Ionic and Neutral Half‐Sandwich Guanidinatoruthenium(II) Complexes and Their Solution Behavior

Ionic and neutral half-sandwich guanidinatoruthenium(II) complexes [(η6-C10H14)RuL(κ2(N,N′){(ArN)2C-N(H)Ar})][OTf] [Ar = 4-MeC6H4, L = 2-methylimidazole (1); Ar = 2-MeC6H4, L = 1,3,5-triaza-7-phosphaadamantane (PTA; 2)], [(ArNH)3C][(η6-C10H14)RuCl3] [Ar = 2-ClC6H4 (3)] and [(η6-C10H14)RuCl(κ2(N,N′){(ArN)2C-N(H)Ar})] [Ar = 2-ClC6H4 (4), 2-FC6H4 (5), 4-ClC6H4 (6), and 4-(NO2)C6H4 (7)] have been isolated and the molecular structures of all but 6 were determined by single-crystal X-ray diffraction. VT 31P{1H} NMR spectroscopy of complex 2 revealed the presence of a mixture of four isomers in a ratio of appproximately 1.4:11.0:1.6:0.1. Theoretical calculations were performed on the syn-syn, syn-anti, anti-syn, and anti-anti conformers of 2, which revealed syn-anti to be the most stable conformer, both in the gas phase and in solution. Furthermore, the energies relating to the interactions between the lone pairs of the nitrogen atoms of the CN3 unit and the antibonding orbital of the central carbon atom in the syn-anti conformer of 2 were investigated by NBO analysis. The 1H NMR spectrum of 3 reveals the presence of two species and their ratio is dependent upon the concentration of 3 in CDCl3 and on the amount of D2O in CD3CN. The two species have been ascribed to the presence of a monomer and a water-bridged dimer. The new complexes 1–7 were screened as pre-catalysts in the transfer hydrogenation of acetophenone and complex 3 was tested as a pre-catalyst in the transfer hydrogenation of a variety of ketones to explore the scope of the reaction.