Syntheses of Group 4 ansa ‐Trovacene Complexes and Conversion of [1]Silatrovacenophanes into Paramagnetic Metallopolymers by Ring‐Opening Polymerization

An improved protocol for the selective dilithiation of [V(η 5 ‐C 5 H 5 )(η 7 ‐C 7 H 7 )] has been developed, which afforded [V(η 5 ‐C 5 H 4 Li)(η 7 ‐C 7 H 6 Li)]⋅PMDTA ( 5 ; PMDTA= N , N , N ′, N ′′, N ′′‐pentamethyldiethylenetriamine) in almost quantitative yield (98 %). In the solid state, the species features a dimeric structure with two terminal and two bridging lithium atoms, with the latter connecting both sandwich subunits. Reaction with suitable Group 4 dihalide compounds enabled the isolation of highly strained silicon‐ and germanium‐bridged [1]trovacenophanes 6 and 7 . Similarly, reaction of 5 with Cl 2 Sn 2 t Bu 4 afforded the rather unstrained complex [V(η 5 ‐C 5 H 4 )(η 7 ‐C 7 H 6 )Sn 2 t Bu 4 ] ( 8 ), which together with 7 represent the first trovacenophanes to incorporate heavier analogues of silicon in the ansa ‐bridge. Ring‐opening polymerization reactions of [V(η 5 ‐C 5 H 4 )(η 7 ‐C 7 H 6 )SiRR′] ( 2 a : R=R′=Me; 6 : R=Me, R′= i Pr) were performed by heating in a solution of toluene in the presence of the Karstedt catalyst, which resulted in the formation of the corresponding soluble poly(trovacenylsilanes) in yields of 41 and 33 %, respectively. As estimated by gel permeation chromatography (GPC), the macromolecules possess molecular weights of M n =10 010 and 5580 g mol −1 with polydispersity indices of 2.31 and 1.64 for 9 and 10 , respectively. ESR spectroscopic studies on 9 and 10 revealed only a single broad resonance in each case without any identifiable 51 V hyperfine coupling.