Organometallic Osmium(II) and Ruthenium(II) Biphenyl Sandwich Complexes: X-ray Crystal Structures and 187Os NMR Spectroscopic Studies in Solution

We report the synthesis of the ruthenium(II) and osmium(II) organometallic sandwich complexes [Ru (eta(6)-bip)(2)](OTf)(2) (1) and [OS(eta(6)-bip)(2)](OTf)(2) (2) containing biphenyl (bip) as the arene ligand, and the X-ray crystal structures of 1 center dot MeOH and 2. The unit cell of the osmium complex contains molecules in which the unbound phenyl ring of the biphenyl ligands exists in both staggered and eclipsed configurations, whereas for the ruthenium complex the rings are only eclipsed. Both crystal structures possess CH/pi and pi-pi stacking interactions. Os-187 (nuclear spin 1/2, natural abundance of 1.64%) has a very low gyromagnetic ratio and is one of the most insensitive nuclei in the periodic table. We show that inverse NMR spectroscopic detection by the use of H-1/Os-187 heteronuclear multiple bond correlation (HMBC) spectroscopy allows the ready observation of the Os-187 resonance of complex 2 via couplings to arene ring protons. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)