Synthesis of ternary group 13/15 chain compounds

Article abstract of DOI:10.1039/c8dt01119b

Herein we present the synthesis and characterisation of the seven-membered group 13/15 chain compound HB{N(H)PtBu₂BH₃}₂ (3) obtained from the reaction of tBu₂PNH₂ (1) with Me₂S·BH₃. Furthermore, we describe the synthesis of the aluminium and gallium compounds tBu₂PN(H)AltBu₂N(H)P(H)tBu₂ (4) and tBu₂(H)PN(H)GatBu₃ (5) derived from the reaction of tBu₂PNH₂ (1) with MtBu₃ (M = Al, Ga).

Full text of DOI:10.1039/c8dt01119b

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COMMUNICATION
Synthesis of ternary group 13/15 chain
compounds†‡
Cite this: DOI: 10.1039/c8dt01119b
Received 23rd March 2018,
Accepted 9th May 2018
Marcel Köster, Annikka Kreher and Carsten von Hänisch
*
DOI: 10.1039/c8dt01119b
rsc.li/dalton
Herein we present the synthesis and characterisation of the seven-
membered group 13/15 chain compound HB{N(H)PtBu BH
obtained from the reaction of tBu PNH (1) with Me S·BH
Furthermore, we describe the synthesis of the aluminium and coupling of phosphine-boranes with B(C
gallium compounds tBu PN(H)AltBu N(H)P(H)tBu (4) and tBu (H) M. Scheer et al. gained access to a new route to polymeric
PN(H)GatBu (5) derived from the reaction of tBu PNH (1) with group 13/15 chains by synthesising the Lewis base stabilised
MtBu (M = Al, Ga).
Polymeric chains containing phosphorus and boron have
2
3
}
2
(3) lately been the focus of attention as new inorganic materials.
2
2
2
3
.
One way to synthesise such polymeric chains is the dehydro-
9
6 5 3
F ) as a catalyst.
2
2
2
2
3
2
2
1
0
3
phosphinoborane [H
2
PBH
2
·NMe
3
]. This compound as well as
P–BH ·NMe can be
treated thermally to prepare [R R P–BH ] (R , R = H, Ph, tBu)
its allyl or alkyl analogues such as Ph
2
2
3
Recently binary interpnictogen compounds which exclusively
incorporate tert-butyl and hydrogen residues have found appli-
cation as metal organic vapour phase epitaxy (MOVPE) precur-
1
2
1
2
2
n
11
polymers without a metal catalyst.
1
sors. Besides industrial application, this compound class has
been investigated with respect to its coordination chemistry
2
and tautomerization. Aminophosphanes (R
2
PNH
2
), for
example, are known to isomerise to the tautomeric iminopho-
sphorane form, which is however best described with a polar
P–N single bond. So lone pairs can either be localised at the
3
Scheme 1 Tautomerization of aminophosphanes.
phosphorus and nitrogen atoms or at the nitrogen atom only
4
(
Scheme 1). Initially, it was estimated that the iminophos-
5
phorane form occurred through cyclomerisation. Later on, the
In this work, we combined the capability of the aminopho-
2 2
synthesis of an open-chained iminophosphorane was reported in sphane tBu PNH (1) to act as a Lewis base and as a Brønsted
4
which substituents that increased the basicity of the phosphorus acid to synthesise new group 13/15 chain compounds.
6
atoms and the acidity of the nitrogen atoms were used.
The reaction of compound 1 and BH
3
·THF was performed
Additionally, reactions of the diaminophosphane tBuP(NH
)
2 2
at −50 °C in THF (Scheme 2). After warming to room tempera-
with the group 13 trialkyls MtBu (M = Al, Ga) led to group 13/15 ture and removing the solvent, the product tBu
2
P(NH
2
)BH
3
(2)
3
7
compounds containing the iminophosphorane form.
was obtained as colourless, needle-shaped crystals with a yield
Aminophosphanes also show a versatile deprotonation of 92% (Fig. 1).
chemistry, for example, the reaction of MeSi(NHPtBu ) with
The IR spectrum of substance 2 displays two characteristic
2
3
[MeSi B–H bands at 2867 cm− and 1200 cm . The BH
1
−1
group
nBuLi
NLiPtBu
leads
·3Et
to
O].
the
trilithium
complex
3
8
1
(
2
)
3
2
reveals a multiplet at 1.53 ppm in the H NMR spectrum as
well as a doublet at −40.6 ppm in the B{ H} NMR spectrum
1
1
1
1
with a coupling constant of J
= 65.6 Hz. For comparison,
B,P
Fachbereich Chemie and Wissenschaftliches Zentrum für Materialwissenschaften
WZMW), Philipps-Universität Marburg, Hans-Meerwein-Straße 4, 35043 Marburg,
Germany. E-mail: haenisch@chemie.uni-marburg.de; Fax: +49-6421-2825653
Dedicated to Professor Alexander C. Filippou on the occasion of his 60th
birthday.
Electronic supplementary information (ESI) available: Experimental details and
crystallographic data. CCDC 1818069 (3), 1818070 (2), 1818071 (4) and 1818072
5). For ESI and crystallographic data in CIF or other electronic format see DOI:
0.1039/c8dt01119b
(
†
‡
(
1
Scheme 2 Reaction pathway for the aminophosphane–borane adduct 2.
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Fig. 2 Molecular structure of 3 in the crystal. Thermal ellipsoids rep-
resent the 70% probability level. Carbon bonded hydrogen atoms are
omitted. Carbon atoms are shown in wire/sticks model for clarity.
Selected bond lengths in (pm) and angles in (°): P(1)–B(1) = 192.61(21),
P(1)–N(1) = 167.80(13), N(1)–B(2) = 141.91(26), N(2)–B(2) = 142.30(21),
P(2)–N(2) = 168.23(12), P(2)–B(3) = 192.56(26); B(1)–P(1)–N(1) = 112.98
(7), N(1)–B(2)–N(2) = 123.88(13), P(1)–N(1)–B(2) = 125.12(10) und P(2)–N
(2)–B(2) = 132.16(11).
Fig. 1 Molecular structure of 2 in the crystal. Thermal ellipsoids rep-
resent the 50% probability level. Carbon bonded hydrogen atoms are
omitted. Carbon atoms are shown in wire/sticks model for clarity.
Selected bond lengths in (pm) and angles in (°): P(1)–N(1) = 165.37(18),
P(1)–B(1)
= 191.7(2); B(1)–P(1)–N(1) = 110.24(10), C(4)–P(1)–C(8) =
1
12.49(10).
the analogue compound tBuP(NH
2
)
2
BH
3
shows a doublet at
1
1
1
similar to that in 2. As in 2, the P–N bond length of 3 (167.80
−
38.4 ppm in the B{ H} NMR spectrum with a coupling con-
1
12
31
(
13) and 168.23(12) pm) represents a P–N single bond, which
stant of JB,P = 75.9 Hz. At 77.4 ppm, the signal in the
P
indicates the exclusive presence of the aminophosphane form.
The distances between the nitrogen and the boron atoms
NMR spectrum of 2 shows a shift very similar to that of com-
1
2
pound tBuP(NH ) BH at 81.8 ppm.
2
2
3
(
N(1)–B(2) = 141.91(26) pm and N(2)–B(2) = 142.30(21) pm) are
The boron–phosphorus bond length is 191.7(2) pm and
within the range of other B–P bond lengths as in
2
15
within the typical range of B(sp )–N distances. With ∡N–B–N
1
close to the ideal angle of 120° for a trigonal planar coordi-
nation. This coordination allows a partial double bond charac-
ter between the boron and the nitrogen atoms and supports
the short B(sp )–N bond length. Thus, the N–B–N group of 3
can be seen as a fragment of borazine, and the comparison
shows similar bond lengths and angles (borazine: N(1)–B(1) =
1
=
1
3
23.88(13)°, the bond angle of the bridging boron atom B2 is
PhtBuP-ProlinolBH3 with 193.2(3) pm. The bond length
between the nitrogen and the phosphorus atom is 165.4(2) pm
and hence similar to other P–N single bonds in compounds
with coordination number 4 at the phosphorus atom, e.g. in
2
1
4
[
Et
3
PNH
Subsequently, we investigated the possibility of adding a
second BH group to the aminophosphane by the reaction of 1
2
]I with 165(2) ppm.
3
1
6
42.9(1) pm; ∡N–B–N = 117.1(1)°).
3 2
with an excess of BH ·SMe . The educts were added to
n-pentane at −20 °C, and the reaction mixture was then heated
to 40 °C (Scheme 3). After removing the solvent, the product
−
1
In the IR spectrum the NH band of 3 appears at 3305 cm
groups at 2870 cm− , which is
1
and the BH band from the BH
3
close to the corresponding values of 2. The BH band of the N–B
2 3 2
HB{N(H)PtBu BH } (3) was obtained as a colourless solid with
a yield of 73% (Fig. 2).
H)–N group can be observed at 2381 cm− , in good agreement
1
(
17
11
1
with the literature known B–H compounds. The B{ H} NMR
spectrum shows – similar to compound 2 – a doublet at
1
−
40.9 ppm with a coupling constant of JB,P = 68.1 Hz for the
BH
group. Compared with the B{ H} NMR signal of borazine
HBNH) at 30.2 ppm, the signal of compound 3 is slightly
shifted downfield. 3 shows two signals at 79.7 ppm and
3
groups and a broad singlet at 32.1 ppm for the N–B(H)–N
1
1
1
(
3
18
3
1
8
8.6 ppm in the P NMR spectrum, which can be related to the
steric strain at the phosphorus atom. The presence of the tert-
butyl- and BH groups leads, as observed in the crystal struc-
ture, to two different PtBu BH groups. A temperature depen-
Scheme 3 Reaction pathway for the seven-membered group 13/15
chain 3.
3
2
3
3
1
dent P NMR measurement reveals a coalescence at 350 K. The
Compound 3 is a group 13/15 chain containing seven same effect can be observed in the H NMR spectrum: two
heteroatoms and consists of two H BPtBu NH fragments signals of the tert-butyl groups (1.30 ppm and 0.97 ppm) appear
1
3
2
bridged by a BH group.
Crystals of 3 were obtained as colourless blocks from cyclo-
at room temperature and one signal (1.13 ppm) at 350 K.
After successfully applying boron compounds as Lewis
pentane at 3 °C. At 192.6(2) pm, the B–P bond length of 3 is acids, we investigated the reactivity of tBu PNH2 (1) with
2
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Scheme 4 Reaction pathway for the aminophosphane/iminophosphor-
ane hybrid compound 4.
heavier group 13 homologues, such as the group 13 alkyls
3
MtBu (M = Al, Ga).
The reaction of 1 with AltBu
3
at −50 °C gave in n-pentane
after warming to room temperature and removal of all volatile
compounds a colourless solid with a yield of 79% (Scheme 4).
As can be seen by IR and NMR spectroscopy as well as by
Fig. 3 Molecular structure of 4 in the crystal. Thermal ellipsoids rep-
resent the 70% probability level. Carbon bonded hydrogen atoms are
omitted. Carbon atoms are shown in wire/sticks model for clarity.
X-ray diffraction, the reaction of 1 with AltBu at low tempera- Selected bond lengths in (pm) and angles in (°): P(1)–N(1) = 160.86(48),
3
tures led to the formation of an aminophosphane/iminophos- P(2)–N(2) = 167.79(51), N(1)–Al(1) = 193.70(49), N(2)–Al(1) = 185.39(54);
P(1)–N(1)–Al(1) = 141.5(2), N(1)–Al(1)–N(2) = 107.77(17).
phorane hybrid compound. The product is a Lewis acid/base
adduct of the iminophosphorane tautomer of 1 coordinating
to the aluminium atom, as well as a covalently bonded, depro-
3
1
in the P NMR spectrum for the doublet at 62.9 ppm, indicat-
tonated aminophosphane formed under the loss of isobutane.
3
1
−
1
ing the presence of the iminophosphorane. The P NMR spec-
trum also shows a singlet signal at 65.5 ppm for the amino-
phosphane group. At high temperature (333 K) the P NMR
shows one broad signal (FWHM = 582 Hz) at 63.2 ppm.
Compound 4 was crystallised from benzene at 7 °C as col-
ourless blocks. There are two different P–N bond lengths in
compound 4. The P1 and N1 atom distance of 160.9(5) pm is
in good agreement with other iminophosphoranes, as for
The IR spectrum of 4 reveals a NH band at 3332 cm and a
−
1
PH band at 2410 cm . These values are in good agreement
3
1
with the literature known compound tBu(H)P(NH)NH AltBu
2
3
−
1
with the NH band at 3350 cm
2
and the PH band at
392 cm− . The existence of a PH band in the IR spectrum of
1 7
1
4
indicates an iminophosphorane form of tBu PNH . The H
2
2
NMR spectrum of 4 displays a singlet for the Al-tBu groups at
.36 ppm and two broad singlets at 1.21 ppm and 0.93 ppm
1
1
9
3 3 3
example (iPr PNSiMe )AlMe (P–N: 160.6(6) pm). At 167.8(5)
for the tert-butyl groups at the phosphorus atoms. The two
pm, the P2–N2 bond length of the aminophosphane group is
larger and in the range of P–N bonds observed in compounds
broad singlets split into two doublets at lower temperature
(213 K), indicating that the tert-butyl groups at the phosphorus
2
and 3. The aluminium compound [Me
2
Al(κ-N,N′-
atoms have different chemical environments. At 333 K the tert-
butyl groups at the phosphorus atoms show one broad signal
at 1.11 ppm. The protons at the nitrogen atoms are overlaid by
the broad tert-butyl groups at room temperature, but at lower
temperature (213 K) they appear as a doublet with a chemical
shift of 0.62 ppm (–P–NH–) and as a doublet of doublets at
Ph
2
PNPPh NSiMe )] contains as compound 4 phosphorus
2
3
atoms in the oxidation states III and V. This compound shows
P–N bond length in the range between 160.181 and 170.0(1)
2
0
pm. Two different values were also observed for the Al–N-
bonds in 4: the deprotonated aminophosphane group shows
an Al1–N2 bond of 185.4(5) pm and the iminophosphorane
group an Al1–N1 bond of 193.7(5) pm. The angle around the
aluminium atom ∡N–Al–N with 107.8(2)° is near to an ideal
tetrahedral angle (Fig. 3).
0
.97 ppm (–HPvNH–). With increasing temperature (333 K)
the two signals combine to one multiplet at 0.90 ppm. This
observation leads to the conclusion that at high temperatures
the proton at the phosphorus atom is not localised and oscil-
lates between the two phosphorus atoms as illustrated in
Scheme 5.
The analogous reaction of GatBu
3
and 1 at −65 °C in
n-pentane yielded 69% of tBu (H)PN(H)GatBu (5) as a colour-
2
3
less powder (Scheme 6).
Compound 5 was identified as the iminophosphorane form
of 1 bound to GatBu as a Lewis acid/base-adduct. The IR spec-
The PH group of the iminophosphorane shows a doublet at
.63 ppm in the H NMR spectrum with a coupling constant of
H,P = 445.0 Hz. The same coupling constant can be detected
1
5
J
1
3
−
1
troscopic analysis of 5 revealed a NH band at 3344 cm and a
PH band at 2399 cm− . These values are similar to those of tBu
1
Scheme 5 Proton exchange between the phosphorus atoms at high
temperatures of compound 4.
Scheme 6 Reaction pathway for the iminophosphorane 4.
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Acknowledgements
This work was supported by the Deutsche Forschungsgemein-
schaft (GRK 1782: “Functionalization of Semiconductors”).
Notes and references
1
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4
Fig. 4 Molecular structure of 5 in the crystal. Thermal ellipsoids rep-
resent the 70% probability level. Carbon bonded hydrogen atoms are
omitted. Carbon atoms are shown in wire/sticks model for clarity.
Selected bond lengths in (pm) and angles in (°): P(1)–N(1) = 160.01(9),
N(1)–Ga(1) = 206.65(12); P(1)–N(1)–Ga(1) = 142.18(6), C(1)–P(1)–C(2) =
6
3
4
5
6
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(
3
H)P(NH)NH GatBu described by Bauer et al. (NH band:
2 3
362 cm− ; PH band: 2356 cm−1). The H NMR spectrum of 5
1
7
1
displays a doublet of doublets at 5.54 ppm for the PH group
1
3
with the coupling constants of JH,P = 460.2 Hz and JH,H
1
=
P
1
31
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6.3 Hz. The JH,P coupling constant also appears in the
NMR spectrum for a doublet at 64.2 ppm. Both signals belong
V
1
to a P H-species, the iminophosphorane group of 5. In the H
NMR spectrum, the tert-butyl groups at the gallium atom form
a singlet at 1.50 ppm, and the ones at the phosphorus atom a
doublet at 0.76 ppm. The relative intensities are 3 : 2.
9
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P–N bond length (160.0(1) pm) is smaller than the P–N bonds of
the compounds 2 and 3. Yet, the value lies in the range of P–N
double bonds as found in the iminophosphorane group of com-
pound 4. At 206.7(1) pm, the bond length between the gallium
and nitrogen atom is relatively long, indicating a weak Lewis
acid/base bond. In contrast to 4, there is no isobutane elimin-
ation process in the formation of compound 5 due to the less
polar Ga–C bond in GatBu compared to Al–C in AltBu . This
1
1
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1
5 M. Möhlen, B. Neumüller, K. Harms, H. Krautscheid,
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3
lower temperature (2) and one at higher temperature (3). The
latter was identified as a group 13/15 compound with a seven-
membered heteroatomic chain. Using the higher homologues
AltBu and GatBu , the aminophosphane 1 yielded the tauto-
3 3
meric iminophosphane species 4 and 5 as Lewis acid/base-
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0 P. Braunstein, R. Hasselbring and D. Stalke, New J. Chem.,
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There are no conflicts to declare.
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