Transition metal ether complex

Structure of the ether complex HfCl4(thf)2fwn

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

In almost all of its complexes, dioxane is a bridging, not chelating, ligand. Structure of the coordination polymer of cobalt(II) chloride and 1,4-dioxane.

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:

WCl6 + OC4H8 → WOCl4 + ClCH2CH2CH2CH2Cl

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 B(ArF)−4 and Al(ORF)−4.

[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

Structure of NiI2(dme)2 as determined by X-ray crystallography. The sum of the angles at O is 352°, indicating a nearly planar ether oxygen. Color code: O = red, I = purple, Ni = blue, C = black.

Structure of FeCl3(diethylether)2. Color code: Cl=green, Fe = blue, O = red.

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	Coordination sphere	color and comment
ScCl3(thf)3	mer-ScO3Cl3	colorless
TiCl4(Et2O)2	cis-TiO2Cl4	yellow
TiCl4(thf)2	cis and trans-TiO2Cl4	yellow Both cis and trans isomers have been reported
TiCl3(thf)3	mer-TiO3Cl3	blue
[TiCl3(thf)2]2	TiO2Cl4	green
ZrCl4(Et2O)2	trans-ZrO2Cl4	white
ZrCl4(thf)2	cis-ZrO2Cl4	white
HfCl4(thf)2	cis-HfO2Cl4	white
VCl3(thf)3	mer-VO3Cl3	pink
[VCl3(thf)2]2	trans-VO2Cl4	red
NbCl4(Et2O)2	trans-NbO2Cl4	yellow
NbCl4(thf)2	trans-NbO2Cl4	yellow
Ta3Cl9(thf)4	TaO2Cl4 and TaOCl5	green
CrCl3(thf)3	mer-CrO3Cl3	pink
MoCl4(thf)2	trans-MoO2Cl4	pink
MoCl4(Et2O)2	trans-MoO2Cl4	beige
MoCl3(thf)3	mer-MoO3Cl3	red
WCl3(thf)3	mer-WO3Cl3	yellow
WCl4(Et2O)2	trans-WO2Cl4	yellow
MnCl3(thf)3	mer-MnO3Cl3	brown-purple
TcCl4(thf)2	cis-TcO2Cl4	yellow
ReCl4(thf)2	cis-ReO2Cl4	green See also: ReCl4(dme)
Fe4Cl8(thf)6	FeO2Cl3, FeO2Cl4	brown
FeCl3(thf)2	FeO2Cl3	the related diethyl ether complex is brown
FeCl3(OEt2)2	FeO2Cl3	brown
Co4Cl8(thf)6	CoO2Cl3, CoO2Cl4	blue isostructural with Fe analogue
[CoCl2(dme)]2	CoO2Cl3	pink
NiCl2(dimethoxyethane)2	cis-NiCl2O4	yellow
[Cu2Cl4(thf)3]n	CuO2Cl4, CuOCl4	orange
ZnCl2(thf)2	ZnO2Cl2	white

Metal carbonyl complexes