Addition of Sn–O i Pr across a C C Bond: Unusual Insertion of an

Communication pubs.acs.org/Organometallics

Addition of Sn−OiPr across a CC Bond: Unusual Insertion of an Alkene into a Main-Group-Metal−Alkoxide Bond Evgeny V. Beletskiy,† Yuyang Wu,‡ Mayfair C. Kung,*,† and Harold H. Kung*,† †

Chemical and Biological Engineering Department and ‡Chemistry Department, Northwestern University, Evanston, Illinois 60208, United States S Supporting Information *

ABSTRACT: An example of unusual addition of a maingroup-metal alkoxide across an alkene CC bond was demonstrated with a dimethylvinylsilyl-substituted Sn-POSS complex (POSS = incompletely condensed polyhedral oligomeric silsesquioxane). The structure of the pentacoordinated Sn chelate product was confirmed by 1H, 13C, and 119Sn NMR and ESI-MS.

A

Scheme 1. Products of Reaction of Tin Isopropoxide with POSS Ligand 1

lkene functionalization by forming a new C−O bond to generate oxygen-containing products plays a crucial role in converting hydrocarbon feedstocks into useful chemicals. Whereas this can be achieved with different reactions such as oxidation, electrophilic addition, and hydroformylation, the desire for high selectivity and yield and to use lower temperature processing has led to investigation of various stoichiometric or metal-facilitated catalytic processes. The Wacker process1 and oxymercuration2 are well-known examples that involve addition of metal (Pd or Hg) and oxygen across CC bonds. Insertion of alkenes into metal−oxygen bonds has been reported also for other transition metals, such as Ir, Rh, Pt, and Au,3−6 as well as cobalt porphyrin systems.7 In spite of these many examples, we found only one report for a maingroup metal: addition of Ge−ONR2 across a CC bond, which proceeded via stabilized Ge(III) and TEMPO radicals.8 Considering the importance of alkene oxygenation, we were interested if other metal−oxygen bonds are capable of adding across CC bonds. Sn−O addition seems of particular interest,9 since Sn is an abundant main-group metal, and the resulting organotin compounds could be potentially demetalated in transformations such as Stille coupling reactions10 and solvolyses.11 We report here our findings of the first example of alkene insertion into a Sn−O bond in a silsesquioxane framework. The discovery originated from our previously reported reaction between incompletely condensed polyhedral oligomeric silsesquioxane (POSS) and Sn isopropoxide (Scheme 1).12 When a 1:2 ratio of Sn isopropoxide to (CH3)2Si(C2H3) POSS 1 was used, the tetrahedrally coordinated POSS-SnPOSS 2 was formed in high yield. This compound exhibited a 119 Sn NMR resonance at δ −438 ppm. However, occasionally, an impurity with δ −330 ppm was found. Interestingly, this impurity was never observed with the SiMe3 analogue of 1. Thus, it appeared that the CC bond played an important role in its formation. After a number of attempts, we discovered that when the molar ratio of Sn isopropoxide to 1 was slightly above © XXXX American Chemical Society

unity, a single Sn species with δ −312 ppm in the 119Sn NMR could be synthesized (Figure S4 in the Supporting Information). Although this compound was noncrystalline and too moisture-sensitive to be isolated in high purity, NMR characterization results detailed below suggested that its connectivity and structure were those of 3 (Scheme 1). The reaction of 1 with a slight excess of Sn isopropoxide was carried out in toluene at 100 °C. After removal of volatiles and dissolution in CDCl3, 1H NMR showed that the alkene resonances had disappeared, while the set of new resonances shown in Figure 1 appeared. Cross-peaks in COSY established this set to consist of an AMX group and two isopropoxide CHs, one being the δ 3.8 ppm resonances of the isopropoxide unit COCH(CH3)2 and the other the δ 4.5 ppm signal of SnOCH(CH3)2 (Figure S5a,b in the Supporting Information). Among the resonances assigned to AMX, two proton resonances were in the δ 3.5−4.0 ppm region and the third Received: November 29, 2015

A

DOI: 10.1021/acs.organomet.5b00973 Organometallics XXXX, XXX, XXX−XXX

Organometallics

■

Communication

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.5b00973. Experimental details, NMR spectra, and ESI-MS spectra (PDF)

■

AUTHOR INFORMATION

Corresponding Authors

*E-mail for M.C.K.: [email protected]. *E-mail for H.H.K.: [email protected].

Figure 1. 1H NMR of the product of 1 + Sn(OiPr)4 (1:1.3).

Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS This work was supported by the Office of Basic Energy Sciences, U.S. Department of Energy, DE-FG02-01ER15184. E.V.B. was supported in part by the Northwestern University Institute of Catalysis for Energy Processes (U.S. Department of Energy, DE-FG02-03-ER15457). Characterization was performed at the Integrated Molecular Structure Education and Research Center (IMSERC) supported in part by NSF CHE1048773 and Int. Institute of Nanotechnology at Northwestern University.

was at δ 2.1 ppm, suggesting a CHCH2O fragment with a stereocenter at the CH. HSQC correlation showed that the δ 2.1 ppm signal corresponded to a CH with δ 33.9 ppm in 13C NMR with 1J(13C−119Sn) = 731 Hz13 (Figure S2 in the Supporting Information) that could be assigned to SiCH(CH2R)Sn14 (Figure S6a,b in the Supporting Information). The ESI-MS analysis showed a cluster at m/z 1233.38 (Figure S10a,b in the Supporting Information) that corresponded to POSS-SnOPr+. These observations indicated that 3 was the product of condensation of POSS silanols with Sn(OiPr)4 followed by an insertion of the alkene into a Sn−OiPr bond. The structure of 3 was further confirmed by correlation NMR experiments. When proton decoupling was turned off during the 119Sn NMR measurements, the Sn signal appeared as a multiplet with four 119Sn−1H coupling constants: 266, 161, and two of 50 Hz (Figure S8 in the Supporting Information).15 In the 1H NMR, the coupling to 119Sn (8.6% abundance) and 117 Sn (7.6%) resulted in small satellite signals (e.g., at δ 4.20− 4.15 and 3.68−3.64 ppm originating from the δ 3.9 ppm triplet; Figure 1). These signals were confirmed to be due to Sn−H interaction by decoupling to 119Sn, which resulted in less intense and more symmetrical 117Sn−1H satellite signals (Figure S9 in the Supporting Information). The coupling constants determined from these measurements were 265 and 55 Hz for Sn−C−CH2, 160 Hz for Sn−CH, and ca. 50 Hz for Sn−O−CH. The large difference in 3J coupling constants for the two diastereotopic protons of CH2 suggested that rotation around the CH−CH2 bond was hindered, presumably due to isopropoxide oxygen lone pair interaction with the Sn Lewis acid. This resulted in a folded, four-membered-ring structure in which the two Sn−C−C−H dihedral angles were different. The large and small 3J (119Sn−1H) values for the CH2 were due to Karplus-type behavior16 similar to the 3J(13C−1H) values in cyclobutane systems.17 The proposed chelate pentacoordinate structure also accounted for an unusual 119Sn NMR chemical shift of −312 ppm, which would be more upfield than analogous structures without the chelation (−247 ppm).18 In conclusion, we have demonstrated the first example of alkene CC bond insertion into a Sn−alkoxide bond. This reaction is analogous to the key step in the Wacker process and oxymercuration but does not utilize a precious or toxic metal. In fact, other than Ge, we could not find other examples of this type of transformation for a main-group element. Thus, there might be other reactions of alkene functionalization utilizing Sn Lewis acids that await discovery.

■

REFERENCES

(1) Baeckvall, J. E.; Akermark, B.; Ljunggren, S. O. J. Am. Chem. Soc. 1979, 101, 2411. (2) Brown, H. C.; Geoghegan, P. J. Am. Chem. Soc. 1967, 89, 1522. (3) Woerpel, K. A.; Bergman, R. G. J. Am. Chem. Soc. 1993, 115, 7888. (4) Li, S.; Sarkar, S.; Wayland, B. B. Inorg. Chem. 2009, 48, 8550. (5) Khusnutdinova, J. R.; Zavalij, P. Y.; Vedernikov, A. N. Organometallics 2007, 26, 2402. (6) Langseth, E.; Nova, A.; Tråseth, E. A.; Rise, F.; Øien, S.; Heyn, R. H.; Tilset, M. J. Am. Chem. Soc. 2014, 136, 10104. (7) Blaauw, R.; Kingma, I. E.; Laan, J. H.; van der Baan, J. L.; Balt, S.; de Bolster, M. W. G.; Klumpp, G. W.; Smeets, W. J. J.; Spek, A. L. J. Chem. Soc., Perkin Trans. 1 2000, 1199. (8) Fang, H.; Ling, Z.; Lang, K.; Brothers, P. J.; de Bruin, B.; Fu, X. Chem. Sci. 2014, 5, 916. (9) Shimada, E.; Inomata, K.; Mukaiyama, T. Chem. Lett. 1974, 3, 689. (10) Stille, J. K. Angew. Chem., Int. Ed. Engl. 1986, 25, 508. (11) Olszowy, H. A.; Kitching, W. Organometallics 1984, 3, 1676. (12) Beletskiy, E. V.; Shen, Z.; Riofski, M. V.; Hou, X.; Gallagher, J. R.; Miller, J. T.; Wu, Y.; Kung, H. H.; Kung, M. C. Chem. Commun. 2014, 50, 15699. (13) Willem, R.; Bouhdid, A.; Kayser, F.; Delmotte, A.; Gielen, M.; Martins, J. C.; Biesemans, M.; Mahieu, B.; Tiekink, E. R. T. Organometallics 1996, 15, 1920. (14) Lautens, M.; Zhang, C. H.; Goh, B. J.; Crudden, C. M.; Johnson, M. J. A. J. Org. Chem. 1994, 59, 6208. (15) Morris, G. A.; Emsley, J. W. Multidimensional NMR Methods for the Solution State; Wiley: Hoboken, NJ, 2012. (16) Quintard, J.-P.; Degueil-Castaing, M.; Barbe, B.; Petraud, M. J. Organomet. Chem. 1982, 234, 41. (17) Denisov, A. Y. U.; Tyshchishin, E. A.; Tkachev, A. V.; Mamatyuk, V. I. Magn. Reson. Chem. 1992, 30, 886. (18) Brand, K.; Labinger, J. A.; Davis, M. E. In 24th North American Catalysis Society Meeting Abstracts; Pittsburgh, PA, USA, June 14− 19, 2015; paper 10193.

B

DOI: 10.1021/acs.organomet.5b00973 Organometallics XXXX, XXX, XXX−XXX