Complexes of elements of groups 9 and 10 with new chiral chelating bisphosphine monosulfide and monoselenide ligands

Article abstract of DOI:10.1039/b111422k

The chiral bisphosphine prepared from the reaction of (S)-α-methylbenzyl amine with two equivalents of chlorodiphenylphosphine can be oxidised by direct reaction with one equivalent of either of the elemental chalcogens sulfur or selenium to prepare new chiral monoxidised bisphosphines. These chiral ligands can be used to prepare complexes with group nine [Rh(I), Ir(I)] and group ten [Pd(II) and Pt(II)] metals. These complexes were characterised by spectroscopic and, in four cases, crystallographic techniques.

Full text of DOI:10.1039/b111422k

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Complexes of elements of groups 9 and 10 with new chiral chelating
bisphosphine monosulfide and monoselenide ligands
Jack W. Faller,a Julio Lloret-Fillolby and Jonathan Parr*by
a
Department of Chemistry, Yale University, 225 Prospect Street, New Haven,
CT 06520-8107, USA
Department of Chemistry, Loughborough University, Loughborough, Leics.,
LE11 3TU, UK
b
Received (in New Haven, CT, USA) 13th December 2001, Accepted 8th January 2002
First published as an Advance Article on the web 18th June 2002
The chiral bisphosphine prepared from the reaction of (S)-a-methylbenzyl amine with two equivalents of
chlorodiphenylphosphine can be oxidised by direct reaction with one equivalent of either of the elemental
chalcogens sulfur or selenium to prepare new chiral monoxidised bisphosphines. These chiral ligands can
be used to prepare complexes with group nine [Rh(I), Ir(I)] and group ten [Pd(II) and Pt(II)] metals. These
complexes were characterised by spectroscopic and, in four cases, crystallographic techniques.
In recent years there has been an increasing interest in che-
lating ligands that comprise mixed donor sets. These ligands
can bring a range of properties to the complexes that they
comprise, such as hemilability or electronic asymmetry. This
latter property is of particular interest if the complexes have
applications as reagents or in homogeneous catalysis. Some of
the most well studied chelating ligands are bisphosphines, so it
is perhaps not surprising that heterobidentate ligands prepared
Fig. 1 The formation of L2 and L3.
from these, particularly bisphosphine monoxides (BPMO’s),
are now being actively studied.1–5
The role of chiral bisphosphines in making complexes that
We report here the new chiral bisphosphine monosulfide L2
are useful for selective homogeneous catalysis is well developed
and monoselenide L3, Fig. 1, along with some complexes with
and so it seems reasonable that monoxidised chiral bisphos-
group nine and ten metals.
phines could be of interest, as they bring to the complexes that
they form the added feature of electronic asymmetry. The
publication of a route to chiral BPMO’s from commercial
Experimental
chiral bisphosphines6 has resulted in a number of publications
detailing the successful use of complexes of such ligands in
catalytic reactions.7
A further family of chiral monoxidised bisphosphines is
General
All reactions were performed under nitrogen unless otherwise
available from the oxidation of chiral bisphosphines by chal-
stated. All reagents were commercial and used as received
cogens other than oxygen. There is a wealth of literature on the
preparation of phosphine sulfides and selenides by direct
except [(cod)MCl]2 (M ¼ Rh, Ir), which were prepared accor-
ding to reported procedures,10 and Et3N and Ph2PCl, which
reaction of the corresponding phosphine with the elemental
were distilled prior to use.
chalcogen.8 Such ligands are potentially very interesting, since
Infrared spectra were recorded as KBr pellets in the range
4000–200 cmꢀ1 on a Perkin–Elmer System 2000 FT-IR spec-
the donor properties of phosphine sulfides and selenides are
trometer. The 1H NMR spectra (250 MHz) were recorded on a
quite different from the parent phosphines and indeed, from
phosphine oxides. A bisphosphine monosulfide or mono-
selenide might well prove to induce a more pronounced elec-
tronic asymmetry and in its complexes may be able to exhibit
different coordination behaviour. Further, it is possible to
imagine a family of chiral monoxidised bisphosphines that
comprise chelate rings that are entirely inorganic, in contrast
Bruker AC250 FT spectrometer with chemical shifts (d) in
ppm to high frequency of SiMe4 and coupling constants (J) in
Hz. The 31P{1H} NMR spectra (36.2 MHz) were recorded on a
JEOL FX90Q spectrometer with chemical shifts (d) in ppm to
high frequency of 85% H3PO4 and coupling constants (J) in
Hz. All spectra were recorded in CDCl3 unless otherwise sta-
to the BPMO’s previously reported. The ligands reported here
ted. Elemental analyses (Perkin–Elmer 2400 CHN Elemental
chelate to form carbon free M–E–P–N–P rings and are related
Analyzer) were performed by the Loughborough University
to achiral ligands that form similar rings, such as imido-
Analytical Service within the Department of Chemistry.
tetraaryldichalcogenodiphosphinates, which have enjoyed a
great deal of success and are capable of coordinating to a wide
range of metals.9
Synthesis of ligands
(S)-(Ph2P)2NC(H)(Me)Ph (L1). (i) A solution of (S)-phenyl-
ethylamine (1.08 cm3, 8.42 mmol) and Et3N (2.25 cm3, 16 mmol)
y Current address: Department of Chemistry, Yale University, 225
Prospect Street, New Haven, CT 06520-8107, USA.
in diethyl ether (10 cm3) was added dropwise to a stirred solution
DOI: 10.1039/b111422k
New J. Chem., 2002, 26, 883–888
883
This journal is # The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2002

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of ClPPh2 (3.0 cm3, 16.71 mmol) in diethyl ether (15 cm3) under
nitrogen. During the addition, the reaction formed a white pre-
cipitate. After 1.5 h the reaction mixture was filtered. The liquid
fraction was evaporated to dryness, giving a yellow oil. Treat-
ment with MeOH (3 cm3) overnight at 0 ꢁC led to the formation
of a white solid, which was collected by filtration and washed
successively with hexane (3 ꢂ 5 cm3) and diethyl ether
(2 ꢂ 3 cm3). Yield 2.7 g, 65%.
[{k2-(S)-{(Ph2P)(Ph2P{S})NC(H)(Me)Ph-P,S}RhCl]2 [L2-
RhCl]2. A solution of [(cod)RhCl]2 (35 mg, 0.0713 mmol) and
L2 (75 mg, 0.144 mmol) in CH2Cl2 (10 cm3) was stirred for 5 h.
The solvent was reduced to ca. 1 cm3 by evaporation under
reduced pressure and the product was precipitated by addition
of diethyl ether (10 cm3). The dark red solid was collected by
filtration and dried in vacuo. Yield: 79 mg, 83%. 31P{1H}
1
1
NMR: 104.6 [dd, JPP ¼ 66.0, JPRh ¼ 158.4, P(III)]; 70.9 [d,
1
1JPP ¼ 66.0, P(V)]. H NMR: 8.11–6.24 (m, 50H, arom.), 4.92
(ii) An alternative preparation followed the same route until
the addition to ClPPh2 was complete. After 10 h of stirring, the
solvent was removed to give a white solid that was washed with
50 cm3 of distilled degassed water. The white solid product was
collected by filtration and was washed successively with hexane
(3 ꢂ 5 cm3) and diethyl ether (3 ꢂ 3 ml) and the solid was dried
under vacuum. Yield: 3.52 g, 85%.
3
(m, 2H, CH), 0.83 (d, JHH ¼ 7.2, 6H, CH3). IR: 1436, 1099,
943, 864, 746, 693 cmꢀ1
.
Anal. found (calcd. for
C64H58N2P4Cl2Rh2S2): C ¼ 58.20 (58.30); H ¼ 4.35 (4.45);
N ¼ 2.10 (2.10)%.
[{k2-(S)-{(Ph2P)(Ph2P{S})NC(H)(Me)Ph-P,S}IrCl]2 [L2Ir-
Cl]2 (Isomer 1). A solution of [(cod)IrCl]2 (65 mg, 0.0968
mmol) and L2 (100 mg, 0.192 mmol ) in CH2Cl2 (10 cm3) was
stirred for ca. 2 h. The solvent was removed by evaporation
under reduced pressure and the residue dissolved in CH2Cl2
(2 cm3). Addition of diethyl ether (10 cm3) formed an orange
precipitate that was collected by filtration and dried in vacuo.
(S)-(Ph2P)N{Ph2P(S)}C(H)(Me)Ph (L2). A solution of L1
(375 mg, 0.77 mmol) in THF (10 cm3) and elemental sulfur
(24.5 mg, 0.77 mmol) was stirred 2.5 h at room temperature
and then filtered through a Celite plug. The volume was
reduced to ca. 1 cm3 under reduced pressure and the product
was precipitated as a white solid by addition of MeOH (2 cm3)
and collected by filtration. Yield: 250 mg, 61%. 31P{1H}
NMR: 71.95 [d, 2JPP ¼ 13.2, P(V)], 52.42 [d, 2JPP ¼ 13.2, P(III)].
1H NMR: 7.76–6.91 (m, 25H, arom.), 5.11 (m, 1H, CH), 1.75
1
Yield: 60 mg, 40%. 31P{1H} NMR: 95.11 [d, JPP ¼ 65.9,
1
P(III)], 72.92 [1JPP ¼ 65.9, P(V)]. H NMR: 8.44–6.46 (m, 50H,
3
arom.), 4.75 (m, 2H, CH), 0.84 (d, JHH ¼ 7.2, 6H, CH3).
IR: 1436, 1097, 939, 770, 747, 692, 618, 595, 571, 542, 521,
496, 459, 398, 376 cmꢀ1. Anal. found (calcd. for C64H58N2-
P4Cl2S2Ir2): C ¼ 51.30 (51.25); H ¼ 4.00 (3.90); N ¼ 1.80
(1.90)%.
3
(d, J ¼ 7, 3H, CH3). IR: 1436, 1090, 944, 848, 673, 774, 742,
691, 673, 515 cmꢀ1. Anal. found (calcd. for C32H29NP2S):
C ¼ 73.50 (73.60); H ¼ 5.45 (5.55); N ¼ 2.50 (2.70)%.
[{k2-(S)-{(Ph2P)(Ph2P{S})NC(H)(Me)Ph-P,S}IrCl]2 [L2Ir-
Cl]2 (Isomer 2). A solution of [(cod)IrCl]2 (67 mg, 0.10 mmol)
and L2 (105 mg, 0.20 mmol) in CH2Cl2 (10 cm3) was stirred for
ca. 6 h. The solvent was removed under reduced pressure and
the residue was dissolved in CDCl3 (1 cm3). Addition of diethyl
ether (10 cm3) led to the formation of an orange precipitate
that was collected by suction filtration and dried in vacuo.
(S)-(Ph2P)N{Ph2P(Se)}C(H)(Me)Ph (L3). A solution of L1
(1 g, 2.04 mmol) in THF (10 cm3) and grey selenium (160 mg,
2.04 mmol) were stirred together for 17 h at room temperature.
The volume was then reduced to ca. 1 cm3 under reduced
pressure and the product was precipitated as a white solid by
addition of MeOH (2 cm3) and collected by filtration. Yield:
2
1
890 mg, 76.6%. 31P{1H} NMR: 70.43 [d, JPP ¼ 8.8, JPSe
¼
2
Yield: 100 mg, 67%. 31P{1H} NMR: 82.01 [d, JPP ¼ 57.2,
757, P(V)], 53.08 [d, 2JPP ¼ 8.8, P(III)]. 1H NMR: 7.72–6.71 (m,
1
P(III)], 77.04 [2JPP ¼ 57.2, P(V)]. H NMR: 8.54–6.28 (m, 50H,
3
25H, arom), 5.22 (m, 1H, CH), 1.77 (d, JHH ¼ 7, 3H, CH3).
3
IR: 1436, 1089, 945, 845, 774, 742, 690, 554 cmꢀ1. Anal. found
(calcd. for C32H29NP2Se): C ¼ 67.60 (67.90); H ¼ 5.15 (5.10);
N ¼ 2.40 (2.50)%.
arom), 4.75 (m, 2H, CH), 1.78 (d, JHH ¼ 8.0, 6H, CH3). IR:
1436, 1104, 1027, 998, 817, 744, 696, 618, 570, 544, 513, 398
cmꢀ1. Anal. found (calcd. for C64H58N2P4Cl2S2Ir2): C ¼ 51.30
(51.25); H ¼ 3.95 (3.90); N ¼ 2.00 (1.90)%.
Synthesis of complexes
{k2-(S)-{(Ph2P)(Ph2P{S})NC(H)(Me)Ph-P,S}PdCl2 (L2Pd-
Cl2). A solution of (cod)PdCl2 (22 mg, 0.077 mmol) and L2 (40
mg, 0.077 mmol) in CH2Cl2 (10 cm3) was stirred for 2 h. The
solvent was removed by evaporation under reduced pressure
and the residue dissolved in the minimum quantity of CDCl3
to give an orange solution, from which crystals of the product
were obtained by slow evaporation. Yield: 49 mg, 91%.
31P{1H} NMR: 98.02 [d, 2JPP ¼ 48.4, P(III)] 75.9 [d, 2JPP ¼ 48.4,
P(V)]. 1H NMR: 8.32–6.34 (m, 50H, arom), 4.88 (m, 2H, CH),
[{k2-(S)-{(Ph2P)2NC(H)(Me)Ph-P,P}RhCl]2 [L1RhCl]2.
A
solution of [(cod)RhCl]2 (56 mg, 0.114 mmol) and L1 (114 mg,
0.23 mmol) in CH2Cl2 (8 cm3) was stirred for 4 h. The solvent
was reduced to ca. 2 cm3 and the product was precipitated as
an orange solid by the addition of diethyl ether (10 cm3). The
solid was collected by filtration and dried in vacuo. Yield: 70
mg, 49%. 31P{1H} NMR: 72.74 (1JRhP ¼ 123.2 Hz.). 1H NMR:
8.10–6.48 (m, 50H, arom), 4.27 (m, 2H, CH), 0.97 (d,
3JHH ¼ 6.8, 6H, CH3). IR: 1435, 1097, 967, 864, 745, 693, 593,
528, 505, 431 cmꢀ1. Anal. found (calcd. for C64H58N2-
P4Cl2Rh2): C ¼ 61.20 (61.40); H ¼ 4.60 (4.65); N 2.05 (2.25)%.
3
1.1 (d, JHH ¼ 7.2, 6H, CH3). IR: 1437, 1104, 997, 936, 918,
878, 773, 751, 727, 691, 645, 588, 524, 493, 478, 401, 364, 318,
226 cmꢀ1. Anal. found (calcd. for C32H29NP2SCl2Pd): C ¼
55.00 (55.10); H ¼ 4.20 (4.15); N ¼ 1.80 (2.00)%.
[{k2-(S)-{(Ph2P)2NC(H)(Me)Ph-P,P}IrCl]2 [L1IrCl]2.
A
{k2-(S)-{(Ph2P)(Ph2P{S})NC(H)(Me)Ph-P,S}PtCl2 (L2Pt-
Cl2). A solution of (cod)PtCl2 (29 mg, 0.075 mmol) and L2 (40
mg, 0.077 mmol) in CH2Cl2 (10 cm3) was stirred for 2 h. The
solvent was removed by evaporation under reduced pressure
and the residue dissolved in the minimum quantity of CDCl3
to give a red solution from which red crystals of the product
solution of [(cod)IrCl]2 (115 mg, 0.17 mmol) and L1 (170 mg,
0.34 mmol) in CH2Cl2 (10 cm3) was stirred overnight. The
solvent was reduced to ca. 2 cm3 by evaporation under reduced
pressure and the product was precipitated by addition of di-
ethyl ether (10 cm3). The brown solid was collected by filtra-
tion and dried in vacuo. Yield: 100 mg, 41%. 31P{1H} NMR:
1
3.48. H NMR: 8.05–6.51 (m, 50H, arom), 4.24 (m, 2H, CH),
3
were obtained after 15 min. Yield: 58 mg, 96%. 31P{1H}
1
0.98 (d, JHH ¼ 6.8, 6H, CH3). IR: 1435, 1098, 970, 857, 746,
NMR: 70.24 [d, JPP ¼ 47.6, 1JPPt ¼ 3976, P(III)], 72.69 [1JPP
¼
693, 569, 534, 515, 439, 217 cmꢀ1. Anal. found (calcd for
C64H58N2P4Cl2Ir2): C ¼ 53.70 (53.60); H ¼ 4.00 (4.10);
N ¼ 2.15 (1.95)%.
47.6, JPPt ¼ 104, P(V)]. H NMR: 8.25–6.12 (m, 25H, arom),
2
1
3
4.95 (m, 1H, CH), 1.10 (d, JHH ¼ 7.2, 3H, CH3). IR: 1437,
1104, 937, 876, 751, 726, 691, 524, 494, 480, 402, 365, 330
884
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cmꢀ1. Anal. found (calcd. for C32H29NP2SCl2Pt): C ¼ 48.95
(48.80); H ¼ 2.95 (3.05); N ¼ 1.65 (1.80)%.
filtration and dried in vacuo. Yield: 97 mg, 73%. 31P{1H}
2
NMR: 103.36 [d, JPP ¼ 57.2, P(III)], 62.73 [2JPP ¼ 57.2,
1
1JPSe ¼ 546, P(V)]. H NMR: 8.31–6.55 (m, 25H, arom), 4.81
(3JHH ¼ 7.2, 1H, CH), 1.11 (d, 3JHH ¼ 7.2, 3H, CH3). IR: 1436,
[{k2-(S)-{(Ph2P)(Ph2P{Se})NC(H)(Me)Ph-P,Se}RhCl]2 [L3-
RhCl]2. A solution of [(cod)RhCl]2 (45 mg, 0.092 mmol) and
L3 (104 mg, 0.183 mmol) in CH2Cl2 (10 cm3) was stirred for
4 h. The solvent was reduced to ca. 2 cm3 by evaporation under
reduced pressure and the product was precipitated by addition
of diethyl ether (10 cm3). The brown solid was collected by
filtration and dried in vacuo. Yield: 122 mg, 94%. Isomer 1:
1102, 928, 875, 743, 689, 549, 519, 492, 369, 325, 293 cmꢀ1
.
Anal. found (calcd.) for C32H29NP2Cl2SePd: C ¼ 51.40 (51.85);
H ¼ 3.65 (3.95); N ¼ 1.70 (1.90)%.
{k2-(S)-{(Ph2P)(Ph2P{Se})NC(H)(Me)Ph-P,Se}PtCl2 (L3-
PtCl2). A solution of (cod)PtCl2 (68 mg, 0.18 mmol) and L3
(100 mg, 0.176 mmol) in CH2Cl2 (10 cm3) was stirred for 2 h.
The solvent was reduced to ca. 1 cm3 by evaporation under
reduced pressure and the product was precipitated by addition
of diethyl ether (15 cm3). The pale yellow solid was collected by
filtration and dried in vacuo. Yield: 102 mg, 69%. 31P{1H}
2
1
31P{1H} NMR: 108.69 [d, JPP ¼ 74.8, JPRh ¼ 158.4, P(III)],
59.04 [2JPP ¼ 74.8, JPSe ¼ 553, P(V)]. H NMR: 8.24–6.46 (m,
50H, arom.), 4.81 (m, 2H, CH), 1.09 (d, 3JHH ¼ 7.6, 6H, CH3).
IR: 1435, 1126, 1096, 863, 744, 695, 545, 505 cmꢀ1. Isomer 2:
1
1
93.40 [d, JPP ¼ 70.4, JPRh ¼ 145.7, P(III)], 50.31 [2JPP ¼ 70.4,
2
1
1JPse ¼ 556, P(V)]. H NMR: 8.22–6.45 (m, 50H, arom.), 4.51
1
2
1
NMR: 73.25 [d, JPP ¼ 52.8, JPPt ¼ 3897, P(III)], 57.8 [2JPP
¼
3
(m, 2H, CH), 1.78(d, JHH ¼ 6.8, 6H, CH3). IR: 1435, 1128,
1
2
1
1097, 856, 743, 693, 539, 506 cmꢀ1. Anal. found (calcd.) for
52.8, JPse ¼ 512, JPPt ¼ 109.9, P(V)]. H NMR: 8.52–5.59 (m,
25H, arom), 4.22 (m, 1H, CH), 1.06 (d, 3JHH ¼ 6.8, 3H, CH3).
IR: 1436, 1102, 932, 870, 743, 688, 554, 525, 492, 373, 320, 291
cmꢀ1. Anal. found (calcd.) for C32H29NP2Cl2SePt: C ¼ 46.30
(46.20); H ¼ 3.10 (3.50); N ¼ 1.60 (1.70)%.
C64H58N2P4Cl2Se2Rh2:
N ¼ 2.0 (1.95)%.
C
54.70 (54.40); H ¼ 4.20 (4.25);
[{k2-(S)-{(Ph2P)(Ph2P{Se})NC(H)(Me)Ph-P,Se}IrCl]2 [L3-
IrCl]2. A solution of [(cod)IrCl]2 (51 mg, 0.076 mmol) and L3
(86 mg, 0.152 mmol) in CH2Cl2 (10 cm3) was stirred overnight.
The solution was initially orange, and the colour changed to
red by the end of the reaction. The solvent was reduced to ca. 1
cm3 by evaporation under reduced pressure and the product
was precipitated by addition of diethyl ether (10 cm3). The
brown solid was collected by filtration and dried in vacuo.
Yield: 162 mg, 67%. Isomer 1: 31P{1H} NMR: 88.21 [d,
X-Ray crystallography
Structural analyses were performed on crystals of L2PdCl2
L2PtCl2 , L3PdCl2 and L3PtCl2 at ꢀ90 1 ꢁC using a Nonius
Kappa CCD diffractometer with graphite-monochromated
+
Mo-Ka radiation (l ¼ 0.71073 A). The crystal data, a sum-
mary of the data collection and the structural refinement
parameters for these are given in Table 1 and selected bond
lengths and angles are collected in Table 2. Structures were
solved by direct methods for the L2 compounds and Patterson
heavy atom methods for the L3 compounds and all were
expanded using Fourier techniques. The non-hydrogen atoms
were refined anisotropically and hydrogen atoms were inclu-
ded but not refined. One might expect that all would be iso-
structural; however, L2PtCl2 and L2PdCl2 crystallise with two
molecules of CHCl3 and have space group P21 instead of
P212121 . Absolute configurations were determined by refer-
ence to the configuration of the ligands as well as observing
lower Rw for the enantiomer.
1
2JPP ¼ 70.4, P(III)], 51.83 [2JPP ¼ 73.1, JPSe ¼ 551, P(V)]. 1H
NMR: 8.10–6.40 (m, 50H, arom.), 4.81 (m, 2H, CH), 1.09 (d,
3JHH ¼ 7.6, 6H, CH3). Isomer 2: 31P{1H} NMR: 85.72 [d,
1
2JPP ¼ 68.0, P(III)], 58.60 [2JPP ¼ 68.0, JPSe ¼ 550, P(V)]. 1H
NMR: 8.12–6.41 (m, 50H, arom.), 4.51 (m, 2H, CH), 1.84 (d,
3JHH ¼ 6.9, 6H, CH3). IR: 1435, 1128, 1097, 856, 743, 693, 539,
506 cmꢀ1. Anal. found (calcd.) for C64H58N2P4Cl2Se2Ir2:
C ¼ 48.40 (48.50); H ¼ 3.70 (3.65); N ¼ 1.75 (1.80)%.
{k2-(S)-{(Ph2P)(Ph2P{Se})NC(H)(Me)Ph-P,Se}PdCl2 (L3-
PdCl2). A solution of (NCPh)2PdCl2 (68 mg, 0.177 mmol) and
L3 (100 mg, 0.176 mmol) in CH2Cl2 (10 cm3) was stirred for
2 h. The solvent was reduced to ca. 1 cm3 by evaporation under
reduced pressure and the product was precipitated by addition
of diethyl ether (10 cm3). The orange solid was collected by
CCDC reference numbers: 175774–175777 (see http:==www.
rsc.org=suppdata=nj=b1=b111422k= for crystallographic data
in CIF or other electronic format.
Table 1 Crystallographic data for the X-ray diffraction studies of L2PdCl2 , L2PtCl2 , L3PdCl2 and L3PtCl2
L2PdCl2
L2PtCl2
L3PdCl2
L3PtCl2
Formula
Crystal system
C34H31Cl8NP2PdS
Monoclinic
P21 (no. 4)
10.2033(5)
16.3289(8)
11.7551(5)
90
96.269(3)
90
1946.8(1)
11.88
C34H31Cl8NP2PtS
Monoclinic
P21 (no. 4)
10.2048(3)
16.3146(9)
11.7788(5)
90
96.615(3)
90
1947.96(13)
50.81
C32H29Cl2NP2PdSe
Orthorhombic
P212121 (no. 19)
11.8372(7)
15.8445(9)
16.8452(7)
90
90
90
3159.4(3)
20.33
C32H29Cl2NP2PtSe
Orthorhombic
P212121 (no. 19)
11.8948(4)
15.3216(5)
16.8763(6)
90
90
90
3075.7(2)
60.28
Space group
+
a=A
+
b=A
+
c=A
a=ꢁ
b=ꢁ
g=ꢁ
+
U=A3
m=cmꢀ1
T=ꢁC
ꢀ90
ꢀ90
ꢀ90
ꢀ90
Refl. measured
Unique refl.
Rint
Data used [I>3s(I)]
Final R
Final Rw
14 270
7818
12 258
7551
13 999
7200
17 433
8171
0.044
3179
0.036
0.041
0.057
3685
0.045
0.051
0.054
2368
0.038
0.041
0.070
2641
0.037
0.039
New J. Chem., 2002, 26, 883–888
885

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+
Table 2 Selected bond lengths (A) and angles (ꢁ) for L2PdCl2 , L2PtCl2 , L3PdCl2 and L3PtCl2
L2PdCl2 (E ¼ S)
L2PtCl2 (E ¼ S)
L3PdCl2 (E ¼ Se)
L3PtCl2 (E ¼ Se)
M–Cl(1) trans to E
M–Cl(2) trans to P
M–E
M–P(1)
E–P(2)
Cl(1)–M–Cl(2)
P(1)–M–Cl(1)
P(1)–M–E
Cl(2)–M–E
P(2)–E–M
P(1)–N–P(2)
2.310(2)
2.369(2)
2.274(2)
2.214(2)
2.011(3)
92.73(7)
87.73(7)
91.21(7)
88.67(7)
101.8(1)
116.0(3)
2.324(3)
2.346(3)
2.260(3)
2.212(3)
2.016(4)
90.7(1)
88.6(1)
92.1(1)
88.7(1)
101.2(2)
115.1(6)
2.321(3)
2.366(2)
2.377(1)
2.218(3)
2.164(2)
93.30(9)
87.33(9)
92.94(8)
86.15(7)
97.55(7)
116.4(4)
2.313(3)
2.312(3)
2.369(1)
2.152(3)
2.129(3)
89.46(12)
90.1(1)
92.44(9)
87.76(8)
98.54(10)
116.5(6)
Results and discussion
Ligand synthesis
By a refinement of the method reported by Krishnamurthy
et al.11 we have prepared the chiral chelating bisphosphine (S)-
N,N-bis(diphenylphosphino)methylbenzylamine (L1) and used
this to prepare two new chiral bisphosphine monochalco-
genides by direct reaction with one equivalent of either
elemental sulfur (L2) or selenium (L3).
The 31P{1H} NMR spectrum of L1 is a singlet at d ¼ 53.20,
whereas L2 exhibits two doublets, at 71.95 [P(V)] and 54.42
[P(III)], with a 2J(31P-31P) coupling of 13.2 Hz. The spectrum of
L3 is similar, with doublets at 70.43 [P(V)] and 53.08 [P(III)],
Fig. 2 The geometric isomers of complexes [k2-(L)-MCl]2 .
2
with a J(31P-31P) coupling of 8.8 Hz. Additionally, the lower
field resonance shows selenium satellites with 1J(31P-77Se) of
756.6 Hz, a value typical for phosphine selenides.12
Prepared in the same way, complexes of L2 are also of the
form [(k2-L2-P,S)M(I)Cl]2 . As L2 has two different donor
groups, in this case there is the possibility of geometric iso-
mers, Fig. 2. The reaction of two equivalents of L2 with
[(cod)Rh(I)Cl]2 for a period of five hours leads to a red solu-
tion, and the red solid product isolated from the reaction at
this time shows both a 31P{1H} and a 1H NMR spectrum
indicative of a single isomer product. The analogous reaction
with L3, however, leads after the same time interval to a
solution that has 31P{1H} and 1H NMR spectra indicative of a
more complex situation, with two isomers present in
approximately equal concentrations. On standing such a
solution for a further three days, the concentrations of these
two components are changed, such that the resonances to
higher field are of greater intensity with respect to those at
lower field in a ratio of 4 : 1. This slow interconversion indi-
cates that, although both isomers are formed initially, there is
a thermodynamically preferred isomer, and that over time, the
less favoured kinetic product isomerises to the more stable
geometry. The rate at which the equilibrium is reached is
somewhat dependent upon the solvent, such that solutions
kept in CDCl3 show a slightly reduced rate of equilibration
with respect to those kept in CH2Cl2 .
This kind of isomerism is also seen for the corresponding
iridium complexes. In the case of L2, after five hours reaction
the 31P{1H}NMR spectrum shows a single set of resonances
indicative of a single isomer product. After a period of five
days in chloroform solution at room temperature, a second set
of resonances is present at intermediate field suggesting the
formation of the second isomer. For the complex with L3, the
rate of isomerisation is somewhat slower.
To further probe the isomerisation processes, we added
aliquots of THF or excess ligand to the solutions of the sam-
ples. Addition of THF to a CH2Cl2 solution of [L3RhCl]2
increases the rate of interconversion. For [L2IrCl]2 and
[L3IrCl]2 similar results are seen, where addition of THF
accelerates the rate of interconversion. The addition of a cat-
alytic quantity of excess ligand in both cases gives a much
There is a well-developed field of coordination chemistry
based upon bisphosphines doubly oxidised by sulfur or sele-
nium, but very few reports of the monoxidised versions have
appeared. In the case of an achiral analogue of L3 prepared
from aniline, the value for 2J(31P-31P) is ca. 110 Hz and
1J(31P-77Se) is 766 Hz.12 In a related system, Smith et al. have
reported N,N-bis(diphenylphosphino)-2-methoxyaniline, an
analogue of L1 that has a coupling between the two phos-
phorus nuclei of 103 Hz.13 We attribute the variation between
the values of the phosphorus-to-phosphorus coupling to the
difference in the basicity of the nitrogens. In these two pre-
viously reported cases, where the amine is aromatic, there is a
marked difference in basicity at the nitrogen with respect to
that of the ligands L2 and L3 reported here, wherein the amine
is essentially alkyl. This in turn will have an effect on the
nature of the (P–N) bonds and thus the extent to which the
phosphorus centres will couple.
The new ligands L2 and L3 present a mixed [P,E] donor set
that can chelate to a metal centre to form a five-membered
inorganic ring. Perhaps the main feature that they offer is
electronic asymmetry, and with specific reference to this
property, we have prepared a number of complexes of transi-
tion metals using these ligands to explore their characteristics.
Complexes of L1–3 with Rh(I) and Ir(I)
Two equivalents of the bisphosphine L1 react with [(cod)-
M(I)Cl]2 (M ¼ Rh or Ir) to give the neutral chloro-bridged
dimers [(k2-L1-P,P)M(I)Cl]2 [L1RhCl]2 and [L1IrCl]2 in pre-
ference to the monoanionic bridge-cleaved products [(k2-L1-
P,P)(cod)M(I)]Cl. This is established by the NMR spectra,
which indicate the presence of complexed L1 and the absence
of cod, and the IR spectra, which show the presence of the
chloro bridge. The chemical shift in the 31P{1H}NMR spectra
show characteristic downfield shifts, and the coupling
1J(31P-103Rh) of 123.2 Hz in [L1RhCl]2 is typical for phos-
phines coordinated to rhodium(I) centres.
886
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greater increase in the rate of isomerisation. These findings
together indicate that the interconversion is catalysed by the
addition of a ligand species, which may suggest that the
mechanism involves an intermediate in which an incoming
ligand forms initially a five-coordinate metal centre. This can
then either undergo a pseudorotation to exchange the ligand
positions or cleavage of one halide bridge followed by rotation
about the remaining M–X–M axis before re-establishment of
the M–X–M bridge to reform the dimer, a process that could
lead to exchange of the P and E positions.
We were interested in assigning geometries to the two iso-
mers and so examined the spectroscopic data to this end. In the
case of the cis isomers, the two P(III) termini of the ligands are
both trans to a single chloro group in the halide bridge, and so
it seems reasonable to assume that the extent to which electron
density is back-donated to the s* orbital of these phosphorus
is reduced with respect to the trans isomers, in which each
phosphorus has a different trans halide. From this, it can be
inferred that the cis isomers will show a greater coupling
between the phosphorus centres, as the degree of back-
donation is reduced with respect to the trans isomers and so
the P(III)–N bond length will be shorter in the cis isomer.
Furthermore, the cis isomer might also be expected to show a
more low-field value for d as the electron density about the
nucleus is, by the same arguments, reduced. In the case of
[L3RhCl]2 , the less stable isomer shows a greater coupling
than the more stable one and resonates at a lower field. In the
case of both [L2IrCl]2 and [L3IrCl]2 the less stable isomer
again shows a greater coupling, although the chemical shift
data is less conclusive. In this case, the chemical shifts for the
more stable isomer occur at a field between the P(V) and P(III)
resonances of the less stable isomer.
Fig. 3 The molecular structure of (k2-L2)PtCl2 , an ORTEP drawing
with 50% probability ellipsoids.
Considering the IR data, and in particular the bands asso-
ciated with the halide bridge, for the cis isomer a greater degree
of asymmetry is expected in the M–X system. In the case of the
complex [L2IrCl]2 it was possible to isolate samples of the two
isomers independently. Comparing the spectra from these two
isomers, there are more n(M–X) absorptions seen for the
initially produced isomer than in the final isomer. The inference
from this data is consistent with that from the 31P{1H}NMR
data, and so we tentatively assign the initially formed isomer to
the cis geometry and the preferred isomer to trans.
Fig. 4 The molecular structure of (k2-L3)PtCl2 , an ORTEP drawing
with 50% probability ellipsoids.
Complexes of L2 and 3 with Pd(II) and Pt(II)
Reaction of L2 or L3 with (cod)M(II)Cl2 (M ¼ Pd or Pt) forms
complexes of general formula (k2-L-P,E)M(II)Cl2 . The che-
mical shift in the 31P{1H} NMR spectra and the values of the
couplings 2J(31P-31P), 1J(31P-77Se), 1J(31P-31Pt) and 2J(31P-
31Pt) all fall within the range of typical values. The structures
of (k2-L2-P,S)Pd(II)Cl2 , (k2-L3-P,Se)Pd(II)Cl2 , (k2-L2-
P,S)Pt(II)Cl2 and (k2-L3-P,Se)Pt(II)Cl2 were all determined by
single crystal X-ray diffraction measurements and are pre-
sented in Figs. 3 and 4. The metrical parameters are presented
in Table 1 and the values of selected bond lengths and angles
are given in Table 2.
The overall structure of the complexes is square planar in
each case with cis disposition of the chloro ligands and in each
case the chelate ring is almost flat. The structures of the pal-
ladium and platinum complexes of the same ligand are iso-
morphous. The conformations of the ligands in all four
complexes are very similar, even though the phosphine sulfide
complexes and phosphine selenide complexes crystallise in
different space groups and one lattice accommodates a solvent.
Comparison of the structures of the two pairs of complexes
allows for discussion of the effect of varying the chalogen. The
distances M–Cl can be used to evaluate and compare the trans
influence of the phosphine sulfide with respect to the phos-
trans to the P(III) terminus of L2. For the corresponding pla-
tinum complex, a similar though smaller variation is seen, with
+
the Pt–Cl trans to the chalcogen 0.022 A shorter than the Pt–
Cl trans to the P(III). For the complexes of L3, the effect is
similar but smaller, with 0.045 A between the two Pd–Cl dis-
+
tances and no measurable difference between the two Pt–Cl
distances. The implication of this latter observation is that the
overall trans influence of the phosphine selenide is in this case
not greatly different from the phosphine itself. For the palla-
dium complex of L3, however, there is a difference between the
two Pd–Cl distances and this may indicate that the extent to
which there is a hard-soft match between the metal and the
chalcogen on the P(V) terminus of the ligand controls the
degree to which the trans influence is expressed.
The distance M–E is significantly longer in the cases where E
is Se than those where E is S, and for the platinum complexes,
there is a corresponding compression of the M–P distance
in the selenium-containing ring compared to the sulfur-
containing ring. This allows an internal compensation for the
change in size and softness of the chalcogen whilst maintaining
the overall geometry of the ring. There is also a corresponding
compression of the angle Pt–E–P from 101.2 to 98.5ꢁ between
the sulfide and the selenide as part of the same reorganisation
of the ring.
phine selenide. For the monosulfide complex of palladium, the
Pd–Cl trans to the chalcogen is 0.059 A shorter than the Pd–Cl
+
New J. Chem., 2002, 26, 883–888
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3
4
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Suranna and R. Wang, Inorg. Chim. Acta, 1998, 280, 150.
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tallics, 1997, 16, 2127.
A. Bader and E. Lindner, Coord. Chem. Rev., 1991, 108, 27.
V. V. Grushin, Organometallics, 2001, 20, 3950; V. V. Grushin, J.
Am. Chem. Soc., 1999, 121, 5831.
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Faller, B. J. Grimond and D. G. D’Alliessi, J. Am. Chem. Soc.,
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P. Bhattacharyya, A. M. Z. Slawin, D. J. Williams and J. D.
Woollins, J. Chem. Soc., Dalton T rans., 1995, 3189; P. Bhatta-
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Woollins and Z. Pikramenou, Chem. Commun., 1999, 61;
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Conclusion
By direct reaction of a simple chiral bisphosphine with ele-
mental sulfur or selenium, we have prepared the first chiral
bisphosphine monosulfide and -selenide. These ligands coor-
dinate metals from group nine or ten to form chelated com-
plexes. The ease of preparation of such ligands would suggest
that there is a wealth of coordination chemistry available using
such new heterobidentate chiral ligands prepared from chiral
bisphosphines and elemental sulfur or selenium.
5
6
7
8
9
Acknowledgement
Two of us (J.P., J.L.-F.) thank Loughborough University for
support and Johnson–Matthey plc for the loan of precious
metal salts. One of us (J.W.F.) acknowledges support from the
National Science Foundation (Grant CHE0092222).
10 G. Giordano and R. H. Crabtree, Inorg. Synth., 1990, 28, 88.
11 R. P. Kamalesh Babu, S. S. Krishnamurthy and M. Nethaji,
Tetrahedron: Asymmetry, 1995, 6, 425; N. C. Payne and D. W.
Stephen, J. Organomet. Chem., 1981, 221, 203; D. F. Clemens
and W. E. Perkinson, Inorg. Chem., 1974, 13, 333.
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