Orthoplatination of primary amines

Article abstract of DOI:10.1021/om800238j

The first efficient and general cycloplatination reaction of primary amines is introduced. A precursor obtained from K₂PtCl₄ and HI undergoes fast substitution by amine ligands; the resulting trans diamine derivative is converted via C-H activation into a cycloplatinated square-planar complex. The reaction proceeds surprisingly fast, under mild conditions and with high yields, even for electron-deficient substrates. The monohapto amine ligand in the product complex may be substituted by alternative donor ligands such as phosphanes or pyridine derivatives. Single-crystal X-ray diffraction studies of a trans compound which is suggested as intermediate, of three target complexes involving electronically different primary amines and of four substitution products are reported and underline the broad range of products accessible by this synthesis.

Full text of DOI:10.1021/om800238j

3124
Organometallics 2008, 27, 3124–3130
Orthoplatination of Primary Amines
Beatrice Calmuschi-Cula and Ulli Englert*
Institute of Inorganic Chemistry, RWTH Aachen UniVersity, Landoltweg 1, D-52074 Aachen, Germany
ReceiVed March 14, 2008
The first efficient and general cycloplatination reaction of primary amines is introduced. A precursor
obtained from K2PtCl4 and HI undergoes fast substitution by amine ligands; the resulting trans diamine
derivative is converted via C-H activation into a cycloplatinated square-planar complex. The reaction
proceeds surprisingly fast, under mild conditions and with high yields, even for electron-deficient substrates.
The monohapto amine ligand in the product complex may be substituted by alternative donor ligands
such as phosphanes or pyridine derivatives. Single-crystal X-ray diffraction studies of a trans compound
which is suggested as intermediate, of three target complexes involving electronically different primary
amines and of four substitution products are reported and underline the broad range of products accessible
by this synthesis.
state, “It is interesting to point out that, in spite of initial
difficulties well established methods have now been developed
for the cyclopalladation of primary amines, however, the
preparation of platinum analogues still remains uncommon.”
In view of the experimental difficulties with the synthesis of
cycloplatinated primary amines, the almost entire lack of
structural information for these compounds is no surprise: Only
one crystal structure of a benzylamine derivative7 is documented
in the Cambridge Structural Database.8 Basic research interests
apart, motivation for the synthesis and structural elucidation of
cycloplatinated primary amines also stems from recent interest
in organoplatinum compounds as potential antitumor drugs.9,10
Introduction
ortho-Metalation of amines with palladium and platinum share
a common history: As early as 1968, Cope and Friedrich
reported C-H activation for electron-rich amines and imines.1
The two noble metals differ, however, significantly in cyclo-
metalation. In general, the reaction proceeds with much higher
yields and for a wider range of substrates in the case of
palladium;2 the initial restriction rules for cyclopalladation no
longer apply.3 On the other hand, “cycloplatination”, the
formation of a C-Pt bond in a metallacycle, even today remains
a challenge. From a kinetic point of view, Pt(II) represents one
of the most inert metal centers in coordination chemistry, and
therefore most reactions proceed much slower than for the lighter
congener palladium. No general precursor for cycloplatination
has been found to date: The reaction of N,N-dimethylbenzy-
lamine with the standard platinum source K2PtCl4 gives at best
a yield of 20%.1 With the same reagent, secondary or primary
amines fail to ortho-metalate. In 1997, cis-PtCl2(dmso)2 emerged
as a more promising reagent,4 but even with this starting material
successful examples of ortho-platination are limited to tertiary
amines. For ferrocenylamines, the same precursor proved to
undergo facile cycloplatination. Despite the good performance
of these reactions with tertiary ferrocenylamines, no experi-
mental procedure has yet been reported for cyclometalation of
primary or secondary ferrocenylamines.5 We are not aware of
any well-documented and convenient general method for the
synthesis of primary ortho-platinated amines at the preparative
scale. A recent communication6 explicitly gives a yield of 10%
for a benzylamine derivative and underlines the difficulties in
systematically synthesizing this class of compounds; the authors
Results and Discussion
In the context of our quest for a straightforward and general
synthesis from primary amines to the cycloplatinated target
molecules we have identified the reaction product of potassium
tetrachloroplatinate with hydroiodic acid as a suitable precursor.
In contrast to our initial idea, the resulting dark powder cannot
simply be addressed as pure K2PtI4, which was structurally
characterized by Olsson and Oskarsson.11 X-ray diffraction
rather shows the additional presence of at least one more
crystalline phase: Several lines in the powder pattern match those
calculated for K2PtI5.12 The chemical reactivity of the precursor
also suggests a more complex nature than K2PtI4: We recall
that Pt(II) compounds are notoriously inert; the presence of one
or more platinum complexes in a higher oxidation state can
explain the short reaction times and mild conditions required
for cycloplatination. Although the quantitative composition of
the precursor varies with subtle details in its preparation, it does
not affect the subsequent cycloplatination step relevant for this
work. We note that Corain and Poe¨ observed the formation of
* Corresponding author. E-mail: ullrich.englert@ac.rwth-aachen.de.
(1) Cope, A. C.; Friedrich, E. C. J. Am. Chem. Soc. 1968, 90, 909.
(2) Schmu¨lling, M.; Ryabov, A.; van Eldik, R. J. Chem. Soc., Dalton
Trans. 1994, 1257.
(7) Avshu, A.; O’Sullivan, R. D.; Parkins, A. W.; Alcock, N. W.;
Countryman, R. M. J. Chem. Soc., Dalton Trans. 1983, 1619.
(8) Allen, F. Acta Crystallogr. Sect. B 2002, B58, 380.
(9) Ruiz, J.; Cutillas, N.; Vicente, C.; Villa, M. D.; Lopez, G.; Lorenzo,
J.; Aviles, F. X.; Moreno, V.; Bautista, D. Inorg. Chem. 2005, 44, 7365.
(10) Ruiz, J.; Lorenzo, J.; Sanglas, L.; Cutillas, N.; Vicente, C.; Villa,
M. D.; Aviles, F. X.; Lopez, G.; Moreno, V.; Perez, J.; Bautista, D. Inorg.
Chem. 2006, 45, 6347.
(3) Vicente, J.; Saura-Llamas, I.; Cuadrado, J.; Ramirez de Arellano,
M. C. Organometallics 2003, 22, 5513.
(4) Ryabov, A. D.; Kazankov, G. M.; Panyashkina, I. M.; Grozovsky,
O. V.; Dyachenko, O. G.; Polyakov, V. A.; Kuz’mina, L. G. J. Chem. Soc.,
Dalton Trans. 1997, 4385.
(5) Ranatunge-Bandarage,; P, R. R.; Robinson, B. H.; Simpson, J.
Organometallics 1994, 13, 500.
(11) Olsson, L. F.; Oskarsson, A. Acta Chem. Scand. 1989, 43, 811.
(12) Thiele, G.; Mrozek, C.; Wittmann, K.; Wirkner, H. Naturwissen-
schaften 1978, 65, 206.
(6) Capape´, A.; Crespo, M.; Granell, J.; Font-Bardia, M.; Solans, X.
Dalton Trans. 2007, 2030.
10.1021/om800238j CCC: $40.75
2008 American Chemical Society
Publication on Web 05/23/2008

Orthoplatination of Primary Amines
Organometallics, Vol. 27, No. 13, 2008 3125
Scheme 1. Synopsis of the Reaction Pathways and Products
Pt complexes with a “higher oxidation state than II” under
similar preparation conditions as early as 1967.13
was quenched after 30 min by partial evaporation of methanol
from the solvent mixture, the trans complex precipitated. When
this compound was redissolved in methanol/water and an
additional equivalent of the primary amine was provided to
promote C-H activation, it underwent cycloplatination to (S,S)-
The potassium iodoplatinate precursor and the primary amine
form the intermediate complex trans-PtI2L2, 2, which in a second
step undergoes ortho-platination to 3. Scheme 1 compiles the
reaction sequence and the compounds prepared by this method.
The ortho-platination may also be conducted as a “one-pot
reaction”, starting from K2PtCl4; in this case, the iodoplatinate
precursor is not isolated at all and the pH of the reaction mixture
is controlled by addition of KOH; see Experimental Section.
A reviewer suggested testing pure K2PtI4, prepared according
to the method of Olsson,14 as an alternative platinum source in
order to clarify the metalation process. Reactions conducted with
this compound under the same conditions but under nitrogen
rather than standard atmosphere gave mixtures of the trans-
configured complex 2a, the cycloplatinated target compound
3a, and large amounts of platinum metal. We conclude that our
mixed-valent precursor described above represents the superior
alternative.
The trans-configured complexes MX2L2 of palladium and
platinum are considered intermediates in cyclometalation; for
the case of palladium, prior experimental evidence has been
obtained.15,16 In order to get insight into the reaction pathway
of the synthesis reported here, the alleged intermediate (S,S)-
2a has been isolated and fully characterized: When the reaction
Figure 1. Arrangement of the six symmetrically independent
molecules of (S,S)-2a in the unit cell. Pt-N min. 2.054(7) Å, max.
2.087(8) Å; Pt-I min. 2.6009(12) Å, max. 2.6199(11) Å; N-Pt-N
min. 176.3(3)°, max. 178.8(3)°; I-Pt-I min. 171.88(3)°, max.
178.77(2)°; dihedral angles subtended by the plane of coordination
and the phenyl rings min. 2.7(4)°, max. 26.2(4)°.
(13) Corain, B.; Poe¨, A. J. J. Chem. Soc. (A) 1967, 1318.
(14) Olsson, L. F.; King, C.; Roundhill, D. M. Inorg. Synth. 1989, 25,
98.
(15) Ryabov, A. Chem. ReV. 1990, 90, 403.
(16) Calmuschi, B.; Jonas, A. E.; Englert, U. Acta Crystallogr. Sect. C
2004, 60, m320.

3126 Organometallics, Vol. 27, No. 13, 2008
Calmuschi-Cula and Englert
Table 1. Experimental X-ray Diffraction Parameters and Crystal Data for 2a and the Cycloplatination Products r-3a, ꢀ-3a, and 3c
complex
(S,S)-2a
r-(R,R)-3a
C16H21PtIN2
563.33
ꢀ-(S,S)-3a
C16H21PtIN2
563.33
(R,R)-3c
empirical formula
fw
C16H22PtI2N2
691.25
C16H19PtF2IN2
599.32
cryst size (mm)
cryst habit, color
cryst syst
space group
a (Å)
0.22 × 0.25 × 0.31
fragment, yellow
triclinic
P1
9.908(3)
14.267(4)
21.596(5)
96.105(5)
91.797(5)
92.448(5)
3030.7(14)
2.272
0.80 × 0.05 × 0.02
rod, light yellow
orthorhombic
P212121
4.6146(3)
11.7364(8)
29.866(2)
0.28 × 0.01 × 0.01
rod, light yellow
monoclinic
P21
11.311(2)
4.6196(9)
0.56 × 0.04 × 0.04
rod, colorless
orthorhombic
P212121
4.5846(13)
11.894(3)
b (Å)
c (Å)
15.981(3)
30.144(9)
R (deg)
ꢀ (deg)
98.687(4)
γ (deg)
V (Å3)
1617.49(19)
2.313
4
825.5(3)
2.266
2
1643.7(8)
2.422
4
D (g · cm-1
Z
)
6
T (K)
130(2)
9.997
1896
100(2)
10.576
1048
130(2)
10.362
524
130(2)
10.432
1112
µ(Mo KR) (mm-1
F(000)
)
θ range (deg)
no. of reflns collected
Rint
no. of unique reflns in refin
no. of reflns with I > 2σ(I)
no. of params refined
R1 (2σ(I))
R1 (all data)
wR2
Flack’s param
2. 06-26.00
2.21-33.78
52 872
0.0626
6147
5720
183
0.0301
0.0331
0.0616
0.002(5)
1.070
2.07-28.35
11 167
0.0736
4030
3594
183
0.0524
0.0600
0.0928
0.029(11)
1.018
2.65-29.82
14 555
0.0836
4304
3441
201
0.0453
0.0572
0.0750
-0.009(9)
1.001
52 490
0.0341
23 702
22 576
1147
0.0348
0.0371
0.0829
0.007(3)
1.027
goodness of fit
diff peak/hole (e/Å3)
1.27/-0.98
-1.09/2.13
-3.24/1.79
-0.46/0.97
3a within a few hours, in agreement with the concept of an
intermediate.
enantiomerically pure 1a two different polymorphs were
encountered. One of these polymorphs, hereafter referred to as
r-3a, crystallizes in the orthorhombic space group P212121. The
alternative modification ꢀ-3a exhibits roughly related lattice
parameters (cf. Table 1) in the monoclinic space group P21 and
slightly less efficient space filling. Figure 2 shows the molecular
structures in both polymorphs. The most significant difference
between molecules in r- and ꢀ-3a pertains to the rotation around
the N-C bond in the monohapto amine ligand.
(S,S)-2a, isolated as outlined above, was characterized by
microanalysis and by spectroscopic methods. The 195Pt chemical
shift amounts to -3354 ppm; a recent review on 195Pt
spectroscopy reports a range between -3336 and -3372 ppm
for the chemical shifts of trans diiodo platinum complexes of
primary amines.17 In addition, single crystals of (S,S)-2a were
studied by X-ray diffraction: The compound is associated with
a solid state structure of surprising18 complexity, featuring six
symmetrically independent square-planar, trans-configured mol-
ecules (Figure 1) that differ mainly with respect to conformation.
Displacement ellipsoid plots of all independent molecules are
provided in the Supporting Information (Figure S1).
Isolation of the trans-configured intermediate (S,S)-2a, albeit
very possible, is not mandatory: As shown in Scheme 1, the
primary amines 1a-c can be directly converted into the
corresponding ortho-platinated complexes 3a-c. In addition to
the unsubstituted 1-phenylethylamine 1a, we deliberately de-
cided to test the electron-rich para methyl derivative 1b and
its electron-deficient para fluoro congener 1c: We recall that
the more popular cyclopalladation was originally limited to
electron-rich substrates.1,3 Reaction times are longer for the
fluoro derivative, but all three target complexes 3a-c may be
obtained in high yields. Best results are achieved using a slight
excess of the amine (see Experimental Section), but a 3:1 molar
ratio between amine and precursor is in principle sufficient. The
products have been isolated and characterized by microanalysis
and spectroscopic methods. In the cases of 3a and 3c, single
crystals suitable for X-ray diffraction have been obtained; prior
to these results, only one structural study on cycloplatinated
benzylamine had been carried out.7 From the metalation of
ortho-Platination is not restricted to 1-phenylethylamine 1a
but tolerates substitution in the para position of the aromatic
ring of the primary amine. The conversion of the methyl-
substituted and hence electron-rich 1b to the cycloplatinated
complex 3b proceeds faster than for the unsubstituted phenyl-
ethylamine 1a, whereas 1c, due to its electron-withdrawing
fluoro substituent, requires a prolonged reaction time to form
3c. Very high yields confirm that our approach tolerates
substitution on the aryl ring of the primary amine. All three
complexes 3a-c show 195Pt resonances at ca. -3300 ppm, a
rather high field for Pt(II) compounds in general but not
surprising for organoplatinum compounds.19 In the 13C spectrum
of 3c the fluoro substitution is reflected in a characteristic
chemical shift for the substituted carbon atom of ca. 160 ppm.
Single-crystal X-ray diffraction proved that the fluoro derivative
is isomorphous with the R-polymorph of 3a: Both compounds
crystallize in the same space group with very similar lattice
pameters, and initial phases for the crystal structure of 3c could
be derived using the model of 3a. The interatomic distance
between the metal center and the nitrogen atom of the ortho-
metalated ligand in compounds 3a and 3c is consistently shorter
than the Pt-N bonds to the σ donor, although this difference is
hardly significant at the level of an individual structure. The
molecular structure of 3c (Figure S2, Supporting Information)
(17) Still, B. M.; Kumar, P. G. A.; Aldrich-Wright, J. R.; Price, W. S.
Chem. Soc. ReV. 2007, 36, 665.
(19) Benn, R.; Reinhardt, R.-D.; Rufinska, A. J. Organomet. Chem. 1985,
282, 291.
(18) Brock, C. P.; Dunitz, J. D. Chem. Mater. 1994, 6, 1118.

Orthoplatination of Primary Amines
Organometallics, Vol. 27, No. 13, 2008 3127
Figure 2. Molecular structures of (R,R)-r-3a (orthorhombic polymorph, left) and (S,S)-ꢀ-3a (monoclinic polymorph, right) in the solid.
Displacement ellipsoids are drawn at 30% probability; H atoms are shown with arbitrary radius. Selected interatomic distances (Å) and
angles (deg) for (R,R)-r-3a [values for (S,S)-ꢀ-3a in square brackets]: Pt1-N1 2.034(4) [2.062(10)], Pt1-N2 2.058(4) [2.067(10)], Pt1-I1
2.6966(3) [2.7075(10)], Pt1-C3 1.999(4) [2.003(12)], N1-Pt1-N2 179.16(16) [177.6(4)], C3-Pt1-I1 174.93(13) [174.7(3)], N1-Pt1-I1
91.71(10)[91.8(3)],N2-Pt1-I187.83(10)[88.2(3)],C3-Pt1-N183.22(17)[83.1(5)],C3-Pt1-N297.23(17)[96.8(4)];Pt1-N2-C9-C16-71.5(4)
[-65.1(12)].
closely matches that of its unsubstituted congener, and differ-
ences are limited to soft intramolecular degrees of conformation.
So far we have discussed the reaction sequence of primary
amines 1 either directly or via the intermediate trans complexes
2 to organoplatinum derivatives 3. These complexes exhibit the
same amine as a chelating ortho-metalated and a monodentate
ligand. The latter moiety may be substituted by a variety of
donor ligands; thus, a wide spectrum of cycloplatinated primary
amines becomes accessible. Two classes of substitution products
have been characterized in the context of this work, namely,
the phosphane complex 4a and the pyridine derivatives 5a-c.
When 3a is stirred in CH2Cl2 at room temperature with
triphenylphosphane, the monohapto primary amine is replaced
in a relatively fast reaction and product 4a was isolated in high
yield by precipitation with hexane. X-ray diffraction revealed
Figure 3. Molecular structure of (S)-4a in the crystal. Displacement
that the bulky triphenylphosphane ligand in (S)-4a leads to a
significant distortion in the idealized square-planar coordination
of the metal center: the angle C21-Pt1-I1 (Figure 3) amounts
to 165.54(15)° and is by far the smallest trans angle in all
structures reported in this work.
ellipsoids are drawn at 30% probability; H atoms are shown with
arbitrary radius. Selected interatomic distances (Å) and angles (deg):
Pt1-N1 2.108(5), Pt1-P1 2.2338(14), Pt1-I1 2.7008(5), Pt1-C21
2.041(6), N1-Pt1-P1 172.43(15), C21-Pt1-I1 165.55(15),
N1-Pt1-I1 87.85(14), P1-Pt1-I1 97.42(4), C21-Pt1-N1 81.1(2),
C21-Pt1-P1 -94.54(16).
Not only in 3a, the cycloplatination product of the unsub-
stituted amine, but also in the para-substituted derivatives 3b
and 3c may the monohapto amines be replaced by alternative
ligands. In addition to phosphanes as shown above, N-donor
ligands such as pyridine derivatives may be employed. The
reactions of 3a-c with 4-picoline are slow, even at elevated
temperatures. In the case of 3b, NMR control at regular intervals
revealed that the reaction in benzene at 65 °C was complete
after 3 days. The substitution of the monodentate amine in 3c
is faster and requires 24 h in refluxing methanol. All three
substitution products 5a-c have been isolated and characterized,
and we have been able to obtain single crystals suitable for X-ray
diffraction studies. 5a-c are isomorphous, crystallizing in the
tetragonal space group I41 with two independent molecules in
the asymmetric unit: Their displacement ellipsoid plots are
reported in Figure 4 and in the Supporting Information, Figures
S3 and S4. These graphical representations of the symmetrically
independent pairs also allow one to appreciate the pseudosym-
metry in the structures, cf. Experimental Section. We had
encountered a closely related structure for (R)-PdCl(C6H4-
CHMeNH2)(pyridine) in the context of cyclopalladation.20
In agreement with our expectation and the prior examples
for cycloplatinated tertiary amines compiled in the CSD,8 the
metal-carbon bond represents the shortest in the coordination
sphere. With respect to the iodo substituents, the crystal
structures communicated in this work feature 22 symmetrically
independent Pt-I bonds. These interatomic distances reflect the
influence of the ligand in trans position. When the trans ligand
is a second iodo substituent as in 2a, Pt-I falls in the range
between 2.6009(12) and 2.6199(11) Å, whereas longer Pt-I
bonds (min. 2.6814(15) Å) are observed for all the other
compounds with C-bonded ligands in trans position. In 3c, with
the electron-deficient chelating amine, the Pt-I distance amounts
to 2.6878(10) Å and is shorter than in both polymorphs of 3a,
the unsubstituted cycloplatinated amine, where values of
(20) Calmuschi, B.; Englert, U. Acta Crystallogr. Sect. C 2002, 58,
m545.

3128 Organometallics, Vol. 27, No. 13, 2008
Calmuschi-Cula and Englert
resulted in black K2PtIx, which was recovered in quantitative yield.
Preparation of the precursor may be achieved within much shorter
reaction times, e.g., 10 min, albeit at the expense of lower yields
in the subsequent cycloplatination reaction.
Cycloplatination. A 1.2 mmol amount of K2PtIx prepared as
above was suspended in 30 mL of MeOH/H2O (2:1). Then 4.8
mmol of ligand 1 was added, and the reaction mixture was heated
to reflux. The color of the reaction mixture changed from dark
brown via yellow to almost colorless, and a white precipitate
formed. This solid was recovered by filtration and washed with 20
mL of cold MeOH/H2O (2:1). Reaction times: For 1a ortho-
platination 4 h, for 1b less than 3 h, and for 1c ca. 1 day. The
intermediate product 2a was isolated and characterized. This
complex may be precipitated after a reaction time of ca. 30 min by
addition of water or by concentration of the reaction mixture as a
yellow crystalline solid. Yields: 96% (1.152 mmol) for 2a, 86%
(1.032 mmol) for 3a, 87.5% (1.05 mmol) for 3b, and 86% (1.032
mmol) for 3c. The difference between the yields and the quantitative
yield represents mostly the trans-PtI2L2 precursor, a product that
could be isolated and used for further ortho-platination.
Cycloplatination without Isolation of the Precursor. K2PtCl4
(500 mg, 1.2 mmol) was dissolved in 5 mL of H2O. Then 0.63 mL
(4.8 mmol) of 57% hydroiodic acid was added to the solution, and
the mixture was stirred at room temperature for 2 h. At this point
20 mL of MeOH and 5 mL of H2O were added, and the pH of the
reaction mixture was adjusted to a value of ca. 2.5 using drops of
a solution of KOH in MeOH/H2O (2:1). Ligand 1a (4.8 mmol)
was added, and the reaction mixture was heated to reflux for 4 h.
The white precipitate formed was recovered by filtration and washed
with 20 mL of cold MeOH/H2O (2:1). Yield: 82% (0.984 mmol)
for 3a.
Substitution Reactions. 4a. 3a (0.5 mmol, 0.282 g) was disolved
in 10 mL of CH2Cl2 at room temperature, and an equimolar amount
of PPh3 (0.131 g) was added. After 4 h the clear reaction mixture
was concentrated, and 4a was precipitated as a white powder by
adition of hexane. Yield: 93% (1.116 mmol).
5a, 5b, 5c. A 0.5 mmol amount of the cycloplatinated amine 3a
(0.282 g), 3b (0.296 g), and 3c (0.300 g) was dissolved in 15 mL
of CH2Cl2. An equimolar amount of 4-picoline (0.0465 g) was
added, and the reaction mixture was heated to reflux for 2 days.
The white precipitate formed was filtered off. Yield: 88% (1.056
mmol) for 5a, 79% (0.948 mmol) for 5b, and 82% (0.984 mmol)
for 5c.
Figure 4. Molecular structures of the two independent molecules
of (R)-5a in the crystal. Displacement ellipsoids are drawn at 30%
probability; H atoms are shown with arbitrary radius. Selected
interatomic distances (Å) and angles (deg) [values for the second
molecule in square brackets]: Pt1-N1 2.056(13), [2.005(13)],
Pt1-N2 2.011(12), [2.024(12)], Pt1-I1 2.6814(15), [2.6912(14)],
Pt1-C8 2.010(15), [1.954(15)], N2-Pt1-N1 175.3(5), [176.1(5)],
C8-Pt1-I1 174.2(4), [174.7(4)], N1-Pt1-I1 93.3(4), [93.2(4)],
N2-Pt1-I1 91.2(4), [90.6(4)], C8-Pt1-N1 80.9(5), [81.5(6)],
N2-Pt1-C8 94.6(6), [94.7(6)]. Dihedral angle between plane of
coordination and pyridine ring: 73.0(5) [82.7(5)].
2.6966(3) and 2.7075(10) Å are encountered. No reliable trend
can be deduced for the less accurate structures 5a-c.
A short discussion of the intermolecular aspects in the crystal
structures is appropriate: The primary amines represent good
donors for classical hydrogen bonds; however, in the absence
of suitable acceptors other than iodide not all N-H groups can
participate in efficient hydrogen bonding. The aryl-bonded
fluorine in 3c and 5c does not accept any classical hydrogen
bond. Shortest interhalide contacts occur in 2a with I · · · I
distances of ca. 4.3 Å, and closest intermetal contacts of ca.
3.9-4.0 Å are observed in 5a-c.
Spectroscopic and Analytical Results. 2a: trans-(S,S)-PtI-
Concluding Remarks
(C6H5CHMeNH2)(H2NCHMeC6H5). NMR. 1H NMR (400
In this contribution we have reported a convenient and general
access to cycloplatinated primary amines. As the organoplatinum
complexes directly obtained by this reaction can undergo
substitution with suitable donor ligands, this approach will pave
the way to a wide range of compounds. The nature of the
iodoplatinate precursor represents an important issue for future
investigation. Furthermore, we intend to study the cytotoxicity
of cycloplatinated primary amines.
Experimental Section
General Comments. NMR spectra were recorded on a Varian
Mercury 200 (19F NMR: 188.15 MHz), a Varian Mercury 300 (31P:
121.45 MHz), a Varian Unity 500 (1H: 500 MHz, 13C: 125 MHz,
195Pt: 107.4 MHz), and a Bruker Avance II (1H: 400 MHz, 13C:
MHz, CD2Cl2): δ 1.71 (d, 6H, J ) 6.92 Hz, CHMe); 3.50-3.90
(br, 4H, NH2); 4.50 (m, 2H, CHMe); 7.29-7.40 (m, 10H,
H2-H6) ppm. 13C NMR (100.6 MHz, CD2Cl2): δ 21.60 (s, 2C,
CH3); 57.79 (s, 2C, CH); 127.71, 128.27 (s, 10C, C2-C6),
141.32 (s, 2C, C1) ppm. 195Pt NMR (107.4 MHz, CD2Cl2): δ
-3354.21 ppm. Anal. Calcd for C16H22PtI2N2: H: 3.21, C: 27.80,
N: 4.05. Found: H: 3.19, C: 27.79, N: 4.02. Mp: 149 °C.
3a, 3b, 3c:. (S,S)- or (R,R)-PtI(4-R-C6H4CHMeNH2)(H2-
NCHMeC6H5-4-R). 3a. NMR. 1H NMR (400 MHz, C6D6): δ
0.93 (d, 3H, J ) 6.56 Hz, CHMe cycloplatinated amine); 1.58
1
100 MHz, 19F: 376.5 MHz) at ambient temperature. H and 13C
resonances are referenced to TMS, 19F spectra to CCl3F, 31P to
H3PO4, and 195Pt to H2PtCl6. Yields refer to the initial amount of
platinum introduced into the reaction.
Preparation of the Iodoplatinate Precursor. K2PtCl4 (500 mg,
1.2 mmol) was dissolved in 5 mL of H2O. Then 0.63 mL (4.8 mmol)
of 57% hydroiodic acid was added to the solution, and the mixture
was stirred at room temperature for 2 h. Evaporation of the water

Orthoplatination of Primary Amines
Organometallics, Vol. 27, No. 13, 2008 3129
nated amine). 195Pt NMR (107.4 MHz, CD2Cl2): -3315.87 ppm.
Anal. Calcd for C16H19PtF2IN2: H: 3.20, C: 32.07, N: 4.67.
Found: H: 3.30, C: 31.99, N: 4.61. Mp: 223 °C with
decomposition.
1
4a: (S)-PtI(4-R-C6H4CHMeNH2)(PPh3). NMR. H NMR
(d, 3H, J ) 6.80 Hz, CHMe noncycloplatinated amine); 3.09,
3.44 (br, 2H, NH2, noncycloplatinated amine); 3.26, 5.23 (br,
2H, NH2, cycloplatinated amine); 3.74 (m, 1H, CH, cycloplati-
nated amine); 4.13 (m, 1H, CH, noncycloplatinated amine); 6.63,
6.74 (m, 2H, H4, H5); 6.64, 6.66 (m, 2H, H2, H3); 6.86 (m, 1H,
H10); 7.02 (m, 2H, H8, H12); 7.03 (m, 2H, H9, H11) ppm. 13C
NMR (100.6 MHz, C6D6): δ 23.00 (s, 1C, CH3, noncycloplati-
nated amine); 24.06 (s, 1C, CH3, cycloplatinated amine); 58.39
(s, 1C, CH, noncycloplatinated amine); 62.96 (s, 1C, CH,
cycloplatinated amine); 121.22, 128.19 (s, 2C, C4, C5); 123.64,
125.22 (s, 2C, C2, C3); 126.36 (s, 1C, C10); 127.92 (s, 2C, C8,
C12); 128.46 (s, 2C, C9, C11); 139.81 (s, 1C, C6); 143.18 (s, 1C,
C7); 155.20 (s, 1C, C1) ppm. 195Pt NMR (107.4 MHz, C6D6): δ
-3302.81 ppm. Anal. Calcd for C16H21PtIN2: H: 3.76, C: 34.11,
N: 4.97. Found: H: 3.72, C: 34.29, N: 5.02. Mp: 199 °C.
(400 MHz, CD2Cl2): δ 1.59 (d, 3H, J ) 6.84 Hz, CHMe); 4.38
(q, 1H, J ) 5.12 Hz, CH); 5.29 (br, 1H, NH); 6.04 (br, 1H,
NH); 6.24 (m, 1H, Ph); 6.38 (dd, 1H, J ) 2.80 Hz, J ) 7.74
Hz, Ph); 6.77 (m, 1H, Ph); 6.94 (m, 1H, Ph); 7.39-7.45 (m,
9H, PPh3); 7.63-7.70 (m, 6H, PPh3) ppm. 13C NMR (100.6
MHz, CD2Cl2): δ ) 25.14 (s, 1C, CH3); 62.67 (s, 1C, CH);
121.10, (s, 1C, Ph); 122.66 (s, 1C, Ph); 124.33 (s, 2C, Ph);
127.71 (d, 6C, JC-P ) 10.06 Hz, meta-C, PPh3); 130.39 (s, 3C,
para-C, PPh3); 134.64 (d, 6C, JC-P ) 10.06 Hz, ortho-C, PPh3);
132.02 (d, 3C, JC-P ) 57.35 Hz, ipso-C, PPh3); 142.48 (s, 1C,
C6); 155.65 (s, 1C, C1) ppm. 31P NMR (121.45 MHz,CD2Cl2):
δ 21.66 (t, 1P, JP-Pt ) 4421.78 Hz, PPh3). 195Pt NMR (107.4
MHz, DMSO): -4253.82 (d, 1Pt, JP-Pt ) 4043.15) ppm. Anal.
Calcd for C26H25PtINP: H: 3.58, C: 44.33, N: 1.99. Found: H:
3.68, C: 44.54, N: 2.00. Mp: 249 °C with decomposition.
5a, 5b, 5c: (S)- or (R)-PtI(4-R-C6H4CHMeNH2)(4-pi-
coline). 5a. NMR. 1H NMR (400 MHz, C6D6): δ 0.82 (d, 3H,
1
3b. NMR. H NMR (400 MHz, C6D6): δ 0.99 (d, 3H, J )
6.60 Hz, CHMe cycloplatinated amine); 1.60 (d, 3H, J ) 6.76 Hz,
CHMe noncycloplatinated amine); 1.87 (s, 3H, 4-Me(Ph) cyclo-
platinated amine); 2.09 (s, 3H, 4-Me(Ph) noncycloplatinated amine);
2.61 (br, 1H, NH, noncycloplatinated amine); 3.35 (br, 2H, NH
noncycloplatinated and NH cycloplatinated amines); 4.00 (m, 2H,
CH, noncycloplatinated and cycloplatinated amines); 6.06 (br, 1H,
NH, cycloplatinated amine); 6.39 (s, 1H, H5); 6.42 (d, 1H, J )
7.60 Hz, H3); 6.61 (d, 1H, J ) 7.56 Hz, H2); 6.69 (d, 2H, J )
8.00 Hz, H8, H12); 6.87 (d, 2H, J ) 7.80 Hz, H9, H11) ppm. 13
C
NMR (100.6 MHz, C6D6): δ 21.08 (s, 2C, 4-CH3(Ph), noncyclo-
platinated and cycloplatinated amines); 23.45 (s, 1C, CH3, non-
cycloplatinated amine); 24.65 (s, 1C, CH3, cycloplatinated amine)
58.53 (s, 1C, CH, noncycloplatinated amine); 62.57 (s, 1C, CH,
cycloplatinated amine); 120.63, (s, 1C, C2); 124.34 (s, 1C, C3);
126.15 (s, 2C, C8, C12); 129.54 (s, 1C, C5); 129.68 (s, 2C, C9, C11);
133.91 (s, 1C, C4); 137.70 (s, 1C, C10); 140.00 (s, 1C, C6); 141.00
(s, 1C, C7); 153.11 (s, 1C, C1) ppm. 195Pt NMR (107.4 MHz,
C6D6): δ -3297.59 ppm. Anal. Calcd for C18H25PtIN2: H: 4.26,
C: 36.56, N: 4.74. Found: H: 4.30, C: 35.77, N: 4.65.
J ) 6.60 Hz, CHMe cycloplatinated amine), 1.40 (s, 1H,
4-Me(Py)); 3.40- 3.60 (b, 2H, NH2); 4.19 (m, 1H, CH);
6.00-8.76 (m, 7H, Ph, Py) ppm. 195Pt NMR (107.4 MHz,
C6D6): δ -3306.29 (s, 1Pt) ppm. Anal. Calcd for C14H17PtIN2:
H: 3.20, C: 31.41, N: 5.23. Found: H: 3.29, C: 32.31, N: 5.35.
Mp: 241 °C with decomposition.
3c. NMR. 1H NMR (400 MHz, CD2Cl2): δ 1.46 (d, 3H, J )
6.60 Hz, CHMe cycloplatinated amine); 1.60 (d, 3H, J ) 6.59
Hz, CHMe noncycloplatinated amine); 3.64 (br, 2H, NH
noncycloplatinated and NH cycloplatinated amines); 3.79 (br,
2H, NH amine noncycloplatinated amine); 4.24 (m, 1H, CH,
cycloplatinated amines); 4.46 (m, 1H, CH, noncycloplatinated
amines); 4.64 (br, 1H, NH, amine, cycloplatinated amine); 6.36
(s, 1H, H5); 6.66 (m, 1H, H3); 6.91 (m, 1H, H2); 7.09 (m, 2H,
H8, H12); 7.38 (m, 2H, H9, H11) ppm. 13C NMR (100.6 MHz,
CD2Cl2): δ 22.91 (s, 1C, CH3, noncycloplatinated amine); 24.25
(s, 1C, CH3, cycloplatinated amine) 57.98 (s, 1C, CH, noncy-
cloplatinated amine); 62.89 (s, 1C, CH, cycloplatinated amine);
1
5b. NMR. H NMR (400 MHz, C6D6): δ 0.88 (d, 3H, J )
6.60 Hz, CHMe cycloplatinated amine), 1.53 (s, 1H, CHMe),
2.09 (s, 1H, 4-Me(Py)); 3.05, 3.59 (m, 2H, NH2); 4.08 (m, 1H,
CH); 6.02-8.38 (m, 7H, Ph, Py) ppm. 195Pt NMR (107.4 MHz,
C6D6): δ -3188.05 (s, 1Pt) ppm. Anal. Calcd for C15H19PtIN2:
H: 3.49, C: 32.80, N: 5.10. Found: H: 3.61, C: 32.77, N: 4.99.
Mp: 218 °C with decomposition.
1
5c. NMR. H NMR (400 MHz, C6D6): δ 1.32, 1.34 (s, 2H,
110.22, (d, 1C, JC-F ) 21.40 Hz, C3); 114.79 (d, 1C, JC-F
)
CHMe, 4-Me(Py)); 2.63, 2.97 (m, 2H, NH2); 4.28 (m, 1H, CH);
6.59-6.69 (m, 7H, Ph, Py) ppm. 19F NMR (188.15 Mhz, C6D6):
δ -113.32 (m, 1F, F) ppm. 195Pt NMR (107.4 MHz, C6D6): δ
-3376.38 (s, 1Pt) ppm. Anal. Calcd for C14H16PtFIN2: H: 2.91,
C: 30.39, N: 5.06. Found: H: 3.01, C: 30.10, N: 4.98.
18.72 Hz, C5); 116.27 (d, 2C, JC-F ) 20.06 Hz, C8, C12); 122.83
(d, 1C, JC-F ) 8.03 Hz, C2); 128.78 (d, 2C, JC-F ) 7.46 Hz,
C9, C11); 138.66 (s, 1C, C7); 141.84 (s, 1C, C6); 149.82 (s, 1C,
C1); 160.20 (d, 1C, JC-F ) 246.53 Hz, C4); 163.04 (d, 1C, JC-F
) 246.53, C10) ppm. 19F NMR (376,3 MHz, CD2Cl2): δ-114.07
(m, 1F, noncycloplatinated amine); -116.70 (m, 1F, cycloplati-
Single-Crystal X-ray Diffraction. Suitable crystals for X-ray
diffraction were obtained by slow evaporation of 2-propanol/

3130 Organometallics, Vol. 27, No. 13, 2008
Calmuschi-Cula and Englert
Table 2. Experimental X-ray Diffraction Parameters and Crystal Data for the Substitution Products 4a and 5a-c
complex
(S)-4a
(R)-5a
(S)-5b
(S)-5c
empirical formula
fw
C26H25PtINP
704.42
C14H17PtIN2
535.29
C15H19PtIN2
549.31
C14H16PtFIN2
553.28
cryst size (mm)
cryst habit, color
cryst syst
space group
a (Å)
0.47 × 0.14 × 0.03
rod, light yellow
monoclinic
P21
9.975(2)
8.3934(19)
14.854(3)
104.246(4)
1205.4(4)
1.941
0.19 × 0.09 × 0.04
rod, colorless
tetragonal
I41
19.0287(5)
0.21 × 0.04 × 0.04
fragment, colorless
tetragonal
I41
18.990(3)
0.30 × 0.10 × 0.10
fragment,light yellow
tetragonal
I41
19.091(3)
b (Å)
c (Å)
16.3448(10)
17.965(6)
16.950(3)
ꢀ (deg)
V (Å3)
5918.3(4)
2.403
16
6478(2)
2.253
16
6177.7(16)
2.379
16
D (g · cm-1
Z
)
2
T (K)
130(2)
7.180
668
100(2)
11.555
3936
100(2)
10.559
4064
130(2)
11.083
4064
µ(Mo KR) (mm-1
F(000)
)
θ range (deg)
no. of reflns collected
Rint
no. of unique reflns in refin
no. of reflns with I > 2σ(I)
no. of params refined
R1 (2σ(I))
R1 (all data)
wR2
Flack’s param
2.11-28.33
1.51-28.26
10 303
0.0284
7188
5915
239
0.0376
0.0506
0.0804
0.042(18)
1.072
1.52-28.61
10 559
0.0800
7493
5003
253
0.0540
0.1033
0.1101
0.07(3)
0.993
1.51-26.00
36 320
0.0480
6080
5370
239
0.0311
0.0367
0.0782
0.053(17)
1.005
16 539
0.0399
5956
5657
272
0.0322
0.0343
0.0788
-0.010(5)
1.018
-1.21/2.17
goodness of fit
diff peak/hole (e/Å3)
-1.14/1.32
-1.20/2.13
-1.12/2.17
CH2Cl2 solutions at room temperature. Crystal data, parameters
for intensity data collection, and convergence results are
compiled in Table 1 (for the intermediate 2a and the direct
products of cycloplatination, r-3a, ꢀ-3a, 3c) and Table 2 (for
the substitution products 4a, 5a-c). Data were collected with
Mo KR radiation (graphite monochromator, λ ) 0.71073 Å)
on a Bruker D8 goniometer with a SMART APEX CCD area
detector. An analytical absorption correction21,22 based on face-
indexing was performed for the well-shaped crystal of 3c,
whereas in the other cases multiscan absorption corrections were
applied by SADABS23 or PLATON.22 Unit cell parameters were
obtained by least-squares refinement of up to 9999 reflections.
The structures were solved by direct methods (SHELXS-97)24
and refined by full matrix least-squares procedures based on
F2 with all measured reflections (SHELXL-97).25 Non-hydrogen
atoms were refined anisotropically. Hydrogen atoms were
introduced in calculated positions (dC-H ) 0.98 Å, dN-H )
0.95 Å) and refined using a riding model. The absolute
configurations of the enantiomerically pure reagents were
confirmed by evaluation of the Flack26 parameter. The crystal
structures of 5a-c are isomorphous and show pronounced
pseudosymmetry with strong correlation between parameters for
atoms in symmetrically independent molecules related by
pseudoinversion. Displacement parameters within each atom pair
were constrained to be equal, and distance restraints were
applied in order to ensure physically meaningful results and
convergence. Nevertheless, it has to be noted that the inherent
pseudosymmetry affects the accuracy of these structures. We
will attempt to perform nonroutine diffraction experiments at
high resolution, possibly for one of the cycloplatinated amines
3a or 3c not affected by pseudosymmetry, in order to obtain
more precise geometry parameters for the molecular structure
of a primary amine. Crystallographic data for all structures have
been deposited with the Cambridge Crystallographic Data Centre
as supplementary publications no. CCDC-681252 (for 2a),
677332 (for r-3a), 681253 (for ꢀ-3a), 681254 (for 3c), 681255
(for 4a), 677333 (for 5a), 681256 (for 5ꢀ), and 681257 (for
5c).
Acknowledgment. The authors thank Manuel Krott for
help with powder diffraction, Toni Gossen for 195Pt NMR
spectra, and an anonymous referee for helpful comments.
Supporting Information Available: Crystallographic informa-
tion for all structures in CIF format; refinement details and
displacement ellipsoid plots for the six independent molecules in
(S,S)-2a, displacement ellipsod plots of (R,R)-3c, (S)-5b, and (S)-
5c in the solid state. This material is available free of charge via
the Internet at http://pubs.acs.org.
(21) De Meulenaer, J.; Tompa, H. Acta Crystallogr. 1965, 19, 1014.
(22) Spek, A. L. J. Appl. Crystallogr. 2003, 36, 7.
(23) Sheldrick, G. M. SADABS, Program for Empirical Absorption
Correction of Area Detector Data; University of Go¨ttingen, 1996.
(24) Sheldrick, G. M. SHELXS97, Program for Crystal Structure
Solution; University of Go¨ttingen, 1997.
(25) Sheldrick, G. M. SHELXL97, Program for Crystal Structure
Refinement; University of Go¨ttingen, 1997.
(26) Flack, H. D. Acta Crystallogr., Sect. A 1983, 39, 876.
OM800238J