2- The ligand in uranocene is C8H8 35 In the metal-olefin interaction, the extent of increase in metal olefin -back-donation would (a) lead to a decrease in C=C bond length (b) change the formal oxidation state of the metal (c) change the hybridisation of the olefin carbon from sp² to sp³. (d) increase with the presence of electron donating substituent on the olefin. In Metal-Olefin interaction, the extent of increase in metal → Olefin л-back donation would strengthen the Metal-Olefin bond which produces a increase in C = C bond length and somewhat single bond character which results a change in hybridisation from sp² to sp³.
Explanation as extracted from the printed page; notation may be imperfect.