The heterogenization of the zwitterionic Rh(I) catalysts (sulfos)Rh(cod) (1) and (sulfos)Rh(CO)2 (2) [sulfos = -O3S(C6H4)CH2C(CH2PPh2)3; cod = cycloocta-1,5-diene] is performed by controlled adsorption on partially dehydroxylated high surface area silica. The immobilization procedure is based uniquely on the capability of the sulfonate tail of sulfos to link the silanol groups of the support via hydrogen bonding. Experimental evidence of the −SO3···HOSi− interaction between 1 or 2 and silica has been obtained from IR, Rh K-edge EXAFS, and CP MAS 31P NMR studies. The grafted catalyst (sulfos)Rh(cod)/SiO2 (1/SiO2) is active for the hydrogenation of alkenes in either flow reactors (ethene, propene) or batch reactors (styrene) in hydrocarbon solvents. The hydroformylation of alkenes, here exemplified by 1-hexene, is catalyzed exclusively in solid−liquid conditions. No Rh leaching is observed in either case. In solid−gas conditions, the catalyst 1/SiO2 is converted by syngas to the catalytically inactive, dicarbonyl derivative (sulfos)Rh(CO)2/SiO2 (2/SiO2). The termination metal products of the solid−gas reactions have been studied by EXAFS, while those of the batch reactions have been authenticated by NMR spectroscopy after extraction with methanol. In all of the cases investigated there was no evidence of the formation of contiguous Rh−Rh sites, indicating that the catalytic active sites are isolated Rh atoms, as in homogeneous phase. A comparison with analogous hydrogenation and hydroformylation reactions catalyzed by the soluble complex 1 in liquid-biphase conditions shows that the immobilized catalyst is more chemoselective and more easily recyclable than the unsupported analogue.

Energy-dispersive EXAFS (EDE), combined with mass spectrometry and a flow microreactor system, has been used to investigate the reaction of an Al 2 O 3 -supported Rh I (CO) 2 species with NO. This combined in situ approach uniquely permits a priori analysis of the structures of the species involved (on a time scale of ca. 2 s) and simultaneous determination of reaction mechanism and kinetic parameters. In the current case, it is found that the Al(O)Rh I (CO) 2 Cl species reacts to form an intermediate Al(O)Rh(NO) 2 Cl Cl species (ν ≈ 0.357 ( 0.125 s -1 , E act ≈ 11 ( 1.25 kJ mol -1 ), which subsequently forms an (AlO) 2 Rh(NO) -Cl species and N 2 O (g) (ν ≈ 2 ( 0.5 × 10 4 s -1 , E act ≈ 40 ( 3.5 kJ mol -1 ) showing a bent (134°) RhNO bond. This combination of rapid and complementary techniques should be applicable to a wide range of disciplines where quantitative structural and kinetic determinations are of importance.

The interaction between supported Rh I (CO) 2 Cl species, prepared by metallo-organic chemical vapor deposition (MOCVD) of [Rh(CO) 2 Cl] 2 to hydroxylated γ-Al 2 O 3 , and NO has been investigated using time-resolved, energy dispersive extended X-ray absorption fine structure (EDE)/mass spectrometry (MS) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). MOCVD of [Rh I (CO) 2 Cl] 2 leads to the formation of a Rh I (CO) 2 Cl{O-Al} adlayer which, when fresh, reacts with NO to form a majority {Al-O} 2 RhCl(NO -) species at room temperature via a two-step mechanism involving an {Al-O}Rh(NO) 2 Cl species. The application of DRIFTS allows a direct association of the bent RhNO bonding in the {Al-O} 2 RhCl(NO)with "highwavenumber" Rh(NO -) species displaying ν(NO) at ca. 1750 cm -1 often observed in supported Rh systems. DRIFTS investigations on analogous Rh I (CO) 2 Cl/TiO 2 systems show the same reactivity toward NO, with a bent nitrosyl being formed rather than the more commonly dominant linear Rh(NO + ) species. DRIFTS also indicates that a second reaction is possible. This becomes increasingly significant for Rh(CO) 2 Cl{O-Al} samples exposed to air for ca. 2-3 days and results in the {Al-O}Rh I (CO) 2 Cl species reacting with NO to form a new species displaying adsorptions at 2150-2110 and 1750-1700 cm -1 . Once formed, this latter species reacts no further at room temperature under NO. The DRIFTS spectrum of this species is interpreted as being due to {Al-O}Rh(CO)(NO)Cl species existing in cis and trans configurations: the isomer with the carbonyl group trans to the Cl ligand being the preferred form at room temperature. The reconversion of the Rh(NO -) species under CO shows complex temperature dependence. The consumption of the Rh(NO -) shows only a weak temperature dependence in terms of EDE, but the observed evolution of NO g shows a strong temperature dependence. The combination of EDE and MS indicates rapid formation of an intermediate species, most likely {Al-O}Rh(CO)(NO)Cl, which at room temperature converts to the geminal dicarbonyl species slowly. The possible origins of this behavior, and the parameters determining the formation of "linear" and/ or "bent" rhodium nitrosyls in support Rh systems are discussed.