Acetylene complexes ligand substitution

Photochemical reactions have been used for the preparation of various olefin, and acetylene complexes (7). Application to the coordination of dienes as ligands has not been used extensively, so far. In this article the preparative aspects of the photochemistry of carbonyls of the group 6 and group 7 elements and some key derivatives, with the exception of technetium, with conjugated and cumulated dienes will be described. Not only carbonyl substitution reactions by the dienes, but also C—C bond formation, C—H activation, C—H cleavage, and isomerizations due to H shifts, have been observed, thereby leading to various types of complexes. 

Metal ij2-acetylene complexes react with further molecules of acetylenes in two different ways, namely ligand exchange or substitution (Scheme 3). 

In conclusion, subtle variations in the molybdothiol-complex catalysts—ligand substitution, coordination donor atom, and central metal ion—have large effects on the catalytic activity of acetylene reduction. The results presented here may offer useful information for a design of catalysts with optimal activity in such complex systems. 

Substitution reactions at Os(CO)4( -alkene) or Os(CO)4 ()] -alkyne) take place through initial dissociation of a ligand. The complexes Os(CO)4(jj -alkyne), where the alkyne is CF3CSCCF3 or HC=CH, compounds are more reactive than Os(CO)5 in substitution and insertion reactions. The acetylene complex is 10 times more reactive than the hexafluoro-2-butyne complex. This is probably due to the ability of the alkyne to act as a four electron donor and stabilize electron-deficient intermediates. The reaction of Os(CO)4( -HC CH) with excess PMes gives a CO insertion product 0s(C0)2(PMe3)2 C(H)=C(H)-C(0) while reaction with the bulkier phosphine PBuj gives a double insertion product, 0s(C0)3(PBu ) C(0)-C(H)=C(H)-C(0) (Scheme 9). ... 

In this section (Section III) we have discussed substitution reactions of ligands in the first class of complexes (see Section II). Except for acetylene complexes, this class exhibits a tendency to react by an associative mechanism with increase of coordination number in the transition state. Data on monodentate olefins are in agreement with this suggestion. Substitution of polydentate ligands is more complicated and usually depends upon the nature of both the replacing ligand and of a fragment to be substituted. Thus substitution involves competition between both possible mechanisms. 

A reaction mechanism involving a transition metal was studied by Decker and Klobukowski218 who investigated the role of the acetylene ligand from a density functional perspective in M(CO)4(C2H2) (M = Fe, Ru or Os). Recent kinetics experiments have shown that the rate of CO substitution in complexes of the type M(CO)4(C2R2) is accelerated by factors of 102-1013 over their respective pentacarbonyl complexes. These substitution reactions have been shown to be dissociative in nature and show a marked metal dependence on the rate. The origin of the increased reactivity of these alkyne complexes was... 

Miscellaneous.— The reaction between dioxygen platinum(ii) complexes and substituted acetylenes takes place via two discernible steps, according to reaction (9), where R = COaMe and R = cyclohexyl. There is a direct attack by the acetylene on the dioxygen ligand. Formation of u-peroxo- -hydroxo-complexes... 

Almost all acetylene complexes have been prepared by one of two methods ligand substitution [Eq. (1)] or reductive complexation [Eq. (2)]. 

The treatment of metal carbonyls (especially those of iron) with acetylenes affords, together with other products, cyclopentadienone and quinone complexes, in which one or two carbonyl groups respectively have been incorporated with two acetylene molecules into a cyclic organic ir-bonding system. These complexes can also be obtained by direct reaction between iron carbonyls and cyclopentadienone or quinone ligands. Other products in these reactions include complexes of substituted ( clobutadienes, and ir-cyclopentadienyl derivatives. Some examples are shown in Figure 49. 

Since 1958 a considerable amount of research activity has centered around these systems, both in the acetylene-iron carbonyl reactions and the direct reactions of olefins with iron carbonyls. The types of unsaturated ligands which are now known to occur in stable iron carbonyl complexes include substituted and nonsubstituted cyclic, acyclic, and nonconjugated dienes as well as some aromatic systems. Furthermore, what may be formally regarded as dienyl cations as well as allyl cations and radicals are found to... 

A number of structures with S-rich dianion ligands have been determined (297-299).831 832 For example, (297) can be synthesized by the reaction of [Ni(CN)4]2 with polysulfide.833 Upon further reaction with CS2 or substituted acetylenes it forms perthiocarbonato and dithiolene complexes, respectively. 

A variety of triazole-based monophosphines (ClickPhos) 141 have been prepared via efficient 1,3-dipolar cycloaddition of readily available azides and acetylenes and their palladium complexes provided excellent yields in the amination reactions and Suzuki-Miyaura coupling reactions of unactivated aryl chlorides <06JOC3928>. A novel P,N-type ligand family (ClickPhine) is easily accessible using the Cu(I)-catalyzed azide-alkyne cycloaddition reaction and was tested in palladium-catalyzed allylic alkylation reactions <06OL3227>. Novel chiral ligands, (S)-(+)-l-substituted aryl-4-(l-phenyl) ethylformamido-5-amino-1,2,3-triazoles 142,... 

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