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Der durch Behandlung des zweikernigen trans‐Fe‐Komplexes (I) mit Tritylhexafluorophosphat dargestellte Titelkomplex (II) ist das erste Beispiel eines Komplexes mit Dihaptocyclobutadienoid‐Liganden; ein analoges Zwischenprodukt wird bei der oxidativen Zersetzung von Tetrahaptocyclobutadienoid‐tricarbonyl‐Fe angenommen.

so the extent to which configuration is lost during dimerization of 1 to 2, will depend on the relative activation energies of the two "forbidden" processes 6 -* 7 and 6 -*• 8. Since both have very low activation energies, the difference between them must be correspondingly small. The conversion of 1 to 2, or of 2 to 1, should therefore take place with partial retention, but much loss, of configuration. This is the case. 16 The loss of configuration in these reactions is due to the formation first of the "wrong" intermediate (6 in the case of 1 -* 2) which has to undergo a "forbidden" conversion to the "right" one (7). If the latter were formed directly, it should collapse to cyclobutane with little or no loss of configuration. Bartlett and Porter16 have indeed found that photolysis of 10 gives 12 with little of the trans isomer; in this case loss of N2 from 10 gives the biradicaloid 11 analogous to 7. Mex ,-, zMe h Mex >-i zMe Et*N=N*Et Et^O ¿Net 10 11Organometal. Chem., 65, C57 (1974).(14) D. J. Ehnholt, unpublished results.

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55% yield: mp 42-43°( lit.6 mp 42-43°); ir (CC14) 1710 cm-1 (C=0); nmr (CC14) 1.15 (s, 6), 2.9 (s, 2), 7.3 (m, 4). l-ierf-Butylethynyl-2,2-dimethylindan-l-ol was prepared as described earlier3 for the general synthesis of tertiary propargyl alcohols by addition of iert-butylethynyllithium to 2,2-dimethyl-1-indanone. Distillation afforded the alcohol in 82% yield (99-100°at 0.5 mm): ir (neat) 3460 cm-1 (O-H), 2250 cm-1 (C=C); nmr (CC14) 1.0 (s, 3), 1.15 (s, 3), 1.23 (s, 9), 2.02 (s, 1), 2.55 (s, 1), 2.78 (s, 1), 7.05 (m, 4).l-(terf-Butylchlorovinylidene)-2,2-dimethylindan (2) was prepared according to the general procedure for the preparation of chloroallenes by Jacobs and Fenton.7 After three successive distillations from a small amount of sodium borohydride to remove unreacted alcohol, the desired chloroallene was obtained in 23% yield: bp 96-100°at 0.3 mm; ir (neat) 1945 cm-1 (C= C=C); nmr (CC14) S 1.22 (s, 9), 1.29 (s, 6), 2.86 (s, 2), 7.08 (m, 4).