Cyclo and Spirozirconation: Synthesis of New Phospholane-Boranes and Polyphosphine-Boranes

The diallylic phosphine-borane Ph(BH3)P(allyl)2 6, reacts with the zirconocene ‘Cp2Zr’ and gives the bicyclocomplex intermediate 7, characterized by 1H and 31P NMR. The electrophilic addition of H+, Br2, PhPCl2(BH3), Ph2PCl(BH3) leads to the corresponding stabilized phospholanes 8, 9, 11 and bicyclophospholane 10, whereas Ph2P(BH3)Li on 9 gives the boro(phospholane–diphosphine) 12. Under the same conditions, the tetraallylsilane (or germane) 13a–b leads to the spirometallacyclopentane 14a–b intermediates. After reaction with Br2, Ph2PLi(BH3) and PhPCl2(BH3), the racemic spirannic tetraphosphines 16a–b and the protected spirannic diphosphine 17b are obtained with a remarkable selectivity. Decomplexation reaction by Et2NH gives corresponding free phosphines 3′–17′.