Photochemical reactions of cyclopentadienylbis(ethene)rhodium with benzenederivatives

During UV irradiation of [CpRh(C2H4)(2)] (1) (Cp = eta(5)-C5H5) in hexane i n the presence of hexamethylbenzene the di- and trinuclear arene bridged co mplexes [(CpRh)(2)(mu-eta(3):eta(3)-C6Me6)] (3) and [(CPRh)(3)(mu(3)-eta(2) :eta(2):eta(2)- C6Me6)] (4) are formed besides known [CPRh(eta(4)-C6Me6)] ( 2). It was shown by a separate experiment that 3 besides small amounts of 4 is formed by attack of photochemically from 1 arising CpRh fragments at th e free double bond of the eta(4)-bonded benzene ring in 2. Irradiation of 1 in the presence of diphenyl (C12H10) affords the compounds [(CpRh)(2)(mu-e ta(3):eta(3)-C12H10)] (5) and [(CPRh)(3)(mu(3)-eta(2)-eta(2):eta(2)- C12H10 )] (6) as analogues of 3 and 4, in the presence of triptycene (C20H14) only [(CpRh)(2)(mu-eta(3):eta(3)-C20H14)] (7) is obtained; the bridging in 5, 6 , and 7 always occurs via the same six-membered ring of the corresponding l igand system. During the photochemical reaction of 1 in the presence of sty rene (C8H8) substitution of the ethene ligands by the vinyl groups with for mation of [CpRh(C2H4) (eta(2)-C8H8)] (8) and known [CpRh(eta(2)-C8H8)(2)] ( 9) is observed exclusively. The new complexes were characterized analytical ly and spectroscopically, in the case of 3 also by X-ray structure analysis .