Unexpected Trimerization of Pyrazine in the Coordination Sphere of Low-Valent Titanocene Fragments

Thomas Jung; Rüdiger Beckhaus; Thorsten Klüner; Sebastian Höfener; Wim Klopper

doi:10.1021/ct900137r

Unexpected Trimerization of Pyrazine in the Coordination Sphere of Low-Valent Titanocene Fragments

J Chem Theory Comput. 2009 Aug 11;5(8):2044-9. doi: 10.1021/ct900137r.

Authors

Thomas Jung¹, Rüdiger Beckhaus¹, Thorsten Klüner¹, Sebastian Höfener¹, Wim Klopper¹

Affiliation

¹ Inorganic Chemistry and Theoretical Chemistry, Institute of Pure and Applied Chemistry, Carl von Ossietzky University, D-26111 Oldenburg, Germany and Institute of Physical Chemistry, Universität Karlsruhe (TH), D-76128 Karlsruhe, Germany.

PMID: 26613146
DOI: 10.1021/ct900137r

Abstract

The titanium mediated trimerization of pyrazine leads to the formation of a tris-chelate complex employing a 4a,4b,8a,8b,12a,12b-hexahydrodiyprazino[2,3-f:2',3'-h]quinoxaline ligand (HATH6, 3). The driving force in the formation of the (Cp*2Ti)3(HATH6) complex 2 is attributed to the formation of six Ti-N bonds. We show that density functional theory (DFT) fails to predict quantitatively correct results. Therefore, post-Hartree-Fock methods, such as second-order Møller-Plesset perturbation theory (MP2), in combination with coupled-cluster (CC) methods must be used. Both MP2 and CCSD(T) levels of theory provide endothermic trimerization energies, showing that the plain pyrazine trimer is not stable with respect to decomposition into its monomers. Complete basis set (CBS) results for the MP2 level of theory were computed using explicitly correlated wave functions. With these, we estimate the CCSD(T) CBS limit of the hypothetical trimerization energy to be +0.78 eV. Thus, the trimerization is facilitated by the formation of six Ti-N bonds with a calculated formation energy of -1.32 eV per bond.