Alkyne reactions complexes

The interaction of aUcynes with iridium hydride complexes can lead to a number of different alkyne complexes. Reaction between two equivalents of 2-butyne and [IrH4(PPhMe2)3] produces one equivalent of butene and the butyne complex [Ir(MeC=CMe)(PPhMe2)3]+ (35) with a structure that differs from the expected square planar. Reaction between the same iridium complex and dimethylacetylenedicarboxylate produces a bis-aUcyne complex (36). ... 

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 ... 

The reaction of alkenes with alkenes or alkynes does not always produce an aromatic ring. An important variation of this reaction reacts dienes, diynes, or en-ynes with transition metals to form organometallic coordination complexes. In the presence of carbon monoxide, cyclopentenone derivatives are formed in what is known as the Pauson-Khand reaction The reaction involves (1) formation of a hexacarbonyldicobalt-alkyne complex and (2) decomposition of the complex in the presence of an alkene. A typical example Rhodium and tungsten ... 

Attempts to exploit the reaction of the dianion with alkyl halides to produce a c/.v-dialkyl complex by using 1,2- or 1,3-dihaloalkanes did not indeed give this result. The reaction of Ru(Por) " with 1,2-dibromoethane was sucessful, but the resulting metallacyclopropane product is better formulated as a /r-complex of ethene, and will be discussed below in the section on alkenc and alkyne complexes. The corresponding reaction of the diiinion with 1,3-dichloropropane gave no evidence for a metallacyclobutane. but instead free cyclopropane was detected by GC analysis and the porphyrin product was Ru(TTP)(THF)2. ... 

Cui, Q., Musaev, D. G., Morokuma, K., 1998a, Why do Pt(PR3)2 Complexes Catalyze the Alkyne Diboration Reaction, but Their Palladium Analogues Do Not A Density Functional Study , Organometallics, 17, 742. 

The copper-alkoxo unit, which is usually synthesized in situ, plays a significant role in metal-promoted transformations of organic substrates by copper(I). To determine the reaction form of the Cu-OPh unit, Floriani and co-workers structurally characterized four complexes (772) (pseudotetrahedral Cu-Cu 3.223 AT (773) (pseudotetrahedral), (774) ( anion linear coordination) and (775) (planar trigonal).57 Using 3,3,6,6-tetramethyl-l-thia-4-cycloheptyne as terminal ligand the structural characterization of a copper(I)-alkyne complex (776) (Cu-Cu 2.940 A) was reported.573... 

Went, Michael J., Synthesis and Reactions of Polynuclear Cobalt-Alkyne Complexes. 41 69... 

The benzoquinone 66 is similarly prepared by the regioselective cycloaddition of 64, derived from 63. The cyclization reaction is based on the electronic effect of the substituent of 65 [34]. The maleoylcobalt complex 67, substituted by PPh3, is unreactive towards terminal alkynes. The reaction course is altered... 

A variety of triazole-based monophosphines (ClickPhos) 141 have been prepared via efficient 1,3-dipolar cycloaddition of readily available azides and acetylenes and their palladium complexes provided excellent yields in the amination reactions and Suzuki-Miyaura coupling reactions of unactivated aryl chlorides <06JOC3928>. A novel P,N-type ligand family (ClickPhine) is easily accessible using the Cu(I)-catalyzed azide-alkyne cycloaddition reaction and was tested in palladium-catalyzed allylic alkylation reactions <06OL3227>. Novel chiral ligands, (S)-(+)-l-substituted aryl-4-(l-phenyl) ethylformamido-5-amino-1,2,3-triazoles 142,... 

In some instances formation of ( 0) may be avoided by employing alkyne displacement reactions. Thus (32) is formed in essentially quantitative yield by reacting L(n-CsH5)(0C)2W = CRl with the bridged alkyne complex fNi2(y-Me3SiC2SiMe3)(n-C5H5)2] (9). 

Schore, N. E. Transition Metal Alkyne Complexes Pauson-Khand Reaction. In Comprehensive Organometallic Chemistry II Abel, E. W., Stone, F. G. A., Wilkinson, G., Eds. Elsevier Oxford, 1995 Vol. 12, pp 703-739. 

Terminal RCH—CH2 1-Hexene C4H9CH=CH2 is isomerized by complex 1 in accordance with the factors influencing the thermodynamic stability of cis- and trans-2 -hexene [15], At the end of the reaction, the alkyne complex 1 was recovered almost quantitatively. No alkene complexes or coupling products were obtained. The corresponding zirconocene complex 2a did not show any isomerization activity. Propene CH3CH=CH2 reacts with complex 6 with substitution of the alkyne and the formation of zirconacydopentanes as coupling products, the structures of which are non-uniform [16]. 

Unsubstituted H2C=CH2 Upon reaction with complexes 2a or 6, ethene gives zirconacy-clopentanes such as 13 and 14 [16]. The formation of these compounds proceeds at low temperature via zirconacydopentenes 15, which disproportionate at room temperature to the starting alkyne complex and complex 14. The latter is formed quantitatively in the reaction of 15 with ethene. 

No defined complexes could be isolated from reactions of complex 1 with acetone Me2C=0. Complexes 2a and 2b react with acetone to give the zirconafuranone 2c, which is an interesting zirconocene precursor in view of its extremely good solubility in hydrocarbon solvents and because of its ability to dissociate into the alkyne complex [2f], It is also possible to cleanly substitute the bis(trimethylsilyl)acetylene unit so as to obtain the complex 47, or, alternatively, to substitute the acetone with formation of the zirconafuranone 95 (Fig. 10.14) [2f],... 

Pauson-Khand cyclopentenone synthesisThe cycloaddition of an alkene with an alkyne complexed with Co2(CO) usually furnishes a mixture of two cy-clopentenones when the alkene is unsymmetrical. The regioselectivity can be improved markedly if the alkene bears a heteroatom that can coordinate with the cobalt complex. Both sulfur and nitrogen ligands can improve the yield and regio-control of this reaction. 

Complex condensation products are obtained by reaction of the alkyne complex with excess of 3,3-dimethyl-l-butyne, which yields two isomeric products of formulas Ru3(CO)6[HC2C(Me)3-COCH2CMe3][HC2CMe3]2 (125). The X-ray structure of one of those adducts (Fig. 19) shows that both dimerization of two alkyne molecules and the insertion of carbon monoxide into the alkyne metal bonds have occurred. The Ru-Ru distances of 2.820,2.828, and 2.686 A in the ring are of interest. The value of 2.686 A is one of the shortest found in a... 

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