Functionalization of Carbon Dioxide with Ethylene at Molybdenum Hydride Complexes

Abstract

The molybdenum tetrahydride species (Triphos)MoH4PPh3 (Triphos = PhP(CH2CH2PPh2)2) generated from sodium triethylborohydride addition to (Triphos)MoCl3 was found to promote CO2 functionalization to afford acrylate, propionate, and formate species. The formation of (Triphos)MoH4PPh3 occurs via a (Triphos)Mo(H)Cl(PPh3) intermediate followed by dismutation of an unobserved six-coordinate molybdenum(II) dihydride complex. Addition of dihydrogen to the dismuation product mixture affords a nearly quantitative yield of (Triphos)MoH4PPh3. The molybdenum tetrahydride species facilitates CO2 insertion into a metal hydride to produce a formate complex, (Triphos)Mo(H)(κ2-CHO2)(PPh3), with an observed rate constant of [2.9(2)] × 10–4 s–1 (25 °C), which is independent of CO2 pressure. Selective formation of acrylate and propionate carbon dioxide–ethylene coupling products, (Triphos)Mo(H)(κ2-C3H3O2)(PPh3) and (Triphos)Mo(H)(κ2-C3H5O2)(PPh3), was achieved by sequential addition of olefin and heterocumulene to (Triphos)MoH4PPh3. A formally zerovalent TriphosMo(η2-C2H4)3 intermediate was characterized by NMR spectroscopy and computational analysis along the pathway for carbon dioxide–ethylene coupling.

Recent Advances in the Chemistry of Metal Carbamates

“…The “weak point” in the apparently unscratchable robustness of carbon dioxide is the susceptibility to nucleophilic attacks at the carbon atom [ 22 , 23 , 24 ]. Thus, a range of nucleophilic reagents, including neutral N -heterocyclic carbenes [ 25 , 26 ], are known to react with CO 2 even under mild conditions, and some chemistry at transition metal centers is provided by the possibility of CO 2 insertion into the bond between a metal atom and a suitable anionic ligand, e.g., alkyl, allyl, alkoxide and hydride [ 27 , 28 , 29 , 30 , 31 , 32 ]. In this context, amines are key reactants towards carbon dioxide, and indeed carbon dioxide/amine systems have been intensively investigated in the field of capture/storage [ 33 , 34 , 35 ] and exploited for the incorporation of the CO 2 moiety within organic structures [ 36 , 37 , 38 , 39 ].…”

Molybdenum-Containing Metalloenzymes and Synthetic Catalysts for Conversion of Small Molecules

“…They synthesized (κ 6 -P,N,N,N,C,P-Ph2PPr PDI)-MoH (17) (PDI = pyridine diamine) by a reduction of (( Ph2PPr PDI)MoI)I (16) with excess K/Hg (Scheme 10) [51]. Complex 17 reacted with CO 2 under 0.2 atm of CO 2 condition, where CO 2 was inserted into Mo-H bond to form η 1 -formate-bound Mo(OC(O)H) species [52,53]. The Mo-formate 13 C NMR resonance appeared at 169.7 ppm and the infrared (IR) frequency was detected at 1625 cm −1 .…”

Synthesis of Acrylic Acid Derivatives from CO2 and Ethylene

“…Zhang et al 52 later discovered that a Mo-tetrahydride complex was also capable of inducing CO 2 -ethylene coupling. The structure was confirmed by NMR and X-ray analysis.…”