Metallaheteroboranes Containing Group 16 Elements: an Experimental and Theoretical Study
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Journal of Organometallic Chemistry 883 (2019) 71e77 Contents lists available at ScienceDirect Journal of Organometallic Chemistry journal homepage: www.elsevier.com/locate/jorganchem Metallaheteroboranes containing group 16 elements: An experimental and theoretical study * Moulika Bhattacharyya, Rini Prakash, R. Jagan, Sundargopal Ghosh Department of Chemistry, Indian Institute of Technology Madras, Chennai 600036, India article info abstract Article history: Thermolysis of diphenyl dichalcogenides, Ph2E2 (E ¼ S, Se and Te) with an insitu generated intermediate, Received 19 November 2018 5 obtained from the reaction of [Cp*WCl4] (Cp* ¼ h -C5Me5) with [LiBH4$THF], yielded new tung- Received in revised form staheteroboranes, [(Cp*W)2(m-EPh)(m3-E)(m-H)(B3H2EPh)], 1 and 2 (1:E¼ S; 2:E¼ Se), and [(Cp*W)2(m- 9 January 2019 TePh)B H (m-H) ], 4. Formation of compounds 1 and 2 substantiate the evidence of [(Cp*W) B H ], Accepted 11 January 2019 5 5 3 2 4 10 which supports our previous studies. Compound 4 has a capped octahedral geometry that is unique due Available online 17 January 2019 to the presence of three W-H-B bridging hydrogens in a closo cluster. Alternatively, the shape of cluster 4 can be defined as oblatoarachno that can be derived from a heptagonal bipyramid. All the compounds Keywords: 1 11 1 13 1 Oblatoarachno have been characterized by mass spectrometry, H, B{ H}, IR and C{ H} NMR spectroscopy in solution Metallaheteroboranes and the structural architectures of 1 and 4 were unequivocally established by X-ray crystallographic Tungsten analysis. The density functional theory calculations also yielded geometries in close agreement with the Diphenyl dichalcogenide observed structures. © 2019 Elsevier B.V. All rights reserved. 1. Introduction In a recent study, we have described the direct evidence for the existence of saturated molybdaborane/tungstaborane compound, Heteroborane chemistry is one of the robust branches of poly- [(Cp*M)2B4H10][16] which was hypothesized earlier as hedral borane chemistry, mainly due to the wide development of [(Cp*M)2B4H8][17]. Therefore, there remains a possibility of similar carboranes and their derivatives [1e3]. In parallel to the expansion analogues in metallaheteroboranes, which can substantiate this of the carboranes, the chemistry of heteroboranes and hetero- result further. Hence, in order to put some insight into this problem, metallaboranes containing group 16 elements have grown in we have reinvestigated the synthesis of group 6 hetero- numbers albeit in a slower rate, especially thiaboranes and thia- metallaborane especially tungstaheteroborane where only a very metallaboranes [4e6]. There is always an urge to synthesize the few structurally characterized compounds are known [18]. The heavier chalcogen containing heterometallaborane and there has reaction led to the isolation of [(Cp*W)2(m-EPh)(m3-E)(m- been a few success in this area [7,8]. From the earlier time, the H)(B3H2EPh)] (E ¼ S and Se) which supports the existence of a strategies and reagents used for this purpose are varied and saturated tungstaborane compound [(Cp*W)2B4H10] as the inter- explored to make interesting cluster geometries [9,10]. Apart from mediate. After perceiving success with S and Se, an investigation to this geometrical importance, many applications are also registered isolate the Te analogues led to the formation of an unexpected such as active homogeneous catalyst precursors in the hydroge- [(Cp*W)2(m-TePh)B5H5(m-H)3], a new entry into the rare class of nation and isomerization of alkenes [11,12]. Current investigations oblatoarachno geometry containing a bridging TePh ligand. Along in our laboratory are focused on the development of new methods with the other tools, density functional theory (DFT) calculations for the synthesis of di-metallaheteroboranes through the activation have been used to provide some insight into the nature of the of diorganyl-dichalcogenide ligands [13,14] or chalcogen powders, bonding of these new molecules. [15] which have been shown to be one of the effective routes for the preparation of dimetallaheteroboranes. 2. Results and discussion 2.1. Synthesis and characterizations of ditungstaheteroboranes, 1e4 * Corresponding author. E-mail address: [email protected] (S. Ghosh). As shown in Scheme 1, treatment of an insitu generated https://doi.org/10.1016/j.jorganchem.2019.01.007 0022-328X/© 2019 Elsevier B.V. All rights reserved. 72 M. Bhattacharyya et al. / Journal of Organometallic Chemistry 883 (2019) 71e77 Scheme 1. Synthesis of dimetallaheteroborane clusters 1e4. intermediate obtained from the reaction of Cp*WCl4 with perpendicular to the W1-W2 bond and nearly parallel to the two [LiBH4$THF] at À78 C, with Ph2E2 [E ¼ S, Se and Te] at 85 C led to Cp* planes. In another way, the core structure can be considered as the isolation of tungstaheteroborane clusters [(Cp*W)2(m-EPh)(m3- a bicapped tetrahedron similar to [(Cp*ReH2)2B4H4][20] proposed E)(m-H)(B3H2EPh)], 1 and 2 (1:E¼ S; 2:E¼ Se) and [(Cp*W)2(m- by Fehlner et al. In compound 1,two{W2B} triangular faces are TePh)B5H5(m-H)3], 4 along with known [(Cp*W)2B5H9], 3 [19]. capped by one boron (B3) and sulphur (S3) atom in a {W2B2} tet- Detailed characterizations of these molecules are described below. rahedron and the W-W edge is further bridged by a sulfido ligand (S1), which led to a short W-W bond of 2.6930(3) Å as compared to 2.1.1. [(Cp*W)2(m-EPh)(m3-E)(m-H)(B3H2EPh)], 1 and 2 (1:E¼ S; 2: usual W-W single bond [19]. It is in between the double and single E ¼ Se) bond distance and very much comparable to that of [(Cp*W)2(m- 2 Compound 1 was isolated as brown sticky semi solid in low S)2(m-h -S2CH2)] [18c]. The shape of 1 can also be visualized as yield. The mass spectral analysis of 1 shows the molecular ion peak oblatoarachno with the removal of two equatorial vertices from þ at m/z 924.1886 corresponding to [M] . The formation of new oblatocloso hexagonal bipyramid with 2n (12 e) Wadean [21] boron-containing species, 1 was indicated by the presence of three skeletal electrons (6 skeletal electron pairs). One of the interesting 11B{1H} signals in 1:1:1 ratio at d ¼ 91.8, 73.3 and À12.2 ppm indi- features of 1 is the presence of three different types of S- ligands, i) 11 cating the presence of different boron environments. The B m3- S, ii) m2-SPh, iii) SPh. The m3-S ligand is connected to the boron chemical shift at d ¼12.2 ppm can be assigned to the boron atom and the observed B(1)-S(3) bond length of 1.845(6) Å is attached with the chalcogen atom which is a part of the cluster comparable to that of other sulphur containing metalla-thiaborane 1 13 1 core. The H and C{ H} NMR spectra imply two equivalents of Cp* compounds [7,8]. The m2-SPh ligand bridge between two tungsten ligands. Further analysis of 1H NMR spectrum shows the presence centres symmetrically with an average metal-sulfur bond length of of a single W-H-B proton at d ¼7.81 ppm. The characteristics 2.493 Å. This is comparable to the symmetric coordination of the fi 2 bands for B-Ht proton stretching frequency is observed at disul de bridges in [(Cp*W)2(m-S)2(m-h -S2CH2)] [18c]. À 2498 cm 1. These spectroscopic data were not adequate to envisage As listed in Table 1, there are many iso-structural metallaboranes the identity of 1. A clear explanation eluded us until the solid-state and metallaheteroboranes known to that of 1, where a planar X-ray structure analysis of 1 was carried out. opened ring connected with two linear metal centers. One of the The solid-state X-ray structure of 1, shown in Fig. 1, is fully earlier examples is unsaturated chromaborane, [(Cp*Cr)2B4H8][22]. consistent with the spectroscopic data. The molecular structure of 1 Later various metallaboranes were synthesized and structurally consists of a planar unit of one sulphur and three boron atoms characterized such as [(Cp*Ta)2B4H10], [23a] [(Cp*ReH2)2B4H4][20] with the same structure but different sep (skeletal electron pair) count. Other than the pure metallaboranes, a series of group 9 heterometallaboranes, [(Cp*M)2B2E2H2][24,25](M¼ Co, Rh, Ir; E ¼ S, Se) are also reported with the similar core. The analogues structurally characterized tungsten and molydaborane compounds shown in Table 1 (entries 4e9) are iso-structural and iso-electronic to 1. Compound 1 indeed is a mediator in the transition between [(Cp*WCO)2B4H6], from which one and two boron atoms are 4 4 replaced by sulphur atoms to form 1 and [(Cp*W)2(m-S)(m-h :h - S2B2H2)] respectively. Even though there is not much deviation in the distance between two boron atoms (B1 and B2) in the M2B2 tetrahedron core of bicapped tetrahedral geometry, the M-M bond distance is considerably shortened in case of chalcogen substituted complexes, mostly when bridging chalcogen present across the M- M bond. All the molybdenum and tungsten complexes, shown in Table 1, demonstrate the direct evidence for the formation of saturated molybda and tungstaborane compounds i.e [(Cp*M)2B4H10] (6 sep) as one of the possible intermediates. In an attempt to extend this chemistry to heavier group-16 el- ements under similar reaction conditions, we have carried out the reaction of tungsten intermediate with Ph Se that led us to isolate Fig. 1. Molecular structure and labeling diagram of 1. Selected bond lengths (Å) and 2 2 ο bond angles ( ): W1-W2 2.6930(3), B1-B2 1.691(9), B1-S3 1.845(6), B1-W2 2.332(7), the Se analogue of 1, that is [(Cp*W)2(m-SePh)(m3-Se)(m- B2-W1 2.244(6), S1-W1 2.5244(14), W2-S3 2.4119(16); B2-B1-S3 123.1(4), S3-B1-W1 H)(B3H2SePh)], 2.