Cyclopentadienylrhodium Coordination to Alkenylarenes

Photochemical reaction of [Rh( η ‐C 5 H 5 )(C 2 H 4 ) 2 ] ( 5 ) with alkenyl benzene derivatives PhC(R 1 )=CHR 2 results in the formation of four types of cyclopentadienylrhodium complexes: the mononuclear ethylene η 2 ‐alkenylbenzene complexes [Rh( η ‐C 5 H 5 )( η ‐C 2 H 4 )( η 2 ‐PhC(R 1 )=CHR 2 )] 9 a (R 1 =H, R 2 =Ph), 9 b (R 1 =Ph, R 2 =H), 9 c (R 1 =CH 3 , R 2 =H), the mononuclear η 4 ‐alkenylbenzene complex [Rh( η ‐C 5 H 5 ){ β , α ,1,2‐ η ‐C 6 H 5 C(Ph)=CH 2 }] ( 10 ), the dinuclear μ ‐ η 4 : η 4 ‐alkenylbenzene complex [ anti ‐{Rh( η ‐C 5 H 5 )} 2 { μ ‐ β , α ,1,2‐ η :3,4,5,6‐ η ‐C 6 H 5 C(Ph)C=CH 2 }] ( 11 ), and the dinuclear rhodaindenyl complexes [Rh( η ‐C 5 H 5 ){1‐3,8,9‐ η ‐{1‐( η ‐C 5 H 5 )}‐3‐R 1 ‐1‐rhodaindenyl}] 12 a (R 1 =Ph), 12 b (R 1 =CH 3 ). Reaction of 5 with triisopropenylbenzene gives the dinuclear complex [{Rh( η ‐C 5 H 5 )} 2 ( μ ‐ β , α ,1,2‐ η : β ′, α ′,4,3‐ η ‐C 6 H 3 {C(CH 3 )=CH 2 } 3 )] ( 13 ). In the complexes 9 , only the olefinic side chain of the alkenylbenzene binds to the metal. In the complexes 10, 11, 12 , and 13 , an arene nucleus coordinates to rhodium as a 1,3‐diene moiety (or part thereof). The rhodaindenyl complexes 12 result from C−H activation of the alkenylbenzene at the β and ortho positions. The crystal and molecular structures of 9 a, 9 b, 10, 11 , and 12 a, b were determined. The role of 9 – 11 and 13 as models for intermediates during alkenylbenzene‐assisted self‐assembly of tricobalt clusters is discussed.