1. We were unable to verify earlier reports concerning these compounds: and Izvestiya Akad. Nauk SSSR, Otdel. Tekh. Nauk 466 (1959);
2. Cf. and J. chem. Soc. (London) 2601 (1961).
3. and J. Amer. chem. Soc., in the press.
4. and J. chem. Soc. (London) 690 (1959), and references cited therein.