(2-Fluoro­phenyl­imino)­tri(1-pyrrolyl)­phospho­rane

The P atom of the title compound, C₁₈H₁₆FN₄P, has a slightly distorted tetrahedral geometry. The P-N bond lengths range from 1.671 (3) to 1.680 (3) Å, while the P=N bond is 1.517 (3) Å. The pyrrolyl groups are arranged around the P atom in a chiral propeller-like geometry.

S1. Comment

We have recently reported that iminophosphoranes of the type Cl₃P═NAr (Ar is 2-fluorophenyl) are important main-group examples of well defined carbodiimide metathesis catalysts (Bell et al., 2000). It is believed that these catalysts follow an addition–elimination pathway for double-bond metathesis. We produced pyrrolyl derivatives of the iminophosphoranes in an effort to rule out the possibility of HCl-mediated metathesis pathways that might arise from the decomposition of trichloroiminophosphoranes. Selection of the pyrrolyl moiety as a chloride replacement was prompted by Petersen's discussion of tripyrrolylphosphorus ligands (Moloy & Petersen, 1995). In particular, pyrrolyl is π-acidic, which allows replacement of chlorine without loss of electrophilicity at the phosphorus center, believed to be an important factor in the carbodiimide metatheses.

The structure determination of the title compound, (I), was undertaken to study the effect of substitution on significant features of the phosphorus center. We report herein the first example of a tripyrrolyl derivative of an iminophosphorane. The only previous example of a pyrrolyl derivative is bispyrrolylcyclophosphazene (Craig et al., 1987). A notable aspect of the crystal structure reported here is the short P═N bond length [1.517 (3) Å], which is significantly shorter than in bispyrrolylcyclophosphazene [1.583 (6) Å]. It is important to note that the P═N bond length is similar to chlorine-derivatized hydrocarbyliminophosphoranes ranging from 1.505 (3) (Antipin et al., 1985) to 1.557 (2) Å (Belaj, 1996).

P—N bond length has been correlated with the orbital electronegativity of the phosphorus substituents (Bullen & Tucker, 1972). The comparable P═N bond length of the trichloro- and tripyrrolyliminophosphoranes indicates a similar electronegativity of the phosphorus substituents.

The P atom is slightly distorted from tetrahedral geometry, with the bond angles around it varying from 101.93 (16) to 117.74 (17)°, the average value being 109.1 (2)°. The pyrrolyl groups make interplanar angles of 45.9 (3), 55.0 (3) and 63.4 (2)° with the 2-fluorophenyl ring. The P atom has chirality due to the propeller-like arrangement of the pyrrolyl rings, although no conclusion can be made about the absolute configuration as the Friedel pairs were not collected for this structure.

Related literature

For related literature, see: Antipin et al. (1985); Belaj (1996); Bell et al. (2000); Bullen & Tucker (1972); Craig et al. (1987); Moloy & Petersen (1995).

S2. Experimental

Potassium pyrrolide (0.518 g, 4.93 mmol) was slowly added to a vigorously stirred solution of Cl₃P═NAr (0.405 g, 1.643 mmol) in hexanes (45 ml) at 195 K. The mixture was stirred for 30 min at 195 K and was then warmed to room temperature and stirred for an additional 14 h. Filtration yielded a colorless liquid that was reduced to 15 ml and cooled to 238 K. The precipitate was removed by filtration and the filtrate was again reduced in volume and cooled to yield colorless crystals (yield: 0.231 g, 41.5%). ¹H NMR (300 MHz, d₈-toluene, p.p.m.): δ 6.79 (m, 4H, aryl), 6.67 (m, 6H, pyrrolyl), 6.08 (m, 6H, pyrrolyl); ³¹P NMR (121 MHz, d₈-toluene, p.p.m.): δ -32.4.

S3. Refinement

H atoms were calculated in idealized isotropic positions [C—H = 0.94 Å and U_iso(H) = 1.2U_iso(C)].

Computing details

Data collection: P3 Diffractometer Control Program (Siemens, 1990); cell refinement: P3 Diffractometer Control Program; data reduction: P3 Diffractometer Control Program; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997).

Figures

Fig. 1. The structure of the title compound with 50% probability displacement ellipsoids and the atom-numbering scheme.

(I)

Crystal data

C18H16FN4P	F(000) = 352
Mr = 338.32	Dx = 1.328 Mg m^−3
Monoclinic, P21	Mo Kα radiation, λ = 0.71073 Å
a = 7.6950 (15) Å	Cell parameters from 24 reflections
b = 14.828 (3) Å	θ = 9–13°
c = 8.0060 (16) Å	µ = 0.18 mm^−1
β = 112.11 (3)°	T = 206 K
V = 846.3 (3) Å^3	Plate, colorless
Z = 2	0.40 × 0.30 × 0.05 mm

Data collection

Siemens P3 diffractometer	1343 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.046
Graphite monochromator	θmax = 25.0°, θmin = 2.7°
ω scans	h = −3→9
Absorption correction: ψ scan (North et al., 1968)	k = 0→17
Tmin = 0.932, Tmax = 0.991	l = −9→9
2400 measured reflections	3 standard reflections every 197 reflections
1572 independent reflections	intensity decay: 1%

Refinement

Refinement on F^2	Hydrogen site location: inferred from neighbouring sites
Least-squares matrix: full	H-atom parameters constrained
R[F^2 > 2σ(F^2)] = 0.038	w = 1/[σ^2(Fo^2) + (0.0413P)^2] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.089	(Δ/σ)max = 0.001
S = 1.10	Δρmax = 0.24 e Å^−3
1572 reflections	Δρmin = −0.23 e Å^−3
218 parameters	Extinction correction: SHELXL97, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
1 restraint	Extinction coefficient: 0.011 (3)
Primary atom site location: structure-invariant direct methods	Absolute structure: Flack (1983)
Secondary atom site location: difference Fourier map	Absolute structure parameter: −0.12 (16)

Special details

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	0.80813 (13)	0.52138 (7)	0.32311 (11)	0.0272 (2)
F1	1.1997 (3)	0.5907 (2)	0.5610 (3)	0.0585 (8)
N1	0.8647 (5)	0.6090 (2)	0.2598 (5)	0.0375 (9)
C1	1.0309 (6)	0.6524 (3)	0.2756 (5)	0.0301 (9)
N2	0.6143 (5)	0.4788 (2)	0.1634 (4)	0.0352 (8)
C2	1.1985 (6)	0.6450 (3)	0.4234 (6)	0.0387 (10)
N3	0.9599 (5)	0.4351 (2)	0.3703 (4)	0.0295 (7)
C3	1.3597 (6)	0.6884 (3)	0.4380 (7)	0.0466 (11)
H3A	1.4706	0.6790	0.5393	0.056*
N4	0.7442 (4)	0.5276 (3)	0.5005 (3)	0.0307 (7)
C4	1.3581 (7)	0.7459 (3)	0.3025 (7)	0.0543 (12)
H4A	1.4675	0.7770	0.3107	0.065*
C5	1.1928 (7)	0.7574 (3)	0.1537 (6)	0.0488 (12)
H5A	1.1904	0.7968	0.0608	0.059*
C6	1.0324 (7)	0.7119 (3)	0.1406 (6)	0.0399 (10)
H6A	0.9217	0.7209	0.0390	0.048*
C7	0.5741 (7)	0.3886 (3)	0.1217 (6)	0.0428 (11)
H7A	0.6570	0.3401	0.1687	0.051*
C8	0.3947 (7)	0.3820 (4)	0.0014 (6)	0.0557 (14)
H8A	0.3319	0.3286	−0.0512	0.067*
C9	0.3202 (6)	0.4697 (4)	−0.0300 (6)	0.0562 (14)
H9A	0.1976	0.4850	−0.1072	0.067*
C10	0.4526 (5)	0.5281 (4)	0.0682 (5)	0.0458 (11)
H10A	0.4388	0.5910	0.0722	0.055*
C11	0.9916 (6)	0.3684 (3)	0.5000 (6)	0.0355 (9)
H11A	0.9353	0.3647	0.5856	0.043*
C12	1.1172 (6)	0.3097 (3)	0.4816 (6)	0.0414 (10)
H12A	1.1641	0.2580	0.5523	0.050*
C13	1.1657 (6)	0.3396 (3)	0.3375 (6)	0.0403 (10)
H13A	1.2501	0.3110	0.2949	0.048*
C14	1.0706 (6)	0.4157 (3)	0.2716 (6)	0.0362 (10)
H14A	1.0775	0.4500	0.1755	0.043*
C15	0.8419 (6)	0.5732 (3)	0.6622 (5)	0.0384 (10)
H15A	0.9449	0.6119	0.6841	0.046*
C16	0.7627 (7)	0.5519 (3)	0.7800 (6)	0.0464 (12)
H16A	0.8006	0.5735	0.8988	0.056*
C17	0.6130 (7)	0.4917 (3)	0.6963 (6)	0.0442 (11)
H17A	0.5345	0.4659	0.7492	0.053*
C18	0.6034 (6)	0.4783 (3)	0.5283 (5)	0.0366 (9)
H18A	0.5153	0.4414	0.4421	0.044*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
P1	0.0224 (5)	0.0319 (5)	0.0272 (4)	−0.0011 (5)	0.0093 (4)	0.0009 (5)
F1	0.0392 (15)	0.075 (2)	0.0531 (15)	−0.0035 (15)	0.0085 (12)	0.0259 (15)
N1	0.0308 (19)	0.038 (2)	0.0446 (19)	−0.0005 (17)	0.0156 (16)	0.0107 (16)
C1	0.028 (2)	0.028 (2)	0.036 (2)	0.0041 (18)	0.0139 (18)	0.0031 (16)
N2	0.0286 (17)	0.046 (2)	0.0295 (16)	−0.0033 (17)	0.0095 (14)	−0.0029 (15)
C2	0.036 (2)	0.037 (2)	0.043 (2)	0.000 (2)	0.015 (2)	0.0051 (18)
N3	0.0287 (17)	0.0318 (18)	0.0315 (16)	0.0001 (16)	0.0154 (15)	0.0033 (15)
C3	0.031 (2)	0.038 (2)	0.061 (3)	−0.005 (2)	0.007 (2)	0.001 (2)
N4	0.0316 (16)	0.0325 (17)	0.0294 (14)	−0.0002 (19)	0.0132 (12)	−0.0038 (17)
C4	0.041 (3)	0.044 (3)	0.084 (3)	−0.007 (2)	0.030 (3)	0.003 (3)
C5	0.052 (3)	0.040 (3)	0.064 (3)	0.001 (2)	0.032 (3)	0.016 (2)
C6	0.044 (2)	0.033 (2)	0.049 (2)	0.006 (2)	0.024 (2)	0.0068 (19)
C7	0.044 (3)	0.048 (3)	0.042 (2)	−0.017 (2)	0.021 (2)	−0.009 (2)
C8	0.049 (3)	0.077 (4)	0.043 (3)	−0.031 (3)	0.020 (2)	−0.021 (3)
C9	0.023 (2)	0.100 (4)	0.040 (2)	−0.007 (3)	0.0056 (19)	−0.006 (3)
C10	0.031 (2)	0.066 (3)	0.039 (2)	0.008 (3)	0.0103 (17)	−0.002 (3)
C11	0.036 (2)	0.037 (2)	0.0367 (19)	0.002 (2)	0.0167 (17)	0.0072 (18)
C12	0.036 (2)	0.032 (2)	0.054 (3)	0.004 (2)	0.015 (2)	0.007 (2)
C13	0.032 (2)	0.037 (2)	0.056 (3)	0.000 (2)	0.021 (2)	−0.009 (2)
C14	0.035 (2)	0.041 (3)	0.041 (2)	0.001 (2)	0.023 (2)	0.0016 (19)
C15	0.042 (2)	0.037 (2)	0.031 (2)	−0.003 (2)	0.0084 (18)	−0.0023 (18)
C16	0.057 (3)	0.054 (3)	0.031 (2)	0.006 (2)	0.020 (2)	−0.0025 (18)
C17	0.054 (3)	0.042 (2)	0.049 (2)	0.004 (2)	0.034 (2)	0.003 (2)
C18	0.035 (2)	0.037 (2)	0.043 (2)	−0.007 (2)	0.0212 (19)	−0.0022 (19)

Geometric parameters (Å, º)

P1—N1	1.517 (3)	C7—C8	1.357 (6)
P1—N4	1.671 (3)	C7—H7A	0.9400
P1—N3	1.676 (3)	C8—C9	1.406 (8)
P1—N2	1.680 (3)	C8—H8A	0.9400
F1—C2	1.361 (5)	C9—C10	1.343 (7)
N1—C1	1.394 (5)	C9—H9A	0.9400
C1—C2	1.388 (6)	C10—H10A	0.9400
C1—C6	1.398 (5)	C11—C12	1.350 (6)
N2—C7	1.386 (6)	C11—H11A	0.9400
N2—C10	1.397 (6)	C12—C13	1.411 (6)
C2—C3	1.362 (6)	C12—H12A	0.9400
N3—C11	1.388 (5)	C13—C14	1.341 (6)
N3—C14	1.393 (5)	C13—H13A	0.9400
C3—C4	1.377 (7)	C14—H14A	0.9400
C3—H3A	0.9400	C15—C16	1.339 (6)
N4—C18	1.392 (5)	C15—H15A	0.9400
N4—C15	1.402 (5)	C16—C17	1.411 (6)
C4—C5	1.388 (7)	C16—H16A	0.9400
C4—H4A	0.9400	C17—C18	1.334 (5)
C5—C6	1.376 (6)	C17—H17A	0.9400
C5—H5A	0.9400	C18—H18A	0.9400
C6—H6A	0.9400
N1—P1—N4	116.7 (2)	C8—C7—H7A	125.8
N1—P1—N3	117.74 (17)	N2—C7—H7A	125.8
N4—P1—N3	104.68 (16)	C7—C8—C9	107.3 (5)
N1—P1—N2	110.59 (19)	C7—C8—H8A	126.3
N4—P1—N2	101.93 (16)	C9—C8—H8A	126.3
N3—P1—N2	103.22 (18)	C10—C9—C8	108.9 (4)
C1—N1—P1	137.2 (3)	C10—C9—H9A	125.6
C2—C1—N1	124.5 (4)	C8—C9—H9A	125.6
C2—C1—C6	115.7 (4)	C9—C10—N2	107.8 (5)
N1—C1—C6	119.7 (4)	C9—C10—H10A	126.1
C7—N2—C10	107.6 (4)	N2—C10—H10A	126.1
C7—N2—P1	126.9 (3)	C12—C11—N3	108.0 (4)
C10—N2—P1	124.9 (3)	C12—C11—H11A	126.0
F1—C2—C3	118.7 (4)	N3—C11—H11A	126.0
F1—C2—C1	117.2 (4)	C11—C12—C13	107.9 (4)
C3—C2—C1	124.1 (4)	C11—C12—H12A	126.1
C11—N3—C14	107.7 (3)	C13—C12—H12A	126.1
C11—N3—P1	128.6 (3)	C14—C13—C12	108.3 (4)
C14—N3—P1	123.6 (3)	C14—C13—H13A	125.9
C2—C3—C4	119.1 (4)	C12—C13—H13A	125.9
C2—C3—H3A	120.4	C13—C14—N3	108.1 (4)
C4—C3—H3A	120.4	C13—C14—H14A	126.0
C18—N4—C15	106.5 (3)	N3—C14—H14A	126.0
C18—N4—P1	127.0 (3)	C16—C15—N4	108.0 (4)
C15—N4—P1	125.8 (3)	C16—C15—H15A	126.0
C3—C4—C5	119.1 (4)	N4—C15—H15A	126.0
C3—C4—H4A	120.5	C15—C16—C17	108.8 (4)
C5—C4—H4A	120.5	C15—C16—H16A	125.6
C6—C5—C4	120.8 (4)	C17—C16—H16A	125.6
C6—C5—H5A	119.6	C18—C17—C16	107.4 (4)
C4—C5—H5A	119.6	C18—C17—H17A	126.3
C5—C6—C1	121.3 (4)	C16—C17—H17A	126.3
C5—C6—H6A	119.4	C17—C18—N4	109.4 (4)
C1—C6—H6A	119.4	C17—C18—H18A	125.3
C8—C7—N2	108.4 (5)	N4—C18—H18A	125.3