Aminotroponiminates: Alkali Metal Compounds ... - ACS Publications

Article pubs.acs.org/Organometallics

Aminotroponiminates: Alkali Metal Compounds Reveal Unprecedented Coordination Modes Crispin Lichtenberg* Institut für Anorganische Chemie, Julius-Maximilians-Universität Würzburg, Am Hubland, 97074 Würzburg, Germany S Supporting Information *

ABSTRACT: The coordination chemistry of alkalimetal aminotroponiminates (ATIs) was investigated based on (i) a lithium ATI, (ii) the first example of a sodium ATI, and (iii) the first example of a structurally characterized potassium ATI. In the lithium derivative of this series, the ATI ligand adopts a well-known κ2N binding mode. In contrast, the sodium and potassium ATIs show two different types of unprecedented polymeric structures in the solid state, unraveling a surprisingly rich coordination chemistry for the ATI ligand family. In the solid-state structure of the potassium compound, ATI ligands bridge the metal atoms in a μ2-κ2N binding mode. The sodium compound reveals a μ2-κ2Nκ5C coordination mode with an unusual interaction of a metal center with a C7 ATI ligand backbone. NMR studies suggest that this type of interaction might also be accessible in solution. It was further studied by DFT calculations. The tendency of monoanionic ATI ligands to interact with transition-metal centers via their C7 ligand backbone was investigated experimentally and theoretically using Rh+ and W0 as examples for potentially arenophilic metals.

■

interaction of a metal center with the π-electron cloud of the conjugated seven-membered ring in the ligand backbone should also be possible (C, Scheme 1). However, this has so far only been reported in a single case for a protonated ligand, H-ATI, interacting with [Ru(C5Me5)]+.13 ATI complexes of the alkali metals are commonly employed as starting materials for the preparation of other ATI compounds in salt metathesis protocols.7 In contrast to their frequent utilization as chemical building blocks, the coordination chemistry of this class of compounds is only little investigated. In this contribution, the coordination chemistry of a series of alkali metal ATIs is presented, revealing unprecedented binding modes. The tendency for the realization of type C binding modes in complexes of Rh+ and W0 as examples for potentially arenophilic metal centers is evaluated.

INTRODUCTION Aminotroponiminates (ATIs) are a well-established class of ligands. The complexation of (semi)metals across large parts of the periodic table has been reported including s-block1,2 and pblock elements,1b,c,3 early1a,4 and late transition metals,5 and the lanthanoides.6,7 Initial fundamental studies on metal ATIs were dedicated to odd electron delocalization and magnetically anomalous compounds.8 Subsequent research was oriented toward the design of new catalysts for hydroamination,2a,6c,9 olefin and propylenoxide polymerization,7,10b alkyne oligomerization,10 or NO disproportionation.11 For all of these investigations, the coordination chemistry and the binding mode of the ATI ligand play a crucial role as they determine properties such as electron delocalization pathways, ligand field splitting, degree of association, or the availability and character of vacant coordination sites. The most prevalent binding motif of monoanionic ATI ligands is the chelating κ2N coordination mode (A, Scheme 1).7 Structurally authenticated exceptions are rare: Only two examples of oligo-nuclear compounds with ATI ligands bridging two lithium atoms in a μ2-κ2N coordination mode have been reported (B, Scheme 1).12 In principle, the

■

RESULTS AND DISCUSSION Alkali Metal ATIs. The asymmetrically phenyl/iso-propyl substituted aminotroponimine [H(ATIPh/iPr)] (1) was chosen as a starting point for these studies.9a The deprotonation of 1 with alkali metal bases at ambient temperature is straightforward and gives the metalated products in high yields (87−99%) as yellow to orange solids (Scheme 2). The lithium compound [Li(ATIPh/iPr)] (2) can be isolated free of neutral donor ligands when using toluene as a solvent. Once a donor solvent such as THF is added, it cannot be removed under reduced pressure or by washing with hexanes. Whereas the bis-thf-adduct of 2 forms an orange oil,14 the adduct [Li(ATIPh/iPr)(thf)(OPPh3)] (2-thf-OPPh3) could be

Scheme 1. Structurally Authenticated (A, B) and Potential (C) Coordination Modes of Anionic ATI Ligandsa

a

Received: January 19, 2016

One resonance structure is shown in each case. X = anionic ligand. © XXXX American Chemical Society

A

DOI: 10.1021/acs.organomet.6b00042 Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics Scheme 2. Synthesis of Alkali Metal ATIs 2, 3-thf, and 4-thfa

a

Only one resonance structure is shown in each case.

isolated as a crystalline yellow solid. 7Li NMR studies reveal similar chemical shifts of δ ≈ 1.5−1.8 ppm for the metal nucleus irrespective of the presence and the nature of a neutral donor ligand (Table S1). This rules out close interactions of the Li+ ion with the aromatic ligand backbone.15−17 The related, tetracoordinate species [Li(ATItBu/tBu)(thf)2] shows a similar 7 Li NMR shift, δ = 1.78 ppm.1c Compound 3-thf is the first example of a sodium ATI. It is soluble in aromatic hydrocarbons and donor solvents such as THF or pyridine. A 23 Na NMR study revealed extremely broad resonances for the sodium nucleus of 3-thf in either C5D5N (fwhm = 1300 Hz) or C6D6 (fwhm = 2300 Hz)18 and a significant low-field shift in the coordinating solvent pyridine (δ = 11.8 ppm) compared to benzene (δ = 4.1 ppm).19 This suggests the possibility of interactions between the sodium nucleus and the aromatic C7 ligand backbone in benzene solution,15,20 albeit the severe signal broadening hampers an unequivocal interpretation. The THF ligand of compound 3-thf could not be removed under reduced pressure or by washing with hexanes. In comparison, the THF ligand of the potassium species 4-thf can be removed by prolonged exposure to high vacuum.21 Both 4 and 4-thf are insoluble in aromatic hydrocarbons, requiring at least small amounts of donor solvents such as THF for solvation. In contrast to the literature known compound [Li(ATIiPr/iPr)(thf)2], the THF ligands in 2-thf-OPPh3,22 3-thf, and 4-thf are substitutionally labile in the presence of excess THF as shown by 1H NMR spectroscopy. Among the few examples of isolated alkali metal ATIs, only lithium derivatives have been structurally characterized.1,12,23 In order to elucidate their coordination chemistry in the solid state, compounds 2-thf-OPPh3, 3-thf, and 4-thf were investigated by single-crystal X-ray diffraction analysis.24 Compound 2-thf-OPPh3 (monoclinic P21/c, Z = 4; Figure 1) shows the expected distorted tetrahedral coordination geometry around Li, the distortion being due to the small bite angle of the ATI ligand (N1−Li1−N2, 79.51(9)°). The Li−N bond lengths of 2.034(2) and 1.988(2) Å differ by 0.05 Å, which might be due to the asymmetric substitution pattern of the ATI ligand.27 The presence of the strong σ-donor OPPh3 induces an elongation of the Li−OTHF bond compared to literature known lithium ATI compounds bearing two THF ligands (Δ ≈ 0.02− 0.04 Å). The sodium compound 3-thf crystallized from a THF/ hexanes solution in the orthorhombic space group P212121 with Z = 4 (Figure 2).28 Unexpectedly, each sodium atom does not only interact with one THF ligand and two nitrogen atoms of an ATI ligand but also with the C7 ligand backbone of a neighboring molecule. In this respect, it is noteworthy that 3thf was crystallized in the presence of an excess of the donor ligand THF. This is the first example of a monoanionic ATI ligand interacting with a metal center via the π-electron cloud

Figure 1. Molecular structure of [Li(ATIPh/iPr)(thf)(OPPh3)] (2-thfOPPh3) in the solid state. Displacement ellipsoids are drawn at the 50% probability level. Hydrogen atoms and one lattice bound molecule of toluene are omitted for clarity. Selected bond lengths (Å) and angles (deg): Li1−N1, 2.034(2); Li1−N2, 1.988(2); Li1−O1, 1.906(2); Li1−O2, 2.014(2); O1−P1, 1.4953(9); C1−N1, 1.3196(16); C2−N2, 1.3224(16); N1−Li1−N2, 79.51(9); N1−Li1− O1, 124.42(12); N1−Li1−O2, 124.46(11); N2−Li1−O1, 120.56(12); N2−Li1−O2, 104.65(10); O1−Li1−O2, 101.31(10); Li1−O1−P1, 148.94(9).

Figure 2. (a) Cutout of the solid-state structure of [Na(ATIPh/iPr)(thf)]∞ (3-thf)∞. Displacement ellipsoids are drawn at the 50% probability level. Hydrogen atoms are omitted for clarity. Atoms exceeding one formula unit are shown as empty ellipsoids. (b) Representation showing the arrangement of (3-thf)∞ as a onedimensional coordination polymer in the solid state. Selected bond lengths (Å) and angles (deg): Na1−N1, 2.3643(15); Na1−N2, 2.3563(15); Na1−O1, 2.3047(14); Na1−C3′, 3.1071(18); Na1−C4′, 2.9313(19); Na1−C5′, 2.8034(18); Na1−C6′, 2.7957(18); Na1−C7′, 3.0604(18); N1−C1, 1.303(2); N2−C2, 1.318(2); N1−Na1−N2, 67.57(5); N1−Na1−O1, 99.24(5); N1−Na1−ct, 132.96(5); N2− Na1−O1, 107.29(5); N2−Na1−ct, 116.84(5); O1−Na1−ct, 120.48(5).

of its C7 ligand backbone; i.e., a μ2(κ2-N)(κ5-C) coordination mode is realized (cf, Scheme 1, C). This coordination mode leads to the formation of a one-dimensional coordination polymer, in which neighboring molecules are related by a twofold screw axis 21 along the crystallographic a-axis (Figure 2b). Taking the centroid of the carbon atoms C3−C7 as a coordination point, the sodium atom is found in a strongly distorted tetrahedral coordination geometry. The distances between Na1 and the atoms C3−C7 of the ATI backbone B


Article

Organometallics

metal centers via the π-electron cloud of the C7 ligand backbone, reactions of 3-thf with precursors containing Rh+ and W0 as potentially arenophilic metal centers were investigated.30,31 Reaction of 3-thf with [Rh(OTf)(cod)] did not give a cationic mixed metal species [NaRh(ATIPh/iPr)(cod)][OTf], but salt elimination was observed to yield the rhodium compound [Rh(ATIPh/iPr)(cod)] (5) as a yellow solid (Scheme 3; OTf = triflate; cod = 1,5-cyclooctadiene).

(2.80−3.11 Å) are within the range of 2.58−3.11 Å reported for Na−C6(arene) interactions in literature-known sodium compounds with at least two additional nitrogen donor ligands.29 In spite of the asymmetric substitution pattern of the ATI ligand, the two Na1−N1/2 bond lengths differ only marginally (Δ = 0.01 Å). The potassium compound 4-thf crystallized in the monoclinic space group P21/n with Z = 4 (Figure 3). It is

Scheme 3. Reactions of 3-thf with RhI Precursors Give [Rh(ATIPh/iPr)(cod)] (5) Irrespective of the Use of Triflate or Chloride Counteranionsa

a

Only one resonance structure is shown.

Alternatively, the more easily accessible rhodium precursor [RhCl(cod)]2 can be used for the synthesis of 5.32 The rhodium complex 5 is easily soluble in common organic solvents such as toluene or THF and moderately soluble in aliphatic hydrocarbons or highly polar solvents such as DMSO. 5 is air stable in the solid state and in solution, even at elevated temperatures of 100 °C. NOESY NMR studies indicate a κ2N coordination mode in the temperature range of 23−100 °C (cross signals were detected for Hcod/HiPr and Hcod/HPh resonances, but not for Hcod/HATI‑backbone) and a square-planar coordination geometry is suggested for the d8-Rh species in solution. Single-crystal X-ray analysis confirmed the expected coordination geometry in the solid state with an angle sum of 360° around the rhodium center (Figure 4; orthorhombic space group Fdd2, Z = 16).28 The Rh−N bond lengths differ due to the asymmetric substitution pattern of the ATI ligand (Δ = 0.05 Å). On average (Rh−N(avg), 2.05 Å), they are slightly elongated compared to those in a dinuclear RhI tetra-carbonyl species based on a bis-ATI ligand (Rh−N(avg) = 2.03 Å).33

Figure 3. (a) Cutout of the solid-state structure of [K(ATIPh/iPr)(thf)]∞ (4-thf)∞. Displacement ellipsoids are drawn at the 50% probability level. Hydrogen atoms are omitted for clarity. Atoms exceeding one formula unit are shown as empty ellipsoids. (b) Representation showing the arrangement of (4-thf)∞ as a onedimensional coordination polymer in the solid state. Selected bond lengths (Å) and angles (deg): K1−N1, 2.916(3); K1−N2, 2.786(3); K1−N1′, 2.836(3); K1−N2′, 2.968(3); K1−O1, 2.859(2); K1−O1′, 2.849(3); N1−C1, 1.328(4); N2−C2, 1.346(4); N1−K1−N2, 55.57(8); N1−K1−O1, 85.32(8); N1−K1−N1′, 176.64(8); N1− K1−N2′, 124.36(8); O1−K1−O1′, 175.30(7).

the first potassium ATI compound to be crystallographically characterized. The ATI and the THF ligand in 4-thf adopt bridging coordination modes. Crystallographically independent units are related by a two-fold screw axis 21 along the crystallographic b-axis (Figure 3b). This leads to a onedimensional μ2-κ2N coordination polymer, which is unprecedented for ATI compounds. The potassium center resides in an octahedral coordination geometry with each of the two THF ligands, the two NPh groups, and the two NiPr groups in trans positions to each other. Whereas the K1−O1/O1′ bond lengths of 2.85−2.86 Å are highly similar, two of the K−N bonds (K1−N1/N2′, 2.92−2.97 Å) are clearly elongated compared to the remaining two K−N bonds (K1−N1′/N2, 2.79−2.84 Å). Interestingly, the general trend of alkali metal− arene interactions becoming more favorable with increasing atomic number of the group 1 element is not mirrored by the solid-state structures of 3-thf and 4-thf.24 ATI Complexes of Rh+ and W0. M−arene interactions of a neutral H-ATI ligand and related monoanionic (amino)tropolonates with highly arenophilic [Ru(C5Me5)]+ moieties have been reported.13 In order to evaluate the tendency of monoanionic ATI ligands to interact with other transition-

Figure 4. (a) Molecular structure of [Rh(ATIPh/iPr)(cod)] (5) in the solid state. Displacement ellipsoids are drawn at the 50% probability level. Hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and angles (deg): Rh1−N1, 2.070(5); Rh1−N2, 2.023(6); Rh1− (C17 = C18), 2.022(6); Rh1−(C21 = C22), 2.016(5); C1−N1, 1.354(7); C2−N2, 1.355(8); C17−C18, 1.396(10); C21−C22, 1.406(8); N1−Rh1−N2, 77.7(2); N1−Rh1−(C17 = C18), 99.2(2); Σ(N/(C = C)−Rh1−N/(C = C)), 360.0(3). C


Article

Organometallics The Rh−cod bonding parameters of 5 compare well to those of structurally related β-diketiminate compounds [Rh(βdiketiminate)(cod)].34 Reaction of 3-thf with [W(CO)3(NCMe)3] led to formation of a deep red crystalline compound [NaW(ATIPh/iPr)(thf)3] (6) under elimination of the acetonitrile ligands (Scheme 4). NMR Scheme 4. Reaction of 3-thf with [W(CO)3(NCMe)3] To Give [NaW(ATIPh/iPr)(thf)3] (6) or [NaW(ATIPh/iPr)(py)5] (7) (py = NC5H5)a

a

One resonance structure is shown in both cases.

spectroscopy confirmed the presence of CO ligands and their interaction with the tungsten center in solution (183W satellites for the CO resonance in the 13C NMR spectrum: 1JCW = 187.7 Hz). IR spectroscopy in the solid state revealed two sets of CO stretching bands with ṽ = 1856 cm−1 and ṽ = 1736, 1697 cm−1. This suggests the presence of terminal CO groups and CO groups bridging (at least) two metal centers.35 The THF ligands in 6 are substitutionally labile in solution as shown by 1 H NMR spectroscopy and can be substituted for stronger σdonors such as pyridine. Accordingly, a compound of the constitution [NaW(ATIPh/iPr)(py)5] (7) was isolated by crystallization from pyridine/MTBE and shows NMR and IR spectroscopic features similar to those of 6 (py = NC5H5; MTBE = methyl-tert-butyl ether). One exception to the spectroscopic similarities is a broadening of 1H NMR resonances of the phenyl group in 7 due to a higher rotational barrier as a consequence of the stronger binding of the neutral ligand (pyridine vs THF).36 Compound 7 crystallized in the orthorhombic space group Fdd2 with Z = 16 (Figure 5).28 The asymmetric unit contains two formula units with similar bonding parameters, only one of which is discussed. Four pyridine molecules per formula unit interact with metal centers (vide inf ra), and solvent voids are occupied by pyridine or MTBE molecules. The tungsten center is coordinated by the ATI ligand in a κ2N coordination mode, by three carbonyl ligands in a facial fashion, and by a pyridine ligand. This results in an octahedral coordination geometry around W. The W−NATI bond lengths of 2.17−2.24 Å differ by 0.07 Å. In the only other crystallographically characterized tungsten compound based on an ATI ligand framework, [W(HATIiPr/iPr)’(CO)4], the ligand is neutral and the NH proton has migrated to the ligand backbone in an imine enamine tautomerization.37 Consequently, the W−N bonds in 7 are on average shortened (Δ = −0.02 Å). One of the carbonyl ligands in 7 is terminal, whereas the remaining two adopt a bridging μ2-κCκO bonding mode acting as W−(CO)−Na isocarbonyl ligands (Figure 5). As a result, the isocarbonyl ligands show not only lower frequencies of the CO stretch in the IR spectrum (vide supra) but also a lengthening of the W− C (Δavg = 0.02 Å) and the CO bonds (Δavg = 0.02 Å) compared to the terminal CO ligand. The sodium atoms adopt a slightly distorted square-pyramidal coordination geometry with the isocarbonyl ligands in trans positions of the equatorial

Figure 5. (a) Cutout of the solid-state structure of [NaW(ATIPh/iPr)(CO)3(py)5]∞ (7)∞.38 Displacement ellipsoids are drawn at the 50% probability level, coordinating solvent molecules are shown as wire frame. Hydrogen atoms and lattice bound solvent molecules are omitted for clarity. Atoms exceeding one formula unit are shown as empty ellipsoids. (b, c) Arrangement of (7)∞ as a one-dimensional coordination polymer in the solid state. Selected bond lengths (Å) and angles (deg): W1−N1, 2.242(8); W2−N2, 2.167(7); W1−N3, 2.311(9); W1−C22, 1.913(10); W1−C23, 1.926(10); W1−C24, 1.930(9); Na1−O3, 2.366(7); Na1−O4, 2.350(8); Na1−N4, 2.475(12); Na1−N5, 2.441(10); Na1−N6, 2.397(9); C1−N1, 1.310(13); C2−N2, 1.347(11); C22−O1, 1.173(14); C23−O2, 1.189(12); C24−O3, 1.190(10); N1−W1−N2, 70.4(3); N3−W1− C22, 178.1(5); C22−W1−C23, 83.7(6); C24−O3−Na1, 133.8(6); O3−Na1−O4, 178.5(4); N4−Na1−N5, 95.7(4); N4−Na1−N6, 171.0(5).

plane. Overall, the bridging coordination mode of the isocarbonyl ligands in conjunction with their cis arrangement around W and their trans arrangement around Na leads to a one-dimensional coordination polymer of 7. The band structure is built of U-shaped asymmetric units that are related by glide reflections along the diagonal of the crystallographic ac plane (Figure 5b,c). This is the first example of a polymeric tungsten carbonylate with only isocarbonyl units as bridging ligands.39 DFT Calculations. Density functional theory (DFT) calculations were performed on a series of Na, Rh, and W ATIs related to 3-thf, 5, and 7, respectively (for details, see the Experimental Section and the Supporting Information). Compound [Na(ATIPh/iPr)(thf)2] (3-(thf)2) was calculated as D


Article

Organometallics a monomeric form of 3-thf, bearing one additional THF ligand compared to its experimentally observed counterpart. A frontier orbital analysis reveals a HOMO and a LUMO with large contributions of pz-type orbitals of the carbon atoms in the C7 ligand backbone (Figure 6a). Thus, coordination of a metal center to this part of the molecule appears reasonable for metals engaging in L→M bonding and/or M→L backdonation.

Figure 7. Schematic representations and relative Gibbs energies of calculated structures 5, 5-pi, and 9−11; cod = 1,5-cyclooctadiene, py = pyridine.

might be experimentally accessible by ligand fine-tuning (e.g., increase of steric bulk at the NATI and Ccod donor atoms; see the Supporting Information). A frontier orbital analysis of 5 reveals a metal-centered dz2 type HOMO and a LUMO with large contributions from pz-type orbitals of the carbon atoms in the ligand backbone (Supporting Information). This makes 5 a less promising candidate for the coordination of Lewis acidic metal centers to the ligand backbone (L→M bonding), but suggests the possibility of coordinating an electron-rich metal center to the ligand backbone (M→L bonding as dominating interaction). Compound [NaW(ATIPh/iPr)(CO)3(py)3] (9) was calculated as a model for the experimentally observed tungsten complex 7 (Figure 7, bottom). Isomers of 9 with either a tungsten (10) or a sodium atom (11, 12) interacting with the ligand backbone were found to be minima on the potential energy surface (for 12, see the Supporting Information). Compound 10 is significantly higher in energy than 9 (ΔGrel = +17.7 kcal· mol−1), which is in agreement with earlier experimental findings on a related mononuclear system.37 Compound 11 is only slightly higher in energy than 9 (ΔGrel = +3.6 kcal·mol−1), suggesting that interactions between sodium ions and the ATI ligand backbone should be accessible for the experimentally observed compounds [NaW(ATIPh/iPr)(L)n] (6, 7) in solution.44

Figure 6. Calculated structures of 3-(thf)2 (a) with its HOMO (left) and LUMO (right) at isovalues of 0.03 and 8 (b). Color code for atoms: gray = C, red = O, blue = N, yellow = Na; hydrogen atoms omitted for clarity.

Indeed, the dinuclear species [Na2(ATIPh/iPr)2(thf)3] (8), for which L→M interactions can be expected, corresponds to a stationary point on the potential energy surface (Figure 6b).40 The Na−C interactions in 8 were analyzed using the Nalewajski−Mrozek (N-M) bond index, which accounts for covalent as well as ionic contributions to bonding.41 N-M indices for interactions of Na1 with C3−C7 show an average value of 0.02.42 The other relevant N-M bond indices amount to 0.11 (Na1−OTHF), 0.17 (Na1−NPh), and 0.22 (Na1−NiPr). In order to relate these numbers to the bonding situation in well-known compounds, [Na(C5H5)(thf)3] and [Na(C5Me5)(thf)3] were calculated as archetypical examples of complexes with bonding interactions between Na+ and an anionic, carbonbased, delocalized π-electron system (Supporting Information). In both cases, the N-M bond indices show average values of 0.04 and 0.14 for Na−CCp/Cp* and Na−OTHF interactions, respectively. Overall, these results confirm that the strongest bonding of the Na1 atom in 8 results from Na1−N interactions and that the short Na1−C(3−7) distances correlate with significant bonding interactions. In agreement with these results, the reaction 2 (3-(thf)2) → 8 + THF was calculated to be slightly exothermic and exergonic (ΔHrel = −6.3 kcal· mol−1; ΔGrel = −1.9 kcal·mol−1). This supports experimental findings in that interactions between Na and the ligand backbone are energetically accessible even in the presence of a potential donor ligand (vide supra).43 The rhodium compound 5 was calculated with the experimentally observed κ2N coordination geometry and as an isomer 5-pi, in which with the metal center is coordinated by the π-electron cloud of the C7 ligand backbone (Figure 7, top). In good agreement with experimental findings, 5 is thermodynamically favored over 5-pi by ΔGrel = −31.0 kcal· mol−1. However, the energy gap between 5 and 5-pi together with the fact that 5-pi represents a local energy minimum on the potential energy surface suggests that analogues of 5-pi

■

CONCLUSIONS A series of Li, Na, and K aminotroponiminates (ATIs) have been synthesized and fully characterized. The studies are based on the literature-known asymmetrically phenyl/iso-propyl substituted ligand H-ATIPh/iPr. The lithium compound [Li(ATIPh/iPr)(thf)(OPPh3)] shows a frequently observed κ2N binding mode. The first example of a sodium ATI, [Na(ATIPh/iPr)(thf)] (3-thf), revealed an unprecedented μ2-κ2Nκ5C coordination mode of the ATI ligand with unusual interactions between the metal center and the π-electron cloud of the C7 ligand backbone in the solid state. Significant Na−C bonding interactions were confirmed by DFT calculations. NMR studies and calculations suggest that this type of interaction is also accessible in solution. The new binding mode leads to a polymeric structure of 3-thf in the solid state. Likewise, the first E


Article

Organometallics

Ph), 163.80 (s, 1-C), 165.78 (s, 2-C) ppm. 7Li NMR (194 MHz, C6D6): δ = 1.52 ppm. Anal. Calc. for C16H17N2Li (244.27 g/mol): C, 78.68; H, 7.02; N, 11.47; found: 78.63; H, 7.31, N, 11.32. mp = 164 °C (decomp). [Li(ATIPh/iPr)(thf)(OPPh3)] (2-thf-OPPh3). OPPh3 (34 mg, 0.12 mmol) was added to a solution of 2 (30 mg, 0.12 mmol) in THF (2 mL). The reaction mixture was layered with hexanes (12 mL) and stored at −30 °C. A yellow crystalline material had precipitated after 2 days, which was isolated by filtration and dried in vacuo. A second crop was obtained after storing the mother liquor for another 2 days at −30 °C. Combined yield: 59 mg, 99 μmol, 83%. 1 H NMR (500 MHz, C6D6/THF-d8 (5:1)): δ = 1.25 (d, 6H, 3JHH = 6.2 Hz, Me), 1.46−1.48 (m, 4H, β-THF), 3.53−3.56 (m, 4H, α-THF), 3.98 (sept, 1H, 3JHH = 6.2 Hz, CHMe2), 5.98 (dd, 1H, 3JHH = 8.8 Hz, 3 JHH = 8.8 Hz, 5-H), 6.54 (d, 1H, 3JHH = 11.6 Hz, 7-H), 6.58 (d, 1H, 3 JHH = 11.1 Hz, 3-H), 6.65 (dd, 1H, 3JHH = 8.8 Hz, 3JHH = 11.1 Hz, 4H), 6.82 (dt, 1H, 3JHH = 7.6 Hz, 4JHH = 0.8 Hz, N(p-Ph)), 6.85−6.89 (m, 3H, N(o/m-Ph)), 6-H (overlapping)), 7.04−7.08 (m, 6H, P(oPh)3), 7.10−7.14 (m, 5H, P(p-Ph)3, N(m/o-Ph) (overlapping)), 7.55−7.59 (m, 6H, P(m-Ph)3) ppm. 13C NMR (126 MHz, C6D6/ THF-d8 (5:1)): δ = 24.17 (s, Me), 25.86 (s, β-THF), 48.43 (s, CHMe2), 67.82 (s, α-THF), 110.29 (s, 7-C), 110.46 (s, 3-C), 110.91 (s, 5-C), 120.48 (s, N(p-Ph)), 123.67 (s, N(o/m-Ph)), 128.71 (d, 2JCP = 12.1 Hz, P(o-Ph)3), 129.12 (s, N(m/o-Ph)), 131.99 (d, 4JCP = 2.6 Hz, P(p-Ph)3), 132.49 (d, 3JCP = 10.0 Hz, P(m-Ph)3), 132.59 (s, 6-C), 132.99 (s, 4-C), 133.04 (d, 1JCP = 104.9 Hz, P(ipso-Ph)3), 155.96 (s, N(ipso-Ph)), 162.59 (s, 1-C), 164.38 (s, 2-C) ppm. 31P NMR (123 MHz, C6D6/THF-d8 (5:1)): δ = 28.17 (s) ppm. 7Li NMR (194 MHz, C 6 D 6 /THF-d 8 (5:1)): δ = 1.83 (s) ppm. Anal. Calc. for C38H40N2O2LiP (594.66 g/mol): C, 76.75; H, 6.78; N, 4.71; found: C, 76.80; H, 6.78; N, 4.47. mp = 85−92 °C (decomp). [Na(ATIPh/iPr)(thf)] (3-thf). [Na(N(SiMe3)2)] (834 mg, 3.50 mmol) was added to a solution of 1 (642 mg, 3.50 mmol) in THF (4.5 mL) to give a deep orange solution. After 10 min, all volatiles were removed from the reaction mixture. The resulting orange solid was washed with hexanes (2 × 2 mL) and dried in vacuo. Yield: 1.15 g, 3.46 mmol, 99%. 1 H NMR (300 MHz, C6D6): δ = 1.05 (d, 6H, 3JHH = 6.1 Hz, Me), 1.24−1.28 (m, 4H, β-THF), 3.27−3.31 (m, 4H, α-THF), 3.77 (sept, 1H, 3JHH = 6.1 Hz, CHMe2), 6.06 (br dd, 1H, 3JHH = 8.9 Hz, 5-H), 6.48 (d, 1H, 3JHH = 11.6 Hz, 7-H), 6.51 (d, 1H, 3JHH = 10.7 Hz, 3-H), 6.67 (ddd, 1H, 3JHH = 8.9 Hz, 3JHH = 10.7 Hz, 4JHH = 1.0 Hz, 4-H), 6.75 (t, 1H, 3JHH = 7.4 Hz, p-Ph), 6.84 (d, 2H, 3JHH = 8.6 Hz, o-Ph), 6.87 (ddd, 1H, 3JHH = 8.9 Hz, 3JHH = 11.6 Hz, 4JHH = 1.0 Hz,, 6-H (partially overlapping with o-Ph)), 7.11 (br t, 2H, 3JHH = 7.8 Hz, mPh) ppm. 1H NMR (400 MHz, C5D5N): δ = 1.25 (d, 6H, 3JHH = 6.2 Hz, Me), 1.62−1.65 (m, 4H, β-THF), 3.65−3.69 (m, 4H, α-THF), 4.07 (sept, 1H, 3JHH = 6.2 Hz, CHMe2), 5.97 (dd, 1H, 3JHH = 8.6 Hz, 3 JHH = 9.0 Hz, 5-H), 6.53 (d, 1H, 3JHH = 10.6 Hz, 3-H), 6.56 (d, 1H, 3 JHH = 11.4 Hz, 7-H), 6.72 (ddd, 1H, 3JHH = 9.0 Hz, 3JHH = 10.6 Hz, 3 JHH = 1.4 Hz, 4-H), 6.89 (t, 1H, 3JHH = 7.3 Hz, p-Ph), 6.96 (ddd, 1H, 3 JHH = 8.6 Hz, 3JHH = 11.4 Hz, 3JHH = 1.4 Hz, 6-H (partially overlapping with o-Ph)), 6.99 (br d, 2H, 3JHH = 7.1 Hz, o-Ph), 7.23 (m, 2H, m-Ph (partially overlapping with solvent resonance)) ppm. 13C NMR (75 MHz, C6D6): δ = 24.41 (s, Me), 25.56 (s, β-THF), 48.19 (s, CHMe2), 67.97 (s, α-THF), 111.39 (s, 3-C), 111.90 (s, 7-C), 112.56 (s, 5-C), 121.07 (s, p-Ph), 123.40 (s, o-Ph), 129.98 (s, m-Ph), 133.24 (s, 6-C), 133.65 (s, 4-C), 156.49 (s, ipso-Ph), 162.46 (s, 1-C), 163.94 (s, 2-C) ppm. 13C NMR (101 MHz, C5D5N): δ = 24.66 (s, Me), 26.27 (s, β-THF), 49.67 (s, CHMe2), 68.30 (s, α-THF), 108.98 (s, 5-C), 109.94 (s, 7-C), 110.10 (s, 3-C), 120.74 (s, p-Ph), 123.58 (s, o-Ph), 129.96 (s, m-Ph), 132.75 (s, 6-C), 133.03 (s, 4-C), 157.99 (s, ipso-Ph), 162.14 (s, 1-C), 163.87 (s, 2-C) ppm. 23Na NMR (106 MHz, C6D6, 0.06 M): δ = 4.1 (br s) ppm. 23Na NMR (106 MHz, NC5D5, 0.06 M): δ = 11.8 (br s) ppm. Anal. Calc. for C20H25N2ONa (332.42 g/mol): C, 72.26; H, 7.58; N, 8.43; found: C, 72.11; H, 7.72; N, 8.32. mp = 112− 116 °C (decomp). [K(ATIPh/iPr)(thf)] (5-thf). KH (13 mg, 0.32 mmol) was added to a solution of 1 (50 mg, 0.21 mmol) in THF (2 mL). A gas evolution was

structurally characterized potassium ATI, [K(ATIPh/iPr)(thf)] (4-thf), also shows a polymeric structure in the solid state. In this case, a rare μ2-κ2N coordination mode is realized with each ATI ligand bridging two metal centers. 3-thf and 4-thf represent the first examples of coordination polymers based on ATI ligands. Reactions of 3-thf with Rh+ and W0 precursors were performed to investigate the potential of monoanionic ATI ligands to interact with transition-metal centers via their C7 ligand backbone. Experimental and theoretical analyses of the isolated products [Rh(ATIPh/iPr)(cod)] (5) and [NaW(ATIPh/iPr)(py)5] (7) revealed no such interactions, but suggest isomers of 7 with Na−ATIbackbone interactions to be energetically accessible. Overall, this study revealed an unexpectedly rich coordination chemistry for the monoanionic ATI ligand family with implications for the design of ATI-based catalysts and their potential mechanistic pathways.

■

EXPERIMENTAL SECTION

General Considerations. All air- and moisture-sensitive manipulations were carried out using standard vacuum line Schlenk techniques or in an MBraun inert atmosphere drybox containing an atmosphere of purified argon. Solvents were degassed and purified according to standard laboratory procedures. NMR spectra were recorded on Bruker instruments operating at 300, 400, or 500 MHz with respect to 1H. 1H and 13C NMR chemical shifts are reported relative to SiMe4 using the residual 1H and 13C chemical shifts of the solvent as a secondary standard. 7Li and 23Na NMR chemical shifts are reported relative to 1 M LiCl in D2O and 1 M NaCl in D2O, respectively. In the NMR spectroscopic characterization of ATI compounds, the CNiPr carbon atom is referred to as 1-C. Infrared spectra were collected on a Bruker FT-IR-Alpha spectrometer. Elemental analyses were performed on a Leco or a Carlo Erba instrument. Single crystals suitable for X-ray diffraction were coated with polyisobutylene or perfluorinated polyether oil in a glovebox, transferred to a nylon loop, and then transferred to the goniometer of a diffractometer equipped with a molybdenum X-ray tube (λ = 0.71073 Å). The structures were solved using direct methods (SHELXS) completed by Fourier synthesis and refined by full-matrix least-squares procedures. CCDC 1446548−1446552 contain the crystallographic information for this work. Computational Details. DFT calculations were performed with the Amsterdam Density Functional program45 using the BP86-D3 functional (local density approximation, VWN correction)46 with gradient47 and dispersion corrections.48 The TZ2P basis set was applied. Core electrons were treated by the small frozen core approximation.49 For calculations including W or Rh, relativistic effects were treated using the scalar zeroth order regular approximation.50 All reported structures show zero imaginary frequencies. Discussed N-M bond indices are based on partioning of tr(ΔP2) with a 3-index set.41 Thermodynamic parameters were calculated at a temperature of 298.15 K and a pressure of 1.00 atm. [Li(ATIPh/iPr)] (2). A solution of [Li(CH2SiMe3)] (200 mg, 2.12 mmol) in toluene (6 mL) was added to a solution of 1 (505 mg, 2.12 mmol) in toluene (6 mL) to give an orange solution. After 1 h, addition of pentane (10 mL) led to precipitation of a yellow solid, which was isolated by filtration, and dried in vacuo. Yield: 450 mg, 1.84 mmol, 87%. 1 H NMR (300 MHz, C6D6): δ = 1.02 (d, 6H, 3JHH = 6.2 Hz, Me), 3.60 (hept, 1H, 3JHH = 6.2 Hz, CHMe2), 6.12 (dd, 1H, 3JHH = 8.7 Hz, 3 JHH = 9.2 Hz, 5-H), 6.49 (d, 1H, 3JHH = 10.7 Hz, 3-H), 6.52 (d, 1H, 3 JHH = 11.6 Hz, 7-H), 6.64 (ddd, 1H, 3JHH = 9.2 Hz, 3JHH = 10.7 Hz, 4 JHH = 1.3 Hz, 4-H), 6.85 (t, 1H, 3JHH = 7.7 Hz, p-Ph), 6.86 (ddd, 1H, 3 JHH = 8.7 Hz, 3JHH = 11.6 Hz, 4JHH = 1.3 Hz, 6-H), 6.90 (d, 2H, 3JHH = 7.7 Hz, o-Ph), 7.11 (br t, 2H, 3JHH = 7.7 Hz, m-Ph) ppm. 13C NMR (75 MHz, C6D6): δ = 24.02 (s, Me), 47.97 (s, CHMe2), 112.73 (s, 3C), 113.49 (s, 7-C), 115.13 (s, 5-C), 122.99 (s, p-Ph), 124.29 (s, oPh), 130.68 (s, m-Ph), 134.14 (s, 6-C), 134.45 (s, 4-C), 153.76 (s, ipsoF


Article

Organometallics

6-H), 6.91 (tt, 1H, 3JHH = 7.5 Hz, 4JHH = 1.2 Hz, p-Ph), 7.01 (dd, 2H, 3 JHH = 8.4 Hz, 4JHH = 1.2 Hz, o-Ph), 7.17−7.21 (m, 2H, m-Ph) ppm. 13 C NMR (126 MHz, THF-d8): δ = 25.28 (s, Me), 26.18 (s, β-THF), 53.69 (s, CHMe2), 68.02 (s, α-THF), 112.23 (s, 7-C), 114.45 (s, 3-C), 114.48 (s, 5-C), 122.81 (s, p-Ph), 125.93 (s, o-Ph), 128.69 (s, m-Ph), 131.73 (s, 4-C), 132.42 (s, 6-C), 155.93 (s, ipso-Ph), 166.78 (s, 1-C), 168.73 (s, 2-C), 231.55 (s, CO; satellites: 1JCW = 187.7 Hz) ppm. mp = 58−63 °C; Anal. Calc. for C31H41N2NaO6W (744.50 g/mol): C, 50.01; H, 5.55; N, 3.76; found: C, 50.12; H, 5.71; N, 4.12. ATR IR: ṽ = 2955 (w), 2870 (w), 1856 (s), 1736 (s), 1697 (s), 1581 (m), 1490 (m), 1460 (w), 1414 (m), 1370 (w), 1271 (w), 1230 (m), 1194 (w), 1169 (w), 1140 (w), 1053 (m), 882 (m), 856 (m), 717 (m), 694 (w) cm−1. [NaW(ATIPh/iPr)(CO)3(py)5] (7). 6 (40 mg, 54 μmol) was dissolved in pyridine (1 mL). The solution was layered with MTBE (4 mL) and cooled to −30 °C. Dark red-brown needles of 7 had formed after 3 days, which were isolated by filtration and dried in a stream of argon. Yield: 34 mg, 37 μmol, 63%. 1 H NMR (500 MHz, 40 °C, THF-d8): δ = 1.24 (d, 6H, 3JHH = 6.3 Hz, Me), 4.07 (sept, 1H, 3JHH = 6.3 Hz, CHMe2), 5.71 (dd, 1H, 3JHH = 9.0 Hz, 3JHH = 9.0 Hz, 5-H), 5.82 (d, 1H, 3JHH = 11.1 Hz, 3-H), 6.27 (ddd, 1H, 3JHH = 9.0 Hz, 3JHH = 11.1 Hz, 4JHH = 1.2 Hz, 4-H), 6.33 (d, 1H, 3JHH = 11.6 Hz, 7-H), 6.57 (ddd, 1H, 3JHH = 9.0 Hz, 3JHH = 11.6 Hz, 4JHH = 1.2 Hz, 6-H), 6.66 (br d, 2H, 3JHH = 7.3 Hz, o-Ph), 6.80 (t, 1H, 3JHH = 7.4 Hz, p-Ph), 7.05 (br dd, 2H, 3JHH = 7.3, 3JHH = 7.4 Hz, m-Ph), 7.20−7.22 (m, 10H, 3,5-py), 7.63 (tt, 5H, 3JHH = 7.6, 4JHH = 1.8 Hz, 4-py), 8.53−8.55 (m, 10H, 2,6-py) ppm. Traces of MTBE were also detected. 13C NMR (126 MHz, 40 °C, THF-d8): δ = 24.72 (s, Me), 53.33 (s, CHMe2), 112.29 (s, 7-C), 113.26 (s, 5-C), 114.47 (s, 3-C), 122.59 (s, p-Ph), 124.04 (s, 3,5-py), 125.52 (s, o-Ph), 128.65 (s, m-Ph), 131.72 (s, 4-C), 132.60 (s, 6-C), 136.03 (s, 4-py), 151.16 (s, 2,6-py), 155.96 (s, ipso-Ph), 166.58 (s, 1-C), 168.28 (s, 2-C), 230.58 (s, CO) ppm. mp = 58−62 °C. Anal. Calc. for C44H42N7NaO3W (923.70 g/mol): C, 57.21, H, 4.58; N, 10.61; found: C, 57.17; H, 4.67; N, 10.62. ATR IR: ṽ = 3054 (w), 2966 (m), 2926 (w), 2274 (s), 1857 (s), 1732 (s), 1695 (s), 1580 (s), 1481 (s), 1437 (s), 1417 (m), 1363 (m), 1271 (m), 1232 (m), 1193 (m), 1143 (m), 1066 (m), 1030 (m), 991 (m), 946 (m), 748 (w), 698 (m), 610 (w).

observed, a colorless solid precipitated, and the color of the liquid phase changed from yellow to orange. After 1 h, the reaction mixture was filtered and all volatiles were removed from the filtrate to give an orange solid, which was washed with hexanes (2 × 2 mL) and dried in vacuo for 1 h. Yield: 70 mg, 0.20 mmol, 95%. The THF ligands can be removed by prolonged drying in vacuo.21 1 H NMR (500 MHz, C6D6/THF-d8 (12:1)): δ = 1.19 (d, 6H, 3JHH = 6.1 Hz, Me), 1.44−1.46 (m, 4H, β-THF), 3.53−3.56 (m, 4H, αTHF), 3.98 (sept, 1H, 3JHH = 6.1 Hz, CHMe2), 5.88 (br dd, 1H, 3JHH = 8.6 Hz, 3JHH = 9.0 Hz, 5-H), 6.34 (d, 1H, 3JHH = 12.6 Hz, 7-H), 6.38 (d, 1H, 3JHH = 10.8 Hz, 3-H), 6.62 (ddd, 1H, 3JHH = 9.0 Hz, 3JHH = 10.8 Hz, 4JHH = 1.0 Hz, 4-H), 6.82 (br t, 1H, 3JHH = 7.7 Hz, p-Ph), 6.83 (ddd, 1H, 3JHH = 8.6 Hz, 3JHH = 12.6 Hz, 4JHH = 1.0 Hz, 6-H (partially overlapping with o-Ph)), 6.98 (br d, 2H, 3JHH = 7.7 Hz, oPh), 7.23 (br t, 2H, 3JHH = 7.7 Hz, m-Ph) ppm. 13C NMR (125 MHz, C6D6/THF-d8 (12:1)): δ = 24.27 (s, Me), 25.84 (s, β-THF), 49.08 (s, CHMe2), 67.82 (s, α-THF), 109.28 (s, 5-C), 109.59 (s, 3-C, 7-C (overlapping)), 119.68 (s, 6-C), 122.92 (s, o-Ph), 129.77 (s, m-Ph), 132.28 (s, p-Ph), 132.88 (s, 4-C), 157.50 (s, ipso-Ph), 162.09 (s, 1-C), 163.18 (s, 2-C) ppm. mp > 220 °C. Elemental analyses were unsatisfactory for this compound, which was ascribed to its air sensitivity.51 [Rh(ATIPh/iPr)(cod)] (5). [RhCl(cod)]2 (82 mg, 0.17 mmol) was added to a solution of 3-thf (110 mg, 0.33 mmol) in toluene (5 mL). After 1 h, the reaction mixture was filtered. From this point on, exclusion of air is no longer necessary. All volatiles were removed from the yellow filtrate under reduced pressure to give a yellow solid, which was washed with hexanes (2 × 3 mL). The solid was dried in vacuo. The filtrate was stored at −30 °C for 12 h to give a second crop of 5, which was isolated by filtration and dried in vacuo. Combined yield: 77 mg, 0.17 mmol, 50%.

1 H NMR (400 MHz, C6D6): δ = 1.41 (d, 6H, 3JHH = 7.2 Hz, Me), 1.74 (br ddd, 2H, 3JHH = 6.9 Hz, 3JHH = 7.2 Hz, 3JHH = 14.2 Hz, He), 1.89 (br ddd, 2H, 3JHH = 6.7 Hz, 3JHH = 6.9 Hz, 3JHH = 13.7 Hz, Hc), 2.26−2.35 (m, 2H, Hd), 2.39−2.48 (m, 2H, Hb), 3.57 (sept, 1H, 3JHH = 7.2 Hz, CHMe2), 3.70 (br dd, 2H, 3JHH = 2.2 Hz, 3JHH = 5.0 Hz, Hf), 3.92 (br dd, 2H, 3JHH = 2.3 Hz, 3JHH = 5.1 Hz, Ha), 6.26 (dd, 1H, 3JHH = 8.8 Hz, 3JHH = 9.0 Hz, 5-H), 6.54 (d, 1H, 3JHH = 11.7 Hz, 3-H), 6.58 (dd, 1H, 3JHH = 8.8 Hz, 3JHH = 11.7 Hz, 4-H), 6.84 (dd, 1H, 3JHH = 9.0 Hz, 3JHH = 11.3 Hz, 6-H), 6.87 (d, 2H, 3JHH = 7.6 Hz, o-Ph), 6.91 (t, 1H, 3JHH = 7.4 Hz, p-Ph), 7.12 (dd, 2H, 3JHH = 7.4 Hz, 3JHH = 7.6 Hz, m-Ph), 7.18 (d, 1H, 3JHH = 11.3 Hz, 7-H) ppm. 13C NMR (101 MHz, C6D6): δ = 20.29 (s, Me), 30.71 (s, CHdHe), 31.25 (s, CHbHc), 50.42 (d, 2JCRh = 0.7 Hz, CHMe2), 77.73 (d, 1JCRh = 12.7 Hz, CHa),78.80 (d, 1 JCRh = 12.3 Hz, CHf), 115.64 (d, 3JCRh = 1.7 Hz, 3-C), 117.86 (d, 3JCRh = 2.1 Hz, 7-C), 119.43 (s, 5-C), 124.79 (s, p-Ph), 126.35 (s, o-Ph), 129.72 (s, m-Ph), 130.99 (s, 6-C), 132.51 (s, 4-C), 149.91 (d, 2JCRh = 1.3 Hz, ipso-Ph), 165.16 (d, 2JCRh = 1.5 Hz, 1-C), 168.64 (s, 2JCRh = 0.8 Hz, 2-C) ppm. mp = 208 °C. Anal. Calc. for C24H29N2Rh: C, 64.28, H, 6.52, N, 6.25; found: C, 64.41; H, 6.50; N, 6.31. [NaW(ATIPh/iPr)(CO)3(thf)3] (6). THF (2 mL) was added to a mixture of 3-thf (50 mg, 0.15 mmol) and [W(CO)3(NCMe)3] (60 mg, 0.15 mmol). After 3 days, the reaction mixture was filtered. The filtrate was layered with hexanes (6 mL) and stored at −30 °C. Dark red-brown crystalline 6 precipitated after 1 day, was isolated by filtration, and dried in a stream of argon. A second crop was obtained from the mother liquor upon storage at −30 °C for several days. Combined yield: 106 mg, 0.14 mmol, 93%. 1 H NMR (500 MHz, THF-d8): δ = 1.49 (d, 6H, 3JHH = 6.4 Hz, Me), 1.76−1.79 (m, 12H, β-THF), 3.60−3.63 (m, 12H, α-THF), 4.18 (sept, 1H, 3JHH = 6.4 Hz, CHMe2), 5.87 (dd, 1H, 3JHH = 9.0 Hz, 3JHH = 9.0 Hz, 5-H), 6.01 (d, 1H, 3JHH = 11.0 Hz, 3-H), 6.38 (ddd, 1H, 3JHH = 9.0 Hz, 3JHH = 11.0 Hz, 4JHH = 1.3 Hz, 4-H), 6.52 (d, 1H, 3JHH = 11.6 Hz, 7-H), 6.67 (ddd, 1H, 3JHH = 9.0 Hz, 3JHH = 11.6 Hz, 4JHH = 1.3 Hz,

■

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.6b00042. NMR spectra, 7Li NMR shifts for 2 in the presence of different neutral ligands, and computational details (PDF) Crystallographic data for 2-thf-OPPh3, 3-thf, 4-thf, 5, and 7 (CIF) Cartesian coordinates of calculated compounds (XYZ)

■

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS C.L. thanks Dr. Viktoria H. Gessner for helpful discussions, Prof. Dr. Holger Braunschweig and Prof. Dr. Hansjö rg Grützmacher for their support, and the Alexander von Humboldt Foundation for a Feodor Lynen return fellowship. G


Article

Organometallics

■

(17) A slight high-field shift of the resonances for C3−C7 atoms of the ligand backbone is observed in 13C NMR spectra of 2-thf-OPPh3 (C6D6/THF-d8 (5:1) compared to 2 (C6D6) (Δ = − 1.5 to − 4.2 ppm). Such changes could theoretically be due to (i) direct interaction of a metal nucleus with the ligand backbone or due to (ii) a change in M−N interactions (since the nitrogen atoms are in conjugation with the ligand backbone). (18) Broad 23Na NMR resonances have been reported for [Na(C5Me5)(NC5H5)3] and were ascribed to large quadrupolar relaxation effects as a result of an asymmetric environment around the Na nucleus (ref 20b). (19) Only a slight high-field shift of the resonances for C3−C7 atoms of the ligand backbone is observed in 13C NMR spectra upon changing the solvent from C6D6 to C5D5N (Δ = − 0.5 to − 3.6 ppm). Such changes could theoretically be due to (i) direct interaction of a metal nucleus with the ligand backbone or due to (ii) a change in M−N interactions (since the nitrogen atoms are in conjugation with the ligand backbone). (20) Strong interactions of a sodium nucleus with an aromatic system lead to negative 23Na NMR shifts (e.g.: δ = − 33.4 and − 22.0 ppm for [Na(C5H5)] and [Na(C5Me5)(NC5H5)3], respectively): (a) Willans, M. J.; Schurko, R. W. J. Phys. Chem. B 2003, 107, 5144−5161. (b) Rabe, G.; Roesky, H. W.; Stalke, D.; Pauer, F.; Sheldrick, G. M. J. Organomet. Chem. 1991, 403, 11−19. (21) Potassium ATIs with iso-propyl or cyclohexyl substituents at nitrogen could also be isolated free of additional donor ligands: (a) ref 6a. (b) Meiners, J.; Herrmann, J.-S.; Roesky, P. W. Inorg. Chem. 2007, 46, 4599−4604. (22) Only one set of THF signals appeared in the 1H NMR spectrum of a solution of 2-thf-OPPh3 in C6D6 in the presence of ca. 10 equiv of THF. (23) A lithium derivative of a ligand containing two ATI motifs has also been structurally characterized: Meyer, N.; Roesky, P. W. Dalton Trans. 2007, 2652−2657. (24) It has been shown that the tendency of alkali metal cations to interact with delocalized π-electrons increases with increasing atomic number of the alkali metal, e.g.: for alkyl and aryl compounds (ref 25 and references therein) or for amidinates (ref 26 and references therein). (25) (a) Hoffmann, D.; Bauer, W.; Schleyer, P. v. R.; Pieper, U.; Stalke, D. Organometallics 1993, 12, 1193−1200. (b) Schade, C.; von Ragué Schleyer, P. Adv. Organomet. Chem. 1987, 27, 169−278. (26) Lichtenberg, C.; Adelhardt, M.; Wörle, M.; Büttner, T.; Meyer, K.; Grützmacher, H. Organometallics 2015, 34, 3079−3089. (27) It has to be noted, however, that crystal packing and dispersion effects can also significantly affect bonding parameters in the solid state, especially for alkali metals with their tendency to show nondirectional bonding interactions. (28) Compounds 3-thf, 5, and 7 crystallized in chiral space groups, and their absolute structures were determined. (29) (a) Corbelin, S.; Kopf, J.; Lorenzen, N. P.; Weiss, E. Angew. Chem., Int. Ed. Engl. 1991, 30, 825−827. (b) Bock, H.; Havlas, Z.; Hess, D.; Näther, C. Angew. Chem., Int. Ed. 1998, 37, 502−504. (c) Fedushkin, I. L.; Skatova, A. A.; Chudakova, V. A.; Fukin, G. K. Angew. Chem., Int. Ed. 2003, 42, 3294−3298. (d) Hawley, A. L.; Stasch, A. Eur. J. Inorg. Chem. 2015, 2015, 258−270. (30) For examples of [Rh(cod)]+ interacting with arene moieties, see: (a) Ishii, Y.; Onaka, K.-I.; Hirakawa, H.; Shiramizu, K. Chem. Commun. 2002, 1150−1151. (b) Kuo, Y.-Y.; Haddow, M. F.; PérezRedondo, A.; Owen, G. R. Dalton Trans. 2010, 39, 6239−6248. (c) Shi, Y.; Blum, S. A. Organometallics 2011, 30, 1776−1779. (31) For examples of [W(CO)3] interacting with arene moieties, see: (a) Barluenga, J.; Trabanco, A. A.; Flórez, J.; García-Granda, S.; LLorca, M.-A. J. Am. Chem. Soc. 1998, 120, 12129−12130. (b) Fischer, P. J.; Weberg, A. B.; Bohrmann, T. D.; Xu, H.; Young, V. G., Jr. Dalton Trans. 2015, 44, 3737−3744. (c) Lee, J.-S.; Young, K. C.; Dongmok, W.; Kimoon, K. J. Organomet. Chem. 1993, 445, 49−54. (32) For an alternative synthesis of [Rh(ATI)(cod)] compounds involving a biphasic system and the in situ deprotonation of an H-ATI

REFERENCES

(1) (a) Dias, H. V. R.; Jin, W.; Wang, Z. Inorg. Chem. 1996, 35, 6074−6079. (b) Sinhababu, S.; Siwatch, R. K.; Mukherjee, G.; Rajaraman, G.; Nagendran, S. Inorg. Chem. 2012, 51, 9240−9248. (c) Siwatch, R. K.; Kundu, S.; Kumar, D.; Nagendran, S. Organometallics 2011, 30, 1998−2005. (2) (a) Datta, S.; Roesky, P. W.; Blechert, S. Organometallics 2007, 26, 4392−4394. (b) Datta, S.; Gamer, M. T.; Roesky, P. W. Dalton Trans. 2008, 2839−2843. (c) Bailey, P. J.; Dick, C. M. E.; Fabre, S.; Parsons, S. Dalton Trans. 2000, 1655−1661. (3) (a) Korolev, A. V.; Ihara, E.; Guzei, I. A.; Young, V. G., Jr.; Jordan, R. F. J. Am. Chem. Soc. 2001, 123, 8291−8309. (b) Korolev, A. V.; Guzei, I. A.; Jordan, R. F. J. Am. Chem. Soc. 1999, 121, 11605− 11606. (4) Steinhuebel, D. P.; Lippard, S. J. Organometallics 1999, 18, 109− 111. (b) Steinhuebel, D. P.; Lippard, S. J. Inorg. Chem. 1999, 38, 6225−6233. (c) Steinhuebel, D. P.; Lippard, S. J. J. Am. Chem. Soc. 1999, 121, 11762−11772. (5) (a) Ewald, A. H.; Sinn, E. Inorg. Chem. 1967, 6, 40−48. (b) Eaton, D. R.; McClellan, W. R.; Weiher, J. F. Inorg. Chem. 1968, 7, 2040−2046. (c) Brunner, H.; Knott, A.; Benn, R.; Rufińska, A. J. Organomet. Chem. 1985, 295, 211−221. (6) (a) Roesky, P. W. Chem. Ber. 1997, 130, 859−862. (b) Roesky, P. W. Eur. J. Inorg. Chem. 1998, 1998, 593−596. (c) Bürgstein, M. R.; Berberich, H.; Roesky, P. W. Organometallics 1998, 17, 1452−1454. (7) For a review article, see: Roesky, P. W. Chem. Soc. Rev. 2000, 29, 335−345. (8) Holm, R. H.; O’Connor, M. J. The Stereochemistry of Bis-Chelate Metal(II) Complexes in Progress in Inorganic Chemistry; Vol 14; Lippard, S. J., Ed.; Wiley: New York, 1971; pp 241−401. (9) (a) Dochnahl, M.; Löhnwitz, K.; Pissarek, J.-W.; Biyikal, M.; Schulz, S. R.; Schön, S.; Meyer, N.; Roesky, P. W.; Blechert, S. Chem. Eur. J. 2007, 13, 6654−6666. (b) Dochnahl, M.; Löhnwitz, K.; Pissarek, J.-W.; Roesky, P. W.; Blechert, S. Dalton Trans. 2008, 2844− 2848. (10) (a) Korolev, A. V.; Guzei, I. A.; Jordan, R. F. J. Am. Chem. Soc. 1999, 121, 11605−11606. (b) Korolev, A. V.; Ihara, E.; Guzei, I. A.; Young, V. G., Jr.; Jordan, R. F. J. Am. Chem. Soc. 2001, 123, 8291− 8309. (11) Franz, K. J.; Lippard, S. J. J. Am. Chem. Soc. 1999, 121, 10504− 10512. (12) Dias, H. V. R.; Jin, W. J. Chem. Crystallogr. 1997, 27, 353−358. (13) Pittracher, M.; Frisch, U.; Kopacka, H.; Wurst, K.; Müller, T.; Oehninger, L.; Ott, I.; Wuttke, E.; Scheerer, S.; Winter, R. F.; Bildstein, B. Organometallics 2014, 33, 1630−1643. (14) [Li-ATIPh/iPr(thf)2] (2-(thf)2) was isolated as an orange oil upon removing all volatiles from a THF solution of 2 under reduced pressure and was characterized NMR spectroscopically: 1H NMR (300 MHz, C6D6) δ = 1.20−1.24 (m, 8H, β-THF), 1.24 (d, 6H, 3JHH = 6.3 Hz, Me), 3.32−3.36 (m, 8H, α-THF), 3.98 (sept, 1H, 3JHH = 6.3 Hz, CHMe2), 6.16 (m, 1H, 5-H), 6.68 (d, 1H, 3JHH = 11.5 Hz, 7-H), 6.76− 6.83 (m, 2H, 3-H, 4-H), 6.93 (t, 1H, 3JHH = 7.3 Hz, p-Ph), 6.99 (dd, 1H, 3JHH = 9.6 Hz, 3JHH = 11.5 Hz, 6-H), 7.05 (br d, 2H, 3JHH = 8.5 Hz, o-Ph), 7.27 (br t, 2H, 3JHH = 7.9 Hz, m-Ph) ppm. 13C NMR (75 MHz, C6D6) δ = 25.45 (s, β-THF), 31.97 (s, Me), 48.13 (s, CHMe2), 68.26 (s, α-THF), 111.42 (s, 7-C), 111.62 (s, 3-C), 112.86 (s, 5-C), 121.45 (s, p-Ph), 123.81 (s, o-Ph), 129.68 (s, m-Ph), 133.32 (s, 6-C), 133.67 (s, 4-C), 155.46 (s, ipso-Ph), 163.24 (s, 1-C), 165.05 (s, 2-C) ppm. (15) Tropolonate anions, in analogy with ATIs, have been shown to exhibit aromatic character: Mó, O.; Yáñez, M.; Esseffar, M.; Herreros, M.; Notario, R.; Abboud, J. L.-M. J. Org. Chem. 1997, 62, 3200−3207. Close interactions between Li+ ions and aromatic ring systems induce high-field shifts of the 7Li NMR resonance (ref 16), which was not observed for 2 compared to 2-thf-OPPh3 or 2-(thf)2 (cf, Table S1). (16) (a) Cox, R. H.; Terry, H. W. J. Magn. Reson. 1974, 14, 317−322. (b) Lichtenberg, C.; Hillesheim, N. S.; Elfferding, M.; Oelkers, B.; Sundermeyer, J. Organometallics 2012, 31, 4259−4266. H


Article

Organometallics ligand, see: Brunner, H.; Knott, A.; Benn, R.; Rufińska, A. J. Organomet. Chem. 1985, 295, 211−221. (33) Villacorta, G. M.; Lippard, S. J. Inorg. Chem. 1988, 27, 144−149. (34) (a) Meier, G.; Steck, V.; Braun, B.; Eißler, A.; Herrmann, R.; Ahrens, M.; Laubenstein, R.; Braun, T. Eur. J. Inorg. Chem. 2014, 2014, 2793−2808. (b) Budzelaar, P. H. M.; Moonen, N. N. P.; de Gelder, R.; Smits, J. M. M.; Gal, A. W. Eur. J. Inorg. Chem. 2000, 2000, 753−769. (35) (a) de la Cruz, C.; Sheppard, N. J. Mol. Struct. 1990, 224, 141− 161. (b) Darensbourg, M. Y.; Jimenez, P.; Sackett, J. R.; Hanckel, J. M.; Kump, R. L. J. Am. Chem. Soc. 1982, 104, 1521−1530. (36) The coalescence temperature is ca. 263 K; five separate signals for the phenyl protons are observed in 1H NMR spectra recorded at 233 K in THF-d8. (37) Kirin, V.; Roesky, P. W. Z. Anorg. Allg. Chem. 2004, 630, 466− 469. (38) For asymmetric unit of 7, see the Supporting Information. (39) Some tungsten carbonylates with isocarbonyl ligands and at least one more type of bridging ligand have been reported, e.g.: (a) Liddle, S. T.; Gardner, B. M. J. Organomet. Chem. 2009, 694, 1581−1585. (b) Kirin, V.; Roesky, P. W. Eur. J. Inorg. Chem. 2004, 2004, 1045−1050. (c) Erker, G.; Dorf, U.; Mynott, R.; Tsay, Y.-H.; Krüger, C. Angew. Chem., Int. Ed. Engl. 1985, 24, 584−585. (40) 8 is suggested as a model of the bonding situation of 3-thf in the solid state (for comparison of bonding parameters, see the Supporting Information). (41) (a) Nalewajski, R. F.; Mrozek, J. Int. J. Quantum Chem. 1994, 51, 187−200. (b) Nalewajski, R. F.; Mrozek, J.; Michalak, A. Int. J. Quantum Chem. 1997, 61, 589−601. (c) Nalewajski, R. F.; Mrozek, J.; Mazur, G. Can. J. Chem. 1996, 74, 1121−1130. (d) Michalak, A.; DeKock, R. L.; Ziegler, T. J. Phys. Chem. A 2008, 112, 7256−7263. (42) Individual values range from 0.01 to 0.02. (43) Expectedly, the association of [Na(ATIPh/iPr)(thf)2] and [Na(ATIPh/iPr)(thf)] to give 8 was calculated to be exothermal and exergonic in the gas phase (ΔHrel = − 49.7 kcal·mol−1; ΔGrel = − 33.7 kcal·mol−1; Supporting Information). (44) This is further supported by calculated isomer 12 (ΔGrel = − 4.4 kcal·mol−1), in which the sodium atom interacts with the ligand backbone and one tungsten bound carbonyl ligand (Supporting Information). (45) ADF2014.05; SCM, Theoretical Chemistry, Vrije Universiteit: Amsterdam, The Netherlands, (http://www.scm.com). (46) Vosko, S. H.; Wilk, L.; Nusair, M. Can. J. Phys. 1980, 58, 1200− 1211. (47) (a) Perdew, J. P. Phys. Rev. B: Condens. Matter Mater. Phys. 1986, 33, 8822−8824. (b) Becke, A. D. Phys. Rev. A: At., Mol., Opt. Phys. 1988, 38, 3098−3100. (48) Grimme, S.; Antony, J.; Ehrlich, S.; Krieg, H. J. Chem. Phys. 2010, 132, 154104. (49) Te Velde, G.; Bickelhaupt, F. M.; Baerends, E. J.; Fonseca Guerra, C.; Van Gisbergen, S. J. A.; Snijders, J. G.; Ziegler, T. J. Comput. Chem. 2001, 22, 931−967. (50) (a) van Lenthe, E.; Baerends, E. J.; Snijders, J. G. J. Chem. Phys. 1993, 99, 4597−4610. (b) van Lenthe, E.; Baerends, E. J.; Snijders, J. G. J. Chem. Phys. 1994, 101, 9783−9792. (c) van Lenthe, E.; Snijders, J. G.; Baerends, E. J. J. Chem. Phys. 1996, 105, 6505−6516. (d) van Lenthe, E.; van Leeuwen, R.; Baerends, E. J.; Snijders, J. G. Int. J. Quantum Chem. 1996, 57, 281−293. (e) van Lenthe, E.; Ehlers, A. E.; Baerends, E. J. J. Chem. Phys. 1999, 110, 8943−8953. (51) Even single crystalline material gave unsatisfactory results. NMR spectra are displayed in the Supporting Information. Elemental analyses for literature known potassium ATIs were not reported (refs 6a, 21b).

I


Aminotroponiminates: Alkali Metal Compounds ... - ACS Publications

Recommend Documents