Other Transition Metal Complexes

Gold(III) organometallics are isoelectronic with cisplatin-like Ptn complexes. For example, complex 10 hydrolyses in water [123] and has shown activity in human tumour xenograft models [124]. However, its mechanism of action is different from that of cisplatin [124,125]. The role of hydrolysis as an activation step for this class of compounds is not yet clear. 

Other examples of organogolds with cytotoxic activity are complexes such as 11, [Au(bipyc-H)(OH)]PF6 [126], and analogues in which the OH has been substituted by bulkier ligands such as 2,6-xylidine-H and p-toluidine-H [127]. For these analogues, hydrolysis may represent an activation step. 

NCI-H460 and T47D), and all were more active than cisplatin. Given the success enjoyed by cisplatin-like platinum coordination complexes, this appears to be a promising area of research. 

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Pd-cataly2ed reactions of butadiene are different from those catalyzed by other transition metal complexes. Unlike Ni(0) catalysts, neither the well known cyclodimerization nor cyclotrimerization to form COD or CDT[1,2] takes place with Pd(0) catalysts. Pd(0) complexes catalyze two important reactions of conjugated dienes[3,4]. The first type is linear dimerization. The most characteristic and useful reaction of butadiene catalyzed by Pd(0) is dimerization with incorporation of nucleophiles. The bis-rr-allylpalladium complex 3 is believed to be an intermediate of 1,3,7-octatriene (7j and telomers 5 and 6[5,6]. The complex 3 is the resonance form of 2,5-divinylpalladacyclopentane (1) and pallada-3,7-cyclononadiene (2) formed by the oxidative cyclization of butadiene. The second reaction characteristic of Pd is the co-cyclization of butadiene with C = 0 bonds of aldehydes[7-9] and CO jlO] and C = N bonds of Schiff bases[ll] and isocyanate[12] to form the six-membered heterocyclic compounds 9 with two vinyl groups. The cyclization is explained by the insertion of these unsaturated bonds into the complex 1 to generate 8 and its reductive elimination to give 9. 

Lewis acids such as SnCl4 also catalyze the reaction, in which case the species that adds to the alkenes is H2C —O— SnC. Montmorillonite KIO clay containing zinc(IV) has been used to promote the reaction. The reaction can also be catalyzed by peroxides, in which case the mechanism is probably a free-radical one. Other transition metal complexes can be used to form allylic alcohols. A typical example is. ... 

Reactions of Other Transition-Metal Complexes with Group-IB. 

S.3.3.3. by Reactions of Other Transition-Metal Complexes with Group-IIB Derivatives... 

Various other transition metal complexes are also useful, including rhodium,195 palladium,196 and molybdenum197 compounds. The catalytic cycle can generally be represented as shown below.198... 

Electrochemiluminescence of Organometallics and Other Transition Metal Complexes... 

In preliminary studies various metal salts such as PdCl2 were attached to the ligands and the complexes characterized by NMR spectroscopy and X-ray crystallography. Typical examples are the palladium complexes (32)—(44) (Scheme 9).66 The catalytic profiles of these and other transition metal complexes prepared by this method still need to be defined. Moreover, solid-phase synthetic versions would be advantageous, and this may well be possible via the (protected) phenol function. 

Double C-H functionalizations involving biphenyl couplings can be mediated by other transition metal complexes (e.g., VOf . Ru02/TFA, Fe(m), TTFA (TI2O3/TFA)), or by light. An early review highlighted this chemistry (Equations (170) and (171)).141... 

Corma and coworkers tested a number of rhodium and other transition metal complexes with ligands based on proline (Fig. 29.23). These authors reported ee-values of 54—90% for the hydrogenation of dehydroamino acid derivatives with a catalyst prepared from ligand 38 [51]. With ligand 39, an ee-value of 34% was recorded for the hydrogenation of ethyl acetamidocinnamate 10 [52]. 

However, because of the mostly very slow electron transfer rate between the redox active protein and the anode, mediators have to be introduced to shuttle the electrons between the enzyme and the electrode effectively (indirect electrochemical procedure). As published in many papers, the direct electron transfer between the protein and an electrode can be accelerated by the application of promoters which are adsorbed at the electrode surface [27], However, this type of electrode modification, which is quite useful for analytical studies of the enzymes or for sensor applications is in most cases not stable and effective enough for long-term synthetic application. Therefore, soluble redox mediators such as ferrocene derivatives, quinoid compounds or other transition metal complexes are more appropriate for this purpose. 

Alkynes react with the bulky germanium hydride (MejSdjGeH to selectively yield (Z)-alkenes (Equation (105)).67 The hydrogermylation of alkynols or alkynes can be catalyzed by a rhodium complex (Equation (106), Table 18) and some of the intermediates were identified (Scheme 16).132 Similar rhodium species react with alkynes to yield alkenyl complexes,133 and other transition metal complexes have been employed as hydrogermylation catalysts including those containing palladium.134,135... 

Although Co carbonyl complexes have been used most often in catalytic PKR, a variety of other transition metal complexes are able to catalyze this reaction. For instance, Cp2Ti(PMe3)2 [36] and Ni(0) catalysts [37] have been reported to afford iminocyclopentenes by the use fBuMe2SiNC instead of CO. Subsequent hydrolysis provides the desired cyclopentenones. Unfavorably, the isolated product yield decreases significantly when applying this reaction sequence. 

Many of these systems employ charged polymers or polyelectrolytes that confer on them particular properties due to the existence of electrical charges in the polymer structure. Oyama and Anson [14,15] introduced polyelectrolytes at electrode surfaces by using poly(vinylpiridine), PVP, and poly-(acrylonitrile) to coordinate metal complexes via the pyridines or nitrile groups pending from the polymer backbone. Thomas Meyer s group at North Carolina [16, 17[ also employed poly(vinylpyridine) to coordinate Ru, Os, Re and other transition-metal complexes by generating an open coordination site on the precursor-metal complex. 

Other transition metal complexes also catalyzed the dimerization of simple butadiene type substrates. For related examples see ... 

The reliable prediction of redox potentials as a function of composition is useful in the synthetic design and application of technetium and other transition metal complexes. A parametric procedure for doing so on the basis of ligand additivity principles has been developed by Lever [28]. Lu etal. [29] used this scheme to correlateTc / ",Tc "/ , andTc hi potentials with the composition of octahedral technetium complexes containing halide, nitrogen, and phosphorus donor ligands. The results are illustrated in Fig. 2 [29], where the observed potentials are plotted according to... 

Multiple metal-metal bonds have since been found in Re and many other transition metal complexes [41]. The structure of the unsupported Re2 unit (2) is shown in Chart 1. Bonds to the ligands in the equator around each metal may be staggered or eclipsed depending on electronic structure, and solvent or unidentate ligands may bind weakly at the axial positions. In some cases, polydentate ligands may bridge the metal-metal-bonded unit (3). 

Murai and Chatani speculated that the two acetylene carbons should be converted into two carbene equivalents to give XVIII during the reaction." To trap this intermediate, the reaction of 6,11-dien-l-yne 69c, which has an olefin moiety in a tether, is carried out in the presence of [RuCl2(CO)3]2 in toluene at 80 °C for 4 h to give tetracyclic compound 71 in 84% yield. It is interesting to note that other transition metal complexes, such as PtCl2, [Rh(OOCCF3)2]2, [IrCl(CO)3] , arid ReCl(CO)s also show catalytic activity for this very complex transformation (Scheme 27). 

Such important studies may be relevant to the activation of dioxygen by other transition-metal complexes and to the investigation of the mechanism of the evolution of dioxygen by photosynthetic man-ganese-oxo complexes. 

Template and capping reactions feature in recent work. A number of sterically hindered H20 and N4 ligands have been prepared in which a quadridentate Schiff base is capped by condensation of salicylaldehyde or pyrrole-2-carbaldehyde with a series of bis(8-aminonaphthyl)alkyl ethers. These ligands combine the versatility of the Schiff base with the protective features well known for certain model porphyrin systems, and appear to be of some interest. The zinc(II) complex and other transition metal complexes have been prepared.340... 

Rather less work has been done with other transition metal complexes using 3,2,3-tet as a ligand. The Cu11,836 859 Os111 44 and Rum410 complexes have been reported, with trans octahedral configurations assigned to the latter two. 

It is found that the hydrolysis of fluorophosphate esters is also accelerated by transition metal ions and complexes. This would be an observation of little general interest, except for the fact that fluorophosphate esters form one of the more commonly encountered types of nerve gases (Fig. 4-51). The hydrolysis of fluorophosphate esters is increased dramatically in the presence of copper(n) and other transition metal complexes, and this sug-... 

The efficient catalytic cycle is ascribed to the characteristic feature that Pd(0) is more stable than Pd(II). Reactions of 7t-allylpalladium complexes with carbon nucleophiles are called Tsuji Trost reactions. In addition to Pd, other transition metal complexes, such as those of Mo [26], Rh [27] and other metals, are used for catalytic allylation. 

Other transition metal complexes catalyze interesting cocyclization of alkynes and alkenes by a completely different mechanism. Efficient 671-clcctrocyclization of the... 

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