Diynes, reactions with metal complexes

VII. Other Reactions of Diynes with Metal Complexes. 199... 

F. Reactions of Metal Complexes with 1,3-Diynes Giving Organic Products. 218... 

OTHER REACTIONS OF DIYNES WITH METAL COMPLEXES... 

The diyne reactions of 1,4-, 1,5-, 1,6-, and 1,7-diynes via transition metal complexes are useful for the synthesis of new cyclic compounds (Muller, 1974 Wagner and Meier, 1974, 1975). t-C5H5Co(CO)2 reacts catalytically with linear l,m-diacetylenes (XXXVIII) to give trimers (XXXIX), formation of which involves the interaction of six acetylene functions (Vollhardt and Bergman, 1974). 

Beyond palladium, it has recently been shown that isoelectronic metal complexes based on nickel and platinum are active catalysts for diyne reductive cyclization. While the stoichiometric reaction of nickel(O) complexes with non-conjugated diynes represents a robust area of research,8 only one example of nickel-catalyzed diyne reductive cyclization, which involves the hydrosilylative cyclization of 1,7-diynes to afford 1,2-dialkylidenecyclohexanes appears in the literature.7 The reductive cyclization of unsubstituted 1,7-diyne 53a illustrates the ability of this catalyst system to deliver cyclic Z-vinylsilanes in good yield with excellent control of alkene geometry. Cationic platinum catalysts, generated in situ from (phen)Pt(Me)2 and B(C6F5)3, are also excellent catalysts for highly Z-selective reductive cyclization of 1,6-diynes, as demonstrated by the cyclization of 1,6-diyne 54a.72 The related platinum bis(imine) complex [PhN=C(Me)C(Me)N=Ph]2Pt(Me)2 also catalyzes diyne hydrosilylation-cyclization (Scheme 35).72a... 

Cu(I)-Catalyzed Reactions of 1,3-Diynes with Metal-Halide Complexes... 

The first complexes to be described were obtained from reactions between MCI2CP2 and metallated alkynes and initially formulated as the dimers M(/r-C=CR)Cp 2. Further studies have clarified the nature of these complexes together with those formed from RC CC CR (R = Me, Bu, Ph, SiMe3) and MCp2. The several structural types obtained contain 1 /1,1 /2, 2/1, and 2/2 ratios of MCp2 to diyne, as shown in Scheme 48. The nature of the complexes formed depends on diyne substituent and metal. 

There are many examples of reactions of diynes with metal species that give mono or binuclear products containing ligands other than simple this section and there are obvious connections with that presented earlier as many of the products are derived from isomerization, rearrangement, and bond-forming reactions of initially formed diyne complexes. 

Metal-promoted 1,2-migration of silyl groups in silylalkynes results in the formation of silylvinylidenes which are subsequently readily desilylated. " Alkynyl-substituted silylvinylidenes have been obtained from silylated diynes and the Fe(N2)(CO)2 P(OMe)3 2/ Fe(CO)2[P(OMe)3]2 2(/t-N2) reagent and similar species are implicated in the reactions of several Group 8 metal complexes with mono- and bis-trialkylsilyl diynes. " ... 

Dienes are less reactive toward transition metals than enynes and diynes, and perhaps for this reason, the development of effective catalyst systems for the cyclization/hydrosilylation of dienes lagged behind development of the corresponding procedures for enynes and diynes. The transition metal-catalyzed cyclization/hydrosilylation of dienes was first demonstrated by Tanaka and co-workers in 1994. Reaction of 1,5-hexadiene with phenyl-silane catalyzed by the highly electrophilic neodymium metallocene complex Cp 2NdCH(SiMe2)3 (1 mol%) in benzene at room temperature for 3 h led to 5- ///76 -cyclization and isolation of (cyclopentylmethyl)phenylsilane in 84% yield (Equation (15)). In comparison, neodymium-catalyzed reaction of 1,6-heptadiene with phenylsilane led to 5- X(9-cyclization to form (2-methylcyclopentylmethyl)phenylsilane in 54% yield as an 85 15 mixture of trans. cis isomers (Equation (16)). 

As is clear from the introductory discussion, most, if not all, of the d-block transition metals are expected to participate in reactions that are related to those discussed here. In addition to the Co-based methodology mentioned earlier, some related reactions of Pd and are known. Also related are the cyclization reactions of metal-carbene complexes containing Cr, Mo, W and other transition metals with alkynes and alkenes and a recently reported Nb- or Ta-promoted diyne-alkyne cyclization reaction, which appears to be closely related to a number of previously developed alkyne cyclotrimerization reactions, such as those catalyzed by Co. Investigations of reactions involving other transition metals may prove to be important especially from the viewpoint of developing asymmetric and catalytic procedures. 

The reaction of dienes, diynes, or en-ynes with transition metals " (usually cobalt) " forms organometalhc coordination complexes. In the presence of carbon monoxide, the metal complexes derived primarily from enynes (alkene-alkynes) form cyclopentenone derivatives in what is known as the Pauson-Khand... 

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