Solvent-controlled lithiation of PC-N-heterocycles: Synthesis of mono- and bis(trimethylsilyl)-tert-butyl-dihydrobenzazaphospholes - A new type of highly bulky and basic phosphine ligands

Article abstract of DOI:10.1016/j.jorganchem.2014.04.014

The influence of solvents on the lithiation of N-methyl-1,3- benzazaphospholes is reported; these are accessible via catalytic phosphonylation of 2-bromoanilines, subsequent reduction to 2-phosphinoanilines and acid-catalysed disproportionative ring closure with excess paraformaldehyde. Reactions with tBuLi in polar solvents (THF, Et₂O), particularly in the presence of tBuOK, lead to 2-lithiobenzazaphospholes (CH-lithiation) whereas hydrocarbons favour normal (hexane) or inverse (toluene) addition at the PC bond. Reactive Li-species were trapped by ClSiMe₃, present during the lithiation in hydrocarbons, and give rise to 2- and 3-trimethylsilyl-dihydro-1,3-benzazaphospholes, respectively. In hexane, via preferred lithiation of the primary adduct, the 2,2′- bis(trimethylsilyl)-dihydro-1,3-benzazaphosphole is the main product. 5-Methyl-1,3-benzazaphosphole, with NH function, reacts in toluene in the normal mode to 3-tert-butyl-1,2-bis(trimethylsilyl)-5-methyl- dihydrobenzazaphosphole. The sterically demanding tert-butyl and trimethylsilyl groups are arranged in anti-position as shown by crystal structure analyses, the second 2-SiMe₃ group in gauche position. The P-tert-butyl-2, 2′-bis(trimethylsilyl)-dihydrobenzazaphospholes represent a new type of sterically congested dialkylaryl phosphine ligands with increased basicity by the +I-effect of the silyl groups and +M-effect of the basic nitrogen in o-position.

Full text of DOI:10.1016/j.jorganchem.2014.04.014

Journal of Organometallic Chemistry 763-764 (2014) 44e51
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Solvent-controlled lithiation of P]CeN-heterocycles:
Synthesis of mono- and bis(trimethylsilyl)-tert-butyl-
dihydrobenzazaphospholes e A new type of highly bulky
and basic phosphine ligands
,
Mohammed Ghalib a, Peter G. Jones b, Joachim W. Heinicke a
*
a Institut für Biochemie, Ernst-Moritz-Arndt-Universität Greifswald, 17487 Greifswald, Germany
b Institut für Anorganische und Analytische Chemie der Technischen Universität Braunschweig, 38023 Braunschweig, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
The influence of solvents on the lithiation of N-methyl-1,3-benzazaphospholes is reported; these are
accessible via catalytic phosphonylation of 2-bromoanilines, subsequent reduction to 2-phosphinoanilines
and acid-catalysed disproportionative ring closure with excess paraformaldehyde. Reactions with tBuLi in
polar solvents (THF, Et2O), particularly in the presence of tBuOK, lead to 2-lithiobenzazaphospholes (CH-
lithiation) whereas hydrocarbons favour “normal” (hexane) or “inverse” (toluene) addition at the P]C
bond. Reactive Li-species were trapped by ClSiMe3, present during the lithiation in hydrocarbons, and give
rise to 2- and 3-trimethylsilyl-dihydro-1,3-benzazaphospholes, respectively. In hexane, via preferred
lithiation of the primary adduct, the 2,20-bis(trimethylsilyl)-dihydro-1,3-benzazaphosphole is the main
product. 5-Methyl-1,3-benzazaphosphole, with NH function, reacts in toluene in the “normal” mode
to 3-tert-butyl-1,2-bis(trimethylsilyl)-5-methyl-dihydrobenzazaphosphole. The sterically demanding
tert-butyl and trimethylsilyl groups are arranged in anti-position as shown by crystal structure
analyses, the second 2-SiMe3 group in gauche position. The P-tert-butyl-2,20-bis(trimethylsilyl)-dihy-
drobenzazaphospholes represent a new type of sterically congested dialkylaryl phosphine ligands with
increased basicity by the þI-effect of the silyl groups and þM-effect of the basic nitrogen in o-position.
Ó 2014 Elsevier B.V. All rights reserved.
Received 19 November 2013
Received in revised form
29 March 2014
Accepted 14 April 2014
Keywords:
Phosphorus heterocycles
P]C compounds
P ligands
Lithiation
Solvent effects
Introduction
[8]; however, complexes with non-zerovalent transition metals [9]
proved to be kinetically labile and, in contrast to phosphabenzene
Compounds with trivalent phosphorus form a well-known class
of ligands with wide variability of electronic and steric properties,
ranging from highly basic phosphides and nucleophilic phosphines
complexes [3a,3b,10], seem to be restricted to electron-rich d10
metal species. Labile benzazaphosphole M(CO)5eAgSbF6 com-
plexes are efficient initiators for ring opening polymerization of
cyclic ethers [11], but applications as ligands in coordination
catalysis are disfavoured by the lability of the relevant complexes.
However, an indirect applicability of these P]C compounds with
respect to transition metal coordination catalysis might be prom-
ising e their transformation towards new types of bulky and basic
phosphines as steering ligands. The polymerization of phos-
phaalkenes to new polyphosphorus materials was recently re-
ported and highlighted [12], and some addition reactions of tBuLi at
the P]C bond of aromatic P]C heterocycles are also known
[13,14]. The 1,3-benzazaphospholes appear particularly useful for
the synthesis of sterically demanding and basic phosphine ligands
because the addition of tBuLi provides N-heterocyclic tert-butyl-
phosphines with high P-basicity, associated with the þM-effect of
the o-amino group in addition to the inductive (þI) and the steric
to more electrophilic phosphites and low-coordinated neutral l3
-
phosphorus species [1]. Whereas phosphine and phosphite ligands
find a wide variety of applications in homogenous transition metal
coordination catalyses [2], examples of the use of neutral dicoor-
dinated P-ligands in such reactions are rather limited, being
restricted to phosphabenzenes and phosphaalkenes [3]. In-
vestigations of various types of 1,3-benzazaphospholes [4e6],
which are reasonably stable
p-excess aromatic P]C ligands [7],
showed formation of kinetically and thermally stable M(CO)5
complexes with zero-valent chromium, molybdenum and tungsten
* Corresponding author. Tel.: þ49 3834 864318.
E-mail address: heinicke@uni-greifswald.de (J.W. Heinicke).
http://dx.doi.org/10.1016/j.jorganchem.2014.04.014
0022-328X/Ó 2014 Elsevier B.V. All rights reserved.

M. Ghalib et al. / Journal of Organometallic Chemistry 763-764 (2014) 44e51
45
influence of the tertiary alkyl substituent at phosphorus. We
observed this addition in the case of bulkier N-substituted 1,3-
benzazaphospholes as a competing reaction to the 2-CH lithiation
by tBuLi(pentane) in THF. A closer investigation of the lithiation of
N-neopentyl-1,3-benzazaphospholes gave evidence that the reac-
tion can be controlled by auxiliaries and the polarity of the solvent.
The presence of KOtBu led to clean CH-lithiation, use of non-polar
solvents to normal (tBu at phosphorus) and inverse (tBu at C2)
addition. The inverse addition was prevented by steric hindrance in
the reaction of N-adamantyl-1,3-benzazaphosphole with tBuLi in
hexane [14]. In the case of 1-methyl-1,3-benzazaphosphole, the
CH-lithiation was strongly favoured in THF or diethyl ether [15].
The aim of the present study was to find out if controlled addition
reactions of tBuLi can be achieved for NMe- and NH-1,3-
benzazaphospholes by use of less polar solvents.
comparison with related species (see below) allowed their un-
ambiguous identification. tBuLi itself did not react significantly
with ClSiMe3 under these conditions. The formation of mainly 7a
can be rationalized in terms of rapid silylation of the primarily
formed normal addition product and preferential lithiation of the
resulting 6a, with the second silylation affording 7a. The inverse
addition is a minor side reaction leading to small amounts of 8a,
formed by desilylation at phosphorus with MeOH. CH-lithiation
was not observed under the above conditions.
For further experiments 3b was used, because the additional
5-methyl group facilitates interpretation of the proton NMR
spectra, which is helpful in the analysis of product mixtures. The
lithiation of 3b in THF with tBuLi (pentane) in the presence of
ClSiMe3 did not provide the expected clean 2-trimethylsilyl-ben-
zazaphosphole 5b but instead a mixture with the addition-
bis(silylation) product 7b in a molar ratio of 33:67%. The ratio of
5b/7b in Et2O, determined by integration of SiMe3 proton signals,
was 25:75% under the same conditions, and was similar in Et2O/
hexane (1:1) (23:77%). Exclusive CH-lithiation and formation of 5b
required reaction with tBuLi (pentane) and KOtBu in THF (ꢀ70
to ꢀ30 ꢁC) and subsequent trimethylsilylation. This shows that the
presence of ClSiMe3 favours addition of tBuLi at the P]C bond,
whereas KOtBu, which coordinates alkyllithium compounds to
form highly polar LochmanneSchlosser-bases [18], strongly sup-
ports CH-lithiation, as known already for various other compound
types [19]. Inverse addition was not observed in these experiments
but became the major reaction if the conversion of 3b with tBuLi
(pentane) was carried out in toluene (ꢀ70 ꢁC) in the presence of
ClSiMe3; the inverse P-silylation product 9b was obtained in ca.
70% yield along with a trace amount of the normal isomer 6b
(Scheme 3).
Results and discussion
Starting materials
For the preparation of the starting materials we used a new
three step route (Scheme 1), in part communicated recently [6c].
The first step is the synthesis of 1a,b by phosphonylation of 2-
bromo (methyl)anilines with diethyl phosphite in toluene in the
presence of Pd(PPh3)4 (2 mol%)/triethylamine using a protocol of
Hirao et al. [16]. The coupling gave good yields and is more
convenient to handle than the original synthesis of 1a by Issleib and
Vollmer [17] by means of photoinduced Michaelis-Becker coupling
of 2-iodoaniline with KOP(OEt)2 in liquid ammonia. Steps two and
three comprise the reduction of the 2-phosphonoaniline with
LiAlH4 to 2a,b and the conversion to 3a,b by subsequent heating
(24 h) with excess paraformaldehyde (4-5 equivalents CH2O) in the
presence of p-toluenesulfonic acid (15 mol%). The latter reaction
combines the condensation of the 2-phosphinoaniline with two
molecules of formaldehyde with concomitant cyclization and
reductive N-methylation. The driving force for the internal transfer
of hydrogen is the gain in energy by aromatization of a dihy-
drobenzazaphosphole intermediate.
Reaction of the NH-benzazaphosphole 3c with 1.5 equivalents
tBuLi (pentane) in toluene in the presence of ClSiMe3 (1.5 equiv.)
resulted in N-silylation and normal addition and furnished the 1,2-
bis(silylated) 3-tert-butyl-dihydrobenzazaphosphole 10c (Scheme
4) in good yield. This, together with lack of even a weak phos-
phorus resonance for the corresponding N-trimethylsilyl-1,3-
benzazaphosphole, which like 2-methyl-N-trimethylsilyl-benza-
zaphospholes should appear downfield shifted [20], suggests rapid
addition of tBuLi at either the primarily formed NLi-species or the
NSiMe3 compound formed therefrom.
Lithiation and substitution reactions
The lithiation of 3a with tBuLi (1.7 M in pentane) in diethyl
ether at ꢀ78 ꢁC led to 2-lithio-1-methyl-1,3-benzazaphosphole 4a,
To introduce functional groups via reagents that themselves
react with tBuLi, the lithiated species must be generated at first and
be sufficiently persistent towards the solvent to allow defined
substitution reactions. This is possible for the relatively stable 2-
lithio-benzazaphospholes, as shown earlier for 4a [15] and for 4b
by reaction with CO2 and workup to the carboxylic acid 11b. The
latter was recently communicated, including a characterization by
crystal structure analysis [6c]. Benzazaphosphole-2-carboxylic
which crystallized from THF/hexane as a m-Li-bridging dimeric bis-
THF solvate. This was stable at room temperature at least one day
and allowed coupling with a variety of electrophilic element ha-
lides or carbonyl compounds to form benzazaphospholes with
functional groups in the 2-position [15]. When the reaction of 3a
with tBuLi (1.6 M) was carried out in a mixture of diethyl ether
with the less polar hexane (1:1 v/v) and a slight excess of chlor-
otrimethylsilane, added before tBuLi (at ꢀ70 ꢁC) to trap reactive
acids are stable compounds and form
h
1-P pentacarbonyl tung-
sten complexes, as shown for 12a, without interference by the acidic
COOH-group (Chart 1). Attempts to synthesize N-methyl-3-tert-
butyl-dihydrobenzazaphosphole-2-carboxylic acids, however, have
so far failed to give defined products, although this was possible in
the case of bulkier N-neopentyl, N-adamantyl and asymmetric N-
(1-aryl)ethyl substituted dihydrobenzazaphosphole-2-carboxylic
organolithium
species,
the
previously
observed
2-
trimethylsilylbenzazaphosphole 5a [15] was not obtained.
Instead, a complex mixture of the addition products 6a, 7a and 8a
was formed in a molar ratio of 17:68:15% (based on 1H NMR
integration) (Scheme 2). Sufficiently different and characteristic
31P, 13C and 1H NMR data of the different compound types and
Scheme 1. Synthesis of N-methyl-1,3-benzazaphospholes 3a,b.

46
M. Ghalib et al. / Journal of Organometallic Chemistry 763-764 (2014) 44e51
Scheme 2. Reactions of 3a with tBuLi and ClSiMe3 under varied conditions with assumed intermediates (the double arrow before 8a symbolizes P-silylation and desilylation by
MeOH).
acids, which all proved to form efficient ethylene oligomerization
catalyst systems with Ni(COD)2 [14].
Particular features of the novel bulkily substituted 3-tert-butyl-
2,20-bis(trimethylsilyl)-dihydrobenzazaphospholes 7a,b are signif-
icant downfield shifts and signal broadenings of the second SiMe3
signal in the proton and 13C NMR spectra, and significantly
Structural aspects
increased 1JPC coupling constants for PCMe3 (
N (
DJ ca.10 Hz) and PeCe
1
The structure of the products was elucidated by conclusive 31P,
1H and 13C solution NMR and high resolution mass spectra. The
assignment of the proton and 13C resonances was facilitated by
typical shift ranges and coupling constants to phosphorus, known
from related, independently synthesized compounds [14].
D
J ca. 15 Hz) compared to 6a and 10c, whereas JPC3a become
smaller (by 3e6 Hz). Detailed information on the structure, the
arrangement of the substituents and distortions of P3 and C2 from
the ring plane is provided by crystal structure analyses of 7b and
10c (Figs. 1 and 2). Both compounds crystallize in the space group
Scheme 3. Reactions of 3b with tBuLi (ꢀ70 ꢁC to r.t.) and ClSiMe3 in various solvents.

M. Ghalib et al. / Journal of Organometallic Chemistry 763-764 (2014) 44e51
47
Scheme 4. Reaction of the NH-benzazaphosphole 3c with tBuLi and ClSiMe3.
P21/c with four molecules in the unit cell. N1 lies effectively within
ꢀ
the plane of the six-membered ring [7b displaced by ꢀ0.002(2) A;
ꢀ
ꢀ
10c by ꢀ0.026(1) A], P3 is only slightly displaced [7b by 0.098(2) A;
ꢀ
10c by 0.024(1) A], but C(2) is markedly displaced out of the plane
ꢀ
ꢀ
[7b by ꢀ0.449(2) A; 10c by ꢀ0.331(2) A] to meet the steric re-
quirements of the five-membered ring. The tert-butyl groups are
arranged nearly perpendicular to the benzene ring plane [7b C(9)-
P(3)-C(3A)-C(7A) 95.93(11), C(9)-P(3)-C(3A)-C(4) 81.81(14); 10c
C(8)-P(3)-C(3A)-C(7A) 95.85(7), C(8)-P(3)-C(3A)-C(4) 84.57(9)].
The 2-trimethylsilyl groups of 7b occupy a gauche [Si(2)-C(2)-P(3)-
C(9) 55.52(9)] and the anti position [Si(1)-C(2)-P(3)-C(9) 174.43(6)]
towards the tert-butyl group at phosphorus. In the 2-monosilylated
10c the anti orientation of the SiMe3 and CMe3 groups is less pro-
nounced [Si(2)-C(2)-P(3)-C(8) 151.83(4)]. The 2- and 1-
trimethylsilyl groups are arranged almost perpendicular [Si(1)-
N(1)-C(2)-Si(2) 90.68(8)] with the NeSiMe3 group deviating
somewhat more from the benzene ring plane [Si(1)-N(1)-C(7A)-
C(7) 21.67(13)] than the NeMe group of 7b [C(8)-N(1)-C(7A)-
C(3A) 174.07(13)]. The N(1)-C(3A) and N(1)-C(2) bond lengths are
similar in 7b and 10c and are consistent with sp2-hybridization of
nitrogen, which allows efficient conjugation with the benzene ring.
These characteristics show that the new dialkylarylphosphine-type
3-tert-butyl-dihydro-1,3-benzazaphospholes with silyl-substituted
(þI-effect) alkyl and o-amino-substituted (þM-effect) aryl group
fulfil the criteria for sterically demanding or congested (two SiMe3
groups adjacent to tBuP) and P-basic ligands.
Fig. 1. Molecular structure of 7b in the crystal (ellipsoids with 50% probability).
ꢁ
ꢀ
Selected bond lengths (A) and angles ( ): P(3)-C(3A) 1.8256(14), C(2)-P(3) 1.8922(14),
P(3)-C(9) 1.9031(15), N(1)-C(7A) 1.3851(18), N(1)-C(2) 1.5006(18), N(1)-C(8)
1.4520(18), C(2)-Si(2) 1.9255(15), C(2)-Si(1) 1.9539(15), SieCH3 1.8674(17)-
1.8808(16); C(7A)-N(1)-C(2) 112.33(11), C(7A)-N(1)-C(8) 119.19(12), N(1)-C(2)-P(3)
104.39(9), Si(2)-C(2)-Si(1) 109.87(7), C(3A)-P(3)-C(2) 88.18(6).
represent a novel heterocyclic type of sterically congested dia-
lkylarylphosphine ligands with þI- and þM-substituents that in-
crease the P-basicity. The synthetic accessibility, reported herein,
paves the way for studies of their use as ligands in homogenous
transition metal catalysed reactions.
Experimental section
General
All operations with air sensitive compounds were carried out
under dry nitrogen or argon using Schlenk techniques. Ethers,
Conclusions
N-Methyl-1,3-benzazaphospholes, accessible from N,P-dipri-
mary o-phosphinoanilines by acid-catalysed condensation with
excess paraformaldehyde, react with tBuLi in different modes,
controlled by the polarity of the medium. In THF or diethyl ether,
particularly in the presence of tBuOK to generate highly polar
Lochmann-Schlosser bases, CH-lithiationwith formation of 2-lithio-
1-methyl-1,3-benzazaphospholes is enabled whereas a highcontent
of hydrocarbons, supported by the presence of ClSiMe3 for silylation
of the resulting reactive Li-species, promotes normal (n-hexane) or
inverse (toluene) addition and formation of silylated dihy-
drobenzazaphospholes. 1,2-Unsubstituted 1,3-benzazaphospholes
undergo N-lithiation combined with normal addition in toluene
and provide 1,2-bis(silyl)-dihydrobenzazaphospholes. The new P-
tert-butyl-2,20-bis(trimethylsilyl)-1,3-dihydrobenzazaphospholes
W(CO)5
Me
P
P
Fig. 2. Molecular structure of 10c in tꢁhe crystal (ellipsoids with 50% probability).
COOH
COOH
ꢀ
Selected bond lengths (A) and angles ( ): P(3)-C(3A) 1.8150(9), C(2)-P(3) 1.8756(9),
N
N
P(3)-C(8) 1.8897(9), N(1)-C(7A) 1.4009(11), N(1)-C(2) 1.4980(12), N(1)-Si(1) 1.7548(8),
C(2)-Si(2) 1.9042(10); Si(2)-CH3 1.8629(11)-1.8710(11); C(7A)-N(1)-C(2) 111.08(7),
C(7A)-N(1)-Si(1) 123.23(6), N(1)-C(2)-P(3) 108.23(6), C(3A)-P(3)-C(2) 88.83(4), Si(1)-
N(1)-C(7A)-C(3A) ꢀ158.57(7), C(2)-N(1)-C(7A)-C(3A) 12.38(11), Si(2)-C(2)-P(3)-C(8)
151.83(4), Si(1)-N(1)-C(2)-Si(2) ꢀ90.68(8).
Me
Me
11b
12a
Chart 1. Compounds 11b and 12a.

48
M. Ghalib et al. / Journal of Organometallic Chemistry 763-764 (2014) 44e51
hexane and toluene were dried over sodium ketyl and freshly
distilled before use. Commercially available starting materials were
used as received unless indicated otherwise. The compounds 2a
[17] and 3c [8a] were prepared as described in the literature. NMR
spectra were recorded on a multinuclear FT-NMR spectrometer
ARX300 (Bruker) at 300.1 (1H), 75.5 (13C), and 121.5 (31P) MHz.
1-Methyl-1H-1,3-benzazaphosphole (3a)
A solution of 2a [17] (160 mg, 1.28 mmol) in toluene (10 mL) was
refluxed with paraformaldehyde (192 mg, 6.40 mmol, 5 equivalents)
inthepresenceof p-toluenesulfonicacidhydrate(36mg,15mol%)for
24 h. The mixture was diluted with diethyl ether (10 mL), extracted
with cold aqueous NaOH (5%) followed bycold 10% aqueous H2SO4 to
remove the catalyst and N-basic impurities, respectively, and dried
with Na2SO4. Removal of the solvent under vacuum gave 114 mg
(60%) colourless liquid. The NMR data are in good agreement
with those of 3a synthesized by condensation of N-methyl-2-
phosphinoaniline with formiminomethylester hydrochloride [15b].
Chemical shifts (d) are given in ppm relative to Me4Si and H3PO4
(85%), respectively. Coupling constants refer to JHH in 1H and JPC in
13C NMR data unless stated otherwise. Assignment numbers follow
the nomenclature (cf. Scheme 1). HRMS measurements were per-
formed in the Institut für Organische Chemie, Universität Göttin-
gen, using a 7T Fourier transform ion cyclotron resonance mass
spectrometer APEX IV (Bruker Daltonics) (ESI) and in the Depart-
ment Chemie, Ludwig-Maximilians-Universität München using an
MS700 (Jeol) (DEI).
1,5-Dimethyl-1H-1,3-benzazaphosphole (3b)
Compound 3b was synthesized by heating 2b (248 mg,
1.78 mmol) with paraformaldehyde (214 mg, 7.13 mmol, 4 equiv-
alents) and p-toluenesulfonic acid hydrate (51 mg, 15 mol%) in
toluene (12 mL) for 24 h at reflux and workup as described for 3a
2-Amino-phenylphosphonic acid diethylester (1a)
A mixture of 2-bromoaniline (0.50 g, 2.91 mmol), Et3N (0.5 mL,
3.56 mmol), diethyl phosphite (0.50 mL, 3.90 mmol) and Pd(PPh3)4
(67 mg, 2 mol%) in toluene (15 mL) was heated at 100 ꢁC for 14 h.
Filtration, removal of the solvent in a vacuum and purification by
column chromatography on silica gel using 4% ethyl acetate/hexane
for elution furnished 0.50 g (75%) pale yellow oil. 1H NMR (CDCl3):
yielding 179 mg (62%) pale yellow oil. 1H NMR (CDCl3):
d 2.39 (s, 3H,
5-CH3), 3.87 (d, 4JPH ¼ 0.8 Hz, 3H, NCH3), 7.16 (br d, 3J ¼ 8.4 Hz, 1H,
H-6), 7.37 (br d, 3J ¼ 8.4 Hz, 1H, H-7), 7.80 (m, 1H, H-4), 8.32 (d,
2JPH ¼ 37.8 Hz, 1H, H-2). 13C{1H} NMR (CDCl3):
d 21.10 (s, 5-CH3),
37.35 (d, 3J ¼ 2.7 Hz, NCH3), 112.02 (s, CH-7), 126.49 (d, 4J ¼ 2.6 Hz,
CH-6), 128.89 (d, 2J ¼ 21.3 Hz, CH-4), 129.38 (d, 3J ¼ 11.9 Hz, Cq-5),
d
¼ 1.32 (t, 3J ¼ 7.4 Hz, 6H, CH3), 4.09 (m, 4H, OCH2), 5.17 (vbr s,
141.29 (d, 2J ¼ 5.3 Hz, Cq-7a), 142.55 (d, 1J ¼ 39.8 Hz, Cq-3a), 161.94
NH2), 6.65 (br t, 3J z 7.5, 7 Hz, 1H, H-5), 6.70 (ddd, 3J ¼ 8.4,
4JPH ¼ 3.3, 4J ¼ 0.8 Hz, 1H, H-3), 7.26 (tt, 3J ¼ 8.3, 7.2, 4J ¼ 1.4 Hz, 1H,
(d, 1J ¼ 54.4 Hz, CH-2). 31P NMR (CDCl3):
d
69.8 (dd, JPH ¼ 38.2,
2
J ¼ 3.0 Hz). HRMS (ESI in MeOHþFA): C9H10NP (163.16), calcd. for
H-4), 7.44 (ddd, JPH ¼ 14.3, 3J ¼ 7.5, 4J ¼ 1.6 Hz, 1H, H-6). 31P{1H}
[MþH]þ 164.0624; found: 164.0624.
3
NMR (CDCl3):
d
¼ 21.2 ppm. The 1H NMR data are in agreement
with earlier reported 100 MHz 1H NMR values [17].
Detection of 3-tert-butyl-1-methyl-2-trimethylsilyl-2,3-dihydro-
1H-1,3- benzazaphosphole (6a), 3-tert-butyl-1-methyl-2-
2-Amino-5-methyl-phenylphosphonic acid diethylester (1b)
bis(trimethylsilyl)-2,3-dihydro-1H-1,3-benzazaphosphole (7a), and
2-tert-butyl-1-methyl-2,3-dihydro-1H-1,3-benzazaphosphole (8a)
A pentane solution of tBuLi (0.38 mL 1.6 M, 0.61 mmol) was
added to a solution of 3a (59.7 mg, 0.40 mmol) and Me3SiCl
(0.08 mL, 0.64 mmol) in hexane/Et2O (1:1) (10 mL) at ꢀ70 ꢁC. The
mixture was allowed to warm slowly to room temperature, stirred
overnight, filtered, and the solid residue was washed with Et2O.
Removal of the solvent provided 107 mg of air-sensitive yellow oil,
analysed by the NMR and HRMS data as a mixture of 6a, 7a, and 8a,
molar ratio 17:68:15% (by 1H NMR integration), corresponding to
yields of 16 mg (15%), 80 mg (57%) and 11 mg (13%).
Compound 1b was prepared in analogy to 1a from 2-bromo-4-
methylaniline (1.20 g, 6.45 mmol), Et3N (1.1 mL, 7.89 mmol),
diethyl phosphite (1.10 mL, 8.60 mmol) and Pd(PPh3)4 (149 mg,
2 mol %) in toluene (20 mL) as a pale yellow oil (1.19 g, 76% yield). 1H
NMR (CDCl3):
d
1.30 (t, 3J ¼ 7.0 Hz, 6H, CH3), 2.19 (s, 3H, 5-CH3), 4.06
(m, 4H, OCH2), 4.95 (br s, 2H, NH2), 6.56 (dd, 3J ¼ 8.1, 4JPH ¼ 6.9 Hz,
1H, H-3), 7.06 (dt, 3J ¼ 8.3, 4J þ JPH ¼ 1.8 Hz, 1H, H-4), 7.23 (dd,
5
3JPH ¼ 14.7, 4J ¼ 1.9 Hz, 1H, H-6). 13C{1H} NMR (CDCl3):
d 16.16 (d,
3J ¼ 6.6 Hz, CH3), 20.09 (s, 5-CH3), 61.77 (d, 2J ¼ 4.0 Hz, OCH2),
107.80 (d, 1J ¼ 183.1 Hz, Cq-1), 116.35 (d, 3J ¼ 13.3 Hz, C-3),125.84 (d,
3J ¼ 13.3 Hz, Cq-5), 132.80 (d, 2J ¼ 6.6 Hz, C-6), 134.72 (d, 4J ¼ 2.7 Hz,
6a e 1H NMR (CD3OD):
d
¼ 0.03 (d, 4JPH ¼ 0.8 Hz, 2-SiMe3), 0.82
C-4), 148.79 (d, 2J ¼ 8.0, Cq-2). 31P{1H} NMR (CDCl3):
d
21.5. HRMS
(d, 3JPH ¼ 11.6 Hz, PCMe3), 2.94 (s, 3H, NCH3), 3.20 (d, 2JPH ¼ 3 Hz, 2-
CHtrans), 6.37 (br shoulders at d of 7a, 3J ¼ 8.0 Hz, H-7), 6.60 (partly
superimposed tdd, H-5), 7.14 (superimposed m, H-6), 7.22 (m,
3J ¼ 7.2, 3JPH ¼ 4.8, 4J ¼ 1.4, 5J ¼ 0.6 Hz, H-4). 13C{1H} NMR (CD3OD):
(ESI in MeOHþFA):
C
11H18NO3P (243.24), calcd. for [MþH]þ
244.1097; found: 244.1099.
2-Phosphino-4-methylaniline (2b)
d
¼ ꢀ2.13 (d, 3J ¼ 6.6 Hz, 2-SiMe3), 26.26 (d, 2J ¼ 15.4 Hz, PCMe3),
A solution of 1b (0.50 g, 2.06 mmol) in diethyl ether (20 mL) was
added dropwise at ꢀ10 ꢁC to LiAlH4 (0.24 g, 6.3 mmol) in diethyl
ether (150 mL). After stirring for 3 d at room temperature water was
added dropwise until the evolution of hydrogen ceased. The
mixture was dried by Na2SO4 and filtered, and the residue was
washed with ether. Removal of solvent in vacuum furnished 0.214 g
30.84 (d, 1J ¼ 25.0 Hz, PCMe3), 37.89 (d, 3J ¼ 2.2 Hz, NeCH3), 53.86
(d, 1J ¼ 39.9 Hz, PCN), 108.16 (s, C-7), 116.60 (d, 3J ¼ 7.3 Hz, C-5),
131.74 (s, C-6), 132.52 (d, 2J ¼ 21.9 Hz C-4), 156.63 (dbr s, Cq-7a);
Cq3a-signal superimposed. 31P{1H} NMR (CD3OD):
d
¼ ꢀ7.0. HRMS
(ESI in MeOHþFA):
C
15H26NPSi (279.43), calcd. for [MþH]þ
280.1645; found: 280.1646.
(75%) pale yellow oil. 1H NMR (CDCl3):
d
¼ 2.26 (s, 3H, 4-CH3), 3.67
7a e 1H NMR (CD3OD):
d
¼ ꢀ0.10 (d, 4J ¼ 0.8 Hz, 9H, 2-SiMe3),
(d, 1JPH ¼ 201.7 Hz, 2H, PH2), 3.92 (br s, 2H, NH2), 6.66 (dd, 3J ¼ 8.1,
4JPH ¼ 2.1 Hz, 1H, H-6), 7.04 (ddt, 3J ¼ 8.1, 4J ¼ 1.5, 5J z 5JPH ¼ 0.7 Hz,
1H, H-5), 7.30 (ddd, 3JPH ¼ 11.4, 4J ¼ 1.5, 5J ¼ 0.6 Hz,1H, H-3). 13C{1H}
0.50 (br s, 9H, 20-SiMe3), 0.92 (d, 3JPH ¼ 11.2 Hz, 9H, PCMe3), 3.05 (s,
3H, NCH3), 6.37 (br d, 3J ¼ 8.0 Hz, 1H, H-7), 6.61 (tdd, 3J ¼ 7.2,
4JPH ¼ 2.0, 4J ¼ 0.8 Hz, 1H, H-5), 7.17 (m, 1H, H-6), 7.27 (ddd, 3J z 7.4,
NMR (CDCl3):
d
20.16 (s, 4-CH3), 110.85 (d, 1J ¼ 9.3 Hz, Cq-2), 114.91
3JPH ¼ 4.8, 4J ¼ 1.4, 5J ¼ 0.6 Hz, 1H, H-4). 13C{1H} NMR (CD3OD):
(br, C-6), 127.57 (d, 3J ¼ 10.6 Hz, Cq-4), 131.56 (s, C-5), 137.99 (d,
d
¼ 2.44 (d, J ¼ 7.3 Hz, 2-SiMe3), 5.35 (br s, 20-SiMe3), 28.68 (d,
3
2J ¼ 29.2 Hz, C-3),146.92 (d, 2J ¼ 2.7 Hz, Cq-1). 31P{1H} NMR (CDCl3):
2J ¼ 14.7 Hz, PCMe3), 34.95 (d, 1J ¼ 35.9 Hz, PCMe3), 37.01 (d,
3J ¼ 1.5 Hz, NCH3), 58.01 (d, 1J ¼ 56.5 Hz, PCN),107.55 (s, C-7),116.78
(d, 3J ¼ 8.1 Hz, C-5), 127.16 (d, 1J ¼ 4.4 Hz, Cq-3a), 130.94 (s, C-6),
132.11 (d, 2J ¼ 21.3 Hz C-4), 156.48 (d, 2J ¼ 2.2 Hz, Cq-7a). 31P{1H}
d
ꢀ150.3. HRMS (ESI in MeOH, FA): C7H10NP (139.13), calcd. for
[MþH]þ 140.0624; found: 140.0624. The NMR data are in good (31P)
and sufficient (1H, 200 MHz) agreement, respectively, with data on
2b, synthesized from N-methylamino benzenephosphonous acid
diethyl ester [21]).
NMR (CD3OD):
d
¼ 9.9. HRMS (ESI in MeOHþFA): C18H34NPSi2
(351.61), calcd. for [MþH]þ 352.2040; found: 352.2042.

M. Ghalib et al. / Journal of Organometallic Chemistry 763-764 (2014) 44e51
49
8a e 1H NMR (CD3OD):
d
¼ 0.94 (br s, PCMe3), 3.12 (s, NCH3),
Table 1
2
3.71 (dd, 3J ¼ 8.8, JPH ¼ 2.4 Hz, 2-CHtrans
EP), 4.34 (ddt,
Crystal data and structure refinement for 7b and 10c.
zu
1JPH ¼ 184.1, 3J ¼ 8.8, J ¼ 1.4 Hz, PH), 6.48 (br d, 3J ¼ 8.0 Hz, H-7), 6.53
(tdd, 3J ¼ 7.2, 4J ¼ 2.0, 4JPH ¼ 0.9 Hz, H-5), 6.95-7.50 (superimposed
Compound
7b
10c
Empirical formula
Formula weight
Temperature
Wavelength
Crystal system
Space group
C19H36NPSi2
365.64
100(2) K
0.71073 A
Monoclinic
C18H34NPSi2
351.61
100(2) K
0.71073 A
Monoclinic
m, H-6, H-4). 13C{1H} NMR (CD3OD):
d
¼ 27.38 (d, 3J ¼ 10.3 Hz,
PCMe3), 39.31 (d, 2J ¼ 19.9 Hz, 2-CMe3), 41.77 (d, 3J ¼ 2.2 Hz, NCH3),
73.35 (d, 1J ¼ 11.7 Hz, PCHN),109.79 (s, C-7),118.69 (d, 3J ¼ 7.3 Hz, C-
5), 123.97 (d, 1J ¼ 11.0 Hz, Cq-3a), 131.13 (d, 2J ¼ 25.7 Hz, C-4), 131.25
(s, C-6; uncertain), 156.98 (s, Cq-7a). 31P{1H} NMR (CD3OD):
ꢀ
ꢀ
P21/c
P21/c
ꢀ
ꢀ
Unit cell dimensions
a ¼ 13.0201(4) A
a ¼ 11.4350(2) A
¼ ꢀ83.5 (d, 1JPH ¼ 185.8 Hz). HRMS (ESI in MeOH þ FA): C12H18NP
ꢀ
ꢀ
d
b ¼ 9.6441(4) A
b ¼ 8.9663(2) A
(207.25), calcd. for [MþH]þ 208.1250; found: 208.1250.
ꢀ
ꢀ
c ¼ 18.1251(6) A
c ¼ 21.1862(5) A
b
¼ 101.452(3)ꢁ
b
¼ 100.654(3)ꢁ
3
ꢀ
3
ꢀ
Volume
Z
Density (calculated)
Absorption coefficient
F(000)
Crystal size
w range for data collection 2.29e28.28ꢁ
Index ranges
2230.61(14) A
4
2134.79(8) A
4
1,5-Dimethyl-2-trimethylsilyl-1H-1,3-benzazaphosphole (5b)
1.089 Mg/m3
0.23 mmꢀ1
800
1.094 Mg/m3
0.24 mmꢀ1
768
A solution of tBuLi in pentane (0.56 mL, 0.90 mmol) was added
slowly at ꢀ70 ꢁC to a solution of 3b (98 mg, 0.60 mmol) and tBuOK
(80.8 mg, 0.72 mmol) in THF (10 mL). The mixture was allowed to
warm slowly (within 5 h) to ꢀ30 ꢁC, then cooled again to ꢀ70 ꢁC.
After Me3SiCl (0.12 mL, 0.96 mmol) was added, the mixture was
warmed to room temperature and stirred overnight. THF was
removed in vacuum and diethyl ether added. Insoluble salts were
separated by filtration (twice washed with ether), and the solvent
was removed yielding 106 mg (75%) 5b as pale yellow oil. 1H NMR
0.40 ꢃ 0.30 ꢃ 0.08 mm3 0.40 ꢃ 0.35 ꢃ 0.35 mm3
2.41e30.88ꢁ
ꢀ16 ꢂ h ꢂ 15,
ꢀ12 ꢂ k ꢂ 12,
ꢀ30 ꢂ l ꢂ 30
93591
6465 [R(int) ¼ 0.028]
99.7% to w ¼ 30.00ꢁ
6465/209
ꢀ17 ꢂ h ꢂ 17,
ꢀ12 ꢂ k ꢂ 12,
ꢀ24 ꢂ l ꢂ 24
47141
5466 [R(int) ¼ 0.044]
98.9% to w ¼ 28.28ꢁ
5466/219
Reflections collected
Independent reflections
Completeness
(CD2Cl2):
d
0.50 (d, 4JPH ¼ 1.1 Hz, 9H, SiMe3), 2.49 (s, 3H, 5-CH3), 4.01
Data/parameters
(d, 4JPH ¼ 1.1 Hz, 3H, NCH3), 7.26 (dt, 3J ¼ 8.7, 4J z 5JPH < 2 Hz, 1H, H-
Goodness-of-fit on F2
1.045
1.034
6), 7.50 (br d, 3J ¼ 8.7 Hz, 1H, H-7), 7.86 (m, 1H, H-4). 13C{1H} and
Final R indices [I > 2
s
(I)] R1 ¼ 0.0367,
R1 ¼ 0.0292,
wR2 ¼ 0.0789
R1 ¼ 0.0335,
wR2 ¼ 0.0822
wR2 ¼ 0.0895
R1 ¼ 0.0503,
wR2 ¼ 0.0975
135-DEPT NMR (CD2Cl2):
d
0.67 (d, 3J ¼ 7.9 Hz, SiMe3), 21.35
R indices (all data)
(s, 5-CH3), 37.67 (d, 3J ¼ 2.6 Hz, NeCH3), 112.71 (s, C-7), 127.32
(d, 4J ¼ 2.6 Hz, C-6), 128.54 (d, 2J ¼ 19.9 Hz, C-4), 129.54
(d, 3J ¼ 11.9 Hz Cq-5), 144.12 (d, 1J ¼ 43.8 Hz, Cq-3a), 146.51
(d, 2J ¼ 4.0 Hz, Cq-7a), 180.22 (d, 1J ¼ 74.3 Hz, Cq-2). 31P{1H} NMR
ꢀꢀ3
ꢀꢀ3
Largest diff. peak and hole 0.43 and ꢀ0.23 e∙A
0.46 and ꢀ0.34 e∙A
(CD2Cl2):
d
114.6. HRMS (ESI in MeOHþFA): C12H19NPSi (235.34),
0.87 mmol) in toluene (10 mL) at ꢀ70 ꢁC. The mixture was allowed
to warm slowly to room temperature and stirred overnight. The
precipitate was separated and washed with diethyl ether. Removal
of the solvent in vacuum provided 123 mg 9b as an air-sensitive
pale yellow oil that was slightly contaminated by the isomeric 6b
calcd. for [MþH]þ 236.1019; found 236.1021.
3-tert-Butyl-1,5-dimethyl-2,2-bis(trimethylsilyl)-2,3-dihydro-1H-
1,3-benzazaphosphole (7b)
A solution of tBuLi in pentane (0.49 mL 1.6 M, 0.78 mmol) was
added to a solution of 3b (85 mg, 0.52 mmol) and Me3SiCl (0.11 mL,
0.88 or 0.83 mmol) in THF (10 mL) at ꢀ70 ꢁC. The mixture was
allowed to warm slowly to room temperature and stirred over-
night. The precipitate was separated and washed with diethyl ether.
Removal of the solvent in vacuum provided 146 mg yellow oil,
consisting of compounds 7b and 5b, molar ratio 67:33% (by 1H NMR
integration of SiMe3 signals), corresponding to 111 mg (58%) and
35 mg (29%) yield. Overlayering a concentrated ethereal solution of
the mixture with hexane provided colourless crystals of 7b.
Selected bond lengths and angles are shown in Fig. 1, for crystal
(yields by NMR ratio ca. 70:5%). 1H NMR (C6D6):
d
¼ ꢀ0.01 (d,
3JPH ¼ 4.5 Hz, 9H, SiMe3), 1.02 (s, 9H, 2-CMe3), 2.16 (s, 3H, 5-CH3),
2
2.77 (s, 3H, NCH3), 3.38 (d, JPH ¼ 2.6, Hz, 1H, PCHN), 6.25 (br d,
3J ¼ 8.1 Hz, 1H, H-7), 6.91 (ddd, 3J ¼ 8.1 4J ¼ 1.8, 5JPH ¼ 0.9 Hz, 1H, H-
7), 7.07 (ddd, 3JPH ¼ 5.8, 4J ¼ 1.8, 5J ¼ 0.9 Hz, 1H, H-4). 13C{1H} NMR
(C6D6):
d
¼ ꢀ2.69 (d, 2J ¼ 11.9 Hz, SiMe3), 21.11 (s, 5-CH3), 27.08 (d,
3J ¼ 10.6 Hz, 2-CMe3), 39.31 (d, 2J ¼ 19.9 Hz, 2-CMe3), 42.08 (d,
3J ¼ 2.7 Hz, NCH3), 75.2 (d, 1J ¼ 19.9 Hz, PCHN), 108.25 (s, C-7),
123.32 (d, 3J ¼ 11.9 Hz, Cq-5), 126.90 (d, 1J ¼ 6.6 Hz, Cq-3a), 129.43 (s,
C-6), 129.64 (d, 2J ¼ 21.2 Hz, C-4), 154.46 (s, Cq-7a). 31P{1H}-NMR
(C6D6):
d
¼ ꢀ91.2; ꢀ5.6 (6b, ꢂ5 mol%). HRMS (ESI in MeOHþFA):
data see Table 1. 7b e 1H NMR (CD2Cl2):
d
¼ ꢀ0.10 (d, 4J ¼ 1.1 Hz, 9H,
C
16H28NPSi (293.46), calcd. for [MþH]þ 294.1801; found: 294.1804.
3
2-SiMe3), 0.48 (br s, 9H, 20-SiMe3), 0.92 (d, JPH ¼ 11.3 Hz, 9H,
PCMe3), 2.26 (s, 3H, 5-CH3), 3.01 (s, 3H, NCH3), 6.25 (br d,
3J ¼ 8.3 Hz, 1H, H-7), 7.0 (ddt, 3J z 8, 4J ¼ 1.8, 5J z 5JPH z 1 Hz, 1H,
3-tert-Butyl-5-methyl-1,2-bis(trimethylsilyl)-2,3-dihydro-1H-1,3-
benzazaphosphole (10c)
3
H-6), 7.13 (ddd, JPH ¼ 4.8, 4J ¼ 1.8, 5J ¼ 0.9 Hz, 1H, H-4). 13C{1H}
3
NMR (CD2Cl2):
d
¼ 2.17 (d, J ¼ 6.6 Hz, 2-SiMe3), 4.98 (br s, 20-
A pentane solution of tBuLi (0.43 mL 1.6 M, 0.68 mmol) was
added to a solution of 3c (67 mg, 0.45 mmol) and excess Me3SiCl
(0.09 mL, 0.72 mmol) in toluene (10 mL) at ꢀ70 ꢁC. The mixture was
allowed to warm slowly to room temperature and stirring
continued overnight. Insoluble solids were filtered off and washed
with Et2O. Removal of the solvent gave 112 mg (71%) pale yellow oil,
which crystallized from n-hexane. Selected bond lengths and an-
gles of 10c are shown in Fig. 2, for crystal data see Table 1. 1H NMR
SiMe3), 20.68 (s, 5-CH3), 28.21 (d, 2J ¼ 14.6 Hz, PCMe3), 34.13 (d,
1J ¼ 37.1 Hz, PCMe3), 36.61 (s, NeCH3), 57.15 (d, 1J ¼ 57.1 Hz, PCN),
106.21 (s, C-7), 124.62 (d, 3J ¼ 8.0 Hz, Cq-5), 126.71 (d, 1J ¼ 5.3 Hz,
Cq-3a), 130.30 (s, C-6), 131.85 (d, 2J ¼ 21.2 Hz, C-4), 153.58 (d,
2J ¼ 2.6 Hz, Cq-7a). 31P{1H} NMR (CD2Cl2):
d
¼ 10.9. HRMS (ESI in
MeOHþFA): C19H36NPSi2 (365.64), calcd. for [MþH]þ 366.2197;
found: 366.2199. The NMR data of the side product 5b are in good
accordance with those given above.
(CDCl3):
d
¼ ꢀ0.01 (d, 4J ¼ 1.1 Hz, 9H, 2-SiMe3), 0.32 (s, 9H,1-SiMe3),
3
0.91 (d, JPH ¼ 12.1 Hz, 9H, CMe3), 2.26 (s, 3H, 5-CH3), 3.54 (d,
2JPH ¼ 4.9 Hz, 1H, PCH), 6.64 (br d, 3J ¼ 7.9 Hz, 1H, H-7), 6.94 (dd,
3J ¼ 7.9, 4J ¼ 2 Hz, 1H, H-6), 6.94 (dd, 3JPH ¼ 5.5, 4J ¼ 2 Hz, 1H, H-4).
2-tert-Butyl-1,5-dimethyl-3-trimethylsilyl-2,3-dihydro-1H-1,3-
benzazaphosphole (9b)
A solution of tBuLi in pentane (0.52 mL 1.6 M, 0.83 mmol) was
added to a solution of 3b (90 mg, 0.55 mmol) and Me3SiCl (0.11 mL,
13C{1H} NMR (CDCl3):
d
¼ ꢀ2.37 (d, 3J ¼ 6.6 Hz, 2-SiMe3), 0.71
(s, 1-SiMe3), 20.56 (s, 5-CH3), 26.32 (d, 2J ¼ 14.6 Hz, CMe3), 31.05

50
M. Ghalib et al. / Journal of Organometallic Chemistry 763-764 (2014) 44e51
(d, 1J ¼ 25.2 Hz, CMe3), 48.99 (d, 1J ¼ 39.8 Hz, PCN), 111.57
(s, 3J ¼ 2.2 Hz, C-7), 126.16 (d, 3J ¼ 8.0 Hz, Cq-5), 127.07
(d, 1J ¼ 8.0 Hz, Cq-3a), 130.22 (s, C-6), 132.44 (d, 2J ¼ 22.6 Hz, C-4),
Acknowledgements
Funding of these investigations and a scholarship (M. G.) by the
Deutsche Forschungsgemeinschaft (HE 1997/14-1) is gratefully
acknowledged. We thank Dr. M. K. Kindermann, G. Thede and M.
Steinich for numerous NMR spectra, Dr. H. Frauendorf and G.
Sommer-Udvarnoki (Georg-August-Universität Göttingen, Institut
für Organische und Biomolekulare Chemie) and Prof. H.-C. Böttcher
and B. Breitenstein (Department Chemie, Ludwig-Maximilians-
Universität München) for HRMS measurements.
153.36 (d, 2J ¼ 2.7 Hz, Cq-7a). 31P{1H} NMR (CDCl3):
d
¼ ꢀ6.3 ppm.
HRMS (DEIþ): C18H34NPSi2 (351.61), calcd. for [M]þ 351.1967;
found: 351.1972.
1,5-Dimethyl-1H-1,3-benzazaphosphole-2-carboxylic acid (11b)
A solution of tBuLi in pentane (0.6 mL, 0.96 mmol) was added
slowly at ꢀ70 ꢁC to a solution of 6 (104 mg, 0.64 mmol) and tBuOK
(85.3 mg, 0.76 mmol) in THF (20 mL). The mixture was allowed to
warm slowly (within 5 h) to ꢀ30 ꢁC, then cooled again to ꢀ70 ꢁC. A
slow stream of gaseous carbon dioxide was passed through for
40 min which turned the orange-red colour, formed during the
lithiation, to yellow. The mixture was allowed to warm slowly to
room temperature and stirring continued overnight to complete
the conversion. Then excess Me3SiCl (0.13 mL, 1.02 mmol) was
added at ꢀ70 ꢁC to trap the lithium. After 2e3 h at room temper-
ature the precipitate was filtered off, twice washed with ether and
the solvent removed in vacuum. The residual yellow solid was
treated with methanol (10 mL) yielding 96 mg (72%) of 7, mp. 210e
215 ꢁC (dec.). The compound is only slightly soluble in methanol or
diethyl ether but readily soluble in THF. Single crystals were ob-
tained by slow concentration of the d8-THF solution. 1H NMR
Appendix A. Supplementary material
CCDC 971420, 971421 contains the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via www.
ccdc.cam.ac.uk/data_request/cif.
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d
2.42 (s, 3H, 5-CH3), 4.22 (d, 4JPH ¼ 1.5 Hz, 3H, NCH3), 7.28
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d 21.30
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(s, 5-CH3), 34.77 (d, 3J ¼ 4.0 Hz, NeCH3), 114.30 (s, C-7), 129.62 (d,
4J ¼ 3.2 Hz, C-6), 129.63 (d, 2J ¼ 20.4 Hz, C-4), 130.67 (d, 3J ¼ 13.3 Hz,
Cq-5), 143.49 (d, 1J ¼ 37.1 Hz, Cq-3a), 145.46 (d, 2J ¼ 8.0 Hz, Cq-7a),
162.38 (d, 1J ¼ 51.7 Hz, C-2), 166.48 (d, 2J ¼ 21.2 Hz, COOH). 31P{1H}
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NMR (d8-THF):
for [M]þ 207.0449; found: 207.0463.
d
115.0. HRMS (DEIþ): C10H11NO2P (207.17), calcd.
Pentacarbonyl-h1P-(1-methyl-1H-1,3-benzazaphosphole-2-
carboxylic acid)tungsten(0) (12a)
A solution of W(THF)(CO)5 was prepared by irradiation of
W(CO)6 (81 mg, 0.23 mmol), dissolved in THF (85 mL), by using a
medium pressure mercury UV-immersion lamp (2.5 h, 20 ꢁC). Then
11a (40.6 mg, 0.21 mmol) was added. After stirring for 24 h the
solvent was removed and the residue extracted with diethyl ether.
Removal of the solvent gave 74 mg (68%) pale brown solid. 1H NMR
(d8-THF):
d
¼ 4.32 (d, 4JPH ¼ 3.4 Hz, 3H, NCH3), 7.34 (tdd, 3J ¼ 8.1, 6.9,
4J ¼ 0.9, JPH ¼ 2.1 Hz, 1H, H-5), 7.61 (ddt, 3J ¼ 8.7, 6.9, 4J ¼ 1.5,
5JPH ¼ 2 Hz, 1H, H-6), 7.89 (br d, 3J ¼ 8.7 Hz, 1H, H-7), 8.02 (tt,
3J z 3JPH z 8.1, 4J z 5J z 0.9 Hz, 1H, H-4). 13C{1H} NMR (d8-THF):
5
b) B. Niaz, F. Iftikhar, M.K. Kindermann, P.G. Jones, J. Heinicke, Eur. J. Inorg.
Chem. (2013) 4220e4227;
c) M. Ghalib, B. Niaz, P.G. Jones, J.W. Heinicke, Tetrahedron Lett. 53 (2012)
5012e5014;
d) B.R. Aluri, B. Niaz, M.K. Kindermann, P.G. Jones, J. Heinicke, Dalt. Trans. 40
(2011) 211e224;
e) B.R. Aluri, M.K. Kindermann, P.G. Jones, I. Dix, J.W. Heinicke, Inorg. Chem. 47
(2008) 6900e6912.
d
¼ 35.38 (s, NeCH3), 115.63 (d, 3J ¼ 4.0 Hz, C-7), 122.53 (d,
3J ¼ 15.9 Hz, C-5), 128.36 (d, 4J ¼ 11.9 Hz, C-6), 129.41 (d, 2J ¼ 5.3 Hz,
C-4), 137.89 (d, 1J ¼ 25.3 Hz, Cq-3a), 146.37 (d, 2J ¼ 2.7 Hz, Cq-7a),
154.21 (d, 1J ¼ 27.9 Hz, COOH),163.45 (d, 2J ¼ 17.2 Hz, COOH), 195.29
(d, sat, 2J ¼ 10.7, 1JCW ¼ 126.0 Hz, 4 cis-CO), 200.15 (d, 2J ¼ 33.2 Hz,
[7] a) L. Nyulászi, Chem. Rev. 101 (2001) 1229e1246;
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Chem. (2001) 2563e2567.
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187e202.
trans-CO). 31P{1H} NMR (d8-THF):
d
¼
84.64 (satellites,
1JPW ¼ 260.8 Hz). IR (KBr): nCO ¼ 2078 (wm), 1928 (vs) cmꢀ1. MS (EI,
70 eV, 90 ꢁC): m/z (%) ¼ 517 (0.3) [Mþ], 461 (0.5), 377 (1.2), 349 (0.6),
306 (0.8), 193 (4.8). HRMS (ESI in MeOH): C14H9NO7PW (518.04),
calcd. for [M(184W)þH]þ 517.9621; found: 517.9623 and correct
isotopic pattern.
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52 (2014) 664e670.
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Crystal structure analysis of 7b and 10c
Crystals of 7b and 10c were mounted on glass fibers in inert oil,
and data (Table 1) were recorded at 100 K on an Oxford Diffraction
Xcalibur E diffractometer using MoKa-radiation. Absorption cor-
rections were based on multi-scans. The structures were refined by
full-matrix least-squares on F2 [22]. Hydrogen atoms were included
using a riding model or rigid methyl groups.
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