Manganese carbonyl-mediated reactions of azabutadienes with phenylacetylene, methyl acrylate and other unsaturated molecules

Article abstract of DOI:10.1016/j.jorganchem.2004.04.042

Reaction of PhCH₂Mn(CO)₅ with l,4-di-aryl-1-aza-1, 3-butadienes gave substituted pyrrolinonyl rings which were η⁴-coordinated to a Mn(CO)₃ group. These are formed by intramolecular CO insertion into a (non-isolated) cyclomanganated intermediate, followed by cyclisation. Other unsaturated reagents (PhC≡CH, CH₂CHCOOMe, PhNCO) gave products arising from insertion of these, including a structurally characterised tri-aryl-η⁵-azacyclohexadienyl-Mn(CO)₃ complex from the reaction with the alkyne.

Full text of DOI:10.1016/j.jorganchem.2004.04.042

Journal of Organometallic Chemistry 689 (2004) 2523–2530
www.elsevier.com/locate/jorganchem
Manganese carbonyl-mediated reactions of azabutadienes with
phenylacetylene, methyl acrylate and other unsaturated molecules
*
Wade J. Mace, Lyndsay Main , Brian K. Nicholson , Daniel J. van de Pas
*
Department of Chemistry, School of Science and Technology, University of Waikato, Private Bag 3105, Hamilton, New Zealand
Received 25 February 2004; accepted 14 April 2004
Abstract
Reaction of PhCH2Mn(CO)5 with l,4-di-aryl-1-aza-1,3-butadienes gave substituted pyrrolinonyl rings which were g4-coordinated
to a Mn(CO)3 group. These are formed by intramolecular CO insertion into a (non-isolated) cyclomanganated intermediate, fol-
lowed by cyclisation. Other unsaturated reagents (PhC„CH, CH2‚CHCOOMe, PhNCO) gave products arising from insertion
of these, including a structurally characterised tri-aryl-g5-azacyclohexadienyl-Mn(CO)3 complex from the reaction with the alkyne.
ꢀ 2004 Elsevier B.V. All rights reserved.
Keywords: Azabutadienes; Manganese; Carbonyl phenylacetylene
1. Introduction
most of the previously reported cyclometallated azabut-
adiene compounds have been prepared indirectly. These
include di- and tetra-ruthenium compounds [14], the di-
manganese compound 4 (from Mn2(CO)9(CNR) and
DMAD [15]), and the manganese complex 5 (from
ClC6H4CH2C(O)Mn(CO)4(CNC6H4CH3) and CF3CC-
CF3) [16]. Only some orthopalladiated examples 6 have
involved direct cyclometallation of an azabutadiene [17].
We now report attempts to prepare directly ortho-
manganated azabutadiene complexes, and their reactiv-
ity towards some unsaturated molecules.
Cyclomanganation of organic substrates to give com-
plexes of the form 1 has proved to be a general process
[1]. Substrates that have been examined include aryl-
and hetero-aryl ketones [2] and imines [3], benzylamines
[4], triphenylphosphine chalcogenides [5] and triphenyl-
phosphine imines [6]. These complexes undergo a series
of interesting reactions involving the Mn–C bond with
alkenes [7], alkynes [8], organic isocyanates [9], sulfur di-
oxide [10] and carbon disulfide [11]. More recently, cyclo-
manganation studies have been extended beyond aryl
substrates to reactions involving a,b-unsaturated ke-
tones (chalcones) where compounds of the type 2 could
be formed [12]. These also reacted with alkynes, in partic-
ular, to give novel products, including g5-pyranyl- and
g5-oxocycloheptadienyl-Mn(CO)3 derivatives [13].
1-Azabutadienes, 3, are pseudo-iso-electronic with
chalcones so appeared to be a potential source of new
organomanganese chemistry. While there has been ex-
tensive use of azabutadienes as g4-butadiene analogues,
*
Corresponding author. Fax: +64-7-838-4219.
E-mail address: b.nicholson@waikato.ac.nz (B.K. Nicholson).
0022-328X/$ - see front matter ꢀ 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2004.04.042

2524
W.J. Mace et al. / Journal of Organometallic Chemistry 689 (2004) 2523–2530
2. Experimental
2.1. General
to reflux for three hours. The solvent was removed under
vacuum, and the residue chromatographed (PLC, 1:1 pe-
troleum spirits/ether) to give three fractions. The first
main fraction afforded the azacyclohexadienyl complex
8a which was recrystallised by vapour diffusion (ether/pe-
troleum spirits) as a cream powder (94 mg, 87%), m.p.
176 ꢁC. m(C„O) (petroleum spirits) 2025(s), 1965(m),
1946(m) cmꢀ1. ES-MS (MeOH/NaOMe, ꢀve ion) m/z
460 (27%, [MꢀH]ꢀ), 492 (100%, [M+OMe]ꢀ).
Electrospray mass spectra were recorded on a VG
Platform II spectrometer, operated as detailed elsewhere
[18]. Spectra were run at a cone voltage of 20 V unless
otherwise specified, and in some cases Na[OMe] was
added to provide ionisation [19]. NMR spectra were ob-
tained in CDCl3 on a Bruker AC400 instrument operat-
ing under standard conditions, with assignments based
on COSY, HSQC and HMBC experiments. IR spectra
were recorded on a Digilab FTS-40 instrument. All reac-
tions were carried out under nitrogen, but no precau-
tions to exclude air were taken during work-up. The
azabutadiene 4-phenyl-1-p-tolyl-1-azabuta-1,3-diene 3a,
its 1,4-diphenyl analogue and PhCH2Mn(CO)5 were
prepared by literature routes [20,21]. PLC and TLC re-
fer to preparative and thin layer chromatography on sil-
ica gel (Merck Kieselgel 60 PF254).
1H NMR d 2.22 (3H, s, CH3), 5.01 (1H, d, 3JHH =4.2
3
Hz, H6), 5.52 (1H, d, JHH =4.2 Hz, H5), 6.29 (1H, s,
3
H3), 6.58 (2H, d, JHH =8.1 Hz, H20/H60), 6.92 (2H, d,
3
3JHH =8.1 Hz, H30/H50), 7.30 (1H, t, JHH =7.3 Hz,
3
H400), 7.34–7.45 (5H, m, Ar–H), 7.58 (2H, d, JHH =8.4
3
Hz, H200/H600), 7.70 (2H, d, JHH =6.8 Hz, H2*/H6*);
13C NMR d 20.8 (CH3), 66.0 (C6), 82.0 (C2), 88.6
(C3), 91.7 (C5), 102.3 (C4), 115.4 (C20/C60), 123.9
(C200/C600), 127.2 (C2*/C6*), 127.9 (C400), 128.9 (Ar–H),
129.3 (C30/C50)0,0 129.4 (Ar–H), 130.3 (C10), 136.9
(C1*), 138.1 (C1 ), 153.1 (C40), 221.7 (Mn(CO)3).
The second fraction was a mixture of minor products
including unreacted azabutadiene. The third fraction (11
mg) was manganese-free, but was not able to be charac-
terized, ES-MS (MeOH/NaOMe) m/z 452 (100%), 905
(27%) which can be assigned as [MꢀH]ꢀ and
[2MꢀH]ꢀ, respectively, for Mr =453.
2.2. Reactions
2.2.1. Reaction of 4-phenyl-1-p-tolyl-1-azabuta-1,3-diene
with PhCH2Mn(CO)5
A solution of the azabutadiene 3a (51 mg, 0.23 mmol)
and PhCH2Mn(CO)5 (80 mg, 0.28 mmol) in petroleum
spirits (60–80 ꢁC fraction 15 ml) was transferred to a
Schlenk flask. The solution was heated under reflux for
6.5 h. The solvent was removed under vacuum, and the
residue was dissolved in dichloromethane and chromato-
graphed (PLC), eluting with petroleum spirits/ether
(1:1), to afford three fractions. The first fractions con-
tained unreacted starting materials, while the third
fraction was collected to afford the g4-1-tolyl-3-phe-
nylpyrrolin-2-onyl complex 7 which was recrystallised
as yellow needles from diethyl ether (32 mg, 35%), m.p.
143 ꢁC. Found: C, 62.03; H, 3.64; N, 3.62%.
C20H14MnNO4 requires C 63.36, H 3.66, N 3.82%, M
387. m(C„O) (heptane) 2034(s), 1962(m), 1945(m)
cmꢀ1. ES-MS: (MeOH/NaOMe, ꢀve ion) m/z 386 (4%,
2.2.3. Reaction of l,4-diphenyl-1-azabuta-1,3-diene and
PhC„CH with PhCH2Mn(CO)5
A petroleum spirits (30 ml) solution containing
PhCH2Mn(CO)5 (160 mg, 0.56 mmol), diphenylazabut-
adiene (100 mg, 0.48 mmol) and PhC„CH (200 ll,
1.96 mmol) was heated under reflux for four hours.
The solvent was evaporated and the residue chromato-
graphed, eluting with ether/petroleum spirits (1:9). The
main band was removed and recrystallised from hot pe-
troleum spirits to give yellow crystals of 8b, (68 mg,
31%). Found: C, 69.96; H, 4.28; N, 3.06%.
C26H17MnNO3 requires 69.78, H 4.05, N 3.13%, M
447. IR (petroleum spirits) m(C„O) 2023(s), 1965(m),
1946(m) cmꢀ1. ES-MS (MeOH/NaOMe, ꢀve ion) m/z
446 (20%, [MꢀH]ꢀ), 478 (100%, [M+OMe]ꢀ).
[MꢀH]ꢀ), 418 (100%, [M+OMe]ꢀ). H NMR: d 2.41
1
3
(3H, s, CH3), 5.98 (1H, d, JHH =2.4 Hz, H4), 6.23
3
(1H, d, JHH =2.4 Hz, H5), 7.3 (4H, m, H200/H300/H500/
3
H600), 7.3 (1H, t, JHH =7.4 Hz, H40), 7.4 (2H, dd,
3JHH =7.5, 7.5 Hz, H30/H50), 7.9 (2H, d, JHH =7.5 Hz,
3
H20/H60); 13C NMR: d 21.4 (CH3), 71.2 (C3), 78.9
(C5), 83.1 (C4), 126.2 (C20/C60), 126.5 (C200/C600), 127.8
(C40), 129.1 (C30/C50), 130.5 (C300/C500), 132.2 (C10),
132.5 (C100), 140.1 (C400), 152.4(C2),221.5(Mn(CO)3).
2.2.2. Reaction of 4-phenyl-1-p-tolyl-1-azabuta-1,3-diene
and PhC„CH with PhCH2Mn(CO)5
A solution of the azabutadiene 3a (52 mg, 0.23 mmol),
PhC„CH (75 ll, 0.68 mmol) and PhCH2Mn- (CO)5 (87
mg, 0.30 mmol) in petroleum spirits (15 ml) was heated
1H NMR d 5.01 (1H, d, 3JHH =4.2 Hz, H6), 5.52 (1H,
d, JHH =4.2 Hz, H5), 6.29 (1H, s, H3), 6.63–7.86 (Ar–
3
H); 13C NMR d 65.3 (C6), 81.4 (C2), 88.7 (C3), 91.7
(C5), 102.4 (C4), 115.2–155.3 (Ar–C), 221.5 (Mn(CO)3).

W.J. Mace et al. / Journal of Organometallic Chemistry 689 (2004) 2523–2530
2525
2.2.4. Reaction of 4-phenyl-1-p-tolyl-1-azabuta-1,3-diene
and CH2‚CHCO2Me with PhCH2Mn(CO)5
(C400), 127.9 (C2*/C6*), 128.9 (C3*/C5*), 0 1290.4 (C300/
C500), 129.5 (C4*), 129.7 (Cl0), 130.3 (C3 /C5 ), 131.0
(Cl*), 136.8 (Cl00), 137.9 (C3), 138.2 (C4), 142.5 (C40),
168.2 (C2)
A solution of the azabutadiene 3a (53 mg, 0.24
mmol), CH2‚CHCO2Me (115 ll, 1.2 mmol) and
PhCH2Mn(CO)5 (79 mg, 0.28 mmol) in petroleum spir-
its (15 ml) was transferred to a Schlenk flask under ni-
trogen. The solution was heated to reflux for 2 h
before the solvent was removed under vacuum. The res-
idue was chromatographed (PLC, 1:1 ethyl acetate/pe-
troleum spirits) giving three fractions. The first and
last were minor fractions containing a mixture of prod-
ucts (no further purification was attempted on these
fractions). The second fraction contained the main
product 9, recrystallised as a yellow powder by vapour
diffusion (benzene/hexane) (28 mg, 39%), m.p. 148 ꢁC.
Found: C, 63.35; H, 4.73; N, 3.27% C23H20MnNO3 re-
quires C 62.03, H. 4.53, N 3.15%, M 445. IR
(CH2C12) m(C„O) 2017(s), 1933(m, br) cmꢀ1, m(C‚O)
1734 cmꢀ1. ES-MS (MeOH, +ve ion) m/z 308 (100%,
[M–Mn(CO)3 +2H]+), 468 (17%, [M+Na]+), 913 (11%,
[2M+Na]+).
The fourth fraction afforded a product tentatively as-
signed as 11 (33 mg, 30% yield) as a dark yellow solid,
m.p.=192 ꢁC. IR (heptane) m(C‚O, C‚N) 1718,
1703, 1676 cmꢀ1. ES-MS (MeOH, +ve ion) m/z 482
1
(100%, [M+Na]+), 941 (36%, [2M+Na]+). H NMR d
2.35 (3H, s, CH3), 6.07 (CH), 6.78–7.82 (Ar–H), 8.96
(NH); 13C NMR d 21.5 (CH3), 67.6 (CH), 120.2–140.4
(Ar–H, Ar), 153.8 (C‚N), 154.6 (C‚O), 168.0 (C‚O).
2.2.6. Attempted reaction of 4-phenyl-1-p-tolyl-1-azabu-
ta-1,3-diene and ButNC with PhCH2Mn(CO)5
A mixture of the azabutadiene 3a (52 mg, 0.24
mmol), ButNC (200 ll, 1.8 mmol) and PhCH2Mn(CO)5
(88 mg, 0.31 mmol) in petroleum spirits (15 ml) was
heated to reflux for 2 h before the solvent was removed
under vacuum. The residue was chromatographed
(PLC, 1:1 petroleum spirits/dichloromethane) to give
three fractions. The first fraction was unreacted azabut-
adiene, while the second was collected to afford 12, re-
crystallised as yellow crystals from hexane (15 mg,
10% yield), m.p. 96 ꢁC. IR (heptane) m(C„N) 2135
cmꢀ1, m(C„O) 1990(m), 1939(m) cmꢀ1, m(C‚O),
m(C‚N) 1713, 1679 cmꢀ1. ES-MS (MeOH, +ve ion)
m/z 480 (100%, [M+H]+). 1H NMR d 1.31 (9H, s,
But), 1.39 (9H, s, But), 1.46 (9H, s, But), 3.83 (1H, d,
3
1H NMR d 2.23 (1H, d, JHH =11.8 Hz, H2), 2.40
3
(3H, s, Me), 3.33 (1H, d, JHH =22.3 Hz, H5), 3.72
3
(1H, d, JHH =22.2 Hz, H5), 3.83 (3H, s, OMe), 6.43
3
(1H, d, JHH =11.7 Hz, H3), 7.04 (2H, d, JHH =8.1
3
3
Hz, H200/H600), 7.22 (2H, d, JHH =8.1 Hz, H300/H500),
7.23 (1H, m, H40), 7.39 (2H, m, H30/H50), 7.53 (1H, s,
H6), 7.66 (2H, m, H20/H60); 13C NMR d 21.1 (Me),
44.7 (C5), 51.6 (OMe), 59.9 (C2), 90.5 (C4), 102.2
(C3), 120.7 (C200/C600), 126.5 (C20/C60), 126.5 (C40),
128.7 (C30/C50), 129.9 (C300/C500), 137.6 (C400), 145.7
(C10), 150.6 (C100), 174.7 (C1), 176.4 (C6).
2
2JHH =14.1 Hz, H3), 4.27 (1H, d, JHH =14.1 Hz, H3),
7.17 (2H, m, H30/H50), 7.18 (1H, m, H40), 7.23 (2H,
m, H20/H60); 13C NMR d 29.9 (C(CH3)3), 30.6
(C(CH3)3), 31.0 (C(CH3)3), 32.7 (C3), 56.4 (C(CH3)3),
56.9 (C(CH3)3), 59.6 (C(CH3)3), 125.7 (C40), 128.3
(C30/C50), 128.7 (C20/C60), 138.9 (C10), 186.2 (C1),
194.8 (C2), 217.0, 221.5 224.4 (Mn–CO, Mn–CNBut)
ES-MS determined that the third fraction contained a
mixture of [Mn(CNBut)6]+ and [Mn(CNBut)5(CO)]+
species, and was not analysed further.
2.2.5. Reaction of 4-phenyl-1-p-tolyl-1-azabuta-1,3-diene
and PhNCO with PhCH2Mn(CO)5
A solution of the azabutadiene 3a (53 mg, 0.24
mmol), PhNCO (80 ll, 0.74 mmol) and PhCH2Mn(CO)5
(71 mg, 0.25 mmol) in petroleum spirits (15 ml) was
heated to reflux for 2 h before the solvent was removed
under vacuum. The residue was chromatographed
(PLC, 1:4 ethyl acetate/petroleum spirits) to give four
fractions, the first two of which were minor fractions
containing unreacted starting materials. The third frac-
tion was collected to afford 10 (24 mg, 30%) as a yellow
solid. IR (CH2C12) m(C‚O) 1715(br) cmꢀ1. ES-MS
(MeCN, +ve ion) m/z 341 (100%, [M+H]+), 363 (45%,
[M+Na]+), 681 (43%, [2M+H]+), 703 (20%,
2.2.7. Reaction of 4-phenyl-1-p-tolyl-1-azabuta-1,3-diene
and CS2 with PhCH2Mn(CO)5
PhCH2Mn(CO)5 (81 mg, 0.284 mmol), the azabutadi-
ene 3a (54 mg, 0.243 mmol) and CS2 (5 ml) were trans-
ferred to an ampoule which was sealed under vacuum.
The ampoule was heated to 85 ꢁC in a Carius tube for
48 h. Small yellow crystals of 13 (2 mg, 3%) crystallised
from the cooled reaction mixture, and were identified by
ES-MS and IR [11]. TLC of the remaining reaction mix-
ture showed a multitude of products which were not fur-
ther investigated.
1
[2M+Na]+), 1043 (8%, [3M+Na]+). H NMR d 2.27
3
(3H, s, CH3), 3.90 (1H, s, NH), 6.05 (1H, d, JHH =2.0
3
Hz, H5), 6.67 (2H, d, JHH =8.4 Hz, H20/H60), 7.01
3
3
(2H, d, JHH =8.3 Hz, H30/H50), 7.22 (1H, t, JHH =7.4
3
Hz, H400), 7.30 (1H, d, JHH =2.0 Hz, H4), 7.39 (2H,
m, H300/H500), 7.43 (2H, m, H3*/H5*), 7.46 (1H, m,
2.3. X-ray crystallography
3
H4*), 7.58 (2H, d, JHH =7.6 Hz, H200/H600), 7.95 (2H,
d, JHH =6.3 Hz, H2*/H6*); 13C NMR d 20.8 (CH3),
X-ray intensity data were collected on a Siemens
SMART CCD diffractometer using standard procedures
3
70.9 (C5), 115.9 (C20/C60), 123.4 (C200/C600), 125.8

2526
W.J. Mace et al. / Journal of Organometallic Chemistry 689 (2004) 2523–2530
and software. Empirical absorption corrections were ap-
plied (SADABS [22]). Structures were solved by direct
methods and developed and refined on F2 using the
SHELX programmes [23]. Hydrogen atoms were included
in calculated positions.
2.3.1. Structure of the g4-pyrrolinonyl complex 7
Yellow needle crystals of 7 were obtained from di-
ethyl ether.
Crystal data: C20H14MnNO4, M=387.26, mono
clinic, space group C2/c, a=24.314(8), b=11.199(4),
3
˚
˚
c=16.664(5) A, b=131.33(3)ꢁ, U 3407.1(19) A , T 168
K, Z=8, Dcalc =1.510 gcmꢀ3, l(Mo Ka)=0.80 mmꢀ1
,
F(000) 1584; 21764 reflections collected with
2ꢁ<h<26ꢁ, 3470 unique (Rint 0.0264) used after correc-
tion for absorption (Tmax, min 0.882, 0.686). Crystal di-
mensions 0.51·0.18·0.16 mm3. Refinement on F2
gave R1 0.0356 [I>2r (I)] and wR2 0.0782 (all data),
Fig. 2. The structure of the 1,2,4-triphenyl-1-azacyclohexa-2,4-dien-6-
yl-manganese tricarbonyl complex 8b. Bond lengths include: Mn(1)–
C(1) 2.202(2), Mn–C(2) 2.121(2), Mn–C(3) 2.160(3), Mn–C(4)
2.107(3), Mn–C(5) 2.142(3), C(1)–N(1) 1.453(3), C(5)–N(1) 1.429(3),
GoF 1.125, residual peaks ( 0.26 eAꢀ3). The structure
˚
of 7 is illustrated in Fig. 1, with selected bond parame-
ters included in the caption to the figure.
˚
C(11)–N(1) 1.420(3) A.
2.3.2. Structure of the g5-azacyclohexadienyl complex 8b
Yellow needle crystals of 8b were obtained from pe-
troleum spirits.
3. Results and discussion
The reactions discussed in detail below are summar-
ised in Scheme 1.
Crystal data: C26H18MnNO3, M=447.36, monoclin-
ic, space group C2/c, a=21.925(7), b=10.950(4),
3
˚
˚
c=17.234(6) A, b=94.768(6)ꢁ, U 4123(2) A , T 163 K,
Z=8, Dcalc =1.441 gcmꢀ3, l(Mo Ka)=0.67 mmꢀ1
,
3.1. Attempted cyclomanganation of 4-phenyl-1-p-tolyl-1-
azabuta-1,3-diene
F(000) 1840; 24528 reflections collected with
2ꢁ<h<26ꢁ, 4067 unique (Rint 0.1033) used after correc-
tion for absorption (Tmax, min 1.000, 0.826). Crystal di-
mensions 0.36·0.18·0.12 mm3. Refinement on F2
gave R1 0.0416 [I>2r (I)] and wR2 0.0450 (all data),
When the azabutadiene 3a was reacted with
PhCH2Mn(CO)5, under the refluxing-heptane condi-
tions used successfully for cyclometallation of chal-
GoF 0.935, residual peaks ( 0.23 eAꢀ3). The structure
˚
cones,
a
yellow product was readily isolated.
Elemental analysis and ES-MS were consistent with
the expected product, a cyclometallated azabutadiene,
but the infrared spectrum was not since the m(CO) pat-
tern was more like that of a Mn(CO)3 moiety than the
characteristic Mn(CO)4 type.
of 8b is illustrated in Fig. 2, with selected bond para-
meters included in the caption to the figure.
An X-ray crystal structure determination was there-
fore carried out. This showed that a substituted pyrrolino-
nyl ring had formed and was coordinated to a Mn(CO)3
group as in 7. The structure is illustrated in Fig. 1. Clearly,
the deprotonated azabutadiene group has combined with
a CO ligand to form the new planar ring structure, and
this acts as a five-electron donor to the manganese, with
two electrons from the N atom, two from the C(4)–C(5)
p bond, and one from C(6). This leaves the C‚O group
free of interaction with the manganese atom, although
˚
the Mnꢁ ꢁ ꢁC(7) is quite short (2.375 A).
There appear to be no previous examples of g4-pyr-
rolinonyl complexes, the closest analogues being some
g2-pyrrolinone-Fe(CO)4 species [24]. This new synthesis
of pyrrolinonyl rings is of interest as such five-membered
rings are involved in several areas of organic chemistry
Fig. 1. The structure of the g4-1-tolyl-3-phenylpyrrolin-2-onyl-man-
ganese tricarbonyl complex 7. Bond lengths include: Mn(1)–N(1)
2.102(2), Mn–C(4) 2.080(2), Mn–C(5) 2.131(2), Mn–C(6) 2.195(2),
Mnꢁ ꢁ ꢁC(7) 2.375(2), C(7)–O(4) 1.214(2), C(4)–C(5) 1.394(3), C(5)–C(6)
˚
1.421(3) A.

W.J. Mace et al. / Journal of Organometallic Chemistry 689 (2004) 2523–2530
2527
Scheme 1.
[25], and different substituents could be incorporated by
choosing the appropriate azabutadiene.
(cf. ꢂ2080 cmꢀ1 for cyclomanganated chalcones [12]).
As the reaction continued the 2034 cmꢀ1 peak increased,
while that at 2076 cmꢀ1 was never more than a small
feature. This is consistent with the process in Scheme
2, where the cyclomanganated azabutadiene is formed,
but rapidly reacts further by CO insertion.
A route to complex 7 can be proposed, by analogy
with chalcone chemistry (Scheme 2) [13]. The first step
is presumably to form the cyclometallated azabutadiene
5b. Under the conditions, and in contrast to chalcone
examples, there is rapid insertion of a CO ligand into
the Mn–C r-bond. Addition of the new Mn–C bond
across the N‚C bond forms the five-membered ring
with the Mn(CO)3 group attaching to one face in a g4
manner to achieve an eighteen-electron configuration.
To investigate the reaction in more detail, it was re-
peated under milder conditions with monitoring by IR
spectroscopy. When a mixture of the azabutadiene and
PhCH2Mn(CO)5 was slowly heated in heptane, no
change was observed until the temperature of the oil
bath reached 70 ꢁC, at which time two new IR peaks ap-
peared at 2034 and 2076 cmꢀ1. The former of these can
be attributed to the pyrrolinonyl complex 7, while the
latter is in the position expected for the highest frequen-
cy m(CO) band for the cyclometallated azabutadiene 5b
3.2. Reaction in the presence of PhCBCH
Although the cyclomanganated complex 5b could not
be isolated, its reactivity in situ with other substrates
was of interest. Several groups have shown that reac-
tions between cyclomanganated aryl ketones or chal-
cones and alkynes proceed via insertion/cyclisation
processes to give novel derivatives [8,13], so the corre-
sponding reaction was investigated here. When a mix-
ture of the azabutadiene 3a, PhCH2Mn(CO)5 and
PhC„CH (ca. 1:1:3) was heated in petroleum spirits a
reaction occurred to give a solution with m(CO) peaks
indicative of a Mn(CO)3 group, but shifted ꢂ10 cmꢀ1
to lower frequencies compared with those of the
Scheme 2.

2528
W.J. Mace et al. / Journal of Organometallic Chemistry 689 (2004) 2523–2530
pyrrolinonyl-complex 7. Work-up provided two prod-
ucts. The major one was identified spectroscopically as
the g5-azacyclohexadienyl complex 8a formed in excel-
lent yield. This is the N-analogue of the g5-pyranyl com-
plexes formed when cyclomanganated chalcones are
reacted with alkynes [13], and a similar route can be as-
sumed. This invokes the cyclomanganated azabutadiene
5b as the first intermediate, which undergoes insertion of
PhC„CH into the Mn–C bond. Cyclisation involving
the N‚C bond leads to the six-membered ring with
the Mn(CO)3 group occupying one face (Scheme 3).
The minor product from the reaction of the azabut-
adiene with PhC„CH was not identified, but appears
to have arisen from CO insertion and double addition
of PhC„CH to give a species which the mass spectrum
suggests has an Mr of 453.
Compounds analogous to 8 have been prepared pre-
viously by reactions of alkynes with RC6H4CH2C(O)-
Mn(CO)4(CNC6H4R0), probably via a cyclomanganated
azabutadiene formed in situ by coupling the isonitrile
with the first equivalent of alkyne [16]. Interestingly,
the azacyclohexadienyl ligands found in that study were
either g4 or g5, depending on the substituents. These
cannot be distinguished reliably by spectroscopic means,
but it seemed probable that 8a contained an g5 ligand in
the absence of electron-withdrawing substituents on the
ring. We could not prepare crystals of 8a suitable for
X-ray crystallography to confirm this, so the corre-
sponding reaction using 1,4-diphenyl-1-azabutadiene
was carried out. This gave 8b in a completely analogous
procedure and this compound crystallised well. The
structure of 8b is shown in Fig. 2 and confirms the g5-at-
tachment of the ligand to the manganese. The C(1)–C(5)
g5-azacyclohexadienyl examples with other substituents
reported by Homrighausen et al. [16].
3.3. Reaction in the presence of CH2@CHCOOMe
Activated alkenes are also known to react with cyclo-
manganated substrates derived from aryl ketones and
chalcones [7,13]. A mixture of the azabutadiene 3a,
PhCH2Mn(CO)5 and CH2‚CHCOOMe reacted to give
one main product which was characterised spectroscop-
ically as 9 in moderate yield. ES-MS and elemental anal-
ysis confirmed the formula as a combination of one
CH2‚CHCOOMe, one deprotonated azabutadiene
molecule and one Mn(CO)3 fragment, while IR data
confirmed a Mn(CO)3 unit and showed from the
m(C‚O) at 1734 cmꢀ1 that the carboxylate group was
not coordinated to the metal. A peak at 1699 cmꢀ1
can be assigned to a non-conjugated C‚N bond. This
information, and a full 2-D NMR study, leads to the
structure 9, in which the CH2‚CHCOOMe has coupled
to the azabutadiene through C-4 to give a disubstituted
methyl 7-azahepta-3,6-dien-2-yloate ligand. This is coor-
dinated to the Mn(CO)3 group via an g3-allyl interac-
tion, with the remaining two electrons coming from
the N atom. Again the formation of this species can
be explained by initial formation of the cyclomanganat-
ed complex 5b, followed by insertion of the alkene into
the Mn–C bond and subsequent rearrangement giving
the product. When an orthomanganated chalcone was
reacted with CH2‚CHCOOMe in CCl4 the main prod-
uct was a substituted methyl 7-oxo-hepta-2,6-dienoate,
which is the protio-demetallated equivalent of 9 [12].
˚
atoms are planar to within 0.024 A, forming a dihedral
angle with the C(1)–N(1)–C(5) plane of 50ꢁ. The Mn–C
bond distances range from 2.107(2) to 2.202(3) A, aver-
3.4. Reaction in the presence of PhNCO
˚
Liebeskind et al. [9] reacted orthomanganated sub-
strates with PhNCO and showed that insertion fol-
lowed by cyclisation led to phthalimidines. In the
present system, PhNCO with PhCH2Mn(CO)5 and
the azabutadiene gave two organic products, both in
˚
age 2.146 A, which indicates slightly stronger bonding of
the ring than in the related (g5-pyranyl)Mn(CO)3 com-
˚
plexes where the average Mn–C distance was 2.188 A
[13]. The structure of 8b is directly comparable to the
Scheme 3.

W.J. Mace et al. / Journal of Organometallic Chemistry 689 (2004) 2523–2530
2529
about 30% yield. The first of these showed an [M+H]+
3.6. Summary
peak at m/z 341 in the ES-MS, giving a mass of 340
which corresponds to a combination of one PhNCO
and one azabutadiene molecule. The IR spectrum
showed a peak at 1715 cmꢀ1 assigned to a free C‚O
group, and the NMR spectra were consistent with
the structure 10. This can be explained by an insertion
of PhNCO into the Mn–C bond of 5b, followed by
cyclisation involving the imine carbon atom to give a
five-membered ring. Subsequent protio-demetallation
would give 10.
The other product from the reaction was shown to
have a mass of 459 from ES-MS. This equates to a
combination of one azabutadiene molecule with two
PhNCO molecules, presumably via a double insertion
process. The IR spectrum contained three peaks in
the C‚O or C‚N region. A possible structure is
shown (11) but this could not be confirmed from
NMR data so should be regarded as a tentative assign-
ment only.
Although no cyclomanganated azabutadiene deriva-
tive 5b could be isolated, it appears that this is the
first-formed compound in the reaction of 3a with
PhCH2Mn(CO)5. This provides an activated form of
the azabutadiene for subsequent coupling. A survey of
‘‘one pot’’ reactions between an azabutadiene and un-
saturated substrates in the presence of PhCH2Mn(CO)5
shows that useful new compounds can be formed.
It is interesting that the three unsaturated molecules
PhC„CH, CH2‚CHCOOMe and PhNCO all appear
to insert initially into the Mn–C bond of a pre-formed
5b to give a seven-membered metallocyclic ring interme-
diate, but that reactions then proceed differently. The al-
kyne-intermediate cyclises by attack at the imine
nitrogen atom to give a six-membered ring, the
PhNCO-intermediate attacks at the imine carbon atom
to give a five-membered ring, while the alkene-derived
species does not undergo a cyclisation reaction at all.
Further work with other azabutadienes and other unsat-
urated molecules is underway to determine the factors
that affect this reactivity.
3.5. Reaction in the presence of ButNC or CS2
These substrates were also examined as ‘‘one-pot’’ re-
agents. However in neither case were products derived
from the azabutadiene isolated. ButNC gave a low yield
of a complex 12 which is not unexpected from a reaction
between PhCH2Mn(CO)5 and an isonitrile, based on
other studies of RMn(CO)5 compounds with isonitriles
[26]. The formation of 12 involves step wise insertion
of first a CO ligand and secondly a ButNC one, with fur-
ther replacement of two terminal carbonyl groups by
isonitriles. (An isomer of 12 with the inserted CO and
ButNC interchanged cannot be excluded spectroscopi-
cally, but is less likely.) It appears that isonitriles are
too effective as Lewis bases and react with
PhCH2Mn(CO)5 before the reaction with the azabutadi-
ene to form 5b can take place.
Acknowledgements
We thank Dr. Jan Wikaira and Professor Ward Rob-
inson, University of Canterbury, for collection of X-ray
intensity data.
Appendix A. Supplementary material
Crystallographic data for the structural analyses have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC Nos. 237998 and 237999. Copies
of this information may be obtained free of charge from
the Director, CCDC, 12 Union Rd., Cambridge CB2
1EZ, UK (fax: +44-1223-336033; e-mail: depos-
it@ccdc.cam.ac.uk or www: http://www.ccdc.cam.a-
c.uk). Supplementary data associated with this article
can be found, in the online version at doi:10.1016/j.jor-
ganchem.2004.04.042.
In a rather unspecific reaction, CS2 gave a low yield
of the trithiocarbonate–tetramanganese compound 13,
which has been found in similar reactions with other cy-
clomanganated substrates [11].
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