Varying electronic structural forms of ruthenium complexes of non-innocent 9,10- phenanthrenequinonoid ligands

摘要

Bis(acetylacetonato)ruthenium complexes [Ru(acac)_2(Q_(1-3))], 1-3, incorporating redox non-innocent 9,10-phenanthrenequinonoid ligands (Q_1 = 9,10-phenanthrenequinone, 1; Q_2 = 9,10-phenanthrenequinonediimine, 2; Q_3 = 9,10-phenanthrenequinonemonoimine, 3) have been characterised electrochemically, spectroscopically and structurally. The four independent molecules in the unit cell of 2 are involved in intermolecular hydrogen bonding and π-π interactions, leading to a 2D network. The oxidation state-sensitive bond distances of the coordinated ligands Q~n at 1.296(5)/1.289(5) ? (C-O), 1.315(3)/1.322 (4) ? (C-N), and 1.285(3)/1.328(3) ? (C-O/C-N) in 1, 2 and 3, respectively, and the well resolved ~~1H NMR resonances within the standard chemical shift range suggest DFT supported variable contributions from valence formulations [Ru~(III)(acac)_2(Q~(?-))] (spin-coupled) and [Ru~(II)(acac)_2(Q~0)], respectively. Complexes 1-3 exhibit one oxidation and two reduction steps with comproportionation constants K_c~10~7-10~(22) for the intermediates. The electrochemically generated persistent redox states 1~n (n = 0, 1-, 2-) and 2~n/3~n (n = 1+, 0, 1-, 2-) have been analysed by UV-vis-NIR spectroelectrochemistry and by EPR for the paramagnetic intermediates in combination with DFT and TD-DFT calculations, revealing significant differences in the oxidation state distribution at the {Ru-Q} interface for 1~n-3~n. In particular, the diminished propensity of the NH-containing systems for reduction results in the preference for Ru~(II)(Q~0) relative to Ru~(III)(Q~(?-)) (neutral compounds) and for Ru~(II)(Q~(?-)) over the Ru~(III)(Q~(2-)) alternative in the case of the monoanionic complexes.