Basics of Organometallic Chemistry — DU B.Sc (hons) Chemistry Previous Year Question Papers

2. Attempt six questions in all. 1. Complete the following : (a) An example of a sandwich compound is (b) An example of Schrock carbene is (c) Number of C-O stretching vibrations observed for C-O in IR region for (d) Effective atomic number of V(CO), is (e) An example of a ligand with three hapticity (n' is ........ (f) The catalyst used in the hydroformylation reaction is ........ (g) Give an example of nucleophilic substitution reaction in organometallic chemistry. (h) Draw the structure of Mn, (CO)10° (i) A catalyst with a lower turnover frequency is an efficient catalyst (True/ 0) Geometry and hybridisation of Fe(CO), as per VBT is (k) Non bonding orbitals in MO diagram of CoCO, a.......... (l) Migratory insertion of a coordinated alkene in M-H bond leads to formation of ......... (alkane/alkyne). (m) The value of x in Mn(CO), Cl is ... (n) C-C stretching frequency in H, C=CH, is (higher/lower.) than Zeise's salt. (o) Define metallacycles. (1x15=15) 2. (a) Based on 18 electron rule, identify the charge, x on coordination sphere for the following complexes : (b) Giving reasons arrange the following in the order of increasing M-C bond strength (i) Does the M-CO bond strength increase or decrease when L of [L M- CO] becomes more electron withdrawing? Justify your answer. (c) Differentiate between metal aikene and metal alkyne compounds giving examples for each. (5x3=15) 3.. Provide a suitable explanation for the following statements : (a) Fischer carbenes are less reactive than Schrock carbenes. (b) For a homogeneous catalyst, the nature of ligands attached to the metal, influences its reactivity and selectivity. (c) Co(n'-Cp), complex is much more readily oxidised than Fe(n'-Cp), (d) Electrophilic substitution in ferrocene often occurs more readily than in benzene. (e) Fe,(CO), and Mn,(CO),, are both dimeric carbonyls, yet their structures are not identical. 4. (a) Give catalytic cycle for Monsanto acetic acid process clearly marking the type of reaction at each step. (b) Differentiate (giving examples) between (i) Homogeneous and heterogeneous organometallic catalyst (c) Using VBT, deduce the structure of 5. (a) Describe two preparative methods for metal carbonyls with the help of examples. (b) C-O stretching frequency for free CO is 2143 cm-' while for the carbonyls [Ti(CO),1, [Cr(CO)6] and [Fe(CO),1t are 1748, 2000 and 2204 cm-l respectively. Explain. (c) Describe Dewar-Chatt-Duncanson model of bonding in Zeise's salt. Explain its structure also. (5x3=15) 6. (a) Complete the following chemical equations : (b) Metallocenes generally violate 18e-rule and yet are stable compounds. (c) (i) Coordinatively saturated organometallic complexes containing B hydrogen are thermally more stable towards B-elimination reactions than the unsaturated analogues. Explain (ii) Oxidative addition to a catalyst increases its electron count. Explain giving an example. (5×3=15)