Among the following which is not the $\pi$-bonded organometallic compound :

Question

( A ) $(CH_3)_4 Sn$
( B ) $Cr(\eta^6 - C_6H_6)_2$
( C ) $K[PtCl_3(\eta^2 –C_2H_4)]$
( D ) $Fe(\eta^5 –C_5H_5)_2$