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
1545