Crystal structure of tert-butyl-N-phenyl-carbonitrilium tetra-chlorido-aluminate.

In the title compound, (C11H14N)[AlCl4], the nitrilium (systematic name: 2,2-dimethyl-N-phenyl-propane-nitrilium) ion adopts a slightly distorted linear configuration [C-N C = 178.87 (16) and N C-C = 179.13 (17)°]. In the crystal, while there are no inter-molecular hydrogen bonds, pairs of nitrilium ions are linked through π-π inter-actions [inter-centroid distance = 3.8091 (13) Å].

Chemical context

Nitrilium salts are highly electrophilic species that can be generated from imidoyl chlorides by abstracting its chloride using a Lewis acid, SbCl5 having been most widely applied (Meerwein, Laasch, Mersch & Nentwig, 1956 ▶; Klages & Grill, 1955 ▶; Kanemasa, 2004 ▶). Recently, we have shown that tri­methyl­silyl triflate (TMSOTf) can also be used as a Lewis acid, generating nitrilium triflates, which are excellent imine synthons in the preparation of 1,3-imino­phosphane ligands (van Dijk et al., 2014 ▶). Inter­estingly, nitrilium tetra­chlorido­aluminates, which can be synthesised using the much cheaper AlCl3, have found little application (Meerwein, Laasch, Mersch & Spille, 1956 ▶; Al-Talib et al. 1992 ▶). Therefore, we also focused on these species of which the title compound is illustrative.

Structural commentary

The asymmetric unit of the crystal (Fig. 1 ▶) contains one nitrilium cation and one tetra­chlorido­aluminate anion, which are ion-separated. The nitrilium cation adopts a slightly distorted linear configuration [C—N C = 178.87 (16) and N C–C = 179.13 (17)°] and features an N C bond length of 1.1353 (19) Å, which is in the range of previously reported nitrilium ions (see Database survey). The tetra­chlorido­aluminate anion has an approximately tetra­hedral geometry and is in the range of those reported previously (Bezombes et al., 2004 ▶).

Figure 1

Mol­ecular structure of tert-butyl-N-phenyl­carbonitrilium tetra­chlorido­aluminate with displacement ellipsoids drawn at the 50% probability level.

Supra­molecular features

In the unit cell, pairs of inversion-related nitrilium cations are linked through π–π inter­actions with an inter-centroid distance of 3.8091 (13) Å. There is a plane-to-plane shift of the phenyl rings of 1.563 (3) Å. The nitrilium cations and tetra­chloridoaluminate anions are arranged in alternating planes parallel to (011).

Database survey

A search in the Cambridge Structural Database (Version 5.35, last update May 2014; Groom & Allen, 2014 ▶) showed five structures of nitrilium salts (Gjøystdal & Rømming, 1977 ▶; MacLaughlin et al., 1983 ▶; Casey et al., 1988 ▶; Bykhovskaya et al., 1993 ▶, Okazaki et al., 2013 ▶), and two structures of nitrilium ylides (Janulis et al., 1984 ▶; Doherty et al., 1999 ▶)). The title compound is very closely related to N-(2,6-di­methyl­phen­yl)-acetonitrilium tetra­fluorido­borate (Gjøystdal & Rømming, 1977 ▶), which has an N C bond length of 1.131 Å, and (N-phen­yl)(tert-but­yl)carbonitrilium tri­fluoro­methane­sulfonate [van Dijk et al., 2014 ▶; N C bond length of 1.125 (3) Å], both of which feature similar bond lengths and angles for the nitrilium group.

Synthesis and crystallization

This experiment was performed under an atmosphere of dry nitro­gen using standard Schlenk-line and glovebox techniques. NMR spectra were recorded at 300 K on a Bruker Advance 500 and referenced inter­nally to residual solvent resonance of CD2Cl2, 1H at δ 5.32, 13C{1H} at δ 53.84. The melting point was measured in a sealed capillary on a Stuart Scientific SMP3 melting point apparatus and is uncorrected. The IR spectrum was recorded on a Shimadzu FTIR–8400S spectrophotometer. Solvents were distilled from the appropriate drying agents CaH2 (DCM), NaK/benzo­phenone (diethyl ether), and P2O5 (CD2Cl2), and kept under an inert atmosphere of dry nitro­gen.

The title compound was obtained as follows: to a suspension of AlCl3 (3.00 g, 22.4 mmol) in DCM (10 ml) cooled to 195 K, an equimolar amount of N-phenyl­pivalimidoyl chloride (4.38 g, 22.4 mmol) in DCM (25 ml) was added dropwise, after which the reaction mixture was warmed to room temperature and stirred for 16 h. All volatiles were removed in vacuo, after which the product was redissolved in DCM (60 ml), layered with diethyl ether (90 ml) and cooled to 193 K for 48 h. The analytically pure product was isolated as a grey crystalline solid (6.23 g, 18.9 mmol, 85%). Recrystallization from DCM at 278 K yielded crystals suitable for X-ray crystallography. The crystals were coated with paratone oil and mounted on a glass fibre in the cooled nitro­gen stream of the diffractometer. M.p. 411 K. 1H NMR (500.2 MHz, CD2Cl2): δ 7.89 [d, 3 J(H,H) = 7.6 Hz, 2H; o-PhH], 7.80 [t, 3 J(H,H) = 7.6 Hz, 1H; p-PhH], 7.66 [t, 3 J(H,H) = 7.6 Hz, 2H; m-PhH], 1.84 [s, 9H; C(CH 3)3]. 13C{1H} NMR (125.8 MHz, CD2Cl2): δ 135.1 (s; p-PhC), 131.0 (s; m-PhC), 128.7 (s; o-PhC), 121.1 [t, 1 J(C,N) = 42.7 Hz; N C], 120.7 [t, 1 J(C,N) = 14.2 Hz; ipso-PhC], 31.7 [s; C(CH3)3], 27.3 [s; C(CH3)3]. IR: 3065 (w), 2990 (w), 1692 (w), 1611 (w), 1588 (w), 1483 (w), 1474 (m), 1456 (m), 1445 (w), 1373 (w), 1296 (w), 1238 (w), 1198 (w), 1186 (w), 1161 (w), 1028 (w), 1005 (w), 939 (w), 928 (w), 876 (w), 845 (w), 781 (w), 758 (s), 692 (w), 677 (m), 669 (w), 652 (w).

Refinement

Crystal data, data collection and structure refinement details are summarized in Table 1 ▶.

Table 1

Experimental details

Crystal data
Chemical formula	(C11H14N)[AlCl4]
M r	329.03
Crystal system, space group	Monoclinic, P21/c
Temperature (K)	153
a, b, c ()	6.4531(6), 13.6967(13), 17.9352(17)
()	93.636(1)
V (3)	1582.0(3)
Z	4
Radiation type	Mo K
(mm1)	0.78
Crystal size (mm)	0.16 0.05 0.03
Data collection
Diffractometer	Bruker APEXII
Absorption correction	Multi-scan (SADABS; Bruker, 2007 ▶)
T min, T max	0.885, 0.977
No. of measured, independent and observed [I > 2(I)] reflections	16388, 4063, 3294
R int	0.035
(sin /)max (1)	0.675
Refinement
R[F 2 > 2(F 2)], wR(F 2), S	0.030, 0.081, 1.03
No. of reflections	4063
No. of parameters	210
H-atom treatment	All H-atom parameters refined
max, min (e 3)	0.35, 0.26

Computer programs: APEX2 and SAINT-Plus (Bruker, 2007 ▶), SHELXS97 and SHELXL97 (Sheldrick, 2008 ▶), PLATON (Spek, 2009 ▶), WinGX (Farrugia, 2012 ▶) and OLEX2 (Dolomanov et al., 2009 ▶).

Crystal structure: contains datablock(s) I, global. DOI: 10.1107/S1600536814022028/kj2242sup1.cif

Structure factors: contains datablock(s) I. DOI: 10.1107/S1600536814022028/kj2242Isup2.hkl

CCDC reference: 1027790

Additional supporting information: crystallographic information; 3D view; checkCIF report

(C11H14N)[AlCl4]	F(000) = 672
Mr = 329.03	Dx = 1.381 Mg m−3
Monoclinic, P21/c	Melting point: 411 K
Hall symbol: -P 2ybc	Mo Kα radiation, λ = 0.71073 Å
a = 6.4531 (6) Å	Cell parameters from 5175 reflections
b = 13.6967 (13) Å	θ = 2.3–28.5°
c = 17.9352 (17) Å	µ = 0.78 mm−1
β = 93.636 (1)°	T = 153 K
V = 1582.0 (3) Å3	Needle, colorless
Z = 4	0.16 × 0.05 × 0.03 mm

Bruker APEXII diffractometer	4063 independent reflections
Radiation source: rotating anode	3294 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.035
Detector resolution: 80 pixels mm-1	θmax = 28.7°, θmin = 1.9°
ω and Phi scans	h = −8→8
Absorption correction: multi-scan (SADABS; Bruker, 2007)	k = −18→18
Tmin = 0.885, Tmax = 0.977	l = −24→24
16388 measured reflections

Refinement on F2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.030	Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.081	All H-atom parameters refined
S = 1.03	w = 1/[σ2(Fo2) + (0.0425P)2 + 0.1953P] where P = (Fo2 + 2Fc2)/3
4063 reflections	(Δ/σ)max = 0.001
210 parameters	Δρmax = 0.35 e Å−3
0 restraints	Δρmin = −0.26 e Å−3

Experimental. Corrections were done with the SADABS program, utilizing the none merged raw data obtained from the integration process. Integration and final cell refinement were done with SAINT.SADABS reports ratio of Tmin/Tmax = 0.797049

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.

	x	y	z	Uiso*/Ueq
Al1	0.96022 (7)	0.22733 (3)	0.35138 (2)	0.02252 (11)
C1	0.5146 (2)	0.96503 (11)	0.27377 (8)	0.0280 (3)
C2	0.5280 (3)	0.91716 (11)	0.34748 (8)	0.0301 (3)
C3	0.6685 (3)	0.82750 (13)	0.34364 (10)	0.0333 (3)
C4	0.6215 (5)	0.99100 (15)	0.40414 (11)	0.0544 (6)
C5	0.3056 (3)	0.88817 (17)	0.36455 (14)	0.0492 (5)
C6	0.4893 (2)	1.04868 (10)	0.14690 (8)	0.0246 (3)
C7	0.6619 (3)	1.09623 (11)	0.12260 (9)	0.0287 (3)
C8	0.6442 (3)	1.13970 (11)	0.05267 (9)	0.0321 (3)
C9	0.4587 (3)	1.13540 (11)	0.00948 (9)	0.0329 (4)
C10	0.2892 (3)	1.08788 (12)	0.03538 (9)	0.0337 (4)
C11	0.3023 (3)	1.04317 (11)	0.10465 (9)	0.0290 (3)
Cl1	1.07491 (7)	0.12249 (3)	0.27615 (2)	0.03826 (11)
Cl2	0.63285 (6)	0.24128 (3)	0.33003 (2)	0.03784 (11)
Cl3	1.03104 (7)	0.17986 (3)	0.46328 (2)	0.03810 (11)
Cl4	1.09572 (6)	0.36715 (3)	0.33438 (2)	0.03407 (11)
N1	0.5044 (2)	1.00304 (9)	0.21740 (7)	0.0270 (3)
H5	0.678 (3)	0.7947 (13)	0.3913 (11)	0.032 (4)*
H6	0.803 (3)	0.8453 (14)	0.3297 (11)	0.042 (5)*
H12	0.449 (3)	1.1638 (13)	−0.0347 (10)	0.031 (4)*
H14	0.781 (3)	1.0977 (13)	0.1524 (10)	0.037 (5)*
H10	0.189 (3)	1.0117 (13)	0.1246 (10)	0.033 (5)*
H4	0.615 (3)	0.7821 (17)	0.3065 (13)	0.059 (6)*
H13	0.760 (3)	1.1708 (14)	0.0343 (10)	0.037 (5)*
H3	0.311 (3)	0.8571 (16)	0.4147 (13)	0.059 (6)*
H8	0.635 (4)	0.9609 (17)	0.4530 (14)	0.067 (7)*
H11	0.165 (3)	1.0868 (15)	0.0039 (12)	0.054 (6)*
H7	0.539 (3)	1.0444 (18)	0.4074 (12)	0.055 (6)*
H1	0.229 (4)	0.9457 (17)	0.3674 (13)	0.061 (7)*
H2	0.243 (4)	0.8431 (19)	0.3264 (15)	0.074 (8)*
H9	0.763 (4)	1.0135 (19)	0.3925 (15)	0.080 (8)*

	U11	U22	U33	U12	U13	U23
Al1	0.0237 (2)	0.0221 (2)	0.0215 (2)	0.00139 (16)	−0.00057 (16)	−0.00156 (15)
C1	0.0313 (8)	0.0270 (7)	0.0263 (8)	0.0037 (6)	0.0048 (6)	0.0011 (6)
C2	0.0392 (9)	0.0296 (8)	0.0220 (7)	0.0008 (6)	0.0055 (6)	0.0068 (6)
C3	0.0368 (9)	0.0350 (8)	0.0279 (8)	0.0042 (7)	0.0003 (7)	0.0072 (7)
C4	0.100 (2)	0.0342 (10)	0.0280 (10)	−0.0045 (11)	−0.0013 (10)	0.0001 (8)
C5	0.0420 (11)	0.0531 (12)	0.0542 (13)	0.0093 (9)	0.0179 (9)	0.0245 (10)
C6	0.0331 (8)	0.0202 (6)	0.0208 (7)	0.0057 (5)	0.0036 (6)	0.0021 (5)
C7	0.0307 (8)	0.0265 (7)	0.0291 (8)	0.0033 (6)	0.0034 (6)	0.0006 (6)
C8	0.0401 (9)	0.0251 (7)	0.0323 (8)	0.0022 (6)	0.0132 (7)	0.0041 (6)
C9	0.0524 (10)	0.0266 (8)	0.0201 (7)	0.0119 (7)	0.0052 (7)	0.0043 (6)
C10	0.0408 (9)	0.0320 (8)	0.0273 (8)	0.0093 (7)	−0.0054 (7)	−0.0009 (6)
C11	0.0319 (8)	0.0253 (7)	0.0300 (8)	0.0026 (6)	0.0040 (6)	0.0008 (6)
Cl1	0.0421 (2)	0.0355 (2)	0.0370 (2)	0.00888 (16)	0.00073 (17)	−0.01397 (16)
Cl2	0.02347 (19)	0.0465 (2)	0.0431 (2)	0.00328 (15)	−0.00125 (16)	0.00606 (17)
Cl3	0.0468 (2)	0.0410 (2)	0.02528 (19)	−0.00252 (17)	−0.00698 (16)	0.00525 (16)
Cl4	0.0377 (2)	0.02523 (18)	0.0400 (2)	−0.00444 (15)	0.00856 (17)	−0.00103 (15)
N1	0.0331 (7)	0.0245 (6)	0.0238 (6)	0.0057 (5)	0.0047 (5)	0.0024 (5)

Al1—Cl3	2.1315 (6)	C2—C5	1.539 (3)
Al1—Cl2	2.1316 (6)	C6—C7	1.384 (2)
Al1—Cl1	2.1347 (6)	C6—C11	1.386 (2)
Al1—Cl4	2.1351 (6)	C6—N1	1.4084 (18)
C1—N1	1.1353 (19)	C7—C8	1.386 (2)
C1—C2	1.473 (2)	C8—C9	1.385 (2)
C2—C4	1.530 (3)	C9—C10	1.378 (3)
C2—C3	1.531 (2)	C10—C11	1.383 (2)
Cl3—Al1—Cl2	110.32 (2)	C4—C2—C5	111.84 (18)
Cl3—Al1—Cl1	109.13 (3)	C3—C2—C5	111.39 (15)
Cl2—Al1—Cl1	109.04 (2)	C7—C6—C11	122.93 (14)
Cl3—Al1—Cl4	110.05 (2)	C7—C6—N1	118.70 (14)
Cl2—Al1—Cl4	107.71 (2)	C11—C6—N1	118.36 (13)
Cl1—Al1—Cl4	110.58 (3)	C6—C7—C8	117.71 (15)
N1—C1—C2	179.13 (17)	C9—C8—C7	120.42 (16)
C1—C2—C4	107.46 (14)	C10—C9—C8	120.51 (15)
C1—C2—C3	108.54 (13)	C9—C10—C11	120.48 (16)
C4—C2—C3	110.50 (17)	C10—C11—C6	117.95 (15)
C1—C2—C5	106.91 (15)	C1—N1—C6	178.87 (16)