On the Electronic Structure of Bis(η⁵-cyclopentadienyl) Titanium

Abstract

Prior to the first reported synthesis of the titanium analogue of ferrocene, bis(η5-cyclopentadienyl)Ti, there was theoretical speculation as to the electronic structure of what would become known as “titanocene”. In time, the original report of a successful synthesis was apparently shown to be incorrect, and a dimeric form of the substance was postulated as the correct structure. In the present work, high level ab initio and DFT calculations are performed on the titanocene monomer to help answer these structural questions, and to compare with early theoretical and experimental efforts. The need for a multi-configurational wave function is analyzed and found to be unnecessary. The present calculations predict that the ground state of titanocene monomer is a triplet with parallel and freely rotating cyclopentadienyl rings, which further suggests that experimentally synthesized “titanocene” is indeed some form of the dimer.

TD-DFT analysis of the electronic spectra of Ti-containing catalysts

“…Photophysical properties were calculated using Time dependent Density Functional Theory (TD-DFT) [35]. The validity of this approach for transition-metal clusters has been checked by several authors [36][37][38]. The functionals employed were the hybrid B3LYP [39][40][41] and the pure mPWPW91, which employs the exchange functional of Perdew and Wang as modified by Barone [42] and the original correlation functional developed by Perdew and Wang [43].…”

Bis(η5-cyclopentadienyl)titanium(II) in the gas phase:

“…Freitag and Gordon [16] calculated using various correlated methods that the triplet ground state ( 3 B 1 ) C 2v titanocene is 21-88 kJ mol À1 (5.0-21.0 kcal mol À1 ) below the lowest energy singlet (C 2v 1 A 1 ). Our value of energy difference between ground state titanocene 1t and lowest energy singlet titanocene 1s obtained at B3LYP/6-311+G(2d,p) level of theory is 33 kJ mol À1 .…”

“…In their quantum chemical survey of the electronic structure of these titanocenes they found that at all levels of theory they used, the triplet geometries were all lower then the lowest energy singlet and that the 3 B 1 (C 2v ) state was a ground state at MP2, B3LYP and CCSD(T) levels of theory. Based on results of their MCSCF calculation, Freitag and Gordon also concluded that a single-reference wave function is appropriate for theoretical treatment of titanocene [16]. Some DFT calculation results concerning titanocene can also be found in papers by Harrod et al [17] and Lee et al [18].…”

“…Therefore, owing to a vertical nature of electron transfer in NRMS, the structure assignment of the apparently stable neutral C 10 H 10 Ti species was rather ambiguous. More then a half century long history of theoretical studies of titanocene was thoroughly reviewed by Freitag and Gordon [16]. They also performed high-level ab initio and density functional theory (DFT) calculations on titanocene with C s , C 2v , D 5h and D 5d symmetries [16].…”

“…More then a half century long history of theoretical studies of titanocene was thoroughly reviewed by Freitag and Gordon [16]. They also performed high-level ab initio and density functional theory (DFT) calculations on titanocene with C s , C 2v , D 5h and D 5d symmetries [16]. In their quantum chemical survey of the electronic structure of these titanocenes they found that at all levels of theory they used, the triplet geometries were all lower then the lowest energy singlet and that the 3 B 1 (C 2v ) state was a ground state at MP2, B3LYP and CCSD(T) levels of theory.…”