1,2-dimethyl-3,4-diäthyl-cyclobutadien-eisentricarbonyl und trimethyl-äthyl-cyclobutadien-eisentricarbonyl

(Cyclobutadiene)iron TricarbonylA Case of Theory before Experiment

“…However, A is still used.) Once it was known that (cyclobutadiene)iron tricarbonyl was stable and that it could be prepared by halogen elimination from vicinal dihalocyclobutenes with Fe 2 (CO) 9 , others used this procedure to prepare diverse alkyl-substituted cyclobutadiene−iron carbonyl complexes: 1,2-dimethyl-3,4-diethyl-, trimethylethyl-, 1-ethyl-2,3-dimethyl-, isopropyl-2,3-dimethyl-, 1,2-dimethyl-3,4-diisopropyl-, trimethylisopropyl-, 1,2-dimethyl-, tetramethyl-, trimethyl-, and 1,3-dimethylcyclobutadiene−iron tricarbonyl, as well as 23 and 24 6 Rowland Pettit (reproduced by permission of Prof. J.…”

Experimental and Theoretical Characterization of the Valence Isomerization of Bi‐2H‐azirin‐2‐yls to Diazabenzenes

“…To prepare such 3,4‐diazidocyclobutenes, we used the known dihalides 15 c 12 (X=Br), cis ‐ 15 d (X=Cl), trans ‐ 15 d 13 (X=Cl, Br, I), a mixture14 of the dibromides 15 e , 15 e′ , and 15 e′′ , or 15 f 15 (X=Br) as well as 15 g ,16 15i ,17 15 j ,18 and 15 k 18 (all X=Cl). Alternatively to the procedure of Brune et al18, 19 via bis(methylene)cyclobutenes, some of these known and several new compounds were accessible more conveniently from alkynes 12 via cyclobutenediones 13 20 and diols 14 ,21 which were transformed into dihalides 15 (X=Cl, Br, I) on treatment with SOCl 2 , PBr 3 , or PI 3 . We prepared 15 f (X=I), 15 h (X=Br), and 15 i (X=Cl, Br) as pure substances, whereas 15 j (X=Cl, Br) and 15 k (X=Cl, Br) resulted each as mixtures with dihalides 15 j′ or 15 k′ and 15 k′′ , respectively.…”

“…We prepared 15 f (X=I), 15 h (X=Br), and 15 i (X=Cl, Br) as pure substances, whereas 15 j (X=Cl, Br) and 15 k (X=Cl, Br) resulted each as mixtures with dihalides 15 j′ or 15 k′ and 15 k′′ , respectively. The equilibration of 3,4‐dihalocyclobut‐1‐enes substituted with alkyl groups is notorious as a rapid process 18. 19 The synthesis of 15 c (X=Br) was performed by a different literature method 12…”