1,3-Pentadien-1-yl-5-ylidene (trimethyl-phosphine) boron

[168643-26-3]  · C8H14BP  · (MW 151.90)

(precursor to metal boratabenzenes)

Physical Data: mp 135-139 °C.

Solubility: soluble in chlorinated and ethereal solvents; sparingly soluble in aromatic solvents.

Form Supplied in: white solid.

Handling, Storage, and Precautions: stable to oxygen and moisture as a crystalline solid, but as a precaution should be stored under an inert atmosphere.

Precursor to Metal Boratabenzenes

Treatment of 1,3-pentadien-1-yl-5-ylidene (trimethylphosphine) boron (‘borabenzene-PMe3’),1 with any of a variety of anionic nucleophiles furnishes B-substituted alkali-metal boratabenzenes (1).2 Mechanistic work has established that this aromatic substitution proceeds via an addition-elimination pathway. Because boratabenzenes can serve as surrogates for cyclopentadienyl ligands, access to electronically and sterically diverse derivatives is useful for transition-metal chemistry.3

In certain cases, h6-boratabenzene complexes can be synthesized without the intermediacy of an alkali-metal boratabenzene, simply through treatment of borabenzene-PMe3 with a transition-metal alkyl or amide (2).4 This conversion presumably involves p-coordination of borabenzene-PMe3 to the transition metal, followed by intramolecular displacement of PMe3.

This approach can circumvent a problem (reduction) that sometimes bedevils reactions of alkali-metal boratabenzenes with transition metals. Thus, efforts to generate Cr(III)-boratabenzene adducts through treatment of Cl3Cr(THF)3 with (C5H5B-Ph)Li fail, furnishing Cr(II)-derived products instead. However, reaction of Ph3Cr(THF)3 with borabenzene-PMe3 affords the desired Cr(III)-boratabenzene complex (2).

1. Hoic, D. A.; Wolf, J. R.; Davis W. M.; Fu, G. C., Organometallics 1996, 15, 1315.
2. Qiao, S.; Hoic, D. A.; Fu, G. C., J. Am. Chem. Soc. 1996, 118, 6329.
3. (a) Fu, G. C., Adv. Organomet. Chem. 2001, 47, 101. (b) Herberich, G. E.; Ohst, H., Adv. Organomet. Chem. 1986, 25, 199.
4. (a) Putzer, M. A.; Rogers, J. S.; Bazan, G. C., J. Am. Chem. Soc. 1999, 121, 8112. (b) Rogers, J. S.; Bu, X.; Bazan, G. C., J. Am. Chem. Soc. 2000, 122, 730.

Gregory C. Fu

Massachusetts Institute of Technology, Cambridge, MA, USA

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