Dimeric phosphinoboranes R′(Hal)B-PHR2 and some of their Reactions [1]

Article abstract of DOI:10.1002/zaac.200700070

Reactions of organylboron halides RBX2 (R = tBu, iPr, Et, Me; X = Cl, Br) with lithium organylphosphides LiPHR′ (R′ = mes, Ph, tBu) in a 1:1 ratio lead to the corresponding 1,3,2,4-di-phospha-dibora-cyclobutanes [R′(H)P-B(Hal)R]₂. Further substitution to 2,4-diphosphino derivatives has only be achieved for [tBu(H)P-B(tBu)PHtBu]₂ (12). Its exocyclic PHtBu groups can be metallated by LiPHtBu, but it is more convenient to use the 1 : 3 reaction of tBuBCl₂ with LiPHtBu for the preparation of [tBu(H)P-B(tBu)PLitBu]₂ (16), which was isolated as a diethyl ether solvate. Compound 12 on irradiation with a mercury vapour lamp splits off tBuPH₂ and generates the bicyclic tBuP[BtBu-PHtBu]₂ (17). The new compounds have been characterized by NMR and Mass spectral data. The tBu groups of compound [Br(tBu)B-PHtBu]₂ (7), are present in an all-trans-configuration. Its B₂P₂ ring is planar.

Full text of DOI:10.1002/zaac.200700070

DOI: 10.1002/zaac.200700070
Dimeric Phosphinoboranes [RЈ(Hal)B-PHR]2 and some of their Reactions [1]
Ralf Jetzfellnera, Heinrich Nötha,*, and Robert T. Paineb
a Munich/Germany, University of Munich, Department of Chemistry
b Albuquerque, NM/USA, University of New Mexico, Department of Chemistry
Received January 30th, 2007.
Dedicated to Professor Wolfgang Beck on the Occasion of his 75th Birthday
Abstract. Reactions of organylboron halides RBX2 (R ϭ tBu, iPr,
Et, Me; X ϭ Cl, Br) with lithium organylphosphides LiPHRЈ (RЈϭ
mes, Ph, tBu) in a 1:1 ratio lead to the corresponding 1,3,2,4-di-
phospha-dibora-cyclobutanes [RЈ(H)P-B(Hal)R]2. Further substi-
tution to 2,4-diphosphino derivatives has only be achieved for
[tBu(H)P-B(tBu)PHtBu]2 (12). Its exocyclic PHtBu groups can be
metallated by LiPHtBu, but it is more convenient to use the 1 : 3
reaction of tBuBCl2 with LiPHtBu for the preparation of
[tBu(H)P-B(tBu)PLitBu]2 (16), which was isolated as a diethyl ether
solvate. Compound 12 on irradiation with a mercury vapour lamp
splits off tBuPH2 and generates the bicyclic tBuP[BtBu-PHtBu]2
(17). The new compounds have been characterized by NMR
and Mass spectral data. The tBu groups of compound
[Br(tBu)B-PHtBu]2 (7), are present in an all-trans-configuration. Its
B2P2 ring is planar.
Keywords: 1,3,2,4-Diphosphadiboracyclobutanes; P-Lithiation;
Bicyclo[1.1.0]triphosphadibora-pentane; NMR; Mass spectra;
X-ray crystallography
Introduction
Phosphinoboranes RЈ2B-PR2 have a high tendency to di-
merize to give four membered cyclo-phosphinoboranes
[RЈ2B-PR2]2 built from alternating tetra-coordinated B and
P atoms [2Ϫ6]. Trimerization of the phosphinoboranes to
1,3,5-triphospha-2,4,6-triboracyclohexanes is less pro-
nounced [3, 4], and oligomerization is even less likely [3Ϫ5].
The oligomerization can be prevented by replacement of
bulky substituents, either at the B or P atoms [2, 4, 5] or by
introduction of electron donating groups such as amino or
alkoxo groups which reduces the Lewis acidic character of
the boron atom by BNϪ or BOϪπ- bonding [2].
Synthesis
The reactions of alkyldihaloboranes with lithium mesityl-
phosphide yields the dimeric phosphinoboranes 1 to 4 as
shown in Equ. (2).
While the very bulky tris(trimethylsilyl)methyl group
supresses
(Me3Si)3CB(PHR)Hal,
dimerization
of
compounds of
type
or
(Me3Si)3CB(PR2)Hal
(Me3Si)3CB(PHR)2 [6] the tBu group, although also
sterically demanding, is not able to prevent dimerization of
tBu(Hal)B-PHR to form [tBu(Hal)B-PHR]2 as reported
here. These latter compounds offer the possibility for
H-Hal abstraction and, therefore, the stepwise formation of
the corresponding diphosphadiboretanes [tBuB-PR]2 as
shown in Equ. (1).
* Prof. Dr. H. Nöth
Department Chemie der Universität München
Butenandtstr. 5Ϫ13
D-81377 München
E-mail: H. Noeth@lrz.uni-muenchen.de
Compounds 1 and 2 are formed exclusively although the
crude product is often slightly contaminated (< 0.5 %) by
the respective boroxine which can be removed by crystalli-
zation. The 11B NMR spectrum of the reaction solution
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R. Jetzfellner, H. Nöth, R. T. Paine
obtained with EtBCl2 is dominated by the signal of 3
(δ11B ϭ 0.1) but there are also very low intensity signals at
43.3 ppm (most likely of [Et(Cl)B]2O) and 61.8 ppm
(EtBCl2). Only a single signal for 3 in the 31P NMR spec-
trum is observed. The reaction (1) carried out with MeBBr2
leads always to some [MeBO]3 as well as [MeBPmes]3 be-
sides 4. The by-products have been repeatedly observed.
They are not due to a slightly incorrect stoichiometry. Re-
peated recrystallizations of 4 increases the presence of
[MeBPmes]3 (δ11B ϭ 59.0). Obviously, 4 decomposes slowly
with HBr elimination.
The reactions at Ϫ45 °C of tBuBBr2 and iPrBBr2 with
LiPHPh in hexane as shown in Equ. (3) lead to compounds
5 and 6. Further substitution to RB(PHPh)2 is not observed
even at 50 °C. This result shows i) that RB(Hal)PHPh di-
merizes rapidly and ii) that HBr elimination from the dimer
by LiPHPh with formation of LiBr and PhPH2 does not
occur. This step requires stronger bases (v. i.).
ucts including 16 which could not be separated into the
components either by fractional crystallization or by distil-
lation. For this reason we treated tBuBCl2 with three equiv-
alents of LiPHtBu in a mixture of hexane and diethyl ether
at Ϫ78 °C in the hope that 12 as an intermediate would
further react with the phosphide to achieve metallation at
the exocyclic P atoms. The reason for this experiment was,
that the 1:2 reaction at Ϫ78 °C not only gave compound 12
but also a species which showed an 11B NMR signal at δ ϭ
Ϫ4.4. In addition, two new 31P NMR signals appeared at
Ϫ92 and Ϫ99 ppm. These signals indicated to a possible
P metallation.
In the 1:3 reaction only these two 31P NMR signals were
observed. Addition of a fourth equivalent of LiPHtBu has
no additional effect. Therefore, the 1: 3 reaction proceeds
according to Equ. (6).
Reactions according to Equ. (4) with LiPHtBu at Ϫ45 °C
in hexane give access to the diphosphadiboracyclobutanes
7 to 11. No monomeric phosphinoboranes RB(Hal)PHtBu
are detected by 11B NMR spectroscopy as intermediates.
The only by-products are small amounts of [RBO]3 (< 5 %)
in case of compounds 9 and 10.
In several of the reactions performed according to Equs.
(3) and (4) the formation of small amounts of RPH2 is also
noted. Whether its formation occurs inter- or intramolecu-
larly remains an open question. For this reason we heated
compound 12 to 120 °C, a temperature at which the com-
pound decomposes. But apart from tBuPH2, no other prod-
ucts could be characterized. Then, we subjected a solution
of 12 in benzene to the light of a mercury vapour lamp.
Besides the 31P NMR signal of tBuPH2 (δ ϭ Ϫ79.6) three
additional signals at δ ϭ Ϫ15, Ϫ30 and Ϫ178 appeared.
The 11B NMR spectrum showed a single signal at δ11B ϭ
Ϫ8.4 for a tetra-coordinated boron atom. Compound 17
crystallized in a very small yield from hexane at Ϫ18 °C,
but the crystals are not suitable for an X-ray structure de-
termination. However, compound 17 is not only charac-
terized by its NMR spectra but also by its mass spectrum
(v. i.). The formation is depicted in Equ. (7). 17 provides a
new type of a bicyclic boron phosphorus compound.
On adding a second equivalent of LiPHtBu to com-
pounds 7 to 11 no reaction occurs at ambient temperature
either by removing HHal or by substituting the halogen
atoms. Similarly, elimination or substitution are not ob-
served with NaN(SiMe3)2, LiNMe2 or LitBu. However, on
heating a 1:1 mixture of compounds 7 to 11 with LiPHtBu
at reflux (RF) for 4 to 20 h produces the dimeric organyl
bis(tbutylphosphino)boranes 12 to 15 as shown in Equ. (5).
There are a number of by-products formed besides com-
pounds 13 to 15. The latter compounds are only charac-
terized by 11B and 31P NMR data, in contrast to com-
pounds 12 which is isolated as a pure species.
Reactions
NMR Spectra
Compound 12 potentially may undergo deprotonation and
tBuPH2 elimination. Treatment of 12 with either LiBu or
LitBu in hexane at Ϫ30 °C leads to a mixture of new prod-
The NMR data of compounds 1 to 11 are listed in Table 1.
They show that all compounds have tetra-coordinated bo-
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Dimeric Phosphinoboranes [RЈ(Hal)B-PHR]2
ron and phosphorus atoms consistent with the formation
of 1,3-diphospha-2,4-diboracyclobutanes. For the series of
compounds 1 Ϫ 4 the boron nuclei become better shielded
the smaller the size of the B-alkyl group. There is a 11B shift
difference of 15.4 ppm between the B-tbutyl and B-methyl
and 3.6 ppm between the B-tbutyl and B-ipropyl deriva-
tives. The 11B shifts for the series of compounds 7 to 10 are
less regular and the differences less pronounced. For the
phenylphosphino compounds 5 and 6, there is only a differ-
ence of 1.8 ppm. For all these compounds only a single 11B
and 31P NMR signal is observed. This indicates that only
one type of isomer is present. This is supported by the 13C
and 1H NMR spectra. In principle the isomers A to F might
form by the dimerization of the monomers:
Table 1 NMR Data of Compounds 1 Ϫ 11
δ11
B
δ31
P
δ13
C
δ13
C
δ1H
δ1H
1
2
7.8a (315) Ϫ104.4 (167) 143.7 C2 141.1 C6 6.85 H3
130.8 C3 26.4 C5 2.84 H5
5.70c PH
1.90 H6
20.8 C6 30.0b C8 1.17 H8
4.2 (304) Ϫ40.5d (180) 142.5 C2 141.0 C4 6.58 H3
130.4 C3 25.6 C5 2.64 H5
5.30e PH
1.93 H6
20.6 C6 20.9 C8 1.35f H7 1.16g H8
1.08h H8Ј
3
Ϫ0.04i (470) Ϫ39.6 (210) 142.7 C2 140.5 C4 6.70 H3
6.65 H3Ј
130.5 C3 25.2j C5 4.79k PH 2.91 H5
20.8 C6 10.2 C8 2.66 H5Ј 1.94, H6, H6Ј
1.73l H7 1.52m H7Ј
0.88n H8 0.68o H8Ј
4
5
6
Ϫ7.6p (520) Ϫ34.0 (290) 144.3 C2 141.1 C4 6.63 H3
4.38q PH
1.91 H6
130.6 C3 25.3 C5 2.48 H5
21.1 C6
0.90 H7
Ϫ7.3 (370) Ϫ69.1r (50) 135.1 C4 131.2 C3 7.06-6.89 4.7s PH
129.9 C2 127.5 C1 1.35 H6
30.9 C6
Ϫ9.1 (740) Ϫ43.7 (160) 135.2 C4 133.1 C3 7.12 H4
6.96t H2,3
130.4 C2 127.5 C1 3.82u PH 1.64v H5
17.7 C6
1.11w H6
7
8
9
0.1x (185) Ϫ49.5 (220) 36.3y C1 35.6 C3 4.08 aaPH 1.31ab H2
30.8 C2 29.5 C4 1.09 H4
3.6ac (170) Ϫ43.5 (260) 34.9ad C1 34.5 C3 4.05 PH 1.31ag H2
af
30.6 C2 29.0ae C4 1.06 H4
Ϫ3.4ah (255) Ϫ20.8 (265) 34.1ai C1 28.9 C2 3.60ak PH 1.31al H2
19.3aj C4
1.53am H3 1.10an H4
10 Ϫ2.9 (980) Ϫ18.4 (580) 31.6 C1 30.2 C21 4.07ao PH 1.34 H2
14.4 C4
1.54ap H3 0.90aq H4
11 Ϫ13.1 (450) Ϫ11.8 (370) 32.8 C1 30.2 C2 3.86ar PH 1.35 H2
0.94as H3
a) 1J(31P11B) ϭ 63 Hz; b) d, 3J(31P13C) ϭ 5 Hz; c) m,N ϭ 330 Hz; d) m,N ϭ
200 Hz; e) m,N ϭ 190 Hz; f) m, 3J(1H1H) ϭ 7 Hz; g) d, 3J(1H1H) ϭ 7 Hz;
h) 3J(1H1H) ϭ 7 Hz; i) t, 1J(31P11B) ϭ 73 Hz; j) N ϭ 15.8 Hz; k) N ϭ 270 Hz;
l) m,N ϭ 19 Hz; m) m,N ϭ 21 Hz; n) t, 3J(1H1H) ϭ 6.9 Hz; o) t, 3J(1H1H) ϭ
7.2 Hz; p) t, 1J(31P11B) ϭ 71 Hz; q) N ϭ 386 Hz; r) d, 1J(31P1H) ϭ 214 Hz;
s) d, 1J(31P1H) ϭ 214 Hz; t) m,N ϭ 14 Hz, u) d, 1J(31P1H) ϭ 200 Hz; v) m,N ϭ
21 Hz; w) d, 3J(1H1H) ϭ 6.6 Hz; x) t,t, 1J(31P11B) ϭ 67 Hz; y) d,t, 1J(31P13C) ϭ
17 Hz; aa) m,N ϭ 336 Hz; ab) m,N 16 Hz; ac) t, 1J(31P11B) ϭ 68 Hz; ad) d, t,
1J(31P13C) ϭ 16 Hz; ae) t, 1J(31P13C) ϭ 4.5 Hz; af) N ϭ 442 Hz; ag) N ϭ
15 Hz; ah) t, 1J(31P11B) ϭ 71 Hz; ai) t, 3J(31P13C) ϭ 14 Hz; aj) t, 3J(31P13C) ϭ
7 Hz; ak) 1J(31P1H) ϭ 1365 Hz; al) N ϭ 15 Hz; am) m, 3J(1H1H) ϭ 7.8 Hz;
Amongst the isomers A to F those of C to F can be ex-
cluded for symmetry reasons provided that the B2P2 ring is
planar. This leaves two isomers with C2v symmetry, A and
B as options. Because the X-ray structure of compound 7,
[(Br)tBuB-PhtBu]2, has an all-trans-structure, we will dis-
cuss the NMR data on this basis.
an) d, 3J(1H1H)
ϭ ϭ N ϭ
7.8 Hz; ao) N 380 Hz; ap) m, 18 Hz; aq) t,
3J(1H1H) ϭ 6.5 Hz; ar) N ϭ 216; as) m, N ϭ 23. Hz.
In 7 each boron atom is bonded to two equivalent P
atoms. Therefore the 11B NMR signal should be a 1:2:1
triplet due to 1J(11B31P) coupling. This coupling is observed
for compounds 1, 3 and 4 [1J(11B31P) ϭ 63, 73 and 71 Hz]
but not for 2 although the 11B line width is similar to that
of 1. The 31P nuclei in compound 4 are well shielded. The
smaller the B-organyl group the less shielded are the 31P
nuclei. In case of compounds 5 and 6 the 31P shifts vary
only little from Ϫ40.5 to Ϫ34.0 ppm. The deshielding
corresponds with an increase of the shielding of the PH
proton.
No such coupling is observed for the phenyl derivatives
5 and 6, but is again observed for the tBu-derivatives 7 to
9 [1J(11B31P) ϭ 67, 69, 71 Hz]. However, only broad unre-
solved 11B resonance signals are observed for compounds
10 and 11. Most likely the quadrupolar relaxation is faster
for the methyl and ethyl derivatives than for the others. This
is indicated by the large line width for compound 10
(980 Hz).
The 31P NMR signals are also rather broad due to the
influence of the quadrupole moment of the boron atom.
The 31P atoms of compounds 7 to 11 are deshielded com-
pared with the mesityl and phenyl derivatives, but they are
still in the range expected for tetra-coordinated P atoms
carrying an organyl group [7]. The size of the organyl group
at the boron atoms as well as the different halogen atoms
have only a small effect on the shielding. Due to the large
1
line width the expected doublet due to J(31P1H) could not
1
be observed for all of the new compounds. But with H
1
decoupling the signals sharpened. The H and 31P NMR
spectra of compounds 7 and 11 are characterized by groups
of signals with high asymmetry. They cannot be interpreted
in terms of 1st order coupling. One has to assume that they
are of the type AAЈH9H9ЈXXЈ [8]. Figure 1 shows the sig-
nals for the PH proton of compound 7. There are six lines
which at higher resolution split up into more signals
which is indicated already by the four rather broad lines in
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The corresponding NMR spectra of compounds 8 to 10
are simpler than those of 7 and 11 but still of higher order.
Neighboring tBu groups are in trans-position to one an-
other as shown by the X-ray structure of compound 7 (vide
infra). Those in opposite places are in cis-position corre-
sponding as shown for isomer B. Table 2 contains NMR
data of compounds 12 to 17. As expected one observes only
one 11B NMR signal for the compounds 12 to 15, but one
cannot recognize a trend in the shielding, nor is it possible
to see BP coupling. Each of these four compounds shows
two highly structured 31P resonances. The less shielded 31P
signals are assigned to the ring P atoms as the shifts are
similar to those found for compound 7 to 10. They also
show larger line widths as expected for P atoms that are
bonded to two boron atoms. The better shielded 31P reson-
ances are assigned to the exocyclic P atoms. All 31P signals
of the ring P atoms are highly structured due to coupling
1
Fig. 1 PH area of the H NMR spectrum of compound 7
1
not only to one but to several H atoms. In contrast, the
exocyclic phosphino groups show a triplet of doublet pat-
1
tern in the H coupled spectrum due to the equivalent ring
P atoms and the P bonded H atom. However, a full assign-
ment of all resonance signals was not possible.
The metallated compound 16 shows an 11B NMR signal
which is better shielded by 2.4 ppm compared with the par-
ent compound 12. There is only a single 7Li resonance.
However, instead of two 31P NMR signals three 31P signals
are recorded. The signal at Ϫ7.8 ppm is assigned to the ring
P atoms. It appears as a doublet in the 1H coupled spectrum
[1J(31P1H) ϭ 331 Hz] consistent with the presence of PH
groups. The other two signals at Ϫ92.5 and Ϫ98.9 ppm on
proton decoupling show only marginally sharper signals. So
these P atoms are not bonded to a hydrogen atom. The
high field shift stands in consonance with a higher negative
charge at the P atoms as expected for a P-Li interaction.
The small difference in the shielding points to the con-
clusion that they have a similar but inequivalent electronic
environment. In accord with these two 31P resonances are
Fig. 2 Area of the proton resonance of the tert.-butyl groups
bonded to the P atoms of compound 7.
Figure 1. The tert.-butyl group at the P atoms shows five
resonance lines (Fig. 2).
Table 2 NMR Data of compounds 12 to 17
δ11
B
δ31
P
δ13
C
δ13
C
δ1H
δ1H
c)
e)
f)
12
Ϫ2.6 (140)
P1 -33.9a) (435)
P2 -51.1b) 285)
35.1 C3
32.6 C5
29.8 C
33.3 d)
4.71 P1H
4.63 P2H
1.37 H4,6
g)
30.0 C8
1.07 H8
1.04 H10
30.0b) C8
13
14
15
16
Ϫ0.6 (225)
Ϫ12.4 (195)
Ϫ8,4 (280)
Ϫ5.0 (145)
Ϫ3.6 (460) P1
Ϫ3.4 (310) P2
Ϫ51.9(410) P1
Ϫ70.1 (385) P2
Ϫ46.8 (535) P1
Ϫ54.5 (490) P2
Ϫ7.8 (175) P1 i)
Ϫ92.5 (200 Hz) P2
Ϫ98.9 (210 Hz P3
29.88 C11
n)
o)
35.32 k) C8
35.01 C4
33.18 C7
15.0 CH3CH2
Ϫ13.1 (260) P2
35.28 l)
33.27 C9
31.86 C5
66.3 CH2O
6
6.06 P1H
1.58 H9
1.54 H7
m)
p)
1.51 H5
1.42 H11
q)
r)
3.01 CH2O
0.96 MeCH2
t)
17
Ϫ8.4 (175)
Ϫ29.7 s) (380) P1
4.74 PH
1.38 H4
1.04 H8
u)
1.49 H6
a) m,N ϭ 290 Hz; b) tdt 2J(31P31P) ϭ 116 Hz, 1J(31P1H) ϭ 360 Hz; c) d, 1J(31P13C) ϭ 17 Hz; d) m.N, 1J(31P13C) ϭ 17 Hz; e) d, 1J(31P13C) ϭ 11 Hz; f) m.N ϭ 780 Hz,
g) m,N ϭ 242 Hz; h) m,N ϭ 90 Hz; i) d, 1J(31P1H) ϭ 331 Hz; k) d, 1J(31P13C) ϭ 12.3 Hz; l) d, 1J(31P13C) ϭ 12.1; m) d, 1J(31P13C) ϭ 14.0 Hz; n) d, 1J(31P1H) ϭ
331 Hz; o) d, 3J(31P1H) ϭ 2.2 Hz; q) d, 3J(31P1H) ϭ 1.7 Hz; r) q, 3J(1H1H) ϭ 6.9 Hz; r) t, 3J(1H1H) ϭ 6.9 Hz; s) significant broadening in the undecoupled spectrum;
t) dd, 1J(31P1H) ϭ 339 Hz; u) d, 1J(31P1H) ϭ 11.0 Hz.
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Z. Anorg. Allg. Chem. 2007, 917Ϫ926

Dimeric Phosphinoboranes [RЈ(Hal)B-PHR]2
Scheme 2 Fragments observed in the mass spectrum of compound 2
Scheme 1 Fragments observed in the mass spectrum of compound 1
a spectrum of higher order with m, N ϭ 21 Hz, while a
two sets of 1H signals for two non equivalent P-tBu groups.
It may well be that a steric effect which is to be expected
for a tBuP[Li(OEt2)2] group, which is rather bulky, may be
responsible for the somewhat different environments. In the
1H NMR spectrum the signals for two of the tBu groups
doublet is recorded for its Me groups.
1
In contrast, all H and 13C NMR spectra of the tbutyl-
phosphinoborane species 8 to 12 are of first order. Its 11B
signals span the range from 0.1 to Ϫ13.1 ppm. The largest
difference of 10.2 ppm is observed between 11 and 12. The
shielding of the 31P nuclei shifts to lower field as the B-
organyl groups become smaller. The halogen atom does not
significantly influence δ11B.
3
appear as doublets due to J(31P1H) ϭ 2.2 and 1.7 Hz. PH
coupling is also observed with the CH2 and CH3 protons
of the ligand diethyl ether. The 13C NMR spectra show four
Due to the relatively sharp 31P resonance signals the 11B
NMR signals of compounds 7 to 9 appear as triplets with
1J(31P11B) ϭ 67, 68, and 171 Hz. However, this coupling is
not found for the ethyl and methyl compounds as the line
widths of the 11B NMR signals are in the order of 900 Hz.
Also, the 31P NMR signals are rather broad with 580 Hz
for 11 and 370 Hz for 12.
1
different tBu groups, and J(31P13C) ϭ 13 Hz is observed
for the ipso-C atoms.
The bicyclic system 17 exhibits a signal at Ϫ8.4 ppm in
the 11B NMR spectrum. This corresponds with a better
shielding of 5.8 ppm compared to the starting material 12.
As expected for the suggested structure of compound 17,
one observes two 31P NMR signals. That at Ϫ29.7 ppm is
assigned to the tetra-coordinated P atoms since it is sharper
in the 1H decoupled spectrum. The other signal at
Ϫ13.1 ppm remains unaffected and it is assigned to the tri-
1
Finally, the H NMR spectra of the P-phenylphosphino
derivatives show simple doublets for the PH proton with
1J(31P1H) ϭ 200 Hz for both compounds. While no 31P1H
coupling was observed for the Me protons of 5 there is a
1
coordinate P atom. The signal of the PH proton in the H-
1
doublet for the Me groups in 6. On the other hand, the H
NMR spectrum appears as a doublet of doublets due to the
coupling with two different types of P atoms [9].
NMR signal of the CH group is of higher order with m,
1H decoupling leads to significantly sharper 31P NMR
N
ϭ 21 Hz. Power et al. reported for compound
[mes2BPHPh]2 a coupling constant J(31P1H) of 254 Hz [7].
For the bromides 7, 8, and 11 the 31P nucleus is continu-
ously deshielded the smaller the B-organyl group. Replace-
ment of Br by Cl leads also to a deshielding. The broad
resonance lines (h1/2 ϭ 220 to 580 Hz) prevent the detection
of PH coupling. The 31P signals get sharper (50Ϫ100 Hz)
on proton decoupling.
1
1
signals. The corresponding H-NMR spectrum appears as
part of an AAЈXXЈ spectrum, the AAЈ spectrum must co-
incide. For compounds 4 and 5 the following data are valid:
2
4
4: N ϭ 190 Hz; J(31P31P) ϭ 429 Hz, J(1H1H) ϭ ϳ0 Hz;
1J(31P1H) ϭ ϩ335 Hz, J(31P1H) ϭ Ϫ Hz, m, N ϭ 330 Hz.
3
The data for compound 5 are: 2J(31P31P) ϭ 412 Hz,
4J(1H1H) ϭ ϳ0 Hz; 1J(31P1H) ϭ ϩ217 Hz, 3J(31P1H) ϭ
Ϫ6 Hz, m, M, N ϭ 190 Hz. Larger m, N values are found
in the 31P NMR spectra of compounds 6 and 7.
Mass Spectra
The H and the 13C NMR spectra of 2 show only one
1
signal for the CH groups of the iPr substituent but two sets
of doublets for its Me groups with J(H,H) ϭ 7.0 Hz. This
For compounds 1, 2 and 4 no parent peak could be detected
in the 70 eV mass spectra, and for compound 3 it shows
up with only 3 % relative intensity. The base peak is either
RBHalϩ (2 and 4), M/2ϩ (3) or tBuBPmesϩ (1). However,
all mass spectra of compounds 1 to 4 show the M/2 cation.
In case of compound 1 this M/2 fragment loses HBr to
produce tBuBPmes.ϩ. Loss of the tBu group from mesHP-
B(Hal)tBu.ϩ generates mesHPϭBBrϩ. Other fragments are
shown in Scheme 1. No mesPϭBRϩ peak appears in the
mass spectra of compounds 2 Ϫ 4. In case of 2 and 4 BP
3
suggests hindered rotation about the B-C bond. The same
1
is true for the Et groups of compound 3. There are two H
NMR signals for the CH2 groups and both of them are
multiplets with m,N ϭ 19 and 21 Hz, respectively, as well
as two triplets for the Me groups (J ϭ 2.9 and 7.2 Hz). This
indicates to the presence of 3J(31P1H). This kind of coupling
1
is also observed for [iPr(Br)B-PHPh2] (6). The H NMR
signal of the CH moiety does not show a simple septet but
Z. Anorg. Allg. Chem. 2007, 917Ϫ926
 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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921

R. Jetzfellner, H. Nöth, R. T. Paine
Scheme 5 Fragments observed in the mass spectrum of compound 5
Scheme 3 Fragments observed in the mass spectrum of compound 3
Scheme 6 Fragments observed in the mass spectrum of compound 7
Scheme 4 Fragment observed in the mass spectrum of compound 4
cleavage leads to the fragment RBBrϩ, and isoprene elimin-
ation from the M/2 cation generates H(Br)B-PHmesϩ
(89 %) in case of compound 2, but the loss of a mesityl
radical to produce iPr(Br)BϭPHϩ (60 %) is less favoured
than the loss of the mesPH group to generate the PrBBr
cation.
The parent peak M.ϩ is present in case of the phenyl
compound 6 (7 %) but is absent for 5. The four membered
B2P2 rings stay partly intact for compounds 5 and 6. They
lose an alkyl radical by B-C bond cleavage. However, apart
from this fragmentation it seems logical that the tBu.ϩ and
iPr.ϩ radical cations (100 % relative intensity). are generated
by loss of neutral B2P2Br2H2R fragments. Typical is also
the appearance of BrBϭPHPhϩ (17 % for 5, 31 % for 6)
(see scheme 6).
Scheme 7 Fragments in the mass spectrum of compound 12
Moreover, M/2ϩ is also recorded (7 Ϫ 34 %), as well as
the formation of RBHalϩ. Scheme 6 depicts the observed
fragments for compound 7.
Fragments that are observed in the mass spectrum of the
bicyclic compound 17 are shown in Scheme 8. The parent
peak M.ϩ is present in a 19 % relative intensity. Typical is
the loss of tBu radicals with formation of peaks at m/z ϭ
The parent peak M.ϩ is observed in the mass spectra of
compounds [tBu(H)P-B(Hal)R]2 (3 Ϫ 33 % rel. intensity).
922
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Z. Anorg. Allg. Chem. 2007, 917Ϫ926

Dimeric Phosphinoboranes [RЈ(Hal)B-PHR]2
Fig. 3 Molecular structure of 7. Thermal ellipsoids are depicted
on 25 % probability level.
Scheme 8 Fragments in the mass spectrum of compound 17
˚
Selected bond lengths (in A): P1-B1 2.023(6), P1-B2 2.029(6), B1-P2
2.028(6), B2-P2 2.031(6), P1-C1 1.886(5), P2-C5 1.870(5), B1-C9 1.609(8),
B1-Br1 2.036(6), B2-Br2 2.038(6), P1-H1 1.25(4), P2-H2 1.18(4). Ϫ Selected
bond angles (in °): B1-P1-B2 93.45(2), P1-B2-P2 86.5(2), B2-P2-B1 93.3(2),
P1-B1-P2 86.7(2), P1-B1-C9 117.9(4), Br1-B1-P2 110.0(4), C9-B1-Br1
112.1(4), C13-B2-Br2 111.6(4), Br2-B2-P1 109.7(4), Br2-B2-P2 109.4(4), Br2-
B2-C13 111.6(4), C5-P2-B2 123.4(4), H1-P1-B1 107,H1-P1 B2 102, H1-P1-
C1 104.4(7), H2-P2-B1 110.7(7), H2-P2-B2 107.7(7), H2-P2-C6 97.7(7). Ϫ
Interplanar angles/°: B2P2/ P1H1C1 86.7, B2P2/H2P2C5 88.5, H1P1C11/
P2H2C5 4.4; B2P2/Br1B1C4 90.0; Br1B1C9/P2H2C5 90.7, Br1B1C0/
P1H1C1 86.7. Ϫ Torsion angles: C1-P1-B1-C9 106.3, C1-P1-B2-C13 -104.3,
Br1-B1-P1-H1 -146.3, H2-P2-B2-C13 -8.0, H2-P2-B2-Br2 -137.7, H2-P2-B1-
Br1 139.5.
345 (61 %) and m/z ϭ 288 (66 %). The loss of a tBuPH
radical from M.ϩ generates a species with m/z ϭ 314
(100 %) which breaks apart into tBu(H)PϭBtBu.ϩ and
tBu(H)PϭBtBu.
In summary: the parent radical cations are either not ob-
served at all or at a very low intensity level in contrast to
M/2.ϩ fragments which are formed by loss of the neutral
phosphinoborane RЈ(H)P-B(Hal)R. But also boraphos-
phene radical fragments RBϭPRЈ.ϩ are formed, and this
shows that the BP bond is not generally readily broken.
Lewis-acidity of the boron atom by introducing substitu-
ents X which are capable of π-bonding [21]. In this respect,
amino groups are most effective, and indeed, most of the
monomeric phosphinoboranes are phosphino-amino-bor-
anes [2]. However, dimerization can also be prevented by
introducing bulky organyl groups at the P atom, like the
mesityl group, or the tBu group [2, 22, 23]. Previously re-
ported dimeric phosphinoboranes are of type [R2P-BX2]2,
X ϭ H, Cl, Br, I, Me [3Ϫ5]. Typical examples that are struc-
turally characterized are [Ph2P-BI2]2 [24] or [tBu2P-
B(H)secBu]2 [20]. The posphinoborane Me2P-BH2 forms
either six-membered trimers [Me2P-BH2]3 [25] or eight-
membered tetramers [Me2P-BH2]4 [26]. The influence of
steric effects is nicely demonstrated by comparing the com-
pounds [Ph2B-P(H)tBu]2 with mes2B-P(H)tBu [12], and in-
deed, most of the organylphosphino-dimesitylboranes are
monomeric [23] which demonstrates the influence of steric
effects. On the other hand, the present study shows that a
single mesityl group at the phosphorus atom is insufficient
to prevent dimerization of compounds of type Mes(H)P-
B(Hal)R even by introduction of a tBu group at the boron
atom. The presence of a BHal group (Hal ϭ Cl, Br) in-
creases the Lewis acidity of the boron center which in turn
favors the dimeric interaction. From this point of view one
can also understand that the phosphinoboranes Ph(H)P-
B(Hal)R, tBu(H)P-P(Hal)R are dimeric.
X-Ray Structure
Figure 3 shows the molecular structure of compound 7. The
monoclinic crystals were obtained from hexane solution.
The four membered B2P2 ring is planar, and the B-P bond
lengths are equal within standard deviations [aver.
˚
2.026(6) A]. Adjacent tBu groups are in trans-position, the
two bromine atoms are arranged in syn-positions as are the
hydrogen atoms of the PH groups. The B-C bond lengths
(1.622(8) and 1.609(8) A) correspond with B-C-single bond
lengths to tetra-coordinated boron atoms (1.59 Ϫ 1.65 A)
[10Ϫ12]. Although the P-C bond lengths are slightly differ-
ent [1.886(5) and 1.870(5) A] they fit into the range for P-
C bond lengths found for alkyl and aryl P bonds to tetra-
˚
˚
˚
˚
coordinated P atoms (1.826 Ϫ 1.868 A, PCalkyl] [10, 13Ϫ15];
˚
(1.76Ϫ1.89 A, PCaryl) [10, 16Ϫ19]. Moreover, the B-Br
bond lengths are similar to other B-Br bonds found for bro-
mine atoms attached to tetra-coordinated B atoms [B-Br:
˚
2.02Ϫ2.07 A] [11, 20].
The P-B-P bond angles are smaller (86.8°) than the B-P-
B bond angles (93.4°). As expected, the C-B-Br bond angles
(aver. 111.8°) are larger than the H-P-C bond angles (104.4,
97.7°). The point group symmetry of the molecule is slightly
distorted C2v.
Discussion
Although in most cases the 1:1 reactions of LiPHR with
RBHal2 give good to excellent yields of the dimeric species
[R(H)P-B(Hal)R]2, we also observed only in case of
Most phosphinoboranes of type R2P-BX2 are dimeric
[3Ϫ5], but one can prevent dimerization by reducing the
Z. Anorg. Allg. Chem. 2007, 917Ϫ926
 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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923

R. Jetzfellner, H. Nöth, R. T. Paine
fraction: Siemens P4 four circle diffractometer equipped with an
area detector and a low temperature device; MoKα radiation,
graphite monochromator. IR: Perkin-Elmer 325, NMR: Bruker
ACP200, Jeol FX 400; MS: Varian Atlas CH-7. The peaks showed
the correct isotope distribution. Mass numbers are quoted for the
[mes(H)P-B(Br)Me]2 small amounts of [mesP-BMe]3,
δ11B ϭ 59.0 [27]. This shows that LiPHR acts as a dehydro-
halogenating agent as has been observed with mesitylphos-
phinoboranes [28]. In contrast, the phenyl compounds
[PhHP-B(Hal)R] do not react with an excess of LiPHPh or
other bases such as NaN(SiMe3)2 either by dehydrohal-
ogenation or substitution. Furthermore, compound
[tBu(H)P-B(Hal)tBu]2 reacts neither at room temperature
nor at 50 °C with a second equivalent of LiPHtBu. The
substitution of the halogen atoms occurs, however, slowly
in refluxing hexane. This generates the dimeric bis(tert.-bu-
tylphosphino)-tert.-butylboranes 12 Ϫ 15 although com-
pounds 13 to 15 were not isolated in a pure state. Com-
pound 12 can be deprotonated with LiPHtBu at the ex-
ocyclic P atoms to generate the dilithium salt 16. As has
been demonstrated by Power and our group [2, 12, 29] P-
lithiophosphinoboranes not only have interesting structures
but are also useful reagents. Therefore, further studies of
the reactivity of 16 will surely lead to a number of interest-
ing new B-P compounds.
1
isotopes H, 11B, 12C, 31P, 35Cl, 79Br.
1,3-Dimesityl-2,4-di-tert.-butyl-2,4-dibromo-1,3,2,4-diphosphadi-
boracyclobutane, (1): Starting materials: tBuBBr2: 0.48 g
(2.1 mmol); LiPHmes: 0.33 g (2.1 mmol). Insoluble product (LiBr):
0.26 g. Raw product: 0.52 g of a yellow powder. Colorless crystals
of 1 from hexane at Ϫ30 °C. Yield: 0.38 g (61 %); m. p. 86Ϫ88 °C.
C26H42B2Br2P2 (598.02): calc. C 52.22, H 7.08, Br 26.72; found C
51.43, H 7.02, Br 26.51 %.
IR /cmϪ1: ν ϭ 3022 w, 2964 st, 2929 st, 2893 m, 2857 st, 2706 w, 2425 m,
1735 w, 1604 st, 1560 w, 1467 st, 1459 m, 1445 st, 1307 w, 1387 w, 1378 st,
1358 m, 1297 st, 1271 m, 1249 w, 1218 w, 1202 w, 1182 w, 1156 w, 1101 w,
1028 m, 1013 st, 993 w, 956 m, 933 w, 908 m, 886 w, 852 st, 821 st,766 m,
720 m, 711 st, 702 m, 647 w, 632 w, 600 st, 568 w, 547 st, 538 w, 516 w, 495 w,
471 w, 452 w, 413 w, 372 m, 312 w.
1.3-Dimesityl-2,4-dibromo-2,4-diisopropyl-1,3,2,4-diphosphadi-
boracyclobutane, (2): Starting materials: iPrBBr2: 0.351 g
(1.64 mmol); LiPHmes: 0.330 g (1.64 mmol). Colorless insoluble
product (LiBr): 0.16 g. Raw product: 0.38 g of a slightly yellow oil.
Colorless crystals from hexane at Ϫ30 °C. Yield: 0.25 g (50 %); m.
p. 88Ϫ91 °C.
The molecular structure of compound 7 is similar to
compound [tBu2P-B(H)secBu]2 [17] except that it has C2v
symmetry and not Ci symmetry as observed for the latter
compound. The B-P bond lengths of 7 are on average
˚
˚
C24H38B2Br2P2 (569.93): calc. C 50.58, H 6.72, Br 28.04; found C
49.11, H 6.87, Br 28.38 %.
IR (Nujol, Hostaflon) /cmϪ1: ν ϭ 3029 w, 2957 st, 2943 st, 2920 m, 2888 m,
2862 st, 2416 m, 2367 w, 2341 w, 2312 w, 1604 st, 1560 w, 1466 m, 1452 st,
1410 m, 1378 st, 1359 w, 1295 m, 1270 w, 1250 w, 1165 w, 1079 w, 1044 st,
1026 m, 967 m, 950 m, 920 w, 883 m, 848 st, 823 m, 719 st, 690 m, 656 w,
604 st, 569 w, 546 st, 454 w, 438 w, 419 w, 384 st, 380 st, 332 w, 307 w, 285 w.
2.028 A. They are 0.015 A longer than in compound
[tBu2P-B(H)secBu]2. This falls into line with [Cl2B-
˚
˚
P(SiMe3)2]2 [2.025(3) A] and [Br2B-P(SiMe3)2]2 [2.03(1) A]
[30]. However, the P-C bond lengths of 7 are shorter (aver.
˚
1.878 A) than those of compound [tBu2P-B(H)secBu]2
˚
(aver. 1.903 A), but the B-C bonds are longer (aver. 1.665
˚
vs. 1.581 A). Exocyclic bond angles are rather similar for
1,3-Dimesityl-2,4-dichloro-2,4-diethyl-1,3,2,4-diphosphadiboracyclo-
butane, (3): Starting materials: EtBCl2: 0.26 g (2.4 mmol);
LiPHmes: 0.37 g (2.4 mmol). Insoluble LiCl : 0.12 g. Raw product:
0.49 g as a yellow oil. Crystallization from hexane yielded a slightly
yellow solid. Yield: 0.28 g (53 %), m. p. 122Ϫ125 °C.
both compounds. The shortening of the B-P bonds is most
likely the consequence of the inductive effect of the Br
atoms.
Surely the most interesting compound reported here is
the bicyclic triphosphinodiborane 17. Unfortunately no
crystal structure is yet available, but NMR and mass spectra
point to a bicyclic structure. In this respect its structure is
akin to the bicyclic diphosphatriboranes P2(BR)3 [2,
31Ϫ34]. This compound as well as the bis(lithium-tert.-
butyl-phosphido) diphosphadiboracyclobutane offer them-
selves as reagents for developing new areas of phosphino-
borane chemistry.
C22H34B2Cl2P2 (452.98): calc. C 58.33, H 7.57, Cl 15.65; found C
59.49, H 8.01 Cl 14.83 %.
IR (Nujol, Hostaflon) /cmϪ1: ν ϭ 3026 m, 2958 st, 2928 st, 2875 st, 2731 w,
2407 m, 2369 w, 2327 w, 2309 m, 1732 w, 1605 st, 1560 m, 1454 st, 1414 m,
1378 m, 1296 m, 1271 w, 1249 w. 1081 w, 1031 st, 1009 m, 968 w, 952 w,
896 w, 850 st, 777 m, 761 w, 720 m, 696 w, 624 w, 609 w, 565 w, 549 st, 516 w,
478 m, 437 w, 389 w, 378 m.
1,3-Dimesityl-2,4-dibromo-2,4-dimethyl-1,3,2,4-diphosphadibora-
cyclobutane, (4): Starting materials: MeBBr2: 0.36 g (1.9 mmol);
LiPHmes: 0.31 g (1.9 mmol). White insoluble product [LiBr with
some (MeBO)3]: 0.20 g. Raw material: 0.5 g of a yellow oil. Crystal-
lisation yielded no pure compound 4. Yield: 0.18 g. m. p. 68Ϫ72 °C.
Experimental Section
General procedure: A solution of the organylboron dihalides in hex-
ane (20 ml for each mmol of the halide) is placed in a 100 ml two
necked flask fitted with a nitrogen inlet, a dropping funnel, a reflux
condensor and a magnetic stirring bar. After cooling to Ϫ45 °C
the lithium organylphosphide, suspended in hexane (15 ml for each
mmol of LiPHR), is added. After addition the stirred suspension
is allowed to attain room temperature. Stirring is continued for 2
to 4 hours. Then the solid is removed by filtration and the filtrate
checked by NMR for completion of the reaction. The hexane is
then removed in vacuo, the residue dissolved in a small amount of
hexane, and after cooling to Ϫ25 °C set aside for crystallization.
All IR spectra were recorded as Nujol/Hostaflon mulls. X-ray dif-
C20H30B2Br2P2: (513.85) calc. C 46.75, H 5.88; found C 57.49, H
7.73 %. These data show that the product is impure 4.
1,3-Diphenylphosphino-2,4-dibromo-2,4-di-tert.butyl-1,3,2,4-diphos-
phadiboracyclobutane, (5): Starting materials: tBuBBr2: 0.23 g
(1.0 mmol); LiPHPh: 0.11 g (1.0 mmol). Yellow insoluble solid:
0.14 g. Raw product: 0.30 g of a yellow oil. On attempted crystalli-
zation: 80 mg of a microcrystalline product slightly contaminated
with another boron compound. Yield 31 %, m. p. 89Ϫ92 °C.
C20H30B2Br2P2 (513.82): calc. Br 31.10; found Br 29.88 %.
IR /cmϪ1: ν ϭ 3046 m, 2950 st, 2853 st, 2358 w, 2331 m, 2296 m, 1955 w,
1648 w, 1607 w, 1583 m, 1480 m, 1465 st, 1436 st, 1377 st, 1358 m, 1306 w,
924
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Z. Anorg. Allg. Chem. 2007, 917Ϫ926

Dimeric Phosphinoboranes [RЈ(Hal)B-PHR]2
1266 m, 1173 w, 1156 w, 1135 m, 1118 m, 1070 m, 1026 w, 1001 w, 947 m,
814 w, 739 st, 694 st, 609 w, 583 m, 426 w, 363 w.
C16H38B2Cl2P2 (384.97): Calc. C 49.92, H 9.95, Cl 18.42; found C
51.17, H 10.20, Cl 18.12 %.
IR /cmϪ1: ν ϭ 3002 w, 2963 st, 2936 st, 2901 m, 2857 st, 2355 st, 1475 m,
1465 st, 1446 w, 1388 w, 1367 m, 1284 w, 1175 st, 1034 m, 1016 m, 961 w,
943 w, 913 w, 854 w, 842 m, 813 m, 784 w, 764 w, 693 w, 680 m, 585 w, 499 w,
484 w, 424 m, 200 w, 376 w, 366 w.
1,3-Diphenyl-2,4-dibromo-2,4-diisopropyl-1,3,2,4-diphosphadibora-
cyclobutane, (6): Starting materials: iPrBBr2: 0.270 g (1.26 mmol);
LiPHPh: 0.15 g (1.26 mmol). Insoluble product: 0.23 g; Raw
product: 0.35 g. Treatment of the white powder with hexane (2 x
3 ml) removed not all adhered PhPH2 (NMR). Yield of 6: 70 mg
(24 %), m.p. 82Ϫ86 °C.
1.2,3,4-Tetra(tert.-butyl)-2,4-di(tert.-butylphosphino)-1,3,2,4-di-
phosphadiboracyclobutane, (12): Starting materials: tBuBCl2: 0.35 g
(2.5 mmol); LiPHtBu: 0.48 g (5.0 mmol).The reaction mixture is
kept at reflux for 20 h. Insoluble product: 0.26 g of a white solid.
Crystals from hexane at Ϫ25 °C. Yield: 20 mg (68 %); m.p.
214 °C dec.
C18H26B2Br2P2 (485.80): calc. Br 32.89; found Br 31.95 %.
IR /cmϪ1: ν ϭ 3054 m, 3020 w, 2926 st, 2859 st, 2359 w, 2294 m, 1885 w,
1582 m, 1495 w, 1482 m, 1462 m, 1436 st, 1378 m, 1328 w, 1268 w, 1185 w,
1157 w, 1102 m, 1070 m, 1000 w, 965 w, 917 m, 902 w, 849 w, 738 st, 694 w,
617 w, 497 w, 482 m, 464 m, 411 w, 399 w.
C24H58B2P4 (492.25): calc. C 58.56, H 11.88; found C 57.32, H
11.48 %.
IR /cmϪ1: ν ϭ 2943 m, 2927 st, 2885 st, 2851 st, 2343 m, 1785 w, 1463 st,
1400 w, 1381 m, 1353 m, 1354 st, 1261 m, 1209 w, 1175 w, 1164 m, 1092 w,
1040 w, 1029 st, 1017 m, 959 m, 945 m, 922 st, 915 w, 874 w, 807 w, 709 w,
684 w, 662 w, 601 w, 578 m, 563 w, 447 w, 428 w, 386 w, 332 w.
1,3-Di-(tert.butyl)-2,4-dibromo-2,4-di-tert.butyl)-1,3,2,4-diphospha-
diboracyclobutane, (7): Starting materials: tBuBBr2: 0.37 g
(1.62 mmol); LiPHtBu: 0.16 g (1.62 mmol). Insoluble product:
160 mg. Raw product: colorless oil, 400 mg. 560 mg (73 %) color-
less crystals from hexane at Ϫ16 °C, m. p. 163Ϫ165 °C.
1,2,3,4-Tetra(tert.-butyl)-2,4-di(lithio-tert.-butylphosphino)-
1,3,2,4-diphosphadiboracyclobutane-tetra(diethyl ether), (16): Start-
ing materials: tBuBCl2: 0.27 g (1.9 mmol); LiPHtBu: 0.56 g
(5.8 mmol). The reaction was started at Ϫ40 °C by dropping a solu-
tion of tBuBCl2 into the suspension of the phosphide in hexane/
diethyl ether (1:1). A yellow orange solid formed slowly. Stirring
was continued at Ϫ15 °C. Insoluble solid: 200 mg. Raw product:
510 mg of a yellow orange solid. Two crystallization from hexane
(Ϫ25°) yielded colorless crystals of 16. Yield: 300 mg (38 %); dec.
> 160 °C.
C16H38B2Br2P2 (473.86): calc. C 40.56, H 8.08, Br 33.72; found C
41.14, H 8.30, Br 33.62 %.
IR /cmϪ1: ν ϭ 3005 w, 2956 st, 2935 st, 2898 m, 2856 st, 2736 w, 2726 w,
2705 w, 2351 st, 1474 m, 1460 w, 1440 w, 1396 w, 1388 m, 1366 m, 1206 w,
1171 st, 1034 m, 1016 m, 963 w, 941 m, 911 m, 859 w, 850 m, 813 st, 776 w,
766 w, 739 st, 722 st, 705 m, 680 m, 604 w, 581 m, 546 w, 534 w, 494 w, 429 m,
399 m, 381 w, 355 m, 340 w, 320 w.
1,3-Di-(tert.butyl)-2,4-dibromo-2,4-diisopropyl-1,3,2,4-diphospha-
diboracyclobutane, (8): Starting materials: iPrBBr2: 0.38 g
(1.78 mmol); LiPHtBu: 0.172 g (1.78 mmol). Insoluble product:
0.16 g. Raw product: 450 mg of a light yellow oil. Slightly yellow
crystals from hexane at Ϫ25 °C. Yield: 260 mg (67 %); m. p.
102Ϫ104 °C.
C40H96O4B2Li2P4 (800.59): calc. C 60.01, H 12.09; found C 59.03,
H 12.24 %.
IR /cmϪ1: ν ϭ 2946 m, 2927 st, 2886 st, 2852 st, 2694 w, 2413 w, 2344 m,
1784 w, 1464 st, 1392 w, 1381 m, 1363 w, 1354 st, 1261 m, 1210 m, 1180 w,
1165 m, 1097 w, 1041 w, 1029 st, 1016 w, 959 m, 946 m, 929 m, 916 w, 894 w,
868 w, 809 w, 710 w, 667 w, 578 w. 562 w, 480 w, 447 w, 429 w, 404 w.
C14H34B2Br2P2 (445.79): calc.: C 37.72, H 7.69, Br 35.85; found C
38.17, H 7.76, Br 35.84 %.
IR /cmϪ1: ν ϭ 3047 w, 2948 st, 2926 st, 2903 m, 2864 st, 2824 m, 2784 w,
2514 w, 2362 m, 2343 st, 2301 w, 2184 w, 1460 st, 1392 m, 1379 st, 1365st,
1289 m, 1271 w, 1206 m, 1182 st, 1117 w, 1102 w, 1083 w, 1039 st, 1029 st,
1018 m, 946 m, 887 w, 862 m, 849 st, 813 m, 742 m, 702 st, 662 w, 616 w,
591 m, 489 w, 437 w, 405 st, 391 w, 315 w.
1,2,3,4,5-Penta(tert.butyl)-1,3,5,2,4-triphosphadibora-bicyclo-
[1.1.1]pentane, (17): A stirred solution of 12 (200 mg, 0.41 mmol)
dissolved in benzene (50 ml) is irradiated at 15 °C with a Hg vapor
lamp (Hanovia S200W) for 6 h. The solution adopted slowly a
bright yellow color. The solvent was evaporated in vacuo. The evap-
orate contained tert.-butylphosphane (NMR). Crystallization of
the residue from a hexane/toluene mixture at Ϫ20 °C rendered a
colorless microcrystalline solid. Yield: 30 mg (18 %), m. p.
186Ϫ189 °C. Due to the small amount of 17 the compound was
only characterized by its NMR and mass spectrum.
1,3-Di-(tert.butyl)-2,4-dichloro-2,4-diethyl-1,3,2,4-diphophadibora-
cyclobutane, (9): Starting materials: EtBCl2: 0.22 g (2.0 mmol);
LiPHtBu: 0.19 g (2.0 mmol). Insoluble product: 200 mg of an
orange solid. Raw product: orange oil from which no crystals could
be obtained in attempts to crystallize from various solvents. The
product decomposes above 120 °C. Yield: 140 mg (43 %) (as deter-
mined from NMR spectra after substracting the signals of by-prod-
ucts. The compound was only characterized by NMR and mass
spectra.
X-ray Structure Determination
A suitable crystal of 7 was selected from crystals covered with a
perfluoro ether oil, fixed on a glass fibre and mounted on the goni-
ometer head which was flushed with cold nitrogen gas (Ϫ80 °C).
The cell constants were determined from the reflections on 5 differ-
ent sets of 15 frames, using the program SMART [35]. Data collec-
tion was performed in the hemisphere mode of the program
SMART with exposure times of 5s per/frame. Reflections on a total
of 1200 frames were collected and reduced by applying the program
SAINT. The programme SADABS [35] was used for absorption
correction. Solution of the structure and refinement were per-
formed with the SHELXTL programs [36]. The positions of PH
hydrogen atoms are obtained from the difference Fourier map and
were freely refined. This led to too short PH distances. Their ther-
1,3-Di-(tert.-butyl)-2,4-dibromo-2,4-dimethyl-1,3,2,4-diphosphadi-
boracyclobutane-tetra(diethyl ether), (10): Starting materials:
MeBBr2: 0.33 g (1.8 mmol); LiPHtBu: 0.172 g (1.8 mmol). Insol-
uble product: 0.21 g, yellow solid. Raw product: yellow oil (10 with
impurities). Yield: 170 mg. Characterization only by NMR.
1,2-Di-(tert.-butyl)-2,4-dichloro-2,4-di-tert.-butyl-1,3,2,4-diphos-
phadiboracyclobutane, (11): Starting materials: tBuBCl2: 0.21 g
(2.2 mmol); LiPHtBu: 0.30 g (2.2 mmol). Insoluble product: 0.11 g
of a yellows solid. Raw product: yellowish oil: 490 mg. Colorless
crystals from hexane at Ϫ30 °C. Yield: 300 mg (71 %); m. p.
122Ϫ123 °C.
Z. Anorg. Allg. Chem. 2007, 917Ϫ926
 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
925

R. Jetzfellner, H. Nöth, R. T. Paine
mal parameters showed no anomaly, and there were no other re-
sidual peaks close to these atoms. Although most of the positions
of the other H atoms were found in the difference map they were
placed in calculated positions and refined by applying a riding
model. Relevant crystallographic data and data related to data col-
lection and structure solution are summarized in Table 3. Ad-
ditional information on the structure solution is deposited with the
Crystallographic Data Centre, Cambridge, and can be obtained
free of charge by quoting the CSD-number 639523.
[5] D. A. Armitage, Inorganic Rings and Cages, E. Arnold Publ.
1972, 109.
[6] R. Jetzfellner, H. Nöth, R. T. Paine, Z. Anorg. Allg. Chem.
2007, 633, 548.
[ 7 ] P. P. Powe r, Angew. Chem. 1990, 102, 527; Angew. Chem. Int.
Ed. Engl. 1990, 29, 481.
[8] Detailed simulations have not been attempted since they
would require a computer programme capable of handling a
22 spin system (Dr. K. Karaghiosoff, Dr. D. Stevenson).
[9] Due to the small quantity of the compound the 13C NMR
spectrum was not be recorded.
[10] D. Scheschkewitz, H. Amil, H. Gornitza, W. W. Schoeller, D.
Bourissou, G. Bertrand, Angew. Chem. 2004, 116, 595; Angew.
Chem. Int. Ed. 2004, 43, 585.
Table 3 Crystal Data and Data Collection Parameters
Compound
7
[11] H. Amil, L. Kranicar, H. Gornitzki, D. Bourissou, G. Ber-
Chem. formula
Form. wght
C8H19BBrP
236.92
0.28 ϫ 0.32 ϫ 0.35
monoclinic
P21 /c
10.481(2)
13.927(3)
15.752(4)
96.17(1)
2286.0(9)
8
1.377
3.682
976
trand, J. Am. Chem. Soc. 2004, 126, 1344.
[12] R. A. Bartlett, H. V. R. Dias, X. Feng, P. P. Power, J. Am.
Chem. Soc. 1989, 111, 1306.
[13] S. J. Lancaster, A. J. Mountford, D. L. Hughes, M. Schor-
mann, M. Bochmann, J. Organomet. Chem. 2003, 680, 193.
[14] F. C. Alyea, A. Costin, G. Ferguson, G. T. Frey, R. G Goel,
R. J. Restivo, J. Chem. Soc. Dalton Trans. 1975, 1294.
[15] D. L. Thorn, J. C. Calabrese, J. Organomet. Chem. 1984,
272, 283.
Cryst. size /mm
Cryst. system
Space group
˚
a /A
˚
b /A
˚
c /A
β /°
3
˚
V /A
Z
ρ(calcd.) /Mg/m3
µ /mmϪ1
[16] P. Mura, J. Coord. Chem. 1999, 48, 503.
F(000)
[17] F. J. Hual, J. L. Atwood, J. Coord. Chem. 1999, 46, 505.
[18] K. A. O. Starzewski, W. M. Kelly, A. Stumpf, D. Freitag, An-
gew. Chem. 1999, 111, 2588; Angew. Chem. Int. Ed. 1999, 38,
2439.
[19] W. P. Hul, H. Britzwanger, A. A. Broehus, H. J. Heres, A. J.
von Linden, A. G. Orpen, Inorg. Chim. Acta 2002, 327, 147.
[20] H. H. Karsch, G. Hanika, B. Huber, J. Riede, G. Müller, J.
Organomet. Chem. 1989, 361, C25.
Index range
2 θ /°
Temp. / K
Refl. collected
Refl. unique
Refl. observed (4σ)
R (int.)
No. variables
Weighting schemea) x/y
GOOF
Ϫ11 Յ h Յ 5Ϫ14 Յ k Յ 15Ϫ18 Յ l Յ 17
48.00
203(2)
4022
3461
2462
0.0379
217
/
1.034
0.0428
0.0914
0.452
[21] H. Nöth, W. Schrägle, Chem. Ber. 1965, 98, 352.
[22] X. Feng, M. M. Olmstead, P. P. Power, Inorg. Chem. 1986,
25, 4615.
Final R (4σ)
Final wR2
Larg. res. peak /e/A3
[23] D. C. Pestana, P. P. Power, J. Am. Chem. Soc. 1991, 113, 8426.
[24] W. Gee, R. A. Shaw, B. C. Smith, G. J. Bullen, Proc. Chem.
Soc. 1961, 432.
2
2
a) wϪ1 ϭ σ2Fo ϩ (xP)2 ϩ yP; P ϭ (Fo ϩ 2Fc2)/3.
[25] W. C. Hamilton, Acta Crystallogr. 1955, 8, 199.
[26] P. Goldstein, R. A. Jacobsen, J. Am. Chem. Soc. 1962, 84,
2457.
[27] The synthesis and properties of this and other 1,3,5,2,4,6-tri-
phosphatriboretanes will be described in a forthcoming paper.
[28] D. Dou, M. Westerhausen, G. L. Wood, G. Linti, E. N.
Duesler, H. Nöth, R. T. Paine, Chem. Ber. 1993, 126, 379.
[29] D. Dou, B. Kaufmann, E. N. Duesler, T. Chen, R. T. Paine,
H. Nöth, Inorg. Chem. 1993, 32, 3056.
Acknowledgments. We thank Fonds der Chemischen Industrie and
Chemetall GmbH for valuable support. We also acknowledge the
invaluable assistance of Mrs. D. Ewald for recording many mass
spectra, Dr. I. Krossing for collecting the X-ray data, and Dr. K.
Karaghiosoff for the discussion of NMR spectra.
References
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Sulfur, Silicon 1994, 87, 41.
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[35] SMART, Version 5, Bruker Co., Madison.
[36] SHELXTL, Version 5, Bruker Co., Madison.
926
www.zaac.wiley-vch.de
 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2007, 917Ϫ926