B(C6F5)(3) as C6F5 transfer agent in zirconium chemistry: Borole sandwich and borole-bridged triple-decker complexes

Treatment of Cp " Zr(C6F5)(OEt2){eta (5)-(3-RC4H3BC6F5)} (1H, R = H; 1Me, R = Me; Cp " = 1,3-C5H3(SiMe3)(2)) in toluene with nitriles R ' CN gives ris e to the adducts Cp " Zr(C6F5)(NCR '){eta (5)-(3-RC4H3BC6F5)} (2H, R = H, R ' = Me; 3H, R = H, R ' = tBu; 3Me, R = Me, R ' = tBu) in high yields. The reaction of III and 1Me with a 4-fold excess of tert-butylisocyanide in tol uene at -20 degreesC leads to the formation of Cp " Zr(C6F5)(CNtBu)(2){eta (5)-(3-RC4H3BC6F5)} (4H, R = H; 4Me, R = Me), while warming to room tempera ture results in the insertion of one molecule of isocyanide into the zircon ium-C6F5 bond to give the eta (2)-iminoacyl complexes Cp " Zr{eta (2)-(C(6) F(5)CNtBu)}(CNtBu){eta (5)-(3-RC4H3BC6F5)} (5H, R = H; 5Me, R = Me), The st ructures of 3H and 5H were confirmed by X-ray diffraction. The reaction of the diene complexes (CpZr)-Zr-R(eta (3)-crotyl)(eta (4)-butadiene) (6a, Cp- R = C5H4SiMe3; 6b, C5H4Me; 6c, Cp; 6d, Cp ") with B(C6F5)(3) in toluene sol ution at room temperature proceeds quantitatively with C-H activation, bute ne elimination, and C6F5 transfer to generate (CpZr)-Zr-R(C6F5){eta (4)-CH2 CHCHCHB(C6F5)(2)} (7a-d). These boryldiene complexes are thermally unstable and smoothly rearrange to give the triple-decker complexes Zr-2(Cp-R)(2)(C 6F5)(2){mu-eta (5):eta (5)-C4H4BCH2-eta (3),kappaF-CHCHCHB(C6F5)(3)} (8a-d) . The formation of these complexes involves the complete transfer of all th ree 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 co mplexes feature a Zr2C4B core, a zwitterionic structure, and an unusually s trong Zr-F donor interaction. On activation with methylalumoxane (MAO), 8a- d polymerize ethene.