Reactions with cationic metal complexes

Iron hahdes react with haHde salts to afford anionic haHde complexes. Because kon(III) is a hard acid, the complexes that it forms are most stable with F and decrease ki both coordination number and stabiHty with heavier haHdes. No stable F complexes are known. [FeF (H20)] is the predominant kon fluoride species ki aqueous solution. The [FeF ] ion can be prepared ki fused salts. Whereas six-coordinate [FeCy is known, four-coordinate complexes are favored for chloride. Salts of tetrahedral [FeCfy] can be isolated if large cations such as tetraphenfyarsonium or tetra alkylammonium are used. [FeBrJ is known but is thermally unstable and disproportionates to kon(II) and bromine. Complex anions of kon(II) hahdes are less common. [FeCfy] has been obtained from FeCfy by reaction with alkaH metal chlorides ki the melt or with tetraethyl ammonium chloride ki deoxygenated ethanol. 

To simplify the following discussion EDTA is assigned the formula H4Y the disodium salt is therefore Na2H2Y and affords the complex-forming ion H2 Y2 in aqueous solution it reacts with all metals in a 1 1 ratio. The reactions with cations, e.g. M2+, may be written as ... 

Then, contrary to what was reported previously, the olefin dissociates from the zirconium metal complex. This conclusion was further supported by other experimental observations. However, it cannot be completely excluded that competition between dissociative and direct rearrangement pathways could occur with the different isomerization processes studied up to now. Note that with cationic zirconocene complexes [Cp2Zr-alkyl], DFT studies suggest that Zr-alkyl isomerizations occur by the classical reaction route, i.e. 3-H transfer, olefin rotation, and reinsertion into the Zr-H bond the olefin ligand appears to remain coordinated to the Zr metal center [89]. 

These examples serve to illustrate several general points about use of chiral catalysts for D-A reactions. A cationic metal center is present in nearly all of the catalysts developed to date and has several functions. It is the anchor for the chiral ligands and also serves as a Lewis acid with respect to the dienophile. The chiral ligands establish the facial selectivity of the complexed dienophile. There are several indications of the importance of the anions to catalytic activity. Anions, in general,... 

John G. R., Kane-Maguire, L. A. P., and Eabom, C., Chem. Commun. 481 (1975) (Elimination of SiMe3 groups in the reaction of cationic metal-7r-enyl complexes with aryltrimethylsilanes). 

Recently the unprecedented example of stereoselective C—Si bond activation in cu-silyl-substituted alkane nitriles by bare CQ+ cations has been reported by Hornung and coworkers72b. Very little is known of the gas-phase reactions of anionic metal complexes with silanes. In fact there seems to be only one such study which has been carried out by McDonald and coworkers73. In this work the reaction of the metal-carbonyl anions Fe(CO) (n = 2, 3) and Mn(CO) (n = 3, 4) with trimethylsilane and SiH have been examined. The reactions of Fe(CO)3 and Mn(CO)4 anions exclusively formed the corresponding adduct ions via an oxidative insertion into the Si—H bonds of the silanes. The 13- and 14-electron ions Fc(CO)2 and Mn(CO)3 were observed to form dehydrogenation products (CO) M(jj2 — CH2 = SiMe2) besides simple adduct formation with trimethylsilane. The reaction of these metal carbonyl anions with SiFLj afforded the dehydrogenation products (CO)2Fe(H)(SiII) and (CO)3Mn(II)(SiII). ... 

A large variety of organometallic compounds, e.g., metal alkoxides and metal carboxylates, has been studied as initiators or catalysts in order to achieve effective polymer synthesis [35]. Many reactions catalyzed by metal complexes are highly specific and, by careful selection of metal and ligands, reactions can be generated to form a desired polymer structure [36, 37]. The covalent metal alkoxides with freep or d orbitals react as coordination initiators and not as anionic or cationic inititors [38]. Fig. 1 summarizes some of the most frequently used initiators and catalysts. 

The reaction of the transition-metal fragments with main group 15 elements directly has proven a very fruitful field for exploration. The methodology has been successful for a wide range of metal complexes. These fall generally into three basic types (1) reactions with cyclopentadienyl metal carbonyls, (2) reactions with homoleptic metal carbonyls and substituted derivatives, and (3) reactions with metal cations in the presence of a multi-dentate chelating ligand. 

Reactions of cationic carbonyl complexes with alcohols are less common than with amines ( 5.8.2.12.4). They occur only with the most reactive carbonyl complexes with high C—O force constants this is because alcohols are poorer nucleophiles and also less basic than amines. Metal carbonyls react with alkoxide ions. See Table 1 for complexes of the Mn, Fe and Co subgroups ". ... 

Some attempts have been made to use a cationic metal complex intercalate as a catalyst these efforts are briefly reviewed in an account of the catalyst type (b) in Fig. 1. The results advocate the possibility of the immobilization of catalyst solution in the interlayer spaces. The catalytic activity of Cu -TSM or Cu Pd -TSM swelled with water or an organic solvent for the reaction involving molecular oxygen is introduced in the following section. 

Silver(I) compounds are often used to generate cationic metal complexes from the corresponding metal halides. Suzuki and coworkers found that -hexylzirconocene chloride (61), derived from 1-hexene and Schwartz reagent 60, can react with aldehydes in the presence of a catalytic amount of AgAsFs to give secondary alcohols [27]. The reaction with hydrocinnamaldehyde, for example, provides the alcohol 62 in 95 % yield (Sch. 14). Allylic alcohols are also obtainable by a similar procedure using 1-hexyne as a starting material. 

Compared to manganese, little work has been carried out on analogous alkyl complexes of rhenium, although that which has may be divided into the same categories, namely, (1) reaction with transition metal hydrides, for example [CpW(H)(CO>3] (2) reaction with Lewis acids, for example, AlCUEt (3) orthometallation reactions (4) reaction with cationic species, for example, (5) reaction with anionic nucleophiles, for example, BF4" (6) reaction with neutral nucleophiles, for example, PPh3-... 

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