A combined parahydrogen and theoretical study of H2 activation by 16-electron d8 ruthenium(0) complexes and their subsequent catalytic behaviour

Abstract

The photochemical reaction of Ru(CO)(3)(L)(2), where L = PPh(3), PMe(3), PCy(3) and P(p-tolyl)(3) with parahydrogen (p-H(2)) has been studied by in-situ NMR spectroscopy and shown to result in two competing processes. The first of these involves loss of CO and results in the formation of the cis-cis-trans-L isomer of Ru(CO)(2)(L)(2)(H)(2), while in the second, a single photon induces loss of both CO and L and leads to the formation of cis-cis-cis Ru(CO)(2)(L)(2)(H)(2) and Ru(CO)(2)(L)(solvent)(H)(2) where solvent = toluene, THF and pyridine (py). In the case of L = PPh(3), cis-cis-trans-L Ru(CO)(2)(L)(2)(H)(2) is shown to be an effective hydrogenation catalyst with rate limiting phosphine dissociation proceeding at a rate of 2.2 s(-1) in pyridine at 355 K. Theoretical calculations and experimental observations show that H(2) addition to the Ru(CO)(2)(L)(2) proceeds to form cis-cis-trans-L Ru(CO)(2)(L)(2)(H)(2) as the major product via addition over the pi-accepting OC-Ru-CO axis.

Parahydrogen-based NMR methods as a mechanistic probe in inorganic chemistry

“…More recent studies involving in situ UV irradiation of solutions containing parahydrogen and Ru(CO) 3 L 2 , where L = PPh 3 , PMe 3 , PCy 3 and P(p-tolyl) 3 , have been described [93]. In this case, two reactions are involved.…”

Contrasting photochemical and thermal reactivity of Ru(CO)2(PPh3)(dppe) towards hydrogen rationalised by parahydrogen NMR and DFT studies

“…In the pyridine doped spectra two hydride resonances of the previously reported double substitution product OC-6-13 (Figure 2) isomer of Ru(H) 2 (CO)(dppe)(pyridine), 5, were also detected at δ -4.17 and -4.57. 12 The ratio of the hydride resonance signal intensities for 3a : 5 were 1 : 0.11 for an 18 fold excess and 1 : 0.2 for a 61 fold excess of pyridine. The higher concentrations of pyridine therefore substantially increase the proportion of Ru(H) 2 (CO)(dppe)(pyridine) formed in this reaction and suggest that a process whereby both CO and PPh 3 are lost from 1 competes with the loss of PPh 3 and CO.…”

“…10,11 We have recently reported an investigation using this approach on the photochemical addition of hydrogen to complexes of the type Ru(CO) 3 (L) 2 , where L = PPh 3 , PMe 3 , PCy 3 , P(p-tolyl) 3 and AsPh 3 , together with studies on alkyne hydrogenation. 12 In this system, the reaction with hydrogen proceeds via the two competing processes shown in Scheme 1. The first of these involves the photochemical loss of CO, and preferential H 2 addition across the more π-accepting OC-Ru-CO axis of the resulting intermediate to form the cis-cis-trans-L isomer of Ru(CO) 2 (L) 2 (H) 2 .…”

In Situ FTIR and NMR Spectroscopic Investigations on Ruthenium‐Based Catalysts for Alkene Hydroformylation

“…[11, 12, 38, 40b, 42] Wilkinson et al studied triphenylphosphine-modified ruthenium-catalyzed hydroformylation and proposed ad issociative reactionm echanism involving 18-and 16-electron complexes, which has been confirmed in many aspects by others (Scheme 1, unsaturated 16-electron speciesa re not shown). [43][44][45][46][47] Startingf rom the ruthenium(0) complex [Ru(CO) 3 -(PPh 3 ) 2 ]( 1), dissociation of ac arbonyl ligand first occurs, followed by oxidative addition of molecular hydrogeny ielding the ruthenium(II) dihydride complex 2.A fter dissociation of PPh 3 ,a lkene activation takes place giving the p complex 3.I nsertion of the alkene into the RuÀHb ond and coordinationo f PPh 3 provides complex 4.M igratory insertion of CO followed by coordination of another carbonyl ligand yields the acyl complex 5.I nt he last step molecular hydrogen is activatedf ollowed by aldehyde elimination and regeneration of complex 2. Formation of the dihydridec omplex has been proposed to be rate-determining.…”