Small molecule activation by sila/germa boryne species.

The inability of p-block elements to participate in π-backbonding restricts them from activating small molecules like CO, H2 , and so forth. However, the development of the main group metallomimetics became a new pathway, where the main-group elements like boron can bind and activate small molecules like CO and H2 . The concept of the frustrated Lewis pair, Boron-Boron multiple bonds, and borylene are previously illustrated. Some of these reported classes of boron species can mimic the jobs of the metal complexes. Hence, we have theoretically studied the binding of CO/N2 molecules at B-center of elusive species like sila/germa boryne stabilized by donor base ligands (cAAC)BE(Me)(L), where E  Si, L  cAACMe , NHCMe , PMe3 , E  Ge, L  cAACMe and (NHCMe )BE(Me)(cAACMe )). The substitutional analogues of (cAACR )BSiR1 (cAAC) and E  P, L  cAACMe ) have been studied by density functional theory (DFT), natural bond orbital, QTAIM calculations and energy decomposition analysis (EDA) coupled with natural orbital for chemical valence (NOCV) analyses. The computed bond dissociation energy and inner stability analyses by the EDA-NOCV method showed that the CO molecule can bind at the B-center of the above-mentioned species due to stronger σ-donor ability while binding of N2 has been theoretically predicted to be weak. The energy barrier for the CO binding is estimated to be 13-14 kcal/mol by transition state calculation. The change of partial triple bond character to single bond nature of the BSi bond and the bending of CBSi bond angle of sila-boryne species are the reason for the activation energy. Our study reveals the ability of such species to bind and activate the CO molecule to mimic the transition metal-containing complexes. We have additionally shown that binding of Fe(CO)4 and Ni(CO)3 is feasible at Si-center after binding of CO at the B-center.

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.

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.

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.