Synthesis and crystal structures of [Ph3PCH2PPh3]I2 dichloromethane disolvate and [Ph3PCH2PPh3](BI4)2

Reaction of BI3 with carbodiphosphorane, C(PPh3)2, gives a mixture of the dicationic compounds, [Ph3PCH2PPh3]I2·2CH2Cl2 and [Ph3PCH2PPh3](BI4)2. Solvents are the source of the protons at the ylidic C atom.


Figure 2
The molecular structure of compound (II), showing the atom labelling and 40% probability displacement ellipsoids. solvated (Fig. 2). For both compounds, the C2/P1/C1/P2/C20 fragment lies in a plane, as shown in Figs. 1 and 2, respectively, with the P1-C1-P2 angle being 124.1 (2) for (I) and 121.7 (3) for (II); see Tables 1 and 2. Such a conformation avoids any significant steric repulsion between the phenyl groups on the adjacent P atoms. The smaller value in compound (II) is attributed to decreased steric repulsion and/ or an absence of electrostatic repulsion (Walker & Poli, 1989). The P-C bond lengths in compound (I) are slightly shorter than those in compound (II); see Tables 1 and 2. In (II), the BI 4 À anions display regular tetrahedral geometry, with I-B-I angles ranging from 108.1 (3) to 110.9 (3) .

Figure 3
A view along the a axis of the crystal packing of compound (I). Only the H atoms (grey balls) participating in hydrogen bonding (dashed lines) have been included (see Table 3).

Figure 4
A view along the a axis of the crystal packing of compound (II). Only the H atom (grey ball) participating in hydrogen bonding (dashed lines) has been included (see Table 4). Table 3 Hydrogen-bond geometry (Å , ) for (I). reported structures of the dicationic species, which all show similar conformations. In these eight structures, the P-C-P angle varies from ca 120.89 to 123.35 , while the P-C bond lengths vary from ca 1.802 to 1.833 Å . The smallest P-C-P angle and the shortest P-C bond length, ca 120.89 and 1.802 Å , respectively, are observed in methylenebis(triphenylphosphonium) dichloride 1,2-dimethoxyethane monosolvate (CSD refcode CADZUE; Petz et al., 2011). While one of the largest P-C-P angles (ca 123.11 ) and longest P-C bond lengths (ca 1.825 Å ) were observed for methylenebis(triphenylphosphonium) bis(tetrachloroindium) dichloromethane monosolvate (CIYGIB; Petz et al., 2008). Interestingly, in compound (I), the P-C bond lengths are short [1.804 (4) and 1.807 (5) Å ], while the P-C-P angle [124.1 (2) ] is one of the largest observed to date.

Synthesis and crystallization
(Ph 3 ) 2 C (0.1 g, 0.19 mmol) and 1 equivalent of BI 3 were mixed in ca 10 ml of DCM and left to stir overnight under inert conditions. The volume of the resulting solution was reduced to ca 3 ml and layered with ca 5 ml of hexane. A crop of crystals formed in a few days [yield 0.02 g, 4% based on (PPh 3 ) 2 C, for (I) and 0.015 g, 5% based on (PPh 3 ) 2 C, for (II)].

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 5. The H atoms were included in calculated positions and treated as riding atoms, with C-H = 0.95-0.99 Å and U iso (H) = 1.2U eq (C). For both compounds, a small number of reflections were affected by the beam stop and were omitted from the final cycles of refinement.