Organometallic compounds: synthesis, bonding and structure, and reactivity. Organometallics in homogeneous catalysis.
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1.The reactions of Ni(CO)4with the ligand (L = PMe3or P(OMe)3)L yields 3 Ni(CO)3L . The reaction is
(c) Interchange (Ia)
(d) Interchange (Id)
Ni(CO)4 [L = PMe3,P(OMe)3]
Ni(CO)4 Total valence electron around
Ni = 10 + 4 x 2 = 18 electron
Substitution reactions at coordinatively saturated tetrahedral complexes with a 18 electron count likeNi(CO)4 or Ni(CO)2(PR3)2 follows a simple first order kinetics.
Since rate does not depend upon the concentration and nature of the ligand suggesting a dissociative mechanism.
2.The correct statement for the aggregating nature of alkyl lithium (RLi) reagent is:
(a) The carbanionnucleophilicity increases with aggregation.
(b) The observed aggregation arises from its electron deficient nature.
(c) Carbanionnucleophilicity does not depend on aggregation.
(d) The extent of aggregation is maximum in polar dative solvents.
CH3Li →the tendency of organolithium compounds to associate in the solid state as well as in solution is due to the fact that in a single molecule (LiR), the number of valence electrons is too low to use all the available Li valence orbitals for 2e–2c bonding. This electron deficiency is compensated by the formation of multicentre bonds e.g. (2e – 4c) bonding.
In this structure methyl group of one (LiCH3)4unit interacts with the Li atoms of neighbouring (Li)4tetrahedron.
3.For the reaction, trans-[IrCl (CO) (PPh3)2] + Cl2→ trans-[IrCl3(CO) (PPh3)2], the correct observation
(a) VCO(product) > VCO(reactant)
(b) VCO(product) < VCO(reactant)
(c) VCO(product) = VCO(reactant)
(d) VCO(product) = VCO(free CO)
Since in product metal Ir is present in the higher oxidation state.So, there is less back bonding to π*orbital of CO.
Hence, V(CO) product >V(CO) reactant
4.The nucleophilic attack on olefins under mild conditions:
(a) Is always facile
(b) Is more facile than electrophilic attack on olefins
(c) Is facile for electron-rich olefins
(d) Requires activation by coordination to metal.
Nucleophilic attack on olefins under mild conditions
So, it requires activation by coordination to metal.
5.The cluster having arachno type structure is:
Step-I: Calculate T.V.E. (total valency electron)
= 8×3 + 2 ×12 = 48
Step-II: Polyhedral electron count
= T.V. E. – (n×12) = 48–36=12 n = number of the metal atom
Step-III: = P.E.C./2 = 12/2 = 6 = (n + 3) = Archano.
6.The carbonyl resonance in 13C NMR spectrum of [(h5– C5 H5)Rh(CO)]3 (103Rh, nuclear spin, I=1/2, 100%) shows a triplet at –65º C owing to the presence of
(a) Terminal CO
(b) μ2– CO
(c) μ3– CO
Doublet of carbonyl carbon indicates the each CO is attached with chemically equivalent two Rh- atoms–that means μ2-CO complex.
Actual structure is: