Treatment of trans-[W(N2)2(dppe)(PEtN MePEt)] (dppe = Ph2PCH2CH 2PPh2; PEtNMePEt = Et2PCH2N(Me)CH2PEt2) with 3 equiv of tetrafluoroboric acid (HBF4·Et2O) at °78 °C generated the seven-coordinate tungsten hydride trans-[W(N 2)2(H)(dppe)(PEtNMeP Et)][BF4]. At higher temperatures, protonation of a pendant amine is also observed, affording trans-[W(N2) 2(H)(dppe)(PEtNMe(H)PEt)][BF 4]2, with formation of the hydrazido complex [W(NNH 2)(dppe)(PEtNMe(H)PEt)][BF 4]2 as a minor product. A similar product mixture was obtained using triflic acid (HOTf). The protonated products are thermally sensitive and do not persist at ambient temperature. Upon acid addition to the carbonyl analogue cis-[W(CO)2(dppe)(PEtN MePEt)], the seven-coordinate carbonyl hydride complex trans-[W(CO)2(H)(dppe)(PEtNMe(H)P Et)][OTf]2 was generated. A mixed diphosphine complex without the pendant amine in the ligand backbone, trans-[W(N2) 2(dppe)(depp)] (depp = Et2P(CH2) 3PEt2), was synthesized and treated with HOTf, selectively generating a hydrazido complex, [W(NNH2)(OTf)(dppe)(depp)][OTf]. Computational analysis probed the proton affinity of three sites of protonation in these complexes: the metal, pendant amine, and N2 ligand. Room-temperature reactions with 100 equiv of HOTf produced NH4 + from reduction of the N2 ligand (electrons come from W). The addition of 100 equiv of HOTf to trans-[W(N2) 2(dppe)(PEtNMePEt)] afforded 0.81 equiv of NH4+, while 0.40 equiv of NH4 + was formed upon treatment of trans-[W(N2) 2(dppe)(depp)] with HOTf, showing that the complexes containing proton relays produce more products of reduction of N2.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Organic Chemistry
- Inorganic Chemistry