Dimetallic complexes

Organometallic compounds which have main group metal-metal bonds, such as S—B, Si—Mg,- Si—Al, Si—Zn, Si—Sn, Si—Si, Sn—Al, and Sn—Sn bonds, undergo 1,2-dimetallation of alkynes. Pd complexes are good catalysts for the addition of these compounds to alkynes. The 1,2-dimetallation products still have reactive metal-carbon bonds and are used for further transformations. 

Desulhirization reactions of transition metal-polysulfido complexes have also been reported. The treatment of a dimetallic complex of titanium, [ Ti(Cp)(OAr) 2(yU-S)(yU-S2)] (Cp=77 -C5H5, Ar=2,6-i-Pr2C6H3), with an equimolar amount of PhsP results in the quantitative formation of [ Ti(Cp)(OAr) 2(yU-S)2] via the transformation of the 1U-S2 ligand to a /t-S ligand (Scheme 44) [93]. The reverse reaction of [ Ti(Cp)(OAr) 2(/t-S)2] with Ss proceeds in a good yield. 

Reviews covering the chemistry of group 2 metal complexes with phosphorus-stabilized carbanions,279 and of molecular clusters of magnesium dimetallated primary phosphanes, are available.2 u Magnesium phosphanes remain rare compounds.281 Lithiation of bromide 98 with BuLi in the presence of tmeda in pentane produces a lithium phosphine dimer subsequent treatment with MgCl2 in EtzO gives the phosphane 99 in 69% overall yield (Equation (19)). The centrosymmetric 99 has Mg-C = 2.217 A Mg-P = 2.77 A (av.).282... 

Condensation of 2,6-diacetylpyridine with bis(3-aminopropane)amine in the presence of small ions such as Mn(n), Co(n), Ni(n) or Cu(n) readily leads to formation of the corresponding monomeric (14-membered) macrocyclic complexes of ligand (83). However, when the large Ag(i) ion is used as the template, then a dimetallic complex of a 28-membered macrocycle of type (88) is produced. This example illustrates well the importance of metal-ion size in promoting template reactions. 

The electronic and magnetic properties of bridged dimetallic complexes such as 104 and 105 have been explored. Oxidation of the CoII-Co11 phenylene-bridged species 104 affords the mixed valence Con-Com complex and the diamagnetic CoIII-Co111 dication.128 Magnetic, IR, and electrochemical evidence on neutral 104 indicates weak Co-Co interaction. 

Related to these dimetallic systems, though not involving transition metals, are the boratastilbene complexes such as a " [ H 5 C 5 B-CH =CH-CH 4 -C H =C H P h ]" (isoelectronic with distyrylbenzene chromophores) that show aggregation-dependent photophysics. In nonpolar solvents, they form tightly bound ion pairs that are poorly luminescent, but in polar solvents, or when the counter ions are encapsulated in crown ethers, strong emission is observed as a result of intramolecular charge transfer.130... 

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