| Summary: | The Group 1 complexes, [M(Me6[18]aneN6)][BArF] (M = Li-Cs; Me6[18]aneN6 = 1,4,7,10,13,16-hexamethyl-1,4,7,10,13,16-hexaazacyclooctadecane; BArF = tetrakis{3,5-bis(trifluoromethyl)-phenyl}borate), are obtained in high yield by reaction of the macrocycle with M[BArF] in anhydrous CH2Cl2 solution, and characterised spectroscopically (1H, 13C{1H}, 7Li, 23Na, and 133Cs 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 [BArF]? 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)(?1-BArF)2]? anion', with long axial K?F interactions). The Rb+ ion sits above the N6 plane, with two long axial Rb?F interactions in one cation and two long, mutually cis Rb?F 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.
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