G. Wagner / Inorganica Chimica Acta 357 (2004) 1320–1324
1323
5. Concluding remarks
tered off, washed with diethylether, and recrystallised
from CH2Cl2/diethylether.
Structurally closely related transition metal nitrile
complexes behave differently in the reaction with nitro-
nes, depending on the metal. Cycloaddition across the
CꢀN bond takes place if the nitrile binds strongly to
the metal and ligand exchange is slow. Metals from the
platinum group are most promising to favour this re-
action pathway. Metals with suitable exchange kinetics
and weak affinity to nitriles prefer to undergo ligand
exchange, and oxygen-bound nitrone complexes are
obtained if oxophilic metals such as Ti or Zr are used. A
third reaction mode, i.e., hydrolysis of the nitrone to the
aldehyde, was observed as the main reaction with Mo
and W but also occurred with other metals as a side
reaction. However, the factors leading to a preference
for this reaction mode, its mechanism and the role of the
metal are not yet understood and subject of a continuing
study in our group.
Yield is 58%.
Anal. Calc. for C30H28Cl2N4O2Pd: C, 55.11; H, 4.32; N,
8.57. Found: C, 55.73; H, 4.29; N, 8.50%. FABþ-MS, m/
z: 677 [M + Na]þ, 617 [M– HCl]þ, 583 [M–2HCl]þ. M.p.
166 °C. IR spectrum (selected bands), cmꢁ1: 1627 vs
1
m(C@N) + m(C@C). H NMR spectrum in CDCl3, d:
2.94 (s, 3H, C–N(Me)–O), 5.89 (s, br, 1H, N–CH –N),
7.40 (t, 7.5 Hz, 2H), 7.50 (m, 3H), 7.68 (m, 3H), and 8.63
(d, 7.5 Hz, 2H) (two Ph). 13C NMR spectrum in CDCl3,
d : 45.8 (br, C–N(Me)–O), 93.7 (br, N–CH–N), 122.6,
128.5, 128.7, 128.9, 129.8, 130.4, 133.5 and 135.8 (two
Ph), 164.9 (C@N).
Yield
is 44%. Anal. Calc. for C32H32Cl2N4O2Pd: C, 56.36; H,
4.73; N, 8.22. Found: C, 56.48; H, 4.88; N, 8.41%.
FABþ-MS, m/z: 705 [M + Na]þ, 610 [M–2HCl]þ. M.p.
150 °C (dec.). IR spectrum (selected bands), cmꢁ1: 1632
In summary, this work shows that Lewis acidity of a
metal alone is not sufficient to bring about a cycload-
dition of nitrones to coordinated nitriles. Factors fa-
vouring competing reactions such as ligand exchange or
hydrolysis have to be considered, and therefore, the
metal strongly influences the outcome of the reaction.
1
vs m(C@N) + m(C@C). H NMR spectrum in CDCl3, d:
2.44 (s, 3H, C6H4Me), 2.95 (s, 3H, C–N(Me)–O), 5.87 (s,
br, 1H, N–CH–N), 7.30 (d, 7.8 Hz, 2H), 7.48 (d, 7.9 Hz,
2H)(C6H4Me), 7.40 (t, 7.6 Hz, 2H), 7.63 (m, 1H) and
8.68 (d, 7.6 Hz, 2H)(Ph). 13C NMR spectrum in CDCl3,
d : 21.5 (C6H4Me), 46.0 (br, C–N(Me)–O), 93.8 (br, N–
CH–N), 122.5, 128.1, 128.6, 128.7, 129.1, 129.3, 130.4,
133.0, 133.5, 139.4 (Ph and C6H4Me), 164.3 (C@N).
6. Experimental
6.1. Materials and instrumentation
Acknowledgements
Transition metal complexes and nitrones were pre-
pared according to published methods. Solvents were
dried using standard techniques, reactions with Ti, Zr,
Mo and W compounds were performed in a nitrogen
atmosphere. Melting points were determined in sealed
tubes on a Kofler melting point apparatus. C, H and
N elemental analyses were carried out on a Leeman
CE 440 automatic analyser. Infrared spectra (4000–
400 cmꢁ1) were recorded on Perkin Elmer 2000 FTIR
and Nicolet Avatar 320 FT-IR spectrometers in KBr
pellets. Positive FAB-MS spectra of the samples in 3-
nitrobenzyl alcohol matrices were obtained on a
Finnigan MAT 900XLT instrument. 1H and 13C
NMR experiments were acquired on Bruker DRX 500
and Bruker AMX 300 spectrometers at ambient tem-
perature.
Johnson Matthey is acknowledged for a generous
loan of Pd compounds, and the Department of Physics
of the University of Augsburg (Germany) and the ITQB
Oeiras (Portugal) for general support of this work. The
EPSRC National Mass Spectrometry Service Centre,
University of Wales Swansea, is acknowledged for re-
cording FAB-MS spectra.
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