1,2-diphosphetene, 1,2-diphosphete, and 1,3-diphosphete metal complexes: novel access by ring contraction, cyelodimerization, and intramolecular redox reactions

Article abstract of DOI:10.1021/om980862x

The reaction of [Cr(CO)₅(THF)] and pentaphenyl-1,2,3-triphospholene affords a single stereoisomer of [(pentaphenyl-1,3-η-1,2,3-triphospholene)(Cr(CO)₅)₂] (6). Visible light photolysis of 6 causes a ring contraction and [(trans-tetraphenyl-1,2-η-1,2-diphosphetene)(Cr-(CO)₅) ₂] (7a) is formed, whose stereochemistry was elucidated by X-ray crystallography. trans-1,2-Dichloro-3,4-di-terf-butyl-1,2-diphosphetene (2a) and [Fe₂(CO)9] form the σ complexes [(trans-1,2-dichloro-3,4-di-tert-butyl-1-η-1,2-diphosphetene)Fe(CO) ₄] (8a) and [(trans-1,2-dichloro-3,4-di-tert-butyl-1,2-η-1,2-diphosphetene)(Fe(CO) ₄)₂] (8b), depending on the relative concentration of the starting materials. 8a has been proven to be an intermediate in the formation of 8b. Heating of neat 8b in a vacuum leads to the elimination of the chlorine substituents in an intramolecular redox reaction and [(3,4-di-tert-butyl-η⁴-1,2-diphosphete)-Fe(CO)₃] (9a) is formed. This is the first specific reaction, leading to a 1,2-diphosphete complex. 9a and its 1,3-isomer 10a react with [Cr(CO)₅(THF)] to form the mono- and diaddition products [1-η-{(3,4-di-tert-butyl-η⁴-1,2-diphosphete)Fe(CO) ₃}Cr(CO)₅] (9b), [1,2-η-{(3,4-di-feru-butyl-η⁴-1,2-diphosphete)Fe(CO) ₃}(Cr(CO)5)2](9c))[1-η-{(2,4-di-tert-butyl-η ⁴-1,3-diphosphete)Fe(CO)₃}Cr(CO)₅] (10b), and [1,3-η-{(2,4-di-tert-butyl-η⁴-1,3-diphosphete)-Fe(CO) ₃}(Cr(CO)₅)₂] (10c), respectively. X-ray crystallographic studies for 9c and 10c give some insight into the bonding situation of the compounds, σ- and π-complexing properties of the diphosphete ligands are almost independent of each other and significant back-bonding from the iron atom to the ligand π* orbitals occurs in both cases.

Full text of DOI:10.1021/om980862x

Organometallics 1999, 18, 2021-2029
2021
1,2-Dip h osp h eten e, 1,2-Dip h osp h ete, a n d 1,3-Dip h osp h ete
Meta l Com p lexes: Novel Access by Rin g Con tr a ction ,
Cyclod im er iza tion , a n d In tr a m olecu la r Red ox Rea ction s†
Frank W. Heinemann, Susanne Kummer, Udo Seiss-Brandl, and
Ulrich Zenneck*
Institut fu¨r Anorganische Chemie, Universita¨t Erlangen-Nu¨rnberg, Egerlandstrasse 1,
D-91058 Erlangen, Germany
Received October 16, 1998
The reaction of [Cr(CO)5(THF)] and pentaphenyl-1,2,3-triphospholene affords a single
stereoisomer of [(pentaphenyl-1,3-η-1,2,3-triphospholene)(Cr(CO)5)2] (6). Visible light pho-
tolysis of 6 causes a ring contraction and [(trans-tetraphenyl-1,2-η-1,2-diphosphetene)(Cr-
(CO)5)2] (7a ) is formed, whose stereochemistry was elucidated by X-ray crystallography. trans-
1,2-Dichloro-3,4-di-tert-butyl-1,2-diphosphetene (2a ) and [Fe2(CO)9] form the σ complexes
[(trans-1,2-dichloro-3,4-di-tert-butyl-1-η-1,2-diphosphetene)Fe(CO)4] (8a ) and [(trans-1,2-
dichloro-3,4-di-tert-butyl-1,2-η-1,2-diphosphetene)(Fe(CO)4)2] (8b), depending on the relative
concentration of the starting materials. 8a has been proven to be an intermediate in the
formation of 8b. Heating of neat 8b in a vacuum leads to the elimination of the chlorine
substituents in an intramolecular redox reaction and [(3,4-di-tert-butyl-η4-1,2-diphosphete)-
Fe(CO)3] (9a ) is formed. This is the first specific reaction, leading to a 1,2-diphosphete
complex. 9a and its 1,3-isomer 10a react with [Cr(CO)5(THF)] to form the mono- and
diaddition products [1-η-{(3,4-di-tert-butyl-η4-1,2-diphosphete)Fe(CO)3}Cr(CO)5] (9b), [1,2-
η-{(3,4-di-tert-butyl-η4-1,2-diphosphete)Fe(CO)3}(Cr(CO)5)2] (9c), [1-η-{(2,4-di-tert-butyl-η4-
1,3-diphosphete)Fe(CO)3}Cr(CO)5] (10b), and [1,3-η-{(2,4-di-tert-butyl-η4-1,3-diphosphete)-
Fe(CO)3}(Cr(CO)5)2] (10c), respectively. X-ray crystallographic studies for 9c and 10c give
some insight into the bonding situation of the compounds. σ- and π-complexing properties
of the diphosphete ligands are almost independent of each other and significant back-bonding
from the iron atom to the ligand π* orbitals occurs in both cases.
In tr od u ction
The CdC double bond of the partly unsaturated cis
(1) or trans (2) isomers of 1,2-diphosphetene rings
1
C2R′2P2R2 does not interact significantly with the two
lone pairs of the phosphorus atoms.2,3 Its ligand proper-
ties reveal a comparable situation, as exclusively the
P-σ lone pairs determine the behavior toward transition
metals. To the best of our knowledge no complex of 1,
2, or topologically related unsaturated P-heterocycles
has been reported as yet, in which the metal is coordi-
nated to the π-electrons of a vinylic CdC double bond
in combination with an adjacent P-M σ-bond. As the
F igu r e 1. Relative orientations of CdC π bond and
phosphorus lone pair orbitals of trans-1,2-diphosphetene
(2) and 1,2,3-triphospholene (3) derivatives.
functions and a suitable transition metal seems to be
possible. The divergency of the Cring-pz orbitals of the
pronounced convex surface of the π ligand of [(η6-2,2-
paracyclophane)Cr(CO)3], for example, is just in that
range.6 The same topological situation of 1 and 2 is
present in 1,2,3-triphospholenes (3).7
π-Complexes of unsaturated heterocycles exhibit fron-
tier orbitals, which depend decisively on the heteroatom
and the symmetry of the ring ligand, and these orbitals
govern the reactivity of such complexes.8 We have
divergency of the phosphorus lone pairs and the Cring
-
pz orbitals can be estimated to be in the range between
15° and 35° on the basis of the P-P-Csubstituent bond
angles (Figure 1), which range from 101° to 107°,4,5
a
simultaneous interaction between both types of donor
†Dedicated to Professor Otto J . Scherer on the occasion of his 65th
birthday.
* To whom correspondence should be addressed: tel, +49 9131
8527464; fax, +49 9131 8527367; e-mail, Zenneck@anorganik.chemie.uni-
erlangen.de.
(1) Kummer, S.; Zenneck, U. In Comprehensive Heterocyclic Chem-
istry II; Katritzky, A. R., Rees, C. W., Scriven, E. F. V., Eds.;
Pergamon: Oxford, 1996; Vol. 1B, 1.37, p 1157.
(2) Mathey, F. Phosphorus Sulfur 1987, 30, 213.
(3) Cowley, A. H.; Dewar, M. J . S.; Goodman, D. W.; Padolina, M.
C. J . Am. Chem. Soc. 1974, 96, 3666.
(5) Maigrot, N.; Ricard, L.; Charrier, C.; Le Goff, P.; Mathey, F. Bull.
Soc. Chim. Fr. 1992, 129, 76.
(6) Kai, Y.; Yasuoka, N.; Kasai, N. Acta Crystallogr. 1978, B43, 2840.
(7) Ecker, A.; Schmidt, U. Chem. Ber. 1973, 106, 1453.
(8) Elschenbroich, C.; Nowotny, M.; Metz, B.; Massa, W.; Graulich,
J . Angew. Chem. 1991, 103, 601; Angew. Chem., Int. Ed. Engl. 1991,
30, 547.
(4) Charrier, C.; Guilhem, J .; Mathey, F. J . Org. Chem. 1981, 46, 3.
10.1021/om980862x CCC: $18.00 © 1999 American Chemical Society
Publication on Web 04/24/1999

2022 Organometallics, Vol. 18, No. 10, 1999
Heinemann et al.
Sch em e 1
utilized this effect for a significant variation of the
properties of known catalysts with carbacyclic π ligands.9
π,σ complexes of the heterocycles 1-3 could be a new
alternative for such an approach. Therefore we found
it worthwhile to investigate the preparation of com-
plexes in which 1-3 can function as four-electron- (π2,σ2)
or even six-electron-donating (π2,σ2,σ2) flat ligands.
The idea is backed by the coordination chemistry of
the diheterodiene species 1,2,4-triphosphole, which may
act as a six-electron-donating ligand toward a Mo(CO)3
fragment by including the P-lone pair into the π electron
system of the ring.11A very bulky substituent on the
saturated σ3-P atom seems to be essential to create such
a planar η5-triphosphole ligand.
Lesser related cases are the fully unsaturated C2R2P2
ligands 1,3-diphosphete (4)10 and 1,2-diphosphete (5),12
where transition metal atoms always interact with the
π electrons of P and C atoms at the same time. Being
antiaromatic π4 species, 4 and 5 do not have an
independent existence at ambient temperature, but
require stabilization as π4 ligands in the coordination
sphere of a transition metal.13 An additional σ2-P-M′
interaction is possible, too, but only with a second
transition metal in the plane of the ring.10,14,15 In the
case of a successful π,σ interaction between 1 or 2 and
a suitable transition metal, an activation of the P-
substituents toward cleavage of the bond seems to be
likely, as only small structural changes within the (P-
heterocycle)M substructure are necessary to convert a
1,2-diphosphetene ligand into a fully unsaturated 1,2-
diphosphete by removing the substituents of the phos-
phorus atoms.
NMR spectra of purified starting material 3a ,18 the
phenyl substituents are oriented exclusively as indi-
cated in Figure 1; thus the P-lone pairs of the adjacent
P atoms 1 and 3 of the CdC double bond are directed
toward the same side of the ring.
Resu lts
Rea ctivity of P en ta p h en yl-1,2,3-tr ip h osp h olen e
3a . 3a was reacted with the highly reactive metal vapor
product [(1,5-COD)2Fe],19 which is an excellent genera-
tor of (1,5-cyclooctadiene)Fe fragments at low temper-
ature. These 12 valence electron (VE) fragments need
donation of six additional electrons by ligands for the
formation of stable 18-VE complexes.20 A product is
formed in the reaction, but it is of limited stability at
room temperature. According to field desorption mass
spectroscopy, it is [(COD)(pentaphenyl-1,2,3-triphos-
pholene)Fe], and NMR spectroscopic evidence suggested
coordination of P atoms P(1) and P(3) to the iron atom,
since the heterocycle forms an AX2 spin system, where
the X nuclei exhibit the proposed coordination shift.
Proof for or against an interaction between the iron
atom and the CdC double bond is not yet possible, as
to date no single crystals have been obtained.
If an excess of [Cr(CO)5(THF)] is allowed to react with
3a at room temperature in THF, the 1,3-P atoms, again,
are the active centers of the heterocycle and two Cr-
(CO)5 fragments are added to form [(1,2,3,4,5-penta-
phenyl-1,3-η-1,2,3-triphospholene)(Cr(CO)5)2] (6). The
isolated yield is nearly quantitative, and there is no hint
that the CdC double bond or P(2) is taking part in the
bonding in the product. This is in line with literature
reports concerning 1,2,3-triphospholene derivatives,
where always only P(1) and P(3) interact with transition
metal atoms.22 According to the NMR spectra of 6,
stereochemistry and symmetry of ligand 3a are main-
tained in the product. Thus the two Cr(CO)5 fragments
are believed to be bonded at the same side of the ring
ligand (Scheme 2).
trans-1,2-Dichloro-3,4-di-tert-butyl-1,2-diphosphet-
ene (2a )16 was chosen for the experiments dealing with
trans-1,2-diphosphetenes, as the chlorine substituents
are promising leaving groups. Neglecting the P-lone pair
electrons, 2a is analogous to 3,4-dichlorocyclobutene,
which was used successfully by Pettit and co-workers,
when they prepared [(η4-cyclobutadiene)Fe(CO)3] as the
first example of a π-cyclobutadiene transition metal
complex.17 1,2,3,4,5-Pentaphenyl-1,2,3-triphospholene
(3a ), on the other hand, was chosen as the second
starting material because of its good availability and
suitable chemical properties.4,7 According to the 31P
(9) Le Floch, P.; Knoch, F.; Kremer, F.; Mathey, F.; Scholz, J .; Scholz,
W.; Thiele, K.-H.; Zenneck, U. Eur. J . Inorg. Chem. 1998, 119.
(10) Reviews: Nixon, J . F. Chem. Rev. 1988, 88, 1327. Regitz, M.;
Binger, P. Angew. Chem. 1988, 100, 1541; Angew. Chem., Int. Ed. Engl.
1988, 27, 1484. Binger, P. In Multiple Bonds and Low Coordination
in Phosphorus Chemistry; Regitz, M., Scherer, O. J ., Eds.; Thieme:
Stuttgart, 1990; p 90. Regitz, M. In Organic Synthesis via Oganome-
tallics (OSM 4, Aachen); Enders, D., Gais, H.-J ., Keim, W., Eds.;
Viehweg: Wiesbaden, 1993; p 93. Nixon, J . F. Coord. Chem. Rev. 1995,
95, 201.
(11) Caliman, V.; Hitchcock, P. B.; Nixon, J . F.; Nyulaszi, L.;
Sakarya, N. Chem. Commun. 1997, 1305.
(12) Binger, P.; Glaser, G.; Albus, S.; Kru¨ger, C. Chem. Ber. 1995,
128, 1261.
(13) Schoeller, W. W.; Busch, T. Angew. Chem. 1993, 105, 635;
Angew. Chem., Int. Ed. Engl. 1993, 32, 617.
(14) Binger, P.; Milczarek, R.; Mynott, R.; Regitz, M.; Ro¨sch, W.
Angew. Chem. 1986, 98, 645; Angew. Chem., Int. Ed. Engl. 1986, 25,
644.
(15) Binger, P.; Biedenbach, B.; Mynott, R.; Benn, R.; Rufinska, A.;
Betz, P.; Kru¨ger, C. J . Chem. Soc., Dalton Trans. 1990, 1771.
Hitchcock, P. B.; Maah, M. J .; Nixon, J . F. Heteroatom Chem. 1991, 2,
253.
(16) Knoch, F.; Kummer, S.; Zenneck, U. Synthesis 1996, 2, 265.
(17) Emerson, G. F.; Watts, L.; Pettit, R. J . Am. Chem. Soc. 1965,
87, 131.
(18) Seiss-Brandl, U.; Dissertation, Universita¨t Erlangen-Nu¨rnberg,
1997.
(19) Mackenzie, R.; Timms, P. L. J . Chem. Soc., Chem. Commun.
1974, 650.
(20) Knoch, F.; Kremer, F.; Schmidt, U.; Zenneck, U.; Le Floch, P.;
Mathey, F. Organometallics 1996, 15, 2713.
(21) Maigrot, N.; Charrier, C.; Ricard, L.; Mathey, F. Polyhedron
1990, 9, 1363.
(22) King, R. B.; Reimann, R. H. Inorg. Chem. 1976, 15, 184.

1,2-Diphosphetene Metal Complexes
Organometallics, Vol. 18, No. 10, 1999 2023
Sch em e 2
F igu r e 2. View of the molecular structure of [(trans-
1,2,3,4-tetraphenyl-1,2-η-1,2-diphosphetene)(Cr(CO)5)2]‚
C6D6 (7a ) in the solid state. Selected bond distances [Å]
and angles [deg]: Cr(1)-P(1), 2.348(2); Cr(2)-P(2), 2.356-
(2); P(1)-C(11), 1.831(6); P(2)-C(21), 1.841(6); C(1)-C(31),
1.480(8); C(2)-C(41), 1.488(8); C(1)-C(2), 1.331(8); C(1)-
P(1), 1.830(6); C(2)-P(2), 1.824(6); P(1)-P(2), 2.271(2);
C(2)-C(1)-P(1), 104.1(5); C(1)-P(1)-P(2), 75.1(2); P(1)-
P(2)-C(2), 74.7(2); P(2)-C(2)-C(1), 105.1(5). There are no
bonding interactions between C6D6 and 7a . Hydrogen
atoms and the C6D6 molecule are omitted for clarity.
An AX2 spin system is observed in the 31P{1H} NMR
spectrum of 6 (121.5 MHz), and the X nuclei are much
more shifted than the A nucleus with respect to the
signals of the free ligand, due to the direct P-Cr
interaction of P(1) and P(3). The existence of a double
doublet for P(2) which is split by 4.5 Hz instead of a
first-order triplet can successfully be simulated. As one
would expect, the stereochemistry of the ligand has not
changed upon complexation.
To force the inclusion of the π electrons of the CdC
double bond into the interaction between the cyclic
ligand and the chromium atoms of 6, CO elimination
reactions have been tried. Heating solutions of 6 was
not successful, as inseparable mixtures are formed.
Visible light photolysis, however, yields a reaction
mixture, whose workup allows isolation of the main
product [(trans-1,2,3,4-tetraphenyl-1,2-η-1,2-diphosphe-
tene)(Cr(CO)5)2] (7a ) by chromatography. To our sur-
prise, no CO loss has taken place, but the central P(2)Ph
unit was lost from the molecule and the two chromium
atoms of 7a now are in a trans position (vide infra). 7a
is therefore a complex of the ligand trans-1,2,3,4-
tetraphenyl-1,2-diphosphetene (2b), and the photolysis
reaction of 6 represents a new access to such complexes
(Scheme 2).
Complexes of 2b can be made directly from the ligand,
but 3a is more readily accessible.4 [trans-(1,2-C2P2Ph4)-
(W(CO)5)2]21 (7b) and [trans-(1,2-C2P2Ph4)(Fe(CO)4)2]4,23
(7c) are closely related to 7a with regard to their
properties. Fe carbonyl species 7c has already been
investigated with respect to its behavior upon heating.
P-P bond cleavage and loss of one molecule of PhCt
CPh were observed.4 As found here, the CdC double
bond did not interact with the metal atoms. Therefore,
no more experiments in this direction have been carried
out with 7a . To prove the proposed stereochemistry, the
structure of 7a was determined by X-ray crystal-
lography. The solid-state molecular structure of 7a is
shown in Figure 2. and some selected bond distances
and angles are summarized in the figure caption.
Figure 2 clearly indicates the trans arrangement of
the two Cr(CO)5 fragments and the P-phenyl substitu-
ents, respectivly. The ring of 7a is nearly planar and
less twisted than in the free ligand 2b. This is indicated
by the angle between the endocyclic bonds P(1)-P(2)
and C(1)-C(2), which is 7.8° for 7a , but 19° for 2b.4 All
bond distances and angles of 7a are in the normal
ranges, which are defined by related compounds such
as 7b and 7c.
Mechanistic considerations of the formation of 7a
from 6 need to explain the fact that at least one P(Ph)-
(Cr(CO)5) moiety rotates by 180° during the course of
the reaction, as one of the two chromium atoms changed
from one side of the ligand ring to the other. If we
suppose a ring-opened structure after the P(2)Ph unit
has left molecule 6, an open chain cis-1,4-diphospha-
butadiene, structure 7a ′, is the most probable interme-
diate, which allows a ring closure immediately after its
formation. A related 1,2-diphosphetene f 1,4-diphos-
phabutadiene rearrangement has been found to date in
only one example, that of ditungsten complex 7b.21 If
the reaction sequence includes 7a ′ as the decisive
intermediate, the 180° rotation of one P(Ph)(Cr(CO)5)
unit is easily understood, as both phosphorus atoms
have to rotate by 90° together with their substituents,
for the ring opening as well as for the ring-closure steps
(Scheme 2).
Rea ctivity of tr a n s-1,2-Dich lor o-3,4-d i-ter t-bu tyl-
1,2-d ip h osp h eten e 2a . 2a was reacted with [Fe2(CO)9].
In contrast to 2b, the reaction of 2a and [Fe2(CO)9]
proceeds well at room temperature.4 Depending on the
relative concentration of the reactants, one or two iron
atoms became bonded to the phosphorus atoms to form
[(trans-1,2-dichloro-3,4-di-tert-butyl-1-η-1,2-diphosphet-
ene)Fe(CO)4] (8a ) and [(trans-1,2-dichloro-3,4-di-tert-
butyl-1,2-η-1,2-diphosphetene)(Fe(CO)4)2] (8b), respec-
tively (Scheme 3). In the reaction mixture, even before
workup, no traces of the corresponding cis isomers are
observable.
(23) Mathey, F.; Charrier, C.; Maigrot, N.; Marinetti, A.; Ricard, L.;
Tran Huy, N. H. Comments Inorg. Chem. 1992, 13, 61.

2024 Organometallics, Vol. 18, No. 10, 1999
Heinemann et al.
F igu r e 3. 31P{1H} NMR spectrum (109.4 MHz, THF) of the reaction products formed by a 1:1 mixture of Fe2(CO)9 and
trans-1,2-dichloro-3,4-di-tert-butyl-1,2-diphosphetene (2a ) at room temperature.
Sch em e 3
isomer. However, the mild reaction conditions are
definitely not in favor of an inversion of phosphorus-
(III) atoms, which are part of a ring system. Further-
more, the trans-diiron complex 8b is believed to be the
thermodynamically favored product.23 There seems to
be no driving force for such an isomerization process,
which anyway would be expected to produce mixtures
of isomers, and these have not been observed.
Rea ctivity of [(tr a n s-1,2-Dich lor o-3,4-d i-ter t-bu -
tyl-1,2-η-1,2-d ip h osp h eten e)(F e(CO)4)2] 8b. As the
dehalogenation of 2a did not occur at room temperature
even with a large excess of [Fe2(CO)9], an intramolecular
redox process was attempted to induce an interaction
of the CdC double bond with at least one of the two
iron atoms by heating neat 8b in a vacuum in a
kugelrohr distillation unit. The process requires heating
at 190 °C, and the product [(3,4-di-tert-butyl-η4-1,2-
diphosphete)Fe(CO)3] (9a ) distills from the flask during
the course of the heating as a pure compound, but again
as an oil (Scheme 3). Thus, in contrast to carbacyclic
3,4-dichlorocyclobutene, the dechlorination of ligand 2a
in the form of its complex 8b requires high tempera-
tures.
To the best of our knowledge, such a dechlorination
is new for P-heterocycles and is the first specific reaction
leading directly to a 1,2-diphosphete complex. Only one
example of such a compound is in the literature, but it
was only formed together with its 1,3-isomer as an
unseparable mixture.12
The spectra of 9a are in complete agreement with the
presence of the proposed 1,2-diphosphete ligand, but,
as before, the observable spectroscopic data do not
distinguish definitely between 1,2- and 1,3-regioisomers.
This is even the case for the 13C{1H} NMR spectrum.
Due to strong but, because of the symmetry of the
molecule, unobservable P-P coupling (vide infra), the
signals of the ring carbon atoms as well as those of the
t-Bu groups are split into pseudo triplets, although AXY
spin systems should be formed for 13C-isotopomers of
1,2-isomer 9a (A ) 13C; X, Y ) 31P(1, 2) are inequivalent
because of coupling with a single 13C nucleus). The
If equimolar amounts of [Fe2(CO)9] and 2a are allowed
to react, an almost statistical mixture of unreacted 2a
and the two complexes 8a and 8b is formed, which
overall contains nearly one Fe(CO)4 unit per ring ligand
(Figure 3). No side products are observable. If this
inseparable mixture is treated again with another mole
of [Fe2(CO)9], the remaining amounts of 2a and primary
product 8a are both converted almost quantitatively into
8b. An excess of [Fe2(CO)9] therefore directly leads to
good yields of pure 8b. We interpret this finding as a
proof that 8a is an intermediate in the formation of 8b.
This means that the reactivities of the free ligand 2a
and monocomplex 8a toward complexation by Fe(CO)4
fragments are almost identical. Otherwise a preference
of the formation of either 8a or 8b in a 1:1 reaction
would have been observed, depending on the relative
reactivities of 2a and 8a . These almost identical reac-
tivities of a free bifunctional ligand and a corresponding
monocomplex stand in contrast to the reactivity of 2b
toward reactive [Fe(CO)4L] complexes.4
No real proof for the stereochemistry of complexes 8a
and 8b has been found as yet since they can only be
isolated as oils. All spectra of the complexes are inter-
preted unambiguously, if an unchanged trans-1,2-
diphosphetene ligand structure is assumed, but this
does not unequivocally rule out the corresponding cis

1,2-Diphosphetene Metal Complexes
Organometallics, Vol. 18, No. 10, 1999 2025
Sch em e 4
corresponding 1,3-isomer [(3,4-di-tert-butyl-η4-1,2-diphos-
phete)Fe(CO)3] (10a ) is known,24 but it also is a low-
melting compound and no structural information is
available. With the exception of mass spectroscopy, the
spectra of 9a and 10a are rather different and thus they
definitely are isomers. However, their main character-
istics are the same. The chemical shifts of the ring
nuclei, for example, are indicative for diphosphete
ligands that are complexed to Fe(CO)3 fragments. A
good argument, but no real proof, for 10a being a 1,3-
diphosphete complex was deduced from a side product,
where one phosphorus atom is complexed to a second
iron atom and a small P-P coupling constant of 4.3 Hz
was observed.24 To answer the question of regioisom-
erism properly, we transformed both [(diphosphete)Fe-
(CO)3] isomers, 9a and 10a , into crystalline compounds,
utilizing the additional donor properties of the phos-
phorus atoms of the complexes.
F igu r e 4. 31P{1H} NMR spectrum (109.4 MHz, THF) of
the reaction products formed by a mixture of [Cr(CO)5-
(THF)] and [(3,4-di-tert-butyl-η4-1,2-diphosphete)Fe(CO)3]
(9a ) at room temperature.
Sch em e 5
Rea ctivity of 1,2- a n d 1,3-Isom er s 9a a n d 10a of
[(d i-ter t-bu tyl-η4-d ip h osp h ete)F e(CO)3]. To avoid
difficult-to-handle reactants or working in an autoclave,
we prepared 10a by a different route, that reported by
Binger and co-workers.24 The visible light photochemical
reaction of [Fe(CO)5] and t-BuCtP25 at ambient tem-
perature in a Duran glass photolysis apparatus is quite
effective (Scheme 4).
9a and 10a both react with [Cr(CO)5(THF)] at room
temperature, to form mono- and diaddition products
[1-η-{(3,4-di-tert-butyl-η4-1,2-diphosphete)Fe(CO)3}Cr-
(CO)5] (9b), [1,2-η-{(3,4-di-tert-butyl-η4-1,2-diphosphete)-
Fe(CO)3}(Cr(CO)5)2] (9c), [1-η-{(2,4-di-tert-butyl-η4-1,3-
diphosphete)Fe(CO)3}Cr(CO)5] (10b), and [1,3-η-{(2,4-
di-tert-butyl-η4-1,3-diphosphete)Fe(CO)3}(Cr(CO)5)2] (10c),
respectively. As in the case of the addition of Fe(CO)4
fragments to 2a , the Cr(CO)5 units are added step by
step, and the monoaddition products 9b and 10b were
shown to be intermediates in the formation of 9c and
10c by the same method (Scheme 5, Figure 4).
1
is very large. A J PP of greater than 200 Hz is exactly
what is required for the above-mentioned observation
of pseudotriplets in the 13C{1H} NMR spectra of 9a . In
the case of 10b, we have been able to obtain 13C{1H}
NMR spectra as well. As the carbon atom signals do not
split upon involving only one of the two phosphorus
atoms in the formation of P-Cr bonds, an element of
symmetry persists, which causes equivalence of both
C-t-Bu units. This is possible only if 10b contains the
1,3-diphosphete ligand.
X-r a y Str u ctu r a l In vestiga tion s on 9c a n d 10c.
As hoped, trinuclear 9c and 10c form good crystals
which have been grown at -30 °C from a THF solution
of 9c and a solvent mixture THF/Et2O in the case of
10c. The molecular structures in the solid state are
shown in Figures 5 (9c) and 6 (10c), and selected bond
distances and angles are summarized in the figure
captions.
As for 8a , neither 9b nor 10b can be prepared without
giving reaction mixtures that contain all three com-
pounds 9a ,b,c and 10a ,b,c, respectively. As a conse-
quence, 9b and 10b can be observed by means of
spectroscopy, but attempts to isolate them failed. NMR
spectra of the FeCr complexes 9b and 10b present good
evidence for the proposed regioisomers. Both 31P{1H}
NMR spectra show the characteristics of AB spin
systems. In the case of the 1,3-complex 10b no P-P
coupling is resolved, whereas the 1,2-complex 9b ex-
1
hibits a P-P coupling constant J PP ) 225.7 Hz (Figure
4). Compared with free asymmetric 1,2-diphosphetene
1
derivatives,1 the J PP constant of fully unsaturated 9b
(24) Binger, P.; Biedenbach, B.; Schneider, R.; Regitz, M. Synthesis
1989, 960.
(25) Becker, G.; Gresser, G.; Uhl, W. Z. Naturforsch. 1981, 36b, 16.
Optimized procedure: Ro¨sch, W.; Hees, U.; Regitz, M. Chem. Ber. 1987,
120, 1645.
In both cases, the X-ray structure analyses prove the
proposed structures. The cyclic ligands are planar,

2026 Organometallics, Vol. 18, No. 10, 1999
Heinemann et al.
Ta ble 1. Selected En d ocyclic Bon d Dista n ces [Å]
of 1,2-Dip h osp h ete a n d 1,2-Dip h osp h eten e
Der iva tives
10c and its interpretation, we believe we have good
reasons for neglecting the influence of the Cr(CO)5
fragments in the case of 9c, too. In both cases σ- and
π-bonding orbitals of the ring ligand are orthogonal and
thus do not mix. The observed effects on the ring ligand
therefore have to be interpreted only on the basis of π
bonding of an electron-rich (Fe) or electron-poor transi-
tion metal atom (Ti). As for the 1,3-diphosphete com-
plexes, we can explain the elongation of the PdP and
CdC double bonds toward values that are between
single and double bonds mainly on the basis of the
donation of π electron density to the metal atom. The
dominating cause of the shortening of the P-C bond
length is an electron back-donation from the π-bonded
metal to ligand π* orbitals. The second effect should be
smaller for the 16-VE species 11b than it is for 11a ,
but in the case of 11b only the P-P bond is more
elongated than for 18-VE complex 9c. As a simple
explanation for this effect has not been found yet, the
problem seems to require a theoretical study.
5a
2a
11bb
9c
C-C
C-P
P-P
1.345
1.874
2.115
1.363
1.825
2.189
1.429
1.815, 1.806
2.175
1.432
1.807, 1.825
2.147
a
Calculated values.13 b [(3,4-Di-tert-butyl-η4-1,2-diphosphete)(η8-
COT)Ti].12
forming a trapezoid for the 1,2-diphosphete of 9c and a
rhombus for the 1,3-diphosphete of 10c, respectively.
The length of all four P-C bonds in 10c are es-
sentially the same (1.78 ( 0.01 Å), and the C-P-C
angles are smaller (84°) than the P-C-P angles (96°).
Almost identical endocyclic bonding distances have been
found also for other (η4-1,3-diphosphete)metal complexes
of the late transition metals such as cobalt26 or in
oligonuclear rhodium complexes, where a (η4-1,3-
diphosphete)Rh unit is σ-bonded to a second rhodium
atom.15 This indicates an almost complete separation
of the orthogonal σ and π coordination properties of the
ligand and a cyclic delocalization of the π electrons
within the ring. The different covalent radii of P and C
atoms cause the rhombic deformation of the otherwise
ideal square of a η4-cyclobutadiene ligand.10,27 The
situation is different only in the case of the 16-VE early
transition metal complex [(2,4-di-tert-butyl-η4-1,3-diphos-
phete)(η8-COT)Ti] (11a ), where alternating P-C bond
lengths are observed.12 This has been related to the
calculated structural data of free unsubstituted 1,3-
diphosphete 4, which exhibits an even more pronounced
parallelogram structure.13 In contrast to the 18-VE late
transition metal complexes, 11a obviously does not
allow a complete π electron delocalization within the 1,3-
diphosphete ligand, probably due to a reduced back-
bonding capacity of the electron-poor early transition
metal center.
Such a 16-VE (COT)Ti complex is the only known
example of a (η4-1,2-diphosphete)M complex.12 As for 9c,
a planar trapezoid is observed for the 1,2-diphosphete
ligand of [(3,4-di-tert-butyl-η4-1,2-diphosphete)(η8-COT)-
Ti] (11b), and the same is true for the calculated
structure of free unsubstituted 1,2-diphosphete 513 and
the dichloro-1,2-diphosphetene 2a .16 The endocyclic
bond distances of these four species have been compiled
in Table 1.
The most striking fact is the very close conformity of
the C-C and C-P bond lengths of 9c and 11b, but the
P-P bond of 11b is 0.028 Å longer than that of 9c. The
P-P bond of 11b is therefore only 0.014 Å shorter than
the P-P single bond of 2a , and this is a value that is
only slightly larger than the sum of the 3σ ranges. The
influence of the metal atoms on the structural features
of 9c or 11b can be studied, when we compare the
endocyclic bond distance data of the complexes with the
calculated values of the free 1,2-diphosphete 5. Both,
the CdC and PdP bonds of 5 are elongated by 0.032
(P-P of 9c) to 0.087 Å (C-C of 9c), but the average
value of the P-C bonds of 9c and 11b is 0.05 Å shorter
than that of 5. On the basis of the structural data of
Con clu sion s
Not only in the case of free 1,2-diphosphetene 2a but
also for the diphosphete complexes 9a and 10a we found
experimental evidence for a stepwise addition of suitable
transition metal complex fragments such as Fe(CO)4
and Cr(CO)5 to these bifunctional P2 ligands. The
finding of closely related σ ligand reactivities of the
uncomplexed species as well as for their monocomplexes
was assumed in the case of 1,3-diphosphete complex
10a , as the donor orbitals point in opposite directions
and the two phosphorus atoms are not bonded directly
to each other. This was not expected for 2a , as neigh-
boring P atoms should interact to some extent and a
chemical reaction of one P atom should influence the
other one. The sterically favorable trans arrangement
of the lone pairs is no argument against a proposed
influence, as in the case of cyclotetraphosphanes, for
example, no report has appeared in the literature of
neighboring P atoms with a trans stereochemistry which
have been both coordinated to transition metal atoms.
Finally, in the case of 1,2-diphosphete complex 9a the
two P-lone pair orbitals are situated in the plane of the
ring at neighboring positions, and they form an angle
of ca. 100°. This can be estimated with some degree of
certainty from the angle between the P-Cr bonds of
complex 9c. Consequently, the two Cr(CO)5 fragments
of 9c do interact (Figure 5), as can be deduced from the
positions of the equatorial carbonyl groups. To minimize
the repulsion between the CO ligands of the two
chromium atoms, the ligand C(53)O(53) of Cr(2) is thus
positioned right in the middle between the two CO
ligands C(41)O(41) and C(44)O(44) of Cr(1). In this cog-
wheel-like conformation, however, only weak repulsion
between the two Cr(CO)5 fragments of 9c remains, but
entropy is lost.
We started our investigations with the aim of using
1,2-diphosphetene or 1,2,3-triphospholene derivatives as
π,σ ligands. This point still remains open, as no stable
complexes have been isolated that contain such a
structural element. On the other hand, the thermally
induced redox reaction of diiron complex 8b would be
difficult to understand without the possibility of devel-
oping an interaction between a P-σ-bonded iron atom
(26) Hitchcock, P. B.; Maah, M. J .; Nixon, J . F. J . Chem. Soc., Chem.
Commun. 1986, 737. Binger, P.; Milczarek, R.; Mynott, R.; Kru¨ger,
C.; Tsay, Y.-H.; Raabe, E.; Regitz, M. Chem. Ber. 1988, 121, 637.
(27) Deeming, A. J . Compr. Organomet. Chem. 1982, 4, 459.

1,2-Diphosphetene Metal Complexes
Organometallics, Vol. 18, No. 10, 1999 2027
Sch em e 6
F igu r e 5. View of the molecular structure of [1,2-η-{(3,4-
di-tert-butyl-η4-1,2-diphosphete)Fe(CO)3}(Cr(CO)5)2] (9c) in
the solid state. Selected bond distances [Å] and angles
[deg]: P(1)-C(1), 1.807(4); P(2)-C(2), 1.825(4); P(1)-P(2),
2.147(2); C(1)-C(2), 1.432(6); Fe(1)-P(1), 2.3343(14); Fe-
(1)-P(2), 2.3107(13), Fe(1)-C(1), 2.174(4); Fe(1)-C(2),
2.150(4); Cr(1)-P(1), 2.3501(14); Cr(2)-P(2), 3.3680(13);
C(1)-P(1)-P(2), 78.7(2); C(2)-P(2)-P(1), 78.6(2); C(2)-
C(1)-P(1), 102.0(3); C(1)-C(2)-P(2), 100.7(3). The hydro-
gen atoms are omitted for clarity.
under current investigation. There is little reason to
assume a primary attack from an external iron carbonyl
complex fragment on either a P-Cl or the CdC double
bond, as this would have been much easier in the case
of free ligand 2a . But 2a is almost quantitatively
converted by Fe(CO)4 fragments into 8b without any
observable side reaction (Figure 3).
This new and specific route to 1,2-diphosphete com-
plex 9a is believed to be of more use, as 2a should be
able to react with several different transition metal
complex fragments, and most of them will dechlorinate
the P-heterocycle at elevated temperatures as well. We
are interested in a better access to (η4-diphosphete)M
complexes, because several of these are robust com-
pounds.10,26,29 Therefore the coligands of such com-
pounds in some cases may be removed without breaking
the M-diphosphete bond.16,30 As (η4-cyclobutadiene)M
or (η4-heterocyclobutadiene)M units are identical in
their electron count with an (η5-cyclopentadienyl)M′
fragment, if M′ is the left neighbor of M in the periodic
table, many useful applications can be imagined for (η4-
diphosphete)M complexes,31 especially as we now have
found access to both regioisomers.
F igu r e 6. View of the molecular structure of [1,3-η-{(2,4-
di-tert-butyl-η4-1,3-diphosphete)Fe(CO)3}(Cr(CO)5)2] (10c)
in the solid state. Selected bond distances [Å] and angles
[deg]: P(1)-C(1), 1.781(7); P(2)-C(2), 1.791(8); P(2)-C(1),
1.776(7), P(1)-C(2), 1.782(7), Fe(1)-P(1), 2.285(3); Fe(1)-
P(2), 2.320(3); Fe(1)-C(1), 2.176(7); Fe(1)-C(2), 2.156(7);
Cr(1)-P(1), 2.352(3); Cr(2)-P(2), 2.371(2); C(1)-P(1)-C(2),
84.0(3); P(2)-C(1)-P(1), 96.1(4); C(1)-P(2)-C(2), 83.9(3);
P(1)-C(2)-P(2), 95.6(4). The hydrogen atoms are omitted
for clarity.
Exp er im en ta l Section
Gen er a l In for m a tion . All reactions were carried out under
an atmosphere of purified and dried nitrogen using Schlenk-
type glassware. Solvents and starting materials were dried
and saturated with nitrogen according to standard procedures.
Instruments used: 1H,13C NMR: J EOL-GX 270 operating
at 270 MHz (1H) and 67.7 MHz (13C), and J EOL-J NM-LA 400
operating at 400 MHz (1H) and 100.4 MHz (13C), respectively;
31P {1H} NMR: J EOL-EX 270 (109.4 MHz), Bruker Avance
DPX 300 (121.5 MHz), and J EOL-J NM-LA 400 (161.7 MHz).
Mass spectra: J EOL J MS 700 (FD or EI mode, 70 eV). IR:
Perkin-Elmer FT-IR Model 16. Elemental analyses were
performed at the microanalytical laboratory of the Institut fu¨r
Anorganische Chemie, University of ErlangensNu¨rnberg. The
with the π electrons of the adjacent CdC double bond,
most probably after loss of one CO ligand, but without
breaking the Fe-P σ bond at the same time. The other
iron atom would be able to insert into to its neighboring
P-Cl bond. This might be the initiating step for the
dechlorination of the ring ligand. Removing the first
chlorine substituent with one iron atom from the ring
allows the formation of an (η3-phospaallyl)Fe unit, a
molecular building block, which has been known for
some time now.28 The removal of the second chlorine
atom is most probably not possible in an intramolecular
reaction because of the trans stereochemistry of the
involved phosphorus atoms (Scheme 6).
(29) Driess, M.; Hu, D.; Pritzkow, H.; Scha¨ufele, H.; Zenneck, U.;
Regitz, M.; Ro¨sch, W. J . Organomet. Chem. 1987, 334, C35. Zenneck,
U. Angew. Chem. 1990, 102, 171; Angew. Chem., Int. Ed. Engl. 1990,
29, 126.
(30) Bo¨hm, D.; Knoch, F.; Kummer, S.; Schmidt, U.; Zenneck, U.
Angew. Chem. 1995, 107, 251; Angew. Chem., Int. Ed. Engl. 1995, 34,
198. Knoch, F.; Bo¨hm, D.; Kummer, S.; Zenneck, U. Z. Kristallogr.
1995, 210, 801. Bo¨hm, D.; Geiger, H.; Knoch, F.; Kremer, F.; Kummer,
S.; Le Floch, P.; Mathey, F.; Schmidt, U.; Zenneck, U. Phosphorus,
Sulfur, Silicon 1996, 109-110, 173.
Up to now we have not found proof for the proposed
intramolecular reaction mechanism, but this point is
(28) Hu, D.; Scha¨ufele, H.; Pritzkow, H.; Zenneck, U. Angew.
Chem.1989, 101, 929; Angew. Chem., Int. Ed. Engl. 1989, 28, 900.
(31) Herrmann, W. A.; Cornils, B. Angew. Chem. 1997, 109, 1074;
Angew. Chem., Int. Ed. Engl. 1997, 36, 1048.

2028 Organometallics, Vol. 18, No. 10, 1999
Heinemann et al.
column chromatography material used was silica gel or neutral
alumina (70-230 mesh) deactivated with 5% degassed water.
Photochemical reactions have been performed with a Hg-vapor
lamp, Philips HPK 125 W, in a locally constructed Duran glass
apparatus, which allows temperature control and pumping of
the reactant solution through the irradiation zone. For kugel-
rohr distillation a Bu¨chi GKR 51 was used, which allows
working between -78° and 250 °C and evacuating the ap-
paratus to a vacuum of 0.005 mbar.
The following starting materials have been prepared as
reported in the literature: trans-1,2-dichloro-3,4-di-tert-butyl-
1,2-diphosphetene (2a ),16 1,2,3,4,5-pentaphenyl-1,2,3-triphos-
pholene (3a ),4 [(1,5-COD)2Fe],19 and PtC-t-Bu.25 All other
materials have been purchased from standard commercial
sources in synthetic quality.
Data of 8a from such a mixture, which was purified by a short
chromatography (3 cm) on alumina/5% water to give a red oil:
1H NMR (C6D6): δ 1.10 (s, 9H, t-Bu); 1.16 (s, 9H, t-Bu). 31P-
{1H} NMR (C6D6): δ 69.05 (d, 1P, P2, J (PP) ) 129.36 Hz);
120.83 (d, P1, J (PP) ) 129.36 Hz). FD-MS [m/z (%)]: 438 (M+,
100, isotopic pattern equals C14H18Cl2FeO4P2).
[(3,4-Di-ter t-bu tyl-η4-1,2-d ip h osp h ete)F e(CO)3] (9a ). 8b
(383 mg, 0.63 mmol) was placed in the hot zone of an evacuated
kugelrohr distillation unit (0.05 mbar). After reaching 190 °C
95 mg of spectroscopically pure 9a (0.28 mmol, 44.4%) con-
densed within 1 h in an ice-cooled glass bulb as a yellow oil.
1H NMR (C6D6): δ 1.00 (s,18 H, t-Bu). 31P{1H} NMR (C6D6):
δ -84.63 (s). 13C{1H} NMR (C6D6): δ 32.38 (pt, -C(CH3)3,
4
2
3J (P,C) + J (P,C) ) 4.12 Hz); 37.45 (pt, -C(CH3)3, J (P,C) +
3J (P,C) ) 2.91 Hz); 134.89 (pt, C-ring, 1J (P,C) + 2J (P,C) )
27.66 Hz); 214.18 (s, CdO). FD-MS [m/z (%)]: 340 (M+, 100,
isotopic pattern equals C13H18FeO3P2). IR (PE): ν(CO) ) 1990,
2060.
[(1,2,3,4,5-P en ta p h en yl-1,3-η-1,2,3-tr ip h osp h olen e)(Cr -
(CO)5)2] (6). A solution of Cr(CO)6 (2.2 g, 10 mmol) in 150 mL
of THF was irradiated for 3 h in a tap water cooled 125 W
photolysis glass apparatus. The resulting solution of [Cr-
(CO)5THF] was added to a solution of 1.8 g (3.5 mmol) of
1,2,3,4,5-pentaphenyl-1,2,3-triphospholene (3a ) in 20 mL of
THF and stirred for 12 h at room temperature. After removal
of the solvent in a vacuum, excess Cr(CO)6 was sublimed at
40 °C. Chromatography on silica/5% water in light petroleum
ether (PE) and PE/toluene mixtures allowed the purification
of the yellow product. Yield: 2.87 g (3.2 mmol, 91%). 1H NMR
(C6D6): δ 8.13-6.60 (m). 31P{1H} NMR (C6D6): δ +88.46 (d, J
) 256.9 Hz); -33.96 (dd, J 1 ) 253.9 Hz, J 2 ) 258.4 Hz);
(simulated) δ +88.46 (d); -33.95 (dd); J ) -256.6 Hz. EI-MS
[1,2-η-{(3,4-Di-ter t-bu tyl-η4-1,2-d ip h osp h ete)F e(CO)3}-
(Cr (CO)5)2] (9c) a n d [1-η-{(3,4-Di-ter t-bu tyl-η4-1,2-d ip h os-
p h ete)F e(CO)3}Cr (CO)5] (9b). A water-cooled solution of
Cr(CO)6 (199 mg, 0.91 mmol) in 45 mL of THF was irradiated
for 8 h in a tap water cooled 125 W photolysis glass apparatus.
The resulting solution of [Cr(CO)5THF] in THF was added to
103 mg (0.30 mmol) of 9a and stirred for 48 h at room
temperature. After removal of the solvent in a vacuum, the
residue was dissolved in a few milliliters of THF and filtered
through Al2O3/5% water. Recrystallization from THF yielded
1
131 mg (0.18 mmol, 60.0%) of yellow 9c. H NMR (CDCl3): δ
[m/z (%)]: 886 (M+, 100, isotopic pattern equals C42H25
-
1.43 (s,18 H, t-Bu). 13C{1H} NMR (C6D6): δ 33.25 (s, -C(CH3)3);
Cr2O10P3); 858 (M+ - CO, 10); 830 (M+ - 2CO, 6); 802 (M+
-
38.22 (pt, -C(CH3)3, J (P,C) + 3J (P,C) ) 6.43 Hz); 126.49 (pt,
2
3CO, 3); 778 (M+ - PPh, 15); 694 (M+ - Cr(CO)5, 40); 666
([(C2P3Ph5)Cr(CO)4]+, 13); 502 (C2P3Ph5+, 8). IR (THF): ν(CO)
) 2061, 1948, 1930.
C-ring, 1J (P,C) + 2J (P,C) ) 11.90 Hz); 209.84 (s, CdO); 213.79
(pt, (CdO), 2J (P,C) + 3J (P,C) ) 5.47 Hz); 218.89 (s, CdO). 31P-
{1H} NMR (CDCl3): δ 28.76 (s). FD-MS [m/z (%)]: 724 (M+,
100). IR (CDCl3): ν(CO) ) 2083, 2067, 2047, 1994, 1965. Anal.
Calcd for C23H18Cr2FeO13P2: C 38.15; H 2.51. Found: C 37.48;
H 2.39.
tr a n s-[(1,2,3,4-Tet r a p h en yl-1,2-η-1,2-d ip h osp h et en e)-
(Cr (CO)5)2] (7a ). A solution of 1.33 g (1.50 mmol) of [(1,2,3,4,5-
pentaphenyl-1,3-η-1,2,3-triphospholene)(Cr(CO)5)2] (6) in 100
mL of THF was irradiated for 8 h in a tap water cooled 125 W
photolysis glass apparatus. After removal of the solvent in a
vacuum the orange-yellow product was purifid by chromatog-
raphy on silica/5% water in PE/toluene, 4:1. Yield: 200 mg
(0.26 mmol, 17%). 1H NMR (acetone-d6): δ 8.22 (m); 7.75 (m);
7.49 (m); 7.42 (m). 13C{1H} NMR (acetone-d6): δ 221.29 (t, J
) 2.5 Hz, COtrans); 215.72 (t, J ) 5.8 Hz, COcis); 149.28 (t, J )
19 Hz); 136.37 (t, J ) 7.4 Hz); 135.59 (t, J ) 10.7 Hz); 134.16
(t, J ) 7.4 Hz); 133.19 (s); 131.09 (s); 130.61; 130.60; 130.56.
31P{1H} NMR (C6D6): δ +91.37 (s). FD-MS [m/z (%)]: 694 (M+,
100). Anal. Calcd for C36H20CrO10P2: C 55.54; H 2.59. Found:
C 56.36; H 2.40.
Reaction mixtures, composed of equimolar amounts of Cr-
(CO)6 and 9a , which were treated in the same manner, formed
unseparable mixtures of 9a , 9b, and 9c. Data of 9b from a
filtered solution of such a mixture: 31P{1H} NMR (C6D6): δ
16.02 (d, 1J (P,P) ) 225.70 Hz); -80.42 [d, 1J (P,P) ) 225.70
Hz]. FD-MS (70 eV) [m/z (%)]: 532 (M+, 100, isotopic pattern
equals C18H18CrFeO8P2).
[(2,4-Di-ter t-bu tyl-η4-1,3-d ip h osp h ete)F e(CO)3] (10a ). A
solution of Fe(CO)5 (1000 mg, 5.1 mmol) in 100 mL of PE was
added to PtC-t-Bu (1530 mg, 15.3 mmol) in a tap water cooled
125 W photolysis glass apparatus and irradiated for 8 h. The
reaction mixture was filtered through a D4 glass frit, the
solvent was removed in a vacuum, and the residue was
distilled in a kugelrohr distillation unit (200° f 0 °C/0.1 mbar)
to yield 844 mg of pure 10a (2.5 mmol, 49.0%). The spectro-
scopic data of 10a are in good agreement with those reported
in the literature.24
[(tr a n s-1,2-Dich lor o-3,4-di-ter t-bu tyl-1-η-1,2-diph osph e-
ten e)F e(CO)4] (8a ) a n d [(tr a n s-1,2-Dich lor o-3,4-d i-t-bu -
tyl-1,2-η-1,2-d ip h osp h eten e)(F e(CO)4)2] (8b). A solution of
trans-1,2-dichloro-3,4-di-tert-butyl-1,2-diphosphetene (2a ) (186
mg, 0.69 mmol) in 30 mL of THF was added to Fe2(CO)9 (522
mg, 1.43 mmol). The reaction mixture was stirred for 24 h at
room temperature. After removing the solvent in a vacuum,
the brown residue was dissolved in light petroleum ether (PE)
and purified by a short (3 cm) chromatography on silica/5%
water. The PE was removed in a vacuum again to yield 349
mg of spectroscopically pure 8b (0.58 mmol, 84.1%) as a red
oil. 1H NMR (C6D6): δ 1.25 (s, 18 H, t-Bu). 13C{1H} NMR
[1,3-η-{(2,4-Di-ter t-bu tyl-η4-1,3-d ip h osp h ete)F e(CO)3}-
(Cr (CO)5)2] (10c) a n d [1-η-{(2,4-Di-t-bu tyl-η4-1,3-d ip h os-
p h ete)F e(CO)3}Cr (CO)5] (10b). Preparation as reported for
9b and 9c: Cr(CO)6 (716 mg, 3.25 mmol); 60 mL of THF;
irradiation for 4 h; 369 mg (1.08 mmol) of 10a . After removal
of the solvent, the residue was dissolved in a small amount of
THF and filtered through Al2O3/5% water, and the same
volume of diethyl ether was added to the yellow solution. The
product crystallized at -30 °C to yield 332 mg (0.46 mmol,
42.6%) of yellow 10c. 1H NMR (CDCl3): δ 1.13 (s, 18 H, t-Bu).
13C{1H} NMR (CDCl3): δ 32.35 (t, -C(CH3)3, 3J (C,P) ) 4.52
2
(C6D6): δ 31.43 (s, -C(CH3)3); 39.10 (pt, -C(CH3)3, J (P,C) +
2
3J (P,C) ) 14.08 Hz); 164.28 (pt, C-ring, 1J (P,C) + J (P,C) )
16.15 Hz); 212.19 (pt, CdO, 2J (P,C) + 3J (P,C) ) 5.38 Hz). 31P-
{1H} NMR (C6D6): δ 157.6 (s). FD-MS [m/z (%)]: 606 (M+, 100,
isotopic pattern equals C18H18Cl2Fe2O8P2). IR (PE): ν(CO) )
1975, 2044.
2
Hz); 34.94 (t, -C(CH3)3, J (C,P) ) 3.31 Hz); 112.17 (t, C-ring,
2
1J (C,P) ) 28.11 Hz); 210.54 (s, CdO); 214.18 (t, CdO, J (C,P)
Unseparable mixtures of 2a , 8a , and 8b were obtained if
equimolar amounts of 2a and Fe2(CO)9 were allowed to react
in the same way. Addition of another mole of Fe2(CO)9 to the
mixture and stirring for 24 h transformed 2a and 8a into 8b.
) 6.22 Hz); 217.99 (s, CdO). 31P{1H} NMR (C6D6): δ 82.11
(s). FD-MS [m/z (%)]: 724 (M+, 100). IR (CDCl3): ν(CO) ) 2082,
2069, 2046, 1992, 1960. Anal. Calcd for C23H18Cr2FeO13P2: C
38.15; H 2.51. Found: C 37.91; H 2.47.

1,2-Diphosphetene Metal Complexes
Organometallics, Vol. 18, No. 10, 1999 2029
Ta ble 2. Exp er im en ta l Da ta for th e X-r a y Diffr a ction Stu d ies on 7a , 9c, a n d 10c
7a
9c
10c
a
empirical formula
molar mass
T, K
C
42H20Cr2D6O10P2
C23H18Cr2FeO13P2
724.16
200(2)
C23H18Cr2FeO13P2
724.16
200(2)
862.61
200(2)
cryst size, mm
cryst syst
space group
measured θ-range, deg
unit cell dimensions
a, Å
0.6 × 0.5 × 0.5
monoclinic
P21/n
0.6 × 0.4 × 0.1
0.4 × 0.2 × 0.15
othorhombic
Pbca
triclinic
P11
2.3-27.0
2.2-25.0
2.0-27.0
11.779(3)
22.671(5)
14.425(3)
90
91.27(2)
90
3851(2)
4
1.487
0.707
none
610
1744
9.671(1)
10.982(1)
15.592(2)
101.48(1)
96.15(1)
113.72(1)
1453.1(3)
2
14.613(7)
19.709(10)
20.598(9)
90
90
90
5932(5)
8
1.622
1.371
none
b, Å
c, Å
R, deg
â, deg
γ, deg
volume, Å3
Z
F
calc, g cm-3
1.655
abs coeff µ, mm-1
abs corr
1.400
delta F2 c
443
refined params
377
2912
F(000)
728
measured reflns
unique reflns
8232
6751
4487
1.275
0.0738
0.2277
0.599, -0.651
7409
6265
4457
1.042
0.0546
0.1542
0.731, -1.358
7850
6463
1599
0.587
0.0514
0.1040
0.419, -0.532
obsd reflnsb
goodness-of-fit on F2
R1a
wR2 (all data)
residual electron density e Å-3; max, min
a
b
The formula represents 7a ‚C6D6. [F0 > 4σ(F)]. c Program XABS2.33
Reaction mixtures, composed of equimolar amounts of Cr-
(CO)6 and 10a , which were treated in the same manner,
formed unseparable mixtures of 10a , 10b, and 10c. Data of
10b from such a mixture: 1H NMR (C6D6): δ 0.82 (s, 18 H,
t-Bu). 13C{1H} NMR (C6D6): δ 31.98 (pt, -C(CH3)3; 3J (P,C) )
4.97 Hz); 34.52 (dd, -C(CH3)3, 2J (P,C) ) 2.51 Hz, 2J (P,C) )
7.18 Hz); 112.21 (dd, C-ring, 1J (P,C) ) 25.20 Hz, 1J (P,C) )
were tied to those of the adjacent carbon atoms by a factor of
1.5. Suitable crystals for X-ray structure analyses were
obtained under the following conditions: 7a , NMR-sample in
C6D6, room temperature, yellow blocks; 9c, THF, -30 °C,
yellow plates; 10c, THF/Et2O 1:1, -30 °C, yellow blocks. The
experimental data for the X-ray diffraction studies on 7a , 9c,
and 10c are summarized in Table 2.
2
59.09 Hz); 212.44 (s, Fe-CO); 214.91 (d, Cr-COtrans, J (P,C)
2
) 12.35 Hz); 218,70 (d, Cr-COcis, J (P,C) ) 3.31 Hz). 31P{1H}
NMR (C6D6): δ 4.80 (s); 114.81 (s). FD-MS [m/z (%)]: 532 (M+,
100, isotopic pattern equals C18H18CrFeO8P2).
Ack n ow led gm en t. Financial support of the project
by the Deutsche Forschungsgemeinschaft, the DFG
Graduiertenkolleg “Phosphorchemie als Bindeglied ver-
schiedener chemischer Disziplinen” (Universita¨t Kai-
serslautern), and the Fonds der Chemischen Industrie
is gratefully acknowledged. We thank Prof. Dr. D.
Sellmann, Erlangen, for providing the X-ray facilities.
X-r a y Str u ctu r e Deter m in a tion s. The data of all struc-
tural investigations were collected on a Siemens P4 diffrac-
tometer with Mo KR radiation (λ ) 0.710 73 Å) and a graphite
monochromator using ω-scans. The structures were solved by
direct methods and refined by full-matrix least-squares meth-
ods (SHELXTL 5.03).32 Non hydrogen atoms were refined
anisotropically; the hydrogen atoms were taken from a differ-
ence Fourier calculation and were isotropically refined in the
case of 7a and 10c. In the case of 9c all hydrogen atoms were
geometrically positioned and allowed to ride on their corre-
sponding carbon atoms. Their isotropic thermal parameters
Su p p or tin g In for m a tion Ava ila ble: The complete set of
structural data for 7a , 9c, and 10c (description of the structure
determination, atomic coordinates, isotropic and anisotropic
thermal factors, bond angles, distances, and ORTEP plots).
This material is available free of charge via the Internet at
http://pubs.acs.org.
(32) SHELXTL 5.03 for Siemens Crystallographic Research Sys-
tems; Siemens Analytical X-Ray Instruments Inc.: Madison, WI, 1995.
(33) Parkin, S.; Moezzi, B.; Hoppe, H. J . Appl. Crystallogr. 1995,
28, 53.
OM980862X