Oxide-supported triruthenium ketenylidence clusters and their catalytic properties

Abstract

A triruthenium ketenylidene cluster, [PPN] 2[Ru 3(CO) 6(μ-CO) 3(μ 3-CCO)] ( 1), as a possible precursor for production of higher oxygenates, was deposited on MgO, SiO 2 and SiO 2Al 2O 3, and the nature of surface species supported on these oxides was characterized by IR and Raman spectroscopy along with their catalytic performance in CO isotopic exchange, alkylation, and hydroformylation. When MgO was dehydrated below 573 K, the sample spectrum of the triruthenium ketenylidene cluster on the MgO support exhibited characteristic bands of [Ru 3(CO) 6(μ-CO) 3(μ 3-CCO)] 2−. A new surface species assigned to [HRu 3(CO) 9(μ 3-CCO)] − ( 2) was characterized by new IR bands at 2068, 2030, and 1999 cm −1, as the MgO was dehydrated at 673 K. On SiO 2 and SiO 2Al 2O 3, IR investigation suggested that the stoichiometric protonation of [Ru 3(CO) 6(μ-CO) 3(μ 3-CCO)] 2− ( 1) with surface hydroxyl groups such as SiOH and Si(OH)Al occurred, giving rise to [HRu 3(CO) 9(μ 3-CCO)] −{SiO −} ( 2) and H 2Ru 3(CO) 9(μ 3-CCO)2{Si(O −)Al} ( 3), respectively. The above mentioned species were demonstrated by the extraction from surface species by IR and NMR investigation. The Raman spectra of MgO and SiO 2 supported triruthenium clusters showed bands assigned to RuRu and Ru 3C stretching modes. In the reactions of CO isotopic exchange, alkylation and hydroformylation, these oxides-supported triruthenium ketenylidene species showed quite different activities. H 2Ru 3(CO) 9(μ 3-CCO)2{Si(O −)Al} ( 3) was active for CO isotopic exchange reaction, while [Ru 3(CO) 6(μ-CO) 3(μ 3-CCO)] 2−{MgO} ( 1) was active with CH 3I at room temperature in alkylation reaction. In hydroformylation of ethylene, MgO-supported triruthenium ketenylidene species showed high activity and selectivity for formation of oxygenates, while the SiO 2Al 2O 3-supported triruthenium ketenylidene cluster exhibited a high activity for the formation of ethane. These results have demonstrated that the support effect is obvious for the formation of various triruthenium ketenylidene species on oxides. Additionally, the preparation of these triruthenium ketenylidene clusters on oxides by surface-mediated organometallic synthesis showed a very high yield and a relatively simple procedure as compared with those by solution synthesis.