Elucidating Solution-State Coordination Modes of Multidentate Neutral Amine Ligands with Group-1 Metal Cations: Variable-Temperature NMR Studies

Abstract

Multidentate neutral amine ligands play vital roles in coordination chemistry and catalysis. In particular, these ligands are used to tune the reactivity of Group-1 metal reagents, such as organolithium reagents. Most, if not all, of these Group-1 metal reagent-mediated reactions occur in solution. However, the solution-state coordination behaviors of these ligands with Group-1 metal cations are poorly understood, compared to the plethora of solid-state structural studies based on single-crystal X-ray diffraction (SCXRD) studies. In this work, we comprehensively mapped out the coordination modes with Group-1 metal cations for three multidentate neutral amine ligands: tridentate 1,4,7-trimethyl-1,4,7-triazacyclononane (Me 3 TACN), tetradentate tris[2-(dimethylamino)ethyl]amine (Me 6 Tren), and hexadentate N,N′,N″-tris-(2-N-diethylaminoethyl)-1,4,7-triaza-cyclononane (DETAN). The macrocycles in the Me 3 TACN and DETAN are identified as the rigid structural directing motif, with the sidearms of DETAN providing flexible “on-demand” coordination sites. In comparison, the Me 6 Tren ligand features more robust coordination, with the sidearms less likely to undergo the decoordinating–coordinating equilibrium. This work will provide a guidance for coordination chemists in applying these three ligands, in particular, the new DETAN ligand to design metal complexes which suit their purposes.

Li vs Na: Divergent Reaction Patterns between Organolithium and Organosodium Complexes and Ligand-Catalyzed Ketone/Aldehyde Methylenation

“…This work unlocks new chemical space by proving the concept that, by tuning the chemical environments of organo-alkali metal complexes, it is possible to lead to diversified and divergent reaction patterns depending on the metal identity and aggregate size. Further work is underway in our groups in four directions: (1) Comprehensively explore the similarities and differences in reaction patterns between 1 -Li and 1 -Na and thoroughly understand their mechanisms; (2) push the strategy into heavier Group-1 metal congeners, i.e., organopotassium, organorubidium, and organocesium; (3) exploit the ligand-catalysis strategy by employing more catalysts, such as bidentate tetramethylethylenediamine (TMEDA) and hexa -dentate N , N ′, N ″-tris-(2- N -diethylaminoethyl)-1,4,7-triaza-cyclononane (DETAN), − and establish catalyst structure-reactivity-selectivity relationships; and (4) expand the methodology from methylenation (CCH 2 bond formation) into general olefination (CCRR′ bond formation, where R and R′ are H, aryls, or alkyls) and systematically study the E / Z selectivity.…”

Octalithium, Tetrasodium, and Decalithium Compounds Based on Pyrrolyl Ligands: Synthesis, Structures, and Activation of the C–H Bonds of Pyrrolyl Rings and C═N Bonds of a Series of Ligands by Organolithium Reagents

“…The chemistry of organometallic compounds of lithium ion has received growing attention from many groups worldwide. – The interest of many scientists stems from the widespread applications of these complexes as indispensable tools for the synthesis of novel inorganic, organometallic, organic, and bioorganic compounds . These organolithium compounds also exhibit aesthetically pleasing structures.…”

Reduction of K+ or Li+ in the Heterobimetallic Electride K+[LiN(SiMe3)2]e–

“…The accessibility of 1 allows for a comprehensive exploration of its reactivity. From the ligand perspective, our group has applied a number of multidentate neutral ligands in Group-1 metal chemistry − and has observed their cation-binding selectivity . Since 1 features a nonbinding electron and two Group-1 cations (Li + and K + ), it offers an unprecedented opportunity to probe selective reduction of Li + or K + .…”