4-Chloro-5-methyl-3-diphenylphosphino-1-phenyl-1,2,3,6- tetrahydrophosphinine as a bidentate P-ligand in a cis chelate Pt(II) complex

Article abstract of DOI:10.1016/j.jorganchem.2004.06.062

Double deoxygenation of a 3-phosphinoxido-1,2,3,6-tetrahydrophosphine oxide (2) led to bisphosphine 3-2 with an inverted ring P atom. The reaction of bidentate P-ligand 3-2 with dichlorodibenzonitrilo platinum(II) yielded the mixture of a novel cis chelat

Full text of DOI:10.1016/j.jorganchem.2004.06.062

Journal of Organometallic Chemistry 689 (2004) 3158–3162
www.elsevier.com/locate/jorganchem
4-Chloro-5-methyl-3-diphenylphosphino-1-phenyl-1,2,3,6-
tetrahydrophosphinine as a bidentate P-ligand in a cis chelate
Pt(II) complex
a,
Gyorgy Keglevich , Melinda Sipos , Denes Szieberth ,
a
b
*
´
´
¨
c
Gyo¨rgy Petocz , Laszlo Kollar
c
}
´
´
a
Department of Organic Chemical Technology, Budapest University of Technology and Economics, 1521 Budapest, Hungary
b
Department of Inorganic Chemistry, Budapest University of Technology and Economics, 1521 Budapest, Hungary
c
´
Department of Inorganic Chemistry, University of Pecs and Research Group for Chemical Sensors of the Hungarian Academy of Sciences,
´
7624 Pecs, Hungary
Received 17 March 2004; accepted 23 June 2004
Available online 20 August 2004
Abstract
Double deoxygenation of a 3-phosphinoxido-1,2,3,6-tetrahydrophosphine oxide (2) led to bisphosphine 3–2 with an inverted ring
P atom. The reaction of bidentate P-ligand 3–2 with dichlorodibenzonitrilo platinum(II) yielded the mixture of a novel cis chelate
complex (7 = PtCl2(3–2)) and a cis bis(3-diphenylphosphino-1,2,3,6-tetrahydrophosphininyl) complex (8 = PtCl2(g1-5)2) containing
two units of monodentate P-ligand 5.
Ó 2004 Elsevier B.V. All rights reserved.
Keywords: Phosphorus heterocycles; Phosphines; Theoretical studies; Platinum complexes; Chelation
1. Introduction
The parent bis(phosphine oxide), 3-diphenylphos-
phinoxide-1-phenyl-1,2,3,6-tetrahydrophosphinine oxide
(2) was obtained by the diastereoselective Michael addi-
tion of diphenylphosphine oxide at the a,b-double bond
of 1,2-dihydrophosphinine oxide (1) [3], as it was
described (Scheme 1) [4].
The preferred conformer, a twist-boat containing the
Ph2P(O) moiety and the oxygen atom of the ring P‚O
in the trans disposition (2*) was established by DFT cal-
culations. A novel intramolecular H-bonding between
the oxygen atom of the Ph2P(O) moiety and the suitable
hydrogen atom of the C(6)H2 unit was found to stabilise
the twist-boat form [5].
The phosphines are important ligands in transition
metal complexes that can be catalysts in a great variety
of homogeneous catalytic reactions among them hydro-
genation and hydroformylation [1]. Especially the chiral
homo- and heterobidentate P-ligands, such as BINAP,
DIOP, DIPAMP and BINAPHOS are of practical inter-
est [2]. In this paper, the preparation and the coordina-
tion properties of a novel bidentate P-ligand containing
one of the phosphine moieties in an unsaturated six-
membered hetero ring, while the other one as an exocy-
clic diphenylphosphino substituent in position 3 is
described.
The bis(phosphine oxide) (2) was deoxygenated by a
standard procedure applying trichlorosilane–pyridine
in boiling benzene [6] to give a diphosphine (3). Accord-
ing to DFT ab initio calculations [7], the isomer with in-
verted P1-atom (3–2) containing the Ph2P group and the
*
Corresponding author. Tel.: +36 1 463 1111/58 53; fax: +36 1 463
3648.
E-mail address: keglevich@oct.bme.hu (G. Keglevich).
0022-328X/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2004.06.062

G. Keglevich et al. / Journal of Organometallic Chemistry 689 (2004) 3158–3162
3159
Scheme 1.
lone electron pair of the ring phosphorus in the cis posi-
tion is more favourable than the diphosphine with pre-
served P1-configuration (3–1). Twist-boat conformer
3–2* is by 0.58 kcal/mol more favourable than the most
stable conformer of 3–1 (Scheme 2).
The diphosphine (3–2) was stored as its diborane
complex (4) from which it could be regenerated by treat-
ment with diethylamine at 78 °C [12] (Scheme 2).
The exocyclic P-moiety of the diphosphine (3–2) was,
however, extremely sensitive towards oxidation. After a
several minutes exposure to air, 3–2 was converted to
hemioxide 5 (dP ꢀ32.1 and 35.6, (M + H)+ = 425) that
was identified as the corresponding monoborane com-
plex (6) (Scheme 4).
It was assumed that the stereochemistry of the start-
ing phosphine (3–2) was preserved in phosphine-boranes
4 and 6.
Diphosphine 3–2 was reacted with one molar equiva-
lent of dichlorodibenzonitrilo platinum(II) at benzene
reflux. 31P NMR analysis of the crystal fractions, ob-
tained by fractional crystallisation on cooling, suggested
that two complexes were formed, cis chelate complex 7
represented as cis-PtCl2(3–2) and cis bis(3-diph-
Due to the high inversion barrier of 35.4 kcal/mol
obtained by DFT ab initio calculations for the 3–
1 ! 3–2 transformation, that is in accord with the
usual activation enthalpy of 29–36 kcal/mol for phos-
phines [8], it had to be assumed that the phosphine
with inverted P-configuration (3–2) was formed di-
rectly on deoxygenation. Although the silane reduc-
tions are known to proceed mostly with retention of
configuration [9], inversion of the P-pyramid was re-
ported in a few cases, especially in the sphere of
P-heterocycles [10]. Silane reductions carried out in
the presence of tertiary amines were also observed to
result in inversion of the P-center in certain cases
[11]. A possible mechanism starting with the protona-
tion of the P‚O moiety by R3HN+ ꢀSiCl3 followed
by a Cl3SiꢀHOꢀ exchange, and finally by the loss of
Cl3SiOH is shown in Scheme 3.
enylphosphino-1,2,3,6-tetrahydrophosphininyl)
plati-
num complex 8 formulated as cis-PtCl2(g1-5)2. In the
latter complex, hemioxide 5 coordinates as a monoden-
tate ligand. The ratio of 7 and 8 was ca. 3:7 (Scheme 5).
Scheme 2.

3160
G. Keglevich et al. / Journal of Organometallic Chemistry 689 (2004) 3158–3162
HN
Ar
Ar
Ar
Ar
3-2
3
HO
Cl3Si
.
SiCl3
.
Cl3Si
P
O
P
OH
P
P
– Cl3SiOH
N
Scheme 3.
Cl
P
Cl
26 ˚C, 6 h
Me2S BH3
H
H
O
.
26 ˚C, 6 min
exposure to air
CH3
CH3
4
O
CHCl3
3
2
5
6
1
Ph2P
Ph2P
H3B
P
.
.
Ph
Ph
5
6
Scheme 4.
Cl
Cl
Cl
78 ˚C, 1 h
PtCl2(PhCN)2
benzene
CH3
Ph
Ph
4
Pt
3
2
5
6
O
O
PPh2
P
P
1
Ph2P
P
+
Ph2P
Pt
Ph
Cl
Cl
Cl
CH3 H3C
Cl
8
7
Scheme 5.
cis Chelate complex 7 can be regarded as a proof for
the stereostructure of diphosphine 3–2, containing the
two P lone pairs on the same side. Bis(tetrahydrophos-
phininyl) monodentate complex 8 was the major compo-
nent containing the 3-substituent in the phosphine oxide
form. The ring phosphine unit seems to be more reactive
towards the platinum(II) center than the diphenyphos-
phine moiety, which is, in turn, highly sensitive towards
oxidation. The phosphine oxide functions in the major
component were formed by oxidation during the
work-up procedure.
Complexes 7 and 8 were purified by repeated recry-
stallisations to afford the products in an almost pure
form, whose structures were confirmed by 31P NMR
spectral data. The 31P NMR spectrum of cis chelate 7
contained doublets at 17.7 and at 50.3 (JP–P = 6.7 Hz)
justifying that the two phosphorus atoms are bound to
the same metal center. Moreover, both doublets were
accompanied by satellites due to the 195Pt–31P coupling
(JPt–P coupling constants were 3496 and 3681 Hz,
respectively). At the same time, the 31P NMR spectrum
of complex 8 contained singulets at dP ꢀ8.2 and at 42.3,
and only the first one was associated with a JPt–P satellite
of 3566 Hz. In both cases (7 and 8), the cis relationship
of the P-moieties was proved by the JPt–P couplings of
diagnostic value (ca. 3600 Hz) referring to the trans posi-
tion of the P-unit and the chloro ligand [13].
The assignment of the 1H and 13C NMR of 7 was car-
ried out by using various 2D techniques including
COSY and HSQC. The methine proton adjacent to
the exocyclic PPh2 group shows a clear JP–H = 48 Hz
coupling to P. Interestingly, one of the two methylene
groups (CH2 adjacent to CH) shows a large separation
of the two protons (2.03 and 2.42 ppm) and only one
of them gives a 31P–1H coupling of similar magnitude
(JP–H = 55 Hz). The other methylene group (bound to
the olefinic moiety) shows an AB pattern centerd at
3.5 ppm due to the close chemical shifts of the two gemi-
nal protons.
Stereostructure and geometrical data of the cis che-
late complex (7) was determined by DFT ab initio calcu-
lations [7]. It can be seen from Fig. 1 that the
tetrahydrophosphinine ring adopts a half-chair confor-
mation in complex 7. It means that the complexation
also affects the conformation of the six-membered
hetero ring, i.e., the twist-boat form is converted to a
half-chair. The change in the conformation may be the
consequence of the steric hindrance due to the coordi-
nating platinum.
It can be concluded that the double deoxygen-
ation of 3-diphenylphosphinoxido-1-phenyl-1,2,3,6-tetra-
hydrophosphinine 1-oxide (2) made available a novel
bidentate P-ligand (3–2) that was useful in the prepara-
tion of a cis chelate platinum(II) complex (7). The other

G. Keglevich et al. / Journal of Organometallic Chemistry 689 (2004) 3158–3162
3161
0.16 g (0.40 mmol) of diphosphine in 25 ml of de-
gassed dichloromethane was treated with 0.47 ml of
2M dimethylsulfide borane in THF solution (0.93 mmol)
at room temperature. After a 4 h reaction time, 0.50 ml
of water was added and the mixture stirred for 10 min.
The precipitated material was removed by filtration
and the organic phase was dried (Na2SO4). Concentra-
tion in vacuo left 0.17 g (98%) of bis(phosphine borane)
4. dP(CDCl3) 7.7 (broad signal) and 30.8 (broad signal),
dC(CDCl3) 22.8 (1J = 34.9, C(6)), 23.7 (C(5)–CH3), 28.8
(1J = 30.7, C(2)), 44.4 (2J = 38.9, C(3)), 124.5 (1J = 5.7,
2J = 12.2, C(5)), 128.5 (1J = 12.1, C(30))a, 128.9
(2J = 9.5, C(300))a, 129.2 (2J = 10.0, C(300))a, 130.4
(C(4)), 131.3 (2J = 9.6, C(200))a, 131.4 (2J = 8.7, C(200))a,
131.7 (1J = 8.9, C(20))a, 132.3 (2J = 2.2, C(400))b,
132.5 (2J = 2.9, C(400))b, a,btentative assignment;
Fig. 1. Perspective view of cis chelate complex 7 with bond lengths
˚
(A), bond angles (°) and torsion angles (°) obtained by B3LYP
calculations. P(1)–C(2) 1.844, C(2)–C(3) 1.542, C(3)–C(4) 1.521,
C(4)–C(5) 1.352, C(5)–C(6) 1.527, C(6)–P(1) 1.840, P(1)–C(10) 1.823,
C(3)–PPh2 1.902, P(1)–Pt 2.264, Pt–PPh2 2.277, P(1)–C(2)–C(3) 105.3,
C(2)–C(3)–C(4) 111.1, C(3)–C(4)–C(5) 127.3, C(4)–C(5)–C(6) 123.5,
C(5)–C(6)–P(1) 114.0, C(6)–P(1)–C(2) 98.7, C(2)–C(3)–PPh2 106.0,
C(4)–C(3)–PPh2 112.6, C(2)–P(1)–C(10) 106.0, C(6)–P(1)–C(10) 108.3,
P(1)–C(2)–C(3)–C(4) 62.7, P(1)–C(6)–C(5)–C(4) ꢀ10.6, P(1)–C(2)–
C(3)–PPh2 –59.9, C(5)–C(4)–C(3)–C(2) ꢀ29.4, C(5)–C(6)–P–C(10)
150.8, P(1)–C(6)–C(5)–CH3 169.7.
ðM ꢀ HÞþ ¼ 435:1468,
C24H28B2ClP2
requires
found
435.1541 for the 11B and 35Cl isotopes.
On exposure to air, 3 was rapidly converted to hem-
ioxide 5 that was identified as the corresponding phos-
phine borane (6) dP(CDCl3) 10.9 (broad signal) and
34.9; dC(CDCl3) 22.0 (1J = 34.8, C(6)), 24.2 (C(5)–
CH3), 29.9 (1J = 29.9, 2J = 2.4, C(2)), 43.9 (1J = 7.8,
2
2J = 67.0, C(3)), 123.1 (1J = 8.5, J = 13.5, C(5)), 128.6
(1J = 11.9, C(30))a, 129.0 (2J = 9.7, C(300))a, 129.3
(2J = 9.8, C(300))a, C(40) overlapped, 130.3 (1J = 1.7,
C(4)), 131.4 (2J = 7.0, C(200))a, 131.5 (2J = 6.5, C(200))a,
131.8 (1J = 9.2, C(20))a, 132.4 (2J = 2.8, C(400))b,
132.6 (2J = 2.8, C(400))b, a,btentative assignment;
product of the complex formation was a bis(3-diph-
enylphosphino-1,2,3,6-tetrahydrophosphininyl) plati-
num(II) complex (8) containing hemioxide 5 as a
monodentate P-ligand.
ðM ꢀ HÞþ
¼ 437:1077, C24H25BClOP2 requires
found
437.1162 for the 11B and 35Cl isotopes.
2. Experimental
31P, 13C and 1H NMR spectra were recorded in
CDCl3 on a Varian Inova 400 spectrometer at 161.89,
100.62 and 400.13 MHz, respectively. Chemical shifts
are given relative to CHCl3 (7.26 and 77.00 ppm for
1H and 13C) or relative to H3PO4 (31P). The couplings
are listed in Hertz. The starting 3-phosphinoxido-tetra-
hydrophosphinine oxide derivative (2) was synthesized
as described earlier [4]. PtCl2(PhCN)2 was prepared by
a known procedure [14].
2.2. Complexation of the bisphosphine (3) by
PtCl2(PhCN)2
To 0.40 mmol of diphosphine 3 in 40 ml of benzene
0.20 g (0.42 mmol) of dichlorodibenzonitrilo plati-
num(II) was added and the mixture was stirred at reflux
for 1 h under nitrogen. Fractional crystallisation from
the benzene solution (repeated with both fractions ob-
tained in the first run) furnished 7 as pale yellow pow-
der-like crystal in pure form and 8 as an off-white
powder-like material in ca. 85% purity (containing 7 as
an impurity).
2.1. Deoxygenation of the bis(phosphine oxide) precursor
(2) – preparation of diborane-diphosphine 4
Complex 7: dP(CDCl3) 17.7 (JPt–P = 3496, JP–P = 6.7,
P(1)), 50.3 (JPt–P = 3681, JP–P = 6.7, C(3)–P); dC
(CDCl3) 23.2 (CH3), 30.5 (C(6)), 31.1 (C(2)), 45.2
(C(3)), 124.0 (C(5)), 130.3 (C(4)), dH (CDCl3) 1.92 (d,
JH–H = 4.0, 3H, CH3), 2.03 (m, 1H, C(2)HaHb), 2.42
(ddd, JH–H = 11.4, JH–H = 11.0, JP–H = 55, 1H,
C(2)HaHb), 3.47 (d, JH–H = 19, 1H, C(6)HaHb), 3.52
(d, JH–H = 19, 1H, C(6)HaHb), 3.78 (dd, JH–H = 9, JP–
H = 48, 1H, C(3)H), 7.2–7.8 (m, 15H, Ph); Anal. calc.
for C24H23P2Cl3Pt (674.83): C, 42.72; H, 3.44; Found:
C, 43.05; H, 3.73%.
0.09 ml (0.9 mmol) of trichlorosilane and 0.20 ml (2.5
mmol) of pyridine were added to 0.18 g (0.41 mmol) of 2
[3] in 25 ml of degassed toluene and the mixture was stir-
red at the boiling point for 6 h under nitrogen. The pre-
cipitated silane was removed by filtration under nitrogen
and the filtrate was evaporated to give the diphosphine
(3) quantitatively (dP(CDCl3) ꢀ32.1 and ꢀ3.1,
(M + H)+ = 409). The diphosphine (3) that was highly
sensitive towards oxygen was identified as its bis(phos-
phine borane) complex (4).

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G. Keglevich et al. / Journal of Organometallic Chemistry 689 (2004) 3158–3162
N. Sakai, S. Mano, K. Nozaki, H. Takaya, J. Am. Chem. Soc.
115 (1993) 7033;
Complex 8: dP(CDCl3) ꢀ8.2 (JPt–P = 3566, P(1)), 42.3
(C(3)–P); dH(CDCl3) 1.35 (d, J = 3.7, 3H, CH3), 2.50 (m,
2H, CH2), 3.05 (m, 1H, CHaHb), 3.2 (m, 1H, CHaHb),
3.7 (m, 1H, C(3)H), 7.2–7.9 (m, 15H, Ph).
I. Ojima, C.-Y. Tsai, M. Tzamarioudaki, D. Bonafoux, in: L.E.
Overman et al. (Eds.), The Hydroformylation Reaction, vol. 56,
Wiley, New York, 2000, pp. 1–354 (Chapter 1, in Organic
Reactions).
[3] Gy. Keglevich, B. Androsits, L. To¨ke, J. Org. Chem. 53 (1988)
4106.
´
[4] Gy. Keglevich, M. Sipos, T. Imre, K. Ludanyi, D. Szieberth, L.
2.3. Quantum chemical calculations
Quantum chemical calculations were carried out
using the GAUSSIAN 98 program package [7]. Geome-
tries of all conformers of 3 were optimised at the
B3LYP/3-21G* level of theory. Energies were further re-
fined with the help of B3LYP/6-31 + G* single point cal-
culations. In case of 7 the determination of geometries
and energies were carried out using the B3LYP func-
tional with the LANL2DZ ECP basis set augmented
with polarisation functions.
To¨ke, Tetrahedron Lett. 43 (2002) 8515.
[5] Gy. Keglevich, M. Sipos, D. Szieberth, L. Nyulaszi, T. Imre, K.
´
´
Ludanyi, L. To¨ke, under publication.
[6] L.D. Quin, K.C. Caster, J.C. Kisalus, K.A. Mesch, J. Am. Chem.
Soc. 106 (1984) 7021.
[7] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A.
Robb, J.R. Cheeseman, V.G. Zakrzewski, J.A. Montgomery,
R.E. Stratmann, J.C. Burant, S. Dapprich, J.M. Millam, A.D.
Daniels, K.N. Kudin, M.C. Strain, O. Farkas, J. Tomasi, V.
Barone, M. Cossi, R. Cammi, B. Mennucci, C. Pomelli, C.
Adamo, S. Clifford, J. Ochterski, G.A. Petersson, P.Y. Ayala, Q.
Cui, K. Morokuma, D.K. Malick, A.D. Rabuck, K. Raghava-
chari, J.B. Foresman, J. Clioslowski, J.V. Ortiz, B.B. Stefanov,
G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R. Gomperts,
R.L. Martin, D.J. Fox, T. Keith, M.A. Al-Laham, C.Y. Peng,
A. Nanayakkara, C. Gonzalez, M. Challacombe, P.M.W. Gill,
B. Johnson, W. Chen, M.W. Wong, J.L. Andres, C. Gonzalez,
M. Head-Gordon, E.S. Replogle, J.A. Pople, GAUSSIAN 98,
Revision A.7, Gaussian Inc., Pittsburgh, PA, 1998.
Acknowledgement
The authors are grateful for the OTKA support
(T042479, T035047).
[8] R.D. Baechler, K. Mislow, J. Am. Chem. Soc. 92 (1970) 3090.
[9] R. Engel, in: R. Engel (Ed.), Handbook of Organophosphorus
Chemistry, Marcel Dekker Inc., New York, 1992 (Chapter 5).
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