Ortho−Nitrosation of Anilines on a Ruthenium Hydridotris(pyrazolyl

Article pubs.acs.org/Organometallics

Ortho−Nitrosation of Anilines on a Ruthenium Hydridotris(pyrazolyl)borato Complex and Oxidation of the Resulting Coordinated Amine Groups Yasuhiro Arikawa,*,† Soseki Yamaguchi,† Yuji Otsubo,† Masayoshi Onishi,‡ and Keisuke Umakoshi† †

Division of Chemistry and Materials Science, Graduate School of Engineering, and ‡Department of Applied Chemistry, Faculty of Engineering, Nagasaki University, Bunkyo-machi 1-14, Nagasaki 852-8521, Japan S Supporting Information *

ABSTRACT: Nitrosation of anilines at the ortho position was found to proceed on a ruthenium hydridotris(pyrazolyl)borato (Tp) complex. Reactions of [TpRuCl2(NO)] (1) with primary anilines 4-NH2C6H4R (R = tBu, H) in the presence of excess Et3N in CH2Cl2 gave amine-chelated nitrosoarene complexes [TpRuCl{N(O)−C6H3R−NH2-κ2N,N}] (R = tBu (2a), H (2b)). Use of 2,4,6-trimethylaniline afforded an aryldiazenido complex [TpRuCl2{NNC6H2(Me)3}] (3) without forming the nitrosation product because of the introduction of the Me substituents at the ortho positions. On the other hand, in the case of secondary amines (N-methylanilines 4-NH(Me)C6H4R (R = tBu, H)), similar reactions gave amine-chelated nitroso complexes [TpRuCl{N(O)−C6H3R−NHMe-κ2N,N}] (R = t Bu (4a), H (4b)) and imine-chelated nitroso complexes [TpRuCl{N(O)−C6H3R−NCH2-κ2N,N}] (R = tBu (5a), H (5b)). Conversion of 4b into 5b by O2 was disclosed by 1H NMR monitoring. Moreover, oxidative reaction of 2a afforded an amide-chelated nitroso complex [TpRuCl{N(O)− C6H3(tBu)−NH-κ2N,N}] (6a) through one-proton release from the NH2 group.

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INTRODUCTION

Scheme 1

C-Nitrosation of arenes has been a well-known active research field of great interest because the resulting nitrosoarenes are biologically and synthetically valuable species.1 The chemical properties of nitrosoarene transition-metal complexes have also been a fascinating topic in connection with their π-conjugated systems.2 Several nitrosations with NO ligands on transitionmetal complexes through direct C−N bond formation have been described, but among them are only a few couplings with arenes: the reaction of [Cp2Zr(Ph)2] with NO,3 the reaction of [CpCr(NO)2(Ph)] with NOPF6,4 thermolysis of [Cp*W(NO)(Ph)2],5 and direct NO+ insertion of cyclometalated [Ru(Ĉ N)([9]aneS3)(L)]+ (C^N = deprotonated phenylpyridine; [9]aneS3 = 1,4,7-trithiacyclononane; L = solvent, t BuNC)6 and [Ru(C^N)([14]aneS4)]+ ([14]aneS4 = 1,4,8,11tetrathiacyclotetradecane).7 We recently reported two types of interesting nitrosation reactions (Scheme 1). One is the nitrosation of [TpRuCl2(NO)] (1) (Tp = hydridotris(pyrazolyl)borato) with 2-vinylpyridines, including C−H bond activation of a vinyl substituent.8 The other is a reaction of 1 with Et3N in the presence of PPh 3 to give a nitrosoethenolato complex, accompanied by oxidative dehydrogenation of Et3N, C−H bond activation, and enamine hydrolysis.9 © 2015 American Chemical Society

Herein we present the nitrosation of 1 with anilines at the ortho position and oxidative processes of the resulting aminechelated nitroso species. Related reactions of the nitrosylruthenium complex [RuCl(bpy)2(NO)](PF6)2 with anilines have been described by Meyer’s group, where treatment of the bis(bpy) complex with a primary aniline gave an aryldiazenido complex [RuCl(bpy)2(NNC6H5)](PF6)2, whereas nitrosation Received: December 12, 2014 Published: March 3, 2015 1056

DOI: 10.1021/om5012769 Organometallics 2015, 34, 1056−1061

Article

Organometallics with N-mono- and N-disubstituted anilines C6H5NMe(R) (R = H, Me) occurred at the para position to afford the nitroso complexes [RuCl(bpy) 2 {N(O)−C 6 H 4 NH(R)}](PF 6 ) (Scheme 2).10 Scheme 2

Figure 1. Molecular structure of 2a. Thermal ellipsoids are set at the 50% probability level. Hydrogen atoms except for amine protons have been omitted for clarity. Selected bond distances (Å) and angles (deg): Ru1−Cl1 = 2.3898(10), Ru1−N1 = 1.921(3), Ru1−N8 = 2.036(3), O1−N1 = 1.249(4), N1−C10 = 1.434(4), N8−C11 = 1.409(5), C10− C11 = 1.396(5), C10−C15 = 1.394(5), C11−C12 = 1.392(5), C12− C13 = 1.375(6), C13−C14 = 1.408(5), C14−C15 = 1.390(5), Ru1− N1−O1 = 128.6(2).

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RESULTS AND DISCUSSION Reactions of 1 with primary anilines 4-RC6H4NH2 (R = tBu, H) in the presence of excess Et3N in CH2Cl2 gave the aminechelated nitrosoarene complexes [TpRuCl{N(O)−C6H3R− NH2-κ2N,N}] (R = tBu (2a), H (2b)) in yields of 72% and 90%, respectively (Scheme 3a). In the absence of Et3N, the

distances of 2a are 2.036(3) and 1.249(4) Å, respectively. The structures were also confirmed by fast atom bombardment mass spectrometry (FAB-MS). Their formation mechanism should be chelation-assisted electrophilic aromatic nitrosation,10c,d,11 which probably involves initial coordination of the aniline nitrogen atom through chloride ligand replacement (Scheme 3b). These results are in contrast to those of the above-mentioned bis(bpy) ruthenium complex, which led to the formation of the aryldiazenido species.10a,b On the other hand, using 2,4,6trimethylaniline in the reaction with 1 afforded the aryldiazenido complex [TpRuCl2{NNC6H2(Me)3}] (3) in 63% yield without forming the nitrosation product (Scheme 4) because of the introduction of the Me substituents at the

Scheme 3. (a) Reactions of 1 with 4-NH2C6H4R (R = tBu, H) and (b) Proposed Mechanism for the Formation of 2

Scheme 4. Reaction of 1 with 2,4,6-Trimethylaniline

ortho positions. The 1H NMR spectrum of 3 indicates retention of the mesityl group. The structure was also confirmed by X-ray structural analysis (Figure 2). The Ru1− N1−N2 (166.41(16)°) and N1−N2−C10 (141.4(2)°) angles are comparable to those of the “singly bent” aryldiazenido complex [RuCl 3 (p-NNC 6 H 4 Me)(PPh 3 ) 2 ] (Ru−N−N, 171.9(5)°; N−N−C, 137.1(5)°).12 The Ru1−N1 (1.7991(14) Å) and N1−N2 (1.163(2) Å) bond distances are also similar to those of [RuCl3(p-NNC6H4Me)(PPh3)2] (Ru−N, 1.784(5) Å; N−N, 1.158(6) Å). However, similar piano-stool type aryldiazenido complexes, [CpRu(NNC6H4OMe)(PPh3)2](BF4)2 (Ru−N−N, 175.4(3)°; N−N−C, 158.9(4)°)13 and [TpRu(NNC6H5){P(OEt)3}2]2+ (Ru−N−N, 178.212°; N−N− C, 171.330°),14 show a near-linear arrangement of the Rubonded N2Ar ligand. Their total charge of 2+ should account for these differences. The IR spectrum of 3 shows a ν(NN)

reaction did not proceed. The IR spectra of 2a and 2b show the disappearance of the ν(NO) stretching vibration of the starting complex. The 1H NMR spectrum of 2a displays characteristic diastereotopic doublet proton signals at δ 5.59 and 4.40. These signals disappeared upon addition of D2O to the NMR sample and were assigned to NH2 protons. The structures were revealed by X-ray crystallographic analyses of 2a and 2b (Figure 1 and Figure S16 in the Supporting Information). The structures verified the presence of the bidentate chelation by the nitrosobenzylamine in which the two nitrogen atoms of the nitroso and amine groups are coordinated to the central ruthenium atom, indicating ortho C−H bond activation. The Ru1−N8 and N1−O1 bond 1057

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isolated and confirmed by X-ray crystallographic analysis (Figure 3). In 5a, the sum of angles around the N8 atom is

Figure 2. Molecular structure of 3. Thermal ellipsoids are set at the 50% probability level. Hydrogen atoms have been omitted for clarity. Selected bond distances (Å) and angles (deg): Ru1−Cl1 = 2.3663(5), Ru1−Cl2 = 2.3885(6), Ru1−N1 = 1.7991(14), N1−N2 = 1.163(2), N2−C10 = 1.419(3), Ru1−N1−N2 = 166.41(16), N1−N2−C10 = 141.4(2).

Figure 3. Molecular structure of 5a. One of the two independent molecules in the unit cell is shown. Thermal ellipsoids are set at the 50% probability level. Crystal solvent molecules and hydrogen atoms except for imine protons have been omitted for clarity. Selected bond distances (Å) and angles (deg): Ru1−Cl1 = 2.3726(17), Ru1−N1 = 1.911(5), Ru1−N8 = 2.065(5), O1−N1 = 1.250(7), N8−C20 = 1.301(8), N1−C10 = 1.442(8), N8−C11 = 1.432(8), C10−C11 = 1.383(8), Ru1−N1−O1 = 129.0(4), Ru1−N8−C20 = 129.1(4), Ru1− N8−C11 = 111.0(4), C11−N8−C20 = 119.7(5).

band at 1904 cm−1, which is at higher frequency than those of trichlorobis(phosphine)ruthenium complexes [RuCl3(NNAr′)(PAr3)2] (1856−1895 cm−1).15 Although the reaction of 1 with the tertiary amine N,Ndimethylaniline, C6H5NMe2, did not proceed, treatment with the secondary amine N-methylaniline, C6H5NH(Me), resulted in the formation of two nitroso species, the amine-chelated complex [TpRuCl{N(O)−C6H4−NHMe-κ2N,N}] (4b) and the imine-chelated complex [TpRuCl{N(O)−C6H4−N CH2-κ2N,N}] (5b) (Scheme 5). Although complete isolation of

nearly 360°, indicating an imine nitrogen (N8) atom. The bond lengths of N8−C20 (1.301(8) Å) and N1−O1 (1.250(7) Å) are typical for double bonds. Isolation of the imine-chelated species 5 indicates that oxidative dehydrogenation occurred. To study the oxidative conversion of 4 into 5, the CDCl3 solution of 4b was monitored by 1H NMR spectroscopy. Under an Ar atmosphere, the spectrum of 4b remained unchanged for 2 days at room temperature, but alteration to an O2 atmosphere caused the spectrum to change from that of 4b to that of 5b completely after 2 days, indicating the intermediacy of 4b. This oxidation reaction mechanism is unclear, but many ruthenium-mediated amine oxidations to give imines have been described in the literature.17 The oxidative formation of 5 prompted us to check the oxidation of 2a. Treatment of 2a with CuCl2 in air afforded the paramagnetic complex [TpRuCl{N(O)−C6H3(tBu)−NHκ2N,N}] (6a) in 83% yield (Scheme 6). The presence of the

Scheme 5. Reactions of 1 with N-Methylanilines 4NH(Me)C6H4R (R = tBu, H)

Scheme 6. Oxidative Reaction of 2a with CuCl2 in Air

4b was unsuccessful,16a the 1H NMR spectrum of 4b shows quartet and doublet signals at δ 7.00 and 2.34 for the proton and the methyl substituent, respectively, in the coordinated amine group.16b On the other hand, in the 1H NMR spectrum of 5b, two characteristic doublet signals (δ 8.64 and 7.40) are observed. The FAB-MS spectrum of 5b exhibits a parent molecular ion signal at m/z 484.1, showing a decrease by m/z 2 compared with that of 4b (m/z 486.1). The structure of 5b was confirmed by X-ray crystallographic analysis. Unfortunately, for the N,N-bidentate chelate {N(O)−C6H4−NCH2}, crystallographic disorder between the NO and NCH2 groups causes uncertainty in the metrical parameters. Thus, the reaction of 1 with the tBu analogue 4-tBuC6H4NH(Me) was carried out to give the amine-chelated complex [TpRuCl{N( O)−C6H3(tBu)−NHMe-κ2N,N}] (4a) and the imine-chelated complex [TpRuCl{N(O)−C6H3(tBu)−NCH2-κ2N,N}] (5a) (Scheme 5). The isolation of 4a failed because of the facile further transformation to 5a,16c while complex 5a was

paramagnetic Ru(III) ion is evidenced by the anisotropic rhombic electron paramagnetic resonance (EPR) spectrum at 77 K (g1 = 2.267, g2 = 2.191, g3 = 1.942; ⟨g⟩ = 2.14) (Figure S15 in the Supporting Information).18 The FAB-MS spectrum of 6a shows a decrease of 1 mass unit in the parent-ion molecular weight compared with 2a. Complex 6a was characterized by X-ray crystallographic analysis, which revealed coordination of nitroso and amido nitrogen atoms to the 1058

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commercially available and used without further purification. NMR spectra were recorded on a Varian Gemini-300 or a JEOL JNM-AL400 spectrometer. 1H NMR chemical shifts in CDCl3 or CD3CN are quoted with respect to TMS or the solvent signal, respectively, and 13 C{1H} NMR chemical shifts are quoted with respect to the solvent signal. Infrared spectra in KBr pellets were obtained on a JASCO FTIR-4100 spectrometer. FAB-MS spectra were recorded on a JEOL JMS-700N spectrometer. EPR spectra in the X band were recorded with a JEOL JES-FA200 spectrometer. Elemental analyses (C, H, N) were performed on a PerkinElmer 2400II elemental analyzer. Preparations of [TpRuCl{N(O)−C6H3R−NH2-κ2N,N}] (R = t Bu (2a), H (2b)). To a solution of [TpRuCl2(NO)] (1) (70 mg, 0.17 mmol) in CH2Cl2 (10 mL) were added 4-tert-butylaniline (51 mg, 0.34 mmol) and Et3N (172 mg, 1.70 mmol). After 1 h of stirring, the mixture was evaporated to dryness. The residue was subjected to column chromatographic separation with silica gel, eluting with CH2Cl2, to give [TpRuCl{N(O)−C6H3(tBu)−NH2-κ2N,N}] (2a) as an orange solid (65 mg, 72%). Aniline (22.4 mg, 0.24 mmol) and Et3N (121 mg, 1.20 mmol) were added to a solution of [TpRuCl2(NO)] (1) (50 mg, 0.12 mmol) in CH2Cl2 (10 mL). The mixture was stirred for 1 h and evaporated to dryness. The residue was subjected to column chromatography with silica gel, eluting with CH2Cl2/acetone (25/1), to give [TpRuCl{N( O)−C6H4−NH2-κ2N,N}] (2b) as an orange solid (51 mg, 90%). Complex 2a: IR (KBr, pellet): ν(BH) 2454 (m) cm−1. 1H NMR (CD3CN): δ 8.15 (d, 1H, 3JHH = 1.8 Hz, pz), 7.98 (d, 1H, 3JHH = 2.1 Hz, pz), 7.96 (dd, 1H, 3JHH = 2.3 Hz, 4JHH = 0.5 Hz, pz), 7.88−7.84 (m, 2H, tBu-C6H3), 7.72 (dd, 1H, 3JHH = 2.4 Hz, 4JHH = 0.7 Hz, pz), 7.52 (d, 1H, 3JHH = 8.2 Hz, tBu-C6H3), 7.37 (d, 1H, 3JHH = 1.7 Hz, pz), 6.49 (t, 1H, 3JHH = 2.1 Hz, pz), 6.33 (d, 1H, 3JHH = 2.0 Hz, pz), 6.21 (t, 1H, 3JHH = 2.2 Hz, pz), 6.12 (t, 1H, 3JHH = 2.2 Hz, pz), 5.59 (d, 1H, 2 JHH = 13 Hz, NH2), 4.40 (d, 1H, 2JHH = 13 Hz, NH2), 1.41 (s, 9H, t Bu). 13C{1H} NMR (CD3CN): δ 165.7 (tBu-C6H3), 153.3 (tBuC6H3), 144.8 (pz), 144.5 (pz), 141.1 (pz), 140.8 (tBu-C6H3), 138.0 (tBu-C6H3), 137.1 (pz), 135.6 (pz), 127.6 (tBu-C6H3), 127.2 (tBuC6H3), 108.8 (pz), 107.6 (pz), 107.3 (pz), 106.5 (pz), 35.6 (tBu), 31.7 (tBu). FAB-MS (m/z): 528.2 ([M]+), 492.2 ([M − Cl − 1]+). Anal. Calcd for C19H24N8BOClRu: C, 43.24; H, 4.58; N, 21.23. Found: C, 42.95; H, 4.16; N, 21.20. Complex 2b: IR (KBr, pellet): ν(BH) 2483 (w) cm−1. 1H NMR (CD3CN): δ 8.15 (d, 1H, 3JHH = 2.0 Hz, pz), 7.96−7.95 (m, 2H, pz and C6H4), 7.83 (d, 1H, 3JHH = 1.9 Hz, pz), 7.78 (dt, 1H, 3JHH = 7.6 Hz, 4JHH = 1.3 Hz, C6H4), 7.70 (d, 1H, 3JHH = 1.8 Hz, pz), 7.60 (d, 1H, 3 JHH = 7.9 Hz, C6H4), 7.44 (t, 1H, 3JHH = 7.2 Hz, C6H4), 7.36 (d, 1H, 3 JHH = 1.7 Hz, pz), 6.49 (t, 1H, 3JHH = 2.2 Hz, pz), 6.34 (d, 1H, 3JHH = 1.9 Hz, pz), 6.20 (t, 1H, 3JHH = 2.2 Hz, pz), 6.11 (t, 1H, 3JHH = 2.3 Hz, pz), 5.67 (d, 1H, 2JHH = 12 Hz, NH2), 4.48 (d, 1H, 2JHH = 12 Hz, NH2). 13C{1H} NMR (CD3CN): δ 165.8 (C6H4), 144.8 (pz), 144.6 (pz), 143.3 (C6H4), 141.2 (pz), 138.1 (pz), 137.2 (pz), 135.6 (pz), 130.5 (C6H4), 129.7 (C6H4), 127.8 (C6H4), 112.4 (C6H4), 107.7 (pz), 107.4 (pz), 106.6 (pz). FAB-MS (m/z): 472.0 ([M]+), 436.1 ([M − Cl − 1]+). Anal. Calcd for C15H16N8BOClRu: C, 38.20; H, 3.42; N, 23.76. Found: C, 38.01; H, 3.68; N, 23.32. Preparation of [TpRuCl2{NNC6H2(Me)3}] (3). A mixture of [TpRuCl2(NO)] (1) (70 mg, 0.17 mmol), 2,4,6-trimethylaniline (120 mg, 0.89 mmol), and Et3N (34 mg, 0.34 mmol) in CH2Cl2 (1.5 mL) was stirred for 2 days. After evaporation to dryness, the residue was subjected to column chromatography with silica gel, eluting with CH2Cl2/acetone (25/1), to give [TpRuCl2{NNC6H2(Me)3}] (3) as a dark brown solid (57 mg, 63%). Complex 3: IR (KBr, pellet): ν(BH) 2532 (w) cm−1, ν(NN) 1904 (s) cm−1. 1H NMR (CDCl3): δ 8.26 (d, 1H, 3JHH = 1.7 Hz, pz), 7.79 (d, 2H, 3JHH = 2.2 Hz, pz), 7.75 (dd, 2H, 3JHH = 2.4 Hz, 4JHH = 0.7 Hz, pz), 7.62 (dd, 1H, 3JHH = 2.2 Hz, 4JHH = 0.7 Hz, pz), 7.01 (s, 2H, C6H2(Me)3), 6.32 (t, 2H, 3JHH = 2.3 Hz, pz), 6.30 (t, 1H, 3JHH = 2.3 Hz, pz), 2.62 (s, 6H, C6H2(Me)3), 2.38 (s, 3H, C6H2(Me)3). 13C{1H} NMR (CDCl3): δ 144.3 (pz), 143.3 (C6H2(Me)3), 142.3 (pz), 137.8 (C6H2(Me)3), 136.3 (pz), 134.9 (pz), 130.0 (C6H2(Me)3), 124.8 (C6H2(Me)3), 107.1 (pz), 106.6 (pz), 21.8 (C6H2(Me)3), 20.5

ruthenium center (Figure 4). This indicates that oxidationinduced one-proton release from the NH2 ligation site

Figure 4. Molecular structure of 6a. Thermal ellipsoids are set at the 50% probability level. Hydrogen atoms except for the amide proton have been omitted for clarity. Selected bond distances (Å) and angles (deg): Ru1−Cl1 = 2.3813(7), Ru1−N1 = 1.9692(15), Ru1−N8 = 1.9706(16), O1−N1 = 1.258(2), N1−C10 = 1.399(3), N8−C11 = 1.344(3), C10−C11 = 1.421(3), C10−C15 = 1.404(3), C11−C12 = 1.424(3), C12−C13 = 1.369(3), C13−C14 = 1.430(3), C14−C15 = 1.386(3), Ru1−N1−O1 = 126.99(12).

occurred. The position of the hydrogen atom on the amide moiety was crystallographically located from the Fourier map. The six C−C bonds of the C6H3(tBu) ring in 6a exhibit the “four long/two short” distortion, indicating the contribution of a quinoid-like canonical structure.19 Compared with the structure of 2a, oxidation led to shortening of the N1−C10 (1.399(3) Å), N8−C11 (1.344(3) Å), and Ru−N8 (1.9706(16) Å) bond distances, but almost no change in the N1−O1 bond distance (1.258(2) Å).

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CONCLUSIONS Chelation-assisted nitrosation of anilines at the ortho position led to the nitrosobenzylamine species, except for the reactions with N,N-dimethylaniline or 2,4,6-trimethylaniline. Use of the latter led to the formation of the aryldiazenido complex [TpRuCl2{NNC6H2(Me)3}] (3). The electrophilic aromatic nitrosation of anilines usually occurs at the para position. The ortho selectivity in our system would support the proposal of initial coordination of the aniline nitrogen atom through chloride ligand replacement. The difficulty of coordination of tertiary amines to the metal may account for the unreactivity of N,N-dimethylaniline. In the case of secondary amines, oxidative dehydrogenation from amine- to imine-chelated species by O2 was disclosed. Moreover, oxidative reaction of the nitrosobenzylamine complex [TpRuCl{N(O)−C6H3(tBu)−NH2κ2N,N}] (2a) gave [TpRuCl{N(O)−C6H3(tBu)−NHκ2N,N}] (6a), indicating oxidation-induced one-proton release from the NH2 ligation site. Unexpectedly, in paramagnetic 6a, the unpaired electron is not delocalized over the π-conjugated nitrosobenzylamido moiety.

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EXPERIMENTAL SECTION

General Information. All reactions were carried out under N2 or Ar unless otherwise noted, and subsequent workup manipulations were performed in air. The starting materials [TpRuCl2(NO)]20 and 4-NH(Me)C6H4tBu21 were prepared according to the previously reported methods. Organic solvents and all other reagents were 1059

DOI: 10.1021/om5012769 Organometallics 2015, 34, 1056−1061

Article

Organometallics (C 6 H 2 (Me) 3 ). FAB-MS (m/z): 497.1 ([M − Cl] + ), 350.0 ([TpRuCl]+). Anal. Calcd for C18H21N8BCl2Ru: C, 40.62; H, 3.98; N, 21.05. Found: C, 40.18; H, 3.82; N, 20.71. Preparations of [TpRuCl{N(O)−C6H3R−NHMe-κ2N,N}] (R = t Bu (4a), H (4b)) and [TpRuCl{N(O)−C6H3R−NCH2-κ2N,N}] (R = tBu (5a), H (5b)). 4-tert-Butyl-N-methylaniline (55 mg, 0.34 mmol) and Et3N (170 mg, 1.68 mmol) were added to a solution of [TpRuCl2(NO)] (1) (70 mg, 0.17 mmol) in CH2Cl2 (10 mL). The mixture was stirred for 5 h and evaporated to dryness. The residue was subjected to column chromatography with silica gel, eluting with CH2Cl2 and CH2Cl2/acetone (50/1), to afford [TpRuCl{N(O)− C 6 H 3 ( t Bu)−NHMe-κ 2 N,N}] (4a) and [TpRuCl{N(O)− C6H3(tBu)−NCH2-κ2N,N}] (5a) (40 mg, 44%) as a dark redbrown solid. However, complete isolation of 4a was unsuccessful because of facile further transformation to 5a. To a solution of [TpRuCl2(NO)] (1) (70 mg, 0.17 mmol) in CH2Cl2 (10 mL) were added N-methylaniline (36.8 mg, 0.34 mmol) and Et3N (340 mg, 3.36 mmol). After 3 h of stirring, the mixture was evaporated to dryness. The residue was subjected to column chromatography with silica gel, eluting with CH2Cl2/acetone (100/ 1), to give [TpRuCl{N(O)−C6H4−NHMe-κ2N,N}] (4b) (18 mg, ∼22%) and [TpRuCl{N(O)−C6H4−NCH2-κ2N,N}] (5b) (29 mg, 35%) as a dark red-brown solid. Complex 4b was contaminated with a small amount of 5b. Complex 4a: 1H NMR (CDCl3): 8.13 (d, 1H, 3JHH = 1.8 Hz, pz), 6.61 (q, 1H, 3JHH = 5.8 Hz, NH), 6.05 (t, 1H, 3JHH = 2.2 Hz, pz), 2.36 (d, 3H, 3JHH = 6.2 Hz, Me), 1.41 (s, 9H, tBu). (Other resonance signals of 4a were unresolved because they overlap with those of 5a.) FAB-MS (m/z): 542.2 ([M]+). Complex 4b: IR (KBr, pellet): ν(BH) 2473 (m) cm−1. 1H NMR (CDCl3): δ 8.38 (d, 1H, 3JHH = 2.0 Hz, pz), 8.06 (dd, 1H, 3JHH = 8.0 Hz, 4JHH = 1.3 Hz, C6H4), 7.83 (d, 1H, 3JHH = 2.3 Hz, pz), 7.71 (d, 1H, 3 JHH = 2.4 Hz, pz), 7.61 (d, 1H, 3JHH = 2.4 Hz, pz), 7.50 (d, 1H, 3JHH = 1.9 Hz, pz), 7.45−7.39 (m, 2H, C6H4), 7.34 (dt, 1H, 3JHH = 7.5 Hz, 4 JHH = 1.4 Hz, C6H4), 7.00 (q, 1H, 3JHH = 5.9 Hz, NH), 6.35 (d, 1H, 3 JHH = 2.0 Hz, pz), 6.30 (t, 1H, 3JHH = 2.1 Hz, pz), 6.19 (t, 1H, 3JHH = 2.2 Hz, pz), 6.04 (t, 1H, 3JHH = 2.3 Hz, pz), 2.34 (d, 3H, 3JHH = 6.2 Hz, Me). 13C{1H} NMR (CDCl3): δ 163.7 (C6H4), 147.9 (C6H4), 143.9 (pz), 143.8 (pz), 139.9 (pz), 136.6 (pz), 135.6 (pz), 134.2 (pz), 129.9 (C6H4), 128.5 (C6H4), 124.4 (C6H4), 112.0 (C6H4), 107.0 (pz), 106.3 (pz), 105.9 (pz), 38.7 (Me). FAB-MS (m/z): 486.1 ([M]+), 450.1 ([M − Cl − 1]+). Complex 5a: IR (KBr, pellet): ν(BH) 2487 (m) cm−1. 1H NMR (CDCl3): δ 8.53 (d, 1H, 2JHH = 11 Hz, NCH2), 8.10 (d, 1H, 3JHH = 1.7 Hz, pz), 7.98 (d, 1H, 3JHH = 2.2 Hz, pz), 7.80 (d, 1H, 3JHH = 2.2 Hz, pz), 7.77−7.73 (m, 2H, tBu-C6H3), 7.65 (d, 1H, 3JHH = 8.3 Hz, t Bu-C6H3), 7.58 (d, 1H, 3JHH = 2.0 Hz, pz), 7.51 (d, 1H, 3JHH = 1.7 Hz, pz), 7.45 (d, 1H, 2JHH = 11 Hz, NCH2), 6.43 (t, 1H, 3JHH = 2.1 Hz, pz), 6.41 (d, 1H, 3JHH = 2.0 Hz, pz), 6.18 (t, 1H, 3JHH = 2.2 Hz, pz), 6.08 (t, 1H, 3JHH = 2.2 Hz, pz), 1.39 (s, 9H, tBu). 13C{1H} NMR (CDCl3): δ 163.2 (tBu-C6H3), 156.1 (tBu-C6H3), 155.8 (NCH2), 145.5 (tBu-C6H3), 143.6 (pz), 142.3 (pz), 140.0 (pz), 136.6 (tBuC6H3), 135.9 (pz), 134.6 (pz), 127.4 (tBu-C6H3), 114.9 (tBu-C6H3), 109.5 (pz), 107.2 (pz), 106.6 (pz), 106.0 (pz), 35.4 (tBu), 31.4 (tBu). FAB-MS (m/z): 540.2 ([M]+), 505.2 ([M − Cl]+). Anal. Calcd for C20H24N8BOClRu: C, 44.50; H, 4.48; N, 20.76. Found: C, 44.18; H, 4.43; N, 20.58. Complex 5b: IR (KBr, pellet): ν(BH) 2488 (m) cm−1. 1H NMR (CD3CN): δ 8.64 (d, 1H, 2JHH = 10 Hz, NCH2), 8.07 (d, 1H, 3JHH = 2.0 Hz, pz), 7.97−7.95 (m, 2H, pz and C6H4), 7.92 (dd, 1H, 3JHH = 8.1 Hz, 4JHH = 1.0 Hz, C6H4), 7.88 (dd, 1H, 3JHH = 2.5 Hz, 4JHH = 0.6 Hz, pz), 7.85 (dt, 1H, 3JHH = 8.1 Hz, 4JHH = 1.4 Hz, C6H4), 7.73 (dd, 1H, 3JHH = 2.4 Hz, 4JHH = 0.7 Hz, pz), 7.55 (dt, 1H, 3JHH = 8.2 Hz, 4 JHH = 1.1 Hz, C6H4), 7.40 (d, 1H, 2JHH = 10 Hz, NCH2), 7.35 (d, 1H, 3JHH = 2.0 Hz, pz), 6.51 (t, 1H, 3JHH = 2.2 Hz, pz), 6.49 (d, 1H, 3 JHH = 2.0 Hz, pz), 6.23 (t, 1H, 3JHH = 2.2 Hz, pz), 6.17 (t, 1H, 3JHH = 2.3 Hz, pz). 13C{1H} NMR (CD3CN): δ 163.7 (C6H4), 161.4 (N CH2), 148.9 (C6H4), 144.0 (pz), 143.4 (pz), 141.4 (pz), 137.8 (pz), 137.1 (pz), 135.7 (pz), 132.3 (C6H4), 131.1 (C6H4), 117.4 (C6H4),

112.2 (C6H4), 107.9 (pz), 107.6 (pz), 106.4 (pz). FAB-MS (m/z): 484.1 ([M]+), 449.1 ([M − Cl]+). Anal. Calcd for C16H16N8BOClRu: C, 39.73; H, 3.33; N, 23.17. Found: C, 39.65; H, 3.52; N, 22.96. Preparation of [TpRuCl{N(O)−C6H3(tBu)−NH-κ2N,N}] (6a). A mixture of [TpRuCl{N(O)−C6H3(tBu)−NH2-κ2N,N}] (2a) (30.0 mg, 0.057 mmol) and CuCl2 (8.0 mg, 0.059 mmol) in CH3CN (5.0 mL) was stirred for 40 h at room temperature in air. After evaporation, the residue was subjected to column chromatography with silica gel, eluting with CH2Cl2, to give a dark brown solid. Recrystallization from CH2Cl2/pentane afforded [TpRuCl{N(O)− C6H3(tBu)−NH-κ2N,N}] (6a) (25 mg, 83%). Complex 6a: IR (KBr, pellet): ν(BH) 2488 (m) cm−1. FAB-MS (m/z): 527.2 ([M]+), 492.2 ([M − Cl]+). Anal. Calcd for C19H23N8BOClRu: C, 43.32; H, 4.40; N, 21.27. Found: C, 43.27; H, 4.41; N, 21.18.

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ASSOCIATED CONTENT

S Supporting Information *

NMR and EPR spectra, X-ray crystallographic data, and CIF files for 2a, 2b, 3, 5a, and 6a. 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 JSPS KAKENHI Grant 22685008 and the priority research project of Nagasaki University. The authors are grateful to Prof. H. Nagashima, Dr. Y. Sunada, and K. Ideta (Kyushu University) for EPR measurements.

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DOI: 10.1021/om5012769 Organometallics 2015, 34, 1056−1061