Metal-metal bonding in pentamethylcyclopentadienylmolybdenum(IV) dinuclear compounds: chloride abstraction from non-bonded Cp∗2Mo2Cl6 to afford bonded [Cp∗2Mo2Cl5]+
Résumé
Chloride abstraction from Cp*2M02Cl 6 (Cp*= η5-C5Me5) is accomplished by interaction with the Lewis acid AICl 3 to afford
the structurally characterized salt [Cp*2Mo2CI5]+[AICI4] -. Crystal data: triclinic, space group P1, a = 8.3903(13), b= 15.797(3),
c =24.036(2) Å, α =86.766(11), β = 80.916(10), γ = 81.616(14) °, V =3110.5(8) Å3, Dc = 1.726 Mg m -3, μ(Mo Kα)= 1.618 mm -1,
R=0.0637. The structure exhibits two four-legged piano stools joined by three bridging Cl atoms. The Mo-Mo distance of
2.866(2) Å is significantly longer than all other reported bonded Mo(IV)-Mo(IV) distances and longer than the single bond
(σ2δ*2δ2) distance in the related Mo(III) complexes [(ring)MoCl2]2 (ring= substitute cyclopentadienyl ring). The reasons for
this lengthening are analyzed and discussed on the basis of structural data and Fenske-Hall MO calculations. [Cp*2Mo2Cl5] +
reacts rapidly with Cl- to afford [Cp*MoCl4]- and exhibits a reversible one-electron oxidation to a neutral Cp*2Mo2Cl5 species
at -0.13 V versus ferrocene/ferricinium. The non-existence of a metal-metal bonded isomeric form of the Cp*2Mo2Cl6 parent
compound is also discussed.
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