Activation of Carbon Monoxide, Water, and Alcohols on Metal Carbonyl Clusters. Homogeneous and Surface‐Mediated Reactions

The Surface of Inorganic Oxides or Zeolites as a Nonconventional Reaction Medium for the Selective Synthesis of Metal Carbonyl Complexes and Clusters

“…About 20 years ago, it was shown that reductive carbonylation at 200 °C of chemisorped [HOs 3 (CO) 10 (OSi⋮)] and [Os(CO) x (OSi⋮) 2 ] n ( x =2,3) gives [Os 3 (CO) 12 ], showing an unexpected mobility of Os carbonyl species even if anchored to the silica surface. Starting from this observation, more recently, α-[Os(CO) 3 Cl 2 ] 2 and various neutral Os carbonyl clusters have been generated from OsCl 3 or [Os 3 (CO) 12 ], in high yields and under mild conditions, on the surface of silica added 41 or not 48,67 with an alkali carbonate …”

“…The practice of carrying out reactions in solution may reflect tradition, but it appeared in the last two decades that one can carry out many organic reactions on solids − (alumina, − silica, − zeolites, clays, , and polymers 2,3 ), generating faster reactions and higher yields than via the traditional solution methods . Recently the surface of inorganic oxides also proved to be a useful reaction medium for the easy high-yield preparation of various metal carbonyl complexes and clusters 7-9a which are of interest as catalysts or catalysts precursors. 9b-g…”

“…Both supported reagent and product can be often fully characterized by various surface methods (e.g., IR, NMR, EXAFS, XPS, extraction, and chemical reactivity methodologies, comparison with molecular models) . In many cases, selectivities and yields are so high and reaction conditions so mild that surface-mediated organometallic syntheses (on silica, Table ; on MgO or Al 2 O 3 , Table ) can be recommended over traditional syntheses in solution (Table ), which often require high pressures, high temperatures, and strongly reducing conditions. − …”

“…In the second approach, rather, basic zeolites such as NaX can produce in their basic cages anionic metal carbonyl species . The third approach involves an increased basicity of silica by dispersion on the surface of an alkali carbonate. , In this latter case, the basicity is controlled by (i) the nature and amount of the alkali carbonate, (ii) temperature, and (iii) the manner by which the alkali carbonate is deposited on silica. The surface basicity is affected not only by the amount of the added alkali carbonate but also by its nature.…”