[mistche20]

Is it true that Cp (c5h5-) can bond in η1, η2, η3, η4, η5 fashion? (I'm not sure about η4)

Also, can C6h6 bond in η5 fashion?

Thanks!!!!!!!!!

[cheese (MSW)]

Think about a TM bonding to C=C.  Can you see that by binding to just one C results in a radical:
M  +  C=C → M-C-C• Now C5H5 is a radical to begin with so need a M-C σ bond and so
only η^1, η^3, η^5–C5H5 are to my knowledge are known.  Examples:  (η-C5H5)Fe(CO)2(η^1-C5H5) Wilkinson’s famous ring whizzer.  Mo(η^1-C5H5)(η^3 –C5H5)(η-C5H5)(NO)  Cotton’s three-ring circus cmpd that lead him to propose the hapticity nomenclature.  Note if all the C atoms are bound to the metal the superscript is dropped.
Of course ferocence Fe(η-C5H5)2 kicked off the whole field of organometallic chemistry: **#@%%!! It can’t be that [Fe(σ-C5H5)2]. It’s a sandwich!   There are thousands of CpM cmplxs known and are an essential ligand in many metallocene catalysts for olefin polymerization.
Wilkinson G (1975) The iron sandwich: a recollection of the first four months.  Journal of Organometallic Chemistry 100, 273–278.
Also, can C6h6 bond in η5 fashion?
For the same reason and as far as I am aware there are no η^1, η^3, η^5 -C6H6 cmplxs of TM. 
η2, η4 –C6R6 cmplxs are known but are extremely rare.  There are hundreds of  η-C6H6 cmplxs but are not as ubiquitous as Cp cmplxs.  (η-C6H6)Cr(CO)3 is probably the best known
Look up the Nobel Citations (1973) for Fischer [Cr((η-C6H6)2] and Wilkinson [Fe(η-C5H5)2] for sandwich compounds.
For further reading try, Organometallics,  Christoph Elschenbroich