Synthesis, spectroscopy, structure, and reactivity of bis-azapentadienyl–ruthenium–phosphine complexes [1]

•The first examples of bis-(η3-azapentadienyl)RuL2 complexes have been synthesized and characterized.•The complexes adopt a variety of structural motifs, which differ in the orientation of the azapentadienyl ligands.•Dynamic interconversions between these structural types are observed.•The azapentadienyl nitrogens are the preferred sites of electrophilic attack.

We report the synthesis, spectroscopy, structure, and reactivity of the first examples of bis-azapentadienyl–ruthenium complexes. The parent compound, [(1,2,3-η3)-(5-tert-butylazapentadienyl)]2Ru(PPh3)2 (1), is produced by reacting Cl2Ru(PPh3)3 with two equivalents of potassium tert-butylazapentadienide. Treatment of 1 with CNCMe3, P(OMe)3, PMe3, or PEt3 (L) in THF at room temperature yields single-ligand substitution products [(1,2,3-η3)-(5-tert-butylazapentadienyl)]2Ru(PPh3)(L) (2, L = CNCMe3; 3, L = P(OMe)3; 4, L = PMe3; 5, L = PEt3), and the double-ligand substitution product, [(1,2,3-η3)-(5-tert-butylazapentadienyl)]2Ru(PEt3)2 (6). Other double-ligand substitution products, [(1,2,3-η3)-(5-tert-butylazapentadienyl)]2Ru(L)2 (7, L = PMe3; 8, L = P(OMe)3), are obtained when 1 is treated with PMe3 or P(OMe)3 in THF at reflux. Compounds 7 and 8 exist in solution as equilibrium mixtures of two structural isomers. Electron-rich compounds 6 and 7 react with triflic acid to generate dicationic products,{[(1,2,3-η3)-(CH2CHCHCHN(H)(CMe3)]2Ru(L)2}2+(−O3SCF3)2 (9, L = PEt3; 10, L = PMe3), in which both azapentadienyl nitrogen atoms have been protonated. All of the compounds reported herein have been characterized by NMR spectroscopy, and the structures of 2, 3, 4, 6, and 9 have been confirmed by single-crystal X-ray diffraction.

Graphical abstractThe first examples of bis-(η3-azapentadienyl)RuL2 complexes have been synthesized, and a variety of structural motifs have been observed by NMR and X-ray diffraction. Treatment of electron-rich members of this family with triflic acid leads to protonation at both azapentadienyl nitrogen centres.Figure optionsDownload full-size imageDownload as PowerPoint slide