Group 9 and 8 metals

Reductive elimination from octahedral complexes of rhodium(III) and irid-ium(III) has been examined mainly for C-H bond formation. While some of the complexes undergo a dissociative mechanism similarly to platinum(IV) and palla-dium(IV) analogs, direct reductive elimination without preliminary ligand loss has also been documented. 

The elimination of H2 from cA,cA-IrH2Cl(L)(PPh3)2 (L = CO, PPh3) is induced by flash photolysis [59]. The quantum yield decreases with increase in the concentration of free L, suggesting the mechanism involving a photo-induced dissociation of L, followed by rapid thermal elimination of H2 from the five-coordinate intermediate IrH2Cl(PPh3)2. 

4 (EtCHO), 1.5-1.6 (H2)]. The EtH and EtCHO eliminations constitute the product-forming step in hydrogenation and hydroformylation of ethylene catalyzed by IrH3(CO)(dppe), respectively. 

Platinum(lV) complexes with a structure analogous to 21 have been isolated (Eq. 9.11) [76], 

6 REDUCTIVE ELIMINATION EROM OTHER METAL COMPLEXES 

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As with the salts of other oxoacids, the thermal stability of nitrates varies markedly with the basicity of the metal, and the products of decomposition are equally varied/ Thus the nitrates of Group 1 and 2 metals find use as molten salt baths because of their thermal stability and low mp (especially as mixtures). Representative values of mp and the temperature (I d) at which the decomposition pressure of O2 reaches 1 atm are ... 

The flame colours of the compounds of several group 1 and 2 metals... 

Figure 7.15 (a) Enthalpy of formation of ternary oxides and nitrides from their binary constituent compounds as a function of the ratio of ionic potential [16]. Reprinted with permission from [16] Copyright (1997) American Chemical Society, (b) Gibbs energy of the oxide-sulfide equilibrium for group 1 and 2 metals at 1773 K as a function of the optical basicity of the metal. 

When it comes to metal-rich compounds of the alkaline earth and alkali metals with their pronounced valence electron deficiencies it is no surprise that both principles play a dominant role. In addition, there is no capability for bonding of a ligand shell around the cluster cores. The discrete and condensed clusters of group 1 and 2 metals therefore are bare, a fact which leads to extended inter-cluster bonding and results in electronic delocalization and metallic properties for all known compounds. 

The bis-benzo-15-crown-5 ferrocene compound [7] containing two vinylic linkages was formed in a mixture of three isomeric components, the cis-cis, cis-trans and trans-trans isomers, which proved inseparable. However, the precedent of insignificant differences found between the magnitudes of the metal cation-induced anodic shifts in the ferrocenyl redox potentials of the respective separated cis and trans isomers [2a] and [2b] led us to use the same isomeric mixture of [7] throughout the subsequent FABMS and electrochemical group 1 and 2 metal cation complexation experiments,... 

The p-t-butylcalix[4]arenediquinone-bis(methylether) [56], which had previously been synthesized by Gutsche and co-workers, was used as a model compound in these studies. The receptors [54] and [55] have been shown by nmr titration techniques to form 1 1 solution state complexes with group 1 and 2 metal, ammonium and alkylammonium guest species. 

Compounds [54] and [55] have been shown to complex group 1 and 2 metal cations and also ammonium and alkylammonium cations by nmr and UV/Vis spectroscopies and also by a number of solid-state X-ray crystallographically determined structures. The quinone moieties in these molecules constitute not only the coordination site but also the redox-active centre. The complexation... 

Only a few group 1 and 2 metal derivatives of selenolates have been structurally characterized. They are prepared with the same methods used for the thiolates.155,158 At present there are no crystal structures of lithium terphenyl selenolates. However, the potassium and rubidium salts, which are dimeric, have been structurally characterized.155 They are isomorphous, both to each other and to the closely related thiolate analogues.1533 Currently, there are no reported terphenylselenolates reported for the alkaline-earth metals. 

Conductivity monitoring is most valuable for studying reactions which have very small spectral changes but which are accompanied by pH changes. The interaction of group 1 and 2 metal ions with cryptands and diaza-crown ethers has been studied by flow/conductivity methods. Conductivity monitoring has been linked to reactions which may follow pulse radiolysis, for example, in examining the... 

Metals in biological systems function in a number of different ways. Group 1 and 2 metals operate as structural elements or in the maintenance of charge and osmotic balance (Table 1.2). Transition metal ions that exist in single oxidation states, such as zinc(II), function as structural elements in superoxide dismutase and zinc fingers, or, as an example from main group +2 ions, as triggers for protein activity—that is, calcium ions in calmodulin or troponin C... 

The cyclopropane 1 reacts with none of the group 1 and 2 metal chlorides. Among early transition metal chlorides, NbCl reacted with i in moderate yield to give the same homoenolate obtained by the reaction of equimolar amounts of titanium homoenolate 2 and NbCl (Scheme 2). TaCl5, CrCl3, MoCls, and WC15 did not give any characterizable products. 

The cations of Group 1 and 2 metals, and those of charge +1 from other groups, are such weak Lewis acids that the hydrated ions do not act as acids. 

The saline carbides are formed most commonly from Group 1 and 2 metals, aluminum, and a few other metals. The s-block metals form saline carbides when their oxides are heated with carbon. The anions present in saline carbides are either C22 or C4. All the C4 carbides, which are called methides, produce methane and the corresponding hydroxide in water ... 

Carbon forms ionic carbides with Group 1 and 2 metals, covalent carbides with nonmetals, and interstitial carbides with d-block metals. Silicon compounds are more reactive than carbon compounds. They can act as Lewis acids. 

Suppose that the instability of carbonates when heated depends on the ability of the metal cation to polarize the carbonate ion and remove an oxide ion from it, thereby releasing carbon dioxide. Predict the order of thermal stability of the Groups 1 and 2 metal carbonates. Comment on the likely stability of aluminum carbonate. 

The Group 1 and 2 metals are lightweight and combine well with other lightweight but more stable metals such as aluminum. A mixture, or alloy, of aluminum and lithium is used in airplanes and racing bike frames. Lithium is often used to make light batteries for laptop computers, digital cameras, and pacemakers. Beryllium... 

Metal /3-diketonates are generally synthesized from the neutral /3-diketones and the appropriate bulk metal or metal salt are synthesized in solvents such as water, dioxane, ethanol, or neat diketone. The use of the bulk metal is limited to the more electropositive elements such as the group 1 and 2 metals, although the method is more widely apphcable with more acidic /3-diketones, such as those with perfluoroalkyl substituents. Electrochemical syntheses... 

The enormous increase in readily available computing power since the 1980s has greatly affected the study of. s-block metal complexes. A long-standing assumption that the Group 1 and 2 metal ions (especially the former) could be successfully modeled as point charges in molecular orbital... 

A summary of key properties of the lanthanides, transition metals, and Group 1 and 2 metals appears in Table 2. 

The group 1 and 2 metals form compounds M3P and M3P2 respectively which are hydrolysed by water and can... 

The group 1 and 2 metal sulfides possess the antifluorite and NaCl lattices respectively (see Section 5.11), and appear to be typical ionic salts. However, the adoption of the NaCl lattice (e.g. by PbS and MnS) cannot be regarded as a criterion for ionic character, as we discussed in Section... 

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