Contributions to the chemistry of boron .240. Studies on benzo-1,3,2-diphosphaborolanes, benzo-1,4,2,3-diphosphadiborinanes and benzo-1,5,2,3,4-diphosphatriborepanes

A series of benzo-1,3,2-diphosphaborolanes C6H4(PR)(2)BR' (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)(5)Cr fragment. In contrast to the R2N-bearing benzo-1,3,2-diphosphaborolanes, the derivative C6H4(PH)(2)BCMe3 (4f) dimerizes by additional B-P bond formation to produce a pentacyclic system (4f)(2). - The reaction of C6H4(PHNa)(2) with B-2(NMe2)(2)Cl-2 in THF/hexane yields the acyclic phosphanylborane Me2NB(PH-C6H4PH2)(2) (15). However, if C6H4[P(iPr)Li](2) is allowed to react with B-2(NMe2)(2)Cl-2, the benzo-1,4,2,3-diphosphadiborinane 13 is obtained, together with its rearrangement product 2-bis(dimethylamino)borylbenzo-1,3,2-diphosphaborolane 14 which dimerizes to (14)(2). - In contrast, the almost planar ring of the 2,3-dimesitylbenzo-1,4,2,3-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 6 pi electron system. Moreover, the benzo-1,5,2,3,4-diphosphatriborepane 18 forms readily from C6H4(PHNa)(2) and Br(Me2N)B-B(NMe2)-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.