Dicyclopentamethylenethiuram Disulfide as Precursor of Mononuclear Complexes: Oxidative Cleavage of Metal-Metal Bond in [CpMo(CO)₃]₂ and Molecular Structure of cis-[CpMo(CO)₂{S₂C-N(CH₂)₅}]

Md. Manzurul Karim^1*, Shafikul Islam², Md. RafikulIslam³, Mohammad R. Karim^4*, Tasneem A. Siddiquee⁴

¹Department of Chemistry, Jahangirnagar University, Savar, Bangladesh.
²Department of Chemistry, Morning Glory School and College, Savar, Bangladesh.
³Department of Chemistry, Barisal Cadet College, Barisal, Bangladesh.
⁴Department of Chemistry, Tennessee State University, Nashville, TN, USA.

DOI: 10.4236/csta.2017.64006                

Abstract

The reaction of [CpMo(CO)₃]₂ with dicyclopentamethylenethiuram disulfide in refluxing xylene resulted a novel mono nuclear complex,

cis-[(CpMo(CO)₂{S₂C-N(CH₂)₅}] as red crystals in moderate yield. The compound was formed by the oxidative cleavage of metal-metal bond in [CpMo(CO)₃]₂ together with a reductive sulfur-sulfur bond scission in the ligand.

Keywords

Dicyclopentamethylenethiuram Disulfide (Dcpmtd), Oxidation Number, Oxida-tive Cleavage, Coordination Number, Mononuclear Complex, X-Ray Crystal Structure

1. Introduction

Dithiocarbamate ligands are versatile ligands with applications in industry [1] , agriculture [2] and biology [3] . Since these ligands contain nitrogen and sulfur donor atoms, they are capable of forming complexes with most of the elements [4] . A number of dithiocarbamate complexes have been reported in literature [5] - [12] with various geometries such as square planar [13] , octahedral [14] [15] and trigonal prismatic [16] . Interestingly, their pyridine [6] [7] [17] , 2,2'-bipyridine [7] [9] triphenylphosphine [18] , and 1,10-phenanthroline [9] [17] adducts have been reported to possess similar donor properties. These ligands may stabilize monatomic metal ions in various oxidation states because of its chelating capacity thus forming mononuclear complexes [19] - [28] . The anionic form of N,N-dialkyl-1, 1-dithio-ligands is stable and the stability stems from the resonance of the anionic form of the ligand (Figure 1) [19] .

Shi et al. reported the reaction between [CpMo(CO)₂]₂ with tetramethylthiuram disulfide which yielded the mononuclear cyclopentadienyl molybdenum dithiocarbamate complex cis-[(CpMo(CO)₂{S₂C-N(CH₃)₂}] [29] . The compound is formed by oxidative cleavage of Mo-Mo triple bond together with a reductive S-S bond scission in tetramethylthiuram disulfide ligand (Scheme 1).

2. Results

We carried out the analogous reaction of dicyclopentamethylenethiuram disulfide with [CpMo(CO)₃]₂ and reported herein the formation of a mononuclear cyclopentadienyl molybdenum dicarbonyl complex, cis-[(CpMo(CO)₂{S₂C-N(CH₂)₅}].

Treatment of [CpMo(CO)₃]₂ with dicyclopentamethylenethiuram disulfide in refluxing xylene gave thermally stable complex cis-[(CpMo(CO)₂{S₂C-N(CH₂)₅}] as major reaction product (Scheme 2) which has been characterized by elemental analysis and spectroscopic methods [30] . The structure of the complex has been determined by single crystal X-ray diffraction [31] which is summarized in Figure 2.

Figure 1. Resonance structures of anioic N,N-dialkyl-1,1-dithio ligand.

Figure 2. Molecular structure of cis-[(CpMo(CO)₂{S₂C-N(CH₂)₅}].

Scheme 1. Oxidative cleavage of Mo-Mo triple bond in thiuram disulfide by [CpMo(CO)₂]₂.

Scheme 2. Synthesis of cis-[(CpMo(CO)₂{S₂C-N(CH₂)₅}].

The molecular structure of cis-[(CpMo(CO)₂{S₂C-N(CH₂)₅}] shows a four-legged piano-stool configuration at Mo(II), being coordinated to a bidentate cyclo pentamethylene dithiocarbamate and two CO ligands, similar to the coordination found in the analogous complex ion cis-[(CpMo(CO)₂{S₂C-N(CH₃)₂}] (Scheme 2) [29] . Bond lengths S(1)-C(3) and S(2)-C(3) have been found 1.708(5) Å, which is consistent with the partial C-S double bond [32] . The average Mo-C(Cp) bond distance in cis-[(CpMo(CO)₂{S₂C-N(CH₂)₅}] has been found to be 2.326 Å, which is similar to the Mo-C(Cp) average bond distance of 2.325 Å as found in cis-[(CpMo(CO)₂{S₂C-N(CH₃)₂}] [29] . Mo-S bond distance in cis-[(CpMo(CO)₂{S₂C-N(CH₂)₅}] was found 2.500 Å which is similar to the average Mo-S bond distance reported in cis-[(CpMo(CO)₂{S₂C-N(CH₃)₂}] (2.503 Å) [29] . Average Mo-CO bond distance in cis-[(CpMo(CO)₂{S₂C-N(CH₂)₅}] is 1.962 Å. Similar average Mo-CO bond distance 1.958 Å was found in cis-[(CpMo(CO)₂{S₂C-N(CH₃)₂}] (Figure 2) [29] .

Selected bond lengths [Å] and bond angles [˚]: Mo(1)-C(1) 1.958(6), Mo(1)-C(2) 1.966(6), Mo(1)-C(9) 2.275(6), Mo(1)-C(10) 2.300(6), Mo(1)-C(13) 2.306(6), Mo(1)-C(12) 2.363(6), Mo(1)-C(11) 2.384(6), Mo(1)-S(1) 2.505(2), Mo(1)-S(2) 2.495(3), S(1)-C(3) 1.708(5), S(2)-C(3) 1.708(5), C(2)-Mo(1)-C(1) 5.7(2), C(2)-Mo(1)-S(1) 81.47(19), C(1)-Mo(1)-S(1) 121.98(18), S(2)-Mo(1)-S(1) 68.55(7).

The complex, cis-[(CpMo(CO)₂{S₂C-N(CH₂)₅}] was obtained by the oxidative cleavage of the Mo-Mo bond in [CpMo(CO)₃]₂ which is consistent with the increase in oxidation number of Mo atom in the complex from +1 to +2. The geometry of the compound can be described as square-pyramidal with Cp-Mo defining the vertex and C(1), C(2), S(1) and S(2) atoms defining the base. The base of this complex is not a regular square because of unequal bond lengths of Mo-S and Mo-C bonds. In complex cis-[(CpMo(CO)₂{S₂C-N(CH₂)₅}], the cyclopentadienyl ligand acts as five electron donor and dithiocarbamate acts as three electron donor ligand. The complex is thermally stable and follows 18-electron rule.

Acknowledgements

The authors acknowledge ministry of science and technology, Bangladesh for financial assistance and Department of chemistry, Jahangirnagar University for providing the laboratory facility.

Supplementary Material

Crystallographic data for cis-[(CpMo(CO)₂{S₂C-N(CH₂)₅}] has been deposited at the Cambridge Crystallographic Centre with CCDC Reference Number CCDC 1567351. Copy of the data can be obtained free of charge via https://www.ccdc.cam.ac.uk/conts/retrieving.html (or from Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK (Tel: [phone]; fax: [phone]; email: [e-mail])).

Conflicts of Interest

The authors declare no conflicts of interest.

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[30]	To a xylene (40 mL) of [CpMo(CO)3]2 (0.200 g, 0.408 mmol) Was Added Dicyclopentamethylenethiuram Disulfide (0.196 g, 0.612mmol) and the Reaction Mixture Was Refluxed for 1 Hour. The Color Was Changed from Red to Red Brown. The Solvent Was Removed under Reduced Pressure and Residue Chromatographed by TLC on Silica. Elution with Cyclohexane/Dichloromethane (3:2 V/V) Gave One Band cis-[(CpMo(CO)2{S2C-N(CH2)5}] (0.167 g, 36.16%) as Red Brown Crystal from Dichloromethane/Hexane Mixture at ?4 oC. Elemental Analysis: Found C = 41.36, H = 3.99, N = 3.70, S = 16.94% and C13H15MoNO2S2 Requires C = 41.34, H = 3.98, N = 3.71, S = 16.96%. IR (υCO) in cm?1: 1857.53(s), 1949.15(s). 1H NMR (ppm): 1.54 (m, 3H), 1.63 (m, 3H), 3.56 (m, 2H), 3.79 (m, 2H), 5.41 (s, 5H). FAB mass (m/z):377 [M+], 349 [M+-CO], 321 [M+-2CO], 257 [M+-2CO-2S], etc.
[31]	Crystal Data for cis-[(CpMo(CO)2{S2C-N(CH2)5}]: Empirical Formula C13H15MoNO2S2, MW = 377.32, Triclinic, Space groupP1, a = 6.449(7) A, b = 10.634(10) A, c = 11.383(12) A, α = 71.94(3)°, β = 82.31(3)°,γ = 76.43(3)°, V =719.9(13) A3, T= 273(2) K, Z= 2, μ=1.197 mm-1, F(000) 380, density (calculated) 1.741 Mg/m3, 7722 Reflections Collected, 3303 Independentreflections [R(int) = 0.0477]. The Final R1 = 0.0486, wR2 = 0.1288 [I > 2σ (I)], R Indices (all data) R1 = 0.0719, wR2 = 0.1566.
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