Comparing Reactivities of Metal Complexes in Solution and on Surfaces by IR Spectroscopy and Time-Resolved in Situ Ellipsometry

The reaction of the [RU(eta(5)-C5H5)(eta(4)-C5H4O)](+) fragment, anchored to self-assembled primer layers of NC5H4(CH2)(2)SiOx or NC(CH2)(16)SiOx on native silicon (Si/SiO2) substrates, with some tertiary phosphines PR3 has been studied by means of in situ ellipsometry. In this way the metal center is effectively inaccessible, and the phosphine can attack only at the cyclopentadienone ligand site. The rate constants derived from in situ;ellipsometry are found to be in surprisingly good agreement with those obtained in homogeneous solution for the reaction of [Ru(eta(5)-C5H5)(eta(4)-C5H4O)L](+) (L = pyridine, CH3CN) with PR3 to yield the eta(3)-cyclopentenoyl complexes [Ru(eta(5)-C5H5)(eta(3)-C5H4O-2-PR3)L](+). The nature of the ruthenium complexes at the surface has been established by IR spectroscopy in combination with XPS measurements. Thus, the present study provides a rare example of a direct comparison of the same intrinsic reaction occurring in homogeneous solution and at the solid-liquid interface.