Intermolecular alkynyl-ligand migration from aryl-palladium(II) to -platinum(II) complexes with and without a CuI catalyst. Reversible transfer of the alkynyl group between copper(I) and palladium(II) complexes

Article abstract of DOI:10.1039/a700021i

Alkynyl-ligand transfer from [PdR(OCPh)L₂] (R = C₆H₄Me-p, L = PEt₃) to [PtR′(I)L₂] (R′ = C₆H₄OMe-p), to give [PdR(I)L₂] and [PtR′(GCPh)L₂], has been enhanced to a large extent by addition of CuI, indicating reversible ligand transfer between Pd^II and Cu^I complexes.

Full text of DOI:10.1039/a700021i

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Intermolecular alkynyl-ligand migration from aryl-palladium(II) to
platinum(II) complexes with and without a CuI catalyst. Reversible
-
transfer of the alkynyl group between copper(I) and palladium(II)
complexes
Kohtaro Osakada,* Reiko Sakata and Takakazu Yamamoto*
Research Laboratory of Resources Utilization, Tokyo Institute of Technology, 4259 Nagatsuta,
Midori-ku, Yokohama 226, Japan
L
L′
Alkynyl-ligand transfer from [PdR(C᎐CPh)L ] (R = C H Me-p,
᎐
2
6
4
MeC6H4 Pd
C
C
Ph MeOC6H4 Pd
I
L = PEt ) to [PtRЈ(I)L ] (RЈ = C H OMe-p), to give [PdR(I)L ]
3
2
6
4
2
L
L′
and [PtRЈ(C᎐CPh)L ], has been enhanced to a large extent by
᎐
2
1
5
addition of CuI, indicating reversible ligand transfer between
II
I
(L = PEt3, L′ = PMe3) –30 °C
Pd and Cu complexes.
L
L′
MeOC6H4 Pd
L′
MeC6H4 Pd
L
I
C
C
Ph (2)
Many dinuclear transition-metal complexes with bridging
1
2
alkynyl ligands in a µ-η :η fashion undergo rapid switching of
1
the co-ordination mode as shown in Scheme 1(i). The reaction
2
6
with facile cleavage of the thermodynamically stable metal–
2
alkynyl σ bond is probably involved as a crucial step in the
fer occurs prior to intermolecular aryl ligand migration both in
reactions (1) and (2).
intermolecular transfer of an alkynyl group between one
transition-metal complex and another [Scheme 1(ii)]. However,
the latter type of alkynyl-ligand-transfer reactions have mainly
been reported for transfers between alkynylcopper() com-
pounds and Group 8–10 transition-metal complexes in a
Reaction (1) is significantly enhanced by addition of CuI
Ϫ3
(
2.09 µmol dm , [Cu]/[Pd] = 0.10) and is completed within 5 min
at 50 ЊC. The results indicate that the reaction proceeds through
two independent pathways as shown in Scheme 2. Pathway (i)
involves direct ligand exchange, possibly having a bimetallic
transition state, while (ii) has the alkynylcopper() intermediate
that promotes the indirect ligand transfer from Pd to Pt. The
3
seemingly irreversible fashion. There have been only a few
reports on the intermolecular alkynyl transfer reaction among
4
Group 8–10 metal centres. In this paper we report migration of
the alkynyl group from aryl(alkynyl)palladium() to aryl(iodo)-
platinum() complexes in the absence and presence of a CuI
catalyst and describe the role of CuI in the reaction.
II
latter pathway requires alkynyl-ligand transfer from the Pd to
I
one Cu centre, but this reaction is unprecedented. Addition of
An aryl(alkynyl)palladium() complex, trans-[Pd(C H -
6
4
Ϫ1
1
†
Spectroscopic data for 1. IR (KBr): ν(C᎐C) 2092 cm . H NMR (400
MHz in C ): δ 0.98 (m, 18 H, CH ), 1.57 (m, 12 H, PCH ), 2.29 (s, 3
H, CH ), 7.00 (t, 1 H, C H H, J = 7), 7.08 (d, 2 H, C H H , J = 7), 7.16
Me-p)(C᎐CPh)(PEt ) ] 1, prepared from the reaction of trans-
᎐
3 2
3
h,5
6
D
6
3
2
[
Pd(C H Me-p)(I)(PEt ) ] 2 and [{Cu(C᎐CPh)(PPh )} ]
at
6
4
3
2
3
4
3
6
4
6
3
2
Ϫ30 ЊC, reacts smoothly at 50 ЊC with equimolar amounts of
trans-[Pt(C H OMe-p)(I)(PEt ) ] 3 to give a mixture of 2
13
(
t, 2 H, C H H , J = 7 Hz), 7.46 and 7.62 (d, 4 H, C H , J = 7 Hz). C-
6 3 2 6 4
1
{ H} NMR (100 MHz in C D ): δ 119.0 (t, PdC᎐, J = 20 Hz), 111.6 (s,
᎐
6
4
3
2
6
6
3
1
1
1
and trans-[Pt(C H OMe-p)(C᎐CPh)(PEt ) ] 4 quantitatively
᎐C᎐C). P-{ H} NMR (160 MHz in C D ): δ 14.5 (s). 2. H NMR (400
6
4
3
2
᎐
6
6
1
31
1
[
equation (1)].† The NMR ( H and P-{ H}) spectra of the
MHz in C
6
D
6
): δ 0.89 (m, 18 H, CH
3
), 1.56 (m, 12 H, PCH
2
), 2.18 (s, 3
3
1
1
H, CH ), 6.90 and 7.21 (d, 4 H, C H , J = 7 Hz). P-{ H} NMR (160
3
6
4
1
MHz in C D ): δ 10.3 (s). 3. H NMR (400 MHz in C D ): δ 0.87 (m,
6
6
6
6
L
L
1
8 H, CH ), 1.71 (m, 12 H, PCH ), 3.43 (s, 3 H, OCH ), 6.77 and 7.32
3 2 3
31 1
MeC6H4 Pd
C
C
Ph MeOC6H4 Pt
I
(d, 4 H, C H , J = 8 Hz). P-{ H} NMR (160 MHz in C D ): δ 8.9
6 4 6 6
Ϫ1 1
[
s, J(PtP) = 1364 Hz]. 4. IR (KBr): ν(C᎐C) 2098 cm
.
H
L
L
NMR (400 MHz in C D ): δ 0.96 (m, 18 H, CH ), 1.66 (m, 12 H,
6
6
3
1
3
PCH ), 3.50 (s, 3 H, OCH ), 6.96 (d, 2 H, C H , J = 7), 7.02 (t, 1 H,
2
3
6
4
(L = PEt3) 50 °C
C H H, J = 7), 7.17 (t, 2 H, C H H , J = 7), 7.48 (d, 2 H, C H H , J = 7),
6
4
6
3
2
1
6
2
2
3
1
7
.61 (d, 2 H, C H H , J = 7 Hz). P-{ H} NMR (160 MHz in C D ): δ
6 2 2 6 6
13 1
L
MeC6H4 Pd
L
L
10.2 [s, J(PtP) = 1320 Hz]. C-{ H} NMR (100 MHz in CD Cl ): δ 55.1
2 2
(
1
OCH ), 109.9 [᎐C᎐C, J(PtC) = 22], 113.7 [CH᎐C᎐Pt, J(PtC) = 50],
3
I
MeOC6H4 Pt
L
C
C
Ph (1)
14.3 [Pt᎐C᎐, t, J(PC) = 15, J(PtC) = 890], 124.8 (para carbon of
C᎐CC H ), 128.2, 130.0 [᎐C᎐C, J(PtC) = 22], 131.0, 139.1, 145.0 [Pt᎐C,
᎐
᎐
6
5
1
t, J(PC) = 10, J(PtC) = 673 Hz], 155.5 (OC). 5. H NMR (400 MHz
at Ϫ30 ЊC in CD Cl ): δ 1.19 (apparent triplet due to virtual coupling,
2
4
2
2
1
8 H, CH ), 3.683 (s, 3 H, OCH ), 6.67 and 7.05 (d, 4 H, C H , J = 8
3 3 6 4
31 1 1
reaction mixture show only the peaks due to complexes 1–4
throughout the reaction, indicating that the aryl groups behave
as spectator ligands and do not undergo migration between the
metal centres in contrast to the aryl ligands bonded to several
Hz). P-{ H} NMR (160 MHz at 25 ЊC in C D ): δ Ϫ21.0 (s). 6.
NMR (400 MHz at Ϫ30 ЊC in CD Cl ): δ 1.19 (apparent triplet due to
virtual coupling, 18 H, CH ), 3.676 (s, 3 H, OCH ), 6.63 and 7.13 (d, 4
H, C H , J = 8), 7.18 (t, 1 H, C H H, J = 7), 7.34 (d, 2 H, C H H ,
J = 7), 7.54 (t, 2 H, C
Ϫ30 ЊC in CD Cl ): δ Ϫ17.3 (s).
‡ The NMR spectra of the reaction mixture after 1 h at Ϫ30 ЊC showed
conversion of ca. 10% of 1 and 5 into 2 and 6, while raising the tem-
perature caused formation of many Pd complexes probably due to
accompanying exchange of the phosphine ligands among the
complexes.
H
6
6
2
2
3
3
6
4
6
4
6
3
2
II
II
6
31
1
Ni and Pd complexes. The reaction (1) obeys the kinetics
6 3 2
H H , J = 7 Hz). P-{ H} NMR (160 MHz at
that is first-order both in [1] and [3] with a rate constant
2
2
Ϫ2
3
Ϫ1 Ϫ1
1
.13 × 10 dm mol
s
at 50 ЊC. Similar reaction between
palladium complexes 1 and trans-[Pd(C H OMe-p)(I)(PMe ) ] 5
6
4
3 2
at Ϫ30 ЊC initially gives 2 and trans-[Pd(C H OMe-p)(C᎐CPh)-
6
4
(
PMe ) ] 6 as shown in equation (2).‡ The alkynyl-ligand trans-
3 2
J. Chem. Soc., Dalton Trans., 1997, Pages 1265–1266
1265

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(i) σ–π Rearrangement of a bridging alkynyl ligand in a bimetallic system
R
R
C
C
C
C
M′
M
M
M′
(ii) Intermolecular transfer of an alkynyl ligand
M
C
C
R
+
M′
M
+
M′
C
C
R
Scheme 1
(
i)
L
Pd
L
L
L
L
R
C
C
Ph R′ Pt
I
R
R
Pd
L
I
R′ Pt
C
C
Ph
Ph
Ϫ3
Fig. 1 Profile of the reaction of compound 1 (27.4 mmol dm ) with
L
L
Ϫ3
CuI (26.3 mmol dm ) at 25 ЊC in C D . Amounts of 1 and the resulting
6
6
2 and MeC H C᎐
᎐
CPh, shown by the molar ratios based on the initial
1
(ii)
6 4
molarity of 1, were obtained by relative peak area ratio in the H NMR
L
Pd
L
L
Pd
L
spectra
R
C
C
+
Ph
+
CuI
C
I
+
Cu
C
C
Scientific Research of Ministry of Education, Science, Culture
and Sports, Japan.
L
L
R′ Pt
I
Cu
C
Ph
R′ Pt
C
C
Ph
+
CuI
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L
L
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4
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2
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L
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C
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L
1
(L = PEt3) 25 °C
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MeC6H4 Pd
I
+
'Cu(C CPh)'
+
MeC6H4C CPh
(3)
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1
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4
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6
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The present study has disclosed alkynyl-ligand transfer from
II
II
Pd to Pt centres in a direct fashion as well as through an
intermediate alkynylcopper() complex. Reversible transfer of
I
II
the ligand between Cu and Pd metal centres has been
observed directly. Aryl(alkynyl)palladium() complexes in this
study have been postulated as the possible intermediates in the
cross-coupling reaction of aryl halides with terminal alkynes
7
8 B. M. Trost and T. R. Verhoeven, in Comprehensive Organometallic
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8
catalysed by Pd complexes in the presence of CuI but their
9
chemical properties have not been reported so far.
Acknowledgements
9
P. Espinet, J. Forniés, F. Martínez, M. Sotes, E. Lalinde, M. Teresa
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This work was partially supported by a Grant-in-Aid for
2
53.
II
§
cis–trans Isomerisation of Pd complexes induced by intermolecular
7
ligand exchange has been reported.
Received 2nd January 1997; Communication 7/00021I
1
266
J. Chem. Soc., Dalton Trans., 1997, Pages 1265–1266