π-Excess σ2P ligands: Synthesis of biaryl-type 1,3-benzazaphosphole hybrid ligands and formation of P^P′-M(CO) 4 chelate complexes

Article abstract of DOI:10.1039/c3dt50981h

Acid-catalyzed cyclocondensations of 2-phosphanylanilines 1 with substituted benzaldehydes or heteroaryl aldehydes open a convenient route to new biaryl-type 1H-1,3-benzazaphosphole hybrid ligands 2a-f with o-phosphanylphenyl, pyridyl, imidazolyl, thienyl or o-methoxyphenyl donor groups (in addition to the σ²P donor) and to bromophenyl substituted benzazaphospholes 2g,h. Excess aldehyde leads to concomitant reductive N-alkylation, as shown by formation of 3h besides 2h. The reactions proceed via dihydrobenzazaphospholes 4, which can be detected under mild conditions. The aromaticity-driven dehydrogenation does not liberate dihydrogen but is accomplished by transfer hydrogenations, mainly by reduction of some of the aldehyde. N-Secondary 2-phosphanylanilines 5 also react with aldehydes to form the corresponding N-substituted benzazaphospholes 6. The formation of (P^P′)M(CO)₄-chelate complexes 8a (M = Cr) and 9a,b (M = Mo) was demonstrated by reaction with M(CO)₄(norbornadiene). The crystal structure of 9a, determined in addition to the solution structure elucidation by multinuclear NMR spectra, confirms the chelate formation and reveals a trigonal environment for the low coordinated phosphorus, with the P-Mo(0) vector bent out of the benzazaphosphole ring plane by 14.4° (0.57 A?), together with axial chirality of the molecules in the racemic crystals by twisting of the benzazaphosphole and phenyl π-planes around the common C(2)-C(21) bond. The Royal Society of Chemistry 2013.

Full text of DOI:10.1039/c3dt50981h

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π-Excess σ2P ligands: synthesis of biaryl-type 1,3-
benzazaphosphole hybrid ligands and formation of
Cite this: Dalton Trans., 2013, 42, 9523
P^P’–M(CO)4 chelate complexes†
Basit Niaz,‡a Mohammed Ghalib,a Peter G. Jonesb and Joachim W. Heinicke*a
Acid-catalyzed cyclocondensations of 2-phosphanylanilines 1 with substituted benzaldehydes or hetero-
aryl aldehydes open a convenient route to new biaryl-type 1H-1,3-benzazaphosphole hybrid ligands 2a–f
with o-phosphanylphenyl, pyridyl, imidazolyl, thienyl or o-methoxyphenyl donor groups (in addition to
the σ2P donor) and to bromophenyl substituted benzazaphospholes 2g,h. Excess aldehyde leads to con-
comitant reductive N-alkylation, as shown by formation of 3h besides 2h. The reactions proceed via di-
hydrobenzazaphospholes 4, which can be detected under mild conditions. The aromaticity-driven
dehydrogenation does not liberate dihydrogen but is accomplished by transfer hydrogenations, mainly
by reduction of some of the aldehyde. N-Secondary 2-phosphanylanilines 5 also react with aldehydes to
form the corresponding N-substituted benzazaphospholes 6. The formation of (P^P’)M(CO)4-chelate
complexes 8a (M = Cr) and 9a,b (M = Mo) was demonstrated by reaction with M(CO)4(norbornadiene).
The crystal structure of 9a, determined in addition to the solution structure elucidation by multinuclear
NMR spectra, confirms the chelate formation and reveals a trigonal environment for the low coordinated
phosphorus, with the P–Mo(0) vector bent out of the benzazaphosphole ring plane by 14.4° (0.57 Å),
together with axial chirality of the molecules in the racemic crystals by twisting of the benzazaphosphole
and phenyl π-planes around the common C(2)–C(21) bond.
Received 14th April 2013,
Accepted 19th April 2013
DOI: 10.1039/c3dt50981h
www.rsc.org/dalton
phosphinine rhodium catalysts for the hydroformylation of
styrene and internal or bulky substituted olefins.5 Additional
Introduction
In contrast to the large amount of research that has been per- donor sites, allowing chelate formation, improve the stability of
formed on bidentate biarylphosphanes and their use in homo- the phosphinine complexes with transition metal cations,
genous transition metal catalysis,1,2 our knowledge of biaryl- which otherwise suffer from the low donor strength of the low-
type σ2P-ligands with additional P-, N- or O-donor sites, and coordinated phosphorus and the loss of aromatic stabilization
complexes thereof, is limited, being restricted essentially to on coordination of cations. The first MeClPt(II) diphosphinine
compounds involving phosphinine moieties, e.g. 2,2′-bisphos- and pyridylphosphinine chelates were still sensitive to addition
phinines, pyridylphosphinines, o-O-functional 2-phenylphos- of moisture or ROH at the PvC bond6,7 but combinations with
phinines and single P,N,P or O,P,O pincer ligands.3,4 The suitable o-substituents and electron-rich RuCp* or IrCp* frag-
interest in coordination compounds of phosphinines was ments led to stable M(II) complexes, and recently even made
stimulated by the discovery of highly active o-aryl-substituted possible the isolation of the first Rh(III) and Ir(III) pyridylphos-
phinine chelate complexes that allowed controlled addition
reactions.8 In the course of our investigations of 1H-1,3-aza-
phospholes9 we recently isolated the first complexes with d10
transition metal cations,10 but our attempts to synthesize d8
metal complexes have failed so far. Even the formation of a cat-
ionic benzazaphosphole Rh(I)(COD) complex was accompanied
by instantaneous addition of traces of moisture,10,11 whereas
phosphinines form stable Rh(I)(COD) complexes.5,12 Therefore,
we searched for routes to 1,3-azaphosphole-based chelate
ligands that might provide more stable chelate complexes. 1H-
1,3-Benzazaphospholes with O-donor groups were obtained
recently by catalytic phosphonylation of o-methoxybenzoyl or
aInstitut für Biochemie, Anorganische Chemie, Ernst-Moritz-Arndt-Universität
Greifswald, Felix-Hausdorff-Str. 4, D-17489 Greifswald, Germany.
E-mail: heinicke@uni-greifswald.de; Tel: +49 3834 864337
bInstitut für Anorganische und Analytische Chemie, Technische Universität
Braunschweig, Hagenring 30, D-38106 Braunschweig, Germany
†Electronic supplementary information (ESI) available: Detection of thiophen-2-
methanol in the synthesis of 2e, 31P and 13C NMR spectra of new compounds,
tables with atomic coordinates, bond lengths and angles of 9a. CCDC 926716.
For ESI and crystallographic data in CIF or other electronic format see DOI:
10.1039/c3dt50981h
‡Present address: Department of Chemistry, Hazara University Mansehra,
Pakistan.
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2-furoyl o-bromoanilides and reductive cyclization with excess unsubstituted phosphanylaniline, under different conditions.
lithium aluminium hydride,9d but N- or P-donor substituted It was found that 1H-benzazaphospholes can be synthesized in
benzazaphospholes were not available by this method. Here reasonable to good yields (33–68%) by heating aldehydes with
we present a route to the latter by acid-catalyzed condensation 1 in toluene or xylene in the presence of 10–15 mol% of
of 2-phosphanyl-4-methylaniline with carbo- or heterocyclic p-toluenesulfonic acid hydrate (PTSA). An equimolar amount
arylaldehydes. We also present the first examples of formation of PTSA, tested in one example, did not improve the yield.
of M(0)(CO)4 chelate complexes with these ligands, whereas Nafion(H+) and Me3SiCl were much less efficient and led to
reactions with non-zero-valent transition metal compounds only partial conversion, mainly to dihydrobenzazaphospholes.
are still under investigation and will be reported separately.
Depending on the molar ratio, NH-functional derivatives 2
(molar ratio 1 : 1) or mixtures with N-CH2R-derivatives 3 (molar
ratio 1 : 1–1 : 2) were formed (Scheme 1). Clean reaction to
N-CH2R-substituted benzazaphospholes can be achieved with
a greater excess of aldehyde, as demonstrated by the acid-cata-
lyzed reaction of 1 with 4–5 equivalents of paraformaldehyde
to 1,5-dimethyl-1,3-benzazaphosphole (62% yield) or, more
efficiently, with o-diformylarenes, both recently published by
us.17 The aforementioned tolerance of tertiary P- and N-Lewis-
basic groups to aromatic aldehydes, combined with their con-
venient synthetic or commercial availability, allowed us to syn-
thesize the bidentate o-phosphanylphenyl and N-heterocyclic-
substituted benzazaphospholes 2a–d. Likewise, 2-thienyl- and
o-methoxyphenyl substituents were introduced (2e, f), whereas
Results and discussion
Syntheses
The first 1H-1,3-benzazaphospholes were synthesized by cyclo-
condensation of 2-phosphanylanilines with iminoester hydro-
chlorides or imidoylchlorides,13,14 similarly to the related
unsaturated As,N-heterocycles.15 The more stable P-hetero-
cycles were also obtained with acyl chlorides or orthoesters. To
introduce additional donor groups into the heterocycles,
however, carbonyl compounds must be used that are better
compatible with the desired functional groups but still
sufficiently reactive to undergo cyclocondensation. Aldehydes
are known to tolerate tertiary N- and P-donor groups and to
undergo cyclocondensations with 2-phosphanylaniline.
Whereas aliphatic aldehydes gave distillable 2-alkyl-2,3-
dihydro-1,3-benzazaphospholes in good yields, benzaldehyde
provided 2-phenyl-2,3-dihydrobenzazaphosphole in low yield
(12%) only,16 but decomposed on heating at 180 °C partly to
2-phenyl-1,3-benzazaphosphole. The yield was again very low
(15%).13b Nevertheless, we were interested to find out if this
potential route to 2-arylbenzazaphospholes could be improved
to function as a general access to functionally substituted
2-aryl-1,3-benzazaphospholes. Therefore, we screened the reac-
tions of various aldehydes with 4-methyl-2-phosphanylaniline
1, which is more advantageous for NMR monitoring than
attempts to synthesize
a 2-(o-hydroxyphenyl)-1,3-benzaza-
phosphole from 1 and salicylaldehyde failed and gave a
mixture with an unidentified main product with δ31P =
134.5 ppm. Bromophenyl-substituted derivatives 2g, h and 3h
were obtained by condensation of 1 with excess 2- and
3-bromobenzaldehyde, respectively, and may be useful for
insertions of zerovalent metals or cross-coupling reactions, but
these aspects were not investigated within this study.
The formation of N-substituted benzazaphospholes of type
3 inspired us to look for ways to introduce substituents from
different aldehydes in the 1- and 2-position. However, attempts
at cross-condensation of 1 with pyridine-2-carboxaldehyde and
formaldehyde (molar ratio 1 : 1 : 1) furnished mixtures, and
N-methylation of 2c by formaldehyde failed. Only acid-
Scheme 1 Acid-catalyzed syntheses of the benzazaphospholes 2 and 3 from 1 and aldehydes in boiling toluene (or xylene for 2e).
9524 | Dalton Trans., 2013, 42, 9523–9532
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thiophene-2-methanol was detected by GCMS. The formation
of thiophene-2-methanol might suggest that two equivalents
of aldehyde should be used in the reaction, one for the cyclo-
condensation and one to trap the hydrogen. The isolation of
3h along with 2h in the conversion of 1 with an excess of
2-bromobenzaldehyde shows, however, that excess aldehyde
not only traps hydrogen by formation of the alcohol, but also,
at least in part, leads to formation of N-CH2R groups, e.g. by
reductive alkylation at nitrogen of the 1H-1,3-benzazaphos-
phole. It is proposed that the transfer of hydrogen proceeds
with P–C bond cleavage via equilibrium amounts of P-proto-
nated species. Benzazaphospholes of type 2 might be formed
via the monocondensation products 4 through equilibrium
amounts of aldehyde addition products. Benzazaphospholes
of type 3, observed only in the case of excess aldehyde, might
be generated via unstable condensation products with two
molecules of aldehyde (Scheme 3). If reduction of a primarily
formed imine to MeC6H3(PH2)NHCH2R, which could con-
dense with RCHO to 3, were to play a major role in the hydro-
gen transfer, as observed for the similarly complex conversion
of benzimidazolines to benzimidazoles,19 then 3 should be
observed also in the 1 : 1 condensation. A small amount of not
completely identified p-toluidyl species, detected by the
characteristic AA′BB′ proton multiplets in the upfield aryl
region, showed in addition minor cleavage of the P–aryl bond.
The fate of the phosphorus is not clear in this case but reduc-
Scheme 2 Reactions of N-secondary 2-phosphanylanilines with aldehydes.
catalyzed conversions of N-secondary phosphanylanilines with
aldehydes RCHO produced N-substituted benzazaphospholes
with substituents other than CH2R at nitrogen. Examples are
the condensation of 5a with pyridine-2-carboxaldehyde to the
N-neopentyl-2-pyridylbenzazaphosphole 6a and the NMR-
monitored reaction of 5b with benzaldehyde to the already
known N-methyl-benzazaphosphole 6b.14 The reaction of 5b
with benzaldehyde was slow without catalysts at 20 °C and led
via diastereoisomers of a primary addition product (δ = −34.1
and −38.9 ppm, ca. 20% each after 15 h) to the diastereoiso-
meric dihydrobenzazaphospholes 7a. After one week at 20 °C
the latter were the main products (δ = −53.5, −64.9 ppm, ca.
80 : 20%). In the presence of PTSA, the conversion of 5b to 7b
was complete within less than 3 h, and much less side pro-
ducts (δ = 3.0, 4.0, −11.1, −0.5 ppm) were formed. The benz-
azaphosphole 6b, however, was obtained only on heating to
reflux (Scheme 2).
+
tive cleavage of PH3, in the presence of PTSA fixed as a PH4
salt (not detected in the gas phase), appears to be possible and
to make a further contribution to the aromatization of the
dihydro-precursors 4.
Attempts to improve the yields of 2c by dehydrogenation of
crude 4c with CCl4/Et3N failed and led to increased amounts
Mechanistic aspects
The above NMR experiment showed that the acid-catalyzed of impurities, as did attempts at dehydrogenation by heating
reaction of 2-phosphanylanilines with aldehydes to benzaza- in the presence of Pd/charcoal (5 mol%), a normal method in
phospholes comprises two principal steps, (i) cyclocondensa- the aromatization of classical air-stable heterocycles.20
tion and (ii) dehydrogenation, the latter driven by the
aromaticity of the 1H-1,3-benzazaphospholes.18 The same was
Properties
observed in the condensations of 1 with pyridine- and thio-
1
phene-2-carboxaldehyde, monitored by H and 31P NMR. After
The new functionally substituted 2-(hetero)aryl-benzazaphos-
pholes are thermally and hydrolytically stable aromatic com-
pounds, in the solid state slightly, in solution more sensitive
to air oxidation. They are well soluble in THF, dichloro-
methane or ethyl acetate but only moderately to sparingly
soluble in toluene, diethyl ether or methanol and insoluble in
combining the reactants at room temperature each two pairs
of diastereoisomeric dihydrobenzazaphospholes were
4
formed as the main products, identified by the typical coup-
ling pattern of the PH and PCHN protons and phosphorus
resonances in the range of secondary phosphanes (4c at δ =
−46.5 and −63.0 ppm and 4e at δ = −48.4 and −58.5 ppm). On
heating, these signals depleted and finally disappeared in
favour of the signals of the benzazaphospholes 2c and 2e,
respectively, as the main products. To obtain information as to
the fate of the two hydrogen atoms eliminated in the conver-
sion of 4 to 2 under inert conditions, the volume and the com-
position of the gas liberated during heating of crude 4e were
determined. It was less than 10% of the amount calculated for
cleavage of H2 and contained only about 1% H2. The main
part was N2, liberated by heating the N2-saturated solution.
This shows that a transfer hydrogenation with 4e as the hydro-
gen donor must have occurred. Indeed, in the solution Scheme 3 Proposed mechanism.
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n-hexane. This allows purification by precipitation from con- phosphorus (Table 1). Compared to the coordination chemical
centrated THF or ether solutions with hexane or MeOH or by shifts of the phosphorus resonance in 1,3-azaphosphole
column chromatography on silica gel under a nitrogen atmos- Cr(CO)5 and Mo(CO)5 complexes (Δδcomplex-ligand ca. 4–8 and
phere. The lack of N-basic properties of the azaphosphole ring ca. −7 ppm21) the coordination chemical shifts for the low-
by involvement of the N lone-pair in the aromatic π-system coordinated phosphorus of 8a and 9a,b are considerably
enables the separation of dihydrobenzazaphosphole impuri- greater. The complex 9b with the more P-basic dicyclohexyl-
ties by extraction with dilute acids except for derivatives with a phosphanyl group displays however a smaller downfield shift
basic group in the 2-(hetero)aryl substituent. The NH-function than the diphenylphosphanyl complex 9a. This suggests that
exhibits weakly acidic properties and displays the proton NMR the downfield drift of the signals of low-coordinated
signals of 2a, 2e, 2g and 2h in the range δ = 9.10–9.62 ppm.
Particularly strong downfield shifts in the presence of the
more P-basic o-dicyclohexylphosphanyl group of 2b (δ =
12.06 ppm), the N-basic 2-pyridyl and 2-imidazolyl groups of
2c (δ = 10.80 ppm) and 2d (δ = 11.37 ppm), respectively, or the
o-methoxy group of 2f (δ = 10.95 ppm) indicate the formation
of hydrogen bonds and preference for a conformation of the
2-aryl-substituents with the donor atom close to NH. The oppo-
site orientation of the 2-aryl group is enforced in chelate com-
plexes involving coordination at the low-coordinated
Scheme 4 Formation of chelate complexes with 2a.
phosphorus and the donor function of the 2-(hetero)aryl
group. Annulated 1,3-azaphospholes, like other σ2P-com-
pounds, are rather π-acidic and known to form metal(0) penta-
carbonyl complexes.9a–c,21 Chelate complexes, however, are not
yet known. Such complexes are formed from 2a and 2b with M
(CO)4(nbd) (M = Cr, Mo; nbd norbornadiene) in THF, as
detected by conclusive NMR data of 8a and 9a,b (Scheme 4).
Detailed structural information was obtained by crystal struc-
ture analysis of the molybdenum complex 9a (Fig. 1).
Structure elucidation
The structure elucidation of the new ligands and metal(0) car-
bonyl complexes was based on conclusive solution NMR and
HRMS data. The assignments are supported by characteristic
shift ranges and H–H, P–H and P–C coupling
constants.9,11,13–15 The coordination of the M(CO)4 fragments
Fig. 1 Structure of 9a (enantiomer with an R-configuration) in the crystal (ellip-
in the six-membered M(0) chelate complexes is evident from
soids with 50% probability). Selected bond lengths (Å) and angles (°): Mo–P(1)
the coordination chemical shifts of both phosphorus reson-
2.5442(5), Mo–P(3) 2.4219(5), Mo–C(9) 1.973(2), Mo–C(10) 2.011(2), Mo–C(12)
ances and the signals of adjacent 13C nuclei, particularly of
2.039(2), Mo–C(11) 2.050(2), C(2)–P(3) 1.7173(17), P(3)–C(3A) 1.7574(18), N(1)–
C-2, but also of C-3a and C-2′. In addition, marked changes of
C(2) 1.369(2), N(1)–C(7A) 1.381(2); P(3)–Mo–P(1) 79.598(13), C(2)–P(3)–Mo
1
the JPC coupling constants are observed, even if the Δδ13C
126.51(6), C(3A)–P(3)–Mo 136.83(6), C(9)–Mo–P(1) 174.05(6), C(10)–Mo–P(3)
values are small (C3a, C2′ and C-i), so that Δ1JPC is a useful
171.81(7), cis-C–Mo–C 87.31(9) to 93.81(9), C(12)–Mo–C(11) 173.79(8), C(2)–
P(3)–C(3A) 92.17(8), N(1)–C(2)–P(3) 110.84(13).
probe for metal coordination of the low-coordinated
Table 1 Characteristic coordination chemical shifts and changes of 1JPC coupling constants in the (P^P’)M(CO)4 complexes (δ in ppm, JPX in Hz)
2a (CDCl3)
8a (CDCl3)
9a (CDCl3)
2b (CDCl3)
9b (CD2Cl2)
31
31
δ
δ
P
P
(JPP),
83.1 (16.1),
−12.0 (16.1)
—
174.1 (50.6)
—
141.9 (42.3)
—
135.2 (15.1)
—
108.5 (65.5),
53.2 (65.5)
25.4, 65.2 (49)
160.0 (27) (noise level)
−14.1 (−23.6)
136.2 (10.6)
−5.7 (−31.7)
130.7 (31.2)
−4.5 (16.1)
135.3 (34.4)
88.4 (41.2),
33.4 (41.2)
85.5 (s),
−11.7 (s)
—
177.0 (49)
—
141.6 (40.0)
—
130.4 (vbr 20)
—
80.5 (44),
28.4 (44)
ring
(JPP
)
)
PR2
Δδ31P (ΔJPP
5.3, 45.4 (25)
161.0 (25.2)
−13.9 (−25.4)
138.1 (11.9)
−3.8 (−30.4)
130.3 (33.2)
−4.9 (18.1)
135.1 (33.1)
−1.1 (24.1)
−5.0, 40.1 (44)
160.9 (22.6)
−16.1 (−26.4)
138.6 (10.6)
−3.0 (−29.4)
127.1 (19)
−3.3 (–)
δ
13C-2 (1JPC
Δδ13C-2 (ΔJ)
13C-3a (1JPC
Δδ13C-3a (ΔJ)
13C-2′ (1JPC
Δδ13C-2′ (ΔJ)
13C-i/α (1JPC) of R2P
Δδ13C-i/α (ΔJ)
)
δ
)
δ
)
δ
136.2 (9)
—
33.7 (9.4)
—
37.4 (14.6)
3.7 (5.2)
−0.9 (25.4)
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phosphorus is caused by steric rather than electronic effects N-methyl-o-phosphanylaniline 5b14,22 were prepared as
on replacement of a π-accepting CO with a σ-donor P-ligand. reported earlier. Commercially available reagents were used as
More detailed information on the constitution and geome- received unless indicated otherwise. NMR spectra were
try of the chelates is provided by the crystal structure analysis measured on a multinuclear FT-NMR spectrometer Bruker
1
of 9a (Fig. 1). The compound crystallizes in the orthorhombic ARX300 at 300.1 (1H), 75.5 (13C), and 121.5 (31P) MHz. H, 13C
space group Pna21 with four molecules in the unit cell. Molyb- and 31P chemical shifts are δ values and given in ppm relative
denum displays a distorted octahedral coordination, the co- to Me4Si and H3PO4 (85%), respectively. Assignment numbers
ordinated phosphanyl group is essentially tetrahedral and the are indicated in Scheme 1. Coupling constants refer to H–H
low-coordinated phosphorus has a trigonal geometry. The (1H NMR) or P–C couplings (13C NMR) unless stated otherwise.
metal lies 0.57 Å out of the benzazaphosphole ring plane, cor- Assignments of 1H, 13C and 31P NMR signals are based on
responding to an angle of 14.4° between the ring plane and typical shift ranges and coupling constants of known benzaza-
the P–Mo vector. The π-planes of the benzazaphosphole and phospholes and their M(CO)5 complexes, tentative assign-
2-phenyl-ring are mutually rotated around the C(2)–C(21) axis ments of 2-aryl, 1-CH2-aryl and cyclohexyl carbon nuclei in
by 33° (cf. torsion angle P(3)–C(2)–C(21)–C(22) −37°) by the addition by using 135 DEPT spectra and increment methods.
steric demands within the chelate ring. This generates axial UV-Vis spectra were measured on a Perkin-Elmer spectral-
asymmetry and consequently there are two molecules each photomer Lambda 800 in MeOH. Melting points were deter-
with R- and S-configuration in the unit cell. The Mo–P(3) bond mined in sealed capillaries. Detection of thiophen-2-methanol
(2.4219(5) Å) is shorter than the Mo–P(1) bond (2.5442(5) Å), by GCMS was carried out using a GC Agilent 6890N and an MS
consistent with the smaller radius of formally sp2- compared Agilent 5973 with Software MS-Chemstation. HRMS measure-
to sp3-hybridized phosphorus. The P(3)–C(2) and P(3)–C(3a) ments were performed in Göttingen using a double focusing
bonds are slightly shortened and the C(3a)–P(3)–C(2) angle is sector-field instrument MAT 95 (Finnigan) (EI 70 eV) or a 7T
slightly increased by the coordination, compared to the values Fourier transform ion cyclotron resonance mass spectrometer
in free benzazaphospholes.9,11 Other bond lengths and angles APEX IV (Bruker Daltonics) (ESI).
are not significantly altered and indicate preservation of aro-
maticity18 in the 1,3-benzazaphosphole ring.
2-(2-Diphenylphosphanylphenyl)-5-methyl-1H-1,3-benzaza-
phosphole (2a). o-Diphenylphosphanyl-benzaldehyde23 (815
mg, 2.81 mmol) and p-toluenesulfonic acid hydrate (PTSA)
(80 mg, 15 mol%) were added to 1 (390 mg, 2.80 mmol) in
toluene (10 mL) and heated to reflux for 24 h. NMR monitor-
ing displayed 2a as the main product (60% by integration of
Conclusions
Biaryl-type 1,3-benzazaphosphole hybrid ligands with o-phos- the methyl signals). Removal of toluene in a vacuum, treat-
phanylphenyl, heterocyclic imine, thienyl or o-alkoxyphenyl ment of the crude product with degassed 5% aq. NaOH–
donor groups can be synthesized in moderate to good yields diethyl ether, drying of the organic phase with Na2SO4, con-
by PTSA-catalyzed cyclocondensation of o-phosphanylanilines centration of the solution and crystallization from dry metha-
1
with the respective functionally substituted (hetero)aryl alde- nol gave ca. 0.6 g (52%) pale-yellow 2a. H NMR (CDCl3): δ =
hydes in boiling toluene or xylene. A larger excess of aldehyde 2.35 (s, 3 H, Me), 6.98 (ddd, 3J = 7.6, 4JPH = 4.2, 4J = 1 Hz, H-6′),
3
4
3
(RCHO) leads to the additional introduction of a CH2R substi- 7.03 (d br, J = 8.4, J ≈ JPH ≈ 1.5, 0.7 Hz, aryl), 7.12 (d br, J =
3
tuent at nitrogen by reductive N-alkylation. Benzazaphospholes 8.4 Hz, 1 H, aryl), 7.19–7.31 (m, 11 H, aryl), 7.34 (td, J = 7.5,
with other N-substituents can be obtained by condensation of 4J = 1.4 Hz, H-4′ or H-5′), 7.68 (dt, JPH = 4.3, J = 1 Hz, 1 H,
the corresponding N-secondary o-phosphanylanilines with H-4), 7.70 (m, 1 H, aryl), 9.31 (br, 1 H NH) ppm. 13C{1H} and
aldehyde. As demonstrated for 2-o-phosphanylphenyl-1,3-benz- DEPT135 NMR (CDCl3): δ = 21.25 (s, Me), 113.25 (s, C-7),
azaphospholes, chelate complexes are formed with suitable M 126.81 (d, 4J = 2.6 Hz, C-6), 127.88 (d, 2J = 20.1 Hz, C-4), 128.59
3
4
3
(0) carbonyl complexes. The potential for stabilization of the (s, C-4′), 128.81 (d, J = 6.7 Hz, 4 C-m), 129.11 (s, C-5′), 129.17
3
3
generally quite labile benzazaphosphole complexes with non- (s, 2 C-p), 129.58 (d, J = 11.9 Hz, Cq-5), 131.33 (dd, J = 11.8,
zerovalent transition metals by the chelate effect still has to be 5.2 Hz, C-6′), 134.06 (d, 2J = 18.6 Hz, 4 C-o), 134.11 (s, C-3′),
1
3
1
explored but the synthetic accessibility of suitable 1,3-benzaza- 135.17 (dd, J = 15.1, J = 5.9 Hz, Cq-2′), 136.24 (d, J = 9.3 Hz,
2
2
phosphole hybrid ligands reported in this study paves the way 2 Cq-i), 140.47 (dd, J = 26.4, 16.0 Hz, Cq-1′), 140.50 (d, J = 6.5
to such investigations.
Hz, Cq-7a), 141.89 (d, 1J = 42.3 Hz, Cq-3a), 174.11 (dd, 1J = 50.6,
3J = 3.9 Hz, Cq-2) ppm. 31P{1H} NMR (CDCl3): δ = −12.0 (d, 4JPP
4
= 16.1 Hz, PPh2), 83.1 (d, JPP = 16.2 Hz, Pring) ppm. MS (EI 70
eV, 350 °C): m/z (%) = 410 (29), 409 (100) [M+], 408 (96), 332
(18), 254 (45), 183 (21), 137 (51), 98 (32). HRMS (ESI, MeOH–
FA): C26H21NP2 (409.11) calcd for [M + H]+ 410.1222; found
Experimental section
General considerations
All reactions with air- or moisture-sensitive compounds were 410.1218.
carried out under a nitrogen atmosphere using Schlenk tech-
2-(2-Dicyclohexylphosphanyl-phenyl)-5-methyl-1H-1,3-benz-
niques and deoxygenated dry solvents. 4-Methyl-2-phosphany- azaphosphole (2b). 2-Dicyclohexylphosphanyl-benzaldehyde24
laniline 1,17 N-neopentyl-o-phosphanylaniline 5a11a and (774 mg, 2.56 mmol) and PTSA (73 mg, 15 mol%) were added
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to 1 (356 mg, 2.56 mmol) in toluene (10 mL) and heated to diethyl ether. A slightly yellow precipitate was obtained when
reflux for 48 h. Replacement of toluene by ether, extraction of dry n-hexane was poured into a concentrated solution of the
the catalyst with degassed 5% aq. NaOH from the ethereal crude product in THF. Separation of the precipitate, washing
solution of the product and purification by column chromato- with THF–hexane (1 : 2) and drying in a vacuum gave 659 mg
graphy using 1% Et2O–n-hexane gave ca. 0.6 g (51%) of pale (33%) of 2d as a nearly colourless solid, mp. 197–199 °C. UV
1
yellow viscous 2b. H NMR (CDCl3): δ = 1.03–1.35 (m br, 10 H, (9.0 × 10−5 M in MeOH): λmax (ε) = 331 (7.700), 272 (sh, 6.200),
cHex), 1.58–1.78 (m br, 10 H, cHex), 1.91–2.06 (m br, 2 H, 261 (7.500), 220 (10.300) nm. 1H NMR (CDCl3): δ = 2.46 (s, 3 H,
3
5
cHex), 2.45 (s, 3 H, Me), 7.17 (d br, J = 8.5 Hz, H-6), 7.25–7.42 Me), 4.03 (d, JPH = 2.4 Hz, 3 H, NMe), 7.05 (s, 1 H, H-4′
3
5
(m br, 2 H, aryl), 7.51–7.62 (m br, 2 H, aryl), 7.82 (dt, JPH
=
or H-5′), 7.17 (d, JPH = 1.2 Hz, 1 H, H-4′ or H-5′), 7.21 (d br,
2.8, J = 1, J = 0.7 Hz, 1 H, H-4), 8.17 (br dt-shape, 1 H, H-6′), 3J = 8.4 Hz, 1 H, H-6), 7.54 (d br, 3J = 8.5 Hz, 1 H, H-7),
4
5
12.06 (vbr, 1 H, NH) ppm. 13C{1H} and DEPT135 NMR (CDCl3): 7.86 (ddd, JPH = 4.1, J ≈ 1.5, J = 0.7 Hz, 1 H, H-4), 11.37 (br,
3
4
5
δ = 21.30 (Me), 26.18 (C-δ), 26.89 (d, J = 8.5 Hz, C-γ), 27.04 (d, 1 H, NH) ppm. 13C{1H} and DEPT135 NMR (CDCl3): δ =
3
3J = 13.3 Hz, C-γ′), 28.81 (d, J = 6.7 Hz, C-β), 29.86 (d, J = 15.6 21.25 (s, Me), 36.11 (d, JPC = 26.0 Hz, NMe), 113.79 (s, C-7),
2
2
4
1
2
Hz, C-β′), 33.68 (d, J = 9.4 Hz, C-α), 113.85 (br s, C-7), 126.72 123.74 (s, C-6), 127.14 (s, C-4′ or C-5′), 127.99 (d, J = 22.3 Hz,
(br s, C-6), 127.41 (br s, C-4′), 127.60 (d, 2J = 21.0 Hz, C-4), C-4), 127.99 (d, 4J = 2.6 Hz, C-4′ or C-5′), 129.93 (d, 3J = 12.6 Hz,
129.23 (br s, C-5′), 129.51 (d, J = 12.1 Hz, Cq-5), 130.4 (vbr d, Cq-5), 140.24 (d, 2J = 7.7 Hz, Cq-7a), 141.66 (d, 1J = 39.6 Hz,
3
1J ≈ 20 Hz, halfwidth each 23 Hz, Cq-2′), 131.34 (vbr d, 2J = Cq-3a), 144.01 (d, J = 16.0 Hz, Cq-2′), 158.67 (d, J = 56.4 Hz,
2
1
22 Hz, halfwidth each 23 Hz, C-3′), 133.56 (br s, C-6′), 140.79 Cq-2) ppm. 31P NMR (CDCl3): δ = 76.1 ppm. MS (EI 70 eV,
(vbr d, halfwidth 24 Hz, Cq-1′), 141.34 (d, J = 5.3 Hz, Cq-7a), 260 °C): m/z (%) = 230 (17), 229 (100) [M+], 228 (35), 201 (13),
2
141.55 (dd, 1J = 40.0, 5J = 2.8 Hz, Cq-3a), 177.0 (br d, 1J = 49 Hz, 161 (11), 160 (12), 95 (17), 77 (13). HRMS (ESI, MeOH–FA):
Cq-2) ppm. 31P{1H} NMR (CDCl3): −11.7 (s, PcHex2), 85.5 (s, C12H12N3P (229.22), calcd for [M + H]+ 230.0842; found
P
ring) ppm. HRMS (ESI, MeOH–FA): C26H33NP2 (421.49), calcd 230.0842.
for [M + H]+ 422.2161; found 422.2163.
5-Methyl-2-(thien-2-yl)-1H-1,3-benzazaphosphole (2e) and
5-Methyl-2-(pyrid-2-yl)-1H-1,3-benzazaphosphole (2c). Pyri- detection of 4e. Thiophene-2-carboxaldehyde (0.56 mL,
dine-2-carboxaldehyde (0.62 mL, 6.52 mmol) and PTSA 6.09 mmol) was added to a solution of 1 (830 mg, 5.97 mmol)
(150 mg, 13 mol%) were added to 1 (850 mg, 6.11 mmol) in and PTSA (103 mg, 10 mol%) in xylene (7 mL). The solution
toluene (10 mL) and refluxed for 24 h. Removal of the solvent, became warm and turbid. NMR-monitoring showed strong
extraction of the catalyst with degassed 5% aq. NaOH from the signals for the diastereoisomers of 4e, four weak signals in the
ethereal solution and purification of the resulting orange oil region δ = −56.3 to −53.8 ppm and some in the region δ = −1.9
by column chromatography using dry 50% CH2Cl2–n-hexane to 4.5 and at 11.8 ppm. After heating the mixture at reflux for
gave 830 mg (60%) of 2c as a yellow solid. UV (3.8 × 10−5 M in 12 h the 31P NMR spectrum showed a very strong peak for 2e
MeOH): λmax (ε) = 367 (sh, 7.400), 336 (12.000), 262 (14.300), and several weak signals. GC analysis of the volatiles, sepa-
1
228 (20.000) nm. H NMR (CDCl3): δ = 2.39 (s, 3 H, Me), 7.14 rated in a vacuum at 50 °C/2 Torr, displayed a peak for thio-
3
4
(d, partly superimposed, J = 8.5, J = 1 Hz, 1 H, H-6), 7.16 (m, phene-2-methanol, confirmed by comparison with pure
partly superimposed, 3J ≈ 7.2, 4.9, 4J ≈ 1 Hz, 1 H, H-5′), 7.49 (d thiophene-2-methanol and additionally by GCMS. The sticky
3
3
br, J = 8.5 Hz, 1 H, H-7), 7.64 (td, J = 7.8, 7.7, J = 1.8 Hz, 1 H, residue was dissolved in diethyl ether and purified by extrac-
3
4
5
H-4′), 7.78 (ddd, JPH = 4.2, J = 1.5, J = 0.7 Hz, 1 H, H-4), 8.03 tion of N-basic and acid impurities with cold aqueous H2SO4
3
4
4
5
(ddt, J = 8.0, JPH = 2.1, J ≈ J = 1 Hz, 1 H, H-3′), 8.49 (d br, and NaOH solution and final column chromatography
3J = 4.9 Hz, 1 H, H-6′), 10.80 (br, 1 H, NH) ppm. 13C{1H} and (n-hexane, followed by 25% Et2O–hexane), yielding 700 mg
DEPT135 NMR (CDCl3, ref. solv.): δ = 21.26 (s, Me), 114.10 (s, (50%) of a pale yellow powder, mp. 160–164 °C. The compound
C-7), 121.69 (d, JPC = 14.2 Hz, C-3′), 122.94 (d, 5J = 2.7 Hz, is easily soluble in methanol, moderately soluble in cold and
3
4
2
C-5′), 128.18 (d, J = 3.4 Hz, C-6), 128.45 (d, J = 21.2 Hz, C-4), much more readily in hot CHCl3. Crystals in the form of yellow
129.99 (d, 3J = 13.3 Hz, Cq-5), 137.71 (s, C-4′), 141.05 (d, 2J = 7.5 platelets formed on cooling. UV (2.1 × 10−5 M in MeOH): λmax
Hz, Cq-7a), 142.55 (d, 1J = 40.1 Hz, Cq-3a), 147.71 (br, C-6′), (ε) = 357 (6.200), 268 (sh, 7.700), 256 (sh, 11.500), 240 (14.500),
151.79 (d, 2J = 20.1 Hz, Cq-2′), 169.05 (d, 1J = 50.0 Hz, Cq-2) 211 (12.700) nm. H NMR (CDCl3): δ = 2.37 (s, 3 H, Me), 7.01
1
ppm. 31P{1H} NMR (CDCl3): δ = 80.0 ppm. MS (EI 70 eV, (ddd, J = 5.2, 3.6, JPH = 1.5 Hz, 1 H, H-4′), 7.09 (dt, J = 8.2,
280 °C): m/z (%) = 227 (14), 226 (94) [M+], 225 (17), 199 (20), 4J ≈ 5JPH ≈ 1.0 Hz, 1 H, H-6), 7.23 (dd, 3J = 5.2, 4J = 1.1 Hz, 1 H,
167 (41), 149 (100), 78 (47), 57 (65). HRMS (ESI, MeOH–FA): H-5′), 7.34 (ddd, 3J = 3.7, 4J = 1.1, 4JPH = 1.8 Hz, 1 H, H-3′), 7.39
3
5
3
C13H11N2P (226.07), calcd for [M + H]+ 227.0733; found (d br, J = 8.3 Hz, 1 H, H-7), 7.71 (m, JPH = 4.0, J ≈ 1.5, J =
3
3
4
5
227.0733.
0.7 Hz, 1 H, H-4), 9.10 (br, 1 H, NH) ppm. 13C{1H} and
5-Methyl-2-(N-methyl-imidazol-2-yl)-1H-1,3-benzazaphos- DEPT135 NMR (CDCl3): δ = 21.21 (s, Me), 113.01 (s, C-7),
phole (2d). 1-Methyl-imidazole-2-carboxaldehyde (960 mg, 123.63 (d, 3J = 11.4 Hz, C-3′), 125.51 (d, J = 5.3 Hz, C-4′ or C-5′),
8.72 mmol) and chlorotrimethylsilane (0.11 mL, 10 mol%) 127.24 (d, 4J = 3.4 Hz, C-6), 128.13 (d, 2J = 21.2 Hz, C-4), 128.23
3
2
were added to 1 (1.21 g, 8.70 mmol) in toluene (10 mL) and (s br, C-5′ or C-4′), 130.04 (d, J = 12.0 Hz, Cq-5), 138.46 (d, J =
refluxed for 24 h. Then the solvent was removed in a vacuum 19.5 Hz, Cq-1′), 140.65 (d, 2J = 7.6 Hz, Cq-7a), 141.78 (d, 1J =
and the acid was extracted with degassed 5% aq. NaOH– 41.2 Hz, Cq-3a), 166.64 (d, 1J = 49.3 Hz, Cq-2) ppm. 31P{1H}
9528 | Dalton Trans., 2013, 42, 9523–9532
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NMR (CDCl3): δ = 75.23 ppm. HRMS (ESI, MeOH–FA): 130.64 (s, C-5′), 131.48 (d, 5J = 2.6 Hz, C-4′), 137.09 (d, 2J = 15.5
C12H10NPS (231.25), calcd for [M + H]+ 232.0344; found: Hz, Cq-1′), 141.29 (d, 2J = 6.9 Hz, Cq-7a), 141.79 (d, 1J = 40.6 Hz,
232.0345.
Cq-3a), 171.81 (d, 1J = 50.5 Hz, Cq-2) ppm. 31P{1H} NMR
Characteristic NMR (CDCl3) signals of 5-methyl-2-thienyl- (CDCl3): δ = 79.0 ppm. MS (EI 70 eV, 350 °C): m/z (%) = 306 (5),
2,3-dihydro-1,3-benzazaphosphole (4e): diastereoisomer with 305 (34), 304 (8), 303 (29) [M+], 226 (19), 149 (18), 121 (28),
1
P–H and 2-thienyl in the syn-position, δ1H = 4.49 (dd, JPH
=
91 (17), 77 (19), 57 (17), 44 (100). HRMS (ESI, MeOH–FA):
188.5, 3J = 15.0 Hz, PH), 5.55 (dd, JPH = 21.3, 3J = 15.0 Hz, C14H11BrNP (304.12), calcd for [M(79Br) + H]+ 303.9885; found
2
H-2), δ31P = −47.0 ppm; diastereoisomer with P–H and 303.9888.
2-thienyl in the anti-position, δ1H = 4.95 (dd, JPH = 185.8, J =
Synthesis of 2-(2-bromophenyl)-5-methyl-1H-1,3-benzaza-
6.6 Hz, PH), 5.67 (d, J = 6.6 Hz, JPH very small, H-2), δ31P = phosphole (2h) and 1-(2-bromobenzyl)-2-(2-bromophenyl)-5-
−58.5 ppm; syn : anti ratio 2 : 1 (based on PH integrals). methyl-1,3-benzazaphosphole (3h). o-Bromobenzaldehyde
1
3
3
2
2-(2-Methoxyphenyl)-5-methyl-1H-1,3-benzazaphosphole (0.95 mL, 8.14 mmol), 1 (750 mg, 5.39 mmol) and PTSA
(2f). o-Methoxybenzaldehyde (318 mg, 2.32 mmol) and PTSA (1.02 g, 5.36 mmol) were heated in toluene (10 mL) to reflux
(64 mg, 15 mol%) were added to 1 (310 mg, 2.23 mmol) in for 72 h, and the mixture was worked up as described for 2g.
toluene (10 mL) and heated to reflux for 48 h. Toluene was The resulting oil was separated into two products by column
removed in a vacuum, and the ethereal solution of the residue chromatography. The 1,2-disubstituted product 3h was
extracted with degassed 5% aq. NaOH. Drying with Na2SO4 obtained as a brownish yellow solid as the first fraction using
and evaporation of ether furnished 525 mg brown oil, still dis- dry 10% CH2Cl2–n-hexane as an eluent, yield 381 mg (15%).
playing aryl impurities in the NMR spectrum. Column chrom- The second fraction using dry 20% CH2Cl2–n-hexane for
atography (n-hexane, followed by 25% Et2O–hexane) gave ca. elution gave 652 mg (40%) of 2h as a brownish yellow oil.
1
250 mg (44%) of a pale yellow oil. 1H NMR (CDCl3): δ = 2.45 (s,
Data of 2h: H NMR (CDCl3): δ = 2.46 (s, 3 H, Me), 7.21 (d
3 H, Me), 4.04 (s, 3 H, OMe), 7.03 (superimposed dd, 3J = br, superimposed, J = 8.3 Hz, 1 H, H-6), 7.21–7.28 (m, super-
8.4–7, J = 1–2.5 Hz, 1 H, H-6), 7.13 (superimposed t, J = 7–8 imposed, 1 H, H-4′), 7.38 (td, J = 7.5, J = 1.2 Hz, 1 H, H-5′),
3
4
3
3
4
3
3
3
4
Hz, 1 H, H-5′), 7.17 (superimposed d, J ≈ 7.5 Hz, 1 H, H-3′), 7.54 (br d, J = 8.4 Hz, 1 H, H-7), 7.69 (dd, J = 8.0, J = 1.1 Hz,
7.32 (tdd 3J = 8.3, 7.2, 3J = 1.6, J = 0.8 Hz, 1 H, H-4′), 7.52 (d br, 1 H, H-3′), 7.76 (dt, J = 7.7, J ≈ JPH = 1.7, 1.6 Hz, 1 H, H-6′),
3
4
4
3J = 8.3 Hz, 1 H, H-7), 7.85 (ddd, 3JPH = 3.8, 4J = 1.7, 5J = 0.7 Hz, 7.86 (ddd, JPH = 3.7, J = 1.6, J = 0.8 Hz, 1 H, H-4), 9.62 (br,
3
4
5
1 H, H-4), 8.21 (ddd, J = 8.0, JPH = 4.2, J = 1.6 Hz, 1 H, H-6′), 1 H, NH) ppm. 13C{1H} NMR (CDCl3): δ = 21.25 (s, Me), 113.43
3
4
10.95 (br, 1 H, NH) ppm. 13C{1H} NMR (CDCl3, ref. solv): δ = (s, C-7), 120.85 (d, JPC = 6.7 Hz, Cq-2′), 127.31 (d, J = 3.2 Hz,
3
4
21.28 (Me), 55.27 (OMe), 112.02 (s, CH-3′), 113.47 (s, CH-7), C-6), 127.79 (s, C-5′), 128.00 (d, 2J = 20.3 Hz, C-4), 129.85 (d
121.80 (s, CH-5′), 123.17 (d, J = 14.5 Hz, Cq-1′), 126.58 (d, J = superimposed, 3J ≈ 11 Hz, Cq-5), 129.89 (s, C-4′), 132.43 (d, 3J =
2
4
2.5 Hz, CH-6), 127.65 (d, 2J = 21.4 Hz, CH-4), 129.46 (super- 12.1 Hz, C-6′), 133.91 (s, C-3′), 135.59 (d, J = 17.1 Hz, Cq-1′),
2
imposed d, 3J = 10.7 Hz, Cq-5), 129.68 (superimposed d, 3J = 22 140.71 (d, J = 6.7 Hz, Cq-7a), 141.65 (d, J = 42.4 Hz, Cq-3a),
2
1
Hz, CH-6′), 129.73 (d, J = 3.4 Hz, CH-4′), 141.07 (d, J = 40.0 172.30 (d, J = 50.4 Hz, Cq-2) ppm. 31P{1H} NMR (CDCl3): δ =
Hz, Cq-3a), 140.76 (d, 2J = 5.5 Hz, Cq-7a), 154.66 (d, 3J = 8.3 Hz, 84.3 ppm. MS (EI 70 eV, 320 °C): m/z (%) = 306 (17), 305 (100),
Cq-2′), 172.97 (d, 1J = 50.6 Hz, Cq-2) ppm. 31P{1H} NMR 304 (22), 303 (99) [M+], 224 (90), 121 (64), 77 (25). HRMS (ESI,
(CDCl3): δ = 76.1 ppm. HRMS (ESI, MeOH–FA): C15H14NOP MeOH–FA): C14H11BrNP, calcd for [M(79Br) + H]+ 303.9885,
5
1
1
(255.25), calc. for [M + H]+ 256.0886; found: 256.0886.
2-(3-Bromophenyl)-5-methyl-1H-1,3-benzazaphosphole (2g).
found 303.9889.
Data of 3h: 1H NMR (CDCl3): δ = 2.45 (s, 3 H, Me), 5.15,
m-Bromobenzaldehyde (1.06 ml, 9.09 mmol) and PTSA (1.56 g, 5.55 (2 d, 2J = 17.4 Hz, 2 H, NCHAHB), 6.21 (m, 1 H, aryl),
3
4
8.20 mmol) were added to 1 (1.13 g, 8.12 mmol) in toluene 7.01–7.04 (m, superimposed, 2 H, aryl), 7.15 (dt, J = 8.6, J ≈
(10 mL) and heated to reflux for 72 h. Toluene was removed 5JPH = 0.7 Hz, 1 H, H-6), 7.27–7.28 (m, br, 3 H, aryl), 7.33–7.39
in a vacuum, the residue dissolved in dichloromethane (m, 1 H, aryl), 7.45–7.50 (m, 1 H, aryl), 7.65–7.70 (m, 1 H, aryl),
and the catalyst extracted with 5% aq. NaOH solution. The 7.91 (br dt, JPH = 4.1, J ≈ J = 0.7 Hz, 1 H, H-4) ppm. 13C{1H}
3
4
5
3
organic phase was dried with Na2SO4 and concentrated. The and DEPT135 NMR (CDCl3): δ = 21.14 (s, Me), 50.29 (d, JPC
=
crude product 2g was purified by column chromatography, 3.5 Hz, NCH2), 113.45 (s, C-7), 121.55 (s, Cq-2″), 124.72 (d,
eluting with 20% CH2Cl2–n-hexane, to give 1.68 g (68%) of 3JPC = 6.8 Hz, Cq-2′), 127.14, 127.30 (C-4″, C-5″), 127.72 (s, C-5′),
1
a pale brownish-yellow viscous oil. H NMR (CDCl3): δ = 2.46 128.45 (d, 2J = 22.1 Hz, C-4), 128.80 (s, C-6″), 130.24 (d, 3J =
3
(s, 3 H, Me), 7.20 (d br, 3J = 8 Hz, H-6), 7.30 (t, 3J = 7.9 Hz, 1 H, 11.2 Hz, Cq-5), 130.47 (s, C-4′), 132.56 (s, C-3″), 132.74 (d, J =
6
2
H-5′), 7.48 (dtd, 3J = 7.9, 4J = 1.8, JPH = 0.8 Hz, 1 H, H-4′), 12.0 Hz, C-6′), 132.82 (s, C-3′), 135.49 (d, J = 17.4 Hz, Cq-1′),
7.52 (d, 3J = 8.5 Hz, 1 H, H-7), 7.71 (dtd, 3J = 7.8, 4J = 1.8, 4JPH
=
135.73 (s, Cq-1″), 141.02 (d, 2J = 6.5 Hz, Cq-7a), 141.83 (d, 1JPC
=
1.2 Hz, 1 H, H-6′), 7.83 (d br, JPH = 4.1 Hz, 1 H, H-4), 7.91 41.0 Hz, Cq-3a), 175.66 (d, JPC = 48.7 Hz, Cq-2) ppm. 31P{1H}
3
1
4
(q, JPH
≈
4J = 1.8 Hz, 1 H, H-2′), 9.32 (br, 1 H, NH) ppm. NMR (CDCl3): δ = 79.4 ppm. MS (EI 70 eV, 170 °C): m/z (%) =
13C{1H} and DEPT135 NMR (CDCl3): δ = 21.23 (s, Me), 475 (19), 474 (9), 473 (37), 471 (29) [M+], 394 (11), 392 (11.5),
3
113.29 (s, C-7), 123.24 (s, Cq-3′), 123.96 (d, J = 13.0 Hz, C-6′), 304 (13), 302 (14), 222 (51), 171 (72), 169 (74), 149 (100), 71
127.55 (d, 4J = 2.6 Hz, C-6), 127.86 (d, 3J = 12.2 Hz, C-2′), (48), 57 (68). HRMS (ESI, MeOH–FA): C21H16Br2NP (473.14),
128.30 (d, 2J = 21.1 Hz, C-4), 130.12 (d, 3J = 12.9 Hz, Cq-5), calcd for [M(79Br2) + H]+ 471.9460, found 471.9463.
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2
2
1-Neopentyl-2-(pyrid-2′-yl)-1,3-benzazaphosphole (6a). Pyri- 218.5 (dd, Jcis-PC = 20, 12 Hz, 2 CO), 226.8 (dd, Jcis-PC = 13,
dine-2-carboxaldehyde (0.31 mL, 3.26 mmol) and PTSA 2Jtrans-PC = 6.6 Hz, 2 CO) ppm; Cq-1′ in noise. 31P{1H} NMR
2
2
(81 mg, 15 mol%) were added to 5a (557 mg, 2.85 mmol) in (CD2Cl2): δ = 53.2 (d, JPP = 65.5 Hz, PPh2), 108.5 (d, JPP
=
toluene (10 mL) and were heated to reflux for 24 h. NMR-moni- 65.5 Hz, Pring) ppm.
toring showed 6a as the main product (ca. 55% relative inten-
Molybdenum(0)(tetracarbonyl)(2-(2-diphenylphosphanyl)-
sity). The catalyst was removed with degassed 5% aq. NaOH. phenyl-5-methyl-1,3-benzazaphosphole-P,P′)
(9a). THF
Drying on Na2SO4, evaporation of toluene in a vacuum and (10 mL) was added to a Schlenk flask, charged with 2a
repeated precipitation from the concentrated solution in THF (58.9 mg, 0.144 mmol) and excess Mo(CO)4(nbd) (51.6 mg,
with hexane (THF–n-hexane ca. 1 : 3) furnished pale yellow 6a, 0.172 mmol). Within a few minutes the colour changed from
yield 400 mg (50%). 1H NMR (CDCl3): δ = 0.67 (s, 9 H, Me), pale yellow to yellow-orange. NMR monitoring after stirring at
4.31 (vbr, 1 H, NCHA), 5.53 (vbr, 1 H, NCHB), 7.16 (tdd, 3J = 7.9, room temperature for 20 h showed incomplete reaction, but
4
4
3
4
7.0, JPH = 1.9, J = 1.0 Hz, H-5), 7.25 (tt, J = 7.5, 4.9, J = 1.3, after heating at 40 °C for 4 h it was complete. The mixture was
J ≈ 1.1 Hz, 1 H, H-5′), 7.38 (tt, 3J = 8.4, 7.0, 4J = 1 Hz, 1 H, H-6), filtered and the solvent and volatiles were removed in a
7.71 (br dd, J = 8.6, J = 1 Hz, 1 H, H-7), 7.75 (td, J = 7.8, 7.5, vacuum (10 h, 10−3 Torr) to give 63 mg (71%) of orange-brown
3
4
3
4J = 1.8 Hz, 1 H, H-4′), 7.87 (dq, J = 7.8, JPH ≈ J ≈ J = 1 Hz, 9a. Crystals were formed from a concentrated solution in C6D6/
3
4
4
5
3
3
4
5
1 H, H-3′), 8.07 (dddd, J = 7.9, JPH = 4.5, J = 1.3, J = 0.6 Hz, CH3OH, single crystals by slow partial evaporation of a concen-
1 H; H-4), 8.69 (dq, J = 4.9, J = 1.8, J = 1 Hz, 1 H; H-6′) ppm. trated solution in CDCl3 (crystal data, Table 2). 1H NMR
3
4
5
13C{1H} NMR (CDCl3): δ = 28.65 (s, CMe3), 35.44 (s, Cq), 54.92 (CDCl3): δ = 2.33 (s, 3 H, Me), 6.62 (br t, J = 8.7, 8.4 Hz, 1 H,
3
3
(d, JPC = 2.6 Hz, NCH2), 115.08 (s, C-7), 120.14 (d, JPC = 11.9 aryl-H), 7.07, 7.09 (2 superimposed br t, J = 7–8 Hz, 2 H, aryl-
4
Hz, C-5), 122.29 (br s, C-5′), 124.76 (d, J = 4.0 Hz, C-6), 125.36 H), 7.20–7.61 (br m, 13 H, aryl-H), 7.58 (br d, J = 7.9, 1 H, aryl-
3
2
(d, J = 11.9 Hz, C-3′), 128.73 (d, J = 22.6 Hz, C-4), 137.04 (s, H), 9.49 (s br, 1 H, NH) ppm. 13C{1H} and DEPT135 NMR
C-4′), 141.36 (d, 1J = 37.2 Hz, Cq-3a), 146.09 (d, 2J = 6.6 Hz, (CDCl3): δ = 21.15 (s, Me), 114.41 (br s, C-7), 125.30 (vbr, C-4′),
Cq-7a), 148.80 (s, C-6′), 155.73 (d, 2J = 23.8 Hz, Cq-2′), 175.26 (d, 126.34 (d, J = 14.6 Hz, C-4), 128.14 (dd, J = 5.5, 3.3 Hz, C-6′),
1J = 47.8 Hz, Cq-2) ppm. 31P{1H} NMR (CDCl3): δ = 89.4 ppm. 128.35 (d, 3J = 9.3 Hz, 4 C-m), 128.58 (d, 4J = 4.5 Hz, C-6),
HRMS (ESI, MeOH–FA): C17H19N2P (282.32), calcd for [M + H]+ 129.89 (br s, 2 C-p), 130.31 (dd, 1J = 33.2, 3J = 6.6 Hz, Cq-2′),
2
3
3
2
283.1359; found 283.3159.
Detection of
130.47 (d, J = 14.6 Hz, Cq-5), 130.87 (br s, C-5′), 133.23 (d, J =
1-methyl-2-phenyl-1,3-benzazaphosphole 13.3 Hz, 4 C-o), 133.95 (τ, |2J + J| = 6.6 Hz, C-3′), 135.13 (dd,
4
(6b). The reaction of 5b with benzaldehyde in toluene with
and without PTSA (15 mol%) was carried out on the NMR
scale to obtain information about the effect of PTSA and about
the reaction intermediates (see mechanistic aspects and 31P
NMR spectra in the ESI†). The final formation of 6b was con-
Table 2 Crystal data and structure refinement for 9a
1
firmed by good accordance of the 31P and H NMR data with
Compound
9a
6b, obtained by cyclocondensation of 5b with benzimino-
methylester hydrochloride.14
Empirical formula
Formula weight
Temperature
Wavelength
Crystal system
Space group
C30H21MoNO4P2
617.36
100(2) K
0.71073 Å
Orthorhombic
Pna21
Detection of chromium(0)(tetracarbonyl)(2-(2-diphenyl-
phosphanyl)phenyl-5-methyl-1,3-benzazaphosphole-P,P′) (8a).
Excess Cr(CO)4(nbd) (128.26 mg, 0.45 mmol) was added to a
solution of 2a (90 mg, 0.22 mmol) in THF (5 mL). 31P NMR
reaction monitoring after 2 h displayed a mixture of 2a and 8a.
After 24 h colourless crystals of Cr(CO)6 had separated and the
filtrate was concentrated to give 118 mg of orange solid 8a,
contaminated by unconverted Cr(CO)4(nbd). The compound
Unit cell dimensions
a = 15.5796(4) Å
b = 9.4484(2) Å
c = 19.0086(4) Å
2798.11(11) Å3
4
Volume
Z
Density (calculated)
Absorption coefficient
F(000)
Crystal size
ϑ range for data collection
Index ranges
1.465 Mg m−3
0.619 mm−1
1
1248
was identified by characteristic NMR data. H NMR (CD2Cl2):
0.40 × 0.25 × 0.10 mm3
2.41 to 30.51°
δ = 2.43 (s, 3 H, Me), 6.69 (t, 3J = 8.4 Hz, 1 H, aryl-H), 7.20, 7.22
(2 superimposed br t, 2 H, aryl-H), 7.15–7.75 (m, 13 H, aryl-H),
−21 ≤ h ≤ 22, −13 ≤ k ≤ 13,
3
−25 ≤ l ≤ 27
7.71 (br d, J = 8.4 Hz, 1 H, aryl-H), 9.44 (br, 1 H, NH) ppm.
13C{1H} and DEPT135 NMR (CDCl3): δ = 21.20 (s, Me), 114.44
(d, 3J = 4.0 Hz, C-7), 123 (vbr, C-4′), 126.28 (d, 2J = 13.3 Hz,
Reflections collected
Independent reflections
Completeness
Absorption correction
Max. and min. transmission
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2σ(I)]
R indices (all data)
70 559
8221 [R(int) = 0.0433]
98.4% to ϑ = 30.51°
Semi-empirical from equivalents
1.00000 and 0.96238
Full-matrix least-squares on F2
8221/2/349
3
3
C-4), 128.02 (dd, J = 6, 4.5 Hz, C-6′), 128.38 (d, J = 9.3 Hz, 4
4
4
C-m), 128.87 (d, J = 4.6 Hz, C-6), 129.87 (d, J = 2.0 Hz, 2 C-p),
3
2
130.35 (d, J = 15.3 Hz, Cq-5), 131.13 (br s, C-5′), 132.95 (d, J =
11.3 Hz, 4 C-o), 134.64 (τ, |2J + 4J| = 6.6 Hz, C-3′), 135.32 (d, 1J =
1.085
3
1
R1 = 0.0242, wR2 = 0.0497
R1 = 0.0290, wR2 = 0.0521
0.392(18)
33.2, J = 5.3 Hz, 2 Cq-i), 136.23 (d, J = 10.6 Hz, Cq-3a), 141.25
(d, J = 2.7 Hz, Cq-7a); nearly noise level: 130.72 (dd, J = 31.2,
3J = 5.3 Hz, Cq-2′), 159.97 (dd, 1J = 27.2, 3J = 11.3 Hz, Cq-2),
2
1
Absolute structure parameter
Largest diff. peak and hole
0.363 and −0.433 e Å−3
9530 | Dalton Trans., 2013, 42, 9523–9532
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1J = 33.1, 3J = 4.0 Hz, 2 Cq-i), 137.95 (dd, 2J = 11.9, 10.6 Hz, thank G. Thede, M. Steinich and Dr M. K. Kindermann for
1
3
2
Cq-1′), 138.10 (dd, J = 11.9, J = 4.0 Hz, Cq-3a), 141.07 (d, J = NMR and LRMS, P. Gierok and Prof. Dr M. Lalk for GC-MS, Dr
1
3
2.7 Hz, Cq-7a), 160.96 (dd, J = 25.2, J = 10.6 Hz, Cq-2), 207.26 H. Frauendorf and G. Sommer-Udvarnoki (Georg-August-
2
2
(dd, Jcis-PC = 12.6, 8.6 Hz, 2 CO), 215.83 (dd, Jtrans-PC = 23.9, Universität Göttingen, Institut für Organische und Biomolekulare
2Jcis-PC = 9.3 Hz, CO), 216.22 (dd, Jtrans-PC = 15.9, Jcis-PC = 9.3 Chemie) and Prof. Dr H.-C. Böttcher (Ludwig-Maximilians-
2
2
Hz, CO) ppm. 31P{1H} NMR (CDCl3): δ = 33.4 (d, 2JPP = 41.2 Hz, Universität München) for HRMS measurements, and Dr Peulecke
2
PPh2), 88.4 (d, JPP = 41.2 Hz, Pring) ppm. Elemental analysis, (LIKat Rostock) for analysis of gas samples.
calcd for C30H21MoNO4P2 (617.38): C 58.36, H 3.43, N 2.27;
found: C 58.15, H 3.57, N 2.14%. MS (ESI in MeOH–FA): calcd
+
for [M(98Mo) − 2CO]+ (C28H21MoNO2P2 ) 563.01, found: 563.01
(and other peaks for the correct isotopic pattern).
Notes and references
Detection of molybdenum(0)(tetracarbonyl)(2-(2-dicyclohexyl-
phosphanyl)phenyl-5-methyl-1,3-benzazaphosphole-P,P′) (9b).
Reaction of 2b (51 mg, 0.121 mmol) and Mo(CO)4(nbd)
(36.3 mg, 0.121 mmol) in THF (10 mL) as described for 9a
furnished 37 mg (73%) of yellow-brown viscous 9b. 1H NMR
(CDCl3): δ = 1.05–1.45 (m, 11 H, cHex), 1.57–1.85 (m, 9 H),
cHex), 2.08–2.23 (m, 2 H, cHex), 2.48 (s, 3 H, 5-Me), 7.23 (d,
3J = 8.1 Hz, 1 H, aryl-H), 7.40 (t, 3J = 7.2 Hz, 1 H, aryl-H),
7.47–7.63 (br m, 3 H, aryl-H), 7.69 (br m, 1 H, aryl-H), 7.79 (d,
3J = 8.1 Hz, 1 H, aryl-H), 9.99 (s br, 1 H, NH) ppm. 13C{1H} and
DEPT135 NMR (CDCl3): δ = 21.38 (s, Me), 26.34 (C-δ), 27.24 (d,
1 (a) D. S. Surry and S. L. Buchwald, Angew. Chem., Int. Ed.,
2008, 47, 6338–6361; (b) R. Martin and S. L. Buchwald, Acc.
Chem. Res., 2008, 41, 1461–1473; (c) C. M. So, Z. Zhou,
C. P. Lau and F. Y. Kwong, Angew. Chem., Int. Ed., 2008, 47,
6402–6406.
2 (a) N. Arshad and C. O. Kappe, Adv. Heterocycl. Chem.,
2010, 99, 33–59; (b) Y. Canac and R. Chauvin, Eur. J. Inorg.
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B. Schaeffner, J. Huang, A. Zapf, R. Kadyrov, A. Boerner and
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(e) M. Berthod, G. Mignani, G. Woodward and M. Lemaire,
Chem. Rev., 2005, 105, 1801–1836.
3
2
3J = 9.3 Hz, C-γ), 27.58 (d, J = 11.9 Hz, C-γ′), 27.94 (d, J = 13.3
Hz, C-β), 27.96 (d, 2J = 10.6 Hz, C-β′), 37.39 (d, 1J = 14.6, 3J = 2.6
Hz, C-α), 114.98 (br s, C-7), 126.36 (vbr, C-4′), 126.34 (d, 2J =
3 (a) P. Le Floch, Coord. Chem. Rev., 2006, 250, 627–681;
(b) F. Mathey and P. Le Floch, Sci. Synth., 2004, 15, 1097–
1156.
1
3
14.6 Hz, C-4), 127.05 (dd, J = 19, J = 7 Hz, Cq-2′), 127.94 (dd,
3
4
3
3J ≈ J ≈ 4 Hz, C-6′), 128.81 (d, J = 4.0 Hz, C-6), 130.95 (d, J =
2
15.6 Hz, Cq-5), 130.70 (br s, C-5′), 133.95 (d, J = 2.7 Hz, C-3′),
138.64 (dd, J = 10.6, J = 4.0 Hz, Cq-3a), 139.44 (t, J = 10 Hz,
Cq-1′), 141.46 (d, J = 2.7 Hz, Cq-7a), 160.90 (dd, J = 22.6, J =
4 (a) C. Müller, L. E. E. Broeckx, I. de Krom and
J. J. M. Weemers, Eur. J. Inorg. Chem., 2013, 187–202;
(b) C. Müller and D. Vogt, C. R. Chim., 2010, 13, 1127–1143;
(c) C. Müller and D. Vogt, Dalton Trans., 2007, 5505–5523.
5 (a) B. Breit, Chem. Commun., 1996, 2071–2072; (b) B. Breit,
R. Winde, T. Mackewitz, R. Paciello and K. Harms,
Chem.–Eur. J., 2001, 7, 3106–3121; (c) L. Weber, Angew.
Chem., Int. Ed., 2002, 41, 563–572.
1
3
2
2
1
3
2
8.0 Hz, Cq-2), 208.34 (dd, Jcis-PC = 11.9, 9.3 Hz, 2 CO), 216.30
2
2
2
(dd, Jtrans-PC = 22.6, Jcis-PC = 10.6 Hz, CO), 218.53 (dd, Jtrans-PC
= 33.2, Jcis-PC = 8.0 Hz, CO trans to PcHex2) ppm. 31P NMR
2
(CDCl3): δ = 28.4 (d, 2JPP = 43 Hz, PcHex2), 80.5 (d, 2JPP = 44 Hz,
P
ring) ppm. HRMS (ESI in THF): C30H33MoNO4P2 (629.47); 9b in
THF is rapidly oxidized by air and displays peaks for [M + 2O]−
and [M + 3O]− (half intensity), stronger peaks for [M + nO − CO]−
and strong peaks for [M + nO − 2CO]− (n = 2, 3) with correct
isotopic pattern; calcd for [M + nO − 2CO]− 606.0861, found:
606.0849.
6 P. Le Floch, S. Mansuy, L. Ricard and F. Mathey, Organo-
metallics, 1996, 15, 3267–3274.
7 B. Schmid, L. M. Venanzi, A. Albinati and F. Mathey, Inorg.
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8 I. de Krom, L. E. E. Broeckx, M. Lutz and C. Müller,
Chem.–Eur. J., 2013, 19, 3676–3684.
Crystal structure analysis
9 (a) R. K. Bansal and J. Heinicke, Chem. Rev., 2001, 101,
3549–3578; (b) A. Schmidpeter, in Phosphorus-Carbon
Heterocyclic Chemistry: The Rise of a New Domain, ed.
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(c) M. S. S. Adam, P. G. Jones and J. W. Heinicke,
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B. Niaz, M. K. Kindermann, P. G. Jones and J. Heinicke,
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Crystals of 9a were mounted on a glass fiber in an inert oil.
Data were recorded at low temperature on a Bruker SMART
1000 CCD using MoKα-radiation (λ = 0.71073 Å). Crystal data
are summarized in Table 2. The structures were solved by
direct methods and refined by full-matrix least-squares on
F2.25 Hydrogen atoms were included using a riding model or
rigid methyl groups.
10 M. Ghalib, PhD thesis, University Greifswald, 2013.
11 (a) B. R. Aluri, M. K. Kindermann, P. G. Jones, I. Dix and
J. W. Heinicke, Inorg. Chem., 2008, 47, 6900–6912;
(b) M. Ghalib, P. G. Jones and J. W. Heinicke, in
preparation.
Acknowledgements
Financial support and a fellowship from the Higher Education
Commission-Pakistan (HEC) and Deutscher Akademischer 12 (a) N. Mezailles, N. Avarvari, L. Ricard, F. Mathey and P. Le
Austauschdienst (DAAD) are gratefully acknowledged. We
Floch, Inorg. Chem., 1998, 37, 5313–5316; (b) M. Doux,
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9532 | Dalton Trans., 2013, 42, 9523–9532
This journal is © The Royal Society of Chemistry 2013