and the solution was refluxed for a few days. The isomerisation
was monitored by means of TLC (in each case the Rf’s of cis
isomers were smaller than those of the trans isomers). The
isomerisation was usually accompanied by a partial demetal-
lation and formation of an immobile yellow species. The
acetonitrile was removed on a rotary evaporator and the result-
ing sample was chromatographed on silica gel with an
appropriate eluent. It was found that extensive heating should
be avoided, as this may lead to a partial conversion to trans
complexes. The yield of the cis complex of bis-chelates
obtained was dependent on the ligand system and varied from
about 50% for Pd(OEtN3C6H3Me-2,3)2 to about 15% for
Pd(OMeN3C6H4Me-2)2. The heteroleptic cis-complexes were
additionally characterized by their mass spectra.
2-[CH2CH3]Ј), 3.54 (s, 6H, NCH3 ϩ [NCH3]Ј), 7.02–7.14 (m,
6H, aromatics). (Calc. for PdC20H28N6O2: C, 48.94; H, 5.75; N,
17.11. Found C, 48.87; H, 567; N, 17.04%).
cis isomer. 1H NMR (300 K, d8-toluene): δ 1.03 (t, J = 7.6 Hz,
3H, CH2CH3), 1.07 (t, J = 7.6Hz, 3H, [CH2CH3]Ј), 2.10 (s, 3H,
2-CH3), 2.12 (s, 3H, 2-[CH3]Ј), 2.22 and 2.87 (m, 2H, CH2), 3.10
(s, 6H, NCH3 ϩ [NCH3]Ј), 6.39 (d, 1H, J = 7.4 Hz), 6.47 (d, 1H,
J = 7.4 Hz), 6.49 (d, 1H, J = 7.6 Hz), 6.56 (d, 1H, J = 6.0 Hz),
6.77 (t, 2H, J = 7.53 Hz). (Calc. for PdC20H28N6O2: C, 48.94; H,
5.75; N, 17.11. Found C, 49.06; H, 5.77; N, 17.14%).
Pd(OMeN3C6H4Me-2)2 (6). The separation was performed
using dichloromethane as eluent (Rftrans = 0.60, Rfcis = 0.12).
1
trans isomer. H NMR (300 MHz, CDCl3): δ 7.16–7.09 (m,
8H, aromatic), 3.63 (s, 6H, NMe), 2.40 (s, 6H, 2-Me). UV-VIS
(CHCl3): 530 (250), 345 (14400), 260 nm (21400 dm3 cmϪ1
molϪ1). (Calc. for PdC16H20N6O2: C, 44.20; H, 4.64; N, 19.32.
Found C, 44.06; H, 4.71; N, 19.42%).
Pd(OButN3C6H4Me-4)2 (1). For this complex, (bearing
no methyl groups in the ortho position of the phenyl ring) the
procedure involving heating of the trans complex in acetonitrile
did not result in formation of the cis isomer. Therefore
the following procedure was applied: the reaction mixture of
the ligand and palladium() acetate in 25 ml of boiling acetone,
(which revealed the presence of both isomers in the TLC), was
rapidly poured into 400 ml of a water–ice mixture. The
resulting pink precipitate containing both isomers was filtered,
dried on air and chromatographed using dichloromethane as
eluent (Rftrans = 0.95, Rfcis = 0.73).
cis isomer. 1H NMR (300 MHz, CDCl3): δ 6.80–6.56 (m, 8H,
aromatic), 3.72 (s, 6H, NMe), 2.40 (s, 6H, 2-Me). UV-VIS
(CHCl3): 540 (140), 340 (10100), 250 nm (15800 dm3 cmϪ1
molϪ1). (Calc. for PdC16H20N6O2: C, 44.20; H, 4.64; N, 19.32.
Found C, 44.41; H, 4.64; N, 19.25%).
Pd(OMeN3C6H3Me-2,4)2 (7). cis and trans isomers were
separated using dichloromethane as eluent (Rftrans = 0.75, Rfcis
=
1
trans isomer. H NMR (300 MHz, CDCl3): δ 7.28–7.02 (dd,
0.28).
J = 7.8 Hz, 8H, aromatic), 2.29 (s, 6H, 4-Me), 1.54 (s, 18H,
CMe3). (Calc. for PdC22H32N6O2: C, 50.92; H, 6.22; N, 16.19.
Found C, 50.80; H, 6.25; N, 16.10%).
trans isomer. 1H NMR (294 K, CDCl3): δ 7.24–6.94 (m, 6H,
aromatic), 3.62 (s, 6H, NMe), 2.36, 2.15 (s, 6H, s, 6H, 2-Me ϩ
4-Me). (Calc. for PdC18H24N6O2: C, 46.71; H, 5.23; N, 18.15.
Found C, 46.85; H, 5.20; N, 18.10%).
1
cis isomer. H NMR (300 MHz, CDCl3): δ 6.52 (AB spec-
1
trum, 8H, aromatic), 2.14 (s, 6H, 4-Me), 1.53 (s, 18H, CMe3).
(Calc. for PdC22H32N6O2: C, 50.92; H, 6.22; N, 16.19. Found C,
50.91; H, 6.04; N, 16.34%).
cis isomer. H NMR (294 K, d8-toluene): δ 6.61 (d, 2H, J =
7.9 Hz, 6-H), 6.37 (br d, 2H, 5-H), 6.28 (br s, 2H, 3-H), 3.07 (s,
6H, NMe), 2.12, 2.03 (s, 6H, s, 6H, 2-Me ϩ 4-Me). (Calc. for
PdC18H24N6O2: C, 46.71; H, 5.23; N, 18.15. Found C, 46.70; H,
5.25; N, 18.20%).
Pd(OButN3C6H5)2 (2). Only the trans isomer was isolated. 1H
NMR (300 MHz, CDCl3): δ 7.37 (dd, 2H), 7.24 (dd, 4H), 7.00
(dd, 4H, aromatic), 1.57 (18H, CMe3). (Calc. for
PdC20H28N6O2: C, 48.96; H, 5.75; N, 17.11. Found C, 48.94; H,
5.66; N, 17.22%).
Pd(OPriN3C6H4Me-2)2 (8). The separation was performed
using dichloromethane as eluent (Rftrans = 0.75, Rfcis = 0.48).
1
trans isomer. H NMR (300 MHz, CDCl3): δ 7.24–7.06 (m,
8H, aromatic), 4.20 (septet, 2H, CHMe2, J = 6.7 Hz), 1.36 (d,
12H, CHMe2), 2.39 (s, 6H, 2-Me). (Calc. for PdC20H28N6O2: C,
48.96; H, 5.75; N, 17.12. Found C, 48.80; H, 5.71; N, 17.02%).
cis isomer. 1H NMR (300 MHz, CD2Cl2): δ 6.80–6.48 (m, 8H,
aromatic), 4.33 (septet, 2H, CHMe2, J = 6.7 Hz), δ = 1.40 (d,
12H, CHMe2), 2.11 (s, 6H, 2-Me). (Calc. for PdC20H28N6O2: C,
48.96; H, 5.75; N, 17.11. Found C, 48.90; H, 5.73; N, 16.92%).
Pd(OButN3C6H3Me-2,3)2 (3). The separation was performed
using dichloromethane as eluent (Rftrans = 0.76, Rfcis = 0.65).
trans isomer. 1H NMR (300 MHz, CDCl3): δ 7.11–6.93 (br m,
6H, aromatic), 1.41 (s, 18H, CMe3), 2.28, 2.27 (s, 6H, s, 6H,
2-Me, 3-Me). (Calc. for PdC24H36N6O2: C, 52.50; H, 6.63; N,
t
15.36. Found C, 52.55; H, 6.70; N, 15.33%).
1
cis isomer. H NMR (300 MHz, CDCl3): δ 6.66–6.47 (br m,
t
6H, aromatic), 1.49 (s, 18H, CMe3), 1.96, 1.92 (s, 6H, s, 6H,
Pd(OEtN3C6H3Me-2,3)2 (9). The separation was performed
using dichloromethane as eluent (Rftrans = 0.75, Rfcis = 0.40).
2-Me, 3-Me). (Calc. for PdC24H36N6O2: C, 52.50; H, 6.63; N,
15.36. Found C, 52.68; H, 6.56; N, 15.25%).
1
trans isomer. H NMR (300 MHz, CDCl3): δ 7.05–6.99 (m,
6H, aromatic), 3.88 (q, 4H, J = 7.2 Hz, NCH2Me), 1.34 (t, 6H,
NCH2CH3), 2.31, 2.27 (s, 6H, s, 6H, 2-Me, 3-Me). (Calc. for
PdC20H28N6O2: C, 48.96; H, 5.75; N, 17.11. Found C, 48.84; H,
5.78; N, 16.98%).
Pd(OMeN3C6H4But-2)2 (4). cis and trans isomers were
separated chromatographically using dichloromethane as
eluent (Rftrans = 0.76, Rfcis = 0.31).
1
trans isomer. 1H NMR (294 K, CDCl3): δ 7.43–7.l7 (overlap-
ping multiplets, 8H, aromatic), 3.54 (s, 6H, NMe), 1.50 (s, 18H,
CMe3). (Calc. for PdC22H32N6O2: C, 50.92; H, 6.22, N, 16.19.
Found C, 51.10; H, 6.35; N, 15.90%).
cis isomer. H NMR (300 MHz, CDCl3): δ 6.68–6.54 (br m,
6H, aromatic), 3.97 (q, 4H, J = 7.2 Hz, NCH2Me), 1.43 (t, 6H,
NCH2CH3), 1.93 (s, 12H, 2-Me, 3-Me). (Calc. for
PdC20H28N6O2: C, 48.96; H, 5.75; N, 17.11. Found C, 49.01; H,
5.75; N, 17.05%).
1
cis isomer. H NMR (294, d8-toluene): δ 7.29 (d, 2H, 3-H ),
6.97 (dd, 2H, 4-H ), 6.75 (br d, 2H, 6-H ), 6.50 (br t, 2H, 5-H ),
3.28 (6H, s, NMe), 1.22 (br s, 18H, CMe3). (Calc. for
PdC22H32N6O2: C, 50.92; H, 6.22; N, 16.19. Found C, 51.12; H,
6.50; N, 15.85%).
Pd(OMeN3C6H3Me-2,5)2 (10). The separation was per-
formed using dichloromethane–hexane (3 : 1) as eluent (Rftrans
=
0.5, Rfcis = 0.1).
1
trans isomer. H NMR (300 MHz, CDCl3): δ 7.03–6.87 (m,
6H, aromatic), 3.63 (s, 6H, NMe), 2.37, 2.29 (s, 6H, s, 6H,
2-Me, 5-Me). (Calc. for PdC18H24N6O2: C, 46.71; H, 5.23; N,
18.15. Found C, 46.70; H, 5.24; N, 18.09%).
Pd(OMeN3C6H3Me-2,Et-6)2 (5). The separation was
performed using CH2Cl2 as eluent. (Rftrans = 0.87, Rfcis = 0.27).
trans isomer. 1H NMR (295 K, CDCl3): δ 1.25 (t, J = 7.5 Hz,
3H, CH2CH3), 1.26 (t, J = 7.6 Hz, 3H, [CH2CH3]Ј), 2.38 (s, 6H,
cis isomer. 1H NMR (300 MHz, CDCl3): δ 6.34 (s, 2H, 6-H ),
6.57 (AB spectrum, 4H, 3-H, 4-H ), 3.71 (s, 6H, NMe), 2.04,
2-CH3
ϩ
2-[CH3]Ј), 2.7–2.94 (m, 4H, 2-CH2CH3
ϩ
J. Chem. Soc., Dalton Trans., 2002, 885–895
887