REACTION OF BIS(TRIMETHYLPHOSPHINE)HEPTAHYDROTETRABORON(1+) CATION WITH TRIMETHYLPHOSPHINE

The reaction of the no-bis(trimethylphosphine)heptahydrotetraboron(1+) cation, B4H7 . 2P(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 o-tris(trimethylphos phine)heptahydrotetraboron(1+) cation, B4H7 . 3P(CH3)(3)(+) (3), which further reacted with P(CH3)(3) to finally give cleaved products, the tetrakis(trimethylphosphine)tetrahydrotriboron(1+) cation, B3H4 . 4P(C H3)(3)(+) (4), and trimethylphosphine-borane(3), BH3. P(CH3)(3). The e ffect of the ionic charges upon the reaction rates was apparent. Thus, the second reaction for 1 was rapid at room temperature while the cor responding reaction for 2 was slow and the negatively charged isoelect ronic species, the B4H9 . P(CH3)(3)(-) anion, did not undergo the seco nd reaction. The above two hypho polyboron complex cations, 3 and 4, w ere characterized by B-11 and P-31 NMR spectroscopy. Like its isoelect ronic counterparts, the cation 3 was highly fluxional; at room tempera ture the three B-P(CH3)(3) groups were equivalent on the NMR time scal e.