Disilanyl bridges

Section II. A regioselective introduction of disilanyl bridges is necessary in the process to synthesize complexes with ligands of types 36 or 37109, and this has been made possible by methylation of the cyclopentadienyl fragments. Due to prototropic rearrangements, the protonated derivatives of 36 and 37 exist as a complicated mixture of isomers. The synthesis of the thallium derivative of 37109 is shown in equation 51. 

In accordance with results obtained from UV-Vis and Mossbauer spectroscopy, the pertinent CV data underline the fact that there is a noticeable transmission effect via the disilanyl bridge in 1. They show a distinct decrease in the HOMO-LUMO gap upon introduction of the Fp group... 

Epc + E = 2.96 V in 5 and 2.26 V in 1). In contrast to this, no shift in the Fc-substituted analogue 11 of either the ferrocene oxidation potential or of the dicyanovinyl reduction potential can be observed. Donor-acceptor interaction seems unlikely via the disilanyl bridge in 11, which again is in accordance with UV-Vis data. As there is some interaction via the cyclohexasilanyl bridge in 8, an enhanced conununication could be expected for the Fp analogue, a topic which currently is under study. 

The choice of silicon as the bridging atom results primarily from the ease with which these compounds can be prepared (vide infra). Nevertheless, certain silicon-containing bridging units have been chosen for electronic reasons for example, it is well known that a disilanyl group qualitatively behaves like an ethylene unit. 

P-H-substituted hydrido-disilanyl complexes L M(H)(SiR2-SiR2H) are activated towards a second oxidative addition reaction and tend to form bridged compounds [L (H)M-SiR2]2. 

The tendency to form bridged complexes is reduced with an increasing steric bulk of the substituents at the disilanyl ligand... 

The silylene migration may be involved in some stoichiometric reactions of hydrodisilanes with transition-metal complexes, forming disilanyl complexes through activation of Si-H bonds. Binuclear Ru and Os complexes 39 having terminal silyl groups and silylene bridges are isolated in the reactions of pentame-thyldisilane with Ru3(CO)12 and Os3(CO)12, respectively, albeit in low yields (Eq. 16) [33]. Similar silylene migration may be involved in the reactions of hydrodisilane with other transition-metal carbonyls such as Fe2(CO)9 and Co2(CO)8 [34]. 

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