Abstract

The Group 1 complexes, [M(Me6[18]aneN6)][BAr(F)] (M = Li-Cs; Me6[18]aneN6 = 1,4,7,10,13,16-hexamethyl-1,4,7,10,13,16-hexaazacyclooctadecane; BAr(F) = tetrakis{3,5-bis(trifluoromethyl)-phenyl}borate), are obtained in high yield by reaction of the macrocycle with M[BAr(F)] in anhydrous CH2Cl2 solution, and characterised spectroscopically ((1)H, (13)C{(1)H}, (7)Li, (23)Na, and (133)Cs NMR), by microanalysis and, for M = Li, K, and Rb, by single crystal X-ray analysis. The structures show N6-coordination to the metal ion; the small ionic radius for Li(+) leads to a puckered conformation. In contrast, the K(+) ion fits well into the N6 plane, with the [BAr(F)](-) anions above and below, leading to two K(+) species in the asymmetric unit (a hexagonal planar [K(Me6[18]aneN6)](+) cation and a '[K(Me6[18]aneN6)(κ(1)-BAr(F))2](-) anion', with long axial KF interactions). The Rb(+) ion sits above the N6 plane, with two long axial RbF interactions in one cation and two long, mutually cis RbF interactions in the other. The unusual sandwich cations, [M(Me3tacn)2](+) (M = Na, K; distorted octahedral, N6 donor set) and half-sandwich cations [Li(Me3tacn)(thf)](+) (distorted tetrahedron, N3O donor set), [Li(Me4cyclen)(OH2)](+), and [Na(Me4cyclen)(thf)](+) (both distorted square pyramids with N4O donor sets) were also prepared (Me3tacn = 1,4,7-trimethyl-1,4,7-triazacyclononane, Me4cyclen = 1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclododecane). Density functional theory (DFT) calculations, using the BP86 and B3LYP functionals, show that the accessibility of the [M(Me3tacn)2](+) sandwich cations depends strongly on the M(+) ionic radius, such that it is sufficiently large to avoid steric clashing between the Me groups of the two rings, and small enough to avoid very acute N-M-N chelate angles. The calculations also show that coordination to the Group 1 cation involves significant donation of electron density from the p-orbitals on the N atoms of the macrocycle, rather than purely electrostatic interactions.

Highlights

  • The coordination chemistry of Group 1 cations with neutral ligands is dominated by oxygen-donor ligands such as alcohols, ethers, and water, including the ubiquitous crown ethers and cryptands which are frequently used as ligands towards Group 1 cations.1,2 The corresponding chemistry with the less electronegative neutral polyaza macrocycles has been much less studied

  • We report here the first systematic study of the synthesis, spectroscopic, and structural characterisation of Group 1 cation (Li+ to Cs+) complexes involving tri, tetra- and hexa-aza macrocycles

  • The results from the BP86 functional are discussed in the main manuscript, while those computed with the B3LYP functional are collected in the Electronic supplementary information (ESI).†

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Summary

Introduction

The coordination chemistry of Group 1 cations with neutral ligands is dominated by oxygen-donor ligands such as alcohols, ethers, and water, including the ubiquitous crown ethers and cryptands which are frequently used as ligands towards Group 1 cations.1,2 The corresponding chemistry with the less electronegative neutral polyaza macrocycles has been much less studied. Hexa-aza macrocyclic complexes The reaction of [Li(thf )4][BArF] with Me6[18]aneN6 in CH2Cl2 led to the isolation of a white crystalline solid (Scheme 1) which was formulated as [Li(Me6[18]aneN6)][BArF] on the basis of microanalytical, 1H, 13C{1H}, and 7Li NMR spectroscopic data.

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