Indoles and indazoles are common moieties in pharmaceuticals and naturally occurring bioactive compounds. The development of light-driven methods using earth-abundant transition-metal catalysts offers an attractive route for functionalization of such compounds. Herein, we report a visible-light-induced method for the C3- and N-alkylation of indoles and indazoles with styrenes, catalyzed by Co complexes based on the macrocyclic Mabiq ligand (Mabiq = 2–4:6–8-bis­(3,3,4,4-tetra­methyl­dihydro­pyrrolo)-10–15-(2,2′-biquinazolino)-[15]-1,3,5,8,10,14-hexaene-1,3,7,9,11,14-N6). The photochemical behavior of two CoIII catalysts was examined: Co­(Mabiq)­Cl2 and the newly synthesized Co­(MabiqBr)­Cl2, which contains the Br-modified ligand. Both complexes undergo visible-light-induced homolysis that is significant to their activity but exhibit differences in reactivity. The alkylation reactions are regioselective, furnishing the alkylated indole and indazole products in a Markovnikov fashion with excellent yields of up to 96% across a broad range of substrates. Notably, in contrast to dual-transition-metal and photoredox-catalyzed cross-coupling reactions, our studies reveal that the Co complex plays a dual roleas a photosensitizer and catalytically active metal center with the Mabiq ligand offering regiocontrol.

We have investigated the ability of Co– and Fe–Mabiq complexes (Mabiq = 2–4:6–8-bis­(3,3,4,4-tetramethyldihydropyrrolo)-10-15-(2,2′-biquinazolino)-[15]-1,3,5,8,10,14-hexaene1,3,7,9,11,14-N6) to act as electrocatalysts for CO2 reduction. We observed marked differences in activity when switching the metal center, as the Fe complex outperforms its Co-containing analogue, both in terms of overpotential (η) and faradaic efficiency (FE). [Fe­(Mabiq)2(MeCN)2]­PF6 ([2] + ) selectively reduces CO2 to CO with an overpotential requirement of 500 mV. We have synthesized and fully characterized the two-electron reduced Na­(OEt2)­[Fe­(Mabiq)] ([2] – ), which consists of an intermediate spin FeII center coupled to a ligand biradical and exhibits a unique S = 1 spin state. Both electrochemical and reactivity studies with [2] – point toward a protonated precatalytic intermediate (I PhOH ). The molecular structure of I PhOH indicates the diketiminate carbon as the site of protonation and the ability of the Mabiq ligand to engage in hydrogen bonding interactions. The noninnocent Mabiq ligand, therefore, acts not only as an electron reservoir but also as a proton storage site. Our ligand system uniquely combines two beneficial features, a redox-active unit and a proton donor site, that in combination with the metal ion reduces overpotentials and facilitates selective CO2 conversion.

This work presents the synthesis and characterization of a 3d-4f bimetallic complex based on the redox-active macrocyclic biquinazoline ligand, Mabiq. The mixed Yb-Ni complex, [(Cp*) 2 Yb(Mabiq)Ni]BArF (3), was synthesized upon reaction of [Ni II (Mabiq)]BArF (2) with Cp* 2 Yb II OEt 2 . The molecular structures of 3 and its sister complex, [(Cp*) 2 Yb(Mabiq)Ni][(Cp*) 2 Yb(OTf) 2 ] (1), confirmed the presence of a Yb(III) center and a reduced Ni-Mabiq unit. Spectroscopy (absorption and NMR), cyclic voltammetry and magnetic susceptibility studies were employed to analyze the electronic structure of 3, which is best described by the [(Cp*) 2 Yb III (Mabiq • )Ni II ] + formulation. Notably, the ligand centered radical is delocalized over both the diketiminate and bipyrimidine units of the Mabiq ligand. The magnetic susceptibility and variable temperature NMR studies for 3 denote coupling between the Ni-Mabiq site and the peripheral Yb center -previously unobserved in 3d-3d Mabiq complexes. The complex nature of the exchange interactions is highlighted by the multiconfigurational ground state for 3, comprising nearly degenerate singlet and triplet states.

Benzene-1,3,5-tri­(dithiocarboxylate) (BTDTC3–), the sulfur-donor analogue of trimesate (BTC3–, benzene-1,3,5-tricarboxylate), is introduced, and its potential as a multidentate, electronically bridging ligand in coordination chemistry is evaluated. For this, the sodium salt Na3BTDTC has been synthesized, characterized, and compared with the sodium salt of the related ditopic benzene-1,4-di­(dithiocarboxylate) (Na2BDDTC). Single-crystal X-ray diffraction of the respective tetrahydrofuran (THF) solvates reveals that such multitopic aromatic dithiocarboxylate linkers can form both discrete metal complexes (Na3BTDTC·9THF) and (two-dimensional) coordination polymers (Na2BDDTC·4THF). Additionally, the versatile coordination behavior of the novel BTDTC3– ligand is demonstrated by successful synthesis and characterization of trinuclear Cu­(I) and hexanuclear Mo­(II)2 paddlewheel complexes. The electronic structure and molecular orbitals of both dithiocarboxylate ligands as well as their carboxylate counterparts are investigated by density functional theory computational methods. Electrochemical investigations suggest that BTDTC3– enables electronic communication between the coordinated metal ions, rendering it a promising tritopic linker for functional coordination polymers.

Rational design of artificial water-splitting catalysts is central for developing new sustainable energy technology.