text: Bulky ligands can preclude the approach of the full complement of ligands that would allow the metal to achieve the 18 electron configuration.
  Examples: 
  *Ti(neopentyl) (8 e)
  *Cp*Ti(CH) (16 e)
  *V(CO) (17 e)
  *Cp*Cr(CO) (17 e)
  *Pt(PBu) (14 e)
  *Co(norbornyl) (13 e)
  *[FeCp] (17 e)
  Sometimes such complexes engage in agostic interactions with the hydrocarbon framework of the bulky ligand.  For example:
  *W(CO)[P(CH)] has 16 e but has a short bonding contact between one C–H bond and the W center.
  *Cp(PMe)V(CHCMe) (14 e, diamagnetic) has a short V–H bond with the alkylidene-H, so the description of the compound is somewhere between Cp(PMe)V(CHCMe) and Cp(PMe)V(H)(CCMe).