Tris(pyrazolyl)methanesulfonate (Tpms) − A Versatile Alternative to Tris(pyrazolyl)borate in Rhodium(I) Chemistry

Abstract

Thallium(I) tris(pyrazol-1-yl)methanesulfonate (TlTpms) has been prepared as a new versatile precursor for Tpms complexes. TlTpms readily reacts with the rhodium(I) complexes [Rh(LL)Cl]2 [LL = (CO)2, cod, nbd] to give the corresponding TpmsRh(LL) complexes [LL = (CO)2 (2a), cod (3), and nbd (4)]. In solution, 2a reversibly forms the binuclear complex TpmsRh(µ-CO)3RhTpms (2b). 3 and 4 react with CO to form 2a. TpmsRh(CO)(PR3) complexes [PR3 = PPh3 (5a), PMe3 (5b), PCy3 (5d), P(Ph)2(PhSO3K) (5e)] have been obtained by reaction of 2a with the corresponding phosphanes. The solid-state structures of 2a, 3, 4, and 5a have been determined by X-ray analysis. 2a, 3, and 5a have square-planar geometries with the Tpms ligand coordinating in a κ2 mode. The non-coordinating pyrazole ring faces either away from (structure 2a) or towards the rhodium atom (structures 3 and 5a). 4 has a trigonal-bipyramidal coordination geometry with a genuine κ3-bonded Tpms ligand. The non-rigid behaviour of the (Tpms)rhodium complexes has been followed by variable-temperature NMR studies. IR studies on 2a and 5a−e show that Tpms is a weakly donating ligand, comparable to the Tp and Tp ligands. Compound 5e is soluble and stable in dilute acids, showing that Tpms, unlike the Tp ligand, is hydrolytically stable.