The mechanism of protonolysis of phenylplatinum(II) bonds in complexes with phenyl trans to nitrogen or carbon donors

Article abstract of DOI:10.1139/v03-113

Addition of acids of the form HX (X = Cl, BF₄, CF ₃SO₃, CF₃CO₂) to complexes [PtPh₂(NN)] (NN = bu₂bpy = 4,4′-di-ferf-butyl-2, 2′-bipyridine) and [PtPh(NCN)] (NCN = 2,6-C₆H ₃(CH₂NMe₂)₂) at -78°C gave the corresponding phenyl(hydrido)platinum(IV) complexes [PtX(H)Ph₂(NN)] and [PtX(H)Ph(NCN)], which decomposed by reductive elimination of benzene at about -20°C to give the platinum(II) complexes [PtXPh(NN)] and [PtX(NCN)]. Further addition of HCl to [PtClPh(NN)] at low temperature gave [PtHCl ₂Ph(NN)], which decomposed above -10°C, to give benzene and [PtCl₂(NN)]. The reaction of DBF₄ in the presence of excess CD₃OD with [PtPh₂(NN)] led to formation of C ₆H₅D and C₆H₄D₂ but with [PtPh(NCN)] no multiple deuterium incorporation was observed in the product benzene. The mechanisms of these reactions are discussed.

Full text of DOI:10.1139/v03-113

1196
The mechanism of protonolysis of
phenylplatinum(II) bonds in complexes with phenyl
trans to nitrogen or carbon donors1
Christopher M. Ong, Michael C. Jennings, and Richard J. Puddephatt
Abstract: Addition of acids of the form HX (X = Cl, BF4, CF3SO3, CF3CO2) to complexes [PtPh2(NN)] (NN =
bu2bpy = 4,4′-di-tert-butyl-2,2′-bipyridine) and [PtPh(NCN)] (NCN = 2,6-C6H3(CH2NMe2)2) at –78 °C gave the corre-
sponding phenyl(hydrido)platinum(IV) complexes [PtX(H)Ph2(NN)] and [PtX(H)Ph(NCN)], which decomposed by
reductive elimination of benzene at about –20 °C to give the platinum(II) complexes [PtXPh(NN)] and [PtX(NCN)].
Further addition of HCl to [PtClPh(NN)] at low temperature gave [PtHCl2Ph(NN)], which decomposed above –10 °C,
to give benzene and [PtCl2(NN)]. The reaction of DBF4 in the presence of excess CD3OD with [PtPh2(NN)] led to for-
mation of C6H5D and C6H4D2 but with [PtPh(NCN)] no multiple deuterium incorporation was observed in the product
benzene. The mechanisms of these reactions are discussed.
Key words: platinum, phenyl, benzene, protonolysis.
Résumé : L’addition, à –78 °C, d’acides de la forme HX (X = Cl, BF4, CF3SO3, CF3CO2) à des complexes
[PtPh2(NN)] (NN = bu2bpy = 4,4′-di-tert-butyl-2,2′-bipyridine) et [PtPh(NCN)] (NCN = 2,6-C6H3(CH2NMe2)2 conduit
aux complexes correspondants phényl(hydrido)platine(IV) [PtX(H)Ph2(NN)] et [PtX(H)Ph(NCN)] qui se décomposent
par élimination réductrice du benzène, à environ –20 °C, pour conduire aux complexes de platine(II) [PtXPh(NN)] et
[PtX(NCN)]. L’addition subséquente de HCl au complexe [PtClPh(NN)], à basse température, conduit au
[PtHCl2Ph(NN)] qui se décompose au-dessus de –10 °C pour donner du benzène et du [PtCl2(NN)]. La réaction du
DBF4 avec du [PtPh2(NN)], en présence d’un excès de CD3OD, conduit à la formation de C6H5D et de C6H4D2; toute-
fois, avec le [PtPh(NCN)], on n’observe aucune incorporation multiple de deutérium dans le benzène obtenu comme
produit. On discute des mécanismes de ces réactions.
Mots clés : platine, phényle, benzène, protonolyse.
[Traduit par la Rédaction] Ong et al. 1205
Introduction
recent studies of protonolysis of platinum–carbon bonds
have involved complexes [PtR2(NN)], in which the alkyl or
aryl groups are trans to nitrogen donor ligands (3–5), and it
was of interest to compare complexes with mutually trans
Pt—C bonded groups. This paper reports a study of the reac-
tions of acids with the complexes cis-[PtPh2(NN)](NN =
bu2bpy = 4,4′-di-tert-butyl-2,2′-bipyridine, 1) and [PtPh-
(NCN)] (NCN = 2,6-C6H3(CH2NMe2)2, 2) in which the
NCN pincer ligand forces the two aryl groups to be mutually
trans (15) (Chart 1).
The activation of alkanes or arenes by platinum(II) com-
plexes is thought to involve the intermediacy of alkyl(hy-
drido)platinum(IV) or aryl(hydrido)platinum(IV) complexes,
and so there has been much interest in such complexes (1–
13). A useful synthetic route to platinum(IV) complexes
[PtX(H)R2(NN)] (NN = bidentate nitrogen-donor ligand,
X = halide, R = alkyl or aryl) is by addition of acid HX to a
platinum(II) complex [PtR2(NN)] and the decomposition of
these platinum(IV) complexes by reductive elimination of
RH to give [PtXR(NN)], which leads to overall protonolysis
of the alkyl–platinum or aryl–platinum bond, can then be
studied (3–5). Hydrido(alkyl)-, hydrido(aryl)-, and hydri-
do(silyl)platinum complexes are proposed in several other
important catalytic reactions, including the hydrosilation re-
actions catalyzed by platinum complexes (14). Most of the
Results
The phenylplatinum complexes 1 and 2
Complex 1 was prepared by reaction of the ligand bu2bpy
with the precursor [PtPh2(µ-SMe2)]n, n = 2 or 3 (16–18), in
Received 9 February 2003. Published on the NRC Research Press Web site at http://canjchem.nrc.ca on 9 September 2003.
This article is dedicated to Dr. John Harrod for his distinguished contributions to organometallic chemistry and its applications in
catalysis and materials science.
C.M. Ong, M.C. Jennings, and R.J. Puddephatt.2 Department of Chemistry, University of Western Ontario, London, ON
N6A 5B7, Canada.
1This article is part of a Special Issue dedicated to Professor John Harrod.
2Corresponding author (e-mail: pudd@uwo.ca).
Can. J. Chem. 81: 1196–1205 (2003)
doi: 10.1139/V03-113
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Ong et al.
1197
Fig. 1. A view of the structure of complex 1. 30% Thermal el-
Chart 1.
lipsoids are shown and hydrogen atoms have been omitted for
clarity.
diethyl ether solution, while complex 2 was prepared by a
modified literature method (15).
The structures of complexes 1 and 2 are shown in Figs. 1
and 2, with selected bond distances and angles listed in Ta-
bles 1 and 2. Each complex contains a roughly square-planar
platinum(II) center, but with cis- and trans-PtC2N2 coordina-
tion, respectively, and in each case the phenyl group lies
roughly orthogonal to the square plane (79° in 1, in which
the two phenyl groups are crystallographically equivalent;
84° in 2, Figs. 1 and 2). This conformation allows platinum–
phenyl dπ-pπ bonding and minimizes steric effects. The Pt—
C(phenyl) bond distance is shorter in 1 (2.023(2) Å, trans to
N) than in 2 (2.111(6) Å, trans to C), as expected since ni-
trogen has the lower trans-influence. However, the distance
Pt(1)—C(1) = 1.956(6) Å in 2 is shorter than either of these
Pt—C(phenyl) distances, as a result of the chelate effect.
Other bond distances and angles are comparable to those re-
ported for related complexes [PtR2(bu2bpy)] (5, 16) or
[PtX{2,6-C6H3(CH2NMe2)2}] (15).
Fig. 2. A view of the structure of complex 2. 30% Thermal el-
lipsoids are shown and hydrogen atoms have been omitted for
clarity.
Reactions with acids
Complex 1 reacted with 1 equiv. of acid HX (X = Cl,
CF3CO2, CF3SO3, BF4) at room temperature to give benzene
and the corresponding product [PtXPh(bu2bpy)] (3a, X = Cl;
3b, X = CF3CO2; 3c, X = CF3SO3; 3d, X = BF4)
(Scheme 1). The complexes were characterized by elemental
1
analysis and by their H NMR spectra, which showed the
presence of nonequivalent t-BuC4H3N units and only a sin-
gle phenylplatinum group.
The reaction of complex 1 in CDCl3 solution with HCl at
–78 °C gave an intermediate hydridoplatinum(IV) complex
1
4a (Scheme 1) that was identified by its H NMR spectrum.
The hydride resonance was observed at δ = –20.15 with
1J(PtH) = 1613 Hz (Table 3). The trans oxidative addition of
HCl was shown by the observation of equivalent t-BuC4H3N
and phenyl groups. Complex 4a decomposed at –20 °C by
reductive elimination of benzene to yield the product
[PtClPh(bu2bpy)] (3a) and no other intermediates were ob-
served. The similar reaction of 1 in CDCl3 with the other ac-
ids failed to give detectable hydride intermediates, but the
reaction with HBF4 or CF3SO3H in CDCl3–CD3CN gave a
hydride intermediate (5) characterized by δ(PtH) = –21.84,
1J(PtH) = 1619 Hz. This is presumed to be a cationic
acetonitrile complex, since the spectral properties were the
same in each case and acetonitrile is a stronger ligand than
either triflate or tetrafluoroborate. Complex 5 decomposed
on warming the solution to –20 °C to give complex 3d.
The complex [PtClPh(bu2bpy)] (3a) reacted with HCl at
room temperature to give benzene and [PtCl2(bu2bpy)] (5).
When the reaction was carried out at –78 °C, the intermedi-
ate hydridoplatinum(IV) complex [PtHCl2Ph(bu2bpy)] (6)
Table 1. Selected bond lengths (Å) and angles
(°) for complex 1.
Bond lengths (Å)
Pt(1)—C(11)
Pt(1)—N(1)
2.023(2)
2.097(3)
Bond angles (°)
N(1)-Pt(1)-N(1A)
N(1A)-Pt(1)-C(11)
N(1)-Pt(1)-C(11)
C(11A)-Pt(1)-C(11)
77.1(2)
97.4(1)
174.5(1)
88.2(2)
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Can. J. Chem. Vol. 81, 2003
Table 3. H NMR data for hydridoplatinum(IV) complexes.
1
Table 2. Selected bond lengths (Å) and angles
(°) for complex 2.
Complex
δ (PtH) 1J(PtH) (Hz)
Bond lengths (Å)
[PtHClPh2(bu2bpy)] (3a)
[PtHPh2(MeCN)(bu2bpy)]+ (5)
[PtHCl2Ph(bu2bpy)] (6)
–20.15
–21.84
–25.94
–21.36
–20.47
1613
1619
1540
1622
1644
Pt(1)—C(1)
Pt(1)—N(1)
Pt(1)—N(2)
Pt(1)—C(13)
1.956(6)
2.079(5)
2.079(5)
2.111(6)
[PtHClPh{2,6-C6H3(CH2NMe2)2}] (8)
[PtHPh(MeCN){2,6-
C6H3(CH2NMe2)2}]+ (9)
Bond angles (°)
N(1)-Pt(1)-N(2)
N(1)-Pt(1)-C(13)
N(2)-Pt(1)-C(13)
N(1)-Pt(1)-C(1)
N(2)-Pt(1)-C(1)
C(1)-Pt(1)-C(13)
164.1(2)
97.8(2)
97.9(2)
82.3(2)
81.9(2)
177.2(2)
Scheme 2.
Scheme 1.
Scheme 3.
1
was detected. The H NMR spectrum contained a hydride
1
resonance at δ = –25.94 with J(PtH) = 1540 Hz, in the
range expected for a hydride trans to chloride (Table 3) (5).
The aromatic region of the spectrum contained six reso-
nances for the bu2bpy ligand and three for the phenyl group,
consistent with the proposed structure that arises from trans
oxidative addition. The hydride complex decomposed at
–20 °C to give benzene and [PtCl2(bu2bpy)] (Scheme 2).
Reaction of [PtPh{2,6-C6H3(CH2NMe2)2}] (2) with acids
HX gave benzene and the corresponding complexes
[PtX{2,6-C6H3(CH2NMe2)2}] (7a, X = Cl; 7b, X = CF3CO2;
7c, X = CF3SO3; 7d, X = BF4) (Scheme 3) (15). Reaction of
complex 2 with HCl in CDCl3 at –78 °C gave the hydri-
doplatinum(IV) complex [PtHClPh{2,6-C6H3(CH2NMe2)2}]
(8) which was characterized by a hydride resonance at δ =
cayed at –20 °C as reductive elimination of benzene oc-
curred to give 7a. Similarly, reaction of 2 in CDCl3–CD3CN
at –78 °C with triflic acid or tetrafluoroboric acid gave
[PtHPh(NCCD3){2,6-C6H3(CH2NMe2)2}]+ (9) identified by
its H NMR spectrum (δ(PtH) = –20.47, J(PtH) = 1644 Hz)
and it decomposed at –20 °C to give benzene and complex
7c or 7d. The complexes 7 were inert to protonolysis under
1
1
1
–21.36 with J(PtH) = 1622 Hz. The hydride resonance de-
© 2003 NRC Canada

Ong et al.
1199
Scheme 4.
mild conditions, and there was no evidence for the addition
of protons to the aryl group, though several electrophiles are
known to add easily to the ipso carbon atom (15).
It is easier to detect these hydridoplatinum(IV) complex in-
termediates when they are generated by protonation of alkyl
or aryl platinum(II) complexes and many details of their
structures and energetics have been determined over recent
years (1–10). Strong dependence on the nature of the
hydrocarbyl group, the supporting ligands, the acid used,
and the solvent medium has been demonstrated (3–5). The
phenylplatinum complexes 1 and 2 are constrained to have
the phenyl group(s) trans to nitrogen or carbon, respectively,
and so a study of the dependence of protonolysis mechanism
on stereochemistry is possible.
Studies of H-D exchange
The reaction of 1 and 2 with DBF4 in CDCl3–CD3OD was
studied to observe H-D exchange and hence, to investigate
reversibility of the protonation and C-H reductive elimina-
tion steps. In each case, the benzene was analyzed by GC–
MS. In the reaction with 1, the ratio of C6H6:C6H5D:C6H4D2
was 0.1:1.0:0.2, indicating significant formation of C6H4D2,
but in the reaction of 2 the ratio was 0.1:1.0:0.01, indicating
very little if any deuterium enrichment beyond C6H5D. Inte-
gration of the phenylplatinum resonances in the product 3a
from reaction with complex 1 indicated that there was about
10% D-incorporation, distributed equally in the ortho, meta,
and para positions. In the reaction with 2 there was no de-
tectable D-incorporation in the C6H3 group of the NCN
ligand. It has been shown previously that electrophilic attack
at the ipso carbon atom of the C6H3 group of the NCN
ligand is easy, but of course the chelate ligand prevents
scrambling if reversible addition of D occurs at this point
and no direct evidence of such reactivity was found (15).
The chemistry shown in Schemes 1–3 illustrates that the
mechanism of protonolysis of the phenylplatinum groups in
1, 2, and 3a is similar in each case. Intermediate hydrido-
1
platinum(IV) complexes are detected by low-temperature H
NMR in all cases. These intermediates are formed essen-
tially quantitatively at –78 °C and they survive for several
hours at this temperature, but they decompose on warming
to –10 to –20 °C by reductive elimination of benzene. No
other intermediates were detectable during reactions that
were monitored by NMR, and there were no very dramatic
differences in reactivity.
The chief difference between 1 and 2 was observed when
the deuterolysis of the phenylplatinum groups was carried
out in CDCl3–CD3OD solvent medium, in which there is a
very large excess of exchangeable deuterium. The cleavage
of the phenylplatinum groups from 1 or 2 under these condi-
tions gave mostly C6H5D, as expected for simple cleavage.
However, complex 1 also gave C6H4D2 in significant yield
and moderate deuterium enrichment in the residual
phenylplatinum group of the product 3a. Free benzene did
Discussion
The intermediacy of hydridoplatinum(IV) complexes in
the protonolysis of metal–carbon bonds in electron-rich
alkyl or aryl complexes of platinum(II) or in C-H activation
by electrophilic platinum complexes, is now accepted as the
general rule, though other mechanisms are possible (1–12).
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Can. J. Chem. Vol. 81, 2003
Fig. 3. Proposed reaction coordinate diagram for the protonolysis
of a phenyl group from either complex 1 or 2 in CDCl3–CD3OD.
Table 4. Relative energies and bond distances as predicted by
the DFT calculations.
Complex
B
C
D
F
G
H
E (kcal mol–1)
Distances (Å)
PtH1
0
3.1
–10.0 2.5
–16.9 –17.0
1.53
2.66
2.07
2.03
3.06
2.93
2.28
2.28
1.87
2.64
2.55
2.03
3.00
2.99
2.28
2.07
1.91
2.43
2.52
2.03
3.00
3.00
2.27
2.07
2.91
2.69
2.64
2.06
2.37
2.38
3.27
2.11
2.30
2.69
2.65
2.07
2.35
2.35
3.23
2.11
2.26
PtH2
2.68
2.08
2.57
3.45
2.35
2.10
2.26
PtC4
PtC1
PtC2
PtC3
PtN1
PtN2
not undergo H-D exchange under the experimental condi-
tions, so the deuterium enrichment occurred during cleavage
of the phenylplatinum group to give 3. A proposed sequence
of reactions leading to H-D exchange is shown in Scheme 4.
The five-coordinate complex 10* is proposed as a key inter-
mediate based on earlier work (4, 5); it can be formed by ad-
dition of D+ to complex 1 or by chloride dissociation from
the resting state complex [PtDClPh2(bu2bpy)] (4a*), which
is not shown in Scheme 4. Reductive elimination with C—D
bond formation then leads naturally to the benzene-d1 com-
plex 11*, for which there are now several known precedents
(4, 7, 10). Deuterium enrichment in the phenylplatinum
groups requires that this reductive elimination reaction be
reversible to form a hydrido(deuteriophenyl)platinum(IV)
cation 10** (Scheme 4). The complex 11* is expected to be
fluxional and to undergo rapid edge-to-edge migration of the
benzene group, and so the position of the deuterium label
will naturally scramble among all possible positions in 11*
and 10** (though only one is shown in Scheme 4). Forma-
tion of C6H4D2 requires further deuterium incorporation,
likely by deprotonation of 10** to give 1* followed by addi-
tion of D+ to give 10*** and C-H reductive elimination to
give 11**. Dissociation or displacement of the coordinated
benzene from 11 is irreversible, so free benzene cannot co-
ordinate and hence, cannot undergo H-D exchange. In prin-
ciple, the reactions of Scheme 4 can continue and give
complete H-D exchange but only modest enrichment is ob-
served. Hence, the benzene dissociation or displacement step
from 11 to give 3 is competitive with the C-H oxidative ad-
dition and PtH–PtD exchange steps. Since the addition of D+
to complex 2 gives no significant amount of C6H4D2, in this
case the C-H reductive elimination is probably irreversible.
The difference between the chemistry of complexes 1 and
2 can be understood in terms of the qualitative reaction coor-
dinate diagram shown in Fig. 3. There is a destabilizing
effect of two strong donor ligands (antisymbiosis) in organo-
platinum chemistry, and so the trans-diaryl arrangement in 2
is less stable than the cis-diaryl arrangement in 1. This rela-
tive stability is maintained through the various intermediates
through to the proposed benzene complex, but is most pro-
nounced in the trans-diaryl complexes. The six-coordinate
hydridoplatinum(IV) complex is the most stable of the inter-
mediates and so the only one that is directly observable in
either case. The difference comes at the benzene loss step.
The trans-ligand controls the rate of ligand loss through the
trans-effect, and so the activation energy for benzene loss is
much lower for 2 than for 1. For 1 the activation energy for
benzene loss from the benzene complex cation (Fig. 3) is
similar to that for the reverse reactions leading to H-D ex-
change, whereas for 2 the benzene loss is much faster and so
the back reactions are not competitive.
The relevance to C—H bond activation is also clear from
Fig. 3. The trans-aryl group in [PtX(NCN)] will labilise the
group X– and so facilitate benzene coordination, but the
overall energetics for oxidative addition of the C—H bond
will be less favorable than in the case of [PtXPh(NN)]. It is
interesting that a platinum(II) complex with a pincer ligand,
which has a nitrogen-donor amide rather than a carbon-
donor aryl group at the center, is capable of activating ben-
zene to give a phenylplatinum(II) derivative (17).
The mechanism by which the five-coordinate hydri-
do(phenyl)platinum(IV) intermediate might be transformed
to the benzene complex was examined by using density
functional theory (DFT) on the model complex [PtHMe-
Ph(NH3)2]+, chosen so as to give a reasonable model for the
complex [PtHPh2(bu2bpy)]+ (10). This model is also useful
since it allows a comparison of the Me···H and Ph···H
reductive elimination pathways. Some data are given in Ta-
ble 4 and summarized in Fig. 4, while the proposed mecha-
nism is summarized in Scheme 5. The five-coordinate
complex B (Fig. 4, Scheme 5) has square-pyramidal stereo-
chemistry. The hydride is slightly displaced towards the
methyl group (HPtC = 85°) and the phenyl group rotates
away from the position in which it is orthogonal to the
C2PtN2 plane to avoid steric effects between the hydride and
the ortho hydrogen atom of the phenyl group (Fig. 4). Com-
plex B can decompose by C-H reductive elimination to give
either a phenyl(methane)platinum(II) complex D or a
methyl(benzene)platinum(II) complex G (Scheme 5). The
formation of D (Scheme 5) occurs in a very similar way to
that found earlier for methane reductive elimination from
methyl(hydrido)platinum(IV) complexes (9), with a late
transition state C (Scheme 5) and the activation energy was
calculated as 3.1 kcal mol–1 (Table 4). The reductive elimi-
nation from B by coupling of the hydride and phenyl groups
proved more difficult to define by DFT. The final state is
predicted to be G (Scheme 5, Fig. 4) in which the benzene
ligand is η2-bonded, with the C-C axis perpendicular to the
plane of the platinum(II) and with the benzene oriented to-
wards the methyl group. The orientation of the benzene in G
© 2003 NRC Canada

Ong et al.
1201
Fig. 4. The predicted structures of the complexes [PtHMePh(NH3)2]+ (B) and [PtMe(C6H6)(NH3)2]+ (F and G) and below the calcu-
lated energies (kcal mol–1) of the complexes B–G.
Scheme 5.
is very similar to that found experimentally in the
hydrido(benzene)platinum(II) complex [PtH(C6H6){κ2-
(Hpz*)BHpz*2}]+, in which benzene is oriented towards the
hydride (10). There is a conformer of G in which the ben-
zene is oriented towards the ammine (H) and it is very close
in energy, presumably because the steric effects of CH3 and
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Can. J. Chem. Vol. 81, 2003
NH3 are essentially the same (Table 4), but H will certainly
be less favored in complexes with bulkier amine or imine
ligands. The hydrogen atoms C1H1 and C2H2 in G and H are
bent away from the platinum by about 10° but otherwise the
benzene molecule is like free benzene. The transition state
was expected to resemble E (Scheme 5), with the hydride
bridging between platinum and the ipso carbon in an analo-
gous way as in C, but no such transition state could be lo-
cated. The only transition state found was F in which the
Pt—H bond is completely broken (PtH1 = 2.91 Å) and the
C—H bond completely formed (C1H1 = 1.09 Å) (Scheme 5,
Fig. 4). Complex F is another η2-bonded benzene complex
of platinum(II) but with atom H1 still oriented roughly per-
pendicular to the plane of platinum(II) and so with the coor-
dinated C-C axis in a less favorable orientation than in G or
H for binding to platinum. The benzene is oriented towards
the ammine ligand in F (Fig. 4). It is possible that the reac-
tion proceeds in two steps, with a first transition state on the
way to C-H reductive elimination (E) but this could not be
defined and is probably close in energy to F; the transition
from F to G just requires rocking about the Pt-C1 axis. The
benzene complex G is more stable than the methane com-
plex C, as expected from the relative ligating abilities of
benzene and methane. Since the transition state for C-H
reductive elimination was not found, the relative energies of
the transition states C and E are not known. Complex E is
placed slightly higher than C or F in Fig. 4, based on
the known selectivity for methane elimination in
methyl(phenyl)platinum(II) complexes with nitrogen-donor
ligands (4). The activation energy for the benzene C-H oxi-
dative addition step, as measured by the energy difference
between G and F, is calculated as 19 kcal mol–1, which can
be compared to experimental activation energies of ∆G = 13
to 14 kcal mol–1 for transformation of the benzene complex
[PtH(C6H6){κ2-(Hpz*)BHpz*2}]+ and similar arene com-
plexes, to the corresponding hydrido(phenyl)platinum(IV)
complexes, such as [PtH2Ph{κ2-(Hpz*)BHpz*2}]+ (10).
Although there are still some questions about the detailed
mechanism of the reductive elimination step to form ben-
zene from complex B, it seems that the initial C···H bond
formation occurs by movement of the hydride parallel to the
Pt-C axis, but then a major sideways motion of the phenyl
group occurs so as to allow side-on η2-coordination of the
forming benzene group. The activation of benzene by oxida-
tive addition (4, 7, 10, 17) is then expected to follow the mi-
croscopic reverse of this sequence.
stable in CD2Cl2–CD3OD solution in the absence of added
acid, as shown by NMR. The complexes [{PtPh2(µ-
SMe2)}n], bu2bpy, and [PtCl{2,6-C6H3(CH2NMe2)2}] were
prepared according to literature methods (15, 18). Solutions
containing HCl or DCl were prepared by reaction of a
known amount of acetyl chloride with MeOH or CD3OD, re-
spectively. The DFT calculations were carried out at the
B3LYP level employing a LANL2DZ basis set, which uses
a relativistic effective core potential for platinum. The pro-
gram used was the Gaussian-94 software package (19) and
the methods used were as described and justified previously
(9).
[PtPh2(bu2bpy)] (1)
To a solution of [{PtPh2(µ-SMe2)}n] (0.494 g, 1.04 mmol)
in Et2O was added bu2bpy (0.280 g, 1.04 mmol). The solu-
tion immediately turned orange in color. After 12 h, the or-
ange precipitate that formed was filtered off, washed with
Et2O, and dried under vacuum. Yield: 54%. 1H NMR
(CDCl3) δ: 8.45 (d, 2H, JHH = 6Hz), 7.94 (s, 2H), 7.45 (d,
4H, JHH = 8Hz, Ho(Ph)), 7.35 (d, 2H, JHH = 7 Hz), 7.01 (t,
4H, JHH = 7 Hz, Hm(Ph)), 6.88 (t, 2H, JHH = 7 Hz, Hp(Ph)),
1.37 (s, 18H, t-Bu). Anal. calcd. for C30H34N2Pt (%): C
58.33, H 5.55; found: C 58.11, H 5.56.
[PtClPh(bu2bpy)] (3a)
To a solution of 1 (0.062 g, 0.099 mmol) in CH2Cl2
(0.5 mL) was added HCl (0.099 mmol). The orange precipi-
tate of the product was filtered off, washed with Et2O, and
1
dried under vacuum. Yield: 73%. H NMR (acetone-d6) δ:
9.31 (d, 1H, JHH = 6 Hz), 8.40 (s, 1H), 8.38 (d, 1H, JHH
=
6 Hz), 8.33 (s, 1H), 7.79 (d, 1H, JHH = 6 Hz), 7.42 (d, 1H,
JHH = 6 Hz), 7.32 (m, 2H, Ho(Ph)), 6.98 (t, 2H, JHH = 7 Hz,
Hm(Ph)), 6.87 (t, 1H, JHH = 7 Hz, Hp(Ph)), 1.44 (s, 9H, t-
Bu), 1.38 (s, 9H, t-Bu). Anal. calcd. for C24H29ClN2Pt (%):
C 50.04, H 5.07; found: C 49.56, H 4.94.
[PtPh(O2CCF3)(bu2bpy)] (3b)
To a solution of 1 (0.068 g, 0.11 mmol) in CH2Cl2 was
added CF3CO2H (9 µL, 0.11 mmol). The reaction mixture
was stirred for 12 h and the solvent was removed under vac-
uum to yield the product as an orange powder. Yield: 56%.
1H NMR (acetone-d6) δ: 8.85 (d, 1H, JHH = 6 Hz), 8.53 (s,
1H), 8.46 (s, 1H), 8.17 (d, 1H, JPtH = 60 Hz, JHH = 6Hz),
7.82 (d, 1H, JHH = 6 Hz), 7.53 (d, 1H, JHH = 6 Hz), 7.37 (d,
2H, JHH = 7 Hz, Ho(Ph)), 7.13 (t, 2H, JHH = 7 Hz, Hm(Ph)),
7.08 (t, 1H, JHH = 7 Hz, Hp(Ph)), 1.46 (s, 9H, t-Bu), 1.39 (s,
9H, t-Bu). Anal. calcd. for C26H29F3N2O2Pt1(%): C 47.78, H
4.47; found: C 47.49, H 4.41.
Experimental section
Syntheses were carried out using a nitrogen atmosphere,
employing either Schlenk or glovebox techniques. Solvents
1
were dried and distilled under N2 prior to use. H and 13C
[PtPh(CF3SO3)(bu2bpy)] (3c)
NMR spectra were recorded using Varian Inova 400 and
600 MHz spectrometers. Chemical shifts are reported rela-
tive to SiMe4. GC–MS experiments were carried out using a
Finnigan Mat 8200 spectrometer; samples were prepared us-
ing CD2Cl2–CD3OD solutions followed by direct injection to
the GC coupled to the MS and isotopic composition of ben-
zene was determined by simulation, based on spectra of au-
thentic samples. The phenylplatinum(II) complexes were
This was prepared similarly by using CF3SO3H. Yield:
64%. 1H NMR (acetone-d6) δ: 8.88 (d, 1H, JHH = 6 Hz), 8.53
(s, 1H), 8.46 (s, 1H), 8.16 (d, 1H, JPtH = 58 Hz, JHH = 6 Hz),
7.84 (d, 1H, JHH = 6 Hz), 7.54 (d, 1H, JHH = 6 Hz), 7.35 (d,
2H, JHH = 7 Hz, Ho(Ph)), 6.98 (t, 2H, JHH = 7 Hz, Hm(Ph)),
6.87 (t, 1H, JHH = 7 Hz, Hp(Ph)), 1.46 (s, 9H, t-Bu), 1.40 (s,
9H, t-Bu). Anal. calcd. for C25H29F3N2O3SPt (%): C 43.54,
H 4.24; found: C 43.56, H 4.31.
© 2003 NRC Canada

Ong et al.
1203
mixture was stirred for 2 h at which time the beige precipi-
tate was filtered off and washed with ether. Yield: 61%. H
NMR (CDCl3) δ: 6.97 (t, 1H, JHH = 7 Hz), 6.79 (d, 2H,
JHH = 7 Hz), 4.00 (s, 4H, JPtH = 45 Hz, N-CH2), 3.06 (s,
12H, JPtH = 36 Hz, NMe2). Anal. calcd. for C12H19ClN2Pt
(%): C 34.17, H 4.54; found: C 34.01, H 4.62.
[PtPh(BF4)(bu2bpy)] (3d)
1
This was prepared similarly by using HBF4. Yield: 48%.
1H NMR (acetone-d6) δ: 8.89 (d, 1H, JHH = 6 Hz), 8.55 (s,
1H), 8.47 (s, 1H), 8.19 (d, 1H, JHH = 6 Hz), 7.85 (d, 1H,
JHH = 6 Hz), 7.55 (d, 1H, JHH = 6 Hz), 7.37 (d, 2H, JHH
=
7 Hz, Ho(Ph)), 7.13 (m, 2H, Hm(Ph)), 7.05 (m, 1H, Hp(Ph)),
1.46 (s, 9H, t-Bu), 1.40 (s, 9H, t-Bu). Anal. calcd. for
C24H29BF4N2Pt (%): C 45.95, H 4.66; found: C 45.47, H
4.80.
[Pt(CF3CO2){2,6-C6H3(CH2NMe2)2}] (7b)
This was prepared similarly using CF3CO2H. Yield: 48%.
1H NMR (CD2Cl2) δ: 6.81 (t, 1H, JHH = 6 Hz), 6.79 (d, 2H,
JHH = 4 Hz), 4.01 (s, 4H, JPtH = 48 Hz, N-CH2), 2.95 (s,
12H, JPtH = 36 Hz, NMe2). Anal. calcd. for C14H19F3O2N2Pt
(%): C 33.67, H 3.83; found: C 33.59, H 3.72.
[PtHClPh2(bu2bpy)] (4a)
To an NMR tube charged with a solution of 1 (0.052 g,
0.085 mmol) in CDCl3 (0.5 mL) at –78 °C was added HCl
1
(0.085 mmol). H NMR in CDCl3 at –80 °C δ: 8.18 (s, 2H),
8.06 (d, 2H, JHH = 6 Hz), 7.86 (d, 2H, JHH = 7 Hz), 7.29 (d,
4H, JHH = 7 Hz, Ho(Ph)), 6.76 (t, 4H, JHH = 7 Hz, Hm(Ph)),
6.67 (t, 2H, JHH = 7 Hz, Hp(Ph)), 1.19 (s, 18H, t-Bu), –20.15
(s, 1H, JPtH = 1613 Hz, Pt-H). Compound 2 was indefinitely
stable at –78 °C but decomposed rapidly at –20 °C to give
C6H6 and [PtClPh(bu2bpy)] (3a) as monitored by NMR.
[Pt(CF3SO3){2,6-C6H3(CH2NMe2)2}] (7c)
This was prepared similarly using CF3SO3H. Yield: 36%.
1H NMR (CD2Cl2) δ: 6.92 (t, 1H, JHH = 7 Hz), 6.76 (d, 2H,
JHH = 7 Hz), 3.98 (s, 4H, JPtH = 41 Hz, N-CH2), 2.99 (s,
12H, JPtH
=
37 Hz, NMe2). Anal. calcd. for
C13H19F3N2O3PtS (%): C 29.16, H 3.58; found: C 29.42, H
3.73.
[PtH(NCCD3)Ph2(bu2bpy)][BF4] (7)
This was prepared similarly in CDCl3–CD3CN (1.0 mL)
by using HBF4. H NMR (CDCl3–CD3CN) δ: 8.45 (s, 2H),
[Pt(BF4){2,6-C6H3(CH2NMe2)2}] (7d)
1
1
This was prepared similarly using HBF4. Yield: 57%. H
8.10 (d, 2H, JHH = 6 Hz), 7.52 (d, 2H, JHH = 6 Hz), 7.18 (d,
4H, JHH = 7 Hz, Ho(Ph)), 6.99 (t, 4H, JHH = 7 Hz, Hm(Ph)),
6.89 (t, 2H, JHH = 7 Hz, Hp(Ph)), 1.36 (s, 18H, t-Bu), –21.84
(s, 1H, JPtH = 1619 Hz, Pt-H). Compound 7 was indefinitely
stable at –78 °C but decomposed rapidly at –20 °C to give
C6H6 and [Pt(BF4)(C6H5)(tbu2bpy)] (3d).
NMR (acetone-d6) δ: 6.72 (t, 1H, JHH = 7 Hz), 6.55 (d, 2H,
JHH = 7 Hz), 3.78 (s, 4H, JPtH = 48 Hz, N-CH2), 2.76 (s,
12H, JPtH = 38 Hz, NMe2). Anal. calcd. for C12H19BF4N2Pt
(%): C 30.46, H 4.05; found: C 30.42, H 4.11.
[PtHClPh{2,6-C6H3(CH2NMe2)2}] (8)
To an NMR tube charged with a solution of 2 (0.046 g,
0.091 mmol) in CDCl3 at –78 °C was added HCl
[PtHCl2Ph(bu2bpy)] (6)
(0.091 mmol). 1H NMR (CDCl3) δ: 7.70 (d, 2H, JHH
=
To an NMR tube charged with a solution of 3a (0.016 g,
0.028 mmol) in CDCl3 (0.6 mL) at –78 °C was added HCl
6 Hz), 7.16 (t, 1H, JHH = 7 Hz), 6.98 (d, 2H, JHH = 7 Hz,
Ho(Ph)), 6.96 (m, 2H, Hm(Ph)), 6.94 (t, 1H, JHH = 7 Hz,
Hp(Ph)), 4.15 (s, 4H, N-CH2), 2.89 (s, 12H, NMe2), –21.36
(s, 1H, JPtH = 1622 Hz, Pt-H). Compound 8 was indefinitely
stable at –78 °C but decomposed rapidly at –20 °C to give
C6H6 and [PtCl{C6H3(CH2NMe2)2}] (7a).
1
(0.028 mmol). H NMR (CDCl3) δ: 9.17 (s, 1H), 8.25 (s,
1H), 7.99 (s, 1H), 7.94 (s, 1H), 7.52 (s, 1H), 7.22 (d, 2H,
JHH = 6.8Hz, Ho(Ph)), 7.15 (s, 1H), 6.89 (t, 2H, JHH = 7 Hz,
Hm(Ph)), 6.76 (t, 1H, JHH = 7 Hz, Hp(Ph)), 1.28 (s, 9H,
t-Bu), 1.22 (s, 9H, t-Bu), –25.94 (s, 1H, JPtH = 1540 Hz, Pt-
H). Compound 6 was indefinitely stable at –78 °C but
decomposed rapidly at –10 °C to give C6H6 and
[PtCl2(bu2bpy)].
[PtHPh(NCCD3){2,6-C6H3(CH2NMe2)2}][CF3SO3] (9)
This was prepared similarly in CDCl3–CD3CN solution at
1
–78 °C by using CF3SO3H. H NMR (CDCl3–CD3CN) δ:
[PtPh{2,6-C6H3(CH2NMe2)2}] (2)
7.92 (t, 1H, JHH = 8 Hz), 7.46 (d, 2H, JHH = 8 Hz), 6.98 (m,
2H, Ho(Ph)), 6.87 (t, 2H, JHH = 7 Hz, Hm(Ph)), 6.75 (t, 1H,
JHH = 7 Hz, Hp(Ph)), 4.10 (s, 4H, N-CH2), 2.86 (s, 12H,
NMe2), –20.47 (s, 1H, JPtH = 1644 Hz, Pt-H). Compound 9
was indefinitely stable at –78 °C but decomposed rapidly at
–20 °C to give C6H6 and [Pt(CF3SO3){C6H3(CH2NMe2)2}]
(7c).
To a solution of [PtCl(C6H3(CH2NMe2)2)] (0.357 g,
0.78 mmol) in ether (10 mL) at 0 °C was added PhLi
(0.43 mL, 0.78 mmol). The mixture was stirred at 0 °C for
5 min, then for 1 h at room temperature. The beige precipi-
tate that had formed was filtered off, washed with pentane,
and recrystallized from CH2Cl2–pentane to yield colorless
1
crystals of the product (15). Yield: 56%. H NMR (CDCl3)
δ: 7.67 (d, 2H, JHH = 6 Hz), 7.11 (t, 1H, JHH = 7 Hz), 6.97
X-ray structure determinations
(d, 2H, JHH = 7 Hz), 6.92 (m, 2H), 6.87 (t, 1H, JHH = 7 Hz),
Crystals of 1 and 2 were grown from acetone and chloro-
form solution, respectively. Crystals were mounted on glass
fibres. Data were collected by using a Nonius Kappa-CCD
diffractometer with COLLECT (20) software. Crystal data
and refinement parameters are listed in Table 5. Data were
scaled using SCALEPACK (21), and empirical absorption
corrections were applied using redundant data and XPREP
(SHELXTL 5.03). Full-matrix least-squares refinement on
4.11 (s, 4H, JPtH = 42 Hz, N-CH2), 2.89 (s, 12H, JPtH
=
44 Hz, NMe2). 13C NMR (CDCl3) δ: 145.54, 139.59, 126.84,
123.19, 122.63, 119.25, 81.22, 54.36.
[PtCl{2,6-C6H3(CH2NMe2)2}] (7a)
To a solution of 2 (0.052 g, 0.105 mmol) in a THF:Et2O
(50:50) mixture was added HCl (0.105 mmol). The reaction
© 2003 NRC Canada

1204
Can. J. Chem. Vol. 81, 2003
Table 5. Crystal data and structure refinement for complexes 1 and 2.
Complex
1·2Me2CO
2
Formula, fw
C36H46N2O2Pt, 733.84
C18H24N2Pt, 463.09
Temperature (K)
Wavelength (Å)
Crystal system
Space group
200(2)
0.71073
Monoclinic
P2/c
293(2)
0.71070
Monoclinic
P2(1)/n
Cell dimensions
a = 12.7265(3) Å
b = 14.2079(2) Å
c = 10.0711(2) Å
β = 69.0990(3)°
1701.2(6), 2
1.433
a = 9.3780(19) Å
b = 14.663(3) Å
c = 12.650(3) Å
β = 107.35(3)°
1660.2(6), 4
1.856
Volume (Å3), Z
Density (calcd.) (Mg m–3)
Abs. coeff. (mm–1)
F(000)
4.156
740
2.112
224
θ Range (°)
2.60–27.48
17 452
3897/0/203
1.029
R1 = 0.0309
wR2 = 0.0732
R1 = 0.0361
wR2 = 0.0752
2.67–24.99
5665
2918/0/190
0.961
R1 = 0.0321
wR2 = 0.081
R1 = 0.0395
wR2 = 0.0852
No. of reflns collected
Data/restraints/param.
Goodness-of fit on F2
Final R indices (I > 2σ(I))
R indices (all data)
F2 was performed after solving using Patterson methods and
the solution package SHELXTL 5.03 (22). Complex 1 con-
tained two molecules of acetone of solvation.3
Puddephatt. Organometallics, 18, 2861 (1999); J.G. Hinman,
C.R. Baar, M.C. Jennings, and R.J. Puddephatt. Organo-
metallics, 19, 563 (2001).
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Johansson, O. Gropen, O.B. Ryan, O. Swang, and M. Tilset. J.
Am. Chem. Soc. 122, 10 831 (2000).
Acknowledgment
We thank the Natural Sciences and Engineering Research
Council of Canada (NSERC) for financial support.
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ww.ccdc.cam.ac.uk/conts/retreiving.html (or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ,
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© 2003 NRC Canada