Ligands alkynyl

Rod-like mononuclear derivatives have been prepared by the reaction of a polymeric alkynyl gold(I) complex with isocyanides. The mesomorphic properties of three types ofgold(I) acetylide complexes, namely, [Au(CC-Ar)(CN-Ar)J, [Au(CC-R)(CN-Ar)J and [Au(CC-Ar)(CN-R)] (Ar = aryl with aliphatic chain, R = alkyl chain), have been systematically examined. 

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The tendency to form ate complexes observed for yttrium is also seen in the preparation of a novel zirconium alkynyl complex. Reaction of Zr(Por)Cl2 (Por = OEP or TPP) with either two or three equivalents of LiC=CR (R = Ph or SiMe ) gives the trisalkynyl complexes Zr(Por)(C=CR)3Li(TFIF). An X-ray crystal structure of Zr(OEP)(C=CPh)2Li(THF) shows that all three alkynyl ligands are on... 

Scheme 3 Coordination modes of an alkynyl ligand to transition metals.

The first polynuclear structures with gold(i) centers coordinated to isocyanide and alkynyl groups were prepared through a novel exchange of alkynyl ligands. This special route became necessary, because the coupling of certain complexes proved elusive (Equation (40)) AuCl complexes of isocyanides with terminal alkynyl groups are subject to decomposition upon treatment with a variety of auxiliary bases. 

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

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. 

Treatment of the azido complexes 19 with CO leads also to the migration of the N3 ligand to the aiienyiidene unit (Scheme 2.9). Nevertheless, the initially formed azido-alkynyl compounds 20 are in this case thermally unstable, evolving slowly into the metallated acrylonitrile derivatives 23 via extrusion of N2. The mechanism of formation of 23 involves the migration of the azido moiety from Cy to the C atom of the alkynyl ligand to generate the allenyl intermediates 21, which by elimination of... 

When these two types of coordination take place at the same metal center, the migration of the alkynyl ligand to the C -carbon atom of the vinylidene can occur, to form enynyl intermediates which, upon protonation by the terminal alkyne, lead to... 

Values of those parameters have already been proposed for many ligands (Ei) and a considerable number of metal centers (S m and 7m), mainly by Lever [64-67, 72] and occasionally by others [14, 15, 24, 27, 29, 35, 38, 41, 48, 71, 73-77]. Examples concerning the former parameter are listed in Table 9 and an extensive list for many carbyne, carbene, vinylidene, allenylidene and alkynyl ligands has been proposed recently by Pombeiro [38]. Tables 10-12 list the proposed S m and 7m values for the binding metal centers so far studied. 

More recently, a novel metal-substituted methylenecyclopropene (triafulvene) derivative was obtained when bis(propyne)zirconocene was treated with one equivalent of tris(pentafluorophenyl)borane, followed by excess of benzonitrile (equation 367)430. The first step involves alkynyl ligand coupling to give the isolable Cp2Zr(//-2,4-hexadiyne)B(C6F5)3 betaine. This undergoes a formal intramolecular nitrile insertion into the Zr—C(sp2) c-bond of the adjacent alkenyl zirconocene unit, leading to the zirconium-boron triafulvene-betaine. X-ray analysis of the triafulvene confirmed the planar... 

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