Heptaphosphanortricyclenes with Oligosilyl Substituents: Syntheses and Reactions

Abstract

Abstract Three new nortricyclic P 7 R 3 derivatives with R = (SiMe 3 ) 2 MeSi– ( 2 ), (SiMe 3 ) 2 PhSi– ( 3 ), and cyclo‐Si 6 Me 11 – ( 4 ) were synthesized from red phosphorus, sodium/potassium alloy, and a chlorooligosilane, and their structures were elucidated with X‐ray diffraction. Reactions of 2 and 3 and of tri(hypersilyl)heptaphosphane 1 [hypersilyl = (SiMe 3 ) 3 Si–] with KO t Bu and LiO t Bu were performed, which led to different results depending on the size of the substituent. With KO t Bu, Si–P bonds were cleaved in 2 and 3 , and the mono‐ and dianions [P 7 R 2 ] – [R = (SiMe 3 ) 2 MeSi: 2a ; R = (SiMe 3 ) 2 PhSi: 3a ] and [P 7 R] 2– [R = (SiMe 3 ) 2 MeSi: 2b ] formed. Crystals of the [K + . 18‐crown‐6] + salt of 2b suitable for X‐ray diffraction could be grown successfully. Compound 1 reacted in an unprecedented way with KO t Bu at –60 °C. An Si–Si bond was cleaved, and a transient silyl anion formed, which immediately rearranged into a transient heptaphosphanide anion [Hyp 2 P 7 ] – ( 1a ) under expulsion of bis(trimethylsilyl)silylene. The silylene immediately inserted into a P–P bond of the basal P 3 ring of 1a , thereby forming two new isomeric anions {Hyp 2 P 7 [Si(SiMe 3 ) 2 ]} – , 1b and 1c . The structure of 1c could be elucidated by X‐ray crystallography, whereas 1b was characterized by 31 P NMR spectroscopy. The proposed reaction mechanism could be further confirmed by performing the reaction between 1 and KO t Bu in the presence of a large excess amount of dimethylbutadiene, which trapped the silylene. Just the formation of anion 1a was observed in that case. Anion 1a was also obtained quantitatively when KO t Bu was replaced by LiO t Bu. Compound 1a reacted with trifluoroacetic acid to give Hyp 2 P 7 H ( 1d ), which was successfully crystallized and examined by X‐ray diffraction. It is the first structural example of a stable and neutral nortricyclic P 7 derivative, R 2 P 7 H. All compounds were chracterized further by 31 P and 29 Si NMR spectroscopy and elemental analyses.