Coupling of isocyanides to alkynes on manganese

Article abstract of DOI:10.1016/S0020-1693(02)00865-4

Novel six-membered nitrogen-containing heterocycles bonded to manganese are produced from the reaction of [p-RC₆H₄CH ₂C(O)Mn(CO)₄(CNC₆H₄-p-R′)] (1) R′=Me or OMe, R=H or Cl with various alky

Full text of DOI:10.1016/S0020-1693(02)00865-4

Inorganica Chimica Acta 334 (2002) 419ꢁ436
/
www.elsevier.com/locate/ica
Coupling of isocyanides to alkynes on manganese
Craig L. Homrighausen 1, John J. Alexander *, Jeanette A. Krause Bauer
Department of Chemistry, University of Cincinnati, Cincinnati, OH 45221, USA
Received 3 January 2002; accepted 4 March 2002
Dedicated to Professor Andrew A. Wojcicki in recognition of his contributions to inorganic chemistry
Abstract
Novel six-membered nitrogen-containing heterocycles bonded to manganese are produced from the reaction of [p-
RC6H4CH2C(O)Mn(CO)4(CNC6H4-p-R?)] (1) R?ꢀMe or OMe, RꢀH or Cl with various alkynes. Trapping of the alkynes by
/
/
an unsaturated manganese-mono(iminoacyl) group generated in situ leads to formation of: [1-(p-tolyl)-2-(p-chlorobenzyl)-3,4,5,6-
tetraphenyl-h5-azacyclohexadienyl]manganese tricarbonyl (2a), [1-(p-methoxy)-2-benzyl-3,4,5,6-tetraphenyl-h5-azacyclohexadie-
nyl]manganese tricarbonyl (2b), [1-(p-tolyl)-2-(p-chlorobenzyl)-3,5-dihydro-4,6-diphenyl-h5-azacyclohexadienyl]manganese tricar-
bonyl (3a), [1-(p-methoxy)-2-(p-chlorobenzyl)-3,5-dihydro-4,6-diphenyl-h5-azacyclohexadienyl]manganese tricarbonyl (3b), [1-(p-
tolyl)-2-(p-chlorobenzyl)-3,5-dimethyl-4,6-bis(carbomethoxy)-h5-azacyclohexadienyl]manganese tricarbonyl (4) and h4-azacyclo-
hexadienyl complexes: [1-(p-tolyl)-2-(p-chlorobenzyl)-3,6-dimethyl-4,5-bis(carbomethoxy)-h4-azacyclohexadienyl]manganese tricar-
bonyl (5a), [1-(p-tolyl)-2-(p-chlorobenzyl)-3,6-bis(carbomethoxy)-4,5-dimethyl-h4-azacyclohexadienyl]manganese tricarbonyl (5b),
[1-(p-tolyl)-2-(p-chlorobenzyl)-4,6-dimethyl-3,5-bis(carbomethoxy)-h4-azacyclohexadienyl]manganese tricarbonyl (5c) and [1-(p-
tolyl)-2-(p-chlorobenzyl)-3,4,5,6-tetrakis(carbomethoxy)-h4-azacyclohexadienyl]manganese tricarbonyl (6). All these products
result from coupling of one iminoacyl group and two molecules of alkyne. Surprisingly, reaction of 1 with hexafluoro-2-butyne
led to formation of an unsaturated five-membered manganacycle [1,1,1,1-tetracarbonyl-2,3-bis(trifluoromethyl)-4-(p-chlorobenzyl)-
5-p-tolyl]-5-azamanganacyclopentadiene (7). The structure, reactivity and formation mechanism of these complexes are discussed.
# 2002 Elsevier Science B.V. All rights reserved.
Keywords: Isocyanides; Alkynes; Manganese; Coupling
1. Introduction
Transitionꢁmetal-mediated coupling reactions be-
tween alkynes and carbon monoxide have resulted in a
large variety of organic compounds [1] along with a
myriad of organometallic complexes [2]. Studies of
metal-mediated coupling reactions between alkynes
and isocyanides have been far fewer [3].
Isocyanides, CNR, are isolobal with CO and hence
might be expected to display similar chemistry [4].
Indeed, many such similarities are apparent. For exam-
ple, isocyanides often replace terminal carbonyl ligands.
bonds to produce complexes containing the iminoacyl
(C(ÄNR)) group [5]. In fact, we and others have shown
that aromatic isocyanides insert into metalÃcarbon
bonds preferentially to carbon monoxide [6,7].
Previous studies in our group have demonstrated that
a dimeric manganese diazabutadiene complex is pro-
duced upon refluxing the (p-tolyl)isocyanide-substituted
manganese acyl complex [p-ClC6H4CH2C(O)Mn-
(CO)4(CNC6H4-p-CH3)] in THF (Scheme 1) [7].
An unsaturated manganese-mono(iminoacyl) inter-
mediate was proposed to occur along the pathway to
the diazabutadiene dimer. More recently, when the
product mixture from the reaction of p-chlorobenzyl
manganese pentacarbonyl and 2,6-dimethylphenyl iso-
cyanide was placed under an atmosphere of carbon
dioxide, a carbamate-bridged manganese dimer was
produced (Scheme 2) [8]. In the proposed mechanism
an unsaturated manganese-mono(iminoacyl) intermedi-
/
/
/
Isocyanides are also known to insert into metalÃ
/carbon
* Corresponding author. Tel.: ꢂ
/
1-513-556 9200; fax: ꢂ1-513-556
/
9239.
1
Present address: Eltron Research Inc., 4600 Nautilus Court
South, Boulder, CO 80301-3241, USA.
0020-1693/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved.
PII: S 0 0 2 0 - 1 6 9 3 ( 0 2 ) 0 0 8 6 5 - 4

420
C.L. Homrighausen et al. / Inorganica Chimica Acta 334 (2002) 419ꢁ436
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2. Results and discussion
2.1. Reactions of alkynes with p-
RC6H4CH2C(O)Mn(CO)4(CNC6H4-p-R?) (1)
Scheme 1.
ate reacts via nucleophilic attack on carbon dioxide by
the imino nitrogen lone pair initiating formation of a
bridging carbamate ligand.
2.1.1. Formation of h5-azacyclohexadienyl complexes
Reaction of p-tolyl (R?ꢀ
/
Me) or p-methoxyphenyl
These observations prompted us to investigate reac-
tivity of the manganese acyl complexes [p-
RC6H4CH2C(O)Mn(CO)4(CNC6H4-p-R?)] (1) with al-
kynes. We wish to report that we have been able to trap
with alkynes the unsaturated manganese-mono(iminoa-
cyl) group generated in situ to produce novel nitrogen-
containing heterocycles bonded to manganese.
(R?ꢀOMe) isocyanide with (p-chlorobenzyl)manganese
/
pentacarbonyl or (phenylacetyl)manganese pentacarbo-
nyl gave the expected acyl complexes 1a, 1b, and 1c.
When 2 equiv. of alkyne were allowed to react with these
acyl complexes in warm THF, h5-nitrogen-substituted
azacyclohexadienyl complexes 2a, 2b, 3a, 3b, and 4 were
produced (Scheme 3).
Scheme 2.

C.L. Homrighausen et al. / Inorganica Chimica Acta 334 (2002) 419ꢁ
/436
421
determined by single-crystal X-ray diffraction analysis.
An ORTEP drawing for 2b is presented in Fig. 1.
Selected bond lengths and angles are presented in
Table 2. The structure of 2b can be described as high-
back piano stool geometry. The dihedral angle between
the planes defined by C4Ã
N1ÃC4 is 53.3(2)8. Angles Ccarbonyl
from 84.3(2) to 94.0(2)8 while the angles Ccarbonyl
/
C5Ã
/
C6Ã
/
C7Ã
/
C8 and by C8Ã
Ccarbonyl range
MnÃ
/
/
Ã
/
MnÃ
/
Ã
/
/
Cring range from 86.1(1) to 173.5(1)8. The five-carbon
segment of the h5-azacyclohexadienyl ligand is essen-
tially planar with a mean deviation from planarity of
˚
0.032 A. Bond lengths between C4Ã
/
C5, C5Ã
C8 of 1.422(4), 1.441(4), 1.445(4), 1.405(4) A,
carbon
/
C6, C6Ã
/
C7,
˚
and C7Ã
/
Scheme 3.
respectively, are intermediate between carbonÃ
/
Lower yields were obtained from generation of the
acyl complex in situ followed by addition of the alkyne
and warming in THF.
single and double bonds implying delocalization
throughout the five-carbon skeleton of the ring. Bond
˚
lengths between N1Ã
/
C4 of 1.460(3) A and N1Ã
/
C8 of
˚
1.455(3) A are typical of nitrogenÃ
/
carbon single bonds.
Angles C4ÃN1ÃC8, C4ÃN1ÃC40, C8Ã
2.1.1.1. Diphenylacetylene. When 1a was heated in THF
in the presence of 2 equiv. of diphenylacetylene, complex
2a was isolated. Complex 2a contains an h5-azacyclo-
hexadienyl ligand resulting from the coupling of two
molecules of diphenylacetylene and a p-tolyl(iminoacyl)
group on manganese. The [1-(p-tolyl)-2-p-(chloroben-
zyl)-3,4,5,6-tetraphenyl-h5-azacyclohexadienyl] ligand
functions as a six-electron donor to manganese. Com-
plex 2a is isoelectronic with cymantrene, CpMn(CO)3.
Spectral data (Table 1) are consistent with the
structure proposed for 2a. The IR spectrum displays
three bands in the terminal CO stretching region in a
pattern characteristic of fac-geometry. The absence of a
band at 2164 cmꢃ1 indicates that the terminal isocya-
nide of the starting p-ClC6H4CH2C(O)Mn(CO)4-
(CNC6H4-p-CH3) (1a) is no longer present. The 1H
NMR spectrum has signals in the aromatic region due
to the phenyl rings, as well as a methyl singlet at 2.25
ppm due to the p-tolyl group. The diastereotopic
benzylic protons appear as an AB quartet centered
/
/
/
/
/
N1ÃC40 of
/
103.6(2), 114.7(2) and 117.8(2)8, respectively, define a
distorted tetrahedral geometry about nitrogen with the
lone pair at the fourth vertex. Adams and Huang have
reported a related structure of a metalated pyridine
formed by a 1,4-cycloaddition of an alkyne to the
enamine grouping in a five-membered cyclomangana
enamine ring of a dimeric manganese complex [3a].
2.1.1.3. Phenylacetylene. Four regioisomeric products
are possible from the reaction of 1 with phenylacetylene
(Scheme 4): A, B, C, and D resulting from head-to-tail,
tail-to-tail, head-to-head, and tail-to-head coupling,
respectively.
When 1a was stirred at 60 8C in THF in the presence
of 2 equiv. of phenylacetylene, IR analysis showed the
disappearance of 1a and the presence of product 3a.
Spectral data (Table 1) are consistent with the formation
of regioisomer D. The IR spectrum displays three bands
in the terminal CO region. The h5-azacyclohexadienyl
ligand proton resonances appear as singlets at 6.00 and
5.04 ppm. Evidence for the assignment of regioisomer D
as the structure of 3a was obtained by employing the
around 3.68 ppm having Jꢀ
15 Hz. The 13C spectrum of
/
2a is only somewhat informative; it contains signals in
the aromatic region due to the phenyl rings. Signals at
20.5 and 40.1 ppm arise from methyl and methylene
carbons, respectively, and five signals at 70.6, 81.8,
106.8, 108.8, and 110.4 ppm are assigned to the five
carbons of the h5-azacyclohexadienyl ligand. These five
signals are in the same range as those previously
reported for unsymmetrically substituted h5-cyclopen-
tadienyl ligands on manganese as well as h5-cyclohex-
adienyl manganese tricarbonyl [9]. The 13C spectrum
displays one signal for the three carbonyl carbons which
1Hꢁ1
H COSY experiment [11]. Regioisomer C was ruled
/
out on the basis of the 1H NMR spectrum. The
spectrum lacks signals indicative of three-bond coupling
between protons on adjacent carbons of the azacyclo-
hexadienyl ligand which would be anticipated for C. The
COSY spectrum (Fig. 2) displays symmetrically dis-
posed crosspeaks (X) between the benzylic protons and
the azacyclohexadienyl proton at 5.04 ppm.
Crosspeaks (Y) are also present between the two
azacyclohexadienyl protons. These two sets of symme-
trically disposed crosspeaks (X) and (Y) can be ex-
plained by considering that electron delocalization
throughout the five-carbon skeleton of the azacyclohex-
adienyl ligand provides a mechanism by which the
nuclear spins (four bonds removed in both cases) can
remains unchanged down to ꢃ
/
56 8C in CDCl3 [10],
indicating facile CO exchange.
2.1.1.2. Structure of [1-p-(methoxyphenyl)-2-benzyl-
3,4,5,6-tetraphenyl-h5-azacyclohexadienyl]manganese
tricarbonyl (2b). The molecular structure of 2b was

422
C.L. Homrighausen et al. / Inorganica Chimica Acta 334 (2002) 419ꢁ436
/
Table 1
Spectral data for compounds 2a, 2b, 3a, 3b, 4, 5aꢁc, 6 and 7
/
a,b
c
d,e
Compound IR
(cmꢃ1
)
1H NMR
13C NMR
2a
2b
2017 (vs), 1962
(m), 1936 (s)
7.53ꢁ
/
6.29 (m) (C6H5, C6H4), 3.68 (AB, q,
221.5 (CO), 152.9, 140.2, 136.9, 134.9, 134.3, 134.1, 132.6, 132.4,
132.1, 131.6, 130.8, 129.9, 129.3, 128.9, 128.5, 128.3, 128.1, 128.0,
127.7, 127.5, 127.4, 127.1, 127.0, 126.7, 125.9, 117.6 (Ph), 110.4,
108.8, 106.8, 81.8, 70.6 (h5-azacyclohexadienyl), 40.1 (CH2), 20.5
(Me)
Jꢀ15 Hz) (CH2), 2.24 (s) (CH3)
2015 (vs), 1957 (s), 7.23ꢁ
1928 (m) Jꢀ15 Hz) (CH2), 3.73 (s) (OCH3)
/
6.39 (m) (C6H5, C6H4), 3.69 (AB, q,
221.9 (CO), 154.6, 148.4, 138.5, 135.3, 134.5, 132.1, 131.9, 130.2,
127.9, 127.7, 127.6, 127.5, 127.3, 126.7, 125.8, 119.8 (Ph), 113.6,
108.8, 107.2, 87.9, 74.8 (h5-azacyclohexadienyl), 55.4 (OMe),
40.5 (CH2)
3a
3b
4
2019 (s), 1955 (s), 7.67ꢁ
1947 (sh, m)
/
6.75 (m) (C6H5, C6H4), 6.05 (s) (H), 5.01 150.8, 139.2, 136.6, 133.8, 132.1, 131.8, 129.3, 128.9, 128.4, 127.0,
(s) (H), 3.86 (AB, q, Jꢀ17.5 Hz) (CH2), 2.20 (s) 126.9, 123.6 118.5 (Ph), 99.2, 89.6, 87.5, 86.4, 77.3 (h5-
(CH3)
2018 (vs), 1954 (s), 7.70ꢁ
1946 (sh, m)
azacyclohexadienyl), 39.9 (CH2), 20.5 (Me)
/
6.65 (m) (C6H5, C6H4), 6.03 (s) (H), 4.93 155.3, 145.4, 138.4, 136.3, 133.5, 132.7, 131.3, 128.6, 128.4, 128.3,
(s) (H), 3.80 (s) (CH2), 3.69 (s) (OCH3)
127.9, 126.7, 126.5, 123.3, 120.9 (Ph), 113.5, 98.4, 88.5, 85.6, 78.7
(h5-azacyclohexadienyl), 54.9 (OMe), 39.2 (CH2)
6.55 (m) (C6H4), 3.94 (s) (OCH3), 3.74 (s) 171.6, 167.7 (CÄO), 147.9, 136.0, 133.7, 132.9, 130.9, 129.5,
2036 (vs), 1977 (s), 7.43ꢁ
1959 (s)
(OCH3), 3.45 (AB, q, Jꢀ15 Hz ) (CH2), 2.48 128.3, 119.6 (Ph), 114.9, 107.5, 101.3, 92.9, 65.4 (h5-azacyclo-
(s) 2.24 (s) 2.03 (s) (CH3) hexadienyl), 53.2, 51.4 (OMe), 36.6 (CH2), 20.7, 17.9, 17.3 (Me)
2015 (vs), 1946 (s), 7.46ꢁ6.47 (m) (C6H4), 4.02 (s) (OCH3), 3.69 (s)
1936 (s) (OCH3), 3.17 (AB, q, Jꢀ16 Hz) (CH2), 2.66 (s)
2.35 (s) 1.81 (s) (CH3)
2016 (vs), 1941 (s), 7.18ꢁ
6.51 (m) (C6H4), 3.84 (AB, q, Jꢀ15 Hz) 185.4 (CÄN(ꢂ)), 169.0, 168.6, (CÄO), 139.4, 138.7, 133.3, 132.5,
1927 (s)
(CH2), 3.60 (s) (OCH3), 3.35 (s) (OCH3), 2.57 130.0, 129.8, 128.8, 124.9 (Ph), 109.9, 99.7, 85.7, 65.8 (h4-
/
5a
5b
/
/
(s) 2.43 (s) 2.28 (s) (CH3)
azacyclohexadienyl), 51.0, 50.5 (OMe), 37.2 (CH2), 29.6, 21.1,
17.3 (Me)
5c
6
2007 (vs), 1930 (s), 7.28ꢁ
1919 (s), (OCH3), 3.48 (AB, q, Jꢀ5 Hz) (CH2), 2.75 (s)
2.37 (s) 1.53 (s) (CH3)
2028 (vs), 1956 (s), 7.19ꢁ
6.67 (m) (C6H4), 3.96 (AB, q, Jꢀ15 Hz) 187.3 (CÄN(ꢂ)), 167.4, 166.9, 166.5, 166.2 (CÄO), 140.0, 137.6,
1949 (sh, m)
/
6.71 (m) (C6H4), 3.88 (s) (OCH3), 3.74 (s)
/
(CH2), 3.96 (s) 3.80 (s), 3.63 (s) 3.42 (s) (OCH3), 133.4, 131.6, 130.3, 128.8, 125.0, 113.0 (Ph), 108.7, 98.7, 79.0,
2.35 (s) (CH3)
60.3 (h4-azacyclohexadienyl), 53.7, 53.4, 51.7, 51.3 (OMe), 37.0
(CH2), 29.7, 21.3 (Me)
7
2090 (m), 2010 (s, 7.19ꢁ
sh), 2006 (vs), 1980 (CH3)
(s)
/
6.62 (m) (C6H4), 3.89 (s) (CH2), 2.34 (s) 215.4, 209.2 (CO), 183.9 (CÄN), 149.5, 137.2, 133.9, 132.9, 130.4,
128.9,120.1, 38.8 (CH2), 20.9 (CH3)
a
b
c
In hexane. vs, very strong; s, strong; m, medium; sh, shoulder.
CO stretching frequencies.
In CDCl3 shifts reported in ppm downfield from internal TMS standard. m, multiplet; s, singlet; d, doublet; q, quartet.
Shifts reported in ppm relative to central deuterated chloroform peak.
No resonance around 200 ppm for the carbonyl carbons of 3a, 3b, 4, and 5b could be discerned, probably due to a combination of relaxation
d
e
time and quadrupolar coupling effects.
communicate. This form of J-coupling could be con-
sidered somewhat analogous to the four-bond coupling
observed in allylic systems [11b,12]. Moreover, regioi-
somer D is the only isomer in which four-bond separa-
tion exists for both sets of coupled nuclei. The 13C
spectrum of 3a contains signals in the aromatic region
due to the phenyl rings. Signals at 20.5 and 39.9 ppm
due to the methyl and methylene carbons, respectively
are observed. Five signals at 77.3, 86.4, 87.5, 89.6, and
99.2 ppm are assigned to the five h5-azacyclohexadienyl
carbons. The signals attributed to carbons C3 (89.6
ppm) and C5 (86.4 ppm) were unambiguously identified
using a 2D HETCOR experiment [13]. Signals for
quaternary carbons in the 2, 4, and 6 positions are not
detected by the 2D HETCOR experiment.
2.1.1.4. Structure
of
[1-p-(methoxyphenyl)-2-p-
(chlorobenzyl)-3,5-dihydro-4,6-diphenyl-h5 -azacyclo-
hexadienyl]manganese tricarbonyl (3b). The molecular
structure of 3b (derived from 1b) was determined by
single-crystal X-ray diffraction analysis. An ORTEP
drawing for 3b is presented in Fig. 3.
Selected bond lengths and angles are presented in
Table 2. The main structural features of 3b are similar to
those of 2b. The dihedral angle of 44.8(3)8 between the
planes defined by C4Ã
/
C5Ã
/
C6Ã
/
C7Ã
/
C8 and by C8Ã
/
N1Ã
/
C4 differs from that in 2b (55.68) by 10.88. This could be
attributed to the difference in steric demands imposed
by the greater number of phenyl groups in 2b. The five-
carbon segment of the h5-azacyclohexadienyl ligand is
essentially planar with a mean deviation from planarity

C.L. Homrighausen et al. / Inorganica Chimica Acta 334 (2002) 419ꢁ
/436
423
Scheme 4.
analogous to A, B, C, D of Scheme 4 depending on the
coupling mode of the alkynes. In fact, we have isolated
and characterized all four regioisomeric products, 4, 5a,
5b and 5c (vide infra). When 1a was stirred at 65 8C in
THF in the presence of 2 equiv. of methyl 2-butynoate,
IR analysis showed the disappearance of 1a and the
presence of a complex mixture. Chromatography on
grade II acidic alumina eluting with 60/40 methylene
chloride/hexane gave a yellow band eventually identified
Fig. 1. ORTEP drawing for complex 2b. Hydrogen atoms omitted for
clarity.
˚
of 0.016 A. As in 2b, bond lengths between C4Ã
/
C5, C5Ã
C8 are intermediate between
carbon single and double bonds implying
delocalization throughout the five-carbon skeleton of
the ring. Angles C4ÃN1ÃC8, C4ÃN1ÃC28, C8ÃN1Ã
/
as
[1-(p-tolyl)-2-(p-chlorobenzyl)-3,5-dimethyl-4,6-
C6, C6Ã
/
C7, and C7Ã
/
bis(carbomethoxy)-h5-azacyclohexadienyl]manganese
tricarbonyl (4). Spectral data (Table 1) are consistent
with the structure depicted for 4 in Scheme 3.
carbonÃ
/
/
/
/
/
/
/
C28 of 103.8(3), 116.0(3) and 117.2(3)8, respectively,
are consistent with distorted tetrahedral geometry about
nitrogen with the lone pair at the fourth vertex.
2.1.1.6. Structure of [1-(p-tolyl)-2-(p-chlorobenzyl)-
3,5-dimethyl-4,6-bis(carbomethoxy)-h5 -azacyclohexa-
dienyl]manganese tricarbonyl (4). The molecular struc-
ture of 4 was determined by a single-crystal X-ray
diffraction study. An ORTEP drawing for 4 is presented
in Fig. 4. The h5-heterocycle features tail-to-head
2.1.1.5. Methyl 2-butynoate. The reaction of the un-
symmetrical alkyne methyl 2-butynoate with 1a could
also be expected to lead to four regioisomeric products
Table 2
Selected bond distances (A) and angles (8) and their estimated standard deviations for compounds 2b, 3b, 4 and 7
˚
2b
3b
4
7
Bond distances
N1ÃC4
N1ÃC8
C4ÃC5
C5ÃC6
C6ÃC7
1.460(3)
1.455(3)
1.422(4)
1.441(4)
1.445(4)
1.405(4)
2.165(3)
2.150(3)
2.151(3)
2.145(3)
2.246(3)
1.470(5)
1.457(5)
1.418(5)
1.430(5)
1.451(5)
1.386(5)
2.205(4)
2.137(4)
2.157(4)
2.134(4)
2.228(4)
1.446(3)
1.453(3)
1.422(3)
1.438(3)
1.443(3)
1.405(3)
2.144(2)
2.140(2)
2.154(2)
2.158(2)
2.208(3)
N1ÃC5
C5ÃC6
C6ÃC7
C6ÃC8
C7ÃC9
Mn1ÃC1
Mn1ÃC2
Mn1ÃC3
Mn1ÃC4
Mn1ÃN1
Mn1ÃC7
1.296(2)
1.471(2)
1.356(2)
1.512(2)
1.507(2)
1.821(2)
1.847(2)
1.872(2)
1.852(2)
2.031(1)
2.039(1)
C7ÃC8
MnÃC4
MnÃC5
MnÃC6
MnÃC7
MnÃC8
Bond angles
C1ÃN1ÃC4
C1ÃN1ÃC8
C4ÃN1ÃC8
C7ÃC8ÃN1
N1ÃC8ÃC2
C7ÃC8ÃC2
114.7(2)
117.8(2)
103.6(2)
117.0(3)
115.5(3)
125.5(3)
116.0(3)
117.2(3)
103.8(3)
119.6(3)
113.9(3)
123.0(4)
116.8(2)
117.9(2)
103.6(2)
115.9(2)
117.6(2)
122.5(2)
Mn1ÃN1ÃC5
Mn1ÃN1ÃC10
Mn1ÃC7ÃC6
C10ÃN1ÃC5
N1ÃC5ÃC6
118.2(1)
121.7(1)
114.8(1)
120.1(1)
113.8(1)
114.2(1)
C5ÃC6ÃC7
(1) C40 for 2b, C28 for 3b, C24 for 4. (2) C33 for 2b, C21 for 3b, C17 for 4.

424
C.L. Homrighausen et al. / Inorganica Chimica Acta 334 (2002) 419ꢁ436
/
Fig. 2. 1Hꢁ1
H COSY spectrum for complex 3a.
/
Fig. 3. ORTEP drawing for complex 3b. All hydrogen atoms except
those on C5 and C7 removed for clarity.
Fig. 4. ORTEP drawing for complex 4. Hydrogen atoms removed for
clarity.

C.L. Homrighausen et al. / Inorganica Chimica Acta 334 (2002) 419ꢁ
/436
425
coupling of the two alkynes analogous to regioisomer D
of Scheme 4. Selected bond lengths and angles are
presented in Table 2. In 4, the dihedral angle between
the planes defined by C4Ã
/
C5Ã
/
C6Ã
/
C7Ã
/
C8 and by C8Ã
/
N1ÃC4 is 52.9(2)8. As observed in the related structures,
/
the h5-azacyclohexadienyl ligand is essentially planar
with a mean deviation from planarity of 0.024 A. The
˚
other structural features of 4 are similar to those of 2b
and 3b.
2.1.2. Formation of h4-azacyclohexadienyl complexes
2.1.2.1. Methyl 2-butynoate. As described above, the
reaction of 1a with 2 equiv. of methyl 2-butynoate led to
a complex mixture as determined by IR analysis.
Chromatography on grade II acidic alumina and elution
with 60/40 methylene chloride/hexane removed 4, while
elution with 75/25 methylene chloride/hexane gave a
second (orange) band. Removal of solvent in vacuo and
recrystallization from methylene chloride/hexane (1/2)
gave an orange solid. 1H NMR analysis showed 10
methyl signals in the same region of the spectrum as the
methyl groups for compound 4. Therefore, the mixture
was believed to contain two regioisomeric azacylohex-
adienyl complexes. Fractional recrystallization from
Fig. 5. ORTEP drawing for complex 5a. Hydrogen atoms removed for
clarity.
adienyl ligand, formed from the coupling of a (p-
tolyl)iminoacyl group and two molecules of methyl 2-
butynoate in tail-to-tail fashion on manganese. The
four-carbon segment of the h4-azacyclohexadienyl li-
gand consists of three carbons arising from alkynes plus
the iminoacyl C; it is essentially planar with a mean
hexane at ꢃ78 8C gave 5b and 5c (vide infra).
/
Elution with THF gave a third (yellow) band.
Removal of solvent in vacuo and recrystallization
from methylene chloride/hexane (1/2) gave a yellow
solid (5a). Spectral data (Table 1) were consistent with
data for the previously described h5-azacyclohexadienyl
complexes. The small amounts of compound 5a isolated
have prevented acquisition of a 13C NMR spectrum.
Only upon completion of a single crystal X-ray diffrac-
tion study (vide infra) was discovered that compound 5a
is an h4-azacyclohexadienyl complex (Scheme 5).
˚
deviation from planarity of 0.009 A. The dihedral angle
is 48.2(1)8 between the planes defined by C5ÃC6ÃC7Ã
C8 and by C5ÃC4ÃN1ÃC8. Bond lengths between C4Ã
C5, C5ÃC6, and C7ÃC8 of 1.465(3), 1.482(3), 1.462(3)
A, respectively, could be described as short CÃC single
bonds while the bond distance for C6ÃC7 of 1.401(3) A
may best be described as a long carbonÃcarbon double
bond (vide infra). The bond length between N1 and C4
/
/
/
/
/
/
/
/
/
˚
/
˚
/
/
˚
of 1.307(3) A is indicative of an NÃ
/
C double bond. The
2.1.2.2. Structure of [1-(p-tolyl)-2-(p-chlorobenzyl)-
3,6-dimethyl-4,5-bis(carbomethoxy)-h4 -azacyclohexa-
dienyl]manganese tricarbonyl (5a). The molecular struc-
ture of 5a was determined by a single-crystal X-ray
diffraction study. An ORTEP drawing for 5a is presented
in Fig. 5. Selected bond lengths and angles are presented
in Table 3. The complex contains an h4-azacyclohex-
through-space distance between C4 and manganese is
˚
2.991 A, well outside the accepted bonding distance of
manganeseÃcarbon single bonds. Angles C4ÃN1ÃC8,
C4ÃN1ÃC24, C8ÃN1ÃC24 of 116.3(2), 122.6(2) and
/
/
/
/
/
/
/
120.0(2)8, respectively, demonstrate trigonal planar
geometry about nitrogen.
Scheme 5.

426
C.L. Homrighausen et al. / Inorganica Chimica Acta 334 (2002) 419ꢁ436
/
Table 3
2.1.2.3. Structure of [1-(p-tolyl)-2-(p-chlorobenzyl)-
4,5-dimethyl-3,6-bis(carbomethoxy)-h4 -azacyclohexa-
dienyl]manganese tricarbonyl (5b). The molecular struc-
ture of 5b was determined by a single-crystal X-ray
diffraction analysis. An ORTEP drawing for 5b is
presented in Fig. 6. Selected bond lengths and angles
are presented in Table 3. The complex contains a h4-
azacyclohexadienyl ligand, formed from the coupling of
two molecules of methyl 2-butynoate in head-to-head
fashion and a p-tolyl(iminoacyl) group on manganese.
The four-carbon segment of the h4-azacyclohexadienyl
ligand consists of carbons arising from the two alkynes;
it is essentially planar with a mean deviation from
˚
Selected bond distances (A) and angles (8) and their estimated standard
deviations for compounds 5a, 5b, 5c and 6
5b
5c
5a
6
Bond distances
N1ÃC4
N1ÃC8
C4ÃC5
C5ÃC6
C6ÃC7
C7ÃC8
MnÃC4
MnÃC5
MnÃC6
MnÃC7
MnÃC8
1.465(3)
1.305(3)
1.464(4)
1.394(4)
1.491(4)
1.458(3)
2.079(3)
2.089(3)
2.089(3)
2.130(2)
1.311(3)
1.486(4)
1.459(4)
1.479(4)
1.402(4)
1.460(4)
1.307(3)
1.480(3)
1.465(3)
1.482(3)
1.401(3)
1.462(3)
1.471(3)
1.304(3)
1.458(3)
1.406(3)
1.478(3)
1.464(3)
2.090(2)
2.078(2)
2.058(2)
2.149(2)
a
a
2.976
2.991
2.145(3)
2.058(3)
2.104(3)
2.105(3)
2.147(2)
2.082(2)
2.068(2)
2.104(2)
˚
planarity of 0.003 A. The dihedral angle is 48.9(2)8
a
a
2.985
2.995
between the planes defined by C4Ã
C4ÃN1ÃC8ÃC7. Bond lengths between C4Ã
C7, and C7Ã
respectively, could be described as short CÃ
bonds while the bond distance for C5Ã
may best be described as a long CÃC double bond (vide
infra). The bond length between N1 and C8 of 1.305(3)
/
C5Ã
/
C6Ã
/
C7 and by
/
/
/
/
C5, C6Ã
/
Bond angles
C24ÃN1ÃC4
C24ÃN1ÃC8
C4ÃN1ÃC8
C7ÃC8ÃN1
N1ÃC8ÃC17
C7ÃC8ÃC17
˚
118.9(2)
123.0(2)
115.1(2)
114.5(2)
121.2(3)
123.5(3)
122.2(2)
119.7(2)
117.1(2)
112.0(2)
115.8(2)
118.4(2)
122.6(2)
120.0(2)
116.3(2)
110.7(2)
114.8(2)
119.0(2)
120.0(2)
123.9(2)
115.0(2)
115.0(2)
122.0(2)
122.4(2)
/
C8 of 1.464(4), 1.491(4), 1.458(3) A,
/C single
/C6 of 1.394(4)
/
˚
A is indicative of an NÃ
/
C double bond. The through-
˚
a
Indicates through space distance.
space distance between C8 and manganese is 2.985 A,
well outside the accepted bonding distance of man-
Spectral data for 5a (Table 1) are similar to data for
the previously described h5-azacyclohexadienyl com-
plexes. The complex displayed H NMR signals in the
ganeseÃ
/
carbon single bonds. Angles C4Ã
/
N1Ã
/
C8, C4Ã
/
N1ÃC24, C8Ã
/
/
N1ÃC24 of 115.1(2), 118.9(2) and
/
1
123.0(2)8, respectively, demonstrate trigonal planar
geometry about nitrogen.
aromatic region due to the phenyl rings. Singlets at 4.02,
3.69, 2.66 and 2.35 ppm are attributed to the carbo-
methoxy methyl and azacylohexadienyl ring methyl
groups, respectively. A singlet at 1.81 ppm is assigned
to the p-tolyl methyl group. The diastereotopic benzylic
protons appear as an AB quartet centered around 3.17
Spectral data for 5b (Table 1) are consistent with data
for previously described azacyclohexadienyl complexes.
The complex displayed 1H NMR signals in the aromatic
region due to the phenyl rings. Singlets at 3.60, 3.35,
2.57 and 2.43 ppm are attributed to the carbomethoxy
methyl and azacylohexadienyl ring methyl groups,
respectively. A singlet at 2.28 ppm is assigned to the
p-tolyl methyl group. The diastereotopic benzylic pro-
tons appear as an AB quartet centered around 3.84 ppm
ppm having Jꢀ16 Hz.
/
having Jꢀ
15 Hz. The 13C spectrum contains signals in
/
the aromatic region due to phenyl rings. Signals at 21.1
and 37.2 ppm are due to p-tolyl methyl and methylene
carbons, respectively. Signals at 51.0, 50.5, and at 169.0,
168.6 ppm were attributed to the carbomethoxy methyl
and carbomethoxy carbonyl carbons, respectively. Four
signals at 65.8, 85.7, 99.7 and 109.9 ppm were assigned
to the h4-azacyclohexadienyl ligand carbons. A signal at
185.4 ppm (not seen in the 13C spectra of the h5
derivatives) has been assigned to the quaternary carbon
of the imine. It seems reasonable, based on deshielding
arguments, that a quaternary carbon of an imine
containing a nitrogen atom with a formal charge of
(ꢂ1) would resonate further downfield from TMS than
/
the carbonyl carbons of the azacyclohexadienyl ligand.
Liu et al. recently reported that the 13C resonance for
the imine-carbon of a number of N-tert-butanesulfinyl
imines ranges from d 151.1 to 192.4 ppm [14]. The
position of this signal suggests that the compound
Fig. 6. ORTEP drawing for complex 5b. Hydrogen atoms removed for
clarity.

C.L. Homrighausen et al. / Inorganica Chimica Acta 334 (2002) 419ꢁ
/436
427
contains an h4-azacyclohexadienyl ligand as shown in
Scheme 5.
2.1.2.4. Structure of [1-(p-tolyl)-2-(p-chlorobenzyl)-
4,6-dimethyl-3,5-bis(carbomethoxy)-h4 -azacyclohexa-
dienyl]manganese tricarbonyl (5c). The small amounts
of 5c isolated have prevented determination of a 13C
NMR spectrum. Only upon completion of a single
crystal X-ray diffraction study (vide infra) was it
discovered this compound was a h4-azacyclohexadienyl
complex (Scheme 5).
An ORTEP drawing for 5c is presented in Fig. 7.
Selected bond lengths and angles are presented in Table
3. This complex also contains a h4-azacyclohexadienyl
ligand, formed from the coupling of a p-tolyl(iminoacyl)
group and two molecules of methyl 2-butynoate in a
head-to-tail fashion on manganese. The four-carbon
segment of the h4-azacyclohexadienyl ligand contains
three carbons arising from alkynes plus the iminoacyl
carbon; it is essentially planar with a mean deviation
Scheme 6.
2.1.2.5. Dimethylacetylene dicarboxylate (DMAD).
When 1a was warmed to 60 8C in the presence of 2
equiv. of DMAD for a 3-h period, IR analysis showed
the complete disappearance of 1a and appearance of the
coupling product 6 (Scheme 6).
Spectral data (Table 1) for the product were consis-
tent with data for the previously described h4-azacyclo-
hexadienyl complexes. The 13C spectrum contains
signals 60.3, 79.0, 98.7, and 108.7 ppm assigned to the
h4-azacyclohexadienyl ligand carbons. A signal at 187.3
ppm has been assigned to the quaternary carbon of the
imine. The position of this signal suggests that 6
contains a h4-azacyclohexadienyl ligand. It was not
until completion of a single crystal X-ray diffraction
study (vide infra) that we confirmed that this compound
was indeed a h4-azacyclohexadienyl complex.
˚
from planarity of 0.016 A. The dihedral angle is 46.6(2)8
between the planes defined by C5Ã
C5ÃC4ÃN1ÃC8. Bond lengths between C4Ã
C6, and C7Ã
respectively, could be described as short CÃ
bonds while the bond distance for C6Ã
may best be described as a long CÃ
infra). The bond length between N1 and C4 of 1.311(3)
/
C6Ã
/
C7Ã
/
C8 and by
/
/
/
/
C5, C5Ã
/
˚
/
C8 of 1.459(4), 1.479(4), 1.460(4) A,
/
C single
˚
C7 of 1.402(4) A
/
2.1.3. Structure of [1-(p-tolyl)-2-(p-chlorobenzyl)-
3,4,5,6-tetrakis(carbomethoxy)-h4-azacyclohexa-
dienyl]manganese tricarbonyl (6)
The molecular structure of 6 was determined by
single-crystal X-ray diffraction analysis. An ORTEP
drawing for 6 is presented in Fig. 8. Selected bond
lengths and angles are presented in Table 3.
/C double bond (vide
˚
A is indicative of an NÃ
/
C double bond. The through-
˚
space distance between C4 and manganese is 2.976 A,
well outside the accepted bonding distance of man-
ganeseÃ
/
carbon single bonds. Angles C4Ã
/
N1Ã
/
C8, C4Ã
/
N1ÃC24, C8Ã
/
/
N1Ã
/
C24 of 117.1(2), 122.2(2) and
119.7(2)8, respectively, demonstrate trigonal planar
geometry about nitrogen.
Fig. 8. ORTEP drawing for complex 6. Hydrogen atoms removed for
clarity.
Fig. 7. ORTEP drawing for complex 5c. Hydrogen atoms removed for
clarity.

428
C.L. Homrighausen et al. / Inorganica Chimica Acta 334 (2002) 419ꢁ436
/
The complex contains a h4-azacyclohexadienyl ligand
assigned an oxidation state of (ꢃI) (Scheme 7). In this
/
resulting from the coupling of two molecules of DMAD
and a (p-tolyl)iminoacyl group on manganese. All four
carbons coordinated to Mn arise from alkynes. The
dihedral angle is 46.3(1)8 between the planes defined by
view 5a, 5b, 5c and 6 would be diene-substituted
pentacarbonyl manganates. However, the negative for-
mal charge on manganese implies a buildup of electron
density on the metal. The positions of CO bands in the
IR spectrum are sensitive to electron density on the
metal. For example, nCO is approximately 1860 cmꢃ1 in
[Mn(CO)5]ꢃ and might be expected to be even lower if
two CO’s were replaced by a diene which is a weaker p-
acid, although this effect would be mitigated by the
formal positive charge on Mn. Brookhart et al. [16] have
prepared Liꢂ[Mn(CO)3(cyclohexadiene)]ꢃ which is ex-
pected to exhibit ion pairing; the CO stretches in this
compound occur at 1929, 1896, 1853, 1832, 1811 and
C4Ã
/
C5Ã
/
C6Ã
/
C7 and by C4Ã
/
N1Ã
/
C8Ã
/
C7. The four-
carbon segment of the h4-azacyclohexadienyl ligand is
essentially planar with a mean deviation from planarity
˚
of 0.017 A. Bond lengths between C4Ã
/
C5, C6Ã
/
C7, and
˚
C8 of 1.458(3), 1.478(3), 1.464(3) A, respectively,
could be described as short CÃ
C7Ã
/
/C single bonds. The bond
˚
C6 of 1.406(3) A may best be described
distance for C5Ã
as a long CÃC double bond (vide infra). The bond
length between N1 and C8 of 1.304(3) A is indicative of
an NÃC double bond. Angles C4ÃN1ÃC8, C4ÃN1Ã
C24, C8Ã C24 of 115.0(2), 120.0(2) and 123.9(2)8,
/
/
˚
1758 cmꢃ1
.
/
/
/
/
/
/
N1Ã
/
However, the positions of the CO bands for our
complexes are in the same range as the previously
described h5-azacyclohexadienyl complexes. Since these
complexes are straightforwardly formulated as Mn(I)
species, a formulation for the h4-complexes different
from that just described seems to be required.
respectively, are indicative of trigonal planar geometry
about nitrogen.
2.1.3.1. Electronic structure of h4-azacyclohexadienyl
complexes. Examination of the CÃ/C bond lengths
(Table 3) in the manganese-bound four-carbon segment
of the ring for compounds 5a, 5b, 5c, and 6 suggests that
two formulations of the electronic structure are possible
as depicted in Scheme 7.
2.1.3.3. Formulation B. Reexamination of the bond
lengths (Table 3) of the ring for compounds 5a, 5b, 5c
and 6 suggests a different interpretation. Since the
2.1.3.2. Formulation A. If all the CÃ
/
C bond lengths in
internal CÃ
6 and C6ÃC7 in 5a and 5c are significantly shorter than
the other CÃC bonds of the four-carbon skeleton, they
may be interpreted as long CÃC double bonds. Then the
/
C bond lengths between C5Ã/C6 in 5b, and
the four-carbon segment are interpreted as intermediate
between single and double bonds, this moiety would
consist of a neutral delocalized skeleton with a hapticity
/
/
/
of four, isolobal with butadiene. The MnÃ
/
C bond
lengths of the h4-four carbon skeleton in 5a, 5b, 5c
and 6 do differ relatively in the same manner as the
end carbons of the four-carbon skeleton would be
considered carbanionic in character. This results in a
formal charge of ꢃ
2 on the h4-manganese-bound
portion of the azacyclohexadienyl ligand. A positively
charged quaternary nitrogen atom and manganese with
/
median MnÃ
/
C bond lengths in h4-1,3-butadiene com-
/ /
plexes (R2C1C2RC2RC1R2) where MnÃ
C1 and MnÃ
C2
˚
are 2.135 and 2.071 A, respectively, lending credence to
this view [15]. The bond lengths between nitrogen and
the non-metalated carbon (C4 in 5a and 5c and C8 in 5b
an oxidation state of (ꢂI) results in an overall neutral
/
species (Scheme 7). This latter formulation is in agree-
ment with the observed positions of the CO bands in the
IR spectra for compounds 5a, 5b, 5c and 6. Further-
and 6) are best described as carbonÃ/nitrogen double
bonds. This requires the formulation of a quaternary
nitrogen atom with a positive formal charge. Since the
molecule is overall neutral, then, in accordance with the
effective atomic number rule, manganese must be
more, the MnÃ
/
C5, MnÃ
/
C8 bond lengths in 5a and 5c
and the MnÃC4, MnÃ
/
/
C7 in 6 and 5b closely agree with
3
˚
C(sp ) median bond distance of 2.173 A [15]
approaching the metallacyclopentene extreme.
the MnÃ
/
The difference in the above two formulations is that
between the description of a C4H6 metal compound as
containing a neutral p-bound butadiene complex as
contrasted with a metallacyclopentene, Scheme 7. For-
mulation B seems reasonable based on the location of
the R groups on the ring of the h4-azacyclohexadienyl
ligand. In complexes 5a, 5b, 5c, and 6 the negative
charge on the formal carbanionic (end) carbons could be
stabilized by electron-withdrawing R groups.
Two important questions about these reactions are:
(1) What may be the mechanism of formation? (2) What
factors determine the h5- or h4-hapticity?
Scheme 7. Formulation of h4-4 complexes.

C.L. Homrighausen et al. / Inorganica Chimica Acta 334 (2002) 419ꢁ
/436
429
Scheme 8.
2.1.3.4. Reaction of 1a with hexafluoro-2-butyne. In an
attempt to determine if the change in hapticity from h5
to h4 occurs when electron-withdrawing alkynes are
employed, complex 1a was allowed to react with excess
hexafluoro-2-butyne [CF3CÅ/CCF3(g)] under 400 psi of
argon. The results are shown in Scheme 8. Spectral data
(Table 1) indicate that the product (7) is different from
the previously described h5- and h4-azacyclohexadienyl
complexes. Most notable is that the IR spectrum shows
four bands in the terminal CO region typical of cis-
disubstituted octahedral geometry. The 1H and 13C
NMR spectra were only somewhat informative; how-
ever, the high-resolution mass spectrum [Mꢂ 511]
indicated that only one molecule of hexafluoro-2-butyne
had been incorporated into 7.
Complex 7 is a mangana-azacyclopentadiene complex
in which one molecule of hexafluoro-2-butyne has
formally inserted into the manganeseÃ
bond. Delis et al. have observed insertion of acetylene
into the iminoacyl carbonÃPd bond of the cationic
complexes [NSNPdà NR)Me]X where (NSNꢀ
(C(Ä
bipy, phen; Rꢀ2,6-Me2C6H3; XꢀBF4) [5a]. Spectral
/
iminoacyl carbon
Scheme 9.
/
/
/
/
for 7, which was determined by a single-crystal X-ray
diffraction analysis. An ORTEP drawing for 7 is pre-
sented in Fig. 9. Selected bond lengths and angles are
presented in Table 2. Compound 7 exhibits structural
features consistent with those of other reported manga-
/
/
data (Table 1) are consistent with the structure depicted
nese metallacycles [1b,17]. The bond length between
˚
C double
N1Ã
/
C5 of 1.296(2) A is indicative of an NÃ
/
˚
bond. The C6Ã
/
C7 bond distance of 1.356(2) A provides
C double bond, demonstrating that
the alkyne has been transformed to an olefinic species.
evidence for a CÃ
/
2.1.3.5. Mechanism of h5-azacyclohexadienyl complex
formation. Scheme 9 depicts three possible pathways
for h5-azacyclohexadienyl complex formation.
Common to all pathways is thermal decarbonylation
of the starting acyl 1 which produces 9, which undergoes
a rapid and preferential insertion of isocyanide into the
MnÃ
/
benzyl carbon bond producing unsaturated 10.
Complex 10 then takes up a molecule of alkyne
producing 11. Complex 11 undergoes insertion of alkyne
into the MnÃ
/
iminoacyl carbon bond producing the five-
membered manganacyclic intermediate 12 analogous to
7. Deshong et al. [2b] have reported that alkynes are
capable of inserting into MnÃ
/
acyl carbon bonds to
Fig. 9. ORTEP drawing for complex 7. Hydrogen atoms removed for
clarity.
produce five-membered metallacyles in which the acyl

430
C.L. Homrighausen et al. / Inorganica Chimica Acta 334 (2002) 419ꢁ436
/
oxygen occupies a coordination site on manganese
analogous to 12. Here the paths branch. The route to
paths A and B (Scheme 9) involves nucleophilic
displacement of the iminoacyl nitrogen by another
molecule of alkyne producing 13. Complex 13 then
undergoes ring formation via one of two pathways. In
pathway A, attack by the iminoacyl nitrogen lone pair
upon the coordinated alkyne converts 13 to 14. Electro-
cyclic rearrangement leads to a species such as 19. Loss
of CO and a rearrangement similar to ring slippage
generates 8. Motz and Alexander [18] have observed
attack upon a coordinated isocyanide by an iminoacyl
nitrogen lone pair followed by rearrangement to gen-
erate a mangana-azacyclobutene ring. Alternatively, 13
could undergo ring formation via pathway B in which
Our results are not yet complete enough to verify the
regiochemistry or hapticity of 20. It is hoped that an X-
ray diffraction study on complex 20 will also provide the
answer to the second question regarding the change in
hapticity from h5 to h4, which is believed to occur when
electron-withdrawing alkynes are used in the coupling
reaction.
2.1.3.7. h4- versus h5-Coordination. The preference for
h4- as opposed to h5-coordination can be rationalized
by the notion that electron-withdrawing alkynes such as
dimethyl acetylene dicarboxylate are capable of stabiliz-
ing the formally carbanionic carbons of a metallacyclo-
pentene (formulation B, Scheme 7). Support for this
view comes from the fact that PhCÅ
/
CPh (containing
the coordinated alkyne inserts into the manganeseÃ
/vinyl
electron-rich phenyl groups) gives an h5-product
whereas DMAD (containing electron-poor carbo-
methoxy groups) gives an h4-product. In cases where
all ring substituents are not the same, composition of the
h4-group seems to be dictated by a preference for
placing electron-withdrawing groups at formally carba-
nionic carbons. If electron-withdrawing ability is con-
carbon bond producing 15. Electrocyclic rearrangement
leads to a species such as 19a?. CO loss and rearrange-
ment leads to 8. Washington et al. [19] have proposed
insertion of a coordinated alkyne into an osmiumÃ
/vinyl
bond of a metallaacylcyclobutene ring, followed by
reductive coupling in order to account for generation
of metalated cyclopentadienones. In pathway C, 12
undergoes substitution of CO by alkyne, generating
16. Insertion of the coordinated alkyne into the man-
sidered to decrease in the order
Ã
/
CO2MeÈÃ
/
CH2C6H4ClÈÃCH3, we can rationalize the fact that,
/
given the regiochemistry of alkyne couplings, methyl-
containing carbons are not part of the h4-moieties in 5a
/
ganeseÃ/vinyl carbon bond produces 17. Complex 17
attains an 18-electron configuration via p-donation
from one olefinic unit of the unsaturated metallocycle.
Electrocyclic rearrangement generates 8. Intermediates
somewhat analogous to 17 have been postulated in the
mechanism for the cobalt-catalyzed trimerization of
alkynes and nitriles to produce pyridines [20]. However,
p-donation from one olefinic unit is not required for
cobalt to attain an 18-electron configuration. We have
shown (vide infra) that complex 7 can be transformed to
a six-membered coupling product implying that com-
pounds analogous to 7 are intermediates along the
reaction pathway. ‘Unhooking’ one of the coordinated
C’s from 8 can lead to h4-products.
and 5c. Instead, the original iminoacyl C containing a Ã
CH2C6H4Cl group is included in the h4-moiety.
Interestingly, this interpretation does not find strong
confirmation in the values of IR CO stretching frequen-
cies. All the tricarbonyl compounds contain the ex-
pected three CO stretching bands: an A mode and the
two components of the split E mode (from C3n idealized
symmetry). The average of the three frequencies spans a
range of only 11 cmꢃ1 from the tetraphenyl compound
(2b; h5; 1967 cmꢃ1) to the tetrakis(carbomethoxy)
compound (6; h4;1978 cmꢃ1). This is perhaps an
example of the Electroneutrality Principle. Moreover,
comparison of the spectra of 5a and 5c, both of which
are h4 and both of which have Ã
CH2C6H4Cl at the formally ‘alkyl’ coordinated C’s
/
CO2Me and Ã
/
2.1.3.6. Reaction of 7 with phenyl acetylene. In an
attempt to demonstrate that an intermediate such as 7
occurs along the pathway to the azacyclohexadienyl
complexes, 7 was treated with phenylacetylene in
refluxing THF for 5 days. IR analysis showed almost
complete disappearance of 7 and the appearance of the
coupling product 20 (Scheme 10).
and which differ only in the regiochemistry at the CÃ
/
C formally double bond, reveals average values of nCO
of 1966 and 1952 cmꢃ1, respectively.
Brookhart [16], Pauson [21], Sweigart [22], Rose-
Munch [23] and their co-workers have reported the
preparation of a large number of h5-cyclopentadienyl
and h5-cyclohexadienyl complexes substituted at var-
ious positions on the rings; these were generally
prepared by nucleophilic additions to [(are-
ne)Mn(CO)3]ꢂ. Trends in the IR spectra on varying
ring substituents are not readily intelligible across a
broad range of compounds. For example [21a], Cp-
Mn(CO)3 displays nCO at 2015, 1945 and 1931 cmꢃ1 and
h5-[1,2-(CO2Me)-2-Ph-C5H2]Mn(CO)3 at 2041, 1982
and 1975 cmꢃ1, a trend in accord with expectation. In
Scheme 10. The regiochemistry and hapticity of 8 remain to be
determined.

C.L. Homrighausen et al. / Inorganica Chimica Acta 334 (2002) 419ꢁ
/436
431
contrast [21b], the trend in the IR spectra of h5-[1-Ph-2-
Cl-C6H4]Mn(CO)3 (nCO at 2025, 1958 and 1948 cmꢃ1
CO from 12 or of the imino nitrogen lone pair 13. See
Scheme 9.
)
and h5-[1-Ph-2-Cl-5-Me-C6H3]Mn(CO)3 (nCO at 2026,
1959 and 1947 cmꢃ1) is not readily rationalized. In some
cases the order of substituents in h5-rings does not
influence the CO stretching frequencies. For example
[21b], [2-Cl-4-Me-C6H4]Mn(CO)3 has nCO at 2024, 1957
and 1943 cmꢃ1 and [2-Me-4-Cl-C6H4]Mn(CO)3 has nCO
at 2025, 1955 and 1945 cmꢃ1. In contrast, [2-NMe2-4-
Me-C6H4]Mn(CO)3 has nCO at 1994 and 1911 cmꢃ1 and
[2-Me-4-NMe2-C6H4]Mn(CO)3 has nCO at 2007, 1928
4. Experimental
4.1. Procedures and materials
M.p.s were determined on a Mel-Temp apparatus
using open-ended capillaries and are uncorrected. NMR
spectra were recorded on a Bruker AM-250 spectro-
meter. Infrared solution spectra were recorded on a 1600
FTIR spectrophotometer. IR cells were 1.0 mm solution
cells with NaCl windows. High-resolution mass spectra
were recorded on a Kratos-80. Unless otherwise noted,
all reactions were performed in dry glassware under an
Ar atmosphere using standard Schlenk techniques.
Dimethylacetylene dicarboxylate and methyl 2-bu-
tynoate were purchased from Fischer Chemical Com-
pany and used as received. Phenylacetylene,
diphenylacetylene, p-chlorobenzyl chloride, hexa-
fluoro-2-butyne, and deuterochloroform were pur-
chased from Aldrich Chemical Company and
dimanganese decacarbonyl from Strem Chemical Com-
pany. All were used as received. p-Methoxyphenyl
isocyanide, p-tolyl isocyanide [24], p-chlorobenzyl man-
ganese pentacarbonyl [7], and (p-tolyl isocyanide)[(p-
chlorophenyl)acetyl]manganese tetracarbonyl [7] were
synthesized according to published procedures. Alumi-
num oxide 90, active acidic grade II (alumina) from EM
and 1918 cmꢃ1
.
Another possibility for explaining differences in the
IR spectra of the carboxymethyl complexes is to
examine how many groups are conjugated with the
rings. This involves looking at the solid-state structures;
there is, of course, no necessary correlation between
these structures and solution structures. Even here, no
trends are evident. The average values of nCO lie in the
order 6ꢀ
/
4ꢀ
/
5aꢀ
/
5bꢀ5c. The numbers of planar
/
(conjugated) carbomethoxy groups in the solid state
are three, one, one, two and one, respectively.
The results are consistent with kinetic control of the
regiochemistry of coupling and electronic as well as
steric control of the structure of the final product.
Unraveling the influences of these effects will require
examining coupling of a greater variety of unsymmetric
alkynes.
3. Conclusion
science and Silica Gel 60, 230ꢁ400 mesh, were used for
/
column chromatography. Tetrahydrofuran was distilled
from sodium benzophenone ketyl. All other laboratory
chemicals were reagent grade and used as received. The
Parr Bomb used for the preparation of 7 was purchased
from Parr Instrument Company, Inc.
Decarbonylation of the manganese acyl complex 1
followed by preferential insertion of aromatic isocya-
nides into manganeseÃ/alkyl carbon bonds generates an
unsaturated manganese (mono)iminoacyl intermediate
in situ. In the presence of alkynes both h5- and h4-
azacyclohexadienyl complexes are produced. When the
manganese acyl complex was allowed to react with 2
equiv. of the unsymmetrical aliphatic alkyne phenylace-
tylene only one regioisomer was produced, suggesting
that the coupling reaction is sensitive to steric factors.
When the manganese acyl complex was treated with 2
equiv. of methyl-2-butynoate, all four possible regioi-
somers were formed. The relative isolated yields of 4 and
4.1.1. X-ray diffraction studies of 2b, 3b, 4, 5a, 5b, 5c, 6
and 7
For X-ray examination and data collection, each
crystal was coated with a light film of epoxy resin and
mounted on a glass fiber. All data were collected using
graphite-monochromated Mo Ka radiation (Tables 4
and 5).
Intensity data for 2b, 3b, 5a and 7 were collected on a
Siemens SMART 1K CCD diffractometer [25]. The
detector was set at a distance of 5.00 cm from the
crystal. A series of data frames measured at 0.38
increments of v were collected with three different 2u
and f values to calculate a preliminary unit cell. For
data collection, frames were measured at 0.38 intervals
of v. In order to correct for high-energy backgrounds in
the images, data frames were collected as the sum of two
exposures and non-correlating events were eliminated.
The data frames were collected in distinct shells, with a
5aꢁc may not reflect their actual relative abundance in
/
the reaction mixture. Because of overlapping IR bands
no exact results are available. However, the relative
amounts in the reaction mixture are 5cꢀ
/
4Â
/
5aꢂ5b,
/
probably demonstrating no large steric influence on
regioselectivity. Reaction of 1a with the electron-with-
drawing alkyne CF3CÅ
unsaturated manganacycle 7 presumably because the
CF3 groups retard incor-
/CCF3 generates a five-membered
very electron-withdrawing Ã
/
poration of a second equivalent of alkyne because of
lower reactivity in nucleophilic displacement either of
maximum u value of approximately 288. The initial 50ꢁ
/

432
C.L. Homrighausen et al. / Inorganica Chimica Acta 334 (2002) 419ꢁ436
/
Table 4
Summary of crystallographic data for 2b, 3b, 4 and 5c
2b
3b
4
5c
Empirical formula
Molecular weight
Color, habit
C
719.7
46H34MnNO4
C34H25ClMnNO4
601.9
C28H25ClMnNO7
577.9
C28H25ClMnNO7
577.9
yellow plates
297
yellow plates
223
yellow rods
295
orange rods
296
Temperature (K)
¯
Space group
˚
Pbca
P21/c
/P1/
P21/c
a (A)
˚
11.1452(5)
19.1470(8)
34.911(2)
90.00
12.092(2)
19.707(4)
12.460(3)
90.00
8.471(4)
11.598(3)
14.867(5)
87.71(2)
85.12(3)
71.67(3)
1381.4(8)
2
16.232(3)
10.725(2)
16.515(3)
90.00
b (A)
˚
c (A)
a (8)
b (8)
g (8)
V (A )
Z
90.00
90.00
96.18(3)
90.00
111.78(3)
90.00
3
˚
7455.9(6)
8
2951.9(10)
4
0.576
2669.7(9)
4
0.642
Absorption coefficient 0.399
(mmꢃ1
0.620
)
Monochromator
Crystal size (mm)
2u range (8)
graphite
graphite
graphite
graphite
0.90ꢄ0.25ꢄ0.15
0.40ꢄ0.35ꢄ0.10
0.30ꢄ0.20ꢄ0.15
0.55ꢄ0.35ꢄ0.30
3.7ꢁ55.12
ꢃ135h 513, ꢃ235k 523, ꢃ165h 516, ꢃ265k 526, 05h 511, ꢃ145k 515,
4.26ꢁ/52.74
3.96ꢁ
/
56.44
/
4.64ꢁ55.12
/
Index ranges
05h 521, 05k 513,
ꢃ43/5l 523
42 327
ꢃ105l 516
19 985
7178
ꢃ195l 519
6789
6357
ꢃ215l 519
6365
6154
Reflections collected
Independent reflections 7611
Min./max. transmis-
sions
Variables
0.857/0.981
0.696/0.928
0.099/0.168
none
470
371
R1ꢀ0.0646, wR2ꢀ0.1034
R1ꢀ0.1965, wR2ꢀ0.1504
0.0924
0.0014(3)
0.582
343
R1ꢀ0.0477, wR2ꢀ0.1232
R1ꢀ0.0705, wR2ꢀ0.1452
0.0277
343
R1ꢀ0.0486, wR2ꢀ0.1066
R1ꢀ0.0890, wR2ꢀ0.1359
0.0167
R indices [I ꢀ2s(I)]
R indices (all data)
Rint
R1ꢀ0.0593, wR2ꢀ0.0904
R1ꢀ0.1302, wR2ꢀ0.1109
0.1002
Extinction coefficient
˚
Res. elec. den. (e A
0.00037(6)
0.307
none
0.494
none
0.562
ꢃ3
)
100 frames of the first data shell were recollected at the
end of the data collection to correct for crystal decay.
The data frames were processed using the program
SAINT [25]. Data were corrected for decay and Lp
effects. Semi-empirical absorption and beam corrections
were applied using SADABS [26].
Intensity data for compounds 4, 5b, 5c and 6 were
collected on a Siemens P3 diffractometer [25]. Lattice
parameters were obtained by least-squares refinement of
the angular settings from 40 reflections lying in a 2u
extinction correction of the form Fc*ꢀ
/
kFc[1ꢂ
/
0.001xFc l3/sin(2u)]ꢃ1/4 was used for compounds 2b
and 3b. For compound 7 all hydrogen atoms were
located directly from the difference map, while in all
other structures hydrogen atom positions were located
directly or calculated based on geometric criteria. All
hydrogen atoms were allowed to ride on their respective
atoms with the exception of compound 3b in which H5
and H7 were fixed where located. Hydrogen atom
2
isotropic temperature factors were defined as U(C)aꢀ
/
range of 10ꢁ
/
308. Intensity data were collected using u ꢁ
/
U(H), where aꢀ1.5 for methyl hydrogens and aꢀ1.2
/
/
2u scans in the range 3.55
/
2u 5558. A decay correction
/
for the remaining hydrogens. For compounds 5b and 7,
methyl group was disordered and each conformation
was set at 0.5 occupancy. Complex 5b crystallizes with a
molecule of solvent which appears to be a partial
molecule of CH2Cl2. Attempts to model the solvent
proved unsatisfactory, thus the solvent contribution was
subtracted from the reflection data using the program
SQUEEZE [28]
was applied to the unique reflections based on three
standard reflections monitored every 300 reflections.
Data were also corrected for Lp effects. For compounds
4 and 5b a semi-empirical absorption correction [26]
based on measured 8 scans was applied; no absorption
corrections were applied for compounds 5c and 6.
Structures were solved by a combination of direct
methods or Patterson analysis using SHELXTL v5.03 [27]
and the difference Fourier technique and were refined by
full-matrix least-squares on F2. Non-hydrogen atoms
4.1.2. Preparation of [1-(p-tolyl)-2-(p-chlorobenzyl)-
3,4,5,6-tetraphenyl-h5-azacyclohexadienyl]manganese
tricarbonyl (2a)
(p-Tolyl isocyanide)[(p-chlorophenyl)acetyl]manga-
nese tetracarbonyl (1a) (0.211 g, 0.465 mmol) was
were refined with anisotropic displacement parameters.
2
A weighting scheme of the form wꢃ1ꢀ
/
s2(Fo )ꢂ
/
(aP)2ꢂ
/
2
2
bP was used, where Pꢀ
/
0.33333Fo ꢂ0.66667Fc . An
/

C.L. Homrighausen et al. / Inorganica Chimica Acta 334 (2002) 419ꢁ
/436
433
Table 5
Summary of crystallographic data for compounds 5a, 5b, 6, and 7
5b
5a
6
7
Empirical formula
Molecular weight
Color, habit
C28H25ClMnNO7
577.88
C28H25ClMnNO7
577.88
C30H25ClMnNO11
665.9
C23H13ClF6MnNO4
571.7
orange plates
293
orange plates
296
orange plates
296
yellow blocks
150
Temperature (K)
¯
¯
¯
Space group
˚
/
P1/
P21/c
/P1/
/P1/
a (A)
˚
11.158(2)
12.018(2)
12.937(2)
111.77(1)
104.27(1)
103.21(2)
1459.4(4)
2
10.1471(1)
14.2234(3)
18.6453(4)
90.00
10.650(2)
10.691(2)
13.854(3)
71.77(3)
87.58(3)
83.15(3)
1487.5(5)
2
10.1503(2)
11.1541(3)
11.9960(3)
69.408(1)
72.022(1)
72.612(1)
1181.37(5)
2
b (A)
˚
c (A)
a (8)
b (8)
g (8)
V (A )
Z
94.342(1)
90.00
3
˚
2683.3(1)
4
0.638
Absorption coefficient 0.587
(mmꢃ1
0.596
0.750
)
Monochromator
Crystal size (mm)
2u range (8)
graphite
0.60ꢄ0.55ꢄ0.20
graphite
0.55ꢄ0.40ꢄ0.20
graphite
0.50ꢄ0.30ꢄ0.15
graphite
0.80ꢄ0.80ꢄ0.40
3.64ꢁ
/
56.12
4.54ꢁ
/
56.62
4.04ꢁ
/
55.12
5.02ꢁ
/
56.4
Index ranges
05h 514, ꢃ155k 515, ꢃ135h 56, ꢃ185k 516, 05h 513, ꢃ135k 513, ꢃ135h 513, ꢃ145k 514,
ꢃ16/5l 516
7101
6752
ꢃ245l 523
17 677
6617
ꢃ185l 518
7220
6853
ꢃ155l 515
13 146
5739
Reflections collected
Independent reflec-
tions
Min./max. transmis-
sions
Scan type
0.727/0.999
0.720/0.998
none
0.475/0.694
u/2u
343
v
u/2u
397
u/2u
325
Variables
343
R1ꢀ0.0453, wR2ꢀ0.1092
R1ꢀ0.0706, wR2ꢀ0.1301
0.0404
R indices [I ꢀ2s(I)]
R indices (all data)
Rint
R1ꢀ0.0525, wR2ꢀ0.1425
R1ꢀ0.0796, wR2ꢀ0.1425
0.0194
R1ꢀ0.0400, wR2ꢀ0.0913 R1ꢀ0.0296, wR2ꢀ0.0778
R1ꢀ0.0637, wR2ꢀ0.1058 R1ꢀ0.0356, wR2ꢀ0.0804
0.0160
none
0.313
0.0207
none
0.331
Extinction coefficient none
ꢃ3
none
0.346
˚
Res. elec. den. (e A
)
0.305
dissolved in 20 ml of THF; diphenylacteylene (0.166 g,
0.930 mmol) was added, after which the reaction
mixture was warmed and maintained at 50 8C for 8 h.
IR analysis showed the disappearance of the starting
materials and the presence of 2a. The solvent was
removed in vacuo and the resulting red residue dissolved
in a minimum volume of CH2Cl2 and loaded onto a
dissolved in a minimum amount of THF were added by
syringe. The reaction was refluxed for 20 h and deemed
complete by IR analysis. Solvent was removed in vacuo;
the resulting red residue was loaded onto a silica gel
column. Elution with C6H14/CH2Cl2 (9/1) removed
small amounts of benzyl manganese pentacarbonyl.
Elution with C6H14/CH2Cl2 (1/1) afforded 2b. Removal
of the solvent in vacuo and repeated recrystallization
grade II acidic alumina column (14.0ꢄ
with C6H14 afforded 2a; recrystallization from C6H14 at
78 8C gave 2a as a yellow solid. Yield: 0.156 g (46%),
m.p. 177ꢁ180 (dec.) MS: m/e (relative intensity) 737
[Mꢂ, not observed], 709 [MꢂꢃCO] (5.9), 653 [Mꢂꢃ
3CO] (11.2), 598 [Mꢂꢃ
Mn(CO)3] (100). Anal. Calc.: C,
/
2.0 cm2). Elution
from C6H14/CH2Cl2 at ꢃ
solid. Yield: 0.048 g (7%), m.p. 174ꢁ
(relative intensity) [Mꢂ] 719 (10), 691 [Mꢂꢃ
580 [Mꢂꢃ
Mn(CO)3] (100).
/
78 8C gave 2b as an orange
176 (dec.). MS: m/e
CO] (35),
ꢃ
/
/
/
/
/
/
/
/
74.80; H, 4.51; N, 1.89%. Found: C, 71.75; H, 4.19; N,
1.71%.
4.1.4. Preparation of [1-(p-tolyl)-2-(p-chlorobenzyl)-
3,5-dihydro-4,6-diphenyl-h5-azacyclohexa-
dienyl]manganese tricarbonyl (3a)
4.1.3. Preparation of [1-(p-methoxyphenyl)-2-benzyl-
3,4,5,6-tetraphenyl-h5-azacyclohexadienyl]manganese
tricarbonyl (2b)
(Phenylacetyl)manganese pentacarbonyl (0.307 g,
0.976 mmol) was dissolved in a minimum amount of
THF, after which p-methoxyphenyl isocyanide (0.130 g,
0.976 mmol) and diphenylacetylene (0.870 g, 4.88 mmol)
(p-Tolyl isocyanide)[(p-chlorophenyl)acetyl]manga-
nese tetracarbonyl (1a) (0.426 g, 0.972 mmol) was
dissolved in THF (20 ml), and phenylacetylene (0.198
g, 0.213 ml, 1.94 mmol) was added by syringe, after
which the reaction was warmed and maintained at
60 8C for 1.5 h. IR analysis showed the disappearance
of the starting materials and the presence of 3a. The

434
C.L. Homrighausen et al. / Inorganica Chimica Acta 334 (2002) 419ꢁ436
/
solvent was removed in vacuo and the resulting orange
residue dissolved in a minimum volume of CH2Cl2 and
2-butynoate (0.144 g, 0.048 ml, 0.478 mmol) was added
by syringe, after which the reaction mixture was warmed
and maintained at reflux for 2 h. IR analysis showed the
disappearance of the starting materials and the presence
of a complex mixture. The solvent was removed in
vacuo, and the resulting orange residue was dissolved in
a minimum volume of CH2Cl2 and loaded onto a grade
loaded onto a grade II acidic alumina column (19.0ꢄ
/
2.0 cm2). Elution with C6H14 removed small amounts of
(p-chlorobenzyl)manganese pentacarbonyl and small
amounts of 3a; elution with C6H14/CH2Cl2 (4/1) re-
moved 3a as a yellow band. Removal of solvent in vacuo
followed by repeated recrystallization from C6H14/Et2O
II acidic alumina column (17ꢄ
1.5 cm2). Elution with
C6H14/CH2Cl2 (2/3) gave a yellow band. Removal of
/
(2/1) at ꢃ
(76%), m.p. 155ꢁ
585 [Mꢂ, not observed], 557 [Mꢂꢃ
3CO] (16), 446 [Mꢂꢃ
Mn(CO)3] (100). Anal. Calc.: C,
/
78 8C gave 3a as a yellow solid. Yield: 0.43 g
157 (dec). MS: m/e (relative intensity)
CO] (6), 501 [Mꢂꢃ
/
solvent in vacuo followed by recrystallization from
/
/
CH2Cl2/C6H14 (1/2) at ꢃ
Yield: 0.016 g (12%), m.p. 112 8C. MS: m/e (relative
intensity) 577 [Mꢂ] (6.6), 493 [Mꢂꢃ
3 CO] (78), 438
[Mꢂꢃ
Mn(CO)3] (100). Elution with (1/4) C6H14/
/
78 8C gave 4 as a yellow solid.
/
69.69; H, 4.30; N, 2.39. Found: C, 69.12; H, 4.66; N,
2.36%.
/
/
CH2Cl2 afforded an orange band. Removal of solvent
in vacuo followed by recrystallization from CH2Cl2/
C6H14 (1/2) gave an orange solid. Yield: 0.030 g (23%).
1H NMR analysis showed 10 methyl signals in the same
region of the spectrum as the methyl groups for
compound 4. Therefore, the mixture was believed to
contain two regioisomeric azacylohexadienyl complexes.
4.1.5. Preparation of [1-(p-methoxyphenyl)-2-(p-
chlorobenzyl)-3,5-dihydro-4,6-diphenyl-h5-
azacyclohexadienyl]manganese tricarbonyl (3b)
(p-Chlorobenzyl)manganese pentacarbonyl (1.00 g,
3.12 mmol) and p-methoxyphenyl isocyanide (0.415 g,
3.12 mmol) were dissolved in a minimum volume of
THF, after which the reaction mixture was stirred at
ambient temperature for 18 h. IR analysis showed the
presence of the expected (p-methoxyphenyl isocyani-
Fractional recrystallization from C6H14 at ꢃ
5c as an orange solid. Yield: 0.005 g (4%), m.p. 172ꢁ
(dec.). MS: m/e (relative intensity) 577 [Mꢂ, not
observed], 493 [Mꢂꢃ3CO] (20), 438 [Mꢂꢃ
Mn(CO)3]
(30), and 5b as a yellow solid. Yield: 0.019 g (14%), m.p.
107ꢁ
108 (dec.). MS: m/e (relative intensity) 577 [Mꢂ]
(10), 493 [Mꢂꢃ3CO] (20), 438 [Mꢂꢃ
Mn(CO)3] (30).
/
78 8C gave
/
175
de)[(p-chlorophenyl)acetyl]manganese
tetracarbonyl
/
/
complex along with remaining (p-chlorobenzyl)manga-
nese pentacarbonyl. Phenylacetylene (0.319 g, 0.343 ml,
6.24 mmol) was added by syringe, after which the
solution was warmed and maintained at 40 8C for 72
h. The solvent was removed in vacuo; the resulting red
residue was dissolved in a minimum volume of CH2Cl2
and loaded onto a grade II acidic alumina column.
Elution with C6H14 afforded a red band. Elution with
Et2O removed an orange band and elution with THF
removed an orange band, all of which contained (p-
chlorobenzyl)manganese pentacarbonyl and 3b. Re-
moval of the solvent in vacuo followed by extraction
/
/
/
Elution with 100% THF gave a yellow band. Removal
of solvent in vacuo followed by recrystallization from
CH2Cl2/C6H14 (1/2) gave 5a as a yellow solid. Yield:
0.009 g (7%), m.p. 191ꢁ
intensity) 577 [Mꢂ, not observed], 493 [Mꢂꢃ
438 [Mꢂꢃ
Mn(CO)3] (30). Anal. Calc.: C, 58.20; H,
/
192 (dec.). MS: m/e (relative
/
3CO] (20),
/
4.36; N, 2.42. Found: C, 57.96; H, 4.36; N, 2.35%.
4.1.7. Preparation of [1-(p-tolyl)-2-(p-chlorobenzyl)-
3,4,5,6-tetrakis(carbomethoxy)-h4-azacyclohexa-
dienyl]manganese tricarbonyl (6)
with C5H12 and recrystallization at ꢃ
an orange solid. Yield: 0.240 g (13%), m.p. 129ꢁ
(dec.). MS: m/e (relative intensity) 601 [Mꢂ, not
observed], 573 [MꢂꢃCO] (20), 517 [Mꢂꢃ
3CO] (8),
462 [Mꢂꢃ
Mn(CO)3] (100).
/
78 8C gave 3b as
/131
(p-Tolyl isocyanide)[(p-chlorobenzyl)acetyl]manga-
nese tetracarbonyl (1a) (0.222 g, 0.508 mmol) was
dissolved in THF (8 ml); dimethylactetylene dicarbox-
ylate (0.144 g, 0.125 ml, 1.02 mmol) was added by
syringe, after which the reaction was warmed and
maintained at 60 8C for a 3-h period. IR analysis
showed the disappearance of the starting materials and
the presence of 6. The solvent was removed in vacuo and
the resulting orange residue dissolved in a minimum
volume of CH2Cl2 and loaded onto a grade II acidic
/
/
/
4.1.6. Preparation of [1-(p-tolyl)-2-(p-chlorobenzyl)-
3,5-dimethyl-4,6-bis(carbomethoxy)-h5-azacyclo-
hexadienyl]manganese tricarbonyl (4), [1-(p-tolyl)-2-
(p-chlorobenzyl)-3,6-dimethyl-4,5-bis(carbomethoxy)-
h4-azacyclohexadienyl]manganese tricarbonyl (5a), [1-
(p-tolyl)-2-(p-chlorobenzyl)-4,5-dimethyl-3,6-
bis(carbomethoxy)-h4-azacyclohexadienyl]manganese
tricarbonyl (5b) and [1-(p-tolyl)-2-(p-chlorobenzyl)-
4,6-(dimethyl)-3,5-bis(carbomethoxy)-h5-
alumina column (15ꢄ
2.0 cm2). Elution with C6H14/
/
CH2Cl2 (4/1) removed small amounts of (p-chloroben-
zyl)manganese pentacarbonyl and small amounts of 6.
Elution with CH2Cl2 afforded 6 as an orange band.
Removal of solvent in vacuo followed by repeated
azacyclohexadienyl]manganese tricarbonyl (5c)
(p-Tolyl isocyanide)[(p-chlorobenzyl)acetyl]manga-
nese tetracarbonyl (1a) (0.100 g, 0.229 mmol) was
dissolved in a minimum volume of THF, and methyl
recrystallization from C6H14/Et2O (2/1) at ꢃ
/
78 8C,
gave 6 as an orange solid. Yield: 0.241 g (71%), m.p.

C.L. Homrighausen et al. / Inorganica Chimica Acta 334 (2002) 419ꢁ
/436
435
168ꢁ
(15), 581 [Mꢂꢃ
[Mꢂꢃ
5CO] (10). Anal. Calc.: C, 54.12; H, 3.75; N,
/
171 (dec.). MS: m/e (relative intensity) 665 [Mꢂ]
3CO] (57), 553 [Mꢂꢃ
4CO] (100), 525
Acknowledgements
/
/
/
J.A.K.B. sincerely thanks Dr. Ewa Skrzypczak-Jan-
kun (University of Toledo) for assistance in using the
SMART 1K CCD diffractometer system for 2b and 3b.
Data were collected through the Ohio Crystallographic
Consortium, funded by the Ohio Board of Regents 1995
Investment Fund (CAP-O75), located at the University
of Toledo, Instrumentation Center in A&S, Toledo, OH
43606.
2.10. Found: C, 54.78; H, 4.02; N, 2.02%.
4.1.8. Preparation of [1,1,1,1-tetracarbonyl-4,5-
bis(trifluoromethyl)-3-(p-chlorobenzyl)-2-(p-tolyl)]-2-
azamanganacyclopentadiene (7)
(p-Tolyl isocyanide)[(p-chlorophenyl)acetyl]manga-
nese tetracarbonyl (1a) (0.503 g, 1.108 mmol) was
dissolved in THF (90 ml) and added to a 300-ml Parr
bomb. The Parr bomb was sealed and hexafluoro-2-
butyne (excess) as determined by the Parr bomb
pressure gauge was admitted to the bomb from a 10 g-
gas canister by employing an Aldrich lecture bottle
regulator. The bomb was then pressurized to 400 psi
with Ar. The temperature was increased to 52 8C and
maintained for 4 h. IR analysis showed the almost
complete disappearance of the starting material and the
presence of 7. Removal of solvent in vacuo and
extraction of the resulting red residue with C6H14
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