Examples

Question 1

HYDROFORMLYATION

What is the oxidation state of Co in [CoCl3(NH3)3]?

Question 2

HYDROFORMLYATION

What is the oxidation state of the transition metal in the following:
(a) [Ni(CN)4]2– (b) WMe6
(c) [PtCl3(C2H4)]– (d) [IrMe(CO)(PPh3)2]

NOTE: hydrogen has an electronegativity close to that of the most electronegative transition metals, however by convention it is usually assumed that H is more electronegative than the metal

Question 3

HYDROFORMLYATION

What is the oxidation state of rhenium in [ReH7(PPh3)2]?

Question 4

HYDROFORMLYATION

How many valence electrons do the following metals have?
(a) Co(0) (b) Rh(I) (c) Ti(IV) (d) Rh(III)

(give you answer in the d^n notation)

Question 5

HYDROFORMLYATION

What is the electron count for the following compounds: (a) WMe6 (b) [PtMe(C2H4)(PPh3)2]+

Question 6

HYDROFORMLYATION

What is the electron count for the following compounds:
(a) [Ni(CN)4]2– (b) [IrMe(CO)(PPh3)2] (c) [CoH(CO)4] (d) [ReH7(PPh3)2]

Question 7

HYDROFORMLYATION

What is the coordination number of the metal in each of the following? (a) [Ni(CN)4]2– (b) [PtMe(C2H4)(PPh3)2]+

Question 8

HYDROFORMLYATION

Sketch the most likely coordination geometry of each of the following?
(a) [Ni(CN)4]2– (CN– = strong field) (b) [NiCl4]2– (Cl– = weak field) (c) Ru(CO)5 (d) [MnMe(CO)4]

Question 9

HYDROFORMLYATION

Classify the following metals as hard, soft or borderline:
Au+ Pd2+ Zr4+ Rh+ Rh3+ Co3+ Ni2+

Question 10

HYDROFORMLYATION

Classify the following bases as hard or soft:
H2O C2H4 Cl– pyrdine PMe3 [SnCl3]– [CN]–

Question 11

HYDROFORMLYATION

List some diatomic ligands which are isoelectronic with CO and which will display
similar bonding characteristics

Question 12

HYDROFORMLYATION

Back-donation places electron density in an orbital which is antibonding with respect to the C–O bond. What will be the effect on the CO bond strength,
the CO bond length, and the CO stretching frequency in the infrared spectrum?

Question 13

HYDROFORMLYATION

Ethene bonds sideways to a transition metal so that an empty orbital on the metal can interact with the electron density in the filled p-orbital of the ethene. Simultaneously, filled dxz orbitals on the metal can overlap the empty p* orbitals of the ethene allowing back-donation to occur. This is sometimes referred to as the Dewar-Chatt-Duncanson model of metal alkene bonding.

Sketch this interaction showing the orbitals concerned and illustrating the flow of electron density?

Question 14

HYDROFORMLYATION

Can you propose other molecules which you think will bond to a transition metal in a manner similar to ethene?

Question 15

MECHANISMS

Use the 18-electron rule to predict the stoichiometry of the following compounds (i.e. what is the value of x?)
(a) [Mn(C5H5)(CO)x] ([C5H5]– = 6 electron donor) (b) [OsMe2(CO)x]

Question 16

MECHANISMS

What mechanism would you expect to operate in each of the following reactions? (a) Mo(CO)6 + PPh3 [Mo(CO)5(PPh3)] + CO
(b) [PtCl(C2H4)(PMe3)2]+ + PMe3 [PtCl(PMe3)3]+ + C2H4

Question 17

MECHANISMS

Name each of the steps in the Mn reaction shown below.
Design an experiment that distinguished between methyl migration (Me group moves) and carbonyl insertion (CO ligand moves). Sometimes migration reactions are incorrectly referred as insertion reactions

Question 18

MECHANISMS

Classify the following reactions. In some cases more than one step may be involved and in those cases identify both steps and the sequence in which they are occurring:

Answer 18

Question 19

MECHANISMS

This catalytic cycle describes one of the best commercial syntheses of acetic acid
NOTE: there are two cycles, an organic one and an organometallic one
(a) What are the raw materials for this synthesis?
(b) Write an equation for the overall reaction.
(c) What are the reactants entering the organometallic cycle?
(d) For each of the complexes, write
i) the oxidation state
ii) the dn number
iii) the electron count
iv) the coordination geometry
(e) Name each of the reaction steps in the organometallic cycle.

Question 20

NUCLEOPHILIC ATTACK ON COORDINATED π-LIGANDS

Sketch the following ligands, (indicating regions of delocalized p-electron density with a dotted bond):
(a) cyclohepta-1,3-diene
(b) but-2-en-1-yl
(c) cycloocta-1,4-diene
(d) bicyclo[2.2.1]hepta-2,5-diene

Question 21

NUCLEOPHILIC ATTACK ON COORDINATED π-LIGANDS

Write formula and assign h number for the following

Question 22

NUCLEOPHILIC ATTACK ON COORDINATED π-LIGANDS

With reference to the catalytic cycle on the next page
(a) identify the raw materials and products
(b) write an equation for the overall reaction
(c) identify the two b-hydride elimination reactions
(d) what organic molecules (as ligands) are formed in each case
(e) identify the step that involves nucleophilic attack on coordinated ethene
(f) what would the product be if the reaction were carried out in D2O?
Construct a cycle for the conversion of propene to acetone.

Question 23

NUCLEOPHILIC ATTACK ON COORDINATED π-LIGANDS

Write an equation for the net overall reaction for this scheme.

Question 24

NUCLEOPHILIC ATTACK ON COORDINATED π-LIGANDS

(a) Predict the outcome of the following reaction. (b) Sketch the organometallic intermediate.

Question 25

METAL-CARBON MULTIPLE BONDS

Predict the outcomes of the following reaction:

Question 26

APPLICATIONS OF SPECTROSCOPY TO ORGANOMETALLIC CHEMISTRY

The reaction of RuCl3 with triphenylphosphine and aqueous methanal in refluxing 2-methoxyethanol affords a compound Z which has weak and strong bands in the IR spectrum at approximately 2000 cm-1, and which also gives a positive test for chloride.
The 31P and part of the 1H NMR spectra are shown below. The only other signals observed in the 1H NMR are a set of intense peaks assigned to phenyl protons.
(a) Propose and justify a formula for Z and sketch all the possible isomers.
(b) Suggest a structure for Z describing in detail how you arrived at your
conclusion and why other isomeric possibilities were eliminated.
(c) Explain the coupling pattern observed for the signal at –7.2 ppm in the 1H NMR

Question 27

APPLICATIONS OF SPECTROSCOPY TO ORGANOMETALLIC CHEMISTRY

The chemical shift difference of two peaks in a low temperature 13C NMR spectrum measured at 75 MHz is 60 ppm.

i) What is this expressed as a difference in frequency?

When the temperature of the sample is raised, the two peaks collapse and begin to coalesce.

ii) What is the approximate rate of the exchange process at the coalescence temperature?

The IR spectrum of the same compound, measured at low temperature, shows peaks due to two different CO ligands at 2050 and 1800 cm–1.

iii) What are these peaks expressed in true frequency (Hz or s–1)?
iv) What rate of exchange, k, would be required to see these peaks coalesce?

What is the key point to be taken from these examples?

Question 28

APPLICATIONS OF SPECTROSCOPY TO ORGANOMETALLIC CHEMISTRY

The di-iron complex [Fe(h-C5H5)(CO)2]2 adopts a structure with both bridging and terminal CO ligands, as evidenced by IR spectroscopy.
At room temperature the 1H NMR spectrum consists of a single peak (see Figure 1), but at low temperature two peaks are observed which are not of identical area (in fact the relative intensity of the two peaks depends on the polarity of the solvent).
Describe what is happening and sketch a mechanism for the process. At room temperature the 13C NMR spectrum shows only one peak for all the carbonyl ligands. Is this consistent with the mechanism you have proposed?

Hint: sketch the possible structures of the complex in 3D abbreviating C5H5 to L – it may be easier to see the possibilities that way.

Question 29

APPLICATIONS OF SPECTROSCOPY TO ORGANOMETALLIC CHEMISTRY

Deduce the structure and fluxional behaviour of the Complex Fe(C5H5)2(CO)2 from the variable temperature
1H NMR spectra shown in Figure 2.
Note that of the two singlets (these are identical in area) observed at 30 ̊C, one remains unchanged as the temperature is lowered, whereas the other changes radically

Question 30

APPLICATIONS OF SPECTROSCOPY TO ORGANOMETALLIC CHEMISTRY

In many alkene complexes, the barrier to alkene rotation about the metal-alkene bond is quite low, and dynamic effects are often observed in the NMR spectra at about room temperature.
The Figure 3 shows the variable temperature 1H NMR of Rh(C2H4)2(h-C5H5) (the Cp signal is not shown)
Draw clear diagrams to show the structure of the complex and explain the dynamic process
Note: coupling to 103Rh is not observed

Question 30

APPLICATIONS OF SPECTROSCOPY TO ORGANOMETALLIC CHEMISTRY

Allyl complexes frequently display dynamic behaviour in solution, particularly in
coordinating solvents. Figure 4a shows the 1H NMR spectrum of [Pd(h-C3H5)(μ-Cl)]2 in CDCl3 at 25 ̊C. When measured in a polar solvent such as DMSO at 25 ̊C the spectrum is similar, though not as sharp. However, when the spectrum is measured in DMSO at 140 ̊C it appears very different (Figure 4b).

Assign the peaks in both spectra and propose a mechanism to account for the high temperature spectrum.

Question 31

METALLACYCLES

Show why 1,2,3-(CH3)3-4,5,6-(CD3)3C6 would be an unlikely product from the cyclotrimerization of CH3C2CD3 catalysed by a cobalt complex.
What are the possible isomers?