β-Cyclomanganated 1,5-diphenylpenta-1,4-dien-3-ones and their reactions with alkynes: Routes to η5-pyranyl- And η5-oxocycloheptadienyl-Mn(CO)3 complexes

Article abstract of DOI:10.1016/S0022-328X(01)01062-2

1,5-Diphenylpenta-1,4-dien-3-ones (4) are cyclometalated with benzylpentacarbonylmanganese to form [[1-phenyl-2-((E)-3-phenylprop-2-en-1-oyl-κO)]ethenyl-κC ¹]tetracarbonylmanganese derivatives (5). Coupling of 5 with alkynes in some cases gives [4-phenyl-2-(2-phenylethenyl)pyranyl-η⁵]tricarbonylmanganese complexes (6) analogous to those previously reported for β-manganated chalcones, but in other cases an alternative cyclisation pathway subsequent to insertion of alkyne into the C-Mn bond leads to [6-oxo-4,7-diphenylcyclohepta-1,4-dienyl-1,2,3,4,5-η]tricarbonylmanganese complexes (7). The X-ray crystal structure determination is reported for one such compound, [6-oxo-2,4,7-triphenylcyclohepta-1,4-dienyl-1,2,3,4,5-η]tricarbonylmanganese (7a), derived from 1,5-diphenylpenta-1,4-dien-3-one and phenylacetylene. The 7-phenyl group is found to occupy the endo position, and a mechanism involving Mn-mediated aryl migration is suggested to explain this stereochemistry. The reaction of 7a with ammonium cerium(IV) nitrate gives a low yield of 2-nitro-3,5,7-triphenylcyclohepta-2,4,6-trien-1-one (9), whose structure was established by X-ray crystal structure analysis. The pyranyl complexes (6) provide the corresponding pyrylium triiodide salts (8) when demetalated with iodine.

Full text of DOI:10.1016/S0022-328X(01)01062-2

Journal of Organometallic Chemistry 633 (2001) 162–172
www.elsevier.com/locate/jorganchem
b-Cyclomanganated 1,5-diphenylpenta-1,4-dien-3-ones and their
reactions with alkynes: routes to h5-pyranylꢀ and
h5-oxocycloheptadienylꢀMn(CO)3 complexes
Warren Tully, Lyndsay Main *, Brian K. Nicholson
Chemistry Department, Uni6ersity of Waikato, Pri6ate Bag 3105, Hamilton, New Zealand
Received 11 May 2001; accepted 30 May 2001
Abstract
1,5-Diphenylpenta-1,4-dien-3-ones (4) are cyclometalated with benzylpentacarbonylmanganese to form [[1-phenyl-2-((E)-3-
phenylprop-2-en-1-oyl-kO)]ethenyl-kC1]tetracarbonylmanganese derivatives (5). Coupling of 5 with alkynes in some cases gives
[4-phenyl-2-(2-phenylethenyl)pyranyl-h5]tricarbonylmanganese complexes (6) analogous to those previously reported for b-man-
ganated chalcones, but in other cases an alternative cyclisation pathway subsequent to insertion of alkyne into the CꢀMn bond
leads to [6-oxo-4,7-diphenylcyclohepta-1,4-dienyl-1,2,3,4,5-h]tricarbonylmanganese complexes (7). The X-ray crystal structure
determination is reported for one such compound, [6-oxo-2,4,7-triphenylcyclohepta-1,4-dienyl-1,2,3,4,5-h]tricarbonylmanganese
(7a), derived from 1,5-diphenylpenta-1,4-dien-3-one and phenylacetylene. The 7-phenyl group is found to occupy the endo
position, and a mechanism involving Mn-mediated aryl migration is suggested to explain this stereochemistry. The reaction of 7a
with ammonium cerium(IV) nitrate gives a low yield of 2-nitro-3,5,7-triphenylcyclohepta-2,4,6-trien-1-one (9), whose structure was
established by X-ray crystal structure analysis. The pyranyl complexes (6) provide the corresponding pyrylium triiodide salts (8)
when demetalated with iodine. © 2001 Elsevier Science B.V. All rights reserved.
Keywords: Manganese; Alkyne; Cyclometallation; Metallacycle; Crystal structures; Pyrylium salts
1. Introduction
We now report on b-manganation of 1,5-diphenyl-
penta-1,4-dien-3-ones (4a–d; Scheme 2) and on prelimi-
nary studies of alkyne-coupling reactions of the
b-manganation products (5). Of interest from a syn-
thetic perspective was whether alkyne insertion into the
CꢀMn bond might result in subsequent alternative cy-
clisation pathways when the donor function
(ArCHꢁCHꢀCꢁO) is potentially reactive at four unsatu-
rated centres rather than the two in the donor group
(ArCꢁO) of b-manganated chalcones.
We have reported the formation of derivatives of
[[1-phenyl-2-phenylcarbonyl-kO]ethenyl-kC1]tetracar-
bonylmanganese (1) in the reaction of chalcones [(E)-
1,3-diarylprop-2-en-1-ones] with benzylpentacarbonyl-
manganese [1a]. These b-cyclomanganated enones are
alkenyl analogues of orthomanganated acetophenones,
and like the latter [2] they undergo synthetically valu-
able reactions with alkenes [1a] and alkynes [1b], some
of which involve cyclisation incorporating the unsatu-
rated donor carbonyl function into a new ring. With
alkynes, the donor carbonyl group is incorporated to
form [h5-pyranyl]Mn(CO)3 complexes (2; Scheme 1),
which on treatment with iodine in carbon tetrachloride,
provide pyrylium triiodide salts (3) [1b].
* Corresponding author. Tel.: +64-7-8384385; fax: +64-7-
8384219.
E-mail address: l.main@waikato.ac.nz (L. Main).
Scheme 1. Syntheses from cyclomanganated chalcones and alkynes.
0022-328X/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(01)01062-2

W. Tully et al. / Journal of Organometallic Chemistry 633 (2001) 162–172
163
the recrystallised product was the pure (E,E)-isomer in
all cases. Elemental analyses on the manganated prod-
ucts (see Section 2.3) provided confirmation of identity.
(E,E)-1,5-Diphenylpenta-1,4-dien-3-one (4a): m.p.
1
107 °C (lit. [4b] 112 °C). H-NMR: l=7.75 (d, 2H,
J=16.0 Hz, H1), 7.61 (m, 4H, H2%, 6%), 7.42 (m, 6H,
H3%, 5%, H4%), 7.09 (d, 2H, J=16.0 Hz, H2). 13C-NMR:
l=189.0 (s, C3), 143.4 (d, C1), 134.9 (s, C1%), 130.6 (d,
C4%), 129.0 (d, C3%, 5%), 128.5 (d, C2%, 6%), 125.5 (d, C2).
(E,E) - 1,5 - Di - (2 - trifluoromethylphenyl)penta - 1,4-
1
dien-3-one (4b): m.p. 131 °C. H-NMR: l=8.09 (dq,
2H, J=15.8, 1.7 Hz, H1), 7.79 (d, 2H, J=7.7 Hz,
H6%), 7.73 (d, 2H, J=7.7 Hz, H3%), 7.61 (t, 2H, J=7.7
Hz, H4%), 7.51 (t, 2H, J=7.7 Hz, H5%), 7.01 (d, 2H,
J=15.8 Hz, H2). 13C-NMR: l=188.3 (s, C3), 139.3
(d, C1), 133.7 (s, C1%), 132.2 (d, C4%), 129.9 (d, C5%),
128.9 (d, C2), 128.0 (d, C6%), 126.3 (d, J=5.3 Hz, C3%).
(E,E)-1,5-Di-(4-bromophenyl)penta-1,4-dien-3-one
Scheme 2. Cyclomanganation of 1,5-diarylpenta-1,4-dien-3-ones.
2. Experimental
2.1. General
1
(4c): m.p. 211 °C. H-NMR: l=7.66 (d, 2H, J=15.9
Benzylpentacarbonylmanganese was prepared by the
standard literature method [3]. Petroleum spirit (b.p.
60–80 °C) was redistilled and CCl4 was of analytical
grade. Other commercial reagents were used without
purification. Cyclomanganation reactions and coupling
reactions with alkynes were conducted under nitrogen,
but subsequent workup was without any precautions to
exclude air. There were no special precautions for the
reactions with iodine or ammonium cerium(IV) nitrate.
Preparative scale layer chromatography (referred to as
PLC in the text) was performed on Merck Kieselgel 60
silica gel, and alumina (Brockmann activity II) was
used for column chromatography. The composition of
mixed solvents is expressed on a volume/volume basis.
NMR spectra were recorded on a Bruker AC300
instrument using CDCl3 as solvent except for pyrylium
triiodide salts for which (CD3)2CO or (CD3)2SO was
used. Infrared spectra (in CH2Cl2 unless specified) were
obtained on a Digilab FTS-45 FTIR instrument and
FAB mass spectra on a VG ZAB 2HF instrument using
a 2-nitrophenol matrix. UV spectra were recorded on a
Uvikon 860 spectrophotometer.
Hz, H1), 7.55 (d, 4H, J=8.5 Hz, H3%, 5%), 7.46 (d, 4H,
J=8.5 Hz, H2%, 6%), 7.03 (d, 2H, J=15.9 Hz, H2).13C-
NMR: l=188.4 (s, C3), 142.2 (d, C1), 133.7 (s, C1%),
132.3 (d, C3%, 5%), 129.8 (d, C2%, 6%), 125.8 (d, C2), 124.9
(s, C4%).
(E,E)-1,5-Di-(4-chlorophenyl)penta-1,4-dien-3-one
1
(4d): m.p. 186 °C. H-NMR: l=7.67 (d, 2H, J=15.9
Hz, H1), 7.53 (d, 4H, J=8.5 Hz, H3%, 5%), 7.38 (d, 4H,
J=8.5 Hz, H2%, 6%), 7.02 (d, 2H, J=15.9 Hz, H2).
13C-NMR: l=188.3 (s, C3), 142.1 (d, C1), 136.5 (s,
C4%), 133.3 (s, C1%), 129.6 (d, C2%, 6%), 129.3 (d, C3%, 5%),
125.8 (d, C2).
2.3. Standard procedure for the preparation of
cyclomanganated (E,E)-1,5-diarylpenta-1,4-dien-3-ones
A solution of the diarylpenta-1,4-dien-3-one (4; 1
mmol) and PhCH2Mn(CO)5 (1.1 mmol) in petroleum
spirit (20 ml) under nitrogen was heated under reflux.
Upon completion of the reaction, as monitored by IR
spectroscopy (ca. 3–4 h), the solvent was removed
under vacuum. Dichloromethane (10 ml) and deacti-
vated neutral alumina (4 g, activity II) were added to
the residue. The mixture was stirred while the CH2Cl2
was removed under vacuum. The alumina with product
adsorbed was transferred onto the top of a column
(2×12 cm) of neutral alumina (activity II). Elution
with CH2Cl2–petroleum spirit (1:8) followed by solvent
evaporation gave the product as a red oil which was
crystallised from petroleum spirit. Yields given are for
the chromatographically pure products prior to crys-
tallisation, which, with the small quantities involved,
resulted in significant losses.
2.2. Standard procedure for the preparation of
(E,E)-1,5-diarylpenta-1,4-dien-3-ones [4a]
Ethanol (10 ml) and a solution of NaOH (2 g) in
water (15 ml) were mixed in a flask immersed in
crushed ice. A solution in Me2CO (ca. 0.5 ml; 8 mmol)
of the appropriate benzaldehyde (ca. 16 mmol) was
added dropwise while stirring and maintaining the tem-
perature at about 25 °C. After a further hour, the
precipitate was collected and washed with water until
the washings were neutral to litmus. The crude product
was dried under vacuum and then recrystallised from
EtOAc in 50–80% yield. NMR spectra indicated that
[[1-Phenyl-2-((E)-3-phenylprop-2-en-1-oyl-kO)]-
ethenyl-kC1]tetracarbonylmanganese (5a): 81%; crys-
tallised as small dark red crystals: m.p. 116 °C. Anal.

164
W. Tully et al. / Journal of Organometallic Chemistry 633 (2001) 162–172
2.4. Coupling reactions with alkynes
Found: C, 62.95; H, 2.98. Calc. for C21H13O5Mn: C,
63.02; H, 3.27%. IR (cm−1): w(CO) 2082 (m), 1997 (vs,
1
This section is divided according to starting b-man-
ganated compound in order to highlight product varia-
tions. In general, reactions were stopped once the
manganese reactant had been consumed, as indicated
by IR monitoring, but in some cases reactions were
continued overnight (see individual cases for details).
br), 1942 (s). H-NMR: l=7.72 (d, 1H, J=16.1 Hz,
H5), 7.59 (m, 2H, H2¦, 6¦), 7.45 (m, 8H, H2%, 6%, H3%, 5%,
H4%, H3¦, 5¦, H4¦), 7.33 (s, 1H, H2), 6.99 (d, 1H,
J=16.1 Hz, H4). 13C-NMR: l=251.2 (s, C1), 219.5 (s,
CO), 214.1 (s, CO), 210.4 (s, CO), 203.9 (s, C3), 150.2
(s, C1%), 145.4 (d, C5), 134.6 (s, C1¦), 133.9 (d, C2),
131.1 (d, C4¦), 129.1 (d, C3¦, 5¦), 128.7 (d, C4%), 128.6
(d, C2¦, 6¦), 128.4 (d, C3%, 5%), 125.3 (d, C2%, 6%), 123.6
(d, C4).
2.4.1. Reactions of [[1-phenyl-2-(3-phenylpropenoyl-
sO]ethenyl-sC1]tetracarbonylmanganese (5a)
[1-(2-Trifluoromethylphenyl)-2-((E)-3-(2-trifluoro-
methylphenyl)prop-2-en-1-oyl-kO)]ethenyl-kC1]tetra-
carbonylmanganese (5b): 85%; crystallised as small
crimson crystals: m.p. 94 °C. Anal. Found: C, 51.81;
H, 1.88. Calc. for C23H11F6O5Mn: C, 51.51; H, 2.07%.
IR (cm−1): w(CO) 2088 (m), 1996 (vs, br), 1951 (s).
1H-NMR: l=8.05 (dq, 1H, J=16.0, 1.7 Hz, H5), 7.77
(m, 3H, H3%, H3¦, H6¦), 7.60 (m, 2H, H5%, H4¦), 7.52 (t,
1H, J=7.6 Hz, H5¦), 7.35 (m, 3H, H2, H4%, H6%), 6.93
(d, 1H, J=16.0 Hz, H4). 13C-NMR: l=251.0 (s, C1),
219.0 (s, CO), 213.2 (s, CO), 204.2 (s, C3), 150.5 (s,
C1%), 141.0 (d, C5), 135.4 (d, C2), 133.2 (s, C1¦), 132.3
(d, C4¦), 131.4 (d, C5%), 130.4 (d, C5¦), 127.8 (d, C6¦),
127.3 (d, C4), 126.4 (d, C3%, C3¦), 126.3 (d, C4%), 125.1
(d, C6%).
2.4.1.1. Coupling of 5a with trimethylsilylacetylene:
preparation
of
[4-phenyl-2-(2-phenylethenyl)-6-tri-
methylsilylpyranyl-p5]tricarbonylmanganese (6a). [[1-
Phenyl-2-((E)-3-phenylprop-2-en-1-oyl-kO)]ethenyl-
kC1]tetracarbonylmanganese (5a) (0.37 g, 0.92 mmol)
and trimethylsilylacetylene (0.25 ml, 1.77 mmol) were
dissolved in nitrogen-flushed CCl4 and refluxed under
nitrogen. When IR monitoring indicated that all 5a had
reacted (4 h), CCl4 was removed under vacuum. To the
residual oil, CH2Cl2 (10 ml) and deactivated neutral
alumina (4 g) were added. The mixture was rotated
(rotary evaporator) while the solvent was removed un-
der vacuum. The alumina with product absorbed was
then transferred to the top of a column (2×12 cm) of
alumina. Elution with CH2Cl2–hexane gave [4-phenyl-
2-(2-phenylethenyl)-6-trimethylsilylpyranyl-h5]tricar-
bonylmanganese (6a) as a red oil (0.34 g, 79%) which
was crystallised from petroleum spirit as small black
crystals: m.p. 121 °C. Anal. Found: C, 63.77; H, 4.76.
Calc. for C25H23O4SiMn: C, 63.82; H, 4.93%. IR
[1-(4-Bromophenyl)-2-((E)-3-(4-bromophenyl)prop-
2 - en - 1 - oyl -kO)]ethenyl - kC1]tetracarbonylmanganese
(5c): 87%; crystallised as small cherry-red crystals: m.p.
109 °C. Anal. Found: C, 45.47; H, 1.67. Calc. for
C21H11Br2O5Mn: C, 45.20; H, 1.99%. IR (cm−1): w(CO)
1
(cm−1): w(CO) 2008 (vs), 1942 (s), 1930 (s). H-NMR:
1
2083 (m), 1998 (vs, br), 1944 (s). H-NMR: l=7.62 (d,
l=7.84 (d, 2H, J=7.1 Hz, H2¦, 6¦), 7.47 (m, 8H, H3¦,
5¦, H4¦, H2§, 6§, H3§, 5§, H4§), 6.88 (d, 1H, J=15.6
Hz, H2%), 6.14 (d, 1H, J=15.6 Hz, H1%), 5.21 (s, 1H,
H5), 4.75 (s, 1H, H3), 0.32 (s, 9H, SiMe3). 13C-NMR:
l=136.9 (s, C1¦ or C1§), 136.1 (s, C1¦ or C1§), 130.7
(d, C2%), 129.2 (d, C3¦, 5¦), 128.8 (d, C3§, 5§), 128.5 (d,
C4¦ or C4§), 128.4 (d, C4¦ or C4§), 127.0 (d, C2§, 6§),
126.4 (d, C2¦, 6¦), 123.1 (d, C1%), 104.4 (s, C2), 99.3 (s,
C4), 91.0 (d, C5), 88.0 (s, C6), 82.0 (d, C3), −2.1 (q,
SiMe3).
1H, J=16.1 Hz, H5), 7.57 (d, 2H, J=8.5 Hz, H3%, 5%),
7.56 (d, 2H, J=8.5 Hz, H3¦, 5¦), 7.44 (d, 2H, J=8.5
Hz, H2¦, 6¦), 7.31 (d, 2H, J=8.5 Hz, H2%, 6%), 7.27 (s,
1H, H2), 6.97 (d, 1H, J=16.1 Hz, H4). 13C-NMR:
l=250.2 (s, C1), 219.4 (s, CO), 213.8 (s, CO), 210.0 (s,
CO), 203.5 (s, C3), 148.2 (s, C1%), 144.1 (d, C5), 134.2
(d, C2), 133.4 (s, C1¦), 132.5 (d, C3¦, 5¦), 131.6 (d, C3%,
5%), 129.9 (d, C2¦, 6¦), 126.8 (d, C2%, 6%), 125.6 (s, C4¦),
123.8 (d, C4), 122.9 (s, C4%).
[1-(4-Chlorophenyl)-2-((E)-3-(4-chlorophenyl)prop-
2 - en - 1 - oyl -kO)]ethenyl - kC1]tetracarbonylmanganese
(5d): 75%; crystallised as bright cherry-red crystals: m.p.
119 °C. Anal. Found: C, 54.01; H, 2.10. Calc. for
C21H11Cl2O5Mn: C, 53.76; H, 2.36%. IR (cm−1): w(CO)
2.4.1.2. Coupling of 5a with phenylacetylene: preparation
of [6-oxo-2,4,7-triphenylcyclohepta-1,4-dienyl-1,2,3,4,5-
p]tricarbonylmanganese (7a). [[1-Phenyl-2-((E)-3-phenyl-
prop-2-en-1-oyl-kO)]ethenyl-kC1]tetracarbonylmanga-
nese) (5a; 0.118 g, 0.29 mmol) and phenylacetylene (0.1
ml, 0.91 mmol) were refluxed overnight in nitrogen-sat-
urated CCl4 (20 ml). The solvent was removed under
vacuum. PLC of the residual oil (Et2O–petroleum spirit
(1:3)) gave one major band. Removal of the band and
extraction with CH2Cl2 followed by solvent removal
under vacuum gave [6-oxo-2,4,7-triphenylcyclohepta-
1,4-dienyl-1,2,3,4,5-h]tricarbonylmanganese (7a; 0.092
1
2083 (m), 2000 (vs, br), 1944 (s). H-NMR: l=7.65 (d,
1H, J=16.1 Hz, H5), 7.52 (d, 2H, J=8.5 Hz, H2¦, 6¦),
7.40 (m, 6H, H2%, 6%, H3%, 5%, H3¦, 5¦), 7.28 (s, 1H, H2),
6.95 (d, 1H, J=16.1 Hz, H4). 13C-NMR: l=250.1 (s,
C1), 219.4 (s, CO), 210.0 (s, CO), 203.5 (s, C3), 148.5 (s,
C1%), 144.0 (d, C5), 137.2 (s, C4¦), 134.6 (s, C4%), 134.2
(d, C2), 133.0 (s, C1¦), 129.7 (d, C3¦, 5¦), 129.5 (d, C3%,
5%), 128.6 (d, C2¦, 6¦), 126.6 (d, C2%, 6%), 123.8 (d, C4).

W. Tully et al. / Journal of Organometallic Chemistry 633 (2001) 162–172
165
kC1]tetracarbonylmanganese (5b) (0.30 g, 0.56 mmol)
and phenylacetylene (0.14 ml, 1.27 mmol) were refluxed
for 4 h in nitrogen-saturated CCl4. Analogous workup
to that for 6a gave [6-phenyl-4-(2-trifluoromethyl-
phenyl)-2-(2-(2-trifluoromethylphenyl))ethenylpyranyl-
h5]tricarbonylmanganese (6c) as a red oil (0.24 g, 70%)
which was crystallised from petroleum spirit as small
red crystals: m.p. 142 °C. Anal. Found: C, 59.38; H,
2.75. Calc. for C30H17O4F6Mn: C, 59.03; H, 2.81%. IR
g, 66%) as a yellow oil which was crystallised by solvent
diffusion (EtOAc–petroleum spirit) as bright yellow
crystals, m.p. 190 °C. Anal. Found: C, 70.95; H, 3.95.
Calc. for C28H19O4Mn: C, 70.89; H, 4.04%. IR (cm−1):
w(CO) 2030 (vs), 1967 (s), 1956 (s). 1H-NMR: l=7.72–
7.20 (m, ArꢀH), 6.64 (1H, dd, J=2.2, 1.1 Hz, H3), 4.79
(1H, d, J=1.1 Hz, H5), 3.97 (1H, dd, J=3.5, 2.2 Hz,
H1), 2.62 (1H, d, J=3.5 Hz, H7). 13C-NMR: l=191.0
(s, CO), 140.6 (s), 138.0 (s), 137.9 (s), 130.6 (d), 130.4
(d), 129.6 (d), 129.1 (d), 129.0 (d), 128.9 (d), 128.5 (d),
127.5 (d), 127.1 (d), 119.2 (s, C2 or C4), 113.5 (s, C2 or
C4), 95.2 (d, C3), 76.0 (d, C5), 58.9 (d, C1), 47.2 (d,
C7). This compound was further characterised by a
single crystal X-ray structure determination.
1
(cm−1): w(CO) 2016 (vs), 1955 (s), 1934 (s). H-NMR:
l=7.97 (d, 1H, J=7.5 Hz, H6§), 7.92 (d, 1H, J=7.4
Hz, H3§), 7.60 (m, 12H), 6.22 (d, 1H, J=15.4 Hz,
H1%), 5.38 (s, 1H, H5), 4.88 (s, 1H, H3). 13C-NMR:
l=135.7 (d, C6§), 135.0 (s), 134.9 (s), 132.7 (d), 131.9
(d), 129.2 (d), 129.0 (d), 128.5 (d), 127.8 (d), 127.3 (d),
127.0 (d), 126.2 (d, J=5.7 Hz, C3¦, C3§) 124.6 (d),
123.3 (d, C2¨, 6¨), 100.2 (s, C2), 94.8 (s, C4 or C6),
94.6 (s, C4 or C6), 86.2 (d, C3), 83.3 (d, C5).
2.4.2. Reactions of [1-(2-trifluoromethylphenyl)-
2-((E)-3-(2-trifluoromethylphenyl)prop-2-en-1-
oyl-sO)]ethenyl-sC1]tetracarbonylmanganese (5b)
2.4.2.3. Coupling of 5b with diphenylacetylene: prepara-
tion of [6-oxo-4,7-di-(2-trifluoromethylphenyl)-2,3-
diphenylcyclohepta - 1,4 - dienyl - 1,2,3,4,5 - p]tricarbonyl-
manganese (7b). Reaction of [1-(trifluoromethylphenyl)-
2-((E)-2-(trifluoromethylphenyl)ethenylcarbonyl-kO)]-
ethenyl-kC1]tetracarbonylmanganese (5b; 0.157 g, 0.29
mmol) and diphenylacetylene (0.1 g, 0.56 mmol) fol-
lowed by workup and purification by PLC as described
for 7a gave [6-oxo-4,7-di-(2-trifluoromethylphenyl)-2,3-
diphenylcyclohepta-1,4-dienyl-1,2,3,4,5-h]tricarbonyl-
manganese (7b; 0.07 g, 35%) as a yellow oil which was
crystallised by diffusion (EtOAc–petroleum spirit) as
small yellow crystals, m.p. 130 °C. This compound was
pure by NMR and was identified by spectral compari-
son with 7a. IR (cm−1): w(CO) 2028 (vs), 1967 (s), 1952
2.4.2.1. Coupling of 5b with trimethylsilylacetylene:
preparation of [4-(2-trifluoromethylphenyl)-2-(2-(2-tri-
fluoromethylphenyl)ethenyl)-6-trimethylsilylpyranyl-p5]-
tricarbonylmanganese
phenyl)-2-((E)-3-(2-trifluoromethylphenyl)prop-2-en-1-
oyl-kO)]ethenyl-kC1]tetracarbonylmanganese
(5b)
(6b).
[1-(2-Trifluoromethyl-
(0.172 g, 0.32 mmol) and trimethylsilylacetylene (0.09
ml, 0.64 mmol) were refluxed for 3 h in nitrogen-satu-
rated CCl4. Carbon tetrachloride was removed under
vacuum. PLC (petroleum spirit) of the residual oil gave
one major band at Rf 0.2 which yielded [4-(2-tri-
fluoromethylphenyl) - 2 - (2 - (2 - trifluoromethylphenyl))-
ethenyl - 6 - trimethylsilylpyranyl - h5]tricarbonylmanga-
nese (6b) as a red oil (0.186 g, 96%) which was crys-
tallised from warm petroleum spirit as small black
crystals: m.p. 95 °C. Anal. Found: C, 54.14; H, 3.49.
Calc. for C27H21O4F6SiMn: C, 53.47; H, 3.49%. IR
1
(s). H-NMR: l=7.50 (m, ArꢀH), 4.41 (1H, s, H5),
3.95 (1H, d, J=3.7 Hz, H1), 3.27 (1H, d, J=3.7 Hz,
H7). 13C-NMR: l=188.2 (s, C6), 139.3–125.6 (several
signals: C-2,3,4, other ArꢀC), 76.2 (d, C5), 66.5 (d, C1),
41.6 (d, C7).
1
(cm−1): w(CO) 2013 (vs), 1948 (s), 1930 (s). H-NMR:
l=7.90 (d, 1H, J=7.7 Hz, H6§), 7.89 (d, 1H, J=7.8
Hz, H3§), 7.63 (m, 4H, H3¦, H6¦, H4§, H5§), 7.49 (t,
1H, J=7.7, H4¦), 7.36 (t, 1H, J=7.6 Hz, H5¦), 7.29
(dq, 1H, J=15.4, 2.0 Hz, H2%), 6.03 (d, 1H, J=15.4
Hz, H1%), 4.83 (s, 1H, H5), 4.62 (s, 1H, H3), 0.27 (s, 9H,
SiMe3). 13C-NMR: l=135.4 (s, C6§), 135.0 (s, C1¦,
C1§), 132.7 (d, C6¦ or C4§ or C5§), 131.8 (d, C4¦),
129.0 (d, C6¦ or C4§ or C5§), 127.7 (d, C5¦), 127.1 (d,
C1%), 127.0 (d, C6¦ or C4§ or C5§), 126.2 (d, J=5.0
Hz, C3¦, C3§), 125.5 (d, C2%), 102.4 (s, C2), 97.4 (s,
C4), 94.5 (d, C5), 88.7 (s, C6), 86.6 (d, C3), −2.4 (q,
SiMe3).
2.4.3. Reaction of [1-(4-Chlorophenyl)-2-((E)-3-
(4-chlorophenyl)prop-2-en-1-oyl-sO)]ethenyl-sC1]tetra-
carbonylmanganese (5d)
2.4.3.1. Coupling with phenylacetylene: preparation of
[6-oxo-4,7-di-(4-chlorophenyl)-2-phenylcyclohepta-1,4-
dienyl-1,2,3,4,5-p]tricarbonylmanganese (7c). Reaction
of [1-(4-chlorophenyl)-2-((E)-3-(4-chlorophenyl)prop-2-
en-1-oyl-kO)]ethenyl-kC1]tetracarbonylmanganese (5d;
0.18 g, 0.38 mmol) and phenylacetylene (0.09 ml, 0.82
mmol) and workup and purification by PLC as
described for 7a above gave [6-oxo-4,7-di-(4-
chlorophenyl)-2-phenylcyclohepta-1,4-dienyl-1,2,3,4,5-
h]tricarbonylmanganese (7c; 0.04 g, 20%) as a yellow
oil which was crystallised by solvent diffusion (EtOAc–
petroleum spirit) as large yellow crystals, m.p. 194 °C.
2.4.2.2. Coupling of 5b with phenylacetylene: preparation
of
[2-phenyl-4-(2-trifluoromethylphenyl)-6-(2-(2-tri-
fluoromethylphenyl)ethenyl)pyranyl - p5]tricarbonylman-
ganese (6c). [1-(2-Trifluoromethylphenyl)-2-((E)-3-(2-
trifluoromethylphenyl)prop - 2 - en - 1 - oyl - kO)]ethenyl-

166
W. Tully et al. / Journal of Organometallic Chemistry 633 (2001) 162–172
Anal. Found: C, 62.09; H, 3.11. Calc. for
(1H, d, J=7.6 Hz, H-6§), 8.23 (1H, d, J=8.3 Hz,
H-6¦), 8.16 (1H, d, J=16.2 Hz, H-1%), 8.07 (m, H-3¦-
5¦,H3§-5§), 0.83 (9H, s, Si(CH3)3). 13C-NMR
((CD3)2CO): l=193.3 (s, C-6), 174.7 (s, C-2), 165.2 (s,
C-4), 142.4 (d, C-2%), 134.5 (s, C-1¦), 134.1 (d), 134.0
(d), 133.0 (d), 132.8 (d), 132.0 (d), 130.7 (d, C-5), 130.0
(s, C-1§), 129.6 (d, C-6§), 128.3 (d, J=4.5 Hz, C-3§),
127.6 (d, J=5.2 Hz, C-3¦), 125.0 (d, C-3), 123.2 (d,
C-1%), −2.86 (q, Si(CH3)3).
C28H17Cl2O4Mn: C, 61.90; H, 3.15%. IR (cm−1): w(CO)
1
2032 (vs), 1968 (s), 1957 (s). H-NMR: l=7.66–7.16
(m, ArꢀH), 6.57 (1H, dd, J=2.2, 1.1 Hz, H3), 4.71
(1H, d, J=1.1 Hz, H5), 3.88 (1H, dd, J=3.6, 2.2 Hz,
H1), 2.58 (1H, d, J=3.6 Hz, H7). 13C-NMR: d 219.6
(s, 2×Mn(CO)), 219.4 (s, MnCO), 190.4 (s, CO), 139.0
(s), 137.6 (s), 136.7 (s), 136.3 (s), 133.6 (s), 130.9 (d),
130.8 (d), 130.3 (d), 129.2 (d), 129.1 (d), 129.0 (d), 128.4
(d), 117.8 (s, C2 or 4), 113.6 (s, C2 or 4), 95.0 (d, C3),
75.5 (d, C5), 58.3 (d, C1), 46.5 (d, C7).
2.5.3. [2-Phenyl-4-(2-trifluoromethylphenyl)-
6-(2-(2-trifluoromethylphenyl)ethenyl)pyrylium triiodide
(8c)
2.5. Preparation of pyrylium triiodide salts
[2-Phenyl-4-(2-trifluoromethylphenyl)-6-(2-(2-tri-
fluoromethylphenyl)ethenyl)pyranyl - h5]tricarbonyl-
manganese (6c; 0.107 g, 0.18 mmol) and iodine (0.089 g,
0.70 mmol) were stirred in CCl4 for 1 h. Solvent was
removed under reduced pressure and ether was added
to the residual oil to precipitate solid [2-phenyl-4-(2-
trifluoromethylphenyl)-6-(2-(2-trifluoromethylphenyl)-
ethenyl)pyrylium triiodide (8c) which was collected
(0.123 g, 85%) and crystallised by solvent diffusion
from MeCN–ether as small black crystals, m.p.
164 °C. Anal. Found: C, 38.28; H, 1.78. Calc. for
C27H17F6I3O: C, 38.06; H, 2.01%. umax (nm) (relative
absorbance intensities) in MeCN: 288 (100), 331 (43),
2.5.1. 4-Phenyl-2-(2-phenylethenyl)-6-trimethylsilyl-
pyrylium triiodide (8a)
[4-Phenyl-2-(2-phenylethenyl)-6-trimethylsilylpyranyl-
h5]tricarbonylmanganese (6a; 0.07 g, 0.15 mmol) and
iodine (0.085 g, 0.67 mmol) were stirred in CCl4 for 1 h.
Solvent was removed under reduced pressure and ether
was added to the residual oil to precipitate solid 4-
phenyl-2-(2-phenylethenyl)-6-trimethylsilylpyrylium tri-
iodide (8a) which was collected (0.073 g, 78%) and
crystallised by solvent diffusion from MeCN–ether as
small black crystals, m.p. 165 °C. Anal. Found: C,
37.62; H, 3.08%. Calc. for C22H18SiI3O: C, 37.10; H,
3.26%. umax (nm) (relative absorbance intensities) in
MeCN: 291 (100), 339 (41), 368 (31). 1H-NMR
((CD3)2CO): l=8.98 (1H, d, J=2.0 Hz, H-3), 8.83
(1H, d, J=2.0 Hz, H-5), 8.65 (1H, d, J=16.2 Hz,
H-2%), 8.49 (2H, d, J=7.2 Hz, H-2§,6§), 8.10 (2H, dd,
J=7.8, 1.8 Hz, H-2¦,6¦), 7.94 (4H, m, H-1%,3§,4§,5§),
7.74 (3H, m, H-3¦,4¦,5¦), 0.82 (9H, s, Si(CH3)3). 13C-
NMR ((CD3)2CO): l=190.0 (s, C-6), 175.6 (s, C-2),
162.3 (s, C-4), 148.1 (d, C-2%), 135.7 (d, C-4§), 135.1 (s,
C-1¦), 133.5 (s, C-1§), 133.3 (d, C-4¦), 130.9 (d, C-
3§,5§), 130.3 (d, C-2¦,3¦,5¦,6¦,2§,6§), 126.0 (d, C-5),
119.8 (d, C-3), 119.7 (d, C-1%), −2.61 (q, Si(CH3)3).
1
364 (34). H-NMR ((CD3)2CO): l=9.10 (1H, s, H-5),
8.86 (1H, dq, J=15.8 Hz, H-2%), 8.72 (2H, d, J=7.3
Hz, H-2¨,6¨), 8.71 (1H, s, H-3), 8.47 (1H, d, J=7.7
Hz, H-2§), 8.08 (11H, m, H-1%,2¦-5¦,3§-5§,3¨-5¨). 13C-
NMR ((CD3)2CO): l=172.4 (s, C-6), 170.3 (s, C-2),
168.4 (s, C-4), 142.0 (d, C-2%), 137.0 (d, C-4¨), 134.7 (s,
C-1¦), 134.2 (d), 134.1 (d), 133.1 (s, C1¨), 132.8 (d),
132.0 (d, C1%), 131.1 (d), 129.9 (d, C2¨,C6¨,C2§), 129.4
(s, C-1§), 128.2 (d, J=4.9 Hz, C-3¦ or C-3§), 127.6 (d,
J=5.4 Hz, C-3¦ or C-3§), 126.6 (s, J=34.7 Hz, C-2¦
or C-2§), 123.2 (d, C-3), 122.8 (s, J=28 Hz, C-2¦ or
C-2§), 120.9 (d, C-5).
2.5.2. 4-(2-Trifluorophenyl)-2-(2-(2-trifluoromethyl-
phenyl)ethenyl)-6-trimethylsilylpyrylium triiodide (8b)
[4-(2-Trifluoromethylphenyl)-2-(2-(2-trifluoromethyl-
phenyl)ethenyl)-6-trimethylsilylpyranyl-h5]tricarbonyl-
manganese (6b; 0.08 g, 0.13 mmol) and iodine (0.069 g,
0.54 mmol) were stirred in CCl4 for 1 h. Solvent was
removed under reduced pressure and ether was added
to the residual oil to precipitate solid 4-(2-trifluoro-
phenyl) - 2 - (2 - (2 - trifluorophenylethenyl) - 6 - trimethyl-
silylpyrylium triiodide (8b) which was collected (0.093
g, 69%) and crystallised by solvent diffusion from
MeCN–ether as small black crystals, m.p. 124 °C. This
compound, pure by NMR, was identified by spectral
comparison with 8a and 8c. umax (nm) (relative ab-
sorbance intensities) in MeCN: 290 (100), 333 (43), 361
2.6. Reaction of [6-oxo-2,4,7-triphenylcyclohepta-1,4-
dienyl-1,2,3,4,5-p]tricarbonylmanganese (7a) with
ammonium cerium(IV) nitrate
[6-Oxo-2,4,7-triphenylcyclohepta-1,4-dienyl-1,2,3,4,5-
h]tricarbonylmanganese (7a; 0.10 g, 0.21 mmol) and
ammonium cerium(IV) nitrate (0.32 g, 0.58 mmol) were
stirred in MeCN (20 ml) for 1 h. Acetonitrile was
removed under vacuum. PLC of the residual oil (Et2O–
petroleum spirit (1:1)) gave one major band at Rf 0.7
which yielded a yellow oil (0.06 g). Crystallisation by
the solvent diffusion method (EtOAc–pentane) gave a
very small quantity of yellow crystals of 2-nitro-3,5,7-
triphenylcyclohepta-2,4,6-trien-1-one (9): m.p. 200 °C.
This compound was characterised by a single crystal
X-ray structure determination (see below).
1
(30). H-NMR ((CD3)2CO): l=8.83 (1H, d, J=16.2
Hz, H-2%), 8.76 (1H, s, H-5), 8.72 (1H, s, H-3), 8.44

W. Tully et al. / Journal of Organometallic Chemistry 633 (2001) 162–172
167
A , Dcalc 1.389 g cm−3 for Z=6, F(000) 1464, v(Mo–
Ka) 0.61 mm−1. Yellow hexagonal-block shaped crystal
from EtOAc–pentane, 1.1×1.0×0.7 mm. A total of
2379 data were collected in the range 2B2qB50°, 2025
unique, 1890 with I\2|(I), corrected for absorption
based on „-scans. All non-H atoms were treated an-
isotropically, phenyl-H atoms and H(1) were included
in calculated positions, while H(2), H(4) and H(6) were
located as the three highest peaks in a penultimate
difference map and were refined with a constrained
CꢀH distance and tied Uiso. Refinement converged with
R1 0.0248 (2|-data), R1 0.0270, wR2 0.0609, Goodness-
of-fit F2 0.999 (all data), no final feature \ꢀ0.38ꢀ
3
Table 1
,
,
Selected bond lengths (A) and bond angles (°) for 7a
Bond lengths
Mn(1)ꢀC(2)
Mn(1)ꢀC(4)
Mn(1)ꢀC(6)
Mn(1)ꢀC(9)
C(1)ꢀC(11)
C(1)ꢀC(2)
C(3)ꢀC(4)
C(4)ꢀC(5)
C(5)ꢀC(51)
C(7)ꢀO(7)
2.295(3)
2.183(3)
2.178(3)
1.813(3)
1.515(4)
1.532(4)
1.428(4)
1.422(4)
1.502(4)
1.224(3)
Mn(1)ꢀC(3)
Mn(1)ꢀC(5)
Mn(1)ꢀC(8)
Mn(1)ꢀC(10)
C(1)ꢀC(7)
2.182(3)
2.178(3)
1.815(3)
1.815(3)
1.523(4)
1.408(4)
1.504(4)
1.436(4)
1.474(4)
C(2)ꢀC(3)
C(3)ꢀC(31)
C(5)ꢀC(6)
C(6)ꢀC(7)
Bond angles
C(9)ꢀMn(1)ꢀC(8)
C(8)ꢀMn(1)ꢀC(10)
C(11)ꢀC(1)ꢀC(2)
C(3)ꢀC(2)ꢀC(1)
C(5)ꢀC(4)ꢀC(3)
C(5)ꢀC(6)ꢀC(7)
O(7)ꢀC(7)ꢀC(1)
91.90(13) C(9)ꢀMn(1)ꢀC(10)
95.56(12) C(11)ꢀC(1)ꢀC(7)
113.9(2)
122.1(2)
125.0(2)
129.6(3)
123.6(2)
85.40(13)
112.5(2)
105.6(2)
120.0(2)
126.4(2)
122.2(3)
114.1(2)
e A−3. That P61 was the correct polarity space group
,
C(7)ꢀC(1)ꢀC(2)
C(2)ꢀC(3)ꢀC(4)
C(4)ꢀC(5)ꢀC(6)
O(7)ꢀC(7)ꢀC(6)
C(6)ꢀC(7)ꢀC(1)
was confirmed by a Flack x parameter of 0.01(2).
Selected bond parameters are given in Table 1.
2.7.2. Crystal structure of
2-nitro-3,5,7-triphenylcyclohepta-2,4,6-trien-1-one (9)
Crystal data: C25H17NO3, MW 379.40, monoclinic,
space group P21/n, a 9.483(7), b 10.393(7), c 19.320(12)
Table 2
,
Selected bond lengths (A) and bond angles (°) for 9
3
A, b 90.32(1)°, V 1904(2) A , Dcalc 1.323 g cm−3 for
Z=4, F(000) 792, v(Mo–Ka) 0.09 mm−1. Yellow
needle-shaped crystal from EtOAc–pentane, 0.56×
0.21×0.12 mm. A total of 2669 data were collected by
„-scans in the range 2B2qB45°, 2491 unique, 1175
with I\2|(I), not corrected for absorption. All non-H
atoms were treated anisotropically, with H atoms in-
cluded in calculated positions. Refinement converged
with R1 0.0774 (2|-data), wR2 0.1909, Goodness-of-fit
,
,
Bond lengths
O(1)ꢀC(1)
O(3)ꢀN(1)
C(1)ꢀC(7)
C(2)ꢀC(3)
C(3)ꢀC(21)
C(5)ꢀC(6)
C(6)ꢀC(7)
1.261(8)
1.234(8)
1.442(9)
1.366(9)
1.495(9)
1.433(8)
1.366(9)
O(2)ꢀN(1)
N(1)ꢀC(2)
C(1)ꢀC(2)
C(3)ꢀC(4)
C(4)ꢀC(5)
C(5)ꢀC(31)
C(7)ꢀC(41)
1.217(8)
1.467(9)
1.453(9)
1.419(9)
1.350(9)
1.485(9)
1.483(9)
Bond angles
O(2)ꢀN(1)ꢀO(3)
O(3)ꢀN(1)ꢀC(2)
O(1)ꢀC(1)ꢀC(2)
C(3)ꢀC(2)ꢀC(1)
C(1)ꢀC(2)ꢀN(1)
C(5)ꢀC(4)ꢀC(3)
C(7)ꢀC(6)ꢀC(5)
124.1(7)
119.0(7)
118.4(7)
134.4(6)
108.8(5)
130.6(7)
132.3(7)
O(2)ꢀN(1)ꢀC(2)
O(1)ꢀC(1)ꢀC(7)
C(7)ꢀC(1)ꢀC(2)
C(3)ꢀC(2)ꢀN(1)
C(2)ꢀC(3)ꢀC(4)
C(4)ꢀC(5)ꢀC(6)
C(6)ꢀC(7)ꢀC(1)
116.9(7)
119.7(7)
121.8(6)
116.7(6)
123.7(6)
125.7(6)
125.6(7)
2
−3
,
on F 1.033 (all data), no final feature \ꢀ0.29ꢀ e A
.
Selected bond parameters in given in Table 2.
3. Results and discussion
3.1. Cyclomanganation of
1,5-diarylpenta-1,4-dien-3-ones (4)
2.7. X-ray crystal structure determinations
The bright red b-cyclomanganation products (5) are
formed from 1,5-diarylpenta-1,4-dien-3-ones (4) and
benzylpentacarbonylmanganese with comparable ease
to those (1) formed [1a] from simple chalcones, and
they appear to be equally stable in air.
The compounds 7a and 9 were characterised by
single-crystal X-ray crystallography. For each, the
space group and crystal quality were established by
precession photography. Accurate cell parameters and
intensity data were collected by ꢀ-scans on a Siemens
With the dienone system of 4, there exists the possi-
bility with excess benzylpentacarbonylmanganese of
successive manganations leading to b,b%-dicycloman-
ganated products in which the carbonyl oxygen acts as
a dual donor. Adams and coworkers have prepared
such a compound from dimethyl acetylenedicarboxylate
and Mn2(CO)10 [6]. However, there was no indication
of a dimanganation product from 4a even over pro-
longed periods for reactions in which benzylpentacar-
bonylmanganese was used in greater than two-fold
excess.
,
P4 diffractometer with Mo–Ka radiation u=0.7107 A)
at −130 °C. The structures were solved by Patterson
methods (7a) or direct methods (9) and routinely devel-
oped. Refinement was full-matrix least-squares based
on F2, using the SHELX programs [5].
2.7.1. Crystal structure of [6-oxo-2,4,7-triphenyl-
cyclohepta-1,4-dienyl-1,2,3,4,5-p]tricarbonylmanganese
(7a)
Crystal data: C28H19MnO4, MW 474.37, hexagonal,
space group P61, a 10.233(2), c 37.509(5) A, V 3401(1)
,

168
W. Tully et al. / Journal of Organometallic Chemistry 633 (2001) 162–172
3.2. Coupling with alkynes
ligand than from the oxocycloheptadienyl ligand, as is
consistent with the structures which show that the
The reaction of the cyclomanganated dienones (5)
with alkynes in some cases gives [4-phenyl-2-(2-
phenylethenyl)pyranyl-h5]tricarbonylmanganese deriva-
tives (6), analogous to those (2) obtained from simpler
b-manganated chalcones (1) [1b], but in other cases
novel seven-membered ring complexes [6-oxo-4,7-
diphenylcyclohepta-1,4-dienyl-1,2,3,4,5-h]tricarbonyl-
manganese (7) were formed (Scheme 3). Various cyclo-
heptadienyl complexes of manganese have been pre-
pared previously from H3Mn3(CO)12 or PhMn(CO)5
and cycloheptatriene [7], or by addition of nucleophiles
to [(cycloheptatriene)Mn(CO)3]+ ions [8], but the
present route appears to be the first for manganese
where the ring is built up in situ, and also the only one
to give a ring incorporating a CꢁO group. Direct
reaction of Mn2(CO)10 with tropone does not give a
corresponding species [9]. However, substituted (h4-tro-
pone)Fe(CO)3 complexes have long been known, syn-
theses involving co-oligomerisation of alkynes and CO
[10]. The same route is involved in the formation of the
h4 cobalt complex (hexachlorotropone-1,2,5,6-h)CoCp
[11]. A chromium h6-tropone complex has been struc-
turally characterised [12].
average MnꢀC(h5) distances are, respectively, 2.188(3)
,
and 2.203 (1) A.
In previously studied simple cycloheptadienyl man-
ganese complexes without the oxo group, carbonyl
stretching frequencies more closely match those of six-
membered ring species with h5 donors, such as the
pyranyl complexes (6) and cyclohexadienyl Mn(CO)3
[8]. In such cycloheptadienyl species both non-coordi-
nated carbon atoms are sp3, permitting a marked fold-
ing of the seven-membered ring so that the h5 section
can bond efficiently and achieve MnꢀC distances simi-
lar to those in smaller ring compounds. By contrast,
similar folding of the ligand in 7a to allow optimum
bonding is restricted by the presence of the sp2 carbon
of the ketone group. Restriction to folding will be
enhanced by the preference of the ketone CO to remain
conjugated to the dienyl p-system; the structure below
shows the C(5)ꢀC(6)ꢀC(7)ꢀO(7) torsion angle is only
7.6°. It is clear that electron-withdrawal from the p-sys-
tem by the conjugated ketone carbonyl will contribute
to the reduction in ligand donor ability towards the
metal.
Possible routes to 6 and 7 are outlined in Scheme 4,
which for clarity does not include the variety of possi-
ble alkene and carbonyl coordinations to the metal.
Regiospecific insertion of the alkyne into the MnꢀC
bond of the cyclomanganated substrate (5a in Scheme 4
for simplicity) would give a seven-membered metallo-
cyclic intermediate (10). As outlined in our previous
paper [1b] and based on the proposal by Booth and
Hargreaves [13], the pyranyl ring of 6 may be formed
Whether it is the six- or seven-membered ring species
which is formed can be established spectroscopically.
Both 6 and 7 give the same type of three-band carbonyl
region infrared spectrum, but the absorptions of the
pyranyl complexes are consistently at lower frequencies
by ca. 20 cm−1 than those of the oxocycloheptadienyl
complexes. This suggests that there is stronger net
electron donation from the h5-system in the pyranyl
Scheme 3. Reactions of cyclomanganated 1,5-diarylpenta-1,4-dien-3-ones with alkynes.

W. Tully et al. / Journal of Organometallic Chemistry 633 (2001) 162–172
169
Scheme 4. Pathways to 6 and 7 (ligand coordinations to Mn, where shown, are indicated by broken arrows, but most are omitted for clarity).
from 10 by rearrangement of the p-system (see electron-
pair movements indicated in 10) as the enone oxygen
bonds to the manganated carbon, the remaining two
p-bonds then coordinating to the metal.
From 12, formation of product 7 requires Ph and Mn
to exchange places on the b and a carbons. A direct
1,2-migration from Cb to Ca with inversion of configu-
ration at Ca would be feasible for the top face (exo)
substituent at Cb but this is H, not Ph, and there is no
product derived from H migration. In any case, if Ph
did migrate (arrow [i] in structure 12) inversion at Ca
would leave Ph exo in the product. This raises the
possibility that phenyl migration may be mediated on
the endo face by MnꢀPh bonding, perhaps through Mn
insertion into the CbꢀPh bond as indicated by [ii] via
the MnꢀPh intermediate 13. Insertion of endo CꢀH into
adjacent h5-coordinated Mn to form MnꢀH intermedi-
ates is established as the basis for thermally induced
hydrogen migrations in tricarbonylcyclohexadienylman-
ganese [16]. Similar hydrogen migrations are mediated
by other p-complexed metals, for instance in tricar-
bonylcycloheptatrienechromium systems in which the
sequential character of hydrogen migration has been
rationalised by Pauson as Cr-assisted endo-H migration
Routes to 7 have been considered which derive
(Scheme 4) from the alternative s-vinyl–h2-alkene
complexes 11a and 11b, formed after dissociation of the
enone oxygen atom from manganese in 10 by rotation
of the exocyclic CꢁC bond into a position where it can
coordinate to the metal. Insertion of the coordinated
CꢁC bond into the CꢀMn bond would bring about
ring-closure, from 11a to form 12 or from 11b to form
14. Such insertion of a coordinated CꢁC group into the
MnꢀC bond has been invoked for some [5+2] cycload-
dition reactions [14], and is analogous to the inter-
molecular alkene insertion reactions at aryl–Mn bonds
of orthomanganted ketones [2a]. Similar coupling of
h1,h2 carbon fragments is well known in the Heck
reaction of aryl or vinyl halides with alkenes, and in a
variety of other palladium-promoted reactions [15].

170
W. Tully et al. / Journal of Organometallic Chemistry 633 (2001) 162–172
without formation of a discrete CrꢀH intermediate [17].
By contrast, as far as we are aware, corresponding
metal-mediated endo-aryl migrations are unknown. In
the current system, the endo CꢀPh bond is the only one
accessible to the s-bonded Mn for insertion in 12, and
collapse of 13 to 7 would be favoured over reversion to
12 by the stabilisation afforded by conjugated p-coordi-
nation in 7. At this stage, an endo-Mn-mediated phenyl
migration, whether or not through a discrete metal–aryl
bonded intermediate, seems to be the most likely expla-
nation for the endo stereochemistry of the phenyl group
in 7.
A mechanism which circumvents the requirement for
Ph migration is one in which the a and b carbons (the
b with the phenyl group attached) ultimately exchange
positions. Initiated by the reverse orientation of insertion
of the p-bond in 11b into the CꢀMn bond, this could be
achieved via the sequence through 14 and 15. However,
by this pathway, as is clear from structures 14a/14b and
15, the original stereochemistry of the enone system
translates into an exo orientation for the phenyl group
in the product (designated 7-exo in Scheme 4), whereas
it is endo in 7. Unless the metal promotes a configura-
tional inversion somewhere on the pathway, it appears
that this a,b-interchange route to 7 cannot apply.
A further puzzle in this initial study is the question of
product preferences in these reactions as a function of
alkyne substituent, for instance, why 5a with pheny-
lacetylene gives the oxocycloheptadienyl complex 7a
whereas with trimethylsilylacetylene it gives the pyranyl
complex 6a. One observation of possible relevance is that
in the phenylacetylene case there was IR evidence at early
stages of the reaction for the formation of some of the
pyranyl complex of type 6, suggesting that some of it may
initially be formed reversibly. With trimethylsily-
lacetylene by contrast, only the pyranyl complex 6 was
formed so if its formation is reversible, this does not
result in product redistribution to the 7 analogue. Fur-
ther study with a wider range of substituents is needed
to explain reactivity patterns.
3.4. Reaction of [6-oxo-2,4,7-triphenylcyclohepta-
1,4-dienyl-1,2,3,4,5-p]tricarbonylmanganese (7a) with
ammonium cerium(IV) nitrate
The potential for organic synthesis of oxidative
demetallation of the (h5-cycloheptadienyl)Mn(CO)3
complexes reported here has been only tentatively ex-
plored so far. Significantly, reaction with I2, which was
successful in the demetalation of pyranyl complexes [1b]
to form stable pyrylium salts, did not demetallate 7a.
However, when the strong oxidant ammonium ceriu-
m(IV) nitrate was used, the tropone 9, in which ring-ni-
tration has accompanied demetalation, was formed
amongst a mixture of products. This suggests untapped
potential in the use of moderate oxidants and elec-
trophiles for the synthesis of cycloheptatrienone deriva-
tives from 7.
3.5. Crystal structures of 7a and 9
The structure of [6-oxo-2,4,7-triphenylcyclohepta-1,4-
dienyl-1,2,3,4,5-h]tricarbonylmanganese (7a) is shown
in Fig. 1, with the numbering scheme used for the
structural discussion. The molecule is an unusual exam-
ple from the well-known class of (h5-dienyl)Mn(CO)3
complexes, with the dienyl fragment coming from a
seven-membered ring related to tropone. The five car-
bon atoms which are bonded to the manganese atom
form a very slightly puckered plane (maximum devia-
3.3. Reaction of pyranyl complexes (6) with iodine to form
pyrylium triiodide salts
,
,
tion 0.09 A) which is 1.608(1) A away from Mn(1). The
individual MnꢀC bonds vary from 2.178(3) to 2.295(3).
The CꢀC distances in the C(1)ꢀC(5) dienyl unit are in
In cases where pyranyl complexes were isolated, they
behaved normally in their reaction with iodine to form
pyrylium triiodide salts (8), the presence of the styryl
substituent on the pyranyl ring (in place of a phenyl
group in the case of the pyranyl complexes formed from
b-manganated chalcones; Scheme 1 [1b]) having no
influence on the course of the reaction. As for their
pyranyl complex precursors, these pyrylium salts have
potential for synthetic modification centred on the alkene
function. Given the enormous variety of heterocyclic
structures that can be obtained by reaction of pyrylium
salts with various reagents [18], there is potential appli-
cation of these reactions in organic synthesis.
,
the range 1.408(4)–1.436(4) A, being shorter, as ex-
pected, than the uncoordinated single sp2–sp2 bond
C(6)ꢀC(7) (1.474(4) A) and the sp2–sp3 bonds
,
C(1)ꢀC(2) and C(1)ꢀC(7) which are 1.532(4) and
,
1.523(4) A, respectively. C(1) and C(7) are twisted out
of the plane of the ligand, away from the manganese
atom and the phenyl substituent on C(1) is endo. The
three phenyl rings on C(1), C(3) and C(5) form dihedral
angles of 83, 34 and 54°, respectively, with the least-
squares plane through C(2–6).
There appear to be four other structure determina-
tions of (heptadienyl)Mn(CO)3 complexes [8,19–21]. As

W. Tully et al. / Journal of Organometallic Chemistry 633 (2001) 162–172
171
membered ring, these parameters closely match those of
a series of aryl-substituted tropones investigated as
possible colchicine analogues [22].
4. Supplementary material
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC no. 168095 for 7a and 168096 for
9. Copies of this information may be obtained free of
charge from The Director, CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK (Fax: +44-1223-336033;
e-mail: deposit@ccdc.cam.ac.uk or www: http://www.
ccdc.cam.ac.uk).
Fig. 1. Structure of [6-oxo-2,4,7-triphenylcyclohepta-1,4-dienyl-
1,2,3,4,5-h]tricarbonylmanganese (7a).
Acknowledgements
We thank Professor Ward Robinson and Jan
Wikaira, University of Canterbury, for collection of
X-ray intensity data, and Professor Michael Bruce and
Dr Chris Adams, University of Adelaide, for mass
spectra.
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