Improved synthesis of KHCr(CO)5 and comparative coordination chemistry from KHCr(CO)5 and KHFe(CO)4

Article abstract of DOI:10.1016/S0022-328X(98)00852-3

A practical procedure for the selective preparation of KHCr(CO)₅ is described. The use of a potassium cation in the coordination chemistry of the [HFe(CO)₄]^- anion is completed and extended to the coordination chemistry of the [HCr(CO)₅]^- anion: CO-substitution by phosphites, phosphines and phosphinites, and H-abstraction by aminophosphines. Most of the observed differences in reactivity between KHFe(CO)₄ and KHCr(CO)₅ can be rationalized by the stronger acidity of KHFe(CO)₄.

Full text of DOI:10.1016/S0022-328X(98)00852-3

Journal of Organometallic Chemistry 571 (1998) 7–13
Improved synthesis of KHCr(CO)5 and comparative coordination
1
chemistry from KHCr(CO)5 and KHFe(CO)4
Jean-Jacques Brunet, Remi Chauvin *, Bruno Donnadieu, Pascale Leglaye, Denis Neibecker
Laboratoire de Chimie de Coordination du CNRS, UPR 8241 lie´e par con6entions,
a` l’Uni6ersite´ Paul Sabatier et a` l’Institut National Polytechnique, 205 Route de Narbonne, 31077 Toulouse cedex 4, France
Received 3 February 1998
Abstract
A practical procedure for the selective preparation of KHCr(CO)5 is described. The use of a potassium cation in the
coordination chemistry of the [HFe(CO)4]− anion is completed and extended to the coordination chemistry of the [HCr(CO)5]−
anion: CO-substitution by phosphites, phosphines and phosphinites, and H-abstraction by aminophosphines. Most of the
observed differences in reactivity between KHFe(CO)4 and KHCr(CO)5 can be rationalized by the stronger acidity of
KHFe(CO)4. © 1998 Elsevier Science S.A. All rights reserved.
Keywords: Hydridocarbonylferrates; Hydridocarbonylchromates; CO-substitution; P-ligands
1. Introduction
ter reducing agents than their iron counterparts derived
from [HFe(CO)4]− [2]. We were however surprised to
find that, contrary to [HFe(CO)4]−, the [HCr(CO)5]−
anion was not readily available. We herein report an
efficient synthesis of KHCr(CO)5 and a general com-
parison of its coordination chemistry with the well-
studied coordination chemistry of KHFe(CO)4 [4].
The relative reducing power of hydridocarbonyl-
metallates has been thoroughly studied versus both the
transition metal (especially of Groups 6 and 8) and the
nature and the number of |-donor ligands [1]. Darens-
bourg et al. showed that CO-replacement by phosphane
ligands enhances the hydridic character (two-electron
transfer) more so than the single electron transfer (SET)
ability of the [M–H]− unit [2]. With the aim of achiev-
ing asymmetric reduction of ketones by a ‘chiral zwitte-
rionic control’ strategy, we recently disclosed the
synthesis of chiral zwitterionic hydridotricarbonylfer-
rate complexes by simultaneous CO-substitution and
K+-metathesis at KHFe(CO)4 with chiral phosphinite
ammonium ligands [3]. The poor reducing ability of
these iron complexes prompted us to extend the strat-
egy to the chromium series ([3]b): indeed, chromium
hydrides derived from [HCr(CO)5]− are generally bet-
2. Improved preparation of KHCr(CO)5 1b
Although ammonium salts of the [HCr(CO)5]− anion
can be selectively prepared by a cumbersome three-step
procedure from Cr(CO)6 [5], or under phase-transfer
conditions (KOH/Et4NHSO4) [6], the coordination
chemistry of [HCr(CO)5]− has been severely limited by
the lack of a routine method to prepare it. Alkali metal
salts of [HCr(CO)5]− were obtained by cation exchange
from ammonium salts ([7]a). By contrast, KHFe(CO)4
1a is easily prepared in a 90–95% yield by mixing
Fe(CO)5 with KOH in methanol or ethanol [4]. This
difference holds to the fact that the dinuclear hydride
[HCr2(CO)10]− acts as a thermodynamic sink for
* Corresponding author. Tel.: +33 5 61333124; fax: +33 5 61
553003; e-mail: chauvin @lcctoul.lcc-toulouse.fr
1 Part of the thesis of P. Leglaye.
0022-328X/98/$ - see front matter © 1998 Elsevier Science S.A. All rights reserved.
PII S0022-328X(98)00852-3

8
J.-J. Brunet et al. / Journal of Organometallic Chemistry 571 (1998) 7–13
Scheme 1. Synthesis of mononuclear potassium hydridocarbonylmetallates.
[HCr(CO)5]− [8], while [HFe2(CO)8]− does not for
[HFe(CO)4]− [9]. Nonetheless, the sodium salt
NaHCr(CO)5 could be tediously prepared in a 50%
yield by protonation of Na2Cr(CO)5, itself generated by
Na/naphtalene reduction of Cr(CO)5(piperidine) [5,10],
and THF solutions of the potassium salt in the presence
of cryptands have been used [11]. Although the reaction
of hydroxide ions with Cr(CO)6 is very slow and non
selective in an aqueous alcohol as solvent [12]a), a
simple procedure for preparing the potassium salt 1b
has been described provided that THF is used as a
co-solvent ([12]b). However, the final ratio between 1b
and K[HCr2(CO)10] 2b appears quite variable and no
rationale accounts for the need of five equivalents of
KOH in a THF–H2O mixture at 55°C, or seven equiv-
alents of KOH in a MeOH–H2O–THF mixture at
46–48°C ([12]b).
We observed that when an ethanol solution of
slightly less than two equivalents of KOH is added to a
dichloromethane solution of Cr(CO)6, 1b is repeatedly
isolated in a 70–78% yield. Some amount of the dinu-
clear hydride 2b also forms which is separated by
simple filtration (see Section 5). This corresponds to the
stoichiometry of Scheme 1, and as for the preparation
of KHFe(CO)4, no excess KOH is needed. The selectiv-
ity of the synthesis is measured from the 1H-NMR
spectrum (1b: lCrH= −7.05 ppm. 2b: lCrH= −19.56
ppm). However, 1b is more sensitive than 1a to protic
sources: the unstable protonated species H2Cr(CO)5
looses H2 and the unsaturated ‘Cr(CO)5’ moiety is
scavenged by another molecule of 1b to give the dinu-
clear hydride 2b ([8]a).
sidered (Scheme 2): to the best of our knowledge, the
only reported phosphane-substituted derivatives of 1b
are the salts of [HCr(CO)4{P(OMe)3}]− and none of
them was prepared by ligand exchange at [HCr(CO)5]−
[1].
3.1. Phosphite ligands
It has been mentioned that CO-substitution on am-
monium salts of [HM(CO)5]− could not be an efficient
route to phosphine or phosphite derivatives (M=
Group
6
metal) [13]. The complex [PPN]+[cis-
HCr(CO)4{P(OMe)3}]− has thus been prepared by
naphtalene/sodium reduction of Cr(CO)4[P(OMe)3]-
(amine) and subsequent protonation with methanol
([7]a, [13,14]). Interestingly, we have now found that
P(OMe)3 does react with the potassium salt 1b in THF
to give K+, [cis-HCr(CO)4{P(OMe)3}]− 3b in a 50%
yield. As in the case of the iron analogue K+, [trans-
HFe(CO)3[P(OMe)3]− 3a, the weak |-donor versus
y-acceptor character of trimethyl phosphite does not
sufficiently enhance the basicity of the chromate anion
of 3b to trigger quantitative deprotonation of
[HCr(CO)5]− [15].
3.2. Phosphine ligands
In the iron series, heating of 1a is required for CO
substitution by bulky phosphines such as PPh3, but the
high basicity of the intermediate triphenylphosphine
hydride complex 5a leads to the neutral complex trans-
Fe(CO)3(PPh3)2 ([4]a). K2Fe(CO)4 is also produced
when the reaction is conducted in THF.
Under similar conditions (two equivalents of PPh3,
refluxing THF, 64 h), a slow reaction of KHCr(CO)5 1b
is evidenced by NMR monitoring. In the 1H-NMR
spectrum ([D8]THF), the doublet of a hydride assigned
to KHCr(CO)4(PPh3) 5b is observed at l= −6.25 ppm
(2JPH=35.1 Hz). In the 31P-NMR spectrum, in addi-
tion to the major signal of 5b (70%, l=81.3 ppm), a
minor signal (30%, l=77.8 ppm) can be assigned, by
analogy with the iron series, to the neutral complex
3. Coordination chemistry of KHFe(CO)4 and
KHCr(CO)5 with phosphanes
By analogy with the synthetically useful CO-substitu-
tion process at KHFe(CO)4 by phosphane ligands [4],
the reactivity of KHCr(CO)5 with phosphites, phosphi-
nes, phosphinites and aminophosphines has been con-

J.-J. Brunet et al. / Journal of Organometallic Chemistry 571 (1998) 7–13
9
Scheme 2. CO-substitution by phosphines, phosphinites or phosphites at hydrido-carbonylmetallates.
trans-Cr(CO)4(PPh3)2. This structure is also supported
The cis-(CO)2, trans-P2 geometry of 7a is assigned on
the basis of solution IR and NMR spectra. The IR
spectrum of 7a in pentane exhibits two strong absorp-
tion bands of nearly equal intensity with a frequency
difference of 39 cm−1, thus implying a cis-Fe(CO)2
arrangement [18]. The NMR data are in accordance
with previous NMR studies on related diphosphine and
diphosphite complexes [4]: the 31P{1H} and 13C{1H,
31P} (carbonyl region) spectra give sharp singlet signals
at 176.3 and 213.7 ppm, respectively. Therefore the
phosphorus atoms are magnetically equivalent, as are
the two carbon atoms of the carbonyl ligands. Further-
by a triplet for the four CO ligands in the 13C-NMR
2
spectrum (l=243.31 ppm, JPC=13.7 Hz). The con-
commitant formation of an equimolar amount of
K2Cr(CO)5 is indicated by the presence of a white
air-sensitive precipitate in the final reaction medium.
However, contrary to KHFe(CO)4, KHCr(CO)5 is not
acidic enough to undergo complete deprotonation by
KHCr(CO)4(PPh3) 5b.
3.3. Phosphinite ligands
1
more, the H (hydride region) and 31P-NMR spectra
Although PPh3 does not selectively displace a single
CO ligand from KHFe(CO)4 1a (vide supra), replacing
one of the phenyl rings at the phosphorus atom of PPh3
by one methoxy group sufficiently lowers the |-donor
ability of the ligand to allow the new complex
KHFe(CO)3[PPh2(OMe)] 4a to be stable in THF solu-
tion in the presence of KHFe(CO)4, and finally isolated
in an 85% yield. The trans stereochemistry is assigned
exhibit well-resolved 1:2:1 triplets with a coupling con-
stant 2JPH=57.7 Hz (CD3CN), in agreement with a
cis-H–P arrangement of two equivalent hydridic hy-
drogens with two equivalent phosphorus atoms ([7]b).
The cis-(CO)2, trans-P2 geometry of 7a is confirmed,
in the solid state, by a X-ray diffraction study of a
monocrystal [19]. The octahedral bonding geometry is
mainly characterized by the OC–Fe–CO angle [95(1)°]
and a very bent P–Fe–P angle [151.6(3)°] (Fig. 1).
However, the hydride ligands could not be located, and
the structure is not discussed further owing to the poor
refinement (R=0.17) because of the poor quality of the
crystal. Several attempts to improve the quality of the
structure by collecting data at low temperature failed
because of a phase transition occuring just below −
15°C.
2
on the basis of the low value of the JPH coupling
constant (4.3 Hz, CD3CN at 20°C), which is close to
values reported for analogous trans-complexes with
PPh3 and P(OMe)3 ligands (2.4 and 3.7 Hz, respec-
tively, CD3CN at 26°C) and very different from the
value reported for the cis isomer of a salt of the
[HFe(CO)3{P(OPh)3}]− anion (41.6 Hz, CD3CN at
ambient temperature) ([7]b).
In methanol, KHFe(CO)4 reacts with two equivalents
of Ph2P(OMe) much less selectively, beside the mono-
substituted anionic complex 4a, the disubstituted com-
plexes H2Fe(CO)2[PPh2(OMe)]2 7a and KHFe(CO)2[P-
Ph2(OMe)]2 8a are identified. According to our previous
studies on analogous phosphine and phosphite com-
plexes [4], the bis(phosphinite) complex 7a could form
from 4a via an elusive neutral monophosphinite dihy-
dride intermediate H2Fe(CO)3[PPh2(OMe)] which
would undergo a fast CO-substitution by a second
equivalent of phosphinite. The conjugated base 8a,
resulting from a deprotonation of 7a by MeOK, is also
observed (Scheme 3) [16]. However, when the methanol
solution is buffered with KHCO3, the basic complex 8a
is no longer formed: the less basic complex 4a is still
present, and 7a is produced in a 25% yield only, along
with the long-known complex 6a (7% yield) [17], further
characterized by 31P- and 13C-NMR (see Section 5).
In the chromium series, KHCr(CO)5 promotes the
decomposition of Ph2P(OMe), leading to more than 20
unidentified 31P-NMR signals [20]. An interpretation of
the failure to isolate 4b could reside in the higher
nucleophilicity of the hydride brought by the stronger
|-donor ability of Ph2P(OMe) with respect to that of
P(OMe)3: unlike [HFe(CO)4]−, [HCr(CO)5]− is not
compatible with the lability of the Me–O–P moiety.
3.4. Tris(amino)phosphine ligands
The reaction of KHFe(CO)4 with P(NMe2)3 does not
proceed by CO-substitution at the iron atom: instead a
formal Me2N-substitution at the phosphorus atom
takes place according to the stoichiometry depicted in
Scheme 4 where the Collman anion [Fe(CO)4]2− and
the neutral complex (CO)4Fe[PH(NMe2)2] 9a are
formed [21,22].

10
J.-J. Brunet et al. / Journal of Organometallic Chemistry 571 (1998) 7–13
Scheme 3. Reaction of Ph2P(OMe) with KHFe(CO)4 in methanol.
mally generates a +P(NMe2)2 equivalent reacting fur-
The analogous reaction in the chromium series does
ther with anionic hydrides to give compounds 9a and
9b. The need of an auxiliary proton source in the case
of chromium shows that given that the reference base
P(NMe2)3, KHCr(CO)5 is less acidic than KHFe(CO)4,
in agreement with the general trend stated for neutral
transition metal hydrides, namely ‘thermodynamic acid-
ity and kinetic acidity generally increase from left to
right across a transition series’ [23].
not occur. However, if tris(dimethylamino)phosphine is
first treated with a stoichiometric amount of acetic acid,
the new neutral chromium complex (CO)5Cr[PH-
1
(NMe2)2] 9b (31P-NMR: l=132.5 ppm; H-NMR: l=
1
7.70 ppm; JPH=315 Hz) is formed and isolated in a
70% yield (Scheme 4). As proposed earlier [21], cleavage
of the P–N bond proceeds via a protonation step
P(NMe2)3+H+ “Me2HN+ –P(NMe2)2 which for-
4. Conclusion
The above results, driven by the search for an anal-
ogy with the coordination chemistry of KHFe(CO)4,
show that KHCr(CO)5 is a versatile precursor for a
coordination chemistry involving phosphanes. Al-
though the iron and chromium hydrides behave simi-
larly from a qualitative viewpoint, observed differences
are accounted for by a lower acidity of KHCr(CO)5 as
compared with that of KHFe(CO)4. Although acidity
and hydridic character are not opposite properties, this
fact is parallel to the well known increase of the hy-
dridic character of transition metal hydrides going from
the right to the left of periodic table [23,24]: beyond
their relative reducing power toward ketones, this trend
is more fundamentally illustrated by the established
increasing ‘dihydride’ versus dihydrogen character of
the congugated acids, H2Fe(CO)4 and H2Cr(CO)5
[25,26].
5. Experimental
All experiments were performed under an argon at-
mosphere using standard Schlenk techniques. THF and
diethyl ether were distilled over Na/benzophenone be-
fore use. Commercial synthesis grade pentane,
dichloromethane, methanol and ethanol were degassed
by bubbling argon before use. Potassium hydroxide
(Technical 86%, Prolabo), trimethyl phosphite
Fig. 1. CAMERON view of the X-ray crystal structure of the
(
dihydride complex 7a (P1, R=0.17), with thermal ellipsoids at 50%
probability level. The hydrogen atoms were not located and the
carbon atoms of the phenyl rings were isotropically refined.

J.-J. Brunet et al. / Journal of Organometallic Chemistry 571 (1998) 7–13
11
Scheme 4. Reaction of hydridocarbonylmetallates with P(NMe2)3 in the presence of a Brønstedt acid: KHFe(CO)4 itself in the case of iron, acetic
acid in the case of chromium.
3
(Aldrich), tris(dimethylamino)phosphine (Fluka), tri-
phenylphosphine (Janssen), hexacarbonylchromium
(Strem), pentacarbonyliron (Fluka) were commercially
available. A sample of Ph2P(OMe) was purchased from
Aldrich or prepared from distilled ClPPh2 (Aldrich) and
methanol in diethyl ether. A Sample of KHFe(CO)4
was prepared as previously described [4]. Elemental
analyses were performed on Perkin Elmer 2400 appara-
tus. IR spectra were recorded on a Perkin-Elmer 1725X
FT-IR spectrometer using CaF2 windows. NMR spec-
tra were recorded on a Brucker AC 200 spectrometer at
200 for 1H, 81 for 31P and 50 MHz for 13C, with
positive chemical shifts at low field expressed in ppm by
internal reference to TMS for 1H and 13C and by
external reference to 85% H3PO4 in D2O for 31P.
1H; CrH); 3.68 (d, JPH=10.0 Hz, 9H; POCH3); 31P-
NMR ([D8]THF): d= +215.3 (dq, 2JPH=52.7 Hz).
13C{1H} ([D8]THF): l=51.59 (s, OCH3); 230.37 and
231.48 (broad, Cr(CO)4).
5.3. Potassium
hydridotetracarbonyl(triphenylphosphine)chromate 5b
A total of 0.363 g (1.56 mmol) of KHCr(CO)5 1b and
0.840 g (3.2 mmol) of PPh3 were stirred for 45 min at
room temperature (r.t.) and then for 64 h at reflux. The
final reaction mixture was filtered and the remaining
solid was washed with 2×5 ml of THF. The combined
THF phases are evaporated to dryness. The resulting
brown solid was washed with 3×10 ml of Et2O, dried,
and analyzed by NMR: 5b corresponds to 70% of the
31P-NMR signal. H-NMR ([D8]THF): l= −6.25 (d,
1
5.1. Potassium hydridopentacarbonylchromate,
KHCr(CO)5 1b
2JPH=35.1 Hz, 1H; FeH); 7.23–7.60 (15H, m, aro-
matic H); 31P-NMR: l (ppm)= +81.3 (d, JPH=35.1
2
A solution of KOH (0.290 g, 4.55 mmol) in 7.5 ml of
absolute ethanol was added to 20 ml of a CH2Cl2
solution of Cr(CO)6 (0.500 g, 2.27 mmol). After stirring
for 10 min the solvent was evaporated to dryness. The
yellow solid residue was treated with 10 ml of THF and
evaporated to dryness: this procedure was repeated
twice in order to eliminate any trace of ethanol and
dichloromethane. The solid was finally extracted with
20 ml of THF and KHCO3 was removed by filtration.
The solvent was then evaporated to give a yellow solid
(0.390 g, 1.68 mmol, 75% yield). Elemental analysis for
C5HCrKO5 (232.2): calc.%: C 25.87, H 0.43; found%: C
25.79, H 0.32. IR (THF): w=2018 (m), 1883 (s), 1852
Hz). 13C{1H} ([D8]THF): l=128.41 (d, JPC=8.3 Hz);
129.18; 135.14 (d, JPC=11.8 Hz) (-o, -m, -p-aromatic
C); 142.69 (d, 1JPC=27.1 Hz, Cipso); 244.22 (broad,
Cr(CO)4).
5.4. Reactions of KHFe(CO)4 with Ph2P(OMe) in the
absence of KHCO3
5.4.1. In THF: potassium hydridotricarbonyl(methyl
diphenylphosphinite)ferrate 4a
A total of 2.0 ml (10.0 mmol) of PPh2(OMe) was
added to a solution of 1.04 g of KHFe(CO)4 (5.0 mmol)
in 20 ml of THF. The solution was stirred at 25°C for
16 h, then evaporated. The residue was washed with
pentane giving 1.68 g (85%) of 4a as a yellow solid.
(sh) cm−1 1H-NMR (CD3CN): l= −7.05 (CrH).
.
13C{1H}-NMR (CD3CN): l=229.06 (Cr(CO)5).
1H-NMR (CD3CN): l= −8.87 (1H, d, JPH=4.3 Hz,
2
3
5.2. Potassium hydridotetracarbonyl(trimethyl
phosphite)chromate 3b
FeH); 3.53 (3H, d, JPH=13.5 Hz, MeO); 7.24–7.46
(6H, m, Ph); 7.66–7.81 (4H, m, Ph). 31P{1H}-NMR
(CD3CN): l= +191.1. 13C{1H}-NMR (CD3CN): l=
52.39 (s, OCH3); 128.39 (d, JPC=7.6 Hz); 129.39;
131.40 (d, JPC=12.2 Hz); 146.90 (d, JPC=37.4 Hz);
A total of 0.150 ml (1.20 mmol) of P(OMe)3 was
added to a solution of 0.267 g (1.15 mmol) of
KHCr(CO)5 in 10 ml of THF. The solution was stirred
at 25°C for 24 h, then evaporated, and the yellow
residue was washed with diethyl ether (3×15 ml) and
dried. A total of 0.190 g (50%) of 3b was obtained.
1H-NMR ([D8]THF): l= −7.25 (d, 2JPH=52.7 Hz,
2
223.36 (d, JPC=14.0 Hz, Fe(CO)3).
5.4.2. In methanol: complexes 7a and 8a
Dihydridodicarbonylbis(methyl
diphenylphos-
phinite)iron 7a. 1H-NMR (CD3CN): l= −9.85 (t,

12
J.-J. Brunet et al. / Journal of Organometallic Chemistry 571 (1998) 7–13
3
2JPH=57.7 Hz, 2 H; FeH2); 3.63 (dd, JPH=5JPH=6.7
Elemental analysis for C9H13N2O5PCr (312.18):
calc.%: C 34.63, H 4.20, N 8.97. Found%: C 35.13, H
1
Hz, 6 H; OCH3); 6.78–7.79 (20 H, m, Ph). H-NMR
(CDCl3): l= −9.91 (t, 2JPH=57.7 Hz, 2 H; FeH2);
4.15, N 8.81. H-NMR (CD3CN): l=2.79 (d, JPH
=
1
3
3.64 (dd, JPH=5JPH=6.5 Hz, 6 H; OCH3); 7.39–7.85
10.5 Hz, 12 H; N(CH3)2); 6.77 (d, JPH=400 Hz, 1 H;
3
1
(20 H, m, Ph). 31P-NMR (CDCl3): l= +176.3 (t,
2JPH=57.7 Hz). 13C-NMR (CDCl3): l=52.86 (q,
1JCH=145 Hz, OCH3); 127.97 (d, 1JCH=162 Hz,
PH). 31P-NMR (CD3CN): l= +142.2 (d, JPH=400
1
Hz). 13C{1H}-NMR (CD3CN): l=42.46 (s, NMe2);
2
217.68 (d, JPC=16.3 Hz, Cr(CO)5). IR (THF): w=
1
Cmeta); 129.83 (d, JCH=160 Hz, Cpara); 130.70 (m,
2066 (s); 2031 (w); 1981 (w); 1949–1941 (s); 1919 (w)
1JCH=162 Hz, 2JPC=26 Hz, Cortho); 142.36 (dd,
1JCP=3JCP=26 Hz, Cipso); 213.67 (t, 2JCP=13 Hz,
1JCPB5 Hz, Fe(CO)2). IR (pentane): w=2001 (s), 1962
cm−1; w(PH)=2403 (w) cm−1
.
(s) cm−1
.
Acknowledgements
Potassium hydridodicarbonylbis(methyl diphenyl-
1
phosphinite)ferrate 8a. H-NMR ([D6] acetone): l= −
This work was supported by the Centre National de
la Recherche Scientifique. The authors wish to thank
Ms L. Noe´ for performing elemental analyses.
9.65 (t, 2JPH=64.3 Hz,
1
H, FeH); 3.39 (t,
3JPH=5JPH=6.7 Hz, 6 H; OCH3); 6.78–7.79 (m, 20 H,
Ph); 31P-NMR (CD3CN): l= +182.2 (d, JPH=64.3
2
Hz).
References
5.5. Reactions of KHFe(CO)4 with Ph2P(OMe) in the
presence of KHCO3 in methanol
[1] For
a review, see: M.Y. Darensbourg, C.E. Ash, Adv.
Organomet. Chem. 27 (1987) 1.
[2] (a) For a discussion, see: M.Y. Darensbourg, S.A. Wander, J.H.
Reibenspies, Organometallics 11 (1992) 3185, and references
therein. (b) M.Y. Darensbourg, C.E. Ash, L.W. Arndt, C.P.
Janzen, K.A. Youngdahl, J. Organomet. Chem. 383 (1990) 191.
(c) P.L. Gaus, S.C. Kao, K. Youngdahl, M.Y. Darensbourg, J.
Am. Chem. Soc. 107 (1985) 2428. (d) S.C. Kao, C.T. Spillett, C.
Ash, R. Lusk, Y.K. Park, M.Y. Darensbourg, Organometallics 4
(1985) 83. (e) S.C. Kao, M.Y. Darensbourg, Organometallics 3
(1984) 646.
[3] (a) J.-J. Brunet, R. Chauvin, G. Commenges, B. Donnadieu, P.
Leglaye, Organometallics 15 (1996) 1752. (b) J.-J. Brunet, R.
Chauvin, J. Chiffre, S. Huguet, P. Leglaye, J. Organomet. Chem.
(1998) (in press).
[4] (a) J.-J. Brunet, G. Commenges, F.-B. Kindela, D. Neibecker,
Organometallics 11 (1992) 1343. (b) J.-J. Brunet, G. Commenges,
F.-B. Kindela, D. Neibecker, ibid 3023. (c) J.-J. Brunet, R.
Chauvin, O. Diallo, F.-B. Kindela, P. Leglaye, D. Neibecker,
Coord. Chem. Rev. (1998) (in press).
[5] M.Y. Darensbourg, S. Slater, Inorg. Synth. 22 (1983) 181.
[6] D.H. Gibson, F.U. Ahmed, K.R. Phillips, Organometallics 1
(1982) 679.
[7] (a) S.C. Kao, M.Y. Darensbourg, W. Schenk, Organometallics 3
(1984) 871. (b) C.E. Ash, M.Y. Darensbourg, M.B. Hall, J. Am.
Chem. Soc. 109 (1987) 4173.
[8] (a) M.Y. Darensbourg, J.C. Deaton, Inorg. Chem. 20
(1981)1644. (b) M.D. Grillone, Inorg. Synth. 23 (1985) 27.
[9] For a discussion of the relative reducing reactivity of NaH-
Fe(CO)4 and NaHFe2(CO)8, see: J.P. Collman, R.G. Finke, P.L.
Matlock, R. Wahren, R.G. Komoto, J.I. Brauman, J. Am.
Chem. Soc. 100 (1978) 1119.
A total of 0.220 ml of Fe(CO)5 (1.6 mmol) was
syringed into a solution of 0.218 g of 86% KOH (3.2
mmol) in 10 ml of methanol. The solution was stirred
at r.t. for 30 min. The IR spectrum of the solution
confirms the presence of KHFe(CO)4 and KHCO3.
After cooling to 0°C, 0.645 ml of Ph2P(OMe) (3.3
mmol) was syringed. The solution was stirred for 24 h
at 0°C, and then evaporated to dryness. The residue
was washed with 3×20 ml of pentane, and 0.270 g of
a light brown solid was obtained, consisting in a mix-
ture of complexes 6a:7a=30:70 (31P-NMR analysis): 7a
is thus obtained in c.a. 25% yield and 6a in c.a. 7%
yield. Green–yellow crystals of complex 7a deposit
from a diluted pentane solution at −10°C, and have
been analyzed by X-ray diffraction.
Tricarbonylbis(methyl diphenylphosphinite)iron 6a.
31P-NMR (CD3CN): l= +184.4. 13C{1H}-NMR
(CD3CN): l=53.96 (s, OCH3); 129.29, 131.69, 133.13
(broad overlaping signals: C-ortho-, meta, para); 140.76
1
2
(d, JPC=27.5 Hz, C-ipso); 231.79 (t, JPC=30.6 Hz,
Fe(CO)3). IR (pentane): w(CO)=1902 (s) cm−1 [17].
5.6. [Bis(dimethylamino)phosphine]pentacarbonyl-
chromium 9b
[10] M.Y. Darensbourg, R. Bau, M.W. Marks, R.R. Burch, J.C.
Deaton, S. Slater, J. Am. Chem. Soc. 104 (1982) 6961.
[11] D.J. Darensbourg, A. Rokicki, M.Y. Darensbourg, J. Am.
Chem. Soc. 103 (1981) 3223.
[12] (a) D.J. Darensbourg, A. Rokicki, Organometallics 1 (1982)
1685. (b) M.D. Grillone, M. Palmisano, Trans. Met. Chem. 14
(1989) 81.
[13] S.G. Slater, R. Lusk, B.F. Schumann, M.Y. Darensbourg,
Organometallics 1 (1982) 1662.
[14] P.L. Gaus, S.C. Kao, M.Y. Darensbourg, L.W. Arndt, J. Am.
Chem. Soc. 106 (1984) 4752.
A solution of tris(dimethylamino)phosphine (0.410
ml, 2.25 mmol) and acetic acid (0.130 ml, 2.25 mmol) in
10 ml of THF was added to 5 ml of a THF solution of
KHCr(CO)5 (0.522 g, 2.25 mmol). After stirring for 15
min at 25°C the solvent was evaporated under vacuum
to afford a yellow residue. This residue was extracted
with pentane (3×15 ml), leaving a pale yellow–white
solid. The pentane solution was evaporated to dryness,
leaving 0.491 g (70%) of spectroscopically pure solid 9b.

J.-J. Brunet et al. / Journal of Organometallic Chemistry 571 (1998) 7–13
13
[20] One of the signals (d= +187.4) might be assigned to the
structure KHCr(CO)4[PPh2(OMe)] 4b. The presence of 4b has
also been supported by a minor elusive hydride signal in the
1H-NMR spectrum (l= −6.69, d, 2JPH=54.2 Hz).
[21] J.-J. Brunet, R. Chauvin, D. Neibecker, Synth. Commun. 27
(1997) 1433.
[15] Traces of neutral complexes Cr(CO)6−m[P(OMe)3]m (m=1, 2)
were spectroscopically detected: R. Mathieu, M. Lenzi, R. Poil-
blanc, Inorg. Chem. 9 (1970) 2030.
[16] Excess KH was reported to deprotonate analogous neutral dihy-
dride diphosphine (4a) and diphosphite (4b) complexes. In the
same reports, KHFe(CO)2(PR3)2 and KHFe(CO)2{P(OR)3}2
were not observed during the synthesis of H2Fe(CO)2(PR3)2 and
H2Fe(CO)2{P(OR)3}2 in a protic solvent. This holds to the
presence of KHCO3 (resulting from the preparation of crude
KHFe(CO)4) which neutralizes MeOK to give MeOH and the
weaker base K2CO3. Under the conditions reported here,
KHCO3 was removed before dissolving KHFe(CO)4 in
methanol.
[22] A preliminary result shows that cleavage of the P–N bond is
actually quite general and is not solely due to the extreme
bulkiness and basicity of P(NMe2)3 (q=157°, w=2061.7 cm−1
:
C.A. Tolman, Chem. Rev. 77 (1977) 313). Indeed, reaction of
Ph2P–NMe2 (q=149°, w=2066.6 cm−1) with KHFe(CO)4 af-
forded
the
known
secondary
phosphine
complex
(CO)4Fe(PHPh2): (a) J.G. Smith, D.T. Thompson, J. Chem. Soc.
(A) (1967) 1694. (b) P.M. Treichel, W.K. Dean, W.M. Douglas,
Inorg. Chem. 11 (1972) 1609 and 1615.
[17] H.L. Conder, M.Y. Darensbourg, J. Organomet. Chem. 67
(1974) 93.
[23] 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, p. 91.
[24] (a) J.A. Labinger, K.H. Komadina, J. Organomet. Chem. 155
(1978) C25. (b) B.D. Martin, K.E. Warner, J.R. Norton, J. Am.
Chem. Soc. 108 (1986) 33.
[25] See for example: (a) R.K. Upmacis, G.E. Gadd, M. Polyakoff,
M.B. Simpson, J.J. Turner, R. Whyman, A.F. Simpson, J.
Chem. Soc. Chem. Commun. (1985) 27. (b) S.P. Church, F.-W.
Grevels, H. Herrmann, K. Schaffner, J. Chem. Soc. Chem.
Commun. (1985) 30.
[18] (a) P. Conway, S.M. Grant, A.R. Manning, F.S. Stephens, J.
Organomet. Chem. 186 (1980) C61. (b) P. Conway, A.R. Man-
ning, F.S. Stephens, J. Organomet. Chem. 186 (1980) C64.
[19] Crystal data for C28H26O4P2Fe: M=544.30, triclinic crystal of
dimensions: 0.35×0.10×0.05 mm3 (space group P1with unit
(
˚
˚
˚
cell a=10.217(2) A, b=11.012(2) A, c=13.271(3) A, h=
107.91(2)°, i=98.62(2)°, k=104.20(2)°, V=1334.6(3) A , Z=
3
˚
2, Dcalc. =1.35 g cm−3, v=7.11 cm−1, F(000)=565. Several
attempts to obtain better crystals failed. Owing to the poor
refinement results, we do not have deposited Supporting Infor-
mation.
[26] For a discussion, see: W. Wang, A.A. Narducci, P.G. House, E.
Weitz, J. Am. Chem. Soc. 118 (1996) 8654.
.