Detection of Unusual Reaction Intermediates during the Conversion of W(N2)2(dppe)2 to W(H)4(dppe)2 and of H2O into H2

Abstract

W(N(2))(2)(dppe-κ(2)P)(2) reacts with H(2) to form WH(3){Ph(C(6)H(4))PCH(2)CH(2)PPh(2)-κ(2)P}(dppe-κ(2)P) and then W(H)(4)(dppe-κ(2)P)(2). When para-hydrogen is used in this study, polarized hydride signals are seen for these two species. The reaction is complicated by the fact that trace amounts of water lead to the formation of H(2), PPh(2)CH(2)CH(2)Ph(2)P(O) and W(H)(3)(OH)(dppe-κ(2)P)(2), the latter of which reacts further via H(2)O elimination to form W(H)(4)(dppe-κ(2)P)(2) and [WH(3){Ph(C(6)H(4))PCH(2)CH(2)PPh(2)-κ(2)P}(dppe-κ(2)P)]. These studies demonstrate a role for the 14-electron intermediate W(dppe-κ(2)P)(2) in the CH activation reaction pathway leading to [WH(3){Ph(C(6)H(4))PCH(2)CH(2)PPh(2)-k(2)P}(dppe-k(2)P)]. UV irradiation of W(H)(4)(dppe-κ(2)P)(2) under H(2) led to phosphine dechelation and the formation of W(H)(6)(dppe-k(2)P)(dppe-k(1)P) rather than H(2) loss and W(H)(2)(dppe-κ(2)P)(2) as expected. Parallel DFT studies using the simplified model system W(N(2))(2)((Ph)HPCH(2)CH(2)PH(2)-κ(2)P)(H(2)PCH(2)CH(2)PH(2)-κ(2)P) confirm that ortho-metalation is viable via both W(dppe-κ(2)P)(2) and W(H)(2)(dppe-κ(2)P)(2) with explicit THF solvation being necessary to produce the electronic singlet-based reaction pathway that matches with the observation of para-hydrogen induced polarization in the hydride signals of [WH(3){Ph(C(6)H(4))PCH(2)CH(2)PPh(2)-κ(2)P}(dppe-κ(2)P)], W(H)(3)(OH)(dppe-κ(2)P)(2) and W(H)(4)(dppe-κ(2)P)(2) during this study. These studies therefore reveal the existence of differentiated and previously unsuspected thermal and photochemical reaction pathways in the chemistry of both W(N(2))(2)(dppe-κ(2)P)(2) and W(H)(4)(dppe-κ(2)P)(2) which have implications for their reported role in N(2) fixation.