Group 8 elements, derivatives

Syntheses of aryl organometallics other than polyhalogenoaryls by thermal decarboxylation are comparatively rare. There are several reasons for this. For transition elements, the thermal stability of simple aryls is often low, especially by comparison with polyhalogenoaryl derivatives, thereby excluding syntheses at elevated temperatures. Electron-withdrawing substituents frequently aid thermal decarboxylation (Section III,A-D), and their absence inhibits major mechanistic paths to both transition metal and main group element derivatives, e.g., SEi (carbanionic) and oxidative addition (Section II). In thermal decomposition of... 

Main group element derivatives containing three or four ferrocenyl thiolate ligands are accessible from the corresponding element chlorides and Fc-SLi. Thus, the reaction of PCI3 with a suspension of 3 equivalents Fc-SLi in toluene — THF (3 1) leads to tris(ferrocenyl thiolato) phosphine, P(SFc)3 the oxide and sulfide, P(0)(SFc)3 and P(S)(SFc)3, are formed as side-products in addition to Fc-SS-Fc. The corresponding tris (ferrocenyl thiolato) element compounds As(SFc)3 and Sb(SFc)3 are also known the antimony derivative decomposes under the influence of either air or light [235]. 

TJ ecently there has been much interest in the synthesis, structure, char-acterization, and thermal decomposition of unusual stable homoleptic metal alkyls MR (I). (The term homoleptic is used to describe a metal complex in which all the ligands are identical (2), i.e. TiR4 and Sn(NR 2)2 are examples of homoleptic metal alkyls and dialkylamides whereas Ti(Cl)R3 and Sn(NR 2)R are heteroleptic compounds. ) There are three classes (2) of these complexes (a) transition metal compounds, (b) diamagnetic lower valent main group element derivatives such as the... 

Similarly, a CF2 group, when not bonded directly to a transition metal, has a fairly consistent chemical shift, falling in the range 110-140. This also appears to be true for both transition metal and main group element derivatives. 

Comparison of solar abundances of iron group elements derived from photospheria absorption and coronal emission lines... 

PM3, developed by James J.P. Stewart, is a reparameterization of AMI, which is based on the neglect of diatomic differential overlap (NDDO) approximation. NDDO retains all one-center differential overlap terms when Coulomb and exchange integrals are computed. PM3 differs from AMI only in the values of the parameters. The parameters for PM3 were derived by comparing a much larger number and wider variety of experimental versus computed molecular properties. Typically, non-bonded interactions are less repulsive in PM3 than in AMI. PM3 is primarily used for organic molecules, but is also parameterized for many main group elements. 

V. Chvalovsky, in B. J. Aylett, ed., Organometallic derivatives of the Main Group Elements, Butterworths, London, 1975. 

Boranes also form derivatives ia which main group elements occupy a bridging position between two boron atoms, rather than a polyhedral vertex. An extensively studied system is -R MB Hg, where R = H, CH, C2H3, halogen, and M = Si, Ge, Sn, Pb (185). The stmcture of l-Br- J.-[(CH3)3Si]-B3H2... 

Main Group Element Carborane Derivatives. Main group element carborane derivatives have been reviewed (231). Only a few alkaline-earth element metaHacarborane derivatives have been characterized. The icosahedral beryUacarborane, /(9j (9-3-[(CH3)3N]-3,l,2-BeC2B H, shown in Figure 24a, has been prepared via the reaction of nido-1 and Be(CH3)2 [0(C2H3)2]2 followed by reaction of the diethyletherate product and... 

Derivatives of the boranes include not only simple substituted compounds in which H has been replaced by halogen, OH, alkyl or aryl groups, etc., but also the much more diverse and numerous class of compounds in which one or more B atom in the cluster is replaced by another main-group element such as C, P or S, or by a wide range of metal atoms or coordinated metal groups. These will be considered in later sections. 

Hellwinkel, D. Penta- and.Hexaorganyl Derivatives of the Main Group Elements. 109, 1-63... 

The radii of cations and anions derived from atoms of the main-group elements are shown at the bottom of Figure 6.13. The trends referred to previously for atomic radii are dearly visible with ionic radius as well. Notice, for example, that ionic radius increases moving down a group in the periodic table. Moreover the radii of both cations (left) and anions (right) decrease from left to right across a period. 

Compounds containing transition metals bonded to main-group elements, such as Hg and Sn, react with Au derivatives to form metal-metal bonds with the elimination of R3MCI ... 

Two principle strategies have been employed for the synthesis of siloxide-containing molecular precursors. The first involves a silanolysis, or condensation, reaction of the Si - OH groups with a metal amido, alkyl, hahde, or alkoxide complex. The second method involves salt metathesis reactions of an alkali metal siloxide with a metal hahde. Much of our work has been focused on formation of tris(tert-butoxy)siloxide derivatives of the early transition metals and main group elements. The largely imexplored regions of the periodic table include the lanthanides and later transition metals. 

Direct metallation of o-halogenophenoxyelement derivatives of silicon, tin, and phosphorus leads to an unstable metallated intermediate which undergoes a rapid 1,3-rearrangement under element-carbon bond formation. This type of reaction seems to be a general method for the synthesis of hydroxyphenyl element derivatives [1-4], We have studied the influence of different organoelement groups on the reaction pathway. The yield increases in the sequence R3Sn < R2P < RjSi P(0)(0R)2. 

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