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

Abstract

The reaction of Cl 3 PNSiMe 3 with 3 equiv of LiHNR (R ) i Pr, Cy, t Bu, Ad) in diethyl ether produces the corresponding tris(amino)(imino)phosphoranes (RNH) 3 PNSiMe 3 (1a, R ) i Pr; 1b, R ) Cy; 1c, R ) t Bu; 1d, R ) Ad); subsequent reactions of 1b−d with n BuLi yield the trilithiated tetraimidophosphates {Li 3 [P(NR) 3 (NSiMe 3 )]} (2a, R ) Cy; 2b, R ) t Bu; 2c, R ) Ad). The reaction of [( t BuNH) 4 P]Cl with 1 equiv of n BuLi results in the isolation of ( t BuNH) 3 PN t Bu (1e); treatment of 1e with additional n BuLi generates the symmetrical tetraimidophosphate {Li 3 [P(N t Bu) 4 ]} (2d). Compounds 1 and 2 have been characterized by multinuclear ( 1 H, 13 C, and 31 P) NMR spectroscopy; X-ray structures of 1b,c were also obtained. Oxidations of 2a−c with iodine, bromine, or sulfuryl chloride produces transient radicals in the case of 2a or stable radicals of the formula {Li 2 [P(NR) 3 (NSiMe 3 )]LiX•3THF} • (X ) Cl, Br, I; R ) t Bu, Ad). The stable radicals exhibit C 3 symmetry and are thought to exist in a cubic arrangement, with the monomeric LiX unit bonded to the neutral radical {Li 2 [P(NR) 3 (NSiMe 3 )]} • to complete the Li 3 N 3 PX cube. Reactions of solventseparated ion pair {[Li(THF) 4 ]{Li(THF) 2 [(µ-N t Bu) 2 P(µ-N t Bu) 2 ]Li(THF) 2 } (6) with I 2 or SO 2 Cl 2 produce the persistent spirocyclic radical {(THF) 2 Li(µ-N t Bu) 2 P(µ-N t Bu)Li(THF) 2 } • (10a); all radicals have been characterized by a combination of variable concentration EPR experiments and DFT calculations.

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

“…Dimethylzinc (2.0 M solution in toluene), din-butylmagnesium (1.0 M solution in heptanes), trimethylaluminum (2.0 M solution in hexanes) and n-butyllithium (2.5 M solution in hexanes) were used as received from Aldrich. ( t BuHN) 3 PNSiMe 3 [4] [12] and [Mg{(N t Bu)(NSiMe 3 )P(NH t Bu) 2 } 2 ] [12] were prepared as described previously. NMR data ( 1 H and 31 P) of complexes 2-4 are included here for comparison with new compounds.…”

“…The reaction of 1 with di-n-butylmagnesium resulted in monodeprotonation of 2 equiv. of 1, yielding a magnesium complex that was assigned the spirocyclic structure (4) (Scheme 1) on the basis of solution NMR data [12]. Significantly, the coordination mode proposed for [P(N t Bu)-(NH t Bu) 2 (NSiMe 3 )] À in 4 was different from that suggested for the zinc and aluminum complexes 2 and 3, respectively [12].…”

“…A fascinating feature of the reactivity of the tri-lithiated derivative (1Li 3 ) is its propensity to undergo oxidation to form a stable, blue paramagnetic species which, in the solid state, exhibits a distorted cubic structure comprised of the dilithium derivative of the radical dianion [P(N t Bu) 3 (NSiMe 3 )] 2ÀÅ and a molecule of lithium iodide [7,8]. In THF solution, solvation of the Li + ions results in rupture of the cubic structure to generate spirocyclic complexes that incorporate this radical dianion [9,10].…”

“…The similar zinc (2) and aluminum (3) complexes were prepared by the alkane elimination reactions of 1 with dimethylzinc [11] or trimethylaluminum [12], respectively, as shown in Scheme 1. The coordination mode of the monoanionic ligand [P(N t Bu)(NH t Bu) 2 (NSiMe 3 )] À in 2 and 3 was deduced on the basis of solution NMR data, but the solid-state structures were not reported [11,12]. The reaction of 1 with di-n-butylmagnesium resulted in monodeprotonation of 2 equiv.…”

“…While no evidence for lithiation of 2 with n-butyllithium exists, the two remaining amino protons of the aluminum complex 3 were sequentially removed with 1 or 2 equiv. of n-butyllithium to yield a mono (3Li) and di-lithiated species (3Li 2 ), respectively, in which the ligand coordination mode was established by X-ray structural determinations (Scheme 2) [12]. The one-electron oxidation of 3Li 2 with iodine produces the persistent, neutral radical [Me 2 Al(l-N t Bu)(l-NSiMe 3 )P(l-N t Bu) 2 Li(THF) 2 ] identified in solution by EPR spectroscopy [12].…”