Metal alkynyl complexes

Dendritic Sphere Based on Alkynyl-Metal Complexes. 47... 

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. 

B. Coupling Reactions of the Alkynyl Ligand in Mono-Alkynyl Metal Complex Precursors... 

The alkynyl-metal complexes are strong carbon bases, with measured pK values for M(C=CBu )L2Cp being 13.6 [ML2 = Fe(CO)(PMe3)j and 20.8 [ML2 = Ru (PMe3)2] [170],... 

The chemistry of bis(alkynyl) metal complexes, including the titanium derivatives, focusing on the synthesis, chemical behavior, structure, and bonding of different type of mononuclear and heterometallic molecules has been discussed in a review.1280 A review focusing the preparation and the reactivity of compounds of the type Cp 2Ti-(ct-C=CR)2 (Cp = Cp, Gp ) has appeared which summarizes special aspects of C-C coupling and cleavage processes in organic reactions.1281... 

With the discovery and use of alkynyliodonium salts, a new class of electrophilic alkynylation reagents has emerged. Because of their impressive reactivity, they could be broadly used to introduce acetylenes on carbon nucleophiles, heteroatoms, or metals. Nevertheless, with the exceptions of the alkynylation of nitrogen and new applications in the synthesis of alkynyl-metal complexes, most research on alkynyliodonium salts has been concentrated in the years 1985-1995, with rare more recent breakthroughs. In particular, very few applications using modem catalytic methods have appeared, in stark contrast to the use of aryhodonium salts in arylation reactions [99]. One of the possible reasons for this drying out of the field is the relatively low stability of alkynyliodonium salts, which often makes their use challenging. 

The chemistry of alkynyl-metal complexes has been reviewed recently.Glassical synthetic routes to half-sandwich alkynyl-ruthenium and alkynyl-osmium complexes of general composition [M(G=GR)(77 -G7,Ht )(L )(L )] are based on the reactions of appropriate halide precursors with lithium/sodium alkynyl reagents or... 

The alkynyl-metal (metal-acetyhde) complex is one of the best building blocks for organometallic dendrimers, since it has some advantages compared to other organometallic complexes [18]. Most of the metal-acetylide complexes are thermally robust and stable, even when exposed to air and moisture. Metal-acetylide complexes are fairly accessible in high yields by well-established synthetic methodology [19]. These features are essential to the construction of dendrimers. 

Etherification using a metal vinylidene has also been combined with G-G bond formation through the reaction of an alkynyl tungsten complex with benzaldehyde (Scheme 14). The addition of an internal alcohol to the incipient /3,/Udialkylvinylidene that is generated leads to dehydration and the formation of a Fischer-type alkylidene complex. Further reactions of this carbene with a range of nucleophiles have provided access to various furan derivatives.374,375... 

Alkynes react readily with a variety of transition metal complexes under thermal or photochemical conditions to form the corresponding 7t-complexes. With terminal alkynes the corresponding 7t-complexes can undergo thermal or chemically-induced isomerization to vinylidene complexes [128,130,132,133,547,556-569]. With mononuclear rj -alkyne complexes two possible mechanisms for the isomerization to carbene complexes have been considered, namely (a) oxidative insertion of the metal into the terminal C-Fl bond to yield a hydrido alkynyl eomplex, followed by 1,3-hydrogen shift from the metal to Cn [570,571], or (b) eoneerted formation of the M-C bond and 1,2-shift of H to Cp [572]. 

Long NJ, Williams CK Angew Chem Int Ed 2003,42 2586-2617 Metal alkynyl sigma complexes synthesis and materials... 

The chemistry of metal complexes featuring alkyne and alkynyl (acetylide) ligands has been an area of immense interest for decades. Even the simplest examples of these, the mononuclear metal acetylide complexes L MC=CR, are now so numerous and the extent of their reaction chemistry is so diverse as to defy efforts at a comprehensive review. " The utility of these complexes is well documented. Some metal alkynyl complexes have been used as intermediates in preparative organic chemistry and together with derived polymeric materials, many have useful physical properties including liquid crystallinity and nonlinear optical behaviour. The structural properties of the M—C=C moiety have been used in the construction of remarkable supramolecular architectures based upon squares, boxes, and other geometries. ... 

In the alkyne chemistry described previously, combination of bis-alkynyl complexes with a second metal complex gives the tweezer complex, which may... 

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. " ... 

As shown in Scheme 4, alkynyl metallates derived from propynoic acid amides can also be used as source of the allenylidene C3 unit, their reactions with the tetrahydrofuran solvates [M(CO)5(THF)] affording the N/O-substimted allenylidene complexes 6 after selective O-alkylation with [R30][BF4] [29]. 

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