The addition of small molecules to (η-C 5H 5) 2Rh 2(CO)(CF 3C 2CF 3) : X. Addition of terminal alkynes; the formation of bridging carbonyl cyclobutenyl intermediates (η-C 5H 5) 2Rh 2(μ-CO)-[η 1,η 3-C 4(CF 3) 2HR] and their facile conversion to binuclear metalladine complexes (η-C 5H 5) 2Rh 2[η 2,η 4-C 4(CF 3) 2HR

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 HCCR (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 HCCR (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 HCCR (R = CH 2CH 2CH 2CCH or CMe=CH 2) in hexane, and again all the products remain in solution. It is possible to separate 2 (R = CH 2CH 2CH 2CCH or CMeCH 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 HCCSiMe 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 HCCR) located in the 3- and 2-positions respectively of the 1-metallacyclopentadiene ring.