Synthesis of water-soluble ruthenium clusters by reaction with PTA (1,3,5-triaza-7-phosphaadamantane)

In the search for new water-soluble ruthenium clusters, [Ru-3(CO)(12)], [Ru5C(CO)(15)] and [Ru6C(CO)(17)] were reacted with ligand PTA (1,3,5-triaza-7-phosphaadamantane) to obtain compounds [Ru-3(CO)(12-)x(PTA)(x)] (x = 1 (4), 2 (5), 3 (6)), [Ru5C(CO)(15-x)(PTA)(x)] (x = 1 (9), 2 (10), 3 (11), 4 (12), 5 (13), 6 (14)), and [Ru6C(CO)(17-x)(PTA)(x)] (x = 1 (15), 2 (16), 3 (17), 4 (18), 5 (19), 6 (20)), respectively. The PTA ligand adds itself to ruthenium clusters very easily thanks to its low cone angle. Column chromatography purification under various conditions was necessary to obtain pure compounds. In total, fourteen new clusters could be synthesized and characterized. The water-solubility property is not reached after the addition of only one ligand but several are needed, the number depending on the core compound. For [Ru-3(CO)(12)] derivatives, one phosphine per ruthenium atom is needed while it is less than one phosphine per ruthenium atom for the other compounds. It is postulated that the PTA forms a solubility envelope around the metal core: the number of PTA ligands necessary for water-solubility decreases proportionally as the nuclearity in the metal core increases. All new compounds were characterized by IR, NMR and HRMS and all analyses assessed the proposed formulae. Furthermore, clusters 4 [Ru-3(CO)(11)(PTA)(1)], 5 [Ru-3(CO)(10)(PTA)(2)], 9 [Ru5C(CO)(14)(PTA)(1)] and 10 [Ru5C(CO)(13)(PTA)(2)] were characterized by single crystal X-ray diffraction. It is observed that the phosphine occupies sites so as to minimize steric interactions. Degradation products of the reaction between [Ru-3(CO)(12)] and PTA were found as a result of air exposure or high temperature treatment and were identified by crystal structure analysis as the mononuclear complexes 7 [Ru(CO)(4)(PTA)(1)] and 8 [Ru(CO)(3)(PTA)(2)]. (C) 2015 Elsevier B.V. All rights reserved.