_P.-Powell-auth.-Principles-of-Organometallic-Chemistry-Springer-Netherlands-1988

Problems
butadiene )tricarbonyliron, E. Identify the protons which give rise to each group of
resonances and discuss the spin-spin couplings which arc observed. (Ignore
coupling through more than three bonds.)
(b) At ambient tempera ture the 13 C n.m.r. spectrum of E (broad-band proton
decoupled) consists ofthree lines at 213.2, 86.4 and 4l.Sppm. downfield from
tetramethylsilane (b = 0). As the temperature of the sample is lowered the
resonance at 213.2<5 broadens, collapses and finally resolves into two lines at
217.4<5 and 211.3<5, with relative intensities 1:2. The rest of the spectrum does
not change with temperature. Assign the spectrum and suggest an explanation
for the variation with temperature. How could the assignments be confirmed?
(c) How can compound E be prepared? How does it react with (i) hydrogen
chloride, (ii) HBF 4 /CO, (iii) MeCOCl/ AlCl 3 (iv) Ph 3 P?
7. The reaction between 1 mmol of K[Rh(PFJ 4 ] and 1 mmol of 1-chloro-3-
methylbut-2-ene (1, 1-dimethylallyl chloride) in diethyl ether gave a yellow
solution and a white precipitate. Fractionation of the yellow solution yielded PF 3
(ca. 1 mmol) and a yellow volatile liquid A.
Analysis of A: found C, 13.8%; H, 2.1 %; P, 21.3%; F, 39.2% and Rh. 23.6%.
The mass spectrum of A showed a highest mass peak at m/z = 436. When
compound A was heated to 60°C it was converted initially into an isomeric
derivative B which subsequently formed a third isomer C. The 1 H n.m.r. spectra of
compounds A, B and C, measured at room temperature, are listed in the table.
These spectra can be assigned by taking into account proton-proton and
proton-rhodium couplings [l(1° 3 Rh) = î: natural abundance of 1 "'Rh isotope
is 100%]. proton-phosphorus couplings are not observed under these conditions.
Interpret these data as fully as you can. Deduce the molecular structures
of the complexes A, B and C and suggest a mechanism for the isomerization.
Chemical Relative *Coupling
shift/b intensity Multiplicity constants/Hz
Compound A
1.7 3 singlet
2.1 3 singlet
2.7 1 doublet of doublets 10.5, 2.0
3.2 1 doublet of doublets 6.5. 2.0
4.9 1 8 lines of equal 10.5. 6.5, l.O(Rh)
intensity
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