Transition metal complexes diynes

Polymeric pseudocrown ether networks have been generated in situ by the photopolymerization of poly(ethylene glycol) diacrylate transition metal complexes <00CM633>, and the effect of metal ion templation was evaluated. The 1,6,13,18-tetraoxa[6.6]paracyclophane-3,15-diyne (termed pyxophanes) was prepared from hydroquinone and l,4-dichlorobut-2-yne it forms size-selective 7i-complexes with alkali metal cations <00CC2377>. Dibenzo[ ]crown-m have been used in numerous elegant studies in which they were the needles that were threaded by diverse reagents the resultant... 

The reductive cyclization of non-conjugated diynes is readily accomplished by treatment of the acetylenic substrate with stoichiometric amounts of low-valent titanium52 523 and zirconium complexes.53 533 Hence, it is interesting to note that while early transition metal complexes figure prominently as mediators of diyne reductive cyclization, to date, all catalyzed variants of this transformation employ late transition metal complexes based on nickel, palladium, platinum, and rhodium. Nevertheless, catalytic diyne reductive cyclization has received considerable attention and is a topic featured in several review articles. ... 

Dimers (259) and trimers (260) have been obtained from non-conjugated diynes in the presence of transition metal complexes - . With Tj -cyclopentadienylcobalt... 

Nitrogen-containing 15-membered trialkyne macrocycles, such as l,6,ll-frw(aiylsulfonyl)-l,6,ll-triazacyclopentadeca-3,8,13-triynes and enediynes as 1,6,11-frw(arylsulfonyl)-1,6,11-triazacyclopentadeca-3-ene-8,13-diynes have been prepared and subjected to a [2+2+2]-cyclotrimerization process catalyzed by transition metal complexes, e.g., RhCl(CO)(PPh3)2 <05JOC2033>. The reaction of pemosylated diethylenetriamine and 2-substituted propan-1,3-... 

Catalytic asymmetric alkaloid synthesis remains a challenge [114], in spite of the pharmaceutical importance of kainic acid [115,116] etc. Chiral transition metal complexes are the catalysts [117] of choice for cyclization of enynes, dienes [118, 119], or diynes [120]. With axially chiral P,N ligands having an achiral gem-dimethyloxazoline unit, alkaloid synthesis can be attained via ene-type cyclization [121]. 

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). 

In both cases, the structure of the organometallic polymers can be designed by the diyne monomers. The regiochemistry of the mainchain connections at each met-allacycle imit is affected by the nature of the substituents on diynes and/or the Ug-ands on the low-valent transition metal complexes. It was also demonstrated that the regioselectivity of the mainchain connections reflects directly on the character of the functional polymers obtained by the polymer reactions. That is, the organotitanium polymers with regiospecific mainchain coimections obtained from titanimn... 

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 ... 

Itoh and coworkers [223] have shown that fullerene derivatives as 6/2-113, which to date have been prepared in a stepwise procedure, can be obtained in a three-component domino process by treatment of diynes 6/2-109, dimethylphenylsilane 6/2-110 and fullerene (C60) in the presence of a Rh-catalyst [223]. Interestingly, using maleic anhydride as dienophile failed to give the desired cycloadduct, whereas Cso -in spite of its strong tendency to form complexes with various transition metals [224] - never suppressed the catalytic silylative cyclization step to give the diene 6/2-112 (Scheme 6/2.24). 

The first tt complexes of 1,3-diynes were reported by Greenfield. Shortly thereafter, Tilney-Bassett described the first heterometallic derivatives. This area has grown steadily since these initial reports and many complexes of this type are now known. Diyne complexes are often simply alkyne-substituted analogues of conventional jr-alkyne complexes. Indeed, transition metal compounds that form -complexes with mono-alkynes can be expected to form complexes with diynes. However, the thermal sensitivity of terminal diynes, especially 1,3-butadiyne, may limit the application of routine reaction conditions in some cases. Further coordination of the ynyl ligand by additional metal fragments is usually determined by the reagent stoichiometry and by steric effects. 

Generally, the preparation of these species is achieved by (a) coordination of preformed diynes to transition metal centers, and (b) coupling reactions of the alkynyl ligand in mono-alkynyl metal complex precursor. 

Transition metal-catalyzed carbocycUzation reactions of tethered diene, enyne, diyne, and vinylallene derivatives represent an important class of transformations in synthetic organic chemistry. This may be attributed to the abihty to significantly increase molecular complexity through the highly selective combination of acyclic components, thereby facilitating the synthesis of complex polycychc products. Recently, rhodium-catalyzed carbocyclization reactions have attracted significant attention due to their immense synthetic versatility and the unique selectivities observed over a range of different transformations. This chapter provides an account of recent developments in rhodium-catalyzed [4-1-2] and [4-i-2-t2] carbocyclization reactions. 

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. 

Diynes in which the distance between the internal acetylenic carbons, (b) and (c) in 244, is not greater than ca. 3-4 A react with certain transition metal compounds, particularly tris(triphenylphosphine)rhodium(i) chloride, to give complexes of type... 

Transition metal catalysts can also be used in photochemical organic synthesis. For example, the photo-Bergman reaction (cycloaromatization see also Scheme 6.62) of (Z)-hex-3-en-l,5-diyne [(Z)-589], which is obtained by photostationary E Z isomerization (Section 6.1.1) from ( )-589, occurs via transition metal-catalysed cycloaromatization reaction followed by photochemical dissociation of the arene ligand from the complex 590 (Scheme 6.289).1530 The product, 1,2-di( -propyl)benzene (591), is obtained in 91% chemical yield. 

---