Synthesis, structure, and reactivity of neutral η3-propargylpalladium complexes

Full text of DOI:10.1021/ja973383i

1938
J. Am. Chem. Soc. 1998, 120, 1938-1939
Synthesis, Structure, and Reactivity of Neutral
η3-Propargylpalladium Complexes
Ken Tsutsumi, Sensuke Ogoshi,* Shinji Nishiguchi, and
Hideo Kurosawa*
Department of Applied Chemistry
Faculty of Engineering, Osaka UniVersity
Suita, Osaka 565, Japan
ReceiVed September 29, 1997
Compared to the considerable progress in the elucidation of
polynuclear allenyl/propargyl complexes,1,2 much less has been
made on the elucidation of the bonding, structure, and reactivity
of the η3-propargyl ligand on a mononuclear metal center,3
especially in neutral complexes.3a,e,f,k Exploration of new chem-
istry of η3-propargylpalladium complexes appears of potentially
synthetic and theoretical significance4 in view of the major role
played by η3-allylpalladiums in organic synthesis.5 We report
here the first synthesis and stability and reactivity aspects of
neutral η3-propargylpalladium complexes.
Figure 1. Molecular structure of 1g. Selected bond distances (Å): Pd-
C1 ) 2.238(7), Pd-C2 ) 2.116(6), Pd-C3 ) 2.156(7), C1-C2 )
1.244(9), C2-C3 ) 1.38(1). Selected angle (deg): C1-C2-C3 )
151.6(7).
(Supporting Information). The treatment of 1a with C6F5Li gave
Pd(tBuCCCH2)(C6F5)(PPh3) (1g, 52%), which exists in the
monomeric η3-propargyl structure both in the solid state (Figure
1)7 and in a solution (VPO; found 638 at 1.08 × 10-2 M; calcd
for monomer 631).
The Pd-CH2 bond in 1g (2.156(7) Å) is considerably longer
than that in 1d (2.070(3) Å), possibly reflecting both intrinsic
difference of bond strength between η1- and η3-coordination8 and
the stronger trans influence of C6F5 than that of Cl.9 The geometry
of η3-propargyl ligand in 1g is similar to that of [Pd(η3-
PhCCCH2)(PPh3)2]BF4;3i,j Pd, P, C4, and η3-propargyl carbons
are located almost on the same plane (dihedral angle between
Pd-P-C4 and C1-C2-C3 ) 3.93°).
The reaction of RCtCCH2Cl with Pd2(dba)3‚CHCl3 (dba )
dibenzylideneacetone) and PPh3 (Pd/PPh3 ) 1/1) in CH2Cl2 at
25 °C afforded new complexes Pd(RCCCH2)(Cl)(PPh3) (1a, R
) tBu, 84%; 1b, R ) (CH3)3Si, 84%; 1c, R ) tBu(CH3)2Si, 46%;
i
1d, R ) Pr3Si, 84%)6 or Pd(iPr3SiCCCH2)(X)(PPh3) (1e, X )
Br, 56%; 1f, X ) I, 61%) if the reaction carried out with added
NaX. These complexes exist as a mixture of the η3-propargyl
monomer (A) and the halide-bridged η1-propargyl dimer (B) in
solution (eq 1, see below). The dimeric structure of 1d in the
The VPO molecular weights of 1d at 35 °C (643 and 717 at
concentrations 3.67 × 10-3 and 1.20 × 10-2 M in chloroform;
calcd for monomer 600 and dimer 1199), and its 1H and 13C NMR
spectra (CDCl3) at room temperature showing two separate sets
of resonances,6 with the relative ratio dependent on the concentra-
tion, indicate that 1d in chloroform exists as an equilibrium
mixture of A and B (eq 1).10 The equilibrium constants between
η3- and η1-propargyl isomers for 1a-f determined by NMR
spectra in CDCl3 and C6D6 at 25 °C show that the η3-propargyl
form is favored by the less bulky substituent R and more polar
solvent (Table 1). Quite remarkably, the equilibrium lies increas-
ingly in favor of the η3-type monomer as chloride is replaced by
bromide, and bromide by iodide. This is in contrast to the more
general trend11 that the ability of the halide ligand to act as a
bridging ligand increases with increasing atomic number; this
tendency was estimated by the degree of bridge splitting by a
hard ligand such as amine. It may well be that the η3-propargyl
coordination may require the softer nature of the palladium center
than the η1-coordination, and this requirement would be better
solid state was confirmed by X-ray crystallographic study
(1) Doherty, S.; Corrigan, J. F.; Carty, A. J.; Sappa, E. AdV. Organomet.
Chem. 1995, 37, 39. Wojcicki, A. New. J. Chem. 1994, 18, 61.
(2) Amouri, H. E.; Gruselle, M.; Besace, Y.; Vaissermann, J.; Jaouen, G.
Organometallics 1994, 13, 2244. Ogoshi, S.; Tsutsumi, K.; Ooi, M.; Kurosawa,
H. J. Am. Chem. Soc. 1995, 117, 10415. and refs 3-5 therein. Doherty, S.;
Elsegood, M. R. J.; Clegg, W.; Scanlan, T. H.; Rees, N. H. J. Chem. Soc.,
Chem. Commun. 1996, 1545.
(3) (a) For Ru, see: Wakatsuki, Y.; Yamazaki, H.; Maruyama, Y.; Shimizu,
I. J. Chem. Soc., Chem. Commun. 1991, 261. (b) For Mo, see: Krivykh, V.
V.; Taits, E. S.; Petrovskii, P. V.; Struchkov, Y. T.; Yanovskii, A. I. MendeleeV
Commun. 1991, 103. (c) For Re, see: Casey, C. P.; Yi, C. S. J. Am. Chem.
Soc. 1992, 114, 6597. (d) For Pt, see: Huang, T.-M.; Chen, J.-T.; Lee, G.-H.;
Wang, Y. J. Am. Chem. Soc. 1993, 115, 1170. (e) For Zr, see: Blosser, P.
W.; Gallucci, J. C.; Wojcicki, A. J. Am. Chem. Soc. 1993, 115, 2994. (f) For
Mo, see: Carfagna, C.; Green, M.; Mahon, M. F.; Rumble, S.; Woolhouse,
C. M. J. Chem. Soc., Chem. Commun. 1993, 879. (g) For Pt, see: Blosser, P.
W.; Schimpff, D. G.; Gallucci, J. C.; Wojcicki, A. Organometallics 1993,
12, 1993. (h) For Pt, see: Stang, P. J.; Crittell, C. M.; Arif, A. M.
Organometallics 1993, 12, 4799. (i) For Pd, see: Ogoshi, S.; Tsutsumi, K.;
Kurosawa, H. J. Organomet. Chem. 1995, 493, C19. (j) For Pt and Pd, see:
Baize, M. W.; Blosser, P. W.; Plantevin, V.; Schimpff, D. G.; Gallucci, J. C.;
Wojcicki, A. Organometallics 1996, 15, 164. (k) For Zr, see: Rodriguez, G.;
Bazan, G. C. J. Am. Chem. Soc. 1997, 119, 343.
(7) Crystal data for 1g: C31H26F5PPd, triclinic, P1h (No. 2), a ) 16.56(3)
Å, b ) 18.00(4) Å, c ) 11.141(9) Å, R ) 101.1(1)°, â ) 107.5(1)°, γ )
63.5(2)°, Z ) 4, Dcalcd ) 1.481 g/cm3, T ) 23 °C, R(Rw) ) 0.057(0.047).
Crystal data for 2g: C67H56F5P3PdPt, monoclinic, P21/n (No. 14), a )
14.642(4) Å, b ) 19.042(4) Å, c ) 20.964(3) Å, â ) 101.85(2)°, Z ) 4,
Dcalcd ) 1.568 g/cm3, T ) 23 °C, R(Rw) ) 0.048(0.028). Details of the
crystallographic determinations are provided in the Supporting Information.
(8) For allyl-Pd bond, see: Ramdeehul, S.; Barloy, L.; Osborn, J. A.; Cian,
A. D.; Fischer, J. Organometallics 1996, 15, 5442.
(4) Tsuji, J.; Mandai, T. Angew. Chem., Int. Ed. Engl. 1995, 34, 2589
(5) Abel, E. W.; Stone, F. G. A.; Wilkinson, G.; Hegedus, L. S.
ComprehensiVe Organometallic Chemistry II; Elsevier Science Ltd.: Oxford,
1995; Vol. 12, Chapter 8.
(9) Albeniz, A. C.; Espinet, P.; Jeannin, Y.; P-Levisalles, M.; Mann, B. E.
J. Am. Chem. Soc. 1990, 112, 6594.
(6) Selected spectral data for 1d. η3-Type monomer: 1H NMR (CDCl3) δ
2.25 (s, 2H); 13C NMR (CDCl3) δ 35.64 (s, CCH2), 104.19 (s, CCH2), 105.17
(d, JCP ) 35.3 Hz, SiCC); 31P NMR (CDCl3) δ 30.72. η1-Type dimer: 1H
NMR (CDCl3) δ 1.95 (s, 2H); 13C NMR (CDCl3) δ 8.10 (s, CCH2), 86.35 (s,
CCH2), 112.70 (s, SiCC); 31P NMR (CDCl3) δ 35.44; mp 196-200 °C (dec.).
Anal. Calcd for C30H38ClPPdSi: C, 60.10; H, 6.39. Found: C, 60.33; H, 6.54.
(10) 13C NMR spectral patterns of each component are similar to those of
authentic samples of 1g and trans-Pd(η1-iPr3SiCCCH2)(Cl)(PPh3)2, which was
prepared similarly to the trimethylsilyl analogue reported: Elsevier, C. J.;
Kleijn, H.; Boersma, J.; Vermeer, P. Organometallics 1986, 5, 716.
(11) Cotton, F. A.; Wilkinson, G. AdVanced Inorganic Chemistry, 5th ed.;
Wiley-Interscience: New York, 1988; p 921.
S0002-7863(97)03383-0 CCC: $15.00 © 1998 American Chemical Society
Published on Web 02/14/1998

Communications to the Editor
J. Am. Chem. Soc., Vol. 120, No. 8, 1998 1939
Table 1. Equilibrium Constant K1 (M-1) of Eq 1
no.
R
X
In C6D6
In CDCl3
1a
1b
1c
1d
1e
1f
tBu
Cl
Cl
Cl
Cl
Br
I
,1
14
30
450
45
21
,1
,1
2.4
16
5.2
,1
Me3Si
tBu(Me)2Si
iPr3Si
iPr3Si
iPr3Si
fulfilled by the iodide. Another result of significance is the
thermodynamic parameters for the equilibrium of 1a in toluene-
d8 (25 to -80 °C), ∆H° ) -9.0 kJ mol-1 and ∆S° ) -33 J
mol-1 K-1 which indicate that the η3-type monomer is favored
at 25 °C not by the enthalpy but by the entropy term.
We investigated reactivities of 1 with some nucleophiles.
Although 1 did not react with MeOH and Et2NH which added to
the CtC bond of cationic η3-propargyl complexes of Pd and
Pt,3d,g,j 1g did react with a Pt(0) nucleophile in a formally
analogous manner. Thus, addition of 1 equiv of Pt(C2H4)(PPh3)2
to 1g in CH2Cl2 for 2 h at 25 °C afforded new complex 2g12
(75%), of which X-ray crystallographic analysis revealed a
remarkable structure containing µ-η2:η3-tBuCCCH2 ligand (Figure
2).7 The C1-C2 bond is longer and the C1-C2-C3 angle
smaller than those of 1g, and the η3-ligand is no longer coplanar
with the Pd-P-C4 plane (dihedral angle between Pd-P1-C4
and C1-C2-C3 ) 49.16°). In contrast to other bimetal
complexes containing µ-η2:η3-RCCCH2 ligands,2 2g does not
possess a metal-metal bond (Pd-Pt ) 3.33 Å). This fact,
together with the great ease of its formation, makes the present
complex quite a unique member of the complexes containing the
similar type of ligands.
Figure 2. Molecular structure of 2g. Selected bond distances (Å): Pd-
C1 ) 2.304(6), Pd-C2 ) 2.153(6), Pd-C3 ) 2.142(6), Pt-C1 )
2.063(6), Pt-C2 ) 2.022(6), C1-C2 ) 1.335(7), C2-C3 ) 1.391(7).
Selected angle (deg): C1-C2-C3 ) 135.5(6).
exclusively (K2 < 10-2 M-1),13 even when treated with 10-fold
excess PPh3.
In summary, we showed the method of controlling η3-propargyl
coordination on mononuclear palladium center by appropriate
choice of substituent R, ligand X, solvent, and amount of PPh3
and their new reactivities. Further investigation including catalytic
reactions is now in progress.15
Acknowledgment. Partial support of this work by Grants-in-aid from
the Ministry of Education, Science, Sports, and Culture and Research
Fellowships of the Japan Society for the Promotion of Science for Young
Scientists is acknowledged (K.T.).
The addition of equimolar PPh3 to 1a-f in CDCl3 generated
η1-propargylpalladium complexes almost quantitatively (eq 2, K2
> 100 M-1),13 while both η3- and η1-propargyl complexes lie in
equilibrium in the case of 1g (K2 ) 25 M-1), showing that the
aryl is a better ligand than the halides to stabilize η3-propargyl
coordination. The corresponding η3-allyl complex, Pd(η3-
tBuCHCHCH2)(C6F5)(PPh3),14 remained η3-coordinated almost
Supporting Information Available: Typical experimental procedures
and spectral data of products, and tables of atomic coordinates and
anisotropic thermal parameters of all atoms, bond distances, and angles
for 1d, 1g, and 2g (78 pages). See any current masthead page for ordering
information and Web access instructions.
JA973383I
(12) Spectral data for 2g: 1H NMR (CDCl3) δ 2.87 (d, JHP ) 7.8, JHPt
)
70.0 Hz, 1H), 2.94 (d, JHP ) 18.9, JHPt ) 79.3 Hz, 1H); 13C NMR (CDCl3)
δ 50.14 (s, CCH2), 108.98 (d, JCP ) 70.3 Hz, JCPt ) 338.4 Hz, CCH2), 112.62
(14) (a) This was prepared analogously to the η3-C3H5 derivative14b and
shown by 1H NMR to contain PPh3 located trans to tBu substituent. (b) Numata,
S.; Okawara, R.; Kurosawa, H. Inorg. Chem. 1977, 16, 1737.
t
(dd, JCP ) 72.6, 39.2 Hz, JCPt ) 338.0 Hz, BuCC); 31P NMR (CDCl3) δ
22.01 (d, JPP ) 28.5 Hz, JPPt ) 3155.7 Hz), 26.49 (d, JPP ) 28.5 Hz, JPPt
)
(15) Complex 1 can be postulated as a new efficient intermediate in catalytic
Stille-type coupling between RCtCCH2Cl and PhSnBu3 to give RCtCCH2-
Ph by the use of Pd2(dba)3‚CHCl3 and PPh3 (Pd/PPh3 ) 1/1) which was more
effective than Pd(PPh3)4 (see Supporting Information). When pyrolyzed in
3419.9 Hz), 27.89 (s, JPPt ) 41.9 Hz); mp 155-158 °C (dec.). Anal. Calcd
for C67H56F5P3PdPt(CH2Cl2)0.5: C, 58.20; H, 4.12. Found: C, 58.57; H, 4.17.
1
(13) Estimated on the basis of the H NMR detection limit (1/10) of the
t
minor component relative to the major one.
C6D6 at 70 °C, 1g indeed gave BuCtCCH2C6F5 (95%).