Dihydrogen Thiolate vs Hydride Thiol: Reactivity of the Series of Complexes MH(CO)(L)(PPh3)2 (M = Ru, Os; L = Pyridine-2-thiolate, Quinoline-8-thiolate) with Acid. X-ray Structure Determination of [Os(CO)(μ2-Spy)(SpyH)(PPh3)]2[BF4]2

Abstract

The complexes MH(CO)(quS)(PPh3)2 (M = Ru, Os; quS = quinoline-8-thiolate) are synthesized in a manner analogous to that for the known complexes MH(CO)(pyS)(PPh3)2 (M = Ru, Os; pyS = pyridine-2-thiolate). The isomer distribution in the quinoline-8-thiolate complexes was determined by an nOe experiment. It is inverted relative to the pyridine-2-thiolate complexes. EHMO calculations on the free chelate anions and the complexes OsH(CO)(L)(PPh3)2 (L = pyridine-2-thiol, quinoline-8-thiol) qualitatively show this to be a consequence of the different electronic properties of the chelate ligand. The electrochemistry of the complexes has been investigated. Protonation of the complexes with HBF4 at low temperature results in the formation of mixtures of dihydrogen complexes [M(η2-H2)(CO)(L)(PPh3)2]BF4 (M = Ru, Os; L = pyridine-2-thiolate, quinoline-8-thiolate) and thiol hydride complexes [MH(CO)(LH)(PPh3)2]BF4 (M = Ru, Os; LH = pyridine-2-thiol, quinoline-8-thiol) in varying tautomer ratios. The structure of the thiol hydride complexes was determined using a heteronuclear decoupling 1H{31P} experiment. At low temperature the complexes [Os(η2-H2)(CO)(quS)(PPh3)2]+ and [Os(H)(CO)(quSH)(PPh3)2]+ are in tautomeric equilibrium. The influence of the chelate and the metal on the relative acidity and stability of the protonated complexes is discussed. The order of acidity of the complexes [M(η2-H2)(CO)(L)(PPh3)2]BF4 is Os > Ru and pyS- > quS-. The majority of the complexes are thermally unstable with respect to loss of dihydrogen gas and/or decomposition. The single-crystal X-ray structure of the dimeric complex [Os(CO)(μ2-Spy)(SpyH)(PPh3)]2[BF4]2, a nonstoichiometric decomposition product of the dihydrogen complex [Os(η2-H2)(CO)(pyS)(PPh3)2]BF4, is presented. It contains a monodentate mercaptopyridinium ligand (SpyH) and face-to-face pyridyl rings, a structural motif which is becoming common for the μ2-Spy- ligand.