En Route to Chiral-at-Metal Ruthenium Complexes Containing Tripodal Tetradentate Ligands

Abstract

Synthetic routes for ruthenium(II) complexes bearing the {Ru(κ4C,N,N′,P-L)} fragment (L = tripodal tetradentate ligand) are explored. Tripodal ligands LH1–LH3 diastereoselectively react with the dimer [{(Cy)RuCl}2(μ-Cl)2] (Cy = η6-p-MeC6H4iPr), affording the p-cymene compounds [(Cy)Ru(κ3N,N′,P-LH)][SbF6] (1–3). Refluxing complexes 1–3 in MeCN gives [Ru(κ3N,N′,P-LH)(NCMe)3][SbF6]2 (4a–6a). In refluxing MeOH, isomers 4a–6a evolve to the corresponding mer complexes 4c–6c. Reaction of [RuCl2(PPh3)3] with LH1 affords [RuCl2(PPh3)(κ3N,N′,P-LH1)] (7) as only one isomer. [RuClH(CO)(PPh3)3] reacts with ligands LH1–LH3 to give [RuH(CO)(PPh3)(κ3N,N′,P-LH)]Cl (8–10). Complexes 8–10 were isolated as a mixture of only two diastereomers as pairs of enantiomers. Refluxing suspensions of complexes 8–10 in 2-ethoxyethanol afforded the corresponding metalated complexes [RuCl(CO)(κ4C,N,N′,P-L)] (11–13), in which the tripodal ligands L1–L3 act as tetradentate ligands. Only one stereoisomer was detected for complexes 11 and 13...