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

lCH2=CHC2H5
Five electron ligands
(i)Na/Hg in THF
A
co
A +---:2:-::5-;;o=-c- O
~~yxne
-80 °C
E contains fluorine and is a 1 : 1 electrolyte.
1 H n.m.r. ( 1 H decoupled; [J relative to TMS,
relative intensities in parenthesis)
A 5.70(5H), -7.40(1H. 1:12:1 pattern)
hexane
8 + c
B 5.61(5H), 1.60(2H), 1.58(2H), 1.55(2H), 0.92(3H)
C 5.61(5H), 1.60(2H), 1.53(1H), 0.92(3H), 0.88(3H)
""' (Ph3C)BF4
~ne
D 5.46(5H), 2.90(2H), 2.34(1H), 2.31(1H), 2.30(1H), 1.63(3H), - 6.13(1H,
1:12:1 pattern)
E 5.99(5H), 4.36(1H), 3.29(1H), 3.20(1H), 2.80(2H), 2.22(3H)
( 183 W has nuclear spinI= i and is 14% abundant, ali other W isotopes ha ve zero
spin].
(University of Southampton).
9. For the compound (1J 1 -C 5 H 5 )Ge(CH 3 )r which contains a cr-bonded metalcyclopentadienyl
group labelled as shown in the figure below, the 1 H n.m.r.
spectrum at - 80°C shows three multiplets at 7.0, 6.0 and 3.5 ppm (relative
intensities 2:2: 1 respectively) and a singlet at 3.0 ppm (relative intensity 9)
downfield from Si(CH 3 ) 4 as reference at Oppm. As the temperature is raised to
- 40°C the three multiplets start to broaden and collapse but the singlet at
3.0 ppm remains sharp. The resonance for the H 8 protons collapses more rapidly
than that for the Hc protons. Finally, at 2 soc the spectrum shows only two sharp
singals, one at 5.6 ppm and the other at 3.0 ppm (relative intensities 5:9
respectively ).
E
Account for the above observations, describe the various exchange processes
which could be occurring at 2 5 oc and indicate which process is the most likely on
the basis of the variations observed in the spectra.
(University of Warwick).
308