Solid-state structure of Tp'PtMe2H, a dimethylhydrido platinum(IV) complex

Article abstract of DOI:10.1021/ja960519o

The solid-state X-ray structure of Tp'PtMe₂H has been determined. This platinum(IV) hydride derivative is stable at room temperature and crystallizes in an orthorhombic cell (space group P(cmn), Z = 4, a = 8.1292(8) ?, b = 13.3862(9) ?, and c = 17.9670(16) ?). The hydride ligand was not located. The complex was synthesized as one of a series of organometallic platinum(IV) derivatives with Tp' (Tp' = hydridotris(3.5-dimethylpyrazolyl)borate) in the coordination sphere. These octahedral platinum(IV) Tp'PtMe₂X and Tp'PtPh₂X complexes were prepared by formal oxidation of platinum(II) intermediates ([K][Tp'PtMe₂] and [K][Tp'PtPh₂]) with electrophiles (HX, MeI, I₂). Thermogravimetric analysis (TGA) was employed to determine the solid-state decomposition temperatures for these platinum(IV) organometallic complexes.

Full text of DOI:10.1021/ja960519o

5684
J. Am. Chem. Soc. 1996, 118, 5684-5689
Solid-State Structure of Tp′PtMe2H, a Dimethylhydrido
Platinum(IV) Complex
Stacy A. O’Reilly, Peter S. White, and Joseph L. Templeton*
Contribution from the Department of Chemistry, UniVersity of North Carolina at Chapel Hill,
Chapel Hill, North Carolina 27599
ReceiVed February 19, 1996X
Abstract: The solid-state X-ray structure of Tp′PtMe2H has been determined. This platinum(IV) hydride derivative
is stable at room temperature and crystallizes in an orthorhombic cell (space group Pcmn, Z ) 4, a ) 8.1292(8) Å,
b ) 13.3862(9) Å, and c ) 17.9670(16) Å). The hydride ligand was not located. The complex was synthesized as
one of a series of organometallic platinum(IV) derivatives with Tp′ (Tp′ ) hydridotris(3,5-dimethylpyrazolyl)borate)
in the coordination sphere. These octahedral platinum(IV) Tp′PtMe2X and Tp′PtPh2X complexes were prepared by
formal oxidation of platinum(II) intermediates ([K][Tp′PtMe2] and [K][Tp′PtPh2]) with electrophiles (HX, MeI, I2).
Thermogravimetric analysis (TGA) was employed to determine the solid-state decomposition temperatures for these
platinum(IV) organometallic complexes.
10
(C6H5)2(SMe2)2 (2) were prepared by literature methods. All other
Introduction
reagents were purchased and used without purification.
Three separate research groups published papers reporting
platinum(IV) alkylhydrido complexes during 1995.1-3 All three
laboratories utilized NMR spectra to characterize the hydride
complexes prior to reductive elimination, which occurred at or
below room temperature in each case. Protonation of platinum-
(II) alkyl precursors was the synthetic route in each instance.
The formation of platinum(IV) and palladium(IV) species as a
result of electrophilic attack on d8 monomers has recently been
summarized in an article by Canty and van Koten.4
Also reported in 1995, by Canty and co-workers, was the
use of the tris(pyrazolyl)borate (Tp) ligand to stabilize a series
of organo palladium(IV) complexes.5 The solid-state X-ray
structure of an octahedral hydroxodimethyl platinum(IV) com-
plex containing the Tp ligand has also been reported.6
With this flurry of activity as a backdrop, we report here the
synthesis and solid-state X-ray structure of Tp′PtMe2H. This
complex is one of a series of platinum(IV) alkyl and aryl
complexes that we have synthesized in an effort to develop a
general route to polypyrazolylborate complexes of platinum-
(IV).
1H and 13C NMR spectra were recorded on a Varian XL 400 (400
MHz) or a Bruker WM 250 (250 MHz) spectrometer. Thermogravi-
metric analyses (TGA) were performed on a Seiko RTG 220. All
elemental analyses were performed by Atlantic Microlab of Norcross,
GA.
[K][Tp′PtPh2]. An NMR tube was charged with 0.019 g (0.040
mmol) of PtPh2(SMe2)2 and 0.021 g (0.062 mmol) of KTp′. Acetone-
1
d6 was added and the reaction was monitored by H NMR. After 1 h
the PtPh2(SMe2)2 signals were gone, and signals compatible with [K]-
[Tp′PtPh2] and KTp′ were the only Tp′ containing species observed.
After 15 h, 25 µL (0.92 mmol) of methyl iodide was added and an 1H
NMR was quickly taken. The intermediate, presumably [K][Tp′PtPh2],
had disappeared; Tp′PtPh2Me and KTp′ were the only identifiable
species present. [K][Tp′PtPh2]: 1H NMR (acetone-d6, δ) 7.46 (m, 4H,
3JPt-H ) 68.0 Hz, Ho) , 6.54 (m, 4H, Hm), 6.39 (m, 2H, Hp), 5.73 (s,
1H, Tp′CH), 5.61 (s, 2H, Tp′CH), 2.33, 2.16, 1.72, 1.67 (s, 6H, 3H,
3H, 6H, Tp′CCH3).
Tp′PtPh2Me. To a THF (5 mL) slurry of 0.129 g (0.329 mmol) of
cis and trans PtCl2(SMe2)2 at 0 °C was added 0.55 mL of 1.8 M (0.99
mmol, 3.0 equiv) phenyllithium in cyclohexane-ether. The reaction
mixture was warmed to room temperature and stirred for 5 h. A drop
of water was added to quench excess phenyllithium, and then the solvent
was removed under vacuum. To the solid PtPh2(SMe2)2, were added
0.112 g (0.333 mmol) of KTp′ and 5 mL of THF. The reaction mixture
was stirred at room temperature for 15 h to give a brown heterogeneous
reaction mixture. To this heterogeneous THF solution was added 0.10
mL (1.6 mmol, 7.9 equiv) of methyl iodide, and the mixture was stirred
at room temperature for 15 min to give a brown solution with a dark
precipitate. The solvent was removed in Vacuo to give a brown solid.
The solid was extracted three times with 10 mL of toluene to extract
the product. The toluene extracts were combined, and the solvent was
removed via rotary evaporation to give a gray-brown solid. The solid
Experimental Section
Materials and Methods. All reactions were performed under
purified nitrogen using standard Schlenk techniques. Tetrahydrofuran
(THF) and hexanes were distilled from sodium benzophenone ketyl;
methylene chloride was distilled from phosphorus pentoxide; acetonitrile
was distilled from calcium hydride; and toluene was distilled from
sodium. NMR solvents were degassed and stored over 4 Å molecular
sieves prior to use. KTp′ (KTp′ ) potassium hydridotris(3,5-dimeth-
9
ylpyrazolyl)borate),7 PtCl2(SMe2)2,8 [Pt(CH3)2(SMe2)]2 (1), and Pt-
was triturated with acetonitrile to give 0.128 g (59% yield) of tan
3
Tp′PtPh2Me. 1H NMR (CDCl3, -28 °C, δ): 7.75 (d, 2H, JPt-H
)
X Abstract published in AdVance ACS Abstracts, June 1, 1996.
(1) Stahl, S. S.; Labinger, J. A.; Bercaw, J. E. J. Am. Chem. Soc. 1995,
117, 9371.
(2) Hill, G. S.; Rendina, L. M.; Puddephatt, R. J. Organometallics 1995,
14, 4966.
(3) De Felice, V.; De Renzi, A.; Panunzi, A.; Tesauro, D. J. Organomet.
Chem. 1995, 488, C13.
(4) Canty, A. J.; van Koten, G. Acc. Chem. Res. 1995, 28, 406.
(5) Canty, A. J.; Jin, H.; Roberts, A. S.; Skelton, B. W.; Traill, P. R.;
White, A. H. Organometallics 1995, 14, 199.
3
4
43.2 Hz, JH-H ) 8.0 Hz , Ho), 7.17 (m, 2H, JPt-H ) 12.0 Hz, Hm),
3
6.91 (m, 2H, Hp), 6.64 (m, 2H, Hm′), 6.56 (d, 2H, JPt-H ) 44.8 Hz,
3JH-H ) 8.4 Hz, Ho′), 5.79 (s, 1H, JPt-H ) 5.6 Hz, Tp′CH), 5.70 (s,
4
2H,4JPt-H ) 4.8 Hz, Tp′CH), 2.48 2.42, 1.37, 1.02 (s, 3H, 6H, 6H, 3H,
Tp′CH3), 1.75 (s, 3H, JPt-H ) 70.4 Hz, PtCH3). 13C NMR (CDCl3,
2
2
20 ° C, δ): 150.1 (s, 2C, JPt-C ) 20 Hz, Tp′CCH3), 149.3 (s, 1C,
(8) van Asselt, R.; Rijnberg, E.; Elsevier, C. J. Organometallics 1994,
13, 706.
(9) Scott, J. D.; Puddephatt, R. J. Organometallics 1983, 2, 1643.
(10) Hadj-Bagheri, N.; Puddephatt, R. J. Polyhedron 1988, 7, 2695.
(6) Canty, A. J.; Fritsche, S. D.; Jin, H.; Skelton, B. W.; White, A. H. J.
Organomet. Chem. 1995, 490, C18.
(7) Tofimenko, S. J. Am. Chem. Soc. 1967, 89, 6288.
S0002-7863(96)00519-7 CCC: $12.00 © 1996 American Chemical Society

Solid-State Structure of Tp′PtMe2H
J. Am. Chem. Soc., Vol. 118, No. 24, 1996 5685
2JPt-C ) 10 Hz, Tp′CCH3), 143.3 (s, 2C, Tp′CCH3), 143.1 (s, 1C, 3JPt-C
mmol, 2.3 equiv) methyllithium in diethyl ether. The reaction mixture
was stirred at 0 °C for 2 h. While still at 0 °C, a drop of water was
added to quench excess methyllithium. The reaction mixture was
warmed to room temperature, and solvent was removed in Vacuo. The
solid was dried under vacuum for 6 h. To the solid [PtMe2(SMe2)]2
were added 0.068 g (0.203 mmol) of KTp′ and 5 mL of THF. The
reaction mixture was stirred at room temperature for 15 h to give a
brown reaction mixture. To this heterogeneous THF solution was added
0.10 mL (1.6 mmol, 7.9 equiv) of methyl iodide, and the mixture was
stirred at room temperature for 1 h at which time a gray precipitate in
a lightly colored solution had formed. The solvent was removed under
vacuum to give a brown solid. The solid was extracted three times
with 5 mL of toluene. The extracts were combined, and the solvent
was removed via rotary evaporation. The resulting tan solid was
triturated with 10 mL of acetonitrile to give 0.0310 g (28% yield) of
white Tp′PtMe3. NMR, IR, and analytical data for Tp′PtMe3 have
previously been reported.11
2
) 10 Hz, Tp′CCH3), 138.0 (broad, 2C, Cm), 132.7 (broad, 2C, JPt-C
2
) 40 Hz, Co), 126.7 (s, 2C, JPt-C ) 20 Hz, Co′), 126.4 (s, 2C, Cp),
1
3
125.8 (s, 2C, JPt-C ) 890 Hz, Cipso), 123.4 (s, 2C, JPt-C ) 10 Hz,
Cm′), 107.8 (s, 2C, 3JPt-C ) 10 Hz, Tp′CH), 107.3 (s, 1C, 3JPt-C ) 10
Hz, Tp′ CH), 14.5 (s, 1C, 3JPt-C ) 6 Hz, Tp′CH3), 12.9 (s, 4C, Tp′CH3),
1
1
12.5 (s, 1C, Tp′CH3), -2.9 (s, 1C, JPt-C ) 660 Hz, JC-H ) 133 Hz,
PtCH3). Anal. Calcd for C28H35BN6Pt: C, 50.84; H, 5.33; N, 12.70.
Found: C, 50.94; H, 5.38; N, 12.61.
Tp′PtPh2I. To a THF (5 mL) slurry of 0.222 g (0.569 mmol) of
cis and trans PtCl2(SMe2)2 at 0 °C was added 1.3 mL of 1.8 M (2.3
mmol, 4.1 equiv) phenyllithium in cyclohexane-ether. The reaction
mixture was warmed to room temperature and stirred for 4 h. A drop
of water was added to quench excess phenyllithium, and then the solvent
was removed under vacuum. To the solid PtPh2(SMe2)2 were added
0.191 g (0.569 mmol) of KTp′ and 5 mL of THF. The reaction mixture
was stirred at room temperature for 15 h to give a brown heterogeneous
reaction mixture. Under positive nitrogen pressure 0.148 g (0.584
mmol) of elemental iodine was added. The reaction mixture im-
mediately turned orange-brown. It was then stirred at room temperature
for 1 h. The solvent was removed under vacuum, and the resulting
solid was extracted three times with 5 mL of toluene. The extracts
were combined. The solvent volume was reduced to 5 mL, and 15
mL of acetonitrile was added. After storing the solution at -30 °C
for 1 week, 0.190 g (51% yield) of yellow crystals of Tp′PtPh2I had
Tp′PtMe2H. To a THF (5 mL) slurry of 0.181 g (0.463 mmol) of
cis and trans PtCl2(SMe2)2 at 0 °C was added 0.75 mL of 1.4 M (1.1
mmol, 2.3 equiv) methyllithium in diethyl ether. The reaction mixture
was stirred at 0 °C for 1.5 h. While still at 0 °C, a drop of water was
added to quench excess methyllithium. The reaction mixture was
warmed to room temperature and solvent was removed in Vacuo. To
the solid [PtMe2(SMe2)]2 were added 0.155 g (0.462 mmol) of KTp′
and 5 mL of THF. The reaction mixture was stirred at room
temperature for 36 h to give a brown heterogeneous reaction mixture.
To the reaction mixture was added 0.50 mL of 1.0 M (0.50 mmol)
anhydrous HCl in diethyl ether. The reaction was stirred at room
temperature for 1 h to give a lightly colored solution with a brown
precipitate. The solvent was removed in Vacuo, and the resulting brown
residue was extracted two times with 5 mL of toluene. The extracts
were combined and the solvent was removed via rotary evaporation.
The gray solid was triturated with 5 mL of acetonitrile at 0 °C. The
resulting light gray solid was dissolved in methylene chloride and
filtered through a Celite column. Removal of the solvent gave 0.107
g (44% yield) of white Tp′PtMe2H. Recrystallization from methylene
chloride and hexanes at room temperature provided crystals for X-ray
analysis. 1H NMR (CDCl3, δ): 5.72 (s, 1H, Tp′CH), 5.71 (s, 2H, 4JPt-H
) 8.0 Hz, Tp′CH), 2.34, 2.29, 2.27, 2.18 (s, 3H, 6H, 3H, 6H, Tp′CH3),
1.19 (s, 6H, 2JPt-H ) 67.5 Hz, Pt(CH3)2), -20.95 (s, 1H, 1JPt-H ) 1358
formed. 1H NMR (CDCl3, δ): 8.49 (d, 2H, 3JPt-H ) 39.6 Hz, 3JH-H
)
7.6 Hz, Ho), 7.07 (m, 2H, 4JPt-H ) 8.0 Hz, Hm), 6.91 (m, 2H, Hp), 6.60
3
3
(m, 2H, Hm′), 6.10 (d, 2H, JPt-H ) 36.8 Hz, JH-H ) 8.4 Hz, Ho′),
4
5.76 (s, 2H, Tp′CH), 5.74 (s, 1H, JPt-H ) 15.2 Hz, Tp′CH), 2.48,
2.45, 1.70, 0.82 (s, 3H, 6H, 6H, 3H, Tp′CH3). 13C NMR (CDCl3, δ):
152.7 (s, 2C, 2JPt-C ) 20 Hz, Tp′CCH3), 149.1 (s, 1C, 2JPt-C ) 40 Hz,
3
Tp′CCH3), 143.8 (s, 2C, Tp′CCH3), 143.5 (s, 1C, JPt-C ) 20 Hz,
Tp′CCH3), 139.0 (s, 2C, 2JPt-C ) 30 Hz, Co), 137.2 (s, 2C, 3JPt-C ) 10
2
3
Hz, Cm), 126.8 (s, 2C, JPt-C ) 40 Hz, Co′), 126.6 (s, 2C, JPt-C ) 30
Hz, Cm′), 124.6 (s, 2C, 4JPt-C ) 10 Hz, Cp ), 120.5 (s, 2C, 1JPt-C ) 740
Hz, Cipso),108.6 (s, 1C, 3JPt-C ) 20 Hz, Tp′CH), 108.4 (s, 2C, 3JPt-C
)
3
30 Hz, Tp′CH), 15.8 (s, 2C, Tp′CH3), 14.4 (s, 1C, JPt-C ) 11 Hz,
Tp′CH3), 13.2 (s, 1C, Tp′CH3), 12.8 (s, 2C, Tp′CH3). Anal. Calcd
for C27H32BIN6Pt‚CH3CN: C, 42.76; H, 4.33; N, 12.03. Found: C,
42.93; H, 4.30; N, 11.74.
Tp′PtPh2H. To a THF (5 mL) slurry of 0.167 g (0.428 mmol) of
cis and trans PtCl2(SMe2)2 at 0 °C was added 0.95 mL of 1.8 M (1.7
mmol, 4.0 equiv) phenyllithium in cyclohexane-ether. The reaction
mixture was warmed to room temperature and stirred for 12 h. A drop
of water was added to quench excess phenyllithium, and solvent was
removed under vacuum to give a brown solid. To the solid PtPh2-
(SMe2)2 were added 0.145 g (0.432 mmol) of KTp′ and 5 mL of THF.
The reaction mixture was stirred at room temperature for 36 h to give
a brown heterogeneous reaction mixture. To the reaction mixture was
added 0.43 mL of 1.0 M (0.43 mmol) of anhydrous HCl in diethyl
ether. The reaction was stirred for 1 h, and then the solvent was
removed in Vacuo to give a brown solid. To isolate the product the
solid was extracted three times with 5 mL of toluene. The extracts
were combined and the solvent was removed via rotary evaporation.
The residual solid was briefly triturated with acetonitrile to give 0.073
g (26% yield) of white Tp′PtPh2H. 1H NMR (CDCl3, -47 °C, δ):
8.09 (d, 2H, 3JPt-H ) 58.8 Hz, 3JH-H ) 8.0 Hz, Ho), 7.09 (m, 2H, 4JPt-H
) 10.4 Hz, Hm), 6.93 (m, 2H, Hp), 6.71 (m, 4H, Hm′, Ho′), 5.90 (s, 1H,
2
Hz, Pt-H). 13C NMR (CDCl3, δ): 149.7 (s, 1C, JPt-C ) 20 Hz,
2
Tp′CCH3), 149.0 (s, 2C, JPt-C ) 20 Hz, Tp′CCH3), 143.5 (s, 2C,
3
Tp′CCH3), 143.3 (s, 1C, Tp′CCH3), 107.3 (s, 1C, JPt-C ) 10 Hz,
TpCH), 106.0 (s, 2C, 3JPt-C ) 10 Hz, TpCH), 14.4 (s, 1C, 3JPt-C ) 10
Hz, Tp′CH3), 12.8 (s, 1C, Tp′CH3), 12.7 (s, 4C, Tp′CH3), -21.6 (s,
2C, 1JPt-C ) 624 Hz, 1JC-H) 130 Hz, 2JH-C ) 4 Hz, Pt(CH3)2). Anal.
Calcd for C17H29BN6Pt: C, 39.01; H, 5.59; N, 16.06. Found: C, 38.92;
H, 5.61; N, 15.78.
X-ray Structure of Tp′PtMe2H (4b). Crystals of Tp′PtMe2H were
grown from methylene chloride/hexanes. The crystal was orthorhombic
(Pcmn space group). The cell dimensions were a ) 8.1292(8) Å, b )
13.3862(9) Å, and c ) 17.9670(16) Å. The cell volume was 1955.2-
(3) Å3 , Z ) 4 molecules per unit cell, Dcalc ) 1.778 g/cm3, λ (Mo KR)
) 0.71073 Å, µ ) 7.26 mm-1, and F(000) ) 1016.68. The X-ray
data were collected on a Rigaku diffractometer using the ω scan mode.
Experimental details are given in Table 1. Of the 5399 unique
reflections, 1549 reflections possessed I > 2.5σ(I), and these were used
in the structure determination. Final agreement indices were R ) 2.7%
and Rw) 3.3%, with hydrogen placed in computed positions 0.96 Å
from the bonded atom and included in the refinement using a riding
model. All other atoms were refined anisotropically. An ORTEP
diagram is shown in Figure 2.
4
Tp′CH), 5.69 (s, 2H, JPt-H ) 6.4 Hz Tp′CH), 2.51, 2.39, 1.43, 1.39
(s, 3H, 6H, 3H, 6H, Tp′CH3), -18.94 (s, 1H, 1JPt-H ) 1360 Hz, Pt-H).
13C NMR (CDCl3, -47 °C, δ): 149.7 (s, 2C, 2JPt-C ) 30 Hz, Tp′CCH3),
149.3 (s, 1C, 2JPt-C ) 20 Hz, Tp′CCH3), 143.5 (s, 2C, Tp′CCH3), 143.3
(s, 1C, Tp′CCH3), 139.2 (s, 2C, 2JPt-C ) 70 Hz, Co), 136.8 (s 2C, 3JPt-C
2
3
) 20 Hz, Cm), 126.7 (s, 2C, JPt-C ) 60 Hz, Co′), 126.5 (s, 2C, JPt-C
Thermogravimetric Analysis (TGA) Studies. Thermogravimetric
studies were conducted using a Seiko RTG 220. In a representative
experiment Tp′PtPh2H (3c) was placed in an aluminum TGA pan. The
sample was heated at a rate of 5 °C per min from 30 to 350 °C under
a nitrogen gas flow of 200.0 mL per min. A diagram of the weight
loss as a function of temperature is shown in Figure 3. The same
1
) 40 Hz, Cm′), 123.9 (s, 2C, JPt-C ) 840 Hz, Cipso), 123.0 (s, 2C,
4JPt-C ) 10 Hz, Cp), 106.9 (s, 1C, JPt-C ) 10 Hz, Tp′CH), 106.1 (s,
3
2C, 3JPt-C ) 20 Hz, Tp′ CH), 14.9 (s, 1C, Tp′CH3), 14.0 (s, 2C, 3JPt-C
) 17 Hz, Tp′CH3), 12.9 (s, 3C, Tp′CH3). Anal. Calcd for C27H33-
BN6Pt: C, 50.08; H, 5.14; N, 12.98. Found: C, 50.11; H, 5.15; N,
13.05.
Tp′PtMe3. To a THF (5 mL) slurry of 0.079 g (0.203 mmol) of cis
and trans PtCl2(SMe2)2 at 0 °C was added 0.33 mL of 1.4 M (0.46
(11) Roth, S. R.; Ramamoorthy, V.; Sharp, P. R. Inorg. Chem. 1990,
29, 3345.

5686 J. Am. Chem. Soc., Vol. 118, No. 24, 1996
O’Reilly et al.
Table 1. Crystallographic data collection parameters for
Tp′PtMe2H (4b)
Scheme 1. Reaction Scheme for the Synthesis of Tp′
Platinum(IV) Complexesa
molecular formula
formula wt, g/mol
crystal dimenss, mm
space group
cell parameters
a, Å
PtC17H29BN6
523.35
0.25 × 0.25 × 0.15
Pcmn
8.1292 (8)
13.3862 (9)
17.9670 (16)
1955.2 (3)
4
b, Å
c, Å
volume, Å3
Z
density calcd, g cm-3
1.778
Collection and Refinement Parameters
radiation (wavelength, Å)
monochromator
scan type
background
2Θ limits, deg
h; k; l ranges
total no. of reflcns
data with I g 2.5σ(I)
R significant [all others],%
Rw significant, [all others],%
GOFa
Mo KR (0.71073)
graphite
ω scan mode
0.1 of scan time
30-40
0, 9; 0, 15; 0, 21
5399
aThe numbering scheme for the pyrazole rings is also given.
1549
2.7, [3.6]
3.3, [3.6]
1.23
(SMe2)2, was combined with a slight excess of KTp′ in acetone-
d6 in an NMR tube and the reaction was monitored by 1H NMR.
After 1 h all of the metal reagent, Pt(Ph)2(SMe2)2, had been
consumed, and only one platinum-containing species was
observed based on clues provided by platinum coupling to aryl
protons (195Pt, I ) 1/2, 33.8% abundant). The resulting spectrum
has been assigned to [K][Tp′PtPh2], a platinum(II) intermediate
analogous to the palladium(II) Tp intermediate generated and
utilized, but not observed, by Canty.5
no. of parameters
largest parameter shift
127
0.001
a Goodness of fit.
instrumental conditions were employed for Tp′PtPh2Me (3a), Tp′PtPh2I
(3b), and Tp′PtMe2H (4b). Decomposition temperatures are given in
Table 5.
The ortho protons of [K][Tp′PtPh2] are observed at 7.46 ppm
with 68.0-Hz platinum coupling. The meta protons are seen at
6.54 ppm and the para at 6.39 ppm. A 2-to-1 pattern was
observed for the pyrazole protons and the methyl groups of the
Tp′ ligand, indicating that a molecular mirror plane contains
one Tp′ ring with the other two rings equivalent. The three
pyrazole rings are not undergoing rapid exchange on the NMR
time scale. Other work has indicated that Tp and B(pyrazole)4-
platinum(II) complexes are fluxional as the pyrazole rings are
exchanged by interchange between four- and five-coordinate
geometries in solution.16 While the 1H NMR of [K][Tp′PtPh2]
here has provided clear evidence that the three pyrazole rings
do not exchange, it is not known whether the predominate
platinum(II) species in solution at room temperature is four- or
five-coordinate.
Tp′PtPh2Me. Addition of excess MeI to the NMR solution
of the reactive platinum(II) [K][Tp′PtPh2] species resulted in
the formation of a platinum(IV) monomer, Tp′PtPh2Me (3a).
This complex can be synthesized on a preparative scale as shown
in Scheme 1.
The aromatic signals of Tp′PtPh2Me in the 1H NMR are broad
at room temperature. Though the two phenyl rings are related
by a molecular mirror plane, in each phenyl ring the individual
ortho and meta protons are inequivalent due to restricted rotation
of the phenyl rings. A 14.8-kcal/mol barrier to phenyl rotation
around the platinum-carbon bond was calculated following
variable-temperature NMR studies.
Results and Discussion
Both the d6 configuration and the high oxidation state of
platinum(IV) promote octahedral coordination, the paradigm of
inorganic chemistry. Given the proclivity of Tp′ to favor
octahedral geometries and the greater electron donating ability
of Tp′ compared to Tp, it seemed worthwhile to pursue a general
synthetic route to Tp′PtX3 complexes. The synthesis of
Tp′PtMe3 from [Pt(Me)3I]4 and KTp′ 11 proved difficult to
generalize. Canty’s work accessed palladium(IV) Tp complexes
through oxidation of palladium(II) Tp intermediates,12 and
electrophilic addition to anionic platinum(II) intermediates
offered a potentially attractive route to a variety of Tp′PtR2X
complexes.
Note that we unsuccessfully attempted several simple prepa-
rations with both platinum(IV) and platinum(II) reagents. Direct
reaction of platinum(IV) halides and the potassium salt of Tp′
(Tp′ ) hydridotris(3,5-dimethylpyrazolyl)borate) in our hands
ruptured the Tp′ ligand backbone and produced platinum
pyrazole complexes or a bis(3,5-dimethylpyrazolyl)borane
dimer13 as the only isolable products. Difficulties arose in the
selection of a suitable platinum(II) source. Ligand exchange
reactions with either Pt(Me)2(COD) (COD ) 1,5-cyclooctadi-
ene) or Pt(Me)2(COE)2 (COE ) cyclooctene) followed by
oxidation were unsuccessful. Clean oxidation of the Tp′ analog
of the previously reported platinum(II) [TpPtMe]x oligomer14
proved elusive.
[K][Tp′PtPh2]. A number of groups have successfully used
platinum(II) sulfide complexes for exchange reactions with
nitrogen donor ligands; the sulfide ligands are extremely
labile.6,8,10,15 The monomeric platinum(II) complex, Pt(Ph)2-
The spectrum of Tp′PtPh2Me at low temperature revealed
two distinct signals for ortho protons: one downfield at 7.75
ppm with 43.2-Hz two-bond platinum coupling, the other upfield
at 6.56 ppm with 44.8-Hz platinum coupling. Because of the
symmetry equivalency of the two phenyl rings, each aromatic
(12) (a) Canty, A. J.; Traill, P. R. J. Organomet. Chem. 1992, 435, C8.
(b) Canty, A. J. Acc. Chem. Res. 1992, 25, 83. (c) Canty, A. J.; Honeyman,
R. T.; Roberts, A. S.; Traill, P. R. J. Organomet. Chem. 1994, 471, C8.
(13) (a) Trofimenko, S. J. Am. Chem. Soc. 1967, 89, 4948. (b) Alcock,
N. W.; Sawyer, J. F. Acta. Crystallogr. 1974, B30, 2899.
(14) Clark, H. C.; Manzer, L. E. Inorg. Chem. 1974, 13, 1996.
(15) Puddephatt, R. J.; Scott, J. D. Organometallics 1985, 4, 1221.
(16) (a) Manzer, L. E. Inorg. Chem. 1976, 15, 2354. (b) Manzer, L.;
Meakin, P. Z. Inorg. Chem. 1976, 15, 3117. (c) Clark, H. C.; Manzer, L.
E. Inorg. Chem. 1974, 13, 1291. (d) Clark, H. C.; Manzer, L., E. J. Am.
Chem. Soc. 1973, 95, 3812. (e) Byers, P. K.; Canty, A. J.; Honeymam, R.
T. AdV. Organomet. Chem. 1992, 34, 1.

Solid-State Structure of Tp′PtMe2H
J. Am. Chem. Soc., Vol. 118, No. 24, 1996 5687
Table 2. 1H NMR Data for 3c and 4b and Other Selected
Platinum(IV) Hydride Complexes
Pt-H, 1JPt-H
ppm Hz
,
trans
ligand
complex
Tp′PtPh2H (3c)
Tp′PtMe2H (4b)
ref
-18.94 1360
-20.95 1358
N
N
Cl
Cl
N
I
this work
this work
[(tmeda)Pt(CH2Ph)(H)(Cl)]a -24
1230
1
2
3
17
[PtCl(H)Me2(tBu2bpy)]b
[Pt(H)XMe2(dmphen)c
trans [PtHI3(PEt3)2]d
-21.80 1590
-22
-16.41
1400
784
a tmeda ) N,N,N′,N′-tetramethylenediamine, CD2Cl2, -78 °C.
b CD2Cl2, -78 °C. c X ) Cl or Br, dmphen ) 2,9-dimethyl-1,10-
phenanthroline, acetone-d6. d CD2Cl2, -40 °C.
coupling to the downfield ortho proton (3JPt-H ) 58.8 Hz). The
Tp′ resonances are similar to those seen for the methyl and
iodide derivatives with platinum coupling to the proton at the
4-position of the two equivalent rings; no platinum coupling to
the 4-position of the unique ring trans to the hydride was
observed.
Figure 1. 1H NMR of the aromatic region of Tp′PtPh2I (3b) in CDCl3.
signal integrated for two protons, one from each phenyl ring.
The differences in chemical shifts may be due to shielding
effects of the five aromatic rings, three pyrazoles and two
phenyls, that surround the crowded metal center. The protons
of the Tp′ ligand are observed in a 2-to-1 ratio with the unique
ring trans to the methyl group. Four-bond platinum coupling
is observed to the 4 position of all of the pyrazole rings. The
protons of the platinum-bound methyl group are observed at
1.81 ppm with 70.8-Hz platinum coupling.
The hydride signal is observed upfield at -18.94 ppm with
1
1360-Hz coupling to platinum. Table 2 gives H NMR data
for platinum(IV) hydride complexes, including the three 1995
1-3
reports
and the 1973 report of a platinum(IV) hydride.17
The effect of the trans ligand on the coupling constant should
be noted. The chemical shift and coupling constant for
Tp′PtPh2H are similar to those of other complexes with trans
nitrogen donor ligands.18,19
In the 13C NMR, two distinct environments for both ortho
and meta carbons are observed, with a large difference in
chemical shifts and substantial platinum coupling. The ipso
carbon is observed at 125.8 ppm with 890-Hz platinum coupling.
Platinum coupling is seen not only throughout the backbone of
the Tp′ ligand but also to the carbon of the methyl group in the
3 position of the unique pyrazole ring. The carbon of the methyl
group bound to the platinum(IV) metal center is observed at
-2.9 ppm with 660-Hz one-bond platinum coupling.
In the 13C NMR larger platinum coupling constants are seen
throughout the phenyl ring for the hydride complex than are
observed for the methyl or iodo derivatives. The ipso carbons
at 123.9 ppm with 840-Hz platinum coupling do not show
coupling to the cis hydride ligand. The Tp′ ligand exhibited
significant platinum coupling and a 2-to-1 pattern due to the
mirror plane.
In an effort to probe the solution stability of Tp′PtPh2H the
complex was refluxed for 15 h in toluene. Neither incorporation
of toluene nor decomposition was observed by 1H NMR
analysis.
Tp′PtPh2I. Oxidation of [K][Tp′PtPh2] with elemental iodine
1
yields Tp′PtPh2I (3b). In the room temperature H NMR, no
1
rotation of the phenyl rings is evident. High-temperature H
NMR studies allowed calculation of a barrier to rotation of 18.1
kcal/mol. The downfield region of the spectrum is shown in
Figure 1. The ortho protons are even farther separated in
Tp′PtPh2I (3b) than in Tp′PtPh2Me (3a) as they occur at 8.49
(3JPt-H ) 39.6 Hz) and 6.10 ppm (3JPt-H ) 36.8 Hz), a chemical
shift difference of 2.39 ppm. Large four-bond platinum coupling
is observed to the 4-position of the Tp′ pyrazole ring trans to
the iodide ligand (4JPt-H ) 15.2 Hz). One of the methyl groups
on the Tp′ ligand is observed at 0.82 ppm, unusually far upfield.
In the 13C NMR spectrum platinum coupling is observed to
Tp′PtMe3. Methyl substitution for chloride in PtCl2(SMe2)2
has previously been reported to give the highly reactive platinum
dimer, [Pt(Me)2(SMe2)]2.9 The analogous ethyl sulfide dimer
has been combined with KTp and oxidized by water/acetone to
give the crystallographically characterized TpPtMe2(OH).6
Would a similar route allow access to platinum(IV) Tp′
complexes? A [K][Tp′PtMe2] intermediate was generated by
ligand exchange of [Pt(Me)2(SMe2)]2 and KTp′; characterization
of this anionic intermediate was not achieved. This putative
anion can be oxidized with MeI to give the previously reported
all of the carbons of the phenyl rings (4JPt-C ) 10 Hz). The
para
11,20
Tp′PtMe3
(3a) in reasonable yields (Scheme 1).
signals for the Tp′ carbons resemble those observed for
Tp′PtPh2Me. Coupling of 11 Hz is observed between platinum
and the methyl group at the 3-position of the unique pyrazole
ring.
Tp′PtMe2H. The surprising thermal stability observed for
Tp′PtPh2H prompted us to explore the synthesis of an analogous
dimethylhydrido platinum(IV) derivative. The anionic inter-
mediate, [K][Tp′PtMe2], can be protonated with anhydrous HCl
in ether to give, in 44% yield, Tp′PtMe2H (4b). The hydride
Tp′PtPh2H. The [K][Tp′PtPh2] intermediate can be proto-
nated with HCl to give Tp′PtPh2H (3c). This platinum(IV) aryl
hydride species is stable in the solid-state and in solution. The
phenyl rings are rotating on the NMR time scale at room
temperature, and the proton signals in the aromatic region are
quite broad. The coalescence temperature for exchange of the
ortho protons was found to be 55 °C, and variable-temperature
NMR studies allowed us to calculate a rotation barrier of 13.6
kcal/mol. Of the three platinum(IV) aryl complexes synthesized,
the hydride exhibited the smallest barrier to phenyl ring rotation,
probably a consequence of steric factors. Again, the pattern of
one downfield doublet and one upfield doublet is observed for
the ortho protons of the phenyl rings, with large platinum(IV)
(17) Anderson, D. W. W.; Ebsworth, E. A. V.; Rankin, D. W. H. J.
Chem. Soc., Dalton Trans. 1973, 854.
(18) For other platinum(IV) hydrides see: (a) Blacklaws, I. M.; Brown,
L. C.; Ebsworth, E. A. V.; Reed, F. J. S. J. Chem. Soc., Dalton Trans.
1978, 877. (b) Arnold, D. P.; Bennett, M. A. Inorg. Chem. 1984, 23, 2110.
(19) A series of compounds also exist with a platinum(IV) hydride in
equilibrium with a platinum(II) tautomer. (a) Wehman-Ooyevaar, I. C. M.;
Grove, D. M.; van der Sluis, P.; Spek, A. L.; van Koten, G. J. Chem. Soc.,
Chem. Commun. 1990, 1367. (b) Wehman-Ooyevaar, I. C. M.; Grove, D.
M.; Kooijman, H.; van der Sluis, P.; Spek, A. L.; van Koten, G. J. Am.
Chem. Soc. 1992, 114, 9916. (c) Wehman-Ooyevaar, I, C. M.; Grove, D.
M.; de Vaal, P.; Dedieu, A.; van Koten, G. Inorg. Chem. 1992, 31, 5484.
(20) TpPtMe3 has also been synthesized; see: King, R. B.; Bond, A. J.
Am. Chem. Soc. 1974, 96, 1338.

5688 J. Am. Chem. Soc., Vol. 118, No. 24, 1996
O’Reilly et al.
Table 4. Selected Bond Angles (deg) for Tp′PtMe2H (4b)
C(1)-Pt(1)-C(1)a
C(1)-Pt(1)-N(11)
90.07(21) N(12)-B(1)-N(12)a 108.8(5)
92.85(18) N(12)-B(1)-N(22) 110.3(4)
C(1)-Pt(1)-N(11)a 177.05(18) Pt(1)-N(11)-N(12) 117.2(3)
C(1)-Pt(1)-N(21)
N(11)-Pt(1)-N(11)a 84.24(14) Pt(1)-N(21)-N(22) 117.0 (4)
N(11)-Pt(1)-N(21) 87.60(17) B(1)-N(22)-N(21) 119.9(6)
92.70(19) B(1)-N(11)-N(12) 119.6 (4)
Table 5. Solid-State Decomposition Temperatures from TGA
complex
temp, °C
Tp′PtPh2Me (3a)
Tp′PtPh2I (3b)
Tp′PtPh2H (3c)
Tp′PtMe2H (4b)
258
260
232
191
Figure 2. ORTEP diagram of Tp′PtMe2H (4b). The hydrogen atom
was not located, and is shown in a calculated position.
Table 3. Bond Lengths (Å) for Tp′PtMe2H (4b) (Symmetry
Equivalent Atoms Are Not Listed)
Pt(1)-C(1)
2.048(5)
2.145(4)
2.169(6)
1.546(6)
1.520(10)
1.377(6)
1.346(6)
1.357(6)
1.371(8)
1.495(8)
C(14)-C(15)
C(15)-C(17)
N(21)-N(22)
N(21)-C(25)
N(22)-C(23)
C(23)-C(24)
C(23)-C(26)
C(24)-C(25)
C(25)-C(27)
1.495(8)
1.497(8)
1.371(8)
1.344(9)
1.359(10)
1.379(11)
1.493(11)
1.387(11)
1.520(12)
Pt(1)-N(11)
Pt(1)-N(21)
B(1)-N(12)
B(1)-N(22)
N(11)-N(12)
N(11)-C(15)
N(12)-C(13)
C(13)-C(14)
C(13)-C(16)
Figure 3. Thermogravimetric analysis (TGA) showing solid-state
decomposition of Tp′PtPh2H (3c).
signal is observed at -20.95 ppm with 1358-Hz platinum
coupling. Both the chemical shift and the coupling constant
values are comparable to other platinum(IV) hydrides (Table
1). The platinum-bound methyl groups appear at 1.19 ppm with
67.5-Hz platinum coupling. A 2-to-1 pattern is observed for
the Tp′ ligand signals. Coupling of 8.0 Hz is observed to the
4-position proton of the two equivalent pyrazole rings. In the
13C NMR the Tp′ ligand is similar to the diaryl derivatives with
platinum coupling throughout the ligand. The platinum methyl
group carbon resonance is upfield at -21.64 ppm with platinum
coupling of 624 Hz, and two-bond coupling to the cis hydride
of 4 Hz is evident.
Platinum(IV) methyl hydride complexes have been implicated
as intermediates in protonation reactions of platinum(II) methyl
complexes.4 Electrophilic attack on d8 square-planar complexes
can yield platinum(IV) methyl hydride intermediates which
reductively eliminate methane. The net reaction is the proto-
nation of a methyl group with cleavage of the platinum(II)-
carbon bond to form methane. In contrast to other platinum(IV)
cis-methyl hydride complexes, Tp′PtMe2H is reluctant to
reductively eliminate methane at room temperature in solution
or in the solid-state.
X-ray Structure of Tp′PtMe2H. Due to the thermal stability
of the complex, it was possible to obtain X-ray quality crystals
of the stable platinum(IV) dimethyl hydride, 4b, by recrystal-
lization from methylene chloride and hexanes at room temper-
ature. An ORTEP diagram is shown in Figure 2; bond lengths
and selected bond angles are shown in Tables 3 and 4,
respectively. The hydride ligand was not located.
The platinum-methyl bond length is 2.048(5) Å, coinciden-
tally equal to the platinum-methyl bond length of 2.048(5) Å
found in TpPtMe2(OH).6 The platinum-nitrogen bond lengths
are 2.145(4) Å and 2.169(6) Å for the two equivalent and one
unique pyrazole rings, respectively. The unique ring is trans
to the hydride ligand and the two equivalent rings are trans to
the methyl groups, so this provides a direct comparison of the
trans influence of a methyl ligand versus a hydride in a platinum-
(IV) monomer. The stronger trans influence ligand, hydride,
causes an increase in the trans platinum-nitrogen bond length
of only 0.024 Å. The bond angle between the platinum-bound
methyl groups is 90.07(21)°, consistent with the octahedral
environment expected for a d6 platinum(IV) metal center.
Solid-State Stabilities. To determine the solid-state decom-
position temperatures for these compounds, thermogravimetric
analyses (TGA) were performed. Previously Goldberg and co-
workers employed TGA and DSC (differential scanning calo-
rimetry) to investigate methyl iodide and ethane reductive
elimination from (dppe)PtMe3I (dppe ) Ph2PCH2CH2PPh2). In
addition to the temperature at which reductive elimination
occurred, the thermodynamics of the processes and an estimation
of platinum(IV)-carbon and platinum(IV)-iodide bond strengths
were reported.21
For all three of the Tp′ platinum(IV) phenyl derivatives
decomposition temperatures were found to be in excess of 230
°C (Table 5). Figure 3 shows the TGA from 30 to 350 °C for
Tp′PtPh2H. It can be seen that after losing about 23% of the
initial mass between 230 and 260 °C, weight loss continues at
higher temperatures. The initial weight loss of 23% does not
correspond to simple benzene reductive elimination. Neither
the organic product nor the platinum species which form at this
high temperature have been identified. For Tp′PtMe2H, de-
(21) Goldberg, K. I.; Yan, J. Y.; Breitung, E. M. J. Am. Chem. Soc.
1995, 117, 6889.

Solid-State Structure of Tp′PtMe2H
J. Am. Chem. Soc., Vol. 118, No. 24, 1996 5689
composition occurs around 190 °C, which is extraordinary
behavior for a platinum(IV) bisalkyl hydride complex. This
unusual stability may be due to the tendency of the Tp′ ligand
to act as an octahedral enforcer; that is, Tp′ may inhibit reductive
elimination by not allowing the metal complex to easily change
its geometry.22 Furthermore, a stable square-planar geometry
is not accessible for the [Tp′PtX] residue. It is now widely
accepted that the initial step for reductive elimination from
platinum(IV) monomers is formation of a five-coordinate
intermediate in many systems.23 The recalcitrance of the
pyrazole arms of the Tp′ to dissociate from the metal center
may account for the robust thermal properties of Tp′PtMe2H.
reductive elimination, we have synthesized a series of thermally
stable Tp′ hydride, alkyl, aryl, and iodide complexes. Unusually
large restricted phenyl rotation barriers were observed for the
aryl derivatives in these sterically demanding complexes. The
room temperature solid-state X-ray structure of Tp′PtMe2H
offers testimony to the stability of this series of Tp′ platinum-
(IV) complexes. This solid-state structure beautifully illustrates
an octahedral environment for an organometallic platinum(IV)
hydride complex.
Acknowledgment. We would like to thank NSF for funding
and Michael R. Clark for performing thermoanalysis experi-
ments. S. A. O’Reilly would also like to thank Dr. D. McMillen
and Dr. S. Westcott for many hours of discussion.
Conclusions
In an effort to explore the chemistry of octahedral d6
platinum(IV) organometallic complexes which resist facile
Supporting Information Available: Tables of atomic
positions, thermal parameters, and complete bond distances and
angles (3 pages). Ordering information is given on any current
masthead page.
(22) Trofimenko, S. Chem. ReV. 1993, 93, 943.
(23) Collman, J. P.; Hegedus, L. S.; Norton, J. R.; Finke, R. G. Principles
and Applications if Organotransition Metal Chemistry; University Science
Books: Mill Valley, CA, 1987.
JA960519O