4-bromophenylboronate derivatives of ring and cage borosilicates

Article abstract of DOI:10.1135/cccc20021051

The reactions between equimolecular amounts of 4-bromophenylboronic acid and di-tertbutylsilanediol or tert-butylsilanetriol in toluene solutions at reflux temperatures afforded the borosilicate ring compound [(4-BrC₆H₄B)O₂

Full text of DOI:10.1135/cccc20021051

4-Bromophenylboronate of Borosilicates
1051
4-BROMOPHENYLBORONATE DERIVATIVES OF RING
AND CAGE BOROSILICATES
a
b2
Anthony G. AVENT , Simon E. LAWRENCEb1, Margaret M. MEEHAN
,
b3
b4,
Tom G. RUSSELL and Trevor R. SPALDING
*
a
School of Physical and Environmental Sciences, University of Sussex, Brighton, Sussex, England,
BN19QJ, U.K.; e-mail: a.g.avent@sussex.ac.uk
Chemistry Department, University College, Cork, Ireland; e-mail: s.lawrence@ucc.ie,
b
1
2
3
4
meehanmm@hotmail.com, tomrussell50@hotmail.com, t.r.spalding@ucc.ie
Received March 28, 2002
Accepted Jun e 19, 2002
Dedicated to Professor Jaromír Plešek to mark the occasion of his 75th birthday and in recognition of
his many outstanding contributions to boron chemistry.
Th e reaction s between equim olecular am oun ts of 4-brom oph en ylboron ic acid an d di-tert-
butylsilan ediol or tert-butylsilan etriol in toluen e solution s at reflux tem peratures afforded
th e borosilicate rin g com poun d [(4-BrC6H4B)O2Si(t-Bu)2]2 (1), an d th e cube-based species
[(t-BuSi)4(4-BrC6H4B)4O10] (2), in m edium (62%) an d low (13%) yields, respectively. Th ese
com poun ds were ch aracterised by m icroan alysis, IR an d NMR (1H, 11B, 13C an d 29Si) spec-
troscopy an d sin gle crystal X-ray crystallograph y. Durin g th e work-up of 2, a sam ple of th e
boroxin e, [(4-BrC6H4BO)3] (3), was isolated an d was ch aracterised by sin gle crystal diffract-
ion .
Keyw ord s: Borosilicate; Boroxin e; Crystal structures; In organ ic rin gs; In organ ic cages.
It is a lon g-term in ten tion of our work to syn th esise in organ ic-organ ic h y-
brid m aterials wh ich con tain two-dim en sion al an d th ree-dim en sion al struc-
ture-form in g borosilicate species. To th is en d, we h ave studied th e syn th esis
of 4-brom oph en ylboron ate con tain in g borosilicate com poun ds wh ich are
based on th e two-dim en sion al Si2B2O4 rin g structure (Diagram 1) an d
R2
Si
O
O
O
BR'
R'B
O
Si
R2
DIAGRAM 1
Collect. Czech. Chem. Commun. (Vol. 67) (2002)
doi:10.1135/cccc20021051

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Avent et al.:
th ree-dim en sion al cube-based Si4B4O10 an d sph ere-based Si2B3O6 structures
(Diagram s 2 an d 3, respectively). Th e brom in e atom of th e 4-brom oph en yl
group offers m an y possibilities as a site with poten tial for couplin g reac-
tion s via, for exam ple, Heck reaction s1.
R
R1
R1
Si
B
O
Si
O
O
Si
R1
R
O
O
O
O
B
O
O
Si
O
B
O
B
BR
RB
RB
O
O
R1
O
O
O
R
Si
R1
Si
R1
R
DIAGRAM 2
DIAGRAM 3
It is an ticipated th at th e com bin ation of th e above borosilicates with suit-
able organ ic reagen ts will perm it th e syn th esis of n ovel ch ain , sh eet an d
th ree-dim en sion al in organ ic-organ ic h ybrid m aterials. We report h ere th e
syn th eses an d sin gle crystal X-ray studies of [(4-BrC6H4B)O2Si(t-Bu)2]2 (1),
an d [(t-BuSi)4(4-BrC6H4B)4O10] (2). Durin g th e presen t work, crystals of th e
boroxin e, (4-BrC6H4BO)3, (3), were isolated in low yield an d th e structure of
th is com poun d was determ in ed by X-ray crystallograph ic tech n iques.
Previously publish ed work on com poun ds related to 1–3 h as reported
details of th e syn th esis an d structures of th e rin g borosilicates
[Ph BO2Si(t-Bu)2]2, (4)2, an d [Ph BO2SiPh 2]2 (5)3,4, th e 4-vin ylph en yl cube-
based com poun d [(t-BuSi)4(4-H2C=CHC6H4B)4O10] (6)5, th e 4-brom o-
ph en ylboron ate derivatives of 5, i.e. [(4-BrC6H4B)O2SiPh 2]2 (7)6, an d th e
sph ere-based com poun d [(t-BuSi)2{O(4-BrC6H4B)O} ] (8)7,8
.
3
EXPERIMENTAL
All reaction s were carried out un der an in ert atm osph ere. Solven ts were dried accordin g to
literature m eth ods an d distilled prior to use. Th e followin g reagen ts were supplied by
Aldrich Ch em ical Co., an d used as supplied: tert-butyltrich lorosilan e, di-tert-butyldich loro-
silan e an d 4-brom oph en ylboron ic acid. Th e silan ols, t-Bu2Si(OH)2 an d t-BuSi(OH)3, were
prepared by literature m eth ods from th e correspon din g ch lorides8–10. In frared spectra
(waven um bers in cm –1) were recorded on a Perkin Elm er Paragon 1000 Fourier tran sform
spectrom eter. Sam ples were prepared as KBr discs. All 1H an d 13C NMR spectra were re-
corded on a Bruker Avan ce 300 MHz spectrom eter an d all 11B an d 29Si NMR spectra were re-
corded on a Bruker 500 MHz spectrom eter. Tetram eth ylsilan e an d boron trifluoride eth erate
were used as stan dards an d deuterated ch loroform as th e solven t. All NMR spectra were re-
corded at am bien t tem perature. Ch em ical sh ifts (δ) are given in ppm , couplin g con stan ts (J)
in Hz. Meltin g poin ts were recorded on an Electroth erm al IA 9000 Series digital m eltin g
Collect. Czech. Chem. Commun. (Vol. 67) (2002)

4-Bromophenylboronate of Borosilicates
1053
poin t apparatus. Elem en tal (C/H) an alyses were carried out on an Exeter An alytical In c.,
CE 440 Elem en tal An alyser at th e Microan alytical Laboratory, Un iversity College, Cork.
Syn th esis of [(4-BrC6H4B)O2Si(t-Bu)2]2 (1)
To a solution of t-Bu2Si(OH)2 (0.20 g, 1.47 m m ol) in toluen e (100 cm 3), was added
4-BrC6H4B(OH)2 (0.25 g, 1.23 m m ol) an d th e m ixture h eated at reflux in a Dean –Stark
apparatus for 3.5 h . Th e reaction m ixture was tran sferred to a rotary film evaporator an d th e
toluen e was rem oved un der reduced pressure. Th e resultin g solid was crystallised from
1,2-dich loroeth an e to give colourless crystals of [(4-BrC6H4B)O2Si(t-Bu)2]2 (1), yield 0.24 g
(62%), m .p. 312–314 °C. For
C28H44B2Br2O4Si2 calculated: 49.3% C, 6.5% H; foun d:
48.5% C, 6.4% H. IR (KBr disc, on ly very stron g or stron g vibration s are reported): 2 962,
2 956, 2 861, 1 473, 1 441, 1 376, 1 343, 1 303, 1 280, 1 148, 831, 696, 666, 568. 1H NMR:
1.12 (s, 18 H); 7.39–7.95 (d, 4 H); 7.89–7.94 (d, 4 H). 13C NMR: 20.34 C(CH3)3; 27.32
C(CH3)3; 126.88, 130.78, 131.22 an d 135.15 all 4-BrC6H4. 11B NMR: 43.3. 29Si NMR: –23.57.
Syn th esis of [(t-BuSi)4(4-BrC6H4B)4O10] (2)
To
a
solution of t-BuSi(OH)3 (0.40 g, 2.94 m m ol) in toluen e (40 cm 3), was added
4-BrC6H4B(OH)2 (0.59 g, 2.94 m m ol) an d th e m ixture h eated at reflux in a Dean –Stark appa-
ratus for 10 h . Th e reaction m ixture was cooled an d stirred overn igh t at room tem perature.
Th e toluen e was rem oved by rotary film evaporation an d th e resultan t powder was dissolved
in h exan e an d filtered. Evaporation of th e h exan e afforded colourless crystals of
[(t-BuSi)4(4-BrC6H4B)4O10] (2), yield 0.11 g (12.7%), m .p. 294–295 °C. For C40H52B4Br4O10Si4
calculated: 41.1% C, 4.5% H, 2.6% B; foun d: 40.9% C, 4.3% H, 2.5% B. IR (KBr disc, on ly
very stron g or stron g vibration s are reported): 2 955, 2 937, 2 863, 1 587, 1 470, 1 415,
1 398, 1 377, 1 348, 1 310, 1 150, 1 131, 1 085, 1 101, 865, 822, 724, 704, 640, 605, 593.
1H NMR: 1.34 (s, 18 H), C(CH3)3; 7.52 (d, 6 H, JH-H = 1.5), C6H4Br; 7.73 (d, 6 H, JH-H = 1.5),
4-BrC6H4. 13C NMR: 16.95 C(CH3)3; 25.74 C(CH3)3; 126.76, 131.13, 130.68 an d 136.52 all
4-BrC6H4. 11B NMR: 44.5. 29Si NMR: –65.96. Prior to th e isolation of 2, colourless n eedle-
sh aped crystals of th e boroxin e [(4-BrC6H4BO)3] (3), were filtered from th e reaction m ixture,
0.04 g, m .p. 282–283 °C. For C18H12B3Br3O3 calculated: 39.4% C, 2.2% H; foun d 39.7% C,
2.1% H. Th is com poun d was iden tified by X-ray crystallograph ic m eth ods.
Crystal Structure An alysis for Com poun ds 1–3
Crystal of 1, 0.40
× 0.40 × 0.25 m m , is m on oclin ic, space group P21/c, form ula
C
28H44B2Br2O4Si2, M = 682.25, a = 9.6973(10) Å, b = 15.589(2) Å, c = 11.2725(14) Å, β =
101.309(10)°, U = 1 671.0(3) Å3, µ = 2.527 m m –1, Z = 2, T = 173 K, S = 1.06, R(Fo) = 0.051,
for 2 244 observed reflection s with I > 2σ(I), wR2(F2) = 0.171 for all 3 096 un ique reflection s,
Tm in = 0.806, Tm ax = 0.953, ∆ρm ax = 0.58 e Å–3, ∆ρm in = –0.87 e Å–3
.
Crystal of 2, 0.30 × 0.30 × 0.12 m m , is m on oclin ic, space group P21/c, form ula
40H52B4Br4O10Si4, M = 1168.06, a = 13.440(3) Å, b = 16.192(3) Å, c = 13.375(2) Å, β =
C
116.167(14)°, U = 2 612.4(8) Å3, µ = 3.222 m m –1, Z = 2, T = 173 K, S = 1.03, R(Fo) = 0.053,
for 2 947 observed reflection s with I > 2σ(I), wR2(F2) = 0.124 for all 4 838 un ique reflection s,
Tm in = 0.662, Tm ax = 0.968, ∆ρm ax = 0.60 e Å–3, ∆ρm in = –0.67 e Å–3
.
A very weakly diffractin g crystal of 3, 0.25 × 0.20 × 0.18 m m , was used for th e an alysis.
Crystals of 3 are orth orh om bic, space group Pnma, form ula C18H12B3Br3O3, M = 548.44, a =
Collect. Czech. Chem. Commun. (Vol. 67) (2002)

1054
Avent et al.:
18.746(3) Å, b = 21.818(3) Å, c = 4.8462(8) Å, U = 1 982.1(5) Å3, µ = 6.121 m m –1, Z = 4, T =
173 K, S = 1.09, R(Fo) = 0.091, for 713 observed reflection s with I > 2σ(I), wR2(F2) = 0.281 for
all 1 884 un ique reflection s, Tm in = 0.743, Tm ax = 1.000, ∆ρm ax = 0.95 e Å–3, ∆ρm in = –1.05 e Å–3
.
All data were collected on a Non ius MACH-3 diffractom eter usin g MoKα graph ite
m on och rom ated radiation , λ = 0.7107 Å, an d corrected for Loren tz, polarisation an d absorp-
tion effects. Th e structures were solved by direct m eth ods an d refin ed by full-m atrix
least-squares on all F2 data usin g SHELXL97 11. Th e h ydrogen atom s were placed in calcu-
lated position s an d allowed to ride on th e paren t atom . CCDC 182475 for 1, CCDC 182473
for 2 an d CCDC 182474 for 3 con tain th e supplem en tary crystallograph ic data for th is pa-
per. Th ese data can be obtain ed free of ch arge via www.ccdc.cam .ac.uk/con ts/retrievin g.h tm l
(or from th e Cam bridge Crystallograph ic Data Cen tre, 12, Un ion Road, Cam bridge, CB2
1EZ, UK; fax: +44 1223 336033; or deposit@ccdc.cam .ac.uk).
RESULTS AND DISCUSSION
The reaction between equim olar am ounts of t-Bu2Si(OH)2 and 4-BrC6H4B(OH)2
in toluene solution at reflux afforded [(4-BrC6H4B)O2Si(t-Bu)2]2 (1), in good
yield (62%). Sim ilar reaction s between ph en ylboron ic4 or 4-brom oph en yl-
boron ic6 acid an d diph en ylsilan diol h ave been reported as altern ative
routes to eigh t-m em bered borosilicate rin g com poun ds from ph en yl-
boron dich loride an d di-tert-butylsilan diol2, or ph en ylboron ic acid an d
12
(EtO)2SiRR′ wh ere R = R′ = Et an d R = Me, R′ = Ph
.
Reaction between equim olar am oun ts of t-BuSi(OH)3 an d 4-BrC6H4B(OH)2
afforded th e cage com poun d [(t-BuSi)4(4-BrC6H4B)4O10] (2), in low yield
(13%). A sm all am oun t of th e boroxin e [(4-BrC6H4BO)3] (3), was also iso-
lated. Th e form ation of com poun d 2 m ay possibly proceed by th e in itial
syn th esis of th e eigh t-m em bered [(4-BrC6H4B)O2Si(t-Bu)OH]2 rin g. How-
ever, com poun d 2 can on ly be form ed by th e com bin ation of two such
rin gs wh en th ey con tain th e Si–OH groups align ed with th e two OH en ti-
ties in cis con figuration s across each rin g as in Diagram 4.
But
HO
Si
O
O
BrC6H4
B
C6H4Br
B
O
O
Si
HO
But
DIAGRAM 4
Subsequen t elim in ation of two water m olecules from two
[(4-BrC6H4B)O2Si(t-Bu)OH]2 m olecules would form th e Si–O–Si bon ds ob-
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4-Bromophenylboronate of Borosilicates
1055
served in 2. At th is stage in our work th e m ode of form ation of th e
boroxin e [(4-BrC6H4BO)3] (3), is un clear an d furth er studies are bein g un -
dertaken to elucidate th is aspect of th e reaction between t-BuSi(OH)3 an d
4-BrC6H4B(OH)2. Com poun d 2 is on ly th e secon d exam ple of an in com -
plete cuboid cage con tain in g four boron an d four silicon atom s. Previously,
[(t-BuSi)4(4-H2C=CHC6H4B)4O10], th e 4-vin ylph en ylboron ate an alogue of 2,
was syn th esised by th e reaction between t-BuSiCl3, 4-CH2=CHC6H4B(OH)2
an d aqueous an ilin e5.
Structural Studies of Compounds 1, 2 and 3
Com poun d [(4-BrC6H4B)O2Si(t-Bu)2]2 (1) is a cyclic silylborate with a cen -
tral eigh t-m em bered rin g con tain in g four B–O–Si lin kages (Fig. 1 an d
Table I) an d a cen tre of sym m etry at th e cen tre of th e B2O4Si2 rin g. Each bo-
ron atom subten ds a 4-brom oph en yl group an d each silicon h as two
tert-butyl groups attach ed. A n otable feature of th e cen tral rin g system in 1
is its apparen t plan arity with atom s B(3) an d O(4) sh owin g m ost deviation
from th e calculated m ean plan e at +0.040(3) an d –0.036(3) Å, respectively.
A secon d n otable feature of th e structure of 1 is th e apparen t coplan arity of
th e borosilicate rin g an d th e ph en yl rin gs attach ed to th e boron atom s. Th e
in terplan ar an gle between th e calculated m ean plan e of th e B2O4Si2 boro-
C23
C13
C22
C12
C21
C11
C24
O2a
Si1
C14
O4
C32a
C33a
C36
C35
Br37
C34a
C31a
C31
B3a
B3
O2
C34
Br37a
O4a
C32
C36a
C33
C35a
C14a
Si1a
C24a
C11a
C21a
C12a
C22a
C13a
C23a
FIG. 1
A view of 1 sh owin g th e n um berin g sch em e. An isotropic displacem en t param eters are drawn
at th e 30% probability level
Collect. Czech. Chem. Commun. (Vol. 67) (2002)

1056
Avent et al.:
silicate rin g an d th e calculated m ean plan e of a ph en yl rin g is 7.9(2)° an d
th e torsion an gle O(2a)–B(3)–C(31)–C(32) is –6.7(7)°. Th is latter datum m ay
be com pared with th at for th e an alogous an gle in [(4-BrC6H4B)O2SiPh 2]2
(7), of 1.3(6)° 6. Th e silicon to oxygen distan ces in 1 are alm ost iden tical at
1.629(3) an d 1.631(3) Å. Th e boron to oxygen are less sim ilar at 1.338(6)
an d 1.352(6) Å. Th e two B–O–Si an gles B(3)–O(4)–Si(1) an d B(3a)–O(2)–Si(1)
are sign ifican tly differen t at 150.7(3) an d 153.0(3)°. In th e n on -brom in ated
an alogue of 1, i.e. [Ph BO2Si(t-Bu)2]2 (4)2, th e B–O–Si an gles are very sim ilar
at 149.1(3) an d 149.9(2)° wh ereas in th e related Si–Ph con tain in g deriva-
tives [Ph BO2SiPh 2]2 (5)4, an d [(4-BrC6H4B)O2SiPh 2]2 (7)6, th e B–O–Si an gles
are 145.3(3) an d 160.9(3) an d 144.7(3) an d 150.7(3)°, respectively. Th e
large ran ge of B–O–Si an gles in borosilicates is n ot surprisin g sin ce, as h as
been sh own previously by structural an d th eoretical studies13, th e deform a-
tion of th ese an gles requires relatively sm all am oun ts of en ergy. Th e struc-
ture of com poun d 1 is typical of borosilicates con tain in g organ oboron
groups with th e O–B–O an gle greater th an 120° at 123.4(4)° wh ilst th e
O–B–C an gles are less th an 120° at 118.3(4)°. Th e O–Si–O an gle in com -
poun d 1 is greater at 112.05(17)° th an th e tetrah edral an gle wh ilst th e
TABLE I
Selected bon d len gth s (in Å) an d an gles (in °) for 1
Bon d len gth s
Si1–O4
Si1–C21
O2–B3A
B3–O4
1.629(3)
1.875(5)
1.338(6)
1.352(6)
Si1–O2
1.631(3)
1.891(5)
1.338(6)
1.575(6)
Si1–C11
B3–O2A
B3–C31
Bon d an gles
O4–Si1–O2
O2–Si1–C21
O2–Si1–C11
B3A–O2–Si1
O2A–B3–C31
B3–O4–Si1
112.05(17)
107.0(2)
105.3(2)
150.7(3)
118.4(4)
153.0(3)
O4–Si1–C21
O4–Si1–C11
C21–Si1–C11
O2A–B3–O4
O4–B3–C31
106.2(2)
107.0(2)
119.5(2)
123.4(4)
118.2(4)
Sym m etry tran sform ation s used to gen erate equivalen t atom s: –x, –y + 2, –z + 1.
Collect. Czech. Chem. Commun. (Vol. 67) (2002)

4-Bromophenylboronate of Borosilicates
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O–Si–C an gles are less th an 109° with m ean value of 106.4(2)°. All oth er
bon d distan ces an d an gles are un rem arkable.
Com poun d 2 (Fig. 2 an d Table II) con tain s a borosilicate fram ework
wh ich m ay be described as an in com plete B4Si4 cube with eigh t B–O–Si an d
two Si–O–Si edges. Altern atively, it m ay be described as con sistin g of two
B2O4Si2 rin gs, as in com poun d 1, join ed con facially via two Si–O–Si bridges.
Un like th e B2O4Si2 rin gs in com poun d 1, h owever, th ose of 2 are distin ctly
n on -plan ar with atom s B(3) an d O(4) deviatin g from th e calculated m ean
plan e con tain in g O(2), Si(1), O(8), B(7), O(6), an d Si(5) by 0.696(7) an d
0.812(4) Å, respectively. Th is is also in m arked con trast to th e equivalen t
B2O4Si2 section s of th e 4-vin ylph en yl an alogue of 2, i.e.,
5
[(t-BuSi)4(4-H2C=CHC6H4B)4O10], com poun d 6 . Here all th e atom s except
on e silicon atom in each B2O4Si2 rin g lie in a plan e with root-m ean -square
deviation of 0.053 Å. Th e silicon atom ’s deviation from th e m ean plan e was
0.705(2) Å com pared with deviation s in th e ran ge –0.062(1) to 0.081(2) Å
for all oth er atom s in th e B2O4Si2 rin g. Oth er n otable differen ces between
com poun ds 2 an d 6 con cern th e ben zen e rin gs in each com poun d. In 6,
th e ben zen e rin gs attach ed to boron atom s in th e con facially join ed B2O4Si2
rin gs were essen tially parallel wh ereas in com poun d 2 th ey are clearly n ot
(Fig. 2). Th e in terplan ar an gle between th e m ean plan es con tain in g th e
C(11) to C(16) atom s attach ed to B(3) an d th e C(21) to C(26) atom s at-
tach ed to B(7a) is 46.4(2)°. Hen ce an y stabilisation of th e structure of
[(t-BuSi)4(4-H2C=CHC6H4B)4O10] (6), due to π–π in teraction s between adja-
cen t ben zen e rin gs (an d vin yl groups in com poun d 6) h as been rem oved in
th e case of [(t-BuSi)4(4-BrC6H4B)4O10] (2).
C15
C16
C5
C1
C23
C22
C24
O6
Si1
O4
B7
C11
C21
Si5
O2
O9a
Si1a
C26
C25
C14
Br27
Br17
O8
B3
C13
C12
O9
FIG. 2
A view of 2 sh owin g th e n um berin g sch em e. An isotropic displacem en t param eters are drawn
at th e 30% probability level. Meth yl groups are om itted for clarity
Collect. Czech. Chem. Commun. (Vol. 67) (2002)

1058
Avent et al.:
Th e Si–O–Si an gles in 2 an d 6 are 147.5(2) an d 154.14(14)°, respectively.
Like B–O–Si an gles, th ere are large variation s in reported Si–O–Si an gles
with values from 89.4 to 180° 14. Th e ran ges of B–O–Si an gles in 2 an d 6 are
135.8(3) to 149.8(4)° an d 137.5(2) to 154.4(2)°, respectively. Th e m ean val-
ues are 142.7 an d 144.8°, respectively.
Mean bon d distan ces in [(t-BuSi)4(4-BrC6H4B)4O10] (2) were 1.361(7) an d
1.628(4) Å for th e B–O an d Si–O bon ds, respectively. Th ese m ay be com -
pared with 1.366(3) an d 1.616(4) Å for th e equivalen t bon ds in
[(t-BuSi)4(4-H2C=CHC6H4B)4O10] (6)5.
TABLE II
Selected bon d len gth s (in Å) an d an gles (in °) for 2
Bon d len gth s
Si1–O9
Si1–O2
O2–B3
B3–C11
Si5–O9A
Si5–C5
B7–O8
1.614(4)
1.634(3)
1.377(6)
1.557(7)
1.615(4)
1.846(5)
1.350(7)
Si1–O8
Si1–C1
B3–O4
O4–Si5
Si5–O6
O6–B7
B7–C21
1.626(4)
1.850(6)
1.352(7)
1.634(4)
1.619(4)
1.364(6)
1.557(7)
Bon d an gles
O9–Si1–O8
O8–Si1–O2
O8–Si1–C1
B3–O2–Si1
O4–B3–C11
B3–O4–Si5
O9A–Si5–O4
O9A–Si5–C5
O4–Si5–C5
O8–B7–O6
O6–B7–C21
Si1–O9–Si5A
107.7(2)
111.36(17)
109.3(2)
142.1(3)
119.2(4)
135.8(3)
108.8(2)
111.3(2)
108.2(2)
122.4(5)
117.9(5)
147.5(2)
O9–Si1–O2
O9–Si1–C1
O2–Si1–C1
O4–B3–O2
O2–B3–C11
O9A–Si5–O6
O6–Si5–O4
O6–Si5–C5
B7–O6–Si5
O8–B7–C21
B7–O8–Si1
106.90(19)
110.8(2)
110.8(2)
120.3(5)
120.5(5)
108.39(19)
111.2(2)
109.0(2)
143.1(3)
119.7(4)
149.8(4)
Sym m etry tran sform ation s used to gen erate equivalen t atom s: –x, –y + 1, –z.
Collect. Czech. Chem. Commun. (Vol. 67) (2002)

4-Bromophenylboronate of Borosilicates
1059
Th e crystal of com poun d 3, [(4-BrC6H4BO)3] (Fig. 3 an d Table III), used
for X-ray m easurem en ts, was n ot of a very h igh stan dard an d con sequen tly,
th e solution of th e crystal structure afforded distan ce an d an gle values with
relatively h igh stan dard un certain ties. However, th e structure solution did
TABLE III
Selected bon d len gth s (in Å) an d an gles (in °) for 3
Bon d len gth s
O1–B1
O2–B1
1.40(2)
1.37(3)
O1–B1A
O2–B2
1.40(2)
1.399(19)
Bon d an gles
B1–O1–B1A
O2–B1–O1
O1–B1–C11
O2–B2–C21
123(2)
B1–O2–B2
121.4(17)
121.5(17)
119(2)
117.5(18)
120.9(18)
120.5(12)
O2–B1–C11
O2A–B2–O2
Sym m etry tran sform ation s used to gen erate equivalen t atom s: x, –y + 1/2, z.
Br17a
C13a
C12a
C14a
C15a
C11a
C16a
O2a
O2
C23a
C23
B1a
O1
C22a
C24
B2
C21
C22
Br27
B1
C11
C16
C12
C13
C15
C14
Br17
FIG. 3
A view of 3 sh owin g th e n um berin g sch em e. An isotropic displacem en t param eters are drawn
at th e 30% probability level
Collect. Czech. Chem. Commun. (Vol. 67) (2002)

1060
Avent et al.:
establish th at, like previously reported boroxin e com poun ds, th e m olecule
con tain ed a B3O3 rin g with each boron atom attach ed to a 4-BrC6H4 group.
Th e m ean value for th e B–O distan ce was 1.39 Å, an d th e m ean values for
th e O–B–O an d B–O–B an gles were 118 an d 122°, respectively. Com parable
15
mean B–O distances are 1.386 Å in (PhBO)3 and 1.384 Å in [(4-MeC6H4BO)3] 16
,
respectively.
Thanks are due to the UCC Foundation, for financial support for the Nonius MACH-3
diffractometer and Enterprise Ireland for financial support to M. M. Meehan.
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