Transition metal ether complex

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.^[2] 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 di-ether 1,4-dioxane is generally a bridging ligand.

Structure of the ether complex HfCl₄(thf)₂.^[1]

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.^[3]

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.^[4]

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:^[5]

WCl₆ + OC₄H₈ → WOCl₄ + ClCH₂CH₂CH₂CH₂Cl

At higher concentrations of thf, polytetrahydrofuran is produced.

Examples

Homoleptic complexes

Ethers are relatively bulky ligands, thus homoleptic (i.e., all ligands being the same) ether complexes are uncommon. Examples often feature weakly coordinating anions such as BAr^F₄⁻ and Al(OR^F)₄⁻.

• [V(thf)₆](BAr^F₄)₂^[6]
• [Mn(thf)₆](Mn(CO)₅]₂^[7]
• [[Fe(thf)₆]][BAr^F24]₂^[8]
• [Ni(thf)₆][Al(OR^F)₄ ]₂^[9]

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.^[10]

Structure of FeCl₃(diethylether)₂.^[11] Color code: Cl=green, Fe = blue, O = red.

Metal chloride-tetrahydrofuran complexes are especially studied.^[12] These compounds are often reagents because they are soluble in organic solvents as well as being anhydrous.

Formula of metal-chloride-ether complexes	Coordination sphere	color
TiCl4(thf)2	TiO2Cl4	yellow[13]
TiCl3(thf)3	TiO3Cl3	blue[12]
[TiCl3(thf)2]2	TiO2Cl4	green[14]
ZrCl4(thf)2	ZrO2Cl4	white[12]
HfCl4(thf)2	HfO2Cl4	white[12]
VCl3(thf)3	VO3Cl3	pink[12]
VCl3(thf)2]2	VO2Cl4	red[14]
NbCl4(thf)2	NbO2Cl4	yellow[15]
Ta3Cl9(thf)4	TaO2Cl4 and TaOCl5[15]
CrCl3(thf)3	CrO3Cl3	pink[12][16]
MoCl4(thf)2	MoO2Cl4	pink[17]
MoCl4(Et2O)2	MoO2Cl4	beige[18]
MoCl3(thf)3	MoO3Cl3	red[17]
WCl4(Et2O)2	WO2Cl4	yellow[19]
MnCl3(thf)3	MnO3Cl3	brown-purple[20]
TcCl4(thf)2	TcO2Cl4	yellow[13]
ReCl4(thf)2	ReO2Cl4	green[21]
Fe4Cl8(thf)6	FeO2Cl3, FeO2Cl4	brown[22]
FeCl3(thf)2	FeO2Cl3[23]	the related diethyl ether complex is brown
FeCl3(OEt2)2	FeO2Cl3	brown[11]
Co4Cl8(thf)6	CoO2Cl3, CoO2Cl4	blue[24]
[CoCl2(dme)]2	CoO2Cl3[25]
NiCl2(dimethoxyethane)2	NiCl2O4	yellow[26]
[Cu2Cl4(thf)3]n	CuO2Cl4, CuOCl4	orange[27]
ZnCl2(thf)2	ZnO2Cl2	white[16]

Metal carbonyl complexes

• M(CO)₅(thf) (M = Cr, Mo, W)^[4]
• Mo(CO)₃(diglyme)