High-yield synthesis and reactivity of stable diiron complexes with bent-phosphinidene bridges

Article abstract of DOI:10.1021/om050617v

Reaction of [Fe₂Cp₂(μ-CO)₂(CO)(PRH ₂)] (Cp = η⁵-C₅H₅; R = Cy, Ph) with [FeCp₂]BF₄ gives the phosphide-bridged complexes [Fe₂Cp₂(μ-PRH)

Full text of DOI:10.1021/om050617v

Organometallics 2005, 24, 5503-5505
5503
High-Yield Synthesis and Reactivity of Stable Diiron
Complexes with Bent-Phosphinidene Bridges
Celedonio M. Alvarez,† M. Angeles Alvarez,† M. Esther Garc´ıa,† Roc´ıo Gonza´lez,†
Miguel A. Ruiz,*,† Hayrullo Hamidov,† and John C. Jeffery‡
Departamento de Quı´mica Orga´nica e Inorga´nica/IUQOEM, Universidad de Oviedo,
E-33071 Oviedo, Spain, and School of Chemistry, University of Bristol, Bristol BS8 1TS, U.K.
Received July 22, 2005
Chart 1
Summary: Reaction of [Fe2Cp2(µ-CO)2(CO)(PRH2)] (Cp
) η5-C5H5; R ) Cy, Ph) with [FeCp2]BF4 gives the
phosphide-bridged complexes [Fe2Cp2(µ-PRH)(µ-CO)-
(CO)2]BF4, which are deprotonated by M(OH) (M ) Na,
K) to give the phosphinidene derivatives [Fe2Cp2(µ-PR)-
(µ-CO)(CO)2] in high yield. The cyclohexylphosphinidene
complex reacts at room temperature with MeI, O2, S8,
or H2CdCHR′ (R′ ) CO2Me) to give selectively [Fe2Cp2-
(µ-PCyMe)(µ-CO)(CO)2]I or neutral derivatives of the
types [Fe2Cp2{µ-P(E)Cy}(µ-CO)(CO)2] (E ) O, S) and
[Fe2Cp2{µ-κ1:κ1,η1-CyPCH2CHR′C(O)}(µ-CO)(CO)].
The chemistry of metal complexes having phosphin-
idene (PR) ligands is a subject of growing interest in
the organometallic area. These versatile ligands can
bind from one to four metal atoms in many different
ways, some of them being the origin of high reactivity.
This is especially so in the case of terminal complexes
having bent PR ligands (A in Chart 1), in which the
metal-phosphorus bond has considerable multiple-bond
character and there is a lone pair at the phosphorus
atom, all of which confers carbene-like reactivity to
these complexes, thus enabling them to act as useful
synthetic reagents in organophosphorus chemistry.1
sought to prepare new phosphinidene-bridged complexes
involving other transition metals. In particular, we
noticed that there were only a few diiron species
previously described in the literature. Moreover, most
of these species were either thermally unstable (such
as the cyclopentadienyl complex [Fe2Cp2(µ-PPh)(CO)4])3
or transient species generated from suitable precursors,
such as [Fe2{µ-P(NiPr2)}2(CO)6],4 [Fe2(µ-PtBu)(CO)6],5
and [Fe3(µ2-PPh)(µ3-PPh)(CO)9]n- (n ) 1, 2).6 All of these
circumstances impose significant restrictions upon the
study of the chemical behavior of the mentioned com-
plexes. Finally, there is just one previous example of
an stable diiron phosphinidene complex, [Fe2{µ-P(OR)}2-
(CO)6], with R being the bulky aryl 4,2,6-C6H2MetBu2,7
but no reactivity appears to have been developed around
that complex. In this paper we report a high-yield
synthetic procedure for the new and stable diiron
complexes [Fe2Cp2(µ-PR)(µ-CO)(CO)2] having bent phen-
yl- or cyclohexylphosphinidene bridges and a prelimi-
nary study of their chemical behavior, illustrative of
their high nucleophilicity.
In contrast, the chemistry of phosphinidene-bridged
complexes of type C or D (Chart 1) has been little
explored, even when the presence of multiple M-P
bonding (type C) or a lone pair at phosphorus (type D)
should lead to useful reactivity. Recently we started a
study aimed at exploring the chemical behavior of
cyclopentadienyl molybdenum complexes of type C (with
t
R ) 2,4,6-C6H2 Bu3) having metal-metal bonds of
formal orders from 1 to 3. We thus discovered several
unusual reactions of the bridging phosphinidene group
such as intramolecular C-H and P-C cleavages, η
coordination of the aryl group, and intermolecular
insertion of 1-alkynes.2 In an extension of this work, we
The above phosphinidene complexes can be prepared
through a two-step procedure. First, dehydrogenation
on the neutral phosphine complexes [Fe2Cp2(µ-CO)2-
(CO)(PRH2)] (R ) Cy (1a),8 Ph (1b))9 is induced by
* To whom correspondence should be addressed. E-mail:
mara@fq.uniovi.es.
(3) (a) Klasen, C.; Effinger, G.; Schmid, S.; Lorenz, I.-P. Z. Naturs-
forch., B 1993, 48, 705. (b) Lorenz, I.-P.; Pohl, W.; Noeth, H.; Schmidt,
M. J. Organomet. Chem. 1994, 475, 211.
† Universidad de Oviedo.
‡ University of Bristol.
(1) Reviews: (a) Lammertsma, K. Top. Curr. Chem. 2003, 229, 95.
(b) Lammerstma, K.; Vlaar, M. J. M. Eur. J. Org. Chem. 2002, 1127.
(c) Mathey, F.; Tran Huy, N. H.; Marinetti, A. Helv. Chim. Acta 2001,
84, 2938. (d) Shah, S.; Protasiewicz, J. D. Coord. Chem. Rev. 2000,
210, 181. (e) Stephan, D. W. Angew. Chem., Int. Ed. 2000, 39, 314. (f)
Schrock, R. R. Acc. Chem. Res. 1997, 30, 9. (g) Cowley, A. H. Acc. Chem.
Res. 1997, 30, 445. (h) Huttner, G.; Knoll, K. Angew. Chem., Int. Ed.
Engl. 1987, 26, 743. (i) Huttner, G.; Evertz, K. Acc. Chem. Res. 1986,
19, 406.
(2) (a) Garc´ıa, M. E.; Riera, V.; Ruiz, M. A.; Sa´ez, D.; Vaissermann,
J.; Jeffery, J. C. J. Am. Chem. Soc. 2002, 124, 14304. (b) Garc´ıa, M.
E.; Riera, V.; Ruiz, M. A.; Sa´ez, D.; Hamidov, H.; Jeffery, J. C.; Riis-
Johannessen, T. J. Am. Chem. Soc. 2003, 125, 13044.
(4) (a) King, R. B. J. Organomet. Chem. 1998, 557, 29. (b) King, R.
B.; Bitterwolf, T. E. Coord. Chem. Rev. 2000, 206-207, 563.
(5) Lang, H.; Zsolnai, L.; Huttner, G. Chem. Ber. 1985, 118, 4426.
(6) (a) Ohst, H. H.; Kochi, J. K. Inorg. Chem. 1986, 25, 2066. (b)
Ohst, H. H.; Kochi, J. K. J. Am. Chem. Soc. 1986, 108, 2897.
(7) Barlett, R. A.; Dias, H. V. R.; Flynn, K. M.; Olmstead, M. M.;
Power, P. P. J. Am. Chem. Soc. 1987, 109, 5699.
(8) Compounds 1a,b were prepared as reported in ref 9 for the
related complex [Fe2Cp2(µ-CO)2(CO)(PHPh2)]. Selected spectroscopic
data for 1a: IR ν(CO) (CH2Cl2) 1935 (s), 1770 (w), 1730 (vs) cm-1 31P-
;
{1H} NMR (CDCl3) δ 17.2 ppm; 1H NMR (CDCl3) δ 4.72 (s, 5H, Cp),
4.50 (d, JHP ) 1, 5H, Cp), 3.28 (dd, JHP ) 327, JHH ) 6, 2H, P-H)
ppm.
10.1021/om050617v CCC: $30.25 © 2005 American Chemical Society
Publication on Web 10/05/2005

5504 Organometallics, Vol. 24, No. 23, 2005
Communications
Scheme 1
Figure 1. ORTEP diagram of compound 3b, with H atoms
omitted for clarity. Selected bond lengths (Å) and angles
(deg): Fe(1)-Fe(2) ) 2.5879(4), Fe(1)-C(1) ) 1.756(2), Fe-
(2)-C(2) ) 1.755(2), Fe(1)-C(3) ) 1.922(2), Fe(2)-C(3) )
1.928(2), Fe(1)-P(3) ) 2.2584(6), Fe(2)-P(3) ) 2.2648(6);
C(1)-Fe(1)-Fe(2) ) 97.3(1), C(2)-Fe(2)-Fe(1) ) 98.1(1),
C(1)-Fe(1)-C(3) ) 86.6(1), C(2)-Fe(2)-C(3) ) 87.0(1),
C(1)-Fe(1)-P(3) ) 91.2(1), C(2)-Fe(2)-P(3) ) 91.8(1), Fe-
(1)-P(3)-C(31) ) 115.0(1), Fe(2)-P(3)-C(31) ) 112.7(1)°.
oxidation with [FeCp2]BF4 to give in high yield the
cationic phosphide complexes [Fe2Cp2(µ-PRH)(µ-CO)-
(CO)2]BF4 (2a,b),10 which display two terminal CO
ligands almost parallel to each other (Scheme 1). To our
knowledge this reaction constitutes a novel synthetic
strategy for cationic phosphide-bridged complexes, and
it seems quite general, since it can be applied to other
diiron complexes having different primary or secondary
phosphines, currently under study. We note that, during
the course of this work, Sugiura et al. reported a
medium-yield (based on the starting [Fe2Cp2(CO)4])
preparation of the triflate salt of the cation present in
2b.11
Scheme 2
The second step in the preparation of the phosphin-
idene complexes 3 is a more conventional deprotonation
of the remaining P-H bond, which can be quantitatively
accomplished in dichloromethane solution using solid
M(OH) (M ) Na, K) or other strong bases. The presence
of the phosphinidene ligand in complexes 3a,b is
denoted by their high 31P chemical shifts12,13 and has
been further confirmed through an X-ray study on the
phenylphosphinidene complex 3b (Figure 1).14 The
phosphorus atom displays a pyramidal environment,
with the phenyl group pointing away from the Cp
ligands as expected on steric grounds, while the Fe-P
and Fe-Fe lengths are consistent with the formulation
of single bonds between these atoms, as proposed
according to the EAN rule. We should note that complex
3b is the first diiron compound having a bent-phosphin-
idene bridge to be structurally characterized.
Both the presence of a lone pair at the phosphorus
atom and the relatively good donor properties of the
cyclopentadienyl ligands cause complexes 3 to be good
nucleophiles, as illustrated by the reactions of the
cyclohexyl derivative 3a (Scheme 2). Thus, complex 3a
is reactive enough to achieve nucleophilic substitution
on methyl iodide at room temperature to give the
corresponding methylcyclohexylphosphide derivative
[Fe2Cp2(µ-PCyMe)(µ-CO)(CO)2]I (4a),15 thus paralleling
the behavior of phosphinidene bridges at anionic metal
centers,16 or the electron-rich [Pt2(µ-PMes)2(dppe)2]
(dppe ) Ph2PCH2CH2PPh2),17 and [Fe2Cp2(µ-PPh)-
(CO)4].3
Compound 3a reacts rapidly at room temperature
with air or elemental sulfur to give the corresponding
derivatives [Fe2Cp2{µ-P(E)Cy}(µ-CO)(CO)2] (E ) O (5a),18
S (5b)19) having phosphinidene oxide or phosphinidene
(9) Alvarez, C. M.; Garc´ıa, M. E.; Ruiz, M. A.; Connelly, N. G.
Organometallics 2004, 23, 4750.
(10) Selected spectroscopic data for 2a: IR ν(CO) (CH2Cl2) 2019 (vs),
1990 (w), 1833 (m) cm-1 31P{1H} NMR (CDCl3) δ 223.4; 1H NMR
;
(CDCl3) δ 8.13 (dd, JHP ) 390, JHH ) 10, 1H, P-H), 5.17 (s, 10H, Cp).
(11) Sugiura, J.; Kakizawa, T.; Hashimoto, H.; Tobita, H.; Ogino,
H. Organometallics 2005, 24, 1099.
(15) Selected spectroscopic data for 4a: IR ν(CO) (CH2Cl2) 2015 (vs),
1985 (w), 1829 (m) cm-1 31P{1H} NMR (CD2Cl2) δ 271.2; 1H NMR (CD2-
;
Cl2) δ 5.37 (s, 10H, Cp), 2.93 (d, JHP ) 12, 3H, Me).
(12) Selected spectroscopic data for 3a: IR ν(CO) (CH2Cl2) 1977 (vs),
(16) (a) Deeming, A. J.; Doherty, S.; Day, M. W.; Hardcastle, K. I.;
Minassian, H. J. Chem. Soc., Dalton Trans. 1991, 1273. (b) Ho, J.; Hou,
Z.; Drake, R. J.; Stephan, D. W. Organometallics 1993, 12, 3145. (c)
Haupt, H.-J.; Schwefer, M.; Egold, H.; Flo¨rke, U. Inorg. Chem. 1995,
34, 5461. (d) Maslennikov, S. V.; Glueck, D. S.; Yap, G. P. A.; Rheingold,
A. L. Organometallics 1996, 15, 2483.
1940 (w), 1773 (m) cm-1 31P{1H} NMR (C6D6) δ 531.6; 1H NMR (C6D6)
;
δ 4.24 (s, 10H, Cp).
(13) Selected spectroscopic data for 3b: IR ν(CO) (CH2Cl2) 1988 (vs),
1952 (w), 1783 (m) cm-1
;
31P{1H} NMR (CD2Cl2) δ 498.2; 1H NMR (CD2-
Cl2) δ 4.90 (s, 10H, Cp).
(14) X-ray data for 3b: dark brown crystals, monoclinic (P21/n), a
) 7.9442(7) Å, b ) 27.055(3) Å, c ) 7.7879(7) Å, â ) 95.843(2)°, V )
1665.1(3) Å3, T ) 173 K, Z ) 4, R ) 0.028 (observed data with I >
2σ(I)), GOF ) 0.992.
(17) Kourkine, I. V.; Glueck, D. S. Inorg. Chem. 1997, 36, 5160.
(18) Selected spectroscopic data for 5a: IR ν(CO) (CH2Cl2) 1985 (vs),
1951 (w), 1788 (m) cm-1 31P{1H} NMR (CDCl3) δ 343.8; 1H NMR
;
(CDCl3) δ 4.87 (s, 10H, Cp).

Communications
Organometallics, Vol. 24, No. 23, 2005 5505
derivative [Fe2Cp2{µ-κ1:κ1,η1-CyPCH2CHRC(O)}(µ-CO)-
(CO)] (6; R ) CO2Me) having a phosphide-acyl ligand
resulting from coupling among the entering alkene, the
phosphinidene group, and a carbonyl ligand.24 Attempts
to isolate compound 6 as a pure material have been
unsuccessful so far. Interestingly, the phosphide-acyl
ligand in 6 is easily protonated by HBF4‚OEt2 to give
the corresponding alkylcyclohexylphosphide derivative
[Fe2Cp2{µ-P(CH2CH2R)Cy}(µ-CO)(CO)2]BF4 (4b),25 which
has the same structure as the methyl compound 4a. The
transformations 2a/3a/6/4b complete the insertion of an
olefin into the P-H bond of the phosphide complex 2a
through a deprotonation/reprotonation sequence involv-
ing a phosphinidene intermediate. This can be then
considered as an alternative to the radical-chain mech-
anism recently proposed for the hydrophosphination of
phenylacetylene and methyl acrylate by the cation
present in 2b.11 As stated above, the phosphinidene
complex 3a reacts with other olefins and alkynes. The
latter reactions are more complex and are currently
under study in our laboratory.
In summary, we have shown that the phosphinidene
complexes [Fe2Cp2(µ-PR)(µ-CO)(CO)2] (R ) Cy, Ph) can
be prepared in high yield through a novel redox-induced
dehydrogenation of coordinated PRH2 ligands, followed
by deprotonation of the resulting PRH-bridged cations.
As illustrated through the reactions of the cyclohexyl-
phosphinidene compound, these complexes are strong
nucleophiles able to react selectively at room tempera-
ture with methyl iodide, oxygen, sulfur, or even some
activated olefins such as methyl acrylate to give neutral
or cationic derivatives of the type [Fe2Cp2{µ-P(E)Cy}-
(µ-CO)(CO)2]n+ (n ) 1, E ) Me; n ) 0, E ) O, S) and
[Fe2Cp2{µ-κ1:κ1,η1-CyPEC(O)}(µ-CO)(CO)] (E ) CH2-
CHCO2Me), which in several cases are difficult to
prepare otherwise. Our results suggest that binuclear
complexes having bent-phosphinidene bridges might be
operative in hydrophosphination of olefins and related
reactions involving P-H bonds of bridging alkyl- or
arylphosphide ligands.
Figure 2. ORTEP diagram of compound 5a, with H atoms
omitted for clarity. Selected bond lengths (Å) and angles
(deg): Fe(1)-Fe(2) ) 2.601(2), Fe(1)-C(1) ) 1.747(5), Fe-
(2)-C(2) ) 1.748(5), Fe(1)-C(3) ) 1.914(5), Fe(2)-C(3) )
1.926(4), Fe(1)-P(1) ) 2.219(2), Fe(2)-P(1) ) 2.216(2),
P(1)-O(4) ) 1.503(3); C(1)-Fe(1)-Fe(2) ) 99.2(1), C(2)-
Fe(2)-Fe(1) ) 99.4(2), C(1)-Fe(1)-C(3) ) 89.3(2), C(2)-
Fe(2)-C(3) ) 90.3(2), C(1)-Fe(1)-P(1) ) 92.0(1), C(2)-
Fe(2)-P(1) ) 91.3(1), Fe(1)-P(1)-O(4) ) 121.6(1), Fe(2)-
P(1)-O(4) ) 120.7(1)°.
sulfide ligands bridging the dimetal center exclusively
through the P atom, as confirmed crystallographically
for 5a (Figure 2).20 We have pointed out recently that
the chemistry of the phosphinidene oxide ligand is
largely unexplored at present.21 In fact, only one other
diiron complex having a P(O)R ligand has been previ-
ously described ([Fe2Cp2{µ-P(O)OH}(µ-CO)(CO)2]).22 On
the other hand, precedents for diiron complexes having
phosphinidene sulfide ligands are also scarce; they are
in fact restricted to the phenyl derivatives [Fe2Cp2{µ-
P(S)Ph}(CO)n] (n ) 3, 4), both of which have no metal-
metal bond.23 The presence of the uncoordinated PdO
and PdS functionalities in complexes 5 might allow
further transformations at the phosphinidene bridge,
currently under exploration.
The most remarkable observation concerning the
chemical behavior of the phosphinidene complex 3a, not
paralleled by other complexes having bent-phosphin-
idene bridges, lies in its ability to react with alkynes or
activated olefins under mild conditions. For example,
3a reacts with methyl acrylate (CH2CHCO2Me) at room
temperature or above to give the very air-sensitive
Acknowledgment. We thank the MCYT of Spain
for financial support (Project BQU2003-05471).
Supporting Information Available: Text giving experi-
mental procedures and spectroscopic data for new compounds
and CIF files giving crystallographic data for compounds 3b
and 5a. This material is available free of charge via the
Internet at http://pubs.acs.org.
(19) Selected spectroscopic data for 5b: IR ν(CO) (CH2Cl2) 1989 (vs),
1957 (w), 1794 (m) cm-1 31P{1H} NMR (CDCl3) δ 345.6; 1H NMR
;
(CDCl3) δ 4.81 (s, 10H, Cp).
(20) X-ray data for 5a: red crystals, monoclinic (P21/c), a ) 8.084-
(7) Å, b ) 12.317(11) Å, c ) 18.743(16) Å, â ) 100.78(1)°, V ) 1833(3)
Å3, T ) 293 K, Z ) 4, R ) 0.049 (observed data with I > 2σ(I)), GOF
) 0.968.
OM050617V
(24) Selected spectroscopic data for 6: IR ν(CO) (CH2Cl2) 1951 (vs),
1785 (s), 1730 (m, CO2Me), 1611 (m, C(O)Fe) cm-1 31P{1H} NMR (CD2-
;
(21) Alonso, M.; Garc´ıa, M. E.; Ruiz, M. A.; Hamidov, H.; Jeffery, J.
C. J. Am. Chem. Soc. 2004, 126, 13610.
Cl2) δ 296.5; 1H NMR (CH2Cl2) δ 4.76, 4.60 (2 × s, 2 × 5H, Cp), 3.69
(s, 3H, OMe).
(22) (a) Schaefer, H. Angew. Chem. 1981, 93, 595. (b) Deppisch, B.;
Schaefer, H. Acta Crystallogr., Sect. C 1983, 39, 975.
(23) Lorenz, I.-P.; Muerschel, P.; Pohl, W.; Kurt, P. Chem. Ber. 1995,
128, 413.
(25) Selected spectroscopic data for 4b: IR ν(CO) (CH2Cl2) 2015 (vs),
1985 (w), 1830 (m), 1736 (m, CO2Me) cm-1 31P{1H} NMR (CD2Cl2) δ
;
276.0; 1H NMR (CD2Cl2) δ 5.27 (s, 10H, Cp), 3.82 (s, 3H, OMe), 3.40,
3.24 (2 × m, 2 × 2H, PCH2CH2).