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Adducts of titanium tetrahalides with neutral Lewis bases. Part I. Structure and stability: a vibrational and multinuclear NMR study

1987; Elsevier BV; Volume: 134; Issue: 1 Linguagem: Inglês

10.1016/s0020-1693(00)84458-8

1873-3255

Eric Turin, Roger M. Nielson, André E. Merbach,

Organometallic Complex Synthesis and Catalysis

Raman, infra-red and multinuclear NMR spectroscopy were used to establish the structure of several TiX4·2L adducts (X=F, Cl, Br; L=Lewis base) in inert solvents. In contrast to the analogous SnX4·2L adducts where a cis-trans equilibrium prevails, most of the TiX4·2L adducts studied were found to have only the cis configuration. Trans isomers were observed but their formation was dependent on the donor ability of the ligand. In dichloromethane solution, the adducts with L=Me2O, Me2S, (MeOCH2-)2, Et2S, THT, Me2Se, MeCN, Me2CO, Cl(MeO)2PO, Cl2(MeO)PO, Cl3PO and Cl2(Me2N)PO were found to have the cis configuration only. For the adducts with L=THF, Cl(Me2N)2PO and TMPA, a cis-trans equilibrium was observed. The thermodynamic parameters were measured for cis-trans isomerization for TiCl4·2TMPA in CHCl3; these parameters are: Kiso277=[trans] / [cis]=0.36, ΔH°iso=− 1.3 ± 1.3 kJ/mol, ΔS°iso=−13.1 + 7.5 J/mol K, and ΔV°iso= − 1.3+0.8 cm3/mol. A complex equilibrium involving cis and trans isomers and the ionic complex [TiCl3·3HMPA]Cl was found to occur for the TiCl4 adduct with L=HMPA. 1H NMR was used to establish the relative stabilities of the cis adducts and the following sequence was obtained: Me2O ∼ MeCN < Me2CO < Me2S < Me2Se < Cl(MeO)2PO < TMPA < CI(Me2N)2PO.