Article

Divalent carbon atom as the proton acceptor in hydrogen bonding.

Department of Quantum Chemistry, Faculty of Chemistry, Nicolaus Copernicus University, Gagarina 7, 87-100, Toruń, Poland.
Physical Chemistry Chemical Physics (Impact Factor: 4.2). 07/2009; 11(27):5711-9. DOI: 10.1039/B901968E
Source: PubMed

ABSTRACT Proton-accepting properties of the divalent carbon atom in carbodiphosphoranes and their simple derivatives as well as in carbenes have been investigated. Both these groups of chemical compounds may be characterized by the formula CL2, where L is a sigma electron donor. Therefore, the carbon atom within both these systems, being in its atomic state, can have one or two lone electron pairs and, as a result, it may form hydrogen bonds of the type D-H...CL2, where C acts as a proton acceptor. Complexes of C(NH3)2, C(PH3)2, C[P(CH3)3]2, CF2, CCl2, and imidazol-2-ylidene with such proton donors as H2O, HCF3, HCN and HCCH have been analyzed by means of high-level quantum chemical methods. Density functional theory (DFT) and second-order Møller-Plesset (MP2) approaches have been applied in conjunction with the aug-cc-pVTZ basis set. The electron density distribution calculated by means of the atoms in the molecules procedure has also been analyzed. Proton-accepting properties of the carbon atom are discussed in detail. It is shown that the divalent carbon atom in the group of chemical systems investigated should be treated as a normal proton acceptor, similar to the much more electronegative O or N atoms. Moreover, hydrogen bonds of the type D-H...CL2 within the complexes investigated have been found to be rather strong. The highest proton accepting ability of the carbon(0) atom found for the (NH3)2C derivative of carbodiphosphorane is explained on the basis of the Leffler-Hammond postulate. Within the group of carbenes, the strongest hydrogen bonds are formed by imidazol-2-ylidene. This is attributed to the significant aromatic character of the imidazol-2-ylidene ring that increases the proton-accepting properties of the carbene carbon atom.

0 Bookmarks
 · 
72 Views
  • [Show abstract] [Hide abstract]
    ABSTRACT: Quantum chemical calculations at the BP86 level with various basis sets (SVP, TZVPP, TZ2P+) have been carried out for transition metal complexes of carbodiphosphorane analogues E(PPh3)2 with E = C–Pb. The nature of the W(CO)4–E(PPh3) bonds was analysed with charge and energy decomposition methods. The equilibrium structures of the tetrylone complexes W(CO)4–E(PPh3)2 possess for E = C, Si, Ge a trigonal bipyramidal coordination at tungsten with the tetrylone ligand occupying an equatorial position. The heavier homologues with E = Sn, Pb exhibit a square pyramidal coordination at tungsten where the tetrylone ligand is at a basal position, while one phenyl group is found trans to the apical CO group which yields a hexacoordinated tungsten complex. The bond dissociation energies for the W(CO)4–E(PPh3)2 bonds are higher than for the W(CO)5–E(PPh3)2 homologues. The bonding analyses of the complexes show that the W–E bonds have a significant contribution from (CO)4W←E(PPh3)2π-donation. All complexes W(CO)4–E(PPh3)2 are suitable targets for synthesis.
    Molecular Physics 09/2013; 111(16-17):2640-2646. · 1.64 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The present review is focused on the application of computational/theoretical methods to the wide and rich chemistry of allenes. Special emphasis is made on the interplay and synergy between experimental and computational methodologies, rather than on recent developments in methods and algorithms. Therefore, this review covers the state-of-the-art applications of computational chemistry to understand and rationalize the bonding situation and vast reactivity of allenes. Thus, the contents of this review span from the most fundamental studies on the equilibrium structure and chirality of allenes to recent advances in the study of complex reaction mechanisms involving allene derivatives in organic and organometallic chemistry.
    Chemical Society Reviews 02/2014; · 30.43 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Quantum chemical calculations at the BP86/TZVPP//BP86/SVP level are performed for the tetrylone complexes [W(CO)(5) -E(PPh(3) )(2) ] (W-1 E) and the tetrylene complexes [W(CO)(5) -NHE] (W-2 E) with E=C-Pb. The bonding is analyzed using charge and energy decomposition methods. The carbone ligand C(PPh(3) ) is bonded head-on to the metal in W-1 C, but the tetrylone ligands E(PPh(3) )(2) are bonded side-on in the heavier homologues W-1 Si to W-1 Pb. The WE bond dissociation energies (BDEs) increase from the lighter to the heavier homologues (W-1 C: D(e) =25.1 kcal mol(-1) ; W-1 Pb: D(e) =44.6 kcal mol(-1) ). The W(CO)(5) ←C(PPh(3) )(2) donation in W-1 C comes from the σ lone-pair orbital of C(PPh(3) )(2) , whereas the W(CO)(5) ←E(PPh(3) )(2) donation in the side-on bonded complexes with E=Si-Pb arises from the π lone-pair orbital of E(PPh(3) )(2) (the HOMO of the free ligand). The π-HOMO energy level rises continuously for the heavier homologues, and the hybridization has greater p character, making the heavier tetrylones stronger donors than the lighter systems, because tetrylones have two lone-pair orbitals available for donation. Energy decomposition analysis (EDA) in conjunction with natural orbital for chemical valence (NOCV) suggests that the WE BDE trend in W-1 E comes from the increase in W(CO)(5) ←E(PPh(3) )(2) donation and from stronger electrostatic attraction, and that the E(PPh(3) )(2) ligands are strong σ-donors and weak π-donors. The NHE ligands in the W-2 E complexes are bonded end-on for E=C, Si, and Ge, but side-on for E=Sn and Pb. The WE BDE trend is opposite to that of the W-1 E complexes. The NHE ligands are strong σ-donors and weak π-acceptors. The observed trend arises because the hybridization of the donor orbital at atom E in W-2 E has much greater s character than that in W-1 E, and even increases for heavier atoms, because the tetrylenes have only one lone-pair orbital available for donation. In addition, the WE bonds of the heavier systems W-2 E are strongly polarized toward atom E, so the electrostatic attraction with the tungsten atom is weak. The BDEs calculated for the WE bonds in W-1 E, W-2 E and the less bulky tetrylone complexes [W(CO)(5) -E(PH(3) )(2) ] (W-3 E) show that the effect of bulky ligands may obscure the intrinsic WE bond strength.
    Chemistry - A European Journal 09/2012; 18(40):12733-48. · 5.93 Impact Factor