Mononuclear Schiff base boron halides: Synthesis, characterization, and dealkylation of trimethyl phosphate

Article abstract of DOI:10.1021/ic0607890

A series of mononuclear boron halides of the type LBX₂ [LH = N-phenyl-3,5-di-tert-butylsalicylaldimine, X = Cl (2), Br (3)] and LBX [LH ₂ = N-(2-hydroxyphenyl)-3,5-di-tert-butylsalicylaldimine, X = Cl (7), Br (8); LH₂ = N-

Full text of DOI:10.1021/ic0607890

Inorg. Chem. 2006, 45, 9213−9224
Mononuclear Schiff Base Boron Halides: Synthesis, Characterization,
and Dealkylation of Trimethyl Phosphate
Amitabha Mitra, Lauren J. DePue, Jeffrey E. Struss, Bijal P. Patel, Sean Parkin, and
David A. Atwood*
Department of Chemistry, UniVersity of Kentucky, Lexington, Kentucky 40506-0055
Received May 9, 2006
A series of mononuclear boron halides of the type LBX2 [LH
(2), Br (3)] and LBX [LH2 N-(2-hydroxyphenyl)-3,5-di-tert-butylsalicylaldimine, X
hydroxyethyl)-3,5-di-tert-butylsalicylaldimine, X Cl (9), Br (10); and LH2
butylsalicylaldimine, X Cl (11), Br (12)] were synthesized from their borate precursors LB(OMe)2 (1) (LH
N-phenyl-3,5-di-tert-butylsalicylaldimine) and LB(OMe) [LH2 N-(2-hydroxyphenyl)-3,5-di-tert-butylsalicylaldimine
)
N-phenyl-3,5-di-tert-butylsalicylaldimine, X
Cl (7), Br (8); LH2
N-(3-hydroxypropyl)-3,5-di-tert-
)
N-(2-
Cl
)
)
)
)
)
)
)
)
(4), N-(2-hydroxyethyl)-3,5-di-tert-butylsalicylaldimine (5), N-(3-hydroxypropyl)-3,5-di-tert-butylsalicylaldimine (6)]. The
boron halide compounds were air and moisture sensitive, and upon hydrolysis, compound 7 resulted in the oxo-
bridged compound 13 that contained two seven-membered boron heterocycles. The boron halide compounds
dealkylated trimethyl phosphate in stoichiometric reactions to produce methyl halide and unidentified phosphate
materials. Compounds 8 and 12 were found to be the most effective dealkylating agents. On reaction with tert-
butyl diphenyl phosphinate, compound 8 produced a unique boron phosphinate compound LB(O)OPPh2 (14)
1
containing a terminal phosphinate group. Compounds 1
EA, and MP. Compounds 5, 6, and 11
−
14 were characterized by H, 13C, 11B, 31P NMR, IR, MS,
−
14 also were characterized by single-crystal X-ray diffraction.
Introduction
substituted anthracene,5 polysaccharides,6 L-cysteine,7 ni-
troles,8,9 tropolonates,10 and salicylaldimines.11
Boron halides have been used extensively over the years
in various organic syntheses, such as ester ring closure1 and
Friedel-Crafts alkylations.2 However, boron trihalides are
very reactive and are difficult to handle. The use of chelated
boron compounds could help overcome this problem. One
advantage of using chelated boron complexes rather than
simple boron Lewis acids (e.g., BCl3) is in the ability to tune
their structure and properties by varying the constituents in
the ligand environments, for example the size of the chelate
rings and their substituents. Schiff base boron compounds
have been studied recently for their possible applications in
catalysis. Some of the recent examples of mononuclear Schiff
base compounds include â-diketonates,3 â-diketiminate,4
Organophosphate esters are active components of nerve
agents and pesticides. Decontamination of organophosphate
nerve gases is required in battle fields, laboratories, storage,
and destruction sites. Examples of some nerve gas agents
and pesticides are shown in Figure 1. All of these compounds
possess a P-O-C linkage (the phosphate-ester linkage) in
their structure. Although extensive research is being carried
out on phosphate ester cleavage using various metal com-
pounds in models of the biological phosphate hydrolysis,12-14
(5) Yamashita, M.; Kamura, K.; Yamamoto, Y.; Akiba, K.-Y. Chem.s
Eur. J. 2002, 8, 2976-2979.
(6) Miyazaki, Y.; Yoshimura, K.; Miura, Y.; Sakashita, H. I.; Katsutoshi.
Polyhedron 2003, 22, 909-916.
(7) Gonzalez, A.; Granell, J.; Piniella, J. F.; Alvarez-Larena, A. Tetra-
hedron 1998, 54, 13313-13322.
* To whom correspondence should be addressed. E-mail: datwood@
uky.edu.
(8) Kliegel, W.; Metge, J.; Rettig, S. J.; Trotter, J. Can. J. Chem. 1998,
76, 1082-1092.
(1) Grieco, P. A.; Hiroi, K.; Reap, J. J.; Noguez, J. A. J. Org. Chem.
1975, 40, 1450-1453.
(9) Kliegel, W.; Metge, J.; Rettig, S. J.; Trotter, J. Can. J. Chem. 1998,
76, 389-399.
(2) Olah, G. Friedel-Crafts and Related Reactions; Interscience: New
York, 1963; Vol. 4.
(10) Hopfl, H.; Hernandez, N. P.; Lima, S. R.; Santillan, R. F.; Farfan, N.
Heteroat. Chem. 1998, 9, 359-368.
(3) Reutov, V. A.; Gukhman, E. V.; Kafitulova, E. Russ. J. Gen. Chem.
2003, 73, 1441-1444.
(4) Qian, B.; Baek, S. W.; Smith, M. R., III. Polyhedron 1999, 18, 2405-
2414.
(11) Wei, P.; Atwood, D. A. Inorg. Chem. 1998, 37, 4934-4938.
(12) Chin, J. Curr. Opin. Chem. Biol. 1997, 1, 514-521.
(13) Bashkin, J. K. Curr. Opin. Chem. Biol. 1999, 3, 752-758.
10.1021/ic0607890 CCC: $33.50
Published on Web 10/14/2006
© 2006 American Chemical Society
Inorganic Chemistry, Vol. 45, No. 23, 2006 9213

Mitra et al.
atom makes the P-O-R bonds susceptible to nucleophilic
attack by the halide anion (Figure 2b). The process could
be made catalytic by conducting the reaction in the presence
of excess BBr3.19,21
The effectiveness of binuclear boron Schiff base halide
compounds for the dealkylation of organophosphate esters
opened up the possibility of a mild soft route for dealkylation
of organophosphates. This finding was significant in the wake
of recent concern for organophosphate nerve agent and
pesticide destruction and decontamination.23-25 To understand
the full utility and scope of this discovery, it is necessary to
study other similar and comparable systems. One preliminary
step is to investigate the use of mononuclear boron Schiff
base compounds in similar reactions. Mononuclear cationic
boron complexes with N-salicylidene-o-aminophenol have
been found to catalyze the polymerization of oxiranes.11
However, these compounds have not been examined in detail
for the dealkylation of phosphates. Previous work indicated
that stoichiometric combinations of LBX2 (LH ) N-(tert-
butyl-3,5-di-tert-butylsalicylaldimine, X ) Br) and trimethyl
phosphate leads to phosphate cleavage.21 A detailed study
of a series of mononuclear boron complexes for phosphate
dealkylation would determine if the presence of two boron
centers in the same compound is necessary for the dealky-
lation.
Figure 1. Structures of various organophosphate nerve gases and
pesticides: (a) sarin gas, (b) VX gas, (c) chloropyrifos, (d) paraoxon, and
(e) parathion.
the use of group 13 compounds in this field is limited. For
example, some phosphate cleavage has been achieved with
organoaluminum reagents15 and aluminum or gallium
amides.16-18 However, these reagents have not been consid-
ered as potential nerve agent or as pesticide decontamination
reagents, probably because of their limited scope or the high
temperature and the long reaction time required. Our research
has focused on using boron and aluminum chelates as
possible organophosphate cleavage agents.19-22 Binuclear
boron halide chelate compounds based on Salen ligands
(Salen ) N,N′-alkylene(or arylene)bis(salicylideneimine))
were shown to dealkylate a wide range of organophosphates
at ambient temperature.19-21 For example, salpen(tBu)[BBr2]2
(salpen(tBu) ) N,N′-propylenebis(3,5-di-tert-butylsalicylide-
neimine)) dealkylates (MeO)3P(O) and (nBuO)3P(O) by 89
and 99%, respectively, in only 30 min.21 This is significant
considering that BCl3 or BBr3 alone is not effective com-
pounds for phosphate dealkylation. In the dealkylation
reaction, RCl or RBr (R ) hydrocarbon residue of the
phosphate) is produced along with a yet unidentified
phosphate material. The active species in this type of reaction
is thought to be a cation formed through the heterolytic
cleavage of a B-X bond (Figure 2a). The cation then
coordinates to the phosphate thereby activating the ester
carbon. This is supported by the ease of formation of this
type of cation by the simple addition of a Lewis base to
L[BX2]2.19 The coordination of the PdO bond to the boron
In this article, the synthesis and full characterization of a
series of mononuclear boron halides of the type LBX and
LBX2 (L ) various Schiff base N,O and N,O,O ligands; X
) Cl, Br) are described. These compounds are shown to be
useful in the dealkylation of organophosphates.
Experimental
General Remarks. All air-sensitive manipulations were con-
ducted using standard benchtop Schlenk line techniques in conjunc-
tion with an inert atmosphere glovebox. All solvents were thor-
oughly dried prior to use. All glassware was cleaned with a base
and an acid wash and then dried in an oven at 130 °C overnight.
The Schiff base ligands N-phenyl-3,5-di-tert-butylsalicylaldimine,
N-(2-hydroxyphenyl)-3,5-di-tert-butylsalicylaldimine, N-(2-hydrox-
yethyl)-3,5-di-tert-butylsalicylaldimine), and N-(3-hydroxpropyl)-
3,5-di-tert-butylsalicylaldimine) were synthesized according to the
literature procedure.26 Nuclear magnetic resonance (NMR) data
were obtained on Varian Gemini-200 and Varian VXR-400
instruments. Chemical shifts were reported relative to SiMe4 for
1H and 13C, BF3‚Et2O for 11B, and 85% H3PO4 for 31P and are
reported in ppm. Infrared (IR) transmission spectra were recorded
at room temperature in a potassium bromide pellet on a Fourier
Transform Magna-IR ESP 560 spectrometer. Elemental analyses
were performed on either a Perkin-Elmer 2400 carbon-hydrogen-
nitrogen (CHN) analyzer or a LECO CHN-2000 analyzer.
(14) Blasko, A.; Bruice, T. C. Acc. Chem. Res. 1999, 32, 475-484.
(15) Kitagawa, Y.; Hashimoto, S.; Iemura, S.; Yamamoto, H.; Nozaki, H.
J. Am. Chem. Soc. 1976, 98, 5030-31.
(16) Pinkas, J.; Wessel, H.; Yang, Y.; Montero, M. L.; Noltemeyer, M.;
Froeba, M.; Roesky, H. W. Inorg. Chem. 1998, 37, 2450-2457.
(17) Pinkas, J.; Chakraborty, D.; Yang, Y.; Murugavel, R.; Noltemeyer,
M.; Roesky, H. W. Organometallics 1999, 18, 523-528.
(18) Pinkas, J.; Loebl, J.; Dastych, D.; Necas, M.; Roesky, H. W. Inorg.
Chem. 2002, 41, 6914-6918.
X-ray data were collected on either a Nonius Kappa-charge-
coupled device (CCD) (compounds 1, 6, 11, 12, and 14; Mo KR
radiation) or a Bruker-Nonius x8 Proteum (compound 13; Cu KR
radiation) diffractometer. All calculations were performed using
the software package SHELXTL-Plus.27-30 The structures were
(19) Keizer, T. S.; De Pue, L. J.; Parkin, S.; Atwood, D. A. J. Am. Chem.
Soc. 2002, 124, 1864-1865.
(20) Keizer, T. S.; De Pue, L. J.; Parkin, S.; Atwood, D. A. Can. J. Chem.
2002, 80, 1463-1468.
(23) Ember, L. Chem. Eng. News 1999, 77, 11.
(24) Ember, L. Chem. Eng. News 2003, 81, 26-27.
(25) Hileman, B. Chem. Eng. News. 2000, 78, 11.
(26) Tas, E.; Kasumov, V. T.; Sahin, O.; Ozdemir, M. Transition Met.
Chem. 2002, 27, 442-446.
(21) Keizer, T. S.; De Pue, L. J.; Parkin, S.; Atwood, D. A. J. Organomet.
Chem. 2003, 40, 103-109.
(22) Mitra, A.; DePue, L. J.; Parkin, S.; Atwood, D. A. J. Am. Chem. Soc.
2006, 128, 1147-1153.
9214 Inorganic Chemistry, Vol. 45, No. 23, 2006

Phosphate Dealkylation with Mononuclear Boron Chelates
Figure 2. (a) Formation of a phosphate-coordinated boron cation. (b) Attack on P-O-R bond by a halide anion.
t
solved by direct methods and successive interpretation of difference
Fourier maps followed by least-squares refinement. All non-
hydrogen atoms were refined anisotropically. The hydrogen atoms
were included using a riding model with isotropic parameters tied
to the parent atom. Crystallographic data were deposited with the
Cambridge Crystallographic Data Center (CCDC reference
numbers: 606640 (1), 606642 (6), 606644 (11), 606643 (12),
606645 (13), and 606641 (14)) and copies of the data can be
obtained free of charge on application to CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK (Fax: +44-1223-336033, e-mail:
deposit@ccdc.cam.ac.uk).
Synthesis of LB(OMe)2 (LH ) N-Phenyl-3,5-di-tert-butyl-
salicylaldimine) (1). To a rapidly stirred solution of N-phenyl-3,5-
di-tert-butylsalicylaldimine (3.00 g, 9.71 mmol) in toluene, B(OMe)3
(6.00 g, 57.69 mmol) was added and refluxed for 16 h. The volatiles
were removed under vacuum and a yellow solid was obtained that
was washed with 20 mL of hexane and dried under vacuum.
Yield: 3.42 g (92%). X-ray quality crystals were grown from a
concentrated toluene solution after slow cooling to -30 °C. mp:
98 °C (dec.). 1H NMR (CDCl3): δ 1.33 (s, 9H, C(CH3)3), 1.48 (s,
9H, C(CH3)3), 3.22 (s, 6H, OCH3), 7.25 (m, 1H, Ph-H), 7.27 (m,
2H, Ph-H), 7.44 (m, 3H, Ph-H), 7.62 (m, 1H, Ph-H), 7.78 (m, 1H,
Ph-H), 8.63 (s, 1H, NdCH). 13C NMR (CDCl3): δ 29.7 (C(CH3)3),
31.7 (C(CH3)3), 34.4 (C(CH3)3), 35.3 (C(CH3)3), 49.9 (OCH3), 118.5
(Ph), 121.4 (Ph), 123.9 (Ph), 126.1 (Ph), 126.7 (Ph), 128.5 (Ph),
129.5 (Ph), 133.5(Ph), 137.2 (Ph), 140.8 (Ph), 148.9 (Ph), 158.5
(Ph), 164.0 (NCH). 11B NMR (CDCl3): δ 2.33 (W1/2 ) 58 Hz).
IR (KBr) ν/ cm-1: 3064w, 2962s, 2903m, 2860m, 1614s, 1575s,
1555w, 1478m, 1464m, 1437m, 1390w, 1360m, 1319w, 1273w,
1248m, 1196m, 1171s, 1130w, 1074w, 1025w, 973w, 903w, 878m,
865s, 823w, 801w, 759s, 728w, 688m. MS electron impact (EI),
positive): 321 (M+, 5%), 350 (M+ - OCH3, 45%), 319 (M+ - 2
OCH3, 10%), 264 (M+ - OCH3 - Bu, 100%). Anal. Calcd for
C23H32O3NB: C 72.44, H 8.46, N 3.67. Found: C 73.61, H 8.72,
N 3.51.
Synthesis of LBCl2 (LH ) N-Phenyl-3,5-di-tert-butylsalicyl-
aldimine) (2). To a rapidly stirred solution of 1 (0.71 g, 1.87 mmol)
in toluene, 1 M BCl3 in heptane (0.68 mL, 0.68 mmol) was added.
The yellow, cloudy mixture was stirred for 13 h. The volatiles were
removed under vacuum. The yellow solid was washed with hexane
and dried under vacuum. Yield: 0.45 g (62%). mp: 255-257 °C
1
(dec.). H NMR (CDCl3): δ 1.32 (s, 9H, C(CH3)3), 1.48 (s, 9H,
C(CH3)3), 7.27 (m, 1H, Ph-H), 7.36 (m, 1H, Ph-H), 7.47 (m, 2H,
Ph-H), 7.66 (m, 2H, Ph-H), 7.78 (m, 1H, Ph-H), 8.29 (s, 1H, Nd
CH). 13C NMR (CDCl3): δ 29.6 (C(CH3)3), 31.3 (C(CH3)3), 34.6
(C(CH3)3), 35.4 (C(CH3)3), 125.2 (Ph), 126.5 (Ph), 129.5 (Ph), 129.7
(Ph), 136.0 (Ph), 144.2 (Ph), 164.2 (NCH). 11B NMR (CDCl3): δ
2.48 (W1/2 ) 57 Hz). IR (KBr) ν/cm-1: 2961s, 2905w, 2869w,
1619s, 1566s, 1555m, 1492w, 1468w, 1392w, 1380w, 1363w,
1254m, 1200m, 1132w, 1015m, 1005m, 918w, 904w, 849m, 762w,
720w, 692m. MS (EI, positive): 390 (M+, 0.5%), 355 (M+ - Cl,
2%), 320 (M+ - 2 Cl, 5%), 309 (M+ - BCl2, 45%), 294 (M+
BCl2 - CH3, 100%). Anal. Calcd for C21H26ONBCl2: C 64.65, H
-
6.72, N 3.59. Found: C 66.11, H 8.44, N 3.51.
Synthesis of LBBr2 (LH ) N-Phenyl-3,5-di-tert-butylsalicyl-
aldimine) (3). To a rapidly stirred solution of 1 (0.48 g, 1.26 mmol)
in toluene, 1 M BBr3 in heptane (0.42 mL, 0.42 mmol) was added
with a syringe. The yellow reaction mixture was stirred for 20 h.
The volatiles were removed under vacuum and the yellow residue
was washed with hexane and dried under vacuum. Yield: 0.45 g
(75%). mp: 284-288 °C (dec.). 1H NMR (CDCl3): δ 1.30 (s, 9H,
C(CH3)3), 1.38 (s, 9H, C(CH3)3), 6.95 (d, 2H, Ph-H), 7.17-7.30
(m, 3H, Ph-H), 7.85 (d, 1H, Ph-H), 7.98 (d, 1H, Ph-H), 9.38 (s,
1H, NdCH). 13C NMR (CDCl3): δ 29.7 (C(CH3)3), 31.4 (C(CH3)3),
34.9 (C(CH3)3), 35.3 (C(CH3)3), 123.4 (Ph), 125.5 (Ph), 128.4 (Ph),
129.3 (Ph), 129.8 (Ph), 130.2 (Ph), 132.8 (Ph), 137.0 (Ph), 138.9
(Ph), 141.6 (Ph), 145.0 (Ph), 153.6 (Ph), 167.7 (NCH). 11B NMR
(CDCl3): δ 2.38 (W1/2 ) 60 Hz). IR (KBr) ν/ cm-1: 2959s, 2901w,
2870w, 1625m, 1594w, 1563s, 1493w, 1469m, 1442w, 1414w,
1381m, 1363w, 1255m, 1203m, 1134w, 1067w, 1030m, 774w,
757w, 690w. MS (EI, positive): 309 (M+ - BBr2, 33%), 294 (M+
(27) Sheldrick, G. M. SHELXS97 and SHELXL97, University of Go¨ttingen,
Germany: Go¨ttingen, Germany, 1997.
(28) Sheldrick, G. M. SHELXTL-plus, Siemens Analytical X-ray Instru-
ments, Inc.: Madison, WI, 1997.
(29) Sheldrick, G. M. SHELXTL, version 5.0; Bruker AXS, Inc.: Madison,
WI, 1998.
(30) Siemens R3m Software, version 4.0; Siemens Analytical X-ray
Instruments, Inc.: Madison, WI, 1990.
Inorganic Chemistry, Vol. 45, No. 23, 2006 9215

Mitra et al.
- BBr2 - CH3, 100%). Anal. Calcd for C21H26ONBBr2: C 52.65,
H 5.47, N 2.92. Found: C 53.00, H 5.15, N 2.85.
2.75 mmol) was added. The reaction mixture was stirred for 13 h.
The golden yellow solution was cannula filtered, and the volatiles
were removed from the filtrate under vacuum to give a yellow solid.
Synthesis of L[B(OMe)] (LH2 ) N-(2-Hydroxyphenyl)-3,5-
di-tert-butylsalicylaldimine) (4). To a rapidly stirred solution of
N-(2-hydroxyphenyl)-3,5-di-tert-butylsalicylaldimine) (3.31 g, 10.21
mmol) in toluene, excess B(OMe)3 (6.50 g, 62.50 mmol) was added
and refluxed for 8 h. The volatiles were removed under vacuum to
yield an orange solid. Yield: 3.06 g (82%). mp: 210 °C (dec.). 1H
NMR (CDCl3): δ 1.30 (s, 9H, C(CH3)3), 1.49 (s, 9H, C(CH3)3),
3.15 (s, 3H, OCH3), 6.86-7.66 (m, 6H, Ph-H), 8.52 (s, 1H,
NdCH). 13C NMR (CDCl3): δ 29.5 (C(CH3)3), 31.2 (C(CH3)3),
34.2 (C(CH3)3), 35.4 (C(CH3)3), 49.7 (OCH3), 114.3 (Ph), 114.7
(Ph), 119.1 (Ph), 125.3 (Ph), 128.2 (Ph), 129.0 (Ph), 131.3 (Ph),
133.0(Ph), 139.8 (Ph), 142.2 (Ph), 150.5 (Ph), 154.6 (Ph), 157.3
(NCH). 11B NMR (CDCl3): δ 5.09. IR (KBr) ν/ cm-1: 2959s,
2905w, 2868w, 1628s, 1556m, 1545m, 1480s, 1419m, 1390m,
1380m, 1362m, 1324s, 1259m, 1202m, 1181s, 1108s, 1039w,
1018m, 1007m, 987m, 886w, 752s. MS (EI, positive): 365 (M+,
11%), 334 (M+ - OCH3, 100%). Anal. Calcd for C22H28O3NB: C
72.34, H 7.73, N 3.83. Found: C 73.20, H 8.33, N 3.60.
1
Yield: 0.96 g (95.0%). mp: 298 °C (dec.). H NMR (CDCl3): δ
1.36 (s, 9H, C(CH3)3), 1.54 (s, 9H, C(CH3)3), 6.97-7.81 (m, 6H,
Ph-H), 8.58 (s, 1H, NdCH). 13C NMR (CDCl3): δ 29.6 (C(CH3)3),
31.2 (C(CH3)3), 34.4 (C(CH3)3), 35.4 (C(CH3)3), 115.0 (Ph), 115.3
(Ph), 120.6 (Ph), 125.8 (Ph), 128.2 (Ph), 129.0 (Ph), 132.0 (Ph),
134.1 (Ph), 140.6 (Ph), 144.1 (Ph), 150.3 (Ph), 153.2 (Ph), 156.3
(NCH). 11B NMR (CDCl3): δ 7.28. IR (KBr) ν/cm-1: 2960s,
2901w, 2869w, 1631s, 1563m, 1549w, 1479s, 1467m, 1424m,
1392m, 1382m, 1363m, 1327m, 1254m, 1202m, 1190s, 1111w,
1031w, 1747m. MS (EI, positive): 286 (M+ - Cl, 100%, 319 (M+
- Cl - O, 15%). Anal. Calcd for C21H25O2NBCl: C 68.23, H
6.82, N 3.79. Found: C 68.75, H 7.65, N 4.04.
Synthesis of L[BBr] (LH2 ) N-(2-Hydroxyphenyl)-3,5-di-tert-
butylsalicylaldimine) (8). To a rapidly stirred solution of 4 (1.00
g, 2.74 mmol) in toluene, excess 1 M BBr3 in heptane (2.78 mL,
2.78 mmol) was added. The reaction mixture was stirred for 13 h.
The solution was concentrated to about one-third of its volume.
The yellow precipitate was cannula filtered and dried under vacuum.
Yield: 0.73 g (64.6%). mp: 234-238 °C (dec.). 1H NMR
(CDCl3): δ 1.34 (s, 9H, C(CH3)3), 1.52 (s, 9H, C(CH3)3), 7.00-
7.83 (m, 6H, Ph-H), 8.81 (s, 1H, NdCH). 13C NMR (CDCl3): δ
29.6 (C(CH3)3), 31.2 (C(CH3)3), 34.4 (C(CH3)3), 35.4 (C(CH3)3),
115.3 (Ph), 118.3 (Ph), 121.3 (Ph), 126.3 (Ph), 128.6 (Ph), 129.0
(Ph), 132.1 (Ph), 134.8 (Ph), 140.7 (Ph), 144.9 (Ph), 150.9 (Ph),
152.8 (Ph), 155.4 (NCH). 11B NMR (CDCl3): δ 6.47 (four-
coordinate boron). IR (KBr) ν/cm-1: 2960s, 2905w, 2869w, 1629s,
1564m, 1549m, 1479s, 1424m, 1392m, 1380m, 1363m, 1328s,
1253m, 1203w, 1189w, 1103w, 1014w, 864w, 769w, 747m, 694w,
664w. MS (EI, positive): 414 (M+, 3%), 334 (M+ - Br, 100%),
318 (M+ - Br - O, 20%). Anal. Calcd for C21H25O2NBBr: C
60.90, H 6.08, N 3.38. Found: C 61.58, H 6.07, N 3.16.
Synthesis of L[B(OMe)] (LH2 ) N-(2-Hydroxyethyl)-3,5-di-
tert-butylsalicylaldimine) (5). To a rapidly stirred solution of N-(2-
hydroxyethyl)-3,5-di-tert-butylsalicylaldimine (3.5 g, 12.6 mmol)
in toluene, B(OMe)3 (4.2 g, 40.8 mmol) was added and refluxed
for 18 h. The volatiles were removed under vacuum, and the yellow
residue was washed with hexane. Yield: 3.2 g (81%). mp: 302-
1
306 °C (dec.). H NMR (CDCl3): δ 1.27 (s, 9H, C(CH3)3), 1.42
(s, 9H, C(CH3)3), 3.17 (s, 3H, OCH3), 3.30-3.48 (m, 2H, NCH2),
3.63-3.86 (m, 2H, OCH2). 7.04 (d, 1H, Ph-H), 7.52 (d, 1H, Ph-
H), 8.30 (s, 1H, NdCH). 13C NMR (CDCl3): δ 29.3 (C(CH3)3),
31.2 (C(CH3)3), 34.1 (C(CH3)3), 35.0 (C(CH3)3), 49.5 (OCH3), 58.9
(NCH2), 59.8 (OCH2), 114.7 (Ph), 125.3 (Ph), 131.9 (Ph), 138.2
(Ph), 140.4, (Ph),157.8 (Ph), 166.8 (NCH). 11B NMR (CDCl3): δ
2.38. IR (KBr) ν/ cm-1: 2954s, 2905w, 2863w, 1644s, 1567w,
1479w, 1462w, 1444w, 1384w, 1360w, 1309w, 1254m, 1210m,
1149s, 1132m, 1017s, 989m, 805w, 774w. MS (EI, positive): 286
(M+ - OCH3, 100%). Anal. Calcd for C18H28O3NB: C 68.15, H
8.90, N 4.42. Found: C 68.25, H 9.18, N 4.23.
Synthesis of L[B(OMe)] (LH2 ) N-(3-Hydroxypropyl)-3,5-
di-tert-butylsalicylaldimine) (6). To a rapidly stirred solution of
N-(3-hydroxypropyl)-3,5-di-tert-butylsalicylaldimine (4.28 g, 14.71
mmol) in toluene, B(OMe)3 (2.00 g, 19.23 mmol) was added and
refluxed for 16 h. The volatiles were removed under vacuum, and
a pale yellow solid was obtained, which was dried under vacuum.
Yield: 4.50 g (92%). mp: 190-192 °C (dec.). 1H NMR (CDCl3):
δ 1.26 (s, 9H, C(CH3)3), 1.43 (s, 9H, C(CH3)3), 1.68-1.86 (m,
1H, CH2), 2.00-2.24 (m, 1H, CH2), 3.23 (s, 3H, OCH3), 3.56-
3.66 (m, 1H, NCH2), 3.92-3.99 (m, 1H, NCH2), 4.09-4.31 (m,
2H, OCH2), 7.03 (d, 1H, Ph-H), 7.53 (d, 1H, Ph-H), 7.99 (s, 1H,
NdCH). 13C NMR (CDCl3): δ 29.4 (C(CH3)3), 30.4 (CH2), 31.2
(C(CH3)3), 34.0 (C(CH3)3), 35.1 (C(CH3)3), 49.7 (OCH3), 54.5
(NCH2), 61.2 (OCH2), 114.8 (Ph), 125.0 (Ph), 132.1 (Ph), 138.7
(Ph), 140.5 (Ph), 157.2 (Ph), 160.7 (NCH). 11B NMR (CDCl3): δ
2.00 (W1/2 ) 140 Hz). IR (KBR) ν/ cm-1: 2955s, 2901m, 2867m,
1661s, 1567m, 1478m, 1448m, 1452m, 1429m, 1392w, 1361m,
1344m, 1307m, 1283w, 1265m, 1244m, 1202m, 1186m, 1153m,
1105s, 1082m, 1039m, 989m, 970m, 923m, 884m, 776w. MS (EI,
positive): 331 (M+, 1%), 300 (M+ - OCH3, 100%). Anal. Calcd
for C19H30O3NB: C 68.89, H 9.13, N 4.23. Found: C 69.55, H
9.28, N 4.31.
Synthesis of L[BCl] (LH2 ) N-(2-hydroxyethyl)-3,5-di-tert-
butylsalicylaldimine) (9). To a rapidly stirred solution of 5 (0.97
g, 3.05 mmol) in toluene, 1 M BCl3 in heptane (1.10 mL, 1.10
mmol) was added. The reaction mixture was stirred for 24 h. Then,
it was cannula filtered and the pale yellow residue was dried under
1
vacuum. mp: >320 °C (dec.). H NMR (CDCl3): δ 1.24 (s, 9H,
C(CH3)3), 1.42 (s, 9H, C(CH3)3), 3.44-3.55 (m, 2H, NCH2), 3.33-
3.44 (m, 2H, OCH2), 7.07 (d, 1H, Ph-H), 7.56 (d, 1H, Ph-H), 8.11
(s, 1H, NdCH). 13C NMR (CDCl3): δ 29.86 (C(CH3)3), 31.4
(C(CH3)3), 34.3 (C(CH3)3), 35.2 (C(CH3)3), 60.5 (NCH2), 61.2
(OCH2), 115.0 (Ph), 125.8 (Ph), 133.7 (Ph), 139.0 (Ph), 141.4 (Ph),
157.2 (Ph), 164.9 (NCH). 11B NMR (CDCl3): δ 2.05 (W1/2 ) 360
Hz). IR (KBr) ν/cm-1: 2960s, 2905w, 2870w, 1640s, 1573m,
1479s, 1444s, 1395m, 1378s, 1363s, 1334m, 1302m, 1283m,
1261m, 1243m, 1214m, 1202m, 1190m, 1138m, 1085m, 1027m,
913w, 879w, 851w, 818w, 802w, 774w. MS (EI, positive): 322
(M+, 1%), (M+ - Cl, 90%). Anal. Calcd for C17H25O2NBCl: C
63.48, H 7.83, N 4.36. Found: C 63.37, H 8.78, N 4.15.
Synthesis of L[BBr] (LH2 ) N-(2-Hydroxyethyl)-3,5-di-tert-
butylsalicylaldimine) (10). To a rapidly stirred solution of 5 (0.54
g, 1.70 mmol) in toluene, 1 M BBr3 in heptane (0.60 mL, 0.60
mmol) was added with a syringe. The clear yellow solution was
stirred for 17 h. The volatiles were removed under vacuum, and
the off-white residue was washed with hexane and dried under
vacuum. Yield: 0.47 g (75%). mp: 228-232 °C (dec.). 1H NMR
(CDCl3): δ 1.32 (s, 9H, C(CH3)3), 1.47 (s, 9H, C(CH3)3), 3.94 (m,
4H, NCH2 and OCH2); 7.17 (d, 1H, Ph-H), 7.59 (d, 1H, Ph-H),
8.25 (s, 1H, NdCH). 13C NMR (CDCl3): δ 29.4 (C(CH3)3), 31.2
(C(CH3)3), 33.2 (C(CH3)3), 35.0 (C(CH3)3), 50.8 (NCH2), 55.0
Synthesis of L[BCl] (LH2 ) N-(2-Hydroxyphenyl)-3,5-di-tert-
butylsalicylaldimine) (7). To a rapidly stirred solution of 4 (1.00
g, 2.74 mmol) in toluene, excess 1 M BCl3 in heptane (2.75 mL,
9216 Inorganic Chemistry, Vol. 45, No. 23, 2006

Phosphate Dealkylation with Mononuclear Boron Chelates
(OCH2), 115.4 (Ph), 125.6 (Ph), 132.2 (Ph), 138.3 (Ph), 140.6, (Ph),
157.8 (Ph), 164.9 (NCH). 11B NMR (CDCl3): δ 2.00 (W1/2 ) 122
Hz). IR (KBr) ν/cm-1: 2958s, 2901w, 2869w, 1644s, 1566m,
1479m, 1469m, 1441m, 1391m, 1378s, 1360m, 1336m, 1304m,
1259m, 1240w, 1203w, 1188m, 1135s, 1042m, 975m, 931w, 877w,
827w, 811w, 775w, 762w. MS (EI, positive): 366 (M+, 30%), 286
(M+ - Br, 55%), 270 (M+ - Br - O, 45%). Anal. Calcd for
C17H25O2NBBr: C 55.77, H 6.88, N 3.83. Found: C 54.98, H 7.36,
N 3.96.
29.8 (C(CH3)3), 31.2 (C(CH3)3), 31.3 (C(CH3)3), 34.3 (C(CH3)3),
35.2 (C(CH3)3), 38.1 (C(CH3)3), 114.9 (Ph), 120.6 (Ph), 121.8 (Ph),
122.0 (Ph), 125.6 (Ph), 126.2 (Ph), 129.6 (Ph), 132.0 (Ph), 133.0
(Ph), 134.2 (Ph), 139.4 (Ph), 141.3 (Ph), 144.9 (Ph), 151.6 (Ph),
159.4 (NCH). 11B NMR (CDCl3): δ 3.19 (W1/2 ) 720 Hz), 7.33
(W1/2 ) 320 Hz). IR (KBr) ν/ cm-1: 2959s, 2909w, 2869w, 1620m,
1586m, 1563m, 1548m, 1486m, 1468m, 1441m, 1414m, 1391m,
1378w, 1362m, 1324w, 1293m, 1263s, 1255s, 1204s, 1187m,
1155m, 1110w, 1016w, 944m, 905m, 749m. MS (EI, positive): 684
(M+, 5%), 334 (M+ - C21H25O3NB, 100%). Anal. Calcd for
C42H50O5NB2: C 73.70, H 7.36, N 4.09. Found: C 73.77, H 7.11,
N 3.62.
Dealkylation of Phosphates. In a typical experiment, the chelate
compound (for 8, 30 mg, 0.07 mmol) was dissolved in 1 mL of
CDCl3 in a glass vial. The solution was transferred to an NMR
tube and trimethyl phosphate (2.83 µL, 0.024 mmol, density 1.197
g/mL) was added with a microsyringe. The mixture was shaken
and monitored by 1H NMR. The percent dealkylation was calculated
from the peak integrations of MeBr produced and the unchanged
phosphate.
Synthesis of L[BCl] (LH2 ) N-(3-hydroxypropyl)-3,5-di-tert-
butylsalicylaldimine) (11). To a rapidly stirred solution of 6 (1.07
g, 3.23 mmol) in toluene, 1 M BBr3 in heptane (1.10 mL, 1.10
mmol) was added. The clear golden-yellow solution was stirred
for 14 h. The volatiles were removed under vacuum, and the yellow
residue was washed with hexane and dried under vacuum. Yield:
0.88 g (81%). X-ray quality crystals were isolated after cooling a
concentrated toluene solution to -30 °C. mp: 192-194 °C (dec.).
1H NMR (CDCl3): δ 1.29 (s, 9H, C(CH3)3), 1.45 (s, 9H, C(CH3)3),
2.02 (q, 2H, CH2), 4.06 (t, 2H, NCH2), 4.24 (t, 2H, OCH2), 7.13
(d, 1H, Ph-H), 7.66 (d, 1H, Ph-H), 7.93 (s, 1H, NdCH). 13C NMR
(CDCl3): δ 28.8 (CH2), 29.4 (C(CH3)3), 31.2 (C(CH3)3), 34.1
(C(CH3)3), 35.1 (C(CH3)3), 53.8 (NCH2), 61.3 (OCH2), 115.4 (Ph),
125.4 (Ph), 133.1 (Ph), 139.2 (Ph), 142.0 (Ph), 155.9 (Ph), 161.3
(NCH). 11B NMR (CDCl3): δ 3.3 (W1/2 ) 166 Hz). IR (KBr) ν/
cm-1: 2960s, 2866w, 1649s, 1572m, 1479m, 1461m, 1441m,
1432w, 1384m, 1365m, 1345m, 1285w, 1265m, 1246w, 1193m,
1164m, 1125w, 1093w, 1024w, 959w, 930w, 872w, 831w, 773w,
758w. MS (EI, positive): 336 (M+, 1%), 300 (M+ - Cl, 100%).
Anal. Calcd for C18H27O2NBCl: C 64.41, H 8.11, N 4.17. Found:
C 65.72, H 6.86, N 4.06.
Synthesis of 14. To a rapidly stirred solution of 8 (0.57 g, 1.56
mmol) in toluene, tert-butyl-diphenylphosphinate (0.41 g, 1.57
mmol) was added. The golden-yellow reaction mixture was refluxed
for 7 h. The volatiles were removed under vacuum, and a yellow
solid was obtained, which was dried under vacuum and washed
1
with hexane. Yield: 0.59 g (68%). mp: 239-240 °C (dec.). H
NMR (CDCl3): δ 1.31 (s, 9H, C(CH3)3), 1.50 (s, 9H, C(CH3)3),
6.64 (m, 1H, Ph-H), 6.86 (m, 1H, Ph-H), 7.14-7.23 (m, 4H, Ph-
H), 7.25-7.39 (m, 4H, Ph-H), 7.44-7.54 (m, 4H, Ph-H), 7.66-
7.79 (m, 2H, Ph-H), 8.57 (s, 1H, NdCH). 13C NMR (CDCl3): δ
29.7 (C(CH3)3), 31.5 (C(CH3)3), 35.7 (C(CH3)3), 38.0 (C(CH3)3),
120.2 (Ph), 128.0 (Ph), 128.2 (Ph), 129.2 (Ph), 131.4 (Ph), 132.8
(Ph), 143.3 (Ph), 157.6 (NCH). 11B NMR (CDCl3): δ 3.57 (W1/2
) 47 Hz). 31P{H} NMR (CDCl3): δ 28.90 (s), δ 33.97 (s). IR
(KBR) ν/cm-1: 2959m, 2909w, 2867w, 1640s, 1564w, 1548w,
1482m, 1440m, 1391m, 1384m, 1365w, 1327m, 1259m, 1212s,
1184m, 1127m, 1082m, 1014s, 994s, 966m, 888w, 750m, 725m,
694m, 544m. MS (EI, positive): 331 (M+, 15%), 334 (M+ - Ph2-
PO2, 45)%), 333 (M+ - Ph2PO2 - H, 100%). Anal. Calcd for
C33H35O4NBP: C 71.88, H 6.40, N: 2.54. Found: C 70.78, H 6.73,
N 1.84.
Synthesis of L[BBr] (LH2 ) N-(3-hydroxypropyl)-3,5-di-tert-
butylsalicylaldimine) (12). To a rapidly stirred solution of 6 (0.69
g, 2.09 mmol) in toluene, 1 M BBr3 in heptane (0.75 mL, 0.75
mmol) was added. The clear yellow solution was stirred for 6 h.
Then, it was concentrated to about one-third of its volume, and
yellow crystals were obtained after cooling at -30 °C overnight.
The crystals were isolated by cannula filtration and dried under
vacuum. Yield: 0.50 g (63% based on the borate). mp: softens at
174 °C and melts at 178-181 °C (dec.). 1H NMR (CDCl3): δ 1.27
(s, 9H, C(CH3)3), 1.42 (s, 9H, C(CH3)3), 2.11 (m, 2H, CH2), 4.31
(s, br, 4H, NCH2 and OCH2), 7.48 (d, 1H, Ph-H), 7.78 (s, br, 1H,
Ph-H), 8.97 (s, 1H, NdCH). 13C NMR (CDCl3): δ 26.3 (CH2),
29.8 (C(CH3)3), 31.4 (C(CH3)3), 34.8 (C(CH3)3), 35.4 (C(CH3)3),
52.3 (NCH2), 63.0 (OCH2), 116.9 (Ph), 127.2 (Ph), 135.9 (Ph),
140.0 (Ph), 145.5 (Ph), 154.5 (Ph), 166.6 (NCH). 11B NMR
(CDCl3): δ 9.7 (W1/2 ) 383 Hz). IR (KBr) ν/ cm-1: 2962s, 2869w,
1638s, 1573s, 1471m, 1459m, 1452m, 1437w, 1386w, 1365m,
1347m, 1285m, 1265m, 1247s, 1196s, 1180m, 1135m, 1097m,
1084m, 1046w, 1000w, 961w, 931w, 874w, 831m, 772m, 755w,
661m, 623m, 607m, 545m. MS (EI, positive): 380 (M+, 5%), 300
(M+ - Br, 100%). Anal. Calcd for C18H27O2NBBr: C 56.87, H
7.16, N 3.69. Found: C 56.04, H 5.91, 3.36.
Results and Discussion
Synthesis of Compounds 1-12. Unlike Schiff base
aluminum compounds (LAlR), the boron chelates (LBR)
cannot be prepared by an alkyl elimination reaction between
the ligand LH2 and BR3 because of the low polarity of the
B-C bond. The common methods for creating boron-ligand
compounds are water elimination using a boronic acid and
alcohol elimination using a borate (represented in the
equations below).31
Hydrolyzed Product (13). Compound 13 was obtained during
the preparation of the halide 7 from the borate 4 by adventitious
exposure to moisture. To a rapidly stirred solution of 4 (1.00 g,
2.74 mmol) in toluene, 1 M BCl3 in heptane (1.00 mL, 1.00 mmol)
was added. The deep brown solution was stirred for 18 h. The
volatiles were removed under vacuum to obtain a yellow solid. The
solid was recrystallized from dichloromethane to give yellow X-ray
quality crystals of 13. Yield: 0.61 g (33%). mp: 303-305 °C (dec.).
1H NMR (CDCl3): δ 1.24 (s, 9H, C(CH3)3), 1.29 (s, 9H, C(CH3)3),
1.31 (s, 9H, C(CH3)3), 1.45 (s, 9H, C(CH3)3), 6.52-7.73 (m, 12H,
Ph-H), 8.51 (s, 2H, NdCH). 13C NMR (CDCl3): δ 29.5 (C(CH3)3),
LH2 + RB(OH)2 f LBR + 2 H2O
LH2 + B(OR)3 f LBOR + 2 ROH
The boron alkyls arising from the boronic acid reaction
are generally stable, whereas the boron alkoxides formed
(31) Vaultier, M.; Carboni, B. In ComprehensiVe Organometallic Chemistry
II: A ReView of the Literature 1982-1994; Abel, E. W., Stone, F. G.
A., Wilkinson, G., Eds.; Elsevier: Oxford, England, 1995; Vol. 11, p
191.
Inorganic Chemistry, Vol. 45, No. 23, 2006 9217

Mitra et al.
Figure 3. Preparation of compounds 1-12.
from the reaction using a borate could be further derivatized
(e.g., to boron siloxides).32
a higher chemical shift compared to the chlorides. The
presence of only one set of Bu peaks and one imine peak
t
for each compound suggested a symmetric solution state
structure.
Binuclear boron halides of the type L[BX2]2 (X ) Cl, Br)
(L ) salen ligands) can be prepared by the exchange reaction
of the binuclear alkoxides L[B(OMe)2]2 with BX3.19-21 In
the present work, similar reactions were employed to
synthesize mononuclear Schiff base boron halide compounds
from their borate precursors. The borate precursors were
prepared in good yield by alcohol elimination between the
Schiff base salicylidenimine ligand and excess trimethyl
borate under reflux. The byproduct MeOH could be removed
under vacuum to drive the reaction to completion. The
salicylidenimine ligands could be prepared easily by the
condensation reaction between 3,5-di-tert-butyl aldehyde and
the corresponding amines according to the literature proce-
dures.26 The synthetic route used for the preparation of
compounds 1-12 is depicted in Figure 3. Thus the halides
2, 3, and 7-12 were prepared from the corresponding borate
precursors 1 and 4-6. The borate precursors, in turn, were
prepared by refluxing Schiff base ligands and excess tri-
methyl borate in toluene. The borates were converted to the
boron halides by combination with BCl3 or BBr3 at room
temperature. All compounds were isolated by removing the
solvent under vacuum or by precipitation after concentration
and cooling to -30 °C. The byproduct B(OMe)3 was
removed under vacuum. The compounds were pale white to
orange in color.
The 11B NMR spectra showed single peaks at δ 2.33, 5.09,
2.38, and 2.00 ppm for the borate compounds, δ 2.48, 7.28,
2.05, and 3.33 ppm for the chlorides, and δ 2.38, 6.47, 2.00,
and 9.7 ppm for the bromides. These shifts indicate the
presence of four-coordinate boron21 in all of the compounds.
The IR spectra have a νB-N stretch in the region 1000-1042
cm-1 for all of the compounds. The mass spectra (EI) of the
borates 1, 4, 5, and 6 showed peaks corresponding to
molecular ions minus methoxy groups, and this was the most
abundant peak for 4, 5, and 6. Compounds 4, 5, and 6 also
showed molecular ions in low abundance. The chloride
compounds 2, 7, 9, and 11 showed molecular ions minus
the chloride in high abundance. Additionally, 2, 9, and 11
showed molecular ion in low abundance. The bromide
compounds 8, 10, and 12 had molecular ion as well as
molecular ion minus bromide in their spectra. However, 3
showed molecular ion minus the BBr2 group (33%) and also
molecular ion minus BBr2 and CH3 (100%). This indicated
that the EI ionization process was sufficiently strong to
separate a boron fragment from the ligand. This was a rare
occurrence for the Schiff base group 13 compounds, which
are usually not observed to release the group 13 element
from the ligand. The elemental analyses of the compounds
were within acceptable limits. In some cases (e.g., 2, 7, 9,
and 11), slightly different values from the calculated values
could be due to the high air and moisture sensitivity of the
compounds.
Spectroscopy. Compounds 1-12 were characterized by
1H, 13C, and 11B NMR, as well as mp, MS, and EA. The 1H
NMR data for all the compounds showed two singlets for
t
the Bu-Ph groups in the range of δ 1.24-1.54 ppm. The
imine peaks appeared at δ 8.63, 8.52, 8.30, and 7.99 ppm
for the borates 1, 4, 5, and 6, δ 8.29, 8.58, 8.11, and
7.93 ppm for the chlorides 2, 7, 9, and 11, and δ 9.38, 8.81,
8.25, and 8.97 ppm for the bromides 3, 8, 10, and 12,
respectively. The imine peaks for the bromides appeared at
Structures. The borate compounds 1 and 6 and the halide
compounds 11 and 12 were structurally characterized by
single-crystal X-ray diffraction studies. The X-ray crystal
structures confirmed the presence of four-coordinate boron
atoms in these compounds (Figures 4-7). The crystal data
collection parameters are shown in Table 1 and selected bond
lengths and angles are shown in Table 2. The B-O bond
(32) Wei, P.; Keizer, T.; Atwood, D. A. Inorg. Chem. 1999, 38, 3914-
3918.
9218 Inorganic Chemistry, Vol. 45, No. 23, 2006

Phosphate Dealkylation with Mononuclear Boron Chelates
Figure 7. Structure of 12. Atoms are shown in 50% probability level.
Hydrogen atoms are omitted for clarity. Only one molecule is shown out
of two molecules in the unit cell.
Figure 4. Structure of 1. Atoms are shown in 50% probability level.
Hydrogen atoms are omitted for clarity.
boron chloride salpen(tBu)[Cl2]2,20 the B-Cl bond lengths
are 1.849(5) and 1.855(5) Å.
The geometry around the boron atom is slightly distorted
tetrahedral in all four compounds. For compound 1, the
largest deviations are shown by the angles O1-B1-N1
(106.8(3)°), O1-B1-O2 (112.1(3)°), and O1-B1-O3
(112.1(3)°), whereas for 6, the largest deviation is shown in
the angle O2-B1-O3 (115.3(2)°). The angle O1-B1-N1
is slightly larger for 6 (109.4(2)°) compared to 1. This could
be caused by the steric restriction that arises because the
boron is part of a second six-membered ring in 6.
For the halide compounds 11 and 12, the largest deviation
from the ideal tetrahedral angle is observed for the angle
O2A-B1A-N1A, which is 112.59(15)° for 11 and 114.64-
(14)° for 12. The angles O1A-B1A-Cl1A (107.83(13)°),
O2A-B1A-Cl1A (113.18(14)°), and N1A-B1A-Cl1A
(102.89(13)°) in 11 are larger than the corresponding angles
O1A-B1A-Br1A (107.09(11)°), O2A-B1A-Br1A (108.82-
(12)°), and N1A-B1A-Br1A (102.00(11)°) in 12. This is
contrary to what would be expected from the Bent’s Rule33
when the higher electronegativity of chlorine compared to
bromine and, thus, less s-character in the B-Cl bond are
considered. The angle O1A-B1A-N1A (110.72(15)° for
11 and 112.48(14)° for 12) is close to the angle found in the
bimetallic boron halides, salpen(tBu)[Cl2]2 (110.1(4)°)20 and
salben(tBu)[BBr2]2 (112.8(6)°).19
A quantitative correlation called the tetrahedral character
(THC) value (Figure 8) has been proposed to determine the
deviation of the geometry around boron in compounds
containing NfB bonds.34 A THC value of 100% refers to a
perfectly tetrahedral geometry and a value of 0% refers to a
trigonal planar geometry around the boron. Compounds 1,
6, 11, and 12 have THC values of 88, 83, 84, and 77%,
respectively. According to the previous observation, the THC
values should increase with increased N-B interaction (i.e.,
decrease in NfB bond length).34 However, the NfB bond
lengths in 1, 6, 11, and 12 (1.628(4), 1.585(4), 1.560(2), and
1.540(2) Å, respectively) do not agree with this observation,
which is possibly because of the restriction imposed by the
ligand.
Figure 5. Structure of 6. Atoms are shown in 50% probability level.
Hydrogen atoms are omitted for clarity.
Figure 6. Structure of 11. Atoms are shown in 50% probability level.
Hydrogen atoms are omitted for clarity. Only one molecule is shown out
of two molecules in the unit cell.
lengths are in the range 1.414(4)-1.485(4) Å for the borates
1 and 6 and 1.394(2)-1.440(2) Å for the halides 11 and 12.
These distances are slightly shorter than the B-N distances
(1.540(2)-1.628(4) Å), which is a reflection of the smaller
covalent radius of oxygen and the coordinative character of
B-N bonds. Nevertheless, the B-N distances reported are
among the shortest known so far. The B-Br bond length
(2.197(2) Å) in 12 is longer than the B-Cl bond length
(1.966(2) Å) in 11, which is a reflection of the greater
covalent radii of Br compared to that of Cl. These distances
are slightly larger compared to the binuclear boron halides
reported previously. For example, in the binuclear Schiff base
boron bromide salben(tBu)[BBr2]2,19 the B-Br lengths are
2.023(8) and 2.077(9) Å, and in the binuclear Schiff base
(33) Bent, H. A. Chem. ReV. 1961, 61, 275-311.
(34) Hopfl, H. J. Organomet. Chem. 1999, 581, 129-149.
Inorganic Chemistry, Vol. 45, No. 23, 2006 9219

Mitra et al.
Table 1. Crystallographic Data and Refinement Details for Compounds 1, 6, and 11-14
1
6
11
12
13
14
empirical
formula
M/g mol-1
crystal size/
mm
crystal
system
space group
a/Å
C23H32BNO3
C19H30BNO3
C
18.15H27.46BCl0.85NO2.15
C18H27BBrNO2
C44H54B2Cl4N2O5
C
36.50H39BNO4P
381.31
331.25
335.00
0.45 × 0.35
380.13
854.31
597.47
0.15 × 0.15
0.90 × 0.15
0.20 × 0.10
0.30 × 0.20
0.12 × 0.08
× 0.03
× 0.08
× 0.25
× 0.08
× 0.05
× 0.05
monoclinic
monoclinic
triclinic
triclinic
orthorhombic
triclinic
Cc
P21/c
P1h
P1h
P212121
12.9606(2)
19.6141(3)
51.9064(7)
90.00
90.00
90.00
13195.2(3)
1.290
12
P1h
11.5730(4)
26.0370(11)
8.5110(3)
90.00
120.9071(19)
90.00
2200.42(14)
1.151
4
16.2045(3)
11.2564(3)
10.4662(5)
90.00
94.7290(11)
90.00
1902.58(11)
1.156
4
11.6315(10)
11.8250(10)
16.5808(2)
100.1133(4)
102.1617(5)
115.9115(5)
1910.10(3)
1.165
11.5811(1)
11.9058(1)
16.5674(1)
101.1731(3)
101.3603(4)
115.8035(3)
1912.52(3)
1.320
12.1241(2)
12.3740(2)
12.4470(2)
73.7525(6)
89.0625(7)
62.5102(6)
1576.34(4)
1.259
b/Å
c/Å
R/°
â/°
γ/°
V/Å3
F
calc/g cm-3
Z
4
4
2
µ/mm-1
T/K
0.074
0.076
0.188
90.0(2)
1.32-27.49
17406
2.157
90.0(2)
1.32-27.50
47040
2.810
0.128
90.0(2)
1.72-27.45
13929
90.0(2)
1.56-25.00
3820
90.0(2)
1.26-25.00
6477
90.0(2)
2.41-67.99
93693
Θ range/°
reflections
measured
unique
3808
3359
8762
8775
23333
7183
reflections
R1 [I > 2σ]
R1 ) 0.0512,
wR2 ) 0.0950
R1 ) 0.0980,
wR2 ) 0.1108
0.0556,
wR2 ) 0.1277
0.1418,
0.0523,
wR2 ) 0.1419
0.0834,
0.0267,
wR2 ) 0.0598
0.0388,
0.0718,
wR2 ) 0.1730
0.1066,
R1 ) 0.0501,
wR2 ) 0.1109
R1 ) 0.1036,
wR2 ) 0.1318
R1 (all data)
wR2 ) 0.1583
wR2 ) 0.1599
wR2 ) 0.0641
wR2 ) 0.1947
Interestingly, the mononuclear borates 1 and 6 do not show
any hydrogen bonding as was observed for binuclear Salen-
[(BOMe)2]2 compounds.35
attributed to νCdN stretching. The mass spectra (EI) had a
molecular ion peak in 5% relative abundance.
An X-ray structure (shown in Figure 11) confirmed the
presence of two four-coordinate boron atoms in 13. The
crystal data collection parameters are shown in Table 1, and
selected bond distances and angles are shown in Table 2.
The boron atoms are part of two seven-membered BOBNC-
CO heterocycles. There is a B-O-B bridge between the
two boron atoms. The bridging B-O bond lengths are 1.404-
(6) and 1.388(6) Å, whereas the B-O(Ph) bond lengths range
from 1.462(6) to 1.481(6) Å. The bridging B-O lengths are
close to those observed in previously reported binuclear
Schiff base boron compounds containing B-O-B bridges
although the B-O(Ph) lengths are slightly shorter. For
example, in the compounds L[(PhB)2(µ-O)] (L ) salen-
(tBu), salpen(tBu), and acpen (acpen ) N,N′-propylenebis-
((methyl)salicylineneimine)), the bridging B-O bond lengths
range from 1.416(5) to 1.419(3) Å, and B-O(Ph) bond
lengths range from 1.493(3) to 1.511(4) Å.36 The B-N bond
lengths for 13 are 1.607(6) and 1.610(6) Å. Each boron atom
is in a distorted tetrahedral environment. The THC values
for B1A and B2A are 75 and 76%, respectively. The most
acute angle for B1A is O2A-B1A-N1A (101.3(3)°) and
for B2A is O3A-B2A-N2A (101.8(3)°). The most obtuse
angle is O2A-B1A-O5A (115.3(4)°) for B1A and O5A-
B2A-O3A (115.2(4)°) for B2A. The B-O-B angle is
117.1(4)°. This angle is significantly smaller compared to
the B-O-B bridged compounds L[(PhB)2(µ-O)] (L )
Salen(tBu) (131.4(3)°), salpen(tBu) (137.5(3)°), and acpen
(128.6°).36
Hydrolysis of Boron Halide Compounds. The boron
halide compounds are moisture sensitive. They are hydro-
lyzed by trace amounts of moisture present in the reaction
medium. Binuclear compound 13, which contains a B-O-B
linkage, was obtained during the preparation of the halide 7
from the borate 4 by adventitious exposure to moisture
(Figure 9). Similar Schiff base compounds with B-O-B
bridges can be prepared intentionally from the combinations
of various Salen ligands with phenylboronic acid (Figure
10)36,37 or boric acid,38 various salicylaldimine derivatives
with boric acid,39 or salicylaldehyde with 2-H2NC6H4Bpin
(pin ) 1,2-O2C2Me4).40
1
t
The H NMR of 13 contained four Bu peaks. The 11B
NMR showed two boron peaks at δ 3.19 and δ 7.33 ppm
corresponding to two four-coordinate boron atoms. The
presence of the second boron peak and two extra tBu peaks
could be caused by the presence of a hydrolyzed compound
“LBOH” produced in the reaction. This hydrolyzed com-
pound presumably condensed to the dinuclear oxo-bridged
compound 13. The IR shows a peak at 1620 cm-1 that is
(35) Wei, P.; Atwood, D. A. Inorg. Chem. 1997, 36, 4060-4065.
(36) Sanchez, M.; Keizer, T. S.; Parkin, S.; Hopfl, H.; Atwood, D. A. J.
Organomet. Chem. 2002, 654, 36-43.
(37) Sanchez, M.; Hopfl, H.; Ochoa, M. E.; Farfan, N.; Santillan, R.; Rojas,
S. Inorg. Chem. 2001, 40, 6405-6412.
(38) Gabriela, V.; Iran, H.; Herbert, H.; Maria-Eugenia, O.; Dolores, C.;
Norberto, F.; Rosa, S.; Elizabeth, G. Inorg. Chem. 2004, 43, 8490-
8500.
(39) Yalcin, N.; Kenar, A.; Arici, C.; Atakol, O.; Tastekin, M. Main Group
Met. Chem. 2001, 24, 247-248.
(40) Webb, J. D.; Darwish, H. A.; Zhang, H.; Wheaton, S. L.; Baerlocher,
F. J.; Vogels, C. M.; Decken, A.; Westcott, S. A. Can. J. Chem. 2005,
83, 1158-1163.
Dealkylation of Trimethyl Phosphate with Various
Mononuclear Compounds. The mononuclear Schiff base
boron halide compounds 2, 3, and 7-12 dealkylated tri-
9220 Inorganic Chemistry, Vol. 45, No. 23, 2006

Phosphate Dealkylation with Mononuclear Boron Chelates
Table 2. Selected Bond Distances (Å) and Angles (deg) for
Compounds 1, 6, 11,a 12,a 13,b and 14
1
B1-O1
B1-O2
B1-O3
B1-N1
1.485(4)
1.414(4)
1.426(4)
1.628(4)
O3-C23
N1-C15
N1-C16
1.412(4)
1.302(4)
1.442(4)
O1-B1-N1
O2-B1-N1
O3-B1-N1
106.8(3)
108.5(3)
108.9(3)
O1-B1-O2
O1-B1-O3
O2-B1-O3
112.1(3)
112.1(3)
108.4(3)
6
Figure 8. THC diagram. (a) Equation for calculating THC % [θn (n )
1-6) are the angles around the boron atom]. (b) Weak interaction between
boron and the donor, which leads to three-coordinate trigonal boron. (c)
Strong interaction between boron and the donor, which leads to tetrahedral
four-coordinate boron.
B1-O1
B1-O2
B1-O3
B1-N1
1.473(3)
1.431(3)
1.444(3)
1.585(4)
O3-C19
N1-C15
N1-C16
1.428(3)
1.286(3)
1.466(3)
O1-B1-N1
O2-B1-N1
O3-B1-N1
109.4(2)
108.2(2)
105.0(2)
O1-B1-O2
O1-B1-O3
O2-B1-O3
107.6(2)
111.2(2)
115.3(2)
phate materials, which remained in solution (Figure 12 and
Table 3). The dealkylation reaction was conducted in NMR
tubes in CDCl3, and the percent conversion was determined
11
1
from the integration of the H NMR peaks for the methyl
B1-O1
B1-O2
1.440(2)
1.401(2)
B1-N1
B1-Cl1
1.560(2)
1.966(2)
halide produced and the unchanged methoxy groups of the
phosphate. The reaction mixture stayed clear throughout the
dealkylation reaction. The possible dealkylation pathway for
the LBX compounds is shown in Figure 13. The best results
were obtained from the monobromide compounds 8 (90%
after 30 min) and 12 (64% after 30 min, 74% after 2 h, and
100% after 24 h). These results are comparable to the
binuclear boron halides studied before.19-21 In compounds
8 and 12 with an ONO environment, either an o-phenylene
or a propylene backbone connects the N and O atoms. These
compounds were far more active than the chloride analogues,
7 and 11. This could be expected from the lower B-Br bond
strength compared to the B-Cl bond strength (bond enthal-
pies for diatomic B-X: 396 kJ mol-1 for B-Br vs 511 kJ
mol-1 for B-Cl) and the consequent ease of formation of
the phosphate coordinated cations. Interestingly, the LBX
(X ) Cl, Br) compounds, 9 and 10, with an ethylene
backbone between the N and O atoms were almost inactive
toward phosphate dealkylation. Compound 3, the dibromide
LBBr2, also showed negligible activity. However, the dichlo-
ride compound, 2, showed moderate activity (17% in 30 min,
61% in 2 h, and 85% in 24 h). The higher activity of chloride
compared to bromide for LBX2 could not be explained by
the B-X bond strength. Thus, a correlation of higher
reactivity and B-X bond strength occurs only for the
monohalide compounds. The LBCl2 compounds are more
reactive than the LBBr2 compounds could be because the
inductive effect of the second chloride makes the formation
of LBCl+ easier to achieve.
O1-B1-N1
O1-B1-O2
O2-B1-N1
110.72(15)
109.40(16)
112.59(15)
O1-B1-Cl1
O2-B1-Cl1
N1-B1-Cl1
107.83(13)
113.18(14)
102.89(13)
12
B1-O1
B1-O2
1.422(2)
1.394(2)
B1-N1
B1-Br1
1.540(2)
2.197(2)
O1-B1-N1
O1-B1-O2
O2-B1-N1
112.48(14)
110.61(15)
114.64(14)
O1-B1-Br1
O2-B1-Br1
N1-B1-Br1
107.09(11)
108.82(12)
102.00(11)
13
B1-O1
B1-O2
B1-O5
B1-N1
1.467(6)
1.478(6)
1.398(6)
1.610(6)
B2-O3
B2-O4
B2-O5
B2-N2
1.473(6)
1.467(6)
1.402(6)
1.611(6)
O1-B1-N1
O1-B1-O2
O1-B1-O5
O2-B1-N1
O2-B1-O5
O5-B1-N1
B1-O5-B2
105.6(3)
111.0(3)
109.5(4)
101.7(3)
115.5(4)
112.8(4)
116.5(4)
O5-B2-N2
O5-B2-O3
O5-B2-O4
O3-B2-N2
O3-B2-O4
O4-B2-N2
112.4(4)
115.3(4)
109.7(4)
102.0(3)
110.8(4)
106.0(3)
14
B1-O1
B1-O2
B1-O3
B1-N1
N1-C15
N1-C16
1.432(2)
1.463(2)
1.476(2)
1.568(3)
1.293(2)
1.413(2)
P1-O3
P1-O4
P1-C22
P1-C28
1.5633(13)
1.4811(13)
1.799(2)
1.8004(19)
O1-B1-N1
O2-B1-N1
O3-B1-N1
O1-B1-O2
O1-B1-O3
O2-B1-O3
109.97(16)
102.22(15)
110.45(16)
114.49(16)
107.91(15)
111.71(16)
O3-P1-O4
O3-P1-C22
O3-P1-C28
O4-P1-C22
O4-P1-C28
C22-P1-C28
P1-O3-B1
116.50(7)
107.33(8)
112.93(8)
111.30(8)
112.93(8)
106.26(9)
132.43(12)
Preparation of a Chelated Monomeric Boron Phosphi-
nate (14) through Dealkylation. Although attempts to get
the structure of the fully dealkylated phosphate triester was
not successful, the dealkylated product, LBOP(O)Ph2 (LH2
) N-(2-hydroxyphenyl)-3,5-di-tert-butylsalicylaldimine) (14),
which was produced from tert-butyl-diphenylphosphinate,
Ph2P(O)OtBu, and the boron bromide compound 8, was
isolated and fully characterized. Molecular phosphates and
phosphonates are interesting because of their possible use
as precursors to solid-state materials.41-44 Examples of
a The values are the mean for the two independent molecules present in
the asymmetric unit. b The values are the mean for the three independent
molecules present in the asymmetric unit.
methyl phosphate at room temperature in stoichiometric
reactions to produce methyl halide and unidentified phos-
Inorganic Chemistry, Vol. 45, No. 23, 2006 9221

Mitra et al.
Figure 9. Formation of the hydrolyzed product 13 from the halide compound 7.
Figure 10. Formation of the binuclear oxo-bridged boron compounds from the Salen ligands.
Figure 11. Structure of the hydrolyzed product 13. Atoms are shown in 50% probability level. Hydrogen atoms are omitted for clarity. Only one molecule
is shown out of the three molecules in the asymmetric unit.
Table 3. Percent Dealkylationa of Trimethyl Phosphate with Schiff
Base Boron Halides
compound
2
3
7
8
9
10
11
12
Figure 12. Reaction between trimethyl phosphate and the mononuclear
Schiff base boron halides.
30 min
2 h
4 h
6 h
8 h
10 h
12 h
24 h
17
61
10
13
9
90
90
92
94
94
94
94
94
2
6
7
7
9
11
11
13
4
4
3
8
64
74
24
40
52
62
68
73
84
monomeric main group or transition metal chelate com-
pounds with terminal phosphinates are rare. Previously
reported metal phosphinate compounds of Ti,45,46 Zr,47 Ta,46
Sn,48,49 Pb,48 Al,50,51 Ga,52,53 and In52 contained bridging
85
18
4
57
100
a Calculated from the integration of H NMR spectra of methyl halide
1
produced and unchanged trimethyl phosphate at room temperature in CDCl3.
(41) Clearfield, A. Chem. Mater. 1998, 10, 2801-2810.
(42) Clearfield, A. Inorganic Ion Exchange Materials; CRC Press: Boca
Raton, FL, 1982.
(43) Lugmair, C. G.; Tilley, T. D. Inorg. Chem. 1998, 37, 1821-1826.
(44) Clearfield, A.; Sharma, C. V. K.; Zhang, B. P. Chem. Mater. 2001,
13, 3099-3112.
(45) Shah, S. A. A.; Dorn, H.; Gindl, J.; Noltemeyer, M.; Schmidt, H. G.;
Roesky, H. W. J. Organomet. Chem. 1998, 550, 1-6.
(46) Dorn, H.; Vejzovic, E.; Lough, A. J.; Manners, I. Can. J. Chem. 2002,
80, 1650-1654.
phosphinate groups, and almost all of the compounds were
di- or polynuclear. A unique example of a mononuclear metal
chelate phosphinate compound is Sn(CH2Ph)2[O2P(C6H11)2]2-
(49) Swamy, K. C. K.; Said, M. A.; Nagabrahmanandachari, S.; Poojary,
D. M.; Clearfield, A., Dalton Trans. 1998, 1645-1651.
(50) Wang, Y.; Parkin, S.; Atwood, D. Chem. Commun. 2000, 1799-
1800.
(47) Swamy, K. C. K.; Veith, M.; Huch, V.; Mathur, S. Inorg. Chem. 2003,
42, 5837-5843.
(48) Shihada, A. F.; Weller, F. Z. Anorg. Allg. Chem. 2001, 627, 638-
644.
(51) Wang, Y.; Parkin, S.; Atwood, D. Inorg. Chem. 2002, 41, 558-
565.
9222 Inorganic Chemistry, Vol. 45, No. 23, 2006

Phosphate Dealkylation with Mononuclear Boron Chelates
Figure 15. Synthesis of 14.
Figure 13. Possible dealkylation pathway for the boron compound LBX.
Figure 16. Crystal structure of compound 14. Atoms are shown in 50%
probability level. Hydrogen atoms are omitted for clarity.
Figure 14. Monomeric tin phosphinate Sn(CH2Ph)2[O2P(C6H11)2]2[HO2-
P(C6H11)2]2.49
could be the existence of a monomer-dimer equilibrium in
the solution. A phosphinate-bridged dimer could form
through the breakage of the B-N linkage, which previously
has been postulated.11 The chemical shift is close to some
other phosphinate compounds. For example, in [(η5-Cp)TiCl2
(µ-Ph2PO2)2] the 31P shift was 34.5 ppm.46 The IR for 14
showed strong νB-N absorption at 1014 cm-1, ν(CdN) at 1640
cm-1, and ν(PdO) at 1212 cm-1. The MS (EI, positive) showed
a molecular ion peak in 15% abundance and a M+- PhPO2
peak in 45% abundance. The base peak (100%) was
attributed to M+ - PhPO2 - H.
[HO2P(C6H11)2]2 (Figure 14).49 In this compound, the phos-
phinate groups participate in intramolecular hydrogen bond-
ing. The aluminum phosphinate Salen chelate compounds,
[Salen(tBu)Al{O2P(H)Ph}]n (n ) 2, ∞), had bridging phos-
phinate groups, and they contained six-coordinate alumi-
num.51 Recently, a Salen aluminum phosphinate compound
(salenOP(O)Ph2), which contained a terminal phosphinate
group, was prepared through dealkylation.54 The methanol
coordinated structure of this compound was reported. Com-
pound 14 is another rare example of a monomeric chelated
compound with a terminal phosphinate group.
Structure of 14. The single-crystal X-ray structure of 14
is shown in Figure 16. Data collection parameters are given
in Table 1, and selected bond lengths and angles are given
in Table 2. The compound contained a four-coordinate boron
and a four-coordinate phosphorus atom. The B-O bond
lengths (1.432(2), 1.463(2), and 1.476(2) Å) were shorter
than the B-N bond length (1.568(3) Å). The P1-O3 bond
length (1.5633(13) Å) was in the single bond range (1.59-
1.60 Å), and the P1-O4 bond (1.4811(13) Å) was close to
the double bond range (1.45-1.46 Å).55 In a previously
reported molecular borophosphonate cage compound
[tBuPO3BEt]4, the average P-O bond length was 1.50 Å,
which was between P-O and PdO.56
Compound 14 was prepared by refluxing 8 and Ph2P(O)-
t
OtBu in toluene (Figure 15). The byproduct BuBr was
removed under vacuum. The formation of this byproduct was
confirmed by repeating the reaction in an NMR tube, which
1
t
showed a H peak corresponding to BuBr. Compound 14
1
t
was soluble in organic solvents. The H NMR showed Bu
peaks at δ 1.31 and δ 1.50 ppm, and an imine peak at δ
8.57 ppm. The 11B NMR showed a single peak at δ 3.57
ppm, which is in the appropriate region for a four-coordinate
boron atom. Interestingly, the 31P NMR had two peaks at δ
28.90 and δ 33.97 ppm in the intensity ratio of 4:3. The
presence of two peaks suggested that there might be some
type of rearrangement in the solution state. One possibility
The geometry around the boron was distorted tetrahedral.
The THC value34 for 14 was 81%. The largest deviation from
(52) Hahn, F. E.; Schneider, B.; Reier, F. W. Z. Naturforsch., B: Chem.
Sci. 1990, 45B, 134-140.
(53) Browning, D. J.; Corker, J. M.; Webster, M. Acta Crystallogr., Sect.
C 1996, C52, 882-884.
(55) Corbridge, D. E. C. The Structural Chemistry of Phosphorus,
Elsevier: Amsterdam, Netherlands, 1974.
(56) Walawalkar, M. G.; Murugavel, R.; Roesky, H. W.; Schmidt, H. G.
Organometallics 1997, 16, 516-518.
(54) Mitra, A.; Parkin, S.; Atwood, D. A. Inorg. Chem. 2006, 45, 3970-
3975.
Inorganic Chemistry, Vol. 45, No. 23, 2006 9223

Mitra et al.
a perfect tetrahedral angle was in the O2-B1-N1 angle
(102.22(15)°) caused by the constraints imposed by the
chelate.
The phosphorus atom was in a distorted tetrahedral
environment. The angle O3-P1-O4 (116.50(7))°) was the
most obtuse angle, whereas the angle C22-P1-C28 (106.26-
(9)°) was the least obtuse. The angle P1-O3-B1 (132.43-
(12)°) was significantly narrower than the Al-O-P angle
(138.8(3)°) in the dimeric aluminum phosphinate compound
[salophen(thf)(tBu)AlO2P(H)Ph]2.51
this problem should be considered. Although the structure
of the fully dealkylated product could not be determined, a
monodealkylated product (compound 14) was fully charac-
terized. Compound 14 is the first example of a chelated boron
phosphinate. Interestingly, the compound had a terminal
phosphinate group, which contrasted with the bridging
phosphinate groups that are found in many other metal
chelates. The dealkylation reaction has the potential to
produce novel structures when used with phosphate di- and
triesters (i.e., phosphonates and phosphates).
Conclusion
Acknowledgment. This work was supported by Kentucky
Science and Engineering Foundation (KSEF Grant 148-502-
04-100). Instruments used in this research were obtained from
the CRIF (NMR, CHE 997841) and MRI (X-ray, CHE
0319176) programs of the National Science Foundation and
from the Research Challenge Trust Fund of the University
of Kentucky. Partial support from the University of Kentucky
Tracy Farmer Center for the Environment is acknowledged.
Thanks also are expressed to the University of Kentucky
Mass Spectrometry Facility and the Center for Applied
Energy Research.
A series of mononuclear Schiff base borates, LB(OMe)2
and LB(OMe) based on N,O and N,O,O ligands, were
prepared. The borates were further derivatized to mono-
nuclear Schiff base boron halides, LBX2 and LBX (X ) Cl,
Br). The boron halides are moisture sensitive, and one of
them on reaction with trace water, produced a binuclear
compound containing a B-O-B linkage and BOBNCCO
heterocycles. Compounds 2, 3, and 7-12 dealkylated trim-
ethyl phosphate to various extents at room temperature. The
monobromide compounds 8 and 12 were the most effective,
and their activity was comparable to the results obtained from
binuclear Salen boron bromide compounds previously re-
ported. However, it should be noted that the mononuclear
compounds were less stable to air and moisture compared
to their binuclear counterparts. For any useful application,
Supporting Information Available: CIF files for compounds
1, 6, and 11-14. This material is available free of charge via the
Internet at http://pubs.acs.org.
IC0607890
9224 Inorganic Chemistry, Vol. 45, No. 23, 2006