tert-Butyl N-(phosphinoyloxy)carbamate

N-Alkyl-O-(diphenylphosphoryl)hydroxylamines have been reported to be potentially useful electrophilic aminating agents, for example in Schmidt reactions (Harger, 1981; Boche & Schrott, 1982a,b; Boche et al., 1988). It was not unreasonable to infer that such systems would act as nitrogen peracid equivalents and could be widely applicable reagents in organic synthesis (Masse & Sturtz, 1988a,b). In the course of exploring this possibility, we prepared the title compound, (I).

The title compound, C 17 H 20 NO 4 P, contains pyramidal N atoms and adopts similar conformations in its three independent molecules (A, B and C). Molecules A and B form a dimer in the crystal structure by way of a pair of N-HÁ Á ÁO hydrogen bonds, as does C with its inversion-generated partner.
Comment N-Alkyl-O-(diphenylphosphoryl)hydroxylamines have been reported to be potentially useful electrophilic aminating agents, for example in Schmidt reactions (Harger, 1981;Boche & Schrott, 1982a,b;Boche et al., 1988). It was not unreasonable to infer that such systems would act as nitrogen peracid equivalents and could be widely applicable reagents in organic synthesis (Masse & Sturtz, 1988a,b). In the course of exploring this possibility, we prepared the title compound, (I).
The asymmetric unit of (I) comprises three independent molecules ( Fig. 1, Table 1). Molecules A and B are related by an approximate local inversion centre and are linked into a dimer by a pair of N-HÁ Á ÁO hydrogen bonds ( Table 2). The third independent molecule (C) forms a similar hydrogenbonded dimer with its symmetry-equivalent partner, generated by a crystallographic inversion centre. The geometries and conformations of all three molecules are essentially the same. The P atoms have tetrahedral geometry. The P-O single bond in (I) is substantially longer [mean 1.616 (2) Å ] than in diphenylphosphinic acid Ph 2 P( O)OH [1.550 (1) Å ; Lyssenko et al., 2002] or in Ph 2 P( O)OBu-t [1.569 (3) Å ; Grice et al., 2004], but comparable to the values in Ph 2 P( O)ONEt 2 [1.599 (1) Å ; Spek & Veldman, 1999] or Ph 2 P( O)ON C(Cl)Pr-i [1.613 (3) Å ; Martynov et al., 1988]. It is noteworthy that the difference between the P O and the P-OR bond lengths is increased from 0.048 (1) Å in Ph 2 P( O)OH and 0.093 (4) Å in Ph 2 P( O)OBu-t to 0.136 (2) Å in (I), 0.128 (1) Å in Ph 2 P( O)ONEt 2 and 0.151 (4) Å in Ph 2 P( O)ON C(Cl)Pr-i. Thus. we may conclude that bonding to an N atom reduces the additionalcomponent of the (formally) single P-O bond. The P-C(Ph) distances in (I) [mean 1.786 (2) Å ] are as expected.

Crystal data
The amino H atoms were located in difference maps and their positions and U iso values were freely refined. The phenyl H atoms were treated as riding on their C atoms with C-H = 0.95 Å and U iso (H) = 1.2U eq (C). The methyl groups were refined as rigid bodies (C-H = 0.98 Å ) allowed to rotate around their linking C-C bonds, with a common refined U iso for the three H atoms.
We thank both the EPSRC and GlaxoSmithKline Pharmaceuticals for a CASE award (to AJB).

Data collection
Bruker SMART CCD 6K diffractometer Radiation source: fine-focus sealed tube Graphite monochromator Detector resolution: 8 pixels mm -1 ω scans 11843 measured reflections 11796 independent reflections 9155 reflections with I > 2σ(I) R int = 0.040 θ max = 30.0°, θ min = 1.5°h Special details Experimental. The data collection nominally covered a hemisphere of reciprocal Space, by 1 run of ω scans each set at different φ and/or 2θ angles and each scan (10 s exposure) covering 0.3° in ω. Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement.