Abstract
Reaction occurs immediately when solutions of (η-C 5H 5) 2Rh 2(μ-CO)(μ-η 2-CF 3C 2CF 3) ( 1) in hexane are treated with HCCR (R = H, CF 3 or Ph), and the cyclobutenyl complexes (η-C 5H 5) 2Rh 2(μ-CO)[μ-η 1,η 3-C 4(CF 3) 2HR] ( 2) separate in near quantitative yield. CO is lost fairly rapidly from solutions of 2 in polar organic solvents, and the metallacyclopentadiene complexes (η-C 5H 5) 2Rh 2[μ-η 2,η 4-C 4(CF 3) 2HR] ( 3) are formed. The reactions between HCCR (R = Pr or CH 2CO 2Me) and 1 in hexane are also fast, but no precipitate is formed; infrared spectroscopy indicates that 2 (R = Pr or CH 2CO 2Me) is present in the reaction solution, but there is rapid conversion into 3 (ca. 80% yield after TLC work up). Slower reactions (2–5 min) occur between 1 and HCCR (R = CH 2CH 2CH 2CCH or CMe=CH 2) in hexane, and again all the products remain in solution. It is possible to separate 2 (R = CH 2CH 2CH 2CCH or CMeCH 2) (up to 65% yield obtained) from the corresponding 3 by immediate TLC, but 2 is converted fairly rapidly into 3 when left in solution. The reaction between 1 and HCCSiMe 3 is significantly slower (ca. 15 min), and gives 3 (R = SiMe 3) (64% yield) and (η-C 5H 5) 2Rh 2(CO) 2CF 3C 2CF 3 (21%) as major products. Another product, spectroscopically identified as (η-C 5H 5) 2Rh 2(μ-CO)[μ-C(O)C(CF 3)C(CF 3)](μ-HC 2SiMe 3) ( 7) can be isolated in significant amount only when TLC of the reaction solution is performed within 10 min of mixing the reactants. Spectroscopic analysis indicates complete regioselectivity in the formation of all metallacyclopentadiene complexes 3, with the H and R groups (from HCCR) located in the 3- and 2-positions respectively of the 1-metallacyclopentadiene ring.
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