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

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 ( 1 d ) was formed. However, the larger OTf − , PF 6 − , and SbF 6 − counterions favored the formation of hexanuclear metallamacrocycles [(Cp*RhL) 6 ⊃2OTf][OTf] 4 ( 1 a ), [(Cp*RhL) 6 ⊃2PF 6 ][PF 6 ] 4 ( 1 b ), and [(Cp*RhL) 6 ⊃2SbF 6 ][SbF 6 ] 4 ⋅ 6CH 3 CN ( 1 c ) 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 1 a , b , and c . Based on the results of 1 H NMR analysis in methanol, the nuclearities of 1 a – c and the two encapsulated anions in each molecular cavity were maintained in solution. In addition, tetranuclear metallamacrocycle 1 d was converted into the hexanuclear metallamacrocycles 1 a′ , b , and c after addition of the appropriate anion as its [NBu 4 ] + salt. The compound 1 a′ was characterized by single‐crystal X‐ray diffraction to have the formula [(Cp*RhL) 6 ⊃2OTf][BF 4 ] 4 ⋅ 2 M eOH ⋅ 2H 2 O. From the interconversion of the hexanuclear metallamacrocycles, we have concluded that the hexanuclear belt‐like host in 1 a – c has an clear selectivity for larger anions, in the sequence SbF 6 − ≈PF 6 − >OTf − >BF 4 − >Cl − .