Acepentalene metal complex

Dilithium Acepentalenediide and Other Metal Complexes of Acepentalene... 

Pentalene (135) and acepentalene (137) are antiaromatic cross-conjugated compounds with two or three fulvene subunits. According to theoretical calculations [142-147], 135 and 137 are unstable species [147, 148] but can be ligands in transition metal complexes. The respective anions, the planar 136 [149, 150] and the slightly bowl-shaped 138 [151, 152], can be generated by deprotonation of a dihydropentalene or by treatment of4,7-bis(trimethylstannyl)-4,7-dihydroacepentalene with methyllithium at -60 °C (Scheme 10.48). 

While some complexes of dihydroacepentalene derivatives have been reported some time ago [178-180], metal complexes of the unstable acepentalene (137), although they were the subject of DFT calculations [181], are still elusive. The acepentalene dianion (138) was obtained as its lithium salt in pure form by treatment of triquinacene (147) with BuLi/KOtBu/TMEDA giving 138 as its impure potassium salt, which was trapped with MegSnCl. The l,7-bis(trimethylstaimyl)-4,7-dihydroacepentalene (148) obtained was then treated with methyllithium, affording pure dilithium acepentalenediide (138-2Li+) (Scheme 10.52) [152]. 

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