Unexpected neutral aza-macrocycle complexes of sodium

Area of Science:

• Inorganic Chemistry
• Coordination Chemistry
• Organometallic Chemistry

Background:

• Sodium cations typically exhibit weak interactions with neutral amine ligands in organic media.
• The coordination chemistry of sodium with neutral polyamines is less explored compared to other alkali metals.

Purpose of the Study:

• To investigate the synthesis and structural characterization of unusual sodium complexes with neutral tri- and tetra-amines.
• To explore novel coordination modes and bonding interactions of sodium cations with nitrogen-donor ligands.

Main Methods:

• Reaction of sodium tetrakis(bis(3,5-trifluoromethyl)phenyl)borate (NaBAr(F)) with neutral tri- and tetra-amines in organic solvents.
• Isolation and structural characterization of the resulting sodium complexes using X-ray crystallography.

Main Results:

• Successful isolation of highly unusual sodium(I) complexes with neutral tri- and tetra-amines in good yields.
• Structural determination revealed primary sodium-nitrogen (Na-N) bonding.
• Identification of a unique sandwich cation, [Na(Me3tacn)2](+), featuring homoleptic N6-coordination from two 1,4,7-trimethyl-1,4,7-triazacyclononane (Me3tacn) ligands.
• Characterization of a distorted 5-coordinate complex, [Na(thf)(Me4cyclam)](+), involving tetrahydrofuran (thf) and 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane (Me4cyclam) ligands.

Conclusions:

• Demonstrated the feasibility of forming stable sodium complexes with neutral amine ligands, challenging previous assumptions.
• The study expands the known coordination chemistry of sodium, showcasing unprecedented coordination numbers and geometries.
• Provides insights into the factors governing Na-N bond formation and the stability of resulting complexes.