Molybdocalix[4]arene N,O-Schiff base ligands

The ‘one-pot’ reaction of 2-hydroxy-3,5-di-tert-butylsalicylaldehyde with in-situ generated ‘amino calixarene’ (from {Mo[(2-NC6H4)2CH2CH2]Cl2(DME)}, KOtBu and tbutylcalix[4]areneH4 LH4) afforded, after work-up, the heterobimetallic salt K(NCMe)2[Mo(NCMe)(OEt)(2-C6H4CH2CH2C6H4NH2-2)L] (1∙2MeCN). By constrast, use of the ‘amino calixarene’ [Mo(NCMe)(2-C6H4CH2CH2C6H4NH2-2)L] afforded the potassium/ethoxide-free complex [Mo(NCMe)(2-C6H4CH2CH2C6H4N-2-CHC6H2-2/-(OH)-3/,5/-tBu)L] (2∙2MeCN). Reaction of 2 (two equivalents) with the dialdehyde [1,3-(CHO)2-5-MeC6H3OH- 2] led, following work-up, to the isolation of the cation-anion pair [C46H42N4O2] 2+[Mo6O19]2-·C2H3N (3). The molecular structures of 1·2MeCN, 2·2MeCN and 3·MeCN are reported, for which it was necessary to use synchrotron radiation for data collection. Complex 1 contains an eliptical calixarene conformation as a result of π-interactions between the K+ and the arene groups and a distorted O5N octahedral geometry at the molybdenum centre, whereas in ‘K+ /ethoxide-free’ 2, the calixarene retains the cone conformation and the metal possesses a distorted octahedral O4N2 coordination environment. In 3, a protonated macrocyclic cation, formed via hydrolysis, has weak intermolecular interactions with the polyoxomolybdate anion.