Acetylene-metal bonding

Ethylenic complexes analogous to these are known and it seems reasonable to suppose that the acetylene metal bond should resemble the ethylene-metal bond in this case. This means that the acetylene, which has two orthogonal p7r-bonds at right angles to each other, would use one filled pir-bond to donate to the manganese and back-donation from the metal would take place mainly into the corresponding anti-bonding pir -mole-cular orbital of the acetylene. 

Tsai et al. have used RAIR extensively in investigations of plasma polymerized acetylene films as primers for rubber-to-metal bonding [12]. Fig. 12 shows RAIR spectra of films having a thickness between about 5.7 and 90.0 nm. A strong band... 

Metal-catalyzed C-H bond formation through isomerization, especially asymmetric variant of that, is highly useful in organic synthesis. The most successful example is no doubt the enantioselective isomerization of allylamines catalyzed by Rh(i)/TolBINAP complex, which was applied to the industrial synthesis of (—)-menthol. A highly enantioselective isomerization of allylic alcohols was also developed using Rh(l)/phosphaferrocene complex. Despite these successful examples, an enantioselective isomerization of unfunctionalized alkenes and metal-catalyzed isomerization of acetylenic triple bonds has not been extensively studied. Future developments of new catalysts and ligands for these reactions will enhance the synthetic utility of the metal-catalyzed isomerization reaction. 

Similar reactions applied to transition metal-acetylene complexes appear capable of separating the 2 carbon atoms originally linked by the acetylenic triple bond 18). Thermal isomerization of metal-acetylene complexes may achieve the same result, showing how metal clusters can catalyze scrambling reactions of acetylenes, e.g.. 

Much of the interest in the polysilanes, polygermanes, and polystannanes involves their sigma delocalization and their sigma-pi delocalization when coupled with arenes or acetylenes. This is not unexpected since silicon exists as a covalent network similar to diamond. In exhibiting electrical conductivity, germanium and tin show more typical metallic bonding. Some polystannanes have been referred to as molecular metals. ... 

Scheme 4.5 shows several possible pathways from r -acetylene metal complexes RE to metal vinylidenes PR. In the first pathway (al + a2), metal vinylidenes PR can be obtained from an intermediate (INI) with a 1,2 hydrogen shift from C to Cp. The second pathway (bl + b2) is through an intermediate (IN2) with an r agostic interaction between the metal center and one C—H bond, which undergoes a 1,2 hydrogen shift to PR. The third pathway (bl + b3 + b4) also starts from IN2 but then goes into another intermediate, the hydrido-alkynyl IN3, which leads to PR with a 1,3 hydrogen shift from the metal center to Cp. 

Compounds with Metal—Metal Bonds. Additions of compounds with metal-metal bonds to acetylenes are rare. Perhaps the addition of acetylenes to cobalt octacarbonyl (29) should be considered an insertion reaction even though the metal-metal bond is not broken since the acetylene finally is bonded to both metal atoms. 

The coordination of oxygen to transition metal ions which occurs mostly in the side-on fashion on surfaces (Section III,A,2 and Appendix B) can be described following the model of acetylene-metal complexes (467). Both 7tu and 7tg orbitals of molecular oxygen have proper symmetry to interact with the bonding set of s, p, and d orbitals on the metal. The bonding orbitals are shown in Fig. 29. 

The proposed structures for these complexes are shown in (XXXVII) and (XXXVIII). The acetylene is bonded to the metal atom through its triple bond, as shown by the lowering of some 200 cm-1 in the C C stretching frequency on complex formation. In addition, the hydroxyl groups interact with the 6p2 or oct -orbitals of the metal atom, as shown by the... 

Both main group and transition metal elements interact with the acetylenic triple bond in a variety of reactions, including hydrogenation, hydrometallation, hydration and cycloadditions. Notably, in most reactions the cyclopropane ring remains intact. 

Fig. 19. Ru6C(CO),5(PhCsCH) (45, 46). The six ruthenium atoms define a slightly distorted octahedron, with the carbide carbon at the center (mean Ru-C — 2.04(2) A). The phenylacetylene ligand is bound to one triangular face of the cluster. Ru-Ru bond lengths fall into two groups those on the face bearing the acetylene average 2.80(4) A, and the remaining metal-metal bonds average 2.92(5) A.

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