Phosphino[tris(trimethylsilyl)methyl]boranes and 2,4- bis[tris(trimethylsilyl)methyl]-1,3,2,4-diphosphadiboretanes [1]

Article abstract of DOI:10.1002/zaac.200600335

The reaction of tris(trimethylsilyl)methylboron dihalides (Me ₃Si)₃CBX₂ (X = Cl, F) with the lithium phosphides LiPHtBu and LiPHmes leads to the phosphinoboranes (Me ₃Si)₃CBX-(PHR), (Me₃Si)₃CB(PHR) ₂ or the 1,3,2,4-diphosphadiboretanes [(Me₃Si) ₃CB(PR)]₂, depending on the ratio of the reagents, the reaction temperature and concentration. High dilution and low temperatures are required for the synthesis of (Me₃Si)₃CB(Hal)PHR (1-3) in order to prevent the formation of (Me₃Si)₃CB(PHR) ₂ (4 and 5). The latter compounds are best prepared in a two step phosphination from (Me₃Si)₃CBHal₂ and LiPHR. At higher temperatures the four-membered 1,3,2,4-diphosphadiboretanes [(Me ₃Si)₃CB(PR)]₂ 6 and 7 are the most stable compounds. On the other hand, compounds of type (Me₃Si) ₃CB(Hal)PR₂, 8 and 9, are thermally more stable than the monophosphinoboranes 1-3. Phosphinoboranes of type (Me₃Si) ₃CB(PR₂)₂ (R = tBu, mes) could not be prepared. NMR and mass spectral data are in accord with the monomeric nature of compounds 1 to 9.

Full text of DOI:10.1002/zaac.200600335

DOI: 10.1002/zaac.200600335
Phosphino[tris(trimethylsilyl)methyl]Boranes and 2,4-
Bis[tris(trimethylsilyl)methyl]-1,3,2,4-diphosphadiboretanes [1]
R. Jetzfellnera, H. Nöth*,a, R. T. Paineb
a Munich, University, Department of Chemistry and Biochemisty
b Albuquerque, NM / USA, University of New Mexico, Department of Chemistry
Received November 28th, 2006.
Abstract. The reaction of tris(trimethylsilyl)methylboron dihalides
(Me3Si)3CBX2 (X ϭ Cl, F) with the lithium phosphides LiPHtBu
and LiPHmes leads to the phosphinoboranes (Me3Si)3CBX-
(PHR), (Me3Si)3CB(PHR)2 or the 1,3,2,4-diphosphadiboretanes
[(Me3Si)3CB(PR)]2, depending on the ratio of the reagents, the
reaction temperature and concentration. High dilution and low
temperatures are required for the synthesis of (Me3Si)3CB(Hal)PHR
(1؊3) in order to prevent the formation of (Me3Si)3CB(PHR)2
(4 and 5). The latter compounds are best prepared in a two step
phosphination from (Me3Si)3CBHal2 and LiPHR. At higher tem-
peratures the four-membered 1,3,2,4-diphosphadiboretanes
[(Me3Si)3CB(PR)]2 6 and 7 are the most stable compounds. On the
other hand, compounds of type (Me3Si)3CB(Hal)PR2, 8 and 9, are
thermally more stable than the monophosphinoboranes 1Ϫ3.
Phosphinoboranes of type (Me3Si)3CB(PR2)2 (R ϭ tBu, mes) could
not be prepared. NMR and mass spectral data are in accord with
the monomeric nature of compounds 1 to 9.
Keywords: Phosphinoboranes; Diphosphadiboretanes; Steric effects
Introduction
Phosphinoboranes of type RЈ2P-BR2. RB(PRЈ2)2 and
B(PRЈ2)3 show a much higher tendency to dimerization, tri-
merization and even polymerization than the corresponding
aminoboranes R2ϪnB(NR2)nϩ1 due to missing or weak
BPϪπ-bonding in spite of the fact that the BP bond is less
polar than the BN bond. This is a consequence of longer
BP bonds as well as the preference of the tri-coordinated P
atom for a trigonal pyramidal geometry. However, it is
possible to force the tri-coordinated P atom of phosphino-
boranes into a planar configuration by use of sterically de-
manding substitutents such as found in the compound
mes2PϭBmes2 [2]. Here, both the B and the P atoms have a
planar environment. Moreover, the BP bond length is much
Compounds A to C [2Ϫ5] were amongst the first boron
phosphorus compounds with planar boron and phosphorus
atoms featuring BPϪπ-bonding. Although compound D
˚
shorter (1.84 A) than found in monomeric phosphino-
˚
contains a double bond [d(BN) ϭ 1.339(5)] A] [6], the
˚
boranes with pyramidal P atoms (1.92 to 1.98 A) [3]. In
planar geometry around the P atom indicates also the pres-
order to induce BPϪπ-bonding it is essential that the B
atoms should, in general, not carry NR2 or OR substituents
because these favour BNϪ or BOϪπ-bonding, i. e. there
should be no competition between BPϪ and BNϪ or
BOϪπ-bonding. Typical examples of phosphinoboranes
showing BPϪπ-bonds include compounds A to E.
˚
ence of a BPϪπ-bond [1.743(5) A] which is even shorter
˚
than in compound A [1.839(8) A]. The presence of a BN-
and a BP-double bond in D is further substantiated by the
allene type structure of the molecule. Both short bond
lengths are of course also due to the presence of a di-coor-
dinated boron atom. A very remarkable compound is the
˚
potassium salt of the anion E. Its BP bond length is 1.767 A
which correspond to a BP bond order of 1.9 [7]. Thus, even
“naked” P atoms carrying formal negative charges may
adopt formal low coordination numbers [8] and form
multiple bonds, avoiding di-, tri- or oligomerization in the
solid state.
a,* Prof. Dr. Dr. h.c.mult. H. Nöth
Department Chemie, Universität München
Butenandtstr. 5Ϫ13
D-81377 München, Germany
E-mail: h.noeth@lrz.uni-muenchen.de
Here we report the results of a study on phosphinobor-
anes with the bulky tris(trimethylsilyl)methyl group. This
might be a substituent that would not only prevent oligo-
b Prof. Dr. R. T. Paine
Department of Chemistry, University of New Mexico
Albuquerque, New Mexico 87131 / USA
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Phosphino[tris(trimethylsilyl)methyl]Boranes
merization of the corresponding phosphinoboranes but also
mightstabilize BP double bonding.
Ϫ60 °C. because at higher temperatures (> Ϫ45 °C) the
1,3,2,4-diphosphadiboretanes 6 and 7 are formed. Instead
of LiPHR the lithium phosphides Li2PR (R ϭ tBu, mes)
can also be used for the phosphination of (Me3Si)3CBCl2.
to produce 6 and 7.
Phosphino[tris(trimethylsilyl)methyl]boranes
On the other hand, the phosphination of (Me3Si)3CBCl2
with LiPR2 (R ϭ tBu, mes) yields only compounds 8 and
9 as shown by Equ. (5) because the introduction of a second
PR2 group as described in Equ. (6) can not be realized,
obviously due to steric overcrowding.
Synthesis
In this study we used exclusively the reaction of lithium
organylphosphides with tris(tri-methylsilyl)methylboron di-
halides for the synthesis of phosphino-tris(trimethylsilyl)-
methyl-boranes. As shown in Equ. (1) monoorganylphos-
phino halo tris(trimethylsilyl)methyl boranes result exclus-
ively when a reagent ratio of 1 : 1 is employed, and when
the reactions are performed at Ϫ60 °C using hexane as the
solvent. Moreover, it is important to use also solutions of
low concentration in order to avoid the formation of by-
products. This result stands in contrast to reports that reac-
tions between mesBCl2 or mesPBr2 with LiPHtBu [4, 9]
produce mixtures of (mesPBtBu)2, (mesPBtBu)3 and
mesBHal(PHtBu).
It should be noted that in some of the reactions leading
to compound 1 31P NMR data revealed the presence of
small amounts of (Me3Si)3CB(PHtBu)2 (< 1 %). It is re-
moved from 1 by recrystallization at Ϫ18 °C from hexane.
In case of compound 2 we observed occasionally the forma-
tion of [(Me3Si)3CBO]3 which is due to oxidation. This can
be avoided by using oxygen free argon as the protecting gas.
Compound 3 decomposed on attempted sublimation with
formation of Me3SiF.
Spectra
The characterization of compounds 1 to 9 by X-ray struc-
ture analysis was, unfortunately, not possible due to insuf-
ficient quality of the crystals obtained from several solvents.
Therefore, NMR, IR and MS spectroscopy was used to de-
duce its structures. NMR data (see Tables 1 and 2) and
mass spectra are in accord with monomeric units contain-
ing tri-coordinated boron and phosphorus atoms.
The 11B NMR signals of compounds 1 to 9 span the
range from 62.8 to 106.6 ppm. In this window one finds
also the 11B NMR data of trialkylboranes, dialkylchloro-
boranes (except the fluorides) and silylboranes [10]. The bo-
ron nuclei of compounds 1 and 2 show chemical shifts close
to B(CH2SiMe3)3 (δ ϭ 78.4) [10] while the boron nucleus
in the fluoride 3 is better shielded by about 14 ppm. This
corresponds to effects which are quite generally found by
comparing boron fluorides and boron chlorides, and the
high field shift is attributed to BFϪπ-bonding [10]. The in-
troduction of a second phosphino group (compounds 4 and
5) deshields the boron nuclei further so that their 11B reson-
ances match with those of trialkylboranes. This can be
taken as convincing evidence for the absence of BPϪπ-
bonding and demonstrates that the phosphino groups are
no better electron donors than alkyl groups as the BP bond
is less polar than the BC bond. However, the (Me3Si)3C
group shows a β-silyl effect [11, 12] on the 11B shifts as
demonstrated by the chemical shift for tBuBCl2 (δ11B ϭ
63.5) and of (Me3Si)3C-BCl2 (δ11B ϭ 56.9) [13], or of
tBuB(Br)PtBu2 (δ11B ϭ 95.1) [14] and (Me3Si)3C-B(Cl)-
PtBu2 (δ11B ϭ 83.3) although the substitution of a Cl atom
by a Br atom leads in general to a slightly better shielding.
On the other hand, the replacement of a Cl atom in
(Me3Si)3C-BCl2 by a PHtBu group results in a deshielding
of 20.3 ppm, while the introduction of a second PHtBu
group causes an additional deshielding but only of
10.2 ppm. The analogous substitution of the Cl atoms by
the PHmes groups leads to shift differences of 10.4 and
6.1 ppm. The replacement of one Cl atom of (Me3Si)3C-BCl2
by a PtBu2 group causes a deshielding of 31.9 ppm, but
only a shift difference of 16.3 ppm is observed by the intro-
duction of a Pmes2 group.
When reaction (1) is performed at Ϫ65 °C at higher con-
centration then compounds of type (Me3Si)3CB(PHR)2
contaminated with compounds 1 to 3 (up to 25 %) are
formed. These bis(phosphino)-boranes are readily prepared
according to Equations (2) or (3).
Under the conditions of reactions (2) or (3) no by-prod-
ucts are observed. However, the diphosphinoboranes 4 and
5 decompose on heating at 150 °C to a number of products
(31P NMR) by RPH2 elimination. We could not separate
these products by fractional crystallization. It is of crucial
importance that reaction (3) is carried out at Ϫ70 to
The chemical shifts for the 31P nuclei are all typical for
pyramidal tri-coordinated P atoms. For the series 1 > 4 >
8 δ31P decreases from Ϫ19.9 to Ϫ0.43 ppm. This trend is
even more pronounced for the series 2 > 5 > 9, and the 31P
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549

R. Jetzfellner, H. Nöth, R. T. Paine
Table 1 11B and 31P chemical shifts of compounds 1 to 9. Half heights in Hz.
1
2
3
4
5
6
7
8
9
δ11
h(1/2)
δ31
h(1/2)
B
76.6
620 Hz
Ϫ19.9
77.3
335 Hz
Ϫ84.4
62.8
410 Hz
Ϫ118.0
86.4
245 Hz
Ϫ13.2
83.4
375 Hz
Ϫ72.8
106.6
285 Hz
Ϫ22.2
79.5
610 Hz
Ϫ
83.8
73.2
210 Hz
Ϫ0.43
30 Hz
390 Hz
Ϫ43.1
45 Hz
a)
b)
c)
d)
e)
P
a) d, 1J(PH) ϭ 245 Hz; b) d, 1J(PH) ϭ 260 Hz, c), d) 1J(PH) ϭ 245 Hz, e) 1J(PH) ϭ 265 Hz.
nuclei of the diphosphadiboretanes 6 are even more de-
shielded. For both compounds, 6 and 7 only one set of H
Table 2 1H and 13C chemical shifts of compounds 1 to 9 ( in deutero-
benzene).
1
and 13C signals is observed for the (Me3Si)3C and the mes
groups. This suggests free rotation of these groups about
the BϪC and PϪC bonds. Most likely, these two diphos-
phadiboretanes are present with an anti-conformation of
the P-substituents because this is the predominant arrange-
ment of substituents in planar diphosphadiboretanes [3].
Typical for the two (Me3Si)3CB(PHR)2 compounds 4 and
5 are the doublets in the 1H coupled 31P NMR spectra with
1J(1H31P) ϭ 253 Hz. In the case of compound 5 one ob-
serves also PP coupling with 2J(31P31P) ϭ 39 Hz. In analogy
to 1 and 2 where the mesityl group induces a better shield-
ing of 64.5 ppm, the corresponding shielding difference be-
tween 1 and 4 is only 6.7 but between 2 and 5 11.6 ppm.
For all compounds, the 13C NMR signals of the
B-bonded C atom cannot be observed, a well known
phenomenon which is due to the quadrupol moment of 11B.
Moreover, also the ipso C atoms of the mesityl groups are
not observed. Exchange of the tBu group by the mes group
substituent reduces the shielding of the 13C atoms of Me3Si
groups in 1, 2, 3, and 5, but this trend is reversed for 6 and
7 as well as for 8 and 9. Magnetic equivalence is observed
for all organyl substituents of the diphosphinoboranes 4
and 5 and for the diphosphadiboretanes 6 and 7.
Compound δ13
C
δ1H
a
1
33.0 CMe3
31.4 CMe
3.8
PHb
c
1.31 CMe3
0.31 SiMe3
6.2
SiMe3
2
142.9 C2,C2Јd 138.0 C4
129.2 C3,C3Јe 24.6 C5
4.69 PHg
6.78 H3,3Јg
61.1 C5f
14.5 CSiMe3 2.39 H3
5.2
SiMe3
2.09 H6
0.36 SiMe3
3
4
5
6
7
142.2 C2,2Јh
129.9 C3,3Јi
21.0 C6
137.9 C2
24.0 C5k
4.8
4.13 PHl
2.72 H-3,3Ј 0.29 SiMe3
CSiMe3 2.35 H5
2.08 H6
m
34.8 CMe3n
32.9 CMe3
7.5
4.16 PHp
1.41 CMe3°
0.38 SiMe3
SiMe3
143.0 C2q
137.5 C4
129.3 C3
25.9 C5
21.0 C6
4.70 PHr
6.39 H3
2.32 H5
2.00 H6
0.52 SiMe3
7.6
SiMe3
s
u
38.9 CMe3t
35.0 CMe3
4.0
1.46 CMe3
0.25 SiMe3
6.68 H3
SiMe3
137.9 C2
136.2 C4
129.0 C3
25.9 C5v
21.2 C6
2.27 H5
14.3 CSiMe3 2.18 H6
4.8
SiMe3
0.29 SiMe3
Mass Spectra
8
9
33.1 C2w
30.2 C1
7.0
SiMe3
61.33 H2x
0.46 SiMe3
y
Mass spectra of compounds 1 to 4 and 6 to 9 (70 eV)
showed no fragments at m/e higher than M·ϩ. This supports
the conclusion drawn from the NMR spectra that these
compounds are molecular monomers. Schemes 1Ϫ8 dem-
onstrate the most important fragments.
144.3 C2z
138.1 C4
129.8 C3
25.63 C5
20.9 C6
5.9
6.58 H3A
2.40 H5
2.11 H6
0.26 SiMe3
SiMe3
a) d, 2J(PC) ϭ 10 Hz; b) d, 1J(PH) ϭ 254 Hz; c) 3J(PH) ϭ 13 Hz;
d) N ϭ 8 Hz; e) N ϭ 14 Hz; f) 1J(PH) ϭ 263 Hz; g) N ϭ 4 Hz; h) N ϭ
7 Hz; i) N ϭ 12 Hz; k) N ϭ 17 Hz, l) 249 Hz; m) N ϭ 7 Hz; n) N ϭ
10 Hz, o) 3J(PH) ϭ 12 Hz; p) 1J(PH) ϭ 267 Hz; q) 3J(PC) ϭ 6 Hz;
r) 1J(PH) ϭ 253 Hz; s) 2J(PC) ϭ 11 Hz; t) N ϭ 27 Hz; u) 3J(PH) ϭ
12 Hz; v) 3J(PC) ϭ 7 Hz; x) 2J(PC) ϭ 12 H, y)3J(PH) ϭ 11 Hz;
z) 2J(PC) ϭ 12 Hz; A) 4J(PH) ϭ 3 Hz.
No molecular ion is observed for compound 1 which
loses HCl readily to give a boraphosphene radical cation
which in turn splits off isobutene to generate a PH unit.
The 100 % peak is the (Me3Si)3CBϩ cation which can form
by two routes: either by loss of a PtBu radical or a PH
radical. Abundant are also Me3Siϩ ions (32 %), while the
loss of a Me radical from the (Me3Si)3CBϭPH radical cat-
ion produces the cation of (Me3Si)2Me2SiC-BϭPH (13 %).
In contrast to 1 compounds 2 and 3 form molecular ions
though only in low intensity (ഠ 2 %). Elimination of a Me
radical gives most likely a cylic cation at m/e ϭ 413. The
more pronounced elimination of a mes radical leads to the
fragment (Me3Si)3CBϭPHțϩ with 68 % relative intensity.
The ion (Me3Si)3CBClϩ results from the parent peak by
loss of a mesPH radical. In analogy to compound 1 the
cation (Me3Si)3CBțϩ is the most abundant fragment
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Phosphino[tris(trimethylsilyl)methyl]Boranes
Scheme 1 The main fragments observed in the mass spectrum of 1 at 70 eV (m/z, rel. %)
Scheme 2 Fragmentation of compound 2 at 70 eV
Scheme 3 Fragmentation of compound 3 at 70 eV
(100 %) in contrast to 3, where the cation (Me3Si3)CBFțϩ
is present with 100 % relative intensity while the cation
(Me3Si)3CBϩ shows only 20 % relative abundance.More-
over, the loss of a mesPH radical is characteristic for the
fragmentation of 2 and 3, while the relative intensities of
the cation (Me3Si)3Cϩ is 5 % for 2 but 90 % for 3.
The mass spectrum of 4 is dominated by the tBu radical
cation (100 %) resulting from PC bond cleavage. The cat-
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551

R. Jetzfellner, H. Nöth, R. T. Paine
Scheme 4 Fragments of 4 in the mass spectrum 70 eV
Scheme 5 Fragments in the MS spectrum of compound 6
Scheme 6 Fragments in the MS spectrum of compound 7
ionic fragment (Me3Si)3CB(PH2)(PHtBu)ϩ results by the
loss of isobutene from the parent ion, while the loss of tBu
generates (Me3Si)3CB(PH)(PHtBu)ϩ as shown by peaks at
m/e ϭ 363 (36 %), and 364 (11 %) and this is accompanied
by a metastable peak at M* ϭ 313.7. Additional intense
cations are (Me3Si)2CBϩ (79 %) and Me3Sițϩ (87 %).
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Phosphino[tris(trimethylsilyl)methyl]Boranes
Scheme 7 The main fragments observed in mass spectrum of 8 at 70 eV (m/z, rel. %)
Scheme 8 Fragments in the mass spectrum of 9 (70 eV)
The mesitylphosphinoborane 5 shows a weak parent
peak. Its BP bonds are readily broken as shown by the for-
mation of the cations (Me3Si)3CBϭPHmesϩ (19 %) and
(Me3Si)3CBțϩ (96 %). The formation of mesțϩ (86 %) sug-
gests that a number of neutral species with a BϭP bond or
a cyclic BP2 system are generated.
process is not clear. The high intensity of the Mețϩ cation
suggests that stable BP fragments, most likely containing
BϭP bonds have to be considered.
Finally, the mass spectrum of compound 7 is charac-
terized by the parent peak and M/2ϩ at m/e ϭ 392 (100 %).
Loss of mes and Me radicals lead to (Me3Si)3CBțϩ (23 %)
and (Me3Si)2Ϫ(Me2Si)C-BPmesϩ (37 %). Me3Sițϩ is quite
abundant (77 %), as well as (Me3Si)3C-Bϩr2ϩ (65 %) and
ț(Me3Si)2CϭBϩ (28 %).
BP cleavage starting from the parent ion of 9 leads to the
țϩ
Pmes2
cation (100 %) and generates by loss of a Pmes2
unit the cation (Me3Si)3CBClϩ (18 %). Moreover, the cat-
ions mesP·ϩ (86 %) and (Me3Si)3CBțϩ are also character-
istic.
Discussion
While the parent peak of the diphosphadiboretane 6 is
not observed it has a reasonable intensity in case for com-
pound 7. Fragmentation starts with the formation of
(Me3Si)3C-BϭPRțϩ by loss of the neutral boraphosphene
species (Me3Si)3CBϭPR. (Me3Si)3CBϭPtBuțϩ is present in
21 % relative intensity, while the cation (Me3Si)3CBϭPmesțϩ
is the 100 % peak. Isobutene is split off from (Me3Si)3CBϭ
PtBu·ϩ followed by loss of a Me radical. The most intense
peak at m/e ϭ 169 is assigned to (Me3Si)2CϭBϩ (100 %).
At which stage in the BP bond is broken the fragmentation
In spite of the considerable steric requirement of the
(Me3Si)3C group attached to the boron atom of
(Me3Si)3CBCl2 this compound allows nevertheless the sub-
stitution of both Cl atoms in a stepwise manner by two
PHR groups (R ϭ tBu, mes) which themselves are also
sterically demanding. However, only one PtBu2 group can
be introduced to generate compounds of type (Me3Si)3-
CBCl(PR2) but not a second one to (Me3Si)3CB(PR2)2.
This is obviously the borderline of the nucleophilic replace-
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553

R. Jetzfellner, H. Nöth, R. T. Paine
distance in Hz between the outermost signals for P,P coupled sys-
tems. The Bruker ACP 200 NMR spectrometer was used to meas-
ure the 1H, 11B, 13C and 31P resonances. A Bruker 270 NMR instru-
ment of Cl by PR2. All the new tris(trimethylsilyl)-meth-
ylboranes are monomeric and show no tendency for dimer-
ization or trimerization in contrast to many other organyl-
phosphino-boranes, e. g. [RB(Br)PPh]2 (R ϭ iPr, tBu), or
[RB(Hal)PtBu]2 (R ϭ Me, Et, iPr, tBu; Hal ϭ Cl, Br) [14].
It needs now to be tested if the analogous compounds
(Me3Si)3CB(Hal)PR2 and (Me3Si)3CB(PRRЈ)2 with R ϭ H,
RЈϭ Me, Et, iPr and R ϭ RЈϭ H, Me, Et will also remain
monomers. Particularly the types with two PHR or PH2
groups should be prone to phosphane elimination forming
cyclic BP ring or even cluster compounds as was demon-
strated here for compounds 4 and 5. These are by them-
selves interesting as they might allow us to check whether
or not a HCl or RPH2 elimination occurs inter and intra-
molecularly. Trapping experiments will be interesting in
order to test whether the expected intermediates
(Me3Si)3CBϭPR and (Me3Si)3CBϭHal exist transiently.
The present series of (Me3Si3)C-B(Hal)-PHR compounds
allow a comparison with analogous amino-halo-phosphi-
noboranes. As expected, the boron nuclei of the amino
group containing compounds are in each case much better
shielded due to the presence of BNϪπ-bonds. Although the
P substituents in the following series of compounds are dif-
ferent the trend is nevertheless convincing:
1
ment was also used for measuring H, 11B and 31P resonances, and
a Jeol FX400 instrument for 1H and 31P. Mass spectra were re-
corded with a Finigan MAT90 or Varian Atlas CH7 instrument.
IR spectra: Perkin Elmer 325, capillary films for liquids or Nujol-
Hostaflon mulls for solids. The observed peaks show expected
intensity calculated for the isotope distribution. Mass data refer to
1H, 11B, 12C, 19F, 28Si, 31P, 35Cl, 79Br.
General Procedures: A solution of either (Me3Si)3BCl2 [16] or
(Me3Si)3CBF2 [16] in hexane (usually 1 mmol in 30 ml) is placed in
a two necked Schlenk vessel, flushed with either N2 or Ar. After
cooling to Ϫ60 °C a suspension of LiPHR (1 mmol) in hexane
(15 mL) is added through a dropping funnel while stirring. Stirring
is continued for about 30 min. The suspension is then allowed to
warm to ambient temperature. The solid is removed by filtration
(G3 frit). The solid is suspended in toluene and checked by NMR
for soluble products (usually no signal). The hexane of the filtrate
is removed in vacuo, and the remaining oils or crystals are crys-
tallized from a minimum amount of hexane, toluene or diethyl
ether at Ϫ25°to Ϫ30 °C. For the preparation of 1 to 3 even more
dilute solutions (1 mmol in 50 ml of hexane) is advisable.
Chloro-tert.-butylphosphino-tris(trimethylsily)methylborane (1): A
solution of (Me3Si)3CBCl2 (3.87 g, 12 mmol) dissolved in 360 ml of
hexane is allowed to react with LiPHtBu [16, 17] (1.20 g, 12 mmol)
suspended in hexane (150 ml). The solid weighed 0.61 g (ϳ12 mmol
of LiCl) and the oily orange oil weighed 4.26 g. After crystalliza-
tion from hexane at Ϫ20 °C 3.61 g of 1 (83 %) were isolated as a
yellow solid which at room temperature turned slowly into a vis-
cous oil. It is readily hydrolysed in contact with moist air.
C14H37BClPSi3 (366.95): calc. C 45.83, H 10.16, Cl 9.66; found C
46.91, H 9.87, Cl 9.61 %.
tBu2N-B(F)-PHCHEt2 δ11B ϭ 39.7 (Me3Si3)3C-B(F)-PHmes δ11B ϭ 62.8
tmp-B(F)-PH(CH(SiMe3)2
37.7
tmp-B(F)-PH(2,4,6-C5iPr3H2) 37.4
tmp-B(Cl)-PH(2,4,6(iPr3C5H2) 45.4 (Me3Si3)3C-BCl-PHtBu
76.6
77.3
tmp-B(Cl)-PHCEt3
iPr2N-B(Cl)-PHCEt3
46.1 (Me3Si3)3C-BCl-PHmes
39.9
IR (ν in cmϪ1): 3678 m, 2989 m, 2960 m, 2909 st, 2857 m, 2349 m, 2294 m,
2103 w, 1927 w, 1869 w, 1460 m, 1442 w, 1383 w, 1363 m, 1302 m, 1263 st,
1254 st, 1188 w, 1174 w, 1048 m, 1027 st, 987 st, 953 w, 935 w, 854 st, 700 m,
759 w, 729 w, 716 m, 680 st, 540 m, 621 st, 572 m, 539 m, 522 w, 509 w,
482 w, 360 st.
Replacement of the phosphino group by an alkyl group
leads to R2N-B(Cl)-R compounds. Their 11B chemical
shifts [11] span a small range from 38 to 41 ppm, and in
the case of the phenyl derivatives from 36 to 44 ppm. The
fluorides show 11B signals close to 31 ppm. These data dem-
onstrate that the phosphino groups have about the same
influence on the shielding as an organyl group. We will
shortly report on other types of simple phosphinoboranes
which will demonstrate that there is a significant difference
between the chemistry of phosphinoboranes and the corre-
sponding aminoboranes
Chloro-mesitylphosphino-tris(trimethylsilyl)methylborane (2): Ob-
tained from (Me3Si)3CBCl2 (1.57 g, 5 mmol) in hexane (150 ml)
and LiPHmes [16, 17] (0.457 g, 5 mmol) in hexane (75 ml). 0.22 g
of a solid is formed (ϳ5 mmol of LiCl). The yellow oil on crystalli-
zation gives yellow needles containing small amounts of (mesBO)3
(11B NMR). Yield: 1.21 g (56 %). C19H39BClPSi3 (429.02): calc. C
53.19, H 9.16; found C 54.02, H 9.53 %.
IR (ν in cmϪ1): 3679 w, 3055 w, 3015 w, 2960 st, 2923 st, 2901 w, 2850 w,
2381 w, 2300 m, 1605 m, 1502 w, 1464 m, 1442 w, 1411 w, 1376 m, 1352 w,
1322 w, 1262 st, 1254 st, 1187 w, 1180 w, 1134 w, 1079 w, 1054 m, 1027 m,
985 m, 943 w, 857 st, 836 st, 799 w, 712 w, 680 w, 621 w.
Experimental Section
The Schlenk-technique has been used for all experiments with dry
nitrogen or argon as the protective gases. Solvents were made anhy-
drous by conventional methods, distilled prior to use and stored
under nitrogen gas. Melting points were determined in capillaries
which were heated under nitrogen to 140 °C and sealed after filling
with samples. C/H/N analyses were performed in microanalytical
laboratory of the department [18]. NMR data were obtained from
C6D6 solutions of the samples using TMS (1H, 13C) as internal
standards, while BF3·OEt2 and 85 % H3PO4 were used as external
standards for 11B and 31P, respectively. Chemical shifts are pre-
sented in ppm units and coupling constants in Hz. N denotes the
Fluoro-mesityphosphino-tris(trimethylsilyl)methylborane
(3):
(Me3Si)3CBF2 (2.44 g, 8.7 mmol) is allowed to react with LiPHmes
(1.37 g, 8.7 mmol) in a total of 400 ml of hexane. A brown solid
formed (0.87 g). The crude compound 3 (yellow to brown in color,
3.02 g) gave light yellow microcrystals by crystallization from hex-
ane. They contained a very small amount of mesPH2 (31P NMR).
Yield: 2.3 g (67 %), m. p. 132Ϫ135 °C. C19H9BFPSi3 (412.57): calc.
55.32, H 9.53; found C 50.32, H 9.78 %.
IR (ν in cmϪ1): 3060 w, 3028 w, 2960 st, 2923 st, 2894 m, 2850 w, 2315 st,
1603 m, 1465 m, 1455 m, 1410 w, 1374 m, 1316 w, 1291 w, 1262 st, 1255 st,
1204 w, 1190 m, 1174 w, 1071 w, 1062 w, 1044 st, 1027 m, 970 w, 935 m,
554
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 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2007, 548Ϫ556

Phosphino[tris(trimethylsilyl)methyl]Boranes
910 w, 858 st, 836 st, 774 w, 757 w, 730 w, 711 w, 681 st, 652 w, 632 w,
613 w, 587 w.
white solid was isolated (2.3 mmol of LiCl). Yield of 8: 0.52 g which
crystallized from hexane at Ϫ30 °C as yellow crystals. These turned
into a waxy material at room temperature. Yield: 0.27 g (58 %).
C18H45BClPSi3 (423.06): calc. C 51.10, H 10.72, Cl 8.38; found C
51.57, H 10.71, Cl 7.99 %.
IR (ν in cmϪ1): 3407 w, 2960 st, 2923 st, 2894 st, 2847 m, 2279 w, 2023 w,
1927 w, 1861 w, 1637 w, 1474 m, 1456 m, 1446 w, 1386 m, 1364 m, 1270 st,
1259 st, 1192 w, 1166 m, 1131 w, 1108 m, 1042 m, 1019 st, 985 w, 857 st,
834 st, 781 m, 755 w, 721 w, 676 st, 654 w, 620 m, 585 w, 502 w, 441 w.
Bis(tert.-butylphosphino)-tris(trimethylsilyl)methylborane (4):
A
suspension of LiHtBu (1.57 g, 16.2 mmol) in hexane (20 ml) is ad-
ded at Ϫ60 °C to a stirred hexane solution of (Me3Si)3CBCl2
(5.22 g, 16.2 mmol; 40 ml). After stirring over night the second
equivalent of LiPHtBu (1.57 g in 20 ml of hexane) is added. After
filtration (1.46 g) and removal of the solvent from the filtrate 4
remained as an orange red oil (7.21 g). Crystallization from small
amounts of hexane at Ϫ20 °C produced an orange red solid. Yield:
4.62 g (70 %); m.p. 152Ϫ154 °C. C18H47BP2Si3 (420.59): calc. C
51.40, H 11.26; found C 50.82, H 10.78 %.
Chloro(dimesitylphosphino)-tris(trimethylsilyl)methylborane
(9):
Prepared as 8 from (Me3Si)3CBCl2 (490 mg, 1. 56 mmol) and
LiPmes2 (430 mg, 1.56 mmol) in hexane (90 ml). 860 mg of an or-
ange colored viscous oil. A yellow orange crystalline material was
obtained by crystallization from hexane at Ϫ30 °C, Yield: 410 mg
(48 %), m.p. 194Ϫ196 °C.
C28H49BClPSi3 (546.42), calc. C 61.46, H 9.03, Cl 6.45; found C
60.15, H 8.70, Cl 6.38 %.
IR (ν in cmϪ1): 3019 m, 2984 st, 2960 st, 2920 st, 2853 m, 2727 w, 2010 w,
1926 w, 1887 w, 1729 w, 1603 st, 1553 m, 1408 m, 1372 m, 1292 w, 1262 st,
1254 st, 1178 w, 1092 m, 1033 st, 1012 st, 962 w, 898 w, 850 st, 834 st, 785 m,
758 w, 721 w, 713 w, 680 st, 659 m, 641 w, 622 st, 585 w, 558 st, 549 m, 505 w,
491 w, 482 m, 424 m, 398 m, 357 w.
IR (ν in cmϪ1): 2955 st, 2896 st, 2858 st, 2405 m, 2392 m, 2291 w, 1926 w,
1873 w, 1471 m, 1458 st, 1406 m, 1392 m, 1360 st, 1320 w, 1253 st,
1201 w, 1195 w, 1102 w,1057 w, 1038 w, 1017 w, 983 m, 978 m, 941 w, 930 w,
941 w, 855 st, 847 st, 793 w, 677 st, 623 m, 585 w, 670 w, 532 m, 480 m, 407 w.
Bis(mesitylphosphino-)tris(trimethylsilyl)methylborane (5): To a
stirred hexane solution of (Me3Si)3CBCl2 (0.52 g, 1.65 mmol,
50 ml) was added a suspension of LiPHmes (0.52 g, 3.3 mmol) in
hexane (40 ml). After stirring over night, 0.24 g of a white solid
was removed. From the filtrate an orange product (1.75 g) was iso-
lated which after crystallization from hexane at Ϫ30 °C gave a yel-
low microcrystalline product. Yield: 0.56 g (62 %). The product
turned into a viscous oil at room temperature. C28H51BP2Si3
(544.73): calc. C 61.74, H 9.44; found C 59.64, H 9.13 %.
IR (ν in cmϪ1): 2955 st, 2925 m, 2854 st, 2728 w, 2482 w, 2380 m, 2369 st,
2313 m, 1921 w, 1722 m, 1602 st, 1570 m, 1462 m, 1445 w, 1410 w, 1375 st,
1318 w, 1291 w, 1261 st, 1252 st, 1192 w, 1177 w, 1131 w, 1103 m, 1085 w,
1028 m, 987 m, 976 m, 914 m, 865 st, 849 st, 793 m, 756 w, 678 st, 622 m,
611 w, 545 m.
Acknowledgement. We thank Fonds der Chemischen Industrie for
invaluable support of our research as well as Chemetall GmbH,
Frankfurt. Moreover, we are indebted to Mr. P. Mayer and Mrs.
D. Ewald for the recording of many NMR and mass spectra.
References
1,3-Bis(tert.butyl)-2,4-bis[tris(trimethylsilyl)methyl]-1,3,2,4-di-
phosphadiboretane (6). To a stirred solution of (Me3Si)3CBF2 [16]
(2.43 g, 89.7 mmol) in hexane (15 ml) was added at Ϫ50 °C, a hex-
ane suspension of Li2PtBu (0.89 g, 8.7 mmol, 30 ml). After 3 d the
deep red colored suspension was subjected to filtration (0.88 g
brown solid), and 2.52 g of a red residue was left after removal
of the solvent. Attempted crystallizations from hexane at Ϫ30 °C
produced only an amorphous solid material. Yield: 1.14 g (40 %);
m. p. 118Ϫ121 °C.
[1] Contribution 264 to “Chemistry of Boron“. For contribution
263 see B. Gemünd, H. Nöth, R. T. Paine, Eur. J. Inorg.
Chem., accepted.
[2] D. C. Pestana, P. P. Power, J. Am. Chem. Soc. 1991, 133,
8426Ϫ8437.
[3] R. T. Paine, H. Nöth, Chem. Rev. 1995, 95, 343Ϫ479.
[4] B. Kaufmann, N. Metzler, H. Nöth, R. T. Paine, Chem. Ber.
1994, 127, 825Ϫ827.
[ 5 ] P. P. Powe r, Angew. Chem. 1990, 102, 527Ϫ538; Angew. Chem.
Int. Ed. Engl. 1990, 102, 492.
[6] G. Linti, H. Nöth, Angew. Chem. 1990, 102, 715Ϫ717; Angew.
Chem. Int. Ed. Engl. 1990, 29, 682.
[7] H. G. v. Schnering, M. Somer, M. Hartwig, K. Peters, Angew.
Chem. 1990, 102, 63Ϫ64; Angew. Chem. Int. Ed. Engl. 1990,
29, 65.
[8] The P atoms in K3BP2are arranged at the corners of a trigonal
prisms, whose centers are occupied by 3 K atoms and a void:
P2(K3ᮀ). The P atoms coordinate to 9 K atoms (instead of
12).
[9] H. V. R. Dias, P. P. Power, J. Amer. Chem. Soc. 1989, 111,
144Ϫ148.
C28H72B2P2Si6 (660.92).
IR (ν in cmϪ1): 2958 st, 2931 m, 2901 m, 2874 m, 2705 w, 1931 w, 1867 w,
1469 m,. 1457 m, 1408 w, 1379 w, 1360 m, 1317 st, 1281 st, 1266 st, 1254 st,
1191 w, 1112 w, 1099 w, 1089 w, 1044 w, 1024 w, 1009 w, 994 w, 976 m, 934 w,
870 st,852 st, 836 st, 799 m, 787 m, 756 w, 717 w, 701 w, 680 st, 643 m, 619 m,
559 w, 535 w, 522 w, 493 w, 479 m, 413 w.
1,3-Bis(mesityl)-2,4-bis[tris(trimethylsilyl)methyl]-1,3,2,4-diphospha-
diboretane (7): Obtained from the reaction of (Me3Si)3CBCl2
(3.13 g, 10 mmol) with Li2Pmes [17, 18] (1.64 g, 10 mmol). After
stirring for 2 d 1.43 g of a white solid was removed. From the or-
ange filtrate a solid was obtained after removal of the solvent in
vacuo. Crystallization from hexane at Ϫ30 °C provided crystalline
orange 7. Yield: 2.35 g (66 %). m. p. 144Ϫ147 °C.
C38H76B2P2Si, (785.13): calc. C 58.13, H 9.76, found C 53.91, H
9.50 %.
IR (ν in cmϪ1): 3088 w, 3061 w, 3027 w, 2957 st, 2927 st, 2904 w, 2860 w,
1606 m, 1497 m, 1472 w, 1439 w, 1407 w, 1374 w, 1291 w, 1254 st, 1190 w,
1124 m, 1107 m, 1027 w, 967 st, 942 st, 853 st, 841 st, 808 w, 784 w, 716 w,
677 st, 634 m, 622 w, 606 w, 595 w, 678 w, 538 w, 506 w, 495 w, 443 w.
[10] H. Nöth, B. Wrackmeyer, Nuclear Magnetic Resonance Spec-
trometry of Boron Compounds, Vol. 14 of NMR, Basic Prin-
ciples and Progress, Editors: P. Diehl, E. Fluck, R. Kosfeld,
Springer Publishers, Berlin, Heidelberg, New York, 1978.
[11] J. B. Lambert, Tetrahedron Lett. 1990, 46, 2677Ϫ2689.
[12] M. R. Ibrahim, W. L. Jorgensen, J. Am. Chem. Soc. 1989,
11, 819Ϫ824.
Chloro(di-tert.-butylphosphino)-tris(trimethylsilyl)methylborane
(8): Prepared from (Me3Si)3CBCl2 (0.34 g, 1.09 mmol) and
LiP(tBu)2 (0.33 g, 2.18 mmol) [18] in hexane (60 ml). 0.1 g of a
[13] R. A. Bartlett, H. V. R. Dias, P. P. Power, Inorg. Chem. 1988,
27, 3919Ϫ3922.
[14] R. Jetzfellner, PhD Thesis, University of Munich, 1997.
Z. Anorg. Allg. Chem. 2007, 548Ϫ556
 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
555

R. Jetzfellner, H. Nöth, R. T. Paine
[15] S. S. Al-Juaid, C. Eaborn, M. N. El-Kheli, B. P. Hitchcock, P.
D. Lickiss, M. E. Molla, J. D. Smith, J. A. Zora, J. Chem. Soc.,
Dalton Trans. 1989, 447Ϫ452.
[16] A. Zunke, M. Riemer, H. Schmidt, K. Issleib, Phosphorus Sul-
fur 1983, 17, 237Ϫ244.
[17] K. Issleib, F. Krech, A. Zschunke, M. Riemer, Phosphorus Sul-
fur 1985, 22, 349Ϫ352.
[18] Analytical data for the mesitylphosphinoboranes are generally
too low. This may be due to boron carbide formation or in-
complete combustion.
556
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