Potassium [1-(tert-but­oxy­carbon­yl)-1H-indol-3-yl]trifluoro­borate hemihydrate

Guillaume Berionni; Peter Mayer; Herbert Mayr

doi:10.1107/S1600536812014225

. 2012 Apr 6;68(Pt 5):m551–m552. doi: 10.1107/S1600536812014225

Potassium [1-(tert-butoxycarbonyl)-1H-indol-3-yl]trifluoroborate hemihydrate

Guillaume Berionni ^a, Peter Mayer ^a,^*, Herbert Mayr ^a

PMCID: PMC3344307 PMID: 22590073

Abstract

The asymmetric unit of the title salt, K⁺·C₁₃H₁₄BF₃NO₂·0.5H₂O, consists of two derivatized indolyltrifluoridoborate anions, two potassium cations and one water molecule. Within the indolyltrifluoroborate anions, the least-square planes consisting of the carboxyl group and the adjacent quarternary C atom of the tert-butyl groups deviate significantly from coplanarity with the indolyl planes [20.44 (11) and 21.02 (10)°]. The potassium ions are coordinated by six atoms (one K⁺ ion by two O and four F atoms, and the second K⁺ ion by one O and five F atoms), however, one of the potassium ions undergoes an additional weak potassium–π interaction (K⋯centroid = 3.722 Å). The packing is stabilized by sequential O—H⋯O hydrogen bonds along [100] between water molecules and also by O—H⋯F hydrogen bonds.

Related literature

For background to organotrifluoroborates and the synthesis, see: Mothes et al. (2008 ▶); Molander et al. (2009 ▶); Kassis et al. (2009 ▶); Reiter et al. (2010 ▶); Darses & Genet (2008 ▶). For related structures, see: Baran et al. (2005 ▶); Davies et al. (2005 ▶, 2007 ▶); Lu & Lin (2011 ▶).

Experimental

Crystal data

K⁺·C₁₃H₁₄BF₃NO₂·0.5H₂O
M _r = 332.17
Orthorhombic,
a = 5.8428 (1) Å
b = 16.3177 (2) Å
c = 32.1286 (5) Å
V = 3063.17 (8) Å³
Z = 8
Mo Kα radiation
μ = 0.38 mm⁻¹
T = 173 K
0.27 × 0.19 × 0.10 mm

Data collection

Nonius KappaCCD diffractometer
24771 measured reflections
7001 independent reflections
6369 reflections with I > 2σ(I)
R _int = 0.027

Refinement

R[F ² > 2σ(F ²)] = 0.032
wR(F ²) = 0.075
S = 1.03
7001 reflections
400 parameters
2 restraints
H atoms treated by a mixture of independent and constrained refinement
Δρ_max = 0.30 e Å⁻³
Δρ_min = −0.24 e Å⁻³
Absolute structure: Flack (1983 ▶), 2995 Friedel pairs
Flack parameter: 0.00 (3)

Data collection: COLLECT (Hooft, 2004 ▶); cell refinement: SCALEPACK (Otwinowski & Minor, 1997 ▶); data reduction: DENZO (Otwinowski & Minor, 1997 ▶) and SCALEPACK; program(s) used to solve structure: SIR97 (Altomare et al., 1999 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: ORTEP-3 (Farrugia, 1997 ▶); software used to prepare material for publication: PLATON (Spek, 2009 ▶).

Supplementary Material

Crystal structure: contains datablock(s) I, global. DOI: 10.1107/S1600536812014225/hp2034sup1.cif

e-68-0m551-sup1.cif^{(45.2KB, cif)}

Structure factors: contains datablock(s) I. DOI: 10.1107/S1600536812014225/hp2034Isup2.hkl

e-68-0m551-Isup2.hkl^{(342.6KB, hkl)}

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Table 1. Hydrogen-bond geometry (Å, °).

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O5—H51⋯F3ⁱ	0.81 (1)	2.14 (1)	2.903 (2)	156 (3)
O5—H51⋯F1ⁱ	0.81 (1)	2.62 (2)	3.188 (2)	128 (2)
O5—H52⋯O5ⁱⁱ	0.81 (1)	2.41 (1)	3.1968 (16)	164 (3)

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Symmetry codes: (i) Inline graphic ; (ii) .

Acknowledgments

The authors thank Professor Peter Klüfers for generous allocation of diffractometer time.

supplementary crystallographic information

Comment

Organotrifluoroborates and, in particular, indolyltrifluoroborates [Molander et al. (2009), Kassis et al. (2009), Reiter et al. (2010)] are synthetically useful nucleophiles for Suzuki-Miyaura cross-coupling and other CC bond-forming reactions [Darses & Genet (2008)].

The asymmetric unit contains two formula units of the title compound (Fig. 1). The B–C bond distances in the two indolyltrifluoroborate anions are found to be 1.596 (3) Å and 1.600 (3) Å. These bond distances are close to the mean distance of 1.619 Å determined from 33 crystal structures of organotrifluoroborates (CSD version 5.33, Nov 2011). In the title compound, the 1-tert-butoxycarbonyl group is not coplanar with the indolyl ring, but deviates with plane-plane angles of 20.44 (11)° and 21.02 (10)°, in which the plane of a tert-butoxycarbonyl group is defined by its C and O atoms with the exception of the methyl groups. This structural feature is observed in several of the dozen of crystal structures of 3-substituted 1-(tert-Butoxycarbonyl)-1H-indolyl derivatives [Baran et al. (2005), Davies et al. (2005), Davies et al. (2007) and Lu & Lin (2011)].

The coordination sphere of K1 consists of two oxygen atoms and four fluorine atoms in bond distances ranging between 2.58 Å and 2.99 Å. Additionally the five-membered ring of an adjacent indolyl moiety is bound by a weak potassium-π interaction (distance K1–Cg(N2, C14—C17) = 3.722 Å). The other potassium ion is coordinated by five fluorine atoms and one oxygen atom in bond distances ranging from 2.62 Å to 2.77 Å. The water molecule is coordinated solely to K1 and forms sequential hydrogen bonds of the type O–H···O along [100]. The other proton of the water molecule acts as donor in hydrogen bonds of the type O–H···F. Layers parallel to ab are formed by the combination of hydrogen bonds and coordination of the potassium ions (Fig. 2). Weak C–H···π interactions between methyl-hydrogen atoms and the six-membered rings of the indolyl moieties are established with C···Cg distances of 3.836 (3) Å and 3.715 (2) Å. The packing of the title compound is shown in Fig. 3.

Experimental

In a 100 ml Schlenck flask under argon, 1.00 g (2.92 mmol,1 eq.) of tert-butyl-3-iodo-1H-indole-1-carboxylate [Mothes et al. (2008)] was dissolved in 20 ml of freshly distilled THF and cooled to -78 °C. With a syringe, 1.37 ml of nBuLi (2.13 M in hexane, 2.92 mmol,1 eq.) was added dropwise, and the solution was stirred for 30 min at this temperature whilst turning orange pale. Neat triisopropyl borate (3.36 mmol, 0.55 ml, 1.15 eq.) was then slowly dropped to the mixture, and after removing the cooling bath the temperature reached 0 °C in 30 min. An aqueous solution of KHF₂ (17.5 mmol, 1.35 g, 6 eq. dissolved in 5 ml of H₂O) was added slowly to the limpid solution under vigorous stirring and after 15 minutes the solvents were removed in vacuo. The waxy solid was dissolved in 50 ml of hot acetone and filtrated. The filtrate was concentrated to 10 ml before adding 10 ml of diethylether. After one night in the fridge, colorless crystalline plates of the title compound were obtained (650 mg, 70%).