O- reagent

Alkyl tetracarbonyl rron(O) reagents in solution decompose more rapidly with increasing concentration and temperature, especially above 0°. Carbon monoxide must be added without delay to convert this intermediate to the more stable acyl iron compound. 

Direct homo-coupling of vinyl halides is a simple way of generating 1,3-dienes. This transformation can be achieved employing various transition metal catalysts such as nickel(O) reagent in the presence of phosphine ligand202 or a nickel(O) reagent in the presence of potassium iodide and thiourea (equation 116)203. 

Because anti/syn ratios in the product can be correlated to the E(0)/Z(0) ratio of the involved boron enolate mixture,10b initial experiments were aimed at the preparation of highly E(0)-enriched boron enolate. The E(0)/Z(0) ratio increases with the bulk of the alkanethiol moiety, whereas the formation of Z(O) enolates prevails with (S )-aryl thioates. (E/Z = 7 93 for benzenethiol and 5 95 for 2-naphthalene thiol esters). E(O) reagent can be formed almost exclusively by reaction of (5)-3,3-diethyl-3-pentyl propanethioate 64 with the chiral boron triflate. High reactivity toward aldehydes can be retained in spite of the apparent steric demand (Scheme 3-22).43... 

Reactions of the alkylidenecycloproparenes with rhodium(I) and platinum(O) reagents lead to metallacycles (Section VI.B.4). ... 

Nickel(O) reagents have been employed in the symmetrical coupling of aryl... 

Acetone Intended for Use as o Reagent shall comply with the requirements and undergo the tests described in Reagent Chemicals (1950),24-5(Ref 18)... 

The condensation of 49 with various Pt(0) reagents has also been demonstrated. The outcome of the reactions depends, to a large extent, on the form of the platinum(O) reagent used. Both /i-tj. t), and dinuclear... 

Cupferron (Baudisch s reagent for iron analysis). Dissolve 6 g of the ammonium salt of Af-hydroxy-Af-nitrosoaniline (cupferron) in 100 mL of H O. Reagent good for 1 week only and must be kept in the dark. 

D.1. Reactions with Nucleophiles. Previously, a jr-allylic palladium complex was generated by reaction of palladium reagents with allylic hydrocarbons prior to reaction with nucleophiles. In the catalytic version of this reaction, an allylic halide or an allylic acetate is used with a palladium(O) reagent. Why use a palladium complex when enolate alkylation is a well-known process (sec. 9.3.A) A typical enolate coupling reaction is the conversion of 2-methylcyclopentane-l,3-dione (373) to the enolate anion by reaction with NaOH, allowing reaction with allyl bromide. Under these conditions only 34% of 374 was obtained. When allyl acetate was used in place of allyl bromide in this reaction and tetra w(triphenylphosphino)palladium was used as a catalyst, a 94% yield of 374 was obtained.224 in this reaction, formation of the Jt-allyl palladium complex facilitated coupling with the nucleophilic enolate derived from 373, which exhibited poor reactivity in the normal enolate alkylation sequence. 

A nickel-catalyzed ene cyclization (sec. 11.13) has been reported that uses Ni(cod)2- The reaction proceeds by initial formation of a ac-allylnickel complex, which facilitates the intramolecular ene reaction with an allylic amine unit. l jt-Allylnickel complexes can be used in coupling reactions with both aryl and alkyl halides. Enolate anions react with nickel(O) reagents to form a complex that subsequently couples to aryl iodides. Semmelhack s final step in the synthesis of cephalotaxinone (446) treated 445 with Ni(cod)2 to... 

Oxidative addition into the transition-metal center is an important reaction in organometallic chemistry. The Cl-C bond in dichlorophosphaethene is sensitive to this oxidative addition. Thus, the Mes -substituted 2,2-dihalophosphaethene 2 was allowed to react with tetrakis(triethylphosphine)platinum(0) to afford the corresponding complex 14 to result in the formation of diplatinum complex 15 [27] (Scheme 9). Bis(trimethylsilyl)amino-substituted dichlorophosphaethene 16 was treated with a nickel(O) reagent to afford the corresponding nickel(II) complex 17 [28] (Scheme 10). Complex 14 displays a carbenoid reaction as mentioned in Sect. 4. 

The Yamamoto method of condensing dihalobenzenes 16 with nickel(O) (Scheme 9) has the advantage of experimental simplicity, but is limited to preparation of homopolymers and random copolymers, and requires stoichiometric amounts of expensive nickel(O) reagents. These can be generated in situ by the reduction of nickel(II) salts in the presence of suitable ligands. 

Synthesis of a-Imidostyrenes. a-Imidostyrenes, useful precursors to vinylamines can be synthesized by introducing an imido group to the a-position of styrenes with the diphenyl sulfoxide-Tf2 O reagent combination. Styrenes with a hydrogen atom at the a-position react with diphenyl(trifluoromethanesulfonyloxy)sulf-onuim triflate to form diphenylstyrylsuifonium triflates which, in turn are converted into the corresponding a-imidostyrenes on treatment with sodium or potassium salts of cyclic imides (eq 9). 

Similarly, the coupling reactions of allyl systems in intermolecular or intramolecular (cyclization) ways is also best performed with nickel(O) reagents (a Corey reaction) [2]. 

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