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

TY - JOUR

T1 - Detection of Unusual Reaction Intermediates during the Conversion of W(N-2)(2)(dppe)(2) to W(H)(4)(dppe)(2) and of H2O into H-2

AU - Eguillor, Beatriz

AU - Caldwell, Patrick J.

AU - Cockett, Martin C. R.

AU - Duckett, Simon B.

AU - John, Richard O.

AU - Lynam, Jason M.

AU - Sleigh, Christopher J.

AU - Wilson, Ian

PY - 2012/11/7

Y1 - 2012/11/7

N2 - W(N-2)(2)(dppe-kappa P-2)(2) reacts with H-2 to form WH3{Ph(C6H4)PCH2CH2PPh2-kappa P-2}(dppe-kappa P-2) and then W(H)(4)(dppe-kappa P-2)(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, PPh2CH2CH2Ph2P(O) and W(H)(3)(OH)(dppe-kappa P-2)(2), the latter of which reacts further via H2O elimination to form W(H)(4)(dppe-kappa P-2)(2) and [WH3{Ph(C6H4)PCH2CH2PPh2-kappa P-2}(dppe-kappa P-2)]. These studies demonstrate a role for the 14-electron intermediate W(dppe-kappa P-2)(2) in the CH activation reaction pathway leading to [WH3{Ph(C6H4)PCH2CH2PPh2-k(2)P}(dppe-k(2)P)]. UV irradiation of W(H)(4)(dppe-kappa P-2)(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-kappa P-2)(2) as expected. Parallel DFT studies using the simplified model system W(N-2)(2)((Ph)HPCH2CH2PH2-kappa P-2)(H2PCH2CH2PH2-kappa P-2) confirm that ortho-metalation is viable via both W(dppe-kappa P-2)(2) and W(H)(2)(dppe-kappa P-2)(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 [WH3{Ph(C6H4)PCH2CH2PPh2-kappa P-2}(dppe-kappa P-2)], W(H)(3)(OH)(dppe-kappa P-2)(2) and W(H)(4)(dppe-kappa P-2)(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-kappa P-2)(2) and W(H)(4)(dppe-kappa P-2)(2) which have implications for their reported role in N2 fixation.

AB - W(N-2)(2)(dppe-kappa P-2)(2) reacts with H-2 to form WH3{Ph(C6H4)PCH2CH2PPh2-kappa P-2}(dppe-kappa P-2) and then W(H)(4)(dppe-kappa P-2)(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, PPh2CH2CH2Ph2P(O) and W(H)(3)(OH)(dppe-kappa P-2)(2), the latter of which reacts further via H2O elimination to form W(H)(4)(dppe-kappa P-2)(2) and [WH3{Ph(C6H4)PCH2CH2PPh2-kappa P-2}(dppe-kappa P-2)]. These studies demonstrate a role for the 14-electron intermediate W(dppe-kappa P-2)(2) in the CH activation reaction pathway leading to [WH3{Ph(C6H4)PCH2CH2PPh2-k(2)P}(dppe-k(2)P)]. UV irradiation of W(H)(4)(dppe-kappa P-2)(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-kappa P-2)(2) as expected. Parallel DFT studies using the simplified model system W(N-2)(2)((Ph)HPCH2CH2PH2-kappa P-2)(H2PCH2CH2PH2-kappa P-2) confirm that ortho-metalation is viable via both W(dppe-kappa P-2)(2) and W(H)(2)(dppe-kappa P-2)(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 [WH3{Ph(C6H4)PCH2CH2PPh2-kappa P-2}(dppe-kappa P-2)], W(H)(3)(OH)(dppe-kappa P-2)(2) and W(H)(4)(dppe-kappa P-2)(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-kappa P-2)(2) and W(H)(4)(dppe-kappa P-2)(2) which have implications for their reported role in N2 fixation.

KW - DIHYDROGEN COMPLEXES

KW - NMR-SPECTROSCOPY

KW - MOLECULAR-HYDROGEN COMPLEXES

KW - TRANSITION-METAL POLYHYDRIDES

KW - TUNGSTEN DINITROGEN COMPLEXES

KW - HEXAHYDRIDE COMPLEXES

KW - CARBONYL-COMPLEXES

KW - PARAHYDROGEN-INDUCED POLARIZATION

KW - IR SPECTROSCOPY

KW - HYDRIDE COMPLEXES

UR - http://www.scopus.com/inward/record.url?scp=84868532419&partnerID=8YFLogxK

U2 - 10.1021/ja302202q

DO - 10.1021/ja302202q

M3 - Article

SN - 0002-7863

VL - 134

SP - 18257

EP - 18265

JO - Journal of the American Chemical Society

JF - Journal of the American Chemical Society

IS - 44

ER -