The dynamic indium-bridged [1.1]ferrocenophane [(Me2Ntsi)In(C5H4)2Fe]2

Salt metathesis reaction between Li(thf)(Me(2)Ntsi) [Me(2)Ntsi = C(SiMe3)(2)SiMe2NMe2] and InX3 gave the new indium dihalides (Me(2)Ntsi)InX2 [X = Cl (2a), I (2b); isolated yields 34% (2a) and 44% (2b)]. Single-crystal X-ray analysis revealed that 2a is a Cl-bridged dimer, while 2b is monomeric. Salt metathesis reaction between dilithioferrocene and 2a and 2b, respectively, gave the new indium-bridged [1.1]ferrocenophane [(Me(2)Ntsi)In(eta(5)-C5H4)(2)Fe](2) (3). Only when 2a was used, could analytically pure 3 be isolated (45%). Revealed by a single-crystal X-ray analysis, compound 3 crystallized as an anti isomer (C-i symmetry). The diinda[1.1]ferrocenophane 3 showed fluxional behavior in solution. The proton NMR spectrum of 3 revealed only five singlets at ambient temperature (500 MHz, 25 degrees C, C6D6 or C7D8): one singlet for SiMe2, SiMe3, and NMe2 each and two singlets for the 16 Cp protons. These facts can be rationalized by assuming a fast degenerate isomerization from one anti isomer to another anti isomer (time-averaged D-2h symmetry). The two singlets at 4.43 and 4.45 ppm (500 MHz, 25 degrees C, C7D8) of the alpha- and beta-protons broadened at lower temperature and coalesced at 5 degrees C. By lowering the temperature further, two sets of signals emerged and became clearly visible at -30 degrees C, with each set consisting of four singlets for the Cp protons of equal intensity. Consistent with the splitting of the Cp signals, all other signals split in two sets of three singlets, indicating Q, symmetric Me2Ntsi moieties. These data show that the [1.1]ferrocenophane 3 exists as a mixture of two isomers in toluene solutions (2:1 ratio at -30 degrees C). Assuming that the thermodynamically favored isomer was found in the crystal lattice, the most intense set of signals was assigned to the anti isomer of 3, while the less intense set of signals was assigned to a syn isomer. The already known diinda[1.1]ferrocenophane {[2-(Me2NCH2)C6H4]In(eta(5)-C5H4)(2)Fe }(2) (1c) was revisited. Compound 1c did not reveal any fluxional behavior in 1D H-1 NMR spectra at ambient temperature, but EXSY spectroscopy revealed an occurring anti-to-anti isomerization of 1c in solution. A cyclic voltammogrant of 3 in thf/0.1 M [Bu4N][PF6] showed only an irreversible oxidation. A rationale is given why the reaction of (Me(2)Ntsi)InX2 [X = Cl (2a), I (2b)] with dilithioferrocene gave a [1.1]ferrocenophane, as similar reactions of (Me(2)Ntsi)ECl2 (E = Al, Ga) with dilithioferrocene gave strained [1]ferrocenophanes.