Bridged surface ligands

In the presence of H2, perhydrocarbyl surface complexes loose their ligands through the hydrogenolysis of their metal carbon bonds to generate putative hydride complexes, which further react with the neighbouring surface ligands, the adjacent siloxane bridges (Eqs. 8-9) [46,47]. 

The tetrahedral nickel isonitrile cluster Ni4(CNR)7 (R = cyclohexyl or f-Bu) contains three bridging isonitrile ligands and a terminal one at each nickel (52) the bridging ligands are mobile on the cluster surface and a ligand dissociation step occurs (33, 390, 391). 

Figure 3. Schematic representation of PMOs with multifunctional organic bridging groups and bifunctional PMOs with multifunctional bridging groups and mercaptopropyl surface ligands.

Figure 4. Nitrogen adsorption isotherms recorded at 77K for the PMO samples with multifunctional groups and the corresponding pore size distributions. PMO-1 and PMO-2 contains tris[3-(trimethoxysilyl)propyl]isocyanurate bridging groups only, while PMO-3 and PMO-4 contains tris[3-(trimethoxysilyl)propyl]isocyanurate bridging groups and mercaptopropyl surface ligands. For clarity the isotherms are offset vertically by 400 ccSTP/g for PMO-1, 300 ccSTP/g for PMO-2 and by 100 ccSTP/g for PMO-3.

PMO materials with ICS bridging groups and mercaptopropyl surface ligands indicating of a I4j32 group.32... 

Pettit [44] has stressed the importance of bridge melhylene ligands un transition metal surfaces- Similarities in product formation with CO/H] and surest a common mechanism for both processes, with methylene possibly being formed by carbide hydrogenation in Fischer-Tropsch reactions. 

Ihe interaction of polynuclear metal complexes with pyrrole-type molecules has also attracted some attention, and it is interesting in connection with possible interactions with surfaces, where vicinal metal atoms may simultaneously interact with the pyrrole molecule. Cluster compounds containing intact coordinated pyrrole ligands are not known, since this reaction invariably involve N-H and/or C-H bond activation to yield derivatives most frequently containing bridging pyrrolyl ligands, as exemplified in Eig. 6.2. 

Heterogeneous Ru catalysts were prepared by thermolysis of Ru3(/t-H)(/t3,77 -ampy)(CO)9 supported on silica and alumina. The face-bridging ampy ligand does not prevent cluster fragmentation on the support surface, and mononuclear Ru surface species are formed. The heterogeneous catalysts are poorer for hydrogenation of phenylacetylene than the cluster is in homogeneous solution. ... 

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