Co-ordination chemistry and metal catalysed carbonylation reactions using 8-(diphenylphosphino)methylaminoquinoline: A ligand that displays monodentate, bidentate and tridentate co-ordination modes

Article abstract of DOI:10.1039/b200401a

Reaction of (diphenylphosphino)methanol with 8-aminoquinoline gives a novel potentially tridentate ligand, 8-(diphenylphosphino)methylaminoquinoline. The co-ordination chemistry of this ligand has been studied. Reaction with [Cp*RhCl₂]₂ gave a P-monodentate complex that was characterised by X-ray crystallography. On addition of one equivalent of silver salts, a 50:50 mixture of a tridentate dicationic complex and the starting material is formed. We describe this somewhat unusual co-ordination behaviour as 2/3 labile. If two equivalents of silver salts are used, the tridentate complex can be isolated and fully characterised. Iridium, ruthenium, palladium and platinum complexes are also described in which the ligand acts as mono- bi-, and tri-dentate. The ligand was also tested as a stabilising ligand in palladium and rhodium catalysed carbonylation reactions.

Full text of DOI:10.1039/b200401a

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Co-ordination chemistry and metal catalysed carbonylation
reactions using 8-(diphenylphosphino)methylaminoquinoline:
a ligand that displays monodentate, bidentate and tridentate
co-ordination modes
Matthew L. Clarke, David J. Cole-Hamilton, Douglas F. Foster, Alexandra M. Z. Slawin and
J. Derek Woollins*
School of Chemistry, University of St. Andrews, St. Andrews, Fife, UK KY16 9ST.
E-mail: jdw3@st-andrews.ac.uk
Received 11th January 2002, Accepted 15th February 2002
First published as an Advance Article on the web 25th March 2002
Reaction of (diphenylphosphino)methanol with 8-aminoquinoline gives a novel potentially tridentate ligand,
8-(diphenylphosphino)methylaminoquinoline. The co-ordination chemistry of this ligand has been studied. Reaction
with [Cp*RhCl2]2 gave a P-monodentate complex that was characterised by X-ray crystallography. On addition of
one equivalent of silver salts, a 50 : 50 mixture of a tridentate dicationic complex and the starting material is formed.
We describe this somewhat unusual co-ordination behaviour as 2/3 labile. If two equivalents of silver salts are used,
the tridentate complex can be isolated and fully characterised. Iridium, ruthenium, palladium and platinum
complexes are also described in which the ligand acts as mono- bi-, and tri-dentate. The ligand was also tested
as a stabilising ligand in palladium and rhodium catalysed carbonylation reactions.
Hemilabile ligands containing P,N donor sets continue to
provide novel applications in catalysis and organometallic
Experimental
chemistry.1 Important examples are the large range of chiral
P,N ligands that have been shown to provide excellent enantio-
selectivity in several asymmetric processes,2 the use of
phosphine-imine ligands (1) in palladium catalysed C–C bond
forming reactions,3 pyridylphosphine (2)–palladium complexes
that catalyse the carbonylation of alkynes,4 and nickel pro-
moted C–C bond forming reactions.5 We have recently become
interested in synthesising new amine containing phosphine lig-
ands and applying them in catalysis. We have prepared a variety
of novel PN ligands and observed a varying propensity towards
the formation of η2-P, N -chelate complexes.6 The co-ordination
chemistry observed for these ligands obviously has a profound
effect on their catalytic properties, and we have recently found
that PN ligands such as (3), that do not readily form stable
chelate complexes have considerable potential in palladium
catalysed C–C bond forming reactions.7
General
All manipulations were carried out under an atmosphere of
nitrogen, unless stated otherwise. All solvents were either
freshly distilled from an appropriate drying agent (THF, Et2O,
CH2Cl2) or obtained as anhydrous grade. H, and 31P NMR
1
spectra were recorded using a “Varian 2000” 300 MHz
spectrometer. IR spectra were recorded as KBr discs (pre-
pared in air) on a Perkin Elmer PE1720 FTIR/RAMAN
spectrometer. Silver salts, diphenylphosphine, formaldehyde,
8-aminoquinoline (Accros Organics Ltd.), were purchased
and used as received. [Cp*MCl2]2 (M = Ir, Rh), [(COD)-
PtCl2], [(PhMe2P)PtCl2]2, and [(Cym)RuCl2]2 (Cym
=
para-cymene) were prepared by literature methods.8–11 All
IR bands above 1000 cmϪ1 have been quoted to serve as a
fingerprint.
X-Ray crystallography
Crystal structures were obtained using a Bruker SMART dif-
fractometer with graphite-monochromated Mo-Kα radiation
(λ = 0.71073 Å) at 293 K. Intensity data were collected using
0.3 or 0.15Њ width ω steps accumulating area detector frames
spanning a hemisphere of reciprocal space for all structures. All
data were corrected for Lorentz, polarisation and long term
intensity fluctuations. Absorption effects were corrected on the
basis of multiple equivalent reflections. Structures were solved
by direct methods and refined by full-matrix least squares
against F 2 (SHELXTL)12 for all data with I > 3σ(I ). See Table
1 for details.
We envisaged that a phosphine ligand that contains two addi-
tional N donor atoms might show interesting co-ordination
behaviour. Furthermore, these types of ligand have not been
studied in transition metal catalysed reactions that are particu-
larly suited to the use of PN ligands. In this paper we report on
the synthesis of a new phosphine ligand (8-(diphenylphos-
phino)methylaminoquinoline) (4) that contains two auxiliary
amine substituents, its co-ordination chemistry and application
in rhodium and palladium catalysed carbonylation reactions.
CCDC reference numbers 177445 and 177446.
See http://www.rsc.org/suppdata/dt/b2/b200401a/ for crystal-
lographic data in CIF or other electronic format.
1618
J. Chem. Soc., Dalton Trans., 2002, 1618–1624
This journal is © The Royal Society of Chemistry 2002
DOI: 10.1039/b200401a

View Article Online
Table 1 Crystal data for compounds (4) and (5)
(4)
(6) as a green/yellow solid in high purity in essentially quanti-
tative yield. Found: C, 51.37; H, 4.33; N, 3.68; C32H34N2-
PRhB2F8 requires: C, 50.97; H, 4.54; N, 3.71%. IR (νmax/cmϪ1
(5)
)
3423, 3058, 1640, 1618, 1588, 1574, 1513, 1437, 1378, 1315,
Empirical formula
M
Crystal system
Space group
a/Å
b/Å
C22H19N2P
342.36
Orthorhombic
Pna21
8.6824(6)
25.822(2)
8.2049(5)
1839.5(2)
4
0.155
7576
2566
0.0388, 0.0743
C32H34Cl2N2PRh
651.39
Orthorhombic
Pna21
21.779(2)
8.4708(8)
16.304(2)
3007.9(5)
4
0.822
12242
4269
0.0390, 0.0749
1261, 1034. 31P NMR (121.4 MHz; CDCl3): δ Ϫ20.1 (JP–Rh
=
=
1
118 Hz). H NMR (300 MHz; CDCl3): δ 1.6 (15H, d, JH–Rh
4.1 Hz), 4.8 (2H, dd app. (app. = apparent), J = 4.8, 15.8 Hz, H1
and H2), 6.7 (1H, m, H3), 7.3–8.2 (14H, m, PArH and quin-
olineH), 8.5 (1H, d, J = 8.3 Hz, H9), 9.55 (1H, d, J = 4.9 Hz, H4).
13C NMR (75. 5 MHz, CDCl3) δ 8.9, 53.4, 101.8, 122 (dd app.
JC–P = 50Hz), 126.7 (d, JC–P = 39 Hz), 129 (d, JC–P = 9 Hz), 129.8,
130.2, 130.3, 130.4, 130.5 132.3 (d, JC–P = 11 Hz), 133.0, 133.3,
133.4, 140.0, 144.3 (d, JC–P = 27 Hz), 157.4. HRMS (ESϩ):
Found: 667.1546, (M Ϫ 2BF4) requires 667.1544.
c/Å
U/Å3
Z
µ/mmϪ1
Reflections measured
Independent reflections
Final R1, wR2[I > 2σ(I )]
[Cp*IrCl2(P-8-dppmaq)] (7)
This compound was obtained in a similar fashion to the
analogous rhodium complex, and precipitated from CH2Cl2
solution with diethyl ether to give a burgundy coloured solid.
Yield: 50 mg, 6.75 × 10Ϫ5 mol, 41%. Found: C, 51.96; H, 4.30;
N, 3.83. C32H34N2PCl2Ir requires: C, 51.89; H, 4.63; N, 3.78%.
IR (νmax/cmϪ1) 3357, 3045, 1612, 1574, 1522, 1479, 1440, 1422,
8-(Diphenylphosphino)methylaminoquinoline (4)
A solution of (diphenylphosphino)methanol (2.585 g, 11.955
mmol) in degassed acetonitrile (30 ml) was added slowly (ca.
2–5 h) to a boiling solution of 8-aminoquinoline in acetonitrile
(1.72 g, 11.955 mmol in 30 ml solvent). The reaction mixture
was held at reflux overnight prior to cooling and the addition of
magnesium sulfate. Filtration (using a filter stick) followed
by removing all volatile material gave the crude product (of
varying purity) in high yield. Size exclusion chromatography
(Biobeads SX80) under anaerobic conditions using degassed
dichloromethane as eluent (product is second fraction) and
removal of solvents in vacuo yielded the analytically pure
material as an orange oil that solidified on standing (1.95 g, 5.70
mmol, 48%). Found: C, 76.95; H, 5.53; N, 7.70. C22H19N2P
requires: C, 77.18; H, 5.59; N, 8.18%. IR (νmax/cmϪ1) 3412, 3070,
1610, 1574, 1524, 1479, 1432, 1385, 1342, 1249, 1228, 1124.
31P NMR (121.4 MHz; CDCl3): δ Ϫ20.4. 1H NMR (300 MHz;
CDCl3): δ 4.2 (2H, dd, J = 5 Hz, other coupling not fully
resolved H1 and H2), 6.6 (1H, s, br, H3), 6.9 (1H, d, J = 7.6 Hz,
H7), 7.15 (1H, dd, J = 0.9, 8.2 Hz, H6), 7.25–7.7 (12H, m, P-aryl,
H5 and H8), 8.1 (1H, dd, J = 1.7, 8.3 Hz, H9), 8.7 (1H, dd, J =
1.7, 4.2 Hz, H4). 13C NMR (75. 5 MHz, CDCl3) δ 43.7 (d,
J = 11 Hz), 105.2, 114.1, 121.1, 127.4, 128.4, 128.5, 128.7 132.7
(d, J = 18.2 Hz), 135.6, 136.6 (d, J = 13.4 Hz), 138.0, 144,7,
147.2.
1379, 1340, 1191, 1122, 1102. 31P NMR (121.4 MHz; CDCl3):
1
δ Ϫ1.64. H NMR (300 MHz; CDCl3): δ 1.4 (15H, d, JH–P
=
1.92 Hz) 5.0 (2H, d, J = 7.2 Hz, H1 and H2), 6.4 (1H, d, J = 8 Hz,
H3), 6.8 (1H, d, J = 8.0 Hz, H7), 6.95 (1H, t, J = 7.8 Hz, H6),
7.2–7.6 (8H, m, PArH and quinolineH), 7.9 (5H, m, PArH
and quinolineH), 8.5 (1H, dd, J = 1.7, 4.0 Hz, H4). 13C NMR
(75. 5 MHz, CDCl3) δ 8.2, 42.4 (d, JC–P = 32 Hz), 92.1, 105.6,
113.6, 121.0, 127.6, 128.0 (d, JC–P = 9.7 Hz), 131.0, 134.7 (d,
JC–P = 8.7 Hz), 135.8, 146.5. HRMS (ESϩ): Found: 669.2012,
M Ϫ 2Cl Ϫ H requires 669.2014.
[Cp*Ir(8-dppmaq)]2BF4 (8)
Compound (8) was prepared similarly to the analogous
rhodium complex, using 50 mg, 6.75 × 10Ϫ5 mol of (7), and 26
mg, 1.35 × 10Ϫ4 mol of silver tetrafluoroborate, giving after
centrifugation, (8) (57 mg, quantitative yield). Found: C, 45.77;
H, 3.98; N, 3.25. C32H34N2PIrB2F8 requires: C, 45.57; H, 4.00;
N, 3.32%. IR (νmax/cmϪ1) 3438, 2919, 1630, 1589, 1574, 1514,
1438, 1382, 1316, 1261, 1083. 31P NMR (121.4 MHz; CDCl3):
1
δ Ϫ38.7. H NMR (300 MHz; CDCl3): δ 1.65 (15H, d, JH–P
=
2.9 Hz), 5.56 (2H, dd app., J = 16, 2.5 Hz, H1 and H2),
7.3–8.2 (14H, m, PArH and quinolineH), 8.4 (1H, d, J = 8.1 Hz,
ArH), 8.8 (1H, t, J = 8.6 Hz, H6) 9.65 (1H, d, J = 5.3 Hz, H4).
13C NMR (75. 5 MHz, CDCl3) δ 7.3, 95.7, 126.8, 127.8, 129.3,
130.2, 130.4 (d, 8 Hz), 130.8, 132.6 (d, JC–P = 11.5 Hz), 133.3
(d, JC–P = 11.5 Hz), 133.7, 140.1, 146.4, 157.6. ESMS 757,
M Ϫ BF4, 669, M Ϫ BF4 Ϫ HBF4.
[Cp*RhCl2(P-8-dppmaq)] (5)
This compound was obtained by the addition of a CH2Cl2
solution of 8-dppmaq (4) to a CH2Cl2 solution of [Cp*RhCl2]2.
After stirring for 30 min, solvent was reduced to near dryness
and Et2O added to give a red precipitate (essentially quanti-
tative yield of pure material) that was dried in vacuo. Recrystal-
lisation by slow diffusion (CH2Cl2/Et2O) gave a few high quality
crystals suitable for an X-ray crystal structure determination.
Found: C, 58.29; H, 4.93; N, 4.07. C32H34N2PRhCl2 requires:
C, 59.00; H, 5.26; N, 4.30%. IR (νmax/cmϪ1) 3359, 3043, 1611,
[(Cym)RuCl2(P-8-dppmaq)] (9)
This compound was obtained in similar fashion to the
monodentate Rh and Ir compounds using 8-dppmaq (81 mg,
2.4 × 10Ϫ4 mol) and [(Cym)RuCl2]2 (72 mg, 1.18 × 10Ϫ4 mol),
and precipitated from a concentrated CH2Cl2 solution with
diethyl ether. Yield: 114 mg, 0.176 mmol, 74%. Found: C, 58.81;
H, 4.76; N, 4.20. C32H33N2PCl2Ru requires: C, 59.26; H, 5.13;
N, 4.32%. IR (νmax/cmϪ1) 3373, 3041, 1612, 1574, 1522, 1481,
1433, 1380, 1339, 1275, 1220, 1194, 1125, 1099. 31P NMR
1574, 1522, 1479, 1440, 1422, 1379, 1340, 1192, 1123, 1026. 31
P
NMR (121.4 MHz; CDCl3): δ 31.5 (JP–Rh = 141 Hz). 1H NMR
(300 MHz; CDCl3): δ 1.4 (15H, d, JH–P = 3.3 Hz), 5.0 (2H, d,
JH–P = 7.4 Hz, H1 and H2), 6.4 (1H, d, br, JH–H = 8 Hz, H3), 6.8
(1H, d, J = 8.0 Hz, H7), 6.95 (1H, t, J = 8.0 Hz, H6), 7.2–7.6 (8H,
m, P-aryl/quinolineH), 7.9 (1H, d, J = 8.0 Hz, H9), 8.0 (4H, t,
J = 8.7 Hz, PArH), 8.5 (1H, d, J = 2.8 Hz, H4). 13C NMR (75. 5
MHz, CDCl3) δ 5.4, 40.8 (d, J = 25 Hz), 95, 102.4, 110.4, 117.7,
124.4, 124.9 (d, J = 8.7 Hz), 127.8, 131.7 (d, J = 8.7 Hz), 132.6,
140.2, 143.3. FAB MS: m/z 651 (MH)ϩ, 615 (M Ϫ Cl)ϩ, 580
(M Ϫ 2Cl)ϩ. HRMS (ESϩ): Found: 615.1201, M Ϫ Cl requires
615.1203.
1
(121.4 MHz; CDCl3): δ 26.4. H NMR (300 MHz; CDCl3):
δ 0.85 (6H, d, J = 6.9 Hz, Cym CH(CH3)2), 1.8 (3H, s, Cym
CH3), 2.4 (1H, m, CymCH) 4.7 (2H, d, J = 7.0 Hz, H1 and H2),
5.2 (2H, d, J = 6.1 Hz), 6.1 (2H, m), 6.8 (1H, d, J = 8 Hz, H7),
7.0 (1H, t, J = 8.2 Hz, H6), 7.1–7.5, (8H, m, ArH), 7.8–8.0 (6H,
m, ArH), 8.5 (1H, dd, J = 4.1, 1.7 Hz). 13C NMR (75. 5 MHz,
CDCl3) δ 17.2, 21.5, 30.1, 39.0 (d, J = 26 Hz), 86.0, 90.0, 104,
108, 114, 121, 127.4, 128.2 (J = 9.4 Hz), 130.8, 131.4, 134.1 (d,
J = 8 Hz), 146.6. HRMS (ESϩ): Found: 649.0888, MHϩ
requires 649.0874.
[Cp*Rh(8-dppmaq)]2BF4 (6)
Addition of two equivalents of silver tetrafluoroborate to a
solution of (5) gave, after filtration through Celite complex
J. Chem. Soc., Dalton Trans., 2002, 1618–1624
1619

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cis- and trans-[(P-8-dppmaq)2PdCl2] (10) and (11)
Found: C, 46.83; H, 3.63; N, 3.68. C30H30N2P2Cl2Ptؒ0.5CH2Cl2
requires: C, 46.43; H, 3.96; N, 3.55%. IR (νmax/cmϪ1), 3385,
3051, 1611, 1573, 1516, 1479, 4 1435, 1380, 1337, 1124, 1103.
31P NMR (121.4 MHz; CDCl3): δ Ϫ15.20 (d ϩ Pt satellites,
To a stirred solution of 8-dppmaq (125 mg, 0.365 mmol)
in dichloromethane (8 ml) was added [(COD)PdCl2] (52 mg,
0.183 mmol) in one portion. This reaction was stirred for one
hour prior to reducing the solvent volume by half, and precipi-
tating the compound with diethyl ether. The precipitate was
washed with Et2O and dried in vacuo to give an orange solid.
Yield: 115 mg, 0.133 mmol, 73%. Found: C, 60.85; H, 4.57;
N, 6.04. C44H38N4PCl2Pd requires: C, 61.30; H, 4.44; N, 6.50%.
IR (νmax/cmϪ1) 3374, 3049, 1612, 1574, 1517, 1479, 1435, 1380,
1339, 1255, 1226, 1101, 819, 742. 31P NMR (121.4 MHz;
CDCl3): δ 25.7 (s, assumed to be cis), 14.2 (s, assumed to be
trans). 1H NMR (300 MHz; CDCl3): δ 4.63 (2H, d, J = 6.9 Hz)
and 4.81 (2H, d, J = 6.9 Hz) (signal for cis and trans isomers),
6.44 (1H, s, br) and 6.50 (1H, s, br) (signals for cis and trans
isomers), 6.9–8.2 (15H, m, ArH for both cis and trans), 8.6 (1H,
d, J = 4.3 Hz). HRMS (ESϩ): Found: 825.1306, C44H38N4P2-
PdCl [M Ϫ Cl]ϩ requires 825.1295.
1
2
2JP–P = 15.6 Hz, JP–Pt = 3519 Hz), 5.70 (d ϩ Pt satellites, J =
1
1
15.6 Hz, J = 3685 Hz). H NMR (300 MHz; CDCl3): δ 1.62
(6H, d, JH–P = 11.3 Hz), 4.71 (2H, d, J = 6.0 Hz, H1 and H2), 5.27
(0.6H, s, CH2Cl2), 6.38 (1H, d, J = 7.7 Hz, H7), 6.50 (1H, s, br,
H3), 6.9–7.7 (18H, m, ArH), 8.0 (1H, d, 8.0 Hz, H6), 8.6 (1H,
dd, J = 1.7, 4.1 Hz, H4). HRMS (ESϩ) Found: 710.1210;
C30H30N2PtP2Cl (M Ϫ Cl)ϩ requires 710.1221.
Carbonylation and hydroformylation reactions
These were conducted in a stainless steel autoclave held at
constant pressure and connected to a ballast vessel from which
CO (or syngas) was fed. Reaction rates were determined by
measuring gas uptake over time, and further confirmed by
GCMS analysis of the reaction products. The identities of the
reaction products were established by comparison of retention
times and mass spectra with authentic samples.
cis-[(8-dppmaq)2PtCl2] (12)
To a stirred solution of 8-dppmaq (133mg, 0.403 mmol)
in dichloromethane (8 ml) was added [(COD)PtCl2] (75 mg,
0.202 mmol) in one portion. This reaction was stirred for one
hour prior to reducing the solvent volume by half, and precipi-
tating the compound with diethyl ether. The precipitate was
washed with Et2O and dried in vacuo to give a purple coloured
solid. Yield: 0.115 mg, 0.121 mmol, 60%. Found: C, 56.24;
H, 3.57; N, 5.76. C44H38N4PCl2Pt requires: C, 55.59; H, 4.03; N,
5.89%. IR (νmax/cmϪ1) 3365, 3057, 1612, 1574, 1516, 1446, 1436,
1380, 1338, 1258, 1227, 1199, 1102. 31P NMR (121.4 MHz;
CDCl3): δ 6.10 (s = Pt satellites, JP–Pt = 3653 Hz). 1H NMR (300
MHz; CDCl3): δ 4.72 (2H, d, J = 5.8 Hz, H1 and H2), 6.54 (1H,
d, J = 7.7 Hz, H3), 6.57 (1H, t, J = 6.7 Hz, H7), 6.98 (6H, t,
J = 7.1 Hz, ArH), 7.15 (1H, t, J = 8.0 Hz, ArH), 7.27 (1H, t, J =
7.3 Hz, ArH), 7.32 (1H, dd, J = 4.1, 8.2 Hz, ArH), 7.56 (4H, t,
J = 8.6 Hz, PArH and quinolineH), 8.0 (1H, dd, J = 7.4, 1.8 Hz,
H9), 8.59 (1H, dd, J = 4.1, 1.7 Hz, H4). 13C NMR (75.4 MHz;
CDCl3): δ 41.7 (d, J = 49 Hz), 102.9, 111.7, 118.4, 124.3, 125.1
(t, J = 5.4 Hz), 128.1, 130.9 (t, J = 4.3 Hz), 132.6, 135.0,
140.2, 144.1. HRMS (ESϩ): Found: 914.1926, C44H38N4P2PtCl
[M Ϫ Cl]ϩ requires 914.1908.
Carbonylation of phenylacetylene. A golden solution of
Pd(OAc)2 (1.83 × 10Ϫ5 mol), 2-PyPPh2 (2) (3.64 × 10Ϫ4 mol),
and p-MeC6H4SO3HؒH2O (7.29 × 10Ϫ4 mol) in MeOH (5 ml)
was added to the autoclave. The solution was flushed with sev-
eral cycles of CO (ca. 20 bar) while stirring. The autoclave was
then pressurised (55 bar) and brought to 60 ЊC. Phenyl acetyl-
ene (1.82 × 10Ϫ2 mol) was then injected and the pressure
brought up to 60 bar. The gas uptake was followed over time.
Hydroformylation of 1-hexene. Rh(acac)CO2 (0.01 mol dmϪ3
)
and 8-dppmaq (0.23 mol dmϪ3) in toluene (4 ml) were added to
the autoclave which was then flushed with syngas. The auto-
clave was then pressurised (14 bar) and stirred at 100 ЊC for one
hour to allow the catalyst to form. Hex-1-ene (1 ml) was
injected and the pressure adjusted to 20 bar. The gas uptake was
followed over time.
Results
(a) Ligand synthesis
A simple way to prepare a PNN type phosphine, would be the
condensation of a diamine with Ph2PCH2OH. This type of
reaction is a useful method of phosphine synthesis as products
of high purity can often be obtained under mild conditions.
Ligand (4), which we have given the acronym 8-dppmaq, is
obtained by the condensation reaction of diphenylphosphino-
methanol with 8-aminoquinoline in refluxing acetonitrile
(Scheme 1). A dilute solution of the phosphine is added slowly
Reaction of (12) with silver salts
To a stirred solution of [(8-dppmaq)2PtCl2] in dichloromethane
was added silver perchlorate or silver tetrafluoroborate (one or
two equivalents) in one portion. This reaction was stirred for
overnight prior to filtration through Celite (or centrifugation),
and dried in vacuo. The crude products were analysed spectro-
scopically. Attempts to obtain analytically pure material by
recyrstallisation/size exclusion chromatography were unsuc-
cessful. IR (νmax/cmϪ1) 3337, 3055, 1620 (sh), 1613, 1576, 1518,
1473, 1437, 1381, 1100. 31P NMR (121.4 MHz; CDCl3): major
2
1
product: δ 4.65 (d, JP–P = 14.2 Hz, JP–Pt = 3686 Hz), 2.60 (d,
2JP–P = 14.2 Hz, 1JP–Pt = 3734 Hz). 1H NMR (300 MHz; CDCl3):
the proton NMR was obtained from the crude mixture, thus
making it difficult to obtain detailed information and meaning-
ful integrals. δ 3.6 (2H, d, J = 15.8 Hz), 4.5 (m), 4.8 (1H, m),
6.6–8.0 (m, ArH), 8.17 (d, J = 7.14 Hz), 8.26 (d, J = 7.14Hz),
8.87 (dd, J = 1.4, 4.1 Hz), 9.74 (d, J = 3 Hz). MS (ESϩ): Found:
878.2148, M Ϫ Cl Ϫ ClO4 requires 878.2142. Also M Ϫ ClO4
present as highest mass ion.
Scheme 1
to the aminoquinoline to prevent di-substitution, although
some side products are observed in the crude product. The
ligand is obtained in analytically pure form after size exclusion
chromatography under anaerobic conditions. On one occasion,
this synthesis gave essentially pure ligand directly with no need
for any purification. Although we anticipated (8) to act as a P,N
bidentate ligand, the possibility of tridentate co-ordination is
also present.
cis-[(PhMe2P)(8-dppmaq)PtCl2] (13)
A solution of 8-dppmaq (98 mg, 0.286 mmol) in CH2Cl2 (5 ml)
was added to
a
solution of the platinum dimer
[(PhMe2P)PtCl2]2 (116 mg, 0.143 mmol). After stirring for one
hour, solvent was reduced to half the volume and Et2O added
to give a purple precipitate. Yield: 110 mg, 0.147 mmol, 52%.
1620
J. Chem. Soc., Dalton Trans., 2002, 1618–1624

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Table 2 Selected bond lengths (Å) and angles (Њ) for (5)
(b) X-Ray crystal structure of (4)
Orange crystals of 8-dppmaq could be obtained by layering a
CH2Cl2 solution with hexane. The crystal structure of (4),
shown in Fig. 1, shows that 8-dppmaq forms a monomeric
Rh(1)–Cl(1)
Rh(1)–Cl(2)
Rh(1)–C(31)
Rh(1)–C(32)
Rh(1)–C(33)
Rh(1)–C(34)
Rh(1)–C(35)
2.413(3)
2.414(3)
2.171(8)
2.168(5)
2.144(8)
2.221(7)
2.219(7)
Rh(1)–P(1)
P(1)–C(1)
P(1)–C(7)
P(1)–C(13)
N(13)–C(14)
C(13)–N(13)
C(14A)–N(21)
2.322(2)
1.806(8)
1.820(7)
1.869(6)
1.372(9)
1.444 (8)
1.349(11)
P(1)–Rh(1)–Cl(1)
C(14)–N(13)–C(13) 124.6(7)
87.91(6)
Cl(1)–Rh(1)–Cl(2)
P(1)–Rh(1)–Cl(2)
91.84(6)
87.26(6)
Fig. 1 X-Ray crystal structure of 8-dppmaq (4). Selected bond lengths
(Å) and angles (Њ): P(1)–C(1) = 1.832(3), P(1)–C(7) = 1.835(4), P(1)–
C(13) = 1.870(3), C(13)–N(13) = 1.429(4), C(14)–N(13) = 1.373(4),
C(14A)–N(21) = 1.374(8); N(13)–C(13)–P(1) = 112.3(2), C(14)–N(13)–
C(13) = 125.9(3).
Fig. 2 X-Ray crystal structure of [Cp*RhCl2(8-dppmaq)] (5).
structure in the solid state in which the aromatic NH forms an
intramolecular hydrogen bond with the quinoline nitrogen
(hydrogen bond acceptor) H(13N) ؒ ؒ ؒ N(21) = 2.14(3) Å;
N(13) ؒ ؒ ؒ N(21) = 2.676(4) Å; N(13)–H(13N) ؒ ؒ ؒ N(21) =
113(3)Њ. Selected bond lengths and angles are shown in the
figure legend.
trans influence. The angles between chloride and phosphine
ligands are close to the idealised 90Њ. Rh–C, Rh–P, and Ph–Cl
bond lengths are fairly typical for this type of complex.6 A
notable feature of this structure is the intramolecular hydrogen
bond between the quinoline nitrogen and the NH functionality
(N(13) ؒ ؒ ؒ N(21) = 2.661(9) Å), which is very similar to that
found in the free ligand. It is possible that the presence of this
hydrogen bond makes the nitrogen atoms less susceptible to co-
ordination to transition metals. The ligand geometry and bond
lengths within the free ligand and the monodentate complex are
very similar. Selected bond lengths and angles are shown in
Table 2.
(c) Rhodium, iridium and ruthenium complexes derived from
8-dppmaq
A brief study of the co-ordination chemistry shown by this
ligand was carried out prior to any catalytic testing. As a start-
ing point, the reaction of this ligand with [Cp*RhCl2]2 (and
subsequent removal of chloride ions) seemed ideal as we had
recently studied the reactions of this metal fragment with sev-
eral other PN ligands.6 Reaction of (4) and [Cp*RhCl2]2 gives
the monodentate complex (5) (see Scheme 2). It is assigned
Addition of one equivalent of silver tetrafluoroborate to the
monodentate complex (5) generates a 1 : 1 mixture of a new
complex and the starting material. The new complex has its
NMR signal significantly upfield from that of the monodentate
compound (δ Ϫ20.1 vs. 31.5 ppm). This is strong evidence that a
four membered chelate ring is present, as this effect has been
observed in all other four membered phosphorus containing
1
rings.13 The H NMR spectrum of this mixture shows the pro-
ton ortho to the quinoline N atom to be significantly shifted
downfield (δ 9.6 vs. 8.5 ppm), which is a characteristic of
aromatic amine co-ordination in other systems. Addition of
two equivalents of AgBF4 to (5) gives only one product, (6).
The spectroscopic data for (6) corresponds to the compound
formed in 50% conversion when one equivalent of silver salt
was added.
Scheme 2
1
monodentate co-ordination by comparison of its IR and H
NMR data with that of the free ligand (no major changes). The
large downfield shift in the 31P NMR signal from (5) (with
respect to the free ligand) is fairly typical of a monodentate
The elucidation of structure (6) was achieved from the fol-
lowing data: 31P NMR indicates the formation of a four mem-
1
1
RhIII complex, as is the magnitude of JP–Rh. The fact that a
bered ring system (NH co-ordination), as does the H NMR
monodentate complex is formed suggests that (4) does not form
extremely strong chelates. We have reported an example of a
cationic complex of type [(η2-L-P, N )Rh(Cp*)Cl]Cl with one
PN ligand.6
The crystal structure of (5) (Fig. 2) shows this complex to be a
monomeric compound of octahedral geometry. The Cp* ligand
occupies three co-ordination sites of this octahedron. There is
an asymmetry regarding the Rh–C bond lengths within the η5-
Cp* ligand (Rh–C between 2.144(8) and 2.221(7) Å) which
reflects whether the carbon is trans to the strongly bound phos-
phine ligand or the chloride ligands, that exert a much lesser
spectrum, which shows a complex group of signals which we
have assigned as H1, H2 and H3 (see Scheme 1 and 3). The signal
due to the NH group (H3) appears as five lines. This compli-
cated signal can be rationalised if N co-ordination prevents
inversion at the (chiral) nitrogen atom, allowing coupling to
nearby protons to be observed. In addition, it is likely that this
proton is now coupling to the NMR active rhodium centre. The
two CH2[N–C(H1H2)–P] protons appear as two broadened
doublets. This multiplicity can be explained by coupling to the
NH proton being observed in the N co-ordinated species.
Alternatively, the diastereotopic nature of the two protons (due
J. Chem. Soc., Dalton Trans., 2002, 1618–1624
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Scheme 4
Scheme 3
to the chiral nitrogen atom) results in a separate signal for each
proton. The signals in this case could be expected to be compli-
cated by coupling to the P atom, the NH proton, and to each
other. Decoupling experiments did not shed any more light on
the exact nature of these signals, but in any case the spectrum
observed is fully consistent with NH co-ordination. Several of
the aromatic protons in the 1H NMR spectrum of (6) have been
shifted downfield with respect to the free ligand or complex (5).
Most notably, the signal assigned ortho to the aromatic N atom
has shifted downfield by ca. 1.1 ppm. This is fully consistent
with aromatic N co-ordination. We have not assigned every
aromatic carbon atom in the (complicated) 13C spectra of 8-
dppmaq (4) or its complexes (5) and (6). However, this spec-
trum also provides support for our proposed structure. In the
spectra of (4) and (5) the furthest downfield peak is the CH
carbon ortho to the aromatic N atom, and is found at 147 and
143 ppm respectively. In complex (6) this signal has shifted
downfield to 157 ppm, which must be considered additional
evidence for co-ordination from the aromatic amine moiety.
Several other aromatic carbons are also shifted downfield from
either the free ligand or the monodentate complex.
The IR spectrum of (6) shows peaks at 1640, 1618, and 1588
cmϪ1 which are significantly different from either the free ligand
(1610, 1574 cmϪ1) or monodentate complex (1611, 1574 cmϪ1).
The structure is finally confirmed by acceptable elemental
analysis and HRMS, which shows peaks corresponding to M Ϫ
2BF4ϩ. We have coined this co-ordination behaviour 2/3 labile.
The ligand has a preference for η1 co-ordination that can be
altered to η3 co-ordination under the appropriate conditions. It
does not appear possible to prepare a bidentate complex with
this type of metal fragment, ligand combination.
Scheme 5
precedent14 to be the cis and trans isomers (Scheme 5). No
attempt was made to separate these, as we felt that they could
well be an equilibrium mixture of the two isomers. The H
1
NMR spectrum, which is not especially informative shows the
CH2 protons (a doublet) appearing as two signals which have
approximately the same peak integration as that seen in the 31
P
NMR spectrum. We tentatively assign the cis complex as that
which is furthest upfield by analogy with the equilibriating
isomers of cis and trans [(PMe2Py)2PtCl2].
If two equivalents of 8-dppmaq are added to [(COD)PtCl2],
a P-monodentate bis-complex L2PtCl2 (12) of cis geometry (as
judged by the magnitude of JP–Pt) is obtained exclusively.
Attempts to obtain a PN chelate complex of formula LPtCl2
by slow addition of one equivalent of ligand to [(COD)PtCl2]
gave a 1 : 1 mixture of the L2PtCl2 complex and unreacted
[(COD)PtCl2]. From this we can conclude that 8-dppmaq shows
a marked preference for monodentate co-ordination with plat-
inum, as a large variety of hemi-labile ligands will form a P,N
chelate complex with platinum under these conditions.15 The 31
P
NMR spectrum of (12) shows the expected singlet with Pt
satellites (JP–Pt = 3653 Hz). The IR spectrum resembles the free
ligand and shows no evidence of a PN chelate. The proton
NMR spectrum of (12) does not show any downfield shift in the
protons adjacent to the quinoline nitrogen donor, or platinum
satellites in the signal attributed to NH. The spectroscopic
evidence unambiguously assigns the complex as that depicted
in Scheme 6.
This ligand shows essentially the same behaviour with
[Cp*IrCl2]2. 8-dppmaq reacts with the iridium dimer to produce
a burgundy coloured solid. The 31P NMR spectrum shows a
singlet at Ϫ1.6 ppm which represents a co-ordination chemical
shift of ϩ19 ppm (cf. Rh complex ∆δ = ϩ51.9 ppm). Reaction
with silver tetrafluoroborate gave a cream coloured solid which
was assigned the tridentate structure by spectroscopy and
chemical analysis. The position of the singlet in the 31P NMR
spectra shows a large shift upfield when the two chloride ligands
are removed by silver salts (η1 complex, δ Ϫ1.6; η3 complex, δ
Ϫ38.7 ppm). The 1H NMR spectrum shows similar features to
those discussed for the Rh complex, although the NH signal
appears somewhat different, as there is no possibility for M–H
coupling.
Scheme 6
We now wished to investigate which, if any of the nitrogen
donors might chelate to platinum if the chloride ligands were
removed. To this end (12) was reacted with one equivalent of
silver perchlorate (CAUTION: although no problems were
encountered during this work, perchlorate salts can be explos-
ive). The 31P NMR spectrum of the compound produced shows
a small amount of starting material (ca. 15–20%), a very small
amount of an unknown impurity, and as the major product, a
complex that displays two coupled doublets as its 31P NMR
The reaction of 8-dppmaq with [(Cym)RuCl2]2 gave the
expected monodentate complex (9) (see Scheme 4). However,
on treatment with either AgBF4 or AgClO4 extensive decomp-
osition took place with formation of an insoluble precipitate.
(d) Palladium and platinum complexes derived from 8-dppmaq
The reaction of two equivalents of 8-dppmaq with [(COD)-
PdCl2] gave an orange solid identified as [(8-dppmaq)2PdCl2] by
HRMS and microanalyses. The 31P NMR spectrum of this
compound contains two singlets that we assign, with literature
2
1
spectrum (δ 4.65, d, JP–P = 14.2 Hz, JP–Pt = 3686 Hz; 2.60, d,
2JP–P = 14.2 Hz, 1JP–Pt = 3734 Hz). The mass spectrum suggests
1622
J. Chem. Soc., Dalton Trans., 2002, 1618–1624

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that this species is monomeric, by showing peaks due to M Ϫ
ClO4 and M Ϫ Cl Ϫ ClO4 as the two highest mass ions. These
two pieces of data suggest that this is a monomeric complex in
which one phosphine is trans to chloride, and one phosphine is
trans to either co-ordinated quinoline nitrogen, perchlorate or
solvent. The fact that the 31P resonances appear at chemical
shifts very similar to the starting complex (12) rules out the
presence of a four membered P–C–N–Pt ring system in which
the NH is co-ordinated. Inspection of the 1H NMR data
immediately suggests that it is the aromatic quinoline nitrogen
that is bound to the platinum. The signal assigned to the proton
ortho to the quinoline nitrogen has shifted upfield to 9.8 ppm.
Other protons in the aromatic region are also shifted somewhat
upfield. The IR spectrum of this compound shows a weak
shoulder on the peak at 1620 cmϪ1. These two peaks are prob-
Fig. 3 PN chelate complexes formed on addition of silver salts to
complexes (12) and (13).
ably due to co-ordinated and unco-ordinated C᎐N stretching
᎐
(e) Rhodium catalysed hydroformylation of hex-1-ene
vibrations. It proved difficult to separate the by-products from
this major complex and confirm the molecular formula by
chemical analysis. Addition of two equivalents of silver per-
chlorate to (12) gave the same mixture of compounds, the only
difference being that the proportion of unknown compound
increased at the expense of unreacted starting material. We have
also attempted these reactions using silver tetrafluoroborate as
halide abstractor. A very similar picture emerges, with one and
two equivalents of silver salts giving a mixture of the unknown
As we felt that the 8-dppmaq ligand could act as either a
mono-, bi-, or tri-dentate ligand, we were intrigued to know if it
was effective at controlling regioselectivity in rhodium catalysed
hydroformylation of hex-1-ene. We also wished to find out what
effect (if any) the presence of the two additional donor atoms
may have on catalyst activity/stability. Reports on the use of
PNx type ligands in hydroformylation are rare. This reaction is
of great interest both academically and industrially. The reac-
tion generally gives a mixture of branched and linear isomers
(Scheme 8), with complete regioselectivity towards the linear
1
compound (≈ 15%, δ 6.8, JP–Pt = 3752 Hz), starting material
(≈ 15%, δ 6.1, JP–Pt = 3653 Hz), and what we have assigned as the
mono-chelate species as the major product (≈70%).
When 8-dppmaq was added to the Pt dimer [(PhMe2P)-
PtCl2]2, cleavage of the chloride bridges occured giving a
product in which the 8-dppmaq and dimethylphenylphosphine
are cis to each other. This can be readily concluded by inspec-
2
1
tion of the 31P NMR data (δ 5.70, d, JP–P = 15.6 Hz, JP–Pt
=
2
1
1
3685 Hz; Ϫ15.20, d, JP–P = 15.6 Hz, JP–Pt = 3519 Hz). The J
coupling constants are typical of an alkylarylphosphine trans
to a chloride ligand. Spectroscopic data are consistent with
structure (13) (see Scheme 7).
Scheme 8
isomer being the ideal goal. Recent pioneering research has
shown that “wide bite angle” ligands are particularly useful in
this respect.16
The 8-dppmaq ligand, in combination with Rh(CO)2acac
catalysed the reaction highly effectively, giving essentially com-
plete conversion in less than an hour (turnover frequency
(TOF) = 1870 hϪ1) at 100 ЊC and 20 bar pressure. Although
selectivity to aldehydes is good (96%), the regioselectivity
towards the terminal aldehyde was very poor (n : i = 1.8).
Triphenylphosphine catalyses the reaction at a faster rate and
gives an n : i ratio of 2.7 under similar conditions.
Scheme 7
When silver perchlorate was added to this monodentate
complex, we observed a new complex that has a fairly similar
31P NMR spectrum (δ 3.61, d, 2JP–P = 16.2 Hz, 1JP–Pt = 3703 Hz;
(f ) Palladium catalysed methoxy carbonylation of
phenylacetylene
2
1
Ϫ18.97, d, JP–P = 16.2 Hz, JP–Pt = 3500 Hz) to the starting
material which was also present as an impurity (even when two
equivalents of silver salts were added). Unfortunately, this
major species could not be readily purified to give completely
pure material. We believe that the chemistry seen when halide
ligands are removed from the two platinum complexes we have
prepared indicates that the 8-dppmaq ligand can bind to a tran-
sition metal as a P,N bidentate chelate (see Fig. 3). The results
also suggest that this co-ordination mode is not especially
favoured for this ligand.
Quite probably the most well known use of a hemilabile ligand
in homogeneous catalysis is the application of palladium
diphenyl(2-pyridyl)phosphine complexes as catalyst for carb-
onylation of alkynes. A combination of palladium acetate,
triflic acid and triphenylphosphine catalyses the formation of
commercially important methyl methacrylate from propyne
with 90% selectivity. However, the reaction proceeds at a very
low rate (ca. 10 turnovers per hour at 115 ЊC). Replacing tri-
phenylphosphine with diphenyl(2-pyridyl)phosphine (2) gives a
remarkable increase in activity with 40,000 turnovers per hour
at 45–60 ЊC. Selectivity is also increased to >99%. It has been
reported that this reaction also works well with other alkynes as
substrates.4
Having at least a partial understanding of how this new
ligand binds to a variety of metal centres, we hoped that the
presence of two additional donor atoms within this phosphine
may increase stability or alter reactivity/selectivity in transition
metal catalysed reactions. We have therefore carried out a
preliminary study in which (4) was used as ligand in two
industrially important carbonylation reactions.
When phenylacetylene was injected into an autoclave con-
taining palladium acetate (0.1%), 2-PyPPh2, p-MeC6H4SO3Hؒ
H2O and pressurised to 55 bar (T = 60 ЊC) a very exothermic
J. Chem. Soc., Dalton Trans., 2002, 1618–1624
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reaction took place with the autoclave temperature rising to
95 ЊC, and complete conversion of phenylacetylene occurring
Acknowledgements
The authors wish to thank the EPRSC for financial support
(M.L.C.), Johnson Matthey for the loan of rhodium() chlor-
ide, the EPRSC mass spectrometry service (Swansea), and the
JREI for equipment grants. The authors also wish to thank
Dr Steve Aucott who generously donated many of the precious
metal starting complexes and Mr Rehan Ahmed whose loan of
diphenylphosphinomethanol is acknowledged!
within a couple of minutes (Scheme 9). The product, CH ᎐
᎐
2
Scheme 9
References
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C(Ph)CO2Me was formed in quantitative yield and good select-
ivity towards the terminal alkene (97%). This reaction was too
fast for an accurate turnover frequency to be measured. How-
ever, 1000 turnovers within minutes is clearly of the same order
of magnitude as that reported by Drent and co-workers4a for
methoxy carbonylation of propyne.
It was of some interest to determine if the 8-dppmaq ligand
would show a similar dramatic effect on this reaction in com-
parison with simple monodentate phosphines. The methoxy
carbonylation of phenylacetylene was carried out under similar
conditions using 8-dppmaq as ligand. However, there appeared
to be very little gas uptake in the first 15 minutes. Consequently
the autoclave was sealed and heated to 100 ЊC for 3.5 hours.
GCMS analysis of the reaction mixture after 4 hours reaction
time showed that approximately 700 reaction turnovers had
occurred within this time. Selectivity was also fairly modest
(86%). 2-Pyridylphosphines remain the ligand of choice for this
reaction. While 8-dppmaq clearly shows some promotional
effect for this reaction (relative to PPh3), the co-ordination, pro-
ton transfer or stabilising qualities of 8-dppmaq are not suf-
ficiently similar to 2-PyPPh2 to give a highly reactive catalytic
system.
8 C. White, A. Yates and P. M. Maitliss, Inorg. Synth., 1992, 29, 228.
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Conclusions
In this work, we have prepared a new phosphine ligand from
8-aminoquinoline. The ligand prefers to bind to the transition
metals studied in a monodentate fashion. However, rhodium
and iridium complexes have been prepared in which the ligand
adopts a tridentate co-ordination mode. There is good evidence
that bidentate (PNaromatic) platinum complexes can be prepared
from this ligand. The ability of this ligand to activate rhodium
and palladium complexes towards carbonylation reactions
has also been evaluated. The novel catalysts do promote both
hydroformylation and methoxy carbonylation reactions, but
they do not match the current state-of-the-art catalysts. Further
studies will concentrate on the synthesis of new multifunc-
tionalised phosphines and their catalytic and co-ordination
chemistry.
16 L. A. Van der Veen, P. C. J. Kamer and P. W. N. M. Van Leeuwen,
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1624
J. Chem. Soc., Dalton Trans., 2002, 1618–1624