Bis-Catecholate, Bis-Dithiocatecholate, and Tetraalkoxy Diborane(4) Compounds: Aspects of Synthesis and Electronic Structure

Article abstract of DOI:10.1021/ic980425a

The synthesis and characterization of a series of bis-catecholate diborane(4) compounds, B₂(1,2-O₂C₆H₄)₂ (3), B₂(1,2-O₂-4-MeC₆H₃)₂ (7), B₂(1,2-O₂-4-MeC₆H₃)₂ (7), B₃(1,2-O₂-4-Bu^tC₆H₃) ₂ (8), B₂(1,2-O₂-3,5-Bu₂^tC ₆H₂)₂ (9), B₂(1,2-O₂-3-MeOC₆H₃)₂ (10), bis-dithiocatecholate diborane(4) compounds, B₂(1,2-S₂C₆H₄)₂ (13), B₂(1,2-S₂-4-MeC₆H₃)₂ (14), and tetraalkoxy diborane(4) compounds, B₂(OCH₂CMe₂CH₂O)₂ (11) and B₂(OCMe₂CMe₂O)₂ (12) from B₂(NMe₂)₄ (1) is described, as are the bis(NHMe₂) adducts of 3 and 9, namely [B₂(1,2-O₂C₆H₄) ₂-(NHMe₂)₂] (4) and [B₂(1,2-O₂-3,5-Bu₂^tC ₆H₂)₂(NHMe₂)₂] (5). The latter two compounds are intermediates in the formation of 3 and 9 from 1. Compound 1 is synthesized by reductive coupling of BCl(NMe₂)₂, which in turn is prepared from reaction of BCl₃ with B(NMe₂)₃ in a 1:2 stoichiometry. We have also characterized [B₂Cl₄-(NHMe₂)₂] (15) formed from addition of HCl to 1 prior to complete reaction with diols, and the salt, [NH₂Me₂]-[B(1,2-O₂C₆H ₄)₂] (16), which arises from addition of cacechol to B(NMe₂)₃. Thus, any B(NMe₂)₃ impurity present after the preparation of 1 needs to be removed by distillation prior to reaction with alcohols. The dimer, [BCl₂-(μ-NMe₂)]₂ (17) has also been characterized. This is formed from reaction of BCl₃ with B(NMe₂)₃ if a 2:1 rather than 1:2 sloichiometry is used. Photoelectron spectra of 1, 3, 8, 11, and 12 are reported along with those of the corresponding diols, catechol, 4-Bu^t-catechol, 2,2-dimethyl-1,3-propanediol, and pinacol. The ionization energies of the B₂(OR)₄ compounds follow the series 8 < 3 < 12 < 11. Replacement of O for N in the B₂N₄ framework increases the IE by ca. 1.65 eV, whereas the presence of an aromatic ring rather than an aliphatic chain decreases the IE by ca. 1.50 eV. The presence of electron donating Bu^t-groups also decreases the IE.

Full text of DOI:10.1021/ic980425a

5282
Inorg. Chem. 1998, 37, 5282-5288
Bis-Catecholate, Bis-Dithiocatecholate, and Tetraalkoxy Diborane(4) Compounds: Aspects
of Synthesis and Electronic Structure
Fiona J. Lawlor, Nicholas C. Norman,*,† Nigel L. Pickett, and Edward G. Robins
Department of Chemistry, The University of Newcastle upon Tyne,
Newcastle upon Tyne NE1 7RU, U.K.
Paul Nguyen, Gerry Lesley, and Todd B. Marder*,‡
Department of Chemistry, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada
Jennifer A. Ashmore and Jennifer C. Green*
Inorganic Chemistry Laboratory, University of Oxford, South Parks Road, Oxford OX1 3QR, U.K.
ReceiVed April 15, 1998
The synthesis and characterization of a series of bis-catecholate diborane(4) compounds, B2(1,2-O2C6H4)2 (3),
B2(1,2-O2-3-MeC6H3)2 (6), B2(1,2-O2-4-MeC6H3)2 (7), B2(1,2-O2-4-ButC6H3)2 (8), B2(1,2-O2-3,5-But2C6H2)2 (9),
B2(1,2-O2-3-MeOC6H3)2 (10), bis-dithiocatecholate diborane(4) compounds, B2(1,2-S2C6H4)2 (13), B2(1,2-S2-4-
MeC6H3)2 (14), and tetraalkoxy diborane(4) compounds, B2(OCH2CMe2CH2O)2 (11) and B2(OCMe2CMe2O)2
(12) from B2(NMe2)4 (1) is described, as are the bis(NHMe2) adducts of 3 and 9, namely [B2(1,2-O2C6H4)2-
(NHMe2)2] (4) and [B2(1,2-O2-3,5-But2C6H2)2(NHMe2)2] (5). The latter two compounds are intermediates in the
formation of 3 and 9 from 1. Compound 1 is synthesized by reductive coupling of BCl(NMe2)2, which in turn
is prepared from reaction of BCl3 with B(NMe2)3 in a 1:2 stoichiometry. We have also characterized [B2Cl4-
(NHMe2)2] (15) formed from addition of HCl to 1 prior to complete reaction with diols, and the salt, [NH2Me2]-
[B(1,2-O2C6H4)2] (16), which arises from addition of catechol to B(NMe2)3. Thus, any B(NMe2)3 impurity present
after the preparation of 1 needs to be removed by distillation prior to reaction with alcohols. The dimer, [BCl2-
(µ-NMe2)]2 (17) has also been characterized. This is formed from reaction of BCl3 with B(NMe2)3 if a 2:1 rather
than 1:2 stoichiometry is used. Photoelectron spectra of 1, 3, 8, 11, and 12 are reported along with those of the
corresponding diols, catechol, 4-But-catechol, 2,2-dimethyl-1,3-propanediol, and pinacol. The ionization energies
of the B2(OR)4 compounds follow the series 8 < 3 < 12 < 11. Replacement of O for N in the B2N4 framework
increases the IE by ca. 1.65 eV, whereas the presence of an aromatic ring rather than an aliphatic chain decreases
the IE by ca. 1.50 eV. The presence of electron donating But-groups also decreases the IE.
Derivatives of diborane(4)1 are an important class of com-
pound in boron chemistry, part of their interest deriving from
the presence of an unsupported two-center, two-electron B-B
bond. There are, however, many aspects of the chemistry of
such species that have been developed only recently. Diborane-
(4) itself, B2H4, is only stable when complexed by Lewis base
ligands such as amines or phosphines,2 while the tetrahalides
B2X4 (X ) F, Cl, Br, I), although having a reasonably well-
established chemistry,3 suffer from low thermal stabilty (with
the exception of B2F4) and preparative difficulties. Tetraorga-
nodiborane(4) compounds, B2R4, are only stable with sterically
demanding R groups such as But or CH2But and mesityl,
examples with the former two having been characterized for
the first time in 1980 by No¨th and co-workers4a and Berndt et
al.,4b and the latter much more recently by Power and co-
workers.5 By far the most stable derivatives are those in which
good π-donor groups are present such as amido (NR2) or alkoxy
(OR), the prototypical examples being B2(NMe2)4 (1)6 and B2-
(OMe)4 (2);7 the former compound 1 is the primary starting
material for much of diborane(4) chemistry due to its thermal
stability and the availability of high yield syntheses. More
recently, as part of an interest in the oxidative addition
chemistry8,9 of the B-B bond and metal-catalyzed diborations10
of alkenes11 and alkynes,9 we have characterized a series of
† Present address: The University of Bristol, School of Chemistry, Bristol
BS8 1TS, U.K.
‡ Present address: Department of Chemistry, University of Durham,
Durham DH1 3LE, U.K.
(4) (a) Biffar, W.; No¨th, H.; Pommerening, H. Angew. Chem., Int. Ed.
Engl. 1980, 19, 56. (b) Schlu¨ter, K.; Berndt, A. Angew. Chem., Int.
Ed. Engl. 1980, 19, 57.
(5) (a) Moezzi, A.; Olmstead, M. M.; Power, P. P. J. Am. Chem. Soc.
1992, 114, 2715. (b) Moezzi, A.; Olmstead, M. M.; Bartlett, R. A.;
Power, P. P. Organometallics 1992, 11, 2383.
(6) Brotherton, R. J.; McCloskey, J. L.; Petterson, L. L.; Steinberg, H. J.
Am. Chem. Soc. 1960, 82, 6242.
(7) Brotherton, R. J.; McCloskey, J. L.; Boone, J. L.; Manasevit, H. M.
J. Am. Chem. Soc. 1960, 82, 6245.
(1) For a brief overview of the synthesis, structure and reactivity of
diborane(4) compounds, see: Lesley, G.; Marder, T. B.; Norman, N.
C.; Rice, C. R. Main Group Chem. News 1997, 5, 4.
(2) Kameda, M.; Driscoll, J. A.; Kodama, G. Inorg. Chem. 1990, 29, 3791
and references therein. See also: Parry, R. W. Phosphorus Sulfur 1994,
87, 177.
(3) See, for example: (a) Massey, A. G. AdV. Inorg. Chem. Radiochem.
1983, 26, 1. (b) Coyle, T. D.; Ritter, J. J. AdV. Organomet. Chem.
1972, 10, 237.
S0020-1669(98)00425-X CCC: $15.00 © 1998 American Chemical Society
Published on Web 09/18/1998

Catecholate, Dithiocatecholate, and Tetraalkoxy Diboranes
Inorganic Chemistry, Vol. 37, No. 20, 1998 5283
stable, crystalline bis-catecholate8a and bis-dithiocatecholate
derivatives, and herein we describe full details of their syntheses,
spectroscopic properties and aspects of bonding derived from
photoelectron spectroscopic measurements and extended Hu¨ckel
molecular orbital (EHMO) calculations. Also described is the
tetraalkoxy compound B2(OCH2CMe2CH2O)2. In a companion
paper12 we describe the solid-state structures of some of the
diborane(4) compounds and related materials.
bis-dimethylamine adduct of B2(1,2-O2C6H4)2, (B2cat2, 3) i.e.,
[B2(1,2-O2C6H4)2(NHMe2)2] (4) as shown in eq 3. Support for
the supposition that the initial precipiate is a bis-amine adduct
comes from parallel studies on the reactivity of 3 which have
resulted in a number of structurally characterized mono- and
bis-4-picoline adducts of 3 (for a bis ligand adduct of 3, see A;
L ) nitrogen base, e.g. amine or pyridine) in which the nitrogen
Results and Discussion
Syntheses. The starting compound for the preparation of all
the diborane(4) compounds described herein was the tetraamido
compound B2(NMe2)4 (1).6 A preparation of 1, which is a
modification of that reported by Brotherton and co-workers,6
is represented as shown in eqs 1 and 2, the first being a
redistribution reaction affording BCl(NMe2)2, and the second,
a reductive coupling resulting in formation of the B-B bond.
BCl3 + 2B(NMe2)3 f 3BCl(NMe2)2
(1)
donor atoms are bonded directly to the boron center(s); these
results have been reported elsewhere.13 In addition, a combina-
tion of elemental analysis and NMR spectroscopic results on
[B2(1,2-O2-3,5-But2-C6H2)2(NHMe2)2] (5) and elemental analysis
of the insoluble parent compound [B2(1,2-O2C6H4)2(NHMe2)2]
(4) are consistent with the proposed formulation.
2BCl(NMe2)2 + 2Na f B2(NMe2)4 (1) + 2NaCl (2)
Treatment of 1 with 2 equiv of catechol in Et2O solution
resulted in the immediate formation of a white precipitate (both
1 and catechol are soluble in Et2O) which we propose is the
B2(NMe2)4 + 2(1,2-(HO)2C6H4) f
(8) (a) Nguyen, P.; Lesley, G.; Taylor, N. J.; Marder, T. B.; Pickett, N.
L.; Clegg, W.; Elsegood, M. R. J.; Norman, N. C. Inorg. Chem. 1994,
33, 4623. (b) Dai, C.; Stringer, G.; Corrigan, J. F.; Taylor, N. J.;
Marder, T. B.; Norman, N. C. J. Organomet. Chem. 1996, 513, 237.
(c) Dai, C.; Stringer, G.; Marder, T. B.; Baker, R. T.; Scott, A. J.;
Clegg, W.; Norman, N. C. Can. J. Chem. 1996, 74, 2026. (d) Dai, C.;
Stringer, G.; Marder, T. B.; Scott, A. J.; Clegg, W.; Norman, N. C.
Inorg. Chem. 1997, 36, 272. (e) Hartwig, J. F.; He, X. Organometallics
1996, 15, 400. (f) Hartwig, J. F.; Xe, H. Angew. Chem., Int. Ed. Engl.
1996, 35, 315. (g) Sakaki, S.; Kikuno, T. Inorg. Chem. 1997, 36, 226.
(h) Clegg, W.; Lawlor, F. J.; Lesley, G.; Marder, T. B.; Norman, N.
C.; Orpen, A. G.; Quayle, M. J.; Rice, C. R.; Scott, A. J.; Souza, F.
E. S. J. Organomet. Chem. 1998, 550, 183. (i) Clegg, W.; Lawlor, F.
J.; Marder, T. B.; Nguyen, P.; Norman, N. C.; Orpen, A. G.; Quayle,
M. J.; Rice, C. R.; Robins, E. G.; Scott, A. J.; Souza, F. E. S.; Stringer,
G.; Whittell, G. R. J. Chem. Soc., Dalton Trans. 1998, 301. (j) Kerr,
A.; Marder, T. B.; Norman, N. C.; Orpen, A. G.; Quayle, M. J.; Rice,
C. R.; Timms, P. L.; Whittell, G. R. J. Chem. Soc., Chem. Commun.
1998, 319. (k) See also: Marder, T. B.; Norman, N. C.; Rice, C. R.;
Robins, E. G. Chem. Commun. 1997, 53.
[B2(1,2-O2C6H4)2(NHMe2)2] + 2NHMe2 (3)
After the reaction mixture containing the white precipiate had
been stirred for several hours, 4 equiv of HCl, as a solution in
Et2O, were then added, resulting in the appearance of a further
amount of white precipitate. This reaction is necessary to
remove both complexed and uncomplexed amine as an am-
monium salt, as shown in eq 4, to afford uncomplexed 3. Sub-
sequent removal of all volatiles followed by extraction into
toluene and low-temperature crystallization yielded 3 as a
colorless crystalline solid.
[B2(1,2-O2C6H4)2(NHMe2)2] (4) + 2NHMe2 + 4HCl f
B2(1,2-O2C6H4)2 (3) + 4[NH2Me2]Cl (4)
(9) (a) Ishiyama, T.; Matsuda, N.; Miyaura, N.; Suzuki, A. J. Am. Chem.
Soc. 1993, 115, 11018. (b) Ishiyama, T.; Matsuda, N.; Murata, M.;
Ozawa, F.; Suzuki, A.; Miyaura, N. Organometallics 1996, 15, 713.
(c) Iverson, C. N.; Smith, M. R., III. J. Am. Chem. Soc. 1995, 117,
4403. (d) Iverson, C. N.; Smith, M. R., III. Organometallics 1996,
15, 5155. (e) Lesley, G.; Nguyen, P.; Taylor, N. J.; Marder, T. B.;
Scott, A. J.; Clegg, W.; Norman, N. C. Organometallics 1996, 15,
5137. (f) Cui, Q.; Musaev, D. G.; Morokuma, K. Organometallics
1997, 16, 1355. (g) Cui, Q.; Musaev, D. G.; Morokuma, K. Organo-
metallics 1998, 17, 742. (h) Cui, Q.; Musaev, D. G.; Morokuma, K.
Organometallics 1998, 17, 1383. (i) Siebert, W.; Pritzkow, H.;
Maderna, A. Angew. Chem., Int. Ed. Engl. 1996, 35, 1501. (j) Clegg,
W.; Scott, A. J.; Lesley, G.; Marder, T. B.; Norman, N. C. Acta
Crystallogr. 1996, C52, 1989 and 1991.
(10) (a) For a review of metal-catalyzed diborations and related reactions,
see: Marder, T. B.; Norman, N. C. In Topics in Catalysis; Leitner,
W., Blackmond, D. G., Eds.; Baltzer Science Publishers: Amsterdam,
1998; Vol. 5, p 63. (b) For metal-catalyzed diboration of dienes, see:
Ishiyama, T.; Yamamoto, M.; Miyaura, N. Chem. Commun. 1996,
2073. Clegg, W.; Johann, T. R. F.; Marder, T. B.; Norman, N. C.;
Orpen, A. G.; Peakman, T. M.; Quayle, M. J.; Rice, C. R.; Scott, A.
J. J. Chem. Soc., Dalton Trans. 1998, 1431. (c) For metal-catalyzed
1,4-diboration of R,â-unsaturated ketones, see: Lawson, Y. G.; Lesley,
M. J. G.; Marder, T. B.; Norman, N. C.; Rice, C. R. Chem. Commun.
1997, 2051. (d) For a related Pd-catalyzed synthesis of ArBpin
compounds from ArX + B2pin2 (Ar ) aryl; pin ) OCMe2CMe2O),
see: Ishiyama, T.; Murata, N.; Miyaura, N. J. Org. Chem. 1995, 60,
7508. Ishiyama, T.; Itoh, Y.; Kitano, T.; Miyaura, N. Tetrahedron
Lett. 1997, 38, 3447.
The related catecholate compounds B2(1,2-O2-3-MeC6H3)2
(6), B2(1,2-O2-4-MeC6H3)2 (7), B2(1,2-O2-4-ButC6H3)2 (8),
B2(1,2-O2-3,5-But2C6H2)2 (9), and B2(1,2-O2-3-MeOC6H3)2 (10)
were prepared in a manner similar to 3, the compounds
becoming more soluble in toluene with increasing hydrocarbon
side-group substitution (3 itself is rather insoluble in most
solvents). The tetraalkoxy compounds, B2(OCH2CMe2CH2O)2
(B2neop2, 11) and B2(OCMe2CMe2O)2 (B2pin2, 12),14 were
(11) (a) Baker, R. T.; Nguyen, P.; Marder, T. B.; Westcott, S. A. Angew.
Chem., Int. Ed. Engl. 1995, 34, 1336. (b) Ishiyama, T.; Yamamoto,
M.; Miyaura, N. Chem. Commun. 1997, 689. (c) Iverson C. N.; Smith,
M. R., III. Organometallics 1997, 16, 2757. (d) Marder, T. B.; Norman,
N. C.; Rice, C. R. Tetrahedron Lett. 1998, 39, 155. (e) Dai, C.; Robins,
E. G.; Scott, A. J.; Clegg, W.; Yufit, D. S.; Howard, J. A. K.; Marder,
T. B. Chem. Commun., in press.
(12) Clegg, W.; Elsegood, M. R. J.; Lawlor, F. J.; Norman, N. C.; Pickett,
N. L.; Robins, E. G.; Scott, A. J.; Nguyen, P.; Taylor, N. J.; Marder,
T. B. Inorg. Chem. 1998, 37, 5289.
(13) (a) Nguyen, P.; Dai, C.; Taylor, N. J.; Power, W. P.; Marder, T. B.;
Pickett, N. L.; Norman, N. C. Inorg. Chem. 1995, 34, 4290. (b) Clegg,
W.; Dai, C.; Lawlor, F. J.; Marder, T. B.; Nguyen, P.; Norman, N.
C.; Pickett, N. L.; Power, W. P.; Scott, A. J. J. Chem. Soc., Dalton
Trans. 1997, 839.
(14) No¨th, H. Z. Naturforsch., Teil B 1984, 39, 1463.

5284 Inorganic Chemistry, Vol. 37, No. 20, 1998
Lawlor et al.
Table 1. Vertical Ionization Energies of the Bands in the
Photoelectron Spectra for the Diborane(4) Compounds 1, 3, 8, 11,
and 12 and also for Catechol, 4-But-catechol, Pinacol, and
2,2-Dimethyl-1,3-propanediol
prepared similarly, as were the dithiocatecholate analogues of
3 and 7, namely B2(1,2-S2C6H4) (13) and B2(1,2-S2-4-MeC6H3)2
(14).
compound
B2(NMe2)4 (1)
vertical ionization energy (eV)
7.16, 7.54, 8.94, 9.64, 12.25,
13.15, 14.67
catechol
8.43, 9.26, 11.42, 12.96, 14.36,
15.88, 17.92
B2cat2 (3)
8.81, 9.39, 12.13, 13.02, 14.02,
15.12, 16.84
8.17, 8.88, 12.70, 14.80, 15.82
8.43, 8.94, 10.85, 12.70, 14.61,
16.46
4-But-catechol
B2Butcat2 (8)
pinacol
B2pin2 (12)
9.89, 10.66, 12.63, 13.78
9.74, 10.74, 11.88, 12.19, 13.50,
14.34, 15.68
2,2-dimethyl-1,3-propanediol
B2neop2 (11)
10.09, 10.73, 13.27, 15.57
10.38, 11.25, 11.59, 12.79-13.73,
15.18,16.23
which manifests itself as a colorless crystalline dimeric material
after workup.
The structures of the complexes 3, 8, 9, 11, and 13-17 have
all been determined by X-ray crystallography, and these results
are presented in the companion paper.12
Photoelectron Spectroscopy. Prior to this work, PES studies
In addition to the main reaction scheme described above, there
are some secondary points which are important in the prepara-
tion of these diborane(4) compounds. First, in the case of 11,
the addition of HCl does not seem to be necessary as 11 does
not appear to form any stable adducts with NHMe2 and is
therefore available directly after addition of the diol HOCH2-
CMe2CH2OH to 1. Second, however, it is important when HCl
addition is required to allow sufficient time for 1 to react with
the catechol or diol. If HCl addition takes place before reaction
3 has gone nearly to completion, an alternative reaction pathway
is followed in which the HCl reacts directly with 1 to give the
complex [B2Cl4(NHMe2)2] (15) as shown in eq 5. In fact, the
reactivity of 1 toward HCl has been studied in some detail by
No¨th and Meister15 and by Malhotra,16 the nature of the product
depending on the relative amounts of 1 and HCl. Thus, No¨th
and Meister observed the following: 1 and 2 equiv of HCl
afforded B2Cl(NMe2)3 and [NH2Me2]Cl; 1 and 4 equiv of HCl
afforded B2Cl2(NMe2)2 and 2[NH2Me2]Cl; 1 and 6 equiv of HCl
afforded 15 and 2[NH2Me2]Cl; while 15 and 2 equiv of HCl
afforded the salt [NH2Me2]2[B2Cl6].
had only been carried out on B2Cl4 and B2F4 and on 1.18
17
Vertical ionization energy data for 1, 3, 8, 11, and 12 and also
for catechol, 4-But-catechol, pinacol, and 2,2-dimethyl-1,3-
propanediol are presented in Table 1, and the He I and He II
spectra for 1, 3, and 12 are shown in Figures 1-3. The other
PE spectra have been deposited as Supporting Information.
The spectrum of 1 (Fig. 1a,b) consists of four bands, which
appear as two overlapping pairs between 7 and 10 eV, and a
number of overlapping peaks above 11 eV. The He I spectrum
is identical to that obtained in the previous study,18 although
the higher resolution obtained here shows fine structure on the
broader band. The previous assignment of the PE spectrum of
118 assumed D2h symmetry; the first four bands were assigned
to the π4, π3, π2, and π1 orbitals principally N pπ in character
(these are labeled au, b1g, b3g, and b2u respectively in the D2h
point group). However, following the most recent structure
determination,19 reassignment within D2 symmetry is given in
Table 2. The dimethylamido groups are twisted out of the BN2
plane so that the N pπ electron pairs are not oriented to gain
maximum overlap with the B pπ orbital. The B pπ orbitals
transform as b2 and b3 in the D2 group while the N pπ orbitals
give a, b1, b2, and b3 symmetry-adapted linear combinations.
The a and b1 linear combinations have the N pπ orbitals out of
phase with one another and no stabilizing interaction with the
boron. These orbitals are expected to lie at higher energy and
give rise to the two lower IE bands at 7.16 and 7.54 eV. The
sharpness of these bands indicates their nonbonding character.
The b2 and b3 orbitals have boron 2p contributions and are
bonding and antibonding across the B-B bond, respectively.
They give rise to the broader bands at 8.94 and 9.64 eV. The
broader band shape of the b2 ionization at 9.64 eV is indicative
B2(NMe2)4 + 4HCl f [B2Cl4(NHMe2)2] + 2NHMe2 (5)
Third, it is important to distill carefully the starting complex
1 as the crude product is usually contaminated with some
B(NMe2)3 and this also reacts with catechols to give ammonium
bis-catecholate borates as shown in eq 6 for catechol itself, i.e.,
[NH2Me2][B(1,2-O2C6H4)2] (16).
(15) No¨th, H.; Meister, W. Z. Naturforsch., Teil B 1962, 17, 714.
(16) Malhotra, S. C. Inorg. Chem. 1964, 3, 862.
(17) (a) Lynaugh, N.; Lloyd, D. R.; Guest, M. F.; Hall, M. B.; Hillier, I.
H.; J. Chem. Soc., Faraday Trans. 2 1972, 68, 2192. (b) Lloyd, D.
R.; Lynaugh, N. J. Chem. Soc., Chem. Commun. 1971, 627.
(18) Cetinkaya, B.; King, G. H.; Krishnaumurthy, S. S.; Lappert, M. F.;
Pedley, J. B. J. Chem. Soc., Chem. Commun. 1971, 1370.
B(NMe2)3 + 2(1,2-(HO)2C6H4) f
[NH2Me2][B(1,2-O2C6H4)2] + 2NHMe2 (6)
(19) (a) Brain, P. T.; Downs, A. J.; MacCallum, P.; Rankin, D. W. H.;
Robinson, H. E.; Forsyth, G. A. J. Chem. Soc., Dalton Trans. 1991,
1195. (b) Brain, P. T. D.Phil. Thesis, University of Oxford, 1991.
Finally, careful control of the stoichiometry of eq 1 is required
as an excess of BCl3 leads to the complex BCl2(NMe2) (17)

Catecholate, Dithiocatecholate, and Tetraalkoxy Diboranes
Figure 1. Short-range He I spectrum (a) and He II spectrum (b) for 1.
Figure 2. He I spectrum (a) and He II spectrum (b) for 3.
Inorganic Chemistry, Vol. 37, No. 20, 1998 5285
Figure 3. He I spectrum (a) and He II spectrum (b) for 12.
Figure 4. Schematic representations of the 4a′′ and 3a′′ nonbonding
oxygen orbitals in catechol as dervied from EHMO calculations.
Table 2. Assignment of the Bands in the PES Spectrum of
B2(NMe2)4 (1)
band
IE (eV)
orbital
1
2
3
4
7.16
7.54
8.94
9.64
a
b1
b3
b2
orbital as the lower of the two so the first band at 8.43 eV is
assigned to the 4a′′ orbital and the second at 9.26 eV is assigned
to the 3a′′ orbital. An analogous assignment has been made
for phenol20 on the basis of an SCF calculation. The increase
in intensity of those two bands, on moving from the He I to the
He II spectrum, probably reflects both the smaller decrease of
the photoionization cross section of oxygen in comparison to
carbon and also the increase commonly found for C pπ orbitals
relative to C-H σ bonding orbitals.21
of significant bonding character. The separations of the first
and second bands (0.4 eV) and the third and fourth band (0.7
eV) give the size of interaction across the B-B bond, the
separation of the average of the first and second bands and the
average of the third and fourth bands of 2 eV is a measure of
the N-B π donation.
Comparison of the catechol spectrum with the 4-But-catechol
spectrum shows a shift of the two bands to lower ionization
energy in the spectrum of the latter. This reflects the inductive
effect of the But group through the σ system and the delocal-
The catechol and 4-But-catechol spectra give two sharp peaks
in the region 8-10 eV. These highest occupied orbitals are
those with the oxygen lone pairs out of phase with the C pπ
orbitals six-carbon ring (Figure 4 shows a schematic diagram
of the electron density for these orbitals derived from the EHMO
calculations). EHMO calculation gives the energy of the 3a′′
(20) Kimura, K.; Katsumatra, S.; Achiba, Y.; Yamazaki, T.; Iwata, S.;
Handbook of He I Photoelectron Spectra of Fundamental Organic
Molecules; Japan Scientific Societies Press: Tokyo, 1981.
(21) Yeh, J.-J. Atomic Calculation of Photoionisation Cross-Sections and
Asymmetry Parameters; Gordon and Breach Science Publishers S.A.:
Newark, NJ, 1993.

5286 Inorganic Chemistry, Vol. 37, No. 20, 1998
Lawlor et al.
Chart 1
Chart 2
ization of electron density through the phenyl group and oxygen
atoms. It should be noted that the first IE of both the catechols
occurs at a lower energy than either parent function, that is either
the corresponding arene or O lone pair. This is a strong
indication that the associated electron is delocalized over both
the oxygens and the ring.
In 3, which has a planar structure, four ionization bands are
expected in the low IE region, two arising from the catechol
pπ orbitals (au and b1g) and two from the interactions with the
in-phase and out-of-phase boron p orbitals (b3g and b2u). All
four orbitals are shown in Chart 1; for clarity only the O pπ
orbitals of the catechol function are included.
Table 3. Assignment of the PES Spectrum of B2pin2 (12)
IE (eV)
orbital
9.74
9.74
10.74
10.74
au
b1g
b3g
b2u
Table 4. Assignment of the PES Spectrum of B2neop2 (11)
IE (eV)
orbital
10.38
10.38
11.25
11.59
au
b1g
b3g
b2u
In the spectrum (Figure 2) the four associated ionization bands
are ill-defined but appear between 8.5 and 10 eV. This
assignment is supported by their increase in relative intensity
in moving from He I to He II photon energies, as was found
for the parent catechol. The separation of the four bands is
less distinct than for 1 even though the planar structure should
favor increased π bonding. One reason is that π donation from
the catechol to the B pπ orbital is confined to the 4a′′ orbital of
catechol. The IE difference found between the first two bands
in catechol should therefore decrease in 3 as is found. Second,
as the electrons are now to a significant extent localized on the
arene rings, the interaction across the B-B bond is less. As a
consequence, the low lying bands only spread across ca. 1.5
eV whereas the highest and the lowest in 1 are separated by
2.5 eV. The band at 12.13 eV must correspond to ionization
from the B-O σ bonds, as there is no analogous peak in the
catechol spectrum. Again, this is supported by the increase in
relative intensity of the band in the He II spectrum.
The spectrum of 8 may be assigned in an identical manner,
with the four bands between 8 and 10 eV corresponding to the
au, b1g, b3g, and b2u orbitals, respectively. However, the relative
intensity change of the band at 10.85 eV, assigned to the B-O
σ orbital is not nearly so marked as in the spectrum of 3. The
magnitude of the shift of the four bands to lower ionization
energy from 3 to 8 is approximately 0.4 eV, compared with the
analogous shift with an approximate magnitude of 0.34 eV from
catechol to 4-But-catechol. This larger shift for the diboron
compounds indicates the greater extent of the π framework in
these compounds, compared to the more limited π framework
in the free catechols.
The two bands at 9.89 and 10.66 eV can be assigned to these
π+ and π- orbitals, respectively. This assignment is supported
by the equal intensities of the two bands in the He II spectrum,
indicating equal oxygen character. The first two IE for pinacol
are higher than those of catechol, the expectation being that
they are more O localized.
The assignment for 12 is given in Table 3. The assignment
of the 10.74 eV band to the b3g and b2u orbitals is supported by
the smaller relative intensity of this band compared with those
from the au and b1g orbitals in the He II spectrum, which
indicates smaller oxygen character and greater boron character.
The separation between the two bands of ca.1 eV is less than
that of the average of the first two and the third and fourth band
of 1, which is ca. 2 eV. This indicates that in these alcohol
derivatives, B-O π interaction is less than the B-N π
interaction found in 1, again despite the more favorable planar
geometry. The B-O σ bond is assigned to the band at 11.88
eV.
The compound 2,2-dimethyl-1,3-propanediol shows the two
bands associated with the nonbonding oxygen orbitals at 10.09
and 10.73 eV, overlapping slightly. The remainder of the
spectrum, as expected, shows a similar shape to that of pinacol.
The assignment for 11 is given in Table 4. The b3g and b2u
have smaller relative intensity in the He I spectrum and a
decrease in photoionization cross section in the He II spectrum.
These effects reflect the decrease in oxygen character and
increase in boron character in comparison with the au and b1g
orbitals. The band due to the ionization from the B-O σ bond
does not show the usual dominance in the He II spectrum and
is consequently not assigned.
In considering the whole series of compounds, the following
trends may be identified. First, the replacement of oxygen for
nitrogen in the N2BBN2 framework leads to an increase in IE
of ca. 1.65 eV; second, the presence of an aromatic ring rather
than an aliphatic chain bonded to the oxygens in the O2BBO2
Pinacol exists in the trans form in all phases (with free rotation
around the C-C bond), meaning that it is not ideal for
comparison with 12, where the pinacolate is locked into the cis
form. The nonbonding, in phase π+ (stabilized by long-range
interactions) and the out of phase π- orbitals for pinacol are
shown in Chart 2 together with the analogous orbitals for the
less stable cis form.

Catecholate, Dithiocatecholate, and Tetraalkoxy Diboranes
Inorganic Chemistry, Vol. 37, No. 20, 1998 5287
allowed to stir at room temperature for an additional 10 h. After this
time, the solvent was removed in vacuo and the product was extracted
into toluene and filtered through Celite. After removal of the toluene
in vacuo, and subsequent washing with MeCN, 4.3 g of white solid 3
was obtained. The MeCN washings were concentrated and cooled (-30
°C) to give an additional 0.9 g of 3. The overall yield of 3 was 5.2 g
(72%). Spectroscopic data for 3. NMR (CD2Cl2): 1H δ 7.38 (m, 4H,
3,6-CH), 7.20 (m, 4H, 4,5-C-H); 13C{1H} δ 147.8 (s, 1,2-CO), 123.5
(s, 3,6-CH), 113.2 (s, 4,5-CH); 11B{1H} δ 31.6. Anal. Calcd for
C12H8B2O4: C, 60.60; H, 3.40. Found: C, 60.80; H, 3.20. MS (EI):
238 (M+, 100), 237 (50), 209 (4), 162 (28), 119 (9), 76 (13), 63 (12).
[B2(1,2-O2-C6H4)2(NHMe2)2] (4). A solution of catechol (0.220 g,
2 mmol) in 5 mL of Et2O was added to a stirred solution of 1 (0.198
g, 1 mmol) in 2 mL of Et2O at room temperature. The resulting reaction
mixture was allowed to stir for 30 min, then the solvent was removed
in vacuo affording the bis-amine adduct (4) as an insoluble white solid
(0.292 g, 89%). Anal. Calcd for C16H22B2N2O4: C, 58.59; H, 6.76.
Found: C, 58.57; H, 6.51.
framework decreases the IE by ca. 1.50 eV; and third, the
presence of electron-donating groups such as But or methyl
groups decrease the IE by ca. 0.40 eV. The first effect is a
consequence of the greater electronegativity of oxygen compared
with nitrogen such that the electrons are more difficult to ionize.
The second and third effects are linked to electron donation
from delocalization and inductive effects, which destabilize the
orbitals.
The ionization energies of the orbitals of the B2(OR)4 series
follow the trend 8 < 3 < 12 < 11, such that ionizations from
the orbitals in 8 occur at lowest IE. This is a consequence of
the effects mentioned above.
Separation in the π type orbitals indicate less π donation to
the boron in the alkoxide than the amido derivatives. In 1 there
is evidence of interaction between the π orbitals across the B-B
bond.
[B2(1,2-O2-3,5-But2-C6H2)2(NHMe2)2] (5). A solution of 3,5-di-
tert-butylcatechol (0.888 g, 4.0 mmol) in Et2O (5 mL) was added to a
solution of 1 (0.396 g, 2.0 mmol) in Et2O (5 mL) at 0 °C which gave
a white precipitate. The solvent was removed by syringe, and the solid
was washed with Et2O (10 mL) before being dried in vacuo (0.75 g,
68%). Spectroscopic data for 5. NMR (CDCl3): 1H δ 6.70 (d, 2H,
6-CH, JHH ) 2.1 Hz), 6.55 (d, 2H, 4-CH, JHH ) 2.1 Hz), 6.27 (v br
s, 2H, NH), 2.45 (br s, 12H, NMe), 1.34 (s, 18H, But), 1.22 (s, 18H,
But); 11B{1H} δ 11.8. Anal. Calcd for C32H54N2O4B2: C, 69.58; H,
9.85; N, 5.07. Found: C, 69.93; H, 10.40; N, 4.87.
Experimental Section
General Considerations. All reactions were performed under an
atmosphere of dry dinitrogen using standard Schlenk or glovebox
techniques. All solvents were dried and distilled prior to use according
to established procedures. Pinacol, 2,2-Me2-1,3-propanediol (neopentyl
glycol), catechol, 3-Me-catechol, 4-Me-catechol, 4-But-catechol, 3,5-
But2-catechol, 1,2-dithiocatechol, and 1,2-dithio-4-Me-catechol were
purchased from Aldrich, and their purity was checked by GC/MS and/
or NMR spectroscopy prior to use.
4
4
Nuclear magnetic resonance experiments were performed on Bruker
AC200, WP200, WM300, AM500, and AMX500 spectrometers at the
following frequencies: 1H, 200, 300, or 500 MHz; 13C{1H}, 50, 75, or
125 MHz; and 11B{1H}, 64 or 160 MHz. 1H chemical shifts were
referenced either to the internal standard tetramethylsilane (TMS) or
B2(1,2-O2-3-MeC6H3)2 (6). Compound 1 (1.00 g, 5.0 mmol) was
dissolved in Et2O (10 mL) at 0 °C and a solution of 3-methylcatechol
(1.24 g, 10 mmol) in Et2O (10 mL) was then added slowly. A white
precipitate formed immediately, and after 30 min, a solution of 1.0 M
HCl in Et2O (25 mL, 25 mmol) was added dropwise and the reaction
mixture allowed to warm to room temperature and stir overnight. The
solvent was then partially removed in vacuo, and the white solid was
extracted into toluene (40 mL) and filtered through Celite, affording a
colorless solution from which white crystals of 6 were obtained over
24 h at -30 °C (0.93 g, 70%). Spectroscopic data for 6. NMR
(CDCl3): 1H δ 7.14 (d, 2H, 6-CH, 3JHH ) 7.5 Hz), 7.01 (t, 2H, 5-CH,
3JHH ) 7.5 Hz), 6.94 (d, 2H, 4-CH, 3JHH ) 7.5 Hz), 2.43 (s, 6H, Me);
13C{1H} δ 147.3 and 146.4 (s, 1 and 2-CO), 124.7 (s, 6-CH), 123.5 (s,
3-CMe), 123.0 and 110.4 (s, 4 and 5-CH), 14.8 (s, Me); 11B{1H} δ
30.5. Anal. Calcd for C14H12B2O4: C, 63.25; H, 4.55. Found: C,
63.25; H, 4.50. HRMS calcd for C14H12B2O4: 266.0922. Found:
266.0919.
B2(1,2-O2-4-MeC6H3)2 (7). Using the same method as that for 6, a
solution of 4-methylcatechol (1.24 g, 10 mmol) in Et2O (10 mL) was
added to a solution of 1 (1.00 g, 5.0 mmol) in Et2O (10 mL) at 0 °C
giving a white precipitate. A 1.0 M solution of HCl in Et2O (25 mL,
25 mmol) was added dropwise and the reaction mixture was allowed
to stir overnight. Reduction of the solvent volume, extraction into
toluene and filtration through Celite afforded white crystals of 7 (0.89
g, 67%). Spectroscopic data for 7. NMR (CDCl3): 1H δ 7.28 (d, 2H,
1
to residual H resonances in the deuterated solvents, all 13C chemical
shifts were referenced to the solvent resonances and are relative to the
external standard TMS, and 11B chemical shifts were referenced to
external BF3‚(OEt2). All spectra were recorded in CDCl3 unless
otherwise stated. Elemental analyses were obtained either from M-H-W
Laboratories (Phoenix, AZ) or the University of Newcastle upon Tyne.
GC/MS analyses were performed on a Hewlett-Packard 5890 series
II/5971A MSD instrument equipped with an HP 7673A autosampler
and a fused silica column (30 m × 0.25 mm × 0.25 mm, cross-linked
5% phenylmethyl silicone). The following operating conditions were
used: injector, 260 °C; transfer line, 280 °C; oven temperature was
ramped from 70 °C to 260 °C at the rate of 20 °C/min. UHP grade
helium was used as the carrier gas. Hrms spectra were recorded on a
Kratos MS-80 instrument. Extended Hu¨ckel molecular orbital (EHMO)
calculations were performed on idealized B2cat2 and on the simplified
model compounds B2(NH2)4 and B2(OCH2CH2O)2 using standard
parameters and charge iteration sequences.22
Photoelectron Spectra. The photoelectron (PE) spectra were
measured using a PES Laboratories 0078 photoelectron spectropho-
tometer which has a hollow cathode He discharge lamp capable of
providing both He I and He II radiation. The samples were held at a
constant temperature in the ranges given below, giving a vapor pressure
of ca. 4 × 10-2 mmHg, and data were collected on the gas-phase
molecules by repeated scans using an Atari microprocessor. The
spectra were calibrated with reference to N2, Xe and He. Recording
temperatures (°C) were as follows: B2(NMe2)4 (1), room temperature;
B2(1,2-O2C6H4)2 (3), 118-140; B2pin2 (12), 20-40; B2(1,2-O2-4-
ButC6H3)2 (8), 120-148; B2(OCH2CMe2CH2O)2 (11), 85-100; cat-
echol, 35-50; 4-Butcatechol, 55-60; pinacol, 25-40; and 2,2-dimethyl-
1,3-propanediol, 35-40.
6-CH, 3JHH ) 8.1 Hz), 7.23 (s, 2H, 3-CH), 7.02 (d, 2H, 5-CH, 3JHH
)
8.1 Hz), 2.45 (s, 6H, Me); 13C{1H} δ 147.8 and 145.6 (s, 1 and 2-CO),
133.5 (s, 4-CMe), 123.9 (s, 5-CH), 113.5 and 112.3 (s, 3 and 6-CH),
21.4 (s, Me); 11B{1H} δ 30.6. Anal. Calcd for C14H12B2O4: C, 63.25;
H, 4.55. Found: C, 63.70; H, 4.40. HRMS calcd for C14H12B2O4:
266.0922. Found: 266.0923.
B2(1,2-O2-4-ButC6H3)2 (8). 4-Butcatechol (10.5 g, 63.3 mmol) was
added to a stirred solution of 1 (5.7 g, 28.8 mmol) in hexane (300 mL)
at room temperature. To this solution was then added 150 mL of a 1
M solution of HCl in Et2O dropwise over a period of 30 min, and the
resulting mixture was allowed to stir at room temperature for 5 h. After
this time, the solvent was removed in vacuo and the product was
extracted into hexane and filtered through Celite. Upon removal of
hexane in vacuo, 8.8 g (88%) of 8 was obtained as a white solid.
Spectroscopic data for 8. NMR (CDCl3): 1H δ 7.36 (m, 2H, 6-CH),
7.17 (m, 4H, 3 and 5-CH), 1.29 (s, 18H, But); 13C{1H} δ 147.7 and
147.3 (s, 1 and 2-CO), 145.4 (s, 4-CBut), 120.3 and 112.0 and 110.2
(s, 3 and 5 and 6-CH), 34.9 (s, C(CH3)3), 31.7 (s, C(CH3)3); 11B{1H}
Preparations. B2(1,2-O2C6H4)2 [2,2′-Bis(1,3,2-benzodioxaborole)]
(3). Catechol (7.3 g, 66.6 mmol) was added to a stirred solution of 1
(6.0 g, 30.3 mmol) in Et2O (250 mL) at room temperature. After
stirring for several hours, the reaction flask was placed in an ice/water
bath and 152 mL of a 1 M solution of HCl in Et2O was added dropwise
over a period of 30 min. The resulting reaction mixture was then
(22) Hoffmann, R. J. Chem. Phys. 1963, 39, 1397.

5288 Inorganic Chemistry, Vol. 37, No. 20, 1998
Lawlor et al.
δ 31.9. Anal. Calcd for C20H24B2O4: C, 68.65; H, 6.90. Found: C,
68.80; H, 7.05. MS (EI): 350 (M+, 18), 335 (100), 319 (3), 307 (8),
295 (2), 251 (4), 160 (8), 132 (11), 89 (3), 77 (3), 57 (4).
MS (EI): 254 (M+, 1), 239 (39), 238 (19), 171 (3), 155 (7), 139 (6),
129 (7), 113 (10), 84 (100), 83 (37), 69 (26), 57 (8).
B2(1,2-S2-C6H4)2 (13). Compound 1 (0.31 mL, 1.76 mmol) was
dissolved in Et2O (5.0 mL) and cooled to 0 °C. To this was added a
solution of benzene-1,2-dithiol (0.500 g, 3.515 mmol) in Et2O (5.0 mL).
A white precipitate was observed immediately. After 5 min, a 1.0 M
solution of HCl in Et2O (8.80 mL, 8.80 mmol) was added dropwise.
The reaction mixture was then stirred for 24 h, after which time the
solvent was removed in vacuo. The remaining white solid was extracted
into toluene (20 mL) and filtered through Celite to give a colorless
solution from which white crystals of 13 formed over 12 h at 5 °C
(0.402 g, 76%). Spectroscopic data for 13. NMR (CDCl3): 1H δ 7.98
(m, 4H, 3,6-CH), 7.43 (m, 4H, 4,5-CH); 13C{1H} δ 143.6 (s, 1 and
2-CS), 126.7 and 125.6 (s, 4,5 and 3,6-CH); 11B{1H} δ 57.9. Anal.
Calcd for C12H8B2S4: C, 47.70; H, 2.65. Found: C, 47.70; H, 4.57.
HRMS Calcd for C12H8B2S4: 301.9695. Found: 301.9704.
B2(1,2-O2-3,5-But2-C6H2)2 (9). Using the same method as for 8, a
solution of 3,5-di-tert-butylcatechol (2.22 g, 10 mmol) in Et2O (10 mL)
was added to a solution of 1 (1.00 g, 5.0 mmol) in Et2O (10 mL) at 0
°C giving a white precipitate. A 1.0 M solution of HCl (25 mL, 25
mmol) was added dropwise and the reaction mixture was allowed to
stir overnight at 0 °C. The product was extracted into toluene (40 mL)
and after filtering through Celite, the volume was reduced by 50%.
After 24 h at -30 °C, white crystals of B2(1,2-O2-3,5-But2-C6H2)2 were
collected, washed with hexanes (40 mL), and dried in vacuo (1.45 g,
63%). Spectroscopic data for 9. NMR (CDCl3): 1H δ 7.28 (d, 2H,
4
4
6-CH, JHH ) 2 Hz), 7.13 (d, 2H, 4-CH, JHH ) 2 Hz), 1.50 (s, 18H,
But), 1.35 (s, 18H, But); 13C{1H} δ 148.3 and 145.6 (s, 1 and 2-CO),
144.0 and 134.9 (s, 3 and 5-CBut), 116.4 and 107.6 (s, 4 and 6-CH),
35.0 (s, C(CH3)3), 34.5 (s, C(CH3)3), 31.9 (s, C(CH3)3), 29.9 (s,
C(CH3)3); 11B{1H} δ 31.6. Anal. Calcd for C28H40B2O4: C, 72.75;
H, 8.70. Found: C, 72.90; H, 8.75. MS (EI): 463 (M + 1+, 19), 462
(M+, 54), 461 (27), 448 (37), 447 (100), 446 (57), 445 (7), 233 (13),
216 (29), 86 (20), 84 (31), 57 (73).
B2(1,2-S2-4-MeC6H4)2 (14). Using a method similar to that above,
a solution of 4-methyl-1,2-dithiocatechol (1.179 g, 7.545 mmol) in Et2O
(10 mL) was added to a solution of 1 (0.67 mL, 3.772 mmol) in Et2O
(10 mL) at 0 °C to give a white precipitate. A 1.0 M solution of HCl
in Et2O (18.86 mL, 18.86 mmol) was added and the reaction was stirred
overnight. Reduction of the solvent volume was followed by extraction
into toluene and filtration through Celite. The volume of filtrate was
reduced and the solution was cooled, affording a white precipitate which
was separated by decanting the solvent. White crystals of 14 were
obtained by cooling a CH2Cl2 solution to 5 °C for 48 h (0.598 g, 48%).
Spectroscopic data for 14. NMR (CDCl3): 1H δ 7.72 (d, 2H, 6-CH,
JHH ) 8.1 Hz), 7.66 (m, 2H, 3-CH), 7.12 (d m, 2H, 5-CH, JHH ) 8.1
Hz), 2.38 (s, 6H, Me); 13C{1H} δ 143.8 and 140.5 (s, 1 and 2-CS),
139.4 (s, 4-CMe), 127.0 and 126.7 and 126.0 (s, 3 and 5 and 6-CH),
21.1 (s, Me); 11B{1H} δ 58.1. Anal. Calcd for C14H12B2S4: C, 50.95;
H, 3.65. Found: C, 51.20; H, 3.67. HRMS calcd for C14H12B2S4:
330.0008. Found: 330.0021.
B2(1,2-O2-3-MeOC6H3)2 (10). A solution of 3-methoxycatechol
(1.00 g, 7.135 mmol) was added to a solution of 1 (0.63 mL, 0.707 g,
3.57 mmol) in Et2O (30 mL). A white precipitate formed immediately.
The reaction mixture was allowed to stir for 4 h after which time a 1
M solution of HCl in Et2O (14.14 mL, 14.14 mmol) was added. After
the mixture had stirred for a further 12 h, the volatiles were removed
in vacuo, and the remaining solid was redissolved in toluene (40 mL)
and filtered through a small amount of Celite to afford a colorless
solution over which hexanes (40 mL) were layered. Solvent diffusion
over 48 h at -30 °C afforded a white solid. (0.771 g, 72%).
Spectroscopic data for 10. NMR (CDCl3): 1H δ 7.18 (t, 2H, 5-CH,
3
3JHH ) 7.5 Hz), 7.02 and 6.80 (d, 4H, 4 and 6-CH, JHH ) 7.5 Hz);
13C{1H} δ 149.2 and 146.3 (s, 1 and 2-CO), 137.5 (s, 3-COMe), 123.6
and 108.0 and 105.9 (s, 4 and 5 and 6-CH), 56.7 (s, OMe); 11B{1H} δ
28.6. Anal. Calcd for C14H12B2O6: C, 56.45; H, 4.06. Found: C,
56.34; H, 4.30. MS (EI): 300 (M + 2+, 3), 298 (M + 1+, 17), 298
(M+, 100), 297 (56), 296 (7), 283 (9), 282 (5), 255 (6), 149 (6), 107
(8), 79 (9).
[B2Cl4(NHMe2)2] (15). This compound was isolated when HCl was
added to 1 before complete reaction with the diols (e.g. pinacol or
neopentyl glycol) had taken place. Spectroscopic data for 15. NMR
(CDCl3): 1H δ 4.75 (br s, 1H, NH), 2.75 (d, 6H, NMe), 3JHH ) 6 Hz);
13C{1H} δ 39.4 (s); 11B{1H} δ 9.5. Anal. Calcd for C4H14N2B2Cl4:
C, 19.30; H, 5.45; N, 10.80. Found: C, 19.05; H, 5.50; N, 10.85.
B2(OCH2CMe2CH2O)2 (11). Neopentyl glycol (2,2-dimethyl-1,3-
propanediol) (2.1 g, 20.2 mmol) was added to a stirred solution of 1
(2.0 g, 10.1 mmol) in Et2O (50 mL) at room temperature. The reaction
mixture was stirred at ambient temperature for 5 h and was then cooled
to -78 °C in a dry ice/acetone bath. To this cooled solution was added
50 mL of a 1 M solution of HCl in Et2O dropwise via an addition
funnel over a period of 2 h. After warming slowly to room temperature,
the solvent was removed in vacuo and the product was extracted into
hexane using a Soxhlet apparatus. Subsequent recrystallization from
hexane/CH2Cl2 (90/10) afforded 1.45 g (64%) of 11 as a white solid.
Spectroscopic data for 11. NMR (CDCl3): 1H δ 3.35 (s, 8H, CH2),
0.91 (s, 12H, CMe2); 13C{1H} δ 71.6 (s, CH2), 31.7 (s, CMe2), 22.1 (s,
CMe2); 11B{1H} δ 28.4. Anal. Calcd for C10H20B2O4: C, 53.15; H,
8.90. Found: C, 52.95; H, 9.00. MS (EI): 226 (M+, 1), 211 (5), 115
(20), 103 (8), 99 (8), 89 (13), 70 (78), 69 (100), 56 (53), 55 (72).
B2(OCMe2CMe2O)2 (12). Pinacol (2.7 g, 22.8 mmol) was added
to a stirred solution of 1 (2.2 g, 11.1 mmol) in Et2O (50 mL) at room
temperature. The reaction mixture was allowed to stir at ambient
temperature for 5 h and then cooled to -78 °C in a dry ice/acetone
bath. To this was added 50 mL of a 1 M solution of HCl in Et2O
dropwise via an addition funnel over a period of 2 h. After warming
slowly to room temperature, the solvent was removed in vacuo and
the product was extracted into hexane and then filtered through Celite.
Upon removal of hexane in vacuo, 2.2 g (76%) of 12 was obtained as
a white solid. Spectroscopic data for 12. NMR (CDCl3): 1H δ 1.27
(s, 24H, Me); 13C{1H} δ 83.4 (s, CMe), 24.9 (s, CMe); 11B{1H} δ 30.7.
[NH2Me2][Bcat2] (16). Neat B(NMe2)3 (0.143 g, 1 mmol) was added
to a solution of catechol (0.222 g, 2 mmol) in Et2O (3 mL). The
resulting precipitate was collected and washed thoroughly with Et2O
(20 mL), followed by drying in vacuo to afford 16 (0.250 g, 91%) as
an insoluble white solid. Spectroscopic data for 16. NMR (CH3CN/
C6D6): 11B{1H} δ 14.0. Anal. Calcd for C14H16NO4B: C, 61.57; H,
5.91. Found: C, 61.67; H, 5.93.
Acknowledgment. T.B.M. thanks the NSERC of Canada
for research funding, N.C.N. and J.C.G. thank the EPSRC for
support, P.N. thanks NSERC for a Postgraduate Fellowship,
F.J.L. and E.G.R. thank EPSCR for studentships, P.N., N.P.,
F.J.L., and G.L. thank the British Council (Ottawa) for travel
scholarships, T.B.M. thanks the University of Newcastle upon
Tyne for a Visiting Senior Research Fellowship, and T.B.M.
and N.C.N. thank NSERC and The Royal Society (London) for
supporting this collaboration through the Bilateral Exchange
Program.
Supporting Information Available: Photoelectron spectra for
catechol, 4-But-catechol, 8, pinacol, 2,2-dimethyl-1,3-propanediol, and
11, Figures 5-10, are available (6 pages). Ordering information is
given on any current masthead page.
IC980425A