Reversible Skeletal Transmetalations of Inorganic Rings: Isolation of Aluminatophosphazenes, a Zwitterionic Phosphazene, and a Donor-Stabilized Alumazine−Phosphazene Hybrid Cation

Synthesis of the cyclic aluminatophosphazene ring N(PCl2NMe)2AlMeCl (5) has been achieved via a skeletal
transmetalation reaction between AlMe3 and the boratophosphazene N(PCl2NMe)2BCl2 (1). Reaction of 5 with various
halogenated Lewis acids such as GaCl3 yielded the fully chlorinated aluminum heterocycle N(PCl2NMe)2AlCl2 (8)
through a methyl−halogen exchange process. In contrast, treatment of 5 with excess AlMe3 resulted in complete
methylation at aluminum to give N(PCl2NMe)2AlMe2 (6). Compound 5 was reacted with various Ag+ salts with
weakly coordinating anions, including Ag[OSO2CF3], which afforded the triflate-substituted heterocycle N(PCl2NMe)2AlMe(OSO2CF3) (9). The reaction of 5 with Ag[BF4] surprisingly produced the previously known fluorinated
boratophosphazene N(PCl2NMe)2BF2 (10). The transformation of 1 to 5 and then to 10 represents a rare, formally
reversible, skeletal transmetalation process involving boron and aluminum. Treatment of 5 with Ag[PF6] led to the
insertion of phosphorus in place of aluminum to form the novel zwitterionic fluorinated phosphorus(V) heterocycle
N(PCl2NMe)2PF4 (11). The ethyl-substituted aluminatophosphazene N(PCl2NMe)2AlMeEt (14) reacted cleanly with
a 1:1 mixture of [Ph3C][B(C6F5)4] and THF to give the novel donor-stabilized alumazine−phosphazene hybrid cation,
[7·THF]+, as the [B(C6F5)4]- salt [N(PCl2NMe)2AlMe·THF][B(C6F5)4] (15).