Electrophilic Functionalization of Donor-Stabilized Phosphanylboranes: A New Pathway toward Heavy 13/14/15 Parent Hydride-Containing Compounds

Abstract

A novel method for the functionalization of donor-stabilized 13/15 compounds is presented. Reacting the IDipp (1,3-bis(2,6-diisopropylphenyl)-imidazolin-2-ylidene) stabilized parent phosphanylborane IDipp·BH₂PH₂ with (in situ generated) main group electrophiles results in mixed 13/14/15 compounds [IDipp·BH₂PH₂ER₃][WCA] (WCA = weakly coordinating anion, ER₃ = CH₃ (2), SiEt₃ (3), Ge(SiMe₃)₃ (4), SnMe₃ (5)) containing the complete series from carbon to tin. In contrast, reactions with the group 15 electrophiles [Cy₂Pn][PF₆] (Pn = P, As) yielded an intriguing P–P coupling reaction, affording [IDipp·BH₂PH₂PHBH₂·IDipp][PF₆] (6). The protonated phosphanylboranes reveal acidic protons at the phosphorus atom, and this can be exploited by reactions with LiGaH₄ and LiAlH₄, resulting in either deprotonation to the parent phosphanylborane or chain extension to yield LB·BH₂PH₂GaH₃ (LB = IDipp (7a), Me₃N (7b)), the first examples of a {GaH₃} unit bound to a primary phosphine. The products can be characterized by multinuclear NMR spectroscopy and single-crystal X-ray structure determination.