Collect. Czech. Chem. Commun. 1997, 62, 1279-1288

Reaction of Bis(trimethylphosphine)heptahydrotetraboron(1+) Cation with Trimethylphosphine

Mitsuaki Kameda and Goji Kodama

Department of Chemistry, University of Utah, Salt Lake City, Utah 84112, U.S.A.


The reaction of the arachno-bis(trimethylphosphine)heptahydrotetraboron(1+) cation, B4H7 . 2 P(CH3)3+ (1), with trimethylphosphine paralleled with that of the isoelectronic arachno-trimethylphosphine-tetraborane(8), B4H8 . P(CH3)3 (2). Thus, it first gave the hypho-tris(trimethylphosphine)heptahydrotetraboron(1+) cation, B4H7 . 3 P(CH3)3+ (3), which further reacted with P(CH3)3 to finally give cleaved products, the hypho-tetrakis(trimethylphosphine)tetrahydrotriboron(1+) cation, B3H4 . 4 P(CH3)3+ (4), and trimethylphosphine-borane(3), BH3 . P(CH3)3. The effect of the ionic charges upon the reaction rates was apparent. Thus, the second reaction for 1 was rapid at room temperature while the corresponding reaction for 2 was slow and the negatively charged isoelectronic species, the B4H9 . P(CH3)3+ anion, did not undergo the second reaction. The above two hypho polyboron complex cations, 3 and 4, were characterized by 11B and 31P NMR spectroscopy. Like its isoelectronic counterparts, the cation 3 was highly fluxional; at room temperature the three B-P(CH3)3 groups were equivalent on the NMR time scale.

Keywords: Tetraborane cation; Triborane cation; Polyborane complex cation.