Zirconocene-mediated preparation of 1,3-, 1,4-, and 2,3-dibora-1,3-butadienes: Their isolation and characterization and use in Suzuki-Miyaura coupling

Article abstract of DOI:10.1021/om960178n

Hydrozirconation of 1-alkynyl pinacolboronates, 1, with HZrCp₂Cl provides gem-borazirconocenes 2. The latter when treated with CuBr gives the homocoupled (1E,3E)-2,3-dibora-1,3-butadienes, 3, in good yield (62-67%). The reaction works even for hindered 2 (R = t-Bu). Structure 3 was assigned on the basis of NMR. Suzuki-Miyaura coupling of 3a (R = n-Bu) with PhI in the presence of CsF leads to the replacement of both boron groups by phenyl and hydrogen to give 6 in 76% yield. Zirconocene-mediated coupling of 1 leads to diastereomeric products: (1E,3E)-1,3-dibora-1,3-butadienes, 4, in 7-26% isolated yields and (1E,3E)-1,4-dibora-1,3-butadienes, 5, in 17-34% isolated yields. The two isomers can be separated by selective precipitation of 5 from the reaction mixture in pentane (-20 °C) followed by silica gel chromatography to give pure 4. The reaction does not work when R in 1 is the t-Bu group. Assignments of structures for 4 and 5 were done on the basis of 1D and 2D NMR experiments. In addition, a single-crystal X-ray analysis of 5a showed it to be a highly planar and linearly oriented molecule. Suzuki-Miyaura coupling of 4a proceeded to replace the terminal boron group exclusively, while the internal boron group of 4a remained intact.

Full text of DOI:10.1021/om960178n

Organometallics 1996, 15, 3323-3328
3323
Zir con ocen e-Med ia ted P r ep a r a tion of 1,3-, 1,4-, a n d
2,3-Dibor a -1,3-bu ta d ien es: Th eir Isola tion a n d
Ch a r a cter iza tion a n d Use in Su zu k i-Miya u r a Cou p lin g
Guillaume Desurmont, Rita Klein, Stefan Uhlenbrock, Eric Laloe¨,
Laurent Deloux,1 Dean M. Giolando, Yong Wah Kim, Schubert Pereira,2 and
Morris Srebnik*,3
Department of Chemistry, University of Toledo, Toledo, Ohio 43606
Received March 7, 1996X
Hydrozirconation of 1-alkynyl pinacolboronates, 1, with HZrCp2Cl provides gem-borazir-
conocenes 2. The latter when treated with CuBr gives the homocoupled (1E,3E)-2,3-dibora-
1,3-butadienes, 3, in good yield (62-67%). The reaction works even for hindered 2 (R )
t-Bu). Structure 3 was assigned on the basis of NMR. Suzuki-Miyaura coupling of 3a (R
) n-Bu) with PhI in the presence of CsF leads to the replacement of both boron groups by
phenyl and hydrogen to give 6 in 76% yield. Zirconocene-mediated coupling of 1 leads to
diastereomeric products: (1E,3E)-1,3-dibora-1,3-butadienes, 4, in 7-26% isolated yields and
(1E,3E)-1,4-dibora-1,3-butadienes, 5, in 17-34% isolated yields. The two isomers can be
separated by selective precipitation of 5 from the reaction mixture in pentane (-20 °C)
followed by silica gel chromatography to give pure 4. The reaction does not work when R in
1 is the t-Bu group. Assignments of structures for 4 and 5 were done on the basis of 1D and
2D NMR experiments. In addition, a single-crystal X-ray analysis of 5a showed it to be a
highly planar and linearly oriented molecule. Suzuki-Miyaura coupling of 4a proceeded to
replace the terminal boron group exclusively, while the internal boron group of 4a remained
intact.
Various dibora compounds bridged by one, two, or
three carbons have been prepared and characterized.4
Dibora compounds have found use in specifically binding
guest molecules.5 They have also been explored as
chiral Lewis acids containing two Lewis acid binding
sites.6 Intriguing diboraheterocyles have been synthe-
sized from the acyclic precursors.7 Boronic esters and
acids are very useful in the Suzuki-Miyaura cross-
coupling reaction.8 The use of a dibora species in that
reaction has not been reported.
As part of our program utilizing zirconocene-mediated
synthesis of new boronic esters,9 we were interested in
preparing a series of 1,3-, 1,4- and 2,3-dibora compounds
from 1-alkynyl pinacolboronates, 1. We envisioned that
2,3-dibora compounds could be obtained from gem-
borazirconocenes10 by copper-mediated coupling.11 Since
the coupling is known to proceed with retention of
stereochemistry, only a single diastereomeric 2,3-dibora-
1,3-butadiene would be expected. The 1,3- and 1,4-
dibora compounds would be accessible by zirconocene-
mediated carbon-carbon bond formation12 of suitable
1-alkynyl boronates.
Resu lts a n d Discu ssion
Syn th esis a n d Isola tion . When a solution of a gem-
borazirconocene, 2, prepared from 1 by hydrozircona-
tion, was treated with CuBr in THF, the yellow color
was discharged and coupling occurred to provide 2,3-
dibora-1,3-butadienes, 3 (eq 1). They were isolated by
X Abstract published in Advance ACS Abstracts, J uly 1, 1996.
(1) Present address: BASF Aktiengesellschaft, ZKP/Forschung
Polyolefine und PVC, 67056 Ludwigshafen, Germany.
(2) Present address: Fresh Products Inc., 4010 South Av, Toledo,
OH 43615.
(3) Address from September 1996: Department of Natural Products,
Hebrew University in J erusalem, POB 12272, J erusalem 91120, Israel.
(4) Some leading references are as follows: (a) Brown, H. C.; Zweifel,
G. J . Am. Chem. Soc. 1961, 83, 3834. (b) Matteson, D. S. Synthesis
1975, 147. (c) Kra¨mer, A.; Pritzkow, H.; Siebert, W. Angew. Chem.,
Int. Ed. Engl. 1988, 27, 927. (d) Katz, H. E. Organometallics 1987, 6,
1134.
(5) Tsugagoshi, K.; Shinkai, S. J . Org. Chem. 1991, 56, 4089.
(6) (a) Nozaki, K.; Masanori, Y.; Takaya, H. Angew. Chem., Int. Ed.
Engl. 1994, 33, 2452. (b) Reilly, M.; Oh, T. Tetrahedron Lett. 1994,
35, 7209.
silica gel chromatography in good yields (Table 1).
(7) Siebert, W. Pure Appl. Chem. 1987, 59, 947.
Compounds 3 are stable to water and air and did not
(8) Miyaura, N.; Suzuki, A. Chem. Rev. 1995, 95, 2457.
(9) For a review, see: Zheng, B.; Deloux, L.; Pereira, S.; Skrzypczak-
J ankun, E.; Cheesman, B. V.; Sabat, M.; Srebnik, M. J . Appl.
Organomet. Chem. 1996, 10, 267.
(11) Yoshifuji, M.; Loots, M. J .; Schwartz, J . Tetrahedron Lett. 1977,
1303.
(10) Deloux, L.; Skrzypczak-J ankun, E.; Cheesman, B. V.; M.;
Srebnik, M. J . Am. Chem. Soc. 1994, 116, 10302.
(12) (a) Negishi, E.; Takahashi, T. Synthesis 1988, 1. (b) Negishi,
E.; Takahashi, T. Aldrichim. Acta 1985, 18, 31.
S0276-7333(96)00178-1 CCC: $12.00 © 1996 American Chemical Society
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3324 Organometallics, Vol. 15, No. 15, 1996
Ta ble 1. (1E,3E)-2,3-Dibor a -1,3-bu ta d ien es, 3
Desurmont et al.
carbon bond,16 since it is generally thought that sterics
dominate in the ring-closure step.14 The pinacolbor-
onate moiety is apparently too large to provide 2,3-
diborabutadienes when other less hindered insertion
pathways are available.
H(1)/H(4),
B(2)/ C(1)/ C(2)/ yield,
c
entry
R
mult, J (Hz) B(3)a
C(4)
C(3)b
%
a
b
c
d
e
f
n-Bu
t-Bu
Ph(CH2)2
Ph(CH2)3
Cl(CH2)3
6.01, t, 7.90
5.91, s
6.08, t, 8.64
6.05, t, 7.96
5.91, t, 7.60
30.6 143.6, 135.7
30.7 149.9 131.1
30.3 143.1 136.2
29.7 143.3 136.2
30.1 142.1 136.9
65
59
67
65
64
62
cyclopentyl 5.87, d, 9.52 30.6 148
133.9
a
b
Relative to BF3‚etherate. Due to the boron quadrupole, C(2)
resonances are all broad and of low intensity. c Isolated.
Ta ble 2. (1E,3E)-1,4-Dibor a -1,3-bu ta d ien es, 5
Η(1)/Η(4), B(1)/ C(1)/ C(2)/
yield,
entry
R
mult
B(4)a C(4)b C(3) %c (GC)
a
c
e
f
n-Bu
5.49, s
6.08, s
5.55, s
4.94, s
5.40, s
30.3 115.6 164.6 34 (52)
30.3 117.0 162.9 17 (43)
30.9 117.5 161.6 24 (31)
30.6 114.0 171.3 28 (31)
30.5 123.6 160.6 33 (52)
In agreement with this hypothesis was our inability
to ring close 1b (R ) t-Bu). One equivalent of 1b did
indeed complex with zirconocene as evidenced by ob-
taining the cis-tert-butylalkenyl pinacolboronate17 after
HCl workup. However when 2 equiv of 1b was used,
only the cis-tert-butylalkenyl pinacolboronate again
could be detected by GCMS and no ring-closure product
was detected (eq 4). Generally, essentially 1:1 mixtures
Ph(CH2)2
Cl(CH2)3
cyclopentyl
phenyl
g
a
b
Relative to BF3‚etherate. Due to the boron quadrupole, C(2)
resonances are all broad and of low intensity. c Isolated.
isomerize or decompose on prolonged heating to 150 °C
under an inert atmosphere.
Recently, No¨th and co-workers prepared two 1,3-bis-
(dialkylamino)-cis-bis(4,5-phenylmethylidene)-1,3-di-
borolane derivatives using zirconocene-mediated cou-
pling of methylene-bridged bis(alkynyl)boranes.13 Since
the alkynes were tethered, only one product was ob-
tained (eq 2).
of 4 and 5 were obtained (Experimental Section). This
would present a formidable problem in isolation since
the Rf values of 4 and 5 are rather similar. Fortunately,
we discovered considerable difference in their solubility
in hydrocarbon solvents. Thus treatment of the crude
reaction mixture containing 4 and 5 with either hexanes
or pentane resulted in precipitation of pure 5, leaving
4 in solution. The latter could then be easily purified
by silica gel chromatography. Yields of combined 4 and
5 were high (Tables 2 and 3). After some experimenta-
tion we found that the addition of 4 equiv of 1,4-dioxane
improved yields considerably.18 As was the case with
butadienes 3, butadienes 4 and 5 are very stable to air,
water, and heat. Prolonged heating at 150 °C or more
under an inert atmosphere did not cause any noticeable
deterioration or isomerization. Furthermore, no equili-
bration of 4 and 5 occurred under the conditions of the
reaction. Either pure 4 or 5 (R ) n-Bu) was recovered
unchanged after stirring with 1 equiv of Cp2Zr in THF
at 25 °C for 48 h.
We tried zirconocene-induced coupling on a series of
1-alkynyl pinacolboronates. In our case, two regioiso-
mers were obtained: 4 and 5 (eq 3). No 2,3-dibora-1,3-
St r u ct u r e Det er m in a t ion . Hydrozirconation is
known to occur in a syn manner.19 Since coupling of
1-alkenylzirconocenes proceeds with retention of ster-
eochemistry,11 (2E,3E)-butadienes, 3, would be the
expected products of homocoupling of 2. NMR data are
consistent with this assignment. Thus only two 13C
resonances in the alkene region of 2 were observed, with
the broadening of C(1) due to the boron quadrupole. C-
(1)/C(4) resonances (∼143-148 ppm) in 3 are at a much
butadienes, 3, were detected. This is in contrast to the
reported coupling of (1-(trimethylsilyl)phenyl)acetylene
in the presence of zirconocene which gave only the 1,4-
disilyl product.14 Hafnium- and titanium-induced cou-
pling of other silylacetylenes also yielded exclusively 1,4-
disilyl products.15 Thus the regioselectivity observed in
our case is in agreement with placing the more bulky
substituents away from the newly formed carbon-
(16) Buchwald, S. L.; Watson, B. T. J . Am. Chem. Soc. 1987, 109,
2544.
(13) Metzler, N.; No¨th, H.; Thomann, M. Organometallics 1993, 12,
2423.
(14) Erker, G.; Zwettler, R.; Kru¨gwe, C.; Hyla-Krypsin, I.; Gleiter,
R. Organometallics 1990, 9, 524.
(15) (a) Sabade, M. B.; Farona, M. F.; Zarate, E. A.; Youngs, W. J .
J . Organomet. Chem. 1988, 338, 347. (b) Nugent, W. A.; Thorn, D. L.;
Harlow, R. L. J . Am. Chem. Soc. 1987, 109, 2788.
(17) Deloux, L.; Srebnik, M. J . Org. Chem. 1994, 59, 6871.
(18) THF was the solvent of choice. Additives such as TMEDA or
HMPTA in various proportions were not as effective as 1,4-dioxane.
The ratio of 4:5 was independent of solvent or additive.
(19) (a) Schwartz, J .; Labinger, J . Angew. Chem., Int. Ed. Engl. 1976,
15, 333. (b) Cardin, D. J .; Lappert, M. F.; Raston, C. L. Chemistry of
Organo-Zirconium and Hafnium Compounds; Wiley: New York, 1986.
+
+

1,3-, 1,4-, and 2,3-Dibora-1,3-butadienes
Organometallics, Vol. 15, No. 15, 1996 3325
Ta ble 3. (1E,3E)-1,3-Dibor a -1,3-bu ta d ien es, 4
H(4), mult
J (Hz)
entry
R
H(1)
B(1)/B(3)a
C(1)b
C(2)
C(3)b
C(4)
yield, %c (GC)
a
c
e
f
n-Bu
5.16, s
5.26, s
5.28, s
5.06, s
5.76, s
6.21, t, 7.7
6.34, t, 7.7
6.19, t, 7.7
5.88, d, 9.9
6.91, s
30.6
30.8
30.9
30.3
30.7
114.8
116.0
116.8
114.8
118.9
166.8
165.3
164.1
171.8
162.3
137.8
137.5
138.4
134.8
140.0
144.51
143.5
142.6
151.6
142.9
26 (39)
7 (36)
15 (60)
34 (45)
16 (43)
Ph(CH2)2
Cl(CH2)3
cyclopentyl
phenyl
g
a
b
Relative to BF3‚etherate. Due to the boron quadrupole, C(2) resonances are all broad and of low intensity. c Isolated.
lower field than that observed for C(1)/C(4) in butadiene
(117.5 ppm), while C(2)/C(3) resonances are in the same
range (135-136 ppm) as the C(2)/C(3) resonance in
butadiene (137.2 ppm). The downfield shift of C(1)/C(4)
can be accounted for by π-back-bonding of the CC double
bond with the formally empty pz orbital on boron. The
deshielding of C(2)/C(3) is governed primarily by me-
someric (π) effects, while C(1)/C(4) resonances remain
relatively unchanged due to competitive π-back-bonding
between the oxygen atoms and boron.20 Peak count is
also consistent with the symmetrical nature of 3. The
11B values (∼30 ppm) indicate considerable B-C(pp)π
interaction leading to coplanarity of the dioxaborolane
F igu r e 1. ORTEP drawing of 5a with 50% probability
ring with the butadiene system (vide infra).21 With 3
thermal ellipsoids. Selected bond distances (Å) and angles
in hand, assignment of symmetrical 522 was straight-
(deg.): O(1)-C(1), 1.457(4); O(1)-B(1), 1.358(4); O(2)-C(2),
forward (Table 2). The H1/H4 resonances in 5 were all
singlets as expected. The C(2)/C(3) peaks are at a much
1.470(4); O(2)-B(1), 1.369(4); C(1)-C(2), 1.553(4); C(1)-
C(3), 1.513(5); C(1)-C(4), 1.530(5); C(2)-C(5), 1.516(5);
lower field than the resonances observed in 3 while the
C(1)/C(4) is shifted upfield and absorbs in the same
range as butadiene. This can be accounted for by the
same reasoning used to explain the shifts in 3.19 Since
the 11B values of 5 are consistent with considerable
B-C(pp)π interaction and since 5 were all crystalline
solids, we decided to determine the structure of 5a in
the solid state.
A search of the Cambridge Crystallographic data base
indicated that 5a 23 is the first reported structure for a
1,4-dibora-1,3-butadiene system. The asymmetric unit
in 5a consists of a five membered heterocyclic ring that
is bonded to the terminal atom of the butadiene moiety
(C(7)). Attached to the second carbon atom of this unit
(C(8)) is an n-butyl group. The second half of the
molecule is generated by a crystallographic inversion
center resulting in a trans position of the ring systems
(Figure 1). All bond distances and angles are in good
C(2)-C(6), 1.522(5); C(7)-C(8), 1.360(4), C(7)-B(1), 1.547(5);
C(1)-O(1)-B(1), 108.9(2); C(2)-O(2)-B(1), 107.1(2); O(1)-
C(1)-C(2), 102.5(2); O(1)-C(1)-C(3), 105.8(3); O(1)-C(1)-
C(4), 107.3(3); C(2)-C(1)-C(3), 113.2(3); C(2)-C(1)-C(4),
115.6(3); C(3)-C(1)-C(4), 111.3(3); O(2)-C(2)-C(1), 103.2(2);
O(2)-C(2)-C(5), 105.7(2); O(2)-C(2)-C(6), 107.0(3); C(1)-
C(2)-C(5), 116.5(3); C(1)-C(2)-C(6), 113.8(3); C(5)-C(2)-
C(6), 109.7(3); C(8)-C(7)-B(1), 128.5(3); O(1)-B(1)-O(2),
112.9(3); O(1)-B(1)-C(7), 120.9(3); O(2)-B(1)-C(7),
126.2(3).
agreementwith the values quoted for similar struc-
tures.21 The heterocyclic ring system exhibits a slight
envelope conformation with O(1)-B(1)-O(2)-C(1) in
the plane and the remaining carbon atom out of the
plane (0.36 Å for C(2)). The most prominent feature of
this molecule is its high planarity and linearity (see
Supporting Information). Least-squares calculations for
the plane consisting of B(1), O(1), C(1), C(2), O(2), C(7),
and C(8) showed a maximum deviation of 0.15 Å for
C(2). The average distance for these atoms from this
plane is just 0.06 Å. An additional calculation of the
dihedral angle between the planar part of the hetero-
cyclic ring and the BCdCC olefin part revealed a value
of 4.48°. In a zirconocene dioxaborolane 1,1-bimetallic
compound21 this angle was found to be close to 90°. The
high planarity in 5a is most likely caused by conjugation
effects. Furthermore, it is noteworthy that the distance
between B(1) and C(7), the first carbon atom of the
butadiene moiety, exhibits with 1.547(5) Å the same
bond length as an sp3-hybridized boron atom to an
alkyne unit in an amino-alkynylborane.24 The thermal
stability of 5a , its flatness, and linearity would appear
to make it an excellent candidate for evaluation as a
liquid crystal.25 The UV of 5a , λmax (CH2Cl2) ) 266 (ꢀ
) 17 247), is consistent with an s-transoid conformation
in solution.
(20) Cheesman, B. V.; Deloux, L.; Srebnik, M. Magn. Reson. Chem.
1995, 33, 724.
(21) The degree of coplanarity is determined by sterics. We have
shown that, in 2b (R ) t-Bu), the plane of the dioxaborolane ring is
tilted almost 90° to the plane of the alkene: Zheng, B.; Deloux, L.;
Skrzypczak-J ankun, E.; Cheesman, B. V.; Pereira, S.; Sabat, M.;
Srebnik, M. J . Mol. Struct. 1996, 374, 291.
(22) Compounds 5 represent a new diborabutadiene system. How-
ever, Metzler and No¨th have reported a zirconocycle incorporating a
1,4-dibora-1,3-butadiene: Metzler, N. Zur Synthese, elektronischen
Struktur und Reaktivita¨t von Alkinylboranen; Ph.D. dissertation,
Ludwig-Maximilians-Universita¨t; Mu¨nchen, Germany, 1994.
(23) Crystal data for 5a (C24H44B2O4): Mr ) 418.24; monoclinic,
space group P21/n with a ) 6.377(1) Å, b ) 17.103(2) Å, c ) 12.266(4)
Å, â ) 94.26(2)°, V ) 1334.0 Å3, F ) 1.07 g cm-3, Z ) 2, F(000) ) 460,
Enraf Nonius CAD 4 diffractometer. The structure was solved by direct
methods. Data were collected at 190 K with Mo KR radiation (λ )
0.710 73 Å). Data were corrected for Lorentz and polarization effects
as well as for decay (0.1%) and absorption [empirical, Tmin ) 0.96, Tmax
) 0.99, µ ) 0.6 cm-1]. From 2896 measured and 2654 unique
reflections, 1389 reflections were considered “observed” [Fo > 3σ(Fo)]
and used for refinement. All non-H atoms were refined with anisotropic
displacement parameters. All H atoms were calculated and allowed
to ride on their corresponding carbon atom with fixed isotropic
contributions (Uiso(fix) ) 1.3Ueq bonding atom). The structure converted
for 136 refined parameters to an R (Rw) value of 0.063 (0.076). The
function minimized was ∑w(|Fo| - |Fc|)2, with w ) 4Fo2/σ2(Fo2).
(24) Metzler, N.; No¨th, H. Chem. Ber. 1995, 128, 711.
(25) Giroud-Godquin, A.-M.; Maitlis, P. M. Angew. Chem., Int. Ed.
Engl. 1991, 30, 375.
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3326 Organometallics, Vol. 15, No. 15, 1996
Desurmont et al.
Unlike the highly crystalline 5, butadienes 4, which
constitute a new dibora-1,3-butadiene system, were oils
whose structures were determined by NMR analysis
(Table 3). The unsymmetrical nature of 4 was evident
from the multiple peaks in their 13C spectra. 1H NMR
spectra of 4 indicated two vinylic protons: one a singlet
and the other a multiplet (except 4g, R ) Ph, which was
also a singlet). 13C NMR of 4 showed four peaks
attributable to the butadiene unit, two of which were
broad resonances of low intensity due to boron quad-
rapolar relaxation. These were assigned to C(1)/C(3).
Correlation and specific assignments were then deter-
mined by 13C-1H HETCOR experiments (Table 3).
Thus C(1) in 4 absorbs in the same range (∼115 ppm)
as it does in 5 (Table 2), and C(3) in 4 (∼137 ppm) is
similar to 3 (Table 1), due to analogous arguments
outlined above. 11B NMR spectra of 4 (∼30 ppm) again
indicated a high degree of orbital interaction.
Su zu k i-Miya u r a cou p lin g has proven to be a
highly successful method for CC bond formation.8 Since
our dibora-1,3-butadiene systems are novel, it was of
interest to see if the boron groups could be differentiated
in the Suzuki-Miyaura coupling reaction. Suzuki-
Miyaura coupling of a dibora species has not been
reported before. Compounds 3a and 4a were investi-
gated since the boron groups on 5 would not be expected
to show chemoselectivity. Reaction of 4a with 1 equiv
of PhI, 2 equiv of CsF,26 and 5 mol % Pd(PPh3)4, in THF
(reflux 2 days), yielded only one product 6 (eq 5), in
protons, H(3) 6.23 (d, J ) 16.5 Hz), H(1) 5.58 (t, J )
8.23 Hz), H(4) 5.11 (dt, J ) 16.5 and 8.23 Hz) in 7.
The three systems described in this paper offer
intriguing possibilities. The planarity of 5a and its very
oriented shape suggest potential for liquid crystal
properties. Selective Suzuki-Miyaura coupling is pos-
sible for 4. Sequential coupling is being investigated
in this respect. Additional studies are being conducted
with 3 to achieve replacement of one boron group and
retention of the other.
Exp er im en ta l Section
Glassware, syringes, and needles were oven dried at 120
°C, assembled while hot, and dried under a flow of Ar. All
reactions were done under a positive pressure of Ar. Solvents
were distilled from sodium benzophenone ketyl and used
1
immediately. All 11B, 13C, and H NMR spectra were recorded
on a Varian VXR-400 spectrometer at 128.3, 100.6, and 400
MHz. Mass spectra were obtained on a GC/MS fitted with a
25 m methylsilicone column. GC analysis were obtained on a
GC Hewlett Packard Model 5790 A. Compounds 1 were
synthesized according to the literature.27 X-ray structure
analysis of 5a was done on a Enraf Nonius CAD 4 diffracto-
meter. UV/vis spectra were obtained on a Hewlett Packard
8452 A diode array spectraphotometer. Microanalysis was
performed in-house on a Perkin-Elmer 2400 CHN elemental
analyzer.
Gen er a l P r oced u r e for th e P r ep a r a tion of 3. The
preparation of 3a is typical. To a stirred suspension of Cp2-
ZrCl(H)28 (1.05 mmol, 0.271 g) in dry THF at 25 °C under an
atmosphere of Argon was added 1a (0.208 g, 1 mmol) in THF
(5 mL). The reaction was stirred for an additional 30 min until
it turned clear and became orange in color. After the addition
of CuBr (1 mmol, 0.143 g) the reaction mixture was stirred
for 10 h to give the desired product, with the deposition of
metallic copper. The reaction mixture was then quenched with
an aqueous solution of saturated ammonium chloride, filtered,
and extracted twice with hexanes. The organic solutions were
combined, dried over Na2SO4, and concentrated. Chromatog-
raphy of the residue on silica (5% ether/hexane) afforded 3a
(0.135 g, 65%) as an oil. 1H NMR (CDCl3): δ ) 5.97 (t, J )
7.90 Hz, 2 H), 2.25 (q, J ) 7.25 Hz, 4 H), 1.35-1.26 (m, 8 H),
1.25 (s, 24 H), 0.89 (t, J ) 7.03 Hz, 6H). 13C NMR (CDCl3): δ
) 143.6, 135.7, 83.0, 32.2, 31.5, 24.9, 22.3, 14.0. 11B NMR
(CDCl3): δ ) 30.6. MS (EI) m/ z (relative intensity): 418 (M+,
0.66).
which differentiation of the two boron atoms indeed had
occurred, with coupling only at the less hindered boron
on C(1). The assignment of 6 follows from its NMR
spectra. H(1) in 4a (5.19, s) is shifted downfield in 6
(6.38 ppm) whereas H(4) in 4a (6.21 ppm) remains
almost unchanged in 6 (6.20 ppm). In 13C, the broad
resonance of C(1) in 4a (114.8 ppm) disappeared while
the C(3) peak in 4a (137.8 ppm) shifted slightly in 6
(135.1 ppm). 13C-1H HETCOR experiments on 6 also
confirmed the connectivity of the new CC bond.
Suzuki-Miyaura coupling of 3a under the same
conditions as for 4a did not lead to the desired replace-
ment of one boron group by phenyl and retention of the
other boron. Rather, concomitant hydrogenation of the
3-boryl group led to 7 (eq 6). The salient features of
the 1H NMR spectra of 7 are the loss of the pinacol
methyl groups and the loss of symmetry in going from
3a to 7 as can be discerned from the three vinylic
3b. P r ep a r a tion as described for the general procedure
using 1b (0.208 g, 1 mmol) provided 3b as crystals obtained
from hexanes by slow evaporation, as a solid (0.113 g, 59%).
(27) Brown, H. C.; Bhat, N. G.; Srebnik, M. Tetrahedron Lett. 1988,
29, 2635.
(26) Wright, S. W.; Hageman, D. Z.; McLure, L. D. J . Org. Chem.
1994, 59, 6095.
(28) Buchwald, S. L.; LaMaire, S. J .; Nielson, R. B.; Watson, B. T.;
King, S. M. Tetrahedron Lett. 1987, 28, 3895.
+
+

1,3-, 1,4-, and 2,3-Dibora-1,3-butadienes
Organometallics, Vol. 15, No. 15, 1996 3327
Mp: 208 °C. 1H NMR (CDCl3): δ ) 5.91 (s, 2 H), 1.28 (s, 24
H), 1.04 (s, 18 H). 13C NMR (CDCl3): δ ) 149.9, 83.4, 34.3,
30.3, 25.2. 11B NMR (CDCl3): δ ) 30.7. MS (EI) m/ z (relative
intensity): 403 (M+ - 15, 0.09). Anal. Calcd for C24H44B204:
C, 68.92; H, 10.62. Found: C, 68.95; H, 10.69.
3c. Preparation as described for the general procedure
using 1c (0.256 g, 1 mmol) afforded 3c (0.171 g, 59%). Mp:
215 °C with decomposition. 1H NMR (CDCl3): δ ) 7.31-7.13
(m, 10 H), 6.08 (t, J ) 8.64 Hz, 2 H), 2.76-2.54 (m, 8 H), 1.25
(s, 24 H). 13C NMR (CDCl3): δ ) 143.1, 142.3, 136.2, 128.5,
128.1, 125.5, 83.0, 36.4, 33.6, 24.9. 11B NMR (CDCl3): δ )
30.3. MS (EI) m/ z (relative intensity): 457 (M+ - 53, 2.5).
Anal. Calcd for C32H44B2O4: C, 74.73; H, 8.62. Found: C,
74.63; H, 8.60.
3d . Preparation as described for the general procedure
using 1d (0.270 g, 1 mmol) afforded 3d (0.175 g, 65%). Mp:
>215 °C with decomposition. 1H NMR (CDCl3): δ ) 7.28-
7.12 (m, 10 H), 6.05 (t, J ) 7.96 Hz, 2 H), 2.62 (t, J ) 7.69 Hz,
4 H), 2.31 (q, J ) 7.32, Hz, 4 H), 1.71 (m, 4 H), 1.23 (s, 24 H).
13C NMR (CDCl3): δ ) 143.3, 142.8, 136.2, 128.4, 128.1, 125.4,
83.0, 35.5, 31.7, 31.4, 24.8. 11B NMR (CDCl3): δ ) 29.7. MS
(EI) m/ z (relative intensity): 357 (M+ - 181, 0.42).
a 46:54 ratio in 79% GC yield. Date for 4c are as follows.
Yield: 0.184 g, 0.36 mmol, 7% . 1H NMR (CDCl3): δ ) 7.30-
7.12 (m, 10 H), 6.34 (t, J ) 7.7 Hz, 1 H), 5.25 (s, 1 H), 2.86 (t,
J ) 8.4 Hz, 2 H), 2.74 (t, J ) 8.4 Hz, 2 H), 2.62 (m, 4 H), 1.31
(s, 12 H), 1.26 (s, 12 H). 13C NMR (CDCl3): δ ) 165.3, 143.5,
143.5, 141.76, 137.5, 128.5, 128.3, 128.0, 125.8, 125.6, 125.5,
116.0, 83.5, 82.6, 36.7, 36.1, 35.3, 33.7, 24.9, 24.9. 11B NMR
(CDCl3): δ ) 30.75. Data for 5c are as follows. Yield: 0.439
g, 0.86 mmol, 17%. Mp: 138 °C. 1H NMR (CDCl3): δ ) 7.26-
7.15 (m, 10H), 5.68 (s, 2H), 2.92 (m, 4H), 2.68 (m, 4H), 1.28 (s,
24H). 13C-NMR (CDCl3): δ ) 162.9, 142.6, 128.6, 128.12,
125.6, 117.5, 83.0, 37.2, 34.4, 24.9. 11B NMR (CDCl3): δ )
31.65. MS (EI) m/ z (relative intensity): 386 (M+ - 128, 0.20).
Anal. Calcd for C32H44B2O4: C, 74.73; H, 8.62. Found: C,
74.52; H, 8.58.
P r ep a r a tion of 4e a n d 5e followed the procedure described
above using 1e (10 mmol, 2.282 g) to afford 4e and 5e in a
66:34 ratio in 91% yield (GC). Data for 4e are as follows.
Yield: 0.336 g, 0.74 mmol, 15%. 1H NMR (CDCl3): δ ) 6.19
(t, J ) 7.7 Hz, 1 H), 5.23 (s, 1 H), 3.51 (t, J ) 6.6 Hz, 2 H),
3.48 (t, J ) 7.0 Hz, 2 H), 2.72 (t, J ) 7.3 Hz, 2 H), 2.40 (q, J
) 7.3 Hz, 2 H), 1.84 (m, 4 H), 1.29 (s, 12 H), 1.23 (s, 12 H). 13
C
NMR (CDCl3): δ ) 164.1, 142.6, 138.4, 116.8, 83.3, 82.4, 44.7,
44.2, 32.5, 32.3, 30.1, 28.9, 24.6, 24.5. 11B NMR (CDCl3): δ )
30.90. MS (EI) m/ z (relative intensity): 443 (M+ - 15, 0.03).
Data for 5e are as follows. Yield: 0.537 g, 1.21 mmol, 24%.
Mp: 143 °C. 1H NMR (CDCl3): δ ) 5.55 (s, 2 H), 3.48 (t, J )
7.0 Hz, 4 H,), 2.73 (t, J ) 7.7 Hz, 4 H), 1.82 (q, J ) 7.7 Hz, 4
H), 1.26 (s, 24 H). 13C NMR (CDCl3): δ ) 161.6, 117.5, 83.1,
44.9, 33.2, 29.5, 24.9, 24.8. 11B NMR (CDCl3): δ ) 30.86. MS
(EI) m/ z (relative intensity): 443 (M+ - 15, 0.06). Anal. Calcd
for C22H38B2Cl2O4: C, 57.65; H, 8.36. Found: C, 57.56; H, 8.34.
P r ep a r a tion of 4f a n d 5f followed the procedure as
described above using 1f (10 mmol, 2.20 g) to give 4f and 5f
in a ratio of 59:41 and a GC yield of 76%. Data for 4f are as
follows. Yield: 0.744 g, 1.69 mmol, 34%. 1H NMR (CDCl3):
δ ) 5.88 (d, J ) 9.9, 1 H), 5.06 (s, 1 H), 3.25 (m, 1 H), 2.93 (q,
J ) 8.8 Hz, 1 H), 1.80-1.37 (m, 16 H), 1.24 (s, 12 H), 1.22 (s,
12 H). 13C NMR (CDCl3): δ ) 83.41, 82.97, 82.73, 45.64, 41.92,
34.40, 32.67, 32.39, 31.56, 27.61, 26.75, 25.99, 25.64, 25.25,
25.15, 24.90. 11B NMR (CDCl3): δ ) 30.30. MS (EI) m/ z
(relative intensity): 427 (M+ - 15, 0.06). Data for 5f are as
follows. Yield: 0.610 g, 1.37 mmol, 28%. Mp: 129 °C. 1H
NMR (CDCl3): δ ) 4.94 (s, 2 H), 3.09 (m, 2 H), 1.76 (m, 4 H),
1.60 (m, 4 H), 1.47 (m, 8 H), 1.24 (s, 24 H). 13C NMR (CDCl3):
δ ) 171.8, 151.6, 134.8, 114.8, 114.0, 82.7, 45.7, 33.01, 25.2,
24.8. 11B NMR (CDCl3): δ ) 30.62. MS (EI) m/ z (relative
intensity): 442 (M+, 0.03). Anal. Calcd for C26H44B2O4: C,
70.61; H, 10.03. Found: C, 69.96; H, 9.96.
P r ep a r a tion of 4g a n d 5g followed the procedure de-
scribed above using 1g (10 mmol, 2.27 g) give 4g and 5g in a
ratio of 45:55 and in GC yield of 95%. Data for 4g are as
follows. Yield: 0.363 g, 0.79 mmol, 16%. Mp: 98 °C. 1H NMR
(CDCl3): δ ) 7.39-7.17 (m, 10 H), 6.91 (s, 1 H), 5.76 (s, 1 H),
1.38 (s, 12 H), 1.08 (s, 12 H). 13C NMR (CDCl3): δ ) 162.3,
142.9, 141.42, 140.15, 140.0, 138.5, 129.8, 128.4, 128.1, 127.9,
127.6, 127.2, 127.1, 118.9, 83.8, 82.8, 25.1, 24.8, 24.5. 11B NMR
(CDCl3): δ ) 30.71. MS (EI) m/ z (relative intensity): 458 (M+,
0.05). Data for 5g are as follows. Yield: 0.741 g, 1.62 mmol,
33%. Mp: 218 °C. 1H NMR (CDCl3): δ ) 7.28-7.24 (m, 10
H), 5.39 (s, 2 H), 0.99 (s, 24 H). 13C NMR (CDCl3): δ ) 160.57,
141.13, 129.71, 127.41, 126.93, 123.60, 83.03, 24.47. 11B NMR
(CDCl3): δ ) 30.47. MS (EI) m/ z (relative intensity): 458 (M+,
3e. Preparation as described for the general procedure
using 1e (0.228 g, 1 mmol) afforded 3e (0.146 g, 64%) as an
oil. 1H NMR (CDCl3): δ ) 5.91 (t, J ) 7.60 Hz, 2 H), 3.47 (t,
J ) 6.88 Hz, 4 H), 2.35 (q, J ) 7.32 Hz, 4 H), 1.70 (m, 4 H),
1.21 (s, 24 H). 13C-NMR (CDCl3): δ ) 142.1, 136.9, 83.2, 44.6,
32.8, 29.0, 24.9. 11B NMR (CDCl3): δ ) 30.1. MS (EI) m/ z
(relative intensity): 458/460 (M+, 0.33/0.11). Anal. Calcd for
C
22H38B2Cl2O4: C, 57.65; H,8.36. Found: C, 57.66; H, 8.38.
3f. Preparation as described for the general procedure using
1f (0.222 g, 1 mmol) to provide 3f as a solid (0.137 g, 62%). 1H
NMR (CDCl3): δ ) 5.87 (d, J ) 9.52 Hz, 2 H), 2.76 (m, 2 H),
1.82-1.75 (m, 4 H), 1.62-1.48 (m, 8 H), 1.25 (s, 24 H), 1.28-
1.20 (m, 4 H). 13C NMR (CDCl3): δ ) 148.0, 83.0, 42.6, 34.1,
25.5, 24.8. 11B NMR (CDCl3): δ ) 30.6. MS (EI) m/ z (relative
intensity): 442 (M+, 0.11). Anal. Calcd for C26H44B2O4: C,
70.61; H, 10.03. Found: C, 70.96; H, 10.00.
Gen er a l P r oced u r e for t h e P r ep a r a t ion of 4 a n d 5.
The preparation of 4a and 5a is typical. To a stirred suspen-
sion of Cp2ZrCl2 (5.0 mmol, 1.42 g) in dry THF (6 mL) at -78
°C under an atmosphere of argon was added dropwise 10 mmol
of n-BuLi, and the solution was allowed to stir for 2 h. Then
1,4-dioxane (20 mmol, 4 equiv, 1.65 mL) was added, followed
by 1a (10.0 mmol, 2.082 g). The cooled bath was immediately
removed to allow the reaction mixture to reach room temper-
ature. The reaction was stirred overnight and quenched with
ethereal HCl (3.17 M, 3 mL) at 0 °C, followed by treatment
with H2O. The resulting solution was extracted twice with
dry ether. The organic solution was dried, concentrated in
vacuo and analyzed by GC (4a :5a ) 43:57 in 91% yield). Then
5a was precipitated at -20 °C in pentane and collected by
filtration. Chromatography of the filtrate on silica (5% ether/
hexane) afforded 4a . Data for 4a are as follows. Yield: 0.551
g, 26%. Suitable crystals for X-ray analysis were grown from
a slowly evaporating hexane solution. Mp: 91 °C. 1H NMR
(CDCl3): δ ) 6.21 (t, J ) 7.6 Hz, 1 H), 5.16 (s, 1 H), 2.56 (t, J
) 7.6 Hz, 2 H), 2.22 (q, J ) 7.0 Hz, 2 H), 1.40-1.23 (m, 8 H),
1.27 (s, 12 H), 0.85 (t, J ) 6.6 Hz, 6 H). 13C NMR (CDCl3): δ
) 166.8,144.5, 137.8, 114.81, 83.30, 82.37, 32.54, 32.18, 31.89,
31.51, 24.85, 22.53, 22.25, 13.92. 11B NMR (CDCl3): δ ) 30.56.
MS (EI) m/ z (relative intensity): 418 (M+, 0.02). Data for 5a
are as follows. Yield: 0.704 g, 34%. Mp: 91 °C. 1H NMR
(CDCl3): δ ) 5.49 (s, 2 H), 2.59 (t, J ) 7 .7 Hz, 4 H), 1.28 (m,
8 H), 1.25 (s, 24 H), 0.87 (t, J ) 7.0 Hz, 6 H). 13C NMR
(CDCl3): δ ) 164.6, 115.6, 82.8, 32.7, 31.8, 24.8, 22.7, 13.9.
11B NMR (CDCl3): δ ) 30.33. MS (EI) m/ z (relative inten-
sity): 418 (M+, 0.01). UV: λmax (CH2Cl2) ) 266 (ꢀ ) 17 247).
Anal. Calcd for C24H44B204: C, 68.92; H, 10.62. Found: C,
68.92, H, 10.60.
0.04). Anal. Calcd for
Found: C, 73.38; H, 7.93.
C28H36B2O4: C, 73.40; H, 7.92.
P r oced u r e for Su zu k i-Miya u r a Cou p lin g of Dibor a -
bu ta d ien es w ith P h en yl Br om id e. Preparation of 7 is
typical. A solution of 3a (0.5 mmol) in 0.209 g in THF (5 mL)
was treated with Pd(PPh3)4 (0.025 mmol, 0.029 g), CsF (1
mmol, 0.152 g), and phenyl iodide (0.5 mmol, 0.102 g). The
reaction mixture was refluxed for 48 h, diluted in hexanes,
washed with brine, and dried over Na2SO4, and concentrated
P r ep a r a tion of 4c a n d 5c followed the procedure described
above using 1c (10 mmol, 2.561 g) and afforded 4c and 5c in
+
+

3328 Organometallics, Vol. 15, No. 15, 1996
Desurmont et al.
in vacuo and chromatographed on silica gel to yield 7 as an
oil (0.092 g, 76%). 1H NMR (CDCl3): δ ) 7.34-7.11 (m, 5 H),
6.23 (d, J ) 16.5 Hz, 1 H), 5.58 (t, J ) 8.23 Hz, 1H), 5.11 (dt,
J ) 16.5 and 8.23 Hz, 1 H), 2.03 (m, 2 H), 1.88 (m, 2 H), 1.32-
1.18 (m, 8H), 0.86-0.81 (m, 6 H). 13C NMR (CDCl3): δ )
141.4, 139.1, 134.1, 131.7, 131.4, 129.5, 127.9, 126.4, 32.4, 32.0,
31.7, 28.4, 22.3, 13.9. MS (EI) m/ z (relative intensity): 242
(M+, 0.83).
22.4, 14.0. 11B NMR (CDCl3): δ ) 32.17. MS (EI) m/ z
(relative intensity): 368 (M+, 0.17).
Ack n ow led gm en t. We thank the University of
Toledo for fellowships that made this research possible
and the State of Ohio Academic Challenges Program for
providing funds for a high-field 400 MHz NMR spec-
trometer.
Su p p or tin g In for m a tion Ava ila ble: X-ray crystallo-
graphic tables (data collection parameters, positional and
thermal parameters, and bond distances and angles) and an
ORTEP diagram (side view) for 5a , NMR spectra for 3a , and
HETCOR plots of 4a ,c and 6 (17 pages). Ordering information
is given on any current masthead page.
P r ep a r a tion of 6 was as described above using 4a (0.5
mmol, 0.209 g). Yield ) 90% (0.166 g). 1H NMR (CDCl3): δ
) 7.31-7.14 (m, 5 H), 6.38 (s, 1 H), 6.20 (t, J ) 8.4 Hz, 1 H),
2.40 (t, J ) 9.2 Hz, 2 H), 2.29 (q, J ) 8.0 Hz, 2 H), 1.51-1.25
(m, 8 H), 1.33 (s, 12 H), 0.92 (t, J ) 10 Hz, 3 H), 0.87 (t, J )
8.8 Hz, 3 H). 13C NMR (CDCl3): δ ) 145.6, 142.0, 138.8, 129.7,
127.95, 126.8, 125.9, 83.4, 32.1, 31.8, 31.3, 28.9, 24.9, 24.8, 22.9,
OM960178N
+
+