Electrophilic addition reactions of the Lewis acids B(C6F5)(2)R [R = C6F5,Ph, H or Cl] with the metallocene hydrides [M(eta-C5H5)(2)H-2] (M = Mo or W), [Re(eta-C5H5)(2)H] and [Ta(eta-C5H5)(2)H-3]

The syntheses of the new compounds [W(eta-C5H5)(eta-C5H4{B(C6F5)(2)R})H-3], where R = (C6F5) 1, Ph 2, H 3 or Cl 4, [Mo(eta-C5H5)(2)(H)(eta(1)-HB(C6F5) (3))] 5, [Mo(eta-C5H5)(2)(H)(eta(1)-H2B(C6F5)(2))] 6, [Mo(eta-C5H4Me)(2)(H) (eta(1)-HB(C6F5)(3))] 7, [Re(eta-C5H5)(eta-C5H4B(C6F5)(3))H-2]. 0.5C(6)H(5) Me 8, [Ta(eta-C5H5)(2)(H)(2)(eta(1)-HB(C6F5)(3))] 9 and [Re(eta-C5H5)(eta-C 5H4{B(C6F5)(2)})(C6F5)] 10 are described. The crystal structures of compoun ds 4 and 10 have been determined. Initial electrophilic addition of the Lew is acid B(C6F5)(3) occurs either by exo-addition to a carbon of a eta-cyclo pentadienyl ring with formation of an exo-{(C6F5)(3)B}C5H5, or by formation of an M-mu-H-B two-electron three-centre bond.