The Solution Structures and Dynamics and the Solid-State Structures of Substituted Cyclopentadienyltitanium(IV) Trifluorides

Organotitanium fluorides (C5Me4R)TiF3 (R = H, Me, Et) sublimate with formation of crystalline dimers. From solution,
we obtained crystals of dimers and tetramers. The tetramer [{(C5Me5)TiF3}4] irreversibly dissociates in the solid
state to dimers (ΔH = 8.33 kcal mol-1). The variable-temperature 1H and 19F NMR spectroscopy measurements
of the toluene-d8 solution of [{(C5Me5)TiF3}2] revealed at 202 K one monomeric, two dimeric (with C2h and Cs
symmetry), two tetrameric (with D2 and C2v symmetry), and two trimeric (both C2 symmetry) molecules. With the
increase in temperature and dilution of the solution, the composition of the solution shifts to the smaller molecules.
The thermodynamic and activation parameters for the reversible dissociation of dimers to monomers in the solution
are ΔH = 9.2 kcal mol-1, ΔS = 24.2 cal mol-1 K-1, ΔH‡ = 12.2 kcal mol-1, ΔS‡ = 9.7 cal mol-1 K-1. The
dissociation path with a weakly double-bridged transition-state dimer was proposed. The thermodynamic parameters
for the reversible dissociation of the C2v tetramer to the dimers in solution are ΔH = 7.9 kcal mol-1 and ΔS =
26.8 cal mol-1 K-1. From both tetramers, the D2 molecule is 0.34(5) kcal mol-1 lower in enthalpy and 6.5(5) cal
mol-1 K-1 lower in entropy than the C2v molecule. The structures of both trimers were proposed. The low-temperature
19F NMR spectra of the CDCl3 solution of [{(C5Me5)TiF3}2] are consistent with equilibria of a monomer, two dimers
(with C2h and Cs symmetry), and a trimer. The vapor pressure osmometric molecular mass determination of CDCl3
solution of [{(C5Me5)TiF3}2] at 302 K is consistent with the equilibrium of the dimer and the monomer.