Linkage and Redox Isomerism in Ruthenium Complexes of Catecholate, Semi-quinone, and o-Acylphenolate Ligands Derived from Tri- and Tetrahydroxy-9,10-anthracenediones

Abstract

The complexes Ru(CO) 2 L 2 (PHAQ-2H) (PHAQ ) 1,2,4-trihydroxy-9,10-anthracenedione (PUR), 1,2,3-trihydroxy-9,10-anthracenedione (AG), and 1,2,5,8-tetrahydroxy-9,10-anthracenedione (QAL); L ) PPh 3 , PCy 3 , PBu 3 ), and Ru(CO)(dppe)(PBu 3 )(PHAQ-2H), containing catecholate-type ligands were prepared. The complex Ru(CO) 2 -(PBu 3 ) 2 (AG-2H) crystallizes in the space group P2 1 /n (No. 14 Var) with a ) 13.317(2), b ) 15.628(2), c ) 21.076(3) Å, β ) 101.660(10)°, Z ) 4; the crystal structure shows it to contain a 2,3-catecholate ligand. The electrochemistry of these complexes was examined, and the semi-quinone complexes [Ru(CO) 2 L 2 (PHAQ-2H)] 1+ and [Ru(CO)(dppe)(PBu 3 )(PHAQ-2H)] 1+ were generated by chemical oxidation. One example of an o-acylphenolate complex, HRu(CO)(PCy 3 ) 2 (PUR-H), is also reported. * To whom correspondence should be addressed.(1) Throughout this paper the following abbreviations are used: purpurin (1,2,4-trihydroxy-9, 10-anthracenedione), PUR; anthragallol (1,2,3trihydroxy-9, 10-anthracenedione), AG; quinalizarin (1,2,5,8-tetrahydroxy-9, 10-anthracenedione), QAL. The removal of one hydroxyl proton is indicated by "-H" and of two hydroxyl protons as "-2H"; removal of three hydroxyl protons and O-methylation is indicated by "-3H+Me". (2) For example, see: (a)

Ruthenium-azoimine-chloranilates Synthesis, Spectra and Electrochemistry of Ruthenium(II)-1-alkyl-2-(arylazo)imidazole-chloranilate Complexes

“…In the complexes where the metal ion is redox active with delocalisable dp-orbitals and/or p-acidic co-ligands having vacant p * -orbitals can participate with additional charge transitions: 3b 1 (catecho lato) fi dp (metal) [17], 3b 1 (catecholato) fi p * (co-ligand) [26]. Usually these transitions appear in the longer wavelength region (>700 nm) and are highly intense in nature (e$10 4 ) [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][20][21][22][23][24]. In [Ru(R-aai-R¢) 2 (CA)], Ru(II) is not a pacceptor system (d 6 ) but the Ru(R-aai-R¢) 2 -fragment is a potent system to receive p-electrons.…”

“…A common feature of the metal-RQ chemistry is the delocalization of active electrons beween the metal and the quinonoid ligand. Thus transition metals are good candidates to stabilize different redox states of the quinonoid system [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. This is mainly due to the closer energy of quinonoid based ligands to those of metal based dporbitals and recently much effort has been devoted to the study of the electrochemical and spectroscopic properties of ruthenium complexes.…”

“…This is mainly due to the closer energy of quinonoid based ligands to those of metal based dporbitals and recently much effort has been devoted to the study of the electrochemical and spectroscopic properties of ruthenium complexes. The presence of p-acidic coligands like CO, [4] pyridines (R-Py), a-diimines (bpy, phen, tpy), [5][6][7][8][9][10][11][12][13][14][15] PPh 3 , [2,3,16] and 2-(arylazo)pyridines [17] efficiently control the energy of metal dp levels. As a result of this, the electron delocalisation between ruthenium and RQ is perturbed in the mixed ligand complexes.…”

“…As a result of this, the electron delocalisation between ruthenium and RQ is perturbed in the mixed ligand complexes. Various approaches have been chosen to establish the participation of metal, coligand and RQ orbitals in the spectroscopic and redox states [9][10][11][12][13]. The modification has been carried out by the synthesis of the ruthenium-RQ system using electron donor/acceptor coligands.…”

“…The cisRuCl 2 fragment in these complexes may be substituted by other donor centers either directly or by the Ag + -assisted route to synthesise hetereoleptic tris-chelates [42,43]. The compounds having a cis-MCl 2 configuration have been used to synthesise catecholato complexes [9][10][11][12][13]. In continuation of comprehensive studies on the chemistry of the catecholato system [21][22][23][24], in this article we describe some ruthenium(II) 1-alkyl-2-(arylazo)imidazole complexes of chloranilic acid.…”