Remarkable S,N,S' tridentate chelation to palladium(n) by the monoanion derived from [Ph2P(S)NH]2CO

Article abstract of DOI:10.1039/b002413i

The reaction between [PdCl2(PhCN)2] and [Ph2P(S)NH]2C=O (H2L) proceeds with monodeprotonation of an amine group in the disulfide ligand to give [Pd(HL)Cl] 1, in which the (HL)~ anion supplies an S,N,S' donor set to palladium(n), leading to disparate S,N c

Full text of DOI:10.1039/b002413i

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Remarkable S,N,SЈ tridentate chelation to palladium(II) by the
monoanion derived from [Ph2P(S)NH]2CO
Pravat Bhattacharyya, Alexandra M. Z. Slawin and J. Derek Woollins*
Department of Chemistry, University of St Andrews, Fife, UK KY16 9ST.
E-mail: jdw3@st-andrews.ac.uk
Received 27th March 2000, Accepted 11th April 2000
The reaction between [PdCl2(PhCN)2] and [Ph2P(S)-
NH] C᎐O (H L) proceeds with monodeprotonation of an
᎐
2
2
amine group in the disulfide ligand to give [Pd(HL)Cl] 1, in
which the (HL)؊ anion supplies an S,N,SЈ donor set to
palladium(II), leading to disparate S,N chelate ring sizes at
the metal.
We have recently investigated1 the imidodiphosphinates
[R2P(E)NP(EЈ)RЈ2]Ϫ (R, RЈ = alkyl, aryl or alkoxy; E, EЈ =
oxygen, sulfur or selenium) as structural analogues of the more
widely known β-diketonates, such as [CH3C(O)CHC(O)CH3]Ϫ.
Despite the ubiquity of the β-diketonates throughout inorganic
chemistry, the anions derived from β-triketones [RC(O)-
CH2C(O)CH2C(O)R] have been largely neglected; although
O,OЈ bidentate and O,OЈ,OЉ tridentate chelation modes
are observed in organotin() complexes of β-triketonate
anions,2 platinum() centres favour C,CЈ metallation to form
platinacyclobutan-3-one rings.3 We considered that the pres-
ence of weakly acidic amine protons and the potential to offer
three chalcogen atoms for co-ordination to metal centres made
Fig. 1 Molecular structure of 1 (C–H atoms omitted for clarity).
Selected bond lengths (Å) and angles (Њ); Pd(1)–Cl(1) 2.296(2), Pd(1)–
S(1) 2.325(2), Pd(1)–S(2) 2.340(2), Pd(1)–N(2) 2.042(5), P(2)–S(2)
2.016(3), P(2)–N(2) 1.651(5), N(2)–C(25) 1.353(8), C(25)–O(25)
1.235(7), C(25)–N(1) 1.389(8), N(1)–P(1) 1.661(6), P(1)–S(1) 1.991(3);
S(2)–Pd(1)–S(1) 177.66(7), S(2)–Pd(1)–N(2) 78.3(2), S(1)–Pd(1)–N(2)
99.4(2), S(2)–Pd(1)–Cl(1) 94.20(7), S(1)–Pd(1)–Cl(1) 88.02(7), N(2)–
Pd(1)–Cl(1) 172.0(2), Pd(1)–S(2)–P(2) 81.94(8), S(2)–P(2)–N(2) 98.0(2),
P(2)–N(2)–Pd(1) 101.3(3), N(1)–P(1)–S(1) 113.6(2), Pd(1)–N(2)–C(25)
137.2(5), N(2)–C(25)–N(1) 117.7(6), C(25)–N(1)–P(1) 126.8(5), P(1)–
S(1)–Pd(1) 98.27(9), C(25)–N(2)–P(2) 121.0(5).
[Ph P(S)NH] C᎐O (H L)4 an ideal candidate for study as a
᎐
2
2
2
structural analogue of β-triketones; here we describe the
unusual tridenticity displayed by the monoanion derived from
H2L at palladium().
Treatment of [PdCl2(PhCN)2] with one molar equivalent of
H2L at room temperature in dichloromethane proceeds with the
elimination of HCl and displacement of two molecules of
benzonitrile from the palladium() co-ordination sphere to give
[Pd(HL-S,N,SЈ)Cl] 1 in good yield (86%).† Compound 1 is
moderately soluble in chlorinated solvents and thf, and stable to
oxygen and moisture. Crystallographic analysis‡ of 1 reveals
monodeprotonation of H2L and subsequent co-ordination by
the (HL)Ϫ anion to Pd(1) in two distinct chelation modes, Fig.
1. The C(25)–O(25) carbonyl vector is directed away from the
metal centre, tridentate coordination of the (HL)Ϫ anion occurs
through the S(1), N(2) and S(2) atoms producing fused
six-membered Pd(1)–S(1)–P(1)–N(1)–C(25)–N(2) and four-
membered Pd(1)–S(2)–P(2)–N(2) palladacycles, with comple-
tion of the donor set at Pd(1) by a chloro ligand Cl(1) bound
trans to N(2). The four membered Pd(1)–S(2)–P(2)–N(2) ring is
essentially planar (mean deviation from planarity 0.04 Å) while
for the six membered chelate ring P(1) lies 0.8 Å from the plane
defined by the remaining five atoms of the hexa-atomic ring
(mean deviation from planarity 0.03 Å). The phosphorus–
sulfur bond lengths are inequivalent in 1, a feature also seen in
the free ligand H2L,4 with P(2)–S(2) in the complex, associated
with the Pd–S–P–N chelate being the longer within the pair.
Co-ordination increases the P–S lengths by ca. 0.06 Å com-
pared with H2L [2.016(3) and 1.991(3) Å in 1, 1.931(1) and
1.942(1) Å in H2L]; conversely the phosphorus–nitrogen dis-
tances, identical within statistical significance in 1 [N(1)–P(1)
1.661(6), N(2)–P(2) 1.651(5) Å], are slightly shorter than the
corresponding lengths in H2L [1.686(2) and 1.702(2) Å]. In
accord with the disparate sizes of the chelate rings the cis S–
Pd–N angles are markedly different [N(2)–Pd(1)–S(2) 78.3(2)Њ,
N(2)–Pd(1)–S(1) 99.4(2)Њ], the trans N(2)–Pd(1)–Cl(1) vector
being restricted to 172.0(2)Њ. Tetra-atomic M–E–P–N metalla-
cycles (E = chalcogen or NR) remain rare in the literature, the
majority of structurally characterised complexes containing
this motif being of first row d-block metals.5 At palladium()
the unsymmetrical ligand (PhO)2P(S)NHP(O)(OPh)2 forms
four-membered S,N chelate rings6 in trans-[Pd{(PhO)2-
P(S)NP(O)(OPh)2-S,N}2] in preference to S,O chelation, the
metallacycle parameters [Pd–N 2.055(3) Å, Pd–S 2.342(1) Å,
N–Pd–S 78.53(8)Њ] show close correspondence to those of 1;
notably S-monodentate co-ordination is observed in trans-
[PdCl2{(EtO)2P(S)NHC6H4NO2-2}2].7 Strong intermolecular
dimer pair hydrogen-bonding interactions seen between
adjacent molecules in the crystal structure of H2L persist in the
structure of 1 (Fig. 2), with H(1n) ؒ ؒ ؒ O(25Ј) 1.79 Å and N(1)–
H(1n) ؒ ؒ ؒ O(25Ј) 177Њ, cf. 1.86 Å and 175.3Њ respectively in the
dimer pairs of H2L.
The 31P{1H} NMR spectrum of 1 comprises two singlets; one
signal resembles the free ligand value (δP 56.1 cf. 52.2 for H2L)
which corresponds to the P(1) atom in the six-membered ring
whereas the other phosphorus environment P(2) (δP 91.6)
experiences substantial deshielding upon N-metallation and
concomitant formation of the four-membered palladacycle.
The characteristic 31P{1H} NMR shifts upon ligation provide a
powerful diagnostic tool, hence we have been able to recognise
similar E,N,EЈ tridentate co-ordination by the anions of
[Ph2P(E)NH]2CO (E = sulfur or selenium) at platinum() and
rhodium() centres.8
DOI: 10.1039/b002413i
J. Chem. Soc., Dalton Trans., 2000, 1545–1546
This journal is © The Royal Society of Chemistry 2000
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suitable for X-ray analysis were grown by vapour diffusion of diethyl
ether into a dichloromethane solution of the complex.
‡ Single crystal X-ray diffraction studies on crystals of [Pd(HL-
S,N,SЈ)Cl] 1 were performed using a Bruker SMART diffractometer
with graphite-monochromated Mo-Kα radiation (λ = 0.71073 Å). The
structures were solved by direct methods, the non-hydrogen atoms were
refined with anisotropic displacement parameters; phenyl hydrogen
atoms were idealised and fixed (C–H 0.95 Å), U(H) = 1.2Ueq(C); the
NH proton H(1n) associated with N(1) was located using a ∆F map and
allowed to refine isotropically subject to a distance constraint. An
attempt to model the slight disorder of the C(19)–C(24) phenyl ring was
made, however this proved unsuccessful. This phenyl ring has been
refined as an idealised rigid body. Structural refinements were by the
full-matrix least-squares method on F2 using the program SHELXTL.9
C25H21ClN2P2OPdS2, M = 633.35, orthorhombic, a = 12.2320(2) Å,
b = 18.5402(2) Å, c = 24.4688(2) Å, U = 5549.13(14) Å3, T = 293 K,
space group Pbca, Z = 8, F(000) = 2544, µ(Mo-Kα) = 1.052 mmϪ1. Of
25983 measured data, 3982 were unique (Rint 0.0834), to give
R1[I > 2σ(I)] = 0.0504 and wR2 = 0.1015. CCDC reference number
186/1932. See http://www.rsc.org/suppdata/dt/b0/b002413i/ for crystal-
lographic files in .cif format.
1 See, for example: A. M. Z. Slawin, M. B. Smith and J. D. Woollins,
J. Chem. Soc., Dalton Trans., 1998, 1537; D. J. Birdsall, A. M. Z.
Slawin and J. D. Woollins, Inorg. Chem., 1999, 38, 4152.
2 A. Imran, R. D. W. Kemmitt, A. W. Markwick, P. McKenna, D. R.
Russell and L. J. S. Sherry, J. Chem. Soc., Dalton Trans., 1985,
549; R. D. W. Kemmitt, S. Mason, M. R. Moore, J. Fawcett and
D. R. Russell, J. Chem. Soc., Chem. Commun., 1990, 1535.
3 B. P. Bachlas, A. Kumar, J. C. Maire and H. Sharma, Bull. Chim. Soc.
Fr., 1983, 46; B. K. Agarwal, B. P. Bachlas and A. Kumar, Synth.
React. Inorg. Met.-Org. Chem., 1985, 15, 907.
Fig. 2 Dimer pair formation in the solid state structure of 1.
In conclusion, N-metallation of H2L in the reaction with
[PdCl2(PhCN)2] produces a complex [Pd(HL)Cl] containing an
S,N,SЈ tridentate (HL)Ϫ anion; the observation of tridenticity
in preference to S,SЈ or S,O bidentate co-ordination modes for
example, is perhaps rationalised by substantial flexibility in the
H2L backbone in alliance with an ionisable NH proton.
We are grateful to the EPSRC for financial support (P. B.)
and to Johnson Matthey plc for the loan of precious metals.
4 P. Bhattacharyya, A. M. Z. Slawin, M. B. Smith and J. D. Woollins,
J. Chem. Soc., Dalton Trans., 1996, 3647.
5 See, for example: A. Brück, U. Englert, W. Kuchen and W. Peters,
Chem. Ber., 1996, 129, 551; M. Bochmann, G. C. Bwembya, S. J.
Coles and M. B. Hursthouse, J. Chem. Soc., Dalton Trans., 1995,
2813; W. Kuchen, W. Peters, M. Sünkeler, R. Wiskemann and
H. Wünderlich, Z. Anorg. Allg. Chem., 1998, 624, 1956.
6 P. Z. Zak, M. Fofana, J. Kamenicek and T. Glowiak, Acta Crystal-
logr., Sect. C, 1989, 45, 1686.
7 J. R. Phillips, A. M. Z. Slawin, D. J. Williams and J. D. Woollins,
Polyhedron, 1996, 15, 3725.
8 P. Bhattacharyya and J. D. Woollins, unpublished work.
9 G. M. Sheldrick, SHELXTL, Version 5.03, program for crystal
structure solution, University of Göttingen, 1994.
Notes and references
† [Pd(HL-S,N,SЈ)Cl] 1. To a solution of [PdCl2(PhCN)2] (43 mg, 0.11
mmol) in dichloromethane (2 cm3) was added H2L (55 mg, 0.11 mmol)
in dichloromethane (2 cm3) and the reaction mixture stirred at room
temperature for 30 min, during which time an orange precipitate
appears. Precipitation of 1 is completed by the addition of hexane (10
cm3). Yield 60 mg, 86%. Found (Calc. for PdC25H21N2P2OS2Cl); C
46.7(47.4), H 3.6(4.4), N 4.6(3.3)%. FABϩ MS; m/z 597, [Mϩ Ϫ Cl]. IR
(KBr, cmϪ1); 3052m (νNH), 1618s (νCO), 1107s, 802s (νPN) and 687s (νPS).
31P{1H} NMR (CDCl3, 36.2 MHz); 56.1 (s), 91.6 (s). Needles of 1
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J. Chem. Soc., Dalton Trans., 2000, 1545–1546