Dibenzotetramethyltetraaza[14]annulene [(tmtaa ... - ACS Publications

Sep 21, 2018 - Department of Chemistry, Temple University, 1901 Northy 13th Street, Philadelphia, Pennsylvania 19122, United States. •S Supporting ...
0 downloads 0 Views 2MB Size
Download PDF
Article Cite This: Inorg. Chem. 2019, 58, 1224−1233

pubs.acs.org/IC

Solution and Solid State Properties for Low-Spin Cobalt(II) Dibenzotetramethyltetraaza[14]annulene [(tmtaa)CoII] and the Monopyridine Complex Soumyajit Dey, Bradford B. Wayland,* and Michael J. Zdilla* Department of Chemistry, Temple University, 1901 Northy 13th Street, Philadelphia, Pennsylvania 19122, United States

Downloaded via IOWA STATE UNIV on January 25, 2019 at 10:23:03 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

S Supporting Information *

ABSTRACT: The single-crystal X-ray structure of solvent-free (tmtaa)CoII reveals three different π−π intermacrocyclic interactions between tmtaa units (tmtaa = dibenzotetramethyltetraaza[14]annulene). Pairs of inequivalent (tmtaa)CoII units in the unit cell link into a one-dimensional π−π stacked array in the solid state. Magnetic susceptibility (χ) studies from 300 to 2 K reveal the effects of intermolecular interactions between (tmtaa)CoII units in the solid state. The effective magnetic moment per CoII center is constant at 2.83 μB from 300 to 100 K and begins to significantly decrease at lower temperatures. The magnetic data are fit to a singlet (S = 0) ground state with a triplet (S = 1) excited state that is 13 cm−1 higher in energy (−2J = 13 cm−1). Toluene solutions of (tmtaa)CoII have 1H nuclear magnetic resonance (NMR) paramagnetic shifts, a solution-phase magnetic moment μeff (295 K) of 2.1 μB, and toluene glass electron paramagnetic resonance spectra that are most consistent with a low-spin (S = 1 /2) CoII with the unpaired electron located in the dyz orbital. Pyridine interacts with (tmtaa)CoII to form a five-coordinate monopyridine complex in which the unpaired electron is in the dz2 orbital. The five-coordinate complex has been structurally characterized by single-crystal X-ray diffraction, and the equilibrium constant for pyridine binding at 295 K has been evaluated by both electronic and 1H NMR spectra. Density functional theory computation using the UB3LYP hybrid functional places the unpaired electron for (tmtaa)CoII in the dyz orbital and that for the monopyridine complex in the dz2 orbital, consistent with spectroscopic observations.

■

INTRODUCTION Low-spin four- and five-coordinate cobalt(II) complexes are d7, S = 1/2 species that exhibit a wide variety of metal-centered radical-like reactions.1−12 Low-spin cobalt(II) complexes are specifically well recognized for reversible dioxygen binding,2 mediation of living radical olefin polymerization,3 and numerous substrate transformations.4−11 Prominent advances in synthetic methods in organic synthesis have been demonstrated using cobalt(II) porphyrin metalloradicalcatalyzed transformations of organic substrates.12 This type of catalysis has recently been extended to cobalt(II) dibenzotetramethyltetraaza[14]annulene4 [(tmtaa)CoII (Figure 1)] that, like porphyrin, is a N42− macrocycle but differs from porphyrin in its antiaromaticity and nonplanarity. Five-coordinate square pyramidal CoII complexes invariably have the unpaired electron in dz2, but the near degeneracy of dz2 with dxz and dyz in four-coordinate, square-planar CoII complexes can give several ground state electron configurations. The occurrence of the odd electron in dz2 for cobalt(II) porphyrins is ascribed to the decrease in the dxz and dyz energy relative to dz2 by the porphyrin π-acceptor interaction, and the (dyz)1 ground configuration for cobalt(II) salen13 reflects the less effective π-acceptor properties of salen compared to those of porphyrin. © 2019 American Chemical Society

Extensive efforts have been made to develop relationships between the cobalt(II) electronic structure and the electron paramagnetic resonance (EPR) g values and 59Co coupling constants that could be used to distinguish between the ground states that arise from having the odd electron in dz2 or dyz (dxz). McGarvey14 concluded that it may not be possible to unambiguously distinguish between the doublet ground states based only on the EPR parameters but that a (dyz)1 ground configuration is most probable when gyy < gzz and that the (dz2)1 configuration is generally indicated by gzz < gyy. This article reports on the solvent-free, solid state X-ray crystal structure and magnetic susceptibility for (tmtaa)CoII (T = 2− 300 K) and the 1H nuclear magnetic resonance (NMR) paramagnetic shifts, magnetic moment, and electronic spectra for (tmtaa)CoII in toluene. The electronic spectral changes and equilibrium constants for formation of the 1:1 pyridine complex [(tmtaa)CoII(py)] along with the single-crystal Xray structure are used in comparisons with cobalt−porphyrin systems. Examination of the electronic structures of the parent versus pyridine coordination complexes uncovers a change in Received: September 21, 2018 Published: January 8, 2019 1224

DOI: 10.1021/acs.inorgchem.8b02644 Inorg. Chem. 2019, 58, 1224−1233

Article

Inorganic Chemistry

the mean C10N4 ring core) distances are found to be 4.685 and 5.001 Å, respectively, as metal centers are displaced from their corresponding least-squares fitted C10N4 [14]annulene planes toward each other by 0.21 and 0.25 Å for Co(1) and Co(2), respectively. The root-mean-square (RMS) displacements of the 14 ring atoms in the two rings are found to be 0.35 and 0.37 Å with respect to their corresponding fitted C10N4 planes. The mean plane separation (MPS) between two molecular rings within the unit cell is found to be 3.436 Å with a lateral shift of 3.634 Å (Figures 2C and 3 illustrate these metrics). There are three different types of π−π interactions observed between the [14]annulene macrocyclic planes of (tmtaa)Co molecules in the crystal system with MPS values of 3.771, 3.436, and 3.862 Å, which give a one-dimensional (1D) π−π stacking array in the solid state (Figure 3). The lateral shifts for the three π−π interactions are 3.469, 3.634, and 4.669 Å with 0°, 31.3°, and 0° interplanar angles, respectively (the 0° interplanar angles are imposed by crystallographic symmetry). In addition, the Ct···Ct distances are calculated to be 5.124, 5.001, and 6.060 Å, respectively, for these π−π interactions. These structural parameters (based on MPS and Ct···Ct distance) indicate moderate, strong, and weak π−π interactions, respectively.17 Alternating adjacent five- and six-membered heterometallacycles and distinct nonplanarity of tmtaa macrocycles contrast with the four consecutive six-membered chelate rings and planarity of porphyrins. These differences play key roles in controlling macrocyclic “hole” sizes and metal−ligand interactions in tmtaa complexes in comparison to those in porphyrins.16,18 The observable result is that Co−Neq bond lengths for (tmtaa)CoII (1.89−1.90 Å) are shorter than the corresponding values for low-spin cobalt(II) porphyrins (∼1.93−1.99 Å).19 The bulk powder sample of (tmtaa)Co exhibits a diffraction pattern consistent with the single-crystal X-ray structure. Figure S1 compares the powder X-ray diffraction (PXRD) patterns of the bulk sample with the simulated patterns obtained from the single-crystal X-ray structure for (tmtaa)Co and provides good agreement, indicating that this material is essentially isolated exclusively in this phase.

Figure 1. Structure and coordinate axis system for (tmtaa)CoII.

the identity of the singly occupied molecular orbital (SOMO) from dyz to dz2 upon axial coordination.

■

RESULTS AND DISCUSSION X-ray Crystal Structure of (tmtaa)CoII. An X-ray structural study for a single crystal of a dimethoxyethane (DME) solvate of (tmtaa)CoII has been reported by Magull et al.15 However, slow diffusion of n-pentane into a benzene solution of (tmtaa)CoII at room temperature under a nitrogen atmosphere results in formation of dark greenish-brown crystals that contain only (tmtaa)CoII. The single-crystal Xray structure for the solvent-free (tmtaa)CoII was determined and refined in the monoclinic P21/c space group (Figure 2). Two inequivalent molecules of (tmtaa)CoII are found in the asymmetric unit (Figure 2B). The macrocyclic ligand in each of the inequivalent (tmtaa)CoII molecules has the expected nonplanar saddle shape that predominantly arises from steric interactions between the methyl and benzo groups.16 Table S1 lists the crystal data and data collection parameters, while selected bond distances and angles are listed in Table S2. The average Co−Neq distances of these two molecules are found to be 1.888 and 1.900 Å for molecule I and molecule II, respectively. The CoII···CoII and Ct···Ct (Ct is the centroid of

Figure 2. (A) Structure of one (tmtaa)CoII molecule from X-ray diffraction (100 K) with thermal ellipsoids set at the 50% probability level. H atoms have been omitted for the sake of clarity. (B) Illustration of the two (tmtaa)CoII molecules in the asymmetric unit in the P21/c space group. (C) Illustration of the intermolecular metrics used in the text.

Figure 3. Diagrams showing (A) 1D packing and (B) strong, moderate, and weak π−π molecular interactions (highlighted) with neighboring molecules. S, M, and W indicate strong, moderate, and weak interactions, respectively. 1225

DOI: 10.1021/acs.inorgchem.8b02644 Inorg. Chem. 2019, 58, 1224−1233

Article

Inorganic Chemistry Magnetic Susceptibility Measurements for Solid (tmtaa)CoII (T = 2−300 K). Magnetic susceptibility measurements were taken for the solid state powder of (tmtaa)CoII over the temperature range from 2 to 300 K. The experimentally determined molar magnetic susceptibility χM(obs) for (tmtaa)CoII, corrected molar paramagnetic susceptibility [χM(P)], and effective magnetic moments (μeff) for one and two (tmtaa)CoII units can be found in Table S3. χM(P) and μeff were obtained by adjusting χM(obs) for diamagnetic contributions [χM(D) = −0.000267 cm3/mol] using Pascal’s constants and temperature-independent paramagnetism [χM(TIP) = 0.000127 cm3/mol] empirically derived from the fitting. The μeff for (tmtaa)CoII is essentially constant at ∼2.84−2.82 μB in the higher temperature range from 300 to 100 K. A μeff of 2.86 μB was previously reported as a part of the original synthesis and characterization of (tmtaa)CoII, but the details of the experiment and nature of the sample were not described.20 The μeff for solid (tmtaa)CoII substantially decreases as the temperature is decreased from 100 to 2 K. The decline in μeff toward zero at low temperatures is ascribed to an antiferromagnetic interaction between two (tmtaa)CoII centers in the unit cell giving a singlet ground state (S = 0) and a triplet state (S = 1) at a slightly higher energy. In the highertemperature region, all four of the microstates arising from the S = 0 (Ms = 0) and S = 1 (Ms = 1, 0, −1) states are essentially equally populated and μeff is constant, but as the temperature is decreased, the S = 0 state becomes preferentially populated and μeff decreases toward zero in the limit. Modeling of the magnetic behavior for solid (tmtaa)CoII necessitates using both of the inequivalent (tmtaa)CoII molecules in the asymmetric unit. Plots of the magnetic susceptibility and effective magnetic moment for two coupled (tmtaa)CoII units (Co2) {μeff(Co 2) = 2.828[2χM(P)T]1/2} as a function of temperature are shown in Figure 4 and Figure S2. The effective magnetic moment for the set of two paramagnetic (tmtaa)CoII molecules at 299.8 K is 4.01 μB, which results from the equilibrium between the ground state with a magnetic moment of zero and the triplet state with an effective magnetic moment of 4.63 μB {μeff (S = 1) = 2.828[4/3(0.006718)(299.8)1/2]; ⟨g⟩ = μeff/[S(S + 1)]1/2 = 3.27}. The solid lines are calculated from the best fit parameters for the two S = 1/2 (tmtaa)CoII sites with g1 = 3.253 and g2 = 3.287 and a J1,2 magnetic coupling constant of −6.4 cm−1, which places the triplet state (S = 1) −2J1,2 (12.8 cm−1) above the singlet state (S = 0). The fact that the S = 0 state has an energy lower than that of the S = 1 state is probably true because of a superexchange type mechanism that involves interligand π−π overlap via the interaction illustrated in Figure 3. The average isotropic g value (⟨g⟩) of ∼3.27 and the associated effective magnetic moment (μeff) of 2.83 μB for (tmtaa)CoII in the solid state powder (μeff) are very large compared to the spin-only values of 2.00 and 1.73 μB for the S = 1/2 state, respectively. The large ⟨g⟩ and μeff values are ascribed to orbital angular momentum because the observed μeff is smaller than the spin-only value for a larger S = 3/2 (μeff = 3.87 μB) ground state, and the temperature independence of the observed μeff for (tmtaa)CoII in the high-temperature region rules out a significant contribution from the thermal population of a high-spin state (S = 3/2). (tmtaa)CoII in a Toluene Solution and Glass. Paramagnetic susceptibility χM(P) and μeff for (tmtaa)CoII in a toluene solution were evaluated by the Evans NMR method. A

Figure 4. Bulk magnetic measurements (T = 2−300 K) for two molecules of (tmtaa)CoII in the asymmetric unit. Dots are experimental points, and lines were calculated for an S = 0 ground state and an S = 1 excited state that was 13 cm−1 higher in energy with the inequivalent (tmtaa)CoII centers having g values of 3.265 and 3.280: (A) 2χM vs T, (B) 1/(2χM) vs T, and (C) μeff vs T.

representative molar paramagnetic susceptibility [χM(P) = 0.001874 cm3/mol] was derived for (tmtaa)CoII by adjusting the observed molar magnetic susceptibility [χM(obs) = 0.001734 cm3/mol] for estimated diamagnetic contributions [χM(D) = −0.000267 cm3/mol] using Pascal’s constants and temperature-independent paramagnetism [χM(TIP) = 0.000127 cm3/ mol]. An effective magnetic moment of 2.10 μB and a ⟨g⟩ of 2.42 for (tmtaa)CoII in a toluene solution were obtained from χM(P) {μeff = 2.828√(0.001874 × 295) = 2.10 μB; ⟨g⟩ = μeff/ √[S(S + 1)] = 2.42}. The μeff and ⟨g⟩ for (tmtaa)CoII in a toluene solution (295 K) are in close agreement with values derived from previously reported EPR spectra for (tmtaa)CoII in toluene glass (90 K) (g1 = 3.83, g2 = 1.64, and g3 = 1.79; ⟨g⟩ = 2.42).22 EPR spectra for (tmtaa)CoII in toluene glass at 4 K are also in close agreement (Figure S4). There is a substantial decrease in the μeff for (tmtaa)CoII in a toluene solution and glass (∼2.1 μB) compared to that of the solid powder (∼2.84 μB), which most probably reflects a smaller orbital angular momentum contribution in solution. EPR spectroscopy of magnetically aligned (tmtaa)CoII in a noncoordinating nematic liquid aided assignment of the g values for the toluene glass (g1 = gxx, g2 = gyy, and g3 = gzz). The observation that gzz is larger than gyy provides strong evidence but not proof that the unpaired electron is in the dyz molecular orbital (MO) (2B2 ground state).21 NMR contact shifts for ligand nuclei can assist 1226

DOI: 10.1021/acs.inorgchem.8b02644 Inorg. Chem. 2019, 58, 1224−1233

Article

Inorganic Chemistry in the assignment of the unpaired electron MO through observation of the sign and magnitude of the electron−nuclear coupling constants.22 1 H NMR Paramagnetic Shifts (δP) for (tmtaa)CoII. The 1 H NMR paramagnetic shifts (δP) for the four chemically nonequivalent sets of hydrogens of (tmtaa)CoII in toluene are plotted versus the inverse of the absolute temperature (T = 183−273 K) in Figure 5. The paramagnetic shift (δP) is defined as the observed shift position (δobs) relative to the hypothetical diamagnetic shift position (δP) that is approximated by the shift positions for the diamagnetic (tmtaa)Ni23 complex (δP = δobs − δD). The linear changes in δP with the inverse of temperature indicate that (tmtaa)CoII functions as a Curie paramagnet, where the population of states does not change over the temperature range of 183−373 K in a toluene solution. The low C2v symmetry, solution dynamics, and large magnetic anisotropy complicate the process of relating the observed paramagnetic shifts with the contact shifts and associated ligand spin densities. However, the relatively large upfield shifts of the methine hydrogens are consistent with substantial positive pπ spin density on the methine carbons in the yz plane, which places negative spin density on the methine H 1s through spin polarization. The methine hydrogen NMR paramagnetic shifts lend further support to assigning the unpaired electron in (tmtaa)CoII to the primarily cobalt(II) dyz MO. Formation and X-ray Diffraction Structure for the Monopyridine Complex (tmtaa)Co(py). Slow diffusion of n-pentane into a solution prepared by dissolution of (tmtaa)CoII in pyridine at room temperature under a nitrogen atmosphere resulted in the formation of dark green triclinic crystals in space group P1̅. The molecular structure of monopyridine complex (tmtaa)CoII(py) is depicted in Figure 6. The crystal data and data collection parameters are listed in Table S1, while selected bond distances and angles are listed in Table S2. The cobalt(II) center adopts an approximate square pyramidal geometry in which the Nax−Co−Neq and Neq−Co− Neq bond angles are close to 90°. The average Co−Neq distance was found to be 0.012−0.024 Å longer than those of the parent four-coordinate structures. The Co−Nax distance is 2.137 Å, and the central CoII is displaced by 0.34 Å from the mean [14]annulene core plane toward the axial pyridine. To the best of our knowledge, this is the first report of the singlecrystal X-ray diffraction structure of a five-coordinate cobalt-

Figure 6. Molecular structure of (tmtaa)Co(py) (100 K) with ellipsoids set at the 50% probability level. H atoms have been omitted for the sake of clarity.

(II) tetraaza[14]annulene complex. The Co−Neq and Co−Nax bond lengths, observed for (tmtaa)Co(py), are shorter than those found for the analogous porphyrin complexes [for CoIIOEPOH(py), Co−Neq = 1.988 Å and Co−Nax = 2.203 Å; for CoIIOEP(DMAP) Co−Neq = 1.982 Å and Co−Nax = 2.191 Å; for CoTPP(CF3)4)(py) Co−Neq = 1.946 Å and Co−Nax = 2.166 Å].19,25 Spectral Changes from Interaction of (tmtaa)Co with Pyridine To Form (tmtaa)Co(py). Whereas spectral and magnetic evidence points to a dyz-based SOMO in (tmtaa)CoII, prior toluene glass EPR studies of (tmtaa)CoII in the presence of pyridine give ligand hyperfine coupling with a single 14N pyridine donor atom, which, along with the g values, conclusively place the unpaired electron in the dz2 MO associated with a 2A1 ground state for (tmtaa)Co(py).22 Differences in the electronic spectra from dissolution of (tmtaa)CoII in benzene and pyridine are illustrated in Figure 7. The ligand-based π−π* transition centered at 372 nm for (tmtaa)CoII in benzene appears to split into two bands at 340 and 384 nm in pyridine, where monopyridine complex (tmtaa)CoII(py) is the dominant species. The appearance of two π−π* transitions could be a result of the pyridine−tmtaa π-interaction that orients the pyridine plane along one of the N−Co−N directions, which is a prominent structural feature observed in the X-ray crystal structure (Figure 6). The remainder of the observed electronic transitions are associated with ligand to metal charge transfer (LMCT) bands that terminate on the metal-based, singly occupied dz2 MO and the higher-energy dxy MO. The broad, lowest-energy LMCT band for (tmtaa)CoII in benzene centered at ∼800 nm (12500 cm−1) minimally shifts to 695 nm (14400 cm−1) and probably

Figure 5. Plot of the 1H NMR paramagnetic shifts (δP) as a function of T−1 for (tmtaa)CoII in toluene-d8 with respect to diamagnetic (tmtaa)Ni.23

Figure 7. Comparison of electronic spectra that result from dissolution of (tmtaa)CoII in C6H6 (solid line) and pyridine (dashed line) at 295 K. 1227

DOI: 10.1021/acs.inorgchem.8b02644 Inorg. Chem. 2019, 58, 1224−1233

Article

Inorganic Chemistry to a higher energy in (tmtaa)CoII(py) as a result of the increase of dz2 by pyridine coordination. NMR spectral changes associated with pyridine coordination are provided in Figure 8. The change in the sign of the methine proton’s paramagnetic shift from a large upfield shift for (tmtaa)CoII to a small downfield shift upon coordination by pyridine in (tmtaa)CoII(py) is consistent with a change in the unpaired electron MO (Table 1). The EPR of (tmtaa)CoII(py)22 places the odd electron in the cobalt dz2 MO that is involved in σ-bonding with pyridine, whereas the odd electron in (tmtaa)CoII is attributed to the cobalt dyz MO. Evaluation of the Equilibrium Constant for the 1:1 Pyridine Complex [(tmtaa)CoII(py)] by 1H NMR and Electronic Spectral Changes. Systematic changes in the 1H NMR and electronic spectra were observed as the mole ratio of pyridine to (tmtaa)CoII species was varied (Figures 8−10). These signatures were utilized to determine the equilibrium constant for pyridine complex formation with (tmtaa)CoII. The 1H NMR spectra in Figure 8 illustrate that (tmtaa)CoII and pyridine complexes of (tmtaa)CoII are in fast exchange in toluene-d8 solutions on the NMR time scale. For the equilibrium coordination of pyridine to (tmtaa)CoII (eq 1), an expression for the mole-fraction-averaged chemical shift between δobs for (tmtaa)CoII (Co) and 1:1 pyridine complex (tmtaa)CoII(py) (Co·py) is given in eq 2, where δ(Co) and δ(Co·py) are the chemical shifts for a given proton of (tmtaa)CoII and (tmtaa)CoII(py), respectively, K1 is the equilibrium constant, and [py] is the concentration of pyridine. The nonlinear least-squares best fit of δobs as a function of pyridine concentration for the methine hydrogen gives a K1(295 K) of 4.75 ± 0.67 and a ΔG°(295 K) of −0.91 ± 0.23 kcal mol−1. Using the methyl hydrogen gives a K1(295 K) of 5.71 ± 0.8 and a ΔG°(295 K) of −1.02 ± 0.13 kcal mol−1 (Figure 9). Averaging the results obtained from using all four of the tmtaa hydrogen NMR shifts gives a K1(295 K) of 4.6 ± 1.1 and a ΔG°(295 K) of −0.89 ± 0.12 kcal mol−1 (Figure 9 and Figure S5).

Table 1. Comparison of the Chemical Shifts (δ at 295 K) for the Proton Resonances of (tmtaa)CoII and (tmtaa)CoII(py) (extrapolated from equilibrium constant measurement, vide infra) molecule

methine (ppm)

methyl (ppm)

O (ppm)

m (ppm)

(tmtaa)CoII (tmtaa)CoII(py)

−72.96 6.60

−20.17 −9.88

32.35 5.89

18.24 3.11

Figure 9. Nonlinear least-squares best fit to 1:1 pyridine complex formation with(tmtaa)CoII given by eq 2 for observed mole-fractionaveraged (tmtaa)CoII 1H NMR shift δobs as a function of pyridine concentration at 295 K {[(tmtaa)CoII]i = 0.05(M); (A) methine hydrogens [K1(295 K) = 4.75 ± 0.67] and (B) methyl hydrogens [K1(295 K) = 5.71 ± 0.8]}.

(tmtaa)CoII + py V (tmtaa)Co(py)

(1)

δobs = [δ(Co) + K1[py]δ(Co·py)] /(1 + K1[py])

(2)

Pyridine-dependent changes in the electronic absorption spectrum can also be used to obtain the equilibrium constant for 1:1 complex formation (K1, eq 1). The eight isosbestic points observed in the 300−900 nm range give full confidence that there are only two species [(tmtaa)CoII and (tmtaa)CoII(py)] as the molar ratio of pyridine to cobalt(II) increases to 3.32 × 105 (Figure 10). Equation 3 gives an expression that parallels eq 2 and relates changes in the electronic absorption at a given wavelength to K1 and the pyridine concentration in terms of the molar extinction coefficients for (tmtaa)CoII and (tmtaa)CoII(py) and the effective apparent molar extinction coefficient, εobs, which is defined as the observed absorbance divided by the initial molar concentration of (tmtaa)CoII {εobs = Aobs/[(tmtaa)CoII]}. εobs = [εA(Co) + K1[py]ε(Co·py)] /(1 + K1[py])

(3)

A nonlinear least-squares best fit of εobs at 338 nm as a function of the pyridine molar concentration at an initial (tmtaa)CoII concentration of 7.12 × 10−5 M (Figure 10) gives a K1 (295 K) of 1.6 ± 0.2 and a ΔG°(295 K) of −0.28 ± 0.06 kcal mol−1. The observation at each wavelength provides

Figure 8. 1H NMR spectral changes of (tmtaa)Co [0.05 (M)] with the gradual changes in the concentration ratio with pyridine-d5 (from 1:0 to 1:16) at 295 K. 1228

DOI: 10.1021/acs.inorgchem.8b02644 Inorg. Chem. 2019, 58, 1224−1233

Article

Inorganic Chemistry

495; ΔG°(295 K) = −3.6 kcal mol−1],26 which is much more thermodynamically favorable than the values for formation of monopyridine complex (tmtaa)CoII [K1(295 K) = 1.56 ± 0.35; ΔG°(295 K) = −0.26 ± 0.13 kcal mol−1] determined by the same method and in the same concentration range. The cobalt−pyridine nitrogen distance in (tmtaa)CoII(py) is shorter (2.137 Å) than the corresponding distance in an analogous porphyrin complexes (Co−N > 2.16 Å).19,22 This implies that the CoII−pyridine bonding in (tmtaa)CoII(py) is at least as effective as it is in the porphyrin complex. This further suggests that an energy term for (tmtaa)CoII compared to (porphyrin)CoII, and not interactions in pyridine complexes, is the dominant source for the difference in the thermodynamics of complex formation. A prominent difference between these low-spin (S = 1/2) cobalt(II) complexes is that cobalt(II) porphyrins have the unpaired electron in the dz2 MO and (tmtaa)CoII has the odd electron in the dyz MO but both of the five-coordinate monopyridine complexes have the unpaired electron in the dz2 MO. An endothermic reorganization energy for the unpaired electron changing to the dz2 MO in (tmtaa)CoII(py) from the dyz MO in (tmtaa)CoII (Figure 12), which is not present in the cobalt(II) porphyrin system, could account for the less thermodynamically favorable pyridine complex formation with (tmtaa)CoII. Spin density plots and SOMO assignments from DFT in the next section provide additional agreement. DFT Computations for (tmtaa)CoII and (tmtaa)CoII(py). DFT computations for (tmtaa)CoII at the UB3LPY level of theory place the unpaired electron in the dyz MO, a 2B2 ground state under C2v symmetry, consistent with spectroscopic and magnetic measurements. This orbital is pointed at the tmtaa methine carbons, explaining the observed contact shifts (vide supra). The frontier orbitals are shown in Figure 11. It is worth noting that in unrestricted calculations, the α and β orbitals are not strictly paired due to spin polarization, which is apparent from the different energies and spatial distributions of these orbitals. In particular, the orbital energies

Figure 10. Ultraviolet−visible spectral changes of (tmtaa)Co (7.12 × 10−5 M) in C6H6 upon addition of pyridine as the molar ratio of pyridine to cobalt(II) changes from 1:0 to 1:3.32 × 105 at 295 K. The inset shows the change in the apparent effective extinction coefficient (εobs) at 338 nm. The solid line represents the nonlinear least-squares best fit for 1:1 complex formation [K1(285 K) = 1.6 ± 0.2].

another independent measurement of K1. A sampling of eight wavelengths gave K1(295 K) values varying from 1.15 to 1.99 (see the Supporting Information) with an average K1(295 K) of 1.56 ± 0.35 and a ΔG°(295 K) of −0.26 ± 0.13 kcal mol−1. Pyridine complex formation with (tmtaa)CoII was studied by 1 H NMR at 5 × 10−2 M and by electronic spectra at 7.1 × 10−5 M. The difference in K1(295 K) values from 1H NMR and electronic spectra is tentatively ascribed to the variation in solvation effects arising from the different solution compositions, including a nearly 3 order of magnitude difference in the initial (tmtaa)CoII concentrations, and corresponding increases in the concentration of the pyridine titrant. Specifically, the increase in solvent polarity at high pyridine concentrations should favor the formation of the more polar pyridine complex in the NMR experiment, which is consistent with the difference in measured equilibrium constants. The equilibrium constant for formation of the monopyridine complex of cobalt(II)tetraphenyl porphyrin using electronic spectral changes was reported by Walker [K1((tpp)CoII(py)) =

Figure 11. Energetic ordering of K−S d orbitals in Co(tmtaa) (left) and Co(tmtaa)(py) (right) calculated at UB3LYP level of theory using the 321g basis set for all atoms. α and β represent opposite spins. Assignments of SOMO indicated by red boxes. 1229

DOI: 10.1021/acs.inorgchem.8b02644 Inorg. Chem. 2019, 58, 1224−1233

Article

Inorganic Chemistry vary drastically between the α and β orbital sets due to differences in electron−electron repulsion and exchange terms. In the cases of Co(tmtaa) and Co(tmtaa)(py), the spatial similarity between electrons in certain α and β orbitals allows us to assign corresponding up- and down-spin electrons as pairs due to their spatial overlap, though their orbital energies differ substantially. Results of DFT calculations for (tmtaa)CoII place one electron with a spin of 1/2 in each of the four α Kohn−Sham MOs that are predominantly cobalt-based dyz, dz2, dxz, and dx2−y2 orbitals and one electron with a spin of −1/2 in each of the similar β dx2−y2, dz2, and dxz MOs (Figure 11). In the Kohn−Sham orbital pictures shown in Figure 11, the dyz orbital is assigned as the SOMO because its corresponding β analogue is unoccupied. In contrast to traditional crystal field orbital energy plots, such as that illustrated in Figure 12, the SOMO is not the HOMO. Rather, the SOMO is energetically positioned at the bottom of the left side of Figure 11. This is because the energies of the Kohn−Sham molecular orbitals include the contribution of electron−electron repulsion terms (often termed in crystal field and molecular orbital theory as the pairing energy), which is greater for paired electrons. In addition, the α orbitals have an increased level of orbital stabilization from greater electron exchange terms due to the presence of four α d electrons versus only three β d electrons. The combination of increased electron−electron repulsion and decreased electron−electron exchange decreases the energy of singly occupied orbitals versus doubly occupied orbitals in lowmultiplicity systems.24 In Figure 11, the SOMO is the dyz orbital but has an energy that is lower than those of all of the other occupied α dz2, dxz, and dx2−y2 orbitals, which have higher energies because they have electrons effectively paired with them in related β orbitals. In the same manner, the unpaired electron in (tmtaa)CoII(py) to a first approximation is found to occur in the Kohn−Sham α dz2 MO. In this case, the α dz2 orbital is the highest-energy occupied spin α Kohn−Sham MO because interaction of the dz2 acceptor orbital with the pyridine

donor substantially elevates the dz2 orbital (Figure 12 and Figure S8). A more direct way of assigning the SOMO orbital is the use of spin density plots, which sum the entire contribution of α and β spins over the whole molecule. Across most of the molecular space, the two spin components cancel each other, leaving a smaller region of net α spin that can be compared to standard orbital shapes. This approach removes the complications of spin polarization and interorbital mixing on orbital shapes. The total odd electron spin density distributions for (tmtaa)CoII and (tmtaa)CoII(py) are shown in Figure 12 and clearly show the shapes of a dyz type orbital for (tmtaa)CoII and a dz2 type orbital for (tmtaa)CoII(py), consistent with SOMO assignments from spectroscopy and K−S orbital analysis. Open shell DFT computations and experiments thus place the unpaired electron for (tmtaa)CoII unambiguously in the dyz type of MO (2B2 ground state) and in a dz2 type MO (2A1 ground state) for (tmtaa)CoII(py).

■

CONCLUSIONS Dissolution of (tmtaa)CoII in toluene gives a μeff of 2.1 μB, which is in close agreement with the previously reported EPR in toluene glass (90 K).22 The 1H NMR paramagnetic shifts and DFT computations support the highly probable placement of the unpaired electron in the dyz orbital and a 2B2 ground state for the four-coordinate (tmtaa)CoII molecule. Pyridine interacts with (tmtaa)CoII exclusively to form five-coordinate complex (tmtaa)CoII(py) with a (dz2)1 electron configuration and 2A1 ground state, previously demonstrated by EPR22 and supported by DFT calculations. The observed small equilibrium constant for pyridine complex formation is proposed as a consequence of the unfavorable energy change associated with donor-induced electron movement from the dyz orbital in (tmtaa)CoII to the dz2 orbital in (tmtaa)CoII(py) (Figure 12). Splitting of the tmtaa ligand-centered π−π* transition into two components in (tmtaa)CoII(py) is ascribed to alignment of the pyridine plane along one of the N−Co−N directions that is observed in the molecular structure from X-ray diffraction. The X-ray diffraction structural study of solvent-free (tmtaa)CoII revealed two inequivalent cobalt(II) macrocycles in the unit cell that have a relatively short intermacrocycle contact. The effects of intermolecular interactions between (tmtaa)CoII units in the solid state are manifested in the magnetic susceptibility (χ) values from 300 to 2 K that are fitted to a singlet (S = 0) ground state with a triplet (S = 1) excited state that is 13 cm−1 higher in energy. The effective magnetic moment per CoII center is constant at 2.83 μB from 300 to 100 K, where there are effectively equal populations in the four microstates of the singlet and triplet. The magnetic moment for the CoII centers (∼2.83 μB) is very large for a lowspin S = 1/2 species in which the electron spin-only magnetic moment is 1.73 μB, but the value is too small for a high-spin CoII (S = 3/2) species in which the minimum electron spinonly value is 3.87 μB. The exceptionally large magnetic moment is ascribed to an orbital contribution associated with the energy proximity of dyz and dxz. The substantial increase in μeff for (tmtaa)CoII in the solvent-free crystal compared to that in solution is proposed to result from intermolecular interactions in the solid decreasing the dyz and dxz energy separation and producing a larger orbital contribution. A more complete understanding of this unusual magnetic behavior will require a thorough theoretical analysis of this low-spin fourcoordinate cobalt(II) system.

Figure 12. One-electron d orbital splitting diagrams describing the pyridine donor-induced change in the unpaired electron location from the dyz orbital for (tmtaa)CoII to the dz2 MO for (tmtaa)CoII(py). The identity of SOMO is supported by spin density plots (top) as well as SOMO isosurfaces (Figure 11). Qualitative orbital energetic ordering (including the contribution of the pairing energy) is given in Figure 11, and quantitative ordering is provided in Figure S8. 1230

DOI: 10.1021/acs.inorgchem.8b02644 Inorg. Chem. 2019, 58, 1224−1233

Article

Inorganic Chemistry

emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

Open shell DFT computations place the unpaired electron for (tmtaa)CoII in a dyz type of MO (2B2 ground state) and in a dz2 type of MO (2A1 ground state) for (tmtaa)CoII(py), which are the same ground state electron configurations deduced from spectroscopic studies. The ordering for the Kohn−Sham MOs (Figure 11) that include interelectronic repulsions contrasts with the ordering in regular one-electron MO diagrams (Figure 12) that ignore interelectronic repulsions and invariably place the singly occupied MO as the highestenergy MO.

■

■

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. ORCID

Michael J. Zdilla: 0000-0003-0212-2557 Notes

EXPERIMENTAL SECTION

The authors declare no competing financial interest.

■

General. All manipulations were performed under a rigorous dry, anaerobic atmosphere of argon/nitrogen gas using standard glovebox and Schlenk line techniques. All reagents were purchased from commercial sources (Aldrich and Strem). Anhydrous solvents such as benzene, pyridine, and n-pentane were purified using an Innovative Technology, Inc., Pure Solv. system. (tmtaa)Co was prepared according to a published procedure.27 1H NMR spectra were recorded on a Bruker Avance 500 MHz spectrometer. Values for chemical shifts (parts per million) are referenced to the residual protio-solvent resonances (C6D6 7.16 ppm and toluene-d8 2.09 ppm). Ultraviolet−visible spectra were recorded on a Shimadzu UV-1800 UV spectrophotometer in the range of 300−1100 nm. The magnetic susceptibility was measured on a Quantum Design Physical Property Measurement System. X-ray Diffraction. X-ray data were collected on a Bruker KAPPA APEX II DUO diffractometer. Single crystals were mounted on a MiTeGen loop using paratone-N oil. For powder XRD, samples were caked onto the end of a glass fiber using paratone-N oil. Samples were cooled using an Oxford Cryostream. Data were obtained using Mo Kα radiation from a sealed tube equipped with a TRIUMPH monochromator and processed using the APEX2 software suite. Structures were determined using direct methods and refined using full-matrix least-squares minimization using the SHELX crystallography package28 with OLEX2 as a GUI and graphics program.29 Powder patterns were obtained with a 180° ϕ scan using Cu Kα radiation from a sealed tube. Powder patterns were simulated using Mercury (CCDC).30 Density Functional Theory. Geometry optimization of (tmtaa) Co was initiated from the crystal structure coordinates, whereas for the pyridine-ligated system, an axial pyridine was added to the optimized structure of (tmtaa)Co and then optimized. All structure optimizations were performed by employing a UB3LYP hybrid functional, using the Gaussian 09 package.31 The Kohn−Sham (K−S) orbital energy diagrams were generated using Chemcraft 1.8. Further details of Kohn−Sham orbital plots and energies are available in the Supporting Information. The method used was Becke’s threeparameter hybrid exchange functional provided by the Lee, Yang, and Parr expression for the nonlocal correlation32 and the Vosko, Wilk, and Nussair 1980 correlation functional (III) for local correction.33 The 3-21G basis set was used for all atoms.

■

AUTHOR INFORMATION

ACKNOWLEDGMENTS The authors gratefully acknowledge support of this research through National Science Foundation Grant 1362016 and the Temple University College of Science and Technology. NMR measurements are supported by a grant from the CURE program from the Pennsylvania Department of Health.

■

REFERENCES

(1) Cuesta, L.; Sessler, J. L. π-Metal complexes of tetrapyrrolic systems. A novel coordination mode in “porphyrin-like” chemistry. Chem. Soc. Rev. 2009, 38, 2716−2729. (2) (a) Lin, W. K.; Alcock, N. W.; Busch, D. H. A molecular mechanics study of dioxygen binding by lacunar cobalt dioxygen carriers. J. Am. Chem. Soc. 1991, 113, 7603−7608. (b) Collman, J. P.; Brauman, J. I.; Doxsee, K. M.; Halbert, T. R.; Hayes, S. E.; Suslick, K. S. Oxygen binding to cobalt porphyrins. J. Am. Chem. Soc. 1978, 100, 2761−2766. (c) Calvin, M.; Barkelew, C. H. The Oxygen-carrying Synthetic Chelate Compounds. IV. Magnetic Properties. J. Am. Chem. Soc. 1946, 68, 2267−2273. (d) Bailes, R. H.; Calvin, M. The Oxygencarrying Synthetic Chelate Compounds. VII. Preparation. J. Am. Chem. Soc. 1947, 69, 1886−1893. (e) Nishikawa, H.; Yamada, S. Planar Quadri-co-ordinate Complexes of Cobalt(II) with Schiff Bases Derived from Salicylaldehyde. Bull. Chem. Soc. Jpn. 1964, 37, 8−12. (f) Earnshaw, A.; Hewlett, P. C.; King, E. A.; Larkworthy, L. F. Transition metal−Schiff’s base complexes. Part III. The magnetic properties of some oxygen-carrying cobalt(II) complexes. J. Chem. Soc. A 1968, 0, 241−246. (g) Floriani, C.; Calderazzo, F. Oxygen adducts of Schiff’s base complexes of cobalt prepared in solution. J. Chem. Soc. A 1969, 946−953. (h) Hoffman, B. M.; Diemente, D. L.; Basolo, F. Electron paramagnetic resonance studies of some cobalt(II) Schiff base compounds and their monomeric oxygen adducts. J. Am. Chem. Soc. 1970, 92, 61−65. (i) Diemente, D.; Hoffman, B. M.; Basolo, F. Electron spin resonance studies of 1:1 cobalt−oxygen adducts. J. Chem. Soc. D 1970, 0, 467−468. (j) Cockle, S. A.; Hill, H. A. O.; Williams, R. J. P. The formation of some superoxo-cobalt(III) complexes: An investigation by E.P.R. spectroscopy. Inorg. Nucl. Chem. Lett. 1970, 6, 131−134. (k) Hipp, C. J.; Baker, W. A., Jr. Electronic and circular dichroism spectra of some tetradentate Schiff base complexes of cobalt(II). J. Am. Chem. Soc. 1970, 92, 792−798. (l) Busetto, C.; Neri, C.; Palladino, N.; Perrotti, E. E.S.R. study of cobalt-oxygen complexes. Inorg. Chim. Acta 1971, 5, 129−132. (m) Ochiai, E.-I. Electronic structure and oxygenation of bis(salicylaldehyde)ethylenediimino cobalt(II). J. Inorg. Nucl. Chem. 1973, 35, 1727−1739. (n) Hoffman, B. M.; Basolo, F.; Diemente, D. Spin-Hamiltonian axes of some cobalt(II) Schiff base complexes from electron paramagnetic resonance in oriented nematic glass. J. Am. Chem. Soc. 1973, 95, 6497−6498. (3) (a) Wayland, B. B.; Poszmik, G.; Mukerjee, S. L.; Fryd, M. Living Radical Polymerization of Acrylates by Organocobalt Porphyrin Complexes. J. Am. Chem. Soc. 1994, 116, 7943−7944. (b) Wayland, B. B.; Basickes, L.; Mukerjee, S. L.; Wei, M.; Fryd, M. Living Radical Polymerization of Acrylates Initiated and Controlled by Organocobalt Porphyrin Complexes. Macromolecules 1997, 30, 8109−8112.

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.8b02644. Crystallographic data and data collection parameters, solid and solution state magnetic measurements, equilibrium constant measurements, and details of density functional studies (PDF) Accession Codes

CCDC 1828450−1828451 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 1231

DOI: 10.1021/acs.inorgchem.8b02644 Inorg. Chem. 2019, 58, 1224−1233

Article

Inorganic Chemistry

Transfer Reactions. J. Am. Chem. Soc. 2015, 137, 5468−5479. (e) Reddy, A. R.; Hao, F.; Wu, K.; Zhou, C.-Y.; Che, C.-M. Cobalt(II) Porphyrin-Catalyzed Intramolecular Cyclopropanation of N-Alkyl Indoles/Pyrroles with Alkylcarbene: Efficient Synthesis of Polycyclic N-Heterocycles. Angew. Chem., Int. Ed. 2016, 55, 1810−1815. (f) Doyle, M. P. Exceptional Selectivity in Cyclopropanation Reactions Catalyzed by Chiral Cobalt(II)−Porphyrin Catalysts. Angew. Chem., Int. Ed. 2009, 48, 850−852. (g) Kuijpers, P. F.; Tiekink, M. J.; Breukelaar, W. B.; Broere, D. L. J.; van Leest, N. P.; van der Vlugt, J. I.; Reek, J. N. H.; de Bruin, B. Cobalt-PorphyrinCatalysed Intramolecular Ring-Closing C−H Amination of Aliphatic Azides: A Nitrene-Radical Approach to Saturated Heterocycles. Chem. - Eur. J. 2017, 23, 7945−7952. (h) te Grotenhuis, C.; van den Heuvel, N.; van der Vlugt, J. I.; de Bruin, B. Catalytic Dibenzocyclooctene Synthesis via Cobalt(III)−Carbene Radical and ortho-Quinodimethane Intermediates. Angew. Chem., Int. Ed. 2018, 57, 140−145. (i) te Grotenhuis, C.; Das, B. G.; Kuijpers, P. F.; Hageman, W.; Trouwborst, M.; de Bruin, B. Catalytic 1,2-dihydronaphthalene and Earyl-diene synthesis via CoIII−Carbene radical and o-quinodimethane intermediates. Chem. Sci. 2017, 8, 8221−8230. (13) von Zelewsky, A.; Fierz, H. Electron Paramagnetic Resonance Spectra of planar low-spin Complexes of Cobalt(II) with Schiff’s Bases. I. N,N′-ethylene-bis(salicylideneimine)-cobalt(II). Preliminary communication Helv. Helv. Chim. Acta 1973, 56, 977−980. (14) (a) McGarvey, B. Theory of the Spin Hamiltonian Parameters for Low Spin Cobalt(II) Complexes. Can. J. Chem. 1975, 53, 2498− 2511. (b) McGarvey, B. Theory of the NMR Paramagnetic Shift of Pseudotetrahedral Complexes of Nickel(II) and Cobalt(II). Inorg. Chem. 1995, 34, 6000−6007. (c) Shakya, R.; Hindo, S. S.; Wu, L.; Allard, M. M.; Heeg, M. J.; Hratchian, H. P.; McGarvey, B.; da Rocha, S. R. P.; Verani, C. N. Archetypical Modeling and Amphiphilic Behavior of Cobalt(II)-Containing Soft-Materials with Asymmetric Tridentate Ligands. Inorg. Chem. 2007, 46, 9808−9818. (d) Hitchman, M. A. Electronic structure of low-spin cobalt(II) Schiff base complexes. Inorg. Chem. 1977, 16, 1985−1993. (15) Magull, J.; Simon, A. Zur Reaktion von MakrozyklenrnitLanthanoiden. I1 Die Strukturen von [K(thf)3]2[(C22H28N4)2Sm2]•4 THF und [(C22H22N,)Co]•DME. Z. Anorg. Allg. Chem. 1992, 615, 81−85. (16) (a) Goedken, V. L.; Pluth, J. J.; Peng, S.-M.; Bursten, B. Structure Relationships between the Four-Coordinate, S = 1, Macrocyclic Complex, [Fe(C22H22N4)], and the Neutral Ligand, C22H24N4. J. Am. Chem. Soc. 1976, 98, 8014. (b) Weiss, M. C.; Bursten, B.; Peng, S.-M.; Goedken, V. L. Effects of peripheral steric constraints and metal ion size on the structure of three five-coordinate macrocyclic ligand complexes of the type [M(C22H22N4)X], M = cobalt(III), iron(III), manganese(II); X = iodine, chlorine, trimethylamine. J. Am. Chem. Soc. 1976, 98, 8021. (17) (a) Piovesan, D.; Minervini, G.; Tosatto, S. C.E. The RING 2.0 web server for high quality residue interaction networks. Nucleic Acids Res. 2016, 44, W367−W374. (b) Avasthi, K.; Shukla, L.; Kant, R.; Ravikumar, K. Folded conformations due to arene interactions in dissymmetric and symmetric butylidene-linker models based on pyrazolo[3,4-d]pyrimidine, purine and 7-deazapurine. Acta Crystallogr., Sect. C: Struct. Chem. 2014, 70, 555−561. (c) Alvarez, S. A cartography of the van der Waals territories. Dalton Trans 2013, 42, 8617−8636. (d) Janiak, C. A critical account on π−π stacking in metal complexes with aromatic nitrogen-containing ligands. J. Chem. Soc., Dalton Trans. 2000, 3885−3896. (18) (a) Wang, Y.; Peng, S.-M.; Lee, Y.-L.; Chuang, M.-C.; Tang, C.P.; Wang, C.-J. Crystal and Molecular Structure of the Macrocyclic Nickel (II) Complex Ni(C22H22H4): Dibenzo[b, i][5, 7, 12, 14] Tetramethyl [1, 4, 8, 11] Tetraazacyclotetradeca-2, 4, 7, 9, 12, 14Hexaeneatonickel (II). J. Chin. Chem. Soc. 1982, 29, 217−224. (b) Andrews, P. C.; Atwood, J. L.; Barbour, L. J.; Croucher, P. D.; Nichols, P. J.; Smith, N. O.; Skelton, B. W.; White, A. H.; Raston, C. L. Supramolecular confinement of C60, S8, P4Se3 and toluene by metal(II) macrocyclic complexes. J. Chem. Soc., Dalton Trans. 1999,

(4) (a) Chirila, A.; Gopal Das, B.; Paul, N. D.; de Bruin, B. Diastereoselective Radical-Type Cyclopropanation of ElectronDeficient Alkenes Mediated by the Highly Active Cobalt(II) Tetramethyltetraaza[14]annulene Catalyst. ChemCatChem 2017, 9, 1413−1421. (b) Chirila, A.; van Vliet, K. M.; Paul, N. D.; de Bruin, B. [Co(MeTAA)] Metalloradical Catalytic Route to Ketenes via Carbonylation of Carbene Radicals. Eur. J. Inorg. Chem. 2018, 2018, 2251−2258. (c) Chirila, A.; Brands, M. B.; de Bruin, B. Mechanistic investigations into the cyclopropanation of electron-deficient alkenes with ethyl diazoacetate using [Co(MeTAA)]. J. Catal. 2018, 361, 347−360. (d) Das, B. G.; Chirila, A.; Tromp, M.; Reek, J. N. H.; de Bruin, B. CoIII−Carbene Radical Approach to Substituted 1H-Indenes. J. Am. Chem. Soc. 2016, 138, 8968−8975. (5) Lin, S.; Diercks, C. S.; Zhang, Y.-B.; Kornienko, N.; Nichols, E. M.; Zhao, Y.; Paris, A. R.; Kim, D.; Yang, P.; Yaghi, O. M.; Chang, C. J. Covalent organic frameworks comprising cobalt porphyrins for catalytic CO2 reduction in water. Science 2015, 349, 1208−1213. (6) Eriksson, K. L. E.; Chow, W. W. Y.; Puglia, C.; Bäckvall, J.-E.; Göthelid, E.; Oscarsson, S. Performance of a Biomimetic Oxidation Catalyst Immobilized on Silicon Wafers: Comparison with Its Gold Congener. Langmuir 2010, 26, 16349−16354. (7) Sugimoto, H.; Kuroda, K. The Cobalt Porphyrin−Lewis Base System: A Highly Selective Catalyst for Alternating Copolymerization of CO2 and Epoxide under Mild Conditions. Macromolecules 2008, 41, 312−317. (8) (a) Silva, T. A.; Diniz, J.; Paixão, L.; Vieira, B.; Barrocas, B.; Nunes, C. D.; Monteiro, O. C. Novel titanate nanotubescyanocobalamin materials: Synthesis and enhanced photocatalytic properties for pollutants removal. Solid State Sci. 2017, 63, 30−41. (b) Lobo, S. A. L.; Brindley, A. A.; Romão, C. V.; Leech, H. K.; Warren, M. J.; Saraiva, L. M. Two Distinct Roles for Two Functional Cobaltochelatases (CbiK) in Desulfovibrio vulgaris Hildenborough. Biochemistry 2008, 47, 5851−5857. (c) Matthews, R. G. CobalaminDependent Methyltransferases. Acc. Chem. Res. 2001, 34, 681−689. (9) (a) Doctorovich, F.; Bikiel, D. E.; Pellegrino, J.; Suárez, S. A.; Martí, M. A. Reactions of HNO with Metal Porphyrins: Underscoring the Biological Relevance of HNO. Acc. Chem. Res. 2014, 47, 2907− 2916. (b) Dube, H.; Kasumaj, B.; Calle, C.; Felber, B.; Saito, M.; Jeschke, G.; Diederich, F. Probing Hydrogen Bonding to Bound Dioxygen in Synthetic Models for Heme Proteins: The Importance of Precise Geometry. Chem. - Eur. J. 2009, 15, 125−135. (c) Fujii, H.; Dou, Y.; Zhou, H.; Yoshida, T.; Ikeda-Saito, M. Cobalt Porphyrin Heme Oxygenase Complex. EPR Evidences for the Distal Heme Pocket Hydrogen Bonding. J. Am. Chem. Soc. 1998, 120, 8251−8252. (10) (a) Wayland, B. B.; Peng, C.-H.; Fu, X.; Lu, Z.; Fryd, M. Degenerative Transfer and Reversible Termination Mechanisms for Living Radical Polymerizations Mediated by Cobalt Porphyrins. Macromolecules 2006, 39, 8219−8222. (b) Peng, C.-H.; Fryd, M.; Wayland, B. B. Organocobalt Mediated Radical Polymerization of Acrylic Acid in Water. Macromolecules 2007, 40, 6814−6819. (11) Goggins, E. M.; Lekich, T. T.; Weare, W. W.; Sommer, R. D.; Ribeiro, M. A.; Pinheiro, C. B. A Periodic Walk through a Series of First-Row, Oxido-Bridged, Heterodimetallic Molecules: Synthesis and Structure. Eur. J. Inorg. Chem. 2016, 2016, 1054−1059. (12) (a) Wang, Y.; Wen, X.; Cui, X.; Zhang, X. P. Enantioselective Radical Cyclization for Construction of 5-Membered Ring Structures by Metalloradical C−H Alkylation. J. Am. Chem. Soc. 2018, 140, 4792−4796. (b) Jiang, H.; Lang, K.; Lu, H.; Wojtas, L.; Zhang, X. P. Asymmetric Radical Bicyclization of Allyl Azidoformates via Cobalt(II)-Based Metalloradical Catalysis. J. Am. Chem. Soc. 2017, 139, 9164−9167. (c) Wang, Y.; Wen, X.; Cui, X.; Wojtas, L.; Zhang, X. P. Asymmetric Radical Cyclopropanation of Alkenes with In SituGenerated Donor-Substituted Diazo Reagents via Co(II)-Based Metalloradical Catalysis. J. Am. Chem. Soc. 2017, 139, 1049−1052. (d) Goswami, M.; Lyaskovskyy, V.; Domingos, S. R.; Buma, W. J.; Woutersen, S.; Troeppner, O.; Ivanović-Burmazović, I.; Lu, H.; Cui, X.; Zhang, X. P.; Reijerse, E. J.; DeBeer, S.; van Schooneveld, M. M.; Pfaff, F. F.; Ray, K.; de Bruin, B. Characterization of PorphyrinCo(III)-‘Nitrene Radical’ Species Relevant in Catalytic Nitrene 1232

DOI: 10.1021/acs.inorgchem.8b02644 Inorg. Chem. 2019, 58, 1224−1233

Article

Inorganic Chemistry 2927−2932. (c) Tsutsui, M.; Bobsein, R. L.; Cash, G.; Pettersen, R. Inorg. Chem. 1979, 18, 758. (19) (a) Scheidt, W. R.; Turowska-Tyrk, I. Crystal and Molecular Structure of (Octaethylporphinato)cobalt(II). Comparison of the Structures of Four-Coordinate M(TPP) and M(OEP) Derivatives (M = Fe-Cu). Use of Area Detector Data. Inorg. Chem. 1994, 33, 1314− 1318. (b) de Melo, C. C.; da Conceicao Moreira, W.; Martins, T. J.; Cordeiro, M. R.; Ellena, J.; Guimaraes, F. F.; Martins, F. T. Saddleshaped macrocycle distortion and symmetry decrease in cobalt (II) meso-tetraphenylporphyrin: Structure of a dichloromethane solvate and DFT calculations. J. Mol. Struct. 2014, 1076, 468−474. (20) Weiss, M. C.; Goedken, V. L. Chemistry of the macrocyclic cobalt(II) complex, [Co(C22H22N4)]. Reactions with halogens, molecular oxygen, alkynes, and nitriles. J. Am. Chem. Soc. 1976, 98, 3389−3392. (21) (a) Pezeshk, A.; Greenaway, F. T.; Dabrowiak, J. C.; Vincow, G. EPR studies of axial ligation of a low-spin cobalt(II) macrocyclic Schiff base complex. Inorg. Chem. 1978, 17, 1717−1725. (b) Pezeshk, A. Newly resolved ESR spectrum of a low-spin cobalt(II) macrocyclic complex in 3-methylpyridine. Inorg. Chem. 1992, 31, 2282−2284. (22) Migita, K.; Iwaizumi, M.; Isobe, T. Nuclear magnetic resonance studies of planar low-spin complexes of cobalt(II) with Schiff bases. N,N’-ethylenebis(salycylideneiminato)cobalt(II) in noncoordinating solvents. J. Am. Chem. Soc. 1975, 97, 4228−4232. (23) Niewahner, J. H.; Walters, K. A.; Wagner, A. Improved Synthesis of Geodken’s Macrocycle through the Synthesis of the Dichloride Salt. J. Chem. Educ. 2007, 84, 477−479. (24) (a) Poli, R.; Cacelli, I. Orbital Splitting and Pairing Energy in Open-Shell Organometallics: A Study of Two Families of 16-Electron Complexes [Cp2M] (M = Cr, Mo, W) and [CpM(PH3)] (M = Co, Rh, Ir). Eur. J. Inorg. Chem. 2005, 2005, 2324−2331. (b) LozanoEspinosa, M.; Garza, J.; Galván, M. Confinement effects on the spin potential of first row transition metal cations. Philos. Mag. 2017, 97, 284−297. (c) Galván, M.; Vela, A.; Gázquez, J. L. Chemical reactivity in spin-polarized density functional theory. J. Phys. Chem. 1988, 92, 6470−6474. (25) Balch, A. L.; Mazzanti, M.; Olmstead, M. M. Cobalt complexes of octaethyloxophlorin. Metal-centered redox chemistry in the presence of a redox-active ligand. Inorg. Chem. 1993, 32, 4737−4744. (26) Walker, F. A. Steric and electronic effeccts in the coordination of amines to a cobalt(II) porphyrin. J. Am. Chem. Soc. 1973, 95, 1150−1153. (27) Miry, C.; Le Brun, D.; Kerbaol, J.-M.; L’Her, M. Cobalt(II)− dibenzotetraaza[14]annulene complex electropolymerization for electrode modification. J. Electroanal. Chem. 2000, 494, 53−59. (28) Sheldrick, G. M. A short history of SHELX. Acta Crystallogr., Sect. A: Found. Crystallogr. 2008, 64, 112−122. (29) Dolomanov, O. V.; Bourhis, L. J.; Gildea, R. J.; Howard, J. A. K.; Puschmann, H. OLEX2: a complete structure solution, refinement and analysis program. J. Appl. Crystallogr. 2009, 42, 339−341. (30) Macrae, C. F.; Bruno, I. J.; Chisholm, J. A.; Edgington, P. R.; McCabe, P.; Pidcock, E.; Rodriguez-Monge, L.; Taylor, R.; van de Streek, J.; Wood, P. A. Mercury CSD 2.0 - new features for the visualization and investigation of crystal structures. J. Appl. Crystallogr. 2008, 41, 466−470. (31) 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.; Keith, T.; 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 C.01; Gaussian, Inc.: Wallingford, CT, 2010. (32) (a) Becke, A. D. Density-functional thermochemistry. III. The role of exact exchange. J. Chem. Phys. 1993, 98, 5648. (b) Lee, C.; Yang, W.; Parr, R. G. Development of the Colle-Salvetti correlationenergy formula into a functional of the electron density. Phys. Rev. B: Condens. Matter Mater. Phys. 1988, 37, 785. (33) (a) Vosko, S. H.; Wilk, L.; Nusair, M. Accurate spin-dependent electron liquid correlation energies for local spin density calculations: a critical analysis. Can. J. Phys. 1980, 58, 1200−1211. (b) Vosko, S. H.; Wilk, L. Influence of an improved local-spin-density correlationenergy functional on the cohesive energy of alkali metals. Phys. Rev. B: Condens. Matter Mater. Phys. 1980, 22, 3812.

1233

DOI: 10.1021/acs.inorgchem.8b02644 Inorg. Chem. 2019, 58, 1224−1233