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Which of following organometallic compound is $\sigma$ and $\pi$ bonded : -
A
$[Fe(\eta^5-C_5H_5)_2]$
B
$K[PtCl_3(\eta^2-C_2H_4)]$
C
$[Co(CO)_5NH_3]^{2+}$
D
$Fe(CH_3)_3$
Detailed Solution
In metal carbonyls, the M–CO bond has both $\sigma$ and $\pi$ character (synergic bonding).
CO donates its lone pair on carbon into an empty metal orbital, forming a $\sigma$ bond.
The metal donates electrons from a filled d orbital back into the empty $\pi^*$ orbitals of CO, forming a $\pi$ bond (back bonding).
So $[Co(CO)_5NH_3]^{2+}$ contains both $\sigma$ and $\pi$ bonded metal–carbon bonds.
Ferrocene and Zeise's salt are classed as $\pi$-bonded organometallic compounds, and $Fe(CH_3)_3$ is $\sigma$-bonded only.
So, as per the answer key, the $\sigma$ and $\pi$ bonded compound is $[Co(CO)_5NH_3]^{2+}$.
CO donates its lone pair on carbon into an empty metal orbital, forming a $\sigma$ bond.
The metal donates electrons from a filled d orbital back into the empty $\pi^*$ orbitals of CO, forming a $\pi$ bond (back bonding).
So $[Co(CO)_5NH_3]^{2+}$ contains both $\sigma$ and $\pi$ bonded metal–carbon bonds.
Ferrocene and Zeise's salt are classed as $\pi$-bonded organometallic compounds, and $Fe(CH_3)_3$ is $\sigma$-bonded only.
So, as per the answer key, the $\sigma$ and $\pi$ bonded compound is $[Co(CO)_5NH_3]^{2+}$.