Gold(I) and platinum(II) complexes with a new diphosphine ligand based on the cyclotriphosphazene platform

Article abstract of DOI:10.1039/b517309b

A new diphosphine ligand system, derivative of (2-hydroxyphenyl) diphenylphosphine and assembled on the cyclotriphosphazene platform was analyzed. Structural analysis of complexes showed the ligands versatile coordination chemistry, capable of monodentate, linear bidentate and cis-bidentate chelations. The new ligand is different from related cyclophosphazene ligands derived from (4-oxyphenyl)diphenylphosphine in having ortho position of pendant phosphine to the phenoxy linker rather than para. It was found that there was no direct interactions between the gold(I) center and the tetrafluoroborate anion. The results show that short contacts between Au(I) and the oxygen atoms occurs in the (2-oxyphenyl)diphosphine hinges.

Full text of DOI:10.1039/b517309b

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Gold(I) and platinum(II) complexes with a new diphosphine ligand
based on the cyclotriphosphazene platform†
Eric W. Ainscough,* Andrew M. Brodie,* Adrian B. Chaplin, Joy M. O’Connor and Carl A. Otter
Received 21st October 2005, Accepted 13th December 2005
First published as an Advance Article on the web 23rd December 2005
DOI: 10.1039/b517309b
A new diphosphine ligand assembled on the cyclotriphosp-
hazene platform forms linear chelate and dimetallic bridged
complexes with Au(I) and a cis-chelate complex with Pt(II).
from NaH and HOC6H4PPh2) and [N3P3(biph)2Cl2]7 (biph =
2,2ꢀ-biphenolato group). The 31P NMR spectrum of L shows the
expected pattern with phosphazene signals at 27.0 (d), 9.6 (t) and
the free phosphine singlet at −15.5 ppm. The reaction between L
and AuBF4 in CH3CN/CH2Cl2 yielded the complex [AuL]BF4 (1).
X-ray quality crystals‡ of 1·CH3CN were grown from
CH3CN/Et2O and the structure of the monocation is shown in
Fig. 1. In this complex L acts as a bidentate chelating ligand
with the gold(I) centre having a slightly distorted linear geometry
[P(4)–Au–P(5) 171.99(3)◦]. The Au–P bond lengths [2.2542(7) and
Diphosphines are an important class of ligands due to the
application of their metal complexes in many catalytic processes.1
The development of specifically trans-spanning diphosphines for
catalytic roles has received much recent attention.2 In particular,
diphosphines with access to wide bite angles are of current interest
in rhodium hydroformylation catalysis.3
The use of cyclic and linear polyphosphazenes as scaffolds for
metal chelators is an area of ongoing interest, mainly due to the
potential applications of the polymers.4 The cyclic compounds
are useful small molecule model compounds for the polymeric
systems but often exhibit interesting coordination chemistries
in their own right. For example, we have recently shown that
hexakis(pyridyloxy)cyclotriphosphazene and its 4-methyl deriva-
tive are versatile multimodal ligands that exhibit a range of
coordination geometries.5
In this paper we describe a new diphosphine ligand system, de-
rived from (2-hydroxyphenyl)diphenylphosphine (HOC6H4PPh2)
and assembled on the cyclotriphosphazene platform (L,
Scheme 1). Structural analyses of complexes of L with gold(I)
and platinum(II) demonstrate that the ligand has a versatile
coordination chemistry, capable of monodentate, linear biden-
tate and cis-bidentate chelating modes. The new ligand dif-
fers from related cyclophosphazene ligands derived from (4-
oxyphenyl)diphenylphosphine in that the pendant phosphine is
ortho to the phenoxy linker rather than para. Hence these latter
ligands favour monodentate coordination.6
˚
2.2643(7) A] are significantly shorter than those in [Au(PPh3)2]BF4
8
˚
[2.321(3) and 2.322(3) A] which is presumably a consequence
of the tethered ligand geometry. No direct interactions between
the gold(I) centre and the tetrafluoroborate anion are apparent,
although there are short contacts between Au(1) and the oxygen
atoms in the (2-oxyphenyl)diphosphine hinges [Au(1) · · · O(1)
˚
and Au(1) · · · O(2) are ca. 3.12 and 3.00 A, respectively]. The
phosphazene ring is essentially planar and the bond lengths and
angles in the ring are typical, however, the value of 95.45(10)◦ for
O(1)–P(1)–O(2) is smaller than usual [the mean value of the two
spirocyclic O–P–O angles is 103.44◦].
Fig. 1 Ortep diagram of the [AuL]+ cation (ellipsoids◦ are drawn at
˚
the 50% probability level). Bond lengths (A) and angles ( ): Au(1)–P(4),
Scheme
1
Synthesis of L. (i) 2,2ꢀ-biphenol/K2CO3 in acetone,
2.2643(7); Au(1)–P(5), 2.2542(7); N(1)–P(1), 1.553(2); N(1)–P(3), 1.548(1);
N(2)–P(1), 1.547(2); N(2)–P(2), 1.552(2); N(3)–P(3), 1.544(2); N(3)–P(2),
1.548(2); P(4)–Au(1)–P(5), 171.99(3); O(1)–P(1)–O(2), 95.45(10).
(ii) HOC6H4PPh2/NaH in THF.
The phosphazene L was prepared from the reaction in THF
between two equivalents of NaOC6H4PPh2 (generated in situ
The reaction between L and two equivalents of [Au(tht)Cl]
(tht = tetrahydrothiophene) in CHCl3 produces the complex
[(AuCl)2L] (2). Crystals§ of 2·2.7CHCl3 were grown by vapour
diffusion of pentane into the CHCl3 solution and the structure of
2 is shown in Fig. 2. In this complex, L acts as a bridging ligand,
coordinating through both phosphine arms to the AuCl centres.
Chemistry-Institute of Fundamental Sciences, Massey University, Private
Bag 11 222, Palmerston North, New Zealand. E-mail: E.Ainscough@
massey.ac.nz, A.Brodie@massey.ac.nz; Fax: +64 6 350 6682; Tel: +64 6
356 9099
† Electronic supplementary information (ESI) available: Experimental
details. See DOI: 10.1039/b517309b
1264 | Dalton Trans., 2006, 1264–1266
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©

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in this structure than 1 and 2, with P(2) and N(1) lying ∼0.17 and
˚
∼0.16 A above and below the mean plane.
To explore further the potential for L to act as a cis-bidentate
diphosphine, its reaction with the [M(CO)4(pip)2] precursors
(M = W or Mo, pip = piperidine) was examined. Complexes of
stoichiometry [W(CO)4L] (4) and [Mo(CO)4L] (5) were isolated af-
ter column chromatography and characterised by microanalytical,
NMR and IR data. The cis-coordination mode is anticipated from
the characteristic pattern10 of carbonyl IR stretching frequencies
[m(CO) cm−1: 2020, 1918, 1892, and 1866 in 4; 2023, 1932, 1900
and 1868 in 5].
The linear bidentate preference of L with Au(I) is interesting
since the Au(I) complexes of ligands that could form chelate
rings of a similar size (for example, the aliphatic carbon bridged
diphosphines) exhibit the monodentate bridging mode.11 The
linear chelating mode is comparable with the trans-spanning
behaviour in complexes of more rigid diphosphines2 although
the structures presented here demonstrate that a flexible bite
angle is available to L that can vary between 100.21(10) and
171.99(3)◦. To our knowledge these complexes are the first struc-
turally characterised cyclotriphosphazene derivatives containing
diphenylphosphine substituents and are also the first structurally
characterised gold complexes of phosphazene based ligands. We
are currently investigating the coordination chemistry of L and
derivatives with other metal ions.
CCDC reference numbers 287631–287633.
For crystallographic data in CIF or other electronic format see
DOI: 10.1039/b517309b
We thank the RSNZ Marsden Fund (MAU208) for financial
support and the Otsuka Chemical Co. Ltd for a gift of cyclot-
riphosphazene.
Fig. 2 Ortep diagram of [(AuCl)2L] (ellipsoids are drawn at t◦he
˚
50% probability level). Selected bond lengths (A) and angles ( ):
Au(1)–P(4), 2.2256(19); Au(1)–P(5), 2.2244(19); Au(1)–Cl(1)2.282(2);
Au(2)–Cl(2), 2.2890(18); N(1)–P(1), 1.571(5); N(1)–P(2), 1.584(5);
N(2)–P(2) 1.577(6); N(2)–P(3), 1.582(5); N(3)–P(1), 1.572(6); N(3)–P(3),
1.573(5); P(4)–Au(1)–Cl(1), 176.21(7); P(5)–Au(2)–Cl(2), 176.73(6);
O(1)–P(1)–O(2), 103.0(2).
The P–Au–Cl angles are nearly linear [176.73(6) and 176.21(7)◦]
and the Au–P and Au–Cl bond lengths are typical.
The phosphine arms in 2 are orientated such that the Au(I)
˚
centres lie ca. 2.27 and 3.54 A above and below the mean
plane of the phosphazene ring. Consequently the Au(I) atoms
˚
are ∼7.75 A apart and the closest Au · · · Au approach between
˚
adjacent molecules is ∼5.77 A indicating that are no strong
aurophilic interactions in 2 as reported for many other digold
complexes of diphosphines.9 There is a weak interaction between
˚
Au(1) and O(1) [Au(1) · · · O(1) 3.20 A] although the Au(2) · · · O(2)
˚
distance at 3.35 A is greater.
The reaction of L with [Pt(COD)Cl2] in CH2Cl2 affords the
complex [PtLCl2] (3) and crystals¶ of 3·4CH3CN (Fig. 3) were
grown from an acetonitrile solution. In this complex the ligand
coordinates as a cis-chelate diphosphine with a bite angle of
100.21(10)◦ giving a distorted square planar geometry about the
Pt(II) centre. The phosphazene ring is significantly more distorted
Notes and references
‡ Crystal data for C62H47AuBF4N4O6P3: M = 1382.66, triclinic, space
˚
group P-1, a = 12.2010(1), b =◦14.2978(1), c = 17.6740(1) A, a = 69.287(1),
3
˚
b = 83.074(1), c = 67.942(1) , U = 2672.54(3) A , T = 83 K, Z = 2,
Dc = 1.718 g cm−3, F(000) = 1380, l(Mo-K) = 2.977 mm−1, 27712
reflections measured (2.30 < 2h < 51.72), 115701 unique (Rint = 0.0627).
Refinement of 749 parameters converged at R1 = 0.0254 [observed data:
10643 |Fo| > 4r(Fo)], wR(F2) = 0.0637 (all data).
§ Crystal data for C62.7H46.7Au2Cl10.1N3O6P5: M = 1845.06, triclinic, space
˚
group P-1, a = 13.8387(1), b = 14.0919(1), c = 18.3886(1) A, a = 93.237(1),
◦
3
˚
b = 104.527(1), c = 100.185(1) , U = 3397.49(6) A , T = 83 K, Z = 2,
Dc = 1.803 g cm−3, F(000) = 1793, l(Mo-K) = 4.880 mm−1, 30919
reflections measured (2.46 < 2h < 54.08), 12898 unique (Rint = 0.024). For
the solution of 2·2.7CHCl3, the electron density of disordered CHCl3 was
removed from the unit cell using PLATON/SQUEEZE. Approximately
2.7 molecules of CHCl3 per cell were removed (314 e− per cell and 869 A
3
˚
was left by the void). Refinement of 703 parameters converged at R1
0.0498 [observed data: 9596 |Fo| > 4r(Fo)], wR(F2) = 0.1295 (all data).
¶ Crystal data for C68H56Cl2N7O6P5Pt: M = 1488.04, monoclinic, space
=
˚
group P2◦(1)/c, a = 13.5768(2), b = 11.1807(2), c = 42.2143(2) A, b =
3
−3
˚
98.811(1) , U = 6348.60(15) A , T = 83 K, Z = 4, Dc = 1.557 g cm
,
F(000) = 2992, l(Mo-K) = 2.480 mm−1, 28324 reflections measured
(5.78 < 2h < 46.52), 9094 unique (Rint = 0.1263). Refinement of 806
parameters converged at R1 = 0.0660 [observed data: 5816 |Fo| > 4r(Fo)],
wR(F2) = 0.1384 (all data).
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