Hexaphenyl­hexa­phosphinane benzene solvate

In the mol­ecular crystal of hexa­phenyl­hexa­phosphinane benzene solvate, C₃₆H₃₀P₆·C₆H₆, representing the trigonal form of phospho­benzene as a solvate, the six-membered ring of P atoms adopts a chair conformation wherein the six phenyl groups are located in equatorial positions. The mol­ecules [mol­ecular symmetry (C_3i)] are stacked infinitely along the c-axial direction.

S1. Comment

Oligophosphines (Baudler & Glinka, 1994), such as hexaphenylcyclohexaphosphine [-phoshphinane ?] (PPh)₆, provide analogies with cycloalkanes since the CR₂ methylene unit is isolobal with the phosphine (PR) unit. The familiar cationic phosphonium center is also isolobal with this unit and is obtained, for example, through methylation reactions of phosphines (Burford et al., 2005). Catena-phosphorus cations represent a newly developing family of compounds and we are currently establishing a comprehensive series of high yielding and facile methods for the synthesis of prototypical polyphosphonium salts from oligophosphines (Weigand et al., 2007). Recently, we reported the synthesis and crystal structures of cyclohexaphosphorus dications, containing a P₆ homocycle composed of two phosphonium centers (1,4-positions) and four phosphine centers (Weigand et al., 2006). In further investigations, we attempted the synthesis of hexaphenylcyclohexaphosphine [-phoshphinane ?], (PPh)₆, according to a modification of the procedure of Henderson et al. (1963). The (PPh)₆ hexamer exists in at least four crystalline forms (Daly, 1965, 1966; Daly & Maier, 1964, 1966). However, for the title solvate, (I), only the cell dimensions of the hexagonal crystal system were reported, with a = 12.68 and c = 20.96 Å (Daly & Maier, 1964). Therefore, we have reinvestigated the crystal structure of hexaphenylcyclohexaphosphine [-phosphinane ?] benzene solvate, which is, to our knowledge, only the second crystallographic characterization of a solvated cyclooligophosphine [-phosphinane ?] after (2,5-Me₂C₆H₃)₆P₆·CHCl₃ (Schmutzler et al., 1993).

A displacement ellipsoid drawing of (I) is shown in Fig. 1 with the corresponding numbering scheme. The centers of both the (PPh)₆ and the benzene molecules are located on the threefold axis as well as the symmetry center, and thus the ring entities are constructed from a single unique P—Ph fragment for the (PPh)₆ molecule and a unique C-atom position for the solvate. The molecules of the cyclohexamer contain an all-phosphorus ring framework adopting a chair conformation with the phenyl groups located in equatorial positions, as required by the 3 symmetry. X-ray investigation shows that the P—P length of 2.2207 (8) Å does not significantly differ from those reported for the other four crystalline forms, with an average value of 2.237 (3) Å. The average aromatic C—C bond length found in the phenyl ring attached to the P atom is 1.384 (2) Å and the C atoms of the phenyl group do not deviate significantly from a regular hexagon. Similarly to the trigonal form of solvent-free (PPh)₆ (Daly, 1965), a slight deviation of the molecule from 3m (D_3d) symmetry is observed. The P—P—C values differ slightly by 1.62 (5)° from each other, the phenyl ring makes an angle of 7.6 (3)° with the 3 axis of the puckered central ring, and the P atom deviates from the phenyl ring plane by 0.041 (2) Å. Distances and angles for the benzene molecule are also presented in Table 1. Specific interactions between the (PPh)₆ molecules and the benzene molecules are not observed. All intermolecular distances are longer than the sum of the appropriate van der Waals radii.

Fig. 2 presents the packing arrangement of the molecules in the unit cell, depicted along the b and c axes. All hexamers in this structure are positioned with their molecular threefold axes parallel to the c axis. The packing of the cyclopolyphosphine [-phosphinane ?] molecules in (I) corresponds to layers in a hexagonal arrangement. These body-centered packing layers have an ABC sequence seperated by the benzene molecules, which also form layers and are located in the `octahedral holes'. Thus, the benzene is surrounded by six individual (PPh)₆ molecules arranged in a pseudooctahedron. Short van der Waals contacts of less than 4.0 Å are observed between the phenyl groups and the solvate. However, there are no contacts of less than 4.0 Å involving the P atom. Nevertheless, this packing is surprisingly similar to that of the unsolvated trigonal (PPh)₆. The difference lies mainly in a more effective layer stacking of the latter caused by the absence of solvate molecules.

Related literature

For related literature, see: Baudler & Glinka (1994); Burford et al. (2005); Daly (1965, 1966); Daly & Maier (1964, 1966); Henderson et al. (1963); Schmutzler et al. (1993); Weigand et al. (2006, 2007).

S2. Experimental

All manipulations were performed under an inert atmosphere of argon. To a solution of PhPCl₂ (179 mg, 1 mmol) in benzene (6 ml) was added PhP(SiMe₃)₂ (254 mg, 1 mmol) in one portion and the solution stirred for 6 h. From the reaction mixture, very small amounts of colorless blocks were obtained after 2 weeks and crystallographically identified as the title compound, (I). The analytical datum for the ³¹P{¹H} NMR shift (δ = -26.4 p.p.m.) is in agreement with that previously reported (Henderson et al., 1963).

S3. Refinement

H atoms were included in calculated positions with distances fixed at 0.95 Å and isotropic displacement parameters corresponding to 1.2U_eq of the carrier C atom. The data set for (I) was truncated at 2θ = 55° as only statistically insignificant data were present above the limit. The largest residual peaks of electron density (0.479 and -0.183 e ų) were found within 0.83 and 1.02 Å of atoms C1 and P1, respectively.

Computing details

Data collection: SMART (Bruker, 1999); cell refinement: SMART (Bruker, 1999); data reduction: SAINT (Bruker, 2006); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997a); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997a); molecular graphics: DIAMOND (Brandenburg, 2000); software used to prepare material for publication: SHELXTL (Sheldrick, 2000).

Figures

	Fig. 1. A view of the molecular structure of (I), showing the atom-labeling scheme. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radii. [Symmetry codes: (i) x-y, x, -z + 1; (ii) y, -x + y, -z + 1; (iii) x-y + 1/3, x - 1/3, -z + 2/3; (iv) y + 1/3, -x + y+2/3, -z + 2/3].
	Fig. 2. Views along (a) the b axis and (b) the c axis, showing the packing of (I) in its molecular structure. H atoms have been omitted for clarity. Light gray denotes phenyl C atoms, medium gray denotes benzene C atoms and black denotes P atoms.

hexaphenylhexaphosphinane benzene solvate

Crystal data

C36H30P6·C6H6	Dx = 1.281 Mg m^−3
Mr = 726.53	Mo Kα radiation, λ = 0.71073 Å
Hexagonal, R3	Cell parameters from 4176 reflections
Hall symbol: -R 3	θ = 2.7–28.3°
a = 12.533 (5) Å	µ = 0.32 mm^−1
c = 20.763 (6) Å	T = 173 K
V = 2824.4 (18) Å^3	Parallelepiped, colourless
Z = 3	0.45 × 0.40 × 0.15 mm
F(000) = 1134

Data collection

Bruker SMART1000/P4 diffractometer	1426 independent reflections
Radiation source: fine-focus sealed tube, K760	1279 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.048
ϕ and ω scans	θmax = 27.5°, θmin = 2.1°
Absorption correction: multi-scan (SADABS; Sheldrick, 1997b)	h = −16→16
Tmin = 0.871, Tmax = 0.954	k = −15→15
6465 measured reflections	l = −26→24

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.030	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.088	H-atom parameters constrained
S = 1.10	w = 1/[σ^2(Fo^2) + (0.0399P)^2 + 2.4743P] where P = (Fo^2 + 2Fc^2)/3
1426 reflections	(Δ/σ)max = 0.001
73 parameters	Δρmax = 0.48 e Å^−3
0 restraints	Δρmin = −0.18 e Å^−3

Special details

Experimental. Crystal decay was monitored by repeating the initial 50 frames at the end of the data collection and analyzing duplicate reflections.

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 F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
P1	0.03927 (3)	0.17046 (3)	0.526123 (16)	0.02631 (14)
C1	0.07438 (12)	0.31045 (12)	0.48036 (7)	0.0299 (3)
C2	0.11195 (14)	0.41695 (14)	0.51600 (9)	0.0424 (4)
H2	0.1163	0.4142	0.5616	0.051*
C3	0.14316 (17)	0.52714 (15)	0.48576 (12)	0.0568 (5)
H3	0.1693	0.5997	0.5106	0.068*
C4	0.13634 (16)	0.53161 (16)	0.41987 (12)	0.0575 (5)
H4	0.1575	0.6073	0.3992	0.069*
C5	0.09891 (16)	0.42664 (18)	0.38372 (9)	0.0512 (5)
H5	0.0944	0.4302	0.3382	0.061*
C6	0.06778 (15)	0.31565 (15)	0.41362 (8)	0.0403 (4)
H6	0.0420	0.2434	0.3885	0.048*
C7	0.71104 (17)	0.45848 (16)	0.33338 (9)	0.0481 (4)
H7	0.7416	0.5448	0.3335	0.058*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
P1	0.0278 (2)	0.0277 (2)	0.0236 (2)	0.01396 (14)	−0.00032 (11)	−0.00097 (12)
C1	0.0248 (6)	0.0272 (6)	0.0376 (7)	0.0130 (5)	0.0009 (5)	0.0021 (5)
C2	0.0366 (8)	0.0318 (8)	0.0556 (10)	0.0146 (6)	−0.0014 (7)	−0.0048 (7)
C3	0.0464 (10)	0.0284 (8)	0.0901 (16)	0.0147 (7)	−0.0014 (9)	−0.0004 (8)
C4	0.0372 (9)	0.0362 (9)	0.0977 (17)	0.0172 (7)	0.0087 (9)	0.0261 (9)
C5	0.0417 (9)	0.0557 (11)	0.0568 (11)	0.0249 (8)	0.0071 (8)	0.0257 (8)
C6	0.0418 (8)	0.0399 (8)	0.0400 (8)	0.0210 (7)	0.0019 (6)	0.0071 (6)
C7	0.0538 (10)	0.0429 (9)	0.0463 (10)	0.0233 (8)	−0.0008 (7)	0.0003 (7)

Geometric parameters (Å, º)

P1—C1	1.8446 (15)	C4—C5	1.377 (3)
P1—P1^i	2.2207 (8)	C4—H4	0.9500
P1—P1^ii	2.2207 (8)	C5—C6	1.389 (2)
C1—C2	1.386 (2)	C5—H5	0.9500
C1—C6	1.392 (2)	C6—H6	0.9500
C2—C3	1.383 (2)	C7—C7^iii	1.3774 (18)
C2—H2	0.9500	C7—C7^iv	1.3774 (18)
C3—C4	1.374 (3)	C7—H7	0.9500
C3—H3	0.9500
C1—P1—P1^i	97.83 (5)	C3—C4—C5	120.15 (16)
C1—P1—P1^ii	96.21 (5)	C3—C4—H4	119.9
P1^i—P1—P1^ii	98.17 (2)	C5—C4—H4	119.9
C2—C1—C6	119.06 (14)	C4—C5—C6	120.26 (18)
C2—C1—P1	116.46 (12)	C4—C5—H5	119.9
C6—C1—P1	124.47 (11)	C6—C5—H5	119.9
C3—C2—C1	120.62 (18)	C5—C6—C1	119.89 (16)
C3—C2—H2	119.7	C5—C6—H6	120.1
C1—C2—H2	119.7	C1—C6—H6	120.1
C4—C3—C2	120.02 (18)	C7^iii—C7—C7^iv	119.997 (2)
C4—C3—H3	120.0	C7^iii—C7—H7	120.0
C2—C3—H3	120.0	C7^iv—C7—H7	120.0

Symmetry codes: (i) x−y, x, −z+1; (ii) y, −x+y, −z+1; (iii) x−y+1/3, x−1/3, −z+2/3; (iv) y+1/3, −x+y+2/3, −z+2/3.