Sodium-mediated magnesiation of thiophene and tetrahydrothiophene : structural contrasts with furan and tetrahydrofuran

Sulfur-containing heterocycles are currently attracting agreat deal of interest in several diverse fields. For instance, substituted tetrahydrothiophenes have received considerable attention due to their extremely wide-ranging chemical and biological applications.These include their use as potent a-glucosidase inhibitors, as an inhibitor of copper amine oxidases and as selective A3 agonists and antagonists. In addition, they have been utilised in chemical transformations, such as catalytic asymmetric epoxidation, catalytic intramolecular cyclopropanation, and asymmetric metal catalysis hydrogenation. From a nanochemical perspective,the adsorption chemistries and physical propertiesof various thiophenes and tetrahydrothiophenes on gold surfaces have recently come to the fore.[7] Polythiophenes are also key compounds in modern materials research, currently utilised in, for example, the fabrication of semi-conducting, fluorescent, and electronic and optoelectronic materials.[8]In this work, metallation (exchange of a hydrogen atom with a metal atom) of the parent heterocycles, tetrahydrothiophene (THT) and thiophene is considered. Metallation is one of the most fundamental reactions in modern day synthesis and is a key tool in the preparation of functionalised aromaticand heterocyclic compounds. It is usually achieved bythe utilisation of commercially accessible organolithiums (or lithium amides); however, these reactions do have theirdrawbacks, including the intolerance of certain functionalgroups, the need for cryoscopic temperatures and the inadvertent reactivity with polar reaction solvents

A monomeric three-coordinate magnesium bis(amide)

The metallation reaction between dibutylmagnesium and 2,6-diisopropyl-N-(trimethylsilyl)aniline gives the unusual monomeric three-coordinate complex (diethyl ether-kappaO)bis[2,6-diisopropyl-N-(trimethylsilyl)anilido-kappaN]magnesium(II), [Mg-(C15H26NSi)(2)(C4H10O)] or [Mg{(Me3Si)(2,6-(Pr2C6H3)-Pr-i)N}(2) (Et2O)]. This low-coordinate species has a distorted trigonal-planar coordination environment, with an additional short Mg-C-ipso contact of 2.799 (2) Angstrom

Chloro(dibenzylamine)dimethylaluminium(III)

The addition of dibenzylamine to Me2A1C1 gives the title alane adduct, [Me2C1AI(NHBz2)] or [A1CI(CH3)2- (CIaHxsN)]. The coordination geometry about the A1 atom is distorted tetrahedral in both the crystalline phase and in solution

Synthesis and structural characterisation of 'solvent-free' lithium-calcium hexamethyldisilazide, [Li{mu-N(SiMe3)(2)}(2)Ca{N(SiMe3)(2)}], exhibiting a double ration of agostic H3C center dot center dot center dot Li and H3C center dot center dot center dot Ca intramolecular interactions

Addition of lithium hexamethyldisilazide to an equimolar amount of calcium bis(hexamethyldisilazide) in toluene gave 'solvent-free'. [Li{mu-N(SiMc(3))(2)}(2)Ca{N(SiMe3)(2)] (1). An X-ray study reveals a dinuclear arrangement based on a planar LiNCaN four-membered ring: both metals engage in additional H3C...M (where M = Lt. Ca) interactions with the mu-N(SiMe3)(2) substituents resulting in a distorted tetrahedral geometry at lithium and a distorted trigonal-bipyramidal geometry at calcium. This contrasts with the previously reported mixed Li-Mg analogue, [Li{mu-N(SiMe3)(2)}(2)Mg{N(SiMe3)(2)}], where only the lithium centre engages in such intramolecular agostic H3C...Li interactions

Intermetallic lithium-magnesium hexamethyldisilazide: Synthesis and structure, discovery of an oxygen-centered variant, and a reaction with benzonitrile that produces a novel amidinate cage compound with a trigonal bipyramidal Li4MgO core

Intermetallic lithium-magnesium hexamethyldisilazide [{(Me3Si)2N}3LiMg], 1, has been synthesized from a nonstoichiometric 2:1 ratio of LHMDS and Mg(HMDS)2 in hexane/toluene solution. Its crystal structure reveals a simple dinuclear arrangement based on a near-planar NMgNLi ring: the Mg center occupies a distorted trigonal planar environment of three N atoms, while the Li center occupies a distorted tetrahedral N2C2 environment due to two additional C-Li interactions with the -N(SiMe3)2 substituents. This structure appears to be retained in arene solution on the basis of the evidence of 1H NMR spectral data. In the presence of trace amounts of oxygen, the surprising peroxide-oxide variant [{(Me3Si)2N}4 Li2Mg2(O2)x(O)y] preferentially crystallizes from solution. X-ray crystallography has established that its structure contains peroxide predominantly [x = 0.715(7); y = 0.285(7)], the presence of which induces an aggregation state increase relative to 1: the four indistinguishable metal centers, held in a square-planar arrangement, side-on-coordinate to the peroxide molecule and bind to two N atoms. The oxygen-scavenging ability of this system has been exploited further in a reaction with benzonitrile. This has yielded a third intermetallic lithium-magnesium crystalline compound, having the composition [{PhC(NSiMe3)2}4Li4Mg(O)]. X-ray crystallography has revealed its remarkable cage structure built around an unprecedented distorted trigonal bipyramidal Li4MgO core, at the center of which lies a 5-O atom. Interestingly, all the metal centers lie out of the benzamidinate NCN ligand planes to indicate a significant degree of -bonding. One NCN ligand also adopts an unusual face-capping mode to a Li3 triangle, the like of which has previously only been observed in transition metal cluster compounds

Structurally-defined direct C-magnesiation and C-zincation of N-heterocyclic aromatic compounds using alkali-metal-mediated metallation

Demonstrating direct synergic ''low polarity metallation'', 1-methylindole is C-magnesiated by (TMEDA)2?Na2MgBu4 and C-zincated by (TMEDA)?Na(tBu)(TMP)Zn(tBu), and 1-methylpyrrole is C-zincated by the same reagent, with all three metal products successfully crystallographically characterised

A new Na/Mg inverse crown ether

A 'missing' member of the inverse crown ether family, namely mu(4)-oxo-tetrakis(mu-2,2,6,6-tetramethylpiperidinido)dimagnesium(II)disodium(I), [Na2Mg2O(C9H18N)(4)], has been synthesized by blocking the alternative aromatic metallation route via the use of sterically hindered 1,3,5-mesitylene as a solvent. [Na2Mg2O(NR2)(4)] (NR2 is 2,2,6,6-tetramethylpiperidinide) is shown to form a cationic planar eight-membered ring with alternating metal and N atoms, which captures at its core an oxide guest that lies on an inversion centre [principal dimensions: Na - O = 2.2405 (11) Angstrom, Na - N = 2.445 (3) and 2.572 (3) Angstrom, Mg - O = 1.8673 (9) Angstrom, and Mg - N = 2.032 (2) and 2.063 (2) Angstrom]

Bis[(μ-cyclopentylamino-N:N)dimethylaluminium(III)]

Reaction of AlMe3 with NH2(C5H9) caused the evolution of methane and produced the dimeric species bis(μ-cyclo­pentyl­amino-N:N)bis[dimethylaluminium(III)], [Al(CH3)2-(C5H10N)]2, which was found to adopt a cis configuration of cyclopentyl groups about a bent AlNAlN ring (which has twofold crystallographic symmetry) instead of the more common trans arrangement

Dichlorobis(dibenzylamino)bis(tetra-hydrofuran)zirconium(IV) toluene hemisolvate

The title complex, [ZrCl2(C4H8O)(2)(C14H14N)(2)].0.5C(7)H(8), was prepared in an unusual manner by utilizing [Mg{N(CH2Ph)(2)}(2)] as a ligand transfer reagent. The Zr atom lies in a distorted octahedral environment where steric repulsion from the large dibenzylamino ligands leads to a widening of the N-Zr-N angle [99.95 (9)degrees] and corresponding compression of other angles [Cl-Zr-Cl 160.95 (3)degrees and O-Zr-O 78.22 (7)degrees]. This distortion is compared with those found in the previously determined structures of the dimethylamino and diethylamino analogues