Article Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
pubs.acs.org/IC
Types of Six-Membered N‑Heterocyclic Germanium Radicals: A Combined Computational and Experimental Study Jiaxiu Yu,†,‡ Yingying Qin,†,‡ Gengwen Tan,§ Huan Wang,⊥ Hecong Cheng,† Wenyuan Wang,*,† and Anyang Li*,†
Inorg. Chem. Downloaded from pubs.acs.org by UNIV AUTONOMA DE COAHUILA on 04/05/19. For personal use only.
†
Key Laboratory of Synthetic and Natural Functional Molecule Chemistry, Ministry of Education, College of Chemistry and Materials Science, Northwest University, Xi’an 710127, China § State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China ⊥ College of Chemistry and Chemical Engineering, Xianyang Normal University, Xianyang 712000, China S Supporting Information *
ABSTRACT: A new stable six-membered cyclic germylene radical C (•L3Ge:; •L3 = •[CH3C(PhCN−Dip)2]2−, where Dip = 2,6-iPr2C6H3) has been synthesized and structurally characterized. Unlike the germanium-centered radical A (L1•Ge:, L1 = [HC(tBuCN−Dip)2]−), C is a π-type radical with spin density mainly distributed on the NC3N backbone, similar to that in the germylene radical B (•L2Ge:; •L2 = • [PhC(PhCN−Dip)2]2−). The electronic effects in sixmembered N-heterocyclic germanium radicals were systematically investigated using density functional theory calculations. The type of radical, which basically depends on the strong inductive effect of substituents on the side C atoms of the NC3N backbone, is confirmed by monitoring the change in the ordering of the frontier molecular orbitals during radical formation. However, the radical with moderately electronegative substituents or two substituents with comparable electron pushing and pulling abilities could not be isolated in experiments, probably because of the kinetic instability during the reduction process from the germylene chloride precursor to radical.
1. INTRODUCTION Most radicals are short-lived species because of their high reactivity. With careful design, some radicals can have relatively longer lifetimes, enabling them to be detected by electron paramagnetic resonance (EPR) spectroscopy and even to be isolated as stable compounds. In the past decades, a variety of stable radicals with heavier main-group elements have been synthesized and structurally characterized.1 Nevertheless, the structural and theoretical investigation of these radicals remains a challenge,2 especially for the low-coordinate radical species (coordination numbers of less than 3). These were rarely reported because of the lack of steric protection due to the very low coordination number. In 2011, the first twocoordinate germanium radical A (Scheme 1; L1•Ge:, L1 = [HC(tBuCN−Dip)2]−, where Dip = 2,6-iPr2C6H3) supported by a β-diketiminate ligand was isolated by Jones and coworkers.3 A is a GeI-centered radical with spin density mainly located in the Ge 4p orbital, which has been validated by the calculations. Recently, using a β-diketiminate ligand with three phenyl substituents on the ligand backbone, we successfully synthesized the low-coordinate stable neutral germylene radical B(•L2Ge:, •L2 = •[PhC(PhCN−Dip)2]2−),4 which contains the same six-membered N-heterocyclic NC3NGe ring as A, in which the unpaired electron is located on the ligand. The singlet occupied molecular orbital (SOMO) of B is a π© XXXX American Chemical Society
Scheme 1. Reported Stable Low-Coordinate Germanium Radicals3,4
antibonding orbital on the NC3N backbone, and its spin density is mainly distributed on N and C atoms, instead of the Ge atom in the case of A. On the basis of the characteristics of their spin-density distributions, we term A as a “p-type” radical and B as a “π-type” radical in this paper. The distinction between A and B could be attributed to different substituents on their β-diketiminate ligands, and the electron density on the metal can be tuned by the introduction of electron-withdrawing or -donating groups on the β-diketiminate ligand.5 In order to correlate the electronic effects in germanium βdiketiminate complexes with the types of germanium radicals, Received: January 6, 2019
A
DOI: 10.1021/acs.inorgchem.9b00034 Inorg. Chem. XXXX, XXX, XXX−XXX
Article
Inorganic Chemistry
[95.72(15)°] and B (95.86°) are almost equal, while they are around 4° larger than that in radical A (91.97°). For the most important bond lengths of C, the Ge−N distances of 1.836(3) and 1.857(4) Å are very close to the corresponding bond lengths of B (1.855 and 1.859 Å) but significantly shorter than the Ge−N distances (both of 1.9988 Å) in radical A. The EPR measurements and theoretical calculations revealed the unpaired electron distributions of C (Figure S8 and Tables S5−S8). Figure 2 shows the spin-density distribution of radical C and a comparison with those of radicals A and B. The differences between the radicals A and B or C could be attributed to their different substituents on the side C atoms of the backbone (C1 and C3). The electron-withdrawing phenyl groups make B and C π-type radicals, while A is a p-type radical because of its electron-donating tert-butyl substituents. The crystal structures of the corresponding precursors, germylene chlorides A-Cl, B-Cl, and C-Cl have been reported previously.4,6,7 Their core structural parameters are very similar (Table S9). Moreover, the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) types for A-Cl, B-Cl, and C-Cl are similar as well, as shown in Figure 3. The reduction from LGe-Cl to the •LGe: radical is proposed to occur in the following way: first LGe-Cl gains an electron to become a radical anion, and then the Cl atom is dissociated from the Ge atom, taking a negative charge away as a result of salt forming with the Na+ cation in the solution. To give insight into the dissociation of Cl−, the geometries of ACl− and C-Cl− are optimized with fixed Ge−Cl distances at the UM06-2X+D3/6-31G* level. Figure 4 shows variations of the potential energies of A-Cl− and C-Cl− along with the distance between Ge and Cl. In comparison to the relatively smooth red curve for C-Cl−, the black curve for A-Cl− has a cusp near 3 Å, which indicates a significant change of the geometry and electronic configuration. Indeed, the bond lengths and angles on the six-membered ring of A-Cl− change significantly with an increase of the Ge−Cl distance from 3.2 to 3.3 Å, while the corresponding bond lengths of C-Cl− exhibit a continuous change in the entire range, as shown in the inset of Figure 4. In the molecules of negatively charged germylene chloride, the single electron preferentially occupies the π-type LUMO of the previous neutral germylene chloride (Figure 3). This orbital has thus become the SOMO in anionic A-Cl− and CCl−. As the Ge−Cl distance increases, the Ge−Cl bond breaks and a Ge-center p-type orbital becomes the new LUMO. For C-Cl−, this π-type molecular orbital (MO) has always been the SOMO, and no electron locates in this p-type LUMO after the dissociation of Cl−. Under this electronic configuration, the spin-density distribution is mainly on the NC3N backbone. The spin-density distribution on Ge is relatively less. Similar to C-Cl−, the Ge-center p-type MO of A-Cl− is higher than the πtype MO, and the energy gap is almost the same at the beginning of Cl anion elimination. Nevertheless, when the Ge−Cl distance changes to near 3.3 Å, the energy order of the π- and p-type MOs suddenly exchanges with a change of the molecular geometry (Figure 5). After this energy-level transition of the two orbitals, a single electron occupies this p-type orbital and remains in this state throughout the dissociation process. This Ge-center p-type SOMO makes the electron spin density concentrated around the Ge atom. It is worth noting that the potential energy surface of A-Cl− has some discontinuities, with the Ge−Cl distance in the range of 8−10 Å (Figure 4). This is mainly due to the fact that the Cl atom is biased toward the substituents on the side of the ring
we systematically investigated the nature characters of sixmembered N-heterocyclic germanium radicals with different substituents on β-diketiminate ligands. In this work, a new lowcoordinate germanium radical was synthesized and structurally characterized. In addition, the precursor for another lowcoordinate germanium radical is described. Density functional theory (DFT) methods were used to simulate the generation pathways of radicals and estimate their stabilities. The computational results matched the experimental data very well and enabled further understanding of the low-coordinate radicals.
2. RESULTS AND DISCUSSION 2.1. Formation Mechanism of p- and π-Type Germanium Radicals. With the usage of β-diketimine [L3H = CH3CH(PhCN−Dip)2], which possesses a methyl and two phenyl groups at the ligand backbone, a new βScheme 2. Synthesis of Radical Germylene C from βDiketiminatogermylene Chloride C-Cl
diketiminatogermanium radical complex C (Scheme 2; •L3Ge:; • 3 L = •[CH3C(PhCN−Dip)2]2−) has been generated via a reductive dehalogenation from the germylene chloride precursor C-Cl (L3GeCl).6 Single crystals of C suitable for X-ray diffraction (XRD) are obtained from a hexane solution at −20 °C. The substituent groups on the backbone C atoms are believed to have a great influence on the core structures of βdiketiminate metal complexes, except the central C atom (C2 in Figure 1).5 As expected, the molecular structure of C (Figure 1) exhibits a nonplanar six-membered C3N2Ge ring, which is similar to the observation in radical B, whereas radical A has a planar ring. The N1−Ge1−N2 bond angles in C
Figure 1. Molecular structure of C. Thermal ellipsoids are drawn at 30% probability level. H atoms are omitted for clarity. Selected bond lengths [Å] and angles [deg]: Ge1−N1 1.836(3), Ge1−N2 1.857(4), N1−C1 1.406(5), N2−C3 1.408(5), C1−C2 1.387(6), C2−C3 1.402(6); N1−Ge1−N2 95.72(15), C1−N1−Ge1 126.4(3), C3− N2−Ge1 126.5(3), C1−C2−C3 125.7(4). B
DOI: 10.1021/acs.inorgchem.9b00034 Inorg. Chem. XXXX, XXX, XXX−XXX
Article
Inorganic Chemistry
Figure 2. Spin-density distributions for radicals A−C at the UM06-2X/6-311+G* level. H atoms are not shown (isosurface ± 0.001 au).
Figure 3. Frontier MOs of germylene chlorides A-Cl, B-Cl, and C-Cl. H atoms are not shown.
Figure 4. Potential energy surfaces of A-Cl− and C-Cl− at the optimized geometries with a fixed Ge−Cl distance. Inset: Variations of the mean Ge−N bond length as a function of the Ge−Cl distance.
in the optimized geometries for A-Cl−, while the electronic configurations (or energy levels of orbitals) do not change in this region. 2.2. Effect of the Substituents. The phenyl ring (in B and C) and tert-butyl group (in A) are typical electronwithdrawing and -donating substituents. The strong electronreleasing tert-butyl group in A pushes electrons toward the Ge atom in the six-membered C3N2Ge ring, while the corresponding electrons are pulled away by the phenyl group in B and C, leading to an electron-rich C3N2Ge ring in A and an electrondeficient C3N2Ge ring in B and C. Therefore, the spin density in A resides at the Ge center, and it is preferred that the spin densities in B and C are on the NC3N backbone. To quantify
Figure 5. Variations of the energies of p- and π-type MOs along with the distance between Ge and Cl of A-Cl− and C-Cl−, where the lower one is always the SOMO. During the dissociation of Cl−, the π- and ptype MOs of C-Cl− keep their energy levels in order, while there is an exchange of energy levels between these two types of MOs of A-Cl−. H atoms are not shown in the MO figures.
the substituent effect and develop new types of radicals, a series of model radicals with different substitutions are calculated by DFT to investigate the correlation between the group electronegativities of substituents and the types of C
DOI: 10.1021/acs.inorgchem.9b00034 Inorg. Chem. XXXX, XXX, XXX−XXX
Article
Inorganic Chemistry radicals. In all of the model systems, the Dip groups are replaced by phenyl groups, and the substituent on the central C atom (C2) of the six-membered ring is replaced by a H atom. Table 1 shows the optimized bond lengths of Ge−N and N−C and the N−Ge−N bond angle of model radicals with Table 1. Optimized Geometries of Model Radicals with Two Identical Substituents and the Corresponding Types of Radicals RSuba
χb
RGe−N (Å)
RC−N (Å)
θN−Ge−N (deg)
type
−PH2 −tBu −CH3 −CH2OH −SH −NH2 −OH −CCH −CHO −COOH −CN −CH2F (M1)c −CH2F (M2)c −CHF2 −CF3
2.154 2.289 2.331 2.491 2.501 2.437 2.585 2.530 2.647 2.769 2.792 2.644 2.644 3.026 3.405
2.041 2.039 2.031 2.030 2.038 2.023 2.044 1.880 1.885 1.889 1.887 1.880 2.037 1.881 1.884
1.319 1.325 1.323 1.325 1.316 1.332 1.313 1.405 1.396 1.392 1.395 1.404 1.321 1.401 1.395
87.87 90.16 87.92 87.69 87.15 88.00 87.63 95.82 95.30 95.72 95.15 95.88 87.39 95.62 95.60
p p p p p p p π π π π π p π π
Figure 6. Spin-density distributions of four isomers of model radicals with CH2F as substituents on the side C atom of the six-membered ring backbone.
geometries and spin-density distributions. Table 2 gives the optimized Ge−N bond lengths and N−Ge−N bond angle and Table 2. Optimized Geometries of Model Radicals with Two Different Substituents and the Corresponding Types of the Radicals
a
The model radical:
χ is the group electronegativity from ref 8. cM1 and M2 are two isomers of the model radical displayed in Figure 6. b
two identical substituents. The structure of these rings can be classified into two types, where the Ge−N bond length is either about 2.0 Å or less than 1.9 Å and the corresponding N−C bond length and N−Ge−N bond angle are either ∼1.3 Å and ∼90° or ∼1.4 Å and ∼95°, respectively. On the basis of the optimized geometries, the calculated spin-density distributions exhibit only two types, without a third type or even an intermediate state. In different substituent functionalized βdiketiminato systems, the π-type radicals are generated by substituents with higher electronegativity, and the lowergroup-electronegativity substituents lead to the p-type radicals. Unfortunately, we could not determine a specific value to distinguish the two types of radicals. Moreover, the radicals with moderately electronegative substituents are probably stable in both types. As shown in Figure 6, the model radicals with CH2F as substituents have two spin-density distributions, only because of the different orientations of CH2F (M1 vs M2). The orientations of the substituents of M3 and M4 are exactly the same, but the two geometries with different spindensity distributions both can be optimized, and their energies are comparable, with a difference of less than 2 kcal/mol (see Table S9). The model radicals with different substituents on two side C atoms (C1 and C3) of the six-membered ring backbone have also been investigated for their effects by calculating their
Subs1
Subs2
χ1 /χ2a
RGe−N1/ RGe−N2(Å)
θN−Ge−N (deg)
type
−CH3 −CH3 −CH3 −CH3 −CH3 −CH3 −CH3 −CH3 −CN −CN −CN −CN −CN −CN −CN
−CH2OH −SH −OH −CH2F −CHF2 −CHO −CN −CF3 −PH2 −But −CH3 −NH2 −SH −OH −COOH
2.331/2.491 2.331/2.501 2.331/2.585 2.331/2.644 2.331/3.026 2.331/2.647 2.331/2.792 2.331/3.405 2.792/2.154 2.792/2.289 2.792/2.331 2.792/2.437 2.792/2.501 2.792/2.585 2.792/2.769
2.030/2.031 2.027/2.045 2.024/2.050 2.043/2.038 2.052/2.038 1.885/1.873 1.887/1.874 1.884/1.876 1.879/1.885 1.876/1.888 1.874/1.887 2.009/2.055 2.023/2.068 2.013/2.066 1.887/1.889
87.87 87.76 88.01 88.16 87.96 95.35 95.63 95.80 95.41 95.53 95.63 88.17 87.67 88.02 95.41
p p p p p π π π π π π p p p π
χ1 and χ2 are the group electronegativities of the two substituents from ref 8.
a
their types of spin density, where methyl and cyano groups are chosen as low- and high-electronegativity groups. The two Ge−N bond lengths are slightly different because of the different substituents on both sides. However, there is still no new type of spin-density distribution, which is similar to the model radicals in Table 1. When methyl is one of the substituted groups, the other group is more electronegative than the methyl group. Only if the group electronegativity is large enough, the optimized free radical tends to be π-type; otherwise, it is p-type. In contrast, the substituents other than cyano in model radicals have less group electronegativity. Consistent with the above discussion, the preferred geometry of the radical with a low-electronegativity substituent is p-type. However, there are several exceptions (e.g., −CH3/−CHF2), indicating that the criteria for group electronegativity are reasonable while insufficient. 2.3. Stability. During the formation process of the germanium radicals, the strong electron-withdrawing substituents could always keep the π-type MO as SOMO and the resulting radical is π-type, whereas the strong electronD
DOI: 10.1021/acs.inorgchem.9b00034 Inorg. Chem. XXXX, XXX, XXX−XXX
Article
Inorganic Chemistry Scheme 3. Synthesis of the Germylene Chloride D-Cl and Its Reduction
published later. The desired radical D could not be isolated under our mature processing procedures. As expected, the frontier MOs of D-Cl are very similar to those of A-Cl and C-Cl (Table S2). The geometries of D-Cl− are optimized with a fixed Ge−Cl distance at the same calculation level as that for A-Cl− and C-Cl−. Figure 8 shows variations of the energies of p- and π-type MOs along with the distance between Ge and Cl of D-Cl−. During the release of Cl−, the energy levels of p- and π-type MOs exchange several times because of the competition of opposing effects between tert-butyl and phenyl on the backbone. As the orbital energy level changes, the Ge−N mean bond length of the ring changes significantly (red curve in Figure 8). The geometry of the radical itself is oscillating rather than staying at a stable configuration in the formation of radicals, which means that the ligands cannot provide good kinetic protections. Thus, the radical D is prone to other chemical reactions, such as ring contractions,10 because of its high reactivity. This instability may be the main barrier to isolate D as a single molecule.
donating substituents could change the energy level order of the frontier MOs, and the p-type MO becomes SOMO, resulting in a p-type radical. The group electronegativity can give a rough estimate of the type of radical, but it is difficult to predict which is more advantageous to be isolated if both of them may be thermodynamically stabilized. The most reliable way to confirm the stability of a compound is based on the experimental results. Thus, radical D (Scheme 3) is designed following a procedure similar to that for the generation of radical C. The precursor for D, germylene chloride D-Cl, is successfully obtained by the reaction of germanium dichloride with lithiated diketimine S2 (see the data in the Supporting Information) and characterized by multinuclear NMR spectroscopy and XRD analysis. Its structure (Figure 7) presents a
3. CONCLUSION On the basis of functionalized β-diketiminato systems, there are only two types of germanium radicals that can be obtained by reductive dehalogenation from their germylene halide. One of them is a p-type radical, which has strong electron-donating substituents on side C atoms of the six-membered ring, resulting in its spin-density distribution being concentrated around the Ge atom resembling a Ge p orbital. The other one is a π-type radical, whose spin density is mainly distributed on the NC3N backbone, corresponding to a π-antibonding orbital, because of the induction of strong electron-withdrawing substituents. The group electronegativity of the substituent can be used to estimate the type of selected radical. For the radical with high-electronegativity group substituents, such as the phenyl group in B and C, the most stable geometries of the corresponding germylene chloride anion LGeCl− retain the same electronic configuration: the single electron occupies the π-type MO on the ring backbone during formation of the radical. However, the stable geometries of LGeCl− have two types of electronic configurations if the low-electronegativity group substituents are on the six-membered ring, such as the tert-butyl in A. At the beginning of dissociation, SOMO is πtype, after which the orbital energy level changes, and the ptype MO becomes a SOMO until dissociation is completed. The germanium radical, which has moderate-electronegativity substituents or two substituents with comparable ability for pushing and pulling electrons on the N-heterocyclic backbone, is unstable enough to be isolated via a reductive dehalogenation from its germylene chloride because the advantaged geometries of the six-membered radical ring cannot be maintained in any stable state.
Figure 7. Molecular structure of D-Cl. Thermal ellipsoids are drawn at 30% probability level. H atoms are omitted for clarity. Selected bond lengths [Å] and angles [deg]: Ge1−N1 1.9776(13), Ge1−N2 1.9863(13), Ge−Cl, 2.3106(6) Å), N1−C21 1.344(2), C20−C21 1.3972, C13−C20 1.406(2), N2−C13 1.332(2); N1−Ge1−N2 92.62(5), C13−N2−Ge1 121.89(10), C21−N1−Ge1 122.53(11), C21−C20−C13 129.10(16).
three-coordinate GeII center in a parallel trigonal-pyramidal environment. The overall geometry and bond lengths of D-Cl [Ge−N, 1.9776(13) and 1.9863(13) Å; Ge−Cl, 2.3106(6) Å] are consistent with those of the known germylene chlorides4,6,7,9 (Table S8). The reduction of D-Cl with sodium naphthalenide leads to a deep-red mixture. The 1H NMR spectra of the hexane extract show that ligand S2 is one of the products and no trace of the magnetic products is observed. The further products D in the ether extract could not be structurally characterized. The reduction of D-Cl with lithium naphthalenide in THF also furnishes mixed products. One of them is a lithium salt of the germylene anion, which is generated via C3N2Ge ring contraction of D-Cl, and would be E
DOI: 10.1021/acs.inorgchem.9b00034 Inorg. Chem. XXXX, XXX, XXX−XXX
Article
Inorganic Chemistry
Figure 8. Variations of the energies of p- and π-type MOs and the Ge−N mean bond length along with the distance between Ge and Cl of D-Cl−. The energy levels of p- and π-type MOs have been exchanges many times. H atoms are not shown in the MO figures. radicals are not sensitive to the functionals and basis sets because the results at the M06-2X14/6-31+G* level are also excellent. Natural bond orbital calculations15 were performed on these optimized structures to get the natural population analysis changes and spin densities at the M06-2X/6-31+G* level (listed in Tables S6 and S7). Table S8 lists a comparison of the computational and experimental results for equilibrium geometries of C-Cl and D-Cl. In the calculation of the potential energy curves of A-Cl−, C-Cl−, and DCl−, the augmented with empirical dispersion correction (D3)16 was added to describe the long-range behavior more accurately in large Ge−Cl distances. These model radicals are all calculated at the M062X/6-31+G* level. All calculations were carried out using the Gaussian 09 software.17
4. EXPERIMENTAL DETAILS Synthesis of C. Sodium (41.1 mg, 1.79 mmol) and naphthalene (38.2 mg, 0.298 mmol) were added in a solution of C-Cl (990 mg, 1.49 mmol) in THF (20 mL). The mixture was stirred at room temperature over 24 h to generate a red-purple solution. When the solvent was evaporated, nearly dark solids were produced. These solids were extracted by cold hexane (50 mL, 0 °C), and the concentrated solution was stored in a −20 °C freezer overnight, affording dark-purple crystals of C (531 mg, 0.845 mmol, 56.7%). Mp: >167 °C (dec). Anal. Calcd for C40H47N2Ge: C, 76.45; H, 7.54; N, 4.46. Found: C, 76.27; H, 7.62; N, 4.39. Synthesis of D-Cl. A solution of 1.6 M nBuLi in hexane (2.45 mL, 3.92 mmol) was added dropwisely to a stirred solution of the new βdiketimine S2 (2.05 g, 3.92 mmol) in diethyl ether (20 mL) at −78 °C in 10 min. The solution was warmed to room temperature and stirred for 12 h, and then GeCl2·dioxane (0.908 g, 3.92 mmol) was added. The reaction mixture was further stirred for 5 h. All volatiles were removed in vacuo. The residue was extracted into toluene (40 mL), and then the extract was filtered, concentrated, and stored in a −30 °C freezer overnight, affording yellow crystals of D-Cl (1.55 g, 63%). Mp: 208−209 °C. 1H NMR (400 MHz, C6D6, 298 K): δ 0.67 (d, 3JHH = 6.4 Hz, 3H, CHMe2), 1.08 (s, 9H, C(CH3)3), 1.16 (d, 3JHH = 6.4 Hz, 3H, CHMe2), 1.17 (d, 3JHH = 6.4 Hz, 3H, CHMe2), 1.19 (d, 3 JHH = 6.4 Hz, 3H, CHMe2), 1.25 (d, 3JHH = 6.4 Hz, 3H, CHMe2), 1.36 (d, 3JHH = 6.8 Hz, 3H, CHMe2), 1.51 (d, 3JHH = 6.4 Hz, 3H, CHMe2), 1.61 (d, 3JHH = 6.4 Hz, 3H, CHMe2), 3.15 (sept, 3JHH = 6.8 Hz, 1H, CHMe2), 3.44 (sept, 3JHH = 6.8 Hz, 1H, CHMe2), 3.87 (sept, 3 JHH = 6.4 Hz, 1H, CHMe2), 4.27 (sept, 3JHH = 6.4 Hz, 1H, CHMe2), 6.23 (s, 1H, NCPhCHCCMe3), 6.82 (m, 1H, NCPhH (p)), 6.88 (m, 2H, NArH (p)), 6.99 (m, 4H, NArH (m)), 7.08 (m, 2H, N CPhH (o)), 7.36 (m, 2H, NCPhH (m)). 13C{1H} NMR (100 MHz, CDCl3, 298 K): δ 23.44 (CHMe2), 24.00 (CHMe2), 24.31 (CHMe2), 24.44 (CHMe2), 26.23 (CHMe2), 26.38 (CHMe2), 27.84 (CHMe2), 28.40 (CHMe2), 28.47 (CHMe2), 28.50 (CHMe2), 28.56 (CHMe2), 28.79 (CHMe2), 32.05 (CMe3), 42.50 (CMe3), 105.45 (PhCCHCCMe3), 123.88, 125.12, 127.26, 127.56, 127.85, 128.72, 128.91, 139.07, 139.47, 141.23, 144.60, 146.30 (aromatic C), 163.47 (CMe3CN), 175.50 (PhCN). Anal. Calcd for C37H48N2GeCl: C, 70.66; H, 7.69; N, 4.45. Found: C, 70.55; H, 7.53; N, 4.40.
■
ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.9b00034. Experimental sections and single-crystal x-ray structure determinations, analyses of C-Cl, S2, and D-Cl, crystal data and structure refinement parameters for compounds C and D-Cl, EPR spectrum of C, computational structures and characters, and the calculated results from DFT methods (PDF) Accession Codes
CCDC 1872884 and 1886354 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing
[email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
■
AUTHOR INFORMATION
Corresponding Authors
*E-mail:
[email protected]. *E-mail:
[email protected].
5. COMPUTATIONAL SETUP
ORCID
For radical C and its precursor C-Cl, the molecular structures were first fully optimized without restrictions by using three different functionals (BP86,11 B3LYP,12 and BHLYP,12a,13) with 6-311+G* basis sets to be compared with our previous work.4 Table S5 lists the key geometries of the GeN2C3 six-membered ring of radical C including A and B. The optimized structures are in good agreement with single-crystal XRD results. These stable geometries of the
Gengwen Tan: 0000-0002-6972-2197 Huan Wang: 0000-0002-7813-7408 Wenyuan Wang: 0000-0003-0898-3278 Anyang Li: 0000-0001-6634-842X Author Contributions ‡
J.Y. and Y.Q. contributed equally to this Article.
F
DOI: 10.1021/acs.inorgchem.9b00034 Inorg. Chem. XXXX, XXX, XXX−XXX
Article
Inorganic Chemistry Notes
(7) Woodul, W. D.; Richards, A. F.; Stasch, A.; Driess, M.; Jones, C. N-Heterocyclic Germylidenide and Stannylidenide Anions: Group 14 Metal(II) Cyclopentadienide Analogues. Organometallics 2010, 29, 3655−3660. (8) Yang, Z.; Shen, E. Molecular electronegativity in density functional theory (II) Direct calculation of group electronegativity and the atomic charges in a group. Science in China Series B-Chemistry 1996, 39, 20. (9) Ding, Y.; Roesky, H. W.; Noltemeyer, M.; Schmidt, H.-G.; Power, P. P. Synthesis and Structures of Monomeric Divalent Germanium and Tin Compounds Containing a Bulky Diketiminato Ligand. Organometallics 2001, 20, 1190−1194. (10) Wang, X.; Liu, J.; Yu, J.; Hou, L.; Sun, W.; Wang, Y.; Chen, S.; Li, A.; Wang, W. GeI−GeI Coupling Reaction Induced by a Mixture of CoBr2 and a Seven-Membered N-Heterocyclic Carbene. Inorg. Chem. 2018, 57, 2969−2972. (11) Perdew, J. P. Density-functional approximation for the correlation energy of the inhomogeneous electron gas. Phys. Rev. B: Condens. Matter Mater. Phys. 1986, 33, 8822−8824. (12) (a) Lee, C.; Yang, W.; Parr, R. G. Development of the ColleSalvetti correlation-energy formula into a functional of the electron density. Phys. Rev. B: Condens. Matter Mater. Phys. 1988, 37, 785−789. (b) Becke, A. D. Densityfunctional thermochemistry. III. The role of exact exchange. J. Chem. Phys. 1993, 98, 5648−5652. (13) Becke, A. D. A new mixing of Hartree-Fock and local densityfunctional theories. J. Chem. Phys. 1993, 98, 1372−1377. (14) Zhao, Y.; Truhlar, D. G. The M06 suite of density functionals for main group thermochemistry, thermochemical kinetics, noncovalent interactions, excited states, and transition elements: two new functionals and systematic testing of four M06-class functionals and 12 other functionals. Theor. Chem. Acc. 2008, 120, 215−241. (15) Glendening, E. D.; Landis, C. R.; Weinhold, F. Natural bond orbital methods. WIREs Comput. Mol. Sci. 2012, 2, 1−42. (16) Grimme, S.; Antony, J.; Ehrlich, S.; Krieg, H. A consistent and accurate ab initio parametrization of density functional dispersion correction (DFT-D) for the 94 elements H-Pu. J. Chem. Phys. 2010, 132, 154104. (17) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H. P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, J. A., Jr.; Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin, K. N.; Staroverov, V. N.; Kobayashi, R.; Normand, J.; Raghavachari, K.; Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega, N.; Millam, J. M.; Klene, M.; Knox, J. E.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Martin, R. L.; Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas, O.; Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J. Gaussian 09, revision E.01; Gaussian, Inc.: Wallingford, CT, 2009.
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS This work was supported by the NSF of China (Grants 21371141 and 21727805) and the Key Science and Technology Innovation Team of Shaanxi Province (Grant 2017KCT-37). Calculations were performed at the chemical HPC center of NWU. We also thank A.L.’s three-year-old daughter for her imagination. She thinks that the sixmembered ring molecules with spin-density distributions look like turtles, which contributed to the cute TOC graphic.
■
REFERENCES
(1) (a) Lee, V. Y.; Sekiguchi, A. Stable Silyl, Germyl, and Stannyl Cations, Radicals, and Anions: Heavy Versions of Carbocations, Carbon Radicals, and Carbanions. Acc. Chem. Res. 2007, 40, 410−419. (b) Lee, V. Y.; Sekiguchi, A. Si., Ge. and Sn-Centered Free Radicals: From Phantom Species to Grams-Order-Scale Materials. Eur. J. Inorg. Chem. 2005, 2005, 1209−1222. (c) Power, P. P. Persistent and Stable Radicals of the Heavier Main Group Elements and Related Species. Chem. Rev. 2003, 103, 789−810. (d) Maar, R. R.; Catingan, S. D.; Staroverov, V. N.; Gilroy, J. B. Formazanate Complexes of Hypervalent Group 14 Elements as Precursors to Electronically Stabilized Radicals. Angew. Chem., Int. Ed. 2018, 57, 9870−9874. (2) (a) Chandra Mondal, K.; Roy, S.; Roesky, H. W. Silicon based radicals, radical ions, diradicals and diradicaloids. Chem. Soc. Rev. 2016, 45, 1080−1111. (b) Nozawa, T.; Ichinohe, M.; Sekiguchi, A. 1,3,5-[(tBu2MeSi)2Si]3C6H3: Isolable Si-centered Triradical with a High-spin Quartet Ground State. Chem. Lett. 2015, 44, 56−57. (c) Taira, K.; Ichinohe, M.; Sekiguchi, A. Isolable Aryl-Substituted Silyl Radicals: Synthesis, Characterization, and Reactivity. Chem. - Eur. J. 2014, 20, 9342−9348. (d) Mondal, K. C.; Roesky, H. W.; Schwarzer, M. C.; Frenking, G.; Tkach, I.; Wolf, H.; Kratzert, D.; Herbst-Irmer, R.; Niepötter, B.; Stalke, D. Conversion of a Singlet Silylene to a stable Biradical. Angew. Chem., Int. Ed. 2013, 52, 1801− 1805. (e) Nozawa, T.; Nagata, M.; Ichinohe, M.; Sekiguchi, A. Isolable p- and m-[(tBu2MeSi)2Si]2C6H4: Disilaquinodimethane vs Triplet Bis(silyl radical). J. Am. Chem. Soc. 2011, 133, 5773−5775. (f) Sekiguchi, A.; Matsuno, T.; Ichinohe, M. Cyclotetrasilenyl: The First Isolable Silyl Radical. J. Am. Chem. Soc. 2001, 123, 12436− 12437. (g) Olmstead, M. M.; Pu, L.; Simons, S. R.; Power, P. P. >Reduction of Ge(Cl)C6H3 mes2-2,6 to give the cyclotrigermenyl radical (GeC6H3 mes2-2,6)3> and the trigermenyl anion salt K(GeC6H3 mes2-2,6)3. Chem. Commun. 1997, 1595−1596. (h) Sekiguchi, A.; Fukawa, T.; Nakamoto, M.; Lee, V. Y.; Ichinohe, M. Isolable Silyl and Germyl Radicals Lacking Conjugation with-Bonds: Synthesis, Characterization, and Reactivity. J. Am. Chem. Soc. 2002, 124, 9865−9869. (i) Ishida, Y.; Sekiguchi, A.; Kobayashi, K.; Nagase, S. 1,6,7-Trigermabicyclo[4.1.0]hept-3-en-7-yl: The Isolable Bicyclic Germyl Radical. Organometallics 2004, 23, 4891−4896. (3) Woodul, W. D.; Carter, E.; Muller, R.; Richards, A. F.; Stasch, A.; Kaupp, M.; Murphy, D. M.; Driess, M.; Jones, C. A Neutral, Monomeric Germanium(I) Radical. J. Am. Chem. Soc. 2011, 133, 10074−10077. (4) Lu, X.; Cheng, H.; Meng, Y.; Wang, X.; Hou, L.; Wang, Z.; Chen, S.; Wang, Y.; Tan, G.; Li, A.; Wang, W. A Two-Coordinate Neutral Germylene Supported by a β-Diketiminate Ligand in the Radical State. Organometallics 2017, 36, 2706−2709. (5) Chen, C.; Bellows, S. M.; Holland, P. L. Tuning steric and electronic effects in transition-metal β-diketiminate complexes. Dalton Trans 2015, 44, 16654−16670. (6) Jin, L.; Wang, X.; Ke, H.; Meng, Y.; Lu, X.; Chen, S.; Wang, W. Syntheses of Chlorogermylene and Chlorostannylene Supported by a β-Diketiminato Ligand Without Active Proton at α-Position. Chin. J. Inorg. Chem. 2016, 32, 839−845. G
DOI: 10.1021/acs.inorgchem.9b00034 Inorg. Chem. XXXX, XXX, XXX−XXX
