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The title compound, C12H9O4P, was prepared by the oxidation of tri-2-furylphosphine. The P=O bond length is 1.478 (2) Å and the C—P bond lengths range from 1.774 (2) to 1.785 (2) Å. The tri-2-furyl-phosphine oxide molecule displays a very distorted confirmation (not propeller-like) due to the large variation in O—P—C—C torsion angles [5.6 (3), 8.5 (3) and 118.0 (3)°]. The crystal structure involves intermolecular C—H...O hydrogen bonds.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S1600536807034125/pk2038sup1.cif
Contains datablocks I, global

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S1600536807034125/pk2038Isup2.hkl
Contains datablock I

CCDC reference: 657776

Key indicators

  • Single-crystal X-ray study
  • T = 290 K
  • Mean [sigma](C-C) = 0.004 Å
  • R factor = 0.034
  • wR factor = 0.099
  • Data-to-parameter ratio = 14.1

checkCIF/PLATON results

No syntax errors found



Alert level B PLAT063_ALERT_3_B Crystal Probably too Large for Beam Size ....... 1.00 mm
Author Response: The collimator that was used was large enough (2 mm) to accommodate the large crystal.

Alert level C PLAT220_ALERT_2_C Large Non-Solvent C Ueq(max)/Ueq(min) ... 2.57 Ratio PLAT242_ALERT_2_C Check Low Ueq as Compared to Neighbors for C1
Alert level G REFLT03_ALERT_4_G Please check that the estimate of the number of Friedel pairs is correct. If it is not, please give the correct count in the _publ_section_exptl_refinement section of the submitted CIF. From the CIF: _diffrn_reflns_theta_max 25.40 From the CIF: _reflns_number_total 2183 Count of symmetry unique reflns 1281 Completeness (_total/calc) 170.41% TEST3: Check Friedels for noncentro structure Estimate of Friedel pairs measured 902 Fraction of Friedel pairs measured 0.704 Are heavy atom types Z>Si present yes
0 ALERT level A = In general: serious problem 1 ALERT level B = Potentially serious problem 2 ALERT level C = Check and explain 1 ALERT level G = General alerts; check 0 ALERT type 1 CIF construction/syntax error, inconsistent or missing data 2 ALERT type 2 Indicator that the structure model may be wrong or deficient 1 ALERT type 3 Indicator that the structure quality may be low 1 ALERT type 4 Improvement, methodology, query or suggestion 0 ALERT type 5 Informative message, check

Comment top

Tertiary phosphines with heterocyclic substituents have attracted a great deal of attention in the design and development of tailor-made ligands for transition-metal coordination (Andersen & Keay, 2001) and important organic reactions (Farina et al., 1988). Although the chemical reactivities of R3P phosphines are by and large determined by steric and electronic factors, these properties are closely inter-related. The increase in steric bulk of the R groups is known to reduce the s-character of the phosphorous lone pair, and makes the ligand more Lewis basic (Andersen & Keay, 2001). With a cone angle of 134°, tri-2-furylphosphine (TFP) has comparable size to that of triphenylphosphine (145°). However, their electronic properties are quite different. TFP is a substantially weaker Lewis base and, therefore a poorer σ-donor than PPh3. It is in fact reported (Allen & Ward, 1980) that the 2-furyl group is the most electron-withdrawing substituent among the tri(hetero)aryl phosphines. As a result, its electronic properties and also its reactivity are expected to be different. It appears that due to its electronic properties, TFP is currently the choice in a wide variety of metal-catalyzed reactions for carbon-carbon and carbon-heteroatom bond formation.

Oxidation of tertiary phosphines to their respective phosphine oxides is well known for PPh3 and related phosphines, and has been accomplished using several techniques including oxidation with H2O2 (Barton et al., 1997) and NO (Lim et al., 2002). An alternative method of synthesis employing oxygen atom transfer routes by metal oxides are also well documented (Mandimutsira et al., 2002). These methods are likely also suitable for tri-2-furylphosphine. A unique reaction reported in the TFP case involved partial oxidation of the ligand while attempted coordination to a Hg(II) center. A mixed ligand/ligand oxide complex of Hg(II) was characterized crystallographically (Bachechi et al., 2005), although the sole oxidized ligand has not been reported. Our initial unexpected synthesis of the title compound (I) was carried out while attempting to coordinate TFP to a Au(I) center in THF solvent. A rational synthesis has since been discovered (See Experimental section for details). Fig. 1 illustrates the molecular structure of (I) along with the atom numbering scheme. The four closest intermolecular interactions are shown in the hydrogen bonding table. All of these interactions are at ranges that are slightly longer than the sum of the atoms van der Waals radii, and are therefore not relatively strong interactions. Not surprisingly, the majority (three) of these interactions are to the oxide moiety.

Related literature top

Oxidation of tertiary phosphines, such as PPh3, to their respective phosphine oxides has been accomplished following several techniques. Oxidation by either H2O2 (Barton et al., 1997) or NO (Lim et al., 2002) has been reported. An alternative method of using oxygen-atom transfer by metal oxides is another of the well established routes (Mandimutsira et al., 2002). These methods are also likely to be suitable for tri-2-furylphosphine (TFP). A unique reaction reported in the TFP case is the partial oxidation of the ligand while attempted coordination to a HgII center. A mixed ligand/ligand oxide complex of HgII was characterized crystallographically (Bachechi et al., 2005), although the crystal structure of the uncomplexed, oxidized ligand has not been reported.

For related literature, see: Allen & Ward (1980); Andersen & Keay (2001); Farina et al. (1988).

Experimental top

tri-2-furylphosphine (TFP) is commercially available and was used as received from Aldrich. The initial synthesis of the TFP oxide was obtained unexpectedly while attempting to coordinate TFP to a Au(I) center. However, the compound can easily be oxidized using the following procedure. TFP (20 mg, 0.086 mmol) is dissolved in 4 ml THF. After addition of a few drops of H2O2 (30%), the solution is stirred for 3 h. After partial evaporation of the solvent and overnight refrigeration, a solid white product is formed. Recrystallization is attained in a THF/diethyl ether (2:1) solution.

The product was characterized using several spectroscopic techniques in addition to the X-ray analysis. 31P-NMR in CDCl3 of the tri-2-furylphosphine oxide (R3PO) shows a single band at a significantly down-field position when compared to the unoxidized ligand, 31P-NMR: (CDCl3, δ, p.p.m.): -10.38 (s). 1H-NMR (CDCl3): 6.57 (1H), 7.18 (1H), 7.80 (1H). The unoxidized TFP ligand (R3P) has a 31P-NMR single band at -77.18 p.p.m., and 1H-NMR (CDCl3): 6.42 (1H), 6.81 (1H), 7.67 (1H). Due to the large size of the crystal used for the diffraction experiment, the beam tunnel that was used was large (2 mm i.d.) to ensure that the crystal was completely inside of the X-ray beam during the diffraction experiment.

Refinement top

H atoms were placed in calculated positions and allowed to ride during subsequent refinement, with Uiso(H) = 1.2Ueq(C) and C—H distances of 0.93 Å for all H atoms.

Structure description top

Tertiary phosphines with heterocyclic substituents have attracted a great deal of attention in the design and development of tailor-made ligands for transition-metal coordination (Andersen & Keay, 2001) and important organic reactions (Farina et al., 1988). Although the chemical reactivities of R3P phosphines are by and large determined by steric and electronic factors, these properties are closely inter-related. The increase in steric bulk of the R groups is known to reduce the s-character of the phosphorous lone pair, and makes the ligand more Lewis basic (Andersen & Keay, 2001). With a cone angle of 134°, tri-2-furylphosphine (TFP) has comparable size to that of triphenylphosphine (145°). However, their electronic properties are quite different. TFP is a substantially weaker Lewis base and, therefore a poorer σ-donor than PPh3. It is in fact reported (Allen & Ward, 1980) that the 2-furyl group is the most electron-withdrawing substituent among the tri(hetero)aryl phosphines. As a result, its electronic properties and also its reactivity are expected to be different. It appears that due to its electronic properties, TFP is currently the choice in a wide variety of metal-catalyzed reactions for carbon-carbon and carbon-heteroatom bond formation.

Oxidation of tertiary phosphines to their respective phosphine oxides is well known for PPh3 and related phosphines, and has been accomplished using several techniques including oxidation with H2O2 (Barton et al., 1997) and NO (Lim et al., 2002). An alternative method of synthesis employing oxygen atom transfer routes by metal oxides are also well documented (Mandimutsira et al., 2002). These methods are likely also suitable for tri-2-furylphosphine. A unique reaction reported in the TFP case involved partial oxidation of the ligand while attempted coordination to a Hg(II) center. A mixed ligand/ligand oxide complex of Hg(II) was characterized crystallographically (Bachechi et al., 2005), although the sole oxidized ligand has not been reported. Our initial unexpected synthesis of the title compound (I) was carried out while attempting to coordinate TFP to a Au(I) center in THF solvent. A rational synthesis has since been discovered (See Experimental section for details). Fig. 1 illustrates the molecular structure of (I) along with the atom numbering scheme. The four closest intermolecular interactions are shown in the hydrogen bonding table. All of these interactions are at ranges that are slightly longer than the sum of the atoms van der Waals radii, and are therefore not relatively strong interactions. Not surprisingly, the majority (three) of these interactions are to the oxide moiety.

Oxidation of tertiary phosphines, such as PPh3, to their respective phosphine oxides has been accomplished following several techniques. Oxidation by either H2O2 (Barton et al., 1997) or NO (Lim et al., 2002) has been reported. An alternative method of using oxygen-atom transfer by metal oxides is another of the well established routes (Mandimutsira et al., 2002). These methods are also likely to be suitable for tri-2-furylphosphine (TFP). A unique reaction reported in the TFP case is the partial oxidation of the ligand while attempted coordination to a HgII center. A mixed ligand/ligand oxide complex of HgII was characterized crystallographically (Bachechi et al., 2005), although the crystal structure of the uncomplexed, oxidized ligand has not been reported.

For related literature, see: Allen & Ward (1980); Andersen & Keay (2001); Farina et al. (1988).

Computing details top

Data collection: CAD-4-PC (Enraf–Nonius, 1993); cell refinement: CAD-4-PC; data reduction: XCAD4 (Harms & Wocadlo, 1995); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL (Bruker, 1998); software used to prepare material for publication: publCIF (Westrip, 2007).

Figures top
[Figure 1] Fig. 1. The molecular structure of I, with the atom-numbering scheme included. Displacement ellipsoids for non-hydrogen atoms are drawn at the 50% probability level. Hydrogen atoms are shown as spheres of arbitrary size.
Tri-2-furyl-phosphine oxide top
Crystal data top
C12H9O4PF(000) = 512
Mr = 248.16Dx = 1.384 Mg m3
Orthorhombic, P212121Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2ac 2abCell parameters from 25 reflections
a = 8.0837 (8) Åθ = 8.1–11.8°
b = 10.9362 (17) ŵ = 0.23 mm1
c = 13.4690 (15) ÅT = 290 K
V = 1190.7 (3) Å3Prism, colorless
Z = 41.0 × 0.49 × 0.48 mm
Data collection top
Enraf–Nonius CAD-4
diffractometer
2043 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tubeRint = 0.018
Graphite monochromatorθmax = 25.4°, θmin = 2.4°
θ/2θ scansh = 09
Absorption correction: ψ scan
(North et al., 1968)
k = 013
Tmin = 0.877, Tmax = 0.895l = 1616
2455 measured reflections3 standard reflections every 120 reflections
2183 independent reflections intensity decay: none
Refinement top
Refinement on F2Hydrogen site location: inferred from neighbouring sites
Least-squares matrix: fullH-atom parameters constrained
R[F2 > 2σ(F2)] = 0.035 w = 1/[σ2(Fo2) + (0.0617P)2 + 0.1689P]
where P = (Fo2 + 2Fc2)/3
wR(F2) = 0.099(Δ/σ)max < 0.001
S = 1.07Δρmax = 0.30 e Å3
2183 reflectionsΔρmin = 0.23 e Å3
155 parametersExtinction correction: SHELXL97, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
0 restraintsExtinction coefficient: 0.029 (3)
Primary atom site location: structure-invariant direct methodsAbsolute structure: Flack (1983), 905 Friedel pairs
Secondary atom site location: difference Fourier mapAbsolute structure parameter: 0.01 (6)
Crystal data top
C12H9O4PV = 1190.7 (3) Å3
Mr = 248.16Z = 4
Orthorhombic, P212121Mo Kα radiation
a = 8.0837 (8) ŵ = 0.23 mm1
b = 10.9362 (17) ÅT = 290 K
c = 13.4690 (15) Å1.0 × 0.49 × 0.48 mm
Data collection top
Enraf–Nonius CAD-4
diffractometer
2043 reflections with I > 2σ(I)
Absorption correction: ψ scan
(North et al., 1968)
Rint = 0.018
Tmin = 0.877, Tmax = 0.8953 standard reflections every 120 reflections
2455 measured reflections intensity decay: none
2183 independent reflections
Refinement top
R[F2 > 2σ(F2)] = 0.035H-atom parameters constrained
wR(F2) = 0.099Δρmax = 0.30 e Å3
S = 1.07Δρmin = 0.23 e Å3
2183 reflectionsAbsolute structure: Flack (1983), 905 Friedel pairs
155 parametersAbsolute structure parameter: 0.01 (6)
0 restraints
Special details top

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 > 2σ(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 (Å2) top
xyzUiso*/Ueq
P10.77262 (6)0.09125 (5)0.24066 (4)0.03648 (18)
O10.8209 (4)0.31874 (17)0.15987 (16)0.0788 (7)
O20.7664 (2)0.09724 (15)0.43842 (11)0.0538 (4)
O30.47834 (19)0.20950 (13)0.23857 (15)0.0480 (4)
O40.8335 (2)0.03428 (14)0.22293 (14)0.0529 (4)
C10.8511 (3)0.1956 (2)0.15066 (16)0.0450 (5)
C20.9358 (5)0.1725 (4)0.0685 (2)0.0816 (10)
H2A0.96960.09670.04480.098*
C30.9645 (5)0.2918 (4)0.0236 (2)0.0881 (12)
H3A1.02270.30710.03460.106*
C40.8941 (6)0.3723 (4)0.0795 (3)0.0953 (13)
H4B0.89340.45590.06680.114*
C50.8257 (3)0.1579 (2)0.35641 (15)0.0380 (5)
C60.9141 (4)0.2562 (3)0.3848 (2)0.0573 (7)
H6A0.96640.31290.34400.069*
C70.9106 (4)0.2547 (4)0.4909 (2)0.0714 (9)
H7A0.96230.31040.53280.086*
C80.8210 (4)0.1604 (3)0.51835 (19)0.0647 (7)
H8A0.79820.13980.58390.078*
C90.5522 (2)0.09714 (18)0.23460 (16)0.0371 (5)
C100.4375 (3)0.0104 (2)0.2246 (2)0.0559 (7)
H10A0.45610.07330.22010.067*
C110.2819 (3)0.0700 (2)0.2222 (2)0.0583 (7)
H11A0.17880.03310.21590.070*
C120.3125 (3)0.1888 (2)0.2306 (2)0.0524 (6)
H12A0.23190.24960.23110.063*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
P10.0337 (3)0.0355 (3)0.0402 (3)0.0013 (2)0.0009 (2)0.0019 (2)
O10.1116 (19)0.0550 (12)0.0698 (12)0.0135 (12)0.0208 (13)0.0142 (9)
O20.0612 (10)0.0566 (10)0.0435 (8)0.0071 (9)0.0058 (7)0.0098 (7)
O30.0412 (8)0.0327 (7)0.0702 (11)0.0022 (6)0.0025 (8)0.0087 (7)
O40.0481 (8)0.0417 (9)0.0689 (10)0.0095 (7)0.0009 (8)0.0094 (8)
C10.0406 (12)0.0552 (14)0.0391 (11)0.0060 (11)0.0013 (10)0.0019 (10)
C20.079 (2)0.117 (3)0.0483 (15)0.013 (2)0.0168 (15)0.0023 (17)
C30.079 (2)0.136 (4)0.0498 (17)0.018 (2)0.0137 (16)0.031 (2)
C40.115 (3)0.098 (3)0.073 (2)0.033 (2)0.009 (2)0.037 (2)
C50.0350 (10)0.0426 (11)0.0363 (10)0.0016 (10)0.0022 (8)0.0044 (8)
C60.0588 (15)0.0679 (17)0.0451 (12)0.0230 (14)0.0018 (11)0.0017 (12)
C70.0658 (17)0.103 (2)0.0450 (14)0.0295 (18)0.0008 (12)0.0156 (14)
C80.0609 (16)0.095 (2)0.0382 (12)0.0053 (16)0.0016 (11)0.0041 (13)
C90.0337 (10)0.0327 (10)0.0450 (11)0.0025 (8)0.0009 (8)0.0004 (10)
C100.0428 (12)0.0328 (11)0.092 (2)0.0000 (9)0.0011 (13)0.0022 (12)
C110.0365 (11)0.0480 (13)0.0902 (19)0.0049 (10)0.0032 (12)0.0032 (13)
C120.0354 (11)0.0480 (13)0.0740 (16)0.0070 (9)0.0017 (11)0.0032 (12)
Geometric parameters (Å, º) top
P1—O41.4777 (16)C3—H3A0.9300
P1—C51.774 (2)C4—H4B0.9300
P1—C11.782 (2)C5—C61.346 (3)
P1—C91.7846 (19)C6—C71.429 (4)
O1—C41.366 (4)C6—H6A0.9300
O1—C11.374 (3)C7—C81.313 (4)
O2—C81.353 (3)C7—H7A0.9300
O2—C51.375 (3)C8—H8A0.9300
O3—C121.364 (3)C9—C101.333 (3)
O3—C91.367 (2)C10—C111.417 (3)
C1—C21.326 (4)C10—H10A0.9300
C2—C31.457 (5)C11—C121.328 (3)
C2—H2A0.9300C11—H11A0.9300
C3—C41.291 (6)C12—H12A0.9300
O4—P1—C5116.31 (11)O2—C5—P1115.06 (16)
O4—P1—C1111.51 (11)C5—C6—C7105.3 (2)
C5—P1—C1104.39 (11)C5—C6—H6A127.3
O4—P1—C9111.01 (10)C7—C6—H6A127.3
C5—P1—C9105.48 (10)C8—C7—C6107.6 (3)
C1—P1—C9107.53 (11)C8—C7—H7A126.2
C4—O1—C1105.8 (3)C6—C7—H7A126.2
C8—O2—C5106.20 (19)C7—C8—O2110.9 (2)
C12—O3—C9106.11 (16)C7—C8—H8A124.6
C2—C1—O1110.8 (3)O2—C8—H8A124.6
C2—C1—P1129.0 (3)C10—C9—O3109.83 (18)
O1—C1—P1120.20 (18)C10—C9—P1132.34 (17)
C1—C2—C3104.9 (3)O3—C9—P1117.82 (14)
C1—C2—H2A127.5C9—C10—C11107.1 (2)
C3—C2—H2A127.5C9—C10—H10A126.5
C4—C3—C2107.4 (3)C11—C10—H10A126.5
C4—C3—H3A126.3C12—C11—C10106.4 (2)
C2—C3—H3A126.3C12—C11—H11A126.8
C3—C4—O1111.2 (4)C10—C11—H11A126.8
C3—C4—H4B124.4C11—C12—O3110.6 (2)
O1—C4—H4B124.4C11—C12—H12A124.7
C6—C5—O2110.0 (2)O3—C12—H12A124.7
C6—C5—P1134.91 (18)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
C8—H8A···O4i0.932.443.325 (3)158
C6—H6A···O4ii0.932.493.394 (3)163
C12—H12A···O4iii0.932.503.309 (3)146
C10—H10A···O3iv0.932.503.397 (3)163
Symmetry codes: (i) x+3/2, y, z+1/2; (ii) x+2, y+1/2, z+1/2; (iii) x+1, y+1/2, z+1/2; (iv) x+1, y1/2, z+1/2.

Experimental details

Crystal data
Chemical formulaC12H9O4P
Mr248.16
Crystal system, space groupOrthorhombic, P212121
Temperature (K)290
a, b, c (Å)8.0837 (8), 10.9362 (17), 13.4690 (15)
V3)1190.7 (3)
Z4
Radiation typeMo Kα
µ (mm1)0.23
Crystal size (mm)1.0 × 0.49 × 0.48
Data collection
DiffractometerEnraf–Nonius CAD-4
Absorption correctionψ scan
(North et al., 1968)
Tmin, Tmax0.877, 0.895
No. of measured, independent and
observed [I > 2σ(I)] reflections
2455, 2183, 2043
Rint0.018
(sin θ/λ)max1)0.604
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.035, 0.099, 1.07
No. of reflections2183
No. of parameters155
H-atom treatmentH-atom parameters constrained
Δρmax, Δρmin (e Å3)0.30, 0.23
Absolute structureFlack (1983), 905 Friedel pairs
Absolute structure parameter0.01 (6)

Computer programs: CAD-4-PC (Enraf–Nonius, 1993), CAD-4-PC, XCAD4 (Harms & Wocadlo, 1995), SHELXS97 (Sheldrick, 1997), SHELXL97 (Sheldrick, 1997), SHELXTL (Bruker, 1998), publCIF (Westrip, 2007).

Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
C8—H8A···O4i0.932.443.325 (3)158.2
C6—H6A···O4ii0.932.493.394 (3)162.8
C12—H12A···O4iii0.932.503.309 (3)145.6
C10—H10A···O3iv0.932.503.397 (3)163.0
Symmetry codes: (i) x+3/2, y, z+1/2; (ii) x+2, y+1/2, z+1/2; (iii) x+1, y+1/2, z+1/2; (iv) x+1, y1/2, z+1/2.
 

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