ChemPhysChem, 15, 3493, 2014

DOI:10.1002/cphc.201402442

C. TrujilloG. Sánchez-Sanz, I. Alkorta, J. Elguero

A computational study of 3-azonia-, 3-phosphonia- and 3-arsonia- spiro[2.2]pentanes and related three-membered heterocycles

A theoretical study, using ab initio MP2/6-311++G(d,p) computational level, has been carried out to characterize several heterocyclic spiro[2.2]pentanes cations, with N, P and As as spiro atoms. The strain and relative stability of the spiropentanes has been obtained through isodesmic reactions. NICS values and 3D NISC isosurfaces have shown σ-aromatic characteristics, similar to those found in cyclopropane. The interaction with the Cl– anion, resulting in four different stationary structures has been studied and characterized by means of the Atoms in Molecules (AIM) methodology, and it has been found Cl-pnicogen, Cl-H and Cl-C interactions have. Amongst them, the most stable structure in all cases corresponds to the opening of one of the three membered rings due to the attack of the Cl atom and C-Cl bond formation. Furthermore, the reaction with 3-boranuidaspiro[2.2]pentane anion has been considered, resulting in the formation of a new compound through the cleavage of the carbon rings of both reactants.

J. Phys. Chem. A. 118, 5540, 2014

DOI:10.1021/jp504483x

 M. Marín-LunaG. Sánchez-Sanz, P. O'Sullivan, I. Rozas

Guanidine complexes of Platinum: a theoretical study

We aim to design dual anticancer agents combining a guanidine-based DNA minor groove binder and a cisplatin-like Pt moiety. Hence, to understand the complexation between Pt and the guanidine or guanidinium moiety, we have calculated the complexes of model Nphenylguanidine/ ium derivatives with PtCl3‾ and PtCl2 in different coordinating modes (mono- and bidentate), with different N atoms of the guanidine/ium moiety and using the B3LYP/6-31+G** and LANL2DZ mixed basis set. Calculated interaction and relative energies, analysis of the electron density and examination of the orbital interactions indicate that the most stable type of complex is a monodentate interaction etween PtCl3‾ and guanidinium established through one of the NH2 groups. Next, we optimised the structure of three bis-guanidinium diaromatic systems developed in our group as DNA minor groove binders and their complexation with PtCl3‾ finding that the formation of Pt complexes of these minor groove binders is favourable and would produce stable monodentate coordinated systems.

Chem. Eur. J. 20, 10360, 2014

 DOI:10.1002/chem.201402551

C. TrujilloG. Sánchez-Sanz, I. Karpaviciene, U. Jahn, I. Cikotiene, L. Rulisek

Divergent Pathways and Competitive Mechanisms of Metathesis Reactions Between 3-Arylprop-2-inyl esters and Aldehydes:  An Experimental and Theoretical Study

Mechanistic studies on the BF3•Et2O catalyzed reaction between 3-arylprop-2-ynyl esters and aldehydes were performed using isotopic labeling experiments and quantum chemical calculations. The reactions are shown to proceed either via classical alkyne-carbonyl metathesis route, or via an unprecedented addition-rearrangement cascade. Depending on the structure of the starting materials and the reaction conditions the products of these reactions can be Morita-Baylis-Hillman adducts (MBHA), unavailable via traditional MBH reactions, or (E)- and (Z)-α,β-unsaturated ketones. 18O-Labeling studies suggested the existence of two different reaction pathways to the products. These pathways were further examined by quantum-chemical calculations employing the DFT(wB97XD)/6-311+G(2d,p) method together with the conductor-like screening model for realistic solvation (COSMO-RS). Using the wB97XD functional, the accuracy of the computed data is estimated to be 1 2 kcal.mol 1 as shown by the careful benchmarking of various DFT functionals against coupled cluster calculations at the CCSD(T)/aug-cc-pVTZ level of theory. Indeed, most of the experimental data were reproduced and explained by theory and it is convincingly shown that the branching point between the two distinct mechanisms is the formation of the first intermediate on the reaction pathway either the four-membered oxete or the six-membered zwitterion. The deep mechanistic understanding of these reactions opens new synthetic avenues to chemically and biologically important α,β-unsaturated ketones.

Phys. Chem. Chem. Phys. 16, 15900, 2014

DOI:10.1039/C4CP01072H

G. Sánchez-Sanz, C. Trujillo, I. Alkorta, J. Elguero

Intramolecular pnicogen interactions in phosphorus and arsenic analogues of proton sponges

A computational study of the intramolecular pnicogen bond in 1,5- and 1,8-bis-substituted naphthalene derivatives (ZXH and ZX2 with Z = P, As and X = H, F, Cl, and Br), structurally related to proton sponges, has been carried out. The aim of this paper is the study of their structural parameters, interaction energies and electronic properties such as electron density on the intramolecular interaction. The calculated geometrical parameters associated to the P···P interaction are in reasonable good agreement with the crystal structures found in the CSD search, in special those of the halogen derivatives. Isodesmic reactions where the 1,8-bis-subtituted derivatives are compared to monosubstituted derivatives have been calculated, indicating that the 1,8 derivatives are more stable than the monosusbtituted ones for those cases with X-Z···Z-X and F-Z···Z-H alignments. Electron densities and Laplacians at the BCP on the pnicogen interactions suggest that they can be classified as pure closed shell interactions with a partial covalent character. Electron density shift maps are consistent with the results for intermolecular pnicogen interactions. Relationships between interatomic distance and electron density at the bond critical points and between interatomic distance and the orbital charge transfer stabilization energies have been found.

J. Phys. Chem. A, 118, 1527, 2014

DOI:10.1021/jp411623h

I. Alkorta, G. Sánchez-Sanz, J. Elguero J.E. Del Bene

Pnicogen Bonds between X=PH3 (X = O, S, NH, CH2) and Phosphorus and Nitrogen Bases. 

Ab initio MP2/aug′-cc-pVTZ calculations have been carried out to investigate the pnicogen bonded complexes formed between the acids O═PH3, S═PH3, HN═PH3, and H2C═PH3 and the bases NH3, NCH, N2, PH3, and PCH. All nitrogen and phosphorus bases form complexes in which the bases are lone pair electron donors. The binding energies of complexes involving the stronger bases NH3, NCH, and PH3 differentiate among the acids, but the binding energies of complexes with the weaker bases do not. These complexes are stabilized by charge transfer from the lone pair orbital of N or P to the σ*P═A orbital of X═PH3, where A is the atom of X directly bonded to P. PCH also forms complexes with the X═PH3 acids as a π electron donor to the σ*P═A orbital. The binding energies and the charge-transfer energies of the π complexes are greater than those of the complexes in which PCH is a lone pair donor. Whether the positive charge on P increases, decreases, or remains the same upon complex formation, the chemical shieldings of 31P decrease in the complexes relative to the corresponding monomers. 1pJ(P–N) and 1pJ(P–P) values correlate best with the corresponding P–N and P–P distances as a function of the nature of the base. 1J(P–A) values do not correlate with P–A distances. Rather, the absolute values of 1J(P–O), 1J(P–S), and 1J(P–N) decrease upon complexation. Decreasing 1J(P–A) values correlate linearly with increasing complex binding energies. In contrast, 1J(P–C) values increase upon complexation and correlate linearly with increasing binding energies.

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