CH 611 Advanced Inorganic Chemistry Synthesis and Analysis. Exam #3 12/12/2011. Print Name

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1 Print Name Wherever possible give further details of each transformation or catalytic cycle by describing the steric/electronic nature of reagent and/or substrate including bonding schematics to illustrate any specific point you would like to get across. 1(a) A catalyst may be defined by two important criteria related to its stability and efficiency. Name both of these criteria and describe how they are defined with respect to stability or efficiency (10 points) A catalyst may be defined by its Turnover Number (TN). Each time the complete catalyst cycle occurs, we consider one catalytic turnover to have been completed. The more stable the catalyst the greater the turnover number the more product is formed. The lifetime of the catalyst before deactivation or decomposition is therefore quantified using the turnover number. The catalytic rate, i.e. efficiency, can be conveniently given in terms of the Turnover Frequency (TOF) measured in turnovers per unit time (often per hour). The greater the turnover frequency the more efficient the catalyst is the quicker the product is formed. It should be noted that efficiency does not necessarily equal stability. The best catalysts will of course be highly stable and kinetically favorable. Some catalysts, however, work extremely fast but will decompose after just a few cycles (high turnover frequency + low turnover number). On the other hand, some catalysts are extremely stable but very slow (high turnover number + low turnover frequency). 1

2 1(b) Draw a generic catalytic cycle scheme including the species listed below (10 points). Catalyst precursor (M ) Active catalyst (M) Substrate (S) Catalyst-substrate complex (M-S) Transition state (M-T) Intermediate (M-I) Off loop species (M-S ) Deactivation product (M ) 2

3 1(c) Using the species listed in 1(b), draw a generic free energy diagram describing transformation of substrate to product (10 points). Describe the impact of a catalyst on the overall reaction kinetics, thermodynamics and equilibrium. Energy A catalysts typically reduces the activation energy required along the reaction coordinate (transition state and intermediate formation) thus allowing for more favorable kinetics towards product formation. The catalyst only increases the rate of a process but does not alter its position of equilibrium, which is decided by the relative thermodynamic stabilities of substrate and products (not the transition states or intermediates along the reaction coordinate). 3

4 2(a) Name each of the following reactions accordingly and suggest anticipated products (15 points) PCy 3 Cross metathesis (self metathesis side reaction) Ring opening metathesis polymerization (ROMP) Eneyne ring closing metathesis 4

5 2(b) Draw a complete catalytic cycle for any 1 of the reactions in 2(a) (15 points). PCy 3 -PCy 3 propogation product (cross metathesis) initiation product cis-isomer C 2 C 2 trans-isomer C 2 C C C 2 C C 2 L 3 C C C 2 C 2 C 2 C C 2 5

6 PCy 3 PCy3 excess n 6

7 = Katz mechanism L n M L n M Trost mechanism oxidative addition reductive elimination isomerization MLn 7

8 3. Name the class of reaction below and draw a catalytic cycle to describe product formation (10 points). This is a hydroformylation reaction. binuclear oxidative addition, 2 O - C 3 reductive elimination n-butanal addition ( association) O C 3 oxidative addition 2-2 1,2-insertion O - addition& 1,1'-insertion 8

9 4(a). Name each of the following reactions accordingly and suggest anticipated products (15 points). Negishi coupling Stille coupling Suzuki-Miyura coupling Sonogashira coupling Pd(P 3 ) 4 Br NEt 3 CuI Buchwald-artwig coupling 9

10 4(b). Draw a complete catalytic cycle for the second reaction from 4(a) (15 pionts). 10