Organometallic homoleptic

Experimental and estimated thermodynamic data of homoleptic dialkylzinc compounds are listed in Table 3. Like many organometallic compounds, the lower dialkylzincs have a positive enthalpy of formation, and only the incorporation of silicon atoms in the /3-position imparts significant thermodynamic stability. The mean Zn-C bond rupture enthalpies, all of which are quite low, follow a similar trend as the bond lengths in these compounds. Thus, the presence of methyl substituents in the a-position weakens the zinc-carbon bonds, while silyl substituents strengthen them. 

Surface organometallic chemistry with rare-earth metals (or lanthanides) on various inorganic oxides has advanced considerably during the past decade but is still in its infancy. A major drawback has been the difficult access and handling of pure (homoleptic) Ln alkyl precursors with reactive Ln-C(alkyl) bonds [101]... 

Although technically organometallic, the homoleptic isocyanide complexes of Tc [Tc(CNR)6]" ... 

In the mid-1960s, Dessy and coworkers [12, 13] provided an extensive survey of the anodic and cathodic reactions of transition metal organometallic species, including binary (homoleptic) carbonyls, and this provided a stimulus for many later detailed studies. Whereas the electrochemistry of heteroleptic transition metal carbonyls is covered elsewhere in this volume, that of the binary carbonyls, which is covered here, provides paradigms for the electrochemistry of their substituted counterparts. A key aspect is the generation of reactive 17-electron or 19-electron intermediates that can play key roles in the electrocatalytic processes and electron-transfer catalysis of CO substitution by other ligands. 

Essentially similar methods can be employed to prepare non-homoleptic organometallic compounds of the Main Group elements, EXmR etc. Some procedures unique to particular classes of compound are important, for example the mercuration of aromatic hydrocarbons by mercuric acetate ... 

As can be seen from Scheme III, lanthanide halides are suitable precursors for the synthesis of homoleptic derivatives such as silylamides [114], cyclopen-tadienyls [115] and aryloxides [116]. Such organometallies can be readily obtained in a pure form by sublimating them from the reaction mixture. They themselves are important precursors in organometallic transformations (vide infra). Heteroleptic complexes of the type CpxLn(halide)y (x + y = 2,3) are important synthetic precursors with respect to formation of various Ln-X bonds via simple metathesis reactions [2-29]. Fig. 4 indicates the lanthanide element bonds which are involved in these ubiquitous heteroleptic cyclopentadienyl systems. 

K. H. Theobold, J. Silvestre, E. K. Byrne, and D. S. Richeson, Homoleptic Mesityl Complexes of Cobalt(II). Synthesis, Crystal Structure, and Theoretical Description of Bis(p-mesityl)dimesityldicobalt, Organometallics 8, 2001-2009 (1989). 

During the Manhattan project, a wide range of compounds was screened in the search for volatile uranium compounds that could be used for separation of isotopes of uranium, since UFe was not an easy compound to handle. The leading organometallic chemist of the day, Henry Gilman, investigated the synthesis of simple alkyls and aryls, concluding that such compounds did not exist, or at least were unstable. Even today, just one neutral homoleptic... 

Molybdenum(II) and molybdenum(III) form an extensive array of multiply bonded dimers, which contain Mo-Mo quadruple and triple bonds respectively. Much of the organometallic chemistry of this class of compound has come principally from the work of one research group. Homoleptic compounds suchas [Mo2Me8]" , [Mo() -allyl)4], which contains bridging and terminal allyl ligands (see Bridging Ligand), are readily synthesized from [Mo2(OAc)4]... 

As used here cluster refers to molecules that contain at least 3 metal atoms and electron configurations suitable for the formation of metal-metal bonds. Molybdenum readily forms strong homoleptic metal-metal bonds (see Homoleptic Compound) and so it is not surprising that molybdenum is readily incorporated into cluster stractures (see Polynuclear Organometallic Cluster Complexes). 

While inorganic complexes of osmium in oxidation states +4 through +8 have been known for many years, the study of high-valent alkyl and aryl complexes of osmium is much more recent. The organometallic complexes include homoleptic see Homoleptic Compound) alkyls and aryls, oxo alkyls and aryls, nitrido/imido alkyls and aryls, and cyclopentadienyl see Cyclopentadienyl) alkyls and aryls. The majority of these are complexes of osmium(VI). 

The amino carbene ligands open a new era of ancillary ligands in organometallic chemistry. One of the pioneering studies is the synthesis of 2-coordinate homoleptic see Homoleptic Compound) complexes of low-valent noble... 

Over the years the homoleptic see Homoleptic Compound) alkyl and aryl complexes were one of the major challenges in organolanthanide chemistry. The simplest organometallic... 

---