Synthesis, crystal and molecular structure of [{C5Me5FeC5Me4CH2}B+{C6H3(CF3)(2)}(4)(-)], the first example of a structurally characterized primary ferrocenylcarbocation

The: synthesis and the first X-ray structural study of a salt of the primar y ferrocenylcarbocation [{C5Me5MC5Me4CH2}(+) B{C6H3(CF3)(2)}(4)(-)] (M = Fe , 1a) are reported. The C-Cp-C-alpha bond shows considerable inclination re lative to the plane of the cyclopentadienyl ring so that the C-alpha atom b ecomes closer to the metal centre, the inclination angle alpha being equal to 23.6 degrees. The Fe-C-alpha distance (2.567(12) Angstrom) is still sign ificantly longer than the covalent Fe-C sigma -bond, which may be considere d as an indication that the donor-acceptor interaction of the carbocationic centre with the metal electron pair is substantially weaker than in the ea rlier studied Ru- and Os-analogues (Ib, Ic) wherein the positive charge was mostly localized on the metal centre (metallonium cations). Thus, complex 1a obviously preserves much more of the carbocationic state than its heavie r analogues. (C) 2000 Elsevier Science B.V. All rights reserved.