Upright or in-plane conformational preference: Dilemma of eta(2)-coordinated C = C double bond in PtX2(CO)(eta(2)-ene) (X = H, Cl, or C6F5) complexes

 
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2008 (EN)
Upright or in-plane conformational preference: Dilemma of eta(2)-coordinated C = C double bond in PtX2(CO)(eta(2)-ene) (X = H, Cl, or C6F5) complexes (EN)

Tsipis, A. C. (EN)

Πανεπιστήμιο Ιωαννίνων. Σχολή Θετικών Επιστημών. Τμήμα Χημείας (EL)
Tsipis, A. C. (EN)

In the present work we employ hybrid density functional calculations (at the B3P86 level) in conjunction with natural bond orbitals (NBOs) and charge decomposition analysis (CDA) to unravel the origin of the in-plane or upright conformational preference of eta(2)-coordinated C = C double bonds in a series of square-planar d(8) metal complexes formulated as cis-[PtX2(CO)(L)] (X = H, Cl, C6F5; L = unsaturated hydrocarbon). We find that both the nucleophilicity of the unsaturated hydrocarbon ligands and the electrophilicity of the cis-[PtX2(CO)] electrophilic fragment play a key role in fine-tuning the conformational preference of the coordinated C = C double bond of the unsaturated hydrocarbon ligands. For the complexes of cis-[PtX2(CO)] electrophiles of low electrophilicity (omega values in the range 1.883-4.486 eV) both geometric arrangements (in-plane and upright) correspond to minima on the potential energy surfaces (PES). The two orientations differing slightly in energy are competitive, and therefore it is a dilemma that leads to the coexistence of both conformers in equilibrium in solutions of the unsaturated hydrocarbon complexes of the cis-[PtX2(CO)] electrophiles of low electrophility. In contrast, in the complexes of the cis-[PtX2(CO)] electrophiles with high electrophilicity (omega > 7.0 eV) only one of the orientations could be located as a minimum in the PES, that of the upright orientation of the C = C double bond, except for the complexes of the perfluoroethene, norbornene, 7,7-dimethylnorbornene, and bicyclo[2.2.2]oct-2-ene ligands. Finally, the behavior of the unsaturated hydrocarbon complexes of the cis-[PtX2(CO)] electrophiles of intermediate electrophilicity (omega values in the range 5.0-7.0 eV) is intermediate between those of the cis-[PtX2(CO)] electrophiles with low and high electrophilicity. In this case it is the nucleophilicity of the unsaturated hydrocarbon ligands in conjunction with steric effects that modulates the conformational preference of the unsaturated hydrocarbon. Generally, the high nucleophilicity of unsaturated hydrocarbon ligands in conjunction with high electrophilicity of platinum-containing fragments favors exclusively the upright orientation. (EN)

ab-initio pseudopotentials (EN)

Πανεπιστήμιο Ιωαννίνων (EL)
University of Ioannina (EN)

Organometallics (EN)

English

2008

<Go to ISI>://000258226100013



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