Enantiomerically pure N chirally substituted 1,3-Benzazaphospholes: Synthesis, reactivity toward t buli, and conversion to functionalized benzazaphospholes and catalytically useful dihydrobenzazaphospholes

Article abstract of DOI:10.1021/om401184n

Catalytic C-P coupling of chiral o-bromoanilines 1a-c to the corresponding o-phosphonoanilines 2a-c, reduction to the phosphines 3a-c, and final acid-catalyzed cyclocondensation represents a convenient access to the title compounds 4a-c. Reaction of 4a,b with tBuLi allows solvent-dependent directed lithiation leading either to 2-lithiobenzazaphospholes with a -Pi - CLi-NR- substructure (in Et₂O/KOtBu), in the case of anisyl substitution accompanied by partial additional lithiation in o-position of the MeO-group, or to regiospecific normal addition with formation of -P(tBu)-CHLi-NR- species. These were trapped by ClSiMe₃, CO ₂, or MeOH to give the corresponding substitution products 7b, 8b, 10b, 11a,b and 12a,b, respectively. 12a,b, containing the P-C-COOH structural unit, forms with Ni(COD)₂ in THF very efficient ethylene oligomerization catalysts with high selectivity for linear α-olefins. The structure elucidation of the products is based on conclusive solution NMR data and crystal structure analyses of the 1-(1S)-anisylethyl compounds 3b and 4b.

Full text of DOI:10.1021/om401184n

Article
pubs.acs.org/Organometallics
Enantiomerically Pure N Chirally Substituted 1,3-Benzazaphospholes:
Synthesis, Reactivity toward tBuLi, and Conversion to Functionalized
Benzazaphospholes and Catalytically Useful
Dihydrobenzazaphospholes
Mohammed Ghalib,† Peter G. Jones,‡ Sergej Lysenko,‡ and Joachim W. Heinicke*,†
†Institut fur Chemie und Biochemie, Ernst-Moritz-Arndt-Universitat Greifswald, 17487 Greifswald, Germany
̈
̈
̈
‡Institut fur Anorganische und Analytische Chemie der Technischen Universitat Braunschweig, 38023 Braunschweig, Germany
̈
S
* Supporting Information
ABSTRACT: Catalytic C−P coupling of chiral o-bromoani-
lines 1a−c to the corresponding o-phosphonoanilines 2a−c,
reduction to the phosphines 3a−c, and final acid-catalyzed
cyclocondensation represents a convenient access to the title
compounds 4a−c. Reaction of 4a,b with tBuLi allows solvent-
dependent directed lithiation leading either to 2-lithiobenz-
azaphospholes with a −PCLi−NR− substructure (in Et2O/
KOtBu), in the case of anisyl substitution accompanied by
partial additional lithiation in o-position of the MeO-group, or
to regiospecific “normal” addition with formation of −P-
(tBu)−CHLi−NR− species. These were trapped by ClSiMe3,
CO2, or MeOH to give the corresponding substitution
products 7b, 8b, 10b, 11a,b and 12a,b, respectively. 12a,b,
containing the P−C−COOH structural unit, forms with Ni(COD)2 in THF very efficient ethylene oligomerization catalysts with
high selectivity for linear α-olefins. The structure elucidation of the products is based on conclusive solution NMR data and
crystal structure analyses of the 1-(1S)-anisylethyl compounds 3b and 4b.
Scheme 1. Reaction Modes of N-Substituted 1,3-
Benzazaphospholes with tBuLi
INTRODUCTION
■
1,3-Benzazaphospholes1,2 constitute a special type of trivalent
phosphorus compound. Like the more familiar phosphaben-
zenes (phosphinines),3 they exhibit dicoordinated phosphorus
and aromatic stabilization,4 but the presence of the nitrogen
electron lone-pair in a position β to phosphorus, supported by
the inductive electron-withdrawing effect of nitrogen, induces
increased π density in the ring and at phosphorus and changes
the reactivity. Whereas the stability of complexes with
transition-metal ions is lowered, and tilted or even side-on P
coordination with π-donor contributions is favored for d10
cations5 over coordination within the ring plane, preferred in
phosphinine complexes,3 the α-metalated 2-lithiobenzaza-
phospholes6 are more stable than 2-lithiophosphinines.7 This
allows CH lithiation of the -PCH−NR− structural unit in
competition with the usual addition of tBuLi at the PC
double bond and reaction control by solvent and auxiliaries
(Scheme 1). The -PCLi−NR− species open organometallic
routes to new σ2P hybrid ligands,6 and the highly reactive
−P(tBu)−CHLi−NR− addition products offer novel strategies
to synthesize bulky P-tert-butyl- and 2-substituted heterocyclic
dialkyl(o-amino)aryl-type phosphine ligands.6a,8 The nature and
size of the N substituents play an important role in the reaction
control. The small methyl group favors CH lithiation in polar
solvents and “inverse” addition in toluene, whereas reactions in
hexane provide a mixture of “normal” and “inverse” addition
products. Bulky N-alkyl groups, however, disfavor CH lithiation
in polar solvents and “inverse” addition in hexane and enable
clean “normal” addition in the latter solvent. This behavior
raises the question whether an asymmetric substituent at
nitrogen might also induce stereoselectivity in the “normal”
addition at the PC bond and prompted us to explore a
Received: December 9, 2013
Published: January 23, 2014
© 2014 American Chemical Society
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Scheme 2. Synthesis of 1−4
convenient route to such benzazaphospholes and to test their
reactivity.
yellow viscous oils after column chromatography on silica. In
the second step, phosphorus was introduced. As found in our
earlier studies,2c the C−P coupling of bulkily substituted N-
secondary o-bromoanilines can be achieved in high yields with
excess triethyl phosphite in the presence of Pd(OAc)2 or PdCl2
under the conditions of the Tavs reaction.10 The milder
conditions of the Hirao coupling with diethyl phosphite in the
presence of a base11 had no advantages in these particular
couplings and required time-consuming optimization and
additional auxiliary phosphine ligands. Therefore, we tested
the Tavs coupling of 1a−c with triethyl phosphite in the
presence of NiCl2, NiBr2, PdCl2, and Pd(OAc)2, respectively.
The Ni(0) complexes, formed on heating with P(OEt)3 at
180−200 °C (detected by NMR in the absence of 1), did not
catalyze the P−C coupling, but the Pd(0) triethyl phosphite
complexes, generated under similar conditions from excess
P(OEt)3 and PdCl2 (6 mol %) or Pd(OAc)2 (3 mol %), proved
amine-tolerant and afforded the N-secondary o-phosphonoani-
lines 2a−c in high yields: 80−84% after purification by column
chromatography on silica. These were reduced by LiAlH4 in
good yields (ca. 70%) to the corresponding 2-phosphinoani-
lines 3a−c, air-sensitive oils (3a) or solids (3b,c) of unpleasant
odor, and finally cyclized with dimethylformamide dimethyla-
cetal (DMFA) to the 1,3-benzazaphospholes 4a−c. In the
absence of catalyst the cyclization required heating for 5 days at
50 °C. After 2 days, NMR monitoring of the conversion of 3b
displayed signals of 4b (δ(31P) 73.2 ppm), phosphaalkene 5b
(R* = (S)-CH(p-anisyl)Me, δ(31P) 43.9 ppm, isomer ratio E:Z
9:1), and its symmetric cyclodimer, a 1,3-diphosphetane
(δ(31P) −27.0 ppm), with an intensity ratio of 55:20:25.
After 7 days at 50 °C 4b was isolated in 81% yield. In the
presence of chlorotrimethylsilane the reaction is much faster
and complete within 1 day. This reagent, used in stoichiometric
amounts, silylates any of the nucleophilic sites and thereby
liberates HCl as the catalyst of the cyclocondensation. After
extraction of N-basic impurities with dilute aqueous sulfuric
acid the title compounds were isolated as moderately air-
sensitive, nearly colorless viscous oils (4a,c) or a pale yellow
solid (4b), crystallizing by slow diffusion of hexane into the
concentrated THF solution.
RESULTS AND DISCUSSION
■
Synthesis. Commercially available chiral (1S)-1-arylethyl-
amines were chosen as starting materials to promote stereo-
selection in the addition reactions of the title compounds with
tBuLi by different sizes and shapes of the α substituents. The
substituent in the para position of the phenyl group was varied,
partially to simplify the NMR spectra and partially to see if this
affects the reactivity toward tBuLi. The primary arylethylamines
were coupled with o-dibromobenzene using the Buchwald−
Hartwig protocol9 with various Pd−phosphine catalysts and
NaOtBu as a base. The moderate steric hindrance at the amino
group by the α-branched substituent favored the arylamination
and allowed high yields of 1a−c (Scheme 2) with a catalyst
formed from Pd2(dba)3 and BINAP (Table 1, entries 1−3) and
good yields with a Pd2(dba)3/DPPF catalyst (entries 4−6),
whereas monodentate phosphine ligands and Pd(OAc)2 or
Pd(PPh3)4 were much less suitable (entries 7 and 8). In the
absence of catalyst under otherwise identical conditions, no
conversion was observed. The products were isolated as pale
Table 1. Pd-Catalyzed Coupling of 1,2-Dibromobenzene
with (1S)-1-Phenylethylamines
ligand
entry (amt, mol %)
Pd compd
(amt, mol %)
base (amt,
equiv)
product
a
(yield, % )
1
2
3
BINAP (7.5)
BINAP (7.5)
BINAP (7.5)
Pd2(dba)3 (5)
Pd2(dba)3 (5)
Pd2(dba)3 (5)
NaOtBu
1a (74)
(1.4)
NaOtBu
(1.4)
1b (75)
1c (74)
NaOtBu
(1.4)
4
5
DPPF (7.5)
DPPF (7.5)
Pd2(dba)3 (5)
Pd2(dba)3 (5)
NaOtBu (1.4
1a (57)
1b (59)
NaOtBu
(1.4)
6
7
8
DPPF (7.5)
Pd2(dba)3 (5)
Pd(OAc)2 (3.0)
Pd(PPh3)4
NaOtBu
1c (58)
1b (6)
1b (0)
(1.4)
P(o-Tol)3 (5)
NaOtBu
(1.4)
Et3N
a
Yield after isolation.
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Structural Aspects. All of the new compounds were
characterized by conclusive 1H, 13C, and also (except for 1a−c)
31P solution NMR data, by [M + H]+ peaks in the ESI-HRMS
spectra, and (for solids) by satisfactory elemental analysis.
Typical chemical shift ranges and coupling constants with the
31P nuclei allowed unambiguous assignment of the signals and
clear identification of the compounds. The phosphorus
resonances of the intermediate phosphaalkenes 5b appear at
Å14). The orientation of the phosphine hydrogen atoms toward
the amine proton might imply weak N−Hδ+···δ−H−P
interactions, but the H01···H(P) distances (2.27, 2.35 Å) are
only marginally shorter than the sum of the van der Waals radii
(2.4 Å,14 which may of course depend on the chemical
environment). Interactions with the P lone pair would require
the opposite orientation of the PH2 group.
The chiral benzazaphosphole 4b (Figure 2) displays the
expected planarity of the fused ring system (mean deviation
2
somewhat higher field than the signals of 4a−c, and the JPH
coupling constant of the major trans isomer of 5b is
significantly smaller (13.9 Hz) than in 4a−c and in the trace
of cis-5b (37.8 Hz), as is typical for Me2N- and Me3SiO-
substituted trans-phosphaalkenes.12
Additional and more detailed structure information was
obtained by X-ray diffraction of single crystals of 3b and 4b,
both crystallizing from THF/hexane in the monoclinic chiral
space group P21 with two molecules in the unit cell. The
absolute configuration was determined by anomalous dis-
persion, confirming the S configuration at the α-C atom of the
N substituents. Bond lengths and angles are within the usual
ranges. For o-phosphinoaniline 3b (Figure 1) all hydrogen
Figure 2. Molecular structure of 4b in the crystal (ellipsoids with 50%
probability). Selected bond lengths (Å) and angles (deg): P3−C2
1.7189(14), P3−C3A 1.7842(12), N1−C2 1.3578(16), N1−C7A
1.3855(16), N1−C8 1.4922(17), C8−C9 1.5177(18), C8−C10
1.5188(17); N1−C2−P3 115.56(10), C2−P3−C3A 88.28(7), C2−
N1−C7A 112.55(11), C2−N1−C8 124.42(11), C7A−N1-C8
122.72(10), C4−C3A-P3 130.11(11), C7A-C3A-P3 111.34(10),
N1−C8−C9 109.57(10), N1−C8−C10 110.73(11), C9−C8−C10
115.34(12), C13−O−C16 116.89(11).
0.005 Å) with C8 lying 0.12 Å out of the plane. The N−C2 and
P−C2 bonds are short in comparison to the N−C7A and P−
C3A bonds, as is typical for 1,3-benzazaphospholes.1 With
respect to 1-neopentyl-1,3-benzazaphosphole,2c bearing a
moderately bulky primary N-alkyl group, the P−C2 (double)
bond is perhaps marginally longer (by 0.0087(14) Å), but N−
C2 and the other bonds of the ring system are very similar. The
α-methyl group at C8 is rotated into a position almost
perpendicular to the benzazaphosphole ring plane (C2−N1−
C8−C9 88.08(14)°), whereas the phenyl group is in a gauche
position on the same side as C2 (C2−N1−C8−C10
40.26(16)°), and its ring plane is nearly perpendicular to that
of the benzazaphosphole-C8 plane (N1−C8−C10−C11
77.21(15)°). π interactions with lithium, shown for various
lithium arene compounds,15 should direct tBuLi with the
organic residue toward 2-CH and might activate tBuLi species
for stereoselective addition at the PC2 bond. Additionally,
interactions with the O-donor group may have an impact on
the reactivity.
Reactivity of 4a−c. General aspects of the reactivity of 1,3-
benzazaphospholes, shown earlier, are the aromaticity, proved
by photoelectron spectroscopic and quantum chemical
studies,4b and the resulting stabilization of the −PCR′−
NR− species toward attack by water, aqueous acids, and bases
and several other electrophilic and nucleophilic reagents.1,2,6
This includes even organolithium reagents in polar solvents
such as diethyl ether and THF and renders feasible the CH
lithiation of 1-methylbenzazaphospholes with R′ = H to give
isolable −PCLi−NMe− reagents, stable at room temper-
ature up to 2 days.6b,c Bulky N substituents, however, favor
competing addition reactions,6a and the use of nonpolar
solvents causes complete suppression of the CH lithiation, even
for 1-methyl-1,3-benzazaphospholes.8
Figure 1. Molecular structure of 3b in the crystal (ellipsoids with 50%
probability). Selected bond lengths (Å) and angles (deg): P−C12
1.8215(9), O−C24 1.3716(10), O−C3 1.4253(12), C1−C21
1.5205(11), C1−C2 1.5275(12), C11−C16 1.4069(12), C11−C12
1.4189(12), C12−C13 1.3978(12); C11−N−C1 124.18(7), C24−O−
C3 117.73(7), N−C1−C21 113.04(7), N−C1−C2 108.43(7), C21−
C1−C2 109.61(7), N−C11−C16 121.24(7), N−C11−C12
120.05(7), C13−C12−P 116.77(6), C11−C12−P 124.35(6).
atoms at P and N were found and refined freely. The
phosphino group adopts an intersecting conformation with
dihedral angles of 47.6(8) and −47.6(7)°, respectively, for
C11−C12−P−H02 and C11−C12−P−H03. The phosphorus
lone pair then lies in the ring plane, indicating a lack of π
interactions, as was similarly shown for gaseous o-phosphino-
phenol and the analogous arsine by combined photoelectron
spectroscopic and quantum chemical studies.13 For the amino
group the situation is different. The small dihedral angle of
2.28(12)° for C1−N−C11−C16 and short N−C11(sp2) and
N−C1(sp3) bond lengths (1.3746(10) and 1.4581(10) Å)
indicate sp2 hybridization of nitrogen and efficient π
conjugation. The packing (for Figure S1 see the Supporting
Information) displays only weak intermolecular P−H···π and o-
C−H···π contacts to the π-rich amino- and methoxy-substituted
phenyl groups of neighboring molecules, but no π stacking. The
intramolecular (N)H01···P contact (2.732(14) Å) is only
slightly shorter than the sum of the van der Waals radii (3.0
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Scheme 3. Lithiation of 4b in the Presence of KOtBu in Ether and Conversion to Silylated and Carboxylated Products
The focus of the reactivity study of the N asymmetrically
substituted compounds 4 is the addition of tBuLi and possible
stereocontrol, but the question of maintenance of preferred 2-
CH lithiation in polar solvents or the dominance of directed
lithiation in o-position of the methoxy group16 of the p-anisyl-
substituted 4b was also addressed and is presented first. In
these experiments lithiation was carried out by addition of the
tBuLi pentane solution to an ethereal solution of 4b and
KOtBu at −70 °C and subsequent slow warming to −30 °C.
Under these mild conditions ether cleavage is avoided, but the
reaction is slow despite the fact that the alkoxide supports the
CH lithiation to 6 via highly polar tBuLi/KOtBu clusters.17 An
excess of tBuLi (1.5 equiv) was required to achieve nearly
quantitative conversion of 4b. The lithiated species were
trapped by ClSiMe3 and in a second experiment by CO2.
Workup, in the latter case via silylation of the lithium
carboxylate and methanolysis of the silyl ester after separation
of LiCl, provided the N-anisylethyl-substituted 2-(trimethylsil-
yl)- and 2-carboxybenzazaphospholes 7b and 8b accompanied
by 7d and 8d with additional SiMe3 and COOH groups in a
position ortho to the methoxy group (Scheme 3). The molar
ratio 7b:7d was ca. 3:1 and that of 8b:8d 1:2, on the basis of
integration of methyl proton signals. The detection of a minor
amount of 4b in the first reaction and the dominance of 8d in
the second reaction, both without hints of solely lithiation in o-
position of the OMe group, suggests that the methoxy-directed
lithiation is favored after the first lithiation step to 6b and
competes then with CH lithiation of 4b. This does not allow a
selective monolithiation of 4b under the above conditions. The
higher amount of ortho lithiation product 8d in the reaction
with CO2 in comparison with that in the trimethylsilylation
(7d) can be explained by incomplete consumption of tBuLi
before addition of the trapping reagents and carboxylate-
supported additional ortho lithiation. The high content of 7b is
in accordance with continued 2-CH lithiation by unconverted
tBuLi in the presence of ClSiMe3, since trapping of the bulky
tBuLi by ClSiMe3 occurs only at higher temperature.
addition product 9b. The latter is highly reactive and rapidly
deprotonates THF, so that trapping with ClSiMe3 afforded a
mixture of 7b with 10b. Dominant or exclusive addition was
achieved in less polar solvent systems. Methanolic quenching of
the lithiation products formed in a 1:1 mixture of hexane and
diethyl ether gave evidence that the addition is strongly
preferred to CH lithiation, is regiospecific for the “normal”
addition, and is moderately diastereoselective with respect to
the asymmetric (1S)-carbon at nitrogen (Scheme 4). NMR
Scheme 4. Addition of tBuLi at 4a,b Followed by
Protonation, Silylation, or Carboxylation
inspection of the crude product mixture displayed only 13 mol
% of 4b as the quenching product of 6b and a 2:1 preference of
one of the diastereosiomers of 10b to the other (58 vs 29 mol
%). When only hexane or toluene was used as solvent, CH
lithiation was completely suppressed in favor of regiospecific
“normal” addition but the diastereoselectivity was lower or
entirely lost. Thus, in hexane two diastereoisomers of the
When the lithiation was carried out in the absence of KOtBu
in THF (−70 to −30 °C) the CH lithiation to 6d was still
preferred but was accompanied by considerable amounts of the
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silylation trapping product 11b were formed in a 1:1 ratio,
whereas reaction in hexane/Et2O (1:1) furnished these
diastereoisomers in a ratio of 62:38. The analogous reaction
of 4a provided the diastereoisomers of 11a similarly in a 65:35
ratio. Lack of signals for two further diastereoisomers involving
the new chirality center at C2 indicates high diastereoselectivity
for the trimethylsilylation, yielding only the products with tBu
and SiMe3 groups at trans positions. This assignment is evident
2
from the rather small JPH coupling constants of the PCH
protons (4.2−4.9 Hz) which hint at an orientation of this
proton trans to the P lone-pair (syn toward tBu) and thus also
of the substituents at the adjacent C and P atoms. Trapping
with CO2, followed by silylation and methanolysis of the silyl
ester after separation from LiCl, likewise gave two major
diastereoisomers of 12a and 12b, respectively, both with small
2JPH values (2.3−2.6 Hz) and thus trans positions of tBu and
COOH, but the selectivity of the substitution was lower and led
also to minor and/or trace amounts of the two other possible
diastereoisomers. It should be noted here that the 2,3-dihydro-
1,3-benzazaphospholes are kinetically less stable than the
aromatic benzazaphospholes. Slow chromatography on silica
gel led to major decomposition of the dihydrobenzaphosphole-
2-carboxylic acid, while storage in solution or flash chromatog-
raphy may cause acid-catalyzed isomerization, as observed also
for 1,3-azaphospholidine-2-carboxylic acids.18 This proceeds
probably via slow ring-opening/ring-closure reactions at the
aminophosphinoacetalic structure unit. For 12b such isomer-
ization was observed after a small amount of pivalinic acid was
separated by flash chromatography on silica gel using hexane/
ethyl acetate (2%) for elution. The NMR spectra then
displayed a change of the diastereoisomer composition. A
phosphorus resonance at 8.5 ppm, observed for a minor isomer
of 12a but not for crude 12b, became the second strongest
signal while the previously second most intense signal at 17.9
ppm became much smaller. In the proton and 13C NMR
spectra a new PCH doublet appeared for this isomer, shifted
Figure 3. o,o′-Proton multiplets of 12b with fine splitting for
diastereoisomer C (right end of B multiplet partially superimposed
by 4-H).
display downfield coordination chemical shifts.19 For the 1-
(1S)-arylethyl-benzazaphospholes and dihydrobenzazaphosp-
holes these properties are each demonstrated by one example:
the tungsten(0) pentacarbonyl complex 13b and the Rh(COD)
Cl complex 14b (Chart 1). The former displays the typical
upfield coordination chemical shift in comparison to the ligand
4b (Δδ(31P) = −39.4 ppm), whereas the latter exhibits the
expected downfield shifts of the diastereoisomers versus 11b
(Δδ(31P) ≈ 40 ppm). Attempts to separate the diaster-
eoisomers of 11b failed. The structures of the complexes were
elucidated by conclusive 13C and proton NMR data with
1
characteristic changes of the JPC coupling constants by the
complexation.
The dihydrobenzazaphosphole-2-carboxylic acids 12 imply a
P−C−COOH structural unit, as in diphenylphosphinoacetic
acid, originally used for the generation of nickel catalysts for the
oligomerization of ethylene in the Shell Higher Olefin
2
slightly downfield with an increased JPH (7.6 Hz) and slightly
1
Process.20 Therefore, they might also be suitable for generation
increased JPC (ΔJ = 1.3 Hz) coupling constant, whereas the
̂
2JPC coupling constant of the COOH carbon resonance, 15.9
Hz in both of the diastereoisomers A and B, becomes 0. This
hints at the formation of a new diastereoisomer with trans
positions (gauche conformations) of 2-H and the P lone pair and
of tBu and COOH, possibly favored by hydrogen bond
interactions of the COOH with the amino group. An unusually
fine splitting of the multiplet of the two ortho protons with an
otherwise typical AA′BB′ coupling pattern hints at weak
through-space interactions to the P lone pair in diastereoisomer
C (Figure 3). Since the N substituent has an S configuration
and the o-H···P interaction requires an orientation of the anisyl
group more or less perpendicular to the NC6H4P plane with
the P lone pair directed toward the anisyl group, the P atom in
diastereoisomer C also has an S and C2 an R configuration.
Single crystals for more direct information on the configuration
at phosphorus and C2 also in the primarily formed
diastereoisomers A and B have not been obtained so far.
Examples of Complexes and Use in Catalysis. The
ligand properties of 1,3-benzazaphospholes and dihydrobenz-
azaphospholes differ sharply. The former are weak donors, form
labile complexes with d10 cations,5 and need π back-bonding for
stable complexes, e.g. LM(CO)5 (M = Cr, Mo, W), indicated
by a low downfield (Cr) or even upfield (Mo, W) 31P
coordination chemical shift.1,2 The P-tert-butyl-2,3-dihydro-1,3-
benzazaphospholes, however, are P-basic phosphines which
of PO− chelate catalysts.21 The bulky tert-butyl group and
increased π density at the aryl carbon in a position ortho to the
amino group, along with steric shielding of the N-donor site by
the branched arylethyl substituent, should even improve the
efficiency of the nickel catalysts for the oligomerization of
ethylene, and this prompted us to screen 12a,b for this purpose
in a batch procedure. The precatalysts were prepared in situ
from equimolar amounts of the ligands and Ni(1,5-COD)2 in
THF, transferred into a stainless steel autoclave, and after
pressurization heated to 70 °C. As in a preliminary test of 1-
neopentyldihydrobenzazaphosphole-2-carboxylic acid,6a the
nickel complexes generated with Ni(COD)2 formed very active
catalysts during heating and, after reaching about 70 °C,
converted ethylene rapidly, as seen by the pressure−time curve,
depicted in Figure 4. The catalyst formation and conversion
were slightly slower for 12a,b/Ni than for the analogous 1-
neopentyl-substituted catalyst, but the conversion was almost
quantitative. The turnover numbers were limited by the
catalyst/ethylene ratio. Waxy polymers and a small portion of
liquid oligomers were provided (Table 2). NMR analysis of the
waxy oligomers showed high selectivity for linear α-olefins
(87−89%) and molecular weights (MNMR) between 750 and
900, on the basis of the integral ratios of olefinic to CH2 and
CH3 protons of swollen polymers (measured at 100 °C). The
oligomers, analyzed by GC of the flash distillate, were also
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̂
Chart 1. η1P Coordination in 13b and 14b and Assumed PO− Chelate Structure of the Ni−Ethylene Oligomerization Catalysts
a
Formed from 12a,b and Ni(1,5-COD)2
a
Legend: Rp, H or growing chain; □, coordination site for C2H4.
formation of a polymer at 70 °C, but with very slow
consumption of ethylene (Figure 4). This could not be
accelerated, since raising the temperature to 100 °C caused
catalyst deactivation. According to the 1H and 13C NMR
spectra the polymer consisted mainly of a mixture of a
polystyrene (PS) and low-molecular-weight linear polyethylene
with a phenyl to vinyl group ratio of roughly 7:1. The CH
proton signals for styryl end groups were very weak. Only trace
signals for phenyl branching by incorporation of styrene into
the polyethylene chain were detected by 13C NMR (α- and β-
C: δ 37.5, 28.2 ppm;23 Cbr superimposed by CH2 signals of PS),
in addition to very weak signals for methyl branching. The
microstructure of the PS part (δ 41.5−41.8 (CH), 42.5−47.3
ppm (CH2)) is complicated and was not analyzed. The
molecular weight of the PE part was estimated by proton
integration and correction for CHCH2 of PS to about 750.
Extraction of the polymer mixture with THF led to enrichment
of the PS part (phenyl to vinyl group ratio 12.6:1) and lower
MNMR value of the PE part but not to full separation of the
polymers. A GPC measurement of this extract using THF
displayed a bimodal molecular weight distribution by a very
broad shoulder at the low-molecular-weight side of the main
curve.
Figure 4. Ethylene consumption in the batch polymerization with
catalysts generated in situ from Ni(COD)2 and (a) 12a, (b) 12b, and
(c) 1-neopentyl-3-tert-butyl-dihydrobenzazaphosphole-2-carboxylic
acid,6a respectively, at 70 °C in THF. Curve d reflects the conversion
in the presence of 12a/Ni in THF/styrene (1:1).
mainly linear α-olefins. This selectivity corresponds well to that
observed for catalysts formed from diphenylphosphinoacetic
acid, phosphino ketones, and o-phosphinophenols, for which P
O− chelate structures were established.20,21 Thus, this structure
̑
type can also be anticipated for the nickel catalysts generated
with 12a,b (Chart 1, right).
CONCLUSIONS
■
In comparison to nickel catalysts based on N-substituted
diphenylphosphinoglycine22 or 3-phenyl-1,3-azaphospholidine-
2-carboxylic acid,18 the efficiency of 12a,b/Ni for ethylene
conversion is improved. Therefore, and because incorporation
of styrene comonomers into the CH2 chain was observed for o-
phosphinophenolate nickel catalysts,23 we tested if copoly-
merization of ethylene with styrene is possible. The experiment
with 12a/Ni in THF/styrene (1:1 by volume) showed
Enantiomerically pure N chirally substituted 1,3-benzazaphosp-
holes 4 are accessible via Pd-catalyzed C−N coupling of the
corresponding chiral primary amines with o-dibromobenzene,
subsequent C−P coupling with triethyl phosphite, reduction
with LiAlH4, and acid-catalyzed cyclization with Me2NCH-
(OMe)2. The reaction of 4 with tBuLi in Et2O in the presence
of KOtBu leads to 2-CH lithiation and allows introduction of
functional groups into this position, but the presence of an
a
Table 2. Oligomerization of Ethylene with Catalysts Formed from 12a,b
b
catalyst (amt,
amt of C2H4, g (mol);
solvent (amt, mL)
C2H4 conversion, g (%);
amt of polymer, g; mp,
c
d
entry
1
μmol)
TON, (mol mol−1
14.8 (99); 7228
)
°C; D, g cm−3
polymer: MNMR
;
α-olefins (%), Me/CC, %
12a (73),
Ni(COD)2 (73)
14.8 (0.53); THF (20)
11.7; 110−114; 0.94
11.6; 108−112; 0.94
6.8; 106−112; 0.94
870; 87, 1.3
900; 89, 1.3
750; 86, 1.6
2
3
12b (75),
Ni(COD)2 (75)
15.9 (0.57); THF (20)
15.5 (97.5); 7368
e
12b (54),
Ni(COD)2 (54)
14.7 (0.52); THF (10),
styrene (10)
7.9 (54); 5215
a
b
Conditions: batch oligo-/polymerization of ethylene in THF, pstart of C2H4 at room temperature 40−45 bar, start of conversion at ca. 70 °C. Solid
residue after flash distillation of volatiles, treatment with MeOH/aqueous concentrated HCl (1:1), washing with MeOH, and drying under vacuum.
c
d
Density of tablets of the solid (pressed at 10 kbar) determined by the sinking method in H2O/EtOH. MNMR based on 1H NMR integrals of CH2
e
and CH3 versus CH protons in swollen polymers at 100 °C. TON relative to C2H4 conversion.
809
dx.doi.org/10.1021/om401184n | Organometallics 2014, 33, 804−816

Organometallics
Article
= 1.5 Hz, 1 H, 6-H), 6.49 (td, 3J = 8.0, 7.2, 4J = 1.5 Hz, 1 H, 4-H), 6.98
anisyl group causes competing additional directed lithiation in
o-position of the methoxy group and subsequent additional
functionalization of this position. Reaction of 4 with tBuLi in
hexane/diethyl ether (without KOtBu) proceeds with a strong
preference, regiospecifically and with moderate diastereoselec-
tivity versus the 1S carbon atom, for the “normal” addition
product with tBu at phosphorus and Li at C2. Quenching by
methanol or highly diastereoselective trimethylsilylation
showed that the addition at the PC bond is moderately
stereoselective under these conditions (2:1 molar ratio of
diastereoisomers). Lithiation in toluene or hexane causes clean
addition but partial or complete loss of diastereoselectivity.
Trapping of the lithiodihydrobenzazaphospholes with CO2
furnishes the respective carboxylic acids: however, with lower
selectivity. These heterocyclic α-phosphino α-amino acids may
slowly isomerize by their heteroacetalic nature and thus are
unsuitable as ligands for asymmetric catalyses. However, the
presence of the P−C−COOH structure unit allows the
formation of nickel catalysts for the oligomerization of ethylene
with the same selectivity as known from phosphinoacetate
nickel catalysts, originally used in the first step of the SHOP
process. The bulky P and N substituents induce high activity.
This and each one of the examples of complexes of the chiral
benzazaphospholes and P- and N-basic dihydrobenzazaphosp-
holes provide the first information on the properties of these
ligands and their potential for catalytic applications. This paves
the way for further exploration of the use of these ligands in
complex chemistry and catalysis.
3
4
(td, J = 8.1, 7.2, J = 1.5 Hz, 1 H, 5-H), 7.19−7.35 (m, 5 H, phenyl-
H), 7.40 (dd, 3J = 7.9, 4J = 1.5 Hz, 1 H, 3-H). 13C{1H} NMR
(CDCl3): δ 25.10 (CH3), 53.51 (NCH), 109.60 (Cq-2), 112.64 (C-6),
117.74 (C-4), 125.68 (2 C-o), 127.00 (C-p), 128.27 (C-5), 128.69 (2
C-m), 132.21 (C-3), 143.86, 144.46 (Cq-i, Cq-1). MS (20 °C): m/z
(%) 277 (9) [M + H]+, 276 (2), 275 (9) [M + 1]+, 262 (13), 260 (14),
173 (18), 171 (19), 105 (100). HRMS (ESI in MeOH + FA):
C14H14BrN (276.17), calcd for [M + H]+ 276.0382, 278.0362; found
276.0381, 278.0361.
2-Bromo-N-[(S)-1-(p-methoxyphenyl)ethyl]aniline (1b). Reac-
tion of 1,2-dibromobenzene (4.08 mL, 33.8 mmol) with (S)-(−)-1-(4-
methoxyphenyl)ethylamine (5.0 mL, 33.9 mmol) in the presence of
DPPF (1.41 g, 7.5 mol %), Pd2(dba)3 (1.55 g, 5 mol %), and NaOtBu
(4.52 g, 47.0 mmol) in toluene (40 mL) and workup as described for
1a (for elution hexane 92%/Et2O 8%) gave 6.15 g (59%) of pale
yellow viscous 1b. Using the same procedure but with BINAP instead
of DPPF provided 7.81 g (75%) of 1b. 1H NMR (CDCl3): δ 1.55 (d,
3J = 6.8 Hz, 3 H, CH3), 3.78 (s, 3 H, OCH3), 4.48 (q, 3J = 6.8 Hz, 1 H,
NCH), 4.82 (br s, 1 H, NH), 6.42 (dd, 3J = 8.1, 4J = 1.5 Hz, 1 H, 6-H),
6.51 (td, 3J = 7.8, 7.5, 4J = 1.5 Hz, 1 H, 4-H), 6.85 (m, 2 H, m-H), 7.00
(td, 3J = 8.1, 7.2, 4J = 1.5 Hz, 1 H, 5-H), 7.25 (m, 2 H, o-H), 7.40 (dd,
4
3J = 7.8, J = 1.5 Hz, 1 H, 3-H). 13C{1H} NMR (CDCl3): δ 25.05
(CH3), 53.04 (NCH), 55.23 (OCH3), 109.72 (Cq-2), 112.87 (C-6),
114.06 (2 C-m), 117.83 (C-4), 126.81 (2 C-o), 128.27 (C-5), 132.22
(C-3), 136.36 (Cq-i), 143.81 (Cq-1), 158.60 (Cq-p). MS (20 °C): m/z
(%) 307 (7) [(81Br)M]+, 305 (7) [(79Br)M]+, 291 (2), 210 (3), 136
(11), 135 (100), 134 (7). HRMS (ESI in MeOH + FA): C15H16BrNO
(306.20), calcd for [M − H]+ 304.0332, 306.0316; found 304.0334,
306.0314; the [M + H]+ peaks display low intensity.
2-Bromo-N-[(S)-1-(p-methylphenyl)ethyl]aniline (1c). Reac-
tion of 1,2-dibromobenzene (3.12 mL, 21.2 mmol) with (S)-(−)-1-
(4-methylphenyl)ethylamine (3.12 mL, 21.2 mmol) in the presence of
DPPF (0.88 g, 7.5 mol %), Pd2(dba)3 (0.97 g, 5 mol %), and NaOtBu
(2.83 g, 29.4 mmol) in toluene (40 mL) and workup as described for
1a (for elution hexane 98%/Et2O 2%) gave 3.58 g (58%) of pale
EXPERIMENTAL SECTION
■
General Remarks. All operations were carried out under dry
nitrogen or argon using Schlenk techniques and freshly distilled dry
solvents. 1,2-Dibromobenzene, asymmetric amines, palladium salts,
Pd2(dba)3 (tris(dibenzylideneacetone)dipalladium(0)), BINAP (2,2′-
bis(diphenylphosphino)-1,1′-binaphthyl), DPPF (1,1′-bis-
(diphenylphosphino)ferrocene), tBuLi solution, ClSiMe3, Ni(COD)2,
and ethylene were purchased and used as received. NMR spectra were
measured on an ARX300 multinuclear FT-NMR spectrometer
(Bruker) at 300.1 (1H), 75.5 (13C), and 121.5 (31P) MHz. Chemical
shifts (δ) are given in ppm relative to Me4Si or Me4Si calibrated
solvent signals and H3PO4 (85%), respectively. Assignment numbers
follow the atom numbering of the nomenclature and are indicated in
the Supporting Information. Coupling constants refer to JHH in 1H and
JPC in 13C NMR data unless stated otherwise. The assignment of the
13C NMR signals is based on 135-DEPT spectra, characteristic P−C
coupling constants, and increment estimations. Low-resolution mass
spectra were measured on an AMD40 single-focus mass spectrometer
(Maurer) with EI (70 eV), and high-resolution mass spectra were
1
3
yellow viscous 1c. H NMR (CDCl3): δ 1.57 (d, J = 6.8 Hz, 3 H,
CH3), 2.33 (s, 3 H, CH3), 4.51 (q, 3J = 6.8 Hz, 1 H, NCH), 4.72 (br s,
1 H, NH), 6.42 (dd, 3J = 8.1, 4J = 1.5 Hz, 1 H, 6-H), 6.51 (td, 3J = 8.1,
4
3
4
7.5, J = 1.5 Hz, 1 H, 4-H), 7.00 (td, J = 7.8, J = 1.5 Hz, 1 H, 5-H),
7.14 (br d, 3J = 7.8 Hz, 2 H, o- or m-H), 7.24 (br d, 3J = 7.8 Hz, 2 H,
m- or o-H), 7.40 (dd, J = 7.5, 4J = 1.5 Hz, 1 H, 3-H). 13C{1H} NMR
3
(CDCl3): δ 20.90 (4-CH3), 24.99 (CH3), 53.07 (NCH), 109.44 (Cq-
2), 112.48 (C-6), 117.49 (C-4), 125.46 (2 C-o), 128.13 (C-5), 129.24
(2 C-m), 132.03 (C-3), 136.39 (Cq-p), 141.35, 143.85 (Cq-i, Cq-1).
MS (20 °C): m/z (%) 292 (1), 291 (8) [(81Br)M]+, 290 (2), 289 (9)
[(79Br)M]+, 277 (8), 276 (9), 173 (10), 171 (11), 119 (100). HRMS
(ESI in MeOH + FA): C15H16BrN (290.20), calcd for [(79Br)M +
Na]+ 312.0359; found 312.0358.
2-[(S)-(1-Phenylethyl)amino]benzenephosphonic Acid Di-
ethyl Ester (2a). A Schlenk flask was charged with 1a (6.0 g, 21.7
mmol), P(OEt)3 (7.5 mL, 43.8 mmol), and PdCl2 (0.23 g, 6 mol %),
connected to a distillation apparatus that allows refluxing of P(OEt)3
and distillation of EtBr, and heated under a slow stream of N2 for ca. 2
h at 180−190 °C (bath). NMR samples were taken every 15−30 min
to monitor the progress of the reaction and obtain optimal yields.
Higher temperatures (>190 °C) led to dark mixtures and considerable
decrease of the yields. The crude product was purified by column
chromatography on silica gel using elution with hexane/EtOAc (14%).
obtained at the Institut fur Organische Chemie, Universitat Gottingen,
̈
̈
̈
using an APEX IV 7 T Fourier transform ion cyclotron resonance mass
spectrometer (Bruker Daltonics) (ESI in MeOH, formic acid).
Elemental analyses were performed with a MICRO CUBE CHN
analyzer from Elementar vario under standard conditions.
2-Bromo-N-[(S)-1-phenylethyl]aniline (1a). A Schlenk flask was
charged with 1,2-dibromobenzene (4.68 mL, 38.8 mmol), (S)-(−)-1-
phenylethylamine (5.0 mL, 39.2 mmol), DPPF (1.61 g, 7.5 mol %),
Pd2(dba)3 (1.78 g, 5 mol %), sodium 2-methylpropanolate (NaOtBu;
5.2 g, 54 mmol), and toluene (40 mL). The mixture was heated for 6 h
at 80 °C and then 20 h at 100 °C. Finally, the solvent was removed
under vacuum, the residue was suspended in diethyl ether (40 mL),
and the suspension was filtered through Celite. The brown-black
filtrate was concentrated under vacuum and purified by column
chromatography on silica gel using hexane/Et2O (5%) for elution.
Evaporation of the solvent furnished 6.42 g (60%) of a pale yellow
viscous oil. 1H NMR (CDCl3): δ 1.57 (d, 3J = 6.8 Hz, 3 H, CH3), 4.51
(q, 3J = 6.8 Hz, 1 H, NCH), 4.73 (br s, 1 H, NH), 6.38 (dd, 3J = 8.1, 4J
1
Removal of solvents provided 6.1 g (84%) of a pale yellow oil. H
NMR (CDCl3): δ 1.34 (td, 3J = 7.2, 4JPH ≈ 1 Hz, 6 H, CH3), 1.56 (d,
3J = 6.6 Hz, 3 H, CH3), 4.12 (m, 4 H, OCH2), 4.50 (quin, 3J = 6.2 Hz,
1 H, NCH), 6.42 (t, 3J ≈ 4JPH = 8.1, 7.8 Hz, 1 H, 3-H), 6.60 (tdd, 3J =
7.5, 7.2, 4JPH = 3.3, 4J = 0.8 Hz, 1 H, 5-H), 7.13−7.37 (m, 7 H, NH, 4-
H, phenyl-H), 7.45 (ddd, 3JPH = 14.8, 3J = 7.8, 4J = 1.5 Hz, 1 H, 6-H).
3
13C{1H} NMR (CDCl3): δ 16.25 (d, J = 6.6 Hz, CH3), 24.92 (s,
CH3), 53.19 (s, NCH), 62.00 (d, 2J = 2.6 Hz, OCH2), 107.99 (d, 1J =
3
3
181.8 Hz, Cq-1), 112.59 (d, J = 11.9 Hz, C-3), 115.67 (d, J = 14.6
Hz, C-5), 125.75 (s, 2 C-o), 126.83 (s, C-p), 128.59 (s, 2 C-m), 133.33
2
4
(d, J = 8.0 Hz, C-6), 133.91 (d, J = 2.7 Hz, C-4), 144.83 (s, Cq-i),
810
dx.doi.org/10.1021/om401184n | Organometallics 2014, 33, 804−816

Organometallics
Article
150.66 (d, 2J = 9.3 Hz, Cq-2). 31P{1H} NMR (CDCl3): δ 21.7. MS (90
°C): m/z (%) 334 (28) [M + 1]+, 392 (21), 319 (100). HRMS (ESI in
MeOH + FA): C18H24NO3P (333.36), calcd for [M + H]+ 334.1567;
found 334.1565.
2 - [ ( S ) - ( 1 - ( p - M e t h o x y p h e n y l ) e t h y l ) a m i n o ] -
benzenephosphonic Acid Diethyl Ester (2b). Heating 1b (6.0 g,
19.6 mmol) with P(OEt)3 (6.86 mL, 40.0 mmol) and PdCl2 (0.21 g, 6
mol %) and workup as described for 2a gave 5.85 g (82%) of 2b as a
N-[(S)-1-(p-Methoxyphenyl)ethyl]-2-phosphinoaniline (3b).
A solution of 2b (5.0 g, 13.8 mmol) in Et2O (20 mL) was reduced
with LiAlH4 (1.57 g, 41.3 mmol) in Et2O (150 mL) and worked up as
described for 3a, yielding 2.61 g (73%) of a pale yellow, air-sensitive
solid. Single crystals of 3b were obtained at 0 °C from THF/hexane.
Crystal data are compiled in Table S1 (Supporting Information) and
1
selected bond lengths and angles in Figure 1. H NMR (CDCl3): δ
1.56 (d, 3J = 6.6 Hz, 3 H, CH3), 3.64 (d, 1JPH = 200.2 Hz, 2 H, PH2),
3.77 (s, 3 H, OCH3), 4.45 (br s, NH-superimposed with CH), 4.52 (q,
3J = 6.6 Hz, 1 H, NCH), 6.40 (dt, 3J = 8.3, J ≈ 1 Hz, 1 H, 6-H), 6.60
pale yellow viscous oil. 1H NMR (CDCl3): δ 1.21 (td, 3J = 7.1, 4JPH
≈
3
1 Hz, 6 H, CH3), 1.41 (d, J = 6.4 Hz, 3 H, CH3), 3.60 (s, 3 H,
3
3
4
4
OCH3), 3.99 (m, 4 H, OCH2), 4.34 (quin, J = 6.4 Hz, 1 H, NCH),
(tt, J = 7.5, 7.2, J ≈ JPH ≈ 1.1 Hz, 1 H, 4-H), 6.85 (m, 2 H, m-H),
3
4
3
3
4
5
6.30 (br t, J ≈ JPH = 8.1, 7.5 Hz, 1 H, 3-H), 6.45 (tdd, J = 7.5, 7.3,
4JPH = 3.3, 4J = 0.6 Hz, 1 H, 5-H), 6.70 (m, 2 H, m-H), 6.97 (br d, J =
5.7, 1 H, NH), 7.03 (br t, 3J = 8.3, 7.3 Hz, 1 H, 4-H), 7.15 (m, 2 H, o-
7.12 (tdd, J = 8.3, 7.4, J = 1.3, JPH ≈ 0.6 Hz, 1 H, 5-H), 7.25 (m, 2
3
3
4
H, o-H), 7.48 (ddd, JPH = 12.5, J = 7.4, J = 1.3 Hz, 1 H, 3-H).
13C{1H} NMR (CDCl3): δ 25.20 (s, CH3), 52.91 (s, OCH3), 55.23 (s,
NCH), 110.30 (d, 1J = 10.6 Hz, Cq-2), 111.20 (s, C-6), 114.06 (s, 2 C-
H), 7.44 (ddd, JPH = 14.8, J = 7.6, J = 1.7 Hz, 1 H, 6-H). 13C{1H}
NMR (CDCl3): δ 16.00 (d, 3J = 6.6 Hz, CH3), 24.84 (s, CH3), 52.05
(s, NCH), 54.81 (s, OCH3), 61.67 (d, 2J = 2.7 Hz, OCH2), 107.45 (d,
1J = 183.2 Hz, Cq-1), 112.12 (d, 3J = 12.0 Hz, C-3), 113.69 (s, 2 C-m),
3
3
4
3
m), 116.73 (d, J = 13.2 Hz, C-4), 126.77 (s, 2 C-o), 131.22 (s, C-5),
2
136.73 (s, Cq-i), 138.11 (d, J = 33.2 Hz, C-3), 149.54 (s, Cq-1),
158.54 (s, Cq-p). 31P{1H} NMR (CDCl3): δ −153.4. MS (90 °C): m/z
(%) 260 (1.4), 259 (10) [M]+, 244 (2), 153 (6), 136 (15), 135 (100).
HRMS (ESI in MeOH + FA): calcd for [M + H]+ 260.1199; found
260.1200. Anal. Calcd for C15H18NOP (259.28): C, 69.48; H, 7.00; N,
5.40. Found C, 69.53; H, 7.02; N, 5.42.
115.08 (d, 3J = 13.3 Hz, C-5), 126.46 (s, 2 C-o), 133.05 (d, 2J = 8.0 Hz,
C-6), 133.65 (d, 4J = 2.2 Hz, C-4), 136.74 (s, Cq-i), 150.71 (d, 2J = 9.3
Hz, Cq-2), 158.18 (s, Cq-p). 31P{1H} NMR (CDCl3): δ 21.8. MS (90
°C): m/z (%) 363 (8) [M]+, 348 (26), 299 (14), 257 (16), 242 (100).
HRMS (ESI in MeOH + FA): C19H26NO4P (363.39), calcd for [M +
H]+ 364.1672; found 364.1672; calcd for [M + Na]+ 386.1492; found
386.1492.
N-([(S)-1-(p-Methylphenyl)ethyl]-2-phosphinoaniline (3c). A
solution of 2c (3.9 g, 11.2 mmol) in Et2O (20 mL) was reduced with
LiAlH4 (1.25 g, 33 mmol) in Et2O (150 mL) and worked up as
described for 3a to give 2.01 g (74%) of pale yellow, air-sensitive 3c.
2-[(S)-(1-(p-Methylphenyl)ethyl)amino]benzenephosphonic
Acid Diethyl Ester (2c). Heating 1c (4.42 g, 15.2 mmol) with
P(OEt)3 (5.14 mL, 4.98 g, 30.0 mmol) and PdCl2 (0.16 g, 6 mol %)
and workup as described for 2a (elution with hexane/EtOAc (10%))
furnished 4.23 g (80%) of 2c as a pale yellow oil. 1H NMR (CDCl3): δ
3
1H NMR (CDCl3): δ 1.57 (d, J = 6.4 Hz, 3 H, CH3), 2.31 (s, 3 H,
CH3), 3.66 (d, 1JPH = 200.2 Hz, 2 H, PH2), 4.53 (q, 3J = 6.6 Hz, 1 H,
NCH), ca. 4.5 (vbr s, 1 H, NH superimposed with CH), 6.41 (d, 3J =
3
8.3 Hz, 1 H, 6-H), 6.60 (br t, J = 7.5, 7.2 Hz, 1 H, 4-H), 7.06−7.13
3
4
3
(superimposed m, 1 H, 5-H), 7.11 (m, 2 H, o- or m-H), 7.23 (m, 2 H,
1.36 (td, J = 7.1, JPH ≈ 1 Hz, 6 H, CH3), 1.56 (d, J = 6.8 Hz, 3 H,
CH3), 2.32 (s, 3 H, p-CH3), 4.13 (m, 4 H, OCH2), 4.49 (quin, 3J = 6.2
Hz, 1 H, NCH), 6.45 (t, 3J ≈ 4JPH ≈ 8.1, 7.5 Hz, 1 H, 3-H), 6.60 (tdd,
3J = 7.5, 7.3, 4JPH = 3.3, 4J = 0.9 Hz, 1 H, 5-H), 7.12 (m, 2 H, o- or m-
H), 7.18 (tt, 3J = 8.4, 7.2, 4J ≈ 5JPH ≈ 1.3 Hz, 1 H, 4-H), 7.26 (m, 2 H,
3
3
4
m- or o-H), 7.47 (ddd, JPH = 12.3, J = 7.4, J = 1.5 Hz, 1 H, 3-H).
13C{1H} NMR (CDCl3): δ 21.04 (s, p-CH3), 25.06 (s, CH3), 53.39 (s,
NCH), 110.50 (d, J = 4.0 Hz, Cq-2), 111.42 (d, J = 2.7 Hz, C-6),
1
3
3
116.93 (d, J = 10.6 Hz, C-4), 125.67 (s, 2 C-o), 129.36 (s, 2 C-m),
131.19 (s, C-5), 136.55 (s, Cq-p), 138.09 (d, 2J = 33.1 Hz, C-3), 141.51
(s, Cq-i), 149.31 (s, Cq-1). 31P{1H} NMR (CDCl3): δ −153.3. HRMS
(ESI in MeOH + FA): C15H18NP (243.28), calcd for [M + H]+
244.1250; found 244.1252.
3
3
4
m- or o-H), 7.46 (ddd, JPH = 14.7, J = 7.7, J = 1.7 Hz, 1 H, 6-H),
7.13 (br d, J = 7.6 Hz, 1 H, NH). 13C{1H} NMR (CDCl3): δ 16.21 (d,
3J = 6.6 Hz, CH3), 20.95 (s, p-CH3), 24.92 (s, CH3), 52.83 (s, NCH),
61.91 (d, 2J = 4.0 Hz, OCH2), 107.87 (d, 1J = 183.1 Hz, Cq-1), 112.54
(d, 3J = 11.9 Hz, C-3), 115.53 (d, 3J = 14.6 Hz, C-5), 125.61 (s, 2 C-o),
1-[(S)-1-Phenylethyl]-1H-1,3-benzazaphosphole (4a). Excess
dimethylformamide dimethylacetale (DMFA; 14.7 mL, 110 mmol)
and ClSiMe3 (1.5 mL, 11.8 mmol) were added to 3a (2.50 g, 10.9
mmol). After this mixture was heated for 24 h at 50 °C, unconverted
DMFA and ClSiMe3 were evaporated under vacuum. The residue was
dissolved in diethyl ether and treated with degassed 10% aqueous
sulfuric acid at room temperature to extract N-basic impurities. The
ether phase was washed with water, dried with Na2SO4, and separated.
Removal of the solvent under vacuum provided 1.9 g (73%) of 4a as a
viscous oil. 1H NMR (CDCl3): δ 1.87 (d, 3J = 6.8 Hz, 3 H, CH3), 5.76
(q, 3J = 6.8 Hz, 1 H, NCH), 7.00 (m, 3J = 8.1 Hz, 2 H, o-H), 7.07 (tdd,
2
129.22 (s, 2 C-m), 133.28 (d, J = 7.7 Hz, C-6), 133.86 (br, C-4),
136.29 (s, Cq-p), 141.77 (s, Cq-i), 150.66 (d, 2J = 9.3 Hz, Cq-2).
31P{1H} NMR (CDCl3): δ 21.8. MS (90 °C): m/z (%) 348 (3.0), 347
(12.1) [M]+, 333 (9.3), 332 (41). HRMS (ESI in MeOH + FA):
C19H26NO3P (347.39), calcd for [M + H]+ 348.1723; found 348.1724.
N-[(S)-1-Phenylethyl]-2-phosphinoaniline (3a). A solution of
2a (5.0 g, 15.0 mmol) in Et2O (20 mL) was added dropwise at −10 °C
to LiAlH4 pellets (1.71 g, 45.0 mmol) in Et2O (150 mL). After it was
stirred for 3 d at room temperature to complete the reduction, the
mixture was cooled to ca. 10 °C, and water was added dropwise to
decompose excess hydride. After the evolution of H2 ceased, the
addition of water was stopped (to avoid formation of a slurry), and the
precipitate was filtered off and thoroughly washed with ether. The
filtrate was dried over Na2SO4 and separated. Evaporation of the
5
3J = 7.9, 7.2, 4J = 1.8, JPH = 0.9 Hz, 1 H, 5-H), 7.11−7.22
3
(superimposed m, 3 H, m-H, p-H), 7.20 (superimposed tt, J = 8.1,
7.2, 4J = 1.5, 5JPH = 0.9 Hz, 1 H, 6-H), 7.41 (br d, 3J = 8.3 Hz, 1 H, 7-
3
3
4
5
H), 8.01 (dddd, J = 7.1, JPH = 4.2, J = 1.5, J = 0.6 Hz, 1 H, 4-H),
8.62 (d, JPH = 37.8 Hz, 1 H, 2-H). 13C{1H} NMR (CDCl3): δ 21.74
2
1
solvent gave 2.54 g (74%) of a pale yellow, highly air-sensitive oil. H
(s, CH3), 57.78 (d, 3J = 2.7 Hz, NCH), 113.10 (s, C-7), 120.22 (d, 3J =
10.6 Hz, C-5), 124.59 (d, 4J = 2.7 Hz, C-6), 125.86 (s, 2 C-o), 127.74
3
1
NMR (CDCl3): δ 1.47 (d, J = 6.8 Hz, 3 H, CH3), 3.55 (d, JPH
=
199.6 Hz, 2 H, PH2), 4.40 (br s, NH superimposed with CH), 4.45 (q,
2
(s, C-p), 128.83 (s, 2 C-m), 129.46 (d, J = 21.3 Hz, C-4), 141.38 (s,
3J = 6.8 Hz, 1 H, NCH), 6.28 (br d, 3J = 8.3 Hz, 1 H, 6-H), 6.50 (tt, 3J
Cq-i), 142.49 (d, 1J = 39.8 Hz, Cq-3a), 142.51 (d, 2J = 5.3 Hz, Cq-7a),
157.58 (d, 1J = 53.1 Hz, C-2). 31P{1H} NMR (CDCl3): δ 73.5. MS (80
°C): m/z (%) 240 (2), 239 (11) [M]+, 163 (2), 148 (2), 135 (45), 105
(100). HRMS (ESI in MeOH + FA): C15H14NP (239.25), calcd for
[M + H]+ 240.0937; found 240.0940.
= 7.4, 4J ≈ 4JPH ≈ 1.2 Hz, 1 H, 4-H), 6.99 (tt, 3J = 8.3, 7.8, 4J ≈ 5JPH
≈
=
3
0.9 Hz, 1 H, 5-H), 7.06−7.26 (m, 5 H, phenyl-H), 7.38 (ddd, JPH
12.4, 3J = 7.5, 4J = 1.7 Hz, 1 H, 3-H). 13C{1H} NMR (CDCl3): δ 25.15
1
(s, CH3), 53.46 (s, NCH), 110.26 (d, J = 10.6 Hz, Cq-2), 111.16 (s,
C-6), 116.78 (d, 3J = 11.9 Hz, C-4), 125.65 (s, 2 C-o), 126.92 (s, C-p),
1-[(S)-1-(p-Methoxyphenyl)ethyl]-1H-1,3-benzazaphosphole
(4b). Reaction of 3b (0.90 g, 3.47 mmol) with DMFA (4.6 mL, 34.4
mmol) in the presence of ClSiMe3 (0.48 mL, 3.78 mmol) and workup
as described for 4a furnished 0.75 g (80%) of 4b as a pale yellow solid.
Single crystals were grown from a concentrated THF solution
overlayered with hexane. Crystal data are compiled in Table S1
2
128.64 (s, 2 C-m), 131.19 (s, C-5), 138.07 (d, J = 33.2 Hz, C-3),
144.64 (s, Cq-i), 149.40 (s, Cq-1). 31P{1H} NMR (CDCl3): δ −153.3.
MS (90 °C): m/z (%) 230 (2), 229 (14) [M]+, 214 (6), 125 (17), 105
(100). HRMS (ESI in MeOH + FA): C14H16NP (229.26), calcd for
[M + H]+ 230.1093; found 230.1093.
811
dx.doi.org/10.1021/om401184n | Organometallics 2014, 33, 804−816

Organometallics
Article
(Supporting Information) and selected bond lengths and angles in
mmol) was added dropwise at −70 °C to a mixture of 4b (43 mg, 0.16
mmol) and KOtBu (21.3 mg, 0.19 mmol) in Et2O (10 mL). Stirring
was continued while the mixture was warmed slowly to −30 °C (5 h).
Then it was cooled again to −70 °C, ClSiMe3 (0.03 mL, 0.24 mmol)
was added, and the mixture was warmed to room temperature. After
the mixture was stirred overnight, volatile components were removed
under vacuum. The residue was extracted with diethyl ether and the
solvent removed from the filtrate, affording 41 mg of a pale yellow oil.
This was identified by NMR and mass spectrometric data as a mixture
of 7b (65 mol %) and 7d (20 mol %) and small amounts of residual 4b
(6 mol %) and diastereoisomeric addition products 10b (4 + 5 mol
%). The NMR data of 4b and 10b are in accordance with those given
1
3
Figure 2. H NMR (CDCl3): δ 1.93 (d, J = 6.8 Hz, 3 H, CH3), 3.75
(s, 3 H, OCH3), 5.83 (q, 3J = 6.9 Hz, 1 H, NCH), 6.82 (m, 2 H, m-H),
7.05 (m, 2 H, o-H), 7.16 (tm, 3J = 7.9, 7.0, 4JPH = 1.9, 4J = 1 Hz, 1 H,
5-H), 7.31 (tt, 3J = 8.1, 7.2, 4J ≈ 5JPH = 1.4 Hz, 1 H, 6-H), 7.54 (br d, 3J
3
3
4
5
= 8.1 Hz, 1 H, 7-H), 8.09 (ddd, J = 8.1, JPH = 4.1, J = 1.8, J = 0.6
Hz, 1 H, 4-H), 8.65 (d, JPH = 37.8 Hz, 1 H, 2-H). 13C{1H} NMR
2
3
(CDCl3): δ 21.64 (s, CH3), 55.23 (s, OCH3), 57.27 (d, J = 2.7 Hz,
NCH), 113.10 (s, C-7), 114.17 (s, 2 C-m), 120.19 (d, 3J = 12.0 Hz, C-
5), 124.56 (d, 4J = 2.6 Hz, C-6), 127.27 (s, 2 C-o), 129.50 (d, 2J = 21.3
Hz, C-4), 133.30 (s, Cq-i), 142.46 (d, 2J = 5.4 Hz, Cq-7a), 142.58 (d, 1J
1
= 39.8 Hz, Cq-3a), 157.61 (d, J = 53.1 Hz, C-2), 159.09 (s, Cq-p).
1
31P{1H} NMR (CDCl3): δ 73.2. MS (90 °C): m/z (%) 269 (7) [M]+,
above and below, respectively. Data for 7b are as follows. H NMR
(CDCl3): δ 0.49 (d, 4JPH = 1.5 Hz, 9 H, SiMe3), 2.04 (d, 3J = 7.2 Hz, 3
H, CH3), 3.79 (s, 3 H, OCH3), 6.03 (q, 3J = 7.2 Hz, 1 H, NCH), 6.72
(d, 3J = 8.3 Hz, 1 H, 7-H), 6.85 (mAA′, 2 H, o- or m-H), 7.01−7.21 (m,
m- or o-H, 5-H, 6-H, 7-H), 8.02−8.08 (m, 4-H). 13C{1H} NMR
163 (41), 148 (40), 135 (100). HRMS (ESI in MeOH+FA): calcd for
[M + H]+ 270.1042; found 270.1047; calcd for [M + Na]+ 292.0862;
found 292.0868. Anal. Calcd for C16H16NOP (269.28): C, 71.37; H,
5.99; N, 5.20. Found: C, 71.58; H, 6.38; N, 5.51.
3
(CDCl3): δ 0.40 (d, J = 8.0 Hz, SiMe3), 17.71 (s, CH3), 55.22 (s,
NMR Detection of Intermediate Phosphaalkene 5b and a
Symmetric 1,3-Diphosphetane as Minor Side Products in the
Synthesis of 4b without Catalyst. A mixture of 3b (2.5 g, 9.64
mmol) and DMFA (1.55 mL, 11.6 mmol) was heated for 2 days at 50
°C. NMR monitoring displayed 31P resonances at δ 73.2 (4b), 65.0 (Z-
5b), 43.9 (E-5b), and −27.0 (1,3-diphosphetane), with relative
intensities 55:5:20:25. After the mixture was heated for a further 3
days at 50 °C, unconverted DMFA was removed under vacuum and
the crude product worked up as described for 4a to give 2.1 g (81%) of
4b. The NMR data of the latter are in good accordance with the values
given above. The intermediate 5b and the 1,3-diphosphetane side
product were identified by characteristic proton NMR data. Data for
3
OCH3), 60.70 (135DEPT d, J = 2.2 Hz, NCH), 114.10 (s, 2 C-m),
116.10 (s, C-7), 119.37 (d, 3J = 10.6 Hz, C-5), 124.10 (d, 4J = 2.7 Hz,
C-6), 127.04 (s, 2 C-o), 129.02 (d, 2J = 19.9 Hz, C-4), 132.17 (s, Cq-i),
144.66 (d, 2J = 4.0 Hz, Cq-7a), 144.79 (d, 1J = 42.5 Hz, Cq-3a), 158.79
1
(s, Cq-p), 180.84 (d, J = 73.0 Hz, Cq-2). 31P{1H} NMR (CDCl3): δ
117.9. HRMS (ESI in MeOH + FA): C19H24NOPSi (341.46), calcd
for [M + H]+ 342.1438; found 342.1440. Data for 7d are as follows. 1H
NMR (CDCl3): δ 0.21 (s, 9 H, 3′-SiMe3), 3.77 (s, 3 H, OCH3), 6.72
(d, 3J = 8.1 Hz, 5′-H); SiMe3 doublet, MeCH, and aryl signals
superimposed by those of 7b. 13C{1H} NMR (CDCl3): δ −1.05 (s,
SiMe3), 0.44 (d, 3J = 9.3 Hz, SiMe3), 17.86 (s, CH3), 55.04 (s, OCH3),
60.94 (135DEPT s, NCH), 109.51 (s, C-5′), 113.11 (s, Cq-3′), 116.19
1
3
5b are as follows. H NMR (CDCl3): δ 1.52 (d, J = 6.6 Hz, 3 H,
4
3
4
CH3), 3.07 (d, JPH = 3.3 Hz, 6 H NMe2), 3.78 (s, 3 H, OCH3), 4.47
(s, C-7), 119.28 (d, J = 10.6 Hz, C-5), 124.01 (d, J = 2.6 Hz, C-6),
(superimposed q, 3J ≈ 6.4 Hz, 1 H, NCH), 6.06 (br d, 1 H, NH), 6.30
(br dd, 3J = 7.8, 4J = 2.8 Hz, 1 H, 6-H), 6.57 (td, 3J = 7.4, 4J = 1.0 Hz, 1
H, 4-H), 6.83 (superimposed m, 2 H, m-H), 6.97 (td, 3J = 7.6, 4J = 1.5
Hz, 1 H, 5-H), 7.27−7.32 (m, 3 H, o-H, 4-H), 8.80 (d, 2JPH = 13.9 Hz,
2
128.46 (s, C-6′), 128.95 (d, J = 21.2 Hz, C-4), 131.49 (s, Cq-1′),
132.17 (superimposed s, C-2′), 144.77 (d, 2J = 4 Hz, Cq-7a), ca. 144.8
(d, Cq-3a, noise level), 164.89 (s, Cq-4′), 180.81 (d, 1J = 73 Hz, Cq-2,
noise level). 31P{1H} NMR (CDCl3): δ 117.5. MS (90 °C): m/z (%)
414 (0.8) [M+ (7d)], 342.5 (0.7), 341.6 (3) [M+ (7b)], 327 (1), 235
(2), 207 (12), 164 (2), 147 (7), 135 (100).
2
0.9 H, E-PCH), 8.53 (d, JPH = 37.8 Hz, 0.1 H, Z-PCH acyclic).
1
Data for the 1,3-diphosphetane side product are as follows. H NMR
(CDCl3): δ 1.51 (d, 3J = 6.9 Hz, 6 H, CH3), 2.42 (s, 12 H NMe2), 3.77
Detection of 1-[(S)-1-(p-Methoxyphenyl)ethyl]-1H-1,3-ben-
zazaphosphole-2-carboxylic Acid (8b) and 1-[(S)-1-(3-Carboxy-
4-methoxyphenyl)ethyl]-1H-1,3-benzazaphosphole-2-carbox-
ylic Acid (8d). A solution of tBuLi in hexane (0.33 mL, 0.53 mmol)
was added dropwise at −70 °C to a mixture of 4b (94 mg, 0.35 mmol)
and KOtBu (47 mg, 0.42 mmol) in diethyl ether (20 mL). Stirring was
continued while the mixture was warmed slowly to −30 °C (5 h).
Then it was cooled again to −70 °C and a slow stream of dry CO2
bubbled in over 40 min (color change from orange to yellow). The
mixture was warmed slowly to room temperature overnight. ClSiMe3
(0.07 mL, 0.55 mmol) was added at −70 °C, and the mixture was
stirred with warming to room temperature and filtered. Removal of the
solvent provided a pale yellow solid, which was treated with excess
MeOH (20 mL) for desilylation. MeOH and Me3SiOMe were
removed under vacuum, the residue was dissolved in diethyl ether, and
N-basic impurities were extracted with degassed 10% aqueous H2SO4.
The ether phase was washed with water and dried over Na2SO4.
Removal of ether under vacuum furnished 81 mg of a yellow solid,
identified by conclusive NMR data as a mixture of 8b (34 mol %, 25
2
(s, 6 H, OCH3), 3.89 (t, JPH = 4.0 Hz, 2 H, P2CH), 4.46
(superimposed q, 3J ≈ 6.4 Hz, 2 H, NCH), 5.03 (br t, 3J ≈ 4JPH ≈ 5.4
Hz, 2 H, NH), 6.35 (br d, 3J ≈ 7.5, 2 H, 6-H), 6.62 (superimposed br
3
t, J ≈ 7.5 Hz, 2 H, 4-H), 6.83 (superimposed m, 4 H, m-H), 6.99
(superimposed t, 3J ≈ 7.5 Hz, 2 H, 5-H), 7.27−7.32 (m, 6 H, o-H, H-
4). Evidence for the diphosphetane nature is given by the triplet at
δ(1H) 3.89 with small coupling to two P atoms, characteristic for
symmetric 2,4-diamino-1,3-diphosphetanes.24,25 For 2,4-bis-
(dimethylamino)-1,3-diphenyl-1,3-diphosphetane, δ(1H) 3.69 (t, JPH
2
= 3.4 Hz), additional evidence was provided by crystal structure
analysis.24
b
1-[(S)-1-(p-Methylphenyl)ethyl]-1H-1,3-benzazaphosphole
(4c). Reaction of 3c (1.95 g, 8.02 mmol) with DMFA (10.7 mL, 80.2
mmol) in the presence of ClSiMe3 (1.12 mL, 8.82 mmol) and workup
1
as described for 4a furnished 1.53 g (75%) of 4c as a viscous oil. H
NMR (CDCl3): δ 1.94 (d, 3J = 7.2 Hz, 3 H, CH3), 2.29 (s, 3 H, CH3),
5.83 (q, 3J = 7.2 Hz, 1 H, NCH), 6.99 (m, 2 H, o- or m-H), 7.09 (m, 2
H, m- or o-H), 7.15 (tdd, 3J = 8.1, 7.2, 4JPH = 1.9, 4J = 0.9 Hz, 1 H, 5-
H), 7.30 (tt, 3J = 8.3, 7.2, 4J ≈ 5JPH ≈ 1.4 Hz, 1 H, 6-H), 7.52 (br d, 3J
= 8.1 Hz, 1 H, 7-H), 8.09 (dddd, 3J = 8.1, 3JPH = 4.2, 4J = 1.1, 5J = 0.7
1
mg) and 8d (66 mol %, 56 mg). Data for 8b are as follows. H NMR
(600 MHz, d8-THF): δ 1.94 (d, 3J = 7.2 Hz, 3 H, CH3), 3.72 (s, 3 H,
OCH3), 6.82 (mAA′, 2 H, m-H), 7.00 (superimposed mBB′ and q, 3 H,
o-H, NCH), 7.05 (superimposed tt, 1 H, 5-H), 7.13 (br t, 3J = 8.4, 7.2
2
Hz, 1 H, 4-H), 8.68 (d, JPH = 37.8 Hz, 1 H, 2-H). 13C{1H} NMR
3
(CDCl3): δ 21.00 (s, CH3), 21.71 (s, CH3), 57.59 (d, J = 2.7 Hz,
3
3
NCH), 113.13 (s, C-7), 120.19 (d, 3J = 11.9 Hz, C-5), 124.58 (d, 4J =
2.7 Hz, C-6), 125.89 (s, 2 C-o), 129.48 (d, 2J = 21.3 Hz, C-4), 129.52
(s, 2 C-m), 137.53, 138.38 (2s, Cq-p, Cq-i), 142.53 (d, 2J = 5.3 Hz, Cq-
Hz, 1 H, 6-H), 8.00 (dd, J = 7.8, JPH = 4.8 Hz, 1 H, 4-H); 7-H
superimposed by signals of 8d in the range 7.24−7.31. 13C{1H} NMR
(CD3OD): δ 17.55 (s, CH3), 55.63 (s, OCH3), 56.96 (d, 3J = 4.0 Hz,
3
1
1
NCH), 114.93 (s, 2 C-m), 118.06 (s, C-7), 121.43 (d, J = 13 Hz, C-
7a), 142.54 (d, J = 39.8 Hz, Cq-3a), 157.63 (d, J = 53.1 Hz, C-2).
5), 127.15 (d, 4J = 2.7 Hz, C-6), 128.42 (s, 2 C-o), 130.71 (d, 2J = 22.6
31P{1H} NMR (CDCl3): δ 73.1. HRMS (ESI in MeOH + FA):
2
C16H16NP (253.28), calcd for [M + H]+ 254.1093; found 254.1097.
Detection of 1-[(S)-1-(p-Methoxyphenyl)ethyl]-2-(trimethyl-
silyl)-1H-1,3-benzazaphosphole (7b) and 1-[(S)-1-(4-Methoxy-
3-(trimethylsilyl)phenyl)ethyl]-2-(trimethylsilyl)-1H-1,3-benza-
zaphosphole (7d). A solution of tBuLi in hexane (0.15 mL, 0.24
Hz, C-4), 134.06 (s, Cq-i), 145.31 (d, J = 7.5 Hz, Cq-7a), 160.21 (s,
Cq-p); Cq-3a, Cq-2 and COOH doublets at noise level. 31P{1H} NMR
(CD3OD): δ 122.05. Data for 8d are as follows. 1H NMR (600 MHz,
d8-THF): δ 1.97 (d, 3J = 7.2 Hz, 3 H, CH3), 3.84 (s, 3 H, OCH3), 7.07
3
(superimposed m, 1 H, 5-H), 7.08 (superimposed d, J ≈ 8 Hz, 1 H,
812
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Organometallics
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3
5′-H), 7.17 (t, 3J = 8.4 Hz, 1 H, 6-H), 7.23 (ddd, 3J = 8.4, 4J = 2.4, J =
0.6 Hz, 1 H, 6′-H), 7.29 (superimposed d (3J ≈ 8.4 Hz) and q, 2 H, 7-
(superimposed ddd, 3J = 7.6, JPH = 4.9, 4J = 1 Hz, 1 H, 4-HA).
13C{1H} NMR (C6D6): δ −1.56 (d, 3J = 8.0 Hz, SiMe3B), −0.73 (d, 3J
= 9.3 Hz, SiMe3A), 16.30 (s, CH3B), 20.34 (s, CH3A), 26.76 (d, J =
15.9 Hz, CMe3A), 26.90 (d, J = 15.9 Hz, CMe3B), 31.64 (d, J = 27.8
4
5
3
2
H, NCH), 7.76 (dd, J = 2.4, J = 0.7 Hz, 1 H, 2′-H), 8.02 (dd, J =
3
7.8, JPH = 4.2 Hz, 1 H, 4-H). 13C{1H} NMR (CD3OD): δ 17.44 (s,
2
1
3
1
1
CH3), 56.53 (s, OCH3), 56.54 (superimposed d, J = 2.7 Hz, NCH),
Hz, CMe3A), 31.93 (d, J = 29.2 Hz, CMe3B), 48.83 (d, J = 43.8 Hz,
3
PCHA), 53.90 (d, 1J = 43.8 Hz, PCHB), 58.76 (d, 3J = 2.7 Hz, NCHA),
113.60 (s, C-5′), 117.75 (s, C-7), 120.86 (s, Cq-3′), 121.58 (d, J =
4
3
13.3 Hz, C-5), 127.46 (d, J = 4.0 Hz, C-6), 130.47 (s, C-6′), 130.89
60.91 (d, J = 4.0 Hz, NCHB), 110.05 (s, C-7A), 112.58 (s, C-7B),
(d, 2J = 22.5 Hz, C-4), 133.20 (s, C-2′), 134.18 (s, Cq-1′), 143.92 (d, 1J
117.03 (d, 3J = 6.6 Hz, C-5B), 117.24 (d, 3J = 8.0 Hz, C-5A), 123.69 (d,
2
1J = 10.6 Hz, Cq-3A), 125.22 (d, J = 13.3 Hz, Cq-3aB), 127.40 (s, C-
1
= 37.1 Hz, Cq-3a), 145.21 (d, J = 7.9 Hz, Cq-7a), 159.57 (s, Cq-4′),
1
2
162.70 (d, J = 53.1 Hz, Cq-2), 166.82 (d, J = 22.6 Hz, 2-COOH),
169.40 (s, 3′-COOH). 31P{1H} NMR (CD3OD): δ 123.4.
pB), 127.53 (s, 2 C-oB), 127.60 (s, 2 C-oA), 127.68 (s, C-pA), 129.25 (s,
2 C-mA), 129.33 (s, 2 CH-mB), 130.32 (s, C-6B), 131.39 (s, C-6A),
132.45 (d, 2J = 22.5 Hz, C-4A), 132.86 (d, 2J = 22.6 Hz, C-4B), 143.84
(s, Cq-iB), 144.81 (s, Cq-iA), 153.00 (s, Cq-7aB), 155.97 (s, Cq-7aA).
31P{1H} NMR (C6D6): δ −4.6, −5.3 (intensity ratio 65:35%). MS
(3S/3R)-3-tert-Butyl-1-[(1S)-1-(p-methoxyphenyl)ethyl]-2,3-
dihydro-1H-1,3-benzazaphosphole (10b). A solution of tBuLi in
hexane (0.58 mL, 0.93 mmol) was added dropwise at −70 °C to 4b
(164 mg, 0.61 mmol) in Et2O/hexane (each 5 mL). The mixture was
warmed slowly to −30 °C (5 h). The resulting orange-red solution of
the lithium reagent was then quenched at −70 °C with methanol (10
mL). After the mixture was warmed to room temperature, the solvents
were removed under vacuum. Diethyl ether was added to the residue,
the insoluble part was filtered off, and ether was removed under
vacuum to give 159 mg of a pale yellow oil. NMR and HRMS data
indicate two diastereoisomers of 10b, A:B 58:29 mol % (by integration
of methyl protons), and 13 mol % of unconverted 4b: calcd yield of
(210 °C): m/z (%) 370.5 (0.5) [M+], 343 (0.9), 264 (4), 208 (12),
136 (15), 135 (100). HRMS (ESI in MeOH + FA): C22H32NPSi
(369.56), calcd for [M + H]+ 370.2114; found 370.2119.
3-tert-Butyl-1-[(1S)-1-(p-methoxyphenyl)ethyl]-2-(trimethyl-
silyl)-2,3-dihydro-1H-1,3-benzazaphosphole (11b). ClSiMe3 (30
μL, 0.24 mmol) was added to 4b (45.8 mg, 0.17 mmol) in Et2O/
hexane (5 mL each), followed by addition of a solution of tBuLi in
hexane (0.16 mL, 0.26 mmol) at −70 °C. The mixture was worked up
as described for 11a to give 50 mg (73%) of a pale yellow oil,
containing two diastereoisomers A and B of 11b, molar ratio 62:38%
(by integration of Me protons). 1H NMR (C6D6): δ 0.10 (d, 4JPH = 1.1
1
3
10b 142 mg, 71%. H NMR (C6D6): δ 0.88 (d, JPH = 12.1 Hz, 9 H,
CMe3B), 0.97 (d, 3JPH = 12.1 Hz, 9 H, CMe3A), 1.13 (d, 3J = 6.8 Hz, 3
H, CH3B), 1.33 (d, 3J = 7.2 Hz, 3 H, CH3A), 3.06 (dd, 2J = 12.6, 2JPH
=
=
=
Hz, 9 H, SiMe3A), 0.13 (d, 4JPH = 1.1 Hz, 9 H, SiMe3B), 0.92 (d, 3JPH
=
2
2
12.1 Hz, 9 H, CMe3A), 0.94 (d, 3JPH = 11.7 Hz, 9 H, CMe3B), 1.53 (d,
3J = 7.2 Hz, 3 H, CH3A), 1.54 (d, 3J = 7.2 Hz, 3 H, CH3B), 3.25 (d, 2JPH
= 4.2 Hz, 1 H, PCHcis‑B), 3.305 (s, 3 H, OCH3A), 3.313 (s, 3 H,
OCH3B), 3.60 (d, 2JPH = 4.5 Hz, 1 H, PCHcis‑A), 4.44 (q, 3J = 6.8 Hz, 1
H, NCHB), 4.45 (q, 3J = 6.9 Hz, 1 H, NCHA), 6.28 (d br, 3J = 8.3 Hz,
3.6 Hz, 1 H, PCHcis to tBu‑B), 3.21 (superimposed dd, J = 12.9, JPH
22 Hz, 1 H, PCHtrans‑B or A), 3.29 (superimposed dd, J = 12.9, JPH
2
2
22.8 Hz, 1 H, PCHtrans‑A or B), 3.29 (s, 3 H, OCH3A), 3.31 (s, 3 H,
2
OCH3B), 3.42 (d, 2J = 12.6, JPH = 3.6 Hz, 1 H, PCHcis‑A), 4.70
(superimposed q, 3J ≈ 7 Hz, 1 H, NCHA), 4.71 (superimposed q, 3J ≈
7 Hz, 1 H, NCHB), 6.42 (br d, 3J = 7.9 Hz, 1 H, 7-HA), 6.47 (br d, 3J =
8.3 Hz, 1 H, 7-HB), 6.66 (m, 2 H, m-HA), 6.62−6.75 (superimposed
m, 2 H, 5-HAB), 6.79 (m, 2 H, m-HB), 6.97 (m, 2 H, o-HA), 7.13 (m,
superimposed, 2 H, o-HB), 7.10−7.23 (superimposed m, 6-HAB),
7.40−7.47 (superimposed m, 4-HAB). 13C{1H} NMR (C6D6): δ 13.50
3
1 H, 7-HB), 6.32 (d br, J = 8.3 Hz, 1 H, 7-HA), 6.58 (superimposed
tdd, J = 7.2, JPH = 2.2, J = 1.1 Hz, 1 H, 5-HB), 6.63 (superimposed
tdd, J = 7.2, JPH = 2.2, J = 1.1 Hz, 1 H, 5-HA), 6.78 (m, 2 H, m-
CHA), 6.79 (m, 2 H, m-CHB), 6.92 (ddd, J = 8.4, 7.1, J = 1.5 Hz, 1
3
4
4
3
4
4
3
4
3
4
H, 6-HB), 7.04 (ddd, J = 8.3, 7.2, J = 1.1 Hz, 1 H, 6-HA), 7.17
(superimposed m, 2 H, o-CHA), 7.24 (m, 2 H, o-CHB), 7.38−7.46 (m,
2 H, 4-HAB). 13C{1H} NMR (C6D6): δ −1.51 (d, 3J = 8.0 Hz, SiMe3B),
2
(s, CH3B), 18.43 (s, CH3A), 27.08 (superimposed d, J = 15.9 Hz,
2
1
CMe3A), 27.38 (superimposed d, J = 14.6 Hz, CMe3B), 30.91 (d, J =
1
1
3
18.6 Hz, CMe3B), 31.13 (d, J = 19.9 Hz, CMe3A), 42.92 (d, J = 21.2
Hz, PCH2B), 43.43 (d, 1J = 21.2 Hz, PCH2A), 54.07 (s, NCHA), 54.42
(s, NCHB), 55.40 (s, OCH3AB), 108.82 (s, C-7A), 108.94 (s, C-7B),
114.67 (s, 2 C-mB), 114.81 (s, 2 C-mA), 117.35 (d, 3J = 6.6 Hz, C-5A),
117.83 (d, 3J = 8.0 Hz, C-5B), 124.61 (d, 1J = 11.9 Hz, Cq-3aA), 125.50
(d, 1J = 13.3 Hz, Cq-3B), 128.97 (135DEPT s, 2 C-oA), 129.68 (s, 2 C-
−0.69 (d, J = 9.3 Hz, SiMe3A), 16.28 (s, CH3B), 20.42 (s, CH3A),
26.77 (d, 2J = 14.6 Hz, CMe3A), 26.92 (d, 2J = 15.9 Hz, CMe3B), 31.67
(d, 1J = 29.2 Hz, CMe3A), 31.94 (d, 1J = 27.9 Hz, CMe3B), 48.82 (d, 1J
= 43.7 Hz, PCHA), 53.71 (d, 1J = 43.8 Hz, PCHB), 55.42 (s, OCH3AB),
3
3
58.23 (d, J = 2.7 Hz, NCHA), 60.35 (d, J = 4.0 Hz, NCHB), 110.03
(s, C-7A), 112.52 (s, C-7B), 114.69 (s, C-mA), 114.79 (s, C-mB), 116.94
2
3
3
1
oB), 131.43 (br s, C-6A and C-6B), 133.30 (d, J = 22.6 Hz, C-4A),
133.39 (d, J = 21.2 Hz, C-4B), 134.03 (s, Cq-iA), 134.61 (s, Cq-iB),
(d, J = 8.0 Hz, C-5B), 117.12 (d, J = 6.6 Hz, C-5A), 123.68 (d, J =
11.9 Hz, Cq-3A), 125.20 (d, 1J = 13.3 Hz, Cq-3aB), 128.64 (135DEPT s,
C-oB), 128.70 (135DEPT s, C-oA), 130.32 (s, C-6B), 131.37 (s, C-6A),
132.47 (d, 2J = 22.6 Hz, C-4A), 132.86 (d, 2J = 22.6 Hz, C-4B), 135.50
(s, Cq-iB), 136.54 (s, Cq-iA), 153.10 (s, Cq-7aB), 156.04 (s, Cq-7aA),
159.52 (s, Cq-pB), 159.77 (s, Cq-pA). 31P{1H} NMR (C6D6): δ −4.7,
−5.2 (intensity ratio 60:40%). MS (210 °C): m/z (%) 399.5 (0.5)
[M+], 343 (1), 264 (4), 208 (12), 136 (15), 135 (100).
3-tert-Butyl-1-[(1S)-1-phenylethyl]-2,3-dihydro-1H-1,3-ben-
zazaphosphole-2-carboxylic Acid (12a). A solution of tBuLi in
hexane (0.60 mL, 0.96 mmol) was added dropwise at −70 °C to 4a
(154 mg, 0.65 mmol) in Et2O/hexane (each 10 mL). After slow
warming to −30 °C (5 h), a stream of CO2 was introduced at −70 °C
for 20 min (color change from orange-red to yellow). The mixture was
warmed slowly to room temperature overnight and cooled again to
−70 °C, and ClSiMe3 (0.13 mL, 1.02 mmol) was added. After it was
warmed to room temperature, the mixture was filtered, the residue was
washed with ether, and the solvent was removed under vacuum,
yielding a yellow solid. Treatment with methanol (5 mL) and
evaporation of the solvent and MeOSiMe3 under vacuum furnished
160 mg of a yellow solid. The NMR spectra displayed three
diastereoisomers of 12a in a A:B:C ratio of 41:31:20 and traces of
the two diastereoisomers of 10a, identified by characteristic
phosphorus resonances (δ(31P) −12.8, −12.2) similar to those of
10b (see above): corrected yield of 12a 150 mg (67%). NMR data of
the major diastereoisomers A and B (most signals of C are
2
155.20 (br s, Cq-7aA), 155.32 (br s, Cq-7aB), 159.78 (s, Cq-pA), 160.00
(s, Cq-pB). 31P{1H} NMR (C6D6): δ −13.4 (B), −14.0 (A). HRMS
(ESI in MeOH + FA): C20H26NOP (327.40), calcd for [M + H]+
328.1825; found 328.1825.
3-tert-Butyl-1-[(1S)-1-phenylethyl]-2-(trimethylsilyl)-2,3-di-
hydro-1H-1,3-benzazaphosphole (11a). ClSiMe3 (38 μL, 0.30
mmol) was added to 4a (45.5 mg, 0.19 mmol) in Et2O/hexane (5 mL
each), followed by addition of a solution of tBuLi in hexane (0.18 mL,
0.29 mmol) at −70 °C. The mixture was slowly warmed to room
temperature, stirred overnight, filtered, and washed with ether.
Removal of the solvent under vacuum gave 50 mg (71%) of a pale
yellow oil, containing two diastereoisomers A and B of 11a, molar ratio
65:35% (by integration of Me protons). 1H NMR (C6D6): δ 0.078 (d,
4
4JPH = 1.1 Hz, 9 H, SiMe3A), 0.085 (d, JPH = 1.1 Hz, 9 H, SiMe3B),
3
3
0.90 (d, JPH = 12.1 Hz, 9 H, CMe3A), 0.93 (d, JPH = 11.7 Hz, 9 H,
3
3
CMe3B), 1.52 (d, J = 7.2 Hz, 3 H, CH3A), 1.53 (d, J = 7.2 Hz, 3 H,
CH3B), 3.22 (d, 2JPH = 4.2 Hz, 1 H, PCHcis‑B), 3.58 (d, 2JPH = 4.9 Hz, 1
H, PCHcis‑A), 4.23, 4.45 (2 superimposed q, 2 H, NCHA,B), 6.22
(superimposed d, 3J > 8.1 Hz, 1 H, 7-HB), 6.25 (d br, 3J > 7.9 Hz, 1 H,
7-HA), 6.57 (superimposed tdd, 3J = 7.2, 4JPH = 2.3, 4J = 1 Hz, 1 H, 5-
3
4
4
HB), 6.61 (superimposed tdd, J = 7.2, JPH = 2.3, J = 1 Hz, 1 H, 5-
HA), 6.87 (td, 3J = 8.3, 7.2, 4J = 1.5 Hz, 1 H, 6-HB), 6.99 (td, 3J = 8.3,
7.2, 4J = 1.5 Hz, 1 H, 6-HA), 7.02−7.35 (m, phenyl-HAB), 7.40
3
3
4
(superimposed ddd, J = 7.6, JPH = 4.9, J = 1 Hz, 1 H, 4-HB), 7.42
813
dx.doi.org/10.1021/om401184n | Organometallics 2014, 33, 804−816

Organometallics
Article
1
3
superimposed) are as follows. H NMR (CD3OD): δ 0.81 (d, JPH
=
155.37 (s, Cq-7aA), 160.01 (s, Cq-pC), 160.54 (s, Cq-pA), 160.63 (s, Cq-
pB), 173.41 (br s, COOC), 177.31 (d, 2J = 15.9 Hz, COOA), 178.24 (d,
2J = 15.9 Hz, COOB); tentative diastereoisomer assignment by
12.6 Hz, 9 H, CMe3B), 0.98 (d, 3JPH = 12.6 Hz, 9 H, CMe3A), 1.59 (d,
3J = 7.2 Hz, 3 H, CH3B), 1.60 (d, 3J = 6.8 Hz, 3 H, CH3A), 4.30 (d, 2JPH
2
= 2.6 Hz, 1 H, PCHcis‑B), 4.54 (d, JPH = 2.6 Hz, 1 H, PCHcis‑A), 4.69
intensity ratios. HRMS (ESI in MeOH + FA): C21H26NO3P (371.41),
(br q, 3J = 6.8 Hz, 1 H, NCHB), 4.97 (br q, 3J = 7.2 Hz, 1 H, NCHA),
calcd for [M + H]+ 372.1723; found 372.1719.
6.54 (br d, 3J = 8.1 Hz, 1 H, 7-HB), 6.57 (br d, 3J = 8.3 Hz, 1 H, 7-HA),
{η1 P-1-[(1S)-1-(p-methoxyphenyl)ethyl]-1H-1,3-
benzazaphosphole}pentacarbonyltungsten(0) (13b). A solution
of W(CO)5(THF) was generated by UV irradiation of W(CO)6 (161
mg, 0.458 mmol) in THF (85 mL) at 20 °C for 2.5 h using a water-
cooled 250 W medium-pressure mercury UV lamp. Neat 4b (110.9
mg, 0.412 mmol) was added, the solution was stirred for 1 day at room
temperature, and the solvent was removed under vacuum. Diethyl
ether was added to the residue, the soluble part was separated by
filtration, and the solvent was evaporated under vacuum, yielding 168
mg (69%) of a very air sensitive pale brown viscous product. 1H NMR
3
4
4
6.62 (superimposed tdd, J = 7.5, JPH = 2.7, J = 1 Hz, 5-HB) 6.65
(superimposed tdd, 3J = 7.5, 4JPH = 2.4, 4J = 1 Hz, 5-HA), 7.12 (td, 3J =
7.8, 7.5, J = 1.5 Hz, 6-HA), 7.19 (td, 3J = 8.3, 7.5, 4J = 1.5 Hz, 6-HB),
4
7.23−7.41 (phenyl-H, 4-H). 13C{1H} NMR (CD3OD): δ 19.08
2
(superimposed s, CH3A), 19.11 (sh, CH3B), 26.34 (d, J = 15.9 Hz,
2
1
CMe3A), 26.48 (d, J = 15.9 Hz, CMe3B), 31.92 (d, J = 22.6 Hz,
1
CMe3B), 32.08 (d, J = 22.6 Hz, CMe3A), 57.60 (s, NCHC), 58.02 (s,
NCHB), 58.58 (s, NCHA), 61.06 (d, 1J = 26.6 Hz, PCHB), 61.35 (d, 1J
1
= 27.8 Hz, PCHA), 66.41 (d, J = 29.1 Hz, PCHC), 109.90 (s, C-7A),
3
110.15 (s, C-7B), 117.97 (d, 3J = 8.0 Hz, C-5A), 119.13 (d, 3J = 8.0 Hz,
(CD3OD): δ 1.98 (d, J = 6.8 Hz, 3 H, CH3), 3.72 (s, 3 H, OCH3),
6.08 (q, 3J = 6.8 Hz, 1 H, CH), 6.85 (mAA′, 2 H, m-CH), 7.17 (mBB′, 2
1
1
C-5B), 122.54 (d, J = 11.9 Hz, Cq-3aA), 124.91 (d, J = 11.9 Hz, Cq-
3aB), [127.18, 128.05, 128.43, 128.51 (2C), 128.65, 129.33 (2C),
129.49 (2C), 129.60 (2C) (phenyl-CHA-C)], 131.39 (s, C-6B), 131.53
(s, C-6A), 132.14 (d, J = 21.3 Hz, C-4A), 132.43 (d, J = 21.2 Hz, C-
4B), 143.05 (s, Cq-iB), 143.10 (s, Cq-iA), 155.32 (s, Cq-7aB), 155.48 (s,
Cq-7aA), 177.29 (d, J = 15.9 Hz, COOA), 178.01 (d, J = 15.9 Hz,
COOB). 31P{1H} NMR (CD3OD): δ 18.1, 17.8, 8.5 (relative
intensities 41:31:20%). HRMS (ESI in MeOH + FA): C20H24NO2P
(341.38), calcd for [M + H]+ 342.1617; found 342.1628.
3-tert-Butyl-1-[(1S)-1-(p-methoxyphenyl)ethyl]-2,3-dihydro-
1H-1,3-benzazaphosphole-2-carboxylic Acid (12b). Compound
4b (127 mg, 0.47 mmol) in Et2O/hexane (10 mL each) was lithiated
with tBuLi in hexane (0.44 mL, 0.70 mmol), treated with CO2 and
then with ClSiMe3 (0.10 mL, 0.79 mmol), and worked up as described
for 12a to give 128 mg of a yellow solid. The NMR spectra indicated
two major diastereoisomers of 12b with δ(31P) (d8-THF) 15.4, 15.1
and intensity ratio of ca. 60:40% and a trace amount of tBuCOOH.
Flash column chromatography on silica gel using hexane (98%)/ethyl
acetate (2%) after several weeks furnished 97 mg (55%) of pure 12b,
but with a changed diastereoisomer distribution, δ(31P) (CD3OD)
17.9, 17.4, 11.7, 8.5 and intensity ratio 18:53:2:27%, assigned to B, A,
D, and C by similar intensity ratios (tBu proton integrals 19:52:4:25)
and characteristic 1H and 13C NMR data, respectively. Data after
3
4
4
H, o-CH), 7.26 (tdd, J = 7.9, 7.0, JPH = 2.8, J = 0.9 Hz, 1 H, 5-H),
7.4 (ddt, 3J = 8.6, 7.1, 4J = 5JPH = 1.5 Hz, 1 H, 6-H), 7.83 (br d, 3J = 8.7
Hz, 1 H, 7-H), 7.98 (tt, 3J ≈ 3JPH = 8.1, 7.8, 4J ≈ 5J = 1.2, 0.9 Hz, 1 H,
4-H), 8.91 (d, 2JPH = 32.9 Hz, 1 H, 2-H). 13C{1H} NMR (CD3OD): δ
21.51 (s, CH3), 55.28 (s, OCH3), 57.19 (s, CH), 114.85 (s, 2 C-m),
115.53 (d, 3J = 4 Hz, C-7), 122.04 (d, 3J = 15.9 Hz, C-5), 126.73 (d, 4J
= 4 Hz, C-6), 127.70 (d, 2J = 13.3 Hz, C-4), 128.07 (s, 2 C-o), 133.77
2
2
2
2
4
1
(d, J = 2.7 Hz, Cq-i), 138.66 (d, J = 22.5 Hz, Cq-3a), 143.82 (s, Cq-
7a), 153.73 (d, 1J = 27.9 Hz, C-2), 160.46 (s, Cq-p), 195.45 (d, 2J = 9.3
Hz, 4 cis-CO), 200.17 (d, J = 29.2 Hz, trans-CO). 31P{1H} NMR
2
(CD3OD): δ 33.8 (satellite d, 1JPW = 242.6 Hz). MS (90 °C): m/z (%)
593 (1) [M+], 377 (0.6), 352 (4), 268 (11), 135 (100). HRMS (ESI in
MeOH): C21H16NO6PW (593.17), calcd for [M(184W) + OH]+
610.0249; found 610.0249; calcd for [M(184W) + ONa]+ 632.0069;
found 632.0067. The detection of the [M + OH]+ and [M + ONa]+
peaks, both with correct isotopic patterns, indicates the high air
sensitivity of 13b in solution. IR (KBr): νCO 2076 (wm), 1924 (vs)
cm−1.
Detection of {η1P-3-tert-butyl-1-[(1S)-1-(p-methoxyphenyl)-
e t h y l ] - 2 - ( t r i m e t h y l s i l y l ) - 2 , 3 - d i h y d r o - 1 H - 1 , 3 -
benzazaphosphole}(1,5-octadiene)rhodium Chloride (14b). A
solution of [Rh(COD)Cl]2 (39 mg, 0.079 mmol) in THF (8 mL) was
added slowly at −30 °C to a solution of 11b (63 mg, 0.16 mmol) in
THF (5 mL). After the mixture was stirred for 2 days at room
temperature, the solvent was removed, the orange-brown residue was
extracted with diethyl ether, and the solvent was removed under
vacuum to give 79 mg of a diastereoisomer mixture (A:B:C by 31P
signal integration ca. 60:35:5) of 14b, contaminated with a small
amount of unconverted [Rh(COD)Cl]2. 1H NMR (C6D6): δ 0.43 (s, 9
1
column chromatography are as follows. H NMR (CD3OD): δ 0.79
(d, JPH = 12.5 Hz, 9 H, CMe3B), 0.98 (d, JPH = 12.5 Hz, 9 H,
3
3
3
3
CMe3A), 1.04 (d, JPH = 11.7 Hz, CMe3D), 1.05 (d, JPH = 12.1 Hz, 9
H, CMe3C), 1.46 (d, 3J = 6.8 Hz, 3 H, CH3C), 1.55 (d, 3J = 6.8 Hz, 3 H,
CH3A), 1.57 (d, 3J = 7.2 Hz, 3 H, CH3B), 1.60 (d, 3J = 7.2 Hz, CH3D),
3.74 (s, OCH3D), 3.76 (s, 3 H, OCH3B), 3.77 (s, 3 H, OCH3A), 3.78
(s, 3 H, OCH3C), 4.23 (d, 2JPH = 2.6 Hz, 1 H, PCHcis‑B), 4.47 (d, 2JPH
=
3
2
H, SiMe3A3), 0.65 (s, 9 H, SiMe3B), 0.91 (d, J = 7.5 Hz, 3 H, CH3A),
2.6 Hz, 1 H, PCHcis‑A), 4.66 (d, JPH = 7.6 Hz, 1 H, PCHtrans‑C), 4.64
(q, 3J = 7.2 Hz, 1 H, NCHB), 4.92 (q, 3J = 7.2 Hz, 1 H, NCHA), 4.94
(q, 3J = 7.2 Hz, 1 H, NCHB), 6.20 (br d, 3J = 8.3 Hz, 1 H, 7-HC), 6.35
(br d, 3J = 8.3 Hz, 1 H, 7-HD), 6.61 (superimposed br d, 3J = 8.3 Hz, 1
H, 7-HAB), 6.59−6.69 (superimposed m, 5-H), 6.85 (m, 2 H, m-CHA),
6.87 (superimposed m, 2 H, m-CHB), 6.89 (superimposed m, 2 H, m-
CHC), 6.98−7.27 (superimposed m, 6-H, 4-H), 7.30 (m, 2 H, o-HB),
7.40 (m, 2 H, o-HA), 7.47 (m, o-HD), 7.60 (m, d fine splitting JPH = 0.9
Hz, 2 H, o-HC). 13C NMR (CD3OD): δ 11.09 (s, CH3C), 18.51 (s,
CH3A), 18.85 (s, CH3B), 26.37 (d, 2J = 15.9 Hz, CMe3A), 26.43 (d, 2J =
15 Hz, CMe3B), 27.34 (d, 2J = 15.9 Hz, CMe3C), 27.54 (superimposed
d, 2J = 15 Hz, CMe3D), 31.92 (d, 1J = 22.5 Hz, CMe3B), 32.09 (d, 1J =
22.5 Hz, CMe3A), 33.25 (d, 1J = 26.5 Hz, CMe3C), 55.64 (br s,
OCH3AC), 55.70 (s, OCH3B), 57.23 (s, NCHA), 57.29 (s, NCHD),
3
0.95 (d, J = 7.2 Hz, 3 H, CH3B), 1.41 (d, JPH = 13.6 Hz, 9 H,
3
PCMe3A), 1.50 (d, JPH = 14.0 Hz, 9 H, PCMe3B), 1.55−1.80, 2.00−
2.30 (m br, 8 H, CH2A,B), 3.27 (s, 3 H, OCH3B), 3.28 (s, 3 H,
OCH3A), 3.83 (m br, 1 H, CHB), 4.13 (m br, 1 H, CHA), 4.32 (m
br, 1 H, CHA,B), 4.30 (superimposed d, 2JPH = 12.5 Hz, PCHB), 4.44
3
2
(q, J = 6.8 Hz, 1 H, NCHA), 4.55 (d, JPH = 11.0 Hz, 1 H, PCHA),
4.57 (q, 3J = 6.6 Hz, 1 H, NCHB), 5.46 (m br, 2 H, CHB), 5.68 (m
br, 2 H, CHA), 6.33 (br d, 3J = 8 Hz, 1 H, H-7B), 6.48 (br d, 3J = 8.3
Hz, 1 H, H-7A), 6.45 (tdd, 3J = 7.5, 7.2, 4JPH = 2.6, 4J = 0.9 Hz, 1 H, H-
3
4
4
5B), 6.54 (tdd, J = 7.5, 7.2, JPH = 2.7, J = 0.9 Hz, 1 H, H-5A), 6.76
3
4
5
(mAA′, 2 H, CH-mA,B), 7.06 (ddt, J = 8.3, 7, J ≈ JPH = 1.3 Hz, 1 H,
H-6A), 7.00−712 (superimposed m, H-4A,B), 7.12 (ddt, 3J = 8.3, 7, 4J ≈
5JPH = 1.3 Hz, 1 H, H-6B), 7.23 (mBB′, 2 H, CH-oB), 7.25 (mBB′, 2 H,
CH-oA). 13C{1H} NMR (C6D6): δ 3.54 (d, J = 2.7 Hz, 2-SiMe3A),
3
1
57.37 (s, NCHB), 57.40 (s, NCHC), 60.89 (d, J = 27.9 Hz, PCHB),
3
61.21 (d, 1J = 27.9 Hz, PCHA), 66.36 (d, 1J = 29.2 Hz, PCHC), 109.68
(s, C-7A), 109.90 (s, C-7B), 113.19 (s, C-7C), 114.60 (s, 2 C-mAC),
114.84 (s, 2 C-mB), 117.83 (two superimposed d, 3J = 8.0 Hz, C-5AB),
3.76 (d, J = 2.7 Hz, 2 SiMe3B), 19.71 (s, CH3B), 23.49 (s, CH3A),
28.57 (s, CH2A), 29.31 (br s, CH2B), 29.54 (d, J = 2.2 Hz, CH2B),
30.03 (br s, CH2A), 30.65 (d, 2J = 5.6 Hz, PCMe3A), 30.86 (d, 2J = 5.3
Hz, PCMe3B), 33.57, (DEPT d, J = 2 Hz, CH2A), 33.90 (d, J = 3 Hz,
CH2B), 34.23 (d, J = 2 Hz, CH2B), 34.47 (d, J = 3.3 Hz, CH2A), 37.20
3
1
119.05 (d, J = 8.0 Hz, C-5C), 122.48 (d, J = 11.9 Hz, Cq-3aAC),
124.85 (d, 1J = 13.3 Hz, Cq-3aB), 129.21 (s, C-6A), 129.75 (s, 2 C-oB),
131.02 (s, 2 C-oA), 131.60 (s, 2 C-oC), 130.70 (s, C-6C), 131.44 (s, C-
6B), 132.22 (d, J = 22.6 Hz, C-4A), 132.34 (d, J = 22.6 Hz, C-4B),
132.86 (d, J = 22.6 Hz, C-4C), 134.40 (s, Cq-iA), 134.71 (s, Cq-iB),
1
1
(d, J = 8 Hz, PCMe3B), 38.07 (d, J = 5 Hz, PCMe3A), 51.87 (s,
OCH3A), 54.03 (s, OCH3B), 55.48 (d, 1J = 11.9 Hz, PCHA,B), 59.52 (d,
2
2
3J = 3 Hz, NCHB), 60.57 (s, NCHA), 65.86 (d, JRhC = 13.3 Hz, 
1
2
2
1
1
135.50 (s, Cq-iC), 154.88 (d, J = 2.7 Hz, Cq-7aC), 155.3 (sh, Cq-7aB),
CHA), 68.75 (d, JRhC = 13.3 Hz, CHB), 69.89 (d, JRhC = 13.3 Hz,
814
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Organometallics
Article
1
CHB), 71.10 (d, JRhC = 13.3 Hz, CHA), 101.78 (DEPT dd, J =
Rise of a New Domain; Mathey, F., Ed.; Pergamon: Amsterdam, 2001;
p 363. (d) Heinicke, J. Trends Organomet. Chem. 1994, 1, 307.
(2) Selected recent work: (a) Niaz, B.; Ghalib, M.; Jones, P. G.;
Heinicke, J. W. Dalton Trans. 2013, 42, 9523. (b) Niaz, B.; Iftikhar, F.;
Kindermann, M. K.; Jones, P. G.; Heinicke, J. Eur. J. Inorg. Chem. 2013,
4220. (c) Aluri, B. R.; Kindermann, M. K.; Jones, P. G.; Dix, I.;
Heinicke, J. W. Inorg. Chem. 2008, 47, 6900.
14.3, 7.7 Hz, CHA), 102.72 (dd, J = 13, 7 Hz, CHB), 104.31
(superimposed m, CHA,B), 112.08 (d, 3J = 4.0 Hz, C-7A), 113.91 (d,
3J = 4 Hz, C-7B), 115.02 (s, 2 C-mA,B), 118.00 (d, J = 9 Hz, C-5A),
3
3
1
118.31 (d, J = 8 Hz, C-5B), 121.0 (dd, J = 33 Hz, Cq-3aA; Cq-3aB at
noise level), 128.72 (DEPT s, 2 C-oB), 130.74 (s, 2 C-oA), 131.41 (br s,
2
2
C-6B), 131.68 (d, J = 9.3 Hz, C-4B), 131.73 (d, J = 9.3 Hz, C-4A),
132.40 (br s, C-6A), 135.08 (s, Cq-iA), 136.19 (s, Cq-iB), 154.69 (d, 3J =
(3) Selected recent reviews: (a) Muller, C.; Broeckx, L. E. E.; de
̈
3
2.7 Hz, Cq-7aB), 155.49 (d, J = 2.7 Hz, Cq-7aA), 159.82 (s, Cq-pB),
Krom, I.; Weemers, J. J. M. Eur. J. Inorg. Chem. 2013, 187; (b) Kollar,
160.45 (s, Cq-pA). 31P{1H} NMR (C6D6): δ 35.5 (d, 1JRhP = 151.1 Hz,
L.; Keglevich, G. Chem. Rev. 2010, 110, 4257. (c) Muller, C.; Vogt, D.
̈
1
1
A), 34.9 (d, JRhP = 151.1 Hz, B), 35.35 (d, JRhP = 151.9 Hz, C),
integral ratio 60:35:5.
Dalton Trans. 2007, 5505. (d) Le Floch, P. Coord. Chem. Rev. 2006,
250, 627.
Crystal Structure Analysis of 3b and 4b. Crystals of 3b and 4b
were mounted on glass fibers in inert oil. Data were recorded at 100 K
on an Oxford Diffraction Xcalibur E diffractometer using Mo Kα
radiation (λ = 0.71073 Å). Crystal data are summarized in Table S1
(Supporting Information). The structures were refined by full-matrix
least squares on F2.27 Hydrogen atoms of NH and PH2 groups were
refined freely (but for the latter with a P−H distance restraint),
methyls were refined as idealized rigid groups allowed to rotate but not
tip, and other H atoms were included using a riding model starting
from calculated positions.
(4) (a) Nyulaszi, L. Chem. Rev. 2001, 101, 1229. (b) Nyulas
Csonka, G.; Reffy, J.; Veszpremi, T.; Heinicke, J. J. Organomet. Chem.
1989, 373, 49.
(5) Ghalib, M.; Konczol, L.; Nyulas
́
zi, L.;
́
́
́
zi, L.; Jones, P. G.; Palm, G. J.;
̈
̈
Heinicke, J. W. Dalton Trans. 2014, 43, 51.
(6) (a) Aluri, B. R.; Kindermann, M. K.; Jones, P. G.; Heinicke, J. W.
Chem. Eur. J. 2008, 14, 4328. (b) Heinicke, J.; Steinhauser, K.;
Peulecke, N.; Spannenberg, A.; Mayer, P.; Karaghiosoff, K. Organo-
metallics 2002, 21, 912. (c) Heinicke, J.; Tzschach, A. Tetrahedron Lett.
1982, 23, 3643.
Ethylene Oligomerization/Polymerization. Solution of 12a and
12b, respectively, in THF (10 mL) were added to a solution of
Ni(COD)2 in cold THF (10 mL) (for quantities see Table 2), and the
mixtures were transferred into the autoclave. This was then pressurized
with ethylene. After control of weight and tightness, heating to 70 °C
and pressure registration were started. After 15 h the autoclave was
cooled to about 10 °C, residual ethylene was released through a
cooling trap, the contents of the autoclave were transferred to a flask,
and the volatiles were flash distilled. The density was determined from
polymer disks, pressurized at 10 kbar by the sinking method in EtOH/
water (with detergent); the NMR spectra were measured in C6D5Br at
100 °C after swelling for 1 day at 100 °C. Further details of the
working technique have been described earlier.26
(7) See e.g.: (a) Le Floch, P.; Carmichael, D.; Mathey, F.
Organometallics 1991, 10, 2432. (b) Teunissen, H. T.; Bickelhaupt,
F. Tetrahedron Lett. 1992, 33, 3537. (c) Teunissen, H. T.; Bickelhaupt,
F. Organometallics 1996, 15, 794.
(8) Ghalib, M.; Jones, P. G.; Heinicke, J. W. Submitted for
publication.
(9) (a) Rivas, F. M.; Riaz, U.; Diver, S. T. Tetrahedron: Asymmetry
2000, 11, 1703. (b) Buchwald, S. L. Acc. Chem. Res. 1998, 31, 805.
(c) Hartwig, J. F. Acc. Chem. Res. 1998, 31, 853.
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Bull. Chem. Soc. Jpn. 1982, 55, 909. (b) Hirao, T.; Masunaga, T.;
Ohshiro, Y.; Agawa, T. Synthesis 1981, 56.
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(b) Becker, G.; Roessler, M.; Uhl, W. Z. Anorg. Allg. Chem. 1981, 473,
7.
ASSOCIATED CONTENT
■
S
* Supporting Information
(13) Nyulas
́
zi, L.; Szieberth, D.; Csonka, G. I.; Reffy, J.; Heinicke, J.;
A table, figures, and CIF files giving experimental and
spectroscopic data for the new compounds and crystallographic
data for 3b and 4b. This material is available free of charge via
the Internet at http://pubs.acs.org. CCDC files 975110 and
975111 also contain crystallographic data for 3b and 4b.
Veszpremi, T. Struct. Chem. 1995, 6, 1.
́
(14) (a) Bondi, A. J. Phys. Chem. 1964, 68, 441. (b) Batsanov, S. S.
Izv. Akad. Nauk, Ser. Khim. 1995, 24; Russ. Chem. Bull. 1995, 44, 18 (in
English).
(15) Sannigrahi, A. B.; Kar, T.; Niyogi, B. G.; Hobza, P.; Schleyer, P.
v. R. Chem. Rev. 1990, 90, 1061.
AUTHOR INFORMATION
(16) (a) Slocum, D. W.; Reinscheld, T. K.; White, C. B.; Timmons,
M. D.; Shelton, P. A.; Slocum, M. G.; Sandlin, R. D.; Holland, E. G.;
Kusmic, D.; Jennings, J. A.; Tekin, K. C.; Nguyen, Q.; Bush, S. J.;
Keller, J. M.; Whitley, P. E. Organometallics 2013, 32, 1674.
(b) Snieckus, V. Chem. Rev. 1990, 90, 879. (c) Klumpp, G. W. Recl.
Trav. Chim. Pay-Bas 1986, 105, 1. (d) Heinicke, J.; He, M.; Karasik, A.
A.; Georgiev, I. O.; Sinyashin, O. G.; Jones, P. G. Heteroat. Chem.
2005, 16, 379.
■
Corresponding Author
*J.W.H.: tel, (+)49 3834-864318; e-mail, heinicke@uni-
greifswald.de.
Notes
The authors declare no competing financial interest.
(17) (a) Schlosser, M. Tetrahedron 1994, 50, 1. (b) Lochmann, L.;
ACKNOWLEDGMENTS
■
̌
Pospísil, J.; Lím, D. Tetrahedron Lett. 1966, 2, 257.
Financial support by the Deutsche Forschungsgemeinschaft
(DFG) is gratefully acknowledged (HE1997/14-1). We thank
Dr. M. K. Kindermann, G. Thede, and M. Steinich for
numerous NMR spectra and Dr. H. Frauendorf and G.
(18) (a) Basvani, K. R. Ph.D. thesis, Greifswald, 2011. (b) Heinicke,
J.; Basvani, K. R.; Jones, P. G. Phosphorus, Sulfur Silicon Relat. Elem.
2011, 186, 678.
(19) Pregosin, P. S., Kunz, R. W. 31P and 13C NMR of Transition
Metal Phosphine Complexes; Springer: Berlin, 1979; Vol. 16.
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(b) Keim, W. In Industrial Applications of Homogeneous Catalysis;
Mortreux, A., Petit, F. Eds.; Springer: Dordrecht, The Netherlands,
1988; p 335.
Sommer-Udvarnoki (Georg-August-Universitat Gottingen, In-
̈
̈
stitut fur Organische und Biomolekulare Chemie) for HRMS
̈
measurements.
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