Metal acetylides, structure

Metal-acetylide complexes including metal-poly(yne) polymers often show unique properties [21-23]. Thus, metal-acetylide dendrimers are of interest because amplification of the functionality due to metal-acetylide units based on three-dimensional assembly with a regular dendritic structure is expected. 

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. ... 

Aeetylldes (Acetylene Derivatives, Inorganic) (Acetylenide or Carbide, in Ger). Acetylides are compds obtained by replacement of one or two hydrogen atoms of acetylene or its homologs or derivatives by a metal. Their structure may be as follows HC i CM1, ... 

Transition metal acetylides combine the properties of acetylenes with those of the transition metals, offering flexibility in the tuning of structural and electronic properties of both the organic and inorganic constituents. Optimization of the molecular and bulk crystalline properties is envisaged to lead to a new class of useful nonlinear optical materials. 

Alkynyl complexes, also known as metal acetylides, possess both rigid linear skeleton and tt-conjugation. In the structural aspect, alkynyls make excellent linear bridging units. By means of the reactions of transmetallation (see Transmetalation), poly-Pt-acetylides are readily synthesized (Scheme 24). Copper(I)-mediated oxidative coupling... 

A few simple beryllium acetylide structures are known. In one of these structures, illustrated as (112), the metal cation is symmetrically coordinated side-on to a triple bond. 

Two poly(cyclodiborazane) polymers containing group-10 transition metal-acetylide groups P50 and P51 were prepared by Chujo et al. and represent a new kind of organometal-lic acetylide polymers functionalized with group-13 boron elements in the main chain.78 The structures of P50 and P51 were confirmed by IR and NMR ( H, 31P, and nB) spectra. The optical properties were studied by UV-vis absorption and emission measurements. It was shown that these polymers display extended -conjugation length via transition metal and boron atom with enhanced air- and moisture stability. 

Formerly, only very strong bases (Na, NaNHj, KNHj) were found to effect isomerization of alkynes, and then only at elevated temperatures and only of 2-alkynes to 1-alkynes. Since internal alkynes are more stable than terminal alkynes, the isomerization is evidently possible because of formation of a metal acetylide. Migration is blocked by a branch in the chain. The base is also highly active in the exchange of benzene C—-D bonds. It converts limonene to p-cymene with evolution of hydrogen at room temperature in high yield. Brown notes that the base can exist as a chelate (a), a structure that may contribute to the high basicity. 

Acetylides and fulminates form highly explosive shock- and heat-sensitive salts with many metals. Acetylides are the metal derivatives of acetylene. Hydrogen attached to carbon atoms bearing a triple bond is acidic in nature. It can be substituted by a metal ion to form acetylides, with the general structure M-C=C-M. These substances are made from acetylene, HC=CH, or alkyl acetylene, RC=CH, by passing acetylene gas or aUcyl acetylene vapors over the aqueous solutions of ammoniacal metal salts, as shown in the following reactions ... 

As a result of the multiple orbitals available for metal-ligand bonding, alkynes readily coordinate with multiple metal centres [12]. Where two metals coordinate to a single alkyne (or acetylide) moiety, a number of different arrangements have been characterised (Fig. 2). An acetylide moiety may coordinate in an end-on fashion via two metal-carbon o-bonds (structure A) with the C = C axis perpendicular to the metal-metal axis (p—r r ). The alkyne can also coordinate parallel to the metal-metal axis (structure B), with each alkyne carbon forming a o-bond to a different... 

In addition to the ternary potassium transition metal acetylides discussed above, the crystal structure of Rb2PdC2 has also been solved. This is isostructural with Na2PdC2. The Rb-C and Rb-Pd bond lengths are comparable to those found in other known structures, meaning the species fits well into the trend of ternary palladium and platinum acetylide compounds. ... 

Research in poly(metal acetylides) such as structure 11, dominates the area of transition metals a-bonded to organic moieties Since the first report of these polymers in the 1970s, many researchers have described the incorporation of various types of transition metals into this class of materials. This class of organometaUic polymers contains rigid-rod structures, making these polymers ideal for electrical and optical applications. 

A number of metal acetylide-containing dendrimers and stars have also been prepared." Scheme 25 shows the synthesis of a first-generation platinum acetylide dendrimer (87) containing 9 platimun complexes in its structure. Dendrimer 87 was made by the reaction of a chloro-substituted platinum complex (85) with an ethynyl functionalized dendron (86) in the presence of Cul." Dendrimers with up to 45 platinum emits were synthesized using this methodology. 

One of the most common methods used to install transition metal centers within carbon-rich structures takes advantage of the easily constructed metal-acetylide bond. In addition to their facile preparation, insertion of a metal center into an unsaturated material can introduce a range of exciting properties not pres-... 

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