Other Complexes Possibly Containing M—H—Si Three-Center Bonds

OTHER COMPLEXES POSSIBLY CONTAINING M—H—SI THREE-CENTER BONDS 

Apart from the dinuclear metal complexes 17-19 there are also some mononuclear metal compounds for which the occurrence of M—H—Si three-center bonds appears possible, judging from currently available data. The first complex in this category, 20, was obtained by Jetz and Graham among other products by reaction of trichlorosilane with Cp2(OC)4Fe2 (65). 

Subsequently three complexes of this type [SiR3 = SiCl3 (66), SiF2Me (67), and SiMe2Ph (6 )] were structurally characterized, but only in one of them (SiR3 = SiF2Me) was the hydrogen located. 

For a more general comparison between complexes containing a three-center bond involving either a silicon or a carbon atom, let us return to the notion that in complexes of this type the E—H bond (E = C, Si) is not completely oxidatively added to the metal moiety (L M) and that the addition process [Eq. (8)] is instead arrested at some point along the 

The main difference between mononuclear complexes containing either a M—H—C or a M—H—Si three-center bond is that most tj2-CH complexes correspond to an earlier stage of the addition reaction than do the 7j2-SiH complexes 7(CMH) coupling constants are usually closer to the values for /(OH), while /(SiMH) values are closer to 2/(SiMH), and the relative lengthening of the C—H distance on 172 coordination is usually smaller than that of coordinated Si—H bonds. For example, in the representative iron complex 21 [the structure of which was determined by neutron diffraction analysis (74)], the coordinated C—H bond 

---