Acetylides ligands

A novel cadmate complex has been formed by the reaction of Cd(NH2>2 with I C=CH in the presence of acetylene in liquid ammonia.250 The potassium salt, K2Gd(CCH)4-2NH3 191, has been structurally characterized. The cadmium center is tetrahedrally coordinated to four acetylide units with which it forms Cd-C bonds of 2.23-2.25 A (Figure 29). The acetylide ligands are 7r-coordinated to two crystallographically distinct potassium ions whose coordination sphere is completed by two ammonia molecules. 

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. ... 

The tantalum(V) calix[4]arene complex 44 provides an interesting scaffold for the construction of an j -PhC2C=CPh ligand upon reaction with an excess of phenylethynyllithium (Scheme 10). The coupling reaction is presumed to proceed via bis-alkynyl 45, which is subsequently attacked at the a-carbon of one of the acetylide ligands to give anion 46, isolated as its lithium salt. The addition of a further equivalent of LiC CPh is probably prohibited by orbital constraints. ... 

Gold(I) acetylide complexes have been prepared from alkynyllithium compounds [Eq. (22)] (63), and a dimeric complex [(PhC=C)Au(/u.-dpe)-Au(C=CPh)] [dpe = bis(diphenylphosphino)ethane] was obtained analogously. The simplest acetylide complexes are perhaps those containing only acetylide ligands. The compounds [Au(C=CPh)]x and [Au(C=C-/-Bu)]4 (1) contain cr- and 7r-bonded acetylide groups, the values of... 

Acetylene-vinylidene rearrangements of silylacetylene-iron carbonyl complexes have been observed,537 while iron-acetylide hydride complexes of the type [Fe(H)(C=CR)(dmpe)2], where dmpe=l,2-bis(dimethylphosphino)ethane, have been found to react with anions to afford substituted alkenyl complexes. It has been proposed538 that a likely reaction course for this latter rearrangement involves initial protonation of the cr-bound acetylide ligand at the carbon (I to the metal centre to form a vinylidene complex. Metal-to-carbon hydride migration in this vinylidene complex with attack by the anion would then lead to the neutral complex (see Scheme 106). A detailed mechanistic investigation has been carried out539 on the novel metathetical... 

The adoption of two different geometries for these isoelectronic Au6Pt clusters is probably due to electronic differences between the carbon monoxide and acetylide ligands, as neither ligand is sterically demanding in these compounds. However, both cluster compounds adopt metal cage geometries that are best described as hemispherical, as expected from their valence electron counts. 

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)...

Related to our work on the bipyridyl acetylides, we have also demonstrated that proper selection of the acetylide ligand makes possible the design of Ptn terpyridyl complexes that exhibit acetylide 3IL excited states [20]. The perylene complexes 3.7 and 3.8 do not display photoluminescence, however, indirect evidence that the triplet excited state is indeed populated was indicated through the sensitization of singlet oxygen. Transient absorption measurements (Fig. 7) confirmed that regardless of the polyimine ligand used, the lowest excited state in these molecules is 3IL localized in the perylenylacetylide moiety. It is clear in Fig. 7a and b that the identical features are observed in the absorption difference spectra of 3.7 and 3.8, whereas the difference spectrum of the phenylacetylide complex is clearly distinct, illustrative of the marked differences between 3IL and 3CT excited absorptions. 

Another report from our laboratory demonstrated how the photophysical properties of Ptn chromophores can be altered by introduction of a terpyridylacetylide unit as the monodentate acetylide ligand, which provides a free tpy-based chelation site for metal ions such as Fe11 and Zn11 [63], For the mononuclear complex, the excited-state properties are consistent with a 3CT manifold, showing a broad structureless emission profile and a long-lived excited state. Once Fe11 is coordinated, the emission... 

Several groups have completed computational studies on the relative stabilities of osmium carbyne, carbene, and vinylidene species. DFT calculations on the relative thermodynamic stability of the possible products from the reaction of OsH3Cl(PTr3)2 with a vinyl ether CH2=CH(OR) showed that the carbyne was favored. Ab initio calculations indicate that the vinylidene complex [CpOs(=C=CHR)L]+ is more stable than the acetylide, CpOs(-C=CR)L, or acetylene, [CpOs() -HC=CR)L]+, complexes but it doesn t form from these complexes spontaneously. The unsaturated osmium center in [CpOsL]+ oxidatively adds terminal alkynes to give [CpOsH(-C=CR)L]+. Deprotonation of the metal followed by protonation of the acetylide ligand gives the vinylidene product. 

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