A boron analogue of furan. the synthesis and coordination chemistry of 2-substituted-1,2-oxaborolides

Article abstract of DOI:10.1021/om049473v

Two general methods have been developed for the synthesis of alkali metal salts of 2-substituted-1,2-oxaborolides (6). 2-Phenyl-1,2-oxaborolide (6b) has been converted to RuCp* complex lib and to Mn(CO)₃ complex 12b, in which the metals are η

Full text of DOI:10.1021/om049473v

5088
Organometallics 2004, 23, 5088-5091
A Bor on An a logu e of F u r a n . Th e Syn th esis a n d
Coor d in a tion Ch em istr y of
2-Su bstitu ted -1,2-Oxa bor olid es
J inhui Chen, Xiangdong Fang, Zoltan Bajko, J eff W. Kampf, and
Arthur J . Ashe, III*
Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109-1055
Received J uly 14, 2004
Summary: Two general methods have been developed for
the synthesis of alkali metal salts of 2-substituted-1,2-
oxaborolides (6). 2-Phenyl-1,2-oxaborolide (6b) has been
converted to RuCp* complex 11b and to Mn(CO)3
complex 12b, in which the metals are η5-bound to the
ligand.
4 and 5 are good ligands, which have been used to
prepare Cp-like transition metal complexes.10-14 Of
particular significance is the observation that zirco-
nium(IV) derivatives of 410 and 514 have high activity
for the polymerization of olefins. Thus it is of consider-
able interest to prepare 6 so that its coordination chem-
istry can be explored. We now wish to report the first
synthesis of the 1,2-oxaborolide ring system and on its
facile conversion to late transition metal complexes.
The precursors to 6, 2-substituted-2,5-dihydro-1,2-
oxaboroles (9), may be easily prepared by either of two
syntheses summarized in Scheme 2. (Allyloxy)(N,N-diiso-
propylamino)vinylborane (8) was prepared in 87% yield
by treatment of (N,N-diisopropylamino)vinylboron chlo-
ride (7)10b with lithium alloxide in THF. Upon addition
of 2 mol % of Grubbs catalyst to 8 in methylene chloride,
cyclization took place smoothly to give 9a in 92% yield.
Alternatively the reaction of 2,2-dibutyl-2,5-dihydro-1,2-
oxastannole (10)15 with PhBCl2 afforded 9b in 83% yield.
Since 10 is available in large quantities from the
reaction of Bu2SnH2 with propargyl alcohol, the latter
preparation is particularly facile.
Although thiophene (1), pyrrole (2), and furan (3) are
the best known and most important five-membered ring
aromatic heterocycles,1 they are not particularly good
η5-ligands toward transition metals. Thiophene2 and
pyrrole3 form few stable π-coordinated transition metal
complexes. To the best of our knowledge only one
complex containing an η5-furan ligand has been re-
ported: the very labile [Cp*Ru(η5-C4H4O)]Cl.4-6 We
have been interested in anionic aromatic ligands, in
which a CH group of a neutral aromatic is replaced by
the isoelectronic BH- group.7-14 In this manner 1, 2,
and 3 are converted to 1,2-thiaborolide (4),10 1,2-aza-
borolide (5),11-14 and 1,2-oxaborolide (6), respectively.
* To whom correspondence should be addressed. E-mail: ajashe@
umich.edu.
(1) Bird, C. W., Ed. Comprehensive Heterocyclic Chemistry II;
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other papers in this series.
The reaction of 9a with t-BuLi in pentane at -78 °C
gave a yellow powder, which after washing with excess
pentane afforded pure Li-6a in 53% yield. Alterna-
tively treatment of 9b in ether with KN(SiMe3)2 gave a
1
86% yield of K-6b. The H NMR spectra of 6a and 6b
in THF-d8 or DMSO-d8 show first-order patterns, which
are consistent with the assigned structures.
(4) Chaudret, B.; J alon, F. A. J . Chem. Soc., Chem. Commun. 1988,
711.
(5) See: Krishnan, R.; Gottlieb, H. E.; Schultz, R. H. Angew. Chem.,
Int. Ed. 2003, 42, 2179.
Of particular significance is the observation that the
1H, 11B, and 13C NMR spectra of 6b are extremely
similar to those of 5b, as is illustrated in Figure 1. The
spectra exhibit high-field 11B chemical shift values,
which are consistent with strong stabilization by π-bond-
ing to boron.16 The high-field 13C NMR shifts for C(3)
are consistent with appreciable carbanionic character,
(6) Furan forms η2-complexes: (a) Cordone, R.; Harman, W. D.;
Taube, H. J . Am. Chem. Soc. 1989, 111, 5969. (b) Chen, H.; Hodges,
L. M.; Liu, R.; Stevens, W. C., J r.; Sabat, M.; Harman, W. D. J . Am.
Chem. Soc. 1994, 116, 5499. (c) Friedman, L. A.; Sabat, M.; Harman,
W. D. J . Am. Chem. Soc. 2002, 124, 7395. (d) Meiere, S. H.; Keane, J .
M.; Gunnoe, T. B.; Sabat, M.; Harman, W. D. J . Am. Chem. Soc. 2003,
125, 2024.
(7) (a) Ashe, A. J ., III; Kampf, J . W.; Mu¨ller, C.; Schneider, M.
Organometallics 1996, 15, 387. (b) Bazan, G. C.; Rodriguez, G.; Ashe,
A. J ., III; Al-Ahmad, S.; Mu¨ller, C. J . Am. Chem. Soc. 1996, 118, 2291.
(c) Bazan, G. C.; Rodriguez, G.; Ashe, A. J ., III; Al-Ahmad, S.; Kampf,
J . W. Organometallics 1997, 16, 2492.
(8) For reviews of boratabenzene chemistry see: (a) Herberich, G.
E. In Comprehensive Organometallic Chemistry; Wilkinson, G., Stone,
F. G. A., Abel, E. W., Eds.; Pergamon: Oxford, U.K., 1982; Vol. 1, p
381. (b) Herberich, G. E.; Ohst, H. Adv. Organomet. Chem. 1986, 25,
199. (c) Herberich, G. E. In Comprehensive Organometallic Chemistry
II; Housecroft, C. E., Ed.; Pergamon: Oxford, U.K., 1995; Vol. 1, p 197.
(d) Fu, G. C. Adv. Organomet. Chem. 2001, 47, 101.
(9) (a) Ashe, A. J ., III; Fang, X.; Kampf, J . W. Organometallics 1998,
17, 2379. (b) Ashe, A. J ., III; Fang, X.; Kampf, J . W. Organometallics
1999, 18, 1821.
(11) (a) Ashe, A. J ., III; Fang, X. Org. Lett. 2000, 2, 2089. (b) Ashe,
A. J ., III; Yang, H.; Fang, X.; Kampf, J . W. Organometallics 2002, 21,
4578.
(12) For reviews of 1,2-azaborolyl, see: (a) Schmid, G. Comments
Inorg. Chem. 1985, 4, 17. (b) Schmid, G. In Comprehensive Heterocyclic
Chemistry II; Shinkai, I., Ed.; Pergamon: Oxford, U.K. 1996; Vol. 3, p
739.
(13) For recent work on 1,2-azaborolyl, see: (a) Liu, S.-Y.; Lo, M.
M.-C.; Fu, G. C. Angew. Chem., Int. Ed. 2002, 41, 174. (b) Liu, S. Y.;
Hills, I. D.; Fu, G. C. Organometallics 2002, 21, 4323.
(14) (a) Nagy, S.; Krishnamurti, R.; Etherton, B. P. PCI Int. Appl.
W09634021; Chem. Abstr. 1997, 126, 19431j. US Patent 5,902,866, May
11, 1999. (b) Ashe, A. J ., III; Yang, H.; Timmers, F. J . PCT Int. Appl.
WO2003087114; Chem. Abstr. 2003, 139, 323949.
(10) (a) Ashe, A. J ., III; Kampf, J . W.; Schiesher, M. Organometallics
2000, 19, 4681. (b) Ashe, A. J ., III; Fang, X.; Kampf, J . W. Organo-
metallics 2000, 19, 4935.
(15) Massol, M.; Satge´, J .; Bouyssie`res, B. Synth. Inorg. Met.-Org.
Chem. 1973, 3, 1.
(16) Wrackmeyer, B. Annu. Rep. NMR Spectrosc. 1988, 20, 1.
10.1021/om049473v CCC: $27.50 © 2004 American Chemical Society
Publication on Web 09/15/2004

Notes
Organometallics, Vol. 23, No. 21, 2004 5089
Sch em e 1
Sch em e 2. Syn th esisa
F igu r e 2. Solid-state Structure of 11b (ORTEP). Thermal
ellipsoids are at the 50% probability level. Hydrogen atoms
have been omitted for clarity. Selected distances (Å):
B(1)-C(3), 1.468(2); B(1)-O(1), 1.427(2); C(1)-C(2), 1.382-
(2); C(2)-C(3), 1.416(2); C(1)-O(1), 1.422(2); B(1)-Ru(1),
2.278(2); C(1)-Ru(1), 2.149(2); C(2)-Ru(1), 2.193(2);
C(3)-Ru(1), 2.230(2); O(1)-Ru(1), 2.217(1); C(Cp)-Ru(1),
2.148(2)-2.186(2).
a
Key: (a) LiOC3H5/THF; (b) (Cy3P)2(PhCH)RuCl2; (c)
PhBCl2; (d) t-BuLi or KN(SiMe3)2; (e) [Cp*RuCl]4; (f)
(AN)3Mn(CO)3PF6.
tances (2.06-2.21 Å) and the Mn-O distance (2.111(1)
Å). These observations are consistent with a somewhat
weaker coordination to boron, and they conform to the
pattern shown by complexes of other heterocyclic boron
ligands.7-12
The intra-ring C-C and B-C distances of the 1,2-
oxaborolyl ligand of 12b are typical of those found for
similarly coordinated heteroaromatic ligands. The C-C
bond distances (1.43-1.39 Å) of 12b are only slightly
different than those shown by (1-phenylboratabenzene)-
Mn(CO)3 (13) (1.42-1.40 Å).18 The intra-ring B-C
distance of 12b (1.514(2) Å) is identical to that shown
by 13. However it is more difficult to draw conclusions
about the B-O and C-O bonds due to the dearth of
compounds with coordination similar to that of 12b. The
C-O bond of 12b (1.404(2) Å) is somewhat longer than
that of furan (1.368 Å).19 On the other hand the B-O
bond of 12b (1.456(2) Å) is well outside the range of the
B-O bonds (1.34-1.38 Å) found for esters of borinic
acids (R2BOR′) (14).20 We speculate that hypothetical
metal coordination to 3 or 14 might reasonably be
expected to expand these bonds.
Finally we note that the CO stretching frequencies
in the IR spectrum of 12b in hexane are 2039, 1966,
and 1948 cm-1, which are virtually identical to those of
13 (2039, 1974, 1960 cm-1),21 but are slightly shifted
from those of CpMn(CO)3 (2028, 1944 cm-1). This
suggests that the boron heterocycles are weaker donors
but better acceptors than Cp.8b
F igu r e 1. Comparison of the 1H NMR, 13C NMR (in
parentheses), and 11B NMR (in circles) chemical shift
values of 5b and 6b in THF-d8.
while the lower field chemical shift values of C(4) and
C(5) suggest that these atoms bear little negative
charge.17 Overall the great similarity in spectra implies
a similarity in the electronic structure of 5b and 6b.
Like 1,2-azaborolides, 1,2-oxaborolides readily form
transition metal complexes. The reaction of 6b with
[Cp*RuCl]4 gave 11b as bright amber crystals in 70%
yield. The crystal structure of 11b shows that it is a
diheteroruthenocene in which the oxaborolyl ring is
η5-bond to Ru in the same manner found for the
corresponding complex of 4a . See Figure 2.
Unfortunately, a partial disorder limits the accuracy
of the bond distances. 11b is more robust than the
isoelectronic furan complex, [Cp*Ru(η5-C4H4O)]Cl, which
was reported to be stable only in solutions of noncoor-
dinating solvents.4
The reaction of 6b with Mn(CO)3(AN)3PF6 in THF
afforded 12b as a yellow crystalline solid in 63% yield.
On recrystallization from pentane, 12b was subject to
single-crystal X-ray analysis. The molecular structure
of 12b, illustrated in Figure 3, shows that the near
planar oxaborolyl ring is η5-bound to the Mn(CO)3 group
in a typical piano-stool fashion. The oxaborolyl ring
shows a small deviation from planarity in that the boron
atom is displaced away from Mn out of the plane defined
by C(1)C(2)C(3)O(1) by 0.12(2) Å. The B-Mn distance
(2.301(1) Å) is somewhat longer than the C-Mn dis-
In summary, we have developed two efficient synthe-
ses of 1,2-oxaborolides from readily available starting
materials. 1,2-Oxaborolides are diheterocyclopentadi-
enides, which are also anionic boron analogues of furan.
(18) Huttner, G.; Gartzke, W. Chem. Ber. 1974, 107, 3786.
(19) (a) Fourme, R. Acta Crystallogr. 1972, B28, 3984. (b) Liescheski,
P. B.; Rankin, D. W. H. J . Mol. Struct. 1989, 196, 1.
(20) For example see: (a) Ashby, M. T.; Sheshtawy, N. A.; Organo-
metallics 1994, 13, 236. (b) Rogers, J . S.; Bazan, G. C.; Sperry, C. K.
J . Am. Chem. Soc. 1997, 119, 9305. (c) Grelwe, P.; Beez, V.; Pritzkow,
H.; Siebert, W. Eur. J . Inorg. Chem. 2001, 381. (d) Ko¨ster, R.; Seidel,
G.; Boese, R.; Wrackmeyer, B. Chem. Ber. 1990, 123, 1013. (e)
Montchamp, J .-L.; Migaud, M. E.; Frost, J . W. J . Org. Chem. 1993,
58, 7679.
(17) (a) Olah, G. A.; Asensio, G.; Mayr, H.; Schleyer, P. v. R. J . Am.
Chem. Soc. 1978, 100, 4347. (b) Ashe, A. J . III; Fang, X.; Kampf, J . W.
Organometallics 1999, 18, 466.
(21) Herberich, G. E.; Becker, H. J . Angew. Chem., Int. Ed. Engl.
1973, 12, 764.

5090 Organometallics, Vol. 23, No. 21, 2004
Notes
The reaction mixture was kept at -78 °C for 1 h and then
slowly warmed to room temperature and stirred for 4 h. The
liquid was removed via cannula filtration, and the residue was
washed with diethyl ether (3 × 5 mL) to obtain the product
They are good ligands toward late transition metals. The
way is now open for the development of new coordina-
tion chemistry of this Cp surrogate.
1
(6.46 g, 85.9%) as a light yellow powder. H NMR (DMSO-d6,
Exp er im en ta l Section
400 MHz): δ 7.48 (m, 2H, ArH), 7.03 (m, 2H, ArH), 6.82 (m,
1H, ArH), 6.47 (t, 1H, J ) 1.6 Hz, H5), 6.11 (dd, 1H, J ) 1.6
Hz, J ) 4.4 Hz, H4), 4.30 (d, 1H, J ) 4.4 Hz, H3). 13C NMR
(DMSO-d6, 100.6 MHz): δ 130.85, 126.23, 126.59, 122.55,
118.78, 85.50 (br). 11B NMR (DMSO-d6, 160.4 MHz): δ 33.34.
1H NMR (THF-d8, 500 MHz): δ 7.61 (d, 2H, J ) 9.5 Hz, ArH),
7.02 (t, 2H, J ) 9.0 Hz, ArH), 6.84 (t, H, J ) 9.0 Hz, ArH),
6.58 (s, 1H, H5), 6.35 (d, 1H, J ) 4.5 Hz, H4), 4.50 (d, 1H, J )
4.5 Hz, H3). 13C NMR (THF-d8, 100.6 MHz): δ 132.46, 128.72,
127.61, 124.44, 120.77, 84.19.
[η5-P e n t a m e t h ylcyclop e n t a d ie n yl][η5-2-p h e n yl-1,2-
oxa bor olyl]r u th en iu m (II) (11b). A 40 mL portion of THF
was added to a mixture of potassium 2-phenyl-1,2-oxaborolide
(0.728 g, 4.0 mmol) and [Cp*RuCl]4 (1.087 g, 4.0 mmol) at -78
°C with magnetic stirring. The mixture was stirred at -78 °C
for 2 h and allowed to warm to and maintained at room
temperature for 20 h. The solvent was removed under reduced
pressure, and the residue was dried in vacuo. The solid residue
was then extracted with pentane (100 mL). The product was
obtained as amber crystals (1.06 g, 70%) by cooling the extracts
to -30 °C and slowly removing the solvent by vacuum. Mp )
84.7 °C (dec). 1H NMR (C6D6, 400 MHz): δ 7.84 (m, 2H, ArH),
7.32 (m, 2H, ArH), 7.22 (m, 1H, ArH), 6.31 (s, 1H, H5), 4.64
(d, 1H, J ) 4.8 Hz, H4), 4.10 (d, 1H, J ) 4.8 Hz, H3), 1.61 (s,
15H, Cp*Me). 13C NMR (C6D6, 100.6 MHz): δ 132.79, 128.01,
127.69, 99.10, 85.32, 83.98, 11.30. 11B NMR (C6D6, 160.4
MHz): δ 19.72. HRMS (EI, m/z): calcd for C19H2311BO102Ru
(M+), 380.0885; found, 380.0886. Anal. Calcd for C9H9BO: C,
60.17; H, 6.11. Found: C, 59.77; H, 5.98.
Gen er a l Meth od s. 1H, 11B{1H}, and 13C{1H} NMR spectra
were recorded on Varian INOVA-400 or 500 MHz spectrom-
eters. The solvents used were chloroform-d1 (CDCl3), benzene-
d6 (C6D6), methyl sulfoxide (DMSO-d6), or tetrahydrofuran-d8
(THF-d8), as indicated. Chemical shifts (δ) are reported in
parts per million (ppm). Proton and carbon chemical shifts are
relative to respective solvent internal standards: 7.27 (for
proton), 77.23 (for carbon) (CDCl3); 7.16, 128.39 (C6D6); 2.50,
39.70 (DMSO-d6); 3.58, 67.40 (THF-d8). Boron-11 chemical
shifts are relative to prospective external reference: δ 0.00
(BF3/Et2O 1.0 M LiCl in D2O). The coupling constants (J ) are
reported in Hz. The following abbreviations are used to
describe peak patterns: “s” for singlet, “d” for doublet”, “t” for
triplet, “q” for quartet, “m” for multiplet, and “br” for broad
peak. Data are presented as follows: chemical shift (multiplic-
ity, integrated intensity, coupling constant, and assignment).
Infrared (IR) spectra were recorded on a Nicolet Mode 5-DX
FT-IR spectrometer using thin films in hexane. Data are
reported in wavenumber (cm-1). High-resolution mass spectra
(HRMS) were recorded on a VG-250S spectrometer with
electron-impact spectra at 70 eV. Elemental analysis was
conducted on a Perkin-Elmer 240 CHN analyzer by the
analytical service in the Department of Chemistry at the
University of Michigan, Ann Arbor. Melting points were
recorded on a Laboratory Devices MEL-TEMP melting point
apparatus with an uncorrected thermometer.
Solvents were freshly distilled prior to use. THF and diethyl
ether were distilled from sodium and benzophenone ketyl
under N2. Pentane and hexane were distilled from sodium
metal. Dibutyltin dihydride was prepared by reaction of
dibutyltin dichloride with lithium aluminum hydride followed
by vacuum distillation. Tricarbonyl tris(acetonitrile) manga-
nese hexafluorophosphate and 2-phenyl-1,2-dihydro-1,2-oxa-
stannole15 were prepared according to literature procedures.
All other reagents were purchased from the commercial ven-
dors and were used as received or distilled if necessary. All
reactions were conducted under an inert atmosphere of argon
or in the glovebox under nitrogen unless otherwise specified.
Syn th esis of 2,5-Dih yd r o-2-p h en yl-1,2-oxa bor ole (9b).
A solution of dichlorophenylborane (7.87 g, 50 mmol) in 25 mL
of pentane was added via cannula technique to a solution of
2,2-dibutyl-2,5-dihydro-1,2-oxastannole (14.45 g, 50 mmol),
prepared according to literature procedure, in 60 mL of
pentane at -78 °C. Upon the addition, the white oxastannole
slurry dissolved and the solution turned light brown. The
reaction mixture was gradually warmed and stirred at room
temperature overnight. The solvent was removed under re-
duced pressure, and the product was obtained via vacuum
distillation (bp 35-38 °C at 0.025 Torr) with a yield of 5.95 g
(82.6%) as a colorless liquid. 1H NMR (C6D6, 400 MHz): δ 8.13
(m, 2H, ArH), 7.28 (m, 3H, ArH), 7.01 (d, 1H, J ) 8 Hz, H3),
6.48 (d, 1H, J ) 8 Hz, H4), 4.44 (m, 2 H, H5). 13C NMR (C6D6,
100.6 MHz): δ 158.94 (C3), 136.29, 132.12, 128.63, 78.85 (C5).
1H NMR (CDCl3, 400 MHz): δ 8.00 (m, 2H, ArH), 7.64 (d, 1H,
J ) 8 Hz, H3), 7.54-7.45 (m, 3H, ArH), 6.68 (d, 1H, J ) 8 Hz,
H4), 4.98 (d, 2H, J ) 1.2 Hz, H5). 13C NMR (CDCl3, 100.6
MHz): δ 158. 54 (C3), 135.56, 131.67, 128.14, 78.82 (C5). 11B
NMR (C6D6, 160.4 MHz): δ 46.5. HRMS (EI, m/z): calcd for
C9H911BO (M+), 144.0746; found, 144.0739. Anal. Calcd for
C9H9BO: C, 75.08; H, 6.30. Found: C, 74.72; H, 6.28.
T r i c a r b o n y l[η5 -2-p h e n y l-1,2-o x a b o r o ly l]m a n g a -
n ese(I) (12b). THF (50 mL) was added to a mixture of
potassium 2-phenyl-1,2-oxaborolide (1.288 g, 7.0 mmol) and
Mn(CO)3(NCCH3)3 PF6 (3.0 g, 7.0 mmol) at -78 °C with
magnetic stirring. The mixture was stirred at -78 °C for 2 h
and allowed to warm to and maintained at room temperature
for 12 h. The solvent was removed under reduced pressure,
and the residue was dried in vacuo. The solid residue was then
extracted with pentane (100 mL). The product was obtained
by recrystallization from pentane at -30 °C as yellow crystals
(1.25 g, 62.5%). Mp ) 64 °C. IR (hexane, film): 2039, 1966,
1948 cm-1 1H NMR (C6D6, 400 MHz): δ 7.56 (m, 2H, ArH),
.
7.17 (m, 3H, ArH), 5.79 (s, 1H, H5), 4.65 (d, 1H, J ) 4.8 Hz,
H4), 3.60 (d, 1H, J ) 4.8 Hz, H3). 13C NMR (C6D6, 100.6 MHz):
δ 222.43, 134.24, 131.31, 128.71, 102.98, 98.23, 65.78. 11B NMR
(C6D6, 160.4 MHz): δ 24.68. HRMS (EI, m/z): calcd for
C
C
12H811BOMn (M+), 281.9896; found, 281.9902. Anal. Calcd for
12H8BMnO4: C, 51.12; H, 2.86. Found: C, 51.49; H, 2.86.
(N,N-Diisop r op yla m in o)a llyloxyvin ylbor a n e (8). A so-
lution of N,N-diisopropylvinylboron chloride (21 g, 121 mmol)
in 30 mL of THF was treated with a solution of lithium
allyloxide (1.0 equiv) in 20 mL of THF at -78 °C. The mixture
was stirred at -78 °C for 2 h and at 25 °C for 3 h. A white
solid formed gradually. After filtration and removal of the
solvent the residue was vacuum distilled to give the product
as a clear colorless liquid (20.5 g, 87%), bp 32-34 °C at 0.05
Torr. 1H NMR (C6D6, 400 MHz): δ 6.03 (dd, 1H, J ) 20.5, 15.0
Hz, vinyl), 5.84 (m, 1H, vinyl), 5.34 (dq, 1H, J ) 15.4, 2.2 Hz,
vinyl), 5.04 (dq, 1H, J ) 10.6, 1.8 Hz, vinyl), 135.7 (br, vinyl),
126.9 (vinyl), 113.7 (vinyl), 66.4 (CH2O), 48.2 (NC), 44.2 (NC),
23.9 (Me), 22.9 (Me). 11B NMR (C6D6, 115.5 MHz): δ 29.9.
HRMS (EI, m/z): calcd for C11H2211BNO (M+), 195.1794; found,
195.1785. Anal. Calcd for C11H22BNO: C, 67.72; H, 11.36; N,
7.18. Found: C, 67.54; H, 11.52; N, 7.01.
P ota ssiu m 2-P h en yl-1,2-oxa bor olid e (6b). A solution of
potassium bis(trimethylsilyl)amide (5.95 g, 41.3 mmol) in 35
mL of diethyl ether was added slowly via cannula to a solution
of 9b (9.11 g, 43.4 mmol) in 15 mL of diethyl ether at -78 °C.
Upon completion of addition, the solution turned light yellow.
N,N-Diisopr opyl-2-am in o-2,5-dih ydr o-1,2-oxabor ole (9a).
A solution of 8 (16.7 g, 85.6 mmol) in 120 mL of CH2Cl2 was
added to a solution of bis(tricyclohexylphosphine)benzylidene

Notes
Organometallics, Vol. 23, No. 21, 2004 5091
Ta ble 1. Cr ysta l a n d Da ta Collection P a r a m eter s
for 11b a n d 12b
11b
12b
empirical formula
fw
C
19H23BORu
C12H8BMnO4
281.93
379.25
temp,K
293(2)
150(2)
wavelength, Å
cryst syst
space group
a, Å
b, Å
c, Å
0.71073
monoclinic
P2(1)/n
8.7654(13)
14.136(2)
13.820(2)
94.583(4)
1706.9(4), 4
1.476
0.71073
monoclinic
P2(1)/c
8.4249(7)
17.0274(14)
8.2670(7)
98.110(2)
1174.07(17), 4
1.595
â, deg
V, Å3, Z
calcd density, Mg/m3
abs coeff, mm-1
F(000)
0.917
776
1.124
568
F igu r e 3. Solid-state structure of 12b (ORTEP). Ther-
mal ellipsoids are at the 50% probability level. Hydro-
gen atoms have been omitted for clarity. Selected dis-
tances (Å): B(1)-C(3), 1.514(2); B(1)-O(1), 1.456(2);
C(1)-C(2), 1.392(2); C(2)-C(3), 1.427(2); C(1)-O(1),
1.404(2); B(1)-Mn(1), 2.301(2); C(1)-Mn(1), 2.057(2);
C(2)-Mn(1), 2.154(1); C(3)-Mn(1), 2.210(1); O(1)-Mn(1),
2.111(1).
cryst size, mm
limiting indices
0.36 × 0.12 × 0.12 0.74 × 0.72 × 0.36
-11 e h e 11,
-18 e k e 18,
-18 e l e 18
-11 e h e 11,
-22 e k e 22,
-11 e l e 11
13 720/2900
no. of reflns collected/ 23 160/22 728
unique
abs corr
semiempirical fr
equivalents
full-matrix
least-squares
on F2
semiempirical fr
equivalents
full-matrix
least-squares
on F2
refinement method
25 °C for 15 min. A white solid formed gradually. After removal
of the solvent and washing with cold pentane the residue was
dried under vacuum to give the product as a light yellow
no. of data/restraints/ 22 728/0/206
params
2900/0/163
1
powder (0.28 g, 53%). H NMR (THF-d8, 400 MHz): δ 6.2 (s,
GOF on F2
1.043
1.058
1H, H5), 6.04 (d, 1H, J ) 4.8 Hz, H4), 3.44 (sept, 2H, J ) 6.6
Hz, NCH), 2.44 (d, 1H, J ) 4.7 Hz, H3), 1.11 (d, 12H, J ) 6.6
Hz, Me). 13C NMR (THF-d8, 100.6 MHz): δ 122.0, 118.8, 58
(br, C(3)), 46.3 (NC), 23.9 (Me). 11B NMR (THF-d8, 115.5
MHz): δ 37.0.
Sin gle-Cr ysta l X-r a y Cr ysta llogr a p h y. Crystals of 11b
and 12b suitable for X-ray diffraction were obtained by
recrystallization from ether/hexane and pentane, respectively.
Crystallographic and data collection parameters are collected
in Table 1. ORTEP drawings of 11b and 12b showing the
atom-numbering scheme used in the refinements are il-
lustrated in Figures 2 and 3, respectively. Additional crystal-
lographic data are available in the Supporting Information.
final R indices
(I>2σ(I)
R indices (all data)
R1 ) 0.0350,
wR2 ) 0.0784
R1 ) 0.0534,
wR2 ) 0.0830
0.772 and -0.790
R1 ) 0.0225,
wR2 ) 0.0634
R1 ) 0.0236,
wR2 ) 0.0641
0.377 and -0.282
largest diff peak and
hole, e/A3
ruthenium(IV) dichloride (Grubb’s catalyst) (1.4 g, 2 mol %)
in 20 mL of CH2Cl2 at 25 °C for 10 h, after which the color
had changed from purple-red to dark brown. The solvent was
removed in vacuo at 0 °C, and the product (13.2 g, 92%) was
1
obtained as a clear colorless liquid, bp 28 °C at 0.05 Torr. H
NMR (C6D6, 400 MHz): δ 6.78 (d, 1H, J ) 7.7 Hz), 6.06 (d,
1H, J ) 7.7 Hz), 4.40 (m, 2H), 3.64 (sept, 1H), 3.46 (sept, 1H,
J ) 6.6 Hz), 1.27 (d, 6H, J ) 6.6 Hz), 1.09 (d, 6H, J ) 6.6 Hz).
13C NMR (C6D6, 100.5 MHz): δ 152.2 (CdC), 53.3 (CH2O), 47.2
(NCH), 45.2 (NCH), 24.0 (CH3), 23.3 (CH3). 11B NMR (C6D6,
115.5 MHz): δ 33.2. HRMS (EI, m/z): calcd for C9H1811BNO,
167.1481; found, 167.1490. Anal. Calcd for C9H18BNO: C,
64.71; H, 10.86; N, 8.38. Found: C, 64.90; H, 10.78; N, 7.84.
Lith iu m N,N-Diisopr opyl-2-am in o-1,2-oxabor olide (6a).
A solution of 9 (0.52 g, 3.11 mmol) in 12 mL of pentane was
treated with a solution of t-BuLi (1.7 M, 1.8 mL) in pentane
at -78 °C. The mixture was stirred at -78 °C for 1 h and at
Ack n ow led gm en t. Partial support of this reseach
has been provided by NSF Grant No. CHE-0108069. We
are grateful to the Boulder Scientific Company for a
generous gift of the Grubbs catalyst.
Su p p or tin g In for m a tion Ava ila ble: X-ray characteriza-
tion of 11b and 12b (CIF). This material is available free of
charge via the Internet at http://pubs.acs.org.
OM049473V