Kartik Chandra Mondal

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=O2N 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−CO2R2; 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.

Arenes [C6H3R(TMS)(OTf); also called benzyne/aryne precursors] containing inter-related leaving groups Me3Si (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 [C6H4(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 C6H3R(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 [C6H4(TMS-F)(OTf)]− exclusively changes to covalent dative σ-bond CAr→S(Me)3F on the attachment of F− to the TMS group of C6H4(TMS)(OTf). Introduction of σ-electron withdrawing group (like OMe, NMe2, and NO2) to the ortho-position of the TMS group of functionalized arynes C6H3R(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.

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 [(S3C(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, (Ph3P)2C(0); Ph3P→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 S3C(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 (S2Cring donor, π-C donor) and stronger donor set like CP3 (σ-C donor) ligands, respectively.

Stabilizing the exotic chemical species possessing multiple bonds is often extremely challenging due to insufficient orbital overlap, especially involving one heavier element. Bulky aryl groups and/or carbene as ligand have previously stabilized the Si-Si, Ge-Ge, and B-B triple bonds. Herein, theoretical calculations have been carried out to shed light on the stability and bonding of elusive silaboryne/germaboryne (Si/Ge-B triple bond) stabilized by donor base ligands ((cAAC)BE(Me)(L); E = Si, L = cAACMe, NHCMe, PMe3; E = Ge, L = cAACMe). The heavier analogues (Sn, Pb) have been further studied for comparison. Additionally, the effects of bulky substituents at the Si and N atoms on the structural parameters and stability of those species have been investigated. Energy decomposition analysis coupled with natural orbital for chemical valence (EDA-NOCV; for Si) showed that cAAC/NHC ligands could stabilize the exotic BSi-Me species more efficiently than PMe3 ligands. The B-Si partial triple bond of the corresponding species possesses a mixture of one covalent electron sharing B-Si σ-bond and two dative π-bonds (B ← Si, B → Si).