Organic Chemistry
Organic Chemistry
6th Edition
ISBN: 9781936221349
Author: Marc Loudon, Jim Parise
Publisher: W. H. Freeman
Question
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Chapter 18, Problem 18.15P
Interpretation Introduction

(a)

Interpretation:

The structures of the transition-metal complexes involved in each of the given mechanistic step are to be shown. The electron count and the metal oxidation state at each step is to be stated.

Concept introduction:

The Wilkinson’s Catalyst is a common name of coordination compound ClRh(PPh3)3. It is basically used for the catalytic hydrogenation of alkenes. The Wilkinson’s catalyst has square-planar structure.

Expert Solution
Check Mark

Answer to Problem 18.15P

The structures of the transition-metal complexes involved in each of the given mechanistic step are shown below.

1. The oxidative addition reaction is shown below.

Organic Chemistry, Chapter 18, Problem 18.15P , additional homework tip  1

2. The ligand substitution of one PPh3 by the alkene is shown below.

Organic Chemistry, Chapter 18, Problem 18.15P , additional homework tip  2

3. 1, 2-insertion of alkene into a RhH bond and readdition of previously expelled PPh3 ligand is shown below.

Organic Chemistry, Chapter 18, Problem 18.15P , additional homework tip  3

4. Reductive elimination of the alkane product to generate the catalyst is shown below.

Organic Chemistry, Chapter 18, Problem 18.15P , additional homework tip  4

Explanation of Solution

The general formula for the calculation of electron count in a given formula is shown below.

Electroncount=Numberofvalenceelectronsoncentralmetalatom+((Numberofelectronsdonatedbyligand))×(Numberofligands)

The number of valence electrons present in rhodium is 9 and the phosphine donates 2 electrons.

1. In oxidative addition reaction, the central metal atom gets oxidized with the addition of two ligands and there is an increase in electron count at the central metal atom.

The oxidative addition reaction is shown below.

Organic Chemistry, Chapter 18, Problem 18.15P , additional homework tip  5

Figure 1

The electron count in ClRh(PPh3)3 is shown below.

Electroncount=9+2×(3)+1×(1)=9+6+1=16

The electron count in ClRh(PPh3)3H2 is shown below.

Electroncount=9+2×(3)+1×(1)+1×(2)=9+6+1+2=18

2. The ligand substitution reaction of one PPh3 by alkene is shown below.

Organic Chemistry, Chapter 18, Problem 18.15P , additional homework tip  6

Figure 2

The electron count in ClRh(PPh3)3H2 is shown below.

Electroncount=9+2×(3)+1×(1)+2(1)=9+6+1+2=18

The electron count in ClRh(PPh3)2H2alkene complex is shown below.

Electroncount=9+2×(2)+2×(1)+1(1)+1(2)=9+4+2+1+2=18

3. 1, 2-insertion of alkene into a RhH bond and readdition of previously expelled PPh3 ligand is shown below.

Organic Chemistry, Chapter 18, Problem 18.15P , additional homework tip  7

Figure 3

The electron count in ClRh(PPh3)2H2alkene complex is shown below.

Electroncount=9+2×(2)+2×(1)+1(1)+1(2)=9+4+2+1+2=18

The electron count in ClRh(PPh3)2Halkyl complex is shown below.

Electroncount=9+2×(2)+1×(1)+1(1)+1(1)=9+4+1+1+1=16

The electron count in ClRh(PPh3)3Halkyl complex is shown below.

Electroncount=9+3×(2)+1×(1)+1(1)+1(1)=9+6+1+1+1=18

4. Reductive elimination of the alkane product to generate the catalyst is shown below.

Organic Chemistry, Chapter 18, Problem 18.15P , additional homework tip  8

Figure 4

The electron count in ClRh(PPh3)3Halkyl complex is shown below.

Electroncount=9+3×(2)+1×(1)+1(1)+1(1)=9+6+1+1+1=18

The electron count in ClRh(PPh3)3 is shown below.

Electroncount=9+2×(3)+1×(1)=9+6+1=16

Conclusion

The catalytic hydrogenation of alkene by wilkinson’s catalyst and electron count is shown in Figure 1, 2, 3 and 4.

Interpretation Introduction

(b)

Interpretation:

The stereochemistry of the product if D2 substitutes H2 in the given reaction is to be stated.

Concept introduction:

The complex that follows 18-electron rule are most stable. The electrons are donated by the ligand to central metal atom. These 18 electrons occupy the bonding molecular orbitals making the compound stable. The catalyst accelerate the rate of reaction. There is always syn addition of hydrogen on alkene takes place. It means addition from same side, it can be from top or from bottom.

Expert Solution
Check Mark

Answer to Problem 18.15P

The reaction between cis-alkene with the deuterium substituted wilkinson’s catalyst is shown below.

Organic Chemistry, Chapter 18, Problem 18.15P , additional homework tip  9

This shows syn-addition of deuterium on alkene.

Explanation of Solution

Reduction of cis-alkene with the deuterium substituted Wilkinson’s catalyst.

Organic Chemistry, Chapter 18, Problem 18.15P , additional homework tip  10

Figure 5

In the reduction of cis-alkene with the deuterium substituted Wilkinson’s catalyst. Hydrogen added on Wilkinson’s catalyst for hydrogenation of alkene is replaced by deuterium. The alkene is present in the plane of the paper, the deuterium can attack the alkene either from below the plane or above the plane.

Therefore, this shows that syn-addition of deuterium also takes place.

Conclusion

The reaction in Figure 5 shows that syn addition of hydrogen takes place even when it is substituted by deuterium.

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Chapter 18 Solutions

Organic Chemistry

Ch. 18 - Prob. 18.11PCh. 18 - Prob. 18.12PCh. 18 - Prob. 18.13PCh. 18 - Prob. 18.14PCh. 18 - Prob. 18.15PCh. 18 - Prob. 18.16PCh. 18 - Prob. 18.17PCh. 18 - Prob. 18.18PCh. 18 - Prob. 18.19PCh. 18 - Prob. 18.20PCh. 18 - Prob. 18.21PCh. 18 - Prob. 18.22PCh. 18 - Prob. 18.23PCh. 18 - Prob. 18.24PCh. 18 - Prob. 18.25PCh. 18 - Prob. 18.26PCh. 18 - Prob. 18.27PCh. 18 - Prob. 18.28PCh. 18 - Prob. 18.29PCh. 18 - Prob. 18.30PCh. 18 - Prob. 18.31PCh. 18 - Prob. 18.32PCh. 18 - Prob. 18.33PCh. 18 - Prob. 18.34PCh. 18 - Prob. 18.35PCh. 18 - Prob. 18.36PCh. 18 - Prob. 18.37PCh. 18 - Prob. 18.38PCh. 18 - Prob. 18.39PCh. 18 - Prob. 18.40PCh. 18 - Prob. 18.41PCh. 18 - Prob. 18.42PCh. 18 - Prob. 18.43PCh. 18 - Prob. 18.44PCh. 18 - Prob. 18.45PCh. 18 - Prob. 18.46APCh. 18 - Prob. 18.47APCh. 18 - Prob. 18.48APCh. 18 - Prob. 18.49APCh. 18 - Prob. 18.50APCh. 18 - Prob. 18.51APCh. 18 - Prob. 18.52APCh. 18 - Prob. 18.53APCh. 18 - Prob. 18.54APCh. 18 - Prob. 18.55APCh. 18 - Prob. 18.56APCh. 18 - Prob. 18.57APCh. 18 - Prob. 18.58APCh. 18 - Prob. 18.59APCh. 18 - Prob. 18.60APCh. 18 - Prob. 18.61APCh. 18 - Prob. 18.62APCh. 18 - Prob. 18.63APCh. 18 - Prob. 18.64APCh. 18 - Prob. 18.65APCh. 18 - Prob. 18.66APCh. 18 - Prob. 18.67APCh. 18 - Prob. 18.68APCh. 18 - Prob. 18.69APCh. 18 - Prob. 18.70APCh. 18 - Prob. 18.71APCh. 18 - Prob. 18.72APCh. 18 - Prob. 18.73APCh. 18 - Prob. 18.74APCh. 18 - Prob. 18.75APCh. 18 - Prob. 18.76APCh. 18 - Prob. 18.77APCh. 18 - Prob. 18.78APCh. 18 - Prob. 18.79APCh. 18 - Prob. 18.80APCh. 18 - Prob. 18.81APCh. 18 - Prob. 18.82APCh. 18 - Prob. 18.83APCh. 18 - Prob. 18.84APCh. 18 - Prob. 18.85APCh. 18 - Prob. 18.86APCh. 18 - Prob. 18.87APCh. 18 - Prob. 18.88APCh. 18 - Prob. 18.89APCh. 18 - Prob. 18.90APCh. 18 - Prob. 18.91APCh. 18 - Prob. 18.92AP
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