Hydrocarbon ligand chemistry

Dimetallocycles have been discovered which exhibit high reactivity with respect to carbon-carbon bond-making and -breaking processes. They allow the synthesis of a variety of simple but important hydrocarbon ligands bridging a dinuclear metal centre. y-Carbene complexes are readily available by several routes and their reactions have implications for both alkyne polymerisation and alkene metathesis. A substantial chemistry of organic species co-ordinated at dinuclear metal centres is in prospect, with significance for metal surface chemistry and catalysis. 

The great majority of Cr1 or Cr° complexes, including those with carbonyl, carbene, or 77-hydrocarbon ligands, are described in the Comprehensive Organometallic Chemistry series. 

Kerber, R.C. (1995) Mononuclear Iron Compounds with ri -ri -Hydrocarbon Ligands, in Comprehensive Organometal-lie Chemistry II, vol. 7 (eds E.W. Abel, F.G.A. Stone, and G. Wilkinson), Pergamon, New York, Chapter 2, pp. 101-229. 

Since 1970 or before, chemists have relied on classical, detailed temperature-dependent line-shape analyses.Indeed, fundamental contributions to our understanding of the dynamics of fluxional metal complexes with vr-hydrocarbon ligands,tertiary phosphorus donors, as well as TT-allyl anions,all stem from these types of measurement. Their contributions to metal carbonyl dynamics and rearrangements in cluster compounds is even more pronounced, and we cite selected studies in this very large area of organometallic chemistry.For slow exchange... 

As the most prevalent structure in organometallic chemistry, sandwich compounds, defined as two cyclic aromatic hydrocarbon ligands flanking one metal center, has played a central role on the stage of organometallic chemistry and catalysis ever since the seminal structure of ferrocene (CpjFe) was elucidated in 1952 [161]. However, this chemistry had never been extended into compound mono-layers of multiple metal atoms in place of the one metal center as the filling of the sandwich until... 

The cluster compounds represent a special and rather broad field in lanthanoid chemistry. Binuclear complexes with bridging atoms or groups but without a direct Ln-Ln bond are found in almost all types of REM compounds and were considered in the corresponding sections of this book. Herein the carbon-containing clusters without hydrocarbon ligands are collected. 

The chemistry of transition metal complexes containing alkylidene, allenylidene, and cumulenylidene ligands, [L M]=C(=C) =CRR n > 2), has been reviewed.An extensive series of Cp (dppe)Fe compounds with an end-bound hydrocarbon ligand have been synthesized, and the iron-carbon bonding studied using Fe Mossbauer spectroscopy. 

This section is dedicated to a description of the chemistries of trinithenium and triosmium clusters that do not contain hydrocarbon ligands. This section should be viewed as an addition to the chemistry described in sections 32.5 and 33 of COMC (1982) and section 12 of COMC (1995) as most of the main themes have been developed in the previous two decades. Overall, the interest in the cluster chemistry of ruthenium and osmium during the period 1994-2004 has tended to focus mainly on higher nuclearity and mixed metal clusters in order to enhance the developments in catalysis and bridge the gap between molecular clusters and nanoparricles. However, triruthenium and triosmium clusters continue to play a pivotal role in the chemistry of ruthenium and osmium. Both classes of clusters can be, and are, used extensively as precursors for the synthesis of higher nuclearity clusters as well as the formation of mono- and bimetallic complexes. No up-to-date review of the chemistry of either Ru3(CO)i2 or Os3(CO)i2 and their compounds is available, but several annual reviews of the chemistry of mthenium and osmium, which include the chemistry of the trinuclear clusters, are available. ... 

This chapter takes a deeper look at the chemistry of transition metal complexes with cross-conjugated hydrocarbon ligands. In each section, issues of their synthesis and structure will be discussed first, followed by some representative reactions. 

The number of works regarding the chemistry of Cp-Rh complexes without other hydrocarbon ligands reported in the 1994-2005 period has been scarce compared to the previous editions, COMC (1982) and COMC (1995). Most of the Rh-Cp complexes reported in the last decade contain other hydrocarbon ligands and hence are described in other sections of this chapter. 

Hydrocarbon ligands which formally contribute five electrons when bonding to a metal are called Dienyl ligands. Five-electron systems are found for cyclic 5-, 6- and 7-membered hydrocarbon ligands and non-cyclic ligands. The 7r-cyclopentadienyl group is the commonest ligand in this class and the chemistry of cyclopentadenyl metal complexes is discussed first. For convenience, the transition metal cyclopentadienide complexes are also discussed in this section. 

This loss of ori/io-hydrogens also occurs in the chemistry of other transition metal-aromatic systems and these reactions may be associated with the general reactivity of atoms and groups in the -position of hydrocarbon ligands attached to transition metals. 

The attachment of a transition metal to an unsaturated hydrocarbon ligand transforms the reactivity properties of the ligand. Whereas the classic chemistry of alkenes and arenes is that of electrophilic addition and substitution reactions, the classic reactivity of multihapto-complexes is their reactions with nucleophiles. Such complexes need not be cationic to be good electrophiles, but it helps, and not surprisingly, the most powerful electrophilic multihapto-complexes have positive charge stabilized by the metal. 

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