Aluminum stable complex formation with

The fluoride ion chemisorbs on clays and oxides by ligand exchange of surface OH", a reaction favored at low pH and on oxide and silicate minerals of low crystallinity. Fluoride, a hard base, has a particular affinity for a hard acid. Soluble AP -fluoride cationic and anionic complexes are quite stable, and can dominate the speciation of dissolved aluminum in low-humus soils. The mobility of A1 can be increased by the presence of F soluble complex formation with A1 may explain the rather high solubility and mobility of F in acid soils. 

The experimental evidence which has accumulated in recent years shows that in every system which has been rigorously investigated the polymerization of olefins by metal halides depends upon the presence of some third substance, the co-catalyst [2-8]. The function of the cocatalyst is to provide the ions which start the polymerization proper, by forming an ionogenic complex with the metal halide. In most systems the metal halide is not consumed in the course of the reaction, so that the term catalyst in its classical sense may be retained in this respect. Exceptions to this are some polymerizations involving aluminum halides in the polymerization of propene [9], and possibly of styrene and a-methyl styrene [10], these catalysts may be inactivated by the formation of stable complexes. In other cases, such as the... 

Complex formation between olefins and Lewis acids has been demonstrated in a number of cases, e.g., isobutene and titanium tetrachloride (66), butene-2 and boron trifluoride (67—69), propylene and aluminum bromide (70), stflbene and various Lewis acids (71), styrene and stannic chloride (72), and in similar systems (73). Monomer-catalyst Ji-complex formation occurs during the polymerization of styrene or a-methyl styrene with chloroacetic acids (74,75). All these complexes are usually very weak and only stable at low temperatures. Evans contends (76) that isobutene and boron trifluoride do not interact because no polymerization occurs in the absence of moisture and therefore he postulates that BF3 HaO is the primary species. This does not rule out the possibility of a weak interaction between isobutene and the Lewis acid. Indeed, Nakana et al. (77) found direct evidence for the existence of boron trifluoride-propene complexes at low temperatures. 

Examination of electronic and thermodynamic factors in the aforementioned conventional enolate formation revealed that steric factors were of fundamental importance in fhe reaction. One alternative is to complex a carbonyl compound with a bulky Lewis acid (Fig. 6.13). Bulky aluminum reagents usually form relatively stable 1 1 complexes irreversibly wifh carbonyl compounds. We first hypothesized that even in the presence of a strong base (LDA or LTMP), a steric environment applied in the aluminum-carbonyl complex would kinetically adjust site-selective deprotonation of carbonyl compounds which offer multiple sites for enohzation and kinetically stabilize fhe resulting bulky enolates by retarding the rate of proton transfer or other undesirable side reactions. These fundamental considerations found particular application in fhe formation and reaction of novel aluminum enolates. 

Alkali alkyls or alcoholates and trialkyl alanes form only 1 1 complexes and no stable 2 1 compounds. On the other hand, various reactions indicate the formation of at least labile 2 1 complexes between triethylalane and sodium phenolate (156, 232). The relationships become relatively complicated in mixtures with three different components, e.g., in the system alkali fluoride or hydride-triethylalane-diethylalane, in which up to 4 moles of aluminum compounds may combine with 1 mole of the alkali salt (158). 

Masking can be achieved by precipitation, complex formation, oxidation-reduction, and kinetically. A combination of these techniques may be employed. For example, Cu " can be masked by reduction to Cu(I) with ascorbic acid and by complexation with I . Lead can be precipitated with sulfate when bismuth is to be titrated. Most masking is accomplished by selectively forming a stable, soluble complex. Hydroxide ion complexes aluminum ion [Al(OH)4 or AlOa"] so calcium can be titrated. Fluoride masks Sn(IV) in the titration of Sn(II). Ammonia complexes copper so it cannot be titrated with EDTA using murexide indicator. Metals can be titrated in the presence of Cr(III) because its EDTA chelate, although very stable, forms only slowly. 

Because organoboranes and organoalanes form relatively stable intermediate complexes with various substrates as a prelude to final product formation, it seems permissible to try to extend the scope of the Woodward-Hoffmann principle to the reorganization pathways of such complexes. Thus, it would be useful, for example, to consider whether the chemical behavior of an allylic aluminum system complexed with a ketone (3) might resemble the thermally allowed [3, 3] sigmatropic rearrangement (4). The value of viewing the collapse of such complexes as potential pericyclic processes will become evident in Section IV,C, where the interplay of kinetic versus thermodynamic control on ketone insertions into carbon-metal bonds is discussed. 

The dimeric dicyclopentadienyl methyl yttrium complex reacts readily with methyl aluminum dichloride with loss of the methyl group and formation of a stable di- u-chloro-bridged dicyclopentadienyl yttrium dimethyl aluminum complex (Holton et al., 1979c), and dicyclopentadienyl yttrium chloride reacts with aluminum hydride in ether with formation of a white crystalline 2 1 1 complex, of which the X-ray structure was determined (Lobkovskii et al., 1982) ... 

The hydrolysis of the aluminum salt may be masked by the addition of neutral substances which form complexes. For example, the aluminum ion can be replaced by alkali ions and it can then take a place in compounds whose reaction is neutral. The acid or alkaline reaction of the masked solution will then reveal the presence of free acids or basic aluminum salts, since the exchange involves the disappearance of only the aluminum ion and not the hydrogen or hydroxyl ions. Alkali oxalates are excellent complex formers with aluminum salts. If sodium oxalate is added to solutions of aluminum salts there is an immediate formation of the sodium salt of aluminum oxalic acid, in which the aluminum is a constituent of a stable complex anion ... 

Whereas sulfolane is relatively stable to about 220°C, above that temperature it starts to break down, presumably to sulfur dioxide and a polymeric material. Sulfolane, also stable in the presence of various chemical substances as shown in Table 2 (2), is relatively inert except toward sulfur and aluminum chloride. Despite this relative chemical inertness, sulfolane does undergo certain reactions, for example, halogenations, ting cleavage by alkah metals, ring additions catalyzed by alkah metals, reaction with Grignard reagents, and formation of weak chemical complexes. 

The process involves reacting butenes and mixtures of propenes and butenes with either a phosphoric acid type catalyst (UOP Process) or a nickel complex-alkyl aluminum type catalyst (IFP Dimersol Process) to produce primarily hexene, heptene, and octene olefins. The reaction first proceeds through the formation of a carbocation which then combines with an olefin to form a new carbocation species. The acid proton donated to the olefin initially is then released and the new olefin forms. Hydrotreatment of the newly formed olefin species results in stable, high-octane blending components. 

Its molecular structure (Figure 37) consists of a centrosymmetric dimer with a bridging H2Al(OR)( U-OR)2Al(OR)H2 entity. The Ta atoms are approximately square pyramidal, with the four phosphorus atoms forming the basal plane (Ta lies 0.64 A out of it). The relatively short Ta—A1 distances are comparable to those found in other transition metal aluminum complexes (Ta—Al 2.79-3.13 A). The hydrogen atoms have not been located, but were evidenced by chemical and spectroscopic techniques (IR 1605, 1540 cm 1 HNMR 16.30p.p.m.). The Ta—(ju-H2)A1 unit is relatively stable, and (54) is inert to carbon monoxide or trimethylamine. It is a poor catalyst in the isomerization of 1-pentene. Formation of complexes analogous to (54) may explain the low yields often obtained from alkoxoaluminohy-drides and metal halides. 

Another simple oligomerization is the dimerization of propylene. Because of the formation of a relatively less stable branched alkylaluminum intermediate, displacement reaction is more efficient than in the case of ethylene, resulting in almost exclusive formation of dimers. All possible C6 alkene isomers are formed with 2-methyl-1-pentene as the main product and only minor amounts of hexenes. Dimerization at lower temperature can be achieved with a number of transition-metal complexes, although selectivity to 2-methyl-1-pentene is lower. Nickel complexes, for example, when applied with aluminum alkyls and a Lewis acid (usually EtAlCl2), form catalysts that are active at slightly above room temperature. Selectivity can be affected by catalyst composition addition of phosphine ligands brings about an increase in the yield of 2,3-dimethylbutenes (mainly 2,3-dimethyl-1-butene). 

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