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 t o self-assembled primer layers of NC5H4(CH2)(2)SiOx or NC(CH2)(16)SiOx on n ative silicon (Si/SiO2) substrates, with some tertiary phosphines PR3 has b een studied by means of in situ ellipsometry. In this way the metal center is effectively inaccessible, and the phosphine can attack only at the cyclo pentadienone ligand site. The rate constants derived from in situ;ellipsome try are found to be in surprisingly good agreement with those obtained in h omogeneous solution for the reaction of [Ru(eta(5)-C5H5)(eta(4)-C5H4O)L](+) (L = pyridine, CH3CN) with PR3 to yield the eta(3)-cyclopentenoyl complexe s [Ru(eta(5)-C5H5)(eta(3)-C5H4O-2-PR3)L](+). The nature of the ruthenium co mplexes at the surface has been established by IR spectroscopy in combinati on with XPS measurements. Thus, the present study provides a rare example o f a direct comparison of the same intrinsic reaction occurring in homogeneo us solution and at the solid-liquid interface.