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49 Cards in this Set
- Front
- Back
What is 'syn gas' ? |
A mixture of CO and H2 and is manufactured from coal. CO2 also produced as a by-product |
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What are Fischer Tropsch reactions? |
A series of reactions using CO2 and H2 with the required pressure, head and catalyst to produce a range of products and is a critical way of making fuel |
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What are the catalysts used for the Monsanto BP acetic acid process: MeOH + CO --> MeCOOH |
Iridium, cobalt or rhodium |
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Why is spectrometry useful for characterisation of CO complexes? |
Can see fragmentation where CO ligands fall off |
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Why is the CO IR stretch easy to identify? |
Not many other stretches in same range |
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If there is only one environment, what must you NOT assume? |
There is only one stretch. Group theory shows there will e multiple stretches but some will not result in a dipole change and therefore be absent from the IR spectra |
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Give the hybridisation for the sigma bonds in the following complexes:
Ni(CO)4 Fe(CO)5 Cr(CO)6 |
Sp3 Dsp3 D2sp3 |
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Draw an energy level for an octahedral ML6 complex |
See book |
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What is the acid behaviour of a CO ligand? |
Weak base, electron pair donor for forward bonding C-O empty pi* orbitals act as Lewis acid |
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Show why there is a triple bond between C and O using a molecular energy diagram |
See pic |
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Why does CO tend not to form complexes with elements with a high oxidation state? What else can we deduce is unlikely to form a complex with CO ligands? |
Because the CO - metal backbonding requires a lot of electron density on the metal. CO therefore unlikely to bid to non-metals such as BF3 |
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Explain why CO ligand bonding is an exams of synergic bonding |
CO forward bonding pushes electrons onto the metal increasing its electron density. This increases the backbonding which in turn helps the forward bonding again |
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Will a stronger bond have a higher or lower IR frequency? |
Higher |
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Why is the bond order going to be less than 3 for the CO bond when C is also acting as a ligand? |
Because electron density from metal will go into CO pi* orbital lengthening the bond and making it weaker |
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What is the IR range for vCO for carbonyl compounds ? |
2150 - 1850 |
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What is the effect of charge on a complex on a CO stretch? |
Negative charge increases electron density on metal increasing backbonding, decreasing the strength of the CO bond so causing a lower frequency or vCO. A positive charge opposite |
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There cannot be more IR active bands than the number of carbonyl groups. What eventuality can cause this? |
Impurities Isotopes |
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For an Mn(CO)4 3- complex, explain why Mn(-3) can exist |
The negative charge is spread Into the backbonding Electroneutrality principle, in reality the Mn is only slightly negative |
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What is a homoeleptic compound ? |
One specific metal with one specific ligand E.g. Cr(CO)6 |
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Why is V(CO)6 possible and V(CO)7 not? |
V is D5 meaning that the complex is going to have an odd number electrons. With 6 ligands it can exist with a total of 17 electrons, but with 7 ligands there are 19 electrons and the extra electron goes into antibondig |
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What are the consequences of a 17 electron complex e.g. Nb(CO)6 |
Paramagnetic so liable to jahn teller and easily reduce to Nb(CO)6 - |
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Why is V(CO)6 possible and V(CO)7 not? |
V is D5 meaning that the complex is going to have an odd number electrons. With 6 ligands it can exist with a total of 17 electrons, but with 7 ligands there are 19 electrons and the extra electron goes into antibondig |
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What are the consequences of a 17 electron complex e.g. Nb(CO)6 |
Paramagnetic so liable to jahn teller and easily reduce to Nb(CO)6 - |
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Why can group 4 metals not form carbonyl complexes |
To satisfy the 18 electron rule would have to be; M(CO)7 4 d electrons not enough to backbond to 7 CO |
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What two complexes are known for group 7 metals with carbonyl ligands? |
M(CO)5- but very air sensitive M(CO)6+ |
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Why is tc unknown in nature |
It's radioactive |
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How can Mn exist with CO ligands without a charge? |
Forms Mn2(CO)10 the extra electron comes from each Mn |
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What is the hybridisation of Mn in Mn2(CO)10 |
Octahedral so d2sp3 |
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How can Fe(CO)5 be identified ? |
Toxic and smelly but not everyone can smell it |
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What evidence is there for Fe(CO)5 being trigonal pyramidal? |
2 stretches can be seen in the IR spectrum, one axial stretch one Equatorial |
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Why is there only one CNMR peak for Fe(CO)5? |
Berry pseudo rotation, spins too fast for CNMR |
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What happens to [Ru(CO)5] at room temp |
Decomposes to [Ru3(CO)12] |
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What can be doe with Fe metal |
Heated to make magnets and metal films |
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What does [Os(CO)5] look like |
Pale yellow solid |
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What happens when hv and MeCO2H are added to [Fe(CO)5]? What can be seen grime HRS spectrum |
Fe - Fe hind formed with 2 bridging carbonyl groups. Will show three CO stretches |
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What evidence is there for an Fe-Fe bond and the existence of a [Fe2(CO)9] complex |
CO stretch on IR Completes 18 electron rule Molecule is diamagnetic |
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What is a carbene? |
A molecule containing a neutral carbon atom with a valence of two and two unshared valence electrons
R=C: |
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Give some examples of how to create carbonylate anions |
Add Li/Hg Add Na/Hg (highly toxic) Hv |
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What occurs when [Mn(CO)10] is added to Br2? |
2[BrMn(CO)5] |
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Distinguiish between the bonding in [Fe3(CO)12] and Ru(CO)12] |
The Fe comple has 3 Fe bonds and semibriding CO. Gives a very distorted shape with different bond lengths. The Ru complex has no briding carbonyls. It is more or less a slightly disorted octahedral environment. Has CO in the plane and 6 CO out of the plane |
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What is a metal cluster? Give an example |
[Ru3(CO)12]. It is a metal solubilised by internal ligands |
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What is the only form group 9 CO complexes can exist? |
As anions, otherwise will not satisfy the 18 electron rule. E.g. [Co(CO)4]- and [Co(CO)5]+ |
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What is the result of adding MeC(=O)Cl to [Mn(CO)5]-? |
M-C bond formation |
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What is required for a thermal substitution? Give an example uaing MeCN. In what positions do subsituted go in octahedral complex? What can be noted about CN- ligands? |
Heat and reflux with solvent containing ligand. E.g. MeCN solvent with [Cr(CO)6]. CN- adds axial first, then cis equitorial then fac. The CN- ligands can then themselves be removed and substituted by other ligands. |
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What are typical reagents for a photochemical substitution and their roles? |
THF, hv and ligand. hv causes dissociation of CO ligands, THF stabilises 16e- intermediate before being displaced by incoming ligand. |
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What reagents are typically used for a chemically assisted CO substitution and how do they bring about the substitution? |
CH2Cl2 and Me3NO. One of the CO groups binds to the Me3NO via the O group. It leaves as CO2 being replaced by NMe3. This is a poor back-bonder and easily replaced by the desired ligand. |
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What reagents are used for an electron transfer catalysed substitution? |
[Ph2CO]' |
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What happens if M-Li is added to a carbonyl metal complex followed by [Me3O]+?
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It will act as a nucleophile attacking the CO to form a complex with a negative charge. The addition of MeO3 produces a Fisher carbene |
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What is the effect of RO groups attacking complexes? |
Can attack ligands and form carbenes |