A computational study of carbene ligand stabilization of biomimetic models of the rotated Hred state of [FeFe]‐hydrogenase

Stabilization of fully rotated conformation at one of the iron center has been achieved for the reduced Fe(I)Fe(I) state in chelated cyclic alkyl amino carbene (CAAC) substituted biomimetic hydrogenase model complex. This study indicates that the spatial orientation of the chelated NHCs at one of the iron center plays a major role in determining the geometry at the other iron center. We also made an attempt at explaining the electronic origin behind the favorability of rotated vs unrotated structure in asymmetrically substituted chelated vs monodentate NHC complexes

Is borazine aromatic? unusual parallel behavior between hydrocarbons and corresponding B-N analogues

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Structure and bonding of metallacyclocumulenes, radialenes, butadiyne complexes and their possible interconversion: a theoretical study

Density functional theory is used to study the dimerization of metallacyclocumulenes (1, 2 and 9) to metal substituted radialenes (3, 4 and 5). These were compared to the dimerization of ethylene to cyclobutane and cumulene to radialene. The bonding of the metallacyclocumulenes were discussed in the light of the Dewar-Chatt-Duncanson model. A possible mechanism for the formation of bis(butadiyne) complex of Ni (8) is also presented. Correlation diagrams constructed for the conversion of the radialene type structure to that of the bis(butadiyne) complex show that it is allowed for both Ti and Ni

Stabilization of tricoordinate pyramidal boron: theoretical studies on CBSiH<SUB>5</SUB>, BSi<SUB>2</SUB>H<SUB>5</SUB>, CBGeH<SUB>5</SUB>, and CBSnH<SUB>5</SUB>

Discovery of new pyramids: Theoretical studies have characterized CBSiH5, BSi2H5, CBGeH5, and CBSnH5, all of which have a tricoordinate pyramidal boron atom as minima on their respective potential energy surfaces. The extent of pyramidalization, as well as the energy for inversion through the planar structure, is dependent on the substituents of the boron atom

Structure and neutral homoaromaticity of metallacyclopentene, -pentadiene, -pentyne, and -pentatriene: a density functional study

Density functional calculations were carried out on a series of metallacycles (1-6) to analyze the bonding and specifically to find the presence of any metal-p interaction in them. While there is no interaction between the metal and the middle carbon atoms in metallacyclopentane (1) and metallacyclopentadiene (4), strong metal-π interaction is found in the other metallacycles. The metallacyclopentene (2) and metallacyclopentyne (5) are found to be neutral bishomoaromatic, while the metallacyclopentatriene (6) is neutral in-plane aromatic. The calculated nucleus-independent chemical shift values and other bonding parameters support the strong cyclic delocalization of electrons in 2, 5, and 6. A comparison of the calculated hydrogenation energies of the parent hydrocarbons and the metallacycles indicates that the metal fragment nearly eliminates the strain energy

Structure, reactivity and aromaticity of acenes and their BN analogues: a density functional and electrostatic investigation

Density functional calculations have been carried out on a series of linearly annelated acenes and their BN analogues. Even though borazine shows aromatic and reactivity behavior parallel with that of benzene, its condensed derivatives show patterns different from those of their hydrocarbon analogues. Nucleus independent chemical shift (NICS) values in acenes suggest that the aromaticity of the inner rings is more than that of benzene, whereas in BN-acenes there is no substantial change in the aromaticity of the individual rings. Molecular electrostatic potential (MESP) is employed to obtain further insights into the bonding and reactivity trends for these systems. The MESP topography patterns of acenes and BN-acenes are substantially different, with BN-acenes showing more localized p electron features compared to those of acenes. The MESP values at the critical points (CPs) indicate overall lowering of aromaticity in these annelated systems. However, this change is gradual among the BN-acenes

Synthesis and characterization of bis(sigma)borate and bis-zwitterionic complexes of rhodium and iridium

Building upon the chemistry of Rh–N,S-heterocyclic carbene complex, [(Cp*Rh)(L2)(1-benzothiazol-2-ylidene)], 2 (Cp*=η5-C5Me5; L=C7H4NS2) with various monoboranes-Lewis adducts, we explored the chemistry of 2 with BH3⋅thf at elevated temperature. As a result, mild thermolysis of 2 with BH3⋅thf led to the formation of bis(sigma)borate [(η4-C5Me5H)Rh(η2-H3BL)], 3 and a bis-zwitterionic species [Cp*RhS(BH2L2)], 4 with the concomitant release of BH3⋅bt (bt=benzothiazole). The RhS3C2N2B2 atoms in 4 generates two six membered rings fused by a common Rh−S bond, which may be considered as a bicycle [4.4.0] cage at the rhodium center. In an effort to generate the iridium analogue of 3, reaction of [Cp*IrCl2]2 with Na[H3B(mbt)] (mbt=2-mercaptobenzothiazole) was carried out that produced bis(sigma)borate complex [(η4-C5Me5H)Ir(η2-H3BL)], 1. The solid state X-ray structures of 1 and 3 showed that the Cp*H ligand coordinated to the metal center in a η4-fashion. In compound 3, the methyl group is oriented towards rhodium center, whereas it is away from Ir center in 1. In addition, the DFT computations were performed to shed light on the bonding and electronic structures of these compounds

New routes to a series of σ-borane/borate complexes of molybdenum and ruthenium

A series of agostic σ-borane/borate complexes have been synthesized and structurally characterized from simple borane adducts. A room-temperature reaction of [Cp*Mo(CO)3Me], 1 with Li[BH3(EPh)] (Cp*=pentamethylcyclopentadienyl, E=S, Se, Te) yielded hydroborate complexes [Cp*Mo(CO)2(μ-H)BH2EPh] in good yields. With 2-mercapto-benzothiazole, an N,S-carbene-anchored σ-borate complex [Cp*Mo(CO)2BH3(1-benzothiazol-2-ylidene)] (5) was isolated. Further, a transmetalation of the B-agostic ruthenium complex [Cp*Ru(μ-H)BHL2] (6, L=C7H4NS2) with [Mn2(CO)10] affords a new B-agostic complex, [Mn(CO)3 (μ-H)BHL2] (7) with the same structural motif in which the central metal is replaced by an isolobal and isoelectronic [Mn(CO)3] unit. Natural-bond-orbital analyses of 5–7 indicate significant delocalization of the electron density from the filled σB&#x2014;H orbital to the vacant metal orbital