Design, Synthesis, and Characterization of Hybrid Metal–Ligand

Jan 22, 2015 - Despite the prevalence of supramolecular architectures derived from metal–ligand or hydrogen-bonding interactions, few studies have f...
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Design, Synthesis, and Characterization of Hybrid Metal−Ligand Hydrogen-Bonded (MLHB) Supramolecular Architectures Samantha K. Sommer, Lev N. Zakharov, and Michael D. Pluth* Department of Chemistry and Biochemistry, Materials Science Institute, University of Oregon, Eugene, Oregon 97403, United States S Supporting Information *

ABSTRACT: Despite the prevalence of supramolecular architectures derived from metal−ligand or hydrogen-bonding interactions, few studies have focused on the simultaneous use of these two strategies to form discrete assemblies. Here we report the use of a supramolecular tecton containing both metal-binding and self-complementary hydrogen-bonding interactions that upon treatment with metal precursors assembles into discrete hybrid metal−ligand hydrogen-bonded assemblies with closed topology. 1H NMR DOSY experiments established the stability of the structures in solution, and the measured hydrodynamic radii match those determined crystallographically, suggesting that the closed topology is maintained both in solution and in the solid state. Taken together, these results demonstrate the validity of using both hydrogen-bonding and metal−ligand interactions to form stable supramolecular architectures.

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INTRODUCTION Directional metal−ligand1−5 and hydrogen-bonding6−9 interactions are established methods used to form synthetic supramolecular architectures and to control molecular selfassembly. In addition to the diverse array of two- and threedimensional supramolecular structures accessible by these two strategies, numerous assemblies have been used in applications ranging from sensing10−14 to catalysis.15−18 Despite the prevalence of structures derived from metal−ligand or hydrogen-bonding interactions, few studies have focused on the simultaneous use of these two strategies to form discrete supramolecular structures constructed exclusively from ligand and transition-metal subunits.19−30 Typically, ligand components containing both metal−ligand and hydrogen-bonding motifs assemble into structures with open topologies, such as chains,31−34 sheets,35−39 and networks.26,40−51 The rational design, formation, and characterization of discrete structures with closed topology formed from integrated metal−ligand and hydrogen-bonding interactions remain a significant challenge. An additional obstacle in generating assembled structures containing both metal−ligand and hydrogen-bonding interactions is determining whether solid- and solution-state structures maintain the same topology. Compounding these challenges, if topologically closed structures are formed, they often form a distribution of structures in equilibrium in solution rather than one discrete structure. This complexity has resulted in few systems that have been fully structurally characterized in both the solution and solid state. An early example of such a structure was derived from 5-aminoorotate and [Pt(PPh3)2]2+, which when combined, crystallized into hydrogen-bonded © XXXX American Chemical Society

tetrads, although other conformations were also observed in the solid state.19 Eroding the structural fidelity, chlorinated solutions of the tetrad were found to be in equilibrium with a hydrogen-bonded dimer.19 A similar report described a transplatinum dimetalated quartet formed through hydrogenbonding interactions of platinum-bound 1-methylcytosine and 9-ethylguanine.25 Although the solid-state structures for this system were counteranion-dependent, solution structures in dimethyl sulfoxide were counterion-independent and favored quartet formation.25 Dinuclear organoplatinum(II) complexes have also been used as metal precursors, which when treated with nicotinic acid, afford hydrogen-bonded cyclic aggregates with hydrogen-bonded corrugated chains present in the solid state.20 Recently, 2-ureido-4-[1H]pyrimidinone and cis-substituted square-planar palladium(II) components were used to make a mixture of molecular triangles and squares via hydrogen-bonding and metal−ligand interactions in chloroform, but no solid-state structural data were reported.21 One major goal of this emerging research area is to rationally develop discrete supramolecular structures containing both metal−ligand and hydrogen-bonding interactions that maintain their structure in both the solution and solid state. Such complexes would further enable the generation and understanding of hybrid metal−ligand hydrogen-bonded (MLHB) structures, thus expanding the accessible chemical space of selfassembly. Motivated by these goals, we report here the design, synthesis, and characterization of a new class of self-assembled Received: November 24, 2014

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DOI: 10.1021/ic502802f Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry structures utilizing hybrid MLHB interactions with closed topology in both the solution and solid state.

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RESULTS AND DISCUSSION Design and Synthesis of Hybrid MLHB Ligands. Motivated by the extensive use of self-complementary amide groups in both biological and synthetic hydrogen-bonded structures,52,53 we reasoned that similar motifs could be used to generate hydrogen-bonding architectures compatible with common metal-binding functional groups.54 The incorporation of both such groups into one rigid ligand should generate one subunit that will allow for the construction of hybrid MLHB structures in the presence of an appropriate metal (Scheme 1). Scheme 1. Design Strategy for Generating Hybrid MLHB Supramolecular Tectons Figure 1. (a) Synthesis, (b) molecular structure, and (c) 31P{1H} NMR spectrum of 7-DPQ. Thermal ellipsoids in the ORTEP diagram are shown at the 50% probability level.

construction of a variety of supramolecular complexes.56−62 Additionally, coupling of the NMR-active 103Rh nucleus to the bound phosphines provides additional information regarding the coordination environment and symmetry in the 31P{1H} NMR spectra. On the basis of these parameters and to test whether the self-complementary hydrogen-bonding interactions stayed intact upon metal binding, we treated [Cp*RhCl2]2 with 2 equiv of 7-DPQ in CHCl3 with the expectation that one 7-

On the basis of these design principles, we chose to use a quinolone-derived system with a pendant metal-binding unit that would provide self-complementarity hydrogen-bonding interactions between the quinolones while also providing separate functionalization to enable metal binding. For a metal-binding site, we chose to incorporate phosphine groups because of their high binding affinity toward late transition metals. The desired phosphine-containing quinolone ligand 7diphenylphosphino-1H-quinolin-2-one (7-DPQ) was prepared in five steps starting from commercially available precursors. The treatment of ethyl vinyl ether with oxalyl chloride provides acid chloride 1,55 which is subsequently coupled to 3iodoaniline to generate amide 2. Cyclization of 2 with H2SO4 furnished a mixture of iodo-substituted isomers, which could not be separated directly. Conversion of the two isomers of cyclized 2 to the corresponding 2-chloroquinolines with SOCl2, however, allowed for isolation of the desired 7-iodo-2chloroquinoline (3) isomer by chromatography. The treatment of 3 with NaOMe generates 7-iodo-2-methyoxyquinoline (4), which can then be coupled to a secondary phosphine. Optimization of the phosphine coupling conditions resulted in efficient coupling of HPPh2 to 4 using catalytic Pd(OAc)2 in MeCN to generate the methoxy-protected ligand (7-DPQOMe), which was subsequently deprotected with HCl to afford 7-DPQ (Figure 1a). Single crystals of 7-DPQ suitable for X-ray diffraction grown by the slow evaporation of CH2Cl2 confirmed the molecular identity and established that 7-DPQ selfassociates to form a 2-fold-symmetric hydrogen-bonded dimer, with a hydrogen-bond distance of 2.786 Å (Figure 1b). The N−H hydrogen atom was located from the residual electron density map and is consistent with the quinolone tautomeric form. Coordination and Self-Assembly of 7-DPQ: Characterization of Hybrid MLHB Complexes. Having established that 7-DPQ forms a hydrogen-bonded 2-fold-symmetric supramolecular techton, we next sought to demonstrate the formation of hybrid MLHB structures. Toward this goal, we chose to use piano-stool complexes of the form [Cp*RhX2]2, which have been used previously as metal subunits in the

Figure 2. (a) Synthesis, (b) 31P{1H} NMR spectrum, and (c) molecular structure of Rh2P2. Thermal ellipsoids of the ORTEP diagram are shown at the 50% probability level. All hydrogen atoms, except for N−H, are omitted for clarity.

DPQ ligand would coordinate to each metal (Figure 2a). The 31 1 P{ H} NMR resonance of the resultant reaction displays a clean doublet at 30.9 ppm (1JP,Rh = 141.6 Hz), which is shifted 35.4 ppm downfield from the free 7-DPQ ligand, consistent with the formation of a single discrete, symmetric 1:1 7-DPQ/ rhodium complex of the form [Cp*Rh(7-DPQ)Cl2]2 (Rh2P2; Figure 2b). The molecular structure of Rh2P2 was confirmed by X-ray crystallography of single crystals obtained by the diffusion of Et2O into a CHCl3 solution of Rh2P2 (Figure 2c). The B

DOI: 10.1021/ic502802f Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

spectrum of the reaction products displays a doublet at 26.6 ppm (1JP,Rh = 137.9 Hz), which is similar to that reported for known [RhIII(bisphosphine)]+ complexes,63 suggesting the formation of [Cp*Rh(7-DPQ)2Cl]2(PF6)2 (Rh2P4; Figure 3b). Additionally, the 4.3 ppm upfield shift in the 31P{1H} NMR spectrum of Rh2P4 relative to that of Rh2P2 is consistent with increased electron density at the phosphine due to an increase in the number of 7-DPQ ligands bound to the rhodium center. Inspection of the 1H NMR of the product shows integrations consistent with 2:1 7-DPQ/rhodium binding, and the downfield shift of the single N−H resonance supports the formation of a symmetric hydrogen-bonding motif in solution. Unambiguous evidence for the structure and closed topology of Rh2P4 was obtained by X-ray crystallography. Single crystals of Rh2P4 suitable for X-ray diffraction were grown by the vapor diffusion of petroleum ether into a CH2Cl2 solution of the complex (Figure 3c). The Rh2P4 complex is centered on a crystallographic inversion center located between the hydrogenbonding 7-DPQ ligands. The piano-stool complex adopts a distorted geometry in the solid state with a P−Rh−P angle of 101.3°, possibly due to the steric demands of the 7-DPQ ligand. Selected bond distances and lengths comparing Rh2P2 and Rh2P4 are shown in Table 1. The distance between rhodium centers in Rh2P4 is 15.584 Å, and the 7-DPQ ligands are separated by 3.614 Å, suggesting π−π interactions between the 7-DPQ ligands. Table 2 provides crystallographic data for 7-DPQ, Rh2P2, and Rh2P4. Overall, Rh2P4 provides a rare example of a discrete MLHB irregular hexagon characterized in the solid state. To further establish that the solid-state structures corresponded to the spectra observed in solution, we used 1H NMR DOSY experiments to investigate the solution structures of Rh2P2 and Rh2P4. We also synthesized Cp*Rh(7-DPQOMe)Cl2 (RhPOMe) from the O-methylated quinoline ligand (7DPQOMe), which cannot form self-complementary hydrogen bonds and thus should have a smaller radius and larger diffusion coefficient than the intact structures of Rh2P2 and Rh2P4. The 1 H NMR DOSY spectra of Rh2P2, Rh2P4, and RhPOMe showed only one discrete species in CD2Cl2 for each compound, suggesting that these complexes were not in equilibrium with higher-order self-assembled constructs (Figure 4).64 To obtain further evidence for the discrete intact MLHB structures, the diffusion coefficients measured from 1H NMR DOSY in CD2Cl2 were used to calculate the hydrodynamic radius of each complex using the Stokes−Einstein equation. If Rh2P2 and Rh2P4 formed discrete molecular species in solution, then we

crystal structure of Rh 2 P 2 shows one 7-DPQ ligand coordinated to the rhodium metal center through the phosphine with an Rh−P distance of 2.332 Å. The 2-foldsymmetric quinolone−quinolone hydrogen-bonded dimer, observed in the crystal structure of 7-DPQ, is maintained in Rh2P2 with a N−H···O hydrogen-bond length of 2.762 Å. The bridging, hydrogen-bonded 7-DPQ ligands in the Rh2P2 structure confirm that the addition of metal−ligand interactions does not perturb the hydrogen-bonding interactions of the ligand system. A systematic increase in the number of 7-DPQ ligands available to coordinate the rhodium center should result in an increase in the dimensionality, which is important for the propagation of larger and more complex closed MLHB architectures. To investigate this possibility, [Cp*RhCl2]2 was treated with an excess of 7-DPQ with KPF6 in a 1:1 CH2Cl2/ H2O solution (Figure 3a). The resultant 31P{1H} NMR

Figure 3. (a) Synthesis, (b) 31P{1H} NMR spectrum, and (c) molecular structure of Rh2P4. The PF6− counterions, solvent molecules, and hydrogen atoms, except for N−H, are excluded for clarity. Thermal ellipsoids in the ORTEP diagram are shown at the 50% probability level.

Table 1. Selected Bond Lengths and Angles for Rh2P2 and Rh2P4 Rh2P2

Rh2P4 Bond Lengths (Å)

Rh(1A)−P(1A)

2.332

NH(1A)−O(2B)

2.762

P(1A)−Rh(1A)−Cl(1A) P(1A)−Rh(1A)−Cl(2A) Cl(1A)−Rh(1A)−Cl(2A) N(1A)−H(1A)−O(2B)

88.29 86.95 95.03 168.47

Rh(1A)−P(1A) Rh(1A)−P(2A) NH(1A)−O(2B) NH(2A)−O(1B)

2.358 2.386 2.847 2.773

P(1A)−Rh(1A)−P(2A) P(1A)−Rh(1A)−Cl(1A) P(2A)−Rh(1A)−Cl(1A) N(1A)−H(1A)−O(2B) N(2A)−H(2A)−O(1B)

101.28 88.22 86.55 175.80 172.84

Bond Angles (deg)

C

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Inorganic Chemistry Table 2. Crystallographic Data for 7-DPQ, Rh2P2, and Rh2P4 formula fw temperature (K) cryst syst space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z ρ (mm−1) μ (mm−1) F(000) cryst size (mm3) limiting indices θ range (deg) completeness to θ (%) total reflns indep reflns R(int) data/restraints/param max, min transmn R1 (wR2) [I > 2σ(I)] R1 (wR2) GOF (F2) max, min peaks (e Å−3)

7-DPQ

Rh2P2

Rh2P4

C21H16NOP 329.32 193(2) triclinic P1̅ 8.866(2) 9.850(3) 10.991(3) 115.602(4) 96.827(4) 93.940(4) 851.7(4) 2 1.284 0.168 344 0.26 × 0.18 × 0.12 −10 ≤ h ≤ 10, −11 ≤ k ≤ 11, −13 ≤ l ≤ 13 2.08−25.00 99.8 8308 3003 0.0198 3003/0/281 0.9802, 0.9577 0.0651 (0.1463) 0.0677 (0.1480) 1.065 1.071, −0.198

C31H31Cl2NO2.50PRh 662.35 100(2) monoclinic P21/n 8.9031(7) 16.4605(13) 21.4740(17) 90 95.7940(10) 90 3130.9(4) 4 1.405 0.796 1352 0.17 × 0.09 × 0.06 −10 ≤ h ≤ 10, −19 ≤ k ≤ 15, −25 ≤ l ≤ 19 1.56−25.00 100.0 28189 5527 0.0850 5527/0/354 0.9538, 0.8765 0.0626 (0.1280) 0.1067 (0.1430) 1.106 1.084, −0.712

C55H53Cl7F6N2O2P3Rh 1331.96 150(2) triclinic P1̅ 12.4931(17) 15.480(2) 15.839(2) 90.066(2) 102.854(2) 111.085(2) 2775.3(7) 2 1.594 0.796 1352 0.22 × 0.04 × 0.02 −14 ≤ h ≤ 14, −18 ≤ k ≤ 18, −18 ≤ l ≤ 18 1.32−25.00 100.0 33173 9782 0.0708 9782/2/693 0.9843, 0.8444 0.0506 (0.1208) 0.0892 (0.1390) 1.000 1.529, −0.752

Figure 4. 1H NMR DOSY spectra (500 MHz, CD2Cl2) of (a) Rh2P2, (b) Rh2P4, and (c) RhPOMe. The CD2Cl2 diffusion peak is excluded from the 1 H NMR DOSY spectral window for clarity.

Table 3. Diffusion Data for Rh2P2, Rh2P4, and RhPOMe Including the Calculated Radii and Radii from the Determined Molecular Structures −10

2

−1

diffusion coefficient (×10 m s ) radius, Stokes−Einstein (Å) radius, crystal structure (Å)

Rh2P2

Rh2P4

RhPOMe

5.0 ± 0.2 10.7 ± 0.5 10.7

4.4 ± 0.3 12.2 ± 0.8 13.0

7.0 ± 0.4 7.6 ± 0.5

would expect the radii calculated from the 1H NMR DOSY data to match the dimensions of Rh2P2 and Rh2P4 determined by crystallography (Table 3). By contrast, if the 7-DPQ hydrogenbond network does not remain intact in solution, we would expect the diffusion coefficients and calculated radii to be

similar to those of RhPOMe. Alternatively, if polymeric structures of Rh2P2 and Rh2P4 were formed in solution, then the 1H NMR DOSY radii would be significantly larger than those obtained from the Rh2P2 and Rh2P4 crystal structures. Comparison of the 1H NMR DOSY spectra of Rh2P2, Rh2P4, D

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Inorganic Chemistry and RhPOMe revealed that RhPOMe has a significantly larger diffusion coefficient and thus a smaller radius, which is expected because it cannot form larger assemblies through hydrogen bonding (Figure 4). As anticipated, the Rh2P2 and Rh2P4 radii calculated from 1H NMR DOSY data are in good agreement with the molecular dimensions found in the solid state, confirming that intact MLHB structures are present in solution as well as the solid state. To determine whether metal coordination significantly perturbed the hydrogen-bonding interactions in 7-DPQ, we calculated the root-mean-squared distance (rmsd) between the 7-DPQ ligands in the crystal structures of 7-DPQ, Rh2P2, and Rh2P4. The rmsd between 7-DPQ and Rh2P2 was 0.125 Å, whereas that between 7-DPQ and Rh2P4 was only 0.0654 Å. Similarly, the rmsd between Rh2P2 and Rh2P4 was 0.127 Å. Taken together, these comparisons indicate only minor structural variations in the hydrogen-bonding network, suggesting that metal coordination does not significantly alter the 7-DPQ hydrogen-bonded subunit structure. This structural stability demonstrates the viability of using similar subunits to assemble higher-order MLHB structures using different coordination motifs.

anisotropically. Hydrogen atoms were treated in calculated positions except those involved in hydrogen bonds, which were found on the residual density map and refined with isotropic thermal parameters. 3-Ethoxy-N-(3-iodophenyl)acrylamide (2). A solution of 3ethoxyprop-2-enoyl chloride (7.90 g, 58.7 mmol) in CH2Cl2 (10 mL) was added dropwise to a solution containing 3-iodoaniline (5.05 g, 29.3 mmol) and pyridine (4.73 mL, 58.7 mmol) in CH2Cl2 (40 mL). The reaction mixture was stirred at room temperature for 3 h, poured into water (100 mL), and extracted with EtOAc (3 × 50 mL). The organic layers were combined and dried over MgSO4, and the solvent was removed under vacuum to afford a brown solid. The crude product was recrystallized from EtOAc by slow evaporation, and crystals were washed with Et2O to afford 2 (7.41 g, 94%) as a white crystalline solid. 1H NMR (300 MHz, CDCl3): δ 7.98 (s, 1H), 7.56 (d, 1H, 12.2 Hz), 7.47 (d, 1H, 7.8 Hz), 7.40 (d, 1H, 7.8 Hz), 7.14 (s, 1H), 7.02 (t, 1H, 7.8 Hz), 5.30 (d, 1H, 9.8 Hz), 3.92 (q, 2H, 7.3 Hz), 1.32 (t, 3H, 7.3 Hz). 13C{1H} NMR (125 MHz, CD2Cl2): δ 165.5, 161.9, 140.4, 133.1, 130.9, 128.8, 119.4, 99.1, 94.1, 68.0, 14.9. 7-Iodo-2-chloroquinoline (3). Solid 2 (5.76 g, 21.3 mmol) was added to concentrated H2SO4 (97%, 10 mL) and stirred at room temperature for 6 h. The resultant reaction mixture was poured into ice water (100 mL). The resultant precipitate was filtered, washed with Et2O (25 mL), and dried to give a beige solid. The crude product (309 mg, 1.38 mmol) was dissolved in CH2Cl2 (15 mL), and SOCl2 (130 μL, 214 μmol) and N,N-dimethylformamide (118 μL, 1.51 mmol) were added. The reaction mixture was refluxed for 3 h, cooled to room temperature, and poured into water (50 mL). After extraction with EtOAc (3 × 50 mL), the combined organic fractions were dried over MgSO4 and evaporated, and the residue was purified by flash chromatography (9:1 hexanes/EtOAc) to afford 3 (0.114 g, 35%) as a white solid. 1H NMR (500 MHz, CD2Cl2): δ 8.41 (s, 1H), 8.09 (d, 1H, 8.7 Hz), 7.84 (d, 1H, 8.7 Hz), 7.56 (d, 1H, 8.7 Hz), 7.40 (d, 1H, 8.3 Hz). 13C{1H} NMR (125 MHz, CD2Cl2): δ 151.9, 148.9, 139.4, 137.9, 136.3, 129.4, 126.4, 123.5, 97.1. HRMS ([M + H]+). Calcd for C9H6NClI: m/z 289.9234. Found: m/z 289.9221. 7-Iodo-2-methyoxyquinoline (4). A solution of 3 (0.208 g, 0.860 mmol) and NaOMe (3.87 mmol, prepared from 89.0 mg of Na in 4.4 mL of MeOH) was heated at 65 °C for 2 h. The reaction mixture was poured into a saturated aqueous NH4Cl solution (10 mL) at 0 °C. After extraction with CH2Cl2, the combined organic layers were dried over MgSO4 and evaporated to afford 4 (0.176 g, 85%) as a white solid. 1H NMR (500 MHz, CD2Cl2): δ 8.25 (s, 1H), 7.95 (d, 1H, 8.7 Hz), 7.65 (d, 1H, 8.3 Hz), 7.45 (d, 1H, 8.36 Hz), 6.95 (d, 1H, 8.7 Hz), 4.03 (s, 3H). 13C{1H} NMR (125 MHz, CD2Cl2): δ 163.3, 148.0, 139.0, 136.6, 133.2, 129.2, 124.7, 114.2, 95.8, 54.0. HRMS ([M + H]+). Calcd for C10H9NOI: m/z 285.9729. Found: m/z 285.9733. 7-Diphenylphosphino-2-methyoxyquinoline (7-DPQOMe). In a glovebox, Pd(OAc)2 (1.0 mg, 4.5 μmol), NEt3 (153 μL, 1.10 mmol), HPPh2 (69.6 μL, 0.403 mmol), and CH3CN (1 mL) were added to a scintillation vial. The deep-red solution was stirred for 10 min at room temperature and then added to a solution of 4 (0.105 g, 0.367 mmol) in CH3CN (3 mL). The resulting orange solution was stirred at 90 °C overnight. The reaction mixture was cooled to room temperature, filtered, and concentrated under vacuum to give a red oily solid. The crude product was then run through a silica plug and washed with CH2Cl2 (15 mL) to afford pure 5 (0.175 g, 85%). 1H NMR (500 MHz, CD2Cl2): δ 7.98 (d, 1H, 8.8 Hz), 7.68 (m, 2H), 7.48 (m, 1H), 7.38 (m, 8H), 6.91 (d, 1H, 8.8 Hz), 3.99 (s, 3H). 31P{1H} NMR (202 MHz, CD2Cl2): δ −4.73. 13C{1H} (125 MHz, CD2Cl2): δ 163.3, 147.0 (d, 7.4 Hz), 140.1 (d, 13.7 Hz), 138.9, 137.4 (d, 11.6 Hz), 134.5 (d, 20.1 Hz), 134.4 (d, 16.9 Hz), 132.7 (d, 16.9 Hz), 129.5, 129.1 (d, 7.4 Hz), 129.0 (d 9.5 Hz), 128.8 (d, 20.1 Hz), 127.9 (d, 7.4 Hz), 125.6, 114.2. HRMS. Calcd for C22H18NOP: m/z 343.1126. Found: m/z 344.1198. 7-Diphenylphosphino-1H-quinolin-2-one (7-DPQ). Solid 5 (1.03 g, 3.00 mmol) was dissolved in concentrated HCl (5 mL) and refluxed for 6 h, after which the pH of the reaction mixture was adjusted to pH 7 with 6 M NaOH. The reaction mixture was extracted with CH2Cl2 (3 × 20 mL), the organic fractions were combined and dried over MgSO4, and the solvent was removed under reduced

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CONCLUSIONS By designing a rigid ligand component with both metal-binding and hydrogen-bonding motifs, we have prepared hybrid metal− ligand hydrogen-bonding complexes. The discrete, isolable MLHB structures were characterized in both solution and the solid state, providing a rare example of a hybrid MLHB assembly with closed topology. Furthermore, 1H NMR DOSY experiments established that the hydrogen bonding is not eroded in solution, and structural insights from the 1H NMR DOSY data are consistent with crystallographically determined structures. A rmsd comparison on the free hydrogen-bonded 7DPQ tecton with Rh2P2 and Rh2P4 indicates that metal coordination does not perturb the hydrogen-bonding network. Taken together, these results provide a foundation for the rational design of more complex, discrete, closed hybrid MLHB architectures to expand the chemical space of accessible supramolecular systems.

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EXPERIMENTAL SECTION

Materials and Methods. All air- and moisture-sensitive reactions were performed under a nitrogen atmosphere using standard Schlenk and glovebox techniques. All chemicals were used as purchased unless noted otherwise. 3-Ethoxyprop-2-enoyl chloride was prepared as previously described.55 Anhydrous and air-free solvents were obtained from a Pure Process Technologies solvent purification system. Deuterated solvents were dried and deoxygenated by distillation over the appropriate drying agent followed by three freeze−pump− thaw cycles. NMR spectra were acquired on a Varian INOVA 500 MHz spectrometer at 25 °C and are referenced internally according to residual solvent resonances. Data for 1H, 31P{1H}, and 13C{1H} NMR spectra are reported as follows: chemical shift (δ, ppm), multiplicity [(s) singlet, (d) doublet, (t) triplet, (m) multiplet], integration, coupling constant (Hz). 1H NMR DOSY spectra were recorded using the PFG double-stimulated echo-pulse sequence. High-resolution mass spectrometry (HRMS) experiments were performed by the Biomolecular Mass Spectrometry Core of the Environmental Health Sciences Core Center at Oregon State University. Diffraction data were collected on a Bruker Smart Apex diffractometer at 150(2) K using Mo Kα radiation (λ = 0.71073 Å). Data reduction was performed in SAINT, and absorption corrections were applied using SADABS. All refinements were performed using the SHELXTL software package.65−67 All non-hydrogen atoms were refined E

DOI: 10.1021/ic502802f Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry pressure to afford 7-DPQ, a light-yellow solid (0.593 g, 60%). 1H NMR (500 MHz, CD2Cl2): δ 10.60 (s, 1H), 7.75 (d, 1H, 8.3 Hz), 7.38−7.33 (m, 10H), 7.14 (d, 1H, 7.33 Hz), 7.08 (m, 1H), 6.57 (d, 1H, 9.8 Hz). 31P{1H} NMR (202 MHz, CD2Cl2): δ −4.50. 13C{1H} (125 MHz, CD2Cl2/MeOD): δ 164.1, 142.4 (d, 13.7 Hz), 141.2, 138.5 (d, 7.4 Hz), 136.7 (10.6 Hz), 134.5 (d, 20.1 Hz), 129.7, 129.2 (d, 7.4 Hz), 128.1 (d, 7.4 Hz), 127.8 (d, 21.1 Hz), 122.3, 120.7, 120.5 (d, 13.7 Hz). HRMS ([M + H]+). Calcd for [C21H17NOP]+: m/z 330.1048. Found: m/z 330.1050. [Cp*Rh(7-DPQ)Cl2]2 (Rh2P2). To a vial containing a solution of 7DPQ (15.0 mg, 45.6 μmol) in CHCl3 (0.5 mL) was added a solution of [Cp*RhCl2]2 (14.1 mg, 22.8 μmol) in CHCl3 (0.5 mL). After stirring for 1 h, the deep-red solution was allowed to slowly evaporate to give Rh2P2 as red crystals (21.6 mg, 74%). 1H NMR (500 MHz, CD2Cl2): δ 7.82−7.72 (m, 6H), 7.70 (d, 1H, 8.8 Hz), 7.58 (m, 1H), 7.53−7.40 (m, 8H), 1.34 (d, 15H, 3.42 Hz). 31P{1H} NMR (202 MHz, CD2Cl2): δ 30.9 (d, 1JP,Rh = 141.6 Hz). MS ([M − Cl]−). Calcd for [C31H31ClNOPRh]−: m/z 602.1. Found: m/z 602.0. [Cp*Rh(7-DPQ)2Cl]2(PF6)2 (Rh2P4). To a solution of [Cp*RhCl2]2 (11.8 mg, 23.9 μmol) in CH2Cl2 (1.5 mL) was added a solution of KPF6 (13.2 mg, 71.8 μmol) in water (1.5 mL). The resultant solution was stirred for 20 min, after which a solution of 7-DPQ (47.3 mg, 144 μmol) in CH2Cl2 (2 mL) was added. After stirring for 5 h at room temperature, the organic layer was isolated, washed with water (3 mL), and reduced to ca. 2 mL with a flow of nitrogen. Ethanol (5 mL) was layered on top of the solution, and slow diffusion overnight led to crystal formation. The solution was then decanted off, and the crystals were dried under vacuum to afford Rh2P4 as orange-red crystals (20.2 mg, 39%). 1H NMR (500 MHz, CD2Cl2): δ 12.83 (s, 1H), 7.91 (m, 3H), 7.83 (m, 2H), 7.62 (m, 5H), 7.55 (m, 2H), 7.49−7.43 (m, 11H), 7.37 (m, 2H), 6.85 (d, 2H, 8.3 Hz), 6.77 (m, 2H), 6.26 (d, 2H, 9.8 Hz), 1.16 (s, 15H). 31P{1H} NMR (202 MHz, CD2Cl2): δ 26.6 (d, 1 JP,Rh = 137.9 Hz). MS ([M + Na]−). Calcd for [C52H47ClF6N2O2P3RhNa]−: m/z 1099.1. Found: m/z 1099.2. Cp*Rh(7-DPQOMe)Cl2 (RhPOMe). To a vial containing a solution of 7-DPQOMe (18.8 mg, 55.0 μmol) in CHCl3 (0.5 mL) was added a solution of [Cp*RhCl2]2 (17.0 mg, 27.5 μmol) in CHCl3 (0.5 mL). After stirring for 1 h, the deep-red solution was allowed to slowly evaporate to give RhPOMe as red crystals (33.5 mg, 95%). 1H NMR (500 MHz, CD2Cl2): δ 8.24 (m, 1H), 8.03 (m, 1H), 7.86 (m, 4H), 7.56−7.40 (m, 2H), 7.58 (m, 7H), 7.00 (d, 1H, 8.7 Hz), 4.07 (s, 3H), 1.41 (s, 15H). 31P{1H} NMR (202 MHz, CD2Cl2): δ 31.9 (d, 1JP,Rh = 144.6 Hz). HRMS ([M − Cl]+). Calcd for [C32H33ClNOPRh]+: m/z 616.1043. Found: m/z 616.1041.

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ASSOCIATED CONTENT

S Supporting Information *

Experimental details, NMR and DOSY spectra, and X-ray crystallographic data in CIF format. This material is available free of charge via the Internet at http://pubs.acs.org.

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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 This work was supported by funding from the University of Oregon (UO). The NMR facilities at the UO are supported by the NSF/ARRA (Grant CHE-0923589). The Biomolecular Mass Spectrometry Core of the Environmental Health Sciences Core Center at Oregon State University is supported, in part, by the NIEHS (Grant P30ES000210) and NIH.

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DOI: 10.1021/ic502802f Inorg. Chem. XXXX, XXX, XXX−XXX

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DOI: 10.1021/ic502802f Inorg. Chem. XXXX, XXX, XXX−XXX