Titanium trifluoride, structure

The pharmaceutical interest in the tricyclic structure of dibenz[6,/]oxepins with various side chains in position 10(11) stimulated a search for a convenient method for the introduction of functional groups into this position. It has been shown that nucleophilic attack at the carbonyl group in the 10-position of the dibenzoxepin structure renders the system susceptible to water elimination. Formally, the hydroxy group in the enol form is replaced by nucleophiles such as amines or thiols. The Lewis acids boron trifluoride-diethyl ether complex and titanium(IV) chloride have been used as catalysts. 

In contrast with the difluorides, the distribution of trifluorides extends to the third series of the transition metals, where iridium and gold trifluorides are fully characterized. In the second series, trifluorides are known for the elements from niobium to rhodium, with the exception of technetium, and in the first series, from titanium to cobalt. All the trifluorides have been characterized structurally, with earlier reports based on X-ray powder-diffraction data, since the compounds were not prepared in single-crystal form until more recently, when high-temperature, crystal-growth techniques became available. 

Although the number of tetrafluorides reported is as large as the number of di- and trifluorides (see Table III), this group of compounds is the least well characterized structurally of the transition metal fluorides. The synthesis of most of the expected tetrafluorides has been reported, with examples from titanium to manganese in the first, from zirconium to palladium (except for technetium) in the second, and from hafnium to platinum (except for tantalum) in the third series. Many of them have been little studied and, in general, they have not proved amenable to crystallographic structural analysis. 

Just about the same time Japanese workers (107) polymerized this dialdehyde with boron trifluoride etherate, p-toluene sulfonic acid, and titanium tetrachloride as well as with aluminum triethyl-water catalyst systems. Completely insoluble products were obtained with the cationic catalysts, whereas partially soluble materials were isolated with the latter initiator. On the basis of infrared evidence, the above structure was assigned to the soluble product. In spite of the fact that ether linkages were found by infrared analysis in the cationic product, the authors concluded that its structure was different from that of the soluble polymer obtained with organometallic catalyst. The structure of the soluble fraction was assumed to be ... 

In contrast to the low yield when hydrogen chloride is employed, an 88% yield of 2,4,6-triphenyl- 1,3,5-triazine (7) is obtained when chlorosulfonic acid is used as catalyst in a molecular ratio of 3 1 (CiSOjH/PhCN) at 0-5 C C and a reaction time of 12 to 24 hours.174 Trifluo-romethanesulfonic acid as a catalyst and solvent trimerizes benzonitrile at 91 °C in a yield of 66%.175 Lewis acids alone, such as aluminum, zinc, iron or titanium chlorides, phosphorus pentachloride, and boron trifluoride, have a considerably lower catalytic activity than the corresponding mixtures of Lewis acid with various promotors, such as mineral acids, organic acids and water. These differences are attributed to a change in the structure of the active complexes with the aryl cyanides. 

Addition compounds of 1,3,5-triazine with several Lewis acids can also be formed in which one or two molecules of the Lewis acid are bound to one molecule of 1,3,5-triazine. The structures of the obtained adducts 4 depend on the nature of the metal cation examples of Lewis acids that can be used in this reaction are aluminum trichloride, titanium(IV) chloride, tin(IV) chloride and antimony(V) chloride.26 In inert solvents, boron trifluoride and 1,3,5-triazine produce a stable adduct with the appearance of fine needles.28... 

The trihalides of titanium can be prepared by reducing the tetrahalides with the metal. With the exception of the trifluoride, which has a magnetic moment of 1.75 BM, as expected for a d ion, all the trihalides have low magnetic moments, indicative of metal-metal interaction. The structures consist of halogen-bridged polymers containing six-coordinate titanium. 

In Section 12.7.B, the Stille coupling reaction reacted a vinyl tin compound with a vinyl triflate, in the presence of palladium(O). Tetravalent tin complexes add to aldehydes and ketones, in the presence of a Lewis acid. Allyltin complexes are, by far, the most widely used of these compounds.297 a typical example is taken from the work of Keck, in which a chiral aldehyde (455) was treated with allyltributyltin, in the presence of various Lewis acids. S As shown in Table 12.19, a mixture of syn (456) and anti (457) products was obtained. The ratio of 456/457 was dependent on the structure of the R group in 455, the solvent and the Lewis acid.The anti product (457) was obtained by using the tert-butyldimethylsilyloxy derivative (sec. 7.3.A.i) of 455 with 2 equivalents of boron trifluoride in dichloromethane. The syn product is obtained preferentially when the benzyloxy derivative of 455 is used with titanium tetrachloride in dichloromethane.298... 

The cationic polymerization of 1,3-dimethylcyclopentadiene can be initiated by boron trifluoride/diethyl ether/tin(IV) chloride, titanium(IV) chloride, and triethylalumi-num/titanium(IV) chloride [410]. The poly (1,3-dimethylcyclopentadienes) that are obtained at — 78 °C are easily soluble with identical portions of 1,4 and 1,2 structures [411]. Under the same conditions, 1-methyl- and 2-methylcyclopentadienes are polymerized to powdery polymers [412]. The same applies to ally Icy clopentadiene and allylmethylcyclopentadiene. The polymerization proceeds exclusively via the C-C double bond in the cyclopentadiene ring with increasing portions of 1,4-structures in the polymers for monomers with growing steric hindrance. 

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