Complexes of Azaphospholes: Synthesis and Structure of Pentacarbonyl-(η1)-2-phosphaindolizinechromium(0), -molybdenum(0), and -tungsten(0)

Article abstract of DOI:10.1002/(SICI)1099-0682(199808)1998:8<1079::AID-EJIC1079>3.0.CO;2-U

The complex chemical behaviour of 2-phosphaindolizines 1 (1,3-azaphospholo[1,5-a]pyridines) towards metal carbonyl compounds was studied. (η¹-2-Phosphaindolizine)M(CO)₅ complexes 2-4 (M=Cr, Mo, W) were formed from 1 and [(THF)M(CO)

Full text of DOI:10.1002/(SICI)1099-0682(199808)1998:8<1079::AID-EJIC1079>3.0.CO;2-U

FULL PAPER
Complexes of Azaphospholes: Synthesis and Structure of
Pentacarbonyl-(η1)-2-phosphaindolizine)chromium(0), -molybdenum(0),
and -tungsten(0)
Neelima Guptaa[°], Chandra B. Jaina[°], Joachim Heinicke*a, Raj K. Bansal*b, and Peter G. Jonesc
Institut für Anorganische Chemie, EMA-Universität Greifswalda,
17487 Greifswald, Germany
Fax (internat.) ϩ49 (0)3834/ 864319
E-mail: heinicke@rz.uni-greifswald.de
Department of Chemistry, University of Rajasthanb,
Jaipur 302004, India
Fax: (internat.) ϩ91(0)141/652784
Institut für Anorganische und Analytische Chemie, Technische Universität Braunschweigc,
Postfach 3329, D-38023 Braunschweig, Germany
E-mail: p.jones@tu-bs.de
Received March 30, 1998
Keywords: Phosphorus heterocycles / P ligands / Transition metals / Carbonyl complexes
The complex chemical behaviour of 2-phosphaindolizines 1
(1,3-azaphospholo[1,5-a]pyridines) towards metal carbonyl
strong upfield signal (δ31P = 6.1) was observed with a
coordination shift of ∆δ = –161.7, which is typical for π-
compounds was studied. (η1-2-Phosphaindolizine)M(CO)5 coordination. Prolonged reaction or work-up led, however, to
complexes 2–4 (M = Cr, Mo, W) were formed from 1 and
[(THF)M(CO)5], the cis-L2Cr(CO)4 complex 5f from 1f and
dismutation yielding 1g and the fac-L3Mo(CO)3 complex 6g.
X-ray structure analysis of 2a indicates an increased 10π-
tetracarbonyl(norbornadiene) chromium(0). The reaction of delocalization compared with 1a and
a
changed
2-phosphaindolizines 1e, 1f, or 1g with tricarbonyl(cyclo-
heptatriene)molybdenum(0) or tricarbonyl(mesitylene)-
tungsten(0) yielded σ-complexes of the types L2M(CO)4 or
L3M(CO)3 rather than isolable π-complexes. In one case a
conformation of the acyl substituent. The influence of
substituents and metals on the 31P and 13C complexation
chemical shifts and coupling constants is discussed.
pholes[10][11][12] but very little is known about their behav-
iour in complex formation. Only two η1-LCr(CO)5 com-
plexes with the ligands 2-phenyl-1,3-benzazaphosphole[13]
and 2-phosphaindolizine[14] have been reported, which exhi-
bit even lower 31P-coordination shifts than related η1-di-
and -triazaphosphole[11][15] and η1-phosphabenzene com-
plexes[16] with sp2(pπ) hybridized phosphorus. This may be
viewed in association with the reduced σ- and the increased
π-charge density at phosphorus[10][14] in these π-excess het-
erocycles. These various aspects prompted us to investigate
complexation reactions of neutral and anionic 1,3-azaphos-
pholes or more easily accessible annelated representatives
thereof and to study the preferred coordination mode and
possible alternatives. We report here on reactions of 2-phos-
phaindolizines[14][17][18] with group VI metal carbonyl com-
plexes and the characterization of the complexes by NMR
and, for 2a, by X-ray structural analysis.
Introduction
The coordination behaviour of five-membered π-excess
heterocycles has found considerable interest[1][2][3][4][5]
.
Mono-, di-, and triphosphole anions exhibit different coor-
dination modes but, like cyclopentadienyl anions, they pref-
erably form η5-complexes[1][2][6] emphasizing the similarities
of PϭC and CϭC structural units[7]. Pyrroles and pyrrole
anions also form various types of complexes with π- and σ-
coordination. Simple sandwich or η5-coordinate (tricarbon-
yl)transition metal(0) complexes of pyrroles or pyrrole
anions, however, need sterical stabilization by suitable sub-
stituents[4]. Thus, tricarbonyl(η5-pyrrole)chromium(0) com-
plexes belong to the most labile π-complexes with benzene-
like ligands, reacting even with THF or benzene by ligand
substitution[8], in sharp contrast to the η5-phosphole or η5-
arsole complexes. 1H-1,3-azaphospholes and their anions,
contain both two-coordinate phosphorus and three-coordi-
nate nitrogen; they are aromatic 6π-systems even in the neu-
tral state and, according to the PϭC/CϭC-similarity prin-
ciple, should resemble the pyrroles[9][10]. There are several
studies on azaphospholes and annelated azaphos-
Results and Discussion
Synthesis of Phosphaindolizine Carbonyl Complexes
Various substituted 2-phosphaindolizines 1 bearing an
[°]
Present Address: University of Rajasthan.
electron-withdrawing substituent R2 such as acyl, carbalk-
Eur. J. Inorg. Chem. 1998, 1079Ϫ1086
WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1998
1434Ϫ1948/98/0808Ϫ1079 $ 17.50ϩ.50/0
1079

N. Gupta, C. B. Jain, J. Heinicke, R. K. Bansal, P. G. Jones
FULL PAPER
oxy or p-nitrophenyl in 3-position and a further substituent
(Me, nBu or Ph) in position 1, 6, or 7 were treated at room
temperature with [(THF)M(CO)5] (M ϭ Cr, Mo, W). This
led to selective formation of (η1-2-phosphaindoli-
zine)M(CO)5 complexes 2؊4. The carbonyl or nitro groups
did not interfere. Extractive purification or recrystallization
of the crude products with hexane afforded powdery or
crystalline, analytically pure, pale to dark yellow complexes.
They were characterized by 31P (Table 1), 1H (Table 2), and
13C NMR (Table 3) as well as by infrared spectroscopy
Solely during the reaction of excess 1g with tricarbonyl-
(Table 4) and (for 2a) by X-ray structural analysis (Figure (cycloheptatriene)molybdenum(0) in tetrahydrofuran at
1). The spectroscopic data and structure are discussed be- room temperature could a strong upfield signal at δ31P ϭ
low.
6.1 with a coordination shift of ∆δ ϭ Ϫ161.7 be observed,
The reaction of 1e with [(THF)Cr(CO)5] to 2e (δ31P ϭ which is close to the phosphorus resonance δ31P ϭ 4.3 and
190.6) was accompanied by formation of a smaller amount ∆δ ϭ Ϫ173.9 of tricarbonyl-η3-(2,4,6-triphenylphosphaben-
of the tetracarbonyl bis(phosphaindolizine) complex 5e zene)chromium(0)[20]. On prolonged reaction or attempted
(δ31P ϭ 201.5). Recrystallization of the crude product af- isolation this signal disappeared, however, and only 1g and
forded, however, only pure 2e. The synthesis of tetracar- the fac-L3Mo(CO)3 complex 6g (δ31P ϭ 181.2) were de-
bonyl bis(phosphaindolizine) complexes can be achieved by tected. This suggests formation of a little stable π-complex
refluxing 1 with tetracarbonyl(norbornadiene)chromium(0) that underwent dismutation. Curiously, if the reaction was
in petroleum ether. In this way, 1f gave an orange-yellow performed in a 1:1 ratio using the same solvent and reaction
mixture of two complexes, 2f (δ31P ϭ 190.8) and 5f (δ31P ϭ conditions, the isomeric mer-L3Mo(CO)3 complex 7g
202.3). Recrystallization from hexane gave 5f. Structure [δ31P ϭ 196.3, d, 2 Ptrans; 203.8, t, 1 Pcis; J(31P-31Pcis) ϭ
2
elucidation is based on 13C and H NMR investigations. 9.3 Hz] was obtained. Formation of 7g was also observed
1
The appearance of two triplets of equal intensity in the 13C- if CDCl3 was used as solvent. Attempts at extractive purifi-
NMR spectrum at δ ϭ 217.0 [2J(31P-13C) ϭ 17.2 Hz, cis cation or reaction in refluxing ether/hexane furnished a
CO] and δ ϭ 224.0 ( JAX ϩJAЈX ϭ 20.2 Hz, trans CO) be- mixture of 6g and 7g. The structure assignment is sup-
sides the signals for the ligand indicates the presence of two ported by proton-coupled phosphorus spectra. In 6g the
equally populated types of carbonyl groups and thus proves proton coupling with the initial phosphorus singlet led to a
5f to be the tetracarbonyl-cis-bis(η1-2-phosphaindolizi- symmetric multiplet with seven resolved lines, lines 1 and 7
ne)chromium(0) complex. It should be mentioned that the being weak, lines 3 and 5 broad. A calculated spectrum[22]
2
2
cis-L2M(CO)4 isomers were also formed preferentially in with δ31P ϭ 173.13, J(31P-31P) ϭ 30 Hz and J(PH1) ϭ
the reaction of triphenylphosphabenzene with tetracar- 30.8 Hz is in good accordance with the experimental coup-
bonyl(norbornadiene) complexes of group VI[16a] whereas ling pattern. It consists of 9 inner lines, two pairs of which
thermal reactions of phosphanes and the metal hexacar- lie close together to form the experimental lines 3 and 5.
bonyls provide mixtures of cis and trans complexes[19]
.
Weak outer lines are hinted at in the spectrum by a raised
base line. In 7g the Pc triplet becomes a double triplet by
coupling with the H-1 proton within the ligand, while the
doublet corresponding to the Ptrans ligands is split into a
multiplet with five strong lines. A simulation using
Scheme 1
δ31P(C6D6) ϭ 193.34, 200.90, 2J(31P-31Pcis) ϭ 9.3 Hz,
2
2J(31P-31Ptrans) ϭ 41 Hz and J(PH1) ϭ 30.8 Hz (δH1
ϭ
6.38) fits with the experimental spectrum (Figure 1). Since
2J(PH1) is similar to the respective coupling in 3g (31.5 Hz)
2
and J(31P-31P) generally larger in trans than in cis com-
plexes these values seem reasonable.
In the reaction of 1f with tricarbonyl(cycloheptatriene)-
In view of the existence of σ- and π-coordination modes molybdenum(0), initial formation of probably 6f was ob-
in carbonyl complexes of phosphabenzene[16][20][21], phos- served by a singlet at δ31P ϭ 178.9 and a line form of the
phole anions[1][2], and π-excess heterocycles such as pyr- proton-coupled phosphorus multiplet resembling rather a
role[3][4][5], we tried to obtain η5-2-phosphaindolizine π- fac-L3Mo(CO)3 than a trans-L2Mo(CO)4 coupling pattern.
complexes. However, isolable π-complexes were obtained However, this complex proved to be unstable in extractive
neither on prolonged irradiation by a high-pressure mer- work-up and subsequently underwent dismutation yielding
cury lamp, e.g. of 4b in hexane, nor on heating, nor from the LMo(CO)5 complex 3f (δ31P ϭ 169.3), which could be
the reactions of 2-phosphaindolizines 1e, 1f, or 1g with isolated in spectroscopically and analytically pure form
tricarbonyl(cycloheptatriene)molybdenum(0) or tricarbon- (Tables 1Ϫ4). Prolonged heating of 1e with tricarbonyl(me-
yl(mesitylene)tungsten(0). Instead, a variety of σ-complexes sitylene)tungsten(0) in THF afforded a mixture of 6e
1
of the types L2M(CO)4 or L3M(CO)3 were formed.
[δ31P ϭ 149.6, J(31P-183W) ϭ 265 Hz, multiplet with five
1080
Eur. J. Inorg. Chem. 1998, 1079Ϫ1086

Complexes of Azaphospholes
FULL PAPER
Figure 1. Proton-coupled phosphorus spectra of 6f (left) and 7f hybridization) may be compared with complexes of elec-
(middle and right)
tron-poor phosphanes, which are weak σ-donor but more
efficient π-acceptor ligands. In fact, ∆δ31P of the 2-phos-
phaindolizine complexes 2؊4 is somewhat lower than
∆δ31P of (MeO)3PMVI(CO)5
and similar to the η1-
[26][27]
[16]
phosphabenzene complexes 2,4,6-Ph3C5H2PMVI(CO)5
.
The electron-withdrawing effect of nitrogen and -M groups
in α-position to phosphorus is partly compensated by the π-
excess character of the 1,3-azaphosphole ring. The stronger
upfield coordination shifts of the pivaloyl and phenacyl de-
rivatives a-d may be attributed to the changed confor-
mations with increased anisotropy and reduced ϪM effects
on phosphorus as compared to the free ligand. The one-
bond 31P-183W couplings of 4 (253Ϫ268 Hz) are larger than
those in (triorganophosphane)W(CO)5 complexes which,
however, increase with the group electronegativity of R in
[23][24][25][26]
R3PW(CO)5
.
Proton NMR: The chemical shifts and almost all coup-
ling constants of free ligands 1aϪh[14][17][18] and their com-
plexes (Table 2) in CDCl3 are very similar. Thus the differ-
ences of respective δ values of the complex 2e and the li-
gand 1e in CDCl3 are less than 0.13. However, a strong
influence on the proton resonance is exerted by deuteroben-
zene. Almost all signals of phosphaindolizine protons in
2Ϫ4 are upfield shifted by ∆δ ϭ 0.6 to 1.1 in C6D6 as com-
pared to the ligands in CDCl3. Methyl groups in position 7
and 1 are also affected, but to a lower extent. Phenyl groups
are at most slightly influenced, indicating stacking interac-
tions between C6D6 and the phosphaindolizine ring. The
lack of an upfield shift of H-5 in the 3-carbalkoxy deriva-
tives 3e, 4e, 2f, and 3f can be attributed to a superimposed
deshielding anisotropy effect of the carbonyl group of
COOR (R ϭ Me, Et). Another exception, the extreme in-
crease of δ(H-5) in 2a (∆δ ϭ 2.75), 4a (∆δ ϭ 2.34), and 5a
(∆δ ϭ 2.58) compared to 1a in CDCl3, is associated with a
change in conformation of the 3-pivaloyl substituent which
is also found for the solid state. In crystalline 1a, the acyl
group is arranged nearly coplanar to the ring system (tor-
sion angle PϪC1ϪCϭO 178°) with the tert-butyl group at
the P-side, whereas in the chromium complex 2a the latter
is oriented to the N-side of the azaphosphole ring, adopting
a staggered conformation (see below). This arrangement
shields the proton in position 5. Concerning proton coup-
lings, the only marked changes between 1 and 2؊4 are the
[a]Each two unresolved lines (calculated 21528, 21530; 21514,
[b]
21512), of which only the stronger one is seen. Ϫ
Small lines
(calculated 23541, 23532; 23440, 23449) are superimposed by noise.
broad lines by 31P-1H coupling] and 4e (δ ϭ 140.2, quartet
by 31P-1H coupling).
The phosphaindolizine carbonyl complexes are less stable
than phosphane carbonyl complexes and are attacked by
water and by air, slowly in the solid state and more rapidly
in solution. In a moist CDCl3 solution of 4a we observed
the phosphorus resonance of 1a. After four days, signals of
1a and an addition product (δ31P ϭ 128.5) are exhibited
(intensity 1:2) and after a further day all of 1a and a part of
the addition product was decomposed to give a hydrolysis
product with δ31P ϭ 21.8. The volatility is low but sufficient
to record EI mass spectra of the complexes LM(CO)5. For
2f, 3f, 4e and 4h the molecular ion peaks Mϩ were ob-
served. The appearance of [M Ϫ CO]ϩ., [M Ϫ 2 CO]ϩ., [M
Ϫ 3 CO]ϩ., [M Ϫ 4 CO]ϩ. and [M Ϫ 5 CO]ϩ. peaks indi-
cates primary decomposition by the successive loss of car-
bon monoxide molecules from the LM(CO)5 moieties.
Further fragmentation follows similar pathways as for the
free ligand[18]
.
Spectra of Phosphaindolizine M(CO)5 Complexes and Structural
Aspects
3
solvent-independent increase of the magnitude of J(PH)
involving the 1-methyl protons by ∆J ϭ 3.7 to 5.3 Hz,
Phosphorus NMR: Preliminary reports of two Cr(CO)5 slightly increasing from chromium to tungsten and from the
complexes of annelated 1,3-azaphospholes, 2-phenyl-1,3- 3-pivaloyl to the 3-carbalkoxy derivatives, and the decrease
benzazaphosphole[13], and a 2-phosphaindolizine[14], had of the magnitude of 2J(31P-1H) of the protons in 1-position
indicated small 31P-coordination shifts of ∆δ ϭ 4.4 and 7.5, of 2b, 4b, 4d, and 3g relative to the respective ligands by
respectively. The larger body of data for 2؊4 (Table 1) now 7Ϫ8 Hz.
reveals a much broader range of ∆δ31P and allows a com-
Carbon NMR: In contrast to organometallic compounds,
parison with LMVI(CO)5 complexes of phosphane and het- phosphane complexes have not been extensively investi-
erocyclic σ2-phosphorus ligands. The coordination shift in gated with respect to the impact of coordination on carbon
complexes R3PMVI(CO)5 becomes smaller with increasing chemical shifts and couplings in the ligands[23][24][25]. In the
group electronegativity of R, for Hal3PMVI(CO)5 even 13C NMR spectra of 2؊4 (Table 3) we observed trans 13CO
negative[23][24][25][26]. η1-Complexes of σ2-phosphorus com- (δ ϭ 197-225) at lower field than cis carbonyls (δ ϭ
pounds possessing a higher s-character at phosphorus (sp2 194Ϫ215) and for both an increasing shielding in the series
Eur. J. Inorg. Chem. 1998, 1079Ϫ1086
1081

N. Gupta, C. B. Jain, J. Heinicke, R. K. Bansal, P. G. Jones
Table 1. 31P-NMR chemical shifts (δ ) of 1Ϫ4 and coordination shifts (∆δ)
FULL PAPER
R1
R2
R3
R4
δ 1
δ 2
M ϭ Cr
∆δ (2؊1) δ 3
M ϭ Mo
∆δ (3؊1) δ 4 (1JPW, Hz) ∆δ (4؊1)
M ϭ W
a
b
c
d
e
f
CH3
H
COC(CH3)3
COC6H5
COC6H5
COC6H5
COOC2H5
COOCH3
CN
H
H
H
H
172.1
179.9
183.6
155.4
184.6
Ϫ16.7
ϩ4.7
135.3
164.3
Ϫ36.8
Ϫ19.3
108.2 (258.2)
133.4 (253.7)
Ϫ63.9
Ϫ46.4
nBu
H
CH3
H
H
CH3 182.5
137.1 (264.2)
140.2 (268.1)
Ϫ45.4
Ϫ25.3
CH3
CH3
H
H
H
H
165.5
165.8
190.6
190.8
ϩ25.1
ϩ25.0
167.5
169.3
169.9
ϩ2.0
ϩ3.5
ϩ5.4
H
g
h
H
CH3 164.5
C6H5
C6H4-NO2(p)
H
H
130.6
105.2 (262.4)
Ϫ25.4
1
Table 2. H-NMR data of the complexes 2؊4[a]
δ
2a
2b
2e
2f
3a 3c 3e 3f 3g 4a
4b
4d
4e
4h
5e
5f
J [Hz]
1-H
7.09
28.3
6.38
31.5
6.95 6.85
27.8 28.3
2J(P,H)
5-H
7.49 9.51 9.95 9.80 7.90 9.48 9.87 9.81 7.48 7.66 9.57 9.55 9.86 7.21 9.91 9.90
4J(P,H)
3J(5-H,6-H)
4J(5-H,7-H)
6-H
1.8
7.2
0.9
1.9
7.3
1.1
1.9
7.3
0.9
1.6
7.3
1.3
1.5
1.9
7.3
0.9
1.4
6.8
1.1
7.1
7.3
0.9
7.3
0.8
7.3
7.2
7.4
7.3
7.2
0.8
[b]
[c]
5.87
1.1
7.0
1.1
6.89 6.12 5.98 6.05 6.16 6.14 5.70 5.91
5.96 6.14 5.95 6.82 6.09
1.5
5J(P,H)
3J(6-H,7-H)
4J(6-H,8-H)
7-H
1.3
7.0
1.4
1.2
7.1
1.4
6.4
1.3
1.3
6.7
1.3
1.3
6.9
1.0
1.2
1.3
7.0
1.3
1.3
6.8
1.5
0.6
6.6
7.0
6.9
6.8
1.0
[d]
[e]
6.24 6.71 7.22 6.41 6.30 6.41 6.43 6.40
6.27 6.45
6.41 6.30 7.15 6.36
1.6
8.9
5J(P,H)
3J(7-H,8-H)
8-H
1.2
9.1
1.4
8.9
1.4
8.9
1.3
9.3
1.5
8.9
1.5
8.9
1.3
9.0
1.3
9.0
1.3
9.1
9.0
9.1
8.9
8.9
6.58 6.47 7.43 6.54 6.66 6.63 6.60 6.57 6.29 6.58 6.70 6.41 6.55 7.08 7.32 6.53
4J(P,H)
R1:
1.1
2.5
2.5
2.5
2.5
1.2
2.4
1.9
2.6
1.1
[f]
CH3
2.21
16.0
2.58 2.12 2.25 2.22 2.13 2.10
16.7 16.7 16.2 16.8 16.9 16.9
2.15
16.6
2.07
17.3
2.35 2.15
3J(P,H)
(m)
(m)
R2:
OCH2/OCH3
CH3
4.47 3.65
1.46
7.1
4.28 3.64
1.26
7.1
4.28
1.25
7.1
4.26 3.61
1.22
7.0
3J(H,H)
COC(CH3)3
o-H
1.19
1.30
1.23
7.83
7.17Ϫ
7.19
7.82
7.20
7.86
7.16Ϫ
7.21
7.43
7.94
m-, p-H
[a]
[b]
[c]
2e and 5e in CDCl3, others in C6D6. Ϫ 6-Bu: α-CH2: δ ϭ 2.12; β-CH2: δ ϭ 1.35; γ-CH2: δ ϭ 1.30; δ-CH3: δ ϭ 0.83. Ϫ 6-Bu: α-
[d]
[e]
[f]
CH2: δ ϭ 2.11; β-CH2: δ ϭ 1.28; γ-CH2: δ ϭ 1.14; δ-CH3: δ ϭ 0.80. Ϫ
δ ϭ 6.88; m-H: δ ϭ 7.37; p-H: δ ϭ 7.18.
7-CH3: δ ϭ 1.66. Ϫ 7-CH3: δ ϭ 1.74. Ϫ 1-C6H5: o-H:
Cr, Mo, W. This can be seen e.g. for the series 2e, 3e, 4e group and reduced π-charge density at C-CO by loss of de-
where each ∆δ is about 10. The magnitude of the two-bond localization compared to the coplanar free ligand. Marked
coupling with the phosphorus decreases for cis carbonyls coordination shifts for C-5 are found in the phenacyl de-
in the order Cr, Mo, W pentacarbonyl (ca. 17, 12, 9 Hz, rivatives, nearly no effect for 3c, shielding for 4b and de-
respectively) and increases with the metal radii for the re- shielding for 4d, whereas δ(3-CO) is slightly influenced by
spective trans carbonyls (ca. 4 << 32 , 32 Hz), causing small the coordination, suggesting a torsion of the phenyl ring
trans couplings in chromium carbonyl P-complexes. around the CϪC(O) axis to give the minimum energy ar-
Marked differences in some carbon chemical shifts and rangement. A general upfield shift on coordination for C-1
coupling constants occur also between free and coordinate and, except for 2a and 4a, also for C-3, with a slight in-
phosphaindolizines and can be attributed to steric and elec- crease from chromium to tungsten, may be assigned to elec-
tronic effects. The solvent influence, in contrast to proton tronic as well as steric influences, viz. the change in hy-
NMR data, is essentially negligible as can be seen, e.g., by bridization of phosphorus, back-bonding and steric shield-
the very small differences of δ13C (< 0.6) and J(31P-13C) ing by the M(CO)5 group. The same holds to an reduced
(Յ1) of 4b in CDCl3 and C6D6. The upfield coordination extent for the α-C atoms of the substituents at C1 and C3,
shift for C-5 and the opposite change for C-3 and the 3- reflecting inductive effects. The lack of noticeable shift dif-
carbonyl groups in 2a and 4a, not observed in other deriva- ferences for C6 to C9 in free and coordinated ligands sug-
tives, are attributed to the distortion of the 3-pivaloyl gests that back donation, ascribed to (dM-π*)π bonding[25]
group, causing enhanced shielding of C-5 by the tert-butyl has a rather localized effect. Indeed, according to PM3 cal-
,
1082
Eur. J. Inorg. Chem. 1998, 1079Ϫ1086

Complexes of Azaphospholes
FULL PAPER
2
3
culations[28] phosphorus has the highest coefficient in the 13C9) and J(31P-3-13CO), whereas J(31P-13C8) are usually
LUMO (π*-orbital) of 2-phosphaindolizine (ε ϭ Ϫ0.77 eV, increased.
c2 ϭ 0.50) and is separated by nodal planes from C1 and
X-ray Analysis of 2a
C3.
A strong decrease in 1J(31P-13C) coupling constants is ob-
X-ray structure analysis of the Cr(CO)5 complex 2a (Fig-
served by complexation. For C1 and C3 one-bond 31P-13C ure 2) shows a planar ring system (mean deviation 3 pm)
coupling constants are in the range 18Ϫ30 Hz and 10Ϫ37 with trigonal planar coordination at phosphorus; the metal
Hz as compared to 38Ϫ44 and 45Ϫ59 Hz, respectively, in lies only slightly outside the plane (12 pm). The endocyclic
the free ligands[14][17][18]. The absolute magnitude of 1J(31P- angle at phosphorus in the rigid five-membered ring is not
13C3) increases with the electron-withdrawing effect of the greatly affected by the steric requirements and thus only
3-substituent R2 in the order C6H4-4-NO2 << COOEt < slightly opened, from 91.9(2)° in 1a[18] to 93.5(1)° in 2a.
COOMe ഠ or < COPh ഠ COtBu. The much lower one- The PϪC bond lengths become more equal [172.4, 171.7(2)
bond couplings in the complexes may be attributed to the pm] on complexation than in the free ligand [174.7(3),
participation of the s-orbital in the hydridization of phos- 170.8(4) pm] and on average shorter (172.1 versus 172.8
1
phorus. The smaller differences between J(31P-13C1) and pm) indicating more effective delocalization. The rotation
1J(31P-13C3) in the complexes reflect a higher degree of de- of the pivaloyl group from a coplanar arrangement (di-
localization and aromaticity than in the ligands themselves. hedral angle PϪC1ϪCϭO 178°) in 1a to a staggered con-
This is consistent with nearly equal PϪC bond lengths in formation with ␽(PϪC1ϪC9ϪO1) ϭ 45.5° in 2a prevents
2a, whereas they differ in 1a. In rounding off this section it the strong -M interactions possible in 1a and is certainly
should be mentioned that two-bond couplings are also re- an important factor in the increase in aromaticity. Another
duced on complexation, 2J(31P-1-13CH3) larger than 2J(31P- factor may be the change in hybridization from p2 to sp2
Table 3. 13C-NMR data of the complexes 2Ϫ4[a]
δ
2a
2e
2f
3c
3e
3f
3g
4a
4b
4d
4e
4h
5f[b]
J in Hz
[c]
C-1
130.3
18.3
147.0
10.0
126.7
Ϫ
132.5
22.9
130.0
18.3
129.6
2.3
132.2
23.0
130.1
18.4
129.1
Ϫ
131.7
22.2
129.5
19.1
129.6
2.4
132.4
22.3
129.6
19.7
130.1
2.3
129.7
22.5
145.4
14.7
127.2
Ϫ
128.6
25.1
143.4
17.0
127.1
Ϫ
121.6
28.3
139.7
12.7
128.2
1.7
120.3
28.6
139.4
13.5
137.1
2.3
130.8
29.4
127.4
28.2
129.8
7.8
134.4
25.5
145.1
36.9
123.8
Ϫ
132.0
23.3
129.3
12.1
128.3
8.0
112.7
<1.0
123.9
<1.0
115.1
11.4
143.6
7.3
1J(CP)
C-3
133.2
19.3
130.0
2.0
113.3
Ϫ
1J(CP)
C-5
3J(CP)
C-6
112.0
113.2
4.8
113.3
113.7
4.7
113.8
4.9
116.8
112.6
125.7
116.2
4.5
113.7
5.1
112.9
4J(CP)
C-7
4.0
4.7
4.7
4.4
Ϫ
127.9
2.0
3.8
120.7
3.0
124.1
3.2
115.3
11.3
143.6
5.7
11.3
14.4
163.0
17.7
60.7
14.4
124.2
3.0
124.7
3.2
123.4
2.9
115.7
11.7
143.3
5.7
11.4
15.6
162.8
16.8
60.6
14.4
124.0
3.0
116.4
11.2
144.0
5.7
11.9
16.0
163.6
17.0
51.3
122.5
2.9
121.2
2.6
129.5
Ϫ
124.3
3.0
116.0
11.7
143.6
4.6
11.6
14.9
163.0
17.4
60.8
14.5
121.3
1.8
4J(CP)
C-8
116.2
17.0
140.6
4.0
115.3
11.3
143.7
5.7
115.9
117.9
11.8
147.6
116.8
11.2
140.6
2.9
118.0
12.4
145.6
117.1
12.4
147.0
118.0
9.5
3J(CP)
C-9
Ϫ
143.7
5.8
11.8
15.3
186.8
20.5
140.3
2J(CP)
R1: CH3
2J(CP)
R2: CO/CN
2J(CP)
OCH2/OCH3
CH3
Ϫ
8.4
8.3
Ϫ
[d]
[e]
[f]
[g]
10.9
14.9
204.9
12.0
11.3
14.5
163.1
17.4
50.6
14.4
11.3
15.3
204.9
12.1
11.5
14.4
163.6
19.6
50.9
117.5
19.7
186.6
20.6
186.3
20.6
27.5
45.7
27.1
1.6
45.7
4J(CP)
C(CH3)3
C-i
140.8
1.8
140.5
1.8
140.6
1.8
137.4
13.6
137.3
7.4
129.4
148.2
1.6
2/3J(CP)
C-o
130.8
2.9
131.3
2.9
131.3
3.0
3/4J(CP)
C-m
129.0
132.5
129.0
132.7
129.0
132.6
C-p
5J(CP)
M(CO)5:
CO(cis)
1J(CW)
2J(CP)
CO(para)
1J(CW)
2J(CP)
215.2
214.6
214.6
203.6
204.3
204.9
208.8
194.9
125.2
8.7
198.4
151.4
30.7
194.5
125.7
8.7
198.2
148.8
32.2
194.6
125.6
8.8
194.4
125.5
9.4
198.7
151.6
32.0
194.2
128.9
8.7
197.8
145.2
31.0
217.0
16.0
221.1
17.2
220.9
17.3
220.9
10.7
209.6
11.7
210.0
11.8
210.6
11.9
225.1
17.2
224.0
198.3
[h]
[i]
5.0
3.9
3.8
31.9
31.9
33.0
32.2
20.2
[a]
[b]
[c]
4e in CDCl3, others in C6D6. Ϫ Coupling constants are not J values but N ϭ ͉JAX Ϫ JAЈX͉ values. Ϫ Merged in C6D6 peak. Ϫ
[d]
[e]
[f]
[g]
7-CH3: δ ϭ 20.9. Ϫ α-C: δ ϭ 32.7; β-C: δ ϭ 32.5; γ-C: δ ϭ 22.4; δϪC: δ ϭ 13.9. Ϫ 7-CH3: δ ϭ 20.4. Ϫ
1-C6H5: i-C: δ ϭ
[h]
133.6 (JPC ϭ 12.8); o-C: δ ϭ 130.9 (JPC ϭ 6.9); m-C: δ ϭ 124.5; p-C: δ ϭ 129.2. Ϫ Not observed due to small intensity of signal. Ϫ
[i]
Not resolved.
Eur. J. Inorg. Chem. 1998, 1079Ϫ1086
1083

N. Gupta, C. B. Jain, J. Heinicke, R. K. Bansal, P. G. Jones
FULL PAPER
Figure 2. Structure of 2a in the crystal. Ellipsoids represent 50%
bonyl [440 mg of Cr(CO)6; 704 mg of W(CO)6 or 528 mg of
Mo(CO)6] in 200 ml of oxygen-free THF was irradiated using a
high-pressure mercury photo lamp with continuous stirring and
monitoring of the volume of CO evolved. [If with Mo(CO)6 the
reaction became slower, the irradiation was interrupted and argon
was bubbled through the solution to diminish the CO concen-
tration, using a separate outlet.] After evolution of 2 mmol (44.8
ml ) of CO the irradiation was stopped. The [(THF)M(CO)5] solu-
tion was added to a solution of the respective 2-phosphaindolizine
1 (2.0 mmol ) in THF and stirred overnight at room temperature.
The solvent was removed in vacuo and the residue extracted with
hexane (2 ϫ 50 ml). Shining crystals were obtained on leaving the
concentrated hexane extract (10Ϫ15 ml) in a refrigerator (Ϫ20°C).
If no crystals separated, the solvent was removed completely to
obtain yellow to orange powdery complexes. 2a, b, e, 3a, c, e, g, 4a,
b, d, e and h were synthesized in this manner. In case of the reaction
of 1e with [(THF)Cr(CO)5], formation of some 5e was observed in
addition to 2e. On recrystallization from hexane pure 2e was ob-
tained. NMR-spectroscopic data are given in Tables 1-3, substance
and IR data in Table 4.
probability levels. H atom radii are arbitrary[a]
[a]
Selected bond lengths [pm] and angles: CrϪC(14) 187.0(3),
Reaction of 1f with Tetracarbonyl(norbornadiene)chromium(0)
(2f and 5f): 207 mg (1.0 mmol) of 1f was refluxed with 256 mg (1.0
mmol) of tetracarbonyl(norbornadiene)chromium(0) in petroleum
ether (50 ml, b.p. 100Ϫ120°C ) for three hours. The colour of the
solution changed from yellow to orange. The reaction mixture was
filtered, and the filtrate placed in a refrigerator (ca. Ϫ20°C). Yel-
low-orange crystals consisting of 2f (δ31P ϭ 190.8) and 5f (δ31P ϭ
CrϪC(16) 189.8(3), CrϪC(15) 190.0(3), CrϪC(18) 190.3(3),
CrϪC(17) 190.6(3), CrϪP 232.50(14), PϪC(7) 171.7(2), PϪC(1)
172.4 (2), C(1)ϪN 138.2(3), NϪC(6) 140.4(3), C(6)ϪC(7) 138.7(3);
C(1)ϪPϪCr 135.95(8), C(7)ϪPϪCr 130.47(8), C(7)ϪPϪC(1)
93.51(11), NϪC(1)ϪP 109.6(2), C(1)ϪNϪC(6) 113.7(2),
C(7)ϪC(6)ϪN 113.2(2), C(6)ϪC(7)ϪP 109.9(2).
1
202.3) precipitated. For H- and 13C-NMR data see Tables 2 and
which makes the phosphorus more similar to carbon. In 2a
the CrϪP bond [232.50(14) pm] is slightly shortened com-
pared to a variety of R3PCr(CO)5 and phosphaalkene
Cr(CO)5 complexes (235-245 pm)[29] and also the CrϪC
bond of trans-CO [187.0(3) pm] is shorter (trans effect) by
3 pm than those of cis-CO (average 190.2 pm). Finally, it
should be mentioned that the averaged PϪCrϪC angles of
cis-and trans-carbonyls are 90.2° and 178.4°, respectively,
corresponding closely to ideal octahedral geometry around
chromium.
3. Extraction of the mixture with hexane afforded spectroscopically
pure 5f, yield 18%, m.p. 135Ϫ137°C.
Reactions of 1g with Tricarbonyl(cycloheptatriene)molyb-
denum(0) (6g and 7g) Ϫ A: 236 mg of 1g (1.35 mmol) and 123 mg
(0.45 mmol) of (cycloheptatriene)Mo(CO)3 were dissolved in THF.
31P NMR (THF/[D8]THF) spectra were recorded (i) after 18 hours
and (ii) after 2 days at room temperature. In the first case we ob-
served signals at δ (rel.int.) ϭ 6.1 (65), 11.4 (12), 167.8 (85) 1g and
181 (8) 6g, in the second case only at δ (rel.int.) ϭ 167.8 (110) and
181.2 (20).
Funding by the Deutsche Forschungsgemeinschaft and financial
support by the Fonds der Chemischen Industrie, Germany, is grate-
fully acknowledged. Furthermore, we appreciate the help by Dr.
M. K. Kindermann and B. Witt for numerous NMR measurements,
I. Stoldt for IR and Dr. A. Müller for mass spectra.
B: 130 mg (0.75 mmol) of 1g was stirred for 2 days with 203 mg
(0.75 mmol) of (cycloheptatriene)Mo(CO)3 in THF (40 ml) at room
temperature. 31P NMR (THF/[D8]THF) control showed only sig-
nals of 7g, δ ϭ 196.3, d; 203.8, t; 2J(31P-31P) ϭ 9 Hz, intensity ratio
2:1. Similarly, 7g is formed preferentially in CDCl3.
C: 120 mg (0.69 mmol) of 1g was refluxed for 2 days with 188
mg (0.69 mmol) of (cycloheptatriene)Mo(CO)3 in ether/hexane
(1:2). The precipitate was separated and washed with little hexane.
The 31P-NMR spectra of the solid, dissolved in C6D6, showed it to
Experimental Section
General Comments: All reactions were carried out under a dry
argon atmosphere using the Schlenk technique. Ϫ NMR spectra
were recorded on Bruker ARX 300 (31P-NMR at 121.5 MHz, 1H-
NMR at 300.1 MHz and 13C-NMR at 75.5 MHz). The chemical
shifts refer to 85% H3PO4 (external) or TMS (internal). Ϫ Mass
spectra were recorded on AMD 40(intectra), IR spectra on System
2000 of Perkin-Elmer. Ϫ The synthesis of the 2-phosphaindolizines
1a-h was recently reported[14][17][18]. [(THF)M(CO)5] were freshly
prepared before use[30], tetracarbonyl(norbornadiene)chromium(0)
was synthesized by refluxing chromium hexacarbonyl with norbor-
nadiene in light petroleum[31]. Tricarbonyl(cycloheptatriene)molyb-
denum(0) and tricarbonyl(mesitylene)tungsten(0) were commer-
cially available and used without further treatment. Melting points
of complexes are uncorrected and were determined in a capillary
under argon.
2
be a mixture of 7g (δ ϭ 193.3, d; δ ϭ 200.9, t; J(31P-31P) ϭ 9.3
Hz) and 6g (δ ϭ 177.1, s); proton-coupled 31P-NMR: 7g δ ϭ 193.3,
dt, 2J(31P-1H) ϭ 30.5 Hz, δ ϭ 200.8, multiplet; 6g δ ϭ 177.1, mul-
tiplet.
Reaction of 3f with Tricarbonyl(cycloheptatriene)molybdenum(0)
(3f and 6f): 207 mg (1.0 mmol) of 1f and 272 mg of (cycloheptatri-
ene)Mo(CO)3 was stirred in THF (50 ml) for two days. 31P-NMR
of the reaction mixture indicated 6f (δ ϭ 178.9) as major product,
along with 3f (δ ϭ 169.3). THF was removed and the residue ex-
tracted with hexane. On concentrating the filtrate, analytically and
1
spectroscopically pure 3f was obtained as a yellow solid. For H-
and 13C-NMR see Table 2 and 3, for substance data see Table 4.
Reaction of 2-Phosphaindolizines 1 with THF·M(CO)5 (2, 3, 4)
Ϫ General Procedure: A solution of 2.0 mmol of metal hexacar-
Reaction of 1e with Tricarbonyl(mesitylene)tungsten(0) ( 4e and
6e ): 111 mg (0.5 mmol) of 1e was heated with 194 mg (0.5 mmol)
1084
Eur. J. Inorg. Chem. 1998, 1079Ϫ1086

Complexes of Azaphospholes
FULL PAPER
Table 4. Substance and IR data of the complexes 2؊4
IR ν (CO)
mp
[°C]
yield
[%]
mol. formula
[m. wt.]
analysis found / calc. (%)
[cmϪ-1
]
C
H
N
2a
2b
2e
3a
3c
3e
3f
2071 m, 2004 w,
1954 s, 1940 s, 1915 sh
Ϫ
90Ϫ92
68Ϫ69
77
78
82
72
65
77
51
64
68
75
70
81
66
C18H16O6NPCr
(425.29)
50.93
50.83
56.21
56.68
46.15
46.50
46.26
46.07
49.34
49.09
42.53
42.03
40.49
40.65
40.16
40.99
39.08
38.80
45.61
44.61
42.13
41.62
36.16
35.25
43.12
43.93
4.02
3.79
3.44
3.72
2.67
2.93
3.28
3.44
2.73
2.47
2.72
2.65
2.43
2.28
1.81
1.72
2.83
2.90
3.14
2.93
2.13
2.10
2.54
2.22
2.16
2.00
3.34
3.29
2.61
2.87
3.29
3.39
2.75
2.99
2.93
2.86
3.04
3.06
3.28
3.16
6.98
6.83
2.37
2.51
2.23
2.26
2.39
2.43
2.24
2.57
4.32
4.27
C23H18O6NPCr
(487.35)
2069 m, 1995 sh,
1956 s, 1929 s,
Ϫ
164Ϫ65
89Ϫ90
C16H12O7NPCr
(413.24)
C18H16O6NPMo
(469.23)
2079 w, 1987 s,
1964 m, 1953 s, 1936 s
2075 m, 2035 w,
124Ϫ25
146Ϫ47
115Ϫ16
135Ϫ38
74Ϫ76
C20H12O6NPMo
(489.22)
C16H12O7NPMo
(457.18)
1986 m, 1961s, 1926 s
2075 m, 1987 m,
1961 s, 1948 s, 1926 s
2072 w,
C15H10O7NPMo
(443.15)
3g
4a
4b
4d
4e
4h
C14H7O5N2PMo
(410.1)
986 s, 1950 s
2077 m, 1995 w,
C18H16O6NPW
(557.14)
1970 sh, 1953 s, 1920 s
2078 m, 1999 w,
66Ϫ67
C23H18O6NPW
(619.20)
1952 s, 1920 sh
2079 m, 2007 m,
1970 s,1943 s, 1908 s
2074 m, 1993 m,
1954 s, 1935 s, 1917 s
2075 m, 1994 w,
166Ϫ68
179Ϫ81
170Ϫ71
C20H12O6NPW
(577.13)
C16H12O7NPW
(545.09)
C24H13O7N2PW
(656.18)
1961 s, 1930 s, 1918 sh
[6]
[7]
V. Caliman, P. B. Hitchcock, J. F. Nixon, L. Nyulaszi, N. Saka-
of tricarbonyl(mesitylene)tungsten(0) in THF (40 ml) for 20 hours
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intensity ratio of 14:8:78. After removal of THF, the residue was
extracted with hexane and filtered. Removal of the solvent in vacuo
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110Ϫ118°C) of 6e as major product with some 4e. Proton-coupled
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L. Nyulaszi, T. Veszpremi, J. Reffy, J. Phys. Chem. 1993, 97,
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1
31P NMR: 6e δ ϭ 149.6, multiplet, J(31P-183W) ϭ 263 Hz; 4e δ ϭ
3
140.2, q, J(31P-1H) ϭ 17 Hz.
[10]
[11]
X-ray Structure Analysis of 2a Ϫ Crystal Data: C18H16CrNO6P,
¯
triclinic, P1, a ϭ 905.9(3), b ϭ 977.8(4), c ϭ 1238.0(4) pm, α ϭ
94.13(3), β ϭ 97.52(3), γ ϭ 116.72(3)°, V ϭ 0.9604 nm3, Z ϭ 2,
µ ϭ 0.71 mm-1, Dx ϭ 1.471 Mg m-3, λ(Mo-Kα) ϭ 71.073 pm, T ϭ
Ϫ130°C. Data Collection: Yellow tablet 0.7 ϫ 0.5 ϫ 0.15 mm, Stoe
STADI-4 diffractometer, 2θmax 50°; 3622 intensities, absorption
correction with ψ-scans (transmissions 0.82Ϫ0.96), 3387 unique re-
flections (Rint 0.021). Structure Solution and Refinement: Direct
methods, refined on F2 using SHELXL-93[32]. Hydrogen atoms:
riding model or rigid methyls. Final wR(F2) 0.077 for all reflections,
conventional R(F) 0.032 for 248 parameters; S 1.06, max. ∆ρ 295
[12]
[13]
[14]
K. Issleib, R, Vollmer, Z. Allg. Anorg. Chem. 1981, 481, 22Ϫ32.
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e nmϪ3
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[17]
[18]
[19]
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Crystallographic data (excluding structure factors) have been de-
posited at the Cambridge Crystallographic Data Centre under the
number CSD 101226. Copies may be obtained free of charge from:
The Director, CCDC, 12 Union Road, Cambridge CB2 1EZ (Fax
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