Enantiopure Calcium Iminophosphonamide Complexes: Synthesis, Photoluminescence, and Catalysis

Article abstract of DOI:10.1002/chem.202004833

The synthesis of calcium complexes ligated by three different chiral iminophosphonamide ligands, L-H (L=[Ph₂P{N(R)CH(CH₃)Ph}₂]), L′-H (L′=[Ph₂P{NDipp}{N(R)CH(CH₃)Ph}]), (Dipp=2,6-ⁱPr_2<

Full text of DOI:10.1002/chem.202004833

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&
Photoluminescence
Enantiopure Calcium Iminophosphonamide Complexes: Synthesis,
Photoluminescence, and Catalysis
Bhupendra Goswami,[a] Thomas J. Feuerstein,[a] Ravi Yadav,[a] Ralf Kçppe,[a] Sergei Lebedkin,[b]
Manfred M. Kappes,[b, c] and Peter W. Roesky*[a]
Dedicated to Prof. Hansgeorg Schnçckel on the occasion of his 80th birthday.
Abstract: The synthesis of calcium complexes ligated by
three different chiral iminophosphonamide ligands, L-H (L=
[Ph2P{N(R)CH(CH3)Ph}2]), L’-H (L’=[Ph2P{NDipp}{N(R)CH(CH3)-
Ph}]), (Dipp=2,6-iPr2C6H3), and L’’-H (L’’=[Ph2P{N(R)CH(CH3)-
naph}2]), (naph=naphthyl) is presented. The resulting struc-
tures [L2Ca], [L’2Ca], and [L’’2Ca] represent the first examples
of enantiopure homoleptic calcium complexes based on this
type of ligands. The calcium complexes show blue–green
photoluminescence (PL) in the solid state, which is especially
bright at low temperatures. Whereas the emission of [L’’2Ca]
is assigned to the fluorescence of naphthyl groups, the PL of
[L2Ca] and [L’2Ca] is contributed by long-lived phosphores-
cence and thermally activated delayed fluorescence (TADF),
with a strong variation of the PL lifetimes over the tempera-
ture range of 5–295 K. Furthermore, an excellent catalytic ac-
tivity was found for these complexes in hydroboration of ke-
tones at room temperature, although no enantioselectivity
was achieved.
Introduction
on earth-abundant metals, also including main-group metals,
has recently become an active and challenging research area.[3]
The well-known aluminum compound Alq3 (q=8-hydroxyqui-
nolinate) and its derivatives may be viewed as proponents of
practically important, highly luminescent complexes of the
main-group metals.[4] For group 1 and group 2 metals, howev-
er, only few molecular compounds with prominent emission
have been described so far.[5]
Over the last few decades, the rapid development in the field
of photophysics and photochemistry is largely dominated by
transition metal-based complexes owing to their highly lumi-
nescent nature.[1] In particular expensive transition metals (i.e.,
Ir, Ru, Pt, and Au) have been studied extensively.[2] This circum-
stance may be a limiting factor for a mass production of eco-
nomical organic light-emitting diodes (OLED) devices for light-
ing applications. Accordingly, a search for alternatives based
Very recently, we have synthesized a chiral version of an imi-
nophosphonamide ligand (L-H) and found that it allows further
derivatization into alkali and group 13 metal complexes.[5b,6]
The complexes [M2(L)2] (M=alkali metals, Figure 1) showed ex-
citing photoluminescence (PL) properties, including bright
long-lived phosphorescence at low temperature and thermally
activated delayed fluorescence (TADF) with a high quantum
yield at ambient temperature. Inspired by the results obtained
for the alkali metal complexes, we aimed to obtain the analo-
gous complexes of L-H and similar
[a] Dr. B. Goswami, Dr. T. J. Feuerstein, Dr. R. Yadav, Dr. R. Kçppe,
Prof. Dr. P. W. Roesky
Institute of Inorganic Chemistry,
Karlsruhe Institute of Technology (KIT)
Engesserstrasse 15, 76131 Karlsruhe (Germany)
E-mail: roesky@kit.edu
[b] Dr. S. Lebedkin, Prof. Dr. M. M. Kappes
Institute of Nanotechnology
ligands also for group 2 metals as
Karlsruhe Institute of Technology (KIT)
Hermann-von Helmholtz-Platz 1
well as characterize their PL prop-
76344, Eggenstein-Leopoldshafen (Germany)
erties. Note that for the whole
[c] Prof. Dr. M. M. Kappes
ligand class of iminophosphonam-
Institute of Physical Chemistry
Karlsruhe Institute of Technology (KIT)
Fritz-Haber Weg 2, 76131 Karlsruhe (Germany)
ides only a few examples of alka-
line earth metal complexes are
known.[7] Moreover, only one het-
Supporting Information and the ORCID identification number(s) for the au-
thor(s) of this article can be found under:
eroleptic calcium complex based
https://doi.org/10.1002/chem.202004833.
on a chiral iminophosphonamide
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VCH GmbH. This is an open access article under the terms of the Creative
Commons Attribution Non-Commercial License, which permits use, distribu-
tion and reproduction in any medium, provided the original work is proper-
ly cited and is not used for commercial purposes.
has been reported, with the chirali-
Figure 1. Enantiopure dimeric
alkali metal complexes with
iminophosphonamide li-
gands.
ty solely introduced at one nitro-
gen center.[8] None of these report-
ed alkaline earth metal complexes
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based on iminophosphonamides showed PL.
Furthermore, from the view point of green and sustainable
chemistry, alkaline-earth metal complexes are considered as
benign catalysts for activation of synthetic intermediates due
to their low electronegativity.[9] Thus, complexes based on alka-
line-earth metals are highly attractive catalysts for a wide
range of chemical transformations including the Tishchenko re-
action,[10] ring-opening polymerization,[11] hydroboration,[12] hy-
droamination,[13] hydrophosphination of alkenes and alkynes,[14]
coupling of alkynes with carbodiimides,[15] and cross dehydro-
coupling.[16] The known catalysts based on alkaline-earth-metal
complexes are mostly heteroleptic in nature.[12b,e,f,17] However,
catalysts based on homoleptic alkaline-earth-metal complexes
are limited possibly due to saturation in the coordination
sites.[10b,12d,14b]
Scheme 1. Synthesis of the ligand L’-H.
3JHH =10 Hz, 3JPH =10 Hz) is assigned to [NHCH(CH3)Ph] whereas
the methyl protons [HNCH(CH3)Ph] appear as a doublet at d=
1.26 ppm (3JHH =6.8 Hz). Finally, the IR spectrum of L’-H shows
the characteristic nNH stretching frequency at 3347 cmÀ1 (Fig-
ure S34).
Single crystals of L’-H suitable for X-ray analysis were grown
from hot n-heptane (Figure 3). The ligand L’-H crystallized in
Herein, we describe an extended series of enantiopure imi-
nophosphonamine ligands bearing different substituents at
the nitrogen atom(s) of the NPN backbone (L-H, L’-H, and L’’-
H, Figure 2). These were used to prepare solvent-free tetra-
coordinated calcium complexes 1–3, respectively. To the best
of our knowledge, these complexes represent the first exam-
ples of enantiopure homoleptic alkaline-earth-metal complexes
based on chiral iminophosphonamides. Furthermore, similar to
the alkali metals ligated by L,[5b] calcium complexes with L and
L’ ligands also show TADF. In addition, all calcium complexes
were found to be very efficient catalysts for the hydroboration
of ketones although no enantioselectivity was observed for the
reaction products.
Results and Discussion
Figure 3. Molecular structure of L’-H in the solid state. All hydrogen atoms
except for the amine proton are omitted for clarity. Selected bond lengths
[Š]: PÀN1 1.536(4), PÀN2 1.660(4); selected bond angles [8]: N1ÀPÀN2
116.7(2).
Synthesis and characterization
Enantiopure iminophosphonamine ligands
The ligand L-H was obtained using the previously reported
procedure.[5b] In order to modify the steric factor of L-H, a new
the orthorhombic chiral space group P212121 with one mole-
ligand L’-H was synthesized by replacing one chiral center (RÀ cule in the asymmetric unit. The PÀN1 (1.536(4) Š) bond is sig-
CH(CH3)Ph) with a Dipp (Dipp=2,6-iPr2C6H3) group. Specifically,
nificantly shorter than the PÀN2 (1.660(4) Š) bond, indicating a
double bond P=N1. Therefore, the hydrogen atom could be as-
signed to N2.[5b] The N1ÀPÀN2 angle of 116.7(2)8 is smaller
than in ligand L-H and comparable to the angle in related achi-
ral compounds.[5b,20] No strand structure was observed in the
crystalline state, suggesting no hydrogen bridging to the
L’-H was synthesized via the Staudinger reaction between the
[18]
known compounds Dipp-N3
and HN[RÀCH(CH3)Ph](PPh2)[19]
(Scheme 1). The ligand was characterized by multinuclear NMR
spectroscopy. The 31P{1H} NMR spectrum of L’-H exhibits a
single peak at d=À10.9 ppm, significantly shifted upfield in
comparison
to
d=36.6 ppm
observed
for
HN[RÀ neighboring molecule.
1
CH(CH3)Ph](PPh2). In the H NMR spectrum, the NH proton ap-
pears as a doublet of doublets at d=2.81 ppm (3JHH =9.5 Hz,
2JPH =9.5 Hz), indicating the absence of any E/Z isomerization
in contrast to L-H.[5b] A signal at d=4.64 ppm (3JHH =6.8 Hz,
Further on, to enhance bulk and the p-character at the nitro-
gen substituents a modified ligand L’’-H was synthesized by
the incorporation of naphthyl substituents. Specifically, it was
synthesized by conducting the Staudinger reaction between
Figure 2. Structural representation of the iminophosphonamine ligands under discussion.
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Scheme 2. Synthesis of the ligand L’’-H. The first step (a) was reported earlier.[21]
[19]
{RÀCH(CH3)naph}N3
and HN{RÀCH(CH3)naph}(PPh2), which
was synthesized from H2N{RÀCH(CH3)naph}, and ClPPh2, as de-
scribed earlier (Scheme 2).[21] Similar to L-H, the H NMR spec-
1
trum of L’’-H also shows E/Z tautomerization. Due to this tau-
tomerization two signal sets for naph(CH)CH3 (d=5.49,
5.17 ppm) and naph(CH)CH3 (d=1.81, 1.21 ppm) are observed.
Appearance of two signal sets in pairs for naph(CH)CH3 (d=
29.9, 25.7 ppm) and naph(CH)CH3 (d=51.2, 46.3 ppm) in the
13C{1H} spectrum further confirms the non-equivalent nature of
the methine and methyl carbon atoms of the ligand L’’-H. The
1
corresponding NH proton in the H NMR spectrum is observed
as a broad signal at d=2.88 ppm. Additionally, in the 31P{1H}
NMR spectrum a singlet at d=3.6 ppm is detected. Finally, in
the IR spectrum of L’’-H the nNH stretching frequency is found
at 3372 cmÀ1.
Figure 4. Molecular structure of L’’-H in the solid state. All hydrogen atoms
except for the amine proton are omitted for clarity. Selected bond lengths
[Š]: P1ÀN1 1.675(4), P1ÀN2 1.544(4); selected bond angles [8]: N1ÀP1ÀN2
119.6(2).
Colorless single crystals of the ligand L’’-H, suitable for X-ray
analysis, were obtained from hot n-heptane. Similar to the
ligand L-H, L’’-H also crystallized in the chiral space group P21
with two molecules in the asymmetric unit (Figure 4). Similar
to the ligand L’-H, no strand structure was observed in the
solid state. The phosphorous atom in the NPN moiety is tetra-
hedrally coordinated. The PÀN1 bond length (1.675(4) Š) is
within the range of a PÀN single bond, whereas the PÀN2
bond length of 1.544(4) Š is in the range of a P=N double
bond. Therefore, the hydrogen atom could be clearly assigned
to the nitrogen atom N1. The N1ÀP1ÀN2 bond angle
(119.6(2)8) is wider than observed for L’-H (116.7(2)8) but nar-
rower than in L-H (121.6(2)8).
Calcium complexes
As the starting point for calcium complexation, we chose our
previously reported enantiopure ligand L-H and reacted it with
[Ca{N(SiMe3)2}2(THF)2] in a 2:1 ratio.
This afforded the corresponding homoleptic complex [L2Ca]
(1) in good yield (Scheme 3). Complex 1 is solvent free and
monomeric in nature.
Complex 1 was further characterized by multinuclear NMR
spectroscopy, elemental analysis and IR spectroscopy. The ab-
sence of the nNH stretching frequency in the IR spectrum and
1
the absence of the NH resonance in the H NMR spectrum indi-
cates complete deprotonation of the iminophosphonamide
ligand in 1. Furthermore, the 31P{1H} NMR spectrum of 1 shows
Scheme 3. Synthesis of complex 1.
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a significant downfield shift in comparison to the metal-free
ligand L-H: d=24.5 (1) versus 2.7 ppm (L-H). In the 1H NMR
spectra, the characteristic resonances that can be assigned to
the methine protons (i.e., Ph(CH)CH3) and the methyl protons
(i.e., Ph(CH)CH3) are observed. In complex 1, the Ph(CH)CH3 res-
onance is well resolved and appears as a doublet of quartets
at d=4.04 ppm, whereas two sets of signals at d=4.73 and
4.38 ppm are observed for the ligand due to E/Z isomerization
and tautomerization.
Similar to the synthesis of 1, the asymmetric ligand L’-H was
reacted with [Ca{N(SiMe3)2}2(THF)2] in a 2:1 ratio to obtain
monomeric homoleptic calcium complex [L’2Ca] (2) (Scheme 4).
1
The absence of a NH signal in the H NMR spectrum of 2
suggests a full conversion of the ligand L’-H. Furthermore, a
doublet of quartets at d=3.67 ppm and a doublet at d=
1.65 ppm are observed, which can be assigned to the
Ph(CH)CH3 and the Ph(CH)CH3 proton resonances, respectively.
These well-resolved resonances indicate a symmetric coordina-
tion of both ligands in solution. However, the signals corre-
sponding to the Dipp groups show broad resonances, which
may be the result of a hindered rotation. The 31P{1H} NMR
spectrum of 2 appears to show a single peak at d=22.6 ppm,
which is significantly shifted downfield compared to the ligand
L’-H (d=À10.9 ppm). Finally, the absence of any nNH stretching
band in the IR spectrum of 2 suggests complete deprotonation
of the ligand by [Ca{N(SiMe3)2}2(THF)2].
Single crystals suitable for X-ray crystallography were ob-
tained from hot n-hexane. Complex 1 crystallizes in the mono-
clinic chiral space group C2. The crystal structure shows two
halves of the molecule in the asymmetric unit. Thus, a crystal-
lographic C2 axis goes along P1ÀCaÀP2. The central calcium
metal ion in 1 is tetracoordinated by four N atoms without any
coordinating solvent and adopts a distorted tetrahedral geom-
etry (Figure 5).
Complex 2 crystallized in the orthorhombic chiral space
group P212121 with one molecule in the asymmetric unit
(Figure 6). The central calcium atom in complex 2 is tetracoor-
Figure 5. Molecular structure of complex 1 in the solid state. All hydrogen
atoms are omitted for clarity. Selected bond lengths [Š]: CaÀN1 2.365(3),
CaÀN2 2.344(2), CaÀP1 2.9884(14), CaÀP2 2.9801(14), P1ÀN1 1.606(3), P2ÀN2
1.605(2); selected bond angles [8]: P2ÀCa-P1 180.0, N2ÀCaÀN1 137.17(9),
N2’ÀCaÀN1’ 137.18(9) N2ÀCaÀN2’ 64.76(11), N1ÀCaÀN1’ 64.64(13), N2ÀCaÀ
N1’ 133.94(9), N2’ÀCaÀN1 133.94(9), N1ÀP1ÀN1’ 103.9(2), N2ÀP2ÀN2’
102.9(2).
Figure 6. Pictorial representation of 2 in the solid state, based on the X-ray
diffraction connectivity data. All hydrogen atoms are omitted for clarity.
The CaÀN bond distances (CaÀN1 2.365(3) Š and CaÀN2
2.344(2) Š) are consistent with literature reports on similar
compounds.[22] The P1ÀCaÀP2 arrangement is clearly linear
(1808), and the two CaN2P planes intersect at an angle of
86.04(3)8. The PÀN bond distances in complex 1 are almost
equal and in the range between single and double bonds. The
NPN bond angle of ligand L-H (121.6(2)8) significantly decreas-
es upon coordination (N1ÀP1ÀN1’ 103.9(2)8 and N2ÀP2ÀN2’
102.9(2)8).
dinated and adopts a distorted tetrahedral geometry. However,
due to systematic twinning the quality of the single crystal X-
ray diffraction data was poor. This problem could not be so far
solved by using different conditions for the crystallization. Nev-
ertheless, the connectivity, which is shown as pictorial repre-
sentation in Figure 6, could be deduced from the difference
Fourier map.
Ligand variation in the coordination sphere of the calcium
center was further realized by the synthesis of the homoleptic
tetracoordinated calcium complex [L’’2Ca] (3). Complex 3 was
Scheme 4. Synthesis of complex 2.
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Scheme 5. Synthesis of complex 3.
Photoluminescence properties
obtained by reaction of L’’-H with [Ca{N(SiMe3)2}2(THF)2] in a
2:1 molar ratio (Scheme 5). Analogous to 1, the appearance of
a single set of resonances for the methine and methyl protons
We recently reported on the unusual PL properties of the alkali
metal complexes [L2M2] (M=Li, Na, K, Rb, Cs) with the ligand
L-H.[5b] In contrast to the fluorescent ligand, these complexes
demonstrate bright blue–green phosphorescence at low tem-
peratures (<100 K) in the solid state, which transforms upon
raising the temperature above ꢀ150 K to TADF emission from
the (relaxed) singlet state S1 thermally populated from the
lower-lying close triplet state T1.[23]
1
in the H NMR spectrum of complex 3 suggests its symmetric
nature. This is in contrast to L’’-H, which showed two different
sets of resonance corresponding to methine [i.e., naph(CH)CH3]
and methyl [i.e., naph(CH)CH3] due to E/Z tautomerization. In
1
the H NMR spectrum of 3, the naph(CH)CH3 appears as a dou-
blet of quartets at d=4.86 ppm, whereas for naph(CH)CH3 a
doublet at d=1.44 ppm is observed. The 31P{1H} NMR spec-
trum shows a single peak at d=27.3 ppm, which is significant-
ly shifted downfield compared to d=3.6 ppm for the ligand.
Complex 3 crystallizes in the monoclinic chiral space group
P21 with one molecule in the asymmetric unit (Figure 7). Unlike
We were further able to show that the TADF results from
the dimeric structure (i.e., the alkali metal participates in the
TADF) and correlates with the mutual orientation of the two li-
gands. Accordingly, we were interested whether this mecha-
nism is also observed for the novel monometallic Ca-based
complexes and how the nitrogen substituents and their re-
spective orientation influence the PL properties.
Similar to the alkali metal complexes [L2M2], all three calcium
complexes 1–3 are colorless crystalline solids showing a broad
blue–green photoluminescence upon UV excitation below
ꢀ400 nm. The emission and excitation (PLE) spectra of 1–3 as
well as the temperature dependencies of the integrated PL in-
tensity are shown in Figure 8.
Figure 7. Molecular structure of 3 in the solid state. All hydrogen atoms are
omitted for clarity. Selected bond lengths [Š] CaÀN1 2.390(2), CaÀN2
2.370(2), CaÀN3 2.394(2), CaÀN4 2.374(2), CaÀP1 3.0033(9), CaÀP2 3.0106(8),
P1ÀN1 1.599(2), P1ÀN2 1.601(2), P2ÀN3 1.604(2), P2ÀN4 1.607(2); selected
bond angles [8]: P1ÀCaÀP2 170.35(2), N1ÀCaÀN2 63.97(6), N3ÀCaÀN4
63.90(7), N1ÀCaÀN3 167.91(7), N2ÀCaÀN4 147.51(7), N1ÀCaÀN4 118.11(7),
N1ÀP1ÀN2 104.01(10), N3ÀP2ÀN4 103.61(10).
in complex 1, where the central calcium atom is exactly in the
plane of the coordinating N2P ligand backbones, in complex 3,
it is slightly above this plane with the angle P1ÀCaÀP2 equal
to 170.35(2)8. The deviation of the central metal from the N2P
backbone is reflected in the dihedral angles of 1.327(10)8 and
6.8878 between N1ÀP1ÀN2 and N1ÀCaÀN2 planes and N3À
P2ÀN4 and N3ÀCaÀN4 planes, respectively. This slight displace-
ment of the calcium atom is likely to minimize the repulsion
between the naphthyl substituents. The CaÀN bond distances
in 3 are in the range from 2.370(2) to 2.394(2) Š, similar to
complexes 1 and 2.
Figure 8. Left: photoluminescence excitation (PLE) and emission (PL) spectra
of compounds 1–3 at 7, 150, and 295 K. The spectra were recorded/excited
at 480/330 nm, respectively. Right: integrated PL intensities plotted against
the temperature in the range of 7–295 K.
In case of calcium complex 1, not only the PL spectra but
also the temperature dependencies of the PL intensity
(Figure 8, right panel) and decay lifetime (Figure S47) are
rather similar to those observed for the dimeric alkali metal
complexes of the same ligand.[5b] The latter dependence shows
a characteristic TADF transition from a long-lived phosphores-
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correlations between the structural and photophysical proper-
ties were observed.[5b]
Finally, in contrast to 1 and 2, only a fast PL component
with a lifetime <10 ns (time resolution of our apparatus) could
be detected for complex 3 at low temperatures as well as
under ambient conditions. This can be assigned to the fluores-
cence of the naphthyl moieties in 3. Its efficiency amounts to
7% at room temperature. Similar to 1 and 2, a substantial de-
crease in the PL efficiency, that is, an increase in nonradiative
excited-state relaxation, was observed for complex 3 by raising
the temperature over the range of 7–295 K (Figure 8).
Catalytic hydroboration of ketones
Figure 9. PL decay time of solid complex 1 versus temperature. The PL was
excited with a ns-pulsed laser at 337 nm, recorded at 480 nm, and fit with
monoexponential curves. The red curve depicts the fit according to Equa-
tion (S1) (see text and the Supporting Information). The fit yielded the
energy separation DE between S1 and T1 states of about 1200 cmÀ1. Below
Tꢀ100 K the emission is predominantly phosphorescence with a lifetime of
ca. 5.6 ms. Increasing the temperature activates the TADF mechanism, result-
ing in an effective PL lifetime of 24 ms at room temperature.
Hydroboration is the addition of BÀH bond across an unsatu-
rated system such as alkenes, alkynes, aldehydes, ketones, and
imines to form compounds with CÀB, CÀO, and CÀN bonds, re-
spectively. In particular, hydroboration of ketones with boranes
(R2BH) is an atom-economical reaction to form borate esters
(R2BOCHR2), which are useful synthetic intermediates for the
formation of functionalized alcohols. For hydroboration of
C=O-containing compounds, pinacolborane (HBpin) or cate-
cholborane (HBcat) are mostly considered as suitable mild re-
ductants.[24]
cence with a lifetime of ca. 5.6 ms below 100 K to much faster
PL kinetics with an effective lifetime of 24 ms at 295 K
(Figure 9). This transition occurs over ꢀ130–180 K and corre-
lates with the nonmonotonic dependence of the integrated PL
intensity versus temperature (Figure 8). The latter also resem-
bles the curves measured for [L2Na2], [L2K2] and [L2Rb2] com-
plexes. A simple TADF model of thermally equilibrated S1 and
T1 states [Eq (S1) in the Supporting Information][23a,c] can be ap-
plied to the data shown in Figure 9 to estimate the energy
separation DE between these states as ca. 1200 cmÀ1
(148 meV). This value is notably larger in comparison with DE
obtained for the alkali metal complexes (ca. 600–750 cmÀ1). A
PL quantum yield of 22% was determined for 1 using an inte-
grating sphere under ambient conditions and excitation at
330 nm (Table S2).
The hydroboration catalysts based on alkaline earth metals
reported so far are mostly heteroleptic in nature.[12b,e,f,17] The
homoleptic catalysts for this chemical transformation are ex-
tremely rare possibly due to saturation in coordination
sites.[12d] With this background, one of the goals of our study
was to probe a performance of tetra coordinated com-
plexes 1–3 as catalysts for hydroboration of ketones. As a pre-
liminary test, the reaction between acetophenone and HBpin
was conducted in C6D6 and monitored continuously via
1H NMR measurements, with a catalyst loading of 1 mol% and
ferrocene as an internal standard. Regardless of which complex
was used, we observed almost complete conversion into the
corresponding alkoxypinacolboronate ester within 5 min at
room temperature. High catalytic activity of 1–3 was found for
various acetophenones substituted at the para position with
electron-withdrawing (Br, NO2) or electron-donating (NH2, CH3,
and OCH3) groups (Table 1). Such catalytic efficiency of 1–3
and fast conversion of the substrates may be related to their
coordinatively unsaturated nature. Perhaps due to this unsatu-
ration in coordination sites the conversion requires less time in
comparison to previously reported homoleptic alkaline earth
metal catalysts.[12d] Since the catalysts 1–3 are enantiopure, one
might expect enantiomeric excess in the product. However,
practically no enantiomeric excess could be observed, also by
conducting the reactions at lower temperature (down to
À208C), likely due to the fast conversion of the ketones into
their corresponding alkoxypinacolboronate esters.
Similar to 1, the PL of complex 2 shows the minor fast fluo-
rescence and major long-lived (t=30 ms at 5 K) phosphores-
cence components below ꢀ20 K (Figure S49). By contrast, a
TADF-like transition to faster PL kinetics occurs already be-
tween ꢀ20 and ꢀ75 K, indicating a much smaller energy gap
DE between S1 and T1 states, roughly estimated as ꢀ330 cmÀ1
(Figure S49). The PL decay above ꢀ20 K is non-monoexponen-
tial. In addition, non-radiative electronic relaxation significantly
reduces the PL intensity upon raising the temperature
(Figure 8), resulting in a low quantum yield of <1% at 295 K
(Table S2). Correspondingly, it is not surprising that the simple
TADF model of equilibrated S1 and T1 states [Eq. (S1)] describes
the PL decay versus temperature (Figure S48) only relatively
poorly. By further increasing the temperature above ꢀ200 K,
the fast (fluorescence) component becomes dominant in 2.
The discrepancy in PL between 1 and 2 might be explained by
different structural (ligand) arrangements in the solid state
(Figures 5 and 6). This explanation would agree with our previ-
ous study on the alkali metal complexes, where pronounced
The catalytic activity of catalysts 1–3 for acetophenone can
be compared with the known catalysts based on alkaline earth
metals. We used 1 mol% of catalyst and observed in most
cases a quantitative conversion in less than 5 min resulting, in
a turnover frequency (TOF) of >1200 hÀ1
.
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Table 1. Hydroboration of ketones using complexes 1–3 as catalysts.[a]
Entry Substrate
Product
Catalyst NMR yield[b]
[%]
1
2
1
2
3
4
5
6
>99
3
1
2
3
>99
1
2
3
>99
96
>99
1
2
3
Figure 10. Extract of the experimental (a, b) and calculated (c, d) Raman
spectra of acetophenone and its complex with 1 (bands associated to aceto-
phenone and its complex are marked by # and *, respectively, those of the
solvent n-heptane are marked by §).
>99
>99
1
2
3
band from 1600 to 1597 cmÀ1 is observed (Figure 10), which in
total confirms an underlying weak calcium–oxygen contact.
The theoretical frequency calculations confirm these experi-
mental findings (Figure 10). The structure of the complexation
between 1 and acetophenone indicates a weak calciumÀ
oxygen bond (3.690 Š); its complexation energy was calculated
to be about À13 kJmolÀ1. The C=O distance of acetophenone
(1.227 Š) is elongated to 1.235 Š upon complexation. However,
this large CaÀO distance is expected for the borane to enable
an attack on the acetophenone molecule during the catalytic
cycle without any enantiomeric excess.
1
2
3
>99
97
>99
[a] Conditions: 1 mol% of catalyst 1–3, C6D6, rt. [b] Yields were calculated
based on 1H NMR spectroscopy, using ferrocene as the internal standard.
The heteroleptic Mg-based catalysts reported by Fohlmeister
and Stasch showed high catalytic activity with a TOF of
>8486 hÀ1 towards a related ketone (i.e., 2-adamantanone).[17b]
Li et al. showed a TOF of 2000 hÀ1 for the reduction of aceto-
phenone by using highly reactive asymmetric b-diketiminate
magnesium(I) complexes.[12g] Furthermore, related to our com-
Conclusions
plexes,
the
amidinate
stabilized
calcium
catalyst,
[PhC(NiPr)2CaI],[12f] showed a TOF of only 9.5 hÀ1. In compari-
son, magnesium-based catalysts such as {CH[C(Me)NAr]2MgnBu}
(Ar=2,6-iPr2C6H3) reported by Arrowsmith et al.[12b] and bulky
amido magnesium methyl-based catalysts from Ma et al.[17a]
showed higher TOFs of 23.5 and 667 hÀ1, respectively. Addi-
tionally, Yadav et al. reported homoleptic calcium and magnesi-
um complexes based on methylpyridinato b-diketiminate li-
The reaction of the chiral iminophosphonamide ligands L-H, L’-
H and L’’-H with [Ca{N(SiMe3)2}2(THF)2] leads to the formation
of the homoleptic calcium complexes [L2Ca] (1), [L’2Ca] (2) and
[L’’2Ca] (3), respectively. All these complexes are tetracoordinat-
ed without coordinating solvent molecules. In the solid state,
complexes 1–3 show spectrally similar blue–green PL, which is
relatively bright in the case of 1 and 3 also at ambient temper-
ature. However, the PL of 3 is the fluorescence of the naphthyl
moieties, whereas the emission of 1 and 2 is contributed by
phosphorescence at cryogenic temperatures and thermally ac-
tivated delayed fluorescence (TADF) at elevated temperatures.
On the other hand, the characteristic parameters such as the
TADF activation temperature and PL efficiency differ signifi-
cantly in 1 and 2. These results suggest that the photophysical
properties of iminophosphonamide complexes of both alkali
and alkaline earth metals, including the TADF process, can be
strongly varied by modification of the ligand. This suggests
that the TADF quantum yield (22% for 1 at room temperature)
might be further increased by a ligand optimization. A high
catalytic activity of complexes 1–3 was demonstrated in inter-
molecular hydroboration of various ketones at room tempera-
ture. Unfortunately, no enantioselectivity could be achieved,
also when conducting the catalytic reactions at low tempera-
ture.
gands, which showed TOFs of about 16 hÀ1 [12d]
The above ex-
.
amples evidence the highly active nature of catalysts 1–3.
These results prompted us to explore its ability to reduce al-
kenes under similar conditions. However, no conversion was
observed in the reaction of styrene with HBpin using com-
plexes 1–3 as catalysts, even at a relatively high temperature
of 1208C.
To gain some insight into the mechanism underlying the
catalytic reaction, vibrational spectroscopic investigations were
carried out accompanied by theoretical DFT calculations. In situ
NMR studies were not conclusive. The complexation of aceto-
phenone to calcium complex 1 in n-heptane solution, which is
a key step of the catalytic cycle, was investigated by Raman
spectroscopy. On one hand, a red-shift of the C=O valence
mode of acetophenone from 1694 to 1651 cmÀ1 is seen upon
complexation of the C=O group to the calcium center, on the
other hand a rather negligible red-shift of its valence phenyl
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NCq), 134.8 (d, 1JPC =121 Hz, ArphosCq), 134.2 (d, 1JPC =127 Hz,
Experimental Section
2
2
ArphosCq), 132.3 (d, JPC =9.8 Hz, o-ArphosÀCH), 132.2 (d, JPC =9.8 Hz,
o-ArphosÀCH), 131.1 (d, 3JPC =2.8 Hz, ArÀCH), 130.9 (d, 3JPC =2.9 Hz,
ArÀCH) 128.7 (ArÀC), 128.5 (ArÀC), 128.2 (ArÀC), 127.0 (ArÀC), 126.2
All manipulations of air-sensitive materials were performed under
the rigorous exclusion of oxygen and moisture in flame-dried
Schlenk-type glassware, either on a dual manifold Schlenk line, in-
terfaced to a high vacuum (10À3 Torr) line, or in an argon-filled
MBraun glove box. Hydrocarbon solvents (toluene, n-heptane, n-
pentane) were dried by using a MBraun solvent purification system
(SPS-800), degassed and stored under vacuo. n-hexane was pre-
dried over CaCl2 before decantation and distillation over potassium
and storage over 4 Š molecular sieves. Tetrahydrofuran (THF) was
distilled under nitrogen over potassium benzophenone ketyl
before storage over lithium aluminum hydride (LiAlH4). All sub-
strates [ketones and 4,4,5,5-tetramethyl-1,3,2-dioxaborolane
(HBpin)] for hydroboration reactions were purchased from either
ABCR or Sigma–Aldrich and used without any further purification.
4
(ArÀC), 123.3 (d, JPC =1.3 Hz, o-ArÀCH), 119.9 (d, JPC =2.5 Hz, ArÀC),
3
50.8 (PÀNCHCH3), 29.1 (CH(CH3)2), 26.1 (d, JPC =4.0 Hz, Ph(CH)CH3),
24.13 (CH(CH3)2), 24.06 ppm (CH(CH3)2); 31P{1H} NMR (C6D6,
162 MHz): d=À10.9 ppm; IR (ATR): n=3347 (w), 3054 (vw), 2971
(w), 2961 (vw), 2864 (w), 1585 (w), 1596 (w), 1450 (m), 1434 (vs),
1401 (vw), 1354 (m), 1295 (w), 1257 (w), 1202 (w), 1185 (w), 1117
(m), 1101 (m), 1087 (m), 1075 (m), 1064 (m), 1028 (w), 1017 (w),
950 (m), 833 (w), 794 (vw), 771 (m), 749 (vs), 695(vs), 625 (s), 649
(vw), 600 (m), 534 (s), 511 (vs), 500 (vs), 447 cmÀ1 (w); elemental
analysis: calcd [%] for [C32H37N2P] (480.64): C 79.97, H 7.76, N 5.83;
found: C 79.42, H 7.63, N 5.80.
Synthesis of P,P-diphenyl-N,N’-bis[(R)-1-naphthylethyl]phosphin-
imidic amide, (R)-HNEPIA (L’’-H): Ph2PN(RÀ*CHMenaph) (7.20 g,
20.26 mmol, 1.00 equiv.) was dissolved in THF (40 mL) and cooled
NMR spectra were recorded on a Bruker Avance III 300 MHz or
Avance III 400 MHz spectrometer. Chemical shifts were measured
relative to the characteristic solvent resonances as internal stand-
ards [7.16 ppm (1H) and 128.06 ppm (13C)]. They are expressed in
ppm and reported relative to tetramethylsilane. 85% phosphoric
acid was used as external reference for 31P- and 31P{1H}-NMR. Ele-
mental analyses were carried out with a Vario Micro Cube (Elemen-
tar Analysensysteme GmbH). IR spectra were obtained on a Bruker
Tensor 37 FTIR spectrometer equipped with a room temperature
DLaTGS detector, a diamond ATR (attenuated total reflection) unit,
and a nitrogen-flushed chamber. In terms of their intensity, the sig-
nals were classified into the categories vs=very strong, s=strong,
m=medium, w=weak and vw=very weak. The Raman spectra
were taken using a Bruker Senterra II Raman microscope using a
laser with an excitation wavelength of 532 nm.
to À208C.
A solution of 2.37 g (R)-a-methylnaphthyl azide
(22.28 mmol, 1.10 equiv.) in THF (20 mL) was added slowly. After
complete addition, the reaction mixture was warmed to ambient
temperature whereupon liberation of N2 was observed. The reac-
tion mixture was stirred for 12 h at ambient temperature. After
evaporation of the solvent under reduced pressure, a viscous solid
was obtained, which was washed with n-pentane (4*20 mL) and
dried in vacuum to obtain the desired product as white powder.
Single crystals of the title compound suitable for X-ray analysis
were obtained by recrystallization from n-heptane.
1
Yield (based on crystals): 6.7 g (63%); H NMR (C6D6, 400 MHz): d=
8.44 (br, 2H, ArÀH), 8.04 (br, 2H, ArÀH), 7.77–7.69 (br, 3H, ArÀH),
7.52–7.19 (m, 10H, ArÀH), 7.09–6.95 (m, 7H, ArÀH), 5.52–5.45 (m,
1H, P=NCH), 5.17 (br, 1H, HNCH), 2.88 (br, 1H, NH), 1.81 (br, 3H, P=
NCHCH3), 1.21 ppm (br, 3H, HNCHCH3); 13C{1H} NMR (C6D6,
100 MHz): d=148.0 (d, JPC =11.3 Hz, ArÀC), 142.6 (ArÀC), 135.6 (d,
The theoretical calculations were performed by means of the pro-
gram package TURBOMOLE 7.3 without constraints of symmetry
using the RI-DFT/BP-86 method[25] and def2-SV(P) basis sets for all
atoms.[26] Vibrational frequencies and Raman intensities were calcu-
lated analytically using the modules aoforce[27] and egrad.[28]
J
PC =23.5 Hz, ArÀC), 134.5 (ArÀC), 134.2 (ArÀCH), 132.9 (d, JPC
=
8.2 Hz, ArÀCH), 132.1 (d, JPC =8.6 Hz, ArÀCH), 131.4 (ArÀCH), 130.8
(ArÀCH), 129.0 (d, JPC =20.5 Hz, ArÀCH), 127.9 (ArÀCH), 127.6 (ArÀ
For synthesis of (R)-a-methylnaphthyl azide the literature proce-
dure was exactly followed.[29] Dipp-azide (Dipp=2,6-iPr2C6H3),[18]
HN[RÀCH(CH3)Ph](PPh2),[19] HN[RÀCH(CH3)naph](PPh2),[21] P,P-diphen-
yl-N,N’-bis((R)-1-phenylethyl)phosphinimidic amide, (R)-HPEPIA (L-
H),[5b] and [Ca{N(SiMe3)2}2(THF)2][30] were also prepared according to
already described procedures.
CH), 126.5 (ArÀCH), 126.1 (d, JPC =8.2 Hz, ArÀCH), 125.5 (d, JPC
=
13.1 Hz, ArÀCH), 125.0 (d, JPC =16.1 Hz, ArÀCH), 124.7 (ArÀCH),
124.3 (ArÀCH), 123.4 (ArÀCH), 122.4 (ArÀCH), 51.2 (P=NCH), 46.3
(HNCH), 29.9 (d, 3JPC =11.8 Hz, P=NCHCH3), 25.7 ppm (HNCHCH3);
31P{1H} NMR (C6D6, 162 MHz): d=3.6 ppm; IR (ATR): n=3372 (m),
3074 (m),3051 (m) 2965 (m), 2921 (w), 2858 (vw), 2826 (vw), 2166
(vw), 2104 (vw), 1594 (m), 1508 (m), 1480 (vw), 1435 (m), 1392 (s),
1374 (m), 1329 (m), 1287 (s) 1261 (m), 1233 (vs), 1165 (s), 1111 (s),
1102 (m), 1080 (w), 1053 (w), 1024 (w),997 (w), 934 (m), 868 (w),
849 (w), 829 (s), 801 (m), 774 (s), 750 (s), 717(m), 694 (m), 639 (m),
612 (w), 545 (w), 524 (m), 483 (w), 434 cmÀ1 (w); elemental analysis
calcd [%] for [C36H33N2P] (524.65): C 82.42; H 6.34, N 5.34; found: C
82.10, H 6.23, N 5.40.
Synthesis of P,P-diphenyl-N-[(R)-1-phenylethyl],N’-(2’,6’-diisopro-
pylaniline)phosphinimidic
amide,
(R)-HPEDippPIA
(L’-H):
Ph2PN(R-*CHMePh) (3.2 g, 10.61 mmol, 1.00 equiv) was dissolved in
30 mL of THF and cooled to À208C. A solution of Dipp-azide
(2.4 g, 11.67 mmol, 1.1 equiv) in 20 mL of THF was added slowly.
After complete addition, the reaction mixture was warmed to am-
bient temperature whereupon liberation of N2 gas was observed.
The reaction mixture was stirred at ambient temperature for 16 h.
After evaporation of the solvent under reduced pressure, a viscous
solid was obtained, which was washed with n-pentane (4*20 mL)
and dried in vacuum to obtain the desired product as white
powder. Single crystals of the title compound suitable for X-ray
analysis were obtained by recrystallization from n-heptane.
Synthesis of complex 1: [Ca{N(SiMe3)2}2(THF)2] (182.0 mg,
0.36 mmol, 1.00 equiv.) and L-H (300.0 mg, 0.71 mmol, 2.00 equiv.)
were dissolved in toluene (30 mL) and stirred at room temperature
for 16 h. After removal of the solvent under reduced pressure re-
sulted into white solid. The resulting white solid was washed with
n-pentane (5 mL). Single crystals suitable for X-ray analysis were
obtained from hot n-hexane. The solvent was decanted, and the
product was washed with cold n-pentane (5 mL).
Yield (based on crystals): 3.57 g (70%); 1H NMR (C6D6, 400 MHz):
d=7.78–7.66 (m, 4H, oÀArphosÀH), 7.25–7.22 (m, 2H, ArÀH), 7.10–
6.94 (m, 12H, o,m,p-ArÀH), 4.64 (ddq, 3JHH =6.8 Hz, 3JHH =10 Hz,
3JPH =10 Hz, 1H, HNCH), 3.67 (sept, JHH =6.9 Hz, 2H, HC(CH3)2), 2.81
Yield (based on crystals): 190 mg (60%). 1H NMR (C6D6, 400 MHz):
d=7.71–7.66 (m, 8H, o-ArphosÀCH), 7.21–7.19 (m, 16H, o-ArÀCH and
m-ArphosÀCH), 7.18–7.17 (m, 4H, ArÀCH), 7.15–7.13 (m, 6H, ArÀCH),
3
(dd, 3JHH =9.5 Hz, 2JPH =9.5 Hz, 1H, NH), 1.26 (d, 3JHH =6.8 Hz, 3H,
HNCHCH3), 1.183 (d, 3JHH =6.9 Hz, 6H, HC(CH3)2), 1.180 ppm (d,
3JHH =6.9 Hz, 6H, HC(CH3)2); 13C{1H} NMR (C6D6, 100 MHz): d=146.2
3
3
7.11–7.06 (m, 6H, ArÀCH), 4.04 (dq, JHH =6.5 Hz, JPH =19.6 Hz, 4H,
3
2
(d, JPC =4.8 Hz, PNHCHCq),144.6 (ArÀCDipp),142.0 (d, JPC =7.2 Hz, P=
Ph(CH)CH3), 1.38 ppm (d, 3JHH =6.5 Hz, 12H, Ph(CH)CH3); 13C{1H}
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3
NMR (C6D6, 100 MHz): d=152.0 (d, JPC =14.0 Hz, ArÀCq), 135.9 (d,
1JPC =85.4 Hz, ArphosÀCq), 132.7 (d, 2JPC =8.8 Hz, o-ArphosÀCH), 130.3
(d, 4JPC =2.7 Hz, ArÀCH), 129.3 (ArÀCH), 127.9 (ArÀCH), 126.1 (ArÀ
CH), 125.9 (ArÀCH), 54.1 (Ph(CH)CH3), 28.4 ppm (d, 3JPC =6.7 Hz,
Ph(CH)CH3); 31P{1H} NMR (C6D6, 162 MHz): d=24.5 ppm; IR (ATR):
n=3058 (vw), 3022 (vw), 2957 (vw), 2913 (vw), 2835 (vw), 1598
(vw), 1489 (m), 1479 (m), 1452 (m), 1433 (m), 1401 (m), 1361 (m),
1346 (m), 1309 (m), 1273 (w), 1236 (s), 1204 (s), 1176 (m), 1167 (m),
1156 (m), 1149 (m), 1118 (m), 1102 (w), 1087 (m), 1060 (m), 1025
(m), 1000 (s), 984 (m), 973 (m), 965 (s), 945 (vs), 911 (m), 859 (m),
837 (m), 822 (m), 780 (s), 772 (s), 761 (m), 749 (m), 719 (s), 714 (s),
695 (s), 622 (m), 608 (m), 597 (m), 574 (m), 565 (m), 510 (s), 463 (s),
446 (m), 434 cmÀ1 (vw); elemental analysis calcd (%) for
[C56H56CaN4P2] (887.09): C 75.82, H 6.36, N 6.32; found: C 75.56, H
6.20, N 6.46.
1082 (vs), 1027 (m), 1014 (m), 1001 (w), 970 (m), 926 (m), 908 (m),
849 (s), 835 (s), 821 (s), 791 (m), 775 (m), 748 (m), 730 (m), 712 (vs),
697 (w), 645 (m), 628 (vw), 617 (m), 575 (m), 560 (m), 543 (vs), 532
(vs), 517 (m), 499 (m), 488 (vw), 432 (m), 420 cmÀ1 (vw); elemental
analysis calcd [%] for [C72H64CaN4P2] (1087.33): C 79.53, H 5.93, N
5.15; found: C 79.72, H 6.28, N 5.18.
Hydroboration reactions
The catalyst, ferrocene (internal standard) and solid substrates
(0.25 mmol ketone, if any) were weighed into an NMR tube in the
argon-filled glove box. C6D6 (about 0.5 mL) was condensed into
the NMR tube and the mixture was frozen at À1968C. The reac-
tants HBpin (0.3 mmol) and ketone (liquid, 0.25 mmol) were inject-
ed onto the solid mixture under nitrogen using an oven-dried Pas-
teur pipette, and the whole sample was melted and mixed just
before insertion into the core of the NMR machine (t0). The com-
pletion of the reaction was indicated by conversion of singlet of
the methyl protons of the ketone into doublet of the final product.
Synthesis of complex 2: Following the similar procedure described
above for 1, the reaction of [Ca{N(SiMe3)2}2(THF)2] (157.0 mg,
0.31 mmol, 1.00 equiv.) and L’-H (300 mg, 0.62 mmol, 2.00 equiv.)
afforded single crystals from n-pentane suitable for X-ray analysis.
The solvent was decanted and the product was washed with cold
n-pentane (5 mL).
NMR data of catalysis: The NMR data (1H, 11B, 13C{1H}) for the hy-
droboration products was consistent with the corresponding litera-
1
ture.
Yield (based on crystals): 220.0 mg (71%); H NMR (C6D6, 400 MHz):
Ph(Me)CHOBpin[31]
d=7.50–7.45 (m, 4H, o-ArphosÀCH), 7.27–7.25 (m, 4H, ArÀCH), 7.14–
7.09 (m, 6H, ArÀCH), 6.99–6.94 (m, 10H, ArÀCH), 6.83–6.74 (m,
3
3
12H, ArÀCH), 3.67 (dq, JHH =6.5 Hz, JPH =24.87 Hz, 2H, Ph(CH)CH3),
3
3.07 (br, 4H, CH(CH3)2), 1.65 (d, JHH =6.5 Hz, 6H, Ph(CH)CH3), 1.06–
0.38 ppm (m, 24H, CH(CH3)2); 13C{1H} NMR (C6D6, 100 MHz): d=
152.5 (d, 3JPC =8.9 Hz, ArÀCq), 144.6 (ArÀCq), 143.0 (d, JPC =4.3 Hz,
2
ArÀCq), 135.8 (ArÀC), 134.9 (d, JPC =8.6 Hz, ArÀCH), 133.9 (ArÀCH),
133.5 (d, JPC =8.9 Hz, ArÀCH), 132.4 (d, JPC =8.1 Hz, ArÀCH), 130.4
(d, JPC =2.5 Hz, ArÀCH), 130.2 (d, JPC =2.6 Hz, ArÀCH), 129.5 (ArÀ
CH), 127.7 (ArÀCH), 127.5 (d, JPC =10.9 Hz, ArÀCH), 126.5 (ArÀCH),
123.3 (ArÀCH), 122.02 (d, JPC =4.8 Hz, ArÀCH), 55.8 (Ph(CH)CH3),
29.6 (d, 3JPC =10.9 Hz, Ph(CH)CH3), 28.5 (CH(CH3)2), 24.1 ppm (br,
CH(CH3)2); 31P{1H} NMR (C6D6, 162 MHz): d=22.6 ppm; IR (ATR): n=
3055 (vw), 2964 (m), 2954 (w), 2919 (w), 2863 (w), 1588 (w), 1492
(m), 1452 (s), 1432 (w), 1380 (vw), 1364 (vw), 1327 (vw), 1308 (m),
1255 (m), 1204 (vs), 1179 (s), 1146 (w), 1111 (w), 1099 (w), 1067 (w),
1047 (m), 1026 (m), 1004 (vw), 992 (vw), 973 (vw), 950 (vw), 931
(vw), 837 (vs), 787 (m), 775 (m), 756 (m), 743 (m), 715 (m), 696 (vs),
662 (m), 609 (m), 583 (m), 564 (s), 524 (s), 514 (m), 490 (m), 477
(m), 451 cmÀ1 (m); elemental analysis calcd [%] for [C64H72CaN4P2]
(999.33): C 76.92, H 7.26, N 5.61; found: C 77.13, H 7.69, N 5.82.
Synthesis of complex 3: Following the similar procedure described
above for 1, the reaction of [Ca{N(SiMe3)2}2(THF)2] (96.0 mg,
0.19 mmol, 1.00 equiv.) and L’’-H (200.0 mg, 0.38 mmol, 2.00 equiv.)
afforded single crystals from n-pentane suitable for X-ray analysis.
The solvent was decanted and the product was washed with cold
n-pentane (5 mL).
1H NMR (C6D6, 400 MHz): d=7.34 (d, 3JHH =6.47 Hz, 2H, o-ArÀH),
3
7.15–7.12 (m, 2H, m-ArÀH), 7.04 (t, JHH =7.34 Hz, 1H, p-ArÀH), 5.38
(q, 3JHH =6.46 Hz, 1H, PhCHCH3), 1.43 (d, 3JHH =6.47 Hz, 3H,
PhCHCH3), 1.02 (s, 6H, BpinÀCH3), 0.99 ppm (s, 6H, Bpin-CH3);
13C{1H} NMR (C6D6, 100 MHz): d=145.4 (ArÀCq), 128.5 (ArÀCH),
127.4 (ArÀCH), 125.7 (ArÀCH), 82.5 (BpinÀC), 72.9 (OCHCH3Ph), 25.8
(PhCHCH3), 24.7 ppm (BpinÀCH3); 11B NMR (C6D6, 128 MHz): d=
22.6 ppm.
(4-NO2Ph)(Me)CHOBpin[31]
1H NMR (C6D6, 400 MHz): d=7.83 (d, 3JHH =8.78 Hz, 2H, o-ArÀH),
7.05 (d, 3JHH =8.52 Hz, 2H, m-ArÀH), 5.19 (q, 3JHH =6.48 Hz, 1H,
OCHCH3), 1.27 (d, 3JHH =6.51 Hz, 3H, OCHCH3), 1.05 (s, 6H, Bpin-
CH3), 1.02 ppm (s, 6H, BpinÀCH3); 13C{1H} NMR (C6D6, 100 MHz): d=
152.1 (ArÀCq), 147.4 (ArÀCH), 126.2 (ArÀCH), 123.6 (ArÀCH), 83.0
(BpinÀC), 71.9 (OCHCH3), 25.3 (OCHCH3), 24.6 ppm (BpinÀCH3);
11B NMR (C6D6, 128 MHz): d=22.4 ppm.
Yield (based on crystals): 120.0 mg (58.1%); 1H NMR (C6D6,
400 MHz): d=7.77–7.70 (m, 8H, o-ArphosÀCH), 7.65–7.60 (m, 12H,
ArphosÀCH), 7.48–7.46 (m, 4H, ArÀCH), 7.14–7.10 (m, 4H, ArÀCH),
7.06–6.99 (m, 20H, ArÀCH), 4.86 (dq, 3JHH =6.4 Hz, 3JPH =19.02 Hz,
3
4H, naph(CH)CH3), 1.44 ppm (d, JHH =6.44 Hz, 12H, naph(CH)CH3);
(4-BrPh)(Me)CHOBpin[32]
13C{1H} NMR (C6D6, 100 MHz): d=147.4 (d, 3JPC =12.67 Hz, ArÀCq),
135.8 (ArÀC), 134.9 (ArÀC), 134.6 (ArÀCH), 132.7 (d, JPC =8.7 Hz, ArÀ
CH), 130.9 (ArÀCH), 130.2 (d, JPC =2.5 Hz, ArÀCH), 129.5 (ArÀCH),
126.7 (ArÀCH), 126.5 (ArÀC), 126.0 (ArÀC), 125.3 (ArÀC), 123.3 (ArÀ
C), 123.2 (ArÀC), 49.7 (naph(CH)CH3), 28.9 ppm (d, 3JPC =8.3 Hz,
naph(CH)CH3); 31P{1H} NMR (C6D6, 162 MHz): d=27.3 ppm; IR (ATR):
n=3052 (vw), 2959 (vw), 2917 (w), 2859 (w), 1595 (w), 1508 (w),
1481 (w), 1456 (m), 1434 (w), 1394 (w), 1364 (w), 1323 (w), 1310
(w), 1300 (w), 1256 (vw), 1235 (vw), 1172 (w), 1144 (w), 1133 (w),
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1H NMR (C6D6, 400 MHz): d=7.23 (d, 3JHH =8.46 Hz, 2H, o-ArÀH),
7.00 (d, 3JHH =8.32 Hz, 2H, m-ArÀH), 5.20 (q, 3JHH =6.44 Hz, 1H,
OCHCH3), 1.32 (d, 3JHH =6.47 Hz, 3H, OCHCH3), 1.02 (s, 6H, BpinÀ
CH3), 0.99 ppm (s, 6H, BpinÀCH3); 13C{1H} NMR (C6D6, 100 MHz): d=
144.3 (ArÀCq), 131.6 (ArÀCH), 127.5 (ArÀCH), 121.2 (ArÀCH), 82.7
(BpinÀC), 72.2 (OCHCH3), 25.5 (OCHCH3), 24.7 ppm (BpinÀCH3);
11B NMR (C6D6, 128 MHz): d=22.4 ppm.
Acknowledgements
Financial support from KIT is gratefully acknowledged. The au-
thors acknowledge computational support by the state of
Baden-Württemberg through bwHPC and the German Re-
search Foundation (DFG) through grant no INST 40/467-1
FUGG. Open access funding enabled and organized by Projekt
DEAL.
(4-MePh)(Me)CHOBpin[33]
Conflict of interest
The authors declare no conflict of interest.
Keywords: calcium · homoleptic · hydroboration
iminophosphonamide · photoluminescence
·
1H NMR (C6D6, 400 MHz): d=7.29 (d, 3JHH =8.07 Hz, 2H, o-ArÀH),
6.97 (d, 3JHH =7.83 Hz, 2H, m-ArÀH), 5.41 (q, 3JHH =6.44 Hz, 1H,
3
OCHCH3), 2.09 (s, 3H, PhCH3), 1.47 (d, JHH =6.46 Hz, 3H, OCHCH3),
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Manuscript received: November 4, 2020
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