Transition-metal derivatives 734 Subject

Cyclopropanes are cleaved by a variety of transition metal derivatives. The first observation was that PtCl4 reacts to give a platinocyclobutane. Cyclobutanes appear to be less reactive, but cubane reacts with [Rh(CO)2Cl]2 leading to C—C bond cleavage. The subject of C—C bond cleavage has been reviewed. 

There seems to be no stemming the flow of the primary literature, and the appearance of Volume 1 of the Chemical Society s Specialist Periodical Report on Organometallic Chemistry will be welcomed by all. Further details of this book, which covers both Main Group and Transition Metal derivatives, can be found in Section B. The Journal of Organometallic Chemistry continues to expand, with 1972 seeing the publication of thirteen volumes (34-46), which include subject reviews, annual reports, and preliminary communications, as well as the usual selection of papers. Fortunately it is now possible to purchase the individual volumes given over to the annual reviews. 

Derivatives of Silicon, Germanium, Tin, and Lead containing Bonds to Transition Metals.—Derivatives containing Group IV metal-Transition metal bonds have in recent years been the subject of substantial activity. A... 

Lower oxidation states are rather sparsely represented for Zr and Hf. Even for Ti they are readily oxidized to +4 but they are undoubtedly well defined and, whatever arguments may be advanced against applying the description to Sc, there is no doubt that Ti is a transition metal . In aqueous solution Ti can be prepared by reduction of Ti, either with Zn and dilute acid or electrolytically, and it exists in dilute acids as the violet, octahedral [Ti(H20)6] + ion (p. 970). Although this is subject to a certain amount of hydrolysis, normal salts such as halides and sulfates can be separated. Zr and are known mainly as the trihalides or their derivatives and have no aqueous chemistry since they reduce water. Table 21.2 (p. 960) gives the oxidation states and stereochemistries found in the complexes of Ti, Zr and Hf along with illustrative examples. (See also pp. 1281-2.)... 

The chemistry of diazines remains an area of intense interest, both academic and industrial, with applications in many areas, from biomedical to materials science and electronics. They are versatile, having very varied reactivity, giving many opportunities for manipulation of substituents. Nucleophilic substitutions, electrophilic substitution in oxy and amino derivatives, organometallic and transition metal-catalysed coupling reactions are all subjects of substantial research effort. There are obvious similarities in reactivity of the three diazine systems but also many interesting and practically important, often subtle, differences. 

Complexation of an amino acid derivative with a transition metal to provide a cyanation catalyst has been the subject of investigation for some years. It has been shown that the complex formed on reaction of titanium(IV) ethoxide with the imine (40) produces a catalyst which adds the elements of HCN to a variety of aldehydes to furnish the ( R)-cyanohydrins with high enantioselectivity[117]. Other imines of this general type provide the enantiomeric cyanohydrins from the same range of substrates11171. 

Combustion of transition metal organometallic compounds produces a mixtures of simple compounds (metal oxides, carbon oxides, water, nitrogen) which is subject to exact analysis. Thermal decomposition or high temperature iodination of the same compounds cannot necessarily be expected to produce simple materials, with the result that identification is often a difficult problem. This is typified by diene derivatives of iron carbonyl10, where side reactions of the dienes (e.g. polymerization) follow disruption of the iron-diene bonds. The oligomeric mixture can be parti-... 

The period under review has seen a small, but apparently real, decrease in the annual number of publications in the field of the vibrational spectroscopy of transition metal carbonyls. Perhaps more important, and not unrelated, has been the change in perspective of the subject over the last few years. Although it continues to be widely used, the emphasis has moved from the simple method of v(CO) vibrational analysis first proposed by Cotton and Kraihanzel2 which itself is derived from an earlier model4 to more accurate analyses. One of the attractions of the Cotton-Kraihanzel model is its economy of parameters, making it appropriate if under-determination is to be avoided. Two developments have changed this situation. Firstly, the widespread availability of Raman facilities has made observable frequencies which previously were either only indirectly or uncertainly available. Not unfrequently, however, these additional Raman data have been obtained from studies on crystalline samples, a procedure which, in view of the additional spectral features which can occur with crystalline solids (vide infra), must be regarded as questionable. The second source of new information has been studies on isotopically-labelled species. 

There are no available data on the formation of hydroperoxides derived from DNA within cells. This is likely explained, at least partly, by the fact that DNA is a poorer target than proteins for OH radical as observed upon exposure of mouse myeloma cells to ionizing radiation . However, indirect evidence for DNA peroxidation within cells may be inferred from the measurement of final degradation products that may derive from thymine and guanine hydroperoxidation as the result of oxidation reactions mediated by OH radical and O2, respectively (Sections n.A.2 and n.E.2). It may be pointed out that the measurement of oxidized bases and nucleosides within DNA has been the subject of intense research during the last decade and accurate methods are now available . This includes DNA extraction that involves the chaotropic Nal precipitation step and the use of desferrioxamine to chelate transition metals in order to prevent spurious oxidation of overwhelming nucleobases to occur . HPLC coupled to electrospray ionization... 

Other donors very often used in combination with fullerenes comprise ferrocene, phthalocyanine, transition metal complexes, aniline derivatives, tetrathiafulvalene and oligoacenes, carotenoids, oligoarylene, and oligothiophene and many examples are collected in recent reviews and books dedicated to this subject.3a,7e 28... 

Of commercial interest are benzo- and other fused aromatic 1,2,3-diazaborine derivatives which have exhibited good antibacterial activity against a variety of microorganisms (155—157). The reaction of pyrazole or C-substituted pyrazoles with boranes yields the pyrazabole system, a class of exceptionally stable compounds. More than 70 species in this system have been reported and the subject comprehensively reviewed (158). These compounds have been used as ligands in transition-metal complexes (159). 

At the present time the preparation of the trifluoromethylated derivatives of low valent transition metals by ligand-exchange reactions appears to be quite general. However, as exemplified by the nickel reaction above, the utility of the method is obviously subject to the inherent stability of the desired product. In many cases, such as the preparation of the trifluoromethyl derivatives of the cyclopentadienyl cobalt system, (CF3)Co(Cp)(CO)I and (CF3)2Co(Cp)(CO), the reaction of the dihalide with (CF3)2Cd glyme represents the simplest reaction... 

The cyanocarbonylchromates(O) [Cr(CO)5CN]- and cis-[CifCOMCN) ] -, which are formed by the oxidation of [Cr l,(CO)s]2-with aqueous solutions of KCN or with (CN)2 or ICN have been discussed earlier (55, 56). Further studies have shown that the reaction of metal carbonyls or their derivatives with solutions of KCN in liquid NH3 is a most advantageous method for the synthesis of new cyanocarbonyl metalates of transition metals, since, in liquid NH3, alkali cyanides are not subject to solvolysis, and also since the broad temperature range of -78 to +120°C may be employed. Thus, we have been able to obtain quantitative yields of the tricyano-tricarbonyl metalates (0)/ac-[M(CO)3(CN)3]3 (M = Cr, Mo, W) by direct reaction of the hexacarbonyls (21) ... 

Recently, the borylene complex [p-B(NMe2) (r 5-C5H5)Mn(CO)2 2] (1) was subject to detailed computational studies and the theoretically predicted and the experimentally derived structural parameters were found to be in very good agreement (Table I).117 Density functional theoretical studies have concluded that borylenes BX can be viable ligands in the design of transition metal complexes, which are thermodynamically stable with... 

Other variations involve transition metal-catalyzed generation of the required hydrazones . In a representative example, the iodoarene derivative 49 was converted to the intermediate 50, which was thereafter subjected to Fischer conditions rendering the indole 51 in a good overall yield (Scheme 30) <2004JOC3336>. 

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