A supramolecular approach to chiral ligand modification: Coordination chemistry of a multifunctionalised tridentate amine-phosphine ligand

Article abstract of DOI:10.1039/b712612c

A novel chiral amine-phosphine tagged with an amido-napthyridine moiety has been synthesised and found to bind complementary pyridinone additives. These additives were found to have a modest but measurable promotional effect on the catalytic activity and/or enantioselectivity of Ir- and Rh-catalysed reductions. One explanation for the relatively poor results obtained with the Ir and Ru catalysts is the formation of complexes, in which the ligand adopts an anionic tridentate coordination mode. Pt and Rh complexes of this type were isolated and characterised. The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.

Full text of DOI:10.1039/b712612c

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PAPER
www.rsc.org/njc | New Journal of Chemistry
A supramolecular approach to chiral ligand modification: coordination
chemistry of a multifunctionalised tridentate amine-phosphine ligandw
´
Jose A. Fuentes, Matthew L. Clarke* and Alexandra M. Z. Slawin
Received (in Durham, UK) 16th August 2007, Accepted 10th December 2007
First published as an Advance Article on the web 10th January 2008
DOI: 10.1039/b712612c
A novel chiral amine-phosphine tagged with an amido-napthyridine moiety has been synthesised
and found to bind complementary pyridinone additives. These additives were found to have a
modest but measurable promotional effect on the catalytic activity and/or enantioselectivity of
Ir- and Rh-catalysed reductions. One explanation for the relatively poor results obtained with the
Ir and Ru catalysts is the formation of complexes, in which the ligand adopts an anionic
tridentate coordination mode. Pt and Rh complexes of this type were isolated and characterised.
points towards the self-assembly of new asymmetric supramo-
Introduction
lecular catalysts. Due to the great importance of transition
metal catalysis, we were particularly interested in expanding
this concept to asymmetric transition metal catalysis. In this
paper, we report our progress towards this goal, including
coordination chemistry experiments that have shed light on
the relatively low catalytic activity observed in the hydrogena-
tion experiments using this first prototype ligand system.
The important advances made in transition metal catalysis
generally rely on the careful and time-consuming optimisation
of catalyst structure to obtain maximum selectivity and cata-
lytic activity. Very subtle changes to catalyst structure can
often make large and unpredictable differences to catalyst
performance, especially to the enantioselectivity of asymmetric
catalysis. Given the great advances made in high throughput
catalyst screening and analysis techniques, the slow step in the
screening of asymmetric catalysts is now catalyst synthesis.
There is therefore great interest in new methodologies that
allow the synthesis of structurally diverse catalyst libraries,
and in the synthesis of distinctive new types of catalysts.1 In
recent years, several new methodologies that facilitate the
synthesis of catalyst libraries have been introduced.2–5 One
of the most intriguing approaches has been using the supra-
molecular synthesis of pseudo bidentate ligands from two
smaller libraries of complementary monodentate ligands.
The self-assembly of bidentate ligands using either coordina-
tion or hydrogen bonding interactions have been reported by
the groups of Reek, Breit and Takacs.4 Our group have been
investigating a conceptually different approach, where intact
chiral catalysts or ligands are modified by binding a small
library of complementary additives. We have recently demon-
strated this new approach to supramolecular catalyst libraries
in metal-free organocatalysis. The results were dramatic: a
range of programmed additives interacted with the organo-
catalyst to deliver supramolecular catalysts that each gave
distinctive catalytic properties. The best chiral additive im-
proved the enantioselectivity from o20% ee without additive
present up to 94% ee.5 Catalysts that lack the desired hydro-
gen bonding sites to bind additives did not show the same
promotional effect. All the mechanistic data obtained thus far
Results and discussion
The amido-napthyridine:pyridinone hydrogen bonding net-
work6 was utilised in our previous catalysts, hence our design
focused on incorporating an amido-napthyridine moiety into a
chiral ligand structure. In part, due to their straightforward
synthesis and our interest in amine-phosphine ligands in
catalysis,7 the simple phosphine-imine ligand was chosen as
the template to investigate the self-assembly approach, and we
envisaged that the ligand and pyridinones would assemble in
the manner shown as 1b (Fig. 1).
School of Chemistry, University of St Andrews, EaStCHEM, St.
Andrews, Fife, UK KY 16 9ST. E-mail: mc28@st-andrews.ac.uk;
Fax: +44 (0)1334 463808; Tel: +44 (0)1334 463850
w Electronic supplementary information (ESI) available: Further ex-
perimental details, NMR spectra of products, and bond lengths and
distances of the X-ray structure determination. See DOI: 10.1039/
b712612c
Fig. 1 Pyridinone additives binding to napthyridine-functionalised
catalysts and ligands.
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Scheme 2 Asymmetric hydrogenation of 2,3,3-trimethylindoline.
presence of additive A1, a reproducible and meaningful en-
antioselectivity was recorded.
Catalyst screening was halted at this early stage, since despite
an indication that the additives had a measurable effect on these
catalysts, the overall activity of this type of catalyst was quite
low. This highlighted to us the importance of understanding the
coordination chemistry of this relatively complex ligand. The
reaction of ligand 5 with catalyst precursors [M(cod)2]BF4 (M =
Rh, Ir) gave several inseparable products, suggesting that the
ligand was not forming a discrete bidentate catalyst, as was
hoped. However, the reaction of 5 with [Rh(acac)(CO)2] pro-
ceeded cleanly to give a single species.
Scheme 1 Conditions: (a) Pyridine, cyanuric fluoride, DCM, ꢁ20 1C;
(b) pyridine, DMF, 140 1C, 30 min, MW irradiation (66% yield); (c)
TFA, DCM, r.t.; then aq. NaOH, r.t. (81% yield); (d) DCM, MgSO4,
r.t. (64% yield).
The expected product of a reaction between this precursor
and a bidentate ligand is a complex of type [Rh(L)(acac)].
However, spectroscopic investigations revealed that the ligand
had been deprotonated by acacꢁ, forming complex 6, where
ligand 5 acts as a tridentate anionic ligand. The complex’s
31P{1H} NMR spectrum showed the expected doublet with
1JP–Rh = 146 Hz. This is somewhat larger than that observed
when phosphines are trans to each other (typically B125 Hz),
and reflects the lower trans influence of the amide ligand. FAB
mass spectroscopy gave the expected mass ion and relative
isotopic intensities. A tridentate complex of this nature can
either bond through nitrogen or oxygen. We have been unable
to grow high quality crystals of this complex for X-ray
analysis, but an X-ray crystal structure determination car-
ried-out on very small micro-crystals of 6 gave a low quality
structure that was sufficient to confirm the connectivity of the
complex, as shown in Scheme 4.8 This preference for proto-
nation of complexed anionic ligands extended to the strongly
bound methyl ligands in [Pt(cod)Me2]. It is well known that
strong acids protonate Pt–Me bonds,9 although examples
where the acid is part of a ligand system are more unusual.10
Ligand 5 reacted cleanly (495% by NMR) with this precursor
at 50 1C to give 7, in which a tridentate anionic coordination
mode for 5 was also observed. This protonation and coordina-
tion also takes place at r.t., although more slowly. The
protonation reaction also takes place in the presence of the
additives. FAB mass spectrometry revealed the expected
MH+ ion and isotope patterns. The proton NMR spectrum
showed a methyl resonance with the expected relative integrals
and 195Pt coupling (1JH–Pt = 42 Hz), and did not show a
The synthesis of ligand 5 was relatively straightforward
using the route shown in Scheme 1. It is worth noting
here that many other coupling reagents failed to couple the
poorly nucleophilic amino-napthyridine to (S)-N-Boc-valine.
The use of an acid fluoride and rapid heating gave
good results, and this is recommended as a useful method
for amide bond formation with poorly nucleophilic amines.
Due to the forcing conditions employed, individual samples of
(S)-4 and (R)-4 were converted to diastereomeric ureas by
reaction with enantiomerically pure (S)-1-phenylethylisocya-
nate. 1H NMR spectra of these ureas showed a single diaster-
eomer in each case, confirming that no racemisation took
place (see ESIw).
Several pyridinones, A1, A2 and A3, were employed to
investigate the self-assembly approach. Before the catalytic
studies were initiated, the complementary binding of the most
soluble additive, A3, to host ligand 5 was examined by 1H
NMR titration experiments. These revealed that the equili-
brium between bound host–additive duplexes and free com-
ponents was 105: 1, confirming its proposed structure as that
shown in Fig. 1. The binding was felt to be sufficiently strong
to prove the potential of the approach. Our initial goal was to
see if the complementary additives would have any effect on
reaction yields or selectivities. Three main classes of reaction
were studied: imine hydrogenation, ketone hydrosilylation and
alkene hydrogenation. When ligand 5 was tested in the Ir-
catalysed hydrogenation of 2,3,3-trimethylindoline (Scheme
2), a rather low activity was observed, although catalysis was
clearly observed. More intriguingly, the addition of additive
A2 increased the reaction rate and ee of these reactions (other
additives were less effective). Combinations of [Rh(cod)Cl]2 or
[Rh(cod)2]BF4 and ligand 5 were found to give very low
activity in the hydrogenation of dimethyl itaconate, with or
without additives. When these in situ-formed Rh complexes
were tested as catalysts for the hydrosilylation of 40-fluoro-
acetophenone (Scheme 3), the catalysts also failed to effec-
tively control the enantioselectivity, but the presence of the
complementary additives had a clear effect; reactions carried-
out without additives gave racemic material, whereas in the
Scheme 3 Hydrosilylation of 4-fluoroacetophenone.
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ligand 5 in catalysis. We have not completely demonstrated the
effectiveness of the ligand additive approach using this ligand
system, and it is still too early to state with certainty whether
the proposed self-assembly mechanism is in operation in
transition metal catalysis. However, the study does suggest
that ligands that can bind complementary additives are a
viable area of investigation if a better ligand design, that does
not present the opportunity for tridentate anionic coordina-
tion modes, can be employed.
Scheme 4 Synthesis of a tridentate Rh complex.
Experimental
All chemicals and solvents were obtained through commercial
sources. Solvents were removed by rotary evaporation on a
Heidolph Labrota 4000. Flash column chromatography was
performed using Davisil silica gel 35–70u 60A (Fluorochem).
Melting points were determined with a Gallenkamp melting
point apparatus no 889339 and are uncorrected. NMR spectra
were recorded on Bruker Avance 300 and 400 instruments.
Chemical shifts are reported in ppm from TMS, with the
solvent resonance as the internal standard. Proton signal
multiplicities are given as s (singlet), d (doublet), t (triplet), q
(quartet), m (multiplet), br (broad) or some combination of
them. All spectra were recorded at r.t., and the solvent for a
particular spectrum is given in parentheses. Infrared spectra
were recorded on a Perkin-Elmer Spectrum GX FT-IR system.
Liquids were analysed as films, solids were analysed as KBr
disks. Mass spectra were recorded on Waters Micromass LCT
(fitted with lockspray for accurate mass) (ESI) or GCT (CI)
instruments. Optical rotations were measured on an Optical
Activity Ltd. AA-1000 digital polarimeter using a 5 ml cell
with a 1 cm path length at r.t. using the sodium D-line, or in a
Perkin-Elmer 341 polarimeter using a 1 ml cell with a 1 cm
path length at 20 1C using the sodium D-line. Microwave
reactions were carried out in a Biotages initiator using 5 ml
heavy-walled reactor vials equipped with an air tight seal. The
temperature was measured by an infrared temperature probe
that measured the temperature on the surface of the vial. The
pressure was measured by directly reading the deflection of the
septa on the vial using a load cell behind the inner part of the
cavity lid.
Scheme 5 Synthesis of a tridentate Pt complex.
Fig. 2 X-Ray structure of Pt complex 7. Key bond lengths (A):
Pt(1)–P(1) = 2.1904(15), Pt(1)–N(11) = 2.094(5), Pt(1)–N(8) =
2.061(5) and Pt(1)–CH3 = 2.083(6).
resonance that could be assigned to an amide proton, consis-
tent with the anionic coordination mode. Coupling to 195Pt is
also evident in the carbon NMR of the Pt–Me group.
Crystals of rac-7 were grown by slow evaporation of a
sample of rac-7 in CDCl3 over several months. The structure
determination unambiguously confirmed the structure in
Scheme 5 (Fig. 2). The Pt–P bond lengths are similar to those
observed in Pt–phosphine dihalide complexes, in which P is
trans to a halide.11 This is consistent with a weak trans
influence of the amido ligand, as expected from the magnitude
Amide 3
1
of JP–Pt. The most significant deviations from square planar
To N-Boc-amino acid fluoride 2 (219 mg, 1.0 mmol) and 1,8-
aminonapthyridine (173 mg, 1.0 mmol) in a 5 ml microwave
process vial were added, under a nitrogen atmosphere, dry
DMF (3 ml) and anhydrous pyridine (0.14 ml, 1.73 mmol).
The reaction mixture was heated by microwave irradiation at
140 1C for 30 min. After being cooled to ambient temperature,
the solvent was evaporated under reduced pressure, and the
reaction crude purified by chromatography on a SiO2 column
using EtOAc as the eluent to give N-Boc amine 3 (246 mg,
66%) as a yellow solid. mp 82–84 1C; [a]2D0 ꢁ30.0 (c 0.333 in
CHCl3); IR (CDCl3): 3242, 2969, 2932, 1689, 1601, 1510, 1407,
geometry arise in the very narrow bite angle of the N^N part
of the ligand (N(8)–Pt(1)–N(11) = 79.60(19)1.
It is not clear if the formation of complexes with a tridentate
anionic coordination mode is a general reaction of phosphine-
imines derived from amino acid amides. The literature sug-
gests amide coordination does not occur without prior depro-
tonation of the ligand and reaction with
a precursor
containing a more labile anion.10 Since it is such a strongly
electron withdrawing substituent, the napthyridine moiety is
likely to be a key feature that renders ligand 5 highly acidic.
1
1393, 1367, 1312, 1277 and 1170 cmꢁ1; H NMR (300 MHz,
CDCl3): d 0.90 (3H, d, J = 6.9 Hz, CH3), 0.97 (3H, d, J = 6.7
Hz, CH3), 1.40 (9H, s, 3 ꢂ CH3), 2.23–2.49 (1H, m, CH), 2.59
(3H, s, CH3), 2.64 (3H, s, CH3), 4.18–4.25 (1H, m, CH), 5.03
(1H, br d, J = 8.7 Hz, NH), 7.07 (1H, s, ArCH), 8.27 (1H, d, J
Conclusions
The isolation of complexes 6 and 7 provides one possible
explanation for the low activity of the metal complexes of
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= 9.0 Hz, ArCH), 8.43 (1H, d, J = 9.0 Hz, ArCH) and 9.03
(1H, br s, NH); 13C NMR (75 MHz, CDCl3): d 17.4 (CH3),
18.1 (CH3), 19.3 (CH3), 25.3 (CH3), 28.3 (CH3), 30.7 (CH),
60.8 (CH), 80.6 (C(CH3)3), 113.7 (ArCH), 118.8 (ArC), 122.4
(ArCH), 135.7 (ArCH), 145.7 (ArC), 152.6 (ArC), 154.2
(CQO), 154.3 (ArC), 162.9 (ArC) and 171.3 (CQO). MS(ES)
m/z: 373.2 [MH]+ (100%), 317.2 (18), 273.2 (41) and 174.1
(28). Found (ES) 373.2234 [MH]+; C20H29N4O3 requires
373.2234.
136.2 (d, J = 9.4 Hz ArC), 138.5 (d, J = 3.5 Hz, ArC), 138.7
(ArC), 145.6 (ArC), 153.1 (ArC), 155.2 (ArC), 162.1 (d, J =
25.1 Hz, CQN), 163.2 (ArC) and 172.6 (CQO). 31P{1H}
NMR (162 MHz, CDCl3): d ꢁ13.45 (s). MS(TOF-ES) m/z:
567.11 [MNa]+ (87%), 545.13 [MH]+ (100), 295.10 (5), 273.12
(41) and 174.08 (6). Found (TOF ES) 545.2465 [MH+];
C34H34N4OP requires 545.2470.
Complex 6
Ligand (S)-5 (120 mg, 0.22 mmol) and [Rh(acac)(CO)2] (73.4
mg, 0.22 mmol) were placed in a Schlenk tube and stirred in
dry de-gassed toluene (4 ml) at r.t. for 1.5 h under an argon
atmosphere. During this time, an orange solid precipitated.
Diethyl ether (7 ml) was added and the reaction mixture was
filtered via cannula. The resulting solid was washed with
diethyl ether (3 ꢂ 5 ml) and dried under vacuum to obtain
complex (S)-6 as a dark orange solid (132 mg, 89%). mp
175–178 1C (decomp.); [a]2D0 +145 (c 0.06 in CHCl3); IR
(CDCl3): 3054, 2960, 2925, 2001, 1614, 1583, 1506, 1436,
Amine 4
N-Boc amine 3 (110 mg, 0.29 mmol) was treated with trifluoro-
acetic acid (0.3 ml, 3.9 mmol) in DCM (5 ml) at r.t. for 24 h.
The reaction mixture was then treated with NaOH (0.4 g, 10
mmol) in water (10 ml) and stirred for 1 h. The organic phase
was separated and the aqueous solution extracted with DCM
(2 ꢂ 15 ml) and Et2O (4 ꢂ 15 ml). The combined organic
layers were washed with brine, dried over anhydrous MgSO4,
filtered and concentrated under reduced pressure to give (S)-
amine 4 as a white solid (64 mg, 81%). mp 144–146 1C; [a]D20
ꢁ15.3 (c 0.333 in CHCl3); IR (KBr): 3355, 3251, 2961, 1698,
1402, 1332, 1234 and 1097 cmꢁ1 1H NMR (300 MHz,
;
CDCl3): d 0.57 (3H, d, J = 6.8 Hz, CH3), 0.87 (3H, d, J =
6.8 Hz, CH3), 2.34–2.48 (1H, m, CH), 2.50 (3H, s, CH3), 2.55
(3H, s, CH3), 3.97 (1H, d, J = 6.4 Hz, CH), 6.90 (1H, s,
ArCH), 6.96–7.02 (1H, m, ArCH), 7.27–7.54 (13H, m, ArCH),
7.81 (1H, d, 3JH–Rh 2.3 Hz, HCQN), 7.84 (1H, d, J = 8.8 Hz,
ArCH) and 8.04 (1H, d, J = 8.8 Hz, ArCH); 13C NMR (75
MHz, CDCl3): d 18.1 (CH3), 18.8 (CH3), 19.6 (CH3), 25.5
(CH3), 34.6 (CH), 87.9 (CH), 118.1 (ArC), 119.5 (ArCH),
121.3 (ArCH), 126.9 (d, J = 40.0 Hz, ArC), 128.7 (d, J = 10.8
Hz, ArCH), 130.8 (ArCH), 131.0 (ArCH), 131.1 (ArCH),
132.0 (d, J = 52.9 Hz, ArC), 132.2 (ArCH), 132.4 (d, J =
49.1 Hz, ArC), 133.2 (ArCH), 133.3 (ArCH), 133.5 (d, J =
12.6 Hz, ArCH), 134.1 (d, J = 12.8 Hz, ArCH), 136.2 (d, J =
16.7 Hz, ArC), 136.9 (d, J = 8.0 Hz, ArCH), 144.2 (ArC),
156.1 (ArC), 160.9 (ArC), 161.7 (d, J = 7 Hz, CQN), 164.0
1597, 1561, 1508, 1397 and 1308 cmꢁ1; H NMR (300 MHz,
1
CDCl3): d 0.86 (3H, d, J = 6.9 Hz, CH3), 1.02 (3H, d, J = 7.0
Hz, CH3), 1.61 (2H, br s, NH2), 2.31–2.46 (1H, m, CH), 2.59
(3H, s, CH3), 2.66 (3H, s, CH3), 3.43 (1H, d, J = 3.6 Hz, CH),
7.05 (1H, s, ArCH), 8.25 (1H, d, J = 9.0 Hz, ArCH), 8.48 (1H,
d, J = 9.0 Hz, ArCH) and 10.35 (1H, br s, NH); 13C NMR (75
MHz, CDCl3): d 16.5 (CH3), 18.4 (CH3), 20.1 (CH3), 25.8
(CH3), 31.4 (CH), 61.1 (CH), 113.7 (ArCH), 118.9 (ArC),
122.5 (ArCH), 135.7 (ArCH), 145.5 (ArC), 153.1 (ArC), 155.2
(ArC), 163.2 (ArC) and 174.7 (CQO). MS(ES) m/z: 273.2
[MH]+ (100%), 256.1 (5), 174 (99) and 72.2 (10). Found (ES)
273.1710 [MH]+; C15H21N4O requires 273.1710.
Ligand 5
1
2
(ArC), 176.4 (CQO) and 191.6 (dd, JC–Rh = 75.6 Hz, JC–P
= 19.0 Hz, CO); 31P{1H} NMR (162 MHz, CDCl3): d 47.77
To a solution of (S)-amine 4 (0.203 g, 0.75 mmol) in DCM (7
ml), was added 2-(diphenylphosphino)benzaldehyde (0.216 g,
mmol) at r.t. The resulting yellow solution was stirred at r.t.
for 24 h, and then filtered and evaporated in vacuo. The crude
mixture was purified by chromatography on a SiO2 column
using EtOAc as the eluent to give compound 5 as a yellow
solid (0.257 g, 64%). mp 101–103 1C; [a]2D0 ꢁ105 (c 0.200 in
CHCl3); IR (CDCl3): 3339, 3056, 2964, 2930, 1696, 1637, 1600,
1
(d, JP–Rh = 145.7 Hz). MS(ES) m/z: 675.2 [MH]+ (100%),
561.4 (38), 187 (12), 105.0 (46) and 99.1 (58). Found (ES)
675.1391 [MH]+; C35H33N4O2PRh requires 675.1391.
Complex 7
A solution of ligand (S)-5 (120 mg, 0.22 mmol) in toluene (2
ml) was added to a solution of [Pt(cod)Me2] (73.4 mg, 0.22
mmol) in toluene (2 ml) in a Schlenk tube under an N2
atmosphere. The reaction mixture was heated at 50 1C and
stirred for 16 h. The reaction was allowed to cool to r.t. and
hexane (4 ml) was added. The resulting precipitate was filtered
and washed with diethyl ether (3 ꢂ 4 ml) to obtain complex
(S)-7 as a yellow solid (106 mg, 64%). mp 4226 1C (decomp.);
[a]2D0 ꢁ13.0 (c 0.20 in CHCl3); IR (CDCl3): 3058, 2961, 2924,
1726, 1614, 1601, 1550, 1507, 1437, 1403, 1373, 1333, 1236 and
1100 cmꢁ1; 1H NMR (400 MHz, CDCl3): d 0.04 (3H, d with Pt
1507, 1435, 1406, 1338, 1312, 1276 and 1182 cmꢁ1; H NMR
1
(300 MHz, CDCl3): d 0.67 (3H, d, J = 6.9 Hz, CH3), 0.80 (3H,
d, J = 6.9 Hz, CH3), 2.12–2.25 (1H, m, CH), 2.59 (3H, s,
CH3), 2.65 (3H, s, CH3), 3.57 (1H, d, J = 4.4 Hz, CH),
6.81–6.85 (1H, m, ArCH), 7.05 (1H, s, ArCH), 7.16–7.33
(11H, m, ArCH), 7.39–7.45 (1H, m, ArCH), 8.22–7.17 (1H,
m, ArCH), 8.25 (1H, d, J = 9.0 Hz, ArCH), 8.46 (1H, d, J =
9.0 Hz, ArCH), 8.81 (1H, d, J = 5.9 Hz, HCQN) and 9.50
(1H, br s, NH); 13C NMR (75 MHz, CDCl3): d 17.8 (CH3),
18.5 (CH3), 19.6 (CH3), 25.9 (CH3), 33.9 (CH), 79.9 (CH),
114.2 (ArCH), 119.0 (ArC), 122.6 (ArCH), 128.3 (d, J = 3.9
Hz, ArCH), 128.8 (d, J = 8.0 Hz, ArCH), 129.2 (d, J = 7.1
Hz, ArCH), 129.4 (ArCH), 129.6 (ArCH), 129.7 (ArCH),
131.6 (ArCH), 133.6 (ArCH), 134.4 (d, J = 13.2 Hz, ArCH),
134.7 (d, J = 13.5 Hz, ArCH), 135.8 (ArCH), 136.0 (ArC),
3
2
satellites, JH–P = 3.6 Hz, JH–Pt = 72.6 Hz, CH3), 0.81 (3H,
d, J = 6.9 Hz, CH3), 0.97 (3H, d, J = 6.8 Hz, CH3), 2.42–2.55
(1H, m, CH), 2.51 (3H, s, CH3), 2.58 (3H, s, CH3), 4.33 (1H, d,
J = 5.0 Hz, CH), 6.95 (1H, s, ArCH), 7.15–7.63 (15H, m,
ArCH), 8.13 (1H, d, J = 8.6 Hz, ArCH) and 8.23 (1H, s with
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Pt satellites, 3JH–Pt = 41.7 Hz, HCQN); 13C NMR (100 MHz,
=
nation. The authors also wish to thank Johnson Matthey for
the loan of precious metal salts.
CDCl3): d ꢁ12.2 (d with Pt satellites, 2JC–P = 6.9 Hz, 1JC–Pt
671.2 Hz, CH3), 18.1 (CH3), 18.6 (CH3), 19.8 (CH3), 25.4
(CH3), 34.8 (CH), 83.3 (CH), 118.4 (ArC), 122.0 (ArCH),
122.1 (ArCH), 124.3 (d, J = 53.7 Hz, ArC), 127.8 (ArC), 128.3
(d, J = 11.2 Hz, ArCH), 128.7 (d, J = 11.0 Hz, ArCH), 130.9
(d, J = 59.4 Hz, ArC), 130.9 (ArCH), 131.1 (ArCH), 131.7
(ArCH), 132.7 (d, J = 7.2 Hz, ArCH), 133.0 (ArCH), 133.8
(ArCH), 133.8 (d, J = 24.5 Hz, ArCH), 134.7 (ArCH), 136.9
(d, J = 8.8 Hz, ArCH), 137.4 (d, J = 13.8 Hz, ArC), 144.5
(ArC), 156.0 (ArC), 156.9 (d, J = 3.4 Hz, CQN), 161.1 (ArC),
162.7 (ArC) and 177.8 (CQO); 31P{1H} NMR (162 MHz,
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4 The latest publications on supramolecular (transition metal) cata-
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1640; (b) X.-B. Jiang, L. Lefort, P. Elspeth-Goudriaan, A. H. M.
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1
CDCl3): d 16.20 (s with Pt satellites, JP–Pt = 3938.8 Hz);
MS(FAB) m/z: 755.2 (81%), 754.2 (100), 753.2 (94), 738.2 (48),
482.0 (21), 377.9 (11) and 199.9 (24). Found (FAB) 753.2244
[M]+; C35H35N4OP195Pt requires 753.2248. Crystals for X-ray
structure determination, obtained as the monohydrate, were
grown after a long period of slow evaporation of rac-7 in an
NMR tube. Found C, 54.60; H, 4.74; N, 7.33. C35H35N4OPPt
+ H2O requires C, 54.47; H, 4.83; N, 7.26%.
X-ray crystallography of rac-7. C35H37N4O2PPt, M =
771.75, yellow prism, 0.08 ꢂ 0.03 ꢂ 0.03 mm, monoclinic,
space group P2(1)/c, Z = 4, a = 8.7388(15), b = 14.988(2),
c = 25.469(4) A, b = 94.227(2)1, V = 3326.7(10) A3, rcalc
=
1.541 Mg mꢁ3, m(Mo-Ka) = 4.302 mmꢁ1 (max./min. trans-
mission = 0.879/0.7125), T = 93 K. Of 28 683 measured data,
5887 were unique (Rint = 0.0686) and 5412 observed [I 4
2s(I)] to give R = 0.0440 and wR2 = 0.1095. Data were
collected using a Rigaku MM007 high brilliance RA generator
(Mo-Ka radiation, confocal optics) and a Saturn70 CCD
system. At least a full hemisphere of data was collected using
o scans. Intensities were corrected for Lorentz polarisation
and absorption effects. The structures were solved by direct
methods. Hydrogen atoms bound to carbon were idealised.
Structural refinements were performed with full-matrix least-
squares based on F2 using SHELXTL.12 There is a disordered
water molecule in two locations, with no hydrogen atoms
located (water molecules are omitted in Fig. 2 for clarity).
CCDC 653579. For crystallographic data in CIF or other
electronic format see DOI: 10.1039/b712612c
5 M. L. Clarke and J. A. Fuentes, Angew. Chem., Int. Ed., 2007, 46,
930.
6 T. R. Kelly, G. J. Bridger and C. Zhao, J. Am. Chem. Soc., 1990,
112, 8024.
7 (a) M. L. Clarke, A. M. Z. Slawin, M. Wheatley and J. D.
Woollins, J. Chem. Soc., Dalton Trans., 2001, 3421; (b) M. L.
Clarke, D. J. Cole-Hamilton and J. D. Woollins, J. Chem. Soc.,
Dalton Trans., 2001, 2721; (c) M. L. Clarke, D. J. Cole-Hamilton,
D. F. Foster, A. M. Z. Slawin and J. D. Woollins, J. Chem. Soc.,
Dalton Trans., 2002, 1624; (d) M. L. Clarke, A. M. Z. Slawin and J.
D. Woollins, Polyhedron, 2003, 22, 19; (e) M. L. Clarke, Adv.
Synth. Catal., 2005, 347, 303; (f) M. L. Clarke, M. B. France, J. A.
Fuentes and E. J. Milton, Beilstein J. Org. Chem., 2007, 3, 18; (g)
M. L. Clarke, M. B. Diaz-Valenzuela and A. M. Z. Slawin,
Organometallics, 2007, 26, 16.
8 M. L. Clarke, J. A. Fuentes and A. M. Z. Slawin, unpublished
results.
9 See, for example: G. J. P. Britovsek, R. A. Taylor, G. J. Sunley, D.
J. Law and A. J. P. White, Organometallics, 2006, 25, 2074.
10 Related amino acid-derived phosphine-imines do not sponta-
neously protonate and adopt anionic tridentate coordination
modes: (a) H. A. Ankersmit, N. Veldman, A. L. Spek, K. Vrieze
and G. Van Koten, Inorg. Chim. Acta, 1996, 252, 339; (b) P.
Pelagatti, A. Bacchi, C. Bobbio, M. Carcelli, M. Costa, C. Pelizzi
and C. Vivorio, Organometallics, 2000, 19, 5440.
11 For an example in an amine-phosphine PtCl2 complex, see: A. J.
Blacker, M. L. Clarke, M. S. Loft, M. F. Mahon, M. E. Hum-
phreys and J. M. J. Williams, Chem.–Eur. J., 2000, 6, 353.
12 G. M. Sheldrick, SHELXTL 6.14, Bruker AXS, Madison, 2004.
Acknowledgements
The authors thank the EPSRC for funding this project, and
for the use of the National Mass Spectrometry Service. Mrs C.
Horsborough and Mrs M. Smith are also thanked for provid-
ing technical assistance. Mr Jan Sadownik (Prof. D. Philp’s
group) is also thanked for his assistance with the Ka determi-
ꢀc
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2008
New J. Chem., 2008, 32, 689–693 | 693