Formation of Double Cubanes [Sn7(NR)8] in the Reactions of Pyridyl and Pyrimidinyl Amines with Sn(NMe2)2:  A Synthetic and Theoretical Study

In contrast to the reactions of Sn(NMe2)2 with unfunctionalized primary amines (RNH2), which yield the simple imido SnII cubanes [SnNR]4, the reactions of 2-pyridyl or 2-pyrimidinyl amines give the mixed-oxidation-state SnII/SnIV double cubanes [Sn7(NR)8]. In addition to [Sn7{2-N(5-Mepy)}8]·2thf (1·2thf) (py = pyridine) and [Sn7{2-N(pm)}8]·0.33thf (2·0.33thf) (pm = pyrimidine), which were communicated previously, the syntheses and structures of the new complexes [Sn7{2-N(4-Mepm)}8]·2thf (3·2thf), [Sn7{2-N(4,6-Me2pm)}8]·4thf (4·4thf), [Sn7{2-N(4-Me-6-MeO-pm)}8] (5), and [Sn7{2-N(4-MeO-6-MeO-pm)}8] (6) are reported. Model DFT calculations on the reactions of Sn(NMe2)2 with 2-pmNH2 or PhNH2, producing the cubanes [Sn{2-N(pm)}]4 and [SnNPh]4 (respectively), and the corresponding double cubanes [Sn7{2-N(pm)}8] and [Sn7(NPh)8], show that the presence of intramolecular Sn···N bonding which spans the cubane halves of the complexes is crucial to the formation of the double-cubane structure.