Synthesis and characterisation of platinum(II) complexes containing heterobidentate S,N-chelating ligands: X-ray crystal structure of cis-[Pt{SPPh2N=C(Me)NH-S,N}(PMe2Ph)2]Cl

Article abstract of DOI:10.1016/S0277-5387(00)00320-X

Deprotonation of the terminal amino group in the N-thiophosphoryl compounds Me₂P(S)N=C(NH₂)₂ (HL¹), Ph₂P(S)N=C(Me)NH₂ (HL²) or Ph₂P(S)N=C(NH₂)₂ (HL³) using potassium tert butoxide in thf, followed by treatment with cis-[PtCl₂(PR₃)₂] (PR₃ = PMe₂Ph or 1/2 dppe) generates monocationic complexes cis-[Pt(L(n)-S,N)(PR₃)₂]Cl (1-6), which have been characterized by ³¹P{¹H} NMR, IR and FAB⁺ mass spectroscopies, and for cis-[Pt(L²-S,N)(PMe₂Ph)₂]Cl (2) by single crystal X-ray diffraction. The molecular structure of 2 reveals bidentate coordination of the platinum(II) centre by a bidentate S,N-chelating [Ph₂P(S)N=C(Me)NH]^- anion, giving a six-membered platinacycle, which adopts a chaise-longue conformation, with a strong hydrogen-bonding interaction between the chloride counterion and the nitrogen-bound proton. (C) 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0277-5387(00)00320-X

www.elsevier.nl/locate/poly
Polyhedron 19 (2000) 809–812
Synthesis and characterisation of platinum(II) complexes containing
heterobidentate S,N-chelating ligands: X-ray crystal structure of
cis-[Pt{SPPh2N_C(Me)NH-S,N}(PMe2Ph)2]Cl
*
Pravat Bhattacharyya, Alexandra M.Z. Slawin, J. Derek Woollins
Department of Chemistry, University of St Andrews, St Andrews, Fife, Scotland KY16 9ST, UK
Received 30 November 1999; accepted 21 January 2000
Abstract
Deprotonation of the terminal amino group in the N-thiophosphoryl compounds Me2P(S)N_C(NH2)2 (HL1), Ph2P(S)N_C(Me)NH2
(HL2) or Ph2P(S)N_C(NH2)2 (HL3) using potassium tert butoxide in thf, followed by treatment with cis-[PtCl2(PR3)2] (PR3sPMe2Ph
or $dppe) generates monocationic complexes cis-[Pt(Ln-S,N)(PR3)2]Cl (1–6), which have been characterised by 31P{1H} NMR, IR and
FABq mass spectroscopies, and for cis-[Pt(L2-S,N)(PMe2Ph)2]Cl (2) by single crystal X-ray diffraction. The molecular structure of 2
reveals bidentate coordination of the platinum(II) centre by a bidentate S,N-chelating [Ph2P(S)N_C(Me)NH]y anion, giving a six-
membered platinacycle, which adopts a chaise-longue conformation, with a strong hydrogen-bonding interaction between the chloride
counterion and the nitrogen-bound proton.
q2000 Elsevier Science Ltd All rights reserved.
Keywords: Thiophosphoryl guanidines; Platinum complexes; Crystal structures
1. Introduction
As a class of potentially chelating bidentate ligands, the
phosphorus(V) derivatised guanidines and amidines
R2P(E)N_C(X)NH2 (Rsalkyl or aryl; Esoxygen or sul-
fur; XsNH2 or alkyl) have been known for some time, but
their coordination chemistry does not appear to have been
well explored [11–16]. The presence in these molecules of
an ionisable nitrogen-boundprotoncoupledwiththepotential
for delocalisation of the resulting uninegative charge through
the p-system of the anion suggests a high degree of similarity
with both imidodiphosphinate and b-diketonate ligands. The
combination of chalcogen and nitrogen donor atoms offered
by these molecules is, however, rarely encountered in their
P–N–P or carbon-backboned counterparts.
Ourselves [1,2] and others [3–8] have studied the co-
ordination chemistry of imidodiphosphinate anions
[R2P(E)NP(E9)R92]y (R, R9salkyl, aryl or alkoxy; E,
E9soxygen, sulfur or selenium), generated from the weak
acids HN(R2PE)(R92PE9), regarded as ‘inorganic’ ana-
logues of the more ubiquitous b-diketonates such as acetyl-
acetonate. Bidentate E,E9 chelation of imidodiphosphinate
ligands at d- and p-block metal centres produces hexa-atomic
metallacycles; crystallographic analyses of several such
metal complexes indicate substantial flexibility within the E–
P–N–P–E9 backbone which enables the adoption of a variety
of chelate ring conformations in the solid state, although
planarity is rarely observed. The facile construction of
imidodiphosphinate ligands, generally by the base-catalysed
clipping together of R2P(E)NH2 and R92P(E9)Cl precursors
or via oxidation of the parent diphosphine R2PNHPR92 using
elemental chalcogen or hydrogen peroxide, has led to appli-
cations for such ligands as metal extraction agents, NMR
shift reagents and recently in a catalytic function in the
aerobic co-oxidation of alkenes and aldehydes [7–10].
Here, we describe our studies on the coordination chem-
istry of the monoanions derived from Me2P(S)N_C(NH2)2
(HL1) and Ph2P(S)N_C(X)NH2 (XsMe (HL2) or NH2
(HL3)) at platinum(II) centres, including one representative
crystal structure.
2. Results and discussion
Deprotonation of the amine nitrogen atom in
HN(R2PE)(R92PE) gives p-delocalised imidodiphosphin-
ate anions [R2P(E)NP(E9)R92]y which have great propen-
* Corresponding author. Tel.: q44-1334-463861; fax: q44-1334-
463384; e-mail: jdw3@st-and.ac.uk
0277-5387/00/$ - see front matter q2000 Elsevier Science Ltd All rights reserved.
PII S0277-5387(00)00320-X
Thursday Apr 13 09:54 AM
StyleTag -- Journal: POLY (Polyhedron) Article: 3396

810
P. Bhattacharyya et al. / Polyhedron 19 (2000) 809–812
accord with the weaker trans influence of N versus S. A
similar variation in 1J(Pt–P) values as a function of the trans
donor atom has been observed in cis-[Pt(S2N2)(PR3)2] and
cis-[Pt(S2N2H)(PR3)2]q, in which the sulfur–nitrogen ani-
2
ons are S,N-bidentate at platinum(II) [17,18]. The J(Pt–
P) couplings for the phosphorus(V) atom P(1) ofthe chelate
in 1–6 (85–102 Hz) are somewhat larger than the values we
have reported in the dithio-imidodiphosphinate complexes
cis-[Pt{(SPPh2)2N}(PR3)2]Cl (60–64 Hz for monodentate
phosphines, 79 Hz for dppe) which contain S,S9-chelating
Fig. 1. Structures of the ligands HL1–3
.
2
[(SPPh2)2N]y anions [19]. The cis J(PIII–Pt–PIII) cou-
plings for the PhMe2P complexes 1–3 (20–25 Hz) are larger
in magnitude compared with the dppe complexes (5–10 Hz),
in which there is an additional 3J(P–P) component through
the ligand backbone of opposite sign. Each of the cis or trans
3J(PIII–Pt–S–PV) couplings for 1–6 have comparable mag-
nitudes, being between 4 and 11 Hz. Upon deprotonation and
chelation the phosphorus atom P(1) of the chelate experi-
ences modest shielding, moving ca. 15 ppm to low frequency
from the free ligand value (dP 48.3 and 42.2 for HL1 and HL2
(d-chloroform), 42.5 for HL3 (d4-methanol)). Formation of
the S,N chelate is exclusive in these instances; there is no
evidence from 31P{1H} NMR spectroscopy for the formation
of isomeric complexes of (L1)y or (L3)y in which the
[R2P(S)NC(NH2)NH]y anion functions as an N,N9 biden-
tate chelate to platinum(II) by the amino groups at the imine
carbon.
In their IR spectra 1–6 exhibit several strong bands in the
region 1400–1700 cmy1; the nNH vibrations (broad bands of
medium intensity between 3400–3100 cmy1) and the nPS
bands (ca. 562 cmy1 for 1 and 4, ca. 588 cmy1 for 2, 3, 5
and 6) are shifted only marginally from the values in the
uncomplexed molecules HL1–3 (HL1 3377, 3142 (nNH) and
558 (nPS); HL2 3361, 3285, 3230 (nNH) and 575 (nPS); HL3
3437, 3350, 3299, 3201 (nNH) and 586 (nPS)).
sity towards bidentate E,E9 chelation at metal centres [1–6].
We believed that the N-thiophosphoryl amidine (HL2) and
guanidines (HL1,3) (Fig. 1) could in a similar way function
as monobasic acids and undergo coordination to metal ions,
to give chelates using a heterobidentate S,N donor array. To
test our hypothesis we attempted to prepare platinum(II)
complexes using the anions derived from HL1–3
.
Treatment of thf solutions of HL1–3 with potassium tert-
butoxide followed by a stoichiometric quantity of cis-[PtCl2-
(PR3)2] (PR3sPMe2Ph or $dppe) proceeds smoothly at
reflux with displacement of the chloro ligands from the metal
coordination sphere and chelation of the (Ln)y anion to give
cationic complexes cis-[Pt(Ln-S,N)(PR3)2]Cl (1–6) isola-
ble in moderate yields (39–65%) from dichloromethane–
diethyl ether, Eq. (1).
cis-[PtCl2 (PR3)2 ]qKLn
(1)
™cis-[Pt(Ln-S,N)(PR3)2 ]ClqKCl
The platinum(II) complexes 1–6 are colourless (1, 2) or
pale yellow (3–6) solids, tolerant to air and moisture, and
are highly soluble in chlorinated solvents and thf. In their
FABq mass spectra all of the complexes give intense peaks
which correspond to an ion of composition [PtL(PR3)2]q.
The 31P{1H} NMR spectra for 1–6 (Table 1) contain exten-
sive information on 195Pt–31P and 31P–31P coupling constants
and are in accord with their structures; the complexes exhibit
first-order AMX spin systems with platinum-195 satellites.
The 1J(Pt–P) coupling constants for the phosphine co-
ligands P(2), P(3) lie in the ranges 2917–3004 Hz (P(3)
trans sulfur) and 3234–3371 Hz (P(2) trans nitrogen) in
The molecular structure of cis-[Pt{SPPh2N_C(Me)NH-
S,N}(PMe2Ph)2]Cl (2) has been determined by single crys-
tal X-ray diffraction, Fig. 2. The coordination sphere at the
metal atom Pt(1) comprises two mutually cis dimethylphen-
ylphosphine ligands, bound through P(2) and P(3), and
(L2)y ligand bound via the terminal sulfur and nitrogen
atoms S(1) and N(14) to form a six-membered Pt(1)–
Table 1
31P{1H} NMR spectral data for [Pt(Ln-S,N)(PR3)2]Cl (1–6) a
dP
1J(Pt–P)/Hz
J(P–P)/Hz
P(1)
P(2)
P(3)
Pt–P(1)
Pt–P(2)
Pt–P(3)
P(1)–P(2)
P(1)–P(3)
P(2)–P(3)
[Pt(L1-S,N)(PMe2Ph)2]Cl (1)
[Pt(L2-S,N)(PMe2Ph)2]Cl (2)
[Pt(L3-S,N)(PMe2Ph)2]Cl (3)
[Pt(L1-S,N)(dppe)]Cl (4)
[Pt(L2-S,N)(dppe)]Cl (5)
[Pt(L3-S,N)(dppe)]Cl (6)
32.2
25.2
28.2
48.9
52.1
50.4
y7.7
y7.7
y7.6
38.5
37.8
38.8
y22.6
y23.5
y22.5
30.3
24.0
26.7
92
88
102
3234
3247
3262
3273
3371
3332
2997
3003
3004
2930
2913
2938
85
87
90
11
10
10
6
10
8
4
22
20
25
10
5
6
b
6
5
8
8
a CDCl3 solutions. P(1)sPS, P(2) trans nitrogen and P(3) trans sulfur.
b Not resolved.
Thursday Apr 13 09:54 AM
StyleTag -- Journal: POLY (Polyhedron) Article: 3396

P. Bhattacharyya et al. / Polyhedron 19 (2000) 809–812
811
enced to external 85% phosphoric acid (d 0)) and IR spectra
(pressed KBr discs) were recorded on JEOL FX90Q NMR
and Perkin-Elmer System 2000 NIR FT-Raman spectrome-
ters respectively. Elemental analyses (PE 2400 CHN ele-
mental analyser) were performed by the University of
Loughborough Analytical Service, FAB mass spectra (pos-
itive ionisation mode, 3-nitrobenzyl alcohol matrix) were
carried out by the EPSRC National Mass Spectrometry Ser-
vice Centre, Swansea.
The platinum(II) complexes cis-[Pt(Ln-S,N)(PR3)2]Cl
(1–6) were prepared by the same general procedure.
To a solution of the ligand HLn (0.2 mmol) and potassium
tert-butoxide (0.25 mmol) in thf (5 cm3) was added cis-
[PtCl2(PR3)2] (0.2 mmol) as a solid in one portion. The
resulting yellow mixture was heated at reflux for 2 h and then
cooled to room temperature. The solvent was removed in
vacuo, the crude product was extracted in dichloromethane
(5 cm3) and the solution filtered through a plugofglasswool-
Celite. The dichloromethane filtrate was concentrated under
reduced pressure to ca. 2 cm3; vapour diffusion of diethyl
ether into the solution over several days gave the complexes
cis-[Pt(Ln-S,N)(PR3)2]Cl (1–6) as either colourless (1, 2)
or pale yellow (3–6) solids. Conversion is quantitative by
31P{1H} NMR spectroscopy, isolated yields of the complexes
were typically 39–65% based on Pt.
Fig. 2. X-ray crystal structure of cis-[Pt{SPPh2N_C(Me)NH-S,N}-
(PMe2Ph)2]Cl (2) (hydrogen atoms bound to carbon omitted for clarity).
Selected bond lengths (A) and angles (8): Pt(1)–S(1) 2.403(2), Pt(1)–
P(2) 2.284(2), Pt(1)–P(3)2.289(2), Pt(1)–N(14)2.060(8), P(1)–S(1)
2.036(4), P(1)–N(1) 1.604(8), N(1)–C(13) 1.335(12), C(13)–N(14)
1.314(12); P(3)–Pt–P(2) 96.17(9), P(2)–Pt(1)–S(1) 85.57(9), S(1)–
Pt(1)–N(14) 90.8(3), N(14)–Pt(1)–P(3) 89.1(3), Pt(1)–S(1)–P(1)
91.75(12), P(1)–N(1)–C(13) 121.5(7), S(1)–P(1)–N(1) 115.3(3),
N(1)–C(13)–N(14) 127.5(9), C(13)–N(14)–Pt(1) 134.5(7).
˚
S(1)–P(1)–N(1)–C(13)–N(14) platinacycle. There is a
hydrogen-bonding interaction between the chloride counter-
ion Cl(1) and the remaining amine proton H(14n) at N(14)
˚
(H(14n)∆Cl(1) 2.34 A, N(14)–H(14n)∆Cl(1) 1648).
Within the chelate ring, the atoms of the Pt(1)–N(14)–
[Pt(L1-S,N)(PMe2Ph)2]Cl (1). Anal. Found: C, 33.40;
H, 4.70; N, 6.10. Calc. for C19H31N3P3ClPtS: C, 34.73; H,
4.76; N, 6.40%. FABq MS: m/z 621 (MqyCl). IR (cmy1):
3302, 3156 (nNH), 562 (nPS).
C(13)–N(1)–P(1) chain are coplanar, S(1) beingdisplaced
˚
by 1.27 A from this plane. There are deviations from square
planarity at the metal centre; the angles between cis atoms
are in the range 85.6–96.28, moreover the P(2)–Pt(1)–P(3)
and N(14)–Pt(1)–S(1) planes are twisted by 138 relative to
each other. The Pt–P and Pt–N distances in 2 (Pt(1)–P(2)
2.284(2), Pt(1)–P(3) 2.289(2) and Pt(1)–N(14)
[Pt(L2-S,N)(PMe2Ph)2]Cl (2). Anal. Found: C, 45.51;
H, 4.58; N, 3.49. Calc. for C30H36N2P3ClPtS: C, 46.18; H,
4.65; N, 3.59%. FABq MS: m/z 744 (MqyCl). IR (cmy1):
3123 (nNH), 588 (nPS).
˚
2.060(8) A) correspond closely with the parameters for
[Pt(L3-S,N)(PMe2Ph)2]Cl (3). Anal. Found: C, 45.78;
H, 4.78; N, 5.75. Calc. for C29H35N3P3ClPtS: C, 44.59; H,
4.52; N, 5.38%. FABq MS: m/z 746 (MqyCl). IR (cmy1):
3439, 3264, 3203 (nNH), 588 (nPS).
˚
[Pt(S2N2)(PMe2Ph)2] (Pt–P 2.271(4) and2.265(3)A, Pt–
˚
N 2.081(8) A) although the Pt–S distance is somewhat
longer in the (L2)y complex (Pt–S 2.403(2) A in 2, c.f.
˚
2.270(5) A for the (S2N2)2y complex) [17].
˚
[Pt(L1-S,N)(dppe)]Cl (4). Anal. Found: C, 39.41; H,
4.69; N, 6.17. Calc. for C29H34N3P3ClPtS: C, 44.64; H, 4.39;
N, 5.39%. FABq MS: m/z 743 (MqyCl). IR (cmy1);3329,
3163 (nNH), 562 (nPS).
In summary S,N bidentate chelates can be readily formed
at platinum(II) by N-thiophosphoryl derivatives of guani-
dines and amidines upon prior deprotonation usingpotassium
tert-butoxide. Efforts are underway to extend the range of
metal complexes which can be obtained using the anions
[Pt(L2-S,N)(dppe)]Cl (5). Anal. Found: C, 50.96; H,
4.77; N, 3.06. Calc. for C40H39N2P3ClPtS: C, 53.19; H, 4.35;
N, 3.10%. FABq MS: m/z 866 (MqyCl). IR (cmy1): 3340
(nNH), 585 (nPS).
derived from HL1–3
.
[Pt(L3-S,N)(dppe)]Cl (6). Anal. Found: C, 50.57; H,
4.42; N, 4.98. Calc. for C39H38N3P3ClPtS: C, 51.80; H, 4.24;
N, 4.65%. FABq MS: m/z 867 (MqyCl). IR (cmy1);3346,
3148 (nNH), 588 (nPS).
3. Experimental
Complexation reactions were performed under an atmos-
phere of oxygen-free nitrogen; subsequent work-up and
recrystallisations were in air. Dichloromethane and thf were
dried and distilled from calcium hydride and sodium respec-
tively, cis-[PtCl2(PR3)2] (PR3sPMe2Ph or $dppe) was
prepared by the addition of stoichiometric quantities of PR3
to cis-[PtCl2(cycloocta-1,5-diene)] in dichloromethane,
potassium tert-butoxide (Aldrich) and other solvents
employed were unpurified. 31P{1H} NMR (36.2 MHz, refer-
3.1. X-ray crystallography
X-ray diffraction studies on crystals of cis-[Pt(L2-
S,N)(PMe2Ph)2]Cl (2) grown from dichloromethane–
hexane by solvent diffusion, were performed using a Bruker
SMART diffractometer with graphite-monochromated Mo
Thursday Apr 13 09:54 AM
StyleTag -- Journal: POLY (Polyhedron) Article: 3396

812
P. Bhattacharyya et al. / Polyhedron 19 (2000) 809–812
˚
Ka radiation (ls0.71073 A). The structure was solved by
direct methods, the non-hydrogen atoms were refined with
anisotropic displacement parameters; hydrogen atoms bound
References
[1]
[2]
[3]
A.M.Z. Slawin, M.B. Smith, J.D. Woollins, J. Chem. Soc., Dalton
Trans. (1998) 1537.
D.J. Birdsall, A.M.Z. Slawin, J.D. Woollins, Inorg. Chem. 38 (1999)
4152.
J. Novosad, M. Necas, J. Marek, P. Veltsistas, C. Papadimitriou, I.
Haiduc, M. Watanabe, J.D. Woollins, Inorg. Chim. Acta 290 (1999)
256.
˚
to carbon were idealised and fixed (C–H 0.95 A); the NH
proton H(14n) associated with N(14) was located by a DF
map and allowed to refine anisotropically. Structural refine-
ments were by the full-matrix least-squares method on F2
using the program SHELXTL-PC [20]. C30H36N2P3ClPtS,
colourless needles, 0.08=0.12=0.15 mm, Ms780.12,
[4]
[5]
R. Rossi, A. Marchi, L. Marvelli, L. Magon, M. Peruzzini, U.
Casellato, R. Graziani, J. Chem. Soc., Dalton Trans. (1993) 723.
R. Cea-Olivares, G. Espinosa-Perez, I. Haiduc, R. Rosler, C. Silvestru,
monoclinic, as9.9790(2), bs29.4825(4), cs10.9449(2)
3
˚
˚
A, bs90.835(1)8, Us3219.7(1) A , Ts293 K, space
group P21/n, Zs4, m(Mo Ka)s4.677 mmy1. Of 13959
measured data 4587 were unique reflections (Rints0.0421)
to give R1s0.0414 (I)2s(I), 3680 observed) and
wR2s0.0881.
¨
Inorg. Chem. 34 (1995) 3352.
[6]
J. Ellermann, P. Gabold, F.A. Knoch, M. Moll, A. Schmidt, M. Schutz,
Z. Naturforsch., Teil B 51 (1996) 201.
[7]
L. Barkoui, M. Charrouf, M.-N. Rager, B. Denise, N. Platzer, H.
Rudler, Bull. Chim. Soc. Fr. 134 (1997) 167.
H. Rudler, B. Denise, J.R. Gregario, J. Vaissermann, J. Chem. Soc.,
Chem. Commun. (1997) 2299.
[8]
Supplementary data
[9]
E. Herrmann, O. Navratil, P. Sladek, Phosphorus Sulfur Silicon Relat.
Elem. 109–110 (1996) 201.
[10]
[11]
[12]
G. Grossmann, E. Herrmann, O. Navratil, Collect. Czech. Chem.
Commun. 55 (1990) 364.
Full lists of structure refinement data, atomic coordinates,
bond lengths and angles, anisotropic displacement parame-
ters and hydrogen atom parameters have been deposited as
supplementary material, no. 137216, at the Cambridge Crys-
tallographic Data Centre, 12 Union Road, Cambridge CB2
1EZ, UK (fax: q44-1223-336033; e-mail: deposit@
ccdc.cam.ac.uk).
¨
N. Inguimbert, L. Jager, M. Taillefer, H.J. Cristau, J. Organomet.
Chem. 529 (1997) 257.
¨
¨
J. Munchenberg, O. Boge, A.K. Fischer, P.G. Jones, R. Schmutzler,
Phosphorus Sulfur Silicon Relat. Elem. 86 (1994) 103.
A. Schmidpeter, J. Ebeling, Angew. Chem. 70 (1967) 534.
M.A.R. Khayat, F.S. Al-Isa, J. Prakt. Chem. 331 (1988) 149.
R. Appel, Chem. Ber 105 (1972) 2476.
[13]
[14]
[15]
[16]
[17]
[18]
G. Capozzi, P. Haake, J. Am. Chem. Soc. 94 (1972) 3249.
P.F. Kelly, J.D. Woollins, J. Chem. Soc., Dalton Trans. (1988) 1053.
P.A. Bates, M.B. Hursthouse, P.F. Kelly, J.D. Woollins, J. Chem.
Soc., Dalton Trans. (1986) 2367.
Acknowledgements
We are grateful to the EPSRC for funding (P.B.), Johnson
Matthey plc for the loan of platinum salts and to Professor
Alfred Schmidpeter, University of Munich, for the generous
[19] J.R. Phillips, A.M.Z. Slawin, D.J. Williams, J.D. Woollins, Poly-
hedron 15 (1996) 3175.
[20] G.M. Sheldrick, SHELXTL, Version 5.03, program for crystal struc-
gift of samples of HL1–3
.
ture solution, University of Gottingen, Germany, 1994.
¨
Thursday Apr 13 09:54 AM
StyleTag -- Journal: POLY (Polyhedron) Article: 3396