research communications
of 4-methyl-2,6,7-trioxa-1-phosphabicyclo[2.2.2]octane
aChemistry Department, Taibah University, PO Box 30002, Code 14177, Al-Madinah Al-Munawarah, Kingdom of Saudi Arabia, and bSchool of Chemistry, University of East Anglia, Norwich, NR4 7TJ, UK
*Correspondence e-mail: musa_said04@yahoo.co.uk, d.l.hughes@uea.ac.uk
The title molecule, C5H9O3P, has a bicyclo[2.2.2] structure with the P atom at the prow and the bridge-head C atom, with the bonded methyl group, at the stern. The three six-membered rings in the bicyclo[2.2.2] structure have essentially identical good boat conformations.
CCDC reference: 1486648
1. Chemical context
Phosphorus-based ligands bind strongly to transition metals and these complexes offer a wide range of properties due to the high volume of accessible substituents (Downing & Smith, 2004; Tolman, 1977; Joslin et al., 2012). Complexation experiments with these ligands can yield mono- or bi-nuclear complexes (van den Beuken et al., 1997). Phosphorus-based complexes are an important class of compounds in and coordination chemistry (Downing & Smith, 2004; Kühl, 2005). In particular, we have noted interesting studies comparing the donor ability of bicyclic phosphites and the related acyclic phosphites; the phosphorus atom in the former shows more positive charge than in the acyclic phosphites and, hence, the donor ability of bicyclic phosphites is lower than that of the related acyclic phosphites (Vande Griend et al., 1977; Joslin et al., 2012). The present work is a continuation of an investigation into the synthesis and study of bi- and tri-cyclic, penta- and hexa-coordinated phosphoranes to form anionic, neutral and (Said et al. 1996; Timosheva, et al. 2006; Kumara Swamy & Satish Kumar, 2006). In this paper, we report the synthesis, clean isolation and of 4-methyl-2,6,7-trioxa-1-phosphabicyclo[2.2.2]octane (Tolman, 1977; Joslin et al., 2012).
2. Structural commentary
The molecular structure of the title compound, Fig. 1, shows a bicyclo[2.2.2] structure with the phosphorus atom as one bridge-head atom and C3, with the bonded methyl group, as the other. The three six-membered rings in the bicyclo[2.2.2] structure have essentially identical, good boat conformations. The P—O bond lengths are very similar, lying in the range 1.613 (2)–1.616 (2) Å; the O—P—O angles at the prow have angles in the range 100.17 (9)–101.34 (10)°, whereas the C—P—C angles at the stern lie in the range 107.99 (17)–109.08 (18)°.
A comparison between acyclic and bicyclic phosphites based on the `hinge' effect has shown (Vande Griend et al., 1977; Joslin et al., 2012) that the O—P—O and P—O—C angles, a and b in Scheme 1, change upon ligation with a metal. Due to the steric profile of the bicyclic phosphite, the changes here in a, a′ and b, b′ upon metal ligation are less than in acyclic phosphites. Verkade had pointed out earlier that the p-orbital overlap between P and O in bicyclic phosphites is less than in acyclic phosphites, making P more positive and therefore reducing the basicity of P relative to that in acyclic phosphites (Vande Griend et al., 1977); hence, the coordination ability of acyclic phosphites is higher than that of bicyclic phosphites (Verkade, 1972). A variety of multi-cyclic phosphorus compounds including their coordination to various metals has been studied. Based on the trends found in basicity, it is expected that the title compound would show a donating ability to metal centres very similar to that of the more commonly studied bicyclic phosphite P(OCH2)3CEt (Verkade, 1972). The average of O—P—O bond angle (a, Scheme 1) in our study is 100.7o, whereas the average O—P—O bond angle in coordinated phosphites (a′, Scheme 1) is larger, e.g. in Ru{P(OCH2)3CEt}Cl2, it is 102.5o (Joslin et al., 2012), the same as in [Rh2I2(C6H5N2O2)2(COMe)2{P(OCH2)3CMe}2] (Venter et al., 2009); this suggests a slightly larger Tolman angle (Tolman et al., 1977) after metal ligation. In another study, the enhanced π-accepting ability of the bicyclic phosphite ligand compared to the PPh3 and other phosphine ligands was demonstrated clearly in the shorter M—P bond distances in the bicyclic phosphite complexes (Erasmus et al., 1998).
3. Supramolecular features
Contacts between molecules are at normal van der Waals distances, the shortest of which is H4B⋯O6′, at 2.58 Å (Table 1). The nearest neighbours of the phosphorus atom are hydrogen atoms at distances of at least 3.09 Å. A view of the packing along the b axis is shown in Fig. 2.
4. Database survey
From a selection of et al., 2016), we note that the P—O bond distances:
results for bicyclic phosphites from the Cambridge Structural Database (Groom1) are shortest in phosphonium ions, as in [Ph3C{P(OCH2)3CMe}]+ (Fang et al., 2000), at ca 1.552 Å,
2) in the phosphates, as O=P(OCH2)3CR, (e.g. Nimrod et al., 1968; Santarsiero, 1992) are ca 1.57 Å,
3) in the metal-coordinated phosphites, M–{P(OCH2)3CR} (e.g. Aroney et al., 1994; Venter et al., 2009; Davis & Verkade, 1990; Predvoditelev et al., 2009; Basson et al., 1992; Erasmus et al., 1998; Joslin et al., 2012; Albright et al., 1977) are ca 1.59 Å, and
4) in our results, correlate with those of other unsubstituted phosphites, (e.g. Wojczykowski & Jutzi, 2006; Milbrath et al., 1976; Predvoditelev et al., 2009) with P—O bond lengths of ca 1.62 Å.
Within each group, there is very little variation in the P—O distances. The bond angles in the bicyclic structure are quite constrained, but we do note a trend, down the four groups of increasing P—O distances, of a corresponding decrease in O—P—O angles from ca 107 to 100°.
5. Synthesis and crystallization
To 4.26 g (35.46 mmol) of 2-(hydroxymethyl)-2-methylpropane-1,3-diol in 70 mL of dry benzene at RT was added 4.26 g (106.38 mmoles in mineral oil 60%) of NaH in small portions over a period of 20 minutes. The mixture was stirred for 3h before 4.87 g (35.46 mmol) of PCl3 were added dropwise over a period of 20 mins in benzene (10 mL) using a dropping funnel. The reaction mixture was stirred overnight before NaCl was removed by filtration under nitrogen cover. Benzene was removed completely under low pressure. 5 mL of diethyl ether was added, followed by 3 mL of n-hexane. The mixture was placed in deep freeze to afford the title compound as a white solid (yield 4.52 g, 86%; m.p. 369–373 K). The product was purified further by at 393 K/0.5 mm to yield crystals. 1H NMR (CDCl3, 400 MHz): 0.73 (s, 3H, CH3), 3.94 (s, 6H, CH2). 13C NMR (CDCl3, 400 MHz): 16.60 (s, 1C, CH3), 31.98 [d, 1C, C(CH3)3], 71.80 (s, 3C, CH2). 31P NMR (CDCl3, 400 MHz): 91.45 p.p.m. IR cm−1: 2950, 1380. Elemental analysis: calculated: C, 40.55; H, 6.13; found: C, 40.83; H, 6.19.
6. Refinement
Crystal data, data collection and structure .
details are summarized in Table 2The H atoms were included in idealized positions and treated as riding atoms: C—H = 0.93– 0.97 Å with Uiso(H) = 1.5Ueq(C) for methyl H atoms and = 1.2Ueq(C) for methylene H atoms.
Supporting information
CCDC reference: 1486648
https://doi.org/10.1107/S2056989016009993/lh5816sup1.cif
contains datablock I. DOI:Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2056989016009993/lh5816Isup2.hkl
Supporting information file. DOI: https://doi.org/10.1107/S2056989016009993/lh5816Isup3.cdx
Supporting information file. DOI: https://doi.org/10.1107/S2056989016009993/lh5816Isup4.cml
Data collection: CrysAlis PRO (Agilent, 2013); cell
CrysAlis PRO (Agilent, 2013); data reduction: CrysAlis PRO (Agilent, 2013); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015); molecular graphics: ORTEPIII (Johnson, 1976) and ORTEP-3 for Windows (Farrugia, 2012); software used to prepare material for publication: SHELXL2014 (Sheldrick, 2015) and WinGX (Farrugia, 2012).C5H9O3P | Dx = 1.443 Mg m−3 |
Mr = 148.09 | Mo Kα radiation, λ = 0.71073 Å |
Orthorhombic, Pna21 | Cell parameters from 2685 reflections |
a = 10.4408 (6) Å | θ = 3.3–32.3° |
b = 6.2129 (5) Å | µ = 0.34 mm−1 |
c = 10.5052 (5) Å | T = 140 K |
V = 681.45 (7) Å3 | Prism, colourless |
Z = 4 | 0.65 × 0.17 × 0.07 mm |
F(000) = 312 |
Oxford Diffraction Xcalibur 3/Sapphire3 CCD diffractometer | 1561 independent reflections |
Radiation source: Enhance (Mo) X-ray Source | 1405 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.043 |
Detector resolution: 16.0050 pixels mm-1 | θmax = 27.5°, θmin = 3.8° |
Thin slice φ and ω scans | h = −13→13 |
Absorption correction: multi-scan (CrysAlis PRO; Agilent, 2013) | k = −8→8 |
Tmin = 0.684, Tmax = 1.000 | l = −13→13 |
10309 measured reflections |
Refinement on F2 | Secondary atom site location: difference Fourier map |
Least-squares matrix: full | Hydrogen site location: inferred from neighbouring sites |
R[F2 > 2σ(F2)] = 0.033 | H-atom parameters constrained |
wR(F2) = 0.084 | w = 1/[σ2(Fo2) + (0.0459P)2 + 0.0252P] where P = (Fo2 + 2Fc2)/3 |
S = 1.11 | (Δ/σ)max < 0.001 |
1561 reflections | Δρmax = 0.24 e Å−3 |
82 parameters | Δρmin = −0.12 e Å−3 |
1 restraint | Absolute structure: Flack x determined using 605 quotients [(I+)-(I-)]/[(I+)+(I-)] (Parsons et al., 2013) |
Primary atom site location: structure-invariant direct methods | Absolute structure parameter: 0.07 (6) |
Experimental. CrysAlisPro, Agilent Technologies, Version 1.171.36.21 Empirical absorption correction using spherical harmonics, implemented in SCALE3 ABSPACK scaling algorithm. |
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes. |
x | y | z | Uiso*/Ueq | ||
P1 | 0.87893 (7) | 0.45449 (13) | 0.75670 (8) | 0.0380 (2) | |
O1 | 0.9057 (2) | 0.5737 (4) | 0.6228 (3) | 0.0470 (6) | |
C2 | 0.8029 (3) | 0.5722 (6) | 0.5302 (3) | 0.0373 (7) | |
H2A | 0.8308 | 0.4974 | 0.4541 | 0.045* | |
H2B | 0.7816 | 0.7189 | 0.5068 | 0.045* | |
C3 | 0.6847 (2) | 0.4614 (5) | 0.5841 (2) | 0.0253 (5) | |
C4 | 0.7208 (3) | 0.2300 (4) | 0.6164 (3) | 0.0349 (6) | |
H4A | 0.6473 | 0.1566 | 0.6524 | 0.042* | |
H4B | 0.7456 | 0.1549 | 0.5393 | 0.042* | |
O5 | 0.8263 (2) | 0.2254 (4) | 0.7070 (2) | 0.0399 (5) | |
O6 | 0.7460 (2) | 0.5660 (4) | 0.7998 (2) | 0.0457 (7) | |
C7 | 0.6445 (3) | 0.5749 (6) | 0.7058 (3) | 0.0371 (7) | |
H7A | 0.6242 | 0.7240 | 0.6871 | 0.045* | |
H7B | 0.5681 | 0.5070 | 0.7397 | 0.045* | |
C8 | 0.5752 (3) | 0.4642 (6) | 0.4878 (3) | 0.0370 (7) | |
H8A | 0.6017 | 0.3921 | 0.4113 | 0.055* | |
H8B | 0.5021 | 0.3919 | 0.5231 | 0.055* | |
H8C | 0.5530 | 0.6105 | 0.4683 | 0.055* |
U11 | U22 | U33 | U12 | U13 | U23 | |
P1 | 0.0322 (4) | 0.0504 (4) | 0.0314 (4) | 0.0023 (3) | −0.0076 (4) | −0.0037 (5) |
O1 | 0.0297 (11) | 0.0630 (15) | 0.0483 (14) | −0.0148 (10) | −0.0050 (10) | 0.0112 (12) |
C2 | 0.0313 (15) | 0.047 (2) | 0.0340 (16) | −0.0046 (13) | −0.0002 (13) | 0.0088 (13) |
C3 | 0.0232 (12) | 0.0319 (13) | 0.0209 (13) | −0.0003 (11) | −0.0002 (10) | −0.0004 (11) |
C4 | 0.0391 (16) | 0.0332 (15) | 0.0323 (14) | 0.0001 (13) | −0.0036 (12) | −0.0026 (13) |
O5 | 0.0448 (12) | 0.0399 (12) | 0.0350 (11) | 0.0094 (10) | −0.0096 (9) | 0.0025 (9) |
O6 | 0.0455 (13) | 0.0625 (17) | 0.0292 (11) | 0.0128 (11) | −0.0079 (9) | −0.0209 (10) |
C7 | 0.0295 (16) | 0.0508 (18) | 0.0310 (14) | 0.0082 (13) | −0.0008 (12) | −0.0080 (13) |
C8 | 0.0305 (16) | 0.053 (2) | 0.0274 (15) | −0.0001 (14) | −0.0049 (12) | 0.0014 (13) |
P1—O5 | 1.613 (2) | C4—O5 | 1.456 (4) |
P1—O1 | 1.614 (3) | C4—H4A | 0.9700 |
P1—O6 | 1.616 (2) | C4—H4B | 0.9700 |
O1—C2 | 1.449 (4) | O6—C7 | 1.450 (4) |
C2—C3 | 1.522 (4) | C7—H7A | 0.9700 |
C2—H2A | 0.9700 | C7—H7B | 0.9700 |
C2—H2B | 0.9700 | C8—H8A | 0.9600 |
C3—C7 | 1.519 (4) | C8—H8B | 0.9600 |
C3—C4 | 1.524 (4) | C8—H8C | 0.9600 |
C3—C8 | 1.527 (4) | ||
O5—P1—O1 | 100.46 (13) | C3—C4—H4A | 109.5 |
O5—P1—O6 | 100.17 (13) | O5—C4—H4B | 109.5 |
O1—P1—O6 | 101.34 (14) | C3—C4—H4B | 109.5 |
C2—O1—P1 | 117.00 (18) | H4A—C4—H4B | 108.1 |
O1—C2—C3 | 110.7 (2) | C4—O5—P1 | 116.88 (18) |
O1—C2—H2A | 109.5 | C7—O6—P1 | 116.95 (18) |
C3—C2—H2A | 109.5 | O6—C7—C3 | 110.7 (2) |
O1—C2—H2B | 109.5 | O6—C7—H7A | 109.5 |
C3—C2—H2B | 109.5 | C3—C7—H7A | 109.5 |
H2A—C2—H2B | 108.1 | O6—C7—H7B | 109.5 |
C7—C3—C2 | 109.1 (3) | C3—C7—H7B | 109.5 |
C7—C3—C4 | 108.6 (2) | H7A—C7—H7B | 108.1 |
C2—C3—C4 | 108.0 (2) | C3—C8—H8A | 109.5 |
C7—C3—C8 | 110.2 (2) | C3—C8—H8B | 109.5 |
C2—C3—C8 | 110.8 (2) | H8A—C8—H8B | 109.5 |
C4—C3—C8 | 110.1 (2) | C3—C8—H8C | 109.5 |
O5—C4—C3 | 110.5 (2) | H8A—C8—H8C | 109.5 |
O5—C4—H4A | 109.5 | H8B—C8—H8C | 109.5 |
O5—P1—O1—C2 | 50.4 (3) | C3—C4—O5—P1 | 1.8 (3) |
O6—P1—O1—C2 | −52.3 (3) | O1—P1—O5—C4 | −52.8 (2) |
P1—O1—C2—C3 | 2.4 (4) | O6—P1—O5—C4 | 50.8 (2) |
O1—C2—C3—C7 | 57.2 (3) | O5—P1—O6—C7 | −54.0 (3) |
O1—C2—C3—C4 | −60.7 (3) | O1—P1—O6—C7 | 49.0 (3) |
O1—C2—C3—C8 | 178.7 (3) | P1—O6—C7—C3 | 3.3 (4) |
C7—C3—C4—O5 | −60.0 (3) | C2—C3—C7—O6 | −60.4 (3) |
C2—C3—C4—O5 | 58.2 (3) | C4—C3—C7—O6 | 57.1 (3) |
C8—C3—C4—O5 | 179.2 (2) | C8—C3—C7—O6 | 177.8 (3) |
D—H···A | D—H | H···A | D···A | D—H···A |
C4—H4B···O6i | 0.97 | 2.58 | 3.495 (4) | 158 |
Symmetry code: (i) −x+3/2, y−1/2, z−1/2. |
Acknowledgements
This work was supported financially by the Research Deanship of Taibah University. BLAlB is thankful to Dr Rawda Okasha for her support and encouragement.
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