Surface hydroxyl group ligands

The numerous surface hydroxyl groups provide attachment points for other functional groups and ligands. 

Formation of 2-propanol and propene was confirmed by GC/MS. Chemisorption of Ti(0 Pr)4 is therefore suggested to be a consequence of nonhydrolytic condensation of the 2-propoxide ligands, which generates V-O-Ti bridges in the absence of surface hydroxyl groups. After removal of volatiles and desorption of physisorbed metal complexes, analysis reveals the presence of two equiv. Ti per V site on the surface, Table 1 (experiments 3 and 4). 

These functional groups contain the same donor atoms as found in functional groups of soluble ligands i.e. the surface hydroxyl group on a hydrous oxide has similar donor properties as the corresponding counterparts in dissolved solutes, such as hydroxides, carboxylates, e.g., (S-OH is a surface group)... 

It is important to distinguish between outer-sphere and inner-sphere complexes. In inner-sphere complexes the surface hydroxyl groups act as o-donor ligands which increase the electron density of the coordinated metal ion. Cu(II) bound inner-... 

The rhenium perhydrocarbyl complex Re(=CBu )(= CHBu )(CH2Bu )2 reacts with the surface hydroxyl groups of a silica(7oo) (Scheme 2.29) to form a well-defined surface species, monografted on silica and containing one alkyl, one alkylidene and one alkylidyne ligands according to mass balance analysis IR, NMR, EXAFS [79-82] and calculations [83, 84]. 

Recent developments have been reported for imido-molybdenum systems. When X = 2,5-dimethylpyrrolyl, more stable surface species can be obtained (although a second minor species, formed by the addition of a surface hydroxyl group to the alkylidene ligand, is also present). Moreover, by tuning the imido ligand, the catalytic activity has been improved dramatically (Table 11.3, bottom rows) [20]. 

Specific adsorption involves replacement of the surface hydroxyl groups by the adsorbing ligand, L, i. e. 

In method A, the ligand silane is used to react with surface hydroxyl groups to form a ligand-functional silica, and then a metal complex precursor is allowed to react with the functionalized surface. In method B, a metal-ligand silane complex is first formed in solution and then allowed to react with surface hydroxyls of the support. 

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