5 }2 ]+ (M=Cu, Au) are reported. Structural data of the rare, trimetallic Cu2 Fe, Ag2 Fe and Au2 Fe complexes [Cu{Fe(CO)5 }2 ][SbF6 ], [Ag{Fe(CO)5 }2 ][SbF6 ] and [Au{Fe(CO)5 }2 ][HOB{3,5-(CF3 )2 C6 H3 }3 ] are also given. The silver and gold cations [M{Fe(CO)5 }2 ]+ (M=Ag, Au) possess a nearly linear Fe-M-Fe' moiety but the Fe-Cu-Fe' in [Cu{Fe(CO)5 }2 ][SbF6 ] exhibits a significant bending angle of 147° due to the strong interaction with the [SbF6 ]- anion. The Fe(CO)5 ligands adopt a distorted square-pyramidal geometry in the cations [M{Fe(CO)5 }2 ]+ , with the basal CO groups inclined towards M. The geometry optimization with DFT methods of the cations [M{Fe(CO)5 }2 ]+ (M=Cu, Ag, Au) gives equilibrium structures with linear Fe-M-Fe' fragments and D2 symmetry for the copper and silver cations and D4d symmetry for the gold cation. There is nearly free rotation of the Fe(CO)5 ligands around the Fe-M-Fe' axis. The calculated bond dissociation energies for the loss of both Fe(CO)5 ligands from the cations [M{Fe(CO)5 }2 ]+ show the order M=Au (De =137.2 kcal mol-1 )>Cu (De =109.0 kcal mol-1 )>Ag (De =92.4 kcal mol-1 ). The QTAIM analysis shows bond paths and bond critical points for the M-Fe linkage but not between M and the CO ligands. The EDA-NOCV calculations suggest that the [Fe(CO)5 ]→M+ ←[Fe(CO)5 ] donation is significantly stronger than the [Fe(CO)5 ]←M+ →[Fe(CO)5 ] backdonation. Inspection of the pairwise orbital interactions identifies four contributions for the charge donation of the Fe(CO)5 ligands into the vacant (n)s and (n)p AOs of M+ and five components for the backdonation from the occupied (n-1)d AOs of M+ into vacant ligand orbitals.

Solid-State Isolation of Cyclic Alkyl(Amino) Carbene (cAAC)-Supported Structurally Diverse Alkali Metal-Phosphinidenides.

Cyclic alkyl(amino) carbene (cAAC)-supported, structurally diverse alkali metal-phosphinidenides 2-5 of general formula ((cAAC)P-M)n (THF)x [2: M=K, n=2, x=4; 3: M=K, n=6, x=2; 4: M=K, n=4, x=4; 5: M=Na, n=3, x=1] have been synthesized by the reduction of cAAC-stabilized chloro-phosphinidene cAAC=P-Cl (1) utilizing metallic K or KC8 and Na-naphthalenide as reducing agents. Complexes 2-5 have been structurally characterized in solid state by NMR studies and single crystal X-ray diffraction. The proposed mechanism for the electron transfer process has been well-supported by cyclic voltammetry (CV) studies and Density Functional Theory (DFT) calculations. The solid state oligomerization process has been observed to be largely dependent on the ionic radii of alkali metal ions, steric bulk of cAAC ligands and solvation/de-solvation/recombination of the dimeric unit [(cAAC)P-M(THF)x ]2 .

Revisiting the Bonding Scenario of Two Donor Ligand Stabilized C2 Species.

Quantum chemical calculations using density functional methods were performed for complexes of type L2C2 with L = NHCMe (1), SNHCMe (2) (S = saturated), cAACMe (3), and diamidocarbene (DACMe) (4). The equilibrium structures of 1-4 possess almost linear C4 cores. A high thermochemical stability of the complexes with respect to dissociation, L2C2 → C2 + 2L, is indicated by the large bond dissociation energy following the order 3 > 4 > 2 > 1. The results show that the use of SNHCMe and DACMe as ligands is preferable over NHCMe. The bonding analysis using charge and energy decomposition methods reveals that (cAACMe)2C2 and (DACMe)2C2 possess genuine cumulene C4 moieties, which results from the electron-sharing bonding between quintet L2 and quintet C2 fragments. In contrast, the bonding in (NHCMe)2C2 and (SNHCMe)2C2 comes from a combination of dative and electron-sharing interactions between doublet L2+ and doublet C2- fragments.

Group†6 Hexacarbonyls as Ligands for the Silver Cation: Syntheses, Characterization, and Analysis of the Bonding Compared with the Isoelectronic Group†5 Hexacarbonylates.

The syntheses of the two novel complexes [Ag{Mo/W(CO)6 }2 ]+ [F-{Al(ORF )3 }2 ]- (RF =C(CF3 )3 ) are reported along with their structural and spectroscopic characterization. The X-ray structure shows that three carbonyl ligands from each M(CO)6 fragment bend towards the silver atom within binding Ag-C distance range. DFT calculations of the free cations [Ag{M(CO)6 }2 ]+ (M=Cr, Mo, W) in the electronic singlet state give equilibrium structures with C2 symmetry with two bridging carbonyl groups from each hexacarbonyl ligand. Similar structures with C2 symmetry (M=Nb) and D2 symmetry (M=V, Ta) are calculated for the isoelectronic group 5 anions [Ag{M(CO)6 }2 ]- (M=V, Nb, Ta). The electronic structure of the cations is analyzed with the QTAIM and EDA-NOCV methods, which provide detailed information about the nature of the chemical bonds between Ag+ and the {M(CO)6 }2 q (q = -2, M = V, Nb, Ta; q = 0, M = Cr, Mo, W) ligands.

Stabilization of Linear C3 by Two Donor Ligands: A Theoretical Study of L-C3 -L (L=PPh3 , NHCMe , cAACMe )*.

Quantum chemical studies using density functional theory and ab initio methods have been carried out for the molecules L-C3 -L with L=PPh3 (1), NHCMe (2, NHC=N-heterocyclic carbene), and cAACMe (3, cAAC=cyclic (alkyl)(amino) carbene). The calculations predict that 1 and 2 have equilibrium geometries where the ligands are bonded with rather acute bonding angles at the linear C3 moiety. The phosphine adduct 1 has a synclinal (gauche) conformation whereas 2 exhibits a trans conformation of the ligands. In contrast, the compound 3 possesses a nearly linear arrangement of the carbene ligands at the C3 fragment. The bond dissociation energies of the ligands have the order 1<2<3. The bonding analysis using charge and energy decomposition methods suggests that 3 is best described as a cumulene with electron-sharing double bonds between neutral fragments (cAACMe )2 and C3 in the respective electronic quintet state yielding (cAACMe )=C3 =(cAACMe ). In contrast, 1 and 2 possess electron-sharing and dative bonds between positively charged ligands [(PPh3 )2 ]+ or [(NHCMe )2 ]+ and negatively charged [C3 ]- fragments in the respective doublet state.

Preparation of a high-coordinated-silicon-centered spiro-cyclic compound.

Silicon compounds containing silicon-silicon bond with a variety of unusual oxidation states are quite important, because their high reactivity leads to the formation of a variety of silicon compounds. The isolation of such compounds with unusual oxidation states requires a resilient synthetic strategy. Herein, we report the synthesis of a silicon based spirocyclic compound containing a hyper-valent silicon atom and a silicon-silicon bond. The computational calculations employing natural bond orbital (NBO) analysis and energy decomposition analysis-natural orbitals for chemical valence (EDA-NOCV) reveal that the nature of bonding between the silicon atoms is of an electron sharing nature.

Redox Active cAAC-Fluorene/Indene Systems Displaying Solvatochromism, Green Luminescence and pH Sensing: Functionalization of Fluorenyl/Indenyl Rings with Radical Carbene.

Two new series of air stable compounds of cAACX = fluorene/indene (X = Me2 , Et2 , Cy) [cAAC = cyclic (alkyl) amino carbene] have been isolated and well characterized by X-ray single crystal diffraction, photoluminescence, cyclic voltammogram (CV) and electron paramagnetic resonance (EPR) studies. Fluorescence studies reveals green light emission of cAAC bonded fluorene, whereas free fluorene generally displays a violet emission. Interestingly, the sterically crowded cAAC-fluorene analogue display solvatochromism and CF3 CO2 H sensing in solution. CV of the these compounds show a quasi-reversible electron transfer process, indicating the functionalization of fluorene/indene with radical anionic form of carbene, confirmed by CV/EPR measurements. DFT/TDDFT calculations and energy decomposition analysis coupled with natural orbital for chemical valence (EDA-NOCV) have been carried out to study different aspects of bonding and electronic transitions. Such a class of redox active and thermally stable organic molecules may be suitable for molecule based spin memory devices in future.

Estimations of Fe0/-1-N2 interaction energies of iron(0)-dicarbene and its reduced analogue by EDA-NOCV analyses: crucial steps in dinitrogen activation under mild conditions.

Metal complexes containing low valence iron atoms are often experimentally observed to bind with the dinitrogen (N2) molecule. This phenomenon has attracted the attention of industrialists, chemists and bio-chemists since these N2-bonded iron complexes can produce ammonia under suitable chemical or electrochemical conditions. The higher binding affinity of the Fe-atom towards N2 is a bit 'mysterious' compared to that of the other first row transition metal atoms. Fine powders of α-Fe0 are even part of industrial ammonia production (Haber-Bosch process) which operates at high temperature and high pressure. Herein, we report the EDA-NOCV analyses of the previously reported dinitrogen-bonded neutral molecular complex (cAACR)2Fe0-N2 (1) and mono-anionic complex (cAACR)2Fe-1-N2 (2) to give deeper insight of the Fe-N2 interacting orbitals and corresponding pairwise intrinsic interaction energies (cAACR = cyclic alkyl(amino) carbene; R = Dipp or Me). The Fe0 atom of 1 prefers to accept electron densities from N2 via σ-donation while the comparatively electron rich Fe-1 centre of 2 donates electron densities to N2 via π-backdonation. However, major stability due to the formation of an Fe-N2 bond arises due to Fe → N2 π-backdonation in both 1 and 2. The cAACR ligands act as a charge reservoir around the Fe centre. The electron densities drift away from cAAC ligands during the binding of N2 molecules mostly via π-backdonation. EDA-NOCV analysis suggests that N2 is a stronger π-acceptor rather than a σ-donor.

The Labile Nature of Air Stable Ni(II)/Ni(0)-phosphine/Olefin Catalysts/Intermediates: EDA-NOCV Analysis.

Metal ions-based inorganic-organic hybrid composites are often reported acting as good to excellent catalysts with various substrate scopes under milder reaction conditions. The active catalyst of a catalytic cycle is sometimes proposed to be a short-lived reactive intermediate species. A three coordinate (L-Me)Ni(II) intermediate species [L-Me=O2 N donor dianionic ligand] can bind with short-lived carbene-ester ligands to produce four coordinate Ni(II) species which can act as carbene transfer intermediate under suitable reaction conditions for C-H functionalization and/or cyclopropanation reactions. The dissociation of phosphine (PPh3 ) from the Ni(II) centre of (L-Me)Ni(II)(PPh3 ) (1 a) and binding of short lived carbene esters (:CR1 -CO2 R2 ; R1 =H, Ph; R2 =aliphatic group; 2-4 and other carbenes; 5-10) to Ni(II) rationalize the phenomenon in solution. Air stable Ni(0)-olefin complexes/intermediates (12-18) have recently been shown to mediate a variety of organic transformations. This analysis will further help organic/organometallic chemists to rationalize the design and synthesis of future catalysts for organic transformation. EDA-NOCV calculations have been performed to shed light on the stability and bonding of those species. Additionally, our analysis provides a proper reason why the analogous (L-Me)Pd-PPh3 complex (1 b) does not dissociate in solution and hence, a similar catalytic product has not been isolated from identical reaction conditions. The stability and the labile nature of Ni(II/0) complexes have been investigated by state-of-the-art EDA-NOCV analyses.

Bonding and stability of dinitrogen-bonded donor base-stabilized Si(0)/Ge(0) species [(cAACMe-Si/Ge)2(N2)]: EDA-NOCV analysis.

Recently, dinitrogen (N2) binding and its activation have been achieved by non-metal compounds like intermediate cAAC-borylene as (cAAC)2(B-Dur)2(N2) [cAAC = cyclic alkyl(amino) carbene; Dur = aryl group, 2,3,5,6-tetramethylphenyl; B-Dur = borylene]. It has attracted a lot of scientific attention from different research areas because of its future prospects as a potent species towards the metal free reduction of N2 into ammonia (NH3) under mild conditions. Two (cAAC)(B-Dur) units, each of which possesses six valence electrons around the B-centre, are shown to accept σ-donations from the N2 ligand (B ← N2). Two B-Dur further provide π-backdonations (B → N2) to a central N2 ligand to strengthen the B-N2-B bond, providing maximum stability to the compound (cAAC)2(B-Dur)2(N2) since the summation of each pair wise interaction accounted for the total stabilization energy of the molecule. (cAAC)(B-Dur) unit is isolobal to cAAC-E (E = Si, Ge) fragment. Herein, we report on the stability and bonding of cAAC-E bonded N2-complex (cAAC-E)2(N2) (1-2; Si, Ge) by NBO, QTAIM and EDA-NOCV analyses (EDA-NOCV = energy decomposition analysis coupled with natural orbital for chemical valence; QTAIM = quantum theory of atoms in molecule). Our calculation suggested that syntheses of elusive (cAAC-E)2(N2) (1-2; Si, Ge) species may be possible with cAAC ligands having bulky substitutions adjacent to the CcAAC atom by preventing the homo-dimerization of two (cAAC)(E) units which can lead to the formation of (cAAC-E)2. The formation of E[double bond, length as m-dash]E bond is thermodynamically more favourable (E = Si, Ge) over binding energy of N2 inbetween two cAAC-E units.

Dinitrogen Binding and Activation: Bonding Analyses of Stable V(III/I)-N2-V(III/I) Complexes by the EDA-NOCV Method from the Perspective of Vanadium Nitrogenase.

The FeVco cofactor of nitrogenase (VFe7S8(CO3)C) is an alternative in the molybdenum (Mo)-deficient free soil living azotobacter vinelandii. The rate of N2 reduction to NH3 by FeVco is a few times higher than that by FeMoco (MoFe7S9C) at low temperature. It provides a N source in the form of ammonium ions to the soil. This biochemical NH3 synthesis is an alternative to the industrial energy-demanding production of NH3 by the Haber-Bosch process. The role of vanadium has not been clearly understood yet, which has led chemists to come up with several stable V-N2 complexes which have been isolated and characterized in the laboratory over the past three decades. Herein, we report the EDA-NOCV analyses of dinitrogen-bonded stable complexes V(III/I)-N2 (1-4) to provide deeper insights into the fundamental bonding aspects of V-N2 bond, showing the interacting orbitals and corresponding pairwise orbital interaction energies (ΔE orb(n)). The computed intrinsic interaction energy (ΔE int) of V-N2-V bonds is significantly higher than those of the previously reported Fe-N2-Fe bonds. Covalent interaction energy (ΔE orb) is more than double the electrostatic interaction energy (ΔE elstat) of V-N2-V bonds. ΔE int values of V-N2-V bonds are in the range of -172 to -204 kcal/mol. The V → N2 ← V π-backdonation is four times stronger than V ← N2 → V σ-donation. V-N2 bonds are much more covalent in nature than Fe-N2 bonds.

Fluorescent organo-antimony compounds as precursors for syntheses of redox-active trimeric and dimeric alkali metal antimonides: an insight into electron transfer reduction processes.

(Tip)2SbCl (1, Tip = 2,4,6-triisopropylphenyl) has been utilized as a precursor for the synthesis of the distibane (Tip)4Sb2 (4) via one-electron reduction using KC8. The two-electron reduction of 1 and 4 afforded the novel trinuclear antimonide cluster [K3((Tip)2Sb)3(THF)5] (6). Changing the reducing agent from KC8 to a different alkali metal resulted in the solid-state isolation of corresponding stable dimeric alkali metal antimonides with the general formula [M2((Tip)2Sb)2(THF)p-x(tol)x] (M = Li (14), Na (15), Cs (16)). In this report, different aspects of the various reducing agents [K metal, KC8, and [K2(Naph)2(THF)]] used have been studied, correlating the experimental observations with previous reports. Additional reactivity studies involving 1 and AgNTf2 (Tf = trifluoromethanesulfonyl) afforded the corresponding antimony cation (Tip)2Sb+NTf2- (19). The Lewis acidic character of 19 has been unambiguously proved via treatment with Lewis bases to produce the corresponding adducts 20 and 21. Interestingly, the precursors 1 and 4 have been observed to be highly luminescent, emitting green light under short-wavelength UV radiation. All the reported compounds have been characterized via NMR, UV-vis, mass spectrometry, and single-crystal X-ray diffraction analysis. Cyclic voltammetry (CV) studies of 1 in THF showed possible two electron reduction, suggesting the in situ generation of the corresponding radical-anion intermediate 1˙- and its subsequent conversion to the monomeric intermediate (Tip)2Sb- (5) upon further reduction. 5 undergoes oligomerization in the solid state to produce 6. The existence of 1˙- was proved using electron paramagnetic resonance (EPR) spectroscopy in solution. CV studies of 6 suggested its potential application as a reducing agent, which was further proved via the conversion of Tip-PCl2 to trimeric (Tip)3P3 (17), and cAACP-Cl (cAAC = cyclic alkyl(amino)carbene) to (cAAC)2P2 (18) and 4, utilizing 6 as a stoichiometric reducing agent.

EDA-NOCV Calculation for Efficient N2 Binding to the Reduced Ni3S8 Complex: Estimation of Ni-N2 Intrinsic Interaction Energies.

The binding of the dinitrogen molecule to the metal center is the first and crucial step toward dinitrogen activation. Favorable interaction energies are desired by chemists and biochemists to study model complexes in the laboratory. An electrochemically reduced form of a previously isolated sulfur-bridged Ni3S8 complex is inferred to bind N2 at multiple Ni centers, and this bonded N2 undergoes reductive protonation to produce hydrazine (N2H4) as the product in the presence of a proton donor. Density functional theory (DFT) calculations and quantum theory of atoms in molecules (QTAIM) analysis have been carried out to shed light on the nature of N2 binding to an anionic trinuclear Ni3S8 complex. Additionally, energy decomposition analysis with the combination of natural orbital for chemical valence (EDA-NOCV) analysis has been performed to estimate the pairwise interaction energies between the Ni center and the N2 molecule under experimental conditions.

Estimations of Fe-N2 Intrinsic Interaction Energies of Iron-Sulfur/Nitrogen-Carbon Sites: A Deeper Bonding Insight by EDA-NOCV Analysis of a Model Complex of the Nitrogenase Cofactor.

The MoFe7S9C1- unit of the nitrogenase cofactor (FeMoco) attracts chemists and biochemists due to its unusual ability to bind aerial dinitrogen (N2) at ambient condition and catalytically convert it into ammonia (NH3). The mode of N2 binding and its reaction pathways are yet not clear. An important conclusion has been made based on the very recent synthesis and isolation of model Fe(I/0)-complexes with sulfur-donor ligands under the cleavage of one Fe-S bond followed by binding of N2 at the Fe(0) center. These complexes are structurally relevant to the nitrogenase cofactor (MoFe7S9C1-). Herein, we report the EDA-NOCV analyses and NICS calculations of the dinitrogen-bonded dianionic complex Fe0-N2 (1) (having a CAr ← Fe π-bond) and monoanionic complex FeI-N2 (2) (having a CAr-Fe σ-bond) to provide a deeper insight into the Fe-N2 interacting orbitals and corresponding pairwise interaction energies (EDA-NOCV = energy decomposition analysis coupled with natural orbital for chemical valence; NICS = nucleus-independent chemical shifts). The orbital interaction in the Fe-N2 bond is significantly larger than Coulombic interactions, with major pairwise contributions coming from d(Fe) orbitals to the empty π* orbitals of N2 (three Fe → N2). ΔE int values are in the range of -61 to -77 kcal mol-1. Very interestingly, NICS calculations have been carried out for the fragments before and after binding of the N2 molecule. The computed σ- and π-aromaticity values are attributed to the position of the Fe atoms, oxidation states of Fe centers, and Fe-C bond lengths of these two complexes.