Hans Dietrich

Low temperature study of the structure of crystalline ethyllithium

Abstract Comparison with the room temperature structure shows that the Li4 clusters in the tetramer units of crystalline ethyllithium tend to increase their symmetry at low temperature. This, and the fact that 4-centre bond peaks CLi3 are observed in difference maps, suggest some covalent bonding inside the tramers. Comparison to the structure of the Li2O complex of 2,6-dimethyllithium reveals how this bonding changes in an environment of basic groups. The latter system might be representative of the lithium clusters assumed to act as reaction centre for organolithium compounds in basic solvents.

Über metallalkyl- und aryl-verbindungen ☆: XXXV. Zur struktur von allyllithium. Darstellung und kristallstruktur einer monomeren allyllithium-verbindung, allyl(pentamethyldiethylentriamin)lithium, LiC3H5(Me2NC2H4N(Me)C2H4NMe2)

Abstract Allyl(pentamethyldiethylenetriamine)lithium represents the first example of a crystalline monomeric allylithium complex. An X-ray diffraction investigation at 117 K revealed the precise structure of the LiC3H5 unit. The structural data show qualitative agreement with the results of previous theoretical calculations. Contrary to theory, however, asymmetrical bonding of the allyl group to lithium is observed, giving Li to terminal C atom distances of 225.5(5) for LiC(1) and 272.0(4) pm for LiC(3). The C3H5 unit is not planar. The central H(2) atom is bent slightly towards the Li atom; all terminal H atoms are bent in the opposite direction, particularly H(11) and H(31) which are anti to H(2).

Pentacoordinate carbon in trigonal-bipyramidal symmetry. The eight-membered x-ray structure of tetrakis(benzylsodium-N,N,N',N'-tetramethylethylenediamine).

Unlike organolithium compounds,’ relatively few structures of the synthetically important organic derivatives of the heavier alkali metals have been reported.2 A new hexane-soluble butylsodium reagent’ facilitates the preparation of crystalline organosodium compounds.3b Thus, metalation of toluene in hexane at -18 OC in the presence of N,N,N’,N’-tetramethylethylenediamine (TMEDA) gave yellow needles of (NaCHzC,H,-TMEDA),.4a

The crystal and molecular structure of the Li2O complex of 2,6-dimethoxyphenyllithium, (C8H9O2Li)6Li2O

Abstract The 2,6-dimethoxyphenyllithium molecule has the crystallographic site symmetry 3 . All lithium atoms of the six formula units of the complex are combined together with the Li2O to form a long cluster, Li8O, in the centre of the molecule. This cluster is composed of two Li4 pyramids, each of which is connected to the oxygen atom via its Li3 base in such a way that the oxygen atom has a nearly octahedral coordination with very short LiO distances. The remaining six Li3 faces of the Li4 pyramides are occupied by the organic residues as in the tetramers of ethyllithium [1] and methyllithium [2]. The final Fo  Fc map suggests weak 4-centre bonds in each of the Li4 pyramids and, as expected, between each of the metallated ring atoms, C(1), and the pyramid face to which it is attached. At the ring atoms C(1) and C(3) there are additional charges which extend in the sp2 and pz areas. The ring is planar but the CCC angles deviate systematically from 120°; the biggest deviation, of −8°, is found at C(1).

Double lithium bridging: The structure of 1,4-dilithio-1,4-diphenyl-cis-2-butene

Abstract The title compound is shown by both X-ray analysis (Fig. 2) and MNDO calculations ( 4 ) to prefer a doubly lithium bridged cis structure ( C 2 rather than C 2v ) in contrast to the trans geometry expected for the isolated 1,4-diphenylbutadiene dianion.

Kristall- und Molekülstruktur von 2,6-Dimethoxyphenyllithium

Abstract The solid state structure of 2,6-dimethoxyphenyllithium has been determined by X-ray diffraction at 117 K. The compound crystallizes in the triclinic system, space group P 1 with cell dimensions a 11.78(1), b 13.44(1), c 20.67(2) A, α 80.60(9), β 78.46(9), γ 88.83(8)°, V 3162 A 3 , Z 16. The final R ( F ) based on 3369 data with I > 2σ(I) was 0.070. The compound forms tetramers with approximate 4 2 m symmetry and having a nearly regular Li 4 tetrahedron core. The tetramer is an aggregate of the two dimers.

Competition among multihapto bonding, solvation, and aggregation. The η1/η2 infinite-chain X-ray structure of indenylsodium · N,N,N′,N′-tetramethyl-1,2-diaminoethane

Abstract Indenylsodium · N,N,N′,N′ -tetramethyl-1,2-diaminoethane ( 1 ; NaC 9 H 7 · tmeda) crystallizes in an infinitely aggregated chain structure. Unlike the known monomeric structure of indenyllithium · tmeda, which favours η 5 -coordination, the sodium cations in 1 are sandwiched between two indenyl units and, unexpectedly, exhibit η 1 - and η 2 -bonding. This reduction in metal coordination to each indenyl unit is due to the opportunites for interaction elsewhere, i.e. to the tmeda ligand and to a second indenyl anion. The C(1) (benzylic) sites of each indenyl unit, in turn, are coordinated in local D 3 h -type symmetry by two metal cations on opposite faces. The structure and bonding in organosodium indenyl, fluorenyl, cyclopentadienyl, benzyl, allylenyl and allyl compounds, and in related substances, are compared. The main structure determining factors include cation radius (viz. the average cation coordination number), the charge distribution in the anion, the competition between π-delocalization due to resonance and charge localization due to the electrostatic influence of the counter-ion, hapticity, solvation and aggregation.

Synthesis and X-ray crystal structure of a 1,1-dithiolate cluster anion containing an Ag61 octahedron [Ag61{s2cc(cn)2}6]6–

The existence of the novel title anion, despite its high electrical charge and the surprising fact that its ag6S12core has the same size as that in the uncharged molecule [Ag61{S2C-N(C3H7)2}6],1 must be due to Ag–Ag interactions.

The eight-membered ring structure of an α-lithio-2,6-dimethylpyridine–tetramethylenediamine (TMEDA) dimer

Unlike monomeric benzyl-lithium, the α-lithiated 2,6-dimethylpyridine–tetramethylethylenediamine complex prefers a dimeric, chair-like, eight-membered ring arrangement involving two intermoleculary chelated lithium atoms and near ideal perpendicular conformations of the α-CH2Li+ groups, as shown by a crystal structure.

X-Ray crystal structure of [{o-C6H4(CHPh)2}{Li(tmeda)}2](tmedaMe2NCH2CH2NMe2). Unsymmetrical lithium bridging and (E,E)-conformation of the phenyl groups

The lithium atoms in the title compound are shown by X-ray analysis to prefer quite different locations, in contrast to the symmetrical double bridging exhibited by other 1,4-dilithium compounds, but in agreement with model MNDO calculations; furthermore, the (E,E) conformation of the two phenyl groups differs from the (E,Z) conformation reported in methyltetrahydrofuran solution.