Phosphorus-based ambidentate chelating ligands: Pyridyl-N- and imido-N-metal coordination in the Py2P(NSiMe3)(2) anion

Monoanionic heteroallylic ligand systems [R-N-E-N-R](-) (E = Si(R-2), S(R-2 ) or S(R), C(R), and P(R-2)) are Versatile chelating substituents both in m ain group and transition metal chemistry as they provide sufficient steric demand and solubility to the products. Their application is only limited by the rigid bite of the ligands as the N . . .N distance cannot be tuned to the various; radii,of different metals. In this paper we present the new co ncept of opening the ligand periphery to additional coordination. The NP(R- 2)N- chelate in classical aminoiminophosphoranates is extended by additiona l coordination sites in the organic substituents (e.g., 2-pyridyl (Py) inst ead of phenyl (Ph)). Py2P{N(H)SiMe3}(NSiMe3) (1) is the starting material f or a new class of complexes as deprotonated 1 contains along with the NPN- chelate the pyridyl ring nitrogen atoms to generate a side-selective Janus face ligand. In [(THF)Sr{Py2P(NSiMe3)(2)}(2)] (2) and [(4,4'-bipy)Ba{Py2P(N SiMe3)(2)}(2]n) (3) both pyridyl rings are involved in metal coordination b ut only one. imido nitrogen atom. Hence, the classical NP(Ph-2)N- chelating ;ligand is converted into a NP(Py-2)N- tripodal ligand. In the coordination to zinc in the complex [Zn{Py2P(NSiMe3)(2)}(2)] (4) one pyridyl ring and o ne imido nitrogen atom.is:employed in metal coordination. Pyridyl substitut ion of the P(V) center gives not only access to new coordination modes but also changes the reactivity of aminoimindphophoranes considerably. [Li(Py2P NSiMe3)](2) (5) is a lithiated phosphanylamine derived from the reduction o f 1 with lithium di(trimethylsilyl)amide. Reaction of 1 with lithium organi cs yields [(THF)(2)Li(Py2P)] (6). Pyridyl substitution facilitates single o r even double P=N bond cleavage, unprecedented in alkyl- or aryl-substitute d aminoiminophosphoranes. This reduction of P(V) species to P(III) compound s supplies easy access to phosphanylamines and secondary phosphanes.