N(R)- or N(S)-[Pd(S-meap)Cl2] in D2O with or without added
KCl gave essentially the same spectrum as observed for [Pd(S-
meap)(D2O)2]2ϩ, i.e. epimerisation occurs rapidly on dis-
solution, confirming the CD observations. The presence of dis-
stirring for 20 min the mixture was filtered and the filtrate acid-
ified with 1 M HCl to give a thick precipitate. The solid was
collected by filtration, washed with ice-cold water and air-dried.
A single treatment with NaOH was not sufficient for complete
conversion of the ester: unchanged material recovered during
the initial filtration was treated once more with base to obtain
the maximum yield of succinimide derivative. Recrystallisation
was effected from ethyl acetate–light petroleum (bp 40–60 ЊC)
yield = 27.5 g (66%) mp = 80 ЊC (uncorrected). δH (d6-acetone)
10.14 (1 H, br, NH), 7.0–7.3 (5 H, m, C6H5), 6.68 (1 H, d, NH),
5.02 (2 H, s, CH2), 4.34 (1 H, q, CH) and 2.66 (2 H, m, CH2).
1
tinct NMe singlets for each diastereoisomer in the H NMR of
[Pd(S-meap)Cl2] (separation 75 Hz) shows the epimerisation to
be slow on the NMR timescale at ambient temperature. Inver-
sion of the NMe centre is considered to succeed Pd–NMe bond
rupture, as outlined for similar platinum() complexes.3 It was
not possible to examine the relation between rates of epimeris-
ation and NMe-H exchange in organic solvents owing to the very
low solubility of the complexes in such media. Compounds
of the cations [M(S-meap)2]2ϩ (M = Pd or Pt) were readily
obtained, but not characterised, as initial NMR studies
revealed a large degree of isomeric complexity for these
systems.
3S-(Methylamino)pyrrolidine
dihydrochloride
(S-meapؒ
2HCl). A solution of 3S-(benzyloxycarbonylamino)succin-
imide (10.9 g, 44 mmol) in dry THF (200 ml) was added drop-
wise to a rapidly stirred suspension of lithium aluminium
hydride (7.5 g) in dry THF (500 ml). The mixture was set to
reflux for 72 h, cooled, then hydrolysed at room temperature by
the successive addition of water (7.5 ml), 15% aqueous NaOH
(7.5 ml) and water (22.5 ml) to the rapidly stirred mixture. The
mixture was stirred overnight and the aluminate cake filtered
off and extracted with hot THF (2 × 200 ml). The filtrate and
extracts were combined and the solvent removed in vacuo to
give a dark oil. The oil was partitioned between 1 M HCl (300
ml) and Et2O (300 ml) and the aqueous phase concentrated in
vacuo to near dryness. Treatment of the residue with EtOH gave
a crystalline solid which was filtered off, washed sparingly with
cold EtOH, then triturated thoroughly with dry Et2O to give a
white solid, yield = 2.50 g (33%). α(589.3 nm, 20 ЊC, free amine,
2% in MeOH = Ϫ14.5Њ). δH (D2O) 4.12 (1 H, m, CH), 3.87 (1 H,
dd, CH), 3.55 (3 H, m, 3 CH), 2.81 (3 H, s, CH3), 2.62 (1 H, m,
CH) and 2.26 (1 H, m, CH).
Experimental
3S-Aminopyrrolidine dihydrochloride (S-apؒ2HCl) was
obtained from Lancaster Synthesis Ltd., the free amine being
extracted (diethyl ether) from a strongly basic solution prior to
each synthesis. Removal of the organic solvent in vacuo gave the
free base as a clear oil. All other reagents were of general
laboratory grade used as supplied unless otherwise specified.
Microanalyses (C,H,N) were performed by Mrs A. Dams of
1
this department. The H and 13C NMR spectra were recorded
on a Bruker WM360 spectrometer operating at 360 and 90
MHz respectively, electronic and circular dichroism spectra
using Perkin-Elmer Lambda 5 and Jobin Yvon CNRS Dichro-
graphe V spectrophotometers, respectively. The solid state CD
measurements were performed on KBr discs containing the
complexes as 1% dispersions in the oven-dried metal halide.
The reported results are the average from 3–6 independent spec-
tra for each complex. It is notable that little variation was
observed on recording the spectra for the N(S) and N(R)-
[Pd(S-meap)Cl2] complexes; larger discrepancies occurred in
the spectra of [Pd(S-ap)Cl2].
[Ni(S-ap)2][ClO4]2. To a stirred solution of Ni(ClO4)2ؒ6H2O
(1.15 g, 3.14 mmol) in MeOH (20 ml) was added a solution of 2
mol equivalents of S-ap (0.54 g) in MeOH (20 ml) giving an
immediate yellow precipitate which was filtered off, washed
with MeOH then Et2O and air-dried. Yield = 0.55 g (41%)
(Found: C, 22.6; H, 4.7; N, 12.9. Calc. for C8H20Cl2N4NiO8: C,
22.35; H, 4.70; N, 13.03%). UV/VIS (methanol): λmax/nm (ε/dm2
molϪ1): 442 (750). CD (methanol): λmax/nm (∆ε/dm2 molϪ1) 424
(ϩ2.32).
Preparations
N-Benzyloxycarbonylasparagine. To a vigorously stirred sus-
pension of S-asparagine (10 g, 0.076 mol) in 1 M NaHCO3 (150
ml) was added in portions over a period of 90 min, 11.4 ml
(0.080 mol) of benzyloxycarbonyl chloride. After stirring for
2 h the mixture was extracted with Et2O (1 × 150 ml), and the
aqueous phase acidified to pH 1–2 with concentrated HCl pre-
cipitating a thick pasty solid. The white precipitate was col-
lected, washed sparingly with cold water, air-dried and
recrystallised from water, yield = 12 g (60%), mp = 159–161 ЊC
(uncorrected). δH (d6-dmso) 12.66 (1 H, br, CO2H), 7.47 (1 H, d,
NH), 7.32 (5 H, s, C6H5), 6.92 (1 H, s, NH), 5.03 (2 H, s, CH2),
4.34 (1 H, q, CH), 3.37 (1 H, br, NH) and 2.50 (2 H, m, CH2).
[Cu(S-ap)2][ClO4]2ؒH2O. As for the nickel() complex above,
using Cu(ClO4)2ؒ6H2O. The initial purple solid product
hydrated in air to give the blue monohydrate. Yield = 1.25 g
(90%) (Found: C, 21.4; H, 4.5; N, 12.4. Calc. for C8H22-
CuCl2N4O9: C, 21.22; H, 4.91; N, 12.38%. UV/VIS (water):
λmax/nm (ε/dm2 molϪ1) 552 (1350). CD (water): λmax/nm (∆ε/dm2
molϪ1) 587 (Ϫ0.63) and 504 (ϩ0.81).
[Cu(S-ap)2Cl]ClO4. To a solution of [Cu(S-ap)2][ClO4]2ؒH2O
(0.5 g, 1.10 mmol) in MeOH (30 ml) was added 1.5 mol equiv-
alents of LiClؒH2O in MeOH (10 ml). After stirring for 10 min a
blue precipitate had formed. The solid was filtered off, washed
with minimum MeOH and air-dried. Yield = 0.22 g (54%)
(Found: C, 26.1; H, 5.5; N, 15.1. Calc. for C8H20CuCl2N4O4: C,
25.91; H, 5.45; N, 15.11%). UV/VIS (nitromethane): λmax/nm
(ε/dm2 molϪ1): 636 (1900). CD (nitromethane): λmax/nm (∆ε/dm2
molϪ1): 725 (ϩ1.87), 576 (ϩ0.55) and 470 (Ϫ0.10).
N-Benzyloxycarbonylasparagine methyl ester. Acetyl chloride
(70 ml, 0.188 mol) was added dropwise to a stirred suspension
of N-benzyloxycarbonylasparagine (50 g, 0.188 mol) in dry
MeOH (500 ml) at Ϫ70 ЊC. After the addition the mixture was
refrigerated at Ϫ15 ЊC overnight. The solvent was removed in
vacuo at < 5 ЊC, and the residue treated with Et2O until a solid
had formed. The mixture was cooled overnight at Ϫ15 ЊC, fil-
tered, and the white solid obtained washed with dry Et2O, water
and finally Et2O to give the dry solid, yield = 52.5 g (99%),
mp = 150–152 ЊC (uncorrected). δH (d6-acetone) 7.36 (5 H, m,
C6H5), 5.08 (2 H, s, CH2), 4.54 (1 H, q, CH), 3.64 (3 H, s, CH3)
and 2.68–2.94 (5 H, m, NH and CH2).
[Cu(S-ap)2Br]ClO4. As for the chloride complex above using
100 mg [Cu(S-ap)2][ClO4]2ؒH2O and a 10% stoichiometric
excess of LiBr in a total volume of 20 ml of MeOH. Diethyl
ether was added to ensure complete precipitation of the ternary
complex. This was collected at the pump, washed (Et2O) and
air-dried. Yield = 75 mg (83%) (Found: C, 23.2; H, 4.6; N,
13.3. Calc. for C8H20BrClCuN4O4 C, 23.4; H, 4.86; N, 13.50%).
UV/VIS (nitromethane): λmax/nm (ε/dm2 molϪ1) 628 (1980). CD
3-(Benzyloxycarbonylamino)-S-succinimide. To a stirred sus-
pension of N-benzyloxycarbonylasparagine methyl ester (47 g,
0.168 mol) in water was added 325 ml of 0.5 M NaOH. After
604
J. Chem. Soc., Dalton Trans., 1999, 599–606