Facile Transformations of a 1,3,5-Triphosphacyclohexadienyl Anion within the Coordination Sphere of Group 13 and 14 Elements: Synthesis of 1,3-Diphosphacyclopentadienyl Complexes and Phosphaorganometallic Cage Compounds

The reactivity of the lithium triphosphacyclohexadienyl complex Li[1,3,5-MeP3C3But3] toward a range
of group 13 and 14 halide complexes has been investigated. The heterocycle reacts with MX (M = Ga,
In, or Tl; X = Cl or I) to give the diphosphacyclopentadienyl (i.e., diphospholyl) complexes [M(η5-1,3-P2C3But3)] in good yield via phosphinidene, PMe, elimination reactions. One complex, M = Tl, has been
structurally characterized and found to exist as a one-dimensional polymer in the solid state. Similarly,
the reactions of Li[MeP3C3But3] with MCl2 (M = Sn or Pb) have given the tetraphosphametallocenes
[M(η5-1,3-P2C3But3)2], which have been structurally characterized. These exhibit fluxional behavior in
solution, which has been examined by variable-temperature NMR studies. The monomeric guanidinato−tin chloride complexes [LSnCl] (L = Cy2NC(NAr)2- or (cis-2,6-Me2C5H8N)C(NAr)2-, Cy = cyclohexyl,
Ar = C6H3Pri2-2,6) have been prepared, structurally characterized, and treated with Li[MeP3C3But3].
Again, this has yielded diphospholyl complexes [LSn(η1-1,3-P2C3But3)] via phosphinidene elimination
processes. In contrast, the reactions of Ph3ECl, E = Sn or Pb, do not proceed via phosphinidene elimination
reactions, but instead by triphosphacyclohexadienyl rearrangement processes that eventually lead to
complexes [Ph3M(η2-P,P-MeP3C3But3)], containing five-coordinate metal centers that are P,P-chelated
by an anionic bicyclic ligand. In the case of the tin complex, a reaction intermediate has been isolated
and shown to contain the first structurally characterized example of a 1,2-diphosphabicyclo[1.1.0]butane
fragment. A mechanism for the formation of this intermediate has been proposed.