Investigation of the coordination chemistry of multidentate azine Schiff-base ligands towards d6 half-sandwich metal complexes

Accepted Manuscript Investigation of the coordination chemistry of multidentate azine Schiff-base ligands 6 towards d half-sandwich metal complexes Sanjay Adhikari, Werner Kaminsky, Kollipara Mohan Rao PII:

S0022-328X(17)30457-6

DOI:

10.1016/j.jorganchem.2017.07.028

Reference:

JOM 20042

To appear in:

Journal of Organometallic Chemistry

Received Date: 6 June 2017 Revised Date:

20 July 2017

Accepted Date: 21 July 2017

Please cite this article as: S. Adhikari, W. Kaminsky, K.M. Rao, Investigation of the coordination 6 chemistry of multidentate azine Schiff-base ligands towards d half-sandwich metal complexes, Journal of Organometallic Chemistry (2017), doi: 10.1016/j.jorganchem.2017.07.028. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. 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.

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Investigation of the coordination chemistry of multidentate azine Schiff-

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base ligands towards d6 half-sandwich metal complexes

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Sanjay Adhikari[a], Werner Kaminsky[b], Kollipara Mohan Rao[a]*

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India. E-mail: [email protected]

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Department of Chemistry, University of Washington, Seattle, WA 98195, USA

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Centre for Advanced Studies in Chemistry, North-Eastern Hill University, Shillong 793 022,

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Graphical abstract Ruthenium, rhodium and iridium bidentate, tridentate and tetradentate azine complexes

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have been prepared by the reaction of metal precursor with multidentate azine Schiff-base

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ligands. Tetradentate azine ligand L1 yielded mononuclear complexes whereas hexadentate

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ligand L2 afforded mono as well as dinuclear complexes. In the mononuclear complexes the

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ligands acted as tridentate as well as bidentate chelating ligand whereas in dinuclear complexes

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the ligand behaved as tetradentate bridging ligand.

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Abstract

The reaction of multidentate azine Schiff-base ligands was investigated towards d6 half-

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sandwich metal complexes. Tetradentate azine ligand L1 reacts with [(arene)MCl2]2 (arene = p-

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cymene, Cp*; M = Ru, Rh and Ir) in 1:2 or 1:1 molar ratio to give mononuclear complexes

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having formula [(arene)M{L1к3(N,N´,N´´)}]2+ whereas the reaction of one equivalent of

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[(arene)MCl2]2 with four fold excess of hexadentate azine ligand L2 afforded mononuclear

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complexes bearing formula [(arene)M{L2к2(N,N´)}]+. The reaction of L2 with [(p-cymene)RuCl2]2

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in 1:1 molar ratio gave dinuclear complex [(p-cymene)2Ru2Cl2L2к4(N,N´,N´´,N´´´)]2+ whereas the

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reaction of L2 with [Cp*MCl2]2 yielded two coordination isomers (dinuclear and mononuclear).

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The coordination isomers were separated by column chromatography and characterized by

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spectral and structural studies. In mononuclear complexes with ligand L1 it acted as tridentate

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chelating ligand coordinating metal center in a tridentate к3 fashion through both the pyridine and

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one azine nitrogen atom leading to the formation of five and six membered chelated rings.

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Ligand L2 in mononuclear complexes coordinated metal in a bidentate к2 mode coordinating

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through both the pyridine nitrogen’s whereas in dinuclear complexes L2 acted as tetradentate

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bridging ligand coordinating both metal atoms in a bidentate к2 fashion through pyridine

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nitrogen’s thus forming a six membered metallacycle with both the metal centers. In the other

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isomer of rhodium and iridium complexes L2 acted as tridentate chelating ligand having bonding

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properties similar with complexes of ligand L1.

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Keywords: Ruthenium, rhodium, iridium, azine Schiff-base ligands

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1.

Introduction

Platinum group metal organometallic complexes are undoubtedly the most studied ones.

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These organometallic complexes have been widely explored and these complexes are a subject

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of fruitful research mainly because of its applications in industrial and biological fields [1-3].

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Particularly half-sandwich metal complexes of the type [(arene)Ru(L)Cl]+ (arene = p-cymene

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and its derivatives, L is a chelating ligand) have been found to exhibit anti-cancer activities.

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These complexes have the potential to act as metal-based anticancer drugs [4-7]. The polycyclic

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arene ligand is relatively inert and is known to stabilize the metal’s oxidation state [8].

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Nevertheless, Cp*Rh and Cp*Ir complexes have also been well researched as an alternative to

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ruthenium based drugs mainly because of its water solubility and an inert facial co-ligand Cp*

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[9]. This has led to a growing interest in the chemistry of pentamethylcyclopentadienyl

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complexes of the type [Cp*M(L)Cl]2+ (M = Rh/Ir, L a chelating ligand) [10, 11]. These

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complexes have also been employed as catalyst for various organic reactions namely C-H

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activation, oxidation of alcohols, reduction of ketones and water oxidation [12, 13].

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Azine ligands in particular represent a well-known class of organic compounds with

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interesting chemical properties having applications in various fields [14]. In this context pyridyl

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azine Schiff-base ligands linked by a single N-N bond are excellent ligands in the field of

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coordination chemistry because of its coordinative flexibility about the N-N bond [15]. Several

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transition metal complexes of azine Schiff-base ligands have been reported which possess

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interesting structural motifs and magnetic properties [16, 17]. The coordination chemistry of di-

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2-pyridyl imine ligands derived from di-2-pyridyl ketone has been explored by various workers

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where the ligands offered interesting coordination modes [18, 19]. Recently Georg Süss-Fink and

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group reported arene ruthenium complexes of the type [(arene)Ru(η2-N,N-L)Cl]+ (arene =

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benzene and p-cymene) and (L = 2, 2'-pyridyl N-aryl imines) where the ligands coordinated

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ruthenium in two different fashions: One coordination mode is through both the pyridyl

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nitrogen’s while the other coordination is through imine nitrogen and one of the pyridyl nitrogen

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[20].

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Recently we investigated the coordination chemistry of pyridyl azine Schiff-base ligands

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where we observed interesting bonding modes associated with the ligand [21]. Pursuing our

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interest with multidentate azine ligands herein we studied the coordination chemistry of

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tetradentate phenyl 2-pyridyl ketone azine L1 and hexadentate di-2-pyridyl ketone azine L2

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azine Schiff-base ligands towards ruthenium, rhodium and iridium complexes. Because of the

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rotational flexibility of these ligands around N-N single bond we anticipated that these ligands

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can give rise to compounds with unusual bonding modes and we therefore explored this

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possibility in the present work. Ligands used in this work are presented in Chart-1.

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2.

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2. 1.

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General

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Experimental

The reagents used were of commercial quality and used without further purification.

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Metal salts RuCl3.nH2O, RhCl3.nH2O and IrCl3.nH2O were purchased from Arora Matthey

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Limited. α-phellandrene, pentamethylcyclopentadiene and 2-benzoylpyridine were purchased

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from Sigma Aldrich. Di-2-pyridyl ketone and hydrazine hydrate were obtained from Alfa Aesar

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and Qualigens. The solvents were dried and distilled prior to use according to standard

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procedures [22]. Precursor metal complexes [(p-cymene)RuCl2]2 and [Cp*MCl2]2 (M = Rh/Ir)

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were prepared according to the published procedures [23, 24]. The azine Schiff-base ligands

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phenyl 2-pyridyl ketone azine (L1) and di-2-pyridyl ketone azine (L2) were prepared according

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to previously described procedures [25, 26]. 1H and 13C NMR spectra were recorded on a Bruker

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Advance II 400 MHz spectrometer using CDCl3 and DMSO-d6 as solvents; chemical shifts were

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referenced to TMS. Infrared spectra (KBr pellets; 400-4000 cm-1) were recorded on a Perkin-

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Elmer 983 spectrophotometer. Mass spectra were recorded with Q-Tof APCI-MS instrument

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(model HAB 273) using acetonitrile as solvent. Absorption spectra were recorded on a Perkin-

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Elmer Lambda 25 UV/Vis spectrophotometer in the range of 200-800 nm at room temperature in

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acetonitrile. Elemental analyses of the complexes were carried out on a Perkin-Elmer 2400

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CHN/S analyzer.

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2.2.

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Structure determination by X-ray crystallography

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Suitable single crystals of complexes (1), (2), (3), (5), (7), (8a) and (9b) were obtained by

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slow diffusion of hexane into acetone or dichloromethane solution. Single crystal data for the

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complexes were collected with an Oxford Diffraction Xcalibur Eos Gemini diffractometer using

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graphite monochromated Mo-Kα radiation (λ = 0.71073 Å). The strategy for the data collection

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was evaluated using the CrysAlisPro CCD software. Crystal data were collected by standard

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‘‘phi–omega scan’’ techniques and were scaled and reduced using CrysAlisPro RED software.

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The structures were solved by direct methods using SHELXS-97 and refined by full-matrix least

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squares with SHELXL-97 refining on F2 [27, 28]. The positions of all the atoms were obtained

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by direct methods. Metal atoms in the complex were located from the E-maps and all non-

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hydrogen atoms were refined anisotropically by full-matrix least-squares. Hydrogen atoms were

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placed in geometrically idealized positions and constrained to ride on their parent atoms with C--

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-H distances in the range 0.95-1.00 Angstrom. Isotropic thermal parameters Ueq were fixed such

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that they were 1.2Ueq of their parent atom Ueq for CH's and 1.5Ueq of their parent atom Ueq in

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case of methyl groups. Crystallographic and structure refinement parameters for the complexes

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are summarized in Table S1 & S2, and selected bond lengths and bond angles are presented in

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Table 1. Figures 1-5 were drawn with ORTEP3 program whereas Figures S15 & S16 were drawn

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by using MERCURY 3.6 program [29]. The crystal structure of complex (2) contains C3H6O (acetone) and complex (8a) contains

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H2O molecule in their solved structure. Crystal structure of complex (9b) contains disordered

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CH2Cl2 and H2O molecule in their solved structure. In the crystal structure of complex (3), a

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disordered acetone molecule was present which has been removed by SQUEEZE method [30].

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2. 3.

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General procedure for preparation of mononuclear tridentate complexes

A mixture of starting metal precursor [(arene)MCl2]2 (arene = p-cymene, Cp*; M = Ru,

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Rh and Ir), ligand L1 (0.1 or 0.2 mmol) and 4 equivalents of NH4PF6 were dissolved in ethanol

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(5 mL) and stirred at room temperature for 2 hours (Scheme-1). A yellow colored compound

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precipitated out from the reaction mixture. The precipitate was filtered, washed with cold

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methanol (2 x 5 ml) and diethyl ether (3 x 10 ml) and air dried.

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2. 3. 1. [(p-cymene)RuL1к3(N,N´,N´´)](PF6)2 (1)

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Yield 105 mg (59%); IR (KBr, cm-1): 3433(m), 2972(m), 1598(m), 1542(m), 1469(w), 841(s);

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J = 4 and 4 Hz), 7.51-8.01 (m, 12H), 7.07 (d, 2H, J = 8 Hz), 6.55 (d, 1H, J = 4 Hz, CH(p-cym)),

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6.44 (dd, 2H, J = 8 and 4 Hz, CH(p-cym)), 5.85 (d, 1H, J = 4 Hz, CH(p-cym)), 3.23 (sept, 1H, CH(p-

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cym)),

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DMSO-d6): δ = 169.5, 167.0, 157.0, 155.6, 155.3, 149.4, 147.3, 145.5, 143.6, 139.1, 137.7,

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137.3, 131.1, 130.4, 129.7, 127.5, 126.3 (C-L2), 107.5, 103.9, 89.7, 86.2, 82.3, 30.7, 23.8, 18.4

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(C-p-cym); HRMS-APCI (m/z) [Found (Calcd)]: [299.0873 (299.0835)] (M-2PF6/2)2+; UV–Vis

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{Acetonitrile, λmax, nm (ε/10-4 M-1 cm-1)}: 211 (1.69), 277 (1.00), 322 (0.66), 396 (0.31); Anal.

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H NMR (400 MHz, DMSO-d6): δ = 9.98 (d, 1H, J = 8 Hz), 9.52 (d, 1H, J = 4 Hz), 8.27 (dd, 2H,

2.01 (s, 3H, CH(p-cym)), 1.12 (dd, 6H, J = 8 and 8 Hz, CH(p-cym));

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C NMR (100 MHz,

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Calc. for C34H32F12N4P2Ru (887.64): C, 46.01; H, 3.63; N, 6.31. Found: C, 46.14; H, 3.78; N,

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6.47 %.

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2. 3. 2. [Cp*RhL1к3(N,N´,N´´)](PF6)2 (2)

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Yield 102 mg (57%); IR (KBr, cm-1): 3409(m), 2924(m), 1599(m), 1554(m), 1471(m), 842(s);

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11H), 7.16 (d, 3H, J = 8 Hz), 1.74 (s, 15H, CH(Cp*)); 13C NMR (100 MHz, CDCl3): δ = 167.3,

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166.7, 155.4, 153.2, 151.1, 143.6, 142.4, 138.8, 135.1, 132.4, 131.6, 130.8, 130.4, 130.1, 129.9,

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129.5, 126.8 (C-L1), 91.3 (Cp*ipso), 8.3 (Cp*Me); HRMS-APCI (m/z) [Found (Calcd)]: [345.2334

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(345.1167)] (M-2PF6/2)2+; UV–Vis {Acetonitrile, λmax, nm (ε/10-4 M-1 cm-1)}: 217 (2.43), 272

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(1.66), 317 (1.15), 366 (0.77); HRMS-APCI (m/z) [Found (Calcd)]: [300.0893 (300.0880)] (M-

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2PF6/2)2+; UV–Vis {Acetonitrile, λmax, nm (ε/10-4 M-1 cm-1)}: 236 (2.27), 275 (1.41), 316 (1.08),

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390 (0.66); Anal. Calc. for C34H33F12N4P2Rh (890.48): C, 45.86; H, 3.74; N, 6.29. Found: C,

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46.03; H, 3.86; N, 6.35 %.

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2. 3. 3. [Cp*IrL1к3(N,N´,N´´)](PF6)2 (3)

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Yield 120 mg (61%); IR (KBr, cm-1): 3412(s), 2927(m), 1597(m), 1556(m), 1475(m), 841(s); 1H

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NMR (400 MHz, CDCl3): δ = 8.69 (d, 2H, J = 4 Hz), 7.84 (t, 2H, J = 8 Hz), 7.64 (d, 2H, J = 8

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Hz), 7.58-7.62 (m, 9H), 7.21 (d, 3H, J = 8 Hz), 1.73 (s, 15H, CH(Cp*));

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CDCl3): δ = 166.8, 165.9, 156.4, 153.8, 153.1, 143.6, 141.6, 140.8, 133.1, 132.4, 131.3, 130.9,

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130.8, 130.4, 130.3, 129.9, 129.0, 128.8 (C-L1), 92.6 (Cp*ipso), 8.1 (Cp*Me); HRMS-APCI (m/z)

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[Found (Calcd)]: [345.2334 (345.1167)] (M-2PF6/2)2+; UV–Vis {Acetonitrile, λmax, nm (ε/10-4

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M-1 cm-1)}: 217 (2.43), 272 (1.66), 317 (1.15), 366 (0.77); Anal. Calc. for C34H33F12N4P2Ir

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(979.79): C, 41.68; H, 3.39; N, 5.72. Found: C, 41.82; H, 3.48; N, 6.21 %.

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C NMR (100 MHz,

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H NMR (400 MHz, CDCl3): δ = 8.71 (d, 2H, J = 4 Hz), 7.86 (t, 2H, J = 8 Hz), 7.56-7.64 (m,

General procedure for preparation of mononuclear bidentate complexes

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A mixture of starting metal precursor [(arene)MCl2]2 (arene = p-cymene, Cp*; M = Ru,

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Rh and Ir) (0.1 mmol), ligand L2 (0.4 mmol) and 4 equivalents of NH4PF6 were dissolved in

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ethanol (10 mL) and stirred at room temperature for 2 hours (Scheme-2). A yellow colored

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compound precipitated out from the reaction mixture. The precipitate was filtered, washed with

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cold methanol (2 x 5 ml) and diethyl ether (3 x 10 ml) and air dried.

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2. 4. 1. [(p-cymene)RuClL2к2(N,N´)]PF6 (4)

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Yield 82 mg (52%); IR (KBr, cm-1): 3438(m), 3159(w), 2961(m), 1618(m), 1471(w), 843(s); 1H

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NMR (400 MHz, CDCl3): δ = 9.94 (d, 1H, J = 8 Hz), 9.60 (d, 1H, J = 4 Hz), 9.01 (t, 1H, J = 4

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Hz), 8.71 (d, 1H, J = 8 Hz), 8.58-8.62 (m, 1H), 8.27 (t, 1H, J = 8 Hz), 8.14-8.20 (m, 2H), 7.94-

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8.03 (m, 2H), 8.04 (d, 2H, J = 8 Hz), 7.96 (t, 2H, J = 4 Hz), 7.82-7.88 (m, 1H), 7.76 (t, 1H, J = 8

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Hz), 5.55 (d, 1H, J = 4 Hz, CH(p-cym)), 5.50 (d, 1H, J = 8 Hz, CH(p-cym)), 5.48 (d, 1H, J = 4 Hz,

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CH(p-cym)), 5.42 (d, 1H, J = 4 Hz, CH(p-cym)), 2.37 (sept, 1H, CH(p-cym)), 1.87 (s, 3H, CH(p-cym)),

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1.07 (d, 3H, J = 8 Hz, CH(p-cym)), 1.05 (d, 6H, J = 8 Hz, CH(p-cym)); 13C NMR (100 MHz, CDCl3):

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δ = 163.5, 163.0, 157.0, 156.6, 153.0, 149.6, 149.3, 145.0, 144.6, 140.0, 137.7, 137.3, 132.1,

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130.8, 129.1, 126.5, 125.3 (C-L2), 108.5, 107.4, 91.7, 88.2, 87.5, 87.0, 30.3, 22.8, 20.0, 17.4 (C-

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p-cym); HRMS-APCI (m/z) [Found (Calcd)]: [ 635.1261 (635.1264)] (M-PF6)+; UV–Vis

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{Acetonitrile, λmax, nm (ε/10-4 M-1 cm-1)}: 209 (1.63), 283 (1.12), 327 (0.70), 401 (0.23); Anal.

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Calc. for C32H30ClF6N6PRu (780.10): C, 49.27; H, 3.88; N, 10.77. Found: C, 49.35; H, 3.96; N,

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10.83 %.

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2. 4. 2. [Cp*RhClL2к2(N,N´)]PF6 (5)

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Yield 78 mg (50%); IR (KBr, cm-1): 3425(m), 3141(w), 2932(m), 1621(m), 1475(w), 844(s); 1H

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NMR (400 MHz, CDCl3 + DMSO-d6): δ = 9.43 (d, 1H, J = 8 Hz), 9.30 (d, 1H, J = 4 Hz), 8.60 (t,

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2H, J = 4 Hz), 8.24 (t, 1H, J = 4 Hz), 8.13 (t, 1H, J = 8 Hz), 7.90-8.05 (m, 5H), 7.76 (t, 1H, J = 8

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Hz), 7.71 (d, 2H, J = 8 Hz), 7.58 (t, 2H, J = 8 Hz), 1.60 (s, 15H, CH(Cp*)); 13C NMR (100 MHz,

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CDCl3 + DMSO-d6): δ = 166.3, 165.4, 152.6, 148.4, 148.0, 146.8, 143.8, 135.1, 134.1, 131.8,

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130.9, 124.2, 122.1, 121.8, 120.9, 119.8, 119.6 (C-L2), 91.9 (Cp*ipso), 8.1 (Cp*Me); HRMS-APCI

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(m/z) [Found (Calcd)]: [637.1376 (637.1354)] (M-PF6)+; UV–Vis {Acetonitrile, λmax, nm (ε/10-4

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M-1 cm-1)}: 206 (1.01), 232 (1.05), 289 (0.56), 328 (0.44); Anal. Calc. for C32H31ClF6N6PRh

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(782.95): C, 49.09; H, 3.99; N, 10.73. Found: C, 49.18; H, 4.09; N, 10.87 %.

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2. 4. 3. [Cp*IrClL2к2(N,N´)]PF6 (6)

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Yield 95 mg (54%); IR (KBr, cm-1): 3398(m), 3018(w), 2823(m), 1623(m), 1476(w), 845(s); 1H

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NMR (400 MHz, CDCl3 + DMSO-d6): δ = 9.45 (d, 1H, J = 4 Hz), 9.33 (d, 1H, J = 8 Hz), 8.74

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(dd, 2H, J = 4 and 4 Hz), 8.25 (t, 1H, J = 8 Hz), 8.14-8.19 (m, 3H), 7.90-8.06 (m, 3H), 7.86 (d,

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2H, J = 4 Hz), 7.63 (t, 2H, J = 4 Hz), 7.40 (d, 1H, J = 4 Hz ), 1.68 (s, 15H, CH(Cp*)); 13C NMR

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(100 MHz, CDCl3 + DMSO-d6): δ = 165.3, 164.8, 154.6, 147.4, 146.4, 145.1, 141.3, 140.5,

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138.1, 135.3 130.9, 123.2, 121.5, 121.1, 120.4, 119.8, 119.6 (C-L2), 93.2 (Cp*ipso), 8.2 (Cp*Me);

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HRMS-APCI (m/z) [Found (Calcd)]: [727.1928 (727.1925)] (M-PF6)+; UV–Vis {Acetonitrile,

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λmax, nm (ε/10-4 M-1 cm-1)}: 216 (1.76), 278 (1.17), 337 (0.68); Anal. Calc. for C32H31ClF6N6PIr

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(872.26): C, 44.06; H, 3.58; N, 9.63. Found: C, 44.18; H, 3.66; N, 9.78 %.

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2. 5.

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complexes

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General procedure for preparation of dinuclear tetradentate and mononuclear tridentate

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A mixture of metal precursor [(arene)MCl2]2 (arene = p-cymene, Cp*; M = Ru, Rh and

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Ir) (0.1 mmol), ligand L2 (0.1 mmol) and 4 equivalents of NH4PF6 were dissolved in ethanol (10

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mL) and stirred at room temperature for 2 hours (Scheme-3). A yellow colored compound

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precipitated out from the reaction mixture. The precipitate was filtered, washed with cold

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methanol (2 x 5 ml) and diethyl ether (3 x 10 ml) and air dried.

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Rhodium and iridium complexes with ligand L2 the coordination isomers were separated

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by silica gel column chromatography (100-200) mesh size using (VDCM : VMeOH = 94:6) for

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complex (8) and (VDCM : VMeOH = 98:2) for complex (9) as eluent.

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2. 5. 1. [(p-cymene)2Ru2Cl2L2к4(N,N´,N´´,N´´´)](PF6)2 (7)

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Yield 110 mg (46%); IR (KBr, cm-1): 3385(m), 3208(w), 2981(m), 1629(m), 1618(m), 1478(w),

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845(s); 1H NMR (400 MHz, CDCl3): δ = 9.17 (d, 2H, J = 4 Hz), 9.03 (d, 2H, J = 4 Hz), 8.35 (t,

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2H, J = 8 Hz), 8.26 (t, 4H, J = 8 Hz), 7.93 (t, 2H, J = 8 Hz), 7.83-7.86 (m, 4H), 5.91 (d, 4H, J = 4

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Hz, CH(p-cym)), 5.65 (d, 4H, J = 4 Hz, CH(p-cym)), 2.62 (sept, 2H, CH(p-cym)), 1.82 (s, 6H, CH(p-cym)),

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1.10 (d, 12H, J = 8 Hz, CH(p-cym)); 13C NMR (100 MHz, CDCl3): δ = 163.2, 161.8, 159.4, 157.5,

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156.2, 154.0, 153.2, 145.3, 144.7, 141.3, 137.6, 135.2, 132.1, 128.1, 127.2, 123.3 (C-L2), 107.5,

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103.8, 92.8, 86.8, 31.5, 23.8, 18.6 (C-p-cym); HRMS-APCI (m/z) [Found (Calcd)]: [453.1321

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(453.0545)] (M-2PF6/2)2+; UV–Vis {Acetonitrile, λmax, nm (ε/10-4 M-1 cm-1)}: 210 (1.84), 281

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(1.54), 323 (1.12); Anal. Calc. for C42H44Cl2F12N6P2Ru2 (1195.81): C, 42.18; H, 3.71; N, 7.03.

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Found: C, 42.28; H, 4.29; N, 7.17 %.

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2. 5. 2. [(Cp*)2Rh2Cl2L2к4(N,N´,N´´,N´´´)](PF6)2 (8a)

217

Yield 101 mg (41%); IR (KBr, cm-1): 3392(m), 3302(w), 2815(m), 1592(m), 1585(m), 1368(w),

218

842(s); 1H NMR (400 MHz, CDCl3 + DMSO-d6): δ = 9.42 (d, 1H, J = 4 Hz), 9.35 (d, 1H, J = 8

219

Hz), 8.74 (d, 1H, J = 4 Hz), 8.50 (d, 1H, J = 8 Hz), 7.89-8.15 (m, 4H), 7.74 (d, 1H, J = 8 Hz),

220

7.62-7.70 (m, 5H), 7.57 (t, 1H, J = 4 Hz), 7.53 (t, 1H, J = 8 Hz), 1.51 (s, 15H, CH(Cp*)), 1.25 (s,

221

15H, CH(Cp*)); 13C NMR (100 MHz, CDCl3 + DMSO-d6): δ = 163.5, 161.0, 156.9, 154.6, 154.4,

222

153.1, 152.4, 149.7, 149.3, 147.5, 145.5, 144.6, 140.9, 139.7, 137.7, 137.2, 132.0, 130.2, 129.8,

223

126.6, 124.9 (C-L2), 97.0, 96.9 (Cp*ipso), 8.3, 8.1 (Cp*Me); HRMS-APCI (m/z) [Found (Calcd)]:

224

[1055.0902 (1055.0913)] (M-PF6)+, [455.0642 (453.0635)] (M-2PF6/2)2+; UV–Vis {Acetonitrile,

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λmax, nm (ε/10-4 M-1 cm-1)}: 209 (1.56), 231 (1.52), 294 (0.86), 329 (0.76); Anal. Calc. for

226

C42H44Cl2F12N6P2Rh2 (1201.50): C, 41.98; H, 3.86; N, 6.99. Found: C, 42.10; H, 3.95; N, 7.09

227

%.

228

2. 5. 3. [Cp*RhL2к3(N,N´,N´´)](PF6)2 (8b)

229

Yield 92 mg (51%); IR (KBr, cm-1): 3284(m), 3163(w), 2965(m), 1598(m), 1582(m), 1474(w),

230

843(s); 1H NMR (400 MHz, CDCl3 + DMSO-d6): δ = 9.43 (d, 1H, J = 8 Hz), 9.30 (d, 1H, J = 4

231

Hz), 8.60 (t, 2H, J = 4 Hz), 8.24 (t, 1H, J = 8 Hz), 8.13 (t, 1H, J = 8 Hz), 7.90-8.05 (m, 5H), 7.76

232

(t, 1H, J = 4 Hz), 7.71 (d, 2H, J = 8 Hz), 7.58 (t, 2H, J = 8 Hz), 1.60 (s, 15H, CH(Cp*)); 13C NMR

233

(100 MHz, CDCl3 + DMSO-d6): δ = 161.0, 160.4, 159.9, 151.7, 148.4, 147.9, 145.8, 144.6,

234

144.3, 140.1, 139.7, 136.9, 135.6, 133.8, 131.2, 126.1, 123.8, 121.6, 121.1, 120.1 (C-L2), 89.2

235

(Cp*ipso), 8.3 (Cp*Me); HRMS-APCI (m/z) [Found (Calcd)]: [301.1665 (301.0832)] (M-

236

2PF6/2)2+; UV–Vis {Acetonitrile, λmax, nm (ε/10-4 M-1 cm-1)}: 208 (1.36), 233 (1.40), 289 (0.74),

237

324 (0.60); Anal. Calc. for C32H31F12N6P2Rh (892.46): C, 43.07; H, 3.50; N, 9.42. Found: C,

238

43.16; H, 3.68; N, 9.51 %.

239

2. 5. 4. [(Cp*)2Ir2Cl2L2к4(N,N´,N´´,N´´´)](PF6)2 (9a)

240

Yield 96 mg (34%); IR (KBr, cm-1): 3421(m), 3286(w), 1602(m), 1591(m), 1272(w), 843(s); 1H

241

NMR (400 MHz, CDCl3 + DMSO-d6): δ = 9.46 (d, 1H, J = 4 Hz), 8.84 (d, 1H, J = 4 Hz), 8.76

242

(d, 1H, J = 4 Hz), 8.23-8.32 (m, 3H), 8.16 (t, 1H, J = 8 Hz), 7.93-8.10 (m, 5H), 7.85 (t, 3H, J = 4

243

Hz), 7.73 (t, 1H, J = 4 Hz), 1.47 (s, 15H, CH(Cp*)), 1.24 (s, 15H, CH(Cp*)); 13C NMR (100 MHz,

244

CDCl3 + DMSO-d6): δ = 165.2, 164.0, 155.7, 154.3, 152.7, 151.4, 149.4, 145.3, 144.3, 143.5,

245

141.1, 137.8, 138.7, 134.7, 132.8, 131.3, 130.5, 126.9, 123.8 (C-L2), 92.8, 88.9 (Cp*ipso), 8.6, 8.1

246

(Cp*Me); HRMS-APCI (m/z) [Found (Calcd)]: [543.1657 (543.1682)] (M-2PF6/2)2+; UV–Vis

247

{Acetonitrile, λmax, nm (ε/10-4 M-1 cm-1)}: 212 (2.08), 266 (1.32), 394 (0.77), 485 (0.44); Anal.

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Calc. for C42H46Cl2F12N6P2Ir2 (1380.32): C, 36.55; H, 3.36; N, 6.09. Found: C, 36.68; H, 3.43;

249

N, 6.02 %.

250

2. 5. 5. [Cp*IrL2к3(N,N´,N´´)](PF6)2 (9b)

251

Yield 95 mg (73%); IR (KBr, cm-1): 3314(m), 3083(w), 2823(m), 1608(m), 1594(m), 1465(w),

252

845(s); 1H NMR (400 MHz, CDCl3): δ = 8.74 (d, 1H, J = 8 Hz), 8.57 (d, 1H, J = 4 Hz), 8.37 (d,

253

1H, J = 4 Hz), 8.20 (t, 2H, J = 8 Hz), 8.03-8.14 (m, 5H), 7.93 (d, 2H, J = 8 Hz), 7.46 (t, 2H, J = 8

254

Hz), 7.35 (t, 2H, J = 8 Hz), 1.72 (s, 15H, CH(Cp*));

255

158.9, 150.4, 148.3, 147.9, 144.8, 144.6, 144.5, 140.4, 138.7, 135.9, 135.6, 132.8, 132.4, 127.0,

256

126.6, 121.9, 121.8, 121.6, 120.1 (C-L2), 90.0 (Cp*ipso), 8.2 (Cp*Me); HRMS-APCI (m/z) [Found

257

(Calcd)]: [346.1136 (346.1119)] (M-2PF6/2)2+; UV–Vis {Acetonitrile, λmax, nm (ε/10-4 M-1 cm-

258

1

259

39.15; H, 3.18; N, 8.56. Found: C, 39.26; H, 3.29; N, 8.62 %.

260

3.

Results and discussion

261

3.1.

Synthesis of the complexes

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C NMR (100 MHz, CDCl3): δ = 160.0,

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)}: 212 (1.34), 234 (1.45), 287 (0.78), 326 (0.63); Anal. Calc. for C32H31F12N6P2Ir (981.77): C,

Tetradentate azine Schiff-base ligand L1 reacted with metal precursors in 1:2 or 1:1

263

molar ratio to yield exclusively mononuclear tridentate complexes (Scheme-1). Our attempt to

264

prepare dinuclear complexes with ligand L1 was unfruitful as it yielded only mononuclear

265

complexes despite varying the metal to ligand ratio. The reaction of (1:2 M:L) molar ratio with

266

ligand L2 led to the formation of mixture of compounds which we were unable to separate by

267

chromatography so we took excess ligand (4 equivalents) and reacted with metal precursor

268

which led to the formation of mononuclear bidentate complexes (Scheme-2). The reaction of L2

269

with [(p-cymene)RuCl2]2 in (1:1 M:L) molar ratio gave exclusively dinuclear tetradentate

270

complex, whereas with [Cp*MCl2]2 (M = Rh/Ir) dimers it yielded two coordination isomers

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where one is mononuclear tridentate complex and the other is dinuclear tetradentate complex

272

(Scheme-3). The coordination isomers were separated by column chromatography. The

273

molecular structures of some of the complexes displayed the interesting coordination behavior

274

associated with the ligands. In mononuclear complexes (1-3) with ligand L1 the ligand acted as

275

tridentate chelating ligand whereas in mononuclear complexes (4-6) the ligand L2 behaved as

276

bidentate chelating ligand. In dinuclear complexes L2 acted as tetradentate bridging ligand

277

whereas in the other isomer the ligand behaved as tridentate chelating ligand. The single crystals

278

of both the mononuclear and dinuclear rhodium complexes were isolated and characterized by

279

single crystal X-ray analysis. All these azine complexes were isolated as cationic salts with PF6

280

counter ion. These complexes were isolated as yellow solids which are stable in air and are non-

281

hygroscopic. These complexes are soluble in common organic solvents like CH3CN, CH2Cl2,

282

(CH3)2O and (CH3)2SO but insoluble in petroleum ether, hexane and diethyl ether.

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3.2.

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Spectral studies of the complexes

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The formations of the cationic complexes were confirmed by their IR spectra. These

285

complexes display a sharp band around 842-846 cm-1 which corresponds to the characteristic P-F

286

stretching frequency of the counter ion [31]. Also the mononuclear and dinuclear complexes

287

exhibited characteristic bands for C=N and C=C. The presence of the medium intense band for

288

C=N stretching frequency around 1590-1640 cm-1 at higher frequency region as compared to the

289

free ligand around 1565-1582 cm-1 suggests the coordination of the ligand occurs through

290

pyridine and imine nitrogen.

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The 1H NMR spectra of the complexes further supports the binding of the ligand to metal

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atom. The 1H NMR spectra of these complexes exhibit signals associated with the ligand protons

293

and signals due to p-cymene and Cp* ring protons. The aromatic proton signals associated with

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the ligands were observed in the downfield region around δ = 7.0-9.8. This shift of ligand proton

295

signals clearly indicates the coordination of the ligand to the metal ion. In the mononuclear

296

ruthenium complexes the binding of the ligand resulted in distinct splitting of the p-cymene

297

protons. The proton signals of the p-cymene ligand consisted of doublets around δ = 6.55-5.85

298

for the four aromatic protons of the p-cymene moiety, one doublet for complex (1) and one

299

doublet of doublet for complex (4) around δ = 1.10-1.17 for the isopropyl group. This splitting of

300

the p-cymene protons is probably due to the coupling of the diastereotopic methyl protons of the

301

isopropyl group and aromatic protons of the p-cymene and it correlates well with similar

302

reported complexes [32]. In complexes (2) and (3), the methyl protons of the Cp* ring was

303

observed as a singlet at δ 1.74 and 1.73 (Figure S1 & S2). The 1H NMR spectrum of the

304

dinuclear ruthenium complex (7) exhibits two sets of doublets each having an integration of 4H,

305

at δ = 5.91 and 5.65 and one doublet comprising of 12H at δ = 1.10 (Figure S3). In ruthenium

306

complexes the methyl protons of the p-cymene moiety was observed as singlet around δ = 1.82-

307

2.01. The methine protons of the isopropyl group displayed septet around δ = 2.37-3.23. The

308

mononuclear rhodium and iridium bidentate and tridentate complexes displayed only one singlet

309

for the methyl protons of the Cp* group around δ = 1.52-1.75 whereas its dinuclear tetradentate

310

complexes possessed two singlets for the Cp* protons around δ = 1.29-1.51 respectively. For

311

instance the 1H NMR spectrum of the mononuclear bidentate iridium complex (6) displayed

312

singlet at δ = 1.68 (Figure S4) whereas tridentate iridium complex (9b) exhibits singlet at δ =

313

1.72 (Figure S5). For the dinuclear tetradentate iridium complex (9a) the Cp* proton signals

314

were observed at δ = 1.47 and 1.29 (Figure S6). Thus the 1H NMR spectra of the complexes

315

strongly supports the formation of mononuclear and dinuclear complexes.

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The

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13

C NMR spectra further support the formation of the complexes. In the

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C NMR

spectra of the complexes the imine carbon resonances shifted downfield and were observed in

318

the region around δ = 160-166 while the aromatic carbon resonances were observed in the region

319

of δ = 120-158. The p-cymene carbon resonances were observed in the expected region. The

320

mononuclear rhodium and iridium complexes exhibited one signal around δ = 8.1-8.3 whereas

321

the dinuclear complexes possessed two signals around δ = 8.1-8.6 for the methyl protons of the

322

Cp* ligand. Similarly mononuclear rhodium and iridium complexes displayed one resonance

323

around δ = 89.2-92.6 whereas the dinuclear complexes exhibited two resonances around 88.9-

324

97.0 for the ring carbon of the Cp* moiety.

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The mass spectra of the complexes further confirmed the integrity of the mono-and

326

dinuclear complexes. In the mass spectra of the tridentate complexes (1–3) with ligand L1 the

327

molecular ion peaks were observed as (M-2PF6/2)2+ at m/z: 299.0873, m/z: 300.0893 and m/z:

328

345.2334 respectively. The mass spectra of the mononuclear bidentate complexes (4-6) with

329

ligand L2 displayed peaks at m/z: 635.1261, m/z: 637.1376 and m/z: 727.1925 which correspond

330

to the loss of the PF6 counter-ion. Also, tetradentate complexes (7), (8a) and (9a) displayed

331

molecular ion peaks at m/z: 453.1321, m/z: 455.0642 and m/z: 543.1657 due to (M-2PF6)2+ ion.

332

Similarly, tridentate rhodium (8b) and iridium (9b) complexes displayed their molecular ion

333

peaks at m/z: 301.1665 and m/z: 346.1136 corresponding to (M-2PF6)2+ ion respectively. The

334

mass spectra values of the complexes are in well agreement with the theoretically expected

335

values.

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Electronic spectra of these azine complexes were recorded in acetonitrile solution at room

337

temperature and the respective plot is shown in (Figure S14). All these complexes displayed

338

three to four absorption bands in the region around 200-500 nm. The absorption bands in the

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higher energy region around 200-310 nm can be assigned as ligand centered (LC) π-π* and n-π*

340

transitions respectively. The lowest energy absorption bands in these complexes around 330-500

341

nm are ascribed as metal to ligand charge transfer (MLCT) dπ(M) to π*(L) transition.

342

3.3.

Description of the crystal structures of complexes

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In addition to the spectroscopic and analytical analysis, the coordination of the ligand to

344

the metal was further established by single crystal X-ray diffraction analysis. In order to have a

345

deeper understanding about the geometry of the complexes, we carried out the single crystal

346

analyses for the complexes. By carrying out the single crystal analyses we established that both

347

the tetradentate and hexadentate azine ligands displayed unexpected bonding modes towards

348

formation of complexes. The details about the data collection, solution and structure refinement

349

parameters for the complexes are summarized in Table S1 & S2. Selected bond lengths, bond

350

angles and metal atom involving ring centroid values are listed in Table 1. The ORTEP plots of

351

the complexes are presented in Figure (1-5) respectively. In general, mononuclear tridentate

352

complexes (1-3) with ligand L1 adopts a regular half-sandwich piano-stool geometry with metal

353

coordinated through η6/ η5 bonded arene ring (arene = p-cymene/Cp*) and nitrogen atoms from

354

chelating pyridyl azine ligand in a tridentate mode. The ligand L1 in mononuclear complexes (1-

355

3) acted as tridentate chelating ligand. L1 ligates metal in a tridentate к3 mode through two

356

pyridine nitrogen’s N(1), N(4) and one azine nitrogen (N2) leading to the formation of five and

357

six membered chelated rings (Figure 1 & 2). The other azine nitrogen N(3) remains

358

uncoordinated in mononuclear complexes. This type of tridentate bonding mode is also observed

359

for Co(II) , Ni(II), Cu(II) and Zn(II) metal complexes with the same ligand [33]. The M-N(py)

360

distances in complexes (1-3) are comparatively longer than M-N(azine) distances (Table 1). The

361

hexadentate azine ligand L2 displayed interesting bonding modes depending upon the

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appropriate molar ratio reaction between precursor complexes and L2. In mononuclear bidentate

363

rhodium complex (5), L2 acted as bidentate chelating ligand coordinating rhodium atom in a

364

bidentate к2 fashion through two pyridine nitrogen atoms N(1) and N(2) forming six-membered

365

metallacycle (Figure 3). In dinuclear tetradentate ruthenium and rhodium complexes (7) and (8a)

366

the hexadentate ligand L2 behaved as tetradentate bridging ligand coordinating both the metal

367

centers in a bidentate к2 fashion. Ligand L2 coordinates M(1) through pyridine nitrogen’s N(1)

368

and N(2) and ligates M(2) through pyridine nitrogen’s N(5) and N(6) forming six membered

369

metallacycle with both the metal centers (where M = Ru and Rh) (Figure 4). The dinuclear

370

complexes also displayed a similar three legged piano-stool geometry around the metal center

371

with coordination sites occupied by arene/Cp*, nitrogen donor atoms from chelating hexadentate

372

azine ligand in a tetradentate mode and terminal chloride. In tridentate iridium complex (9b) the

373

ligand L2 acted as tridentate chelating ligand coordinating Ir(1) in a tridentate к3 manner through

374

pyridine nitrogen’s N(1), N(4) and azine nitrogen N(2) (Figure 5). The geometry of the metal

375

center in these complexes is pseudo octahedral wherein the arene ligands serve as seat and

376

chloride and azine ligand forms the legs. The metal to carbon average distances (M = Ru, Rh and

377

Ir) in mononuclear complexes are {2.222 (1), 2.167 (2), 2.180 (3), 2.156 (5), 2.177 (9b) Å}. In

378

dinuclear complexes the average M(1)-C distances are {2.232 (7), 2.155 (8a) Å} while the

379

average M(2)-C distances are {2.164 (7), 2.151 (8a) Å} respectively. In all these complexes, the

380

arene/Cp* ligands are essentially planar and distance between the metal to centroid of the p-

381

cymene/Cp* ring in mononuclear complexes are {1.713 (1), 1.791 (2), 1.815 (3), 1.781 (5) and

382

1.801 (9b) Å} while in dinuclear ruthenium and rhodium complexes (7) and (8a) the M(1)-CNT

383

and M(2)-CNT distances are equal 1.690 (7) and 1.771 (8a) Å (Table 1). The bond lengths in

384

these complexes are very similar to previously reported three legged piano-stool complexes

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(Table 1) [34]. With respect to the bond angle values the N-M-N and N-M-Cl angles are close to

386

90° which is consistent with the piano stool arrangement of various groups about the metal

387

center. These bond angle values are comparable with previously reported complexes having

388

similar coordination environment (Table 1) [35]. Overall all the geometrical parameters are as

389

anticipated. Although, we were unsuccessful to isolate single crystal for some of the complexes

390

however the spectroscopic data’s strongly supports the formation of the complexes.

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Further the crystal packing of complex (7) shows a dimeric unit formed via inter-

392

molecular non-covalent C-H·····Cl (2.927 Å) interaction between the aromatic hydrogen of p-

393

cymene moiety and chloride attached to ruthenium (Figure S15). The crystal structure of

394

complex (8) crystallized with one water molecule which formed three different types of inter-

395

molecular non-covalent interactions the first between the hydrogen atom of water molecule and

396

chloride O-H·····Cl (2.546 Å) and the second and third between hydrogen atoms from pyridine

397

and chloride C-H·····Cl (2.927 & 2.746 Å (Figure S16). These non-covalent interactions play an

398

important role in the formation of supramolecular architectures.

399

3.4.

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Further discussions of molecular structures

Mononuclear tridentate and dinuclear tetradentate ruthenium, rhodium and iridium azine

401

complexes have been synthesized from symmetrical tetradentate and hexadentate azine ligand.

402

The introduction of the substituents attached to the imino carbon plays a crucial role in

403

determining the structural flexibility of the bridging azine ligand. The phenyl substituent in

404

ligand L1 produces a steric environment which forces the pyridine rings to come closer and

405

coordinate metal in tridentate mode. This steric effect of the phenyl ring may also be the reason

406

due to which the dinuclear complexes could not form with ligand L1. The presence of the phenyl

407

ring maximizes the steric hindrance between the neighboring phenyl group which in turn forces

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L1 to behave in a tridentate mode. But when both the phenyl group is substituted with pyridine

409

ring it becomes easy for the ligand L2 to form mononuclear as well as dinuclear complexes. In

410

the dinuclear complexes the multidentate azine Schiff-base ligand (L2) acts as a bridge to

411

communicate between the two metal centers.

412

Conclusion

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In this work, we have successfully synthesized d6 half-sandwich metal complexes bearing

414

tetradentate and hexadentate azine Schiff-base ligands. The ligands used in this work exhibited

415

interesting binding modes. In the mononuclear complexes, (1-3) L1 acted as tridentate chelating

416

ligand coordinating metal atom in a tridentate fashion through two pyridine nitrogen’s and one

417

azine nitrogen. This coordination led to formation of five and six membered chelate ring around

418

the metal center. In mononuclear rhodium complex (5) L2 coordinated rhodium in a bidentate

419

mode through two pyridine nitrogen atoms. Ligand L2 yielded two coordination isomer for the

420

rhodium and iridium precursor whereas exclusively one isomer for the ruthenium precursor. In

421

dinuclear ruthenium and rhodium complex (7) and (8a) ligand L2 behaved as tetradentate

422

bridging ligand coordinating both the metal centers in a bidentate fashion through the four

423

pyridine nitrogen’s thus forming six membered metallacycle with both the metal centers. In

424

complex (9b) the iridium center is coordinated by L2 in a tridentate mode through two pyridine

425

nitrogen’s and one of the azine nitrogen. It is interesting to note that ruthenium afforded only one

426

isomer in distinction rhodium and iridium yielded two coordination isomers. In general this work

427

carried out by us displays the use of multidentate azine Schiff-base ligands to form complexes

428

with interesting coordination modes.

429

Acknowledgements

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Sanjay Adhikari thanks, UGC, New Delhi, India for providing financial assistance in the form of

431

university fellowship (UGC-Non-Net). We thank DST-PURSE SCXRD, NEHU-SAIF, Shillong,

432

India for providing Single crystal X-ray analysis and other spectral studies.

433

Supplementary material

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434

CCDC 1554273 (1), 1554274 (2), 1554275 (3), 1554276 (5), 1554277 (7), 1554278 (8a)

435

and 1554279 (9b) contains the supplementary crystallographic data for this paper. These data can

436

be

437

[email protected], or by contacting The Cambridge Crystallographic Data Centre,

438

12, Union Road, Cambridge CB2 1EZ, UK; Fax: +44 1223 336033.

439

References

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[1]

L. Ronconi, P.J. Sadler, Coord. Chem. Rev. 251 (2007) 1633.

441

[2]

G. Gasser, N.M. Nolte, Curr. Opin. Chem. Bio. 16 (2012) 84.

442

[3]

S.Y. Mudi, T.M. Usman, S. Ibrahim, Am. J. Chem. Appl. 2 (2015) 151.

443

[4]

Y.K. Yan, M. Melchart, A. Habtemariam, P.J. Sadler, Chem. Comm. (2005) 4764.

444

[5]

A.F.A. Peacock, P.J. Sadler, Chem. Asian J. 3 (2008) 1890.

445

[6]

W.H Ang, A. Casini, G. Sava, P.J. Dyson, J. Organomet. Chem. 696 (2011) 989.

446

[7]

Q. Wu, K. Zheng, S. Liao, Y. Ding, Y. Li, W. Mei, Organometalllics 35 (2016) 317.

447

[8]

448

[9]

449

[10]

452

charge

via

www.ccdc.cam.ac.uk/data_request/cif,

SC

of

by e-mailing

AC C

EP

TE D

M AN U

free

L.A. Huxham, E.L.S. Cheu, B.O. Patrick, B.R. James, Inorg. Chim. Acta 352 (2003) 238. Y. Geldmacher, M. Oleszak, W.S. Sheldrick, Inorg. Chim. Acta 393 (2012) 84.

M.A. Scharwitz, I. Ott, Y. Geldmacher, R. Gust, W. Sheldrick, J. Organomet. Chem. 693 (2008) 2299.

450 451

obtained

[11]

M. Gras, B. Therrien, G. Suss-Fink, A. Casini, F. Edafe, P.J. Dyson, J. Organomet. Chem. 695 (2010) 1119. 21

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[12]

J. Canivet, G.Suss-Fink, P. Stepnicka, Eur. J. Inorg. Chem. 2007, 4736.

454

[13]

Z. Lui, P.J. Sadler, Acc. Chem. Res. 47 (2014) 1174.

455

[14]

J. Safari, S. Gandomi-Ravandi, RSC Adv. 4 (2014) 46224.

456

[15]

Y.-F. Yue, E.-Q gao, C.-J. Fang, T. Zheng, J. Liang, C.-H. Yan, Cryst. Eng. Comm. 10 (2008) 614.

[16]

Z. Xu, S. White, L.K. Thompson, D.O. Miller, M. Ohba, H. Okawa, C. Wilson, J.A.K. Howard, J. Chem. Soc. Dalton Trans. (2000) 1751.

459

SC

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RI PT

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[17]

E.-Q. Gao, Y.-F. Yue, S.-Q. Bai, Z. He, C.-H. Yan, J. Am. Chem. Soc. 126 (2004) 1419.

461

[18]

J. Yorke, C. Dent, A. Decken, A. Xia, Inorg. Chem. Comm. 13 (2010) 54.

462

[19]

M. Bakir, O. Brown, J. Mol. Struc. 641 (2002) 183.

463

[20]

M.U. Raja, B. Therrien, G. Suss-Fink, Inorg. Chem. Comm. 29 (2013) 194.

464

[21]

S. Adhikari, W. Kaminsky, M.R. Kollipara, J. Organomet. Chem. 836-837 (2017) 8.

465

[22]

D.D. Perrin, W.L.F. Armarego, Purification of Laboratory Chemicals, fourth ed.,

[23]

P.A. Vekariya, P.S. Karia, J.V. Vaghasiya, S. Soni, E. Suresh, M.N. Patel, Polyhedron,

[25]

AC C

110 (2016) 73.

E. Amadei, M. Carcelli, S. Ianelli, P. Cozzini, P. Pelagatti, C. Pelizzi, Dalton Trans. (1998) 1025.

472 473

[26]

474

[27]

475

EP

[24]

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M.A. Bennett, T.N. Huang, T.W. Matheson, A.K. Smith, S. Ittel, W. Nickerson, Inorg. Synth. 21 (1982) 74.

468 469

TE D

Butterworths Heinemann, London, 1996.

466 467

M AN U

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C.J. Sumby, P.J. Steel, New, J. Chem. 29 (2005) 1077. G.M. Sheldrick, (1997) SHELXL-97, Program for the Refinement of Crystal Structures. University of Göttingen, Germany.

22

ACCEPTED MANUSCRIPT

476

[28]

G.M. Sheldrick, Acta Crystallogr. (2015). C71, 3.

477

[29]

L.J. Farrugia, J. Appl. Crystallogr. 32 (1999) 837.

478

[30]

(a) A.L. Spek, PLATON, A Multipurpose Crystallographic Tool, Utrecht University, Utrecht, The Netherlands, 2008; (b) A.L. Spek, J. Appl. Crystallogr. 36

480

(2003) 7.

RI PT

479

[31]

O. Prakash, P. Singh, G. Mukherjee, A.K. Singh, Organometallics, 31 (2012) 3379.

482

[32]

A. Pastuszko, K. Niewinna, M. Czyz, A. Jozwiak, M. Malecka, E. Buddzisz, J. Organomet. Chem. 64 (2013) 754.

[33]

(a) F. Tuna, G. Clarkson, N. W. Alcock, M. J. Hannon, Dalton Trans, 2003, 2149; (b). D-

M AN U

483 484

SC

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B. Dang, B. An, W-J. Niu, Y. Bai, Spectrochimica Acta Part A 91 (2012) 338; (c) E.

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Amadei, M. Carcelli, S. Ianelli, P. Cozzini, P. Pelagatti, C. Pelizzi J. Chem. Soc., Dalton

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Trans. 1998 1025. [34]

(a) O. Dayan, M. Tercan, N. Ozdemir, J. Mol. Str. 1123 (2016) 35; (b) Z. Almodares, S.J.

TE D

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Lucas, B.D. Crossley, A.M. Basri, C.M. Pask, A.J. Hebden, R.M. Phillips, P.C.

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McGowan, Inorg. Chem. 53 (2014) 727; (c) T. Tsolis, M.J. Manos, S. Karkabounas, I.

491

Zelovitis, A. Garoufis, J. Organomet. Chem. 768 (2014) 1.

493 494 495 496

[35]

(a) G Gupta, G. Sharma, B. Koch, S. Park, S.S. Lee, J. Kim, New. J. Chem. 37 (2013) 2573; (b) H. Turkmen, I. Kani, B. Cetinkaya, Eur. J. Inorg. Chem. (2012) 4494; (c) S.

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Adhikari, D. Sutradhar, S. L. Shepherd, R. M. Phillips, A. K. Chandra, K. M. Rao, Polyhedron 117 (2016) 404.

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Chart-1 Ligands used in the present study

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Scheme-1. Synthesis of mononuclear tridentate complexes with L1

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Scheme-2. Synthesis of mononuclear bidentate complexes with L2

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Scheme-3. Synthesis of mononuclear tridentate and dinuclear tetradentate complexes with L2

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Figure 1 (a) ORTEP plot of complex (1) and (b) ORTEP plot of complex (2) with 50%

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probability thermal ellipsoids. Counter anions, hydrogen atoms, and solvent molecules are

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omitted for clarity.

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Figure 2 ORTEP plot of complex (3) with 50% probability thermal ellipsoids. Counter anions,

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Figure 3 ORTEP plot of complex (5) with 50% probability thermal ellipsoids. Counter anions,

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solvent molecules and hydrogen atoms are omitted for clarity.

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Figure 4 (a) ORTEP plot of complex (7) and (b) ORTEP plot of complex (8a) with 50% probability thermal ellipsoids. Counter

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Figure 5 ORTEP plot of complex (9b) with 50% probability thermal ellipsoids. Counter anions, solvent molecules and hydrogen

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Table 1 Selected bond lengths (Å) and bond angles (°) of complexes. 1

2

3

5

7

8a

9b

M(1)-CNT M(2)-CNT M(1)-Cave M(2)-Cave M(1)-N(1) M(1)-N(2) M(1)-N(4) M(2)-N(5) M(2)-N(6) M(1)-Cl(1) M(2)-Cl(2)

1.713 ----2.222 ----2.0993(18) 2.0257(17) 2.0952(18) --------1.271(4) 2.3897(11)

1.791 ----2.167 ----2.118(5) 2.049(5) 2.140(5) -----------------

1.815

1.781

2.180

2.156

2.103(4) 2.035(5) 2.099(4)

2.103(3) 2.117(3)

1.690 1.690 2.232 2.164 2.110(2) 2.094(3)

1.771 1.777 2.155 2.151 2.107(5) 2.108(5)

2.110(2) 2.094(3) 2.3875(9) 2.3875(9)

2.092(5) 2.116(5) 2.404(1) 2.389(1)

1.801 ---2.177 ---2.097(5) 2.093(5) 2.107(5) -------------

N(1)-M(1)-N(2) N(2)-M(1)-N(4) N(1)-M(1)-N(4) N(1)-M(1)-Cl(1) N(2)-M(1)-Cl(1) N(5)-M(2)-N(6) N(5)-M(2)-Cl(2) N(6)-M(2)-Cl(2)

75.22(7) 78.22(7) 93.61(7) ---------------------

75.6(2) 76.0(2) 91.2(2) ---------------------

74.5(2) 77.5(2) 90.3(2)

85.3(1)

83.6(1)

85.7(2)

87.14(8) 87.77(8)

85.54(7) 86.81(8) 83.6(1) 85.54(7) 86.81(8)

86.5(1) 89.8(1) 84.0(2) 88.6(1) 88.6(1)

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Complex

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74.9(2) 75.6(2) 89.64(19) ----------------

CNT represents the centroid of the arene/Cp* ring; Cave represents the average bond distance of the arene/Cp* ring carbon and metal

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In d6 metal complexes, azine ligands expressed variety of bonding modes.

Tetradentate azine ligand yielded only mononuclear tridentate complexes.

Hexadentate azine ligand yielded two coordination isomers for rhodium and iridium

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analogue whereas only one isomer for ruthenium.