Orthomercurated and cycloaurated derivatives of the iminophosphorane Ph3P{double bond, long}NPh

Article abstract of DOI:10.1016/j.ica.2006.02.009

Ortho-lithiation of Ph₃P{double bond, long}NPh followed by reaction with HgCl₂ gave good yields of [Hg{C₆H₄(PPh₂{double bond, long}NPh)-2}Cl], 3, which was characterised spectroscopically and by an X-

Full text of DOI:10.1016/j.ica.2006.02.009

Inorganica Chimica Acta 360 (2007) 1310–1315
www.elsevier.com/locate/ica
Orthomercurated and cycloaurated derivatives of the
iminophosphorane Ph P@NPh
3
Samuel D.J. Brown, William Henderson, Kelly J. Kilpin, Brian K. Nicholson *
Department of Chemistry, University of Waikato, Private Bag 3105, Hamilton, New Zealand
Received 18 January 2006; accepted 2 February 2006
Available online 15 March 2006
Dedicated with respect to Michael Lappert in recognition of his many contributions to chemistry, and in gratitude to him for his mentoring of BKN over
the years.
Abstract
Ortho-lithiation of Ph
3
P@NPh followed by reaction with HgCl
2 6 4 2
gave good yields of [Hg{C H (PPh @NPh)-2}Cl], 3, which was char-
acterised spectroscopically and by an X-ray crystal structure determination. This is an isomer of the product of direct mercuration of
Ph
3
P@NPh which occurs on the N-bonded phenyl ring [J. Vicente, J.A. Abad, R. Clemente, J. Lopez-Serrano, M.C. Ramirez de Arel-
ꢀ
lano, P.G. Jones, D. Bautista, Organometallics, 22 (2003) 4248]. Transmetallation of 3 with [AuCl
rated complex [Au{j -C,N-C H (PPh @NPh)-2}Cl ], with a five-membered metallocyclic ring incorporating four different elements.
4
]
gave the corresponding cycloau-
2
6
4
2
2
ꢀ
2006 Elsevier B.V. All rights reserved.
Keywords: Iminiphosphorane; Mercurated; Cycloaurated; X-ray crystal structures
1
. Introduction
Iminophosphoranes, R P@NR are a readily accessible
0
3
class of compound through the Staudinger reaction of
N
0
0
P
R P with R N , or from R PBr and R NH [1–5]. The
N
3
3
3
2
2
P
electronic and steric properties can be tuned through
Cl
0
M(CO)4
appropriate choice of R and R . Alper showed many
Pd
0
years ago that the Ph P@NR examples underwent reac-
3
tion with Pd(OAc) to give cyclopalladiated complexes 1
2
2
(1)
(
2) M = Mn or Re
[
6]. More recently, Vicente et al. have prepared a more
extensive range of cyclopalladiated examples, and exam-
ined their reactivity towards alkynes and isonitriles [7].
We have shown previously that direct cyclo-manganation
As far as we are aware these are the only cyclometal-
lated derivatives of iminophosphoranes involving transi-
tion metals that have been prepared directly, though
other examples of both transition- and main-group metal
and -rheniation of Ph P@NPh occurs readily to give 2
3
[
8].
derivatives have been synthesised via ortho-lithiation of
0
Ph P@NR followed by coupling with appropriate metal
3
halides [9–12].
*
We and others have been developing Au(III) chemistry
based on cycloaurated C,N-donor ligands which confer
Corresponding author. Fax: +64 7 838 4219.
E-mail address: b.nicholson@waikato.ac.nz (B.K. Nicholson).
0
020-1693/$ - see front matter ꢀ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2006.02.009

S.D.J. Brown et al. / Inorganica Chimica Acta 360 (2007) 1310–1315
1311
stability on this high oxidation state. So far most studies
have concentrated on N,N-dimethylbenzylamine, and phe-
nyl- or benzyl-pyridines as the substrate giving both five-
and six-membered chelate rings [13–21]. The resulting
square-planar complexes are also of interest for possible
biological activity, since they are formally analogous to
cis-Platin species, and pharmacological properties have
been recognised for some cycloaurated Au(III) species
132.6 (d, JPC = 2.9 Hz), 133.3 (s), 133.3 (s), 133.4 (s),
133.5 (s), 135.8 (s),137.1 (s), 138.5 (d, J = 12.4 Hz),
PC
3
1
3
199
149.0 (s); P d 8.6, J( Hg–P) 326 Hz. ESMS (MeOH)
m/z 612 [M+Na] , 590 [M+H] . IR m(P@N) 1304 cm
+
+
ꢀ1
.
(b) A N -flushed Schlenk flask was charged with PhBr
2
(0.30 mL, 0.44 g, 2.8 mmol) and Et O (10 mL). A solution
2
ꢀ
1
of BuLi (2 mL of 1.6 mol L
solution, 3.2 mmol) was
added and the mixture stirred for 15 min. Solid Ph P@NPh
3
[
22–27]. For many of these compounds direct cycloaura-
(1.0 g, 2.8 mmol) was added in one portion. The solution
turned orange as the solid dissolved and then a yellow pre-
cipitate formed. After stirring for 1.5 h, HgCl2 (0.82 g,
3.0 mmol) was added in one portion. The mixture became
colourless, with a white precipitate forming. After 1 h the
solvent was evaporated and the residue extracted with
CH Cl (2 · 10 mL). The filtered extracts were treated with
ꢀ
tion with [AuCl4] is not viable, so transmetallation from
the corresponding ortho-metallated mercury derivative is
commonly employed [28–32].
We decided to explore the Au(III) chemistry of
Ph P@NPh, and this required the prior synthesis of the
3
ortho-mercurated (on a P-bonded phenyl ring) intermedi-
ate. In this paper we report the syntheses and structures
of the mercurated and aurated derivatives 3 and 4,
respectively.
2
2
Et O (20 mL) and crystals of the product formed after stor-
2
ing at ꢀ20 ꢁC overnight (1.01 g, 60%).
2
.1.2. Preparation of (2-Cl AuC H )Ph P@NPh (4)
2
6
4
2
2
. Experimental
(2-ClHgC H )Ph P@NPh (0.35 g, 0.59 mmol) was dis-
6
4
2
solved in degassed acetonitrile (30 mL). [Me N][AuCl ]
4
4
2
.1. General
(0.24 g, 0.59 mmol) and [Me N]Cl (0.06 g, 0.55 mmol) were
4
added and the flask was wrapped in foil to exclude light.
The mixture was stirred for 2 d. The solvent was evapo-
rated under vacuum and the residue was dissolved in
CH Cl . Filtration removed the white by-product
Reactions were routinely carried out under a nitrogen
atmosphere using Schlenk techniques and solvents that
were distilled under nitrogen from appropriate drying
agents before use. Electrospray mass spectra were recorded
on a VG Platform II spectrometer, operated as detailed
elsewhere [33]. Assignments were confirmed by simulation
of the characteristic isotope patterns using the ISOTOPE pro-
gram [34]. The peaks reported are the most intense in the
isotopic envelope. NMR spectra were obtained on a Bru-
ker AC300 instrument operating under standard condi-
tions. IR spectra were recorded on a Digilab Scimitar
2
2
[Me N][HgCl ]. The filtrate was slowly evaporated until
4
3
the first sign of crystallisation and was stored at ꢀ20 ꢁC
overnight to give yellow crystals of (2-Cl AuC H )-
2
6
4
Ph P@NPh (0.217 g, 59%). C H NPCl Au Æ CH Cl
2
24 19
2
2
2
requires: C, 42.68; H, 3.01; N, 1.99. Found: C, 43.23; H,
1
2.95; N, 2.10%. NMR (CDCl ): H: d 5.30 (s, CH Cl ),
3
2
2
6.97–7.13, 7.30–7.36, 7.41–7.52, 7.54–7.58, 7.68–7.77,
1
3
8.40–8.42 (all m, Ar–H); C: d 124.1 (s), 125.3 (s), 126.2
(d, JPC = 2.0 Hz), 128.3 (s), 128.4 (d, JPC = 1.4 Hz), 128.5
(s), 129.5 (s), 129.6 (s), 129.7 (d, JPC = 18 Hz), 129.8 (s),
133.4 (s), 133.5 (s), 133.6 (s), 133.8 (d, JPC = 3 Hz), 134.5
instrument as KBr disks. Ph P@NPh was prepared by a lit-
3
erature method [35] and [Me N][AuCl ] from [Me N]Cl
4
4
4
and chloroauric acid.
3
1
(
d, JPC = 2.8 Hz), 142.7 (s), 149.5 (s), 149.7 (s); P d
+
2
.1.1. Preparation of (2-ClHgC H )Ph P@NPh (3)
65.6. ESMS (MeOH) m/z 616 [MꢀCl+MeOH] , 584
6
4
2
+
ꢀ1
(
a) Ph P@NPh (1.0 g, 2.83 mmol) was dissolved in dry,
[MꢀCl] . IR m(P@N) 1244 cm
.
3
degassed ether (30 mL). A solution of BuLi in hexane
ꢀ
1
(
1.6 mol L , 2.0 mL, 3.2 mmol) was added and the mix-
2.2. X-ray crystallography
ture was stirred for 3 h. After cooling to ꢀ84 ꢁC with an
ethyl acetate slush bath, a solution of HgCl2 (0.84 g,
X-ray intensity data were collected on a Siemens
SMART CCD diffractometer using standard procedures
and software. Empirical absorption corrections were
applied (SADABS [36]). Structures were solved by direct
3
.1 mmol) in thf (10 mL) was added. The solution was
allowed to slowly warm to room temperature, and stirring
was continued for 24 h. The solvent was evaporated under
vacuum and the residue extracted with CH Cl (20 mL).
2
methods and developed and refined on F using the SHELX
2
2
After filtration and evaporation the residue was redissolved
programs [37] operating under WinGX [38,39]. Hydrogen
atoms were included in calculated positions.
in the minimum volume of CH Cl and stored at ꢀ20 ꢁC to
2
2
give off-white crystals of (2-ClHgC H )Ph P@NPh (0.41 g,
6
4
2
2
5%). C H NPClHg requires: C, 48.99; H, 3.25; N, 2.38.
2.2.1. Structure of (2-ClHgC H )Ph P@NPh (3)
2
4
19
6
4
2
1
Found: C, 49.62; H, 3.61; N, 2.31%. NMR (CDCl ): H: d
Colourless block crystals of 3 were obtained from
3
6
7
1
1
.71–6.75, 6.93–6.96, 7.02–7.07, 7.28–7.33, 7.44–7.5, 7.68–
CH Cl .
2
2
1
3
.73 (all m, Ar–H); C: d 119.4 (s), 124.0 (d, JPC
=
Crystal data: C H NPClHg, M = 588.41, monoclinic,
24 19
space group P2 /c, a = 10.2061(1), b = 12.8252(2), c =
1
16.1800(1) A, b = 104.713(1)ꢁ, U 2048.44(4) A , T 83 K,
4.7 Hz), 128.3 (d, JPC = 14.6 Hz), 128.0 (s), 129.2 (s),
29.4 (s), 130.0 (s), 130.8 (s), 131.8 (d, JPC = 3.1 Hz),
3
˚
˚

1312
S.D.J. Brown et al. / Inorganica Chimica Acta 360 (2007) 1310–1315
ꢀ
3
ꢀ1
Z = 4, Dcalc = 1.908 g cm , l (Mo Ka) = 7.732 mm
,
Table 1
Structural parameters for the orthomercurated compound 3 and the
cycloaurated compound 4
F(000) 1128; 12073 reflections collected with 2ꢁ < h < 26ꢁ,
175 unique (Rint 0.0162) used after correction for absorp-
tion (Tmax,min 0.307, 0.157). Crystal dimensions 0.38 ·
4
3, M = Hg
4, M = Au
3
2
˚
Bond lengths (A)
0
.24 · 0.20 mm . Refinement on F gave R1 0.0177
I > 2r(I)] and wR2 0.0427 (all data), Goodness-of-fit
.164. The structure of 3 is illustrated in Fig. 1, with
selected bond parameters summarised in Table 1.
M–C(12)
M–N(1)
M–Cl(1)
2.066(3)
2.637(2)
2.3303(7)
2.035(5)
2.034(4)
2.368(1)
2.289(1)
1.618(4)
1.790(5)
1.433(6)
1.403(6)
[
1
M–Cl(2)
P(1)–N(1)
P(1)–C(11)
N(1)–C(41)
C(11)–C(12)
1.589(2)
1.814(3)
1.409(4)
1.396(4)
2
(
.2.2. Structure of (2-Cl AuC H )Ph P@NPh Æ CH Cl
2
6
4
2
2
2
4 Æ CH Cl )
2
2
Yellow crystals of 4 as the mono solvate were obtained
from CH Cl .
Bond angles (ꢁ)
N(1)–M(1)–C(12)
C(12)–M–Cl(1)
Cl(1)–M–Cl(2)
M(1)–N(1)–P(1)
P(1)–N(1)–C(41)
N(1)–P(1)–C(11)
2
2
80.07(9)
170.16(8)
84.86(17)
174.9(1)
90.70(4)
113.2(2)
123.2(3)
101.3(2)
Crystal data: C H NPCl Au Æ CH Cl , M = 705.16,
2
4
19
2
2
2
orthorhombic, space group P2 2 2 , a = 9.3827(4), b =
1
1 1
3
˚ ˚
1
3.5335(6), c = 19.5831(9) A, U 2486.7(2) A , T 83 K,
106.7(1)
126.4(2)
106.8(1)
ꢀ
3
ꢀ1
Z = 4, Dcalc = 1.884 g cm , l (Mo Ka) = 6.425 mm
F(000) 1360; 15096 reflections collected with 2ꢁ < h < 26ꢁ,
065 unique (Rint 0.0211) used after correction for absorp-
tion (Tmax,min 0.360, 0.286). Crystal dimensions 0.26 ·
.24 · 0.20 mm . Refinement on F gave R1 0.0220
I > 2r(I)] and wR2 0.0535 (all data), Goodness-of-fit
.004, Flack x parameter 0.010(5). The structure of 4 is
,
5
Group, University of Canterbury, New Zealand. Details
are published elsewhere [21]. This gave an IC50 of
3
2
0
[
1
ꢀ
1
7546 ng ml or 10.7 lM.
illustrated in Fig. 2, with selected bond parameters summa-
rised in Table 1.
3. Results and discussion
3.1. Synthesis and properties of 3
2
.3. Biological activity
Since it is known that direct mercuration of Ph P@NPh
3
An assay of the gold compound 3 against a P388 Murine
occurs at the N-bonded phenyl ring [7], we have developed
Leukemia cell line was performed by the Marine Chemistry
a synthesis of the derivative of Ph P@NPh with mercury on
3
Cl(1)
Hg(1)
C(12)
C(11)
C(32)
C(31)
P(1)
N(1)
C(42)
C(41)
C(21)
C(22)
Fig. 1. The structure of the orthomercurated complex 3.

S.D.J. Brown et al. / Inorganica Chimica Acta 360 (2007) 1310–1315
1313
C(22)
C(32)
C(21)
C(31)
P(1)
C(11)
C(12)
C(41)
N(1)
C(42)
Au(1)
Cl(1)
Cl(2)
Fig. 2. The structure of the cycloaurated complex 4.
the P-bonded phenyl ring via an intermediate lithiated spe-
cies (c.f. [9–12]), as in Scheme 1.
early paper on the lithiation of Ph P@NPh showed that
3
exchange of groups on phosphorus occurred readily with
BuLi [40]. Hence the method was modified by producing
PhLi in situ (from Li/Br exchange between PhBr and BuLi)
This provided moderate yields of 3, with the mercury
attached to one of the P-bonded phenyl groups. This is
the isomer of the compound produced from a direct merc-
uration reaction, where attachment is on the N-bonded
phenyl group [7]. Initially lithiation was carried out with
BuLi. Examination of the crude reaction mixture by elec-
trospray mass spectrometry showed the presence of several
by-products, including Bu(2-ClHgC H )PhP@NPh. An
before adding Ph P@NPh. This led to much improved
3
yields of 3.
The new compound was characterised by elemental
1
13
31
analysis and H, C and P NMR spectroscopy. The
3
1
P signal for 3 comes at d 8.6 ppm, the relatively small
shift from that at 3.6 ppm for the free ligand suggesting a
simple metallation rather than a cyclometallated species
involving coordination of the N atom to Hg as well [41].
6
4
1
99
The appearance of Hg satellites on the P signal strongly
supported metallation at a P-bonded, rather than an N-
bonded, phenyl ring. To confirm this a single-crystal X-
ray structure determination was carried out. The molecule
is shown in Fig. 1. It confirms the position of the –HgCl
group at an ortho site on a P-bonded phenyl ring. The
geometry at Hg shows a small deviation from linearity
P
N
P
Hg(OAc) /LiCl
2
[
C–Hg–Cl 170.16(8)ꢁ] and a smaller P(1)–C(11)–C(12)
angle of 106.8(1)ꢁ than the other two P(1)–C(11)–C angles
BuLi
[
av. 115.9(1)ꢁ]. These accommodate a weak N(1). . .Hg(1)
N
P
˚
interaction {2.637(2) A cf. a normal Hg–N(imine) bond
˚
of ca. 2.25 A [42]} which is obviously significant but is
HgCl
not sufficient to regard 3 as a true cyclometallated deriva-
tive. However it is sufficient to constrain an overall confor-
mation where the pseudo-cyclic ring is planar to within
(
3)
HgCl2
N
Li
˚
P
± 0.13 A. The N-bonded phenyl ring is twisted 8ꢁ from this
plane, compared with the free ligand where the correspond-
ing twist is 11ꢁ (c.f. the true cyclometallated complexes dis-
cussed below). Only small differences are seen for the rest
Scheme 1.
of the ligand when compared to Ph P@NPh itself [43].
3

1314
S.D.J. Brown et al. / Inorganica Chimica Acta 360 (2007) 1310–1315
The electrospray mass spectrum of 3 in methanol gave a
strong peak at m/z 590 which corresponds to the [M+H]
ion, which suggests that the N atom is available for chem-
ical ionisation by protonation, and not obstructed by the
weak Hg. . .N interaction.
bonding of the N atom to Au has lengthened both the
+
P@N and the N(1)–C(41) bonds compared to the free
ligand [43], and to the mercurated example 3. Finally,
the higher trans-influence of C versus N is reflected in the
longer Au–Cl(1) distance compared to Au–Cl(2).
The biological activity of the gold(III) compound 3 was
screened against a P388 Murine Leukaemia cell line, and
3
.2. Synthesis and properties of 4
ꢀ1
showed an IC50 value of 7546 ng ml (11 lM). This repre-
sents significant activity, but is less than for other cyclomet-
allated species [21]. Compound 3 was poorly soluble in
biologically relevant solvents so derivatives modified to
improve hydrophilicity can be expected to show higher
activity.
Compound 4 is conveniently prepared by a simple trans-
metallation reaction between the mercury compound 3 and
ꢀ
[
AuCl ] , Scheme 2, following the precedents established
4
for other potential C,N bonding ligands [28–32].
The electrospray mass spectrum in methanol showed
major peaks at m/z 584 and 616 which can be assigned to
+
+
[
MꢀCl] and [MꢀCl + MeOH] , respectively. In this case
4. Conclusions
+
there is no [M+H] signal at m/z 619, indicating that the N
3
1
atom is no longer available for protonation. The P NMR
We have shown that Ph P@NPh forms stable mercury
3
signal at d 65 ppm shows a large shift from the free ligand
and gold derivatives with metallation at an ortho-carbon
atom of a P-bonded phenyl group via a lithiated intermedi-
ate. The gold compound forms a strong secondary interac-
tion with the nitrogen atom, but there is only a weak one
for the mercury example. The mercury compound should
find extensive use in preparing cyclometallated complexes
of other metals by transmetallation, while the gold complex
would be a good precursor for an extensive range of new
derivatives by ligand exchange reactions with the labile
(
and from the value in 3) consistent with incorporation into
a five-membered metallocyclic ring [41]. One of the advan-
tages of having a phosphorus atom in the ligand is that the
3
1
large changes in P chemical shifts from non-cyclised to
cyclised forms is potentially useful for examining the
reactivity of cycloaurated systems – in the (damp)AuCl2
complexes some ligands displaced the N-donor atom; cor-
responding opening of the metallocyclic ring for 4 could be
3
1
readily screened using P NMR. Full cyclometallation was
confirmed by the crystal structure determination which
revealed the molecule shown in Fig. 2. This has a square
Cl groups. The compounds reported here using Ph P@NPh
3
can be regarded as the prototypes for an extensive series
given the ease with which the substituents on the P and
N atoms can be varied to tune the steric, electronic and
physical properties of the ligand.
˚
planar (to ± 0.05 A) Au(III) centre, attached to two Cl
ligands, and to the N and an ortho-C atom of
the Ph P@NPh ligand. This generates a five-membered
3
metallocyclic ring which is significantly puckered, with
Acknowledgement
˚
deviations of +0.24 [N(1)] and ꢀ0.20 A [P(1)] from the
least-squares plane. The metallocyclic plane and the Au
coordination plane are twisted to give an angle of 14ꢁ
between them. In the related cyclomanganated derivative
We thank Dr. Tania Groutso, University of Auckland,
for collection of X-ray intensity data.
2
the metallocyclic ring was essentially planar, so there is
Appendix A. Supplementary material
clearly flexibility in these rings arising from the incorpora-
3
tion of the sp P atom. The Au–N(1) and Au–C(12) dis-
Crystallographic data for the structural analyses have
been deposited with the Cambridge Crystallographic Data
Centre, CCDC nos. 293123 and 293124. Copies of this
information may be obtained free of charge from the
Director, CCDC, 12 Union Road, Cambridge CB2 1EZ,
UK (fax: +44 1223 336033; e-mail: deposit@ccdc.cam.
ac.uk or www: http://www.ccdc.cam.ac.uk). Supplemen-
tary data associated with this article can be found, in the
online version, at doi:10.1016/j.ica.2006.02.009.
˚
tances are the same length (2.035(4) A) and give a N(1)–
Au(1)–C(12) angle of 84.9(2)ꢁ, very similar to that in the
orthomanganated example [8], suggesting the ‘bite’ is rela-
tively rigid. In this example the N-bonded phenyl ring is
twisted to 54ꢁ from the metallocycle plane. The strong
[AuCl ]-
N
N
Au
Cl
References
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4
P
HgCl
Cl
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