The Activation of Hydrogen by First-Row Transition-Metal Complexes. Final Report
- Columbia Univ., New York, NY (United States)
We have assigned the vibrational spectra of Os1 and Os2 complexes of propene, butene, and acetylene, and have used them for the assignment of the vibrational frequencies of surface alkenes and alkynes. We have measured the rates of H• transfer from (C5R5)Cr(CO)3H to olefins of many structural types, and have learned that even one substituent on the carbon to which the H• is transferred slows down the reaction considerably. We have shown that these Cr hydrides are useful catalysts for chain transfer during radical polymerization reactions. We have determined the strengths of several M–H bonds (in particular Cr–H ones), and have confirmed that the hydrides of first-row transition metals are particularly useful for generating radicals. We have used H• transfer to terminal methylenes to generate radicals that cyclize. We have shown that (C5R5)Cr(CO)3H can be regenerated under H2 and is therefore catalytic, but that (P–P)V(CO)4H cannot be regenerated from H2 and therefore can only be used stoichiometrically for radical generation. (The V-H bonds are weaker than the Cr–H ones, and the H• transfer to an olefin is therefore faster.) We have found that, under five atm of H2 pressure, cobaloximes catalyze H• transfer; they efficiently remove an H• from cyclized radicals, and therefore can be used to catalyze the cycloisomerization of some olefins. We have explored the one- and two-electron oxidation of (Ph3P)6Cu6H6. One-electron oxidation (which is reversible) generates a cation radical, whereas two-electron oxidation generates loss of a hydride (i.e., two electrons and a proton). We have found that the hydricity of (Ph3P)6Cu6H6 is between 36 and 50 kcal/mol. We have shown that uncongested organic radicals (i.e., TEMPO) can catalyze H• transfer from (C5R5)Cr(CO)3H to congested radicals like Ar3C•. We have examined the one-electron oxidation of [CpV(CO3H]–, and have inferred from the results that the reduction of alkyl iodides with [CpV(CO3H]– occurs by one-electron transfer. We have been able to use that reagent to catalyze radical cyclizations from H2 and appropriate alkyl iodides.
- Research Organization:
- Columbia Univ., New York, NY (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), Basic Energy Sciences (BES). Chemical Sciences, Geosciences, and Biosciences Division
- DOE Contract Number:
- FG02-97ER14807
- OSTI ID:
- 1604425
- Report Number(s):
- DOE-FG02-97ER14807
- Country of Publication:
- United States
- Language:
- English
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