Thiazoline- and oxazoline-annulated (η1-P)-1,3-azaphosphole-(pentacarbonyl)chromium, -molybdenum and -tungsten complexes

Article abstract of DOI:10.1016/S0022-328X(98)01075-4

The heterocycles 2,3-dihydro-1,3-azaphospholo[5,1-b]thiazole 1 and -oxazole 4 react with [(THF)M(CO)₅] 2 (M=Cr, Mo, W) selectively to give (η¹-P)-(2,3-dihydro-1,3-azaphospholo[5,1-b]thiazole and -oxazole)M(CO)₅ complexes 3

Full text of DOI:10.1016/S0022-328X(98)01075-4

Journal of Organometallic Chemistry 577 (1999) 337–341
Thiazoline- and oxazoline-annulated
(h1-P)-1,3-azaphosphole-(pentacarbonyl)chromium, -molybdenum and
-tungsten complexes
Chandra B. Jain a,1, Dinesh C. Sharma a,2, Neelima Gupta a,3, Joachim Heinicke a,*,
Raj K. Bansal b
a Institut fu¨r Anorganische Chemie, Ernst-Moritz-Arndt Uni6ersita¨t Greifswald, Soldmannstrasse 16, D-17487 Greifswald, Germany
b Department of Chemistry, Uni6ersity of Rajasthan, Jaipur 302 004, India
Received 25 September 1998
Abstract
The heterocycles 2,3-dihydro-1,3-azaphospholo[5,1-b]thiazole 1 and -oxazole 4 react with [(THF)M(CO)5] 2 (M=Cr, Mo, W)
selectively to give (h1-P)-(2,3-dihydro-1,3-azaphospholo[5,1-b]thiazole and -oxazole)M(CO)5 complexes 3 and 5, respectively. The
compounds are structurally characterized by NMR data which is discussed in relation to those of the free ligands. Supported by
PM3 calculation of 1 and 4, the preference to h1-P-coordination is discussed in terms of control by d(M)“p* back-bonding.
© 1999 Elsevier Science S.A. All rights reserved.
Keywords: Annulated azaphospholes; Transition metals; Pentacarbonyl complexes; h1-P coordination; NMR spectroscopy
1. Introduction
cently investigated the possible coordination modes of
pyrido annulated derivatives, namely 2-phosphaindoli-
zines, and observed the selective coordination through
s2-P. (h1-2-Phosphaindolizine)M(CO)5 complexes, re-
lated to (2-phenyl-1,3-benzazaphosphole)W(CO)5 [12]
and some di- and triazaphosphole–M(CO)5 complexes
[6,7], were obtained with (THF)M(CO)5 whereas with
tricarbonyl(cycloheptatriene)molybdenum(0) or tricar-
bonyl(mesitylene)tungsten(0) a variety of s-complexes
Recently, various 1,3-azaphospholes annulated to
pyridine, pyrazine, thiazoline, oxazoline or benzothia-
zole rings have become available through [4+1]-cyclo-
condensation of N-cycloiminium salts with phosphorus
trichloride [1–5]. Chemical properties of these het-
eroaromatic compounds incorporating a dicoordinate
phosphorus are of current interest [6–8]. They have
been found to show versatile reactivity towards elec-
trophilic substitution [9,10], hydrolysis [1,5], 1,2-addi-
tion on PꢀC bond [10] and [1+4]-cycloaddition on
phosphorus [11]. In view of the presence of a p-excess
azaphosphole ring in these compounds, we have re-
* Corresponding author. Tel.: +49-3834-864-337; fax: +49-3834-
864-319.
E-mail address: neinicke@rz.uni-greifswald.de (J. Heinicke)
1 Present address: University of Rajasthan.
2 Present address: University of Rajasthan.
3 Present address: University of Rajasthan.
Scheme 1.
0022-328X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(98)01075-4

338
C.B. Jain et al. / Journal of Organometallic Chemistry 577 (1999) 337–341
no marked influence on the complex chemical proper-
ties. It should be mentioned in this place that in the
(thiazole)Cr(CO)5 complex coordination was found to
be preferred through s2-nitrogen instead of sulfur [17].
This implies that back bonding in this type of aromatic
heterocycles is effected by d(M)“p* interactions. PM3
calculations of 1 and 4 show the LUMO to be low-lying
p*-orbitals (−0.97 and −0.77 eV) and to possess high
coefficients at s2-phosphorus (c2=0.37 and 0.34). This
and the similarities of the electron systems in 1 and 3 or
4 and 5, as seen from the 13C-NMR data, suggest that
the back-donation in 3 and 5 is due to strong d(M)“
p* rather than to d(M)“d(P) interactions. A compari-
son of PM3 orbital energies of unsubstituted
1H-1,3-azaphosphole with ionization potentials of this
species calculated using high-level ab initio methods
[18,19] shows higher deviations in the correlation with
experimental ionization potentials but the general trend
is the same so that the PM3 values of the higher,
-M-substituted derivatives may be regarded to be suffi-
ciently reliable.
Scheme 2.
of the types L2M(CO)4 or L3M(CO)3 were formed, but
no isolable p-complexes [13]. In 1,3-azaphospholes
without aromatic annulation the preferences of s- and
p-coordination may be different. The 2,3-dihydro-1,3-
azaphospholo[5,1-b]thiazole and -oxazole derivatives,
easier accessible than 1,3-azaphospholes [14–16], may
be used as model compounds if the impact of the
Group 16 heteroatom is not remarkable. In this context
we explored the reactions of 2,3-dihydro-1,3-azaphos-
pholo[5,1-b]thiazoles and -oxazoles with (THF)M(CO)5
(M=Cr, Mo, W).
2.2. Spectroscopic analysis of complexes 3 and 5
Pentacarbonyl metal complexes 3a–c and 5a–c were
2. Results and discussion
1
characterized by 31P-, H- and 13C-NMR, as well as IR
2.1. Reaction of 2,3-dihydro-1,3-azaphospholo[5,1-b]-
thiazole 1 and -oxazole 4 with (THF)M(CO)5
and mass spectroscopy. 31P-NMR data for complexes 3
and 5 together with those of 1 and 4 as reference and
the coordination shifts Dl are given in Table 1. A
strong upfield coordination shift of 31P-NMR signal for
W(CO)5 complexes 3c and 5c (Dl= −38 and −53) in
C6D6 is accompanied by satellite peaks showing a large
1JPW coupling constant of about 260 Hz, which is in the
range characteristic of s2l3-phosphorus-tungsten pen-
tacarbonyl coordination [20,21]. This reveals evidence
that sulfur or oxygen of the annulated hetero ring does
The ligand ethyl(7-methyl-2,3-dihydro-1,3-azaphos-
pholo[5,1-b]thiazole)-5-carboxylate 1 reacts with an
equimolar amount of (THF)M(CO)5 2 (M=Cr, Mo,
W) at room temperature (r.t.) to give selectively (h1-P)-
(2,3-dihydro-1,3-azaphospholo[5,1-b]thiazoline)M(CO)5
complexes 3 (Scheme 1).
The reaction of 5-benzoyl-7-methyl-2,3-dihydro-1,3-
azaphospholo[5,1-b]oxazole 4 with (THF)M(CO)5 at
r.t. proceeds analogously and led to the formation
of (h1-P)-(2,3-dihydro-1,3-azaphospholo[5,1-b]oxazole)-
M(CO)5 complexes 5 (Scheme 2).
1
not interfere with P-coordination. The JPW coupling in
3c and 5c (ca. 260 Hz) is comparable to that (253–268
Extraction of the crude products 3a, c and 5a, c with
hexane afforded analytically and spectroscopically
pure, yellow crystalline or powdery complexes. In case
of Mo(CO)5 complexes, the reaction was not complete
after 3–4 days at 20°C or even by using an excess
amount (1.2 equivalents) of 2b as revealed by 31P-NMR
of the reaction mixture. A mixture of the free ligand
and Mo(CO)5 complex (1+3b and 4+5b) was ob-
tained which could not be isolated in pure form by
repeated crystallization or fractional extraction.
The results show that coordination at phosphorus is
preferred to coordination at sulfur despite the reduced
basicity of s2-phosphorus in the heteroaromatic ligand
1. This underlines the impact of p-back-bonding in this
type of complexes and a considerable acceptor strength
of 1,3-azaphospholes. The heteroatom in position 1 has
Table 1
31P-NMR data-chemical shifts (l) of 1, 3, 4 and 5 and coordination
shifts (Dl) of 3 and 5
Compound
M
Solvent
l (ppm)
1JPW (Hz)
Dl
1
CDCl3
C6D6
CDCl3
174.8
175.3
189.7
169.0
139.8
137.1
198.5
193.5
187.9
177.2
169.6
140.4
3a
3b
3c
Cr
+14.9
−5.8
Mo CDCl3
W
CDCl3
C6D6
CDCl3
C6D6
260.9
261.0
−35.0
−38.2
4
5a
5b
Cr
C6D6
−5.6
−21.3
−23.9
−53.1
Mo CDCl3
C6D6
5c
W
C6D6
260.0

C.B. Jain et al. / Journal of Organometallic Chemistry 577 (1999) 337–341
339
Table 2
In the mass spectra of 3a, 3c and 5a the molecular
1H-NMR data of complexes 3 and 5a
ion peaks were observed. [M-5CO]+ or [M–(Cr/
’
W)5CO]+ forms the base peak. The appearance of
’
l (ppm) J (Hz)
3ab
3bb
3cb
5ac
5bc
5cc
3.70
6.2
3.64
5.5
6.2
2.0
+
+
+
[M–CO]+ , [M–2CO] , [M-3CO] , [M–4CO]
’
’
’
’
and [M–5CO]+ peaks indicates the primary decompo-
sition by successive loss of carbon monoxide molecules.
Further fragmentation involves loss of metal atom and
five-substituents.
’
2-CH2
3JHH
3.72 3.73 3.73 3.68
7.4 7.4 7.4 6.1
4.80 4.79 4.81 3.63 4.71–4.75
5.01
8.1
3-CH2
4JPH
4.6
7.4
2.9
7.4
4.6
7.4
4.5
6.1
(m)
3JHH
7-CH3
2.24 2.23 2.19 2.12
15.1 15.1 15.7 15.4
2.21
15.0
3JPH
15.4
3. Experimental details
a 5a and 5c in C6D6; others in CDCl3.
b 5-COOEt: CH3 ca. l 1.39, CH2 ca. l 4.35, 3JHH=7.1 Hz.
c 5-COPh: o-H ca. l 7.94, m-H ca. l 7.15, p-H ca. l 7.24.
Hexane, ether, THF and toluene were dried under
argon with sodium/benzophenone and freshly distilled
before use. All reactions were carried out under an
atmosphere of purified argon using standard Schlenk
techniques. Melting points were determined in closed
capillaries in inert atmosphere and were uncorrected.
NMR data were recorded on a multinuclear FT-NMR
Hz) reported for (h1-2-phosphaindolizine)M(CO)5 com-
plexes [13] indicating similar coordination properties of
s2-phosphorus in both cases.
Following the same trend as observed in the case of
2-phosphaindolizine complexes, the extent of coordina-
tion shift Dl depends strongly on the electron with-
drawing substituent in a-position to phosphorus [13],
Dl for complexes 5 bearing a 5-benzoyl substituent
being more negative (in upfield region) as compared to
those for 3 with a 5-ethoxycarbonyl substituent. Some-
what stronger coordination shifts (Dl 8–10) in the
higher field region for 3 and 5 than in the 2-phosphain-
dolizine complexes having identical a-substituents may
be attributed to the stronger p-acceptor properties in
the former complexes.
spectrometer Bruker ARX-300; H- at 300.1 MHz, 13C-
1
at 75.5 MHz and 31P- at 121.5 MHz with reference to
TMS (internal) and 85% H3PO4 (external), respectively.
CDCl3 was used as solvent unless otherwise indicated.
Mass spectra (EI, 70 eV) were measured on a Intectra
AMD-40 single focusing sector-field mass spectrometer,
IR spectra on a Perkin-Elmer 2000 FT-IR spectrometer
system. (THF)M(CO)5 was freshly prepared before use
by photolysis of metal hexacarbonyl in THF [22].
3.1. Synthesis of
2,3-dihydro-1,3-azaphospholo[5,1-b]thiazole (1) and
-oxazole (4)
1
In H-NMR spectra (CDCl3) of 3a–c (Table 2) all
the protons exhibit a slight downfield shift (Dl=0.03–
0.24) with respect to the free ligand 1. A marked feature
in the proton NMR spectra of both the complexes, 3
and 5, is the increase in JPH coupling constants with
The ligands ethyl(7-methyl-2,3-dihydro-1,3-azaphos-
pholo[5,1-b]thiazole)-5-carboxylate 1 and 5-benzoyl-7-
methyl-2,3-dihydro-1,3-azaphospholo[5,1-b]oxazole 4
were prepared according to methods reported previ-
ously [4,5].
3
respect to free ligands: JPH for 7-methyl protons by ca.
4
4.5 Hz and JPH for 3-CH2 protons by ca. 2 Hz.
A comparison of the 13C-NMR data of 3 and 5
(Table 3) and 2-phosphaindolizine complexes [13] re-
veals that variation in the nature of the hetero-ring
annulated to the azaphosphole ring does not effect
greatly the chemical shifts and the coupling constants
of metal carbonyl carbons. Chemical shift values of
para-CO are observed at lower field (l=198–221) than
the cis-CO (l=194–215); also both carbonyls are most
deshielded in chromium and least in tungsten com-
plexes. The two-bond PC coupling constant is minimal
(4 Hz) for para-CO in chromium complexes which
increases in the order Cr, Mo, W (ca. 4, 30, 32 Hz) and
decreases for cis-CO (ca. 16, 11, 9 Hz). While a slight
upfield shift is observed for C-7 and C-5 carbon, their
one-bond coupling constant with phosphorus decreases
strongly from 46–47 to 13–23 Hz for C-7 and from
52–59 to 12–28 Hz for C-5. Moreover, in the case of
5a and 5b the signal observed for C-5 is unresolved.
3.2. Synthesis of (p1-P)-(ethyl{7-methyl-2,3-dihydro-
1,3-azaphospholo[5,1-b]thiazole}-5-carboxylate)-
pentacarbonyl metalVI complexes (3a–c) and
(p1-P(5-benzoyl-7-methyl-2,3-dihydro-1,3-azaphos-
pholo[5,1-b]oxazole)pentacarbonyl metalVI complexes
(5a–c)
3.2.1. General procedure
Metal hexacarbonyl (4 mmol) (0.88 g of Cr(CO)6;
1.056 g of Mo(CO)6; 1.408 g of W(CO)6) was dissolved
in THF (300 ml) and irradiated with an UV medium
pressure lamp until 89.6 ml of CO was collected. The
resulting yellow to orange solution was added to a
solution of 4 mmol of 1 (0.916 g) or 4 (0.981 g) in THF
(10–20 ml). After stirring 1–2 days the mixture was
filtered, solvent removed in vacuo and the residue ex-
tracted with hexane (2×50 ml). On leaving the hexane

340
C.B. Jain et al. / Journal of Organometallic Chemistry 577 (1999) 337–341
Table 3
13C-NMR data of compounds 1, 3, 4 and 5a
l (ppm) J (Hz)
1
3a
33.9
53.9
2.2
143.8
18.9
129.8
13.6
146.3
5.8
162.1
17.9
14.2
60.9
12.6
14.6
3c
33.9
53.7
2.0
140.8
27.9
128.2
20.4
146.2
4.2
161.9
17.4
14.3
61.0
12.8
15.1
4b
74.7
48.3
4.3
143.9
58.8
114.9
47.4
159.6
9.5
5a
72.9
48.9
2.9
5b
73.7
49.1
2.9
5c
72.9
48.7
2.2
141.8
12.0
111.1
23.0
158.5
2.0
C-2
35.2
51.9
3.2
C-3
3JCP
C-5
146.3
52.1
132.8
46.0
144.7
12.1
162.9
20.4
14.4
60.4
14.1
23.5
146.6
143.8
1JCP
C-7
c
c
112.4
15.2
158.5
112.5
13.4
158.8
1JCP
C-8
2JCP
5-CO
2JCP
CH3
CH2
7-CH3
2JCP
185.9
22.8
185.1
18.7
185.8
19.3
184.9
18.3
10.3
22.3
9.5
12.1
9.7
14.0
9.6
12.5
C6H5
C-i
139.4
1.4
129.1
8.5
127.9
131.4
139.6
2.4
130.0
3.0
129.1
132.5
138.6
2.3
130.1
4.1
128.8
132.5
139.3
3.0
130.4
3.0
129.0
132.6
3JCP
C-o
4JCP
C-m
C-p
M(CO)5
CO(cis)
1JCW
214.6
194.3
125.3
9.4
214.6
203.1
195.1
125.2
9.4
2JCP
17.4
16.0
10.6
CO(para)
221.2
199.0
150.4
31.9
220.9
209.2
198.0
d
1JCW
2JCP
4.1
4.1
29.5
31.6
a 5a and 5c in C6D6; others in CDCl3.
b Ref. [5].
c Unresolved.
d Not observed due to low intensity.
solution in refrigerator yellow–orange needles de-
posited. Alternatively, the solvent was removed com-
pletely to afford a yellow powdery complex. In case of
3b and 5b, the isolated product was found to be a
mixture of complex and a smaller amount of the free
ligand which could not be purified by repeated extrac-
tion or recrystallization with hexane.
184 (100), 156.4 (23), 71.2 (56), 29 (92). Anal. Found:
C, 29.37; H, 2.11; N, 2.10%. C14H12NO7PSW (553.13)
calc.: C, 30.40; H, 2.19; N, 2.53%.
5a: Yield 1.22 g (70%); yellow powder; m.p. 101–
102°C. IR (in nujol): w 2070m, 1996vst, 1983vst,
1971vst, 1954vst, 1931vst, 669st, 646st cm−1. MS (EI,
70 eV): m/z (%) 438.4 (1) [M+], 410 (1), 382.1 (1), 354.2
(2), 325.9 (11), 298 (63), 245.9 (100), 230.7 (17), 220.6
(26), 168.5 (12), 77.3 (81), 52 (51). Anal. Found: C,
50.36; H, 3.08; N, 2.99%. C18H12NO7PCr (437.3) calc.:
C, 49.44; H, 2.76; N, 3.20%.
5c: Yield 1.36 g (60%); yellow crystalline solid; m.p.
110–112°C. IR (in nujol): w 2076st, 1979vst, 1950vst,
1930vst, 594st, 572st cm−1. Anal. Found: C, 38.4; H,
2.47; N, 2.26%. C18H12NO7PW (569.1) calc.: C, 37.98;
H, 2.13; N, 2.46%.
3a: Yield 1.156 g (69%); yellow crystalline needles;
m.p. 142–143°C. IR (in nujol): w 2072m, 1985sh,
1956vst, 1937vst, 1929vst; 1275m, 671st, 647st cm−1
.
MS (EI, 70 eV): m/z (%) 422.1 (12) [M+], 394.1 (2),
366.0 (1), 337.8 (4), 309.8 (19), 281.7 (100), 230 (26),
209.5 (31), 184.4 (17), 52 (46). Anal. Found: C, 40.00;
H, 3.07; N 3.22%. C14H12NO7PSCr (421.29) calc.: C,
39.91; H, 2.87; N, 3.32%.
3c: Yield 2.27 g (95%); yellow powder; m.p. 123–
124°C. (DTA minimum: 142°C at 10 K min−1). IR (in
nujol): w 2078m, 1980vst, 1954vst, 1927vst; 1276st,
593st, 572st cm−1. MS (EI, 70 eV): m/z (%) 556.7 (1),
553.9 (35, M+[184W]), 500 (27), 497.6 (54), 470.5 (6),
442.4 (7), 416.2 (39), 414.2 (48), 412 (36), 229.6 (30),
PM3 calculation [23]
Total charge on phosphorus
p-Charge on phosphorus
HOMO [p] (eV)
1
4
+0.461 +0.425
−0.069 −0.097
−8.45 −8.41

C.B. Jain et al. / Journal of Organometallic Chemistry 577 (1999) 337–341
341
[6] A. Schmidpeter, K. Karaghiosoff, in: M. Regitz, O.J. Scherer
(Eds.), Multiple Bonds and Low Coordination in Phosphorus
Chemistry, Thieme, Stuttgart, 1990, p. 261.
[7] R.K. Bansal, K. Karaghiosoff, A. Schmidpeter, Tetrahedron 50
(1994) 7675.
[8] J. Heinicke, Trends Organomet. Chem. 1 (1994) 307.
[9] (a)R.K. Bansal, N. Gupta, V. Kabra, C. Spindler, K. Karaghio-
soff, A. Schmidpeter Heteroat. Chem. 3 (1992) 359. (b) A.
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n Orbital (eV); lone pair on
phosphorus
−10.03 −9.88
−0.97 −0.77
LUMO [p*] (eV)
Coefficient on phosphorus in
0.37
0.34
LUMO (c2)
Selected PM3 eigenvalues of unsubstituted 1H-1,3-
azaphosphole: −0.06 (p*, LUMO), −8.43 (p,
HOMO), −9.77 (p), −9.76 (n), −12.01 (s), −13.80
(p); for ab initio and experimental ionization potentials
see ref. [18].
[12] K. Issleib, R Vollmer, Z. Allg. Anorg. Chem. 481 (1981) 22.
[13] N. Gupta, C.B. Jain, J. Heinicke, R.K. Bansal, P.G. Jones, Eur.
J. Inorg. Chem. (1998) 1079.
Acknowledgements
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Financial support from the Deutsche Forschungsge-
meinschaft and Fonds der Chemischen Industrie, Ger-
many is gratefully acknowledged.
[18] T. Veszpremi, L. Nuylaszi, J. Reffy, J. Heinicke, J. Phys. Chem.
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