Heterogeneous reactions afforded the first detection (by IR and NMR spectroscopy) of a secondary (η1-allyl)manganese carbonyl complex, CH3CHCHCH(CH3)Mn(CO)5, which results from the reaction of solid NaMn(CO)5 with 4-bromo-2-pentene in benzene or in saturated hydrocarbons at temperatures up to 5 °C. The analogous reaction of NaCo(CO)4 gives CH3-CHCHCH(CH3)C(O)Co(CO)4, the product of CO insertion into CH3CHCHCH(CH3)Co-(CO)4, which constitutes approximately 10% (by IR spectroscopy) of the equilibrium mixture with CH3CHCHCH(CH3)C(O)Co(CO)4 under CO at 1 atm and 5 °C. Addition of PPh3 to this mixture leads to the formation of isolable CH3CHCHCH(CH3)C(O)Co(CO)3PPh3. Similar reactions of 4-bromo-2-pentene with NaMn(CO)4PPh3 and NaCo(CO)3PPh3 do not give metal-carbon-bonded species, nor do room-temperature reactions of 4-bromo-2-pentene with NaMn-(CO)5 and NaCo(CO)4. Instead, the products include 2-pentenes, 1,3-pentadienes, 4,5-dimethyl-2,6-octadiene isomers, BrMn(CO)5, Mn2(CO)10, Co2(CO)8, and η3-(CH3CHCHCHCH3)Co(CO)3· Reactions of dimethyl chlorosuccinate, ethyl 2-bromopropionate, methyl 3-bromopropionate, and dimethyl dibromosuccinate with NaMn(CO)5 and NaCo(CO)4 give varying amounts of alkylmetal carbonyl compounds and products of β-elimination. The characteristics of these transformations suggest radical mechanisms initiated by single electron transfer (SET). Radical pairs formed by SET are implicated as intermediates in both substitutions and eliminations.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Organic Chemistry
- Inorganic Chemistry