Photochemical C-H activation and ligand exchange reactions of CpRe(PPh{sub 3}){sub 2}H{sub 2}. Phosphine dissociation is not involved
- Univ. of Rochester, NY (United States). Dept. of Chemistry
The dihydride CpRe(PPh{sub 3}){sub 2}H{sub 2} (1) catalyzes H/D exchange between C{sub 6}D{sub 6} and other arenes or alkanes. Compound 1 also undergoes photochemical phosphine substitution with PMe{sub 3} to give CpRe(PPh{sub 3})(PMe{sub 3})H{sub 2} and then CpRe(PMe{sub 2}){sub 2}H{sub 2}. Mechanistic studies of these reactions are inconsistent with [CpRe(PPh{sub 3})H{sub 2}] as an intermediate. An alternative mechanism is presented proposing that the active species for H/D exchange is the 14-electron cyclic allyl intermediate [({eta}{sup 3}-C{sub 5}H{sub 7})Re(PPh{sub 3}){sub 2}] (E), in which both hydrides have migrated from the rhenium to the cyclopentadienyl ligand. This intermediate accounts for the fact that (1) deuterium does not exchange into the hydride ligands of complex 1 during the H/D exchange catalysis and (2) phosphine substitution occurs by an associative pathway. The precursor to intermediate E, [({eta}{sup 4}-C{sub 5}H{sub 6})Re(PPh{sub 3}){sub 2}H] (D), can undergo reversible orthometalation, allowing H/D exchange between the hydride ligands and the ortho phosphine positions. Evidence is presented to support this new mechanism as well as to rule out other feasible mechanisms.
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- DOE Contract Number:
- FG02-86ER13569
- OSTI ID:
- 343705
- Journal Information:
- Organometallics, Journal Name: Organometallics Journal Issue: 9 Vol. 18; ISSN ORGND7; ISSN 0276-7333
- Country of Publication:
- United States
- Language:
- English
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