Abstract
Colourless blocks of 1,3-di-tert-butyl-2-chloro-1,3,2-di-aza-phospho-rinane, C11H24ClN2P (1), were obtained by sublimation in vacuo slightly above room temperature. The asymmetric unit of the monoclinic crystal structure of the six-membered N-heterocyclic compound is defined by one mol-ecule in a general position. The six-membered ring of the mol-ecule adopts a cyclo-hexane-like chair conformation; the chair at one side is to some extent flattened as a result of the approximately trigonal-planar coordination of both nitro-gen atoms. In detail, this modified chair conformation is characterized by an angle of 53.07 (15)° between the plane defined by the three carbon atoms and the best plane of the two nitro-gen atoms and the two carbon atoms bound to them, and an angle of 27.96 (7)° between the latter plane and the plane defined by the nitro-gen and phospho-rus atoms. The tert-butyl groups are oriented equatorially and the chloro substituent is oriented axially. The P-Cl bond length of 2.2869 (6) Å is substanti-ally longer than the P-Cl single-bond length in PCl3 [2.034 Å; Galy & Enjalbert (1982 ▸). J. Solid State Chem. 44, 1-23]. Inspection of the inter-molecular distances gives no evidence for inter-actions stronger than van der Waals forces. The closest contact is between the Cl atom and a methyl-ene group of a neighbouring mol-ecule with a Cl⋯C distance of 3.7134 (18) Å, excluding a significant influence on the P-Cl bonding.
Highlights
Colourless blocks of 1,3-di-tert-butyl-2-chloro-1,3,2-diazaphosphorinane, C11H24ClN2P (1), were obtained by sublimation in vacuo slightly above room temperature
The six-membered ring of the molecule adopts a cyclohexane-like chair conformation; the chair at one side is to some extent flattened as a result of the approximately trigonal–planar coordination of both nitrogen atoms
This modified chair conformation is characterized by an angle of 53.07 (15) between the plane defined by the three carbon atoms and the best plane of the two nitrogen atoms and the two carbon atoms bound to them, and an angle of 27.96 (7) between the latter plane and the plane defined by the nitrogen and phosphorus atoms
Summary
Over the past two decades, P-chlorofunctionalized N-heterocyclic phosphanes (NHPCls) received considerable attention, mainly as precursors of N-heterocyclic phosphenium ions (NHPs) that are valence isoelectronic compounds of the wellknown N-heterocyclic carbenes (NHCs) (Papke et al, 2017), and as educts of tetrakis(amino)diphosphanes (e.g. Bezombes et al, 2004; Blum et al, 2016; Edge et al, 2009; Frank et al, 1996), some of which reversibly dissociate to stable phosphinyl radicals (‘jack-in-the-box dipnictines’; Hinchley et al, 2001), and as starting materials in the synthesis of mixed-valent tetrakis(amino)tetraphosphetes (Breuers et al, 2015; Frank et al, 1996). Temperature-dependent dynamical NMR investigations showed that in solution these substances are not subject to a fast conformation change, like the ring-inversion process of cyclohexane, and that in the predominant conformation the chloro substituent is expected to be in the axial position and the residues on the nitrogen atoms are oriented ‘diequatorial’ This gives rise to a quite complex 1H-NMR spectrum with an AA0KK0QTX pattern (X = P, AA0KK0 = C4 and C6 protons, Q and T = C5 protons; Hutchins et al, 1972). The number and position of the signals in the 1H-NMR spectrum are dependent on concentration, which was attributed to intermolecular chlorine-exchange mechanisms Even though this parent class of six-membered NHPCls has been known for quite some time, no crystal structure analysis has far been reported. It should be noted that the crystal structure determination described here confirms the suggestions of Hutchins et al (1972) concerning the structure of 2-chloro1,3,2-diazaphophorinanes, derived by NMR spectroscopy
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