Synthesis and molecular structure of tris[(trimethylsilyl)silyl] (diisopropylamino)(diphenylphosphino)borane [1]

Article abstract of DOI:10.1002/zaac.200600210

The 1:1 reaction of [(Me₃Si)₃SiLi·3THF] with (iPr₂N)BCl₂ in hexane provides [{Me₃Si) ₃Si} · (iPr₂N)BCl] (2) in good yield as a colorless crystalline solid. This compound combined

Full text of DOI:10.1002/zaac.200600210

DOI: 10.1002/zaac.200600210
Synthesis and Molecular Structure of
Tris[(trimethylsilyl)silyl](diisopropylamino)(diphenylphosphino)borane [1]
Maomin Fana, Robert T. Painea,*, E. N. Dueslera, and Heinrich Nöthb,*
a Albuquerque, NM /USA, University of New Mexico, Department of Chemistry
b Munich/Germany, University of Munich, Department of Chemistry
Received July 10th, 2006.
Abstract. The 1:1 reaction of [(Me3Si)3SiLi·3THF] with
(iPr2N)BCl2 in hexane provides [{(Me3Si)3Si}·(iPr2N)BCl] (2) in
and 11B NMR spectroscopy and the molecular structure of 3 was
determined by X-ray structure analysis.
good yield as
combined in
a
a
colorless crystalline solid. This compound
1:1 ratio with LiPPh2 in DME gives
[{(Me3Si)3Si}·(iPr2N)B(PPh2)] (3) as a yellow crystalline solid. The
Keywords: Phosphinoboranes; Aminoboranes; Silyl boranes; NMR
spectra; Crystal structures
new compounds were characterized by IR, MS and 1H, 13C{1H}
Introduction
report here the synthesis and molecular structure determi-
nation for the molecule [{(Me3Si)3Si}B-(NiPr2)(PPh2)](3),
that is sufficiently congested that the phosphane lone pair
becomes inactive toward simple metal carbonyl fragments.
Aminophosphino boranes display interesting reactivity and
coordination chemistry properties and much of the work
with these reagents has been summarized in a review
[2].Since 1995, additional advances, mostly directed to the
development of new low coordination number conditions,
unusual ring and cage structures and new polymeric materi-
als, have continued to appear in the literature [3Ϫ34]. In
some of our studies, we have sought to construct sterically
crowded N-B-P environments that might be introduced into
more complex molecules. As part of that work, we have
explored syntheses of tri-coordinate borane fragments with
connectivities N-B(Si)-X. Pertinent to this, we described in
1981 the synthesis of several tris(trimethylsilyl)silyl boranes
Reactions
The 1:1 combination of [(Me3Si)3SiLi·3THF] [39, 40] with
(iPr2N)BCl2 [41] in hexane rapidly eliminates LiCl with
formation of [{(Me3Si)3Si}B(Cl)(NiPr2)] (2) that is isolated
in 94 % yield, following recrystallization, as an analytically
pure, colorless, crystalline solid. The compound displays
a single 11B NMR resonance at δ ϭ 43.0, and this
shift is similar to that reported previously for
[{Me3Si)3Si}B(Cl)(tmp)], δ ϭ 48.5 [38]. As is typically
found with other aminoboranes, the shift for the (tmpB)
fragment is slightly deshielded compared to the (iPr2NB)
and
borates
including
the
amino
derivatives
[{(Me3Si)3Si}B(NMe2)2] and [{(Me3Si}3Si]2B(NMe2)] [35].
Subsequently, Haase and Klingebiel reported the formation
of [{(Me3Si}3Si]B(F){N(SiMe3)2}] (1a) that undergoes ther-
mally promoted 1,2-Me3SiF elimination with formation of
the imino borane [{(Me3Si)3Si}BϵN(SiMe3)] [36]. The syn-
thesis and characterization of additional examples of 1,
[{(Me3Si)3M}B(F){N(R)(SiMe)3}], MϭC, Si; RϭMe, Et,
iPr, SiMe3, CMe3, and a molecular structure determination
for the imino borane (Me3C)BϵN(SiMe3) also have been
described [37]. More recently, Marschner and coworkers [38]
published the synthesis of [{(Me3Si)3Si}B(Cl)(tmp)] (tmpϭ
2,2,6,6-tetramethylpiperidinyl). For our synthesis appli-
cations, we are also interested in the B-B(Si)-P unit and we
1
fragment [2, 42]. The H and 13C NMR spectra show that
the silyl methyl groups are equivalent; however, the isopro-
pyl methyl and methine groups each display two inequiva-
lent environments consistent with hindered rotation about
the B-N bonds.
Compound 2 combined in a 1:1 ratio with Ph2PLi in
DME provides [{(Me3Si)3Si} B(NiPr2)(PPh2)] (3) as an ana-
lytically pure yellow crystalline solid in 80 % yield following
standard workup and recrystallization. It is worth noting
that attempts to obtain 3 using hexane as the reaction sol-
vent were unsuccessful. The FAB-MS analysis of 3 reveals
a parent ion along with expected fragment ions. The 11B
NMR spectrum contains a single broad resonance at δ ϭ
55 that is typical of three coordinate aminophosphino bor-
anes [2]. The 31P NMR spectrum also displays a single res-
onance at δ ϭ Ϫ31.7, and this shift can be compared
against the shift for [(Et2N)B(PPh2)2], δ ϭ Ϫ37.1 [43]. As
* Prof. Dr. Dr.h.c. H. Nöth
Department Chemie der Universität
Butenandtstr. 3Ϫ5
D-81377 München
E-mail: h.nöth@lrz.uni-muenchen.de
1
found for 2, the H and 13C NMR spectra show a single
Z. Anorg. Allg. Chem. 2006, 632, 2443Ϫ2446
 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
2443

M. Fan, R. T. Paine, E. N. Duesler, H. Nöth
carbonyl reagents including Cr(CO)6, [Cr(CO)5·THF],
[Cr(CO)5·NMe3],
Mo(CO)6,
[Mo(CO)4(CH3CN)2],
[Mo(CO)4(NBD)], W(CO)6, [W(CO)5·THF], Fe(CO)5,
Fe2(CO)9 and Ni(CO)4. None of these combinations led to
the isolation of a complex. It appears, therefore, that 3 is a
poor donor toward these metal carbonyl acceptor frag-
ments and this is likely a result of steric crowding at the
phosphorus atom.
Experimental Section
Standard inert-atmosphere techniques were used for the manipu-
lation of reagents. Infrared spectra were recorded on a Mattson
2020 FT-IR spectrometer from KBr pellets. Mass spectra were ob-
tained from the Midwest Center for Mass Spectrometry. NMR
spectra were recorded on Bruker WP-250 and JEOL GSX-400
spectrometers from samples vacuum sealed in NMR tubes contain-
ing appropriate lock solvents. Spectra were referenced with Me4Si
(1H, 13C), 85 % H3PO4 (31P) and F3BႧOEt2 (11B) and downfield
shifts relative to the reference were assigned positive δ values.
Figure 1 Plot of the molecular structure of compound 3.Thermal
ellipsoids are presented on a 25 % probability scale.
˚
Selected bond lengths (in A): B-P 1.982(5), B-N 1.391(7), B-Si1 2.063(5),
P-Cl0 1.840(4), P-C16 1.834(4), N-C22 1.495(6), N-C25 1.491(6), Si1-Si2
2.365(2), Si1-Si3 2.378(2), Si1-Si4 2.386(2). Ϫ Selected bond angles (in de-
grees) Ϫ Si1-B-P 104.8(2), Si1-B-N 128.0(3), P-B-N 127.1(3), B-N-C22
121.7(4), B-N-C25 120.5(4), C22-N-C25 117.8(4), C10-P-C16 102.4(2), C10-
P-B 115.1(2), C16-P-B 101.0(2), Si2-Si1-Si3 106.8(1), Si2-Si1-Si4 107.1(1),
Si3-Si1-Si4 104.3(1), Si2-Si1-B 100.2(1), Si3-Si1-B 115.3(1), Si4-Si1-B
121.9(2).
Tris[(trimethylsilyl)silyl](diisopropylamino)(chloro)borane (2). A
solution of [(Me3Si)3SiLi·3THF] (5.0 g, 10.6 mmol) [39, 40] in hex-
ane (30 mL) was added to a stirred solution of iPr2NBCl2 (1.93 g,
10.6 mmol) [41] in hexane (20 mL) held at Ϫ78 °C. The mixture
was stirred (30 min) and then warmed to 23 °C and stirred (1d).
Solid LiCl formed and was removed by filtration. The filtrate was
vacuum evaporated leaving a sticky oil (3.74 g) that was crystallized
from hexane. Yield 3.5 g (84 %) colorless crystals: m.p. 142-144 °C.
methyl group resonance for the (Me3Si)3Si group and in-
equivalent CH3 and CH groups for the NiPr2 fragment.
C15H41NBSi4Cl (394.107):calc. C 45.72, H 10.49, N 3.55; found; C
45.50, H 10.33, N 3.62 %.
Molecular Structure
NMR (C6D6): 1H-NMR: δ ϭ 0.36 (s, 27H, SiCH3), 0.93 (d, J ϭ 6.7 Hz, 6H,
iPrCH3), 1.38 (d, J ϭ 7.1 Hz; 6H, iPrCH3), 3.07 (sept, J ϭ 7.1 Hz, 1H,
iPrCH), 4.04 ppm (sept, J ϭ 6.7 Hz, 1 H, iPrCH). Ϫ 13C{1H}-NMR: δ ϭ
3.08 (SiCH3), 22.04 (iPrCH3), 23.56 (iPrCH3), 47.71 (iPrCH), 56.34 ppm
(iPrCH). Ϫ 11B{1H}-NMR: δ ϭ 43 (h1/2 ϭ 190 Hz). IR /cmϪ1: ν ϭ 2969 (s),
2893 (m), 1472 (m), 1447 (m), 1395 (m), 1368 (m), 1310 (m), 1244 (s), 1184
(m), 1146 (m), 1117 (w), 1005 (m), 835 (vs), 748 (m), 685 (m), 623 (m),
583 (w).
The molecular structure of 3 was determined by X-ray dif-
fraction techniques and a view of the molecule is shown in
Figure 1. The compound contains planar coordinated N
and B atoms and a pyramidal coordinated P atom (sum of
˚
angles 318.5°). The B-N bond length 1.391(7) A is short,
and together with the mutually planar coordination of the
B and N atoms, indicate significant π-overlap between these
atoms. The iPr2N-B bond length compares favorably with
Tris[(trimethylsilyl)silyl](diisopropylamino)(diphenylphosphino)-
borane (3). N-Butyl lithium (Aldrich, 2 mL, 2.5 M in hexane) was
added with stirring to Ph2PH (Aldrich, 0.93 g, 5 mmol) in hexane
(50 mL) at Ϫ78 °C. The mixture was stirred (10 min) and then
warmed to 23 °C (3h). A yellow solid (Ph2PLi) separated and was
recovered by filtration. The solid was rinsed with fresh hexane (2 x
10 mL) and dried in vacuum. A sample of Ph2PLi (0.551 g;
2.87 mmol) was dissolved in DME (15 mL) and added to a solution
of 2 (1.13 g, 2.87 mmol) in DME at 23 °C. This mixture was stirred
(12h) and the volatiles removed in vacuo. The yellow residue was
treated with hexane (40 mL) and insoluble LiCl was removed by
filtration. The filtrate was vacuum evaporated leaving a yellow solid
(1.50 g) that was recrystallized from cold hexane leaving yellow
crystals of 3. Yield 1.24 g (80 %); m.p. 168-170 °C.
t
i
values in [Me3SiPBNiPr2]2 1.384(5) A [44], [ BuPBN Pr2]2
˚
i
˚
˚
1.37(1) A [45], [HPBN Pr2]2 1.377(3) A [7] and in metal car-
˚
bonyl complexes [{HPBNiPr2}2·Cr(CO)5] 1.36(1) A (avg)
[7], [( Pr2N)2BP(H)(SiPh3)·Cr(CO)5] 1.41(1) A (avg) [21]
and [( Pr2N)B(PH2)2·[Cr(CO)5]2] 1.37(3) A [7]. The B-P
bond length, 1.982(5) A, is at the long end of the range of
i
˚
i
˚
˚
B-P single bond lengths found in acyclic boron-phosphorus
˚
compounds 1.9Ϫ2.0 A [2]. The B-Si bond length,
˚
2.063(5) A, are similar to values in the silylborazine
˚
[{(Me3Si)Si}(Me)2B3N3(Me)3], 2.097(4) A [46], and in the
t
˚
iminoborane BuNϵBSi(SiMe3)3, 1.976(4) A [37]. A series
of transition metal complexes containing (Me3Si)3SiB(X)
fragments A show B-Si bond lengths in the range
2.030(8)Ϫ2.052(11) [47].
Since aminophosphino boranes are generally good li-
gands toward transition metal carbonyl fragments [2], we
examined the reactions of 3 with a set of standard metal
C27H51NBSi4P (543.841): calc. C 59.63, H 9.45, N 2.58; found; C
59.50, H 9.43, N 2.71 %.
˚
Mass spectrum (30 eV):m/e 544 (Mϩ), 529 (M-CHϩ3 ), 471 (M-TMSϩ). Ϫ
NMR (C6D6) 1H-NMR: δ ϭ 0.41 (s, 27H, SiCH3), 0.76 (d, Jϭ7.0 Hz, 6H,
i
iPrCH3), 1.27 (d, Jϭ7.0 Hz, 6H, iPrCH3), 4.47 (m, J ϳ 7 Hz, 2H, PrCH
overlapped), 6.99 -7.11 (Ph), 7.41-7.67 ppm (Ph). Ϫ 13-C{1H}-NMR: δ ϭ
4.21 (SiCH3), 25.00 (iPrCH3), 26.16 (iPrCH3), 55.41 (iPrCH), 59.39 (iPrCH),
2444
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 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2006, 2443Ϫ2446

Synthesis and Molecular Structure of Tris[(trimethylsilyl)silyl](diisopropylamino)(diphenylphosphino)borane
References
Table 1 Crystal data for 3.
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Chem. formula
Form. wt.
C27H51BNPSi4
543.8
0.28 x 0.35 x 0.46
monoclinic
P21/n
10.170(2)
17.327(3)
19.580(4)
96.58(3)
3427.5(11)
4
1.054
0.236
1184
Ϫ10 Յ h Յ 10
Ϫ18 Յ k Յ 18
Ϫ21 Յ l Յ 21
3 to 45
9988
4479
Cryst. size /mm
Cryst. system
Space group
˚
a /A
˚
b /A
˚
c /A
β /°
3
˚
V /A
Z
ρ(calcd.)/(Mg/m3)
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F (000)
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1.92
307
No. variables
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GOOF
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wϪ1 ϭ σ2(F) ϩ 0.0003F2
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