Alkynes, -complexes with

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... 

Green and coworkers19 prepared the title compound and other related monoalkyne complexes by reaction of the corresponding bis(alkyne) complex with triphenylphosphine (or other phosphines) in good yields. The method described here works for several alkynes, for example, 2-butyne or phenyl-acetylene, and also for phosphines, for example, PEt3 or P(OPh)3. 

These reactions can be used to prepare a novel series of complexes where cyclic alkynes can be stabilized by coordination to platinum(O).831,832 The compounds are feasible because coordination of a triple bond to platinum causes a distortion of the alkyne from linearity by displacement of the alkynic substituents back away from the platinum. Also these methods can be used to prepare platinum(O) alkyne complexes with substituents other than triphenylphosphine.833-836... 

To our knowledge there is no example in the literature of a stable alkene (or alkyne) complex with magnesium as central atom, n Complexes have, however, been postulated as intermediates in the rearrangement reactions of some alkenyl Grignard reagents (86). 

Two potentially informative infrared probes in alkyne complexes with ancillary carbonyl ligands are (1) v(C=C) absorptions and (2) v(CO) absorptions. The first provides direct information about the carbon-carbon multiple bond of the bound alkyne ligand, but it is usually weak and has proven particularly difficult to detect in M(CO)(RC=CR)(S2CNEt2)2 complexes (57). The second provides only indirect information about the metal-alkyne moiety, but its intensity and unambiguous assignment as y(CO) have stimulated an extensive literature data bank to assist interpretation. 

Cp(CO)2M[CR=CRC(R)6] with M = Mo, W Cp = tj5-C5H5, tj5-C5H4Me, or i75-C9H7 and R = Me, Et, "Pr, or "Bu (70). The net conversion of CpM(CO)3R reagents plus alkyne to the alkenylketone products [Eq. (57)] corresponds to 1 1 adduct formation, but the reaction is mechanistically complex. Formation of alkyl alkyne and acyl alkyne complexes with loss of CO precedes addition of CO to form the final product. 

In 1974, Dickson and Fraser reviewed the already substantial area of cobalt-alkyne complexes.1 Since then the number of examples and applications of this class of organometallic compounds, especially dinuclear complexes, has increased enormously. This review will present the chemistry of polynuclear cobalt-alkyne complexes, with emphasis on the more recent developments. Although there have been many exciting fundamental discoveries, this is a maturing area of research that is finding many important applications in organic synthesis,2 such as the use of [Co2(jU-alkyne)(CO)6] complexes in the synthesis of enediyne antitumor antibiotics.3-4... 

A recent report has described a series of Ni(0)-alkynylphopshine complexes (21) featuring the unusual coordination of the alkyne moiety in preference over the phosphine moiety (Scheme 20). The reaction of these Ni(0)-alkyne complexes with HCl and the isolation of the resulting Ni(ll) T] -vmy complexes (22) has provided a rare opportunity to study alkyne insertion reactions. The Ni-P bond in (22) undergoes another insertion see Insertion) by CO2 or CS2 to give 5-coordinate, zwitterionic see Zwitterion) complexes (23). 

Mukaiyama-type reaction of cobalt-alkyne complexes with ketene acetals gives the syn product exclusively, a reaction used as a key in a relay to bengamide E (Scheme 201). Total synthesis of blastomycinone utilizing a Mukaiyama-type reaction has been reported (Scheme 202). It is interesting to note the complete reversal of selectivity compared to the uncomplexed aldehyde (Scheme 203). 

Carbonyl, Phosphine, Alkene, and Alkyne Complexes with jr-Ligands 2... 

Derdau, V., Laschat, S., Dix, I., Jones, P. G. Cobalt-Alkyne Complexes with Diphosphine Ligands as Mechanistic Probes forthe Pauson-Khand Reaction. Organometallics 1999,18, 3859-3864. 

Figure 25. The Cu(I)-and Ag(I)-bis(alkyne) complexes with mono- and dirhenoethyne ligands.

Reaction of Ta-alkyne complexes with R R2C=0. The Ta complexes formed from TaCls/Zn with unsymmetrical alkynes react with carbonyl compounds to form two rcgioisomcric allylic alcohols with a ratio depending on the substituents on the alkync (both steric and electronic effects) as well as the size of the substituents in the carbonyl group. The complexes from acetylenic esters react with carbonyl compounds mainly at the position or to the ester group, whereas complexes from acetylenic amides react mainly at the position fi to the amide. 

Note that heating the 1-alkyne complexes with amines in toluene alone leads 2-alke-namides." ... 

CARBONYL, PHOSPHINE, ALKENE, AND ALKYNE COMPLEXES WITH rr-LIGANDS... 

Table 3. Alkyne scission by reaction of alkyne complexes with cluster-building reagents.

Terminal alkyne complexes with ruthenium react with carbon dioxide and amines to yield urethanes, as shown in reaction 8. ... 

In Table 2 appear complexes of transition metals with acetylenic compounds. A study was made of the structure and interconversion of acetylene complexes with binuclear transition metals, where acetylene lies parallel or perpendicular to the metal-metal bond" . Carbonyl alkyne complexes with binuclear iron give good separations in reverse-phase HPLC 4... 

The Zr center is considered to take +4 oxidation state in Cp2Zr(C2H4) in the experimental field. In this case, the oxidation state of Zr does not change at all in this metathesis. However, it is also likely to consider that the Zr center takes +2 oxidation state, because ethylene is understood to form a strong Tt-back donation interaction with the Zr center. In this case, the oxidation state of Zr increases by +2 by this metathesis like that of Pd in the thioboration of alkyne. Maybe, the oxidation state of Zr in Cp2Zr(C2H4) is considered to be intermediate between +2 and +4 and this metathesis is similar to the metathesis of a Pd(0) alkyne complex with thioborane. 

Compound 64 is a true nickel(O) alkyne complex with no agostic interactions between Ni and the methyl groups of the ligands. In the crystal the molecules are associated by four intermolecular hydrogen-bond interactions between neighboring butynediol ligands. This leads to the formation of chain polymers. 

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