Bent metallocene

In organometallic chemistry, bent metallocenes are a subset of metallocenes. In bent metallocenes, the ring systems coordinated to the metal are not parallel, but are tilted at an angle. A common example of a bent metallocene is Cp₂TiCl₂. Several reagents and much research is based on bent metallocenes.

Like regular metallocenes, bent metallocenes are synthesized by a variety of methods but most typically by reaction of sodium cyclopentadienide with the metal halide. This method applies to the synthesis of the bent metallocene dihalides of titanium, zirconium, hafnium, and vanadium:

In the earliest work in this area, Grignard reagents were used to deprotonate the cyclopentadiene.

Niobocene dichloride, featuring Nb(IV), is prepared via a multistep reaction that begins with a Nb(V) precursor:

Bent metallocene dichlorides of molybdenum and tungsten are also prepared via indirect routes that involve redox at the metal centres.

Tebbe's reagent

Schwartz's reagent.

Ansa-metallocene, X is the linker group, often (CH₂)_n or R₂Si (R = alkyl)

Titanocene dicarbonyl.

Bent metallocenes have ideallized C_2v symmetry. The non-Cp ligands are arrayed in the wedge area. For bent metallocenes with the formula Cp₂ML₂, the L-M-L angle depends on the electron count. In the d²-complex molybdocene dichloride (Cp₂MoCl₂) the Cl-Mo-Cl angle is 82°. In the d¹ complex niobocene dichloride, this angle is more open at 85.6°. In the d⁰-complex zirconocene dichloride the angle is even more open at 92.1°. This trend reveals that the frontier orbital, which is d_z2, is oriented in the MCl₂ plane but does not bisect the MCl₂ angle.

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