Dimerization of Olefins
J. Am. Chem. Soc., Vol. 118, No. 26, 1996 6233
added dropwise. The solution was stirred at -78 °C for 1 h and the
solvent was removed in vacuo. The white solid was dissolved in hexane
and filtered. The solution was reduced in vacuo and the flask was
cooled to -30 °C. White crystals were isolated (0.28 g, 73%). 1H
NMR (300 MHz, CD2Cl2) δ 4.99 (m, 1H, H5); 3.47 (dd, 1H, JHH ) 7.3
Hz, H4); 3.30 (t, 1H, H1); 2.38 (dd, 1H, JHH ) 12.9 Hz, H2); 2.33 (d,
1H, JHH ) 13.2 Hz, H3); 0.03 (d, 3H, JHP ) 4.7 Hz, CH3). 13C NMR
(75.4 MHz, CD2Cl2) δ (allylic) 117.2 (d, JCP ) 4.2 Hz, C2); 60.7 (s,
C1); 56.0 (d, JCP ) 36.8 Hz, C3); (PCy3) 35.3 (d, JCP ) 17.4 Hz, C1);
30.6 (d, JCP ) 13.4 Hz, C2) 28.1 (d, JCP ) 10.6 Hz, C3); 27.0 (s, C4);
-17.9 (d, JCP ) 13.2 Hz, CH3). 31P NMR (121.5 MHz, 20 °C, CD2Cl2)
δ 42.2.
[(C3H5)Pd(CH3)(PnBu3)] (6b). The following procedure is a
modification of that reported by Nakamura.34 A Schlenk flask was
charged with 0.866 g (2.25 mmol) of [(C3H5)Pd(Cl)(nBu3)] (5b) and
Et2O (40 mL) was added to give a suspension. The reaction mixture
was cooled to -78 °C and 750 µL of a 3 M solution of MeMgBr in
Et2O was added dropwise. The solution was stirred at -78 °C for 3
h. The resulting pale green solution was filtered, leaving a white solid
(MgBrCl). The solution was reduced in vacuo and filtered again to
remove additional MgBrCl. The solvent was then removed in vacuo
and a yellow oil was isolated (1.430 g, 52%). 1H NMR (250 MHz,
CDCl3) δ 5.0 (m, 1H, H5); 3.45 (m, 2H); 2.45 (dd, 1H); 2.3 (d, 1H);
0.05 (d, 3H, CH3).
[(C3H5)Pd(OEt2)(PCy3)]+[BAr′4]- (7a: Ar′ ) [3,5-C6H3(CF3)2]).
A Schlenk flask was charged with 0.26 g (0.58 mmol) of [(C3H5)Pd-
(CH3)(PCy3)] (6a) and 0.59 g (0.58 mmol) of [H+(OEt2)2(BAr′4)-]. The
reaction flask was cooled to -78 °C and Et2O (10 mL) was added.
The reaction was warmed slightly to form a clear solution, which was
cooled to -78 °C and stirred for 1 h. The solvent was reduced in
vacuo to precipitate a beige powder, which was washed with hexane
and isolated (0.58 g, 73%). In solution, an ether complex and an aquo
complex of 7a are observed in approximately a 7:3 ratio, respectively.
1H NMR (300 MHz, -20 °C, CD2Cl2) δ 7.72 (s, 8H, Ar′); 7.56 (s, 4H,
Ar′), 5.79 (m, 1H, H5); 5.08 (bt, 1H, H1); 4.01 (dd, 1H, H2); 3.80 (b,
1H, H4); 3.10 (bd, 1H, H3). 13C NMR (75.4 MHz, -20 °C, CD2Cl2)
[(H3CO(O)CCH2CH2)Pd(PCy3)(L)]+[BAr′4]- (18: Ar′ ) 3,5-
C6H3(CF3)2; L ) OEt2, OH2). A Schlenk flask was charged with
0.290 g (0.21 mmol) of [(C3H5)Pd(OEt2)(PCy3)]+[BAr′4]- (7a). The
reaction flask was cooled to -78 °C and 10 mL of CH2Cl2 was added.
Methyl acrylate (114 µL, 1.26 mmol) was added. The solution was
warmed to 0 °C and stirred for 3 h. The solvent was removed in vacuo,
leaving a yellow oil. The oil was dissolved in a minimum amount of
Et2O/hexane and cooled to -30 °C. Pale yellow crystals (0.90 g, 30%)
were isolated. 1H NMR (300 MHz, 20 °C, CD2Cl2) δ 7.72 (s, 8H,
Ar′); 7.56 (s, 4H, Ar′); 3.87 (s, 3H, OCH3); 2.75 (td, JHP ) 2.1 Hz,
2H); 1.96 (td, JHP ) 2.4 Hz, 2H); 1.0-2.0 (m, cyclohexyl). 13C NMR
(75.4 MHz, 20 °C, CD2Cl2) δ 240.6 (CdO), 56.6 (OCH3), 40.4 (Câ),
15.2 (CR); (BAr4′) 163.1 (q, C1), 136.1 (C2), 130.0 (m, C3), 126.0 (q,
CF3), 118.8 (C4); (PCy3) 35.3 (d, C1), 31.4 (C2), 28.7 (d, C3), 27.4
(C4). 31P NMR (121.5 MHz, 20 °C, CD2Cl2) δ 49.54, 46.07. Anal.
Found: C, 49.32; H, 4.43. Calcd: C, 49.36; H, 4.43.
X-ray Structural Analysis of [(H2O)(H3CO(O)CCH2CH2)-
Pd(PCy3)]+[BAr′4]- (18). A single crystal of 18 (0.20 × 0.20 × 0.40
mm) was grown from a concentrated solution of Et2O and hexane at
-30 °C. The crystal was triclinic (P1, No. 2) with the following cell
dimensions determined from 50 reflections (λ(Mo) ) 0.71073 Å): a
) 12.816(7) Å, b ) 14.879(15) Å, c ) 18.537(9) Å; R ) 79.10(6)°,
â ) 89.28(4)°, γ ) 85.72(6)°; z ) 2; V ) 3461(4) Å3; Fw ) 1503.40
(PdC62H74BF24O5P); Dc ) 1.442 g m-3
.
Data were collected at -120 °C on a Rigaku diffractometer with a
graphite monochromator using Mo KR radiation. A total of 9559 data
were collected of which 6187 unique reflections with I g 2.5σ(I) were
observed (5° e 2θ e 45°; maximum h, k, l ) 13, 16, 19; data octants
) +/-h, +k, +/-l; ω scan method; scan speed ) 2 deg min-1). Three
standards were collected every 100 reflections with no significant
change in intensity. An absorption correction was applied using the
ψ scan method58 with a range of transmission factors of 0.85 to 0.94.
The structure was solved using direct methods. The asymmetric
unit consists of one ion pair in a general position. Hydrogen atoms
were idealized with C-H ) 0.96 Å. The structure was refined by
full-matrix least squares and corrected for anamolous dispersion. There
are 847 parameters (data to parameter ratio of 7.30); final R ) 0.055
(Rw ) 0.063). The error of fit was 1.78 with a maximum ∆σ-1 of
0.021. The deepest hole was -0.93 e Å-3 and the highest peak was
1.52 e Å-3. Selected interatomic distances and angles are summarized
in Tables 1 and 2, respectively.
δ (BAr′4) 161.7 (q, JCB ) 49.2, C1); 134.7 (s, C2); 128.7 (qq, JCF
)
32.2, C3); 124.5 (q, 272.1, CF3); 117.5 (bt, C4); (PCy3) 34.3 (d, 21.2,
C1); 30.1 (d, 16.1, C2); 27.4 (d, 1.7, C3); 26.0 (s, C4); (allylic) 120.3
(b, C2); 86.8 (d, JCP ) 22.9 Hz, C3); (Et2O) 66.9 (b, CH2CH3); 15.2 (s,
CH2CH3). 31P NMR (121.5 MHz, 20 °C, CD2Cl2) δ 39.7 (Et2O
complex); δ 41.3 (H2O complex). Anal. Found: C, 50.30; H, 4.35.
Calcd: C, 50.15; H, 4.43.
[(C3H5)Pd(OEt2)(PnBu3)]+[BAr′4]- (7b: Ar′ ) [3,5-C6H3(CF3)]).
A Schlenk flask was charged with 0.616 g (1.69 mmol) of
[(C3H5)Pd(CH3)(PnBu3)] (6b). The reaction flask was cooled to -78
°C and Et2O (10 mL) was added. To the yellow palladium solution
was added 1.71 g (1.69 mmol) of [H+(OEt2)2(BAr′4)-]. The resulting
yellow solution was stirred at -78 °C for 1 h. The reaction was filtered,
leaving a small amount of insoluble material. Hexane was added to
the filtrate to facilitate precipitation. The solvent was then reduced in
Measurement of the Rate of Interconversion between [(C3H5)-
(PCy3)Pd(C2H4)]+[BAr′4]- 8r and 8â. The sample was prepared in
a drybox by charging the palladium complex [(C3H5)Pd(OEt2)-
(PCy3)]+[BAr′4]- (7a) (12 mg, 0.009 mmol) and CD2Cl2 into an NMR
tube at ambient temperature. The NMR tube was cooled to -78 °C
under an argon atmosphere and ethylene was introduced via syringe
(excess ethylene was removed by purging the solution with argon for
approximately 30 min). The NMR tube was introduced into a precooled
(-90 °C) NMR probe and gradually warmed. 1H and 31P NMR spectra
were recorded. The rate of interconversion of 8r and 8â at the
coalescent temperature (-74 °C, Bruker AMX-300 spectrometer) is
calculated from the frequency seperation of the two PCy3 resonances
in the slow-exchange limit, k ) π(VΑ - VΒ)/x2 (k ) 300 s-1 at -74
°C). The free energy of activation obtained from the Eyring equation
vacuo and the resulting yellow solution was cooled to -30 °C.
A
yellow powder was isolated (0.320 g, 15%). 1H NMR resonances (300
MHz, -80 °C, CD2Cl2) δ 7.72 (s, 8H, Ar′); 7.56 (s, 4H, Ar′); 5.65 (m,
1H, H5); 4.75 (bt, 1H, H1); 3.75 (dd, 1H, H2); 2.6 (bd, 1H). 31P NMR
(121.5 MHz, -80 °C, CD2Cl2) δ 16 (Et2O complex); 11 (H2O complex).
is 9.3 kcal mol-1
37.04.
.
31P NMR (121.5 MHz, -90 °C, CD2Cl2) δ 35.93,
Measurement of the Rate of Interconversion (Allyl Rocking)
[(C3H5)Pd(PCy3)2]+[BAr′4]- (9: Ar′ ) 3,5-C6H3(CF3)2). A Schlenk
flask was charged with 100 mg (0.073 mmol) of
[(C3H5)Pd(OEt2)(PCy3)]+[BAr′4]- (7a) and 21 mg (0.073 mmol) of
PCy3. The reaction flask was cooled to -78 °C and 5 mL of CH2Cl2
was added. The solution was warmed to -40 °C and stirred for 3 h.
The solvent was removed in vacuo, leaving a yellow oil, which was
dissolved in a minimum amount of Et2O/hexane and cooled to -78
°C. A white solid (0.06 g, 52%) was isolated. 1H NMR (300 MHz,
-20 °C, CD2Cl2) δ 7.72 (s, 8H, Ar′); 7.56 (s, 4H, Ar′); 5.36 (m, 1H,
H5); 4.47 (bs, 2H, H1 and H4); 2.91 (bs, 2H, H2 and H3). 13C NMR
(75.4 MHz, -20 °C, CD2Cl2) δ 119.5 (t, C2); 70.6 (t, C1 and C3); (BAr4′)
163.1 (q, C1), 136.1 (C2), 130.0 (m, C3), 126.0 (q, CF3), 118.8 (C4);
(PCy3) 36.0 (b, C1), 30.5 (C2), 27.6 (d, C3), 26.2 (C4). 31P NMR (121.5
MHz, -90 °C, CD2Cl2) δ 36.5 (dd).
between [(C3H5)(PCy3)Pd(C2H4)]+[BAr′4]- 9 and 9′. The sample was
prepared in
a drybox by charging the palladium complex
[(C3H5)Pd(PCy3)2]+[BAr′4]- (9) (10 mg, 0.006 mmol) and CD2Cl2 into
an NMR tube at ambient temperature. The NMR tube was introduced
into a precooled (-90 °C) NMR probe and gradually warmed. 31P
NMR spectra were recorded. Line broadening experiments were carried
out for 9 and 9′ beginning at a temperature where the complexes were
static (the phosphorus signals appeared as an AB quartet) to a
temperature where the complexes were dynamic (the phosphorus signals
appeared as a broad singlet). Experimental line shapes were compared
to line shapes calculated using the DNMR3 program43-46 (for an
(58) Gabe, E. J.; Le Page, Y. L.; Charland, J. P.; Lee, F. L.; White, P.
S. J. Appl. Crystallogr. 1989, 22, 384.