Metal halides, donor-acceptor complexes

In Friedel-Crafts acylation of aromatics with acid chlorides and Lewis acid metal halides the reactive electrophile is considered to be formed in the interaction of the reagent and the catalyst. First the highly polarized donor-acceptor complex 1 is formed, which can further give other complexes and ion pairs.24 The various... 

A considerable amount of research has been concerned with the nature of the electrophiles that are involved in Friedel-Crafts acylation reactions. We will summarize the main points. Acyl halides and carboxylic acid anhydrides have been known, for many years, to form stable complexes with a variety of acid catalysts. A well-defined product is formed between acetyl fluoride and boron trifluoride at low temperatures. Analytical and conductivity data characterized the material as acetylium tetrafluoroborate, and this was further confirmed by IR measurements. In the system acetyl chloride-aluminum chloride the acetylium ion can be differentiated from the donor-acceptor complex involving the carbonyl group by means of their IR carbonyl stetching frequencies. A number of other acyl fluorides have been shown to form well-defined acylium salts by interaction with a number of metal fluorides. Acylium salts can also be prepared from acyl chlorides by means of metathetical reactions involving anhydrous salts such as silver hexafluoroantimonate. As well as characterization by means of IR spectroscopy, acylium salts have been studied in non-nucleophilic solvents by NMR spectroscopy. The NMR data for the ben-... 

The positive modifiers are exemplified by Higashimura s system of monomer + HX (equivalent to HMX) + ZnX2, where the C-X bond of the ester (organic halide) is activated by the metal halide. The transition state (II) for this reaction has been given above. Evidently, the active species PnX.ZnX2 is a reversibly formed donor (PnX) - acceptor (ZnX2) complex. 

The lanthanide phthalocyanine complexes, obtained by conventional methods starting from metal salts at 170-290°C and phthalonitrile (Example 26), contain one or two macrocycles for each metal atom [5,6,8,63,82,84-98]. Thus, according to Refs. 6,63, and 85, the complexes having compositions LnPc2H, XLnPc (X- is halide anion), and Ln2Pc3 (a super-complex ) were prepared from phthalonitrile as a precursor the ratio of the reaction products depends on the synthesis conditions and the metal nature. The ionic structure Nd(Pc)+Nd(Pc)2 was suggested [85] and refuted [63] for the neodymium super-complex Nd2Pc3 the covalent character of the donor-acceptor bonds in this compound and other lanthanide triple-decker phthalocyanines was proved by the study of dissociation conditions of these compounds [63]. 

Donor-Acceptor Molecular Complexes in Alternating Copolymerization and in the Polymerization of Metal Halide-Complexed Vinyl Monomers... 

Organic nitriles, in particular acetonitrile, form stable electron-donor-acceptor (EDA) complexes with a number of Lewis acids such as BX3(X = Cl, Br, 1), SnC, AICI3, and with many transition metal halides, the nitrile group acting as the electron donor ... 

A complex in general is any species formed by specific association of molecules or ions by donor-acceptor interactions (see Topic C9). In aqueous solution the most important complexes are those formed between a metal cation and ligands, which may be ions (e.g. halides, cyanide, oxalate) or neutral molecules (e.g. ammonia, pyridine). The ligand acts as a donor and replaces one or more water molecules from the primary solvation sphere, and thus a complex is distinct from an ion pair, which forms through purely electrostatic interactions in solvents of low polarity (see Topic El). Although complex formation is especially characteristic of transition metal ions it is by no means confined to them. 

The copolymerization of a donor monomer with a weaker acceptor monomer, such as methyl methacrylate or acrylonitrile, in the presence of a complexing agent (a metal halide or an organoaluminum halide) yields an equimolar, alternating copolymer, regardless of initial monomer charge and with or without free-radical precursor (1). 

Processes taking place in ionic melt-solvents are considerably affected by impurities contained in the initial components of the melt or formed during preparation (mainly, melting) of solvents due to the high-temperature hydrolysis of melts or their interactions with container materials (AI2O3, SiOj, etc.) or active components of atmosphere (O2, CO2, etc.). The list of these impurities is wide enough and includes multivalent cations of transition metals, different complex anions (0x0- or halide anions). The effect of the mentioned admixtures on the processes in ionic melts depends mainly on the degree of their donor-acceptor interactions with constituent parts of the melt. 

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