Inorganic Chemistry respectively]. The resonance for the pyrazolopyridine proton H1a (the proton nearest to the metal center) was not detected in DMSO-d6 in 1c−3c. The signals originating from benzimidazole CH C4b and quaternary C7b carbons in 3c and the 7b−L3 tautomer are observed near the same positions [C4b at 118.97 (7b−L3) and 117.22 (3c) ppm; C7b at 122.95 (7b−L3) and 124.54 (3c) ppm] and differ significantly from those in the 4b′−L3 tautomer (quaternary C4b′ at 129.38 ppm; CH carbon C7b′ at 111.17 ppm). These data provide further evidence of 7b−L3 tautomer coordination to ruthenium in 3c. The coordination of L4 results in a significant downfield shift for the resonances corresponding to H8′ (by 0.28 ppm), H10′ (by 0.43 ppm), and H18′ (by 0.88 ppm). Carbon resonances C14′ (166.55 ppm) and C18′ (156.61 ppm) also differ relative to the free ligand, by 8.18 and 6.14 ppm, respectively, indicating bidentate paullone coordination via the pyridine (N19′) and azomethine nitrogens (N13′) to ruthenium with the formation of a five-membered chelate ring. The azepine methylene protons H7′ of 4c display no diastereotopic splitting (singlet at 3.61 ppm), as was the case for free L4 and [MCl(η6-p- cymene)(L4)]Cl (M = Ru, Os).21 Ligand L5 (with an endocyclic double bond C6′N5′) adopts a configuration with an exocyclic double bond C6′N13′ upon coordination and protonated N5′ instead of the N13′ atom (Chart 4). As a result, the triplet corresponding to H13′ at 7.81 Chart 4. Tautomers of L5 ppm for L5 disappears and proton H5′ of 5c emerges as a singlet at 9.67 (Z isomer) and 9.07 (E isomer) ppm. Because of this rearrangement of the ligand tautomeric form, a large 15N shift for the protonated amidine N atom from 77.4 (L5) to 107.46 (Z isomer) and 107.95 ppm (E isomer) is observed (Table S4 in the Supporting Information). The methylene groups of the azepine ring [H7′; 3.47 and 4.77 ppm (E isomer); 3.69 and 4.92 ppm (Z isomer)] and α- picolylamine moiety [H14′; 5.22 and 5.84 ppm (E isomer) and 4.99 and 5.16 ppm (Z isomer)] in 5c show diastereotopic splitting, as reported for [MCl(η6-p-cymene)(L5)]Cl,21 where- as for the L5 proton H7′, resonance, in accordance with fast inversion of the seven-membered azepine ring, was found at 3.41 ppm as a singlet and proton H14′ gives rise to a doublet at 4.51 ppm. The L5 ligand in 5c undergoes significant downfield shifts for H7′ (by 0.06−1.51 ppm), H14′ (by 0.48−1.33 ppm), and H18′ [by 0.52 (Z isomer) and 0.6 (E isomer) ppm]. Carbon signals C14′ and C18′ were shifted compared to those of the free ligand by 15.24 (Z isomer), 15.08 (E isomer), 5.57 (Z isomer), and 5.7 (E isomer) ppm, indicating bidentate paullone coordination via the nitrogens N19′ and N13′ to the ruthenium center, as reported for [MCl(η6-p-cymene)(L5)]Cl.21 Article Cross-peaks of high intensity in the 1H,1H ROESY NMR spectra of 1c−3c between the η6-arene ring protons H1d, H5d, H2d, and H4d and the nearest benzimidazole H4b proton reveal strong couplings. Thus, the 4-formylphenoxyacetyl-η6-benzyla- mide in 1c−3c in a DMSO-d6 solution must be oriented in such a manner that its substituent R, or H3d, lies above the chelate ring (Figure S8 in the Supporting Information). The closest η6-arene ring pyrazolopyridine proton H1a was not observed in 1c−3c in DMSO-d6. Similar solution structures were suggested for [MCl(η6-p-cymene)(L)]Cl (M = Ru, Os; L = L1−L3).25 Note that orientation of the cymene ring with the isopropyl group above the chelate ring is the preferred orientation in the crystal structures.25 The structures of 4c and 5c in DMSO-d6 were determined from 1H,1H ROESY NMR plots and were compared with the solution and X-ray structures of [MCl(η6-p-cymene)(L)]Cl.21 The X-ray structures of p-cymene analogue complexes facilitate the interpretation of the solution structures of 4c and 5c (E/Z isomers). The cross-peak originating from H8′,H14′ is more intense than that of H10′,H14′ (i.e., the H14′ proton is closer to H8′ than H10′), thus the chelating moiety in 4c is rotated out of the plane of the paullone indole ring with a torsion angle ΘC14′− N13′−C9′−C10′ > 90°, as observed in [MCl(η6-p-cymene)(L4)]Cl21 (Figure S9 in the Supporting Information). The orientation of the 4-formylphenoxyacetyl-η6-benzylamide group in 4c may be deducted from the intensity of the 1H−1H ROESY cross-peaks between protons of the paullone ligand (H8′, H10′, and H18′) and those of the η6-arene ring. Despite the absence of cross- peaks of H14′ with H3d and H7d and the same intensities of the cross-peaks between H18′ and η6-arene ring protons, the most intense couplings, H8′, H10′ with H1d, H5d, assume the η6-arene ring orientation preferably with a substituent R above the chelate ring away from the pyridine ring. Couplings H8′,H7d and H10′,H7d are in accordance with the proposed η6-arene orientation (Figure S10 in the Supporting Information). The arene ligand orientation with its substituent above the chelate ring was also observed in a DMSO-d6 solution for 5c. For example, the H14′ protons of both isomers oriented toward the arene ring (at 5.16 ppm for the Z isomer and at 5.22 ppm for the E isomer) show couplings with H7d (Figure S11 in the Supporting Information). The intensity of the cross-peaks in the 1H,1H ROESY NMR plot between protons of the paullone, H18′, and the η6-arene ring indicates a strong coupling between H18′ and H1d/H5d. This observation is in agreement with the η 6 - arene ring orientation with the substituent above the chelate ring toward the pyridine ring (Figure S12 in the Supporting Information). In the Z isomer, the azepine methylene group (H7′) is directed toward the arene ring and shows the 1H,1H ROESY NMR cross-peaks with η6-arene ring protons. In the E isomer, it points away from the arene ring, and as result, there are no 1H−1H ROESY couplings with H1d−H5d (Figure S13 in the Supporting Information). Solid-State Structures. The molecular structures of [RuCl2(η6-arene)(DMSO)], where η6-arene = 4-formylphenox- yacetyl-η6-benzylamide, and L2·DMSO are shown in Figures S14 and S15 in the Supporting Information, respectively. The structures of cis,cis-[RuIICl2(DMSO)2(L1)]·H2O and mer-[RuIICl(DMSO)3(L2−H)]·H2O are shown in Figure 1. Selected bond distances and angles are quoted in the legend. The complex cis,cis-[RuIICl2(DMSO)2(L1)]·H2O crystallized in the triclinic centrosymmetric space group P1̅ and mer- [RuIICl(DMSO)3(L2−H)]·H2O in the monoclinic space 12675 dx.doi.org/10.1021/ic201801e | Inorg. Chem. 2011, 50, 12669−12679