I've noticed that my book does not mention metals as a possible substituent for mono-substituted benzenes, but it doesn't begin to explain why. Also I have had trouble finding reasons why online. Specifically I am interested to know why you don't see metals bonded to benzene with a covalent sigma bond. I am not interested in metal benzene complexes. As much in depth help that anyone can offer would be greatly appreciated.
Two of the most commonly used examples of benzene-metal bonds directly to the carbon of benzene are as follows:
As you implied in your post, examples of benzene bonding to metals through its -bonds abound in the literature. Bonds of metals directly to a carbon of a benzene ring are far less common. The examples above (the structures in short form are PhMgBr and PhLi, where Ph represents a "phenyl" group - C6H5) have the metal directly bonded to the C of the benzene ring, but the bond would not be classified as covalent. On the bonding continuum (covalent, polar covalent, ionic), I would place them somewhere between polar covalent and ionic, but closer to ionic. The reason is for ...
The expert examines metals covalently bonded to benzene. Covalent sigma bond of benzene is determined.