Carboxylation of pincer PCP platinum methoxide complexes under formation of metalla carbonates

Article abstract of DOI:10.1016/j.poly.2011.08.028

The ligand 2,6-bis[(diphenylphosphino)methyl]benzene ((PCP)H) was prepared and characterised in an improved manner. With platinum it forms the complex (PCP)PtOTf which reacts with sodium methoxide to give (PCP)PtOMe as the major product together with a sm

Full text of DOI:10.1016/j.poly.2011.08.028

Polyhedron 32 (2012) 24–29
Contents lists available at SciVerse ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Carboxylation of pincer PCP platinum methoxide complexes under formation of
metalla carbonates
⇑
Athimoolam Arunachalampillai, Nagarajan Loganathan, Ola F. Wendt
Centre for Analysis and Synthesis, Department of Chemistry, Lund University, P.O. Box 124, S-221 00 Lund, Sweden
a r t i c l e i n f o
a b s t r a c t
Article history:
Available online 3 September 2011
The ligand 2,6-bis[(diphenylphosphino)methyl]benzene ((PCP)H) was prepared and characterised in an
improved manner. With platinum it forms the complex (PCP)PtOTf which reacts with sodium methoxide
to give (PCP)PtOMe as the major product together with a small amount of [(PCP)Pt]2-
methoxide reacts with carbon dioxide to give (PCP)PtO(CO)OMe. Also the dinuclear [(PCP)Pt]2(
O(CO)OMe) is formed in this reaction if (PCP)PtOTf is present. The crystal structures for [(PCP)PtOH2]OTf,
PCP)PtOMe, [(PCP)Pt]2- -H and [(PCP)Pt]2( -O(CO)OMe) are reported.
Ó 2011 Elsevier Ltd. All rights reserved.
l-H. The platinum
Keywords:
Platinum
Carbon dioxide
Pincer ligands
Alkoxide complexes
Carbonate complexes
l
-
l
l
1. Introduction
2. Experimental
The use of carbon dioxide as a raw material is attractive because
it is abundant, cheap and non-toxic and transition metal mediated
activation has received considerable attention lately. Among the
reactions involving CO2 that have the highest success probability
in the short run are those where the (OCO)-fragment is intact in
the product, such as carbonates, since these require the least en-
ergy input [1]. There has also been significant progress in making
polymeric carbonates from epoxides and CO2 [2], whereas the car-
boxylation of alcohols is still a challenge with the best homoge-
neous catalysts being tin or early transition metal alkoxides [3].
We have investigated the reactivity of transition metal-carbon
bonds towards carbon dioxide using palladium ligated with triden-
tate PCP pincer ligands [4], and we decided to expand these inves-
tigations to include alkoxides, since, compared with the many
studies of the reactivity of metal-carbon bonds, there is much less
information on the reactivity of late metal alkoxides and several
studies also suggest a difference in fundamental mechanisms, e.g.
for b-elimination [5]. Late metal alkoxides are potentially interest-
ing for catalytic transformations of carbon dioxide because of the
high reactivity towards carbon dioxide reported for such species
[6]. Lately there have been reports on the reactivity of nickel alkox-
ides and amides towards CO2 and also on the insertion of CO2 into a
PCP platinum amides [7], but little has been reported on the reac-
tion of platinum alkoxides towards carbon dioxide. Here we report
on the synthesis, stability and CO2 insertion reactivity of a (PCP)
platinum methoxide complex.
2.1. General procedures and materials
All experiments with air-sensitive compounds were carried out
under an atmosphere of nitrogen in a glove box or using standard
Schlenk or high vacuum-line techniques [8]. All non-deuterated
solvents were vacuum-transferred from sodium/benzophenone ke-
tyl directly to the reaction vessel, except chlorinated solvents which
were distilled from calcium hydride. Commercial grade CO2 was
dried using P2O5 and a dry ice-acetone mixture prior to use. Ben-
zene-d6 was dried over sodium/benzophenone ketyl and vacuum
transferred directly to the NMR tube. All the other commercially
available reagents were purchased from Sigma–Aldrich and used
as received. 1H, 13C and 31P NMR spectra were recorded on a Varian
Unity INOVA 500 spectrometer working at 499.77 MHz (1H). The
NMR spectroscopic measurements were performed in benzene-d6
unless otherwise stated. (COD)PtClN(SiMe3)2 was prepared accord-
ing to a reported procedure [9]. Chemical shifts are given in ppm
downfield from TMS using residual solvent peaks (1H NMR, 13C
NMR) or H3PO4 as reference. Elemental analyses were performed
by H. Kolbe, Mülheim an der Ruhr, Germany.
2.2. Synthesis of 2,6-bis[(diphenylphosphino)methyl]benzene, (PCP)H,
(1)
This ligand was synthesised using a slightly modified literature
procedure [10]. To a solution of
a,
a0-dichloro-m-xylene (0.78 g,
4.5 mmol) in THF (30 mL) a potassium diphenylphosphide solution
(2.0 g, 8.9 mmol) in THF was added over a period of 10 min. The
mixture was stirred vigorously for 6 h and the solvent was
⇑
Corresponding author. Fax: +44 1223 336 033.
E-mail address: ola.wendt@organic.lu.se (O.F. Wendt).
0277-5387/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2011.08.028

A. Arunachalampillai et al. / Polyhedron 32 (2012) 24–29
25
1
1
evaporated in vacuo; the mixture was re-dissolved in ether (75 mL)
and filtered through a glass frit with celite. Evaporation of the ether
solution afforded the ligand as a low melting solid. Yield: 1.92 g
(90.1%). Anal. Calc. for C32H28P2: C, 81.00; H, 5.95; P, 13.05. Found:
C, 80.76; H, 5.90; P, 13.00%. 1H NMR: d 3.22 (bs, 4H, PCH2), 6.69 (d,
2H, 3J = 7.5 Hz, p-H of centre phenyl), 6.79 (s, 1H, o-H of centre
phenyl), 6.85 (t, 1H, 3J = 7.5 Hz, m-H of centre phenyl), 7.19 (m,
12H, P-phenyl) and 7.26 (m, 8H, P-phenyl). 13C{1H} NMR: d 35.87
133.43 (t, JPt–C = 47.7 Hz, Pt–C) and 148.20 (t, JP–C = 9.1 Hz, i-C
of P-phenyls). 31P{1H} NMR: d 31.8 (s, with platinum satellites,
JPt–P = 3142 Hz).
2.5. Synthesis of (PCP)Pt–O(CO)OMe (9)
To a pale yellow coloured solution of 7 (0.10 g, 0.14 mmol) in
benzene (5 mL) 3 atm of dry carbon dioxide was added and the
mixture was stirred for 10 min. The solution was concentrated to
2 mL and left standing at room temperature. Colourless crystalline
plates of 9 were formed and these were filtered and dried. Yield:
0.10 g (96%). Anal. Calc. for C34H30O3P2Pt: C, 54.92; H, 4.07; P,
8.33. Found: C, 55.06; H, 4.20; P, 8.26%. 1H NMR: 3.33 (t, 4H,
1
5
3
(d, JP–C = 14.3 Hz, PCH2), 127.10 (dd, JP–C = 2.9 and JP–C = 6.9 Hz,
p-C of the centre phenyl), 128.21 (t, 4JP–C = 1.9 Hz, m-C of the centre
phenyl), 128.5 (d, 2JP–C = 6.7 Hz, o-C of P-phenyls), 130.55 (t, 3JP–C
=
7.2 Hz, o-C of the centre phenyl), 132.99 (s, p-C of P-phenyls),
4
2
133.14 (s, m-C of P-phenyls), 137.30 (dd, JP–C = 1.5 and JP–C
=
1
2JP–H = 4.5 Hz, PCH2), 3.49 (s, –COOMe), 6.90 (t, 1H, JH–H = 7.5 Hz,
p-H of the centre phenyl), 6.93 (d, 2H, JH–H = 7.5 Hz, m-H of the
3
7.9 Hz, i-C of the centre phenyl) and 138.10 (d, JP–C = 13.8 Hz, i-C
of P-phenyls). 31P{1H} NMR: d ꢀ9.3 (s).
3
3
centre phenyl), 6.98 (tt, 12H, JH–H = 1.5 and 7.0 Hz, phenyls),
7.88 (tq, 8H, JH–H = 1.0 and 6.0 Hz, phenyls). 13C{1H} NMR: d
3
2.3. Synthesis of (PCP)Pt–Cl (3), (PCP)Pt–I (3a), (PCP)Pt–OTf (4) and
[(PCP)Pt–OH2]CF3SO3 (5)
1
3
42.34 (t, JP–C = 18.2 Hz, PCH2), 53.34 (s, –OMe), 122.72 (t, JP–C
=
9.1 Hz, m-C of the centre phenyl), 125.20 (s, p-C of the centre phe-
3
Complexes3, 3a and 4 were prepared according to reported pro-
cedures [9–11]. Recrystallisation of complex 4 from a wet dichloro-
methane and hexane mixture afforded colourless crystals of 5
quantitatively. Anal. Calc. for C33H29F3O4P2SPt: C, 47.43; H, 3.50;
P, 7.41. Found: C, 47.35; H, 3.58; P, 7.35%. 1H NMR: d 3.27 (t, 4H,
2JP–H = 4.5 Hz, PCH2), 6.82 (d, 2H, 3JH–H = 7.5 Hz, p-H of centre phe-
nyl), 128.65 (t, JP–C = 5.3 Hz, m-C of P-phenyls), 130.47 (s, p-C of
1
2
P-phenyls), 132.52 (s, JPt–C = 52.8 Hz, Pt–C), 133.27 (t, JP–c
=
6.8 Hz, o-C of P-phenyls), 140.0 (s, o-C of the centre phenyl),
1
148.20 (t, JP–C = 9.1 Hz, i-C of P-phenyls) and 160.2 (s, Pt–O–C).
31P{1H} NMR: d 36.9 (s, with platinum satellites, JPt–P = 3091 Hz).
IR:
m .
(C@O) 1661 cmꢀ1
3
nyl), 6.95 (t, 1H, JH–H = 7.5 Hz, m-H of centre phenyl), 7.00 (t, 4H,
3
3JH–H = 7.5 Hz, P-phenyl), 7.05 (t, 8H, JH–H = 7.5 Hz, P-phenyl) and
2.6. Crystallography
3
7.80 (q, 8H, JH–H = 7.5 Hz, P-phenyl). 13C{1H} NMR: d 41.82,
123.08, 126.09, 128.20, 128.88, 131.03, 131.68, 133.32 and
Intensity data were collected at 293 K with an Oxford Diffrac-
tion Xcalibur 3 system using -scans and MoK (k = 0.71073 Å)
145.20. 31P{1H} NMR: d 39.9 (s, with platinum satellites, JPt–P
3019 Hz). 19F NMR: d ꢀ77.58 (s).
=
x
a
[12]. CCD data were extracted and integrated using Crysalis RED
[13]. The structures were solved using direct methods and refined
by full-matrix least-squares calculations on F2 using SHELXTL 5.1
[14]. Non-H atoms were refined with anisotropic displacement
parameters, unless otherwise indicated. Hydrogen atoms were
constrained to parent sites, using a riding model. In the structure
of complex 5 there are two remaining large difference Fourier
peaks but they are located <1 Å from the platinum atom. In the
crystal structure of complex 6 we tried to resolve the disorder in
the benzene and triflic acid molecules using restraints but this
was unsuccessful. The crystal quality of compound 8 was low giv-
ing poor data. Thus, only a few non-H atoms were refined with
anisotropic displacement parameters and most were refined iso-
tropically. All atoms could be located but the solvent molecules
were disordered and these were instead treated using a SQUEEZE
procedure [15]. Overall this gives a model with many remaining
alert A’s in the CIF-check and the structure is only reliable insofar
as connectivity is concerned. All crystallographic data is available
in CIF format. CCDC reference numbers 778661–778664.
2.4. Synthesis of [(PCP)Pt]2-l-H (6) and (PCP)Pt–OMe (7)
To a colourless solution of 4 (0.25 g, 0.3 mmol) in THF (10 mL),
NaOMe (0.08 g, 1.5 mmol) was added and the mixture was stirred
for 3 h. The solution was filtered and the THF was evaporated in va-
cuo. The slightly coloured solid was dissolved in benzene (25 mL),
leaving behind colourless crystals of 6, which were filtered and
dried. Yield: 0.023 g (11%). Anal. Calc. for C64H55P4Pt2: C, 57.40;
H, 4.21; P, 9.26. Found: C, 56.35; H, 4.10; P, 9.20%. 1H NMR (dichlo-
romethane-d2): d ꢀ6.59 (quintet with platinum satellites, 1H,
1
2
2JP–H = 9.0 Hz and JPt–H = 504 Hz, hydride), 3.52 (t, 4H, JP–H
=
4.0 Hz, PCH2), 6.93 (t, 8H, 3JH–H = 8.0 Hz, phenyl), 7.07 (m, 4H, phe-
nyl), 7.14–7.27 (m, 11H, phenyl). 13C{1H} NMR (dichloromethane-
1
3
d2): d 44.45 (t, JP–C = 18.7 Hz, PCH2), 123.26 (t, JP–C = 9.7 Hz, m-C
of the centre phenyl), 126.70 (s, p-C of the centre phenyl), 128.5
(s, o-C of the centre phenyl), 128.8 (t, 3J = 5.3 Hz, m-C of P-phenyls),
131.35 (s, p-C of P-phenyls), 131.51 (t, JPt–C = 55.3 Hz, Pt–C), 132.82
2
1
(t, JP–C = 6.2 Hz, o-C of P-phenyls) and 145.30 (t, JP–C = 7.7 Hz, i-C
of P-phenyls). 31P NMR (dichloromethane-d2): d 38.1 (d, with
2
1
3
platinum satellites, JP–H = 6 Hz, JPt–P = 2892 Hz, JPt–P = 32 Hz).
Evaporation of the benzene solution afforded slightly coloured so-
lid 7 which was recrystallised from a benzene/ether mixture. Yield:
0.15 g (71%). Anal. Calc. for C33H30OP2Pt: C, 56.65; H, 4.32. Found:
3. Results and discussion
3.1. Synthesis and characterisation of the platinum alkoxide
C, 56.55; H, 4.30%. 1H NMR: d 3.55 (t, 4H, JP–H = 4.5 Hz, PCH2),
The diphenyl phosphine ligand 1 was first synthesised in 1983,
but no thorough characterisation data have been reported
[10,11b]. To improve the synthetic procedure we employed the
commercially available potassium diphenyl phosphide, reacting
2
3
4.41 (s, with platinum satellites, 3H, JPt–H = 23.5 Hz, Pt–OMe),
3
6.96 (d, 2H, JH–H = 6.0 Hz, m-H of the centre phenyl), 7.00 (t, 4H,
3JH–H = 8.0 Hz, p-H of the P-phenyls), 7.05 (t, 8H, JH–H = 7.0 Hz, o-
3
3
H of the P-phenyls), 7.13 (t, 1H, JH–H = 7.5 Hz, p-H of the centre
this with a,
a0-dichloro xylene in THF. This afforded the ligand ana-
3
phenyl), 8.01 (q, 8H, JH–H = 6.0 Hz, m-H of the P-phenyls).
lytically pure in 90% yield. It was characterised by multinuclear
NMR spectroscopy and elemental analysis. Cyclometallation was
then achieved using a procedure recently reported by us giving
the chloro complex 3, cf. Scheme 1 [9].
Platinum alkoxides have sometimes been synthesised through
salt metathesis of the halides and initially we attempted this
13C{1H} NMR: d 43.47 (t, JP–C = 18.9 Hz, PCH2), 63.60 (t, JP–C
=
1
4
3
5.8 Hz, Pt–OMe), 122.47 (t, JP–C = 9.5 Hz, m-C of the centre phe-
nyl), 124.40 (s, p-C of the centre phenyl), 128.18 (s, o-C of the cen-
3
tre phenyl), 128.68 (t, JP–C = 5.2 Hz, m-C of P-phenyls), 130.35 (s,
2
p-C of P-phenyls), 133.25 (t, JP–c = 6.5 Hz, o-C of P-phenyls),

26
A. Arunachalampillai et al. / Polyhedron 32 (2012) 24–29
Scheme 1.
reaction for the synthesis of the tert-butoxide derivatives of 3. We
chose the tert-butoxide to avoid any elimination reactions thinking
that the bulky tert-butoxide should be sterically compatible with
the diphenyl phosphine moiety. However, 3, and its iodo analogue
3a, failed to react with sodium tert-butoxide in THF also at ele-
vated temperatures. This has been observed earlier and the usual
solution has been to use triflate or, as reported recently for nickel
derivatives, fluoride as the leaving group [16]. Thus, we synthes-
ised the triflate complex 4 using the standard silver triflate reac-
tion as reported in the literature [11c]. Upon recrystallisation
from dichloromethane/hexane under ambient conditions we ob-
tained a material that is probably the corresponding aqua complex
5, cf. Scheme 2. It was characterised by multinuclear NMR spec-
troscopy, elemental analysis and X-ray crystallography. Although
no obvious coordinated water peak could be observed in the 1H
NMR there is a peak at d 0.40 ppm corresponding to free water
although dry benzene was used. This indicates that in solution
there is some ion pairing at least partly displacing the water mol-
ecule. The molecular structure is given in Fig 1 and crystal data and
details about data collection are given in Table 1.
The structure is the expected mononuclear pseudo square pla-
nar platinum exhibiting the typical bent-back P–Pt–P angle
(165.5°) because of the limitations from the rigid ligand backbone,
as is almost always seen for PCP complexes. The complexes form
hydrogen bonded dimers together with two triflate anions with
O–O distance of 2.668(11) Å (O1–O3) and 2.715(4) Å (O1⁄–O4)
indicating fairly strong hydrogen bonds. Thus, an 8-membered ring
is formed from the two sulfur and six oxygen atoms. We formulate
complex 5 as an aqua complex, but of course it cannot be ruled out
that it is a hydroxide complex with a molecule of triflic acid in the
crystal lattice. However, the hydroxide would be highly basic and
probably react with the triflic acid [17]. Furthermore, looking at
bond distances seems to support our formulation; the Pt–O dis-
tance is 2.156(7) Å which is in line with similar aqua complexes,
whereas corresponding hydroxides usually display shorter dis-
tances [18]. Similar triflate displacements are well known [19].
However, also 4 was unreactive towards sodium tert-butoxide
and we conclude that the steric demand of the PCP ligand is not
compatible with the bulky tert-butoxide. It has been reported pre-
viously that tert-butoxides are too bulky to react with pincer li-
Fig. 1. DIAMOND drawing of 5. Hydrogen atoms are omitted for clarity. Selected
bond distances (Å): Pt1–C1 1.995(9), Pt1–O1 2.156(7), Pt1–P2 2.294(3), Pt1–P1
2.298(3).
two products, which were fairly easily separated with the minor
one being sparingly soluble in benzene. By filtering, it could be iso-
lated analytically pure in 11% yield and it was identified as the
dinuclear hydride, 6, cf. Scheme 3.
The hydride is observed as a quintet (d = ꢀ6.59 ppm) in 1H NMR
2
spectroscopy with JHP = 9 Hz. The structure of complex 6 was
unambiguously (apart from the number and positions of the
hydrogens) confirmed using X-ray crystallography. A perspective
view of the molecular structure (excluding the phosphine phenyl
groups) is shown in Fig. 2, including selected bond distances and
angles. The two coordination planes are situated at a 67° angle to-
wards each other. In addition to 6 the unit cell contains highly dis-
ordered molecules of benzene, THF and triflate. The position of the
hydrogens in complex 6 is clearly a case of ‘‘proton ambiguity’’,
where a reasonable structure would be a cationic, dinuclear
gated palladium [5b] and we then reacted
4 with sodium
methoxide at room temperature in THF. This gave a mixture of
Scheme 2.

A. Arunachalampillai et al. / Polyhedron 32 (2012) 24–29
27
Table 1
Crystal data for 5, 6, 7 and 8.
5
6
7
8
Formula
Formula weight
Space group
a (Å)
b (Å)
c (Å)
C
33H29F3O4P2PtS
C75H68F3O4P4Pt2S
1636.41
P2(1)/n
15.4226(3)
17.5298(3)
25.4852(4)
90
97.309(2)
90
6834.1(2)
4
C36H33OP2Pt
738.65
P1
C74H62F6O9P4Pt2S2
1787.42
P1
835.65
P1
ꢀ
ꢀ
ꢀ
9.6441(14)
13.8854(19)
14.012(3)
119.084(13)
93.431(17)
104.595(12)
1549.6(4)
2
8.824(2)
12.5170(19)
14.712(2)
91.936(12)
104.959(16)
104.199(17)
1513.6(5)
2
9.9203(2)
16.1494(4)
23.4661(7)
72.573(2)
83.991(2)
74.829(2)
3460.45(15)
2
a
(deg)
b (deg)
c
(deg)
V (Å3)
Z
Dcalc (g cmꢀ3
)
1.791
4.754
1.590
4.270
1.621
4.768
1.715
4.265
l
(mmꢀ1
)
h (range/deg)
2.23–32.30
8361
6926
0.0729
0.1795
2.27–32.76
49860
22441
0.0400
0.0929
2.10–32.65
13124
9323
0.0609
0.1485
2.13–19.59
8237
5589
0.0965
0.2933
No. of reflections collected
No. of unique reflections
R(F) (I > 2
r
(I))a
wR2(F2) (all data)b
Sc
0.979
0.841
0.809
4.843
Rint
CCDC
0.0308
778661
0.0453
778662
0.0692
778663
0.0182
778664
a
b
c
R =
wR2 = [
S = [
R
(|Fo| ꢀ |Fc|)/
R|Fo|.
R
w(|Fo| ꢀ |Fc|)2/
R .
|Fo|2]0.5
R
w(|Fo| ꢀ |Fc|)2/(m ꢀ n)]1/2.
Scheme 3.
Fig. 2. DIAMOND drawing of 6. Hydrogen atoms phenyl rings on the phosphines are omitted for clarity. Selected bond distances (Å) and angles (deg): Pt1–C1 2.062(5), Pt1–P1
2.2662(12), Pt1–P2 2.2836(13), Pt1–Pt2 2.9131(3), Pt2–C33 2.073(5), Pt2–P3 2.2759(14), Pt2–P4 2.2976(14), P1–Pt1–P2 153.91(5), P3–Pt2–P4 160.94(5).
platinum monohydride with a triflate counteranion. The platinum
methoxide complex could undergo a b-hydride elimination as is of-
ten observed for such ligands [20] and the so formed hydride could
displace the triflate of unreacted 4 to give complex 6. This is also
compatible with the coupling pattern of the hydrides. They appear
as a quintet with coupling to the 4 equivalent phosphorus atoms
and applying 31P broadband decoupling the quintet collapses to a
singlet. More importantly, applying off-resonance (from the
hydride peak) 1H decoupling the 31P spectrum of 6 displays an
ill-resolved doublet with a 2JPH coupling constant of approximately
6 Hz, a value which is in the same region as in the proton
spectrum; this clearly indicates the presence of one hydride.

28
A. Arunachalampillai et al. / Polyhedron 32 (2012) 24–29
characterised as the methoxide complex 7. The 31P{1H} NMR reso-
nance is seen at 31.8 ppm and the 1H NMR spectrum displays a
methoxide resonance at 4.41 ppm with typical platinum satellites.
Compound 7 is fairly thermally stable but we were unable to syn-
thesise it without some accompanying formation of 6, as men-
tioned earlier [23]. Still, due to their different solubilities, 7 was
easily obtained in an analytically pure form. Compound 7 is also
sensitive to moisture forming what is probably the hydroxide. No
systematic study of its thermal stability was performed. The com-
pound was also characterized by X-ray crystallography and the
molecular structure is shown in Fig 3. It displays a mononuclear
distorted square-planar coordination geometry with only weak
intermolecular forces. The lattice contains one molecule of ben-
zene solvent/platinum and the methoxy oxygens form interactions
to the solvent, typical for
(D = 3.47 Å; d = 2.61 Å; h = 155°) [24].
a
weak Oꢁ ꢁ ꢁC–H hydrogen bond
Having obtained the methoxide complex 7 we were very inter-
ested in its reactivity towards carbon dioxide. Initially we therefore
reacted 4 with NaOMe in THF and then stripped the solvent, added
benzene and reacted the resulting solution with carbon dioxide
in situ. From this reaction we harvested a small amount of a crys-
talline material that was subjected to an X-ray analysis and turned
out to be the dinuclear carbonate complex, 8, cf. Scheme 4. The
molecular structure is shown in Fig. 4. In addition to the dinuclear
cationic species shown in Fig. 4 the unit cell contains one triflate
moiety and disordered solvent. We did not optimise the reaction
conditions to obtain 8 and it was never isolated in a large amount
enough to allow micro analysis. It cannot be excluded that the iso-
lation of the di-nuclear species was in part due to its lower solubil-
ity and that it was formed concomitantly with 9. However, to avoid
this dimerization we instead reacted the isolated platinum meth-
oxide with carbon dioxide in benzene (Scheme 5). This immedi-
ately gave the monomeric hemicarbonate 9, which was isolated
and fully characterised by micro analysis and multinuclear NMR
spectroscopy. Unfortunately, it failed to give X-ray quality crystals
and we were only able to generate very poor data sets. The meth-
oxy group of the terminal carbonate is seen as a peak at 3.49 and
53.34 ppm in the 1H and 13C NMR spectra [25]. The 13C carbonyl
carbon resonance is found at 160.2 ppm similar to what has been
observed in terminal alkyl carbonate complexes of manganese
and tin [26]. It displays an HMBC correlation with the 1H NMR peak
of the methoxy group.
Fig. 3. DIAMOND drawing of 7. Hydrogen atoms are omitted for clarity. Selected
bond distances (Å) and angles (deg): Pt1–C1 2.054(7), Pt1–O1 2.086(6), Pt1–P2
2.263(2), Pt1–P1 2.270(2), P2–Pt1–P1 166.61(7).
Scheme 4.
Interestingly, the 31P spectrum also shows the presence of long-
range platinum satellites with a 3J coupling constant of ca 32 Hz;
with poor decoupling all peaks broaden and the satellites can eas-
ily be mistaken for a triplet, which would indicate the presence of
two equivalent hydrides. Integration also supports the formulation
of a monohydride. The Pt–Pt distance is 2.913(1) Å, which is in the
lower range compared to similar complexes indicating the pres-
ence of some metal–metal interaction [21]. The dimerisation could
be triggered by the lower solubility of the dimer [22].
In conclusion we have been able to show that with a (PCP) plat-
inum framework the tert-butoxide complex is unattainable proba-
bly for steric reason but the corresponding methoxide complex can
After removal of
6 by filtration, the remaining solution
contained a single product which was isolated in 71% yield and
Fig. 4. DIAMOND drawing of 8. Hydrogen atoms are omitted for clarity. Selected bond distances (Å).

A. Arunachalampillai et al. / Polyhedron 32 (2012) 24–29
29
[5] (a) J.R. Fulton, A.W. Holland, D.J. Fox, R.G. Bergman, Acc. Chem. Res. 35 (2002)
44;
(b) C.M. Fafard, O.V. Ozerov, Inorg. Chim. Acta 360 (2007) 286;
(c) N.A. Smythe, K.A. Grice, B.S. Williams, K.I. Goldberg, Organometallics 28
(2009) 277;
(d) I. Matas, J. Cámpora, P. Palma, E. Álvarez, Organometallics 28 (2009) 6515.
[6] (a) D.J. Darensbourg, K.M. Sanchez, A.L. Rheingold, J. Am. Chem. Soc. 109
(1987) 290;
(b) D.J. Darensbourg, W.-Z. Lee, A.L. Phelps, E. Guidry, Organometallics 22
(2003) 5585;
(c) H. Yasuda, J.C. Choi, S.-C. Lee, T. Sakakura, Organometallics 21 (2002) 1216;
(d) D.S. Glueck, L.J.N. Winslow, R.G. Bergman, Organometallics 10 (1991) 1462.
[7] (a) S. Park, Bull. Korean Chem. Soc. 22 (2001) 1410;
(b) J. Cámpora, I. Matas, P. Palma, E. Álvarez, C. Graiff, A. Tiripicchio,
Organometallics 26 (2007) 3840.
[8] B.J. Burger, J.E. Bercaw, in: A. Wayda, M.Y. Darensbourg (Eds.), New
Developments in the Synthesis, Manipulation and Characterization of
Organometallic Compounds, vol. 357, American Chemical Society,
Washington, DC, 1987.
[9] A. Athimoolam, M.T. Johnson, O.F. Wendt, Organometallics 27 (2008) 4541.
[10] (a) M.A. Bennett, H. Jin, A.C. Willis, J. Organomet. Chem. 451 (1993) 249;
(b) S. Fischer, O.F. Wendt, Acta Cryst. E60 (2004) m69.
[11] (a) F. Gorla, L.M. Venanzi, A. Albinati, Organometallics 13 (1994) 43;
(b) H. Rimml, L.M. Venanzi, J. Organomet. Chem. 259 (1983) C6;
(c) J.M. Seul, S. Park, J. Chem. Soc., Dalton Trans. (2002) 1153.
[12] Crysalis CCD, Oxford Diffraction Ltd. Abingdon, Oxfordshire, UK, 2005.
[13] Crysalis RED, Oxford Diffraction Ltd. Abingdon, Oxfordshire, UK, 2005.
[14] G.M. Sheldrick, Acta Cryst. A64 (2008) 112.
Scheme 5.
be synthesised together with a small amount of metal hydride
complex. The methoxide readily undergoes insertion to form a
methyl carbonate complex. The functionalisation of the platina
carbonate is the subject of on-going investigations.
Acknowledgement
Financial support from the Swedish Research Council, the Crafo-
ord Foundation, the Knut and Alice Wallenberg Foundation and the
Royal Physiographic Society in Lund is gratefully acknowledged.
[15] A.L. Spek, Acta Cryst. D65 (2009) 148.
[16] (a) R.D. Simpson, R.G. Bergman, Angew. Chem. Int. Ed. Engl. 31 (1992) 220;
(b) P.L. Holland, R.A. Andersen, R.G. Bergman, J. Huang, S.P. Nolan, J. Am.
Chem. Soc. 119 (1997) 12800;
Appendix A. Supplementary data
(c) J. Cámpora, I. Matas, P. Palma, C. Graiff, A. Tiripicchio, Organometallics 24
(2005) 2827.
[17] H.E. Bryndza, W. Tam, Chem. Rev. 88 (1988) 1163.
[18] (a) R.P. Hughes, A.J. Ward, J.A. Golen, C.D. Incarvito, A.L. Rheingold, L.N.
Zakharov, Dalton Trans. (2004) 2720;
(b) C. Scriban, D.S. Glueck, J.A. Golen, A.L. Rheingold, Organometallics 26
(2007) 1788;
(c) J.J. Adams, N. Arulsamy, D.M. Roddick, Organometallics 28 (2009) 1148.
[19] G.A. Lawrance, Chem. Rev. 86 (1986) 17.
CCDC 778661–778664 contains the supplementary crystallo-
graphic data for compounds 5, 6, 7 and 8. These data can be ob-
tained free of charge via http://www.ccdc.cam.ac.uk/conts/
retrieving.html, or from the Cambridge Crystallographic Data Cen-
tre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223-336-
033; or e-mail: deposit@ccdc.cam.ac.uk.
[20] J.F. Hartwig, Organotransition Metal Chemistry–From Bonding to Catalysis,
University Science Books, Sausolito, CA, 2010. p. 402.
References
[21] A. Albinati, S. Chaloupka, J. Eckert, L.M. Venanzi, M.K. Wolfer, Inorg. Chim. Acta
259 (1997) 305 (See also ref 18c).
[22] This has been observed for (PCP) iridium nitrogen complexes: R. Ghosh, M.
Kanzelberger, T.J. Emge, G.S. Hall, A.S. Goldman, Organometallics 25 (2006)
5668.
[23] Platinum methoxides have been shown to undergo b-elimination already at
room temperature: see ref 17 and H.E. Bryndza, J.C. Calabrese, M. Marsi, D.C.
Roe, W. Tam, J.E. Bercaw, J. Am. Chem. Soc. 108 (1986) 4805.
[24] G.R. Desiraju, T. Steiner, The Weak Hydrogen Bond In Structural Chemistry and
Biology; IUCr Monographs on Crystallography 9, Oxford University Press, New
York, 1999.
[1] (a) S.N. Riduan, Y. Zhang, Dalton Trans. 39 (2010) 3347;
(b) T. Sakakura, K. Kohno, Chem. Comm. (2009) 1312;
(c) T. Sakakura, J.-C. Choi, H. Yasuda, Chem. Rev. 107 (2007) 2365.
[2] (a) D.J. Darensbourg, Chem. Rev. 107 (2007) 2388;
(b) G.W. Coates, D.R. Moore, Angew. Chem. Int. Ed. 43 (2004) 6018.
[3] (a) T. Sakakura, Y. Saito, M. Okano, J.-C. Choi, T. Sako, J. Org. Chem. 63 (1998)
7095;
(b) A. Dibenedetto, C. Pastore, M. Aresta, Catal. Today 115 (2006) 88;
(c) M. Aresta, A. Dibenedetto, C. Pastore, Inorg. Chem. 42 (2003) 3256 (For a
review see ref 1(b) or (c)).
[25] For a platinum methyl carbonate structure, see: A. Immirzi, A. Musco, Inorg.
Chim. Acta 22 (1977) L35.
[26] (a) S.M. Mandal, D.M. Ho, M. Orchin, Organometallics 12 (1993) 1714;
(b) L. Ferro, P.B. Hitchcock, M.P. Coles, H. Cox, R.J. Fulton, Inorg. Chem. 50
(2011) 1879.
[4] (a) R. Johansson, M. Jarenmark, O.F. Wendt, Organometallics 24 (2005) 4500;
(b) R. Johansson, O.F. Wendt, Dalton Trans. (2007) 488;
(c) R. Johansson, O.F. Wendt, Organometallics 26 (2007) 2426;
(d) M.T. Johnson, R. Johansson, M.V. Kondrashov, G. Steyl, M.S.G. Ahlquist, A.
Roodt, O.F. Wendt, Organometallics 29 (2010) 3521.