Synthesis and structure of alkynylplatinum(IV) complexes containing the pincer group [2,6-(dimethylaminomethyl)phenyl-N, C, N]-

Article abstract of DOI:10.1016/j.inoche.2004.11.001

An alkynyliodine(III) reagent IPh(CCSiMe₃)(O₃SCF ₃) reacts readily with Pt(O₂CAr)(NCN) to give Pt(O ₂CAr)(O₃SCF₃)(CCSiMe₃)(NCN), and addition of sodium iodide gives isolable Pt(O₂CAr)I(CCSiMe ₃)(NCN) as the first examples of alkynylplatinum(IV) 'pincer' complexes. Reaction of phenyl(trimethylsilylalkynyl)iodine(III) triflate with Pt^II(O₂CAr)(NCN) (Ar = Ph, 4-trifluoromethylphenyl (Ar_F); NCN = [C₆H₃(CH₂NMe ₂)₂-2,6]) at ambient temperature gives solutions of Pt^IV(O₂CAr)(OTf)(C≡CSiMe₃)(NCN) [Ar = Ph (1a); Ar = Ar_F (1b)]. Addition of sodium iodide (NaI) to 1 results in the isolation of Pt^IV(O₂CAr)I(C≡CSiMe ₃)(NCN) [Ar = Ph (2a); Ar = Ar_F (2b)] in >90% yields. In these first examples of alkynyl(pincer)platinum(IV) complexes, the pincer group is present as a mer-[NCN]^- tridentate donor and the alkynyl group is located cis to the pincer carbon donor, and the triflate (1a, 1b) and iodide groups (2a, 2b) are located trans to the pincer carbon; an X-ray structural analysis has been completed for 2b.

Full text of DOI:10.1016/j.inoche.2004.11.001

Inorganic Chemistry Communications 8 (2005) 55–57
www.elsevier.com/locate/inoche
Synthesis and structure of alkynylplatinum(IV)
complexes containing the pincer group
[2,6-(dimethylaminomethyl)phenyl-N,C,N]À
a,
a
b
b
Allan J. Canty *, Thomas Rodemann , Brian W. Skelton , Allan H. White
a
School of Chemistry, University of Tasmania, Private Bag 75, Hobart, TAS 7001, Australia
b
Chemistry M313, University of Western Australia, Crawley, WA 6009, Australia
Received 10 October 2004; accepted 1 November 2004
Abstract
Reaction of phenyl(trimethylsilylalkynyl)iodine(III) triflate with PtII(O2CAr)(NCN) (Ar = Ph, 4-trifluoromethylphenyl (ArF);
NCN = [C6H3(CH2NMe2)2-2,6]) at ambient temperature gives solutions of PtIV(O2CAr)(OTf)(C„CSiMe3)(NCN) [Ar = Ph (1a);
Ar = ArF (1b)]. Addition of sodium iodide (NaI) to 1 results in the isolation of PtIV(O2CAr)I(C„CSiMe3)(NCN) [Ar = Ph (2a);
Ar = ArF (2b)] in >90% yields. In these first examples of alkynyl(pincer)platinum(IV) complexes, the pincer group is present as a
mer-[NCN]À tridentate donor and the alkynyl group is located cis to the pincer carbon donor, and the triflate (1a, 1b) and iodide
groups (2a, 2b) are located trans to the pincer carbon; an X-ray structural analysis has been completed for 2b.
Ó 2004 Elsevier B.V. All rights reserved.
Keywords: Platinum(IV); Pincer; Intramolecular; Alkynyls; Iodonium; Iodine(III)
There is considerable current interest in alkynylplati-
num chemistry [1–4], including for complexes containing
intramolecularly coordinating tridentate groups as
ancillary ligands [5–10], in particular [NCN]À pincer
groups [5–9]. However, there is a limited range of re-
ported alkynylplatinum(IV) complexes [11–14], and
there are no reported examples of platinum(IV) com-
plexes containing [NCN]À pincer groups. The synthesis
of alkynyl(pincer)platinum(IV) complexes appears to
have been elusive, e.g. the alkynylplatinum(II) bond in
alkynyl(pincer)platinum(II) complexes is not stable to
halogen-containing oxidants [6]. Cyclic voltammetry
studies for this class of platinum(II) complex [6,7], and
related complexes [10], reveal irreversible oxidation pro-
cesses. We report here a convenient synthetic route to
alkynyl(pincer)platinum(IV) complexes employing a
readily obtained iodonium reagent [15] as oxidant to
transfer [C„CSiMe3]+ to a platinum(II) substrate con-
taining the archetypal pincer group [2,6-(dimethylami-
nomethyl)phenyl-N,C,N]À (NCN) [16].
1
Addition of IPh(C„CSiMe3)(O3SCF3) to Pt(O2
1,2
CAr)(NCN) [Ar = Ph, 4-CF3C6H4 (ArF)] in acetone
gave complexes 1a and 1b as yellow solutions and, on
1
The reagents IPh(C„CSiMe3)(OTf) [15] and Pt(O2CPh)(NCN)
[17] were prepared as reported.
2
Preparation of Pt(O2CArF)(NCN): silver 4-trifluoromethylbenzo-
ate (9.0 mg, 0.39 m mol) was added to a solution of PtCl(NCN) [18]
(16 mg, 0.38 m mol) in acetone (5 mL). The suspension was stirred for
15 h in the absence of light, then filtered through Celite. The solvent
was removed in a vacuum to give the product as a white solid (18 mg,
95%). 1H NMR (acetone-d6) (300 MHz): d 8.27 (d, 3J = 7.6 Hz, 2H,
H2), 7.71 (d, 3J = 7.6 Hz, 2H, H3), 6.93 (dd, 3J = 6.3, 8.4 Hz, 1H, H4–
*
Corresponding author. Tel.: +61 3 6226 2162; fax: +61 3 6226
3
3
NCN), 6.80 (d, J = 7.7 Hz, 2H, H3–NCN), 4.10 (s, JPt–H = 47.6 Hz,
3
4H, NCH2), 3.04 (s, JPt–H = 36.9 Hz, 12H, NCH3).
2858.
E-mail address: allan.canty@utas.edu.au (A.J. Canty).
1387-7003/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2004.11.001

56
A.J. Canty et al. / Inorganic Chemistry Communications 8 (2005) 55–57
addition of sodium iodide, complexes 2a and 2b were
isolated in 91% and 93% yield, respectively (Scheme
O2CAr
NMe2
Pt O2CAr
NMe2
NMe2
X
(i)
Pt
3
1). The isolated complexes have satisfactory micro-
NMe2
1
analyses (C, H, N), and 1a–2b exhibit H NMR spec-
4,5,6,7
tra
in accord with the configuration revealed by
SiMe3
the X-ray structural analysis for 2b, 8 e.g. two N-methyl
environments consistent with the presence of inequiva-
lent groups above and below the Pt(NCN) coordination
plane, and large 2J coupling for the geminal CH2
1a: Ar = Ph, X = OTf
1b: Ar = ArF, X = OTf
2a: Ar = Ph, X = I
(ii)
2b: Ar = ArF, X = I
groups. Infrared spectra of complexes 2a and 2b exhibit
m(C„C) of 2078 cmÀ1
6,7
.
Scheme 1. Synthesis of alkynyl(pincer)platinum(IV) complexes: (i)
IPh(C„CSiMe3)(O3SCF3), acetone, 30 min, 25 °C; (ii) NaI, acetone,
30 min, 25 °C.
In the solid state Pt(O2CArF)I(C„CSiMe3)(NCN)
(2b) has distorted octahedral coordination for platinum
3
(Fig. 1), based on a meridionally coordinated pincer
group, an iodo ligand trans to the pincer carbon donor,
and alkynyl and 4-trifluoromethylbenzoate groups ori-
ented mutually trans. One molecule devoid of crystallo-
graphic symmetry comprises the asymmetric unit. The
Typical synthesis, where solvents were dried and distilled, and all
procedures carried out under argon: phenyl[(trimethylsilyl)ethynyl]iod-
onium triflate (0.15 m mol) was added to a stirred solution of the
platinum(II) reagent (0.15 m mol) in acetone (10 ml) and stirring was
continued for another 30 min. For complexes 1a and 1b acetone-d6 was
also used as a solvent to allow NMR characterisation. Sodium iodide
(0.2 m mol) was added and the solution was stirred for a further 30
min. The solvent was removed in a vacuum and the residue was
extracted with a minimum amount of dichloromethane. The suspen-
sion was filtered and the solvent removed in a vacuum. The residue was
washed with a small amount of cold diethyl ether to give the product.
Crystals of 2b were obtained at 0 °C from a solution of the complex in
dichloromethane/diethyl ether.
˚
C(01)–C(02) distance, 1.205(4) A, appears to be a nor-
mal triple bond. As is often the case with tridentate
ligands of this type, the ligand is non-planar, with
quasi-two symmetry about the metal-central carbon
bond, the pendant C–N arrays twisting out of plane to
either side of the central aromatic ring. The aroate
plane lies quasi-normal to the C(01), O(11), N(21,61)
coordination plane (C2O2/CON2 interplanar dihedral,
89.1(1)°).
Reactions of alkynyliodine(III) species with soft
nucleophiles are believed to occur via Michael addition
to the electron-deficient b-carbon, followed by rear-
rangement to give the alkynyl group bonded to the
nucleophile [19]. Organoplatinum(II) species, including
pincer complexes, often act as nucleophiles, thus facili-
tating [C„CSiMe3]+ transfer. Syntheses of the new class
of complexes reported here occurs under mild condi-
tions, the exchange of triflate for other groups at the
platinum(IV) centre is facile, and the complexes isolated
are stable at ambient temperature. Thus, it is anticipated
that the synthetic protocol described herein provides the
basis for a wider investigation of alkynyl(pincer)plati-
num(IV) chemistry.
4
Pt(O2CPh)(OTf)(C„CSiMe3)(NCN) (1a). 1H NMR (acetone-d6)
(300 MHz): d 7.85 (d, 3J = 8.1 Hz, 2H, H2), 7.59–7.48 (m, 2H, H4, H4–
NCN), 7.45–7.36 (m, 2H, H3), 7.24 (d, 3J = 8.1 Hz, 2H, H3–NCN),
2
4.77 (d, J = 14.8 Hz, JPt–H = 30.4 Hz, 2H, NCH2), 4.61 (d, J = 14.8
3
2
3
Hz, JPt–H = 39.0 Hz, 2H, NCH2), 3.37 (s, JPt–H = 41.7 Hz, 6H,
3
3
NCH3), 2.97 (s, JPt–H = 24.3 Hz, 6H, NCH3), 0.08 (s, 9H, Si(CH3)3).
5
Pt(O2CArF)(OTf) (C„CSiMe3)(NCN) (1b). 1H NMR (acetone-
d6) (300 MHz): d 8.06 (d, 3J = 8.2 Hz, 2H, H2), 7.78–7.72 (m, 2H, H3),
7.40 (t, 3J = 7.5 Hz, 1H, H4–NCN), 7.24 (d, 3J = 7.8 Hz, 2H, H3–
NCN), 4.77 (d, 2J = 15.1 Hz, JPt–H = 33.0 Hz, 2H, NCH2), 4.62 (d,
3
2J = 15.1 Hz, JPt–H = 37.6 Hz, 2H, NCH2), 3.37 (s, JPt–H = 41.9 Hz,
3
3
3
6H, NCH3), 2.99 (s, JPt–H = 24.0 Hz, 6H, NCH3), 0.08 (s, 9H,
Si(CH3)3).
6
Pt(O2CPh)I(C„ CSiMe3)(NCN) (2a). 1H NMR (acetone-d6) (300
MHz): d 8.04 (d, 3J = 8.2 Hz, 2H, H2), 7.46–7.31 (m(b), 4H, H3, H4,
H4–NCN), 7.01 (d, 3J = 7.7 Hz, 2H, H3–NCN), 4.65 (d, 2J = 14.8 Hz,
3JPt–H = 33.1 Hz, 2H, NCH2), 4.40 (d, J = 14.8 Hz, JPt–H = 35.5 Hz,
2
3
3
3
2H, NCH2), 3.41 (s, JPt–H = 42.1 Hz, 6H, NCH3), 3.08 (s, JPt–
H = 26.4 Hz, 6H, NCH3), 0.08 (s, 9H, Si(CH3)3). IR (KBr disk): m
(C„C) 2078 cmÀ1
.
7
Pt(O2CArF)I(C„CSiMe3)(NCN) (2b). 1H NMR (acetone-d6)
(300 MHz): d 8.20 (d, 3J = 8.6 Hz, 2H, H2), 7.71 (d, 3J = 8.6 Hz,
2H, H3), 7.41 (t, 3J = 7.6 Hz, 1H, H4–NCN), 7.03 (d, 3J = 7.7 Hz, 2H,
H3–NCN), 4.67 (d, 2J = 14.8 Hz, JPt–H = 32.9 Hz, 2H, NCH2), 4.42
3
Acknowledgement
(d, 2J = 14.8 Hz, JPt–H = 35.2 Hz, 2H, NCH2), 3.41 (s, JPt–H = 42.0
3
3
3
Hz, 6H, NCH3), 3.08 (s, JPt–H = 25.9 Hz, 6H, NCH3), 0.08 (s, 9H,
We thank the Australian Research Council for finan-
cial support.
Si(CH3)3). IR (KBr disk): m (C„C) 2078 cmÀ1
Structure determination for 2b: C25H32F3IN2O2PtSi, M = 799.6,
.
8
ꢀ
triclinic, space group P1, a = 10.0061(6), b = 10.8050(7), c = 13.6912(9)
3
˚
˚
A, a = 85.450(1), b = 70.118(1), c = 89.947(1), V = 1387.1(2) A , Dc
(Z = 1) = 1.914 g cmÀ3, 27502 (=sphere); 2hmax = 75°) CCD diffrac-
tometer reflections (absorption corrected) reduced to 14219 unique
(Rint = 0.037), 12056 with F > 4r(F) being used in full-matrix least-
squares refinement (anisotropic displacement parameters for non-
Appendix A. Supplementary material
Crystallographic data has been deposited with the
Cambridge Crystallographic Data Centre (Deposition
No. 247684). Copies of the information can be obtained
hydrogen atoms, (x, y, z, Uiso)H constrained), R = 0.034, Rw (statistical
weights) = 0.073.

A.J. Canty et al. / Inorganic Chemistry Communications 8 (2005) 55–57
57
Fig. 1. Projection of a molecule of Pt(O2CArF)I(C„CSiMe3)(NCN) (1b), showing 50% displacement ellipsoids for the non-hydrogen atoms,
˚
˚
hydrogen atoms having arbitrary radii of 0.1 A. Selected bond lengths (A) and angles (°), Pt–C(1, 01)1.966(3), 1.951(3); Pt–N(21, 61) 2.136(3),
2.125(3); Pt–I 2.7469(3); Pt–O(11) 2.090(2); C(01)–C(02) 1.205(4); C(02)–Si(2) 1.828(3) and C(01)–Pt–C(1) 85.4(1); C(01)–Pt–N(21, 61) 93.5(1),
86.3(1); C(01)–Pt–O(11) 175.7(1); C(01)–Pt-I 90.83(9); Pt–C(01)–C(02) 172.7(3); C(01)–C(02)–Si(2) 165.4(3); C(1)–Pt–N(21, 61) 81.4(1), 81.1(1);
C(1)–Pt–O(11) 98.9(1); C(1)–Pt–I 176.09(8); I–Pt–N(21, 61) 97.92(8), 99.58(8); O(11)–Pt–N(21, 61) 87.3(1), 93.4(1); I–Pt–(O11) 84.86(7).
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