The EPR signal of Cp2TiIIIH2AlCl2 in tetrahydrofuran shows an alternating line-width effect involving the MI = ±1 and MI = 0 spin states of the two bridge hydrogens, and indicating the existence of a dynamic molecular process in which the involved coupling constant undergoes an out-of-phase modulation. Evaluation of the temperature dependence of the line-width effect leads to an activation energy of 4 kcal/mol, which implies that complete breaking of a chemical bond is not involved. It is proposed that one hydrogen is more tightly bonded to the Al, the other to the Ti, and that the molecular motion concerns the flopping to the reverse conformation. When di-π-cyclopentadienyltitanium dichloride (Cp2TiCl2) in tetrahydrofuran is reduced with metallic sodium in the presence of freshly sublimed AlCl3, a paramagnetic species is formed after several hours stirring at room temperature. The reaction solution gives a strong electron resonance signal. Double integration of the first derivative spectrum indicates some 60% of the initial amount of titanium ([Ti] = 10 x 10-3 mol/1) is present in the signal-producing form. The essential feature of the spectrum is the interaction of the unpaired electron of a TiIII species with one nucleus of Al (I = 5 2), giving rise to six equivalent hyperfine lines. On extreme dilution further hyperfine structure is resolved (Fig. 1). Each of the six lines is split into a 1/2/1 triplet by two equivalent hydrogen nuclei, and furthermore a splitting of each component into an uneven number of very narrow lines is. © 1969.
