(4) . Use either acceptable method of electron counting to determine the number
ID: 1029903 • Letter: #
Question
(4) . Use either acceptable method of electron counting to determine the number of metal ona formal metal valence electrons in nickelocene and CpNi(IPr)CI (3). What is the formal metal oxidation state in each? The X-ray crystal structure of nickelocene is presented in eClass in a format that can be manipulated and studied in three dimensions (WWW). How does knowing what the structure of nickelocene looks like in the solid state help confirm its electron count? (2) Provide two factors that "drive" the reaction of Cp2Ni with IPr HCI. Explain briefly. (3). Describe how the bonding of an N-heterocyclic carbene to a metal center differs from more "conventional" Fischer and Schrook carbenes.Explanation / Answer
4. The total valence electrons = Contribution from ligands + No. of valence electrons from metals.
In Nickelocene, there are 2 cyclopentadienyl ligands having 5 electron count for each Cp ligand. In addition, Nickel has 8 '3d' electrons and 2 '4s' electrons. Thus the total valence metal electrons for nickelocene=10+5+5=20.
In CpNi(IPr)Cl, there are total 5 valence electrons from Cyclopentadienyl ligand, 2 valence electrons from Isopropyl ligand, 1 valence electron from Chlorine ligand and Nickel has 8 '3d' electrons and 2 '4s' electrons. Thus the total valence metal electrons for CpNi(IPr)Cl = 5+2+1+10= 18.
2. Metal oxidation state of Ni in Nickelocene is '0' since the cyclopentadienyl ligands are neutral ligands.
Metal oxidation state of Ni in CpNi(IPr)Cl is 'I' since both cyclopentadienyl and isopropyl ligands are neutral and Cl is an anionic monodentate ligand. Hence Ni develops an oxidation state of +1 so that the the coordination complex as a whole is neutral.
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