The title compound, [Zn(C6H5)2(C5H5N)2], (I), forms conformationally chiral molecules residing on a twofold axis. The molecules are stacked along c, and these stacks are associated by edge-to-face π–π interactions. Crystals of (I) belong to the Sohncke space group P21212 and the crystal lattice of (I) is chiral. The crystal batch that was examined consisted of a mixture of enantiomerically pure crystals and crystals twinned by inversion.
Supporting information
CCDC reference: 735112
Bromobenzene (4.1 ml, 0.039 mol) was added to a stirred mixture of magnesium
(1.1 g, 0.045 mol) and diethyl ether (40 ml). The mixture was stirred
overnight at ambient temperature. The solution was added dropwise to a
suspension of zinc chloride (2.6 g, 0.019 mol) in diethyl ether (10 ml) at 273 K. The reaction mixture was stirred at ambient temperature overnight,
evaporated and sublimated at 10-2 mbar (1 mbar = 100 Pa). The white product
was dissolved in toluene (4 ml). An excess of pyridine (1 ml) was added,
whereupon a precipitate formed. The mixture was heated to reflux, and slowly
allowed to reach ambient temperature, whereupon colourless crystals of (I)
formed.
All H atoms were included in calculated positions and refined using a riding
model with C—H = 0.93 Å and Uiso(H) = 1.2Ueq(C).
Data collection: CrystalClear (Rigaku, 2000); cell refinement: CrystalClear (Rigaku, 2000); data reduction: CrystalClear (Rigaku, 2000); program(s) used to solve structure: SIR92 (Altomare et al., 1993); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 (Farrugia, 1997) and PLATON (Spek, 2009); software used to prepare material for publication: SHELXL97 (Sheldrick,2008).
Diphenyldipyridinezinc(II)
top
Crystal data top
[Zn(C6H5)2(C5H5N)2] | F(000) = 392 |
Mr = 377.79 | Dx = 1.375 Mg m−3 |
Orthorhombic, P21212 | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: P 2 2ab | Cell parameters from 5959 reflections |
a = 11.931 (2) Å | θ = 3.2–25.5° |
b = 12.157 (2) Å | µ = 1.35 mm−1 |
c = 6.2921 (13) Å | T = 100 K |
V = 912.6 (3) Å3 | Prism, white |
Z = 2 | 0.4 × 0.3 × 0.2 mm |
Data collection top
Rigaku R-AXIS IIC image-plate system diffractometer | 1672 independent reflections |
Radiation source: rotating-anode X-ray tube, Rigaku RU-H3R | 1644 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.022 |
Detector resolution: 105 pixels mm-1 | θmax = 25.5°, θmin = 3.2° |
ϕ scans | h = −14→14 |
Absorption correction: multi-scan (CrystalClear; Rigaku, 2000) | k = −14→14 |
Tmin = 0.551, Tmax = 0.767 | l = −7→7 |
5959 measured reflections | |
Refinement top
Refinement on F2 | Secondary atom site location: difference Fourier map |
Least-squares matrix: full | Hydrogen site location: inferred from neighbouring sites |
R[F2 > 2σ(F2)] = 0.017 | H-atom parameters constrained |
wR(F2) = 0.046 | w = 1/[σ2(Fo2) + (0.0302P)2 + 0.1732P] where P = (Fo2 + 2Fc2)/3 |
S = 1.04 | (Δ/σ)max < 0.001 |
1672 reflections | Δρmax = 0.26 e Å−3 |
124 parameters | Δρmin = −0.36 e Å−3 |
0 restraints | Absolute structure: Flack (1983) |
Primary atom site location: structure-invariant direct methods | Absolute structure parameter: 0.061 (10) |
Crystal data top
[Zn(C6H5)2(C5H5N)2] | V = 912.6 (3) Å3 |
Mr = 377.79 | Z = 2 |
Orthorhombic, P21212 | Mo Kα radiation |
a = 11.931 (2) Å | µ = 1.35 mm−1 |
b = 12.157 (2) Å | T = 100 K |
c = 6.2921 (13) Å | 0.4 × 0.3 × 0.2 mm |
Data collection top
Rigaku R-AXIS IIC image-plate system diffractometer | 1672 independent reflections |
Absorption correction: multi-scan (CrystalClear; Rigaku, 2000) | 1644 reflections with I > 2σ(I) |
Tmin = 0.551, Tmax = 0.767 | Rint = 0.022 |
5959 measured reflections | |
Refinement top
R[F2 > 2σ(F2)] = 0.017 | H-atom parameters constrained |
wR(F2) = 0.046 | Δρmax = 0.26 e Å−3 |
S = 1.04 | Δρmin = −0.36 e Å−3 |
1672 reflections | Absolute structure: Flack (1983) |
124 parameters | Absolute structure parameter: 0.061 (10) |
0 restraints | |
Special details top
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 (Å2) top | x | y | z | Uiso*/Ueq | |
C1 | 0.35104 (12) | 0.51973 (12) | 0.5765 (2) | 0.0126 (3) | |
C2 | 0.33527 (13) | 0.60603 (13) | 0.4290 (3) | 0.0140 (3) | |
H2 | 0.3915 | 0.6585 | 0.4142 | 0.018 (5)* | |
C3 | 0.23879 (13) | 0.61611 (12) | 0.3052 (3) | 0.0155 (3) | |
H3 | 0.2316 | 0.6748 | 0.2113 | 0.021 (5)* | |
C4 | 0.15420 (13) | 0.53868 (13) | 0.3222 (3) | 0.0154 (3) | |
H4 | 0.0901 | 0.5445 | 0.2388 | 0.017 (5)* | |
C5 | 0.16567 (13) | 0.45229 (14) | 0.4649 (3) | 0.0160 (3) | |
H5 | 0.1094 | 0.3997 | 0.4766 | 0.018 (5)* | |
C6 | 0.26204 (13) | 0.44414 (13) | 0.5897 (2) | 0.0143 (3) | |
H6 | 0.2674 | 0.3866 | 0.6866 | 0.017 (5)* | |
C7 | 0.39766 (13) | 0.36116 (14) | 1.0858 (3) | 0.0150 (3) | |
H7 | 0.3504 | 0.4215 | 1.1009 | 0.021 (5)* | |
C8 | 0.37750 (14) | 0.26805 (14) | 1.2085 (3) | 0.0185 (3) | |
H8 | 0.3179 | 0.2663 | 1.3038 | 0.021 (5)* | |
C9 | 0.44804 (15) | 0.17815 (14) | 1.1869 (3) | 0.0195 (3) | |
H9 | 0.4360 | 0.1144 | 1.2654 | 0.020 (5)* | |
C10 | 0.53713 (14) | 0.18426 (13) | 1.0461 (3) | 0.0177 (3) | |
H10 | 0.5865 | 0.1256 | 1.0305 | 0.018 (5)* | |
C11 | 0.55105 (14) | 0.27996 (13) | 0.9284 (2) | 0.0149 (3) | |
H11 | 0.6104 | 0.2836 | 0.8329 | 0.022 (5)* | |
N1 | 0.48256 (11) | 0.36714 (10) | 0.94604 (19) | 0.0128 (3) | |
Zn1 | 0.5000 | 0.5000 | 0.72282 (3) | 0.01101 (8) | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
C1 | 0.0131 (6) | 0.0153 (9) | 0.0094 (6) | 0.0002 (6) | 0.0018 (5) | −0.0027 (6) |
C2 | 0.0143 (7) | 0.0138 (7) | 0.0140 (7) | −0.0032 (6) | 0.0012 (6) | −0.0009 (6) |
C3 | 0.0202 (7) | 0.0132 (7) | 0.0129 (7) | 0.0041 (6) | −0.0003 (6) | 0.0006 (6) |
C4 | 0.0120 (7) | 0.0197 (7) | 0.0144 (8) | 0.0023 (6) | −0.0025 (6) | −0.0026 (6) |
C5 | 0.0123 (7) | 0.0180 (7) | 0.0179 (9) | −0.0041 (6) | 0.0010 (6) | −0.0025 (7) |
C6 | 0.0158 (8) | 0.0136 (7) | 0.0136 (8) | 0.0003 (7) | 0.0005 (6) | 0.0017 (6) |
C7 | 0.0140 (7) | 0.0176 (8) | 0.0132 (7) | −0.0005 (7) | 0.0001 (6) | −0.0025 (6) |
C8 | 0.0189 (7) | 0.0248 (8) | 0.0119 (7) | −0.0067 (7) | 0.0006 (6) | −0.0009 (7) |
C9 | 0.0285 (8) | 0.0168 (8) | 0.0131 (8) | −0.0066 (7) | −0.0053 (7) | 0.0020 (6) |
C10 | 0.0235 (8) | 0.0127 (7) | 0.0168 (9) | 0.0031 (6) | −0.0060 (6) | −0.0024 (6) |
C11 | 0.0156 (7) | 0.0174 (8) | 0.0117 (7) | 0.0019 (7) | −0.0002 (6) | −0.0014 (6) |
N1 | 0.0140 (7) | 0.0131 (6) | 0.0112 (5) | 0.0001 (5) | −0.0022 (5) | −0.0006 (4) |
Zn1 | 0.00980 (12) | 0.01206 (12) | 0.01117 (12) | 0.00009 (11) | 0.000 | 0.000 |
Geometric parameters (Å, º) top
C1—C6 | 1.407 (2) | C7—N1 | 1.344 (2) |
C1—C2 | 1.413 (2) | C7—C8 | 1.391 (2) |
C1—Zn1 | 2.0158 (15) | C7—H7 | 0.9299 |
C2—C3 | 1.395 (2) | C8—C9 | 1.386 (3) |
C2—H2 | 0.9300 | C8—H8 | 0.9300 |
C3—C4 | 1.384 (2) | C9—C10 | 1.386 (2) |
C3—H3 | 0.9300 | C9—H9 | 0.9300 |
C4—C5 | 1.388 (2) | C10—C11 | 1.389 (2) |
C4—H4 | 0.9299 | C10—H10 | 0.9301 |
C5—C6 | 1.396 (2) | C11—N1 | 1.343 (2) |
C5—H5 | 0.9301 | C11—H11 | 0.9300 |
C6—H6 | 0.9300 | N1—Zn1 | 2.1505 (12) |
| | | |
C6—C1—C2 | 115.04 (14) | C8—C7—H7 | 118.7 |
C6—C1—Zn1 | 124.11 (11) | C9—C8—C7 | 118.82 (16) |
C2—C1—Zn1 | 120.37 (11) | C9—C8—H8 | 120.6 |
C3—C2—C1 | 122.80 (14) | C7—C8—H8 | 120.6 |
C3—C2—H2 | 118.6 | C8—C9—C10 | 119.09 (15) |
C1—C2—H2 | 118.6 | C8—C9—H9 | 120.7 |
C4—C3—C2 | 119.90 (15) | C10—C9—H9 | 120.2 |
C4—C3—H3 | 120.2 | C9—C10—C11 | 118.52 (15) |
C2—C3—H3 | 119.9 | C9—C10—H10 | 120.8 |
C3—C4—C5 | 119.52 (14) | C11—C10—H10 | 120.7 |
C3—C4—H4 | 120.2 | N1—C11—C10 | 122.97 (15) |
C5—C4—H4 | 120.2 | N1—C11—H11 | 118.7 |
C4—C5—C6 | 119.91 (15) | C10—C11—H11 | 118.4 |
C4—C5—H5 | 120.0 | C11—N1—C7 | 118.04 (14) |
C6—C5—H5 | 120.1 | C11—N1—Zn1 | 118.68 (11) |
C5—C6—C1 | 122.83 (15) | C7—N1—Zn1 | 122.77 (11) |
C5—C6—H6 | 118.6 | C1—Zn1—C1i | 125.65 (8) |
C1—C6—H6 | 118.6 | C1—Zn1—N1i | 107.11 (5) |
N1—C7—C8 | 122.53 (15) | C1—Zn1—N1 | 107.60 (5) |
N1—C7—H7 | 118.7 | N1i—Zn1—N1 | 98.45 (7) |
Symmetry code: (i) −x+1, −y+1, z. |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
C9—H9···C5ii | 0.93 | 2.87 | 3.765 (2) | 162 |
C4—H4···C10iii | 0.93 | 2.90 | 3.703 (2) | 146 |
Symmetry codes: (ii) −x+1/2, y−1/2, −z+2; (iii) −x+1/2, y+1/2, −z+1. |
Experimental details
Crystal data |
Chemical formula | [Zn(C6H5)2(C5H5N)2] |
Mr | 377.79 |
Crystal system, space group | Orthorhombic, P21212 |
Temperature (K) | 100 |
a, b, c (Å) | 11.931 (2), 12.157 (2), 6.2921 (13) |
V (Å3) | 912.6 (3) |
Z | 2 |
Radiation type | Mo Kα |
µ (mm−1) | 1.35 |
Crystal size (mm) | 0.4 × 0.3 × 0.2 |
|
Data collection |
Diffractometer | Rigaku R-AXIS IIC image-plate system diffractometer |
Absorption correction | Multi-scan (CrystalClear; Rigaku, 2000) |
Tmin, Tmax | 0.551, 0.767 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 5959, 1672, 1644 |
Rint | 0.022 |
(sin θ/λ)max (Å−1) | 0.606 |
|
Refinement |
R[F2 > 2σ(F2)], wR(F2), S | 0.017, 0.046, 1.04 |
No. of reflections | 1672 |
No. of parameters | 124 |
H-atom treatment | H-atom parameters constrained |
Δρmax, Δρmin (e Å−3) | 0.26, −0.36 |
Absolute structure | Flack (1983) |
Absolute structure parameter | 0.061 (10) |
Selected geometric parameters (Å, º) topC1—Zn1 | 2.0158 (15) | N1—Zn1 | 2.1505 (12) |
| | | |
C1—Zn1—C1i | 125.65 (8) | C1—Zn1—N1 | 107.60 (5) |
C1—Zn1—N1i | 107.11 (5) | N1i—Zn1—N1 | 98.45 (7) |
Symmetry code: (i) −x+1, −y+1, z. |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
C9—H9···C5ii | 0.930 | 2.870 | 3.765 (2) | 162.11 |
C4—H4···C10iii | 0.930 | 2.899 | 3.703 (2) | 145.51 |
Symmetry codes: (ii) −x+1/2, y−1/2, −z+2; (iii) −x+1/2, y+1/2, −z+1. |
Optical resolution is usually time consuming (Faigl et al., 2008), but in a few rare cases spontaneous resolution may occur. It has been estimated to occur for less than 10% of crystalline racemates (Jacques et al., 1981) and involves the crystallization of a racemate in one of the 65 Sohncke space groups (Flack, 2003). Chiral molecules which are stereochemically labile in solution may undergo total spontaneous resolution, also known as crystallization-induced asymmetric transformation (Jacques et al., 1984). This is a phenomenon where the whole batch of crystals originates from a single-crystal nucleus and a fast enantiomerization in the solution converts all material in solution into the crystallizing enantiomer. Under favourable circumstances the entire amount of racemate may be converted to a pure enantiomer in quantitative yield. It has been observed that slow stirring may be beneficial for crystallization-induced asymmetric transformation (Kondepudi et al., 1990; McBride & Carter, 1991; Pagni & Compton, 2002). Since a racemic mixture is transformed into an optically active substance without the use of chiral reagents or catalysts, crystallization-induced asymmetric transformation is an important strategy for absolute asymmetric synthesis i.e. the creation of optically active substances from achiral or racemic starting materials only (Feringa & Van Delden, 1999). Over the years we have studied the total spontaneous resolution of stereochemically labile chemical reagents (Lennartson et al., 2009; Vestergren et al., 2000, 2003; Håkansson et al., 1999) and potential substrates (Johansson & Håkansson, 2005; Lennartson, Salo et al., 2005; Andersson et al., 1986, Lennartson et al., 2007). During a study of (diphenyl)zinc complexes, it was found that diphenyl(dipyridyl)zinc(II), (I), crystallizes in the Sohnke space group P21212.
The molecules of (I) are located on a twofold axis, and the molecules are therefore C2 symmetric. The coordination geometry around Zn1 is distorted tetrahedral (Fig. 1). The molecules of (I) are conformationally chiral due to the orientations of the aromatic rings surrounding the central Zn atom as in Fig. 2. The enantiomerization barrier between the two enantiomers can be expected to be very low, and the conformational chirality of (I) will be immediately lost upon dissolution of the crystals, one of the requirements for total spontaneous resolution.
Only a limited number of diphenylzinc structures are reported in the Cambridge Structural Database (CSD, version 5.29 of November 2007; Allen, 2002). Unsolvated diphenylzinc forms a dimer with two three-coordinate Zn atoms bridged by two phenyl groups (Markies et al., 1990). There are another five structures where diphenylzinc coordinates crown ethers (Markies et al., 1991; Fabicon et al., 1999; Kooijman et al., 2007), two examples of coordination to glyme ligands (Markies et al., 1992) and a complex with thiophene (Dickson et al., 2000). The thiophene complex is dimeric with two distorted tetrahedral Zn atoms bridged by two phenyl groups, and the structure is therefore very different from (I). The other seven complexes also differ from (I), since the C—Zn—C angles are considerably larger, approximately 140–150° compared with 125.65 (8)° in (I). The C—Zn—C angle in the (2)-(diphenyl)zinc(18-crown-6)rotaxane is 174.5 (1)° (Fabicon et al., 1999). These differences are rational, since pyridine appears to coordinate stronger than the ligands previously employed. The Zn—N distances in (I) are 2.1505 (12) Å, while the Zn—O distances in the rotaxane approaches 3 Å. Monomeric Lewis base free dialkylzinc compounds are reported to be linear (Almenningen et al., 1982; Lewinski et al., 2007), and this rule also applies to monomeric diarylzinc compounds, viz. dimesitylzinc (Cole et al., 2003). Weaker coordinating ligands would therefore be expected to give rise to larger C—Zn—C angles. A few structures with one phenyl group attached to Zn have also been published, e.g. di-µ-phenoxido-bis[(diethyl ether)phenylzinc(II)], which we recently reported (Lennartson & Håkansson, 2008). The dinuclear phenylzinc amide bis[µ2-phenyl-C,C)-{µ2-4,6-bis(dimethylamino)ethylamido}dibenzofuran-N,N',N'',N''']dizinc (Hlavinka & Hagadorn, 2005) is also related to (I), since it has an N-donor ligand rather than the O-donor ligands which appear to be more abundant among the structures previously reported in the CSD.
The molecules in (I) are stacked along c, and molecules of the same chiral sense will fit perfectly on top of each other. There are no unambiguous indications of interactions within these stacks, although there is one intermolecular distance (2.89 Å) within the sum of the van der Waals radii between H8 and C6 (at x, y, 1 + z). Each stack is surrounded by four adjacent stacks, and these stacks appears to be held together by means of edge-to-face π–π-interactions resulting in a network structure (Fig. 3). Each aromatic ring acts both as a donor and as an acceptor. There are two independent sets of interactions in (I), the shortest intermolecular distances being H9···C5 (at 1/2-x, -1/2+y, 2 - z) with a distance of 2.87 Å and H4···C10(1/2 + x, 1/2 - y, 1 - z) with a distance of 2.90 Å. Due to the molecular symmetry, each molecule will be engaged in eight interactions, four of each kind.
Organozinc reagents readily undergo nucleophilic addition to aldehydes and ketones, and the reaction of (I) with a prochiral aldehyde is expected to give rise to a chiral product. If crystallization-induced asymmetric transformation of (I) could be preformed[performed?], it would perhaps be possible to use (I) as a chiral reagent and to obtain an optically active alcohol. This would be similar to the reaction of octahedral `chiral-at-Mg' Grignard reagents with prochiral aldehydes, which give up to 22% enantiomeric excess (Vestergren et al., 2003). Reaction conditions that prevent the reagent from dissolving are required, e.g. a solid-state reaction with an aldehyde. The formation of a solid-state melt could, however, be a potential problem. A problem encountered during crystallization of (I), compared to the Grignard reagents, is a tendency for twinning by inversion. Three crystals from the same crystal batch were picked for absolute structure determination, and two of these crystals were found to be twinned, and almost racemic. Complete spontaneous resolution of (I) would therefore require rigorously controlled crystallization conditions (Gervais et al., 2002; Perez-Garcia & Amabilino, 2002). Determination of an e.e. in a microcrystalline bulk sample of (I) using solid-state CD spectroscopy (Lennartson, Vestergren et al., 2005) would be very difficult due to the high air sensitivity of (I).