Anion‐Templated Assembly of Half‐Sandwich Rhodium‐Based Multinuclear Metallamacrocycles

Abstract

A series of half-sandwich rhodium-based metallamacrocycles with tetra- and hexanuclearities have been synthesized. They are assembled by linking the deprotonated 2,4-diacetyl-5-hydroxy-5-methyl-3-(3-pyridinyl)cyclohexanone (HL) ligand in the presence of counteranions. When the counteranion was the tetrahedral BF(4)(-) ion, tetranuclear metallamacrocycle [(Cp*RhL)(4)][BF(4)](4) (1d) was formed. However, the larger OTf(-) , PF(6)(-) , and SbF(6) (-) counterions favored the formation of hexanuclear metallamacrocycles [(Cp*RhL)(6)⊃2OTf][OTf](4) (1a), [(Cp*RhL)(6)⊃2PF(6)][PF(6)](4) (1b), and [(Cp*RhL)(6)⊃2SbF(6)][SbF(6)](4)⋅6CH(3)CN (1c) when the reactions were performed under the same conditions. Single-crystal X-ray analysis indicated that, in the solid state, two counteranions were encapsulated in each belt-like host molecule of hexanuclear metallamacrocycles 1a, b, and c. Based on the results of (1)H NMR analysis in methanol, the nuclearities of 1a-c and the two encapsulated anions in each molecular cavity were maintained in solution. In addition, tetranuclear metallamacrocycle 1d was converted into the hexanuclear metallamacrocycles 1a', b, and c after addition of the appropriate anion as its [NBu(4)](+) salt. The compound 1a' was characterized by single-crystal X-ray diffraction to have the formula [(Cp*RhL)(6)⊃2OTf][BF(4)](4) ⋅2MeOH⋅2H(2) O. From the interconversion of the hexanuclear metallamacrocycles, we have concluded that the hexanuclear belt-like host in 1a-c has an clear selectivity for larger anions, in the sequence SbF(6) (-) ≈PF(6) (-) >OTf(-) >BF(4) (-) >Cl(-) .