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supported by DFT calculations. □ INTRODUCTION. Tetrylenes are heavier group 14 carbene analogues. Their chemistry is of importance for synthetic and...
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Germanium and Tin Monoxides Trapped by Oxophilic Germylene and Stannylene Ligands Yunxia Gao,†,‡ Ying Yang,*,‡ Wenjun Zheng,*,† Yuanyuan Su,† Xiang Zhang,† and Herbert W. Roesky*,§ †

Institute of Organic Chemistry & College of Chemical and Materials Science & Key Laboratory of Magnetic Molecules and Magnetic Information Materials, Ministry of Education, Shanxi Normal University, Gongyuan Street 1, Linfen, Shanxi Province, 041004, People’s Republic of China ‡ School of Chemistry and Chemical Engineering, Central South University, Lushannan Road 932, Changsha, Hunan Province 410083, People’s Republic of China § Institut für Anorganische Chemie, Universität Göttingen, Tammannstrasse 4, 37077 Göttingen, Germany S Supporting Information *

ABSTRACT: Germanium and tin monoxides (MO, M = Ge, Sn) were trapped by the 1,2,4-diazaphospholide-based germylene and stannylene M[3,5-tBu2dp]2 (M = Ge (2), Sn (3)), resulting in the Lewis acid−base adduct of composition M(μ-O)[M{η1(N)-(3,5-tBu2dp)}2]2 (M = Ge (4), Sn (5)). Compounds 4 and 5 were characterized by single-crystal X-ray structural analysis. The bonding features of 4 and 5 were supported by DFT calculations.

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INTRODUCTION Tetrylenes are heavier group 14 carbene analogues. Their chemistry is of importance for synthetic and industrial applications.1−3 Considerable effort has been made in the synthesis of oxophilic tetrylenes, heavier carbon monoxide homologues such as GeO and SnO species. However, stannanones mostly form cage,4 ladder,5,6 or cluster7 structures rather than remaining in the simple monomeric MO form (M = Ge, Sn). Until recently, the situation has been improved by using a pincer tetrylene, a benzannulated lutidine-bridged bisstannylene, as a supporter to stabilize the formal divalent tin(II) and lead(II) monoxides.8 This prompted us to explore the potential for capturing molecular SnO or even the lighter congener of GeO utilizing non-pincer ligands. In this context, we used the monoanionic 3,5-di-tert-butyl-1,2,4-diazaphospholide ligand ([3,5-tBu2dp]−) (1−)9−17 to prepare the 1,2,4diazaphospholide-based germylene and stannylene M[η2(N,N)3,5-tBu2dp]2 (M = Ge (2), Sn (3)) as molecular traps. Treating hydrolyzed Ge[N(SiMe3)2]2 and Sn[N(SiMe3)2]2 with 2 and 3, respectively, resulted in the complex M(μ-O)[M{η1(N)-(3,5tBu2dp)}2]2 (M = Ge (4), Sn (5)), which contained the formally trapped MO (M = Ge, Sn) moiety.

Attempts to prepare 2 through the metathesis of 3,5-di-tertbutyl-1,2,4-diazaphospholide potassium (K[1])9 with GeCl2· dioxane were not successful. Instead, heterobimetallic ate complexes [Ge(3,5-tBu2dp)3K·(η6-tol)] (2′) and [Ge(3,5tBu2dp)3K)]2(μ-1,4-dioxane) (2″) (Scheme S1 and Figures S1 and S2 in the Supporting Information) were isolated.20 Bis(η2-N,N-3,5-di-tert-butyl-1,2,4-diazaphospholide)tin(II) (3; Scheme 1) was prepared by reacting Sn[N(SiMe3)2]218,21 with 1 in a way similar to that described for 2. The 31P{1H} NMR spectrum of 3 exhibited two sharp singlets at δ 84.73 and 82.89 ppm, which are comparable to the sharp singlets reported for the nitride stannylene [(η1:η1(N,N)-tBu2dp)(η1(N)tBu 2dp) 2(μ3-Sn) 2(μ4-N)(μ3 -Sn) 2(η 1:η 1 (N,N)-tBu 2dp) 2] (δ 81.6, 97.1 ppm).12 A significant upfield resonance was detected in the 119Sn{1H} NMR spectrum at δ −742 ppm, similar to the resonance at δ −720 ppm displayed for the dimeric pyrazolato stannylene [{Sn(η1-3,5-(CF3)2pz)2}2],22 indicating that the tin(II) center is in a uniform environment.23 Attempts to obtain single crystals of 2 in high enough quality for X-ray crystal diffraction analysis have so far been unsuccessful, but preliminary structural investigations showed that 2 has structural characteristics similar to those of 3. Singlecrystal X-ray diffraction analysis of 3 exhibited a monomeric homoleptic composition (Figure 1). A trigonal-planar geometry was observed around the tin(II) atom, when the lone pair electrons were taken into consideration.24,25 The slipped η2(N,N)-1,2,4-diazaphospholide would best be described as a monodentate ligand26 (Sn(1)−N(2) 2.198(3) Å, Sn(1)···N(1) 2.460(3) Å). The intermolecular dimeric structure of 3 (Figures

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RESULTS AND DISCUSSION Bis(η 2 -N,N-3,5-di-tert-butyl-1,2,4-diazaphospholide)germanium(II) (2) was obtained by reacting Ge[N(SiMe3)2]218 with H[3,5-tBu2dp] (1)19 (Scheme 1) in a 65% yield. In the 1H NMR spectrum of 2, two distinct singlet resonances at δ 1.45 and 1.33 ppm characterize the feature of η1 ↔ η2 tautomerism of the deprotonated diazaphospholide ligand in solution. In addition, the 13C{1H} and 31P{1H} NMR spectra each showed two sets of resonances due to the dynamic tautomerism. © XXXX American Chemical Society

Received: April 14, 2017

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DOI: 10.1021/acs.inorgchem.7b00918 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry Scheme 1. Syntheses of Compounds 2−5

The presence of empty orbitals and a lone pair on the M(II) atoms (M = Ge, Sn) indicates that 2 and 3 should exhibit Lewis acid and Lewis base bifunctionality and will react with either electrophilic or nucleophilic reagents. Germylenes and stannylenes such as M[N(SiMe3)2]2 (M = Ge, Sn)27,28 have been shown to be broadly reactive with small molecules such as CO2, OCS, and CS2.29−31 They may be inert to CO but may bind the heavier homologues of CO.8 Bis-ligated 2 and 3 were therefore used as trapping reagents to stabilize the [MO] unit. The [GeO] and [SnO] species were generated in situ by hydrolyzing Ge[N(SiMe3)2]2 and Sn[N(SiMe3)2]2, respectively, according to the procedure described previously.8 The following addition of 2 or 3 at a ratio of 1:2 resulted in the compound M(μ-O)[M-{η1(N)-(3,5-tBu2dp)}2]2 (M = Ge (4), Sn (5)). They were isolated as colorless crystals (Scheme 1). Single-crystal X-ray diffraction analysis of 4 showed that the [Ge(3)O] unit was trapped by two formal η1(N)-germylene moieties via O−Ge(1) and O−Ge(2) bonds (Figure 2). The central Ge(3) atom has a 0.6:0.4 occupation disorder at positions Ge(3) and Ge(3A) (Figure S5 in the Supporting Information).20 The deviations of the O atom from the Ge2Ge(3) (0.035 Å) and Ge2Ge(3A) (0.004 Å) planes are very small. The Ge(3)−O bond (1.853(5) Å) is slightly shorter than the Ge(1)−O (1.869(4) Å) and Ge(2)−O (1.911(4) Å) bonds32 (versus GeO 1.6468(5) Å).33 The interatomic Ge(3)···N(2) and Ge(3)···N(4) distances (2.213(7) and

Figure 1. Molecular structure of 3 with thermal ellipsoids at the 30% probability level. The ellipsoids of the tBu groups are shown isotropic. Hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and angles (deg): Sn(1)−N(2) 2.199(3), Sn(1)···N(1) 2.460(3), Sn(1)− N(3) 2.193(3), Sn(1)···N(4) 2.408(3); N(3)−Sn(1)−N(2) 89.52(12), N(2)···Sn(1)···N(4) 121.84(11).

S3 and S4 in the Supporting Information) and its discussion are given in the Supporting Information.20 Stannylenes stabilized by azolyl derivatives predominantly adopt the η1 or η1:η1 form,12,22 but 3 is the first example of a group 14 element compound in such an edge-bound, slipped η2 mode.

Figure 2. Molecular structures of (a) 4 and (b) 5 with thermal ellipsoids at the 30% probability level. The ellipsoids of the tBu groups are shown isotropic. Hydrogen atoms and terminal methyl group disorder are omitted for clarity. Selected bond lengths (Å) and angles (deg) with DFT calculation results (C2 symmetry) in brackets are as follows. 4: Ge(3)−O(1) 1.853(5) [1.878], Ge(1)−O(1) 1.869(4) [1.913], Ge(2)−O(1) 1.911(4) [1.913], Ge(1)−N(1) 2.046(5) [2.072], Ge(1)−N(3) 2.008(5) [2.052], Ge(2)−N(5) 2.022(5) [2.072], Ge(2)−N(7) 2.009(5) [2.052]; Ge(1)−O(1)−Ge(2) 113.5(2) [116.86], Ge(1)−O(1)−Ge(3) 112.7(3), Ge(2)−O(1)−Ge(3) 133.7(3). 5: Sn(3)−O(1) 2.052(2) [2.036], Sn(3)··· N(2) 2.567(3) [2.664], Sn(3)···N(4) 2.655(4) [2.736], Sn(1)−O(1) 2.048(2) [2.051], Sn(1)−N(3) 2.225(3) [2.238], Sn(1)−N(1) 2.237(3) [2.253], Sn(2)−O(1) 2.062(2) [2.051], Sn(2)−N(5) 2.204(4) [2.253], Sn(2)−N(7) 2.223(3) [2.238]; O(1)−Sn(3)···N(2) 74.86(10) [75.23], Sn(1)−O(1)−Sn(2) 123.33(11) [120.23], Sn(1)−O(1)−Sn(3) 117.47(11), Sn(2)−O(1)−Sn(3) 119.20(12). B

DOI: 10.1021/acs.inorgchem.7b00918 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

values for Sn(1) and Sn(2) of 5. Similar observations have been also reported for some tin(II) species, such as Sn{N[Si(CH3)3]2}2.41 The valence states of the tin atoms in 5 were examined using 119 Sn Mössbauer spectroscopy (Figure 3).20

2.309(8) Å, respectively) are much longer than the interatomic Ge(1)−N(1) and Ge(1)−N(3) distances (2.046(5) and 2.008(5) Å, respectively) as well as the sum of the singlebond covalent radii (Ge−N 1.92 Å).34 This observation indicated that the related intramolecular interactions are weak. The Ge(3A) site exhibits a similar situation. Previously, no similar example has been reported with such a Ge(3) environment supported by one formal Ge−O bond and two N···Ge intramolecular interactions. A comparable Ge(II) compound was realized by the N,N,O ligand to provide covalent N and O bonding and coordinative N bonding to the Ge(II) center.35 Similarly, as revealed by single-crystal X-ray structural analysis, the [Sn(3)O] unit of 5 is trapped by two molecules of 3. The Sn(1) and Sn(2) atoms are each bound by two 1,2,4diazaphospholides in the η1(N) coordination mode, in contrast to the slipped η2(N,N) coordination mode observed in 3. The oxygen atom is almost perfectly situated in the Sn3 plane, with an out-of-plane deviation of 0.006 Å. The Sn−O−Sn angles are close to 120° (Sn(1)−O(1)−Sn(3) 117.47(11)°, Sn(1)− O(1)−Sn(2) 123.33(11)°, Sn(2)−O(1)−Sn(3) 119.20(12)°), and the sum of the angles at the O atom is 360.00(33)°. The bond angles at the Sn(1) atom (N(3)−Sn(1)−N(1) 91.30(12)°, N(3)−Sn(1)−O(1) 87.17(11)°, N(1)−Sn(1)− O(1) 86.92(11)°) and the Sn(2) atom in 5 are close to 90°, indicating that the lone pair of electrons in the Sn(1) and Sn(2), respectively, exhibits s characteristics. The Sn−O bond lengths (Sn−O 2.048(2)−2.062(2) Å) are close to the sum of the covalent Sn−O bond radii (2.03 Å), which may be typical for an ionic character due to the large differences in the electronegativities of Sn and O.36,37 The Sn(3) center of 5 was observed to be in a bent two-coordinate environment and to contain a rare O−Sn···N linkage38−40 with an acute angle (74.86(10)°). The Sn(3)···N(2) distance (2.567(3) Å) is significantly longer than the Sn(1)−N and Sn(2)−N bond lengths (2.204(4)−2.237(3) Å), indicating that intramolecular interactions between the Sn(3) and N(2) atoms are weak. The 31P{1H} NMR spectrum of 5 displayed two sharp resonances at δ 82.9 and 80.1 ppm, which are consistent with two sets of resonances in the 1H and 13C{1H} NMR spectra, suggesting that the ligand environments are significantly different in solution and in the solid state. The 119Sn{1H} NMR spectrum of 5 showed two broad resonances at δ −372.3 and −398.3 ppm after 20480 scans, which present moderate deviations from the calculated 119Sn NMR chemical shifts at δ −223.9 ppm (average) for Sn(1) and Sn(2) and δ −420.4 ppm for Sn(3).20 The tin(II) atom can expand its coordination sphere through weak interactions with solvent or donor molecules in solution, and this might also be sensitive to temperature. A high-field shift of stannylene could even be detected when the deuterated solvent was changed from toluene-d8 to THF-d8, due to the solvent coordination to the empty p orbital at the tin atom.8 The resulting chemical shift δ(119Sn) of 5 reflected qualitatively the strength of interactions or dissociation between the tin(II) atom and the potential donor site, possibly both intra- and intermolecularly. Our calculations were performed with an isolated model while being simplified by neglecting the effect of complicated interactions, such as the weak interactions of Sn(1)/Sn(2) and the adjacent N atoms of ligands with possible slipped η2 coordination in the solution (Figure 2). Therefore, a downfield shift deviation (Δδ 148 ppm) was found between the calculated and experimental

Figure 3. Measured (bottom) and simulated (top A, B) Mössbauer spectra for 5.

119

Sn

The spectrum can be simulated as two resonances, indicative of the presence of nonequivalent tin atoms. The values of isomer shifts (δ) and quadrupole splitting (ΔEQ) are typical for divalent tin (δ = 3.35 and 3.10 mm s−1; ΔEQ = 1.87 and 2.21 mm s−1)20 at room temperature. We compared the core geometry of 5 with that of SnO trapped by a pincer bis-stannylene molecule.8 The Sn(3)−O bond length (2.052(2) Å) in 5 is slightly shorter than the Sn(3)O bond in the pincer bis-stannylene (2.079(2) Å).8 However, the Sn(1)−O and Sn(2)−O bond lengths (2.048(3) and 2.062(2) Å) in 5 are slightly shortened and are similar to the Sn(3)−O bond length. Therefore, it can be argued that the three Sn−O bonds in 5 are to some extent shorter than those with the rigid pincer-type bis-stannylene ligand, probably because the pincer ligands are overall slightly stronger donors than the stannylene ligands in 5.8 M(3) atoms seem to interact in a similarly strong manner with the central O atoms as the two M(3,5-tBu2dp)2 ligands. What was the key to making the M(1)−O and M(2)−O bonds relatively short in 4 and 5? The additional interactions of the “naked” Sn atom with the N donor atoms seemed to further make a significant adjustment of electronic situations at the Sn atoms in 5. To gain a better understanding of the bonding nature, we optimized the geometries of 4 and 5 at the B3LYP/ 6-311G(d,p)+LANL2dz level and calculated the natural bond orbital (NBO) charge distribution42,43 and Mayer bond index44 using NBO 3.145 in Gaussian09 software.20 For each compound two structures of C1 and C2 symmetry were established (Figure S6 in the Supporting Information)20 with comparable energies (ΔE = 2.7 kcal/mol for 4 and 1.3 kcal/mol for 5). The DFT calculation results (C2 symmetry) of the optimized geometries of 4 and 5 are given in the caption to Figure 2 in brackets. The calculated Mayer bond indexes of key M−O and M−N bonds in 4 and 5 as well as APT/NBO charges of M atoms and O atoms are given in Table S1 in the Supporting Information to illustrate the key bonding interactions.20 C

DOI: 10.1021/acs.inorgchem.7b00918 Inorg. Chem. XXXX, XXX, XXX−XXX

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NMR (243 MHz, CDCl3, 23 °C): δ 89.7 (s), 19.7 (s) ppm. IR (KBr, Nujol mulls, cm−1): 1460 (s), 1261 (vs), 1095 (vs), 1020 (vs), 799 (vs). Anal. Calcd for C20H36GeN4P2 (Mr = 467.11): C, 51.43; H, 7.77; N, 11.99. Found: C, 51.51; H, 7.85; N, 11.86. Synthesis of Sn[η2(N,N)-3,5-tBu2dp]2 (3). In a fashion similar to the preparation of 2, the reaction of 1 (0.40 g, 2.0 mmol) and Sn[N(SiMe3)2]2 (0.44 g, 1.0 mmol) was carried out to afford 3 as colorless crystals (0.38 g, 74%). Mp: 165−167 °C. 1H NMR (600 MHz, CDCl3, 23 °C): δ 1.36 (s, 12 H, CH3), 1.33 (s, 24 H, CH3) ppm. 13C{1H} NMR (150 MHz, CDCl3, 23 °C): δ 195.71, 195.29 (d, 1 JP−C = 63.0 Hz, PCN), 190.32, 189.91 (d, 1JP−C = 61.5 Hz, PCN), 35.60 (d, 2JP−C = 15.0 Hz, CCH3), 33.12 (d, 2JP−C = 39.0 Hz, CCH3), 32.97 (d, 3JP−C = 7.5 Hz, CH3), 32.15 (d, 3JP−C = 6.0 Hz, CH3) ppm. 31 1 P{ H} NMR (243 MHz, CDCl3, 23 °C): δ 84.73 (s), 82.89 (s) ppm. 119 Sn NMR (224 MHz, CDCl3, 23 °C): δ −742 ppm. IR (KBr, Nujol mulls, cm−1): 1461 (s), 1377 (m), 1260 (s), 1093 (m), 1019 (s), 875 (w), 799 (s). Anal. Calcd for C20H36SnN4P2 (Mr = 513.18): C, 46.81; H, 7.07; N, 10.92. Found: C, 46.63; H, 7.01; N, 10.85. Single crystals suitable for X-ray diffraction analysis were obtained from n-hexane at room temperature. Synthesis of Ge(μ-O)[Ge{η1(N)-(3,5-tBu2dp)}2]2 (4). The fresh hydrolysis of Ge[N(SiMe3)2]2 was carried out by following the reported procedure.8 To a solution of Ge[N(SiMe3)2]2 (0.39 g, 1.0 mmol) in THF (15 mL) was added a solution of water (18 mg, 1.0 mmol) in THF (5 mL) at −78 °C. Then 2 (0.94 g, 2.0 mmol) in THF (20 mL) was immediately added to the mixture with vigorous stirring. The solution was gradually warmed to ambient temperature with an additional 2 h of stirring to complete the reaction. Colorless crystals of 4 were obtained from the solution after several days at 2 °C (0.31 g, 30.0%). Mp: 196−198 °C. 1H NMR (600 MHz, CDCl3, 23 °C): δ 1.38 (s, 54 H, CH3), 1.32 (s, 18 H, CH3) ppm; 13C{1H} NMR (150 MHz, CDCl3, 23 °C): δ 193.39, 193.02 (d, 1JP−C = 55.5 Hz, PCN), 35.84 (d, 2JP−C = 16.5 Hz, CCH3), 33.02 (d, 2JP−C = 7.5 Hz, CCH3), 32.52 (d, 3JP−C = 9.0 Hz, CH3) ppm. 31P{1H} NMR (243 MHz, CDCl3, 23 °C): δ 86.9 (br), 79.2(s) ppm. IR (KBr, Nujol mulls, cm−1): 1595 (w), 1461 (s), 1377 (m), 1260 (s), 1093 (m), 1019 (s), 875 (w), 865 (vw), 798 (s), 722 (w). Anal. Calcd for C40H72Ge3N8OP4 (Mr = 1022.71): C, 46.97; H, 7.09; N, 10.95. Found: C, 46.88; H, 7.02; N, 10.90. Single crystals suitable for X-ray diffraction analysis were obtained from toluene at 2 °C. Synthesis of Sn(μ-O)[Sn{η1(N)-(3,5-tBu2dp)}2]2 (5). To a solution of 3 (1.03 g, 2.0 mmol) in THF (20 mL) was slowly added a freshly hydrolyzed Sn[N(SiMe3)2]2 (0.44 g, 1.0 mmol) in THF (20 mL) at 0 °C over 2 h with stirring. The solution was filtered through Celite, and the filtrate was concentrated to about 10 mL to afford 5 as colorless crystals after several days at 2 °C (0.64 g, 55.0%). Mp: 198−202 °C. 1H NMR (600 MHz, CDCl3, 23 °C): δ 1.38 (s, 36 H, CH3), 1.28 (s, 36 H, CH3) ppm. 13C{1H} NMR (150 MHz, CDCl3, 23 °C): δ 195.67, 195.29 (d, 1JP−C = 55.5 Hz, PCN), 35.76 (d, 2JP−C = 16.5 Hz, CCH3), 33.07 (d, 2JP−C = 52.50 Hz, CCH3), 32.00 (s, CH3) ppm. 31P{1H} NMR (243 MHz, CDCl3, 23 °C): δ 82.9 (s), 80.1 (s) ppm. 119Sn NMR (224 MHz, CDCl3, 23 °C): δ −372.3, − 398.3 ppm (after 20480 scans). IR (KBr, Nujol mulls, cm−1): 1592 (w), 1462 (s), 1377 (m), 1260 (s), 1091 (m), 1019 (s), 864 (vw), 799 (s), 722 (vw). Anal. Calcd for C40H72N8OP4Sn3 (Mr = 1161.01): C, 41.38; H, 6.25; N, 9.65. Found: C, 41.43; H, 6.20; N, 9.59. Single crystals suitable for X-ray diffraction analysis were obtained from n-hexane at room temperature.

The bonding nature of the core skeleton of M3O can be well described by the coordination effect (σ coordination in M(1)− O/M(2)−O and M(3)−O moieties) between the unoccupied lone-pair orbitals of M atoms (LP*, mainly p orbitals) and the occupied lone pair orbitals of O atom (LP, mainly spn, n ≈ 2, or pz orbitals). From the coefficients of these bonding orbitals we can see that, in each bonding orbital, the contribution of the LP orbital of the O atom is predominant (over 90%), which clearly indicates that M−O bonds are highly polarized and can be roughly described as being formed by ionic interactions. This conclusion is supported by the calculated APT and NBO charges on the O atom.20 Note that the two-electron filled pz orbital of the O atom almost has no interaction with the unoccupied pz orbital of M(3). These results can well explain the structural characters. (i) M−O bonds are all single σ-coordination bonds; thus, they have similar bond orders and bond lengths. (ii) The nearly planar structure of the M3O moiety is the result of nearly sp2 hybridization of the s, px, and py orbitals of the O atom. (iii) An explanation for the relatively short M(1)−O and M(2)−O bonds in 4 and 5 might be that two types of σ bonds are formed involving a shorter σ-sharing bond and a longer σ-dative bond depending on the different coordinating ligands used for the preparation of the complexes.

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CONCLUSIONS We have demonstrated that germanium and tin monoxides can be stabilized by a 1,2,4-diazaphospholide ligated germylene (2) and stannylene (3), generating the Lewis acid−base pair adducts 4 and 5. DFT calculations of 4 and 5 suggested that all of the M−O bonds in 4 and 5 are strongly polarized σ bonds. The occupied lone pair orbital (pz) of the O atom contains two electrons that have little π interaction with the nearly unoccupied pure pz orbital of M(3) or the LP* orbitals of M. This appears to be responsible for the somewhat convergent M−O bond lengths in 4 and 5, respectively.

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EXPERIMENTAL SECTION

General Comments. All manipulations were carried out under a nitrogen atmosphere under anaerobic conditions using standard Schlenk, vacuum line, and glovebox techniques. The solvents were thoroughly dried, deoxygenated, and distilled under a nitrogen atmosphere prior to use. CDCl3 was dried using CaH2 before use, and DMSO-d6 was dried over molecular sieves before use. The 1H NMR, 13C{1H} NMR, 119Sn{1H} NMR, and 31P{1H} NMR spectra were recorded with a Bruker DRX-600 spectrometer. IR measurements were carried out on a NICOLET 360 FT-IR spectrometer from Nujol mulls prepared in a drybox. Elemental analysis was performed on an Elementar vario MACRO cube (Germany). Melting points were measured in sealed argon-filled capillaries without temperature correction with an XT4-100A apparatus (Electronic and Optical Instruments, Beijing). Synthesis of Ge[η2(N,N)-3,5-tBu2dp]2 (2). To a solution of 1 (0.40 g, 2.0 mmol) in n-hexane (20 mL) was added Ge[N(SiMe3)2]2 (0.39 g, 1.0 mmol) in n-hexane (20 mL) by syringe. After the solution was stirred for 12 h, the volatile components were removed under reduced pressure. The resulting residue was dried for 2 h under high vacuum, and the solid was dissolved in warm n-hexane (50 mL). The solution was filtered through Celite, and the filtrate was then concentrated to give 2 as colorless crystals at room temperature (0.30 g, 65%). Mp: 219−220 °C. 1H NMR (600 MHz, DMSO-d6, 23 °C): δ 1.45, 1.33 (2s, 36 H, CH3) ppm. 13C{1H} NMR (150 MHz, DMSO-d6, 23 °C): δ 192.15, 191.74 (d, 1JP−C = 61.5 Hz, PCN), 190.13, 189.77 (d, 1JP−C = 54.0 Hz, PCN), 36.28 (s, CCH3), 35.30 (d, 3 JP−C = 7.5 Hz, CH3), 34.70 (d, 3JP−C = 7.5 Hz, CH3) ppm. 31P{1H}

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.7b00918. Experimental procedures and spectroscopic data for 2′ and 2″, more detailed DTF calculation results, DFT coordinates, and crystallographic data for 2′ and 3−5 (PDF) D

DOI: 10.1021/acs.inorgchem.7b00918 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry Accession Codes

(12) Pi, C.; Elguero, J.; Wan, L.; Alkorta, I.; Zheng, W.; Weng, L.; Chen, Z.; Wu, L. 1,2,4-Diazaphospholide Complexes of Tin(II): From Nitride Stannylene to Stannylenated Ammonium Ions. Chem. - Eur. J. 2009, 15, 6581−6585. (13) Pi, C.; Wan, L.; Liu, W.; Pan, Z.; Wu, H.; Wang, Y.; Zheng, W.; Weng, L.; Chen, Z.; Wu, L. 1,2,4-Diazaphospholide Complexes of Barium: Mechanism of Formation and Crystallographic Characterization. Inorg. Chem. 2009, 48, 2967−2975. (14) Pi, C.; Wang, Y.; Zheng, W.; Wan, L.; Wu, H.; Weng, L.; Wu, L.; Li, Q.; Schleyer, P. v. R. A Persistent Dipotassium 1,2,4Diazaphospholide Radical Complex: Synthesis, X-Ray Structure, and Bonding. Angew. Chem., Int. Ed. 2010, 49, 1842−1845. (15) Zheng, W.; Alkorta, I.; Yang, D.; Wan, L.; Zhao, M.; Elguero, J. Synthesis and Structural Characterization of 1,2,4-Diazaphospholide Complexes of Titanium(IV) and Titanium(III). Inorg. Chem. 2011, 50, 12408−12410. (16) Liu, D.; Wang, Y.; Pi, C.; Zheng, W. Synthesis and Structural Characterization of Homoleptic 1,2,4-Diazaphospholide Alkaline Earth Metal Complexes. Organometallics 2014, 33, 6013−6017. (17) Zhao, M.; Li, P.; Xie, X.; Su, J.; Zheng, W. Synthesis and structural characterization of 2,6-bis(1,2,4-diazaphospholyl-1-yl)pyridine zinc and 2,6-bis(1,2,4-diazaphospholyl-1-yl)pyrazine copper complexes. Polyhedron 2015, 85, 302−311. (18) Lappert, M. F.; Power, P. P.; Slade, M. J.; Hedberg, L.; Hedberg, K.; Schomaker, V. Monomeric bivalent group 4B metal dialkylamides M[NCMe2(CH2)3CMe2]2(M = Ge or Sn), and the structure of a gaseous disilylamide, Sn[N(SiMe3)2]2, by gas electron diffraction. J. Chem. Soc., Chem. Commun. 1979, 369−370. (19) Schmidpeter, A.; Willhalm, A. 1H-1,2,4-Diazaphospholes via 2Phosphaallyl Chlorides. Angew. Chem., Int. Ed. Engl. 1984, 23, 903− 904. (20) The Supporting Information. (21) Harris, D. H.; Lappert, M. F. Monomeric, volatile bivalent amides of group IV elements, M(NR1 2)2 and M(NR1R2)2(M = Ge, Sn, or Pb; R1=Me3Si, R2=Me3C). J. Chem. Soc., Chem. Commun. 1974, 895−896. (22) Breher, F.; Rüegger, H. Distannenes Turned Inside Out: Bis(stannylenes) with an Unusual Structural Motif. Angew. Chem., Int. Ed. 2005, 44, 473−477. (23) A modest 1J(119Sn,117Sn) coupling constant of 1340 Hz was reported for the dimer [R2SnSnR2] (R = CH(SiMe3)2): Zilm, K. W.; Lawless, G. A.; Merrill, R. M.; Millar, J. M.; Webb, G. G. Nature of the tin-tin double bond as studied by solid-state and solution nuclear magnetic resonance. J. Am. Chem. Soc. 1987, 109, 7236−7238. We did not observe 1J(119Sn,117Sn) coupling in our case, suggesting that 3 exists in a monomeric species in solution. (24) Yang, D.; Guo, J.; Wu, H.; Ding, Y.; Zheng, W. Synthesis and structural characterization of two-coordinate low-valent 14-group metal complexes bearing bulky bis(amido)silane ligands. Dalton Trans. 2012, 41, 2187−2194. (25) Hitchcock, P. B.; Lappert, M. F.; Misra, M. C. Homoleptic, three-co-ordinate group 8c noble metal(0) complexes having GeII or SnII ligands, [M{M′(NR2)2}3] (M = Pd or Pt, M′= Ge or Sn, R = SiMe3), and the X-ray structure of one of them (M = Pd, M′= Sn). J. Chem. Soc., Chem. Commun. 1985, 863−864. (26) Guzei, I. A.; Yap, G. P. A.; Winter, C. H. Tantalum Complexes Bearing η1-, η2-, and “Slipped” η2-Pyrazolato Ligands. Inorg. Chem. 1997, 36, 1738−1739. (27) Asay, M.; Jones, C.; Driess, M. N-Heterocyclic Carbene Analogues with Low-Valent Group 13 and Group 14 Elements: Syntheses, Structures, and Reactivities of a New Generation of Multitalented Ligands. Chem. Rev. 2011, 111, 354−396. (28) Zabula, A. V.; Hahn, F. E. Mono- and Bidentate Benzannulated N-Heterocyclic Germylenes, Stannylenes and Plumbylenes. Eur. J. Inorg. Chem. 2008, 2008, 5165−5179. (29) Stewart, C. A.; Dickie, D. A.; Parkes, M. V.; Saria, J. A.; Kemp, R. A. Reactivity of Bis(2,2,5,5-tetramethyl-2,5-disila-1-azacyclopent-1-yl) tin with CO2, OCS, and CS2 and Comparison to That of Bis[bis(trimethylsilyl)amido]tin. Inorg. Chem. 2010, 49, 11133−11141.

CCDC 1057381−1057384 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.

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AUTHOR INFORMATION

Corresponding Authors

*E-mail for Y.Y.: [email protected]. *E-mail for W.Z.: [email protected]. *E-mail for H.W.R.: [email protected]. ORCID

Herbert W. Roesky: 0000-0003-4454-1434 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We gratefully acknowledge financial support from the National Natural Science Foundation of China (NSFC; Grant Nos. 21272143, 21271057), the Program for Changjiang Scholar and Innovative Research Team in University (No. IRT1156), and the Special Fund for Agro-scientific Research in the Public Interest (No. 201503108). Support of the Deutsche Forschungsgemeinschaft (RO 224/68-1) is gratefully acknowledged.

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REFERENCES

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DOI: 10.1021/acs.inorgchem.7b00918 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry (30) Ochiai, T.; Szilvási, T.; Franz, D.; Irran, E.; Inoue, S. Isolation and Structure of Germylene-Germyliumylidenes Stabilized by NHeterocyclic Imines. Angew. Chem., Int. Ed. 2016, 55, 11619−11624. (31) Pelzer, S.; Neumann, B.; Stammler, H.-G.; Ignat’ev, N.; Hoge, B. The Bis(pentafluoroethyl)germylene Trimethylphosphane Adduct (C2F5)2Ge·PMe3: Characterization, Ligand Properties, and Reactivity. Angew. Chem., Int. Ed. 2016, 55, 6088−6092. (32) The average length of Sn(3)−O and Sn(3A)−O bonds (1.8815(5) Å) is 0.069 Å shorter than the sum of single-bond covalent radii (Ge−O 1.95 Å): Pyykkö, P.; Atsumi, M. Molecular Single-Bond Covalent Radii for Elements 1−118. Chem. - Eur. J. 2009, 15, 186−197. (33) Li, L.; Fukawa, T.; Matsuo, T.; Hashizume, D.; Fueno, H.; Tanaka, K.; Tamao, K. A stable germanone as the first isolated heavy ketone with a terminal oxygen atom. Nat. Chem. 2012, 4, 361−365. (34) Pyykkö, P.; Atsumi, M. Molecular Single-Bond Covalent Radii for Elements 1−118. Chem. - Eur. J. 2009, 15, 186−197. (35) Zaitsev, K. V.; Cherepakhin, V. S.; Churakov, A. V.; Peregudov, A. S.; Tarasevich, B. N.; Egorov, M. P.; Zaitseva, G. S.; Karlov, S. S. Extending the family of stable heavier carbenes: New tetrylenes based on N,N,O-ligands. Inorg. Chim. Acta 2016, 443, 91−100. (36) Ochiai, T.; Franz, D.; Irran, E.; Inoue, S. Formation of an IminoStabilized Cyclic Tin(II) Cation from an Amino(imino)stannylene. Chem. - Eur. J. 2015, 21, 6704−6707. (37) Ochiai, T.; Franz, D.; Wu, X.-N.; Inoue, S. Isolation of a germanium(II) cation and a germylene iron carbonyl complex utilizing an imidazolin-2-iminato ligand. Dalton Trans. 2015, 44, 10952−10956. (38) One known structurally determined case in the available literature is the heteroleptic two-coordinate prochiral tin(II) compound Sn[N(SiMe3)2][O-2,6-tBu2-4-Me-C6H2], exhibiting a significantly shorter Sn−N (2.079(3) Å) and slightly longer but comparable Sn−O (2.053(2) Å) bond length and considerably wider O−Sn−N angle (96.4(1)°). forming a typical trigonal-planar geometry about the metal center: Braunschweig, H.; Chorley, R. W.; Hitchcock, P. B.; Lappert, M. F. The first monomeric prochiral tin(II) complexes Sn[N(SiMe3)2]X [X = OC6H2tBu2-2,6-Me-4, 1 or NCMe2(CH2)3CMe2, 2]; the X-ray structure of 1 and oxidative addition reactions of 2. J. Chem. Soc., Chem. Commun. 1992, 1311− 1313. (39) Barrau, J.; Rima, G.; El Amraoui, T. New bivalent germanium, tin and lead compounds with M-O bond. Inorg. Chim. Acta 1996, 241, 9−10. (40) Rimo, X.; Sita, L. R. Mechanistic details for metathetical exchange between XCO (X = O and RN) and the tin(II) dimer, {Sn[N(SiMe3)2](μ-OBut)}2. Inorg. Chim. Acta 1998, 270, 118−122. (41) Broeckaert, L.; Turek, J.; Olejník, R.; Růzǐ čka, A.; Biesemans, M.; Geerlings, P.; Willem, R.; De Proft, F. Combined NMR and DFT Study on the Complexation Behavior of Lappert’s Tin(II) Amide. Organometallics 2013, 32, 2121−2134. (42) Stephens, P.; Jalkanen, K.; Kawiecki, R. Theory of vibrational rotational strengths: comparison of a priori theory and approximate models. J. Am. Chem. Soc. 1990, 112, 6518−6529. (43) Ghosez, P.; Michenaud, J. P.; Gonze, X. Dynamical atomic charges: The case of ABO3 compounds. Phys. Rev. B: Condens. Matter Mater. Phys. 1998, 58, 6224−6240. (44) Lee, C.; Yang, W.; Parr, R. G. Development of the Colle-Salvetti correlation-energy formula into a functional of the electron density. Phys. Rev. B: Condens. Matter Mater. Phys. 1988, 37, 785−789. (45) Stephens, P. J.; Devlin, F. J.; Chabalowski, C. F.; Frisch, M. J. Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields. J. Phys. Chem. 1994, 98, 11623−11627.

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DOI: 10.1021/acs.inorgchem.7b00918 Inorg. Chem. XXXX, XXX, XXX−XXX