Ru-Complex Framework toward Aerobic Oxidative Transformations of

Nov 30, 2017 - It includes the following transformations involving {Ru(acac)2} coordinated β-diketiminate in 1 and ketodiimine in 2 with the simultan...
0 downloads 7 Views 3MB Size
Download PDF
Article Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX

pubs.acs.org/IC

Ru-Complex Framework toward Aerobic Oxidative Transformations of β‑Diketiminate and α‑Ketodiimine Sanjib Panda, Abhishek Mandal, Prabir Ghosh, and Goutam Kumar Lahiri* Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India S Supporting Information *

ABSTRACT: The impact of the {Ru(acac)2} (acac− = acetylacetonate) framework on the transformations of C−H and C−H/C−C bonds of coordinated β-diketiminate and ketodiimine scaffolds, respectively, has been addressed. It includes the following transformations involving {Ru(acac)2} coordinated β-diketiminate in 1 and ketodiimine in 2 with the simultaneous change in metal oxidation state: (i) insertion of oxygen into the C(sp2)−H bond of β-diketiminate in 1, leading to the metalated ketodiimine in 2 and (ii) Bronsted acid (CH3COOH) assisted cleavage of unstrained C(sp2)− C(sp2)/CN bonds of chelated ketodiimine (2) with the concomitant formation of intramolecular C−N bond in 3, as well as insertion of oxygen into the C(sp3)−H bond of 2 to yield −CHO function in 4 (−CH3 → −CHO). The aforesaid transformation processes have been authenticated via structural elucidation of representative complexes and spectroscopic and electrochemical investigations.

■

Scheme 1. Reported Oxidative Functionalization of Cβ−H of “nacnac” Derivatives Involving O2a

INTRODUCTION The aryl-substituted β-diketiminate (nacnac) moiety has drawn continuing attention in organometallic and coordination chemistry over the decades by virtue of its diverse binding modes to metal ions, as well as its tunable electronic and steric features.1,2 Besides the robust nature of nacnac in complex frameworks,1b,3h its “noninnocent” features including ligand based reactivity and redox activity have also been demonstrated.1a,b,3−7 The β-carbon (Cβ) of metal coordinated nacnac is known to react with electrophiles such as dienophiles (in cycloaddition reactions) to form bicyclic structures,3 activation of small diatomic molecules (H2, N2, O2) by interaction with their LUMOs,4 and methyl cation migration,5a among many others.5 However, oxidative transformation of methine C−H of nacnac (Cβ) derivatives using molecular oxygen is limited to a few recent reports involving p-, d-, and f-block metal complexes to furnish a wide variety of oxygenated nacnac backbones, L1− L4 as depicted in Scheme 1.4 Isolation of the free ketodiimine ligand (L1, Scheme 1) from in situ generated M−nacnac complexes (M = Cu, Zn)4b requires vigorous O2 purging. Though the catalytic role of metal complexes of preformed L1 for olefin polymerization has been documented,8 reactivity of metal coordinated L1 in the specific context of organometallic chemistry remains unexplored. In this regard, this article highlights a facile oxidation route of nacnac on a heavier metal derived molecular platform followed by its unusual reactivity profile. The newly designed coordinatively saturated {Ru(acac)2} derived nacnac framework (1) undergoes oxygenation of its vinylogous C(sp2)−H bond under aerial atmosphere to ketodiimine derivative, 2 (Scheme © XXXX American Chemical Society

a

Transformed nacnac moieties are selectively shown for clarity.

2). Furthermore, the subsequent acid prompted reaction of 2 leads to unprecedented transformations of the ketodimine moiety including (i) unstrained aliphatic C−C/CN bond cleavage9 with the concomitant formation of a C−N bond in 3 and (ii) selective oxygenation of an inert C(sp3)−H bond to yield the −CHO group in 4 (Scheme 2), revealing a metal driven activation of substrate10 as well as small molecule (O2).11 Herein, we report the synthetic account of 1−4, structural authentication of the transformation processes in Scheme 2, and spectroscopic and electrochemical features of the complexes. Received: August 23, 2017

A

DOI: 10.1021/acs.inorgchem.7b02172 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry Scheme 2. Metal Coordination Assisted Facile Organic Transformations

Scheme 4. Synthetic Outline for 3 and 4

chemical processes of L1 on the selective molecular backbone of 2. Identification of 1−4 has been established by elemental analysis (Experimental Section), mass spectrometry (Figure S1, Supporting Information), single crystal X-ray structures of representative complexes (Figures 1 and 2; Table 1; Figures S2−S5 and Tables S1−S9, Supporting Information), and their NMR spectral features. The change in bond distances, redox potentials, broad paramagnetic to diamagnetic 1H NMR signals, disappearance of RuIII based EPR, distinctive electronic spectra on moving from 1 to 2, and CO vibration of L1 in 2 at about 1660 cm−1 (13C NMR of CO: 186 ppm) (see later) collectively corroborate the change in metal oxidation state in the reaction sequence of 1 → 2. Furthermore, the involvement of aerial oxygen for the conversion of 1 → 2 has been established by 18O2 labeling experiments with the representative complex 1a, which displays ESI-MS corresponding to 2a (18O/16O = 61.5:38.5), in agreement with the computer simulated isotropic pattern (Figure S6, Supporting Information). The crystal structures of representative 1b, 1c, 2a, and 2b and 3a and 4b are shown in Figures 1 and 2, respectively. The average Ru−N bond distance in 2 (2b, 1.966 Å) is shorter than that in 1 (1b, 2.006 Å) possibly due to the stronger (dπ)RuII → (pπ*)L1 π-back-bonding interaction in the former. The conversion of nacnac in 1 to L1 in 2 has also been reflected in shortening and lengthening of C−N and C2− C3/C3−C4 bond distances, respectively. The CO distance at about 1.24 Å in 2 supports its unperturbed identity. The single (C3−N1, 1.352(6) Å) and double (C2−N2, 1.284(5) Å) bonds of L5 in 3 result in significant variation in corresponding Ru−N1 (2.000(3) Å) and Ru−N2 (2.016(4) Å) bond distances, respectively. The C3−O5 bond length (1.224(5) Å) of L5 in 3 is slightly shorter than the CO distance of L1 (1.240(3) Å) in 2. The impact of asymmetry in L6 in 4 owing to the CH3 and CHO functions with respect to symmetric L1 (two CH3 functions) in 2 has nicely been reflected in bond distances involving the RuII−L fragments. The enhanced charge delocalization in the direction of the imine group (C2−N1) attached to the CHO as compared to C4−N2 linked to the CH3 function leads to the lengthening of C2−N1 and Ru−N2 relative to C4−N2 and Ru−N1 bonds. This in effect makes the CO distance of L6 in 4 (C3−O5, 1.241(13) Å) shorter than that of L1 in 2 (1.25(1) Å). The bond parameters of 1−4 in Table 1 are in good agreement with those obtained by DFT calculations (Tables S2−S9 and Figure S7, Supporting Information). Spectral Aspects. The paramagnetic and diamagnetic features of 1 and 2, respectively, have been expectedly reflected in their broad or widespread (δ, −6 to +15 ppm) and usual (δ, 0 to +10 ppm) 1H NMR signatures. The symmetric 2 shows NMR resonances corresponding to half of the molecule. Disappearance of the methine proton of free nacnac (δ,

■

RESULTS AND DISCUSSION Synthesis and Crystal Structure. The starting [RuIII(acac)2(nacnac)] complexes (1a−1c) have been obtained from H-nacnacR,R (R = H, OMe, Cl) and precursor complex [RuII(acac)2(CH3CN)2] (acac = L = acetylacetonate) in refluxing ethanol and in the presence of Et3N base under dinitrogen atmosphere (Scheme 3). The presence of three Scheme 3. Synthetic Outline for 1 and 2a

a

Reagents and conditions: (i) EtOH, Et3N, 373 K, N2, 6 h; (ii) EtOH, O2 ballon, 333 K, ∼3 h.

anionic ligands (acac and nacnac) facilitates the stabilization of the paramagnetic Ru(III) (t2g5) state in 1 as has been reported earlier in numerous {Ru(acac)2} derived systems.12 Complex 1 (green) is however found to be sensitive to air and undergoes irreversible transformation to 2 (purple) in different solvents such as EtOH/MeOH, CHCl 3 , CH 2 Cl 2 , CH 3 CN, or (CH3)2CO even under ambient condition, where the methine C−H bond of coordinated nacnac in 1 has been oxidized to CO (ketodiimine, L1) with the simultaneous reduction of the metal oxidation state from Ru(III) in 1 to Ru(II) in 2. The rate of conversion of 1 → 2 varies based on the nature of the substituents in the Ar groups of nacnac, and it follows the order 1c < 1b < 1a (Scheme 3, see later), and this indeed has restricted the full characterization of 1a or 1b. Furthermore, the ketodiimine moiety (L1) in 2 undergoes unusual fragmentation/oxidation stimulated by metal chelation and Brønsted acid (glacial AcOH) assistance under aerial conditions (Scheme 4). These include (i) cleavage of α-C( O)−C(N) and CN bonds of 2 and formation of a new C−N bond to yield {RuIII(acac)2} coordinated α-iminocarboxamidato (L5) in 3 as well as (ii) selective oxidation of the saturated C−H bond of 2, leading to {RuII(acac)2} chelated bis(imino)oxopentanal (L6) in 4. The use of 10 equiv of glacial AcOH is found to provide the maximum yield of 3 or 4. The facile formation of 3 and 4 from 2 indeed demonstrate unique B

DOI: 10.1021/acs.inorgchem.7b02172 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

Figure 2. ORTEP diagrams of 3a (molecule A) and 4b (molecule A). Ellipsoids are drawn at 30% and 50% probability levels, respectively. Hydrogen atoms are omitted for clarity.

(Figure 3). The upfield shifted CHO function (13C NMR, δ(CHO) = 190 ppm) is the reflection of RuII → L6 back bonding. The anisotropic EPR of 1a−1c (Figure 4 and Table S10, Supporting Information) with ⟨g⟩/Δg ≈ 2.06/0.3 implies metal dominated spin with minor contribution from nacnac.13 This has also been evident from ∼25% spin localization on nacnac (Figure 5 and Figure S9, Table S11,Supporting Information).7 This in effect leads to the mixed electronic structural form of 1, [RuIII(acac)2(nacnac)] (major) and [RuII(acac)2(nacnac•)] (minor). Appreciably high g anisotropy (⟨g⟩ > 2.15) and Δg (0.55) (Figure 4 and Table S10, Supporting Information) along with metal dominated spin (>80%) (Figure 5 and Figure S9, Table S11, Supporting Information) suggest [RuIII(acac)2(L5)] configuration of 3. It however suggests slight spin localization (>10%) on L5. The delocalization of negative charge over the [N1−C3−O5] fragment has been manifested in the decrease of ν(CO) to ∼1630 cm−1 in 3 with respect to 1660 cm−1 in 2. Complexes 1c, 2a−2c, 3a−3c, and 4a−4c exhibit multiple absorptions in the UV−visible region in CH3CN (Figure 6 and Table S12, Supporting Information), which have been analyzed by TD-DFT calculations of representative 1c, 2a, 3a, and 4a (Figure S10 and Table S13, Supporting Information). There is a fairly good agreement between the experimental data and TD-DFT calculations. Complexes 2a−2c, 3a−3c, or 4a−4c show slight variation in spectral profile based on the substituents in the ligand framework. The weak and intense bands of 1c at 640 nm (ε = 1100 M−1 cm−1) and 342 nm (ε = 26710 M−1 cm−1) are assigned to be mixed metal−ligand (nacnac) and largely ruthenium targeted LMCT (ligand (acac/ nacnac) to metal charge transfer) transitions. Complexes 2a− 2c display one very weak band at around 830 nm followed by

Figure 1. ORTEP diagrams of 1b, 1c (molecule A), 2a, and 2b (molecule B). Hydrogen atoms are omitted for clarity. Thermal ellipsoids are drawn at 50% probability level.

approximately +4.8 ppm) in the 1H NMR of 2, as well as the appearance of CO of L1 in the 13C NMR of 2 (Figure S8, Supporting Information, and Experimental Section) corroborate the conversion of C−H of nacnac in 1 to CO in 2. The paramagnetic 3 exhibits broad 1H NMR (Figure S8, Supporting Information) and Ru(III) based anisotropic EPR (see later). Unlike 2, Ru(II) derived unsymmetric 4 shows four CH3 (acac), one CH3 (L6), and one CHO signals due to selective oxidation of one of the CH3 groups to CHO of L1 C

DOI: 10.1021/acs.inorgchem.7b02172 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry Table 1. Selected Bond Lengths (Å)

a

bond

1b

1ca (molecule A)

2a

2ba (molecule B)

3aa (molecule A)

4ba (molecule A)

Ru(1)−N(1) Ru(1)−N(2) Ru(1)−O(1) Ru(1)−O(2) Ru(1)−O(3) Ru(1)−O(4) C(2)−N(1) C(4)−N(2) C(2)−C(3) C(3)−C(4) C(3)−O(5) C(3)−N(1) C(2)−N(2) C(1)−O(6)

2.009(2) 2.003(2) 2.071(2) 2.020(2) 2.061(2) 2.024(2) 1.338(4) 1.326(4) 1.400(4) 1.397(4)

2.012(3) 2.007(3) 2.064(2) 2.029(2) 2.067(2) 2.021(2) 1.336(4) 1.333(4) 1.398(5) 1.397(5)

1.978(2) 1.974(2) 2.0346(19) 2.0182(17) 2.0529(17) 2.0504(18) 1.311(3) 1.316(3) 1.486(4) 1.481(4) 1.240(3)

1.973(5) 1.960(6) 2.024(4) 2.001(6) 2.035(4) 2.037(7) 1.31(1) 1.31(1) 1.48(1) 1.47(1) 1.25(1)

2.000(3) 2.016(4) 2.030(3) 2.004(3) 2.031(3) 1.998(3)

1.934(8) 2.002(8) 2.052(7) 2.031(6) 2.029(7) 2.020(7) 1.333(14) 1.285(13) 1.468(16) 1.499(15) 1.241(13)

1.499(6) 1.224(5) 1.352(6) 1.284(5)

1.164(15)

Unit cells of 1c, 3a, 4b, and 2b contain two (molecule A and molecule B) and three (molecule A, molecule B, and molecule C) molecules.

Figure 3. Segmented 1H NMR (400 MHz) of 2a (red) and 4a (blue) in CDCl3 at 298 K.

The complexes 2a−2c display reversible one oxidation and one reduction (Figure 7 and Table S14, Supporting Information). The MO compositions of 2n (n = 0, +1, −1) (Tables S20−S28, Supporting Information) predict the involvement of {Ru(acac)2} (∼90%) fragment and CO/ CN components of L1 (∼90%) towards the oxidation (2+, S = 1/2) and reduction (2−, S = 1/2) processes, respectively. The metal based oxidation (Ru(II) → Ru(III)) and the reduction of L1 while moving from 2 → 2+ ([RuIII(acac)2(L1)]) and 2 → 2− ([RuII(acac)2(L1•−)]), respectively, have also been supported by the EPR of the electrogenerated 2+ and 2− (Figure 4 and Table S10, Supporting Information), as well as Mulliken spin density distributions (Figure 5 and Figure S9, Table S11, Supporting Information). This in effect reveals the noninnocent feature of L1 in 2. The large positive shift (>1 V) of RuII/RuIII potential on moving from 1 to 2 can be attributed to the change in electronic nature of the ligand frameworks,10a,b anionic βdiketiminate (nacnac) in the former to the strongly π-accepting neutral ketodiimine (L1) in the latter. The complexes 3a−3c undergo reversible one-electron oxidation and reduction processes within the potential window of ±2.0 V versus SCE in CH3CN (Figure 7 and Table S14, Supporting Information). The primarily ligand (L5) based oxidation (∼80%) and metal based reduction with partial involvement of L5 (∼30%) as predicted by their MO compositions (Tables S29−S31, Supporting Information) and Mulliken spin distribution of 3+ (S = 1) (Figure 5 and Figure S11, Table S11, Supporting Information), implying [Ru III (acac) 2 (L 5• )] + and a mixed [Ru II (acac) 2 (L 5 )] − / [RuIII(acac)2(L5•−)]− (S = 0) electronic configurations for 3+

two moderately intense bands around 540 and 370 nm corresponding to primarily L1 targeted mixed metal/ligand based transitions. The weak and rather ill-defined three close by transitions between 550 and 390 nm for 3a−3c represent ruthenium targeted LMCT and L5 or acac targeted MLCT transitions. The spectral features of 4 appear to be similar to those of 2, displaying one very weak band around 870 nm and two moderately intense bands at about 540 and 430 nm corresponding to L6 targeted MLCT (metal−ligand charge transfer) transitions. Electrochemistry and Electronic Structural Aspects. The cyclic and differential pulse voltammograms of 1c, 2a−2c, and 3a−3c are shown in Figure 7 and Table S14, Supporting Information. The one-electron nature of the oxidation or reduction process in Figure 7 has been confirmed by constant potential coulometry. The primarily ligand based (62%) irreversible oxidation with partial metal contribution (29%) as revealed by the DFT calculated MO compositions (Tables S15−S19, Supporting Information) suggest a mixed electronic configuration of 1c+ (S = 1), [RuIII(acac)2(nacnac•)]+ (major) and [RuIV(acac)2(nacnac)]+ (minor). On the other hand, MO compositions predict a reverse situation of metal dominated (59%) reduction with partial ligand contribution (26%) leading to the electronic structural form of [RuII(acac)2(nacnac)]− (major) and [RuIII(acac)2(nacnac•−)]− (minor) for 1c− (S = 0). This in effect implies the potential bidirectional (fractional) noninnocence of coordinated nacnac.7,14 The instability of both 1c+ and 1c− on the coulometric time scale has prevented us from checking their spectral features. D

DOI: 10.1021/acs.inorgchem.7b02172 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

The change in metal oxidation state in moving from 1 to 2 can be attributed to the stronger π-acceptor feature of ketodiimine ligand (L1) in 2 with respect to nacnac in 1 as has also been evidenced by their redox potentials (Table S14, Supporting Information). The necessary change in multiplicities for the activation of O2 (GS triplet, 3Σg− ; ES singlet, 1 Δg and 1Σg+) in this pathway may be assisted by its interaction with the complex under strong crystal field.15 The minority contribution of alternate valence tautomeric form {RuIInacnac•} of 1 (radical pathway in Scheme 5) cannot however be excluded due to the partial (∼25%) involvement of nacnac in the spin distribution process (Table S11, Supporting Information) as has also been reflected in the relatively small EPR g anisotropy value13 (⟨g⟩ ≈ 2.06, Δg ≈ 0.3, Figure 4 and Table S10, Supporting Information) of 1. It is to note that if the two spin tautomers are close in energy, the approach of the oxygen molecule could potentially induce a spin state change at the metal/ligand interface leading to a different electronic state at the bond breaking/bond forming process from its electronic ground state. This indeed has led to the consideration of both the possibilities in Scheme 5. The alternate approach of M−O− O−C(β) peroxo bridged intermediate4b seems to be unlikely for the coordinatively saturated system as in 1 due to the formation of a less favored seven coordinated intermediate. The likely involvement of initial weak interaction of O2 with the metal ion in facilitating the 1 → 2 transformation process in Scheme 5 even at the ambient condition cannot however be ruled out. In this regard, the trapping of one of the short-lived intermediates during the conversion process of 1c → 2c (see Experimental Section) indeed extends further insights into the mechanistic outline. The identity of the intermediate (blue) has been ascertained by different spectral analysis, which exhibits the following distinct features with special reference to the precursor complex 1c (green) as well as the final product 2c (purple). (i) Free radical type EPR with slight metal based anisotropy (⟨g⟩/Δg = 2.008/0.046) (Figure 9). (ii) Mass (m/z) of 673 (Figure S13a, Supporting Information). (iii) UV−vis spectral profile with intense peaks at 598, 394, and 278 nm (Figure S13b, Supporting Information). (iv) Spectral change for the conversion of intermediate blue species to 2c with time (Figure S13c, Supporting Information). (v) Raman spectral band16 at 893 cm−1 (Figure S13d, Supporting Information). The collective consideration of the aforesaid spectral features (i−v) reveals the radical identity of the intermediate species, which may suggest the involvement of the radical pathway over the anionic route in Scheme 5. Transformation of 2 → 3 and 4. A tentative mechanistic outline for acid prompted Ru chelation assisted conversion of ketodiimine (L1) in 2 to iminocarboxamidato (L5) function in 3 is shown in Scheme 6. The protonation of highly basic keto function in C possibly initiates the C−C bond cleavage, leading to the formation of a strained unsaturated azirine ion derived chelate (D). The subsequent hydrolysis of D followed by the removal of CH3CHO from F results in metal coordinated L5 in 3. The reaction sequence is also coupled with the change in metal oxidation state (RuII to RuIII). The transformation of 2 to 3 (Scheme 6) may be prompted via the involvements of (a) an in situ generated ring strain in D,17 favored by the backdonation from RuII, (b) an energy releasing fragmentation step in F,18,9h and (c) electron-rich acac−/L5 in stabilizing the oxidized Ru(III) state with much negative Ru(II)/Ru(III)

Figure 4. X-band EPR spectra in CH3CN/toluene (1:1) at 100 K.

and 3−, respectively. This in turn attributes the bidirectional noninnocent features of the newly developed L5 in 3.13 Kinetics of 1 → 2. The rate of transformation of 1a → 2a has been followed spectrophotometrically in deaerated CH3CN in the presence of O2 atmosphere by initial flushing of O2 over the temperature range of 303−333 K (Figure 8, Table 2 and Figure S12, Table S32, Supporting Information). The rate of transformation for 1b → 2b or 1c → 2c has also been estimated at 333 K (Figure S12 and Table S33, Supporting Information), which follows the order (k in s−1) 1a ((9.7 ± 0.2) × 10−6) > 1b ((8.8 ± 0.3) × 10−6) > 1c ((6.7 ± 0.2) × 10−6) at 333 K. Detailed kinetic study at different temperatures for 1a → 2a shows a pseudo-first-order rate (with respect to 1a) with ΔH⧧ (enthalpy of activation) and ΔS⧧ (entropy of activation) values of 2.1 ± 0.1 kcal mol−1 and −75.3 ± 0.3 cal mol−1 K−1, respectively, which implies the involvement of an associatively activated pathway. Transformation of 1 → 2. Two probable reaction pathways for the oxidation of methine C−H of “nacnac” in coordinatively saturated 1 are depicted in Scheme 5. First step of the anionic pathway in Scheme 5 involves the generation of peroxide anion (A) via the interaction of 1 (SOMO ∼60% nacnac, ∼30% Ru) and O2, which spontaneously rearranges to give the hydroperoxo species (B). The subsequent heterolytic cleavage of O−O bond in B leads to thermodynamically stable ketone derivative 2 with the simultaneous reduction of RuIII to RuII. E

DOI: 10.1021/acs.inorgchem.7b02172 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

Figure 5. Mulliken spin density plots (0.003 isovalue) of 1 (S = 1/2), 2n (n = +1, −1; S = 1/2), and 3 (S = 1/2).

formation processes of 1 → 2 and 2 → 3 and 4 in Scheme 2 have been established via structural and spectroscopic characterization of 1−4. The redox noninnocence of nacnac, L1, and L5 in 1, 2, and 3, respectively, has also been addressed by experimental (electrochemistry, EPR) studies in conjunction with DFT calculations. Finally, the observed metal (RuII/III) redox assisted functionalization of inert bonds of coordinated nacnac or L1 in 1 or 2, respectively, (Scheme 2) would enhance the future scope relating to the reactivity profile of metal coordinated nacnac derivatives.

couple with regard to that in 2 [0.28 V (2a) and −0.71 V (3a) versus SCE] (Table S14, Supporting Information). The oxidation of saturated sp3 C−H in 4 under aerial atmosphere may proceed through the generation of a carbon radical at the allylic position with respect to the imine function of 2 by a possible reactive hydroxyl radical formation (RuII → RuIII + e−; O2 + H+ + e− → OH•)19b followed by activating O2.19 Periodic monitoring of the conversion of 2 to 3 and 4 by mass spectrometry excludes the alternate high valent metal− oxygen species triggered reaction pathway.20 Further oxidation of the second CH3 group of L6 in 4 is thermodynamically an uphill process and thus provides selectivity. This may be facilitated due to the following factors: (a) Substantially higher barrier for the activation of O2, since nucleophilicity of the newly generated carbon radical would be decreased in the presence of a large number of electron withdrawing groups. This may be justified by the deshielding of 1H NMR peak of CH3 group as observed on moving from L1 in 2a to L6 in 4a, Figure 3. (b) Lesser statistical abundance of C−H bonds. (c) Second oxidation also requires to overcome high activation energy of entropy.

■

EXPERIMENTAL SECTION

Materials. The precursor complexes cis-Ru(acac)2(CH3CN)221 and the ligand aryl-substituted β-diketimine (nacnac-H)22 were prepared according to the literature procedures. EtOH was dried using activated magnesium.23 Other chemicals and solvents were of reagent grade and used as received. For spectroscopic and electrochemical studies, HPLC grade solvents were used. 18O2 was bought from ICON isotope. Physical Measurements. The electrical conductivity was checked using an autoranging conductivity meter (Toshcon Industries, India). EPR spectra were recorded on Bruker EMX Plus. Cyclic voltammetric and differential pulse voltammetric measurements of the complexes were done using a PAR model 273A electrochemistry system. Glassy carbon working, platinum wire auxiliary, and saturated calomel reference electrodes were used in a standard three-electrode configuration with tetraethylammonium perchlorate (TEAP) as the supporting electrolyte (substrate concentration ≈10−3 M; standard scan rate 100 mV s−1). 1H/13C NMR spectra were recorded on a Bruker Avance III 400 or 500 MHz spectrometer. The elemental analyses were recorded on a Thermoquest (EA 1112) microanalyzer.

■

CONCLUSION In the context of recent growing interest of C−H, C−C bond functionalization, the present article demonstrates late transition metal mediated insertion of oxygen to the stable Csp2−H in 1 or Csp3−H bond in 4 and cleavage of unstrained C−C to form intramolecular C−heteroatom bond in 3. The transF

DOI: 10.1021/acs.inorgchem.7b02172 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

spectrum was recorded in a WITec micro-Raman spectrometer equipped with a 532 nm Nd:YAG laser excitation. Kinetic Studies. Kinetics experiments were carried out under O2 atmosphere by dissolving 1 (∼3.5 × 10−4 M) in deaerated CH3CN. The compound solution in a 3 mL cuvette with rubber septum was vigorously purged with O2 (O2 balloon) for 1 min before each experiment. The change in absorbance at 544 nm for 1 → 2 was monitored for the rate calculation. The pseudo-first-order rate constant (k) for 1 → 2 was calculated based on nonlinear exponential fit in Origin Pro8 software by the following equation: y = y0 + A1 exp(−x/t1), where y and y0 correspond to absorbance at 544 nm at time t and at time t = 0 respectively; x corresponds to time periods (t in min) over which the absorption changes take place; A1 is pseudofirst-order coefficient, and the value of pseudo-first-order rate constant (k in s−1) is [1/(t1 × 60)]. Crystallography. X-ray diffraction data were collected using a Rigaku Saturn-724+ CCD single crystal X-ray diffractometer using Mo Kα radiation. The data collection was evaluated by using the Crystal Clear-SM Expert software. The data were collected by the standard ωscan technique. The structure was solved by direct method using SHELXS-97 and refined by full matrix least-squares with SHELXL2012, refining on F2.24 All data were corrected for Lorentz and polarization effects, and all non-hydrogen atoms were refined anisotropically. The remaining hydrogen atoms were placed in geometrically constrained positions and refined with isotropic temperature factors, generally 1.2Ueq of their parent atoms. Hydrogen atoms were included in the refinement process as per the riding model. CCDC 1502335 (1b), CCDC 1501986 (1c), CCDC 1502333 (2a), CCDC 1502334 (2b), CCDC 1501980 (3a), and CCDC 1501981 (4b) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/ cif. The alert B in the checkCIF of 2b and 4b can be ignored as it has developed due to weakly diffracting crystal and twining problem, respectively. Computational Studies. Full geometry optimization was performed by using the density functional theory method at B3LYP (for 2 and 4) or (U)B3LYP (for 1 and 3) level.25 Except ruthenium, all other elements were assigned the 6-31G* basis set. The LANL2DZ basis set with effective core potential was employed for the ruthenium atom.26 All calculations were performed with the Gaussian 09 program package.27 Chemissian 1.728 was used to calculate the fractional contributions of various groups to each molecular orbital. All calculated structures were visualized with ChemCraft.29 Vertical electronic excitations based on (R)B3LYP/(U)B3LYP optimized geometries were computed for 1c, 2a, 3a, and 4a using the timedependent density functional theory (TD-DFT) formalism30 in acetonitrile using conductor-like polarizable continuum model (CPCM).31 Electronic spectra were calculated using the SWizard program.32,33 Preparation of Complexes. Synthesis of [Ru(acac)2(nacnacR,R)] (1a−1c) and [Ru(acac)2(L1 R,R)] (2a−2c). The complexes were prepared by following the general synthetic routes using respective preformed nacnac-HR,R ligands (where R,R are the para-substituents of N-bearing aryl groups). To the orange solution of Ru(acac)2(CH3CN)2 in degassed EtOH in an oven-dried clean twoneck round-bottom flask, the yellow solution of the respective nacnacHR,R derivatives in degassed EtOH followed by Et3N was added. The solution was refluxed under a dinitrogen atmosphere for 6 h. The solution gradually turned green. Evaporation of solvent under vacuum afforded a green solid, which was subjected to purification by column chromatography using a neutral alumina and petroleum ether/ dichloromethane as the eluent. The removal of solvent under vacuum resulted in corresponding complexes 1a−1c. Complex 1 was sensitive to air, was stable only under deaerated conditions, and converted to 2 (purple) on exposure to air to different extents (1c < 1b < 1a) depending on the substitutent effect in the nacnac framework. The complexes 1a and 1b were found to be partially converted to 2 during the chromatographic process; therefore

Figure 6. Electronic spectra of 1c, 2a−2c, 3a−3c and 4a−4c in CH3CN.

Figure 7. Cyclic (black) and differential pulse (green) voltammograms in CH3CN/0.1 M Et4NClO4/GC versus SCE; scan rate 100 mV s−1.

Electrospray mass spectrometry was checked on a Bruker’s Maxis Impact (282001.00081) spectrometer. IR spectra of the complexes as KBr pellets were recorded on a Nicolet spectrophotometer. Raman G

DOI: 10.1021/acs.inorgchem.7b02172 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

Figure 8. (a) UV−vis change at 541 and 648 nm in the presence of oxygen for 1a → 2a conversion at 323 K. Rate is assigned based on the growing feature of the 541 nm peak (inset). (b) Plot of ln(k/T) versus 1/T for the reaction of 1a with O2.

Table 2. Temperature Dependent Kinetic Data for 1a → 2a temp (K) 303 313 323 333

k (s−1) 6.44 7.54 8.66 9.74

× × × ×

−6

10 10−6 10−6 10−6

ΔH⧧ (kcal mol−1)

ΔS⧧ (cal mol−1 K−1)

2.1 ± 0.1

−75.3 ± 0.3

full characterization of 1c was performed. In order to obtain 2 from 1, the reaction was carried out under O2 atmosphere for 3 h. [RuIII(acac)2(nacnacH,H)], 1a. Ru(acac)2(CH3CN)2 (100 mg, 0.26 mmol), EtOH (50 mL), nacnacH,H (65.5 mg, 0.26 mmol), Et3N (0.036 mL, 0.26 mmol). Yield: 130 mg (91%). MS (ESI+, CH3CN): m/z {1a}+ calcd, 549.13; found, 549.11. Molar conductivity (CH3CN): ΛM = 2 Ω−1 cm2 M−1. [RuIII(acac)2(nacnacOMe,OMe)], 1b. Ru(acac)2(CH3CN)2 (100 mg, 0.26 mmol), EtOH (50 mL), nacnacOMe,OMe (81.4 mg, 0.26 mmol), Et3N (0.036 mL, 0.26 mmol). Yield: 149 mg (94%). Crystallization was done by slow evaporation of its dichloromethane−hexane (2:1) solution. MS (ESI+, CH3CN): m/z {1b}+ calcd, 609.15; found, 609.19. Molar conductivity (CH3CN): ΛM = 4 Ω−1 cm2 M−1. [RuIII(acac)2(nacnacCl,Cl)], 1c. Ru(acac)2(CH3CN)2 (100 mg, 0.26 mmol), EtOH (50 mL), nacnacCl,Cl (83.7 mg, 0.26 mmol), Et3N (0.036 mL, 0.26 mmol). Yield: 141 mg (87%). Crystallization was done by slow evaporation of its dichloromethane−hexane (2:1) solution. MS (ESI+, CH3CN): m/z {1c}+ calcd, 617.05; found, 617.09. 1 H NMR (400 MHz, CDCl3) [δ/ppm]: 15.31, 14.92, 7.13, 6.92, 6.60, 6.00, 5.30, 2.02, 1.30, −0.27, −2.16, −5.48. Anal. Calcd. for C27H29N2O4Cl2Ru: C, 52.52, H, 4.73; N, 4.54. Found: C, 52.74, H, 4.67; N, 4.83. Molar conductivity (CH3CN): ΛM = 2 Ω−1 cm2 M−1. [RuII(acac)2(L1 H,H)], 2a. Complex 1a (50 mg, 0.091 mmol), EtOH (30 mL). Yield: 45 mg (88%). Slow evaporation of its dichloromethane−hexane (2:1) solution gave crystals of 2a. MS (ESI+, CH3CN): m/z {2a}+ calcd, 564.12; found, 564.11. 1H NMR (400

Figure 9. X-band EPR spectra of the intermediate blue species 100 K in CH3CN.

Scheme 6. Tentative Pathway for C−C/CN Bond Cleavage in 2 to Form a New C−N Bond in 3

MHz, CDCl3) [δ/ppm]: δ 6.45−7.39 (br, 10H, aromatic), δ 5.11 (s, 2H, acac), δ 2.23 (s, 6H, CH3 of L1), δ 1.92 (s, 6H, CH3 of acac), δ 1.71 (s, 6H, CH3 of acac). 13C NMR (101 MHz, CDCl3) [δ/ppm]: δ 188.15 (CO, L1), δ 186.08 (CN, L1), δ 176 (C−O, acac), δ 99− 152 (aromatic C), δ 21−30 (CH3). Some of the 13C signals were merged due to similar chemical shift values. Anal. Calcd. for

Scheme 5. Probable Pathway for Oxidation of 1 to 2

H

DOI: 10.1021/acs.inorgchem.7b02172 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

4.06; N, 4.94. IR (KBr, cm−1): 1672 [ν(CO)]. Molar conductivity (CH3CN): ΛM = 7 Ω−1 cm2 M−1. [RuII(acac)2(L6 H,H)], 4a. Complex 2a (50 mg, 0.089 mmol), EtOH (20 mL), glacial AcOH (42 μL, 0.89 mmol). Yield: 11.8 mg (23%). MS (ESI+, CH3CN): m/z {4a}+ calcd, 578.10; found, 578.09. 1H NMR (400 MHz, CDCl3) [δ/ppm]: δ 9.76 (s, 1H, CHO), δ 6.2−7.39 (br, 10H, aromatic), δ 5.31 (s, 1H, acac), δ 4.97 (s, 1H, acac), δ 2.51 (s, 3H, CH3 of L6), δ 1.88−1.94 (s, 12H, CH3 of acac). 13C NMR (126 MHz, CDCl3) [δ/ppm]: δ 190.26 (CHO, L6), δ 188.28 (CO, L6), δ 187.39 (CN, close to CHO function of L6), δ 185.95 (CN, far from CHO function of L6), δ 168−182 (C−O, acac), δ 98−155 (aromatic C), δ 20−30 (CH3). Some of the 13C signals were merged due to similar chemical shift values. Anal. Calcd for C27H28N2O6Ru: C, 56.05; H, 4.88; N, 4.84. Found: C, 56.33; H, 4.66; N, 4.99. IR (KBr, cm−1): 2712 [(weak, ν(CHO)], 1670 [ν(CO)]. Molar conductivity (CH3CN): ΛM = 6 Ω−1 cm2 M−1. [RuII(acac)2(L6 OMe,OMe)], 4b. Complex 2b (50 mg, 0.080 mmol), EtOH (20 mL), glacial AcOH (38 μL, 0.80 mmol). Yield: 10.8 mg (21%). Crystals of 4b were obtained from dichloromethane−hexane (2:1) solvent mixture. MS (ESI+, CH3CN): m/z {4b + H}+ calcd, 639.12; found, 639.16. 1H NMR (400 MHz, CDCl3) [δ/ppm]: δ 9.73 (s, 1H, CHO), δ 6.15−7.37 (br, 8H, aromatic), δ 5.33 (s, 1H, acac), δ 5.06 (s, 1H, acac), δ 3.83 (s, 6H, OCH3), δ 2.52 (s, 3H, CH3 of L6), δ 1.78−1.97 (s, 12H, CH3 of acac). 13C NMR (126 MHz, CDCl3) [δ/ ppm]: δ 190.09 (CHO, L6), δ 188.12 (CO, L6), δ 187.26 (CN, close to CHO function of L6), δ 185.15 (CN, far from CHO function of L6), δ 168−182 (C−O, acac), δ 98−155 (aromatic C), δ 55−56 (OCH3), δ 20−30 (CH3). Some of the 13C signals were merged due to similar chemical shift values. Anal. Calcd for C29H32N2O8Ru: C, 54.62, H, 5.06; N, 4.39. Found: C, 54.83; H, 4.97; N, 4.46. IR (KBr, cm−1): 2716 [(weak, ν(CHO)], 1662 [ν(C O)]. Molar conductivity (CH3CN): ΛM = 3 Ω−1 cm2 M−1. [RuII(acac)2(L6 Cl,Cl)], 4c. Complex 2c (50 mg, 0.079 mmol), EtOH (20 mL), glacial AcOH (39 μL, 0.79 mmol). Yield: 9.3 mg (18%). MS (ESI+, CH3CN): m/z {4c + H}+ calcd, 647.02; found, 647.03. 1H NMR (400 MHz, CDCl3) [δ/ppm]: δ 9.73 (s, 1H, CHO), δ 6.1−7.32 (br, 8H, aromatic), δ 5.33 (s, 1H, acac), δ 5.06 (s, 1H, acac), δ 2.52 (s, 3H, CH3 of L6), δ 1.78−1.97 (s, 12H, CH3 of acac). 13C NMR (126 MHz, CDCl3) [δ/ppm]: δ 190.33 (CHO, L6), δ 188.34 (CO, L6), δ 187.44 (CN, close to CHO function of L6), δ 185.95 (CN, far from CHO function of L6), δ 168−182 (C−O, acac), δ 98−152 (aromatic C), δ 20−30 (CH3). Some of the 13C signals were merged due to similar chemical shift values. Anal. Calcd for C27H26N2O6Cl2Ru: C, 50.15, H, 4.06; N, 4.34. Found: C, 50.23; H, 4.26; N, 4.58. IR (KBr, cm−1): 2722 [(weak, ν(CHO)], 1687 [ν(CO)]. Molar conductivity (CH3CN): ΛM = 4 Ω−1 cm2 M−1.

C27H30N2O5Ru: C, 57.54, H, 5.37; N, 4.97. Found: C, 57.81; H, 5.42; N, 5.14. IR (KBr, cm−1): 1664 [ν(CO)]. Molar conductivity (CH3CN): ΛM = 6 Ω−1 cm2 M−1. [RuII(acac)2(L1 OMe,OMe)], 2b. Complex 1b (50 mg, 0.082 mmol), EtOH (30 mL). Yield: 46 mg (89%). Slow evaporation of its dichloromethane−hexane (2:1) solution gave crystals of 2b. MS (ESI +, CH3CN): m/z {2b}+ calcd, 624.14; found, 624.11. 1H NMR (500 MHz, CDCl3) [δ/ppm]: δ 6.49−7.5 (br, 8H, aromatic), δ 5.13 (s, 2H, acac), δ 3.81 (s, 6H, OCH3), δ 2.22 (s, 6H, CH3 of L1), δ 1.94 (s, 6H, CH3 of acac), δ 1.71 (s, 6H, CH3 of acac). 13C NMR (126 MHz, CDCl3) [δ/ppm]: δ 187.9 (CO, L1), δ 185.83 (CN, L1), δ 176 (C−O, acac), δ 99−158 (aromatic C), δ 55.43 (OCH3), δ 21−30 (CH3). Some of the 13C signals were merged due to similar chemical shift values. Anal. Calcd. for C29H34N2O7Ru: C, 55.85, H, 5.49; N, 4.49. Found: C, 56.02; H, 5.42; N, 4.64. IR (KBr, cm−1): 1655 [ν(C O)]. Molar conductivity (CH3CN): ΛM = 4 Ω−1 cm2 M−1. [RuII(acac)2(L1 Cl,Cl)], 2c. Complex 1c (50 mg, 0.081 mmol), EtOH (30 mL). Yield: 41.5 mg (81%). MS (ESI+, CH3CN): m/z {2c}+ calcd, 632; found, 632.16. 1H NMR (500 MHz, CDCl3) [δ/ppm]: δ 6.39−7.50 (br, 8H, aromatic), δ 5.15 (s, 2H, acac), δ 2.22 (s, 6H, CH3 of L1), δ 1.94 (s, 6H, CH3 of acac), δ 1.72 (s, 6H, CH3 of acac). 13C NMR (126 MHz, CDCl3) [δ/ppm]: δ 188.13 (CO, L1), δ 186.09 (CN, L1), δ 176.65, 175.74 (C−O, acac), δ 99−150 (aromatic C), δ 21−30 (CH3). Some of the 13C signals were merged due to similar chemical shift values. Anal. Calcd. for C27H28N2O5Cl2Ru: C, 51.26, H, 4.46; N, 4.43. Found: C, 51.47; H, 4.34; N, 4.67. IR (KBr, cm−1): 1672 [ν(CO)]. Molar conductivity (CH3CN): ΛM = 1 Ω−1 cm2 M−1. Intermediate for 1c → 2c Conversion (C27H29N2O6Cl2Ru). The intermediate was trapped via chromatographic separation on a silica gel (mesh 100−200) column using dichloromethane as the eluent by careful monitoring the change in color 1c (green) → intermediate (blue) → 2c (purple) (Figure S13, Supporting Information). MS (ESI +, CH3CN): m/z {intermediate + Na}+ calcd, 672.50; found, 672.98. Raman (cm−1): 893. UV−vis [λ, nm]: 795, 598, 394, 278, 224. General Procedure for Preparation of [Ru(acac)2(L5)] (3) and [Ru(acac)2(L6)] (4). To the purple solution of Ru(acac)2(L1) in EtOH in an oven-dried clean round-bottom flask, glacial AcOH in EtOH was added dropwise under stirring in an ice-bath. After completion of addition, the reaction mixture was heated at 343 K and stirred under aerial atmosphere for 8 h. The solution gradually turned to brownishred. The crude mixture was concentrated under reduced pressure and purified on a neutral alumina column with 2:1 petroleum ether/ dichloromethane mixture as eluent, which afforded initially a brown solution corresponding to [Ru(acac)2(L5)] (3) followed by a brick-red solution of [Ru(acac)2(L6)] (4). Evaporation of solvent yielded the complexes in solid form. [RuIII(acac)2(L5 H,H)], 3a. Complex 2a (50 mg, 0.089 mmol), EtOH (20 mL), glacial AcOH (42 μL, 0.89 mmol). Yield: 32.4 mg (68%). Crystals of 3a were obtained from its dichloromethane−hexane (2:1) solvent mixture. MS (ESI+, CH3CN): m/z {3a + H}+ calcd, 538.10; found, 538.09. 1H NMR (400 MHz, CDCl3) [δ/ppm ]: 10.57 (s), 6.04 (s), 5.30 (s), 4.63 (s), 4.32 (s), 1.94 (s), 1.61 (s), 1.23 (s), 0.86 (s), −6.50 (s), −10.38 (s), −12.41 (s), −20.69 (s). Anal. Calcd for C25H27N2O5Ru: C, 55.86, H, 5.07; N, 5.21. Found: C, 55.73; H, 5.28; N, 5.42. IR (KBr, cm−1): 1629 [ν(CO)]. Molar conductivity (CH3CN): ΛM = 4 Ω−1 cm2 M−1. [RuIII(acac)2(L5 OMe,OMe)], 3b. Complex 2b (50 mg, 0.080 mmol), EtOH (20 mL), glacial AcOH (38 μL, 0.80 mmol). Yield: 31.4 mg (64%). MS (ESI+, CH3CN): m/z {3b + H}+ calcd, 598.12; found, 598.14. 1H NMR (400 MHz, CDCl3) [δ/ppm]: 10.68, 4.70, 4.10, 2.75, 1.78, 1.33, 1.24, −7.23, −10.95, −12.57, −20.23. Anal. Calcd for C27H31N2O7Ru: C, 58.86; H, 6.44; N, 4.31. Found: C, 58.53; H, 6.67; N, 4.56. IR (KBr, cm−1): 1605 [ν(CO)]. Molar conductivity (CH3CN): ΛM = 4 Ω−1 cm2 M−1. [RuIII(acac)2(L5 Cl,Cl)], 3c. Complex 2c (50 mg, 0.079 mmol), EtOH (20 mL), glacial AcOH (39 μL, 0.79 mmol). Yield: 29 mg (61%). MS (ESI+, CH3CN): m/z {3c + H}+ calcd, 606.02; found, 606.04. 1H NMR (400 MHz, CDCl3) [δ/ppm]: 10.67, 7.30, 7.10, 7.08, 6.62, 6.60, 5.30, 4.67, −7.36, −11.20, −12.79, −20.44. Anal. Calcd for C25H25N2O5Cl2Ru: C, 49.59; H, 4.16; N, 4.63. Found: C, 49.87; H,

■

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.7b02172. Bond lengths and angles (crystal and DFT), MO compositions, mass spectra, 1H and 13C NMR, ORTEP diagrams, DFT optimized structures, kinetic plots, electronic spectra, Raman spectrum, TD-DFT table (PDF) Accession Codes

CCDC 1501980, 1501981, 1501986, and 1502333−1502335 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing data_request@ccdc. cam.ac.uk, or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033. I

DOI: 10.1021/acs.inorgchem.7b02172 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

■

Diketiminato Complexes and Application in Catalysis. Organometallics 2013, 32, 7345−7356. (f) Yempally, V.; Fan, W. Y.; Arndtsen, B. A.; Bengali, A. A. Intramolecular C−C Bond Coupling of Nitriles to a Diimine Ligand in Group 7 Metal Tricarbonyl Complexes. Inorg. Chem. 2015, 54, 11441−11449. (g) Schreiber, D. F.; Ortin, Y.; MüllerBunz, H.; Phillips, A. D. Application of Electron-Withdrawing Coordinatively Unsaturated η6-Arene β-Diketiminato-Ruthenium Complexes in Lewis Acid Catalyzed Diels-Alder Reactions. Organometallics 2011, 30, 5381−5395. (h) Basuli, F.; Huffman, J. C.; Mindiola, D. J. Reactivity at the β-Diketiminate Ligand Nacnac− on Titanium(IV) (Nacnac− = [Ar]NC(CH3)CHC(CH3)N[Ar], Ar = 2,6[CH(CH3)2]2C6H3). Diimine-alkoxo and Bis-anilido Ligands Stemming from the Nacnac− Skeleton. Inorg. Chem. 2003, 42, 8003−8010 and references therein. (4) (a) 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. (b) Yokota, S.; Tachi, Y.; Itoh, S. Oxidative Degradation of β-Diketiminate Ligand in Copper(II) and Zinc(II) Complexes. Inorg. Chem. 2002, 41, 1342−1344. (c) Scheuermann, M. L.; Fekl, U.; Kaminsky, W.; Goldberg, K. I. Metal−Ligand Cooperativity in O2 Activation: Observation of a “Pt−O−O−C” Peroxo Intermediate. Organometallics 2010, 29, 4749−4751. (d) Scheuermann, M. L.; Luedtke, A. T.; Hanson, S. K.; Fekl, U.; Kaminsky, W.; Goldberg, K. I. Reactions of Five-Coordinate Platinum(IV) Complexes with Molecular Oxygen. Organometallics 2013, 32, 4752−4758. (e) Holze, P.; Corona, T.; Frank, N.; BraunCula, B.; Herwig, C.; Company, A.; Limberg, C. Activation of Dioxygen at a Lewis Acidic Nickel(II) Complex: Characterization of a Metastable Organoperoxide Complex. Angew. Chem., Int. Ed. 2017, 56, 2307−2311. (f) Zhang, J.; Zhang, Z.; Chen, Z.; Zhou, X. Oxidation and Coupling of β-Diketiminate Ligand in Lanthanide Complexes: Novel Eight-Nuclear Lanthanide Clusters with μ-, μ3-Cl, and μ4-O Bridge. Dalton Trans. 2012, 41, 357−359. (g) Hill, M. S.; Pongtavornpinyo, R.; Hitchcock, P. B. Aggregation Behaviour of Thallium(I) β-Diketiminates. Chem. Commun. 2006, 3720−3722. (5) (a) Fekl, U.; Kaminsky, W.; Goldberg, K. I. A Stable FiveCoordinate Platinum(IV) Alkyl Complex. J. Am. Chem. Soc. 2001, 123, 6423−6424. (b) Venugopal, A.; Ghosh, M. K.; Jürgens, H.; Törnroos, K. W.; Swang, O.; Tilset, M.; Heyn, R. H. (β-Diketiminato)dimethylgold(III): Synthesis, Structure, and Reactivity. Organometallics 2010, 29, 2248−2253. (c) Ferro, L.; Coles, M. P.; Day, I. J.; Fulton, J. R. Taking Advantage of Hg-C Bonds: Synthesis of the First Homoleptic Bis-β-diketiminate Complex Bound through the γCarbons. Organometallics 2010, 29, 2911−2915. (d) Hadzovic, A.; Song, D. Synthesis, Characterization, and Reactivity of a Versatile Dinuclear Palladium β-Diiminate Complex. Organometallics 2008, 27, 1290−1298. (6) (a) Woodul, W. D.; Carter, E.; Müller, R.; Richards, A. F.; Stasch, A.; Kaupp, M.; Murphy, D. M.; Driess, M.; Jones, C. A Neutral, Monomeric Germanium(I) Radical. J. Am. Chem. Soc. 2011, 133, 10074−10077. (b) Tomson, N. C.; Arnold, J.; Bergman, R. G. Halo, Alkyl, Aryl, and Bis(imido) Complexes of Niobium Supported by the β-Diketiminato Ligand. Organometallics 2010, 29, 2926−2942. (c) Lohrey, T. D.; Bergman, R. G.; Arnold, J. Oxygen Atom Transfer and Intramolecular Nitrene Transfer in a Rhenium β-Diketiminate Complex. Inorg. Chem. 2016, 55, 11993−12000. (d) Hitchcock, P. B.; Lappert, M. F.; Nycz, J. E. Synthesis, structure and reductive dechlorination of the C-centred phosphorus(III) β-diketiminate PCl(Ph)L [L= C{C(Me)NC6H3Pri2-2,6}{C(Me)NHC6H3Pri2-2,6}]. Chem. Commun. 2003, 1142−1143. (e) Ragogna, P. J.; Burford, N.; D’eon, M.; McDonald, R. Inhibited chelation in the new γ-phosphinoβ-diketiminate to give phosphine→arsine coordination. Chem. Commun. 2003, 1052−1053 and references therein. (f) Zhu, H.; Chai, J.; Chandrasekhar, V.; Roesky, H. W.; Magull, J.; Vidovic, D.; Schmidt, H.; Noltemeyer, M.; Power, P. P.; Merrill, W. A. Two Types of Intramolecular Addition of an Al-N Multiple-Bonded Monomer LAlNAr′ Arising from the Reaction of LAl with N3Ar′(L)HC[(CMe)-

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected] (G.K.L.). ORCID

Goutam Kumar Lahiri: 0000-0002-0199-6132 Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS Financial support was received from DST (SERB) and CSIR (fellowship to S.P., A.M. and P.G.), New Delhi. The help of Prof. R. J. Butcher, Department of Chemistry, Howard University, USA, in solving the structure of 4b and the valuable comments of Prof. I. N. N. Namboothiri and Prof. D. Maiti, Department of Chemistry, IIT Bombay, India, are also gratefully acknowledged.

■

REFERENCES

(1) (a) Camp, C.; Arnold, J. On the Non-Innocence of “Nacnacs”: Ligand-based Reactivity in β-Diketiminate Supported Coordination Compounds. Dalton Trans. 2016, 45, 14462−14498. (b) BourgetMerle, L.; Lappert, M. F.; Severn, J. R. The Chemistry of βDiketiminatometal Complexes. Chem. Rev. 2002, 102, 3031−3065. (c) Chen, C.; Bellows, S. M.; Holland, P. L. Tuning Steric and Electronic Effects in Transition-Metal β-diketiminate Complexes. Dalton Trans. 2015, 44, 16654−16670. (d) Stender, M.; Eichler, B. E.; Hardman, N. J.; Power, P. P.; et al. Synthesis and Characterization of HC{C(Me)N(C6H3-2,6-i-Pr2)}2MX2 (M = Al, X = Cl, I; M = Ga, In, X = Me, Cl, I): Sterically Encumbered β-Diketiminate Group 13 Metal Derivatives. Inorg. Chem. 2001, 40, 2794−2799. (e) Phillips, A. D.; Thommes, K.; Scopelliti, R.; Gandolfi, C.; Albrecht, M.; Severin, K.; Schreiber, D. F.; Dyson, P. J. Rational Design of Highly Cytotoxic η6-Arene β-Diketiminato−Ruthenium Complexes. Organometallics 2011, 30, 6119−6132. (2) (a) LeBlanc, F. A.; Berkefeld, A.; Piers, W. E.; Parvez, M. Accelerated Ligand Metalation in a β-Diketiminato Scandium Dimethyl Complex Activated with Bis(pentafluorophenyl)borane. Organometallics 2012, 31, 810−818. (b) Wright, R. J.; Power, P. P.; Scott, B. L.; Kiplinger, J. L. Uncommon η3-(N,C,C’)-1-Azaallyl Bonding Mode for the Nacnac Ligand: A Bis(β-diketiminato)uranium(III) Iodide Complex. Organometallics 2004, 23, 4801−4803. (c) Basuli, F.; Watson, L. A.; Huffman, J. C.; Mindiola, D. J. Phosphaazaallene and Phosphinylimide Complexes Stemming from a Terminal and Four-coordinate Titanium Phosphinidene. Dalton Trans. 2003, 4228−4230. (d) Carrera, N.; Savjani, N.; Simpson, J.; Hughes, D. L.; Bochmann, M. Syntheses and Structures of Thermally Stable Diketiminato Complexes of Gold and Copper. Dalton Trans. 2011, 40, 1016−1019. (e) Dias, H. V. R.; Flores, J. A. The First β-Diketiminate− Ag(I) Complexes. Macrocyclic Dinuclear and Tetranuclear Ag(I)Complexes and Linear Coordination Polymer Ag(I)-Complex. Inorg. Chem. 2007, 46, 5841−5843. (3) (a) Radzewich, C. E.; Coles, M. P.; Jordan, R. F. Reversible Ethylene Cycloaddition Reactions of Cationic Aluminum β-Diketiminate Complexes. J. Am. Chem. Soc. 1998, 120, 9384−9385. (b) Phillips, A. D.; Laurenczy, G.; Scopelliti, R.; Dyson, P. J. Facile, Thermoreversible Cycloaddition of Small Molecules to a Ruthenium(II) Arene β-Diketiminate. Organometallics 2007, 26, 1120−1122. (c) Gregory, E. A.; Lachicotte, R. J.; Holland, P. L. A Cationic ThreeCoordinate Iron(II) Complex and the Reaction of β-Diketiminate with Ethyl Diazoacetate. Organometallics 2005, 24, 1803−1805. (d) West, N. M.; White, P. S.; Templeton, J. L.; Nixon, J. F. Cycloaddition Reactions of Terminal Alkynes and Phosphaalkynes with an Isolable 5Coordinate β-Diiminate Platinum(IV) Dihydrosilyl Complex. Organometallics 2009, 28, 1425−1434. (e) Schreiber, D. F.; O’Connor, C.; Grave, C.; Müller-Bunz, H.; Scopelliti, R.; Dyson, P. J.; Phillips, A. D. Synthesis, Characterization, and Reactivity of the First Osmium βJ

DOI: 10.1021/acs.inorgchem.7b02172 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry (NAr)]2, Ar′) 2,6-Ar2C6H3, Ar) 2,6-iPr2C6H3). J. Am. Chem. Soc. 2004, 126, 9472−9473. (7) (a) Khusniyarov, M. M.; Bill, E.; Weyhermüller, T.; Bothe, E.; Wieghardt, K. Hidden Noninnocence: Theoretical and Experimental Evidence for Redox Activity of a β-Diketiminate (1−) Ligand. Angew. Chem., Int. Ed. 2011, 50, 1652−1655. (b) Takaichi, J.; Morimoto, Y.; Ohkubo, K.; Shimokawa, C.; Hojo, T.; Mori, S.; Asahara, H.; Sugimoto, H.; Fujieda, N.; Nishiwaki, N.; Fukuzumi, S.; Itoh, S. Redox Chemistry of Nickel(II) Complexes Supported by a Series of Noninnocent β-Diketiminate Ligands. Inorg. Chem. 2014, 53, 6159− 6169 and references therein. (8) (a) Azoulay, J. D.; Rojas, R. S.; Serrano, A. V.; Ohtaki, H.; Galland, G. B.; Wu, G.; Bazan, G. C. Nickel α-Keto-β-Diimine Initiators for Olefin Polymerization. Angew. Chem., Int. Ed. 2009, 48, 1089−1092. (b) Azoulay, J. D.; Koretz, Z. A.; Wu, G.; Bazan, G. C. Well-Defined Cationic Methallyl α-Keto-β-Diimine Complexes of Nickel. Angew. Chem., Int. Ed. 2010, 49, 7890−7894. (9) (a) Chiba, S.; Zhang, L.; Ang, G. Y.; Hui, B. W. Generation of Iminyl Copper Species from α-Azido Carbonyl Compounds and their Catalytic C−C Bond Cleavage under an Oxygen Atmosphere. Org. Lett. 2010, 12, 2052−2055. (b) Zhang, C.; Feng, P.; Jiao, N. CuCatalyzed Esterification Reaction via Aerobic Oxygenation and C−C Bond Cleavage: An Approach to α-Ketoesters. J. Am. Chem. Soc. 2013, 135, 15257−15262. (c) He, C.; Guo, S.; Huang, L.; Lei, A. Copper Catalyzed Arylation/C−C Bond Activation: An Approach toward αAryl Ketones. J. Am. Chem. Soc. 2010, 132, 8273−8275. (d) Sun, M.; Shen, G.; Bao, W. Regioselective Cleavage of Unstrained C−C Bond and C−H Bond: Palladium−Copper Catalyzed Deacetophenonylative Arylation of Coumarin Derivatives. Adv. Synth. Catal. 2012, 354, 3468−3474. (e) Chan, Y. W.; Chan, K. S. Metalloradical-Catalyzed Aliphatic Carbon−Carbon Activation of Cyclooctane. J. Am. Chem. Soc. 2010, 132, 6920−6922. (f) Huang, X.; Li, X.; Zou, M.; Song, S.; Tang, C.; Yuan, Y.; Jiao, N. From Ketones to Esters by a Cu-Catalyzed Highly Selective C(CO)−C(alkyl) Bond Cleavage: Aerobic Oxidation and Oxygenation with Air. J. Am. Chem. Soc. 2014, 136, 14858−14865. (g) Zhang, M.; Ji, P.; Liu, Y.; Guo, C. Transition-Metal-Free Synthesis of Carbonyl-Containing Oxindoles from N-Arylacrylamides and αDiketones via TBHP- or Oxone-Mediated Oxidative Cleavage of C(sp2)−C(sp2) Bonds. J. Org. Chem. 2015, 80, 10777−10786. (h) Ruhland, K. Transition-Metal-Mediated Cleavage and Activation of C−C Single Bonds. Eur. J. Org. Chem. 2012, 2012, 2683−2706. (10) (a) Khusnutdinova, J. R.; Milstein, D. Metal−Ligand Cooperation. Angew. Chem., Int. Ed. 2015, 54, 12236−12273. (b) Hindson, K.; de Bruin, B. Cooperative & Redox Non-Innocent Ligands in Directing Organometallic Reactivity. Eur. J. Inorg. Chem. 2012, 2012, 340−342. (11) Meyer, F.; Tolman, W. B. Forums on Small-Molecule Activation: from Biological Principles to Energy Applications. Inorg. Chem. 2015, 54, 5039. (b) Yao, S.; Driess, M. Lessons from Isolable Nickel(I) Precursor Complexes for Small Molecule Activation. Acc. Chem. Res. 2012, 45, 276−287 and references therein. (12) (a) Mandal, A.; Kundu, T.; Ehret, F.; Bubrin, M.; Mobin, S. M.; Kaim, W.; Lahiri, G. K. Varying Electronic Structural Forms of Ruthenium Complexes of Non-Innocent 9,10- Phenanthrenequinonoid Ligands. Dalton Trans. 2014, 43, 2473−2487. (b) Mondal, P.; Das, A.; Lahiri, G. K. The Electron-Rich {Ru(acac)2} Directed Varying Configuration of the Deprotonated Indigo and Evidence for Its Bidirectional Noninnocence. Inorg. Chem. 2016, 55, 1208−1218. (c) Mondal, P.; Ray, R.; Das, A.; Lahiri, G. K. Revelation of Varying Bonding Motif of Alloxazine, a Flavin Analogue, in Selected Ruthenium(II/III) Frameworks. Inorg. Chem. 2015, 54, 3012−3021. (d) Das, D.; Das, A. K.; Sarkar, B.; Mondal, T. K.; Mobin, S. M.; Zališ, S.; Urbanos, F. A.; Kaim, W.; Lahiri, G. K.; Fiedler, J.; JiménezAparicio, R. The Semiquinone-Ruthenium Combination as a Remarkably Invariant Feature in the Redox and Substitution Series [Ru(Q)n(acac)3−n]m, n = 1−3; m=(−2), − 1, 0, + 1, (+2); Q = 4,6-Ditert-butyl-N-phenyl-o-iminobenzoquinone. Inorg. Chem. 2009, 48, 11853−11864.

(13) (a) Chakraborty, S.; Laye, R. H.; Paul, R. L.; Gonnade, R. G.; Puranik, V. G.; Ward, M. D.; Lahiri, G. K. A. Dinuclear Bis(bipyridine)ruthenium(II) Complex, [(bpy) 2 Ru I I {L 2 − }RuII(bpy)2]2+, Incorporating an Unusual Non-innocent Bridging Ligand Containing a p-benzoquinonediimine Fragment: Synthesis, Structure, Redox, and UV/VIS/NIR and EPR Spectroelectrochemical Properties. J. Chem. Soc., Dalton Trans. 2002, 1172−1179. (b) Patra, S.; Sarkar, B.; Mobin, S. M.; Kaim, W.; Lahiri, G. K. Separating Innocence and Non-Innocence of Ligands and Metals in Complexes [(L)Ru(acac)2]n (n = − 1, 0, + 1; L = o-Iminoquinone or oIminothioquinone). Inorg. Chem. 2003, 42, 6469−6473. (c) Ghosh, P.; Banerjee, S.; Lahiri, G. K. Ruthenium Derivatives of in Situ Generated Redox-Active 1,2-Dinitrosobenzene and 2-Nitrosoanilido. Diverse Structural and Electronic Forms. Inorg. Chem. 2016, 55, 12832−12843. (14) (a) Mandal, A.; Schwederski, B.; Fiedler, J.; Kaim, W.; Lahiri, G. K. Evidence for Bidirectional Noninnocent Behavior of a Formazanate Ligand in Ruthenium Complexes. Inorg. Chem. 2015, 54, 8126−8135. (b) Das, A.; Scherer, T. M.; Mondal, P.; Mobin, S. M.; Kaim, W.; Lahiri, G. K. Experimental and DFT Evidence for the Fractional NonInnocence of a β-Diketonate Ligand. Chem. - Eur. J. 2012, 18, 14434− 14443. (c) Das, A.; Mobin, S. M.; Lahiri, G. K. Recognition of Fractional Non-innocent Feature of Osmium Coordinated 2,2′Biimidazole or 2,2’-Bis(4,5-Dimethylimidazole) and their Interactions with Anions. Dalton Trans. 2015, 44, 13204−13219. (15) (a) Mikheikin, I. D.; Vorontsova, I. K.; Abronin, I. A. Reactivity of Molecular Oxygen on the Surface of Ionic Crystals. Int. J. Quantum Chem. 2002, 88, 489−495. (b) Moro-oka, Y. Reactivities of Active Oxygen Species and Their Roles in the Catalytic Oxidation of Inactive Hydrocarbon. Catal. Today 1998, 45, 3−12. (16) (a) Chen, P.; Solomon, E. I. O2 Activation by Binuclear Cu Sites: Noncoupled Versus Exchange Coupled Reaction Mechanisms. Proc. Natl. Acad. Sci. U. S. A. 2004, 101, 13105−13110. (b) Ginsbach, J. W.; Peterson, R. L.; Cowley, R. E.; Karlin, K. D.; Solomon, E. I. Correlation of the Electronic and Geometric Structures in Mononuclear Copper(II) Superoxide Complexes. Inorg. Chem. 2013, 52, 12872−12874. (c) Solomon, E. I.; Ginsbach, J. W.; Heppner, D. E.; Kieber-Emmons, M. T.; Kjaergaard, C. H.; Smeets, P. J.; Tian, L.; Woertink, J. S. Faraday Discuss. 2011, 148, 11−39. (d) Bonnot, F.; Tremey, E.; von Stetten, D.; Rat, S.; Duval, S.; Carpentier, P.; Clemancey, M.; Desbois, A.; Niviere, V. Formation of High-Valent Iron−Oxo Species in Superoxide Reductase: Characterization by Resonance Raman Spectroscopy. Angew. Chem., Int. Ed. 2014, 53, 5926−5930. (e) Lehnert, N.; Neese, F.; Ho, R. Y. N.; Que, L., Jr.; Solomon, E. I. Electronic Structure and reactivity of Low-Spin Fe(III)Hydroperoxo Complexes: Comparison to Activated Bleomycin. J. Am. Chem. Soc. 2002, 124, 10810−10822. (f) Shin, B.; Sutherlin, K. D.; Ohta, T.; Ogura, T.; Solomon, E. I.; Cho, J. Reactivity of a Cobalt(III)−Hydroperoxo Complex in Electrophilic Reactions. Inorg. Chem. 2016, 55, 12391−12399. (g) Kozlowski, P. M.; Nazarenko, V. V.; Jarzecki, A. A. DFT Analysis of Interligand Vibrations in a Hydroperoxo Complex of Cobalt Bleomycin. Inorg. Chem. 2006, 45, 1424−1426. (h) Tejel, C.; Ciriano, M. A.; Jimenez, S.; Passarelli, V.; Lopez, J. A. Stabilization of the Hydroperoxido Ligand: A 1κO, 2κO’ Dimetallic Coordination Mode. Angew. Chem., Int. Ed. 2008, 47, 2093−2096. (17) (a) Liu, H.; Dong, C.; Zhang, Z.; Wu, P.; Jiang, X. TransitionMetal-Free Aerobic Oxidative Cleavage of C−C Bonds in α-Hydroxy Ketones and Mechanistic Insight to the Reaction Pathway. Angew. Chem., Int. Ed. 2012, 51, 12570−12574. (b) Liang, D.; He, Y.; Liu, L.; Zhu, Q. A Metal-Free Tandem Demethylenation/C(sp2)−H Cycloamination Process of N-Benzyl-2-aminopyridines via C−C and C−N Bond Cleavage. Org. Lett. 2013, 15, 3476−3479. (18) Huang, L.; Cheng, K.; Yao, B.; Xie, Y.; Zhang, Y. Iron-Promoted C−C Bond Cleavage of 1,3-Diketones: A Route to 1,2-Diketones under Mild Reaction Conditions. J. Org. Chem. 2011, 76, 5732−5737. (19) (a) Mitroka, S.; Zimmeck, S.; Troya, D.; Tanko, J. M. How Solvent Modulates Hydroxyl Radical Reactivity in Hydrogen Atom Abstractions. J. Am. Chem. Soc. 2010, 132, 2907−2913. (b) Page, S. E.; Sander, M.; Arnold, W. A.; McNeill, K. Hydroxyl Radical Formation K

DOI: 10.1021/acs.inorgchem.7b02172 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

Local Density Approximation Ionization Threshold. J. Chem. Phys. 1998, 108, 4439−4450. (31) (a) Barone, V.; Cossi, M. Quantum Calculation of Molecular Energies and Energy Gradients in Solution by a Conductor Solvent Model. J. Phys. Chem. A 1998, 102, 1995−2001. (b) Cossi, M.; Barone, V. Time-dependent Density Functional Theory for Molecules in Liquid Solutions. J. Chem. Phys. 2001, 115, 4708−4718. (c) Cossi, M.; Rega, N.; Scalmani, G.; Barone, V. Energies, Structures, and Electronic Properties of Molecules in Solution with the C-PCM Solvation Model. J. Comput. Chem. 2003, 24, 669−681. (32) Gorelsky, S. I. SWizard program, http://www.sg-chem.net/, University of Ottawa, Ottawa, Canada, 2013. (33) Gorelsky, S. I.; Lever, A. B. P. Electronic Structure and Spectra of Ruthenium Diimine Complexes by Density Functional Theory and INDO/S. Comparison of the Two Methods. J. Organomet. Chem. 2001, 635, 187−196.

upon Oxidation of Reduced Humic Acids by Oxygen in the Dark. Environ. Sci. Technol. 2012, 46, 1590−1597. (c) Zhou, P.; Zhang, J.; Zhang, Y.; Liu, Y.; Liang, J.; Liu, B.; Zhang, W. Generation of Hydrogen Peroxide and Hydroxyl Radical Resulting from OxygenDependent Oxidation of L-Ascorbic acid via Copper Redox-Catalyzed Reactions. RSC Adv. 2016, 6, 38541−38547. (d) Dick, A. R.; Sanford, M. S. Transition Metal Catalyzed Oxidative Functionalization of Carbon-Hydrogen Bonds. Tetrahedron 2006, 62, 2439−2463. (20) Kojima, T.; Nakayama, K.; Ikemura, K.; Ogura, T.; Fukuzumi, S. Formation of a Ruthenium(IV)-Oxo Complex by Electron-Transfer Oxidation of a Coordinatively Saturated Ruthenium(II) Complex and Detection of Oxygen-Rebound Intermediates in C−H Bond Oxygenation. J. Am. Chem. Soc. 2011, 133, 11692−11700. (21) Kobayashi, T.; Nishina, Y.; Shimizu, K. G.; Satô, G. P. Diacetonitrilebis(β-diketonato)Ruthenium(II) Complexes. Their Preparation and Use as Intermediates for the Synthesis of MixedLigand β-Diketonato Ruthenium(III) Complexes. Chem. Lett. 1988, 17, 1137−1140. (22) Gong, S.; Ma, H. β-Diketiminate Aluminium Complexes: Synthesis, Characterization and Ring-Opening Polymerization of Cyclic Esters. Dalton Trans. 2008, 3345−3357. (23) Armarego, W. L. F.; Perrin, D. D. Purification of Laboratory Chemicals, 4th ed.; Butterworth Heinemann: Oxford, Boston, 1996. (24) (a) Sheldrick, G. M. A short history of SHELX. Acta Crystallogr. Acta Crystallogr., Sect. A: Found. Crystallogr. 2008, 64, 112−122. (b) Program for Crystal Structure Solution and Refinement; University of Goettingen: Germany, 1997. (c) Sheldrick, G. M. Crystal structure refinement with SHELXL. Acta Crystallogr. Acta Crystallogr., Sect. C: Struct. Chem. 2015, 71, 3−8. (25) Lee, C.; Yang, W.; Parr, R. G. Development of the Colle-Salvetti Correlation-Energy Formula into a Functional of the Electron Density. Phys. Rev. B: Condens. Matter Mater. Phys. 1988, 37, 785−789. (26) (a) Andrae, D.; Haeussermann, U.; Dolg, M.; Stoll, H.; Preuss, H. Energy-adjusted ab initio Pseudo Potentials for the Second and Third row Transition Elements. Theor. Chim. Acta 1990, 77, 123. (b) Fuentealba, P.; Preuss, H.; Stoll, H.; von Szentpaly, L. A. Proper Account of Core-Polarization with Pseudopotentials: Single ValenceElectron Alkali Compounds. Chem. Phys. Lett. 1982, 89, 418−422. (27) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H. P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, J. A., Jr.; Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin, K. N.; Staroverov, V. N.; Kobayashi, R.; Normand, J.; Raghavachari, K.; Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega, N.; Millam, J. M.; Klene, M.; Knox, J. E.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Martin, R. L.; Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas, O.; Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J. Gaussian 09, revision A.02; Gaussian, Inc.: Wallingford, CT, 2009. (28) Leonid, S. Chemissian, version 1.7; 2005−2010. Available at http://www.chemissian.com. (29) Zhurko, D. A.; Zhurko, G. A. ChemCraft 1.5 2004; Plimus: San Diego, CA. Available at http://www.chemcraftprog.com. (30) (a) Bauernschmitt, R.; Ahlrichs, R. Treatment of Electronic Excitations within the Adiabatic Approximation of Time Dependent Density Functional Theory. Chem. Phys. Lett. 1996, 256, 454−464. (b) Stratmann, R. E.; Scuseria, G. E.; Frisch, M. J. An Efficient Implementation of Time-Dependent Density-Functional Theory for the Calculation of Excitation Energies of Large Molecules. J. Chem. Phys. 1998, 109, 8218−8225. (c) Casida, M. E.; Jamorski, C.; Casida, K. C.; Salahub, D. R. Molecular Excitation Energies to High-Lying Bound States from Time-Dependent Density Functional Response Theory: Characterization and Correction of the Time-Dependent

■

NOTE ADDED AFTER ASAP PUBLICATION This paper was published on the Web on November 30, 2017, with minor errors in Scheme 1. The corrected version was reposted on December 1, 2017.

L

DOI: 10.1021/acs.inorgchem.7b02172 Inorg. Chem. XXXX, XXX, XXX−XXX