Presence Of Et2O Research Articles

Synthesis and Characterization of Neutral and Cationic Magnesium Complexes Supported by NHC Ligands

A series of neutral N-heterocyclic carbene (NHC) magnesium alkyl complexes was synthesized by reaction of IMes (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene) and IPr (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) with Grignard reagents. In the presence of THF, the mononuclear species [Mg(IMes)(R)(Br)(THF)] (1, R = Me; 2, R = Et) and [Mg(IPr)(R)(Br)(THF)] (3, R = Me; 4, R = Et) were isolated. Complex 4 was further methylated to afford the Mg–THF adduct [Mg(IPr)(Me)2(THF)] (5), which crystallizes as the dimer [{(Mg(IPr)(Me)}2(μ-Me)2] (5′), thus evidencing the labile THF coordination in these systems. In contrast, in the presence of Et2O, the dinuclear Mg(II) species [{(Mg(NHC)(Br)}2(μ-Me)2] (6, NHC = IMes; 7, NHC = IPr), [{(Mg(IMes)(Ph)}2(μ-Br)2] (8), [{(Mg(IMes)(CH2Ph)}2(μ-Cl)2] (9), and [{(Mg(IPr)(Ph)}2(μ-Br)2] (10) were isolated and characterized. The protonolysis reaction between the protio ligand [IMes-H]Cl and EtMgBr afforded the Mg(II) dihalido dimer [{(Mg(IMes)(Br)}2(μ-Cl)2] (11...

Intramolecular hydroalkoxylation of syn- and anti-1-R-2-arylhex-4-en-1-ols. Efficient stereoselective synthesis of tri- and tetrasubstituted tetrahydrofurans

Reactions of syn- and anti-4-(4-bromophenyl)-2-methylnon-1-en-5-ols and 3-(4-bromophenyl)-5- methyl-1-phenylhex-5-en-2-ols with trifluoromethanesulfonic acid and salicylaldehyde derivatives in the presence of Et2O · BF3 (Prins reaction) or with salicylaldehydes in the presence of trimethyl orthoformate and p-toluenesulfonic acid stereoselectively afforded tri- and tetrasubstituted tetrahydrofurans with one or two fused heterocycles and various functional groups (COOEt, Br, MeC=CH2). The reactivity of the synthesized compounds toward thiophen-2-ylboronic acid in the Suzuki reaction was studied, and hydrolysis and reduction (LiAlH4) of the ester group therein gave the corresponding carboxylic acids and alcohols. One of the obtained tetrahydrofuran derivatives was converted into amide, aldehyde, and aldehyde oxime. Stereochemical configuration of substituents was retained in all chemical transformations.

Lithium and Potassium Complexes with dbn‐ and dbu‐Based Enamido Phosphine Ligands: Syntheses and Applications

The phosphines 6‐diphenylphosphino‐1,8‐diazabicyclo[5.4.0]undec‐7‐ene (dbuPH) and 7‐diphenylposphino‐1,5‐diazabicyclo[4.3.0]non‐5‐ene (dbnPH), containing amidine subunits, were successfully deprotonated by n‐butyllithium or benzylpotassium. In the presence of Et2O or THF, the well‐defined complexes [{Li(dbnP)(Et2O)}2] (1), [{Li(dbuP)(Et2O)}2] (2), [{K(dbnP)(THF)}∞] (3b) and [{K(dbuP)(THF)2}2] (4) were obtained, while in the absence of such donors, polymeric [{K(dbnP)}∞] (3a) was formed. These alkali‐metal derivatives are useful precursors for salt‐metathesis reactions, and they allow the transfer of the enamido phosphine ligands to appropriate transition metals, as demonstrated by the syntheses of the new rhodium complexes [Rh(dbnP)(cod)] (5) and [Rh(dbuP)(cod)] (6). The reaction of 1 and 2 with Ph2PCl underlined the ambident character of dbnP– and dbuP– as nucleophiles and led to the new diphosphines dbn(PPh2)2 (two isomers C‐7 and N‐7) and dbu(PPh2)2 (N‐8), in which either the carbon or the nitrogen atom of the former enamido moiety was substituted.

Oxidative-substitution reactions of electron-rich aromatic compounds with BF 3-activated iodonium ylides

The treatment of electron-rich aromatic substrates with phenyliodonium bis(carbonyl)methylides in the presence of Et 2O·BF 3 leads to bis(carbonyl)alkylation of the aromatic nucleus.

CP/MAS NMR and X-ray crystallographic characterization of trans-PdX2(PPh2vinyl)2 (X = Cl, I); UV and Et2O·BF3 reaction studies, including the formation of [Pd(µ-Cl)(PPh2vinyl)2]2[BF4]2

The complexes PdCl2(PPh2vinyl)2 and PdI2(PPh2vinyl)2 have been prepared and crystallographically characterized as their trans square planar isomers. Trans-PdCl2(PPh2vinyl)2 exists in a centrosymmetric structure with a planar PdCl2P2 core whereas trans-PdI2(PPh2vinyl)2 shows no local Pd-centred symmetry and significant distortion of the PdI2P2 core from planarity. Crystallographic data is in accord with the 31P{1H} CP/MAS NMR spectra of the two complexes, which display a single resonance for the chloro-complex and two resonances for the iodo-complex. UV irradiation of CH2Cl2 solutions of PdCl2(PPh2vinyl)2 followed by re-dissolution in CDCl3 indicates no permanent chemical change. However, post-irradiation CP/MAS 31P{1H} NMR spectroscopy demonstrates the presence of trans-PdCl2(PPh2vinyl)2 in two solid state structures, plus cis-PdCl2(PPh2vinyl)2. PdI2(PPh2vinyl)2 exists only in its trans form in both solid state and solution. Irradiation results in phosphine displacement and the formation of sym-[PdI2(PPh2vinyl)]2 and free phosphine, the latter being characterized as Ph2P(O)vinyl following aerobic oxidation. PdCl2(PPh2vinyl)2 reacts in the presence of Et2O·BF3 to afford [Pd(µ-Cl)(PPh2vinyl)2]2[BF4]2 whereas PdI2(PPh2vinyl)2 is recovered in 95% yield, with the remaining material undergoing phosphine abstraction to form sym-[PdI2(PPh2vinyl)]2.Key words: palladium, phosphine, alkene, isomerization, CP/MAS.

The crystal structure of [Ni(dmf) 6 ][NiCl 4 ] and comments on the hydrolysis of coordinated amides and peptides in metal complexes

Solutions of nickel(II) chloride in N,N-dimethylformamide (DMF) in the presence of Et2O slowly give bluegreen crystals of [Ni(dmf)6][NiCl4] whose structure has been confirmed by X-ray crystallography. The complex crystallises with three crystallographically distinct [Ni(dmf)6]2+ cations in the asymmetric unit, Ni(1) on a general position and Ni(2) and Ni(3) on centres of symmetry. There are also two unique [NiCl4]2− anions, both on general positions. N,N-Dimethylformamide is O-bonded to nickel as coordination via nitrogen would cause the loss of the resonance energy of the amide group. All Ni—O bond lengths are within the expected range for such complexes [2.029(4)–2.084(4) \rA]. The C=O bond lengths, which range from 1.219(7) to 1.259(7) \rA, are not significantly different from those for uncomplexed dmf (1.232 ± 0.004 \rA), suggesting that there is very little polarisation of the C=O bond by nickel(II). Oxygen-bonded dmf undergoes rapid hydrolysis in metal complexes, for example the base hydrolysis of [Co(NH3)5dmf]3+ to give the formato complex is some 104-fold faster than that of the free ligand. Copper(II)-catalysed amide and peptide bond hydrolysis is subject to ca. 106-fold rate enhancements. The origin of these rate enhancements, which appear to be due to transition state effects rather than ground state effects, is discussed in detail.

Si-C-Bond cleavage in 1-organylsilatranes by bromine or iodine chloride

The Si-C bond in I-organylsilatranes is cleaved by bromine or iodine chloride to yield 1-bromo- or 1-chlorosilatrane respectively. In the presence of Et2O or THF and under the action of dioxane dibromide, I-halosilatrane

New Method for Derivatization of Squaric Acid to Highly Substituted Cyclobutenones: Lewis Acid-Catalyzed Reaction of Cyclobutene-1,2-dione Monoacetal and Its Vinylog with Unsaturated Organosilanes, and Subsequent Ring Transformation of the Adducts

Abstract Described herein is a novel method for regio-controlled synthesis of highly substituted cyclobutenones having an unsaturated substituent at 4-position, starting from commercially available squaric acid. Both cyclobutene-1,2-dione monoacetal (4,4-diethoxycyclobutenone) and its vinylog (2,4-diethoxycyclobutenone), which were easily obtained from diethyl squarate, reacted with allylsilanes in the presence of Et2O·BF3 to afford 4-allyl-4-ethoxycyclobutenones having various substituents at 2-position regioselectively. These products were efficiently transformed to highly substituted bicyclo[3.2.0]heptenones by refluxing in xylene. The synthetic utility of this process was demonstrated in the construction of tricyclic ring systems. Further extension of the Lewis acid-catalyzed reaction of the monoacetal using an allenylsilane, a silyl enol ether, and a silyl ketene acetal also afforded the corresponding 4-substituted products. In contrast to the above 4-allylated products, 4-propargylated and 4-acylmethylated products did not undergo an analogous ring transformation under the same conditions.

Glycosyl Imidates, 55. Synthesis of the Pentasaccharide Moiety of an Asterosaponin

AbstractReaction of 2‐O‐acetyl‐protected O‐galactosyl trichloroacetimidate 3 as glycosyl donor and 2,4‐di‐O‐unprotected xylopyranoside 2 as glycosyl acceptor furnished in the presence of Et2O · BF3 as catalyst regioselectively β‐(1→4)‐connected disaccharide 4 which gave upon subsequent reaction with O‐quinovosyl trichloroacetimidate 5 as donor β‐(1→2)‐connection, thus affording trisaccharide 6. Removal of the 2‐O‐acetyl group from the galactosyl moiety yielded acceptor 7; its glycosylation with donor 5 furnished β‐connected tetrasaccharide 8. This compound was transformed via 1‐O‐desilylation and then treatment with trichloroacetonitrile in the presence of a base into O‐tetraosyl trichloroacetimidate 10 as glycosyl donor. Reaction of 10 with 3‐O‐unprotected 2,4‐di‐O‐acetyl‐ and 2,4‐di‐O‐benzyl‐protected quinovosides 13 and 16 furnished the desired fully O‐protected pentasaccharides 17 and 18, respectively. Hydrogenolytic O‐debenzylation of 18 furnished the O‐unprotected target molecule 19 which was characterized as its O‐acetyl product 20.

Synthesis and Structure of [Et2OZn(SC6H2tBu3)2], the First T‐Shaped Zinc Complex

The stacking of aryl groups once again appears to be structure‐determining. The title complex, which is accessible by reaction of [Zn(CH2SiMe3)2] with two equivalents of 2,4,6‐tBuC6H2SH in the presence of Et2O, has an SZnS angle of ca. 160° and ZnS distances of only 2.196 Å. In contrast, the ZnO distance is relatively large and explains the ready cleavability of the ether ligands. Zinc thiolates are of interest as model complexes for zinc‐containing proteins.

Hydrogen-bonding effect on the dual emission of salicylic acid

The effect of hydrogen bonding, taking diethyl ether (Et 2O) as the hydrogen-bonding partner, on the dual emission of salicylic acid (SA) has been investigated with both steady-state and time-domain experiments. It has been observed that in place of dual emission, only a single fluorescence band is observed int he presence of Et 2O. This has been attributed to the fact that all SA molecules are converted into hydrogen-bonded complexes. Further, two configurations for the SA-Et 2O complexes are suggested to explain the dynamical behaviour at low temperatures.

Reaction of furfural and its diethylacetal with alkyl diazoacetates and dimethyl diazomalonate in the presence of boron trifluoride etherate or rhodium acetate

1. The reaction of alkyl diazoacetates (ADA) with furfural in the presence of Et2O·BF3 at 20°C leads mainly to the product of the formal implantation of the alkoxycarbonylmethylene fragment into the aldehyde C-H bond, while in the same reaction in the presence of (Rh(OAc)2, a mixture of isomeric 2,5-di (2-furyl)-4-alkoxycarbonyl-1,3-dioxalanes is formed in a 60% overall yield. 2. The reaction of furfural diethylacetal with ADA in the presence of Et2O·BF3 at 20°C gave yields of up to 60% of 1-(2-furyl)-1-alkoxycarbonyl-2,2-diethoxyethanes that C1-C2are products of the formal implantation of the alkoxycarbonylmethylene fragment into the C1-C2 bond. However, in the presence of Rh(OAc)2 in the same reaction, the alkyl esters of 3-diethoxy-methyl-2-oxabicyclo[3.1.0]-3-hexene-6-carboxylic and 6,6-diethoxy-1,3-hexadien-5-one-1-carboxylic acid are formed in 60–70% overall yields. 3. The reaction of furfural diethylacetal with dimethyl diazomalonate catalyzed by Rh(OAc)2 at 20°C leads to the dimethyl ester of Z-6,6-diethoxy-1,3-hexadien-5-one-1,1-di-carboxylic acid in a 63% yield.

Reaction of dialkylphosphorous acids with sterically hindered benzoquinonimines

1. Dialkylphosphorous acids in the presence of Et2O·BF3 add to the 1-phenylimine of 3,5-di-tert-butyl-4-benzoquinone at the C=N bond to form dialkyl α-aminoquinolphosphonates. 2. Diethylphosphorous acid reacts with 3,5-di-tert-butyl-1,4-benzoquinone to give O,O-diethyl-3,5-di-tert-butyl-4-hydroxyphenyl phosphate.

ChemInform Abstract: REACTIONS OF CYCLOPENTADIENE WITH CARBONYL‐RUTHENIUM AND ‐OSMIUM COMPLEXES

AbstractRu3(CO)12 und H4Ru4(CO)12 reagieren mit Cyclopentadien unter Ausschluß von Sauerstoff zu dem Komplex (Ia), der durch Überführung in (Ib) charakterisiert wurde.

Reactions of cyclopentadiene with carbonyl-ruthenium and -osmium complexes

Both Ru3(CO)12 and [H4Ru4(CO)12] react rapidly with cyclopentadiene in the absence of oxygen to yield [RuH(CO)2(η-C5H5)], (II; M = Ru), quantitatively, characterised in part via high-yield conversion into [RuH(CO)(PPh3)(η-C5H5)]. In the presence of oxygen [{Ru(CO)2(η-C5H5)}2], (III; M = Ru), is obtained in ca. 70% yield. The complex [Ru(CO)3(η-C5H6)], (I; M = Ru), has been isolated and shown to be a direct precursor of (II). Treatment of (I; M = Ru) with [Ph3C][BF4] gives [Ru(CO)3(η-C5H5)][BF4], while triphenyl-phosphine displaces C5H6 forming [Ru(CO)3(PPh3)2]. Carbonylation (100 atm) of [RuH(CO)(PPh3)(η-C5H5)] in the presence of Et2O·BF3 gives [Ru(CO)2(PPh3)(η-C5H5)][BF4] in high yield. A minor product of the reaction of Ru3(CO)12 and C5H6 is tentatively identified as [Ru3H(CO)9(η3-C5H5)], (IV); a related fluxional osmium complex, [Os3H2(CO)9(η2-C5H4)], is obtained on treating [H2Os3(CO)10] with C5H6. Low-yield formation of (I; M = Os) and (II; M = Os) from reaction of Os3(CO)12, [H2Os3(CO)10], or [H2Os(CO)4] with C5H6 is described.