Approaches to bi- and trimetallic platinum and palladium complexes using the DPPEPM ligand

Article abstract of DOI:10.1016/j.inoche.2003.08.004

Bis{(diphenylphosphinoethyl)phenylphosphino}methane (DPPEPM) reacts with [PtR₂(cod)] in 1:1 ratio to give [PtR₂ (DPPEPM-PP)] (2a, R = Me; 2b, R = Ph), whereas with [PtCl₂(cod)] or [PdCl ₂(cod)] it yields the ionic species [M(DPPEPM-PP)₂] ²⁺ (3 and 4). With [MClMe(cod)], the product is [MMe(DPPEPM-PPP)]⁺ (5, M = Pt; 6, M = Pd), in which one of the internal P atoms of the ligand is uncoordinated. These complexes undergo oxidation of the free P atom to give 7 and 8 on standing in solution. Complexes 2-4 may be used to construct bimetallic and trimetallic mixed metal complexes. The molecular structures of 7 and [PtMe₂(μ-DPPEPM)PdCl ₂] (11) are reported.

Full text of DOI:10.1016/j.inoche.2003.08.004

Inorganic Chemistry Communications 6 (2003) 1307–1310
www.elsevier.com/locate/inoche
Approaches to bi- and trimetallic platinum and palladium
complexes using the DPPEPM ligand
*
Padma Nair, Gordon K. Anderson , Nigam P. Rath
Department of Chemistry and Biochemistry, University of Missouri-St. Louis, 8001 Natural Bridge Road, St. Louis, MO 63121, USA
Received 31 July 2003; accepted 11 August 2003
Published online: 10 September 2003
Abstract
Bis{(diphenylphosphinoethyl)phenylphosphino}methane (DPPEPM) reacts with [PtR2(cod)] in 1:1 ratio to give [PtR2
(DPPEPM-PP)] (2a, R ¼ Me; 2b, R ¼ Ph), whereas with [PtCl2(cod)] or [PdCl2(cod)] it yields the ionic species [M(DPPEPM-PP)2]2þ
(3 and 4). With [MClMe(cod)], the product is [MMe(DPPEPM-PPP)]þ (5, M ¼ Pt; 6, M ¼ Pd), in which one of the internal P atoms
of the ligand is uncoordinated. These complexes undergo oxidation of the free P atom to give 7 and 8 on standing in solution.
Complexes 2–4 may be used to construct bimetallic and trimetallic mixed metal complexes. The molecular structures of 7 and
[PtMe2(l-DPPEPM)PdCl2] (11) are reported.
Ó 2003 Elsevier B.V. All rights reserved.
Keywords: Platinum and palladium complexes; Crystal structure(s); Tetraphosphine ligands
A number of phosphorus-containing ligands have
been employed in the synthesis of homobimetallic com-
plexes. Preparation of heterobimetallic complexes is less
straightforward, however, because of the tendency for
formation of symmetrical species. One method that can
favor heterometallic species is the use of heterodifunc-
tional ligands, such as Ph2Ppy [1], Ph2PCH2AsPh2 [2], or
R2PC5H4 [3]. Alternatively, unsymmetrical complexes
can be prepared using simple bridging ligands, such as
Ph2PCH2PPh2 (dppm), but they must be constructed in a
stepwise manner. Thus, reaction of [MoCl(g5-C5H5)
(CO)2(dppm-P)] with [Pt(C2H4)(PPh3)2] gives the mixed
metal complex [Mo(g5-C5H5)(CO)2(l-dppm)Pt(PPh3)]
[4]. We have shown that the g1-dppm cations [PtR
(dppm-PP)(dppm-P)]þ can serve as precursors to plati-
num–rhodium complexes [5], and to mixed metal com-
plexes of platinum with silver, gold or mercury [6].
Similarly, the g1-dppm derivatives [PtR2(dppm-P)2]
have been used to prepare diplatinum complexes of the
type [PtR2(l-dppm)2PtR02] [7]. StanleyÕs tetra- and
hexaphosphine ligands have been used primarily in the
synthesis of homobimetallic compounds, but mixed
metal complexes of these ligands have been prepared
also [8]. We have shown previously that platinum and
palladium precursors react with the tetraphosphine
bis[(diphenylphosphinoethyl)phenylphosphino]methane
(DPPEPM) in 2:1 ratio to generate symmetrical homo-
bimetallic complexes of the form [MX2(l-DPPEPM)
MX2] (M ¼ Pt, X ¼ Cl, methyl, benzyl, phenyl, 4-tolyl;
M ¼ Pd, X ¼ Cl) [9]. Here we describe reactions of plat-
inum and palladium precursors with DPPEPM in 1:1
ratio, and subsequent reactions to produce heterobime-
tallic derivatives.
Treatment of meso-DPPEPM (1) with 1 mol equiv of
[PtR2(cod)] (R ¼ Me, Ph) in dilute acetone solution pro-
duces the monometallic complex [PtMe2(DPPEPM-PP)]
(2a) and [PtPh2(DPPEPM-PP)] (2b) in good yield
(Scheme 1). Each complex is characterized by four reso-
nances in its 31P{1H} NMR spectrum. Complex 2a ex-
hibits a doublet at )12.4 ppm (3JPP ¼ 31 Hz) and a
3
doublet of doublets at )28.7 ppm (2JPP ¼ 68, JPP ¼ 31
Hz), due to the uncoordinated P atoms, and a doublet of
doublets at 42.0 ppm (2JPP ¼ 68, 4 Hz, 1JPtP ¼ 1814 Hz)
and a doublet at 49.4 ppm (2JPP ¼ 4 Hz, 1JPtP ¼ 1829 Hz),
* Corresponding author. Tel.: +1-314-516-5311; fax: +1-314-516-
5342.
E-mail address: ganderson@umsl.edu (G.K. Anderson).
1387-7003/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2003.08.004

1308
P. Nair et al. / Inorganic Chemistry Communications 6 (2003) 1307–1310
P
P
P
P
PtR2(cod)
MClMe(cod)
1
MCl2(cod)
P
P
P
P
P
P
P
P
+
Pt
M
R
R
Me
P
P
P
P
R = Me
R = Ph
2a
2b
2
+
M = Pt
M = Pd
5
6
M
P
P
P
P
M = Pt
M = Pd
3
4
Scheme 1. Reactions of DPPEPM with [PtR2(cod)] (R ¼ Me, Ph), [MCl2(cod)] and [MClMe(cod)] (M ¼ Pd, Pt).
2
due to the two coordinated P atoms. The magnitudes of
the couplings to 195Pt are consistent with a phosphine
ligand lying trans to an alkyl group. The NMR spectrum
of 2b is similar [10]. When dilute solutions are employed
the monometallic complex is formed almost quantita-
tively, but with more concentrated samples the diplati-
num complexes [Pt2R4(l-DPPEPM)] [9] and some free
ligand are observed also.
two that exhibit large JPP couplings indicative of their
mutually trans disposition, and a fourth that shows
coupling to each of the other three P atoms. In 5, this
1
fourth signal also shows the smallest JPtP value, indi-
cating that it lies trans to the methyl group. If allowed to
stand in acetone solution the uncoordinated P atom
becomes oxidized, as evidenced by the disappearance of
the low frequency signal and the appearance of a new
signal at ca. 35 ppm, to give [MMe{DPPEPM(O)-
PPP}]Cl, 7 (M ¼ Pt) and 8 (M ¼ Pd). The structure of 7
has been determined by X-ray crystallography [13], and
its molecular structure is shown in Fig. 1.
One might expect that the analogous reaction of
with
DPPEPM
[PtCl2(cod)]
would
produce
[PtCl2(DPPEPM-PP)], but this is not the case. When
dilute solutions of the two reagents are mixed in equi-
molar amounts, the major product is indeed a complex
with four nonequivalent (two coordinated and two un-
1
coordinated) P atoms. The magnitudes of the JPtP
coupling constants (2370 and 2665 Hz) indicate that
each phosphine lies trans to another phosphine, how-
ever, instead of a chloride. The product is formulated as
the [Pt(DPPEPM-PP)2]2þ cation (3) [11], and the nature
of the cation has been confirmed by high-resolution
mass spectrometry. The 1H NMR spectrum of 3 exhibits
eight resonances due to the PCH2CH2P hydrogens,
which can be separated into two sets of four on the basis
of COSY experiments. The central CH2 hydrogens give
rise to broad peaks at 4.55 and 0.87 ppm, each of which
simplifies to a doublet upon 31P decoupling. The reac-
tion with [PdCl2(cod)] proceeds similarly. The 31P{1H}
NMR spectrum of [Pd(DPPEPM-PP)2]2þ (4) also ex-
hibits signals due to two uncoordinated and two coor-
dinated P atoms [11]. Again, the central CH2 group of
the DPPEPM ligand gives rise to two widely separated
1H resonances at 4.35 and 0.91 ppm.
Reactions of DPPEPM with [PtClMe(cod)] and
[PdClMe(cod)] follow yet a different path. The products
are formulated as the cations 5 and 6 (Scheme 1) [12], in
which the chloride has been displaced from the metal.
DPPEPM acts a tridentate ligand, with one of the in-
ternal P atoms remaining uncoordinated. In each case,
the 31P{1H} NMR spectrum exhibits four resonances,
one at low frequency due to the uncoordinated P atom,
Fig. 1. Molecular structure of [PtMe{DPPEPM(O)-PPP}]þ (7). Selected
ꢀ
bond distances (A) and angles (deg): Pt(1)–P(1) 2.2953(8), Pt(1)–P(2)
2.3276(8), Pt(1)–P(4) 2.2859(8), Pt(1)–C(42) 2.131(3); P(1)–Pt(1)–P(2)
84.48(3), P(1)–Pt(1)–P(4) 174.92(3), P(2)–Pt(1)–P(4) 98.76(3), P(1)–
Pt(1)–C(42) 88.38(11), P(2)–Pt(1)–C(42) 172.84(10), P(4)–Pt(1)–C(42)
88.33(10), P(2)–C(21)–P(3) 118.87(17).

P. Nair et al. / Inorganic Chemistry Communications 6 (2003) 1307–1310
1309
P
P
P
P
Pt
Me
Me
R = Me
2a
PtPh2(cod)
MCl2(cod)
P
P
P
P
P
+
P
P
P
P
P
P
P
P
Pt
Me
P
Me
P
2
+
Pt
Pt
M
M
Pt
Pt
Me
Me
Ph
Cl
Me
Me
Me
Me
Ph
Cl
P
10
M = Pt
M = Pd
9
12
M = Pt
M = Pd
11
13
PtMe2(cod)
P
P
P
P
2
+
M
P
P
P
P
M = Pt
M = Pd
3
4
Scheme 2. Preparation of mixed metal complexes.
The monometallic complexes 2–4 may be employed
to prepare mixed metal derivatives. Addition of 1 mol
equiv of [PtPh2(cod)] to an acetone solution of 2a
produces the mixed diplatinum complex [PtMe2(l-
DPPEPM)PtPh2] (9) quite cleanly (Scheme 2) [14], al-
though traces of [Pt2R4(l-DPPEPM)] (R ¼ Me, Ph) are
also formed. Reaction of 2a with [PtCl2(cod)] yields a
mixture of [PtMe2(l-DPPEPM)PtCl2] (10) and the
trimetallic complex [{PtMe2(l-DPPEPM)}2Pt]2þ (12).
The 31P{1H} NMR spectrum of 10 consists of four
We have shown that it is possible, by careful addition
of 1 equiv of a suitable platinum or palladium precursor
to DPPEPM, to produce complexes containing two co-
ordinated and two uncoordinated phosphine moieties,
i.e., it is possible to add one metal center to one ‘‘half’’ of
the tetradentate ligand. The remaining free diphosphine
1
resonances, the JPtP couplings being typical of two P
atoms lying trans to methyl groups, and two lying trans
to chlorides. The structure of 10 has been determined
by X-ray crystallography, and its molecular structure is
shown in Fig. 2 [15]. The 31P{1H} NMR spectrum of
12 contains two signals with small 195Pt couplings, due
to the two P atoms lying trans to methyls, and two
signals that are very similar to those found for the
central P atoms in 3. Complex 10 would be formed by
displacement of cod from [PtCl2(cod)] by the free
phosphine groups in 2a, whereas further reaction of 10
with a second equivalent of 2a would generate 12.
When the reaction is performed in reverse order,
namely, by addition of DPPEPM to [PtCl2(cod)] to
give 3, followed by addition of [PtMe2(cod)], the
trimetallic complex 12 is formed quantitatively. Here
the two uncoordinated diphosphine units in 3 would
displace cod from two molecules of [PtMe2(cod)]
(Scheme 2).
Fig. 2. Molecular structure of [PtMe2(l-DPPEPM)PtCl2] (10). Se-
ꢀ
lected bond distances (A) and angles (deg): Pt(1)–P(1) 2.240(1), Pt(1)–
P(2) 2.243(1), Pt(1)–C(6) 2.259(2), Pt(1)–C(7) 2.271(2), Pt(2)–P(3)
2.252(1), Pt(2)–P(4) 2.227(1), Pt(2)–Cl(3) 2.319(2), Pt(2)–Cl(4)
2.287(2); P(1)–Pt(1)–P(2) 86.33(5), P(1)–Pt(1)–C(6) 91.22(8), P(1)–
Pt(1)–C(7) 179.01(7), P(2)–Pt(1)–C(6) 177.29(8), P(2)–Pt(1)–C(7)
92.68(7), C(6)–Pt(1)–C(7) 89.77(10), P(3)–Pt(2)–P(4) 85.83(4), P(3)–
Pt(2)–Cl(3) 94.33(5), P(3)–Pt(2)–Cl(4) 176.46(6), P(4)–Pt(2)–Cl(3)
174.04(5), P(4)–Pt(2)–Cl(4) 92.01(6), Cl(3)–Pt(2)–Cl(4) 88.11(7), P(2)–
C(5)–P(3) 121.1(2).

1310
P. Nair et al. / Inorganic Chemistry Communications 6 (2003) 1307–1310
2JPP ¼ 68 Hz, 3JPP ¼ 4 Hz, 1JPtP ¼ 1814 Hz), 49.4 (d, 3JPP ¼ 4 Hz,
1JPtP ¼ 1829 Hz). For 2b, 31P{1H} NMR: dP )28.0 (dd, 2JPP ¼ 78
Hz, 3JPP ¼ 30 Hz, 3JPtP ¼ 15 Hz), )12.8 (d, 3JPP ¼ 30 Hz), 37.9 (d,
unit may be employed subsequently to generate unsym-
metrical diplatinum, or mixed platinum–palladium,
derivatives. These include the expected bimetallic species
9–11, and the unexpected trimetallic complexes 12 and
13. Studies of the chemistry of the bi- and trimetallic
complexes are continuing.
1
1
2JPP ¼ 78 Hz, JPtP ¼ 1723 Hz), 41.6 (s, JPtP ¼ 1733 Hz).
3
[11] For 3, 31P{1H} NMR (acetone-d6): dP )27.7 (dt, JPP ¼ 32 Hz,
3
2JPP ¼ 4JPP ¼ 18 Hz), )12.7 (d, JPP ¼ 32 Hz), 34.3 (ddd,
1
2
2JPP ¼ 18 Hz, JPtP ¼ 2370 Hz), 44.7 (dd, JPP ¼ 18 Hz,
1JPtP ¼ 2665 Hz). HRMS: observed, 1508.3933; calcd. for
12
C
H81P195Ptþ, 1508.3887. For 4, 31P{1H} NMR: dP )26.9 (dt,
8
2 3
82
3JPP ¼ 32 Hz, JPP ¼ 16 Hz), )12.6 (d, JPP ¼ 32 Hz), 47.4 (ddd,
2JPP ¼ 16 Hz), 57.3 (dd, JPP ¼ 16 Hz).
2
Supporting information available
[12] For 5, 31P{1H} NMR (acetone-d6): dP )19.5 (dd, JPP ¼ 24 Hz,
2
3JPP ¼ 9 Hz), 28.9 (ddd, JPP ¼ 384, 19, 9 Hz, JPtP ¼ 2833 Hz),
2
1
Complete spectroscopic characterization for all
compounds, and full X-ray structural details for [PtMe
(DPPEPM(O)-PPP)]Cl (7) and [PtMe2(l-DPPEPM)
PtCl2] (10).
2
1
43.7 (ddd, JPP ¼ 24, 19, 5 Hz, JPtP ¼ 1785 Hz), 54.8 (dd,
2JPP ¼ 384, 5 Hz, JPtP ¼ 2718 Hz). For 6, 31P{1H} NMR: dP
1
2
3
3
)17.0 (dd, JPP ¼ 26 Hz, JPP ¼ 11 Hz), 31.3 (ddd, JPP ¼ 374, 23
3
2
Hz, JPP ¼ 11 Hz), 39.3 (dt, JPP ¼ 37, 26, 26 Hz), 56.0 (dd,
2JPP ¼ 374, 26 Hz).
[13] Crystals of
7
are triclinic, space group Pðꢀ1Þ, with
ꢀ ꢀ ꢀ
a ¼ 10:7382ð11Þ A, b ¼ 10:8073ð11Þ A, c ¼ 18:6111ð19Þ A,
Acknowledgements
a ¼ 99:493ð8Þ°, b ¼ 99:685ð8Þ°, c ¼ 112:983ð7Þ°, V ¼ 1895:7ð3Þ
A , Z ¼ 2, and qcalcd: ¼ 1:609 g cmꢀ3 for fw ¼ 918.18. A total of
3
ꢀ
Thanks are expressed to the National Science Foun-
dation (Grant No. CHE-9508228) for support of this
work, and to NSF (Grant Nos. CHE-9318696, 9309690
and 9974801), the US Department of Energy (Grant No.
DE-FG02-92CH10499) and the University of Missouri
Research Board for instrumentation grants.
9725 independent reflections were collected at 120(2) K in the h
range 2.12–29.00°, wR2 ¼ 0:0546 and R1 ¼ 0:0301.
[14] For 9, 31P{1H} NMR (acetone-d6): dP 32.3 (dd, JPP ¼ 19, 6 Hz,
2
1JPtP ¼ 1654 Hz), 40.5 (dd, 2JPP ¼ 19, 7 Hz, 1JPtP ¼ 1785 Hz), 40.5
2
1
2
(d, JPP ¼ 6 Hz, JPtP ¼ 1820 Hz), 48.8 (d, JPP ¼ 7 Hz,
1JPtP ¼ 1811 Hz). HRMS: observed, 1061.1636; calcd. for
C
H43P195Ptþ2 (M–CH3,2C6Hþ), 1061.1611. For 10, 31P{1H}
12
42
4
5
NMR: dP 36.4 (br s, 1JPtP ¼ 3535 Hz), 39.2 (br s, 1JPtP ¼ 1743 Hz),
1
1
41.5 (br s, JPtP ¼ 3648 Hz), 48.5 (br s, JPtP ¼ 1786 Hz). For 11,
31P{1H} NMR: dP 40.3 (br s, JPtP ¼ 1740 Hz), 48.9 (br s,
1
References
1JPtP ¼ 1795 Hz), 61.0 (br s), 64.8 (br s). For 12, 31P{1H} NMR:
2
1
2
[1] J.P. Farr, F.E. Wood, A.L. Balch, Inorg. Chem. 22 (1983) 3387.
[2] A.L. Balch, R.R. Guimerans, J. Linehan, F.E. Wood, Inorg.
Chem. 24 (1985) 2021.
dP 30.3 (t, JPP ¼ 16 Hz, JPtP ¼ 2375 Hz), 40.2 (d, JPP ¼ 9 Hz,
1JPtP ¼ 1790 Hz), 43.1 (t, JPP ¼ 16 Hz, JPtP ¼ 2693 Hz), 49.7 (d,
2 1
2JPP ¼ 9 Hz, JPtP ¼ 1791 Hz). HRMS: observed, 1958.3901;
1
12
calcd. for
C
2
H93P195Ptþ3 , 1958.4122. For 13, 31P{1H} NMR: P
[3] R.M. Bullock, C.P. Casey, Acc. Chem. Res. 20 (1987) 167.
[4] M.Cano,P.Ovejero,J.V.Heras,J.Organomet.Chem.486(1995)63.
[5] C. Xu, G.K. Anderson, N.P. Rath, Inorg. Chim. Acta 265 (1997)
241.
86
8
1
41.1 (br t, JPP ¼ 8 Hz, JPtP ¼ 1756 Hz), 43.5 (br), 49.4 (d,
2JPP ¼ 8 Hz, JPtP ¼ 1789 Hz), 56.0 (t, JPP ¼ 15 Hz). HRMS:
1
2
C
H93P106Pd195Pt2þ, 1869.3509.
86
8
12
observed, 1869.3434; calcd. for
[6] C. Xu, G.K. Anderson, L. Brammer, J. Braddock-Wilking, N.P.
Rath, Organometallics 15 (1996) 3972.
[15] Crystals of 10 are triclinic, space group Pðꢀ1Þ, with
ꢀ ꢀ ꢀ
a ¼ 12:3043ð2Þ A, b ¼ 13:7558ð2Þ A, c ¼ 13:9551ð2Þ A,
a ¼ 104:6490ð10Þ°, b ¼ 101:7410ð10Þ°, c ¼ 100:1730ð10Þ°,
cmꢀ3 for
[7] F.S.M. Hassan, D.M. McEwan, P.G. Pringle, B.L. Shaw, J.
Chem. Soc., Dalton Trans. (1985) 1501.
3
ꢀ
V ¼ 2171:56ð6Þ A , Z ¼ 2, and qcalcd: ¼ 1:800
g
[8] S.E. Saum, F.R. Askham, S.A. Laneman, G.G. Stanley, Polyhe-
dron 9 (1990) 1317.
[9] P. Nair, G.K. Anderson, N.P. Rath, Organometallics 22 (2003)
fw ¼ 1176.80. A total of 11,046 independent reflections were
collected at 170(2) K in the h range 1.86–29.93°, wR2 ¼ 0:0641 and
R1 ¼ 0:0323. Due to the small sizes of the methyl and chloride
ligands attached to platinum, the ligands show positional disorder.
The disorder was resolved using partial occupancies of 50% for the
ligands on both metals.
1494.
[10] For 2a, 31P{1H} NMR (acetone-d6): dP )28.7 (dd, JPP ¼ 68 Hz,
2
3JPP ¼ 31 Hz, JPtP ¼ 17 Hz), )12.4 (d, JPP ¼ 31 Hz), 42.0 (dd,
3
3