Compounds with bonds to P, As or Sb

IV-substituted and B-substituted borazines are readily prepared by suitable choice of amine and borane starting materials or by subsequent reaction of other borazines with Grignard reagents, etc. Thermolysis of monocyclic borazines leads to polymeric materials and to polyborazine analogues of naphthalene, biphenyl, etc.  

A quite different structural motif is found in the curious cyclic hexamer [(BNMc2)6] which can be obtained as orange-red crystals by distilling the initial product formed by dehalogenation of (Me2N)2BCl with Na/K alloy (  

The Be ring has a chair conformation (dihedral angle 57.6°) with mean B-B distances of 172pm. All 6 B and all 6 N are trigonal planar and the 6-exocyclic NMe2 groups are each twisted at an angle of 65° from the adjacent B3 plane, with 

B-N 140pm. Structurally, this cyclohexaborane derivative resembles the radialenes, particularly the isoelectronic [Ce(=CHMe)6] in which the Ce ring likewise adopts the chair conformation. 

jELfNEK, J. D. Kennedy and B. StIbr, J. Chem. Soc., Chem. Commun., 677-8 (1994) and references cited therein. L. Schneider, U. Enclert and P. Paetzold, Z. anorg. allg. Chem. 620, 1191-3 (1994). H.-P. Hansen, U. E. Englert and P. Paetzold. Z. anorg. allg. Chem. 621, 719-24 (1995). 

Finally, the conceptual isoelectronic replacement of C-C by B-N can be applied to carba-boranes, thus leading (by appropriate synthetic routes) to azaboranes in which one or more of the cluster vertices of the borane is occupied by an N atom. So far, the following species have been characterized, the relevant cluster geometries and numbering schemes being given by the indicated structures on pp. 153-85 arachno- 

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