Noninnocence of Indigo: Dehydroindigo Anions as Bridging Electron-Donor Ligands in Diruthenium Complexes

Abstract

Complexes of singly or doubly deprotonated indigo (H2Ind) with one or two [Ru(pap)2](2+) fragments (pap = 2-phenylazopyridine) have been characterized experimentally [molecular structure, voltammetry, electron paramagnetic resonance (EPR), and UV-vis-near-IR spectroelectrochemistry] and by time-dependent density functional theory calculations. The compound [Ru(pap)2(HInd(-))]ClO4 ([1]ClO4) was found to contain an intramolecular NH---O hydrogen bond, whereas [{Ru(pap)2}2(μ-Ind(2-))](ClO4)2 ([2](ClO4)2), isolated as the meso diastereoisomer with near-IR absorptions at 1162 and 991 nm, contains two metals bridged at 6.354 Å distance by the bischelating indigo dianion. The spectroelectrochemical study of multiple reversible reduction and oxidation processes of 2(n) (n = 4+, 3+, 2+, 1+, 0, 1-, 2-, 3-, 4-) reveals the stepwise addition of electrons to the terminal π-accepting pap ligands, whereas the oxidations occur predominantly at the anionic indigo ligand, producing an EPR-identified indigo radical intermediate and revealing the suitability of deprotonated indigo as a σ- and π-donating bischelating bridge.

Pseudo electron-deficient organometallics: limited reactivity towards electron-donating ligands

“…1 They are also known to be extremely unstable and most organometallics follow the 18-electron rule. Some stable coordinatively unsaturated 16-electron (16-e) complexes have been isolated in particular by the groups of Koelle, Tilley, Suzuki, among others, [2][3][4][5][6][7][8][9][10][11][12] but little is known about the reactivity of air and moisture stable 16-e complexes and about their properties in solution. Half-sandwich metal complexes are a particular class of organometallics which has attracted an enormous attention for the design of catalysts, 13 anticancer drug candidates, [14][15][16][17][18][19][20][21][22]23,24 and as building blocks for supramolecular chemistry.…”

“…The hydrogen atoms are omitted for clarity. Selected bond distances (Å) and angles (°): 6: Os1-Cg 1.690 Os1-S1 2.2582(14) Os1-S2 2.2568(14) S1-Os1-Cg 135.69 S2-Os1-Cg 136.41 S1-Os1-S2 87.68(5) 8: Ir1-Cg 1.818 Ir1-S1 2.249(3) Ir1-S2 2.246(3) S1-Ir1-Cg 137.34 S2-Ir1-Cg 134.31 S1-Ir1-S2 88.35(11).…”

Redox‐Induced Oxidative C−C Bond Cleavage of 2,2′‐Pyridil in Diruthenium Complexes

“…The possibility of the formation of either five‐membered or six‐membered chelate ring is extended by the 2,2′‐pyridil derivatives. In all the complexes 1 – 3 , five‐membered chelate rings are preferred over six‐membered chelates which is not uncommon . The tris‐chelated ruthenium centers in both dinuclear and mononuclear complexes 1 – 3 display commonly observed distorted octahedral geometry due to the presence of an asymmetric environment around the metal ion with respect to coordinating centers and the different bridging and ancillary ligands .…”

“…In all the complexes 1-3,f ive-membered chelate rings are preferred over six-membered chelates which is not uncommon. [12] The tris-chelated ruthenium centers in both dinuclear and mononuclear complexes 1-3 display commonly observed distorted octahedral geometry due to the presenceo fa n asymmetrice nvironment aroundt he metal ion with respect to coordinating centers and the different bridging and ancillary ligands. [13] The water molecule in the crystal lattice of 2 forms intermolecular hydrogen bonds at 2.189 (O2·H7D) with the parentm olecule and at 2.708 (O6·H7E) with the neighboring molecule ( Figure S5, Supporting Information).…”

Solvent‐Mediated Functionalization of Benzofuroxan on Electron‐Rich Ruthenium Complex Platform

“…The observeds maller g anisotropy for 2a + /2b + (< g > = 2.089/2.076, Dg = 0.272/0.268;F igure 4a nd Ta ble 2) is in agreement with the spin density plot (Figure 5a nd Ta ble 3) of appreciable spin accumulation on the bridge. [22] Furthermore, the metal-dominated spin for the triplet (S = 1) state of doubly oxidized 2 2 + (Figure 5a nd Ta ble 3) was attributedt ot he {Ru III (L 2 ) 0 Ru III }c onfiguration. Bridge( L 2 )c entered (1,4-diazabutadiene fragment) successive reduction processes [7a, 8] in 2 n (n = À,2 À)w ere corroborated by MO compositions (see Ta blesS3 and S13-S22 in the Supporting Information) and Mulliken spin density plots (Figure 5a 1/2;S cheme 5), it displayed af ree radical in the EPR spectrum at g % 2(Table 2and Figure 4).…”