In recent years our group was interested in the synthesis and stabilisation of all-C-deprotiometallacyclobutadienes (e.g. Cp’2M(η3-Me3SiC3SiMe3), Cp’= η5-unsubstituted and substituted cyclopentadienyl) of group 4 metals.Following up on a series of unsuccessful attempts to access such structures, in one of our latest contributions to these efforts, we presented the synthesis of pure and solid Li2(Me3SiC3SiMe3) (1), the ideal synthon for this task. The reaction of 1 and rac-(ebthi)TiCl2 in 1:1 stoichiometry eventually leads to the first all-C-deprotiotitanacyclobutadiene (2). The molecular structure unambiguously shows the four-membered metallacycle bearing two C=C double bonds and two Ti-C single bonds (Figure 1, left). With the help of a detailed quantum mechanical investigation this exotic bonding situation can be best described as open shell singlet biradical. During the formation of 2, the formal allenediide ligand transfers an electron to the titanocene(IV), forming a titanocene(III) centre and a formal alleneylide fragment as ligand (Figure 1, middle and right). In follow-up experiments, we investigated the insertion of simple carbonyl compounds into one Ti-C bond forming labile six membered metallacycles which undergo subsequent reaction to enynes and formal Ti oxido species.

Successfull synthesis of the first all-C-deprotiotitanacyclobutadiene?

ACS Spring Meeting 2021

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