Preparation and Characterisation of the Dinuclear Dinitrogen Complex, Trichloro-p-d in it rogenbis( tet ra hydrof u ran)(chlorotet rakis[ d imethyl-(phenyl)phosphine]rhenium(r))chromium(~~~) [ ( PMe2Ph),CIReN2CrC13-(thf121 By
Titanium(IV) iV,W-dialkyldithiocarbamates of the type Ti(S2CNR2)"Cl4 ( = 2, 3, or 4; R = Me, z'-Pr, z'-Bu, or, when = 3, Et) have been prepared by reaction of titanium(IV) chloride with anhydrous sodium VV^-dialkyldithiocarbamates in refluxing dichloromethane (or benzene). Molecular weight, conductance, and infrared data demonstrate that these complexes are monomeric nonelectrolytes in which all of the dithiocarbamate ligands are bidentate. Therefore, the Ti(IV) atom may be assigned coordination numbers 6, 7, and 8 when = 2, 3, and 4, respectively. The C--N, C -S, and Ti-Cl stretching frequencies depend systematically on the coordination number. Coordination number 7 has been confirmed for Ti(S2CNMe2)3Cl by X-ray diffraction; the molecule has a pentagonal-bipyramidal structure with the chlorine atom in an axial position. Mass spectra of the monochloro compounds show that monomeric Ti(S2CNR2)3Cl species exist in the gas phase. A cis configuration is indicated for the six-coordinate Ti(S2CNR2)2Cl2 complexes by dipole moments of ~9 D (for R = z'-Pr or z'-Bu) in benzene solution. Variable-temperature proton nmr spectra of the Ti(S2CNR2)"Cl4_n complexes in dichloromethane (+40 to -90°) indicate that (1) metal-centered rearrangement is fast on the nmr time scale at temperatures above -90°and (2) there is hindered rotation about C-N single bonds in the diisopropyl derivatives. Activation parameters for exchange of isopropyl methyl groups between the two nonequivalent sites are essentially the same for all three Ti(S2CN-(z'-Pr),)"Cl4_n complexes ( = 2, 3, or 4): AH* = 9.4 kcal/mol; AS* = -12 eu; AG*(-26°) = 12.4 kcal/mol. A gear like rotation mechanism is proposed.
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