Complexes and Their Derivatives

Many of the electrochemical studies of metal carbonyl derivatives, and indeed of other species, have sought to correlate redox potentials with other physical or spectroscopic properties. These studies will be described briefly where appropriate but the reader may wish to refer to a review (33) of such correlations in coordination chemistry. A more theoretical basis has also been provided for the often noted relationship between ° and infrared carbonyl, nitrosyl, or isocyanide stretching frequencies (34). 

Recently (35, 36), attempts have been made to predict the potential of oxidation, ElJ2, of a complex M,L on the basis of a ligand parameter, pL [Eq. (1)]. is the potential when the metal site M( is occupied by CO, and is 

The use of Eq. (1) is exemplified by the chemistry of [MoL(NOXdppe)2]2 where M, is Mo(NOXdppe)2 (36). For L = Cl, SCN (Z = 0), and NCR (R = Me or Ph, Z = 1), a plot of fi1/2 versus pL is linear, but [Mo(COXNOXdppe)2] + is irreversibly oxidized at a potential 0.3 V more positive than expected. J1P NMR spectroscopy subsequently revealed the cis-nitrosylcarbonyl geometry, contrasting with the trans arrangement for the halide and nitrile complexes. Interestingly, the product of the oxidation of cis-[Mo(COXNOXdppe)2]+ is a dication which is reversibly reduced at the potential predicted for the trans isomer. The redox-induced isomerization mimics that of isoelectronic cis-[Mo(CO)2(dppe)2] (Section II,C,6). Other examples of the predictive power of Eq. (1) are to be found in Sections II,C,4 and II,D. 

The seven-coordinate complexes [MX(CO)2(dmpe)2] (M = Nb, X = Cl M = Ta, X = H, Cl, Me, etc.) (38,39) are reversibly oxidized in acetone. Neither the radical cations nor the products of a second, irreversible electron-transfer step have been further characterized. 

Many derivatives of the Group VI metal carbonyls, [M(CO)6] (M = Cr, Mo, or W) undergo reversible one-electron oxidation or reduction, and stable, sometimes isolable, metal- or ligand-based radicals have been fully characterized. The redox potentials of representative complexes are listed in Table I. 

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Dicyclopentadienyliron finds limited application as a catalyst. It was used earlier as an antiknock additive for gasoline. The complex also is used to synthesize other metal jr-complexes and their derivatives. 

The metalloporphyrin complexes and their derivatives have been studied from the standpoint of model compounds of hemoglobin. The polymer-metalloporphyrin complexes are also formed by the reaction in Scheme 8, and a few qualitative investigations have been made with poly(L-lysine)9,10, poly(L-histidine)11, and poly(vinylimidazole)12 as the polymer ligand. Blauer9 has studied the complex formation of heme with poly(L-lysine) and has discussed the effects of the molecular weight and secondary structure of poly(L-lysine) on complex formation. 

The 18-electron rale is not obeyed as consistently by these types of oiganome-tank compounds a by the carbonyl and nitrosyl complexes and their derivatives. For example, in addition to ferrocene. M(i 5-CsHs)2 compounds are known for most of the other elements of the first transition series (M — V, Cr, Mn.Co, Ni) and these cannot obey ihe 18-electron rule. However, only ferrocene shows exceptional thermal stability (stable to 500 C) and is not oxidized by air. Furthermore, cobaltocene, a 19-electron species, is readily oxidized to the 18-electron cobaltocenium ion. (Co(ip-CsH )3)4 , which reflects much of the thermal stability of ferrocene. Mixed cyclopentadienyl carbonyl complexes are common K -CjHjMCO) ]. [(if-CjH )-Cr(CO), . [( -CjHOMnCCOjJ, [(>r-C,H,>Fe(CO ,, . [fo -CjiyCoCoy. and (ip-CsH,)Ni(CO) 2. Of interest is the fact that among these compounds, the odd-atomic-number elements (V. Mn, and Co) form monomers and the even-atomic-number elements (Cr. Fe. and Ni) Ibrm dimers, which is in direct contrast to the behavior shown by the simple carbonyl complexes. Cyclopentadienyl derivatives are now known for every main group and transition metal of the periodic table and for most of the -block metals.89... 

A noteworthy work on complexes of this type has been on the oxyallyl complexes (171) and their related dimers (172). Despite the fact that only electrophilic substitution is observed in the reactions of these complexes and their derived (oxyallyl)Fe(CO)4 cations, these compounds, or structurally very similar ones, have been proposed as intermediates in iron carbonyl mediated [4 + 3] cycloaddition reactions of a ,a -dibromoketones and dienes. " ... 

Homoleptic allyl complexes and their derivatives are prepared by reacting allylmag-nesium chloride with metal halides . 

The photochemically studied group VIIA dimers are mainly the Mj(CO),o complexes and their derivatives which contain unbridged, single metal-metal bonds. As with the group VIA dimers, flash photolysis and kinetic studies argue for an additional photoproduced intermediate besides the expected M(CO)j radicals, but the radical species still dominate the photochemistry of these compounds. ... 

Cp complexes and their derivatives also undergo insertion of the metal into a ligand C-H bond. For example, the dimer in Figure 3.34 forms from the reduction of Djmeuesuiting from the... 

Table 3 presents several examples of organic chemical treatments used to modify ITO surface electronic properties. Chemical structures of these organic materials used to modifiy ITO electrode surfaces are also shown in Fig. 4. Chemical structures of carboxylated and phosphonated ruthenium complexes and their derivatives are not shown in Fig. 4. 

Clearfield, A. Warner, D. K. Saldarriaga-Molina, C. H. Ropal, R. Bernal, I. Structural studies of (jt-C5H5)2MX2 complexes and their derivatives. The structure of bis(jt -cyclopentadienyl)titanium dichloride. Can. J. Chem. 1975, 55, 1622-1629. 

A number of rmsaturated polyazamacrocyclic complexes and their derivatives exhibit unusual properties, such as high metal-like conductivities or, conversely, semiconductor behaviour [90-96], Metallophthalocyanines and subphthalocyanines are promising non-linear optical materials for application in optoelectronic devices [97, 98] Porphyrins have been used in organic light-emitting diodes [99],... 

The field of heterogeneous catalysis employing immobilized homogeneous catalysts continues to expand. Several transition metal complexes and their derivatives have been immobilized on the surface of silica materials... 

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