Lithiation of (^tBuNH)₃PNSiMe₃ and Formation of Tetraimidophosphate Complexes Containing M₃O₃ Rings (M = Li, K):  X-ray Structure of the Stable Radical {(Me₃SiN)P(μ₃-N^tBu)₃[μ₃-Li(THF)]₃(O^tBu)}

Abstract

The reaction of ((t)BuNH)(3)PNSiMe(3) (1) with 1 equiv of (n)BuLi results in the formation of Li[P(NH(t)Bu)(2)(N(t)Bu)(NSiMe(3))] (2); treatment of 2 with a second equivalent of (n)BuLi produces the dilithium salt Li(2)[P(NH(t)Bu)(N(t)Bu)(2)(NSiMe(3))] (3). Similarly, the reaction of 1 and (n)BuLi in a 1:3 stoichiometry produces the trilithiated species Li(3)[P(N(t)Bu)(3)(NSiMe(3))] (4). These three complexes represent imido analogues of dihydrogen phosphate [H(2)PO(4)](-), hydrogen phosphate [HPO(4)](2)(-), and orthophosphate [PO(4)](3)(-), respectively. Reaction of 4 with alkali metal alkoxides MOR (M = Li, R = SiMe(3); M = K, R = (t)Bu) generates the imido-alkoxy complexes [Li(3)[P(N(t)Bu)(3)(NSiMe(3))](MOR)(3)] (8, M = Li; 9, M = K). These compounds were characterized by multinuclear ((1)H, (7)Li, (13)C, and (31)P) NMR spectroscopy and, in the cases of 2, 8, and 9.3THF, by X-ray crystallography. In the solid state, 2 exists as a dimer with Li-N contacts serving to link the two Li[P(NH(t)Bu)(2)(N(t)Bu)(NSiMe(3))] units. The monomeric compounds 8 and 9.3THF consist of a rare M(3)O(3) ring coordinated to the (LiN)(3) unit of 4. The unexpected formation of the stable radical [(Me(3)SiN)P(mu(3)-N(t)Bu)(3)[mu(3)-Li(THF)](3)(O(t)Bu)] (10) is also reported. X-ray crystallography indicated that 10 has a distorted cubic structure consisting of the radical dianion [P(N(t)Bu)(3)(NSiMe(3))](.2)(-), two lithium cations, and a molecule of LiO(t)Bu in the solid state. In dilute THF solution, the cube is disrupted to give the radical monoanion [(Me(3)SiN)((t)BuN)P(mu-N(t)Bu)(2)Li(THF)(2)](.-), which was identified by EPR spectroscopy.

Cubic and Spirocyclic Radicals Containing a Tetraimidophosphate Dianion [P(NR)3(NR‘)]•2-

“…Inspection of EPR spectrum of 3d in the absorption mode ( Figure 5) reveals an exponential decay pattern at both the high-and low-field ends of the resonance, which is characteristic of hyperfine coupling to more than one equivalent nucleus with I > 1, such as 7 Li. Integration of the spectral simulation published previously 15 does not reproduce this pattern. In consequence, the EPR spectrum of 3d was simulated anew, assuming the C3 symmetry which is expected for this cubic radical.…”

“…14,15 The remarkable stability of these radicals can be attributed to the delocalization of spin density over two or four nitrogen atoms, respectively, as well as the presence of bulky isopropyl or tert-butyl substituents to impede their reactivities.…”

“…14 This finding prompted a reexamination of the EPR data reported previously for the lithium tert-butoxide adduct {Li2[P(N t Bu)3(NSiMe3)]•(LiO t Bu)•3THF} • (3d). 15 A good simulation of the EPR spectrum of this species had been obtained assuming dissociation of the cubic framework to yield the monocyclic radical {(THF)2Li(-N t Bu)(-NSiMe3)P(N t Bu)2]} •  ; however, the fact that 3a does not dissociate in solution would suggest that 3d also retains its cubic structure, as the LiX bonds which cement these frameworks are stronger for X = O than X = Cl. Inspection of EPR spectrum of 3d in the absorption mode ( Figure 5) reveals an exponential decay pattern at both the high-and low-field ends of the resonance, which is characteristic of hyperfine coupling to more than one equivalent nucleus with I > 1, such as 7 Li.…”

“…In consequence, we consider that the simulation in Figure 5c is a more accurate representation of the EPR spectrum in Figure 5b than the simulation described previously. 15 The HFCCs that were used to create the new simulation (Table 4) are more accurate values for this radical, which, in the final analysis, appears to retain its cubic structure in dilute THF solutions.…”

Organo-aluminum, zinc and magnesium derivatives of the imidotris(amido)phosphate Me3SiNP(NHtBu)3

“…of n-butyllithium. In an alternative approach to tetraimidophosphates we have shown that ( t BuNH) 3 PNSiMe 3 (1) [4] can be sequentially deprotonated with n-butyllithium to give Li[P(N t Bu)(NH t Bu) 2 (NSiMe 3 )] (1Li) [5], Li 2 [P-(N t Bu) 2 (NH t Bu)(NSiMe 3 )] (1Li 2 ) [5] and Li 3 [P(N t Bu) 3 -(NSiMe 3 )] (1Li 3 ) [4]. The anions in these complexes can be considered analogues of dihydrogen phosphate [H 2 PO 4 ] À , hydrogen phosphate [HPO 4 ] 2À and orthophosphate [PO 4 ] 3À , respectively.…”