Synthesis and Small Molecule Reactivity oftrans-Dihydride Isomers of Ru(NHC)₂(PPh₃)₂H₂(NHC = N-Heterocyclic Carbene)

Abstract

Addition of IMe4 (1,3,4,5-tetra­methyl­imidazol-2-ylidene) to Ru­(PPh3)3­HCl (in the presence of H2) or Ru­(PPh3)4­H2 gave the all-trans isomer of Ru­(IMe4)2­(PPh3)2­H2 (1a), whereas 1,3-diethyl-4,5-dimethylimidazol-2-ylidene (IEt2­Me2) reacted with Ru­(PPh3)4­H2 to form cis,cis,trans-Ru­(IEt2­Me2)2­(PPh3)2­H2 (2b). H/D exchange of 1a with C6D6 (elevated temperature) or D2 (room temperature) gave Ru­(IMe4)2­(PPh3)2­HD (1a-HD) and Ru­(IMe4)2­(PPh3)2­D2 (1a-D 2 ). CO reacted with 1a to give a mixture of Ru­(IMe4)2­(PPh3)­(CO)­H2 (3) and Ru­(IMe4)2­(CO)3 (4); 2b reacted in a similar manner, although more slowly, allowing isolation of the monocarbonyl species Ru­(IEt2­Me2)2­(PPh3)­(CO)­H2 (5). Insertion of CO2 into one of the Ru–H bonds of 1a and 2b generated mixtures of major and minor isomers of the κ2-formate complexes Ru­(IMe4)2­(PPh3)­(OCHO)H (7/8) and Ru(IEt2Me2)2(PPh3)(OCHO)H (9/10). The hydridic nature of 1a and 2b was apparent by their reactivity toward MeI, which gave [Ru­(IMe4)2­(PPh3)2­H]I (11), Ru­(IEt2­Me2)2­(PPh3)­HI (12), [Ru­(IEt2­Me2)2­(PPh3)2­H]I (13), and Ru­(IEt2­Me2)­(PPh3)2­HI (14). Complexes 1a, 2b, 5, 9, 11, 13, and 14 were structurally characterized.

Stoichiometric and catalytic C–F bond activation by the trans-dihydride NHC complex [Ru(IEt2Me2)2(PPh3)2H2] (IEt2Me2= 1,3-diethyl-4,5-dimethylimidazol-2-ylidene)

“…Very recently, we reported an example of such a species in the form of the mixed carbene-phosphine complex [Ru(IEt 2 Me 2 ) 2 (PPh 3 ) 2 H 2 ] (1; IEt 2 Me 2 = 1,3-diethyl-4,5-dimethylimidazol-2-ylidene). 14 The unusual trans-arrangement of the two hydride ligands imparts highly nucleophilic character to Ru-H, as evidenced by the formation of methane and [Ru(IEt 2 -Me 2 ) 2 (PPh 3 ) 2 HI] upon addition of the electrophile MeI. We now report our initial findings on both the stoichiometric and catalytic reactivity of 1 towards aromatic fluorocarbons.…”

“…This reagent has become quite commonplace for the formation of transition metal bifluoride ([FHF] − ) complexes, 25 but has, on occasion, also produced metal fluoride species. However, increasing the stoichiometry to 1 : 3 Ru : HF gave instead the previously reported cation [Ru(IEt 2 Me 2 ) 2 (PPh 3 ) 2 H] + , 14 which was shown crystallographically to be formed as the relatively unusual [H 2 F 3 ] − salt, 5 (see ESI †). 0.33 eq.…”

“…Solvents were purified using an MBraun SPS solvent system (hexane, Et 2 O) or under a nitrogen atmosphere from sodium benzophenone ketyl (benzene). 14 [Ru(IEt 2 Me 2 ) 2 (PPh 3 ) 2 HF] (2). NMR spectra were recorded on Bruker Avance 400/ 500 and Avance III 500 MHz NMR spectrometers and referenced as follows: 1 (1).…”

“…4 Transition metal NHC complexes have also been employed for C-F bond formation through hydrofluorination, [5][6][7] but have perhaps received more attention in processes in which C-F bonds are broken (Scheme 1), either through cross-coupling 8 or, of particular relevance to the work reported in this manuscript, hydrodefluorination (HDF). 14 The unusual trans-arrangement of the two hydride ligands imparts highly nucleophilic character to Ru-H, as evidenced by the formation of methane and [Ru(IEt 2 -Me 2 ) 2 (PPh 3 ) 2 HI] upon addition of the electrophile MeI. Very recently, we reported an example of such a species in the form of the mixed carbene-phosphine complex [Ru(IEt 2 Me 2 ) 2 (PPh 3 ) 2 H 2 ] (1; IEt 2 Me 2 = 1,3-diethyl-4,5-dimethylimidazol-2-ylidene).…”

Contrasting Photochemical and Thermal Catalysis by Ruthenium Arsine Complexes Revealed by Parahydrogen Enhanced NMR Spectroscopy

“…have shown how photochemical loss of PMe 3 from Ru (H)(SiMe 3 )(PMe 3 ) 4 yields a 16 electron species, Ru(H)(SiMe 3 )(PMe 3 ) 3 , that is capable of HH, SiH, CH and SiC bond activations, and established that alkyl hydride complexes can be detected in the reaction chemistry of such complexes [22] . Replacing the phosphine in such ruthenium complexes by an N‐heterocyclic carbene expands the range of reactions that complexes of this type can undergo [23–25] . Photolysis of an NMR sample within an NMR spectrometer has become an established method to study photochemical reactions [26–33] .…”