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Article Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX

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Trithia-diborinane and Bis(bridging-boryl) Complexes of Ruthenium Derived from a [BH3(SCHS)]− Ion Koushik Saha,† Urminder Kaur,†,§ Sourav Kar,†,§ Bijan Mondal,† Benson Joseph,† P. K. Sudhadevi Antharjanam,‡ and Sundargopal Ghosh*,† †

Department of Chemistry and ‡SAIF, Indian Institute of Technology Madras, Chennai 600036, India

Inorg. Chem. Downloaded from pubs.acs.org by TEMPLE UNIV on 02/04/19. For personal use only.

S Supporting Information *

ABSTRACT: The field of diborinane is sparsely explored area, and not many compounds are structurally characterized. The room-temperature reaction of [{Cp*RuCl(μ-Cl)}2] (Cp* = η5-C5Me5) with Na[BH3(SCHS)] yielded ruthenium dithioformato [{Cp*Ru(μ,η3-SCHS)}2], 1, and 1thioformyl-2,6-tetrahydro-1,3,5-trithia-2,6-diborinane complex, [(Cp*Ru){(η2-SCHS)CH2S2(BH2)2}], 2. To investigate the reaction pathway for the formation of 2, we carried out the reaction of [(BH2)4(CH2S2)2], 3, with 1 that yielded compound 2. To the best of our knowledge, it appears that compound 2 is the first example of a ruthenium diborinane complex where the central six-membered ring [CB2S3] adopts the chair conformation. Furthermore, room temperature reaction of 1 with [BH3·thf] resulted in the isolation of agostic-bis(σ-borate) complex, [Cp*Ru(μ-H)2BH(S-CHS)], 4. Thermolysis of 4 with trace amount of tellurium powder led to formation of bis(bridging-boryl) complex, [{Cp*Ru(μ,η2-HBS2CH2)}2], 5, via dimerization of 4 followed by dehydrogenation. Compound 5 can be considered as a bis(bridging-boryl) species, in which the boryl units are connected to two ruthenium atoms. Theoretical studies and chemical bonding analyses demonstrate the reason for exceptional reactivity and stability of these complexes.

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INTRODUCTION Recent years have witnessed significant growth in the field of transition metal borane chemistry ranging from supraicosahedral clusters to unusual structures involving one or two boron atoms.1,2 Consequently, there has been continuous studies for the understanding of chemical bonding of metal− boron interaction.3 The electronic contributions of metal and boranes to the nonclassical cluster structure are expressed in such a way that the reaction varieties are not seen for transition metal complexes or boranes individually.4 As a result, the field of metallaborane chemistry continues to yield surprises, with various structural types and unusual reactivities.3−5 The synthetic development of metallaboranes emerged from two major methodologies:6 (i) treatment of anionic boranes with metal precursors and (ii) the condensation reactions of cyclopentadienyl metal polychlorides with monoboron reagents.6,7 Although the former method yields only thermodynamically stable products, monoborane condensation often leads to uncontrolled products formation. In the recent past, we have explored the reactivity of various chalcogen-based borate ligands, such as, Li[BH3ER] and Li[BH2E3] (E = S, Se, or Te; R = phenyl or ferrocenyl) with pentamethylcyclopentadienyl based metal halides, which led to the formation of a wide range of new types of transition metal borane complexes with interesting topologies.8 After discovering that the reactions of these chalcogen-based borate ligands led to interesting compounds, a reinvestigation of a related system became attractive. Therefore, we pursued this © XXXX American Chemical Society

chemistry with a modified borohydride reagent, Na[BH3(SCHS)] and [Cp*RuCl(μ-Cl)]2. Although the objective of generation of higher nuclearity clusters was not achieved, interesting ruthenium complexes were isolated. Herein we present the viable synthetic routes for the isolation of trithiadiborinane, agostic-bis(σ-borate), and bis(bridging-boryl) complexes of ruthenium. The computational results reported here efficiently demonstrate the bonding of these compounds and their potential reactivity with small molecules.

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RESULTS AND DISCUSSION Reactivity of Na[BH3(SCHS)] with [Cp*RuCl(μ-Cl)]2. In search of an alternative borane source for the synthesis of transition-metal−boron complexes, we have explored the reactivity of a modified borohydride reagent, Na[BH3(SCHS)]9 with [Cp*RuCl(μ-Cl)]2 that led to the formation of 1 (Scheme 1). It was isolated as orange crystals with a 28.59% yield and was characterized by 1H and 13C{1H} NMR, IR spectroscopy, and single crystal X-ray diffraction studies. The mass spectrum of 1 showed a molecular ion peak at m/z 628.9560 [M + H]+. The 11B{1H} NMR showed no resonances, and the 1H NMR showed two signals at δ = 1.61 and 4.70 ppm for the Cp* and dithioformato ligands. The spectroscopic and mass spectrometric data were not adequate to predict the identity of 1. An unambiguous explanation Received: September 27, 2018

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DOI: 10.1021/acs.inorgchem.8b02759 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry Scheme 1. Syntheses of Ruthenium Dithioformato Compounds 1, 2, and 4

Compound 2 displayed 1H NMR resonances at δ = 6.52 ppm due to methine proton and δ = 4.64 and 3.92 ppm due to the methylene protons, respectively. Presence of terminal hydrogens associated with boron atoms were confirmed by 1H{11B} NMR spectroscopy (δ = 4.14 and 3.45 ppm). High resolution mass spectrometry experiment was carried out on 2 and the result provided molecular mass consistent with the formula C12H22B2S4Ru. Single crystal X-ray diffraction study showed compound 2 as 1-thioformyl-2,6-tetrahydro-1,3,5-trithia-2,6-diborinane complex of ruthenium (Figure 2a). The average B−S bond length

eluded us until an X-ray diffraction study revealed the molecular structure of 1 as [{Cp*Ru(μ,η3-SCHS)}2]. The solid-state X-ray structure of 1, shown in Figure 1a, clearly

Figure 1. (a) Molecular structure and labeling diagram of 1. Selected bond lengths (Å) and angles (deg): Ru1−C11 2.116(6), S2−C11 1.703(8), S1−C11 1.752(7), S2−Ru1 2.4137(17), S1−Ru1 2.4048(16), S1−Ru1 2.3733(16); S2−C11−S1 123.6(4). (b) the HOMO of 1 showing its donating ability.

shows that each metal is coordinated to an {η3-SCHS} unit and one sulfur atom from the another dithioformato ligand. The observed Ru−Ru distance of 3.7 Å eliminates the possibility of having any Ru−Ru interaction. Two different sets of C−S bond distances (S2−C11 = 1.703(8) Å and S1− C11 = 1.752(7) Å) have been observed in 1 that exhibit a partially delocalized bonding situation of the dithioformato ligand. Trithia-diborinane Ruthenium Complex, 2. Along with compound 1, we have isolated another compound, 2, in 20.50% yield. This reaction also yielded some air and moisture sensitive compounds that we were not able to isolate in their pure form. Therefore, the yield of compounds 1 and 2 are poor, and several efforts to increase the yield does not improve the situation. The 11B{1H} NMR spectrum of compound 2 reveals sharp peaks at δ = −5.0 and −15.6 ppm in 1:1 ratio that suggests the presence of two chemically nonequivalent boron environments. In addition, the 11B NMR spectrum showed two triplets which indicates the presence of the {BH2} units.

Figure 2. (a) Molecular structure and labeling diagram of 2. Selected bond lengths (Å) and angles (deg): C12−Ru1 2.11(2), C11−S1 1.66(2), C11−S2 1.87(2), C12−S3 1.881(15), C12−S4 1.671(15), Ru1−S1 2.388(7), Ru1−S2 2.487(6), Ru1−S4 2.371(6), S1−B2 1.80(2), S2−B1 1.84(3), S3−B1 1.95(3), S3−B2 2.07(3); S1−C11− S2 102.1(13), S3−C12−S4 116.8(12), C12−Ru1−S4 43.3(4). (b) HOMO of 2 depicting the localized orbitals.

(avg 1.915 Å) is within the single B−S distances.9 One of the interesting features of 2 is the presence of a thioformyl (CHS) unit bonded to ruthenium having a short C−S distance (1.671(15) Å). This may be due to the presence of ruthenium that brings the carbon and sulfur atoms in close proximity. Ruthenium atom in 2 exists in +2 oxidation state. The borate units (B1 and B2) possess one negative charge each, and the sulfur atom (S3) between the borate units possesses one positive charge. This ultimately makes the trithia-diborinane B


Article

Inorganic Chemistry Table 1. Selected Structural and Spectroscopic Data of Diborinane Derivatives and Complexes10−14

a

NMR spectra were recorded in CDCl3 solvent unless stated. bE = heteroatom in the central ring. cconformation of the central six membered ring. In [D8]-thf. e2,6-Diisopropylphenyl. f2,6-Dimethyl-phenyl. gIn CD2Cl2.

d

complexes remain as a sparsely explored area mainly due to the lack of proper synthetic routes. Although handful of heterocyclic borane compounds are reported, very few diborinane compounds, mainly derivatives, are known to date.10−14,20−22 Although some examples of the trithiadiborinane compounds have been reported, there have been no reports on metal complexes of trithia-diborinane species. Compound 2 is the first example of a trithia-diborinane stabilized ruthenium complex. To gain insight into the mechanism for the formation of compound 2, we carefully monitored the reaction of Na[BH3(SCHS)] with [Cp*RuCl(μ-Cl)]2 under various reaction conditions. One of the reaction conditions, i.e., thermolysis of the reaction mixture at 60 °C for 18 h yielded compound 3 as colorless solid along with compounds 1 and 2. The 11B{1H} chemical shift appearing at δ = −16.9 ppm corresponds to tetrahedral boron. The 1H NMR showed a peak at δ = 1.91 ppm for the terminal hydrogens associated with boron atoms. The molecular ion peak in ESI-MS spectrum suggests the molecular formula as C2H12B4S4. On the basis of the spectroscopic and single-crystal X-ray data, compound 3 was characterized as [(BH2)4(CH2S2)2] having an adamantane geometry. This compound was reported in 1984 by Binder et al. in good yield.23 The core geometries

{CH2S3(BH2)2} moiety a monoanionic species. The sixmembered ring containing the {CB2S3} moiety adopts a chair conformation similar to that of the reported diborinane species, such as bis(γ-picoline)-1,4-diethyl-2,5-bis(trimethylsilyl)-1,4-diborinane and [BH2CH2SMe]2.10,11 It is unlike that of other substituted diborinanes, such as [(BNMe2)(CH2)(N−Ar)]2 (Ar = mesityl, Dip and Xyl), where the central six-membered ring adopts a boat conformation.12 Meller et al. reported the first transitionmetal−diborinane adduct in 1986, [(BMe) 2 (NH){N(SiMe3)}2(S){W(CO)5}].13 Recently, Braunschweig et al. reported bis(cAAC)-stabilized 3,6-dicyano-1,2,4,5-tetrasulfa3,6-diborinane where the central {B2S4} ring displays boat conformation and this was the first example of structurally and NMR-spectroscopically characterized {B2S4}-heterocycle.14 Selected examples of the structurally characterized diborinane derivatives are listed in Table 1, and it is clear that the tetracoordinated boron atoms in the diborinane species are more shielded and appear in the upfield region as compared to the tricoordinated boron atoms.10−14 Enormous growth has been observed in the field of boroncontaining ring compounds.15−17 The attention was mainly focused on the classes of the borole and boralane rings.18,19 In contrast, the diborinane species and their chemistry with metal C


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Inorganic Chemistry

structure of 4. The different C−S bond distances (C11−S1 = 1.687(13) Å and C11−S2 = 1.569(15) Å) denote unsaturation in the {SCHS} moiety and suggest possible base stabilization to the {BH3} unit. Although the experimental data on bond parameters suggest compound 4 is a base-stabilized agostic-bis(σ-borane) complex, the DFT calculations26 show a delocalized situation (Figures S26 and S27). Thus, compound 4 may be considered in between borate and borane descriptions. The QTAIM analysis effectively captures two important pictures: (i) dative interaction of the S2 lone pair with B1 (with S → B bond polarization), which stabilizes the borane moiety and (ii) forward electrostatic interactions of BH bond with Ru center (Figure S27b,c). This was further supported by the NBO analysis that showed the existence of two 3c−2e Ru−H−B bonds with maximum BH (85%) to Ru (15%) forward donation. In addition, the NBO-based second-order-perturbation-energy analyses showed a minor back-donation of the electron density into the vacant B−H orbital that results in a weak delocalization interaction of 8.94 kcal·mol−1. The HOMO of 4, depicted in Figure 3b, suggests that both the S atoms are engaged in bonding with p orbitals of CH and BH3. However, a large amount of electron density is localized on Ru center, which is in antibonding interaction with the forward BH donation. This “acceptor” nature of 4 and relatively “open” pseudo-octahedral geometry is suitable to test the scope of 4 with electron-rich species. Compound 4 is very labile in nature. It slowly converts to 1 by losing BH3 at room temperature. This conversion was even faster when PPh3 was added to 4 that formed [BH3·PPh3] adduct. Ruthenium Bis(bridging-boryl) Complex, 5. Inspired by the work of Sabo-Etienne and co-workers on σ-borane to borylene transformation by dehydrogenation,27 we photolyzed as well as thermolyzed 4. Photolysis of 4 led to decomposition of the starting material; however, 4, under thermolytic condition, in the presence of small amount of tellurium powder, produced compound 5 with 10.20% yield (Scheme 2).28 The 11B{1H} NMR showed two closely separated signals

(CB2S3 ring) of compounds 2 and 3 are very similar to each other. This prompted us to carry out the reaction of ruthenium dithioformato complex, 1, with compound 3. Indeed, the reaction at room temperature led to the formation of compound 2 in 49.77% yield. Therefore, we believe that in due course of reaction of Na[BH3(SCHS)] with [Cp*RuCl(μCl)]2, compound 3 might have formed in situ and further reacted with 1 to yield compound 2. To gain insight into the bonding and electronic structure of 2, we have undertaken computational studies based on DFT (density functional theory) methods at the pbepbe/def2-svp level of theory starting from the X-ray coordinate. The optimized geometry is almost in agreement with the solid-state structure. The HOMO−LUMO gap of 2.093 eV at the GGA PBE level of theory is well-matched with the high stability of compound 2. The HOMO is localized on Ru and S atoms of thioformyl group (Figure 2b), whereas HOMO−9 and HOMO−11 show that d-orbital of Ru and p-orbital of S participated in bonding (Figure S23). We have checked the Laplacian plot of electron density of 2 along the S−Ru−S plane which showed a bond critical point (bcp) between Ru1− S1 and Ru1−S2 (Figure S24). Reactivity of Ruthenium Dithioformato Compound, 1 with [BH3·thf]. The HOMO of 1 shown in Figure 1b clearly indicates its donating ability through the S ends (the HOMO is largely centered on both the S atoms), which allowed us to test its reactivity with small molecules such as borane, silane, alkyne, and so on. Although silanes and alkynes do not react with 1, treatment of 1 with [BH3·thf] led to the formation of compound 4 with 61.26% yield (Scheme 1). The 11B{1H} NMR showed a signal at upfield region (δ = 19.1 ppm) for shielded boron atom. The 1H NMR chemical shifts confirm the presence of one Cp* ligand, two Ru−H−B protons, one terminal B−H, and one thioformato ligand (SHCS). The spectroscopic data along with the solid-state X-ray crystal structure (Figure 3a) distinctly showed a mononuclear

Scheme 2. Synthesis of Ruthenium Bridging-Boryl Compound 5

Figure 3. (a) Molecular structure and labeling diagram of 4. Selected bond lengths (Å) and angles (deg): S1−Ru1 2.249(3), B1−Ru1 2.143(12), C11−S1 1.687(13), C11−S2 1.569(15), B1−S2 2.048(18); S1−C11−S2 125.7(7), S2−B1−Ru1 111.4(7). (b) HOMO of 4 demonstrating its acceptor possibility.

(δ = 65.3 and 64.1 ppm). The 1H and 13C{1H} NMR spectra showed the presence of methylene groups and a single set of Cp* protons. A single crystal X-ray diffraction study revealed the structure of 5 to be [{Cp*Ru(μ,η2-HBS2CH2)}2] (Figure 4), where the boryl ligands {−SCH2SBH−} bridge two {Cp*Ru} units. Since the first appearance of X-ray structure of such complexes in 1990, only a handful of structurally characterized metal bridging-boryl complexes are reported (Figure S30).29,30 In the context of existing examples, compound 5 is unique as the

complex, where the single boron atom is connected to the ruthenium center through two B−H−M bridges that makes the metal−boron separation considerably shorter (2.143(12) Å).24 The observed Ru−B distance can be compared with those of [Cp*Ru(μ-H)2BL] (2.216(6) Å, L = 2-mercaptobenzothiazolyl) and [RuH{(μ-H)2BMeCH2SMe}(PCy3)2] (2.266(8) Å, Cy = cyclohexyl).25 A unique {Ru-μH−B−S− C-S} metallaheterocycle is evidenced from the molecular D


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Inorganic Chemistry

structure determination. Likewise, the large HOMO−LUMO gaps are in accord with the high stabilities (Table S1), and the 11 B chemical shifts accurately (with error range ca. 2−4 ppm) reflecting the observed shifts (Table S2). Although the DFT, MO and NBO analyses preclude any Ru−Ru interaction, Laplacian plot of charge density analyses suggest a strong interaction between Ru1 and Ru2 (Figure 5). The results convincingly demonstrate the crucial role of the bridging (HBSCH2S) ligands that shorten the intermetallic Ru−Ru distance (see electronic structure analysis of 5 in the Supporting Information). The observed Ru−Ru bond distance of 2.6196(6) Å in 5 falls in the short range compared to those of reported compounds containing a Ru−Ru single bond, for example, metallaborane cluster, [nido-1,2-(Cp*Ru) 2 (μ-H)B 4 H 9 ] (2.8527(4) Å), 32 triply bridging borylene [(μ 3 -BH)(Cp*RuCO)2(μ-CO){Fe(CO) 3}] (2.7584(2) Å), 33 and vinyl-borylene complex (Z)-[(Cp*RuCO)2(μ-CO)B(CPh)(CH-Ph)] (2.7584(4) Å).34 However, this is longer than compounds that showed the presence of RuRu bonds, for example, [Cp*2Ru2H3B(N,N-dimethylphenylenediamine)]35 (Ru−Ru 2.455(1) Å) and [(Cp*Ru)2 (μ-CO)(μ-H)(μBcat)]31 (2.404(3) Å). In contrast, it is comparable to [Ru(NO)(μ-P(C6H5)2)(P(CH3)(C6H5)2)]236 (2.629(2) Å) that contains a formal double bond. The natural bond orbital (NBO) analysis on 5 showed the Wiberg bond index value of 0.35. Therefore, it is reasonable to assume that 5 contains a formal double bond. The natural charge analysis also shows that both the B and S atoms bear positive charge (B1, B2; qB = 0.11; S2, S3; qS = 0.327); thus, they may be considered a donor. However, the Ru center acts as an acceptor (qRu = −0.58). Interestingly, neither the MO nor the NBO analysis showed the presence of any double bond character in 5. As a result, we have checked its Laplacian plot

Figure 4. (a) Molecular structure and labeling diagram of 5. Selected bond lengths (Å) and angles (deg): B2−S1 1.722(11), B2−Ru1 2.181(9), B2−Ru2 2.196(9), C23−S1 1.772(13), C23−S2 1.850(15), B1−S4 1.805(9), B1−Ru2 2.191(8); S1−C23−S2 116.5(7), Ru1− B2−Ru2 73.5(3), S1−B2−Ru2 123.4(7). (b) HOMO of 5.

structure is simple and does not require bulky ligand on boron atom due to the chelate stabilization provided by the rest of the bridging group. The average Ru−B bond length of 2.185 Å is reasonably shorter than that of IV (Figure S30) and [(Cp*Ru)2(μ-H)(μ-CO)(μ-BCat)];31 however, they are similar to those of 4. Four acute bite angles (two ∠Ru−B−Ru and ∠Ru−S−Ru) fetch both the Ru centers to close proximity that resulted in a shorter Ru−Ru contact (2.6196(6) Å). Theoretical Insights on the Bonding of Compound 5. To gain further insight into the bonding of 5, we have undertaken computational studies based on density functional theory (DFT) methods starting from the X-ray coordinate at the pbepbe/def2-svp level of theory. The electronic structure calculations/yield geometry is in agreement with the solid-state

Figure 5. Contour line diagrams of Laplacian of electron density of 5 along the (a) Ru1−B1−Ru2 plane and (c) plane perpendicular to Ru−Ru bond, respectively. Solid red lines indicate areas of charge concentration (∇2ρ(r) < 0), while dashed black lines show areas of charge depletion (∇2ρ(r) > 0). Blue dots indicate bond critical points (BCPs)]. (b) and (d) Respective ELF plots. E


Inorganic Chemistry of electron density that showed a bond critical point (bcp) and bond path between two Ru centers (Figure 5). As shown in Figure 5, an area of charge concentration along the Ru1−Ru2 bond was observed with high covalent character. This has also been reflected by higher values of the electron density (ρb = 112.25) and a negative value of the energy density [H(r) = −64644.8] at bcp. In order to understand the interaction of the bridging boryl ligands in 5 with two Cp*Ru fragments, we have also performed the Fenske−Hall MO calculation provided in Figures S28 and S29. The theoretical calculation on compound 5 explain the bonding situation explicitly and indicate that the bridging boryl ligands in 5 are responsible for the short Ru−Ru bond. This bis(bridging-boryl) complex is a novel entry to the class of transition-metal−boryl complexes.

ACKNOWLEDGMENTS

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REFERENCES

(1) (a) Roy, D. K.; Mondal, B.; Shankhari, P.; Anju, R. S.; Geetharani, K.; Mobin, S. M.; Ghosh, S. Supraicosahedral Polyhedra in Metallaboranes: Synthesis and Structural Characterization of 12-, 15- and 16-Vertex Rhodaboranes. Inorg. Chem. 2013, 52, 6705−6712. (b) Zhang, J.; Xie, Z. Recent Progress in the Chemistry of Supercarboranes. Chem. - Asian J. 2010, 5, 1742−1757. (c) Robertson, A. P. M.; Beattie, N. A.; Scott, G.; Man, W. Y.; Jones, J. J.; Macgregor, S. A.; Rosair, G. M.; Welch, A. J. 14-Vertex Heteroboranes with 14 Skeletal Electron Pairs: An Experimental and Computational Study. Angew. Chem., Int. Ed. 2016, 55, 8706−8710. (d) Ghosh, S.; Beatty, A. M.; Fehlner, T. P. The Reaction of Cp*ReH6, Cp* = C5Me5 with Monoborane to Yield a Novel Rhenaborane. Synthesis and Characterization of arachno-Cp*ReH3B3H8. Collect. Czech. Chem. Commun. 2002, 67, 808−812. (e) Ghosh, S.; Shang, M.; Fehlner, T. P. A Novel Coordinated Inorganic Benzene. The synthesis and Characterization of {η5-C5Me5Re}2{μ-η6:η6-B4H4 Co2(CO)5}. J. Am. Chem. Soc. 1999, 121, 7451−7452. (f) Ghosh, S.; Noll, B. C.; Fehlner, T. P. Expansion of Iridaborane Clusters by Addition of Monoborane. Novel Metallaboranes and Mechanistic Detail. Dalton Trans 2008, 371−378. (2) (a) Marder, T. B., Lin, Z., Eds. Contemporary Metal Boron Chemistry I. Borylenes, Boryls, Borane σ-complexes, and Borohydrides; Springer, 2008; Vol. 130. (b) Braunschweig, H.; Dewhurst, R. D.; Gessner, V. H. Transition metal borylene complexes. Chem. Soc. Rev. 2013, 42, 3197−3208. (c) Bose, S. K.; Geetharani, K.; Sahoo, S.; Reddy, K. H. K.; Varghese, B.; Jemmis, E. D.; Ghosh, S. Synthesis, Characterization, and Electronic Structure of New Type of Heterometallic Boride Clusters. Inorg. Chem. 2011, 50, 9414−9422. (d) Anju, R. S.; Saha, K.; Mondal, B.; Dorcet, V.; Roisnel, T.; Halet, J.-F.; Ghosh, S. Chemistry of Diruthenium Analogue of Pentaborane(9) With Hetero-cumulenes: Towards Novel Trimetallic Cubanetype Clusters. Inorg. Chem. 2014, 53, 10527−10535. (e) Yuvaraj, K.; Roy, D. K.; Geetharani, K.; Mondal, B.; Anju, V. P.; Shankhari, P.; Ramkumar, V.; Ghosh, S. Chemistry of Homo and Hetero-metallic Bridged-Borylene Complexes. Organometallics 2013, 32, 2705−2712. (f) Roy, D. K.; Mondal, B.; Anju, R. S.; Ghosh, S. Chemistry of Diruthenium and Dirhodium Analogues of Pentaborane (9): Synthesis and Characterization of Metal N,S-Heterocyclic Carbene and B-agostic Complexes. Chem. - Eur. J. 2015, 21, 3640−3648. (3) (a) Muetterties, E. L., Ed. Boron Hydride Chemistry; Academic Press, New York, 1975. (b) Fehlner, T. P.; Halet, J.-F.; Saillard, J.-Y. Molecular Clusters. A Bridge to Solid-State Chemistry; Cambridge University Press: New York, 2007. (c) Housecroft, C. E. Boranes and Metalloboranes: Structure, Bonding and Reactivity; Halsted Press: New York, 1990. (d) Krishnamoorthy, B. S.; Thakur, A.; Chakrahari, K.; Bose, S. K.; Hamon, P.; Roisnel, T.; Kahlal, S.; Ghosh, S.; Halet, J.-F. Theoretical and Experimental Investigations on Hypoelectronic Heterodimetallaboranes of Group 6 Transition Metals. Inorg. Chem. 2012, 51, 10375−10383. (e) Geetharani, K.; Krishnamoorthy, B. S.; Kahlal, S.; Mobin, S. M.; Halet, J.-F.; Ghosh, S. Synthesis and Characterization of Tantalaboranes. Comparison of the Geometric and Electronic Structures of [(Cp*TaX)2B5H11] (X = Cl, Br and I). Inorg. Chem. 2012, 51, 10176−10184. (f) Ghosh, S.; Shang, M.; Fehlner, T. P. Comparison of the Geometric and Molecular Orbital Structures of (Cp*Cr)2B4H8 and (Cp*Re)2B4H8, Cp* = η5-C5Me5. Structural Consequences of Delocalized Electronic Unsaturation in a Metallaborane Cluster. J. Organomet. Chem. 2000, 614, 92−98.

CONCLUSION In summary, [BH3(SCHS)]− ion found to be a suitable precursor for the synthesis of trithia-diborinane and dithioformato metal complexes. Compound 2 is the first structurally characterized trithia-diborinane complex of ruthenium where the central ring [CB2S3] adopts a chair confirmation . We have fur ther established that [(BH2)4(CH2S2)2], 3, plays a key role in the formation of 2. The synthetic method that we have developed may be extended to synthesize other transition metal diborinane complexes. Synthesis of agostic-borate complex, 4, from 1 presented the simplest synthetic route that does not require preformed boron-containing bulky ligands. In contrast, compound 5 does not possess any bulky ligand on boron atom. Investigations to evaluate the scope of synthesis of boryl complexes concerning early transition metals are underway. ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.8b02759. Synthesis procedures; 1H, 11B{1H}, 13C{1H} NMR and mass spectra; X-ray analysis details; DFT-computed results for 1-5 and other computational details (PDF) Accession Codes

CCDC 1828320−1828321, 1828323, and 1867996 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/ data_request/cif, or by emailing [email protected]. uk, or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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This research was funded by CEFIPRA, grant number 5905-1. DST-FIST, India, is gratefully acknoweldged for the HRMS facility. K.S. thanks CSIR, India, for the research fellowship. S.K. and B.M. thank IIT Madras for research fellowships. B.J. thanks University Grant Commission (UGC), India, for a fellowship. Computational facilities, IIT Madras, is gratefully acknowledged.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Tel.: +91-44-22574230. Fax: +91 44-22574202. ORCID

Bijan Mondal: 0000-0002-7359-8926 Sundargopal Ghosh: 0000-0001-6089-8244 Author Contributions §

U.K. and S.K. are equal second authors.

Notes

The authors declare no competing financial interest. F


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