Coordination and organometallic complexes of iron containing oe-phenylenebis(dimethylphosphine) (pdmp). Crystal and molecular structure of [Fe(η2-C2H4)(pdmp)2]

Article abstract of DOI:10.1039/b002012p

Routes to hydrido- and organo-iron complexes of the bidentate ligand o-phenylenebis(dimethylphosphine), o-C6H4(PMe2)2 (pdmp), have been developed, starting from trans-[FeCl₂(pdmp)2]. Reduction of trans-[FeC2(pdmp)2] with LiAlH4 gives the dihydride, cw-[FeH2(pdmp)2], there being no evidence for an intermediate monohydride [FeHCl(pdmp)2]. Treatment of /ra/w-[FeCl₂(pdmp)₂] with an excess of methyllithium gives [FeMe2(pdmp)2], isolated as a cis//ra;;s-mixture, the methyl groups of which are cleaved by an excess of HX to give [FeX2(pdmp)₂] (X = Cl, Br), predominantly in the form of the c/s-isomers. Other new complexes include [FeCI(Me)(pdmp)2] (m//ra;u-mixture) and [Fe(L)(pdmp)2] [L = CO, T|2-C2H4, n2-C8H8, nM,4-C8H6(SiMe3)2, r]2-C4H6, r|2-PhC2Ph and r|2-MeC₂Me]. Treatment of/ra/j.c-[FeCl2(pdmp)2] with sodium-naphthalene generates the hydrido(naphthyl)iron(n) complex [FeH(r(1-CIOH7)(pdmp)2] as a cis/trans-mixlute in tautomeric equilibrium with a zerovalent iron naphthalene complex [Fe(r|2-C,0H8)(pdmp)2]. Single crystal X-ray analysis shows that [Fe(n2-C2H4)(pdmp)2] has a distorted octahedral structure in which the ethylene is twisted by ca. 15° relative to the FeP4 skeleton, probably because of steric effects. In solution the coordinated ethylene rotates about the coordination axis with a free energy of activation ΔC^t at 324 K of 67 kJ mol^-1, as estimated from variable temperature 'H and 31P NMR spectra. In the cyclooctatetraene complexes [Fe(r|2-C8Hg)(pdmp)2] and [Fe{(nM,4C8H6)(SiMe3)2}(pdmp)2] there is also a lower energy process in which the Fe(pdmp)2 unit migrates between the double bonds of the eight-membered ring. The strong electron-donating ability of the Fe(pdmp)2 fragment is indicated by the low value of v(CO) in [Fe(CO)(pdmp)2], the highly shielded 'H and I3C nuclei of coordinated ethylene in [Fe(n2-C2H4)(pdmp)2], the Fe-C and C=C bond lengths in the Fe-C2H4 unit [2.052(8) and 1.418(10) A, respectively], and the facile reversible protonation of the coordinated ethylene by methanol or ethanol. Treatment of [Fe(n2-C2H4)(pdmp)2] with HBF4-OEt2 gives initially a complex ris-[Fe(BF4)(Et)(pdmp)2], in which the ethyl group may be agostic, and finally ra-[Fe(BF4)2(pdmp)2]. The coordinated BF4 groups of the latter compound are displaced by acetonitrile to give c/5-[Fe(NCMe)2(pdmp)2](BF4)2. The BPh4 salts of the cations [FeBr(NCMe)(pdmp)2]'1' and [Fe(NCMe)2(pdmp)2]2+ have also been isolated as mixtures of cis/trans-isomers from ra-[FeX2(pdmp)2] (X = Cl, Br) and acetonitrile. The Royal Society of Chemistry 2000.

Full text of DOI:10.1039/b002012p

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Coordination and organometallic complexes of iron containing
o-phenylenebis(dimethylphosphine) (pdmp). Crystal and molecular
structure of [Fe(ꢀ2-C2H4)(pdmp)2]
Martin A. Bennett,* Evert J. Ditzel, Allen D. Hunter, Karl Khan, Mike R. Kopp,
Horst Neumann, Glen B. Robertson and Harald Zeh
Research School of Chemistry, Australian National University, Canberra, A.C.T. 0200,
Australia. E-mail: bennett@rsc.anu.edu.au
Received 6th March 2000, Accepted 23rd March 2000
Published on the Web 3rd May 2000
Routes to hydrido- and organo-iron complexes of the bidentate ligand o-phenylenebis(dimethylphosphine),
o-C6H4(PMe2)2 (pdmp), have been developed, starting from trans-[FeCl2(pdmp)2]. Reduction of trans-[FeCl2-
(pdmp)2] with LiAlH4 gives the dihydride, cis-[FeH2(pdmp)2], there being no evidence for an intermediate
monohydride [FeHCl(pdmp)2]. Treatment of trans-[FeCl2(pdmp)2] with an excess of methyllithium gives
[FeMe2(pdmp)2], isolated as a cis/trans-mixture, the methyl groups of which are cleaved by an excess of HX
to give [FeX2(pdmp)2] (X = Cl, Br), predominantly in the form of the cis-isomers. Other new complexes include
[FeCl(Me)(pdmp)2] (cis/trans-mixture) and [Fe(L)(pdmp)2] [L = CO, η2-C2H4, η2-C8H8, η2-1,4-C8H6(SiMe3)2,
η2-C4H6, η2-PhC2Ph and η2-MeC2Me]. Treatment of trans-[FeCl2(pdmp)2] with sodium–naphthalene generates
the hydrido(naphthyl)iron() complex [FeH(η1-C10H7)(pdmp)2] as a cis/trans-mixture in tautomeric equilibrium
with a zerovalent iron naphthalene complex [Fe(η2-C10H8)(pdmp)2]. Single crystal X-ray analysis shows that
[Fe(η2-C2H4)(pdmp)2] has a distorted octahedral structure in which the ethylene is twisted by ca. 15Њ relative to
the FeP4 skeleton, probably because of steric effects. In solution the coordinated ethylene rotates about the
coordination axis with a free energy of activation ∆G‡ at 324 K of 67 kJ molϪ1, as estimated from variable
temperature 1H and 31P NMR spectra. In the cyclooctatetraene complexes [Fe(η2-C8H8)(pdmp)2] and [Fe{(η2-1,4-
C8H6)(SiMe3)2}(pdmp)2] there is also a lower energy process in which the Fe(pdmp)2 unit migrates between the
double bonds of the eight-membered ring. The strong electron-donating ability of the Fe(pdmp)2 fragment is
indicated by the low value of ν(CO) in [Fe(CO)(pdmp)2], the highly shielded 1H and 13C nuclei of coordinated
ethylene in [Fe(η2-C H )(pdmp) ], the Fe–C and C᎐C bond lengths in the Fe–C H unit [2.052(8) and 1.418(10) Å,
᎐
2
4
2
2
4
respectively], and the facile reversible protonation of the coordinated ethylene by methanol or ethanol. Treatment of
[Fe(η2-C2H4)(pdmp)2] with HBF4ؒOEt2 gives initially a complex cis-[Fe(BF4)(Et)(pdmp)2], in which the ethyl group
may be agostic, and finally cis-[Fe(BF4)2(pdmp)2]. The coordinated BF4 groups of the latter compound are displaced
by acetonitrile to give cis-[Fe(NCMe)2(pdmp)2](BF4)2. The BPh4 salts of the cations [FeBr(NCMe)(pdmp)2]ϩ and
[Fe(NCMe)2(pdmp)2]2ϩ have also been isolated as mixtures of cis/trans-isomers from cis-[FeX2(pdmp)2] (X = Cl, Br)
and acetonitrile.
Building on the pioneering studies of Nyholm and coworkers
on the coordination chemistry of o-phenylenebis(dimethyl-
arsine), o-C6H4(AsMe2)2 (pdma),1 Warren and Bennett,2 and,
more recently, Levason and coworkers3–6 have shown that the
corresponding ditertiary phosphine, o-C6H4(PMe2)2 (pdmp),
forms complexes with the d-block elements in which the metal
atom attains unexpectedly high formal oxidation states, e.g. ϩ3
and ϩ4 in trans-[MX2(pdmp)2]nϩ (X = Cl, Br, M = Mn,2
Fe,2,3 Ni,2,4 Os,2,5 n = 1, 2), ϩ3 in [CuCl(pdmp)2]2ϩ and [Cu-
we thought it worthwhile to make a preliminary survey of the
organometallic chemistry of the Fe(pdmp)2 moiety. The results
are reported in this paper.
Results and discussion
Since most of the Fe(pdmp)2 complexes reported here are
pseudooctahedral, their 31P-{1H} NMR data, collected in
Table 1, provide useful stereochemical information.
(pdmp)2]3ϩ 2
[OsO2(pdmp)2]2ϩ 6
,
and ϩ6 in trans-[OsO2Cl2(pdmp)] and trans-
The stability of such compounds can be
The starting material for most of the syntheses is trans-
[FeCl2(pdmp)2], trans-1, which precipitates as a pale green,
diamagnetic solid when pdmp is added to a solution of ferrous
chloride in ethanol.2 If the preparation is carried out in thf
instead of ethanol, a mixture of the red-brown cis- and green
trans-isomers can be isolated. Supersaturated solutions contain-
ing mixtures of cis- and trans-1 are formed when the organo- or
hydrido-complexes of pdmp (see below) react with chlorinated
solvents, thus enabling the 31P parameters of these poorly sol-
uble complexes to be determined. As expected, trans-1 shows a
singlet whereas cis-1 shows a pair of well separated triplets aris-
ing from an A2X2 spin system. The cis-dihalides [FeX2(pdmp)2]
(X = Cl 1, Br 2) are also obtained by addition of an excess of
HX to the dimethyl compound [FeMe2(pdmp)2] (see below).
.
attributed to a combination of the geometrical rigidity and
strong electron-donating ability of pdmp. However, the appli-
cation of pdmp in organometallic chemistry has not been as
widespread as that of its more flexible aliphatic counterparts
of similar steric bulk, viz., 1,2-bis(dimethylphosphino)ethane,
Me2PCH2CH2PMe2 (dmpe) or 1,2-bis(diethylphosphino)-
ethane, Et2PCH2CH2PEt2 (depe) (see refs. 7 and 8 for recent
examples). This remains true even though the earlier low-
yielding syntheses of pdmp2,7,9,10 have been replaced by a
reliable, high-yield alternative.11 In view of the extensive low
oxidation state, organometallic and C–H activation chemistry
based on 3d8 fragments such as Fe(dmpe)2 and Fe(depe)2,12–21
DOI: 10.1039/b002012p
J. Chem. Soc., Dalton Trans., 2000, 1733–1741
This journal is © The Royal Society of Chemistry 2000
1733

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Table 1 31P-{1H} NMR data for Fe–pdmp complexesa
Complex
Isomer
Solvent
δP
[FeCl2(pdmp)2] 1
trans
cis
trans
cis
CDCl3
CDCl3
CD3CN
CD3CN
59.7 (s)b
58.4 (t), 72.2 (t, 2JPP 49)b
62.7 (s)c
[FeX(NCMe)(pdmp)2]ϩ 3a
60.6 (q, sep 48.2, 52.3, 52.8), 66.7 (q, sep 53.2, 51.3, 54.3), 70.8 (q, sep
43.9, 52.0, 42.5)c
[FeX(NCMe)(pdmp)2]ϩ 3b
trans
cis
CD3CN
CD2Cl2
CD3CN
CD2Cl2
CD3CN
CD3CN
acetone-d6
C6D6
C6D6
C6D6
C6D6
C6D6
61.1 (s)c
58.8 (s)d
58.4 (t, sep 57.0), 64.4 (q, sep 52.4), 75.7 (q, sep 53.6)c
57.2 (8-line m), 62.6 (q, sep 53.0), 74.0 (6-line m)d
[Fe(NCMe)2(pdmp)2]2ϩ
4
trans
cis
60.7 (s)e
59.6 (t), 63.3 (t, 2JPP 42.4)e
58.3 (t), 62.1 (t, 2JPP 43.5) f
[Fe(CO)(pdmp)2] 5
57.6 (s)
[Fe(η2-C2H4)(pdmp)2] 6
[Fe(η2-C8H8)(pdmp)2] 7
50.8 (t), 69.8 (t, 2JPP 46.9)
46.0–48.4 (11-line m), 50.0–52.5 (6-line m), 63.6–66.2 (8-line m)
46.7 (m), 47.7 (m), 51.9 (m), 65.8 (m)
45.4 (6-line m, sep 13.8, 43.6, 43.6), 51.8 (6-line m, sep 13.8, 47.8, 47.8),
[Fe{η2-1,4-C8H6(SiMe3)2}(pdmp)2] 8
[Fe(η2-C4H6)(pdmp)2] 9
59.0 (6-line m, sep 118.7, 48.7, 43.6)
[Fe(η2-PhC2Ph)(pdmp)2] 10
cis-[FeH2(pdmp)2] 11
cis-[Fe(AlH4)Cl(pdmp)2] 12
[FeMe2(pdmp)2] 13
C6D6
C6D6
C6D6
C6D6
C6D6
C6D6
C6D6
thf-d8
thf-d8
Et2O
C6D6
C6D6
CD2Cl2
52.6 (t), 63.8 (t, 2JPP 43.0)
61.8 (t), 70.7 (t, 2JPP 29.8)
68.0 (m)
trans
cis
trans
cis
trans
cis
74.2 (s)
59.8 (t), 69.6 (t, 2JPP 34.6)
[FeCl(Me)(pdmp)2] 14
68.7 (s)
53.1 (1:2:1 td), 64.4–65.4 (7-line m), 78.3 (8-line m)
73.2 (s), 73.5 (s)
44.7 (br m), 61.4 (br m), 67.5 (br m)
69.3 (s)
[FeH(η1-C10H7)(pdmp)2] 15
trans-[FeHCl(pdmp)2] 17
[Fe(BF4)(C2H5)(pdmp)2] 18
trans
cis
66.3 (s)
47.1 (8-line m), 58.2–68.5 (15-line m), 66.4–68.0 (8-line m)
cis-[Fe(BF4)2(pdmp)2] 19
53.0 (t), 70.6 (t, 2JPP 42.0)
a Separations and couplings in Hz. b Data from solutions of 6 or 11 in CDCl3 that had been set aside for ca. 0.5 h. c Data from cis/trans-1 in CD3CN.
d Data from BPh4 salt of 3b in CD2Cl2. e Data from BPh4 salt of 4 in CD3CN. f Data from BF4 salt of 4 in acetone-d6.
Addition of cis-1 or cis-2 to neat acetonitrile gives immedi-
ately at room temperature a mixture of cis- and trans-[FeX-
(NCMe)(pdmp)2]X [X = Cl 3a, Br 3b], as shown by the 31P-{1H}
NMR spectra. The cation of 3b (3, X = Br; cis/trans-mixture)
was isolated as its BPh4 salt. On heating to 80 ЊC for 24 h in the
presence of NaBPh4, the bis(acetonitrile) complex [Fe(NCMe)2-
(pdmp)2](BPh4)2 4a is formed, also consisting of an approxi-
mately 1:1 mixture of cis- and trans-isomers. There is no
reaction between trans-1 and acetonitrile at room temperature,
but at 80 ЊC in the presence of NaBPh4 the 1:1 mixture of
cis- and trans-4a is formed again. The crystalline solid that sep-
arates on cooling appears to be pure trans-4a according to an
X-ray crystallographic study.22 The isolation of pure cis-4 as its
BF4 salt 4b is discussed below. In its 31P-{1H} NMR spectrum
trans-3b shows a singlet whereas in cis-3b all the phosphorus
atoms are inequivalent and give rise to three complex multi-
plets in a 2:1:1 ratio arising from an ABCD spin system.
1
Correspondingly, the H NMR spectrum of trans-3b contains
a pair of quintets due to the inequivalent P–Me groups,
Scheme 1 (i) Na/Hg, CO; (ii) Na/Hg, C2H4; (iii) K2C8H8; (iv) Li2{1,4-
whereas in cis-3b all the P–Me groups are inequivalent
C8H6(SiMe3)2}; (v) C4H6Mgؒ2thf; (vi) NaC10H8, PhC2Ph; (vii) Na/Hg,
and appear as eight doublets. The 31P NMR spectra of cis-
H2 or LiAlH4; (viii) MeLi (excess); (ix) pdmp.
and trans-[Fe(NCMe)2(pdmp)2]2ϩ 4 resemble those of the
corresponding isomers of 1 and 2. Acetonitrile complexes
trans-[FeCl(NCMe)(L–L)2]BPh4 (L–L = pdma,23 depe24) and
complexes [FeH(C10H7)(dmpe)2] obtained from trans-[FeCl2-
(dmpe)2] and NaC10H8 (2 equiv.) is a convenient room temper-
ature source of the 16-electron Fe(dmpe)2 fragment,12 but the
analogous pdmp system seems generally to work only at ca.
65 ЊC (see below). Reaction of trans-1 with sodium-amalgam
in thf gives a deep red, thermally unstable solution which we
have been unable to characterise but which functions as a source
of Fe(pdmp)2 in some of its reactions. Thus, in the presence
of CO, the red 18e complex [Fe(CO)(pdmp)2] 5 is formed in
high yield. Its IR spectrum in thf shows one ν(CO) band at
1825 cmϪ1, cf. 1812 cmϪ1 (C6D6),12 1830 cmϪ1 (thf)26 for
[Fe(CO)(dmpe)2].12 The 31P NMR spectrum contains only a
24
trans-[Fe(NCMe)2(depe)2](BPh4)2 are known, but the cis-
isomers of these cations or of [FeCl2(L–L)2] have not been
reported and are presumably more labile than their pdmp
analogues.
An unsuccessful attempt was made to generate the cation
[FeCl(N2)(pdmp)2]ϩ, an analogue of [FeCl(N2)(dmpe)2]ϩ,25 by
treatment of a suspension of trans-1 in ethanol with NaBPh4
under dinitrogen.
Despite its low solubility, trans-1 reacts rapidly with reducing
agents and alkylating agents, as outlined in Scheme 1. In the
dmpe series, the cis/trans-mixture of hydrido(2-naphthyl)
1734
J. Chem. Soc., Dalton Trans., 2000, 1733–1741

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₁
singlet, indicating that complex 5, which is probably trigonal
bipyramidal with equatorial CO, is highly fluxional at room
temperature.
Hz) and 6.40 (W = 35 Hz), attributable to the coordinated and
₂

uncoordinated protons, respectively, of the eight-membered
ring. These coalesce at higher temperature and separate at
Ϫ60 ЊC into six multiplets of equal intensity at δ 2.51, 3.28,
Sodium-amalgam reduction of trans-1 under ethylene gives
the iron(0)–ethylene complex [Fe(η2-C2H4)(pdmp)2] 6. After
separation from a pyrophoric by-product, this can be isolated in
good yield as a red, crystalline, air-sensitive solid. The 1H NMR
spectrum at 20 ЊC shows a broad resonance at δ 1.24 corre-
sponding to two of the ethylene protons; the resonance due to
the other two is masked by broad singlets due to the P–Me
groups. On cooling the latter sharpen and resolve into four
singlets.
5.22, 5.42, 6.38 and 6.51; the protons of the coordinated C᎐C
᎐
bond are probably masked by the P–Me resonances. In addition
to rotation of the C8H8 ring about the iron–alkene bond, there-
fore, there is a lower energy process in which the Fe(pdmp)2 unit
migrates between the double bonds. In contrast, the eight-
membered ring in [Mn(CO)2(η5-C5H5)(η2-C8H8)] shows no
fluxional behaviour below its decomposition temperature (ca.
75 ЊC).34 The lower energy process is hindered in the corre-
sponding η2-1,4-bis(trimethylsilyl)cyclooctatetraene complex,
[Fe{η2-1,4-C8H6(SiMe3)2}(pdmp)2] 8, which is formed in high
yield from the reaction of trans-1 with Li2{1,4-C8H6(SiMe3)2}.
At room temperature, the 31P-{1H} NMR spectrum shows four
The 31P-{1H} NMR spectrum at 20 ЊC in C6D6 consists of a
pair of triplets, corresponding to the presence of a pair of
mutually cis-pdmp ligands. In the 1H NMR spectrum of [Fe(η2-
C2H4)(o-C6H4{P(CD3)2}2)] 6-d12 at 0 ЊC, the ethylene protons
appear as a pair of broad resonances at δ 1.22 and 0.90, which
sharpen on cooling to a pair of multiplets; in the 13C NMR
spectrum of 6 at room temperature the ethylene carbon atoms
resonate at δ 17.04. These data are consistent with a represen-
tation of 6 either as a trigonal bipyramidal iron(0) complex with
ethylene occupying an equatorial site or as a pseudooctahedral
iron() complex (ferracyclopropane); confirmation is provided
by the X-ray crystal structure discussed below. The marked
upfield shifts of the ethylene 1H and 13C nuclei presumably
reflect strong back-bonding into the ethylene π*-orbital,
although comparison with the value for the average chemical
shift of the ethylene protons in [Fe(η2-C2H4)(dmpe)2] (δ 0.59)
suggests that back-bonding from the Fe(dmpe)2 fragment may
be even stronger.
As the temperature of the solution of 6-d12 is raised, the
ethylene resonances reversibly broaden and coalesce to a singlet
at δ 1.0; the free energy of activation ∆G‡ for the fluxional
process at the coalescence temperature (324 K) calculated from
the equation k = π∆ν/√227 is 67.3 kJ molϪ1. An independent
estimate of ∆G‡ can be made from the broadening of the 31P
resonances of 6, which becomes evident at 50–60 ЊC. The line-
widths at half-height of the deconvoluted 31P NMR peaks at
324 K and 273 K were 40.0 Hz and 3.54 Hz, respectively, and
1
separate multiplets and the H NMR spectrum shows broad
multiplets at δ 2.79(1H), 3.52(1H) and 6.30(2H); the absence of
proton resonances in the region δ 5–6 implies that the iron atom
is probably bound to carbon atoms 6 and 7, thus placing the
bulky SiMe3 groups as far as possible from the Fe(pdmp)2 unit.
Attempts to prepare a butadiene complex by reaction of
trans-1 with Na/Hg in the presence of butadiene were unsuc-
cessful, but treatment with but-2-ene-1,3-diylmagnesium,
C4H6Mgؒ2thf,35,36 gives the deep red, very air-sensitive complex
[Fe(η2-C4H6)(pdmp)2] 9 whose complex 31P-{1H} NMR spec-
trum indicates that the phosphorus atoms are inequivalent, as
1
expected. The H NMR spectrum in C6D6 shows three broad
resonances of equal intensity at δ 6.35, 5.25 (doublet) and 4.95
assignable to the uncoordinated diene protons and a peak at
δ 2.95 that may be due to one of the coordinated diene protons.
Reduction of trans-1 with Na/Hg in the presence of alkynes
such as diphenylacetylene or but-2-yne did not yield alkyne
complexes cleanly, but use of NaC10H8 in the presence of an
excess of diphenylacetylene gives [Fe(η2-PhC2Ph)(pdmp)2] 10 as
a red, air-stable solid. Complex 10 shows bands in its solid state
IR spectrum at 1710 and 1685 cmϪ1, cf. 1720 cmϪ1 in [Fe(η2-
PhC2Ph)(dmpe)2],12 and the acetylenic carbon atoms give a sig-
nal at δ 143.4 in the 13C NMR spectrum. The 31P-{1H} and 1H
NMR spectra are consistent with the presence of a pair of
mutually cis-pdmp ligands. These data indicate that the alkyne
is acting as a 2e donor in a trigonal bipyramidal structure simi-
lar to that of the η2-ethylene complex 6. The corresponding
but-2-yne complex, [Fe(η2-MeC2Me)(pdmp)2], was formed
similarly to complex 10 and identified on the basis of its A2X2
31P-{1H} NMR spectrum. The compound could not be isolated
because it decomposed in solution to a second, unidentified
species containing four inequivalent phosphorus atoms.
Sodium-amalgam reduction of trans-1 under hydrogen gas
gave a low yield of the dihydride cis-[FeH2(pdmp)2] 11, which
could be separated only with difficulty from a pyrophoric by-
product. Complex 11 is obtained in higher yield and purity as a
yellow solid by reduction of trans-1 with an excess of LiAlH4
and subsequent hydrolysis. If the hydrolysis step is omitted, an
intermediate orange solid can be isolated, whose composition,
based on microanalysis and mass spectrometry, corresponds to
the formula [Fe(AlH4)Cl(pdmp)2] 12. The 31P-{1H} NMR spec-
trum consists of a complex, symmetrical multiplet centred at
δ 68.0; the 1H NMR spectrum contains four one-proton triplet
resonances in the range δ 0.2–2.2, which may be due to Al–H
protons, in addition to a pair of 12H-resonances suggestive of
the presence of cis-pdmp ligands. The nature of this intermedi-
ate requires further investigation. In contrast to the LiAlH4
reduction of [FeCl2(dmpe)2] or [FeCl2(depe)2],18,37,38 the mono-
hydride trans-[FeHCl(pdmp)2] could not be detected as an
intermediate.
₁
₁
application of the equation k = π(W * Ϫ W Њ), which is valid in
₂
₂

the slow exchange regime,27 gave a value of ∆G‡ of 66.8 kJ
molϪ1 (W * and W Њ are the linewidth at half height at temper-
₁
₁
₂

₂

ature T and the natural linewidth, respectively). As in the case
of [Fe(η2-C2H4)(dmpe)2],12 the process responsible for these
changes must be a 90Њ rotation of the coordinated ethylene, but
the dmpe complex is stereochemically more mobile than the
pdmp complex, 6. Its olefinic protons appear as a single broad
resonance at 25 ЊC and split into two resonances only at
Ϫ25 ЊC; similarly, its 31P{1H} resonances are broad at 25 ЊC.
In agreement with previous experimental and theoretical
work,27–31 these differences imply a strong connection between
the processes of olefin rotation and pseudorotation of the FeP4
unit, the latter process having a higher barrier for the more rigid
pdmp system.
The coordinated ethylene of complex 6 is firmly bound but is
displaced by CO at room temperature and atmospheric pressure
over a period of several days to give the carbonyl complex 5.
The protonation of complex 6 is discussed below.
In the course of investigating alternative routes to complex 6,
we found that bis(cyclooctatetraene)iron(0), [Fe(η6-C8H8)(η4-
C8H8)],32,33 reacts with pdmp to give [Fe(η2-C8H8)(pdmp)2] 7 as
a red, thermally robust and fairly air-stable complex. Complex
7 can also be made directly from the reaction of trans-1 with
K2C8H8, but in much lower yield and purity. The 31P-{1H}
NMR spectrum consists of complex overlapping multiplets
showing the four phosphorus atoms to be inequivalent, suggest-
ing that the eight-membered ring is non-planar, probably with
a tub conformation similar to that found in [Mn(CO)2(η5-
Reaction of trans-1 with two equivalents of methyllithium
gives the dimethyl complex [FeMe2(pdmp)2] 13, which we
isolated in 64% yield as a mixture of the cis- and trans-isomers.
Monitoring by 31P NMR spectroscopy showed that cis-13 was
1
C5H5)(η2-C8H8)].34 At room temperature, the H NMR spec-
₁
trum contains a pair of broad resonances, at δ 3.30 (W = 180
₂

J. Chem. Soc., Dalton Trans., 2000, 1733–1741
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Table 2 Selected bond distances (Å) and interbond angles (Њ) in
formed initially but this underwent partial isomerisation as
the solution was concentrated, and at equilibrium the ratio
of trans- to cis-13 in d8-thf was ca. 1:4. Consistent with the
electron-rich nature of the fragment Fe(pdmp)2, the iron–
methyl resonances of both isomers in C6D6 are highly shielded,
viz. a quintet at δ Ϫ1.80 (JPH 5.9 Hz) for trans-13 and a multi-
plet at δ Ϫ0.27 for cis-13. As in the case of the ethylene com-
plexes, however, the shieldings are not as high as those of the
corresponding dimethyliron() complexes containing dmpe,
viz., trans-[FeMe2(dmpe)2]: δ Ϫ2.02(toluene-d8);39 cis-[FeMe2-
(dmpe)2]: δ Ϫ0.99(toluene-d8),39 Ϫ0.64(C6D6).40
[Fe(η2-C2H4)(pdmp)2] 6
Molecule 1
Molecule 2
Fe(1)–C(21)
Fe(1)–C(22)
C(21)–C(22)
Fe(1)–P(11)
Fe(1)–P(12)
Fe(1)–P(13)
Fe(1)–P(14)
2.052(8)
Fe(2)–C(51)
Fe(2)–C(52)
C(51)–C(52)
Fe(2)–P(21)
Fe(2)–P(22)
Fe(2)–P(23)
Fe(2)–P(24)
2.052(8)
2.047(8)
1.427(14)
2.174(2)
2.147(2)
2.168(2)
2.139(2)
2.045(9)
1.409(14)
2.173(2)
2.154(2)
2.176(2)
2.142(2)
Addition of one equivalent of HCl in ether to a mixture of
cis- and trans-13 in toluene gives a red-brown solid containing
the corresponding chloro(methyl)iron() complexes, cis- and
trans-[FeCl(Me)(pdmp)2] 14. The trans-isomer was obtained
in reasonable purity, as shown by 31P NMR spectroscopy, by
washing the mixture with pentane, in which it is poorly soluble.
The chloro(methyl) complexes could not be obtained by treat-
ment of trans-1 with one equivalent of methyllithium, nor
could they be detected as intermediates in the formation of
the dimethyl complex 13. Treatment of complex 13 with more
than two equivalents of HCl or HBr in ether precipitated
brown-red and brown-green solids, respectively, identified as
containing mainly cis-1 and cis-2, on the basis of their elemen-
tal analysis and 31P-{1H} NMR spectra in CD3CN (see above).
C(21)–Fe(1)–C(22)
C(21)–Fe(1)–P(12)
C(22)–Fe(1)–P(14)
P(11)–Fe(1)–P(13)
P(11)–Fe(1)–P(12)
P(13)–Fe(1)–P(14)
P(12)–Fe(1)–P(14)
40.2(4)
110.0(3)
106.9(3)
179.6(1)
84.6(1)
85.3(1)
104.0(1)
C(51)–Fe(2)–C(52)
C(52)–Fe(2)–P(23)
C(52)–Fe(2)–P(22)
P(21)–Fe(2)–P(23)
P(21)–Fe(2)–P(22)
P(23)–Fe(2)–P(24)
P(22)–Fe(2)–P(24)
40.7(4)
109.5(4)
106.6(4)
179.2(1)
85.3(1)
85.1(1)
104.3(1)
whereas reactions with benzene and terminal alkynes occur at
room temperature.
Protonation reactions
As expected for an alkene coordinated to an electron-rich, low-
valent metal centre,43 the ethylene in [Fe(η2-C2H4)(pdmp)2] 6 is
readily protonated. Addition of one equivalent of HBF4ؒOEt2
to a solution of 6 in ether gave a pale yellow, air- and moisture-
sensitive solid, the 1H NMR spectrum of which in CD2Cl2
shows broad multiplets due to an ethyl group at δ 0.60(2H) and
δ 1.44(3H). The 31P-{1H} NMR spectrum contains a complex
pattern of overlapping multiplets due to inequivalent phos-
phorus atoms. The microanalysis corresponds approximately
to the formula [Fe(BF4)(C2H5)(pdmp)2] 18, but further work
is required to establish whether the compound would be
better represented as an agostic ethyl complex, [Fe(CH2CH2-
µ-H)(pdmp)2]BF4.44 The 31P-{1H} NMR spectrum of the yellow
solution of complex 6 in ethanol is very similar to that of 18,
suggesting that even ethanol is sufficiently acidic to protonate
the coordinated ethylene; removal of ethanol regenerates com-
plex 6 almost quantitatively. This behaviour is reminiscent of
the protonation of [FeH2(dmpe)2] by ethanol to give [FeH-
(η2-H2)(dmpe)2]ϩ, the labile η2-dihydrogen of which is readily
replaced by ClϪ to give trans-[FeHCl(dmpe)2].18 The dihydride
11 also reacts with methanol and ethanol but we have not been
able to identify conclusively the analogous cation [FeH(η2-H2)-
(pdmp)2]ϩ.
Reaction of trans-1 with sodium–naphthalene (two equivalents)
The IR spectrum of the very air-sensitive solid (15) isolated
from this reaction carried out under argon in thf shows ν(FeH)
bands at 1721 and 1765 cmϪ1, and the 1H NMR spectrum con-
tains multiplet hydride resonances at δ Ϫ13.6 and Ϫ18.2. The
chemical shifts are close to those reported12 for cis- and trans-
[FeH(η1-2-C10H7)(dmpe)2], respectively. Unexpectedly, however,
the 31P-{1H} NMR spectrum shows two sharp singlets at δ 73.2
and 73.5, whereas trans-[FeH(η1-2-C10H7)(dmpe)2] has the
expected singlet, at δ 74.2.12 In addition, there are three very
broad resonances at δ 44.7, 61.4 and 67.5 in a ratio of 1:1:2 in
the 31P-{1H} NMR spectrum of the pdmp complex, whereas
the corresponding complex multiplets in cis-[FeH(η1-2-
C10H7)(dmpe)2] in the range δ 50–75 are well-resolved. We
suggest tentatively that [FeH(η1-C10H7)(pdmp)2] 15 contains
both 1- and 2-naphthyl derivatives, each as a cis/trans-mixture,
and that the cis-isomers are in rapid equilibrium with an
undetected, zerovalent iron naphthalene complex, [Fe(η2-
C10H8)(pdmp)2] 16. Treatment of compound 15 with an excess
of DCl gives naphthalene containing no deuterium, i.e. deuter-
olysis must proceed entirely via the reactive tautomer 16. In
contrast, reaction of cis-[FeH(η1-2-C10H7)(dmpe)2] with DCl
gives naphthalene containing ca. 20% of 2-C10H7D, as shown
Addition of an excess of HBF4ؒOEt2 to complexes 6, 7 or 11
cleaves the Fe–H (11) or Fe–C (6, 7) bonds to give the mauve-
grey solid cis-[Fe(BF4)2(pdmp)2] 19. The corresponding bis-
2
(triflato) complex cis-[Fe(CF3SO ) (pdmp) ] can be made
3
2
2
by H NMR spectroscopy and GC-MS; a similar result has
similarly by use of triflic acid. We assume that in these com-
pounds the anions are bound weakly to iron in a monodentate
fashion,45 perhaps similarly to the perchlorate groups in the
monoclinic modification of trans-[Co(ClO4
plex 19 immediately forms an orange solution in acetonitrile
from which the salt cis-[Fe(NCMe)2(pdmp)2](BF4)2, cis-4b,
can be isolated as a yellow powder. The 31P-{1H} NMR spec-
trum shows that the pdmp groups retain their cis-arrangement
and there is no trace of the corresponding trans-isomer (see
above).
been reported for the reaction of DCl with cis-[RuH(η1-2-
C10H7)(dmpe)2].41
Attempts to obtain a dinitrogen complex analogous to
[Fe(η1-N2)(depe)2]42 by treatment of trans-1 in thf with
sodium–naphthalene under nitrogen gave a mixture of 15 and
the dihydride 11. The same mixture is formed if a solution of 15
in thf is exposed to nitrogen; in n-hexane or cyclohexane, how-
ever, 11 is not observed. This behaviour has not been investi-
gated further.
Addition of an equimolar quantity of HCl to complex 15
gives mainly 1 as a cis/trans-mixture and unchanged starting
material. Only a small amount of a compound assumed to be
trans-[FeHCl(pdmp)2] 17, identified by its quintet hydride
resonance and singlet 31P-{1H} NMR signal (Table 1), could be
detected. Complex 15 is unaffected by ethylene at room tem-
perature and reacts to give [Fe(η2-C2H4)(pdmp)2] 6 only at
65 ЊC; in contrast, cis-[FeH(η1-2-C10H7)(dmpe)2] reacts with
ethylene at room temperature.12 Preliminary experiments show
that complex 15 also reacts with hex-3-yne only at 65 ЊC,
) (pdma) ].46 Com-
2
2
Molecular structure of [Fe(ꢀ2-C2H4)(pdmp)2] 6
Crystals of 6 contain two crystallographically independent but
metrically similar molecules in each asymmetric scattering unit.
The molecules are separated by normal van der Waals contacts
and exhibit virtual C2 symmetry. Diagrams of each, one viewed
parallel and one viewed perpendicular to the virtual twofold
axis, are shown in Fig. 1, together with the atom numbering
schemes; hydrogen atoms of the pdmp ligands are omitted for
1736
J. Chem. Soc., Dalton Trans., 2000, 1733–1741

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associated contraction of the P(axial)–C(phenyl) relative to the
P(equatorial)–C(phenyl) distance [1.830(4) Å, 1.849(3) Å,
respectively; ∆/σ ≈ 4] is also evident.
Conclusion
The electron-rich fragment Fe(pdmp)2, like its more extensively
studied Fe(dmpe)2 counterpart, forms complexes with CO
and with unsaturated hydrocarbons in which there is strong
back-bonding to the added ligands. The π-donor ability of
Fe(pdmp)2 may be slightly less than that of Fe(dmpe)2 as a
consequence of the presence of the aromatic linking group but
this feature may serve to stiffen the chelate ring so that one-
ended dissociation is less likely. The greater rigidity may also be
responsible for the apparently higher barrier to rotation of
coordinated ethylene in the Fe(pdmp)2 complex. The iron chem-
istry of pdmp differs from that of dmpe and depe in other
subtle ways, e.g. the zerovalent iron tautomer [Fe(η2-C10H8)-
(L–L)2] plays a more significant role in the chemistry of
[FeH(η1-C10H7)(L–L)2] for L–L = pdmp than for L–L = dmpe,
and the behaviour of cis-[FeH2(pdmp)2] towards protons is
more complex than that established for the dmpe and depe
analogues. These differences may also arise from the tighter and
more compact binding of the aromatic-based ligand but at
present we cannot offer a detailed explanation. So far, we have
been unable to isolate intermediates that could be used to gen-
erate the Fe(pdmp)2 fragment at room temperature and thus
allow access under mild conditions to a wider range of zero-
valent iron complexes of pdmp. This problem may limit the
utility of Fe(pdmp)2 as an electron-rich fragment in organo-
metallic chemistry.
Fig. 1 Molecular structure of [Fe(η2-C2H4)(pdmp)2] 6, viewed (a)
parallel and (b) perpendicular to the virtual twofold axis, with atom
labelling and 30% probability ellipsoids.
clarity. Selected bond lengths and interbond angles are listed in
Table 2. The coordination geometry about the metal atom can
be described as approximately trigonal bipyramidal, with two
axial and two equatorial phosphorus atoms of pdmp and the
third equatorial site occupied by the mid-point of dihapto-
ethylene, or as a slightly distorted octahedron with the ethylene
occupying one edge. In both molecules the ethylene ligands are
twisted by about 15Њ relative to the FeP4 skeleton, probably
owing to intramolecular steric interaction between the ethylene
hydrogen atoms and neighbouring phosphorus and methyl
groups of the pdmp ligands. In addition, the ethylene ligands
also exhibit an in-plane tilting displacement, which is
manifested in the inequivalence of the P(equatorial)–Fe–C
angles and of the P ؒ ؒ ؒ C non-bonding contact distances. This
deformation is, again, metrically similar in both molecules
[∆{P(equatorial)–Fe–C} = 3.1, 2.9Њ] but, unlike the twist
deformation, it does not conform to the virtual C2 symmetry of
the Fe(pdmp)2 fragment.
Experimental
All reactions and subsequent manipulations were carried out
under dry nitrogen or argon with use of standard Schlenk tech-
niques. Solvents were dried and distilled before use by standard
methods. NMR spectra were recorded at 20 ЊC on Varian
XL200E (2H at 30.7 MHz, 13C at 50.3 MHz, 31P at 81.0 MHz),
Gemini 300BB and Varian VXR300 (13C at 75.4 MHz, 31P at
121.4 MHz) and Inova 500 spectrometers and were referenced
to the residual protons of deuterated solvents (1H), the signals
of the solvent (13C), and to external 85% H3PO4 (31P). 31P-{1H}
NMR data are listed in Table 1. Variable temperature NMR
spectra were measured on the VXR300 instrument. IR spectra
were measured on Perkin-Elmer 683 grating or 1800 Fourier-
transform spectrometers. Mass spectra were measured by the
electron impact (EI) method at 70 eV on a VG Micromass
7070F spectrometer or by the fast-atom bombardment (FAB)
technique on a VG ZAB2-SEQ spectrometer. Elemental
analyses were performed in-house.
The Fe–C(ethylene) distance in complex 6 [2.052(8) Å] is sig-
nificantly less than those reported for the trigonal bipyramidal
iron(0) complexes [Fe(CO)4(η2-C2H4)] 20 [2.117(3) Å],47
[Fe(CO)3(PPh3)(η2-C2H4)] 21 [2.095(7), 2.102(7) Å],48 [Fe(CO)2-
{P(OMe)3}2(η2-C2H4)] 22 [2.111(4) Å],49 and [Fe(CO)2-
{(C2F5)2PCH2CH2P(C2F5)2}(η2-C2H4)] 23 [2.125(4), 2.113(4)
Å],50 all of which contain auxiliary ligands that are probably
stronger π-acceptors than pdmp. Correspondingly, the C–C
(ethylene) distance in 6 [av. 1.418(10) Å] exceeds those in 22 and
23 [1.369(6) and 1.362(7) Å, respectively], although it is not
significantly different from that in 21 [1.398(8) Å]. These data
indicate strong Fe–C2H4 back-donation in 6 induced by the
strong σ-donor and poor π-acceptor abilities of the Fe(pdmp)2
fragment. The Fe–C2H4 unit in 6 has ferracyclopropane char-
acter, as is evident from the average dihedral angle between the
H–C–H planes of 64Њ, cf. 0Њ for free ethylene and 109Њ 47Ј for
the eclipsed form of ethane.
The compounds pdmp,11 dmpe,51 trans-[FeCl2(dmpe)2],40
[Fe(η6-C8H8)(η4-C8H8)],33 K2[C8H8],52 Li2[1,4-C8H6(SiMe3)2]53
and C6H4Mgؒ2thf35,36 were prepared by published procedures.
The ligand o-C6H4{P(CD3)2}2, pdmp-d12, was made similarly to
pdmp with use of CD3I in place of CH3I. Anhydrous ferrous
chloride was made by reduction of anhydrous FeCl3 with iron
powder in thf;54 the resulting solid was heated in vacuo at 85 ЊC
to give a material whose composition corresponded approxi-
mately to the formula [FeCl2(thf)].55
Preparations
trans-[FeCl2(pdmp)2], trans-1.2 Method (i). A vigorously
stirred solution of [FeCl2(thf)] (1.98 g, 9.9 mmol) in ethanol (70
cm3) was treated dropwise with pdmp (3.6 cm3, 19.2 mmol).
After an initial red coloration, a green precipitate formed. The
suspension was stirred for 1 h at room temperature and the light
green precipitate was separated from the pale pink solution by
filtration. After the solid had been washed with ethanol (3 × 20
cm3) and dried in vacuo, the yield was 4.50 g (87%).
As was also observed in complex 23, the Fe–P(axial) bond
distances in 6 [av. 2.172(2) Å] are significantly greater than the
Fe–P(equatorial) distances [av. 2.145(2) Å]; a presumably
J. Chem. Soc., Dalton Trans., 2000, 1733–1741
1737

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Method (ii). A vigorously stirred solution of [FeCl2(thf)] (1.90
g, 9.5 mmol) in thf (50 cm3) was treated dropwise with pdmp
(3.45 cm3, 19.2 mmol). The mixture was stirred for 1 h at room
temperature and the mixture of brown-red and green solids
(cis- and trans-1) was separated from the colourless solution by
filtration. After the solid had been washed with hexane (3 × 20
cm3) and dried in vacuo, the yield was 4.3 g (87%). The mixture
was converted into trans-1 after stirring in ethanol for 1 h
(Found: C, 46.6; H, 6.5; Cl, 13.1; P, 22.2%; C20H32Cl2FeP4
requires: C, 45.9; H, 6.2; Cl, 13.55; P, 23.7%); FAB-MS (eth-
anol) m/z 522(Mϩ), 487(Mϩ Ϫ Cl).
[Fe(CO)(pdmp)2] 5. To a stirred suspension of 1% sodium-
amalgam (5 mmol Na, excess) in thf (60 cm3) under an atmos-
phere of CO was added solid trans-1 (0.50 g, 0.96 mmol). The
mixture was stirred for 2 h and the deep red solution was separ-
ated by decantation. Solvent was removed in vacuo and the solid
residue was purified by crystallisation from hexane at Ϫ25 ЊC to
give complex 5 as a red crystalline solid. The yield was 0.28 g
(61%) (Found: C, 52.3; H, 7.0%. C21H32FeOP4 requires: C, 52.5;
1
H, 6.7%). H NMR (C6D6) δ 1.55 (s, 24 H, PMe), 7.15 (br,
4 H), 7.37 (br, 4 H) (C6H4); IR (thf) 1825 cmϪ1 (νCO); EI-MS m/z
480 (Mϩ), 452 (Mϩ Ϫ CO).
[Fe(ꢀ2-C2H4)(pdmp)2] 6. To a rapidly stirred suspension of 1%
sodium-amalgam (10 mmol Na) in thf (100 cm3) under ethylene
was added solid trans-1 (1.50 g, 2.87 mmol). After 1 h the deep
red solution was separated by decantation and evaporated to
dryness in vacuo. The residual solid was crystallised from
hexane at Ϫ25 ЊC to give complex 6 as large red crystals, some
of which were of X-ray quality. The yield was 0.95 g (69%)
(Found: C, 54.7; H, 7.7; Fe, 11.5%. C22H36FeP4 requires: C,
55.0; H, 7.6; Fe, 11.6%). 1H NMR (C6D6) δ 0.94 (s, 14 H, PMe,
CH2CH2), 1.24 (br s, 2 H, CH2CH2), 1.53 (s, 6 H, PMe), 1.63 (s,
6 H, PMe), 7.08 (br s, 4 H), 7.31 (br s, 4 H) (C6H4); 13C-{1H}
NMR (C6D6) δ 14.36 (m, PMe, JCH 124 Hz), 17.04 (m, C2H4,
JCH 144 Hz), 18.38 (m, PMe, 1JCH 128 Hz), 21.08 (m, PMe, 1JCH
126 Hz), 26.66 (m, PMe, 1JCH 126 Hz), 126.4 (m, C6H4, 1JCH 163
Hz), 150 (br s, C6H4), 153 (br s, C6H4); EI-MS m/z 452
(Mϩ Ϫ C2H4).
cis-[FeCl2(pdmp)2], cis-1. A suspension of freshly prepared
cis-[FeMe2(pdmp)2] 12 (see below) (0.32 g, 0.66 mmol) in tolu-
ene (30 cm3) was cooled to Ϫ25 ЊC and treated dropwise from a
syringe with a solution of HCl in ether (2.0 cm3, 1.43 M, 2.9
mmol) to give a red-brown precipitate. The colourless super-
natant liquid was removed by cannulation and the residue was
washed with pentane (3 × 15 cm3) and dried in vacuo. The yield
was 0.22 g (64%) (Found: C, 45.7; H, 6.3%. C20H32Cl2FeP4
requires: C, 45.9; H, 6.2%).
cis-[FeBr2(pdmp)2], cis-2. A suspension of [FeMe2(pdmp)2] 12
(see below) (0.18 g, 0.37 mmol) in toluene (30 cm3) was cooled
to Ϫ25 ЊC and treated dropwise with a solution of HBr in ether
(4.0 cm3, 0.2 M, 0.8 mmol) to give a red-brown precipitate. The
colourless supernatant liquid was removed by cannulation
and the brown solid was washed with pentane (2 × 10 cm3) to
give cis-2 (0.10 g, 44%) (Found: C, 40.3; H, 5.6; Br, 26.0%.
C20H32Br2FeP4 requires: C, 39.2; H, 5.3; Br, 26.1%).
[Fe(ꢀ2-C8H8)(pdmp)2] 7. Method (a). A solution of pdmp
(1.26 g, 6.36 mmol) in thf (50 cm3) was treated with solid
[Fe(η6-C8H8)(η4-C8H8)] (0.84 g, 3.18 mmol) and the mixture
was stirred for 18 h, after which time the reaction was complete
as judged by 31P NMR spectroscopy. The deep red solution was
evaporated to dryness in vacuo to give a brick-red powder.
Recrystallisation from ether gave violet crystals of 7 (1.41 g,
80%).
cis- and trans-[FeBr(NCMe)(pdmp)2]BPh4, 3b. To a mixture
of cis-2 (55 mg, 0.09 mmol) and NaBPh4 (33 mg, 0.1 mmol) was
added a solution of acetonitrile (3 µl) in CH2Cl2 (5 cm3). The
orange-brown supernatant liquid was separated by decantation
from a white precipitate (presumably NaBr) and evaporated to
dryness under reduced pressure. The residue was redissolved in
the minimum volume of CH2Cl2 and hexane was added slowly
to the solution to give the mixture of cis- and trans-3b as
an orange-brown solid (Found: C, 62.0; H, 6.4%. C46H55-
BBrFeNP4 requires: C, 61.9; H, 6.2%). cis-3b: 1H NMR
(CD2Cl2) δ 0.62 (d, 3 H, PMe, JPH 8.0 Hz), 0.69 (d, 3 H, PMe,
JPH 7.6 Hz), 1.18 (d, 3 H, PMe, JPH 9.1 Hz), 1.51 (d, 3 H, PMe,
JPH 9.9 Hz), 1.80 (br s, 3 H, MeCN), 1.90 (d, 3 H, PMe, JPH
7.1 Hz), 1.92 (d, 3 H, PMe, JPH 5.4 Hz), 2.07 (d, PMe, 3 H,
JPH 7.1 Hz), 2.19 (d, 3 H, PMe, JPH 7.1 Hz), 6.88 (t, 4 H,
J 7.2 Hz), 7.03 (t, 8 H, J 7.2 Hz), 7.35 (m, 8 H) (BPh4), 7.48
(ABq, 8 H, J 8.4 Hz, C6H4). trans-3b: 1H NMR (CD2Cl2) δ 1.66
(qnt, 12 H, PMe), 2.12 (qnt, 12 H, PMe). FAB-MS (ethanol)
m/z 573 (Mϩ ϩ H), 531 [FeBr(pdmp)2].
Method (b). A suspension of trans-1 (0.20 g, 0.38 mmol) in thf
(20 cm3) was treated dropwise with a freshly prepared solution
of K2[C8H8] (ca. 0.5 mmol) and the mixture was stirred at room
temperature for 12 h. The solvent was removed in vacuo and the
dark red residue was extracted with hexane at Ϫ25 ЊC. Crystal-
lisation from hexane gave complex 7 in 5–10% yield (Found: C,
60.6; H, 7.6; Fe, 9.9%. C28H40FeP4 requires: C, 60.45; H, 7.25;
1
Fe, 10.0%). H NMR (C6D6) δ 0.58 (d, 3H, PMe, JPH 5.3 Hz),
0.66 (d, 3 H, PMe, JPH 5.2 Hz), 1.07 (d, 3 H, PMe, JPH 6.7 Hz),
1.52 (d, 3 H, PMe, JPH 6.0 Hz), 1.60 (d, 3 H, PMe, JPH 8.1 Hz),
1.66 (d, 3 H, PMe, JPH 6.3 Hz), 1.81 (d, 3 H, PMe, JPH 6.2 Hz),
1.88 (d, 3 H, PMe, JPH 6.5 Hz), 3.30 (br, 2 H, C8H8), 6.40 (br,
6 H, C8H8), 7.1–7.5 (br m, C6H4); EI-MS m/z 556 (Mϩ), 452
[Fe(pdmp)2ϩ].
cis- and trans-[Fe(NCCD3)2(pdmp)2](BPh4)2, 4a-d6. A suspen-
sion of cis-1 (30 mg, 0.06 mmol) in CD3CN was treated with
NaBPh4 (24 mg, 0.07 mmol). After the mixture had been stirred
for 5 min, an orange solution had formed together with a white
solid, which was removed by centrifugation. The 31P-{1H}
NMR spectrum of the orange solution showed the presence of
cis- and trans-3a-d6. Additional NaBPh4 (24 mg, 0.07 mmol)
was added and the mixture was heated at 60–80 ЊC for 96 h. At
this stage the 31P-{1H}NMR spectrum showed the presence of
[Fe{ꢀ2-1,4-C8H6(SiMe3)2}(pdmp)2] 8. Dropwise addition of
n-butyllithium in hexane (3.25 cm3, 1.6 M, 5.2 mmol) to a solu-
tion of 1,4-C8H8(SiMe3)2 (0.65 g, 2.60 mmol) in thf (30 cm3) at
Ϫ30 ЊC caused the initially colourless solution to turn orange.
trans-1 (1.33 g, 2.54 mmol) was added to the solution at
Ϫ30 ЊC. The mixture was allowed to warm to room temperature
and was stirred for 12 h. The dark red solution was filtered and
evaporated to dryness in vacuo. Recrystallisation of the residue
1
from hexane gave complex 8 as a red solid (1.38 g, 78%). H
2
trans-4a-d6 (δ 61.0), cis-4a-d6 [δ 59.9 (t), 63.6 (t, JPP 42.4 Hz)]
NMR (C6D6) δ 0.29 (s, 9 H, SiMe3), 0.49 (s, 9 H, SiMe3), 0.50 (d,
3 H, PMe, JPH 6.9 Hz), 0.58 (d, 3 H, PMe, JPH 5.2 Hz), 0.86 (d,
3 H, PMe, JPH 6.6 Hz), 1.16 (d, 3 H, PMe, JPH 8.5 Hz), 1.36
(d, 3 H, PMe, JPH 6.1 Hz), 1.65 (d, 3 H, PMe, JPH 6.2 Hz), 1.71
(d, 3 H, PMe, JPH 6.5 Hz), 1.80 (d, 3 H, PMe, JPH 6.1 Hz), 2.79
(br, 1 H), 3.52 (br, 1 H), 6.30 (m, 2 H) (C8H6; coordinated
olefinic protons probably masked by P–Me resonances), 6.9–7.3
(br m, C6H4); EI-MS m/z 700 (Mϩ), 628 (Mϩ Ϫ SiMe3 ϩ 1), 452
[Fe(pdmp)2ϩ].
and some unchanged cis- and trans-3a-d6. Another 20 mg of
NaBPh4 was added and the mixture was heated again at 80 ЊC
for 12 h. The 31P-{1H}NMR spectrum showed the main prod-
uct to be cis-4-d6, together with a small amount of trans-4-d6.
The product was isolated by evaporating to dryness and wash-
ing the yellow solid with ether (Found: C, 72.6; H, 6.65; N,
2.3%. C70H72D6B2FeN2P4 requires: C, 73.7; H, 6.7; N, 2.4%); IR
(cmϪ1, Nujol) 2100w [ν(CN)].
1738
J. Chem. Soc., Dalton Trans., 2000, 1733–1741

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[Fe(ꢀ2-C4H6)(pdmp)2] 9. A suspension of trans-1 (0.52 g, 1.0
mmol) in thf (50 cm3) was treated with [C4H6Mgؒ2thf] (ca. 1.2
equiv.) and the mixture was stirred for 14 h at room temper-
ature. Filtration through Celite and evaporation to dryness
in vacuo gave 9 as a very air-sensitive red solid, which was
(0.92 g, 64%). Recrystallisation from ether gave pure cis-13 in
the first fraction and a 1:1 mixture of cis- and trans-13 in the
second fraction (Found: C, 54.8; H, 8.4%. C22H38FeP4 requires:
1
C, 54.8; H, 7.9%). cis-13: H NMR(C6D6) δ Ϫ0.27 (m, 6 H,
FeMe), 0.68 (d, 6 H, PMe, JPH 3.9 Hz), 1.20 (d, 6 H, PMe, JPH
5.8 Hz), 7.30 (br m, 8 H, C6H4); trans-13: 1H NMR(C6D6)
δ Ϫ1.80 (qnt, 6 H, FeMe, JPH 5.9 Hz), 1.46 (s, 24 H, PMe), 7.30
(br m, 8 H, C6H4).
1
recrystallised from thf/hexane (1:4). The yield was 68%. H
NMR(C6D6) δ 0.5–1.8 (br m, 26 H, PMe, 2 H of C4H6), 2.95
(br s), 4.95 (br s), 5.25 (d), 6.35 (br s) (each 1 H of C4H6), 6.95–
7.35 (br m, 8 H, C6H4); EI-MS m/z 452 [Fe(pdmp)2ϩ].
[FeCl(Me)(pdmp)2] 14. A solution of cis- and trans-13 (0.35 g,
0.70 mmol) in toluene (100 cm3) was cooled in dry ice and
treated dropwise with an ether solution of HCl (7.50 cm3, 0.095
M, 0.70 mmol). The initially red solution turned brown and a
red-brown precipitate formed. The mixture was evaporated to
dryness in vacuo and the residual solid was washed with pentane
(3 × 20 cm3). The solid (0.31 g) contained a mixture of cis- and
trans-14 together with small amounts of cis-13, cis-1 and trans-
1 (Found: C, 49.1; H, 6.6%. C21H35ClFeP4 requires: C, 50.2; H,
7.0%). trans-14: 1H NMR(C6D6) δ Ϫ2.73 (qnt, 3 H, FeMe, JPH
7.0 Hz), 1.28 (qnt, 12 H, PMe), 2.18 (qnt, 12 H, PMe). cis-14:
1H NMR(C6D6) δ Ϫ0.72 (ddt, 3 H, FeMe, sep, 8.7, 5.6, 1.6 Hz),
0.26 (d, 3 H, PMe, JPH 6.5 Hz), 0.66 (d, 3 H, PMe, JPH 4.7 Hz),
0.89 (d, 3 H, PMe, JPH 8.2 Hz), 1.49 (d, 3 H, PMe, JPH 5.2 Hz),
1.61 (d, 3 H, PMe, JPH 7.6 Hz), 1.79 (d, 3 H, PMe, JPH 7.0 Hz),
1.84 (d, 3 H, PMe, JPH 7.1 Hz), 1.88 (d, 3 H, PMe, JPH 5.9 Hz),
6.84 (t, 1 H, J 6.5 Hz), 6.98 (t, 1 H, J 7.0 Hz), 7.08 (q, 4 H, J 7.4
Hz), 7.43 (q, 2 H, J 7.4 Hz) (C6H4). EI-MS m/z 503 (Mϩ), 489
(Mϩ Ϫ Me), 452 [Fe(pdmp)2ϩ].
[Fe(ꢀ2-PhC2Ph)(pdmp)2] 10. A mixture of trans-1 (0.17 g,
0.32 mmol) and diphenylacetylene (0.12 g, 0.65 mmol) in thf
(30 cm3) was treated dropwise with a solution of NaC10H8
freshly prepared from naphthalene (2.5 mg, 0.33 mmol) and
sodium (0.5 g, excess) in thf (50 cm3). The colour changed from
green to red. After the solution had been stirred for 2 h at room
temperature, solvent was removed in vacuo. Naphthalene was
removed from the residue by sublimation at 40 ЊC 10Ϫ4 mm and
the residue was recrystallised from hexane to give complex 10 in
ca. 30% yield (Found: C, 64.5; H, 6.9; Fe, 8.6%. C34H42FeP4
1
requires: C, 64.8; H, 6.7; Fe, 8.9%). H NMR(C6D6) δ 0.75 (d,
6 H, PMe, JPH 4.5 Hz), 1.09 (t, 6 H, PMe, JPH 3.4 Hz), 1.37
(t, 6 H, PMe, JPH 2.3 Hz), 1.82 (d, 6 H, PMe, JPH 5.1 Hz);
EI-MS m/z 452 [Fe(pdmp)2ϩ]; IR (cmϪ1, KBr) 1710m, 1685m
[ν(C᎐C)].
᎐
cis-[FeH2(pdmp)2] 11. Method (a). Solid trans-1 (0.155 g, 0.30
mmol) was added to a suspension of 1% sodium-amalgam
(2 mmol Na) in thf (30 cm3) and the mixture was stirred vigor-
ously for 3 h at room temperature under hydrogen. The dark red
supernatant liquid was removed by cannulation and evaporated
to dryness in vacuo to give a red, pyrophoric solid. Extraction
with hexane and several recrystallisations from this solvent gave
a poor yield of a yellow solid identified by its 1H and 31P-{1H}
NMR spectra as complex 11.
Method (b). An excess of LiAlH4 (0.50 g, 13 mmol) was added
to a vigorously stirred suspension of trans-1 (0.50 g, 0.96 mmol)
in thf (200 cm3). After ca. 0.5–1 h the starting complex had
been consumed and an olive-green solution had formed. This
was filtered to remove the excess of LiAlH4 and distilled water
(0.10 cm3) was added, causing vigorous gas evolution. The
resulting yellow solution was evaporated to dryness in vacuo
and the residue was recrystallised from hexane to give complex
11 as a yellow, microcrystalline solid. The yield was 0.37 g
(85%) (Found: C, 51.1; H, 7.6%. C20H34FeP4 requires: C, 52.9;
H, 7.5%). 1H NMR(C6D6) δ Ϫ13.08 (br m, 2 H, FeH), 1.18 (br
s, 6 H, PMe), 1.56 (br s, 6 H, PMe), 1.70 (br s, 6 H, PMe), 1.85
(br s, 6 H, PMe), 7.30 (br m, 8 H, C6H4); EI-MS m/z 452
(Mϩ ϩ 2); IR (cmϪ1, Nujol) 1762m br [ν(FeH)].
cis- and trans-[Fe(BF4)(Et)(pdmp)2] 18. A red solution of
complex 6 (0.17 g, 0.35 mmol) in ether (50 cm3) was treated
dropwise with a dilute solution of HBF4ؒOEt2 in ether until the
supernatant liquid became pale orange. The flocculent, pale
yellow precipitate was collected by filtration and dried in vacuo.
The yield of compound 19 was quantitative (Found: C, 45.0;
H, 6.9%. C22H37BF4FeP4 requires: C, 44.2; H, 6.9%). 1H
NMR(CD2Cl2) δ 0.60 (br m, 2 H, CH2), 0.80–1.1 (m, 12 H,
PMe), 1.44 (br m, 3 H, CH2CH3), 1.6–2.0 (br m, 12 H, PMe),
7.5–8.1 (m, 8 H, C6H4).
The 31P-{1H} NMR spectrum of the yellow solution of com-
plex 6 in ethanol was almost the same as that of complex 18,
suggesting that either [Fe(OEt)(η1-C2H5)(pdmp)2] or [Fe(η2-
C2H5)(pdmp)2]ϩ had been formed. There were also weak peaks
2
at δ 62.8 (t), 69.8 (t, JPP 35.3 Hz), possibly due to cis-
[Fe(OEt)2(pdmp)2].
cis-[Fe(BF4)2(pdmp)2] 19. Treatment of a solution of complex
6 (0.18 g, 0.38 mmol) in ether (40 cm3) with an excess of
HBF4ؒOEt2 caused discharge of the red colour and precipi-
tation of complex 19 as a mauve-grey solid, which was separ-
ated by filtration and dried in vacuo. The yield was quantitative
(Found: C, 38.4; H, 5.7%. C20H32B2F8FeP4 requires: C, 38.4; H,
5.15%). The compound is very hygroscopic and attempted
cis-[Fe(AlH4)Cl(pdmp)2] 12. An excess of LiAlH4 (0.05 g, 1.3
mmol) was added to a vigorously stirred suspension of trans-1
(0.10 g, 0.19 mmol) in thf (40 cm3). After ca. 1 h the result-
ing olive green solution was filtered and evaporated to dryness
in vacuo. Crystallisation of the residue from toluene gave cis-
[Fe(AlH4)Cl(pdmp)2] (0.08 g, 81%) as an orange microcrystal-
line solid (Found: C, 46.4; H, 6.45%. C20H36AlClFeP4 requires:
C, 46.3; H, 7.0%). 1H NMR(C6D6) δ 0.24 (t, 1 H, AlH), 1.32 (t,
1 H, AlH), 1.47 (s, 12 H, PMe), 1.87 (s, 12 H, PMe), 1.90 (t, 1 H,
AlH), 2.21 (t, 1 H, AlH), 7.40 (br, 8 H, C6H4); EI-MS m/z 487
(Mϩ Ϫ AlH4), 452 [Fe(pdmp)2ϩ].
recrystallisation from CH2Cl2/ether gave
a monohydrate
(Found: C, 37.1; H, 5.3%. C20H34B2F8FeOP4 requires: C, 37.3;
H, 5.3%). 1H NMR(CD2Cl2) δ 0.55 (t, 6 H, PMe, sep, 8.8 Hz),
2
1.32 (d, 6 H, PMe, JPH 10.0 Hz), 1.94 (br m, 6 H, PMe), 2.26
(br m, 6 H, PMe), 7.47–8.15 (br m, 8 H, C6H4); IR (Nujol)
1158–1056 cmϪ1 (vs br, BF4).
Complex 19 could be formed similarly from complexes 7
or 11.
[FeMe2(pdmp)2] 13. A vigorously stirred suspension of trans-
1 (1.57 g, 3.00 mmol) in thf (100 cm3) was treated dropwise at
room temperature with an ether solution of methyllithium (4.20
cm3, 1.44 M, 6.00 mmol) and stirring was continued for 2 d. The
solution was evaporated to dryness in vacuo and the residual
orange solid was extracted with toluene (50 cm3). The orange
solution was evaporated to dryness in vacuo and the solid was
crystallised from hexane to give a mixture of cis- and trans-13
cis-[Fe(NCMe)2(pdmp)2](BF4)2ؒH2O, cis-4b. Addition of
acetonitrile (10 cm3) to complex 19 (50 mg, 0.08 mmol) gave
immediately a pale orange solution. Evaporation to dryness in
vacuo and crystallisation of the residue from CH2Cl2/ether gave
cis-4b quantitatively as a yellow powder (Found: C, 39.3; H,
5.5; N, 3.6%. C24H40B2F8FeN2OP4 requires: C, 39.7; H, 5.55; N,
1
2
3.9%). H NMR (acetone-d6) δ 0.93 (t, 6 H, PMe, JPH ϩ 4JPH
2
8.4 Hz), 1.57 (t, 6 H, PMe, JPH ϩ 4JPH 10.1 Hz), 2.09 (t, 6 H,
J. Chem. Soc., Dalton Trans., 2000, 1733–1741
1739

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2
2
PMe, JPH ϩ 4JPH 8.7 Hz), 2.29 (t, 6 H, PMe, JPH ϩ 4JPH 8.4
Hz), 2.65 (t, 6 H, J 1.7 Hz, MeCN), 2.85 (br s, H2O), 7.7–8.0 (m,
4 H), 8.4 (m, 4 H) (C6H4); IR (cmϪ1, Nujol) 2100 w [ν(CN)].
phine ligand hydrogens as fixed contributors at idealised sites
(C–H = 0.95 Å, normal angles) with BH = 1.1 BC]. Anisotropic
thermal parameters were specified for all non-hydrogen atoms
and a secondary extinction parameter β was also included in the
refinement scheme.60 Neutral atom scattering factors with dis-
persion corrections for Fe, P & C were taken from ref. 61. At
convergence R = 0.058, wR = 0.063, goodness of fit = 2.10, maxi-
mum shift to error ratio = 0.04 and the maximum ∆ρ in a final
difference map was 0.45 e ÅϪ3. Data reduction and refinement
were performed with programs contained in the ANUCRYS
package.62 Fig. 1 was drawn with ORTEP.63
Reaction of trans-1 with sodium–naphthalene. A suspension
of trans-1 (161 mg, 0.3 mmol) in thf (20 cm3) was treated at
room temperature with a solution of NaC10H8 that had been
prepared from sodium (240 mg, ca. 10 mmol) and naphthalene
(1.34 g) in thf (30 cm3). The mixture gradually turned yellow
and was stirred for a further 2 h. The solvent was removed in
vacuo and the solid residue was extracted with pentane (3 × 15
cm3). The solution was evaporated to dryness and the excess of
naphthalene removed at room temperature/10Ϫ4 mm to give a
very air-sensitive, orange-yellow solid believed to contain cis-
and trans-[FeHR(pdmp)2] (R = 1- or 2-C10H7) 15 (see text and
Table 1). The yield was 124 mg (71%). 1H NMR (thf-d8) δ Ϫ18.2
(m, FeH of trans-15), Ϫ13.6 (m, FeH of cis-15), 0.55–1.85 (m,
PMe), 6.40–8.15 (m, aromatic); IR (Nujol) 1721, 1765 cmϪ1
[ν(FeH)].
CCDC reference number 186/1914.
Acknowledgements
We thank the Izaak Walton Killam Memorial Foundation for
the award of a Visiting Fellowship to A. D. Hunter and the
Alexander von Humboldt Foundation for the award of a von
Lynen Fellowship to M. R. Kopp.
Reaction of 15 with DCl. A solution of 15 prepared in situ
from trans-1 (86 mg, 0.164 mmol) was treated with a solution
of 37% DCl in D2O (0.03 cm3, 0.375 mmol). The mixture was
stirred for 30 min and evaporated to dryness, and the residue
was extracted with hexane. Naphthalene (40 mg, 87% of the
initial amount) was recovered from the solution and identified
by comparison of its EI-mass spectrum with that of a reference
sample. The 2H NMR spectrum showed that no deuterium had
been incorporated.
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1741