Titanium—iron bonds

Mercury-transition metal bonds have been described for all members of Groups V-VIII of the transition series except, apparently, technetium. They commonly involve a low oxidation state of the transition element and are particularly numerous for the chromium, iron and cobalt families.1 In addition, mercury-titanium bonded species have been postulated as unstable reaction intermediates.2... 

In order to overcome the poor electrophilicity ofimines, nitrones arc used as partners for reaction with iron acyl enolates 428. Benzaldehyde phenylnitrone (5) reacts rapidly with the aluminum-based enolate at —78 C to give a crude /J-hydroxyamino iron acyl 6 (68% yield). Treatment with aqueous titanium trichloride in tetrahydrofuran at room temperature causes a selective reduction of the N—O bond and affords the /1-amino iron acyl 7 with inverse configuration compared to the addition ofimines (99% yield d.r. 11 23). 

Bonding is used extensively on steel. The reaction occurs with a high hydrogen dilution of the BCI3 to prevent substrate attack. An iron boride is formed. 1 1 Not all metals, however, are suitable to bonding. For instance, the bonding of titanium by CVD in a chloride-based system is more difficult since the titanium substrate is highly susceptible to HCl attack and the rate of diffusion is low. 

Laser Hardening and Modification. Lasers are used to surface harden ductile steels and improve the toughness to a depth of 0.35 min or more. Lasers can also be used to bond solid or powder coatings to a surface. Typical coalings are nickel or titanium carbide on iron, and nickel, cobalt, manganese, and titanium carbide. TiC. on aluminum. I1 sc of lasers with other specialized coating methods is common. 

Diastereoselective epoxidation of an allylic alcohol. Epoxidation of either a cis-or Irons-allylic alcohol substituted in the y-position by an alkoxy function by either m-ehloroperbenzoic acid or r-butyl hydroperoxide/VO(acac), results mainly in the anti-cpoxide (9, 109). Epoxidation of the allylic alcohol 1 with m-chloroperbenzoic acid conforms to this pattern, but epoxidation with f-butylhydroperoxide and VO(acac)2 mediated by titanium (IV) isopropoxide favors formation of the jyn-epoxide by a (actor of 10 1. The methyl group attached to the double bond is necessary for this unusual syn-selectivity when it is lacking, epoxidation with f-butyl hydroperoxide/ Ti(l V) is anti-sclcctivc, but less so than epoxidation with the peracid.1... 

Crystal field theory is one of several chemical bonding models and one that is applicable solely to the transition metal and lanthanide elements. The theory, which utilizes thermodynamic data obtained from absorption bands in the visible and near-infrared regions of the electromagnetic spectrum, has met with widespread applications and successful interpretations of diverse physical and chemical properties of elements of the first transition series. These elements comprise scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel and copper. The position of the first transition series in the periodic table is shown in fig. 1.1. Transition elements constitute almost forty weight per cent, or eighteen atom per cent, of the Earth (Appendix 1) and occur in most minerals in the Crust, Mantle and Core. As a result, there are many aspects of transition metal geochemistry that are amenable to interpretation by crystal field theory. 

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