Agostic interactions bridging

MR donor bonds, is o-bond metathesis. Alternatively, as the Lewis-acid strength of M increases, the tendency toward agostic or bridging interactions can finally result in H—H bond scission and formal migration of hydride to the metal atom,... 

Further LEED work done with intensity-voltage measurements to determine the distance between the median plane of the C6 skeleton and the surface plane of the metal would seem to be important for distinguishing between the cases of on-top or threefold hollow sites for the agostic interactions of the C-H bonds. The former should require a greater metal surface to Q, plane distance. Direct distinctions between the alternative hollow-site models and the twofold bridging sites may require the use of the more recently developed photoelectron diffraction technique. 

The unsaturated methyl complex Mo2(p-ri1 ri2-Me)(p-PCy2)(CO)2 has a weak agostic interaction and undergoes facile dehydrogenation in the presence of metal carbonyl reagents, giving methylidyne-bridged products... 

The only example of Si H M agostic interaction supported by a phosphorus bridge was discovered by Driess et al. in the complexation of a silylated triphosphine ligand to a chromium tricarbonyl complex [Eq. (20)].143,144 A bigger metal (M = Mo) or smaller substituent at silicon (R = Ph) leads to the normal triphosphine complexes. The presence of a Si H "M interaction in 59 is deduced from the lack of C3 symmetry (evident from NMR), the red shift of the IR band for the coordinated Si-H bond (1994 cm-1 vs. 2142 cm-1), and the observation of a reduced Si-H coupling (135.7 Hz for the coordinated Si-H bond vs. 210.9 and 228.6 Hz for the free Si-H bonds). The X-ray structure determination of 59 shows that one of the phosphine ligands is tilted away from the chromium atom so that the... 

Palladium(I) dimeric complexes are also known where the Pd-Pd bond is supported by electron-deficient hydrido or silyl ligands. In the case of SiR2H bridges, an agostic interaction (see Agostic Bonding) of one of the Pd atoms with the Si-H bond is observed (9). The same feature has been found for some phosphido-bridged Pd(I) dimers. 

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