2- tert -Butoxy-1-phenyl-1-(2,2,6,6-tetramethyl-piperidin-1-yloxy)ethane

The title compound, C21H35NO2, contains a piperidine ring in a chair conformation, with a pyramidal N atom and a single (exocyclic) N—O bond in an equatorial orientation.

The title compound, C 21 H 35 NO 2 , contains a piperidine ring in a chair conformation, with a pyramidal N atom and a single (exocyclic) N-O bond in an equatorial orientation.

Comment
Nitroxide-mediated polymerization (NMP) has emerged in recent years as a successful controlled or 'living' radical polymerization technique which can be used to prepare polymers of target molecular weight, narrow polydispersity and complex architecture (block and graft copolymers, star polymers, etc.) (Matyjaszewski, 2003). Successful NMP requires the use of a monomolecular initiator, identified as an alkoxyamine, which is derived from a nitroxide. This alkoxyamine should be prepared separately and then added in a known concentration to the monomer to be polymerized. Synthetic routes to alkoxyamines include the trapping of alkyl radicals by free nitroxides at moderate temperatures (Braslau et al., 1997;Miura et al., 1998) and a catalytic route involving Mn-salen complexes [H 2 salen is bis(salicylidene)ethylenediamine; Dao et al., 1998]. The title compound, (I), has been synthesized in the course of these studies (Cameron et al., 2000).
The molecular structure of (I) (Fig. 1) is similar in its main features to the other N-oxy-2,2,6,6-tetramethylpiperidinyl derivatives reported by Ermert & Vasella (1993), Jahn et al. (2001Jahn et al. ( , 2002 and Leitich et al. (2002). The piperidine ring adopts a chair conformation with the N-O1 bond in an equatorial orientation. The N-O1 distance is typical for a single bond (Allen et al., 1987), while the N atom has pyramidal geometry, corresponding to sp 3 hybridization.

Experimental
A solution of 2,2,6,6-tetramethylpiperidinyloxy (TEMPO; 0.187 g, 1.20 mmol) and di-tert-butylperoxalate (0.148 g, 0.63 mmol) in styrene (5 ml) was prepared. The mixture was degassed by three freeze/pump/thaw cycles and backflushed with argon after the final cycle. The resulting solution was sealed, then heated overnight at 313 K. After cooling, the solution was dried in vacuo to constant mass. The crude solid product obtained was then purified by flash chromatography on silica gel, eluting with a mixture of 40-60 petroleum ether/ethyl acetate (90:10 v/v). After removal of the solvent, a white crystalline solid was obtained in 79% yield. The characterization data of the isolated product were in agreement with those given in the literature (Bon et al., 1999 Table 1 Selected geometric parameters (Å , ).

Figure 1
The molecular structure of (I), showing atomic displacement ellipsoids at the 50% probability level.

Special details
Experimental. The data collection nominally covered full sphere of reciprocal space, by a combination of 4 sets of ω scans; each set at different φ and/or 2θ angles and each scan (20 sec exposure) covering 0.3° in ω. Crystal to detector distance 4.85 cm. Crystals are shattering when cut, therefore a crystal larger than the beam diameter was used and the intensities were corrected by SADABS program (actual absorption is negligible).

sup-2
Acta Cryst. (2005). E61, o716-o717 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.