Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
CYL 100 Inorganic Part Home assignment and Solved problems for self study- Part 2 Organometallic Chemistry (18e rule, carbonyls, sandwich compounds, unique reactions) Solved problems for self study- Part 2 Points to remember; • Follow only one counting method initially. Easier one is neutral atom counting method although more realistic is oxidation count method. • Note that square planar late transition metal compounds and titanium group metals may show 16 electron stability as well • All carbon based ligands even if they have a formal + charge are more electronegative when compared to the transition metal to which it is bonded • Compare a metal – metal bond in a complex to the Cl-Cl bond of Cl2 if you are unable to sort out the electron source of the bond. • A metal – metal bond like Cl-Cl bond does to contribute to the oxidation state of the metal to which it is attached 1. Consider 18 electron rule as a guide and determine the value of n in the following complexes i) iii) (v) Na2Fe(CO)n W(η6-C6H6)(CO)n Cr(η3-C5H5)(CO)n(CH3) ii) iv) (vi) MnBr(CO)n Rh(η5-C5H5)(CO)n IrBr2(CO)n (PPh3)2(CH3) solution i) iii) (v) 2. Na2Fe(CO)n n= 4 n =3 W(η6-C6H6)(CO)n 3 Cr(η -C5H5)(CO)n(CH3) n = 4 ii) iv) (vi) MnBr(CO)n n = 5 Rh(η5-C5H5)(CO)n n=2 IrBr2(CO)(PPh3)2(CH3) n =1 A metal complex having the empirical formula FeC9H7O3Cl, has one ligand as a substituted cyclopentadienyl group. It is an ionic compound and has poor solubility in hydrocarbon solvents. The compound gives a white precipitate on treatment with AgNO3 solution. Assuming that it obeys the 18 electron rule, suggest its structure. solution CH3 Fe OC CO CO Cl 3. In a carbonyl complex with linear CO-M-CO group, how will νCO change when a) one CO is replaced by Et3N b) a positive charge is put on the complex c) a negative charge is placed on the complex. Solution νco will change as follows, a) Since Et3N is a sigma donor only and not an acceptor, the back donation from M to the CO’s will increase and hence υco will decrease. b) less back bonding because of positive charge and hence υco increases c) back bonding increases because of negative charge, and hence υco decreases. 4. Give a scheme for the synthesis of Mn(CO)4(PPh3)[C(O)CH3] starting from Manganese acetate, Mn(OAc)2. Solution 2 Mn(OAc)2 + 4 Na + 10 CO high temp high pressure Mn2(CO)10 + 4 NaOAc Mn2(CO)10 + 2 Na 2 NaMn(CO)5 NaMn(CO)5 + CH3I CH3Mn(CO)5 CH3Mn(CO)5 + CO CH3C(O)Mn(CO)5 + PPh3 CH3C(O)Mn(CO)5 ( migratory insertion) CH3C(O)Mn(CO)4PPh3 hv Or at step 3 direct reaction with acyl chloride instead of MeI. Step 1 other reducing agents e.g. AlEt3 can also be used. 5. Fluorene, a polycyclic organic compound, forms an ionic organometallic compound with a CpFe fragment and obeys the 18e rule. It has the molecular formula [(C5H5)Fe(C13H10)]+[PF6]− (A). Treatment of A with a base results in another 18e organometallic complex B with the formula [(C5H5)Fe(C13H9)]. Draw reasonable structures of complexes A and B. Fluorene H H H H H H H solution H H H PF6 Fe H H A Fe B 6. Which among the following compounds will not undergo oxidative addition of methyl iodide ? Give reasons (a) Ir(PPh3)2(CO)Cl (b) [RhI2(CO)2](c) η5-Cp2Ti(Me)Cl Solution (c) As titanium is already in its highest oxidation state of +4 and therefore no d electrons present for further oxidation 7. Mark against each statement the appropriate type of reaction or reactions from the list (oxidative addition, reductive elimination, migratory insertion and β-H transfer) (a) cis orientation of the participating ligands is a must. (b) This reaction does not occur for d0 metal complexes. (c) This reaction is enthalpy favoured and entropy prohibited. (d) A vacant coordination site on the metal centre is a prerequisite. (e) The more electron rich the metal centre, the more facile is the reaction. (f) There is an increase in the electron count of the metal complex by two units during this reaction. Solution (a) Red elimination and migratory insertion (b) Oxidative addition (c) Migratory insertion (d) Oxidative addition and β-H transfer (e) Oxidative addition (f) Oxidative addition and β-H transfer 8. Using the concept of oxidative addition and reductive elimination, give a suitable mechanism for the formation of each of the products in the following reaction (Et3Si-H may be considered as a non polar/weakly polar system) Ph2 P OC Ir Br Solution P Ph2 H + excess Et3Si-H Et3Si Ph2 P + HBr + Et3Si-SiEt3 Ir H CO P Ph2 H Ph2 P OC oxidative addition Et3Si Ir + Et3Si-H Ir Br 16e Br P Ph2 18e CO Ph2 P Ph2 reductive Et Si P elimination 3 Ir -HBr OC 16e P Ph2 + Et3Si-H H Et3Si Ph2 P oxidative addition Ir H 18 e CO P Ph2 + Et3Si-H Ph2 P H Ir OC 16e P Ph2 P Ph2 oxidative addition H reductive elimination -Et3Si-SiEt3 Et3Si Ph2 P Ir Et3Si 18e CO P Ph2 Home Assignement 11 problems Inorganic Part Part 2 (submit on March 27 Friday) 1. The complex [M(η6-C6H6)(CO)2]2 obeys 18 electron rule and has one metal- metal double bond. Predict M and sketch the probable structure of the complex. 2. Determine the unknown quantity a) [CpW(CO)x]2 [has W-W single bond] b) [(CO)3Ni-Co(CO)3]z c) [CpMn(CO)x]2 (has Mn = Mn double bond] d) [(Cp)3Ni3(μ3-CO)2]z (no metal metal bonds) ( hint: consider unit as a whole) e) [CpM(CO)3]2 (has a single M-M bond; M = Ist row TM] 3. Trimetallic complexes of phosphido bridges are well known. Assuming that the 18e rule is followed, postulate the structure of [Mn(μ-PH2)(CO)4]3. 4. Arrange the following in the decreasing order of back donation Cr(CO)6; [Ti(CO)6]-2 ; [Mn(CO)6]+ ; [Ir(CO)6]3+; [V(CO)6]- 5. The compound (η5-C5H5)Co(CO)2 (A) upon UV irradiation, resulted in the evolution of equimolar amount of a gas and formation of a new compound B. While the infrared spectrum of A showed absorptions around 1988 cm-1, the spectrum of B showed absorptions only around 1798 cm-1. Compounds A and B both obey 18 electron rule and both has the cyclopentadienyl group in the η5 mode. Draw the structure of compound B. 6. Select the best choice in each of the following and briefly justify the reason for your choice a) Complex with the shortest C-O bond Ni(CO)4, b) [Co(CO)4]-, [Fe(CO)4]2- Complex with the lowest C-O stretching frequency V(CO)6- Cr(CO)6 Fe(CO)62+ 7. Ferrocene is thermally stable and not air sensitive but cobaltocene is readily oxidized to cobaltocenium ion. Why ? 8. The following are some reactions of first row transition-metal containing sandwich compounds, having η5-Cp ligands leading to products with 18 electrons. Identify the transition metals A, B and C present in these compounds. K H2 A H Na/Hg B A excess C2H4 - KC5H5 H B H H CO C - 1/2 C5H5 dimer OC C CO CO 9. Benzene, on heating with D2 and the precatalyst η5- Cp2TaH3, gets converted to monodeuterobenzene and finally to hexadeutero benzene. The reaction involves only oxidative additions (both C6H5-H and D-D) and reductive eliminations. Suggest a mechanism for the formation of monodeutero benzene (C6H5-D) from benzene. ( hint: the active form of the catalyst is a 16 electron species ) 10. The given metal-alkene intermediate is unstable and undergoes a rearrangement resulting in the formation of three different arylalkene complexes of the general formula Pd(PPh3)2(Br)(H)(η2 -alkene). Predict the structures of the three arylalkene palladium complexes. Br Pd Ph3P PPh3 CH C H2 H2C CH3 11. Wilkinsons catalyst, RhCl(PPh3)3 catalyzes the reaction of trimethylsilyl hydride [(CH3)3Si-H] with ethylene to give ethyltrimethylsilane[(CH3)3Si-CH2CH3]. Show steps involved and mark the electron count and type of reaction at each step.