Behavior of 1,3-di(tert-butyl)-2,4-bis(tetramethylpiperidino)-1,3,2,4- diphospha-diboretane towards boron halides and adduct formation of a bicyclo[1.1.0]diphosphadiboretane with tris(pentafluorophenyl)borane [1]

Article abstract of DOI:10.1515/znb-2006-0305

While the diphosphadiboretane (tBuP=Btmp)₂, 1, reacts with boron trihalides BX³ (X = Cl, Br, I) with BN cleavage producing a number of unidentifiable products, a new tricyclic BP ring system 2, containing B ₃P₃,

Full text of DOI:10.1515/znb-2006-0305

Behavior of 1,3-Di(tert-butyl)-2,4-bis(tetramethylpiperidino)-1,3,2,4-di-
phospha-diboretane towards Boron Halides and Adduct Formation of a
Bicyclo[1.1.0]diphosphadiboretane withTris(pentafluorophenyl)borane [1]
Klaus Knabela, Heinrich No¨tha, and Robert T. Paineb
a Department of Chemistry, University of Munich, Butenandtstr. 5 – 13, D-81377 Mu¨nchen, Germany
b Department of Chemistry, University of New Mexico, Albuquerque, New Mexico, USA
Reprint requests to Prof. Dr. H. No¨th. E-mail: H.Noeth@lrz.-uni-muenchen.de
Z. Naturforsch. 61b, 265 – 274 (2006); received December 8, 2005
Dedicated to Prof. Dr. H.-G. Schno¨ckel on the occasion of his 65th birthday
While the diphosphadiboretane (tBuP=Btmp)2, 1, reacts with boron trihalides BX3 (X = Cl, Br, I)
with BN cleavage producing a number of unidentifiable products, a new tricyclic BP ring system 2,
containing B3P3, PB2C2 and C6 rings, results from the combination of PhBCl2 and 1. B-Chlorocat-
echolborane and 1 give access to the diborylphosphane 3, tmpBCl-PtBu-cat (cat = C6H4O2B). This
shows that the selectivity of the reactions increases as the Lewis acidity of boron halide decreases. The
structure of compounds 2 and 3 were determined by X-ray structure analysis. The bicyclic (tmpBP)2
4 forms no adducts with MeI, CF3SO2Me or Ph3C(SnCl5). However, it adds B(C6F5)3 to give 10,
the first BX3 adduct of this bicycle that is fully characterized including its molecular structure.
Key words: Diphosphadiboretanes, Bicyclodiphosphadiboretane, Reactivity, NMR Spectra, X-Ray
Structure Analysis
Introduction
Reactions of (tmpB=PCMe3)2 with Some Boron
Halides
The reaction chemistry of 1,3,2,4-diphosphadi-
boretanes [2 – 7], the bicylic [1.1.0]diphospha-di-
boretanes (R2NBP)2 (R2N=Et2N, iPr, 2,2,6,6-tetra-
methylpiperidino (tmp) group) [8, 9], and tricycl-
ic (R2NB)2P2(EXn) cages [2, 10] has been par-
tially explored with several classical Lewis acids
and a multitude of metal carbonyls [2 – 14]. In par-
ticular, the trihalides of Al, Ga or In react with
1,3,2,4-diphosphadiboretanes either with formation of
adducts (tmpB=PR)2 · EX3 [15, 16] or by BP bond
opening to generate a boraphosphinidene molecule
tmpB=PR(EX3) [17]. Adduct formation is also ob-
served in the case of the bicyclic (tmpB)2P2 with metal
carbonyls, e. g. CpMn(CO)3 [18]. However, the behav-
ior of the two types of BP compounds towards boron
halides has not yet been reported except for the forma-
tion of the adduct (tmpBP)2(BBr3)2 [18], which was
characterized only by analytical and NMR methods.
Reactions of boron trihalides BX3 with 1 may lead
to a variety of interesting and still unknown boron
phosphorus compounds. Several possibilities are de-
picted in Scheme 1. Most likely the first step results in
the formation of addition products A or B. The boron
trihalides may of course also attack at the nitrogen
atom of the tmp substituent. So far we have never ob-
served BX3 addition to this group although this might
be expected since cleavage of the BN bond of tmp-
boranes is quite common. Ring opening of the 1,3,2,4-
diphosphadiboretanes generates product C which may
form a new ring D. Provided that BN cleavage occurs
to generate the unknown diphosphadiboretanesE these
may react with more BX3 to give either compounds of
type G or F. Compounds of type F have already been
reported [19], but not yet for boron halide groups.
In the present study, we examined reactions of 1
Some reactions of boron halides with the diphospha- with BCl3, BBr3 and BI3 using reactant ratios from
diboretane (tmpB=PtBu)2, 1, are reported here, one 1 : 1 to 1 : 2. In all cases mixtures of various boron
of them yielding an unexpected new BP heterocyclic compounds were observed by 11B NMR spectroscopy,
system.
but no single reaction product was isolated in a pure
c
0932–0776 / 06 / 0300–0265 $ 06.00 ꢀ 2006 Verlag der Zeitschrift fu¨r Naturforschung, Tu¨bingen · http://znaturforsch.com
- 10.1515/znb-2006-0305
Downloaded from De Gruyter Online at 09/12/2016 11:43:24PM
via free access

266
K. Knabel et al. · Tris(pentafluorophenyl)borane
Scheme 1.
state. In case of BCl3 the 11B NMR data show clearly companied by tmpBCl2 and tmpB(Cl)Ph. For maximal
that BN bond cleavage takes place with formation of yield of 2 a 3 : 8 (1 : PhBCl2) stoichio◦metry was re-
tmpBCl2 (δ11B = 33.8 ppm) [20]). The 1 : 1 reaction quired as shown in eq. (1). Below −40 C no reaction
of 1 with BBr3 in toluene at −50◦ led to two broad according to eq. (1) was noted.
11B NMR signals at −8.8 and 18.4 ppm suggesting
It is obvious that a number of consecutive reactions
are necessary to arrive at compound 2.
the formation of two products, but at room tempera-
ture new signals emerged. The reaction of 1 with BI3
led to the iodoborane tmp2BI (δ11B = 26.5 ppm) [21]).
In addition, during the reaction of BI3 with 1 a dou-
blet (δ11B = −57.4 ppm, with 1J(BP) = 40 Hz) and a
triplet (δ11B = −43.1 ppm with 1J(BP) = 50 Hz) was
observed indicating the formation of BI3 adducts at the
P-atoms.
Most likely PhBCl2 adds to 1 by opening of
B-P bonds with formation of the diborylphosphane
PhClB-tBuP-BCl(tmp). Elimination of tmpBCl2 from
this intermediate should generate tBuP=BPh which
on trimerization could form the six-membered
(tBuP=BPh)3. Addition of PhBCl2 to this ring across
one of its BP bonds would generate a cyclic intermedi-
The boron trihalides are obviously too reactive ate ClPhB(tBuPBPh)3Cl. Orthoboration of one of the
to allow selective reactions. Therefore, we replaced phenyl groups by HCl elimination could then form a
them by the less Lewis acidic PhBCl2. In this case benzodiboryl system. Addition of the HCl generated
the reaction products were independent of the stoi- in this process to two BP bonds should finally yield
chiometry used. The tricyclic 9-bora-2,4,6-triborata- the tricyclic compound 2. This reaction sequence is,
bicyclo[4.3.01,6]-nonane, 2, was the main product ac- of course, speculative but some of the steps are typi-
- 10.1515/znb-2006-0305
Downloaded from De Gruyter Online at 09/12/2016 11:43:24PM
via free access

K. Knabel et al. · Tris(pentafluorophenyl)borane
267
cal in BP chemistry. According to eq. (1) the yield of
2 should not exceed 51% based on boron. The actual
yield was 54%.
The rather unexpected formation of 2 shows, how-
ever, that a reduced Lewis acidic character of the boron
halide might induce higher selectivity with 1, and one
may surmise that a monohaloborane would be an even
better choice than PhBCl2. This is indeed the case as
observed for the reaction of 1 with catecholchlorobo-
rane which yields the diborylphosphane 3 as shown in
eq. (2). In contrast to the formation of 2 no BN bond
cleavage was observed in this case.
NMR Spectra and Molecular Structures of 2 and 3
Fig. 1. Plot of the molecular structure of compound
The structure of compound 2 could be deduced from
its NMR data. These showed two broad 11B NMR sig-
nals at 29.8 and −4.0 ppm in a 1 : 3 ratio, assigned to a
tricoordinated boron atom and three tetracoordinated
boron atoms, respectively. Although atom B2 is not
chemically equivalent to B1 and B3, both are bound
to two P atoms, one Cl and one C atom. Therefore,
the chemicals shifts for these three boron atoms should
not differ much. This explains that only one signal is
observed for these two atoms. No BP coupling was
noted for all 11B resonances, a well known phenom-
enon which is due to the large quadrupole moment of
the boron atom as well as the asymmetry induced by
the substituents. There are three 31P resonances, two
2. Thermal ellipsoids are presented on a 25% probabil-
˚
ity scale. Selected bond lengths (in A): P1–B1 2.029(4),
P1–B2 2.013(4), P1-B4 1.956(5), P1–C30 1.887(3), P2–B2
2.003(4), P2–B3 1.995(4), P2–C17 1.880(4), P2–H2 1.24,
P3–B1 2.016(4), P3–B3 2.039(4), P3–C7 1.872(4), B1–C1
1.589(5), B1–Cl1 1.909(4), B2–Cl2 1.865(4), B2–C21
1.608(5), B3–C31 1.616(5), B3–Cl3 1.883(4), B4–C22
1.537(5), B4–C41 1.571(6), C7–C10 1.532(5), C7–C8
1.535(5), C22–C23 1.401(6). – Selected bond angles (in de-
grees): P2–B3–P3 106.0(2), B3–P2–B2 115.0(2), P1–B2–P2
108.1(2), B1–P3–B3 122.3(2), P3–B1–P1 110.3(2), B4–P1–
B1 92.2(2), P1-B1-P3 110.4(2), B2–P1–B1 113.3(2), B1–
P1–C30 117.1(2), B4–P1–B2 92.2(2), B3–P1–C30 117.0(2),
B3–P2–C7 112.0(2), B2–P2–C17 117.3(2), B3–P2–H2
99.7, B2–P2–H2 106.5, B1–P3–C7 112.0(2), B1–P3–H3
102.4, C1–B1–C11 112.6(3), P2–B2–C21 116.4(2), P1–B2–
Cl2 111.3(2), C21–B2–Cl2 110.6(3), P2–B2–Cl2 110.1(2),
P3–B1–Cl1 104.1(2), P1–B4–C41 130.0(3), Cl3–B3–C31
125.0(3). – Torsion angles: P1–B4–P3–B2 −46.0, B–4–P3–
B2–P2 30.2, P3–B2–P2–B3 27.8, B2–P2–B3–P1 −70.4; P2–
B3–P1–B4 51.1, B3–P1–B4–P3 1.5, B4–P1–B2–Cl2 89.5,
B4-C22-C21-B2 −4.3, C21-B2-P1-B4 −27.3, C21-C22-B4-
P1 −17.9, C22–C21–B2–P1 23.2.
1
of them are doublets in the H coupled spectra indi-
cating the presence of PH groups. The assignment to
atom P1 is unambiguous as there is no H atom bonded
to this P atom. Because δ31P and 1J(31P1H) are rather
similar for the PH type P atoms no assignment either
3
to P2 or P3 is possible. This is true also or J(31P1H)
the methyl groups and the quarternary C atoms show-
ing 1,2J(31P13C) coupling. In addition, 13 13C signals
were observed for the benzo- and phenyl groups. Ob-
viously the C atoms of two phenyl rings are magneti-
cally equivalent. Actually, 14 signals should be found
because NMR signals of 13C atoms bonded to the 11B
atoms are generally not recordable. As no specific de-
coupling experiments had been performed no informa-
tion regarding the relative positions of the tBu and Ph
found for the protons of the tBu groups; although there
are three signals for tBu groups, the coupling con-
3
stants J(31P1H) are equal for all on them (14 Hz).
1
In addition there are two signals for the HP protons
1
which are doublets of doublets with J(31P1H) = 370
3
and 350 Hz, and J(31P1H) = 3 Hz for both. The aro-
matic CH potons give rise to many signals in the region
5.6 to 7.6 ppm. Unspectacular are the 13C resonances
for the tBu group: there are three signals each for
- 10.1515/znb-2006-0305
Downloaded from De Gruyter Online at 09/12/2016 11:43:24PM
via free access

268
K. Knabel et al. · Tris(pentafluorophenyl)borane
that atom B3 is part of the six- and five-membered
rings.
The diborylphosphane 3 is a new type of a dibo-
rylphosphane. Its NMR data are in accord with the
suggested structure. Fig. 2 shows its molecular struc-
ture as determined by X-ray crystallography. The two
tricoordinated boron atoms are present in a planar en-
vironment, and the structural parameter values of the
catecholatoboryl unit compare well with those already
reported [22, 23]. Due to an acute OBO bond angle
of 110.8(4)◦, the two P-B-O bond angles are larger
than 120◦: 126.7(4) and 122.1(4)◦. The BP bonds
˚
are 1.884(6) (to B1) and 1.933(5) A (to B2). The
shorter bond to the catecholatoboryl moiety may be
due to the stronger Lewis acidic character of this boron
atom compared with B2 which carries the tetram-
ethylpiperidino group. Its six-membered ring shows
a twist conformation with a planar nitrogen atom, a
rather rare conformation for tetramethylpiperidino bo-
ranes. The most often observed conformation for the
tmp group with its planar N atom is the semichair con-
formation [24 – 26].
Fig. 2. Plot of the molecular structure of compound 3. Ther-
mal ellipsoids are presented on a 25% probability level. Se-
˚
lected bond lengths (in A): P1–B1 884(6), P1–B2 1.933(5),
B1–O1 1.389(6), B1–O2 1.390(6), Cl1–B2 1.808(5),
B2–N1 1.395(6), N1–C11 1.526(5), N1–C15 1.530(5),
O1–C1 1.379(5), O2–C2 1.380(5), C1–C2 1.373(7), C4–C5
1.390(8). – Selected bond angles (in degrees): C7–P1–B1
107.9(2), C7–P1–B2 114.0(2), B1–P1–B2 97.6(2), P1–B1–
O1 126.7(3), P1–B1–O2 122.2(3), O1–B1–O2 110.8(4),
P1–B2–Cl1 117.5(2), P1–B2–N1 122.8(4), N1–B2–Cl1
119.8(4), C11–N1–C15 117.6(3), B1–O1–C1 105.4(3), B1–
O2–C2 105.2(3). Angle between planes (in ◦): O2B/P1 B2
C7 = 117.3, C11 N1 C15/ P1 B2 Cl1 127.2.
The B2–N1 bond is comparatively long with
2
2
˚
1.395(6) A for an sp B-sp N bond. The C2N plane
forms an angle with the B2P1Cl1 plane of 37.6◦, and
this still allows BN-π-bonding. On the other hand, the
O2B plane is twisted against the B1P1B2 plane by
41.8◦, while the torsion angle C7P1B2Cl1 is 15.1◦, the
closest angle to planarity. A pyramidal configuration is
found for the P atom.
groups can be given. However, these were determined
by X-ray crystallography.
Compound 2 crystallizes in the monoclinic system
space group C/2c with Z = 8. Fig. 1 depicts its mole-
cular structure. The six-membered B3P3 ring adopts a
strongly distorted tub shape while the five-membered
C2B2P ring is present in an envelope conformation
with atom P1 flipped up. The phenylene ring is copla-
nar with the B2C21C22B4 plane. The torsion angles
for the six-membered B3P3 ring range from −70.4◦
to 51.1◦ with B2–P1–B1–P3 as small as −1.7◦. The
phenyl and tBu groups are arranged in anti conforma-
tion.
Reaction of Bis(tetramethylpiperidino)bi-
cyclo(1.1.0)-1,2,3,4-diphosphadiboretane
with Lewis Acids
The bicyclic diphosphadiboretane 4 is an interest-
ing molecule. Steric strain in its P2B2 three mem-
bered rings offers high reactivity. 4 reacts with potas-
sium with opening of the PP bond to form an 1,3,2,4-
diphosphadiboretanide anion 5 [8]. It also adds oxida-
tively stannylenes or platinum(0) complexes with for-
mation of tricyclic systems such as 7 or 8 [22], or adds
transition metal fragments such as CpMn(CO)2 to give
6 [18]. Also, BBr3 adds to 4 in a 1 : 2 ratio to give the
adduct 9 [18] while diborane cleaves its B-N bonds
with formation of tmpBH2 [18].
The BP bonds are practically of equal lengths
˚
(avg. 2.021(4) A); only the bond B1–P1 is shorter
˚
(1.956(5) A), a consequence of the tricoordinated
B1 atom. This shortening is also observed for the
˚
B1–C1 bond (1.550(6) A) compared with the BC bond
lengths of the phenyl groups bonded to tetracoordi-
Attempts to react 4 with the electrophiles
˚
nated B atoms (range of 1.593(6) to 1.619(6) A). Ph3C[SnCl5] or MeI were unsuccessful even un-
Two of the three BCl bonds are of equal lengths der reflux conditions. However, methyltriflate reacted
(1.886 A) while the bond B3–Cl3 is significantly already at −60 ◦C but no well defined reaction
˚
˚
longer (1.912(5) A). This may be due to the fact product was found. The Lewis acidic boron compound
- 10.1515/znb-2006-0305
Downloaded from De Gruyter Online at 09/12/2016 11:43:24PM
via free access

K. Knabel et al. · Tris(pentafluorophenyl)borane
269
Fig. 3. Plot of the molecular structure of compound
10. Thermal ellipsoids are presented on a 25% prob-
˚
ability scale. Selected bond lengths (in A): P1–P2
2.280(2), P1–B1 1.919(6), P1–B2 1.909(5), P2–B1 1.905(5),
P2–B2 1.896(5), B1–N1 1.368(6), B2–N2 1.380(6), P1–B3
2.120(6), B3 C19 1.636(6), B3–C25 1.622(7), B3–C31
1.632(6); C–F1 to F5: 1.356(5), 1.345(5), 1.341(5), 1.347(5),
C 1.351(5). – Selected bond angles (in degrees): B1–P1–
B23 81.9(2), B2–P1–B3 132.2(2), B1–P1–B3 132.5(2), B3–
P1–P2 52.9(2), B3–P1–P2 115.9(2), B1–P1–P2 53.1(2), B3–
P1–P2 115.9(2), B2–P2–B1 82.6(2), B1–P2–P1 53.7(2), B2–
P2–B1 82.6(2), B1–N1–C1 118.3(4), B1–N1–C5 120.9(4),
C1–N1–C5 120.0(4), B2–N2–10 117.9(4), B2–N2–C14
120.5(4), C10–N2–C14 119.0(4). Angles between planes
(in ◦): P1B2P2/P1B1P2 105.0, C1N1C5/P1B1P2 11.5,
C10N2C14/P2B2P1 10.9.
Formulae 5 to 9
The presence of the tmp group is demonstrated by
two proton NMR signals at 1.18 ppm for the methyl
groups and a broad multiplet centered around 1.25 ppm
for the CH2 units. The intensity ratio for these two sig-
nals is 2 : 1. Compared with other tmp-boranes [24 –
26] the proton signals are found at unusually high field.
B(C6F5)3 forms only a 1 : 1 addition product 10◦as
shown in eq. (3). The addition sets in at about −30 C.
Two broad 11B NMR signals in a ratio of 1 : 2 were There is only a single signal for the methyl groups at
25 ◦C indicating free rotation of the tmp groups about
observed for 10 at −7.0 and 40.6 ppm. Also two very
broad 31P signals at −294.8 and −244.6 ppm were its BN bond. On the other hand, two 13C NMR signals
recorded. We assign the latter to the P atom that is were observed for the methyl groups besides two sin-
coordinated to B(C6F5)3 on the basis of its larger glets for the other CH2 groups of the tmp ring, and a
line width because this P atom is bonded to three single signal for the CMe2 atom. In case of hindered
boron atoms. Compared with the 31P resonances found rotation about the BN bonds four non-equivalent Me
for compound 4 the tetracoordinated P atom is better groups should be observable.
shielded by 5 ppm, while the tricoordinated P atom is
deshielded by 45 ppm. Due to the large line width no
PP coupling could be observed.
The molecular structure of 10 is shown in Fig. 3.
The compound crystallizes in the triclinic space group
¯
P1 with Z = 2. The bicyclic structure is retained by
Three 19F resonances demonstrate that the penta- the addition of B(C6F5)3. The roof angle between the
fluorophenyl groups are magnetically equivalent with two P2B units is 105.2◦, which is close to that found
free rotation about their BC bonds.
for 4 [8]. However, it is much smaller than in the
- 10.1515/znb-2006-0305
Downloaded from De Gruyter Online at 09/12/2016 11:43:24PM
via free access

270
K. Knabel et al. · Tris(pentafluorophenyl)borane
cation tBuP(Btmp)2P+ [14]. The four B–P bonds are ethylpiperidino groups of 1 with formation of tmpBCl2
of equal lengths (3σ-criterion). The average length is and Ph(tmp)BCl as shown in eq. (2). At which stage the
˚
1.907 A, which is practically the same as found in 4 orthoboronation of a phenyl group occurs remains an
˚
(1.91 A).
In the solid state, the BN bonds are comparatively
open question as well as at which stage the PH group
formation sets in. In order to formulate a stoichiomet-
ric equation for the formation of 2 from PhBCl2 and 1
one has to assume that not only tmpBCl2 is formed, the
formation of which is definitely observed amongst the
reaction products by 11B NMR (δ = 37.6 ppm) [20],
but also Ph(tmp)BCl, to which a signal at δ = 40 ppm
can be assigned [34].
˚
˚
short (1.368 and 1.380 A), close to the value of 1.◦34 A
for a B=N double bond. Nevertheless, above 30 C in
solution there seems to be free rotation about these
bonds, which is obviously frozen in the solid state.
The BP bond to the tetracoordinated B atom is
2.210 A and lies on the longer side for borane
˚
The PH groups show up in the 31P NMR spectra
as broad doublets, but no BP coupling is observed.
The relative orientation of the two P-H bonds and P-
CMe3 bonds could not be determined by NMR ex-
periments but turned out to be trans as determined
by X-ray structure analyses of 2. The structure de-
termination also showed a planar benzo group, a
PB2C2 ring in envelope conformation, and a highly
distorted six-membered B3P3 ring as deduced from
the ring torsion angles (for data see Fig. 1). In con-
trast, all known phosphinoboranes of type [R2P-BH2]3
posses a chair conformation. To our knowledge no
crystal structure of a six-membered phosphinoborane
[R2P-B(Hal)2]3 is known in contrast to known struc-
tures for [R2P-BH2]3 [40, 41] and trimeric phosphi-
noborenes (RP-BR’)3 [2]. It is not unexpected that
the BP bond at the tricoordinated B4 atom is shorter
phosphane adducts [27 – 33], but corresponds to the
2.181 A found for Ph3P-B(C6F5)3 [34].
˚
Discussion and Conclusions
Reactions of 1 with BX3 (X = Cl, Br, I) were er-
ratic. In case of BCl3 the main product was tmpBCl2.
Its 11B NMR signal was accompanied by several
other less intense signals indicating to the presence
of tetracoordinated boron atoms. None of these sig-
nals showed BP coupling. Therefore, it is difficult to
assign these resonances to BCl substituted phosphino-
boranes. Surprisingly, only two 11B NMR signals were
observed by following the reaction of 1 with BBr3 at
low temperature. However, the chemical shifts do not
fit with a BBr3 adduct to a triorganylphosphanesuch as
Br3B·PMe3 (δ11B = −14.5 ppm [35]) or Br3B·PPh3
(δ11B = −14.2 ppm [36]). Adducts of BBr3 with phos-
phinoboranes are unknown at present. The reaction of
1 with BI3 furnished only three 11B NMR signals. That
at low field seems to be due to tmpBI2 [20], while two
more signals in the range for tetracoordinated boron
atoms show BP coupling. This indicates the formation
of either a BI3 adduct with 1 or a phosphine-borane
containing tetracoordinated B and P atoms. So far only
phosphinoboranes of the type (X2B-PR2)3 [X = F,
R = Me [37]; (X = Cl, R = Me, Et, Ph [37, 38]; X = Br,
R = Me, Et, Ph [34 – 36]; X = I, R = Me. Ph [34, 35]) or
of the type [Hal2B-PHR]3, or [HalRB-PR2]3 have been
characterized by NMR methods, and the crystal struc-
tures of only a few of type [H2P-PR2]3 (R = Me [39];
R = Ph [39]; R = SiMe3 [40]) have been reported.
˚
by 0.046 A than the average B-P bond length to the
tetracoordinated B atoms. Similarly, the BC bond at
˚
the tricoordinated B4 atom is 0.043 A shorter than
those at the tetracoordinated B atoms. In general, B-P
bond lengths of phosphane-boranes are influenced by
the boron substituent as well as by the steric de-
mand of the triorganylphosphanecomponents [23– 28,
37 – 43].
Finally it is worthwhile noting that the lengths of the
boron-bondedC=C group of the five membered B2C2P
˚
ring is elongated by 0.051 A compared with the other
C-C bonds of the benzo ring. Therefore, the endocyclic
C-C-C bond angles vary significantly.
Compound 3 is a typical diborylphosphane, but
it is so far unique as no diborylphosphane carry-
By contrast, the reaction of 1 with PhBCl2 leads to ing a O2B and a B(N)Cl boryl group is yet known.
the well-defined new tricyclic BP compound 2 con- Those known either carry aryl groups and/or amino
taining three tetracoordinated P atoms two of which groups [2]. Amongst these, compounds RP(Bmes2)2
are bonded to a hydrogen atom. One of the four and mesP(BmesCl)2 show planar or almost planar con-
boron atoms of this heterocycle is tricoordinated, the figuration at the P atoms (360◦ and 354.3◦, repectively)
other three are tetracoordinated. The compound is [44, 45]. In contrast, the P atom of 3 has a pyramidal
formed by breaking the BN bonds to the tetram- conformation. The sum of bond angles at the P atom
- 10.1515/znb-2006-0305
Downloaded from De Gruyter Online at 09/12/2016 11:43:24PM
via free access

K. Knabel et al. · Tris(pentafluorophenyl)borane
271
is 319.5◦, while the B-P-B bond angle is 97.6◦. There-
fore, there is no BP-π-bonding in 3, and, consequently
the BP bonds involving the BO2 group and the BClN
˚
˚
group (1.884(6) A and 1.933(5) A) are longer than
˚
in PhP(Bmes2)2 (1.871(2) A) and mesP(BClmes)2
˚
(1.853(4) A [44, 45]. The shorter of the two BP bonds
in 3 is due to the small O-B-O bond angle (110.8(4)◦)
and B-O-π-bonding as well as the inductive effect of
the oxygen atoms. The longer BP bond results from
BN-π-bonding as shown by the short BN bond length
˚
of 1.395(6) A and the presence of a planar N atom.
The tmp ring, however, does not show the usual chair
or half chair conformation as found for many boranes
carrying a tmp group [45– 48] but is twisted. However,
in solution only a single signal for the Me groups is
observed in the 13C NMR spectrum, indicating free ro-
tation about its B-N bond and/or ring inversion.
While the diphosphadiboretanes readily form 1 : 1
and 1 : 2 complexes with transition metal carbonyl
fragments [2], there is scarce information about adduct
formation of the bicyclic B2P2-species 4 particularly
with Lewis acids of the main group elements. So far
only 4 · BBr3 has been characterized by NMR spec-
troscopy, while attempts to prepare 4 · (BH3)n (n =
1,2) failed and led to BN bond cleavage (The expected
(HB)2P2 or its oligomer could not be detected amongst
the reaction products [19]).
Scheme 2. Selected bond lengths and angles for three bicy-
clodiboretanes.
might have expected that the formation of 10 would
lead to different B1-P1-B2 and B1-P2-B2 bond angles,
this is not the case as shown by values of 81.9(2) and
82.6(2)◦, respectively. Out of the three examples of the
bicyclic BP compounds discussed here there are two
which are of a new type. This shows that there are
most likely many other still unexpected small and large
BnPm molecules to be detected, which may also be in-
teresting precursors for new materials.
Experimental Section
All experiments have been performed by the Schlenk
technique using dry N2 or Ar as protecting gases. Starting
materials were prepared according to literature procedures.
Solvents were applied in an anhydrous state stored under N2.
Most NMR spectra were recorded with a JeolEX 400 instru-
ment; chemical shifts are referenced to TMS, 11BF3OEt2,
85% H3PO4, and either C6D6 or CDCl3 were used as sol-
vents. IR spectra were recorded with a Nicolet-FT-IR spec-
trometer as Nujol/Hostaflon mulls. Liquids were placed be-
tween CsI plates. Data collection for X-Ray structure detger-
minations were carried out with a Siemens P4 diffractome-
ter using Mo-Kα radiation, a graphite monochromator, a low
temperature device LT2 and an area detector.
The structure of 4 suggests that this compound
should not be a strong Lewis base, neither at the N
nor the P atoms, since the lone pair at the P atoms
have s-orbital character and the B-N bond is involved
in π-bonding. On the other hand, the bicyclic nature
of 4 suggests high reactivity. Compound 10 is now
the first fully characterized 1 : 1 borane adduct of 4. In
Scheme 2 structural data of three bicyclic P2P2 com-
pounds are listed. The PP bond lengths shrink as one
moves from the parent compound to the adduct 10 and
the cation (tmpB)2P(PtBu)+. The adduct formation,
however, does not result in two very different B-P-B
bond angles.
7,8-Benzo-1,2,5-tri(tert-butyl)-2,4,6-trichloro-2,4,9-tri-
phenyl-1,3,5-phosphonia-9-bora-2,4,6-triborata-bicyclo-
[4,3,01,6]nonane (2)
˚
The BP bond to the B(C6F5)3 unit (2.120(6) A)
is longer than the BP bonds to the tmpB groups
[1.896(5)– 1.919(5) A], a feature that was to be ex-
A solution of (tmpB-PCMe3)2 (0.45 g, 1 mmol) in hexane
(20 ml) was added within 30 min to a stirred solution of
PhBCl2 (0.25 ml, 1.9 mmol) in hexane (10 ml). During this
process the orange solution turned yellow. After the addition
the solution was reduced to half its volume in vacuo. Col-
orless crystals of 2 separated within one day by storing the
solution at −78 ◦C. Yield 0.21 g (56% based on 1).
˚
pected, because similar trends have been observed for
phosphine boranes [27]. It is also interesting to note
that the sum of bond angles for the P2B3 unit is 347◦,
which is larger than found for the (tmp)2B2P2(tBu)
+
cation (336◦). This is an indication that there is
NMR (all in d8-toluene): 1H NMR: δ = 0.71 (d, 9H
an even higher degree for a p,p-orbital interaction in
10 than calculated for this cation [17]. Although one CMe3), 2J(PH) = 14 Hz); 1.16 (d, 9H, CMe3), 2J(PH) =
- 10.1515/znb-2006-0305
Downloaded from De Gruyter Online at 09/12/2016 11:43:24PM
via free access

272
K. Knabel et al. · Tris(pentafluorophenyl)borane
Table 1. Crystallographic pa-
Compound
2
3
10
rameters and data relevant for
data collection and structure
solution of compounds 2, 3
and 10.
Chem. formula
Form. wght.
C39H55B4Cl3P3
766.33
0.07×0.08×0.15
monoclinic
C2/c
38.075(6)
11.076(3)
19.859(5)
90.00
90.45(1)
90.00
8375(3)
8
1.216
0.360
3240
C19H31B2Cl N O2P
393.49
C36H36B3F15N2P2
876.04
Cryst. size [mm]
Cryst. system
Space group
0.10×0.10×0.10
0.05×0.10×0.10
triclinic
triclinic
¯
¯
P1
P1
˚
a w−1 = σ2Fo2 +(xP)2 +yP; P =
a [A]
7.9701(8)
10.3649(12)
13.1695(15)
81.429(2)
82.041(2)
76.929(2)
1041.7(2)
2
11.4667(9)
12.2388(11)
15.0510(13)
70.609(1)
75.964(2)
89.353(2)
1927.4(3)
2
˚
(Fo2 +2F 2)/3.
b [A]
c
˚
c [A]
α [◦]
β [◦]
γ [◦]
˚
V [A3]
Z
ρ(calcd.) [Mg/m3]
1.255
0.273
420
1.509
0.217
892
µ [mm−1
F(000)
]
Index range
−42 ≤ h ≤ 27
−12 ≤ k ≤ 12
−22 ≤ l ≤ 22
46.50
−10 ≤ h ≤ 8
−13 ≤ k ≤ 13
−16 ≤ l ≤ 16
58.36
−15 ≤ h ≤ 11
−15 ≤ k ≤ 15
−19 ≤ l ≤ 19
57.88
2θ [◦]
Temp, [K]
193
193(2)
193(2)
Refl. collected
Refl. unique
Refl. observed (4σ)
R (int.)
17681
5000
4470
0.0334
6056
3212
1870
0.0300
11309
5939
3117
0.0722
No. variables
Weighting schemea x/y
GOF
451
0.0326/3.6457
1.089
243
0.1531/0.000
1.049
531
0.0615/0.000
0.950
Final R(4σ)
0.0454
0.1213
0.921
0.0726
0.2022
0.635
0.0582
0.1134
0.290
Final wR2
3
˚
Larg. res. peak [e/A ]
14 Hz); 1.31, (d, 9H CMe3), 2J(PH) = 14 Hz); 4.18 (dd,
1H, PH, J(PH) = 370 Hz, J(PH) = 3 Hz); 5.11 (dd, 1H, found C 57.11, H 7.86, N 3.56.
C
19H31NO2BClP (393.49): calcd. C 57.99, H 7.94, N 3.56;
1
3
PH, 1J(PH) = 350 Hz, 3J(PH) = 3 Hz); 6.92, 6.95, 6.97,
7.00, 7.03, 7.05, 7.11, 7.14, 7.20, 7.23, 7.26, 7.29, 7.31, 7.33,
7.36, 7.38, 7.41, 7.46, 7.52, 7.55, 7.75, 7.77, 7.93(m), 8.27
(m), 8.40, 8.41, 8.44, 8.52, 8.55. – 13C NMR: δ = 30.8 (s,
CMe3), 31.3 (s, CMe3), 31.9 (s, CMe3), 37.5 (s, CMe3), 38.6
(s, CMe3), 40.3 (s, CMe3), 127.9, 131,7, 133.5, 134.0, 134.8
135.0, 135.7, 136.5, 136.7, 136.8, 138.6, 138.7. – 11B NMR:
NMR (all in d8-toluene) 1H NMR: δ = 1.45 (s, 3H,
tmpMe); 1.47 (s, 3H, tmpMe); 1.49 (m, 2H, C3H2); 1.50 (s,
3H, tmpMe); 1.52 (s, 3H, tmpMe); 1.65 ( s, 9H, CMe3); 1.78
(m, 4H, CH2); 7.06 (m); 7.20 (m, 4H). – 13C NMR: δ = 14.4
(s, C4); 30.0 (CMe3); 31.0 (s, CH2); 32.1 (s, CH2); 32.3 (s,
CH2); 32.6 (s, CH2); 32.7 (s, CH2); 35.4 (s, CMe3); 57.2 (s,
CMe2); 112.0 (p-C); 122.3 (m-C); 148.8 (o-C). – 11B NMR:
δ = 33.4 (h1/2 = 90 Hz); 37.4 (h1/2 = 340 Hz). – 31P NMR:
δ = −75.6 (h1/2 = 200 Hz).
1
δ = 29.8 (h1/2 = 280 Hz), −4.0 (h1/2 = 420 Hz). – 31P{ H}
NMR: δ = −12.5 (h1/2 = 220 Hz), −14.23 (h1/2 = 190 Hz),
−21.8 (h1/2 = 220 Hz). P(H)-NMR: δ = −12.3 (d, 1JPH) =
370 Hz); −14.7 (d, 1J(PH) = 350 Hz); −21.8 (s).
2,4-Bis(tetramethylpiperidino)-1-phosphonia-2-phosphato-
3,4-dibora[1,1,0]bicyclobutane-tris(pentafluorpheny)borate
(10)
Catecholatoboryl(2,2,6,6-tetramethylpiperidinochlorobor-
yl)tert-butylphosphane, (3)
To an orange solution of 3,4-bis(tetramethylpiperidino)-
1,2-diphospha-3,4-dibora[1.1.0]-bicyclobutane in toluene
To the clear orange solution of 1 (0.78 g, 1.62 mmol) (10 ml) was added with stirring a solution of B(C6F5)3
in toluene (50 ml) was added a toluene solution (10 ml) (70 mg, 0.13 mmol) in toluene (85 ml). The mixture was
of B-chlorocatecholborane (0.5 g, 3.24 mmol). The mixture stirred for several days until a deep yellow solution had
was stirred over night. Then the solution was reduced to formed. 12 ml of the solvent were removed in vacuo. The
◦
◦
half of its volume in vacuo. It was kept at −30 C. Crys- remaining solution was kept at −30 C. After standing for
tals started settling after a few hours. The colorless prisms three months 0.1 g (85%) of colorless prisms was i◦so-
were isolated after 8 h. Yield: 1.10 g of 3, 86%, m. p. 154 ◦C. lated which had single crystal quality; m. p. 147 – 149 C.
- 10.1515/znb-2006-0305
Downloaded from De Gruyter Online at 09/12/2016 11:43:24PM
via free access

K. Knabel et al. · Tris(pentafluorophenyl)borane
273
C36H36N2B3F15P2 (875.88): calcd. C 49.36, H 4.14, N 3.20; was performed in the hemisphere mode implemented in the
found C 47.24, H 3.91, N 2.81.
SMART program. After data reduction the structure was
solved using the SHELXTL program. Non-hydrogen atoms
were refined anisotropically, the positions of the PH hydro-
gen atoms were taken from a difference Fourier map and re-
fined isotropically. All other hydrogen atoms were placed in
calculated positions and refined in the riding mode. Crys-
tallographic data are summarized in Table 1 together with
data referring to structure solution and refinement. Addi-
tional data have been deposited with the Cambridge Crys-
tallographic Data Centre, CCDC 296126 – 296128. Copies
of the data can be obtained free of charge on application
to The Director, CCDC, 12 Union Road, Cambridge CB2
1EZ, UK (Fax: int.code+(1223)336-033; e-mail for inquiry:
fileserv@ccdc.cam.uk.
NMR (all in d8-toluene): 1H NMR: δ = 1.18 (24 H,
CH3); 1.25 (m, 12 H, C4,C3,C5-CH2). – 13C NMR: δ = 16.3
(t, mp-C4), 33.2 (CH3); 38.1 (CH3); 41.4 (tmp-C3,5); 56.5
(CMe2). – 11B NMR: δ = −7.0 (h1/2 = 480 Hz); 40.6
(h1/2 = 400 Hz). – 19F NMR: δ = −163.6 (m-CF); −156.1
(p-CF); −127.6 (o-CF). – 31P NMR: δ = −298.3 (h1/2
2100 Hz); −244.6 (h1/2 = 2300 Hz).
=
MS (70 eV): m/z (%) = 512 (45, B(C6F5)3+.), 365 (35,
M-B(C6F5)3+).
X-ray structures
The single crystals were mounted on a glass fibre with
perfluoroether oil and fixed on the goniometer head while
cooling to −80 ◦C with a nitrogen cold stream using a
LPT2 device. After alignment of the crystal 5 sets of 15
frames each at different setting angles were recorded with
an area CCD detector. Reflections on these frames were used
to calculate the parameters of the unit cell. Data collection
Acknowledgements
We are indebted to Fonds der Chemischen Industrie and
Chemetall GmbH for continued support, and to Mr P. Mayer
for the recording of many NMR spectra. We are also grateful
to Dr. J. Knizek for collecting the X-ray data sets and for the
cooperation in structure solution.
[1] Part 258 of the series “Contributions to the Chemistry [15] B. Kaufmann, H. No¨th, R. T. Paine, K. Polborn,
of Boron”, for contribution 257 see H. No¨th, A. Troll,
Europ. J. Inorg. Chem. 3524 (2005).
M. Thomann, Angew. Chem. 105, 1534 (1993);
Angew. Chem. Int. Ed. 32, 1446 (1993).
[2] R. T. Paine, H. No¨th, Chem. Rev. 95, 343 (1995).
[3] G. Fritz, W. Ho¨lderich, Z. Anorg. Allg. Chem. 431, 61
(1977).
[4] P. Ko¨lle, H. No¨th, R. T. Paine, Chem. Ber. 119, 2681
(1986).
[5] P. Ko¨lle, G. Linti, H. No¨th, G. L. Wood, C. K. Narula,
R. T. Paine, Chem. Ber. 121, 871 (1988).
[6] B. Kaufmann, H. No¨th, R. T. Paine, K. Polborn,
[16] D. Dou, B. Kaufmann, E. N. Duesler, T. Chen, R. T.
Paine, H. No¨th, Inorg. Chem. 32, 3056 (1993).
[17] K. Knabel, T. M. Klapo¨tke, H. No¨th, R. T. Paine,
I. Schwab, Eur. J. Inorg. Chem. 1099 (2005).
[18] G. Linti, H. No¨th, Z. Anorg. Allg. Chem. 593, 124
(1991).
[19] B. Kaufmann, Ph. D. Thesis, University of Munich
(1992).
M. Thomann, Angew. Chem. 105, 1535 (1993); [20] H. No¨th, S. Weber, Z. Naturforsch. 38b, 1460 (1983).
Angew. Chem., Int. Ed. 32, 1446 (1993).
[7] G. Linti, H. No¨th, R. T. Paine, Chem. Ber. 126, 875
(1993).
[8] P. Ko¨lle, G. Linti, H. No¨th, K. Polborn, J. Organomet.
Chem. 355, 7 (1988).
[21] Compound tmp2BI has not yet been reported,
but comparison with the 11B chemical shifts of
bis(amino)boron iodides (δ = 25 – 27 ppm) suggests
its formation (H. No¨th, B. Wrackmeyer, NMR Spec-
troscopy of Boron Compounds, Springer Publishers,
Heidelberg, Berlin, New York (1978), Table XLVII.
[22] W. Clegg, M. R. J. Elsegood, F. J. Lawlor, N. C. Nor-
man, P. Nguyen, N. J. Taylor, T. B. Marder, Inorg.
Chem. 37, 5289 (1988).
[23] R. B. Coapes, F. E. S. Souca, M. A. Fox, A. S. Batsans,
A. E. Goeta, D. S. Yufit, M. A. Lees, J. A. K. Howard,
A. J. Scott, W. Clegg, T. B. Marder, J. Chem. Soc. Dal-
ton Trans. 1201 (2001).
[9] B. Kaufmann, G. Linti, H. No¨th, R. T. Paine, Chem.
Ber. 129, 557 (1996).
[10] G. L. Wood, E. N. Duesler, Ch. K. Narula, R. T. Paine,
H. No¨th, J. Chem Soc. Chem. Comm. 496 (1987).
[11] G. Linti, H. No¨th, K. Polborn, R. T. Paine, Angew.
Chem. 102, 715 (1990), Angew. Chem. Int. Ed. 29, 682
(1990).
[12] D. Dou, M. Westerhausen, G. L. Woods, G. Linti, E. N.
Duesler, H. No¨th, R. T. Paine, Chem. Ber. 126, 875
(1993).
[24] H. No¨th, M. Schwarz, S. Weber, Chem. Ber. 118, 4726
(1985).
[13] T. Chen, E. N. Duesler, R. T. Paine, H. No¨th, Inorg.
Chem. 36, 802 (1997).
[25] P. Ko¨lle, H. No¨th, R. T. Paine, W. Rattay, Z. Natur-
forsch. 43b, 1439 (1988).
[14] T. Chen, E. N. Duesler, R. T. Paine, H. No¨th, Inorg.
Chem. 37, 490 (1998).
[26] H. No¨th, H. Stolpmann, M. Thomann, Chem. Ber. 127,
81 (1994).
- 10.1515/znb-2006-0305
Downloaded from De Gruyter Online at 09/12/2016 11:43:24PM
via free access

274
K. Knabel et al. · Tris(pentafluorophenyl)borane
[27] U. Monkowius, S. Nogai, H. Schmidbaur, J. Chem.
Soc. Dalton Trans. 987 (2003).
[38] R. H. Buddolph, M. P. Brown, R. C. Cass, R. Long,
H. B. Silver, J. Chem. Soc. 1822 (1961).
[28] B. Rapp, D. J. Drake, Inorg. Chem. 12, 2868 (1973).
[29] M. S. Lube, R. L. Wells, Inorg. Chem. 35, 5007 (1996).
[30] A. Marinetti, S. Jus, F. Labrue, A. Lemarchand, J. P.
Genet, L. Ricard, Synthesis 2095 (2001).
[39] W. Gee, J. B. Holden, R. F. A. Shaw, B. C. Smith,
J. Chem. Soc. 1171 (1965).
[40] G. J. Bullen, P. R. Mallison, J. Chem. Soc., Dalton
Trans, 1295 (1973).
[31] E. Vedejes, O. Daugulis, L. A. Harper, J. A. Mackay,
D. R. Powell, J. Org. Chem. 68, 5020 (2003).
[32] C. A. Jaska, A. J. Lough, I Manners, Inorg. Chem. 43,
1090 (2004).
[33] J. C. Huffman, W. A. Shupinski, K. G. Caulton, Cryst.
Struct. Comm. 11, 1435 (1982).
[34] H. Jacobsen, H. Benke, S. Doring, G. Kehr, G. Erker,
R. Fro¨hlich, O. Mayer, Organometallics 18, 1724
(1999).
[35] M. L. Denniston, D. R. Martin, J. Inorg. Nucl. Chem.
36, 1461 (1974).
[41] W. C. Hamilton, Acta Crystallogr. 8, 199 (1955).
[42] L. M. Trefonas, F. S. Matthews, W. N. Lipscomb, Acta
Crystallogr. 14, 273 (1961).
[43] G. L. Wood, D. Dou, C. K. Narula, E. N. Duesler, R. T.
Paine, H. No¨th, Chem. Ber. 123, 1455 (1990).
[44] R. A. Bartlett, H. V. Rasika Dia, X. Feng, P. P. Power,
Inorg. Chem. 27, 3919 (1988).
[45] G. Linti, PhD Thesis, University of Munich (1990).
[46] A. Weiss, H. Pritzkow, W. Siebert, Eur. J. Inorg. Chem.
1607 (2002).
[47] T. Habereder, H. No¨th, Z. Anorg. Allg. Chem. 627, 789
(2001).
[36] H. No¨th, B. Wrackmeyer, Nuclear Magnetic Reso-
nance Spectroscopy of Boron, See lit [21], Tables [48] B. Kaufmann, R. Jetzfellner, E. Leissring, K. Issleib,
XLVII and XLVIII.
[37] A. B. Burg, R. I. Wagner, US Patent 3 025 326 (1962).
H. No¨th, M. Schmidt, Chem. Ber. 130, 1677 (1997).
[49] B. Kaufmann, H. No¨th, R. T. Paine, Chem: Ber. 129,
557 (1999).
- 10.1515/znb-2006-0305
Downloaded from De Gruyter Online at 09/12/2016 11:43:24PM
via free access