In chemistry, a transition metal ether complex is a coordination complex consisting of a transition metal bonded to one or more ether ligand. The inventory of complexes is extensive. Common ether ligands are diethyl ether and tetrahydrofuran. Common chelating ether ligands include the glymes, dimethoxyethane (dme) and diglyme, and the crown ethers. Being lipophilic, metal-ether complexes often exhibit solubility in organic solvents, a property of interest in synthetic chemistry. In contrast, the diether 1,4-dioxane is generally a bridging ligand.
Bonding, structure, reactions
Ethers are L-type ligands. They are σ-donors that exert weak field ligands. They resemble water ligands as seen in aquo complexes. They do not, however, readily participate in hydrogen bonding. The ether oxygen is nearly trigonal planar in its complexes.
Being weakly basic, ether ligands tend to be easily displaceable. Otherwise, ether ligands are relatively unreactive. Cyclic ethers such as thf can ring-open or even deoxygenated when bound to highly electrophilic metal halides. Thus treatment of tungsten hexachloride with one equivalent of thf gives 1,4-dichlorobutane:
At higher concentrations of thf, polytetrahydrofuran is produced.
Examples Homoleptic complexes Ethers are relatively bulky ligands, thus homoleptic (all ligands being the same) ether complexes are uncommon. Examples often feature weakly coordinating anions such as and . [V(thf)6](BArF4)2 [Mn(thf)6](Mn(CO)5]2 [Fe(thf)6][BArF4]2 [Ni(thf)6][Al(ORF)4]2
Metal halide complexes
Metal chloride-tetrahydrofuran complexes are especially studied. These compounds are reagents because they are "organic-soluble" source of anhydrous halides. The following trends are observed: for diethyl ether forms isolable complexes with only highly electrophilic halides, thf forms more extensive set of complexes with a more extensive set of metal chlorides. Heavier, late metal halides (RuCl3 to CdCl2 and OsCl4 to HgCl2) do not form isolable complexes with simple ethers.
Formula of M–Cl–ether complexes Coordinationspherecolor and comment ScCl3(thf)3 mer-ScO3Cl3colorless TiCl4(Et2O)2 cis-TiO2Cl4yellow TiCl4(thf)2 cis and trans-TiO2Cl4yellow Both cis and trans isomers have been reported TiCl3(thf)3 mer-TiO3Cl3blue [TiCl3(thf)2]2 TiO2Cl4green ZrCl4(Et2O)2 trans-ZrO2Cl4white ZrCl4(thf)2 cis-ZrO2Cl4white HfCl4(thf)2 cis-HfO2Cl4white VCl3(thf)3 mer-VO3Cl3pink [VCl3(thf)2]2 trans-VO2Cl4red NbCl4(Et2O)2 trans-NbO2Cl4yellow NbCl4(thf)2 trans-NbO2Cl4yellow Ta3Cl9(thf)4 TaO2Cl4 and TaOCl5green CrCl3(thf)3 mer-CrO3Cl3pink MoCl4(thf)2 trans-MoO2Cl4pinkMoCl4(Et2O)2trans-MoO2Cl4beige MoCl3(thf)3 mer-MoO3Cl3red WCl3(thf)3 mer-WO3Cl3yellowWCl4(Et2O)2trans-WO2Cl4yellow MnCl3(thf)3 mer-MnO3Cl3brown-purple TcCl4(thf)2 cis-TcO2Cl4yellow ReCl4(thf)2 cis-ReO2Cl4green See also: ReCl4(dme) Fe4Cl8(thf)6 FeO2Cl3, FeO2Cl4brown FeCl3(thf)2 FeO2Cl3the related diethyl ether complex is brown FeCl3(OEt2)2 FeO2Cl3brown Co4Cl8(thf)6 CoO2Cl3, CoO2Cl4blue isostructural with Fe analogue[CoCl2(dme)]2CoO2Cl3pink NiCl2(dimethoxyethane)2cis-NiCl2O4yellow [Cu2Cl4(thf)3]n CuO2Cl4, CuOCl4orange ZnCl2(thf)2 ZnO2Cl2white
Metal carbonyl complexes M(CO)5(thf) (M = Cr, Mo, W) Mo(CO)3(diglyme)
Related topics Ethers are widely used as ligands beyond transition metal chemistry. Few alkali metal halides form isolable adducts, but the divalent alkaline earth complexes are well known, such as .
References