An iron(II) dihydrogen hydrido complex containing the tripodal tetraphosphine ligand P(CH2CH2PMe2)3

Article abstract of DOI:10.1039/b401954g

The dihydrogen hydrido complex [FeH(H₂)(PP₃)] ⁺ 1 (PP₃ = P(CH₂CH₂PMe ₂)₃ 2) was formed by the protonation of the dihydrido complex FeH₂(PP₃) 3 wi

Full text of DOI:10.1039/b401954g

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An iron(II) dihydrogen hydrido complex containing the tripodal
tetraphosphine ligand P(CH2CH2PMe2)3
Leslie D. Field,*a Hsiu L. Li,a Barbara A. Messerle,*b Ronald J. Smernika and Peter Turnera
a School of Chemistry, University of Sydney, NSW 2006, Australia
b School of Chemical Sciences, University of New South Wales, NSW 2052, Australia
Received 9th February 2004, Accepted 3rd March 2004
First published as an Advance Article on the web 29th March 2004
The dihydrogen hydrido complex [FeH(H2)(PP3)]ϩ 1 (PP3 = P(CH2CH2PMe2)3 2) was formed by the protonation
of the dihydrido complex FeH2(PP3) 3 with methanol or ethanol. The observation of H–D coupling in partially
deuterated isotopomers of 1 and measurement of T 1 relaxation times for the hydrido and dihydrogen resonances of 1
confirmed the presence of the η2-dihydrogen ligand. Complex 1 shows dynamic NMR behaviour in both the 31P and
1H NMR spectra with facile exchange between the protons in the η2-dihydrogen ligand and the η1-hydrido ligand.
The dihydrogen ligand of 1 is easily displaced by both anionic and neutral ligands to afford the corresponding
hydrido complexes [FeHX(PP3)]ϩ (X = CO 11, X = PPh3 12) or FeHX(PP3) (X = Cl 13, X = Br 14, X = I 15, X = N3
16). Small quantities of the alkoxy hydrido complexes FeH(OR)(PP3) (R = Me 4; R = Et 5) are observed in methanol
and ethanol solutions containing 1. In methanol solution, FeH(OMe)(PP3) 4 reacts to form the carbonyl hydrido
complex [FeH(CO)(PP3)]ϩ 11 and isotopic labelling confirms that the carbonyl ligand of 11 is derived from the
methanol solvent. The mechanism of methanol oxidation presumably proceeds through β-hydride elimination from
FeH(OMe)(PP3) to produce formaldehyde as an intermediate which is further dehydrogenated to form the carbonyl
ligand. [FeH(H2)(PP3)]ϩ 1 and FeHCl(PP3) 13 react rapidly with paraformaldehyde to also form [FeH(CO)(PP3)]ϩ 11.
Complex 11 also decarbonylates acetaldehyde to afford the methyl carbonyl complex [FeMe(CO)(PP3)]ϩ 17. The
structure of 17 was confirmed by X-ray crystallography.
Introduction
Results and discussion
Preparation of [FeH(H2)(PP3)]؉ 1
Tripodal tetradentate phosphines constrain the stereochemistry
of the resultant metal complexes to a high degree and in some
cases this can lead to enhanced catalytic activity compared to
analogous complexes containing mono- and bidentate ligands.1
In octahedral complexes, the presence of a tripodal tetradentate
ligand enforces a cis relationship between the two remaining
ligands.
Iron() dihydrido complexes of the form FeH2P4 containing
bidentate13 or tripodal tetradentate9 phosphine ligands undergo
reversible protonation in alcohol solvents to afford dihydrogen
hydrido complexes of the form [FeH(H2)P4]ϩ.14
Dissolution of FeH2(PP3) 312a in methanol or ethanol
afforded the dihydrogen hydrido complex [FeH(H2)(PP3)]ϩ 1 as
the major product. A small quantity of the corresponding
alkoxy hydrido complex FeH(OR)(PP3) (R = Me 4, R = Et 5) is
also formed (Scheme 1). FeH(OMe)(PP3) 4 has been previously
reported from the solvolysis of FeHCl(PP3).12b,15
Complexes of molecular hydrogen have now been observed
for a large number of metals and many molecular hydrogen
complexes exhibit hydrogen exchange between the dihydrogen
and hydrido ligands.2 The exchange is more facile when the
two ligands are mutually cis. Crystal structures of Fe(H2)(H)2-
3
(PEtPh2)3 and RuH(H2)I(PCy3)2,4 where the dihydrogen and
hydrido ligands are constrained to be cis, show close contact
between dihydrogen and hydrido hydrogen atoms indicating
some degree of bonding. Protonation of Group 8 dihydrido
complexes containing the tripodal phenyl-substituted ligand
P(CH2CH2PPh2)3 (PP3Ph) to give the dihydrogen/hydrido
complexes has been studied in depth5 and dihydrogen hydrido
complexes of iron,6 ruthenium7 and osmium8 containing the
phenyl substituted ligand P(CH2CH2PPh2)3 as well as an iron
complex containing the methyl substituted ligand P(CH2-
Scheme 1
Removal of the alcohol solvent and reconstitution in
an aprotic solvent, regenerated the dihydrido complex 3. The
addition of a methanol or ethanol solution of sodium tetra-
phenylborate precipitated 1 as the tetraphenylborate salt.
9
CH2CH2PMe2)3 and iron and ruthenium complexes contain-
ing the cyclohexyl substituted ligand P(CH2CH2PCy2)3 (PP3-
Cy)10 have all been reported to exhibit exchange between
η2-dihydrogen and η1-hydrido sites. The facile synthesis of the
tripodal tetraphosphine ligand P(CH2CH2PMe2)3 (PP3)11 and
iron complexes containing PP3,12 have allowed this comparison
to be extended to include [FeH(H2)(PP3)]ϩ 1.
NMR Characterisation of [FeH(H2)(PP3)]؉ 1
The 31P{1H} NMR spectrum (Fig. 1(a)) of 1 at 300 K contains
two resonances, a sharp quartet at δ 179.8 ppm assigned to the
central phosphorus atom PC and a broadened doublet at δ 64.6
ppm assigned to the terminal phosphorus atoms PT and PU
which are exchanging at this temperature. At 253 K, separate,
broad resonances were observed for PT and PU (Fig. 1(b)). At
213 K, sharp multiplet resonances were observed for PT at
δ 64.2 ppm and PU at δ 67.3 ppm (Fig. 1(c)). The resonance
for PC was almost invariant through this temperature range,
moving slightly upfield to δ 179.0 ppm at 213 K.
In this paper we report the synthesis of [FeH(H2)(PP3)]ϩ 1 by
the protonation of the dihydrido complex Fe(H)2(PP3) 3 by
methanol and ethanol.
D a l t o n T r a n s . , 2 0 0 4 , 1 4 1 8 – 1 4 2 3
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 4
1418

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Scheme 2
those with propylene-bridged ligands due to the smaller bite
angle and reduced flexibility of the polydentate system with
shorter arms. Distortion of the metal centre would have a direct
influence on the orbitals interacting with the dihydrogen and
hydrido ligands and hence the bond strength and ligand
dynamics.
The presence of a dihydrogen ligand in 1 was also supported
by measurement of T 1 relaxation values and by the presence of
H–D coupling in partially deuterated isotopomers. At 195 K
and 400 MHz, the T 1 relaxation values determined by the
inversion recovery method were 12.8 0.5 ms for the broad
Fig.
1
Variable temperature 31P{1H} NMR spectra (162 MHz,
acetone-d6) of [FeH(H2)(PP3)]ϩ 1 (BPh4 salt).
dihydrogen resonance and 121
9 ms for the hydrido
The high field region of the 1H NMR spectrum (Fig. 2(a)) of
1 at 300 K contains a single broad resonance at δ Ϫ10.2 ppm.
At 253 K, separate, broad resonances were observed for the
dihydrogen and hydrido protons (Fig. 2(b)). At 213 K, the
hydride appeared as a sharp 31P-coupled multiplet resonance
resonance, consistent with the proposed formulation.17 At 240
K, the T 1 values were 29 1 and 48 2 ms for the dihydrogen
and hydrido resonances, respectively, indicating significant
exchange between the two sites.
H–D Coupling constants are typically in the range 25–35 Hz
for η2-(H–D) complexes and usually less than 5 Hz for hydrido
deuterido complexes.18 Partial replacement of protons for
deuterons in the molecular hydrogen complex 1 was achieved by
dissolving the dihydrido complex 3 in methanol-d4 (Scheme 2).
Due to the intramolecular exchange between the η2-dihydrogen
and η1-hydride sites, most of the iron-bound protons were
replaced by deuterons in both the dihydrogen and hydrido
ligands, giving predominantly the trideuterated complex
6. There remained, however, a low concentration of residual
protons, including those from the dihydrido complex and from
isotopic impurities in the deuterated solvent.
Due to the large excess of deuterons over protons, the mono-
protonated complexes, 7 and 8 were present in much higher
concentration than complexes containing two (9, 10) or three
(1) metal-bound protons. Of the two monoprotonated
complexes, 8 contains no protons in the region shown in Fig. 3
(i.e. the region of the η2-dihydrogen resonance) and 7 is the
major product seen (Fig. 3(a)). Complex 7 gives rise to a 1 : 1 : 1
triplet at δ Ϫ8.91 ppm, with 1JHD = 31.1 Hz, consistent with the
η2-(H–D) formulation. The diprotonated complexes, 9 and 10
were observed as minor products. The dihydrogen resonances
of 9 and 10 were isotopically shifted by approximately 40 ppb
from 7 to low field, and had almost identical chemical shifts.
The dihydrogen resonance of 9 appeared as a 1 : 1 : 1 triplet at
δ Ϫ8.87 ppm (1JHD = 31.1 Hz) due to coupling in the H–D
ligand, whilst that of 10 appeared as a singlet.
The addition of approximately 0.1 ml of CH3OH to the
solution (approximately 0.5 ml) increased the concentration
of the species that contain more protons. The dihydrogen
resonance of the fully protonated complex 1 was observed as a
singlet at δ Ϫ8.83 ppm, isotopically shifted by approximately
40 ppb further downfield than those of the diprotonated
complexes 9 and 10 (Fig. 3(b)). The addition of a further
0.15 ml of protonated methanol further increased the
proportion of the di- and tri-protonated species (Fig. 3(c)).
There are two possible stereoisomers of 1, i.e. with the
hydrido ligand either cis or trans to the central phosphorus
PC. The NMR spectra show that only one isomer is present.
(2JH–P(C) = 43.9 Hz, JH–P(T) = 58.8 Hz, JH–P(U) = 14.9 Hz) at
δ Ϫ13.05 ppm (Fig. 2(c)). At this temperature the dihydrogen
resonance appeared as a broad singlet (w1/2 = 35 Hz) at δ Ϫ8.86
ppm. No coupling to the 31P nuclei was apparent in the
dihydrogen resonance. The broadness of this resonance is due
to the short T 1 relaxation, typical for dihydrogen resonances
(see below). From the lineshape of the exchange-broadened 1H
NMR spectrum ∆G≠ for the η2-H2/η1-H exchange can be
estimated at 53.7 kJ molϪ1 at 300 K. This contrasts to the
related system [FeH(H2)(P(CH2CH2CH2PMe2)3)]ϩ where the
corresponding η2-H2/η1-H exchange could not be frozen out on
the NMR timescale and this indicates an approximate exchange
barrier ∆G≠ < 28 kJ molϪ1 at 165 K.9,16 Exchange between η2-
dihydrogen and η1-hydrido sites has been observed for related
complexes containing the tripodal tetraphosphine ligands
PP3Ph,6 P(CH2CH2CH2PMe2)3 9 and PP3Cy10 and the nature of
the ligand set should influence the strength of the metal–
dihydrogen bond and the dynamics of the dihydrogen ligand.
The fact that the iron complex [FeH(H2)(P(CH2CH2-
CH2PMe2)3)]ϩ with the longer straps on the tripodal ligand has
a substantially lower barrier to exchange than [FeH(H2)-
(P(CH2CH2PMe2)3)]ϩ 1, is notable. This could be the result
of crowding the dihydrogen/hydrido ligands in [FeH(H2)-
(P(CH2CH2CH2PMe2)3)]ϩ, weakening the bonds to the metal
centre. Alternatively, metal complexes where the metal centres
are coordinated by ethylene-bridged PP3 ligands are substanti-
ally more strained and distorted from octahedral geometry than
2
2
Fig. 2 High field region of variable temperature 1H NMR spectra
(400 MHz, acetone-d6) of [FeH(H2)(PP3)]ϩ 1 (BPh4 salt).
D a l t o n T r a n s . , 2 0 0 4 , 1 4 1 8 – 1 4 2 3
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Reactions of [FeH(H2)(PP3)]؉ 1 and FeHCl(PP3) 13 with
methanol
In methanol solutions of 1, a small quantity of the methoxy
hydrido complex FeH(OMe)(PP3) 4 is present and on heating,
the carbonyl hydrido complex [FeH(CO)(PP3)]ϩ 11 is formed.
Complete conversion of 1 to 11 is achieved on heating at 60 ЊC
for 2 h. The carbonyl ligand in 11 was shown to originate from
the methanol solvent by the use of 13C-methanol which resulted
in the formation of [FeH(13CO)(PP3)]ϩ. In ethanol solutions of
1, although a small quantity of the ethoxy hydrido complex
FeH(OEt)(PP3) 5 is present, no carbonyl complexes are formed
on heating.
The oxidation of methanol probably proceeds via a β-hydride
elimination of formaldehyde from the methoxy hydrido
complex 4 formed in methanol solution (Scheme 4). β-Hydride
elimination of formaldehyde from the methoxy hydrido
complex 4 also generates the dihydrido complex 3, which would
be rapidly protonated by the methanol to regenerate 1.
Subsequent reaction of 1 with the formaldehyde would result in
the formation of 11 (Scheme 5).
Fig. 3 1H NMR spectra (400 MHz, 220 K, MeOD) of partially
deuterated isotopomers of
1 (methoxide salts) at decreasing
concentration of deuterium (a) > (b) > (c). Only the η2-(H–H) and η2-
(H–D) resonances are shown.
The similarity of the coupling constants between 31P and
2
the hydrido ligand of 1 (2JH–P(C) = 43.9 Hz, JH–P(T) = 58.8 Hz,
Scheme 4
2JH–P(U) = 14.9 Hz) to other cationic octahedral complexes of
the type [FeHX(PP3)]ϩ (X = CO 11, 2JH–P(C) = 39.4 Hz, 2JH–P(T)
=
2
2
61.0 Hz, JH–P(U) = 16.5 Hz; X = PPh3 12, JH–P(C) = 44.7 Hz,
2JH–P(T) = 64.0 Hz, 2JH–P(U) = 18.6 Hz) for which the assignment
of stereochemistry has been confirmed using the NOESY
experiment, suggests that 1 has the same stereochemistry as 11
and 12 i.e. with the hydrido trans to PU.12b It should be noted
2
2
that JH–P(C) and JH–P(U) are of nearly equal magnitude for
neutral complexes of the type FeHX(PP3) (X = Cl, Br, I, N3).12
The complexes [MH(H2)P((CH2)2PPh2)3]ϩ (M = Fe,6 Ru,7 Os8)
and [RuH(H2)P((CH2)2PCy2)3]ϩ 10 are reported to have the same
stereochemistry as 1 whereas [FeH(H2)P((CH2)3PMe2)3]ϩ is
reported to have the opposite stereochemistry i.e. with the
hydrido trans to PC.9
Scheme 5
Substitution reactions of [FeH(H2)(PP3)]؉ 1
Evidence for β-hydride elimination from FeH(OMe)(PP3) 4
comes from the reaction of FeHCl(PP3) 13 with methanol.
Dissolution of 13 in methanol affords an equilibrium mixture
of 13 and 4 in the ratio 1.4 : 1, respectively.12b On standing the
mixture of 13 and 4 at room temperature, or on heating
the same mixture, [FeH(H2)(PP3)]ϩ 1 is formed, presumably via
β-hydride elimination from 4 to form the dihydride 3 and
subsequent protonation. Further standing or heating of the
mixture of 13 and 4 affords the carbonyl hydride 11.
Complex 1 undergoes simple substitution reactions with a
number of anionic and neutral ligands with displacement of the
dihydrogen ligand to give the corresponding hydrido complexes
[FeHX(PP3)]ϩ (X = CO 11, X = PPh3 12) or FeHX(PP3) (X = Cl
13, X = Br 14, X = I 15, X = N3 16) (Scheme 3). The complexes
11, 12 and 14–16 have all been prepared previously by the
substitution of the chloro ligand of FeHCl(PP3) 13 in alcohol
solution.12b
In addition, either [FeH(H2)(PP3)]ϩ 1 or FeHCl(PP3) 13 react
rapidly with paraformaldehyde in ethanol solution to form
[FeH(CO)(PP3)]ϩ 11.
A number of rhodium and ruthenium complexes are known
to act as catalysts for the dehydrogenation of alcohols,19
including transfer hydrogenation reactions20 and in some cases
decarbonylation of methanol to afford carbonyl hydrido
complexes has been reported.19a,d
Solutions of [FeH(H2)(PP3)]ϩ 1 in ethanol are stable,
although gradual loss of 31P signal is observed on heating
ethanol solutions of 1 for several days with the formation of
Scheme 3
D a l t o n T r a n s . , 2 0 0 4 , 1 4 1 8 – 1 4 2 3
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Table 1 Crystallographic data for [FeMe(CO)(PP3)]ϩ 17 (Cl salt, THF
solvate)
Table 2 Selected bond lengths (Å) and angles (Њ) for [FeMe(CO)-
(PP3)]ϩ 17 (Cl salt, THF solvate)
Formula of the refinement model
C18H41ClFeO2P4
504.69
Monoclinic
P21/n (no. 14)
14.502(2)
9.132(2)
19.697(3)
103.820(3)
2532.8(7)
1.324
Fe(1)–C(1)
Fe(1)–C(2)
Fe(1)–P(1)
Fe(1)–P(2)
Fe(1)–P(3)
Fe(1)–P(4)
O(1)–C(2)
2.14(1)
1.84(1)
2.178(2)
2.234(2)
2.230(2)
2.246(2)
1.04(1)
C(2)–Fe(1)–C(1)
C(2)–Fe(1)–P(1)
C(1)–Fe(1)–P(1)
C(2)–Fe(1)–P(3)
C(1)–Fe(1)–P(3)
P(1)–Fe(1)–P(3)
C(2)–Fe(1)–P(2)
C(1)–Fe(1)–P(2)
P(1)–Fe(1)–P(2)
P(3)–Fe(1)–P(2)
C(2)–Fe(1)–P(4)
C(1)–Fe(1)–P(4)
P(1)–Fe(1)–P(4)
P(3)–Fe(1)–P(4)
P(2)–Fe(1)–P(4)
92.3(6)
178.1(4)
89.3(5)
94.6(3)
80.5(2)
84.76(7)
93.0(4)
174.1(4)
85.27(7)
96.51(6)
97.5(3)
Model molecular weight
Crystal system
Space group
a/Å
b/Å
c/Å
β/Њ
V/Å3
Dc/g cmϪ3
Z
4
Crystal size/mm
Crystal colour
Crystal habit
Temperature/K
λ(Mo-Kα)/Å
µ(Mo-Kα)/mmϪ1
T (Gaussian)min, max
2θmax/Њ
0.398 × 0.294 × 0.116
Orange
Prism
150(2)
0.71073
0.964
0.693, 0.893
56.56
81.7(2)
83.6(1)
158.8(1)
100.14(7)
hkl Range
N
Nind (Rmerge
Ϫ19 18, Ϫ12 12, Ϫ26 26
24965
6050 (0.0280)
3945
)
Nobs (I > 2σ(I ))
Nvar
209
Residuals R1(F), wR2(F 2)
GoF (all)
0.0934, 0.2708
1.242
Residual extrema
Ϫ1.230, 1.255
an unidentified black precipitate and this suggests that
β-hydride elimination from the ethoxy hydride 5 is less facile
than from the methoxy hydride 4. However, acetaldehyde reacts
with FeHCl(PP3) 13 in ethanol solvent to give the methyl carb-
onyl complex 17 (Scheme 6) presumably via a mechanism
analogous to that in Scheme 5 but where the last step involves
methyl migration from a coordinated acetyl group. Complex 17
has been prepared independently by the reaction of the
chloro methyl complex 1812a with carbon monoxide in tetra-
hydrofuran.
Fig. 4 ORTEP22 depiction (20% thermal ellipsoids, non-hydrogen
atoms) of the complex cation of 17 (Cl salt, THF solvate).
19.23 Conversely, the C–O bond in 17 (1.04(1) Å) is shorter than
that for 19 (1.17(2) Å). This indicates less back-bonding from
Fe to CO in 17 compared with 19 which is also reflected in the
ν(CO) of 1935 cmϪ1 for 17 cf. 1927 cmϪ1 for 19. Complex 19
also has the less hindered hydride ligand located in the position
cis to the central phosphorus atom.
[FeMe(CO)(PP3)]ϩ 17 is the first structurally characterised
complex of the PP3 ligand containing an iron–methyl bond.
The Fe–CH3 bond length (2.14(1) Å) is similar to those in other
Scheme 6
iron complexes containing four phosphorus atoms e.g. trans-
᎐
FeMe(C᎐CPh)(dmpe) 20 (dmpe = 1,2-bis(dimethylphosphino)-
᎐
2
X-Ray crystal structure of 17
ethane)24 and cis-FeMe2(PP)2 21 (PP = 1,2-bis(2,2-diethyl-1,3-
propanedioxyphosphino)ethane)25 (2.144(3)–2.179(5) Å).
Crystals of 17, suitable for X-ray diffraction analysis, were
obtained from a tetrahydrofuran solution of FeMeCl(PP3)
18 under carbon monoxide. The crystal data parameters are
summarised in Table 1. Selected bond lengths and angles are
listed in Table 2.
Conclusions
The dihydrogen hydrido complex [FeH(H2)(PP3)]ϩ 1 was
prepared by the protonation of FeH2(PP3) 3 in methanol or
ethanol. The presence of a dihydrogen ligand was confirmed by
measurement of T 1 relaxation times for 1 and H–D coupling
in partially deuterated isotopomers. There is facile exchange
between the coordinated η2-(H2) and η1-H and exchange
processes were observed in both the 31P and 1H NMR spectra of
1. The dihydrogen ligand of 1 is easily displaced by anionic and
neutral ligands and this provides a convenient and clean
synthetic route to a range of iron hydrido complexes.
The structure determination confirmed that the methyl group
was cis to the central phosphorus atom (Fig. 4), as had been
1
shown previously by H NOESY spectroscopy.12a This stereo-
chemistry is consistent with all other methyl iron–PP3 com-
plexes studied to date.12a,21 The Fe–PP3 fragment is similar to
3
that found in [FeCl(PPh3)(PP3)]ϩ 12a and [Fe(η -PhC᎐C–C᎐
᎐
᎐
᎐
CHPh)(PP3)]ϩ.12c The Fe–PC bond (2.178(2) Å) is significantly
shorter than the Fe–PU and Fe–PT bonds (2.230(2)–2.246(2) Å)
as expected for the PP3 ligand.12a,c The four phosphorus and
two carbon atoms deviate from octahedral geometry due to the
small bite angle of the PP3 ligand as shown by the PT–Fe–PT
angle of 158.8(1)Њ. The PC/PT–Fe–CH3 angles (80.5(2)–89.3(5)Њ)
are smaller than the PU/PT–Fe–CO angles (93.0(4)–97.5(3)Њ)
indicating that the methyl ligand sits in the smaller “pocket” cis
to the central phosphorus atom as also observed for all other
octahedral Fe–PP3 complexes.12,21
Heating a methanol solution of 1, results in the formation
of the carbonyl hydrido complex [FeH(CO)(PP3)]ϩ 11. Using a
13C-labelled solvent, the carbonyl ligand was shown to originate
from the methanol solvent by sequential dehydrogenations, pre-
sumably via an intermediate metal formyl complex. Complex 1
also reacted with paraformaldehyde to afford the carbonyl
hydrido complex [FeH(CO)(PP3)]ϩ 11 and this supports the
mechanistic proposal which invokes formaldehyde (from
partially oxidised methanol) as a reaction intermediate.
The Fe–CO bond (1.84(1) Å) is longer than the corre-
sponding bond (1.69(1) Å) in [FeH(CO)(P(CH2CH2PPh2)3)]ϩ
D a l t o n T r a n s . , 2 0 0 4 , 1 4 1 8 – 1 4 2 3
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2JP(C)–P(E) = 32.8 Hz); 64.6 (d, 3P, PE, see Fig. 1). 31P{1H} NMR
spectrum (162 MHz, acetone-d6, 213 K): δ 179.0 (dt, 1P,
Experimental
All synthetic manipulations involving air sensitive materials
were carried out under an inert atmosphere of argon in an
argon-filled dry box or under a nitrogen atmosphere using
standard Schlenk techniques. Tetrahydrofuran (THF), benzene
and hexane were dried over sodium before distillation from
sodium and benzophenone under nitrogen. Ethanol and
methanol were distilled from magnesium under nitrogen. PP3 2,
FeH2(PP3) 3, FeHCl(PP3) 13 and FeMeCl(PP3) 18 complexes
were prepared using literature methods.12a
2
2
PC, JP(C)–P(T) = 31.8 Hz, JP(C)–P(U) = 33.2 Hz); 64.2 (dd, 2P, PT,
2JP(T)–P(U) = 22.6 Hz); 67.3 (dt, 1P, PU). 1H{31P} NMR spectrum
(400 MHz, acetone-d6, 223 K): δ Ϫ13.08 (s, 1H, Fe–H); Ϫ8.85
(s, 2H, Fe–H2); 1.99, 2.17, 2.18, 2.46 (4 × m, 4 × 2H,
–PCCHHCHHPT–); 1.95, 2.19 (2 × m, 2 × 2H, –PCCH2CH2-
PU–); 1.54, 1.62 (2 × s, 2 × 6H, 2 × PT(CH3)); 1.65 (s, 6H,
3
PU(CH3)2); 7.45 (br, 8H, BPhortho); 7.09 (t, 8H, JH–H = 7.1 Hz,
BPhmeta); 6.93 (t, 4H, BPhpara). 13C{1H} NMR spectrum
(101 MHz, methanol, 300 K): δ 22.9 (br, –P(CH3)); 26.8 (m,
–PECH2CH2PC–, 1JP(C)–C = 25.7 Hz); 34.0 (m, –PECH2CH2PC–,
2JP(C)–C = 12.5 Hz). IR νmax (Nujol, BPh4 salt): 1866 cmϪ1 (Fe–
H). Anal.: Calc. for C36H53BFeP4: C, 63.9; H, 7.9. Found: C,
63.6; H, 8.0%.
1H, 13C and 31P NMR spectra were recorded on Bruker
AMX400 and AMX600 spectrometers at the temperatures
1
quoted. H and 13C chemical shifts were internally referenced
to residual solvent resonances. 31P spectra were referenced
to external neat trimethyl phosphite at 140.85 ppm. The
labelling convention for the 31P nuclei is given in structure 1.
Infrared spectra were recorded on a Perkin-Elmer 1600 series
FTIR. Elemental analyses were carried out at the Joint
Elemental Analysis Facility, The University of Sydney or the
Campbell Microanalytical Laboratory, University of Otago,
New Zealand. Melting points were recorded on a Gallenkamp
heating stage and are uncorrected.
Dihydrogen substitution reactions of [FeH(H2)(PP3)]؉ 1
Dihydrogen substitution reactions of [FeH(H2)(PP3)]ϩ 1 with
anionic ligands (ClϪ, BrϪ, IϪ, and N3Ϫ) and neutral ligands (CO
and PPh3) were carried out in NMR tubes, typically containing
approximately 10 mg of 1 in 0.5 ml of ethanol or methanol. The
solutions were heated at approximately 60 ЊC for 1 h and the
reactions were followed by 31P NMR spectroscopy. There was
complete conversion of the starting material and a single
product [FeHXPP3]ϩ (X = CO 11, X = PPh3 12), FeHXPP3
(X = Cl 13, X = Br 14, X = I 15, X = N3 16) was formed in each
reaction. The products were spectroscopically identical to those
produced independently from FeHClPP3.12b
Crystal structure determination
The crystallographic data for 17 (Cl salt, THF solvate) are
summarized in Table 1. An orange prism-like crystal was
attached with Exxon Paratone N, to a short length of fibre
supported on a thin piece of copper wire inserted in a copper
mounting pin. The crystal was quenched in a cold nitrogen gas
stream from an Oxford Cryosystems Cryostream. A Bruker
SMART 1000 CCD diffractometer employing graphite mono-
chromated Mo-Kα radiation generated from a sealed tube was
used for the data collection. Cell constants were obtained from
a least squares refinement against 963 reflections located
between 6 and 54Њ 2θ. Data were collected at 150(2) K with
ω scans to 56.56Њ 2θ. The data integration and reduction were
undertaken with SAINT and XPREP,26 and subsequent
computations were carried out with the teXsan,27 WinGX,28
and XTAL29 graphical user interfaces. The intensities of 128
standard reflections recollected at the end of the experiment did
not change significantly during the data collection. A Gaussian
absorption correction26,30 was applied to the data. The structure
was solved by direct methods with SIR97,31 and extended and
refined with SHELXL-97.32 The asymmetric unit contains the
complex cation, a chloride counterion and a THF molecule
disordered over two sites. The populations of the THF sites
were refined and then fixed at 0.5. The fully occupied
non-hydrogen atom sites were modelled with anisotropic
displacement parameters and the partially occupied solvate
sites were modelled with isotropic displacement parameters.
A riding atom model with group displacement parameters
was used for the hydrogen atoms. The molecule has large
displacement parameters that may be a foil for positional
disorder. Distance restraints were required for the C(7)–C(8)
and C(11)–C(12) bonds. An ORTEP22 depiction of the
molecule with 20% displacement ellipsoids is provided in Fig. 4.
CCDC reference number 230875.
Reaction of [FeH(H2)(PP3)]؉ 1 with methanol to form
[FeH(CO)(PP3)]؉ 11
FeH2(PP3) 3 (10 mg, 28 µmol) was dissolved in methanol
(0.5 ml), to give the dihydrogen hydrido complex [FeH(H2)-
(PP3)]ϩ 1. A small quantity of the methoxy hydrido complex
FeH(OMe)(PP3) 4 was also evident by 31P NMR. The solution
was heated at 60 ЊC for 2 h and [FeH(CO)(PP3)]ϩ 11 was formed
as the sole product. Complex 11 formed in this way was
identical, in every respect, to authentic samples of 11 prepared
by the reaction of FeHCl(PP3) 13 with carbon monoxide.12b
When 13C-labelled methanol was used as solvent, [FeH(13CO)-
(PP3)]ϩ 11-13C was formed, as evidenced by an extra doublet
coupling in each 31P resonance. Again 11-13C formed in this way
was identical in every respect to authentic samples prepared
from the reaction of FeHCl(PP3) 13 with 13C-labelled carbon
monoxide.12b
Reaction of [FeH(H2)(PP3)]؉ 1 or FeHCl(PP3) 13 with para-
formaldehyde to form [FeH(CO)(PP3)]؉ 11
Fe(H)2(PP3) 3 (ca. 10 mg, 28 µmol) was dissolved in ethanol
(0.5 ml), to give a solution of the dihydrogen hydrido complex
[FeH(H2)(PP3)]ϩ 1. A small quantity of the ethoxy hydrido
complex FeH(OEt)(PP3) 5 was evident by 31P NMR. Paraform-
aldehyde (5 mg, 0.17 mmol) was added and within 10 min at
room temperature, all the paraformaldehyde had dissolved and
[FeH(CO)(PP3)]ϩ 11 was formed as the sole product. Complex
11 formed in this way was identical, in every respect, to
authentic samples of 11 prepared by the reaction of
FeHCl(PP3) 13 by reaction with carbon monoxide.12b
Similarly, FeHCl(PP3) 13 (ca. 10 mg, 26 µmol) was dissolved
in ethanol (0.5 ml). A small quantity of the ethoxy hydrido
complex FeH(OEt)(PP3) 5 was evident by 31P NMR. Paraform-
aldehyde (5 mg, 0.17 mmol) was added and within 10 min at
room temperature, all the paraformaldehyde had dissolved and
[FeH(CO)(PP3)]ϩ 11 was formed as the sole product.
See http://www.rsc.org/suppdata/dt/b4/b401954g/ for crystal-
lographic data in CIF or other electronic format.
[FeH(H2)(PP3)]؉ 1
FeH2(PP3) 3 (23 mg, 65 µmol) was dissolved in methanol (5 ml)
and a solution of sodium tetraphenylborate (25 mg, 73 µmol) in
methanol (5 ml) was added. The resulting precipitate was
isolated by filtration, washed with methanol (10 ml) and dried
in vacuo to give [FeH(H2)(PP3)]ϩ 1 (BPh4 salt) (37 mg, 84%) as a
cream coloured solid, mp 223–227 ЊC (decomp.). 31P{1H} NMR
spectrum (162 MHz, acetone-d6, 300 K): δ 179.8 (q, 1P, PC,
[FeMe(CO)(PP3)]؉ 17
A solution of FeMeCl(PP3) 18 (10 mg, 25 µmol) in THF
(0.5 ml) was placed under an atmosphere of carbon monoxide.
D a l t o n T r a n s . , 2 0 0 4 , 1 4 1 8 – 1 4 2 3
1422

View Article Online
8 C. Bianchini, K. Linn, D. Masi, M. Peruzzini, A. Vacca and
F. Zanobini, Inorg. Chem., 1993, 32, 2366.
9 N. Bampos and L. D. Field, Inorg. Chem., 1990, 29, 587.
10 G. Jia, S. D. Drouin, P. G. Jessop, A. J. Lough and R. H. Morris,
Organometallics, 1993, 12, 906.
11 N. Bampos, L. D. Field, B. A. Messerle and R. J. Smernik, Inorg.
Chem., 1993, 32, 4084.
12 (a) L. D. Field, B. A. Messerle, R. J. Smernik, T. W. Hambley and
P. Turner, Inorg. Chem., 1997, 36, 2884–92, and references therein;
(b) L. D. Field, B. A. Messerle and R. J. Smernik, Inorg. Chem.,
1997, 36, 5984–90; (c) L. D. Field, B. A. Messerle, R. J. Smernik, T. W.
Hambley and P. Turner, J. Chem. Soc., Dalton Trans., 1999, 2557.
13 M. V. Baker, L. D. Field and D. J. Young, J. Chem. Soc., Chem.
Commun., 1988, 546.
14 For reviews on the protonation of metal hydrides by alcohols, see:
(a) L. M. Epstein and E. Shubina, Coord. Chem. Rev., 2002, 231,
165; (b) L. Brammer, Dalton Trans., 2003, 3145.
The resulting precipitate provided crystals suitable for X-ray
diffraction. The precipitate was isolated by filtration and dissol-
ved in ethanol (1 ml). A solution of sodium tetraphenylborate
(10 mg, 29 µmol) in ethanol (2 ml) was added, resulting in the
formation of a yellow precipitate, which was isolated by
filtration, washed with methanol (10 ml) and dried in vacuo to
give [FeMe(CO)(PP3)]ϩ 17 (BPh4 salt), mp >300 ЊC. 31P{1H}
NMR spectrum (162 MHz, BPh4 salt, acetone-d6, 300 K):
δ 176.9 (dt, 1P, PC, JP(C)–P(T) = 30.5 Hz, JP(C)–P(U) = 28.6 Hz);
71.7 (dd, 2P, PT, 2JP(T)–P(U) = 21.0 Hz); 65.5 (dt, 1P, PU). 1H{31P}
NMR spectrum (600 MHz, BPh4 salt, acetone-d6, 293 K):
δ Ϫ0.72 (s, 1H, Fe–CH3); 2.33, 2.82 (2 × m, 2 × 2H,
–PCCH2CHHPT–); 2.43, 2.67 (2 × m, 2 × 2H, –PCCHHCH2PT–);
2.40 (m, 2H, –PCCH2CH2PU–); 2.14 (m, 2H, –PCCH2CH2PU–);
1.84, 1.89 (2 × s, 2 × 6H, 2 × –PT(CH3)); 1.85 (s, 6H,
–PU(CH3)2); 7.63 (br, 8H, BPhortho); 7.22 (t, 8H, 3JH–H = 7.1 Hz,
BPhmeta); 7.08 (t, 4H, BPhpara). 13C{1H} NMR spectrum (101
MHz, acetone-d6, 300 K, carbonyl resonance only): δ 217.2
(ddt, 1C, CO, 2JP(C)–C = 40.7 Hz, 2JP(T)–C = 19.6 Hz, 2JP(U)–C = 16.0
Hz). IR νmax (Nujol, BPh4 salt): 1935 cmϪ1 (–CO).
2
2
15 When 10 mg of FeH2(PP3) 3 was dissolved in 0.5 ml of methanol,
the ratio 1 : 4 was 7 : 1 at room temperature. When 10 mg of
FeH2(PP3) 3 was dissolved in 0.5 ml of ethanol, the ratio 1 : 5 was
35 : 1 at room temperature. FeH(OEt)(PP3) 5 has not been isolated
as a pure compound and has only been observed as a minor
component in mixtures. The 31P{1H} NMR resonances of 5 (162
2
MHz, ethanol, 300 K) at δ 176.2 (dt, 1P, PC, JP(C)–P(T) = 27.5 Hz,
2JP(C)–P(U) = 12.2 Hz); 53.3 (dd, 2P, PT, 2JP(T)–P(U) = 18.3 Hz); 48.0 (dt,
1P, PU) are almost identical to those reported for 4.12b
.
16 Note that the H/η2-D2
D/η2-HD exchange in the dideuterated
Acknowledgements
isotopomer of [FeH(H2)(P(CH2CH2CH2PMe2)3)]ϩ was estimated to
have a ∆G≠ of 38 kJ molϪ1 at 200 K.9.
We gratefully acknowledge financial support from the
Australian Research Council, the Australian Government for
an Australian Postgraduate Award (R. J. S.) and the University
of Sydney for an H. B. and F. M. Gritton Award (R. J. S.).
17 See, for example: (a) R. H. Crabtree and M. Lavin, J. Chem. Soc.,
Chem. Commun., 1985, 1661; (b) R. H. Crabtree, M. Lavin
and L. Bonneviot, J. Am. Chem. Soc., 1986, 108, 4032; (c) D. G.
Hamilton and R. H. Crabtree, J. Am. Chem. Soc., 1988, 110, 4126;
(d ) M. T. Bautista, K. A. Earl, P. A. Maltby, R. H. Morris,
C. T. Schweitzer and A. Sella, J. Am. Chem. Soc., 1988, 110, 7031; (e)
P. J. Desrosiers, L. Cai, Z. Lin, R. Richards and J. Halpern, J. Am.
Chem. Soc., 1991, 113, 4173; ( f ) X. Luo, J. A. K. Howard and
R. H. Crabtree, Magn. Reson. Chem., 1991, 29, S89.
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D a l t o n T r a n s . , 2 0 0 4 , 1 4 1 8 – 1 4 2 3
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