Preparation, molecular structure and reactivity of mono- and di-nuclear sulfonato rhodium(I) complexes

Abstract

The reaction of [Rh(η³-C₃H₅)(PPrⁱ₃)₂] 1 or [Rh(η³-CH₂Ph)(PPrⁱ₃)₂] 2 with an equimolar amount of RSO₃H (R = Me, p-tolyl, CF₃, F, Camph) led to the formation of the monomeric sulfonatorhodium(I) complexes [Rh{η²-O₂S(O)R}(PPrⁱ₃)₂] 3–7 in excellent yield. An alternative route for the preparation of 4 (R = p-tolyl) and 5 (R = CF₃) is based on the reaction of PPrⁱ₃ with the dinuclear compounds [{Rh(C₈H₁₄)₂[µ-O₂S(O)R]}₂], which were obtained either from [{Rh(C₈H₁₄)₂(µ-Cl)}₂] 8 or [{Rh(C₈H₁₄)₂(µ-OH)}₂] 9 as starting materials. Compounds 3–7 react smoothly with hydrogen by oxidative addition to give the dihydridorhodium(III) complexes [RhH₂{η²-O₂S(O)R}(PPrⁱ₃)₂]. Moreover, on treatment of 3–6 with CO and C₂H₄ the chelating bond of the sulfonate ligand is partially opened and the carbonyl and ethene complexes trans-[Rh{η¹-OS(O)₂R}(L)(PPrⁱ₃)₂] (L = CO or C₂H₄) are formed. The bis(stibine)rhodium(I) derivative trans-[Rh{η¹-OS(O)₂CF₃}(C₂H₄)(SbPrⁱ₃)₂] was obtained from [{Rh(C₂H₄)₂[µ-O₂S(O)CF₃]}₂] and SbPrⁱ₃. Reaction of the compounds [Rh{η²-O₂S(O)CF₃}(olefin)(PPrⁱ₃)] (olefin = C₈H₁₄ or C₂H₄) with benzene led to the displacement of the sulfonate ligand and to the formation of the half-sandwich-type complexes [Rh{η⁶-C₆H₆)(olefin)(PPrⁱ₃)][CF₃SO₃] containing a rather labile benzene–rhodium bond. The preparation of the vinylidene complex trans-[Rh{η¹-OS(O)C₆H₄Me-p}(CCHPh)(PPrⁱ₃)₂] is also described and the crystal and molecular structures of three compounds have been determined. The four-co-ordinate sulfonato complexes 3–6 are active catalysts in the C–C coupling reaction of ethene and diphenyldiazomethane. Besides the three isomeric 1∶1 adducts of C₂H₄ and CPh₂, quite unexpectedly also the 2∶1 adduct 3,3-diphenylpent-1-ene is formed.