Pyridine-based sulfoxide pincer complexes of rhodium and iridium

The new pyridine-based sulfoxide pincer ligand 1 (2-(diethylaminomethyl)-6-(tert-butylsulfinylmethyl)pyridine = S(O)NN) reacts cleanly with Rh(2)(COE)(4)Cl(2) to form the neutral water- and air-stable Rh(I) complex [Rh(S(O)NN)(NCCH(3))], 1. The cationic complexes [Rh(S(O)NN(NCCH(3))][BF(4)] (2) and [Ir(S(O)NN)(COE)][BF(4)] (5) were obtained by the reaction of 1 with the appropriate metal precursors. The corresponding carbonyl complexes [Rh(S(O)NN)(CO)][PF(6)] (4) and [Ir(S(O)NN)(CO)][BF(4)] (7) exhibit nu CO in the IR spectra that shows that ligand I is a relatively poor a-donor ligand compared to the more common PNP-type ligands, resulting in rather electron-poor metal centers. The carbonyl compounds can be deprotonated to the remarkably stable dearomatized complexes Rh(S(O)NN*)(CO) (8) and Ir(S(O)NN*)(CO) (9). DFT studies on 8 revealed a high electron delocalization over the pyridine ring system and the sulfur atom, which explains the high stability of 8 toward reprotonation. Complete protonation of 8 was achieved in acetic acid.