Dinuclear Rhenium Complexes

The present volume is the fourth in the series and covers the topics lithium in biology, the structure and function of ceruloplasmin, rhenium complexes in nuclear medicine, the anti-HIV activity of macrocyclic polyamines and their metal complexes, platinum anticancer dmgs, and functional model complexes for dinuclear phosphoesterase enzymes. The production of this volume has been overshadowed by a very sad event—the passing away of the senior editor, Professor Robert W. Hay. It was he who conceived the idea of producing this series and who more than anyone else has been responsible for its continuation. A tribute by one of his many friends, Dr. David Richens, is included in this Volume. 

Fletcher et al. reported another interesting neutral dinuclear rhenium complex 28 (see Fig. 15) which interacts strongly with H2P04 , reasonably with Cl" but only... 

Binuclear complexes of naphthalene (VIII) and of benzene (IX) with [Os(NH3)5]2+ and [Ru(NH3)5]2+ moieties were reported by Taube et al. (19), in which anti- //-1,2-rj2 3,4- 2) coordination of the arene is present. This bonding mode was first observed by Pasman et al. (20) in the binuclear Rhenium complex X. Wolczanski et al. (21) obtained complex XI from the mononuclear complex [Ta(0—Si Bu3)3 2-(N,C)-pyridine ] and benzene. Each tantalum atom is bound unsymmetrically to one C=C bond of benzene with a weak interaction to a third carbon atom the bonding may be described as a distorted tj3-enyl. In the dinuclear cobalt complex XII, the xylene functions as a bis(enyl)-ligand (12,22). 

Four- and five-ring systems diimine ligands and their corresponding dinuclear rhenium complexes (Figure 29) were also prepared. However, while the diimines exhibited smectic and nematic phases between 100 and 400°C, none of the dirhenium complexes was mesomorphic. 

The dinuclear rhenium disulfido complex with n,rj -S2 ligands (ReCp )2(/U-S2)2 (Cp =7j -C5Me4Et) (type IIa2 complex in Fig. 2) undergoes an insertion reaction of acetylene and ethylene into the S-S bond according to Scheme 57. 

The [TcO(OH2)(CN)4] complex is, as shown by the complex formation constants in Table II, more reactive than the corresponding complexes of either the Re(V) or W(IV). This, coupled with the fact that the dinuclear species [Tc203(CN)8]4 is formed rapidly whenever there are appreciable amounts of the [TcO(OH)(CN)4]2 complex present (71), i.e., below pH ca. 5.5, prohibits any experiment around these acidic conditions. A marked difference in the [H+] dependence for the Tc(V) compared to the above-mentioned Re(V) and W(IV) systems originates from the fact that the Tc(V) is much more reactive and had to be studied at pH values significantly higher than the )Ka2 value of ca. 4. This yielded results similar to the insert (a) in Fig. 16 for the rhenium(V) and only the exchange rate constants and the activation parameters for the hydroxo oxo complex for Tc(V) could thus be obtained (Table V). 

It is also worth noting that the Mn—Sn distance in MeCp(OC)2Mn-(H)SnPh3 is much greater than the Re—Si distance in Cp(CO)2Re(H)-SiPh3. The increased size of the atoms involved (relative to Mn and Si), therefore, cannot be responsible for the absence of a three-center bond in the rhenium silyl compound. The preference of the Cp(OC)2Mn moiety for this kind of bonding is manifested by the dinuclear complexes of type 11 [with Mn-Pt 280.4(3), Mn—H 169(15), Pt—H 200(15) pm in lib] (22a). 

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