Cyclopentadienyl carbonyl complexes with other ligands

Two commonly used synthetic methodologies for the synthesis of transition metal complexes with substituted cyclopentadienyl ligands are important. One is based on the functionalization at the ring periphery of Cp or Cp metal complexes and the other consists of the classical reaction of a suitable substituted cyclopentadienyl anion equivalent and a transition metal halide or carbonyl complex. However, a third strategy of creating a specifically substituted cyclopentadienyl ligand from smaller carbon units such as alkylidynes and alkynes within the coordination sphere is emerging and will probably find wider application [22]. 

Osmium forms a wide variety of alkyl and aryl complexes including homoleptic alkyl and aryl complexes and many complexes with ancillary carbonyl (see Carbonyl Complexes of the Transition Metals), cyclopentadienyl (see Cyclopenta-dienyl), arene (see Arene Complexes), and alkene ligands (see Alkene Complexes). It forms stronger bonds to carbon and other ligands than do the lighter elements of the triad. Because of this, most reactions of alkyl and aryl osmium complexes are slower than the reactions of the corresponding ruthenium complexes. However, because osmium is more stable in higher oxidation states, the oxidative addition (see Oxidative Addition) of C-H bonds is favored for osmium complexes. The rate of oxidative addition reactions decreases in the order Os > Ru Fe. 

This is a special volume of Inorganic Syntheses that focuses on complexes that are likely to be useful as starting materials for the preparations of new transition metal coordination and organometallic compounds. There are chapters on complexes with weakly coordinated and therefore easily displaced ligands, low-valent complexes that undergo oxidative-addition reactions, substituted metal carbonyl complexes, nucleophilic metal carbonyl anions, transition metal clusters, a variety of cyclopentadienyl complexes, lanthanide and actinide complexes, and a range of other useful ligands and complexes. 

Thermolysis of the mononuclear (1,4-diphenyl-l-azabutadiene)iron complex 45 gives a diastereomeric mixture of the trinuclear complexes 46a and 46b, which are regarded as analogs of ferrocene with the ry -azaferracyclopenta-dienyl ligand 46. " Co-thermolysis of 45 with other metal carbonyl species produces heterodinuclear 77 -azaferra-cyclopentadienyl complexes 47 (Scheme 4). 

The synthesis of a trinuclear cyclopentadienyl trihydrido complex having carbonyl ligands had been reported prior to the synthesis of 6 and 7. Treatment of (CpRu)2(CO)2( -CO)( -CHR) 17 with H2 (1 atm) under UV irradiation provides fluxional complex 18. The fluxionality involves the passage of tj-CsHs and CO ligands from one side of the Ru3 plane to the other. Protonation of 18 yields a non-fluxional cation 19 in which all three cyclopentadienyl ligands are on the same side of the RU3 plane (Equation (3)). Compound 18 has been shown to react readily with a wide... 

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. 

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