Syntheses and structures of new alkali-metal boraamidinates and ferrocenyl aminoboranes

Article abstract of DOI:10.1039/c0nj00279h

The ferrocenyl bis(amino)boranes FcB[N(H)R]₂ (Fc = ferrocenyl; 1a, R = ^tBu, 1b, R = Dipp) and 1,1′-Fc{B[N(H) ^tBu]₂}₂ (2) are obtained by the reactions of [Li][N(H)R] with the corresponding ferrocenyl

Full text of DOI:10.1039/c0nj00279h

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PAPER
www.rsc.org/njc | New Journal of Chemistry
Syntheses and structures of new alkali-metal boraamidinates
and ferrocenyl aminoboraneswzy
Andrea M. Corrente and Tristram Chivers*
Received (in Montpellier, France) 14th April 2010, Accepted 24th May 2010
DOI: 10.1039/c0nj00279h
t
The ferrocenyl bis(amino)boranes FcB[N(H)R]2 (Fc = ferrocenyl; 1a, R = Bu, 1b, R = Dipp)
and 1,10-Fc{B[N(H)tBu]2}2 (2) are obtained by the reactions of [Li][N(H)R] with the
corresponding ferrocenyl dibromoboranes FcBBr2 and 1,10-Fc(BBr2)2. In a similar manner
1,4-[N(H)tBu]2BC6H4B[N(H)tBu]2 (3) is prepared in good yield by treatment of
1,4-Br2BC6H4BBr2 with five equivalents of [Li][N(H)tBu] in toluene. Compound 3 is converted
to the highly air-sensitive tetralithio derivative [Li4][1,4-(NtBu)2BC6H4B(NtBu)2] (4), by
n
deprotonation with BuLi in hexanes. Alkali-metal derivatives of a monoanionic boraamidinate
[M][PhB(NDipp){N(H)Dipp}] [M = Li (5), K (6)] are produced by reactions of PhB[N(H)Dipp]2
n
with one equivalent of BuLi in hexanes or [K][CH2Ph] in THF, respectively. The use of
two equivalents of [K][CH2Ph] generates the dipotassium reagent [K2][PhB(NDipp)2] (7)
in excellent yield. The X-ray structures of 1a, 1b, 2, 4ꢀ6THF, 5ꢀ2THF and 7ꢀ3THF were
determined. The complex 4ꢀ6THF incorporates one terminal and one bridging THF molecule
for each Li+ cation. The boraamidinate ligand in 5ꢀ2THF is connected in an N-monodentate
fashion to the Li+ cation, which is solvated by two THF molecules. In the solid state
7ꢀ3THF forms an extended structure as a result of Z1-amide–Z6-arene coordination
to the two K+ cations, which are coordinated by one or two THF molecules,
respectively.
unique consequences: (a) fewer anionic ligands are necessary for
Introduction
stabilizing higher oxidation states4,5 and (b) novel redox beha-
viour leading to the formation of persistent or, in some cases,
stable radicals is observed.6 As with amidinates, the electronic
and steric properties of bams can be tuned by varying the
substituents on either nitrogen or boron. Recently, we described
the synthesis and structures of the first boraguanidinates,7 i.e.
isoelectronic analogues of guanidinates,8 in which the substi-
tuent on boron is a dialkylamino group. Current investigations
of bam ligands are focused on lanthanide complexes and their
potential as catalysts.9,10
Boraamidinates (bams)1 [RB(NR0)2]2ꢁ (A) are dianionic ligands
that are isoelectronic with monoanionic amidinates [RC(NR0)2]ꢁ
(B).2 The bam ligand adopts a wide range of bonding modes in
main group and transition-metal complexes, most commonly
chelating or bridging arrangements.1,3 Replacement of the CR
fragment in the ligand backbone with a BR unit imposes two
The synthesis of new types of bams is of interest in order to
expand the chemistry of this versatile ligand. For example, the
introduction of a linker group between two boron atoms
would generate a tetraanionic ligand (C). In light of the
formation of stable radicals that incorporate the anion radical
[PhB(NtBu)2]ꢂꢁ,6 C is a potential source of biradical systems
incorporating p-block elements.11 A second modification of
the bam ligand that warrants investigation is single deproto-
nation of bamH2 to form a monoanionic ligand D that still
contains an –NH functionality. In addition to being isoelec-
tronic, these monoanions would have the same charge as the
well-studied amidinate ligands.2 Finally, the availability of
hitherto unknown dipotassiated bam reagents is desirable
in order to facilitate the separation of alkali-metal halide
by-products in metathetical reactions with main group or
transition-metal halides.12
Department of Chemistry, University of Calgary, Calgary,
Alberta T2N 1N4, Canada. E-mail: chivers@ucalgary.ca;
Fax: +1 403 289-9488; Tel: +1 403 220-5741
w Dedicated to the late Professor Pascal le Floch in appreciation of his
many outstanding contributions.
z This article is part of a themed issue on Main Group chemistry.
y CCDC reference numbers [CCDC 773247–773252]. For crystallo-
graphic data in CIF or other electronic format see DOI: 10.1039/
c0nj00279h
With these objectives in mind we describe here the syn-
thesis, spectroscopic and structural characterization of (a) the
t
ferrocenyl aminoboranes FcB[N(H)R]2 [R = Bu (1a), Dipp
(1b); Fc = ferrocenyl, Dipp = 2,6-diisopropylphenyl] and
ꢃc
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Fc[B{N(H)tBu}2]2 (2), (b) 1,4-[N(H)tBu]2BC6H4B[N(H)tBu]2
(3) and the tetralithiated derivative [{Li(THF)}4(m-THF)2]-
[1,4-(NtBu)2BC6H4B(NtBu)2] (4ꢀ6THF), (c) alkali-metal derivatives
of a monoanionic boraamidinate [M][PhB(NDipp){N(H)Dipp}]2
(M = Li (5), K (6)), and (d) the dipotassium reagent
[K2(THF)3][PhB(NDipp)2] (7).
were solved by direct methods using SHELXS-9718a and
refinement was carried out on F2 against all independent
reflections by the full-matrix least-squares method using the
SHELXL-9718b program. All non-hydrogen atoms were refined
with anisotropic thermal parameters. The hydrogen atoms
were calculated geometrically and refined using a riding
model. For complexes 4ꢀ6THF and 7ꢀ3THF, electron density
in two regions was attributed to disordered solvent molecules
(4ꢀ6THF: diethyl ether; 7ꢀ3THF: hexane) for which no suitable
model could be found. These regions of electron density were
removed from the reflections data using the program
SQUEEZE (PLATON),18c leaving a total void of 355.7 A3
and 327.4 A3, respectively. Crystallographic data for 1a, 1b
and 2 are summarised in Table 1 and those for 4ꢀ6THF, 5ꢀ
2THF and 7ꢀ3THF are given in Table 2.y
Experimental section
Reagents and general procedures
All reactions and the manipulation of moisture- and/or air-
sensitive products were performed under an argon atmosphere
using standard Schlenk line techniques or in an inert-atmosphere
glove box. Solvents were dried with appropriate drying agents,
distilled before use and stored over molecular sieves. Prior to
use, all glassware was carefully dried. Dicyclopentadienyl iron
(Cp2Fe) was purchased from Eastman Organic Chemical
Company and all other chemicals were obtained from Aldrich
Chemical Company and used as received. The reagents
[Li][N(H)Dipp] and [Li][N(H)tBu] were prepared by the addi-
Syntheses
FcB[N(H)tBu]2, 1a. A solution of FcBBr2 (1.37 g, 3.85 mmol)
in toluene (15 mL) was added to a stirred slurry of [Li][N(H)tBu]
(0.609 g, 7.70 mmol) in toluene (15 mL) at ca. ꢁ80 1C. After 1 h,
the cold bath was removed and the reaction mixture was
allowed to warm to room temperature and stirred for 4 h. After
filtration to remove LiBr, volatiles were taken off in vacuo
yielding an orange solid (1.005 g, 2.96 mmol, 76%). Orange,
X-ray quality crystals of 1a were grown from a concentrated
hexanes/toluene solution at 5 1C. HRMS: calculated m/z for
[C18H29BN2]: 340.1773. Found: 340.1757. 1H NMR (C6D6,
n
tion of BuLi (2.5 M in hexane) to an equimolar amount of
DippNH2 or tBuNH2, respectively, in hexanes and purity was
checked by 1H NMR spectroscopy. The reagents FcBBr2,13
1,10-Fc(BBr2)2,14 1,4-Br2BC6H4BBr2,15 benzylpotassium,16
17
and PhB[N(H)Dipp]2 were prepared by literature methods.
Deuterated solvents were purchased from Cambridge Isotope
Laboratories, dried over molecular sieves for at least one week
and degassed using the freeze–pump–thaw method.
3
25 1C): d 4.28 (t, 2H, C5H4, JH–H = 1.59 Hz), 4.12 (t, 2H,
3
C5H4, JH–H = 1.59 Hz), 4.06 (s, 5H, C5H5), 3.35 (2H, br
s, –NH), 1.21 (s, 18H, –C(CH3)3). 11B NMR (C6D6, 25 1C):
d 29.2. 13C NMR (C6D6, 25 1C): d 74.4 (C5H4), 69.4 (C5H4),
69.2 (C5H5), 49.0 (–C(CH3)3), 33.6 (–C(CH3)3).
Instrumentation
All NMR spectra were collected at room temperature using a
Bruker DRX 400 spectrometer. All chemical shifts are reported
in parts per million (ppm) with higher frequency taken as
positive. Chemical shifts for 1H and 13C{1H} NMR spectra are
reported with respect to tetramethylsilane and were calibrated
based on the signal of the residual solvent peak. A solution of
FcB[N(H)Dipp]2, 1b. A solution of FcBBr2 (0.720 g,
2.02 mmol) in toluene (10 mL) was added to a stirred slurry
of [Li][N(H)Dipp] (0.742 g, 4.05 mmol) in toluene (15 mL) at
ca. ꢁ80 1C. After 1 h the cold bath was removed and the
reaction was allowed to warm to room temperature and stirred
for 18 h. The reaction mixture was filtered to remove LiBr and
volatiles were taken off in vacuo yielding an orange solid
(0.746 g, 1.36 mmol, 67%). Orange, X-ray quality crystals of
1b were grown from a concentrated toluene solution at 5 1C.
Anal. Calcd. for C34H45BN2Fe: C, 74.46; H, 8.27; N, 5.11%.
Found: C, 74.31; H, 8.05; N, 5.06%. 1H NMR (C6D6, 25 1C):
d 7.21–7.03 (m, 6H, Dipp), 4.28 (br, 2H, –CH(CH3)2), 4.07
7
1.0 M LiCl in D2O was used as the external standard for Li
NMR spectra and 11B{1H} NMR chemical shifts are reported
with respect to a solution of BF3ꢀOEt2 in C6D6. Elemental and
mass spectrometry analyses (using a Waters GCT Premier
spectrometer) were carried out by the Analytical Services
Laboratory of the Department of Chemistry, University of
Calgary.
Crystal structure determinations
3
(s, 5H, C5H5), 4.01 (t, 2H, C5H4, JH–H = 1.67 Hz), 3.87
Single crystals of FcB[N(H)tBu]2 (1a), FcB[N(H)Dipp]2 (1b),
1,10-Fc{B[N(H)tBu]2}2 (2), [{Li(THF)}4(m-THF)2][1,4-(NtBu)2-
BC6H4B(NtBu)2] (4ꢀ6THF), [Li(THF)2][PhB(NDipp){N(H)-
Dipp})] (5ꢀ2THF) and [K2(THF)3][PhB(NDipp)2] (7ꢀ3THF)
suitable for X-ray analysis were covered with Paratone oil and
mounted on a glass fibre in a stream of N2 at 173 K on a Nonius
KappaCCD diffractometer (MoKa radiation, l = 0.71073 A)
using COLLECT (Nonius, B.V. 1998) software. The unit cell
parameters were calculated and refined from the full data set.
All crystal cell refinement and data reduction were carried out
using the Nonius DENZO package. After data reduction, the
data were corrected for absorption based on equivalent reflec-
tions using SCALEPACK (Nonius, B.V. 1998). The structures
(t, C5H4, 3JH–H = 1.67 Hz), second iPr septet under resonance
at 3.87 ppm, 3.41 (2H, br s, –NH), 1.37–1.04 (br, 24H,
–CH(CH3)2). 11B NMR (C6D6, 25 1C): d 30.3. 13C NMR
(C6D6, 25 1C): d 147.6 (Dipp), 146.1 (Dipp), 123.6 (Dipp), 73.9
(C5H4), 71.0 (C5H4), 68.9 (C5H5), 28.9 (–CH(CH3)2), 25.7
(–CH(CH3)2), 24.7 (–CH(CH3)2), 23.7 (–CH(CH3)2), 23.1
(–CH(CH3)2).
Fc{B[N(H)tBu]2}2, 2. A solution of 1,10-Fc(BBr2)2 (0.268 g,
0.51 mmol) in toluene (10 mL) was added to a stirred slurry of
[Li][N(H)tBu] (0.161 g, 2.03 mmol) in toluene (10 mL) at ca.
ꢁ80 1C. After 1 h the cold bath was removed and the reaction
mixture was allowed to warm to room temperature and stirred
ꢃc
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Table 1 Selected crystal data and refinement parameters for 1a, 1b and 2a
1a
1b
2
Empirical formula
Fw
Cryst. system
Space group
C18H49BFeN2
340.09
Orthorhombic
Pna21
C34H45BFeN2
548.38
Monoclinic
C2/c
C26H48B2FeN4
494.15
Triclinic
ꢀ
P1
a/A
b/A
c/A
a/1
17.365(4)
5.996(1)
35.480(7)
90.00
90.00
90.00
21.451(4)
10.016(2)
28.699(6)
90.00
99.88(3)
90.00
10.265(2)
12.189(2)
13.101(3)
109.70(3)
102.12(3)
103.19(3)
1427(1)
2
b/1
g/1
V/A3
Z
3670(1)
8
6075(2)
8
T/1C
r
ꢁ100
ꢁ100
ꢁ100
calcd/g cmꢁ3
1.231
0.820
1.199
0.521
1.150
0.548
m(MoKa)/mmꢁ1
Crystal size/mm3
F(000)
0.28 ꢄ 0.08 ꢄ 0.04
0.20 ꢄ 0.16 ꢄ 0.04
0.40 ꢄ 0.40 ꢄ 0.32
1456
2352
536
Y Range/1
3.28–25.02
22 275
5629
2.25–27.46
30 049
6921
0.0583
0.0525
2.97–25.03
24 390
5021
0.0200
0.0366
0.0966
1.043
0.996
Reflns collected
Unique reflns
Rint
0.0d
R1 [I 4 2s(I)]b
wR2 (all data)c
GOF on F2
Completeness
0.0428
0.1121
1.126
0.943
0.1380
1.081
0.995
P
1
P
P
P
a
b
c
2
4
d
l(MoKa) = 0.71073 A. R1 = ||Fo| ꢁ |Fc||/ |Fo|. wR2 = [ w(Fo ꢁ Fc2)2/ wFo ]2. Flack parameter: 0.50(2).
Table 2 Selected crystal data and refinement parameters for 4ꢀ6THF, 5ꢀ2THF and 7ꢀ3THFa
4ꢀ6THF
46H88B2Li4N4O6
842.58
Monoclinic
P21/c
10.003(2)
14.712(3)
19.859(4)
91.29(3)
2922(1)
2
5ꢀ2THF
C38H56BLiN2O2
590.60
Monoclinic
P21/n
14.028(3)
16.356(3)
16.606(3)
103.66(3)
3702(1)
4
7ꢀ3THF
C42H63BK2N2O3
732.95
Monoclinic
P21/c
10.456(2)
15.323(3)
27.854(6)
90.91(3)
4462(2)
4
Empirical formula
Fw
Cryst. system
Space group
a/A
b/A
C
c/A
b/1
V/A3
Z
T/1C
r
ꢁ100
ꢁ100
ꢁ100
calcd/g cmꢁ3
0.958
0.060
1.060
0.063
1.091
0.248
m(MoKa)/mmꢁ1
Crystal size/mm3
F(000)
0.20 ꢄ 0.20 ꢄ 0.20
0.14 ꢄ 0.14 ꢄ 0.12
0.20 ꢄ 0.12 ꢄ 0.08
924
1288
1584
Y Range/1
2.65–25.03
32 486
5107
0.0188
0.0679
0.2254
1.074
0.990
2.79–25.03
56 077
6541
0.0666
0.0740
2.57–25.03
37 588
7805
0.0417
0.0859
0.2078
1.093
0.991
Reflns collected
Unique reflns
Rint
R1 [I 4 2s(I)]b
wR2 (all data)c
GOF on F2
Completeness
0.1958
1.059
0.998
P
1
P
P
P
l(MoKa) = 0.71073 A. R1 = ||Fo| ꢁ |Fc||/ |Fo|. wR2 = [ w(Fo ꢁ Fc2)2/ wFo ]2.
a
b
c
2
4
for 18 h. The reaction mixture was filtered to remove LiBr
and volatiles were taken off in vacuo yielding an orange solid
(0.136 g, 0.28 mmol, 54%). Orange, X-ray quality crystals of 2
1,4-[N(H)tBu]2BC6H4B[N(H)tBu]2, 3. A solution of 1,4-
Br2BC6H4BBr2 (0.858 g, 2.05 mmol) in toluene (15 mL) was
added to a slurry of [Li][N(H)tBu] (0.898 g, 10.0 mmol) in
toluene (10 mL) at ca. ꢁ80 1C. After 30 min the reaction
mixture was allowed to warm to room temperature and stirred
for 18 h. Volatiles were removed in vacuo and the product was
extracted in hexanes. After filtration to remove LiBr and
excess [Li][N(H)tBu], volatiles were removed in vacuo resulting
in an oily solid that completely solidified overnight at room
1
were grown from a concentrated toluene solution at 5 1C. H
3
NMR (C6D6, 25 1C): d 4.28 (t, 4H, C5H4, JH–H = 1.73 Hz),
3
4.21 (t, 4H, C5H4, JH–H = 1.73 Hz), 3.47 (4H, br s, –NH),
1.25 (s, 36H, –C(CH3)3). 11B NMR (C6D6, 25 1C): d 29.2.
13C NMR (C6D6, 25 1C): d 75.2 (C5H4), 69.8 (C5H4), 49.1
(–C(CH3)3), 33.7 (–C(CH3)3).
ꢃc
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3
(d, 6H, –CH(CH3)2, JH–H = 6.12 Hz), 1.03 (d, 18H,
temperature to give 3 as a colourless solid (0.597 g, 1.54 mmol,
75%). HRMS: calculated m/z for [C22H44N2B]: 386.3752.
Found: 386.3752. 1H NMR (C6D6, 25 1C): d 7.66 (s, 4H,
–C6H4–), 2.88 (br s, 4H, –NH), 1.16 (s, 36H, –C(CH3)3).
1H NMR (THF-d8, 25 1C): d 7.22 (s, 4H, –C6H4–), 2.93 (br
s, 4H, –NH), 1.13 (s, 36H, –C(CH3)3). 11B NMR (C6D6,
25 1C): d 30.0. 13C NMR (C6D6, 25 1C): d ipso carbon not
observed, 132.0 (–C6H4–), 49.3 (–C(CH3)3), 33.6 (–C(CH3)3).
3
–CH(CH3)2, JH–H = 5.96 Hz). 11B NMR (THF-d8, 25 1C):
d 24.9. 13C NMR (THF-d8, 25 1C): 145.7 (aryl), 138.8 (aryl),
134.4 (aryl), 127.3 (aryl), 126.1 (aryl), 123.1 (aryl), 122.7 (aryl),
114.3 (aryl), 68.4 (–OCH2CH2), 28.9 (–C(CH3)2), 28.0
(–C(CH3)2), 26.5 (–OCH2CH2), 24.9 (–C(CH3)2), 24.3
(–C(CH3)2).
[K2][PhB(NDipp)2], 7. A solution of [K][CH2Ph] (0.385 g,
2.96 mmol) in THF (10 mL) was added to a solution of
PhB[N(H)Dipp]2 (0.650 g, 1.48 mmol) in THF (10 mL) at
room temperature. After 20 min volatiles were removed
in vacuo and the resulting product was treated with 10 mL of
hexanes. Removal of volatiles in vacuo gave 7 as a yellow solid
(0.705 g, 1.36 mmol, 93%). Anal. Calcd. for C30H39BN2K2: C,
69.74; H, 7.61; N, 5.42%. Found: C, 68.19; H, 7.63; N, 5.22%.
1H NMR (THF-d8, 25 1C): d 7.52 (d, 2H, ortho-aryl protons of
Ph group), 6.89 (m, 2H, meta-aryl protons of the Ph group),
6.77 (t, 1H, para-aryl proton of Ph group), 6.64 (d, 4H,
meta-protons of Dipp groups), 6.01 (t, 2H, para-protons of
[{Li(THF)}4(l-THF)2][1,4-(NtBu)2BC6H4B(NtBu)2], 4ꢀ6THF.
n
A 2.5 M solution of BuLi in hexanes (2.23 mL, 5.60 mmol)
was added to a solution of 3 (0.54 g, 1.40 mmol) in hexanes
(10 mL) at 0 1C. The reaction was warmed to room tempera-
ture, stirred for 18 h and volatiles were removed in vacuo
giving a colourless solid. Purification by recrystallization from
THF gave 4ꢀ6THF (0.409 g, 0.485 mmol, 35%). X-Ray quality
crystals were grown from a solution of 4 in a THF/Et2O
solution. Accurate CHN analysis could not be obtained owing
to the highly air-sensitive nature of 4. 1H NMR (THF-d8,
25 1C): d 6.98 (s, 4H, –C6H4–), 3.61 (–OCH2CH2), 1.77
(–OCH2CH2), 0.93 (s, 36H, –C(CH3)3). 11B NMR (THF-d8,
3
Dipp groups), 4.04 (sept., 4H, –CH(CH3)2, JH–H = 6.17 Hz),
7
25 1C): d 33.6. Li NMR (THF-d8, 25 1C): d 1.22. 13C NMR
3.62 (m, –OCH2CH2), 1.78 (m, –OCH2CH2), 1.08 (d, 12H,
3
–CH(CH3)2, JH–H = 6.17 Hz), 0.92 (d, 12H, –CH(CH3)2,
(C6D6, 25 1C): d ipso carbon not observed, 132.3 (–C6H4–),
68.4 (–OCH2CH2), 51.4 (–C(CH3)3), 38.8 (–C(CH3)3), 26.5
(–OCH2CH2).
3JH–H = 6.17 Hz). 11B NMR (THF-d8, 25 1C): d 24.2. 13C
NMR (THF-d8, 25 1C): 162.9 (aryl), 139.2 (aryl), 135.1 (aryl),
126.8 (aryl), 124.0 (aryl), 122.3 (aryl), 109.3 (aryl), 68.4
(–OCH2CH2), 27.8 (–C(CH3)2), 26.8 (–OCH2CH2), 25.2
(–C(CH3)2), 24.8 (–C(CH3)2).
[Li][PhB(NDipp){N(H)Dipp}], 5. A 2.5 M solution of nBuLi
in hexanes (2.5 mL, 2.5 mmol) was added to a solution of
PhB[N(H)Dipp]2 (1.01 g, 2.5 mmol) in hexanes (15 mL) at ca.
ꢁ30 1C. The reaction mixture was warmed to room tempera-
ture over ca. 20 min and stirred for an additional 1.5 h.
Removal of volatiles in vacuo gave 5 as a colourless solid
(0.991 g, 2.07 mmol, 89%). Anal. Calcd. for C30H40BN2Li: C,
80.72; H, 9.03; N, 6.28%. Found: C, 79.36; H, 8.98; N, 6.18%.
1H NMR (THF-d8, 25 1C): d 7.30 (m, 2H, aryl protons),
7.0–6.96 (m, 5H, aryl protons), 6.8–6.74 (m, 3H, aryl proton),
Results and discussion
Synthesis, spectroscopic characterization and X-ray structures
t
of FcB[N(H)R]2 (1a, R = Bu, 1b, R = Dipp) and
1,10-Fc{B[N(H)tBu]2}2 (2)
Ferrocene (Cp2Fe) was the first linker group considered for the
preparation of bis-bams because of the ready availability of
ferrocenyl bis(dibromoborane) 1,10-Fc(BBr2)2.14 In order to
provide a benchmark for the evaluation of the influence of the
Fc group compared to the Ph on redox behaviour of the
dianions [ArB(NtBu)2]2ꢁ (Ar = Ph,6 Fc), the initial targets
6.58 (t, 1H, aryl proton), 3.91 (sept., 2H, –CH(CH3)2, 3JH–H
=
6.87 Hz), 3.58 (–NH, under residual solvent peak of THF),
3
3.41 (sept., 2H, –CH(CH3)2, JH–H = 6.72 Hz), 1.29 (d, 6H,
3
–CH(CH3)2, JH–H = 6.87 Hz), 1.13 (d, 6H, –CH(CH3)2,
3
3JH–H = 6.87 Hz), 0.81 (d, 12H, –CH(CH3)2, JH–H
=
t
were the ferrocenyl bams [FcB(NR)2]2ꢁ (R = Bu, Dipp).
6.72 Hz). 7Li NMR (THF-d8, 25 1C): d 0.23. 11B NMR
(THF-d8, 25 1C): d 26.4. 13C NMR (THF-d8, 25 1C): 156.6
(aryl), 144.0 (aryl), 143.0 (aryl), 141.5 (aryl), 134.2 (aryl),
127.9 (aryl), 126.9 (aryl), 123.1 (aryl), 123.0 (aryl), 122.9 (aryl),
117.7 (aryl), 28.8 (–C(CH3)2), 28.3 (–C(CH3)2), 25.3 (–C(CH3)2),
25.0 (–C(CH3)2), 24.3 (–C(CH3)2).
Substitution of the halogen atoms in ferrocenyl dihaloboranes
for dialkylamino groups has previously been accomplished by
the reaction of 1,10-Fc(BBr2)2 with different amounts of
secondary amine.13b More recently, it was demonstrated that
FcBBr2 reacts with two equivalents of lithium anilide to afford
FcB[N(H)Ph]2;19 the mono-substituted tert-butyl derivative,
FcBBr[N(H)tBu], was also prepared. However, no structural
characterisation for either compound was reported. In the
current study the new ferrocenyl aminoboranes FcB[N(H)R]2
[K][PhB{N(H)Dipp}(NDipp)], 6. A solution of [K][CH2Ph]
(0.166 g, 1.27 mmol) in THF (10 mL) was added to a solution
of PhB[N(H)Dipp]2 (0.562 g, 1.27 mmol) in THF (10 mL) at
room temperature. After 10 min, volatiles were removed
in vacuo and the resulting product was treated with 10 mL
of hexanes. Removal of volatiles in vacuo gave 6 as a cream-
coloured solid (0.578 g, 1.05 mmol, 82%, based on 6ꢀTHF). 1H
NMR (THF-d8, 25 1C): d 7.34 (m, 2H, aryl protons of Ph
group), 6.95–6.78 (m, 8H, aryl protons), 6.32 (t, 1H, aryl
proton), 3.79 (overlapping sept., 4H, –CH(CH3)2), 3.62
(m, –OCH2CH2), –NH is observed at 3.62 ppm when the
reaction is carried out in THF-d8, 1.78 (m, –OCH2CH2), 1.10
t
(1a, R = Bu; 1b, R = Dipp) were synthesized in 65–75%
yields by the reaction of FcBBr2 with two equivalents of
[Li][N(H)R] (R = tBu, Dipp) in toluene (Scheme 1a). A
similar protocol was used to prepare 1,10-ferrocenyl bis-
[di-(tert-butylamino)borane], 2, in 54% yields from 1,10-
Fc(BBr2)2 and four equivalents of [Li][N(H)tBu] (Scheme 1b).
1
The identities of 1a, 1b and 2 were established by H, 13C
and 11B NMR data together with C,H,N analyses or, in the
case of 1a, high resolution mass spectra. The 1H NMR spectra
ꢃc
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Scheme 1
of the tert-butylamino derivatives 1a and 2 show resonances for
C5H5, C5H4, NH and C(CH3)3 protons with appropriate relative
intensities, while the derivative 1b showed the expected resonances
for the C6H3 and CH(CH3)2 protons of the Dipp groups, in
addition to those for C5H5, C5H4, and NH. The 11B NMR
chemical shifts of 1a, 1b and 2 are in the narrow range 29–30 ppm.
X-Ray quality orange crystals of 1a, 1b, and 2 were grown
from toluene or hexanes/toluene solutions. The molecular
structures are depicted in Fig. 1 and 2; selected bond lengths
and angles are compared in Table 3.
Fig. 2 Molecular structure of 1,10-Fc{B[N(H)tBu]2}2 (2) with hydrogen
atoms omitted for clarity, other than those located on the nitrogen
atoms. Thermal ellipsoids are shown at 30% probability.
Table 3 Selected bond lengths (A) and bond angles (1) for 1a, 1b
and 2
The unit cell of 1a contains two independent molecules, as
was found for FcBBr2.20 For both 1a and 1b, planar geometry
is observed at boron; the bond angles at boron are close to
trigonal for 1b (ca. 119–1221), but significantly distorted
(ca. 114–1231) in 1a. The B–N bond lengths in both 1a and
1b are intermediate between a single and double bond as
expected for N(2p) - B(2p) p-bonding. Crystallographic
analysis of 1,10-Fc(BBr2)2 has revealed that Lewis acidic
ferrocenyl boranes have weak iron–boron interactions resulting
in the tilting of the B–C bond towards the metal centre, as
indicated by a B–C1–C2–C3 dihedral angle of ca. 101.21 The
amino substituents in 1a and 1b significantly decrease the
Lewis acidity of the boron centre, reducing this angle to
ca. 41 in 1a and even further in 1b where the boron moiety
lies in the plane of the Cp ring. The structural parameters of
the 1,10-diborylated ferrocene 2 are very similar to the analogous
mono-borylated derivative 1a, with no notable differences in
B–N bond lengths or angles.
1a
1b
2
B1–N1
B1–N2
1.421(6)
1.414(7)
1.437(6)
1.394(7)
122.5(4)
114.8(4)
122.6(4)
123.2(4)
114.0(4)
122.7(4)
1.418(4)
1.419(3)
N/A
1.415(3)
1.413(3)
1.414(3)
1.414(3)
122.0(2)
116.8(2)
121.3(2)
122.2(2)
116.5(2)
121.3(2)
B2–N3a
B2–N4a
N/A
N1–B1–N2
N1–B1–C1
N2–B1–C1
N3–B2–N4a
N3–B2–C19a
N4–B2–C19a
118.8(2)
119.1(2)
122.1(2)
N/A
N/A
N/A
a
These values correspond to the second molecule in the asymmetric
unit of 1a.
The attempted dilithiation of 1a with two equivalents
of nBuLi, which readily deprotonates PhB[N(H)tBu]2,22 in
hexanes, toluene or THF was unsuccessful. No reaction was
Fig. 1 Molecular structures of FcB[N(H)tBu]2 (1a, left) and FcB[N(H)Dipp]2 (1b, right). For clarity, only H atoms attached to N and a-carbons
of Dipp groups are shown. Thermal ellipsoids are shown at 30% probability.
ꢃc
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observed even after extended reaction times at elevated
temperatures, suggesting that replacement of the Ph substituent
by the electron-rich metallocene decreases the acidity of the
intermediate between a single and double bond, as expected.
The arrangement of solvent THF molecules in 4ꢀ6THF
(i.e. one terminal and one bridging THF per Li+ ion) has
been observed previously in the mono-bam complex
[Li(THF)2(m-THF)][PhB(NDipp)2].17 Although the average
n
–NH protons to such an extent that BuLi is insufficient as a
metallating reagent. Subsequently, 1a was treated with the
t
stronger base BuLi. With this reagent, however, competition
22
N–Li distance in both unsolvated {Li2[PhB(NtBu)2]}2 and
between metallation of the –NHtBu groups and the Cp ring
highly solvated [Li(THF)2(m-THF)][PhB(NDipp)2]17 are nearly
identical, the average length of this bond in the bis-bam
4ꢀ6THF is approximately 0.05 A shorter than in either of the
mono-bams.
1
was indicated by multiple products in the H NMR spectra.23
The deprotonation of 1b with [Li][N(SiMe3)2] was also attempted
as this reagent does not react with ferrocene;24 however, no
reaction was observed. Given the difficulties encountered in
the attempted deprotonation of 1a and 1b, we turned our
attention to the use of the phenylene (–C6H4–) group as a
linker for bis-bam ligands of the type C.
The new bis-bam reagent 4ꢀ6THF is extremely air-sensitive
and rapidly turns pink in solution or in the solid state
upon exposure to air, indicative of oxidation to a radical
species even in the presence of only trace amounts of oxygen
(i.e. B8 ppm). This observation is reminiscent of the beha-
viour of {Li2[PhB(NtBu)2]}2.6b In that case, the pink colour
was attributed to the Li+ derivative of the anion radical
Synthesis, X-ray structure and reactions of
[Li4][(NtBu)2C6H4B(NtBu)2]ꢀ6THF (4ꢀ6THF)
ꢁ
[PhB(NtBu)2]ꢂ formed upon one-electron oxidation of the
The reaction of 1,4-Br2BC6H4BBr2, and five equivalents of
[Li][N(H)tBu] in toluene, produces an oil that solidifies over-
night at room temperature to give 3 in 75% yield (Scheme 2).
If only four equivalents of amide are used, the product 3 is
contaminated with minor impurities. The necessity of using an
excess of amide has previously been noted in the synthesis of
dilithio bams;17,22 any unreacted amide is removed by filtra-
tion. Multinuclear NMR spectra and high-resolution mass
spectrometric data were consistent with complete replacement
of all four Br substituents in 1,4-Br2BC6H4BBr2 by –N(H)tBu
corresponding dianion. This persistent radical is also formed
upon treatment of {Li2[PhB(NtBu)2]}2 with one-half equivalent
of I2 and it was identified on the basis of a simulation of the
Scheme 3
1
groups. The H NMR spectrum of 3 exhibits singlets at 7.66,
2.88 and 1.16 ppm with relative intensities of 4 : 4 : 36
corresponding to C6H4, NH and C(CH3)3 protons, respec-
tively. A single resonance is observed in the 11B NMR
spectrum at 30 ppm.
Tetra-lithiation of 3 using four equivalents of nBuLi in
hexanes results in a colourless precipitate of 4, the first
example of a tetra-lithio bis-boraamidinate (Scheme 2). The
molecular structure of 4 is illustrated in Fig. 3 and pertinent
bond lengths and angles are found in Table 4, along with those
of {Li2[PhB(NtBu)2]}2 for comparison.
As depicted in Fig. 3, the –C6H4– unit of 4ꢀ6THF lies on an
inversion centre. The structural parameters involving the
boron centres for 4ꢀ6THF are similar to those of the unsolvated
complex {Li2[PhB(NtBu)2]}2.22 The geometry about boron is
planar, but greatly distorted from trigonal, with bond angles
in the range 109.8–125.51. The B–N bond lengths are
Fig. 3 Molecular structure of [Li4][(NtBu)2C6H4B(NtBu)2]ꢀ6THF, 4ꢀ
6THF. Hydrogen atoms omitted for clarity. Symmetry transforma-
tions used to generate equivalent atoms: ꢁx + 1, ꢁy + 1, ꢁz.
Thermal ellipsoids are shown at 30% probability.
Scheme 2
ꢃc
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Table 4 Selected bond lengths (A) and bond angles (1) for 4ꢀ6THF
and {Li2[PhB(NtBu)2]}2
{Li2[PhB(NtBu)2]}2
a
4
B1–N1
B1–N2
Li1–N1
Li1–N2
Li2–N1
Li2–N2
N1–B1–N2
N1–B1–C1
N2–B1–C1
1.437(3)
1.442(3)
1.970(4)
1.992(4)
2.013(4)
1.989(4)
109.8(2)
125.5(2)
124.8(2)
1.448(3)
1.449(3)
2.077(4)
2.052(4)
2.027(4)
2.022(4)
109.5(2)
124.9(2)
125.5(1)
a
Data taken from ref. 22.
EPR spectrum.6b The controlled oxidation of 4ꢀ6THF with
one-half equivalent of I2 at ꢁ80 1C in THF also generates a
pink solution. However, this solution exhibits a very complex
EPR spectrum and attempts to simulate it assuming the
formation of the expected one-electron oxidation product
suggested the presence of more than one radical species, whose
identities could not be established. The complexity of the
redox behaviour of 4ꢀ6THF presumably results from the
presence of more than one redox-active site.
Fig. 4 Molecular structure of [Li(THF)2][PhB(NDipp){N(H)Dipp}],
5ꢀ2THF. For clarity, hydrogen atoms on carbon atoms have been
omitted and only a-carbons of Dipp groups shown. Thermal ellipsoids
are shown at 30% probability.
Table 5 Selected bond lengths (A) and bond angles (1) for 5ꢀ2THF,
DippbamH2 and [Li2(THF)3][Dippbam]
Synthesis and spectroscopic characterization of
[M][PhB(NDipp){N(H)Dipp}] (5, M = Li; 6, M = K) and
X-ray structure of 5ꢀ2THF
[Li2(THF)3]-
[
Dippbam]a
a
5ꢀ2THF
DippbamH2
B1–N1
B1–N2
N1–Li1
N2–Li2
1.396(4)
1.448(4)
1.908(5)
N/A
121.1(2)
119.1(2)
119.7(2)
120.0(2)
120.0(2)
119.1(2)
130.2(2)
N/A
1.420(3)
1.414(3)
N/A
1.415(5)
1.446(4)
2.022(6)
2.049(7)
111.4(3)
125.2(3)
122.9(3)
130.4(3)
83.7(3)
135.5(3)
126.4(3)
124.4(3)
79.2(2)
In view of the isoelectronic relationship and similar charges of
monoanionic boraamidinates of the type [bam(H)]ꢁ (D) and
the corresponding amidinates (B), we have developed efficient
syntheses of alkali-metal derivatives of this new class of ligand.
The equimolar reaction of PhB[N(H)Dipp]2 with nBuLi in
hexanes proceeds cleanly to give [Li][PhB(NDipp){N(H)Dipp}]
(5), in ca. 90% yield. The 1H NMR spectrum of 5 is consistent
with a mono-lithiated derivative. In addition to aryl resonances
that integrate to the expected values, there are two septets
integrating to 2H each (attributed to CH(CH3)2 protons), a
broad singlet assigned to the remaining –NH group and three
methyl resonances with relative intensities of 6 : 6 : 12
N/A
N1–B1–N2
N1–B1–C1
N2–B1–C1
B1–N1–C7
B1–N1–Li1
C7–N1–Li1
C19–N2–B1
C19–N2–Li1
B1–N2–Li2
N1–Li1–O1
N1–Li1–O2
O1–Li1–O2
118.5(2)
118.7(2)
122.8(2)
124.6(2)
N/A
N/A
128.0(2)
N/A
N/A
N/A
N/A
N/A
121.1(3)
131.3(3)
104.3(3)
163.0(4)
87.6(2)
98.6(3)
N/A
a
7
(CH(CH3)2 protons). The 11B and Li NMR spectra exhibit
Data taken from ref. 17.
single resonances at 26.4 and 0.23 ppm, respectively. X-Ray
quality crystals of 5ꢀ2THF were obtained from a concentrated
THF/hexane solution cooled to ca. ꢁ18 1C and the molecular
structure is illustrated in Fig. 4. Selected bond lengths and
angles are compared with those of PhB[N(H)Dipp]2
structural differences between 5ꢀ2THF and [Li2(THF)3][Dippbam]17
are the coordination numbers of the anionic nitrogen and the
lithium centres, which are both three-coordinate in the former
but four-coordinate in the latter. The nitrogen atoms interact
with both lithium centres in [Li2(THF)3][Dippbam], while the
coordination sphere of the lithium cations is completed by
two THF molecules (one terminal and one bridging THF)
in 5ꢀ2THF.
(
DippbamH2) and [Li2(THF)3][PhB(NDipp)2] in Table 5.
The molecular structure of 5ꢀ2THF is comprised of the
monoanionic [DippbamH]ꢁ ligand bonded in an N-monodentate
fashion to the lithium cation, which is solvated by two THF
molecules. Monodentate structures of lithium amidinates are
known, however they contain even bulkier groups on nitrogen,
such as substituted terphenyls.25,26 Two notable examples for
direct comparison with 5ꢀ2THF are lithium formamidinate
The geometry about B1 in 5ꢀ2THF is trigonal planar
(bond angles are ca. 119–1211), cf. 118.5–1231 for DippbamH2,
and ca. 111–1251 in [Li2(THF)3][Dippbam].17 The geometry
about N1 is also planar. The B1–N1 distance is shorter than
B1–N2 by ca. 0.05 A. There is a slight elongation of the B–N
bond distance of the protonated nitrogen atom in 5ꢀ2THF
when compared to that in DippbamH2. There is no significant
difference between the B–N bond lengths in 5ꢀ2THF and
[Li2(THF)3][Dippbam], however, the N1–Li bond length is
[Li(THF)2][HC(NDipp)2]27
and
lithium
amidinate
[Li(THF)2][p-TolC(NDipp)2]28 (Tol = –C6H4Me), in which
the lithium ion interacts with both nitrogen atoms. In the
formamidinate, however, monodentate structures were
obtained when the THF molecules coordinated to the lithium
cation were replaced with TMEDA.29 The most notable
ꢃc
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ca. 0.13 A shorter in the monolithiated [DippbamH]ꢁ than the
average value in the dilithiated [Dippbam]2ꢁ
.
The mono-potassiated derivative, [K][PhB(NDipp){N(H)Dipp}]
(6), was prepared in 82% yield from the 1 : 1 reaction of
DippbamH2 and benzylpotassium in THF. The deep red colour
of [K][CH2Ph] is immediately consumed upon addition to
DippbamH2, yielding a golden solution; potassium hexamethyl-
disilazide (KHMDS) can also be used as the deprotonating
reagent. Numerous attempts to obtain X-ray quality crystals
from the resulting pale yellow solid failed and, instead, only
an amorphous powder precipitated from solution. However,
1H NMR data are consistent with the formation of the mono-
potassiated derivative; aryl resonances integrating to 11H, over-
lapping septets integrating to 4H, a 1H singlet for the remaining
–NH proton and two doublets (6 : 18 relative intensities) for the
methyl protons of the isopropyl groups are observed. The
11B NMR spectrum displays a single resonance at 24.9 ppm,
which is shifted upfield from DippbamH2 (11B d 29 ppm).17
Synthesis, spectroscopic characterization and X-ray structure of
[K2(THF)3][PhB(NDipp)2], 7ꢀ3THF
Fig. 5 Crystal structure of a discrete [K2(THF)3][PhB(NDipp)2] unit
(7ꢀ3THF). For clarity, all hydrogen atoms and carbon atoms of THF
solvent molecules have been omitted and only a-carbon atoms on
Dipp groups are shown. Thermal ellipsoids are shown at 30% proba-
bility. Symmetry elements used to generate equivalent atoms:
The metathetical chemistry of bam ligands has primarily been
based on dilithiated reagents.1 However, lithium halides are
difficult to separate from the main products of these reactions
and, in some cases, they become incorporated in the products.5,9
These difficulties provided the incentive for the synthesis of the
first dipotassiated derivative of a bam ligand.
1
1
1
1
ꢁx, y + , ꢁz + ; ꢁx, y ꢁ , ꢁz + .
2
2
2
2
The reagents KH, [K][HMDS] and [K][CH2Ph] were evaluated
as a base for the deprotonation of DippbamH2. Potassium
hydride was unreactive, while [K][HMDS] gave only the mono-
potassiated derivative, 6. However, benzylpotassium proved to
be effective, producing [K2][PhB(NDipp)2] (7) in ca. 90% yield
as a yellow solid, which is soluble in THF and to a lesser extent
in toluene, but insoluble in hexanes and Et2O (Scheme 3). The
1H NMR spectrum of this solid is consistent with double
deprotonation and only one resonance is observed in the
11B NMR spectrum at 24.2 ppm. X-Ray quality crystals of
7ꢀ3THF were obtained by cooling a concentrated solution of 7
in a mixture of THF and either hexanes or toluene. The
molecular structure of 7ꢀ3THF is shown in Fig. 5, the extended
structure is illustrated in Fig. 6, and selected structural para-
meters are presented in Table 6.
Fig.
6 Representation of the extended solid-state structure of
[K2(THF)3][PhB(NDipp)2] (7ꢀ3THF). For clarity all hydrogen atoms
and selected carbon atoms have been omitted. Thermal ellipsoids are
shown at 30% probability.
Although three molecules of THF are incorporated into the
structure of 7 during crystallization, the 1H NMR spectrum of
the crude product suggests that the potassium cations are not
solvated; however, attempts to crystallize 7 in the absence
of THF were unsuccessful. A similar observation has been
made in the preparation of [K][N(H)Trip] (Trip = 2,6-
(2,4,6-iPr3C6H2)2C6H3), for which no solvation of the potassium
cation was observed in the crude material (by 1H NMR
and elemental analysis) although the reaction was carried
out in THF.30
Table 6 Selected bond lengths (A) and bond angles (1) for 7ꢀ3THF
B1–N1
B1–N2
N1–K1
N2–K2
K1–centroid
K2–centroid
K1–O1
K2–O2
K2–O3
1.407(5)
1.422(5)
2.673(3)
2.709(3)
2.905(3)
2.834 (3)
2.773(4)
2.704(4)
2.655(4)
N1–B1–N2
N1–B1–C1
N2–B1–C1
C7–N1–B1
C7–N1–K1
B1–N1–K1
C19–N2–B1
C19–N2–K2
B1–N2–K2
124.7(4)
116.3(3)
119.0(4)
121.6(3)
118.8(2)
115.4(3)
134.2(3)
101.1(2)
119.8(2)
In the solid state, 7ꢀ3THF forms an extended structure
resulting from arene–metal interactions. The potassium cation
is coordinated in an Z1-amide–Z6-arene fashion, similar to the
bonding mode observed for potassium formamidinates
[K][HC(NMes2){HC(NMes2)H}]31 and {K[HC(NDipp)2]2-
K(THF)2}n32 (Mes = 2,4,6-Me3C6H2) as well as for the potassium
amidinate [K][PhC(NSiMe3)(NDipp)].33 The potassium–
nitrogen bond distances are comparable to that found in
ꢃc
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[K][HC(NMes2)] (2.719(1) A).31 The K(1)–centroid and K(2)–
centroid contacts of 2.905(3) and 2.834(3) A, respectively, are
similar to the values reported for [K][HC(NMes2){HC(NMes2)H}]
and [K][PhC(NSiMe3)(NDipp)].31 The potassium ions K(1)+ and
K(2)+ are solvated by one or two THF molecules, respectively.
The distorted trigonal planar geometry about boron is
similar to that of the boron atom in [Li2(THF)3][PhB(NDipp)2].17
However, since the nitrogen atoms only interact with a single
potassium cation, their geometry differs significantly from that
of the dilithiated analogue, in which the nitrogen atoms are a
part of two puckered four-membered rings with the boron
centre and a lithium atom.17 Both nitrogen atoms in 7ꢀ3THF
have bond angles that deviate substantially from trigonal
geometry, ca. 115–1211 for N1 and 101–1341 for N2.
87, 461; (c) J. Konu, M. S. Balakrishna, T. Chivers and
T. W. Swaddle, Inorg. Chem., 2007, 46, 2627.
4 D. R. Manke and D. G. Nocera, Inorg. Chem., 2003, 42,
4431.
5 T. Chivers, C. Fedorchuk, G. Schatte and M. Parvez, Inorg.
Chem., 2003, 42, 2084.
6 (a) T. Chivers, D. J. Eisler, C. Fedorchuk, G. Schatte,
H. M. Tuononen and R. T. Boere
(b) T. Chivers, D. J. Eisler, C. Fedorchuk, G. Schatte,
H. M. Tuononen and R. T. Boere, Inorg. Chem., 2006, 45, 2119.
´
, Chem. Commun., 2005, 3930;
´
7 A. M. Corrente and T. Chivers, Inorg. Chem., 2008, 47, 10073.
8 For a recent review of bulky guanidinates, see: C. Jones, Coord.
Chem. Rev., 2009, 254, 1273.
9 A. M. Corrente and T. Chivers, Inorg. Chem., 2010, 49, 2457.
10 (a) S. Harder, Dalton Trans., 2010, DOI: 10.1029/c001966f;
(b) S. Harder and D. Naglav, Eur. J. Inorg. Chem., 2010, 2010, 2836.
11 For reviews, see: (a) F. Breher, Coord. Chem. Rev., 2007, 251, 1007;
(b) T. Chivers and J. Konu, Comments Inorg. Chem., 2009, 30, 131.
12 The incorporation of lithium halides in the final products of
metathetical reaction of lithium bams with element halides occurs
in the formation of Group 13 and lanthanide complexes.5,9
.
Conclusions
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H. W. Lerner, M. C. Holthausen and M. Wagner, Z. Anorg. Allg.
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16 P. L. Bailey, R. A. Coxall, C. M. Dick, S. Fabre, L. C. Henderson,
C. Herber, S. T. Liddle, D. Lorono-Gonzalez, A. Parkin and
S. Parsons, Chem.–Eur. J., 2003, 9, 4820.
We have described the syntheses and structures of several new
reagents that will be useful in the future development of the
chemistry of bams. These include the bis-[di-(tert-butylamino)-
boranes] 1,10-Fc{B[N(H)tBu]2}2 and [N(H)tBu]2BC6H4B[N(H)tBu]2
as well as the extremely air-sensitive tetralithio derivative of
the latter. Efficient syntheses of alkali-metal derivatives of the
monoanion [PhB(NDipp){N(H)Dipp}]ꢁ and the first dipotassium
salt of a bam [K2][PhB(NDipp)2] are also reported. In the
[Li(THF)2]+ derivative the DippbamHꢁ ligand forms an
N-monodentate complex with the cation, while the Dippbam2ꢁ
dianion in the dipotassium salt forms an extended structure via
Z1-amide–Z6-arene coordination to the cations. Main group,
transition-metal and lanthanide complexes of the monoanionic
bam ligand will be of especial interest in comparison with the
well-studied chemistry of isoelectronic amidinate analogues.
The dipotassium reagent will be advantageous compared to
dilithium derivatives in metathetical reactions with element
halides.
17 T. Chivers, C. Fedorchuk and M. Parvez, Inorg. Chem., 2004, 43, 2643.
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22 T. Chivers, C. Fedorchuk, G. Schatte and J. K. Brask, Can. J.
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Acknowledgements
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We thank Prof. S. Harder for providing details of ref. 10 prior
to publication. Financial support from the Natural Sciences
and Engineering Research Council (Canada) and Alberta
Ingenuity (A. M. C.) is gratefully acknowledged.
27 M. L. Cole, A. J. Davies, C. Jones and P. C. Junk, J. Organomet.
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References
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ꢃc
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