Synthesis of Trithia-Borinane Complexes Stabilized in Diruthenium Core : [ ( Cp * Ru ) 2 ( η 1S ) ( η 1-CS ) { ( CH 2 ) 2 S 3 BR } ] ( R = H or SMe )

The thermolysis of arachno-1 [(Cp*Ru)2(B3H8)(CS2H)] in the presence of tellurium powder yielded a series of ruthenium trithia-borinane complexes: [(Cp*Ru)2(η-S)(η-CS){(CH2)2S3BH}] 2, [(Cp*Ru)2(η-S)(η-CS){(CH2)2S3B(SMe)}] 3, and [(Cp*Ru)2(η-S)(η-CS){(CH2)2S3BH}] 4. Compounds 2–4 were considered as ruthenium trithia-borinane complexes, where the central six-membered ring {C2BS3} adopted a boat conformation. Compounds 2–4 were similar to our recently reported ruthenium diborinane complex [(Cp*Ru){(η-SCHS)CH2S2(BH2)2}]. Unlike diborinane, where the central six-membered ring {CB2S3} adopted a chair conformation, compounds 2–4 adopted a boat conformation. In an attempt to convert arachno-1 into a closo or nido cluster, we pyrolyzed it in toluene. Interestingly, the reaction led to the isolation of a capped butterfly cluster, [(Cp*Ru)2(B3H5)(CS2H2)] 5. All the compounds were characterized by 1H, 11B{1H}, and 13C{1H} NMR spectroscopy and mass spectrometry. The molecular structures of complexes 2, 3, and 5 were also determined by single-crystal X-ray diffraction analysis.


Synthesis of Ruthenium Borinane Complexes, 2-4
As shown in Scheme 1, the pyrolysis of 1 in the presence of tellurium powder in toluene yielded compounds 2-4 along with compounds [{Cp*Ru(µ,η 3 -SCHS)} 2 ] and [Cp*Ru(µ-H) 2 BH(SCHS)] [33].The 11 B{ 1 H} NMR spectra at room temperature display single resonance at δ = −4.1,7.4, and 4.9 ppm for compounds 2, 3, and 4, respectively, indicating the presence of a single boron atom.While the 1 H NMR spectrum of compounds 2 and 4 shows the presence of a terminal B-H proton at δ = 3.75 and 2.58 ppm, respectively, compound 3 does not show any indication of a B-H terminal.Instead, it shows a resonance at δ = 2.06 ppm, indicating the presence of a (SCH 3 ) unit.Apart from that, both 2 and 3 display resonances in the region δ = 3.96-1.69ppm, which may be attributed to the presence of methylene protons.Both compounds display signals for two sets of Cp* protons around 1.79 and 1.72 ppm in a 1:1 ratio.The presence of the Cp* ligands, methylene, and SCH 3 units are also supported by 13 C{ 1 H} NMR spectroscopy.Apart from that, the 13 C{ 1 H} NMR spectra also show a resonance at δ = 288.6 and 285.8 ppm, indicating the presence of a C=S group in the molecules of 2 and 3 respectively.Furthermore, the mass spectra show molecular ion peaks (ESI + ) at m/z = 686.9603,732.9479, and 686.9604 for compounds 2, 3, and 4 respectively.Although we isolated the majority of Te powder after workup, we are not in a position to comment on the exact role of chalcogen powder, in particular Te powder, in the formation of complexes 2-4 from 1. ].While the central six-membered ring adopts a chair conformation in diborinane [33], 2 and 3 adopt a boat conformation.A significant difference between 2 and 3 is the presence of the {SMe} moiety instead of a terminal hydrogen attached to the boron atom in compound 3.The B-S bond length (av.1.921 Å) in 2 and 3 is within the B-S single bond distance and is in accord with the ruthenium diborinane complex [33].One of the interesting features observed in these molecules is the presence of the thioformyl unit bonded to the ruthenium atoms.While the diborinane has only one ruthenium atom, compounds 2 and 3 has two ruthenium atoms bridged by one thiocarbonyl unit on one side and B-S on the other side.The C-S distance in the thiocarbonyl unit (1.612(15) Å in 2 and 1.617(7) Å in 3) is found to be shorter than that of 1.The Ru1-Ru2 distances of 2.759(6) Å in 2 and 2.759(6) Å in 3 are significantly shorter when compared to 1, but are well within the reported Ru-Ru single bond distance [69].The ruthenium atoms are connected to two sulfur atoms S2 and S4 present in the (C2S3B) ring and the bridging sulfur is connected to the ring boron atom B1.Although we failed to crystallize compound 4, it was characterized in comparison to its spectroscopic data with 2 and 3. Based on the spectroscopic data, compound 4 is expected to have a structure similar to that of compound 3 where instead of the SMe group, a terminal H is attached to the B atom (Scheme 1).
Recently, our group reported for the first time a trithia-diborinane stabilized ruthenium complex, [(Cp*Ru){(η 2 -SCHS)CH 2 S 2 (BH 2 ) 2 }] [33].Although some examples of trithia-diborinane compounds have been reported, there are no examples of metal complexes of such trithia-diborinane species except the one reported by us [33].Compounds 2-4 are the monoborinane derivatives, and are a novel entry to the class of transition metal borinane complexes.The few structurally characterized borinane and diborinane derivatives are listed in Table 1.
In order to check whether arachno-[(Cp*Ru) 2 (B 3 H 8 )(CS 2 H)], 1, can be converted to a nido or closo geometry with the release of hydrogen, we pyrolyzed 1.Interestingly, the reaction led to the formation of 5 having a capped butterfly geometry, instead of a nido or closo geometry (Scheme 2).The mass spectrometry of the new compound gives a molecular ion peak at m/z = 613.0588that corresponds to C 21 H 37 Ru 2 B 3 S 2 Na.The room-temperature 11 B{ 1 H} NMR spectrum of 5 rationalizes the presence of two boron environments, which appear at δ = 43.6 and −24.1 ppm.Besides the BH terminal protons, one B-H-B and one Ru-H-B proton is observed in the 1 H NMR spectrum.Furthermore, the 1 H NMR spectrum implies the presence of two equivalent Cp* ligands in 5.   Table 1.Selected structural and spectroscopic data of borinane derivatives and complexes [33,[75][76][77][78].

General Procedures and Instrumentation
All manipulations were conducted under an Ar/N2 atmosphere using standard Schlenk techniques or glove box techniques.The solvents were distilled prior to use under argon.Compound arachno-1 was prepared according to the literature method [69], while other chemicals were obtained commercially and used as received.The external reference [Bu4N][B3H8] for the 11 B NMR was synthesized with the literature method [83].Preparative thin layer chromatography was performed with Merck 105554 silica-gel TLC plates (Merck, Darmstadt, Germany).The NMR spectra were recorded on a 400 or 500 MHz Bruker FT-NMR spectrometer (Bruker, Billerica, MA, USA).Residual solvent protons were used as reference (δ, ppm CDCl3, 7.26), while a sealed tube containing [Bu4N(B3H8)] in [d6]-benzene (δB, ppm, −30.07) was used as an external reference for the 11 B NMR.The FT-IR spectrum was recorded using a Jasco FT/IR-4100 spectrometer (JASCO, Easton, MD, USA).The HRMS (ESI) spectra were obtained using a Bruker Micro TOF-II instrument (Bruker, Billerica, MA, USA).Note that all the reported compounds were isolated by the preparative thin layer chromatographic technique (TLC), using silica-gel-coated aluminum TLC plates.The impure reaction mixture was slowly loaded on the TLC and eluted by using the hexane/CH2Cl2 mixture in inert

General Procedures and Instrumentation
All manipulations were conducted under an Ar/N 2 atmosphere using standard Schlenk techniques or glove box techniques.The solvents were distilled prior to use under argon.Compound arachno-1 was prepared according to the literature method [69], while other chemicals were obtained commercially and used as received.The external reference [Bu 4 N][B 3 H 8 ] for the 11 B NMR was synthesized with the literature method [83].Preparative thin layer chromatography was performed with Merck 105554 silica-gel TLC plates (Merck, Darmstadt, Germany).The NMR spectra were recorded on a 400 or 500 MHz Bruker FT-NMR spectrometer (Bruker, Billerica, MA, USA).Residual solvent protons were used as reference (δ, ppm CDCl 3 , 7.26), while a sealed tube containing [Bu 4 N(B 3 H 8 )] in [d 6 ]-benzene (δ B , ppm, −30.07) was used as an external reference for the 11 B NMR.The FT-IR spectrum was recorded using a Jasco FT/IR-4100 spectrometer (JASCO, Easton, MD, USA).The HRMS (ESI) spectra were obtained using a Bruker Micro TOF-II instrument (Bruker, Billerica, MA, USA).Note that all the reported compounds were isolated by the preparative thin layer chromatographic technique (TLC), using silica-gel-coated aluminum TLC plates.The impure reaction mixture was slowly loaded on the TLC and eluted by using the hexane/CH 2 Cl 2 mixture in inert atmosphere.Elution with the particular solvent mixture allowed us to separate the compounds in pure form.

Synthesis of Compound 5
In a flame-dried Schlenk tube, compound 1 (0.1 g, 0.169 mmol) was suspended in toluene (20 mL), and was stirred at 80 • C for 18 h.The solvent was evaporated in vacuum, and the residue was extracted into hexane/CH 2 Cl 2 (70:30 v/v) and passed through Celite.After the removal of the solvent from the filtrate, the residue was subjected to chromatographic workup using silica-gel TLC plates.Elution with hexane/CH 2 Cl 2 (70:30 v/v) yielded orange 5 (0.030 g, 30%).

Conclusions
The present work describes the synthesis of various borinane complexes of a group-8 heavier transition metal (i.e., ruthenium) from a dithioformato stabilized arachno-diruthenium pentaborane cluster.The new molecules have similar structures, but they differ in terms of the boron atom's position in the central six-membered ring {C 2 S 3 B}.With a single boron atom in the six-membered ring {C 2 S 3 B}, these mono-borinanes can be called 1,3,5-trithia-4-borinane and 1,3,5-trithia-2-borinane complexes of ruthenium.In all the mono-borinane complexes, the six-membered ring {C 2 BS 3 } adopt a boat confirmation, which is in contrast to our previously reported trithia-diborinane complexes of ruthenium, [(Cp*Ru){(η 2 -SCHS)CH 2 S 2 (BH 2 ) 2 }], which adopt a chair conformation.The method reported in this article describing the synthesis of trithia-borinane complexes is unique and may be further utilized to introduce one or more boron atoms to the six-membered ring {C 2 BS 3 }.The isolation of these complexes opens up a gateway for the synthesis of early and late transition metal trithia-borinane complexes.Furthermore, in an attempt to convert arachno-[(Cp*Ru) 2 (B 3 H 8 )(CS 2 H)], 1, to a closo or nido geometry, we performed the pyrolysis of 1 that led to the formation of a capped butterfly cluster.With seven-skeletal-electron-pairs (sep), it satisfies the electron count for a BH capped arachno-butterfly structure.These results demonstrate that both the transition metal and the ligands play an important role in the formation of these complexes.It is interesting to see that the properties and reactivity of molecules can be largely controlled by a variation in the metal or ligand.

Scheme 1 . 14 Figure 1 .
Scheme 1. Reaction of [(Cp*Ru) 2 (B 3 H 8 )(CS 2 H)], 1, in the presence of tellurium powder.The single-crystal X-ray diffraction study disclosed the core geometry (C 2 S 3 B ring) of compounds 2 and 3 to be very similar to each other (Figure 1a,b).The only difference between the two is the position of the boron atom in the central six-membered ring {C 2 S 3 B}.Compounds 2 and 3 can be called as 1,3,5-trithia-4-borinane and 1,3,5-trithia-2-borinane complexes of ruthenium, respectively, which is similar to our recently reported diborinane [(Cp*Ru){(η 2 -SCHS)CH 2 S 2 (BH 2 ) 2 }] [33].Unlike diborinane, compounds 2 and 3 have only one boron atom in the six-membered ring {C 2 S 3 B} and are the monoborane derivatives of [(Cp*Ru){(η 2 -SCHS)CH 2 S 2 (BH 2 ) 2 }].While the central six-membered ring adopts a chair conformation in diborinane[33], 2 and 3 adopt a boat conformation.A significant difference between 2 and 3 is the presence of the {SMe} moiety instead of a terminal hydrogen attached to the boron atom in compound 3.The B-S bond length (av.1.921 Å) in 2 and 3 is within the B-S single bond distance and is in accord with the ruthenium diborinane complex[33].One of the interesting features observed in these molecules is the presence of the thioformyl unit bonded to the ruthenium atoms.While the diborinane has only one ruthenium atom, compounds 2 and 3 has two ruthenium atoms bridged by one thiocarbonyl unit on one side and B-S on the other side.The C-S distance in the thiocarbonyl unit (1.612(15) Å in 2 and 1.617(7) Å in 3) is found to be shorter than that of 1.The Ru1-Ru2 distances of 2.759(6) Å in 2 and 2.759(6) Å in 3 are significantly shorter when compared to 1, but are well within the reported Ru-Ru single bond distance[69].The ruthenium atoms are connected to two sulfur atoms S2 and S4 present in the (C 2 S 3 B) ring and the bridging sulfur is connected to the ring boron atom B1.Although we failed to crystallize compound 4, it was characterized in comparison to its spectroscopic data with 2 and 3. Based on the spectroscopic data, compound 4 is expected to have a structure similar to that of compound 3 where instead of the SMe group, a terminal H is attached to the B atom (Scheme 1).Inorganics 2019, 7, x FOR PEER REVIEW 5 of 14
spectra were recorded in a CDCl3 solvent unless stated.b E = hetero atom in the central ring.c conformation of the central six-membered ring.d In [D6]-acetone.e In CD2Cl2.f Data not available.
spectra were recorded in a CDCl3 solvent unless stated.b E = hetero atom in the central ring.c conformation of the central six-membered ring.d In [D6]-acetone.e In CD2Cl2.f Data not available.−5.0 and −15.6 1.915 chair Inorganics 2019, 7, x FOR PEER REVIEW 6 of spectra were recorded in a CDCl3 solvent unless stated.b E = hetero atom in the central ring.c conformation of the central six-membered ring.d In [D6]-acetone.e In CD2Cl2.f Data not available.
were recorded in a CDCl3 solvent unless stated.b E = hetero atom in the central ring.c conformation of the central six-membered ring.d In [D6]-acetone.e In CD2Cl2.f Data not available.
were recorded in a CDCl3 solvent unless stated.b E = hetero atom in the central ring.c conformation of the central six-membered ring.d In [D6]-acetone.e In CD2Cl2.f Data not available.
were recorded in a CDCl3 solvent unless stated.b E = hetero atom in the central ring.c conformation of the central six-membered ring.d In [D6]-acetone.e In CD2Cl2.f Data not available.were recorded in a CDCl3 solvent unless stated.b E = hetero atom in the central ring.c conformation of the central six-membered ring.d In [D6]-acetone.e In CD2Cl2.f Data not available.
were recorded in a CDCl 3 solvent unless stated.b E = hetero atom in the central ring.c conformation of the central six-membered ring.d In [D 6 ]-acetone.e In CD 2 Cl 2 .f Data not available.