Allyl derivatives, sandwich compounds and half sandwich compounds

It contains
Preparation and properties of:
Allyl derivatives of nickel,
Sandwich compounds of Fe, Cr and
half sandwich compounds of Cr, Mo.

1. NAIR VIJAYALAKSHMI PADMAKUMAR TABLE NO.:11 M.Sc. CHEMISTRY PART-I INORGANIC CHEMISTRY PREPARATON AND PROPERTIES OF: 1. Allyl derivatives of Nickel 2. Sandwich compounds of Fe, Cr and half sandwich compounds of Cr, Mo

2. Allyl derivatives of Nickel Diallyl Nickel, Ni(η 3 C 3 H 5 ) 2 : Preparation: NiCl 2 + 2C 3 H 5 MgBr Ether , -10 ℃ η-(C 3 H 5 ) 2 Ni + 2MgClBr

3. Properties: Physical properties: Yellow, pyrophoric compound that melts at 1 C. At low temperature of -10 C, it is in orange yellow crystalline form and recrystallises from pentane. Chemical properties: Insertion reaction: An organic or inorganic substrate is inserted into the metal-carbon bond. Ni(η 3 C 3 H 5 ) 2 + CO 2 →[Ni(OCOC 3 H 5 )(η 3 -C 3 H 5 )] → Diallyl nickel intermediate γ-lactone -Ni

4. Sandwich componds of Fe,Cr Ferrocene: Fe(η 5 -C 5 H 5 ) 2 : Preparation: First metallocene-T.J.Kealey and P.L.Pauson in 1951, were trying to synthesize fulvalene by oxidation of cyclopentadienyl magnesium bromide (Grignard reagent) with FeCl 3 . Instead they obtained orange crystals containing Fe(II), C 10 H 10 Fe. Later on, named as ferrocene by M.C.Whiting.

5. Fe +++ Fe + + [Fe(η 5 -C 5 H 5 ) 2 ] Using sodium cyclopentadiene: FeCl 2 +2C 5 H 5 Na (η 5 -C 5 H 5 ) 2 Fe + 2NaCl Using cyclopentadiene with a metal halides: 2C 5 H 6 + 2Et 2 NH + FeCl 2 (η 5 -C 5 H 5 ) 2 Fe + 2Et 2 NH + Cl - Properties: orange coloured crystalline compound, diamagnetic and thermally stable. M.P. is 173 ℃. stable in air and water, decomposes above 500℃ in absence of air. THF THF C 5 H 5 MgBr C 5 H 5 MgBr

6. insoluble in water but soluble in organic solvents. alkalis and acids do not attack this complex. gets oxidised to blue paramagnetic ferricinium ion [(π-C 5 H 5 ) 2 Fe(III)] + . Chemical properties: It is an aromatic compound and thus undergo electrophilic subtitution. Nitration:

7. Bromation: Alkylation:

8. Acylation: Mannich reaction:

9. Bis(benzene) chromium: [Cr(η 6 -C 6 H 6 ) 2 ] Preparation: CrCl 3 + ⅔Al + AlCl 3 + 2C 6 H 6 → [Cr(C 6 H 6 ) 2 ]AlCl 4 + ⅔AlCl 3 [Cr(C 6 H 6 ) 2 ]AlCl 4 + 1/2Na 2 S 2 O 4 → [Cr(C 6 H 6 ) 2 ]+ NaAlCl 4 + SO 2 Metal vapour synthesis: condensed at 77K Cr (g) + C 6 H 6 → [Cr(η 6 -C 6 H 6 ) 2 ] Properties: Dark brown solid M.P. is 284 ℃

10. do not undergo Friedel Craft acylation, sulphonation and nitration weaker aromatic character Chemical properties: Arene displacement reaction: Oxidation reaction: 2[Cr(η 6 -C 6 H 6 ) 2 ] + H 2 O + 1/2O 2 → 2[Cr(η 6 C 6 H 6 ) 2 ] + OH -

11. Half sandwich compounds of Cr, Mo Cyclic polyhapto ligand bound to an ML n center where L is an unidentate ligand, (η 6 -C 6 H 6 )ML 3 . Also known as two-legged piano stool compounds Preparation: M=Cr,Mo [Cr(η 6 -C 6 H 6 )(CO) 3 ] [Mo( η 6 -C 6 H 6 )(CO) 3 ]

12. Properties: Yellow solid [Cr(η 6 -C 6 H 6 )(CO) 3 ]- M.P. is 162 ℃ [Mo(η 6 -C 6 H 6 )(CO) 3 ]- M.P. is 125 ℃ stable 18-electron coordination compounds with variety of chemical and material applications The X-ray data indicate that the plane of the benzene ring is nearly parallel to the plane defined by oxygen atoms of the carbonyl ligands and so the structure resembles a benzene seat mounted on three carbonyl legs tethered by the metal atom and are thus also known as piano stool complexes.

13. REFERENCES R.C.Mehrotra and A.Singh, Organometallic Chemistry-A unified approach. D.Banerjea, Coordination Chemistry. Dr.Indrajeet Kumar, Organometallic Compounds. www.wikipedia.com www.youtube.com

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