Alkenyl complexes, reaction with

Terminal alkynes undergo the above-mentioned substitution reaction with aryl and alkenyl groups to form arylalkynes and enynes in the presence of Cul as described in Section 1.1.2.1. In addition, the insertion of terminal alkynes also takes place in the absence of Cul, and the alkenylpalladium complex 362 is formed as an intermediate, which cannot terminate by itself and must undergo further reactions such as alkene insertion or anion capture. These reactions of terminal alkynes are also treated in this section. 

Alkylideneaminocarbene complexes 76, which are aza analogs of alkenyl-carbene complexes, upon reaction with alkynes primarily give formal [3+2] cycloadducts analogous to the 1-aminocarbene complexes (Scheme 16) [74,75]. Aumann et al. proposed that this should be considered as a formal 1,3-dipo-... 

Wulff et al. examined the necessary reaction conditions for a,fi-unsaturated aminocarbene complexes to react in a benzannulation reaction [23]. The reaction of dimethylamino(alkenyl)carbene complexes 18 with terminal alkynes in non-coordinating and non-polar solvents afforded phenol products in acceptable yields (Scheme 12). 

Intermolecular hydroalkoxylation of 1,1- and 1,3-di-substituted, tri-substituted and tetra-substituted allenes with a range of primary and secondary alcohols, methanol, phenol and propionic acid was catalysed by the system [AuCl(IPr)]/ AgOTf (1 1, 5 mol% each component) at room temperature in toluene, giving excellent conversions to the allylic ethers. Hydroalkoxylation of monosubstituted or trisubstituted allenes led to the selective addition of the alcohol to the less hindered allene terminus and the formation of allylic ethers. A plausible mechanism involves the reaction of the in situ formed cationic (IPr)Au" with the substituted allene to form the tt-allenyl complex 105, which after nucleophilic attack of the alcohol gives the o-alkenyl complex 106, which, in turn, is converted to the product by protonolysis and concomitant regeneration of the cationic active species (IPr)-Au" (Scheme 2.18) [86]. 

The effect of stoichiometry, substituent, and temperature were investigated in reactions between the hydride HCo(tdppep) (19) and a number of alkynes.175 The cr-acetylide complex (20) and the (7-alkenyl (21) are formed from the stoichiometric reaction with ethyl propiolate. However, when a ten-fold excess of ethyl propiolate is used, the acetylide complex is formed quantitatively and one equivalent of alkyne is hydrogenated to alkene. Forcing conditions and a large excess of... 

The reactivity of OsHCl(CO)(P Pr3)2 toward alkynols depends on the substituents at the C(OH) carbon atom of the alkynol (Scheme 14).47 The reaction with 2-propyn-1 -ol initially affords the alkenyl compound 6s(CI I=CI ICII2OI I)Cl(CO) (P Pr3)2 in 85% yield, as a result of the anti-addition of the Os—H bond to the carbon-carbon triple bond of the alkynol. In chloroform-df solution this complex decomposes to a mixture of products, containing the derivatives OsCl2(CHCH=CH2) (CO)(P Pr3)2 and 6s(CHCHCH6)Cl(CO)(P Pr3)2 (Eq. 5). 

In general, the syntheses of these complexes are achieved through (i) nucleophilic addition/substitution reactions of silver(i) fluoride or (ii) transmetallation reactions with other metal alkyl, alkenyl, and aryl complexes. 

Akiyama developed a novel [3+2] cycloaddition reaction of alkenyl Fischer carbene complexes 11 with simple imines 12 in the presence of a catalytic amount of GaCb to produce 3-alkoxy-2,5-disubstituted-3-pyrroline derivatives 13 <00JA11741>. 

These reactions are compared with those of the equivalent 1-alkenyl HgCl compounds. Some differences are observed, notably that the mercury complexes will react with PhSe—SePh, while the tin complexes undergo no reaction at all. The reactions with ChHg, QHgCl and RHgCl, however, are broadly similar to that shown in reaction 26. 

Recently, a proposal has been put forth that a /raor-addition process may be possible through dinuclear ruthenium intermediates.34 As shown in Scheme 5, reaction of tetraruthenium aggregate A with phenylacetylene results in the fully characterized bridging dinuclear alkenyl complex B. The authors propose a direct /ra .r-dclivcry of hydride through a dinuclear intermediate may be active in the hydrosilylation catalyzed by A, though compound B itself is unreactive to Et3SiH. 

Lactams Lactams represent a special type of C=N system due to the tautomerization between the lactam (keto amine) and lactim (hydroxyimine) forms. The lactim form is much more favored for cyclic than for non-cyclic amides of carbocyclic acids. In the reaction of complex 2b with N-methyl-e-caprolactam, a simple ligand exchange reaction occurs and complex 87 can be isolated. With P-propiolactam, the alkenyl-amido complex 88 is formed, which indicates an agostic interaction. The reaction of complex 1 with e-caprolactam gives, after elimination of the alkyne and of molecular hydrogen, complex 89 with a deproto-nated lactam in a r]2-amidate bonding fashion [47]. 

Palladium complexes have been used for the electroreductive cycliza-tion of Ai-alkenyl-2-bromoanilines to the corresponding indoline derivatives (Scheme 69) [101]. The postulated carban-ion intermediate undergoes a reaction with the electrophiles (H+, CO2). 

Protonation of alkenyl complexes has been used [56,534,544,545] for generating cationic, electrophilic carbene complexes similar to those obtained by a-abstraction of alkoxide or other leaving groups from alkyl complexes (Section 3.1.2). Some representative examples are sketched in Figure 3.27. Similarly, electron-rich alkynyl complexes can react with electrophiles at the P-position to yield vinylidene complexes [144,546-551]. This approach is one of the most appropriate for the preparation of vinylidene complexes [128]. Figure 3.27 shows illustrative examples of such reactions. 

A synthetic application of the sonolysis of iron carbonyls is the preparation of useful ferrilactones. The alkenyl epoxides (2, R = H, Ph, 1-hexanyl) are smoothly converted to the corresponding ferrilactone complexes (3) on reaction with Fe2(CO)9 suspended in THF and sonicated at room temperature [53]. Such complexes undergo several synthetically useful transformations (Scheme 3.7) including oxidation with Ce(IV) as a route to P-lactone natural products or P-lactam antibiotics and reaction with CO to afford 5-lactones [54]. Somewhat surprisingly this reaction is efficient even in diethyl ether, a volatile solvent which delivers low cavitation energy. 

At this point it is worthy of mention that solutions of these alkenyl-hydrido isomers react with hydrogen, at room temperature, to yield styrene and the starting [lrH2(NCMe)3(P Pr3)]BF4 complex. Deuterium treatment of the alkenyl-hydrido isomers shows an easy H/D hydride exchange, which suggests that the reaction with hydrogen is more favorable than C—H reductive elimination. Therefore, the hydrogenahon is dominated by an iridium(lll) species, and most probably iridium(l) species are not involved under catalytic conditions. 

When only one heteroatom of the dinucleophile possesses a hydrogen substituent, the reactions lead instead to alkenyl complexes rather than carbene compounds. Effectively, treatment of diphenylallenylidenes 1 and 6 with pyrazoles yields the heterocyclic derivatives 61 (Scheme 2.25) [76]. Interestingly, the dissymmetric 3-methylpyrazole (R=H, R = Me) provides only one regioisomer, in which the methyl group points towards the metal. This process, which formally corresponds to the addition of two nitrogen nuclei at C and Cy and a hydrogen atom at Cp, is assumed to take place through an initial nucleophilic attack at the Ca position. 

The reactions of butatrienylidene iridium complexes with CO depend strongly on the trans ligand. The trans chloro complex 11 reversibly adds CO to form a five-coordinate butatrienylidene complex 31 whereas the trans azido complex yields with CO an alkenyl(azido)ethynyl complex (32) and the trans methyl complex the alky-nylalkenyl complex 33 (Scheme 3.31) [3]. 

Lanthanide-catalyzed enyne cyclization/hydrosilylation was also applied to the synthesis of silylated alkylidene cyclohexane derivatives. For example, reaction of the 3-silyloxy-l,7-enyne 17 with methylphenylsilane catalyzed by Gp 2YMe(THF) at 50°G for 8h gave 18 in quantitative yield as a 4 1 mixture of trans cis isomers (Equation (11)). Employment of methylphenylsilane in place of phenylsilane was required to inhibit silylation of the initially formed yttrium alkenyl complex, prior to intramolecular carbometallation (see Scheme 8). 

I.1.3 Reactions with 1,2-. 1,3-, and 1,4-dienes. The reaction of conjugated dienes with aryl and alkenyl halides can be explained by the following mechanism. Insertion of a conjugated 1,3-diene into an aryl or ulkenylpalladium bond gives the T-allylpalladium complex 243 as an intermediate, which reacts further... 

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