Acidity measurements on pyridines in tetrahydrofuran using lithiated silylamines

Fraser, Robert R.; Mansour, Tarek S.; Savard, Sylvain

doi:10.1021/jo00217a050

Cited by 240 publications

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“…Until very recently, the pK a value of 25.8 [67] for HN-A C H T U N G T R E N N U N G (SiMe 3 ) 2 was the limiting factor for the use as a metallating reagent, because only the alkaline-earth-metal bis-A C H T U N G T R E N N U N G [bis(trimethylsilyl)amides] were suitable synthons that were soluble in common organic solvents and available in good yields. [30] Therefore, past investigations were limited to substrates with very acidic hydrogen atoms.…”

Section: Metallation Reactions: the Metallation Power Of [Cai(ph)-a Cmentioning

confidence: 99%

Heavy Grignard Reagents: Challenges and Possibilities of Aryl Alkaline Earth Metal Compounds

Westerhausen

Gärtner

Fischer

et al. 2007

Chemistry A European J

162

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Compounds of the type aryl--M--X, with M=Ca, Sr, Ba and X as any kind of ligand (such as halide, phosphanide, amide, aryl), are presented. The low reactivity of the heavy alkaline earth metals calcium, strontium, and barium enforces an activation prior to use for the direct synthesis. The insertion of these metals into C--I bonds of aryl iodides (direct synthesis) yields aryl metal iodides and has to be performed at low temperatures and in THF. Aryl alkaline-earth-metal compounds show some characteristics: 1) the ease of ether cleavage enforces low reaction temperatures, 2) for Sr and Ba the Schlenk equilibrium is shifted towards homoleptic MI2 and MPh2, 3) high solubility of diaryl alkaline-earth-metal derivatives in THF even at low temperatures initiated quantum chemical investigations on the aggregation behavior, and 4) a strong low field shift of the 13C resonances of the ipso carbon atoms in NMR spectra was observed. First results from quantum chemical calculations on diaryl dicalcium(I) suggest a long Ca--Ca bond with a considerable Ca--Ca bond dissociation energy. Initial results on a selection of applications such as metallation, metathesis, and addition reactions of aryl calcium compounds are presented as well.

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Section: Metallation Reactions: the Metallation Power Of [Cai(ph)-a Cmentioning

confidence: 99%

Heavy Grignard Reagents: Challenges and Possibilities of Aryl Alkaline Earth Metal Compounds

Westerhausen

Gärtner

Fischer

et al. 2007

Chemistry A European J

162

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“…slight excess of amine or uptake included arylmethanes (7), benzene derivatives (8), hindered of moisture in methanol-0-d. The results appear in Table 1 .4 amines (9), and alkylpyridines (10). In this paper we wish to describe pK measurements on a series of 5-membered aromatic 'In all cases that we have examined, there has been no observable heterocycles and some of their benz-fused derivatives.…”

mentioning

confidence: 99%

Acidity measurements in THF. V. Heteroaromatic compounds containing 5-membered rings

Fraser¹,

Mansour²,

Savard³

1985

Can. J. Chem.

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The pKa's of 13 heterocyclic aromatic compounds have been measured in tetrahydrofuran (THF) using 13C nmr spectroscopy. The acidifying effect of a nitrogen heteroatom is seen to be quite large (4–6 pK units versus C—H) on an adjacent C—H bond but small on a more remote hydrogen. Most of these aromatic heterocycles are sufficiently acidic, pKa < 34, to be completely deprotonated by lithium tetramethylpiperidide in THF. Benzoxazole appears to be an extremely strong carbon acid, its ring-opened isomer having a pKa of less than 15.7.

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“…62.4 [g] 31.4 5.07 [g] 82.3 [d] 64.2 [d] -5.18 [d] 16 PtBu 2 (6 b) 84.6 [g,h] 64.6 [g,h] - However, when the stronger base NaN(SiMe 3 ) 2 (pK a (THF) HN(SiMe 3 ) 2 = 25.8; [22] 1.1-1.5 equiv) was added to [D 8 ]THF solutions of 3 b,c and 4 b, high conversions to the phosphido complexes 5 b (80 %), 5 c (95 %), and 6 b (90 %) were achieved. [5] Deprotonation reactions could also be effected with nBuLi.…”

Section: Introductionmentioning

confidence: 99%

Generation and Reactions of Ruthenium Phosphido Complexes [(η⁵‐C₅H₅)Ru(PR′₃)₂(PR₂)]: Remarkably High Phosphorus Basicities and Applications as Ligands for Palladium‐Catalyzed Suzuki Cross‐Coupling Reactions

Planas

Hampel

Gladysz

2005

Chemistry A European J

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Reactions of [(eta5-C5H5)Ru(PR'3)2(Cl)] with NaBAr(F) [BAr(F)-=B{3,5-[C6H3(CF3)2]}4-; PR'3=PEt3 or 1/2Et2PCH2CH2PEt2) (depe)] and PR2H (R=Ph, a; tBu, b; Cy, c) in C6H5F, or of related cationic Ru(N2) complexes with PR2H in C6H5F, gave the secondary phosphine complexes [(eta5-C5H5)Ru(PR'3)2(PR2H)]+ BAr(F)- (PR'3=PEt3, 3 a-c; 1/2depe, 4 a,b) in 65-91 % yields. Additions of tBuOK (3 a, 4 a; [D6]acetone) or NaN(SiMe3)2 (3 b,c, 4 b; [D8]THF) gave the title complexes [(eta5-C5H5)Ru(PEt3)2(PR2)] (5 a-c) and [(eta5-C5H5)Ru(depe)(PR2)] (6 a,b) in high spectroscopic yields. These complexes were rapidly oxidized in air; with 5 a, [(eta5-C5H5)Ru(PEt3)2{P(=O)Ph2}] was isolated (>99 %). The reaction of 5 a and elemental selenium yielded [(eta5-C5H5)Ru(PEt3)2{P(=Se)Ph2}] (70 %); selenides from 5 c and 6 a were characterized in situ. Competitive deprotonation reactions showed that 5 a is more basic than the rhenium analog [(eta5-C5H5)Re(NO)(PPh3)(PPh2)], and that 6 b is more basic than PtBu3 and P(iPrNCH2CH2)3N. The latter is one of the most basic trivalent phosphorus compounds [pK(a)(acetonitrile) 33.6]. Complexes 5 a-c and 6 b are effective ligands for Pd(OAc)2-catalyzed Suzuki coupling reactions: 6 b gave a catalyst nearly as active as the benchmark organophosphine PtBu3; 5 a, with a less bulky and electron-rich PR2 moiety, gave a less active catalyst. The reaction of 5 a and [(eta3-C3H5)Pd(NCPh)2]+ BF4- gave the bridging phosphido complex [(eta5-C5H5)Ru(PEt3)2(PPh2)Pd(NCPh)(eta3-C3H5)]+ BAr(F)- in approximately 90 % purity. The crystal structure of 4 a is described, as well as substitution reactions of 3 b and 4 b.

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Acidity measurements on pyridines in tetrahydrofuran using lithiated silylamines

Cited by 240 publications

References 0 publications

Heavy Grignard Reagents: Challenges and Possibilities of Aryl Alkaline Earth Metal Compounds

Heavy Grignard Reagents: Challenges and Possibilities of Aryl Alkaline Earth Metal Compounds

Acidity measurements in THF. V. Heteroaromatic compounds containing 5-membered rings

Generation and Reactions of Ruthenium Phosphido Complexes [(η⁵‐C₅H₅)Ru(PR′₃)₂(PR₂)]: Remarkably High Phosphorus Basicities and Applications as Ligands for Palladium‐Catalyzed Suzuki Cross‐Coupling Reactions

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Acidity measurements on pyridines in tetrahydrofuran using lithiated silylamines

Cited by 240 publications

References 0 publications

Heavy Grignard Reagents: Challenges and Possibilities of Aryl Alkaline Earth Metal Compounds

Heavy Grignard Reagents: Challenges and Possibilities of Aryl Alkaline Earth Metal Compounds

Acidity measurements in THF. V. Heteroaromatic compounds containing 5-membered rings

Generation and Reactions of Ruthenium Phosphido Complexes [(η5‐C5H5)Ru(PR′3)2(PR2)]: Remarkably High Phosphorus Basicities and Applications as Ligands for Palladium‐Catalyzed Suzuki Cross‐Coupling Reactions

Contact Info

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Generation and Reactions of Ruthenium Phosphido Complexes [(η⁵‐C₅H₅)Ru(PR′₃)₂(PR₂)]: Remarkably High Phosphorus Basicities and Applications as Ligands for Palladium‐Catalyzed Suzuki Cross‐Coupling Reactions