Activation of the CN Triple Bond of Substituted Benzonitriles in the Presence of Ru 3(CO) 12, Acetic Acid and Molecular Hydrogen. Crystal Structure of (μH) 2Ru 3-(CO) 9(μ 3NCH 2C 6H 4OMe)

Abstract

Reactions of Ru 3(CO) 12 with p-methoxybenzonitrile and p-nitrobenzonitrile have been studied in refluxing cyclohexane and the complexes formed were characterized by IR, 1H NMR spectroscopy and mass spectrometry. In the presence of acetic acid and p-methoxybenzonitrile, (μ-H)Ru 3(CO) 10(μ-NHCH 2- C 6H 4OMe) is the main reaction product, whilst when acetic acid is replaced by H 2 at atmospheric pressure the main reaction products are (μ-H)Ru 3(CO) 10 (μ- NCHC 6H 4OMe) and (μ-H) 2Ru 3(CO) 9(μ 3-NCH 2C 6H 4OMe). The crystal structure of (μ-H) 2Ru 3(CO) 9(μ 3- NCH 2C 6H 4OMe) has been determined by X-ray diffraction methods. Crystals are triclinic, space group P 1 , with a=11.255(6), b=12.205(8), c=8.831(6) Å, α=108.98(2), β=99.43(2), γ=95.78(2)°, V= 1116(1) Å 3, Z=2. Full-matrix least-squares refinement (324 variables, 2938 observed reflections) converged to give R and R w values of 0.0318 and 0.0435 respectively. The structure consists of an isosceles triangular cluster of Ru atoms (with the longer edges bridged by hydrides) bound to nine terminal carbonyls and triply bridged by the NCH 2C 6H 4OMe group. Reaction of Ru 3(CO) 12 with p-nitrobenzonitrile and acetic acid only leads to decomposition. Addition of H 2 at atmospheric pressure to a cyclohexane solution of Ru 3- (CO) 12 and p-nitrobenzonitrile leads to (μ-H)Ru 3- (CO) 10(μ-NCHC 6H 4NO 2) and (μ-H) 2Ru 3(CO) 9- (μ 3-NCH 2C 6H 4NO 2). In refluxing cyclohexane, (μ-H)- Ru 3(CO) 10(μ-NCHC 6H 4X) complexes (X=H, OMe, NO 2) are slowly converted into (μ-H) 2Ru 3(CO) 9- (μ 3-NCH 2C 6H 4X) (X=H, OMe, NO 2), and in n-octane at 100 °C, besides (μ-H) 2Ru 3(CO) 9(μ 3- NCH 2C 6H 4X), minor amounts of (μ-H)Ru 3(CO) 10- (μ-NHCH 2C 6H 4X) are also formed. These results are discussed in terms of possible reaction pathways and of the role of acetic acid in the reaction of Ru 3- (CO) 12 with benzonitrile and its substituted derivatives.