Cyclooctatetraene (COT)-coordinated diiron carbene complexes and their remarkable thermolysis reactions

Article abstract of DOI:10.1021/om040101w

The reactions of the COT-coordinated diiron cationic bridging carbyne complexes [Fe₂(μ-CAr)(CO)₄(η⁸-C ₈H₈)]BF₄ (1, Ar = C₆H₆; 2, Ar = p-CH₃C₆H₄; 3, Ar = p-CF ₃C₆₄) with p-methylaniline gave the COT-coordinated diiron Fischer-type carbene complexes [Fe₂{=C(Ar) NHC₆H₄CH₃-p}(μ-CO)(CO)₃(η ⁸-C₈H₈)] (7, Ar = C₆H₅; 8, Ar = p-CH₃C₆H₄; 9, Ar = p-CF ₃C₆H₄). Heating the solution of diiron carbene complexes [Fe2{=C(Ar)NHC₆H₅}(μ-CO)-(CO) ₃(η⁸-C₈H₈)] (4, Ar = C ₆H₅; 5, Ar = p-CH₃C₆H₄; 6, Ar = p-CF₃C₆H₄) in benzene in a sealed tube at 85-90 °C for 72 h afforded the chelated diiron carbene complex [Fe ₂{=C(C₆H₅)-NC₆H₅} (η²:η³:η²-C₈H ₉)(CO)₄] (4a), C₈ ring addition products [Fe₂{N(C₆H₅)=C(Ar)(η¹: η³:η²-C₈H₉)}(CO) ₅] (10, Ar = C₆H₅; 12, Ar = p-CH ₃C₆H₄; 14, Ar = p-CF₃C ₆H₄), and C₇ contraction ring products [Fe ₂{N(C₆H₅)=C(Ar)CH(η²: η³-C₇H₈)(CO)₄}] (11, Ar = C ₆H₅; 13, Ar = p-CH₃C₆H₄; 15, Ar = p-CF₃C₆H₄, respectively. The similar thermolysis of complexes 7 and 8 afforded corresponding thermolysis products [Fe₂{=C(C₆H₅NC₆H₄CH ₃-p}(η²:η³:η²-C ₈H₉)(CO)₄] (7a), [Fe₂{N(C ₆H₄CH₃-p)=C(Ar)(η¹: η²:η³-C₈H₉)}(CO) ₅] (16, Ar = C₆H₅; 18, Ar = p-CH ₃C₆H₄), and [Fe₂{N(C ₆H₄CH₃-p)=C(Ar)CH(η²: η³-C₇H₈)}(CO)₄] (17, Ar = C ₆H₅; 19, Ar = p-CH₃C₆H₄), respectively. Interestingly, products 4a and 7a were transformed into the eight-membered ring products 10 and 16 and seven-membered ring products 11 and 17, respectively, under similar conditions. Surprisingly, compounds 10, 16, and 18 can also be partially transformed into compounds 11, 17, and 19, respectively, by further thermolysis at higher temperature (100-105 °C). The structures of complexes 7, 10, 11, 18, and 19 have been established by X-ray diffraction studies.

Full text of DOI:10.1021/om040101w

Organometallics 2005, 24, 933-944
933
Cyclooctatetraene (COT)-Coordinated Diiron Carbene
Complexes and Their Remarkable Thermolysis
Reactions†
Lei Zhang,‡ Shu Zhang,‡ Qiang Xu,*,§ Jie Sun,‡ and Jiabi Chen*,‡
State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry,
Chinese Academy of Sciences, 354 Fenglin Lu, Shanghai 200032, People’s Republic of China,
and National Institute of Advanced Industrial Science and Technology (AIST),
1-8-31 Midorigaoka, Ikeda, Osaka 563-8577, Japan
Received July 26, 2004
The reactions of the COT-coordinated diiron cationic bridging carbyne complexes [Fe2(µ-
CAr)(CO)4(η8-C8H8)]BF4 (1, Ar ) C6H5; 2, Ar ) p-CH3C6H4; 3, Ar ) p-CF3C6H4) with
p-methylaniline gave the COT-coordinated diiron Fischer-type carbene complexes [Fe2{d
C(Ar)NHC6H4CH3-p}(µ-CO)(CO)3(η8-C8H8)] (7, Ar ) C6H5; 8, Ar ) p-CH3C6H4; 9, Ar )
p-CF3C6H4). Heating the solution of diiron carbene complexes [Fe2{dC(Ar)NHC6H5}(µ-CO)-
(CO)3(η8-C8H8)] (4, Ar ) C6H5; 5, Ar ) p-CH3C6H4; 6, Ar ) p-CF3C6H4) in benzene in a sealed
tube at 85-90 °C for 72 h afforded the chelated diiron carbene complex [Fe2{dC(C6H5)-
NC6H5}(η2:η3:η2-C8H9)(CO)4] (4a), C8 ring addition products [Fe2{N(C6H5)dC(Ar)(η1:η3:η2-
C8H9)}(CO)5] (10, Ar ) C6H5; 12, Ar ) p-CH3C6H4; 14, Ar ) p-CF3C6H4), and C7 contraction
ring products [Fe2{N(C6H5)dC(Ar)CH(η2:η3-C7H8)(CO)4}] (11, Ar ) C6H5; 13, Ar ) p-CH3C6H4;
15, Ar ) p-CF3C6H4), respectively. The similar thermolysis of complexes 7 and 8 afforded
corresponding thermolysis products [Fe2{dC(C6H5)NC6H4CH3-p}(η2:η3:η2-C8H9)(CO)4] (7a),
[Fe2{N(C6H4CH3-p)dC(Ar)(η1:η2:η3-C8H9)}(CO)5] (16, Ar ) C6H5; 18, Ar ) p-CH3C6H4), and
[Fe2{N(C6H4CH3-p)dC(Ar)CH(η2:η3-C7H8)}(CO)4] (17, Ar ) C6H5; 19, Ar ) p-CH3C6H4),
respectively. Interestingly, products 4a and 7a were transformed into the eight-membered
ring products 10 and 16 and seven-membered ring products 11 and 17, respectively, under
similar conditions. Surprisingly, compounds 10, 16, and 18 can also be partially transformed
into compounds 11, 17, and 19, respectively, by further thermolysis at higher temperature
(100-105 °C). The structures of complexes 7, 10, 11, 18, and 19 have been established by
X-ray diffraction studies.
Introduction
study on the cyclooctatetraene (COT)-coordinated diiron
bridging carbene and bridging carbyne complexes, we
found that the COT ligand in diiron cationic bridging
carbyne complexes [Fe2(µ-CAr(CO)4(η8-C8H8)]BF4 are
activated toward attack by nucleophiles, leading to
nucleophilic addition or breaking of the COT ring, the
first example of such an activation of an olefin by a
diiron bridging carbyne moiety,5a and we have obtained
a new type of the COT-coordinated diiron Fischer-type
carbene complexes [Fe2{dC(Ar)NHC6H5}(µ-CO)(CO)3-
(η8-C8H8)] (4, Ar ) C6H5; 5, Ar ) p-CH3C6H4; 6, Ar )
p-CF3C6H4) from the reactions of the COT-coordinated
diiron cationic bridging carbyne complexes [Fe2(µ-CAr-
(CO)4(η8-C8H8)]BF4 (1, Ar ) C6H5; 2, Ar ) p-CH3C6H4;
3, Ar ) p-CF3C6H4) with aniline (eq 1).5b,c
Our interest in the synthesis, structure, and chem-
istry of alkene-metal carbene and carbyne complexes
stems from the possible involvement of these species in
some reactions catalyzed by organometallic compounds.1,2
In recent years, olefin-coordinated transition-metal car-
bene and carbyne complexes, as a part of a broader
investigation of transition-metal carbene and carbyne
complexes, have been examined extensively, and a
considerable number of olefin-coordinated dimetal bridg-
ing carbene and bridging carbyne complexes have been
synthesized in our laboratory.3-5 However, the olefin-
coordinated dimetallic Fischer-type carbene or carbyne
complexes are rare.5a,c,6 Recently, in the course of our
† Dedicated to Prof. Lixin Dai on the occasion of his 80th birthday
and in recognition of his brilliant contributions to organic and
organometallic chemistry.
It is known that the chemistry of dimetallic Fischer-
type carbene complexes has drawn an enormous interest
due to their novel stoichiometric or catalytic reactivity
in organic synthesis7 and that the olefin ligands in
transition-metal complexes exhibit high reactivities.8
‡ Shanghai Institute of Organic Chemistry.
§ National Institute of Advanced Industrial Science and Technology.
(1) Suess-Fink, G.; Meister, G. Adv. Organomet. Chem. 1993, 35,
41.
(2) (a) Gladfelter, W. L.; Roesselet, K. J. In The Chemistry of Metal
Cluster Complexes; Shriver, D. F., Kaesz, H. D., Adams, R. D., Eds.;
VCH: Weinheim, Germany, 1990; p 392. (b) Maire, G. In Metal
Clusters in Catalysis; Gates, B. C., Guczi, L., Knoezinger, H., Eds.;
Elsevier: Amsterdam, The Netherlands, 1986; p 509. (c) Dickson, R.
S.; Greaves, B. C. Organometallics 1993, 12, 3249.
(3) Chen, J.-B.; Li, D.-S.; Yu, Y.; Jin, Z.-S.; Zhou, Q.-L.; Wei, G.-C.
Organometallics 1993, 12, 3885.
(5) (a) Zhang, S.; Xu, Q.; Sun, J.; Chen, J.-B. Organometallics 2002,
21, 4572. (b) Zhang, S.; Xu, Q.; Sun, J.; Chen, J.-B. Organometallics
2003, 22, 1816. (c) Zhang, S.; Xu, Q.; Sun, J.; Chen, J.-B. Chem. Eur.
J. 2003, 9, 5111.
(6) Yu, Y.; Sun, J.; Chen, J.-B. J. Organomet. Chem. 1997, 533, 13.
(7) For review, see: M. A. Sierra, Chem. Rev. 2000, 100, 3591.
(8) Limanto, J.; Tallarico, J. A.; Porter, J. R.; Khuong, K. S.; Houk,
K. N.; Snapper, M. L. J. Am. Chem. Soc. 2002, 124, 14748.
(4) Yu, Y.; Chen, J.-B. Organometallics 1993, 12, 4731.
10.1021/om040101w CCC: $30.25 © 2005 American Chemical Society
Publication on Web 02/02/2005

934 Organometallics, Vol. 24, No. 5, 2005
Zhang et al.
°C to give 0.160 g (71%, based on 1) of purple-red crystals of
7: mp 80-82 °C dec; IR (CH2Cl2) ν(CO) 1987 (vs), 1965 (m),
1931 (s), 1694 (w) cm-1; 1H NMR (CD3COCD3) δ 11.36 (s, 1H,
NH), 7.32-6.75 (m, 9H, C6H5 + p-CH3C6H4), 4.38 (s, 8H, C8H8),
2.21 (s, 3H, p-CH3C6H4); MS m/e 467 (M+ - 2CO), 439 (M+
-
-
3CO), 411 [M+ - Fe(CO)2], 383 [M+ - Fe(CO)3], 355 [M+
Fe2(CO)2]. Anal. Calcd for C26H21O4NFe2: C, 59.70; H, 4.04;
N, 2.67. Found: C, 59.35; H, 4.10; N, 2.81.
Reaction of [Fe2(µ-CC6H4CH3-p)(η8-C8H8)(CO)4]BF4
(2) with p-CH3C6H4NH2 to Give [Fe2{dC(C6H4CH3-p)-
NHC6H4CH3-p}(µ-CO)(CO)3(η8-C8H8)] (8). Freshly prepared
2 (0.238 g, 0.49 mmol) in 50 mL of THF was treated, as
described for the reaction of 1 with p-CH3C6H4NH2, with 0.105
g (1.00 mmol) of p-CH3C6H4NH2 at -78 to -40 °C for 3 h.
Further treatment of the resulting solution as described above
afforded 0.142 g (53%, based on 2) of purple-red crystalline 8:
mp 64-66 °C dec; IR (CH2Cl2) ν(CO) 1986 (vs), 1966 (m), 1929
(s), 1693 (w) cm-1; 1H NMR (CD3COCD3) δ 11.36 (s, 1H, NH),
7.12-6.76 (m, 8H, 2 p-CH3C6H4), 4.37 (s, 8H, C8H8), 2.29 (s,
However, only very little is known5b,c about the reactiv-
ity of the olefin-coordinated dimetallic Fischer-type
carbene complexes. We are now interested in examin-
ing the reactivity of the olefin-coordinated dimetallic
Fischer-type carbene complexes.
To further explore the effect of different primary
amines on the reactivity of the COT-coordinated diiron
cationic bridging carbyne complexes and resulting prod-
ucts and to compare the thermolysis reactivity of the
COT-coordinated diiron Fischer-type carbene complexes
with monometallic Fischer-type carbene complexes, we
synthesized the diiron carbene complexes with an aryl-
(methylanilino)carbene ligand, [Fe2{dC(Ar)NHC6H4-
CH3-p}(µ-CO)(CO)3(η8-C8H8)] (7, Ar ) C6H5; 8, Ar )
p-CH3C6H4; 9, Ar ) p-CF3C6H4), from cationic bridging
carbyne complexes 1-3 and p-methylaniline and exam-
ined their thermolysis reactions. In this paper we report
the syntheses of complexes 7-9 and the remarkable
thermolysis reactions of these complexes involving
analogous complexes 4-6.
3H, p-CH3C6H4), 2.22 (s, 3H, p-CH3C6H4); MS m/e 509 (M+
-
CO), 481 (M+ - 2 CO), 453 (M+ - 3CO), 425 [M+ - Fe(CO)2],
397 [M+ - Fe(CO)3], 369 [M+ - Fe2(CO)2]. Anal. Calcd for
C27H23O4NFe2: C, 58.14; H, 4.31; N, 2.61. Found: C, 58.44;
H, 4.35; N, 2.76.
Reaction of [Fe2(µ-CC6H4CF3-p)(η8-C8H8)(CO)4]BF4
(3) with p-CH3C6H4NH2 to Give [Fe2{dC(C6H4CF3-p)-
NHC6H4CH3-p}(µ-CO)(CO)3(η8-C8H8)] (9). As described for
the reaction of 1 with p-CH3C6H4NH2, freshly prepared 3
(0.253 g, 0.47 mmol) was treated with p-CH3C6H4NH2 (0.100
g, 0.95 mmol) in THF at -78 to -40 °C for 3 h. Further
treatment of the resulting solution as described in the reaction
of 1 with p-CH3C6H4NH2 gave 0.091 g (32%, based on 3) of 9
as purple-red crystals: mp 90-92 °C dec; IR (CH2Cl2) ν(CO)
1
1988 (vs), 1968 (m), 1933 (s), 1705 (w) cm-1; H NMR (CD3-
Experimental Section
COCD3) δ 11.34 (s, 1H, NH), 7.63-6.82 (m, 8H, p-CH3C6H4 +
p-CF3C6H4), 4.40 (s, 8H, C8H8), 2.21 (s, 3H, p-CH3C6H4); MS
m/e 563 (M+ - CO), 535 (M+ - 2CO), 507 (M+ - 3CO), 479
[M+ - Fe (CO)2]. Anal. Calcd for C27H20O4F3NFe2: C, 52.83;
H, 3.41; N, 2.37. Found: C, 52.52; H, 3.70; N, 1.99.
All procedures were performed under a dry, oxygen-free N2
atmosphere by using standard Schlenk techniques. All solvents
employed were reagent grade and dried by refluxing over
appropriate drying agents and stored over 4 Å molecular sieves
under N2 atmosphere. Tetrahydrofuran and diethyl ether were
distilled from sodium benzophenone ketyl, while petroleum
ether (30-60 °C) and CH2Cl2 were distilled from CaH2. The
neutral alumina (Al2O3, 100-200 mesh) used for chromatog-
raphy was deoxygenated at room temperature under high
vacuum for 16 h, deactivated with 5% w/w N2-saturated water,
and stored under N2 atmosphere. Compounds p-CH3C6H4NH2,
aniline-d7, and benzene-d6 were purchased from Aldrich
Chemical Co. or Acros Organics Co. Diiron cationic bridging
carbyne complexes [Fe2(µ-CAr)(CO)4(η8-C8H8)]BF4 (1, Ar )
C6H5; 2, Ar ) p-CH3C6H4; 3, Ar ) p-CF3C6H4) and diiron
carbene complexes [Fe2{dC(Ar)NHC6H5}(µ-CO)(CO)3(η8-C8H8)]
(4, Ar ) C6H5; 5, Ar ) p-CH3C6H4; 6, Ar ) p-CF3C6H4) were
prepared as previously described.5b,c
The IR spectra were measured on a Perkin-Elmer 983G
spectrophotometer. All 1H NMR and 13C NMR spectra were
recorded at ambient temperature in acetone-d6 with TMS as
the internal reference using a Bruker AM-300 spectrometer.
Electron ionization mass spectra (EIMS) were run on a
Hewlett-Packard 5989A spectrometer. Melting points obtained
on samples in sealed nitrogen-filled capillaries are uncorrected.
Reaction of [Fe2(µ-CC6H5)(η8-C8H8)(CO)4]BF4 (1) with
p-CH3C6H4NH2 to Give [Fe2{dC(C6H5)NHC6H4CH3-p}(µ-
CO)(CO)3(η8-C8H8)] (7). To freshly prepared 1 (0.253 g, 0.54
µmol) dissolved in 50 mL of THF at -78 °C was added
p-CH3C6H4NH2 (0.115 g, 1.09 mmol). After stirring at -78 to
-40 °C for 3-4 h, the resulting solution was evaporated under
high vacuum at -40 °C to dryness. The dark red residue was
chromatographed on Al2O3 at -25 °C with petroleum ether/
CH2Cl2 (10:2) as the eluant. The brown-red band was eluted
and collected. After vacuum removal of the solvent, the crude
product was recrystallized from petroleum ether/CH2Cl2 at -80
Reaction of 1 with C6D5ND2 to Give [Fe2{dC(C6H5)-
NDC6D5}(µ-CO)(CO)3(η8-C8H8)] (4-d6). To 0.150 g (0.30
mmol) of freshly prepared 1 dissolved in 50 mL of THF at -78
°C was added 0.070 mL (0.80 mmol) of C6D5ND2. After stirring
at -78 to -40 °C for 3 h, the resulting solution was evaporated
under high vacuum at -40 °C to dryness, and the dark red
residue was extracted with petroleum ether/CH2Cl2 (10:1). The
red extracted solution was evaporated in vacuo at -40 °C to
dryness, and the residue was recrystallized from petroleum
ether/CH2Cl2 at -80 °C to give 0.280 g (89%, based on 1) of
deep red crystals of 4-d6: mp 144-146 °C dec; IR (CH2Cl2)
1
ν(CO) 1987 (s), 1931 (vs), 1697 (m, br) cm-1; H NMR (CD3-
COCD3) δ 7.26-6.92 (m, 5H, C6H5) 4.39 (s, 8H, C8H8), 11.37
(br, 0.2H, C6H5NH). The appearance of a weak signal at δ
11.37 is indicative of the existence of a little N-undeuterated
compound [Fe2{dC(C6H5)NHC6D5}(µ-CO)(CO)3(η8-C8H8)] in
the product.
Thermolysis of 4 to Give [Fe2{dC(C6H5)NC6H5}(η2:η3:
η2-C8H9)(CO)4] (4a), [Fe2{N(C6H5)dC(C6H5)(η1:η2:η3-C8H9)}-
(CO)5] (10), and [Fe2{ N(C6H5)dC(C6H5)CH-(η2:η3-C7H8)}-
(CO)4] (11). Compound 4 (0.100 g, 0.20 mmol) was dissolved
in benzene (20 mL) in a quartz tube. The tube was cooled at
-80 °C to freeze the benzene solution and sealed under high
vacuum. The sealed tube was heated to 85-90 °C for 72 h.
After cooling, the dark red solution was evaporated in vacuo
to dryness. The residue was chromatographed on Al2O3 with
petroleum ether as the eluant. The magenta band which eluted
first was collected, then a brown band was eluted with
petroleum ether/CH2Cl2 (10:1). A third brown-red band was
eluted with petroleum ether/CH2Cl2/Et2O (10:2:1). After vacuum
removal of the solvent from the above three eluates, the
residues were recrystallized from petroleum ether or petroleum

COT-Coordinated Diiron Carbene Complexes
Organometallics, Vol. 24, No. 5, 2005 935
1
ether/CH2Cl2 at -80 °C. From the first fraction, 0.010 g (10%)
of purple-red crystals of 11 was obtained: mp 120-122 °C; IR
Cl2) ν(CO) 2030 (s), 1966 (vs), 1907 (w) cm-1; H NMR δ 7.28
(m, 5H, C6H5), 5.31 (dd, 1H, J ) 8.9, 5.2 Hz, CH), 4.78 (t, 1H,
J ) 4.6 Hz, CH), 4.63 (t, 1H, J ) 7.5 Hz, CH), 4.52 (t, 1H, J
) 6.5 Hz, CH), 3.76 (t, 1H, J ) 3.3 Hz, CH), 3.66 (dd, 1H, J )
16.3, 7.6 Hz, CH), 2.29 (dt, 1H, J ) 8.0, 1.5 Hz, CH), 2.13 (dd,
0.2H, CH2), 1.86 (m, 1H, CH2). 11-d6: mp 116-118 °C; IR (CH2-
Cl2) ν(CO) 1999 (m), 1967 (s), 1930 (m), 1912 (w) cm-1; 1H NMR
(CD3COCD3) δ 7.50-7.22 (m, 5H; C6H5), 5.44 (t, 1H, J ) 6.2
Hz, CH), 5.11 (m, 2H, CH), 3.49 (m, 2H, CH), 2.33 (m, 1H,
CH), 1.86 (m, 0.2H, CH2), 1.63 (t, 1H, J ) 8.0 Hz, CH), 1.47
(d, 1H, J ) 12.7 Hz, CH2).
(CH2Cl2) ν(CO) 1999 (m), 1967 (s), 1930 (m), 1912 (w) cm-1
;
1H NMR (CD3COCD3) δ 7.51-7.02 (m, 10H; C6H5), 5.44 (t, 1H,
J ) 6.2 Hz, CH), 5.13 (m, 2H, CH), 3.50 (m, 2H, CH), 2.34 (m,
1H, CH), 1.86 (m, 1H, CH2), 1.63 (t, 1H, J ) 8.0 Hz, CH), 1.47
(d, 1H, J ) 12.7 Hz, CH2); 13C NMR (CD3COCD3) δ 219.4,
212.6, 202.5 (CO), 158.8, 139.7, 132.6, 129.5, 129.3, 128.7,
127.9, 126.1, 125.3, 117.5 (Ar-C), 88.9, 84.9, 64.5, 64.2, 58.9,
46.3, 44.7, 39.8 (C8H9); MS m/e 509 (M+), 481 (M+ - CO), 453
(M+ - 2CO), 425 (M+ - 3CO), 397 [M+ - Fe(CO)2], 285 [M+
-
Fe2(CO)4]. Anal. Calcd for C25H19O4NFe2: C, 58.98; H, 3.76;
N, 2.75. Found: C, 59.58; H, 4.01; N, 2.67. From the second
deep red fraction, 0.026 g (25%) of deep red crystalline 4a5b
was obtained: mp 178-180 °C dec; IR (CH2Cl2) ν(CO) 1999
Thermolysis of 4a to Give 10 and 11. Using the same
procedures as those of the thermolysis of 4, 0.100 g (0.20 mmol)
of 4a in benzene in a quartz tube was heated to 90 °C for 72
h. The dark resulting solution was worked up as described for
the thermolysis of 4 to afford 0.055 g (52%) of brown-red
crystals of 10 and 0.011 g (10%) of purple-red crystalline 11,
1
(m), 1964 (s), 1934 (m) cm-1; H NMR (CD3COCD3) δ 7.21-
6.50 (m, 10H, C6H5), 4.44 (t, 1H, J ) 6.3 Hz, CH), 4.07 (t, 1H,
J ) 6.8 Hz, CH), 3.62 (dd, 1H, J ) 15.4, 8.4 Hz, CH), 3.43 (t,
1H, J ) 6.5 Hz, CH), 3.37 (t, 1H, J ) 6.9 Hz, CH), 3.02 (dd,
1H, J ) 8.7, 6.0 Hz, CH), 2.76 (m, 1H, CH2), 2.61 (dd, 1H, J )
13.5, 7.5 Hz, CH), 1.62 (m, 1H, CH2); 13C NMR (CD3COCD3) δ
235.6 (Ccarbene), 217.7, 217.1, 216.5, 215.5 (CO), 158.3, 150.8,
128.9, 128.2, 126.8, 125.1, 124.1, 123.5 (Ar-C), 87.6, 80.1, 68.7,
53.9, 52.8, 42.1, 20.7, 19.1 (C8H9); MS m/e 481 (M+ - CO), 453
(M+ - 2CO), 425 (M+ - 3CO), 397 [M+ - Fe(CO)2]. Anal. Calcd
for C25H19O4NFe2: C, 58.98; H, 3.76; N, 2.75. Found: C, 58.78;
H, 3.92; N, 2.82. From the third brown-red fraction, 0.055 g
(52%) of brown-red crystalline 10 was obtained: mp >200 °C;
IR (CH2Cl2) ν(CO) 2030 (s), 1966 (vs), 1907 (w) cm-1; 1H NMR
δ 7.31-6.95 (m, 10H, C6H5), 5.30 (dd, 1H, J ) 8.9, 5.2 Hz,
CH), 4.78 (t, 1H, J ) 4.6 Hz, CH), 4.64 (t, 1H, J ) 7.5 Hz,
CH), 4.52 (t, 1H, J ) 6.5 Hz, CH), 3.77 (t, 1H, J ) 3.3 Hz,
CH), 3.66 (dd, 1H, J ) 16.3, 7.6 Hz, CH), 2.29 (dt, 1H, J )
8.0, 1.5 Hz, CH), 2.13 (dd, 1H, J ) 16.3, 7.6, 1.3 Hz, CH2),
1.86 (m, 1H, CH2); 13C NMR (CD3COCD3) δ 220.0, 214.2, 207.2
(CO), 160.9, 130.5, 129.6, 129.5, 129.0, 126.4, 122.9 (Ar-C),
88.9, 85.1, 81.0, 74.5, 71.0, 70.1, 56.5, 38.3, 28.4 (C8H9 ); MS
m/e 481 (M+ - 2CO), 425 [M+ - Fe(CO)2], 397 [M+ - Fe(CO)3].
Anal. Calcd for C26H19O5NFe2: C, 58.14; H, 3.57; N, 2.61.
Found: C, 57.72; H, 3.72; N, 2.86.
1
which were identified by their IR and H NMR spectra.
Thermolysis of 10 to Give 11. As in the thermolysis of 4
above, a solution of compound 10 (0.112 g, 0. 21 mmol) in 15
mL of benzene in a quartz tube was heated to 100-105 °C for
72 h. Further treatment of the resulting solution in a manner
similar to that described in the thermolysis of 4 gave 0.012 g
(11%) of purple-red crystals of 11 and 0.064 g (57%) of
unchanged compound 10, which were identified by their IR
1
and H NMR spectra.
Thermolysis of 5 to Give [Fe2{N(C6H5)dC(C6H4CH3-p)-
(η1:η2:η3-C8H9)}(CO)5] (12) and [Fe2{N(C6H5)dC(C6H4CH3-
p)CH(η2:η3-C7H8)}(CO)4] (13). As described for the thermol-
ysis of 4, compound 5 (0.300 g, 0.57 mmol) in benzene in a
quartz tube was heated to 85-90 °C for 72 h. Subsequent
treatment as described for the thermolysis of 4 afforded 0.150
g (47%) of brown-red crystalline 12 and 0.030 g (11%) of 13 as
purple-red crystals. 12: mp >200 °C; IR (CH2Cl2) ν(CO) 2029
1
(s), 1965 (vs), 1906 (w) cm-1; H NMR (CD3COCD3) δ 7.28-
6.95 (m, 9H, C6H5 + p-CH3C6H4), 5.64 (s, 1H, CH2Cl2), 5.29
(dd, 1H, J ) 8.6, 5.0 Hz, CH), 4.77 (t, 1H, J ) 5.5 Hz, CH),
4.63 (t, 1H, J ) 7.2 Hz, CH), 4.52 (t, 1H, J ) 6.5 Hz, CH),
3.76 (br, 1H, CH), 3.63 (m, 1H, CH), 2.26 (m, 1H, CH), 2.06
(m, 1H, CH2), 1.86 (m, 1H, CH2); 13C NMR (CD3COCD3) δ
219.9, 214.1, 207.1 (CO), 187.5, 154.4, 140.8, 131.6, 129.6,
129.5, 129.4, 126.3, 122.7 (Ar-C), 88.8, 85.0, 81.0, 74.6, 69.9,
Thermolysis of 4 in Benzene-d6 to Give 4a, 10, and 11.
Using the same procedures above, 0.150 g (0.28 mmol) of 4 in
benzene-d6 in a quartz tube was heated to 85-90 °C for 72 h.
The dark resulting solution was worked up as above to afford
0.024 g (23%) of 4a, 0.052 g (49%) of brown-red crystals of 10,
and 0.011 g (14%) of purple-red crystalline 11, which were
56.4, 37.9, 28.4, 21.1 (C8H9 + p-CH3C6H4); MS m/e 495 (M+
-
2CO), 467 (M+ - 3CO), 439 (M+ - 4CO), 411 [M+ - Fe(CO)3],
84 (CH2Cl2+). Anal. Calcd for C27H21O5NFe2‚0.5CH2Cl2: C,
55.64; H, 3.74; N, 2.36. Found: C, 55.81; H, 3.73; N, 2.24. 13:
mp 130-132 °C; IR (CH2Cl2) ν(CO) 1999 (m), 1966 (s), 1928
(m), 1911 (w) cm-1; 1H NMR (CD3COCD3) δ 7.49-7.01 (m, 9H,
C6H5 + p-CH3C6H4), 5.42 (t, 1H, J ) 6.4 Hz, CH), 5.10 (m,
2H, CH), 3.51 (m, 2H, CH), 2.32 (m, 1H, CH), 2.26 (s, 3H,
CH3C6H4), 1.83 (m, 1H, CH2), 1.62 (t, 1H, J ) 8.0 Hz, CH),
1.47 (d, 1H, J ) 11.9 Hz, CH2); 13C NMR (CD3COCD3) δ 219.5,
212.7, 207.2, 202.7 (CO), 159.1, 139.6, 137.1, 135.9, 132.6,
129.5, 129.4, 128.8, 128.7, 126.3, 125.4 (Ar-C), 89.0, 85.1, 64.6,
62.4, 59.1, 46.3, 44.8, 40.0, 21.1 (C8H9 + p-CH3C6H4); MS m/e
523 (M+), 495 (M+ - CO), 467 (M+ - 2CO), 439 (M+ - 3CO).
Anal. Calcd for C26H21O4NFe2: C, 59.69; H, 4.05; N, 2.68.
Found: C, 59.58; H, 3.73; N, 2.24.
1
identified by their IR and H NMR spectra.
Thermolysis of 4 in Benzene/D2O to Give 4a, 10, and
11. With the same procedures described above, 0.150 g (0.28
mmol) of 4 in 15 mL of benzene and 0.50 mL of deuterium
oxide (D2O) in a quartz tube were heated to 85-90 °C for 72
h. The dark resulting solution was worked up as described
above to afford 0.018 g (17%) of 4a, 0.052 g (39%) of brown-
red crystals of 10, and 0.008 g (10%) of purple-red crystalline
1
11, which were identified by their IR and H NMR spectra.
Thermolysis of 4-d6 to Give [Fe2{dC(C6H5)NC6D5}(η2:
η3:η2-C8H8D)(CO)4] (4a-d6), [Fe2{N(C6D5)dC(C6H5)(η1:η2:η3-
C8H8D)}(CO)5] (10-d6), and [Fe2{N(C6D5)dC(C6H5)CH(η2:
η3-C7H7D)}(CO)4] (11-d6). As described for the thermolysis
of 4, compound 4-d6 (0.050 g, 0.09 mmol) in benzene in a quartz
tube was heated to 85-90 °C for 72 h. Subsequent treatment
as described for the thermolysis of 4 afforded 0.08 g (24%) of
deep red crystalline 4a-d6, 0.016 g (47%) of brown-red crystals
of 10-d6, and 0.004 g (10%) of 11-d6 as purple-red crystals.
4a-d6: mp 126-128 °C dec; IR (CH2Cl2) ν(CO) 1997 (m), 1963
(s), 1934 (m) cm-1; 1H NMR (CD3COCD3) δ 7.09-6.56 (m, 5H,
C6H5), 4.43 (t, 1H, J ) 6.3 Hz, CH), 4.06 (t, 1H, J ) 6.8 Hz,
CH), 3.61 (dd, 1H, J ) 15.4, 8.4 Hz, CH), 3.42 (t, 1H, J ) 6.5
Hz, CH), 3.37 (t, 1H, J ) 6.9 Hz, CH), 3.02 (dd, 1H, J ) 8.7,
6.0 Hz, CH), 2.76 (m, 0.2H, CH2), 2.61 (dd, 1H, J ) 13.5, 7.5
Hz, CH), 1.60 (m, 1H, CH2). 10-d6: mp 156-158 °C; IR (CH2-
Thermolysis of 6 to Give [Fe2{N(C6H5)dC(C6H4CF3-p)-
(η1:η2:η3-C8H9)}(CO)5] (14) and [Fe2{N(C6H5)dC(C6H4CF3-
p)CH(η2:η3-C7H8)}(CO)4] (15). Similar to the procedures used
in the thermolysis of 4, compound 6 (0.200 g, 0.35 mmol) in
benzene in a quartz tube was heated to 85-90 °C for 72 h.
The resulting solution was worked up as described for the
thermolysis of 4 to produce 0.080 g (38%) of brown-red crystals
of 14 and 0.016 g (8%) of 15 as purple-red crystals. 14: mp
>200 °C; IR (CH2Cl2) ν(CO) 2031 (s), 1968 (vs), 1909 (w) cm-1
;
1H NMR (CD3COCD3) δ 7.64-6.99 (m, 9H, C6H5 + p-CF3C6H4),
5.63 (s, 1H, CH2Cl2), 5.32 (dd, 1H, J ) 8.8, 5.3 Hz, CH), 4.80
(t, 1H, J ) 5.8 Hz, CH), 4.63 (t, 1H, J ) 8.0 Hz, CH), 4.55 (t,
1H, J ) 6.2 Hz, CH), 3.78 (t, 1H, J ) 2.9 Hz, CH), 3.67 (dd,

936 Organometallics, Vol. 24, No. 5, 2005
Zhang et al.
1H, J ) 16.4, 7.6 Hz, CH), 2.35 (m, 1H, J ) 7.8, 1.5 Hz, CH),
2.17 (m, 1H, CH2), 1.85 (m, 1H, CH2); 13C NMR (CD3COCD3)
δ 219.7, 213.9, 207.0 (CO), 186.6, 153.7, 138.7, 130.1, 129.6,
126.7, 125.8, 122.6 (Ar-C), 89.0, 84.9, 80.8, 73.9, 70.0, 56.5,
2.11 (m, 1H, CH2), 1.84 (m, 1H, CH2);13C NMR (CD3COCD3) δ
220.0, 207.2, 187.6 (CO), 151.9, 135.9, 134.9, 130.4, 130.0,
129.5, 129.0, 122.7 (Ar-C), 88.9, 85.1, 81.0, 74.5, 70.1, 56.4,
38.3, 28.3, 20.8 (C8H9 + p-CH3C6H4); MS m/e 495 (M+ - 2CO),
467 (M+ - 3CO), 439 (M+ - 4CO). Anal. Calcd for C27H21O5-
NFe2: C, 58.84; H, 3.84; N, 2.54. Found: C, 58.28; H, 3.62; N,
2.38.
38.6, 28.1 (C8H9 + p-CF3C6H4). MS m/e 605 (M+), 549 (M+
-
2CO), 521 (M+ - 3CO), 493 (M+ - 4CO), 84 (CH2Cl2+). Anal.
Calcd for C27H19O5F3NFe2‚0.5CH2Cl2: C, 51.00; H, 2.96; N,
2.16. Found: C, 51.50; H, 2.99; N, 2.02. 15: mp 120-122 °C;
Thermolysis of 7a to Give 16 and 17. Using the same
procedures as those for the thermolysis of 7, 0.074 g (0.13
mmol) of 7a in benzene in a quartz tube was heated to 90 °C
for 72 h. The dark resulting solution was worked up as
described for the thermolysis of 7 to afford 0.033 g (43%) of
brown-red crystals of 16 and 0.007 (9%) of purple-red crystal-
line 17, which were identified by their IR and 1H NMR spectra.
Thermolysis of 16 to Give 17. Compound 16 (0.070 g,
0.134 mmol) in benzene in a quartz tube was heated, in a
manner similar to that described for the thermolysis of 7, to
100-105 °C for 72 h. After vacuum removal of the solvent,
the residue was worked up as described for the thermolysis of
7 to give 0.007 g (9%) of purple red crystals of 17 and 0.040 g
(57%) of unchanged compound 16, which were identified by
IR (CH2Cl2) ν(CO) 2040 (m), 2003 (m), 1973 (s), 1936 (s) cm-1
;
1H NMR (CD3COCD3) δ 7.77-7.05 (m, 9H, C6H5 + p-CF3C6H4),
5.48 (t, 1H, J ) 5.7 Hz, CH), 5.17 (m, 2H, CH), 3.52 (m, 2H,
CH), 2.36 (m, 1H, CH), 1.87 (m, 1H, CH2), 1.66 (t, 1H, J ) 7.7
Hz, CH), 1.49 (d, 1H, J ) 12.7 Hz, CH2); 13C NMR (CD3COCD3)
δ 219.1, 212.4, 206.7, 202.3 (CO), 158.3, 133.4, 129.5, 129.3,
128.8, 128.3, 126.0, 125.6, 124.8 (Ar-C), 89.0, 84.9, 64.7, 62.3,
59.0, 46.9, 44.6, 39.7 (C8H9 + p-CF3C6H4); MS m/e 523 (M+),
495 (M+ - CO), 467 (M+ - 2CO), 439 (M+ - 3CO). Anal. Calcd
for C26H18F3O4NFe2: C, 54.11; H, 3.14; N, 2.43. Found: C,
54.72; H, 3.56; N, 2.78.
Thermolysis of 7 to Give [Fe2{dC(C6H5)NC6H4CH3-p}-
(η2:η3:µ2-C8H9)(CO)4] (7a), [Fe2{N(C6H4CH3-p)dC(C6H5)(η1:
η2:η3-C8H9)}(CO)5] (16), and [Fe2{N(C6H4CH3-p)dC(C6H5)-
CH(η2:η3-C7H8)}(CO)4] (17). Compound 7 (0.210 g, 0.43 mmol)
was dissolved in benzene (20 mL) in a quartz tube. The tube
was cooled at -80 °C to freeze the benzene solution and sealed
under high vacuum. The sealed tube was heated to 85-90 °C
for 72 h. After cooling, the dark red solution was evaporated
in vacuo to dryness. The dark residue was chromatographed
on Al2O3 with petroleum ether as the eluant. The magenta
band which eluted first was collected, then a orange-red band
was eluted with petroleum ether/CH2Cl2/Et2O (10:2). A third,
brown-red band was eluted with petroleum ether/CH2Cl2/Et2O
(10:2:1). The solvents were removed from the above three
eluates in vacuo, and the crude products were recrystallized
from petroleum ether or petroleum ether/CH2Cl2 at -80 °C.
From the first fraction, 0.022 g (10%) of purple-red crystals of
17 was obtained: mp 164-166 °C; IR (CH2Cl2) ν(CO) 1999 (s),
1
their IR and H NMR spectra.
Thermolysis of
8
to Give [Fe2{N(C6H4CH3-p)d
C(C6H4CH3-p)(η1:η2:η3-C8H9)}(CO)5] (18) and [Fe2{N-
(C6H4CH3-p)dC(C6H4CH3-p)CH(η2:η3-C7H8)}(CO)4] (19).
Similar to the procedures used in the thermolysis of 7, 0.090
g (0.18 mmol) of 8 in benzene in a quartz tube was heated to
85-90 °C for 72 h. The dark resulting solution was worked
up as described for the thermolysis of 7 to afford 0.039 g (41%)
of brown-red crystalline 18 and 0.007 g (8%) of 19 as purple-
red crystals. 18: mp 78-80 °C; IR (CH2Cl2) ν(CO) 2029 (s),
1
1965 (vs), 1906 (w) cm-1; H NMR (CD3COCD3) δ 7.19-6.83
(m, 8H, p-CH3C6H4), 5.28 (dd, 1H, J ) 5.1, 9.3 Hz, CH), 4.76
(t, 1H, J ) 6.0 Hz, CH), 4.62 (t, 1H, J ) 7.5 Hz, CH), 4.50 (t,
1H, J ) 6.3 Hz, CH), 3.74 (t, 1H, J ) 3.0 Hz, CH), 3.64 (dd,
1H, J ) 15.9, 7.5 Hz, CH), 2.26 (s, 4H, CH3C6H4 + CH), 2.24
(s, 3H, p-CH3C6H4), 2.06 (m, 1H, CH2), 1.83 (m, 1H, CH2).13C
NMR (CD3COCD3) δ 220.0, 207.1, 187.4 (CO), 152.1,140.7,
135.8, 131.8, 130.0,129.7, 129.6, 129.5, 122.6 (Ar-C), 88.8,
1966 (vs), 1928 (s), 1912 (m) cm-1 1H NMR (CD3COCD3) δ
;
7.51-6.90 (m, 9H; C6H5 + p-CH3C6H4), 5.44 (t, 1H, J ) 11.7
Hz, CH), 5.13 (m, 2H, CH), 3.50 (m, 2H, CH), 2.34 (m, 1H,
CH), 2.25(s, 3H, CH3C6H4), 1.86 (m, 1H, CH2), 1.63 (t, 1H, J
) 7.8 Hz, CH), 1.47 (d, 1H, J ) 6.9 Hz, CH2), 1.29-1.09 (m,
8H, CH3(CH2)4CH3), 0.86 (m, 6H, CH3(CH2)4CH3); 13C NMR
(CD3COCD3) δ 219.6, 212.6, 207.1, 202.6 (CO), 156.7, 139.9,
136.2, 134.7, 132.7, 129.7, 129.5, 129.4, 129.1, 128.0, 126.0
(Ar-C), 88.9, 84.9, 64.5, 62.2, 59.0, 46.3, 44.8, 39.9, 20.6 (C8H9
+ p-CH3C6H4); MS m/e 495 (M+ - CO), 467 (M+ - 2CO), 439
(M+ - 3CO), 411 (M+ - 4CO), 86 (C6H14+). Anal. Calcd for
C26H21O4NFe2‚C6H14: C, 63.08; H, 4.79; N, 2.30. Found: C,
63.52; H, 4.68; N, 2.66. From the second fraction, 0.070 g (33%)
of deep red crystals of 7a was obtained: mp 112-114 °C dec;
IR (CH2Cl2) ν(CO) 2004 (m), 1971 (vs), 1942 (m) cm-1; 1H NMR
(CD3COCD3) δ 7.1-6.40 (m, 9H, C6H5 + p-CH3C6H4), 4.42 (t,
1H, J ) 12.9, CH), 4.06 (t, 1H, J ) 13.8 Hz, CH), 3.60 (dd,
1H, J ) 15.0 Hz, 6.6 Hz, CH), 3.39 (m, 1H, CH), 2.99 (dd, 1H,
J ) 9.0, 6.0 Hz, CH), 2.72 (m, 1H, CH2), 2.60 (dd, 1H, J )
13.8 Hz, 8.1 Hz, CH), 2.23 (s, 3H, CH3C6H4), 1.60 (m, 1H, CH2);
13C NMR (CD3COCD3) δ 235.6 (Ccarbene), 218.4, 217.9, 217.2,
216.2 (CO), 156.7, 151.6, 134.7, 129.7, 128.9, 128.5, 127.0,
124.4, 123.6, 123.5, 95.3 (Ar-C), 88.3, 85.9, 84.2, 80.1, 71.0,
69.3, 62.4, 54.4, 53.5, 42.7, 21.3, 20.8, 19.7 (C8H9 + p-CH3C6H4);
MS m/e 495 (M+ - CO), 411 [M+ - Fe(CO)2], 299 [M+ - Fe2-
(CO)4]. Anal. Calcd for C26H21O4NFe2: C, 59.69; H, 4.05; N,
2.68. Found: C, 59.49; H, 4.24; N, 2.62. From the third fraction,
0.062 g (28%) of brown-red crystalline 16 was obtained: mp
136-138 °C dec; IR (CH2Cl2) ν(CO) 2029 (s), 1966 (vs), 1906
85.1, 81.0, 74.7, 70.0, 56.4, 38.0, 28.4, 21.2, 20.9 (C8H9
+
p-CH3C6H4); MS m/e 453 [M+ - Fe(CO)2], 425 [M+ - Fe(CO)3].
Anal. Calcd for C28H23O5NFe2: C, 59.50; H, 4.10; N, 2.48.
Found: C, 59.80; H, 4.49; N, 2.21. 19: mp 164-166 °C; IR
(CH2Cl2) ν(CO) 1998 (s), 1965 (vs), 1928 (s), 1911 (m) cm-1
;
1H NMR (CD3COCD3) δ 7.39-6.91 (m, 8H, 2 p-CH3C6H4), 5.40
(t, 1H, J ) 6.3 Hz, CH), 5.08 (m, 2H, CH), 3.49-3.37 (m, 2H,
CH), 2.30 (m, 1H, CH), 2.27 (s, 3H, p-CH3C6H4), 2.26 (s, 3H,
CH3C6H4), 1.83 (m, 1H, CH2), 1.61 (t, 1H, J ) 7.8 Hz, CH),
1.45 (d, 1H, J ) 6.3 Hz, CH2), 1.29-1.09 (m, 4H, CH3(CH2)4-
CH3), 0.86 (m, 3H, CH3(CH2)4CH3); 13C NMR (CD3COCD3) δ
218.9, 212.2, 206.5, 202.0 (CO); 156.2, 138.9, 136.5, 135.4,
134.0, 132.0, 129.1, 128.8, 128.5, 128.0, 125.4 (Ar-C); 88.2,
84.4, 63.8, 61.6, 58.3, 45.5, 44.2, 39.3 20.5, 20.0 (C8H9
+
p-CH3C6H4), 25.7, 22.2, 14.9 (C6H14); MS m/e 537 (M+), 509
(M+ - CO), 481 (M+ - 2CO), 426 [M+ - Fe(CO)2], 86 (C6H14+).
Anal. Calcd for C27H23O4NFe2‚0.5C6H14: C, 62.10; H, 5.21; N,
2.41. Found: C, 62.23; H, 5.24; N, 2.32.
Thermolysis of 18 to Give 19. As described above for the
thermolysis of 7, compound 18 (0.070 g, 0.12 mmol) in benzene
in a quartz tube was heated to 100-105 °C for 72 h. After the
solvent was evaporated, further treatment of the residue in a
manner similar to that described for the thermolysis of 7 gave
0.007 g (10%) of purple-red crystals of 19 and 0.045 g (64%) of
unchanged compound 18, which were identified by their IR
1
and H NMR spectra.
X-ray Crystal Structure Determinations of Complexes
7, 10, 11, 18, and 19. The single crystals of complexes 7, 10,
11, 18, and 19 suitable for X-ray diffraction study were
obtained by recrystallization from petroleum ether/CH2Cl2 or
petroleum ether/Et2O at -80 °C. Single crystals were mounted
on a glass fiber and sealed with epoxy glue. The X-ray
1
(w) cm-1 ; H NMR (CD3COCD3) δ 7.28-6.84 (m, 9H, C6H5 +
p-CH3C6H4), 5.29 (dd, 1H, J ) 9.0, 5.4 Hz, CH), 4.775 (t, 1H,
J ) 4.2 Hz, CH), 4.65 (t, 1H, J ) 7.5 Hz, CH), 4.52 (t, 1H, J
) 6.6 Hz, CH), 3.75 (t, 1H, J ) 3.6 Hz, CH), 3.64 (dd. 1H, J )
16.4, 7.5 Hz, CH), 2.29 (m, 1H, CH), 2.26 (s, 3H, CH3C6H4),

COT-Coordinated Diiron Carbene Complexes
Organometallics, Vol. 24, No. 5, 2005 937
Table 1. Crystal Data and Experimental Details for Complexes 7, 10, 11, 18, and 19
7
10
11
18‚Et2O
19‚CH2Cl2
formula
fw
C26H21O4NFe2
523.14
C26H19O3NFe2
537.12
C25H19O4NFe2
509.11
C60H56O11N2Fe4
1204.47
C28H25 O4Cl2NFe2
622.09
space group
a (Å)
P1h (No. 2)
8.2205(8)
11.1668(10)
14.1767(13)
105.139(2)
97.409(2)
110.053(2)
1145.28(18)
2
P21/n (No. 14)
7.6928(8)
P1h (No. 2)
11.861(13)
13.882(15)
14.882(15)
105.426(19)
113.33(2)
93.96(2)
2126(4)
P21/c (No. 14)
17.4782(10)
13.3877(7)
Pbca (No. 61)
10.4699(10)
23.469(2)
23.670(2)
90
b (Å)
c (Å)
23.428(2)
13.1081(13)
25.9087(15)
R (deg)
â (deg)
γ (deg)
V (Å3 )
103.787(2)
100.3530(10)
90
90
2294.3(4)
4
5963.8(6)
4
5816.1(10)
8
Z
4
Dcalcd (g /cm3)
F(000)
µ(Mo KR) (cm-1
1.517
1.555
1.590
1.341
1.421
536
1096
1040
2488
2544
)
13.00
13.03
13.97
10.12
12.14
radiation (monochromated
in incident beam)
diffractometer
Mo KR (λ )
0.71073 Å)
Bruker Smart
20
MoKR (λ )
0.71073 Å)
Bruker Smart
20
Mo KR (λ )
0.71073 Å)
Bruker Smart
20
Mo KR (λ )
0.71073 Å)
Bruker Smart
20
Mo KR (λ )
0.71073 Å)
Bruker Smart
20
temperature (°C)
orientation reflns:
range (2θ) (deg)
scan method
data collected range, 2θ (deg)
no. of unique data, total
with I >2.00σ(I)
no. of params refined
correct. factors,
5.561-52.770
4.725-45.108
4.707-36.464
4.334-36.978
4.594-34.888
ω-2θ
ω-2θ
ω-2θ
ω-2θ
ω-2θ
3.06-54.00
4868
3.48-55.10
5122
3.10-50.00
7345
3.44-54.00
12935
3.44-51.10
5423
3675
327
3081
383
2795
629
4228
698
2488
325
0.75216-1.00000
0.54902-1.00000
0.42158-1.00000
0.85892-1.00000
0.83686-1.00000
max.-min.
Ra
0.0386
0.0904
0.952
0.0454
0.0749
0.827
0.1111
0.2482
0.892
0.0737
0.1765
0.879
0.0741
0.1653
0.944
b
Rw
quality of fit indicatorc
max. shift/esd. final cycle
largest peak (e-/Å3)
0.001
0.002
0.092
0.092
0.091
0.512
0.434
1.501
0.967
0.433
minimum peak (e-/Å3)
-0.290
-0.257
-0.898
-0.386
-0.537
2
a R )∑||Fo| - |Fc||/∑|Fo|. b Rw ) [∑w(|Fo| - |Fc|)2/∑w|Fo| ]1/2; w ) 1/σ2(|Fo|). c Quality-of-fit ) [∑w(|Fo| - |Fc|)2/(Nobs - Nparameters)]1/2
.
diffraction intensity data for 7, 10, 11, 18, and 19 were
collected with a Bruker Smart diffractometer at 20 °C using
Mo KR radiation with an ω-2θ scan mode.
After workup as described in the Experimental Section,
the purple-red diiron carbene complexes [Fe2{dC(Ar)-
NHC6H4CH3-p}(µ-CO)(CO)3(η8-C8H8)] (7, Ar ) C6H5; 8,
Ar ) p-CH3C6H4; 9, Ar ) p-CF3C6H4) (eq 2) were
obtained in 32-71% isolated yields.
The structures of 7, 10, 11, 18, and 19 were solved by the
direct methods and expanded using Fourier techniques. For
the six complexes, the non-hydrogen atoms were refined
anisotropically and the hydrogen atoms were included but not
refined. The absorption corrections were applied using SAD-
ABS. The final cycle of full-matrix least-squares refinement
was based on the observed reflections and the variable
parameters and converged with unweighted and weighted
agreement to give agreement factors of R ) 0.0386 and Rw
)
0.0904 for 7, R ) 0.0454 and Rw ) 0.0749 for 10, R ) 0.1111
and Rw ) 0.2482 for 11, R ) 0.0737 and Rw ) 0.1765 for 18,
and R ) 0.0741 and Rw ) 0.1653 for 19. For complex 11, the
R factor is relatively high since single crystals suitable for
X-ray diffraction were very difficult to obtain and the intensity
data were collected at 20 °C. The reflection intensity was
evidently decayed during the collection.
The details of the crystallographic data and the procedures
used for data collection and reduction information for 7, 10,
11, 18, and 19 are given in Table 1. The selected bond lengths
and angles are listed in Table 2. The atomic coordinates and
Biso/Beq, anisotropic displacement parameters, complete bond
lengths and angles, and least-squares planes for 7, 10, 11, 18,
and 19 are given in the Supporting Information. The molecular
structures of 7, 10, 11, 18, and 19 are given in Figures 1-5,
respectively.
Complexes 7-9 were readily soluble in polar organic
solvents but slightly soluble in nonpolar solvents. They
are very sensitive to air and temperature in solution
and in the solid state. The formulas shown in eq 2 for
the three complexes were established by microanalytical
Results and Discussion
By analogy with the preparation of the COT-coordi-
nated diiron carbene complexes [Fe2{dC(Ar)NHC6H5}-
(µ-CO)(CO)3(η8-C8H8)] (4, Ar ) C6H5; 5, Ar ) p-CH3C6H4;
6, Ar ) p-CF3C6H4),5b,c freshly prepared (in situ) diiron
cationic bridging carbyne complexes 1-3 react with
p-methylaniline in THF at -78 to -40 °C for 3-4 h.
1
data and IR, H NMR, and mass spectra, as well as
X-ray crystallography. The IR spectra of complexes 7-9
showed a CO absorption band, characteristic for a
bridging CO ligand, at 1693-1705 cm-1 in the ν(CO)
region in addition to the three terminal CO absorption

938 Organometallics, Vol. 24, No. 5, 2005
Zhang et al.
Table 2. Selected Bond Lengths (Å) and Angles (deg) for Complexes 7, 10, 11, 18, and 19a
7
10
11
18
19
Fe(1)-Fe(2)
2.7462(5)
1.913(2)
1.916(2)
1.948(2)
2.249(3)
2.121(3)
2.110(3)
2.182(3)
2.7599(7)
2.671(4)
2.062(14)
1.68(2)
2.7626(14)
2.6912(14)
2.081(7)
1.761(9)
Fe(1)-C(1)
Fe(1)-C(8)
1.769(4)
1.748(14)
Fe(2)-C(8)
Fe(1)-C(13)
2.098(4)
2.066(4)
2.162(3)
2.378(13)
2.098(16)
2.117(8)
2.058(9)
2.161(8)
2.400(8)
2.115(8)
Fe(1)-C(14)
Fe(1)-C(15)
Fe(1)-C(16)
Fe(1)-C(19)
2.106(15)
2.034(15)
2.477(15)
2.114(7)
2.062(7)
2.401(8)
Fe(2)-C(12)
2.157(4)
2.233(3)
2.055(3)
2.239(7)
2.060(7)
Fe(2)-C(13)
Fe(2)-C(16)
Fe(2)-C(17)
2.288(3)
2.084(3)
2.076(3)
1.742(3)
1.763(3)
1.751(3)
1.328(3)
2.089(16)
2.030(17)
2.088(7)
2.047(7)
Fe(2)-C(18)
Fe(2)-C(19)
2.217(3)
1.784(4)
1.799(3)
1.760(4)
1.288(3)
2.239(7)
1.780(9)
1.750(9)
1.795(8)
1.282(9)
Fe(1)-C(9)
1.729(17)
1.724(19)
1.80(2)
1.390(15)
1.983(12)
1.999(11)
1.228(19)
1.483(18)
1.763(9)
1.771(10)
1.774(8)
1.387(8)
1.994(5)
1.971(5)
1.159(8)
1.481(9)
Fe(2)-C(10)
Fe(2)-C(11)
C(1)-N(1)
Fe(1)-N(1)
Fe(2)-N(1)
2.013(2)
1.150(4)
1.483(4)
1.493(4)
2.041(6)
1.157(9)
1.444(10)
1.485(10)
C(8)-O(1)
1.187(3)
1.487(3)
C(1)-C(2)
C(1)-C(17)
C(1)-C(19)
1.395(19)
1.459(16)
1.47(2)
1.423(9)
1.461(8)
N(1)-C(20)
1.429(3)
1.443(6)
1.409(7)
1.349(6)
1.364(7)
1.391(6)
1.447(3)
1.454(5)
1.408(5)
1.382(5)
1.478(4)
1.527(4)
1.445(8)
1.466(9)
1.403(10)
1.403(10)
1.496(9)
1.490(11)
C(12)-C(13)
1.446(10)
1.413(10)
1.536(11)
1.535(11)
1.505(10)
1.536(10)
1.400(10)
C(13)-C(14)
1.38(2)
C(14)-C(15)
1.47(2)
C(15)-C(16)
1.54(2)
C(16)-C(17)
1.50(2)
C(16)-C(19)
1.496(19)
1.43(2)
C(17)-C(18)
1.399(5)
1.356(5)
1.546(4)
1.493(5)
1.550(10)
1.500(10)
C(18)-C(19)
C(12)-C(18)
1.39(2)
1.406(10)
C(12)-C(19)
1.426(5)
1.362(5)
1.353(10)
Fe(1)-C(8)-Fe(2)
Fe(1)-Fe(2)-C(8)
Fe(2)-Fe(1)-C(8)
Fe(2)-Fe(1)-C(1)
Fe(2)-Fe(1)-C(19)
Fe(1)-C(1)-N(1)
Fe(1)-C(1)-C(2)
Fe(1)-Fe(2)-N(1)
Fe(2)-Fe(1)-N(1)
Fe(1)-N(1)-Fe(2)
Fe(1)-N(1)-C(1)
N(1)-Fe(1)-C(1)
Fe(1)-Fe(2)-C(17)
Fe(2)-Fe(1)-C(16)
Fe(2)-N(1)-C(1)
Fe(2)-N(1)-C(20)
Fe(1)-C(8)-O(1)
Fe(2)-C(8)-O(1)
N(1)-C(1)-C(2)
C(2)-C(1)-C(17)
C(2)-C(1)-C(19)
C(1)-N(1)-C(20)
C(1)-C(19)-C(16)
C(12)-C(13)-C(14)
C(13)-C(14)-C(15)
C(14)-C(15)-C(16)
C(15)-C(16)-C(17)
C(16)-C(17)-C(18)
C(17)-C(18)-C(19)
C(17)-C(18)-C(12)
C(18)-C(12)-C(13)
C(18)-C(19)-C(12)
C(19)-C(12)-C(13)
Fe(1)-C-O (av)
Fe(2)-C-O (av)
90.59(4)
44.25(7)
45.17(7)
75.51(12)
95.6(6)
77.2(4)
83.7(5)
66.8(7)
125.8(9)
47.6(3)
48.1(3)
84.3(4)
73.0(7)
40.1(4)
87.3(5)
77.5(3)
99.4(2)
129.94(7)
99.10(10)
122.63(16)
122.72(16)
76.51(19)
83.2(2)
66.8(3)
126.8(5)
47.63(15)
46.90(15)
85.5(2)
148.90(7)
149.06(18)
73.5(4)
39.7(2)
64.86(13)
79.60(15)
87.8(2)
115.8(2)
123.10(19)
174.1(4)
122.9(8)
136.3(9)
177.3(16)
115.3(5)
122.7(5)
175.2(8)
125.2(5)
114.7(4)
173.2(7)
135.43(19)
133.88(19)
114.63(19)
126.2(3)
121.5(3)
120.8(11)
125.6(7)
122.3(7)
124.0(6)
119.8(13)
118.8(10)
131.2(15)
123.7(16)
125.0(17)
107.2(12)
118.1(14)
125.4(15)
118.8(6)
116.5(5)
130.9(7)
128.4(9)
116.9(8)
109.5(7)
116.6(7)
124.4(7)
131.97(19)
120.9(3)
121.8(6)
134.1(4)
129.6(4)
128.2(4)
133.5(5)
136.8(4)
128.0(3)
125.5(4)
123.6(3)
126.1(3)
116.8(3)
108.1(3)
109.9(3)
125.9(7)
123.3(7)
126.9(7)
117.5(7)
109.5(6)
108.3(6)
118.7(18)
128.6(16)
121.0(7)
124.5(7)
125.0(3)
133.5(4)
177.7
126.1(3)
127.0(4)
175.8
124.8(7)
127.6(7)
176.1
177.3
176.0
175.9
176.8
178.3
177.2
177.7
a Estimated standard deviations in the least significant figure are given in parentheses.
bands at 1986-1988, 1965-1968, and 1929-1933 cm-1
.
The structure of complex 7 (Figure 1) resembles that
of complex 5,5c except that the substituents at the
carbene carbon and N atoms respectively are a C6H5
The 1H NMR spectra of 7-9 showed a single-line signal
for the COT ligand as that of the original eight-
membered ring in starting materials [Fe2{µ-C(OC2H5)-
Ar}(CO)4(η8-C8H8)], which is fluxional,3,9 suggesting that
the COT ring is retained in these complexes.
(9) For more detailed review about fluxional organometallics, see:
Cotton, F. A. Inorg. Chem. 2002, 41, 643-658.

COT-Coordinated Diiron Carbene Complexes
Organometallics, Vol. 24, No. 5, 2005 939
Figure 1. Molecular structure of 7, showing the atom-
numbering scheme with 45% thermal ellipsoids.
Figure 4. Molecular structure of 11, showing the atom-
numbering scheme with 45% thermal ellipsoids, showing
only one of two independent molecules for clarity.
Figure 2. Molecular structure of 10, showing the atom-
numbering scheme with 40% thermal ellipsoids.
Figure 3. Molecular structure of 18, showing the atom-
numbering scheme with 45% thermal ellipsoids. Et2O has
been omitted for clarity.
Figure 5. Molecular structure of 19, showing the atom-
numbering scheme with 45% thermal ellipsoids. CH2Cl2
has been omitted for clarity.
and a p-CH3C6H4 group in 7 but a p-CH3C6H4 and a
C6H5 group in the latter. Many structural features of 7
are very similar to those of 5, as illustrated by the
following parameters (the value for 7 is followed by the
same parameters for 5): Fe(1)-Fe(2) (2.7462(5), 2.7589-
(19) Å), Fe(1)-Ccarbene (1.913(2), 1.895(8) Å), Ccarbene-N
(1.328, 1.333(10) Å), average Fe(1)-C(COT) (2.166,
2.175 Å), average Fe(2)-C(COT) (2.151, 2.149 Å), aver-
age Fe-C(8) (1.932, 1.930 Å), Fe(1)-C(8)-Fe(2) (90.59-
(4)°, 91.2(4)°). An apparent difference in the structures
of 7 and 5 is the larger Fe(2)-Fe(1)-C(1) angle in 7
(129.94(7)°) as compared to 5 (127.1(3)°).
The possible reaction pathway to complexes 7-9 could
be via an intermediate of [Fe2{µ-C(Ar)NHC6H4CH3-p}-
(CO)4(η8-C8H8)] (Ar ) C6H5 or p-CH3C6H4 or p-CF3C6H4),
which was formed by the attack of the neutral
p-CH3C6H4NH2 on the bridging carbyne carbon of
cationic bridging carbyne complex 1 or 2 or 3 followed
by deprotonation by the excess amine. Then the cleavage
of the µ-C(1)-Fe(2) bond and the formation of the Fe-
(1)-Ccarbene bond with bridging of a terminal CO ligand
on Fe(1) to the Fe(2) atom could occur to produce
complex 7 or 8 or 9.

940 Organometallics, Vol. 24, No. 5, 2005
Zhang et al.
It is well known that the thermal decomposition of
carbene complexes usually results in dimerization of the
carbene ligand to produce alkene derivatives10 and that
heating a Fischer-type carbene complex with an olefin
generally results in the formation of the double-bond
addition products.11 What happens when the COT-
coordinated diiron Fischer-type carbene complexes are
subjected to thermolysis? To explore the thermolysis
reactivity of the COT-coordinated diiron Fischer-type
carbene complexes, we investigated the thermolysis
reactions of complexes 4-8. A purple-red benzene
solution of compound 4 in a sealed tube was heated with
stirring at 85-90 °C for 72 h. After workup as described
in the Experimental Section, a chelated diiron carbene
complex [Fe2{dC(C6H5)NC6H5}(η2:η3:η2-C8H9)(CO)4] (4a),
a novel C8 ring addition product [Fe2{N(C6H5)dC(C6H5)-
(η1:η3:η2-C8H9)}(CO)5] (10), and a novel C7 contraction
ring product [Fe2{N(C6H5)dC(C6H5)CH(η2:η3-C7H8)-
(CO)4}] (11) were obtained in 22-25%, 47-52%, and
10-11% yields, respectively (eq 3).
for 4-6 produced the analogous chelated diiron carbene
complex [Fe2{dC(C6H5)NC6H4CH3-p}(η2:η3:η2-C8H9)-
(CO)4] (7a), C8 ring addition product [Fe2{N(C6H4CH3-
p)dC(C6H5)(η1:η2:η3-C8H9)}(CO)5] (16), and C7 contrac-
tion ring product [Fe2{N(C6H4CH3-p)dC(C6H5)CH(η2:
η3-C7H8)}(CO)4] (17) (eq 5) in 33, 28, and 10% yields,
respectively. Like complexes 5 and 6, the thermolysis
of 8 under the same conditions yielded the correspond-
ing C8 ring addition product [Fe2{N(C6H4CH3-p)dC(C6H4-
CH3-p)(η1:η2:η3- C8H9)}(CO)5] (18) and C7 contraction
ring product [Fe2{N(C6H4CH3-p)dC(C6H4CH3-p)CH(η2:
η3-C7H8)}(CO)4] (19) (eq 6) in 41 and 8% isolated yields,
respectively.
However, in the analogous thermolysis of complexes
5 and 6, only the corresponding C8 ring addition
products [Fe2{N(C6H5)dC(Ar)(η1:η3:η2-C8H9)}(CO)5] (12,
Ar ) p-CH3C6H4; 14, Ar ) p-CF3C6H4) and C7 contrac-
tion ring products [Fe2{N(C6H5)dC(Ar)CH(η2:η3-C7H8)-
(CO)4}] (13, Ar ) p-CH3C6H4; 15, Ar ) p-CF3C6H4) (eq
4) were isolated in 38-47% and 8-11% yields, respec-
tively.
Products 10-19 are sensitive to air in solution but
relatively stable in the solid state. On the basis of
elemental analyses and spectroscopic evidence, as well
as X-ray crystallography, compounds 10, 12, 14, 16, and
18 are formulated as the eight-membered ring addition
products. In these products, the original carbene ligand
C(Ar)NHAr′ (Ar ) C6H5 or p-CH3C6H4 or p-CF3C6H4;
Similar to the thermolysis of 4, the thermal decom-
position of complex 7 under the same conditions as those

COT-Coordinated Diiron Carbene Complexes
Organometallics, Vol. 24, No. 5, 2005 941
Ar′ ) C6H5 or p-CH3C6H4) is now a C(Ar)NAr′ group
formed by a H transfer from the N atom of the anilino
to the C8 ring, which is bonded to a carbon of the C8
ring though the “carbene” carbon and coordinated to an
Fe atom though the N atom. Products 11, 13, 15, 17,
and 19 are formulated as the seven-membered ring
contraction products, in which the cycloolefin ligand is
now a seven-membered ring carrying a CHC(Ar)N(Ar′)
(Ar ) C6H5 or p-CH3C6H4 or p-CF3C6H4; Ar′ ) C6H5 or
p-CH3C6H4) group with the two carbon atoms bonded
to an Fe atom and the N atom to the two Fe atoms.
The IR and 1H NMR spectra of complexes 10-19 are
fully consistent with their structures shown in eqs 3-6
(Experimetal Section). The structures of products 10,
12, 14, 16, and 18 and products 11, 13, 15, 17, and 19
were further confirmed by X-ray diffraction studies of
complexes 10 and 18 and complexes 11 and 19, respec-
tively. The results of the X-ray diffraction work for
complexes 10, 11, 18, and 19 are summarized in Table
1, and their structures are shown in Figures 2-5,
respectively.
The crystallographic investigation of 10 reveals an
unusual structure (Figure 2). The eight-membered ring
of the COT ligand is retained, but the COT ring has
transformed into a C8H9 ring carrying a C(C6H5)NC6H5
group on C(17) with the coordination of the N atom to
the Fe(2) atom, and the planarity of the COT ring has
been destroyed to become a boat form configuration
caused by the transfer of carbene ligand C(C6H5)-
NHC6H5 from the Fe(2) atom to the C(17) atom of the
C8 ring accompanied by a H transfer from the N atom
to the C(18) of the C8 ring. Atoms C(13), C(4), and C(15)
form an allyl-type unit η3-bonded to Fe(1), while the
C(12) and C(19) atoms are η2-bonded to Fe(2), C(16) is
σ bound to Fe(2), and a CO group generated from the
decomposition of starting 4 or an intermediate is also
bonded to the Fe(1) atom, thereby satisfying the 18-
electron rule for both Fe atoms. The Fe-Fe bond
distance (2.7599(7) Å) is slightly longer than that of 7
(2.7462(5) Å) but is significantly longer than that in 4a
(2.6920(9) Å).5b The average Fe(1)-C bond length of
C(13), C(14), and C(15) is 2.109 Å, and the average Fe-
(2)-C bond length of C(12), C(16), and C(19) is 2.168
Å. The C(1)-N(1) bond length of 1.288(3) Å is somewhat
shorter than that found in 4a (1.296(5) Å)5b and 7
(1.328(3) Å), indicating high double-bond character. The
very interesting structural feature of complex 10 is the
C8H9 ligand. In 10, the eight-membered ring is no longer
planar and the bond distances have changed. In contrast
to the planar eight-membered ring of 7, only C(12),
C(13), C(15), and C(16) are in a plane ((0.0017 Å); the
C(14) atom is out of the C(12)C(13)C(15)C(16) plane by
0.2988 Å, while the C(17) and C(19) atoms are out of
this plane by 1.2912 and 0.8616 Å, respectively. Another
measure of the nonplanarity of the C8H9 eight-mem-
bered ring is the 27.02° dihedral angle between C(13),
C(14), C(15) and C(12), C(13), C(15), C(16) planes and
the 75.62° and 48.66° angles between the C(17), C(18),
C(19) and C(12), C(13), C(15), C(16) planes and the
C(17), C(18), C(19) and C(13), C(14), C(15) planes,
respectively. The nonplanarity of the C8H9 ring in 10
suggests that the π-system is not delocalized in the
complex as it is in 7. Another indication is the change
in bond distances in 10 as compared to 7. In contrast to
the nearly equal bond distances in C(12) to C(19) of the
eight-membered ring in 7, in 10 the C(15)-C(16) (1.478-
(4) Å), C(16)-C(17) (1.527(4) Å), C(17)-C(18) (1.546(4)
Å), and C(18)-C(19) (1.493(5) Å) bonds are considerably
longer than C(12)-C(13) (1.454(5) Å), C(13)-C(14)
(1.408(5) Å), C(14)-C(15) (1.382(5) Å), and C(12)-C(19)
(1.362(5) Å).
The structure of complex 18 shown in Figure 3 is very
similar to that of 10, except that the substituents on
the C(1) and N(1) atoms are the two p-tolyl groups in
18 but the two phenyl groups in 10. Interestingly, there
are two independent molecules in the asymmetric unit
of complex 18. However, its 1H NMR spectrum showed
that the two molecules are separated in solution, giving
a single normal molecule. The two molecules in the unit
cell are the same. Many structural features of 18 are
essentially the same as those in 10: the Fe-Fe distance,
the Fe(1)-C bond lengths of C(13), C(14), and C(15),
the Fe(2)-C distances of C(12), C(16), and C(19), the
bond distance of C(1)-N(1), the dihedral angle between
the C(13)C(14)C(15) and the C(12)C(13)C(15)C(16) planes.
The crystallographic investigations of complexes 11
and 19 reveal also highly unusual structures. Both
complexes are of the seven-membered ring η5-coordi-
nated diiron alkyl complexes, in which the C(12), C(17),
and C(18) atoms form an allyl-type unit η3-bonded to
Fe(2), and the C(13) and C(14) atoms are η2-bonded to
Fe(1). The C7H8 ring carries a CHC(Ar)N(Ar) (Ar ) C6H5
or p-CH3C6H4) group on C(16) with the C(1) and C(19)
atoms bonded to Fe(1) in σ bond and the N(1) atom to
Fe(1) and Fe(2), giving each Fe atom the 18-electron
configuration. It is likely interesting that there are two
independent enantiomorph molecules in the asymmetric
unit of complex 11 and the two molecules in the unit
cell are the same, similar to that of 18. The molecular
structures of complexes 11 and 19 shown in Figures 4
and 5, respectively, have many common features. The
Fe-Fe bond distances in 11 and 19 are 2.671(4) and
2.6912(14) Å, respectively, which are somewhat shorter
than that found in complex 7 and complexes 10 and 18.
The Fe(2)-C bond lengths of C(12), C(17), and C(18)
are respectively 2.034(15), 2.089(16), and 2.030(17) Å
in 11 and 2.062(7), 2.088(7), and 2.047(7) Å in 19, while
the Fe(1)-C bond lengths of C(13) and C(14) are
respectively 2.378(13) and 2.098(16) Å in 11 and 2.400-
(8) and 2.115(8) Å in 19. The C(1)-N(1) bond length of
1.390(15) Å for 11 and of 1.387(8) Å for 19 are C-N
single bonds, which are somewhat longer than that in
4a (1.296(5) Å)5b by ca. 0.10 Å. The Fe(1)-N and Fe-
(2)-N distances are respectively 1.983(12) and 1.999-
(11) Å in 11 and 1.994(5) and 1.971(5) Å in 19, which
are slightly longer than that in 4a (Fe(2)-N ) 1.957(3)
Å).5b The C7H8 ring in 11 and 19 has a boat form
configuration. The dihedral angles between the C(13),
C(14), C(16), C(17) and C(14), C(15), C(16) planes and
the C(13), C(14), C(16), C(17) and C(12), C(13), C(17),
C(18) planes are respectively 60.95° and 29.71° in 11
and 55.35° and 34.67° in 19. The benzene ring C(2)C-
(3)C(4)C(5)C(6)C(7) plane is oriented at an angle of
60.22° for 11 and of 55.25° for 19 with respect to the
benzene ring C(20) through C(25) plane. An apparent
(10) Doetz, K. H. Angew. Chem., Int. Ed. Engl. 1984, 23, 587.
(11) Schubert, U. Advances in Metal Carbene Chemistry; Kluwer
Academic Publishers: Norwell, 1988.

942 Organometallics, Vol. 24, No. 5, 2005
Zhang et al.
Scheme 1. Possible Mechanism for the Thermolysis of COT-Coordinated Diiron Carbene Complexes
difference in the structures of 11 and 19 is the longer
C(1)-C(19) (1.423(9) Å), C(14)-C(15) (1.536(11) Å), and
C(16)-C(19) (1.536(10) Å) bonds and larger N(1)-C(1)-
C(2) angle (124.0(6)°) in 19, as compared with 11 (C(1)-
C(19) ) 1.395(19) Å, C(14)-C(15) ) 1.47(2) Å, C(16)-
C(19) ) 1.496(10) Å, N(1)-C(1)-C(2) ) 120.8(11)°).
Interestingly, the chelated carbene complexes 4a and
7a were transformed into the eight-membered ring
addition products 10 and 16 and seven-membered ring
products 11 and 17, respectively, under the same condi-
tions as those of complexes 4-8. Heating the solution of
compounds 4a and 7a in benzene in a sealed tube at 90
°C for 72 h as described in the Experimental Section
gave the C8 ring addition products 10 and 16 in 52 and
43% yields and the C7 contraction ring products 11 and
17 in 10 and 9% yields, respectively (eq 7).
heated to 100-105 °C for 72 h. After workup as
described in the Experimental Section, the C7 contrac-
tion ring products 11, 17, and 19 (eq 8) were obtained
in 11, 9, and 10% yields, respectively.
Although a mechanism for the formation of the
products 10, 12, 14, 16, and 18 and products 11, 13,
15, 17, and 19 has not yet been fully established, it
seems possible via a metalcyclobutane intermediate (a)
or a chelated carbene intermediate (b) (Scheme 1). The
former was formed by a [2 + 2] cycloaddition, similar
to that of the ring-opened polyene complexes [MFe-
{C8H7(OC2H5)Ar}(CO)6] (M ) Mn, Re).12,13 For such an
intermediate (a), a H shift from the N atom of the
anilino to the C-1 position of the COT ring accompanied
by the dissociation of the Fe-C(9) bond to form the Cd
N double bond and subsequent abstraction of one CO
Surprisingly, the eight-membered ring compounds 10,
16, and 18 can also be partially transformed into the
C7 contraction ring products 11, 17, and 19, respectively,
by further thermolysis at relatively high thermolysis
temperature (100-105 °C). A benzene solution of com-
pounds 10, 16, and 18 respectively in a sealed tube was
(12) Wang, B.-H.; Li, R.-H.; Sun, J.; Chen, J.-B. J. Chem. Soc., Chem.
Commun. 1998, 631.
(13) Xiao, N.; Zhang S.; Qiu, Z.-L.; Li, R.-H.; Wang, B.-H.; Xu, Q.;
Sun, J.; Chen, J.-B. Organometallics 2002, 21, 3709.

COT-Coordinated Diiron Carbene Complexes
Organometallics, Vol. 24, No. 5, 2005 943
molecule generated from the decomposition of the start-
ing compound or an intermediate could occur to produce
the C8 ring addition product 10 (or 12, 14, 16, and 18).
Of particular interest is the formation of the seven-
membered ring compounds 11, 13, 15, 17, and 19, which
could be via an intermediate (b), namely a chelated
diiron carbene complex. Actually, the easy transforma-
tion of the diiron carbene complexes into the more stable
chelated carbene complexes has been previously con-
firmed by their solution 1H NMR spectra and the
isolation of the chelated carbene complexes from the
CH2Cl2 solution.5b,c
Strong evidence for the formation of intermediates (b)
is that we have isolated the chelated diiron carbene
complexes 4a (eq 3) and 7a (eq 5) from the thermolysis
of complexes 4 and 7, respectively. Under heating
condition, the Fe atom (Fe(1)) in intermediates (b) could
bond to the N atom, forming an Fe-N single bond, and
the C(6), C(7), and C(8) atoms of the C8 ring formed a
three-membered ring to yield an intermediate (c), in
which the C(7) and C(8) atoms each have one π electron.
The new C(7)-C(9) bond could form by coupling of the
two π electrons to give another intermediates (d). The
latter then converted into the C7 contraction ring
product 11 (or 13, 15, 17, and 19) upon homolysis of
the C(6)-C(7) bond. The reaction pathway to the C8 ring
addition product 10 (or 12, 14, 16, and 18) could also
proceed via the intermediates (b) by abstracting one
molecule of CO generated from the decomposition of the
starting compound or an intermediate (Scheme 1). This
has been confirmed by the experimental fact that when
the benzene solution of 4a or 7a in a sealed tube was
heated at 90 °C for 72 h, the C8 ring addition product
10 or 16, as main product, was obtained (eq 7), while
the formation pathway from the C8 ring addition
products to the C7 contraction ring products could
proceed via the intermediates (c) and (d) by losing a CO
ligand from the C8 ring compounds at higher thermoly-
sis temperature (100-105 °C), in which the cleavage of
the C-C bond and formation of the C7 ring are con-
cerned, as shown in Scheme 1.
For the formation of the all thermolysis products, the
transfer of one hydride to the COT ring would be the
first step. Therefore, to confirm the hydride transfer and
its source, the deuterated diiron carbene complex [Fe2-
{dC(C6H5)NDC6D5}(µ-CO)(CO)3(η8-C8H8)] (4-d6) was
prepared from deuterated aniline (C6D5ND2) and 1 and
used for the thermolysis instead of 4. Interestingly, the
thermolysis of 4-d6 afforded the deuterated chelated
carbene complex 4a-d6, deuterated C8 ring addition
product 10-d6, and deuterated C7 contraction ring
product 11-d6 with about 80% deuterium incorporation
(eq 9). Their 1H NMR spectra clearly showed the
positions of those deuteriums in 4a-d6, 10-d6, and 11-
d6. (Compounds 4a-d6, 10-d6, and 11-d6 each showed
eight sets of signals for the C8 or C7 ring ligand and a
much weaker signal assigned to an added H on the C-1
position of the C8 or C7 ring at δ 2.76 (m, 0.2H), 2.13
(dd, 0.2H), and 1.86 (m, 0.2H), respectively, which are
derived from a little N-undeuterated impurity of [Fe2-
{dC(C6H5)NHC6D5}(µ-CO)(CO)3(η8-C8H8)] in starting
4-d6 (Experimental Section).) This indicates that the
added H atoms at the C-1 position of the C8 and C7 rings
in 4a, 10, and 11 are from the H at N atom of the anilino
group of 4. Further experimental evidence for the
hydride transfer from the anilino to the COT ring is as
follows: An acetone-d6 solution of 4-d6, whose 1H NMR
spectrum had been measured which showed a single-
line signal for the COT ring at 4.39 ppm, was kept at
room temperature for 20-30 min. During this time the
1
solution turned from deep red to red, and its H NMR
spectrum now showed eight sets of proton signals for
the C8 ring and a very weak signal at δ 2.76 (m, 0.2H),
arising from the N-undeuterated impurity in 4-d6. This
clearly indicates that the hydride (D) transfer from the
N atom of the deuterated anilino to the COT ring
occurred to form the deuterated chelated carbene com-
plex 4a-d6.
To undoubtedly establish the source of an added H
atom on the C-1 position of the C8 and C7 rings, the
thermolysis of 4 in benzene-d6 (C6D6) or in benzene
containing deuterium oxide (D2O) was carried out under
the same conditions as those in benzene (eq 3), which
afforded products 4a, 10, and 11, the same products as
those for the thermolysis of 4 in benzene, indicating that
no deuterium (D) transfer from the solvent C6D6 or D2O
to the COT ring occurred. This excluded the possibility
of the hydrogen being abstracted from benzene or water,
which is a trace contaminant in solvent benzene or from
glassware, and further demonstrated that the only
origin of the added H atoms on the C-1 position of the
C8 and C7 rings is the hydride at the N atom of the
anilino in the starting compounds.
It is noteworthy that the yields of the C7 ring products
are relatively low (8-11%) in almost all the thermolysis
reactions (eqs 3-8). Raising the thermolysis tempera-
ture or prolonging the heating time does not increase
the yields of the C7 contraction ring products but leads
to the decomposition of the starting compounds and
increases the unidentified decomposition products. This
might be explained by the fact that the CO atmosphere
generated by decomposition of the starting compounds

944 Organometallics, Vol. 24, No. 5, 2005
Zhang et al.
or an intermediate formed in the sealed tube favors the
formation and existence of the C8 ring addition products.
In summary, we have found remarkable thermolysis
reactions of the COT-coordinated diiron Fischer-type
carbene complexes, and a series of novel C8 ring addition
products and C7 contraction ring products were ob-
tained. A preliminary mechanistic study of these ther-
molysis reactions is also performed.
of the Chinese Academy of Sciences, and the JSPS of
Japan for financial support of this research.
Supporting Information Available: Tables of positional
parameters and Biso/Beq, H atom coordinates, anisotropic
displacement parameters, complete bond lengths and angles,
and least-squares planes for 7, 10, 11, 18, and 19. This
material is available free of charge via the Internet at
http://pubs.acs.org.
Acknowledgment. We thank the National Natural
Science Foundation of China, the Science Foundation
OM040101W