Ziegler-Natta catalyst is an organometallic compound of which metal?

Which of the following statements is incorrect?
$(1)$ $Al_4C_3$ is an organometallic compound.
$(2)$ Metal carbonyls are organometallic compounds.
$(3)$ $TEL$ (Tetraethyl lead) is a $\pi$-bonded organometallic compound.
$(4)$ Frankland reagent is a $\sigma$-bonded organometallic compound.

Which of the following is not a $\pi -$ bonded organometallic complex?

An example of a $\sigma$-bonded organometallic compound is:

Which of the following carbonyls will have the strongest $C-O$ bond?

The Wilkinson catalyst is