Synthesis and reactivity of a platinum(II) complex with a chelating dehydro(arylboronic anhydride) ligand. Transmetalation of arylboronic acid

Article abstract of DOI:10.1021/om0509903

The reaction of ArB(OH)₂ (Ar = C₆H₄OMe-4, Ph, C₆H₄COMe-4) with PtI₂(dppe) in THF in the presence of Ag₂O and H₂O at room temperature produced a Pt complex with a chelating dehydro(arylboronic anhydride) ligand, Pt(OBArOBArO)(dppe) (1a, Ar = C₆H₄OMe-4; 1b, Ar = Ph; 1c, Ar = C₆H₄COMe-4). The complexes were characterized by NMR spectroscopy and X-ray crystallography. Reactions of protonic acids, such as HCl, CF₃COOH, and CH₃COOH, with 1a yielded complexes with chloro and carboxylate ligands, PtX₂(dppe) (2, X = Cl; 3, X = OCOCF₃; 4, X = OCOMe). The complexes 1a - c react with arylboronic acids bearing the same aryl group as the ligands of the complexes to form diarylplatinum complexes, PtAr₂(dppe) (5a, Ar = C₆H ₄OMe-4; 5b, Ar = Ph; 5c, Ar = C₆H₄COMe-4), respectively. Reactions of 4-MeCOC₆H₄B(OH)₂ with Ib and of PhB(OH)₂ with 1c in 2:1 molar ratios form mixtures of three diarylplatinum complexes in a statistical ratio.

Full text of DOI:10.1021/om0509903

Organometallics 2006, 25, 1735-1741
1735
Synthesis and Reactivity of a Platinum(II) Complex with a
Chelating Dehydro(arylboronic anhydride) Ligand. Transmetalation
of Arylboronic Acid
Ivayla Pantcheva† and Kohtaro Osakada*
Chemical Resources Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta,
Midori-ku, Yokohama 226-8503, Japan
ReceiVed NoVember 17, 2005
The reaction of ArB(OH)2 (Ar ) C6H4OMe-4, Ph, C6H4COMe-4) with PtI2(dppe) in THF in the presence
of Ag2O and H2O at room temperature produced a Pt complex with a chelating dehydro(arylboronic
anhydride) ligand, Pt(OBArOBArO)(dppe) (1a, Ar ) C6H4OMe-4; 1b, Ar ) Ph; 1c, Ar ) C6H4COMe-
4). The complexes were characterized by NMR spectroscopy and X-ray crystallography. Reactions of
protonic acids, such as HCl, CF3COOH, and CH3COOH, with 1a yielded complexes with chloro and
carboxylate ligands, PtX2(dppe) (2, X ) Cl; 3, X ) OCOCF3; 4, X ) OCOMe). The complexes 1a-c
react with arylboronic acids bearing the same aryl group as the ligands of the complexes to form
diarylplatinum complexes, PtAr2(dppe) (5a, Ar ) C6H4OMe-4; 5b, Ar ) Ph; 5c, Ar ) C6H4COMe-4),
respectively. Reactions of 4-MeCOC6H4B(OH)2 with 1b and of PhB(OH)2 with 1c in 2:1 molar ratios
form mixtures of three diarylplatinum complexes in a statistical ratio.
complexes of these metals. Recently, our group as well as that
of Clarke et al. have reported the transmetalation of arylboronic
acids with Pt complexes.9,10 The reaction of arylboronic acids
with trans-PtPh(I)(PMe2Ph)2 in the presence of Ag2O/H2O
afforded a platinum complex containing an arylboronate ligand,
trans-Pt(OB(OH)C6H4OMe-4)(Ph)(PMe2Ph)2.9 This complex
further reacts with a mixture of 4-MeOC6H4B(OH)2 and Ag2O
in the presence of H2O to yield trans-Pt(C6H4OMe-4)(Ph)(PMe2-
Ph)2 via the activation of the B-C bond of the arylboronate
ligand of the complex or that of the added arylboronic acid,
and the transfer of the aryl group from arylboronic acid to PtPh-
(Br)(dppe) occurs in the presence of NBu4F to form PtPh2-
(dppe).10
Introduction
Arylboronic acids have been employed as a convenient source
of aryl groups in synthetic organic reactions catalyzed by Pd,
Rh, Ni, and Pt complexes.1 These reactions, including cross-
coupling with organic halides (Suzuki-Miyaura coupling)2 and
the 1,4-addition of an aryl group to R,â-unsaturated carbonyl
compounds,3 are believed to involve the activation of the B-C
bond promoted by transition metals as a crucial step. Despite
the wide use of the above catalytic reactions, there have been
a few reports on the stoichiometric reactions of arylboronic acids
with transition-metal complexes, yielding aryltransition-metal
complexes via the activation of the B-C bond. The transmeta-
lation of aryllithium, arylmagnesium, and arylaluminum reagents
provides a general method of preparing aryltransition-metal
complexes.4 Arylpalladium5-7 and arylrhenium8 complexes have
been obtained from the transmetalation of arylboronic acid with
In this paper, we report the preparation of platinum(II)
complexes with a chelating dehydro(arylboronic anhydride)
ligand and their reaction with arylboronic acids, affording
diarylplatinum complexes via the transfer of aryl groups from
boron to platinum.
† On leave from the Department of Chemistry, Sofia University
“St. Kl. Ohridsky”, 1, J. Bourchier blvd., 1000 Sofia, Bulgaria.
(1) (a) Miyaura, N.; Suzuki, A. Chem. ReV. 1995, 95, 2457. (b) Miyaura,
N. AdV. Met.-Org. Chem. 1998, 6.
Results and Discussion
(2) Recent selected papers: (a) Hanazawa, T.; Koyama, A.; Wada, T.;
Morishige, E.; Okamoto, S.; Sato, F. Org. Lett. 2003, 5, 523. (b) Navarro,
O.; Kelly, R. A., III; Nolan, S. P. J. Am. Chem. Soc. 2003, 125, 16194. (c)
Nguyen, H. N.; Huang, X.; Buchwald, S. L. J. Am. Chem. Soc. 2003, 125,
11818. (d) Yamamoto, Y.; Ishii, J.-I.; Nishiyama, H.; Itoh, K. J. Am. Chem.
Soc. 2004, 126, 3712. (e) Grasa, G. A.; Hillier, A. C.; Nolan, S. P. Org.
Lett. 2001, 3, 1077. (f) Li, J.-H.; Liu, W.-J. Org. Lett. 2004, 6, 2809. (g)
Sinclair, D. J.; Sherburn, M. S. J. Org. Chem. 2005, 70, 3730. (h) Hanazawa,
T.; Koyama, A.; Nakata, K.; Okamoto, S.; Sato, F. J. Org. Chem. 2003,
68, 9767.
(3) (a) Sakai, M.; Hayashi, H.; Miyaura, N. Organometallics 1997, 16,
4229. (b) Sakuma, S.; Sakai, M.; Itooka, R.; Miyaura, N. J. Org. Chem.
2000, 65, 5951. (c) Yamamoto, Y.; Fujita, M.; Miyaura, N. Synlett 2002,
767. (d) Itooka, R.; Iguchi, Y.; Miyaura, N. J. Org. Chem. 2003, 68, 6000.
(e) Kuriyama, M.; Tomioka, K. Tetrahedron Lett. 2001, 42, 921. (f) Takaya,
Y.; Ogasawara, M.; Hayashi, T.; Sakai, M.; Miyaura, N. J. Am. Chem. Soc.
1998, 120, 5579. (g) Hayashi, T.; Takahashi, M.; Takaya, Y.; Ogasawara,
M. J. Am. Chem. Soc. 2002, 124, 5052.
PtI2(dppe) reacts with a 2-fold molar amount of ArB(OH)2
(Ar ) C6H4OMe-4, Ph, C6H4COMe-4) in THF to produce
Pt(OBArOBArO)(dppe) (1a, Ar ) C6H4OMe-4; 1b, Ar ) Ph;
1c, Ar ) C6H4COMe-4) with a six-membered ring composed
of one Pt, three O, and two B atoms. The reaction proceeds
(5) Nishikata, T.; Yamamoto, Y.; Miyaura, N. Organometallics 2004,
23, 4317.
(6) (a) Nishihara, Y.; Onodera, H.; Osakada, K. Chem. Commun. 2004,
192. (b) Osakada, K.; Onodera, H.; Nishihara, Y. Organometallics 2005,
24, 190.
(7) Spectroscopic characterization of diarylpalladium complex formed
via transmetalation of arylboronic acid: Aliprantis, A. O.; Canary, J. W. J.
Am. Chem. Soc. 1994, 116, 6985.
(8) Simpson, R. D.; Bergman, R. G. Organometallics 1992, 11, 3980.
(9) Pantcheva, I.; Nishihara, Y.; Osakada, K. Organometallics 2005, 24,
3815.
(4) Osakada, K. Transmetalation. In Current Methods in Inorganic
Chemistry; Yamamoto, A., Kurosawa, H., Eds.; Elsevier: Amsterdam, 2003;
Vol. 3, p 233.
(10) Clarke, M. L.; Heydt, M. Organometallics 2005, 24, 6475.
10.1021/om0509903 CCC: $33.50 © 2006 American Chemical Society
Publication on Web 02/18/2006

1736 Organometallics, Vol. 25, No. 7, 2006
PantcheVa and Osakada
smoothly in the presence of Ag2O and H2O and is completed
in 3-6 h at room temperature (eq 1).
Figure 1. ORTEP drawings of (a) 1b and (b) 1c with ellipsoids at
the 30% probability level. One of the crystallographically inde-
pendent half-molecules of 1b and one of the two independent
molecules of 1c are shown. Selected bond distances (Å) and angles
(deg) of 1b (two independent molecules): Pt1-O1 ) 2.043(2),
Pt1-O2 ) 2.033(3), Pt1-P1 ) 2.214(1), Pt1-P2 ) 2.2133(8),
B1-O1 ) 1.322(4), B2-O2 ) 1.324(4), B1-O3 ) 1.398(6), B2-
O3 ) 1.393(4), Pt2-O4 ) 2.042(2), Pt2-P3 ) 2.259(7), B3-O4
) 1.320(4), B3-O5 ) 1.391(5); O1-Pt1-O2 ) 91.4(1), Pt1-
O1-B1 ) 124.6(2), Pt1-O2-B2 ) 125.4(2), O1-B1-O3 )
126.0(3), O2-B2-O3 ) 125.5(4), B1-O3-B2 ) 126.7(2), O4-
Pt2-O4′ ) 90.0(1), Pt2-O4-B3 ) 124.4(2), B3-O5-B3′ )
125.4(3), O4-B3-O5 ) 124.8(4). Selected bond distances (Å) and
angles (deg) of 1c (two independent molecules): Pt1-O1 )
2.026(6), Pt1-O2 ) 2.031(6), Pt1-P1 ) 2.209(2), Pt1-P2 )
2.213(2), B1-O1 ) 1.34(1), B2-O2 ) 1.33(1), B1-O3 )
1.37(1), B2-O3 ) 1.40(1); O1-Pt1-O2 ) 91.4(2), Pt1-O1-B1
) 124.2(6), Pt1-O2-B2 ) 125.3(6), O1-B1-O3 ) 126.8(9),
O2-B2-O3 ) 125.4(8), B1-O3-B2 ) 126.5(7); Pt2-O6 )
2.051(6), Pt2-O7 ) 2.054(6), Pt2-P3 ) 2.210(2), Pt2-P4 )
2.231(2), B3-O6 ) 1.33(1), B4-O7 ) 1.30(1), B3-O8 )
1.38(1), B4-O8 ) 1.41(1); O6-Pt2-O7 ) 90.0(2), Pt2-O6-B3
) 122.6(6), Pt2-O7-B4 ) 124.2(6), O6-B3-O8 ) 128.0(9),
O7-B4-O8 ) 126.9(8), B3-O8-B4 ) 124.0(7).
There are two possible pathways for the formation of 1a-c;
one involves stepwise replacement of two iodo ligands with
arylboronate groups and the ensuing intramolecular dehydration
of the OH groups of the two arylboronate ligands, and the other
is initial formation of arylboronic anhydride, which undergoes
a metathesis reaction with the diiodoplatinum complex. The
dehydration of two B(OH) groups giving a product with
B-O-B bonds occurs easily in both the absence and the
presence of transition metals. Arylboronic acids are equilibrated
with the corresponding arylboroxine via reversible cleavage and
the formation of B-O bonds. The cyclization of arylboronic
acid accompanied by dehydration occurs in the presence of the
Rh complex to form bicyclic boron-containing anions.11 A Pt
complex with a similar six-membered cyclic structure, Pt(O3B2-
(OH)2)(C6H14N2) (C6H14N2 ) trans-1,2-cyclohexanediamine),
has been prepared by the reaction of K2B4O7 with Pt(OH)2-
(C6H14N2) in the presence of B(OH)3.12
Figure 1 shows the molecular structures of 1b,c determined
by X-ray crystallography. The complexes have a square-planar
geometry around the Pt(II) center, which is coordinated by
chelating dppe and dehydro(arylboronic anhydride) ligands. The
six-membered ring formed by the coordination of the dehydro-
(arylboronic anhydride) to Pt is essentially planar. The Pt-O
bonds of one and one-half crystallographically independent
molecules of 1b (2.033(3), 2.042(2), and 2.043(2) Å) and of
two molecules of 1c (2.026(6), 2.031(6), 2.051(6), and 2.054-
(6) Å) are similar to those reported for Pt(O3B2(OH)2)-
(C6H14N2)12 (ca. 2.0 Å) or slightly longer. The average Pt-O
bond distance of the complexes is shorter than the Pt-O bond
of trans-Pt(OB(OH)C6H4OMe-4)(Ph)(PMe2Ph)2 (2.094(6) Å),
owing to the large trans influence of the phenyl ligand situated
at the trans position of the complex.9 The distances between
the coordinating oxygen and boron atoms (1.30-1.34 Å) are
shorter than the B-OB bonds (1.37-1.41 Å); the standard
covalent bond length is 1.36 Å. The B-O bond distances
reported for compounds containing a boroxine ring ranged from
1.35 to 1.48 Å.13 The B-O-B and O-B-O angles of 1b,c
are larger than 124°, whereas the O-Pt-O angle is fixed close
to 90° (91.4(1), 90.0(1), 91.4(2), and 90.0(2)°).
positions are normal because of the presence of tricoordinate
boron nuclei in the ligands of transition-metal complexes.13,16
1a reacts with 2-fold molar amounts of HCl and of CF3COOH
to form complexes with chloro and trifluoroacetate ligands, 2
and 3, as shown in eq 2. The NMR spectra of the reaction
The 31P{1H} NMR spectra of 1a-c contain a single signal
at 25-26 ppm flanked by 195Pt satellites (J(PtP) ) 3536-3567
Hz). The peak positions are close to those reported for
mononuclear Pt(II) complexes with dppe and O ligands, Pt-
(OSiEt3)2(dppe) (25.9 ppm, J(PtP) ) 3591 Hz)14 and Pt(S-
VANOL)(dppe) (24.7 ppm, J(PtP) ) 3633 Hz).15 Broad 11B{1H}
NMR signals of 1b,c are observed at 24-25 ppm, and their
mixtures showed the formation of 4-MeOC6H4B(OH)2 and the
boroxine formed by the dehydrative cyclotrimerization of such
a compound. The products were characterized by NMR
(11) (a) Nishihara, Y.; Nara, K.; Osakada, K. Inorg. Chem. 2002, 41,
4090. (b) Nishihara, Y.; Nara, K.; Nishide, Y.; Osakada, K. Dalton Trans.
2004, 1366.
(12) Miyamoto, T.; Ichida, H. Chem. Lett. 1991, 435.
(13) Beckett, M. A.; Brassington, D. S.; Owen, P.; Hursthouse, M. B.;
Light, M. E.; Malik, K. M. A.; Varma, K. S. J. Organomet. Chem. 1999,
585, 7 and references therein.
(15) (a) Brunkan N. M.; White, P. S.; Gagne´, M. R. Organometallics
2002, 21, 1565. (b) Becker, J. J.; White, P. S.; Gagne´, M. R. Organometallics
2003, 22, 3245.
(16) (a) Das, M. K.; Mariategui, J. F.; Niedenzu, K. Inorg. Chem. 1987,
26, 3114. (b) Cornet, S. M.; Dillon, K. B.; Enthwise, C. D.; Fox, M. A.;
Goeta, A. E.; Goodwin, H. P.; Marder, T. B.; Thompson, A. L. Dalton
Trans. 2003, 23, 4395. (c) Islam, T. M.; Yoshino, K.; Nomura, H.; Mizuno,
T.; Sasane, A. Anal. Sci. 2002, 18, 363. (d) Islam, T. M.; Yoshino, K.;
Sasane, A. Anal. Sci. 2004, 19, 455.
(14) Banditelli, G.; Pizzoti, M.; Bandini, A. L.; Zucchi, C. Inorg. Chim.
Acta 2002, 330, 72.

Transmetalation of Arylboronic Acid
Organometallics, Vol. 25, No. 7, 2006 1737
spectroscopy and elemental analyses, and 3 was characterized
1
by X-ray diffraction analysis. The H and 31P{1H} NMR data
of the complexes are characteristic of platinum(II) complexes
with Cl and O ligands at the trans positions of phosphorus
nuclei.17 The reaction of CH3COOH with 1a in an NMR tube
indicates the formation of Pt(OCOMe)2(dppe) (4).
The reaction of 4-MeOC6H4B(OH)2 with 1a in a 2:1 molar
ratio in THF at room temperature produced a diarylplatinum-
(II) complex, Pt(C6H4OMe-4)2(dppe) (5a), in 85% yield, as
shown in eq 3.
Figure 2. Plots of concentrations of 4-MeOC6H4B(OH)2 and 5a
during the reaction of 4-MeOC6H4B(OH)2 with 1a in a 2:1 molar
ratio. The amounts of 4-MeOC6H4B(OH)2 and 5a at each time were
determined by comparing the relative 1H NMR peak areas of OMe
hydrogen signals using diphenylmethane as an internal standard.
Plots denoted by black triangles correspond to the intermediate
complex with a 4-methoxyphenyl ligand and an O-coordinating
ligand (see text).
Pt-C and Pt-P bond distances determined by X-ray crystal-
lography are in the normal range when compared with the
parameters of diarylplatinum complexes reported previously.18
The reaction proceeds smoothly at room temperature without
any other additives, whereas the reaction of 4-MeOC6H4B(OH)2
with trans-Pt(OB(OH)(C6H4OMe))(Ph)(PMe2Ph)2 to give trans-
Pt(C6H4OMe)(Ph)(PMe2Ph)2 requires the addition of Ag2O and
H2O.9
ligand, because the dehydro(arylboronic anhydride) ligand could
undergo B-O bond cleavage in the presence of arylboronic acid
(vide infra). The amounts of intermediates are plotted in Figure
2 by assuming that the H NMR signal at 3.66 ppm is caused
by one OMe group contained in the complex.
1
The reactions of PhB(OH)2 with 1b and of 4-MeCOC6H4B-
(OH)2 with 1c in NMR scale (THF-benzene-d8) also form the
corresponding diarylplatinum complexes 5b,c, respectively.
Figure 3 shows a change in the 31P{1H} NMR spectra during
the former reaction: a decrease in signal peak area at 25.1 ppm
(J(PtP) ) 3541 Hz) due to 1b and an increase in the signal
peak area of the 5b produced (41.3 ppm, J(PtP) ) 1690 Hz).
Two signals at 45.2 ppm (J(PtP) ) 1700 Hz) and 30.0 ppm
(J(PtP) ) 4195 Hz) are also observed during the reaction and
are assigned to the unsymmetrical intermediate complexes with
a phenyl ligand and an O-coordinating ligand, respectively.
Reactions of 4-MeCOC6H4B(OH)2 with 1b and of PhB(OH)2
with 1c in a 2:1 molar ratio were conducted to monitor both
the transmetalation and scrambling of aryl groups by 31P{1H}
NMR spectroscopy. Figure 4 shows the 31P{1H} NMR spectrum
of the reaction mixture after aryl group transfer from B to Pt.
The three possible diarylplatinum complexes 5b,c and Pt(C6H4-
COMe)(Ph)(dppe) are formed in an almost 1:1:2 ratio, indicating
that the random scrambling of aryl groups occurs during
transmetalation. Pt(C6H4COMe)(Ph)(dppe) was characterized by
comparing its NMR data with those of the complex prepared
independently of the reaction of 4-MeCOC6H4B(OH)2 with PtI-
(Ph)(dppe) in the presence of Ag2O.
Scheme 1 depicts possible pathways for the reaction of
arylboronic acid with the dehydro(arylboronic anhydride) ligand
bound to Pt, leading to the formation of a new aryl-platinum
bond. Reaction i involves the addition of an O-H bond of
arylboronic acid to a Pt-O bond of the complex to produce
intermediate A. The subsequent intramolecular metathesis-type
bond exchange between the Pt-O bond of the arylboronate
ligand and the B-C bond of the other O ligand forms an aryl-
platinum bond. The aryl ligand introduced to the product is
derived from the dehydrido(arylboronic anhydride) ligand of
the starting complex. Reaction ii proceeds via a direct metathesis
of the added arylboronic acid with the Pt-O bond of the
complex to form a new bond between the Pt center and the
aryl group in the arylboronic acid.
1H and 13C NMR spectra of the reaction mixture in THF
indicate the formation of anisole. An aqueous extract of the
products shows 11B NMR and IR peaks assigned to boric acid.
The above reaction is considered to form an anhydride of boric
acid formulated as (B3O5H)n, which is converted into boric acid
upon hydrolysis. Figure 2 shows changes in the amounts of
1
4-MeOC6H4B(OH)2 and 5a, as monitored by H NMR spec-
troscopy in THF-d8, during the reaction. The amount of 1a was
not determined precisely, because 1a did not dissolve completely
in the solvent. The signal of the OMe hydrogen of 4-MeOC6H4B-
(OH)2 (3.76 ppm in THF-d8) decreases in its intensity in peak
area during the reaction for 9 h. The signal of 5a (3.75 ppm)
increases in intensity in peak area for a period of 9 h and attains
a 99% yield after that. The peak area change of these 1H NMR
signals corresponds to that of the 31P{1H} NMR peaks for the
1
same sample. A H NMR signal at 3.66 ppm and a pair of
31P{1H} NMR signals at 44.8 and 29.0 ppm are also observed
in the spectra during the reaction. These signals are assigned to
an intermediate Pt complex for the formation of 5a, because
they keep increasing in peak area for the initial 4 h and then
decrease until 9 h after start of the reaction. The Pt-P coupling
constant of the former 31P{1H} NMR signal is 1716 Hz,
indicating that the signal can be assigned to the phosphorus
nucleus at the trans position of the aryl ligand. A much larger
J(PtP) value of the latter signal (4200 Hz) suggests that the
phosphorus atom is bonded at the trans position of an oxygen-
coordinating ligand. There are several possible structures of the
(17) Anandhi, U.; Holbert, T.; Lueng, D.; Sharp, P. R. Inorg. Chem.
2003, 42, 1282.
(18) (a) Eaborn, C.; Odell, K. J.; Pidcock, A. J. Chem. Soc., Dalton Trans.
1978, 357. (b) Gugger, P.; Limmer, S. O.; Watson, A. A.; Willis, A. C.;
Wild, S. B. Inorg. Chem. 1993, 32, 5692. (c) Brunkan, N. M.; Gagne´, M.
R. Organometallics 2002, 21, 4711. (d) Al-Allaf, T. A. K.; Schmidt, H.;
Merzweiler, K.; Wagner, C.; Steinborn, D. J. Organomet. Chem. 2003, 678,
48.

1738 Organometallics, Vol. 25, No. 7, 2006
PantcheVa and Osakada
Figure 4. 31P{1H} NMR spectrum of reaction mixture of
4-MeCOC6H4B(OH)2 with 1b after transmetalation in THF-
benzene-d6. Peaks denoted by asterisks correspond to that of Pt-
(C6H4COMe-4)(Ph)(dppe).
Scheme 1
Figure 3. Change in 31P{1H} NMR spectra during reaction of PhB-
(OH)2 with 1b in THF-benzene-d6. Peaks denoted by black dots
are due to intermediate complexes with phenyl and O-coordinating
ligands (see text).
Scheme 2
The above reactions involve the activation of the Pt-O bond
and the formation of the Pt-C bond involving the four-
membered intermediate shown in Scheme 2. The addition of
an O-H bond to the Pt-O bond causes the exchange of the
arylboronate ligand (reaction i), whereas that of the B-C bond
produces arylplatinum complexes and compounds containing a
B-O-B bond (reaction ii).
Scheme 3 depicts a pathway for the formation of the aryl-
platinum bond, which involves the initial cleavage of a B-O
bond of the complex by arylboronic acid. The addition of an
O-H bond of the arylboronic acid to a bond between boron
and oxygen atoms at the â- and γ-positions of a platinacycle
forms intermediate B (reaction i). The Ar-B group of the
intermediate B is derived from arylboronic acid and undergoes
an intramolecular metathesis reaction with the Pt-O bond,
giving an arylplatinum complex. Reaction pathway ii involves
the activation of the bond between the coordinating oxygen atom
and adjacent boron atom by arylboronic acid to form an
intermediate complex with an OH ligand, C.
containing the aryl ligand D or E. The reaction with the Pt-O
bond of the boronate ligand of B yields the arylplatinum
hydroxide complex F, accompanied by the elimination of cyclic
boron-containing compounds. The complexes obtained by the
reactions in Schemes 1 and 3 can be transformed into diaryl-
The aryl group in the ligand undergoes a metathesis reaction
with the Pt-O bond of the OH ligand to produce complexes

Transmetalation of Arylboronic Acid
Organometallics, Vol. 25, No. 7, 2006 1739
Scheme 3
Scheme 4
Intermediate A formed in reaction i of Scheme 1 causes a
metathesis reaction of O-H and B-O bonds to regenerate a
cyclic complex with a dehydro(arylboronic anhydride) ligand
having a different aryl ligand from the starting complex.
Most stoichiometric transmetalations of arylboronic acids with
transition-metal complexes are assisted by the addition of a
nucleophile such as OH- or Ag2O as well as fluoride. These
additives may play two possible roles during the reaction: one
involves the formation of arylborate by the coordination of an
anion to the boron center of arylboronic acid, and the other
involves addition of the nucleophile, which promotes the
activation of the bond between a transition metal and a halogeno
ligand as well and produces a cationic complex with an
electrophilicity higher than that of the neutral complex. Trans-
metalation without base addition has also been reported. The
reaction of arylboronic acid with a dicationic palladium complex
forms a monocationic phenylpalladium complex, accompanied
by the elimination of HBF4 without base addition.5 The alkoxide
ligand bonded to Re shows a high reactivity toward arylboronic
acid to cause transmetalation under mild conditions.8 The Pt
complexes in this study also exhibit a high reactivity toward
arylboronic acid to induce the aryl group transfer from boron
to platinum.
In conclusion, we succeeded in preparing and characterizing
six-membered cyclic platinum(II) complexes containing three
O, two B, and one Pt atom. The Pt-O bond of the complexes
reacted with arylboronic acid to afford diarylplatinum(II)
complexes. The aryl group transfer from boron to platinum
proceeds via the intermolecular metathesis of Pt-O and B-C
bonds or the intramolecular metathesis of the acyclic intermedi-
ate formed by the arylboronic acid induced cleavage of a B-O
bond of the complex.
platinum complexes by further intramolecular or intermolecular
metathesis-type reactions between the B-C and Pt-O bonds.
The experimental results obtained at present are not sufficient
to compare the plausibility of the reactions shown in Schemes
1 and 3 as pathways for the formation of the aryl-platinum
bond. These reactions, occurring in a parallel manner, account
for the scrambling of the aryl group in the reactions of
4-MeCOC6H4B(OH)2 with 1b and of PhB(OH)2 with 1c. The
preferential formation of the monoaryl complex F by reaction
ii in Scheme 3, followed by the reaction of arylboronic acid
with the OH ligand of F, is also consistent with the formation
of diaryl complexes accompanied by the scrambling of the aryl
groups between the complex and arylboronic acid. The hydrox-
ide ligand of complex C (and F) shows a more pronounced
nucleophilic nature than the arylboronate ligand in the com-
plexes of the above reactions and undergoes a metathesis
reaction with electrophilic boron-containing ligands more eas-
ily.19,20 On the other hand, reaction ii in Scheme 3, involving a
metathesis reaction of the B-O bond close to the Pt center,
suffers from a more severe steric congestion between the
substituents of the complex and arylboronic acid than reaction
i in Scheme 1 and reaction i in Scheme 3.
Experimental Section
General Procedures and Materials. All experiments were
carried out under N2 or Ar using the standard Schlenk technique.
The NMR spectra (1H, 11B{1H}, 13C{1H}, 19F{1H}, 31P{1H}) were
recorded on JNM-La-500, JEOL EX-400, and Varian 300 spec-
trometers. Residual peaks of solvent were used as the reference
The results can be explained well by assuming that the
random scrambling of aryl groups occurs prior to transmetala-
tion. Scheme 4 depicts a possible reaction pathway that leads
to the exchange of aryl groups.
1
for H NMR and 13C{1H} NMR (acetone-d6, δ 29.8). External
references were used for 11B{1H} NMR (BF3‚OEt2), 31P{1H} NMR
(85% H3PO4), and 19F{1H} (CFCl3). IR spectra were taken on a
Shimadzu FTIR8100A (KBr, 4000-400 cm-1) spectrophotometer.
Elemental analyses were carried out with a Yanaco MT-5 CHN
Autocorder and a LECO VTF-900 Oxygen Analyzer. Arylboronic
acids and dppe were commercially available (Tokyo Chemical
Industry Co., Ltd. or Aldrich Chemical Co. Inc.) and used as
received. PtI2(dppe) was prepared as described in the literature.21
(19) (a) Yoshida, T.; Okano, T.; Otsuka, S. J. Chem. Soc., Dalton Trans.
1976, 993. (b) Appleton, T. G.; Bennett, M. A. Inorg. Chem. 1978, 17,
738. (c) Bennett, M. A.; Yoshida, T. J. Am. Chem. Soc. 1978, 100, 1750.
(d) Strukul, G.; Michelin, R. A. J. Am. Chem. Soc. 1985, 107, 7563. (e)
Belluco, U.; Bertani, R.; Coppetti, S.; Michelin, R. A.; Mozzon, M. Inorg.
Chim. Acta 2003, 343, 329.
(20) (a) Merwin, R. K.; Schnabel, R. C.; Koola, J. D.; Roddick, D. M.
Organometallics 1992, 11, 2972. (b) Romeo, R.; Scolaro, L. M.; Plutino,
M. R. Transition Met. Chem. 1998, 23, 789. (c) Suzaki, Y.; Osakada, K.
Bull. Chem. Soc. Jpn. 2004, 77, 139.
(21) Kistner, C. R.; Hutchinson, J. H.; Doyle, J. R.; Storlie, J. C. Inorg.
Chem. 1963, 2, 1255.

1740 Organometallics, Vol. 25, No. 7, 2006
PantcheVa and Osakada
Synthesis of Pt(OBArOBArO)(dppe) (1a, Ar ) C6H4OMe-
4; 1b, Ar ) C6H5; 1c, Ar ) C6H4COMe-4). To a THF/H2O (50
mL/1 mL) solution of PtI2(dppe) (847 mg, 1.0 mmol) were added
Ag2O (753 mg, 3.2 mmol) and 4-MeO-C6H4B(OH)2 (304 mg, 2.0
mmol) at room temperature. The reaction mixture was stirred for
3 h. After filtration of the black solid, composed of AgI and
unreacted Ag2O, the resulting solution was added dropwise to
hexane (500 mL) to yield 1a as a white solid, which was filtered
off and dried under vacuum. Yield: 751 mg, 86%. Anal. Calcd for
C40H38B2O5P2Pt: C, 54.76; H, 4.37; O, 9.12. Found: C, 54.35; H,
4.52; O, 8.95. 1H NMR (300 MHz, CDCl3): δ 8.08-8.03 (m, 8H,
PC6H5-o), 7.94 (d, 4H, 3J(H-H) ) 8.1 Hz, BC6H4OMe-4-o), 7.43-
7.41 (m, 12H, PC6H5-m, p), 6.84 (d, 4H, 3J(H-H) ) 8.7 Hz, BC6H4-
OMe-4-m), 3.81 (s, 6H, OMe), 2.44-2.39 (m, 4H, PCH2). 31P{1H}
NMR (121.5 MHz, CDCl3): δ 25.2 (s with satellites, J(PtP) )
3537 Hz).
Figure 5. (a) ORTEP drawing of 3 with ellipsoids at the 30%
probability level. One of the two crystallographically independent
molecules is shown. Selected bond distances (Å) and angles (deg):
Pt1-O1 ) 2.078(4), Pt1-O3 ) 2.096(4), Pt1-P1 ) 2.221(2),
Pt1-P2 ) 2.207(2); O1-Pt1-O3 ) 85.8(2), P1-Pt1-P2 )
86.60(6), O1-Pt1-P1 ) 96.7(1), O3-Pt1-P1 ) 175.6(1), O3-
Pt1-P2 ) 173.7(1), O3-Pt1-P2 ) 90.5(1). (b) ORTEP drawing
of 5a with ellipsoids at the 30% probability level. Selected bond
distances (Å) and angles (deg): Pt1-C1 ) 2.093(6), Pt1-C8 )
2.080(6), Pt1-P1 ) 2.286(1), Pt1-P2 ) 2.289(1); C1-Pt1-C8
) 87.9(2), P1-Pt1-P2 ) 86.34(5), C1-Pt1-P1 ) 94.9(2), C1-
Pt1-P2 ) 176.4(2), C8-Pt1-P1 ) 171.9(2), C8-Pt1-P2 )
91.3(2).
Complexes 1b,c were prepared similarly as colorless crystals
from the corresponding arylboronic acids in 69% and 82% yields,
respectively.
Data for 1b are as follows. Anal. Calcd for C38H34B2O3P2Pt: C,
1
55.84; H, 4.19; O, 5.87. Found: C, 55.85; H, 4.20; O, 5.82. H
NMR (300 MHz, C6D6): δ 8.57 (d, 4H, 3J(HH) ) 7.5 Hz, BC6H5-
o), 7.94 (m, 8H, PC6H5-o), 7.79-7.34 (m, 6H, BC6H5-m, p), 6.90
(br s, 12H, PC6H5-m,p), 1.72-1.67 (m, 4H, PCH2). 31P{1H} NMR
(121.5 MHz, C6D6): δ 25.2 (s, J(PtP) ) 3536 Hz). 11B{1H} NMR
(160.4 MHz, acetone-d6): δ 24.94 (br).
(OH)2 (30 mg, 0.2 mmol), and the reaction mixture was stirred at
room temperature for 16 h. The solvent was evaporated to dryness
under reduced pressure. The residue that formed was washed with
water. Evaporation of water of the washing at 80 °C under vacuum
gave boric acid (12.8 mg, 52%). Data for H3BO3 are as follows.
1H NMR (300 MHz, acetone-d6): δ 5.82 (s, OH, boroxine), 2.90
(s, OH, boric acid), 2.87 (s, OH, water), 11B NMR (160.4 MHz,
acetone-d6): δ 19.9 (s). Addition of hexane to the solid product
after washing with water caused separation of a white solid which
was washed with hexane to give 5a as a white solid (69.1 mg,
85%). Evaporation of the hexane extract gave anisole (11 mg, 51%).
NMR data for C6H5OMe are as follows. 1H NMR (300 MHz,
CDCl3): δ 7.25 (2H, t, C6H5-o), 6.9 (m, 3H, C6H5-m,p), 3.75 (s,
3H, OMe), 13C NMR (75 MHz, CDCl3): 159.7, 129.5, 120.7, 114.0,
55.1. NMR data for 5a are as follows. 1H NMR (300 MHz,
Data for 1c are as follows. Anal. Calcd for C42H38B2O5P2Pt: C,
1
55.96; H, 4.25; O, 8.87. Found: C, 55.43; H, 4.15; O, 8.78. H
NMR (300 MHz, CDCl3): δ 8.06-7.98 (m, 12H, BC6H4COMe-o,
PC6H5-o), 7.87 (d, 4H, 3J(H-H) ) 7.5 Hz, BC6H4COMe-m), 7.48-
7.42 (12H, PC6H5-m,p), 2.60 (s, 6H, COMe), 2.46-2.41 (m, 4H,
PCH2). 31P{1H} NMR (121.5 MHz, CDCl3): δ 26.4 (s, J(PtP) )
3567 Hz). 11B{1H} NMR (160.4 MHz, acetone-d6): δ 24.5 (br).
Reaction of HCl with 1a. To a THF (2 mL) solution of 1a (43.9
mg, 0.05 mmol) was added HCl (3.7% in H2O, 83 µL, 0.1 mmol).
The reaction mixture was stirred at room temperature for 2 h.
Addition of hexane gave PtCl2(dppe) (2) as a white solid, which
was filtered off and dried under vacuum (32.3 mg, 97%). Anal.
Calcd for C26H24B2Cl2P2Pt: C, 47.00; H, 3.64; Cl, 10.67. Found:
1
C, 47.30; H, 3.69; O, 10.09. H NMR (300 MHz, acetone-d6): δ
3
CDCl3): δ 7.51-7.31 (m, 20H), 7.02 (t, 4H, J(HH) ) 7.3 Hz,
7.99-7.92 (m, 8H, PC6H5-o), 7.59-7.53 (m, 12H, PC6H5-m,p),
2.65-2.59 (m, 4H, PCH2). 31P{1H} NMR (121.5 MHz, acetone-
d6): δ 43.2 (s, J(PtP) ) 3595 Hz). Evaporation of the solvent from
hexane solution gave a solid (13.5 mg) containing a mixture of
4-MeOC6H4B(OH)2 and (4-MeOC6H4)3B3O3 in a 2:3 ratio. Their
1H NMR data were compared with those obtained from com-
mercially available products.
Reaction of CF3COOH with 1a. To a THF solution containing
1a (43.9 mg, 0.05 mmol) was added CF3COOH (neat, 11.4 µL,
0.1 mmol). The reaction mixture was stirred at room temperature
for 2 h. The resulting solution was added to hexane to give
Pt(OCOCF3)2(dppe) (3) as a white precipitate in 91% yield (37.3
mg). The hexane fraction contained a mixture of arylboronic acid
and its anhydride in a 1:2 ratio (13.1 mg). Crystals of 3 suitable
for X-ray analyses were grown by slow diffusion of hexane into a
THF solution. Anal. Calcd for C30H24F6O4P2Pt: C, 43.97; H, 2.95;
F, 13.91. Found: C, 44.16; H, 2.71; F, 13.84. 1H NMR (300 MHz,
acetone-d6): δ 7.97-7.95 (m, 8H, PC6H5-o), 7.63-7.54 (m, 12H,
PC6H5-m,p), 2.69-2.64 (m, 4H, PCH2). 31P{1H} NMR (121.5 MHz,
acetone-d6): δ 34.8 (s, J(PtP) ) 3841 Hz). 19F{1H} NMR (282.5
MHz, C6D6): δ -74.4 (s).
3
4J(PH) ) 14.7 Hz, PtC6H4-o), 6.41 (d, 4H, J(H-H) ) 7.2 Hz,
PtC6H4-m), 3.61 (s, 6H, OMe), 2.28-2.23 (m, 4H, PCH2). 31P-
{1H} NMR (121.5 MHz, CDCl3): δ 41.9 (s, J(PtP) ) 1711 Hz).
1H NMR (300 MHz, C6D6): δ 7.56-7.47 (m, 12H), 7.04-6.98
3
(m, 12H), 6.74 (d, 4H, J(HH) ) 9.4 Hz, PtC6H4-m), 3.31 (s, 6H,
OMe), 1.91-1.85 (m, PCH2); 31P{1H} NMR (121.5 Hz, C6D6): δ
42.2 (s, J(PtP) ) 1691 Hz).
The reaction on an NMR scale was carried out by the following
procedure. To 1a (22 mg, 0.025 mmol) in THF-d8 (1 mL) were
added 4-MeOC6H4B(OH)2 (7.5 mg, 0.050 mmol) and Ph2CH2 as
an internal standard (12.5 µL, 0.075 mmol). The changes in the
1
reaction mixture were followed by H and 31P{1H} NMR spec-
troscopy.
Reactions of Arylboronic Acids with 1a-c on an NMR Scale.
In general experiments, NMR tubes were loaded with complexes
1a-c (0.050 mmol) and the corresponding boronic acids in 1:2
molar ratios in a THF/C6D6 mixed solvent system. The changes in
the crude reaction mixtures were detected by 31P{1H} NMR
spectroscopy. In most cases the complexes formed were not isolated
but characterized spectroscopically.
Reaction of CH3COOH with 1a. The reaction of 1a with a
stoichiometric amount of CH3COOH was followed by 31P{1H}
NMR spectroscopy using THF/C6D6 as solvent. The product of the
reaction was identified as Pt(OCOCH3)2(dppe) (4).
Reaction of 4-MeOC6H4B(OH)2 with 1a. To a THF solution
(2 mL) containing 1a (88 mg, 0.10 mmol) was added4-MeOC6H4B-
Preparation of Pt(C6H4COMe-4)(Ph)(dppe). To a THF/H2O
solution (5/0.5 mL) containing Pt(I)(Ph)(dppe) (159.5 mg, 0.20
mmol) were added 4-COMeC6H4B(OH)2 (49.19 mg, 0.30 mmol)
and Ag2O (74.16 mg, 0.32 mmol) in this order. The reaction mixture
was stirred at room temperature for 48 h. After filtration of the
residue, composed of AgI and unreacted Ag2O, the resulting

Transmetalation of Arylboronic Acid
Organometallics, Vol. 25, No. 7, 2006 1741
Table 1. Crystal Structure Data and Refinement Details for Complexes 1b,c, 3, and 5a
1b
1c
3‚THF
5a
formula
Mr
C38H34B2O3P2Pt
817.34
C42H38B2O5P2Pt
901.42
C32H28O4.5F6P2Pt
855.60
C40H38O2P2Pt
807.78
cryst syst
space group
a/Å
b/Å
monoclinic
C2/c (No. 15)
30.007(4)
15.3558(11)
26.908(6)
90
123.706(6)
90
10 314(3)
12
orthorhombic
Pca21 (No. 29)
16.026(2)
21.295(2)
22.041(2)
90
90
90
7522(1)
8
0.3846
monoclinic
P21/c (No. 14)
14.916(2)
18.975(2)
22.898(3)
90
93.4410(2)
90
6469(1)
8
triclinic
P1h (No. 2)
10.382(2)
11.367(2)
14.227(3)
92.374(2)
93.196(3)
98.853(4)
1654.2(5)
2
c/Å
R/deg
â/deg
γ/deg
V/Å3
Z
µ(Mo KR)/ mm-1
F(000)
0.4194
4848
1.579
0.4492
3344
1.757
0.4356
804
1.622
3584
1.592
Dc/g cm-3
cryst size/mm
2θ range/deg
no. of unique rflns
no. of rflns used (>2σ(I))
no. of variables
R
0.30 × 0.20 × 0.05
5.0-55.0
11 148
10 126
674
0.25 × 0.25 × 0.10
5.0-55.0
8823
8823
1013
0.30 × 0.30 × 0.30
5.0-55.0
14 530
10 643
876
0.32 × 0.08 × 0.04
5.0-55.0
7107
6571
444
0.0287
0.0480
0.0400
0.0419
Rw
0.0373
0.0892
0.0457
0.0650
GOF
1.001
0.837
0.915
0.999
solution was mixed with hexane (70 mL) to cause separation of
Pt(C6H4COMe-4)(Ph)(dppe) as a white residue, which was filtered
off and dried under vacuum. Yield: 135.6 mg, 86%. 1H NMR (300
MHz, C6D6): δ 7.82-7.60 (m, 4H, PtC6H4COMe-4-o,m), 7.46-
7.34 (m, 8H, PC6H5-o), 7.07-6.87 (m, 17H), 2.08 (s, 3H, COMe),
1.87-1.80 (m, 4H, PCH2). 31P{1H} NMR (121.5 MHz, C6D6): δ
42.8 (J(PtP) ) 1668 Hz), trans to Ph, 41.9 (J(PtP) ) 1718 Hz),
trans to C6H4COMe-4.
Crystal Structure Determination. Crystals suitable for X-ray
diffraction study were obtained by recrystallization from THF/
hexane solutions and mounted in glass capillary tubes on a Rigaku
AFC-7R automated CCDC diffractometer equipped with Mo KR
radiation (λ ) 0.7107 Å). The data were collected to a maximum
2θ value of 55.0°. A total of 720 oscillation images were collected.
A sweep of data was done using ω scans from -110.0 to 70.0° in
0.5° steps, at ø ) 45.0° and φ ) 0.0°. The detector swing angle
was -20.42°. A second sweep was performed using ω scans from
-110.0 to 70.0° in 0.5° steps, at ø ) 45.0° and φ ) 90.0°. The
crystal-to-detector distance was 44.84 mm. Readout was performed
in the 0.070 mm pixel mode. Calculations were carried out by using
the program package Crystal Structure for Windows. The structure
was solved by direct methods and expanded using Fourier
techniques. A full-matrix least-squares refinement was used for the
non-hydrogen atoms with anisotropic thermal parameters.
The absolute configuration of the crystal of 1c could not be
determined from crystallographic results, due to insufficient quality
of the diffraction data. The two independent molecules in the crystal
show orientations of the phenyl planes different from each other.
Figure 5 depicts crystallographic structures of 3 and 5b. Crystal
structure data and refinement details are given in Table 1.
Acknowledgment. This work was supported by a Grant-
in-Aid for Scientific Research from the Ministry of Education,
Science, Sports, and Culture of Japan and partially supported
by The 21st Century COE Program “Creation of Molecular
Diversity and Development of Functionalities”. We are grateful
to Dr. Mikio Yamasaki of Rigaku Corp. for helpful discussions
of the crystallographic results. I.P. acknowledges a fellowship
for foreign researchers by the Japan Society for the Promotion
of Science.
Supporting Information Available: Crystallographic data and
complete tables of non-hydrogen and selected hydrogen parameters,
bond lengths and angles, calculated hydrogen atom parameters, and
anisotropic thermal parameters (CIF files) of 1b,c, 3, and 5b.
This material is available free of charge via the Internet at
http://pubs.acs.org.
OM0509903