Ligand Exchange and Oxidative Addition on a Silica-Supported Rhodium Complex, trans-[(⋮SiO)Rh(PMe3)2(CO)

Abstract

The surface organometallic fragment [RhI(P(CH3)3)2(CO)], 1, was prepared by the reaction of trans-[CH3Rh(P(CH3)3)2(CO)] with partially dehydroxylated silica. 1 is attached to the silica surface by a covalent bond to oxygen. The reactions of 1 with organic and inorganic substrates were followed by transmission infrared and solid-state NMR spectroscopies. Ligand exchange reactions were observed when 1 was treated with 13CO and P(CH(CH3)2)3. In the presence of excess PR3 (R is methyl or isopropyl), cationic [Rh(PR3)3CO]+ was formed. In the presence of HCl/DCl, Cl2, CCl3Br, CH3I, and CH2CHCH2Cl, 1 underwent oxidative addition to give Rh(III) surface species, characterized by a shift of the ν(CO) modes ca. 100 cm-1 to higher frequency and displacement of the 31P chemical shifts to lower field. In the case of HCl/DCl, ν(Rh−H/D) modes were also observed. Oxidative addition of CH3I to 1 occurs without CO insertion, but the formation of acyl complexes was induced by addition of excess P(CH3)3 or CO. The reaction of 1 with CH2CHCH2Cl exhibits biphasic kinetic behavior, implying consecutive elementary reactions of oxidative addition followed by spontaneous CO insertion into the metal−carbon bond. The demonstration of these reactions on an oxide surface supports the idea that, under carefully controlled conditions, surface reactivity can be interpreted by using concepts from organometallic chemistry.