The synthesis and properties of some group V pyrrole analogs and boron tropylium analogs.

2,2$\sp\prime$,5,5$\sp\prime$,-Tetrakismethylenebistibolane and its bibismolane analog were prepared by a multistep synthesis from 2,5-dibromo-1,5-hexadiene. The band gap of 2,2$\sp\prime$-5,5$\sp\prime$-tetrakismethylenebistibolane was found to be significantly larger than that of its conjugated isomer 2,2$\sp\prime$,5,5$\sp\prime$-tetramethylbistibole. This was in qualitative agreement with our expectations based on the Hoffmann model. 1,1-Dimethyl-4,5-cyclopentenostannepin was prepared according to a literature procedure. Mechanistic studies on the thermal decomposition of 1,1-dimethyl-4,5-cyclopentenostannepin were consistent with the generation of dimethylstannylene as an intermediate. 1-Methyl-4,5-cyclopentenoborepin was prepared by reaction of 1,1-dibutyl-4,5-cyclopentenostannepin with methylboron dibromide. 1-Phenyl-4,5-cyclopentenoborepin was prepared by reaction of 1,1-dimethyl-4,5-cyclopentenostannepin and phenylboron dibromide. The NMR characteristics of the borepins were studied, and were found to be consistent with substantial conjugation of the boron atom to the $\pi$-system. The properties of the borepin ring system as a ligand with transition metals was investigated. 1-Methyl-4,5-benzoborepin(tricarbonyl)chromium was found to be thermally stable to 124$\sp\circ$C. 1-Methyl-4,5-benzoborepin(tricarbonyl)chromium showed no tendency to undergo the haptotropic shift of the chromiumtricarbonyl group from the borepin ring to the benzene ring. A series of substituted 4,5-cyclopentenoboratepins were prepared by a reaction between 1-methyl-4,5-cyclopentenoborepin or 1-phenyl-4,5-cyclopentenoborepin and a nucleophile. Methyllithium, phenyllithium, and potassium cyanide were used as nucleophiles. It was found by NMR spectroscopy that the structures of the substituted 4,5-cyclopentenoboratepins were consistent with the seven membered boratepin ring form, no evidence of the boratenorcaradiene valence tautomer was found. The $\sp1$H-NMR signals of potassium 1-cyano-1-methyl-4,5-cyclopentenoboratepin, lithium 1-methyl-1-phenyl-4,5-cyclopentenoboratepin, and potassium 1-cyano-1-phenyl-4,5-cyclopentenoboratepin showed a temperature dependent and reversible shift in frequency with temperature. A possible explanation for this temperature dependent shift is that there may be a dependence in the proportion of exo to endo conformers upon temperature.PhDOrganic chemistryPure SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/128425/2/9013937.pd