Unique ring-methyl deprotonation of η4-1,2-dimethyl-3,4-di(tert-butyl)cyclobutadiene complexes of palladium(II) bearing phosphine ligand

Article abstract of DOI:10.1016/S0020-1693(03)00145-2

We report unique ring-methyl deprotonation of an η⁴-cyclobutadiene complex [PdCl₂(η⁴-C₄^tBu ₂Me₂)]₂ (1). Reaction of 1 with 2 equiv. of triphenylphosphine in the presence of triethylamine afforded an exo-methylene-η³-cyclobutenyl palladium complex [Pd(μ-Cl)(η³-C₄(=CH₂)( ^tBu)₂Me)(PPh₃)]₂ (3) in quantitative yield. The reaction of complex 1 with 2 equiv. of DPPE gave a cationic complex [Pd(η³-C₄(=CH₂)(^tBu) ₂Me)(DPPE)][Cl] (4a) with the release of HCl. Upon treated with triethylamine and AgOTf, a cationic complex [Pd(η³-C₄(=CH₂)(^tBu) ₂Me)(DPPE)][OTf] (4b) was isolated as yellow microcrystalline solids. The cationic exo-methylene-η³-cyclobutenyl structure of 4 was revealed by spectral data together with a crystallographic study for complex 4a.

Full text of DOI:10.1016/S0020-1693(03)00145-2

Inorganica Chimica Acta 352 (2003) 105Á109
/
www.elsevier.com/locate/ica
Unique ring-methyl deprotonation of h4-1,2-dimethyl-3,4-di(tert-
butyl)cyclobutadiene complexes of palladium(II) bearing phosphine
ligand
Kazushi Mashima *, Daisuke Shimizu, Tsuneaki Yamagata, Kazuhide Tani
Department of Chemistry, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan
Received 12 July 2002; accepted 3 September 2002
Dedicated to Professor M.A. Bennett for his contributions to inorganic and organometallic chemistry
Abstract
We report unique ring-methyl deprotonation of an h4-cyclobutadiene complex [PdCl2(h4-C4tBu2Me2)]2 (1). Reaction of 1 with 2
equiv. of triphenylphosphine in the presence of triethylamine afforded an exo-methylene-h3-cyclobutenyl palladium complex [Pd(m-
Cl)(h3-C4(Ä
complex [Pd(h3-C4(Ä
cationic complex [Pd(h3-C4(Ä
/
CH2)(tBu)2Me)(PPh3)]2 (3) in quantitative yield. The reaction of complex 1 with 2 equiv. of DPPE gave a cationic
/
CH2)(tBu)2Me)(DPPE)][Cl] (4a) with the release of HCl. Upon treated with triethylamine and AgOTf, a
/
CH2)(tBu)2Me)(DPPE)][OTf] (4b) was isolated as yellow microcrystalline solids. The cationic exo-
methylene-h3-cyclobutenyl structure of 4 was revealed by spectral data together with a crystallographic study for complex 4a.
# 2003 Elsevier Science B.V. All rights reserved.
Keywords: Ring-methyl deprotonation; Palladium(II); Ligand; Triethylamine; DPPE
1. Introduction
Metal-assisted CÃ
much interest in view of not only its fundamental
methyl activation of methyl-substituted cyclobutadiene
complexes of Group 10 metals is possible on the basis of
the isolobal relation [17] among half-sandwich com-
/
H bond activation has attracted
plexes of a general formula (hn-CnRn)MLx (nꢀ
/
6 for
Group 9
Group 10 metals). Thus,
M(0)ꢀ
metals, and nꢀ
/
Group 8 metals, nꢀ
/
5 for M(I)ꢀ
/
organometallic reactions but also synthetic application
H bond activation of the
/
4 for M(II)ꢀ
/
in organic reactions [1]. The CÃ
/
we report the first example of ring-methyl activation of
h4-cyclobutadiene complex of palladium, and we pre-
pared and characterized unique exo-methylene-h3-cy-
clobutenyl palladium complexes.
ring-methyl groups of cyclopentadienyl and arene
ligands bound to transition metals is a particular
example of the fundamental reactions. The deprotona-
tion of the ring-methyl group of the h5-pentamethylcy-
clopentadienyl ligand using appropriate base has been
reported to give fulvene complexes or their derivatives
involving the alkylation of the ring-methyl groups [2Á
The CÃH bond activation of the C6Me6 ligand bound in
an h6-fashion to Fe [5Á
16] afforded
/
4].
2. Results and discussion
/
/
13] and Ru [14Á
/
Treatment of [PdCl2(h4-C4tBu2Me2)]2 (1) with 2 equiv.
of triphenylphosphine in dichloromethane, in the ab-
sence of base such as triethylamine, simply led to the
formation of [PdCl2(h4-C4tBu2Me2)(PPh3)] (2) in 51%
yield (Eq. (1)), which is in sharp contrast to the reported
observation that the peraryl-cyclobutadiene ligand
bound to the palladium atom has been found to be
labile, giving phosphine complexes PdX2(PR3)2 [18].
unique exo-methylene-h5-cyclohexadienyl and exo-o-
xylylene complexes. To the best of our knowledge, no
ring-methyl activation of h4-cyclobutadiene complex
has been reported so far. We anticipated that the ring-
* Corresponding author. Fax: ꢁ
/
81-6-6850 6296.
E-mail address: mashima@chem.es.osaka-u.ac.jp (K. Mashima).
0020-1693/03/$ - see front matter # 2003 Elsevier Science B.V. All rights reserved.
doi:10.1016/S0020-1693(03)00145-2

106
K. Mashima et al. / Inorganica Chimica Acta 352 (2003) 105Á109
/
On the other hand, addition of NEt3 to the mixture of
1 and PPh3 in dichloromethane caused ring-methyl
deprotonation, giving an exo-methylene-h3-cyclo-
butenyl
palladium
complex
[Pd(m-Cl)(h3-C4(Ä
/
CH2)(tBu)2Me)(PPh3)]2 (3) in quantitative yield. The
1H NMR spectrum of 3 displayed ring-methyl and tert-
butyl protons as one doublet at d 0.68 ppm of methyl
proton and two singlets at d 1.23 and 1.56 ppm due to
two sets of tert-butyl protons, being in contrast to the
rather simple pattern observed in the 1H NMR spectrum
of 2 with two singlets at d 1.76 and 1.46 ppm due to
methyl and tert-butyl protons. The most informative
data of 3 is two signals appearing at d 3.78 and 4.11
ppm, assignable to the exo-methylene protons. The 31P
NMR spectrum of 3 shows one singlet at d 23.8 ppm,
chemical shift value indicating the coordination of PPh3
to the palladium atom. The dimeric formulation of 3
was further supported by FAB mass and IR spectral
data.
Fig. 1. Molecular structure of the cationic part of 4a with numbering
scheme. Hydrogen atoms are omitted for clarity.
We were able to crystallize 4a suitable for a crystal-
lographic study, despite the poor quality of the crystals
of 4b. Fig. 1 shows the structure of the cationic part of
4a, and its selected bond distances and angles are shown
in Table 1. The bond distances in an h3-allyl moiety
˚
˚
[C(1)Ã
/
C(2)ꢀ
/
1.436(3) A and C(2)Ã
/
C(3)ꢀ
/
1.464(3) A]
˚
and the bond distances of PdÃ
/
C(1) [2.189(2) A], PdÃ
/
˚
˚
C(3) [2.215(2) A] are compar-
C(2) [2.275(2) A] and PdÃ
able to those found for some cyclic-h3-allyl palladium
complexes [19Á22]. In contrast, the longer distance of
PdÃC(4) [2.352(2) A] clearly indicates that the exocyclic
/
/
˚
/
methylene moiety is uncoordinated to the palladium
atom. The sum of the angles around C(4) is 360.08,
consistent with the planar sp2 carbon. The four-mem-
In sharp contrast to the case of PPh3, reaction of
complex 1 with 2 equiv. of DPPE in dichloromethane at
room temperature induced spontaneous ring-methyl
activation to give [Pd(h3-C4(Ä
/
CH2)(tBu)2Me)(DP-
Table 1
˚
Selected bond lengths (A) and angles (8) for 4a
PE)][Cl] (4a) with the release of HCl. The same reaction
upon treated with triethylamine and AgOTf gave a
Bond lengths
cationic
complex
[Pd(h3-C4(Ä
/
CH2)(tBu)2Me)(DP-
PdÃ
PdÃ
PdÃ
PdÃ
PdÃ
PdÃ
/
C(1)
C(2)
C(3)
C(4)
P(1)
P(2)
2.189(2)
2.275(2)
2.215(2)
2.352(2)
2.3097(5)
2.3017(5)
/
PE)][OTf] (4b) as yellow microcrystalline solids in 56%
yield. The exo-methylene-h3-cyclobutenyl structure of
4b was confirmed by spectral data and combustion
analysis, though spectral data of 4a were essentially the
same as those found for 4b. The cationic part of 4b was
observed as a parent ion peak in its FAB mass spectrum.
The 31P NMR spectrum of 4b displayed two doublets
centered at d 44.3 and 47.4 ppm with the coupling
constant of 18.9 Hz due to DPPE. The 1H NMR
spectrum of 4b is almost the same as that of 3 except
for the signals of DPPE. The asymmetric environment
of the cyclobutenyl ring was evident from three singlet
signals in a 3:3:1 ratio due to two tert-butyl and one
methyl groups, and exo-methylene protons appeared as
two doublets centered at d 4.55 and 4.67 ppm with a
small coupling constant of 1.4 Hz.
/
/
/
/
Bond angles
C(1)Ã
C(1)Ã
C(2)Ã
C(3)Ã
C(1)Ã
C(3)Ã
C(4)Ã
P(1)Ã
C(2)Ã
C(1)Ã
C(2)Ã
C(1)Ã
/
C(2)
C(4)
C(3)
C(4)
C(5)
C(10)
C(14)
1.436(3)
1.492(3)
1.464(3)
1.509(3)
1.498(3)
1.510(3)
1.343(3)
86.49(2)
90.2(2)
/
/
/
/
/
/
/
PdÃ
C(1)Ã
C(2)Ã
C(3)Ã
C(4)Ã
/P(2)
/
/
C(4)
/
/
C(3)
C(4)
C(3)
91.8(2)
88.5(2)
87.8(2)
/
/
/
/

K. Mashima et al. / Inorganica Chimica Acta 352 (2003) 105Á
/109
107
bered ring is no longer planar, and hence the ring carbon
C(4) is slightly bent as evident from the dihedral angle
[13.9(2)8] between the least-square planes [C(1), C(2)
and C(3)] and [C(1), C(3) and C(4)]. DPPE coordinates
to the palladium atom to form a puckered five-
membered structure.
washed with hexane (twice, 5 ml each) and dried in
vacuo. The residual was suspended in dichloromethane
(2 ml) and then the suspension was added to hexane (20
ml) to afford the product as a yellow powder (60.2 mg,
51% yield), m.p. 180Á
185 8C (dec.). 1H NMR (300
/
MHz, CDCl3, 35 8C): d 1.46 (s, 18H, C(CH3)3), 1.76
(brs, 6H, CH3), 7.35 (m, 9H, C6H5), 7.70 (m, 6H, C6H5).
31P{1H} NMR (121 MHz, CDCl3, 35 8C): d 23.8 (s).
FAB MS (m/z): 630 [Mꢁꢂ
/
H], 558 [Mꢁꢂ
/
Hꢂ
/
2Cl].
3.3. Preparation of [Pd(m-Cl)(h3-C4(Ä
Me)(PPh3)]2 (3)
/
CH2)(tBu2)-
To a solution of triphenylphosphine (0.124 g, 0.471
mmol) and 1 (0.142 g, 0.192 mmol) in dichloromethane
(7 ml) was added NEt3 (0.06 ml, 0.4 mmol). The reaction
mixture was stirred for 20 h at room temperature. After
removal of the precipitated solids by centrifugation, the
solution was washed with water (twice, 10 ml each).
After dried over MgSO4, all volatiles were removed
under reduced pressure. The residual was dissolved in
dichloromethane (2 ml) and then the solution was added
to hexane (20 ml), giving 3 as yellow powder (0.214 g,
In summary, we demonstrated the first example of
base-induced ring-methyl activation of h4-cyclobuta-
diene complexes of palladium. Thus, two palladium
complexes,
(3) and [Pd(h3-C4(Ä
XꢀCl; 4b: Xꢀ
[Pd(m-Cl)(h3-C4(Ä
CH2)(tBu)2Me)(DPPE)][X] (4a:
OTf), were prepared and their unique
/
CH2)(tBu)2Me)(PPh3)]2
/
/
/
exo-methylene-h3-cyclobutenyl structure was confirmed
by spectral data together with a crystallographic study
for complex 4a.
93% yield), m.p. 120Á
MHz, CDCl3, 35 8C): d 0.68 (d, JPÃH
/
125 8C (dec.). 1H NMR (300
4
ꢀ7.7 Hz, 3H,
/
CH3), 1.23 (s, 9H, C(CH3)3), 1.56 (s, 9H, C(CH3)3), 3.78
(s, 1H, CH2), 4.11 (s, 1H, CH2), 7.37 (m, 9H, C6H5),
7.71 (m, 6H, C6H5). 31P{1H} NMR (121 MHz, CDCl3,
3. Experimental
35 8C): d 27.8 (s). FAB MS (m/z): 630 [Mꢁꢂ
/
3.1. General procedures
Pd(C4CHt2Bu2Me)(PPh3)],
561
[Mꢁꢂ
Cl) cmꢂ1
284 (vs), 239 (m). Anal. Calc. for C64H76Cl2P4Pd2: C,
/PdCl2-
(C4CHt2Bu2Me)(PPh3)]. IR (nujol): n(PdÃ
/
All manipulations involving air- and moisture-sensi-
tive organometallic compounds were carried out using
standard Schlenk techniques under argon. Organic
solvents were dried over appropriate reagents and
distilled under argon before use. Complex
[PdCl2(C4tBu2Me2)]2 (1) was prepared according to the
literature procedure [23]. 1H NMR (300 MHz) and
31P{1H} NMR (121 MHz) were measured on a VAR-
64.54; H, 6.43. Found: C, 64.26; H, 6.46%.
3.4. Preparation of [Pd(h3-C4(Ä
(DPPE)][OTf] (4b)
/
CH2)(tBu)2Me)-
To a solution of DPPE (0.164 g, 0.412 mmol) and 1
(0.151 g, 0.204 mmol) in dichloromethane (6 ml) was
added NEt3 (0.06 ml, 0.43 mmol) via syringe. The
resulting solution was poured into a Schlenk-containing
AgOTf (0.108 g, 0.420 mmol) and then the reaction
mixture was stirred for 2.5 h at room temperature. The
precipitated AgCl was removed by centrifugation and all
volatiles of the supernatant solution were removed
under reduced pressure. The residual dissolved in
dichloromethane (8 ml) was poured into ether (25 ml).
Precipitated NEt3HCl was removed by centrifugation
and the supernatant solution was concentrated under
reduced pressure to remove all volatiles. The residual
was dissolved in dichloromethane (10 ml) and then the
solution was washed with water (twice, 10 ml each) to
separate ammonium salts. After dried over MgSO4, all
volatiles were removed under reduced pressure. The
residual was dissolved in dichloromethane (2 ml), and
then the solution was added to hexane (20 ml) to afford
IAN-MERCURY300. H{31P} NMR was measured on
1
a VARIAN-MERCURY500. Mass spectrometric data
were obtained using FAB techniques on a JEOL SX-102
spectrometer. IR spectra were recorded by the use of
JASCO FT/IR-230. Elemental analyses were performed
on a PerkinÁElmer 2400 microanalyzer in Faculty of
/
Engineering Science, Osaka University. All melting
points were measured in sealed tubes and were not
corrected.
3.2. Preparation of [PdCl2(h4-C4(tBu2)Me2)(PPh3)]
(2)
Triphenylphosphine (66.9 mg, 0.255 mmol) and 1
(68.8 mg, 0.0931 mmol) were dissolved in dichloro-
methane (5 ml). The reaction mixture was stirred for 1.5
h at room temperature. All volatiles were removed
under reduced pressure, and then the residual was

108
K. Mashima et al. / Inorganica Chimica Acta 352 (2003) 105Á109
/
4b as yellow microcrystals (0.191 g, 56% yield), m.p.
195Á
203 8C (dec.). 1H NMR (300 MHz, CDCl3, 35 8C):
d 0.89 (s, 9H, C(CH3)3), 0.96 (s, 9H, C(CH3)3), 1.85 (t,
4JPÃH
10.3 Hz, 3H, CH3), 1.8Á1.9 (m, 1H, CH2CHH),
2.6Á3.2 (m, 3H, CH2CHH), 4.55 (d, JHÃH
1H, Ä
Table 2
Data collection and structure determination for 4a
/
Empirical formula
Formula weight
Temperature (K)
C41H50Cl4P2Pd
ꢀ
/
/
852.95
153(1)
0.71069
2
/
ꢀ
/
1.4 Hz,
˚
Wavelength (A)
/
CHH), 4.67 (d, 1H, Ä
/
CHH), 7.40Á
/
7.80 (m, 20H,
¯
triclinic, P1
C6H5). 31P{1H} NMR (121 MHz, CDCl3, 35 8C): d 44.3
Crystal system, space group
Unit cell dimensions
2
(d, JPÃP
ꢀ
18.9 Hz), 47.4 (d). IR (KBr): n(SO2) cmꢂ1
/
˚
a (A)
12.3251(8)
18.1119(12)
9.6112(7)
99.9488(16)
95.181(2)
100.670(2)
2060.1(2)
2
1264 (s). FAB MS (m/z): 695 [Mꢁꢂ
/
OTfꢂ], 504 [Mꢁ
Calc. for
˚
b (A)
OTfꢂꢂC4CH2t Bu2Me2].
C41H47F3O3P2Pd: C, 58.26; H, 5.60. Found: C, 58.04;
H, 5.41%.
/
Anal.
˚
c (A)
ꢂ
/
a (8)
b (8)
g (8)
3
V (A )
˚
3.5. Preparation of [Pd(h3-C4(Ä
(DPPE)][Cl] (4a)
/
CH2)(tBu)2Me)-
Z
Dcalc (mg mꢂ3
)
1.375
0.815
880
Absorption coefficient (mmꢂ1
F(0 0 0)
)
A solution of 1 (77.9 mg, 0.105 mmol) and DPPE
(96.4 mg, 0.242 mmol) in dichloromethane (5 ml) was
stirred at room temperature for 2 h. The resulting yellow
solution was concentrated and then was poured into
hexane (20 ml). Yellow solid of 4a was collected and
Crystal size (mm3)
0.34ꢃ
2.58Á27.48
05h 516, ꢂ
125l 512
/0.24ꢃ
/
0.18
u range (8)
Limiting indices
/
/
/
/
235
/
k 5
/
23,
ꢂ/
/
/
Reflections collected/unique
22255/9312 [Rint
98.5 (%)
ꢀ
/
5.4593]
Completeness to thetaꢀ
/
27.48
then dried under reduced pressure, 84% yield, m.p. 142Á
/
Absorption correction
Max./min. transmission
Refinement method
semi-empirical from equivalents
0.8636, 0.5663
full-matrix least-squares on F2
9312/0/633
1.062
1
147 8C (dec.). The H NMR, 31P NMR and FAB MS
spectra were superimposable with those of the cationic
part of 4b.
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I ꢀ
R indices (all data)
/
2s(I)]
R1ꢀ
R1ꢀ
0.708 and ꢂ
/
0.0328, wR2ꢀ
0.0383, wR2ꢀ
0.586
/
0.0847
3.6. Crystallographic data collections and structure
determination of 4a
/
/0.0866
Largest difference peak and hole
ꢂ3
/
˚
(e A
)
Yellow single crystals were obtained by repeated
recrystallization of 4a from dichloromethane and hex-
ane: complex 4a crystallized as including HCl. Indexing
was performed from two oscillations, which were
exposed for 2 min. The camera radius was 127.4 mm.
Resolution was performed in the 0.1 mm pixel mode.
Cell constants and an orientation matrix for data
collection were determined by the least-squares refine-
ment, using the setting angles of 15 478 reflections in the
nic part of palladium complex, an anionic chlorine
atom, dichloromethane as a solvate molecule, and a
hydrogen chloride molecule were found in the crystal-
lographic asymmetric unit. Non-hydrogen atoms were
anisotropically refined. All H atoms were isotropically
refined. The hydrogen atoms of HCl are bound to Cl
anion through a hydrogen bond. The function mini-
mized was [Sw(Fo2ꢂFc2)2] (wꢀ
/
/
1/[s2(Fo2)ꢁ(0.0504P)2ꢁ
/
/
1.0132P]), where Pꢀ
/
(Max(Fo2,0)ꢁ
/
2Fc2)/3 with s2(Fo2)
range 2.258B
/
u B27.488 on a Rigaku RAXIS-RAPID
/
˚
with monochromatized Mo Ka (0.71069 A) radiation.
For the data collection, reflections were measured at a
temperature of 153(1) K to a maximum 2u value of
55.08. A total of 52 images, corresponding to 2608
oscillation angles, were collected with two different
goniometer setting Table 2. Exposure time was 30 s
per degree. Readout was performed in the 0.1 mm pixel
mode. Intensity data were corrected for Lorentz and
polarization effects. A semi-empirical absorption correc-
tion was applied, which resulted in transmission factors
ranging from 0.5663 to 0.8636. Of 22 255 measured
from counting statistics. The function R1 and wR2 were
(SjjFojꢂ
/
jFcjj)/SjFoj and [Sw(Fo2ꢂ
/
Fc2)2/S(wFo4)]1/2, re-
spectively. All calculations of least-squares refinements
were performed with SHELXL-97 programs on Origin
3400 computer of Silicon Graphics, Inc. at the Research
Center for Structural Biology Institute for Protein
Research, Osaka University.
4. Supplementary material
reflections, 9312 reflections (5.08B
/
2u B55.08) were
/
unique (Rint 0.0546) and used for the structure solu-
tion and refinement.
The structure of complex 4a was solved by a direct
method (SIR-97) [24] and refined on F2 by the full-
matrix least-squares method (SHELXL-97) [25]. A catio-
ꢀ
/
The atomic positional parameters have been depos-
ited with the Cambridge Crystallographic Data Centre,
CCDC No. 206850 for compound 4a. Copies of this
information may be obtained free of charge from The
Director, CCDC, 12 Union Road, Cambridge, CB2

K. Mashima et al. / Inorganica Chimica Acta 352 (2003) 105Á
/109
109
(j) J.R. Miura, J.B. Davidson, G.C. Hincapie, D.J. Burkey,
Organometallics 21 (2002) 584.
1EZ, UK (Fax: ꢁ44-1223-336-033; e-mail: deposit@
ccdc.cam.ac.uk or www: http://www.ccdc.cam.ac.uk
/
[4] Fulvene complexes of group 9 metals: (a) B. Gloaguen, D. Astruc,
J. Am. Chem. Soc. 112 (1990) 4607;
(b) D. Glueck, R.G. Bergman, Organometallics 9 (1990) 2862;
(c) D.W. Hoard, P.R. Sharp, Inorg. Chem. 32 (1993) 612;
(d) O.V. Gusev, S. Sergeev, I.M. Saez, P.M. Maitlis, Organome-
tallics 13 (1994) 2059;
Acknowledgements
This research was supported by a Grant-in-Aid for
Scientific Research on Priority Areas (A) ‘‘Exploitation
of Multi-Element Cyclic Molecules’’ from the Ministry
of Education, Culture, Sports, Science, and Technology,
Japan.
(e) M.J. Atherton, J. Fawcett, J.H. Holloway, E.G. Hope, A.
Karacar, D.R. Russell, G.C. Saunders, J. Chem. Soc., Dalton
Trans. (1996) 3215;
(f) M.J. Atherton, J. Fawcett, J.H. Holloway, E.G. Hope, D.R.
Russell, G.C. Saunders, J. Organomet. Chem. 582 (1999) 163;
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McKee, M. Nieuwenhuyzen, D.R. Russell, G.C. Saunders, J.
Chem. Soc., Dalton Trans. (1998) 1477;
(h) K. Fujita, R. Yamaguchi, Chem. Lett. (1999) 707;
(i) K. Fujita, M. Nakamura, R. Yamaguchi, Organometallics 20
(2001) 100.
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