Boron halide chelate compounds and their activity towards the demethylation of trimethylphosphate

Article abstract of DOI:10.1139/v02-050

Salen(t-Bu)H₂ (N,N′-ethylenebis(3,5-di-tert-butyl(2-hydroxy)benzylidenimine) and its derivatives were used to prepare boron compounds having the formula L(BCl₂)₂ (L = salen(t-Bu) (1), salpen(t-Bu) (2), salben(t-Bu) (3), salpten(t-Bu) (4), salhen(t-Bu) (5)). These are formed from the reaction of the corresponding (L[B(OMe)₂]₂ with BCl₃. In addition to being a new type of boron compound, they are also potential two-point Lewis acids. Indeed, they demonstrate Lewis acidic behavior in the dealkylation of trimethylphosphate. All of the compounds were characterized by mp, elemental analysis, ¹H and ¹¹B NMR, IR, MS, and in the case of 2 by X-ray crystallography.

Full text of DOI:10.1139/v02-050

1463
Boron halide chelate compounds and their activity
towards the demethylation of trimethylphosphate
Timothy S. Keizer, Lauren J. De Pue, Sean Parkin, and David A. Atwood
Abstract: Salen(t-Bu)H2 (N,N>-ethylenebis(3,5-di-tert-butyl(2-hydroxy)benzylidenimine) and its derivatives were used to
prepare boron compounds having the formula L(BCl2)2 (L = salen(t-Bu) (1), salpen(t-Bu) (2), salben(t-Bu) (3),
salpten(t-Bu) (4), salhen(t-Bu) (5)). These are formed from the reaction of the corresponding L[B(OMe)2]2 with BCl3.
In addition to being a new type of boron compound, they are also potential two-point Lewis acids. Indeed, they dem-
onstrate Lewis acidic behavior in the dealkylation of trimethylphosphate. All of the compounds were characterized by
1
mp, elemental analysis, H and 11B NMR, IR, MS, and in the case of 2 by X-ray crystallography.
Key words: boron, salen, dealkylation.
Résumé : On a utilisé le salen(t-Bu)H2 (N,N>-éthylènebis(3,5-di-tert-butyl(2-hydroxy)benzylidènimide) et ses dérivés
pour préparer des composés du bore de formules L(BCl2)2 (L = salen(t-Bu) (1), salpen(t-Bu) (2), salben(t-Bu) (3),
salpten(t-Bu) (4) et salhen(t-Bu) (5) qui se forment par réaction du L[B(OMe)2]2 avec du BCl3. En plus de
correspondre à un nouveau type de composé du bore, ces produits sont potentiellement des acides de Lewis en deux
points. Ils démontrent effectivement un comportement d’acide de Lewis dans la désalkylation du phosphate de
1
triméthyle. Tous les composés ont été caractérisés par leurs points de fusion, une analyse élémentaire, par RMN du H
et du 11B, par infrarouge et spectrométrie de masse et, dans le cas du produit 2, par diffraction des rayons X.
Mots clés : bore, salen, désalkylation.
[Traduit par la Rédaction] Keizer et al. 1468
Introduction
tions, allowing for further derivatization of the boron atoms
and thereby increasing their potential utility (13).
Over the years, the dianionic Salen ligands (salen(t-Bu) =
N,N>-ethylenebis(3,5-di-tert-butyl(2-oxo)benzylidenimine))
(Fig. 1) have been used in many applications (1, 2). The ver-
satility of the ligand allows for the isolation of both
monometallic and bimetallic derivatives usually involving
the group 13 elements. For example, many compounds have
been reported for aluminum (3–5), gallium (5, 6), and in-
dium (7, 8). However, boron compounds of this type have
been studied less extensively (9–11). Examples of Salen (L)
boron compounds include alkoxide (L[B(OR)2]2, R = Me,
Et) (9), siloxide (L[B(OSiOPh3)2]2 (10), fluoride (L[BF2]2)
(12), and acetate (L[B(OAc)2]2) (11) derivatives. Although
these compounds are interesting from a fundamental stand-
point, they are limited in usefulness because of their lack of
reactivity or Lewis acid potential. In this paper we report the
high-yield syntheses of new Salen-supported boron chloride
derivatives, L[BCl2]2 (1–5). Preliminary work indicates that
these chloride compounds will undergo salt elimination reac-
For instance, boron compounds could be useful as two-
point Lewis acids. Many biological systems use a bis-metal
complex to promote the binding and hydrolysis of phosphate
esters (14). In recent years, synthetic derivatives containing
d-block metals such as cobalt (15, 16), zinc (17–20), and
copper (21, 22) have been used as catalysts for this reaction.
A potentially important development in this area is the re-
cent demonstration that boron bromide compounds such as
salpen(t-Bu)[BBr2]2 can catalytically dealkylate a wide variety
of phosphate esters (23). Herein, the boron chloride com-
pounds L[BCl2]2 (1–5) will be synthesized, characterized,
and examined as dealkylation agents for trimethylphosphate.
Results and discussion
Synthesis and characterization of 1–5
The boron chlorides (1–5) were prepared in nearly quanti-
tative yield by combining the corresponding salen(t-
Bu)[B(OMe)2]2 reagent with BCl3 (Scheme 1). The resulting
compounds have two four-coordinate boron atoms held in a
bidentate manner by the Salen ligand. Each boron atom is
bound by two chlorides, a nitrogen, and an oxygen from the
Salen ligand. This reaction is unique and unusual in that all
of the methoxide groups are replaced with chloride groups.
It is known that boron trichloride mixed with trimethylborate
(eq. [1]) undergoes a ligand redistribution to form BCl(OMe)2
and BCl2(Ome) (24). Thus, the reaction described in
Scheme 1 is expected to produce compounds with various
combinations of chlorides and methoxides on the boron
Received 5 January 2002. Published on the NRC Research
Press Web site at http://canjchem.nrc.ca on 31 October 2002.
Dedicated to Professor Tris Chivers for his contributions to
Canadian chemistry.
T.S. Keizer, L.J. De Pue, S. Parkin, and D.A. Atwood.1
Department of Chemistry, University of Kentucky, Lexington,
KY 40506–0055, U.S.A.
1Corresponding author (e-mail: datwood@pop.uky.edu).
Can. J. Chem. 80: 1463–1468 (2002)
DOI: 10.1139/V02-050
© 2002 NRC Canada

1464
Can. J. Chem. Vol. 80, 2002
Fig. 1. Nomenclature of the Salen ligand precursors used herein.
Scheme 1.
atoms. However, only the desired products L[BCl2]2 (1–5)
were formed. The presence of the chelate apparently stabi-
lizes the dihalide derivative relative to the other possibilities.
shows strong B-Cl stretches between 697–743 cm–1. In the
mass spectrum, the compounds show the parent ion with the
isotope pattern appropriate for four chlorines and two
borons. The most abundant peak for the compounds is the
parent ion minus chlorine with the correct isotope pattern for
three chlorines and two borons.
1
The H NMR data for 1–5 contain two singlets for the t-
Bu-Ph groups in the range ꢀ: 1.22–1.45 ppm. There are mul-
tiple CH2 peaks corresponding to the backbone protons from
the ligand ranging from ꢀ: 1.55–4.62 ppm depending on
ligand type. There is one imine singlet for each compound in
the range ꢀ: 8.19–8.52 ppm. These values decrease with in-
creasing backbone length. Thus, the most shielded shift
(8.2 ppm) is associated with 4 and 5 and the less shielded
shift at 8.5 ppm is associated with 1. This might indicate a
slight increase in nitrogen basicity for electron releasing
“carbon rich” ligands and a moderate decrease in basicity
for the “carbon poor” 1, with a comparatively lower induc-
tive effect. The 13C NMR data also supports this trend. The
chemical shift for the C=N group for 1–5 (166.7–
163.4 ppm) decreases with the increase in the backbone
length. The effect is more distinct between 1 (166.7 ppm)
and 2 (164.9 ppm) than between 4 (163.7 ppm) and 5
(163.4 ppm). Thus, the inductive effect on the C=N is fur-
ther evident when the backbone is increased from two car-
bons to three carbons rather than five carbons to six carbons.
The 11B NMR shows broad single peaks ranging from ꢀ:
5.99–6.39 ppm with w1/2 ranging from 28.2–56.7 Hz, which
are in the region for tetrahedral boron (25). The IR data
The structure of 2 (Fig. 2) was determined by X-ray crys-
tallography. The geometry around the two boron atoms is
slightly distorted from a tetrahedral geometry. Other Salen
boron derivatives also show this distortion (9). The bite an-
gles of the ligand on the boron atoms (N-B-O) are 110.1(4)°
and 111.8(4)° (Table 1). These are slightly larger than other
Salen-supported boron systems such as salenN3H[B(OMe)2]2,
which has an angle of 105.9(3)° (10). This deviation is in
keeping with an increased sp hybridization in the N,O bonds
and more obtuse angles with these atoms for 2 resulting
from an increase in p character for the B—Cl bonds by com-
parison to B—OMe bonds (26). The (N-B-O) angles are sig-
nificantly larger than the (N-Al-O) angle in salben(t-
Bu)[AlMeCl]2 (96.0(4)°) and the (N-Ga-O) angle in
salphen(t-Bu)[Ga(Et)2]2 (92.5(2)°) (5). Thus, the angle de-
creases as the atoms increase in size, and displaces further
“out” of the chelate. The B—Cl bond lengths are 1.849(5) Å,
1.855(5) Å, 1.841(5) Å, and 1.907(5) Å. These are compara-
ble to a similar Schiff base compound, dichloro-[2-(1-imino-
2,2,2-trichloroethyl)-4-methoxyphenoxido-O,N]boron, which
© 2002 NRC Canada

Keizer et al.
1465
Fig. 2. Crystal structure of salpen(t-Bu)[BCl2]2 (2).
Fig. 3. Bimetallic (a) and monometallic (b and c) metal compounds with Salen ligands.
Table 1. Selected bond lengths (Å) and angles (°) for compound 2.
Table 2. Percent dealkylation of trimethylphosphate.
% Conversiona
30 min
% Conversiona
24 h
Bond
lengths
L[BCl2]2
(Å)
Bond angles
(°)
B(1)—O(1)
B(1)—N(1)
B(1)—Cl(1)
B(1)—Cl(2)
C(1)—N(1)
B(2)—O(2)
B(2)—N(4)
B(2)—Cl(3)
B(2)—Cl(4)
C(2)—N(2)
1.422(5)
1.561(5)
1.849(5)
1.855(5)
1.295(4)
1.418(5)
1.548(5)
1.907(5)
1.841(5)
1.294(4)
O(1)-B(1)-N(1)
O(1)-B(1)-Cl(1)
N(1)-B(1)-Cl(1)
O(1)-B(1)-Cl(2)
N(1)-B(1)-Cl(2)
Cl(1)-B(1)-Cl(2)
O(2)-B(2)-N(2)
O(2)-B(2)-Cl(4)
N(2)-B(2)-Cl(4)
O(2)-B(2)-Cl(3)
N(2)-B(2)-Cl(3)
Cl(4)-B(2)-Cl(3)
110.1(4)
108.2(3)
109.7(3)
111.7(3)
106.5(3)
110.6(3)
111.8(4)
109.1(3)
111.0(3)
110.5(3)
104.9(3)
109.4(2)
1
2
3
4
5
14
20
11
42
7
45
32
53
62
47
aYields were calculated from the amount of MeCl produced to the
1
amount of trimethylphosphate remaining in the H NMR.
One unique aspect of these compounds (Fig. 3(a)) is that
there are no corresponding transition metal derivatives.
Rather, transition metals adopt fully chelated five-coordinate
and more often six-coordinate complexes with the Salen lig-
ands (Figs. 3(b) and 3(c)) (1). These ligands are very versatile
in the fact that the “backbone” of the ligand may be altered.
For instance, the length of the backbone may be increased to
the point that binding to a single metal is ineffectual. Thus,
the existence of 1–5 may indicate the possibility of isolating
transition metals of the form L[MX2]2.
has B—Cl bonds lengths of 1.855(7) Å and 1.841(7) Å (27).
A noticeable trend in the length of the NJB dative bond oc-
curs with the exchange of the substituents on the boron atom
(28). The NJB lengths for 2 are 1.561(5) Å and 1.548(5) Å.
These are shorter than the NJB bond length of
salen[B(OMe)2]2 (1.615(2) Å) (9). An inverse relationship
exists between the lengths of the C=N and NJB bonds.
Where the NJB bond shortens the C=N bond lengthens.
The C=N bond for 2 is 1.295(4) Å which is longer than that
of the borate C=N bond (1.288(2) Å). The C=N and NJB
bond lengths of 2 compare closely to those in the boron bro-
Demethylation of trimethylphosphate with compounds
1–5
It is known that boron trichloride will demethylate aryl
ethers (29). Nevertheless, it has been found that BCl3 alone
is ineffective towards the demethylation of trimethylphos-
phate. Compounds (1–5), however, are capable of demethyl-
ating trimethylphosphate (Table 2). When compounds 1–5
mine derivative salben(t-Bu)[BBr2]2 (1.295(4)
1.539(5) Å, respectively) (23).
Å and
© 2002 NRC Canada

1466
Can. J. Chem. Vol. 80, 2002
Table 3. Crystal structure data.
cooled under nitrogen. All air-sensitive manipulations were
conducted using standard bench top inert-atmosphere tech-
niques in conjunction with an inert-atmosphere glove box.
The ligand precursors (30) salen(t-Bu)H2, salpen(t-Bu)H2,
salben(t-Bu)H2, salpten(t-Bu)H2, and salhen(t-Bu)H2 were
synthesized according to the literature procedure. Salen(t-
Bu)[B(OMe)2]2, salpen(t-Bu)[B(OMe)2]2, salben(t-Bu)[B(OMe)2]2,
salpten(t-Bu)[B(OMe)2]2, and salhen(t-Bu)[B(OMe)2]2 were
prepared as reported previously (9). NMR data (1H, 11B)
were obtained on JEOL-GSX-400 and 200 MHz instru-
Salpen(t-Bu)[BCl2]2 (2)
Pale yellow, plate
C33H48B2Cl4N2O2·(1/2)C7H8
714.22
145(1)
Triclinic
P-1
9.086(3)
14.604(4)
14.947(4)
Color, shape
Chemical formula
Formula weight
Temperature (K)
Crystal system
Space group
a (Å)
b (Å)
c (Å)
ꢁ (°)
1
ments. Chemical shifts are reported relative to SiMe4 for H
and 13C and relative to BF3·Et2O in CDCl3 for 11B and are in
ppm. Infrared data were recorded as KBr pellets on a Mathe-
son Instruments 2020 Galaxy Series Spectrometer and are
reported in cm–1. EI (positive) (direct probe) spectra were
acquired on a Kratos Concept IH at 70 eV. Elemental analy-
ses were obtained on Vario EL III Elementar. X-ray data
for 2 were obtained on a Nonius CCD unit employing
Mo Kꢁ radiation.2 The structures were refined using the
Siemens software package SHELXTL 4.0. All of the non-
hydrogen atoms were refined anisotropically. The hydrogen
atoms were put into calculated positions. Absorption correc-
tions were not employed. Further details of the structure
analyses are given in Table 3.
84.29(2)
81.62(2)
89.24(2)
1952.4(10)
ꢂ (°)
ꢃ (°)
Volume (Å3)
Z
2
Dcalcd. (mg m–3)
Absorption coefficient (mm–1)
Crystal size (mm)
Diffractometer, scan
ꢄ range for data collection (°)
Reflections measured
Independent reflections
Data/restraints/parameters
Goodness of fit on F2
Final R indices [I > 2ꢅ(I)]
R indices (all data)
1.215
0.336
0.12 × 0.10 × 0.04
Nonius CCD
1.38–22.50
10 240
5122 (Rint = 0.0984)
5122/414/424
1.046
R1 = 0.0700, wR2 = 0.1006
R1 = 0.1409, wR2 = 0.1172
Salen(t-Bu)[BCl2]2 (1)
To a stirring solution of salen(t-Bu)[B(OMe)2]2 (2.5 g,
3.93 mmol) in toluene (75 mL) was added 1M BCl3 in
heptane (7.8 mL, 7.80 mmol). The reaction mixture was
stirred for 24 h. The solution was concentrated to 5 mL, fil-
tered, and dried. Yield: 2.41g (94%); mp 314–320°C (de-
composition temperature (dec.)). IR (KBr pellet) (cm–1):
2962 (s), 2905 (m), 2862 (w), 1627 (s), 1622 (m), 1573 (m),
1456 (m), 1427 (w), 1359 (w), 1310 (w), 1258 (m), 1210
(w), 1138 (w), 1026 (s), 995 (w), 917 (m), 869 (m), 769 (w),
470 (m), 706 (vs). 1H NMR (CDCl3) ꢀ: 1.22 (s, 18H, C(CH3)3),
1.45 (s, 18H, C(CH3)3), 4.62 (br s, 4H, NCH2), 7.10 (d, 2H,
C6H2), 7.73 (d, 2H, C6H2), 8.52 (s, 2H, N=CH) 13C NMR
(CDCl3) ꢀ: 29.3 (C(CH3)3), 31.1 (C(CH3)3), 34.4 (NCH2),
35.1 (NCH2), 54.5 (C(CH3)3), 115.6 (Ph), 126.2 (Ph), 135.7
(Ph), 139.7 (Ph), 144.2 (Ph), 154.7 (Ph), 166.7 (N=CH).
11B NMR (CDCl3) ꢀ: 6.21 (w1/2 = 43.9 Hz). MS (%): 654
([M]+, 5), 617 ([M – Cl], 100), 582 ([M – 2Cl], 15), 547
([M – 3Cl], 55). Anal. calcd. for B2C32H46N2O2Cl4: C 58.87,
H 7.11, N 4.29; found: C 58.52, H 7.18, N 4.20.
are added to a stoichiometric amount of trimethylphosphate,
methyl chloride is produced. However, these species are less
reactive than the boron bromide analogue, salpen(t-
Bu)[BBr2]2 (23). For example, compound 2 demethylates
20% of the trimethylphosphate within 30 min whereas
salpen(t-Bu)[BBr2]2 demethylates 89% of the trimethyl-
phosphate within 30 min. This heightened activity may be
explained by the fact that the B—Cl bond is less labile than
the B—Br bond. In demonstration of this, it has been found
that THF does not displace the chloride from 2 as readily as
in the boron bromide compound, which forms an in situ cat-
ion (23). By analogy then, trimethylphosphate does not dis-
place the chloride as well as bromide resulting in a decrease
in dealkylation efficiency of the boron chloride compared
with the boron bromide chelate. The bromide derivative can
be made catalytic for the dealkylation of a wide range of
phosphate esters, including trimethylphosphate, by the addi-
tion of BBr3 (23). In this process it was not necessary to have
two connected sites. This was confirmed by using a mono-
metallic boron compound under the same conditions.
Salpen(t-Bu)[BCl2]2 (2)
To a stirring solution of salpen(t-Bu)[B(OMe)2]2 (1.0 g,
1.54 mmol) in toluene (50 mL) was added 1M BCl3 in
heptane (3.1 mL, 3.10 mmol). The reaction mixture was
stirred for 24 h. The solvent was removed and washed with
5 mL of hexanes. Filtration and vacuum drying afforded
salpen(t-Bu)[BCl2]2. Yield: 0.85g (83%); mp 234°C. IR
(KBr pellet) (cm–1): 2963 (s), 2862 (w), 1631 (s), 1569 (m),
1557 (m), 1454 (m), 1429 (w), 1394 (w), 1364 (m), 1346
Experimental
General remarks
All glassware was rigorously cleaned and dried in an oven
at 130°C for 24 h prior to use. They were assembled hot and
2 Supplementary data may be purchased from the Depository of Unpublished Data, Document Delivery, CISTI, National Research Council
Canada, Ottawa, ON K1A 0S2, Canada (http://www.nrc.ca/cisti/irm/unpub_e.shtml for information on ordering electronically). CCDC
174675 contain the supplementary data for this paper. These data can be obtained, free of charge, via www.ccdc.cam.ac.uk/conts/retriev-
ing.html (or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge, U.K.; fax +44 1223 336033; or de-
posit@ccdc.cam.ac.uk).
© 2002 NRC Canada

Keizer et al.
1467
(w), 1259 (m), 1223 (m), 1190 (w), 1115 (m), 1018 (s), 981
(w), 915 (w), 876 (m), 769 (m), 697 (s), 642 (m). H NMR
IR (KBr pellet) (cm–1): 2952 (s), 2904 (w), 2862 (w), 1632
(s), 1573 (m), 1458 (m), 1433 (w), 1359 (w), 1295 (w), 1254
(m), 1215 (w), 1079 (w), 1010 (m), 974 (w), 847 (m), 771
1
(CDCl3) ꢀ: 1.29 (s, 18H, C(CH3)3), 1.43 (s, 18H, C(CH3)3),
2.75 (m, 2H, CH2), 4.09 (m, 4H, NCH2), 7.12 (d, 2H, C6H2),
7.73 (d, 2H, C6H2), 8.38 (s, 2H, N=CH). 13C NMR (CDCl3)
ꢀ: 29.6 (C(CH3)3), 30.0 (CH2), 31.4 (C(CH3)3), 34.6
(NCH2), 35.3 (NCH2), 54.8 (C(CH3)3), 115.7 (Ph), 126.2
(Ph), 135.4 (Ph), 139.8 (Ph), 144.2 (Ph), 154.7 (Ph), 164.9
(N=CH). 11B NMR (CDCl3) ꢀ: 6.05 (w1/2 = 46.7 Hz). MS
(%): 668 ([M]+, 2), 631 ([M – Cl], 100). Anal. calcd. for
B2C33H48N2O2Cl4: C 59.44, H 7.26, N 4.20; found: C 60.08,
H 7.82, N 3.96.
1
(m), 712 (s), 641 (w). H NMR (CDCl3) ꢀ: 1.27 (s, 18H,
C(CH3)3), 1.43 (s, 18H, C(CH3)3), 1.55 (m, 4H, CH2), 2.02
(m, 4H, CH2), 3.91 (m, 4H, NCH2), 7.18 (d, 2H, C6H2), 7.68
(d, 2H, C6H2), 8.19 (s, 2H, N=CH). 13C NMR (CDCl3) ꢀ:
25.7 (CH2), 29.5 (C(CH3)3), 31.1 (C(CH3)3), 34.3 (NCH2),
35.0 (NCH2), 54.4 (C(CH3)3), 125.2 (Ph), 125.6 (Ph), 128.1
(Ph), 129.0 (Ph), 134.6 (Ph), 154.6 (Ph), 163.4 (N=CH).
11B NMR (CDCl3) ꢀ: 6.39 (w1/2 = 28.2 Hz). MS (%): 673
([M – Cl], 100), 658 ([M – Cl – Me], 10), 638 ([M – 2Cl],
50). Anal. calcd. for B2C36H54N2O2Cl4: C 60.99, H 7.68,
N 3.95; found: C 61.40, H 8.04, N 3.66.
Salben(t-Bu)[BCl2]2 (3)
To a stirring solution of salben(t-Bu)[B(OMe)2]2 (0.5 g,
0.75 mmol) in toluene (50 mL) was added 1M BCl3 in
heptane (1.5 mL, 1.50 mmol). The reaction mixture was
stirred for 24 h. The solution was concentrated to 5 mL,
filtered, and dried. Yield: 0.41g (81%); mp 316–318°C
(dec.). IR (KBr pellet) (cm–1): 2949 (s), 2893 (w), 2862 (w),
1631 (s), 1574 (m), 1470 (w), 1405 (w), 1361 (w), 1254 (m),
1219 (m), 1204 (w), 1095 (w), 1018 (m), 1008 (m), 872 (s),
Dealkylation of the trimethylphosphate
In an NMR tube, trimethylphosphate was added to an
equimolar solution of the compound (1–5) in CDCl3 and
held at room temperature for 30 min and 24 h. The reaction
1
was monitored by H NMR (Table 2).
Addition of a Lewis base
1
In an NMR tube, 5 equiv of THF were added to a solution
771 (m), 743 (m), 705 (m), 641 (w). H NMR (CDCl3) ꢀ:
of 2 in CDCl3. 11B NMR (CDCl3) ꢀ: 6.04 (w1/2 = 52.6 Hz).
1.22 (s, 18H, C(CH3)3), 1.41 (s, 18H, C(CH3)3), 2.17 (m,
4H, CH2), 4.03 (m, 4H, NCH2), 7.20 (d, 2H, C6H2), 7.70 (d,
2H, C6H2), 8.21 (s, 2H, N=CH). 13C NMR (CDCl3) ꢀ: 26.7
(CH2), 29.6 (C(CH3)3), 31.1 (C(CH3)3), 34.2 (NCH2), 35.0
(NCH2), 52.5 (C(CH3)3), 125.3 (Ph), 125.9 (Ph), 128.2 (Ph),
129.0 (Ph), 137.8 (Ph), 154.5 (Ph), 164.2 (N=CH). 11B NMR
(CDCl3) ꢀ: 5.99 (w1/2 = 49.5 Hz). MS (%): 681 ([M]+, 2),
645 ([M – Cl], 100), 610 ([M – 2Cl], 20). Anal. calcd. for
B2C34H50N2O2Cl4: C 59.98, H 7.41, N 4.12; found: C 61.35,
H 7.36, N 4.01.
Conclusion
A range of chelated boron compounds have been synthe-
sized and fully characterized. They demonstrate that further
derivatization of boron alkoxide compounds with Salen are
possible and that some are active in the dealkylation of
trimethylphosphate. It has been demonstrated that 1–5 are
inefficient dealkylating compounds by comparison to the
bromide analogues (23). Future work in this area entails in-
creasing the activity of the boron chloride compounds and
broadening their use as Lewis acid activators.
Salpten(t-Bu)[BCl2]2 (4)
To a stirring solution of salpten(t-Bu)[B(OMe)2]2 (0.68 g,
1.00 mmol) in toluene (50 mL) was added 1M BCl3 in
heptane (2.0 mL, 2.0 mmol). The reaction mixture was
stirred for 24 h. The solution was concentrated to 5 mL, fil-
tered, and dried. Yield: 0.64g (98%); mp 261–262°C (dec.).
IR (KBr pellet) (cm–1): 2961 (s), 2869 (w), 1630 (s), 1575
(m), 1474 (m), 1437 (m), 1395 (w), 1363 (m), 1251 (m),
1217 (w), 1190 (w), 1135 (w), 1078 (m), 1025 (m), 914 (m),
Acknowledgements
This work was supported by the National Science Founda-
tion NSF-CAREER award (CHE 9816155). L.J.D. was sup-
ported by the National Science Foundation Research
Experiences for Undergraduates (NSF-REU) program (CHE
-0097668) in the summer of 2001. NMR instruments used in
this research were obtained with funds from the Chemical
Research Instrumentation Fund (CRIF) program of the
National Science Foundation (CHE 997841) and from the
Research Challenge Trust Fund of the University of Kentucky.
1
8749 (m), 771 (m), 731 (s), 644 (w). H NMR (CDCl3) ꢀ:
1.28 (s, 18H, C(CH3)3), 1.45 (s, 18H, C(CH3)3), 1.59 (m,
2H, CH2), 2.19 (m, 4H, CH2), 3.98 (m, 4H, NCH2), 7.19 (d,
2H, C6H2), 7.69 (d, 2H, C6H2), 8.19 (s, 2H, N=CH).
13C NMR (CDCl3) ꢀ: 23.4 (CH2), 29.2 (C(CH3)3), 29.5
(CH2), 31.2 (C(CH3)3), 34.3 (NCH2), 35.0 (NCH2), 54.2
(C(CH3)3), 115.3 (Ph), 125.8 (Ph), 134.7 (Ph), 139.5 (Ph),
143.7 (Ph), 154.2 (Ph), 163.7 (N=CH). 11B NMR (CDCl3) ꢀ:
5.90 (w1/2 = 37.6 Hz). MS (%): 696 ([M]+, 5), 659 ([M – Cl],
100), 624 ([M – 2Cl], 20). Anal. calcd. for B2C35H52N2O2Cl4:
C 60.49, H 7.55, N 4.03; found: C 60.48, H 8.56, N 3.82.
References
1. M.J. Harvey and D.A. Atwood. Chem. Rev. 101, 37 (2001).
2. L. Canali and D.C. Sherrington. Chem. Soc. Rev. 28, 85 (1999).
3. S.J. Dzugan and V.L. Goedken. Inorg. Chem. 25, 2858 (1986).
4. W.-H. Leung, E.Y.Y. Chan, E.K.F. Chow, I.D. Williams, and
S.-M. Peng. J. Chem. Soc. Dalton Trans. 1229 (1996).
5. M.A. Van Aelstyn, T.S. Keizer, D.L. Klopotek, S. Liu,
M. Munoz-Hernandez, P. Wei, and D.A. Atwood. Organo-
metallics, 19, 1796 (2000).
Salhen(t-Bu)[BCl2]2 (5)
To a stirring solution of salhen(t-Bu)[B(OMe)2]2 (1.0 g,
1.46 mmol) in toluene (50 mL) was added 1M BCl3 in
heptane (2.9 mL, 2.92 mmol). The reaction mixture was
stirred for 24 h. The solution was concentrated to 5 mL, fil-
tered, and dried. Yield: 0.91g (91%); mp 302–304°C (dec.).
6. M.S. Hill and D.A. Atwood. Eur. J. Inorg. Chem. 67 (1998).
7. D.A. Atwood, J.A. Jegier, and D. Rutherford. Bull. Chem.
Soc. Jpn. 70, 2093 (1997).
© 2002 NRC Canada

1468
Can. J. Chem. Vol. 80, 2002
8. M.S. Hill and D.A. Atwood. Main Group Chem. 2, 191 (1998).
9. P. Wei and D.A. Atwood. Inorg. Chem. 37, 4934 (1998).
10. P. Wei, D.A. Atwood, and T.S. Keizer. Inorg. Chem. 38, 3914
(1999).
19. W.H. Chapman and R. Breslow. J. Am. Chem. Soc. 117, 5462
(1995).
20. P. Molenveld, S. Kapsabelis, J.F.J. Engbersen, and D.N. Reinhoudt.
J. Am. Chem. Soc. 119, 2948 (1997).
11. B.N. Ghose. Synth. React. Inorg. Met.-Org. Chem. 16, 1383
(1986).
12. D. Agustin, G. Rima, H. Gornitzka, and J. Barrau. J. Organomet.
Chem. 592, 1 (1999).
13. M. Sanchez, T.S. Keizer, S. Parkin, H. Hopfl, and D.A Atwood.
J. Organomet. Chem. 654, 36 (2002).
14. P. Hendry and A.M. Sargeson. Prog. Inorg. Chem. 38, 201
(1990).
15. D.R. Jones, L.F. Lindoy, and A.M. Sargeson. J. Am. Chem.
Soc. 106, 7807 (1984).
16. D.H. Vance and A.W. Czarnik. J. Am. Chem. Soc. 115, 12 165
(1993).
21. K.P. McCue and J.R. Morrow. Inorg. Chem. 38, 6136 (1999).
22. P. Scrimin, G. Ghirlanda, P. Tecilla, and R. A. Moss.
Langmuir, 12, 6235 (1996).
23. T.S. Keizer, L.J. Depue, S. Parkin, and D.A. Atwood. J. Am.
Chem. Soc. 124, 1864 (2002).
24. E. Wiberg and W.Z. Sutterlin. Anorg. Allg. Chem. 222, 92
(1935).
25. R.G. Kidd. In NMR of newly accessible nuclei. Vol. 2. Aca-
demic Press. 1983.
26. H.A. Bent. J. Chem. Educ. 37, 616 (1960).
27. F. Bigi, R. Maggi, G. Sartori, G. Casnati, and G. Bocelli.
Gazz. Chim. Ital. 122, 283 (1992).
17. N.V. Kaminskaia, C. He, and S.J. Lippard. Inorg. Chem. 39,
3365 (2000).
18. M. Yamami, H. Furutachi, T. Yokoyama, and H. Okawa. Inorg.
Chem. 37, 6832 (1998).
28. H. Hopfl. J. Organomet. Chem. 581, 129 (1999).
29. B.C. Ranu and S. Bhar. Org. Prep. Proced. Int. 28, 371 (1996).
30. L. Deng and E.N. Jacobsen. J. Org. Chem. 57, 4320 (1992).
© 2002 NRC Canada