Silylene ligands

A theoretical basis for the description of the cationic complex [Cp Ru(PR3)2 = = SiR2]+ can also be given. For a d6 CpML2 system, a complete splitting of the three orbitals (octahedral symmetry) is to be expected. Consequently, a coordinated silylene ligand (without any base) should prefer the indicated (Fig. 10) conformation. 

CJC1484> and from the reaction of (Cp )2Sm with A2-diazasilole 83 the silylene complex (Cp )2Sm(83) was isolated. It is noteworthy that these complexes are rather labile. Thus, even THF substitutes the silylene ligand in (Cp )2Sm(83) <20030M1160>. 

In the case of the reactions with trihydrosilanes, employment of 2 equiv RSiH3 gives the doubly silylene-bridged complex as a cis-trans mixture, whereas treatment with 4-5 equiv RSiH3 leads the formation of complex with two pt-7)2-HSiR2 ligands and a /x-silylene ligand (Scheme 6).42... 

The first complex with a metal-metal bond that is bridged by only a single silylene ligand has been prepared in a low yield by treatment of chloro(hydro)silane with base in the presence of Fe2(CO)9 [Eq. (33)].65 However, this product is reported to be inflammable in air and stable only at low temperature. 

Slow isomerization with respect to the substituents on the bridging silylene ligand was reported for a diruthenium complex CpfRu2(/u-Si PhOMe)(jU,-OMe)(ju,-H) [Eq. (59)].50 This reaction proceeds at room temperature and the conversion reaches 60% after 24 h. 

Pt(ri2-H-SiH2SiH(SiH3))(dhpe)]+. These finding were rationalized in terms of a better stabilization of the silylene ligand in 76 when either a-donating (Me) or ji- donating substituents are present. 

There are two plausible reasons explaining the difference. One is based on the difference in the substituents on the heteroatom. The substituents on a silylene ligand are alkyl and/or aryl groups, whereas those on a cationic phosphenium ligand are amino and/or alkoxy groups. Hetero... 

Key questions regarding the reactivity of silylene complexes concern their potential role in metal-catalyzed transformations. For the participation of intermediate silylene complexes in a catalytic cycle, low-energy chemical pathways must exist for the conversion of simple silanes to silylene ligands via activation processes at the metal center. Most probably, a key step in such silylene-forming processes would be the a-migration of a group from silicon to the metal. In search of such a reaction, we prepared the methyl silyl complex shown in Eq. 3. This complex is quite... 

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