Supramolecular chemistry of half-sandwich organometallic building blocks based on RuCl2(p-cymene)Ph2PCH2Y

A new series of neutral organometallic building blocks based on piano-stool ruthenium(II) complexes, RuCl₂(p-cymene)Ph₂PCH₂Y Y = -NHC₆H₄(2-CO₂H) (2a), -NHC₆H₄(3-CO₂H) (2b), -NHC₆H₃(3-CO₂H)(6-OCH₃) (2c), -NHC₆H₄(4-CO₂H) (2d), -NHC₆H₃(2-CO₂H)(4-OH) (2e), -NHC₆H₃(3-OH)(4-CO₂H) (2f), -NHC₆H₃(2-CO₂H)(5-CO₂H) (2g) and -OH (2h)], were synthesised in high yields (>88%) from {RuCl₂(p-cymene)}₂ and the appropriate phosphines 1a-1h. The new tertiary phosphine 1b was prepared by Mannich condensation of NH₂C₆H₄(3-CO₂H) with Ph₂PCH₂OH in MeOH. Solution NMR (³¹P{¹H}, ¹H), FT-IR and microanalytical data are in full agreement with the proposed structures. Single crystal X-ray studies confirm that, in each case, compounds 2a, 2b and 2d-2h have piano-stool arrangements with typical Ru-P, Ru-Cl and Ru-C_centroid bond lengths. From our crystallographic studies, factors that influence the supramolecular assemblies of these ruthenium(II) complexes include: (i) the type of functional group present, (ii) the geometric disposition of the -N(H)CH₂PPh₂, -CO₂H and -OH groups around the central benzene scaffold, and (iii) the solvents used in the recrystallisations. Hence in isomers 2a and 2b, molecules are associated into head-to-tail dimer pairs through classical intermolecular O-H?O hydrogen bonding. This feature is also observed in isomer 2d but dimer pairs are further associated to give a 1-D chain through assisted intermolecular N-H?Cl hydrogen bonding. The additional 4-hydroxo group in 2e promotes a ladder arrangement via intermolecular O-H?O and O-H?Cl hydrogen bonding. In contrast the isomeric compound 2f does not show head-to-tail O-H?O hydrogen bonding but instead O-H?Cl and N-H?O intermolecular hydrogen bonding is observed. Depending on the choice of solvent (MeOH or DMSO), 2g forms extended networks based on chains (2g · DMSO · 1.5MeOH) or tapes (2g · 3MeOH). In 2h, a single intramolecular O-H?Cl hydrogen bond is observed for each independent molecule. The X-ray structure of one representative tertiary phosphine, 1f, has also been determined.