Phosphines with N-heterocyclic boranyl substituents

Article abstract of DOI:10.1039/c3dt52441h

A lithio-diazaborole reacted with diamino-chlorophosphines via metathesis to yield previously unavailable phosphinoboranes bearing amino substituents at both the phosphorus and boron atoms, and with Ph₂PCl and Mes*PCl₂via chloride tr

Full text of DOI:10.1039/c3dt52441h

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Phosphines with N-heterocyclic boranyl substituents†
M. Kaaz,a J. Bender,a D. Förster,a W. Frey,b M. Niegerc and D. Gudata,
Cite this: DOI: 10.1039/x0xx00000x
A lithioꢀdiazaborole reacted with diaminoꢀchlorophosphines via metathesis to yield previously
unavailable phosphinoboranes bearing amino substituents at both the phosphorus and boron
atoms, and with Ph2PCl and Mes*PCl2 via chloride transfer and reductive PP coupling to give
a chloroꢀdiazaborole and the corresponding diphosphine or diphosphene, respectively.
Diazaboroles with phenylphosphinoꢀ and PH2ꢀsubstituents were nonetheless accessible via
inverse metathesis upon treatment of a bromoborane precursor with phosphides PhnPH2ꢀnM (n
= 0 – 2, M = Li, K). The products were characterised by spectroscopic data and in most cases
by singleꢀcrystal Xꢀray diffraction studies which show the molecules to exhibit strongly
pyramidal coordination at the phosphorus atom and long BP bonds of 1.93 – 1.95 Å. The
insensitivity of the BP distance towards substituent effects and the tolerance of large sterically
induced torsional twists along the BP bond axis suggest the presence of pure single bonds
Received 00th January 2012,
Accepted 00th January 2012
DOI: 10.1039/x0xx00000x
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without any contribution from P
ꢀB dative πꢀinteractions. This view was confirmed by DFT
studies which indicate further that the molecules lack a significant electrophilic character at
boron but may act as potential σꢀdonor/πꢀacceptor ligands through the phosphorus atom.
Introduction
In addition, tuning of the Lewisꢀacidity and ꢀbasicity at the B
and P atoms by specific substituent effects has been employed
to overcome the preference of trivalent phosphorus atoms for a
pyramidal coordination geometry with a high energetic barrier
1
Phosphinoboranes (boranyl phosphines) R2BPR'2 have drawn
a good deal of attention as heavier congeners of the more
familiar aminoboranes, R2BNR'2. Both types of molecules can
towards planarization, which reduces the
πꢀoverlap of the
draw sizable stability from E
which may in principle occur intermolecularly via creation of
dative ꢀbonds between boron and pnictogen atoms of different
molecules, or intramolecularly via dative ꢀbonding (Chart 1).
ꢀB Lewisꢀacid/base interactions
phosphorus loneꢀpair with the empty pꢀorbital at boron and thus
the BP double bond character.1 In particular, the groups of
Power 2 and Stephan 3 have reported on phosphinoboranes with
nearly or exactly planar coordination at both the boron and
σ
π
Intermolecular interactions generate usually cyclic oligomers
(frequently dimers) of rather low reactivity that are often
perceived as analogues of cycloalkanes and have dominated the
early stages of the development of phosphinoborane chemistry.1
3
phosphorus atoms and concomitantly short BP bonds (cf. PB
= 1.786(4) Å for monomeric tBu2PB(C6F5)2 (
1) vs. PBavg =
2.057(3) Å for dimeric [R2PB(C6F5)2]2 with R = Et, Ph). Even if
the presence of a strong πꢀbonding contribution in 1 and related
systems is beyond doubt,1,2 it is remarkable that these species
R'2E BR2
R'2E BR2
R2B ER'2
still seem to display some Lewisꢀambiphilic character; e. g. the
3
capability of
1
to effect heterolytic cleavage of H2 resembles
Chart 1 Schematic representation of the stabilisation of amino- and phosphino-
boranes by intermolecular and intramolecular E
closely the analogous reactivity of frustrated Lewis pairs.
As alternative approach to the strengthening of PB ꢀbonding
ꢀB electron donation (E = N, P)
π
Dedicated strategies for the stabilisation of monomeric contributions, monomeric phosphinoboranes have also been
phosphinoboranes have systematically been developed since the successfully stabilised by the introduction of amino groups at
1980ies. Monomer formation is generally fostered by boron.4 The low inversion barrier at nitrogen facilitates N
ꢀ
Bꢀ
increasing steric demand of substituents, in particular at boron.
πꢀdonation to saturate the Lewisꢀacidity at boron, which renders
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Bꢀ
Journal Name
DOI: 10.1039/C3DT52441H
Pꢀ
π
ꢀbonding energetically unattractive and removes hence metal phosphides R'2PM (M = alkaline metal).1b As the anion
7
the main driving force for planarization at phosphorus. stabilising effect of amino substituents is very limited and
P
ꢀ
4a
4f
Phosphinoboranes with
(Chart 2) exhibit therefore pyramidal coordination at obviously unsuitable for the synthesis of target compounds 4a-
phosphorus and elongated B–P distances (BP 1.948(3) Å for . Considering that the phosphorus atoms in P(NR2)2 units
and 1.982(5) Å for ) which slightly exceed the sum of covalent exhibit, however, distinct electrophilic character, metathesis
radii (1.93 Å 1a) and are addressed as single bonds.1 Aside from with a boronꢀcentred nucleophile should be a viable alternative.
B
ꢀaminoꢀsubstituents like
2
and
3
amino substituted phosphides are not known, this route is
2
c
3
the structural aspects, the weakening of the electrophilic A suitable reagent is
Nꢀheterocyclic lithioꢀborane 6 which was
character at boron brings also the phosphine character to the first prepared by Nozaki et al. (scheme 1) in 2006,8 and has
fore, and BꢀNR2 substituted phosphinoboranes act therefore as since developed into a versatile tool for the creation of boronꢀ
well behaved as 2eꢀdonor ligands towards transition metals via element bonds in metathesis reactions with various organic and
their phosphorus lone pair.1b
organometallic electrophiles.6,9 The bulky
NꢀDipp (Dipp = 2,6ꢀ
diꢀisopropylꢀphenyl) substituents in this species must be
considered an additional benefit as they provide efficient steric
protection at the boron centre which should help to stabilise
phosphinoborane monomers.
Cl
N
Mes
PH
(Me3Si)3Si
B
B
PPh2
(iPr)2N
2
3
2 C10H8Li
THF
Dipp
N
Dipp
N
Bu
Dmp
N
BBr
BLi(THF)2
Dipp
N
t
NMe2
Ph
P
H
H
H
N
N
Dipp
N
Dipp
- 2 C10H8
- LiBr
B
PR2
PR2
=
P
P
P
P
P
N
Dipp
N
tBu
N
NMe2
Ph
Ph
Dmp
5
6
4a
4b
4c
4d
4e
4f
Scheme 1 Preparation of lithiated N-heterocyclic borane
al. 8
6 according to Nozaki et
Chart 2 Molecular structures of selected B-amino substituted phosphinoboranes
(Mes = mesityl, Dmp = 2,6-dimethylphenyl, Dipp = 2,6-di-isopropylphenyl)
Following the protocol of Nozaki et al.,8,9b lithioꢀborane
generated by reaction of bromoꢀdiazaborole with excess
6 was
Before this background, we became interested in preparing
5
derivatives like 4a-c which combine an
Nꢀheterocyclic borolyl
lithium powder in the presence of naphthalene. We noted that
quantitative conversion of the starting materials (as established
by 11B NMR spectroscopy) required more forcing conditions
than originally reported (24 h reaction time at ꢀ18 °C rather
than 12 h at ꢀ40 °C 8), presumably due to lower reactivity of the
Li powder used. After the reaction was complete, unreacted
metal and precipitated salts were removed by filtration through
celite. The synthesis of 4a was carried out by cooling the deep
(NHB) fragment 5 with a diaminophosphinyl unit. Incorporation
of the boron atom into a rigid and electron rich heterocycle
maximises N
residual electrophilic character at this site, so that the NHB unit
may be simply regarded as strong ꢀdonor substituent at the
ꢀBꢀπꢀconjugation and should eliminate any
σ
diaminophosphinyl unit (a similar concept has been pursued in
case of NHBꢀstabilised silylenes and their homologues 6).
Phosphinoꢀdiazaboroles are thus expected to behave no more as
Lewis ambiphiles but as monofunctional phosphines which
should perform as strong donor ligands in metal complexes.
Apart from the fact that phosphinoboranes carrying exclusively
amino substituents are so far unknown, these species seem
appealing as they can be formally viewed as dimerization
purple solution of crude
6 to ꢀ78 °C and subsequent addition of
a
hexane solution containing an excess of chloroꢀ
bis(dimethylamino)phosphine 7a (Scheme 2).
Dipp
N
NMe2
ClP(NMe2)2 7a
THF/hexane
-78 °C
B
P
P
4a
products of two carbene analogues (a nucleophilic
heterocyclic diazaborolyl and an electrophilic diaminoꢀ
phosphenium ion) via dative B P interaction.
Nꢀ
N
Dipp
NMe2
Dipp
N
- LiCl
- LiCl
ꢀ
BLi(THF)2
N
Dipp
We report here the synthesis and full characterisation of tetraꢀ
aminoꢀsubstituted phosphinoboranes which combine NHB
Dipp
N
R
N
R
N
4b (R = tBu)
B
4c (R = Dmp)
6
moieties with acyclic (4a) or
Nꢀheterocyclic phosphinyl units
ClP
7b,c
N
Dipp
N
R
N
R
(
4b ). In addition, the preparation and characterisation of some
,c
diaminoꢀsubstituted phosphinoboranes grouping NHB and
nucleophilic phosphinyl fragments (4d-f) will be described.
THF/hexane, -78 °C
Scheme 2 Synthesis of phosphinoboranes 4a-c
Results and discussion
For the synthesis of bisꢀheterocyclic derivatives 4b,c, lithioꢀ
borane was first purified by extraction into hexane and
separation of all hexaneꢀinsoluble components. Metathesis
reactions were then carried out by addition of THF solutions
6
Syntheses and spectroscopic studies
Phosphinoboranes R2BPR'2 are generally prepared by salt
metathesis starting from haloboranes R2BX (X = halogen) and
2 | J. Name., 2012, 00, 1-3
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DOI: 10.1039/C3DT52441H
containing equimolar amounts of
Nꢀheterocyclic chloro
Dipp
N
phosphines 7b,c at ꢀ78 °C (Scheme 2). Reaction monitoring by
31P and 11B NMR disclosed that 4a-c constituted the only
detectable reaction products in addition to unreacted starting
material (7a) and minor amounts of hydrolysis products.
2 Ph2PCl
THF/hexane
- 78 °C
+
Ph2P-PPh2
BCl
+
4d
N
Dipp
(< 5%)
Dipp
N
- LiCl
8
10
BLi(THF)2
Target phosphinoboranes 4a-c were isolated in decent yields as
colourless, air and moisture sensitive solids and were identified
and characterised by spectroscopic and singleꢀcrystal Xꢀray
diffraction studies. The presence of direct phosphorusꢀ boron
bonding was immediately evident from the broadening of 31P
NMR signals due to partially relaxed spin coupling to the
quadrupolar 10B (19.9% nat. abundance, I = 3) and 11B (80.1%
N
- LiCl
Dipp
N
Dipp
6
Mes*PCl2
THF/hexane
- 78 °C
+ 0.5
BCl
Mes*P=PMes*
N
Dipp
8
9
Scheme 3 Reactions of
6 with Ph2PCl and Mes*PCl2
1
nat. abundance, I = 3/2) nuclei. Determination of JBP coupling
The outcome of these reactions is easily rationalised if one
acknowledges that mainꢀgroup organometallics like are not
only potent nucleophiles, but may also act as reducing agents.
The generation of 10 is then readily explained via a formal twoꢀ
step pathway involving first Li/Cl exchange between
ClPPh2 to give and LiPPh2, followed by salt metathesis of the
formed phosphide with a second equivalent of the chloroꢀ
phosphine. A similar mechanism may be invoked to explain the
constants was feasible from neither 11B nor 31P NMR spectra.
The 31P chemical shifts of 4a-c (70 – 100 ppm) compare to
those of related symmetrical diphosphines (80 – 90 ppm for
6
(i
Pr2N)2PP(NiPr2)2 and bisꢀdiazaphospholenyls 10), and the 11B
6 and
chemical shifts (23.5 – 25.9 ppm) are slightly larger than those
8
9b
9b
of
featuring a hydrogen instead of the bromoꢀsubstituent at boron.
An unexpected result was obtained when was reacted with
5
(20.9 ppm) and the diazaborole 5-H
(22.9 ppm)
6
formation of 9. A heuristic explanation for the preference of 6
chloroꢀdiazaphospholene 7d (R = Dipp) in hexane. Reaction
monitoring by 31P and 11B NMR revealed that a mixture of 5-H
and two phosphorus containing products (with 31P chemical
shifts of 95.8 and 117.4 ppm) had formed. Even if none of these
species was as yet positively identified, a phosphinoborane
structure is definitely excluded as both signals appear as narrow
lines that show no sign of 31P,10/11B spin coupling. We presume
that metathesis is impeded due to steric overcrowding, and that
the observed products arise rather from a process involving
to react with Mes*PCl2 and Ph2PCl via reductive coupling and
with diamino chlorophosphines (in the reactions leading to 4a-
c) via salt metathesis becomes feasible if one relates the
observed reactivity of a substrate R2PCl to the electronic
properties of R: amino groups permit better delocalisation of
the positive partial charge in the R2P fragment by πꢀ(hyper)ꢀ
conjugation than halogen or phenyl substituents and render the
phosphorus atom a weaker electrophile,12 which obviously
disfavours the formal reduction of the phosphorus centre in a
coupling process and brings metathesis reactions to the fore.
In order to verify the phosphinoborane nature of the side
cleavage of a coordinated THF molecule in 6. Investigations
aiming at further elucidation of the reaction pathway (including
reaction studies in deuterated solvents) are currently under way
but have not yet provided any decisive results, and we want to
refrain at this point from a further discussion of this aspect.
product in the reaction of
species via conventional metathesis of a boron electrophile
6 with ClPPh2, we tried to access this
1b
with a phosphorus nucleophile. The expected product 4d was
Trying to extend the metatheses of
6 to further halophosphines
indeed formed selectively in the reaction of
5 with LiPPh2 and
in order to access phosphinoꢀdiazaboroles with a wider range of
substitution patterns, we further investigated reactions with
Mes*PCl2 (Mes* = 2,4,6ꢀtriꢀtertꢀbutylphenyl) and Ph2PCl. The
31P and 11B NMR spectra of reaction mixtures revealed that
isolated in good yield after standard workꢀup. Analogous
transformations permitted to convert secondary or primary
phosphides PhPHLi and KPH2 into PHꢀfunctionalised
phosphinoboranes 4e,f (Scheme 4).
treatment of
6 with Mes*PCl2 at ꢀ78 °C produced a mixture of
9a
chloroborane
8
(δ 9
11B 22 ppm) and diphosphene 11 (Scheme
MPR1R2
3) which was identified by means of its characteristic 31P
chemical shift of 573.5 ppm and a singleꢀcrystal Xꢀray
diffraction study of a crystalline sample isolated in low yield
from the reaction mixture. The NMR spectroscopic survey of
Dipp
N
Et2O
-78 °C or rt
Dipp
N
R1
R2
BBr
B
P
- MBr
N
Dipp
N
Dipp
the reaction of
6
with ClPPh2 (complete conversion of the
5
4d (R1 = R2 = Ph)
4e (R1 = Ph, R2 = H)
4f (R1 = R2 = H)
starting material required addition of two equivalents) disclosed
that a product addressed as phosphinoborane 4d (broad 31P
NMR signal at ꢀ61.1 ppm,) had formed in low yield (< 5%
according to integration of 31P NMR signals) whereas the main
Scheme 4 Synthesis of phosphinoboranes 4d-f (M = Li (4d,e), K (4f))
All three compounds 4d-f are colourless, thermally stable solids
which are much less sensitive to air and moisture than 4a-c; in
particular, 4e was found to be perfectly stable in contact with
air or water in the solid state and in solution. Characterisation
was accomplished by spectroscopic data and in case of 4e,f by
products were identified as chloroborane
diphosphine 10
31P ꢀ15.6, Scheme 3).
8 and tetraphenyl
(
δ
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DOI: 10.1039J/oCu3DrnT5a2l4N41aHme
singleꢀcrystal Xꢀray diffraction studies. The 11B NMR data of
4d-f are very similar to those of 4a-c whereas the 31P chemical
shifts follow the same trend as those of phenyl phosphines
Ph3ꢀnPHn (n = 0 – 3), moving to progressively higher field with
increasing number n of hydrogen substituents.
A primary exploration of the chemical properties revealed that
4e reacts with nꢀbutyl lithium to afford phosphidoborane 11
(Scheme 5) which gives rise to a singlet at slightly larger
chemical shift (δ
31P ꢀ116.1 vs. ꢀ130.4 for 4e) in the 31P NMR
spectrum. A similar reactivity had previously been noted by
Power et al. for secondary phosphinoboranes Mes2BP(H)R (R =
alkyl, aryl, SiMe3).13 The identification of 11 was confirmed by
a preliminary singleꢀcrystal Xꢀray diffraction study. Even if
severe disorder and limited data quality impeded satisfactory
refinement of the molecular structure, the data prove the
existence of dimeric molecules featuring a central Li2P2 ring
formed by association of two monomeric units via pairwise
Li…P interactions, trigonal planar coordination at boron as well
as tetrahedral coordination at phosphorus, and a strongly
twisted arrangement of the CPh–P–BN2 unit (a representation of
the molecular structure is included in the ESI). We attribute the
deviation of these structural features from those of Power's
monomeric boryl phosphides [Mes2BPMes][Li(12ꢀcrownꢀ4)2]
and Mes2BP(R)Li(THF)2, which exhibit planar arrangement of
the C–P–BC2 skeleton and substantial boronꢀphosphorus double
bond character,13 to a combination of insufficient steric
protection at phosphorus and the repression of BP double bond
character due to the reduced Lewisꢀacidity of the boron atom.
Dipp
N
Dipp
N
n-BuLi
THF, rt
B
P(H)Ph
0.5
B
P(Ph)Li(THF)
- BuH
N
Dipp
N
Dipp
2
4e
11
Scheme 5 Generation of a phosphidoborane by lithiation of 4e
Single-crystal X-ray diffraction studies
The molecular structures of 4a-c, 4e, and 4f are displayed in
Figs. 1 and 2, and selected structural parameters are listed in
Table 1.
All molecules exhibit the expected monomeric structures. The
BN2C2 rings are planar (which implies implicitly trigonal planar
coordination geometries for both the boron and the endocyclic
nitrogen atoms), and endocyclic distances (B–N 1.418(4) to
1.445(2) Å, C–N 1.397(3) to 1.405(3) Å, C–C 1.332(2) to
1.344(2) Å) differ not significantly from the structural data of
previously reported diazaboroles.6,8,9 Likewise, the PN2C2 rings
in 4b,c exhibit bond distances (P–N 1.737(1) to 1.753(1) Å, N–
C 1.420(2) to 1.428(2) Å, C–C 1.329(2) to 1.334(3) Å) and
envelope conformations which repeat wellꢀknown features of
Figure 1 ORTEP-style representation of the molecular structures of (from top to
bottom) 4a-c in the crystal. Thermal ellipsoids are drawn at 50% probability level;
hydrogen atoms are omitted for clarity.
The phosphorus atoms exhibit distinctly trigonal pyramidal
coordination geometry, with the sums of bond angles ranging at
the lower end of the span reported for phosphinoboranes (296°
– 360°).15 The B–P distances are rather insensitive to changes
of the substituents at phosphorus (a slight bond elongation by 2
pm in 4b,c is attested to reflect the effect of increasing steric
congestion) and lie at the upper end of the range of known bond
distances in acyclic monomeric phosphinoboranes (1.786 to
P
ꢀsubstituted diazaphospholenes.14 The slightly pyramidal
coordination at the ꢀbound nitrogen atoms in 4a-c reflects the
P
influences of steric congestion and mutual repulsion between
loneꢀpairs at the adjacent N and P atoms.14
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1.986 Å, mean value 1.897(6) Å).15 The coincidence of strong 0° – which grants optimum
π
ꢀoverlap between the loneꢀpair at
pyramidalisation at phosphorus and elongated B–P bond phosphorus and the empty pꢀorbital at boron – and confirm that
distances goes with the previously observed inverse correlation these compounds exhibit the same conformational preference as
between both parameters which has been attributed to two most previously known phosphinoboranes (including beside
sources, viz. variation of PBꢀ
phosphorus.2 Comparison with the available reference data
gives a first indication that ꢀbonding in is negligible and the 6°). In contrast, 4c exhibits a strongly twisted structure (
πꢀbonding and rehybridisation at species with strong πꢀbonding contributions also derivatives
15
4a
with a low degree of double bond character like
2
with
φ
φ
=
=
π
4
BP bonds should therefore be addressed as pure single bonds.
67°) which approaches a situation where
blocked by orthogonal arrangement ( = 90°) of the R'2P and
BR2 units. A similar distortion has previously been established
πꢀbonding is totally
φ
4f
for
3
(φ = 62°) and is consistently explained as being
enforced by steric repulsion between the extremely bulky
substituents. Quite remarkably, the strong torsional distortion of
4c as compared to 4b leaves the BP distance invariant, which is
hardly compatible with the presence of a perceptible πꢀbonding
1a
contribution and gives thus further support to the perception
of the BP bonds as pure single bonds.
Computational studies
In order to verify our interpretation of the structural features of
the phosphinoꢀdiazaboroles under study, we performed DFT
calculations, using 4b and a simplified derivative 4' featuring
the same heterocyclic framework with methyl instead of the
bulkier
archetypal model compounds. The computations were carried
out with the
B97XꢀD functional,16 which includes longꢀrange
tBu and Dipp substituents at all nitrogen atoms as
ω
and dispersion corrections, in combination with a ccꢀpVDZ
basis set; the same computational model has recently been
shown to allow a realistic structural modelling of sterically
encumbered bisꢀdiazaphospholenyls.10c Energy optimisation of
the molecular structures of 4b and 4' produced results that are
not only quite similar to each other, but show also qualitatively
and quantitatively good agreement with the experimentally
determined structural parameters of 4b (see Table 2 and ESI).
Table 2 Comparison of selected calculated structural parameters (at the
ωB97XꢀD/ccꢀpVDZ level) for 4' and 4b with experimental data for 4b
Figure 2 ORTEP-style representation of the molecular structures of 4e (top) and
4f (bottom) in the crystal. Thermal ellipsoids are drawn at 50% probability level;
hydrogen atoms of CH bonds are omitted for clarity. One orientation of the
disordered iso-propyl group in 4e is displayed.
B–P [Å]
Sum of bond angles [°]
twist angle
at B
at P
at NP a)
φ
[°]
0
0
4' Calcd.
4b Calcd.
1.948
1.950
359.5
358.8
290.6
294.5
337.9
344.4
Table 1 Selected structural parameters for 4a-c, 4e and 4f
344.4
4b
Exp.
1.951(2)
359.1(4)
292.1(2)
348.1(4)
343.1(4)
3(1)
B–P [Å]
Sum of bond angles [°]
twist angle
b) [°]
at B
at P
at NP a)
φ
4a 1.9303(15)
357.9(3)
317.3(2)
354.1(3)
354.5(3)
348.1(4)
343.1(4)
348.5(3)
351.3(4)
ꢀ
7(1)
a) Nitrogen atoms in P –N bonds
4b
4c
1.951(2)
1.953(2)
359.1(4)
360.0(4)
292.1(2)
293.8(2)
3(1)
Experimentally determined and computed molecular structures
of 4b differ mainly in the alignment of the tertꢀbutylꢀ and Dippꢀ
substituents, which we attribute to the unfeasibility of
modelling computationally the influences imposed by crystal
packing effects. The structural features of the bisꢀheterocyclic
core of 4' deviate from those of 4b chiefly in showing an even
stronger pyramidalisation at the Nꢀ and Pꢀatoms in the PN2C2
67(1)
4e
4f
1.931(3)
1.923(2)
359.3(6)
359.6(4)
299(2)
284(4)
1(3)
3(5)
ꢀ
a) nitrogen atoms in P –N bonds; b) angle between the perpendiculars to the
local P and B planes when viewed down the P–B bond axis (cf. ref. 2)
ring, which indicates that steric repulsion between the
Nꢀtertꢀ
Further support for this interpretation is gained from an analysis
of the torsional alignment of R'2P and BR2 fragments with
butyl groups and the diazaphospholene ring in 4b is presumably
more important than between substituents at the boron and
phosphorus heterocycles. Without going into detail, this finding
respect to the BP bond axis. The twist angles
φ (as defined in
Table 1) in 4a,b,d,e of 1° to 7° come close to the ideal value of
This journal is © The Royal Society of Chemistry 2012
J. Name., 2012, 00, 1-3 | 5

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ARTICLE
DOI: 10.1039J/oCu3DrnT5a2l4N41aHme
corroborates also that the pyramidal coordination of the confined to the N2C2 framework as in other
diazaphospholeneꢀnitrogen atoms is mainly of electronic origin diazaphospholenes.14
P
ꢀsubstituted
(i.e. attributable to mutual repulsion of the nitrogen and Similar results as for 4' were also obtained from analysis of the
phosphorus loneꢀpairs). KSꢀorbitals of 4b, with the exception that the first four
Inspection of the KohnꢀSham (KS) orbitals of 4' reveals that the unoccupied orbitals constitute *ꢀorbitals of the aromatic rings
HOMO (we will use HOMO and LUMO instead of the clumsy of the Dipp substituents, and the *(PN)ꢀtype orbitals are
π
σ
– even though more exact – notations "highest occupied/lowest assigned only to the two next higher levels.
unoccupied KSꢀorbital") is strongly delocalised, containing The perception of a true covalent boronꢀphosphorus bond
contributions from the
and the phosphorus loneꢀpair with a weakly BPꢀ
contribution (Fig. 3). The LUMO is merely an antibonding reactions of 4': comparison of the values of
π
ꢀelectron systems of both heterocycles (rather than a dative Lewisꢀdonor/acceptor interaction) is also
ꢀbonding supported by calculated energies for BP bond breaking
Ezpe,corr (which
*(PN) orbital and has no prominent coefficient at boron, include corrections for vibrational zeroꢀpoint energies and basis
σ
ꢀ
σ
whereas the LUMO+1 exhibits contributions from all atoms of set superposition error) computed at
ωB97XꢀD/ccꢀpVDZ level
the central N4BP unit and can be characterised as
σ*(PN) and reveals that heterolytic bond cleavage to give a phosphenium
π
*(BN) antibonding, and (BP) bonding; the largest cation/diazaborolide anion pair requires, not surprising, by far
π
coefficients are likewise found on the phosphorus atom.
more energy (
ꢀ
Ezpe,corr = 174.9 kcal molꢀ1) than homolytic
Ezpe,corr = 64.6 kcal molꢀ1).
cleavage to produce a radical pair (
ꢀ
Taken together, the computational results consistently confirm
our initial hypotheses that the effect of aminoꢀsubstituents
suppresses both the electrophilic character at boron and the
development of BPꢀ
best described as a pure
π
ꢀbonding. The phosphorusꢀboron bond is
ꢀbond, leaving the idea to describe
σ
species like 4b as Lewisꢀdonor/acceptor adducts of carbeneꢀ
analogue phosphenium and diazaborolyl fragments a purely
formal analogy. The structure of the KSꢀorbitals indicates that
phosphinoꢀdiazaboroles may serve as Pꢀdonor ligands.
Conclusions
It has been established that nucleophilic lithioꢀdiazaboroles
show twoꢀsided reactivity towards chlorophosphine substrates.
Reactions with diaminoꢀchlorophosphines proceed like those
9
with silyl and transition metal halides
via metathesis to
produce phosphinoꢀdiazaboroles, and gave for the first time
access to phosphinoboranes bearing ꢀaminoꢀsubstituents.
Synthesis of a diazaphospholenylꢀdiazaborole bearing ꢀDipp
P
N
substituents on both rings was impeded by steric overcrowding,
but the detection of products pointing to a possible THF
activation stimulates further investigation of this reaction with
the prospect to prove involvement of a phospheniumꢀborolide
ion pair as transient intermediate. In contrast, reactions with
aryl (di)chlorophosphines occur via formation of a chloroꢀ
diazaborole and reductive coupling of the phosphine substrate
to create a diphosphine or diphosphene, respectively. The
Figure 3 Visual representations of selected Kohn-Sham orbitals of 4' calculated at
the ωB97X-D/cc-pVDZ level of theory (top, LUMO+1; middle, LUMO; bottom,
HOMO). Isodensity surfaces were drawn for a value of 0.05 a.u.
Analysis of the remaining occupied KSꢀorbitals in the frontier
orbital region discloses that
πꢀbonding interactions are confined
to the heterocyclic PN2C2 and BN2C2 moieties, and that in no
expected
accessible via metatheses of
P
ꢀarylphosphinoꢀdiazaboroles were nonetheless
bromoꢀdiazaborole with
case any significant π(BP) interaction is present. These findings
a
are in accord with an NBO analysis 17 which shows that the BP
bonding interaction arises from a single LMO that is rather
evenly distributed between both atoms (45% B, 55% P),
phosphides PhnPH2ꢀnM (n = 0 – 2, M = Li, K).
Crystallographic studies showed the products formed to possess
phosphorus atoms with strongly pyramidal coordination sphere,
and elongated boronꢀphosphorus bonds which do not show
large variation in length upon change of substituents and
tolerate large sterically induced torsional distortions around the
bond axis. These findings fully back the anticipation that the
indicative of a covalent
σꢀbond. Secondꢀorder perturbation
theory analysis of the Fock matrix in the NBO basis indicates
that the empty pꢀorbital at boron participates in strong
conjugation in the BN2C2 ring, which is dominated by N
interactions with second order perturbation energies
π
π
ꢀ
ꢀ
ꢀ
E
B
(2) of
boronꢀphosphorus interaction is best described as a pure
σꢀbond
92.9 kcal molꢀ1; P
ꢀB donation remains marginal (
E
(2) = 7.8
which is unaffected by any dative P Bꢀ ꢀoverlap. The results
ꢀ
π
kcal molꢀ1). Delocalisation in the PN2C2 ring is small and
of DFT studies corroborate this view and indicate that
6 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 2012

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ARTICLE
DOI: 10.1039/C3DT52441H
6
phosphinoꢀdiazaboroles are potential ligands which are inclined 3.3 Hz,
to engage in ꢀdonor/ ꢀacceptor interactions with a transition CH(
CH(CH3)2), 26.3 (s, CH(
C
H3)2), 22.6 (d, JCP = 2.5 Hz,
σ
π
C
H3)2). – 31P{1H} NMR: δ = 100.0 (broad). – Anal. for
metal through the phosphorus atom, but display apparently no C30H50BN4P (508.54 g molꢀ1): calcd. C 70.86, H 9.91, N
electrophilic character at boron. It remains to be seen if the 11.02%; found C 69.27, H 9.12, N 10.59%.
marked delocalisation of the HOMO permits also to develop
alternative coordination modes (at least for derivatives with less 2-(1,3-BIS(2,6-DI
steric protection around the boron heterocycle). We are 1,3-DI
currently exploring possible uses of phosphinoꢀdiazaboroles as A solution of
-
ISOPROPYLPHENYL)-1,3,2-DIAZABOROLYL)-
(
TERT
-
BUTYL)-1,3,2-DIAZAPHOSPHOLENE (4
B)
5
(1.00 g, 2.14 mmol), lithium powder (148 mg,
strongly electron donating ligands, as well as further ways to 21.4 mmol) and naphthalene (137 mg, 1.07 mmol in THF (20
use the functionality of derivatives with primary and secondary mL) was cooled to ꢀ18 °C and stirred for 24 h. The dark purple
phosphino groups for further transformations.
suspension was filtered through celite and evaporated to
dryness. The residue was taken up in 30 mL of hexane, and
again filtered through a layer of celite to remove insoluble
components. The dark red filtrate was cooled to ꢀ78 °C. A
solution of 7b (502 mg, 2.14 mmol) in THF (10 mL) was added
drop wise with stirring. The suspension turned yellow, and
stirring was continued for 30 min at ꢀ78 °C and then 1 h at rt.
Insoluble salts were removed by filtration through celite.
Volatiles were evaporated under reduced pressure to yield 680
mg of 4b (yield 54 %). A crystalline sample (m. p 175 °C) was
obtained by recrystallisation from hexane. – 1H NMR (C6D6): δ
Experimental
Materials and Methods
All manipulations were carried out under dry argon using
standard Schlenk technique. Solvents were purified by standard
procedures. NMR spectra: Bruker Avance 250 (1H: 250 MHz,
11B: 80.2 MHz, 13C: 62.9 MHz, 31P: 101.2 MHz) in C6D6 or
CDCl3 at 30 °C. Chemical shifts were referenced to ext. TMS
(1H, 13C), BF3(OEt2) (11B;
H3PO4 (31P;
= 40.480742 MHz). Coupling constants are
Ξ = 32.083974 MHz), or 85 %
4
Ξ
= 7.11ꢀ7.25 (m, 6 H, C6H3), 6.09 (d, 2 H, JPH = 0.9 Hz =CH),
3
3
given as absolute values. Elemental analysis: PerkinꢀElmer
2400CHSN/O Analyser and Elementar Micro Cube. The large
deviations between calculated and found analytic compositions
for 4a-c are attributable to the high airꢀsensitivity of these
compounds. Melting Points were determined with a Büchi Bꢀ
545 melting point apparatus in sealed capillaries.
5.94 (d, 2 H, JPH = 5.7 Hz, =CH), 3.36 (sept, 4 H, JHH
6.8.Hz, CH), 1.41 (d, 12 H, 3JHH = 6.8 Hz, CH3), 1.19 (d, 12 H,
3JHH = 6.8 Hz, CH3), 0.79 (s, 18 H, Bu). – 11B{1H} NMR: δ =
=
t
25.8 (broad). – 13C{1H} NMR: δ = 146.0 (s,
oꢀC6H3), 141.2 (s,
i
ꢀC6H3), 127.1 (s,
(s,
Hz, N
= 1.6 Hz,
Hz, CH(
p
ꢀC6H3), 124.0 (d, 2JPC = 4.8 Hz, =CH), 123.4
2
m
ꢀC6H3), 121.7 (d, JPC = 2.6 Hz, =CH), 54.8 (d, 2JPC = 11.6
Diazaborole 5 9b diazaphospholenes 7b,c 19 PhPH2,20 and KPH2
, ,
C
(CH3)3), 29.4 (d, 3JPC = 8.7 Hz, NC(
H(CH3)2), 26.0 (s, CH(
C
H3)3), 28.6 (d, 5JPC
H3)2), 22.8 (d, JPC = 1.5
21 were synthesised as described. Lithium powder was prepared
by washing commercially available lithium dispersion (Sigma
Aldrich, 25 wt % in mineral oil, > 0.05% Na) with hexane and
drying under vacuum.
6
C
C
C
H3)2). – 31P{1H} NMR: δ = 70.1 (s). – Anal. for
C36H56BN4P (586.65 g molꢀ1): calcd. C 73.71, H 9.62, N 9.55%;
found C 72.10, H 9.47, N 9.20%.
Synthetic Procedures
2-(1,3-BIS(2,6-DI
-ISOPROPYLPHENYL)-1,3,2-DIAZABOROLYL)-
1-(1,3-BIS(2,6-DI
N,N,N’,N’-TETRAMETYL
-
ISOPROPYLPHENYL)-1,3,2-DIAZABOROLYL
PHOSPHINEDIAMINE (4
-
1,3-BIS(2,6-DIMETHYLPHENYL)-1,3,2-DIAZAPHOSPHOLENE (4
C
)
-
A)
The synthesis was carried out analogously to that of 4b starting
from 1.00 g of and 708 mg of 7c. Crude 4c was isolated in 56
A solution of
5 (500 mg, 1.07 mmol), lithium powder (74 mg,
5
10.7 mmol), and naphthalene (69 mg, 0.56 mmol) in THF (10
mL) was cooled to ꢀ18 °C and stirred for 24 h. The dark purple
suspension was filtrated through celite. The deep purple filtrate
was cooled to ꢀ78 °C, and excess chloroꢀbis(dimethylamino)
phosphine (0.1 mL) was slowly added with stirring. The
solution turned yellow, and stirring was continued for 30 min at
ꢀ78 °C und further 30 min at rt. All volatiles were removed
under reduced pressure. The residue was dissolved in 40 mL
hexane and filtered through celite to remove insoluble salts.
The filtrate was concentrated to a volume of 20 mL and stored
% yield. A crystalline sample (m. p. 181 °C) was obtained by
recrystallisation from hexane. – H NMR (C6D6): δ = 7.20ꢀ7.08
1
(m, 6 H, C6H3), 6.90ꢀ6.70 (m, 6 H, C6H3), 6.21 (d, 2 H, d, JPH
=
2.0 Hz, =CH), 5.49 (d, 2 H, JPH = 2.9 Hz, =CH), 3.26 (sept, 4
3
5
H, JHH = 6.8 Hz, CH(CH3)2), 2.30 (d, 12 H, JPH = 0.9 Hz,
3
CH3), 1.15 (d, 12 H, JHH = 6.8 Hz, CH(CH3)2), 1.06 (d, 12 H,
3JHH = 6.8 Hz, CH(CH3)2). – 11B{1H} NMR: δ = 23.5 (broad). –
13C{1H} NMR: δ = 145.6 (s,
o
ꢀC6H3), 140.8 (s,
i
ꢀC6H3), 144.0
ꢀC6H3),
pꢀC6H3), 124.9 (d, JPC = 4.8 Hz,
2
3
(d, JPC = 11.2 Hz,
i
ꢀC6H3), 133.2 (d, JPC = 2.5 Hz,
o
2
129.8 (s,
=CH), 123.9 (s,
2.5 Hz, =CH), 28.8 (d, JPC = 1.1 Hz,
CH( H3)2), 22.9 (s, CH(
31P{1H} NMR: δ = 80.1 (broad). – Anal. for C44H56BN4P
(682.74 g molꢀ1): calcd. C 77.41, H 8.27, N 8.21%; found C
75.78, H 8.03, N 7.94%.
m
ꢀC6H3), 127.3 (s,
2
at ꢀ20 °C to yield 620 mg (yield 57%) of 4a of m.p. 130 °C. –
m
ꢀC6H3), 123.5 (s,
m
ꢀC6H3), 121.5 (d, JPC
H(CH3)2), 26.4 (s,
CH3)2), 20.9 (s, CH3), 20.7 (s, CH3). –
=
4
1H NMR (C6D6): δ = 7.16 (m, 6 H, C6H3), 6.31 (d, 2 H, JPH
=
5
C
3
1.1 Hz, =CH), 3.30 (sept, 4 H, JHH = 6.8 Hz, CH), 2.46 (d, 12
C
3
3
H, JPH = 9.2 Hz, PNCH3), 1.32 (d, 12 H, JHH = 6.8 Hz, CH3),
1.18 (d, 12 H, JHH = 6.8 Hz, CH3). – 11B{1H} NMR: δ = 25.9
3
(broad). – 13C{1H} NMR (C6D6): δ = 145.8 (s,
oꢀC6H3), 139.9
3
(s, iꢀC6H3), 127.3 (s, pꢀC6H3), 123.1 (s, mꢀC6H3), 121.4 (d, JCP
2
5
= 3.3 Hz, =CH), 46.5 (d, JCP = 3.3 Hz, NCH3), 28.7 (d, JCP
=
This journal is © The Royal Society of Chemistry 2012
J. Name., 2012, 00, 1-3 | 7

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ARTICLE
Journal Name
DOI: 10.1039/C3DT52441H
6
1,3-BIS(2,6-DI
1,3,2-DIAZABOROLE (4D)
-
ISOPROPYLPHENYL)-2-DIPHENYLPHOSPHINO
-
CH(
ꢀ130.4 (broad d, JPH = 225 Hz). – Anal. for C32H42BN2P
CH3)2), 22.8 (d, JPC = 2.2 Hz, CH(C
H3)2). – 31P NMR: δ =
1
Nꢀbutyl lithium (0.675 mL of a 1.6 M solution in hexane, 1.08 (496.47 g molꢀ1): calcd. C 77.41, H 8.53, N 5.64 %; found C
mmol) was added at rt to a solution of diphenylphosphine (187 76.35 H 8.570 N 5.53 %.
ꢁ
L, 1.08 mmol) in Et2O (10 mL). The mixture was stirred for
30 min. The resulting dark yellow solution was added to a 1,3-BIS(2,6-DIISOPROPYLPHENYL)-2-PHOSPHINO-1,3,2-
cooled (ꢀ78 °C) solution of (500 mg, 1.08 mmol) in Et2O (15 DIAZABOROLE (4
mL). The reaction mixture was stirred for 30 min at this Et2O (15 mL) was added to a mixture of
5
F)
5
(500 mg, 1.08 mmol)
temperature and then allowed to warm slowly to rt. Solvents and KPH2 (86 mg, 1.2 mmol). The suspension was stirred for
and volatiles were removed under reduced pressure. The 24 h at rt. Solvents and volatiles were removed under reduced
residue was taken up in hexane (20 mL) and filtered through pressure. The residue was taken up in hexane (20 mL) and the
celite. The filtrate was concentrated to a volume of 5 mL and resulting suspension filtered through celite. The filtrate was
stored at ꢀ20°C to yield 386 mg (yield 63 %) of 4d as stored at ꢀ20 °C to yield 370 mg of 4f (yield 82 %) as
1
1
crystalline precipitate, m. p. 174 °C. – H NMR (C6D6): δ = crystalline precipitate of m. p. 149 °C. – H NMR (C6D6): δ =
7.29 (m, 4 H, ꢀPh), 7.13 (m, 2 H, ꢀC6H3), 7.00 (m, 4 H, 7.21 (m, 2 H, ꢀC6H3), 7.14 (m, 4 H, ꢀC6H3), 6.24 (d, 2 H,
(CH3)2),
(CH3)2), 1.14 (d, 1.58 (d, JPH = 198 Hz, PH2), 1.27 (d, JHH = 6.9 Hz,
o
p
m
ꢀ
p
m
4
3
C6H3), 6.90ꢀ6.78 (m, 6 H, m/pꢀPh), 6.34 (d, 2 H, d, JPH = 1.5 4JPH = 0.6 Hz, =CH), 3.16 (sept, JHH = 6.9 Hz, C
H
3
1
3
Hz, =CH), 3.25 (sept, 4 H, JHH = 6.8 Hz, C
H
12 H, JHH = 6.8 Hz, CH(CH3)2), 1.09 (d, 12 H, JHH = 6.8 Hz, CH(CH3)2), 1.18 (d, JHH = 6.9 Hz, CH(CH3)2). – 11B{1H}
3
3
3
CH(CH3)2). – 11B{1H} NMR: δ = 26.0 (broad). – 13C{1H} NMR: δ = 27.5 (broad). – 13C{1H} NMR: δ = 146.2 (s,
o
ꢀC6H3),
ꢀC6H3), 120.8
H(CH3)2), 24.6 (s,
H3)2). – 31P NMR: δ =
H(CH3)2), 26.2 (s, ꢀ250.3 (broad t, JPH = 200 Hz). – Anal. for C26H38BN2P
H3)2), 22.7 (d, JPC = 1.4 Hz, CH(
H3)2). – 31P{1H} (420.38 g molꢀ1): calcd. C 74.29, H 9.11, N 6.66%; found C
2
NMR: δ = 145.8 (s,
6.7 Hz, ꢀPh), 135.3 (d, JPC = 19.5 Hz,
C6H3), 127.8 (m/pꢀPh), 123.5 (s, ꢀC6H3), 122.1 (d, JPC = 2.5 CH(
Hz, =CH), 28.8 (d, JPC = 1.5 Hz,
o
ꢀC6H3), 139.2 (s,
i
ꢀC6H3), 136.3 (d, JPC
=
138.7 (s,
i
ꢀC6H3), 128.0 (s,
(d, JPC = 1.4 Hz, =CH), 28.5 (s, C
pꢀC6H3), 123.7 (s, m
3
2
i
o
ꢀPh), 127.9 (s,
p
ꢀ
2
6
m
CH3)2), 23.9 (d, JPC = 2.0 Hz, CH(C
5
1
C
6
CH(
C
C
NMR: δ = ꢀ60.7 (broad d). – Anal. for C38H46BN2P (572.57 g 73.86, H 9.31, N 6.63%
molꢀ1): calcd. C 79.71, H 8.10, N 4.89%; found C 79.31, H
7.99, N 4.87%.
REACTIONS OF 6 WITH MES*PCL AND PH2PCL AND 4D:
2
The preparation of
phosphines was carried out by analogy to the syntheses of 4b,c
The resulting mixtures were analysed by 31P and 11B NMR
6 and reaction with the appropriate chloroꢀ
1,3-BIS(2,6-DIISOPROPYLPHENYL)-2-(PHENYLPHOSPHINO)-
1,3,2-DIAZABOROLE (4E)
.
Nꢀbutyl lithium (1.06 mL of a 1.6 M solution in hexane, 1.71 spectroscopy. Applying the same workꢀup procedure produced
mmol) was added at ꢀ78 °C to a solution of phenylphosphine crystalline borane 5-H (in the reaction with 4d and
(185 L, 1.71 mmol) in Et2O (15 mL). The mixture was stirred diphosphene (in the reaction with Mes*PCl2) as only isolable
for 1 h at ꢀ78 °C and then allowed to warm to rt. The resulting products.
solution was added to a suspension of (850 mg, 1.71 mmol) in
Et2O (20 mL). The reaction mixture was stirred for 30 min and
then evaporated to dryness under reduced pressure. Soxhlet nꢀButyl lithium (250
)
ꢁ
9
5
METALATION OF 4E:
ꢁL of a 1.6 M solution in hexane, 0.40
extraction of the residue with hexane and subsequent removal mmol) was slowly added to a solution of 4e (200 mg, 0.40
of solvent under reduced pressure gave 650 mg of 4d (yield 81 mmol) in THF (10 mL). The resulting yellow solution was
%). Crystals of m. p. 118 °C were obtained by recrystallisation stirred for 30 min. Solvents and volatiles were removed under
1
3
from hexane. – H NMR (CDCl3): δ = 7.31 (t, 2 H, JHH = 7.6 reduced pressure, and the residue taken up in hexane (20 mL).
3
4
Hz,
C6H3), 7.10 (dd, 2 H, JHH = 7.6 Hz, JHH = 1.7 Hz,
6.94 (m, 1 H, ꢀPh), 6.83 (m, 4 H, ꢀPh), 6.63 (m, 4 H,
6.31 (d, 2 H, d, JPH = 1.1 Hz, =CH), 3.30 (d, 1 H, JPH = 225 Recrystallisation from hexane produced a small crop of
p
ꢀC6H3), 7.23 (dd, 2 H, JHH = 7.6 Hz, JHH = 1.7 Hz,
m
ꢀ
The resulting suspension was filtered through celite. The crude
ꢀC6H3), product was isolated by removal of the solvent under reduced
ꢀPh), pressure and characterised by 31P and 11B NMR spectroscopy.
3
4
m
p
m
o
4
1
3
Hz, PH), 3.12 (sept, 2 H, JHH = 6.8 Hz, CH(CH3)2), 2.79 (sept, crystalline material which was further identified by a singleꢀ
2 H, JHH = 6.8 Hz, C
CH(CH3)2), 1.15 (d, 6 H, JHH = 6.8 Hz, CH(CH3)2), 1.10 (d, 6
3
3
H
(CH3)2), 1.28 (d, 6 H, JHH = 6.8 Hz, crystal Xꢀray diffraction study. – 11B NMR: δ = 32.4 (broad s).
–
31P NMR: δ = ꢀ116.1 (broad s).
3
3
3
H, JHH = 6.8 Hz, CH(CH3)2), 0.84 (d, 6 H, JHH = 6.8 Hz,
CH(CH3)2). – 11B{1H} NMR: δ = 26.3 (broad d). – 13C{1H}
X-ray diffraction studies
Crystals of 4a-c 4e, and 4f suitable for Xꢀray diffraction
ꢀPh), 131.1 (d, JPC = 7.5 Hz, analysis were obtained by recrystallization of purified products
ꢀPh), 127.4 (s, ꢀC6H3), 126.3 from hexane. Diffraction data were collected at 100 K (4a-c
ꢀC6H3), 123.33 (s, ꢀC6H3), 120.8 (d, 4e), or 110 K (4f) using a Bruker Kappa APEXII Duo
2JPC = 2.1 Hz, =CH), 28.4 (d, JPC = 1.7 Hz,
H(CH3)2), 28.2 diffractometer with MoꢀKα radiation ( = 0.71073 Å). A
(s, H(CH3)2), 25.2 (s, CH( H3)2), 23.5 (d, JPC = 2.5 Hz, combination of scans was carried out to obtain at least
NMR: δ = 146.3 (s,
o
ꢀC6H3), 145.7 (s,
o
ꢀC6H3), 138.4 (s,
iꢀ
,
2
1
C6H3), 134.0 (d, JPC = 15.8 Hz,
o
3
i
ꢀPh), 127.8 (d, JPC = 7.5 Hz,
m
p
,
(s, ꢀPh), 123.35 (s,
p
m
m
5
C
6
λ
C
C
ω and Φ
8 | J. Name., 2012, 00, 1-3
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DOI: 10.1039/C3DT52441H
a unique data set. The crystal structures were solved by direct hydrogen atoms at phosphorus in 4e,f were localised by
methods (SHELXSꢀ97 22), and refined with a fullꢀmatrix leastꢀ electron density determination and refined freely using
squares scheme on F2 (SHELXLꢀ97 22). Nonꢀhydrogen atoms isotropic thermal displacement parameters. One isopropyl
were refined anisotropically and H atoms (except those on group in 4e is disordered. Details of the crystal structure are
phosphorus in 4e,f) with a riding model. The positions of the listed in Table 3 and in the ESI.
Table 3 Summary of crystallographic data for 4a-c, 4e, 4f
4a
C30H48BN4P
957947
4b
C36H56BN4P
957948
4c
C44H56BN4P
957949
4e
C32H42BN2P
957950
4f
C26H38BN2P
957951
Formula
CCDC
Mol. Wt.
506.50
586.63
682.71
496.46
420.36
Crystal system
Space group
Monoclinic
P21/c
Monoclinic
P21/c
Triclinic
P ‾1
Orthorhombic
P212121
Triclinic
P ‾1
a/Å
b/Å
c/Å
α/°
17.9692(13)
10.7572(9)
17.2353(14)
90
114.004(2)
90
3043.4(4)
4
1.105
11.7029(8)
12.3599(8)
24.3641(18)
90
96.785(3)
90
3499.5(4)
4
1.113
12.4257(4)
12.4802(5)
13.2635(5)
97.682(2)
98.396(2)
103.761(2)
1945.80(12)
2
12.0947(13)
13.6131(12)
17.9876/14)
90
90
90
2961.6(5)
4
1.113
7.5063(5)
9.4119(6)
18.3880(14)
77.441(3)
86.774(4)
78.004(3)
1240.23(15)
2
β/°
γ/°
V/Å3
Z
Calcd. density (g cmꢀ3)
Abs. coeff. (mmꢀ1)
F(000)
1.165
0.106
736
1.126
0.126
456
0.114
1104
0.108
1280
0.115
1072
Crystal size (mm)
0.65 x 0.52 x 0.44
2.97 to 30.51
0.046
0.26 x 0.18 x 0.18
1.67 to 26.47
0.053
0.60 x 0.41 x 0.21
1.58 to 25.35
0.037
0.27 x 0.13 x 0.10
1.88 to 25.35
0.060
0.47 x 0.27 x 0.22
2.26 to 27.47
0.039
θ
range (°)
R(int)
Reflections measured
34117
48124
31455
20575
23221
Reflections unique [I > 2σ(I)]
9269
7217
7097
5423
5671
0.997
0.996
0.998
1.00
0.999
Completeness to
Absorption correction
θ
Semiꢀempirical
from equivalents
0.7461 and 0.7128
9269 / 0 / 325
1.004
0.046
0.120
0.402 and ꢀ0.291
ꢀ
Semiꢀempirical
from equivalents
0.6370 to 0.7454
7217 / 0 / 393
1.055
0.0528
0.1498
0.695 and ꢀ0.485
ꢀ
Semiꢀempirical
from equivalents
0.7457 and 0.7223
7097 / 0 / 455
1.033
0.0389
0.0979
0.316 and ꢀ0.369
ꢀ
Semiꢀempirical
from equivalents
0.7451 and 0.7129
5423 / 13 / 327
1.012
0.0462
0.0910
0.237 and ꢀ0.222
0.06(11)
Semiꢀempirical
from equivalents
0.7461 and 0.7086
5671 / 0 / 277
1.036
0.0503
0.1245
1.025 and ꢀ0.901
ꢀ
Max. and min. transmission
Data/restraints/parameters
Goodness of fit on F2
R1 (I > 2σ(I))
wR(F2) (all data)
Largest diff. (e Åꢀ3)
Flack parameter
Research and the Ministry for Science, Research and Arts
BadenꢀWürttemberg) for the computational resources.
Computational studies
23
DFT calculations were carried out with the Gaussian 09
16
package using the
ωB97XꢀD functional by HeadꢀGordon in
Notes and references
combination with a ccꢀpVDZ basis set as obtained from the
basis set exchange homepage.24 Numerical integrations were
performed on an ultrafine grid. Energy optimisation of
molecular geometries was carried out in C1 symmetry.
Harmonic frequencies and zeroꢀpoint energies (ZPE) at
optimized structures were calculated at the same level and
showed all molecular geometries to present local minima (only
a
Institut für Anorganische Chemie, University of Stuttgart,
Pfaffenwaldring 55, 70550 Stuttgart, Germany. Fax: +49 711 685 64186
Eꢀmail: gudat@iac.uniꢀstuttgart.de.
b Institut für Organische Chemie, University of Stuttgart, Pfaffenwaldring
55, 70550 Stuttgart, Germany.
c
Laboratory of Inorganic and Analytical Chemistry, University of
Helsinki, P.O. Box 55 (A.I. Virtasen aukio 1), FINꢀ00014 Helsinki,
Finland.
positive eigenvalues of the Hessian matrix) on the potential
25
energy surface. MOLDEN
was used for visualization.
†
Dedicated to Professor Dr. Werner Uhl on the occasion of his 60th
Listings of computed energies and molecular coordinates are
given in the Supporting Information.
birthday.
Electronic Supplementary Information (ESI) available: crystallographic
data of 4a-c,e,f (cifꢀfiles, CCDCꢀ957947 to 957951), plots of 31P and 11B
NMR spectra of 4a-f, graphical representation of the molecular structure
of crystalline 11, graphical representations, atomic coordinates, and
Acknowledgements
We thank the Academy of Finland for a Research Fellowship
and Deutscher Akademischer Austauschdienst (DAAD) for
financial support. We thank the bwꢀgrid project (bwGRiD
(http://www.bwꢀgrid.de), member of the German DꢀGrid
initiative, funded by Federal Ministry for Education and
energies of computed molecular structures of 4b and 4’
. See
DOI: 10.1039/b000000x/
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ARTICLE
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10 | J. Name., 2012, 00, 1-3
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DOI: 10.1039/C3DT52441H
reductive coupling
metathesis
Ar
N
Ar
N
Mes*
R2N
R2N
(R2N)2PCl
1/2
P
P
(thf)2LiB
P
B
Mes*PCl2
*Mes
+
N
Ar
N
Ar
Ar
N
ClB
N
Ar
σ
LUMO is *(PN)
=> P-centred
σ-donor/π-acceptor
Metathesis of N-heterocyclic lithioboranes and diaminochlorophosphines yields previously
unavailable tetraamino-phosphinoboranes predicted to feature phosphorus rather than boron
centred electrophilicity.