代做LH Inorganic IIIa / 03 33983 Chemistry Examinations 2023代写C/C++语言

日期：2024-05-16 12:29

COLLEGE OF ENGINEERING & PHYSICAL SCIENCES

SCHOOL OF CHEMISTRY

Year 3  Degree of MSci/BSc with Honours

Chemistry

Chemistry with Industrial Experience

Chemistry with Business Management

Chemistry with Pharmacology

Chemistry with a Modern Language

Degree of B.A./BSc Liberal Arts & Sciences

LH Inorganic IIIa / 03 33983

January Examinations 2023

1.         The following question refers to the substitution reactions of the square planar complexes cis-[Pt(PMe3)Cl2(NH3)], A, and trans-[Pt(PMe3)Cl2(NH3)], B.

(a)    Explain how you would synthesise complex A starting from the [PtCl4]2-  anion.  (2 marks)

(b)    Explain why the rate of substitution of NH3 by NHEt2 is faster for complex B than for complex A. (3 marks)

(c)    On recording kinetics data for the substitution of NH3 by NHEt2 for complex B in two different solvents, the plot below of kobs vs [NHEt2] was obtained.

Discuss the mechanism of substitution for this ligand exchange reaction and state the rate law that applies.  Explain the fully the reason for the behaviour observed when the reaction is carried out in the different solvents. (5 marks)

(d)    If the trimethylphosphine ligand in the platinum complex was replaced with a  tri-t-butylphosphine ligand, how would you expect kobs to change for the same exchange reaction when carried out in methanol solvent?  Explain your reasoning. (2 marks)

2.         The hydrosilylation of alkenes is widely used in the production of silicone polymers, and is described by the model reaction given below:

(a)     [RhCl(PPh3)3] is the pre-catalyst.  Calculate the number of valence electrons for this species, and explain what must occur, to produce the active catalyst. (2 marks)

(b)    Based on the reaction shown above, construct a plausible catalytic cycle for the hydrosilylation process, identifying clearly the key fundamental reactions that are involved in the different stages of the catalytic cycle, i.e. assembly, modification and expulsion.  Ensure you sketch clearly the coordination environment around the central rhodium atom at each stage, and note any changes in the oxidation state and number of valence electrons for the rhodium atom. (7 marks)

(c)     The model reaction above shows the formation of a linear product. However, branched products (as shown opposite) are also possible from this process. Discuss the step in the catalytic cycle that determines the formation of linear or branched products and what simple change could be made to the catalyst to influence the linear:branched ratio?  Illustrate your answer with appropriate diagram(s). (3 marks)

3.         (a)    Assign each of the two electronic spectra (I and II) to one of the complexes

given below. Provide a full justification for your answer. As part of your justification, you should explain why you haven’t chosen the two unassigned complexes.

(9 marks)

(b)    For each of the spectra I and II assign an electronic transition to each of the bands. (3 marks)

4.         (a)    MCl2 reacts with bidentate ligands L1  and L2  (structures shown below) to form.

two different complexes [M(L1)m]x  and [M(L2)n]y  (where M = transition metal, m and n = number of ligands,x andy = charge).

Given information (i) – (iii), assign a structure for each of the complexes and suggest the identity of M. As part of your answer, you should fully explain each of the points (i) – (iii).

(i)        For peaks corresponding to d-d transitions in the electronic spectrum: [M(L1)m]x, ε = 1.1 × 102 M−1 cm−1; [M(L2)n]y, ε = 4.2 M−1 cm−1 .

(ii)       At 300 K: [M(L1)m]x, μ = 2.9 μB ; [M(L2)n]y, μ ~ 0

At 350 K: [M(L1)m]x, μ = 4.9 μB ; [M(L2)n]y, μ = 4.9 μB

(iii)      In both complexes the M-N bond length is observed to be longer at

350 K than the M-N bond length at 300 K.

(10 marks)

(b)    With reasoning, explain where you would expect to find ligand L1  in the spectrochemical series. (2 marks)