Synthesis of Acyclic NPNCN Systems and Metalation Reactions with Organolithium, -magnesium, and -aluminum Reagents

The preparation of a new family of acyclic DippN(H)P(Ph)NRCR‘NR systems (2a−c) has
been achieved by the reaction of the mono(amino)chlorophosphine PhP(Cl)N(H)Dipp (1; Dipp
= 2,6-(iPr)2C6H3) with 1 equiv of Li[CR‘(NR)2] (2a, R = tBu, R‘ = nBu; 2b, R = Cy, R‘ = tBu;
2c, R = Cy, R‘ = nBu). Metalation reactions of 2a−c using nBuLi, Me3Al, and Bu2Mg have
shown that the NPNCN backbone is susceptible to nucleophilic attack. Reactions of 2a or
2b with nBuLi or Me3Al, respectively, produce the complexes Li[DippNPhP−P(nBu)PhNDipp]·Et2O (3) and Al(Me)2[DippNPhP−P(Me)PhNDipp] (4). These complexes involve a new type
of N,N‘ bidentate ligand with a chiral phosphorus center bearing bulky organic substituents
on the nitrogen atoms. Reaction of 2c with Bu2Mg proceeds in a different manner, producing
the amidinate complex Mg[CyNC(nBu)NCy][DippNP(nBu)Ph]·Et2O (5). A more direct route
to 3 and the analogous methyl-substituted complex Li[DippNPhP−P(Me)PhNDipp]·Et2O (6),
involving the reaction of 1 with the appropriate organolithium reagent in the molar ratio
2:3, has been developed. The oxidation product of 3, {Li[DippNPhP(O)P(nBu)PhNDipp]}2
(7), has also been synthesized via an alternative route. Complexes 1, 2a,b, and 5−7 were
fully characterized by multinuclear NMR spectroscopy, elemental analysis, and X-ray
crystallography.