Synthesis and Structures of Base-Stabilized Cationic

Dec 5, 2018 - angles: 337.9(1)° in 6a, 328.8(1)° in 5a). Strong coordination of DMAP to the silicon center is demonstrated by the relatively short S...
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Synthesis and Structures of Base-Stabilized Cationic Silanethionetungsten Complexes and Reaction with MeOH Takako Muraoka, Shun Tanabe, and Keiji Ueno* Division of Molecular Science, Graduate School of Science and Technology, Gunma University, Kiryu 376-8515, Japan

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ABSTRACT: The cationic silanethione-coordinated transition-metal complexes [Cp*(OC)3W{SSiR2(DMAP)}]TFPB (R = Me (6a), Ph (6b), Cp* = η5-C5Me5, DMAP = 4-(dimethylamino)pyridine, TFPB− = B{3,5(CF3)2C6H3}4−) were isolated by H− abstraction from silylsulfanyl complexes Cp*(OC)3WSSiR2H (5) with Ph3CTFPB, followed by the addition of DMAP. The reaction of 6b with 1 equiv of MeOH afforded methoxysilylsulfanyl complex Cp*(OC)3W(SSiPh2OMe) (7) and [H· DMAP]TFPB (8).

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silanethione complexes by the addition of sulfur atom to the MSi bonds in silylene complexes Cp*(OC)2M(SiMes2)(SiMe3) (M = W (3), Mo (4); Cp* = η5-C5Me5; Mes = 2,4,6Me3C6H2)9a because a similar strategy, that is, oxygen addition to silylene complexes 3 and 4, was successfully utilized for the synthesis of silanone complexes 1 and 2.6 However, the sulfuraddition reaction afforded metallacycle complex Cp*W( S){C(SiMe3)CO2SiMes2S} or Cp*Mo(S){SC(SiMe3)CO2SiMes2S} via a silanethione-coordinated complex as a key intermediate.9 Therefore, we have explored another synthetic route to access silanethione complexes. In this paper, we report the synthesis of the first cationic silanethione complexes by H− abstraction from silylsulfanyl complexes Cp*(OC)3WSSiR2H (R = Me (5a), Ph (5b)). Silylsulfanyltungsten complexes Cp*(OC)3WSSiR2H (5) were prepared by the reactions of Li[Cp*(OC)3WS] with R2SiHCl (eq 1). 1H NMR spectra of 5a and 5b showed the

he chemistry of R2SiE compounds (E = O, S) has attracted much attention because they are heavier congeners of ketones. The R2SiE compounds are extremely reactive due to the highly polarized Si+−E− bond and oligomerize readily to give polymeric compounds (R2Si− E)n.1 Several R2SiE compounds have been synthesized by taking advantage of kinetic and thermodynamic stabilization, that is, the introduction of bulky substituents on Si, coordination of Lewis base to Si, and addition of Lewis acid on E (Scheme 1a,b).2−5 Coordination to transition-metal Scheme 1. Stabilization of R2SiE Species (E = O, S)a

Si−H signals at 5.23 (septet, 3JH−H = 3.2 Hz) and 6.11 (s) ppm, respectively. X-ray crystal structure determination of 5a (Figure 1) revealed the four-legged piano-stool structure with one SSiMe2H and three CO ligands. The W−S bond distance (2.5587(11) Å) is comparable to those reported for structurally resembled sulfanyltungsten complexes (2.49−2.56 Å).10 The S−Si bond (2.1165(16) Å) is also within the range of usual S−Si single bonds (2.06−2.17 Å).11 The treatment of 5 with Ph3CTFPB (TFPB− = B{3,5(CF3)2C6H3}4−) in Et2O at −30 °C, followed by the addition

a

(a) Kinetic stabilization, (b) thermodynamic stabilization, and (c) complexation.

fragments as a ligand is also a promising way to stabilize the R2SiE species (Scheme 1c). Five silanone (R2SiO)coordinated complexes6,7 have been reported so far, including three complexes 1 and 2 reported by us.6 In contrast with silanone complexes, the chemistry of silanethione (R2SiS)coordinated complexes has remained unexplored. To our knowledge, only one example of isolated silanethionecoordinated complex has been reported so far in the literature.8 In our previous work, we attempted to synthesize the © XXXX American Chemical Society

Received: December 5, 2018

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DOI: 10.1021/acs.organomet.8b00877 Organometallics XXXX, XXX, XXX−XXX

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structure with a base-stabilized silanethione (DMAP)Me2Si S and three CO ligands. The long interatomic distance between Si and W atoms (3.965(1) Å) as well as the wide W− S−Si bond angle (117.67(5)°) clearly show the η1-coordination mode of the silanethione ligand. The SiS bond distance (2.0790(14) Å) is in the middle between reported SiS double bond (1.95−2.08 Å),4,5,8,12 and Si−S single-bond distances (2.06−2.17 Å),11 indicating the partial double-bond character of the Si−S bonding. The contribution of sp2 hybridization to Si in 6a is also suggested by the planarization of the Si atom (the sum of the C−Si−C and C−Si−S bond angles: 337.9(1)° in 6a, 328.8(1)° in 5a). Strong coordination of DMAP to the silicon center is demonstrated by the relatively short Si−N bond distance (1.840(3) Å) compared with those reported for nitrogen-to-silicon coordination bonds (1.83− 1.94 Å).7a,13 The W−S bond distance in 6a (2.5464(9) Å) is within the range of known sulfur-to-tungsten coordination bond distances (2.51−2.58 Å);14 however, it is also identical to those of sulfanyl complex 5a and other structurally resembled complexes to 5a.10,15 Thus the nature of the W−S bond in 6a appears to be a mixture of a single and a dative bonding. On the basis of the structural features described above, bonding in 6a can be depicted as a resonance of canonical forms A, B, and C (eq 3). The fact that νCO stretching

Figure 1. ORTEP drawing of 5a. H atoms except for H1 are omitted for clarity. Selected bond distances (Å) and angles (deg): W−S 2.5587(11), S−Si 2.1165(16), W−C1 1.984(4), W−C2 1.994(5), W−C3 2.008(4); S−W−C1 136.41(13), C2−W−C3 115.27(16), W−S−Si 112.92(5).

of 1 equiv of 4-(dimethylamino)pyridine (DMAP) to the resultant mixtures within 5 min afforded DMAP-stabilized cationic silanethionetungsten complexes [Cp*(OC)3W{S = SiR2(DMAP)}]TFPB (R = Me (6a), Ph (6b)) in high yields with a concomitant formation of Ph3CH (eq 2). Complex 6

frequencies of 6 (6a: 2020 and 1923 cm−1; 6b: 2023 and 1922 cm−1) are identical to those of 5 (5a: 2021, 1940, and 1922 cm−1; 5b: 2023, 1942, and 1925 cm−1) suggests the significant contribution of canonical forms B and C and thus the localization of the positive charge on the base-stabilized silanethione ligand rather than on the tungsten center. Cationic silanethione complexes 6 are thermally stable and remained unchanged in C7D8 at 70 °C at least 2 days. Reaction of 6b with methanol took place readily to give methoxysilylsulfanyl complex Cp*(OC)3W(SSiPh2OMe) (7) quantitatively with a concomitant formation of the colorless precipitate [H·DMAP]TFPB (8) (eq 4). Complexes 7 and 8

should be formed via H− abstraction from SSiR2H ligand in 5 by Ph3C+, followed by the coordination of DMAP to the silicon center in the resultant R2SiS ligand. The 29Si NMR spectra of complexes 6a and 6b showed the singlet signals assignable to the Si atom of the silanethione ligands at 35.0 and 13.8 ppm, respectively, which are within or near the range of those reported for base-stabilized silanethione compounds (22−42 ppm).4b X-ray crystal structure determination (Figure 2) revealed that the cationic complex in 6a bears a four-legged piano stool

Figure 2. ORTEP drawing of 6a. H atoms and TFPB− fragment are omitted for clarify. Selected bond distances (Å) and angles (deg): W− S 2.5464(9), S−Si 2.0790(14), Si−N1 1.840(3), W−C1 1.986(4), W−C2 1.995(4), W−C3 2.011(4), W−S−Si 117.67(5), S−Si−N1 109.06(11), S−Si−C4 118.02(14), S−Si−C5 108.48(15), C4−Si−C5 111.41(19).

were isolated in 29 and 24% yield, respectively. This reaction would proceed via the formation of D by the substitution of DMAP with methanol or E by the addition of MeOH to the SiS bond, followed by the abstraction of H+ from the EH bond (E = O or S) by resultant free DMAP (Figure 3). B

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Angew. Chem., Int. Ed. 2007, 46, 4159−4162. (c) Ghadwal, R. S.; Azhakar, R.; Roesky, H. W.; Proepper, K.; Dittrich, B.; Goedecke, C.; Frenking, G. Donor-Acceptor Stabilized Silaformyl Chloride. Chem. Commun. 2012, 48, 8186−8188. (d) Rodriguez, R.; Troadec, T.; Gau, D.; Saffon-Merceron, N.; Hashizume, D.; Miqueu, K.; Sotiropoulos, J.-M.; Baceiredo, A.; Kato, T. Synthesis of a Donor-Stabilized Silacycopropan-1-one. Angew. Chem., Int. Ed. 2013, 52, 4426−4430. (e) Do, D. C. H.; Protchenko, A. V.; Á ngeles Fuentes, M. A.; Hicks, J.; Kolychev, E. L.; Vasko, P.; Aldridge, S. Angew. Chem., Int. Ed. 2018, 57, 13907−13911. (f) Sarkar, D.; Nesterov, V.; Szilvasi, T.; Altmann, P. J.; Inoue, S. The Quest for Stable Silaaldehydes: Synthesis and Reactivity of a Masked Silacarbonyl. Chem. - Eur. J. 2019, 25, 1198. (g) Filippou, A. C.; Baars, B.; Chernov, O.; Lebedev, Y. N.; Schnakenburg, G. Silicon-Oxygen Double Bonds: A Stable Silanone with a Trigonal-Planar Coordinated Silicon Center. Angew. Chem., Int. Ed. 2014, 53, 565−570. (h) Alvarado-Beltran, I.; Rosas-Sanchez, A.; Baceiredo, A.; Saffon-Merceron, N.; Branchadell, V.; Kato, T. A Fairly Stable Crystalline Silanone. Angew. Chem., Int. Ed. 2017, 56, 10481− 10485. (i) Wendel, D.; Reiter, D.; Porzelt, A.; Altmann, P. J.; Inoue, S.; Rieger, B. Silicon and Oxygen’s Bond of Affection: An Acyclic Three-Coordinate Silanone and Its Transformation to an Iminosiloxysilylene. J. Am. Chem. Soc. 2017, 139, 17193−17198. (4) Selected examples for base-stabilized silanethiones, see: (a) Arya, P.; Boyer, J.; Carre, F.; Corriu, R.; Lanneau, G.; Lapasset, J.; Perrot, M.; Priou, C. Formation and Reactivity of Silicon-Sulfur and SiliconSelenium Double Bonds. The First X-ray Structure of a Silanethione. Angew. Chem., Int. Ed. Engl. 1989, 28, 1016−1018. (b) Corriu, R. J. P.; Lanneau, G. F.; Mehta, V. D. Aminosilylation of Hetercumulenes and the Intermolecular Decomposition of Their Silyl-Functionalized Adducts. J. Organomet. Chem. 1991, 419, 9−26. (c) So, C.-W.; Roesky, H. W.; Oswald, R. B.; Pal, A.; Jones, P. G. Synthesis and Characterization of [{PhC(NBut)2}Si(S)SBut]: a Silicon Thioester Analogue with the Si(=S)-S-Skeleton. Dalton Trans 2007, 5241− 5244. (d) Yao, S.; Xiong, Y.; Driess, M. N-Heterocyclic Carbene (NHC)-Stabilized Silanechalcogenones: NHC→Si(R2)=E (E = O, S, Se, Te). Chem. - Eur. J. 2010, 16, 1281−1288. (e) Yeong, H.-X.; Xi, H.-W.; Li, Y.; Lim, K. H.; So, C.-W. A Silyliumylidene Cation Stabilized by an Amidinate Ligand and 4-Dimethylaminopyridine. Chem. - Eur. J. 2013, 19, 11786−11790. (5) Examples for base-free silanethiones, see: (a) Suzuki, H.; Tokitoh, N.; Nagase, S.; Okazaki, R. The First Genuine Silicon-Sulfur Double-Bond Compound: Synthesis and Crystal Structure of a Kinetically Stabilized Silanethione. J. Am. Chem. Soc. 1994, 116, 11578−11579. (b) Suzuki, H.; Tokitoh, N.; Okazaki, R.; Nagase, S.; Goto, M. Synthesis, Structure, and Reactivity of the First Kinetically Stabilized Silanethione. J. Am. Chem. Soc. 1998, 120, 11096−11105. (c) Iwamoto, T.; Sato, K.; Ishida, S.; Kabuto, C.; Kira, M. Synthesis, Properties, and Reactions of a Series of Stable Dialkyl-Substituted Silicon-Chalcogen Doubly Bonded Compounds. J. Am. Chem. Soc. 2006, 128, 16914−16920. (6) (a) Muraoka, T.; Abe, K.; Haga, Y.; Nakamura, T.; Ueno, K. Synthesis of a Base-Stabilized Silanone-Coordinated Complex by Oxygenation of a (Silyl)(silylene)tungsten Complex. J. Am. Chem. Soc. 2011, 133, 15365−15367. (b) Muraoka, T.; Abe, K.; Kimura, H.; Haga, Y.; Ueno, K.; Sunada, Y. Synthesis, Structures, and Reactivity of the Base-Stabilized Silanone Molybdenum Complexes. Dalton Trans 2014, 43, 16610−16613. (c) Muraoka, T.; Kimura, H.; Trigagema, G.; Nakagaki, M.; Sakaki, S.; Ueno, K. Reactions of Silanone(silyl) tungsten and − molybdenum Complexes with MesCNO, (Me2SiO)3, MeOH, and H2O: Experimental and Theoretical Studies. Organometallics 2017, 36, 1009−1018. (7) (a) Xiong, Y.; Yao, S.; Driess, M. Coordination of a SiO Subunit to Metal: Complexes of Donor-Stabilized Silanone Featuring a Terminal SiO→M Coordination (M = Zn, Al). Dalton Trans 2010, 39, 9282−9287. (b) Fukuda, T.; Hashimoto, H.; Sakaki, S.; Tobita, H. Stabilization of a Silaaldehyde by its η2 Coordination to Tungsten. Angew. Chem., Int. Ed. 2016, 55, 188−192.

Figure 3. Structures of possible intermediates D and E.

Silanones and silanethiones have been reported to react with MeOH to form methoxysilanol R2Si(OMe)−OH3i,16 and methoxysilanethiol R2Si(OMe)−SH5b,c via the addition of a MeO−H bond across the SiO and SiS bonds, respectively. Methanolysis of silanone complexes 1 and 2a also afforded methoxysilanol in good yields.6c In contrast with the silanone complexes, the reaction of methanol with silanethione complex 6b afforded not methoxysilanethiol Ph2Si(OMe)−SH but Cp*(OC)3W(SSiPh2OMe) (7) and [H·DMAP]TFPB (8). This difference is attributable to the positive charge on silanethione complex [Cp*(OC)3W{S SiPh2(DMAP)}]+, which facilitates the proton abstraction from the intermediate D or E by free DMAP.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.8b00877. Experimental details and crystallographic and spectroscopic data (PDF) Accession Codes

CCDC 1880955−1880956 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], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Keiji Ueno: 0000-0003-0567-7697 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by JSPS KAKENHI grant numbers JP26410066, JP15H00916, JP15K05446, and JP17K05802. REFERENCES

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DOI: 10.1021/acs.organomet.8b00877 Organometallics XXXX, XXX, XXX−XXX