Studies on benzo-1,3,2-diphosphaborolanes, benzo-1,4,2,3-diphosphadiborinanes and benzo-1,5,2,3,4-diphosphatriborepanes

Article abstract of DOI:10.1002/cber.19971301120

A series of benzo-1,3,2-diphosphaborolanes C₆H₄(PR)₂BR′ (R = H, iPr, SiMe₃; R′ = R₂N, R) has been prepared by several routes and characterized by spectroscopic and - in part - by X-ray diffraction methods. They feature pyramidal P atoms with the substituents in antiperiplanar positions. The P atoms act as coordination sites for the (CO)₅Cr fragment. In contrast to the R₂N-bearing benzo-1,3,2-diphosphaborolanes, the derivative C₆H₄(PH)₂BCMe₃ (4i) dimerizes by additional B-P bond formation to produce a pentacyclic system (4f)₂. - The reaction of C₆H₄(PHNa)₂ with B₂(NMe₂)₂Cl₂ in THF/hexane yields the acyclic phosphanylborane Me₂NB(PH-C₆H₄PH₂)₂ (15). However, if C₆H₄[P(/Pr)Li]₂ is allowed to react with B₂(NMe₂)₂Cl₂, the benzo-1,4,2,3-di-phosphadiborinane 13 is obtained, together with its rearrangement product 2-bis(dimethylamino)borylbenzo-l,3,2diphosphaborolane 14 which dimerizes to (14)2. -In contrast, the almost planar ring of the 2,3-dimesitylbenzo1,4,2,3-diphosphadiborinane (16) possesses P and B atoms with a planar geometry. Short B-B and B-P bonds suggest that this new heterocycle can be regarded as a 6π electron system. Moreover, the benzo-l,5,2,3,4-diphosphatriborepane 18 forms readily from C₆H₄(PHNa)₂ and Br(Me₂N)B-B(N-Me₂)-B(NMe₂)Br to give a tub-shaped seven-membered C₂B₃P₂ ring system with the P atoms in a pyramidal and the B atoms in a planar environment. WILEY-VCH Verlag GmbH,sss 1997.