Influence of Multisite Metal–Ligand Cooperativity on the Redox Activity of Noninnocent N₂S₂ Ligands

Abstract

Metal–ligand cooperativity (MLC) relies on chemically reactive ligands to assist metals with small-molecule binding and activation, and it has facilitated unprecedented examples of catalysis with metal complexes. Despite growing interest in combining ligand-centered chemical and redox reactions for chemical transformations, there are few studies demonstrating how chemically engaging redox active ligands in MLC affects their electrochemical properties when bound to metals. Here we report stepwise changes in the redox activity of model Ru complexes as zero, one, and two BH3 molecules undergo MLC binding with a triaryl noninnocent N2S2 ligand derived from o-phenylenediamine (L1). A similar series of Ru complexes with a diaryl N2S2 ligand with ethylene substituted in place of phenylene (L2) is also described to evaluate the influence of the o-phenylenediamine subunit on redox activity and MLC. Cyclic voltammetry (CV) studies and density functional theory (DFT) calculations show that MLC attenuates ligand-centered redox activity in both series of complexes, but electron transfer is still achieved when only one of the two redox-active sites on the ligands is chemically engaged. The results demonstrate how incorporating more than one multifunctional reactive site could be an effective strategy for maintaining redox noninnocence in ligands that are also chemically reactive and competent for MLC.

Cooperative B–H bond activation: dual site borane activation by redox active κ2-N,S-chelated complexes

“…Thus, this may be due to the distinctive contribution of [(L NCS − )Ru III ] species. 14,18 Although the EPR spectra of any open-shell metal based paramagnetic species typically exhibit rhombohedral signals at low temperature, no Please do not adjust margins Please do not adjust margins observable hyperfine splitting was observed for these species due to the 14 N (I = 1) nucleus. 19,20a The UV-Vis spectra of mer-2a-b show a strong absorption band at 240 nm due to the π→π* transitions and a weak absorption at 430 nm (Figure S30).…”

“…Thus, this may be due to the distinctive contribution of [(L NCS − )Ru III ] species. 14,18 Although the EPR spectra of any open-shell metal based paramagnetic species typically exhibit rhombohedral signals at low temperature, no observable hyperfine splitting was observed for these species due to the 14 N (I = 1) nucleus. 19,20 a …”

“…12,13 On the other hand, for the B-H activation the engagement of MLC with multifunctional reactive sites with redox-active ligands is more useful for accessing key organic transformations. 14 As part of our current interest in activation of boranes utilizing cooperative reactivity, 15 we have synthesized a number of molybdenum(II) hydroborate species, in which BH 3 is stabilized through Mo-H-B(H 2 )-E molybdacycles (E ¼ S, Se or Te). 16 Further, very recently, we have established cooperative Si-H and B-H bond activations by a k 2 -N,S-chelated borate complex, trans-mer-1b that led to the formation of six-membered ruthenahetero-cycles through hemilabile ring-opening of Ru-N bonds.…”

“…12,13 On the other hand, for the B–H activation the engagement of MLC with multifunctional reactive sites with redox-active ligands is more useful for accessing key organic transformations. 14…”

Correction to “Ru(II) Complexes with a Chemical and Redox-Active S2N2 Ligand: Structures, Electrochemistry, and Metal–Ligand Cooperativity”

“…The tentative redox assignments made for the cyclic voltammogram (CV) of compound 3 are incorrect and were revised in a recent publication . The CV data reported remain unchanged, and the revised assignments do not alter the conclusions of this work, but we wish to acknowledge the error and direct readers to where they can find the correct assignments.…”