Photochemistry of Solution and Surface-Confined Alkyl- and Benzyltricarbonylcyclopentadienyltungsten Complexes

Bernard Klein, Romas J. Kazlauskas, Mark S. Wrighton

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23 Scopus citations

Abstract

A variety of surface-confined species (η5-C5H5)W(CO)3R (R = Cl, CH3, C2H5, CH2C6H5) has been synthesized and characterized and their photochemistry examined and compared to solution analogues. High surface area (400 m2/g) SiO2, [SiO2], has been functionalized first with −SiMe2C5H5 by reaction of surface OH groups with ClSiMe2C6H6 or EtOSiMe2C5H5. The resulting [SiO2]SiMe2C5H5 can then be treated in a series of conventional synthetic steps to yield [SiO2]SiMe2(η5-C6H4)W(CO)3R (R = Cl, CH3, C2H5). Elemental analyses and infrared spectroscopy has been used to establish that the average coverage is generally submonolayer, with an average separation between W centers of 10–20 Å. Chloromethylated polystyrene reacts with [η5-C5H5)W(CO)3] to yield (η5-C5H5)W(CO)31-CH2C6H4[P]) or with C6H5Na followed by conventional synthetic procedures to yield [P]C6H4CH2(η5-C5H4)W(CO)3R (R = CH3, C2H5). In all cases near-UV (355 nm) irradiation yields chemistry consistent with efficient, dissociative loss of CO as the primary reaction following photoexcitation as has been found for the analogous solution species (Φ366 ≈ 0.35 ± 0.05). Direct spectroscopic evidence for the photogeneration of surface-confined, 16-valence-electron intermediates comes from the infrared analysis of Nujol suspensions of [SiO2]SiMe2(η5-C5H4)W(CO)3R (R = CH3, C2H5) irradiated at 77 K. For R = CH3 warm-up of the irradiated sample yields nearly complete regeneration of the starting complex by back-reaction with the photoejected CO, whereas for R = C2H5 warm-up yields some regeneration of the starting complex and some conversion to [SiO2]SiMe2(η5-C5H4)W(CO)2(H)(C2H4). Unlike the analogous complex in solution, prolonged irradiation of the [SiO2]SiMe2(η5-C5H4)W(CO)3R does not yield WW bonded products, consistent with the immobilized centers remaining anchored sufficiently far apart that WW bonds cannot form. Irradiation of (η5-C5H5)W(CO)31-CH2C6H4[P]) at 77 K does not allow the observation of a 16-valence-electron intermediate rather (η5-C5H5)W(CO)23-CH2C6H4-[P]) is formed. These and similar results for the solution species R = CH2C6H5 and CH(CH3)C6H5 allow an upper limit for the activation energy for the conversion of an η1-benzyl to η3-benzyl to be set at ∼6 kcal/mol. Irradiation of (η5-C5H5)W(CO)3CH2CH2C6H5 leads to a blue 16-valence-electron species at 77 K which gives trans-(η5-C5H5)W(CO)2(H)(styrene) upon warming. This styrene-hydride rearranges slowly at 300 K (t1/2 = ∼400 s) to form (η5-C5H6)W(CO)23-CH(CH3)C6H5).

Original languageEnglish (US)
Pages (from-to)1338-1350
Number of pages13
JournalOrganometallics
Volume1
Issue number10
DOIs
StatePublished - Jan 1 1982

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