Migratory insertion and CO substitution reactions of the β,γ-unsaturated esters and amides [Fe2(CO)5(μ-PPh2)μ-η 1:η2-{NuC(O)CH2}C=CH2}] (Nu = OMe, OEt, OPri, NHPh, NHB

Article abstract of DOI:10.1016/S0022-328X(00)00823-8

Reaction of the β,γ-unsaturated esters and amides [Fe₂(CO)₅(μ-PPh₂)(μ-η ¹(O):η¹(C):η²(C)-{NuC(O)CH ₂}C=CH₂)] (Nu = OMe, 1a; R = OEt, 1b; R = OPrⁱ, 1c, R = N

Full text of DOI:10.1016/S0022-328X(00)00823-8

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 620 (2001) 150–164
Migratory insertion and CO substitution reactions of the
b,g-unsaturated esters and amides
[Fe2(CO)5(m-PPh2)(m-h1:h2-{NuC(O)CH2}CꢀCH2}] (Nu=OMe,
OEt, OPri, NHPh, NHBut): synthesis and characterisation of
acyl-bridged [Fe2(CO)4L2(m-PPh2)(m-CꢀO{CꢀCH2}CH2C(O)Nu)]
(L2=dppm, dppe) and alkenyl-bridged
[Fe2(CO)4{P(Ome)3}2(m-PPh2)(m-h1:h2-{NuC(O)CH2}CꢀCH2)]
Simon Doherty a,*, Graeme Hogarth b, Mark Waugh a, Tom H. Scanlan a,
Mark R.J. Elsegood a, William Clegg a
a Department of Chemistry, Bedson Building, The Uni6ersity of Newcastle upon Tyne, Newcastle upon Tyne NE1 7RU, UK
b Department of Chemistry, Uni6ersity College London, 20 Gordon Street, London WC1H 0AJ, UK
Received 30 August 2000; received in revised form 28 September 2000; accepted 28 September 2000
This contribution is dedicated to Professor Arthur J. Carty on the occasion of his 60th birthday
Abstract
Reaction of the b,g-unsaturated esters and amides [Fe2(CO)5(m-PPh2)(m-h1(O):h1(C):h2(C)-{NuC(O)CH2}CꢀCH2)] (Nu=OMe,
1a; R=OEt, 1b; R=OPri, 1c, R=NHPh, 1d, R=NHBut, 1e) with dppe and dppm results in displacement of the acyl carbonyl
and migratory insertion to give the a,b,-unsaturated acyl derivatives [Fe2(CO)4(h2-dppe)(m-PPh2)(m-CꢀO{CꢀCH2}CH2C(O)Nu)]
(Nu=OMe, 2a; R=OEt, 2b; R=OPri, 2c, R=NHPh, 2d, R=NHBut, 2e) and [Fe2(CO)4(m-dppm)(m-PPh2)(m-
CꢀO{CꢀCH2}CH2C(O)Nu)] (R=OMe, 3a; R=OEt, 3b; R=OPri, 3c, R=NHPh, 3d), respectively. Single-crystal X-ray analyses
of 2a and 3a has revealed that the dppe ligand in the former chelates, with one arm binding trans and one cis to the phosphido
bridge, while the dppm and phosphido group in the latter both bridge the iron-iron bond and are trans to one another. In
contrast, reaction of 1a–c with trimethylphosphite results in displacement of the ester carbonyl oxygen to give
[Fe2(CO)5{P(OMe)3}(m-PPh2)(m-h1(C):h2(C)-{NuC(O)CH2}CꢀCH2}] (Nu=OMe, 4a; R=OEt, 4b; R=OPri, 4c) followed by CO
substitution to give [Fe2(CO)4{P(OMe)3}2(m-PPh2)(m-h1(C):h2(C)-{Nu(O)CCH2}CꢀCH2)] (Nu=OMe, 6a; R=OEt, 6b; R=OPri,
6c) with no evidence for the formation of the corresponding acyl-bridged derivative. Thermolysis of toluene solutions of 4a–c
result in loss of CO and coordination of the oxygen atom of the ester carbonyl to give [Fe2(CO)4{P(OMe)3}(m-PPh2)(m-
h1(O):h1(C):h2(C)-{NuC(O)CH2}CꢀCH2)] (Nu=OMe, 5a; R=OEt, 5b; R=OPri, 5c), an intermediate in the formation of 6a–c.
Complexes 5a and 6a have been characterised by single-crystal X-ray crystallography. © 2001 Elsevier Science B.V. All rights
reserved.
Keywords: Diiron; Migratory insertion; Acyl; Diphosphine; Alkenyl; Decarbonylation; Trigonal twist
1. Introduction
Migratory insertion of carbonyl into a metal–alkyl
bond is a synthetically useful transformation which is
utilised in a number of important stoichiometric and
catalytic reactions [1]. For instance, chiral iron enolates
* Corresponding author. Tel.: +44-191-2226644; fax: +44-191-
2226929.
E-mail address: simon.doherty@newcastle.ac.uk (S. Doherty).
0022-328X/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(00)00823-8

S. Doherty et al. / Journal of Organometallic Chemistry 620 (2001) 150–164
151
mode has been identified in which the acyl acts as a
five-electron donor through additional coordination of
the a,b-double bond [10].
derived from the corresponding acyl compounds have
been used to prepare b- and g-lactams via complex
multistep intramolecular cyclisations [2], and palla-
dium acyl complexes are key intermediates in the syn-
thesis of a,b-unsaturated carboxylic acids, esters
amides, aldehydes and ketones, often with elaborate
architectures [3]. In addition iron acyl complexes are
convenient precursors to non-heteroatom and het-
eroatom stabilised carbene complexes [4].
The most common migratory insertion reaction is
that involving carbon monoxide and a s-bond of a
mononuclear metal–alkyl or alkenyl complex [5]. Al-
though less numerous, there has recently been an in-
creasing number of reports of carbonyl insertion into
unsaturated metal bound hydrocarbons such as s-h-
alkenyls, to generate the corresponding binuclear a,b-
unsaturated acyl derivatives [6]. In contrast to the
widespread use of mononuclear a,b-unsaturated acyl
complexes in organic synthesis, there are surprisingly
few reports of the use of their diiron counterparts in
metal mediated synthesis. However, recent studies by
Gilbertson have demonstrated that these complexes
may also have a rich and varied reactivity with poten-
tial applications in organic synthesis. For instance,
(1)
We have recently been involved in a detailed study
of the reactivity of the s-h-allenyl ligand in
[Fe2(CO)6(m-PPh2){m-h1:h2-C(H)ꢀCꢀCH2}] towards a
range of nucleophilic reagents [11], reasoning that the
cumulated fragment –CHꢀCꢀCH2 could be a poten-
tially versatile building block for the synthesis of a
wide range of organic products. Our studies have re-
vealed that [Fe2(CO)6(m-PPh2){m-h1:h2-C(H)ꢀCꢀCH2}]
reacts with a range of amines and alcohols to give the
b,g-unsaturated amides and esters [Fe2(CO)5(m-PPh2)-
(m - h1(O):h1(C):h2(C)–{NuC(O)CH2}CꢀCH2}] (1a–e),
6ia a highly unusual nucleophile–carbonyl–allenyl
coupling sequence (Eq. (1)) [12]. We became interested
in the carbonyl insertion reactions of these complexes
since the product of this transformation would be a
highly functionalised a,b-unsaturated acyl, capable of
binding to the metal centre through either the alkene
or carbonyl group, and suitable for further functional-
isation. Herein, we report that [Fe2(CO)5(m-PPh2)-
[Fe2(CO)6(m-SPrn){m-OꢀC(CHꢀCHCH3)}]
undergoes
exo-selective Diels–Alder reactions with Danishefsky’s
diene (Scheme 1a) [7], stereo and regioselective [3+2]
cycloaddition reactions with nitrones, to give the cor-
responding 4-isoxazolidenes (Scheme 1b) [8], and ki-
netic resolution in its reaction with enantiomerically
pure nitrones, derived from proline, to give the ex-
pected bicyclic isoxazolidene as a single diastereoiso-
mer (Scheme 1c) [9].
(m-h1(O):h1(C):h2(C)–{NuC(O)CH2}CꢀCH2}]
reacts
with dppm and dppe to give the corresponding phos-
phine substituted a,b-unsaturated acyl derivatives
whereas trimethylphosphite reacts 6ia carbonyl substi-
tution to give the corresponding alkenyl derivatives
(Scheme 2).
In the vast majority of binuclear complexes the acyl
ligand acts as a three-electron donor, through oxygen
and carbon. Recently however, an alternative binding
Scheme 1.

152
S. Doherty et al. / Journal of Organometallic Chemistry 620 (2001) 150–164
Scheme 2.
2. Experimental
placed on a 300×30 mm2 alumina column. Elution
with an n-hexane–dichloromethane mixture (50:50, v/v)
gave a single major band identified as 2a. Crystallisa-
tion from dichloromethane–n-hexane gave 2a as or-
2.1. General comments
ange crystals in 65% yield (0.220 g). IR (w(CO), cm−1
,
Unless otherwise stated, all manipulations were car-
ried out in an inert atmosphere glove box or by using
standard Schlenk line techniques. Diethyl ether and
hexane were distilled from Na–K alloy, tetrahydro-
furan from potassium and dichloromethane from
C6H14): 2013 s, 1961 m, 1940 m, 1901 m, 1747 w, 1653
w. 31P{1H} (121.498 MHz, CDCl3, l): 167.9 (dd,
2JPP=123.0 Hz, 2JPP=11.0 Hz, m-PPh2), 85.9 (dd,
2JPP=123.0 Hz, 2JPP=23.1 Hz, dppe), 79.4 (dd, 2JPP
=
23.1 Hz, 2JPP=11.0 Hz, dppe). 1H-NMR (200.132
MHz, CDCl3, l): 8.01–7.92 (m, 2H, C6H5), 7.38–6.76
(m, 26H, C6H5), 6.50–6.42 (m, 2H, C6H5), 6.19 (s, 1H,
CꢀCHaHb), 5.63 (s, 1H, CꢀCHaHb), 3.51 (s, 3H,
OCH3), 3.16–2.78 (m, 2H, P–CH2–CH2–P), 2.66–2.31
CaH2. CDCl3 was pre-dried with CaH2 and vacuum
transferred and stored over 4 A molecular sieves. H-
1
,
and 31P-NMR spectra were recorded on a JEOL
LAMBDA 500 or Bruker AC 200, AMX 300 and DRX
500 machines. Column chromatography was carried
out with alumina purchased from Aldrich Chemical
Company and deactivated with 6% w/w water prior to
loading. The diiron complexes [Fe2(CO)6(m-PPh2){m-
2
(m, 2H, P–CH2–CH2–P), 2.13 (d, 1H, JHH=16.5 Hz,
(O)CCHcHd), 1.85 (d, 1H, 2JHH=16.5 Hz,
(O)CCHcHd). 13C{1H}-NMR (125.65 MHz, CDCl3, l):
2
2
288.7 (d, JPC=16.6 Hz, m-acyl), 218.1 (td, JPC=12.6
Hz, 2JPC=25.5 Hz, CO), 214.3 (m, CO), 172.0 (s,
C(O)–OCH3), 148.6 (s, CꢀCH2), 140.9–127.3 (m,
h1:h2-(H)CꢀCꢀCH2}]
[11c],
[Fe2(CO)5(m-PPh2)(m-
(1a–e)
h1(C):h2(C):h1(O)–{Nu(O)CCH2}CꢀCH2)]
[12a] and [Fe2(CO)5{P(OMe)3}(m-PPh2)(m-h1:h2-{NuC-
(O)CH2}CꢀCH2}] (4a–c) [12b] were prepared as de-
scribed previously.
C6H5), 133.9 (d, 4JPC=10.7 Hz, CꢀCH2), 51.5 (s,
1
OCH3), 33.8 (s, CH2–C(O)OCH3), 31.6 (dd, JPC
=
2
25.5 Hz, JPC=15.4 Hz, P–CH2–CH2–P), 30.4 (ddd,
1JPC=26.7 Hz, JPC=14.2 Hz, JPC=4.7 Hz P–CH2–
CH2–P). Anal. Calc. for C48H41Fe2O6P3: C, 61.70; H,
4.42. Found: C; 61.62; H, 4.28.
2
3
2.1.1. Synthesis of [Fe2(CO)4(v-PPh2)(p2-dppe)-
(v-OꢀC–C{CH2}–CH2–C(O)OMe)] (2a)
A diethyl ether solution of [Fe2(CO)5(m-PPh2)(m-
Compounds 2b–e were prepared according to the
procedure described above for 2a.
h1(C):h2(C):h1(O)–{MeO(O)CCH2}CꢀCH2)]
(1a)
(0.200 g, 0.373 mmol) and dppe (0.746 mmol, 0.300 g)
was stirred for 16 h. The solvent was then removed
under reduced pressure and the residue dissolved in the
minimum amount of dichloromethane (2–3 ml), ab-
sorbed onto deactivated alumina, desolvated and
2.1.2. Synthesis of [Fe2(CO)4(v-PPh2)(p2-dppe)-
(v-OꢀC–C{CH2}–CH2–C(O)OEt)] (2b)
Isolated as dark red crystals in 65% yield from a
dichloromethane solution layered with n-hexane at

S. Doherty et al. / Journal of Organometallic Chemistry 620 (2001) 150–164
153
room temperature (r.t.). IR (w(CO), cm−1, C6H14):
IR (w(CO), cm−1, C6H14): 2013 s, 1959 m, 1940 m,
1903 w. 31P{1H} (121.498 MHz, CDCl3, l): 168.6 (dd,
2JPP=123.0 Hz, 2JPP=10.5 Hz, v-PPh2), 84.5 (dd,
2013 s, 1961 m, 1940 m, 1901 m, 1747 w, 1655 w.
2
31P{1H} (202.35 MHz, CDCl3, l): 168.1 (dd, JPP
=
=
2
122.0 Hz, 2JPP=10.0 Hz, m-PPh2), 85.8 (dd, JPP
2JPP=123.0 Hz, 2JPP=23.5 Hz, dppe), 79.0 (dd, 2JPP
=
2
2
2
1
122.0 Hz, JPP=23.0 Hz, dppe), 79.6 (dd, JPP=23.0
Hz, 2JPP=10.0 Hz, dppe). 1H-NMR (500.0 MHz,
CDCl3, l): 8.00–7.96 (m, 2H, C6H5), 7.43–6.79 (m,
26H, C6H5), 6.46 (m, 2H, C6H5), 6.18 (s, 1H,
CꢀCHaHb), 5.63 (s, 1H, CꢀCHaHb), 4.01 (q, 2H,
3JHH=6.8 Hz, OCH2CH3), 3.02 (m, 2H, P–CH2–
CH2–P), 2.48 (m, 2H, P–CH2–CH2–P), 2.13 (d,
23.5 Hz, JPP=10.5 Hz, dppe). H-NMR (500.0 MHz,
3
CDCl3, l): 7.99–6.80 (m, 33H, C6H5), 6.56 (t, JHH
=
8.8 Hz, 2H, C6H5), 6.32 (s, 1H, NH), 6.19 (s, 1H,
CꢀCHaHb), 5.75 (s, 1H, CꢀCHaHb), 3.18–2.82 (m, 2H,
P–CH2–CH2–P), 2.61–2.38 (m, 2H, P–CH2–CH2–P),
2.17 (d, 2JHH=15.8 Hz, 1H, (O)CCHcHd), 1.99 (d,
2JHH=15.8 Hz, 1H, (O)CCHcHd). 13C{1H}-NMR
(125.65 MHz, CDCl3, l): 290.6 (br s, m-acyl), 217.9 (br
s, CO), 214.5 (m, CO), 168.5 (s, C(O)–NHPh), 149.9 (s,
2
2JHH=14.5 Hz, 1H, (O)CCHcHd), 1.87 (d, JHH=14.5
Hz, 1H, (O)CCHcHd), 1.18 (t, 3JHH=6.8 Hz, 3H,
OCH2CH3). 13C{1H}-NMR (125.65 MHz, CDCl3, l):
289.1 (br s, m-acyl), 218.2 (br s, CO), 214.6 (m, CO),
171.7 (s, C(O)–OCH2CH3), 148.9 (s, CꢀCH2), 140.6–
4
CꢀCH2), 140.7–119.3 (m, C6H5), 133.9 (d, JPC=8.0
1
Hz, CꢀCH2), 38.4 (s, CH2C(O)), 31.7 (dd, JPC=23.9
Hz, 2JPC=15.2 Hz, P–CH2–CH2–P), 30.4 (m, P–
CH2–CH2–P). Anal. Calc. for C53H44Fe2NO6P3: C,
63.94; H, 4.45; N, 1.41. Found: C; 63.76; H, 4.61; N,
1.36.
4
127.4 (m, C6H5), 133.9 (d, JPC=8.9 Hz, CꢀCH2), 60.3
(s, OCH2CH3), 34.1(s, CH2–C(O)OEt), 31.5 (dd,
2
1JPC=25.8 Hz, JPC=14.4 Hz, P–CH2–CH2–P), 30.3
(ddd, 1JPC=30.0 Hz, 2JPC=14.6 Hz, 3JPC=5.3 Hz,
P–CH2–CH2–P), 14.2 (s, OCH2CH3). Anal. Calc. for
C49H43Fe2O6P3: C, 62.05; H, 4.57. Found: C; 61.73; H,
4.42.
2.1.5. Synthesis of [Fe2(CO)4(v-PPh2)(p2-dppe)-
(v-OꢀCh–Ci{CkH2}–ClH2–Cm(O)NHBut)] (2e)
Isolated as dark red crystals in 55% yield from a
dichloromethane solution layered with n-hexane at r.t.
IR (w(CO), cm−1, C6H14): 2013 s, 1959 m, 1938 m,
1903 w, 1722 w, 1691 w. 31P{1H} (121.498 MHz,
2.1.3. Synthesis of [Fe2(CO)4(v-PPh2)(p2-dppe)-
(v-OꢀC–C{CH2}–CH2–C(O)OPri )] (2c)
2
2
Isolated as dark red crystals in 60% yield from a
dichloromethane solution layered with n-hexane at r.t.
IR (w(CO), cm−1, C6H14): 2013 s, 1961 m, 1940 m,
1903 w. 31P{1H} (121.498 MHz, CDCl3, l): 167.8 (dd,
2JPP=122.2 Hz, 2JPP=10.6 Hz, m-PPh2), 85.3 (dd,
CDCl3, l): 167.9 (dd, JPP=123.8 Hz, JPP=11.1 Hz,
m-PPh2), 87.3 (dd, 2JPP=123.8 Hz, 2JPP=23.7 Hz,
2
2
dppe), 79.1 (dd, JPP=23.7 Hz, JPP=11.1 Hz, dppe).
1H-NMR (500.0 MHz, CDCl3, l): 7.98–6.54 (m, 30H,
C6H5), 6.09 (s, 1H, CꢀCHaHb), 5.58 (s, 1H, CꢀCHaHb),
2JPP=122.2 Hz, 2JPP=23.1 Hz, dppe), 79.5 (dd, 2JPP
=
4.60 (s, 1H, NH), 3.07–2.91 (m, 2H, P–CH2–CH2–P),
2
1
2
23.1 Hz, JPP=10.6 Hz, dppe). H-NMR (500.0 MHz,
CDCl3, l): 8.00–7.96 (m, 2H, C6H5), 7.43–6.79 (m,
26H, C6H5), 6.48–6.14 (m, 2H, C6H5), 6.15 (s, 1H,
CꢀCHaHb), 5.62 (s, 1H, CꢀCHaHb), 4.89 (sept, 1H,
3JHH=6.4 Hz, CH–(CH3)2), 3.03 (m, 2H, P–CH2–
CH2–P), 2.47 (m, 2H, P–CH2–CH2–P), 2.10 (d,
2.59–2.50 (m, 2H, P–CH2–CH2–P), 1.76 (d, JHH
=
16.5 Hz, 1H, (O)CCHcHd), 1.61 (d, 2JHH=16.5 Hz, 1H,
(O)CCHcHd), 1.23 (s, 9H, NHC(CH3)3). 13C{1H}-NMR
(125.65 MHz, CDCl3, l): 290.3 (d, 2JPC=18.8 Hz,
2
2
m-acyl), 218.2 (dt, JPC=13.8 Hz, JPC=26.2 Hz, CO),
214.3 (m, CO), 170.7 (s, C(O)–NHBut), 150.9 (s,
2
4
2JHH=15.9 Hz, 1H, (O)CCHcHd), 1.87 (d, JHH=15.9
CꢀCH2), 140.6–127.2 (m, C6H5), 133.9 (d, JPC=9.4
Hz, 1H, (O)CCHcHd), 1.61 (d, 3JHH=6.4 Hz, 6H,
Hz, CꢀCH2), 51.1 (s, NHC(CH3)3), 38.4 (s, CH2–
CH–(CH3)2). 13C{1H}-NMR (125.65 MHz, CDCl3, l):
C(O)NHBut), 31.9 (dd, JPC=24.8 Hz, JPC=16.0 Hz,
1
2
2
2
2
288.2 (d, JPC=16.7 Hz, m-acyl), 218.4 (td, JPC=29.0
Hz, 3JPC=16.7 Hz, CO), 214.6 (m, CO), 171.2 (s,
C(O)–CH3), 149.1 (s, CꢀCH2), 140.9–127.3 (m, C6H5),
P–CH2–CH2–P), 30.7 (ddd, 1JPC=27.6 Hz, JPC
=
14.6 Hz, 3JPC=5.9 Hz, P–CH2–CH2–P), 28.7 (s,
NHC(CH3)3). Anal. Calc. for C45H48Fe2NO6P3: C,
62.79; H, 4.96; N, 1.44. Found: C; 62.58; H, 4.87; N,
1.75.
4
133.9 (d, JPC=9.6 Hz, CꢀCH2), 67.6 (s, CH–(CH3)2),
34.6 (s, CH2–C(O)OPri), 31.5 (dd, 1JPC=25.4 Hz,
2JPC=15.9 Hz, P–CH2–CH2–P), 30.4 (ddd, JPC
=
1
2
3
27.6 Hz, JPC=13.8 Hz, JPC=5.8 Hz, P–CH2–CH2–
P), 21.9 (s, CH–(CH3)2). Anal. Calc. for
C50H45Fe2O6P3: C, 62.39; H, 4.71. Found: C; 62.24; H,
4.49.
2.1.6. Synthesis of [Fe2(CO)4(v-PPh2)(v-dppm)-
(v-OꢀC–C{CH2}–CH2–C(O)OMe)] (3a)
A
toluene solution of [Fe2(CO)5(m-PPh2)(m-
h1(C):h2(C):h1(O)–{MeO(O)CCH2}CꢀCH2)]
(1a)
(0.200 g, 0.373 mmol) and dppm (0.286 g, 0.746 mmol)
was heated at 75°C for 3 h, after which time the solvent
was removed to give a dark oily residue. This was
dissolved in dichloromethane, absorbed onto deacti-
vated alumina and desolvated under high vacuum,
2.1.4. Synthesis of [Fe2(CO)4(v-PPh2)(p2-dppe)-
(v-OꢀC–C{CH2}–CH2–C(O)NHPh)] (2d)
Isolated as dark red crystals in 65% yield from a
dichloromethane solution layered with n-hexane at r.t.

154
S. Doherty et al. / Journal of Organometallic Chemistry 620 (2001) 150–164
placed on a 300×30 mm2 alumina column and eluted
with n-hexane–dichloromethane (50/50, v/v) to give a
major red–orange band which was crystallized from
dichloromethane–n-hexane to give 4a as orange crys-
tals in 75% yield (0.257 g). IR (w(CO), cm−1, C6H14):
1990 m, 1957 s, 1923 m, 1911 m, 1739 w,. 31P{1H}
dichloromethane solution layered with n-hexane at r.t.
IR (w(CO), cm−1, C6H14): 1990 m, 1957 s, 1921 m,
1911 w. 31P{1H} (121.498 MHz, CDCl3, l): 210.0 (dd,
2JPP=55.2 Hz, 2JPP=110.7 Hz, m-PPh2), 53.0 (dd,
2
2
2JPP=55.2 Hz, JPP=60.4 Hz, dppm), 43.8 (dd, JPP
=
110.7 Hz, 2JPP=60.4 Hz, dppm). 1H-NMR (500.0
MHz, CDCl3, l): 7.85–6.86 (m, 30H, C6H5), 5.09 (s,
1H, CꢀCHaHb), 4.97 (s, 1H, CꢀCHaHb), 4.18 (sept,
2
(121.498 MHz, CDCl3, l): 209.9 (dd, JPP=54.7 Hz,
2JPP=110.8 Hz, m-PPh2), 53.2 (dd, 2JPP=54.7 Hz,
2JPP=60.0 Hz, dppm), 44.1 (dd, 2JPP=110.8 Hz,
2JPP=60.0 Hz, dppm). 1H-NMR (200.132 MHz,
2
3JHH=6.4 Hz, 1H, CH–(CH3)2), 3.49 (ddd, JPH
=
2
2
23.5, JPH=13.4, JHH=3.0, 1H, P–CH2–P), 2.89 (m,
1H, P–CH2–P), 2.00 (d, 2JHH=16.8 Hz, 1H,
(O)CCHcHd), 1.82 (d, 2JHH=16.8 Hz, 1H,
CDCl3, l): 7.68–6.88 (m, 30H, C6H5), 5.09 (s, 1H,
2
CꢀCHaHb), 5.01 (s, 1H, CꢀCHaHb), 3.47 (ddd, JPH
=
2
2
23.8 Hz, JPH=13.4 Hz, JHH=3.3 Hz, 1H, P–CHH–
P), 2.88 (m, 1H, P–CHH–P), 2.86 (s, 3H, OCH3), 2.03
(O)CCHcHd),
0.89
(d,
3JHH=6.1
Hz,
3H,
CH(CH3)CH3), 0.78 (d, 3JHH=6.1 Hz, 3H,
2
2
(d, JHH=16.8 Hz, 1H, (O)CCHcHd), 1.92 (d, JHH
=
CH(CH3)CH3). 13C{1H} NMR (125.65 MHz, CDCl3,
16.8 Hz, 1H, (O)CCHcHd). 13C{1H}-NMR (125.65
l): 301.4 (td, JPC=21.0 Hz, JPC=Hz, m-CO), 219.8
2
3
2
3
2
2
MHz, CDCl3, l): 301.2 (td, JPC=21.5 Hz, JPC=3.6
Hz, m-acyl), 219.7 (t, 2JPC=22.5 Hz, CO), 218.2 (t,
2JPC=19.0 Hz, CO), 217.4 (s, CO), 213.4 (s, CO), 171.5
(s, C(O)–OCH3), 147.6 (s, CꢀCH2), 141.4–127.6 (m,
C6H5), 133.3 (d, 4JPC=8.3 Hz, CꢀCH2), 51.1 (s,
OCH3), 35.4 (m, CdHH–C(O)OCH3 and P–CH2–P).
Anal. Calc. for C47H39Fe2O7P3: C, 61.33; H, 4.27.
Found: C; 61.08; H, 4.39.
(t, JPC=24.0 Hz, CO), 218.3 (t, JPC=18.5 Hz, CO),
217.5 (s, CO), 213.3 (s, CO), 170.8 (s, Co(O)–OPri),
148.2 (s, CbꢀCH2), 141.4–127.6 (m, C6H5), 133.3 (d,
4JPC=7.6 Hz, CꢀCgH2), 67.2 (s, CH(CH3)2), 35.6 (m,
CdHH–C(O)OPri
and
P–CH2–P),
21.7
(s,
CH(CH3)CH3), 21.5 (s, CH(CH3)CH3). Anal. Calc. for
C49H43Fe2O7P3: C, 62.05; H, 4.57. Found: C; 62.37; H,
5.08.
Compounds 3b–d were prepared using a procedure
similar to that described above for 3a.
2.1.9. Synthesis of [Fe2(CO)4(v-PPh2)(v-dppm)-
(v-OꢀC–C{CH2}–CH2–C(O)NHPh)] (3d)
2.1.7. Synthesis of [Fe2(CO)4(v-PPh2)(v-dppm)-
(v-OꢀC–C{CH2}–CH2–C(O)OEt)] (3b)
Prepared following the procedure used for 3a except
1d and dppm were heated in toluene at 85°C for 3 h.
Isolated as orange–red crystals in 65% yield from a
dichloromethane solution layered with n-hexane at r.t.
IR (w(CO), cm−1, C6H14): 1990 s, 1957 s, 1921 m, 1912
w. 31P{1H} (121.498 MHz, CDCl3, l): 210.3 (dd,
2JPP=54.1 Hz, 2JPP=111.2 Hz, m-PPh2), 53.4 (dd,
Isolated as orange–red crystals in 75% yield from a
dichloromethane solution layered with n-hexane at r.t.
IR (w(CO), cm−1, C6H14): 1990 m, 1957 s, 1923 m,
1911 w. 31P{1H} (121.498 MHz, CDCl3, l): 210.1 (dd,
2JPP=55.3 Hz, 2JPP=110.8 Hz, m-PPh2), 53.4 (dd,
2
2
2
2
2JPP=55.3 Hz, JPP=59.6 Hz, dppm), 44.1 (dd, JPP
=
2JPP=54.1 Hz, JPP=60.6 Hz, dppm), 44.1 (dd, JPP
=
110.8 Hz, 2JPP=59.6 Hz, dppm). 1H-NMR (500.0
MHz, CDCl3, l): 7.85–6.86 (m, 30H, C6H5), 5.09 (s,
1H, CꢀCHaHb), 4.99 (s, 1H, CꢀCHaHb), 3.47 (ddd,
2JPH=26.8 Hz, 2JPH=13.2 Hz, 2JHH=3.1 Hz, 1H,
P–CHH–P), 3.23 (m, 2H, OCH2CH3), 2.89 (m, 1H,
P–CHH–P), 2.02 (d, 1H, 2JHH=16.8 Hz,
(O)CCHcHd), 1.91 (d, 1H, 2JHH=16.8 Hz,
(O)CCHcHd), 0.82 (t, 3JHH=5.5 Hz, OCH2CH3).
13C{1H}-NMR (125.65 MHz, CDCl3, l): 301.4 (td,
111.2 Hz, 2JPP=60.6 Hz, dppm). 1H-NMR (500.0
MHz, CDCl3, l): 7.91–6.78 (m, 35H, C6H5), 6.40 (s,
1H, NH), 5.17 (s, 1H, CꢀCHaHb), 5.07 (s, 1H,
2
CꢀCHaHb), 3.57 (m, 1H, P–CHH–P), 2.84 (dd, JPH
=
10.7 Hz, 2JPH=22.6 Hz, 1H, P–CH2–P), 1.90 (d,
2JHH=15.9 Hz, 1H, (O)CCHcHd), 1.83 (d, 1H, JHH
=
2
15.0 Hz, (O)CCHcHd). 13C{1H}-NMR (125.65 MHz,
2
CDCl3, l): 303.9 (br t, JPC=23.2 Hz, m-acyl), 219.3 (t,
2JPC=23.2 Hz, CO), 218.1 (t, 2JPC=18.1 Hz, CO),
217.5 (s, CO), 213.2 (s, CO), 168.3 (s, C(O)–NHPh),
149.0 (s, CꢀCH2), 142.0–123.8 (m, C6H5), 133.3 (d,
4JPC=8.0 Hz, CꢀCH2), 39.4 (m, CH2–C(O) and P–
CH2–P). Anal. Calc. for C52H42Fe2NO6P3:C, 63.63; H,
4.31; N, 1.43. Found: C; 63.67; H, 4.90; N, 1.40.
3
2
2JPC=22.2 Hz, JPC=3.6 Hz, m-acyl), 219.8 (t, JPC
=
2
21.6 Hz, CO), 218.2 (t, JPC=19.6 Hz, CO), 217.4 (s,
CO), 213.4 (s, CO), 171.1 (s, Co(O)–OCH2CH3), 147.8
(s, CꢀCH2), 141.4–127.6 (m, C6H5), 133.3 (d, 4JPC=8.3
Hz, CꢀCH2), 59.9 (s, OCH2CH3), 35.5–35.3 (m, CH2–
C(O) and P–CH2–P), 13.9 (s, OCH2CH3). Anal. Calc.
for C48H41Fe2O7P3·0.5CH2Cl2: C, 59.63; H, 4.33.
Found: C; 59.49; H, 4.27.
2.1.10. Synthesis of [Fe2(CO)4{P(OMe)3}(v-PPh2)-
(v-p1(C):p2(C):p1(O)–{MeO(O)CH2}CꢀCH2)] (5a)
Thermolysis of
a toluene solution (20 ml) of
2.1.8. Synthesis of [Fe2(CO)4(v-PPh2)(v-dppm)-
(v-OꢀC–C{CH2}–CH2–C(O)OPri)] (3c)
Isolated as deep orange crystals in 70% yield from a
[Fe2(CO)5{P(OMe)3}(m-PPh2)(m-h1:h2 -{MeO(O)CH2}-
CꢀCH2)] (4a) (0.200 g, 0.303 mmol) for 6 h resulted in
a gradual darkening of the solution. Removal of the

S. Doherty et al. / Journal of Organometallic Chemistry 620 (2001) 150–164
155
volatiles gave a dark red solid which was chro-
matographed on alumina, eluting with n-hexane–
dichloromethane (60:40, v/v), to give a major band
which afforded 5a as deep red crystals in 70% yield
(0.134 g) after crystallisation by slow diffusion of n-
hexane into a concentrated dichloromethane solution.
IR (w(CO), cm−1, C6H14): 2004 m, 1952 m, 1928 s,
(w(CO), cm−1, C6H14): 2004 m, 1952 m, 1927 s, 1903 w,
1647 w. 31P{1H} (121.498 MHz, CDCl3, l): 184.6 (d,
2JPP=113.2 Hz, m-PPh2), 172.1 (d, 2JPP=113.2 Hz,
P(OMe)3). 1H-NMR (500.0 MHz, CDCl3, l): 7.47–7.07
(m, 10H, C6H5), 4.96 (sept, 3JHH=6.1 Hz, 1H,
OCH(CH3)2), 3.92 (d, 2JHH=21.7 Hz, 1H,
CHcHdC(O)iPr), 3.52 (d, 2JPH=10.7 Hz, 9H,
P(OCH3)3), 3.06 (d, 2JHH=21.7 Hz, CHcHdC(O)iPr),
1905 w, 1660 w. 31P{1H} (121.498 MHz, CDCl3, l):
2
3
184.4 (d, 2JPP=122.6 Hz, m-PPh2), 172.8 (d, JPP
=
2.80 (br t, JPH=3JPH=9.8 Hz, CꢀCHaHb), 2.20 (br t,
1
3
122.6 Hz, P(OMe)3). H-NMR (500.0 MHz, CDCl3, l):
3JPH=3JPH=Hz, CꢀCHaHb), 1.20 (d, JHH=6.5 Hz,
7.48–7.06 (m, 10H, C6H5), 3.96 (d, 2JHH=20.3 Hz, 1H,
3H, OCH(CH3)CH3), 1.16 (d, 3JHH=6.5 Hz, 3H,
OCH(CH3)CH3) 13C{1H}-NMR (125.7 MHz, CDCl3,
l): 219.2 (dd, 2JPC=7.8 Hz, 2JPC=44.4 Hz, CO), 218.7
(dd, 2JPC=20.7 Hz, 2JPC=23.7 Hz, CO), 218.2 (d,
2JPC=16.6 Hz, CO), 214.9 (d, 2JPC=18.6 Hz, CO),
185.6 (s, C(O)Pri), 168.5 (s, CꢀCH2), 141.7–127.2 (m,
C6H5), 71.8 (s, OCH(CH3)2), 62.6 (s, CꢀCH2), 53.3 (s,
CH2C(O)Et), 51.9 (br s, P(OCH3)3), 21.7 (s,
OCH(CH3)CH3), 21.6 (s, OCH(CH3)CH3). Anal. Calc.
for C26H30Fe2O9P2: C, 47.30; H, 4.58. Found: C, 47.12;
H, 4.55.
2
CHcHdC(O)Me), 3.70 (s, 3H, OCH3), 3.50 (d, JPH
=
11.0 Hz, 9H,P(OCH3)3), 3.10 (dd, 2JHH=21.7 Hz,
4JPH=2.7 Hz, CHcHdC(O)Me), 2.80 (ddd, JHH=2.4
2
Hz, 3JPH=8.3 Hz, 3JPH=11.3 Hz, 1H, CꢀCHaHb), 2.20
(br t, JPH,=7.4 Hz, CꢀCHaHb). 13C{1H} NMR (125.7
3
MHz, CDCl3, l): 219.3 (dd, 2JPC=15.0 Hz, 2JPC=39.0
Hz, CO), 218.7 (dd, 2JPC=21.0 Hz, 2JPC=23.0 Hz,
2
2
CO), 217.8 (d, JPC=12.4 Hz, CO), 215.1 (d, JPC
=
2
14.4 Hz, CO), 186.4 (s, C(O)Me), 168.3 (d, JPC=28.9
2
Hz, CꢀCH2), 141.4–127.2 (m, C6H5), 62.8 (br t, JPC
=
2JPC=8.0 Hz, CꢀCH2), 53.5 (s, OCH3), 52.7 (s,
CH2C(O)Me), 51.9 (d, 2JPC=5.2 Hz, P(OCH3)3). Anal.
Calc. for C24H26Fe2O9P2·CH2Cl2: C, 41.87; H, 3.94.
Found: C, 42.03; H, 3.74.
2.1.13. Synthesis of [Fe2(CO)4(v-PPh2)-
{P(OMe)3}2(v-p1(C):p2(C)–{MeO(O)CCH2}CꢀCH2)]
(6a)
Compounds 5b–c were prepared according to the
procedure described above for 5a.
Heating a toluene solution (20 ml) of [Fe2(CO)5(m-
PPh2)(m-h1(C):h2(C):h1(O)–{MeO(O)CCH2}CꢀCH2)]
(1a) (0.200 g, 0.373 mmol) and trimethyl phosphite
(0.090 ml, 0.746 mmol) at 75°C for 3 h, resulted in a
colour change from orange to deep red. The solvent
was removed to give a red solid which was purified by
column chromatography, eluting with, n-hexane/
dichloromethane (40:60, v/v) to give 6a as a single
major band. Slow diffusion of n-hexane into a concen-
trated dichloromethane solution gave orange crystals of
6a in 70% yield (0.200 g). IR (w(CO), cm−1, C6H14):
2004 s, 1963 s, 1932 s, 1915 w. 31P{1H} (121.498 MHz,
2.1.11. Synthesis of [Fe2(CO)4{P(OMe)3}(v-PPh2)-
(v-p1(C):p2(C):p1(O){EtO(O)CH2}CꢀCH2)] (5b)
Isolated as red crystals in 67% yield by slow diffusion
of n-hexane into a dichloromethane solution. IR
(w(CO), cm−1, C6H14): 2004 m, 1952 m, 1927 s, 1907 w,
1653 w. 31P{1H} (121.498 MHz, CDCl3, l): 184.5 (d,
2JPP=120.0 Hz, m-PPh2), 172.5 (d, 2JPP=120.0 Hz,
P(OMe)3). 1H-NMR (500.0 MHz, CDCl3, l): 7.45–7.08
(m, 10H, C6H5), 4.13 (br d, 3JHH=27.2 Hz, 2H,
OCH2CH3), 3.95 (br d, 2JHH=21.4 Hz, 1H,
CHcHdC(O)Me), 3.51 (br d, 2JPH=8.5 Hz, 9H,
3
CDCl3, 273 K, l): 183.4 (d, JPP=39.1 Hz P(OMe)3,
2
6a1), 181.2 (d, JPP=108.7 Hz, P(OMe)3, 6a1), 180.3 (d,
2
P(OCH3)3),
3.09
(br
d,
2JHH=21.4
Hz,
2JPP=103.8 Hz, P(OMe)3, 6a2), 177.5 (t, JPP=2JPP
=
CHcHdC(O)Me), 2.80 (br s, CꢀCHaHb), 1.87 (br s,
CꢀCHaHb), 1.20 (br s, 3H, OCH2CH3). 13C{1H}-NMR
(125.7 MHz, CDCl3, l): 219.1 (dd, 2JPC=16.6 Hz,
103.8 Hz, PPh2, 6a2), 170.6 (d, 2JPP=103.8 Hz,
P(OMe)3, 6a2), 149.0 (dd, JPP=108.7, 39.1 Hz, PPh2,
6a1). H-NMR (500.0 MHz, CDCl3, l): 7.62–7.10 (m,
10H, C6H5), 4.19 (d, JPH=11.9 Hz, 1H, (O)CCHcHd),
2
1
2
2
3
2JPC=42.3 Hz, CO), 218.6 (dd, JPC=21.7 Hz, JPC
=
2
3
22.7 Hz, CO), 218.1 (d, JPC=10.4 Hz, CO), 215.0 (d,
2JPC=14.4 Hz, CO), 186.1 (s, C(O)Et), 168.5 (d,
2JPC=28.9 Hz, CꢀCH2), 141.5–127.2 (m, C6H5), 63.5
(s, OCH2CH3), 62.7 (s, CꢀCH2), 52.9 (s, CH2C(O)Et),
3.59 (d, JPH=11.0 Hz, 18H, P(OCH3)3), 3.02 (br m,
1H, CꢀCHaHb), 2.84 (br m, 1H, (O)CCHcHd), 2.22 (s,
1H, CꢀCHaHb). Anal. Calc. for C27H35Fe2O12P3: C,
42.89; H, 4.67. Found: C; 43.01; H, 4.39.
Compounds 6b–c were prepared according to the
procedure described above for 6a.
2
51.9 (d, JPC=5.2 Hz, P(OCH3)3), 13.9 (s, OCH2CH3).
Anal. Calc. for C25H28Fe2O9P2.CH2Cl2: C, 42.72; H,
4.14. Found: C, 43.04; H, 4.10.
2.1.14. Synthesis of [Fe2(CO)4(v-PPh2){P(OMe)3}2(v-
p1(C):p2(C)–{EtO(O)CCH2}CꢀCH2)] (6b)
2.1.12. Synthesis of [Fe2(CO)4{P(OMe)3}(v-PPh2)-
(v-p1(C):p2(C):p1(O){iPrO(O)CH2}CꢀCH2)] (5c)
Isolated as red crystals in 63% yield by slow diffusion
of n-hexane into a dichloromethane solution. IR
Isolated as deep orange crystals in 65% yield by slow
diffusion
of
methanol
into
a
concentrated
dichloromethane solution at r.t. IR (w(CO), cm−1
,

156
S. Doherty et al. / Journal of Organometallic Chemistry 620 (2001) 150–164
3
C6H14): 2004 s, 1963 s, 1932 s, 1915 w. 31P{1H} (121.498
6.1 Hz, 3H, CH(CH3)2), 1.23 (d, JHH=6.1 Hz, 3H,
CH(CH3)2).
MHz, CDCl3, l): 183.3 (br s, P(OMe)3, major isomer),
180.7 (d, JPP=76.4 Hz, P(OMe)3, major and minor
2
2.2. X-ray crystallographic studies
isomers), 175.9 (br s, PPh2, minor isomer), 170.9 (br s,
P(OMe)3, minor isomer), l 148.4 (br s, PPh2, major
1
All measurements were made on a Bruker AXS
SMART CCD area-detector diffractometer, at 160 K,
using graphite-monochromated Mo–Ka radiation (u=
isomer). H-NMR (500.0 MHz, CDCl3, l): 7.62–7.09
(br m, 10H, C6H5), 4.20 (d, 3JPH=16.2 Hz, 1H,
(O)CCHcHd), 4.16–4.10 (m, 2H, OCH2CH3), 3.59 (d,
3JPH=11.0 Hz, 18H, P(OCH3)3), 3.05 (br m, 1H,
CꢀCHaHb), 2.83 (br m, 1H, (O)CCHcHd), 2.30 (s, 1H,
,
0.71073 A) and narrow frame exposures (0.3° in ꢀ). Cell
parameters were refined from the observed ꢀ angles of
all strong reflections in each data set. Intensities were
corrected semiempirically for absorption based on sym-
metry-equivalent and repeated reflections. The struc-
tures were solved by direct methods and refined on F2
values for all unique data by full-matrix least squares.
Table 1 gives further details. All non-hydrogen atoms
were refined anisotropically. H-atoms, located in differ-
ence maps, were constrained with a riding model except
for those attached to C(1) and C(3) in 5a, and C(1) in
6a, which had their coordinates refined freely because of
non-standard geometry; U(H) was set to 1.2 (1.5 for
methyl groups) times Ueq for the parent atom. Highly
disordered CH2Cl2 solvent, estimated as half a molecule
per molecule of complex 3a, was treated by the SQUEEZE
option of PLATON [13a]. Other programs used were
Bruker AXS SMART and SAINT for diffractometer con-
trol and frame integration [13b], Bruker SHELXTL for
structure solution, refinement and molecular graphics
[13c], and local programs.
3
CꢀCHaHb), 1.29 (t, JHH=7.0 Hz, 3H, OCH2CH3).
2.1.15. Synthesis of [Fe2(CO)4(v-PPh2)-
{P(OMe)3}2(v-p1(C):p2(C)–{iPrO(O)CCH2}CꢀCH2)]
(6c)
Isolated as orange crystals in 64% yield by slow
diffusion of n-hexane into a concentrated dichloro-
methane solution. IR (w(CO), cm−1, C6H14): 2004 s,
1963 s, 1932 s, 1915 w. 31P{1H} (121.498 MHz, CDCl3,
l): 183.3 (br s, P(OMe)3, major isomer), 180.8 (br s,
P(OMe)3, major and minor isomers), 175.2 (br, s, m-
PPh2, minor isomer), 170.9 (br s, P(OMe)3, minor iso-
1
mer), l 147.3 (br s, m-PPh2, major isomer). H-NMR
(500.0 MHz, CDCl3, l): 7.83–7.09 (br m, 10H, C6H5),
4.94 (br m, 1H, CH(CH3)2), 4.15 (d, 3JPH=13.1 Hz, 1H,
3
(O)CCHcHd), 3.59 (d, JPH=11.0 Hz, 18H, P(OCH3)3),
3.08 (br m, 1H, CꢀCHaHb), 2.82 (br m, 1H,
3
(O)CCHcHd), 2.26 (s, 1H, CꢀCHaHb), 1.28 (d, JHH
=
Table 1
Summary of crystal data and structure determination for compounds 2a, 3a, 5a and 6a
Compound
2a
3a·0.5CH2Cl2
5a
6a
Formula
Mr
C48H41Fe2O7P3
934.4
C47H39Fe2O7P3.0.5CH2Cl2
962.9
C25H28Cl2Fe2O9P2
717.0
C27H35Fe2O12P3
756.2
Temperature (K)
Crystal system
Space group
160
Monoclinic
C2/c
173
160
Monoclinic
P21/n
160
Monoclinic
P21/c
Orthorhombic
Pbcn
,
a (A)
44.912(2)
11.3227(5)
17.9056(8)
110.746(2)
8515.1(7)
8
11.7295(14)
24.299(3)
31.701(4)
8.7969(5)
20.1332(11)
17.1050(9)
98.168(1)
2998.7(3)
4
20.4629(14)
9.7074(6)
17.8652(12)
113.783(2)
3247.4(4)
4
,
b (A)
,
c (A)
i (°)
V (A )
3
,
9035.4(18)
8
0.86
Z
v (mm−1
qmax (°)
)
0.85
28.8
1.30
28.8
1.10
28.8
28.9
Reflections measured
Unique reflections
Reflections with F2\2|(F2)
Rint (on F2)
26256
10 022
7507
0.0479
542
0.0479
0.1103
1.043
55092
11 108
8495
0.0560
533
0.0560
0.1197
1.109
18828
7087
5164
0.0446
405
0.0375
0.0874
0.965
19540
7672
6303
0.0292
411
0.0354
0.0948
1.098
No. of parameters
a
R
[I\2|(I)]
b
wR (all data)
GOF c (S)
−3
,
Max, min diff map (e A
)
0.93, −0.61
0.48, −0.56
0.59, −0.71
0.52, −0.31
a Conventional R=SꢀꢀFoꢀ−ꢀFcꢀꢀ/SꢀFoꢀ for ‘observed’ reflections having Fo2\2|(F2o).
b wR=[S(F2o−Fc2)2/Sw(Fo2)2]1/2 for all data.
c GOF=[Sw(F2o−Fc2)2/(no. unique reflections−no. of parameters)]1/2
.

S. Doherty et al. / Journal of Organometallic Chemistry 620 (2001) 150–164
157
Scheme 3.
3. Results and discussion
bridge, a doublet of doublets at l 42.1 (2JPP=113.2,
34.1 Hz) and a high-field doublet at l −18.1 (2JPP
=
3.1. Migratory insertion reactions: synthesis and charac-
terisation of bridging acyl complexes
34.1 Hz), which most likely correspond to the coordi-
nated and uncoordinated phosphorus centres of the
h1-dppe complex I, respectively. Thermolysis of this
mixture resulted in smooth conversion to the m-acyl
complex 2a.
Thermolysis of a toluene solution of [Fe2(CO)5(m-
PPh2)(m - h1(O):h1(C):h2(C)–{NuC(O)CH2}CꢀCH2)]
(1a–e) and 1,2-bis(diphenylphosphino)ethane (dppe) re-
sults in carbonyl migration and formation of acyl-
bridged [Fe2(CO)4(h2-dppe)(m-PPh2)(m-CꢀO{CꢀCH2}-
CH2C(O)Nu)] (2a–e), as the sole products. The reac-
tion is conveniently monitored by TLC and IR spec-
troscopy, with the appearance of a new w(CꢀO) band at
1560 cm−1 typical of a carbonyl absorption of a bridg-
ing acyl ligand. Complexes 2a–e were purified by
column chromatography and characterised by 1H-,
31P{1H}- and 13C{1H}-NMR spectroscopy and in the
case of 2a single-crystal X-ray crystallography. The
1H-NMR spectra of 2a–e contain four distinct sets of
resonances, two doublets in the region l 1.6–2.2 with a
geminal coupling constant of ca. 16 Hz, corresponding
to the diastereotopic methylene protons adjacent to the
ester/amide carbonyl, and two singlets in the region l
5.6–6.2 associated with the vinyl portion of the acyl
bridge. The 31P{1H}-NMR spectrum of 2a contains a
low-field doublet of doublets at l 167.9 (2JPP=123.0
Under similar conditions 1a–d react with dppm via
loss of CO and 1,2-migratory insertion to give the
corresponding
dppm-acyl-bridged
derivatives
[Fe2(CO)4(m - dppm)(m - PPh2)(m - CꢀO{CꢀCH2}CH2C-
1
(O)R)] (3a–d). The H- and 13C{1H}-NMR spectra are
qualitatively similar to those of 2a–d. For instance, the
31P{1H}-NMR spectrum of 3a contains a low-field dou-
blet of doublets at l 209.9 (2JPP=110.8, 54.7 Hz) and
high-field doublets of doublets at l 53.2 (2JPP=54.7,
60.0 Hz) and 44.1 (2JPP=110.8, 60.0 Hz), which corre-
spond to the phosphido group and the inequivalent
ends of the dppm, respectively. The magnitude of the
phosphorus–phosphorus coupling constants suggests a
trans arrangement of the bridging phosphido group and
dppm. Although both cis and trans arrangements of the
phosphorus containing ligands in dppm-phosphido
bridged diiron complexes are possible [14], the most
common stereochemistry appears to be that in which
the phosphorus ligands adopt a trans arrangement. In
the case of 1a in which the ester coordinated carbonyl
occupies a site trans to the phosphido-bridge the forma-
tion of 3a can be most aptly considered as a carbonyl
displacement reaction with retention of stereochemistry
at iron, presumably via an h1-dppm intermediate.
Full structural details of the bridging acyl ligand and
the mode of coordination of the diphosphine were
provided by single-crystal X-ray analyses of 2a and 3a.
Perspective views of the molecular structures of 2a and
3a, together with the atomic numbering scheme, are
illustrated in Figs. 1 and 2, respectively, and a selection
of bond lengths and angles for both compounds is
listed in Table 2. The two iron atoms in 2a are sepa-
2
Hz, JPP=11.0 Hz) and further doublets of doublets at
l 85.9 (2JPP=123.0, 23.1Hz) and 79.4 (2JPP=23.1, 11.0
Hz). The magnitude of the phosphorus–phosphorus
coupling constants is a firm indication that the dppe
acts in a cis chelating fashion with one phosphorus cis
and the other trans to the phosphido-bridge [14]. In the
13C{1H}-NMR spectrum, a low-field signal at l 288.7
corresponds to the acyl carbon and is in the region
characteristic of a m-acyl bridging ligand [15]. Addition
of dppe to 1a–e is expected to result in displacement of
the coordinated ester carbonyl, as has previously been
observed with trimethylphosphite [12] (vide infra), fol-
lowed by an intramolecular phosphine promoted car-
,
bonyl migration to give 2a–e (Scheme 3).
A
rated by a distance of 2.6928(5) A and bridged asym-
31P{1H}-NMR spectrum of a toluene solution of 1a and
a slight excess of dppe, recorded before heating, con-
tained three distinct well-separated signals, a low-field
doublet at l 173.1 (2JPP=113. 2 Hz), for the phosphido
metrically by phosphido ligand [Fe(1)–P(3)=
a
,
,
2.2393(8) A; Fe(2)–P(3)=2.2091(7) A] and a 3-electron
donor a,b-unsaturated acyl ligand, oxygen bound to
Fe(2) [Fe(2)–O(1)=1.9820(17) A] and carbon bound
,

158
S. Doherty et al. / Journal of Organometallic Chemistry 620 (2001) 150–164
Table 2
,
to Fe(1) [Fe(1)–C(1)=1.955(2) A]. The acyl C(1)–O(1)
,
Selected bond lengths (A) and bond angles (°) for 2a and 3a
,
bond length of 1.266(2) A is similar to previously
reported values [6b,17,18] and longer than a typical
conjugated C–O double bond. The remaining carbon–
carbon bonds within the bridging acyl ligand [C(2)–
2a
3a
Bond lengths
Fe(1)–Fe(2)
Fe(1)–P(3)
Fe(2)–P(3)
Fe(2)–P(1)
Fe(2)–P(2)
Fe(1)–C(1)
Fe(2)–O(1)
C(1)–O(1)
C(1)–C(2)
C(2)–C(3)
C(2)–C(4)
C(4)–C(5)
C(5)–O(2)
C(5)–O(3)
2.6928(5)
2.2393(8)
2.2091(7)
2.2350(7)
2.2086(8)
1.955(2)
1.9820(17)
1.266(3)
1.501(4)
1.330(4)
1.515(4)
1.494(4)
1.191(3)
1.325(4)
Fe(1)–Fe(2)
Fe(1)–P(3)
Fe(2)–P(3)
Fe(1)–P(1)
Fe(2)–P(2)
Fe(1)–C(1)
Fe(2)–O(1)
C(1)–O(1)
C(1)–C(2)
C(2)–C(3)
C(2)–C(4)
C(4)–C(5)
C(5)–O(2)
C(5)–O(3)
2.6394(5)
2.1950(8)
2.2026(8)
2.2222(8)
2.2596(8)
1.952(3)
1.9915(17)
1.274(3)
1.494(4)
1.326(4)
1.510(3)
1.495(4)
1.197(4)
1.351(3)
,
,
C(3)=1.330(4)
A
and C(2)–C(4)=1.515(4) A,
,
C(4)–C(5) 1.494(4) A] are consistent with localised
Bond angles
Fe(1)–P(3)–Fe(2)
P(3)–Fe(2)–P(2)
P(3)–Fe(2)–P(1)
P(3)–Fe(2)–C(10)
O(1)–C(1)–C(2)
C(1)–C(2)–C(3)
C(4)–C(5)–O(3)
C(4)–C(5)–O(2)
O(2)–C(5)–O(3)
74.50(2)
110.71(3)
161.18(3)
96.58(8)
113.6(2)
120.7(2)
112.2(3)
125.5(3)
122.3(3)
Fe(1)–P(3)–Fe(2)
P(3)–Fe(1)–P(1)
P(3)–Fe(2)–P(2)
O(1)–C(1)–C(2)
C(1)–C(2)–C(3)
C(1)–C(2)–C(4)
C(4)–C(5)–O(3)
C(4)–C(5)–O(2)
O(2)–C(5)–O(3)
73.77(3)
143.03(3)
152.45(3)
112.5(2)
122.6(2)
116.7(2)
110.3(3)
126.7(3)
123.0(3)
double and single bonds. These carbon–carbon and
carbon–oxygen bond lengths are similar to values re-
ported previously in related a,b-unsaturated acyl com-
plexes such as [Fe2(CO)4(m-PPh2)(m-dppm)(m-OꢀC–C-
Fig. 1. Molecular structure of [Fe2(CO)4(h2-dppe)(m-PPh2)(m-
CꢀO{CꢀCH2}CH2C(O)OMe)] (2a). Phenyl hydrogen atoms and the
CH2Cl2 molecule of crystallisation have been omitted. Carbonyl
carbons have the same numbers as oxygen atoms.
(Ph)ꢀCHPh)]
[6h],
[Fe2(CO)6(m-SBut)(m-OꢀC–C-
(OEt)ꢀCH2)] [6b] and [Fe2(CO)4(m-dppm)(m-PCy2)(m-
OꢀC–C(Ph)ꢀCH2)] [17]. In a number of cases the bond
length pattern in a,b-unsaturated acyl complexes is best
described as delocalised to account for the near equal
lengths of the carbon–carbon bonds [6,11i]. In a typical
example, the two carbon–carbon bonds in the a,b-un-
saturated acyl bridge in [Fe2(CO)5{P(OMe)3}(m-
PPh2){m-OꢀC–CHꢀCMe(NHR)}] (R=iPr, CH2Ph)
[11i] are of similar length and the carbon–nitrogen
bond length is in the region characteristic of an
iminium salt. This bond length equivalence is most
likely due to the presence of an amino group at the
three-position which forms an extended delocalised sys-
tem. The dppe coordinates in a chelating manner with
one arm binding trans [P(1)–Fe(2)–P(2)=161.18(3)°]
and the other cis [P(2)–Fe(2)–P(2)=110.71(3)°] to the
phosphido-bridge, consistent with the JPP couplings of
123.0 and 11.0 Hz, respectively. The bridging acyl
ligand is cis to the phosphido and the carbonyl C(1)–
O(1) lies approximately parallel to the iron–iron bond,
the largest deviation form the least squares mean plane
Fig. 2. Molecular structure of [Fe2(CO)4(m-dppm)(m-PPh2)(m-
CꢀO{CꢀCH2}CH2C(O)OMe)] (3a), Phenyl hydrogen atoms have
been omitted. Carbonyl carbons have the same numbers as oxygen
atoms.
,
containing Fe(1), Fe(2), C(1), O(1) being 0.031 A. The
core structural features of 2a and 3a, in particular the
cis disposition of the phosphido-bridge and the acyl

S. Doherty et al. / Journal of Organometallic Chemistry 620 (2001) 150–164
159
group, the bond lengths and angles within the bridging
hydrocarbyl ligand and the metal–metal and metal–
phosphido are essentially the same. The most striking
difference between the structures of 2a and 3a is a
the b,g-unsaturated esters and amides [Fe2(CO)5(m-
PPh2)(m - h1(O):h1(C):h2(C) – {ROC(O)CH2}CꢀCH2}]
(1a–c) to give the corresponding alkenyl complexes
[Fe2(CO)5{P(OMe)3}(m-PPh2)(m-h1:h2-{ROC(O)CH2}-
CꢀCH2}] (4a–c) [12]. The solid-state structure of
[Fe2(CO)5{P(OMe)3}(m-PPh2)(m-h1:h2-{iPrOC(O)CH2}-
CꢀCH2}] (4c) showed that the trimethylphosphite occu-
pies a site trans to the phosphido-bridge, revealing that
the displacement occurs with retention of stereochem-
istry at iron. In an extension of these studies we have
reacted 1a–c with excess trimethylphosphite in an at-
tempt to promote stepwise displacement and carbonyl
migration to generate the corresponding phosphite sub-
stituted a,b-unsaturated acyl complexes. Heating tolu-
ene solutions of 1a–c and trimethylphosphite results in
substitution of the ester coordinated carbonyl to give
[Fe2(CO)5{P(OMe)3}(m-PPh2)(m-h1:h2-{ROC(O)CH2}-
CꢀCH2}] (4a–c) followed by carbonyl substitution to
give the s-h-alkenyl derivatives [Fe2(CO)4{P(OMe)3}2-
(m-PPh2)(m-:h1:h2-{ROC(O)CH2}CꢀCH2}] (6a–c). No-
tably, there was no evidence for migratory insertion to
give the corresponding a,b-unsaturated acyl complexes.
In earlier work, Hogarth showed that thermolysis of
a toluene solution of the a-phenyl ethenyl complex
,
lengthening of the Fe–O bond from 1.9820(17) A in 2a
,
,
to 1.9915(17) A in 3a (D=0.0095 A). The molecular
structure of 3a clearly shows the trans arrangement of
the phosphido-bridge and the diphosphine [P(3)–Fe(1)–
P(1)=143.03(3)°, P(3)–Fe(2)–P(2)=152.45(3)°].
A number of binuclear complexes bridged by an
a,b-unsaturated acyl ligand have appeared in the litera-
ture and in the vast majority of cases this ligand acts as
a bridging three-electron donor by binding through the
carbonyl oxygen and carbon atoms, in this regard 2a–e
and 3a–d are unexceptional. The most straightforward
route to a,b-unsaturated acyl complexes involves migra-
tory insertion of CO into the s-bond of a binuclear
s-h-alkenyl binuclear complex, although alternative
methods have been developed and include: reaction of
an acid chloride with Na[Fe2(CO)6(m-PPh2)] [6b], car-
bonylative amination of the multi-site bound acetylide
[Fe2(CO)6(m-PPh2)(m-h1:h2-CꢁCR)] [6g], carbonylation
of the alkylidene bridged [Fe2(CO)5{P(OMe)3}(m-
PPh2)(m-CHCMe(NHR)}] [11i] and reaction of
[NEt3H][Fe2(CO)6(m-CO)(m-SR)] with alkynes or
vinylmercuric halides [6c,d].
[Fe2(CO)4(m-dppm)(m-PPh2)(m-PhCꢀCH2)]
afforded
three products, one of which was [Fe2(CO)3(m-dppm)(m-
PPh2){m-OꢀC–C(Ph)ꢀCH2}], bridged by a five-elecron
donor a,b-unsaturated acyl [10]. This prompted us to
examine the thermal stability of [Fe2(CO)5{P(OMe)3}(m-
PPh2)(m-h1:h2-{ROC(O)CH2}CꢀCH2}] (4a–c), specifi-
cally to examine its conversion into 6a–c and/or
possibility of promoting carbonyl migration to form
similar five-electron donor acyl derivatives. Thermolysis
of toluene solutions of 4a–c resulted in loss of CO and
coordination of the ester carbonyl to form complexes
[Fe2(CO)4{P(OMe)3}(m - PPh2)(m - h1(O):h1(C):h2(C)–
{ROC(O)CH2}CꢀCH2}] (5a–c). Coordination of the
ester carbonyl was clearly evident from the IR spectrum,
which showed a shift of the carbonyl band from 1735
cm−1 in 4a to 1660 cm−1 in 5a. The 31P{1H}-NMR
spectrum of 5a contains doublets at l 184.4 and 172.8
(2JPP=122.6 Hz), the magnitude of the coupling con-
stant confirming a trans arrangement of the phosphorus
containing ligands. The 1H-NMR spectrum contains
four multiplets associated with the hydrocarbyl bridge.
The alkenyl protons appear as multiplets at l 2.80 and
2.20 and the diastereotopic methylene protons as a
doublet at l 3.96 (2JHH=20.3 Hz) and doublet of
Seyferth has suggested that the stability of thiolate
bridged a,b-unsaturated acyl (vinyl acyl) complexes of
the type [Fe2(CO)6(m-SR)(m-h1:h1-OꢀC–CHꢀCR1R2)] is
related to the electron-donating ability of the substi-
tuted vinyl group attached to the bridging acyl carbon
atom. The most stable a,b-unsaturated acyl complexes
are those with two alkyl substituents on the CꢀC double
bond, whereas those with only a single alkyl or aryl
substituent attached to the b-carbon atom readily lose
CO to afford the corresponding alkenyl bridged deriva-
tive, with first order kinetics. In contrast, phosphido-
bridged a,b-unsaturated acyl complexes are, in general,
more stable with respect to loss of CO. For instance,
[Fe2(CO)4(m-dppm)(m-PPh2){m-OꢀC–C(Ph)ꢀCH2}] [6h]
and [Fe2(CO)5{P(OMe)3}(m-PPh2)(m-OꢀC–CHꢀCMe-
(NHR)}] (R=iPr, CH2Ph) [11i] are both stable in
refluxing toluene for prolonged periods, with no evi-
dence for loss of CO. Similarly 3a–e are stable under
these conditions, with no evidence for decarbonlyation
even after 12 h at reflux. Although we cannot yet
provide a definitive explanation for the stability of 3a–e,
with respect to decarbonylation, it is tempting to suggest
that the presence of a bulky substituent on the a-carbon
atom is an important factor, as has previously been
noted by Seyferth [6b–d].
4
doublets at l 3.10 (2JPP=20.3, JPH=2.7 Hz). The 13C
signals associated with the m-h1:h2-alkenyl ligand in
5a–c appear in the region expected for such ligands and
are similar to those in 1a–c. Isolation of 5a–c suggests
that it is a likely intermediate in the formation of 6a–c
from 1a–b and trimethylphosphite. Indeed, treatment of
a deep red dichloromethane solution of 5a–c with
trimethylphosphite at room temperature results in
3.2. Carbonyl substitution reactions
We have shown previously that trimethylphosphite
readily displaces the metal-coordinated ester carbonyl in

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S. Doherty et al. / Journal of Organometallic Chemistry 620 (2001) 150–164
3.3. Variable temperature NMR studies
The room temperature 31P{1H}-NMR spectrum of
[Fe2(CO)4{P(OMe)3}2(m - PPh2)(m - CꢀO{CꢀCH2}CH2C-
(O)R)] (6a) contains a sharp doublet at l 186.2 and
several exchange broadened signals at l 149, 170, 176
and 183. To investigate this exchange process further a
variable temperature 31P{1H}-NMR study was under-
taken. The low temperature limiting spectrum of 6a
(Fig. 3) reveals two distinct sets of signals that corre-
spond to a 60:40 mixture of two isomers in slow
exchange, herein referred to as 6a1 and 6a2, respectively
[
, major isomer 6a1; ꢀ, minor isomer 6a2]. One set
comprises a doublet of doublets at l 149.0 (2JPP
=
108.7, 39.1 Hz) and two doublets at l 183.4 (2JPP=39.1
Hz) and 181.2 (2JPP=108.7 Hz) and the other a triplet
at l 177.5 (2JPP=2JPP=103.8 Hz) and two doublets at
l 170.6 (2JPP=103.8 Hz) and 180.3 (2JPP=103.8 Hz).
The disparate magnitudes of the phosphorus–phospho-
rus coupling constants associated with the former set of
resonances strongly suggests that one of the
trimethylphosphites in this isomer, 6a1, is located cis to
the phosphido bridge and the other trans, whereas the
similarity in the phosphorus–phosphorus coupling con-
stants in the latter set is consistent with both
trimethylphosphites trans to the phosphido bridge, i.e.
isomer 6a2. Clearly these two isomers are related by a
Scheme 4.
displacement of the ester coordinated carbonyl and
quantitative conversion into orange–yellow 6a–c
within 10 min (Scheme 4). This transformation is most
conveniently monitored by IR spectroscopy which
clearly shows the disappearance of the band corre-
sponding to the coordinated ester carbonyl (1660
cm−1) and the appearance of a band due to the unco-
ordinated ester carbonyl (1730 cm−1).
Fig. 3. Low temperature limiting 31P{1H}-NMR spectrum of [Fe2(CO)4{P(OMe)3}2(m-PPh2)(m-CꢀO{CꢀCH2}CH2C(O)OMe)] (6a) recorded at 253
K showing the assignment of isomers 6a1 and 6a2
[
, isomer 6a1 one P(OMe)3 trans and one cis to PPh2; ꢀ, isomer 6a2 both P(OMe)3 trans to
PPh2].

S. Doherty et al. / Journal of Organometallic Chemistry 620 (2001) 150–164
161
of isomer 6a1 and 6a2 via a restricted trigonal twist at
one of the phosphite substituted iron centres. This
process interchanges one isomer, with both
trimethylphosphites trans to the phosphido bridge
(2JPP=107.6 Hz), with the other isomer, in which one
phosphite occupies the site trans to the iron–iron bond
(2JPP=39.1 Hz), while the other occupies the site trans
to the phosphido-bridge. The free energy of activation
associated with the trigonal twist is close to the re-
ported values of 15.0 kcal mol−1 for [Os3(CO)10-
{P(OMe)3}2] and 13.8 kcal mol−1 for [Os3(CO)9-
{P(OMe)3}3] [16] each of which is significantly higher
than the values reported for [Fe2(CO)5{P(OMe)3}(m-
Scheme 5.
trigonal twist of one of the Fe(CO)2P fragments
(Scheme 5). As the temperature is raised the two signals
at l 181.2 and 180.3 rapidly coalesce and sharpen into
a doublet at l 180.9 (2JPP=76.8 Hz) while the remain-
ing resonances broaden over a much larger temperature
range. At 253 K the signals belonging to the phos-
phido-bridges (l 177.5 and 149.0) begin to exchange as
do those associated with the remaining trimethylphos-
phites (l 183.4 and 170.6). The temperature dependence
of the 31P{1H}-NMR spectra clearly shows that above
room temperature the two isomers interconvert rapidly.
Not surprisingly the room temperature 1H-NMR
spectrum of 6a consists of four distinct resonances
associated with protons of the bridging b,g-unsaturated
PPh2){m-C(H)CMe(NHPri)}] (DG‡=of 9.5 kcal mol−1
)
and [Fe2(CO)5{P(OMe)3}(m-PPh2){m-OꢀCCHCꢀCMe-
(NHCH2Ph)}] (DG‡=10.4 kcal mol−1).
3.4. X-ray crystal structures of [Fe2(CO)4{P(OMe)3}-
(v-PPh2)(v-p1(O):p1(C):p2(C)–{MeOC(O)CH2}-
CꢀCH2}] (5a) and [Fe2(CO)4{P(OMe)3}2(v-PPh2)-
(v-:p1:p2-{MeOC(O)CH2}CꢀCH2}] (6a)
A single-crystal X-ray study was carried out to deter-
mine the precise structural features of 5a, the result of
which is shown in Fig. 5, with selected bond lengths
and angles listed in Table 3. The molecular structure
confirms that the ester carbonyl oxygen coordinates to
Fe(2) to form a five-membered metallacycle, such that
O(1) is trans to P(2) [O(1)–Fe(2)–P(2)=153.26(5)°],
ester; doublets at l 4.3 (J=14.7 Hz) and 3.18 (2JPP
=
13.0 Hz) a doublet of doublets at l 2.95 (2JPP=8.0,
14.0 Hz) and a broad unresolved triplet at l 2.25.
Variable temperature 1H-NMR studies revealed that
these signals broaden as the temperature is lowered and
eventually sharpen to give rise to a set of eight near
equal intensity resonances, fully consistent with the
presence of two isomers in slow exchange.
,
with Fe(2)–O(1) [2.0930(16) A] and C(4)–O(1)
,
[1.226(3) A] bond lengths similar to those recently
reported for [Fe2(CO)4{h2-C(CO2Me)ꢀCH(CO2Me)ꢀ
O}(m-PPh2)(m-dppm)] [14a] and [Fe2(CO)5(m-PPh2)(m-
h1:h2-{iPrOC(O)CH2}CꢀCH2}] [12b]. The remainder of
the coordination sphere of Fe(2) is completed by the
a-carbon atom of the bridging b,g-unsaturated ester
Our interpretation of the variable temperature
31P{1H}-NMR studies has been supported by magneti-
sation transfer experiments (EXSY). An EXSY spec-
trum (Fig. 4), recorded at 278 K, clearly shows that the
signals at l 149.0 and 177.5, associated with the phos-
phido-bridges of the two isomers, exchange. This spec-
trum also shows that the signals at l 183.4 and 181.2,
which correspond to the trimethylphosphites of one
isomer, exchange with those at l 180.3 and 170.6,
respectively, the trimethylphosphites in the other iso-
mer. Exchange rates, extracted from the 2D intensity
matrix using the programme D2DNMR, have been
used to estimate the free energy of activation for this
exchange process [19]. The rate of interconversion of
6a1 to 6a2 is approximately 22 s−1, which equates to a
free energy of activation for the process of 14.4 kcal
,
[Fe(2)–C(2)=1.944(2) A] and two carbonyls. The co-
ordination geometry at Fe(1) is trigonal bipyramidal
and consists of two carbonyls, trimethylphosphite,
which occupies the site trans to the phosphido bridge
[P(2)–Fe(1)–P(1)=169.69(3)°], and the C(1)–C(2)
,
bond [1.395(3) A] of the alkenyl group [Fe(1)–C(1)=
,
,
2.169(2) A, Fe(1)–C(2)=2.117(2) A].
A single-crystal X-ray analysis of 6a was also under-
taken, to provide full structural details of the bridging
ligand and the positions of substitution of the phos-
phite ligands. The molecular structure is shown in Fig.
6 and a selection of bond lengths and angles is listed in
Table 4. The molecular structure clearly shows two iron
mol−1
. The absence of exchange peaks between
trimethylphosphites within an isomer clearly suggests
that s,h-alkenyl flipping is slow on the NMR
timescale.
,
atoms separated by a distance of 2.6128(4) A and
bridged asymmetrically by a phosphido group [Fe(1)–
,
,
The spectroscopic characteristics described above and
free energy of activation for this exchange are consis-
tent with a dynamic process that involves interchange
P(3)=2.2398(6) A, Fe(2)–P(3)=2.2225(6) A] and a
b,g-unsaturated ester, s-bonded to Fe(2) [Fe(2)–
2
,
C(2)=1.984(2) A] and h -bonded to Fe(1) [Fe(1)–C(1)

162
S. Doherty et al. / Journal of Organometallic Chemistry 620 (2001) 150–164
,
,
2.154(2) A; Fe(1)–C(2)=2.118(2) A]. The C(1)–C(2)
presumably to avoid unfavourable steric interactions
between the substituents on Ca and the phenyl rings of
the bridging phosphido group.
,
bond length of 1.402(3) A is comparable to values
reported previously for binuclear alkenyl complexes [19]
and is slightly longer than expected for a carbon–
carbon double bond. The coordination sphere of both
iron atoms is completed by two carbonyls and one
trimethylphosphite. The trimethylphosphite located on
Fe(1) is trans to the phosphido-bridge [P(3)–Fe(1)–
P(1)=178.72(3)°] while the other, attached to Fe(2), is
cis to the phosphido bridge [P(2)–Fe(2)–P(3)=
99.40(2)°]. The alkenyl ligand adopts the familiar endo
conformation with respect to the phosphido bridge [20],
We have shown that diiron complexes bridged by
a,b-unsaturated ester and amides react with bidentate
phosphines via a pathway involving site selective
displacement of the ester/amide coordinated carbonyl
trans to the phosphido-bridge to give an h1-dppe
intermediate which then undergoes an intramolecular
phosphine assisted migratory carbonyl insertion to
afford the corresponding a,b-unsaturated ester/amide.
In 2a–e the dppe coordinates in a bidentate manner to
Fig. 4. 31P-EXSY spectrum of [Fe2(CO)4{P(OMe)3}2(m-PPh2)(m-CꢀO{CꢀCH2}CH2C(O)OMe)] (6a) recorded at 278 K, showing exchange of
isomer of 6a1 and 6a2.

S. Doherty et al. / Journal of Organometallic Chemistry 620 (2001) 150–164
163
Fig. 5. Molecular structure of give [Fe2(CO)4{P(OMe)3}(m-PPh2)(m-
h1(O):h1(C):h2(C)–{NuC(O)CH2}CꢀCH2}]
(5a). Phenyl and
trimethylphosphite hydrogen atoms have been omitted. Carbonyl
carbons have the same numbers as oxygen atoms.
Fig. 6. Molecular structure of give [Fe2(CO)4{P(OMe)3}2(m-PPh2)(m-
CꢀO{CꢀCH2}CH2C(O)OMe)] (6a). Phenyl and trimethylphosphite
hydrogen atoms have been omitted. Carbonyl carbons have the same
numbers as oxygen atoms.
Table 3
,
Selected bond lengths (A) and bond angles (°) for 5a
Table 4
,
Selected bond lengths (A) and bond angles (°) for 6a
Bond lengths
Fe(1)–Fe(2)
Fe(2)–P(2)
Fe(1)–C(1)
Fe(2)–C(2)
Fe(2)–C(6)
Fe(1)–C(8)
C(1)–C(2)
C(3)–C(4)
C(4)–O(2)
2.6076(5)
2.1707(7)
2.169(2)
1.944(2)
1.747(3)
1.755(3)
1.395(3)
1.489(3)
1.319(3)
Fe(1)–P(2)
Fe(1)–P(1)
Fe(1)–C(2)
Fe(2)–O(1)
Fe(2)–C(7)
Fe(1)–C(9)
C(2)–C(3)
C(4)–O(1)
2.2310(7)
2.1602(7)
2.117(2)
2.0930(16)
1.805(3)
1.778(3)
1.522(3)
1.226(3)
Bond lengths
Fe(1)–Fe(2)
Fe(2)–P(3)
Fe(2)–P(2)
Fe(1)–C(2)
C(1)–C(2)
C(3)–C(4)
C(4)–O(2)
2.6128(4)
2.2225(6)
2.1412(7)
2.118(2)
1.402(3)
1.507(3)
1.343(3)
Fe(1)–P(3)
Fe(1)–P(1)
Fe(1)–C(1)
Fe(2)–C(2)
C(2)–C(3)
C(4)–O(1)
2.2398(6)
2.1716(6)
2.154(2)
1.984(2)
1.540(3)
1.206(3)
Bond angles
Bond angles
Fe(1)–P(3)–Fe(2)
P(2)–Fe(2)–P(3)
P(1)–Fe(1)–Fe(2)
Fe(1)–C(1)–C(2)
Fe(1)–C(2)–C(3)
C(3)–C(4)–O(1)
O(1)–C(4)–O(2)
71.68(2)
99.40(2)
125.05(2)
P(1)–Fe(1)–P(3)
Fe(1)–Fe(2)–P(2)
Fe(2)–C(2)–Fe(1)
178.72(3)
138.26(2)
79.06(7)
72.22(12)
109.55(19)
111.2(2)
Fe(1)–P(2)–Fe(2)
P(2)–Fe(2)–O(1)
P(1)–Fe(1)–C(2)
C(2)–C(3)–C(4)
Fe(2)–O(1)–C(4)
O(1)–C(4)–O(2)
72.64(2)
153.26(5)
93.20(7)
108.9(2)
112.82(15)
123.6(2)
P(1)–Fe(1)–P(2) 169.69(3)
P(1)–Fe(1)–C(1)
C(1)–C(2)–C(3)
C(3)–C(4)–O(1)
C(3)–C(4)–O(2)
96.49(7)
117.7(2)
121.0(2)
115.4(2)
69.47(12) Fe(1)–C(2)–C(1)
123.63(15)
125.8(2)
123.0(2)
C(2)–C(3)–C(4)
C(3)–C(4)–O(2)
the iron atom bound to the acyl oxygen, whereas in
3a–d the dppm bridges the two metal atoms and is
trans with respect to the phosphido–bridge. Under
similar conditions 1a–c react with trimethylphosphite
to give [Fe2(CO)4(m-PPh2){P(OMe)3}2(m-h1(C):h2(C)–
{RO(O)CCH2}CꢀCH2)], most likely via a stepwise pro-
cess involving displacement of the ester coordinated
carbonyl, loss of carbon monoxide and reformation of
the metallacycle ring and a subsequent displacement
with a second molecule of trimethylphosphite. We have
also shown that the a-functionalised alkenyl complex
[Fe2(CO)4(m - PPh2){P(OMe)3}2(m - h1(C):h2(C)–{MeO-
(O)CCH2}CꢀCH2)] (6a) exists as a mixture of two
isomers that interconvert via a trigonal twist process,
and that s,h-exchange via the windshield wiper process
is slow on the NMR timescale.
4. Supplementary material
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC nos. 148651 (2a), 148652 (3a),

164
S. Doherty et al. / Journal of Organometallic Chemistry 620 (2001) 150–164
[7] S.R. Gilbertson, X. Zhao, D.P. Dawson, K.L. Marshall, J. Am.
Chem. Soc. 115 (1993) 8517.
[8] (a) S.R. Gilbertson, D.P. Dawson, O.D. Lopez, K.L. Marshall,
J. Am. Chem. Soc. 117 (1995) 4431. (b) S.R. Gilbertson, O.D.
Lopez, J. Am. Chem. Soc. 119 (1997) 3399.
148653 (5a), 148654 (6a). 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.
com.ac.uk or http://www.ccdc.cam.ac.uk).
[9] S.R. Gilbertson, O.D. Lopez, Angew. Chem. Int. Ed. Engl. 38
(1999) 1116.
[10] S. Doherty, G. Hogarth, Inorg. Chem. Commun. 1 (1998) 257.
[11] (a) S. Doherty, M. Waugh, T.S. Scanlan, M.R.J. Elsegood, W.
Clegg, Organometallics 18 (1999) 679. (b) S. Doherty, J.F.
Corrigan, A.J. Carty, E. Sappa, Adv. Organomet. Chem. 37
(1995) 39. (c) S. Doherty, M.R.J. Elsegood, W. Clegg, N.H.
Rees, T.S. Scanlan, M. Waugh, Organometallics 16 (1997) 3221.
(d) N. Carleton, J.F. Corrigan, S. Doherty, R. Pixner, Y. Sun,
N.J. Taylor, A.J. Carty, Organometallics 13 (1994) 4179. (e) S.
Doherty, G. Hogarth, M. Waugh, T.S. Scanlan, W. Clegg,
M.R.J. Elsegood, Organometallics 18 (1999) 3178. (f) S. Do-
herty, M.R.J. Elsegood, W. Clegg, T.S. Scanlan, N.H. Rees,
Chem. Commun. (1996) 1545. (g) S. Doherty, M.R.J. Elsegood,
W. Clegg, M.F. Ward, M. Waugh, Organometallics 16 (1997)
4251. (h) S. Doherty, M.R.J. Elsegood, W. Clegg, D. Mampe,
Organometallics 15, (1996) 5302. (i) S. Doherty, G. Hogarth,
M.R.J. Elsegood, W. Clegg, N.H. Rees, M. Waugh,
Organometallics 17 (1998) 3331.
[12] (a) S. Doherty, M.R.J. Elsegood, W. Clegg, M. Waugh,
Organometallics 15 (1996) 2688. (b) S. Doherty, M.R.J. Else-
good, W. Clegg, D. Mampe, Organometallics 16 (1997) 1186.
[13] (a) A.L. Spek, PLATON, University of Utrecht, The Netherlands,
2000. (b) SMART and SAINT software for CCD diffractometers,
Bruker AXS Inc., Madison, WI, 1994. (c) G.M. Sheldrick,
SHELXTL user manual, version 5, Bruker AXS Inc., Madison,
WI, 1994.
Acknowledgements
We thank the University of Newcastle upon Tyne for
financial support (S.D.) and the EPSRC for funding for
a diffractometer (W.C.). We thank Dr A.E. Aliev
(UCL) for help with EXSY experiments.
References
[1] J.P. Collman, L.S. Hegedus, J.R. Norton, R.G. Finke, Principles
and Applications of Organotransition Metal Chemistry, Univer-
sity Science Books, Mill Valley, CA, 1987.
[2] (a) S.G. Davies Pure Appl. Chem. 60 (1988) 13. (b) K. Black-
surn, S.G. Davies K.H. Sutton, M. Whittaker, Chem. Soc. Rev.
(1988) 1714. (c) G. Bashiardes, S.G. Davies, Tetrahedron Lett.
28 (1987) 5563. (d) R.P. Beckett, S.G. Davies, A.A Mortlock,
Tetrahedron Asymmetry 3 (1992) 123.
[3] J. Tsuji, Transition Metal Reagents and Catalyst. Innovations in
Organic Synthesis, Wiley, Chichester, 2000.
[4] (a) M. Brookhart, Y. Lou, E.W. Goldman, D.A. Timmers, G.D.
Williams, J. Am. Chem. Soc. 113 (1991) 927. (b) M. Brookhart,
W.B. Studabaker, Chem. Rev. 87 (1987) 411. (c) W. Petz,
Iron–Carbene Complexes, Springer-Verlag, Berlin, 1993.
[5] (a) L. Cassar, A. Giarruso, Gazz. Chim. Ital. 103 (1973) 793. (b)
M.C Baird, J.T. Mague, J.A. Osborn, G. Wilkinson, J. Chem.
Soc. A. (1967) 1347. (c) H. Brix, W. Beck, J. Organomet. Chem.
234 (1982) 151. (d) D.L. Reger, L.J. Mintz, L.J. Lebioda, J. Am.
Chem. Soc. 108 (1986) 1940. (e) D.L. Reger, S.A. Klaeren, J.E.
Babin, R.D. Adams, Organometallics 7 (1988) 181.
[6] (a) D. Seyferth, K.S. Brewer, T.G. Wood, M. Cowie, R.W. Hilts,
Organometallics 11 (1992) 2570. (b) D. Seyferth, J.B. Hoke, J.C.
Dewan, P. Hofmann, M. Schnellbach, Organometallics 13 (1994)
3452. (c) D. Seyferth, C.M. Archer, D.P. Ruschke, M. Cowie,
R.W. Hilts Organometallics 10 (1991) 3363. (d) D. Seyferth, J.B.
Hoke, G.B. Womack, Organometallics 9 (1990) 2662. (e) D.
Seyferth, J.B. Hoke, D.R. Wheeler, J. Organomet. Chem. 341
(1988) 421. (f) D. Seyferth, C.B. Womack, J.C. Dewan,
Organometallics 4 (1985) 398. (g) G.N. Mott, R. Granby, S.A.
MacLaughlin, N.J. Taylor, A.J. Carty, Organometallics 1 (1982)
189. (h) G. Hogarth, K. Shukri, S. Doherty, A.J. Carty, G.D.
Enright, Inorg. Chim. Acta. 291 (1999) 178. (i) K. Henrick, J.A.
Iggo, A.C. Kemball, M.J. Mays, P.R. Raithby, J. Chem. Soc.
Dalton Trans. (1987) 2669.
[14] (a) G. Hogarth, M.H. Lavender, J. Chem. Soc. Dalton Trans.
(1994) 3389. (b) G. Hogarth, M.H. Lavender, J. Chem. Soc.
Dalton Trans. (1992) 2759. (c) G. Hogarth, M.H. Lavender, K.
Shukri, Organometallics 14 (1995) 2325. (d) D. Glushove, G.
Hogarth, M.H. Lavender, J. Organomet. Chem. 528 (1997) 3.
[15] (a) Y.-F. Yu, J. Gallucci, A. Wojcicki, J. Am. Chem. Soc. 105
(1983) 4826. (b) R.P Rosen, J.B. Hoke, R.R. Whittle, G.L.
Geoffroy, J.P. Hutchinson, J.A. Zubieta, Organometallics 3
(1984) 836.
[16] (a) J. Cooke, J. Takats, Organometallics 14 (1995) 698. (b) R.F.
Alex, R.J. Pomeroy, Organometallics
6 (1987) 2437. (c) J.
Cooke, R.E.D. McClung, J. Takats, R.D. Rogers, Organometal-
lics 15 (1996) 4459.
[17] G. Hogarth, M.H. Lavender, K. Shukri, J. Organomet. Chem.
527 (1997) 247.
[18] Z. Xue, W.J. Seiber, C.B. Knobler, H.D. Kaesz, J. Am. Chem.
Soc. 112 (1990) 1825.
[19] E.W. Abel, T.P.J. Coston, K.G. Orrell, V. Sik, D. Stephenson, J.
Magn. Reson. 79 (1986) 34.
[20] S.A. MacLaughlin, S. Doherty, N.J. Taylor, A.C. Carty,
Organometallics 11 (1992) 4315.