Synthesis and structural characterization of an authentic platinum(IV) carbonyl compound

Article abstract of DOI:10.1021/om970651c

The oxidative addition of Br₂ to [NBu₄]₂[Pt-(C₆F₅)₄] followed by halide extraction with AgClO₄ in the presence of CO gave [NBu₄][trans-Pt^IV(C₆F

Full text of DOI:10.1021/om970651c

6024
Organometallics 1997, 16, 6024-6027
Syn th esis a n d Str u ctu r a l Ch a r a cter iza tion of a n
Au th en tic P la tin u m (IV) Ca r bon yl Com p ou n d
J uan Fornie´s,* Miguel A. Go´mez-Saso, Antonio Mart´ın, Francisco Mart´ınez,
Babil Menjo´n, and J avier Navarrete
Departamento de Qu´ımica Inorga´nica, Instituto de Ciencia de Materiales de Arago´n,
Universidad de Zaragoza-Consejo Superior de Investigaciones Cient´ıficas,
E-50009 Zaragoza, Spain
Received J uly 29, 1997X
Summary: The oxidative addition of Br2 to [NBu4]2[Pt-
(C6F5)4] followed by halide extraction with AgClO4 in the
presence of CO gave [NBu4][trans-PtIV(C6F5)4Br(CO)],
the first Pt(IV) carbonyl derivative to be structurally
characterized. It is demonstrated that the previously
reported [NEt4][PtBr3H2(CO)] complex is, in fact, the Pt-
(II) derivative [NEt4][PtBr3(CO)].
tion state.8,9 For a given metal the availability of
electron density decreases as its oxidation state in-
creases, and this trend is normally evidenced by an
increase in ν(CO) values.
The first reported metal carbonyl compound was the
Pt(II) derivative [Pt2(µ-Cl)2Cl2(CO)2].10 Since then many
carbonyl compounds of platinum in a oxidation state of
II or lower have been described,11 whereas only a few
Pt(IV) carbonyl compounds have been reported.12-16
This latter category comprises a series of hydridos
carbonyl derivatives of Pt(IV),14 including the structur-
ally characterized15 complex [NEt4][PtBr3H2(CO)]. In
In tr od u ction
Carbon monoxide is one of the most common and
useful ligands in organotransition metal chemistry.1 Its
ability to bind to low-valent metals was at first puzzling,
although it could be satisfactorily explained by postulat-
ing the existence of a synergic bond with two compo-
nents: carbon-to-metal σ-donation and metal-to-carbon
π-back-donation.2,3 For a long time, this bonding model
was found to apply to almost every stable metal carbonyl
compound, and as a result of this, the idea emerged that
π-back-donation was needed for metal carbonyls to be
stable. This idea is, however, not upheld as an increas-
ing number of metal carbonyl compounds in which CO
acts as a mainly σ-donor ligand4 are being reported.
These examples appear when the electrons of the metal
center are unavailable for π-back-bonding with CO, as
is the case, for instance, in d0 metal ions6,7 or in late-
and post-transition metals in a medium-to-high oxida-
(7) In some instances, the appreciable population of the CO π* MO
in carbonyl d0 group
4 metal complexes has been attributed to
electronic interaction with neighboring ligands, see: Procopio, L. J .;
Carroll, P. J .; Berry, D. H. Polyhedron 1995, 14, 45-55. Howard, W.
A.; Parkin, G.; Rheingold, A. L. Polyhedron 1995, 14, 25-44. Guo, Z.;
Swenson, D. C.; Guram, A. S.; J ordan, A. F. Organometallics 1994,
13, 766-773. Antonelli, D. M.; Tjaden, E. B.; Stryker, J . M. Organo-
metallics 1994, 13, 763-765. Howard, W. A.; Trnka, T. M.; Parkin, G.
Organometallics 1995, 14, 4037-4039.
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Bodenbinder, M.; Bach, C.; Willner, H. Eur. J . Solid State Inorg. Chem.
1996, 33, 917-930. Aubke, F. J . Fluorine Chem. 1995, 72, 195-201.
Aubke, F.; Wang, C. Coord. Chem. Rev. 1994, 137, 483-524. Weber,
L. Angew. Chem. 1994, 106, 1131; Angew. Chem., Int. Ed. Engl. 1994,
33, 1077-1078.
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F. Angew. Chem. 1996, 108, 2104-2106; Angew. Chem., Int. Ed. Engl.
1996, 35, 1974-1976. Dias, H. V. R.; J in, W. C. Inorg. Chem. 1996,
35, 3687-3694. Wang, C. Q.; Lewis, A. R.; Batchelor, R. J .; Einstein,
F. W. B.; Willner, H.; Aubke, F. Inorg. Chem. 1996, 35, 1279-1285.
Rack, J . J .; Webb, J . D.; Strauss, S. H. Inorg. Chem. 1996, 35, 277-
278. Bodenbinder, M.; Balzerjollenbeck, G.; Willner, H.; Batchelor, R.
J .; Einstein, F. W. B.; Wang, C.; Aubke, F. Inorg. Chem. 1996, 35, 82-
92. Dias, H. V. R.; J in, W. J . Am. Chem. Soc. 1995, 117, 11381-11382.
Dias, H. V. R.; Lu, H.-L. Inorg. Chem. 1995, 34, 5380-5382. Wang, C.
Q.; Bley, B.; Balzerjollenbeck, G.; Lewis, A. R.; Siu, S. C.; Willner, H.;
Aubke, F. J . Chem. Soc., Chem. Commun. 1995, 2071-2072. Hulburt,
P. K.; Rack, J . J .; Luck, J . S.; Dec, S. F.; Webb, J . D.; Anderson, O. P.;
Strauss, S. H. J . Am. Chem. Soc. 1994, 116, 10003-10014.
(10) Schu¨tzenberger, P. Ann. Chim. Phys. (Paris) 1868, 15, 100-
106. Schu¨tzenberger, P. Bull. Soc. Chim. Fr. 1868, 10, 188-192.
(11) Cross, R. J . In Comprehensive Organometallic Chemistry II;
Abel, E. W., Stone, F. G. A., Wilkinson, G., Eds.; Elsevier Science
Ltd.: Oxford, U.K., 1995; Vol. 9, Section 7.1, pp 392-411. Hartley, F.
R. In Comprehensive Organometallic Chemistry; Wilkinson, G., Stone,
F. G. A., Abel, E. W., Eds.; Pergamon Press: Oxford, U.K., 1982; Vol.
6, Section 39.1, pp 474-494.
X Abstract published in Advance ACS Abstracts, December 1, 1997.
(1) Bates, R. W. In Comprehensive Organometallic Chemistry II;
Abel, E. W., Stone, F. G. A., Wilkinson, G., Eds.; Elsevier Science
Ltd.: Oxford, U.K., 1995; Vol. 12, Chapter 4, pp 349-386. Elschenb-
roich, C.; Salzer, A. Organometallics, 2nd ed.; VCH: Weinheim,
Germany, 1992; Section 14.5, pp 220-238. Pruchnik, F. P. Organo-
metallic Chemisty of the Transition Elements; Plenum Press: New York
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Inorganic Chemistry, 5th ed.; J ohn Wiley & Sons: New York, 1988;
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3.6.a, pp 110-117.
(2) Mingos, D. M. P. In Comprehensive Organometallic Chemistry;
Wilkinson, G., Stone, F. G. A., Abel, E. W., Eds.; Pergamon Press:
Oxford, U.K., 1982; Vol. 3, Section 19.2, pp 2-27. Braterman, P. S. In
Structure and Bonding; Springer: Berlin, Germany, 1972; Vol. 10, pp
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J .; Williams, A. A. J . Chem. Soc. 1954, 4403-4411.
(3) The multiple character of the M-C bond in metal carbonyl
compounds had already been suggested much earlier, see: Gilliland,
W. L.; Blanchard, A. A. J . Am. Chem. Soc. 1926, 48, 410-420. Pauling,
L. The Nature of the Chemical Bond; Cornell University Press: Ithaca,
NY, 1939.
(4) Lynn, M. A.; Bursten, B. E. Inorg. Chim. Acta 1995, 229, 437-
443. See, however, ref 5.
(5) High ν(CtO) and associated FCO values in cationic and neutral
“non-classical” metal carbonyls have alternatively been interpreted in
terms of electrostatic effects, see: Goldman, A. S.; Krogh-J espersen,
K. J . Am. Chem. Soc. 1996, 118, 12159-12166. These authors conclude
that “the magnitude of σ-bonding has a negligible effect on FCO”.
(6) Selg, P.; Britzinger, H. H.; Andersen, R. A.; Horva´th, I. T. Angew.
Chem. 1995, 107, 877; Angew. Chem., Int. Ed. Engl. 1995, 34, 791-
793.
(12) Dell’Amico, D. B.; Calderazzo, F.; Marchetti, F.; Merlino, S. J .
Chem. Soc., Dalton Trans. 1982, 2257-2260.
(13) (a) Crocker, C.; Goggin, P. L.; Goodfellow, R. J . Chem. Soc.,
Chem. Commun. 1978, 1056-1057. (b) King, R. B.; Bond, A. J . Am.
Chem. Soc. 1974, 96, 1338-1343.
(14) (a) Rachkovskaya, L. N.; Eremenko, N. K.; Matveev, K. I. Russ.
J . Inorg. Chem. 1972, 17, 1173-1175. (b) Rachkovskaya, L. N.;
Eremenko, N. K.; Matveev, K. I. Dokl. Akad. Nauk SSSR 1970, 190,
1396-1398; Chem. Abstr. 1970, 72, 139098t. (c) Rachkovskaya, L. N.;
Eremenko, N. K.; Matveev, K. I. Izv. Sib. Otd. Akad. Nauk SSSR, Ser.
Khim. Nauk 1970, 5, 78-84; Chem. Abstr. 1971, 74, 60302n.
(15) Mironov, Yu. I.; Plyasova, L. M.; Bakakin, V. V. Kristallografiya
1974, 19, 511-515; Chem. Abstr. 1974, 81, 42541e.
(16) (a) Scott, J . D.; Puddephatt, R. J . Organometallics 1986, 5,
1253-1257. (b) Gillard, R. D.; Pilbrow, M. F. Polyhedron 1982, 1, 689-
692.
S0276-7333(97)00651-1 CCC: $14.00 © 1997 American Chemical Society

Notes
Organometallics, Vol. 16, No. 26, 1997 6025
yield). Anal. Found (Calcd for C41H36BrF20NOPt): C, 40.07
this paper, we demonstrate that the latter complex is,
in fact, the Pt(II) carbonyl compound [NEt4][PtBr3(CO)].
Moreover, we also report on the synthesis and first
structural characterization of an authentic Pt(IV) car-
bonyl compound which contains a mainly σ-donor CO
ligand.
(40.57); H, 2.92 (2.99); N, 1.81 (1.15). IR (Nujol): ν(CtO) )
2166 cm-1 19F NMR (282.2 MHz, CDCl3, 20 °C): δ ) -110.0
.
(3J (195Pt,F) ) 130 Hz, 4 F, o-F), -115.3 (3J (195Pt,F) ) 77 Hz, 4
F, o-F), -160.2 (4 F, p-F), -163.1 (4 F, m-F), -164.2 (4 F, m-F).
Crystals suitable for X-ray diffraction analysis were ob-
tained by slow diffusion of a layer of n-hexane (20 mL) into a
solution of 30 mg of 2 in 5 mL of CH2Cl2 at -30 °C.
Exp er im en ta l Section
Cr yst a l Da t a a n d Da t a Collect ion P a r a m et er s.
Methods for preparing K2[PtCl6]17 and [NBu4]2[Pt(C6F5)4]18
as well as the instrumentation19 used to characterize com-
plexes 1 and 2 have been published elsewhere.
C
42.25H38.5BrCl2.5F20NOPt, Mw ) 1319.8, triclinic, a ) 12.304-
(13) Å, b ) 13.265(14) Å, c ) 16.79(2) Å, R ) 89.1(1)°, â )
68.20(9)°, γ ) 83.36(8)°, U ) 2526.39 Å3 (by least-squares
refinement on diffractometer angles for 36 centered reflections
in the range 15° < 2θ < 22°), T ) 200 K, space group P1h,
graphite-monochromated Mo KR radiation, λ ) 0.710 73 Å, Z
) 2, Dc ) 1.59 g cm-3, F(000) ) 1336, colorless with dimensions
of 0.3 × 0.2 × 0.2 mm, µ(Mo KR) ) 36.7 cm-1, semiempirical
absorption correction based on ψ scans, transmission factors
0.3369-0.5204; Siemens STOE/AE2 four-circle diffractometer,
ω-θ scans, data collection range 4.0° < 2θ < 48.0°, +h, (k,
(l, three standard reflections showed no significant variation
P r ep a r a tion of [NEt4][P tBr 3(CO)] (1). Method a. The
procedure to prepare [NEt4][PtBr3H2(CO)] was repeated as
reported in ref 14a. The product obtained was identified as
1. Method b. A suspension of K2[PtCl6] (0.675 g, 1.388 mmol)
in a mixture of 90% formic acid (15 mL) and concentrated
hydrobromic acid (5 mL) also containing NEt4Br (0.624 g, 2.97
mmol) was refluxed until it became a clear, yellow solution
(ca. 4 h). Then the solution was evaporated, and the yellow
solid formed was filtered, washed with small amounts (3 mL
each) of cool water, 2-PrOH, and Et2O, and eventually dried
(0.772 g, 94% yield). Anal. Found (Calcd for C9H20Br3NOPt):
C, 17.97 (18.23); H, 3.31 (3.40); N, 2.28 (2.36). IR (Nujol): ν-
(CtO) 2088 cm-1. MS (FAB-): m/ z 460 [PtBr3(CO)]-.
Crystals suitable for X-ray diffraction analysis were ob-
tained by slow diffusion of a layer of n-hexane (20 mL) into a
solution of 25 mg of 1 in 5 mL of CH2Cl2 at 5 °C.
in intensity; 8347 reflections measured, 7926 unique (Rint
0.0514) giving 3361 data with F > 5.0σ(F).
)
Str u ctu r e Solu tion a n d Refin em en t. The structure was
solved and developed by Patterson and Fourier methods
(program SHELXTL-PLUS).21 All non-hydrogen atoms except
the solvent atoms (CH2Cl2) were assigned anisotropic displace-
ment parameters. Four atomic sites in an interstitial zone
were modeled as a pair of partially occupied disordered CH2-
Cl2 molecules. A common isotropic displacement parameter
was refined for the two Cl atoms of each disordered CH2Cl2
moiety. Loose restraints to equality were applied to the C-Cl
distances and Cl-C-Cl angles in only one of the solvent
molecules. The data-to-parameter ratio in the final refinement
Cr ysta l Da ta a n d Da ta Collection P a r a m eter s. C9H20
-
Br3NOPt, Mw ) 593.08, triclinic, a ) 7.300(5) Å, b ) 9.236(6)
Å, c ) 11.625(8) Å, R ) 88.32(6)°, â ) 88.23(2)°, γ ) 82.28(8)°,
U ) 776.0(9) Å3 (by least-squares refinement on diffractometer
angles from 72 centered reflections, including Friedel pairs,
20.6° < 2θ < 34.9°), T ) 173(1) K, space group P1h, graphite-
monochromated Mo KR radiation, λ ) 0.710 73 Å, Z ) 2, Dc )
2.538 g cm-3, F(000) ) 544, yellow; approximate crystal
was 5.5. The weighting scheme was w ) [σ2(F) + 0.004056F2]-1
.
The final wR2 was 0.0569, with conventional R ) 0.0553 (R
factors defined in ref 21), for 605 parameters, gof ) 1.0791,
max ∆/σ ) 0.002, max ∆F ) 1.18 e Å-3 (-1.38 e Å-3).
dimensions of 0.27 × 0.23 × 0.20 mm; µ(Mo KR) ) 167.4 cm-1
,
semiempirical absorption correction based on ψ scans, trans-
mission factors 0.356-0.263; Siemens STOE/AE2 four-circle
diffractometer, ω/θ scans, data collection range 1.75° < θ <
24.99°, +h, (k, (l, three standard reflections showed no
significant variation in intensity; 2901 reflections measured,
2667 unique (Rint ) 0.0216) which were used in all calculations.
Str u ctu r e Solu tion a n d Refin em en t. The structure was
solved by Patterson and Fourier methods and refined aniso-
tropically by full-matrix least squares on F2 (program SHELXL
93).20 Hydrogen atoms were included using a riding model or
as rigid methyl groups. The weighting scheme was w ) [σ2-
(Fo2) + (0.057P)2]-1, where P ) 1/3[max{Fo2,0} + 2Fc2]. The
final wR2(F2) was 0.0878, with conventional R(F) 0.0375 (R
factors defined in ref 20), for 140 parameters, gof ) 1.096, max
∆/σ ) 0.001, max ∆F ) 1.14 e Å-3 (-2.39 e Å-3) located at less
than 1.39 Å from the platinum atom.
Resu lts a n d Discu ssion
It had been reported that the carbonylation of K2-
[PtCl4] in dilute hydrochloric or hydrobromic solutions
gave [Pt(CO)2]n,22 whose treatment with an excess of
Fe2(SO4)3 resulted in formation of hydridocarbonyl
complexes of formula PtX2H2(CO), where X ) Cl or Br.14
The analogous iodo-derivative was prepared by treating
PtCl2H2(CO) with an excess of KI.14a These neutral
species take up one further equivalent of X-, yielding
the corresponding anions [PtX3H2(CO)]-.14 The formu-
lation of these compounds relied mainly on analytical
and IR spectroscopic data, except for complex [NEt4]-
[PtBr3H2(CO)] which was also studied by X-ray diffrac-
tion methods.15 There are, however, a number of
anomalous features associated with the IR data:14 (1)
the ν(CO) values are too low, considering the high
oxidation state of the metal center; (2) with the excep-
tion of X ) Cl, the ν(CO) shifts observed on going from
the neutral to the anionic species are the opposite of
what would be expected for an increase in negative
charge; and (3) one of the given ν(Pt-H) absorptions
appears to invariably coincide with the ν(CO) band,
regardless of the global charge and of the nature of X.
P r ep a r a tion of [NBu 4][tr a n s-P t(C6F 5)4Br (CO)] (2). Br2
(0.3 mmol) in CCl4 was added to a CH2Cl2 (15 mL) solution of
[NBu4]2[Pt(C6F5)4] (400 mg, 0.297 mmol) at -60 °C. After 15
min, AgClO4 (62 mg, 0.3 mmol) was added and a slow stream
of CO was passed through the suspension while the temper-
ature was allowed to rise to 0 °C. The suspension then was
filtered, and the filtrate was concentrated to ca. 3 mL. By
adding cold 2-PrOH, a white solid was obtained, which was
filtered and washed with 2-PrOH and n-hexane (54 mg, 15%
(17) Grube, H.-L. In Handbuch der Pra¨parativen Anorganischen
Chemie, 3rd ed.; Brauer, G., Ed.; Ferdinand Enke: Stuttgart, Germany
1981; Vol. 3, p 1712.
(18) Uso´n, R.; Fornie´s, J .; Mart´ınez, F.; Toma´s, M. J . Chem. Soc.,
Dalton Trans. 1980, 888-894.
(21) The X-ray diffraction data were processed on a local area VAX
cluster (VMS V5.5-2) with the commercial package SHELXTL-PLUS,
Release 4.21/V, Siemens Analytical X-ray Instruments, Inc., Madison,
WI, 1990.
(22) Matveev, K. I.; Rachkovskaya, L. N.; Eremenko, N. K. Izv. Sib.
Otd. Akad. Nauk SSSR, Ser. Khim. Nauk 1968, 81-87; Chem. Abstr.
1968, 69, 92505u.
(19) Fornie´s, J .; Menjo´n, B.; Sanz-Carrillo, R. M.; Toma´s, M.;
Connelly, N.; Crossley, J . G.; Orpen, A. G. J . Am. Chem. Soc. 1995,
117, 4295-4304.
(20) Sheldrick, G. M. SHELXL-93 Program for the Refinement of
Crystal Structures from Diffraction Data; University of Go¨ttingen:
Go¨ttingen, Germany 1993.

6026 Organometallics, Vol. 16, No. 26, 1997
Notes
Ta ble 1. Com p a r a tive IR Vibr a tion a l Da ta (in
cm -1) of Som e Ha loca r bon yl Com p lexes of
P la tin u m
Ta ble 2. Com p a r a tive Cr ysta l P a r a m eter s of
Br om oca r bon ylp la tin a te Der iva tives
[NEt4][PtIVBr3H2(CO)]a
[NEt4][PtIIBr3(CO)]b
ν(CtO)
X ) Cl X ) Br X ) I X ) Cl X ) Br X ) I
ν(Pt-H)a/ν(13CtO)b
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
Z
9.44(2)
11.92(3)
7.58(2)
90.0(5)
98.2(5)
90.0(5)
2
7.300(5)
9.236(6)
11.625(8)
88.32(6)
88.23(2)
82.28(8)
2
[PtIVX3H2(CO)]-,a 2100
2090
2080 2055
2035 2025
2043 2029
[PtIIX3(CO)]-,b
[PtIVX2H2(CO)]a
[PtII2X4(CO)2]c
2096.5 2089.5 2078 2050
2125
2146
2085
2135
2050
2109
a
b
See ref 14a. See ref 26. c See ref 32.
space group
P1h
P1h
a
b
See ref 15. This work.
These anomalies led us to question both the oxidation
state assigned to the Pt center and the presence of
hydride ligands in those complexes. We, therefore,
decided to check the formulation of the best character-
ized compound of that family, i.e., [NEt4][PtBr3H2(CO)]
for which the X-ray structure had also been reported.
However, X-ray diffraction is not the most suitable
technique for unambiguously detecting and locating
hydride substituents in metal complexes.23 For hydride
location by X-ray diffraction to be reasonably reliable,
good quality crystals and careful data collection (prefer-
ably at low temperature) are generally required.24 The
X-ray diffraction analysis of [NEt4][PtBr3H2(CO)] gave
large esd values, even in the cell parameters and a final
R ) 0.105.15 Hence, the statement that “the coordina-
tion of Pt atom in the complex anion is octahedral with
2 H atoms in trans-position” should be considered with
caution.
F igu r e 1. Thermal ellipsoid diagram of the anion of 1.
Ta ble 3. Selected In ter a tom ic Dista n ces (Å) a n d
An gles (d eg) for th e An ion of 1
Pt-Br(1)
Pt-Br(2)
Pt-Br(3)
2.444(2)
2.434(2)
2.432(2)
Pt-C(1)
C(1)-O
1.830(10)
1.159(12)
We have repeated the published synthesis of
[NEt4][PtIVBr3H2(CO)]14a and have obtained a solid
sample with the following spectroscopic properties: (1)
the IR spectrum is identical to that of a sample of
[NEt4][PtIIBr3(CO)] (1);25 the absorption originally at-
tributed to a ν(Pt-H) mode is indeed very weak and
can be assigned to the ν(13CO) vibration26 (Table 1). (2)
The 1H NMR spectrum does not contain any hydride
signal, at least in the range registered (+10 to -30
ppm). (3) The chemical shift of the 195Pt NMR signal
coincides with that reported for [PtIIBr3(CO)]-;27 more-
over, the signal appears as a singlet instead of as the
triplet expected for a dihydride species. Additionally,
the X-ray crystal structure was redetermined, giving cell
parameters which are virtually identical to those previ-
ously reported for [NEt4][PtIVBr3H2(CO)],15 as shown in
Table 2. When comparing the two sets of parameters,
the different choice of cell axes in each case should be
noted. An ellipsoid drawing of the anion of 1 is given
in Figure 1, and a selection of bond distances and angles
is shown in Table 3. The Pt(II) center is in the usual
square-planar environment with all four angles between
adjacent substituents very close to the ideal 90° value.
The Pt-Br distances are very similar, regardless of the
different trans influence that would be expected for the
Br(1)-Pt-Br(2)
Br(2)-Pt-Br(3)
Br(1)-Pt-C(1)
Br(3)-Pt-C(1)
90.72(7)
90.46(7)
90.0(3)
89.0(3)
Br(1)-Pt-Br(3)
Br(2)-Pt-C(1)
Pt-C(1)-O
176.93(4)
175.7(3)
177.7(8)
Br- and CO ligands.28 These Pt-Br distances do not
significantly deviate from the mean value reported for
terminal Pt-Br bonds in four-coordinate Pt(II) com-
plexes (2.438 Å).29 The Pt-C(1)-O unit is almost linear
(174(2)°), and the Pt-C(1) distance (1.830(10) Å) is in
the range of Pt-CO distances observed in four-coordi-
nate carbonyl derivatives of Pt(II) (1.75-1.98 Å).30 The
C(1)-O distance (1.159(12) Å) is near to the upper end
of the corresponding range of CtO distances in the
same kind of complexes (1.06-1.18 Å).30 All of the
distances and angles in [NEt4][PtIIBr3(CO)] (1) are
similar to those reported for [NEt4][PtIVBr3H2(CO)]. It
might be argued that the small size of the hydride
ligands and their presumed trans arrangement in the
latter compound could be responsible for these negligible
structural differences. However, the presence of hydride
ligands can be ruled out on the basis of spectroscopic
data (see above). Thus, it can be concluded that the
(28) Appleton, T. G.; Clark, H. C.; Manzer, L. E. Coord. Chem. Rev.
1973, 10, 335-422.
(29) Orpen, A. G.; Brammer, L.; Allen, F. H.; Kennard, O.; Watson,
D. G.; Taylor, R. J . Chem. Soc., Dalton Trans. 1989, S1-S83.
(30) Data (34) were retrieved from the Cambridge Structural
Database (see ref 31). Upper value of PtII-CO distance (1.98 Å), see:
Hutton, A. H.; Shabanzaden, B.; Shaw, B. L. J . Chem. Soc., Chem.
Commun. 1983, 1053-1055. Lower value of PtII-CO distance (1.75
Å), see: Canziani, F.; Garlaschello, L.; Malatesta, M. C.; Albinati, A.
J . Chem. Soc., Dalton Trans. 1981, 2395-2404. Upper value of CtO
distance (1.18 Å), see: Berenguer, J . R.; Fornie´s, J .; Lalinde, E.;
Mart´ınez, F. Organometallics 1995, 14, 2532-2537. Lower value of
CtO distance (1.06 Å), see: Andreini, B. P.; Dell’Amico, D. B.;
Calderazzo, F.; Venturi, M. G.; Pelizzi, G.; Segre, A. J . Organomet.
Chem. 1988, 354, 357-368.
(23) Bau, R.; Teller, R. G.; Kirtley, S. W.; Koetzle, T. F. Acc. Chem.
Res. 1979, 12, 176-183. Ibers, J . A. In Transition Metal Hydrides; Bau,
R., Ed.; Advances in Chemistry Series No. 167; American Chemical
Society: Washington, DC, 1978; pp 26-35.
(24) Crabtree, R. H. In Comprehensive Coordination Chemistry;
Wilkinson, G., Gillard, R. D., McCleverty, J . A., Eds.; Pergamon
Press: Oxford, U.K., 1987; Vol. 2, Chapter 19, pp 689-714.
(25) A sample of 1 was obtained by
a one-pot synthesis (see
Experimental Section) which is a slight modification of the method
used to prepare Cs[PtBr3(CO)], see: Cleare, M. J .; Griffith, W. P. J .
Chem. Soc. A 1969, 372-380.
(26) Goggin, P. L.; Norton, M. G.; Mink, J . Inorg. Chim. Acta 1978,
26, 125-128.
(31) Allen, F. H.; Davies, J . E.; Galloy, J . J .; J ohnson, D.; Kennard,
O.; Macrae, C. F.; Mitchell, E. M.; Mitchell, G. F.; Smith, J . M.; Watson,
D. G. J . Chem. Inf. Comput. Sci. 1991, 31, 187-204.
(27) Boag, N. M.; Goggin, P. L.; Goodfellow, R. J .; Herbert, I. R. J .
Chem. Soc., Dalton Trans. 1983, 1101-1107.

Notes
Organometallics, Vol. 16, No. 26, 1997 6027
Ta ble 4. Selected In ter a tom ic Dista n ces (Å) a n d
An gles (d eg) for th e An ion of 2
Pt-C(1)
Pt-Br
Pt-C(2)
Pt-C(8)
1.91(3)
2.474(4)
2.10(2)
2.09(2)
Pt-C(14)
Pt-C(20)
C(1)-O
2.13(2)
2.11(2)
1.13(3)
Pt-C(1)-O
174(2)
93(1)
89.7(9)
86(1)
90.1(9)
89.8(8)
89.1(7)
89.1(6)
C(8)-Pt-C(14)
C(8)-Pt-Br
89.7(8)
89.1(6)
91.3(8)
91.0(7)
91.1(6)
177.0(8)
179.5(6)
178.9(7)
C(1)-Pt-C(2)
C(1)-Pt-C(8)
C(1)-Pt-C(14)
C(1)-Pt-C(20)
C(2)-Pt-C(8)
C(2)-Pt-C(20)
C(2)-Pt-Br
C(14)-Pt-C(20)
C(14)-Pt-Br
C(20)-Pt-Br
C(1)-Pt-Br
C(2)-Pt-C(14)
C(8)-Pt-C(20)
Pt-CO bond in 2 (PtIV-C(1) 1.92(3) Å) is appreciably
longer than that observed in 1 (PtII-C(1) 1.830(10) Å).
This elongation is consistent with the expected decrease
in the π-back contribution of the Pt-CO bond on going
from Pt(II) to Pt(IV). The C(1)-O distance in 2 (1.13-
(3) Å) is in turn very similar to that found in 1 (1.159-
(12) Å), which once again evidences the well-known low
sensitivity of the C-O distance to variations in multiple
bond order.35 The PtCO unit is almost linear (Pt-
C(1)-O 174(2)°), and the Pt-C6F5 distances are similar
to those found in other six-coordinate pentafluorophenyl
derivatives of Pt(IV).36
Metal carbonyl complexes in which the CO molecule
acts mainly as a σ-donor ligand are known to readily
undergo substitution reactions, and thus, only by the
careful use of very poor nucleophilic anions in supera-
cidic conditions have Aubke and co-workers been able
to prepare and isolate an interesting series of nonclas-
sical metal carbonyl derivatives.8,9 Complex 2 is rea-
sonably stable at room temperature in the solid state
and in solution. The global negative charge on the
complex as well as its saturated character (both elec-
tronic and coordinative) can contribute to the stability
of 2. The anion of 2 in solution has a remarkably static
behavior, as revealed by its 19F NMR spectrum which
shows a single resonance for the para-F atoms (δ )
-160.2 ppm) but two signals for each the ortho-F (δ )
-110.0 and -115.3 ppm) and the meta-F atoms (δ )
-163.1 and -164.2 ppm), thus implying that the rota-
tion of the C6F5 rings around the Pt-C bond is restricted
at room temperature. Given that at least in the solid
state (Figure 2) all four C6F5 groups are arranged
helically around the Br-Pt-CO axis (mean dihedral
angle ) 45°), it can be considered that they have a
protective effect on the Pt-bound CO ligand.
F igu r e 2. Thermal ellipsoid diagram of the anion of 2.
complex originally formulated as [NEt4][PtIVBr3H2(CO)]
is, in fact, the Pt(II) carbonyl compound [NEt4][PtIIBr3-
(CO)] (1). Considering the reported ν(CtO) and ν(Pt-
H) values (Table 1), we suggest that all the anions
[PtIVX3H2(CO)]- (X ) Cl, Br or I) should be formulated
as [PtIIX3(CO)]-. As a result, the nature of the parent,
neutral, “five-coordinate” species “PtIVX2H2(CO)” be-
comes more than dubious. Once again, the low ν(CO)
values reported for these species are inconsistent with
the high oxidation state suggested for the metal center
(Table 1).32 The same inconsistency is observed in other
neutral or even cationic Pt(IV) carbonyl derivatives
reported, namely the compounds fac-[PtIMe3(SMe2)-
16a
(CO)] (not isolated, ν(CtO) ) 2090 cm-1
)
and
[PtClIMe{CH(py)Et}(py)(CO)]+Cl- (isolated, ν(CtO) )
2060 cm-1),16b the formulation of which should, in our
opinion, be reconsidered. Higher ν(CO) values have, in
turn, been reported for [PtMe3{(C3H3N2)2BH2}(CO)],
which readily loses the CO molecule (not isolated, ν-
i
(CtO) ) 2125 cm-1),13b and for [NH2 Pr2][PtCl5(CO)]
(isolated, ν(CtO) ) 2191 cm-1).12
Considering its very high ν(CO) value, complex [NH2-
iPr2][PtCl5(CO)] appears to be the most firmly estab-
lished example of an isolated carbonyl derivative of Pt-
(IV). It has been obtained by oxidative addition of Cl2
i
to the substrate [NH2 Pr2][PtIICl3(CO)] in thionyl chlo-
ride solution.12 The new complex [NBu4][PtIV(C6F5)4-
Br(CO)] (2) has been prepared following a related
synthetic procedure: oxidative addition of Br2 to the Pt-
(II) substrate [NBu4]2[Pt(C6F5)4] followed by halide
extraction with AgClO4 in the presence of CO. The IR
spectrum of 2 shows a sharp ν(CO) absorption at 2166
cm-1. Given that this value is higher than that ob-
served for free CO (ν(CtO) ) 2143 cm-1),33 it follows
that the CO molecule in 2 is acting mainly as a σ-donor
ligand, as expected for carbonyl complexes of Pt(IV). The
crystal structure of 2 was determined by X-ray diffrac-
tion methods. An ellipsoid drawing of the anion [trans-
PtIV(C6F5)4Br(CO)]- appears in Figure 2. Selected bond
distances and angles are given in Table 4. The Pt(IV)
center is in the usual octahedral environment with the
Br- and CO ligands located in trans positions. The Pt-
Br distance (2.474(4) Å) is approximately the mean
value observed in anionic six-coordinate Pt(IV) com-
plexes containing terminal Pt-Br bonds (2.47 Å).34 The
Ack n ow led gm en t. We thank the Direccio´n General
de Ensen˜anza Superior for financial support (Grant No.
PB95-0003-C02-01) and Gobierno de Navarra for a
grant to M.A.G.-S.
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal-
lographic data, atomic parameters, anisotropic displacement
coefficients, and complete bond distances and angles for 1 and
2 (12 pages). Ordering information is given on any current
masthead page.
OM970651C
(34) Data (26) were retrieved from the Cambridge Structural
Database (see ref 31).
(32) Note that the ν(CO) frequencies reported for complexes [PtIVX2H2-
(CO)] (ref 14a) are lower even than the corresponding values of the
neutral Pt(II) derivatives [Pt2X4(CO)2], see: Malatesta, L.; Naldini, L.
Gazz. Chim. Ital. 1960, 90, 1505-1515.
(33) Nakamoto, K. Infrared and Raman Spectra of Inorganic and
Coordination Compounds, 4th ed.; J ohn Wiley & Sons: New York,
1986.
(35) Cotton, F. A.; Wing, R. M. Inorg. Chem. 1965, 4, 314-317.
(36) Casas, J . M.; Mart´ın, A.; Oliva, J .; Toma´s, M. Inorg. Chim. Acta
1995, 229, 291-298. Deacon, G. B.; Lawrenz, E. T.; Hambley, T. W.;
Rainone, S.; Webster, L. K. J . Organomet. Chem. 1995, 493, 205-213.
Fornie´s, J .; Fortun˜o, C.; Go´mez, M. A.; Menjo´n, B.; Herdtweck, E.
Organometallics 1993, 12, 4368-4375.