Group 6 carbene complexes derived from lithiated azoles and the crystal structure of a molybdenum thiazolinylidene complex

Article abstract of DOI:10.1016/S0022-328X(99)00445-3

Fischer-type (alkoxy)azolyl carbene complexes and Oefele-Lappert-type azolylinylidene complexes were synthesised by reaction of 1-phenylpyrazol-3-yllithium, 4-methylthiazol-2-yllithium, benzothiazol-2-yllithium, 1-methylimidazol-2-yllithium with M(CO)₅L (L=CO, THF or Cl^-; M=Cr, Mo or W) and subsequent alkylation with CF₃SO₃CH₃. The alkylation of Fischer-type carbene complexes containing an azolyl as the organic substituent proceeded via ring opening of tetrahydrofuran. When the alkylation is carried out in THF, the carbocation CH₃O(CH₂)₄⁺ acts as an electrophile. Protonation rather than alkylation of coordinated imidazolyl furnished cyclic imine complexes. Changing the donor atom of a coordinated thiazole from N to C by deprotonation and alkylation afforded a carbene complex.

Full text of DOI:10.1016/S0022-328X(99)00445-3

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 590 (1999) 158–168
Group 6 carbene complexes derived from lithiated azoles and the
crystal structure of a molybdenum thiazolinylidene complex
Helgard G. Raubenheimer a,*, Yolanda Stander b, Eugene K. Marais b,
Catharine Thompson b, Gert J. Kruger b, Stephanie Cronje a, Maggel Deetlefs a
a Department of Chemistry, Uni6ersity of Stellenbosch, P/Bag X1, Matieland, 7602, South Africa
b Department of Chemistry and Biochemistry, Rand Afrikaans Uni6ersity, PO Box 524, Aucklandpark, 2006, South Africa
Received 8 June 1999; accepted 19 July 1999
Abstract
8
Fischer-type (alkoxy)azolyl carbene complexes and Ofele–Lappert-type azolylinylidene complexes were synthesised by reaction
of 1-phenylpyrazol-3-yllithium, 4-methylthiazol-2-yllithium, benzothiazol-2-yllithium, 1-methylimidazol-2-yllithium with M(CO)5L
(L=CO, THF or Cl−; M=Cr, Mo or W) and subsequent alkylation with CF3SO3CH3. The alkylation of Fischer-type carbene
complexes containing an azolyl as the organic substituent proceeded via ring opening of tetrahydrofuran. When the alkylation is
carried out in THF, the carbocation CH3O(CH2)+4 acts as an electrophile. Protonation rather than alkylation of coordinated
imidazolyl furnished cyclic imine complexes. Changing the donor atom of a coordinated thiazole from N to C by deprotonation
and alkylation afforded a carbene complex. © 1999 Elsevier Science S.A. All rights reserved.
Keywords: Carbene complexes; Group 6 metals; Azolinylidene complexes; Transmetallation
1. Introduction
electrophiles to afford classic Fischer-type hydroxy or
alkoxycarbene products [5,6]. The preparation of hete-
rocyclic Group 6 carbonyl carbene complexes by other
synthetic routes has been reported initially by both
The chemistry of carbene complexes has developed
rapidly since the notion of a metalꢀcarbon double bond
was first postulated [1]. A great variety of preparative
routes has afforded several hundreds of compounds,
some of which are valuable in both organic syntheses
and in catalytic processes [2]. Nevertheless, the develop-
ment of new methodologies towards preparation of
carbene complexes remains an important synthetic en-
deavour. The synthesis of carbene complexes derived
from heterocyclic compounds continues to attract a
great deal of attention [3] and these compounds have
emerged as useful precursors in catalysis [4].
8
Ofele and co-workers [7–9] and Lappert and co-work-
ers [10,11], and more recently by others [12,13]. Earlier
work in our laboratory has indicated an approach to
prepare tungsten azolylinylidene complexes [14] that is
probably more flexible than the method originally used
by Lappert. Our transmetallation route utilises an an-
ionic metal carbonylhalide and a lithiumazolyl com-
pound as opposed to the conventional metal
hexacarbonyl and electron-rich alkene reagents. Azolyls
could, however, also react with a carbonyl ligand in the
Fischer manner and we thus embarked on a study to
compare and contrast the preferential formation of
The majority of the Group 6 metal carbonyl carbene
complexes have been synthesised by the functionalisa-
tion of a coordinated carbonyl ligand. The resulting
anionic acyllithium compounds are then treated with
8
Fischer-type or Ofele–Lappert-type carbene complexes
from simple azolyllithium and pyrazolyllithium precur-
sors, when brought into contact with metal hexa-
carbonyl complexes. In addition, anionic metalcar-
bonyl halides and substituted carbonyl complexes
M(CO)5(THF) (M=Cr, W) were used as the transition
metal sources.
* Corresponding author. Tel.: +27-21-8083850; fax: +27-21-
8083849.
E-mail address: hgr@land.sun.ac.za (H.G. Raubenheimer)
0022-328X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(99)00445-3

H.G. Raubenheimer et al. / Journal of Organometallic Chemistry 590 (1999) 158–168
159
2. Results and discussion
heterolytic cleavage and the formation of the bu-
toxy(methoxy)organo carbene complex (Scheme 2). To
determine the role of the heterocyclic system in this
event, methyl- and phenyllithium were also employed as
reactants. No THF ring opening occurred, showing
that the electron-withdrawing effect of the heterocyclic
ring is necessary to partly suppress total acylate alkyla-
tion by CH+3 . A contributing structure such as (c) in
Scheme 2 is lacking in the alkyl and aryl carbene
complexes and direct complex alkylation occurs.
13C-{1H}-NMR spectra of complexes 1–3 (Table 2)
exhibited shifts for the aromatic carbons of 1-
phenylpyrazolyl between l 107–155, which is some-
what downfield from the resonances (l 107–140) in the
free pyrazole [15,16]. The presence of far-downfield
resonances for complexes 1, 2 and 3 at l 263.1, l 317.6
and l 299.7 as well as the absence of a signal for H5 in
the 1H-NMR spectra, confirms the presence of the
carbene carbons situated at C5.
The analytical and physical data for the products are
presented in Table 1 and the spectroscopic results ap-
pear in Table 2. Previously described complexes have
been identified by comparison of their melting points
and spectral data with known values and have been
omitted from the tables. The Li+ and CF3SO3− counter-
ions are not shown in the schemes.
2.1. Synthesis and characterisation of 1-phenylpyrazolyl
Group 6 carbene complexes 1–6
Reaction of lithiated 1-phenylpyrazole with M(CO)6
(M=Cr, Mo or W) and subsequent alkylation in
CH2Cl2 afforded the three Fischer-type complexes 1, 2
and 3 (Scheme 1). Performing the alkylation in tetrahy-
drofuran (THF) also yielded complexes 1–3 and simul-
taneously, the complexes 4, 5 and 6 that have been
O-alkylated by a butoxy(methoxy) group. Recrystallisa-
tion afforded air- and moisture-sensitive dark red,
needle-like crystals of 1–3 and brown–red crystals of
4–6.
We rationalized the unexpected formation of 4–6 in
terms of generating a new electrophilic centre by
nucleophilic attack of an oxygen lone pair in THF on
the polarised CH3 group in methyltriflate. In turn, the
oxy-anion of the acylmetallate performs a nucleophilic
attack on the a-carbon of the THF ring leading to
13C-{1H}-NMR spectra of complexes 4–6 (Table 2)
display analogous aromatic carbon shifts to complexes
1–3 and the carbene carbon resonances appear at l
263.3, l 315.7 and l 298.9, respectively. Note the
relatively large chemical shift in the molybdenum com-
pound. Carbene complexes similar to complexes 4–6
have been reported in a patent [17], but no characterisa-
tion data are available.
Cis and trans isomers of tungsten aminocarbene com-
plexes at room temperature [18] and of alkoxycarbene
Table 1
Analytical and physical data
Complex
m.p. (°C)
Colour
Analysis (%) a
C
H
N
1
2
3
4
5
6
7
8
9
10
11
12
16
17
18
20
21
22
23
67–68
68–69
66–67
87–88
88–89
86–87
63–64
79–80
53 b
Dark red
Dark red
Dark red
Brown–red
Brown–red
Brown–red
Dark red
Dark brown
Dark red
Dark red
Red
Brown
Yellow
Yellow
Pale yellow
Yellow
50.5 (50.8)
45.7 (45.5)
37.9 (37.7)
53.0 (53.4)
48.7 (48.6)
41.0 (41.3)
49.4 (49.0)
44.9 (44.6)
37.9 (37.7)
44.2 (44.4)
45.2 (45.6)
33.2 (33.6)
39.8 (39.5)
26.3 (26.6)
34.1 (34.4)
33.5 (33.0)
37.4 (37.2)
39.7 (39.4)
39.6 (39.4)
2.6 (2.7)
2.3 (2.4)
1.7 (2.0)
3.8 (4.0)
3.6 (3.7)
3.0 (3.1)
3.5 (3.4)
3.0 (3.1)
2.2 (2.6)
3.6 (3.7)
1.7 (1.9)
1.6 (1.4)
2.0 (2.2)
1.7 (1.5)
2.7 (2.9)
1.6 (1.5)
1.54 (1.7)
2.5 (2.3)
2.1 (2.3)
7.2 (7.4)
6.8 (6.6)
5.5 (5.5)
6.1 (6.2)
5.5 (5.7)
4.4 (4.8)
3.5 (3.2)
2.8 (2.9)
2.3 (2.4)
3.3 (3.5)
3.8 (3.8)
2.9 (2.8)
10.4 (10.2)
6.8 (6.9)
3.9 (4.0)
3.0 (3.0)
4.6 (4.8)
4.8 (4.6)
4.6 (4.6)
62–63
83 b
85 b
58–59 b
63–64 b
90–91
90–91
89 b
Yellow
Pale yellow
Yellow
75–76
91–92
a Required values given in parentheses.
b Decomposition without melting.

160
H.G. Raubenheimer et al. / Journal of Organometallic Chemistry 590 (1999) 158–168
Table 2
Spectroscopic data
Complex
a
1
2
3
lH
lC
7.63–7.18 (7H, m, aromatic protons), 4.38 (3H, s, OCH3)
a
263.1 (Cr=C), 215.9 (COtrans), 213.5 (COcis), 152.8–115.6 (aromatic carbons), 66.4 (OCH3)
b
m/z
378 ([M]+, 4), 350 ([M−CO]+, 44), 294 ([M−3CO]+, 41), 266 ([M−4CO]+, 61), 238 ([M−5CO]+, 71), 223
([Cr{C(O)(C¸N¹(P¹h¹)N¹ꢁ¹C¹H¹CºH)}]+, 73), 52 ([Cr]+, 43)
w (CO) c
2064 (s), 1988(w), 1967 (sh), 1952 (vs)
a
lH
lC
7.70–7.18 (7H, m, aromatic protons), 4.35 (3H, s, OCH3)
a
317.6 (Mo=C), 212.7 (Cotrans), 205.3 (COcis), 153.4–107.5 (aromatic carbons), 67.9 (OCH3)
b
m/z
422 ([M]+,B30), 394 ([M−CO]+,B30), 338 ([M−3CO]+, 63), 310 ([M−4CO]+, 41), 282 ([M−5CO]+, 36), 267
¸¹¹¹¹¹¹º
([Mo{C(O)(CN(Ph)NꢁCHCH}]+, 29), 96 ([Mo]+, 41)
w (CO) c
2072 (s), 1998 (w), 1975 (sh), 1960 (vs)
a
lH
lC
7.58–7.10 (7H, m, aromatic protons), 4.30 and 4.20 (3H, 2×s, OCH3, J=21.0)
299.7 (WꢁC), 205.3 (Cotrans, d, J(183Wꢀ13C)=125.0), 196.8 (COcis, d, J(183Wꢀ13C)=64.3), 155.7–117.3 (aromatic
carbons), 68.7 and 67.9 (OCH3)
a
b
m/z
510 ([M]+,B15), 482 ([M−CO]+,B15), 426 ([M−3CO]+, 100), 398 ([M−4CO]+,B14), 370 ([M−5CO]+, 46),
¸¹¹¹¹¹¹º
355 ([W{C(O)(CH(Ph)NꢁCHCH)}]+, 21)
w (CO) c
2072 (s), 1992 (w), 1972 (sh), 1956 (vs)
a
4
lH
7.57–7.12 (7H, m, aromatic protons), 4.67 (2H, t, H1, J(H1ꢀH2)=6.1), 3.20 (3H, s, OCH3), 3.13 (2H, t, H4,
J(H4ꢀH3)=5.8), 1.37–1.18 (4H, 2×m, H2 and H3)
lC
263.3 (CrꢁC), 223.3 (COtrans), 216.0 (COcis), 152.9–115.6 (aromatic carbons), 81.1 (C1), 71.7 (C4), 58.5 (OCH3),
25.6 (C2 and C3)
a
b
m/z
450 ([M]+, 4), 366 ([M−3CO]+, 12), 338 ([M−4CO]+, 4), 310 ([M−5CO]+, 50), 77 ([Ph]+, 15), 52 ([Cr]+, 100)
2064 (s), 1985 (w), 1965 (sh), 1956 (vs)
w (CO) c
a
5
6
lH
7.58–7.14 (7H, m, aromatic protons), 4.63 and 4.52 (2H, 2×t, H1, J(H1ꢀH2)=8.0), 3.24 and 3.20 (3H, 2×s,
OCH3), 3.13 (2H, t, H4, J(H4ꢀH3)=7.9), 1.38–1.17 (4H, 2×m, H2 and H3)
315.7 (MoꢁC), 212.9 (COtrans), 205.4 (COcis), 153.4–114.7 (aromatic carbons), 83.2 (C1)
494 ([M]+,B5), 412 ([M−3CO]+,B5), 356 ([M−5CO]+,B5)
a
lC
m/z
b
w (CO) c
2071 (s), 1994 (w), 1956 (vs), 1922 (sh)
lH
7.62–7.16 (7H, m, aromatic protons), 4.68 and 4.58 (2H, 2×t, H1, J(H1ꢀH2)=6.0), 3.25 (3H, s, OCH3), 3.16
(2H, t, H4, J(H4ꢀH3)=5.7), 1.36–1.23 (4H, 2×m, H2 and H3)
a
lC
298.9 (WꢁC), 205.4 (COtrans, d, J(183Wꢀ13C)=124.7), 196.9 (COcis, d, J(183Wꢀ13C)=64.2), 155.8–117.2 (aromatic
carbons), 83.3 and 82.7 (C1), 71.7 (C4), 58.5 (OCH3), 25.6 and 25.4 (C2 and C3)
582 ([M]+,B1), 498 ([M−3CO]+, 5), 143 ([M−5CO]+, 5), 77 ([Ph]+, 5)
2071 (s), 1955 (vs)
a
b
m/z
w (CO) c
a
7
8
lH
8.24–7.50 (4H, m, aromatic protons), 5.32 (2H, t, H1%, J(H1%ꢀH2%)=6.3), 3.52 (2H, t, H4%, J(H4%ꢀH3%)=6.1), 3.37
(3H, s, OCH3), 2.19 (2H, m, H2%), 1.90 (2H, m, H3%)
a
lC
322.9 (CrꢁC), 225.9 (COtrans), 216.7 (COcis), 171.4 (C2), 153.9 (C9), 135.1 (C8), 128.1 (C5), 126.8 (C6), 125.7 (C4),
122.3 (C7), 80.7 (C1%), 71.9 (C4%), 58.6 (OCH3), 26.7 (C2%), 26.2 (C3%)
b
m/z
441 ([M]+, 3), 413 ([M−CO]+, 9), 329 ([M−4CO], 9), 301 ([M−5CO], 100), 52 ([Cr]+, 99), 45 ([HCS]+, 35)
2066 (m), 2007 (w), 1979 (s, sh), 1958 (vs)
w (CO) c
a
lH
8.24–7.51 (4H, m, aromatic protons), 5.17 (2H, t, H1%, J(H1%ꢀH2%)=6.3), 3.51 (2H, t, H4%, J(H4%ꢀH3%)=6.1), 3.37
(3H, s, OCH3), 2.18 (2H, m, H2%), 1.88 (2H, m, H3%)
a
lC
313.0 (MoꢁC), 214.7 (COtrans), 206.0 (COcis), 172.6 (C2), 153.9 (C9), 135.3 (C8), 128.0 (C5), 126.8 (C6), 125.7
(C4), 122.3 (C7), 82.3 (C1%), 71.9 (C4%), 58.6 (OCH3), 26.5 (C2%), 26.2 (C3%)
b
m/z
485 ([M]+, 1), 457 ([M−CO]+, 3), 401 ([M−3CO]+, 5), 373 ([M−4CO]+, 2), 345 ([M−5CO]+, 2), 96 ([Mo]+
,
63), 45 ([HCS]+, 93)
w (CO) c
2073 (m), 2007 (w), 1978 (s, sh), 1958 (vs)
a
9
lH
8.25–7.52 (4H, m, aromatic protons), 5.18 and 5.04 (2H, 2×t, H1%, J(H1%ꢀH2%)=6.6), 3.51 (2H, t, H4%,
J(H4%ꢀH3%)=6.2), 3.37 (3H, s, OCH3), 2.17 (2H, m, H2%), 1.88 (2H, m, H3%)
a
lC
295.9 (WꢁC), 205.2 (COtrans), 197.3 (COcis, d, J(183Wꢀ13C)=127), 175.1 (C2), 153.9 (C9), 135.4 (C8), 128.1 (C5),
126.9 (C6), 125.8 (C4), 122.4 (C7), 83.0 (C1%), 71.9 (C4%), 58.6 (OCH3), 26.4 (C2%), 26.3 (C3%)
573 ([M]+, 1), 545 ([M−CO]+, 3), 489 ([M−3CO]+, 2), 433 ([M−5CO]+, 3), 45 ([HCS]+, 100)
2074 (m), 2003 (w), 1974 (s, sh), 1954 (vs)
b
m/z
w (CO) c
a
10
lH
7.14 (1H, s, H5), 5.22 (2H, t, J=6.3, H1%), 3.48 (2H, t, J=6.1, H4%) 3.34 (3H, s, OCH3), 2.55 (3H, s, NCCH3),
2.12 (2H, m, H2%), 1.83 (2H, m, H3%)
a
lC
320.0 (CrꢁC), 225.6 (COtrans), 217.0 (COcis), 172.0 (C2), 156.5 (C4), 119.0 (C5), 80.2 (C1%), 72.0 (C4%), 58.6
(OCH3), 26.7 (C2%), 26.2 (C3%), 14.0 (NCCH3)
b
m/z
405 ([M]+, 10), 377 ([M−CO]+, 16), 293 ([M−4CO]+, 14), 265 ([M−5CO]+, 100)
1065 (m), 2004 (w), 1976 (s, sh), 1955 (vs)
w (CO) c

H.G. Raubenheimer et al. / Journal of Organometallic Chemistry 590 (1999) 158–168
161
Table 2 (Continued)
Complex
a
11
lH
lC
8.26–7.53 (4H, m, aromatic protons), 5.02 (3H, s, OCH3)
a
324.9 (CrꢁC), 225.8 (COtrans), 216.7 (COcis), 171.1 (C2), 153.9 (C9), 135.2 (C8), 128.1 (C5), 126.8 (C6), 125.8 (C4),
122.4 (C7), 66.8 (OCH3)
b
m/z
369 ([M]+, 4), 341 ([M−CO]+, 11), 313 ([M−2CO]+, 8), 285 ([M−3CO]+, 22), 257 ([M−5CO]+, 31), 229
([M−5CO]+, 81), 52 ([Cr]+, 100), 45 ([HCS]+, 4)
w (CO) c
2067 (m), 2009 (w), 1983 (s, sh), 1954 (vs)
a
12
lH
8.25–7.53 (4H, m, aromatic protons), 4.88 and 4.76 (3H, 2×s, OCH3)
297.7 (WꢁC), 205.1 (COtrans), 197.2 (COcis, d, J(183Wꢀ13C)=125.5), 174.9 (C2), 153.9 (C9), 135.5 (C8), 128.1
(C5), 127.0 (C6), 125.8 (C4), 122.5 (C7), 69.2 (OCH3)
a
lC
b
m/z
501 ([M]+, 1), 473 ([M−CO]+, 43), 445 ([M−2CO]+, 39), 417 ([M−3CO]+, 65), 389 ([M−4CO]+, 62), 318
¸¹¹¹¹º
([W{CꢁNC6H4S-o}]+, 87)
w (CO) c
2075 (m), 2005 (w), 1977 (s, sh), 1956 (vs)
a
16
17
18
20
lH
7.36 (1H, s, H2), 6.84 (2H, 2×s, H4 and H5), 3.67 (3H, s, NCH3)
220.6 (COtrans), 215.1 (COcis), 141.0 (C2), 134.4 (C4), 121.3 (C5), 34.1 (NCH3)
274 ([M]+, 14), 246 ([M−CO]+, 4), 218 ([M−2CO]+, 2), 190 ([M−3CO]+, 5), 162 ([M−4CO]+, 28), 134
([M−5CO]+, 89), 52 ([Cr]+, 90)
a
lC
b
m/z
w (CO) c
2065 (w), 1929 (vs)
a
lH
7.58 (1H, s, H2), 7.04 (1H, m, H4), 6.83 (1H, s, H5), 3.72 (3H, s, NCH3)
202.6 (COtrans), 198.6 (COcis, J(183Wꢀ13C)=43), 142.6 (C2), 135.4 (C4), 121.7 (C5), 34.1 (NCH3)
406 ([M]+,B5), 350 ([M−2CO]+, 8), 322 ([M−3CO]+, 13), 294 ([M−4CO]+, 7), 266 ([M−5CO]+, 15), 183
([W]+, 15)
a
lC
b
m/z
w (CO) c
2071 (m), 1933 (vs), 1916 (sh)
a
lH
6.97 (1H, s, H5), 4.03 (3H, s, NCH3), 2.43 (3H, s, NCCH3)
lC
220.7 (MoꢁC), 212.5 (COtrans), 206.5 (COcis), 145.7 (C4), 120.3 (C5), 41.7 (NCH3), 15.0 (NCCH3)
349 ([M]+, 37), 321 ([M−CO]+, 15), 293 ([M−2CO]+, 21), 265 ([M−3CO]+, 32), 237 ([M−4CO]+,76), 209
([M−5CO]+, 79), 169 ([Mo{SꢁCꢁNꢁ(CH3)}]+, 49)
a
b
m/z
w (CO) c
2067 (m), 1985 (w), 1945 (vs), 1945 (vs)
a
lH
7.71 (1H, m, H4), 7.60 (1H, m, H7), 7.62–7.38 (2H, m, H5 and H6), 4.27 (3H, s, NCH3)
218.1 (WꢁC), 202.0 (Cotrans), 197.2 (COcis, J(183Wꢀ13C)=125.7), 144.6 (C9), 136.9 (C8), 127.0 (C5), 125.3 (C6),
120.9 (C4), 113.7 (C7), 41.6 (NCH3)
a
lC
b
m/z
473 ([M]+, 78), 445 ([M−CO]+, 15), 417 ([M−2CO]+, 39), 389 ([M−3CO]+, 99), 361 ([M−4CO]+, 95), 333
¸¹¹¹¹º
([M−5CO]+, 100), 318 ([W{CꢁNC6H4S-o}]+, 12)
w (CO) c
2067 (m), 1982 (w), 1940 (vs), 1940 (vs)
a
21
22
lH
8.89 (1H, s, H2), 7.08 (1H, s, H5), 2.59 (3H, s, NCH3)
lC
220.7 (COtrans), 214.5 (COcis), 157.2 (C4), 156.0 (C2), 116.0 (C5), 18.6 (NCCH3)
¸¹¹¹¹¹¹¹¹º
a
b
m/z
w (CO) c
291 ([M]+, 7), 207 ([M−3CO]+, 3), 179 ([M−4CO]+, 12), 151 ([M−5CO]+, 44), 99 ([CꢁNC(CH3)ꢁCHS]+, 100)
2070 (w), 1943 (vs), 1924 (s, sh)
a
lH
8.70 (1H, s, H2), 2.45 (3H, s, NCCH3), 2.36 (3H, s, SCCH3)
a
lC
220.8 (COtrans), 214.5 (COcis), 153.1 (C4), 151.1 (C2), 128.3 (C5), 16.1 (NCCH3), 12.4 (SCCH3)
305 ([M]+, 7), 277 ([M−CO]+, 3), 249 ([M−2CO]+, 3), 221 ([M−3CO]+, 4), 193 ([M−4CO]+, 15), 165
b
m/z
([M−5CO]+, 79), 113 ([¸Cꢁ¹N¹C¹(¹C¹H¹3)¹ꢁC¹(¹C¹H¹)3ºS]+, 100), 52 ([Cr]+, 76)
w (CO) c
2069 (w), 1942 (vs), 1923 (s, sh)
a
23
lH
6.97 (1H, s, H5), 4.04 (3H, s, NCH3), 2.43 (3H, s, NCCH3)
a
lC
227.2 (C2) 222.2 (COtrans), 217.0 (COcis), 146.6 (C4), 120.1 (C5), 40.7 (NCH3), 15.1 (NCCH3)
305 ([M]+, 43), 277 ([M−CO]+, 22), 249 ([M−2CO]+, 17), 221 ([M−3CO]+, 25), 193 ([M−4CO]+, 50), 165
([M−5CO]+, 99),84 ([CrS]+), 52 ([Cr]+, 100)
b
m/z
w (CO) c
2060 (m), 1981 (w), 1938 (vs)
a Measured in CDCl3, coupling constants in Hz.
b Coupling constants in Hz, intensities given relative to strongest peak.
c Measured in hexane.
complexes at much lower temperatures have been re-
ported [19]. This phenomenon is now also evident in
the H-NMR spectra of complexes 3 and 6 at room
for both the OCH3 and OCH2 protons, respectively.
The intensities of the peaks for related isomers are
approximately the same, suggesting that they occur in
roughly a 1:1 ratio. The failure to observe this phe-
1
temperature, in the form of two sets of separate peaks

162
H.G. Raubenheimer et al. / Journal of Organometallic Chemistry 590 (1999) 158–168
¸¹¹¹¹¹¹¹º
¸¹¹¹¹º
¸¹¹¹¹¹¹º
Scheme 1. Reagents: (i) LiCN(Ph)NꢁCHCH; (ii) CF3SO3CH3; (iii) CH2Cl2; (iv) THF; (v) LiCꢁNC6H4S-o; (vi) LiCꢁNCHꢁCHN(CH3); (vii)
CF3SO3H.
nomenon before can only be ascribed to the lower reso-
lution NMR spectrometers used when the original stud-
ies were performed. The coupling constants between the
cis and trans carbonyl groups and 183W for complexes 3
and 6 in the 13C-{1H} NMR spectra could be calculated,
but the signals corresponding to the coupling intensities
between the carbene carbon and 183W were very weak.
The A21 peak in the infrared spectra of all six com-
plexes occurs as a shoulder at a higher frequency than
the E vibration. With the exception of complex 6, the
forbidden B1 peak indicates that the 1-phenylpyrazolyl
moiety causes distortion of the carbonyls from idealised
C46 symmetry.
Reaction of lithiated benzothiazole with M(CO)6
(M=Cr, Mo or W) and subsequent alkylation in THF
afforded complexes 7–9 and 11 and 12. Performing the
alkylation in CH2Cl2 gave 11 and 12 exclusively. The
same THF ring-opening mechanism as discussed for
complexes 4–6 is again applicable to the formation of
complexes 7–9. We have not been able to isolate the
molybdenum analogue in analytically pure form. The
characterisation data for the complexes (Table 2)
confirm their structural assignments.
2.3. Interaction of a lithiated imidazole with M(CO)6
(M=Cr, Mo, W)
2.2. Synthesis and characterisation of 4-methylthiazolyl
(10) and benzothiazolyl alkoxycarbene complexes (7 to
9, 11 and 12) of the Group 6 metals
Group 6 carbene complexes derived from imidazole
8
derivatives have formerly been reported by Ofele and
co-workers [7,9], who used HCr(CO)−5 as source of
metal carbonyl. The synthesis of Fischer-type carbene
complexes using 1-methylimidazol-2-yllithium as nucleo-
philic reagent has, however, not been mentioned before.
Addition of M(CO)6 (M=Cr, Mo or W) to a THF so-
lution of 1-methylimidazol-2-yllithium, followed by
It is mentioned her¸e¹¹¹¹¹¹¹¹¹º
that the complex
(CO)5Cr[C{O(CH2)4OCH3}{CꢁNC(CH3)ꢁCHS}] (10)
was obtained as a by-product in the attempted reaction
between a neutral chromium pentacarbonyl complex
[Cr(CO)5(THF)], and 4-methylthiazol-2-yllithium. Its
formation is ascribed to the incomplete conversion of
[Cr(CO)6] to [Cr(CO)5(THF)], as well as to the presence
of the THF-derived alkylation agent involved in the for-
mation of complexes 4–9 (vide supra). The structure
8
methylation now also yielded only the Ofele–Lappert-
type complexes 13–15. Although these three complexes
are known and fully characterised [9], this route to 1,3-
dimethylimidazol-2-inilidene has not been utilised be-
fore and leaves the option of protonation rather than
alkylation in the first step. Such a procedure, however,
afforded the new imino complexes 16 and 17. Matching
1
is supported by MS, IR, H- and 13C-{1H} NMR re-
sults.

H.G. Raubenheimer et al. / Journal of Organometallic Chemistry 590 (1999) 158–168
163
results have already been obtained in our laboratory
[14,20] where, as in this event, it is implied that the
most stable thermodynamic product appears to favour
C-protonation and N-coordination. The structures pro-
posed were based on elemental analysis as well as
conclusive spectral data including mass spectrometry.
during protonation. One could ask whether an N-coor-
dinated azole would change into the C-coordinated
form upon deprotonation. The experiment conducted
involved the chromium thiazole complex 21. Previous
reports of coordinated thiazoles have indicated the
possibility of both N- and S-coordination [21]. In this
case however, only N-coordination was evident from
NMR analysis, as has been observed before [22] in the
synthesis of the benzothiazole analogue of this
complex.
2.4. Interaction of a thiazolyllithium with
M(CO)5(THF)
M(CO)5R− complexes (R=alkyl, aryl) of the Group
6 metals usually do not form on addition of organo-
lithium compounds to M(CO)5(THF). In the carbanion
4-methylthiazol-2-yllithium, the negative charge could
be effectively delocalised onto the N-atom and such
a substitution seemingly becomes possible. Treatment
Treatment of 21 with BuLi, followed by methylation
and chromatographic purification afforded 22 as pale
yellow and 23 as yellow crystals. The parallel formation
of these two complexes in a ratio of ca. 1:3 indicates the
exceptional stability of the C-coordinated anion and the
acidity of the proton at C4 that competes for the butyl
anion with the C2 proton in the N-coordinated form 21.
We are now utilising the second result in a modified
form by initially blocking the C2 position with CH3 or
SCH3.
of
a solution of 4-methylthiazol-2-yllithium with
M(CO)5(THF) (M=Mo, W) followed by methylation
in CH2Cl2 and chromatographic purification, yielded
the pure complexes 18 and 19. A similar procedure with
benzothiazol-2-yllithium and W(CO)5(THF) afforded
complex 20 (Scheme 3). These three heterocyclic car-
bene complexes could thus be synthesised via this route
employing milder conditions than the previously de-
scribed method [10].
2.6. An alternati6e method for the preparation of
compounds 13 and 15 and for preparing the known
related bis(carbene) complexes (24 and 25)
The spectroscopic data for complex 19, previously
produced by halide substitution from [W(CO)5Cl]−
[14], and data for the other new compounds are in line
with their proposed structures.
Substitution of halide in M(CO)5X− compounds by
lithiated azoles, followed by alkylation, is known to
produce carbene complexes [14]. Since all the complexes
have been described before [9,23], we mention that such
a transmetallation of 2-lithiated 1-methylimidazole
(Scheme 4) furnished both the mono carbene complexes
13 and 15 and the bis(carbene) complexes 24 and 25
albeit in fairly low yields. Imidazolyls are the only
azolyls we know of that furnish bis(carbene) complexes
in addition to the mono(carbene) complexes.
2.5. Rearrangement of an N-coordinated thiazole
during consecuti6e lithiation and alkylation
We have indicated above that a C-coordinated imida-
zolyl converts into the N-coordinated form (16, 17)
Scheme 2. THF heterolytic ring cleavage.

164
H.G. Raubenheimer et al. / Journal of Organometallic Chemistry 590 (1999) 158–168
¸¹¹¹¹¹¹¹¹º
¸¹¹¹¹º
¸¹¹¹¹¹¹¹¹¹º
Scheme 3. Reagents: (i) LiCꢁNC(CH3)ꢁCHS; (ii) LiCꢁNC6H4S-o; (iii) THF; (iv) CF3SO3CH3; (v) CHꢁNC(CH3)ꢁCHS; (vi) BuLi.
3. Crystal structure of
[(CO5)Mo{CN(CH3)C(CH3)ꢂCHS}] (18)
thereby attained, thus minimising interactions with the
carbonyl ligands.
¸¹¹¹¹¹¹¹¹¹¹¹¹º
,
Selected bond lengths (A) and angles (°) for 18 are
given in Table 3.
4. Summary
The six ligands form an octahedral configuration
around the central Mo atom (Fig. 1). The bond to the
Lithiated pyrazoles [14] and imidazoles substitute
THF or halide ligands from M(CO)5L to from
azolinylidine compounds upon alkylation. With L=
,
carbonyl ligand trans to the thiazolyl ligand (1.955 A) is
,
0.04 A shorter than the other (cis) metalꢀcarbonyl
,
8
bonds (2.039 A). In line with these results, a search of
CO, imidazolyls afforded similar Ofele–Lappert-type
the Cambridge Structural Database [24] for pentacar-
bonyl molybdenum complexes yielded 93 structures,
with an average bond length of the opposing carbonyl
carbene complexes whereas all the other azolyls studied
yield Fischer-type carbene complexes. When the alkyl-
,
of 1.992 A, while the average bond lengths for the other
,
carbonyls were longer, namely 2.048 A. Such structures
show a tendency towards an inverse relationship be-
tween the MoꢀCligand and the MoꢀCtrans bond lengths,
however, since there are only seven structures including
the present one, it is not possible to draw a definite con-
clusion (Fig. 2). The fact that the C(6)ꢀN(1) distance
,
(1.351 A) is shorter than that between C(8) and the ni-
,
trogen (1.393 A) is in accordance with results for
acyclic aminocarbon complexes with no free rotation
around the carbonꢀnitrogen bond at room temperature
[25].
,
The thiazole ligand is planar within 0.02 A with the
plane being twisted 44° from the plane through Mo,
C(2), C(3), C(5) and C(6). An eclipsed conformation is
¸¹¹¹¹¹¹º
Scheme 4. Reagents: (i) LiCꢁNCHꢁCHN(CH3); (ii) THF; (iii)
CF3SO3CH3.

H.G. Raubenheimer et al. / Journal of Organometallic Chemistry 590 (1999) 158–168
165
Table 3
Selected
,
bond
lengths
(A)
and
angles
(°)
for
¸¹¹¹¹¹¹¹¹¹¹¹º
[(CO5Mo{CN(CH3)C(CH3)ꢁCHS}] (18)
Bond lengths
S(1)ꢀC(6)
MoꢀC(6)
N(1)ꢀC(8)
C(7)ꢀC(8)
1.711(3)
2.247(4)
1.393(5)
1.326(6)
S(1)ꢀC(7)
N(1)ꢀC(6)
N(1)ꢀC(10)
1.711(5)
1.351(4)
1.467(5)
Bond angles
C(6)ꢀN(1)ꢀC(8)
C(6)ꢀN(1)ꢀC(10)
N(1)ꢀC(6)ꢀS(1)
S(1)ꢀC(6)ꢀMo
118.0(3)
C(6)ꢀS(1)ꢀC(7)
C(8)ꢀN(1)ꢀC(10)
N(1)ꢀC(6)ꢀMo
94.1(2)
120.1(3)
133.8(2)
121.9(3)
105.9(3)
119.9(2)
ation is carried out in THF with CF3SO3CH3, the
carbocation CH3O(CH2)+4 formally acts as an elec-
trophile. Protonation of imidazolyl complexes do not
afford carbene complexes but coordinated imines and
consecu-tive deprotonation and alkylation of an N-co-
ordinated thiazole leads to carbene complex formation.
5. Experimental
Fig. 2. Comparison of MoꢀCligand and MoꢀCtrans bond lengths.
5.1. General
column chromatography (FCC) was performed using
Merck Kieselgel 60 (particle size 0.063–0.200 mm)
washed with dry diethyl ether and dried overnight under
vacuum.
Melting points were determined on a standardized
Bu¨chi 535 apparatus and infrared spectra were deter-
mined on a Perkin–Elmer 841 apparatus. Mass spectra
were recorded on a Finnegan Mat 8200 instrument
(electron impact at 70 eV) and NMR spectra (1H-NMR
at 200 MHz and 13C-{1H} NMR at 50 MHz) on a VXR
200 FT spectrometer. Elemental analyses were carried
out by the Division of Energy Technology, CSIR,
Pretoria.
All reactions and manipulations were carried out
under an atmosphere of nitrogen using standard
Schlenck techniques. THF and diethyl ether were dis-
tilled under nitrogen from sodium wire and benzophe-
none, pentane and hexane from sodium wire and
CH2Cl2 from CaH2.
The compounds [M(CO)5Cl]−[NEt4]+ (M=Cr, W),
were prepared directly before use according to a litera-
ture method [26]. Deuterated solvents, the Group 6
metal hexacarbonyls, 4-methylthiazole, benzothiazole,
1-phenylpyrazole, CF3SO3H, CF3SO3CH3, (Aldrich), n-
BuLi (Merck) and 1-methylimidazole (Fluka) were pur-
chased and used without further purification. Flash
5.2. Preparation of Group 6 complexes 1–6
A solution of 1-phenylpyrazole (0.6 cm3, 4.8 mmol) in
40 cm3 THF at −78°C was treated with BuLi in hexane
(ca. 1.6 M, 3.12 cm3, 4.8 mmol) for 45 min. M(CO)6
(M=Cr, Mo, W; 0.88 g, 1.06 g, 1.41 g, 4.0 mmol), was
added in solid form to the lithium salt solution at
−78°C, stirred for 2 h at this temperature and gradually
warmed to room temperature (r.t.). After methylation
with CF3SO3CH3 (0.48 cm3, 4.0 mmol) at −50°C for 30
min, the solution was slowly warmed to r.t. Removal of
the solvent, washing with CH2Cl2 (3×20 cm3) and FCC
with hexane/diethyl ether (5:1.5) afforded the pure com-
plexes (% yields: 1, 26.4; 2, 17.9; 3, 29.5; 4, 17.2; 5, 15.9
and 6, 22.5). Recystallization at −20°C from hexane
yielded air and moisture sensitive needle-like dark red
and brown–red crystals of 1–3 and 4–6, respectively.
¸¹¹¹¹¹¹¹¹¹¹¹º
Fig. 1. ORTEP plot of 18 [(CO5Mo{CN(CH3)C(CH3)ꢁCHS}].

166
H.G. Raubenheimer et al. / Journal of Organometallic Chemistry 590 (1999) 158–168
5.3. Preparation of Group 6 complexes 7–9
5.6. Preparation of Group 6 complexes 16 and 17
A solution of benzothiazol-2-yllithium, prepared
from benzothiazole (0.33 cm3, 3.0 mmol) in 40 cm3
THF at −78°C and BuLi in hexane (ca. 1.6 M, 1.9
cm3, 3.0 mmol), was slowly added to a solution of
M(CO)6 (M=Cr, Mo, W; 0.66, 0.79, 1.06 g, 3.0 mmol)
in 50 cm3 THF at −78°C and stirred for 2.5 h at this
temperature. Upon reaching r.t., the reaction mixture
was stirred for a further 30 min. Methylation with
CF3SO3CH3 (0.34 cm3, 3.0 mmol) at −78°C, stirring
overnight with gradual warming to r.t., solvent re-
moval, washing with CH2Cl2 (3×20 cm3) and cold
FCC (−15°C) with hexane–CH2Cl2 (4:1; 3:1–1:2 and
2:1–3:1, respectively), afforded the pure powder-like
complexes (% yields: 7, 32; 8, 22 and 9, 27).
The analogous procedure using 1-methylimidazole
(0.32 cm3, 4.0 mmol), BuLi in hexane (ca. 1.6 M, 2.6
cm3, 4.0 mmol), M(CO)6 (M=Cr, W; 0.88, 1.41 g, 4.0
mmol), protonation with CF3SO3H (0.35 cm3, 4.0
mmol) and cold FCC (−20°C) with hexane–diethyl
ether (1:9), afforded the pure complexes (% yields: 16,
9.52 and 17, 11.2).
5.7. Preparation of Group 6 complexes 18 and 19
M(CO)6 (M=W, Mo; 1.06, 0.79 g, 3.0 mmol) in 100
cm3 THF was irradiated with UV light for 3 h to
prepare the corresponding M(CO)5(THF) complex. A
solution of 4-methylthiazol-2-yllithium, prepared from
4-methylthiazole (0.27 cm3, 3.0 mmol) in 40 cm3 THF
at −78°C and BuLi in hexane (ca. 1.6 M, 1.9 cm3, 3.0
mmol), was added to the M(CO)5(THF) solution at
−78°C and stirred for 2 h. The reaction mixture was
allowed to warm slowly to r.t., stirred for a further 2 h
and the THF removed in vacuo. After dissolving the
residue in CH2Cl2, it was methylated with CF3SO3CH3
(0.34 cm3, 3.0 mmol) at −78°C. Overnight stirring with
warming to r.t., filtration through Celite and cold FCC
(−15°C) with hexane–CH2Cl2 (3:1) afforded the pure
complexes (% yields: 18, 36 and 19, 44).
5.4. Preparation of Group 6 complexes 11 and 12
A solution of benzothiazol-2-yllithium, prepared
from benzothiazole (0.33 cm3, 3.0 mmol) in 40 cm3
THF at −78°C and BuLi in hexane (ca. 1.6 M, 1.9
cm3, 3.0 mmol), was slowly added to M(CO)6 (M=Cr,
W; 0.66, 1.06 g, 3.0 mmol) in 50 cm3 THF at −78°C.
The solution was stirred for 3 h at this temperature,
gradually warmed to r.t., the solvent removed, the
residue washed with hexane (3×20 cm3) and dissolved
in CH2Cl2. Methylation with CF3SO3CH3 (0.34 cm3,
3.0 mmol) at −20°C for 30 min, warming to r.t.,
filtration through a silica plug and cold FCC (−15°C)
with hexane–CH2Cl2 (4:1 and 5:1, respectively) af-
forded the pure complexes (% yields: 11, 28 and 12, 31).
Dissolving 11 in diethyl ether, layering with hexane and
cooling to −80°C produces red microcrystals of the
chromium complex. Reducing the eluent volume of 12
and cooling to −20°C yields brown crystals of the
tungsten complex.
5.8. Preparation of Group 6 complex 20
The analogous procedure using benzothiazole (0.33
cm3, 3.0 mmol), BuLi in hexane (ca. 1.6 M, 1.9 cm3, 3.0
mmol), W(CO)5(THF), methylation with CF3SO3CH3
(0.34 cm3, 3.0 mmol) and cold FCC (−10°C) with
hexane–CH2Cl2 (3:1), afforded the pure complex (%
yield: 21). Recrystallisation from diethyl ether at
−50°C produces yellow crystals of the tungsten complex.
5.9. Preparation of Group 6 complex 21
5.5. Preparation of Group 6 complexes 13–15
Cr(CO)6 (0.66 g, 3.0 mmol) in 100 cm3 THF was
irradiated with UV light for 3 h to prepare the corre-
sponding Cr(CO)5(THF) complex. This solution was
added to 4-methylthiazole (0.27 cm3, 3.0 mmol) in 30
cm3 THF at r.t. and stirred for 1 h. Solvent removal,
FCC with hexane–diethyl ether (7:3), reducing the elu-
ent volume and cooling to −25°C afforded yellow
crystals of the complex (% yield: 77).
To a solution of 1-methylimidazol-2-yllithium, pre-
pared from 1-methylimidazole (0.32 cm3, 4.0 mmol) in
40 cm3 THF at −45°C and BuLi in hexane (ca. 1.6 M,
2.6 cm3, 4.0 mmol), solid M(CO)6 (M=Cr, Mo, W;
0.88, 1.06, 1.41 g, 4.0 mmol) was added at −70°C and
the solution stirred for 2 h at this temperature. The
reaction mixture was slowly warmed to r.t., cooled to
−50°C and protonated with CF3SO3CH3 (0.48 cm3, 4.0
mmol). Overnight stirring with gradual warming to r.t.,
solvent removal, washing with hexane (3×20 cm3),
filtering through a silica plug using CH2Cl2 and cold
FCC (−20°C) using hexane–diethyl ether (1:9) af-
forded the pure complexes (% yields: 13, 19.7; 14, 23.2
and 15, 24). Recrystallisation at −20°C from hexane
yielded yellow crystals in all three cases.
5.10. Preparation of Group 6 complexes 13, 15, 24 and
25
The analogous procedure using 1-methylimidazole
(0.15 cm3, 2.0 mmol), BuLi in hexane (ca. 1.6 M, 1.3
cm3, 2.0 mmol), [M(CO)5Cl]−[NEt4]+ (M=Cr, W; 0.72
g, 0.98 g, 2.0 mmol), methylation with CF3SO3CH3

H.G. Raubenheimer et al. / Journal of Organometallic Chemistry 590 (1999) 158–168
167
(0.24 cm3, 2.0 mmol) and FCC with hexane–CH2Cl2
References
(1:3) afforded the pure yellow complexes (% yields: 13,
28.2; 15, 22; 24, 8.44 and 25, 11.2).
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5.11. Preparation of Group 6 complexes 22 and 23
A solution of 21 (0.59 g, 2.0 mmol) in 40 cm3 THF
was treated with BuLi in hexane (ca. 1.6 M, 1.3 cm3,
2.0 mmol) for 30 min at −78°C. The reaction mixture
was slowly warmed to r.t. and treated with CF3SO3CH3
(0.23 cm3, 2.0 mmol) for 30 min at −50°C. Gradual
warming to r.t., solvent removal, filtering through a
silica plug using CH2Cl2 and cold FCC (−20°C) with
hexane–diethyl ether (4:1) afforded the pure complexes
(% yields: 22, 8 and 23, 26). Yellow crystals of 23 were
obtained by solvent removal, washing with pentane
(3×20 cm3), dissolution in diethyl ether, layering with
pentane and cooling to −25°C. Pale-yellow crystals of
22 were obtained by eluent volume reduction and cool-
ing to −30°C.
8
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(C10H7MoNO5S). An Enraf–Nonius CAD4F diffrac-
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Ka) of wavelength u=0.71073 A was used to collect the
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were unique and the Rint value is 0.0241. The crystal
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(
was found to be triclinic, space group P1 with two
complete chemical units per cell. The unit cell dimen-
,
sions a, b, c (A) are 7.759(1), 9.721(2), 10.172(2), re-
spectively, and the values for h, i, k (°) are 87.26(2),
70.15(1), 66.55(2), respectively.
A total of 192 parameters were refined with a final
R value of 0.0236, (R=ꢀꢁꢁFoꢁ−ꢁFcꢁꢁ/ꢀꢁFoꢁ) and Rw
2 1/2
of 0.0608, (Rw=[ꢀ(ꢁF2oꢁ−ꢁFc2ꢁ)2/ꢀwꢁFoꢁ ]
;
w=1/
[|2(F2o)+(0.0220P)2+0.72P] where P=(max(F2o, 0)+
2F2c)/3). The structure was solved by interpretation of a
Patterson synthesis which yielded the position of the
molybdenum and refinement was by full-matrix least
squares, with all non-H atoms allowed anisotropic ther-
mal motion. Hydrogens were placed from a difference
map and refined isotropically.
SHELX-97 [27] was used to solve and refine the struc-
tures, ORTEP-3 [28] was used to generate Fig. 1, while
the program VISTA v. 2.0 [24] (part of the Cambridge
Crystallographic Data Centre software) was used to
draw Fig. 2.
8
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