Cationic Rh complexes with novel spiro tetraarylpentaborate anions prepared from arylboronic acids and aryloxorhodium complexes

Article abstract of DOI:10.1039/b315902g

Ar-B(OH)₂ (1a: Ar = C₆H₄OMe-4, 1b: Ar = C₆H₃Me₂-2,6) react immediately with Rh(OC ₆H₂Me-4)(PMe₃)₃ (2) in 5 : 1 molar ratio at room temperature to generate [Rh(PMe₃)₄] ⁺[B₅O₆Ar₄]^- (3a: Ar = C₆H₄OMe-4, 3b: Ar = C₆H₃Me ₂-2,6). p-Cresol (92%/Rh), anisole (80%/Rh) and H₂O (364%/Rh) are formed from 1a and 2. The reaction of 1a with 2 for 24 h produces [Rh(PMe₃)₄]^-[B₅O₆(OH) ₄]^- (4) as a yellow solid. This is attributed to hydrolytic dearylation of once formed 3a because the direct reaction of 3a with excess H₂O forms 4. An equimolar reaction of 2 with phenylboroxine (PhBO)₃ causes transfer of the 4-methylphenoxo ligand from rhodium to boron to produce [Rh(PMe₃)₄]⁺[B ₃O₃Ph₃(OC₆H₄Me-4)] ^- (5). Arylboronic acids 1a and 1b react with Rh(OC₆H ₄Me-4)(PR₃)₃ (6: R = Et, 8: R = Ph.) and with Rh(OC₆H₄Me-4)(cod)(PR₃) (11: R = ⁱPr, 12: R = Ph) to form [Rh(PR₃)₄] ⁺[B₅O₆Ar₄]^- (7a: R = Et, Ar = C₆H₄OMe-4, 7b: R = Et, Ar = C₆H ₃Me₂-2,6, 9a: R = Ph, Ar = C₆H ₃Me₂-2,6) and [Rh(cod)(PR₃)(L)] ⁺[B₅O₆Ar₄]^- (13b: R = ⁱPr, L = acetone, Ar = C₆H₃Me₂-2,6, 14a: R = Ph, L = PPh₃, Ar = C₆H₄OMe-4, 14b: R = Ph, L = PPh₃, Ar = C₆H₃Me₂-2,6), respectively. Hydrolysis of 14a yields [Rh(cod)(PPh₃) ₂]^-[B₅O₆(OH)₄] ^- (15) quantitatively.

Full text of DOI:10.1039/b315902g

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Cationic Rh complexes with novel spiro tetraarylpentaborate
anions prepared from arylboronic acids and aryloxorhodium
complexes
Yasushi Nishihara, Kyoko Nara, Yasuhiro Nishide and Kohtaro Osakada*
Chemical Resources Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku,
Yokohama 226-8503, Japan
Received 5th December 2003, Accepted 12th March 2004
First published as an Advance Article on the web 2nd April 2004
Ar–B(OH)2 (1a: Ar = C6H4OMe-4, 1b: Ar = C6H3Me2-2,6) react immediately with Rh(OC6H4Me-4)(PMe3)3 (2) in
5 : 1 molar ratio at room temperature to generate [Rh(PMe3)4]ϩ[B5O6Ar4]Ϫ (3a: Ar = C6H4OMe-4, 3b: Ar = C6H3Me2-
2,6). p-Cresol (92%/Rh), anisole (80%/Rh) and H2O (364%/Rh) are formed from 1a and 2. The reaction of 1a with
2 for 24 h produces [Rh(PMe3)4]ϩ[B5O6(OH)4] Ϫ (4) as a yellow solid. This is attributed to hydrolytic dearylation
of once formed 3a because the direct reaction of 3a with excess H2O forms 4. An equimolar reaction of 2 with
phenylboroxine (PhBO)3 causes transfer of the 4-methylphenoxo ligand from rhodium to boron to produce
[Rh(PMe3)4]ϩ[B3O3Ph3(OC6H4Me-4)]Ϫ (5). Arylboronic acids 1a and 1b react with Rh(OC6H4Me-4)(PR3)3 (6: R = Et,
8: R = Ph) and with Rh(OC6H4Me-4)(cod)(PR3) (11: R = iPr, 12: R = Ph) to form [Rh(PR3)4]ϩ[B5O6Ar4]Ϫ (7a: R = Et,
Ar = C6H4OMe-4, 7b: R = Et, Ar = C6H3Me2-2,6, 9a: R = Ph, Ar = C6H3Me2-2,6) and [Rh(cod)(PR3)(L)]ϩ[B5O6Ar4]Ϫ
(13b: R = iPr, L = acetone, Ar = C6H3Me2-2,6, 14a: R = Ph, L = PPh3, Ar = C6H4OMe-4, 14b: R = Ph, L = PPh3,
Ar = C6H3Me2-2,6), respectively. Hydrolysis of 14a yields [Rh(cod)(PPh3)2]ϩ[B5O6(OH)4]Ϫ (15) quantitatively.
Crystallographic structures of 3a and 3b were reported in the
Introduction
1
preceding communication.8 The H NMR spectrum of 3a in
Weakly coordinating anions1 are used in a wide variety of
acetone-d6 shows two signals of ortho and meta hydrogens at
academic and industrial investigations. Large anions with low
δ 7.98 and 6.87 and a broad signal of the PMe3 hydrogens at
basicity are suited to generate and stabilize highly reactive
δ 1.53. The 31P{1H} NMR spectrum of 3a in acetone-d6 shows a
organic2 and organometallic3 cationic species owing to weak
simple doublet at a position (δ Ϫ15.40, J(RhP) = 134 Hz) simi-
interaction between the cation and the anion. Fluorinated
lar to that reported for [Rh(PMe3)4]ϩClϪ.10 The 13C{1H} NMR
tetraarylborates4 and polyhedral carboranes5 are used as
signals assigned to para, ortho and meta carbons are observed at
anions for olefin polymerization catalysts6 and for new
δ 162.1, 137.2 and 113.4, respectively. No signal assignable to
materials of film type Li polymer batteries.7 Boron-containing
organic and inorganic anions have become more important
recently because of their weak interaction with cations as well
the ipso carbon bonded to boron was detected. The 11B NMR
spectrum of 3a contains two signals at δ 4.76 and 28.18 which
are assigned to the tetracoordinate boron and tricoordinate
as because of their stable B–C and B–O bonds. Synthesis of
boron, respectively.
new types of non-coordinating anions that are easily obtained
from commercially available organoboron compounds would
Prolonged reactions of 1a and 1b with 2 (24 h) lead to
deposition of an orange insoluble solid of [Rh(PMe3)4]ϩ-
provide new materials. Herein we report the preparation of new
[B5O6(OH)4]Ϫ (4) in 58 and 52% yields, respectively (eqn. (2)).
spiro tetraarylpentaborate anions [B5O6Ar4]Ϫ in good to high
The 31P{1H} NMR spectrum of 4 showed a doublet at the iden-
yields by Rh-complex-promoted condensation of arylboronic
tical position to that of 3a, indicating that the cationic rhodium
acids and their dearylation via hydrolysis. A part of this work
1
complex remained intact. The H NMR spectrum shows the
has been reported preliminarily.8
signal of OH hydrogen at δ 3.76 and absence of aromatic
hydrogens. The two 11B NMR signals are observed at higher
field (δ 2.24 and 20.22) than the corresponding signals of 3a
Results and discussion
Preparation of [Rh(PMe3)4]؉[B5O6Ar4]؊
(δ 4.76 and 28.18). The pentaborate ([B5O6(OH)4]Ϫ)11 was
obtained by the reaction of boric acid with MF (M = Li, Na,
NH4, etc.) and found to be more stable than many other oxobo-
ric acid anions.
Reactions of 4-methoxyphenylboronic acid (1a) and 2,6-di-
methylphenylboronic acid (1b) with Rh(OC6H4Me-4)(PMe3)3
(2)9 in a 5 : 1 molar ratio for 15 min in acetone produce the
rhodium complexes with new spiro tetraarylpentaborates,
[Rh(PMe3)4]ϩ[B5O6Ar4]Ϫ (3a: Ar = C6H4OMe-4, 64%, 3b: Ar =
C6H3Me2-2,6, 55%), at room temperature. The yields of 3a and
3b are improved by the addition of an equimolar amount of
PMe3 to 2, to 73 and 79%, respectively (eqn. (1)).
(2)
An NMR experiment of the reaction of H2O with 3a in
acetone-d6 showed a decrease of the H2O signal and formation
of anisole and 4 at room temperature (eqn. (3)). The 11B NMR
spectrum after 4 h contained the signal of 4 only. The amount
of the formed anisole corresponds to that of decreased H2O,
indicating that the four 4-methoxyphenyl groups of 3a are
replaced by the OH groups from H2O during the reaction. The
hydrolytic dearylation of 3a in reaction (3) takes place also in
(1)
D a l t o n T r a n s . , 2 0 0 4 , 1 3 6 6 – 1 3 7 5
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 4
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(3)
reaction (2). The reaction of 1a with 2 forms 3a immediately
and causes subsequent conversion of 3a into 4 by H2O which is
generated from condensation of the arylboronic acid.
Fig. 1 shows plots of the organic and inorganic products dur-
ing the 5 : 1 molar reactions of 1a and of 1b with 2 in acetone-d6
1
at room temperature monitored by H NMR spectroscopy. As
shown in Fig. 1(a), arylboronic acid 1a is consumed within 3
min accompanied by the formation of H2O (364%/Rh) and
p-cresol (92%/Rh). The yield of p-cresol does not change
throughout the reaction. The amount of anisole formed at that
time (80%/Rh) is smaller than that of p-cresol, but increases
during further reaction for 500 min up to 420%/Rh. Decrease
of initially formed H2O also takes place gradually to 157%/Rh
in 500 min. The reaction of 1b with 2 in 5 : 1 molar ratio forms
m-xylene (140%/Rh), H2O (256%/Rh) and p-cresol (96%/Rh)
after 6 min accompanied by a decrease of 1b to 117%/Rh
(Fig. 1(b)). Further reaction for 600 min causes an increase
of m-xylene to 492%/Rh and decrease of H2O to 122%/Rh.
Almost quantitative formation of p-cresol at the beginning of
the reactions in eqn. (2) is attributed to the rapid activation of
the Rh–O bond by the arylboronic acid. Difference in the
amounts of H2O formed at the beginning of the two reactions
indicate that the formation of 3b requires a longer time than
that of 3a and occurs concurrently with the hydrolysis of the
B–Ar bond of the products.
Scheme 1
sation with two other boronic acid molecules or direct B–O
bond formation between the aryloxo ligand and boroxine leads
to the formation of a borate intermediate A with a six-mem-
bered ring.13 Metathesis of the B–OArЈ bond of A with an O–H
bond of the arylboronic acid in the reaction mixture releases
p-cresol accompanied by formation of intermediate B. Further
condensation of the arylboronic acid with B followed by cycliz-
ation of the second boroxine ring results in extrusion of Ar–H
to form 3a. Thus, the reaction of 1a with 2 produces 3a
instantly, which is followed by hydrolysis of the B–C bond of
3a. The profile of the reaction of 1b with 2 (Fig. 1(b)) is consist-
ent with the mechanism in Scheme 1. Completion of the
hydrolysis of the B–C6H3Me2-2,6 bond is slower than that of
the B–C6H4OMe-4 bond in the reaction of 1a.
The intermediate A in Scheme 1 can be obtained from the
reaction of the aryloxorhodium complex with arylboroxine14
which is equilibrated with the arylboronic acid via cycloconden-
sation under usual conditions. The reaction was conducted in
order to examine the plausibility of the reaction pathway.
Complex 2 leads to aryloxo ligand transfer to the boron center
of (PhBO)3 at room temperature to yield [Rh(PMe3)4]ϩ[B3O3-
Ph3(OC6H4Me-4)]Ϫ (5) (61%) (eqn. (4)). The 31P{1H} NMR
spectrum of 5 in acetone-d6 shows a broad singlet at room tem-
perature, while a sharp doublet at δ Ϫ16.13 (J(RhP) = 133 Hz) is
observed at Ϫ50 ЊC. Two 11B NMR signals at δ 4.47 and 28.50
are assigned to tetracoordinate boron and tricoordinate boron,
respectively.
(4)
The 1H NMR spectrum shows aromatic hydrogen signals
due to a 4-methylphenoxo group and three phenyl groups. The
signals of meta and para hydrogens in the phenyl rings are
observed in a 2 : 1 peak area ratio. As shown in Fig. 2, addition
Fig. 1 Plots of the organic and inorganic products during the
reactions (a) of 1a with 2 ([1a]0 = 0.098 M, [2]0 = 0.020 M) and (b) of 1b
with 2 ([1b]0 = 0.68 M, [2]0 = 0.14 M) in acetone-d6 at room temperature.
Mechanism for formation of 3
Scheme 1 depicts a plausible pathway for the formation of 3a
and 3b. The aryloxo ligand of 2 is known to be highly basic and
nucleophilic,9 similar to the aryloxo ligand of Pd() and Pt()
complexes with PMe3 ligands.12 Transfer of the aryloxo ligand
to the electrophilic boronic acid accompanied by cycloconden-
Fig. 2 Plots of the organic and inorganic products during the reaction
of 5 with H2O ([5]0 = 0.031 M, [H2O]0 = 0.14 M) in acetone-d6 at room
temperature.
D a l t o n T r a n s . , 2 0 0 4 , 1 3 6 6 – 1 3 7 5
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of H2O to 5 causes immediate formation of p-cresol and con-
sumption of H2O within 15 min. Although excess H2O is con-
sumed in a short period, the amount of the formed benzene is
much smaller than that of H2O. This reaction involves not only
the activation of the B–C bond by H2O but also hydrolysis of
the B–O bond of six-membered ring to regenerate PhB(OH)2.
This contrasts with that the reaction of H2O with 3a which
causes hydrolysis of the B–Ar bond rather than the activation
of the B–O bond of the spiro tetraarylpentaborate.
Preparation of [Rh(PEt3)4]؉[B5O6Ar4]؊ and
[Rh(PPh3)3]؉[B5O6(C6H4OMe-4)4]؊.
We next conducted the reactions of arylboronic acids with
Rh(OC6H4Me-4)(PEt3)3 (6), which was prepared according to
the preparation method of 2 and characterized by X-ray crys-
tallography (Fig. 3). The reactions of 1a and 1b with 6 produce
[Rh(PEt3)4]ϩ[B5O6Ar4]Ϫ (7a: Ar = C6H4OMe-4, 48%, 7b: Ar =
C6H3Me2-2,6, 43%), similarly to reaction (1) (eqn. (5)).
Fig. 4 ORTEP drawing of [Rh(PEt3)4]ϩ[B5O6(C6H3Me2-2,6)4]Ϫ (7b) at
30% ellipsoid level. Hydrogen atoms are omitted for clarity. Selected
bond distances (Å) and angles (Њ): Rh(1)–P(1) 2.323(3), Rh(1)–P(2)
2.334(2), Rh(1)–P(3) 2.327(3), Rh(1)–P(4) 2.315(3); P(1)–Rh(1)–P(2)
92.88(9), P(1)–Rh(1)–P(3) 145.6(1), P(1)–Rh(1)–P(4) 96.7(1), P(2)–
Rh(1)–P(3) 96.94(9), P(2)–Rh(1)–P(4) 144.6(1), P(3)–Rh(1)–P(4)
94.1(1).
(5)
lengths of 7b are almost identical to those of 3b (1.46(1)–
1.474(7), 1.33(1)–1.39(1) and 1.56(1)–1.58(1) Å), respectively.
The reaction of 1a with Rh(OC6H4Me-4)(PPh3)3 (8), pre-
pared according to the preparation procedure of Rh(OPh)-
(PPh3)3,16 in 5 : 1 molar ratio in the presence of equimolar PPh3
produces [Rh(PPh3)3]ϩ[B5O6(C6H4OMe-4)4]Ϫ (9a) as an orange
1
solid in 49% yield (eqn. (6)). The H NMR spectrum of 9a
contains aromatic hydrogen signals at δ 7.98 and 6.86 due to the
tetraarylpentaborate anion and at δ 7.53–7.35 due to the three
PPh3 ligands of [Rh(PPh3)3]ϩ.17 The 31P{1H} NMR spectrum
showed a doublet at δ 24.28 with J(RhP) = 145 Hz. The reac-
tions of H2O with 7a and with 9a are compared with that with
3a. Fig. 5 depicts hydrolytic dearylation of isolated 3a (a) and
7a (b) accompanied by liberation of anisole. Complex 3a with
PMe3 ligands is turned into its dearylated complex 4 more
rapidly than 7a having PEt3 ligands. Complex 9a is stable in
acetone solution and undergoes dearylation much more slowly
than 3a and 7a. Thus hydrolytic dearylation of the tetraaryl-
pentaborate is influenced by the cation, and the reaction
rates increase in the order, [Rh(PPh3)3]ϩ < [Rh(PEt3)4]ϩ
[Rh(PMe3)4]ϩ..
<
Fig. 3 ORTEP drawing of Rh(OC6H4Me-4)(PEt3)3 (6) at the 30%
ellipsoid level. Hydrogen atoms are omitted for clarity. Selected bond
distances (Å) and angles (Њ): Rh(1)–P(1) 2.207(2), Rh(1)–P(2) 2.318(2),
Rh(1)–P(3) 2.331(1), Rh(1)–O(1) 2.122(3), O(1)–C(1) 1.321(5); P(1)–
Rh(1)–P(2) 97.27(4), P(1)–Rh(1)–P(3) 101.87(5), P(1)–Rh(1)–O(1)
175.17(8), P(2)–Rh(1)–P(3) 157.14(4), P(2)–Rh(1)–O(1) 80.73(9), P(3)–
Rh(1)–O(1) 81.67(9), Rh(1)–O(1)–C(1) 123.2(3).
Complex 7a is highly unstable to air even in the solid state,
whereas 7b is stable enough for X-ray crystallography. An
ORTEP drawing of 7b is shown in Fig. 4 and selected bond
distances and angles of the anions are summarized in Table 1.
The bond parameters of 3a and 3b reported previously8 and
Naϩ[B5O6(OH)4]Ϫ are also shown. The coordination structure
of [Rh(PEt3)4]ϩ is similar to those of 3a, 3b and [Rh(PMe3)4]ϩ-
ClϪ 10 although this is the first X-ray analysis of [Rh(PEt3)4]ϩ
cation. The Rh–P bonds (2.315(3)–2.333(2) Å) of 7b are
longer than those (2.283(2)–2.292(3) Å) of 3b, which bears the
same tetraarylpentaborate anion. Each boroxine ring is flat due
to the delocalization caused by pπ–pπ interaction between filled
p-orbitals of oxygen and vacant p-orbitals of boron.15 Tetraco-
ordinate B–O bond (1.45(1)–1.50(1) Å) and tricoordinate B–O
bond (1.30(1)–1.40(1) Å), and B–C bond (1.56(1)–1.60(1) Å)
(6)
As shown in eqn. (7), reaction of 1b and [PPN]ϩ[OC6H4-
Me-4]Ϫ (PPN = bis(triphenylphosphino)iminium, Ph P᎐N᎐
᎐
᎐
3
PPh3) in a 5 : 1 molar ratio produces [PPN]ϩ[B5O6(C6H3Me2-
2,6)4]Ϫ (10) in 78% yield. The NMR signals of the anion part
are the same as that of 3b. Reaction for 24 h at room temper-
ature does not produce the dearylated product containing
[B5O6(OH)4]Ϫ although the reaction mixture contains H2O
formed via condensation of the arylboronic acid. PPNϩ, which
often stabilizes the reactive organometallic anion,18 serves to
prevent 10 from undergoing hydrolytic dearylation of the tetra-
arylpentaborate anion. This result suggests that the hydrolysis
of the B–C bond of the anion does not occur spontaneously,
but by assistance of the Rh-containing cation.
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Table 1 Selected bond distances (Å) and angles (Њ) of the anions of 3a, 3b, 7b, 15 and Naϩ[B5O6(OH)4]Ϫ
3a
3b
7b
15
Naϩ[B5O6(OH)4]Ϫ
Ref.
8
8
This work
This work
11a
B(1)–O(1)
B(1)–O(3)
B(1)–O(4)
B(1)–O(6)
B(2)–O(1)
B(2)–O(2)
B(3)–O(2)
B(3)–O(3)
B(4)–O(4)
B(4)–O(5)
B(5)–O(5)
B(5)–O(6)
1.462(9)
1.472(9)
1.478(8)
1.46(1)
1.337(9)
1.404(9)
1.392(9)
1.304(9)
1.33(1)
1.47(1)
1.46(1)
1.474(7)
1.474(7)
1.34(1)
1.36(1)
1.39(1)
1.33(1)
1.348(7)
1.363(8)
1.363(8)
1.348(7)
1.48(1)
1.45(1)
1.47(1)
1.50(1)
1.35(1)
1.37(1)
1.39(1)
1.34(1)
1.32(1)
1.40(1)
1.37(1)
1.30(1)
1.47(1)
1.48(1)
1.46(1)
1.47(1)
1.36(1)
1.39(2)
1.41(2)
1.33(1)
1.34(1)
1.38(1)
1.41(1)
1.33(1)
1.482(9)
1.475(10)
1.462(10)
1.444(10)
1.324(9)
1.397(9)
1.393(9)
1.340(9)
1.363(10)
1.377(10)
1.340(9)
1.354(9)
1.41(1)
1.375(9)
1.345(9)
O(1)–B(1)–O(3)
O(1)–B(1)–O(4)
O(1)–B(1)–O(6)
O(3)–B(1)–O(4)
O(3)–B(1)–O(6)
O(4)–B(1)–O(6)
111.5(6)
107.7(6)
109.4(6)
107.7(6)
108.6(6)
112.0(6)
111.9(8)
107.5(6)
107.5(6)
109.3(6)
109.3(6)
111.4(8)
113.4(9)
107.4(1)
106.7(1)
109.9(1)
109.0(1)
110.3(9)
110.2(8)
109.4(9)
109.5(8)
108.6(9)
107.5(9)
111.7(8)
110.1(5)
107.8(5)
109.2(5)
109.3(5)
108.9(5)
111.5(5)
(7)
Scheme 2
hydroxo ligand with an Ar group of the counter anion
[B5O6Ar4]Ϫ to give [B5O6Ar3(OH)]Ϫ. High affinity of the boron
atom of the anion towards oxygen enhances the metathesis of
the Rh–O bond and the B–C bond via transfer of the OH group
from Rh to B and concomitant transfer of the aryl group
from B to Rh. Chart 1 depicts the intermediate of the concerted
reaction that forms the new Rh–C and B–O bonds. Reductive
elimination of Ar–H from the resulting [RhHAr(PR3)n]ϩ
regenerates [Rh(PR3)n]ϩ. Yoshida et al. reported20 the reaction
of H2O with a hydridorhodium() complex to afford the Rh()
Fig. 5 Plots of the organic and inorganic products during the
reactions (a) of H2O with 3a ([3a]0 = 0.088 M, [H2O]0 = 0.35 M) and (b)
of H2O with 7a ([7a]0 = 0.037 M, [H2O]0 = 0.18 M) in acetone-d6 at room
temperature.
Scheme 2 depicts a possible pathway for the hydrolysis of the
B–C bond catalyzed by the cationic rhodium complexes
[Rh(PMe3)4]ϩ, [Rh(PEt3)4]ϩ and [Rh(PPh3)3]ϩ. A hydrido(hy-
droxo)rhodium() complex, [RhH(OH)(PR3)n]ϩ, is formed in
the reaction mixture via oxidative addition of H2O to the Rh()
center. The intermediate of the oxidative addition, [Rh(P-
Me3)4(H2O)]ϩ, has been reported.19 Although the oxidative add-
ition is not a thermodynamically favorable process,10 the
[RhH(OH)(PR3)n]ϩ, once formed, causes facile exchange of the
Chart 1
D a l t o n T r a n s . , 2 0 0 4 , 1 3 6 6 – 1 3 7 5
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complex the hydroxo ligand of which can undergo dissociation
and shows high nucleophilicity.
These complexes are characterized by 1H and 31P{1H}
NMR spectra in acetone-d6 and comparison of the signals with
those of [Rh(cod)(PPh3)2]ϩ[PF6]Ϫ.22 Hydrolytic dearylation of
complex 14a with H2O gives 15 (eqn. (10)).
Preparation of [Rh(cod)(PiPr3)(acetone)]؉[B5O6Ar4]؊ and
[Rh(cod)(PPh3)2]؉[B5O6Ar4]؊
Rh(OC6H4Me-4)(cod)(PiPr3) (11) and Rh(OC6H4Me-4)(cod)-
(PPh3) (12) were prepared by the reaction of a slight excess of
PiPr3 or PPh3 with [Rh(OC6H4Me-4)(cod)]2 according to the
synthetic method of Rh(OPh)(cod)(PCy3).21 Fig. 6 depicts an
ORTEP drawing of 12, which is the first example of X-ray
analysis for Rh(OAr)(cod)(PR3). The bond distances of Rh(1)–
C(5) and Rh(1)–C(6) are larger than those of Rh(1)–C(1),
Rh(1)–C(2) due to a larger trans influence of PPh3 relative to
the aryloxo ligand.
(10)
An ORTEP drawing of 15 upon crystal structure determination
is shown in Fig. 7 and selected bond distances and angles of the
anion are presented in Table 1. The structure of the anion part
of complex 15, [B5O6(OH)4]Ϫ is similar to that of the reported
Naϩ[B5O6(OH)4]Ϫ 11a the distances of B(tetracoordinated)–O
(1.46(1)–1.48(1) Å in 15 and 1.444(10)–1.482(9) Å in Naϩ-
[B5O6(OH)4]Ϫ), B(tricoordinated)–O (1.33(1)–1.41(1) Å in 15
and 1.324(9)–1.397(9) Å in Naϩ[B5O6(OH)4]Ϫ) and B–OH
(1.36(1)–1.37(1) Å in 15 and 1.336(9)–1.377(10) Å in Naϩ-
[B5O6(OH)4]Ϫ) bonds are almost identical between the Na
salt and 15. This is the first example of the crystallographic
structure of the cation [Rh(cod)(PPh3)2]ϩ. The coordination
geometry around the rhodium is square-planar.
Fig. 6 ORTEP drawing of Rh(OC6H4Me-4)(cod)(PPh3) (12) at the
30% ellipsoid level. Hydrogen atoms are omitted for clarity. Selected
bond distances (Å) and angles (Њ): Rh(1)–P(1) 2.329(1), Rh(1)–O(1)
2.029(2), Rh(1)–C(1) 2.102(3), Rh(1)–C(2) 2.093(3), Rh(1)–C(5)
2.196(3), Rh(1)–C(6) 2.179(3), O(1)–C(9) 1.317(3), C(1)–C(2) 1.387(4),
C(5)–C(6) 1.356(5); P(1)–Rh(1)–O(1) 82.96(6), M(12)–Rh(1)–P(1)
94.66(8), M(12)–Rh(1)–M(56) 87.7(1), O(1)–Rh(1)–M(56) 94.5(1),
Rh(1)–O(1)–C(9) 131.6(2). M(12) and M(56) are the midpoints of the
olefinic bonds in the 1,5-cyclooctadiene ligands.
Fig. 7 ORTEP drawing of [Rh(cod)(PPh3)2]ϩ[B5O6(OH)4]Ϫ (15) at the
30% ellipsoid level. Hydrogen atoms and two molecules of acetone are
omitted for clarity. Selected bond distances (Å) and angles (Њ): Rh(1)–
P(1) 2.322(2), Rh(1)–P(2) 2.389(2), Rh(1)–C(1) 2.181(8), Rh(1)–C(2)
2.216(8), Rh(1)–C(5) 2.237(8), Rh(1)–C(6) 2.252(9); P(1)–Rh(1)–P(2)
94.0(1), M(12)–Rh(1)–P(1) 92.2(3), M(12)–Rh(1)–M(56) 84.5(4), P(2)–
Rh(1)–M(56) 91.2(3). M(12) and M(56) are the midpoints of the
olefinic bonds in the 1,5-cyclooctadiene ligands.
The reaction of five molar equivalents of 1b with 11 in the
presence of PiPr3 in acetone at room temperature forms
[Rh(cod)(PiPr3)(acetone)]ϩ[B5O6(C6H3Me2-2,6)4]Ϫ (13b) as a
yellow solid in 50% yield (eqn. (8)).
Conclusions
In summary, we demonstrated unprecedented formation of the
tetraarylpentaborates [B5O6Ar4]Ϫ from arylboronic acids and
aryloxorhodium() complexes. The basic and nucleophilic aryl-
oxo ligand is transferred from Rh to an electrophilic B center of
arylboronic acids or boroxine. Formation of intermediate
monocyclic borate anions and the subsequent condensation of
it with arylboronic acid led to cyclization of the second borox-
ine ring of the spiro [B5O6Ar4]Ϫ. The tetraarylpentaborate
anions undergo hydrolysis of the B–C bonds to generate
[B5O6(OH)4]Ϫ, which is catalyzed by Rh-containing cations.
(8)
The 1H NMR spectrum of 13b shows the vinyl hydrogen signals
of the cod ligand at δ 4.89 and 4.03 and the presence of a cod
and a PiPr3 ligand. The reaction of five molar equivalents of 1a
and 1b with 12 in acetone–toluene (3 : 2) at room temperature
generates an orange solid [Rh(cod)(PPh3)2]ϩ[B5O6Ar4]Ϫ (14a:
Ar = C6H4OMe-4, 14b: Ar = C6H3Me2-2,6) in 46 and 75% yields
(eqn. (9)).
Experimental
General procedures
All manipulations were carried out under argon atmosphere
using standard Schlenk techniques. Hexane and toluene grade
(9)
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Table 2 Analytical results for the complexesa
Complex
C (%)
H (%)
[Rh(PMe3)4]ϩ[B5O6(C6H4OMe-4)4]Ϫ (3a)
48.74
54.04
23.05
53.80
53.19
54.12
58.68
73.49
67.08
73.83
60.25
68.28
62.45
66.37
70.32
55.41
(48.28)
(54.37)
(23.10)
(53.48)
(53.33)
(54.31)
(58.56)
(73.17)
(67.07)
(74.20)
(60.61)
(68.08)
(62.37)
(66.51)
(70.60)
(55.15)
6.54
7.42
6.45
7.08
9.28
7.69
8.44
5.26
5.01
6.00
8.43
5.90
7.56
5.72
6.35
4.86
(6.28)
(7.61)
(5.96)
(7.17)
(8.98)
(7.44)
(8.20)
(5.44)
(5.37)
(6.24)
(8.51)
(6.15)
(7.55)
(5.56)
(6.05)
(5.03)
[Rh(PMe3)4]ϩ[B5O6(C6H3Me2-2,6)4]Ϫ (3b)
[Rh(PMe3)4]ϩ[B5O6(OH)4]Ϫ (4)
[Rh(PMe3)4]ϩ[B3O3Ph3(OC6H4Me-4)]Ϫ (5)
Rh(OC6H4Me-4)(PEt3)3 (6)
[Rh(PEt3)4]ϩ[B5O6(C6H4OMe-4)4]Ϫ (7a)
[Rh(PEt3)4]ϩ[B5O6(C6H3Me2-2,6)4]Ϫ (7b)
Rh(OC6H4Me-4)(PPh3)3 (8)
[Rh(PPh3)3]ϩ[B5O6(C6H4OMe-4)4]Ϫ (9a)
[Ph3P᎐N᎐PPh3]ϩ[B5O6(C6H3Me2-2,6)4]Ϫ (10)b
᎐
᎐
Rh(OC6H4Me-4)(cod)(PiPr3) (11)
Rh(OC6H4Me-4)(cod)(PPh3) (12)
[Rh(cod)(PiPr3)(acetone)]ϩ[B5O6(C6H3Me2-2,6)4]Ϫ (13b)
[Rh(cod)(PPh3)2]ϩ[B5O6(C6H4OMe-4)4]Ϫ (14a)c
[Rh(cod)(PPh3)2]ϩ[B5O6(C6H3Me2-2,6)4]Ϫ (14b)d
[Rh(cod)(PPh3)2]ϩ[B5O6(OH)4]Ϫ (15)
1
a Calculated values are given in parentheses. b N; 1.26 (1.43%). c Obtained as 14aؒ0.5C6H14. The presence of solvated hexane was confirmed by H
NMR. d Obtained as 14bؒ0.5C6H14. The presence of solvated hexane was confirmed by 1H NMR.
were distilled from sodium and benzophenone prior to use or
purchased from Kanto Chemicals Co. Ltd.
Reaction of 1a and 1b with 2: formation of
[Rh(PMe3)4]؉[B5O6(OH)4]؊ (4)
NMR spectra (1H, 13C{1H}, 31P{1H} and 11B) were recorded
on JNM-La-500, JEOL EX-400 and Varian 300 spectrometers.
To an acetone (5 cm3) solution of 2 (235 mg, 0.54 mmol) and
PMe3 (0.056 cm3, 0.54 mmol) was added 4-methoxyphenyl-
boronic acid (1a) (408 mg, 2.68 mmol) at room temperature.
Stirring of the mixture for 24 h at room temperature caused
separation of an orange solid. The volatiles were removed
under reduced pressure, and the orange residue was washed
with toluene (10 cm3 × 3) and then with a minimum amount of
hexane to yield 4 as an air-sensitive orange solid (196 mg, 0.31
mmol, 58%). Complex 4 was recrystallized from acetone–hexa-
ne at room temperature and obtained as orange crystals. Com-
plex 4 was obtained also from the reaction of 1b with 2 under
1
Residual peaks of solvent were used as the reference for H
NMR (δ: acetone-d6, 2.04 chloroform-d, 7.26 toluene-d8, 2.09)
and 13C{1H} NMR (δ: acetone-d6, 29.8 toluene-d8, 20.4). The
external references were used for 31P{1H} NMR (85% H3PO4)
and 11B NMR (BF3ؒOEt2). Arylboronic acids 1a, 1b and
[PPN]ϩClϪ were purchased from Tokyo Chemical Industry Co.,
Ltd. or from Aldrich Chemical Co., Inc. [RhCl(cod)]2,23
[Rh(OMe)(cod)]2,24 phenylboroxine,25 Rh(OC6H4Me-4)(PMe3)3
(2),10 and [PPN]ϩ[OC6H4Me-4]Ϫ 26 were synthesized according
to the literature procedures. Elemental analyses were carried
out with a Yanaco MT-5 CHN Autocorder. Table 2 shows ana-
lytical results of the complexes.
1
the above conditions in 52% yield. H NMR (300 MHz, acet-
one-d6, 25 ЊC): δ 3.76 (s, 4H, OH ), 1.55 (br s, 36H, PCH3);
13C{1H} NMR (100.4 MHz, acetone-d6, 25 ЊC): δ 20.7 (PCH3);
31P{1H} NMR (121.5 MHz, acetone-d6, 25 ЊC): δ Ϫ15.38 (d,
J(RhP) = 134 Hz); 11B NMR (160.4 MHz, acetone-d6, 25 ЊC): δ
20.22 (br s, 4B, B2), 2.24 (s, 1B, B1).
Preparation of [Rh(PMe3)4]؉[B5O6Ar4]؊ (3a: Ar ؍ C6H4OMe-4,
3b: Ar ؍ C6H3Me2-2,6)
To an acetone (5 cm3) solution of 2 (132 mg, 0.30 mmol) and
PMe3 (0.031 cm3, 0.30 mmol) was added 4-methoxy-
phenylboronic acid (1a) (229 mg, 1.51 mmol) at room temper-
ature. Stirring the solution for 15 min caused a change in the
color of the solution from orange to red. The volatiles were
removed under reduced pressure to give a red oily material,
which was washed successively with toluene (10 cm3 × 3) and
with a minimum amount of hexane and dried under vacuum
to yield 3a as an air-sensitive yellow–orange solid (217 mg,
0.22 mmol, 73%). Complex 3a was recrystallized from acetone–
Reaction of 1a with 2 on NMR scale
To an acetone-d6 (0.60 cm3) solution of 2 (5.1 mg, 0.012 mmol)
in an NMR tube was added 1a (9.0 mg, 0.059 mmol) at room
temperature. The 1H NMR spectra were recorded over 510 min.
The change in molar ratio of organic and inorganic products
was monitored using 1,4-dimethylnaphthalene as an internal
standard. The results are shown in Fig. 1(a).
Reaction of 1b with 2 on NMR scale
1
hexane at room temperature as orange crystals. H NMR (300
To an acetone-d6 (0.60 cm3) solution of 2 (36 mg, 0.082 mmol)
in an NMR tube was added 1b (62 mg, 0.41 mmol) at room
temperature. The 1H NMR spectra were recorded over 600 min.
The change in molar ratio of organic and inorganic products
was monitored using 1,4-dimethylnaphthalene as an internal
standard. The results are shown in Fig. 1(b).
MHz, acetone-d6, 25 ЊC): δ 7.98 (d, J = 9 Hz, 8H, ortho), 6.87 (d,
J = 9 Hz, 8H, meta), 3.78 (s, 12H, OCH3), 1.53 (br, 36H, PCH3);
13C{1H} NMR (100.4 MHz, acetone-d6, 25 ЊC): δ 162.1 (para),
137.2 (ortho), 113.4 (meta), 55.1 (OCH3), 20.6 (PCH3); 31P{1H}
NMR (121.5 MHz, acetone-d6, 25 ЊC): δ Ϫ15.40 (d, PMe3,
J(RhP) = 134 Hz); 11B NMR (160.4 MHz, acetone-d6, 25 ЊC):
δ 28.18 (br s, 4B, B2), 4.76 (s, 1B, B1).
Preparation of [Rh(PMe3)4]؉[B3O3Ph3(OC6H4Me-4)]؊ (5)
Complex 3b was prepared analogously from 2 (234 mg,
0.53 mmol), PMe3 (0.097 cm3, 0.94 mmol), and 1b (402 mg,
2.68 mmol) in 79% yield and recrystallized from acetone–
To an acetone (5 cm3) solution of 2 (152 mg, 0.35 mmol) and
PMe3 (0.40 cm3, 0.39 mmol) was added phenylboroxine
(140 mg, 0.45 mmol) at room temperature. Stirring the solution
for 15 min caused a change in the color of the solution from
orange to red. The volatiles were removed under reduced pres-
sure to give a red oily material, which was washed successively
with toluene (10 cm3 × 3) and with a minimum amount of
hexane and dried under vacuum to yield 5 as an air-sensitive
yellow–orange solid (177 mg, 0.21 mmol, 61%). Complex 5 was
recrystallized from acetone–hexane at room temperature as
1
hexane as orange crystals. H NMR (300 MHz, acetone-d6,
25 ЊC): δ 6.95 (t, J = 7 Hz, 4H, para), 6.83 (d, J = 7 Hz, 8H,
meta), 2.43 (s, 24 H, CH3), 1.46 (m, 36H, PCH3); 13C{1H} NMR
(100.4 MHz, acetone-d6, 25 ЊC): δ 140.6 (ortho), 127.6 (para),
126.4 (meta), 22.7 (CH3), 20.7 (PCH3); 31P{1H} NMR (121.5
MHz, acetone-d6, 25 ЊC): δ Ϫ15.38 (d, PMe3, J(RhP) = 134 Hz);
11B NMR (160.4 MHz, acetone-d6, 25 ЊC): δ 29.73 (br s, 4B, B2),
4.67 (s, 1B, B1).
D a l t o n T r a n s . , 2 0 0 4 , 1 3 6 6 – 1 3 7 5
1371

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orange crystals. 1H NMR (400 MHz, acetone-d6, 25 ЊC): δ 8.11
(d, J = 8 Hz, 4H), 7.72 (d, J = 8 Hz, 2H), 7.34 (m, 6H), 7.04 (d,
J = 8 Hz, 2H), 6.95 (d, J = 8 Hz, 2H), 6.92 (t, J = 8 Hz, 1H), 6.73
(d, J = 8 Hz, 2H), 2.09 (s, 3H, CH3), 1.42 (br s, 36H, PCH3);
13C{1H} NMR (100.4 MHz, acetone-d6, 25 ЊC): δ 135.6, 133.1,
130.2, 127.8, 126.7, 124.8, 120.4, 20.6 (PCH3). The CH3 carbon
was not observed due to overlapping with that of PMe3. The
spectrum at Ϫ50 ЊC showed the signal of CH3 carbon (δ 20.4)
and PCH3 carbons (δ 19.9) separately. The ipso carbon signal
was not observed due to its low intensity. 31P{1H} NMR (161.7
Preparation of Rh(C6H4OMe-4)(PPh3)3 (8)
This complex was prepared by modifying the procedure for
Rh(C6H4OMe-4)(PMe3)3 using PPh3 at 60 ЊC for 24 h. Complex
8 was obtained in 59% yield as an orange solid. 1H NMR (400
MHz, in toluene-d8, 25 ЊC): δ 7.30 (m, 18H, ortho), 7.22 (m,
27H, meta), 1.90 (s, 3H, p-CH3); 31P{1H} NMR (161.7 MHz,
toluene-d8, 25 ЊC): δ 99.61 (dt, PB, J(RhP) = 172 Hz, J(PP) =
39 Hz), 29.18 (dd, PA, J(RhP) = 156 Hz, J(PP) = 39 Hz).
Preparation of [Rh(PPh3)3]؉[B5O6Ar4]؊ (Ar ؍ C6H4OMe-4)
(9a)
MHz, acetone-d6, Ϫ50 ЊC): δ Ϫ16.13 (d, J(RhP) = 133 Hz); 11
B
NMR (160.4 MHz, acetone-d6, 25 ЊC): δ 28.50 (br s, 2B, B2),
4.47 (s, 1B, B1).
To an acetone–toluene (3 : 2) (5 cm3) suspension of 8 (79 mg,
0.079 mmol) and PPh3 (21 mg, 0.080 mmol) was added 1a (60
mg, 0.39 mmol) at room temperature. The reaction mixture
immediately became an orange homogeneous solution. After
the mixture was stirred for 15 min at room temperature, the
volatiles were removed under reduced pressure to give an
orange residue. A residue was washed with toluene (5 cm3 × 3)
and a minimum amount of hexane and dried under vacuum to
yield an orange solid (57 mg, 0.039 mmol, 49%) of 9a. 1H NMR
(400 MHz, acetone-d6, 25 ЊC): δ 7.98 (d, J = 8 Hz, 8H, ortho),
7.53–7.35 (m, 45H, PPh3), 6.86 (d, J = 8 Hz, 8H, meta), 3.77 (s,
12H, OCH3); 31P{1H} NMR 161.7 MHz, acetone-d6, 25 ЊC):
δ 24.28 (d, J(RhP) = 145 Hz); 11B NMR (160.4 MHz, acetone-
d6, 25 ЊC): δ 29.55 (br s, 4B, B2), 1.92 (s, 1B, B1).
Reaction of H2O with 5 on NMR scale
To an acetone-d6 (0.70 cm3) solution of 5 (18 mg, 0.022 mmol)
in an NMR tube was added H2O (0.0018 cm3, 0.10 mmol) at
room temperature. The 1H NMR spectra (300 MHz) were
recorded over 60 min. The change in molar ratio of p-cresol,
benzene and H2O was monitored using 1,4-dimethyl-
naphthalene as an internal standard. The results are shown in
Fig. 2.
Preparation of Rh(C6H4OMe-4)(PEt3)3 (6)
This complex was prepared by modifying the procedure for
Rh(C6H4OMe-4)(PMe3)3 9 using PEt3 (20% in toluene solution)
in 44% yield as dark orange blocks. 1H NMR (400 MHz, acet-
one-d6, 25 ЊC): δ 6.84 (d, J = 8 Hz, 2H, ortho), 6.64 (d, J = 8 Hz,
2H, meta), 2.08 (s, 3H, p-CH3), 1.60 (m, 18H, PCH2), 1.19 (m,
9H, PBCH2CH3), 1.08 (apparent triplet by virtual coupling,
18H, PACH2CH3); 13C{1H} NMR (100.4 MHz, acetone-d6,
25 ЊC): δ 170.0 (ipso), 129.2 (ortho), 120.4 (meta), 119.0 (para),
21.5 (d, PBCH2, J(PC) = 26 Hz), 20.6 (p-CH3), 16.9 (apparent
triplet by virtual coupling, PACH2), 9.4 (PBCH2CH3), 8.9
(PACH2CH3); 31P{1H} NMR (161.7 MHz, acetone-d6, 25 ЊC):
δ 36.01 (dt, PB, J(RhP) = 168 Hz, J(PP) = 42 Hz), 17.01 (dd, PA,
J(RhP) = 144 Hz, J(PP) = 42 Hz).
Reaction of H2O with 3a on NMR scale
To an acetone-d6 (0.60 cm3) solution of 3a (53 mg, 0.053 mmol)
in an NMR tube was added H2O (0.0038 cm3, 0.21 mmol) at
1
room temperature. The H NMR spectra were recorded over
360 min. The change in molar ratio of organic and inorganic
products was monitored using 1,4-dimethylnaphthalene as an
internal standard. The results are shown in Fig. 5(a).
Reaction of H2O with 7a on NMR scale
To an acetone-d6 (0.60 cm3) solution of 7a (26 mg, 0.023 mmol)
in an NMR tube was added H2O (0.20 cm3, 0.11 mmol) at room
Preparation of [Rh(PEt3)4]؉[B5O6Ar4]؊ (7a: Ar ؍ C6H4OMe-4.
7b: Ar ؍ C6H3Me2-2,6)
1
temperature. The H NMR spectra were recorded over 4170
min. The change in molar ratio of anisole and H2O was moni-
tored using 1,4-dimethylnaphthalene as an internal standard.
The results are shown in Fig. 5(b).
To an acetone (5 cm3) solution of 6 (137 mg, 0.24 mmol) and PEt3
(20% in toluene solution, 0.20 cm3, 0.27 mmol) was added 1a (185
mg, 1.22 mmol) at room temperature. Stirring the solution for 15
min caused a change in the color of the solution from orange to
red. The volatiles were removed under reduced pressure to give a
red oily material, which was washed successively with toluene (10
cm3 × 3) and with a minimum amount of hexane, and dried
under vacuum to yield 7a as an air-sensitive orange–red solid
(134 mg, 0.12 mmol, 48%). Complex 7a was recrystallized from
Preparation of [PPN]؉[B5O6(C6H3Me2-2,6)4]؊ (10)
To an acetone (5 cm3) solution of [PPN]ϩ[OC6H4Me-4]Ϫ
(346 mg, 0.536 mmol) was added 1b (402 mg, 2.68 mmol) at
room temperature. Stirring the solution for 24 h led to a change
in the color of the solution from pale yellow to colorless. The
volatiles were removed under reduced pressure to give a white
solid, which was washed successively with toluene (10 cm3 × 3),
and with diethyl ether (10 cm3 × 2), and dried in vacuo to give 10
1
acetone–hexane at room temperature as red crystals. H NMR
(300 MHz, acetone-d6, 25 ЊC): δ 7.98 (d, J = 9 Hz, 8H, ortho), 6.87
(d, J = 9 Hz, 8H, meta), 3.79 (s, 12H, OCH3), 1.88 (m, 36H,
PCH2), 1.19 (t, J = 7.2 Hz, 36H, PCH2CH3); 13C{1H} NMR
(100.4 MHz, acetone-d6, 25 ЊC): δ 162.0 (para), 137.0 (ortho),
113.2 (meta), 55.1 (OCH3), 21.2 (m, PCH2CH3), 9.6 (PCH2CH3);
31P{1H} NMR (121.5 MHz, acetone-d6, 25 ЊC): δ 7.12 (d, PEt3,
J(RhP) = 134 Hz); 11B NMR (160.4 MHz, acetone-d6, 25 ЊC):
δ 29.24 (br s, 4B, B2), 1.91 (s, 1B, B1).
Complex 7b was prepared from 6 (177 mg, 0.314 mmol) and
1b (236 mg, 1.57 mmol) in 43% yield and recrystallized
from acetone–hexane as red crystals. 1H NMR (300 MHz,
acetone-d6, 25 ЊC): δ 6.93 (t, 4H, para, J = 7 Hz), 6.87 (d, 8H,
meta, J = 7 Hz), 2.43 (s, 24 H, CH3), 1.90 (m, 24H, PCH2), 1.21
(m, 36H, PCH2CH3); 13C{1H} NMR (100.4 MHz, acetone-d6,
25 ЊC): δ 140.5 (ortho), 127.5 (para), 126.3 (meta), 22.7 (CH3),
21.2 (m, PCH2CH3), 9.6 (PCH2CH3); 31P{1H} NMR (121.5
MHz, acetone-d6, 25 ЊC): δ 7.21 (d, J(RhP) = 137 Hz); 11B NMR
(160.4 MHz, acetone-d6, 25 ЊC): δ 31.57 (br s, 4B, B2), 1.37 (s,
1B, B1).
1
as a white solid (464 mg, 0.418 mmol, 78%). H NMR (300
MHz, acetone-d6, 25 ЊC): δ 7.73–7.62 (m, 18H, Ph(PPN)), 7.57–
7.51 (m, 12H, Ph(PPN), 6.94 (t, J = 7 Hz, 4H, para), 6.82 (d,
J = 7 Hz, 8H, meta), 2.42 (s, 24H, CH3); 13C{1H} NMR (100.4
MHz, acetone-d6, 25 ЊC): δ 140.3 (ortho), 134.3 (para of PPN),
132.9 (m, ortho of PPN), 130.1 (m, meta of PPN), 127.9 (d,
J(PC) = 108 Hz, ipso of PPN), 127.4 (para), 126.2 (meta), 22.7
(CH3), the ipso carbons bonded to boron were not observed.
31P{1H} NMR (121.5 MHz, acetone-d6, 25 ЊC): δ 22.56 (s); 11B
NMR (160.4 MHz, acetone-d6, 25 ЊC): δ 30.51 (br s, 4B, B2),
1.26 (s, 1B, B1).
Preparation of Rh(OC6H4Me-4)(cod)(PiPr3) (11) and
Rh(OC6H4Me-4)(cod)(PPh3) (12)
To a dichloromethane (10 cm3) solution of [Rh(OMe)(cod)]2
(340 mg, 0.70 mmol) was added p-cresol (199 mg, 1.84 mmol) at
room temperature. After the mixture was stirred for 5 min, the
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pale yellow precipitate of [Rh(OC6H4Me-4)(cod)]2 was filtered
off, washed with dichloromethane (10 cm3 × 3), and dried under
vacuum. PiPr3 (90% in toluene solution, 1.6 cm3, 7.5 mmol) was
added to a toluene (10 cm3) suspension of [Rh(OC6H4Me-4)-
(cod)]2 at room temperature. After being stirred for 2 h at 60 ЊC,
the mixture became a homogeneous light orange solution. The
solvent was removed under reduced pressure, and the yellow
residue was extracted with hexane at 60 ЊC. The extracts
were cooled to room temperature to yield yellow crystals of 11
CH2 of cod); 13C{1H} NMR (100.4 MHz, acetone-d6, 25 ЊC):
δ 161.9 (para), 137.0 (ortho), 134.9 (br s, ortho of PPh3), 131.6
(para of PPh3), 129.3 (br s, meta of PPh3), 113.2 (meta), 99.1 (br
s, CH of cod), 55.1 (OCH3), 31.1 (br s, CH2 of cod), the ipso
carbons of PPh3 were not observed; 31P{1H} NMR (121.5
MHz, acetone-d6, 25 ЊC): δ 24.34 (d, J(RhP) = 146 Hz); 11B
NMR (160.4 MHz, acetone-d6, 25 ЊC): δ 29.41 (br s, 4B, B2),
1.95 (s, 1B, B1).
Complex 14b was obtained similarly in 75% yield. 1H NMR
(400 MHz, acetone-d6, 25 ЊC): δ 7.53–7.35 (m, 30H, PPh3), 6.95
(t, J = 8 Hz, 4H, para), 6.85 (d, J = 8 Hz, 8H, meta), 4.67 (m, 4H,
CH of cod), 2.56 (m, 4H, CH2 of cod), 2.42 (s, 24H, CH3), 2.26
(m, 4H, CH2 of cod); 13C{1H} NMR (100.4 MHz, acetone-d6,
25 ЊC): δ 140.4 (ortho), 135.0 (br s, ortho of PPh3), 131.7 (para
of PPh3), 129.4 (br s, meta of PPh3), 127.5 (para), 126.3 (meta),
99.8 (br s, CH of cod), 31.1 (br s, CH2 of cod), 22.7 (CH3), the
ipso carbons of PPh3 were not observed; 31P{1H} NMR (121.5
MHz, acetone-d6, 25 ЊC): δ 24.35 (d, J(RhP) = 145 Hz); 11B
NMR (160.4 MHz, acetone-d6, 25 ЊC): δ 31.50 (br s, 4B, B2),
1.38 (s, 1B, B1).
1
(245 mg, 0.51 mmol, 36%). H NMR (400 MHz, acetone-d6,
25 ЊC): δ 6.72 (d, J = 8 Hz, 2H, ortho), 6.41 (d, J = 8 Hz, 2H,
meta), 4.72 (m, 2H), 3.45 (m, 2H), 2.38 (m, 2H), 2.42 (m, 5H, H
and PCH(CH3)2), 2.09 (s, 3H, p-CH3), 1.93 (m, 2H), 1.76 (m,
2H), 1.38 (dd, J(PH) = 13 Hz, J(HH) = 7 Hz, 18H, PCH(CH3)2);
13C{1H} NMR (100.4 MHz, acetone-d6, 25 ЊC): δ 168.0 (ipso),
129.8 (ortho), 122.7 (para), 121.5 (meta), 99.7 (CH of cod), 64.4
(CH of cod), 33.9 (CH2 of cod), 28.6 (CH2 of cod), 23.2
(p-CH3), 23.0 (PCH(CH3)2), 20.2 (PCH(CH3)2); 31P{1H} NMR
(161.7 MHz, acetone-d6, 25 ЊC): δ 34.66 (d, J(RhP) = 153 Hz).
Complex 12 was obtained in 63% yield as an air-stable yellow
solid and recrystallized from cold toluene to produce yellow
1
crystals. H NMR (400 MHz, in toluene-d8, 25 ЊC): δ 7.57 (br,
Reaction of 1a with 12 on NMR scale
15H, PPh3), 7.00 (d, J = 8 Hz, 2H, ortho), 6.81 (d, J = 8 Hz, 2H,
meta), 5.32 (m, 2H, CH of cod), 2.90 (m, 2H, CH of cod), 2.26
(s, 3H, p-CH3), 2.22 (m, 4H, CH2 of cod), 1.60 (m, 4H, CH2 of
cod). 31P{1H} NMR (161.7 MHz, toluene-d8, Ϫ85 ЊC): δ 22.31
(d, J(RhP) = 164 Hz).
To an acetone-d6 (0.60 cm3) solution of 12 (14 mg, 0.024 mmol)
in an NMR tube was added 1a (18 mg, 0.12 mmol) at room
temperature. The H NMR spectra (400 MHz) were recorded
over 72 h. The change in molar ratio of organic and inorganic
products was monitored using 1,4-dimethylnaphthalene as an
internal standard.
1
Reaction of 2,6-dimethylphenylboronic acid (1b) with 11: prepar-
ation of [Rh(cod)(PiPr3)(acetone)]؉[B5O6Ar4]؊ (Ar ؍ C6H3Me2-
2,6) (13b)
Hydrolytic decomposition of 14a and 14b: formation of
[Rh(cod)(PPh3)2]؉[B5O6(OH)4]؊ (15)
To an acetone (5 cm3) solution of 11 (106 mg, 0.222 mmol) and
PiPr3 (90% in toluene solution, 0.05 cm3, 0.24 mmol) was added
2,6-dimethylphenylboronic acid (1b) (166 mg, 1.11 mmol) at
room temperature. After being stirred for 15 min the volatiles
were removed under reduced pressure to give a yellow oily
material, which was washed with toluene–hexane (1 : 1) solu-
tion (10 cm3 × 3) and with a minimum amount of hexane, and
dried under vacuum to yield 13b as a yellow solid (111 mg,
Complex 15 is obtained from 14a and 14b with H2O in acetone
as insoluble orange solid. 1H NMR (400 MHz, acetone-d6,
25 ЊC): δ 7.55 (m, 12H, ortho of PPh3), 7.49 (m, 6H, para of
PPh3), 7.37 (m, 12H, meta of PPh3), 4.58 (m, 4H, CH of cod),
3.75 (s, 4H, OH ), 2.57 (m, 4H, CH2 of cod), 2.32 (m, 4H, CH2
of cod); 31P{1H} NMR (161.7 MHz, acetone-d6, 25 ЊC): δ 24.26
(d, J(RhP) = 145 Hz); 11B NMR (160.4 MHz, acetone-d6,
25 ЊC): δ 20.40 (br s, 4B, B2), 1.77 (s, 1B, B1).
1
0.111 mmol, 50%). H NMR (400 MHz, acetone-d6, 25 ЊC):
δ 6.95 (t, J = 7 Hz, 4H, para), 6.83 (d, J = 7 Hz, 8H, meta), 4.89
(s, 2H, CH of cod trans to PiPr3), 4.03 (s, 2H, CH of cod trans
to acetone), 2.69–2.20 (m, 5H, CH2 of cod and PCH(CH3)2),
2.42 (s, 24H, CH3), 2.08 (s, 6H, acetone), 1.37 (dd, J(PH) = 13
Hz, J(HH) = 7 Hz, 18H, PCH(CH3)2); 13C{1H} NMR (100.4
MHz, acetone-d6, 25 ЊC): δ 140.4 (ortho), 127.5 (para), 126.3
(meta), 104.4 (CH of cod), 70.4 (d, J(PC) = 15 Hz, CH of cod),
33.7 (CH2 of cod), 28.2 (CH2 of cod), 22.7 (CH3), 22.3
(PCH(CH3)2), 20.2 (PCH(CH3)2); 31P{1H} NMR (161.7 MHz,
acetone-d6, 25 ЊC): δ 36.43 (d, J(RhP) = 141 Hz); 11B NMR
(160.4 MHz, acetone-d6, 25 ЊC): δ 31.56 (br s, 4B, B2), 2.23 (s,
1B, B1).
X-Ray diffraction
Single crystals of 6, 7b, 12 and 15 suitable for X-ray diffraction
studies were grown by appropriate methods (see text). Crystal-
lographic data and details of refinement are summarized in
Table 3. The crystals were sealed in glass capillary tubes and
mounted on a Rigaku AFC-5R automated four-circle dif-
fractiometer. Intensities were collected by the ω–2θ scan
method adopted, and an empirical absorption correction
(ψ scan) along with Lorentz correction were applied. The
intensities of three standard reflections, measured every 150
reflections were monitored throughout the data collection. All
calculations were performed using the Crystal Structure27 crys-
tallographic software package. The structure was solved by
direct methods28 and expanded using Fourier techniques.29 All
non-hydrogen atoms were refined with anisotropic thermal
parameters, whereas all hydrogen atoms were located by assum-
ing ideal geometry and included in the structure calculation
without further refinement of the parameters.30
Preparation of [Rh(cod)(PPh3)2]؉[B5O6Ar4]؊ (14a: Ar ؍
C6H4OMe-4, 14b: Ar ؍ C6H3Me2-2,6)
To an acetone–toluene (3 : 2) (5 cm3) suspension of 12 (163 mg,
0.28 mmol) and PPh3 (147 mg, 0.56 mmol) was added 4-meth-
oxyphenylboronic acid (1a) (213 mg, 1.40 mmol) at room tem-
perature. Stirring for 15 min caused a change in the reaction
mixture to an orange solution. The volatiles were removed
under reduced pressure to give an orange oily material, which
were washed with toluene (10 cm3 × 3) and with a minimum
amount of hexane, and dried in vacuo to yield 14a as an air-
sensitive yellowish orange solid (171 mg, 0.13 mmol, 46%). Re-
crystallization from acetone-d6 at room temperature produced
CCDC reference numbers 225878–225881.
See http://www.rsc.org/suppdata/dt/b3/b315902g/ for crystal-
lographic data in CIF or other electronic format.
Acknowledgements
1
dark orange crystals of 14a. H NMR (400 MHz, acetone-d6,
This work was financially supported by a Grant-in-Aid for
Scientific Research from the Ministry of Education, Science,
Sports, Technology and Culture of Japan. We are grateful
to Prof. Norio Miyaura (Hokkaido University) for helpful
25 ЊC): δ 7.98 (d, J = 8 Hz, 8H, ortho), 7.54–7.35 (m, 30H,
PPh3), 6.86 (d, J = 8 Hz, 8H, meta), 4.67 (m, 4H, CH of cod),
3.78 (s, 12H, OCH3), 2.56 (m, 4H, CH2 of cod), 2.27 (m, 4H,
D a l t o n T r a n s . , 2 0 0 4 , 1 3 6 6 – 1 3 7 5
1373

View Article Online
Table 3 Crystal data and details of the structure refinement of 6, 7b, 12 and 15
6
7b
12
15
Formula
C25H52OP3Rh
C56H96B5O6P4Rh
C33H34OPRh
C44H46B5O10P2Rhؒ
2Me2CO
1069.90
Monoclinic
P21/n (no. 14)
19.578(8)
9.863(5)
27.813(6)
90
103.15(3)
90
5229.8(4)
4
0.446
2216
1.359
0.40 × 0.35 × 0.05
5.0–50.0
9195
4103
649
Mr
564.51
Orthorhombic
Pbca (no. 61)
18.949(4)
18.153(6)
17.641(3)
90
90
90
6068.1(3)
8
0.733
2400
1.236
0.75 × 0.65 ×0.60
5.0–50.0
6966
4256
323
0.038
0.051
1146.22
Monoclinic
P21/n (no. 14)
14.300(2)
27.509(6)
16.606(5)
90
93.23(2)
90
6521.7(3)
4
0.402
2440
1.167
0.35 × 0.30 × 0.20
5.0–50.0
10329
4154
745
580.51
Crystal system
Space group
a/Å
b/Å
c/Å
α/Њ
β/Њ
Triclinic
¯
P1 (no. 2)
11.918(3)
12.525(2)
9.851(2)
106.79(1)
90.22(2)
79.76(2)
1383.6(5)
2
0.697
600
1.393
0.50 × 0.43 × 0.30
5.0–55.0
6369
5306
359
γ/Њ
V/Å3
Z
µ(Mo-Kα)/mmϪ1
F(000)
Dc/g cmϪ3
Crystal size/mm
2θ Range/Њ
No. of unique reflns.
No. of used reflns.
No. of variables
R
0.056
0.067
0.030
0.043
0.056
0.067
a
Rw
GOF
1.001
1.004
0.950
0.978
a Weighting scheme [σ(Fo)2]Ϫ1
.
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13 W. Kliegel, K. Drueckler, B. O. Patrick, S. J. Rettig and J. Trotter,
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discussion on the reaction mechanism. We also thank Dr
Yoshiyuki Nakamura (Tokyo Institute of Technology) for
measurements of 11B NMR spectra.
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D a l t o n T r a n s . , 2 0 0 4 , 1 3 6 6 – 1 3 7 5
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D a l t o n T r a n s . , 2 0 0 4 , 1 3 6 6 – 1 3 7 5
1375