Synthesis and structures of aluminum and magnesium complexes of tetraimidophosphates and trisam idothiophosphates:: EPR and DFT investigations of the persistent neutral radicals {Me2Al[(μ-NR)(μ-NtBu)P(μ-NtBu)2]Li(THF)2}• (R = SiMe3, tBu)

Reactions of (RNH)(3)PNSiMe3 (3a, R = Bu-t; 3b, R = Cy) with trimethylaluminum result in the formation of {Me-2-Al[(mu-(NBu)-Bu-t)(mu-NSiMe3)P((NHBu)-Bu-t)(2)]} (4) and the dimeric trisimidometaphosphate {Me2Al[(mu-NCy)(mu-NSiMe3)P(mu-NCy)(2)P-(mu-NCy)(mu-NSiMe3)]AIMe(2)} (5a), respectively. The reaction of SP((NHBu)-Bu-t)(3) (2a) with 1 or 2 equiv of AIMe(3) yields {Me2Al[(mu-S)(mu-(NBu)-Bu-t)P((NHBu)-Bu-t)(2)]} (7) and {Me2Al[(mu-S)(mu-(NBu)-Bu-t)P(mu-(NHBu)-Bu-t)(mu-(NBu)-Bu-t)]AlMe2} (8), respectively. Metalation of 4 with (BuLi)-Bu-n produces the heterobimetallic species {Me2Al[(mu-(NBu)-Bu-t)(mu-NSiMe3)P(mu-(NHBu)-Bu-t)(mu-(NBu)-Bu-t)]-Li(THF)(2)} (9a) and {[Me2Al][Li](2)[P((NBu)-Bu-t)(3)(NSiMe3)]} (10) sequentially; in THF solutions, solvation of 10 yields an ion pair containing a spirocyclic tetraimidophosphate monoanion, Similarly, the reaction of ((BuNH)-Bu-t)(3)(PNBu)-Bu-t with AIMe(3) followed by 2 equiv of (BuLi)-Bu-n generates {Me2Al[(mu-(NBu)-Bu-t)(2)(mu(2)-(NBu)-Bu-t)(2)(mu(2)-THF)[Li(THF)](2)} (11a), Stoichiometric oxidations of 10 and 11a with iodine yield the neutral spirocyclic radicals {Me2Al[(mu-NR)(mu-(NBu)-Bu-t)P(mu-(NBu)-Bu-t)(2)]Li-(THF)(2)}(center dot) (13a, R = SiMe3; 14a, R = Bu-t), which have been characterized by electron paramagnetic resonance spectroscopy. Density functional theory calculations confirm the retention of the spirocyclic structure and indicate that the spin density in these radicals is concentrated on the nitrogen atoms of the PN2Li ring, When 3a or 3b is treated with 0.5 equiv of dibutylmagnesium, the complexes {Mg[(mu-(NBu)-Bu-t)(mu-(NHBu)-Bu-t)P((NHBu)-Bu-t)(NSiMe3)](2)} (15) and {Mg[(mu-NCy)(mu-NSiMe3)P(NHCy)(2)](2)} (16) are obtained, respectively. The addition of 0.5 equiv of MgBu2 to 2a results in the formation of {Mg[(mu-S)(mu-(NBu)-Bu-t)P((NHBu)-Bu-t)(2)](2)} (17), which produces the hexameric species {[MgOH]-[(mu-S)(mu-(NBu)-Bu-t)P((NHBu)-Bu-t)(2)]}(6) (18) upon hydrolysis. Compounds 4, 5a, 7-11a, and 15-17 have been characterized by multinuclear (H-1, C-13, and P-31) NMR spectroscopy and, in the case of 5a, 9a center dot 2THF, 11a, and 18, by X-ray crystallography.