A Synthetic Approach to Cross-Conjugated Organometallic

Oct 12, 2016 - Combined structural and electrochemical studies suggest that the gem-DEE ligand, as a σ-donor, is weaker than phenylethynyl but strong...
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A Synthetic Approach to Cross-Conjugated Organometallic Complexes Based on geminal-Diethynylethene and CoIII(cyclam) Sean N. Natoli, Tyler J. Azbell, Phillip E. Fanwick, Matthias Zeller, and Tong Ren* Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, United States S Supporting Information *

ABSTRACT: A series of CoIII(cyclam) complexes ([1a,b]Cl, [2a−c]PF6, [3]Cl2, [4a](OTf)4, [4b](PF6)2, and [5]Cl2) (cyclam = 1,4,8,11tetraazacycloctetradecane) bearing a geminal-diethynylethene ligand (gemDEE) is reported. Syntheses of these acyclic cross-conjugated complexes were accomplished in satisfactory yields, and structural characterizations established that the geometrical feature of gem-DEE is largely preserved upon metalation. Combined structural and electrochemical studies suggest that the gem-DEE ligand, as a σ-donor, is weaker than phenylethynyl but stronger than butadiynyl in CoIII(cyclam) complexes. Voltammetric analysis indicated a weak but discernible Co−Co coupling across the gem-DEE bridge in [3]Cl2 and [4a](OTf)4, while the addition of a second acetylide in the trans position diminished such coupling in [4b](PF6)2. DFT analysis revealed significant dπ−π mixing around the cobalt centers with extended π-overlap in the highest occupied orbitals and substantial σ-based mixing in the lowest unoccupied orbitals of [3]Cl2 and [4a](OTf)4, the latter of which likely contributes to the weak Co−Co coupling.

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INTRODUCTION

Chart 1. Acyclic Cross-Conjugated System Representative of gem-DEE

Carbon-rich organometallic compounds have fascinated synthetic and materials chemists for decades because of their structural rigidity and extended π-conjugation, which has led to unique electronic and optoelectronic properties.1 The field has been dominated by mono- and oligo-nuclear metal alkynyl compounds, for which syntheses, structures, and bonding have been carefully examined over the past 60 years.2 In particular, many dinuclear compounds with either an oligoyn-diyl or an oligoen-diyl bridge have been developed as prototypic molecular wires,3 for which the degree of charge delocalization was assessed based on voltammetry and metal-centered mixed valency.4 Though less common, the molecular conductance properties of metal alkynyl compounds have been measured in nanojunctions,5 and robust flash memory devices with metal alkynyls serving as the active species have been recently realized.6 Many of the aforementioned studies have been based on linearly conjugated alkynyl ligands, whereas the studies of transition metal compounds with cross-conjugated alkynyl ligands remain scarce. Cross-conjugation is defined as the conjugation between two unsaturated π-segments that, although not conjugated to each other, are conjugated to an intervening unsaturated segment.7 The synthesis of geminaldiethynylethene (gem-DEE, Chart 1) was pioneered by BöhmGössl et al.,8 Alberts et al.,9 and Gleiter et al.10 and further refined and elaborated by the laboratories of Diederich11 and Tykwinski.12−14 Efforts by the latter enable facile preparation of gem-DEE and its use as the building block for intricate carbon© XXXX American Chemical Society

rich scaffoldings, while also providing a rich source of ligands for metal-alkynyl chemistry. The first examples of gem-DEE-containing metal compounds were reported by Tykwinski and co-workers, where a Pt(PPh3)2 fragment was coordinated by two σ-gem-DEE in transpositions.15 The Pt(II) compound was subsequently converted to a cis-compound when both triphenylphosphines were replaced with a bidentate chelating phosphine.16 Our laboratory reported ferrocenyl capped 3-(dibromomethylidene)penta-1,4diyne and probed the Fc−Fc interaction therein using voltammetry.17 Subsequently, our laboratory explored the role of gem-DEE as a monodentate ligand for both Ru2(DMBA)4 (DMBA = N,N′-dimethylbenzamidinate)18 and CrIII and FeIII complexes of cyclam (cyclam = 1,4,8,11-tetraazacyclotetradecane).19,20 Bruce and co-workers reported a unique approach in assembling bimetallic compounds of a gem-DEE type bridge: Stepwise reaction of oxalyl dichloride with 2 equiv of Cp*Ru(dppe)C2H resulted in a diruthenium compound bridged by penta-1,4-diyn-3-one. 2 1 More recently, Received: August 15, 2016

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DOI: 10.1021/acs.organomet.6b00657 Organometallics XXXX, XXX, XXX−XXX

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Organometallics Scheme 1. Syntheses of Compounds [2a−c]PF6, [3]Cl2, [4a](OTf)4, [4b]PF6, and [5]Cl2a

a Conditions: (i) X = CN, R = H, excess NaCN, H2O, reflux 12 h; X = C2Ph, R = TIPS, 0.9 equiv Li−C2Ph, THF, 12 h; X = gem-DEE-TIPS, R = TIPS, 0.9 equiv of Li-gem-DEE-TIPS, THF, 12 h; (ii) CuCl/TMEDA (cat.), O2, MeOH, 6 h; (iii) 1.9 equiv [Co(cyclam)Cl2]Cl, Et3N, MeOH, reflux 24 h; (iv) X = MeCN, 4 equiv AgOTf, MeCN, reflux 48 h; X = C2TMS, 3 equiv Li−C2TMS, THF, 12 h.

TMS-gem-DEE-TIPS13 in the presence of Et3N with an isolated yield of 79%. Both complexes [1a,b]Cl are diamagnetic, which is typical of a CoIII center with strong-field ligands. C-Dentate ligand substitution at the cobalt−chloro bond in [1a,b]Cl led to the formation of a new cobalt−carbon bond in complexes [2a−c]PF6 (Scheme 1). Complex [2a]PF6 was readily obtained in an isolated yield of 68% via a salt metathesis reaction between [1a]Cl and excess NaCN in a refluxing aqueous solution.28 (Caution! NaCN is highly toxic.) Surprisingly, the reaction of [1a]Cl with 1.2 equiv of Li−C2Ph resulted in a relatively low yield ( [3]Cl2 > [5]Cl2 ≫ [4b](PF6)2. Having similar Co−Co distances, ΔE for the single gem-DEE-bridged systems [3]Cl2, [4a](OTf)4, and [4b](PF6)2 appears to be more dependent on the identity of the ligand trans to the bridge. This trans-effect is clearly highlighted upon careful comparison of the ΔE values between complex [4a](OTf)4, with axial bound solvents, to complex [4b](PF6)2, with strong σ-donor in the axial position. It is welldocumented that electrostatic contributions can also affect electrochemically measured couples.37 However, in the case between [3]Cl2 and [4b](PF6)2 with similar Co−Co distances and like charge, it appears that the change in coupling values are more dependent on through-bond interactions. Likewise, the doubling of charge in [4a](OTf)4 does not have an equal effect on its measured coupling value. It is clear upon evaluation of complex [5]Cl2 that there is a reduction in interaction as the bridge elongates consistent with the conventional wisdom of exponential decay of electronic coupling over distance.38 DFT Calculations. Previously, Luthi and co-workers explored the electronic delocalization in gem-DEE and related organic molecules using both density functional theory (DFT) and ab initio methods.39 Our laboratory also investigated metal−metal interactions across a gem-DEE bridge based on DFT calculations of hypothetical [M]-gem-DEE-[M] with [M] representing 3d metal complexes of dppe.40 In order to rationalize electrochemical behaviors of the cobalt species reported herein based on orbital interactions, spin-restricted density functional calculations were performed on the geometrically optimized model cations [1a′]+, [3′]2+, [4a′]4+, [4b′]2+, and [5′]2+ at the B3LYP/LanL2DZ level using the Gaussian 03 suite.41 Bond lengths and angles are in agreement with single crystal analysis, with only slight elongation in the Co−C bonds (ca. 0.05 Å) but still within expected distances for

Figure 7. CVs of [3]Cl2 (top), [4a](OTf)4 (middle top), [4b](PF6)2 (middle bottom), and [5]Cl2 (bottom) in 0.1 M MeCN solution of Bu4NBF4 at a scan rate of 0.10 V/s.

Table 4. Redox Potentials (V, vs Fc/Fc+) for [3]Cl2, [4a](OTf)4, [4b](PF6)2, and [5]Cl2

a

complex

Epc(A′)

ΔE(A′) (mV)a

Epc(B′)

[3]Cl2 [4a](OTf)4 [4b](PF6)2 [5]Cl2

−1.58 −1.38 −2.04 −1.58

77 86 33 58

−1.95 −1.94 −2.30 −1.87

DPV analysis based on Richardson−Taube method35 F

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Organometallics

Figure 8. Molecular orbital diagrams of HOMOs and LUMOs of compounds [3′]2+, [4a′]4+, and [4b′]2+ obtained from DFT calculation.

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the covalent radius of a cobalt and carbon atoms. While a complete description of the obtained DFT results and structural optimizations is provided in the Supporting Information, a concise description of the electrochemically relevant HOMO and LUMO orbitals of [3′]2+, [4a′]4+, and [4b′]2+ is presented here. As shown in Figure 8, the HOMOs are the antibonding combination of the Co dxz and the π⊥(DEE) (perpendicular, out-of-plane (CC)) orbitals and vinyl π(CC)). This filled−filled type antibonding interaction with π(CC) is characteristic of metal alkynyl complexes.42 The rich π−dπ mixing observed in the HOMOs suggests that via oxidation occupied orbitals are promising conduits for electronic coupling between cobalt centers.40 Indeed, a Robin−Day class II mixed valency was identified recently upon the oxidation of −NMe2 moiety in trans-[Co(cyclam)(C2C6H4NMe2)2]+, where it was surmised that occupied orbitals served as the super exchange pathway.43 However, since reductions are commonly observed herein, the LUMO orbitals are more relevant than the occupied orbitals.27,40 Significant differences in orbital mixing across the LUMOs are apparent in Figure 8: The contours of [3′]2+ and [4a′]4+ are dominated by the Co dz2 interacting strongly with σ*(CC) orbitals of the gem-DEE bridge, while such mixing is absent in the LUMO of bis-alkynyl complex [4b′]2+. This σbased mixing in [3′]2+ and [4a′]4+, although weaker than πbased mixing, does provide a route for Co−Co interaction, agreeing with the aforementioned electrochemical results. Comparison of the LUMO contours in [3′]2+ and [4a′]4+ reveal more orbital density on the trans ligands in [3′]2+ than that in [4a′]4+, leaving [4a′]4+ with more contribution across the bridge, which likely has led to the slight increase in ΔE. Clearly, complexes [4a](OTf)4 and [4b](PF6)2 represent extremes for Co−Co coupling, reaffirming the significance of the trans-effect and choice of axial ligands within Co(cyclam) species.

EXPERIMENTAL SECTION

General Procedures. Phenylacetylene and (trimethylsilyl)acetylene were purchased from GFS Chemicals. Sodium cyanide and silver triflate were purchased from Alfa Aesar. n-BuLi was purchased from Sigma-Aldrich. All reagents were used as received. Starting materials [Co(cyclam)Cl2]Cl,44 TMS-gem-DEE-TMS,12 and TIPSgem-DEE-TMS13 were prepared according to literature procedures. Tetrahydrofuran was freshly distilled over sodium/benzophenone. UV−vis spectra were obtained with a Jasco V-670 spectrophotometer. FT-IR spectra were measured on a Jasco FT/IR-6300 as neat samples. 1 H NMR spectra were obtained using a Varian Mercury 300 NMR, with chemical shifts (δ) referenced to the residual solvent signal (CH3OH, CHCl3, or CH3CN). Splitting of the N−H peaks in the 1H NMR spectra is due to the trans-III arrangement of the cyclam ring, which cannot be isomerized upon metalation.25−29 13C NMR analysis was unsuccessful, due to limited solubility of the reported complexes. Electrospray ionization mass spectrometry (ESI-MS) spectra were recorded on a Waters 600 LC/MS. Elemental analysis (EA) was performed by Atlantic Microlab, Norcross, GA. Solvates typical of Co III (cyclam) complexes were observed for all of the EA reported.25−29 Voltammograms were recorded on a CHI620A voltammetric analyzer with a glassy carbon working electrode (diameter = 2 mm), a Pt-wire auxiliary electrode, and a Ag/AgNO3 reference electrode filled with 10 mM AgNO3 and 0.1 M Bu4NBF4 in dry MeCN. The concentration of analyte is always 1.0 mM in 4 mL of dry MeCN (thoroughly degassed by Ar purging). Potentials were corrected using an internal ferrocene standard at the end of runs. Preparation of [Co(cyclam)(gem-DEE-H)Cl]Cl ([1a]Cl). In a round bottom flask, 100 mg (0.27 mmol) of [Co(cyclam)Cl2]Cl was dissolved in 50 mL of MeOH. To the solution was added 1.0 mL (7.2 mmol) of Et3N and 0.1 mL (0.37 mmol) of gem-DEE-TMS. The solution was refluxed for 24 h, and a gradual shift in solution color from green to red was observed. Solvent was removed, and purification was performed on a silica gel pad by rinsing with EtOAc and then eluting [1a]Cl with a EtOAc/MeOH (5:1) mixture. Compound [1a] Cl was then recrystallized by the addition of Et2O to a concentrated solution in MeOH yielding an orange crystalline material. Yield: 110 mg (0.25 mmol) (93% based on Co). Data for [1a]Cl: ESI-MS (MeOH) 397-[Co(cyclam)(gem-DEE-H)Cl]+. Elem. Anal. Found (Calcd) for C19H39N4O3CoCl2 ([1a]Cl·2 H2O·CH3OH) C, 46.24 (45.52); H, 7.90 (7.84); N, 11.33 (11.17). IR(cm−1) −CC−H 2108 (s), (Co−CC−) 2065 (s). 1H NMR (CD3OD, δ) 4.984 (br s, 2H, N−H), 4.831 (br s, 2H, N−H), 3.381 (s, 1H, CCH), 2.841−2.359 (m, 16H, CH2), 2.057 (s, 3H, CH3), 1.933 (s, 3H, CH3), 1.827 (t, 2H, CH2, J = 14.4 Hz), 1.492 (q, 2H, CH2). Absorption spectrum (MeOH) λmax nm (εmax, L mol−1 cm−1) 492 (110), 323 (810). Preparation of [Co(cyclam)(gem-DEE-TIPS)Cl]Cl ([1b]Cl). In a round bottom flask, 100 mg (0.27 mmol) of [Co(cyclam)Cl2]Cl was dissolved in 50 mL of MeOH. To the solution was added 1.0 mL (7.2 mmol) of Et3N and 0.10 mL (0.38 mmol) of gem-DEE-TIPS. The solution was refluxed for 24 h. A gradual shift in solution color was observed from a green to a rust color. Solvent was removed, and the compound was purified on a silica gel pad by rinsing with DCM and then eluting the compound with a DCM/MeOH (5:1) mixture. The

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CONCLUSIONS A series of acyclic cross-conjugated organometallic complexes based on the gem-DEE ligand have been prepared and characterized. The excellent stability of complex [3]Cl2 allows for both further derivatization to yield complexes [4a](OTf)4 and [4b](PF6)2 and the opportunity to probe the Co−Co interactions across the gem-DEE bridge. DFT calculations revealed that the modest Co−Co interactions observed in [3]Cl2 and [4a](OTf)4 are likely the result of weak but observable σ-based orbital mixing across the LUMOs. Together, the compounds reported herein contribute significantly to the underexplored area of metal alkynyl chemistry based on cross-conjugated ligands. G

DOI: 10.1021/acs.organomet.6b00657 Organometallics XXXX, XXX, XXX−XXX

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Organometallics

(MeOH) 778-[Co(cyclam)(gem-DEE-TIPS)2]+. Elem. Anal. Found (Calcd) for C44H82N4Si2O2CoPF6 ([2c]PF6·2H2O) C, 55.41 (55.09); H, 8.74 (8.62); N, 5.82 (5.84). IR (cm−1) −CC−TIPS 2140 (s), (Co−CC−) 2089 (s). 1H NMR (CDCl3, δ) 4.22 (br s, 4H, N−H), 2.95−2.51 (m, 16H, CH2), 2.05 (s, 6H, CH3), 2.00 (s, 6H, CH3), 1.84 (t, 2H, CH2, J = 15.3 Hz), 1.56 (q, 2H, CH2), 1.05 (s, 42H, TIPS). Absorption spectrum (MeOH) λmax nm (εmax, L mol−1 cm−1) 455 (266). Preparation of [{Co(cyclam)Cl}2(μ-gem-DEE)]Cl2 ([3]Cl2). In a round bottom flask, 100 mg (0.27 mmol) of [Co(cyclam)Cl2]Cl was dissolved in 50 mL of MeOH. To the solution was added 1.0 mL (7.2 mmol) of Et3N and 59 mg (0.14 mmol) of [1a]Cl. The solution was refluxed for 24 h. Solvent was removed, and the compound was purified on a silica gel pad by rinsing with EtOAc and then eluting the desired compound [3]Cl2 using a EtOAc/MeOH (1:3) mixture as a red band. Compound [3]Cl2 was then recrystallized by the addition of Et2O to a concentrated solution in MeOH:CHCl3 yielding an orange crystalline material. Yield: 85 mg (0.11 mmol) (82% based on [1a]Cl). Data for [3]Cl2: ESI-MS (MeOH) 345-[{Co(cyclam)Cl}2(μ-gemDEE)]2+, 727-[{{Co(cyclam)Cl}2(μ-gem-DEE)}Cl]+. Elem. Anal. Found (Calcd) for C29H65N8O5Co2Cl7 ([3]Cl2·5H2O·CHCl3) C, 35.62 (35.84); H, 6.55 (6.74); N, 11.68 (11.53). IR (cm−1) (Co−C C−) 2112. 1H NMR (CD3OD, δ) 4.98 (br s, 4H, N−H), 4.85 (br s, 4H, N−H), 2.88−2.04 (m, 32 H, CH2), 2.05 (s, 6H, CH3), 1.83 (t, 4H, CH2, J = 15.3 Hz), 1.552 (q, 4H, CH2). Absorption spectrum MeOH) λmax nm (εmax, L mol−1 cm−1) 507 (170), 348 (650). Preparation of [{Co(cyclam)NCMe}2(μ-gem-DEE)]OTf4 ([4a](OTf)4). In a round bottom flask, 200 mg (0.26 mmol) of [3]Cl2 was added to an MeCN solution containing 4 equiv of AgOTf. After 48 h of refluxing, the solution was allowed to cool to room temperature, and the silver salts were filtered off. To the eluent was added Et2O which yielded an orange precipitate. Purification was performed on a silica gel pad using an EtOAc/MeCN (1:1) mixture. Complex [4a](OTf)4 was then recrystallized by the addition of Et2O to a concentrated solution of MeCN yielding an orange crystalline material. Yield: 221 mg (0.17 mmol) (65% based on [3]Cl2). Data for [4a](OTf)4: ESI-MS (MeOH) 459-[{Co(cyclam)OTf}2(μ-gemDEE)]2+, 1068-[{{Co(cyclam)OTf}2(μ-gem-DEE)}}OTf]+. Elem. Anal. Found (Calcd) for C 3 4 H 5 9 N 9 O 1 3 Co 2 S 4 F 1 2 ([4a](OTf)4(−C2H3N)·H2O) C, 32.39 (32.00); H, 4.77 (4.66); N, 9.95 (9.88). IR (cm−1) 2118 (Co−CC−). 1H NMR (CD3CN, δ) 4.75 (br s, 4H, N−H), 4.45 (br s, 4H, N−H), 2.80−2.40 (m, 32 H, CH2), 1.96 (s, 6H, CH3), 1.93 (t, 4H, CH2), 1.54 (q, 4H, CH2). Absorption spectrum (MeOH) λmax nm (εmax, L mol−1 cm−1) 477 (243). Preparation of [{Co(cyclam)C2TMS}2(μ-gem-DEE)](PF6)2 ([4b](PF6)2). A Schlenk flask was charged with 100 mg (0.13 mmol) of [3]Cl2 suspended in dried THF, to which was added 3 equiv of Li− C2TMS (0.39 mmol). The solution was stirred under N2 for 12 h, and a gradual change in color from orange to yellow was observed. Purification was performed on a silica gel pad using DCM/MeOH (5:1) as the eluent. Recrystallization was performed by slow diffusion of hexane into a concentrated DCM solution yielding a yellow material. Crystal structures of [4b]Cl2 were hampered by solvent disorder. In attempts to obtain crystalline material, a saturated solution of NaPF6 was added to a dissolved solution of [4b]Cl2 in MeOH causing a yellow solid to precipitate. The precipitate was then recrystallized by the addition of hexane to a concentrated solution in DCM yielding a yellow crystalline material, but only poor quality samples were obtained for X-ray diffraction. Yield for [4b](PF6)2: 86 mg (0.08 mmol) (59% based on [3]Cl2). Data for [4b](PF6)2: ESI-MS (MeOH) 408-[{Co(cyclam)C2TMS}2(μ-gem-DEE)]2+, 849-[{{Co(cyclam)C2TMS}2(μ-gem-DEE)}}Cl]+. Elem. Anal. Found (Calcd) for C40H86N8O5Co2Cl2Si2P2F12 ([4b](PF6)2·4H2O·CH2Cl2·CH3OH) C, 37.12 (37.13); H, 6.94 (6.70); N, 8.74 (8.66). IR (cm−1) 2092 (CC−H), 2029(Co−CC−). 1H NMR (CD3OD, δ) 4.37 (br s, 8H, N−H), 2.81−2.39 (m, 32 H, CH2), 2.08 (s, 6H, CH3), 1.75 (t, 4H, CH2, J = 13 Hz), 0.88 (q, 4H, CH2) 0.07 (s, 18H, TMS). Absorption spectrum (MeOH) λmax nm (εmax, L mol−1 cm−1) 458 (217), 357 (581).

compound was then recrystallized in a MeOH/Et2O solution yielding an orange crystalline material. Yield: 128 mg (0.22 mmol) (79% based on Co). Data for [1b]Cl: ESI-MS (MeOH) 554-[Co(cyclam)(gemDEE-TIPS)Cl]+. IR(cm−1) −CC−SiiPr3 2141 (s), (Co−CC−) 2117. Elem. Anal. Found (Calcd) for C27H57N4O3CoCl2Si ([1b]Cl· 3H2O) C, 50.29 (50.38); H, 8.59 (8.93); N, 8.67 (8.70). 1H NMR (CDCl3, δ) 5.48 (s, 2H, N−H), 4.41 (s, 2H, N−H), 3.24−2.62 (m, 18H, CH2), 2.13 (s, 3H, CH3), 2.11 (s, 3H, CH3), 2.06−2.00 (m, 2H, CH2, J = 15.6 Hz), 1.05 (s, 21H, TIPS). Absorption spectrum (MeOH) λmax nm (εmax, L mol−1 cm−1) 489 (152), 333 (802). Preparation of [Co(cyclam)(gem-DEE-H)CN]PF6 ([2a]PF6). In a round bottom flask, 100 mg (0.23 mmol) of [1a]Cl was dissolved in 25 mL of H2O. To the solution was added 22 mg (0.46 mmol) of NaCN which was set to reflux overnight. A yellow precipitate was obtained upon the addition of a concentrated solution of sodium hexafluorophosphate to the reaction solution at room temperature. Purification was performed on a silica gel pad by rinsing with EtOAc and then eluting [2a]PF6 with a EtOAc/MeOH (5:1) mixture. Compound [2a]PF6 was then recrystallized by the addition of hexane to a concentrated solution in DCM yielding a yellow crystalline material. Yield: 84 mg (0.16 mmol) (68% based on [1a]Cl). Data for [2a]PF6: ESI-MS (MeOH) 388-[Co(cyclam)(gem-DEE-H)CN]+. Elem. Anal. Found (Calcd) for C19H33N5OCoPF6 ([2a]PF6·H2O) C, 41.73 (41.39); H, 5.97 (6.03); N, 12.22 (12.70). IR (cm−1) −C C−TIPS 2130 (s), (Co−CC−) 2102 (s). 1H NMR (CD3OD, δ) 5.10 (br s, 2H, N−H), 4.71 (br s, 2H, N−H), 3.38 (s, 1H, CCH), 2.91−2.06 (m, 16H, CH2), 2.06 (s, 3H, CH3), 1.95 (s, 3H, CH3), 1.83 (t, 2H, CH2, J = 15.3 Hz), 1.35 (q, 2H, CH2). Absorption spectrum (MeOH) λmax nm (εmax, L mol−1 cm−1) 444 (220). Preparation of [Co(cyclam)(gem-DEE-TIPS)(C2Ph)]PF6 ([2b]PF6). A Schlenk flask charged with 220 mg (0.37 mmol) of [1b]Cl suspended in dried THF, to which was added 0.9 equiv of Li−C2Ph (0.33 mmol). The solution was stirred under N2 for 12 h, and a change in color from orange to yellow was observed. Solvent was removed, and a concentrated solution of sodium hexafluorophosphate was added yielding a yellow precipitate. Purification was performed on a silica gel pad using DCM/MeOH (5:1) as the eluent. Recrystallization was performed by slow diffusion of hexane into a concentrated DCM solution yielding a yellow material. Yield: 140 mg (0.18 mmol) (49% based on [1b]Cl). Data for [2b]PF6: ESI-MS (MeOH) 620[Co(cyclam)(gem-DEE-TIPS)(C2Ph)]+. Elem. Anal. Found (Calcd) for C35H58N4OCoPF6Si ([2b]PF6·H2O) C, 53.83 (53.70); H, 7.08 (7.47); N, 7.45 (7.16). IR (cm−1) −CC−H 2108 (s), (Co−C C−) 2065 (s). 1H NMR (CD3OD, δ) 7.36 (d, 2H, Ar−H, J = 8.4 Hz), 7.12 (t, 2H, Ar−H, J = 6.9 Hz), 7.02 (t, 1H, Ar−H, J = 8.7 Hz), 4.49 (br s, 2H, N−H), 4.31 (br s, 2H, N−H), 2.84−2.28 (m, 16H, CH2), 2.06 (s, 3H, CH3), 1.94 (s, 3H, CH3), 1.77 (t, 2H, CH2, J = 15.9 Hz), 1.28 (q, 2H, CH2), 1.02 (s, 21H, TIPS). Absorption spectrum (MeOH) λmax nm (εmax, L mol−1 cm−1) 456 (122), 360 (471). Preparation of [Co(cyclam)(gem-DEE-TIPS)2]PF6 ([2c]PF6). Method A. A Schlenk flask charged with 200 mg (0.54 mmol) of [Co(cyclam)Cl2]Cl suspended in dried THF, to which was added 1.9 equiv of Li-gem-DEE-TIPS (1.04 mmol). The solution was stirred under N2 for 12 h, and a change in color from green to brown-yellow was observed. Solvent was removed, and a concentrated solution of sodium hexafluorophosphate was added yielding a brown-yellow precipitate. Purification was performed on a silica gel pad using DCM/ MeOH (5:1) as the eluent. Recrystallization was performed by slow diffusion of hexane into a concentrated DCM solution yielding a yellow material. Yield: 110 mg (0.12 mmol) (22% based on Co). Method B. A Schlenk flask charged with 150 mg (0.25 mmol) of [1b]Cl suspended in dried THF, to which was added 0.9 equiv of Ligem-DEE-TIPS (0.23 mmol). The solution was stirred under N2 for 12 h, and a change in color from orange to yellow was observed. Solvent was removed, and a concentrated solution of sodium hexafluorophosphate was added yielding a yellow precipitate. Purification was performed on a silica gel pad using DCM/MeOH (5:1) as the eluent. Recrystallization was performed by slow diffusion of hexane into a concentrated DCM solution yielding a yellow material. Yield: 140 mg (0.15 mmol) (60% based on [1b]Cl). Data for [2c]PF6: ESI-MS H

DOI: 10.1021/acs.organomet.6b00657 Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics Preparation of [{Co(cyclam)Cl2}(μ-gem-DEE)2)]Cl2 ([5]Cl2). In a round bottom flask, 200 mg (0.46 mmol) of [1a]Cl was dissolved in 50 mL of methanol which is saturated with O2. To the solution was added Hay catalyst (0.05 g CuCl (0.5 mmol), 0.20 mL (1.3 mmol) of TMEDA in 3 mL of MeOH), and the solution was purged with O2 for 6 h. Solvent was removed, and the blue mixture was placed in a freezer overnight. The residue was then rinsed with DCM to remove excess Hay catalyst before being further purified on a silica gel pad and eluting with a MeOH/EtOAc (3:1) mixture. Compound [5]Cl2 was then recrystallized by the addition of Et2O to a concentrated solution in MeOH:CHCl3 yielding an orange crystalline material. Yield: 181 mg (0.21 mmol) (45% based on [1a]Cl). Data for [5]Cl2: ESI-MS (MeOH) 396-[{Co(cyclam)Cl} 2 (μ-gem-DEE) 2 ] 2+ , 828-[{{Co(cyclam)Cl}2(μ-gem-DEE)2}Cl]+. Elem. Anal. Found (Calcd) for C37H72N8Co2Cl4O5 ([5]Cl2·4H2O·CH3OH) C, 45.65 (45.88); H, 7.32 (7.49); N, 11.18 (11.57). IR (cm−1) (Co−CC−) 2107. 1H NMR (CD3OD, δ) 4.98 (br s, 4H, N−H), 4.83 (br s, 4H, N−H), 2.88−2.35 (m, 32 H, CH2), 2.03 (s, 6H, CH3), 1.93 (s, 6H, CH3), 1.87 (t, 4H, CH2, J = 14.7 Hz), 1.53 (q, 4H, CH2). Absorption spectrum (MeOH) λmax nm (εmax, L mol−1 cm−1) 486 (218), 328 (10158). X-ray Data Collection, Processing, and Structure Analysis and Refinement for Crystals. X-ray diffraction data were collected on either a Rigaku RAPID-II image plate diffractometer using Cu Kα (λ = 1.54184 Å) radiation ([2a](PF6), [4a](OTf)4,and [4b](PF6)2) or a Nonius Kappa CCD using Mo Kα (λ = 0.71073 Å) radiation ([1a]Cl, [2b](PF6), [3]Cl2, and [5]Cl2). The structures were solved using the structure solution program DIRDIF200845 and refined using SHELXTL suite of programs.46 Computational Details. The geometries of [1a′]+, [3′]2+, [4a′]4+, [4b′]2+, and [5′]2+ in the ground state were fully optimized from the crystal structures reported in this work, using the density functional method B3LYP (Beck’s three-parameter hybrid functional using the Lee−Yang−Parr correlation function) and employing the LanL2DZ basis set. The calculation was accomplished by using the Gaussian03 program package.41

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.6b00657. UV−vis and IR spectra for all complexes presented, differential pulse voltammograms for [3]Cl2, [4a](OTf)4, [4b](PF6)2, and [5]Cl2, computational details and relevant geometric parameters for the optimized structures of [3′]+, [4a′]4+, and [4b′]2+, and the CIF files for [1a]+, [2a−c]+, [3]2+, [4a]4+, [4b]2+, and [5]2+ giving X-ray crystallographic data for their structural determination(PDF) Computed Cartesian coordinates for [1a]+, [2a,b]+, [3]2+, [4a]4+, and [5]2+ (CIF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We gratefully acknowledge financial support from the National Science Foundation (CHE 1362214) and Purdue University. REFERENCES

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DOI: 10.1021/acs.organomet.6b00657 Organometallics XXXX, XXX, XXX−XXX