Study On Polysilanyl Substituted Cyclopentadienyl Car-bonyliron Complexes

Silicon-silicon bonds in polysilanes have high electron energy level, which is close to that of transition metal compounds. This makes the transition metal com-pounds easily to combine with silicon-silicon bonds in a proper form, leading to acti-vation of the Si-Si bonds. Therefore, the synthesis of transition metal complexes, containing polysilanyl groups, and the activation of the Si-Si bonds by transition met-als have attracted extensive attention in the field of organosilicon chemistry.In this thesis, possible activation of Si-Si bonds by transition metals in polysi-lanyl substituted bis(cyclopentadienyl)tetracarbonyldiiron complexes has been inves-tigated, and a new Si-Si bond activation reaction has been found. In addition, during the course of the study, a new method for one-step synthesis of Fe-Si-bonded com-plexes has also been discovered.Firstly, a series of new disilanyl substituted cyclopentadiene ligands C5H4R (40a-40j) were synthesized. The reaction between40a-40j and pentacarbonyliron were carried out on in p-xylene under the refluxing condition. When the reaction was performed for5h, polysilanyl substituted bis(cyclopentadienyl)tetracarbonyldiiron complexes41containing Fe-Fe bonds were obtained. When time of reaction was ex-tended to24h, unexpected activation of Si-Si bonds in complexes41were observed, and a series of compounds42containing Fe-Si bonds from the cleavage of Si-Si bonds by iron were successfully isolated.Details of the Si-Si bond activation processes were investigated. It was found that the Si-Si bond was not activated when41was alone refiuxed in p-xylene. But in the presence of ligands40and pentacarbonyliron under refiuxing p-xylene, the acti-vation of Si-Si bonds of41could easily occur, probably due to the formation of in-termediate48which might play a key role in activation of the Si-Si bonds. In addition to the product42, a by-product44and cross products45and46which containing the added ligands were also obtained. On the basis of these results, a possible mechanism of the reaction was suggested, which involves formation of the intermediate52from the reaction of41with48, as the critical step. And subsequent reductive elimination reactions of52produce the final Si-Si bond activated products.Secondly, a new approach for direct synthesis of Fe-Si-bonded complexes (η5-C5H4R)Fe(CO)2SiR’3(62a-62o) by reaction of cyclopentadienes40with penta-carbonyliron in the presence of hydrosilanes64had been developed. Thus, when the reaction of40and pentacarbonyliron in refluxing p-xylene was performed in the presence of64, the desired complexes were successfully obtained in good yields, providing a simple one-step synthetic route to obtain the products from the readily available starting materials, wherein the substituents R and R’could vary over a wide range, including R=disilanyl, silyl, H and alkyl; R’3=Ph3and Me2Ph. A plausible mechanism involving interception of coordinatively unsaturated iron species (η4-C5H5R)Fe(CO)2by oxidative addition of the Si-H bond is believed to be respon-sible for the preferred formation of the desired product.The two types of new reactions described above are of considerable theoretical and applicational significance. The finding of the Si-Si bond activation reaction in polysilanyl substituted bis(cyclopentadienyl)tetracarbonyldiiron complexes presents new and interesting examples of Si-Si bond activation in systems containg Si-Si bonds linked through η-ligands to transition metals. The discovery of new approach for synthesis of Fe-Si-bonded complexes provides a simple, effective and practical way for the synthesis of (η5-C5H4R)Fe(CO)2SiR’3. In the process of the above studies,36new transition metal silyl complexes have been synthesized and fully characte-rized, of which10representive compounds have been strucuturally deterimined by X-ray diffraction methods.