Acid−Base Hydrolytic Chemistry Route to Thin Films Containing Terminal Donor Ligands and Organometallic Complexes for Heterogenization of Metal Complex Catalysis

A general synthetic approach based on the hydrolysis of R‘ 3 Si−NR 2 with organic compounds containing acidic protons, to construct thin films of donor ligands on inorganic oxide surfaces that are subsequently used to support a variety of organometallic complexes, is reported. The reaction of surface hydroxyl groups on silica, glass, quartz, and single-crystal silicon with SiCl 4, followed by NEt 2 H, affords surface-anchored Si−NEt 2 moieties which, upon simple acid−base hydrolysis with HO−(CH 2 ) n −XR 2 ( n = 3, X = N, R = C 2 H 5; n = 3, X = P, R = C 6 H 5; n = 4, X = P, R = C 2 H 5 ), HO−C 6 H 4 −XR 2 (X = P, R = C 6 H 5; X = N, R = C 2 H 5 ), and HO−CH(CH 3 )−(CH 2 ) 3 −N(C 2 H 5 ) 2 at ambient temperature, yield thin films containing terminal phosphine and amine donor ligands. These ligands are then used to covalently anchor organometallic complexes of Ni(0), Rh(I), Ru(II), and Pd(0) via bridge-splitting or ligand-displacement reactions. The synthesis of solution models to the surface-bound species and the characterization of the latter using numerous surface analytical techniques have proven useful in determining the conditions for the deposition process and in the evaluation of the structure of the supported metal complexes. A thin film of [Si]−O−(CH 2 ) 3 PPh 2 Ni(CO) 2 PPh 3 on glass catalyzes the oligomerization of phenylacetylene resulting in a product distribution different from that of a similar reaction in solution. The enhanced activity and selectivity of the organometallic Ni(0) thin films suggests that a positive role is played by the orientation of the surface-bound organometallic species in catalysis.