The Crystal and Molecular of a Dimer of a Cyclobutadiene Derivative. The Crystal Structure of BIS-(2-Bromopyridine)-Dodecahydrodecaborane

Citation

Fritchie, Charles Julius (1963) The Crystal and Molecular of a Dimer of a Cyclobutadiene Derivative. The Crystal Structure of BIS-(2-Bromopyridine)-Dodecahydrodecaborane. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/0JNR-XX66. https://resolver.caltech.edu/CaltechTHESIS:04232012-084021160

Abstract

I. The crystal and molecular structures of a dimer of a cyclobutadiene derivative.

The molecular structure of this compound, previously suggested by other chemical work, has been conclusively established. Bond lengths and angles within the tricyclooctadiene skeleton were established with a precision exceeding that of any other study of a substituted cyclobutane and of any save one study of a substituted cyclobutene. Lengthening of the average C-C single and double bond in a C_4 ring is confirmed, and a shortening of the average external bond is also found. All bonds are normal (considering the above effects) except a C-C single bond in the configuration F-C-C-F, which is found to be 1.500 ± 0.009 Å rather than the expected 1.58 Å. The difference is attributed to change in the carbon hybridization state by the presence of the fluorine atoms.

The cyclobutane ring is accurately planar, but the two cyclobutene rings are slightly folded, with dihedral angles of 177° and 178° between the two halves. This folding is probably due to steric crowding within the molecule. The angles between the mean planes of the three rings, fused in a stairstep arrangement, are 113.3° and 113.7°.

II. The crystal structure of BIS (2-bromopyridine)-dodecahydrodecaborane.

The crystal structure of this compound has been determined, all atoms including hydrogen being located by examination of Patterson syntheses and use of the heavy atom technique. The compound has the same borohydride skeleton within experimental error as diacetonitrile-dodecahydrodescaborane, the first of the B_(10)H_(12)R_2 compounds with R an electron donor to be studied crystallographically. The B-B bond distances in the borohydride radical differ from those in the parent compound, B_(10)H_(14), and the positions of bridge hydrogens attached to borone 5 through 10 in B_(10)H_(14) are changed. There are two hydrogen bridges in the B_(10)H_(12)R_2 compounds, compared with four in B_(10)H_(14). Bond distances in the bromopyridine ligands are unchanged by attachment to the borohydride skeleton, but some angles are slightly abnormal. The abnormalities can be explained in terms of intramolecular steric repulsion.

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