The photolysis of Fe(CO)3{P(OPh)3}2 and reaction of the photoproduct with alkynes: Crystal structures of Fe(CO)2{P(OPh)3}2(η2-PhCCPh), Fe(CO)2{P(OPh)3}2{η1:η 1-C(O)C(Me)C[CH(OEt)2]C(O)}

Article abstract of DOI:10.1016/S0022-328X(00)00384-3

UV-irradiation of Fe(CO)₃{P(OPh)₃}₂ (1) afforded an orthometallated iron hydride HFe(CO)₂{P(OPh)₃}{(PhO)₂POC₆H ₄} (2) which was reacted in situ with alkynes R¹C=CR². Internal alkynes reacted to give either η²-alkyne Fe(CO)₂{P(OPh)₃}₂(η²-R ¹CCR²) [3a, R¹= R² = Ph; 3b, R¹= Ph, R² = CH(OEt)₂] or maleoyl Fe(CO)₂{P(OPh)₃}₂{η¹:η ¹-C(O)C(R¹)C(R²)C(O)} [4a, R¹= Ph, R² = Me; 4b, R¹= R² = Me; 4c, R² = Me, R² = CH(OEt)₂; 4d, R1 = Me, R² = CH₂OH; 4e, R¹ = R² = CH₂OH] complexes. The terminal alkyne HC=CPh reacted with 2 to give the ferrole derivative Fe₂(CO)₄{P(OPh)₃}₂(PhCCH) ₂ (5). The crystal structures of 3a, 4c and 5 were determined. Complex 3a is trigonal bipyramidal about the iron atom with trans apical phosphite ligands and an equatorial arrangement of the CO groups and alkyne CC moiety. Complex 4c is octahedral with trans phosphite ligands and cis carbonyl groups. The alkyne ligand has undergone double carbonylation to generate a ferracyclopentenedione (maleoyl) ring that occupies the remaining two coordination sites at the metal centre. Complex 5 is formally a derivative of Fe₂(CO)₉ in which an Fe(CO)₂{P(OPh)₃} moiety is π-bonded to a ferracyclopentadiene ring arising from the tail-to-tail coupling of two HC=CPh ligands.

Full text of DOI:10.1016/S0022-328X(00)00384-3

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 612 (2000) 61–68
The photolysis of Fe(CO)3{P(OPh)3}2 and reaction of the
photoproduct with alkynes: crystal structures of
Fe(CO)2{P(OPh)3}2(h2-PhCCPh),
Fe(CO)2{P(OPh)3}2{h1:h1-C(O)C(Me)C[CH(OEt)2]C(O)} and
Fe2(CO)4{P(OPh)3}2(PhCCH)2
M. Barrow a, N.L. Cromhout a, D. Cunningham b, A.R. Manning a,*, P. McArdle b
a Department of Chemistry, Uni6ersity College Dublin, Belfield, Dublin 4, Ireland
b Department of Chemistry, Uni6ersity College Galway, Galway, Ireland
Received 11 May 2000; received in revised form 15 June 2000
Abstract
UV-irradiation of Fe(CO)3{P(OPh)3}2 (1) afforded an orthometallated iron hydride HFe(CO)2{P(OPh)3}{(PhO)2POC6H4} (2)
which was reacted in situ with alkynes R1CꢀCR2. Internal alkynes reacted to give either h2-alkyne Fe(CO)2{P(OPh)3}2(h2-
R1CCR2) [3a, R1=R2=Ph; 3b, R1=Ph, R2=CH(OEt)2] or maleoyl Fe(CO)2{P(OPh)3}2{h1:h1-C(O)C(R1)C(R2)C(O)} [4a,
R1=Ph, R2=Me; 4b, R1=R2=Me; 4c, R1=Me, R2=CH(OEt)2; 4d, R1=Me, R2=CH2OH; 4e, R1=R2=CH2OH]
complexes. The terminal alkyne HCꢀCPh reacted with 2 to give the ferrole derivative Fe2(CO)4{P(OPh)3}2(PhCCH)2 (5). The
crystal structures of 3a, 4c and 5 were determined. Complex 3a is trigonal bipyramidal about the iron atom with trans apical
phosphite ligands and an equatorial arrangement of the CO groups and alkyne CC moiety. Complex 4c is octahedral with trans
phosphite ligands and cis carbonyl groups. The alkyne ligand has undergone double carbonylation to generate a ferracyclopen-
tenedione (maleoyl) ring that occupies the remaining two coordination sites at the metal centre. Complex 5 is formally a derivative
of Fe2(CO)9 in which an Fe(CO)2{P(OPh)3} moiety is p-bonded to a ferracyclopentadiene ring arising from the tail-to-tail
coupling of two HCꢀCPh ligands. © 2000 Elsevier Science B.V. All rights reserved.
Keywords: Iron carbonyl; Phosphite; Orthometallation; Alkyne; Maleoyl; Ferrole
product HFe(CO)2{P(OPh)3}{(PhO)2POC6H4} proceed
selectively to afford only one of three product types
1. Introduction
depending on the acetylenic substituents.
The reactions of iron carbonyls with alkynes afford a
wealth of organometallic derivatives with a diverse
array of structures [1] and with numerous practical
applications to organic synthesis [2]. All too often,
however, these reactions are plagued by a lack of
selectivity. Complex mixtures leading to a myriad of
reaction products are obtained and reaction mecha-
nisms are often unclear. In this paper we describe the
photolysis of the iron carbonyl Fe(CO)3{P(OPh)3}2 and
show that the reactions of alkynes with the photo-
2. Results and discussion
The chemistry of Fe(CO)3{P(OPh)3}2 (1) is relatively
under-represented in the literature compared to that of
its phosphine analogue Fe(CO)3(PPh3)2 for which con-
venient and high yielding syntheses are available [3].
Literature methods for the preparation of 1 give this
complex in only ca. 15% yield [4]. We now report that
reflux of Fe(CO)5 with P(OPh)3 in mesitylene followed
by addition of methanol to the cooled reaction mixture,
afforded 1 in ca. 65% yield with no contamination from
* Corresponding author. Tel.: +353-1-7062311; fax: +353-1-
7062127.
E-mail address: anthony.manning@ucd.ie (A.R. Manning).
0022-328X/00/$ - see front matter © 2000 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(00)00384-3

62
M. Barrow et al. / Journal of Organometallic Chemistry 612 (2000) 61–68
We describe here the reactions of HFe(CO)2-
{P(OPh)3}{(PhO)2POC6H4} (2) with a series of alkyne
ligands; these reactions are summarised in Scheme 1. In
a typical procedure, a stoichiometric amount of the
alkyne was added to a toluene solution of 2, generated
in situ by UV-irradiation of 1, and the mixture was
allowed to stir at room temperature overnight. A single
product was obtained in each instance although iso-
lated yields were generally modest. It was found, how-
ever, that the yields of 3 and 4 were improved if the
reactions were conducted in the presence of a Lewis
acid: for example, an increase in yield from 12 to 65%
of the isolated product 3a was obtained on addition of
hydrated ZnCl2 to the reaction of 2 with diphenyl-
acetylene. Anhydrous ZnCl2 compromised both the
yield and selectivity of the reaction affording ca.
25% 3a and other unidentified products. For the acetal-
functionalised alkynes, addition of ZnCl2·nH2O af-
forded the alkyne–aldehyde and Fe(CO)2(Cl)2-
{P(OPh)3}2, identified by comparison with an authen-
tic sample. For these reactions anhydrous MgSO4
was therefore employed as Lewis acid. The mode
of action of these additives is not clear to us present-
ly. The yields, melting points, analyses and infra-
Fe(CO)4{P(OPh)3}. The crystal structure of 1 has re-
cently been described [5].
Previous work from this laboratory has shown that
the photolysis of 1 results in CO loss and the formation
of a new compound 2, which may be isolated as a
moderately air-sensitive oil [6]. The structure of 2 was
deduced from its IR spectrum (two high frequency wCO
bands at 2034 and 1986 cm−1 indicating cis carbonyl
ligands and an oxidised metal centre) and from its
subsequent reactions with a variety of ligands (see
below). It was formulated as the orthometallated iron
hydride HFe(CO)2{P(OPh)3}{(PhO)2POC6H4}; this as-
1
signment is supported by H-NMR spectroscopic data:
a broadened multiplet centred at l −9.36 is at-
tributable to the metal-bound H ligand.
In the presence of two-electron donor ligands L,
complex 2 undergoes an intramolecular reductive elimi-
nation (deorthometallation) and ligand addition to af-
ford Fe0 complexes Fe(CO)2{P(OPh)3}2(L). With
substrates such as HCl or H2, FeII complexes
Fe(CO)2{P(OPh)3}2(X)(Y) (X=H; Y=H, Cl) are ob-
tained [6]. This latter mode of reactivity was exploited
by Schubert and co-workers to prepare derivatives with
X=H and Y=SiR3 [7].
Scheme 1. Reactions of HFe(CO)2{P(OPh)3}{(PhO)2POC6H4} (2) with alkynes R1CCR2.

M. Barrow et al. / Journal of Organometallic Chemistry 612 (2000) 61–68
63
Table 1
Yields, melting points, analyses and infrared spectral data for 3–5
a
Compound
Yield
(%)
M.p.
(°C)
Analyses
%C
IR spectra b
%H
%P
w(CꢀO)
Other
3a
3b
4a
65
56
43
125–126 68.2(68.6)
85 64.1(64.9)
4.5(4.4)
4.1(5.0)
4.4(4.2)
7.1(6.8)
6.9(6.7)
7.0(6.9)
1980(8.0), 1914(10)
2000(5.8), 1934(10)
2041(9.4), 1987(10)
w(CꢀC) 1827(3.1)
w(CꢀC) 1789(1.2)
w(CꢁC) 1606(3.1), w(CꢁO)
1618(4.6)
w(CꢁC) 1605(3.1), w(CꢁO)
1618(4.2)
w(CꢁC) 1606(2.8), w(CꢁO)
1621(2.4)
w(CꢁC) 1606(3.6), w(CꢁO)
1621(2.8)
144–146 65.1(65.1)
135–136 59.6(60.4)
121–122 62.9(62.0)
120–121 61.6(61.6)
4b·12CH2Cl2
48
39
38
4.3(4.2)
4.5(4.8)
4.1(4.2)
7.6(7.0)
7.7(6.7)
7.0(7.2)
2045(9.2), 1994(10)
2039(7.4), 1983(10)
2040(8.3), 1985(10)
c
4c
4d
4e
42
42
144–146 59.9(60.4)
101–102 62.8(62.2)
4.1(4.2)
3.8(4.0)
7.1(7.1)
5.7(5.7)
2040(9.1), 1985(10)
2009(7.5), 1978(10) 1930(6.2),
1920(sh) d
w(CꢁO) and w(CꢁO) 1610(6.7)
5·12CH2Cl2
c
a Found with calculated values in parentheses.
b Spectra recorded as KBr disks; values in cm−1 with relative peak heights in parentheses.
c Contains 1CH2Cl2 of crystallisation.
2
d sh=shoulder.
Table 2
NMR spectroscopic data for 3–5
Compound Nucleus Spectral data a
3a
3b
1H b
13C c
31P e
1H
7.50–6.85 (m, Ph)
217.8 (br d s, CO), 151.6–121.1 (Ph), 91.9 (br s, CꢀC)
152.6 (s)
7.49–6.86 (m, 35H, Ph), 5.50 (s, 1H, CH), 3.83 (m, 2H, 2×CHHCH3), 3.70 (m, 2H, 2× CHHCH3), 1.28 (t, 6H,
CH3)
215.8 (br s, CO), 215.1 (br s, CO), 151.0–120.6 (Ph), 85.7 (br s, CꢀC), 84.9 (br s, CꢀC), 92.3 (s, CH), 61.4 (s,
CH2), 15.7 (s, CH3)
13C
4a
1H
7.21–6.90 (m, 35H, Ph), 1.79 (s, 3H, CH3)
13C
261.1 (t, 2JCP=31 Hz, CꢁO), 258.7 (t, 2JCP=30 Hz, CꢁO), 206.2 (m, 2×CꢀO), 167.4 (s, CꢁC), 167.1 (s, CꢁC),
151.0–121.1 (Ph), 12.8 (s, CH3)
4b
4c
1H
13C
1H
7.42–6.78 (m, 30H, Ph), 1.65 (s, 6H, CH3)
260.5 (t, 2JCP=30 Hz, CꢁO), 206.0 (t, 2JCP=20 Hz, CꢀO), 162.1 (s, CꢁC), 151.0–120.8 (Ph), 13.58 (s, CH3)
7.35–6.70 (m, 30H, Ph), 5.59 (s, 1H, CH), 3.57 (m, 2H, 2× CHHCH3), 3.36 (m, 2H, 2× CHHCH3), 2.05 (s, 3H,
CꢁCCH3), 1.00 (t, 6H, JHH=7.1 Hz, CH2CH3)
13C
261.3 (t, 2JCP=30 Hz, CꢁO), 259.7 (t, 2JCP=30 Hz, CꢁO), 206.4 (t, 2JCP=24 Hz, CꢀO), 206.1 (t, 2JCP=24 Hz,
CꢀO), 169.9 (s, CꢁC), 162.8 (s, CꢁC), 151.5–121.4 (Ph), 98.0 (s, CH), 63.3 (s, CH2), 15.4 (s, CH2CH3), 12.0 (s,
CH3)
31P
1H
145.2 (s)
4d
7.36–6.90 (m, 30H, Ph), 4.36 (s, 2H, CH2), 3.43 (s, 1H, OH), 1.65 (s, 3H, CH3)
259.1 (t, 2JCP=31 Hz, CꢁO), 258.0 (t, 2JCP=31 Hz, CꢁO), 206.0 (t, 2JCP=20 Hz, CꢀO), 205.2 (t, 2JCP=20 Hz,
CꢀO), 165.0 (s, CꢁC), 161.8 (s, CꢁC), 151.0–120.1 (Ph), 59.1 (s, CH2), 11.1 (s, CH3)
7.26–6.91 (m, 30H, Ph), 4.36 (s, 4H, CH2), 3.08 (s, 2H, OH)
13C
4e
5
1H
13C
1H
261.3 (t, 2JCP=29 Hz, CꢁO), 205.7 (t, 2JCP=21 Hz, CꢀO), 165.4 (s, CꢁC), 151.2–120.7 (Ph), 58.0 (s, CH2)
7.39–6.38 (m, Ph)
13C
217.9 (br d, 2JCP=27.3 Hz, Fe2ꢂCO), 209.0 (br d, 2JCP=23.7 Hz, Fe1ꢂCO) 172.2 (br d, 2JCP=15.1 Hz, 2× CPh),
151.3–120.8 (Ph), 107.6 (s, 2×CH)
170.3 (s), 161.9 (s)
31P
a Obtained in CDCl3 solution; chemical shifts in ppm.
b 270 MHz; referenced to tetramethylsilane.
c 67.8 MHz; referenced to internal CDCl3.
d br=broad.
e 121 MHz; referenced to 85% phosphoric acid in D2O with downfield shifts reported as positive.

64
M. Barrow et al. / Journal of Organometallic Chemistry 612 (2000) 61–68
spectrum of 3a exhibits broadened resonances for both
the carbonyl and acetylenic carbon atoms at l 217.8
and 91.9, respectively; that of 3b, which contains the
unsymmetrical alkyne PhCꢀCCH(OEt)2, exhibits sepa-
rate but broadened carbonyl carbon resonances (l
215.8 and 215.1) suggesting the possibility of a dynamic
process in this complex at temperatures above ambient.
The structure of 3a was determined by an X-ray
diffraction study. The molecule resides on a crystallo-
graphic two-fold axis containing the iron atom and
bisecting the alkyne ligand. An ORTEX [9] diagram of
the molecule is shown in Fig. 1 with selected bond
lengths and angles. The configuration about the central
iron atom is approximately trigonal bipyramidal with
the phosphite ligands occupying the trans apical sites
[PꢂFeꢂP bond angle=177.04(2)°]. The FeꢂP bond dis-
red spectral data of the products are presented in
Table 1; NMR spectroscopic data are contained in
Table 2.
2.1. p2-Alkyne complexes
The simple ligand-addition products Fe(CO)2-
{P(OPh)3}2(L) 3 were obtained only for L=PhCꢀCPh
and PhCꢀCCH(OEt)2. The structures of 3 were inferred
from the infrared and NMR spectroscopic data: in
particular, a band at 1827 cm−1 in the IR spectrum of
3a was identified as a wCꢀC stretching frequency by
comparison with that reported for Fe(CO)2{P(OMe)3}2-
(PhCCPh) (6) (wCꢀC=1832 cm−1) [8]. The 13C-NMR
,
tances at 2.1702(5) A are substantially lengthened com-
pared to the parent tricarbonyl complex 1 which has
,
FeꢂP=2.1408(8) and 2.1421(8) A [5]. The asymmetry
of the phosphite ligands noted in 1 is also observed in
3a where one of the FeꢂPꢂO bond angles at 112.20(5)°
is considerably smaller than the remaining two
[118.20(5) and 120.58(6)°].
The carbonyl ligands and the acetylenic CC moiety
comprise the equatorial plane of the molecule. The
distance from the Fe atom to the centroid of the
2
,
h -diphenylacetylene is 1.9554(15) A and the bite angle
(C2ꢂFeꢂC2%) of this ligand is 36.10(11)°. The alkyne is
bent into cis geometry with a PhꢂCꢂC angle of
148.42(9)°, which may be compared with a value of
148.9(2)° in 6. These PhꢂCꢂC angles are at the upper
end of a range of 135–154° reported for the diphenyl-
acetylene ligand in mononuclear metal complexes [10];
the larger the angle, the smaller the deviation from the
ideal linear geometry of the free PhCꢀCPh ligand. The
Fig. 1. ORTEX diagram of the molecular structure of 3a. Selected
,
bond lengths (A) and angles (°): FeꢂP1, 2.1702(5); FeꢂC1, 1.769(2);
FeꢂC2, 2.0566(16); C2ꢂC2%, 1.274(4); C2ꢂC11, 1.447(3); P1ꢂFeꢂP11,
177.04(2);
C1ꢂFe1ꢂC11,
111.06(12);
C1ꢂFeꢂC2,
142.35(8);
C2ꢂFeꢂC21, 36.10(11); FeꢂP1ꢂO21, 112.20(5); FeꢂP1ꢂO31, 120.58(6);
FeꢂP1ꢂO41, 118.20(5). Symmetry operator %= −x, y, 1/2−z.
,
CC bond length in 3a is 1.274(4) A and is comparable
,
to that in 6 [1.263(6) A]; these values lie towards the
shorter end of the reported range of coordinated
,
diphenylacetylene CC distances of 1.24–1.35 A [10].
2.2. Maleoyl complexes
Complexes 4a–e were obtained on reaction of 2 with
the internal alkynes listed in Scheme 1. These species
are distinguished by considerably higher wCO stretching
frequencies (Table 1) than for the h2-alkyne complexes
3 and by the absence of any IR bands attributable to an
acetylenic CC group. Instead, weak IR absorption
bands at ca. 1606 cm−1 and 13C-NMR signals in the
region 160–165 ppm indicated the presence of olefinic
carbons and suggested that oligomerisation of the
alkyne had occured. In fact, these compounds were
identified as ferracyclopentenedione complexes by an
X-ray diffraction analysis of a representative example,
4c.
Fig. 2. ORTEX diagram of the molecular structure of 4c (major
,
conformation). Selected bond lengths (A) and angles (°): FeꢂP1,
2.1631(12); FeꢂP2, 2.1747(12); FeꢂC1, 1.812(4); FeꢂC2, 1.773(8);
FeꢂC3, 1.959(7); FeꢂC6, 2.004(5); C3ꢂC4, 1.520(6); C4ꢂC5, 1.321(7);
C5ꢂC6, 1.503(7); C3ꢂO3, 1.247(6); C6ꢂO4, 1.222(6); P1ꢂFeꢂP2,
167.89(4); C1ꢂFeꢂC2, 97.4(2); C2ꢂFeꢂC6, 91.6(3); C3ꢂFeꢂC6, 80.8(2);
C1ꢂFeꢂC3, 90.3(2); FeꢂC6ꢂC5, 113.8(4); FeꢂC3ꢂC4, 115.4(5).

M. Barrow et al. / Journal of Organometallic Chemistry 612 (2000) 61–68
65
Fig. 3. A view of two symmetry-related molecules of 4c depicting the maleoyl disorder.
An ORTEX diagram of the major conformation (the
disorder is described below) of molecule 4c is shown in
Fig. 2 together with selected bond lengths and angles.
The alkyne ligand has undergone double carbonylation
to generate a five-membered maleoyl-type metallacycle.
The bonding within this ring is similar to that in the
related compounds Fe(CO)4[h1:h1-C(O)C2Et2C(O)] (7)
[11] and Fe(CO)4[h1:h1-C(O)C(Me)C(C2Me)C(O)] (8)
[12]. There is no evidence for delocalisation in the ring:
The maleoyl residue in molecule 4c adopts two dis-
tinct orientations in the asymmetric unit of the crystal
structure. In the average structure, the conformation
(EtO)2CHꢂC(4)ꢁC(5)ꢂMe represents the major maleoyl
orientation (0.805 site occupancy) and is superimposed
upon MeꢂC(4)ꢁC(5)ꢂCH(OEt)2, the minor orientation
(remaining 0.195 site occupancy). Molecules of 4c crys-
tallise such that the maleoyl groups of neighbouring
molecules reside about an inversion centre and in close
proximity; a dimer showing the disorder is depicted in
Fig. 3. Phenyl rings surround this disorder volume
element.
,
C4ꢂC5 [1.321(7) A] is a typical CꢂC double bond;
,
,
C3ꢂC4 [1.520(6) A] and C5ꢂC6 [1.503(7) A] are single
bonds. The FeꢂCO (ketonic) bond lengths of 1.959(7)
,
and 2.004(5) A are in the range of values found for
FeIIꢂC(sp2) bonds, although slightly shorter than the
2.3. Ferrole complexes
,
mean value (2.05 A) [13] and the corresponding dis-
,
,
tances in both 7 (mean 2.009 A) and 8 (mean 2.024 A).
The relative electron richness of the Fe(CO)2{P(OPh)3}2
fragment compared to Fe(CO)4 may account for the
more strongly deshielded 13C-NMR resonance of these
carbons (ca. l 260) compared to those in 7 and 8 (ca. l
The binuclear iron ferrole 5 is the third structural
type observed in this study. Ferrole complexes are
amongst the most common of the iron alkyne deriva-
tives and numerous X-ray studies have been reported
[1,15]. The molecular structure of 5 is shown in Fig. 4
with selected bond lengths and angles. The Fe1ꢂFe2
,
240). The distances C3ꢂO3 [1.247(6) A] and C6ꢂO4
,
,
[1.222(6) A] are slightly, but not significantly, longer
distance of 2.552(2) A is at the upper end of the range
,
than normal CꢁO bonds (1.21 A) [13]. The coordina-
reported for the ferrole complexes [1]. It may be con-
tion about the FeII centre is completed by two CO
ligands co-planar with the maleoyl ring and by two
trans phosphites above and below this plane. Distor-
tions from octahedral geometry are relatively small
apart from the C3ꢂFeꢂC6 angle of 80.8(2)° imposed by
the ring [and the correspondingly large C1ꢂFeꢂC2 angle
of 97.4(2)°] and a significant displacement of the trans
phosphite ligands in the direction of the ring
[P1ꢂFeꢂP2=167.89(4)°]. This inclination of the axial
ligands appears to be a common feature of iron-male-
oyl structures [11,12,14].
trasted with an FeꢂFe distance of 2.515(1) A in the
,
parent ferrole Fe2(CO)6(C2H2)2 [16] and is comparable
,
to that observed in Fe2(CO)6{C2(OH)(Et)}2 [2.544(3) A]
[11].
The symmetrical ferracyclopentadiene ring results
from the tail-to-tail coupling of the unsymmetrical ter-
minal alkyne HCꢀCPh. The CꢂC bond lengths within
this ring are equivalent with values intermediate be-
tween single and double bonds [range 1.397(10)–
,
1.416(11) A]. This bond length equalisation has been
explained by two different charge redistribution mecha-

66
M. Barrow et al. / Journal of Organometallic Chemistry 612 (2000) 61–68
1
nisms viz., p delocalisation and metal-induced s, p
rehybridisation [17].
The ferrole ring protons were not detected in the H-
NMR spectrum of 5: possibly they are sufficiently
deshielded to be obscured by the phenyl resonances of
the P(OPh)3 ligands.
As in the majority of structurally characterised ferrole
complexes, 5 adopts the non-sawhorse conformation in
which the CO and P(OPh)3 ligands on the two iron atoms
are staggered. The result is to place one of the CO ligands
on Fe2 in a semi-bridging position where it is able to
accept some of the electronic charge accumulated on the
ring iron atom by the formal dative bond Fe2“Fe1.
However, in 5 this interaction is highly asymmetric: the
important dimensions are Fe2ꢂC3=1.763(9), Fe1ꢂC3=
Complex 5 was also accessible on treatment of
Fe(CO)2{P(OPh)3}2(PhCCPh) (3a) with HCꢀCPh. The
reaction was slow, occuring on a timescale comparable
with that of the reaction of 2 with HCꢀCPh, and
affording the product, 5, in similar yield. There was no
spectroscopic evidence for the formation of ferrole spe-
cies other than 5: the coupling of PhCꢀCPh and HCꢀCPh
was not observed.
There was also no evidence in the reactions of either
2 or 3a with HCꢀCPh for the formation of the vinylidene
complex Fe(CO)2{P(OPh)3}2(ꢁCꢁCHPh) although Berke
and co-workers have demonstrated the facility with
which Fe(CO)2L2 {L=PEt3, P(OMe)3} fragments in-
duce this rearrangement [20].
,
2.666(14) A and Fe2ꢂC3ꢂO3=173.3(12)°. The Fe1ꢂC3
,
distance has been observed to vary from 2.80 to 2.32 A
in different derivatives of this structural class [1]. Thus,
,
the value of 2.67 A in 5 is comparatively long. The
Fe2ꢂC3ꢂO3 angle is larger than any previously reported
suggesting that the structure of 5 may be intermediate
between the sawhorse and non-sawhorse forms. Theoret-
ical studies have shown that very small energy differences
exist between the two geometries [18].
The solution-state spectroscopic data for 5 are in
accordance with the solid state structure. The carbonyl
region of the 13C-NMR spectrum exhibits two doublet
resonances (Table 2) which were assigned by comparison
with literature data. The ferrole ring carbon resonances
occur at l 172.2 and 107.6: the more deshielded doublet
signal was assigned to the ring carbons C5 and C8
directly bonded to Fe1 and strongly coupled to P1; the
high-field singlet resonance was identified as the H-sub-
stituted carbon atoms C6 and C7 by a DEPT NMR
experiment. These chemical shifts are in line with those
observed in similarly substituted ferrole ring systems [19].
3. Conclusions
The reaction of the orthometallated iron hydride 2
with alkynes has been shown to selectively afford either
h2-alkyne (3), maleoyl (4) or ferrole (5) derivatives
depending on the alkyne chosen. The relatively high-yield
syntheses of 4 are noteworthy since it is well documented
that maleoyl formation from alkynes and metal car-
bonyls is severely limited by low selectivity [21]. In a
future publication we will describe the reactivity of the
complex 3a and develop the mechanistic relationship
between 3a, 4 and 5.
4. Experimental
4.1. General methods
All reactions were performed under N2 using solvents
predried by standard procedures. Alkynes and
triphenylphosphite were purchased from Aldrich and
used without further purification. Infrared spectra were
1
recorded on a Perkin–Elmer 1710FT spectrometer. H
and 13C{1H}-NMR spectra were obtained on a Jeol
JNM-GX270 FT-NMR spectrometer; 31P{1H}-NMR
spectra were obtained on a Varian 300 MHz FT-NMR
spectrometer. Elemental analyses were performed in the
Microanalytical Laboratory, University College Dublin.
Fig. 4. ORTEX diagram of the molecular structure of 5. Selected bond
,
lengths (A) and angles (°): Fe1ꢂFe2, 2.552(2); Fe1ꢂP1, 2.105(4);
4.2. Synthesis of Fe(CO)3{P(OPh)3}2 (1)
Fe1ꢂC1, 1.787(8); Fe1ꢂC2, 1.773(8); Fe1ꢂC3, 2.666(14); Fe1ꢂC5,
1.988(7); Fe1ꢂC8, 1.976(7); Fe2ꢂP2, 2.148(3); Fe2ꢂC3, 1.763(9);
Fe2ꢂC4, 1.757(10); Fe2ꢂC5, 2.098(9); Fe2ꢂC6, 2.099(9); Fe2ꢂC7,
2.134(9); Fe2ꢂC8, 2.159(9); C5ꢂC6, 1.416(11); C6ꢂC7, 1.397(10);
C7ꢂC8, 1.411(10); Fe1ꢂC5ꢂC6, 112.9(5); C5ꢂC6ꢂC7, 115.5(6);
C6ꢂC7ꢂC8, 114.5(6); C7ꢂC8ꢂFe1, 114.1(5); C8ꢂFe1ꢂC5, 81.7(3);
P1ꢂFe1ꢂFe2, 133.91(8); C1ꢂFe1ꢂC2, 85.3(4); Fe1ꢂFe2ꢂP2, 147.59(8);
C3ꢂFe2ꢂC4, 92.1(5).
A solution of triphenylphosphite (40 ml, 152 mmol)
and iron pentacarbonyl (10 ml, 76 mmol) in mesitylene
(80 ml) was heated at reflux for 20 h. The reaction
mixture was allowed to cool and was then filtered.
Methanol (ca. 150 ml) was added to the filtrate and the

M. Barrow et al. / Journal of Organometallic Chemistry 612 (2000) 61–68
67
solution cooled in ice for ca. 1 h. The resulting precipi-
tate was collected by filtration and washed with
petroleum ether (40–60°C) to afford 1 as an analyti-
cally pure white solid (37.5 g, 65% yield). M.p. 121–
122°C. IR (cm−1) wCO 1927(10), 1917(9.6) (KBr).
31P{1H}-NMR 182.0 (s).
overnight. The mixture was filtered, concentrated to
dryness and the residue was purified by column chro-
matography on alumina. Elution with 1:1 hexanes–
dichloromethane afforded
a
pale red material
containing unidentified by-products of the photolysis.
The required product was obtained as a yellow–orange
material on elution with dichloromethane or THF.
Recrystallisation from toluene–hexane or CH2Cl2–hex-
ane mixtures afforded the product as a yellow solid.
4.3. Synthesis of HFe(CO)2{P(OPh)3}-
{(PhO)2POC6H4} (2)
A stirred solution of 1 (0.500 g, 0.66 mmol) in
toluene (50 ml) was cooled in an ice–water bath and
irradiated with a 125 W mercury vapour lamp until the
starting material was consumed (typically 1–2 h) as
determined by IR spectroscopy. The resulting solution
4.5. Reaction of 3a and HCꢀCPh
Phenylacetylene (0.03 ml, 0.27 mmol) was added to a
solution of 3a (0.20 g, 0.220 mmol) in toluene (15 ml)
and the mixture was allowed to stir overnight at r.t. It
was concentrated and the residue was chromatographed
on alumina as described above to give 5 (38% yield).
of 2 was used directly in further reactions. IR (cm−1
)
wCO 2034(10), 1984(7.8) (toluene). 1H-NMR (d6-ben-
zene) 7.8–6.0 (m, Ph), −9.36 (br m, FeꢂH).
4.6. X-ray data collection and structure refinement
4.4. General procedure for the synthesis of 3–5
X-ray quality single crystals of 3a, 4c and 5 were
grown from either benzene–hexane or toluene–hexane
solutions. X-ray data were collected on an Enraf Non-
ius CAD4 diffractometer with graphite monochroma-
A stoichiometric amount of the required alkyne was
added to a solution of 2 prepared as described above.
Approximately 0.01 g of the appropriate Lewis acid
(ZnCl2·nH2O or anhydrous MgSO4) was introduced
and the resulting mixture was allowed to stir at r.t.
,
tised Mo–Ka radiation (l=0.7093 A) at 293(2) K.
Data were corrected for Lorentz and polarisation ef-
Table 3
Summary of crystal data and details of the data collection and refinement for 3a, 4c and 5
Complex
3a
4c
5
Empirical formula
Molecular weight (g mol−1
Colour, habit
Crystal size (mm)
Crystal system
C52H40FeO8P2
910.63
Orange, block
0.50×0.38×0.35
C48H44FeO12P2
930.62
Yellow, block
0.43×0.32×0.24
Triclinic
C56H42Fe2O10P2
1048.59
Yellow, block
0.42×0.37×0.25
)
Monoclinic
Monoclinic
(
Space group
C2/c
25.022(2)
10.005(2)
19.228(2)
90
111.88(2)
90
4466.9(11)
4
1.354
1888
P1
9.214(2)
P21/c
11.133(2)
47.549(10)
11.451(2)
,
a (A)
,
b (A)
12.398(2)
20.413(3)
90.720(10)
97.00(1)
99.97(2)
2278.2(7)
,
c (A)
h (°)
i (°)
k (°)
90
118.39(10)
90
5332.7(17)
4
1.403
2328
0.665
3
,
Volume (A )
Z
2
Dcalc (Mg m−3
F(000)
)
1.357
968
0.463
v (mm−1
)
0.465
q range for data collection
hkl range
Reflections collected
Unique reflections
2–25
2–25
2–25
−3–32, −3–13, −15–23
4944
4542
0–5, –18–18, −30–30
8867
7762
0–5, −14–34, −16–14
7480
6896
Reflections with [I\2|(I)]
Data/restraints/parameters
Goodness-of-fit
3769
4542/0/285
1.078
3543
7762/214/725
0.891
5738
6896/144/758
1.362
Final R indices [I\2|(I)]
R indices (all data)
Density range in final D-map (e A
R1=0.045, wR2=0.129
R1=0.051, wR2=0.134
1.01, −0.33
R1=0.060, wR2=0.147
R1=0.140, wR2=0.174
0.58, −0.58
R1=0.108, wR2=0.297
R1=0.123, wR2=0.309
1.72, −1.32
−3
,
)

68
M. Barrow et al. / Journal of Organometallic Chemistry 612 (2000) 61–68
fects but not for absorption. The structures were solved
by direct methods, SHELXS-86 [22], and refined by
full-matrix least squares using SHELXL-97 [23]. Hydrogen
atoms were included in calculated positions using the
default SHELXL-97 CꢂH settings with displacement
parameters 20–50% larger than the atoms to which they
were attached (depending on carbon type). Calculations
were performed on a Silicon Graphics R4000 computer.
Details of the X-ray data collection and structure
refinement are summarised in Table 3.
Data Centre, CCDC no. 143982, 143983 and 143984 for
compounds 3a, 4c and 5, respectively. Copies of this
information may be obtained free of charge from The
Director, CCDC, 12 Union Road, Cambridge, CB2
1EZ, UK (Fax: +44-1223-336033; e-mail: deposit@
ccdc.cam.ac.uk or www: http://www.ccdc.cam.ac.uk).
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Seyferth, C.M. Archer, J.C. Dewan, Organometallics 10 (1991)
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In the penultimate stages of refinement of 4c {when
R[F2\2|(F2)] was 0.08}, it was noted that considerable
disorder is present in the maleoyl residue. The
CH(OCH2CH3)2 group (attached to the alkenyl C4) has
large displacement parameters; this is not uncommon for
structures incorporating the acetal group [24]. At this
refinement stage, the highest peaks in the residual elec-
tron density map (ca. 1 e A−3) lay in close proximity to
,
the methyl group C12 (bonded to the neighbouring
,
alkenyl C5) at distances ca. 1.3–1.6 A and angles of
100–120° (in a chain) suggesting that either residual
solvent or some component of disorder was present in
this volume element of the crystal structure. These
residual peaks were initially included as minor ethoxy
sites in subsequent refinement cycles with a fixed site
occupancy factor of 0.25. A model of the minor acetal
site at the major methyl position (s.o.f.=0.75) was
fashioned using DFIX bond/angle restraints in combina-
tion with moderate DELU/ISOR SHELXL-97 controls
anchored at the alkenyl C4ꢁC5 part of the ligand. In the
succeeding refinement cycles, the site occupancy factors
of the major and minor acetal site refined freely to 0.805
and 0.195, respectively, and were fixed in the final
least-squares refinement cycles. Disorder in one of the
ethoxy groups in the major maleoyl site was noted
(0.630/0.175) and modelled; disorder in one of the phenyl
rings was also present in {C43A,…C48A/C43B,…C48B}
which refined to 63 and 37% occupancy factors, respec-
tively. The R-factor drops from 6.9 to 6.0% by the
successful modelling of the acetal/phenyl ring disorder
giving a final shift/error ratio of 0.02.
The crystal of 5 decayed by 60% during the data
collection as noted from the intensities of the three
standard reflections thus limiting the precision of our
results; however, the overall structure of 5 was unequiv-
ocally established. In the crystal structure, solvent of
crystallisation was obvious at an intermediate stage of the
refinement process; this was successfully modelled as
three orientations of a benzene solvent of crystallisation,
which is loosely held in a large void in the crystal lattice.
[22] G.M. Sheldrick, Acta Crystallogr. Sect. A 46 (1990) 467.
[23] G.M. Sheldrick, SHELXL-97, A Program for the Refinement of
Crystal Structures, University of Go¨ttingen, Germany, 1997.
[24] P. Butler, J.F. Gallagher, A.R. Manning, Inorg. Chem. Com-
mun. 1 (1998) 343.
5. Supplementary material
Crystallographic data for the structural analyses have
been deposited with the Cambridge Crystallographic
.