Reactivity of a P–H Functionalized Al/P-Based Frustrated Lewis Pair – Hydrophosphination versus Classic Adduct Formation

Article abstract of DOI:10.1002/zaac.201700340

The P–H functionalized Al/P-based frustrated Lewis pair (FLP) Mes(H)P–C[Al{CH(SiMe₃)₂}₂]=C(H)–tBu (3) has the typical functionality of FLPs with Lewis acidic and basic centers in a single molecule and is able to transfer the P bound H atom to activated substrates. Nevertheless, 3 reacted with NH₃ only by adduct formation with the N atom coordinated to Al (5). The relatively low basicity of the P atom prevented the formation of a hydrogen bridge between P and Al. Similarly, benzil and 3 afforded a simple adduct (6) with only one C=O group bonded to P and Al. The second C=O group and the P–H moiety were unaffected. 6 has two stereogenic centers, and the resulting diastereomers were identified by crystal structure determinations. Migration of the P bound H atom was only observed for substrates containing basic N atoms. Nitriles gave heterocyclic iminophosphine adducts (7) in which the N–H groups were coordinated to the Al atoms. An isocyanate and two isothiocyanates afforded adducts via Al–X and P–C bond formation (X = O, S), and phosphaurea derivatives (8a to 8c) resulted from H shift to the exocyclic N atoms. A carbodiimide reacted with 3 by the formation of a phosphaguanidine (8d) with the imine N atom coordinated to Al. The latter reactions proceed under mild conditions and represent formally the hydrophosphination of unsaturated substrates.

Full text of DOI:10.1002/zaac.201700340

Journal of Inorganic and General Chemistry
DOI: 10.1002/zaac.201700340
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
Reactivity of a P–H Functionalized Al/P-Based Frustrated Lewis
Pair – Hydrophosphination versus Classic Adduct Formation
Werner Uhl,*[a] Lukas Keweloh,[a] Alexander Hepp,[a] Frank Stegemann,[a] Marcus Layh,[a] and
Klaus Bergander[b]
Dedicated to Professor Thomas Schleid on the Occasion of his 60th Birthday
Abstract. The P–H functionalized Al/P-based frustrated Lewis pair
(FLP) Mes(H)P–C[Al{CH(SiMe3)2}2]=C(H)–tBu (3) has the typical
nations. Migration of the P bound H atom was only observed for sub-
strates containing basic N atoms. Nitriles gave heterocyclic iminophos-
functionality of FLPs with Lewis acidic and basic centers in a single phine adducts (7) in which the N–H groups were coordinated to the
molecule and is able to transfer the P bound H atom to activated sub-
strates. Nevertheless, 3 reacted with NH3 only by adduct formation
with the N atom coordinated to Al (5). The relatively low basicity of
the P atom prevented the formation of a hydrogen bridge between P
Al atoms. An isocyanate and two isothiocyanates afforded adducts via
Al–X and P–C bond formation (X = O, S), and phosphaurea derivatives
(8a to 8c) resulted from H shift to the exocyclic N atoms. A carbodiim-
ide reacted with 3 by the formation of a phosphaguanidine (8d) with
and Al. Similarly, benzil and 3 afforded a simple adduct (6) with only the imine N atom coordinated to Al. The latter reactions proceed under
one C=O group bonded to P and Al. The second C=O group and the mild conditions and represent formally the hydrophosphination of un-
P–H moiety were unaffected. 6 has two stereogenic centers, and the saturated substrates.
resulting diastereomers were identified by crystal structure determi-
These compounds are highly interesting with respect to the
Introduction
specific soft- or hardness of the contributing metal atoms and
showed a reactivity pattern that differed from that of the Al/P-
FLP 1. Hydroalumination of a P-H functionalized alkynyl-
phosphine opened facile access to a new class of FLPs (3),
which show the typical FLP behavior, but feature a reactive
P–H bond.[16] Activation of substrates by coordination to the
Lewis acidic and basic centers and migration of the P–H
hydrogen atom to the activated species should allow the gener-
ation of unusual structural motifs. Accordingly, reaction of 3
with trimethylsilyl azide afforded a 1-phospha-tetrazene deriv-
ative (4) (Scheme 1), which is stabilized by an interaction to
the Lewis acidic aluminum atom.[16] Similar hydrogen transfer
reactions under relatively mild conditions have been observed
Frustrated Lewis pairs (FLPs) show a fascinating reactivity
in diverse stoichiometric or catalytic transformations and have
been applied in numerous chemical reactions.[1] Their unique
properties result from the presence of coordinatively unsatu-
rated Lewis acidic and basic centers in single molecules or
bimolecular systems and result in the coordination and cooper-
ative activation of a wide variety of substrates. Investigations
into the reactivity of boron-based systems are most frequently
reported,[1] but it has been shown in recent studies that Al/P-
based systems form an interesting alternative class of highly
efficient FLPs.[2–6] A facile route for the synthesis of geminal
Al/P-FLPs (e.g. 1; Scheme 1) is based on hydroalumination of
suitable alkynylphosphines with sterically shielded dialkylalu-
minum hydrides.[3,4a,5] These compounds have been used for
the coordination of numerous substrates including carbon diox-
ide,[3,6] carbonyl compounds,[3,6,7] chalcogen atoms,[8] boron
halides,[9] transition metal atoms,[10] etc. and for the catalytic
dehydrogenation of ammineboranes[11] or in phase-transfer ca-
talysis.[12] Transmetallation comprising an Al/Mg exchange af-
forded a unique phosphinylvinyl Grignard reagent (2), which
allowed the synthesis of Ga/P- and In/P-based FLPs.[13–15]
* Prof. Dr. W. Uhl
Fax: +49-251-8336660
E-Mail: uhlw@uni-muenster.de
[a] Institut für Anorganische und Analytische Chemie
Universität Münster
Corrensstraße 30
48149 Münster, Germany
[b] Organisch-chemisches Institut der Universität Münster
Corrensstraße 40
Scheme 1. Al/P-based FLPs, a Grignard reagent and an adduct of 3
with N3-SiMe3.
48149 Münster, Germany
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upon treatment of 3 with PhCN and PhNCO,[16] while the free coupling constant decreases from 31.8 Hz in 3 to 23.3 Hz in
phosphine Mes(H)P–CϵC–tBu was unreactive towards these 3a, which in accordance with the Karplus relation is indicative
reagents up to 100 °C. for the configuration change (trans to cis with respect to the
These reactions may be described by the addition of P–H P and H positions).[25] Similar effects have previously been
bonds to the activated substrates. Hydrophosphination of ole- observed in adducts of Al/P-based FLPs.[6b] 3a was stable at
fins or heterocumulenes is a powerful method for the prepara- room temperature and no further changes in the NMR spectra
tion of organic phosphorus compounds with high atomic effi- were observed. Out of convenience and due to the high sta-
ciency. Standard reaction conditions, however, typically re- bility of 3 all secondary reactions were carried out with the cis
quire activation of the phosphine by radical starters,[17] acid/ product 3.
base catalysis[18] or most effectively the use of transition[19,20]
or lanthanide metal catalysts.[20,21] The addition of the P–H
fragment is Markovnikow or anti-Markovnikov depending on
the reaction conditions. Hydrophosphination reactions without
activation are rare, but there have been recent efforts to find
suitable conditions that avoid metal catalysts and/or toxic sol-
Scheme 2. Rearrangement of compound 3 [R = CH(SiMe3)2].
vents[22] including the synthesis of phosphaguanidines from
R2PH·BH3 and carbodiimides.[23] The reactions of 3 may be
Previously we reported on investigations into the reactivity
considered as FLP mediated hydrophosphinations,[19] and this
manuscript presents systematic investigations into this topic in
more detail. Reactions of 3 with azides have been reported
previously.[14,16]
of the Al/P-FLP 1 towards NH3 and BH3. Both substrates af-
forded the respective adducts with the boron atom coordinated
to phosphorus and the nitrogen atom bonded to aluminum.
While a B–H–Al bridge was observed for the borane adduct,
no hydrogen bonding resulted for the NH3 derivative.[11] More
recently, reactions with borenium cations and B/P-based FLPs
have led to an NH2-substituted phosphine-borane,[26] an NH3
adduct of a borenium cation[26] and the catalytic dehydrogena-
tion of ammine-boranes, respectively.[11,27] We exposed a solu-
tion of compound 3 in n-pentane to an atmosphere of dry NH3
and isolated a simple Lewis-acid-base adduct (5) in 79% yield
(Scheme 3).
Results and Discussion
Hydroalumination of Mes(H)P–CϵC–tBu (an improved
synthesis is given in the Experimental Section) with
[(Me3Si)2CH]2Al–H resulted in the formation of the Al/P-
based FLP Mes(H)P–C[Al{CH(SiMe3)2}2]=C(H)–tBu (3)[16]
which represents the kinetically favored product of a cis-ad-
dition of aluminum and hydrogen atoms (H and Al in cis posi-
tion of the resulting alkene) and has the phosphorus atom in a
trans position to hydrogen. Molecules with this configuration
are usually obtained in the first step of hydroalumination reac-
tions with alkynes. Smaller substituents result in rearrange-
ment, which requires intermolecular activation by a Lewis acid
and affords the thermodynamically stable trans products with
aluminum and hydrogen atoms on different sides of the alk-
enes.[24] Only the presence of large substituents or coordinative
saturation of the aluminum atoms prevent the approach of a
Lewis acid and the transformation of the kinetically favored
product. The persistence of the cis configuration in 3 at room
temperature is likely attributed to the bulky substituents on
aluminum since in case of related, but sterically less encum-
bered FLPs such as Mes2P–C(AltBu2)=C(H)–Ph (1)[3] sponta-
neous rearrangement was observed and only the thermodynam-
ically favored trans products were detected and isolated.
Attempts to achieve thermal rearrangement of 3 and to yield
the trans product 3a at temperatures of up to 120 °C were not
successful, but irradiation of 3 in an NMR tube with a broad-
band UV source in benzene afforded 3a after 3 h at room
temperature in quantitative yield as determined by NMR spec-
troscopy (Scheme 2). The rearrangement was evident from a
downfield shift in the 31P NMR spectrum [δ = –80.8 ppm (3),
1
–69.7 ppm (3a)] and highfield shifts in the H NMR spectrum
[δ = 5.33 ppm (3), 5.22 ppm (3a) PH; δ = 6.69 ppm (3),
1
5.83 ppm (3a) PC=CH]. The JPH coupling constants are with
Scheme 3. Reactions of compound 3 with NH3, benzil, RЈCϵN, and
3
221.4 und 226.0 Hz, respectively, not affected, but the JPH heterocumulenes RЈ–N=C=X [R = CH(SiMe3)2].
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Similar to the NH3 adduct of 1 it did not show an interaction a sealed NMR tube to 70 °C (about 10% after 1 d). Complete
between hydrogen atoms of the coordinated NH3 molecule and decomposition required heating to 100 °C for 16 h. cis-
the lone pair at phosphorus (N···P 386 pm) (Figure 1). The
missing hydrogen bonding was evident from the NMR spectra
of 5, which were very similar to those of the starting material 3
with virtually identical chemical shifts and coupling constants
[δ(31P), δ(1H), JPH] in the Lewis basic part of the molecule.
Mes(H)P–C(H)=C(H)–tBu was identified by NMR spec-
troscopy (31P, δ = –96.8 ppm; JPH = 219.1, JPH = 23.5 Hz)
as the main product, which results from protolytic cleavage
of the Al–C(vinyl) bond of the FLP backbone. An analogous
phosphaalkene, trans-Mes2P–C(H)=C(H)–Ph, was observed as
a frequent side product in decomposition reactions of FLP
1.[30] (Me3Si)2CH2 was detected as another by-product upon
thermal degradation of 5 [1H NMR: δ = 0.06 ppm (SiMe3),
–0.37 ppm (CH2)]. Treatment of 3 with BH3 afforded also an
adduct, which, however, could not be isolated in a crystalline
form. We abstain from a detailed discussion.
1
3
3
An only small increase in the JPH coupling constant by 6 Hz
is consistent with the retention of the trans arrangement of the
alkenyl group. The NH3 signal in the 15N NMR spectrum (δ =
+
21 ppm) was comparable to that of NH4 (δ = 27 ppm) and
shifted downfield relative to free ammonia (δ = 0.0 ppm). An
increase in the 1JNH coupling constant from 61 (NH3) to 65 Hz
in the adduct 5 may further indicate the coordination of the
NH3 molecule.[28] The 1H NMR resonances of the α-hydrogen
atoms of the CH(SiMe3)2 groups show, as expected, a signifi-
cant high-field shift compared to 3 [δ = –1.27(av.) vs.
–0.50 ppm] which is characteristic of the increased coordina-
tion number and electron density at the aluminum atom.[29]
The bulky CH(SiMe3)2 groups are magnetically inequivalent
and gave two and four different signals for the respective CH
and SiMe3 protons. 5 was stable in solution at room tempera-
ture, but decomposed slowly upon heating a C6D6 solution in
In the solid state, the molecule 5 adopts an eclipsed confor-
mation relative to the P/Al axis (N–Al–P–Cipso 7.4°) with NH3
and the mesityl group on the same side of the molecule (Fig-
ure 1). One CH(SiMe3)2 group (C20) is on the same side as
the vinyl substituent, while the other one (C10) resides on the
same side as the lone pair of electrons at phosphorus. The two
carbon atoms of the olefin and the attached atoms Al, P, H and
C(Me3) are coplanar. The P–C bond lengths (Table 1) are sim-
ilar to those of the starting material, whereas the Al–C dis-
tances are significantly longer (201 vs. 196 pm) as a result of
the increase of the coordination number at the aluminum atom.
The Al–N bond is with 203.1(2) pm relatively long, but in
the typical range of distances in adducts of trialkylaluminum
compounds with ammonia[31] or simple primary or secondary
amines.[32] It may indicate a comparatively weak bond consis-
tent with the facile loss of NH3 as observed in the mass spec-
trum.
Treatment of 3 with benzil afforded adduct 6 in 90% yield
(Scheme 3). Only one of the C=O groups is coordinated to the
acidic and basic centers of the FLP by P–C and Al–O bonds,
and no hydrogen transfer was observed even at elevated tem-
perature. The NMR spectra of 6 differ considerably from those
of 3 with downfield shifts in the 31P [δ = –80.8 ppm (3) to
1
δ = –17.9 ppm (6)] and H NMR spectra [PH (δ = 5.33 to δ =
8.33 ppm); PC=CH (δ = 6.69 to δ = 7.56 ppm)], which are
indicative of an increased coordination number at the phos-
phorus atom. Accordingly, we observed a significant increase
1
3
1
in JPH, JPH(vinyl), and JPC(Mes) coupling constants from
221.4 (3) to 465.6 (6), 31.8 to 72.1 and 10.5 to 55.7 Hz,
respectively. The two different CO groups are easily distin-
guishable in the 13C NMR spectrum by their characteristic
chemical shifts [δ = 98.5 ppm (C–O); δ = 200.3 ppm (C=O)]
Figure 1. Molecular structure of compound 5. Displacement ellipsoids
are drawn at the 40% level. Hydrogen atoms (except H1, H2 and those
on NH3; arbitrary radii) are omitted for clarity.
Table 1. Bond lengths /pm of compounds 5–7, 8a, 8b, and 8d.
Parameter
5
6(RS/SR)
6(RR)
7a
7b
8a
8b
8d
Al–X
203.1(2)
200.7(2)
200.5
183.2(2)
184.3(2)
–
135.5(3)
–
–
183.6(2)
205.8(2)
201.3
177.5(2)
180.4(2)
191.2(2)
134.0(3)
138.1(2)
–
182.5(1)
206.5(1)
200.5
179.0(1)
181.1(1)
190.8(1)
134.3(2)
138.3(2)
–
192.2(2)
202.2(2)
201.3
180.4(2)
184.7(2)
185.8(2)
134.2(2)
131.7(2)
133.3(2)
196.4(2)
203.3(2)
200.6
181.8(2)
184.4(2)
180.3(2)
132.9(2)
128.7(2)
–
190.3(1)
203.2(2)
200.4
180.7(2)
183.6(2)
182.8(2)
133.2(2)
126.9(2)
132.4(2)
237.93(7)
202.1(2)
199.8
178.8(2)
183.7(2)
183.4(2)
134.4(2)
169.7(2)
132.2(2)
197.6(1)
200.7(1)
201.9
178.5(1)
184.5(1)
185.6(1)
134.3(2)
131.9(1)
134.4(1)
Al–C(C=C)
Al–CH(Si2)(av)
P–C(C=C)
P–C(Mes)
P–C(X)
C=C
C–Xring (X = O, N, S)
C–Nterm.
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and JPC coupling constants [66.6 (1JPC) and 4.7 Hz (2JPC)]. and O in the apical position (distance to the plane 52.5 pm;
The compound is unsymmetrical and all atoms or sub-groups folding angle 41.1°; Figure 2). The four atoms P1, C30 and
of the CH(SiMe3)2, Mes and PCPh substituents gave different the unreacted carbonyl group form a second molecular plane,
resonances in the 1H and 13C NMR spectra. The resonances of which is almost perpendicular (83.2°) to the first one. This
the atoms in o- and m-positions of the terminal C(=O)–Ph leads to a close intramolecular C=O···H–P contact (245 pm,
group coincide.
angle O–H–P 97°), which may help to stabilize this conforma-
Compound 6 has two stereo centers [P*, C*(OP)] and dif- tion relative to the R,R/S,S-isomer where this interaction is im-
ferent diastereomers were identified by crystal structure deter- possible (Figure 3). P–H···O distances below 300 pm were de-
minations. The R,S isomer crystallized in the non-centrosym- tected in few structurally authenticated compounds but their
metric space group P212121, while its diastereomer with R,R significance and energetic contribution is not clear.[33] P–H···X
or S,S configuration crystallized as a mixture of enantiomers hydrogen bonding has been found in FLP adducts with
in the centrosymmetric space group P1. Crystals of the latter hydrogen halides (X = F – I)[15b,34] and has been confirmed by
¯
have been picked from a crystalline fraction of 6 by accident. a characteristic[35] downfield shift of the P–H resonances in
Powder X-ray diffraction analysis showed the R,S/S,R mixture the 1H NMR spectra to δ Ͼ 9 ppm. Al–C bond lengths increase
to be the only component. Reflections of the second dia- significantly relative to the starting material (Table 1) which is
stereomer were not found as determined by comparison of the
experimental pattern with a powder pattern, which was calcu-
lated from the data of the single crystal structure determi-
nations. This may indicate the presence of only a few crystals
of the R,R/S,S isomer in the mixture. Diastereomers should
show different NMR spectra, but we observed only data of a
single species, which may be caused by a fast exchange in
solution. The adducts of benzaldehyde with FLPs such as 1
have similar PC2OAl heterocycles and showed a comparable
exchange, which was explained by cleavage of the endocyclic
P–C(carbonyl) bond and rotation about the Al–O bond.[5,7c]
The C–O carbon atoms of the heterocycle have a chiral sur-
rounding, but splitting of resonances was observed only at low
temperature. A similar exchange may occur with the benzil
adduct 6. Variable temperature NMR experiments in C7D8 re-
sulted in a sharpening of the PCPh signals at 240 K, the JHH
coupling constants could be resolved, which is consistent with
a hindered rotation of this group. Further cooling to 200 K on
a 400 MHz NMR spectrometer gave only broad resonances.
Only when the sample was cooled to 178 K on a 600 MHz Figure 2. Molecular structure of compound 6 (R/S isomer; P212121).
spectrometer the 31P NMR resonance at δ = –17.9 ppm splits
into two separate signals at δ = –14.2 and –13.7 ppm in an
Displacement ellipsoids are drawn at the 40% level. Hydrogen atoms
(except H1 and H2; arbitrary radii) are omitted for clarity.
approximate ratio of 1:1. The doublet of the P–H hydrogen
1
atom in the H NMR spectrum did also split into two signals
but overlap prevented an unambiguous assignment. A clearly
resolved splitting pattern (approximate ratio of 1:1) could be
assigned and integrated only for the hydrogen atoms of the
two different o-Me groups and one m-H atom (δ = 2.87 ppm
splits into 2.95 and 2.83 ppm; δ = 1.52 ppm splits into 1.30
and 1.20 ppm; δ = 6.13 ppm splits into 5.74 and 5.61 ppm).
These results may indicate equilibrium between both dia-
stereomers in solution, which is facilitated by cleavage of the
P–C bond similar to the situation in the related benzaldehyde
adducts. Accordingly, the P–C(C–O) bonds in the molecular
structures (191 pm) are relatively long and again comparable
to that of benzaldehyde adducts.[5,7c] The R,S form may crys-
tallize preferentially from the solution due to a weak
P–H···O=C hydrogen bond in the solid state (see below) which
is not present in the second diastereomer.
The five-membered PCAlOC heterocycle of compound 6
(R,S isomer) adopts an envelope conformation with P, Al, and
¯
Figure 3. Molecular structure of compound 6 (R/R isomer; P1). Dis-
placement ellipsoids are drawn at the 40% level. Hydrogen atoms (ex-
C in the molecular plane (largest deviation from plane 0.2 pm) cept H1 and H2; arbitrary radii) are omitted for clarity.
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consistent with the increased coordination number at alumi- carbon atom and ring closure.[16] Compounds 7 are both color-
num. The Al–C(vinyl) distances are with 206 pm longer than less, whereas the PhCN product was yellow. In the absence of
the Al–C distances to the bulky alkyl groups (201 pm), which hydrogen atoms directly bound to phosphorus the reaction of
may be influenced by hyperconjugation by a lone pair of elec- related P/B-based FLPs with organic nitriles led only to the
trons at the oxygen atom with the Al–C σ*-orbital. A similar formation of stable Lewis acid-base adducts,[38] while
trend was observed in e.g. HX adducts of FLPs.[15b,34] The P– Ni(cod)2 in the presence of Me2AlCl and PMe3 catalyzed the
C distances show an opposite trend and are shorter than in 3 as intramolecular arylcyanation of exocyclic double bonds.[39]
a result of the increased oxidation state of the four-coordinate Compound 7a may be compared to the carbodiimide adduct
phosphorus atom. The P–C(vinyl) distances are shorter than 8d of FLP 3 that is formed by hydrogen transfer and to a
the P–C(Mes) distances.
protonated carbodiimide [tBuN=C=N(H)–C(Ph)=C(H)tBu]+.[40]
The structure of the R,R/S,S isomer (Figure 3) is similar but Carbodiimides with one hydrogen atom bound to nitrogen
now the C(PO) atom adopts an apical position (distance from were calculated to be stabilized by electropositive substituents
the plane of the remaining ring atoms 53.8 pm; folding angle on the second nitrogen atom.[41,42]
34.2°) and the P–H and C=O groups are on opposite sides of
The 31P NMR resonances of 7 show a characteristic down-
the molecular plane, which prevents the formation of a field shift consistent with a three-coordinate phosphorus atom.
3
hydrogen bond. The formation of the benzil adduct 6 may be The low coordination number is further confirmed by JPH
compared to related results reported in the literature for Al/P- coupling constants of Ͼ43 Hz, which increased compared to
based[5,7b,7c] and other FLPs.[15c,36] 1 and benzil yielded an that of the starting material (31.8 Hz), but are still consistent
addition product containing a seven-membered heterocycle with retention of the trans orientation of phosphorus and
with P–O and Al–O single bonds and an endocyclic C=C hydrogen atoms. The signal for the P–H hydrogen atom disap-
double bond (cis-enediolate). It seems likely that the steric peared and is replaced by a resonances of NH groups at δ =
shielding of the phosphorus atom determines the outcome of 5.75 ppm (7a) and 8.46 ppm (7b), respectively, which feature
the reaction and two bulky groups at phosphorus prevent the 3JPH coupling constants of 6.5 and 10.2 Hz. The resonance of
approach of the keto carbon atom (C–Ph group) and favor the the nitrogen atom of the imine group is shifted downfield com-
formation of a P–O bond and the generation of a seven-mem- pared to that of free nitriles[28] and the C=N groups show a
bered heterocycle.[37] Accordingly, benzophenone and 1 characteristic signal in the 13C NMR spectrum at δ = 179.8
showed a completely different reaction. The corresponding ad- and 207.5 ppm, which corroborates the similarity of 7a and 8d
duct was stable only at low temperatures, did not show a [δ(C=N) = 178.7 ppm]. A downfield shift of the CH(SiMe3)2
P–C interaction and reacted further by elimination of isobut- hydrogen atoms (δ Ͻ –0.74 ppm) relative to 3 indicates again
ene, reduction of benzophenone and formation of diphenyl- the increase of the coordination number of the aluminum atom.
methanolate complexes.[7a]
7b shows only one set of resonances for the Mes (o-Me, m-
The nitriles H8C4N–CϵN and PhCH2–CϵN showed a dif- H), SiMe3 and CH2Ph substituents at room temperature and a
ferent reactivity and reacted with 3 to afford the FLP adducts splitting of these resonances (pyrrolidyl instead of benzyl) was
7a and 7b in good yields (Scheme 3) by hydrophosphination observed for compound 7a. When respective NMR samples
of the CϵN triple bonds with the transfer of the P–H were measured at 220 and 200 K we observed only a small
hydrogen atom to nitrogen. This result is comparable temperature dependent shift in case of compound 7a, while
to a previously reported reaction of 3 with PhCN,[16] the spectra of 7b show evidence of dynamic behavior with a
which in the first step afforded the simple adduct cis- broadening of the resonances on cooling, before individual
Mes(H)P–C[Al{(CH(SiMe3)2}2]=C(H)-tBu·NCPh. Quantum signals [o-Me, m-H(Mes); o-, m-H(Ph), CH2Ph; CHSi,
chemical calculations suggested that the strongly exothermic CH(SiMe3)2] were resolved at 200 K. This may be associated
adduct formation is followed by ring closure with P–C bond with a hindered rotation of the respective groups, which is only
formation and proton transfer. The hydrogen shift may be facil- apparent at low temperature in case of 7b (ΔG϶
=
itated by the solvent or reactive species such as free FLP. In 10.4 kcal·mol–1) but already significant at room temperature in
case of PhCN, rearrangement and hydrophosphination was case of 7a. The splitting is caused by the chiral surrounding of
slow at room temperature (7 d) and required heating to 50 °C the phosphorus atom, and the different behavior of 7a and 7b
for completion within 12 h. In contrast, 7a was formed readily may depend on the different inversion barriers. In case of 7a
after only a few hours at room temperature, and the nitrile the barrier may be influenced by the delocalization of the lone
adduct could not be detected by NMR spectroscopy. pair of electrons of the pyrrolidyl nitrogen atom into the imine
PhCH2–CN behaved similar to PhCN, and the final product group.
was only obtained after 2 d at room temperature. Both interme-
The molecular structures of compounds 7 (Figure 4) feature
diates, the nitrile adduct (31P, δ = –76.7 ppm; 1JPH = 222.3 Hz; five-membered PCAlNC heterocycles in an envelope confor-
three-coordinate P) and the heterocyclic addition product anal- mation with coplanar carbon (2ϫ), aluminum and nitrogen
1
ogous to 6 (31P, δ = –26.3 ppm; JPH = 474.1 Hz; P–H bond atoms (largest deviation from plane for N, 3 pm) and the py-
intact) were identified by NMR spectroscopy. The high reac- ramidal phosphorus atoms 42 and 32 pm above the planes
tivity of H8C4N-CϵN may be attributed to the electron with- [folding angles 20.1° (7a) and 15.9° (7b)]. The adjacent vinyl
drawing effect (-I) of the pyrrolidyl substituent, which should and pyrrolidyl groups (7a) are coplanar, while the CH2Ph
facilitate nucleophilic attack of the phosphorus atom on the group (7b) is perpendicular to the heterocycle to reduce steric
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interactions to the Mes and CH(SiMe3)2 groups. The planar
The formation of compounds 8 was easily recognizable from
arrangement of the CN2 fragment allows delocalization characteristic changes in the NMR spectra similar to those dis-
of π-electron density from the lone pair of electrons at the cussed above for compounds 7. They include the disappear-
pyrrolidyl nitrogen atom into the C=N bond which results in ance of the PH signal and its characteristic large coupling con-
1
almost identical C–N bond lengths [131.7(2) and 133.3(2) pm; stant (1JPH = 221.4 Hz) in the H NMR spectrum and the ap-
Table 1]. The Al–C bond lengths to the CH(SiMe3)2 substitu- pearance of new, slightly broadened, signals for the hydrogen
ents are longer than those in 3 and reflect the larger coordina- atoms of the N-H groups in the same region of the spectrum
tion number. The P–C bond lengths are very similar to those [δ = 5.58 ppm (8a); 5.1 ppm (8d)] or shifted downfield [δ =
of the starting material. The Al–N distances are with 192.2(2) 6.70 ppm (8b); 8.11 ppm (8c)] relative to 3. Further evidence
3
and 196.4(2) pm shorter than usually observed for imine ad- provided the small increase of the JPH coupling constants to
ducts of alkylaluminum compounds.[43]
the vinylic hydrogen atoms (43.6 to 48.3 Hz; three-coordinate
phosphorus), the high field shift of the CH(SiMe3)2 protons (δ
= –0.57 to –0.72 ppm; coordination number four at aluminum)
1
in the H NMR spectra as well as the characteristic signal of
the P–C=X groups in the 13C NMR spectra at δ = 178.7 (C=N),
195.1 ppm (C=O) and δ = 214.8 and 217.4 ppm (C=S). The
characteristic downfield shift of the thiocyanate derivatives rel-
ative to the C=O/N derivatives is well documented.[44]
As in the case of compounds 6 and 7 the overall spectra are
complicated and show dynamic behavior. The 1H NMR spectra
of compounds 8a to 8c at room temperature show only one set
of signals for the CH(SiMe3)2 (1ϫCH, 2ϫSiMe3) and the
Mes (o-Me, m-H) groups. In case of 8a and 8b cooling to
200 K led to hindered rotation and freezing of ring fluctuations
and therefore all groups become magnetically inequivalent
(2ϫCH, 4ϫSiMe3, 2ϫo-Me, 2ϫm-H). The activation en-
ergy of the rotation was determined to be at about 12.2 (Tc ≈
260 K) and 10.5 kcal·mol–1 (Tc ≈ 220 K), respectively. In case
of compound 8c the signals broaden, but do not resolve into
separate signals. Compound 8d behaved differently. At room
temperature all signals were extremely broad in the 31P and 1H
NMR spectra and the signals of the cyclohexyl groups (except
CH) could not be assigned. Two different CH(SiMe3)2 groups
and inequivalent o-Me and m-H groups were observed. When
the temperature was raised to 340 K the signals sharpened and
the individual signals of each of the above groups became
equivalent. When the temperature was dropped to 210 K the
NH resonance at δ = 5.1 ppm splits into two broad signals at
δ = 4.80 and δ = 5.27 ppm that integrated in a ratio of 2.5:1.
Similarly the 31P NMR signal at δ = –21.1 ppm separated into
two peaks at δ = –22.5 and δ = –23.7 ppm, which showed the
same ratio as the NH peaks. The other resonances also sepa-
rated into the expected number of signals consistent with the
presence of two separate species at 210 K, but all signals re-
mained broad indicating that the system was still dynamic.
This observation may be explained by a hindered rotation
about the (N)C–N(H)C bond and the different orientation of
the N–H group, which in the solid state adopts a trans arrange-
ment with respect to the phosphorus atom (see Figure 5). An
equilibrium between the cis and trans forms may occur in solu-
tion. The broad resonances and signal overlap did not allow the
complete assignment of resonances to the minor component.
The molecular structures of compounds 8a to 8c are similar,
and that of 8a is shown as a representative example in Fig-
ure 5. Single crystals of compound 8c were obtained from n-
Figure 4. Molecular structure of compound 7a; compound 7b is sim-
ilar. Displacement ellipsoids are drawn at the 40% level. Hydrogen
atoms (except H1 and H2; arbitrary radii) are omitted for clarity.
In a further series of experiments the functionalized FLP 3
was treated with heterocumulenes RЈ–N=C=X (Scheme 3) at
–30 °C (tBu–N=C=O) or –50 °C (tBu–N=C=S, Ph–N=C=S,
H11C6–N=C=N–C6H11). After usual work-up, compounds 8
were obtained as colorless (8a, 8d) or yellow (8b, 8c) crystals
in good yields of 69 to 90%. The reactions probably proceed
via the typical reaction course of FLPs by coordination of the
heterocumulenes to the Lewis acidic center followed by ring
closure and hydrogen transfer (see above). Investigations into
the properties of 1 and comparable FLP systems have shown
that charge distribution favors the initial coordination of the
most electronegative atoms to the aluminum atom, but steric
shielding is also of great importance.[3,6b] The very bulky
CH(SiMe3)2 groups of 3 are likely to increase the importance
of steric influences and favor the product with least steric
strain. In case of 1 the simple addition products with isocyan-
ates feature five-membered PCAlOC heterocycles with exocy-
clic C=NR double bonds, while 3 reacts with the given reac-
tants by hydrogen transfer from phosphorus to nitrogen and
formation of PCAlXC heterocycles with endocyclic C=X
double bonds. The difference may be attributed to the prefer-
ence of hydrogen atoms to coordinate the more basic C=N–R
fragments (compared to C=O or C=S). Steric repulsion be-
tween the bulky substituents at Al and N may further disfavor pentane or cyclopentane, but the crystallographic data were of
coordination of N–R to aluminum.
poor quality and will not be discussed any further. 8d (Fig-
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Journal of Inorganic and General Chemistry
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clohexyl group is perpendicular to the molecular plane, and
the observed molecular conformation may help to minimize
steric interaction with the bulky CH(SiMe3)2 substituents. Al–
C and P–C distances show the same trends as discussed for
compounds 7. The Al–O/N bonds are with 190.3(2) and
197.6(1) pm slightly shorter than those of 6 or 7 but in the
typical range of bonds to four-coordinate aluminum atoms.
The Al–S bond in 8b is with 237.93(7) pm significantly longer,
but in the expected range.[46] The heterocumulene fragments
X=C–NHR (X = O, S, N) are approximately coplanar to the
molecular plane. The C–N(HR) bond lengths are with 132.2(2)
to 134.4(1) pm between the typical values of single and a
double bond and indicate π-delocalization.
Figure 5. Molecular structure of compound 8a; compound 8b is sim-
ilar. Displacement ellipsoids are drawn at the 40% level. Hydrogen
atoms (except H1 and H2; arbitrary radii) are omitted for clarity.
Conclusions
The P–H functionalized FLP Mes(H)P–C[Al{CH(SiMe3)2}2]=
C(H)–tBu (3) has unique chemical properties, which makes it
a highly interesting starting material for the application in vari-
ous secondary reactions. It has the typical FLP functionality
with coordinatively unsaturated Lewis acidic aluminum and
Lewis basic phosphorus atoms, which allow the coordination
and activation of dipolar substrates. Transfer of the phosphorus
bound hydrogen atom to activated substrates results in the gen-
eration of unusual structural motifs stabilized by coordination
to aluminum. In continuation of previous work, we treated 3
with different dipolar compounds. The P–H bond was not af-
fected upon treatment with NH3. A simple adduct resulted
from Al–N bond formation, and the phosphorus atom remained
three-coordinate without any significant bonding interaction to
the ammonia hydrogen atoms. Benzil reacted by coordination
of one of the C=O groups to the FLP via Al–O and P–C bonds.
The P–H group is not affected and the remaining C=O group
is in an exocyclic position. This situation reflects the normal
coordination mode of carbonyl compounds (benzaldehyde, ke-
tenes, CO2) to FLPs, but diketones usually behave different
and coordinate to the Al/P FLPs via both oxygen atoms to
yield cis-enediolates.
ure 6) represents a rare example of an FLP adduct with a car-
bodiimide ligand.[5,45] The preliminary of 8c structure was
found to compare well with those of 8a and 8b. They feature
five-membered AlC2XP heterocycles in an envelope conforma-
tion with an approximately planar AlC2X fragment [largest de-
viation from plane: 2 pm O (8a); 12 pm S (8b)] and the pyram-
idal phosphorus atom above the plane [distance from plane
57 pm, folding angle 27.4° (8a); 66 pm, 34.5° (8b)]. The dis-
tortion is larger in the sulfur analogue 8b, which may be
caused by the longer bond lengths for sulfur (Table 1). The
respective AlC2PN heterocycle of 8d adopts also an envelope
conformation (Figure 6), but the aluminum rather than the
phosphorus atom deviates most significantly from the plane
formed by the remaining atoms [largest deviation: 7 pm (C and
N); distance of Al from plane 76 pm, folding angle 31.9°].
This difference may depend on steric interactions. 8d is the
only compound that has a substituent attached the endocyclic
heteroatom of the coordinated C=X group. The respective cy-
These results confirm that steric limitations are important in
FLP chemistry. In 3 one mesityl group and one hydrogen atom
are bonded in terminal positions to phosphorus. The resulting
relatively low steric shielding allows the attack of the carbonyl
carbon atom, which adopts a coordination number of four in
the product. Usually two mesityl groups are attached to the
phosphorus atom, and the approach of the carbonyl carbon
atom is hindered. A P–O bond is formed instead with a low
coordination number of two at the respective oxygen atom in
the product. The application of compounds that have a more
basic nitrogen atom is required to observe hydrogen shift to
the coordinated substrates (isocyanate, isothiocyanate, carbodi-
imide). This promising method opens facile access to com-
pounds with interesting structural motifs such as iminophos-
phines or phosphaguanidines. These results verify the applica-
bility of this P–H functionalized FLP in various secondary re-
actions with two important aspects that influence the outcome
of these reactions: The hydrogen transfer capacity from phos-
Figure 6. Molecular structure of compound 8d. Displacement ellip-
soids are drawn at the 40% level. Hydrogen atoms (except H2 and
H222; arbitrary radii) are omitted for clarity.
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3
4
6.76 (dd, JPH = 38.2, JHH = 2.0 Hz, 1 H, PC=CH), 6.69 (s, 2 H, m-
phorus to the activated substrates and the relatively low steric
shielding of the phosphorus atoms.
1
4
H), 5.24 (dd, JPH = 219.8, JHH = 2.0 Hz, 1 H, PH), 2.56 (s, 6 H, o-
Me), 2.05 (s, 3 H, p-H), 1.46 (s, 9 H, CMe3), 1.40 (s br., 1JNH ≈ 65 Hz,
3 H, NH3), 0.31, 0.30, 0.24, 0.19 (s, 9 H, SiMe3), –1.24 (s, JSiH
10.7 Hz, 1 H, CHSi), –1.29 (s, 2JSiH = 10.5 Hz, 1 H, CHSi). 13C NMR
(101 MHz, C6D6, 300 K): δ = 161.7 (d, 2JPC = 9.2 Hz, PC=CH), 144.6
2
=
Experimental Section
General: All procedures were carried out in an atmosphere of purified
argon in dried solvents (n-pentane, n-hexane with LiAlH4; 1,1,1-tri-
fluorotoluene, and 1,2-difluorobenzene with molecular sieves). NMR
spectra (chemical shift data in δ) were recorded in C6D6 at ambient
probe temperature using the following instruments, Bruker Avance I
(1H, 400.13; 31P 161.98; 13C, 100.62; 29Si 79.49, 11B, 128.38; 15N
40.55 MHz), Bruker Avance III (1H, 400.03; 13C, 100.59; 31P,
161.92 MHz), Agilent DD2 600 (1H, 599.51; 31P, 242.68 MHz) and
referenced internally to residual solvent resonances (1H, 13C). 13C
NMR spectra were all proton decoupled. The assignment of NMR
spectra is based on HSQC, HMBC, DEPT135, 29SiDEPT19.5, HN-
HMBC, HSi-HSQC and H,H-ROESY data. Elemental analyses were
determined by the microanalytic laboratory of the Westfälische
Wilhelms Universität Münster. IR spectra were recorded as paraffin
mull between KBr plates on a Shimadzu Prestige 21 spectrometer, UV
spectra with a CARY Bio 100 spectrophotometer, electron impact mass
spectra with a Varian mass spectrometer. Commercial H8C4N–CN,
PhCH2–CN, Ph–NCS, tBu–NCS and tBu–NCO were dried with mo-
lecular sieves, H11C6–N=C=N–C6H11 and Ph–C(O)–C(O)–Ph were
dried in vacuo. FLP 3 was synthesized from HAl[CH(SiMe3)2]2 and
Mes(H)P–CϵC–tBu;[16] an optimized procedure for the synthesis of
the phosphine is given below.
1
2
(d, JPC ≈ 44 Hz, PC=CH), 143.4 (d, JPC = 12.6 Hz, o-C), 138.4 (p-
1
3
C), 134,2 (d, JPC = 19.3 Hz, ipso-C), 129.8 (d, JPC = 2.6 Hz, m-C),
38.2 (d, 3JPC = 4.2 Hz, CMe3), 30.7 (d, 4JPC = 6.1 Hz, CMe3), 24.5 (d,
3JPC = 11.0 Hz, o-Me), 20.9 (p-Me), 5.7 (SiMe3), 5.7 (d, 5JPC = 0.9 Hz,
5
SiMe3), 5.5 (SiMe3), 5.5 (d, JPC = 1.1 Hz, SiMe3), 2.3, 1.8 (s br.,
CHSi). 31P NMR (162 MHz, C6D6, 300 K): δ = –79.2. 29Si NMR
(79 MHz, C6D6, 300 K): δ = –2.2, –2.29, –2.32, –2.4. 15N NMR
(41 MHz, C6D6, 300 K): δ = 21 (NH3). IR (paraffin, KBr): ν˜ = 3326
w, 3283 w, 3178 w ν(NH); 2951 vs, 2918 vs, 2853 vs. (paraffin); 2322
w ν(PH); 1597 w, 1569 w ν(C=C), aryl; 1464 vs, 1377 vs. (paraffin);
1306 w, 1246 s δ(CH3); 1200 w, 1175 vw, 1161 vw, 1112 w, 1090 w,
1051 m, 1134 m ν(CC); 1011 m δ(CHSi2); 922 w, 843 vs, 777 m, 750
m ρ[CH3(Si)]; 723 m (paraffin); 669 w, 644 w, 624 w ν(SiC); 556 w,
523 w, 490 w, 469 m, 450 w δ(CC), ν(AlC), ν(PC) cm–1. MS
(EI, 20 eV, 298 K): m/z (%): 578 (10) [M – NH3]+, 563 (7)
[M – NH3 – Me]+, 419 (50) [M – NH3 – CH(SiMe3)2]+.
NMR Spectroscopic Data of the Protolysis Product
cis-Mes(H)P–C(H)=C(H)–tBu: 1H NMR (400 MHz, C6D6, 300 K): δ
3
3
3
= 6.79 (s, 2 H, m-H), 5.98 (ddd, JPH = 23.5, JHH = 13.0, JHH
3.0 Hz, 1 H, PC=CH), 5.54 (ddd, JPH = 2.0, JHH = 13.0, JHH
4.0 Hz, 1 H, PCH=C), 5.08 (ddd, JPH = 219.1, JHH = 4.0, JHH
=
=
=
2
3
3
1
3
4
3.0 Hz, 1 H, PH), 2.45 (s, 6 H, o-Me), 2.10 (s, 3 H, p-Me), 1.33 (s, 9
H, CMe3). 31P NMR (162 MHz, C6D6, 300 K): δ = –96.8.
Synthesis
of
Mes(H)P–CϵC–tBu:
A
solution
of
Mes(Cl)P–CϵC–tBu[47] (0.50 g, 1.87 mmol) in THF (15 mL) was
cooled to 0 °C and treated with a solution of Li[secBu3BH] in THF
(1.0 m, 1.9 mL; within 5 min). The mixture was warmed to room tem-
perature. All volatiles were removed in vacuo, and the solid residue
was extracted with n-hexane (15 mL). Filtration, concentration of the
filtrate and cooling to –30 °C afforded colorless crystals (0.39 g,
Synthesis of Compound 6: Solid Ph–C(O)–C(O)–Ph (0.085 g,
0.41 mmol) was added to a cooled (–50 °C) solution of compound 3
(0.24 g, 0.41 mmol) in n-pentane (20 mL). The mixture was warmed
to room temperature and stirred overnight. The concentrated solution
was cooled to 0 °C to yield colorless crystals of 6 (0.29 g, 90%). M.p.
160 °C (dec.). C43H70AlO2PSi4 (789.33): C 65.4 (calcd. 65.4); H 8.8
1.67 mmol, 89%). Characterization: See reference[16]
.
1
(8.9)%. H NMR (400 MHz, C6D6, 300 K): δ = 8.79 [m br, 1 H, o-
Formation of trans-Mes(H)P–C[Al{(CH(SiMe3)2}2]=C(H)tBu (3a):
In an NMR experiment solution of cis-Mes(H)P–
C[Al{(CH(SiMe3)2}2]=C(H)tBu (3) in C6D6 was irradiated at room
temperature over a period of 3 h with a broadband UV source to yield
the thermodynamically favored trans-Mes(H)P–C[Al{(CH(SiMe3)2}2]=
C(H)tBu (3a). H NMR (400 MHz, C6D6, 300 K): δ = 6.86 (s, 2 H,
m-H), 5.83 (dd, JPH = 23.3, JHH = 2.8 Hz, 1 H, PC=CH), 5.22 (dd,
1JPH = 226.0, JHH = 2.8 Hz, 1 H, PH), 2.53 (s, 6 H, o-Me), 2.10 (s,
3 H, p-Me), 0.98 (s, 9 H, tBu), 0.38, 0.35 (s, 18 H, SiMe3), –0.47 (s,
2 H, CHSi). 13C NMR (101 MHz, C6D6, 300 K): δ = 156.8 (PC=CH),
144.1 (d, 2JPC = 12.6 Hz, o-C), 138.9 (p-C), 135.4 (PC=CH), 129.3 (d,
3JPC = 3.3 Hz, m-C), 128.0 (ipso-C), 37.0 (d, JPC = 8.1 Hz, CMe3),
29.6 (CMe3), 23.2 (d, JPC = 10.7 Hz, o-Me), 21.1 (p-Me), 10.0
(CHSi), 4.92, 4.88 (SiMe3). 31P NMR (162 MHz, C6D6, 300 K): δ =
–69.7. 29Si NMR (79 MHz, C6D6, 300 K): δ = –2.55, –2.56.
1
4
H(PCPh)], 8.33 (dd, JPH = 465.6, JHH = 2.6 Hz, 1 H, PH), 8.31 [dd,
a
3JHH = 8.0, JHH = 1.8 Hz, 2 H, o-H(OCPh)], 7.56 (dd, JPH = 72.1,
4JHH = 2.6 Hz, 1 H, PC=CH), 7.35 [m br., 1 H, m-H(PCPh)], 6.96 [m,
2 H, m-H(OCPh)], 6.94 [m, 1 H, p-H(OCPh)], 6.83 [pseudo-triplet,
3JHH ≈ 7.5 Hz, 1 H, p-H(PCPh)], 6.59 [d, JPH = 3.8 Hz, 1 H, m-
4
3
4
1
3
4
H(Mes)], 6.38 [m br., 1 H, o-H(PCPh)], 6.33 [m br., 1 H m-H(PCPh)],
6.13 [s br., 1 H, m-H(Mes)], 2.87 (s, 3 H, o-Me), 1.82 (s, 3 H, p-Me),
1.52 (s, 3 H, o-Me), 0.88 (s, 9 H, CMe3), 0.61 (s, 2JSiH = 6.4 Hz, 9 H,
4
2
2
SiMe3), 0.60 (s, JSiH = 6.4 Hz, 9 H, SiMe3), 0.4 (s, JSiH = 6.1 Hz, 9
2
2
H, SiMe3), 0.16 (s, JSiH = 6.1 Hz, 9 H, SiMe3), –0.43 (s, JSiH
11.2 Hz, 1 H, CHSi), –0.85 (s, 2JSiH = 10.4 Hz, 1 H, CHSi). 13C NMR
(101 MHz, C6D6, 300 K): δ = 200.3 (d, JPC = 4.7 Hz, C=O), 172.5
(d, JPC = 10.1 Hz, PC=CH), 144.9 [d, JPC = 10.5, o-C(Mes)], 143.3
[d, JPC = 3.2 Hz, p-C(Mes)], 142.4 [d, JPC = 6.2 Hz, o-C(Mes)],
139.7 [d, 2JPC = 3.0 Hz, ipso-C(PCPh)], 134.6 [d, 3JPC = 4.4 Hz, ipso-
=
3
2
3
2
2
4
2
3
Synthesis of Mes(H)P–C[Al{(CH(SiMe3)2}2]=C(H)tBu·NH3 (5): A C(OCPh)], 133.5 [p-C(OCPh)], 132.1 [o-C(OCPh)], 131.0 [d, JPC
solution of 3 (0.22 g, 0.38 mmol) in n-hexane (20 mL) was frozen in 9.3 Hz, m-C(Mes)], 129.7 [d, JPC = 11.1 Hz, m-C(Mes)], 128.8 [s
=
3
liquid nitrogen. The reaction flask was evacuated and filled with
NH3(g). The mixture was stirred for 1 h at –78 °C. A white solid
precipitated which dissolved when the mixture was slowly warmed to
br., m-C(PCPh)], 128.3 [p-C(PCPh)], 128.3 [m-C(OCPh)], 127.2 [o-
C(PCPh)], 127.1 [m-C(PCPh)], 126.9 [o-C(PCPh)], 126.5 (s br.,
1
1
PC=CH), 120.1 [d, JPC = 55.7 Hz, ipso-C(Mes)], 98.5 (d, JPC
=
room temperature. All volatiles were removed in vacuo and the residue 66.6 Hz, PCO), 38.5 (d, 3JPC = 12.0 Hz, CMe3), 29.2 (d, 4JPC = 1.1 Hz,
3
3
was dissolved in n-pentane. Concentrating this solution and storing it CMe3), 25.3 (d, JPC = 6.1 Hz, o-Me), 22.3 (d, JPC = 6.2 Hz, o-Me),
5
at –30 °C yielded colorless crystals of compound 5 (0.18 g, 79%).
20.9 (d, JPC = 1.1 Hz, p-Me), 5.9, 5.72, 5.67, 4.9 (SiMe3), 4.8, 4.5 (s
M.p. 158 °C (dec.). C29H63AlNPSi4 (596.13): C 58.0 (calcd. 58.4); H br., CHSi). 31P NMR (162 MHz, C6D6, 300 K): δ = –17.9. 31P NMR
10.6 (10.7); N 2.2 (2.4)%. 1H NMR (400 MHz, C6D6, 300 K): δ =
(243 MHz, C7D8, 178 K): δ = –14.2, –13.7. 29Si NMR (79 MHz, C6D6,
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Journal of Inorganic and General Chemistry
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3
300 K): δ = –1.8, –2.0, –2.1, –2.8. IR (paraffin, KBr): ν˜ = 1668 m, [pseudo-t overlap, JHH ≈ 7 Hz, 2 H, o-H(Ph)], 7.00 [m overlap, 1 H,
1595 w, 1560 m ν(C=O), ν(C=C), aryl; 1462 vs, 1377 vs. (paraffin); p-H(Ph)], 6.76 [m overlap, 2 H, m-H(Mes)], 6.74 [m overlap, 2 H(o-
3
1304 vw, 1242 m δ(CH3); 1200 vw, 1180 vw, 1156 vw, 1107 w, 1082 H(Ph)], 3.20 (d, JPH = 6.2 Hz, 2 H, CH2), 2.56 (s, 6 H, o-Me), 2.06
w, 1067 w, 1036 m ν(CC), ν(CO); 1011 m δ(CHSi2); 930 w, 843 vs,
789 w, 748 w, 733 w ρ[CH3(Si)]; 722 m (paraffin); 671 w, 615 w
ν(SiC); 573 vw, 550 vw, 521 vw, 463 w δ(CC), ν(AlC), ν(AlO), ν(PC)
cm–1. MS (EI, 20 eV, 413 K): m/z (%): 629 (8) [M – CH(SiMe3)2]+,
578 (3) [M – PhC(O)C(O)Ph]+, 563 (8) [M – PhC(O)C(O)Ph – Me]+.
(s, 3 H, p-H), 1.01 (s, 9 H, CMe3), 0.38 (s, 18 H, SiMe3), 0.25 (s, 18
2
H, SiMe3), –0.88 (s, JSiH = 10.3 Hz, 2 H, CHSi). 13C NMR
1
(101 MHz, C6D6, 300 K): δ = 207.5 (d, JPC = 14.2 Hz, C=N), 158.5
(d, 2JPC = 5.1 Hz, PC=CH), 144.8 [d, 2JPC = 15.0 Hz, o-C(Mes)], 141.1
4
[d, JPC = 1.5 Hz, p-C(Mes)], 140.6 (s very br., PC=CH), 132.4 [d,
1
3JPC = 4.9 Hz, ipso-C(Ph)], 130.7 [d, JPC = 17.6 Hz, ipso-C(Mes)],
Synthesis of Compound 7a: H8C4N–CϵN (0.056 mL, 0.56 mmol) 130.4 [o-C(Ph)], 130.0 [d, 3JPC = 5.1 Hz, m-C(Mes)], 129.6 [m-C(Ph)],
was added with a syringe to a cooled (–70 °C) solution of compound
3 (0.32 g, 0.55 mmol) in n-pentane (20 mL). The mixture was warmed CMe3), 29.2 (d, 4JPC = 2.9 Hz, CMe3), 24.5 (d, 3JPC = 13.6 Hz, o-Me),
128.0 [p-C(Ph)], 44.0 (d, 2JPC = 19.3 Hz, CH2), 36.9 (d, 3JPC = 5.4 Hz,
5
to room temperature and stirred overnight. Storing the concentrated
21.1 (p-Me), 5.4 (d, JPC = 1.8 Hz, SiMe3), 5.2 (SiMe3), 3.9 (s br.,
solution at –30 °C afforded a colorless precipitate of 7a (0.32 g, 85%).
CHSi). 31P NMR (162 MHz, C6D6, 300 K): δ = –3.7. 29Si NMR
The product was recrystallized from 1,2-difluorobenzene; the obtained (79 MHz, C6D6, 300 K): δ = –2.07, –2.11. 15N NMR (41 MHz, C6D6,
1
crystals were used for X-ray crystal structure determination, melting 300 K): δ = 235. Low temperature NMR: H NMR (400 MHz, C7D8,
point determination and microanalysis. M.p. 60 °C (dec.). 220 K): δ = 8.38 (d, JPH = 10.2 Hz, 1 H, NH), 7.00–6.97 [t overlap-
3
C34H68AlN2PSi4·(C6H4F2) (789.33): C 60.7 (calcd. 60.9); H 9.0 (9.2),
ping, 1 H, p-H(Ph)], 6.96 [pseudo-t overlap, 2 H, m-H(Ph)], 6.91 (d
overlap, JPH = 46.0 Hz, 1 H, PC=CH), 6.71 [s br., 1 H, m-H(Mes)],
1
3
3
N 3.6 (3.6)%. H NMR (400 MHz, C6D6, 300 K): δ = 6.91 (d, JPH
=
4
43.8 Hz, 1 H, PC=CH), 6.75 (d, JPH = 5.2 Hz, 1 H, m-H), 6.65 (s, 1 6.57 [d overlap, 1 H, m-H(Mes)], 6.57 [d overlap, 1 H, o-H(Ph)], 3.22,
H, m-H), 5.75 (d, 3JPH = 6.5 Hz, 1 H, NH), 3.16 (m, 1 H, NCH2), 2.83 2.82 (m, 1 H, CH2), 2.79, 2.38 (s, 3 H, o-Me), 2.07 (s, 3 H, p-Me),
(m, 2 H, NCH2), 2.77 (s, 3 H, o-Me), 2.47 (s, 3 H, o-Me), 2.10 (m, 1 1.05 (s, 9 H, CMe3), 0.55, 0.45, 0.37, 0.27 (s, 9 H, SiMe3), –0.87,
H, NCH2), 2.01 (s, 3 H, p-Me), 1.01 (s, 9 H, CMe3), 1.00, (m, 1 H, –0.75 (s, 1 H, CHSi). 31P NMR (162 MHz, C7D8, 220 K): δ = –4.9.
NCH2CH2), 0.86 (m, 2 H, NCH2CH2), 0.72 (m, 1 H, NCH2CH2), 0.50 IR (paraffin, KBr): ν˜ = 3310 vw, 3271 m ν(NH); 2963 vs, 2918 vs,
(s, 18 H, SiMe3), 0.48, 0.43 (s, 9 H, SiMe3), –0.74, –0.79 (s, 1 H, 2901 vs, 2859 vs. (paraffin); 1653 w, 1601 m, 1551 s ν(C=N), ν(C=C),
1
CHSi). 13C NMR (101 MHz, C6D6, 300 K): δ = 179.8 (d, JPC
=
=
aryl; 1458 vs, 1373 vs. (paraffin); 1281 m, 1244 vs. δ(CH3); 1200 w,
1074 w, 1020 s ν(CC); 1009 s δ(CHSi2); 928 s, 910 s, 841 vs, 799 s,
2
2
13.2 Hz, CN2), 158.2 (d, JPC = 8.1 Hz, PC=CH), 145.2 (d, JPC
2
1
2.3 Hz, o-C), 145.0 (d, JPC = 27.5 Hz, o-C), 142.8 (s, very br., JPC 777 vs, 748 s ρ[CH3(Si)]; 727 s (paraffin); 698 s, 644 m, 613 w ν(SiC);
4
1
≈ 40 Hz, PC=CH), 140.4 (d, JPC = 1.6 Hz, p-C), 131.2 (d, JPC
=
573 vw, 548 w, 521 s, 480 m 455 w, 424 w δ(CC), ν(AlC), ν(AlN),
22.3 Hz, ipso-C), 130.0 (m-C), 129.8 (d, 3JPC = 8.0 Hz, m-C), 48.8 (d, ν(PC) cm–1. MS (EI, 20 eV, 313 K): m/z (%): 680 (2) [M – Me]+, 536
3JPC = 9.4 Hz, NCH2), 47.4 (NCH2), 36.3 (d, JPC = 4.2 Hz, CMe3), (100) [M – CH(SiMe3)2]+.
3
4
29.4 (d, JPC = 3.0 Hz, CMe3), 25.4, (NCH2CH2), 25.0 (o-Me), 23.6
(NCH2CH2), 23.4 (d, 3JPC = 27.3 Hz, o-Me), 21.0 (p-Me), 6.0, 5.7, 5.7
Synthesis of Compound 8a: tBu–NCO (0.052 mL, 0.45 mmol) was
added at –30 °C to a solution of compound 3 (0.26 g, 0.45 mmol) in
n-pentane (10 mL). The mixture was warmed to room temperature and
stirred overnight. The solvent was removed in vacuo, and the residue
(SiMe3), 5.5 (d, JPC = 3.6 Hz, SiMe3), 4.1, 3.7 (s br., CHSi). 31P
5
NMR (162 MHz, C6D6, 300 K): δ = –21.0. 29Si NMR (79 MHz, C6D6,
300 K): δ = –2.10, –2.05, –1.96, –1.93. 15N NMR (41 MHz, C6D6,
1
300 K): δ = 155 (NH). Low temperature NMR: H NMR (400 MHz, recrystallized from 1,1,1-trifluorotoluene at –30 °C to yield colorless
3
C7D8, 220 K): δ = 6.99 (d, JPH = 43.6 Hz, 1 H, PC=CH), 6.68 (d, crystals of compound 8a (0.21 g, 69%). M.p. 145 °C (dec.).
4JPH = 4.3 Hz, 1 H, m-H), 6.53 (s, 1 H, m-H), 5.70 (d, JPH = 6.0 Hz,
C34H69AlNOPSi4 (678.22): C 59.8 (calcd. 60.2); H 10.1 (10.3), N 1.9
3
3
1 H, NH), 3.13 (m, 1 H, NCH2), 2.81 (s, 3 H, o-Me), 2.78, 2.68 (m,
1 H, NCH2), 2.54 (s, 3 H, o-Me), 2.00 (m, 1 H, NCH2), 2.02 (s, 3 H, 45.7 Hz, 1 H, PC=CH), 6.69 (d, JPH = 2.1 Hz, 2 H, m-H), 5.58 (s, 1
(2.1)%. 1H NMR (400 MHz, C6D6, 300 K): δ = 6.81 (d, JPH
=
4
p-Me), 1.05 (s, 9 H, CMe3), 1.09, (m overlap, 1 H, NCH2CH2), 0.83
H, NH), 2.53 (s, 6 H, o-Me), 1.97 (s, 3 H, p-Me), 0.99 (s, 9 H, CCMe3),
2
(m, 2 H, NCH2CH2), 0.63–0.43 (m overlap, 1 H, NCH2CH2), 0.58, 0.92 (s, 9 H, NCMe3), 0.53, 0.48 (s, JSiH = 6.0 Hz, 18 H, SiMe3),
0.58, 0.57, 0.51 (s, 9 H, SiMe3), –0.70, –0.70 (s, 1 H, CHSi). 31P
–0.72 (s, 2 H, CHSi2). 13C NMR (101 MHz, C6D6, 300 K): δ = 195.1
NMR (162 MHz, C7D8, 220 K): δ = –22.1. IR (paraffin, KBr): ν˜ = (d, 1JPC = 12.3 Hz, NCO), 156.3 (d, 2JPC = 5.9 Hz, PC=CH), 141.6 (d,
1
3450 vw, 3372 vw ν(NH); 2953 vs, 2926 vs, 2853 vs. (paraffin); 1629
w, 1603 w, 1528 s, 1508 m ν(C=N), ν(C=C), aryl; 1458 vs, 1377 s
(paraffin); 1294 w, 1269 w, 1244 m δ(CH3); 1198 w, 1153 vw, 1099 5.2 Hz, CMe3), 29.3 (d, JPC = 3.4 Hz, CMe3), 28.7 (d, JPC = 0.7 Hz,
4JPC = 1.8 Hz, p-C), 139.5 (PC=CH), 132.1 (d, JPC = 29.3 Hz, ipso-
3
3
C), 130.0 (d, JPC = 1.8 Hz, m-C), 54.7 (NCMe3), 36.9 (d, JPC
=
4
4
w, 1080 w ν(CC), ν(CN); 1020 m δ(CHSi2); 928 w, 916 w, 840 vs,
797 w, 777 w, 750 m ρ[CH3(Si)]; 718 w (paraffin); 667 w, 613 vw
ν(SiC); 521 w, 463 w δ(CC), ν(AlC), ν(AlN), ν(PC). cm–1. MS
NCMe3), 24.3 (s br., o-Me), 21.0 (p-Me), 5.6 (d, 5JPC = 0.8 Hz, SiMe3),
5
5.4 (d, JPC = 1.2 Hz, SiMe3), 4.3 (s br., CHSi2); the resonance of o-
C Mes was not found. 31P NMR (162 MHz, C6D6, 300 K): δ = –15.7.
(EI, 20 eV, 323 K): m/z (%): 659 (1) [M – Me]+, 515 (100) 29Si NMR (79 MHz, C6D6, 300 K): δ = –1.8, –2.2. Low temperature
[M – CH(SiMe3)2]+.
NMR: 1H NMR (400 MHz, C7D8, 220 K): δ = 6.89 (d, 3JPH = 45.5 Hz,
4
1 H, PC=CH), 6.58, (d, JPH = 5.2 Hz, 1 H, m-H), 6.52 (s, 1 H, m-H),
Synthesis of Compound 7b: PhCH2–CN (0.068 mL, 0.59 mmol) was
5.58 (s, 1 H, NH), 2.70, 2.37 (s, 3 H, o-Me), 1.96 (s, 3 H, p-Me), 1.03
added at –78 °C to a solution of compound 3 (0.35 g, 0.60 mmol) in (s, 9 H, CCMe3), 0.82 (s, 9 H, NCMe3), 0.61, 0.61, 0.56, 0.54 (s, 9 H,
n-pentane (20 mL). The mixture was warmed to room temperature and
SiMe3), –0.99, –0.53 (s, 1 H, CHSi2). 31P NMR (162 MHz, C7D8,
stirred for 2 d. The solvent was removed in vacuo, and the solid residue 220 K): δ = –18.1. IR (paraffin, KBr): ν˜ = 3370 vw ν(NH); 2951 vs,
was recrystallized from a concentrated solution in n-pentane at –30 °C 2922 vs, 2853 vs. (paraffin); 1688 vw, 1655 vw, 1547 m, 1518 m,
yielding colorless crystals of compound 7b (0.31 g, 74%). M.p. 145 °C 1510 sh ν(CO), ν(C=C), aryl; 1460 vs, 1377 vs. (paraffin); 1273 w,
(dec.). C37H67AlNPSi4 (696.25): C 63.8 (calcd. 63.8); H 9.7 (9.7), N
1244 s δ(CH3); 1209 w, 1155 vw, 1082 vw, 1026 w ν(CC), ν(CN);
1007 w δ(CHSi2); 934 w, 922 w, 841 vs, 777 w, 748 w ρ[CH3(Si)];
723 w (paraffin); 673 w, 610 vw ν(SiC); 519 w, 506 w, 479 w, 463 w
1
3
2.3 (2.0)%. H NMR (400 MHz, C6D6, 300 K): δ = 8.46 (d, JPH
=
3
10.2 Hz, 1 H, NH), 6.82 (d, JPH = 46.4 Hz, 1 H, PC=CH), 7.04
Z. Anorg. Allg. Chem. 2017, 1978–1990
www.zaac.wiley-vch.de 1986
© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Journal of Inorganic and General Chemistry
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
δ(CC), ν(AlC), ν(PC), ν(AlO) cm–1. MS (EI, 20 eV, 323 K): m/z (%):
(s, 9 H, CMe3), 0.58 (s, 18 H, SiMe3), 0.51 (s, 18 H, SiMe3), –0.57
662 (1) [M – Me]+, 518 (100) [M – CH(SiMe3)2]+.
(s, 2 H, CHSi2). 31P NMR (162 MHz, C6D6, 220 K): δ = 17.7 ppm.
IR (paraffin, KBr): ν˜ = 3304 m, 3289 sh ν(NH); 2953 vs, 2922 vs,
2853 vs. (paraffin); 1601 w, 1593 w, 1505 m ν(C=C), aryl; 1454 vs,
1377 vs. (paraffin); 1348 sh, 1312 w, 1292 w, 1242 s δ(CH3); 1198 w,
1028 m ν(CC), ν(CN); 1003 m δ(CHSi2); 924 w, 839 vs, 775 m, 745
m ρ[CH3(Si)]; 725 m (paraffin); 696 m, 667 s, 627 w ν(SiC); 609 w,
548 w, 505 w, 461 w δ(CC), ν(AlC), ν(PC) cm–1. MS (EI, 20 eV,
353 K): m/z (%): 698 (2) [M – Me]+, 554 (100) [M – CH(SiMe3)2]+.
UV/Vis: λmax (n-pentane, 5 °C): 381 nm.
Synthesis of Compound 8b: tBu-NCS (0.067 mL, 0.53 mmol) was
added at –50 °C to a solution of compound 3 (0.31 g, 0.53 mmol) in
n-pentane (20 mL). The mixture was warmed to room temperature and
stirred overnight. Storing the concentrated solution at 0 °C yielded yel-
low crystals of compound 8b (0.33 g, 90%). M.p. 120 °C (dec.).
C34H69AlNPSSi4 (694.29): C 58.4 (calcd. 58.8); H 9.8 (10.0), N 1.8
3
(2.0)%. 1H NMR (400 MHz, C6D6, 300 K): δ = 6.80 (d, JPH
=
4
46.0 Hz, 1 H, PC=CH), δ = 6.70 (s overlap, 1 H, NH), 6.68 (d, JPH
= 2.0 Hz, 2 H, m-H), 2.47 (s, 6 H, o-Me), 1.97 (s, 3 H, p-Me), 0.98
Synthesis of Compound 8d: Dry H11C6–N=C=N–C6H11 (0.11 g,
2
(s, 9 H, CCMe3), 0.96 (s, 9 H, NCMe3), 0.52, 0.50 (s, JSiH = 6.3 Hz, 0.53 mmol) was added to a cooled (–50 °C) solution of compound 3
2
18 H, SiMe3), –0.57 (s, JSiH = 10.4 Hz, 2 H, CHSi2). 13C NMR
(0.32 g, 0.55 mmol) in n-pentane (30 mL). The solution was warmed
1
(101 MHz, C6D6, 300 K): δ = 214.8 (d, JPC = 30.8 Hz, NCS), 155.8 to room temperature and stirred overnight. The concentrated solution
2
2
(d, JPC = 3.7 Hz, PC=CH), 145.1 (d, JPC = 15.1 Hz, o-C), 142.0 (d, was stored at 0 °C to yield colorless crystals of compound 8d (0.32 g,
4JPC = 1.7 Hz, p-C), 141.9 (d br., JPC = 51.0, PC=CH), 133.3 (d, 1JPC 74%). M.p. 225 °C (dec.). C42H82AlN2PSi4 (785.43): C 64.2 (calcd.
1
= 29.5 Hz, ipso-C), 130.1 (d, 3JPC = 4.5 Hz, m-C), 57.9 (NCMe3), 37.2 64.2); H 10.3 (10.5), N 3.4 (3.6)%. 1H NMR (400 MHz, C6D6,
(d, 3JPC = 5.0 Hz, CMe3), 29.6 (d, JPC = 2.4 Hz, CMe3), 27.4 (d, 4JPC
300 K): δ = 6.76 (d, JPH = 43.6 Hz, 1 H, PC=CH), 6.68 (d, JPH =
4
3
4
3
= 2.1 Hz, NCMe3), 23.9 (d, JPC = 13.9 Hz, o-Me), 21.1 (p-Me), 5.7 4.7 Hz, 1 H, m-H), 6.65 (s br., 1 H, m-H), 5.1 (s br., 1 H, NH), 3.35
5
(d, JPC = 2.4 Hz, SiMe3), 5.5 (SiMe3), 4.8 (s br., CHSi2). 31P NMR (s very br., 1 H, NCH), 3.34 (m, 1 H, NHCH), 2.78 (s, 3 H, o-Me),
(162 MHz, C6D6, 300 K): δ = 18.2 ppm. 29Si NMR(79 MHz, C6D6,
2.42 (s, 3 H, o-Me), 1.99 (s, 3 H, p-Me), 1.00 (s, 9 H, CMe3), 0.52 (s
300 K): δ = –1.8, –2.0. 15N NMR (41 MHz, C6D6, 300 K): δ = 178
br., 36 H, SiMe3), –0.59 (s, 1 H, CHSi2), –0.67 (s, JSiH = 10.4 Hz, 1
2
1
(NH). Low temperature NMR: H NMR (400 MHz, C7D8, 200 K): δ H, CHSi). The remaining H atoms of the C6H11 groups could not be
= 6.88 (d, 3JPH = 45.1 Hz, 1 H, PC=CH), 6.72 (s, 1 H, NH), 6.54, 6.52
assigned (very broad lines between δ = 2.2–0.3). 13C NMR (101 MHz,
(s br. overlap, 1 H, m-H), 2.69, 2.30 (s, 3 H, o-Me), 1.93 (s, 3 H, p- C6D6, 300 K): δ = 178.7 (s br., CN2), 155.5 (s br., PC=CH), 145.2 (o-
2
4
Me), 1.04 (s, 9 H, NCMe3), 0.85 (s, 9 H, CCMe3), 0.64, (s br, 27 H,
C), 144.4 (d, JPC = 35.5 Hz, o-C), 140.7 (PC=CH), 140.3 (d, JPC
=
=
SiMe3), 0.60 (s br, 9 H, SiMe3), –0.54, –0.46 (s, 1 H, CHSi2). 31P 1.5 Hz, p-C), 133.7 (d, JPC = 25.5 Hz, ipso-C), 129.9 (d, JPC
1
3
NMR (162 MHz, C7D8, 200 K): δ = 16.7 ppm. IR (paraffin, KBr): ν˜ 7.6 Hz, m-C), 129.6 (m-C), 58.2 (NCH), 54.4 (HNCH), 36.2 (CMe3),
= 3304 vw ν(NH); 2953 vs, 2922 vs, 2853 vs. (paraffin); 1601 vw, 35.5, 33.5, 30.8 (CH2), 29.7 (CMe3), 26.0, 25.5 (CH2), 25.1 (o-Me),
3
1512 w ν(C=C), aryl; 1460 vs, 1377 vs. (paraffin); 1302 w, 1242 m 25.0 (CH2), 23.6 (d, JPC = 28.2 Hz, o-Me), 21.0 (p-Me), 6.9, 6.3 (s
δ(CH3); 1198 w, 1080 m, 1045 s ν(CC), ν(CN); 1006 s δ(CHSi2); 920
w, 841 vs, 777 m, 745 m ρ[CH3(Si)]; 721 m (paraffin); 669 w, 627 w
ν(SiC); 521 m, 463 s δ(CC), ν(AlC), ν(PC), ν(AlS) cm–1. MS
br., SiMe3), 3.4 (CHSi2). 31P NMR (162 MHz, C6D6, 300 K): δ =
–21.1 (s br.). 29Si NMR (79 MHz, C6D6, 300 K): δ ≈ –2. Low tempera-
ture NMR; major isomer: 1H NMR (400 MHz, C7D8, 210 K): δ = 6.79
3
4
(EI, 20 eV, 353 K): m/z (%): 678 (2) [M – Me]+, 534 (100) (d, JPH = 43.9 Hz, 1 H, PC=CH), 6.53 (d, JPH = 4 Hz, 1 H, m-H),
[M – CH(SiMe3)2]+.
6.50 (s br., 1 H, m-H), 5.27 (s br., 1 H, NH), 2.75 (s, 3 H, o-Me), 2.43
(s, 3 H, o-Me), 1.99 (s, 3 H, p-Me), 1.05 (s, 9 H, CMe3), 0.63, 0.61,
0.55, 0.44 (s br., 9 H, SiMe3), –0.53, –0.66 (s, 1 H, CHSi2). 31P NMR
(162 MHz, C7D8, 210 K): δ = –22.5. Minor isomer: 1H NMR
Synthesis of Compound 8c: Ph–NCS (0.042 mL, 0.35 mmol) was
added at –50 °C to a solution of compound 3 (0.21 g, 0.36 mmol) in
n-pentane (30 mL). The mixture was warmed to room temperature and
stirred overnight. Storing the concentrated solution at 0 °C yielded yel-
low crystals of compound 8c (0.23 g, 89%). M.p. 196 °C (dec.).
C36H65AlNPSSi4 (714.29): C 60.3 (calcd. 60.5); H 9.1 (9.2), N 1.8
(2.0)%. 1H NMR (400 MHz, C6D6, 300 K): δ = 8.11 (s, 1 H, NH),
3
(400 MHz, C7D8, 210 K): δ = 6.79 (d, JPH = 43.9 Hz, 1 H, PC=CH),
4
6.53 (d, JPH = 4.0 Hz, 1 H, m-H), 6.50 (s br., 1 H, m-H), 4.80 (s br.,
1 H, NH), 2.77 (s, 3 H, o-Me), 2.39 (s, 3 H, o-Me), 1.99 (s, 3 H, p-
Me), 1.05 (s, 9 H, CMe3), 0.69, 0.60, 0.54, 0.50 (s, 9 H, SiMe3), –0.58,
–0.60 (s, 1 H, CHSi2). 31P NMR (162 MHz, C7D8, 210 K): δ = –23.7.
IR (paraffin, KBr): ν˜ = 3426 w ν(NH); 2969 vs, 2943 vs, 2878 vs,
2839 vs, 2725 m (paraffin); 1576 s, 1560 s, 1524 w ν(CN), ν(C=C),
aryl; 1466 vs, 1449 vs, 1402 m, 1377 vs. (paraffin); 1341 sh, 1323 m,
1302 m, 1240 m δ(CH3); 1196 m, 1163 m 1142 m, 1115 m, 1088 m,
1055 m, 1044 m ν(CC), ν(CN); 1005 w δ(CHSi2); 988 w, 928 m, 891
w, 841 m, 816 m, 766 w ρ[CH3(Si)]; 721 s (paraffin); 664 w ν(SiC);
600 w, 561 w, 550 w, 525 w, 513 w, 475 m, 457 m, 436 m, 430 m
δ(CC), ν(AlC), ν(PC), ν(AlN) cm–1. MS (EI, 20 eV, 383 K): m/z (%):
770 (2) [M – Me]+, 625 (100) [M – CH(SiMe3)2]+.
3
6.93 (s, 2 H, o-H), 6.86 (d, JPH = 48.3 Hz, 1 H, PC=CH), 6.79 (m, 2
4
H, m-H), 6.72 (m, 1 H, p-H), 6.71 [d, JPH = 1.8 Hz, 2 H, m-H(Mes)],
2.53 (s, 6 H, o-Me), 1.98 (s, 3 H, p-Me), 0.99 (s, 9 H, CMe3), 0.53 (s,
2
2JSiH = 6.0 Hz, 18 H, SiMe3), 0.45 (s, 18 H, SiMe3), –0.58 (s, JSiH
=
10.6 Hz, 2 H, CHSi2). 13C NMR (101 MHz, C6D6, 300 K): δ = 217.4
(d, 1JPC = 26.4 Hz, NCS), 156.5 (d, JPC = 3.2 Hz, PC=CH), 145.5 [d,
2
1
2JPC = 15.2 Hz, o-C(Mes)], 142.4 [p-C(Mes)], 141.5 (d br., JPC
=
1
45.4 Hz, PC=CH), 138.2 [ipso-C(Ph), 132.4 [d, JPC = 27.8 Hz, ipso-
C(Mes)], 130.3 [d, JPC = 5.0 Hz, m-C(Mes)], 129.5 [m-C(Ph)], 128.0
[p-C(Ph)], 124.2 [d, JPC = 2.5 Hz, o-C(Ph)], 37.2 (d, JPC = 5.5 Hz,
CMe3), 29.6 (d, 4JPC = 1.9 Hz, CMe3), 24.0 (d, 3JPC = 13.5 Hz, o-Me), X-ray Crystallography: Crystals suitable for X-ray crystallography
21.1 (p-Me), 5.7 (d, JPC = 2.8 Hz, SiMe3), 5.5 (SiMe3), 4.8 (s br.,
CHSi2). 31P NMR (162 MHz, C6D6, 300 K): δ = 19.3 ppm. 29Si NMR
(79 MHz, C6D6, 300 K): δ = –1.6, –1.8. 15N NMR (41 MHz, C6D6,
3
4
3
5
were obtained by recrystallization from n-pentane (5, 6, 7b, 8b, 8d),
1,1,1-trifluorotoluene (8a), or 1,2-difluorobenzene (7a). Intensity data
was collected with a Bruker Venture diffractometer with multilayer
optics and Mo-Kα radiation. Data reduction was carried out using the
1
300 K): δ = 206. Low temperature NMR: H NMR (400 MHz, C7D8,
220 K): δ = 8.06 (s, 1 H, NH), 6.89 (d, JPH = 48.0 Hz, 1 H, PC=CH), program SAINT+.[48] The crystal structures were solved by direct
3
6.74 (m, 2 H, o-Ph), 6.65 (m, 2 H, m-Ph), 6.64 (m, 1 H, p-Ph), 6.59
(s, br., 2 H, m-Mes), 2.54 (s, br., 6 H, o-Me), 1.98 (s, 3 H, p-Me), 1.02 isotropically followed by anisotropic refinement by full-matrix least-
methods using SHELXTL.[49] Non-hydrogen atoms were first refined
Z. Anorg. Allg. Chem. 2017, 1978–1990
www.zaac.wiley-vch.de 1987
© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Journal of Inorganic and General Chemistry
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
Table 2. Crystal data and structure refinement for compounds 5–7.
5
6
6
7a·DFB
7b
Empirical formula
Crystal system
Space group
Z
C29H63AlNPSi4
triclinic
P1
C43H70AlO2PSi4
orthorhombic
P212121
C43H70AlO2PSi4
triclinic
P1
C40H72AlF2N2PSi4
monoclinic
P21/c
4
153(2)
C37H67AlNPSi4
monoclinic
P21/n
c)
¯
¯
2
4
2
4
T /K
100(2)
1.075
173(2)
1.132
1176.58(6)
1201.32(6)
3276.1(2)
90
100(2)
1.143
100(2)
1.070
Dcalc /g·cm–3
a /pm
1.099
906.62(8)
1154.4(1)
1883.4(2)
92.536(3)
103.288(3)
104.960(2)
1.8420(3)
0.247 (Mo-Kα)
2.38–30.11
1100.77(6)
1175.67(6)
1888.4(1)
101.160(2)
99.305(2)
101.847(2)
2.2943(2)
0.216 (Mo-Kα)
2.02–30.03
1989.35(8)
1375.28(6)
1893.57(8)
90
112.894(1)
90
4.7725(3)
0.212 (Mo-Kα)
1.85–30.13
1696.97(8)
1518.63(8)
1707.92(8)
90
100.965(2)
90
4.3211(4)
0.219 (Mo-Kα)
1.81–28.36
b /pm
c /pm
α /°
β /°
90
90
γ /°
V /nm3
4.6306(4)
0.214 (Mo-Kα)
1.84–30.10
μ /mm–1
Θ range /°
Independent reflec- 10427 [Rint = 0.0508] 13540 [Rint = 0.0396] 13286 [Rint = 0.0306] 14029 [Rint = 0.0463] 10791 [Rint = 0.0892]
tions
Parameters
370
0.054
0.1333
0.589, –0.409
482
482
0.0389
0.0985
0.467, –0.409
473
0.0479
0.1372
0.761, –0.682
419
0.0503
0.1359
0.469, –0.286
R1 [I Ͼ 2σ(I)]a)
wR2 (all data)b)
Largest diff. peak
and hole /e·nm–3
0.0432
0.0931
0.33, –0.195
a) R1 = Σ||Fo| – |Fc||/Σ|Fo|. b) wR2 = {Σw(|Fo|2 – |Fc|2)2/Σ|Fo|2}1/2. c) Absolute structure parameter 0.01(2).
Table 3. Crystal data and structure refinement for compounds 8a, 8b, and 8d.
8a
8b
8d
Empirical formula
Crystal system
Space group
C34H69AlNOPSi4
monoclinic
C2/c
C34H69AlNPSSi4
monoclinic
P21/c
C42H82AlN2PSi4
triclinic
P1
¯
Z
8
4
2
T /K
120(2)
1.051
100(2)
1.052
153(2)
1.074
Dcalc /g·cm–3
a /pm
b /pm
c /pm
α /°
1778.0(1)
1774.0(1)
2815.3(2)
90
105.204(2)
90
8.5693(9)
0.221 (Mo-Kα)
1.94–30.15
12628 [Rint = 0.0414]
492
1306.40(6)
1510.41(7)
2226.81(9)
90
94.312(1)
90
4.3815(3)
0.262 (Mo-Kα)
2.21–30.12
12843 [Rint = 0.0363]
627
1103.01(4)
1199.29(4)
2111.30(8)
93.035(1)
100.046(1)
116.7559(9)
2.4280(2)
0.202 (Mo-Kα)
1.92–30.06
14037 [Rint = 0.0229]
473
β /°
γ /°
V /nm3
μ /mm–1
Θ range /°
Independent reflections
Parameters
R1 [I Ͼ 2σ(I)]a)
wR2 (all data)b)
Largest diff. peak and hole /e·nm–3
0.0489
0.1436
0.753, –0.355
0.0527
0.1294
1.009, –0.882
0.0379
0.1060
0.385, –0.374
a) R1 = Σ||Fo| – |Fc||/Σ|Fo|. b) wR2 = {Σw(|Fo|2 – |Fc|2)2/Σ|Fo|2}1/2
.
squares calculation based on F2 using SHELXTL. The hydrogen atoms
were positioned geometrically and allowed to ride on their respective
Crystallographic data (excluding structure factors) for the structures in
this paper have been deposited with the Cambridge Crystallographic
parent atoms (except P–H and N–H, their positions were taken from Data Centre, CCDC, 12 Union Road, Cambridge CB21EZ, UK. Copies
an electron density map and refined isotropically). Compound 7a crys- of the data can be obtained free of charge on quoting the depository
¯
tallized with one molecule of 1,2-difluorobenzene per formula unit. numbers CCDC-1571660, (5), CCDC-1571657 (6; P1), CCDC-
Compound 5 crystallized as a non-merohedral twin, which was treated 1571658 (6; P212121), CCDC-1571662 (7a), CCDC-1571661 (7b),
using BASF and HKL5 instructions. One CH fragment of a CH(SiMe3)2
group of compound 5 (C10), a complete CH(SiMe3)2 group of com-
pound 8a (C20) and two CH(SiMe3)2 groups of compound 8b were
disordered and refined on split positions [0.60 : 0.40 (5); 0.59 : 0.41
(8a); 0.66 : 0.34 (C10), 0.26 : 0.24 : 0.50 (C20) (8b)]. Further crystal-
lographic data is summarized in Table 2 (5–7) and Table 3 (8a, 8b,
and 8d).
CCDC-1571663 (8a), CCDC-1571664 (8b), and CCDC-1571659 (8d)
(Fax: +44-1223-336-033; E-Mail: deposit@ccdc.cam.ac.uk, http://
www.ccdc.cam.ac.uk)
Keywords: Frustrated Lewis pairs; Hydrophosphination; Alu-
minum; Phosphorus; Heterocumulenes
Z. Anorg. Allg. Chem. 2017, 1978–1990
www.zaac.wiley-vch.de 1988
© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Journal of Inorganic and General Chemistry
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
Uzelac, A. Hernan-Gomez, D. R. Armstrong, A. R. Kennedy, E.
Hevia, Chem. Sci. 2015, 6, 5719–5728.
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Received: September 4, 2017
Published Online: October 16, 2017
Z. Anorg. Allg. Chem. 2017, 1978–1990
www.zaac.wiley-vch.de 1990
© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim