supplementary materials

For many main group elements as well as transition and rare earth metals, preferred coordination numbers in coordination compounds are apparent. While coordination numbers of 4, 6 and 8 have been found to be dominant in most cases and, as a consequence, vast structural information has been collected for such compounds in solution and in the solid state, information about other coordination numbers is comparatively limited. Especially for smaller coordination numbers the literature is scant or hitherto completely unknown for many elements. One reason for this certainly is that sometimes challenging synthesis procedures have to be followed and, thus, a general but simple synthetic protocol is desireable. Since such compounds may act as versatile and potent catalysts in many industrial processes and might even show interesting pharmacological properties, we were interested in developing an easy-access-route for their synthesis. Applying bulky ligands might open up a pathway in this aspect. In order to be able to compare metrical parameters in envisioned reaction products, we determined the crystal structure of the title compound. The latter one has already been reported earlier (Cameron et al. (1979)), however, no hydrogen atoms were included in the refinement thus ruling out the possibility to assess the role of C–H···X contacts.

The length of the N–P bonds deviate by 0.05 Å with the – formal – P–N-double bond found at around 1.55 Å. The P–N–P angle was measured at more than 146 °. The marked widening of this angle in comparison to the value expected for a sp²-hybridized nitrogen atom can be explained by the repulsive interaction of the phenyl-moieties on both P atoms. The phenyl groups on each phosphorus atom are approximately orientated perpendicular to each other. The least-squares planes defined by their carbon atoms intersect at an angle of 82.19 (6) ° in case of the P(O)Ph₂-moiety and at angles of 79.82 (5) °, 80.91 (6) ° and 83.28 (6) °, respectively, in case of the PPh₃-moiety. Due to the formation of an intramolecular C–H···O contact (see below), the least-squares plane defined by the P(O)–N–P motif encloses an angle of only 29.40 (9) ° with one of the aromatic carbocycles on the PPh₃-moiety (Fig. 1). For the same reason, both phenyl groups of the P(O)Ph₂-moiety adopt a slightly ecliptic conformation with respect to the P(O) motif, the respective dihedral angles were found at about 19 ° and 26 °.

In the crystal structure, intermolecular C–H···O contacts are present whose range falls by more than 0.3 Å below the sum of van-der-Waals radii of the atoms participating. These can be observed between one of the H atoms in meta-position of a phenyl group on the PPh₃-moiety and the O atom of the P(O)Ph₂-moiety and connect the molecules to infinte chains along [0 1 1] (Fig. 2). Furthermore, intramolecular C–H···O contacts invariably involving hydrogen atoms in ortho-position on one of the phenyl groups of the PPh₃-moiety as well as both phenyl groups of the P(O)Ph₂-moiety are present. However, the latter two ones are not very pronounced. Additionally, a set of C–H···π contacts are evident involving H atoms and aromatic systems both on the PPh₃-moiety as well as the P(O)Ph₂-moiety. Their details are listed in Table 1 (with C_g(1) = C41···C46, C_g(2) = C31···C36 and C_g(3) = C11···C16). In total, the C–H···O contacts as well as the C–H···π contacts connect the molecules to a three dimensional network. In terms of graph-set analysis (Etter et al. (1990); Bernstein et al. (1995)), the intermolecular C–H···O contacts can be assigned a C¹₁(8) descriptor on the unitary level while the intramolecular C–H···O contact involving the phenyl group of the PPh₃-moiety necessitates a S¹₁(7) descriptor. For the other two intramolecular C–H···O contacts, a S¹₁(5) each is feasible. An analysis of C_g···C_g interactions shows the closest distance between two centers of gravity to occur between a phenyl group on the PPh₃-moiety and a phenyl group on the P(O)Ph₂-moiety. The distance was measured at 3.6012 (11) Å.

The packing of the title compound in the crystal structure is shown in Figure 3.