Dataset Information

Unravelling the Photochemical Transformations of Chromium(I) 1,3 Bis(diphenylphosphino), [Cr(CO)4(dppp)]+, by EPR Spectroscopy.

ABSTRACT: UV-induced photochemical transformations of the paramagnetic [Cr(CO)4(Ph2PCH2CH2CH2PPh2)]+ complex (abbreviated [Cr(CO)4(dppp)]+) in dichloromethane was investigated by CW EPR spectroscopy. Room-temperature UV irradiation results in the rapid transformation of [Cr(CO)4(dppp)]+ into trans-[Cr(CO)2(dppp)2]+. However, low-temperature (77-120 K) UV irradiation reveals the presence of an intermediate mer-[Cr(CO)3(?1-dppp)(?2-dppp)]+ complex which photochemically transforms into trans-[Cr(CO)2(dppp)2]+. The derived spin Hamiltonian parameters for these complexes were confirmed by DFT calculations. The photoinduced reaction is shown to be concentration-dependent, leading to a distribution of the three complexes ([Cr(CO)4(dppp)]+, mer-[Cr(CO)3(?1-dppp)(? 2-dppp)]+, and trans-[Cr(CO)2(dppp)2]+). A bimolecular photoinduced mechanism is proposed to account for the formation of mer-[Cr(CO)3(?1-dppp)(?2-dppp)]+ and trans-[Cr(CO)2(dppp)2]+.

SUBMITTER: Luckham SLJ

PROVIDER: S-EPMC7009024 | biostudies-literature | 2019 Jun

REPOSITORIES: biostudies-literature

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Publications

Unravelling the Photochemical Transformations of Chromium(I) 1,3 Bis(diphenylphosphino), [Cr(CO)4(dppp)]+, by EPR Spectroscopy.

Luckham Stephen L J SLJ Folli Andrea A Platts James A JA Richards Emma E Murphy Damien M DM

Organometallics 20190613 12

UV-induced photochemical transformations of the paramagnetic [Cr(CO)4(Ph2PCH2CH2CH2PPh2)]+ complex (abbreviated [Cr(CO)4(dppp)]+) in dichloromethane was investigated by CW EPR spectroscopy. Room-temperature UV irradiation results in the rapid transformation of [Cr(CO)4(dppp)]+ into trans-[Cr(CO)2(dppp)2]+. However, low-temperature (77-12 ...[more]

PMID: 32055085

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Project description:Chromium complexes containing a bis(diphenylphosphino) ligand have attracted significant interest over many years due to their potential as active catalysts for ethylene oligomerisation when combined with suitable co-catalysts such as triethylaluminium (TEA) or methylaluminoxane (MAO). While there has been considerable attention devoted to the possible reaction intermediates and the nature of the Cr oxidation states involved, the potential UV photoactivity of the Cr(I) complexes has so far been overlooked. Therefore, to explore the photoinduced transformations of bis(diphenylphosphino) stabilized Cr(I) complexes, we used continuous-wave (CW) EPR to study the effects of UV radiation on a cationic [Cr(CO)4(dppp)]+[Al(OC(CF3)3)4]- complex (1), where dppp represents the 1,3 bis-(diphenylphosphino)propane ligand, Ph2P(C3H6)PPh2. Our preliminary investigations into the photochemistry of this complex revealed that [Cr(CO)4(dppp)]+ (1) can be readily photo-converted into an intermediate mer-[Cr(CO)3(κ1-dppp)(κ2-dppp)]+ complex (2) and eventually into a trans-[Cr(CO)2(dppp)2]+ complex (3) in solution at room temperature under UV-A light. Here, we show that the intermediate species (2) involved in this transformation can be identified by EPR at much lower temperature (140 K) and at a specific wavelength (highlighting the wavelength dependency of the reaction). In addition, small amounts of a 'piano-stool'-type complex, namely [Cr(CO)2(dppp-η6-arene)]+ (4), can also be formed during the photoconversion of [Cr(CO)4(dppp)]+ using UV-A light. There was no evidence for the formation of the [Cr(L-bis-η6-arene)]+ complex (5) in these UV irradiation experiments. For the first time, we also evidence the formation of a 1-hexene coordinated [Cr(CO)3(dppp)(1-hexene)]+ complex (6) following UV irradiation of [Cr(CO)4(dppp)]+ in the presence of 1-hexene; this result demonstrates the unprecedented opportunity for exploiting light activation during Cr-driven olefin oligomerisation catalysis, instead of expensive, difficult-to-handle, and hazardous chemical activators.

Dataset Information

Unravelling the Photochemical Transformations of Chromium(I) 1,3 Bis(diphenylphosphino), [Cr(CO)4(dppp)]+, by EPR Spectroscopy.

Publications

Unravelling the Photochemical Transformations of Chromium(I) 1,3 Bis(diphenylphosphino), [Cr(CO)<sub>4</sub>(dppp)]<sup>+</sup>, by EPR Spectroscopy.

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