Group 4 metals Titanium Zirconium

The effect of the metals used was then examined (Table 5.4). When the group 4 metals, titanium, zirconium, and hafnium, were screened it was found that a chiral hafnium catalyst gave high yields and enantioselectivity in the model reaction of aldimine lb with 7a, while lower yields and enantiomeric excesses were obtained using a chiral titanium catalyst [17]. 

We first studied group 4 metals (titanium, zirconium and hafnium) supported on a silica dehydroxylated especially at 700 °C (Table 3.8). Following the laboratory-developed strategy, surface-species have been well-characterized by classical techniques (IR, solid-state NMR gas evolvement, reactivity, etc.). Catalysis results show that titanium is the most active even if its activity is far less than that of homogeneous catalysts. In addition, an important amount of metal was lost by lixiviation even if this phenomenon seemed to stop after a certain time. 

Hydrogen reduction has a major advantage in that the reaction generally takes place at lower temperature than the equivalent decomposition reaction. It is used extensively in the deposition of transition metals from their halides, particularly the metals of Groups Va, (vanadium, niobium, and tantalum) and Via (chromium, molybdenum, and tungsten). The halide reduction of Group IVa metals (titanium, zirconium, and hafnium) is more difficult because their halides are more stable. 

Most metals can be electrolytically deposited from water-free melts of the corresponding metal salts. It is well known that aluminum, lithium, sodium, magnesium, and potassium are mass produced by electrolytic deposition from melts. Industrial processes for the melt-electrolytic production of beryllium, rare earth metals, titanium, zirconium, and thorium are also already in use. Pertinent publications [74, 137, 163] describe the electrolytic deposition of chromium, silicon, and titanium from melts. Cyanidic melts are used for the deposition of thick layers of platinum group metals. It is with this technique that, for instance, adhesion of platinum layers on titanium materials is obtained. Reports concerning the deposition of electrolytic aluminum layers [17, 71-73, 94, 96, 102, 164, 179] and aluminum refinement from fused salts [161] have been published. For these processes, fused salt... 

This chapter is a review of the characteristics and properties of the interstitial carbides formed by the metals of Group IV titanium, zirconium, and hafiiium. The rationale for reviewing these compounds together in one chapter is their similarity in atomic bonding, composition, and crystallography as shown in Ch. 3 and summarized as follows ... 

This chapter is a review of the properties and general characteristics of the interstitial nitrides formed by the metals of Group IV (titanium, zirconium, and hafiiium) and Group V (vanadiiun, niobium, and tantalum). As mentioned in Ch. 10, these six nitrides are the only refiactory transition-metal nitrides. Th have similar properties and characteristics and, of the six, titanium nitride has the greatest importance from an application standpoint. 

For the purpose of the present chapter, the definition of metallocene catalysts is limited to the bis(cyclopentadienyl)-based complexes of the group 4 transition metals (titanium, zirconium, or hafnium). The focus is exclusively on group 4 metallocenes since they uniquely have demonstrated... 

This strategy has been found to be more efficient than using Gaussian functions and has now been used to extend the NDDO-based family of methods to the remaining main group elements [22], the AMI parameterisation of second row elements [39] and the transition metals titanium and zirconium [40] as well as our work extending the PM3 method to iron [26, 32],... 

Unlike zirconium, the group IV metal titanium does not form the hydrometalation product but rather a (r -C5Q)-complex. The first titanium-fullerene complex 1 was prepared by reaction of the bis(trimethylsilyl)-acetylene complex of titanocene with equimolar amounts of Cjq (Scheme 7.1). 

The group IV B elements titanium, zirconium, and hafnium exhibit the normal isotope effect. Most of the data for the titanium-hydrogen system have been obtained at elevated temperatures. However, extrapolation of the available data (II, 13,31) to room temperature indicates a normal effect for hydrogen and deuterium. The group VB metals vanadium, niobium, and tantalum, on the other hand, exhibit inverse isotope effects indeed, these are the only pure metals that exhibit the inverse effect near room temperature. Extensive data have been reported for these systems. The P-C-T data obtained by Wiswall and Reilly (32) for vanadium hydrogen and deuterium clearly show a greater stability for... 

The A2 structure is seen from Table 11-2 to be the preferred one for the alkali metals, barium, the fifth-group metals, and the sixth-group metals it is also observed as one aiiotropic form for titanium, zirconium, iron, and thallium. The factors determining the choice of the A2 structure by certain elements are not known. 

A somewhat surprising group of coordination compounds consists of the volatile heavy metal nitrates, such as those of copper, zinc, mercury, titanium, zirconium and hafnium. The structures of some of these, in the gaseous state, have been determined thus Cu(N03)2 contains two bidentate, almost planar, staggered nitrato groups. Some derivatives of metal nitrates have also been found to be volatile for example, Fe(N03)3 N204 and Al(N03)3 2MeCN.39... 

Metallocenes (Fig. 2) are sandwich structures, typically incorporating a transition metal such as titanium, zirconium, or hafnium in the center. The metal atom is linked to two aromatic rings with five carbon atoms and to two other groups—often chlorine or alkyl. The rings play a key role in the polymerization activity (23-27). Electrons associated with the rings influence the metal, modifying its propensity to attack carbon-carbon double bonds of the olefins. The activities of these metallocenes combined by aluminum alkyls, however, are too low to be of commercial interest. Activation with methylaluminoxane, however, causes them to become 10-100 times more active than Ziegler-Natta catalysts. 

The abundances of the elements of the titanium group were compared to those of the zinc group in Table 13-1. It will be recalled that unlike the zinc group metals, which are rare but easily isolated, the titanium group metals are abundant, but purified with difficulty. Note from the (very rough) figures given that titanium is 50 times as abundant as zinc, zirconium is 3000 times as abundant as cadmium, and hafnium 30 times as abundant as mercury. 

Recent Group IV chemistry has seen an upsurge in the number of amide derived species, and this has included fluoride derivatives. None of these compounds are of oxidation state -(-III or less, which are the subject of this review, but refer to titanium, zirconium or hafnium where the metal is the +IV state [1,9-12] and, consequently, not covered here. 

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