β-diketonate, β-ketoiminate, and β-diiminate complexes of difluoroboron

Article abstract of DOI:10.1002/ejic.200800243

A series of β-diketonate, keto(aryl)iminato, and β-bis(aryl)- iminato complexes of difluoroboron, twenty in total, have been prepared to assess the impact of chelate ring and aniline substitution on the structural, electrochemical, and photophysical properties of these ubiquitous chelates. DFT (B3LYP/6-31G*) calculations supplemented the experimental results and both demonstrated that replacing oxygen with the more electron-donating aniline groups serves to only fine-tune the electronic properties because both the HOMO and LUMO energies are affected by such substitution. The electronic properties of all compounds are most greatly influenced by the nature of the substituents bound to the carbon portion of the chelate ring. Each difluoroboron complex undergoes two ligand-based, one-electron reductions where the first reduction potential becomes less favorable with increasing aniline substitution. Similarly, replacing oxygen with the more electron-donating aniline groups gives rise to slightly red-shifted absorption and emission processes. Substitution on the aniline ring has little, if any, influence on the electronic properties of the resultant complexes. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.

Full text of DOI:10.1002/ejic.200800243

FULL PAPER
DOI: 10.1002/ejic.200800243
β-Diketonate, β-Ketoiminate, and β-Diiminate Complexes of Difluoroboron
Felipe P. Macedo,[a] Chengeto Gwengo,[a] Sergey V. Lindeman,[a] Mark D. Smith,[b] and
James R. Gardinier*[a]
Keywords: Chelates / Boron / Electrochemistry / UV/Vis spectroscopy / Density functional calculations
A series of β-diketonate, keto(aryl)iminato, and β-bis(aryl)-
iminato complexes of difluoroboron, twenty in total, have
been prepared to assess the impact of chelate ring and ani-
line substitution on the structural, electrochemical, and pho-
tophysical properties of these ubiquitous chelates. DFT
(B3LYP/6-31G*) calculations supplemented the experimental
results and both demonstrated that replacing oxygen with
the more electron-donating aniline groups serves to only
fine-tune the electronic properties because both the HOMO
and LUMO energies are affected by such substitution. The
electronic properties of all compounds are most greatly influ-
enced by the nature of the substituents bound to the carbon
portion of the chelate ring. Each difluoroboron complex un-
dergoes two ligand-based, one-electron reductions where
the first reduction potential becomes less favorable with in-
creasing aniline substitution. Similarly, replacing oxygen
with the more electron-donating aniline groups gives rise to
slightly red-shifted absorption and emission processes. Sub-
stitution on the aniline ring has little, if any, influence on the
electronic properties of the resultant complexes.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
Introduction
There is a long-standing interest in β-diketonato and re-
lated chelate complexes (Figure 1) of main group and tran-
sition metals for both fundamental studies and a myriad of
practical applications.[1] Recent success in utilizing steri-
cally-demanding β-diiminate ligands to stabilize unusual
transition[2] and main-group[3] metal complexes has spurred
resurgent interest in this class of chelates. Important for
both applied and fundamental coordination chemistry
studies is knowledge of the electronic properties of the li-
gands in their chelated forms. Such information permits as-
sessment of the extent to which the ligands may serve either
as true spectator ligands or as “non-innocent” electron res-
ervoirs, offering new possibilities for (often unanticipated)
reaction chemistry. For this purpose, studies of complexes
whose Lewis acid centers are electrochemically silent are
critical for evaluating the potential for the ligand to remain
non-innocent.
Figure 1. From left to right: β-diketonato, β-ketoiminato, and β-
diiminato chelate complexes. M = metal or metalloid; R1, R3
=
organyl; R2, R1Ј, R3Ј = H, or organyl.
chemistry,[9] and luminescence behavior have been re-
ported.[10] We were interested in incorporating β-ketoimin-
ato and β-diiminato chelates of difluoroboron and of met-
als as functional “sensing” groups in molecular assemblies
and for the stabilization of low-oxidation state species.[11]
While detailed studies on the photophysics of fluorescent
and phosphorescent behavior as well as of exciplex forma-
tion involving difluoroboron diketonate derivatives are
available,[9–10] detailed reports concerning the electronic
properties of β-ketoiminato, and β-diiminato derivatives
were not, to the best of our knowledge. For this purpose, it
became necessary to learn whether the interesting electronic
properties found in the diketonates were retained in the β-
ketoiminato and β-diiminato derivatives. If so, we wanted
to assess the impact of substitution on the “tunability” of
the photo- and electrochemical properties of such systems.
To this end, we report now on our findings regarding the
structural and electronic properties of a series of diketon-
ato, ketoiminato, and diiminato complexes of difluorobo-
ron. Also, in an effort to make comparisons between the
different ligands more intuitive, we will introduce the fol-
lowing non-standard shorthand notation, (R1RЈ1,R2,R3RЈ3),
with reference to Figure 1. The presence of two superscripts
The difluoroboron moiety is one Lewis acid particularly
well-suited for such studies, especially because the known
β-diketonato, β-ketoiminato, and β-diiminato com-
plexes[4–6] are reported to be air-stable and, in some cases,
interesting reaction chemistry,[7] electrochemistry,[8] photo-
[a] Department of Chemistry, Marquette University,
Milwaukee, WI 53201-1881, USA
Fax: +1-414-288-7066
E-mail: james.gardinier@marquette.edu
[b] Department of Chemistry and Biochemistry, University of
South Carolina,
Columbia, SC 29208, USA
Supporting information for this article is available on the
WWW under http://www.eurjic.org or from the author.
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Chelate Complexes of Difluoroboron
RЈ1
(
and RЈ3) refers to a β-diiminate, the presence of only prepared by a known multi-step route (Scheme 2).[13,14] Fi-
one superscript (RЈ1 or RЈ3) refers to a β-ketoiminate, nally, the difluoroboron complexes were prepared by the
whereas the absence of superscripts implies a β-diketonate. straightforward HF elimination reaction in toluene, where
Thus, the hypothetical free ligand and BF2 complex in Fig- the evolved HF (which did not appear to interfere with the
ure 2a and Figure 2b, respectively, would be designated as reaction pathway) was passed into a 1  KOH scrubbing
H(CH3,H,CF3m–(OMe)C6H4) and BF2(tBuDipp,Et,MenBu) ac- solution.
cording to the above shorthand notation. The substituent
Table 1. Difluoroboron chelate complexes prepared in this study.
priority follows from the usual order for donor heteroatoms
(O Ͼ N), then organyls with (R1Ј/R3Ј) Ͼ (R1/R3).
β-Diketonate
β-Ketoiminate
β-Diiminate
BF2(tBu,H,tBu)
BF2(Me,H,Me)
BF2(Ph,H,Me)
BF2(Ph,H,Ph)
BF2(tBu,H,tBuPh
)
BF2(tBuPh,H,tBuPh
)
BF2(Me,H,Me4BrPh
)
BF2(Me4BrPh,H,Me4BrPh
)
BF2(Ph,H,Me4BrPh
)
BF2(Ph4BrPh,H,Me4BrPh
)
BF2(Ph,H,PhPh
)
BF2(Ph,H,Ph2BrPh
BF2(Ph,H,Ph4BrPh
)
)
BF2(Ph,H,Ph2Br4Tolyl
)
BF2(Ph,H,Ph4pzPh
BF2(Ph,H,Ph2pz4Tolyl
BF2(Ph,Ph,Ph4BrPh
)
)
BF2(Ph,Ph,Ph)
)
BF2(pAnis, H, pAnis) BF2(pAnis, H, pAnis4BrPh
)
pAnis = 4-MeOC6H4
m-(OMe)C6H4
Figure 2. Hypothetical (a) free ligand H(CH3,H,CF3
)
and (b) difluoroboron complex BF2(tBuDipp,Et,MenBu) Dipp = di-
isopropylphenyl.
Results and Discussion
Synthesis
The difluoroboron chelates that were prepared in this
study are listed in Table 1 and several details of the synthe-
ses are worth noting. First, while most of the diketones are
commercially available, the triphenyl diketone, H(Ph,Ph,Ph)
is not. Of the several literature methods for the preparation
of this compound,[12] we found that the ozonolysis of tet-
raphenylcyclopentanedione[12a] was, by far, the simplest and
the most reliable route. Most of the ketoiminates and some
of the diiminates could be prepared by acid-catalyzed con-
densation reactions between the diketones and anilines
(Scheme 1). For derivatives originating from the unsymmet-
rical benzoylacetone, H(Ph,H,Me), NMR studies show sub-
stitution first occurs at the acetyl portion of the chelate and
then, slowly, and with lower yields, the second substitution
occurs at the benzoyl portion. This observation is in agree-
ment with the known lower reactivity of aryl- vs. aliphatic
ketones. In this vein, we were unable to prepare β-diiminato
derivatives of the 1,3-diaryl diketones, H(Ph,H,Ph),
H(Ph,Ph,Ph), and H(4-MeOC6H4,H,4-MeOC6H4) by acid
condensation; the second condensation step did not occur
even after prolonged heating, or with higher reaction tem-
peratures, or even when using concentrated HCl as a cata-
lyst. Apparently, the already low reactivity of 1,3-diaryl di-
ketones is significantly further diminished upon initial sub-
stitution of the electron-donating aniline substituent. Simi-
Scheme 1. Preparation of the β-ketoiminate and β-diiminate li-
gands by acid-catalyzed condensation, and of difluoroboron che-
late complexes by HF elimination.
Scheme 2. Preparative route to β-ketoimino and β-diimine deriva-
tives H(tBu,H,tBuPh) and H(tBuPh,H,tBuPh).
larly, all attempts to obtain H(tBu,H,tBuPh
H(tBuPh,H, tBuPh) with tert-butyl groups on the chelate
)
and
The difluoroboron complexes are all air-stable. Those
ring, by acid-catalyzed condensation failed to provide any with aliphatic groups on the chelate ring are colorless while
of the desired products; presumably steric considerations in- those with two aryl groups on the chelate ring are yellow.
hibit the reaction as the starting materials are fully reco- Moreover, derivatives with aliphatic groups on the chelate
vered. Thus, H(tBu,H,tBuPh) and H(tBuPh,H,tBuPh) were ring are soluble in most ethereal, aromatic, and halocarbon
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J. R. Gardinier et al.
FULL PAPER
solvents, are modestly soluble in hot hexanes and alcohols,
but are only slightly soluble in cold hexanes or pentane.
The solubility of the derivatives decreases with increasing
number of aromatic groups such that the diphenyl diketone
derivatives are insoluble in hot hexanes.
Solid-State Structures
A total of twelve new difluoroboron chelate derivatives
have been structurally characterized. The molecular struc-
tures of a representative β-diketonate, β-ketoiminate, and β-
diiminate are given in Figure 3 while those of the remaining
derivatives are found in the Supporting Information. Se-
lected features of the intramolecular geometry of each de-
rivative prepared in this study and of some previously
known derivatives are provided in Table 2. As expected, the
B–N bonds (1.567 Å average) are about 0.1 Å longer than
the B–O bonds (1.467 Å average). Thus, on traversing the
series of diketonate, ketoiminate and diiminate complexes,
the BF2 group is displaced further away from the chelate
ring and the FBF angle becomes more acute. The pertinent
metrical parameters for the ensuing discussion of NMR
spectroscopic data are the average BE2 distance (E = N or
O) and FBF angle of 1.483 Å and 110.7° for the diketon-
ates, 1.518 Å and 110.4° for the ketoiminates, and 1.541 Å
and 107.7° for the diiminates. Analysis of bond lengths in
the ketoiminates suggests that the major resonance contri-
bution to bonding is the alkoxy-imine form (Scheme 3, left).
Figure 3. ORTEP diagrams of (a) BF2(tBu,H,tBu), (b)
BF2(tBu,H,tBuPh), and (c) BF2(tBuPh,H,tBuPh). Hydrogen atoms
removed for clarity. Ellipsoids are shown at 50% probability level.
Table 2. Selected features of intramolecular geometry of some structurally characterized difluoroboron chelates.
[a]
Compound
B–O
[Å]
B–N
[Å]
C–O
[Å]
C–N
[Å]
C=C (O) C=C (N) B–PlC
EBE
[°]
EBE-PlC PlC-aryl dihedral[b]
[Å]
[Å]
[Å]
[°]
[°]
Diketonate[g]
BF2(Me,H,Me)[c]
BF2(tBu,H,tBu)
BF2(Me,H,Ph)[d]
BF2(Ph,H,Ph)[e]
1.475
1.490
1.487
1.483
1.481
–
–
–
–
–
1.287
1.302
1.305
1.294
1.309
–
–
–
–
–
1.358
1.388
1.387
1.380
1.385
–
–
–
–
–
0.142
0.378
0.00
0.251
0.00
111.10
109.47
111.47
110.97
111.80
9.41
25.38
0.00
17.05
0.00
–
–
0.00
3.69
2.36
BF2(pAnis,H, pAnis)[f]
Ketoiminate
BF2(Me,H,Me4BrPh
BF2(tBu,H,tBuPh
)
1.466 1.566 1.318 1.318 1.363
1.458 1.579 1.321 1.322 1.360
1.457 1.588 1.322 1.318 1.362
1.450 1.577 1.317 1.318 1.358
1.457 1.563 1.314 1.324 1.360
1.460 1.569 1.316 1.318 1.365
1.465 1.559 1.314 1.324 1.375
1.469 1.564 1.312 1.322 1.367
1.469 1.568 1.318 1.320 1.368
1.473 1.570 1.321 1.330 1.368
1.464 1.572 1.319 1.318 1.383
1.477 1.572 1.320 1.338 1.378
1.418
1.427
1.426
1.430
1.408
1.408
1.413
1.415
1.414
1.412
1.428
1.403
0.226
0.368
0.371
0.182
0.283
0.067
0.246
0.084
0.087
0.339
0.108
0.387
109.86
109.53
109.39
110.77
109.74
110.14
109.79
110.37
110.56
109.04
108.93
109.63
14.65
24.47
24.52
11.40
18.66
4.32
15.97
5.52
5.82
73.73
85.33
84.99
75.29
)
BF2(Ph,H,PhPh
)
14.75, 52.91, 65.04
11.18, 52.95, 64.53
13.54, 54.26, 81.79
1.24, 51.48, 76.12
6.03, 64.84, 61.20
13.98, 43.76, 76.22
32.70, 81.83, 80.66, 65.94
12.40, 39.75, 58.88
BF2(Ph,H,Ph4BrPh
BF2(Ph,H,Ph2BrPh
)
)
BF2(Ph,H,Ph4pzPh
)
BF2(Ph,H,Ph2pztol
)
21.80
6.81
25.45
BF2(Ph,Ph,Ph4BrPh
)
BF2(pAnis,H,pAnisBrPh
)
Diiminate[g]
BF2(MeMe,H,MeMe [h]
BF2(MeMe,H,MeiPr [i]
BF2(Meptol,H,Meptol [j]
BF2(Me4BrPh,H,Me4BrPh
BF2(tBuPh,H,tBuPh
)
)
–
–
–
–
–
1.523
1.534
1.552
1.544
1.550
–
–
–
–
–
1.326
1.331
1.344
1.337
1.340
–
–
–
–
–
1.384
1.387
1.393
1.393
1.395
0.000
0.238
0.147
0.000
0.399
110.18
110.42
108.62
108.99
109.41
0.00
15.37
9.19
0.00
25.92
–
–
)
76.13
86.77
88.01, 86.57
)
)
[a] Plc = Mean plane of E2C3 chelate ring; E = N,O as appropriate. [b] Given in the order R1, R3, R3Ј, R2, see Figure 1 for labelling. [c]
CSD IHEDUU ref.[15] [d] CSD BZACBF ref.[16] [e] CSD XOCJOO ref.[18] [f] CSD SANKUO ref.[19] [g] Average values. [h] CSD JENLOD
ref.[20] [i] CSD YALLIH ref.[21] [j] CSD BOHFUZ ref.[17]
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Chelate Complexes of Difluoroboron
over the temperature range 213–373 K. This observation is
particularly evident since complexes with symmetrically
equivalent fluorines (derivatives with planar chelate rings,
or those with exchange-averaged solution structures due to
fast ring-flipping processes, etc.) are expected to have only
one triplet 11B NMR resonance near 0 ppm indicative of
symmetric tetracoordinate boron[23] and a single quartet
resonance [with a satellite septet resonance from the 18.8%
naturally-abundant 10B (I = 3) isotope] in the 19F NMR
spectrum. On the other hand, static ring-puckered struc-
tures as found in most of the solid-state structures (Table 1),
would impose symmetric inequivalence of fluorines, and
two sets of doublet resonances (for B–F coupling) would be
anticipated in the 11B spectrum. In this scenario, the 19F
NMR spectrum would be expected to consist of two sets of
doublet-of-quartet resonances for each type of fluorine, due
to both geminal F–F coupling and to one-bond 11B–19F
coupling (with appropriate satellites resonances for 10B–19F
coupling). For most of the compounds, the former (sym-
metric) case applies, demonstrated by the spectra of
BF2(Ph,H,Ph4BrPh) shown in part A of Figure 4. As illus-
trated in Figure 4(B) for BF2(Ph,H,Ph), the spectra of the
diketonates are unusual in that the expected B–F coupling
is not observed presumably due in part to fast relaxation of
the quadrupolar boron nucleus,[24] and, in part, due to the
unusual nature of the diketonates (vide infra). For ketoimi-
nates with (asymmetric) ortho-aniline substitution, the flu-
orines are symmetrically inequivalent and more complex
spectra are observed in accord with the above discussion
and as seen in the spectra of BF2(Ph,H,Ph2BrPh), Figure 4
(C). For such asymmetric cases, the F–F geminal coupling
constant is generally about 90 Hz while the disparate B–F
coupling constants of about 20 Hz (for the resonance near
δ = –130 ppm), and 8 Hz (for the resonance near δ =
–142 ppm) further emphasize the difference in the environ-
ments about each fluorine. It was not possible to access a
more symmetric conformation, even on heating to 373 K. It
is noteworthy that for the twenty compounds studied here,
unexpected trends in the 19F chemical shift and the magni-
tude of the JB–F coupling constant are observed. For the
diketonate complexes, the average 19F chemical shift and
JB–F coupling constant are δF = –139.6 with JB–F ca. 0 Hz
while the average values for the ketoiminate and diiminate
complexes are δF = –135.0, JB–F = 15 Hz and δF = –131.2,
JB–F = 29 Hz, respectively. Normally, one expects the chem-
ical shift and the magnitude of the scalar coupling to in-
crease with increasing electronegativity of groups bound to
boron (increasing the s-character of the B–F bond). We ten-
tatively attribute this unusual behavior to the differences in
shielding caused by the magnetic anisotropy associated with
the ring currents above and below the chelate rings. The
Scheme 3. Possible resonance forms for difluoroboron β-ketoimin-
ates.
That is, for the complete series of difluoroboron chelates
derived from either the parent acetylacetone (Me,H,Me)
and 4-bromoaniline or tetramethylheptanedione (tBu,H,tBu)
and aniline, the B–O bonds are shorter in the ketoiminate
than in the corresponding diketonate while the B–N dis-
tance is longer in the ketoiminate than the average found in
the analogous diiminate. These observations suggest that,
in the ketoiminate, the B–N rather than the B–O interaction
is dative in nature. Analysis of bond length alternations
along the ketoiminate chelate backbone further supports
such an assessment. As one example, the C–C bond on the
keto side of the ring is significantly (ca. 0.04 Å) shorter than
the C–C bond on the imine side, as might be expected from
the resonance form on the left of Scheme 3. Substitution on
the aniline ring has very little, if any, impact on the bond
lengths within the six-membered chelate ring. Interestingly,
the chelate ring is often (but not always) distorted from
planarity giving a half-boat conformation brought about by
folding the E–B–E (E = N or O, as appropriate) moiety
along the E···E hinge axis, affording “axial” and “equato-
rial” B–F bonds. The B–F bond lengths vary without a
length prejudice when in axial or equatorial position and
average 1.38 Å. The chelate ring puckering (measured by
perpendicular distance from boron to the mean E2C3 che-
late ring, PlC, or by the dihedral of the mean plane of the
E–B–E group and PlC, Table 2) appears to be a function of
the crystal packing arrangement, as there is no clear corre-
lation between electronic or intramolecular steric considera-
tions of R1, R1Ј, R3, R3Ј groups. This is particularly evident
from the seemingly capricious nature of ring-puckering in
the series of chelates derived from dibenzoylmethane
(Ph,H,Ph) and triphenyl diketone (Ph,Ph,Ph). In fact, de-
tailed analysis of crystal-packing interactions show that the
BF2 moiety is always involved in weak CH–F non-covalent
interactions,[22] where the number and nature of the interac-
tions depend, of course, on the types of groups present
along the chelate periphery. In general, fluorines with more
intermolecular noncovalent interactions have longer B–F
bonds than more innocent fluorines.
NMR Spectroscopic Studies
With the possible exception of ketoiminates with ortho- structural studies indicate that the BF2 group is closest to
aniline substitution (to be discussed later), the 11B and 19F the chelate ring with the most obtuse FBF angle, allowing
NMR (and to a lesser extent the 1H and 13C), spectroscopic the fluorines (above and below the plane of the chelate ring)
data (Figure 4) reveal that the difluoroboron chelates gen- to penetrate more deeply into the ring currents compared
erally achieve more symmetric conformations in solution to the ketoiminate and the diiminate complexes with fluor-
compared to the static solid-state ring-puckered structures, ines that are progressively located further away from the
but no dynamic processes could be detected for any chelate chelate ring; the fluorines of the diketonate complexes are
Eur. J. Inorg. Chem. 2008, 3200–3211
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J. R. Gardinier et al.
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Figure 4. Representative 11B and of 19F NMR spectra obtained for CDCl3 solutions of C2v symmetric BF2(Ph, H, Ph) (top) and C1
symmetric BF2(Ph, H, Ph2BrPh).
most shielded, followed in order by those on the ketoimin- structive to examine the results obtained from time-depend-
ate and diiminate complexes. The trend in magnitude of the ent density functional calculations (B3LYP/6-31G*, using
B–F coupling constants may then be reconciled if the in- PM3 energy-minimized structures), which represented a
creased shielding effectively makes the fluorines “less reasonable compromise between computational speed and
electronegative” than in the absence of the chelate ring cur- structural accuracy (see Supporting Information for a com-
rents.
parison of results derived from different basis sets). Regard-
less of the basis set, the computational results qualitatively
agreed with those of previous calculations for related dike-
tonate complexes[8] and the experimental structural trends
in electronic data reported here. Figure 5 provides frontier
orbitalsobtainedfromsingle-pointenergycalculationsforthe
Theoretical Studies
In order to facilitate the discussion of the electronic
properties of the difluoroboron chelate complexes it is in-
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Chelate Complexes of Difluoroboron
PM3-energy-minimized structures of the three chelates BF2- tion across the carbon backbone of the chelate rings. As
(tBu,H,tBu), BF2(tBu,H,tBuPh), and BF2(tBuPh,H,tBuPh).
noted previously,[8] replacing aliphatic groups on the carbon
backbone of the chelate ring with aromatic groups is suf-
ficient to substantially lower the HOMO–LUMO energy
gap (predominantly by changing the LUMO energy) in the
β-diketonate series. The increase in HOMO–LUMO energy
gap on traversing between BF2(Ph,H,Ph) (∆E = 3.97 eV)
and BF2(Ph,Ph,Ph) (∆E = 4.17 eV) is presumably due to
steric interactions that reduce the extent of conjugation in
the latter (by lowering the probability of coplanar arrange-
ment of phenyl and chelate rings). Similar arguments ex-
plain the trends calculated (and found) for the energy gaps
in keto(aryl)iminates and bis(aryl)iminate derivatives with
aryl groups decorating both the chelate ring carbon and the
nitrogen atoms. Finally, the electronic impact of changing
substitution on the aniline groups is calculated to be mini-
mal owing to the negligible contribution of aniline group
substituents to either the HOMO or LUMO.
Figure 5. Frontier orbitals for BF2(tBu, H, tBu) (left), BF2(tBu, H,
tBuPh) (middle), BF2(tBuPh, H, tBuPh) (right) from DFT (B3LYP/
6-31G*) calculations.
These frontier orbitals are representative for the remain-
ing series of diketonate, ketoiminate, and diiminate chelates
in that the HOMO and LUMO are mainly centered on the
chelate rings. Figure 6 provides a summary of the relative
HOMO and LUMO energies of a series of fifteen com-
pounds with varying substitution patterns of heteroatom
and chelate ring substituents, from which, a number of fea-
tures can be extracted. First, the HOMO and LUMO ener-
gies increase along the series: β-diketonate Ͻ β-ketoiminate
Ͻ β-diiminate, presumably due to the greater electron-do-
nating nature of (aniline’s) nitrogen compared to oxygen.
Also apparent from Figure 6 is that the electronic properties
of the diketonates are more tuneable than those of the cor-
responding ketoiminates, which are, in turn, more tuneable
than those of diiminates. That is, the variation in the
HOMO and LUMO energies with substitution along the
chelate ring backbone is greatest for the diketonates and
smallest for the diiminates. For chelate rings with only ali-
phatic substituents on the carbon backbone, the energy of
the HOMO varies more than the LUMO on increasing ani-
line substitution whereas the reverse is true for derivatives
with any aryl groups on the chelate ring backbone; the en-
ergy of the LUMO varies more than that of the HOMO.
Coarse-tuning of the HOMO–LUMO energy gap of the
chelates is best achieved by changing the degree of conjuga-
Electronic Properties
A summary of the electronic properties of the difluo-
roboron complexes prepared in this study is given in
Table 3. The observed properties mirrored those anticipated
from the calculations, and those observed for the diketonate
series are in agreement with earlier findings. That is, the
chelates are all weak electron-acceptors whose properties
can be fine-tuned by varying substituents along the periph-
ery. The replacement of electronegative oxygen atom with
the more electron-donating aniline substituent renders the
chelate a poorer acceptor, as shown for the tert-butyl com-
pounds in Figure 7.
Figure 7. Cyclic voltammograms for CH3CN solutions of
BF2(tBuPh,H,tBuPh) (top), BF2(tBu,H,tBuPh) (middle), and of
BF2(tBu,H,tBu) (bottom) obtained at a scan rate of 100 mV/s with
(NBu4)(PF6) as supporting electrolyte.
In this series, the diketonate exhibits a reversible re-
duction at –1.6 V (vs. Ag/AgCl), while the ketoiminate and
diiminate reductions occur at –1.8 V and –1.9 V, respec-
tively. It should be noted that of the compounds reported
here, the reversible nature (ia/ic = 1) of the reduction waves
is unique to the tert-butyl derivatives; the remainder of the
chelates exhibit irreversible waves characteristic of EC be-
havior where the anticipated anodic portion of the wave is
either absent or notably less intense than expected. Regard-
Figure 6. Effect of methyl and phenyl substitution on the relative
energies of frontier orbitals for various chelate complexes [obtained
from DFT (B3LYP/6-31G*) calculations].
Eur. J. Inorg. Chem. 2008, 3200–3211
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J. R. Gardinier et al.
FULL PAPER
Table 3. Electronic properties of difluoroboron chelate complexes.
Compound
E1/2
Absorbance[b]
Emission[b] Calculated lowest-energy excitation
(V vs. Ag/AgCl)[a]
(oxid.) (red.)
λmax (ε, –1 cm–1
)
λmax
λ [eV] λ [nm] f[c]
Assignment [eV]
β-Diketonates
BF2(tBu,H,tBu)
BF2(Me,H,Me)
BF2(Ph,H,Me)
BF2(Ph,H,Ph)
BF2(Ph,Ph,Ph)
BF2(pAnis,H,pAnis)
n.o.[d] –1.46
221(1424)
228 (6440)
291 (23980)
377
315
5.00
5.19
4.32
3.83
3.59
3.56
248
239
287
324
345
348
0.059 HOMO (–7.07)ǞLUMO (–2.06)
0.298 HOMO (–7.22)ǞLUMO (–2.16)
0.328 HOMO (–6.92)ǞLUMO (–2.55)
0.956 HOMO (–6.89)ǞLUMO (–2.72)
0.173 HOMO (–6.59)ǞLUMO (–2.44)
1.000 HOMO (–6.12)ǞLUMO (–2.37)
n.o.
n.o.
n.o.
n.o.
1.98
–1.40
–1.12
286 (16703)
261 (3941)
269 (9147)
314 (10345) 376 (20904) 523
320 (8296)
329 (27231) 371
366 (47210) 414
–1.93; –0.82
–0.83
–2.18, –1.06 251 (6695)
273 (9193)
410 (56767) 443
β-Ketoiminates
BF2(tBu,H,tBuPh
BF2(Me,H,Me4BrPh
BF2(Ph,H,Me4BrPh
)
2.10
2.14
2.05
–1.73
214 (4758)
305 (24742) 403
331
4.29
4.29
4.02
289
289
309
0.260 HOMO (–6.14)ǞLUMO (–1.59)
0.168 HOMO (–6.38)ǞLUMO (–1.73)
0.431 HOMO (–6.32)ǞLUMO (–2.00)
)
)
–1.70, –1.81 219 (8626)
–1.42, –2.22 225 (6394)
301 (12705)
253 (4507)
342 (23917) 436, 471,
387s[e]
BF2(Ph,H,PhPh
)
2.00
2.16
2.00
–1.20, –1.88
265 (8729)
264 (8998)
258 (5588)
265 (7515)
360 (22552) 405, 419,
440, 469s
3.95
3.86
3.81
314
321
325
0.455 HOMO (–6.18)ǞLUMO (–1.97)
0.083 HOMO (–6.31)ǞLUMO (–2.09)
0.350 HOMO (–6.27)ǞLUMO (–2.10)
BF2(Ph,H,Ph2BrPh
BF2(Ph,H,Ph4BrPh
)
–1.16, –1.88
360 (35593) 432, 408,
469s
)
–1.15, –1.83 232 (8513)
362 (25961) 490, 472,
513, 524s
BF2(Ph,H,Ph2Br4Tolyl
BF2(Ph,H,Ph4pzPh
)
2.10
1.71
–1.19, –1.91
–1.31, –1.80
360 (33121) 418, 407s
3.78
3.50
328
354
0.078 HOMO (–6.26)ǞLUMO (–2.05)
0.233 HOMO (–5.99)ǞLUMO (–2.03)
)
264 (18664) 366 (27348) 411, 427,
473, 491s
BF2(Ph,H,Ph2pz4Tolyl
BF2(Ph,Ph,Ph4BrPh
BF2(pAnis,H, pAnis4BrPh
)
1.90
1.95
1.76
–1.20, –1.92 230 (25717) 256 (23367) 362 (25569) 419
–1.22, –1.76 226 (16168) 249 (10769) 356 (25700) 474
–1.24, –1.99 236 (21251)
3.86
3.89
3.65
322
319
340
0.028 HOMO (–6.11)ǞLUMO (–1.81)
0.096 HOMO (–6.24)ǞLUMO (–1.97)
0.264 HOMO (–5.90)ǞLUMO (–2.01)
)
)
381 (45764) 449
β-Diiminates
BF2(Me4BrPh,H,Me4BrPh
)
1.56
1.52
1.59
–2.09
–1.83
218 (9860)
231 (7647)
246 (4374)
264 (2844)
282 (6186)
334 (32565) 419
343 (38530) 365
353 (27384) 440, 470,
399s
4.30
4.18
4.18
288
296
297
0.568 HOMO (–5.94)ǞLUMO (–1.49)
0.597 HOMO (–5.50)ǞLUMO (–1.21)
0.428 HOMO (–5.94)ǞLUMO (–1.56)
BF2(tBuPh,H,tBuPh
BF2(Ph4BrPh,H,Me4BrPh
)
)
–1.59, –2.04 249 (6913)
[a] CH3CN, (NBu4)(PF6) supporting electrolyte, 100 mV/s scan rate. [b] CH3CN, 298 K. [c] Oscillator strength. [d] n.o. = not observed.
[e] s: solid-state emission, (298 K).
less, the trend holds that the diketonates are easiest and the tron-donating aniline group allows for fine-tuning of the
diiminate the most difficult to (irreversibly) reduce. Within absorption spectrum, since the HOMO and LUMO ener-
a given series of chelate, the acceptor strength increases gies are destabilized by approximately the same extent, as
with the chelate substituent’s capacity for extending π-con- discussed above. Thus, within a series of chelates derived
jugation, as observed elsewhere for the diketonates.[8] For from the same diketonate, there is only a slight blue-shift in
instance, for the ketoiminates derived from 4-bromoaniline, the absorption (or emission) spectra with increasing aniline
the reduction becomes more favorable along the series substitution, if it can be detected. Finally, while difluorobo-
BF2(Me,H,Me4BrPh) (–1.8 V), BF2(Ph,H,Me4BrPh) (–1.4 V),
BF2(Ph,H,Ph4BrPh) (–1.2 V), as anticipated for lowering the
energy of the LUMO as a result of increased conjugation.
Also, of interest is that an anodic wave for an irreversible
oxidation is found for each diiminate near 1.6 V while for
each ketoiminate the wave is found near the acetonitrile sol-
vent window at about 2.1 V. Presumably, the oxidation for
each diketonate occurs outside the potential window, due
to the electron-poor nature of the chelate.
The steady-state absorption spectroscopic data of the
chelates parallels the results from theoretical TD-DFT cal-
culations (collected in Table 3), which show that the
HOMO–LUMO energy gap (approximated by the onset of
the lowest energy absorption band) is most effectively
coarse-tuned by extending conjugation of the chelate ring.
Figure 8 displays the red-shift in the lowest energy absorp-
tion band for the ketoiminate series, BF2(Me,H,Me4BrPh),
BF2(Ph,H,Me4BrPh), BF2(Ph,H,Ph4BrPh) that typifies the ef-
fect of replacing chelate-ring alkyls with phenyl groups in
aniline, emphasizing the coarse-tuning of HOMO–LUMO energy
any of the chelate series. Substitution of oxygen for an elec- gap by substitution of groups capable of extending π-conjugation.
Figure 8. Absorption spectra for ketoimine derivatives of 4-bromo-
3206
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Eur. J. Inorg. Chem. 2008, 3200–3211

Chelate Complexes of Difluoroboron
used to prepare H(pzAnMe),[25] the diketone H(Ph,Ph,Ph),[12]
ron diketonates have been reported to be fluorescent in the
solid state and solution, reports on the luminescent behav-
ior of ketoiminate and diminate derivatives are scarce. All
the nitrogenous chelate derivatives reported here are lumi-
nescent in the solid state giving green-blue emission but are
only very weakly emissive in fluid solution at room tem-
perature, if emission can be detected at all (Figure 9). The
similarity between the spectra of these chelates and those
of the diketonates suggests that the emission is fluorescent
in nature.
the β-ketoimines H(tBu,H,tBuPh),[13] H(Me,H,Me4BrPh),[26]
H(Ph,H,Me4BrPh),[27]
H(Ph,H,PhPh),[28]
H(Ph,H,Ph2BrPh),[29]
H(Ph,H,Ph4BrPh),[30] and the β-diimine H(tBuPh,H,tBuPh).[14] Most
of the difluoroboron diketonate derivatives have been reported pre-
viously[4,9,15–21] and a summary of the characterization data for the
known ligands and complexes can be found in the Supporting In-
formation; the exception is BF2(Ph,Ph,Ph) described below. All
other β-diketones and chemicals were obtained commercially and
were used as received. Elemental Analysis was performed by Mid-
west Microlab Inc., Indianapolis, IN. Melting point determinations
were made on samples contained in glass capillaries using an Elec-
trothermal 9100 apparatus and are uncorrected. 1H and 13C NMR
spectra were recorded with a Varian 300 MHz spectrometer. Chem-
ical shifts were referenced to solvent resonances at: δH = 7.27, δC
= 77.23 ppm for CDCl3. The 11B (samples in quartz tubes) and 19
F
NMR spectra were recorded with a Varian 400 MHz spectrometer
and were referenced to external samples of BF3·OEt2 and
CF3CO2H (δ = 0.00 ppm). Absorption measurements were re-
corded with an Agilent 8453 spectrometer. Steady-state emission
spectra were obtained with a JASCO FP-6500 spectrofluorometer.
Electrochemical measurements were collected with a BAS CV-50V
instrument for ca. 0.2 m CH3CN solutions of the complexes, with
0.25  NBu4PF6 as the supporting electrolyte, in a three-electrode
cell comprised of a Ag/AgCl electrode, a platinum working elec-
trode and a glassy-carbon counter electrode.
Ketoiminines
Figure 9. Normalized solid-state emission spectra for representative
ketoiminate and diiminate of difluoroboron.
H(Ph,Ph,Ph4BrPh): A mixture of 0.63 g (2.1 mmol) H(Ph,Ph,Ph),
0.43 g (2.5 mmol) 4-bromoaniline and p-toluenesulfonic acid
(about 2 mol-%) in 30 mL of toluene was heated at reflux in a
Dean–Stark apparatus for 16 h. Solvent was removed by vacuum
distillation and the solid residue was washed with methanol, fil-
tered, and dried under vacuum to leave 0.51 g (54% yield)
Conclusions
A series of twenty difluoroboron chelates of β-diketon-
ate, β-ketoiminate, and β-diiminates have been prepared
and the relationship between structural substitutions and
their effect on electronic properties was examined both ex-
perimentally and by density functional calculations. The
substitution of electron-withdrawing oxygen for more elec-
H(Ph,Ph,Ph4BrPh
)
as
a
yellow solid; m.p. 164.5–165.0 °C.
C27H20BrNO (454.37): calcd. C 71.37, H 4.44, N 3.08; found C
71.02, H 4.43, N 2.97. 1H NMR (300 MHz, CDCl3, 22 °C): δ =
7.43–7.37 (m, 2 H), 7.36–7.29 (m, 2 H), 7.23–7.15 (m, 2 H), 7.10–
6.97 (m, 8 H), 6.87 (m, 1 H), 6.84 (m, 1 H), 6.82 (d, 2 H), 6.79 (m,
1 H) ppm. 13C NMR (75 MHz, CDCl3, 22 °C): δ = 195.1, 161.5,
tron-donating aniline groups renders the electroactive bo- 142.4, 138.8, 138.7, 134.0, 133.6, 131.8, 129.8, 129.1, 128.7, 128.3,
128.2, 127.5, 127.4, 125.7, 125.2, 117.5, 112.3 ppm. UV/Vis
(CH3CN): λmax (log ε) = 379 nm (4.41).
ron-based luminophores poorer acceptors and generally re-
sults in lower-energy absorption/emission processes. The
dominant factor in the tunability of HOMO–LUMO en-
ergy gap is the extent of conjugation along the chelate ring
backbone. Steric interactions between adjacent aryl substi-
tutents appear to disrupt this conjugation. Electrochemical
studies verify that none of the chelate ligands are innocent
spectators, as they are all weak electron acceptors where
their potency is maximized for the derivatives of diben-
zolymethane. Also, of those compounds studied only the
tert-butyl derivatives show reversible redox behavior, pre-
H(Ph,H,Ph4pzPh): A mixture of 1.2 g (3.1 mmol) H(Ph,H,Ph4BrPh),
0.23 g (3.4 mmol) pyrazole, 0.79 g (0.57 mmol) K2CO3, 0.07 mL
(about. 20 mol-%) DMEDA, and 0.030 g (about 5 mol-%) CuI in
4 mL of xylenes was heated at reflux for 72 h. The product mixture
was then washed with deionized water, extracted with dichloro-
methane and separated. The collected organic phases were dried
with magnesium sulfate, filtered, and the solvent was removed in
vacuo. Column chromatography (silica gel) using 2:1 hexanes/ethyl
acetate (Rf = 0.52) afforded 0.85 g (72% yield) of H(Ph,H,Ph4pzPh
as a yellow solid; m.p.130–131 °C. C24H19N3O (365.43): calcd. C
)
1
sumably steric interactions prevent intermolecular decom- 78.88, H 5.24, N 11.50; found C 79.02, H 5.55, N 11.14. H NMR
(300 MHz, CDCl3, 22 °C): δ = 12.96 (br. s, 1 H, N/O-H), 7.99 (d,
J = 6.7 Hz, 2 H, arom.), 7.83 (d, J = 3 Hz, 1 H, pz-H5), 7.68 (d, J
= 2 Hz, 1 H, pz-H3), 7.53–7.33 (m, 10 H), 6.88 (d, J = 8.9 Hz, 2
H, arom), 6.44 (dd, J = 3, 2 Hz, 1 H, pz-H4), 6.14 [s, 1 H, -C(O)-
CHC(N)-] ppm. 13C NMR (75 MHz, CDCl3, 22 °C): δ = 190.0,
161.4, 141.2, 139.9, 138.0, 136.6, 135.7, 131.6, 130.1, 128.9, 128.6,
128.55, 127.5, 126.8, 124.1, 119.7, 107.8, 97.5 ppm. UV/Vis (nm,
CH3CN): λmax (log ε) = 382 (4.45), 274 (4.34).
position pathways. Thus, proper consideration of the elec-
tronic properties and steric demands of these chelating li-
gands should allow the realization of new examples of low
oxidation state transition-metal complexes by our group.
Experimental Section
General Considerations: Solvents were dried and distilled prior to
H(Ph,H,Ph2Br4Tolyl):
A mixture of dibenzoylmethane (2.7 g,
use except where indicated otherwise. Literature procedures were
12 mmol), 2-bromotoluidine (2.7 g, 14 mmol) and (about 2 mol-%)
Eur. J. Inorg. Chem. 2008, 3200–3211
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3207

J. R. Gardinier et al.
FULL PAPER
p-toluenesulfonic acid in 30 mL of toluene was heated at reflux for
18 h, and the solvent removed in vacuo. Column chromatography
(silica gel, 5:1 hexane/ethyl acetate, Rf = 0.5) followed by recrystalli-
zation by cooling a refluxing hexanes solution to room temperature
afforded 2.6 g (63% yield) of H(Ph,H,Ph2Br4Tolyl) as a yellow solid;
H(MeBrPh,H,MeBrPh) (1.14 g, 28%) was obtained as yellow needles
after recrystallization from hexane at –20 °C; m.p. 107–108 °C.
C17H16Br2N2 (408.13): calcd. C 50.03, H 3.95, N 6.86; found C
50.34, H 3.97, N 7.13. 1H NMR (300 MHz, CDCl3, 22 °C): δ =
12.60 (br. s, 1 H, NH), 7.39 (part of AAЈBBЈ, J = 8.6 Hz, 4 H,
m.p. 113–114 °C. C22H18BrNO (392.29): calcd. C 67.36, H 4.62, N aniline), 6.82 (part of AAЈBBЈ, J = 8.6 Hz, 4 H, aniline), 4.89 [s, 1
1
3.57; found C 67.20, H 4.76, N 3.80. H NMR (300 MHz, CDCl3,
H, -C(N)CHC(N)-], 1.98 (s, 3 H, -CH3) ppm. 13C NMR (75 MHz,
CDCl3, 22 °C): δ = 159.8, 144.8, 132.0, 124.3, 116.4, 98.2,
22 °C): δ = 12.73 (br. s, 1 H, N/O-H), 8.00 (d, J = 7.3 Hz, 2 H,
arom.), 7.52–7.41 (m, 3 H, arom.), 7.40–7.30 (m, 6 H, arom.), 6.70 21.0 ppm. UV/Vis (CH2Cl2): λmax (log ε) = 349 (4.56), 233 nm
(part of AB, J = 8.1 Hz, 1 H, arom.), 6.37 (part of AB, J = 8.2 Hz,
(4.52). A sample of H(Me,H,MeBrPh) (1.05 g, 4.13 mmol, 41%,
1 H, arom.), 6.17 [s, 1 H, -C(O)CHC(N)-], 2.21 (s, 3 H, CH3) ppm. based on acetylacetone) as pale yellow needles was obtained after
13C NMR (75 MHz, CDCl3, 22 °C): δ = 190.2, 161.2, 139.9, 136.1,
eluting a second yellow band (Rf = 0.42) from the column and
after recrystallization from hexane at –20 °C, to afford the known
136.0, 135.7, 133.4, 131.7, 130.0, 128.8, 128.6, 128.5, 128.2, 127.7,
125.8, 117.6, 98.0, 20.7 ppm. UV/Vis (CH3CN): λmax (log ε) = 376 ketoiminate as yellowish crystals; m.p. 53–55 °C. 1H NMR
(4.30), 257 nm (4.20).
(300 MHz, CDCl3, 22 °C): δ = 12.60 (br. s, 1 H, N/O-H), 7.39 (d,
J = 8.6 Hz, 4 H), 6.82 (d, J = 8.6 Hz, 4 H), 4.89 [s, 1 H, -C(O)-
CHC(N)-], 1.98 (s, 3 H, -CH3) ppm. 13C NMR (75 MHz, CDCl3,
22 °C): δ = 196.7, 159.7, 138.1, 132.3, 126.3, 118.8, 98.4, 29.4,
20.0 ppm. UV/Vis (CH2Cl2): λmax (log ε) = 330 (4.41), 229 (4.19).
H(Ph,H,Ph2pz4Tolyl):
A mixture of dibenzoylmethane (3.0 g,
14 mmol), 4-methyl-2-pyrazoylaniline (2.4 g, 14 mmol) and p-tolu-
enesulfonic acid (about 2-mol-%) in 30 mL of toluene was heated
at reflux for 16 h and the solvent removed in vacuo. Column
chromatography (silica gel, 3:1 hexanes/ethyl acetate, Rf = 0.6)
followed by recrystallization by cooling a refluxing hexanes solu-
tion to room temperature afforded 4.4 g (85% yield) of
H(Ph4BrPh,H,Me4BrPh):
A mixture of 4-bromoaniline (4.50 g,
26.2 mmol), benzoylacetone (2.02 g, 12.5 mmol) and pTsOH
(4.9 mg, 0.25 mmol, 2 mol-%) in 80 mL of toluene was heated at
reflux overnight with a Dean–Stark trap to remove water. After
removing solvent by rotary evaporation the crude product mixture
was subject to column chromatography on silica gel using 1:4 ace-
tone/hexane as an eluent to give the desired product in the first
H(Ph,H,Ph2pz4Tolyl
) as a yellow solid; m.p. 50 °C (glass).
C25H21N3O (379.46): calcd. C 79.13, H 5.58, N 11.07; found C
79.44, H 5.87, N 10.69. 1H NMR (300 MHz, CDCl3, 22 °C): δ =
12.70 (br. s, 1 H, N/O-H), 7.96 (m, 2 H, arom.), 7.84 (d, J = 2.3 Hz,
1 H, pz-H5), 7.76 (d, J = 1.7 Hz, 1 H, pz-H3), 7.54–7.38 (m, 2 H,
arom.), 7.38–7.09 (m, 7 H, arom.), 6.88 (part of AB, J = 8.2 Hz, 1
H, aniline), 6.73 (part of AB, J = 8.2 Hz, 1 H, aniline), 6.48 (dd, J
= 2.3, 1.7 Hz, 1 H, pz-H4), 6.08 [s, 1 H, -C(O)CHC(N)-], 2.30 (s, 3
H, CH3) ppm. 13C NMR (75 MHz, CDCl3, 22 °C): δ = 190.0,
161.80, 161.78, 141.14, 140.07, 135.8, 135.6, 131.5, 131.0, 130.4,
129.8, 128.51, 128.50, 128.47, 128.3, 127.5, 127.0, 126.5, 107.4,
97.7, 20.9 ppm. UV/Vis (nm, CH3CN): λmax (log ε) = 382 (4.20).
yellow band (Rf
= 0.68). A 0.35 g (10%) sample of pure
H(PhBrPh,H,MeBrPh) was obtained after recrystallization from hex-
anes at –20 °C; m.p. 163–165 °C. C22H18Br2N2 (470.21): calcd. C
56.20, H 3.86, N 5.96; found C 56.58, H 4.12, N 5.63. 1H NMR
(300 MHz, CDCl3, 22 °C): δ = 12.50 (br. s, 1 H, NH), 7.43 (part
of AAЈBBЈ, J = 8.7 Hz, 2 H, aniline), 7.33 (m, 5 H, phenyl), 7.15
(part of AAЈBBЈ, J = 8.5 Hz, 2 H, aniline), 6.78 (part of AAЈBBЈ,
J = 8.5 Hz, 2 H, aniline), 6.50 (part of AAЈBBЈ, J = 8.7 Hz, 2 H,
aniline), 5.17 [s, 1 H, -C(N)CHC(N)-], 2.00 (s, 3 H, -CH3) ppm.
13C NMR (75 MHz, CDCl3, 22 °C): δ = 166.2, 154.8, 148.5, 141.4,
137.0, 132.0, 131.7, 129.1, 128.7, 128.4, 123.6, 123.4, 116.4, 115.2,
102.2, 21.7 ppm. UV/Vis (CH2Cl2): λmax (log ε) = 365 (4.46), 267
H(pAnis,H,pAnis4BrPh):
A mixture of 4-bromoaniline (0.13 g,
0.77 mmol), H(pAnis,H,pAnis) (0.22 g, 0.77 mmol) and pTsOH
(3.1 mg, 0.015 mmol, 2 mol-%) in 80 mL of toluene was heated at
reflux overnight with a Dean–Stark trap to remove water. The sol-
vent was removed by rotary evaporation and the crude product was
purified on a silica gel column using ethyl acetate/hexane (1:5) as
the eluent to give the product in a yellow band (Rf = 0.37). After
removing solvent under vacuum and recrystallization by cooling a
hot saturated hexanes solution to –20 °C, 0.16 g (47%) of H-
(pAnis,H,pAnisBrPh) was obtained as yellow needles; m.p. 62–64 °C.
C23H12BrNO3 (430.26): calcd. C 64.21, H 2.81, N 3.26, found C
64.03, H 3.02, N 3.33. 1H NMR (300 MHz, CDCl3, 22 °C): δ =
12.70 (br. s, 1 H, N/O-H), 7.95 (d, J = 9.1 Hz, 2 H), 7.33 (d, J =
8.9 Hz, 2 H), 7.24 (d, J = 8.9 Hz, 2 H), 6.95 (d, J = 8.9 Hz, 2 H),
6.87 (d, J = 9.1 Hz, 2 H), 6.66 (d, J = 8.9 Hz, 2 H), 6.06 [s, 1 H,
-C(O)CHC(N)-], 3.87 (s, 3 H, -OCH3), 3.84 (s, 3 H, -OCH3) ppm.
13C NMR (75 MHz, CDCl3, 22 °C): δ = 189.0, 162.6, 161.1, 160.3,
139.4, 132.7, 131.9, 130.1, 129.5, 127.9, 124.6, 116.8, 114.3, 113.8,
97.2, 55.6, 55.5 ppm. UV/Vis (CH2Cl2): λmax (log ε) = 389 (4.62),
287 (4.48), 229 nm (4.53).
(4.37), 230 nm (4.47). The known H(Ph,H,MeBrPh
) (1.51 g,
9.31 mmol, 74%, based on benzoylacetone) was obtained after elu-
tion of a second yellow band from the column (Rf = 0.51) and
recrystallization from hexanes at –20 °C; m.p. 130–132 °C. 1H
NMR (300 MHz, CDCl3, 22 °C): δ = 13.10 (br. s, 1 H, N/O-H),
7.91 (part of AAЈBBЈ, J = 8.0 Hz, 2 H, aniline), 7.45 (m, 5 H,
phenyl), 7.06 (part of AAЈBBЈ, J = 8.0 Hz, 2 H, aniline), 5.92 [s, 1
H, -C(O)CHC(N)-], 2.14 (s, 3 H, -CH3) ppm. 13C NMR (75 MHz,
CDCl3, 22 °C): δ = 189.1, 161.7, 139.9, 137.9, 132.4, 131.2, 128.5,
127.2, 126.3, 119.0, 94.9, 20.5 ppm. UV/Vis (CH2Cl2): λmax (log ε)
= 361 (4.50), 250 (4.30), 229 nm (4.32).
Difluoroboron Diketonates
BF2(Ph,Ph,Ph): A mixture of H(Ph,Ph,Ph) (1.0 g, 3.4 mmol) and
BF3·Et2O (0.48 g, 3.4 mmol) in 15 mL of toluene was heated at
reflux for 12 h. After removing the solvent by vacuum distillation
and washing the insoluble solid with dichloromethane, 1.10 g (95%
yield) of BF2(Ph,Ph,Ph) was obtained as a yellow-green solid; m.p.
Diimines
H(Me4BrPh,H,Me4BrPh):
A mixture of 4-bromoaniline (3.61 g, 315–317 °C. C21H19BF2O2 (348.16): calcd. C 72.45, H 4.34; found
21.0 mmol), acetylacetone (1.00 g, 9.99 mmol) and pTsOH
(0.0039 g, 0.20 mmol, 2 mol-%) in 80 mL of toluene was heated at
reflux overnight with a Dean–Stark trap to remove water. The sol-
vent was removed by rotary evaporation and the crude product was
purified on a silica gel column using acetone/hexane (1:4) to give
the product in the first yellow band (Rf = 0.53). A sample of pure
C 72.78, H 4.63. 1H NMR (300 MHz, CDCl3, 22 °C): δ = 7.48–
7.37 (m, 6 H, Ph), 7.34–7.21 (m, 7 H, Ph), 7.06 (dd, 2 H, Ph) ppm.
13C NMR (75 MHz, CDCl3, 22 °C): δ = 189.2, 137.4, 137.2, 137.0,
136.0, 134.2, 133.1, 132.5, 132.0, 78.0 ppm. 11B NMR (128 MHz,
CDCl3, 22 °C): δ = 0.52 (s, ω1/2 = 19 Hz) ppm. 19F NMR
(376 MHz, CDCl3, 22 °C): δ = –138.5 ppm. UV/Vis (CH2Cl2): λmax
3208
www.eurjic.org
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 3200–3211

Chelate Complexes of Difluoroboron
(log ε) = 376 (4.32), 314 (3.92), 273 nm (3.96). Other characteriza-
BF2(Ph,H,Ph2BrPh): mixture of H(Ph,H,Ph2BrPh
A ) (0.36 g,
tion can be found in Table 2 and Table 3.
0.95 mmol) and BF3·OEt2 (0.14 g, 0.95 mmol) afforded 0.22 g
(55% yield) of BF2(Ph,H,Ph2BrPh) as a yellow solid; m.p. 203.5–
204.0 °C. C21H15BBrF2NO (426.07): calcd. C 59.20, H 3.55, N
Difluoroboron Ketoiminates
1
BF2(tBu,H,tBuPh):
A
mixture of H(tBu,H,tBuPh
)
(0.33 g,
3.29; found C 59.41, H 3.74, N 3.30. H NMR (300 MHz, CDCl3,
22 °C): δ = 8.09 (m, 2 H, Ph), 7.65 (m, 1 H, aniline), 7.58 (m, 1 H,
aniline), 7.51 (m, 2 H, Ph), 7.46–7.24 (m, 7 H, Ph, aniline), 7.11
(m, 1 H, aniline), 6.46 [s, 1 H, -C(O)CHC(N)-] ppm. 13C NMR
(75 MHz, CDCl3, 22 °C): δ = 133.6, 133.2, 131.0, 130.0, 129.4,
129.0, 128.96, 128.3, 128.1, 127.9, 121.1, 96.8 ppm. 11B NMR
(128 MHz, CDCl3, 22 °C): δ = 0.92 (dd, JB-F = 21, 8 Hz) ppm. 19F
0.99 mmol) and BF3·OEt2 (0.14 g, 0.99 mmol) afforded 0.23 g
(76% yield) of BF2(tBu,H,tBuPh) as a colorless solid; m.p. 167–
168 °C. C17H24BF2NO (307.19): calcd. C 66.47, H 7.87, N 4.56;
found C 66.53, H 7.99, N 4.25. 1H NMR (300 MHz, CDCl3,
22 °C): δ = 7.44–7.20 (m, 5 H, phenyl), 5.87 [s, 1 H, -C(O)CHC(N)-
], 1.29 [s, 9 H, (CH3)3CC(O)], 1.12 [s, 9 H, (CH3)3CC(N)] ppm. 13
C
NMR (376 MHz, CDCl3, 22 °C): δ = –129.2 (dq, JF-F = 90, JB-F
=
NMR (75 MHz, CDCl3, 22 °C): δ = 180.8, 167.9, 141.1, 128.4,
128.1, 128.0, 92.3, 31.1, 27.9 ppm. 11B NMR (128 MHz, CDCl3,
22 °C): δ = 0.60 (t, JB–F = 14.9 Hz) ppm. 19F NMR (376 MHz,
CDCl3, 22 °C): δ = –137.5 (q, JB-F = 14.9 Hz) ppm. Other charac-
terization can be found in Table 2 and Table 3. Crystals suitable for
single-crystal X-ray diffraction were grown by slow cooling of a
hexanes solution.
21 Hz), –142.2 (dq, JF-F = 90, JB-F = 8 Hz) ppm. Other characteri-
zation can be found in Table 2 and Table 3. Crystals suitable for
single-crystal X-ray diffraction were grown by slow diffusion of a
layer of hexanes into a dichloromethane solution.
BF2(Ph,H,Ph4BrPh):
A ) (0.73 g,
mixture of H(Ph,H,Ph4BrPh
1.9 mmol) and BF3·OEt2 (0.27 g, 1.9 mmol) afforded 0.75 g (91%
yield) of BF2(Ph,H,Ph4BrPh) as a yellow solid; m.p. 256–258 °C.
C21H15BBrF2NO (426.07): calcd. C 59.20, H 3.55, N 3.29; found
BF2(Me,H,Me4BrPh):
A ) (0.11 g,
mixture of H(Me,H,Me4BrPh
0.43 mmol) and BF3·OEt2 (0.060 g, 0.43 mmol) afforded 0.090 g
(67% yield) of BF2(Me,H,Me4BrPh) as a colorless solid; m.p. 144–
145 °C. C11H11N1O2BBrF2 (301.93): calcd. C 43.76, H 3.67, N
1
C 58.87, H 3.59, N 3.22. H NMR (300 MHz, CDCl3, 22 °C): δ =
8.06 (m, 2 H, Ph), 7.60 (t, J = 7.2 Hz, 1 H, p-Ph), 7.50 (m, 2 H,
Ph), 7.43–7.23 (m, 8 H, Ph, aniline), 7.05 (part of AAЈBBЈ, J =
8.6 Hz, 2 H, aniline), 6.43 [s, 1 H, -C(O)CHC(N)-] ppm. 13C NMR
(75 MHz, CDCl3, 22 °C): δ = 170.9, 139.8, 133.3, 132.1, 131.0,
129.0, 128.9, 128.79, 128.78, 128.77, 128.0, 121.4, 97.2 ppm. 11B
NMR (128 MHz, CDCl3, 22 °C): δ = 1.01 (t, JB-F = 15.0 Hz) ppm.
19F NMR (376 MHz, CDCl3, 22 °C): δ = –134.3 (q, JB-F = 15.0 Hz)
ppm. Other characterization can be found in Table 2 and Table 3.
Crystals suitable for single-crystal X-ray diffraction were grown by
slow diffusion of a layer of hexanes into a dichloromethane solu-
tion.
1
4.64; found C 44.08, H 3.67, N 4.72. H NMR (300 MHz, CDCl3,
22 °C): δ = 7.57 (part of AAЈBBЈ, J = 8.5 Hz, 2 H, arom.), 7.10
(part of AAЈBBЈ, J = 8.5 Hz, 2 H, arom.), 5.56 [s, 1 H, -C(O)-
CHC(N)-], 2.20 [s, 3 H, -C(O)CH3],1.96 [s, 3 H, -C(N)CH3] ppm.
13C NMR (75 MHz, CDCl3, 22 °C): δ = 171.7, 138.9, 138.7, 128.2,
122.4, 99.1, 23.1, 21.5 ppm. 11B NMR (128 MHz, CDCl3, 22 °C):
δ = 0.31 (t, JB–F = 15.2 Hz) ppm. 19F NMR (376 MHz, CDCl3,
22 °C): δ = –134.5 (q, JB-F = 15.2 Hz) ppm. Other characterization
can be found in Table 2 and Table 3. Crystals suitable for single-
crystal X-ray diffraction were grown by slow cooling of a methanol
solution.
BF2(Ph,H,Ph2Br4Tolyl): A mixture of H(Ph,H,Ph2Br4Tolyl) (1.1 g,
2.7 mmol) and BF3·OEt2 (0.38 g, 2.7 mmol) afforded 1.0 g (83%
yield) of BF2(Ph,H,Ph2Br4Tolyl) as a yellow solid; m.p. 215–216 °C.
C22H17BBrF2NO (440.09): calcd. C 60.04, H 3.89, N 3.18; found
BF2(Ph,H,Me4BrPh):
A ) (0.80 g,
mixture of H(Ph,H,Me4BrPh
2.5 mmol) and BF3·OEt2 (0.36 g, 2.5 mmol) afforded 0.83 g (91%
yield) of BF2(Ph,H,Me4BrPh) as a colorless solid; m.p. (dec.)
Ͼ150 °C. C16H13BBrF2NO (364.00): calcd. C 52.80, H 3.60, N
1
C 60.00, H 3.77, N 2.99. H NMR (300 MHz, CDCl3, 22 °C): δ =
1
8.08 (m, 2 H, Ph), 7.62–7.55 (m, 1 H, Ph), 7.54–7.46 (m, 3 H, Ph),
7.43–7.34 (m, 3 H, Ph), 7.33–7.25 (m, 2 H, Ph), 7.21 (s, 1 H, ani-
line), 7.14 (part of AB, J = 8.1 Hz, 1 H, aniline), 6.44 [s, 1 H,
-C(O)CHC(N)-], 2.27 (s, 3 H, CH3) ppm. 13C NMR (75 MHz,
CDCl3, 22 °C): δ = 173.3, 172.3, 139.8, 136.9, 134.9, 134.0, 133.2,
131.0, 129.5, 129.0, 128.7, 128.3, 128.1, 122.4, 120.6, 96.8,
21.0 ppm. 11B NMR (128 MHz, CDCl3, 22 °C): δ = 0.89 (dd, JB-F
= 21, 8 Hz) ppm. 19F NMR (376 MHz, CDCl3, 22 °C): δ = –129.4
(dq, JF-F = 88, JB-F = 21 Hz), –142.4 (dq, JF-F = 88, JB-F = 8 Hz)
ppm. Other characterization can be found in Table 2 and Table 3.
Crystals suitable for single-crystal X-ray diffraction were grown by
slow diffusion of a layer of hexanes into a dichloromethane solu-
tion.
3.85; found C 52.63, H 3.70, N 3.54. H NMR (300 MHz, CDCl3,
22 °C): δ = 8.00 (d, J = 7.6, 7.1 Hz, 2 H, m-Ph), 7.59 (part of
AAЈBBЈ, J = 8.5 Hz, 2 H, aniline), 7.56 (t, J = 7.1 Hz, 1 H, p-Ph),
7.48 (t, J = 7.6 Hz, 2 H, o-Ph), 7.16 (part of AAЈBBЈ, J = 8.5 Hz,
2 H, aniline), 6.24 [s, 1 H, -C(O)CHC(N)-], 2.11 [s, 3 H, -C(N)CH3]
ppm. 13C NMR (75 MHz, CDCl3, 22 °C): δ = 172.0, 139.9, 132.9,
132.8, 128.1, 127.7, 126.3, 122.4, 95.9, 22.1 ppm. 11B NMR
(128 MHz, CDCl3, 22 °C): δ = 0.64 (t, JB-F = 14.8 Hz) ppm. 19F
NMR (376 MHz, CDCl3, 22 °C): δ = –135.0 (q, JB-F = 14.8 Hz)
ppm. Other characterization can be found in Table 2 and Table 3.
BF2(Ph,H,PhPh): A mixture of H(Ph,H,PhPh) (1.9 g, 6.5 mmol) and
BF3·OEt2 (0.93 g, 6.5 mmol) afforded 2.2 g (97% yield) of
BF2(Ph,H,PhPh [9a]
as a yellow solid; m.p. 195.0–196.5 °C.
)
C21H16BF2NO (347.17): calcd. C 72.65, H 4.65, N 4.03; found C
BF2(Ph,H,Ph4pzPh):
A
mixture of H(Ph,H,Ph4pzPh
)
(0.46 g,
72.27, H 4.86, N 4.29. 1H NMR (300 MHz, CDCl3, 22 °C): δ =
1.3 mmol) and BF3·OEt2 (0.18 g, 1.3 mmol) afforded 0.45 g (86%
8.05 (m, 2 H, Ph), 7.57 (m, 1 H, Ph), 7.48 (m, 2 H, m-Ph), 7.37– yield) of BF2(Ph,H,Ph4pzPh) as a yellow solid; m.p. 229–230 °C.
7.13 (m, 10 H, Ph), 6.41 [s, 1 H, -C(O)CHC(N)-] ppm. 13C NMR
(75 MHz, CDCl3, 22 °C): δ = 172.3, 170.8, 140.66, 140.65, 133.0,
C24H18BF2N3O (413.23): calcd. C 69.76, H 4.39, N 10.17; found C
69.98, H 4.15, N 10.23. 1H NMR (300 MHz, CDCl3, 22 °C): δ =
8.06 (part of AAЈBBЈ, J = 8.05 Hz, 2 H, aniline), 7.86 (d, 1 H, pz-
H5), 7.69 (d, 1 H, pz-H3), 7.63–7.44 (m, 5 H, Ph), 7.40–7.19 (m, 7
130.7, 129.0, 128.9, 128.8, 128.7, 127.9, 127.5, 127.1, 97.0 ppm. 11
B
NMR (128 MHz, CDCl3, 22 °C): δ = 1.11 (t, JB-F = 15.0 Hz) ppm.
19F NMR (376 MHz, CDCl3, 22 °C): δ = –134.5 (q, JB-F = 15.0 Hz) H, Ph), 6.46 [s, 1 H, -C(O)CHC(N)-], 6.42 (dd, J = 2.1 Hz, 1 H,
ppm. Other characterization can be found in Table 2 and Table 3.
Crystals suitable for single-crystal X-ray diffraction were grown by
slow diffusion of a layer of hexanes into a dichloromethane solu-
tion.
pz-H4) ppm. 13C NMR (75 MHz, CDCl3, 22 °C): δ = 172.7, 170.9,
141.5, 139.0, 138.8, 134.8, 133.2, 130.9, 129.0, 128.9, 128.8, 127.9,
126.9, 119.3, 108.1, 97.2 ppm. 11B NMR (128 MHz, CDCl3, 22 °C):
δ = 1.11 (t, JB–F = 15.0 Hz) ppm. 19F NMR (376 MHz, CDCl3,
Eur. J. Inorg. Chem. 2008, 3200–3211
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
3209

J. R. Gardinier et al.
FULL PAPER
22 °C): δ = –134.4 (q, JB-F = 15.0 Hz) ppm. Other characterization
can be found in Table 2 and Table 3. Crystals suitable for single-
crystal X-ray diffraction were grown by slow diffusion of a layer of
hexanes into a dichloromethane solution.
yield) of BF2(tBuPh,H,tBuPh) as a very pale yellow solid; m.p. 197–
201 °C. C23H29BF2N2 (382.30): calcd. C 72.26, H 7.65, N 7.33;
found C 71.98, H 7.93, N 7.47. 1H NMR (300 MHz, CDCl3,
22 °C): δ = 7.35–7.20 (m, 10 H, Ph), 5.87 [s, 1 H, -C(N)CHC(N)-
], 1.19 [s, 18 H, -C(CH3)3] ppm. 13C NMR (75 MHz, CDCl3,
22 °C): δ = 210.0, 173.2, 142.6, 129.3, 128.0, 127.1, 93.6, 31.7 ppm.
11B NMR (128 MHz, CDCl3, 22 °C): δ = 0.92 (t, JB F = 29.0 Hz)
BF2(Ph,H,Ph2pz4Tolyl): A mixture of H(Ph,H,Ph2pz4Tolyl) (2.0 g,
5.4 mmol) and BF3·OEt2 (0.76 g, 5.4 mmol) afforded 0.76 g (33%
yield) of BF2(Ph,H,Ph2pz4Tolyl) as a yellow solid; m.p. 153–155 °C.
C25H20BF2N3O (427.26): calcd. C 70.28, H 4.72, N 9.83; found C
70.17, H 5.01, N 9.80. 1H NMR (300 MHz, CDCl3, 22 °C): δ =
8.07–8.04 (m, 2 H, Ph), 7.77 (dd, J = 3 Hz, 1 H, pz-H5), 7.72 (part
of AB, J = 8 Hz, 1 H, aniline), 7.60 (s, 1 H, aniline), 7.54–7.48 (m,
2 H, Ph), 7.47 (d, J = 2 Hz, 1 H, pz-H3), 7.33 (part of AB, J =
8 Hz, 1 H, aniline), 7.29–7.22 (m, 2 H, Ph), 7.16 (m, 2 H, Ph), 6.76
(d, J = 8.3 Hz, 2 H, Ph), 6.32 (dd, J = 3, 2 Hz, 1 H, pz-H4), 6.24 [s,
1 H, -C(O)CHC(N)-], 2.35 (s, 3 H, CH3) ppm. 13C NMR (75 MHz,
CDCl3, 22 °C): δ = 172.7, 172.3, 140.7, 139.6, 135.6, 135.5, 133.3,
131.2, 130.54, 130.45, 130.2, 129.4, 129.1, 129.0, 128.7, 128.6,
128.2, 128.0, 126.7, 107.8, 21.1 ppm. 11B NMR (128 MHz, CDCl3,
22 °C): δ = 1.06 (dd, JB-F = 20, 9 Hz) ppm. 19F NMR (376 MHz,
CDCl3, 22 °C): δ = –127.4 (dq, JF-F = 90, JB-F = 20 Hz), –139.7
(dq, JF-F = 90, JB-F = 9 Hz) ppm. Other characterization can be
found in Table 2 and Table 3. Crystals suitable for single-crystal X-
ray diffraction were grown by slow diffusion of a layer of hexanes
into a dichloromethane solution.
ppm. NMR (376 MHz, CDCl3, 22 °C): δ = –136.3 (q, JB-F
=
29.0 Hz) ppm. Other characterization can be found in Table 2 and
Table 3. Crystals suitable for single-crystal X-ray diffraction were
grown by slow cooling of a hexanes solution.
BF2(Me4BrPh,H,Me4BrPh):
A )
mixture of H(Me4BrPh,H,Me4BrPh
(0.58 g, 1.4 mmol) and BF3·OEt2 (0.20 g, 1.4 mmol) afforded 0.21 g
(33% yield) of BF2(Me4BrPh,H,Me4BrPh) as a colorless solid; m.p.
dec. 250 °C. C17H15BBr2F2N2 (455.94): calcd. C 44.78, H 3.32, N
1
6.14; found C 44.92, H 3.01, N 6.07. H NMR (300 MHz, CDCl3,
22 °C): δ = 7.52 (part of AAЈBBЈ, J = 8.6 Hz, 4 H, aniline), 7.12
(part of AAЈBBЈ, J = 8.6 Hz, 4 H, aniline), 5.25 [s, 1 H, -C(N)
CHC(N)-], 1.92 (s, 6 H, CH3) ppm. 13C NMR (75 MHz, CDCl3,
22 °C): δ = 185.4, 132.3, 129.4, 121.6, 21.7 ppm. 11B NMR
(128 MHz, CDCl3, 22 °C): δ = 0.54 (t, JB-F = 30.0 Hz) ppm. 19F
NMR (376 MHz, CDCl3, 22 °C): δ = –129.0 (q, JB-F = 30.0 Hz)
ppm. Other characterization can be found in Table 2 and Table 3.
Crystals suitable for single-crystal X-ray diffraction were grown by
slow cooling of a methanol solution.
BF2(Ph,Ph,Ph4BrPh):
A ) (0.31 g,
mixture of H(Ph,Ph,Ph4BrPh
BF2(Me4BrPh,H, Ph4BrPh): A mixture of H(Me4BrPh,H, Ph4BrPh
)
0.67 mmol) and BF3·OEt2 (0.095 g, 0.67 mmol) afforded 0.33 g
(97% yield) of BF2(Ph,Ph,Ph4BrPh) as a yellow solid; m.p. 205–
206 °C. C27H19BBrF2NO (422.26): calcd. C 64.58, H 3.81, N 2.79;
found C 64.62, H 3.97, N 2.96. 1H NMR (300 MHz, CDCl3,
22 °C): δ = 7.43–7.29 (m, 4 H, Ph), 7.23–7.15 (m, 2 H, arom), 7.10-
6.97 (m, 8 H, Ph), 6.85 (part of AAЈBBЈ, J = 7.3 Hz, 2 H, aniline),
6.80 (part of AAЈBBЈ, J = 7.3 Hz, 2 H, aniline) ppm. 13C NMR
(75 MHz, CDCl3, 22 °C): δ = (CN not obsd.), 135.4, 132.8, 131.9,
131.1, 130.1, 129.2, 129.0, 128.7, 128.4, 127.94, 127.90, 127.3,
121.5, 120.8 ppm. 11B NMR (128 MHz, CDCl3, 22 °C): δ = 0.59
(t, JB-F = 14.1 Hz) ppm. 19F NMR (376 MHz, CDCl3, 22 °C): δ =
–133.3 (q, JB-F = 14.1 Hz) ppm. Other characterization can be
found in Table 2 and Table 3. Crystals suitable for single-crystal X-
ray diffraction were grown by slow diffusion of a layer of hexanes
into a dichloromethane solution.
(0.19 g, 0.41 mmol) and BF3·OEt2 (0.058 g, 0.41 mmol) afforded
0.18 g (85% yield) of BF2(Me4BrPh,H, Ph4BrPh) as a yellow solid;
m.p. 201–202 °C. C22H17BBr2F2N2 (518.01): calcd. C 51.01, H 3.31,
N 5.41; found C 50.76, H 3.02, N 5.53. 1H NMR (300 MHz,
CDCl3, 22 °C): δ = 7.56 (part of AAЈBBЈ, J = 8.5 Hz, 2 H, aniline),
7.32–7.16 (m, 9 H, Ph, aniline), 6.98 (part of AAЈBBЈ, J = 8.5 Hz,
2 H, aniline), 5.45 [s, 1 H, -C(N)CHC(N)-], 2.02 (s, 3 H, -CH3)
ppm. 13C NMR (75 MHz, CDCl3, 22 °C): δ = 132.4, 131.6, 129.8,
129.5, 129.2, 129.0, 128.5, 121.8, 120.1, 98.2, 21.9, (CN not obsd.)
ppm. 11B NMR (128 MHz, CDCl3, 22 °C): δ = 0.89 (t, JB-F
=
30.0 Hz) ppm. 19F NMR (376 MHz, CDCl3, 22 °C): δ = –128.2 (q,
JB-F = 30.0 Hz) ppm. Other characterization can be found in
Table 2 and Table 3.
Supporting Information (see also the footnote on the first page of
this article): Characterization data for known difluoroboron dike-
tonates, details of X-ray crystallographic studies, tables of X-ray
data, details of computational studies, frontier orbital diagrams.
The supplementary crystallographic data for this paper are con-
tained in CCDC-678449 [for BF2(tBu,H,tBu)], -678673 [for
BF2(tBu,H,tBuPh)], -678674 [for BF2(tBuPh,H,tBuPh)], -678450 [for
BF2(pAnis,H,pAnis4BrPh):
A )
mixture of H(pAnis,H,pAnis4BrPh
(0.38 g, 0.87 mmol) and BF3·OEt2 (0.12 g, 0.87 mmol) afforded
0.27 g (64% yield) of BF2(pAnis,H,pAnis4BrPh) as a yellow solid;
m.p. 173.5–174.5 °C. C23H19BBrF2NO (486.12): calcd. C 56.83, H
1
3.94, N 2.88; found C 57.11, H 3.82, N 3.24. H NMR (300 MHz,
CDCl3, 22 °C): δ = 8.02 (part of AAЈBBЈ, J = 9.0 Hz, 2 H, arom.),
7.36 (part of AAЈBBЈ, J = 8.7 Hz, 2 H, aniline), 7.20 (part of
AAЈBBЈ, J = 8.9 Hz, 2 H, arom.), 7.04 (part of AAЈBBЈ, J =
8.7 Hz, 2 H, aniline), 6.98 (part of AAЈBBЈ, J = 9.0 Hz, 2 H,
arom.), 6.80 (part of AAЈBBЈ, J = 8.9 Hz, 2 H, arom.), 6.32 [s, 1
H, -C(O)CHC(N)-], 3.90 (s, 3 H, OCH3), 3.81 (s, 3 H, -OCH3)
ppm. 13C NMR (75 MHz, CDCl3, 22 °C): δ = 163.9, 161.6, 132.1,
131.0, 130.1, 128.8, 120.9, 114.4, 114.3, 55.8, 55.6 ppm. 11B NMR
(128 MHz, CDCl3, 22 °C): δ = 0.99 (t, JB-F = 15.5 Hz) ppm. 19F
NMR (376 MHz, CDCl3, 22 °C): δ = –135.4 (q, JB-F = 15.5 Hz)
ppm. Other characterization can be found in Table 2 and Table 3.
Crystals suitable for single-crystal X-ray diffraction were grown by
slow diffusion of a layer of hexanes into a dichloromethane solu-
tion.
BF2(Me,H,MeBrPh)],
-678447 [for BF2(Ph,H,PhPh)], -678448 [for BF2(Ph,H,Ph4BrPh)],
-678670 [for -678668 [for BF2-
BF2(Ph,H,Ph2BrPh)],
-678669
[for
BF2(MeBrPh,H,MeBrPh)],
(Ph,H,Ph4pzPh)], -678671 [for BF2(Ph,H,Ph2pz4tolyl)], -678672 [for
BF2(Ph,Ph,PhBrPh)], and -678667 [for BF2(pAnis,H,pAnisBrPh)].
These data can be obtained free of charge from The Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
Acknowledgments
J. R. G. thanks Marquette University and the Petroleum Research
Fund for financial support.
Difluoroboron Diiminates
BF2(tBuPh,H,tBuPh):
5.7 mmol) and BF3·OEt2 (0.81 g, 5.7 mmol) afforded 1.7 g (79%
A ) (1.9 g,
mixture of H(tBuPh,H,tBuPh
[1] a) R. C. Mehrotra, R. Bohra, D. P. Gaur in Metal β-Diketon-
ates and Allied Derivatives, Academic Press, New York, 1978;
3210
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© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 3200–3211

Chelate Complexes of Difluoroboron
b) L. Bourget-Merle, M. F. Lappert, J. R. Severn, Chem. Rev.
2002, 102, 3031–3065.
[12] a) P. S. Bailey, T. M. Ferrell, J. Org. Chem. 1981, 46, 5028–
5030; b) A. Padwa, T. Brookhart, J. Org. Chem. 1979, 44, 4021–
4030.
[13] R. Knorr, A. Weiss, Chem. Ber. 1981, 114, 2104–2115.
[14] R. Knorr, A. Weiss, Chem. Ber. 1982, 115, 139–160.
[15] CSD registration number IHEDUU: A. G. Mirochnik, B. V.
Bukvetsky, E. V. Gukhman, P. A. Zhikhareva, V. E. Karasev,
Zh. Obshch. Khim. 2002, 72, 737–740.
[16] CSD registration number BZACBF: A. W. Hanson, E. W. Ma-
caulay, Acta Crystallogr., Sect. B 1972, 28, 1961–1967.
[17] CSD registration number BOHFUZ: B. Qian, S. W. Baek,
M. R. Smith III, Polyhedron 1999, 18, 2405–2414.
[18] CSD registration number XOCJOO: A. G. Mirochnik, B. V.
Bukvetsky, E. V. Gukhman, P. A. Zhikhareva, V. E. Karasev,
Izv. Akad. Nauk SSSR, Ser. Khim. 2001, 50, 1612–1615.
[19] a) CSD registration number SANKUO: A. G. Mirochnik, B. V.
Bukvetskii, E. V. Fedorenko, V. E. Karasev, Russ. Chem. Bull.
2004, 53, 291–296; b) E. Cogné-Laage, J.-F. Allemand, O. Ruel,
J.-B. Baudin, V. Croquette, M. Blanchard-Desce, L. Jullien,
Chem. Eur. J. 2004, 10, 1445–1455.
[20] CSD registration number JENLOD: N. Kuhn, A. Kuhn, M.
Speis, D. Blaser, R. Boese, Chem. Ber. 1990, 123, 1301–1306.
[21] CSD YALLIH: K.-H. Park, W. J. Marshall, J. Org. Chem.
2005, 70, 2075–2081.
[22] F. Grepioni, G. Cojazzi, S. M. Draper, N. Scully, D. Braga,
Organometallics 1998, 17, 296–307.
[23] H. Nöth, B. Wrackmeyer in Nuclear Magnetic Resonance Spec-
troscopy of Boron Compounds, Springer-Verlag, New York,
1978.
[2]
Select Examples: a) K. M. Smith, Organometallics 2005, 24,
778–784; b) J. M. Smith, A. R. Sadique, T. R. Cundari, K. R.
Rodgers, G. Lukat-Rodgers, R. J. Lachicotte, C. J. Flaschen-
reim, J. Vela, P. L. Holland, J. Am. Chem. Soc. 2006, 128, 756–
769; c) Y. M. Badiei, A. Krishnaswamy, M. M. Melzer, T. H.
Warren, J. Am. Chem. Soc. 2006, 128, 15056–15057; d) Z. J.
Tonzetich, A. J. Jiang, R. R. Shrock, P. Muller, Organometallics
2006, 25, 4725–4727.
For instance: a) A. H. Cowley, Z. Lu, J. N. Jones, J. A. Moore,
J. Organomet. Chem. 2004, 689, 2562–2564; b) D. Vidovic, J. A.
Moore, J. N. Jones, A. H. Cowley, J. Am. Chem. Soc. 2005, 127,
4566–4567; c) S. Singh, H.-J. Ahn, A. Stasch, V. Jancik, H. W.
Roesky, A. Pal, M. Biadene, R. Herbst-Irmer, M. Noltemeyer,
H. G. Schmidt, Inorg. Chem. 2006, 45, 1853–1860; d) Y. Yang,
T. Schulz, M. John, Z. Yang, V. M. Jimenez-Perez, H. W. Roe-
sky, P. M. Gurubasavaraj, D. Stalke, H. Ye, Organometallics
2008, 27, 769–777.
[3]
[4]
[5]
N. M. D. Brown, P. Bladon, J. Chem. Soc. A 1969, 526–532.
a) Y. P. Singh, P. Rupani, A. Singh, A. K. Rai, R. C. Mehrotra,
R. D. Rodgers, J. L. Atwood, Inorg. Chem. 1986, 25, 3076–
3081; b) K. Itoh, K. Okazaki, M. Fujimoto, Aust. J. Chem.
2003, 56, 1209–1214.
N. Kuhn, A. Kuhn, J. Lewandowski, M. Spies, Chem. Ber.
1991, 124, 2197–2201.
[6]
[7] N. Kuhn, A. Kuhn, R. Boese, N. Augart, J. Chem. Soc., Chem.
Commun. 1989, 975–976.
[8] a) Y. L. Chow, C. I. Johansson, Y.-H. Zhang, R. Gautron, L.
Yang, A. Rassat, S.-Z. Yang, J. Phys. Org. Chem. 1996, 9, 7–
16; b) R. L. Belford, A. E. Martell, M. Calvin, J. Inorg. Nucl.
Chem. 1956, 2, 11–31.
[9] a) K. Itoh, K. Okazaki, A. Sera, Y. L. Chow, J. Chem. Soc.,
Chem. Commun. 1992, 1608–1609; b) K. Itoh, M. Fujimoto,
M. Hashimoto, New J. Chem. 2002, 26, 1070–1075; c) K. Itoh,
K. Okazaki, Y. Toyotomi, Heterocycles 2002, 57, 2065–2079;
d) K. Itoh, K. Okazaki, Y. L. Chow, Helv. Chim. Acta 2004,
87, 292–302.
[10] a) G. Haucke, P. Czerney, H. G. Ilge, D. Steen, H. Hartmann,
J. Mol. Struct. 1990, 219, 411–416; b) Y. L. Chow, C. J. Johans-
son, J. Phys. Chem. 1995, 99, 17566–17572; c) Y. L. Chow, S.-
S. Wang, C. I. Johansson, Z.-L. Liu, J. Am. Chem. Soc. 1996,
118, 11725–11732.
[11] For instance, O. T. Beachley Jr, J. R. Gardinier, M. R.
Churchill, Organometallics 2000, 19, 4544–4549.
[24] a) N. N. Shapet’ko, L. N. Kurkovskaya, V. G. Medvedeva, A. P.
Skoldinov, L. K. Vasyanina, Zh. Strukt. Khim. 1969, 10, 936–
942; b) J. Bacon, R. J. Gillespie, J. W. Quail, Can. J. Chem.
1963, 41, 3063–3069.
[25] B. J. Liddle, R. M. Silva, T. J. Morin, F. P. Macedo, R. Shukla,
S. V. Lindeman, J. R. Gardinier, J. Org. Chem. 2007, 72, 5637–
5646.
[26] M. M. Khodaei, A. R. Khosropour, M. Kookhazadeh, Can. J.
Chem. 2005, 83, 209–212.
[27] E. E. Turner, J. Chem. Soc. Trans. 1917, 111, 1–4.
[28] D. F. Martin, G. A. Janusonis, B. B. Martin, J. Am. Chem. Soc.
1961, 83, 73–75.
[29] J. Grimshaw, A. P. De Silva, J. Chem. Soc. Perkin Trans. 2 1981,
1010–1014.
[30] S. Sahoo, J. Mol. Catal. A 2006, 244, 179–182.
Received: March 8, 2008
Published Online: June 3, 2008
Eur. J. Inorg. Chem. 2008, 3200–3211
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
3211