Arylplatinum complexes with arylboronate ligands. Their preparation, structure, and relevance to transmetalation

Article abstract of DOI:10.1021/om049050t

The reactions of arylboronic acids with trans-PtPh(I)(PMe ₂Ph)₂ afford new arylboronato platinum complexes, trans-PtPh(OB(OH)Ar)(PMe₂Ph)₂, and diarylplatinum complexes, trans-PtPh(Ar)(PMe₂Ph)₂.

Full text of DOI:10.1021/om049050t

Organometallics 2005, 24, 3815-3817
3815
Arylplatinum Complexes with Arylboronate Ligands.
Their Preparation, Structure, and Relevance to
Transmetalation
Ivayla Pantcheva, Yasushi Nishihara,† and Kohtaro Osakada*
Chemical Resources Laboratory, Tokyo Institute of Technology,
4259 Nagatsuta, Midori-ku, Yokohama 226-8503, Japan
Received December 2, 2004
Scheme 1
Summary: The reactions of arylboronic acids with trans-
PtPh(I)(PMe2Ph)2 afford new arylboronato platinum
complexes, trans-PtPh(OB(OH)Ar)(PMe2Ph)2, and dia-
rylplatinum complexes, trans-PtPh(Ar)(PMe2Ph)2.
Transmetalation of arylboronic acid with the com-
plexes of late transition metals, Pd,1 Rh,2 and Pt,3 is
involved as a crucial step in synthetic organic reactions
such as the cross-coupling and 1,4-addition reactions
catalyzed by these metals. There have been only a few
reports on the stoichiometric transmetalation of aryl-
boronic acids with organotransition-metal complexes,
although transmetalation of organomagnesium and
organoaluminum compounds provides a common route
to the alkyl and aryl complexes of transition metals.
Arylpalladium halogeno complexes undergo transmeta-
lation by arylboronic acids to produce diarylpalladium
complexes in the presence of a base such as OH- or
Ag2O. This reaction has been studied in relation to the
mechanism of the cross-coupling reaction catalyzed by
the Pd complexes. The added base is proposed to have
a dual role in the transmetalation: activation of the
B-C bond of the arylboronic acid and of the Pd-halogen
bond of the complex.4,5 A dicationic palladium complex
with labile MeCN ligands, [Pd(dppe)(NCMe)2]2+, reacts
with arylboronic acid without addition of base to yield
a complex with a Pd-Ph bond.6 PtCl2(P(OAr)3)2 also
catalyzes the cross-coupling reaction of arylboronic acids
with aryl halides, which probably involves a transmeta-
lation reaction.3 Studies on the stoichiometric reaction
of arylboronic acids with Pt complexes would reveal
detailed mechanisms of transmetalation using Pt com-
plexes. In this paper, we report the reaction of aryl-
boronic acids with a phenylplatinum iodo complex in the
presence of base and isolation of a new type of plati-
num(II) complex having an arylboronato (O-B(OH)-
Ar) ligand.7
The reactions of ArB(OH)2 (Ar ) C6H4OMe-4, C6H4-
OMe-2) with trans-PtPh(I)(PMe2Ph)2 in the presence of
Ag2O and H2O produce the diarylplatinum complexes,
trans-PtPh(Ar)(PMe2Ph)2 (1a, Ar ) C6H4OMe-4; 1b, Ar
) C6H4OMe-2), at room temperature (24-72 h), as
shown in Scheme 1. Reaction i includes intermolecular
transfer of the aryl group from B to Pt.
The reaction mixtures after 4-6 h contain new Pt
complexes with an arylboronate ligand, trans-PtPh(OB-
(OH)Ar)(PMe2Ph)2 (2a, Ar ) C6H4OMe-4; 2b, Ar )
C6H4OMe-2). Figure 1 shows the molecular structures
of 1a and 2a determined by X-ray crystallography.8 Both
complexes have typical square-planar geometry around
the Pt(II) center. The Pt-C bond distance of 2a
(2.000(9) Å) is shorter than those of 1a (2.095(6) and
2.096(6) Å), which is ascribed to the trans influence of
the aryl ligand being greater than that of the aryl-
boronate ligand. The geometry of 2a with the aryl-
boronato and phenyl ligands at mutually trans positions
renders the Pt-O bond (2.094(6) Å) longer than those
of the previously reported alkoxoplatinum complexes.9
The B-O1 bond length (1.32(1) Å) is slightly shorter
than B-O2 (1.39(1) Å), and both distances fall into the
distance of triangular BO3 groups of the organoboron
compounds.10 Complexes 2a and 2b, once isolated, are
stable in solution; the 1H and 31P{1H} NMR spectra do
† Present address: Department of Chemistry, Okayama University,
3-1-1 Tsushimanaka, Okayama 700-8530, Japan.
(1) For reviews on the Suzuki-Miyaura reaction see: (a) Miyaura,
N.; Suzuki, A. Chem. Rev. 1995, 95, 2457. (b) Miyaura, N. In Advances
in Metal-Organic Chemistry; Liebeskind, L. S., Ed.; JAI: London, 1998;
Vol. 6, pp 187-243. (c) Stanforth, S. P. Tetrahedron 1998, 54, 263-
303. (d) Tamao, K.; Miyaura, N. In Topics in Current Chemistry;
Springer-Verlag: Berlin, 2002; Vol. 219, p 11.
(2) (a) Hayashi, T.; Takahashi, M.; Takaya, Y.; Ogasawara, M. J.
Am. Chem. Soc. 2002, 124, 5052. (b) Hayashi, T.; Senda, T.; Ogasawara,
M. J. Am. Chem. Soc. 2000, 122, 10716.
(3) Bedford, R. B.; Hazelwood, S. L.; Albisson, D. A. Organometallics
2002, 21, 2599.
(7) There have been no reports on transition-metal complexes having
an arylboronato ligand (M-O-B(OH)-Ar). A limited number of
complexes with similar coordination bonds have been reported. See:
Bartlett, R. A.; Ellison, J. J.; Power, P. P.; Shoner, S. C. Inorg. Chem.
1991, 30, 2888 (M-O-B-Ar2, M ) Fe, Mn). Miyamoto, T.; Ichida, H.
Chem. Lett. 1991, 435 (Pt-O-B(OH)-O-). Vidovic, D.; Moore, J. A.;
Jones, J. N.; Cowley, A. H. J. Am. Chem. Soc. 2005, 127, 4566 (Al-
O-B(N-)2).
(4) Aliprantis, A. O.; Canary, J. W. J. Am. Chem. Soc. 1994, 116,
6985.
(5) (a) Nishihara, Y.; Onodera, H.; Osakada, K. Chem. Commun.
2004, 192. (b) Osakada, K.; Onodera, H.; Nishihara, Y. Organometallics
2005, 24, 190.
(6) Nishikata, T.; Yamamoto, Y.; Miyaura, N. Organometallics 2004,
23, 4317.
10.1021/om049050t CCC: $30.25 © 2005 American Chemical Society
Publication on Web 07/09/2005

3816 Organometallics, Vol. 24, No. 16, 2005
Communications
Figure 1. ORTEP drawings of (a) 1a and (b) 2a with 50%
thermal ellipsoid plotting. Hydrogen atoms are omitted for
clarity. Selected distances (Å) and angles (deg) of 1a: Pt-
C1 ) 2.095(6), Pt-C7 ) 2.096(6), Pt-P1 ) 2.283(2), Pt-
P2 ) 2.283(3); P1-Pt-P2 ) 177.84(7), P1-Pt-C1 )
90.1(2), P1-Pt-C7 ) 90.7(2), P2-Pt-C1 ) 88.1(2), P2-
Pt-C7 ) 91.2(2), C1-Pt-C7 ) 179.0(2). Selected distances
(Å) and angles (deg) of 2a: Pt-C1 ) 2.000(9), Pt-O1 )
2.094(6), Pt-P1 ) 2.283(3), Pt-P2 ) 2.277(3); P1-Pt-C1
) 91.6(3), P1-Pt-P2 ) 172.8(1), P1-Pt-O1 ) 87.0(2),
P2-Pt-O1 ) 91.5(2), P2-Pt-C1 ) 89.8(3), C1-Pt-O1 )
178.4(3).
Figure 2. Time profile of the reaction of (4-methoxyphe-
nyl)boronic acid with PhPt(I)(PMe2Ph)2 in the presence of
Ag2O: (O) PtPh(I)(PMe2Ph)2; (0) 1a; (9) 2a. PtPh(I)(PMe2-
Ph)2 (0.16 mmol), Ag2O (0.26 mmol), and (4-methoxy-
phenyl)boronic acid (0.24 mmol) are reacted in THF/H2O
(8 mL/0.4 mL) in the presence of Ph2CH2 (internal stan-
dard, 0.24 mmol). Part of the solution (ca. 0.7 mL) is
transferred to a Schlenk flask periodically. After removal
of the solvent of each sample by evaporation, the product
1
not change for 24 h at room temperature. The 1H NMR
spectra contain an apparent triplet due to virtual
coupling at 1.18-1.30 ppm. The 31P{1H} and 11B NMR
spectra of 2a and 2b in C6D6 exhibit signals with
reasonable positions and coupling constants (δP -3.36
for 2a (J(PtP) ) 2890 Hz) and -2.36 for 2b (J(PtP) )
3002 Hz); δB 29.64 for 2a and 28.27 for 2b). Figure 2
depicts the change in amounts of the complexes during
reaction i using (4-methoxyphenyl)boronic acid. The
starting complex trans-PtPh(I)(PMe2Ph)2 is consumed
and converted into a mixture of 2a and uncharacterized
Pt complexes.11,12 Further reaction leads to the forma-
tion of 1a almost quantitatively.
Ag2O may play dual roles in the reactions of Scheme
1: abstraction of the iodo ligand from the starting
complex and activation of the arylboronate ligand. Since
OH- could coordinate to the B center of the arylboronate
bonded to Pt and activate the B-C bond, the reaction
of OH- with 2a was conducted. Stirring a THF solution
of 2a, 4-methoxyphenylboronic acid, and TBAOH- (TBA
) NBu4+) in a 1:1.5:1.6 molar ratio produces a mixture
of the phenylplatinum hydroxo complex PtPh(OH)-
(PMe2Ph)2 and 2a in a 60:40 molar ratio. Since the
reaction mixture of Ag2O with PtPh(I)(PMe2Ph)2 also
forms PtPh(OH)(PMe2Ph)2 in part, this complex may be
is characterized by H NMR.
involved in the upper reactions of Scheme 1. PtPh(OH)-
(PMe2Ph)2, prepared as shown above, has a trans
structure initially but undergoes isomerization to pro-
duce a mixture of cis and trans isomers during the
reaction.13 Addition of a large excess amount of (4-
methoxyphenyl)boronic acid to the reaction mixture
regenerates 2a via reversible exchange of the OH and
arylboronato ligands in the presence of a base. The
reaction of 2a, (4-methoxyphenyl)boronic acid, and
TBAOH- in a 1:1.5:10 molar ratio forms mixtures of
PtPh(OH)(PMe2Ph)2 and 1a in a 58:62 molar ratio after
3 h and in a 25:75 molar ratio after 36 h. Scheme 2
summarizes the results of the reactions.
A mixture of 2a and (4-methoxyphenyl)boronic acid
in the presence of Ag2O and H2O also produces 1a.
Formation of diarylplatinum complexes requires a base
such as Ag2O or OH-, because leaving a mixture of 2a
and (4-methoxyphenyl)boronic acid in THF does not
produce the diarylplatinum complex at all. Addition of
(2-methoxyphenyl)boronic acid to a THF solution of 2a
results in partial conversion of the complex into 2b via
exchange of the arylboronate ligand, even in the absence
of Ag2O. This ligand exchange makes it difficult to
determine by crossover experiments whether the forma-
tion of 1a from 2a in Scheme 2 is an intramolecular
reaction.
(8) Crystal data and details of the structure refinement of 1a:
C
29H34OP2Pt, Mr ) 655.62, 0.32 × 0.28 × 0.05 mm, monoclinic, a )
7.585(3) Å, b ) 39.428(4) Å, c ) 9.540(3) Å, â ) 110.67(2)°, V )
2669(1) Å3, space group P21/a (No. 14), Z ) 4, Dcalcd ) 1.631 g cm-3
,
In summary, we succeeded in the isolation of plati-
num complexes that contain a unique arylboronate
F(000) ) 1296.00, µ(MoKR) ) 5.38 mm-1, Mo KR radiation (λ )
0.710 70 Å), 6687 total reflections measured, 6241 unique reflections
(Rint ) 0.033), 4249 observations (I > 3.00σ(I)), 298 variables, R(I >
3.00σ(I)) ) 0.035, Rw(I > 3.00σ(I)) ) 0.035. Crystal data and details of
the structure refinement of 2a: C29H35BO3P2Pt, Mr ) 699.44, 0.30 ×
0.22 × 0.04 mm, monoclinic, a ) 13.683(9) Å, b ) 9.430(3) Å, c )
23.089(5) Å, â ) 92.10(3)°, V ) 2977(2) Å3, P21/n (No. 14), Z ) 4, Dcalcd
) 1.560 g cm-3, F(000) ) 1384.00, µ(Mo KR) ) 4.83 mm-1, Mo KR
radiation (λ ) 0.710 70 Å), 7567 total reflections measured, 7271
unique reflections (Rint ) 0.041), 4080 observations (I > 3.00σ(I)), 325
variables, R(I > 3.00σ(I)) ) 0.054, Rw(I > 3.00σ(I)) ) 0.046.
(9) (a) Strukul, G.; Michelin, R. A.; Orbell, J.; Randaccio, L. Inorg.
Chem. 1983, 22, 3706. (b) Bryndza, H. E.; Tam, W. Chem. Rev. 1988,
88, 1163 and references therein. (c) Osakada, K.; Kim, Y.-J.; Yamamoto,
A. J. Organomet. Chem. 1990, 382, 303.
(12) Yield of 2a determined by 1H NMR of the reaction mixture after
6 h is lower than the yield of the isolated complex from the reaction
under the same conditions. It may be due to conversion of a part of
the uncharacterized Pt complexes formed at this stage into 2a during
isolation process.
(13) Bennett et al. reported that the reaction of KOH with [PtPh-
(acetone)(PMe2Ph)2]+ produced PtPh(OH)(PMe2Ph)2 as a mixture of
the cis and trans isomers (Arnold, D. P.; Bennett, M. A. J. Organomet.
Chem. 1980, 199, 119). Our attempts to prepare PtPh(OH)(PMe2Ph)2
via the reaction of NBu4+OH- with the cationic complex also formed a
cis and trans mixture of the complex. The NMR spectra of the reaction
mixture in Scheme 2 contain signals whose positions and coupling
constants are identical with the data of Bennett. The initial product
of our reactions is trans-PtPh(OH)(PMe2Ph)2, although it could not be
isolated due to facile change of it into the cis isomer.
(10) Behm, H. Acta Crystallogr., Sect. C 1988, 44, 1348.
(11) Gillespie, R. J.; Bytheway, I.; Robinson, E. A. Inorg. Chem.
1998, 37, 2811.

Communications
Organometallics, Vol. 24, No. 16, 2005 3817
Scheme 2
ligand (O-B(OH)-Ar) from the reaction of arylboronic
acid with a phenylplatinum iodo complex. These new
complexes can be regarded as possible intermediates of
the stoichiometric transmetalation of arylboronic acid
with Pt complexes on the basis of the results of the
reactions in Schemes 1 and 2, although a part of the
detailed reaction mechanism remains obscured.
Diversity and Development of Functionalities”. I.P.
acknowledges the JSPS (Japanese Society for Promotion
of Science) for a postdoctoral fellowship for foreign
researchers.
Supporting Information Available: Text giving experi-
mental details and characterization data for the new com-
pounds prepared in this paper and text and tables giving
details of the X-ray crystal structure determinations of 1a and
2a; X-ray data are also given as CIF files. This material is
available free of charge via the Internet at http://pubs.acs.org.
Acknowledgment. This work was supported by a
Grant-in-Aid for Scientific Research on Priority Areas
(No. 15036223 “Dynamic Complexes”) from the Ministry
of Education, Science, Sports, and Culture of Japan and
by a 21st Century COE program “Creation of Molecular
OM049050T