N-Boranyl-N-(trimethyl­silyl)pyrrolidine

The mol­ecule of the title compound, C₇H₂₀BNSi, exhibits normal sp³-hybridized B and N centres and the pyrrolidine ring has a slightly distorted envelope conformation. The B-N bond distance is longer than that found for related derivatives and possibly reflects the conformation of the ring and the effect of N-atom silylation.

Key indicators

• Single-crystal X-ray study
• T = 100 K
• Mean [sigma](C-C) = 0.002 Å
• R factor = 0.031
• wR factor = 0.090
• Data-to-parameter ratio = 14.2

checkCIF/PLATON results

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Alert level C
PLAT153_ALERT_1_C The su's on the Cell Axes are Equal (x 100000) .        500 Ang.
PLAT222_ALERT_3_C Large Non-Solvent    H     Ueq(max)/Ueq(min) ...       3.92 Ratio
PLAT230_ALERT_2_C Hirshfeld Test Diff for    Si     -   C6      ..       5.10 su

Alert level G
REFLT03_ALERT_1_G ALERT: Expected hkl max differ from CIF values
           From the CIF: _diffrn_reflns_theta_max           33.89
           From the CIF: _reflns_number_total               2436
           From the CIF: _diffrn_reflns_limit_ max hkl   13.   13.   15.
           From the CIF: _diffrn_reflns_limit_ min hkl  -10.  -12.  -12.
           TEST1: Expected hkl limits for theta max
           Calculated maximum hkl   13.   16.   18.
           Calculated minimum hkl  -13.  -16.  -18.

   0 ALERT level A = In general: serious problem
   0 ALERT level B = Potentially serious problem
   3 ALERT level C = Check and explain
   1 ALERT level G = General alerts; check

   2 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   1 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
   0 ALERT type 4 Improvement, methodology, query or suggestion
   0 ALERT type 5 Informative message, check

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S1. Comment

As part of a broader study aimed at using various borane derivatives as hydroborating agents for octenes, we have recently begun to explore the use of activated amine adducts of BH₃. Our goal in this work was to prepare and structurally characterize a relatively stable silylated secondary amine adduct of BH₃ as a potentially active hydroborating reagent for alkenes.

The molecular structure of (I), (Fig. 1), reflects sp³ hybridized geometries for boron and nitrogen, consistent with the formation of a regular dative covalent bond to boron. Viewing (I) down the N–Si bond vector shows that the B–N bond roughly bisects the C5–Si–C7 angle to give a staggered conformation around the Si–N bond [C7–Si–N–B = 69 (1)°]. The BH₃ group therefore fits within the space generated by the closest two methyls of the SiMe₃ group.

The B–N bond of (I) (Table 1) is significantly longer than that of B(C₆F₅)₃.(pyrrolidine) [1.628 Å; Mountford et al., 2003], (pyrrolidine)₂(BH₂)₂ [1.596 Å; Jaska et al., 2003] and BH₃.(pyrrolidine) (1.591 Å; Chitsaz et al., 2002). The origin of this effect is unclear, since the present structure exhibits no repulsive (short) B···Si steric interactions that might favour marked elongation of the B–N bond. Indeed the B–N–Si bond angle [108.8 (1)°] is close to the ideal sp³ hybridized value of 109.5°.

It is possible that silylation of the pyrrolidine nitrogen in (I) reduces its σ-donor power, culminating in a weaker, longer N–B bond. Also relevant is the fact that the pyrrolidine ring of (I) adopts a slightly distorted envelope conformation, with N as the flap atom; N is displaced by 0.602 (3) Å from the mean plane of the other four atoms. The ring carbon atoms C2 and C3 tip towards the BH₃ unit leading to a short intramolecular contact between H3B and B [3.02 (1) Å]. It has also a pseudo mirror plane passing through atom N and the mid-point of C2—C3 bond, as evidenced by the torsion angles (Table 1). This conformation is not observed for the pyrrolidine adduct of BH₃ where the envelope conformation of the pyrrolidine ring is folded away from the BH₃ group, presumably due to the absence of the bulky SiMe₃ group.

There are no short intermolecular contacts between molecules of (I) in the crystal lattice and the 4-molecule unit cell (Fig. 2) shows the expected packing.

Related literature

For related literature, see: Jaska et al. (2003); Mountford et al. (2003); Chitsaz et al. (2002).

S2. Experimental

B₂H₆ (b.p. 181 K) was generated by the reaction of BF₃(OEt₂) (51.6 mmol, 6.53 ml) and NaBH₄ (1.46 g, 38.7 mmol) in bis(2-methoxyethyl) ether (20 ml) under nitrogen prior to being condensed at 166 K (liquid nitrogen/iso-octane slurrey). The liquid B₂H₆ was reacted with a solution of N-(trimethylsilyl)pyrrolidine (17.2 mmol, 3.0 ml) in hexane. Colorless crystals of (I) were obtained after 5 d.

S3. Refinement

H atoms were located in difference syntheses and refined isotropically [C—H = 0.893 (15)–1.010 (12) Å, B—H = 1.104 (14)–1.121 (13) Å and U_iso(H) = 0.013 (3)–0.051 (5) Ų].

Computing details

Data collection: CrysAlis CCD (Oxford Diffraction, 2006); cell refinement: CrysAlis RED (Oxford Diffraction, 2006); data reduction: CrysAlis RED; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: WinGX (Farrugia, 1999); software used to prepare material for publication: WinGX.

Figures

	Fig. 1. The molecular structure of the title molecule, with the atom-numbering scheme. Displacement ellipsoids are drawn at the 70% probability level.
	Fig. 2. (a) A packing diagram for (I). H atoms have been omitted for clarity. (b) CPK model of the unit-cell contents of (I) including H atoms.

N-Boranyl-N-(trimethylsilyl)pyrrolidine

Crystal data

C7H20BNSi	F(000) = 352
Mr = 157.14	Dx = 1.04 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2yn	Cell parameters from 4177 reflections
a = 8.613 (5) Å	θ = 3.8–33.9°
b = 10.321 (5) Å	µ = 0.17 mm^−1
c = 11.753 (5) Å	T = 100 K
β = 106.080 (5)°	Block, colorless
V = 1003.9 (9) Å^3	0.4 × 0.3 × 0.2 mm
Z = 4

Data collection

Oxford Diffraction Xcalibur2 CCD diffractometer	2436 independent reflections
Radiation source: fine-focus sealed tube	1970 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.016
Detector resolution: 8.4190 pixels mm^-1	θmax = 33.9°, θmin = 4.0°
ω scans	h = −10→13
Absorption correction: multi-scan (Blessing, 1995)	k = −12→13
Tmin = 0.934, Tmax = 0.971	l = −12→15
6834 measured reflections

Refinement

Refinement on F^2	0 restraints
Least-squares matrix: full	All H-atom parameters refined
R[F^2 > 2σ(F^2)] = 0.031	w = 1/[σ^2(Fo^2) + (0.0589P)^2] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.090	(Δ/σ)max = 0.001
S = 1.06	Δρmax = 0.39 e Å^−3
2436 reflections	Δρmin = −0.21 e Å^−3
171 parameters

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
C1	0.85439 (13)	0.12797 (11)	0.34325 (10)	0.0169 (2)
C2	0.68293 (13)	0.15220 (11)	0.35366 (10)	0.0194 (3)
C3	0.66737 (13)	0.30030 (12)	0.36165 (10)	0.0194 (3)
C4	0.82484 (12)	0.35392 (11)	0.34436 (10)	0.0153 (2)
C5	1.24120 (13)	0.41217 (11)	0.40765 (11)	0.0198 (3)
C6	1.06149 (15)	0.29146 (14)	0.17331 (11)	0.0239 (3)
C7	1.24759 (15)	0.11565 (12)	0.36983 (13)	0.0257 (3)
B	1.00502 (16)	0.24707 (13)	0.53477 (12)	0.0185 (3)
N	0.94841 (11)	0.24928 (8)	0.38998 (8)	0.0124 (2)
Si	1.12767 (3)	0.26715 (3)	0.33653 (3)	0.01435 (12)
H1A	0.9113 (13)	0.0563 (12)	0.3895 (10)	0.021 (3)*
H1B	0.8533 (14)	0.1164 (13)	0.2613 (11)	0.023 (3)*
H2A	0.6659 (14)	0.1066 (13)	0.4225 (10)	0.024 (3)*
H2B	0.6058 (14)	0.1173 (12)	0.2842 (10)	0.021 (3)*
H3A	0.5724 (14)	0.3351 (12)	0.2980 (11)	0.022 (3)*
H3B	0.6545 (15)	0.3236 (13)	0.4371 (12)	0.028 (3)*
H4A	0.8639 (13)	0.4323 (12)	0.3881 (10)	0.017 (3)*
H4B	0.8130 (13)	0.3645 (11)	0.2611 (10)	0.013 (3)*
H5A	1.1743 (16)	0.4884 (14)	0.3951 (12)	0.037 (4)*
H5B	1.2849 (14)	0.3980 (12)	0.4911 (11)	0.023 (3)*
H5C	1.3241 (16)	0.4273 (13)	0.3727 (11)	0.033 (4)*
H6A	0.9977 (19)	0.2279 (14)	0.1352 (13)	0.042 (5)*
H6B	1.1574 (19)	0.2906 (14)	0.1439 (14)	0.041 (4)*
H6C	1.0107 (16)	0.3754 (17)	0.1528 (11)	0.046 (4)*
H7A	1.3255 (19)	0.1171 (15)	0.3272 (12)	0.051 (4)*
H7B	1.2976 (18)	0.1068 (15)	0.4542 (14)	0.051 (5)*
H7C	1.1859 (17)	0.0430 (16)	0.3421 (12)	0.047 (4)*
H8A	0.9040 (16)	0.2120 (13)	0.5674 (12)	0.033 (4)*
H8B	1.0372 (15)	0.3472 (13)	0.5678 (10)	0.030 (4)*
H8C	1.1110 (16)	0.1800 (14)	0.5637 (11)	0.040 (4)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0208 (5)	0.0125 (5)	0.0170 (6)	−0.0037 (4)	0.0045 (4)	−0.0025 (5)
C2	0.0176 (5)	0.0210 (6)	0.0194 (6)	−0.0059 (4)	0.0047 (5)	−0.0015 (5)
C3	0.0166 (5)	0.0226 (6)	0.0197 (6)	0.0008 (4)	0.0061 (5)	−0.0010 (5)
C4	0.0167 (5)	0.0131 (5)	0.0161 (5)	0.0031 (4)	0.0046 (4)	0.0012 (4)
C5	0.0172 (5)	0.0173 (6)	0.0248 (6)	−0.0016 (4)	0.0057 (5)	−0.0027 (5)
C6	0.0239 (6)	0.0307 (7)	0.0183 (6)	−0.0053 (5)	0.0080 (5)	−0.0028 (5)
C7	0.0218 (6)	0.0198 (6)	0.0342 (7)	0.0042 (5)	0.0054 (6)	−0.0068 (6)
B	0.0217 (6)	0.0198 (6)	0.0128 (6)	−0.0014 (5)	0.0027 (5)	0.0012 (5)
N	0.0144 (4)	0.0098 (4)	0.0125 (4)	0.0001 (3)	0.0029 (4)	−0.0002 (3)
Si	0.01368 (16)	0.01410 (18)	0.01535 (19)	0.00015 (10)	0.00415 (12)	−0.00203 (12)

Geometric parameters (Å, º)

C1—N	1.5095 (14)	C5—H5B	0.959 (12)
C1—C2	1.5357 (17)	C5—H5C	0.931 (14)
C1—H1A	0.967 (12)	C6—Si	1.8606 (15)
C1—H1B	0.968 (12)	C6—H6A	0.893 (15)
C2—C3	1.5395 (18)	C6—H6B	0.980 (16)
C2—H2A	0.982 (12)	C6—H6C	0.971 (17)
C2—H2B	0.968 (12)	C7—Si	1.8551 (14)
C3—C4	1.5296 (16)	C7—H7A	0.943 (16)
C3—H3A	1.010 (12)	C7—H7B	0.969 (15)
C3—H3B	0.955 (13)	C7—H7C	0.925 (16)
C4—N	1.5068 (14)	B—N	1.6354 (17)
C4—H4A	0.967 (12)	B—H8A	1.104 (14)
C4—H4B	0.961 (11)	B—H8B	1.112 (13)
C5—Si	1.8553 (13)	B—H8C	1.121 (13)
C5—H5A	0.962 (14)	N—Si	1.8303 (13)
N—C1—C2	105.47 (9)	Si—C6—H6A	112.9 (10)
N—C1—H1A	107.0 (7)	Si—C6—H6B	108.4 (9)
C2—C1—H1A	115.4 (7)	H6A—C6—H6B	106.2 (12)
N—C1—H1B	108.7 (8)	Si—C6—H6C	111.4 (8)
C2—C1—H1B	110.8 (7)	H6A—C6—H6C	111.1 (12)
H1A—C1—H1B	109.2 (10)	H6B—C6—H6C	106.7 (11)
C1—C2—C3	105.57 (8)	Si—C7—H7A	108.1 (10)
C1—C2—H2A	110.7 (7)	Si—C7—H7B	111.0 (9)
C3—C2—H2A	113.0 (7)	H7A—C7—H7B	111.4 (13)
C1—C2—H2B	108.8 (7)	Si—C7—H7C	112.2 (9)
C3—C2—H2B	111.7 (8)	H7A—C7—H7C	104.5 (12)
H2A—C2—H2B	107.0 (10)	H7B—C7—H7C	109.5 (12)
C4—C3—C2	104.82 (9)	N—B—H8A	109.2 (7)
C4—C3—H3A	109.8 (7)	N—B—H8B	108.9 (6)
C2—C3—H3A	112.0 (7)	H8A—B—H8B	109.1 (9)
C4—C3—H3B	111.6 (8)	N—B—H8C	107.9 (7)
C2—C3—H3B	110.0 (8)	H8A—B—H8C	110.3 (10)
H3A—C3—H3B	108.7 (10)	H8B—B—H8C	111.4 (9)
N—C4—C3	104.97 (9)	C4—N—C1	102.14 (9)
N—C4—H4A	107.6 (7)	C4—N—B	110.97 (8)
C3—C4—H4A	115.0 (7)	C1—N—B	110.02 (8)
N—C4—H4B	108.0 (7)	C4—N—Si	112.67 (7)
C3—C4—H4B	109.2 (7)	C1—N—Si	112.16 (7)
H4A—C4—H4B	111.7 (9)	B—N—Si	108.77 (7)
Si—C5—H5A	111.9 (8)	N—Si—C7	108.42 (6)
Si—C5—H5B	110.3 (8)	N—Si—C5	108.43 (5)
H5A—C5—H5B	109.2 (11)	C7—Si—C5	113.07 (7)
Si—C5—H5C	108.0 (8)	N—Si—C6	108.71 (6)
H5A—C5—H5C	107.2 (11)	C7—Si—C6	108.96 (6)
H5B—C5—H5C	110.2 (11)	C5—Si—C6	109.17 (6)
N—C1—C2—C3	20.37 (11)	C4—N—Si—C7	−167.46 (7)
C1—C2—C3—C4	4.88 (11)	C1—N—Si—C7	−52.87 (9)
C2—C3—C4—N	−28.50 (11)	B—N—Si—C7	69.06 (8)
C3—C4—N—C1	41.07 (11)	C4—N—Si—C5	69.43 (9)
C3—C4—N—B	−76.15 (10)	C1—N—Si—C5	−175.98 (7)
C3—C4—N—Si	161.60 (7)	B—N—Si—C5	−54.05 (8)
C2—C1—N—C4	−37.80 (11)	C4—N—Si—C6	−49.15 (9)
C2—C1—N—B	80.10 (10)	C1—N—Si—C6	65.44 (8)
C2—C1—N—Si	−158.69 (7)	B—N—Si—C6	−172.63 (7)