Chemistry of organosilicon compounds. 292. An NMR study of the formation of silyloxonium ions by using tetrakis[3,5-bis(trifluoromethyl)phenyl]borate as counteranion

Kira, Mitsuo; Hino, Takakazu; Sakurai, Hideki

doi:10.1021/ja00043a013

Cited by 117 publications

(138 citation statements)

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“…[28,32] Consistent with weak or non-coordination of the counterions, 3 and 4 each displayed a single 19 F NMR signal at d-78.0 (CF 3 SO 3 À ) [38] and À62.0 (BArF À ) [39] ppm, respectively. As shown in Fig.…”

Section: Resultsmentioning

confidence: 94%

Hydrogenation and hydrogenolysis of furfural and furfuryl alcohol catalyzed by ruthenium(II) bis(diimine) complexes

Gowda

Parkin

Ladipo

2012

Applied Organom Chemis

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The catalytic activity of ruthenium(II) bis(diimine) complexes cis-[Ru(6,6′-Cl 2 bpy) 2 (OH 2 ) 2 ](Z) 2 (1, Z = CF 3 SO 3 ; 2, Z = (3,5-(CF 3 ) 2 C 6 H 3 ) 4 B, i.e. BArF) and cis-[Ru(4,4′-Cl 2 bpy) 2 (OH 2 ) 2 ](Z) 2 (3, Z = CF 3 SO 3 ; 4, Z = BArF) for the hydrogenation and/or the hydrogenolysis of furfural (FFR) and furfuryl alcohol (FFA) was investigated. The molecular structures of cis-[Ru(4,4′-Cl 2 bpy) 2 (CH 3 CN) 2 ](CF 3 SO 3 ) 2 (3′) and dimeric cis-[(Ru(4,4′-Cl 2 bpy) 2 Cl) 2 ](BArF) 2 (5) were characterized by X-ray crystallography. The structures are consistent with the anticipated reduction in steric hindrance about the ruthenium centers in comparison with corresponding complexes containing 6,6′-Cl 2 bpy ligands. While compounds 1-4 are all active and highly selective catalysts for the hydrogenation of FFR to FFA under modest reaction conditions, 3 and 4 showed decreased activity. This is best explained in terms of reduced Lewis acidity of the Ru 2+ centers and reduced steric hindrance about the metal centers of catalysts 3 and 4. cis-[Ru(6,6′-Cl 2 bpy) 2 (OH 2 ) 2 ](BArF) 2 (2) also displayed high catalytic efficiency for the hydrogenation of FFA to tetrahydrofurfuryl alcohol. Presumably, this is because coordination of C=C bonds of FFA to the ruthenium center is poorly inhibited by non-coordinating BArF counterions. Interestingly, cis-[Ru(6,6′-Cl 2 bpy) 2 (OH 2 ) 2 ] (CF 3 SO 3 ) 2 (1) showed some catalytic activity in ethanol for the hydrogenolysis of FFA to 2-methylfuran, albeit with fairly modest selectivity. Nonetheless, these results indicate that ruthenium(II) bis(diimine) complexes need to be further explored as catalysts for the hydrogenolysis of C-O bonds of FFR, FFA, and related compounds.

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Section: Resultsmentioning

confidence: 94%

Hydrogenation and hydrogenolysis of furfural and furfuryl alcohol catalyzed by ruthenium(II) bis(diimine) complexes

Gowda

Parkin

Ladipo

2012

Applied Organom Chemis

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“…In the reaction of 3 a with H(OEt 2 )(THF)TFPB at about À60 8C a new 29 Si NMR resonance was observed at d = 49.7 ppm, remarkably downfield from that of 3 a (d = À3.0 ppm in CD 2 Cl 2 at 25 8C). [27,28] The 29 Si NMR chemical shift of the product is consistent with similar ether-coordinated silylium species prepared by Sakurai and co-workers [29] (see Table 1) and suggested that the solvated silicon cation 7 a + was formed at low temperature (Scheme 3). The 1 H NMR spectrum at this temperature was consistent with this interpretation and showed sets of peaks assigned to ferrocenyl and SiMe 2 groups together with resonances characteristic of free diethyl ether and one set consistent with a coordinated THF molecule.…”

Section: Simentioning

confidence: 98%

“…Some broadening of the coordinated THF reso- nances was observed, and was possibly indicative of coordinative exchange of the ligand. [29] In the 13 C NMR spectrum, corresponding resonances for ferrocenyl and SiMe 2 groups, coordinated THF, and free ether molecules were observed. No other species, aside from the expected TFPB anion, were detected in any of the spectra, which indicated clean ring-opening protonolysis of the sila [1]ferrocenophane.…”

Section: Simentioning

confidence: 98%

“…The isolation of species that approach the ideal trigonal-planar geometry have required the use of bulky and/or electron-donating ligands, extremely noncoordinating anions, and inert solvents. Lambert and co-workers have shown that, while abstraction of H À from Mes 3 SiH is not possible due to steric congestion about silicon, [Mes 3 Si] + can be generated through reaction at the exposed end of the allyl group of Mes 3 Si(allyl) and is an almost completely isolated cation in the presence of a noncoordinating counterion such as tetrakis(pentafluorophenyl)borate (TPFPB), as evidenced by 29 Si NMR spectroscopy (d = 225 ppm).…”

Section: Introductionmentioning

confidence: 99%

“…[8,9] Along with the debate surrounding the isolation of ideal silylium species, a great deal of interest has arisen over coordinated silylium ions, which can still possess a large degree of cationic character associated with the silicon center. This is due to their strong Lewis acidity and potential as highly reactive synthetic reagents, as well as their possible role as Abstract: The ring-opening reactions of a series of sila [1] + (7c + ) at low temperatures, by reaction of the corresponding sila [1]ferrocenophanes (3 a, 3 b, and fcSiiPr 2 (3 c), respectively) with H(OEt 2 )(S)TFPB (S = Et 2 O or THF; TFPB = tetrakis [3,5- 13 C, and 29 Si NMR spectroscopy. A preparative-scale reaction of 3 b with H(OEt 2 )(THF)TFPB at À60 8C and subsequent addition of excess pyridine gave isolable red crystals of 8b-[TFPB]·CHCl 3 , which were characterized by 1 reactive intermediates in a wide variety of synthetic transformations.…”

Section: Introductionmentioning

confidence: 99%

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Ring‐Opening Protonolysis of Sila[1]ferrocenophanes as a Route to Stabilized Silylium Ions

Bourke

MacLachlan

Lough

et al. 2005

Chemistry A European J

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The ring-opening reactions of a series of sila[1]ferrocenophanes with protic acids of anions with various degrees of noncoordinating character have been explored. Ferrocenyl-substituted silyl triflates FcSiMe2OTf (5 a) and Fc(3)SiOTf (5 b) (Fc=(eta5-C5H4)Fe(eta5-C5H5)) were synthesized by means of HOTf-induced ring-opening protonolysis of strained sila[1]ferrocenophanes fcSiMe2 (3 a) and fcSiFc2 (3 b) (fc=(eta5-C5H4)2Fe). Reaction of 3 a and 3 b with HBF4 yielded fluorosubstituted ferrocenylsilanes FcSiMe2F (6 a) and Fc3SiF (6 b) and suggested the intermediacy of a highly reactive silylium ion capable of abstracting F- from the [BF4]- ion. Generation of the solvated silylium ions [FcSiMe2THF]+ (7a+), [Fc3SiTHF]+ (7b+) and [FcSiiPr2OEt2]+ (7c+) at low temperatures, by reaction of the corresponding sila[1]ferrocenophanes (3 a, 3 b, and fcSiiPr2 (3 c), respectively) with H(OEt2)(S)TFPB (S=Et2O or THF; TFPB=tetrakis[3,5-bis(trifluoromethyl)phenyl]borate) was monitored by using low-temperature 1H, 13C, and 29Si NMR spectroscopy. In situ reaction of 7a+, 7b+, and 7c+ with excess pyridine generated [FcSiMe2py]+ (8a+), [Fc3Sipy]+ (8b+), and [FcSiiPr2py]+ (8c+), respectively, as observed by 1H, 13C, and 29Si NMR spectroscopy. A preparative-scale reaction of 3 b with H(OEt2)(THF)TFPB at -60 degrees C and subsequent addition of excess pyridine gave isolable red crystals of 8b-[TFPB]CHCl3, which were characterized by 1H and 29Si NMR spectroscopy as well as by single-crystal X-ray diffraction.

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Ionic and Organometallic‐Catalyzed Organosilane Reductions

Larson

Fry²

2008

Organic Reactions

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This chapter presents a critical review of synthetically useful variations of ionic methods for hydrogenation of organic compounds. In practice ionic hydrogenation involves the formal introduction of hydride from a donor source to an electron‐deficient carbon center. In this chapter, organosilicon hydrides are used as the source of ionic hydride with the goal of completing and updating earlier review work. Organosilicon compounds with at least one Si‐H bond have the ability to serve as mild‐air and water‐stable sources of hydrides and, thus, have reducing properties. In general, organosilicon hydrides do not undergo spontaneous reactions with organic compounds unless the organic substrate is a reasonably strong electrophile or the silane is first activated by the interaction of a nucleophilic species with a nucleophilic center. The organosilicon hydrides are covalent compounds that have little or no nucleophilic properties on their own. The use of these hydrides often provides a means of effecting reductions of organic substrates under very mild conditions and with excellent functional group selectivity. Consideration of the nature of the Si‐H bonds provides insight into the chemical behavior of these hydrides. Enhanced hydridic nature manifests itself in the chemical behavior of hydrosilanes.

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Chemistry of organosilicon compounds. 292. An NMR study of the formation of silyloxonium ions by using tetrakis[3,5-bis(trifluoromethyl)phenyl]borate as counteranion

Cited by 117 publications

References 0 publications

Hydrogenation and hydrogenolysis of furfural and furfuryl alcohol catalyzed by ruthenium(II) bis(diimine) complexes

Hydrogenation and hydrogenolysis of furfural and furfuryl alcohol catalyzed by ruthenium(II) bis(diimine) complexes

Ring‐Opening Protonolysis of Sila[1]ferrocenophanes as a Route to Stabilized Silylium Ions

Ionic and Organometallic‐Catalyzed Organosilane Reductions

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