Peter R. Markies

X-ray structural analyses of organomagnesium compounds

Publisher Summary This chapter discusses the X–ray structural analyses of organomagnesium compounds. Organomagnesium compounds are well-established tools in organic chemistry. Compared to the long history of the synthetic applications of organomagnesium compounds, the investigation of their structure and bonding covers a much shorter period. By the use of gas-phase electron diffraction (GED), it is possible to determine the structure of molecules in the gas phase. A major drawback of GED is that only small molecules can be resolved completely; for larger molecules, the degrees of freedom must be limited during the calculations by assuming and optimizing values for many of the structural parameters. In almost all structure determinations of simple Grignard or diorganylmagnesium compounds, the magnesium atoms are surrounded by four ligands. In the absence of coordinating solvents such as ethers, most organomagnesium compounds tend to form polymeric structures. Solid and volatile organomagnesium compounds can be slowly sublimed in a static high vacuum. On the symmetrization of di-Grignard reagents to the analogous halogen-free compounds, both polymeric and cyclic species may be expected. Although the tetrahedral coordination geometry is preferred by organomagnesium compounds, many examples have been structurally characterized, which show deviating coordination numbers. Increased coordination numbers for magnesium are also found for an ethylmagnesium-chloride/magnesium-chloride adduct. Fascinating structures can be obtained on the complexation of organomagnesium compounds with polyether ligands.

The coordination modes of simple diarylmagnesium species: Some representative X-ray crystal structures

The coordination modes of simple diarylmagnesium species have been investigated by crystal structure studies of representation compounds. In the case of diphenylmagnesium (1), both the solvated monomeric complex Ph2Mg·[THF]2 (1a) and the solvent-free compound [Ph2Mg]n (1b) were characterized. A polymeric structure was found for 1b, with tetrahedrally coordinated magnesium atoms interconnected by μ,η1-bridging phenyl groups to form linear chains. Bis(p-tolyl)magnesium (3) crystallized in a remarkable double structure that contained dimeric and monomeric units in a 1:2 ratio. In the dimer, two aryl groups are μ,η1-bridging.

Complexation of diphenylzinc with simple ethers. Crystal structures of the complexes Ph2Zn · glyme and Ph2Zn · diglyme

Abstract The complexation behavior of diphenylzinc with a series of mono-, di- and tri-coordinating ethers has been investigated. Two stable crystalline 1 : 1 adducts, with ethyleneglycol dimethyl ether (glyme) ( 1 ) and diethyleneglycol dimethyl ether (diglyme) ( 2 ) were isolated and characterized by an X-ray diffraction study. Complex 1 has a normal tetra-coordinated zinc atom; 2 represents the first example of a complex penta-coordinated diorganozinc compound, and has a rather unusual geometry.

Intramolecularly coordinated arylmagnesium compounds: effects on the Schlenk equilibrium

Abstract A series of phenylmagnesium bromides (1, 3–8) with ortho-substutients capable of forming intra-molecular coordinative bonds along with the correspondng diarylmagnesium compounds (1a, 3a–6a, 8a) have been synthesized. The thermodynamic parameters ΔHs, and ΔSs for the Schlenk equilibria (2 ArMgBr &/rhar2; Ar2Mg + MgBr2) have been determined by variable temperature NMR spectroscopy. Crystal structures were obtained of 5,6,7,8,9-tetrahydrodibenz[d,g][1,6]oxamagnesecin (2a) and bis(2,6-di(methoxymethyl)phenyl)magnesium (4a). The extent of intramolecular coordination in these compounds as determined in the solid state, is used in the discussion of the influence of substituents on the Schlenk equilibrium parameters. Unusual penta- or hexa-coordination is encountered and explained as a consequence of intramolecular coordination.

The crystal and molecular structure of polymeric [(dineopentylmagnesium)2 · (neopentylmagnesium bromide)2]n: an unsolvated alkylmagnesium species

Abstract The structure of an unsolvated adduct of dineopentylmagnesium and neopentylmagnesium bromide has been determined by a single crystal X-ray diffraction study. It consists of a polymeric chain of composition [(Np 2 -Mg) 2 · (NpMgBr) 2 ] n , involving an alternating pattern of two Np 2 Mg and two NpMgBr fragments connected by bridging neopentyl and bromide groups, in which all Mg atoms are tetracoordinate. Crystals of C 15 H 33 Mg 2 Br are triclinic, space group P 1, with unit cell dimensions a 9.654(1) A, b 9.876(1) A, c 11.334(2) A, α 85.35(1)°, β 67.93(1)°, γ 74.59(1)°, Z = 2, V 965.3 (2) A 3 , R = 0.0819 for 2447 reflections with I > 3.0σ( I ).

Intra-annular reactions of the (1,3-xylylene)-18-crown-5 system: synthesis and crystal structure of [2-(bromomagnesio)-1,3-xylylene]-18-crown-5, [2-(bromomercurio)-1,3-xylylene]-18-crown-5 and bis[(1,3-xylylene-18-crown-5)-2-yl]mercury

Abstract The Grignard compound [2-(bromomagnesio)-1,3-xylylene]-18-crown-5 ( 4 ) was prepared from the aryllithium compound (2-lithio-1,3-xylylene)-18-crown-5 The 1 : 1 reaction of 9 with HgBr 2 yielded the corresponding organomercury compound [2-(bromomercurio)-1,3-xylylene]-18-crown-5 ( 10 ), which The crown ether Grignard 4 was treated with deuterium oxide, chlorotrimethylstannane, iodine and berizophenone to give the products (2- d -1,3-xy

The remarkable crystal structure of the dimeric species [bis(ortho-anisyl)magnesium · THF]2

Abstract The crystal structure of dimeric bis( ortho -methoxyphenyl)magnesium tetrahydrofuranate, 1 , has been determined, and found to be remarkably unsymmetrical. The magnesium atoms in 1 have different coordination numbers and are connected by two ortho -methoxyphenyl groups each bridging in a unique fashion.