Cyclic and High Polymeric nido-Carboranylphosphazenes as Ligands for Transition Metals¹

l-Methyl-(-(2-propynyl)-3,3,5,5-tetrachlorocyclotriphosphazene (6) reacts with bis(acetonitrile)-decaborane to yield l-methyl-l-[(o-carboranyl)methylene]-3,3,5,5etetrachlorocyclotriphosphazene (7). Species 7 was converted by base to the nido-carboranyl anion or dianion derivatives, which react with Rh(PPh₃)₃Cl or with Mo(CO)₆ or W(CO)₆ to form the appropriate (metallocarboranyl)phosphazene derivatives (10 or 12). Compound 7 polymerizes when heated, and the high polymeric analogues (13,14, and 16) behave in a similar manner to the cyclotriphosphazene derivatives in the formation of metallocarboranyl derivatives. Species 7 is unusual in its reaction with piperidine. The four halogen atoms are replaced by piperidine groups, and a boron atom is removed from the cage, but an internal counterion at skeletal nitrogen is generated rather than the expected piperidinium ion. An X-ray structural investigation of this species (8) confirmed the presence of a planar cyclotriphosphazene ring linked to the carboranyl unit through a methylene spacer group. A proton was connected to the phosphazene skeletal nitrogen atom furthest from the carboranyl group. The P-N bonds adjacent to the site of the carborane attachment were of normal length (1.575 Á), but the two bonds furthest from this site were exceptionally long (1.68 Á), presumably a consequence of ring protonation.