Insertion reactions, of alkynes

The French group of Rudler has reported several insertion reactions of alkynes into a ja-alkylidene carbon tungsten bond (313, 314). 

Oligomerization of alkynes probably occurs by multiple insertions of acetylene into metal-carbon bonds. An insertion reaction of alkynes is shown as follows ... 

Insertion reaction of alkyne and zirconium-silene complexes 883, which are generated from disilylzirconocenes 882 prepared from the reaction of zirconocene dichloride with 2equiv. of Me2PhSiLi, affords... 

Insertion reactions of alkynes into palladium-element bonds is an important route to palladium(ii)-alkenyl complexes. Insertion of alkynes into palladium-boron bonds arising from oxidative addition of boron halides gives complexes 38 (Scheme 8). An X-ray structure was reported for = COeBu Alkenyl- and dienylpalladium(ii) compounds 39... 

A-Heterocycles were synthesized via insertion of 1,1-dimethylallene into Pd-G bonds of cyclopalladated a-tetralone ketimines. Insertion reactions of alkynes into the Pd-G bond of cyclopalladated ferrocenylimines have also been described.Biomimetic hydrolysis of benzoates has been carried out with a water-soluble cyclopalladated aryl oxime, which was proposed as a potential green catalyst. Ghiral cyclopalladated liquid crystals 88 were obtained from amino acids and could possibly serve as enantioselective catalysts. " Palladacycle 89 has been derived from an anthracene-based Schiff base. 

General procedure for insertion reaction of alkynes into 2,6-dia-zasemibullvalene 6-la. 2,6-Diazasemibullvalene 6-la (0.5 mmol, 136 mg) in 2 mL of toluene was treated with dimethyl acetylenedicarboxylate (1.0 mmol, 123 pi) or diethyl analogue (1.0 mmol, 160 pi), and the reaction mixmre was stirred at 90 °C for 3 h. After the removal of solvent in vacuum, purification by column chromatography (silica gel, petroleum ether/diethyl ether/triethylamine = 100 3 1) gave 6-7a or 6-7b as pure products. 

The classical synthetic methodologies for alkenyl complexes based on the nucleophilic additions to 7r-alkyne complexes and the insertion reactions of alkynes into [M]-H and [M]-R bonds have been employed to prepare a number of alkenyl, butadienyl, and analogous derivatives. Nevertheless, the chemistry of vinylidene and allenylidene complexes has disclosed new routes to alkenyl derivatives, most of them incorporating heterocyclic systems. 

Initial step is the formation of a dicobalthexacarbonyl-alkyne complex 5 by reaction of alkyne 1 with dicobaltoctacarbonyl 4 with concomitant loss of two molecules of CO. Complex 5 has been shown to be an intermediate by independent synthesis. It is likely that complex 5 coordinates to the alkene 2. Insertion of carbon monoxide then leads to formation of a cyclopentenone complex 6, which decomposes into dicobalthexacarbonyl and cyclopentenone 3 ... 

For the diboration reactions of alkynes catalyzed by Pt(0) complexes, the reaction mechanism involves the oxidative addition of diborane to the Pt(0) center, followed by the insertion of alkyne into the Pt-B bond and reductive... 

In most of the reactions of heteroatom-substituted carbene complexes with alkynes the first event is insertion of the alkyne into the carbon-metal double bond. If vinylcarbene complexes undergo insertion reactions with alkynes, (1,3-butadien-l-yl)carbene complexes result (Figure 2.27). 

Silylstannylation is also observed in the Pd(PPh3)4-catalyzed reaction of alkynes with disilanyl stannanes, in which both Si-Si and Si-Sn bonds are present. The alkynes undergo insertion into the Si-Sn bond, to regio-and stereoselectively yield (/8-disilanylalkenyl)stannanes [Eq. (25)].73 With terminal alkynes, the stannyl group adds regioselectively to the internal carbon atom. Aliphatic alkynes are not reactive in this system. 

A double insertion of carbon monoxide has been observed for the amine-induced reaction of alkynes with dodecacarbonyltriiron leading to cydobutenediones (Scheme 1.7) [28]. 

Several of the reactions described in Section 6.16.2.4.6.1 are two-step reactions. After the initial [2+1] addition of the silylene to the multiple bond, a second insertion reaction of a silylene into a reactive Si-X bond of the cyclopropane derivative takes place yielding four-membered ring compounds. Examples are the reactions with alkynes, nitriles, imines, and ketones. 

Insertion reactions of Os3H2(CO)10 have been used to give the clusters Os3H(/x,f/2-vinyl)(CO)10 from alkynes 150-153,160,161), and formamido... 

Dirhodium(II) tetrakis(carboxamides), constructed with chiral 2-pyrroli-done-5-carboxylate esters so that the two nitrogen donor atoms on each rhodium are in a cis arrangement, represent a new class of chiral catalysts with broad applicability to enantioselective metal carbene transformations. Enantiomeric excesses greater than 90% have been achieved in intramolecular cyclopropanation reactions of allyl diazoacetates. In intermolecular cyclopropanation reactions with monosubsti-tuted olefins, the cis-disubstituted cyclopropane is formed with a higher enantiomeric excess than the trans isomer, and for cyclopropenation of 1-alkynes extraordinary selectivity has been achieved. Carbon-hydro-gen insertion reactions of diazoacetate esters that result in substituted y-butyrolactones occur in high yield and with enantiomeric excess as high as 90% with the use of these catalysts. Their design affords stabilization of the intermediate metal carbene and orientation of the carbene substituents for selectivity enhancement. 

A mononuclear tantalum-benzyne complex (121) has been prepared by thermolysis of 120 [Eq. (20)].14 An X-ray crystal structure was reported for 121. Bond lengths for the benzyne unit are given in Table III. Complex 121 exhibits a rich insertion chemistry similar to that of Ti, Zr, and Ru benzyne complexes. Insertion reactions of 121 with ethylene, 2-butyne, acetonitrile, and carbon dioxide give 122, 123, 124, and 125, respectively (Scheme 15). Diphenylacetylene does not couple with 121, presumably because of steric constraints. Reagents with acidic protons such as methanol or terminal alkynes cleave the Ta—C bond to give butyl isocyanide and carbon monoxide, but... 

Insertion and condensation reactions of alkynes have been well known for many years (1,191). Alkyne dimerization to form either cyclobutadiene (192) or metallocyclopentadiene products (193), trimerization to arenes (194), condensation of two alkynes and carbon monoxide to cyclo-pentadienones (195), and condensation of alkyne and isonitriles to cyclo-pentadienimines (196) are common reactions. This section surveys alkyne insertion products originating from monomeric Mo(II) and W(II) reagents. 

The insertion reactions of CO, alkenes, and alkynes are particularly important. An early example (Berthelot, 1869) is ... 

Dirhodium(ll) tetrakis[methyl 2-pyrrolidone-5(R)-oarboxylate], Rh2(5R-MEPV)4, and its enantiomer, Rh2(5S-MEPY)4, which is prepared by the same procedure, are highly enantioselective catalysts for intramolecular cyclopropanation of allylic diazoacetates (65->94% ee) and homoallylic diazoacetates (71-90% ee),7 8 intermolecular carbon-hydrogen insertion reactions of 2-alkoxyethyl diazoacetates (57-91% ee)9 and N-alkyl-N-(tert-butyl)diazoacetamides (58-73% ee),10 Intermolecular cyclopropenation ot alkynes with ethyl diazoacetate (54-69% ee) or menthyl diazoacetates (77-98% diastereomeric excess, de),11 and intermolecular cyclopropanation of alkenes with menthyl diazoacetate (60-91% de for the cis isomer, 47-65% de for the trans isomer).12 Their use in <1.0 mol % in dichloromethane solvent effects complete reaction of the diazo ester and provides the carbenoid product in 43-88% yield. The same general method used for the preparation of Rh2(5R-MEPY)4 was employed for the synthesis of their isopropyl7 and neopentyl9 ester analogs. 

Sulfur dioxide reacts generally with transition metal alkyl, aryl, and a-allyl complexes to give sulfinate complexes. The reaction, first described in 1964 by Wojcicki and Bibler, resembles well-known insertion reactions of CO, C2F4, SnCl2, tetracyanoethy-lene, and other unsaturated species into metal-alkyl bonds, but there are important stereochemical and mechanistic differences Sulfur dioxide insertion into metal-alkene and metal-alkyne bonds have not been reported. However, PdCl2 has been used as a catalyst for copolymerization of ethylene and SO2 to polysulfones and insertion into a Pd-ethylene bond is a conceivable reaction step. 

The reactions of alkynes or alkenes with Ni-R bonds are important in organic synthesis, particularly when they involve metallacyclic precursors because these reactions lead to synthetically valuable poly- or heterocyclic derivatives. A crucial question in this context is the regioselectivity of the insertion reaction. To address this issue, a systematic study has been carried out on the insertion of various unsymmetrical alkynes into the Ni-C(sp ) bond of the nickellacycle (8) (Scheme 14) structural analysis of the fairly stable 7-membered ring Ni-aUcenyl products (9) indicates that the insertions are primarily governed by electronic factors. ... 

For metal-carbonyl reactions, CO insertion often accompanies alkyne insertions. A broad spectrum of reactivity is illustrated by the insertion reactions of CpCo(CO)2 ... 

Insertion reactions between alkynes and Ni(acac)(PPh3)(CH3) [e.g., reaction (b)] have been explored for a series of alkynes. Reactions were found to be first-order in alkyne and first-order in metal complexes. Rates of insertion follow the first order ... 

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