Metal unsymmetrical

For alkylation of phosphines containing C-H bonds their alkali salts are usually treated with alkyl halides. Thus primary and secondary phosphines can be obtained by metalation of phosphine itself with sodium in liquid ammonia and subsequent alkylation 208 phosphirane, which is unstable, is also prepared in this way, from sodium phosphide and ethylene dichloride.209 High yields of primary phosphines are afforded by alkylating lithium phosphide, which is formed almost quantitatively by metalating phosphine with butyl-lithium.210 Since the hydrogen can be replaced stepwise by metal, unsymmetrical secondary and tertiary phosphines can be built up from PH3 or a primary phosphine.211 Use of alkali phosphides is not limited to alkylation potassium diphenylphosphide reacts quantitatively with iodobenzene, yielding triphenyl-phosphine.212... 

Lithium metal in tetrahydrofuran can also be used as the coupling reagent, and unsymmetrical ditins can be prepared when the reaction is conducted in stages (162,163). 

Of these dyes, Acid Yellow 151 (37) still has the greatest market among the yellows. As reported by USITC, production had increased to 1989 tons in 1985 from 706 tons in 1975. It is produced by coupling diazotized 2-amino-l-phenol-4-sulfonamide to acetoacetanilide followed by metallizing with cobalt to obtain a 1 2 cobalt complex. Acid Orange 24 (38), which is sulfanilic acid coupled to resorcinol to which diazotized mixed xyUdines have been coupled, is an unsymmetrical primary diasazo dye with a bihinctional coupling component. 

Unsymmetrical cleavage of B2H by metal hydrides gives metal tetrahydroborate salts, also called metal borohydrides or hydroborates. 

Several methods for the preparation of unsymmetrical sulfur diimides RN=S=NR have been developed. One approach involves the addition of a catalytic amount of an alkali metal to a mixture of two symmetrical sulfur diimides, RN=S=NR and RT8i=S=NR. A second method makes use of alkali-metal derivatives of [RNSN] anions.Eor example, derivatives in which one of the substituents is a fluoroheteroaryl group can be prepared by the reaction of the anionic nucleophile [RN=S=N] with pentafluoropyridine. Sulfur diimides of the type RN=S=NH (R = 2,4,6- Bu3C6H2S) have also been prepared. "... 

When a mixture of alkenes 1 and 2 or an unsymmetrically substituted alkene 3 is treated with an appropriate transition-metal catalyst, a mixture of products (including fi/Z-isomers) from apparent interchange of alkylidene moieties is obtained by a process called alkene metathesis. With the development of new catalysts in recent years, alkene metathesis has become a useful synthetic method. Special synthetic applications are, for example, ring-closing metathesis (RCM) and ring-opening metathesis polymerization (ROM) (see below). 

The synthetic applicability is rather limited, due to the various side-reactions observed, such as eliminations and rearrangement reactions. The attempted coupling of two different alkyl halides in order to obtain an unsymmetrical hydrocarbon, usually gives the desired product in only low yield. However the coupling reaction of an aryl halide with an alkyl halide upon treatment with a metal (the Wurtz-Fittig reaction) often proceeds with high yield. The coupling of two aryl halides usually does not occur under those conditions (see however below ) since the aryl halides are less reactive. 

Random incorporation of two different acetoacetates can also be avoided by converting one of the acetoacetates to a derivative which carries the future pyridine nitrogen. For example, treatment of ethyl acetoacetate with ammonia gives the corresponding P-aminocrotonate 32. The aldehyde (34) required for preparation of such an unsymmetrical compound is prepared by reaction of the product from direct metallation of 33 with dimethylformamide. Condensation of that aldehyde with methyl acetoacetate and the p-aminocrotonate from isopropyl acetoacetate leads to isradipine (35) [9]. The same aldehyde with ethyl acetoacetate and the P-aminocrotonate from ethyl acetoacetate gives darodipine (36) [10]. In much the same vein, condensation of the ben-zaldehyde 37 with methyl acetoacetate and its P-aminocrotonate derivative affords riodipine (38) [11]. 

Ring enlargement from subphthalocyanines has been used to synthesize unsymmetrically substituted metal-free phthalocyanines of the AAAB type (see p 738). 

An unsymmetrically substituted tris(phthalocyanine) 3 has been prepared by the reaction of acetatolutetium(III) phthalocyanine dihydrate (2) with metal-free 2 3.9 10.16 17,23 24-tetra(15-crown-5)phthalocyanine (1). 

If two differently substituted alkali-metal phthalocyanines are used (in the same molar ratio), unsymmetrically substituted bis(phthalocyanines) can be obtained. 

Tin amidinates display a rich coordination chemistry with the metal in both the di- and tetravalent oxidation states. The first results in this area were mainly obtained with N-silylated benzamidinate ligands. Typical reactions are summarized in Scheme 48. A stannylene containing unsymmetrically substituted amidinate ligands, [o-MeC6H4C(NSiMe3)(NPh)]2Sn, has been prepared accordingly and isolated in the form of colorless crystals in 75% yield. ... 

Unsymmetrical as well as symmetrical anhydrides are often prepared by the treatment of an acyl halide with a carboxylic acid salt. The compound C0CI2 has been used as a catalyst. If a metallic salt is used, Na , K , or Ag are the most common cations, but more often pyridine or another tertiary amine is added to the free acid and the salt thus formed is treated with the acyl halide. Mixed formic anhydrides are prepared from sodium formate and an aryl halide, by use of a solid-phase copolymer of pyridine-l-oxide. Symmetrical anhydrides can be prepared by reaction of the acyl halide with aqueous NaOH or NaHCOa under phase-transfer conditions, or with sodium bicarbonate with ultrasound. 

The stoichiometric hydroamination of unsymmetrically disubstituted alkynes is highly regioselective, generating the azametaUacycle with the larger alkyne substituent a to the metal center [294, 295]. In others words, the enamine or imine formed results from an anti-Markovnikov addition. Unfortunately, this reaction could not be applied to less stericaUy hindered amines. 

Nb(Et2C c)4X is a 1 1 electrolyte in which the metal is probably eight-coordinated by sulfur atoms from four bidentate dithiocarbamate groups. Infrared data suggest that the ligands are unsymmetrically bonded. 

By judicious choice of reaction conditions an acyclic Ni11 complex (784) could be isolated, which serves as a valuable starting material for the preparation of unsymmetrical and mixed metal complexes by subsequent reaction with various amines. Also, a symmetrical Schiff base macrocycle of larger size has been obtained as a minor byproduct upon condensation of (784) with 1,3-diaminopropane. The resulting Ni11 complex (785) is again bimetallic, although room to bind four metal ions is in principle available.1367... 

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