Solution-state 15N NMR and solid-state single-crystal XRD study of heterosubstituted diazaboroles and borinines prepared via an effective and simple microwave-assisted solvent-free synthesis

Article abstract of DOI:10.1016/j.jorganchem.2012.09.018

A quick and simple, solvent-free synthesis of nitrogen-basedboroles and borinines derived from 1,2-diaminobenzene and 1,8-diaminonaphthalene is reported and compared with the traditional synthetic method. Characterization by ¹⁵N NMR spectroscop

Full text of DOI:10.1016/j.jorganchem.2012.09.018

Journal of Organometallic Chemistry 723 (2013) 122e128
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
15
Solution-state N NMR and solid-state single-crystal XRD study of
heterosubstituted diazaboroles and borinines prepared via an effective and simple
microwave-assisted solvent-free synthesis
*
Cathryn A. Slabber, Craig D. Grimmer, Ross S. Robinson
School of Chemistry, University of KwaZulu-Natal, Private Bag X01, Scottsville, Pietermaritzburg 3209, South Africa
a r t i c l e i n f o
a b s t r a c t
Article history:
A quick and simple, solvent-free synthesis of nitrogen-basedboroles and borinines derived from
1,2-diaminobenzene and 1,8-diaminonaphthalene is reported and compared with the traditional
synthetic method. Characterization by 15N NMR spectroscopy of 12 compounds and single crystal X-Ray
diffraction of 4 compounds provides supporting evidence for donation of electron density, from the
N-atom to the vacant pz orbital of the B-atom. Furthermore comparison of the hitherto unreported
crystal structure of 2-(4-Methylphenyl)-naptho[1,8-de][1,3,2]diazaborinine with similar compounds
made in these laboratories reveals that solid-state packing and the dihedral angle between naphthyl and
phenyl rings is determined by competing inter- and intra-molecular forces.
Received 4 June 2012
Received in revised form
17 September 2012
Accepted 26 September 2012
Keywords:
Borane
Microwave chemistry
Solid-state reaction
15N NMR spectroscopy
X-ray diffraction
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
Miyaura reactions, but their use is limited when compared with that
of the dioxoborole-based reagents [5].
While the use of boron-containing compounds is popular for
such reactions as the SuzukieMiyaura reaction and the Petasis
reaction, the vast majority of the literature deals with the use of
boronic acids or alkylated dioxoboroles, most of which have been
based upon unstable boranes, such as catecholborane (HBCat) and
pinacolborane (HBPin). These reagents have been reported to
undergo disproportionation reactions (Scheme 1), resulting in
lower reaction yields, and are air- and moisture-sensitive [1,2].
In order to avoid the problems encountered when working with
reagents based on HBCat and HBPin, other heterosubstitutedboranes
such as 2-phenyl-1,3,2-benzodiazaborole (HBPda) (Fig. 1) have been
investigated [3]. These reagents are more stable with regards to
storage and handling, but are also less reactive towards olefins,
requiring the use of rhodium(I)-based catalysts, such as Wilkinson’s
Catalyst (Rh(PPh3)3Cl), to form the alkylated borole reagents needed
for further reactions (Scheme 2), and these reactions are at present
limited to the formation of terminal boron-carbon bonds [2,4]. Dia-
zaborole reagents have been successfully used as reagents in Suzukie
Consequently, an alternative method of creating these reagents
was sought in order to make the reaction more cost-effective and to
expand the scope of the reaction. Literature had presented
a possible method which makes use of commercially available
boronic acids and simple 1,2-diols or diamines to create a wide
range of dioxo- or diazaboroles and borinines (Scheme 3) [6,7].
However, these reactions make use of hazardous solvents such as
benzene and toluene, and therefore, in an attempt to find
a “greener” method, a solventless approach was desired. This is
possible, as these compounds have previously been made in
a solvent less method using a ball mill [8]. Our thoughts then
turned to the use of microwave irradiation instead of ball-milling,
as this could potentially reduce the reaction time dramatically.
Should this methodology prove successful, this could provide
a rapid and easy method of creating similar heterosubstituted
boroles and borinines as a large variety of boronic acids are
commercially available, and others can be created using Grignard-
type procedures [9,10]. These reagents could then be utilized
further in SuzukieMiyaura or Petasis-type reactions [11].
In this article we present the successful implementation of
microwave irradiation in the creation of a number of diazaboroles
and diazaborinines using a simple and effective solvent-free reac-
tion methodology. We also present the first X-ray crystal structure
* Corresponding author.
E-mail address: robinsonr@ukzn.ac.za (R.S. Robinson).
0022-328X/$ e see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2012.09.018

C.A. Slabber et al. / Journal of Organometallic Chemistry 723 (2013) 122e128
123
H
N
BH
H
B
N
N
O
O
R
Rh(I) cat
+
R
BH
+ BH3
O
O
O
O
O
O
N
B
B
H
H
3eq
Scheme 2. Rh(I)-catalysed alkylation of HBPda.
Scheme 1. The disproportionation reaction of HBCat.
both the solution and the microwave reactions showed no evidence
of side products. As in the previous reactions with 1, a Dean and
Stark trap was employed for the solution reactions, while the
microwave synthesis reaction products were allowed to air dry.
As with compounds 3aef, the 15N chemical shifts of compounds
5aef (Table 4) show a significant downfield shift relative to the
starting amine (Fig. 4), again indicating the probability of electron
back-donation occurring between the nitrogen and boron.
Onremovalof the solutionreactionof 4 and2d fromheat, crystals
were observed to be forming as the solution cooled. This prompted
the growth of single crystals of 5d suitable for X-ray diffraction
analysis, as very little solid state structural information has been
reported for any compound containing such a nitrogeneboron bond
[16]. A perspective view of the molecule is given in Fig. 5.
of 2-(4-Methylphenyl)-naphtho[1,8-de][1,3,2]diazaborinine and
compare it with the structures of other similar compounds deter-
mined in these laboratories.
2. Results and discussion
In order to test the possibility of creating diazaboroles using this
methodology, o-phenylenediamine 1 was combined with a number
of commercially available boronic acids 2aef with both electron-
donating and electron-withdrawing substituents (Scheme 4). Two
different methods were evaluated in order to determine whether
any advantage is gained by using microwave irradiation over the
standard synthesis conditions of refluxing toluene.
To date, crystal structures have been determined for compounds
5a [17], 5b [18], 5d [this work], and 5e [19]. Selected structural data
for these compounds are given in Table 5.
To our delight, the desired products 3aef were obtained in very
good yields in all cases (Table 1) [12]. While the yields are not as
high as those reported by Kaupp et al. [8], access to a microwave
oven in a synthetic laboratory is far more common than a ball-mill
and the microwave procedure reported here requires a far shorter
reaction time. Further purification of the products was not required
as the products of the solution reactions precipitated out of solution
on cooling to room temperature, and the NMR analyses of the
products from the microwave reactions showed no side products.
The use of a Dean and Stark trap in the solution reactions allowed
for the removal of the water produced in the reaction, while the
products from the microwave reactions were allowed to air dry.
As standard procedure, complete NMR analyses were carried
out on compounds 3aef, including measurement of 15N NMR
chemical shifts via either 15Ne1H HSQC or HMBC experiments. In
all cases, it is interesting to note that the 15N chemical shifts of
compounds 3aef (Table 2) are in the region between that typical of
sp3-hybridized nitrogen atoms (0e90 ppm) and the region corre-
sponding to sp2-hybridized nitrogen atoms (from 220 ppm) [13]
(Fig. 2). This could corroborate the prevailing thought that elec-
tron donation occurs from the lone pair of electrons present on
nitrogen atoms to the vacant pz orbital situated on the boron atoms
(Fig. 3) [2,14,15]. This theory is further supported by DFT calcula-
tions carried out by Weber et al. [16], which show orbital overlap
between the nitrogen atoms and the boron atoms in the HOMO
calculations for structurally similar compounds.
We first note that there are no significant differences between
ꢀ
the BeC bond lengths. The value of 1.568A measured for compound
5b appears longer, but with a relatively high standard deviation of
ꢀ
0.004A (that takes no account of systematic errors) it cannot be
described as significantly different from the other BeC distances.
ꢀ
However, the average BeN distance of 1.441(1)A determined for
compound 5d is significantly longer than the (very similar) values
measured for the other three compounds. Differences in the BeN
distances in diazaboroles can be explained in terms of the back
donation of electron density hypothesis, a hypothesis which is
underpinned by ELF calculations of the type carried out by Berski,
et al. [20]. These calculations show that a partial double bond exists
between the boron and nitrogen atoms, and that two or more
resonance hybrids need to be considered; BeN distances in the
ꢀ
ꢀ
range 1.413A to 1.442A are predicted, the exact value depending on
the extent of back donation of the nitrogen lone pair into the vacant
pz orbital on the boron atom. Compound 5d is distinguished from
compounds 5a, 5b and 5e by the attachment to the boron atom of
an electron donating tolyl group. For this reason, the electron
density on the boron atom in 5d will be higher than that on the
boron atom in the other three compounds; back donation will be
correspondingly less, the BeN bond will have less double bond
character and so the bond lengthens. In fact, the BeN bond lengths
ꢀ
determined for compounds 5a, 5b and 5e (average ¼ 1.413A) are
Due to the success of the coupling reactions with 1, the same
methodology was used in reactions with 1,8-diaminonaphthalene
4. As with the reactions with 1, very good results were obtained
(Table 3). Again, the same comment on the yield and reaction time
of the microwave procedure vs the ball-milling procedure applies
(vide supra). Further purification of the products was not required
for these reactions either as the NMR analyses of the products from
ꢀ
significantly shorter than those of w1.437A reported by Weber,
et al. [16], consistent with a high degree of back donation when
electron withdrawing groups are attached to the boron atom. We
now examine the dihedral angles shown for compounds 5a, 5b, 5d
and 5e in Table 5. These angles provide a measure of the twist of the
phenyl group out of the plane defined by the atoms of the
Hn-1
H
N
BH
N
H
XHn
X
X
HO
HO
-2H2O
B
R
B
R
+
XHn
Hn-1
X = O, N
Fig. 1. 2-Phenyl-1,3,2-benzodiazaborole (HBPda).
Scheme 3. Synthesis of boroles from boronic acids.

124
C.A. Slabber et al. / Journal of Organometallic Chemistry 723 (2013) 122e128
Table 2
15N NMR shifts for compounds 3aef.
Compound
15N NMR signal (ppm)
3a
3b
3c
3d
3e
3f
104
111
107
110
109
113
napthodiazaborinine grouping. For compounds 5a and 5b the
dihedral angle is small (6e8ꢀ) and so these two molecules are
essentially planar. In contrast, the dihedral angles of 23ꢀ and 19ꢀ
measured for compounds 5d and 5e respectively are large,
rendering these two molecules non-planar. This would not be
expected from a consideration of intramolecular non-bonded
repulsions, in particular between the ortho protons of the phenyl
group and the NeH protons; these are expected to be much the
same for all four molecules in view of the close similarity in the BeC
distances (vide supra). More likely is that differences in the dihedral
angle are due to crystal packing forces. Consistent with this inter-
pretation is that the packing motifs for compounds 5a and 5b are
quite different from those of compounds 5d and 5e. For the former,
the planar molecules stack parallel to each other along one of the
Scheme 4. Synthesis of compounds 3aef from o-phenylenediamine1 and boronic
acids 2aef.
Table 1
Synthesis of 1,3,2-benzodiazaboroles 3aef.
Entry Boronic
acid
Product
Yielda Yieldb
H
N
B
1
2a
95
95
unit cell axes with the stacks stabilised by attractive
tions [21]. For compound 5e, the molecules stack in a staircase
motif with successive molecules (steps) bound alternately by
interactions between naptho groups, and CeH(methyl)/ (naptho)
sep interac-
N
H
sep
3a
p
interactions. In fact, the latter interaction is facilitated by the
out-of-plane bending of the phenyl group (see Fig. A.1). For
compound 5d there is no stacking discernable in the crystal
structure: rather the moelcules adopt a zig-zag motif through the
crystal (see Fig. A.2). We do not believe that this is because of any
intermolecular steric effect due to the methyl group; after all, the
van der Waals radii for the chlorine atom (in 5b) is very similar to
that of a methyl group [22], and compound 5b is nearly planar.
More likely is that it can be ascribed to the electron richness of the
H
N
B
Cl
2
2b
97
92
N
H
3b
3c
H
N
CH
3
tolyl group, which has a result that
pep repulsions between
B
O
parallel stacked molecules would be strong e too strong to be
compensated for by attractive sep interactions [21].
3
2c
94
88
N
H
3. Conclusions
H
N
We have successfully synthesised a range of diazaboroles in very
good to excellent yields with no evidence of any side products,
using microwave irradiation under solvent-free conditions. This
simple methodology allows the rapid synthesis of boron reagents,
which could be used in other popular applications, such as the
SuzukieMiyaura and the Petasis reactions. 15N NMR spectroscopic
B
CH
3
4
5
2d
2e
89
95
82
87
N
H
3d
H
N
analysis of these twelve compounds showed
a significant
CH
3
B
B
S
Pyridine/pyrrole
Amide
Amine
47
N
H
550
0ppm
90
135
220
3e
H
N
110
H
N
NH2
6
2f
90
73
N
H
CH
3
B
CH3
H C
3
N
H
NH2
3f
a
Reaction conditions: 1 (2 mmol), 2 (2 mmol) Toluene (50 ml), 110 ꢀC, 3 h.
Reaction conditions: 1 (0.4 mmol), 2 (0.4 mmol) 150 ꢀC, 150 W, 15 min.
Fig. 2. Diagrammatic representation of therelative 15N NMR chemical shifts (not to scale).
b

C.A. Slabber et al. / Journal of Organometallic Chemistry 723 (2013) 122e128
125
Table 4
15N NMR shifts for compounds 5aef.
Compound
15N NMR signal (ppm)
5a
5b
5c
5d
5e
5f
101
101
101
101
101
100
downfield shift in the position of the signal, away from the region of
typical sp3-hybridized amines and towards the region typical of
sp2-hybridized amines. These observations support the theory of
electron back-donation from the nitrogen lone pair to the vacant pz-
orbital on the boron atom. Also supportive of the idea of back
donation is an analysis of the BeN bond lengths, measured by
means of X-Ray diffraction analysis of four diaminonaphthalene-
based borinines. The X-ray analysis also shows (unexpectedly)
that not all four molecules are planar, an observation that is
explained in terms of crystal packing effects e very different
packing motifs are obtained for the near planar molecules on one
hand, and the non-planar molecules on the other.
Fig. 3. Back-donation of the nitrogen lone pair into the vacant pz boron orbital.
Table 3
Synthesis of naphtho[1,8-de][1,3,2]diazaborinines 5aef.
Entry Boronic
acid
Product
Yielda Yieldb
H
N
B
1
2a
85
90
N
H
4. Experimental
5a
4.1. General procedures for the synthesis of compounds 3aef
H
N
4.1.1. Method A
B
Cl
O
To a solution of o-phenylenediamine in toluene (2 mmol in
50 ml) was added the boronic acid (2 mmol) in one portion. The
round-bottomed flask was equipped with a Dean and Stark trap,
and the solution was stirred and heated to reflux at 110 ꢀC for 3 h.
The precipitate was isolated by filtration and washed with minimal
solvent (toluene).
2
2b
75
88
N
H
5b
H
N
CH
3
4.1.2. Method B
B
3
2c
80
95
Theo-phenylenediamine (0.4 mmol) and boronic acid
(0.4 mmol) were added to a microwave tube and sealed with
a microwave septum. The tube was shaken to mix and subjected to
microwave irradiation at 150 ꢀC for 15 min (150 W) under a closed
system. 1H, 11B and 13C NMR spectra in DMSO-d6 were used to
confirm the product obtained by this method was identical to that
obtained for Method A.
N
H
5c
H
N
B
CH3
4
2d
80
75
N
H
4.2. General procedures for the synthesis of compounds 5aef
5d
4.2.1. Method C
To a solution of 1,8-diaminonaphthalene in toluene (2 mmol in
50 ml) was added the boronic acid (2 mmol) in one portion. The
round-bottomed flask was equipped with a Dean and Stark trap,
H
N
CH
3
B
S
5
2e
76
80
Pyridine/pyrrole
N
H
Amide
Amine
550
0ppm
90
135
220
5e
H
N
101
64
B
H
N
6
2f
84
75
CH
H2N
H2N
3
N
H
B
R
H C
3
N
H
5f
a
Reaction conditions: 4 (2 mmol), 2 (2 mmol) Toluene (50 ml), 110 ꢀC, 3 h.
Reaction conditions: 4 (0.4 mmol), 2 (0.4 mmol) 150 ꢀC, 150 W, 15 min.
Fig. 4. Diagrammatic representation of the relative 15N chemical shifts of compounds
5aef (not to scale).
b

126
C.A. Slabber et al. / Journal of Organometallic Chemistry 723 (2013) 122e128
2H, 2x CHeCqeB) 7.90 ppm (d, J ¼ 8.2 Hz, 2H, 2x CHeCqeCl)
9.16 ppm (s, 2H, 2x NH); 11B NMR (160 MHz, DMSO-d6)
28.4 ppm (s); 13C NMR (125 MHz, DMSO-d6)
111.3 ppm (d, 2C,
d
d
2x CHeCHeCqeN) 118.9 ppm (d, 2C, 2x CHeCHeCqeN) 128.5 ppm
(d, 2C, 2x CHeCqeB) 134.7 ppm (s, 1C,CHeCqeCl) 135.6 ppm (d, 2C,
2x CHeCqeCl) 137.5 ppm (s, 2C, 2x CqeN); 15N NMR (50 MHz,
DMSO-d6)
d 111 ppm (s); HRMS calcd for C12H9BN2Cl: 227.0547;
found 227.0551.
4.4.2. Method B
84 mg, 92%.
4.5. 2-(4-Methoxyphenyl)-1,3,2-benzodiazaborole (3c) [26]
Fig. 5. ORTEP plot (50% ellipsoids) of 5d.
4.5.1. Method A
419 mg, 94%.1H NMR (500 MHz, DMSO-d6)
d3.81 (s, 3H, CH3)
6.76e6.80 ppm (m, J ¼ 5.7 Hz, J ¼ 3.2 Hz, 2H, 2x CHeCHeCqeN)
6.98 ppm (d, J ¼ 8.7 Hz, 2H,2x CHeCqeO) 6.99e7.03 ppm (m,
J ¼ 5.7 Hz, J ¼ 3.2 Hz, 2H,2x CHeCqeN) 7.82 ppm (d, J ¼ 8.6 Hz, 2H,
2x CH-Cq-B) 8.94 ppm (s, 2H, 2x NH); 11B NMR (160 MHz, DMSO-
and the solution was stirred and heated to reflux at 110 ꢀC for 3 h.
The solvent was removed in vacuo.
4.2.2. Method D
d6)
d d 55.4 (q, 1C,
28.9 ppm (s); 13C NMR (125 MHz, DMSO-d6)
The1,8-diaminonaphthalene (0.4 mmol) and boronic acid
(0.4 mmol) were added to a microwave tube and sealed with
a microwave septum. The tube was shaken to mix and subjected to
microwave irradiation at 150 ꢀC for 15 min (150 W) under a closed
system. 1H, 11B and 13C NMR spectra in DMSO-d6 were used to
confirm the product obtained by this method was identical to that
obtained for Method C.
CH3) 111.0 ppm (d, 2C, 2x CHeCHeCqeN) 114.1 ppm (d, 2C, 2x CHe
CqeO) 118.9 ppm (d, 2C, 2x CHeCHeCqeN) 135.4 (d, 2C, 2x CHeCqe
B) 138.1 ppm (s, 2C, 2x CqeN) 160.7 ppm (s, 1C, CqeOCH3) 15NMR
(50 MHz, DMSO-d6)
d 107 ppm; HRMS calcd for C13H12BN2O:
223.1043; found 223.1041.
4.5.2. Method B
79 mg, 62%.
4.3. 2-Phenyl-1,3,2-benzodiazaborole (3a) [24]
4.6. 2-(4-methylphenyl)-1,3,2-benzodiazaborole (3d) [27]
4.3.1. Method A
367 mg, 95%. 1H NMR (500 MHz, CDCl3)
d 6.80e6.84 ppm (m,
4.6.1. Method A
369 mg, 89%.1H NMR (500 MHz, DMSO-d6)
d 2.33 ppm (s, 3H,
J ¼ 5.2 Hz, J ¼ 3.2 Hz, 2H, 2x CHeCHeCqeN) 7.04e7.07 ppm (m,
J ¼ 5.2 Hz, J ¼ 3.2, 2H,2x CHeCHeCqeN) 7.38e7.43 ppm (m, 3H,
CHeCHeCH) 7.88e7.91 ppm (m, 2H, 2x CHeCHeCqeB) 9.08 ppm
CH3) 6.77e6.81 ppm (m, J ¼ 5.7 Hz, J ¼ 3.2 Hz, 2H, 2x CHeCHeCqeN)
7.01e7.05 ppm (m, J ¼ 5.7 Hz, J ¼ 3.2 Hz, 2H, 2x CHeCHeCqeN)
7.23 ppm (d, J ¼ 8.2 Hz, 2H, 2x CHeCqeB) 7.78 ppm (d, J ¼ 7.9 Hz,
2H, 2x CHeCqeCH3) 9.01 ppm (s, 2H, 2x NH); 11B NMR (160 MHz,
(s, 2H, 2x NH); 11B NMR (160 MHz, DMSO-d6)
d
28.8 ppm (s); 13C
NMR (125 MHz, DMSO-d6)
d 111.2 ppm (d, 2C, 2x CHeCHeCqeN)
DMSO-d6) d
29.5 ppm (s); 13C NMR (125 MHz, DMSO-d6) 21.6 ppm
119.4 ppm (d, 2C, 2x CHeCHeCqeN) 128.0 ppm (2x d, 2C, CHe
CHeCH) 129.7 ppm (d, 1C,CHeCHeCH) 132.9 ppm (d, 2C, CHe
CqeB) 136.3 (s, 2C, 2x CqeN); 15N NMR (50 MHz, DMSO-d6)
(q,1C, CH3) 111.2 ppm (d, 2C, 2x CHeCHeCqeN) 118.6 ppm (d, 2C, 2x
CHeCHeCqeN) 129.0 ppm (d, 2C, 2x CHeCqeB) 133.9 ppm (d, 2C, 2x
CHeCqeCH3) 137.7 ppm (s, 2C, 2x CqeN) 139.1 ppm (s, 1C, CqeCH3);
d
104 ppm (s); HRMS calcd for C12H10BN2: 193.0937; found
15N NMR (50 MHz, DMSO-d6)
207.1094; found 207.1098.
d 110 ppm; HRMS calcd for C13H12BN2:
193.0938.
4.3.2. Method B
75 mg, 95%.
4.6.2. Method B
68 mg, 78%.
4.4. 2-(4-Chlorophenyl)-1,3,2-benzodiazaborole(3b) [25]
4.7. 2-[4-(methylsulfanyl)phenyl]-1,3,2-benzodiazaborole (3e)
4.4.1. Method A
440 mg, 97%.1H NMR (500 MHz, DMSO-d6)
d 6.80e6.84 ppm (m,
4.7.1. Method A
454 mg, 95%. 1H NMR (500 MHz, DMSO-d6)
d 2.50 ppm (s, 3H,
J ¼ 5.7 Hz, J ¼ 3.2 Hz, 2H, 2x CHeCHeCqeN) 7.03e7.07 ppm (m,
J ¼ 5.7 Hz, J ¼ 3.2 Hz, 2H,2x CHeCHeCqeN) 7.49 ppm (d, J ¼ 8.2 Hz,
SCH3) 6.78e6.81ppm (m, J ¼ 5.7 Hz, J ¼ 3.2 Hz, 2H, 2xCHeCHeCqeN)
7.00e7.05 ppm (m, J ¼ 5.6 Hz, J ¼ 3.2 Hz, 2H, 2x CHeCHeCqeN)
7.30 ppm (d, J ¼ 8.3 Hz, 2H, 2x CHeCqeS) 7.82 ppm (d, J ¼ 8.3 Hz,
2H, 2x CHeCqeB) 9.08 ppm (2, 2H, 2x-NH); 11B NMR (160 MHz,
Table 5
Selected X-Ray data for compounds 5a, 5b, 5d, and 5e.
DMSO-d6) d d 14.7 ppm
28.0 ppm (s);13C NMR (125 MHz, DMSO-d6)
Compound
BeC bond
distance (A)
BeN bond
distance (A)
Dihedral
(q,1C, SCH3) 111.1 ppm (d, 2C, 2x CHeCHeCqeN) 118.7 ppm (d, 2C, 2x
CHeCHeCqeN) 125.6 ppm (d, 2C, 2x CHeCqeS) 134.3 ppm (d, 2C, 2x
CHeCqeB) 137.7 ppm (s, 2C, 2x CqeN) 140.1 ppm (s, 1C, CqeCH3);
a
ꢀ
angle (ꢀ)b
ꢀ
5a
5b
5d
5e
1.562(2)
1.568(4)
1.559(1)
1.559(3)
1.414(2)
1.411(2)
1.441(1)
1.414(2)
8(1)
6(1)
23(1)
19(1)
15NMR (50 MHz, DMSO-d6)
d 109 ppm; HRMS calcd for
C13H12BN2S: 239.0814; found 239.0812.
a
Averaged value.
b
4.7.2. Method B
Angle between mean planes through phenyl group carbon atoms and the non-
hydrogen atoms of the napthodiazaborinane grouping.
83 mg, 87%.

C.A. Slabber et al. / Journal of Organometallic Chemistry 723 (2013) 122e128
127
4.8. 2-(2-Methylpropyl)-1,3,2-benzodiazaborole (3f)
8.19 ppm (s, 2H, 2x NH) 11B NMR (160 MHz, DMSO-d6)
28.7 ppm (s) 13C NMR (125 MHz, DMSO-d6)
55.5 ppm (q, 1C,
d
d
4.8.1. Method A
CH3) 105.9 ppm (d, 2C, 2x CHeCqeN) 113.7 ppm (d, 2C, 2x CHeCqe
O) 116.5 ppm (d, 2C, 2x CHeCqeCq) 119.9 ppm (s, 2C, 2x CqeN)
128.1 ppm (d, 2C, 2x CHeCHeCH) 134.8 ppm (d, 2C, 2x CHeCqe
B) 136.4 ppm (s, 1C, CHeCqeCq) 142.9 ppm (s, 1C, CqeCqeCq)
161.5 ppm (s, 1C, CqeOeCH3) 15N NMR (50 MHz, DMSO-d6)
313 mg, 90%.1H NMR (500 MHz, DMSO-d6)
d 0.96 ppm (d,
J ¼ 6.5 Hz, 6H, 2x CH3) 1.07 ppm (d, J ¼ 7.1 Hz, 2H, CHeCH2eB),1.91e
1.99 ppm (m, J ¼ 6.7 Hz, 1H, (CH3)2eCHeCH2) 6.70e6.73 ppm (m,
J¼ 5.6Hz, J¼ 3.2Hz,2H,CHeCHeCqeN)6.91e6.94ppm(m, J¼ 5.6Hz,
J ¼ 3.2 Hz, 2H, 2x CHeCHeCqeN) 8.33 ppm (s, 2H, 2x NH) 11B NMR
d
101 ppm; HRMS calcd for C17H14BN2O: 273.1199; found 273.1201.
(160 MHz, DMSO-d6)
d
31.7 ppm (s) 13C NMR (125 MHz, DMSO-d6)
d
23.0 ppm (t, 1C, CH2) 25.9 ppm (q, 2C, 2x CH3) 26.2 ppm (d, 1C,
4.11.2. Method D
CH) 110.6 ppm (d, 2C, 2x CHeCHeCqeN) 118.0 ppm (d, 2C, 2x CHe
103 mg, 95%.
CHeCqeN) 137.4 ppm (s, 2C, 2x CqeN) 15N NMR (50 MHz, DMSO-
d6)
d
113 ppm; HRMS calcd for C10H15BN2: 174.0516; found 174.0521.
4.12. 2-(4-Methylphenyl)-naphtho[1,8-de][1,3,2]diazaborine (5d)
[28]
4.8.2. Method B
49 mg, 70%.
4.12.1. Method C
411 mg, 80%.1H NMR (500 MHz, DMSO-d6)
d 2.35 ppm (s, 3H, CH3)
4.9. 2-Phenylenaphtho[1,8-de][1,3,2]diazaborine (5a) [17]
6.58 ppm (dd, J ¼ 7.4 Hz, J ¼ 0.85 Hz, 2H 2x CHeCqeN) 6.89 ppm
(dd,,J ¼ 8.2 Hz, J ¼ 0.90 Hz, 2H, 2xCHeCqeCq) 7.09 ppm (dd, J ¼ 7.8 Hz,
2H, 2x CHeCHeCH) 7.25 ppm (dd, J ¼ 8.0 Hz, J ¼ 0.60 Hz, 2H,2x CHe
CqeCH3) 7.82 ppm (d, J ¼ 7.9 Hz, 2H, 2x CHeCqeB) 8.19 ppm (s, 2H, 2x
4.9.1. Method C
413 mg, 85%. 1H NMR (500 MHz, DMSO-d6)
d 6.60 ppm (dd,
J ¼ 7.5 Hz, J ¼ 0.75 Hz, 2H, 2x CHeCqeN) 6.91 ppm (dd, J ¼ 8.3 Hz,
J ¼ 0.72 Hz, 2H,2x CHeCqeCq) 7.09 ppm (dd, J ¼ 7.8 Hz, 2H, 2x CHe
CHeCH) 7.42e7.48 ppm (m, 3H, CHeCHeCH) 7.92e7.94 ppm (m,
J ¼ 7.7 Hz, J ¼ 1.7 Hz, 2H, CHeCqeB) 8.24 ppm (s, 2H, 2x NH) 11B NMR
NH) 11B NMR (160 MHz, DMSO-d6) 29.2 ppm (s) 13C NMR (125 MHz,
d
DMSO-d6)
d 21.6 ppm (q, 1C, CH3) 106.0 ppm (d, 2C, 2x CHeCqeN)
116.6 ppm (d, 2C, 2x CHeCqeCq) 120.0 ppm (s, 2C, 2x CqeN)
128.1 ppm (d, 2C, 2x CHeCHeCH) 128.7 ppm (d, 2C, 2x CHeCqe
CH3) 133.2 ppm (d, 2C, 2x CHeCqeB) 136.4 ppm (s, 2C, 2x CHeCqe
Cq) 139.9 ppm (s,1C, CqeCH3) 142.9 ppm (s, 2C, 2x CqeCqeCq) 15N
(160 MHz, DMSO-d6) d
30.0 ppm (s) 13C NMR (125 MHz, DMSO-d6)
d
106.1 ppm (d, 2C, 2x CHeCqeN) 116.7 ppm (d, 2C, 2x CHeCqeCq)
120.1 ppm (s, 2C, 2x CqeN) 127.9 ppm (d, 4C, CHeCHeCH and 2x
CHeCHeCqeCq) 130.4 ppm (d, 1C, CHeCHeCH) 133.1 ppm (d, 2C, 2x
CHeCqeB) 136.4 ppm (s,1C, CHeCqeCq) 142.8 ppm (s,1C, CqeCqeCq)
NMR (50 MHz, DMSO-d6)
257.1250; found 257.1248.
d 101 ppm; HRMS calcd for C17H14BN2 :
15N NMR (50 MHz, DMSO-d6)
243.1094; found 243.1092.
d
101 ppm; HRMS calcd for C16H12BN2:
4.12.2. Method D
77 mg, 75%.
4.9.2. Method D
4.13. 2-[4-(Methylsulfanyl)phenyl]enaphtho[1,8-de][1,3,2]
diazaborine (5e) [19]
98 mg, 90%.
4.10. 2-(4-Chlorophenyl)enaphtho[1,8-de][1,3,2]diazaborine (5b)
[18]
4.13.1. Method C
441 mg, 76%. 1H NMR (500 MHz, DMSO-d6)
d 2.52 ppm (s, 3H,
SCH3) 6.58 ppm (dd, J ¼ 7.4 Hz, J ¼ 0.85 Hz, 2H, 2x CHeCqeN)
6.89 ppm (dd, J ¼ 8.1 Hz, J ¼ 0.82 Hz, 2H, 2x CHeCqeCq) 7.07 ppm
(m, J ¼ 7.7 Hz, 2H, 2x CHeCHeCH) 7.31 ppm (d, J ¼ 8.4 Hz, 2H, 2x CHe
CqeSCH3) 7.87 ppm (d, J ¼ 8.3 Hz, 2H, 2x CH-Cq-B) 8.22 ppm (s, 2H, 2x
4.10.1. Method C
415 mg, 75%. 1H NMR (500 MHz, DMSO-d6)
d 6.58 ppm (dd,
J ¼ 7.3 Hz, J ¼ 0.85 Hz, 2H, 2x CHeCqeN) 6.91 ppm (dd, J ¼ 8.3 Hz,
J ¼ 0.84 Hz, 2H, 2x CHeCqeCq) 7.08 ppm (dd, J ¼ 7.8 Hz, 2H, 2x CHe
CHeCH) 7.49e7.53 ppm (m, 2H, CHeCqeCH) 7.94e7.97 ppm (m,
2H, 2x CHeCqeB) 8.30 ppm (s, 2H, 2x NH) 11B NMR (160 MHz, DMSO-
NH) 11B NMR (160 MHz, DMSO-d6) 28.7 ppm (s) 13C NMR (125 MHz,
d
DMSO-d6) d 14.7 ppm (q, 1C, SCH3) 106.1 ppm (d, 2C, 2x CHeCqeN)
116.6 ppm (d, 2C, 2x CHeCqeCq) 120.1 ppm (s, 2C, 2x CqeN)
125.2 ppm (d, 2C, 2x CHeCqeSCH3) 128.1 ppm (d, 2C, 2x CHeCHe
CH) 133.6 ppm (d, 2C, 2x CHeCqeB) 136.4 ppm (s, 2C, 2x CHeCqe
Cq) 141.0 ppm (s, 1C, CqeS) 142.8 ppm (s, 2C, 2x CqeCqeCq) 15N
d6) d d 106.2 ppm (d, 2C,
28.8 ppm (s) 13C NMR (125 MHz, DMSO-d6)
2x CHeCqeN) 116.8 ppm (d, 2C, 2x CHeCqeCq) 120.2 ppm (s, 2C, 2x
CqeN) 128.1 ppm (d, 2x CHeCHeCH or CHeCqeCl) 128.2 ppm (d, 2x
CHeCHeCHorCHeCqeCl)135.0ppm(d,2C, 2xCHeCqeB)135.5ppm
(s, 1C, CHeCqeCl or CHeCqeCq) 136.4 ppm (s, 1C, CHeCqeCl or CHe
CqeCq) 142.3 ppm (s, 1C, CqeCqeCq) 15N NMR (50 MHz, DMSO-d6)
NMR (50 MHz, DMSO-d6)
290.1049; found 290.1050.
d 100 ppm HRMS calcd for C17H15BN2S:
d
101 ppm; HRMS calcd for C16H11BN2Cl: 277.0704; found 277.0701.
4.13.2. Method D
93 mg, 80%.
4.10.2. Method D
88 mg, 88%.
4.14. 2-(2-Methylpropyl)-naphtho[1,8-de][1,3,2]diazaborine (5f)
4.11. 2-(4-Methoxyphenyl)enaphtho[1,8-de][1,3,2]diazaborine (5c)
[28]
4.14.1. Method C
376 mg, 84%; 1H NMR (500 MHz, DMSO-d6)
d 0.77 ppm (d,
J ¼ 7.4 Hz, 2H, CH2eB) 0.95 ppm (d, 6.6 Hz, 6H, 2x CH3eCHeCH2) 1.9e
2.0 ppm (m, 1H, CH3eCHeCH2) 6.39 ppm (dd, J ¼ 7.5 Hz, J ¼ 0.95 Hz,
2H, 2xCHeCqeN)6.83ppm(dd,J¼8.4Hz,J¼ 0.83Hz, 2H, 2xCHeCqe
Cq) 7.02 ppm (m, J ¼ 7.8 Hz, 2H, 2x CHeCHeCH) 7.70 ppm (s, 2H, 2x
4.11.1. Method C
437 mg, 80%. 1H NMR (500 MHz, DMSO-d6)
d 3.81 ppm (s, 3H,
CH3) 6.58 ppm (dd, J ¼ 7.4 Hz, J ¼ 0.95 Hz, 2H, 2x CHeCqeN)
6.88 ppm (dd, J ¼ 8.2 Hz, J ¼ 0.76 Hz, 2H, 2x CHeCqeCq)
7.00 ppm (d, J ¼ 8.7 Hz, 2H, 2x CHeCqeO) 7.07 ppm (t, J ¼ 8.0 Hz,
2H, 2x CHeCHeCH) 7.89 ppm (d, J ¼ 8.7 Hz, 2H, 2x CHeCqeB)
NH) 11B NMR (160 MHz, DMSO-d6) 32.6 ppm (s) 13C NMR (125 MHz,
d
DMSO-d6)
d 24.8 ppm (d,1C, CH3eCHeCH2) 25.4 ppm (q, 2C, 2xCH3e
CHeCH2) 25.8 ppm (t, 1C, CH2eB) 104.9 ppm (d, 2C, 2x CHeCqeN)

128
C.A. Slabber et al. / Journal of Organometallic Chemistry 723 (2013) 122e128
115.6ppm(d, 2C, 2xCHeCqeCq)119.4ppm(s, 2C, 2xCqeN)127.5ppm
(d, 2C, 2x CHeCHeCH) 135.9 ppm (s, 2x CHeCqeCq) 142.4 ppm (s, 2C,
Appendix A. Supplementary material
2x CqeCqeCq) 15N NMR (50 MHz, DMSO-d6)
d
100 ppm (s); HRMS
Supplementary material related to this article can be found at
http://dx.doi.org/10.1016/j.jorganchem.2012.09.018.
calcd for C14H17BN2: 224.1104; found 224.1109.
4.14.2. Method D
References
67 mg, 75%.
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4.15. X-ray crystallographic study
Single crystals of compound 5d were grown by slow evaporation
ofa solution of thecompound indichloromethanefollowing filtration
through a silica plug. Crystal data: C17H15BN2 (MW ¼ 258.12 g molꢁ1);
0.08 ꢂ 0.12 ꢂ 0.38 mm; monoclinic; space group P21/n (No. 14);
¼ 113.0(1)ꢀ; Z ¼ 4,
ꢀ
a ¼ 10.783(1), b ¼ 10.149(1), c ¼ 13.535(2) A,
b
3
V ¼ 1363.6(2)A ; Dcalcd ¼ 1.257gcmꢁ3
;
m
¼ 0.074 mmꢁ1. Intensity data
ꢀ
were collected on a Oxford Diffraction Xcalibur CCD diffractometer
ꢀ
ꢀ
with monochromated MoK
a
radiation (
l
¼ 0.71073 A), at 22 C, in the
q
range 2e25ꢀ. The structure was solved by means of direct methods
using SHELXS-97 [23], and refined on F2 on all data by full matrix
least-squares methods. A riding model with idealised geometry was
usedforallhydrogenatoms.Anisotropicrefinement(241parameters)
of all non-hydrogen atoms converged at R1 ¼ 0.0494 [3953 unique
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o1873.
reflections with I > 2
s
(I)], wR2 (all 5103 data) ¼ 0.0631 and a max.
3
ꢀ
residual electron density of 0.49 e.A .
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Acknowledgements
The authors wish to thank the University of KwaZulu-Natal
and the NRF for financial support. The authors also wish to
thank Dr Jan Gertenbach (University of Stellenbosch) for the
X-ray data collection of compound 5d, and Prof John Field
(University of KwaZulu-Natal) for the interpretation of the crys-
tallographic data.