Calixarenes as ligands for dimetal units: the state of the art. Structure of a new quadruply-bonded dimolybdenum compound

Abstract

Reaction of [Mo 2( cis-DAniF) 2(CH 3CN) 4](BF 4) 2, DAniF= N, N′-di- p-anisylformamidinate, with the dianion of H 4- p- tert-butylcalix[4]arene, H 4L produces the quadruply-bonded compound Mo 2( cis-DAniF) 2(H 2L) where the calix[4]arene dianion spans the Mo 2 4+ unit that is also bridged by two cis formamidinate anions. In the crystal there are four crystallographically independent but chemically similar dimolybdenum molecules, the only difference being the type of molecules occupying the pockets of the calixarenes, namely benzene in two of them and water molecules partially occupying the other two. The Mo–Mo distances of 2.122(3), 2.125(3), 2.118(3) and 2.127(3) Å are typical of those found in other quadruply-bonded Mo 2 4+ complexes. Here, we also review the chemistry of calixarenes with metal–metal bonded units.