| Abstract: | A number of novel (tricarbonyl)chromium complexes of heptalenes 10 – 13, 16 – 20 and 23 – 25 have been prepared by reaction of the heptalenes with Cr(CO)3L3] (L=NH3, Py; cf. Schemes 3–6). Surprisingly, the off‐state complexes 17 and 19 , in which the Cr(CO)3 group complexes on the diester ring, have been obtained with excellent regioselectivity. The directing effect of ester C=O groups on the regioselectivity of the Cr(CO)3 coordination to heptalene rings has been discussed. These complexes undergo thermal rearrangements via 1,2‐intra‐ring shift and inter‐ring migration of the Cr(CO)3 fragment to give the thermodynamically more stable on‐state complexes 16 and 27 , respectively (cf. Schemes 8 and 9). The analogous thermal behavior of other prepared complexes has also been investigated. A new procedure for the selective preparation of complexes 10 and 13 , in which the Cr(CO)3 group is coordinated to the phenyl ring of the styryl substituent has also been developed (Scheme 7). The attachment of the Cr(CO)3 fragment to the phenyl group has a visible influence on the UV/VIS behavior of the on‐state complexes 10 and 13a , as well as on the photochemical behavior of the DBS isomers 13a / 13b (cf. Scheme 10). |
