Philip W. Kletnieks

Zeolite-supported organorhodium fragments: essentially molecular surface chemistry elucidated with spectroscopy and theory.

Structures of zeolite-anchored organorhodium complexes undergoing conversions with gas-phase reactants were characterized by infrared spectra bolstered by calculations with density functional theory and analysis of the gas-phase products. Structurally well-defined zeolite-supported rhodium diethylene complexes were synthesized by chemisorption of Rh(C(2)H(4))(2)(acac) (acac = CH(3)COCHCOCH(3)) on dealuminated Y zeolite, being anchored by two Rh-O bonds, as shown by extended X-ray absorption fine structure (EXAFS) spectroscopy. In contrast to the nonuniformity of metal complexes anchored to metal oxides, the near uniformity of the zeolite-supported species allowed precise determination of their chemistry, including the role of the support as a ligand. The anchored rhodium diethylene complex underwent facile, reversible ligand exchange with deuterated ethylene at 298 K, and ethylene ligands were hydrogenated by reverse spillover of hydrogen from support hydroxyl groups. The supported complexes reacted with CO to form rhodium gem-dicarbonyls, which, in the presence of ethylene, gave rhodium monocarbonyls. The facile removal of ethylene ligands from the complex in H(2)-N(2) mixtures created coordinatively unsaturated rhodium complexes; the coordinative unsaturation was stabilized by the site isolation of the complexes, allowing reaction with N(2) to form rhodium complexes with one and with two N(2) ligands. The results also provide evidence of a new rhodium monohydride species incorporating a C(2)H(4) ligand.

A Site-Isolated Rhodium-Diethylene Complex Supported on Highly Dealuminated Y Zeolite: Synthesis and Characterization

The reaction of Rh(C2H4)2(acac) with the partially dehydroxylated surface of dealuminated zeolite Y (calcined at 773 K) and treatments of the resultant surface species in various atmospheres (He, CO, H2, and D2) were investigated with infrared (IR), extended X-ray absorption fine structure (EXAFS), and 13C NMR spectroscopies. The IR spectra show that Rh(C2H4)2(acac) reacted readily with surface OH groups of the zeolite, leading to loss of acac ligands from the Rh(C2H4)2(acac) and formation of supported mononuclear rhodium complexes, confirmed by the lack of Rh-Rh contributions in the EXAFS spectra; each Rh atom was bonded on average to two oxygen atoms of the zeolite surface with a Rh-O distance of 2.19 A. IR, EXAFS, and 13C NMR spectra show that the ethylene ligands remained bonded to the Rh center in the supported complex. Treatment of the sample in CO led to the formation of site-isolated Rh(CO)2 complexes bonded to the zeolite. The sharpness of the nu(CO) bands in the IR spectrum gives evidence of a nearly uniform supported Rh(CO)2 complex and, by inference, the near uniformity of the mononuclear rhodium complex with ethylene ligands from which it was formed. The supported complex with ethylene ligands reacted with H2 to give ethane, and it also catalyzed ethylene hydrogenation at 294 K.

A Zeolite-Supported Molecular Ruthenium Complex with η6-C6H6 Ligands: Chemistry Elucidated by Using Spectroscopy and Density Functional Theory

An essentially molecular ruthenium-benzene complex anchored at the aluminum sites of dealuminated zeolite Y was formed by treating a zeolite-supported mononuclear ruthenium complex, [Ru(acac)(eta(2)-C(2)H(4))(2)](+) (acac=acetylacetonate, C(5)H(7)O(2)(-)), with (13)C(6)H(6) at 413 K. IR, (13)C NMR, and extended X-ray absorption fine structure (EXAFS) spectra of the sample reveal the replacement of two ethene ligands and one acac ligand in the original complex with one (13)C(6)H(6) ligand and the formation of adsorbed protonated acac (Hacac). The EXAFS results indicate that the supported [Ru(eta(6)-C(6)H(6))](2+) incorporates an oxygen atom of the support to balance the charge, being bonded to the zeolite through three Ru-O bonds. The supported ruthenium-benzene complex is analogous to complexes with polyoxometalate ligands, consistent with the high structural uniformity of the zeolite-supported species, which led to good agreement between the spectra and calculations at the density functional theory level. The calculations show that the interaction of the zeolite with the Hacac formed on treatment of the original complex with (13)C(6)H(6) drives the reaction to form the ruthenium-benzene complex.