The preparations of C-mono- and C,C′-bis(indenylmethyl) and C-mono- and C,C′-bis(fluorenylmethyl) derivatives of nido-2, 3-dicarbahexaborane(8) (C2B4H8) are described. These carboranes are multifunctional, presenting several aryl and carboranyl sites for metal η5 or η6 coordination, and are designed as structural modules for use in the construction of multiunit metal sandwich complexes and proposed electron-delocalized solid-state arrays. The carborane syntheses were conducted via the method of Hosmane and Grimes, involving the reaction of alkynes with B5H9 in the presence of (C2H5)3N. However, these preparations required a priori the syntheses of the first known difluorenyl and diindenyl alkynes, as well as an improved synthesis of (9-fluorenylmethyl) acetylene. In the formation of the bis(indenylmethyl)acetylene from 1-lithioindene, an unexpected 1 → 2 rearrangement occurred to give the 2-substituted product exclusively. The new alkynes and carboranes were characterized via multinuclear NMR, IR, and mass spectroscopy, and the properties of the rado-RR′C2B4H6 carboranes toward bridge deprotonation, complexation with Fe2+, and subsequent fusion to generate R2R′2C4B8H8 products were explored. All of the new RR′C2B4H6 species are deprotonated by NaH in THF to give the RR′C2B4H5- anions, and the monosubstituted anions (R = indenylmethyl, fluorenylmethyl; R′ = H) undergo slow Fe2+-promoted fusion to form R2C4B8H10. However, the disubstituted R2C2B4H5- anions do not fuse, owing to steric hindrance by the bulky R groups; the diindenyl species forms a complex of the type (R2C2B4H4)Fe(THF)x (x = 2 or 3), which does not react further. Treatment of the neutral diindenyl carborane with FeCl2 gave in low yield an apparent intramolecular sandwich complex in which the iron is proposed to be η5-coordinated to the C5 rings of both indenyl groups.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry