3-(2-Bromo­phenyl)-4-(triiso­propyl­silyl)­sydnone

Sydnones are, in most cases, extremely stable crystalline compounds that exhibit a distinct polarity. The five-membered heterocyclic ring that characterizes a sydnone is subject to electrophilic substitution. Only with a strongly activating group present will an attached aryl group compete effectively for the electrophile, due to the considerable partial positive change at the quaternary N atom of the sydnone ring. The title compound, C₁₇H₂₅BrN₂O₂Si, is of interest due to an intra­molecular shift of the silyl-protecting group that occurs between the syndone ring and the aryl ring when treated with n-butyllithium. This was observed while attempting to replace the aryl bromine. With a curiosity into a rationale for this shift, we have examined a series of precursors, this being the first.

Key indicators

• Single-crystal X-ray study
• T = 296 K
• Mean [sigma](C-C) = 0.004 Å
• R factor = 0.042
• wR factor = 0.120
• Data-to-parameter ratio = 26.2

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry


 Alert Level C:



GOODF_01  Alert C The least squares goodness of fit parameter lies
          outside the range 0.80 <> 2.00
          Goodness of fit given =      0.755


 0 Alert Level A = Potentially serious problem

 0 Alert Level B = Potential problem

 1 Alert Level C = Please check

---

S1. Comment

Sydnones are dipolar heteroaromatic compounds first prepared in Sydney, Australia (Earl & Mackney, 1935). They undergo electrophilic aromatic substitution with common electrophiles and this type of reactivity has been extended to the formation of bridged ring analogs via intramolecular processes. For the latter, suitable ortho-substituted arylsydnones have been required, however, the majority of these have been available only through tedious multistep protocols from the corresponding ortho-substituted anilines. We have been interested in more direct routes to ortho-substituted arylsydnones and lithiation strategies have come to the fore. Thus, the molecule described herein was envisaged as a lithiation precursor to a variety of different ortho-substituted arylsydnones via metal-halogen exchange with n-butyllithium, trapping of the incipient anion with a suitable electrophile, and subsequent removal of the silyl protective group with fluoride ion. Interestingly, when an attempt was made to utilize this compound for ortho-substituted arylsydnone synthesis, via reaction with 2.2 equivalents of n-butyllithium at 195 K in dry tetrahydrofuran, migration of the silyl moiety to the ortho-aryl position occurred in high yield. Accordingly, the title compound [and its congeners], (I), have become valuable precursors to ortho-silylarylsydnones; the latter would be difficultly accessible by any other synthetic scheme. It is not clear with the present data how general this novel migration will be and whether or not it is an intra- or intermolecular process, however, further research will help to answer these interesting questions.

The sydnone and phenyl-ring systems found in the compounds are themselves planar, but the rings within a structure lie nearly perpendicular to each other, having an angle of 80.62 (10)°. The bond distances and angles around each atom are within accepted values. In examining the molecule relative to the 1,5 shift, it is noted that the contact distance between the Si atom and Br atom is 4.81 Å, and that between Si and C12 is 4.28 Å.

S2. Experimental

The title compound was prepared by treatment of 3-(2-bromophenyl)sydnone (Applegate & Turnbull, 1988) in dry tetrahydrofuran at 195 K with 1.5 equivalents of lithium diisopropylamide followed by 2 equivalents of triisopropylsilyl chloride.

Computing details

Data collection: CAD-4 Software (Enraf-Nonius, 1989); cell refinement: CAD-4 Software; data reduction: XCAD (McArdle, 1995); program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEX (McArdle, 1995); software used to prepare material for publication: OSCAIL (McArdle, 1995).

Figures

Fig. 1. The molecular structure of (I) showing 30% probability displacement ellipsoids for all non-H atoms. H atoms have been omitted for clarity.

3-(2-Bromophenyl)-4-(triisopropylsilyl)sydnone

Crystal data

C17H25BrN2O2Si	F(000) = 824
Mr = 397.39	Dx = 1.368 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71069 Å
Hall symbol: -P 2yn	Cell parameters from 25 reflections
a = 11.7560 (18) Å	θ = 3.2–12.9°
b = 12.772 (2) Å	µ = 2.20 mm^−1
c = 12.8527 (18) Å	T = 296 K
β = 91.820 (12)°	Rectangular solid with sharp bounding edges, colorless
V = 1928.8 (5) Å^3	0.35 × 0.30 × 0.25 mm
Z = 4

Data collection

Enraf-Nonius CAD-4 diffractometer	2262 reflections with I<2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.012
Graphite monochromator	θmax = 30.0°, θmin = 2.3°
ω/2θ scans	h = −16→16
Absorption correction: analytical (Alcock, 1970)	k = 0→17
Tmin = 0.477, Tmax = 0.591	l = 0→18
6088 measured reflections	3 standard reflections every 120 reflections
5605 independent reflections	intensity decay: <0.1%

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)] = 0.042	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.120	H-atom parameters constrained
S = 0.76	w = 1/[σ^2(Fo^2) + (0.0615P)^2] where P = (Fo^2 + 2Fc^2)/3
5605 reflections	(Δ/σ)max = 0.001
214 parameters	Δρmax = 0.41 e Å^−3
0 restraints	Δρmin = −0.40 e Å^−3

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
Br1	−0.07650 (3)	0.58368 (3)	0.23990 (3)	0.07333 (14)
Si1	0.25799 (6)	0.70689 (6)	0.07415 (6)	0.04265 (18)
O1	0.22264 (19)	0.68413 (17)	0.38982 (16)	0.0652 (6)
O5	0.37655 (19)	0.62431 (19)	0.30698 (18)	0.0728 (6)
N2	0.1204 (2)	0.7300 (2)	0.36492 (18)	0.0599 (6)
N3	0.12206 (19)	0.74113 (16)	0.26418 (16)	0.0462 (5)
C4	0.2160 (2)	0.70632 (19)	0.2156 (2)	0.0447 (6)
C5	0.2852 (3)	0.6668 (2)	0.2991 (2)	0.0547 (7)
C11	0.0198 (2)	0.7865 (2)	0.2175 (2)	0.0468 (6)
C12	−0.0755 (2)	0.7262 (2)	0.1995 (2)	0.0525 (7)
C13	−0.1705 (3)	0.7695 (3)	0.1510 (2)	0.0679 (9)
C14	−0.1686 (3)	0.8740 (3)	0.1235 (3)	0.0737 (9)
C15	−0.0751 (3)	0.9348 (3)	0.1442 (3)	0.0721 (9)
C16	0.0216 (3)	0.8919 (2)	0.1913 (2)	0.0570 (7)
C21	0.1335 (2)	0.7403 (2)	−0.0168 (2)	0.0454 (6)
C22	0.0447 (3)	0.6541 (2)	−0.0312 (2)	0.0639 (8)
C23	0.1714 (3)	0.7760 (3)	−0.1233 (2)	0.0671 (9)
C31	0.3208 (2)	0.5731 (2)	0.0536 (2)	0.0559 (7)
C32	0.2431 (3)	0.4818 (2)	0.0820 (3)	0.0795 (10)
C33	0.3636 (3)	0.5588 (3)	−0.0571 (3)	0.0812 (11)
C41	0.3714 (2)	0.8097 (2)	0.0597 (2)	0.0573 (7)
C42	0.3282 (3)	0.9202 (2)	0.0825 (3)	0.0814 (11)
C43	0.4818 (3)	0.7881 (3)	0.1225 (3)	0.0903 (12)
H13	−0.2349	0.7290	0.1370	0.102*
H14	−0.2323	0.9035	0.0902	0.111*
H15	−0.0764	1.0054	0.1265	0.108*
H16	0.0859	0.9326	0.2051	0.085*
H21	0.0947	0.8000	0.0142	0.068*
H22A	−0.0227	0.6825	−0.0645	0.096*
H22B	0.0263	0.6261	0.0355	0.096*
H22C	0.0745	0.5993	−0.0736	0.096*
H23A	0.2071	0.7188	−0.1579	0.101*
H23B	0.2246	0.8327	−0.1150	0.101*
H23C	0.1064	0.7992	−0.1642	0.101*
H31	0.3879	0.5684	0.1005	0.084*
H32A	0.1760	0.4828	0.0375	0.119*
H32B	0.2218	0.4887	0.1532	0.119*
H32C	0.2828	0.4169	0.0732	0.119*
H33A	0.4020	0.4927	−0.0620	0.122*
H33B	0.4155	0.6143	−0.0726	0.122*
H33C	0.3002	0.5604	−0.1060	0.122*
H41	0.3914	0.8092	−0.0137	0.086*
H42A	0.3118	0.9259	0.1550	0.122*
H42B	0.2602	0.9336	0.0413	0.122*
H42C	0.3854	0.9705	0.0656	0.122*
H43A	0.5350	0.8437	0.1114	0.135*
H43B	0.5138	0.7230	0.1004	0.135*
H43C	0.4658	0.7841	0.1952	0.135*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Br1	0.0800 (3)	0.0556 (2)	0.0850 (3)	−0.01240 (17)	0.01275 (19)	−0.00641 (17)
Si1	0.0396 (4)	0.0421 (4)	0.0460 (4)	0.0025 (3)	−0.0021 (3)	−0.0014 (3)
O1	0.0803 (15)	0.0651 (13)	0.0495 (12)	0.0012 (11)	−0.0089 (11)	0.0052 (10)
O5	0.0659 (14)	0.0733 (14)	0.0778 (16)	0.0144 (12)	−0.0199 (12)	0.0052 (12)
N2	0.0718 (18)	0.0617 (16)	0.0462 (14)	0.0018 (13)	−0.0001 (12)	0.0025 (12)
N3	0.0525 (13)	0.0428 (12)	0.0429 (13)	−0.0019 (10)	−0.0020 (10)	−0.0038 (10)
C4	0.0459 (15)	0.0400 (13)	0.0478 (15)	0.0053 (12)	−0.0060 (12)	−0.0048 (12)
C5	0.0639 (19)	0.0469 (15)	0.0527 (18)	−0.0014 (15)	−0.0090 (15)	0.0049 (13)
C11	0.0470 (15)	0.0521 (16)	0.0413 (14)	0.0071 (13)	0.0027 (12)	−0.0046 (12)
C12	0.0559 (18)	0.0512 (17)	0.0503 (16)	−0.0011 (13)	0.0012 (13)	−0.0093 (13)
C13	0.0552 (19)	0.086 (2)	0.062 (2)	0.0013 (17)	−0.0016 (16)	−0.0136 (18)
C14	0.068 (2)	0.086 (2)	0.065 (2)	0.022 (2)	−0.0097 (17)	0.0054 (19)
C15	0.084 (3)	0.060 (2)	0.073 (2)	0.0211 (18)	0.0025 (18)	0.0032 (16)
C16	0.0582 (18)	0.0510 (17)	0.0618 (18)	0.0044 (14)	0.0044 (15)	−0.0018 (14)
C21	0.0399 (14)	0.0501 (15)	0.0462 (15)	0.0046 (12)	−0.0006 (12)	−0.0046 (12)
C22	0.0549 (18)	0.072 (2)	0.0636 (19)	−0.0063 (15)	−0.0116 (15)	−0.0099 (16)
C23	0.066 (2)	0.083 (2)	0.0520 (18)	0.0058 (18)	−0.0049 (15)	0.0096 (16)
C31	0.0518 (17)	0.0504 (16)	0.0652 (19)	0.0138 (13)	−0.0033 (14)	−0.0056 (13)
C32	0.096 (3)	0.0442 (18)	0.098 (3)	0.0035 (17)	−0.002 (2)	0.0012 (17)
C33	0.087 (3)	0.082 (3)	0.076 (2)	0.028 (2)	0.013 (2)	−0.0188 (18)
C41	0.0505 (16)	0.0574 (18)	0.0640 (19)	−0.0076 (13)	0.0021 (14)	0.0016 (14)
C42	0.082 (2)	0.0521 (19)	0.110 (3)	−0.0134 (18)	−0.004 (2)	−0.0034 (19)
C43	0.057 (2)	0.100 (3)	0.113 (3)	−0.016 (2)	−0.020 (2)	0.015 (2)

Geometric parameters (Å, º)

Br1—C12	1.893 (3)	C22—H22A	0.9599
Si1—C31	1.883 (3)	C22—H22B	0.9599
Si1—C41	1.884 (3)	C22—H22C	0.9599
Si1—C21	1.892 (3)	C23—H23A	0.9599
Si1—C4	1.899 (3)	C23—H23B	0.9599
O1—N2	1.366 (3)	C23—H23C	0.9599
O1—C5	1.415 (4)	C31—C32	1.532 (4)
O5—C5	1.205 (3)	C31—C33	1.536 (4)
N3—N2	1.303 (3)	C31—H31	0.9800
N3—C4	1.360 (3)	C32—H32A	0.9599
N3—C11	1.448 (3)	C32—H32B	0.9599
C4—C5	1.419 (4)	C32—H32C	0.9599
C11—C12	1.372 (4)	C33—H33A	0.9599
C11—C16	1.388 (4)	C33—H33B	0.9599
C12—C13	1.378 (4)	C33—H33C	0.9599
C13—C14	1.380 (5)	C41—C43	1.531 (4)
C13—H13	0.9300	C41—C42	1.532 (4)
C14—C15	1.365 (5)	C41—H41	0.9800
C14—H14	0.9300	C42—H42A	0.9599
C15—C16	1.384 (5)	C42—H42B	0.9599
C15—H15	0.9300	C42—H42C	0.9599
C16—H16	0.9300	C43—H43A	0.9599
C21—C23	1.523 (4)	C43—H43B	0.9599
C21—C22	1.525 (4)	C43—H43C	0.9599
C21—H21	0.9800
C31—Si1—C41	109.68 (13)	H22A—C22—H22C	109.5
C31—Si1—C21	114.63 (13)	H22B—C22—H22C	109.5
C41—Si1—C21	108.53 (13)	C21—C23—H23A	109.5
C31—Si1—C4	104.23 (13)	C21—C23—H23B	109.5
C41—Si1—C4	107.65 (13)	H23A—C23—H23B	109.5
C21—Si1—C4	111.88 (12)	C21—C23—H23C	109.5
N2—O1—C5	110.5 (2)	H23A—C23—H23C	109.5
N3—N2—O1	103.8 (2)	H23B—C23—H23C	109.5
N2—N3—C4	117.3 (2)	C32—C31—C33	110.2 (3)
N2—N3—C11	114.6 (2)	C32—C31—Si1	114.7 (2)
C4—N3—C11	128.0 (2)	C33—C31—Si1	112.3 (2)
N3—C4—C5	102.9 (2)	C32—C31—H31	106.3
N3—C4—Si1	132.69 (19)	C33—C31—H31	106.3
C5—C4—Si1	124.4 (2)	Si1—C31—H31	106.3
O5—C5—O1	119.1 (3)	C31—C32—H32A	109.5
O5—C5—C4	135.4 (3)	C31—C32—H32B	109.5
O1—C5—C4	105.5 (2)	H32A—C32—H32B	109.5
C12—C11—C16	121.4 (3)	C31—C32—H32C	109.5
C12—C11—N3	120.6 (2)	H32A—C32—H32C	109.5
C16—C11—N3	118.0 (3)	H32B—C32—H32C	109.5
C11—C12—C13	119.8 (3)	C31—C33—H33A	109.5
C11—C12—Br1	120.3 (2)	C31—C33—H33B	109.5
C13—C12—Br1	119.9 (2)	H33A—C33—H33B	109.5
C12—C13—C14	119.0 (3)	C31—C33—H33C	109.5
C12—C13—H13	120.5	H33A—C33—H33C	109.5
C14—C13—H13	120.5	H33B—C33—H33C	109.5
C15—C14—C13	121.3 (3)	C43—C41—C42	110.2 (3)
C15—C14—H14	119.4	C43—C41—Si1	114.4 (2)
C13—C14—H14	119.4	C42—C41—Si1	112.5 (2)
C14—C15—C16	120.3 (3)	C43—C41—H41	106.4
C14—C15—H15	119.8	C42—C41—H41	106.4
C16—C15—H15	119.8	Si1—C41—H41	106.4
C15—C16—C11	118.1 (3)	C41—C42—H42A	109.5
C15—C16—H16	120.9	C41—C42—H42B	109.5
C11—C16—H16	120.9	H42A—C42—H42B	109.5
C23—C21—C22	109.0 (2)	C41—C42—H42C	109.5
C23—C21—Si1	112.35 (19)	H42A—C42—H42C	109.5
C22—C21—Si1	115.16 (19)	H42B—C42—H42C	109.5
C23—C21—H21	106.6	C41—C43—H43A	109.5
C22—C21—H21	106.6	C41—C43—H43B	109.5
Si1—C21—H21	106.6	H43A—C43—H43B	109.5
C21—C22—H22A	109.5	C41—C43—H43C	109.5
C21—C22—H22B	109.5	H43A—C43—H43C	109.5
H22A—C22—H22B	109.5	H43B—C43—H43C	109.5
C21—C22—H22C	109.5
C31—Si1—C4—N3	−137.1 (3)	C5—O1—N2—N3	−0.9 (3)
C41—Si1—C4—N3	106.5 (3)	C4—N3—N2—O1	0.6 (3)
C21—Si1—C4—N3	−12.7 (3)	C11—N3—N2—O1	178.5 (2)
C31—Si1—C4—C5	44.2 (3)	N2—N3—C4—C5	−0.1 (3)
C41—Si1—C4—C5	−72.2 (3)	C11—N3—C4—C5	−177.6 (2)
C21—Si1—C4—C5	168.6 (2)	N2—N3—C4—Si1	−179.0 (2)
C31—Si1—C21—C23	−80.4 (2)	C11—N3—C4—Si1	3.5 (4)
C41—Si1—C21—C23	42.6 (2)	N2—N3—C11—C12	−79.4 (3)
C4—Si1—C21—C23	161.2 (2)	C4—N3—C11—C12	98.1 (3)
C31—Si1—C21—C22	45.2 (3)	N2—N3—C11—C16	100.9 (3)
C41—Si1—C21—C22	168.2 (2)	C4—N3—C11—C16	−81.5 (3)
C4—Si1—C21—C22	−73.2 (2)	N3—C4—C5—O5	178.2 (3)
C41—Si1—C31—C32	169.7 (2)	Si1—C4—C5—O5	−2.7 (5)
C21—Si1—C31—C32	−67.9 (3)	N3—C4—C5—O1	−0.4 (3)
C4—Si1—C31—C32	54.7 (3)	Si1—C4—C5—O1	178.62 (18)
C41—Si1—C31—C33	−63.4 (3)	C16—C11—C12—C13	2.4 (4)
C21—Si1—C31—C33	59.0 (3)	N3—C11—C12—C13	−177.2 (3)
C4—Si1—C31—C33	−178.4 (2)	C16—C11—C12—Br1	−178.1 (2)
C31—Si1—C41—C43	−49.4 (3)	N3—C11—C12—Br1	2.2 (4)
C21—Si1—C41—C43	−175.3 (2)	C11—C12—C13—C14	−1.5 (4)
C4—Si1—C41—C43	63.4 (3)	Br1—C12—C13—C14	179.1 (2)
C31—Si1—C41—C42	−176.2 (2)	C12—C13—C14—C15	−0.5 (5)
C21—Si1—C41—C42	57.8 (3)	C13—C14—C15—C16	1.6 (5)
C4—Si1—C41—C42	−63.4 (3)	C14—C15—C16—C11	−0.7 (5)
N2—O1—C5—O5	−178.1 (3)	C12—C11—C16—C15	−1.3 (4)
N2—O1—C5—C4	0.8 (3)	N3—C11—C16—C15	178.3 (3)