Metal-acetylide complexes

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. 

Metal-acetylide complexes have been used as a unit of organometallic polymers that have metallic species in the main chain [20]. Representative examples are metal-poly(yne) polymers (19) of group 10 metals depicted in Scheme 5. These polymers are easily prepared from M(PR3)2Cl2 (M=Pt, Pd) and dialkynyl compounds catalyzed by Cu(I) salts in amine. Recently, this synthetic method was successfully applied to the construction of metal-acetylide dendrimers. 

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. ... 

Most attention thus far has focused on metal acetylide complexes (see Table VII like ferrocenyl systems, they are generally accessible by straightforward procedures in high yields, are thermally and oxidatively stable, and can be modified in a facile manner to afford polymeric analogues (Fig. 12). 

Table XIII contains data for organometallic complexes that do not fall into one of the preceding categories. The nonlinearities of the chloro complexes were used in conjunction with those of terminal acetylenes to demonstrate the importance of electronic communication between ligated metal and acetylide ligand in derivative metal acetylide complexes formed from combining these precursors.49133 134 Evaluation of vinylidene, as with sesqui-fulvalene and carbene, is only experimentally straightforward following metal complexation. The vinylidene cation [Ru(C=CHC6H4-4-N02)...

Table XIV contains data for computationally derived second-order hyperpolarizabilities, principally by Marder, Ratner, and their co-workers, and more recently by Humphrey et al. The focus of these studies has been similar to that of experimental investigations, namely ferrocenyl, metal carbonyl, and metal acetylide complexes, and very recently carboranes. Calculated values were all obtained using ZINDO, the methodology for which is described in Section II,E.

Theoretical studies indicate that electron density in the HOMO of the metal acetylide complex is concentrated on the /3 carbon, and consequently... 

The authors have previously reported33 a new convenient method of preparing transition metal-acetylide complexes of the type cis- and frans-(PR3)2M(C=CR)2 according to Eq. 10, and have shown that the complex having tri-n-butylphosphine as the ligand is air-stable and highly soluble in a variety of organic solvents. This new M-C bond formation reaction... 

Protonation of metal-acetylide complexes affords the corresponding vinylidene complexes e.g. 20 and 99, Figure 1.48). Proceeding from 20 to 99 leads to a lowering of (3 values, by a factor of five. As the vinylidene complexes can be easily deprotonated to give back to the alkynyl precursors, and this sequence can be repeated, these complex pairs can provide an interesting protically switchable NLO system. 

In addition to those formed by surfactant amphiphiles, two other types of lyotropic mesophases are generally recognized, neither of which exhibits a cmc. The first of these are lyotropic phases of rigid-rod polymers that can form mesophases in both aqueous and non-aqueous solvents " these mesophases are of the nematic or hexagonal type. Examples include polymeric metal acetylide complexes and DNA." The other type is usually formed from flat and largely aromatic molecules which stack to give lyotropic columnar phases, also referred to as chromonic phases." " This latter class is formed from systems with ionic or strongly hydrophilic peripheral functions, and forms mesophases... 

Equations 13.10-13.12 show three examples of the synthesis of vinylidene complexes by reactions of metal-acetylide complexes with acid or base. The molybdenum(II) acetylide complex in Equation 13.10 reacts with acid to protonate the p-carbon and generate a cationic vinylidene complex. In this case, the vinylidene complex is thermodynamically unstable. Warming to 0 °C leads to rearrangement of this species to the tautomeric alkyne complex. In contrast, the more electron-rich molybdenum-acetylide complex in Equation 13.11 containing three phosphite donors generates a vinylidene complex upon addition of a proton from alumina to the 3-carbon of the acetylide. The vinylidene form of the complex is apparently more stable than the alkyne complex in this case. 

The reaction of alkynyliodonium salts with electron-rich transition metals usually results in an oxidative addition under formation of a metal-acetylide complex. Although this type of intermediates has been postulated in many catalytic reactions, this section is limited to the cases in which the metal complexes could be isolated and characterized. 

Most of the mixed metal acetylide complexes of this particular group are those associated with Cp, Cp and carbonyl ligands. A number of synthetic studies have been carried out for polynuclear C2 complexes derived from ethynyl and diethyne-diyl iron complexes. Reaction of the ethynyliron complexes [ ( -C5R5)Fe (CO)2 -C = C H] (R = H, 1 R = Me, 2) with [Ru3(CO)i2] in refluxing benzene affords triruthenium /i- j j, j -acetylide eluster eompounds [Ru3(CO)9(/<-H)... 

Mixed Metal Acetylide Complexes ph3PAuC2Ph + AgCjPh -----... 

Compound 77 also reacts with [Mo2Cp2(CO)4] at room temperature or with [CpMoCo(CO>7] at 50 °C to yield mixed metal acetylide complexes 89, [Cp Fe (CO)2C4H Cp2Mo2(CO)4>] and 90, [Cp Fe(CO)2C4H CpMoCo(CO)5 ]. On further reaction with [Co2(CO)g], 89 gives 91 (Scheme 26). ... 

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