Diyne complexes

C. Formation of Diyne Complexes by Coupling of Alkynyl Moieties. 153... 

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. 

The 62-e diyne complexes 115 and 116 are effective scaffolds for the trimeriza-tion of the diynes and codimerization of diyne and alkynes, resulting in extended carbon chains coordinated to the cluster. Thus, reactions with R C=CC=CR (R = Ph, Me) afforded Ru4(M4-PPh) /i4-RCC(CsCR )CPhC-p -CCPhCRC (C=CR ) (CO)s (118 R = Ph, Me). The former was also found as a minor product from Ru4(/i4-PPh)(CO)i3 and PhC=CC=CPh. " These are 64-e clusters containing a /44-PPh ligand capping an RU4 face, together with a C12 ligand formed from... 

Detailed studies of these systems have enabled a rationalization of the observed chemistry to be made, involving as possible intermediates (a) the ful-vene complexes MHCp CsMe4(CH2) or MH2Cp CsMe3(CH2)2, (b) the r -diyne complexes M( 7 -RC2C=CR)Cp 2, and (c) the j" -metallacumulenes, M(/) -RCCCCR)Cp 2. i - ... 

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. 

Trimerization of 1-alkynes to substituted cyclobutadienes occurs in reactions of RhCl(l-alaninate)Cp with HC CR (R = Ph, tol), which afford Rh -C4HR2 (C=CR) Cp (310) possibly via intermediate dialkynylrhodium(III) complexes. Reductive coupling to an /j -diyne complex, which coordinates the third molecule of alkyne, is followed by further coupling to the rhodacyclopentadiene and reductive elimination of the cyclobutadiene (Scheme 72). ... 

The diyne complexes Co2(/u.-fj -RC2C=CR)(CO)6 (R = Ph, Fc) give irreversible reduction waves even at 213 K which indicates that fast chemical reactions follow the electrochemical production of the corresponding radical anions [Co2(jU-)j -RC2C=CR)(C0)6]. The ESR spectra of the anion radical generated in situ were not consistent with the presence of two different Co centers. In the case of the ferrocenyl-substituted complex, two distinct oxidation waves separated by 70 mV are observed, which indicates a modest degree of interaction between the Fc cores through the cluster. 

As surmized in a recent review article there are literally hundreds of polymeric systems featuring organometallic complexes within a conjugated organic backbone. Given recent reviews of these systems, here we shall restrict discussion to the various polymeric species and ceramic materials derived from diyne complexes and from coordination of metal fragments to polymers featuring C=CC=C repeat units. 

Interestingly, seven-membered conjugated diyne complex 16 is produced by the acid-promoted Nicholas reaction of the dicobalt-coordinated bispropargylic complex (Equation (7)). The cyclization proceeds via an intramolecular coupling reaction between a propargyiic cation and an alkene produced after dehydration. The molecular structure of seven-membered diyne complex 16 is confirmed by X-ray analysis, although the decomplexation is not successfully carried out. 

Tamao and Ito proposed a mechanism for the nickel-catalyzed cyclization/hydrosilylation of 1,7-diynes initiated by oxidative addition of the silane to an Ni(0) species to form an Ni(ii) silyl hydride complex. Gomplexation of the diyne could then form the nickel(ii) diyne complex la (Scheme 1). Silylmetallation of the less-substituted G=C bond of la, followed by intramolecular / -migratory insertion of the coordinated G=G bond into the Ni-G bond of alkenyl alkyne intermediate Ila, could form dienylnickel hydride intermediate Ilia. Sequential G-H reductive elimination and Si-H oxidative addition would release the silylated dialkylidene cyclohexane and regenerate the silylnickel hydride catalyst (Scheme 1). 

Rigid-rod bisiridium(III) cr-diyne complexes have also been prepared from Vaska s complex and the bisphenyliodonium triflates of butadiyne and 1,2- and 1,4-diethynylben-zenes45. The reactions were conducted in acetonitrile and, under such conditions, the products are doubly charged bimetallic salts in which acetonitrile occupies one coordination... 

Diynes. The (propargyl acetate)Co,(CO)s complex 1 couples with the trialkyn-ylalane 2 in CH2CI2 at 0° (or better, —78°) to give, after aqueous work-up, the diyne complex 3. The free diyne (4) is obtained by demetallation with CAN. 

The formation of 1,5-diyne complexes as side-products in some reactions of cations 92 with metal alkyls [41] and the facile, regioselective reduction of a propargylic chloride complex by Zn/HOAc, used in the synthesis of the insect pheromone 5-(Z)-tetradecenyl acetate [221], provided early evidence for the intermediacy of (propargyl)Co2(CO)5 mdicals. In a similar vein, the binuclear molybdenum-complexed propargyl cations react with Na/Hg to produce... 

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