2-Diphenylphosphinoazacyclopentadienylmanganese tricarbonyl as a new bridging ligand

Article abstract of DOI:10.1016/S0022-328X(99)00530-6

Treatment of [Mn₂(CO)₁₀] with diphenyl(2-pyrrolyl)phosphine (Ph₂P-2-C₄H₃NH) leads to simple substitution products, the product of P-C bond cleavage [Mn₂(μ-H)(μ-PPh₂)(CO)₈], but the most interesting product (21%) is the trinuclear compound [Mn₃(μ₃-P,N,η⁵-Ph₂PC ₄H₃N)(CO)₁₁], the X-ray structure of which shows it to contain the bidentate ligand, 2-diphenylphosphinoazacyclopentadienylmanganese tricarbonyl, Mn(η⁵-Ph₂PC₄H₃N)(CO) ₃, which bridges across a Mn₂(CO)₈ unit as a novel four-electron donating chiral N,P-ligand.

Full text of DOI:10.1016/S0022-328X(99)00530-6

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 592 (1999) 235–239
2-Diphenylphosphinoazacyclopentadienylmanganese tricarbonyl as
a new bridging ligand
Antony J. Deeming *, Mukesh K. Shinhmar
Department of Chemistry, Uni6ersity College London, 20 Gordon Street, London WC1H OAJ, UK
Received 23 June 1999; accepted 12 July 1999
Abstract
Treatment of [Mn2(CO)10] with diphenyl(2-pyrrolyl)phosphine (Ph2P-2-C4H3NH) leads to simple substitution products, the
product of PꢀC bond cleavage [Mn2(m-H)(m-PPh2)(CO)8], but the most interesting product (21%) is the trinuclear compound
[Mn3(m3-P,N,h5-Ph2PC4H3N)(CO)11], the X-ray structure of which shows it to contain the bidentate ligand, 2-diphenylphosphi-
noazacyclopentadienylmanganese tricarbonyl, Mn(h5-Ph2PC4H3N)(CO)3, which bridges across a Mn2(CO)8 unit as a novel
four-electron donating chiral N,P-ligand. © 1999 Elsevier Science S.A. All rights reserved.
Keywords: Manganese; Pyrrolylphosphine; Azacyclopentadienyl; Clusters
[Re2(m-PPh2)(m-C,S-C4H3S)(CO)8], respectively [5]. Be-
cause of these major differences, we wished to establish
whether the ligand Ph2P-2-C4H3NH would behave like
the analogous thienyl phosphine and undergo PꢀC
bond cleavage to give m-pyrrolyl complexes with Mn
and Re carbonyls. An alternative mode of reaction of
the pyrrole ring, not possible for thiophene, is deproto-
nation at nitrogen which could lead to h5-coordination
of an azacyclopentadienyl ring. The azacyclopentadi-
enyl complex [Mn(h5-C4H4N)(CO)3] has been long
known [6]. Our results show that combinations of these
possibilities occur. PꢀC cleavage and deprotonation to
give an azacyclopentadienyl ligand system but the
chemistry is generally quite unlike that of diphenyl(2-
thienyl)phosphine.
1. Introduction
The ligand 2-Ph2PC4H3NH [1] preferentially coordi-
nates as a simple tertiary phosphine through the phos-
phorus atom, but in doing so, the pyrrole ring may
subsequently become bonded to an adjacent metal
atom if one is present. For example, we have shown
that the ligand reacts with [Ru3(CO)12] to give the
product [Ru3(m-H)(m3-2-Ph2PC4H2NH)(CO)9] in which
the phosphorus atom is coordinated and the pyrrole
has been orthometallated at a second metal atom [2].
Treatment of this product with more [Ru3(CO)12] leads
to PꢀC cleavage and the products [Ru4(m4-PPh)(m4-2-
C4H2NH)(CO)11] with a C,C-bonded pyrrolyne ligand
and its C,N-bonded isomer [2]. However, this type of
chemistry, dominated by orthometallation and CꢀH
bond cleavage, does not occur so readily with
[Mn2(CO)10] or [Re2(CO)10]. For example, in our work
we have shown that diphenyl(2-thienyl)phosphine un-
dergoes CꢀH cleavage with [Ru3(CO)12] [3] or
[Os3(CO)12] [4] to give m3-2-Ph2PC4H2S systems whereas
[Mn2(CO)10] or [Re2(CO)10] react with the same ligand
leading to a PꢀC bond cleavage to give the m-thienyl
complexes [Mn2(m-PPh2)(m-h1,h5-C4H3S)(CO)6] and
2. Results and discussion
The progress of the reaction of [Mn2(CO)10] with
diphenyl(2-pyrrolyl)phosphine in refluxing toluene was
followed by recording the IR spectrum of the solution
periodically. After 1 h the solution contained consider-
able amounts of the simple axially-substituted product
[Mn2(Ph2P-2-C4H3NH)(CO)9]. IR signals for this spe-
cies decreased to a low level after 7 h by which time
there was a little more change in the IR spectrum. The
* Corresponding author. Fax: +44-171-3807463.
E-mail address: a.j.deeming@ucl.ac.uk (A.J. Deeming)
0022-328X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(99)00530-6

236
A.J. Deeming, M.K. Shinhmar / Journal of Organometallic Chemistry 592 (1999) 235–239
Table 1
reaction mixture was worked-up by TLC separation on
silica. Some unreacted [Mn2(CO)10] and a little of the
substitution product [Mn2(Ph2P-2-C4H3NH)(CO)9]
(7%) were isolated. The latter was characterised spec-
troscopically by comparison with related complexes of
,
Selected bond lengths (A) and angles (°) for the compound [Mn3(m3-
P,N,h5-Ph2PC4H3N)(CO)11
]
Bond lengths
Mn(1)ꢀMn(2)
Mn(1)ꢀP(1)
Mn(1)ꢀC(11)
Mn(1)ꢀC(12)
Mn(1)ꢀC(13)
Mn(1)ꢀC(14)
Mn(2)ꢀN(1)
Mn(2)ꢀC(21)
Mn(2)ꢀC(22)
Mn(2)ꢀC(23)
Mn(2)ꢀC(24)
Mn(3)ꢀN(1)
Mn(3)ꢀC(1)
2.913(1)
Mn(3)ꢀC(2)
Mn(3)ꢀC(3)
Mn(3)ꢀC(4)
Mn(3)ꢀC(31)
Mn(3)ꢀC(32)
Mn(3)ꢀC(33)
P(1)ꢀC(1)
N(1)ꢀC(1)
N(1)ꢀC(4)
C(1)ꢀC(2)
C(2)ꢀC(3)
2.167(4)
2.147(4)
2.122(4)
1.804(5)
1.793(5)
1.797(5)
1.831(4)
1.381(6)
1.397(5)
1.423(5)
1.409(6)
1.393(7)
1
2.287(1)
1.835(5)
1.804(5)
1.825(5)
1.831(5)
2.096(3)
1.851(5)
1.849(4)
1.808(5)
1.789(5)
2.156(3)
2.165(4)
type axial-[Mn2(L)(CO)9] [7]. The H-NMR spectrum
showed the expected four pyrrolyl ring protons at l
7.88, 6.98, 6.94 and 6.38, quite similar shifts to those of
the signals for the free ligand at l 8.10, 6.95, 6.51 and
6.31. Therefore coordination is through the phosphorus
atom while the pyrrole ring is hanging free and not
attached directly to the metal atoms. In addition, a low
yield of the known complex [Mn2(m-H)(m-PPh2)(CO)8]
[8] (4%) was obtained by PꢀC bond cleavage but the
main and most interesting product was [Mn3(m3-
P,N,h5-Ph2PC4H3N)(CO)11], isolated as a red microcys-
talline solid (21%). This complex gave ten IR
C(3)ꢀC(4)
Bond angles
Mn(1)ꢀMn(2)ꢀN(1) 88.7(1)
Mn(2)ꢀMn(1)ꢀP(1)
Mn(1)ꢀP(1)ꢀC(1)
Mn(1)ꢀP(1)ꢀC(51)
Mn(2)ꢀN(1)ꢀC(1)
P(1)ꢀC(1)ꢀN(1)
120.6(1)
126.3(2)
117.8(3)
83.1(1)
113.2(1)
Mn(1)ꢀP(1)ꢀC(41) 116.0(1)
absorptions assigned to w(CO), consistent with its
polynuclear nature, and a peak at m/z=723 was ob-
tained as the highest mass ion in the FABMS consistent
1
with this formula. Unfortunately the H- and 13C{1H}-
NMR spectra were very broad and of little use in
establishing its structure. The compound is not para-
magnetic but possibly paramagnetic impurities are
present. Its formulation is therefore based largely on its
single-crystal structure determination (Scheme 1).
The molecular structure of [Mn3(m3-P,N,h5-
Ph2PC4H3N)(CO)11] is shown in Fig. 1 and selected
bond lengths and angles are in Table 1. The three
manganese atoms, Mn(1)ꢀMn(3) in the trinuclear com-
pound, are coordinated to 4, 4 and 3 CO ligands,
respectively. One way to consider the cluster is that it
Scheme 1.
contains
a
2-diphenylphosphino-substituted azacy-
clopentadienyl manganese tricabonyl unit which acts as
a four-electron donor bridge across a Mn2(CO)8 sub-
unit. The organic ligand itself has been deprotonated at
the nitrogen atom, allowing the formation of the
Mn(2)ꢀN(1) bond and h5 coordination of the azacy-
clopentadienyl ring to Mn(3). This is contrast to the
reaction of this ligand with [Ru3(CO)12] in which the
ligand undergoes CꢀH cleavage ortho to the PPh2 sub-
stituent rather than NꢀH bond cleavage as in this case
[2]. The dimanganese unit Mn(1)Mn(2) adopts a con-
formation approximately half way between eclipsed and
staggered with a P(1)Mn(1)Mn(2)N(1) torsional angle
of 24.8°. It is possible to compare the coordination of
the tertiary phosphine and the azacyclopentadienyl
groups in this structure. The MnꢀCO distance trans to
nitrogen is the shortest in the molecule [Mn(2)ꢀC(24)
Fig. 1. Molecular structure of the cluster [Mn3(m3-P,N,h5-
Ph2PC4H3N)(CO)11].
,
1.789(5) A], shorter than that trans to phosphorus
,
[Mn(1)ꢀC(13) 1.825(5) A] and the average of the other

A.J. Deeming, M.K. Shinhmar / Journal of Organometallic Chemistry 592 (1999) 235–239
237
,
MnꢀCO bond lengths at Mn(2) [also 1.825 A]. There-
Mn or Re) [9] and [Os3(m-H){m-2-C4H3NMn(CO)3}-
(CO)10] [10,11].
fore, we believe that the azacyclopentadienyl ring coor-
dinated through nitrogen has a weak trans influence,
less that those of CO or tertiary phosphine. The sub-
stituents Mn(2) and P(1) at the h5-pyrrolyl ring are
The room temperature reaction of [Mn2(CO)10] with
diphenyl-2-pyrrolylphosphine in toluene under UV
photolysis gave no indication of the formation of
[Mn3(m3-P,N,h5-Ph2P-2-C4H3N)(CO)11] but instead two
PꢀC cleavage products were obtained in reasonable
yield: [Mn2(m-H)(m-PPh2)(CO)8] (52%) and a derivative
of this [Mn2(m-H)(m-PPh2){Ph2P-2-C4H3NH}(CO)7]
(20%). Also the thermal treatment of [Mn2(CO)10] with
diphenyl-3-pyrrolylphosphine gave [Mn2(m-H)(m-PPh2)-
(CO)8] and the substitution complex [Mn2(Ph2P-3-
C4H3NH)(CO)9] which was also formed photo-
chemically. Thermal treatment of [Re2(CO)10] with
diphenyl-2-pyrrolylphosphine at 190°C gave the com-
pound [Re2(m-H)(m-PPh2)(CO)8] (37%) as the only
isolable product. Thus none of these reactions which
occur by PꢀC cleavage resulted in the formation of
m-pyrrolyl complexes as in the formation of m-thienyl
dimanganese and dirhenium complexes from diphenyl-
2-thienylphosphine [5].
,
bent out of the plane of the ring by 0.491 and 0.350 A,
respectively away from the Mn(3)(CO)3 group. Bending
back of substituents is commonly associated with the
bonding of unsaturated rings to metal atoms but, in
this case this may be enhanced by interactions of CO
ligands at Mn(3) with those at Mn(1) and Mn(2). The
shortest CꢀC contacts between CO ligands are
,
C(22)…C(31) [3.284(6) A] and C(33)ꢀC(11) [3.358(6)
5
,
A]. If the substituents, Mn(2) and P(1), at the h -
pyrrolyl ring were in the plane of the ring, these dis-
tances would be unfavourably short.
The probable route to this Mn3 compound (Scheme
2) is the reaction of [Mn2(CO)10] with the unattached
pyrrole ring of [Mn2(Ph2P-2-C4H3NH)(CO)9], a com-
pound which we have shown to be formed in the early
stages of the reaction. This would generate a dangling
azacyclopentadienyl manganese tricarbonyl group
which then could displace CO from the adjacent Mn
atom to form the bridged system isolated. An alterna-
tive is that [Mn2(Ph2P-2-C4H3NH)(CO)9] decarbony-
lates and undergoes oxidative addition with NꢀH bond
cleavage to give [Mn2(m-H)(m-Ph2P-2-C4H3N)(CO)8],
which reacts with further [Mn2(CO)10] to give the ob-
served product. Other examples of compounds involv-
ing coordination of the nitrogen atom of azacyclo-
pentadienyl manganese tricarbonyl, [Mn(C4H4N)(CO)3]
are [M(h-C5H5)(CO)2(m-h1,h5-C4H4N)Mn(CO)3] (M=
3. Experimental
Following the method described for diphenyl-2-
pyrrolylphosphine [1], we were able to separate the
mixed isomeric product by column or TLC chromatog-
raphy (SiO2) to give diphenyl-2-pyrrolylphosphine as a
white solid (45%) and diphenyl-3-pyrrolylphosphine as
a colourless oil (40%). [Mn2(CO)10] or [Re2(CO)10] were
used as supplied by Strem.
Scheme 2.

238
A.J. Deeming, M.K. Shinhmar / Journal of Organometallic Chemistry 592 (1999) 235–239
3.1. Treatment of [Mn2(CO)10] with
diphenyl-2-pyrrolylphosphine in refluxing toluene
g) and diphenyl-3-pyrrolylphosphine (0.507 mmol) in
toluene (100 cm3) gave unreacted [Mn2(CO)10] (0.007 g)
and [Mn2(Ph2P-3-C4H3NH)(CO)9] as an orange solid
(0.077 g, 25%).
A solution of [Mn2(CO)10] (0.197 g) and Ph2P-2-
C4H3NH (0.136 g, 1 mol per mol of Mn2) in toluene (40
cm3) was heated under reflux under nitrogen for 8 h. By
monitoring the IR spectrum of the reacting solution
[Mn2(Ph2P-2-C4H3NH)(CO)9] was shown to be formed
as a major product after 1.5 h but this gave very weak
signals at the later stages of the reaction. Solvent was
removed under reduced pressure and TLC work-up of
the orange–brown residue [SiO2; eluent, hexane–
dichloromethane (5:3 v/v)] produced four bands yield-
3.3. Photochemical treatment of [Mn2(CO)10] with
diphenyl-2-pyrrolylphosphine
A solution of [Mn2(CO)10] (0.240 g) and Ph2P-2-
C4H3NH (0.161 g) in toluene (100 cm3) was treated
with UV irradiation for 20 h. The solvent was removed
from the orange solution under reduced pressure and
TLC or the residual orange solid [SiO2; eluent, hexane–
dichloromethane, 5:3 v/v] gave two bands, the first of
which was characterized as [Mn2(m-H)(m-PPh2)(CO)8] as
a yellow solid (0.168 g, 52%) (see above). The second
band gave [Mn2(m-H)(m-PPh2){Ph2P-2-C4H3NH}(CO)7]
as orange crystals (0.091 g, 20%) by evaporation of a
ing
unreacted
[Mn2(CO)10]
(0.053
g)
and
[Mn2(m-H)(m-PPh2)(CO)8] as a yellow solid (0.010 g,
4%) which was characterized by comparison of its
spectra with those reported [8]; Anal. Calc. for
C20H11O8PMn2: C, 46.2; H, 2.1; P, 5.95. Found: C,
45.8; H, 2.5; P, 6.4%; w(CO) (cm−1) (cyclohexane):
2093w, 2063m, 2010vs, 2000m, 1965s; parent molecular
dichloromethane
C35H25O7NPMn2: C, 56.55; H, 3.4; N, 1.9; P, 8.30.
Found: C, 55.9; H, 3.5; N, 1.8; P, 8.6%; w(CO) (cm−1
solution;
Anal.
Calc.
for
1
ion observed in FABMS (MNBA medium); H-NMR
)
(CDCl3, 298 K): l 7.85, 7.35 (Ph multiplets), −16.12
(d, JPH=35.5 Hz, hydride). The third band gave
[Mn2(Ph2P-2-C4H3NH)(CO)9] as an orange solid (0.021
g, 7%); w(CO) (cm−1) (cyclohexane): 2091w, 2012m,
1995vs, 1973m, 1962vw, 1942m, weak parent molecular
(cyclohexane): 2089m, 2011s, 1993vs, 1970s, 1959vw,
1937s; a weak parent molecular ion was observed in the
FABMS (MNBA medium); NMR spectra are very
broad and data are not reported here.
1
ion in FABMS (MNBA medium); H-NMR (CDCl3,
3.4. Treatment of [Re2(CO)10] with
298 K): l 7.88 (br s, NH), 7.40 (m, Ph), 6.96 (m, H2/H5,
pyrrolyl), 6.38 (m, H4, pyrrolyl). The final band gave
[Mn3(m3-P,N,h5-Ph2P-2-C4H3N)(CO)11] as a red micro-
cystalline solid (0.077 g, 21%), w(CO) (cm−1) (cyclohex-
ane): 2067w, 2049m, 2000s, 1991w, 1980m, 1967s,
1955w, 1942vw, 1926sh, 1899m; parent molecular ion in
FABMS (MNBA medium); 1H- and 13C-NMR data are
not reported because these were both very broad and
ill-defined.
diphenyl-2-pyrrolylphosphine at 190°C
A 20 cm3 Carius tube was charged with [Re2(CO)10]
(0.199 g, 0.305 mmol) and diphenyl-2-pyrrolylphos-
phine (0.077 g, 1 mol per mol Re2) in decane (5 cm3).
The mixture was degassed by three freeze-pump-thaw
cycles, sealed under vacuum and heated at 190°C for 24
h. The colourless suspension had become orange and
TLC work-up [SiO2; eluent, hexane–dichloromethane,
5:3 v/v] gave only one tractible product: [Re2(m-H)(m-
PPh2)(CO)8] as a very pale yellow solid (0.088 g, 37%)
by evaporation of a dichloromethane solution; w(CO)
(cm−1) (cyclohexane): 2108m, 2084s, 2076sh, 2014vs,
1998vs, 1983vw; parent molecular ion was observed in
the FABMS (MNBA medium); 1H-NMR (CDCl3,
298°C): l 7.82 (ddd, J=1.5, 7.3, 11.5 Hz, 4H, ortho),
7.80–7.28 (m, 6H, meta/para), −15.02 (d, J=4.6 Hz,
ReHRe); 13C{1H}-NMR (CDCl3, 298°C): l 185.1 (d,
J=28.0 Hz, 2CO trans to PPh2), 183.7 (d, J=3.1 Hz,
2CO), 182.3 (d, J=6.7 Hz, 4CO), 138.8 (d, J=40.3
Hz, ipso), 134.5 (d, J=11.7 Hz, ortho), 129.8 (s, para),
128.8 (d, J=10.6 Hz, meta); 31P{1H}-NMR (CDCl3,
298°C): l 42.9 (s).
3.2. Treatment of [Mn2(CO)10] with
diphenyl-3-pyrrolylphosphine in toluene
A solution of [Mn2(CO)10] (0.105 g, 0.270 mmol) and
diphenyl-3-pyrrolylphosphine (0.069 g, 1 mol per mol
Mn2) in refluxing toluene (40 cm3) gave a red–orange
suspension after 8 h which gave a dark orange solid on
removal of solvent. TLC work-up [SiO2; eluent, hex-
ane–dichloromethane (1:1 v/v)] gave three bands which
gave unreacted [Mn2(CO)10] (0.012 g) and [Mn2(m-H)(m-
PPh2)(CO)8] as a yellow solid (0.013 g, 9%). The third
band gave [Mn2(Ph2P-3-C4H3NH)(CO)9] as an orange
solid (0.031 g, 19%) by evaporation of a dichloro-
methane solution; Anal. Calc. for C25H14O9NPMn2: C,
49.0; H, 2.3; N, 2.3; P, 5.05. Found: C, 50.0; H, 2.8; N,
2.4; P, 5.5%; w(CO) (cm−1) (cyclohexane): 2089m,
2010s, 1993vs, 1970s, 1959vw, 1937s, weak parent
molecular ion in FABMS (MNBA medium). Photo-
chemical treatment of a solution of [Mn2(CO)10] (0.198
3.5. Crystal structure determination of [Mn3-
(v3-P,N,p5-Ph2PC4H3N)(CO)11]
A suitable orange–red crystal (size: 0.22×0.28×
0.30 mm) was selected from a batch of crystals obtained

A.J. Deeming, M.K. Shinhmar / Journal of Organometallic Chemistry 592 (1999) 235–239
239
by slow evaporation of a mixed hexane–dichloro-
Acknowledgements
methane solution. The structure was determined with a
Nicolet R3V/m diffractometer using graphite-
We grateful to the EPSRC for support for the diffrac-
tometer and University College London for support for
this research.
,
monochromated Mo–Ka radiation (u=0.71073 A).
The unit cell was determined from the setting angles of
30 orientation reflections in the 2q range 16–28°. Inten-
sity data collected at 291(1) K were corrected for crystal
decay based on the 8% intensity loss of three check
reflections, for Lorentz and polarization effects, and for
absorption (empirical absorption correction based on
C-scans). The structure was solved by direct methods
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,
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,
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[12] G.M. Sheldrick, SHELXTL-PLUS, University of Go¨ttingen, re-
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[13] G.M. Sheldrick, SHELXL 93, Program for refinement of crystal
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Fractional atomic coordinates for the complex to-
gether with additional material comprising thermal
parameters and full tables of bond lengths and angles
are available from the Cambridge Crystallographic
Data Centre, CCDC number 133929.
.