Evaluation of the donor role of octamethylcyclotetrasilazane

Abstract

NMes; and (MC14)20MT where M = Ti. The stereochemistry of these neutral complexes and the coordination of the metal centers have been assessed in the light of spectral, conductivity, and chemical evidence, and possible molecular structures are proposed. Lewis base participation of the tetrameric (Si-N) ring is seen to involve only two of the four available nitrogen centers in (M-N) bonding and this bidentate behavior is reconciled with the favored metal hexacoordination of these powerful Lewis acids. Hexamethylcyclotrisiiazane [Me2SiNH]3, abbreviated HMT, and titanium(IV) chloride give (TiCl4)2 HMT as a neutral six-coordinate complex, and the donor behavior (bidentate) of the trimeric silazane ring is similarly discussed.In an earlier investigation of the reactions between hexamethylcyclotrisiiazane (Me2SiNH)8, abbreviated HMT, and titanium(III) chloride or vanadium (III) chloride we showed that six-cooordinate adducts of the type MC13 HMT are formed in which all three of the skeletonal nitrogen atoms of the ligand are involved in metal-nitrogen bonding.1 Having established HMT as a nitrogen donor (terdentate), it seemed reasonable to suppose that its tetrameric analog octamethylcyclotetrasilazane (Me2SiNH)4, abbreviated OMT, would behave in similar fashion. Indeed, with a maximum of four nitrogen atoms formally available for coordination, this tetrameric ring clearly has intriguing potential as a multidentate ligand. The present investigation is essentially concerned with an evaluation of the exact donor role of OMT following a study of its reactions with titanium(IV) chloride, titanium(III) chloride, vanadium(III) chloride, and chromium(III) chloride. Experimental SectionMaterials. HMT and OMT were prepared by ammonolysis of dimethyldichlorosilane following the method of Osthoff and Kantor.2 Titanium(IV) chloride (Hopkin and Williams, Essex), titanium(III) chloride and vanadium(III) chloride (K and K Laboratories, Plainview, N. Y.), and chromium(III) chloride (Pfaltz and Bauer Inc., Flushing, N. Y.) were obtained as anhydrous materials and their respective adducts were prepared by standard procedures described in the literature; MC13 • 3THF where M = Ti,3 V,4 and Cr,5 MCl3-2NMe3 where M = Ti,6 V,7 and Cr.7 All solvents were stored over calcium hydride and phosphoric oxide and distilled in vacuo when required.Physical Measurements and Analyses. Infrared spectra (4000-200 cm-1) were recorded on a Perkin-Elmer 621 spectrometer with Nujol and fluorolube mulls held between Csl plates. Conductivity measurements were performed using a Wayne Kerr Universal B221 conductance bridge. The conductivity cell used was calibrated with standard aqueous KC1 solutions and readings were taken at 298.0 ± 0.1 °K on samples of approximately 10-4 M concentration in dichloromethane solution. Absorption spectra were recorded on a Cary 14 spectrophotometer with samples either as solutions in 1-cm

Substitution reactions of metallic complexes of .beta.,.beta.',.beta.''-triaminotriethylamine. X. Synthesis and characterization of chromium(III) complexes of .beta.,.beta.',.beta.''-triaminotriethylamine and kinetics of primary and secondary aquation of the dichloro(.beta.,.beta.'.beta.''-triaminotriethylamine)chromium(III) cation

“…Similarly, the rate was unchanged in nitric or hydrochloric acids. Excellent linear Arrhenius plots were obtained by standard methods over the temperature range [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] °C from the data in Table IV. The following activation parameters were calculated; AH* = 12.3 ± 0.49 kcal/mol; AS* = 23.0 ± 1.3 cal deg™1 mol™1.…”