Allylpalladium dimers with metals connected by binucleating dithiooxamidates in two different coordination modes: Solution behavior and solid-state structure

Article abstract of DOI:10.1021/ic201616s

A series of allylpalladium dimers having metals connected by binucleating dialkyldithiooxamidate [N(R)SC-CS(R)N]^2- [R = methyl, ethyl, isopropyl, benzyl, isoamyl, (S)-1-(1-phenyl)ethyl, meso-(1-phenyl)ethyl, and rac-(1-phenyl)ethyl] were prepar

Full text of DOI:10.1021/ic201616s

ARTICLE
pubs.acs.org/IC
Allylpalladium Dimers with Metals Connected by Binucleating
Dithiooxamidates in Two Different Coordination Modes: Solution
Behavior and Solid-State Structure
Santo Lanza,*,† Francesco Nicolꢀo,† Hadi Amiri Rudbari,† Maria Rosaria Plutino,‡ and Giuseppe Bruno†
†Dipartimento di Chimica Inorganica, Chimica Analitica e Chimica Fisica, and ‡Istituto per lo Studio dei Materiali Nanostrutturati
(ISMN-CNR, OU Palermo, unitꢀa di Messina), c/o Dipartimento di Chimica Inorganica, Chimica Analitica e Chimica Fisica,
Universitꢀa di Messina, Salita Sperone, 31 Contrada Papardo, 98166 Messina, Italy
ABSTRACT: A series of allylpalladium dimers having metals connected
by binucleating dialkyldithiooxamidate [N(R)SCꢀCS(R)N]2ꢀ [R =
methyl, ethyl, isopropyl, benzyl, isoamyl, (S)-1-(1-phenyl)ethyl, meso-
(1-phenyl)ethyl, and rac-(1-phenyl)ethyl] were prepared by reacting
the monochelate [(η3-allyl)Pd(N(R)SCꢀCS(R)NH k-S,S Pd)] with
[(η3-allyl)PdCl]2 in chloroform. At low temperature (20 °C), the
bimetallic complexes [(η3-allyl)Pd]2(μ-dialkyldithiooxamidate k-N,N0
Pd, k-S,S0 Pd0) (kinetic compounds) are formed in a short reaction time
(10 min). At a higher temperature (50 °C) and a longer reaction time
(24 h), the corresponding bimetallic isomers [(η3-allyl)Pd]2(μ-dialkyl-
dithiooxamidate k-N,S Pd, k-N0,S0 Pd0) (thermodynamic compounds)
are obtained. Both kinetic and thermodynamic compounds can exist as
endo or exo isomers, depending on the reciprocal orientation of the allyl
cuspids. Both endo and exo isomers are only detectable in solution when the alkyl substituents are chiral alkyl groups. Moreover,
diffractometric modeling agrees with the presence of both isomers in the solid state even when the alkyl substituent is an achiral alkyl
group. In a chloroform solution, endo and exo isomers undergo isomeric conversion owing to the apparent allyl rotation that follows
the PdꢀN bond rupture in the (η3-allyl)Pd(N^N) frame of kinetic compounds or in the (η3-allyl)Pd(N^S) frame of
thermodynamic compounds. The dithiooxamidate [N(R)SCꢀCS(R)N]2ꢀ, when engaged in a k-N,S Pd, k-N0,S0 Pd0 coordination
mode, behaves as a hybrid hemilabile binucleating ligand. At room temperature and in a chloroform solution, the kinetic compounds
rearrange into the thermodynamically more stable isomers in about 3 or 4 days. The higher stability of the thermodynamic species
was evaluated by means of computational studies in accordance with the maximum hardness principle. Finally, the crystal structures
of [(η3-allyl)Pd]2(μ-diethyldithiooxamidate k-N,S Pd, k-N0,S0 Pd0), [(η3-allyl)Pd]2(μ-meso-(1-phenyl)ethyldithiooxamidate k-N,
S Pd, k-N0,S0 Pd0), and [(η3-allyl)Pd]2(μ-rac-(1-phenyl)ethyldithiooxamidate k-N,N0 Pd, k-S,S0 Pd0) are reported.
’ INTRODUCTION
k-N,S binucleation mode if the amidic nitrogen atoms bear
secondary carbon atoms (ꢀCH2R) as substituents.9 Further-
more, it has been demonstrated that the hardness or softness of
the metal fragments in a heterobimetallic complex produces
specific interactions with the sulfur or nitrogen chelating system
of the binucleating DTO.10 Moreover, it has been observed that
the steric hindrance of the ancillary ligands in a given metal
fragment can also favor the formation of one of the two possible
linkage isomers of the k-N,N0 MLn k-S,S0 M0L0n bimetallic
complexes.11 Finally, it has been shown that the bulkiness of
nitrogen DTO substituents can direct the synthesis of homo-
bimetallic complexes in an “exo” k-N,S coordination mode
toward one of the two possible conformers.8
Secondary dithiooxamides (DTOs), HN(R)SCꢀCS(R)NH
(hereafter referred to as H2R2DTO), can behave as ditopic
ligands, which can bind two metal fragments in a variety of
coordination modes because of their different donor sites and
their freely rotating N(R)CS moieties.
The k-N,S MLn, k-N0,S0 M0L0n and k-S,S0 MLn, k-N,N0
M0L0n modes (A and B in Chart 1) have been extensively
investigated.1ꢀ6 However, even the less common “exo” k-N,S
MLn mode (C in Chart 1) has been suggested7 and recently well
documented.8
The different ways in which two metal fragments can be
connected depends on a delicate balance of the following steric
and electronic factors: (i) the nature of the alkyl substituents of
amidic nitrogen atoms in the ligand; (ii) the hardꢀsoft character
of both coordinated metals and ligand donor sites; (iii) the
nature of the ancillary ligands in the binucleated metal fragments.
Accordingly, it has been observed that DTO, if reacted with some
chloro-bridged dimers, forms homobimetallic complexes in a
The present paper explores the capability of a secondary DTO
to act as a binucleating ligand when the ancillary ligands in the
binucleated metal frames have modest steric crowding. The aim
Received: July 27, 2011
Published: October 18, 2011
r
2011 American Chemical Society
11653
dx.doi.org/10.1021/ic201616s Inorg. Chem. 2011, 50, 11653–11666
|

Inorganic Chemistry
ARTICLE
Chart 1. Coordination Modes of Dialkyldithiooxamidate as a Binucleating Ligand
is to achieve full control of the stereochemistry of the poly-
metallic systems built by means of multifunctional binucleating
ligands.
highest reasonable symmetry, and each stationary point was confirmed
to be a minimum on the potential energy surface by yielding zero
imaginary vibrational frequencies in the vibrational frequency analysis.
The geometries were constructed by GaussView 3.09, available from
Gaussian Inc. (Pittsburgh, PA),16 which was also used to produce
pictures of the orbitals. The best agreement with X-ray crystal structure
data was achieved using the PBE1PBE17,18 functional in conjunction
with the large 6-311++G(2df,2p) and full-relativistic effective core
potential aug-cc-pVTZ-PP19 basis set used for carbon, nitrogen, hydro-
gen, sulfur, and palladium.
’ EXPERIMENTAL PART
All chemicals were standard reagent grade and were used without
further purification. Column chromatography was conducted on alumi-
num oxide (activated, neutral, Brockman grade I).
1H and 13CNMR spectra were recorded at room temperature in
CDCl3, on a Bruker ARX 300 spectrometer at 300 and 75 MHz,
respectively, and on a VNMRS Varian Instruments spectrometer at
500 MHz, using the residual proton resonance of the solvent as the δ
reference.
General procedures for the preparation of homobinuclear com-
plexes [(η3-allyl)Pd]2(μ-RaRb-DTO j-N,S Pd, j-N0,S0 Pd0) [Ra = Rb
= methyl, 1; Ra = Rb = ethyl, 2; Ra = Rb = isopropyl, 3; Ra = Rb =
benzyl, 4; Ra = Rb = isoamyl, 5; Ra = Rb = 1-(S)-(1-phenyl)ethyl, 6;
Ra = 1-(S)-(1-phenyl)ethyl; Rb = 1-(R)-(1-phenyl)ethyl, 7]:
A total of 1 mmol (365 mg) of [(η3-allyl)PdCl]2 was dissolved in
chloroform (100 mL) and then reacted with 2 mol equiv of the selected
H2R2DTO species. The solution turned orange and was left to stand for
1/2 h at room temperature. After the addition under stirring of 2 g of
sodium bicarbonate, the solution turned bright yellow. After filtration of
bicarbonate, the yellowfiltrate, whichcontained[(η3-allyl)Pd(H-R2-DTO
k-S,S Pd)], was reacted with 1 mmol (365 mg) of [(η3-allyl)PdCl]2.
The mixture was refluxed for 24 h at 50 °C, the solvent was removed, and
the crude product was redissolved in a minimum amount of chloroform
and loaded on an alumina column equilibrated with petroleum ether.
Elution with a petroleum ether/chloroform mixture (90:10) gave a
yellow fraction from which the homobimetallic [(η3-allyl)Pd]2(μ-R2-
DTO k-N,S Pd, k-N0,S0 Pd0] was crystallized.
[(η3-Allyl)Pd(HR2-DTO k-S,S Pd)] was prepared following a re-
ported procedure.11 Secondary DTOs, H2R2DTO [R = methyl, ethyl,
isopropyl, benzyl, isoamyl, 1- (S)-(1-phenyl)ethyl, and meso/rac-
(1-phenyl)ethyl], were prepared according to literature methods.12
The meso-DTO H-(R)-1-(1-phenyl)ethyl)NSCꢀCSN-(S)-1-(1-phenyl)-
ethyl)-H was obtained by fractional crystallization from ethanol and an
equimolar mixture of meso- and rac-(1-phenyl)ethyldithiooxamide ob-
tained from rac-(1-phenyl)ethylamine. [(η3-Allyl)PdCl]2 is a commer-
cial product (Aldrich).
X-ray structure determination of [(η3-allyl)Pd]2(μ-diisoamyl-DTO
k-N,S Pd, k-N0,S0 Pd0), [(η3-allyl)Pd]2(μ-meso-(1-phenyl)ethyl-DTO
k-N,S Pd, k-N0,S0 Pd0) (meso-(1-phenyl)ethyl-DTO = [(R)-1-(1-phenyl)-
ethyl)-NSCꢀCSN-(S)-1-(1-phenyl)ethyl)]2ꢀ) and [(η3-allyl)Pd]2(μ-rac-
(1-phenyl)ethyl-DTO k-N,N0 Pd, k-S,S0 Pd0) (rac-(1-phenyl)ethyl-DTO =
[(1-(R)-(1-phenyl)ethyl)-NSCꢀCSN-(1-(R)-(1-phenyl)ethyl)]2ꢀ
/
)
[(η3-Allyl)Pd]2[μ-(methyl)2-DTO j-N,S Pd, j-N0,S0 Pd0] (1).
[(1-(S)-(1-phenyl)ethyl)-NSCꢀCSN-(1-(S)-(1-phenyl)ethyl)]2ꢀ
Yield: 0.37 g (41.7%). 1H NMR (300 MHz, CDCl3): δ 5.46 (m, 2H, allyl
(50:50) was done.
CH2 CH CH2), 4.03 and 3.57 (2d, 4H, allyl CHHsynCHCHHsyn, Jsyn
=
Yellow/orange crystals of suitable quality for X-ray analysis were
selected from those crystallized from a chloroform/petroleum ether
solution of each of the above three complexes.
7.2 Hz), 3.79 (s, 6H, NCH3), 3.41 and 2.64 (2d, 4H, allyl CHHanti
CHCHHanti, Janti = 12.6 Hz). 13C NMR (75 MHz, CDCl3): δ 115.00
(allyl CH2 CHCH2), 69.54 and 58.20 (allyl CH2CHCH2), 50.7
(NCH3). Anal. Calcd for C10H16N2S2Pd2: C, 27.22; H, 3.66; N, 6.35.
Found: C, 27.41; H, 3.74; N, 6.49.
Data were collected at room temperature with a Bruker APEX II CCD
area-detector diffractometer using Mo Kα radiation (λ = 0.710 73 A).
Data collection, cell refinement, data reduction, and absorption correc-
tion were performed using multiscan methods with Bruker software.13
The structures were solved by direct methods using SIR2004.14
The non-hydrogen atoms were refined anisotropically by the full-
matrix least-squares method on F2 using SHELXL.15 All of the hydrogen
atoms were placed at calculated positions and constrained to ride on
their parent atoms. Molecular structures are shown in Figures 6ꢀ8.
Computational Study. All calculations were performed with the
Gaussian 03 suite of programs.16 Geometry optimizations and harmonic
frequencies for the complexes were calculated with density functional
theory using the PBE1PBE functional with different basis sets for the
idealized C2 and Cs symmetries. The geometries were restricted to the
[(η3-Allyl)Pd]2[μ-(ethyl)2-DTO j-N0,S0 Pd j-N,S Pd0] (2).
1
Yield: 0.43 g (45.6%). H NMR (300 MHz, CDCl3): δ 5.44 (2 m,
2H, allyl CH2CHCH2), 4.17 (m, 4H, NCH2CH3), 4.00 and 3.55 (2d,
4H, allyl CHHsynCHCHHsyn, Jsyn = 7.2 Hz), 3.36 and 2.63 (2d, 4H, allyl
CHHantiCHCHHanti, Janti = 14.2 Hz), 1.29 (t, 6H, NCH2CH3, 3JHꢀH
=
6.8 Hz). 13C NMR (75 MHz, CDCl3): δ 114.5 (allyl CH2CHCH2), 68.6
and 56.24 (allyl CH2CHCH2), 49.78 (NCH2CH3). 20.50 (NCH2CH3).
Anal. Calcd for C12H20N2S2Pd2: C, 30.71; H, 4.30; N, 5.97. Found: C,
30.68; H, 4.36; N, 6.08.
[(η3-Allyl)Pd]2[μ-(isopropyl)2-DTO j-N,S Pd, j-N0,S0 Pd0]
(3). Yield: 0.40 g (40.0%). 1H NMR (300 MHz, CDCl3): δ 5.32
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dx.doi.org/10.1021/ic201616s |Inorg. Chem. 2011, 50, 11653–11666

Inorganic Chemistry
ARTICLE
(m, 2H, allyl CH2CHCH2), 4.94 (sl, 2H, NCH(CH3), 3JHꢀH = 6.3 Hz),
4.42 and 4.16 (2d, 4H, allyl CHHsynCHCHHsyn, Jsyn = 6.6 Hz), 2.94 and
2.91 (2d, 4H, allyl CHHantiCHCHHanti, Janti = 12.2 Hz), 1.20 and 1.10
(2d, 12H, NCH(CH3), 3JHꢀH = 6.3 Hz). 13C NMR (75 MHz, CDCl3):
δ 112.36 (allyl CH2CHCH2), 67.81 and 57.43 (allyl CH2CHCH2),
50.60 (NCH(CH3)2), 22.26 and 21.71 (NCH(CH3)2. Anal. Calcd for
C14H24N2S2Pd2: C, 33.81; H, 4.86; N, 5.63. Found: C, 33.92; H, 4.93;
N, 5.70.
alumina column equilibrated with petroleum ether. Two yellow fractions
were collected. The first one of lighter color was discarded while the
other was collected which, upon crystallization, gave [(η3-allyl)Pd]2(μ-
RaRb-DTO k-N,N0 Pd, k-S,S0 Pd0) complexes as yellow microcrystals.
[η3-Allyl)Pd]2[μ-(methyl)2-DTO j-N,N0 Pd, j-S,S0 Pd0] (8).
1
Yield: 0.41 g (46.2%). H NMR (300 MHz, CDCl3): δ 5.55 and 5.29
(2m, 2H, allyl CH2CHCH2), 4.02 and 3.57 (2d, 4H, allyl CHHsynCH-
CHHsyn, Jsyn = 7.2 Hz), 3.60 (s, 6H, NCH3), 3.00 and 2.95 (2d, 4H,
CHHantiCHCHHanti, Janti = 12.6 Hz). 13C NMR (75 MHz, CDCl3): δ
116.5 and 113.3 (allyl CH2CHCH2), 71.15 and 58.2 (allyl CH2CHCH2),
48.00 (NCH3). Anal. Calcd for C10H16N2S2Pd2: C, 27.22; H, 3.66; N,
6.35. Found: C, 27.53; H, 3.58; N, 6.42.
[(η3-Allyl)Pd]2[μ-(benzyl)2-DTO j-N,S Pd, j-N0,S0 Pd0] (4).
Yield: 0.46 g (38.6%). 1H NMR (300 MHz, CDCl3): δ 7.38ꢀ7.21 (10H,
2
NCH2C6H6), 5.46 (AB spin system, 4H, NCH2C6H6, JHꢀH = 14.2
Hz), 5.17 (m, 2H, allyl CH2CHCH2), 5.73 and 3.52 (2d, 4H,
CHHsynCHCHHsyn, Jsyn = 7.97 Hz), 2.85 and 2.53 (2d, 4H, CHHanti
CHCHHanti, Janti = 12.82 Hz). 13C NMR (75 MHz, CDCl3): δ 138.0,
128.4, 127.7, 127.4, 126.9 (NCH2C6H5), 114.17 (allyl CH2CHCH2),
69.15 and 67.12 (allyl CH2CHCH2), 64.24 (ꢀNCH2ꢀ). Anal. Calcd for
C22H24N2S2Pd2: C, 44.53; H, 4.08; N, 4.72. Found: C, 44.61; H, 4.18;
N, 4.76.
[η3-Allyl)Pd]2[μ-(ethyl)2-DTO j-N,N0 Pd, j-S,S0 Pd0] (9).
1
Yield: 0.38 g (40.3%). H NMR (300 MHz, CDCl3): δ 5.50 and 5.29
(2m, 2H, allyl CH2CHCH2), 4.00 and 3.60 (2d, 4H, CHHsynCHCHHsyn
,
Jsyn = 7.2 Hz), 3.98 (m, 4H, NCH2CH3), 2.99 and 2.93 (2d, 4H,
3
CHHantiCHCHHanti, Janti = 14.2 Hz), 1.26 (t, 6H, NCH2CH3, JHꢀH
=
6.8 Hz). 13C NMR (75 MHz, CDCl3): δ 115.45 and 113.21 (allyl
CH2CHCH2), 61.06 and 57.48 (allyl CH2CHCH2), 53.90 (NCH2ꢀ),
13.89 (NCH2CH3). Anal. Calcd for C12H20N2S2Pd2: C, 30.71; H, 4.30; N,
5.97. Found: C, 30.86; H, 4.32; N, 6.02.
[(η3-Allyl)Pd]2[μ-(isoamyl)2-DTO j-N,S Pd, j-N0,S0 Pd0] (5).
Yield: 0.49 g (44.1%). 1H NMR (300 MHz, CDCl3): δ 5.54 (m, 2H, allyl
CH2CHCH2), 4.13 (m, ABX2 spin system, 4H, NCH2CH2CH(CH3)2,
3.92 and 3.55 (2d, 4H, allyl CHHsynCHCHHsyn, Jsyn = 7.7 Hz), 3.34 and
2.61 (2d, 4H, CHHantiCHCHHanti, Janti = 12.6 Hz), 1.72 and 1.64 (2 m,
6H, NCH2CH2CH(CH3)2, 0.99 (d, 12H, NCH2CH2CH(CH3)2,
3JHꢀH = 6.6 Hz). 13C{1H} NMR (75 MHz, CDCl3): δ 114.44 (allyl
CH2CHCH2), 68.70 and 49.67 (allyl CH2CHCH2), 60.52 (NCH2CH2-
CH(CH3)2), 36.47 (NCH2CH2CH(CH3)2), 26.80 (NCH2CH2CH-
(CH3)2), 22.86 and 22.79 (NCH2CH2CH(CH3)2) Anal. Calcd for
C16H28N2S2Pd2: C, 36.58; H, 5.37; N, 5.33. Found: C, 36.69; H, 5.32;
N, 5.24.
[η3-Allyl)Pd]2[μ-(isopropyl)2-DTO j-N,N0 Pd, j-S,S0 Pd0]
1
(10). Yield: 0.33 g (29.7%). H NMR (300 MHz, CDCl3): δ 5.32
and 5.29 (2d, 2H, allyl CH2CHCH2), 4.91 (sl, 2H, NCH(CH3)2, 3JHꢀH
=
6.3 Hz), 4.15 and 3.97 (2m, 4H, CHHsynCHCHHsyn, Jsyn = 7.2 Hz),
2.94 and 2.91 (2d, 4H, CHHantiCHCHHanti, Janti = 12.2 Hz), 1.20 and
1.10 (2d, 12H, NCH(CH3)3, JHꢀH = 6.3 Hz). 13C NMR (75 MHz,
3
CDCl3): δ 113.45 and 111.61 (allyl CH2CHCH2), 60.83 and 57.57
(allyl CH2CHCH2), 55.73 (NCH(CH3)2), 22.21 and 21.96 (NCH-
(CH3)2). Anal. Calcd for C14H24N2S2Pd2: C, 33.81; H, 4.86; N, 5.63.
Found: C, 33.72; H, 5.01; N, 5.68.
[(η3-allyl)Pd]2(μ-((S)-1-(1-phenyl)ethyl))2-DTO k-N,S Pd,
[η3-Allyl)Pd]2[μ-(benzyl)2-DTO j-N,N0 Pd, j-S,S0 Pd0] (11).
1
k-N0,S0 Pd0) (6): Yield: 0.28 gr (22.4%). H NMR (300 MHz,
1
Yield: 0.37 gr (31.0%). H NMR (300 MHz, CDCl3): δ 7.34ꢀ7.17
CDCl3), δ (ppm): 7.44- 7.22 (10H, NꢀCH(CH3)-C6H6), 6.18 (m, 2H,
NꢀCH(CH3)-C6H6), 5.14, 5.13, 4.74, and 4.72 (4 m, 2H, Allyl CH2 CH
CH2), 3.67, 3.67, 3.49, 3.48, 3.46, 3.45, 3.05, and 3.05 ppm (8d, 4H, Allyl
CHHsyn-CHꢀCHHsyn, Jsyn= 7.1 Hz), 2.87, 2.87, 2.47, 2.47, 2.41, 2.40,
1.83, and 1.82 ppm (8d, 4H, Allyl CHHanti-CHꢀCHHanti, Janti= 12.6
Hz). 1.71, 1.69, 1.63, and 1.61 ppm (4d, 6H, NꢀCH(CH3)-C6H6,
3JHꢀH= 6.6 Hz). 13C NMR (75 MHz, CDCl3), δ (ppm): 163.60, 143.30,
128.10, 128.00, 126.80, 126.70, 126.60 (NꢀCH(CH3)-C6H5), 112.70,
112.10 (Allyl CH2-CHꢀCH2), 68.40, 68.26, 62.30 (Allyl CH2ꢀCH-
CH2), 50.90, 50.30 (N-CH(CH3)-C6H5), 18.00, 17.60 (NꢀCH(CH3)-
C6H5). Anal. Calcd for C24H28N2S2Pd2: C 46.38, H 4.54, N 4.51;
Found: C 46.19, H 4.44, N 4.39.
(10H, NCH2C6H6), 5.26 and 4.92 (2m, 2H, allyl CH2CHCH2), 5.23
and 5.22 (two AB spin systems, 4H, NCH2ꢀ), 3.99 and 2.98 (2d, 4H,
CHHsynCHCHHsyn, Jsyn = 7.00 Hz), 2.92 and 2.26 (2d, 4H, CHHanti
CHCHHanti, Janti = 12.82 Hz). 13C NMR (300 MHz, CDCl3): δ 138.6,
128. 4, 127.1, 126.7 (NCH2C6H5), 114.5 and 113.7 (allyl CH2CHCH2),
68.25 and 64.17 (allyl CH2CHCH2), 62.14 (NCH2ꢀ). Anal. Calcd for
C22H24N2S2Pd2: C, 44.53; H, 4.08; N, 4.72. Found: C, 44.31; H, 4.00;
N, 4.80.
[η3-Allyl)Pd]2[μ-(isoamyl)2-DTO j-N,N0 Pd, j-S,S0 Pd0] (12).
Yield: 0.48 gr (43.2%). 1H NMR (300 MHz, CDCl3): δ 5.50 and
5.28 (2m, 2H, allyl CH2CHCH2), 4.00 and 3.56 (2d, 4H, CHHsyn
-
[(η3-allyl)Pd]2(μ-(meso-(1-phenyl)ethyl)-DTO k-N,S Pd, k-
N0,S0 Pd0] (7): Yield: 0.25 gr (20.0%). 1H NMR and 13C NMR, spectra
identical to those of 6
Anal. Calcd for C24H28N2S2Pd2: C 46.38, H 4.54, N 4.51; Found: C
46.30, H 4.35, N 4.39.
General procedures for the preparation of homobinuclear com-
plexes [(η3-allyl)Pd]2(μ-RaRb-DTO j-N,N0 Pd, j-S,S0 Pd0) (Ra=Rb =
Methyl, 8; Ra=Rb = Ethyl, 9; Ra=Rb = Isopropyl, 10; Ra=Rb = Benzyl,
11; Ra=Rb = isoamyl, 12; Ra=Rb = 1-(S)-(1-phenyl)ethyl, 13; Ra=
1-(S)-(1-phenyl)ethyl, Rb= 1-(R)-(1-phenyl)ethyl, 14.; Ra=Rb = (1-
(S)-1-phenyl)ethyl/(1-(R)-1-phenyl)ethyl (50:50); 15:
CHCHHsyn, Jsyn = 7.1 Hz), 3.93 (m, ABX2 spin system, 4H, NCH2CH2-
CH(CH3)2, 2.97 and 2.92 (2d, 4H, CHHantiCHCHHanti, Janti = 12.6 Hz),
1.70 and 1.56 (2m, 6H, NCH2CH2CH(CH3)2, 0.97 (d, 12H, NCH2-
CH2CH(CH3)2, 3JHꢀH = 6.6 Hz). 13C NMR (75 MHz, CDCl3): δ 115.4
and 113.2 (allyl CH2CHCH2), 61.00 and 57.6 (allyl CH2CHCH2), 58.1
(NCH2CH2CH(CH3)2), 36.7 (NCH2CH2CH(CH3)2), 26.7 (NCH2CH2-
CH(CH3)2), 22.78 and 22.68 (NCH2CH2CH(CH3)2). Anal. Calcd for
C16H28N2S2Pd2: C, 36.58; H, 5.37; N, 5.33. Found: C, 36.61; H, 5.32;
N, 5.39.
[(η3-Allyl)Pd]2[μ-[(S)-1-(1-phenyl)ethyl]]2-DTO k-N,N0 Pd,
k-S,S0 Pd0] (13). Yield: 0.23 gr (18.4%). 1H NMR (300 MHz, CDCl3):
δ 7.42ꢀ7.21 (10H, NCH(CH3)C6H6), 6.10 (m, 2H, NCH(CH3)-
C6H6), 5.34 and 4.55 (2m, 2H, allyl CH2CHCH2), 4.04 (d, 2H,
CHHsynCHCHHsyn, near to sulfur atoms, Jsyn = 6.8 Hz), 3.17 and 2.54
(2d, 2H, CHCHsynCHCHCHsyn, near to nitrogen atoms, Jsyn = 6.8 Hz),
2.97 (d, 2H, CHHantiCHCHHanti, near to sulfur atoms, Janti = 12.6 Hz),
2.30 and 1.36 (2d, 2H, CHHantiCHCHHanti, near to nitrogen atoms,
[(η3-allyl)PdCl]2 (1 mmol, 365 mg) was dissolved in chloroform
(100 mL) and two molar equivalents of the desired H2R2DTO species.
The solution turned orange and was left to stand at room temperature
for 1/2 h. On addition, under stirring, of 2 g of sodium bicarbonate, the
solution turned bright yellow. After filtration of the bicarbonate, the
yellow filtrate, which contained [(η3-allyl)Pd(H-R2-DTO k-S,S Pd)],
was reacted with [(η3-allyl)PdCl]2 (1 mmol, 365 mg) at room tem-
perature for 1/2 h. The solvent was then removed and the crude product
was redissolved in the minimum amount of chloroform and loaded on an
Janti = 12.6 Hz). 1.66, 1.65, 1.57, 1.56 (4d, 6H, NCH(CH3)C6H6, 3JHꢀH
=
6.6 Hz). 13C NMR (75 MHz, CDCl3): δ 143.8, 128.09, 126.76, 126.70,
126.50 (NCH(CH3)C6H5), 113.58, 111.65 (allyl CH2CHCH2), 61.57,
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Scheme 1. Synthesis of [(η3-Allyl)Pd]2(μ-dialkyldithiooxamidate j-N,S Pd, j-N0,S0 Pd0) Complexes
Chart 2. Stereomers of [(η3-Allyl)Pd]2(μ-dialkyldithiooxa-
midate k-N,S Pd, k-N0,S0 Pd0) with Their Stereochemical
Descriptors
The structural assignment is based on the 1H NMR spectra of
the new homobimetallic complexes, which are consistent with C2
or Ci symmetry. In fact, the two allylpalladium frames connected
as indicated above can point with the allyl cuspids either to the
same or to opposite sides of the mean plane of the molecule.
These stereochemistries provide the bimetallic complex having
Ci symmetry (exo isomer) and that having C2 symmetry (endo
isomer). The latter is chiral and, as such, should exist in solution
as a racemate (Chart 2).
The stereochemistry of the above compounds can be properly
described by taking into account that an allylpalladiun frame
linked to two different donor atoms defines a chiral plane. This
chiral plane can be termed by means of A,C descriptors, which
can easily be deduced by viewing the molecule from the central
allyl carbon toward palladium.2,11 In such a view, the other two
atoms coordinated to the metal, sulfur and nitrogen, follow a
clockwise direction based on decreasing CIP priority in C,
whereas these atoms follow the anticlockwise direction in A.
The chirality in allylpalladium complexes has been envisaged by
other authors as a central chirality and, as such, has been
indicated by means of R,S descriptors.20 Regardless of the
nomenclature, each enantiomer of endo isomers has its palla-
dium centers in the same configuration, while the exo isomer is a
meso form in which the palladium centers have opposite
configurations.
61.26, 58.10, 57.70 (allyl CH2CHCH2), 59.90 (NCH(CH3)C6H5),
18.75 and 17.47 (NCH(CH3)C6H5). Anal. Calcd for C24H28N2S2Pd2:
C, 46.38; H, 4.54; N, 4.51. Found: C, 46.39; H, 4.49; N, 4.63.
[(η3-Allyl)Pd]2[μ-[meso-(1-phenyl)ethyl]-DTO k-N,N0 Pd,
k-S,S0 Pd0] (14). Yield: 0.27 gr (21.6%). 1H NMR (300 MHz, CDCl3):
δ 7.35ꢀ7.13 (10H, NCH(CH3)C6H6), 6.03 (m, 2H, NCH(CH3)-
C6H6), 5.30, 4.46, 4.20 (m, 2H, allyl CH2CHCH2), 4.06, 4.00, 4.00, 3.98,
3.13, 3.13, 2.49, 2.48 (8d, 4H, CHHsynCHCHHsyn, Jsyn = 7.1 Hz), 2.94,
2.94, 2.94, 2.92, 2.32, 2.32, 2.19, 2.18 (8d, 4H, CHHantiCHCHHanti, Janti
1H NMR spectra of [(η3-allyl)palladium)2(μ-R2DTO k-N,S
Pd, k-N0,S0 Pd0)] bimetallic compounds (R = methyl, 1; ethyl, 2;
isopropyl, 3; benzyl, 4; isoamyl, 5) show only one set of signals,
i.e., a multiplet for the central allyl proton, two doublets
for ꢀCHHsynꢀ and two doublets for ꢀCHHantiꢀ allyl protons, and
the expected resonances for the given alkyl group. These are the
spectral feature that can be expected for a bimetallic compound
having C2 or Ci symmetry.
When two allylpalladium moieties are bridged by symmetrical
binucleating ligands21 and the motion of the allyl unit is slow on
the NMR time scale, both endo and exo isomers can be observed.
We can be confident that both isomers can exist in solution at
room temperature because NCH2ꢀ protons in ethyl, isoamyl,
and benzyl groups appear as ABX3, ABX2, and AB spin systems,
respectively. Furthermore, resonances of the geminal methyl
units in isopropyl and isoamyl groups are split, meaning that a
fast allyl pseudorotation can reasonably be ruled out. For this
reason, we found it surprising that diastereomers like those
depicted in Chart 1 could show coincident NMR resonances.
We therefore attempted to detect both C2- and Ci- symmetrical
isomers in solution by using chiral auxiliaries as substituents of
the binucleating DTO. We prepared the binuclear complexes
[(η3-allyl)palladium)2[μ-[1-(S)-(1-phenylethyl]]2DTO k-N,S
Pd, k-N0,S0 Pd0)] (6) and [(η3-allyl)palladium)2[μ-[meso-
[(1-phenyl)ethyl]2DTO k-N,S Pd, k-N0,S0 Pd0)] (7) following
the above-reported synthetic procedure using the chiral N,N-
bis[1-(S)-(1-phenylethyl)]dithiooxamide and the corresponding
= 12.5 Hz). 1.61, 1.60, 1.50, 1.49 (4d, 6H, NCH(CH3)C6H6, 3JHꢀH
=
6.4 Hz). 13C NMR (75 MHz, CDCl3): δ 143.60, 143.40, 128.50, 128.00,
126.80, 126.70, 126.60, 126.50 (NCH(CH3)C6H5), 113.60, 112.10,
111.10 (allyl CH2CHCH2), 61.50, 61.30, 60.00 (allyl CH2CHCH2),
57.85, 57.80 (NCH(CH3)C6H5), 18.05, 18.03, 17.12, 17.10 (NCH-
(CH3)C6H5). Anal. Calcd for C24H28N2S2Pd2: C, 46.38; H, 4.54; N,
4.51. Found: C, 46.41; H, 4.57; N, 4.55.
[(η3-Allyl)Pd]2[μ-(rac-(1-phenyl)ethyl-DTO k-N,N0 Pd, k-S,
S0 Pd0] (15). This compound was prepared exclusively for the purpose
of growing X-ray-quality crystals. Its NMR spectra were identical with
those of 13. The yield and other analytical data were not determined.
’ RESULTS AND DISCUSSION
j-N,S Pd, j-N0,S0 Pd0 Coordination Mode. The reaction of
[(η3-allyl)palladium(HR2DTO k-S,S Pd)] (HR2DTO = N,N-
dialkyldithiooxamidate; R = methyl, 1; ethyl, 2; isopropyl, 3;
benzyl, 4; isoamyl, 5) with [(η3-allyl)PdCl]2 in a 2:1 ratio,
performed in chloroform at 45 °C in 24 h, gave dimers in which
two allylpalladium fragments are connected by a binucleating
dithiooxamidate frame R2DTO2‑ in an N,S coordination mode
[(η3-allyl)palladium)2(μ-R2DTO k-N,S Pd, k-N0,S0 Pd0)]
(Scheme 1).
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Figure 1. 1H NMR spectrum of 6. The spectrum of 7 is identical.
Chart 3. Stereomers of [(η3-Allyl)Pd]2[μ-[1-(S)-(1-pheny-
lethyl)]2dithiooxamidate k-N,S Pd, k-N0,S0 Pd0] with Their
Stereochemical Descriptors
achiral meso form N-[1-(S)-1-phenylethyl)]-N0-[1-(R)-1-phe-
nylethyl)]dithiooxamide, respectively.
Both syntheses gave two isomeric mixtures that show identical
NMR spectra where 2:4:2 allyl ꢀCHHsyn doublets, 2:2:1:1:1:1
allyl CHHanti doublets, and four equally intense NCH(CH3)-
C6H5 doublets are easily detectable (Figure 1).
The observed spectra account for both chiral (6) and achiral
(7) diastereomers.
Indeed, [(η3-allyl)palladium)2[μ-[1-(S)-(1-phenylethyl)]2D-
TO k-N,S Pd, k-N0,S0 Pd0)] may exist as the isomeric mixture
shown in Chart 3.
The above chart depicts three diastereomers, labeled AS,AS,
CS,CS, and AS,CS. In AS,AS and CS,CS, a C2 axis connects the
two (η3-ally)Pd(RNSC)ꢀ fragments; hence, each of them
1
shows only one group of signals in the H NMR, i.e., two
doublets (syn protons), two doublets (anti protons), and last
one doublet (methyl groups). In contrast, in the AS,CS stereo-
mer, the (allyl)Pd(RNSC)ꢀ halves are diastereotopic; hence,
1
each half of the molecule has its own set of signals. In the H
NMR spectrum, the four groups of signals have the same
intensity, indicating that the three isomers have formed with
the expected statistical ratio (25, 25, and 50%).
CR,AS and CS,AR are two Ci-symmetrical meso forms; each one
is constituted by enantiotopic halves rotated 180° with respect to
the inversion center. Clearly, the stereochemistry of the above
compounds arises from the two different ways in which two
enantiomorphic carbon atoms can be placed with respect to the
enantiotopic half-spaces; according to Prelog and Helmchen, this
is pseudoasymmetry.22,23 We already pointed out that pseudoa-
symmetry should be viewed as an important issue in inorganic
As stated above, [(η3-allyl)Pd]2[μ-(meso-(1-phenyl)ethyl]2-
1
DTO k-N,S Pd, k-N0,S0 Pd0] also shows the same H NMR
spectrum of the corresponding chiral compound. Despite
their very close similarity, the two spectra have a different
stereochemical meaning. In fact, the above symmetric meso
compound is a mixture of the isomers: indicated in Chart 4,
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stereochemistry because the great variety of coordination geo-
metries can supply a number of compounds constituted by
enantiotopic halves.11
CR,AS and CS,AR isomers are a new variety of inorganic
pseudochiral compounds. In fact, pseudoasymmetry, observed in
Cs-symmetric metal complexes sporadically,9,11,24,25 is here re-
ported for the first time in a Ci-symmetric organometallic
molecule. The remaining pair of isomers, AR,AS and CR,CS,
constitute an enantiomeric pair.
The 1H NMR spectrum of [(η3-allyl)Pd]2[μ-[meso-(1-phenyl)-
ethyl]2-DTO k-N,S Pd, k-N0,S0 Pd0] features well the isomeric
mixture described above. In fact, each pseudochiral isomer shows
its own set of signals, while the AR,AS/CR,CS pair has two sets of
signals because each enantiomer is constituted by diastereotopic
halves. The four sets of signals in the meso compounds also show
the same intensity with respect to one another because each
isomer exists in solution in the expected statistical ratio, i.e., 25%
(AR,CS), 25% (AS,CR), and 50% (AR,AS/CR,CS).
Chart 4. Stereomers of [(η3-Allyl)Pd]2[μ-meso-(1-phenyl)-
ethyldithiooxamidate k-N,S Pd, k-N0,S0 Pd0] with Their
Stereochemical Descriptors
Bidimensional NOESY spectra of both [(η3-allyl)palladium)2-
(μ-meso-phenylethyl)2DTO k-N,S Pd, k-N0,S0 Pd0)] and[(η3-allyl)-
palladium)2[1-(S)(1-phenylethyl)]2DTO k-N,S Pd, k-N0,S0
Pd0)] are identical (Figure 2). In particular, in both spectra,
there are opposite phase cross peaks between allyl and the DTO
resonances of the various diastereomers of which homobimetallic
complexes are made.
As for the allyl resonances, synꢀsyn and antiꢀanti exchanges
were observed. This clearly indicates that allyl pseudorotation
occurs in solution, which changes the diastereomers into one
another. The observed exchanges are consistent with a mecha-
nism that involves dissociation of the PdꢀN bond. We previously
proposed a similar mechanism for other binuclear and trinuclear
metal complexes containing a palladium allyl moiety linked to a
Figure 2. Bidimensional EXSY spectrum of 6. Exchange cross peaks are indicated by arrows. The spectrum of 7 is identical.
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Scheme 2. Hybrid Binucleating Ligand Containing Two
Chemically Different Donor Functions
Scheme 3. Proposed Mechanism for Apparent Allyl Rotation
in [(η3-Allyl)Pd]2(μ-dialkyldithiooxamidate j-N,S Pd, j-N0,
S0 Pd0)
nitrogen chelating system.2,3 This happens because a hard
ligandꢀsoft metal interaction is produced when an allyl fragment
is bound by means of a homofunctional N^N-chelating system.
Such an unfavourable interaction allows the PdꢀN bond to
break, and this is the first step of the proposed allyl pseudorota-
tion mechanism. At the same time, we were able to demonstrate
that allyl pseudorotation is not observed when an allylpalladium
frame is linked to a sulfur-chelating system.2 Afterall, when a
(η3-allyl)palladium frame is bound to a homofunctional S^S
chelating system (i.e., a soft donor system bound to a soft metal),
the resulting soft ligandꢀsoft metal strong interaction does not
allow the PdꢀS bond to break, and as a result, allyl pseudorota-
tion is not observed.
In the above homobimetallic complexes, two allylpalladium
fragments are joined to each other by a secondary DTO in an N,S
coordination mode. When linked in such a way, the binucleating
DTO behaves as a double-hybrid ligand.
A hybrid ligand is a polydentate ligand that contains at least
two different types of chemical functionalities capable of binding
to metal centers (Scheme 2). Although it may be considered as
being derived from a pair of homofunctional ligands, its proper-
ties are new compared to either of its parent compounds.26 Such
ligands, either chelating or binucleating, can be represented by
the formalism proposed by Braunstein.27
Hybrid ligands are closely linked to the concept of hemil-
ability, which refers to systems containing at least one substitu-
tionally labile donor function Z while the other donor group D
remains firmly bound to the metal. The term “hemilabile” was
first used to indicate phosphineꢀamine and phosphineꢀether
ligands, which would bind a given metal but would readily
dissociate the “hard” ligand component.28 However, the phe-
nomenon itself had been observed earlier.29
present report shows the allyl isomerization process in two
allylpalladium moieties binucleated by coupled hemilabile N^S
pairs; in both (η3-allyl)Pd(N^S)ꢀ fragments, the allyl motion
seems to take place through the k1 form of the hemilabile
N^S-chelating system.38
j-N,N0 Pd, j-S,S0 Pd0 Coordination Mode. By reacting
[(η3-allyl)palladium(HR2DTO k-S,S Pd)] (HR2DTOꢀ = N,N-
dialkyldithiooxamidate; R = methyl, 8; ethyl, 9; isopropyl, 10;
benzyl, 11; isoamyl, 12) with [(η3-allyl)PdCl]2 in a 2:1 ratio, in
chloroform at 20 °C for 1/2 h, the following process takes place:
the binuclear complexes [(η3-allyl)Pd]2(μ-R2DTO k-N,N0 Pd,
k-S,S0 Pd0] (R = methyl, 8; ethyl, 9; isopropyl, 10; benzyl, 11;
isoamyl, 12) are formed in moderate yield (Scheme 4).
1H NMR spectra of complexes 8ꢀ12 show two distinct allyl
systems, each constituted by three physically associated signals
(NOE cross peak in the bidimensional spectra), i.e., a complex
3
Thus, a DTO frame linked to two allylpalladium moieties in an
N,S coordination mode undergoes dissociation of one hard ligand
component, i.e., the amidic nitrogen (step a in Scheme 3); then a
rotation around the PdꢀS bond takes place (step b); after that,
isomerization of the T-shaped intermediate occurs (step c),
followed by the remaking of the PdꢀN bond (step d).
multiplet (central CH), a lower J doublet (CHHsyn), and a
higher 3J doublet (CHHanti). Obviously, one of the two allyl spin
systems refers to the (η3-C6H5)Pd(N^N)ꢀ fragment, the other
to the (η3-C6H5)Pd(S^S)ꢀ group. Alkyl resonances also appear
as a single group of signals because of the Cs symmetry of the new
complexes.
Isomerization processes of allylpalladium mononuclear com-
plexes bearing P^N,20b,30ꢀ32 C^N,33 P^PS,20a,34 P^PO,35 N^S,36
and N^O37 hemilabile ligands have been widely studied. The
Two stereomers having Cs symmetry could account for the
observed NMR spectra; one of these has both allyl cuspids
directed toward the same side of the molecular plane (endo in
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Scheme 4. Synthesis of [(η3-Allyl)Pd]2(μ-dialkyldithiooxamidate j-S,S0 Pd j-N,N0 Pd0) Complexes
Chart 5. Stereomers of [(η3-Allyl)Pd]2(μ-dialkyldithiooxa-
midate k-N,N0 Pd, k-S,S0 Pd0) Species
intense doublets due to the syn protons (clearly distinguishable
although very close to one another), and two doublets due to the
anti protons (3:1 intensity); the other is made of two central allyl
CH multiplets, three 2:1:1 (syn protons), and three 2:1:1
doublets (anti protons) and refers to the (η3-C3H5)Pd(N^N)ꢀ
fragment. Finally, four equally intense doublets are observed for
the methyl protons of the phenylethyl groups. This spectrum is
consistent with the presence, in solution, of the four stereomers
of compound 14 (Chart 6).
Both endo and exo isomers have a Cs-symmetrical skeleton,
and therefore they are constituted by enantiotopic halves. In each
of these isomers, two enantiomorphic groups can be positioned
in two different ways, allowing two couples of diastereomeric
meso forms to be formed.
With regards to the stereochemical descriptors for such
stereomers, we suggest the terms endo/exo to indicate the
reciprocal position of the allyl cuspids (Chart 5). The above
endo and exo forms exist as two pseudochiral diastereomers that
can be termed according to the procedures proposed previously.11
Thus, the pseudochiral isomers c have the substituent 1-
(R)-(1-phenyl)ethyl on the left-hand side with respect to the
nearest allyl cuspid, while the corresponding a isomers have the
substituent 1-(R)-(1-phenyl)ethyl on the right-hand side with
respect to the same reference point.
Chart 5) and the other having allyl CH pointed toward opposite
sides of the said plane (exo in Chart 5) The geminal hydrogen
atoms in the methylene groups of 9, 11, and 12, as well as the
geminal methyl groups in 10, are diastereotopic. This means that
the allyl isomerization processes are of high energy, thus allowing
both isomers to exist in solution.
Bidimensional EXSY spectra of 13 show NOE cross peaks
between DTO hydrogen atoms and syn, but not anti, allyl
protons (Figure 3).
This allows the allyl protons near the nitrogen-chelating system
to be distinguished from those near the sulfur atoms. Analogous
selective NOEs for allyl derivatives have been reported by Pregosin
et al. and attributed to the CH syn twisting toward the metal out of
the allyl plane.39 Synꢀsyn and antiꢀanti exchange cross peaks were
not observed. However, this does not rule out the allyl pseudorota-
tion in the (η3-C6H5)Pd(N^N)ꢀ fragment; in fact, exchange cross
peaks between the syn and anti doublets cannot be observed
because the resonances of syn and anti protons are isochronous in
the two stereomers. The allyl pseudorotation in the (η3-C6H5)Pd-
(N^N)ꢀ fragment of 13 is, however, documented by the presence
of exchange cross peaks between the methyl doublets of the
phenylethyl substituents. This allyl rearrangement that intercon-
verts the two stereomeric forms of 13 arises from dissociation of a
PdꢀN bond in the (η3-C6H5)Pd(N^N)ꢀ fragment.
We found it surprising that diastereomers like those depicted
in Chart 5 could show coincident NMR resonances. We there-
fore attempted to detect the two Cs-symmetrical isomers using
chiral auxiliaries as substituents in the binucleating DTO.
We synthesized the binuclear complex [(η3-allyl)Pd]2-
[μ-[1-(S)-(1-phenylethyl)]2DTO k-N,N0 Pd, k-S,S0 Pd0] (13)
and [(η3-allyl)Pd]2[μ-(meso-(1-phenyl)ethyl]2-DTO k-N,N0
Pd, k-S,S0 Pd0] (14).
The 1H NMR spectrum of 13 shows two groups of signals; the
first, near the sulfur-chelating system, contains a multiplet
(central CH) and two doublets (syn and anti protons) in a
1:2:2 ratio. The other, near the nitrogen donor atoms, shows a
central CH multiplet, two doublets, and two CHHanti doublets in
a 1:1:1:1:1 ratio. Lastly, four equally intense doublets are due to
the methyl groups of the phenylethyl substituents.
The k1 form of the N^N donor system is not anticipated to
contribute in any way to endo/exo isomerization. Indeed, neither
in mononuclear [(η3-allyl)Pd(H-meso-(1-phenyl)ethyl-DTO k-
S,S Pd)]2 nor in binuclear [(2-phenylpyridine)Rh(μ-isoamyl-
DTO k-N,N Rh k-S,S Pd)Pd(η3-allyl)],10 which contain similar
k-S,S Pd systems, has allyl movement been observed.
The observed resonances are assigned to the two diastereo-
mers like those depicted in Chart 5 when R = 1-(S)-1-pheny-
lethyl; in the spectrum, the allyl resonances of the two stereomers
are isochronous, while syn and anti protons of the allyl system
near the nitrogen atoms appear as split doublets because of the
presence of two homochiral substituents opposite to each other
with respect to the symmetry plane of a Cs molecular skeleton.
The 1H NMR spectrum of 14 exhibits two groups of signals for
the allyl protons. The one that refers to the (η3-C3H5)Pd(S^S)ꢀ
fragment is constituted by a multiplet (central CH), four equally
Again in the EXSY spectrum of 14, NOE cross peaks allow the
allyl system signals near sulfur atoms to be groups and enable
them to be distinguished from the ones near the nitrogen-
chelating system (Figure 4).
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Chart 6. Stereomers of 14 with Their Stereochemical Descriptors
Figure 3. Bidimensional EXSY spectrum of 13. Exchange cross peaks due to the methyl groups signals are evidenced by the expansion.
Allyl hydrogen atoms close to the N^N group are well
separated so that exchange cross peaks can easily be detected
between the multiplets because of the central CH and the
doublets of syn hydrogen atoms and anti hydrogen atoms.
Once again, the synꢀsyn and antiꢀanti exchanges are consistent
with an allyl pseudorotation mechanism, which involves (a)
dissociation of one PdꢀN bond, (b) rotation around the
remaining PdꢀN bond, (c) isomerization of the T-shaped
intermediate, and (d) reforming of the PdꢀN bond.2
As stated earlier, an essential feature of hemilabile ligands is to
have at least one substitutionally labile donor function while
the other donor group(s) remain firmly bound to the metal
center(s). This condition is certainly met by the binucleating
DTO in the k-N,S coordination mode (complexes 1ꢀ7).
However, the concept of hemilability cannot be extended to
dinuclear complexes such as 8ꢀ14. In fact, these compounds could
be regarded as being formed from a complex as a ligand (frame A in
Chart 7) and by a complex as a metal (frame B in Chart 7).
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Figure 4. Bidimensional EXSY spectrum of 14. Exchange cross peaks are indicated by arrows.
Chart 7. [η3-Allyl)Pd]2(μ-dialkyldithiooxamidate k-S,S0 Pd
k-N,N0 Pd0) Complexes Viewed as Being Made by a Complex
as a Ligand and a Complex as a Metal (See the Text)
At this stage, we can only argue that the change in the
coordination mode of the ligand implies the breaking of the
PdꢀS bond in the (η3-allyl)Pd(S^S)ꢀ frame. [(η3-Allyl)Pd]2-
(μ-R2-DTO k-N,N0 Pd, k-S,S0 Pd0) species contain the (η3-
allyl)Pd(N^N)ꢀ frame in which the labile Pd(N^N) interaction
allows the apparent allyl rotation via PdꢀN bond rupture; in the
other frame, a more stable Pd(S^S) interaction requires more
energy to produce the rearrangement of the binucleating ligand
via PdꢀS bond rupture.
The change in the coordination mode of the binucleating
ligands in complexes 8ꢀ14 was not surprising, in that both
groups of compounds 1ꢀ7 and 8ꢀ14 were obtained via the same
chemical reaction (Schemes 1 and 4), albeit performed in
different experimental conditions. Compounds 1ꢀ7 were syn-
thesized under thermodynamic control (higher temperature and
longer reaction time), while the corresponding isomers 8ꢀ14
were prepared under kinetic control (lower temperature and
shorter reaction time).
From this point of view, A does not contain a hybrid
hemilabile ligand but simply a homofunctional chelating
system.
At this point, it is necessary to consider that when species
8ꢀ14 are left in solution, they undergo the following rearran-
gement shown in Scheme 5 The above process shows a half-life
of about 1 day, depending on the nature of the alkyl substit-
uents of 8ꢀ14; this is in agreement with the preparative
separation of the two isomers and with their characterization
in solution without mutual interference.
The spontaneous transformation of the k-N,N0 Pd, k-S,S0 Pd0
species (8ꢀ14) into the corresponding k-N,S Pd, k-N0,S0 Pd0
ones (1ꢀ7) is mainly ruled by the stability of the thermodynamic
compounds with respect to the kinetic ones.
The thermodynamic stability of metalꢀligand interaction
(HSAB principle)40 is a well-assessed issue. Furthermore, be-
cause chemical hardness is related to the highest occupied
Detailed studies will be needed to assess the mechanism of the
rearrangement of the binucleating ligand in the k-N,N k-S,S
homobimetallic complexes 8ꢀ14.
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Scheme 5. Spontaneous Transformation of [(η3-Allyl)Pd]2(μ-dialkyldithiooxamidate j-N,N0 Pd, j-S,S Pd0) in the Corre-
sponding j-N,S Pd j-N0,S0 Pd0 Isomers
Figure 5. Electronic structures of model systems.
Figure 6. Perspective view of compound 5 showing its aymmetric unit
(filled drawings) with the numbering scheme and its centrosymmetric
equivalent (empty drawings). The two disorderd allyl positions are
represented by solid (85% of occupancy) and dotted (15%) lines,
respectively. Thermal ellipsoids are drawn at the 30% probability level,
molecular orbital (HOMO)/lowest unoccupied molecular orbi-
tal (LUMO) gap of a molecular species as half the energy gap of
the two orbitals [η = (ELUMO ꢀ EHOMO)/2], the molecular
stability can be evaluated using the maximum hardness principle,
which states that molecules arrange themselves to be as hard as
possible.41
while the hydrogen size is arbitrary.
Solid-State Structures. [(η3-Allyl)Pd]2(μ-isoamyl-DTO j-N,S
Pd, j-N0,S0 Pd0)] (5). In the solid state, compound 5 is placed in a
crystallographic center of symmetry that is right in the middle
point of the central CꢀC bond of the DTO in a planar-transoid
conformation (Figure 6). The molecular unit is centrosymmetric
and is made up of equivalent halves. The isoamyl groups show a
fixed conformation in the crystal packing. The terminal CH2
carbon atoms of the allyl groups lie in the palladium coordination
plane, while the central CH atom is split on opposite points with
respect to the coordination plane. The central allyl CH disorder
in η3-allylpalladium complexes is usually interpreted as the result
of overlap of two conformations having a different position of the
central CH, although several authors have interpreted such a
disorder to be the result of thermal motion of the central allyl CH
group.45 In the crystal packing of compound 5, the occupancy of
the allyl cuspid oriented in the same direction of the nearest
isoamyl group is 0.85, while it is 0.15 when the allyl CH is
oriented in the opposite direction. This observed distribution
ratio of the allyl orientation can be interpreted in two ways. First,
we could presume that only the exo isomer exists (0.15, a; 0.85, b;
0, c; 0, d; Scheme 3) in the solid state because both conformers
exhibit a centrosymmetrical arrangement. Second, the occupancy
of the allyl cuspid oriented on the same side of the isoamyl group
could also be 0.15 based on the distribution 0.075a + 1/2(0.075 c) +
1/2(0.075d) (Chart 8) For the remaining 0.85, the occupancy
We therefore performed theoretical calculations on a simpli-
fied model of both groups of complexes 1ꢀ7 and 8ꢀ14 in which
a hydrogen atom was placed as the substituent on the amidic
nitrogen atoms instead of the alkyl groups.
In the model system of molecules 8ꢀ14 (k-N,N0 Pd, k-S,S0 Pd0),
we found that the HOMOꢀLUMO gap is 3.837 eV, while this
gap is 3.946 eV for compounds 1ꢀ7 (k-N,S Pd, k-N0,S0 Pd0).
The larger gap for the latter compounds indicates that k-N,S Pd,
k-N0,S0 Pd0 species are the harder isomers. The harder isomers
are more stable, and this fact matches with the greater stability
(9.47 kcal) computed for the k-N,S isomer with respect to the
corresponding k-N,N k-S,S species.
The electronic structures of model systems (Figure 5) show
that the LUMOs have a similar composition, which can be
described as a pz* system of the NSCꢀCSN frame in both the
k-N,S and k-N,N k-S,S isomers . In contrast, HOMOs for the
two isomeric models are quite different in composition from each
other. In the k-N,S model, the HOMO is mainly formed by a
combination of the pz atomic orbital of nitrogen and sulfur atoms
and the dxy orbital of both palladium atoms, while in the k-N,N
k-S,S model, the contribution of the dxy orbital in k-N,N
palladium atom is somewhat lower.
The point we highlight is how a functional choice of hardꢀ
soft-donor chelating ligands can direct inorganic syntheses
toward isomeric preferences42,43 or toward self-assembled mol-
ecular square architectures.44
1
could be due to the distribution 0.775 b + /2(0.075c) +
1/2(0.075d) (Chart 8). Thus, the latter interpretation is
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Chart 8. Orientation of Allyl Cuspids with Respect to the
Nearest Isoamyl Group Observed in the Solid State for
Complex 5 (See the Text)
Figure 7. Perspective view of compound 7 constituted by the aym-
metric unit (filled drawings) showing the numbering scheme and the
centrosymmetric half part (empty drawings). The position of the
disorderd allyl with largest occupancy (55%) is denoted by solid lines
and the other one (45%) by dotted lines. Thermal ellipsoids are drawn at
the 30% probability level, while the hydrogen size is arbitrary.
Chart 9. Orientation of Allyl Cuspids with Respect to the
Nearest Phenyelthyl Group Observed in the Solid State for
Complex 7 (See the Text)
compatible with the existence of 15% of the endo isomer in the
crystal packing. This fact does not conflict with the observed
symmetry of the crystal because species c and d, when equimolar,
are a centrosymmetric racemate.
[(η3-Allyl)Pd]2[μ-(meso-DTO) k-N,S Pd, k-N0,S0 Pd0)] (7). The
unit cell 7 lies in a crystallographic center of symmetry, in the
middle point of the CꢀC axis (Figure 7). The centrosymmetric
molecule is made up of equivalent halves. In the solid state, the
chiral alkyl groups show a fixed conformation. The CH2 terminal
carbon atoms of the allyl groups lie in the palladium coordination
planes, while both allyl CH grooups are split into two opposite
positions with respect to the said molecular planes. In the crystal
packing of 7, the occupancy of allyl cuspids oriented in the same
direction of the phenyl ring of the nearest (1-phenyl)ethyl
substituent is 0.55, while it is 0.45 when the allyl CH group is
oriented in the opposite direction. The observed distribution
ratio may again be explained in two different ways. First, we could
consider that the two pseudochiral exo isomers are the only
species present in the solid state (0.45, a; 0.55, b; 0, c; 0, d;
Chart 9) because both a and b meso forms exhibit a centrosym-
metric arrangement. However, the occupancy of the allyl
cuspid oriented on the same side of the phenyl group could
centrosymmetric racemate. We would point out that the latter
distribution is very similar to the isomeric composition observed in
solution.
[(η3-Allyl)Pd]2[μ-(rac-DTO) k-S,S0 Pd, k-N,N0 Pd0)] (15). In
the solid state, 15 lies on a crystallographic 2-fold axis passing
through the two palladium atoms (Figure 8). The crystal packing
is centrosymmetric because it is constituted by equimolar
quantities of chiral bimetallic molecules having opposite config-
uration, i.e., [(η3-allyl)Pd]2[μ-[1-(S)-(1-phenylethyl)]2-DTO
1
also be 0.55 based on the distribution 0.225a, /2(0.225c) +
1/2(0.225 d) (Chart 9). For the remaining 0.55, the occupancy
1
is due to the following distribution 0.55b + /2(0.225c) +
1/2(0.225d). The presence of c and d (endo isomer) in the
solid state is in agreement with the observed crystallographic
symmetry, in that an equimolar mixture of c and d constitutes a
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’ REFERENCES
(1) Lanza, S.; Bruno, G.; Nicolꢀo, F.; Scopelliti, R. Tetrahedron:
Asymmetry 1996, 7, 3347–3350.
(2) Lanza, S.; Bruno, G.; Nicolꢀo, F.; Rotondo, A.; Scopelliti, R.;
Rotondo, E. Organometallics 2000, 19 (13), 2462–2469.
(3) Lanza, S.; Bruno, G.; Nicolꢀo, F.; Callipari, G.; Tresoldi, G. Inorg.
Chem. 2003, 42, 4545–4552.
(4) Lanza, S.; Callipari, G.; Loiseau, F.; Serroni, S.; Tresoldi, G. Inorg.
Chem. 2005, 44, 6717–6724.
(5) Veit, R.; Girerd, J. J.; Kahn, O.; Jeannin, Y.; Robert, F.; El Murr,
N. Inorg. Chem. 1984, 23, 4448–4454.
(6) Ye, Q. Y.; Nakaro, Y.; Frauenhoff, G. R.; Whitcomb, D. R.;
Takusagava, F.; Busch, D. H. Inorg. Chem. 1991, 30, 1503–1510.
(7) Girerd, J. J.; Jeannin, S.; Jeannin, Y.; Kahn, O. Inorg. Chem. 1978,
17, 3034–3040.
(8) Cotton, F. A.; Li, Z.; Liu, C. Y.; Murillo, C. A. Inorg. Chem. 2007,
46, 7840–7847.
(9) Lanza, S.; Bruno, G.; Nicolꢀo, F.; Rotondo, A.; Tresoldi, G. Eur. J.
Inorg. Chem. 2002, 65–72.
(10) Lanza, S.; Giannetto, A.; Bruno, G.; Nicolꢀo, F.; Tresoldi, G. Eur.
J. Inorg. Chem. 2009, 2647–2654.
(11) Lanza, S.; Nicolꢀo, F.; Cafeo, G.; Amiri Rudbari, H.; Bruno, G.
Inorg. Chem. 2010, 49, 9236–9246.
(12) Hurd, R. N.; De La Mater, G.; McElheny, C. G.; Turner, R. J.;
Figure 8. View of compound 15 evidencing the 2-fold axes passing
through the palladium atoms and showing the numbering scheme of the
aymmetric unit denoted by filled drawings. Each allyl ligand is split into
two positions with equal occupancy (50%) as a consequence of
symmetry. Thermal ellipsoids are drawn at the 30% probability level,
while the hydrogen size is arbitrary.
Vallingford, V. H. J. Org. Chem. 1961, 26, 3980–3987.
(13) (a) COSMO, version 1.60; Bruker AXS Inc.: Madison, WI,
2005. (b) SAINT, version 7.06A; Bruker AXS Inc.: Madison, WI, 2005.
(c) SADABS, version 2.10; Bruker AXS Inc.: Madison, WI, 2005.
(14) SIR2004: Burla, M. C.; Caliandro, R.; Camalli, M.; Carrozzini,
B.; Cascarano, G. L.; De Caro, L.; Giacovazzo, C.; Polidori, G.; Spagna,
R. J. Appl. Crystallogr. 2005, 38, 381–388.
k-N,N0 Pd, k-S,S0 Pd0] and [(η3-allyl)Pd]2[μ-[1-(R)-(1-phenyl-
ethyl)]2-DTO k-N,N0 Pd, k-S,S0 Pd0]. Each enantiomer is
C2-symmetrical, and this implies that the occupancies of the
two positions of the disordered allyl groups are equal (0.5).
Crystal data of 15 agree with H NMR spectra, which show
equimolar mixtures of endo and exo isomers in solution.
1
(15) Sheldrick, G. M. SHELXL97; University of G€ottingen: G€ottingen,
Germany, 1997.
(16) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A.; Vreven, T.; Kudin,
K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.;
Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.;
Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa,
J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.;
Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Adamo, C.; Jaramillo, J.;
Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.;
Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.; Voth, G. A.;
Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich, S.; Daniels,
A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.;
Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.;
Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.;
Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham,
M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.;
Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian
03, revision B.04; Gaussian, Inc.: Pittsburgh, PA, 2003.
(17) Adamo, C.; Barone, V. J. Chem. Phys. 1999, 110, 6158–6170.
(18) Ernzerhof, M.; Scuseria, G. E. J. Chem. Phys. 1999, 110,
5029–5036.
’ CONCLUSION
In this paper, we heve reported the synthesis and study of
some homobimetallic complexes having two allylpalladium moi-
eties joined by a binucleating DTO in both k-N,S Pd, k-N0,S0 Pd0
and k-N,N0 Pd, k-S,S0 Pd0 coordination modes.
These linkage isomers show apparent allyl rotation: either in
the (η3-allyl)Pd (N^N)ꢀ frame of k-N,N0 Pd, k-S,S0 Pd0 species
or in both (η3-allyl)Pd(N^S)ꢀ frames of k-N,S Pd, k-N0,S0 Pd0
compounds. In the latter, the alkyldithiooxamidate group is
therefore a double-hybrid hemilabile binucleating ligand. This
implies that the use of DTO- containing chiral alkyl substituents
as binucleating hybrid ligands could pave the way for studies on
their role in hemilabile systems, which could easily carry and
transfer chiral information.
k-N,N0 Pd, k-S,S0 Pd0 complexes in solution slowly change
into the corresponding k-N,S Pd, k-N0,S0 Pd0 isomers pre-
sumably after breaking of the PdꢀS bond in the (η3-allyl)Pd
(S^S)ꢀ frame.
(19) (a) Figgen, D.; Rauhut, G.; Dolg, M.; Stoll, H. Chem. Phys.
2005, 311, 227–244. (b) Peterson, K. A.; Puzzarini, C. Theor. Chem. Acc.
2005, 114, 283–296.
In other words, in k-N,N0 Pd, k-S,S0 Pd0 complexes, PdꢀN
bond rupture produces stereoisomerization (allyl pseudorotation)
at the NMR time scale, while PdꢀS bond breaking causes linkage
isomerization over a much longer time scale. It would therefore be
interesting to explore the possible catalytic activity in bimetallic
systems where each of the two metals can produce a vacant
coordination site under different energetic conditions.
(20) (a) Faller, J. W.; Sarantopoulos, N. Organometallics 2004,
23, 2008–2014. (b) Faller, J. W.; Stokes-Huby, H. L.; Albrizzio, M. A.
Helv. Chim. Acta 2001, 84, 3031ꢀ3042.
(21) (a) Gꢁomez-de la Torre, F.; de la Hoz, A.; Jalꢁon, F. A.; Manzano,
B. R.; Rodríguez, A. M.; Elguero, J.; Martínez-Ripoll, M. Inorg. Chem.
2000, 39, 1152–1162. (b) Gꢁomez-de la Torre, F.; de la Hoz, A.;
Jalꢁon, F. A.; Manzano, B. R.; Otero, A.; Rodríguez, A. M.; Rodríguez-Perez,
M. C.; Aurea Echevarría, P.; Elguero, J. Inorg. Chem. 1998, 37,
6606–6614. (c) Berenguer, J. R.; Forniꢁes, J.; Lalinde, E.; Martínez, F.
Organometallics 1996, 15, 4537–4546. (d) Tsukada, N.; Sato, T.; Mori,
H.; Sugawara, S.; Kabuto, C.; Miyan, S.; Inoue, Y. J. Organomet. Chem.
2001, 627, 121–126. (e) Scrivanti, A.; Benetollo, F.; Venzo, A.;
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: lanza@unime.it.
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Bertoldini., M.; Beghetto, V.; Matteoli, U. J. Organomet. Chem. 2007,
692, 3577–3582.
(39) (a) Albinati, A.; Amman, C. J.; Pregosin, P. S.; Ruegger, P. S.
Organometallics 1990, 9, 1826–1833. (b) Albinati, A.; Kunz, R. W.;
Amman, C. J.; Pregosin, P. S. Organometallics 1991, 10, 1800–1806.
(40) Pearson, R. G. J. Am. Chem. Soc. 1963, 85, 3533–3539.
(41) (a) Pearson, R. G. Acc. Chem. Res. 1993, 26, 250–255. (b) Pearson,
R. G. J. Chem. Educ. 1999, 76, 267–275.
(42) Del Campo, O.; Carbayo, A.; Cuevas, J. V.; García-Erbosa, G.;
Mu~noz, A. Eur. J. Inorg. Chem. 2009, 15, 2254–2260.
(43) Fave, C.; Hissler, M.; Sꢁenꢁechal, K.; Ledoux, I.; Zyss, J.; Rꢁeau, R.
Chem. Commun. 2002, 16, 1674–1675.
(22) (a) Prelog, V. Proc. K. Ned. Akad. Wet., Ser. B: Phys. Sci. 1968,
B71, 108–123. (b) Prelog, V. Problems in chemical topology. Twenty-first
organic chemistry Symposium of American Chemical Society; American
Chemical Society: Columbus, OH, 1969; pp 72ꢀ84.
(23) Helmchen, G. Recent Developments in the Relations between
Geometry and Stereochemistry; Lecture presented at the Annual Chemical
Congress of the Chemical Society; Royal Society of Chemistry: London,
Mar 30, 1977.
(24) (a) Goldberg, S. I.; Baileyl, W. D. J. Am. Chem. Soc. 1971,
93, 1046–1047. (b) Goldberg, S. I.; Baileyl, W. D. J. Am. Chem. Soc. 1974,
96, 6381–6387.
(25) Ganter, C.; Brassat, L.; Glinsb€ockel, C.; Ganter, B. Organome-
tallics 1997, 16, 2862–2867.
(44) Angurell, I.; Ferrer, M.; Gutiꢁerrez, A.; Martínez, M.; Rodríguez,
L.; Rossel, O.; Engeser, M. Chem.—Eur. J. 2010, 16, 13960–13964.
(45) Redon, R.; Torrens, H.; Ekkehardt Hahn, F.; L€ugger, T.;
Hernandez-Ortega, S.; Toscano, R. A.; Morales-Morales, D. J. Mol.
Struct. 2003, 655, 423–433.
(26) Braunstein, P.; Naud, F. Angew. Chem., Int. Ed. 2001, 40,
680–699.
(27) Braunstein, P. J. Organomet. Chem. 2004, 689, 3953–3967.
(28) Jeffrey, J. C.; Rauchfuss, T. B. Inorg. Chem. 1979, 18, 2658–2666.
(29) (a) Braunstein, P.; Matt, D.; Mathey, F.; Thavard, D. J. Chem.
Res. 1978, 232, 3041. (b) Braunstein, P.; Matt, D.; Dusausoy, Y.; Fischer,
J.; Mitschler, A.; Ricard, L. J. Am. Chem. Soc. 1981, 103, 5115–5125.
(c) Braunstein, P.; Matt, D.; Dusausoy, Y. Inorg. Chem. 1983,
22, 2043–2047. (d) Braunstein, P.; Fischer, J.; Matt, D.; Pfeffer, M.
J. Am. Chem. Soc. 1984, 106, 410–421.
(30) (a) Braunstein, P.; Naud, F.; Dedieu, A.; Rohmer, M. M.; DeCian,
A.; Rettig, S. Organometallics 2001, 20, 2966–2981. (b) Braunstein, P.;
Zhang, J.; Welter, R. Dalton Trans. 2003, 507–509.
(31) Ankersmit, H. A.; Loken, B. H.; Kooijman, H.; Spek, A. L.;
Vrieze, K.; van Koten, G. Inorg. Chim. Acta 1996, 252, 141–155.
(32) Fernꢁandez-Galꢁan, R.; Jaloꢁn, F. A.; Manzano, B. R.; Rodríguez-
de la Fuente, J.; Vrahami, M.; Jedlicka, B.; Weissensteiner, W.; Jogl, G.
Organometallics 1997, 16, 3758–3768.
(33) Scheele, U. J.; John, M.; Dechert, S.; Meyer, F. Eur. J. Inorg.
Chem. 2008, 373–377.
(34) (a) Faller, J. W.; Wilt, J. C. Organometallics 2005, 24,
5076–5083. (b) Faller, J. W.; Milheiro, S.; Parr, J. J. Organomet. Chem.
2008, 693, 1478–1493. (c) Milheiro, S. C.; Faller, J. W. J. Organomet.
Chem. 2011, 696, 879–886.
(35) Brassat, J.; Englert, U.; Keim, W.; Keitel, D. P.; Killat, S.;
Suranna, J. P.; Wang, R. Inorg. Chim. Acta 1998, 280, 150–162.
(36) (a) Canovese, L.; Visentin, F.; Uguagliati, P.; Chessa, G.; Pesce,
A. J. Organomet. Chem. 1998, 566, 61–71. (b) Canovese, L.; Visentin, F.;
Uguagliati, P.; Lucchini, V.; Bandoli, G.; Chessa, G. Inorg. Chim. Acta
1998, 275ꢀ276, 385–394.
(37) Yang, H.; Khan, M. A.; Nicholas, K. M. Organometallics 1993,
12, 3485–3494.
(38) Variable-temperature (VT) experiments have not been per-
formed in the complexes bearing chiral amine-derived ligands because
allyl signals of various diastereomers could have not collapsed because of
the presence of chiral centers in the molecular plane. Only NCH-
(CH3)C6H5 doublets could collapse because in these complexes they
are correlated by a symmetry operation. However, these doublets are so
close to each other that the results of the rate measurement would be of
marginal significance. Rates and activation parameters are inaccessible
also for kinetic complexes (k-N,N0 Pd, k-S,S0 Pd0) bearing achiral amine-
derived ligands. In these complexes, the allyl group in the (η3-allyl)Pd-
(S^S)ꢀ frame does not isomerize; thus, the molecular plane cannot
become symmetrical. As a consequence, NCH2 protons cannot become
equivalent. Furthermore, VT experiments performed on k-N,N0 Pd, k-S,
S0 Pd0 complexes could be affected also by the change of these species
into the N,S Pd, k-N0,S0 Pd0 compounds. Thus, only in the thermo-
dynamic complexes (k-N,S Pd, k-N0,S0 Pd0) could the ABXn signals of
NCH2 groups become a more simple A2Xn spin system without other
complications. Actually, we tried to perform VT experiments on these
latter complexes. Unfortunately, we obtained very poor results: in
deuterated tetrachloroethane at about 80 °C, the ABXn signals were
still far from collapsing to the A2Xn spectral pattern.
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