B(C₆F₅)₃ as C₆F₅ Transfer Agent in Zirconium Chemistry: Borole Sandwich and Borole-Bridged Triple-Decker Complexes

Treatment of Cp‘ ‘Zr(C6F5)(OEt2){η5-(3-RC4H3BC6F5)} (1H, R = H; 1Me, R = Me; Cp‘ ‘ =
1,3-C5H3(SiMe3)2) in toluene with nitriles R‘CN gives rise to the adducts Cp‘ ‘Zr(C6F5)(NCR‘){η5-(3-RC4H3BC6F5)} (2H, R = H, R‘ = Me; 3H, R = H, R‘ = tBu; 3Me, R = Me, R‘ =
tBu) in high yields. The reaction of 1H and 1Me with a 4-fold excess of tert-butylisocyanide
in toluene at −20 °C leads to the formation of Cp‘ ‘Zr(C6F5)(CNtBu)2{η5-(3-RC4H3BC6F5)}
(4H, R = H; 4Me, R = Me), while warming to room temperature results in the insertion of
one molecule of isocyanide into the zirconium−C6F5 bond to give the η2-iminoacyl complexes
Cp‘ ‘Zr{η2-(C6F5CNtBu)}(CNtBu){η5-(3-RC4H3BC6F5)} (5H, R = H; 5Me, R = Me). The
structures of 3H and 5H were confirmed by X-ray diffraction. The reaction of the diene
complexes CpRZr(η3-crotyl)(η4-butadiene) (6a, CpR = C5H4SiMe3; 6b, C5H4Me; 6c, Cp; 6d,
Cp‘ ‘) with B(C6F5)3 in toluene solution at room temperature proceeds quantitatively with
C−H activation, butene elimination, and C6F5 transfer to generate CpRZr(C6F5){η4-CH2CHCHCHB(C6F5)2} (7a−d). These boryldiene complexes are thermally unstable and
smoothly rearrange to give the triple-decker complexes Zr2(CpR)2(C6F5)2{μ-η5:η5-C4H4BCH2-η3,κF-CHCHCHB(C6F5)3} (8a−d). The formation of these complexes involves the complete
transfer of all three C6F5 substituents of one B(C6F5)3 molecule, as well as C−H activation
and the loss of one C6F5 group as pentafluorobenzene. The triple-decker complexes feature
a Zr2C4B core, a zwitterionic structure, and an unusually strong Zr−F donor interaction.
On activation with methylalumoxane (MAO), 8a−d polymerize ethene.