benzimidazole rings: Structural diversity and catalysis

Journal Pre-proofs Research paper Ruthenium(II) complexes of pyridine-carboxamide ligands bearing appended benzothiazole/benzimidazole rings: Structural diversity and catalysis Paranthaman Vijayan, Samanta Yadav, Sunil Yadav, Rajeev Gupta PII: DOI: Reference:

S0020-1693(19)30944-2 https://doi.org/10.1016/j.ica.2019.119285 ICA 119285

To appear in:

Inorganica Chimica Acta

Received Date: Revised Date: Accepted Date:

30 June 2019 2 October 2019 15 November 2019

Please cite this article as: P. Vijayan, S. Yadav, S. Yadav, R. Gupta, Ruthenium(II) complexes of pyridinecarboxamide ligands bearing appended benzothiazole/benzimidazole rings: Structural diversity and catalysis, Inorganica Chimica Acta (2019), doi: https://doi.org/10.1016/j.ica.2019.119285

This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

© 2019 Published by Elsevier B.V.

Ruthenium(II) complexes of pyridine-carboxamide ligands bearing appended benzothiazole/benzimidazole rings: Structural diversity and catalysis Paranthaman Vijayan, Samanta Yadav, Sunil Yadav and Rajeev Gupta* Department of Chemistry, University of Delhi, Delhi 110 007, India

Corresponding Author E-mail: [email protected] (Rajeev Gupta) Phone: +91 – 11 – 2766 6646 Ext. 172 Website: http://people.du.ac.in/~rgupta/ ORCID: 0000-0002-3143-5643 1

Abstract A series of ruthenium(II) complexes (1-6) of pyridine-carboxamide ligands, HLBT/BI (HLBT = N(benzo[d]thiazol-2-yl)picolinamide and HLBI = N-(1H-benzo[d]imidazol-2-yl)picolinamide), have been synthesized. All Ru(II) complexes have been characterized by using various spectroscopic techniques (FTIR, UV-Visible, 1H, 13C, 31P NMR and ESI-MS), conductivity and elemental analyses. The solid-state structures of all Ru(II) complexes, except 2, were substantiated by the single crystal X-ray diffraction technique that revealed versatile coordination modes of two bidentate ligands varying between NN and NO modes. All Ru(II) complexes exhibited a distorted octahedral geometry with a bidentate ligand while other coordination sites are occupied by either anionic Cl or neutral co-ligands (CO, PPh3, CH3CN or (CH3)2SO). These well-defined ruthenium(II) complexes have been utilized as the homogeneous catalysts for the alkylation of amines using alcohols ensuing hydrogen borrowing strategy. Out of six complexes, 1 and 2 were found highly effective catalysts towards the N-alkylation of different amines with assorted alcohols. The alkylated products were obtained in excellent yields with good tolerance to a large variety of functional groups. To evaluate the role of putative Ruhydride species as the intermediate during the catalytic cycle, the respective RuH complexes (7 and 8) were synthesized by the reaction of complexes 1 and 2 with NaBH4. Both RuH

complexes

were

characterized

using

different

spectroscopic

techniques

and

crystallography. Importantly, both RuH complexes, 7 and 8, were directly able to alkylate imine using alcohol thus confirming the involvement of Ruhydride species as the intermediates during the proposed catalytic cycle. Keywords: Ruthenium(II) complexes; Pyridine-carboxamide ligands; Crystal structures; Coordination modes; Ruhydride complexes; N-alkylation

2

1. Introduction Construction of C-N bond is one of the most prominent and fundamental reactions in organic synthesis [1-3]. Alkylated amines are significant due to their utility in agrochemicals, dyes, polymers, pharmaceuticals and as the pharmacophores for the synthesis of bioactive molecules; such as Cinacalet, Resvertaral derivatives, R116010, etc. (Figure 1) [4,5]. Synthesis of Nalkylated amines using alcohols is not only attractive, greener and environmentally friendly [6] but also low-cost and alternative to traditional synthetic methods utilizing harsh alkyl halides [7]. R OH N H

R

R

Resvertaral derivatives H N

CH3 N

N

N

R116010

+ Base

Reduction

S

R1

Catalyst Oxidation

H3C

N H

R

OH

Catalyst-H2 N H

CF3

R

O

Imine formation R R1NH2

Cinacalet

N

R1

H2O

Figure 1. Representative examples for bioactive drugs and hydrogen borrowing methodology for the N-alkylation of amine. Traditional methods, exploited for the synthesis of alkylated amines, suffer due to low yield, limited substrate scope and high toxicity of many alkylated agents. Therefore, continuous efforts have been subjected into the transition metal-catalyzed N-alkylation reactions using alcohols through borrowing hydrogen (BH) or hydrogen auto transfer (HAT) strategies (Figure 1) [8-10]. For such reactions, many successful catalysts have been derived from using precious metals such as Rh, Ir, Ag, Au and Os whereas catalysts based on non-precious earth-abundant metals have met limited success [11] with the exception of a few selected cases involving Mn [11a], Co [11b] and Ni [11c]. In this context, ruthenium complexes have been found highly successful as the homogeneous catalysts in such catalytic reactions as the environmental-friendly and atom economically viable options [11d,k-m,12,13]. Pyridine-carboxamide has emerged as an exciting functional group for the design of stable and robust ligand systems for developing various catalysts [14-16]. Such features are 3

associated with excellent coordinating ability of pyridine-carboxamide based ligands together with good -donor ability of an anionic N-amidate group [17]. The benzothiazole and benzimidazole functional groups are versatile functional groups, not only effective in coordination chemistry but also in promoting various catalytic reactions [18]. In this work, we have utilized two pyridine-carboxamide based bidentate ligands for the synthesis of mononuclear ruthenium(II) complexes and focused on the N-alkylation of amines using alcohols. In particular, we present a series of ruthenium(II) complexes (1-6) of pyridine-carboxamide based potentially bidentate ligands having appended heterocyclic rings. Interestingly, these pyridine-carboxamide ligands chelate Ru(II) ion in their mono-anionic form either as the NO donors or as the NN donors (Scheme 1). Such Ru(II) complexes were then employed for the N-alkylation of assorted amines using various alcohols.

N

N M

N X

M O

O

N X

N

N

N N mode

N O mode

X = S or NH

Scheme 1. Two coordination modes of pyridine-carboxamide ligands observed in this work.

2. Results and discussion 2.1 Synthesis and Characterization This work presents two similar pyridine-carboxamide ligands, N-(benzo[d]thiazol-2yl)picolinamide (HLBT) and N-(1H-benzo[d]imidazol-2-yl)picolinamide (HLBI), synthesized using a previously reported procedure [19a]. These ligands were used for the synthesis of ruthenium(II) complexes, 1-6, by using prefabricated Ru(II) precursors; [RuHCl(CO)(PPh3)3)] [20a], [Ru(CO)2Cl2]n [20b] and cis-[RuCl2(DMSO)4] [20c] (Scheme 2). Both ligands, HLBT and HLBI, acted as the mono-anionic bidentate ones; however, provided NN donors in complexes 1 and 2 and NO donors in complexes 36. Interestingly, metal complexation in complexes 36 4

resulted in the migration of proton from amidic N-H group to the heterocyclic ring and as a result benzothiazole/benzimidazole rings are in their protonated form [19]. For complexes 1 and 2, a hydridic precursor was used, which deprotonated the amidic N-H group leading to NN coordination. In the remaining cases (3 – 6), the benzimidazole/benzothiazole moiety plausibly acted as a base resulting in a zwitterionic ligand with an electron-withdrawing azolium moiety. As a result, the O-atom becomes more nucleophilic and led to NO coordination. All metal complexes were obtained as the air-stable, non-hygroscopic, crystalline materials with solubility in common organic solvents. The identity of complexes 16 was established through the collective studies comprising of CHNS analyses, conductivity, FTIR, UV-Vis, NMR (1H, 31P)

13C,

and ESI-MS spectroscopy as well as crystallography.

O N E

[Ru(CO)ClH(E)3]

X N N

Ru

Toluene/ 110 oC

Cl

O

E X = S (1); NH (2); E = PPh3 N O

H N N

NH X

[Ru(CO)2Cl2]n

N

N Cl O

CH3OH/ 70 oC

X

Ru Z

O Y X ,Y, Z = S, CH3CN, Cl (3) X, Y, Z = NH, Cl, CO (4) X = S (HLBT); X = NH (HLBI)

H N

[Ru(DMSO)4Cl2]

N

CH3CH2OH/ 70 oC

N Cl O

X

Ru

O

S O Cl X = S (5); NH (6)

S

Scheme 2. Preparative routes for the synthesis of ruthenium(II) complexes 1-6 discussed in this work.

5

2.2 Spectroscopic studies FTIR spectra of complexes 14 (Fig. S1-S4) showed peaks for the terminally coordinated carbonyl group (ṽC≡O) between 1935-2060 cm−1. Such signals were observed at a slightly higher frequency than that of the precursor complexes [21a]. The ṽamide stretches (1627–1629 cm−1) were found red-shifted from their corresponding ligands in case of complexes 1 and 2. Such a fact suggests the involvement of deprotonated anionic Namidate in bonding [19]. However, ṽamide stretches for complexes 36 (Fig. S3-S6) were found between 1507-1535 cm-1 which were noted to be shifted to lower frequencies from their respective ligands; suggesting coordination of anionic Oamidate group to the ruthenium ion [19]. Further, stretches between 3205-3554 cm-1 are assigned to ṽN-H groups from the protonated heterocyclic rings for complexes 36. Such ṽN-H stretches are significantly different when compared to the corresponding ligands and convincingly assert that the protons have been migrated from amidic N-H group to the appended benzothiazole/benzimidazole ring [19]. The FTIR spectra of Ru(II) complexes therefore confirm mode of coordination of ligands to metal either via N-pyridyl and N-amidate (NN) or N-pyridyl and O-amidate (NO). The solution conductivity measurements exhibited non-electrolytic nature for all Ru(II) complexes [21b]. UV-visible spectra of complexes 1-6 (Fig. S9) in DMF displayed max between 294-370 nm and such bands are tentatively assigned to the LMCT transitions. The easiest characterization of the present Ru(II) complexes was through their 1H NMR spectra (Fig. S10-S17). For these complexes; pyridyl, benzothiazole/benzimidazole and triphenylphosphine protons were observed as doublets, triplets and multiplets in the range of 6.68-7.72 ppm whereas benzimidazole-NH groups were observed at 11.62-12.17 ppm [21c]. In complexes 5 and 6, CH3 groups of the coordinated DMSO were noted at 3.13-3.52 ppm.

13C-

NMR spectra of complexes 1-4 (Fig. S18-S23) showed C≡O resonances between 196.6-204.2 ppm that is comparable with other ruthenium(II) carbonyl complexes available in literature [21d]. In addition, signals between 44.7-50.1 ppm corresponded to the CH3 groups of sulphur coordinated DMSO for complexes 5 and 6. 31P NMR spectra (Fig. S24-S27) displayed one sharp singlet at 49.8-50.3 ppm for complexes 1 and 2; suggesting the presence of magnetically equivalent triphenylphosphine groups placed trans to each other [21a]. The ESI-MS spectra of complexes 1-6 showed the most abundant peak assigned to [MCl]+, [M2Cl]+ or [M+H+]+ species (Fig. S28-S38). In all cases, observed isotopic distribution patterns matched excellently to that of the simulation patterns (Fig. S28-S38). 6

2.3 Crystal Structures The analytical and spectroscopic data provided tentative information about the composition and molecular formulae but do not substantiate the coordination mode of the pyridine-carboxamide ligand and overall structure of Ru(II) complexes. Therefore, solid-state molecular structures of all Ru(II) complexes but 2 were determined by the single crystal X-ray diffraction analyses (Table 1). The crystal structures of Ru(II) complexes 1 and 36 along with partial atom numbering

scheme

are

shown

in

Figure

2.

Complex

1

was

synthesized

using

[Ru(H)Cl(CO)(PPh3)3)] precursor and therefore exhibited coordinated PPh3 groups. On the other hand, phosphine-free ruthenium(II) precursors, [Ru(CO)2Cl2]n and cis-[RuCl2(DMSO)4], were used for the synthesis of complexes 36 and therefore displayed the presence of assorted coligands. Interestingly, in complexes 36, both ligands HLBT and HLBI coordinated as the bidentate NO donors whereas NN donor mode was noted in 1. Complexes 1 and 3 crystallized in triclinic cell with Pī space group whereas complexes 46 crystallized in monoclinic cell with space groups, P21/n or P21/c. All Ru(II) complexes illustrated slightly distorted octahedral geometry where ligand HLBT/BI coordinated in a bidentate mode creating a five-membered chelate ring involving neutral Npyridyl and anionic Namidate (NN) or neutral Npyridyl and anionic Oamidate (NO) groups. The remaining coordination sites are occupied a combination of chloride ion(s), carbonyl(s), PPh3 group(s), DMSO(s) and CH3CN. Importantly, complexes 36 show protonated state of the appended benzothiazole/benzimidazole ring due to the migration of a proton from amidic N-H group to the appended heterocyclic ring during the synthesis [19]. The molecular structure of 1 displays ligand HLBT coordinating in NN mode whereas additional sites are occupied by two trans PPh3 groups, a CO and a chloride ion. The structures of complexes 3 and 4 are very similar except the associated ligand. In both cases, ligand coordinates in NO mode whereas two chloride ions and two neutral co-ligands complete the octahedral geometry. Interestingly, two chloride ions in complex 3 are present in cis position while they occupy trans position in 4 [23]. In complex 3, an acetonitrile molecule is present in place of CO in 4. The benzothiazole ring in 3 is mono-protonated while the benzimidazole ring in 4 is doubly-protonated. As a result of doubly-protonated benzimidazole ring, ligand-field strength of the chelating ligand reduces, making Ru(II) ion electron-deficient that allows coordination of two CO ligands in complex 4. Consequently, complexes 3 and 4 exhibited distorted octahedral geometry 7

based on CCl2N2O and C2Cl2NO coordination environment. Complexes 5 and 6 are nearly identical except the associated ligand. Both these complexes display NO chelating ligand in addition to two trans chloride ions and two cis DMSO molecules. The structures of 5 and 6 show that Ru(II) ion is present in S2Cl2NO coordination environment. In complex 1, Ru-Namidate distance was 2.115 Å whereas complexes 3 – 6 exhibited RuOamidate distances varying between 2.072 – 2.121 Å (Table 2). On the other hand, Ru-Npyridyl bond lengths were ranging between 2.117 – 2.154 Å for all six complexes. Complexes 1, 3 and 4 displayed Ru-CO distances at 1.868, 1.840 and 1.855/1.896 Å (Table 2). In all complexes, Ru-Cl bond distances were encompassing between 2.368 – 2.422 Å. The average Ru-Cl bond distances were slightly shorter than that of cis-[RuCl2(DMSO)4] precursor [22b]. Complex 3 had a coordinated CH3CN with a distance of 1.999 Å while complexes 5 and 6 exhibited Ru-SDMSO bond distances between 2.234 – 2.251 Å. The Ru-SDMSO bond distances, both for 5 and 6, were shorter than that of cis-[RuCl2(DMSO)4] precursor [22c]. Complex 1 displayed Ru–P distances of 2.394 and 2.426 Å [21d] for two trans positioned PPh3 groups maintaining P-Ru-P angle of 175.93 (Table S1). In complexes 4–6, two chloride atoms occupy trans position with Cl-Ru-Cl angles of 176.43, 173.21 and 172.85, respectively. In contrast, two cis-located chloride atoms in complex 3 exhibit an angle 91.82. The Npyridyl– Ru–CO angle was noted to be larger than that of Npyridyl–Ru–SDMSO angle (Table S1) due to steric hindrance caused by the methyl groups of DMSO. For all complexes, angle involving fivemembered chelate ring of amide-based ligand varied marginally, suggesting little difference as a result of NN versus NO coordinations.

8

1 P1 N1 Cl1

S1

O1

N2 N3 Ru1 C50 O2 P2

3

4

Cl2

N4

N2 N1

Ru1

Cl1

Cl2

O1 C1

N1

S1 O2

O3

N3

C2

Ru1

N2 O1 C1

N4 N3

O2

Cl1

5

Cl1

S1

N2 Cl1

O1

N1

S2

Ru1

N3

N2

S3

N1 O3

6

N3

Ru1

O2

O3

Cl2

S1 Cl2

O1

N4

S2 O2

Figure 2. Thermal ellipsoidal representations (40% probability) of complexes 1 and 36. Lattice solvent molecules are omitted for clarity whereas only selected hydrogen atoms are shown.

9

Table 1. X-ray data collection and structure refinement parameters for complexes 1 and 3-8. HLBT 5

HLBI

1

3

7

4

6

8

Empirical formula

C50H38ClN3O2 P2RuS

C18H15Cl2N5O2 RuS

C17H21Cl2N3O3 RuS3

C50H39N3O2P2 RuS

C17H10Cl2N5O 3Ru

C18H26Cl2N4O 4RuS2

C50H40N4O2P2 Ru

Formula weight

943.35

537.38

583.52

908.91

504.27

598.52

891.87

Temperature (K)

298(2)

273(2)

293(2)

298(2)

298(2)

293(2)

298(2)

Wavelength (Å)

0.71073

0.71073

0.71073

0.71073

0.71073

0.71073

0.71073

Crystal system

Triclinic

Triclinic

Monoclinic

Monoclinic

Monoclinic

Monoclinic

Monoclinic

Space group

Pī

Pī

P21/c

P21/n

P21/n

P21/c

P21/n

Unit cell dimensions a(Å)

12.0945(4)

8.1187(6)

12.0368(3)

10.8987(4)

10.2686(6)

10.7023(3)

13.1771(4)

b(Å)

12.4586(3)

11.9641(7)

11.7297(3)

16.1704(5)

12.0973(8)

9.9414(3)

18.7693(6)

c(Å)

17.1428(5)

12.2397(8)

15.8171(4)

24.0492(8)

15.7733(10)

25.7280(7)

17.1873(6)

α°

73.056(3)

74.092(3)

90

90

90

90

90

β°

78.839(3)

86.817(4)

91.623(2)

91.034(3)

91.326(2)

101.593(3)

102.858(4)

γ°

65.550(3)

70.785(3)

90

90

90

90

90

Volume (Å ) Z Density Mg/m3 (calculated) Absorption coefficient mm-1

2241.46(13)

1078.86(13)

2232.29(10)

4237.7(2)

1958.9(2)

2681.51(14)

4144.3(2)

2 1.398

2 1.654

4 1.736

4 1.425

4 1.720

4 1.483

4 1.429

0.570

1.095

1.247

0.539

1.102

0.968

0.502

F(000)

964 0.22 x 0.210 x 0.17 3.416 to 25.000° -14<=h<=14, -14<=k<=14, -20<=l<=20 27864

536 0.21 x 0.20 x 0.17 2.179 to 24.998° -9<=h<=9, -14<=k<=14, -14<=l<=14 22022

1176 0.32 x 0.15 x 0.10 3.386 to 29.564° -16<=h<=15, -16<=k<=16, -21<=l<=20 32420

1864 0.24 x 0.17 x 0.09 3.538 to 25.319° -15<=h<=15, -22<=k<=22, -33<=l<=33 11930

996 0.24 x 0.16 x 0.11 2.342 to 28.351° -13<=h<=13, -16<=k<=16, -21<=l<=21 87746

1216 0.20 x 0.18 x 0.17 3.421 to 24.998°. -12<=h<=12, -11<=k<=11, -30<=l<=30 32836

1832 0.22 x 0.15 x 0.12 3.316 to 25.000°. -15<=h<=15, -22<=k<=22, -20<=l<=20 17835

7888 [R(int) = 0.0282] 99.8 %

3797 [R(int) = 0.2031] 99.9 %

5715 [R(int) = 0.0335] 99.8 %

6777 R(int) = 0.0535 99.4 %

4900 [R(int) = 0.0257] 100.0 %

4705 [R(int) = 0.0388] 99.7 %

7289 [R(int) = 0.0320] 99.8 %

Full-matrix least-squares on F2

Full-matrix least-squares on F2

Full-matrix least-squares on F2

Full-matrix least-squares on F2

Full-matrix least-squares on F2

Full-matrix least-squares on F2

Full-matrix least-squares on F2

7888 / 0 / 541

3797 / 0 / 264

5715 / 0 / 262

6777 / 0 / 536

4900 / 0 / 261

4705 / 0 / 285

7289 / 0 / 540

1.019

1.027

1.026

0.849

1.097

1.001

0.716

R1 = 0.0267, wR2 = 0.0624 R1 = 0.0308, wR2 = 0.0645 0.488 and -0.411

R1 = 0.0790, wR2 = 0.1784 R1 = 0.1225, wR2 = 0.2013 1.250 and -1.320

R1 = 0.0311, wR2 = 0.0668 R1 = 0.0428, wR2 = 0.0728 0.420 and -0.416

R1 = 0.0531, wR2 = 0.1173 R1 = 0.1098, wR2 = 0.1547 0.436 and - 0.340

R1 = 0.0252, wR2 = 0.0606 R1 = 0.0301, wR2 = 0.0645 0.370 and -0.713

R1 = 0.0293, wR2 = 0.0681 R1 = 0.0332, wR2 = 0.0702 0.389 and -0.412

R1 = 0.0363, wR2 = 0.0943 R1 = 0.0456, wR2 = 0.1029 0.478 and -0.460

3

Crystal size (mm3) Theta range for data collection Index ranges Reflections collected Independent reflections Completeness to theta = 25° Refinement method Data / restraints / parameters Goodness of-fit on 2

F Final R indices [I>2sigma(I)] R indices (all data) Largest diff. peak and hole (e.Å-3)

10

Table 2. Selected bond lengths (Å) for complexes 1 and 3-8. 1

3

4

5

6

Ru(1)-C(50)

1.868(2)

Ru(1)-C(1)

1.839(10)

1.896(2)

Ru(1)-O(1)

2.1117(16)

2.1198(17)

Ru(1)-N(2)

2.1156(16)

Ru(1)-N(1)

2.154(7)

2.1175(15)

Ru(1)-N(1)

2.1222(18)

2.123(2)

Ru(1)-N(1)

2.1473(17)

Ru(1)-O(1)

2.073(6)

2.1209(13)

Ru(1)-S(1)

2.2337(6)

2.2372(7)

Ru(1)-P(1)

2.3936(5)

Ru(1)-Cl(1)

2.379(2)

2.3680(6)

Ru(1)-S(2)

2.2511(7)

2.2503(7)

Ru(1)-Cl(1)

2.4224(5)

Ru(1)-Cl(2)

2.397(2)

2.4012(6)

Ru(1)-Cl(1)

2.3991(7)

2.4139(7)

Ru(1)-P(2)

2.4257(5)

Ru(1)-N(3)

1.999(8)

------------

Ru(1)-Cl(2)

2.4202(7)

2.3960(7)

Ru(1)-C(2)

------------

1.855(2)

7

8

Ru(1)-N(1)

2.149(3)

2.130(2)

Ru(1)-N(2)

2.222(3)

2.208(2)

Ru(1)-P(1)

2.3764(11)

2.3356(7)

Ru(1)-P(2)

2.3658(11)

2.3708(7)

Ru(1)-C(50)

1.831(5)

-----------

Ru(1)-H(1A)

1.55(4)

-----------

Ru(1)-C(49)

------------

1.835(3)

Ru(1)-H(12)

------------

1.570(3)

2.4 Electrochemistry All six Ru(II) complexes (1-6) were subjected to electrochemical investigation in order to understand their redox behavior and extent of stabilization of +2 oxidation state of ruthenium ion (Figure S39). All six ruthenium complexes exhibited rich electrochemistry in the potential ranging from +1.1 V to 1.9 V (vs SCE) in DMF with a scan rate of 0.1 V s-1. For complexes 1, 5 and 6; reversible and/or quasi-reversible redox responses were observed in the positive potential region with E1/2 values of 1.11 (ΔE = 80 mV), 0.81 (ΔE = 130 mV) and 0.80 V (ΔE = 200 mV), respectively. Such responses are assigned to RuIII/RuII redox couple [24]. Complexes 24 showed irreversible oxidative responses with Epa at 1.07, 1.06 and 1.10 V, respectively for the RuIII/RuII redox couple [24b]. All six Ru(II) complexes additionally exhibited reductive responses in the negative potential region varying from 1.60 V to 2.00 V. Complexes 1 and 3 showed reversible and quasi-reversible redox responses at E1/2 1.81 V (ΔE = 80 mV) and 1.89 V (ΔE = 110 mV), respectively. The remaining complexes, 2 and 46, showed irreversible responses (Epc) at 1.84, 11

1.85, 1.83 and 1.91 V, respectively. Such responses are tentatively assigned to ligand-based reduction events originating from two different amide-based ligands [18c]. A close similarity in the reduction potentials suggests that two different chelating ligands behave in a similar manner. The cyclic voltammetric results suggest that the present pyridine-carboxamide ligands stabilize Ru(II) state to a large extent [24b]. 2.5 Catalytic properties The present redox-active ruthenium complexes (1-6) offering metal-coordinated labile sites, appended heterocyclic rings and protonated heterocyclic rings in metal’s vicinity offered notable catalytic opportunities. We attempted to investigate their catalytic abilities for the direct Nalkylation of amines by using alcohols. N-alkylation of amine using alcohol proceeds through insitu formed Ru-hydride species that carries out the imine hydrogenation. This reaction provides a greener approach to N-alkylated amines without using harsh chemicals and/or reagents [25-26]. To achieve this goal, all six ruthenium(II) complexes (1-6) were tested as the catalysts for a reaction between benzyl alcohol and 2-aminopyridine as the model substrates. In such a reaction; catalyst, catalyst-loading, solvent, base, temperature and time were varied in order to achieve optimized reaction conditions (Table 3). As a first set of control experiment, absence of a catalyst or a base did not produce any product (entries 1 and 2). The use of different Ru(II) precursors, as the catalysts, resulted in very poor yield (entries 3-5). Next, different bases were utilized; KOtBu, K2CO3, NaOH and KOH (entries 6–9) wherein KOH was found to be the most effective base (entry 9) while NaOH also showed decent results (entry 8). It is clear from entries 10-13 that toluene is the best solvent when compared to other solvents; benzene, DMF, dioxane and THF. Finally, remaining Ru(II) complexes, 2-6, were also tested as the catalysts (entries 1522) and a comparison asserts that all complexes are effective catalysts for the N-alkylation reaction; however, complexes 1 and 2 were the best. On decreasing the catalyst loading from 1mol% to 0.5-mol%; the product yield was significantly affected (entries 14, 18 and 20) and therefore 1-mol% catalyst load was used in the subsequent reactions. To rule out the possibility of generation of [Ru]-nanoparticles during the catalytic reaction and their potential role as the true catalyst, mercury poisoning test was performed [11a]. The presence of a drop of mercury during the catalytic reaction showed insignificant effect on the product yield. Thus, the present Ru(II) complexes functioned as the true catalysts and did not produce [Ru]-nanoparticles during the catalytic reactions. 12

Table 3. Control experiments for the optimization of catalytic reaction conditions.a Ru (0.5-1.0 mol%) Toluene, 100 0C N

NH2 + HO

NH N

H2O

Entry

Catalyst

Base

Solvent

Conversion/Yieldb

1

-

KOH

Toluene

0/0

2

1

-

Toluene

0/0

3

[RuHCl(CO)(PPh3)3]

KOH

Toluene

21/14

4

[Ru(CO)2Cl2]n

KOH

Toluene

17/9

5

cis-[RuCl2(DMSO)4]

KOH

Toluene

27/18

6

1

KOtBu

Toluene

15/ND

7

1

K2CO3

Toluene

24/10

8

1

NaOH

Toluene

81/69

9

1

KOH

Toluene

96/86

10

1

KOH

Benzene

40/18

11

1

KOH

DMF

0/0

12

1

KOH

Dioxane

20/ND

13

1

KOH

THF

25/ND

14

1c

KOH

Toluene

77/61

15

2

KOH

Toluene

95/83

16

2

NaOH

Toluene

77/65

17

3

KOH

Toluene

76/65

18

3c

KOH

Toluene

69/57

19

4

KOH

Toluene

91/82

20

4c

KOH

Toluene

65/54

21

5

KOH

Toluene

72/59

22

6

KOH

Toluene

90/82

aReaction

conditions: catalyst (1-mol%); 2-aminopyridine (1 mmol); benzyl alcohol (1.2 mmol); base (4 mmol); solvent (toluene, 5 mL); temperature (100 °C). bProduct conversion was determined by the gas chromatography whereas yield represents isolated product yield. cCatalyst (0.5 mol%). ND: Not determined. 13

Table 4. Scope of N-alkylation reactions by using various amines and assorted alcohols.a,b

R1

Ru Catalyst (1 mol%) Toluene, 100 0C, 12 hr R 1

R2

NH2 + HO

N H

R2

H2O

NH

NH N

S NH

S

Cl

NH N

N

N

4g, 91%

c

4b, 85%

H3CO

NH

NH

Cl H CO 3

4c, 93%

4m, 65% O

O

O

4d, 97%c

NH

4e, 99%c

O

4l, 77%

NH

4h, 90%

c

NH

4k, 75%

4f, 88%

NH

O

NH N

N

4a, 89%c S

H3CO

Cl

NH

Cl

4j, 96%

NH

4n, 75%

4i, 93%

NH

O

Cl

NH

4o, 82%

aReaction

conditions: catalyst 1 (1-mol%); amine (1 mmol); alcohol (1.2 mmol); toluene (5 mL); base (4 mmol); temperature (100 °C); Time (12 h). cIsolated yield. These optimized reaction conditions created opportunities for exploring N-alkylation reactions using assorted amines and alcohols. The optimization reaction conditions had asserted that complex 1 was the most effective out of six Ru(II) complexes; therefore, catalyst 1 was used to explore substrate scope and the results are summarized in Table 4. A variety of substituted amines such as para-anisidine, 3,4-(methylenedioxy)aniline and cyclohexyl amine were selectively alkylated using benzyl alcohol, 4-chlorobenzyl alcohol and naphthylmethyl alcohol to produce the assorted products in yield ranging from 65–99%, similar to the previously reported 14

examples [12e, 12f]. It is gratifying to note that both electron-donating and electron-withdrawing groups were well-tolerated to provide excellent yields of the products (4c-4e and 4h-4j). To our delight, use of heterocyclic-amines, such as 2-aminopyridine (4a, 4f, 4k) and 2aminobenzothiazole (4b, 4g, 4l) were equally effective. Notably, use of cyclohexyl amine also produced the corresponding products in excellent yields (4e, 4j, 4o). Similarly, steric hindrance from a bulky substrate, naphthylmethyl alcohol only resulted in moderately lower yield of the product (4k-4o). Importantly, a gram-scale reaction using cyclohexyl amine and benzyl alcohol was not only successful but also produced the desired product in nearly quantitative yield (Table 4, entry 4e). These reactions confirm remarkable catalytic performance of the present Ru(II) complexes in promoting N-alkylation reactions.

Cl Ru

OH

-(KCl + H2O)

KOH

N N H

O Ru

H

H OH

I

N N Ru

H

II

Ru

III N N H

H2N O

N H2O

H

Scheme 3. Tentative mechanistic pathway for the N-alkylation of amine using alcohol.

15

2.5.1 Mechanistic considerations Based on the present catalytic results and previously reported ruthenium-catalyzed N-alkylation reactions [25d], a tentative mechanism is proposed in Scheme 3. Reaction of catalyst 1 with benzyl alcohol in presence of a base in-situ generated the Ru(II)-alkoxide species (I) which upon -hydride elimination generates the Ru(II)-hydride species (II) and intermediate aldehyde. Dehydrative condensation of aldehyde with amine forms the imine species [25e]. Subsequently, coordination of imine followed by the insertion of Ru−H bond generates species III which upon alcoholysis yields the alkylated-amine as the final product while regenerating the Ru-alkoxide species (I) for further catalysis. The stability of intermediates III may depend on the steric and electronic properties of the imine or iminium ion [13e,27a,27b]. Unfortunately, we were not able to isolate the intermediate Ru-hydride species (II) during the catalytic reaction due to its fast reaction with imine species producing the final alkylated-amine product. However, to understand and evaluate the role of Ru-hydride species as an intermediate during the N-alkylation reaction; we attempted its direct synthesis. For this purpose, complexes 1 and 2 were treated with NaBH4 in ethanol (Scheme 4) [14c]. Importantly, this reaction produced the corresponding Ru-hydride complexes, 7 and 8, that were isolated and characterized by various spectroscopic techniques. For example, proton NMR spectra displayed the Ru-H signal at 13.01 and 12.86 ppm for complexes 7 and 8, respectively. Further, the RuH stretch for complexes 7 and 8 was observed at 2008 and 2010 cm-1, respectively. Finally, molecular structures of both complexes 7 and 8 were determined by the single crystal X-ray diffraction (Figure 4). In both cases, crystal structures clearly established the presence of RuH group whereas the remaining ligating sites were identical to that of complex 1 and 2, respectively. Essentially, coordinated chloride group in complexes 1 and 2 was replaced by the hydride in 7 and 8 during the reaction of complexes 1 and 2 with NaBH4. For 7 and 8, RuH bond distance was 1.55(4) and 1.57(3), respectively whereas other bonding parameters were more or less similar to that of its precursor complex 1 (Tables 2 and S1). O

O N E

X N N

Ru Cl E

NaBH4 Ethanol

O

N E

X N N

Ru H E

O

X = S (7); NH (8) E = PPh3

X = S (1); NH (2) E = PPh3

16

Scheme 4. Synthetic protocol for the preparation of RuH complexes 7 and 8 from complexes 1 and 2 using NaBH4 in EtOH.

7

P2

8

O1

S1

P1

N2 N1 N3 H1A Ru1C50 O2 P1

O1 N2

N4

N1 Ru1C50 H12 O2 N3 P2

Figure 4. Thermal ellipsoidal representations (40% probability) of complexes 7 and 8. Hydrogen atoms are omitted for clarity. With the proposed intermediate II in hand (as complexes 7 and 8); an important experiment was performed to confirm its role in the catalysis and to prove the reaction mechanism. The reaction of isolated (E)-N-benzylidenepyridin-2-amine, as a substrate, with complex 7 as a representative intermediate without base produced the alkylated amine product 4a in 75% yield [27b]. This reaction therefore proves that once Ruhydride species is generated during the catalytic reaction; it is capable of directly reacting with the in-situ formed imine species producing the amine product. This reaction further asserts that the role of the base is limited only during the generation of the Ru-alkoxide species.

3. Conclusion To conclude, a series of ruthenium complexes (1-6) of pyridine-carboxamide ligands, HLBT/BI, (HLBT = N-(benzo[d]thiazol-2-yl)picolinamide and HLBI = N-(1H-benzo[d]imidazol-2yl)picolinamide) were synthesized and thoroughly characterized. The crystal structures of these Ru(II) complexes revealed coordination of a bidentate ligand either in NN or NO mode. In these complexes, the Ru(II) ion exhibited a distorted octahedral geometry with a bidentate NN/ NO ligand while the remaining coordination sites were occupied by either anionic Cl or 17

neutral co-ligands (CO, PPh3, CH3CN or (CH3)2SO). These Ru(II) complexes were utilized as the homogeneous catalysts for the alkylation of amines using alcohols. Out of six complexes, 1 and 2 were found highly active catalysts towards the N-alkylation of different amines with assorted alcohols. Both these catalysts tolerated a wide range of functional and steric groups on the substrates and afforded the corresponding alkylated amines in excellent yields. To evaluate the role of putative RuH species as an intermediate during the catalytic cycle, the respective RuH complexes (7 and 8) were synthesized and characterized using various spectroscopic techniques and crystallography. Importantly, both RuH complexes, 7 and 8, were directly able to alkylate imine using alcohol thus confirming the involvement of Ruhydride species as the intermediates during the proposed catalytic cycle.

4. Experimental Section 4.1 Materials and Methods All high purity reagents were purchased from Sigma Aldrich Company and were used without further purification. Solvents were purified and/or dried according to the standard procedures [28]. All synthetic manipulations were routinely performed under an oxygen atmosphere unless otherwise noted. Thin-layer chromatography (TLC) was carried out on Merck 1.05554 aluminum sheets precoated with silica gel 60 F254 and the spots were visualized under the UV light. Column chromatography purifications were performed by using Merck silica gel 60 (0.063-0.200 mm). The ligands HLBT and HLBI were synthesized according to a previously reported method with slight modifications [19]. The prefabricated ruthenium(II) precursors, [RuHCl(CO)(PPh3)3], [Ru(CO)2Cl2]n and cis-[RuCl2(Me2SO)4], were synthesized according to the procedures reported in the literature [20a-20c]. The elemental analysis (C, H, N and S) data were obtained with an Elementar Analysen Systeme GmbH Vario EL-III instrument. The FTIR spectra were recorded with PerkinElmer Spectrum-two spectrometer having Zn-Se ATR. The absorption spectra were recorded either with PerkinElmer Lambda 25 or Lambda 950 spectrophotometers. The conductivity measurements were carried out with a digital conductivity bridge from Popular Traders, India (Model number: PT 825). The NMR (1H,

13C

and

31P)

spectral measurements were carried out

with a Jeol 400 MHz spectrometer with chemical shifts relative to TMS (1H and

13C)

and o-

phosphoric acid (31P). The organic products in catalysis were monitored by using PerkinElmer 18

Clarus-580 gas chromatograph equipped with an auto-injector, a flame ionization detector (FID) and Elite-5 column (0.25 mm ID, 30-meter length). The mass spectra were performed on an advanced Q-TOF mass spectrometer using electrospray ionization mode. The cyclic voltammetric (CV) experiments were performed using a CH instruments electrochemical analyzer (Model 1120A). The cell contained a glassy carbon electrode, a Pt wire auxiliary electrode and Ag+/Ag as the reference electrode. The stock solutions were prepared ca. 1mM as complexes and ca. 0.1 M TBAP as supporting electrolyte. Although, CV experiments were done using Ag+/Ag as the reference electrode; the potentials were corrected and are reported versus saturated calomel electrode (SCE) throughout the manuscript. 4.2 Synthesis of ruthenium(II) complexes [Ru(LBT)(CO)Cl(PPh3)2] (1) A suspension of [RuHCl(CO)(PPh3)3] (0.100 g) in 15 mL toluene was treated with ligand HLBT (0.0268 g) and the mixture was refluxed at 110 C which resulted in a color change from yellow to orange. The reaction was monitored by thin-layer chromatography (TLC) using silica coated aluminum sheets with a 95:5 mixture of chloroform/methanol as the mobile phase. After completion of the reaction, volume was reduced to half using rotary evaporator and diethyl ether was added until the precipitation was complete. The product was then collected by filtration and dried under vacuum. Single crystals suitable for X-ray analysis were obtained by the vapor diffusion of diethyl ether into a saturated dichloromethane solution of the complex. Yield: 0.074 g, 75%. MP: 205 °C; Anal. Cald. for: C50H38ClN3O2P2RuS: C, 63.66; H, 4.06; N, 4.45; S, 3.40%. Found: C, 63.11; H, 4.01; N, 4.36; S, 3.36%. FTIR spectrum (Zn-Se ATR, cm-1: 3052 (ṽC-H), 1935 (ṽC≡O), 1629 (ṽC=O), 755 (ṽC-S), 1433 (Ph-P-Ph). Conductivity (DMF, ca. 1 mM, 298 K): M = 2.5 Ω-1 cm2 mol-1. UV/Vis spectrum (DMF, λmax (ԑ, mol-1cm-1)): 438, 348, 303; 1H NMR spectrum (400 MHz, CDCl3) δ (ppm): 8.37 (d, J = 5.3 Hz, 1H), 8.03 (d, J = 7.7 Hz, 1H), 7.64 (dd, J = 14.7, 7.7 Hz, 2H), 7.56 (d, J = 7.7 Hz, 1H), 7.40 (d, J = 5.1 Hz, 12H), 7.28 (d, J = 7.3 Hz, 1H), 7.14 (d, J = 7.5 Hz, 1H), 7.08 (t, J = 7.3 Hz, 6H), 6.96 (t, J = 7.4 Hz, 12H), 6.68 (t, J = 6.6 Hz, 1H).

13C

NMR spectrum (101 MHz, CDCl3) δ (ppm): 204.21, 168.02, 164.45, 154.09,

150.20, 147.65, 137.01, 135.02, 133.80, 131.63, 131.52, 129.49, 127.65, 127.13, 124.66, 122.08, 120.82, 120.46.

31P

NMR spectrum (162 MHz, CDCl3) δ (ppm): 50.31 (s). Mass spectrum

(ESI+): m/z calcd. For [C50H38ClN3O2P2RuS] 943.3911, Found 910.1312 [M-Cl]+. 19

[Ru(LBI)(CO)Cl(PPh3)2] (2) This complex was synthesized using ligand HLBI (0.025 g) and [RuHCl(CO)(PPh3)3] (0.100 g) by using an identical method as described for 1. Recrystallization was accomplished from dichloromethane-diethyl ether. Yield: 0.074 g, 78%. MP: 198 °C; Anal. Cald. for: C50H39ClN4O2P2Ru: C, 64.83; H, 4.24; N, 6.05%. Found: C, 64.55; H, 4.01; N, 6.01%. FTIR spectrum (Zn-Se ATR, cm-1: 3589 (ṽNH), 3056 (ṽC-H), 1936 (ṽC≡O), 1627 (ṽC=O), 746 (ṽC-S), 1434 (Ph-P-Ph). Conductivity (DMF, ca. 1 mM, 298 K): M = 19.5 Ω-1 cm2 mol-1. UV/Vis spectrum (DMF, λmax (ԑ, mol-1cm-1)): 354, 293; 1H NMR spectrum (400 MHz, CDCl3) δ (ppm): 11.74 (s, 1H), 7.83 (d, J = 7.9 Hz, 1H), 7.75 (d, J = 7.7 Hz, 1H), 7.46 (m, 16H), 7.23 (s, 1H), 7.17 (m, 6H), 7.06 (m, 12H), 6.32 (t, J = 6.4 Hz, 1H). 13C NMR spectrum (101 MHz, CDCl3) δ 203.03, 168.11, 156.29, 154.40, 141.97, 135.46, 133.95, 133.03, 129.37, 129.24, 127.85, 127.76, 127.65, 125.14, 120.61, 120.00, 117.72, 109.67. 31P NMR spectrum (162 MHz, CDCl3) δ (ppm): 49.84 (s). Mass spectrum (ESI+): m/z calcd. For [C50H39ClN4O2P2Ru] 926.3408, Found 893.1789 [M-Cl]+2. [Ru(LBTH)(CO)(CH3CN)Cl2] (3) A mixture of [Ru(CO)2(Cl)2]n (0.050 g) and HLBT (0.0550 g) in CH3OH/CHCl3 (1:1 v/v; 15 mL) solvent mixtures was refluxed for 4 h at 65 C which resulted in a color change from yellow to orange. After completion of the reaction, the resultant mixture was filtered, reduced to 1/3rd volume by rotary evaporator and triturated with diethyl ether until the precipitation of solid was complete. The product was then collected by filtration and dried under vacuum. Single crystals suitable for X-ray analysis were obtained by the slow diffusion of diethyl ether to a acetonitrile solution of complex. Yield: 0.091 g, 85%. MP: 225 °C; Anal. Cald. for: C16H14Cl2N4O2RuS: C, 38.56; H, 2.83; N, 11.24; S, 6.43. Found: C, 38.42; H, 2.95; N, 11.02; FTIR spectrum (Zn-Se ATR, cm-1: 3281 (ṽNH), 3076 (ṽC-H), 1946 (ṽC≡O), 1649 (ṽC=O), 755 (ṽC-S). Conductivity (DMF, ca. 1 mM, 298 K): M = 18.06 Ω-1 cm2 mol-1. UV/Vis spectrum (DMF, λmax (ԑ, mol-1cm-1)): 334. 1H

NMR (400 MHz, DMSO-d6) δ (ppm): 9.16 (d, J = 5.1 Hz, 1H), 8.51 (d, J = 7.7 Hz, 1H), 8.38

(t, J = 7.8 Hz, 1H), 8.18 (d, J = 8.0 Hz, 1H), 7.99 – 7.95 (m, 1H), 7.70 (d, J = 8.1 Hz, 1H), 7.60 (d, J = 8.1 Hz, 1H), 7.50 (t, J = 7.3 Hz, 1H).

13C

NMR spectrum (101 MHz, CDCl3) δ (ppm):

196.62, 174.94, 171.27, 152.79, 150.68, 146.75, 140.82, 130.13, 129.97, 129.34, 127.16, 126.93, 124.59, 123.46, 113.67, 112.91, 111.58, 87.98. Mass spectrum (ESI+): m/z calcd. For [C16H14Cl2N4O2RuS] 498.35, Found 460.9364 [M-Cl]+.

20

[Ru(LBIH)(CO)2Cl2] (4) This complex was synthesized from ligand HLBI (0.0522 g) and [Ru(CO)2(Cl)2]n (0.0500 g) by using a procedure similar to that described for complex 3. Recrystallization was achieved by diffusing diethyl vapors to a acetonitrile solution of complex 4. Yield: 0.071 g, 82%. MP: 208 °C; Anal. Cald. for: C15H12Cl2N4O3Ru: C, 38.47; H, 2.58; N, 11.96. Found: C, 38.14; H, 2.76; N, 12.11; FTIR spectrum (Zn-Se ATR, cm-1: 3205 (ṽNH), 3065 (ṽC-H), 2060 (ṽC≡O), 1986 (ṽC≡O), 1535 (ṽC=O). Conductivity (DMF, ca. 1 mM, 298 K): M = 8.0 Ω-1 cm2 mol-1. UV/Vis spectrum (DMF, λmax (ԑ, mol-1cm-1)): 363. 1H NMR spectrum (400 MHz, DMSO-d6) δ (ppm): 9.08 (d, J = 5.3 Hz, 1H), 8.43 (d, J = 7.4 Hz, 1H), 8.31 (t, J = 8.4 Hz, 1H), 7.95 – 7.83 (m, 2H), 7.61 (dd, J = 6.0, 3.2 Hz, 1H), 7.38 (dd, J = 6.0, 3.2 Hz, 1H), 7.17 (dd, J = 5.9, 3.2 Hz, 1H), 3.85 (s, 3H). 13C NMR spectrum (101 MHz, CDCl3) δ (ppm): 199.26, 198.03, 169.63, 166.10, 154.62, 152.98, 140.27, 133.48, 128.83, 126.15, 125.99, 122.96, 121.85, 120.18, 89.33. Mass spectrum (ESI+): m/z calcd. For [C15H12Cl2N4O3Ru] 396.9875, Found 396.9865 [M-2Cl]+. [Ru(LBTH)(Cl)2(Me2SO)2] (5) A solution of HLBT (0.0263 g) in 10 mL CH3OH/CHCl3 (1:1 v/v) was added dropwise to a boiling solution of cis-[Ru(Cl)2(Me2SO)4] (0.0500 g) in an ethanol/dichloromethane (1:1, 10 mL). The solution was refluxed for 6 h which resulted in a color change from light orange to dark red. After completion of the reaction, solution was filtered, and the filtrate was left for slow evaporation. After four days, yellowish orange colored crystals suitable for X-ray diffraction were obtained. Yield: 0.054 g, 90%. MP: 230 °C; Anal. Cald. for: C17H23Cl2N3O3RuS3: C, 34.87; H, 3.96; N, 7.18; S, 16.43. Found: C, 34.41; H, 4.01; N, 7.02; S, 16.22. FTIR spectrum (Zn-Se ATR, cm-1: 3554 (ṽNH), 2989 (ṽC-H), 1507 (ṽC=O) 1080 (ṽS=O) 758 (ṽC-S). Conductivity (DMF, ca. 1 mM, 298 K): M = 8.8 Ω-1 cm2 mol-1. UV/Vis spectrum (DMF, λmax (ԑ, mol-1cm-1)): 435, 343. 1H

NMR spectrum (400 MHz, DMSO-d6) δ (ppm): 10.25 (d, J = 5.1 Hz, 1H), 8.46 (d, J = 7.1

Hz, 1H), 8.17 (t, J = 8.4 Hz, 1H), 8.07 (d, J = 7.8 Hz, 1H), 7.84 (t, J = 6.6 Hz, 1H), 7.65 (d, J = 7.9 Hz, 1H), 7.58 (t, J = 7.6 Hz, 1H), 7.47 (d, J = 7.5 Hz, 1H), 3.52 (s, 6H), 3.13 (s, 2H), 2.50 (s, 4H).

13C

NMR spectrum (101 MHz, CDCl3) δ (ppm): 177.83, 156.88, 154.06, 151.08, 142.42,

141.04, 139.47, 130.99, 128.21, 125.41, 123.26, 113.34, 87.28, 50.11, 46.50, 44.71. Mass spectrum (ESI+): m/z calcd. For [C17H23Cl2N3O3RuS3] 585.55, Found 547.9483 [M-Cl]+.

21

[Ru(LBIH)(Cl)2(Me2SO)2] (6) This complex was synthesized from ligand HLBI (0.0522 g) and cis-[Ru(Cl)2(DMSO)4] (0.0500 g) by using a procedure similar to that described for complex 5. Recrystallization was attained by leaving the filtrate for slow evaporation. Yield: 0.105 g, 85%. MP: 221 °C; Anal. Cald. for: C17H24Cl2N4O3RuS2: C, 35.92; H, 4.26; N, 9.86; S, 11.28. Found: C, 35.47; H, 4.38; N, 9.68; S, 11.04. FTIR spectrum (Zn-Se ATR, cm-1: 3353 (ṽNH), 3066 (ṽC-H), 1515 (ṽC=O) 1054 (ṽS=O) 735 (ṽC-S). Conductivity (DMF, ca. 1 mM, 298 K): M = 8.9 Ω-1 cm2 mol-1. UV/Vis spectrum (DMF, λmax (ԑ, mol-1cm-1)): 448, 331. 1H NMR spectrum (400 MHz, DMSO-d6) δ (ppm): 12.17 (s, 1H), 10.23 (d, J = 4.8 Hz, 1H), 8.33 (d, J = 7.8 Hz, 1H), 8.08 (td, J = 7.6, 1.4 Hz, 1H), 7.75 (ddd, J = 7.3, 5.7, 1.5 Hz, 1H), 7.50 (dd, J = 6.0, 3.2 Hz, 2H), 7.33 (dd, J = 6.0, 3.2 Hz, 2H), 3.38 (s, 6H), 3.13 (s, 6H).

13C

NMR spectrum (101 MHz, CDCl3) δ (ppm): 175.68, 155.61, 154.68, 151.89,

141.09, 138.36, 1329.87, 127.42, 126.19, 124.52, 124.10, 112.69, 87.25, 49.13, 46.09, 45.36. Mass spectrum (ESI+): m/z calcd. For [C17H24Cl2N4O3RuS2] 568.50, Found 568.5648 [M+]. [Ru(LBT)(H)CO(PPh3)2] (7) A methanolic solution of NaBH4 ( 0.019 g) was added to a solution of complex 1 (0.100 g) in methanol under the magnetic stirring that was continued for 6 h. After completion of the reaction, reaction mixture was passed through a pad of celite in a medium porosity frit and left for evaporation that afforded crystalline product. Yield: 0.075 g, 75%. MP: 205 °C; Anal. Cald. for: C50H38ClN3O2P2RuS: C, 66.07; H, 4.32; N, 4.62; S, 3.53%. Found: C, 66.42; H, 4.09; N, 4.36; S, 3.36%. FTIR spectrum (Zn-Se ATR, cm-1: 3025 (ṽC-H), 2008 (ṽRu-H) 1916 (ṽC≡O), 1597 (ṽC=O), 755 (ṽC-S), 1423 (Ph-P-Ph). Conductivity (DMF, ca. 1 mM, 298 K): M = 5.5 Ω-1 cm2 mol-1. UV/Vis spectrum (DMF, λmax (ԑ, mol-1cm-1)): 426, 331, 271; 1H NMR spectrum (400 MHz, CDCl3): 13.01 (t, J = 20.4 Hz, 1H), δ 8.02 (d, J = 8.0 Hz, 1H), 7.84 (d, J = 7.7 Hz, 1H), 7.76 (d, J = 7.7 Hz, 1H), 7.49 – 7.42 (m, 13H), 7.39 (d, J = 6.7 Hz, 2H), 7.28 – 7.22 (m, 2H), 7.17 (t, J = 7.3 Hz, 6H), 7.04 (t, J = 7.5 Hz, 12H), 6.27 (t, J = 6.3 Hz, 1H). 31P NMR spectrum (162 MHz, CDCl3) δ (ppm): 49.51 (s). Mass spectrum (ESI+): m/z calcd. For [C50H39ClN4O2P2Ru] 908.9461, Found 910.1312 [M+H]. [Ru(LBI)(CO)(H)(PPh3)2] (8) This complex was synthesized from complex 2 by using a procedure similar to that described for complex 7. Recrystallization was accomplished by diffusing vapors of diethyl ether to a dichloromethane solution of complex 8. Yield: 0.070 g, 72%. MP: 214 °C; Anal. Cald. for: 22

C50H40N4O2P2Ru: C, 67.33; H, 4.52; N, 6.28%. Found: C, 67.01; H, 4.41; N, 6.18%. FTIR spectrum (Zn-Se ATR, cm-1: 3589 (ṽNH), 3056 (ṽC-H), 2010 (ṽRu-H), 1936 (ṽC≡O), 1627 (ṽC=O), 746 (ṽC-S), 1434 (Ph-P-Ph). Conductivity (DMF, ca. 1 mM, 298 K): M = 16.1 Ω-1 cm2 mol-1. UV/Vis spectrum (DMF, λmax (ԑ, mol-1cm-1)): 429, 330, 281; 1H NMR spectrum (400 MHz, CDCl3) δ (ppm): 12.86 (t, J = 20.2 Hz, 1H), 11.74 (s, 1H), 7.82 (d, J = 8.2 Hz, 1H), 7.75 (d, J = 7.8 Hz, 1H), 7.50 – 7.40 (m, 17H), 7.18 (t, J = 7.4 Hz, 5H), 7.05 (t, J = 7.6 Hz, 13H), 6.32 (t, J = 6.6 Hz, 1H). 31P NMR spectrum (162 MHz, CDCl3) δ (ppm): 47.00 (s). Mass spectrum (ESI+): m/z calcd. For [C50H40N4O2P2Ru] 892.1670, Found 893.1789 [M+H]. 4.3 Typical procedure for N-alkylation of aromatic amines with alcohols A 10 mL round-bottomed flask, with a stirring bar, was charged with 1-mol % of ruthenium(II) catalyst, 1 mmol of amine, 1.2 mmol of alcohol, 4 mmol of KOH and 3 mL of toluene. The reaction mixture was heated at 100 oC with stirring for 10 h on an oil bath. Upon completion (as monitored by TLC), the reaction mixture was cooled to room temperature, quenched with water (3 mL) and the organic products were extracted with ethyl acetate (3 x 10 mL). The combined organic layers were dried over anhydrous sodium sulphate; passed through a pad of celite using ethyl acetate and concentrated by rotary evaporator to afford the crude organic product. This product was purified by using preparative thin layer chromatography using 5% ethyl acetatehexanes using as the eluent. The product conversion was determined by GC whereas a few representative compounds were characterized by 1H NMR spectroscopy (see Figure S40-S44; Supplementary Information). The reported isolated yields are an average of two runs. 4.4 Characterization data of few representative products: 3.3.1.1. N-benzylpyridin-2-amine: Yield: 160 mg (89 %); 1H NMR (400 MHz, CDCl3) δ 8.03 (d, J = 5.0 Hz, 2H), 7.31 (d, J = 6.5 Hz, 2H), 7.25 (d, J = 7.7 Hz, 1H), 6.56 (dd, J = 15.3, 8.7 Hz, 2H), 6.43 (d, J = 8.3 Hz, 1H), 6.33 (d, J = 8.4 Hz, 1H), 5.34 (s, 1H), 4.45 (d, J = 5.4 Hz, 2H). (Figure S40). 3.3.1.2. N-benzylbenzo[d]thiazol-2-amine: Yield: 150 mg (85%); Colorless solid, 1H-NMR (400 MHz, CDCl3) δ 7.57 (d, J = 7.9 Hz, 1H), 7.48 (d, J = 8.1 Hz, 1H), 7.41 – 7.24 (m, 6H), 7.08 (t, J = 7.9 Hz, 1H), 6.13 (s, 1H) (Figure S41). 3.3.1.3. N-Benzyl-4-methoxyaniline: Yield: 191 mg (93%); Yellow oil; 1H-NMR (400 MHz, CDCl3) δ 8.47 (s, 1H), 7.88 (s, 2H), 6.93 (d, J = 8.7 Hz, 2H), 6.71 (d, J = 8.8 Hz, 2H), 6.64 (d, J = 8.7 2H), 4.66 (s, 2H), 3.81 (s, 3H) (Figure S42). 23

3.3.1.4. N-Benzylbenzo[d][1,3]dioxol-5-amine: Yield : 204 mg (97%); White solid; 1H NMR (400 MHz, CDCl3) δ 7.87 (dd, J = 6.8, 2.9 Hz, 5H), 6.64 (d, J = 8.3 Hz, 1H), 6.28 – 6.24 (m, 1H), 6.06 (dd, J = 8.3, 2.3 Hz, 1H), 5.82 (s, 2H), 4.67 (s, 2H) (Figure S43). 3.3.1.5. N-(benzo[d][1,3]dioxol-5-ylmethyl)naphthalen-2-amine: Yield: 180 mg (75%); 1H NMR (400 MHz, CDCl3) δ 8.01 (s, 3H), 7.85 – 7.78 (m, 4H), 7.49 – 7.45 (m, 3H), 4.86 (s, 2H), 3.48 (s, 2H) (Figure S44). 4.5 X-ray crystal structure determination Suitable single crystals were mounted on a glass fiber with epoxy cement. X-ray data of the samples were collected on Oxford CCD diffractometer having X-calibur sapphire measurement device at 273-293(2) K having graphite monochromated Mo-Kα radiation source (λ=0.71073 Å) [28]. The data collection, cell refinement and reduction steps were done by CrysAlisPro version 1.171.33.49b. The structures were initially solved by the direct methods using SIR-92 program and were further refined by the full matrix least square techniques on F2 using SHELXL2016/2018 [29]. All calculations were carried out with WinGX crystallographic package [30]. All non-hydrogen atoms were located from the difference Fourier map and refined anisotropically. All hydrogen atoms were fixed by HFIX at ideal positions and were included in the refinement process using riding model with isotropic thermal parameters. The crystallographic data collection and structure refinement parameters are provided in Table 1.

Acknowledgements RG acknowledges Council of Scientific & Industrial Research (01(2841)/16/EMR-II), New Delhi for the financial support. PV thanks SERB, New Delhi for the award of National Postdoctoral Fellowship (PDF/2016/000011). Authors thank CIF-USIC of this university and IIT Ropar for the instrumental facilities including crystallographic data collection.

Appendix A. Supplementary data Supplementary data include figures for FTIR, UV-Vis, NMR (1H, 13C and 31P) and mass spectra; and cyclic voltammograms of Ru(II) complexes and 1H NMR spectra of a few representative organic products. CCDC Nos. 1937358-1937364. Supplementary data to this article can be found online at -----------------.

24

References 1. (a) C. S. Yeung, V. M. Dong, Chem. Rev. 111 (2011) 1215–1292. (b) G. Guillena, D. J. Ramon, M. Yus, Chem. Rev. 110 (2010) 1611–1641 (c) S. Bahn, S. Imm, L. Neubert, M. Zhang, H. Neumann, M. Beller, ChemCatChem 3 (2011) 1853–1864. 2. (a) T. C. Nugenta, M. El-Shazlya, Adv. Synth. Catal. 352 (2010) 753-819. (b) Modern Amination Methods; A. Ricci, Ed. Wiley-VCH: Weinheim (2000). (c) Amino Group Chemistry: From Synthesis to the Life Sciences, A. Ricci, Ed., Wiley-VCH, Weinheim. (2008). (d) Amines: Synthesis, Properties, and Applications, Lawrence, S. A. Ed., Cambridge University, Cambridge (2006). 3. (a) W. Zhou, M. Fan, J. Yin, Y. Jiang, D. Ma, J. Am. Chem. Soc. 137 (2015) 11942–11945. b) D.S. Surry, S.L. Buchwald, Angew. Chem. Int. Ed. 47, (2008) 6338–6361. 4. (a) J. L. McGuire, Pharmaceuticals: Classes, Therapeutic Agents, Areas of Application; Wiley-VCH: Weinheim, Germany, (2000) 1-4. (b) A. R. Cartolano, G. A. Vedage, In KirkOthmer Encyclopedia of Chemical Technology; John Wiley & Sons, Inc. New York, 2 (2004) 476-498. 5. (a) S. Elangovan, J. Neumann, J. Baptiste Sortais, K. Junge, C. Darcel, M. Beller, Nat. Commun. 7 (2016) 12641-12657. (b) S. Gomez, J. A. Peters, T. Maschmeyer, Adv. Synth. Catal. 344 (2002) 1037-1057. (c) R. N. Salvatore, C. H. Yoon, K. W. Jung, Tetrahedron 57 (2001) 7785-7811. 6. (a) S. Pan, T. Shibata, ACS Catal. 3 (2013) 704-712. (b) S. Bahn, S. Imm, L. Neubert, M. Zhang, H. Neumann, M. Beller, ChemCatChem 3 (2011) 1853-1864. (c) J. Norinder, A. Börner, ChemCatChem 3, (2011) 1407-1411. (d) G. E. Dobereiner, R. H. Crabtree, Chem. Rev. 110 (2010) 681-703. 7. (a) R. N. Salvatore, A. S. Nagle, K. W. Jung, J. Org. Chem., 2002, 67, 674-683. (b) C. Chiappe, D. Pieraccini, Green Chem. 5 (2003) 193-197. 8. (a) M. H. S. A. Hamid, P A. Slatford, J. M. J. Williams, Adv. Synth. Catal. 349 (2007) 15551564. (b) T. D. Nixon, M K. Whittlesey, J. M. J. Williams, Dalton Trans. 5 (2009) 753-762. 9. (a) A. J. A. Watson, J. M. J. Williams, Science, 329 (2010) 635-636. (b) C. Gunanathan, D. Milstein, Science, 341 (2013) 249-260. (c) M. Pera-Titus, F. Shi, ChemSusChem, 2014, 7, 720-722. (d) K. Shimizu, M. Nishimura, A. Satsuma, ChemCatChem 1 (2009) 497-503.

25

10. (a) G. Guillena, D. J. Ramón, M. Yus, Chem. Rev. 110 (2010) 1611-1641. (b) T. D. Nixon, M. K. Whittlesey, J. M. J. William, Dalton Trans. 5 (2009) 753-762. (c) F. Aloso, F. Foubelo, J. C. Gonzalez-Gomez, R. Martınez, D. J. Ramon, P. Riente, M. Yus, Mol. Diversity, 14 (2010) 411–424. (d) R. H. Crabtree, Organometallics, 30 (2011) 17-19. 11. (a) A. Mukherjee, A. Nerush, G. Leitus, L. J. W. Shimon, Y. B. David, N. A. E. Jalapa, D. Milstein, J. Am. Chem. Soc. 138 (2016) 4298-4301. (b) M. Vellakkaran, K. Singh, D. Banerjee ACS Catal. 7 (2017) 8152-8158. (b) S. Rosler, M.Ertl, T. Irrgang, R. Kempe, Angew. Chem. Int. Ed. 54 (2015) 15046-15050. (d) R. Kawahara, K.-I. Fujita, R. Yamaguchi, J. Am. Chem. Soc. 132 (2010) 15108-15111. (e) R. Kawahara, K.-I. Fujita, R. Yamaguchi, Adv. Synth. Catal. 353 (2011) 1161-1168. (f) N. Zotova, F. J. Roberts, G. H. Kelsall, A. S. Jessiman, K. Hellgardt, K. K. M. Hii, Green Chem. 14 (2012) 226-232. (g) M. Dixit, M. Mishra, P. A. Joshi, D. O. Shah, Catal. Commun. 33 (2013) 80-83. (h) Y. S. Zhao, S. W. Foo, S. Saito, Angew. Chem., Int. Ed. 50 (2011) 3006-3009. (i) K. Shimizu, K. Kon, W. Onodera, H. Yamazaki, J. N. Kondo, ACS Catal. 3 (2013) 112-117. (i) M. Bertoli, A. Choualeb, A. J. Lough, B. Moore, D. Spasyuk, D. G. Gusev, Organometallics 30 (2011) 3479-3482. (j) P. Satyanarayana, G. M. Reddy, H. Maheswaran, M. L. Kantam, Adv. Synth. Catal. 2013, 355, 1859-1867. (k) F. E. Fernandez, C. Puerta, P. Valerga, Organometallics 31 (2012) 6868-6879. (l) A. J. A Watson, A. C. Maxwell, J. M. J. Williams, J. Org. Chem. 76 (2011) 2328-2331. (m) R. Cano, D. J. Ramon, M. Yus, J. Org. Chem. 76 (2011) 5547-5557. 12. (a) M. H. S. A. Hamid, C. L. Allen, G. W. Lamb, A. C. Maxwell, H. C. Mayturn, A. J. A. Watson, J. M. J. J. Williams, J. Am. Chem. Soc. 131 (2009) 1766-1774. (b) A. Tillack, D. Hollmann, D. Michalik, M. Beller, Tetrahedron Lett. 47 (2006) 8881-8885. (c) A. Arcelli, B. T. Khai, G. Porci, J. Organomet. Chem. 235 (1982) 93-96. (d) Y. Watanabe, Y. Tsuji, H. Ige, Y. Ohsugi, T. Ohta, J. Org. Chem. 49 (1984) 3359-3363. (e) S. P. Shan, X. Xiaoke, B. Gnanaprakasam, T. T. Dang, B. Ramalingam, H. V. Huynh, A. M. Seayad, RSC Adv. 5 (2015) 4434-4442. (f) X. Xiaoke, H. V. Huynh, ACS Catal. 57 (2015) 4143-4151. 13. (a) W. Baumann, A. Spannenberg, J. Pfeffer, T. Haas, A. Kockritz, A. Martin, J. Deutsch, Chem.- Eur. J. 19 (2013) 17702–17706. (b) D. Weickmann, W. Frey, B. Plietker, Chem.-Eur. J. 19 (2013) 2741-2748. (c) X. Cui, Y. Deng, F. Shi, ACS Catal. 3 (2013) 808-811. (d) S. Agrawal, M. Lenormand, B. Martin-Matute, Org. Lett. 14 (2012) 1456-1459. (e) D. Pingen, C. Müller, D. Vogt, Angew. Chem., Int. Ed. 49 (2010) 8130-8133. (f) C. Gunanathan, D. 26

Milstein, Angew. Chem., Int. Ed. 47 (2008) 8661-8664. (g) M. H. S. A. Hamid, J. M. J Williams, Chem. Commun. 2007, 725-727. 14. (a) Z. Almodares, S. J. Lucas, B. D. Crossley, A. D. Basri, C. M. Pask, A. J. Hebden, R. M. Phillips, P. C. McGowan, Inorg. Chem. 53 (2014) 727-736. (b) S. Mokesch, M. S. Novak, A. Roller, M. A. Jakupec, W. Kandioller, B. K. Keppler, Organometallics 34 (2015) 848-857. (c) E. P. McMoran, J. A. Goodner, D. R. Powell, L. Yang, Inorg. Chim. Acta 421 (2014) 465-472. 15. (a) A. Rajput, R. Mukherjee, Coord. Chem. Rev. 257 (2013) 350-368. (b) M. J. Rose, P. K. Mascharak, Coord. Chem. Rev. 252 (2008) 2093-2114. (c) D. S. Marlin, P. K. Mascharak, Chem. Soc. Rev. 29 (2000) 69-74. (d) P. Kumar, R. Gupta, Dalton Trans., 45 (2016) 18769 – 18783. (e) P. Kumar, S. Kaur, R. Gupta, K. Bowman-James (2018) Pincers Based on Dicarboxamide and Dithiocarboxamide Functional Groups; Chapter – 14; Ed. David Morales-Morales; Elsevier. (f) G. Kumar, A. P. Singh, R. Gupta, Eur. J. Inorg. Chem. 2010, 5103-5112. (g) A. P. Singh, A. Ali, R. Gupta, Dalton Trans. 39 (2010) 8135-8138. (h) A. P. Singh, G. Kumar, R. Gupta, Dalton Trans. 40 (2011) 12454-12461. 16. (a) P. Kumar, V. Kumar, R. Gupta, RSC Adv. 5 (2015) 97874-97882. (b) G. Kumar, R. Gupta, Inorg. Chem. 51 (2012) 5497-5499. (b) S. Srivastava, B. K. Gupta, R. Gupta, Cryst. Growth Des. 17 (2017) 3907−3916. 17. (a) P. J. Donoghue, J. Tehranchi, C. J. Cramer, R. Sarangi, E. I. Solomon, W. B. Tolman, J. Am. Chem. Soc. 133 (2011) 17602-17605. (b) M. R. Halvagar, W. B. Tolman, Inorg. Chem. 52 (2013) 8306-8308. (c) T. Kojima, K. Hayashi, Y. Matsuda, Inorg. Chem. 43 (2004) 67936804. (d) C. G. Mortimer, G. Wells, J. P. Crochard, E. L. Stone, T. D. Bradshaw, M. F. Stevens, A. D. Westwell, J. Med. Chem. 49 (2006) 179 -185. 18. (a) V. O. Rodionov, S. I. Presolski, S. Gardinier, Y.-H. Lim, M. G. Finn, J. Am. Chem. Soc. 129 (2007) 12696-12704. (b) D. Bansal, R. Gupta, Dalton Trans. 46 (2017) 4617 – 4627. (c) D. Bansal, A. Mondal, N. Lakshminarasimhan, R. Gupta, Dalton Trans. 48 (2019) 7918 – 7927. (d) D. Bansal, R. Gupta, Dalton Trans. 48 (2019) DOI: 10.1039/C9DT02404B. 19. (a) D. Bansal, R. Gupta, Dalton Trans. 45 (2016) 502-507. (b) D. Bansal, G. Kumar, G. Hundal, R. Gupta, Dalton Trans. 43 (2014) 14865-14875.

27

20. (a) Y. Ogiwara, M. Miyake, T. Kochi, F. Kakiuchi, Organometallics 36 (2017) 159-164. (b) M. L. Berch, A. Davision, J. Inorg. Nucl. Chem., 35 (1973) 3763-3767. (c) I. P. Evans, A. Spencer, G. Wilkinson, J. Chem. Soc., Dalton Trans. (1973) 204-209. 21. (a) P. Vijayan, P. Viswanathamurthi, P. Sugumar, M. N. Ponnuswamy, M. D. Balakumaran, P. T. Kalaichelvan, K. Velmurugan, R. Nandhakumar, R. J. Butcher, Inorg. Chem. Front., 2, (2015) 620–639; (b) W. J. Geary, Coord. Chem. Rev. 7 (1971) 81-122. (c) S Pandey, D Bansal, R. Gupta, New. J. Chem. 42 (2018) 9847-9856. (d) P. Kalaivani, R. Prabhakaran, P. Poornima, F. Dallemer, K. Vijayalakshmi, V. Vijayapadma, K. Natarajan, Organometallics, 31 (2012) 8323–8332. 22. (a) F. Basuli, S.-M. Peng, S. Bhattacharya, Inorg. Chem. 40 (2001) 1126–1133. (b) E. Alessio, G. Mestroni, G. Nardin, W.M. Attia, M. Calligaris, G. Sava, S. Zorzet, Inorg. Chem. 27 (1998) 4099-4106. (c) A. R. Davies, F. W. B. Einstein, N. P. Farrell, B. R. James, R. S. McMillan, Inorg. Chem 17 (1978) 1965-1969. 23. (a) B. J. Sarmah, D. K. Dutta, J. Organomet. Chem., 695 (2010) 781–785., (b) B. Deb, P. P. Sarmah, D. K. Dutta, Eur. J. Inorg. Chem. 2010, 1710–1716 24. (a) J. Heinze, Angew. Chem., Int. Ed. Engl. 23 (1984) 831-847. (b) S. Chakraborty, M. G. Walawalkar, G. K. Lahiri, J. Chem. Soc. Dalton Trans. 2000, 2875-2883. 25. (a) M. Kaloglu, N. Gurbuz, D. Semeril, I. Ozdemir, Eur. J. Inorg. Chem. 2018, 1236–1243. (b) R. Ramachandran, G. Prakash, P. Viswanathamurthi, J. G. Malecki, Inorg. Chim. Acta. 477 (2018) 122-129. (c) J. J. A. Celaje, X. Zhang, F. Zhang, L. Kam, J. R. Herron, T. J. Williams, ACS Catal. 7 (2017) 1136–1142. (d) F-L. Yang, Y-H. Wang, Y-F. Ni, X. Gao, B. Song, X. Zhu, X-Q. Hao, Eur. J. Org. Chem. (2017) 3481–3486 (e) M. Maji, K. Chakrabarti, B. Paul, B. Chandra Roy, S. Kundu, Adv. Synth. Catal. 15 (2018) 722-729. 26. (a) D. Srimani, Y. Ben-David, D. Milstein, Angew. Chem., Int. Ed. 52 (2013) 4012-4015. (b) K. Iida, T. Miura, J. Ando, S. Saito, Org. Lett. 15 (2013) 1436-1439 (c) F. Kallmeier, B. Dudziec, T. Irrgang, R. Kempe, Angew. Chem., Int. Ed. 56 (2017) 7261-7265. 27. (a) X. Yu. Y. Li. H. Fu. X. Zheng H. Chen, R. Li, Appl. Organometal. Chem. 32 (2018) e4277-e4284. (b) R. Ramachandran, G. Prakash, S. Selvamurugan, P. Viswanathamurthi, J. G. Malecki, V. Ramkumar, Dalton Trans. 43 (2014) 7889–7902. 28. CrysAlisPro, ver.1.171.33.49b, Oxford Diffraction Ltd, (2009).

28

29. A. Altomare, G. Cascarano, C. Giacovazzo, A. Guagliardi, J. Appl. Crystallogr. 26 (1993) 343-350. 30. L. J. Farrugia, WinGX version 1.64, An integrated system of Windows Programs for the Solution, Refinement and Analysis of Single- Crystal X-ray Diffraction Data, Department of Chemistry, University of Glasgow, (2003).

29

Ruthenium(II) complexes of pyridine-carboxamide ligands bearing appended benzothiazole/benzimidazole rings: Structural diversity and catalysis Paranthaman Vijayan, Samanta Yadav, Sunil Yadav and Rajeev Gupta* Department of Chemistry, University of Delhi, Delhi 110 007, India

Graphical Abstract [Ru – Cl]

P1 N1 Cl1

O1

[Ru – H]

P2

S1

Toluene, 100 0C, 120C, hr 12 hr Toluene, 100 Ru catalyst (1-mol%) R

R1 + HO NH 2 NH + HOR2 2

S1

N2 N1 N3 H1A Ru1C50 O2 P1

N2 N3 Ru1 C50 O2 P2

R1

O1

1

R2 H2OH H 2O2O

NR1 NR2 H H

R2

The Ru(II) complexes of pyridine-carboxamide ligands have been synthesized, characterized and utilized as the homogeneous catalysts for the alkylation of amines using alcohols. In two cases, intermediate RuH complexes were synthesized and crystallographically characterized to shed light on the catalytic mechanism.

30

Ruthenium(II) complexes of pyridine-carboxamide ligands bearing appended benzothiazole/benzimidazole rings: Structural diversity and catalysis Paranthaman Vijayan, Samanta Yadav, Sunil Yadav and Rajeev Gupta* Department of Chemistry, University of Delhi, Delhi 110 007, India

Highlights 

Eight new Ru(II) complexes of pyridine-carboxamide ligands have been synthesized and characterized

 These Ru(II) complexes exhibited a distorted octahedral geometry with coordination modes of two bidentate ligands varying between NN and NO modes

 Ru(II) complexes were utilized for the alkylation of amines using alcohols ensuing hydrogen borrowing strategy

 Ruhydrides, as the putative intermediates during the catalysis, were synthesized and characterized including crystallography

31

Conflict of Interest and Authorship Conformation Form

Please check the following as appropriate:

o

All authors have participated in (a) conception and design, or analysis and interpretation of the data; (b) drafting the article or revising it critically for important intellectual content; and (c) approval of the final version.

o

This manuscript has not been submitted to, nor is under review at, another journal or other publishing venue.

o

The authors have no affiliation with any organization with a direct or indirect financial interest in the subject matter discussed in the manuscript

o

The following authors have affiliations with organizations with direct or indirect financial interest in the subject matter discussed in the manuscript:

Author’s name

Affiliation

Rajeev Gupta

University of Delhi

P. Vijayan

University of Delhi

Samanta Yadav

University of Delhi

Sunil Yadav

University of Delhi

32