Tris(pyrazolyl)methanesulfonate (Tpms) - A versatile alternative to tris(pyrazolyl)borate in rhodium(I) chemistry

Thallium(I) tris(pyrazol-1 -yl)methanesulfonate (TlTpms) has been prepared as a new versatile precursor for Tpms corn plexes. TlTpms readily reacts wi th the rhodium(I) complexes [Rh(LL)C-1](2) [LL = (CO)(2), cod, nbd] to give the corresponding TpmsRh(LL) complexes [LL = (CO)(2) (2a), cod (3), and nb d (4)1. In solution, 2a reversibly forms the binuclear complex TpmsRh(mu -C O)(3)RhTpms (2b), 3 and 4 react with CO to form 2a. TpmsRh(CO)(PR3) complex es [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-sta te structures of 2a, 3, 4, and 5a have been determined by X-ray analysis. 2 a, 3, and 5a have square-planar geometries with the Tpms ligand coordinatin g in a kappa (2) mode, The noncoordinating pyrazole ring faces either away from (structure 2a) or towards the rhodium atom (structures 3 and 5a). 4 ha s a trigonal-bipyramidal coordination geometry with a genuine kappa (3)-bon ded 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(CF3 ' M e) and Tp(CF3 ' CF3) ligands. Compound 5e is soluble and stable in dilute a cids, showing that Tpms, unlike the Tp ligand, is hydrolytically stable.