Phosphonio-benzophospholide zwitterions as bridging 8e-donor ligands: Synthetic and mechanistic studies

Article abstract of DOI:10.1002/zaac.200400393

Reactions of the phosphonio-benzophospholide π-complexes 3a,b[Cr] with [M(CO)₅(olefin)] or of the σ-complexes 2a,b(M] (M = Cr, Mo, W) with [M(CO)₃(aren)] lead to the first binuclear complexes 4a,b[CrM] featuring phosphonoio-benzophospholides as μ-bridging 8e-donor ligands to two group 6 metal atoms. The constitution of the products was determined by spectroscopic and X-ray diffraction studies. Mixed complexes with both group 6 and 7 metals were not accessible. Mechanistic studies showed that the reactions follow a complicated mechanism whose single steps may involve transfer of either M(CO)_n fragments or single CO ligands between complexes; the latter are associated with a σ/π-coordination isomerization of the benzophospholide unit. Competition between both reaction channels can lead to the formation of product mixtures whose composition is controlled by the relative thermodynamic stabilities of the products. Computational studies suggest that in the more stable isomer of heterobimetallic complexes 4a,b[MM′] end-on coordination to the heavier and side-on coordination to the lighter metal atom is preferred.

Full text of DOI:10.1002/zaac.200400393

Phosphonio-benzophospholide Zwitterions as Bridging 8e-Donor Ligands:
Synthetic and Mechanistic Studies
a
b
c
a
d
´
´
´
´
Istvan Bakk , Dietrich Gudat*, Stefan Häp , Martin Nieger , Laszlo Nyulaszi , and Laszlo Szarvas
Stuttgart, Institut für Anorganische Chemie der Universität
Received September 1st, 2004.
Dedicated to Professor Manfred Meisel on the Occasion of his 65th Birthday
Abstract. Reactions of the phosphonio-benzophospholide π-com-
plexes 3a,b[Cr] with [M(CO)5(olefin)] or of the σ-complexes
2a,b[M] (M ϭ Cr, Mo, W) with [M(CO)3(aren)] lead to the first
binuclear complexes 4a,b[CrM] featuring phosphonoio-benzophos-
pholides as µ-bridging 8e-donor ligands to two group 6 metal
atoms. The constitution of the products was determined by spectro-
scopic and X-ray diffraction studies. Mixed complexes with both
group 6 and 7 metals were not accessible. Mechanistic studies
showed that the reactions follow a complicated mechanism whose
single steps may involve transfer of either M(CO)n fragments or
single CO ligands between complexes; the latter are associated with
a σ/π-coordination isomerization of the benzophospholide unit.
Competition between both reaction channels can lead to the for-
mation of product mixtures whose composition is controlled by the
relative thermodynamic stabilities of the products. Computational
studies suggest that in the more stable isomer of heterobimetallic
complexes 4a,b[MMЈ] end-on coordination to the heavier and side-
on coordination to the lighter metal atom is preferred.
Keywords: Phosphorus heterocycles; Benzophospholides; Binuclear
complexes; Bridging ligands; Reaction mechanisms
Phosphonio-Benzophospholid-Zwitterionen als verbrückende 8e-Donorliganden:
Synthetische und mechanistische Untersuchungen
Inhaltsübersicht. Reaktionen der Phosphonio-Benzophospholid-π-
Komplexe 3a,b[Cr] mit [M(CO)5(olefin)] oder der σ-Komplexe
2a,b[M] (M ϭ Cr, Mo, W) mit [M(CO)3(aren)] führten zu den er-
sten binuklearen Komplexen 4a,b[CrM], in denen Phosphonio-Ben-
zophospholide als µ-verbrückende 8e-Donorliganden gegenüber
zwei Metallatomen der Gruppe 6 auftreten. Die Konstitution der
Produkte wurde durch spektroskopische Untersuchungen und
Röntgenstrukturanalysen bestimmt. Gemischte Komplexe mit
Metallatomen der Gruppen 6 und 7 wurden nicht erhalten. Mecha-
nistische Studien legten nahe, dass die Reaktionen einem komple-
xen Mechanismus folgen, dessen einzelne Schritte unter Übertra-
gung entweder eines M(CO)n-Fragments oder einzelner CO-Ligan-
den zwischen Komplexen verlaufen; bei letzteren erfolgt gleichzeitig
eine σ/π-Koordinationsisomerisierung der Benzophospholidein-
heit. Konkurrenz zwischen beiden Reaktionskanälen kann zur Bil-
dung von Produktmischungen führen, deren Zusammensetzung
durch die relativen thermodynamischen Stabilitäten der einzelnen
Produkte bestimmt wird. Computerchemische Untersuchungen le-
gen nahe, dass im stabileren Isomer heterobimetallischer Komplexe
4a,b[MMЈ] end-on Koordination an das schwerere und side-on-
Koordination an das leichtere Metallatom bevorzugt wird.
Introduction
plexes resemble π-complexes of genuine phospholyl anions
and the “end-on” complexes σ-complexes of phosphinins
[3]. As both types of benzophospholide complexes still exhi-
bit a free coordination site, they may themselves act as li-
gands [3] and support the formation of binuclear com-
plexes. As first examples of such specimen we have recently
reported on the formation of homobinuclear Mn- and Re-
compounds (C1, C2); here, each zwitterion acts as µ-bridg-
ing 4e-donor ligand that binds to one metal atom via the
phosphorus lone-pair and to the second one via the π-elec-
trons of a single PC bond in the phosphole ring [4]. In this
work we report on studies directed at the synthesis of
homo- and hetero-binuclear complexes in which the full 8e-
donating capacity of phosphonio-benzophospholides is ex-
ploited. In addition to the synthetic investigations, we will
discuss the results of mechanistic studies which suggested
that the formation of the target complexes via a deceptively
We have recently shown that zwitterionic phosphonio-sub-
stituted benzo[c]phospholides are ambiphilic ligands and
may bind to transition metal atoms “end on” via the phos-
phorus lone-pair (A, Scheme 1) or “side-on” via the π-elec-
trons of the phosphole ring (B) [1, 2]. The “side-on” com-
* Prof. Dr. Dietrich Gudat
Institut für Anorganische Chemie der Universität Stuttgart
Pfaffenwaldring 55
D-70550 Stuttgart
Fax: ϩ49 (0)711 685 4241
E-mail: gudat@iac.uni-stuttgart.de
a Technical University of Budapest, Budapest
b current address: Siegwerke GmbH, St. Augustin
c Institut für Anorganische Chemie der Universität Bonn
d current address: BASF AG, Ludwigshafen
Z. Anorg. Allg. Chem. 2005, 631, 47Ϫ54
DOI: 10.1002/zaac.200400393
© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim
47

I. Bakk, D. Gudat, S. Häp, M. Nieger, L. Nyulaszi, L. Szarvas
[Cr(CO)5(coe)]. Although attempts to isolate any of the
products failed, four components were identified by com-
parison of their spectral data with those of authentic
samples as the mononuclear complexes 2a[Cr], 2a[Mo] (pre-
pared by analogy to 2a[Cr] from 1a and [Mo(CO)5(coe)]),
3a[Cr], and the binuclear complex 4a[Cr2]. The remaining
species (which could not be independently prepared) was
tentatively assigned as the hetero-binuclear complex
4a[Cr,Mo].
The unspecific outcome of the reactions of the π-com-
plexes 3a[M] with [MЈ(CO)5(coe)]) (M, MЈ ϭ Cr, Mo)
prompted us to study the possibility of transferring a 12e-
W(CO)3-fragment from [W(CO)3(tol)] to the σ-complex
2a[Cr] as alternative access to a mixed binuclear complex.
The reaction afforded indeed a single product which was,
however, identified as the same complex 4a[Cr,W] as had
been obtained from 3a[Cr] and [W(CO)5(coe)], and not the
expected isomer [W(CO)3(µ-{η5:W,η1:Cr}-1a)Cr(CO)5].
The formal change of place of the two metal atoms sug-
gested that the reaction involved a more complicated
mechanism than a simple ligand substitution. This was veri-
fied by 31P NMR studies which allowed to detect several
intermediates. Comparison of the change in relative product
ratios with time disclosed that the starting complex 2a[Cr]
reacted during the initial stages predominantly via formal
loss of two CO-ligands to give the π-complex 3a[Cr]. Both
species then decayed at the expense of the homo-binuclear
complex 4a[Cr2] and the tungsten σ-complex 2a[W], until
finally all intermediates were converted into 4a[Cr,W].
Scheme 1 Dinuclear complexes with µ-bridging phosphonio-phos-
pholide as 4e-donor ligands (M ϭ Mn, Re).
simple ligand substitution may in fact involve more compli-
cated reaction pathways.
Scheme 2 Molecular constitution of mono- and binuclear com-
plexes of phosphonio-phospholides with group 6/7 metal carbonyl
fragments. R ϭ Ph (2a ؊ 4a), Et (2b ؊ 4b). M ϭ Cr, Mo, W, Mnϩ
(for 3a).
Attempts to prepare heterobimetallic complexes with
group 6/7 metals
Results and Discussion
Syntheses of homo- and heterobimetallic complexes
with group 6 metals
Considering that the free ligand 1a forms σ-complexes with
manganese carbonyls [4], we attempted as well the synthesis
of mixed Cr/Mn-complexes by reaction of the π-complex
3a[Cr] with [Mn(CO)5Br] in THF. Surprisingly, a 31P NMR
spectroscopic survey disclosed that no hetero-bimetallic
complex was formed but that quantitative conversion of the
starting material into the σ-complex 2a[Cr] had occurred.
Furthermore, the homo-bimetallic complex 4a[Cr2] was ob-
served as an intermediate in the initial phase of the reaction
and disappeared at the end. No further intermediates were
detected when the reaction was conducted at 0 °C.
A hypothesis to rationalize the formation of the σ-com-
plex 2a[Cr] is to consider a transfer of two CO ligands from
the manganese to the chromium carbonyl fragment, and
concomitant η5- to η1-coordination isomerization [2] of the
benzophospholide. As a possible source of the CO trans-
ferred, one can conceive formation of [Mn2Br2(CO)8] [5]
from Mn(CO)5Br with loss of one CO per Mn-atom and,
regarding that the chloride complex [Mn2Cl2(CO)8] is
known to loose two CO ligands in donating solvents to give
[Mn2Cl2(CO)6(solv)2] [6], finally the formation of
[Mn2Br2(CO)6(THF)2] with loss of a second CO per Mn-
atom. IR spectra of the product mixture formed from
[Mn(CO)5Br] and 3a[Cr] displayed in the νCO region, be-
By analogy to the reaction of [Cr(CO)5(coe)] (coe ϭ cyclo-
octene) with triphenylphosphonio-benzo[c]phospholide 1a
to give 2a[Cr] [1], treatment of [Cr(CO)5(coe)] with the π-
complex 3a[Cr] afforded the binuclear species 4a[Cr2]
(Scheme 2) as the only spectroscopically detectable reaction
product. A similar sequence lead from the ligand 1b via the
π-complex 3b[Cr] to 4b[Cr2]. The binuclear complexes were
isolated as red crystalline solids that can be handled for
short times in air and are moderately thermally stable;
4b[Cr2] decomposes slowly in boiling benzene with loss of
the Cr(CO)5 unit to give 3b[Cr].
As an extension to the reactions just described, treatment
of 3a[Cr] with a complex [MЈ(CO)5(coe)] containing a dif-
ferent metal atom MЈ should allow selective access to het-
erobimetallic analogues of 4a[Cr2]. Whereas this proved
true for the reaction of 3a[Cr] with [W(CO)5(coe)] to give
4a[Cr,W], the analogous reaction with [Mo(CO)5(coe)] pro-
duced according to a 31P NMR spectroscopic assay at least
five different complexes with the ligand 1a. Quite surpris-
ingly, a mixture of identical composition was obtained when
the π-complex 3a[Mo] (prepared by analogy to 3a[Cr] from
1a and [Mo(CO)3(tol)]; tol ϭ toluene) was reacted with
48
© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim
zaac.wiley-vch.de
Z. Anorg. Allg. Chem. 2005, 631, 47Ϫ54

Phosphonio-benzophospholide Zwitterions
tively, and Ϫ110 < ∆δcoord < Ϫ135 for binuclear complexes;
coupling constants drop from approx. 90 Hz in the free li-
gands to 58 Ϫ 70 Hz in mononuclear complexes (without
clear differentiation between σ- and π-complexes) and some
50 Hz in binuclear complexes. The increasing coordination
shifts of σ-complexes with increasing atomic weight of the
metal atom [8] and the high shielding of the phosphorus
atoms in π-coordinated phosphole rings [3] reproduce
known trends. Although the large coordination shifts in
benzophospholide π-complexes can be related to popu-
lation of the ligand π*-orbital by MǞL back donation [7],
the qualitative arguments applied fail to give a satisfactory
explanation for the observed decrease in ∆δcoord upon at-
tachment of a second metal atom to the phosphorus atom
in a π-complex 3[M].
The IR spectra of the compounds under study display in
the carbonyl region patterns of three (2a[M], 3a,b[M]) or
five bands (4a,b[M2]), respectively. The assignment to νCO
modes of M(CO)5 and M(CO)3 moieties is given in Table
22). The bands in both subspectra of the binuclear com-
plexes 4[M2] display small but consistent blue-shifts as com-
pared to the mononuclear complexes 2a[M] and 3[M],
respectively. We interpret this effect in terms of a synergistic
enhancement of the π-acidity of the benzophospholide li-
gand which results from the larger drain in electron density
associated with LǞM charge transfer to two rather than
one metal fragment. It had been pointed out previously [1]
that the π-acceptor capacity of the phosphonio-benzophos-
pholide 1a in mononuclear η1(P)-complexes matches that
of PPh3 but is lower than those of trimethyl phosphite or
2,4,6-triphenylphosphinin, respectively.
Scheme 3 Binuclear complexes via Cr(CO)5 metathesis between σ-
and π-complexes.
side the bands of 2a[Cr], three absorptions (ν¯ ϭ 2046, 2011,
1981 cmϪ1; further bands in the 1960-1900 cmϪ1 region
would be hidden under the absorptions of 2a[Cr]) that are
close to the bands of an authentic sample of [Mn2Br2(CO)8]
(ν ϭ 2042, 2011, 1976 cmϪ1 in CH2Cl2) and literature data
¯
for [Mn2Cl2(CO)6(THF)2] (ν
ϭ
2034, 2020, 1960,
¯
1931 cmϪ1 [6]). Even if we interpret this finding as evidence
for the presence of a binuclear complex with a Mn2(CO)6
core, uncertainties such as the solvent dependence1) of the
spectrum of [Mn2Br2(CO)8] and the unavailability of refer-
ence data for [Mn2Br2(CO)6(THF)2] make a more concise
structural assignment unfeasible. The involvement of
[Mn2Br2(CO)8] as possible source of CO was further sub-
stantiated by its reaction with an equimolar amount of
3a[Cr] which afforded likewise a quantitative yield of
2a[Cr]; 31P NMR studies revealed the transient occurrence
of 4a[Cr2] and the cation 3a[Mn؉] (possibly with a BrϪ or
[Mn(CO)5]Ϫ counter ion).
Although CO transfer from [Mn(CO)5Br] explains the
conversion of 3a[Cr] into 2a[Cr], it cannot account for the
observation of the homo-binuclear complex 4a[Cr2]. The
formation of this species can be rationalized, however, by
metathesis of a Cr(CO)5 fragment between 2a[Cr] and
3a[Cr] to give 4a[Cr2] and free ligand 1a (Scheme 3). Con-
ducting the appropriate control experiment revealed that
the expected reaction indeed took place. Evaluation of rela-
tive signal intensities allowed to determine the equilibrium
constant at a temperature of 303 K as K ϭ 0.011(3), and
Crystal structure determinations
The crystals of the σ(P)-complexes 2a[Mo], 2a[W] (both
¯
space group P1) and the π-complex 3a[Mo] (space group
the free enthalpy as ∆G ϭ 3(1) kcal molϪ1 KϪ1
.
P21/n) are isotypic to those of the previously reported com-
pounds 2a[Cr] and 3a[Cr], respectively. Apart from devi-
ations in metal-ligand distances which reflect the different
size of the metal atoms, all bond distances and angles agree
within experimental error with the corresponding data for
2a[Cr] and 3a[Cr] [1]. The deviations between analogous
molecules affect in particular the MϪP distances in the σ-
Spectroscopic studies
The novel binuclear complexes 4a[Cr2], 4b[Cr2], 4a[CrW]
and the reference compounds 2a[Mo], 2a[W], and 3a[Mo]
were unequivocally characterized by an extensive body of
spectroscopic data (cf. experimental section). The most
interesting piece of information, at least from the point of
molecular structure elucidation, is the possibility to assign
the benzophospholide coordination mode from easily ac-
cessible solution 31P NMR data. As is evident from the data
in Table 1, different complex types differ clearly in the mag-
nitudes of the coordination shift (∆δcoord) of the ring phos-
˚
complexes 2a[M] (2.504(1) A for M ϭ W and 2.513(1) for
˚
M ϭ Mo vs. 2.376(1) A for M ϭ Cr [1]) and the distances
between the metal atom and the centroid of the π-bound
˚
phosphole ring in 3a[M] (2.064(4) A for M ϭ Mo vs.
˚
1.874(3) A for M ϭ Cr [1]).
The molecular structure of 4a[Cr2] (space group Pbca) is
shown in Figure 1. The crystals of 4b[Cr2] contain one sol-
vent molecule (THF) per formula unit and crystallize in a
2
phorus atom and the coupling constant JPP. In particular,
ranges of ∆δcoord are < Ϫ75 and > Ϫ140 for mononuclear
complexes with η1(P)- and η5(π)-bound ligands, respec-
2) The low number of visible frequencies for M(CO)5 fragments
owes to the fact that not all IR active fundamentals are resolved
whereas the observation of three bands for M(CO)3 fragments indi-
cates a perceptible perturbation of the local C3v symmetry by the
“unsymmetric” benzophospholide ligand.
1) As judged by the deviation of the spectrum of a CH2Cl2 solution
with respect to the reported literature data [5] which were obtained
in CHCl3.
Z. Anorg. Allg. Chem. 2005, 631, 47Ϫ54
zaac.wiley-vch.de
© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim
49

I. Bakk, D. Gudat, S. Häp, M. Nieger, L. Nyulaszi, L. Szarvas
Table 1 31P NMR data of mono- and binuclear complexes of phosphonio-benzophospholides (at 30 °C in THF)
Formula
P(ring)
PR3
δ31
Ref.
δ31
P
∆δcoord a)
P
2JPP /Hz
2a[Cr]
2a[Mo]
2a[W]
3a[Cr]
3b[Cr]
3a[Mo]
3a[Mn؉]c)
4a[Cr2]
4b[Cr2]
4a[CrMo]
4a[CrW]
[{η1(P)-1a}Cr(CO)5]
158.8
141.7
113.1
30.0
28.0
47.1
29.3
78.8
75.5
53.0
24.2
Ϫ30.0
Ϫ46.1
Ϫ74.7
14.1
14.3
13.7
21.5
24.0
19.6
27.0
17.7
24.2
67.4
69.3
67.4
66.1
61.0
69.9
57.8
51.5
47.0
48.0
49.6
[1]
[{η1(P)-1a}Mo(CO)5]
[{η1(P)-1a}W(CO)5]
b)
[{η5-1a}Cr(CO)3]
Ϫ157.8
Ϫ151.9
Ϫ140.7
Ϫ159.5
Ϫ110.0
Ϫ104.4
Ϫ135.8
Ϫ164.6
[1]
[{η5-1b}Cr(CO)3]
[{η5-1a}Mo(CO)3]
[{η5-1a}Mn(CO)3]ϩ
[4]
[{µ-η1(P):η5-1a}Cr(CO)5Cr(CO)3]
[{µ-η1(P):η5-1b}Cr(CO)5Cr(CO)3]
[{µ-η1(P):η5-1a}Mo(CO)5Cr(CO)3]
[{µ-η1(P):η5-1a}W(CO)5Cr(CO)3]
d)
17.6
b) 1
d) 1
a) ∆δcoord ϭ δ(complex) Ϫ δ(ligand);
J
WP
ϭ 232.4 Hz; c) [BF4]Ϫ salt in CD2Cl2;
J
WP
ϭ 263.2 Hz
Table 2 IR spectra (νCO-region) of mono- and binuclear complexes
of phosphonio-benzophospholides with group 6 metal atoms (in
CH2Cl2).
ν(CO)/cmϪ1
MЈ(CO)5
Ref.
M(CO)3
2a[Cr]
2a[Mo]
2a[W]
3a[Cr]
3b[Cr]
3a[Mo]
4a[Cr2]
4b[Cr2]
M ϭ -, MЈ ϭ Cr
M ϭ -, MЈ ϭ Mo
M ϭ -, MЈ ϭ W
M ϭ Cr, MЈ ϭ -
M ϭ Cr, MЈ ϭ -
M ϭ Mo, MЈ ϭ -
2064, 1942, 1913 [1]
2073, 1948, 1918
2071, 1940, 1912
[1]
1925, 1835, 1826
1924, 1839, 1821
1929, 1838, 1826
M ϭ Cr, MЈ ϭ Cr 1932, 1857, 1844 2071, 1954
M ϭ Cr, MЈ ϭ Cr 1932, 1857, 1834 2071, 1953
4a[CrW] M ϭ Cr, MЈ ϭ W 1938, 1857, 1843 2078, 1951
¯
different space group (P1) but the molecular structure is
quite similar and is not displayed3). A listing of important
bond distances and angles for both compounds is given in
Table 3.
The presence of different phosphonio groups in 4a,b[Cr2]
leaves the remaining part of the molecules untouched and
all bond lengths in the benzophospholide core and both
metal carbonyl moieties are identical within experimental
error. The intra-ligand bonds are further indistinguishable
from those in mononuclear 3a[Cr] [1], suggesting a similar
extent of bond-lengthening in the phosphole ring by π-in-
teraction with the M(CO)3 fragment in all three com-
pounds. A slant of the P1-Cr1 bond out of the mean plane
of the phosphole ring induces a weak pyramidalization
(sum of angles 355.5(3)°) at P1) in 4a[Cr2] which is absent
in 4b[Cr2] (sum of angles 359.5(3)°) and is without doubt
attributable to steric interference between the Cr(CO)5 and
Fig. 1 Molecular structure of 4a[Cr2]. Thermal ellipsoids are drawn
at 50 % probability level, and H atoms have been omitted for clar-
ity. Selected bond lengths and angles are given in Table 3.
tively. This observation allows certainly to rule out mutual
steric interference between the two metal carbonyl moieties.
It may further, in connection with the blue-shift of νCO
bands in 4a,b[Cr2], be interpreted as evidence for a strength-
ening of the metal-ligand bond by increased MǞL back
donation; however, conceding that the effect is very small,
one should be careful as to avoid over-interpretation.
˚
Ph3P fragments. Both the P1-Cr1 (2.347(1), 2.352(1) A) and
Mechanistic considerations and computational studies
˚
Cr2-Ar distances (1.832(2), 1.839(5) A) in 4a,b[Cr2] are
shorter than in the mononuclear complexes 2a[Cr] (P1-Cr1
2.3760(5) A [1]) and 3a[Cr] (Cr2-Ar 1.877(1) A [1]), respec-
The outcome of all reactions of phosphonio-benzophos-
pholide complexes described in this work can be rational-
ized by a common mechanism involving sequences of two
competing elementary steps, viz. transfer of intact M(CO)n
fragments, or transfer of single CO ligands accompanied by
σ/π-coordination isomerisation of the phosphonio-benzo-
phospholide ligand. The formation of 4a[CrW] from 2a[Cr]
and [W(CO)3(tol)] is thus readily explained by a sequence
˚
˚
3) A preliminary single crystal X-ray diffraction study of 4a[CrW]
confirmed the postulated structure with a W(CO)5 and a Cr(CO)3
unit and similar features as for the dichromium complexes. As suc-
cessful refinement failed due to problems with modelling the dis-
order of two solvent molecules, the data are not discussed further.
50
© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim
zaac.wiley-vch.de
Z. Anorg. Allg. Chem. 2005, 631, 47Ϫ54

Phosphonio-benzophospholide Zwitterions
˚
Table 3 Selected bond distances (in A) and angles (in °) for the
In order to cut down the cost of the computations, the
ligand 1a used in the experimental studies was modeled by
the PH3-substituted compound 1c. All reaction energies
were computed at the B3LYP/3-21g* level and are given in
Scheme 5. The computation of ∆E3 with M ϭ MЈ ϭ Cr
was repeated at higher computational levels and also the
Gibbs energy for this reaction was calculated, to give ∆G°
values (at 293 K) of Ϫ0.5, 0.7, and 1.2 kcal molϪ1 KϪ1 at
the B3LYP/3-21G*, B3LYP/LAN2DZP, and B3LYP/6-
311G* levels, respectively. All results are reasonably close
together and to the experimentally determined value of ∆G
for the corresponding reaction of 1a (vide supra) if one con-
siders that the computations were performed on model
compounds in the gas phase.
The computed values of ∆E3 are generally small, suggest-
ing that the attachment of two metal carbonyl fragments
to the same ligand does not introduce an exceedingly large
amount of steric strain. The trends in ∆E1,2 reveal further
a clear preference of the heavier metal for terminal and of
the lighter metal for side-on coordination which is more
pronounced for tungsten than for molybdenum. These find-
ings suggest that the observed formation of 4a[CrW] re-
flects indeed a higher stability relative to the other possible
isomer, and prompted us as well to assign the constitution
of the spectroscopically detectable, yet unisolable, complex
4a[CrMo] accordingly.
binuclear complexes 4a[Cr2] and 4b[Cr2]. The numbering scheme
for all three compounds is identical to the one used in Figure 1.
4a[Cr2]
4b[Cr2]
P1ϪC2
C2ϪC3
C3-C8
1.798(2)
1.461(2)
1.431(2)
1.425(2)
1.739(2)
1.761(2)
2.347(1)
1.884(2)
1.903(2)
1.909(2)
1.903(2)
1.909(2)
1.832(2)
1.827(2)
1.850(2)
1.838(2)
355.5(3)
1.801(4)
1.458(6)
1.442(6)
1.416(6)
1.728(4)
1.762(4)
2.352(1)
1.864(6)
1.908(6)
1.905(6)
1.896(5)
1.913(6)
1.839(5)
1.829(5)
1.819(5)
1.840(6)
359.5(3)
C8-C9
P1ϪC9
P2ϪC2
P1-Cr1
Cr1ϪC1A
Cr1-C1B
Cr1-C1C
Cr1-C1D
Cr1-C1E
a)
Cr2-Ar
Cr2-C2A
Cr2-C2B
Cr2-C2C
Σangles(P1)
a) Ar ϭ Centroid of the phosphole ring
(Scheme 4) involving as the first step the loss of two CO
ligands from 2a[Cr] to give 3a[Cr] and a tungsten complex
(presumably [W(CO)5(THF)], although this was not de-
tected spectroscopically). Reaction of this species with
3a[Cr] affords the final product 4a[CrW] whereas transfer
of a Cr(CO)5 moiety from unreacted 2a[Cr] to 3a[Cr] pro-
duces 4a[Cr2] and the free ligand 1a; the latter is immedi-
ately quenched by [W(CO)5(THF)] to yield 2a[W]. The final
conversion of all intermediates into 4a[CrW] requires that
the intermediate steps are reversible. The same sequence can
account as well for all products formed in the reactions of
3a[Cr] / [Mo(CO)5(coe)] or 3a[Mo] / [Cr(CO)5(coe)], respec-
tively, and the observation of the same product distribution
in both reactions further supports the idea of reversible re-
action steps. It is reasonable to assume that the same pro-
cesses may also occur during the deceptively simple “homo-
nuclear” reactions involving only complexes with like metal
atoms. Last, but not least, the involvement of CO transfer
and Cr(CO)5 exchange processes in the reaction of 3a[Cr]
with manganese complexes has already been mentioned.
Assuming reversible mutual transformations between
benzophospholide complexes suggests that the final prod-
ucts are formed under thermodynamic control. The failure
to obtain Mn-containing binuclear complexes with bridging
benzophospholides, and the transfer of CO ligands from
[Mn(CO)5Br] to 3a[Cr], may thus be assumed to reflect the
known low stabilities of Mn-P [4] and Mn-CO [9][10] σ-
bonds. Likewise, the observed formation of 4a[CrW] rather
than the anticipated product with π-coordinated W(CO)3
and η1(P)-bound Cr(CO)5 fragments from [W(CO)3(tol)]
and 2a[Cr] could point to a higher stability of the former
isomer. In order to evaluate a possible influence of the me-
tal atoms on the stabilities of isomeric binuclear complexes
we performed computational studies of the “intramolecu-
lar” and “intermolecular” ligand redistribution reactions
(1) Ϫ (3) shown in scheme 5.
Conclusions
It was demonstrated that treatment of mononuclear σ- or π-
complexes of phosphonio-benzophospholides with reagents
capable of transferring appropriate M(CO)n fragments gives
rise to binuclear complexes with two group 6 metals and µ-
{η5:M,η1:MЈ}-bridging benzophospholide units. Mechan-
istic studies revealed that many of these reactions cannot
be considered simple substitution processes but follow com-
plicated mechanisms whose elementary steps involve either
a transfer of intact M(CO)n fragments or, alternatively, a
transfer of single CO ligands and concomitant coordination
isomerization of the benzophospholide moiety. Compe-
tition between both types of elementary reactions may yield
product mixtures whose composition appears to be con-
trolled by the relative thermodynamic stabilities of the com-
ponents. As a consequence, unstable isomers or mixed bi-
nuclear complexes of group 6/7 metals remain inaccessible
and the isolation of pure products is in principle restricted
to cases where one exceedingly stable product is formed in
large excess.
The results obtained here suggest further that side reac-
tions via CO transfer and concomitant σ/π-isomerisation
may as well complicate other reactions of carbonyl com-
plexes of phosphonio-benzophospholide ligands (e.g. sub-
stitution or ligand redistribution with non-carbonyl com-
pounds) and may restrict the use of these compounds in
synthesis or catalysis. It can be envisaged that the mechan-
istic considerations presented here may also have import-
ance for studies of complexes of other types of ligands that
Z. Anorg. Allg. Chem. 2005, 631, 47Ϫ54
zaac.wiley-vch.de
© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim
51

I. Bakk, D. Gudat, S. Häp, M. Nieger, L. Nyulaszi, L. Szarvas
Scheme 4 Proposed mechanism for the reaction of the π-complexes 3a[Cr] with [W(CO)3(tol)].
Scheme 5 Computed energies (in kcal mol-1 at the B3LYP/3-21g* level) for ligand metathesis reactions. 1c denotes the parent 1-phos-
phonio-benzo[c]phospholide.
signs of chemical shifts denote shifts to lower frequencies, coupling
constants are given as absolute values; prefixes i-, o-, m-, p- denote
atoms of phenyl substituents and atoms in the benzophospholide
ring are denoted as C-4, 5-H, etc. MS: Kratos Concept 1H, Xe-
FAB, m-NBA matrix. IR spectra: Nicolet FT-IR Magna 550, NaCl
cells. Elemental analysis: Perkin-Elmer 2400CHSN/O Analyser.
Melting points were determined in sealed capillaries. IR and 31P
NMR data are listed in Tables 1 and 2, respectively.
are in principle capable to undergo σ/π-coordination iso-
merisation such as phosphinins or certain substituted pyri-
dine derivatives.
Experimental Section
General Remarks: All manipulations were carried out under dry
argon. Solvents were dried by standard procedures. NMR spectra:
Bruker DPX 300 (1H: 300.13 MHz, 31P 121.5 MHz, 13C:
75.3 MHz) in thf-D8 at 30 °C; chemical shifts referenced to ext.
TMS (1H, 13C), 85 % H3PO4 (Ξ ϭ 40.480747 MHz, 31P); positive
DFT calculations were carried out with the Gaussian 98 program
package [11]. The molecular structures were energy optimized at
the B3LYP/3-21G* level, using the experimental data available
52
© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim
zaac.wiley-vch.de
Z. Anorg. Allg. Chem. 2005, 631, 47Ϫ54

Phosphonio-benzophospholide Zwitterions
from X-ray diffraction studies as starting points. The reaction ener-
gies and free reaction enthalpies for reaction (2) in Scheme 5 were
recomputed at the B3LYP/3-21G*, B3LYP/LAN2DZP, and
B3LYP/6-311G* levels, respectively, using molecular structures
which were re-optimized at the same level of theory. The molecular
structures obtained from these computations are minima on the
potential energy surface (only positive eigenvalues of the Hessian
matrix).
portion of the crude product (120 mg, 0.24 mmol) and
[Cr(CO)5(coe)] (75 mg, 0.24 mmol) were then dissolved in THF
(30 ml) and stirred for 2 hours at room temperature. The reaction
mixture was concentrated to 5 ml and hexane (20 ml) was added.
The precipitate formed was filtered off and dried in vacuum.
Recrystallization from n-hexane/THF afforded 150 mg (91 %, with
respect to 3a[Cr]) of deep red crystals, mp. 208 °C (dec.).
1H NMR: δ ϭ 8.0Ϫ7.5 (m, 10 H, Ph), 7.21 (m, 1 H, 7-H), 6.98 (m, 1 H, 6-
2
H), 6.81 (m, 1 H, 5-H), 6.46 (m, 1 H, 4-H), 5.37 (dd, 1 H, JPH ϭ 35.0 Hz,
Complexes 2a[Cr] and 3a[Cr] were prepared as described earlier [1].
Complexes 2a[Mo], 2a[W], and 3a[Mo] were prepared by analogy
to the corresponding chromium complexes from 1a and
[M(CO)5(coe)] (M ϭ Mo, W) or [MoCO)3(toluene)], respectively.
4
4JPH ϭ 2.8 Hz, JHH ϭ 0.8 Hz, 3-H), 3.2 Ϫ 3.0 (m, 2H, CH2), 1.2 (dt, 3 H,
3
2
3JPH ϭ 19.7 Hz, JHH ϭ 7.5 Hz). Ϫ 236.6 (d, JPC ϭ 3.2 Hz, 4 CO), 215.5
(d, 2JPC ϭ 14.9 Hz, CO), 213.7 (s, 3 CO), 135.5 (s, p-C), 135.4 (s, p-C), 135.3
(d, JPC ϭ 9.8 Hz, o-C), 135.1 (d, JPC ϭ 9.8 Hz, o-C), 130.7 (d, JPC
2
2
3
ϭ
3
12.3 Hz, m-C), 129.3 (s, C-5/6), 126.1 (s, C-5/6), 124.0 (d, JPC ϭ 8.4 Hz, C-
4/7), 122.7 (d, 3JPC ϭ 2.9 Hz, 2.6 Hz, C-4/7), 121.2 (d, JPC ϭ 85.0 Hz, i-C),
1
2a[Mo]: yield 81 %, mp. 159 °C (dec.); Anal. for C31H20MoO5P2:
calcd. C 59.07 H 3.20 %; found: C 58.15 H 4.19 %.
1
n
121.0 (d, JPC ϭ 85.0 Hz, i-C), 114.9 (dd, JPC ϭ 6.8 Hz, 1.3 Hz, C-3a/7a),
112.0 (dd, JPC ϭ 13.3 Hz, 1.9 Hz, C-3a/7a), 87.1 (d, JPC ϭ 8.1 Hz, C-3),
n
1
2
4
1H NMR: δ ϭ 8.1 (dd, 1 H, JPH ϭ 36.9 Hz, JPH ϭ 5.9 Hz, 3-H), 7.89 Ϫ
7.58 (m, 15 H, Ph), 7.53 (m, 1 H, 6.5 Ϫ 6.6 (m, 2 H), 6.85 (m, 1 H, all 4-H
Ϫ 7-H). Ϫ
1
1
2
57.2 (dd, JPC ϭ 32.3 Hz, 94.4 Hz, C1), 23.1 (dd, JPC ϭ 59.8 Hz, JPC
ϭ
3.2 Hz, CH2), 7.5 (d, 2JPC ϭ 5.2 Hz, CH3). Ϫ MS (ϩ)-Xe-FAB, mNBA): m/
z(%): 674 (60) [Mϩ], 482 (55) [Mϩ-Cr(CO)5], 398 (100) [MϩϪCr, Ϫ8 CO].
2a[W]: yield 81 %, mp. 156 °C (dec.); Anal. for C31H20O5P2W:
calcd. C 51.84 H 2.81 %; found: C 50.92 H 3.46 %.
1H NMR: δ ϭ 8.4 (dd, 1 H, 2JPH ϭ 35.6 Hz, 4JPH ϭ 5.8 Hz, 3-H), 7.5 Ϫ 6.8
(m, 15 H, Ph), 7.7 (m, 1 H, 6.8 Ϫ 6.5 (m, 3 H, all 4-H Ϫ 7-H). Ϫ
Complex 4a[CrW]: Complex 3a[Cr] (100 mg, 0.19 mmol) and
[W(CO)5(coe)] (78 mg, 0.19 mmol) were reacted as described above
for 4a[Cr2]. Work-up yielded 180 mg (62 %) of a deep red crystal-
line solid, mp. 217 °C (dec.). Anal. for C34H20CrO8P2W: calcd. C
47.80 H 2.35 %; found: C 46.66 H 2.18 %.
3a[Mo]: yield 92 %, mp. 212 °C (dec.); Anal. for C29H20MoO3P2:
calcd. C 60.64 H 3.51 %; found: C 60.3 H 3.3 %.
1H NMR: δ ϭ 8.3 Ϫ 7.7 (m, 15 H, Ph), 7.0-7.2 (m, 2 H), 6.72 (m, 1 H), 6.32
2
4
(m, 1 H, all 4-H to 7-H), 5.39 (dd, 1 H, JPH ϭ 34.6 Hz, JPH ϭ 2.8 Hz, 3-
1H NMR: δ ϭ 8.0 Ϫ 7.6 (m, 15 H, Ph), 7.0 Ϫ 6.8 (m, 4 H, all 4-H Ϫ 7-H),
2
H). Ϫ 235.8 (s, 3 CO), 197.8 (s, 4 CO), 194.6 (d, JPC ϭ 8.0 Hz, CO), 144.7
(dm, JPC ϭ 12.9 Hz, C-3a/7a), 143.6 (dm, JPC ϭ 7.0 Hz, C-3a/7a), 135.2
(d, JPC ϭ 2.3 Hz, p-C), 135.2 (d, JPC ϭ 9.7 Hz, o-C), 130.1 (d, JPC
2
4
2
3
6.0 (dd, 1 H, JPH ϭ 39.4 Hz, JPH ϭ 3.8 Hz, 3-H). Ϫ
3
2
3
ϭ
1-Ethyldiphenylphosphonio-benzo[c]phospholide (1b) was pre-
pared by reduction of 1a with two equivalents of sodium naph-
thalenide (2 h in THF at ambient temperature) and quenching of
the resulting sodium 1-diphenylphosphino-benzophospholide with
excess ethyl iodide. Solid NaI was filtered off, the reaction mixture
concentrated in vacuum, and the product was precipitated by ad-
dition of hexane; yield 83 % after recrystallization from hexane;
mp. 201 °C.
1
3
12.6 Hz, m-C), 128.8 (dd, JPC ϭ 57.8 Hz, JPC ϭ 3.1 Hz, C-3), 128.0 (dm,
3JPC ϭ 8.8 Hz, C-4/7), 124.6 (s, C-5/6), 124.0 (s, C-5/6), 122.2 (dd, JPC
ϭ
1
3
n
89.8 Hz, JPC ϭ 1.0 Hz, i-C), 121.5 (dd, JPC ϭ 2.3 Hz, 2.6 Hz, C-4/7), 53.6
(dd, 1JPC ϭ 26.9 Hz, 97.6 Hz, C-1). Ϫ MS (ϩ)-Xe-FAB, mNBA): m/z (%) ϭ
854 (80) [Mϩ], 770 (65) [Mϩ], 714 (30) [MϩϪ5 CO], 662 (20) [MϩϪ8 CO,
ϪCr].
Reactions of phosphonio-benzophospholide complexes with metal car-
bonyl complexes. The appropriate reactants (approx. 0.1 mmol
each) were dissolved in 3 Ϫ 5 ml of THF. Part of the solution was
then transferred to an NMR tube and the progress of the reaction
monitored by 31P NMR spectroscopy.
2
4
1H NMR: δ ϭ 7.9 (dd, 1 H, JPH ϭ 42.8 Hz, JPH ϭ 6.4 Hz, 3-H), 7.8 -7.5
2
(m, 10 H, Ph-H), 7.6Ϫ6.5 (m, 4 H, 4-H to 7-H), 3.05 (dq, 2 H, JPH
12.7 Hz, JHH ϭ 7.5 Hz, CH2), 1.33 (dt, 3 H, JHH ϭ 7.5 Hz, CH3).
ϭ
3
3
Complex 4a[Cr2]. A mixture of 3a[Cr] (100 mg, 0.19 mmol) and
[Cr(CO)5(coe)] (60 mg, 0.20 mmol) were dissolved in THF (10 ml).
The resulting solution was stirred for 5 h at ambient temperature.
The solution was then concentrated in vacuum to 0.5 ml and hex-
ane (20 ml) was added. The dark red precipitate formed was filtered
off, washed with little hexane, and dried in vacuum to yield 130 mg
(yield 95 %) of product of mp. 219 °C. Anal. for C34H20Cr2O8P2:
calcd. C 56.52 H 2.79 %; found: C 56.95 H 3.06 %.
Crystal structure determinations
2a[Mo]: yellow crystals, C31H20MoO5P2, M ϭ 630.4, crystal size
¯
0.40 x 0.30 x 0.25 mm, triclinic, space group P1 (No. 2): a ϭ
˚
˚
˚
10.3519(2) A, b ϭ 11.1430(3) A, c ϭ 13.6726(4) A, Ͱ ϭ 110.688(2)°,
3
˚
β ϭ 93.005(2)°, γ ϭ 110.270(2)°, V ϭ 1356.3(1) A , Z ϭ 2,
ρ(calcd) ϭ 1.543 Mg mϪ3, F(000) ϭ 636, m ϭ 0.64 mmϪ1, 19783
reflections (2 θmax ϭ 56.6°) measured on a Nonius Kappa-CCD
1H NMR: δ ϭ 8.3 Ϫ 7.7 (m, 15 H, Ph), 7.66 (m, 1 H), 7.05 (m, 1H), 6.72
2
4
˚
(m, 1H), 6.36 (m, 1 H, 4-H to 7-H), 5.35 (dd, 1 H, JPH ϭ 34.3 Hz, JPH
ϭ
diffractometer at 123(2) K using MoKα radiation (λ ϭ 0.71073 A),
2.6 Hz, 3-H). Ϫ 13C{1H} NMR: δ ϭ 235.7 (d, JPC ϭ 3.1 Hz, 3 CO), 221.0
2
6394 unique [Rint ϭ 0.036] used for structure solution (Direct
Methods, SHELXS-97 [12]) and refinement (full-matrix least-
squares on F2, SHELXL-97 [12]) with 352 parameters, empirical
absorption correction from multiple reflections, H-atoms with a
riding model, R1 (I > 2σ(I)) ϭ 0.023, wR2 ϭ 0.056, largest diff.
(d, 2JPC ϭ 4.2 Hz, 1 CO), 214.5 (d, JPC ϭ 15.1 Hz, 4 CO), 135.2 (d, 2JPC
ϭ
2
4
1
9.9 Hz, o-C), 134.9 (d, JPC ϭ 2.9 Hz, p-C), 134.0 (dd, JPC ϭ 50.5 Hz,
3JPC ϭ 3.0 Hz, C-3), 130.2 (d, JPC ϭ 12.4 Hz, m-C), 128.0 (dd, JPC
ϭ
3
3
3
3
1.8 Hz, JPC ϭ 8.4 Hz, C-4/7), 125.8 (dd, JPC ϭ 0.9 Hz, 7.6 Hz, C-3a/7a),
124.0 (s, C-5/6), 124.7 (s, C-5/6), 123.0 (dd, JPC ϭ 2.5 Hz, 2.5 Hz, C-4/7),
122.2 (dd, JPC ϭ 89.7 Hz, JPC ϭ 1.1 Hz, i-C), 113.6 (dd, JPC ϭ 1.8 Hz,
n
1
3
2
Ϫ3
˚
peak and hole 0.337 and Ϫ0.586 e A
.
1
13.6 Hz, C-3a/7a), 57.2 (dd, JPC ϭ 35.7 Hz, 97.1 Hz, C-1). Ϫ MS (ϩ)-Xe-
FAB, mNBA): m/e(%) ϭ 722 (25) [Mϩ], 530 (60) [MϩϪCr(CO)5], 446 (100)
[MϩϪCr, Ϫ8 CO].
2a[W]: yellow crystals, C31H20O5P2W, M ϭ 718.3, crystal size 0.25
¯
x 0.20 x 0.10 mm, triclinic, space group P1 (No. 2): a ϭ
˚
˚
˚
Complex 4b[Cr2]. Ligand 1b (150 mg, 0.43 mmol) and [Cr(CO)3-
(napth)] (114 mg, 0.43 mmol) were stirred in 30 ml of THF for 12
hours at room temperature. The reaction mixture was then concen-
trated to approx. 5 ml and hexane (20 ml) was added. The precipi-
tate formed was filtered off and dried in vacuo. The product was
identified as the π-complex 3b[Cr] by 31P NMR spectroscopy. A
10.3356(4) A, b ϭ 11.1304(4) A, c ϭ 13.6737(4) A, Ͱ ϭ 110.692(2)°,
3
˚
β ϭ 93.051(2)°, γ ϭ 110.313(2)°, V ϭ 1352.0(1) A , Z ϭ 2,
ρ(calcd) ϭ 1.764 Mg mϪ3, F(000) ϭ 700, µ ϭ 4.43 mmϪ1, 11233
reflections (2 θmax ϭ 50.0°) measured on a Nonius Kappa-CCD
diffractometer at 123(2) K using MoKα radiation (λ ϭ 0.71073 A),
4715 unique [Rint ϭ 0.044] used for structure solution (Direct
˚
Z. Anorg. Allg. Chem. 2005, 631, 47Ϫ54
zaac.wiley-vch.de
© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim
53

I. Bakk, D. Gudat, S. Häp, M. Nieger, L. Nyulaszi, L. Szarvas
Methods, SHELXS-97 [12]) and refinement (full-matrix least-
squares on F2, SHELXL-97 [12]) with 352 parameters, empirical
absorption correction from multiple reflections, H-atoms with a
riding model, R1 (I > 2σ(I)) ϭ 0.023, wR2 ϭ 0.055, largest diff.
Cambridge DB2 1EZ, UK (Fax: int.codeϩ(1223)336-033; e-mail:-
teched@chemcrys.cam.ac.uk).
Acknowledgement. We thank Dr. Jörg Daniels, Universität Bonn,
for his help with the preliminary X-ray diffraction study of
4a[CrW] and the Deutsche Forschungsgemeinschaft for financial
support.
Ϫ3
˚
peak and hole 1.318 and Ϫ1.735 e A
.
3a[Mo]: yellow crystals, C29H20MoO3P2, M ϭ 574.3, crystal size
0.15 x 0.10 x 0.05 mm, monoclinic, space group P21/n (No. 14):
˚
˚
˚
a ϭ 8.6002(6) A, b ϭ 13.3527(12) A, c ϭ 21.3535(16) A, β ϭ
3
Ϫ3
˚
97.847(5)°, V ϭ 2429.2(3) A , Z ϭ 4, ρ(calcd) ϭ 1.570 Mg m
,
References
F(000) ϭ 1160, µ ϭ 0.70 mmϪ1, 11996 reflections (2 θmax ϭ 50.0°)
[1] D. Gudat, S. Häp, L. Szarvas, M. Nieger, Chem. Commun.
2000, 1637Ϫ1638.
measured on a Nonius Kappa-CCD diffractometer at 123(2) K
˚
using MoKα radiation (λ ϭ 0.71073 A), 4219 unique [Rint ϭ 0.067]
[2] Z. Bajko, J. Daniels, D. Gudat, S. Häp, M. Nieger, Organomet-
allics 2002, 21, 5182Ϫ5189.
used for structure solution (Patterson Methods, SHELXS-97 [12])
and refinement (full-matrix least-squares on F2, SHELXL-97 [12])
with 316 parameters, H-atoms with a riding model, R1 (I >
2σ(I)) ϭ 0.044, wR2 ϭ 0.089, largest diff. peak and hole 0.584 and
[3] F. Mathey, Coord. Chem. Rev. 1994, 137, 1Ϫ52; P. Le Floch,
F. Mathey, Coord. Chem. Rev., 1998, 178Ϫ180, 771Ϫ791; K.
B. Dillon, F. Mathey, J. F. Nixon, Phosphorus: The Carbon
Copy, John Wiley, Chichester, 1998 and references therein.
[4] D. Gudat, B. Lewall, M. Nieger, I. Detmer, L. Szarvas, P. Saar-
enketo, G. Marconi, Chem. Eur. J. 2003, 9, 661Ϫ670.
[5] E. W. Abel, G. Wilkinson, J. Org. Chem. 1958, 24, 1501Ϫ1505.
[6] M. C. Van Derveer, J. M. Burlitch, J. Organomet. Chem., 1980,
197, 357Ϫ368.
[7] D. Gudat, M. Nieger, K. Schmitz, L. Szarvas, Chem. Commun.
2002, 1820Ϫ1821.
[8] K. R. Dixon, in: Multinuclear NMR, J. Mason (Ed.), Plenum:
New York 1987, 369ff.
Ϫ3
˚
Ϫ0.373 e A
.
4a[Cr2]: colorless crystals, C34H20Cr2O8P2, M ϭ 722.5, crystal size
0.18 x 0.12 x 0.06 mm, orthorhombic, space group Pbca (No. 61):
˚
˚
˚
a ϭ 17.8340(3) A, b ϭ 15.7619(3) A, c ϭ 22.7827(3) A, V ϭ
6404.2(2) A , Z ϭ 8, ρ(calcd) ϭ 1.499 Mg mϪ3, F(000) ϭ 2928,
3
˚
µ ϭ 0.83 mmϪ1, 64905 reflections (2 θmax ϭ 56.6°) measured on a
Nonius Kappa-CCD diffractometer at 123(2) K using MoKα radi-
˚
ation (λ ϭ 0.71073 A), 7910 unique [Rint ϭ 0.049] used for structure
solution (Direct Methods, SHELXS-97 [12]) and refinement (full-
matrix least-squares on F2, SHELXL-97 [12]) with 415 parameters,
H-atoms with a riding model, R1 (I > 2σ(I)) ϭ 0.030, wR2 ϭ 0.077,
[9] P. M. Treichel, in: Comprehensive Organometallic Chemistry,
G. Wilkinson (Ed.), Pergamon: Oxford 1982, Vol 4, 26f.
[10] T. Ziegler, V. Tschinke, C. Ursenbach, J. Am. Chem. Soc. 1987,
109, 4825Ϫ4837.
Ϫ3
˚
largest diff. peak and hole 0.365 and Ϫ0.480 e A
.
4b[Cr2]: colorless crystals, C30H20Cr2O8P2 I thf, M ϭ 746.5, crystal
¯
size 0.30 x 0.12 x 0.04 mm, triclinic, space group P1 (No. 2): a ϭ
˚
˚
˚
11.2577(4) A, b ϭ 12.0239(4) A, c ϭ 13.0066(5) A, Ͱ ϭ 86.188(2)°,
[11] Gaussian 98 (Rev. A.7), M. J. Frisch, G. W. Trucks, H. B.
Schlegel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, V. G.
Zakrzewski, J. A. Montgomery, R. E. Stratmann, J. C. Burant,
S. Dapprich, J. M. Millam, A. D. Daniels, K. N. Kudin, M.
C. Strain, O. Farkas, J. Tomasi, V. Barone, M. Cossi, R.
Cammi, B. Mennucci, C. Pomelli, C. Adamo, S. Clifford, J.
Ochterski, G. A. Petersson, P. Y. Ayala, Q. Cui, K. Moro-
kuma, D. K. Malick, A. D. Rabuck, K. Raghavachari, J. B.
Foresman, J. Cioslowski, J. V. Ortiz, B. B. Stefanov, G. Liu,
A. Liashenko, P. Piskorz, I. Komaromi, R. Gomperts, R. L.
Martin, D. J. Fox, T. Keith, M. A. Al-Laham, C. Y. Peng, A.
Nanayakkara, C. Gonzalez, M. Challacombe, P. M. W. Gill,
B. G. Johnson, W. Chen, M. W. Wong, J. L. Andres, M. Head-
Gordon, E. S. Replogle and J. A. Pople, Gaussian, Inc., Pitts-
burgh PA, 1998.
3
˚
β ϭ 75.108(2)°, γ ϭ 83.558(2)°, V ϭ 1689.4(1) A , Z ϭ 2,
ρ(calcd) ϭ 1.467 Mg mϪ3, F(000) ϭ 764, µ ϭ 0.79 mmϪ1, 14140
reflections (2 θmax ϭ 50.0°) measured on a Nonius Kappa-CCD
˚
diffractometer at 123(2) K using MoKα radiation (λ ϭ 0.71073 A),
5881 unique [Rint ϭ 0.082] used for structure solution (Direct
Methods, SHELXS-97 [12]) and refinement (full-matrix least-
squares on F2, SHELXL-97 [12]) with 424 parameters and 36 re-
straints, empirical absorption correction from multiple reflections,
H-atoms with a riding model, R1 (I > 2σ(I)) ϭ 0.056, wR2 ϭ 0.134,
Ϫ3
˚
largest diff. peak and hole 0.972 and Ϫ0.692 e A
.
Crystallographic data (excluding structure factors) for the struc-
tures reported in this work have been deposited with the Cambridge
Crystallographic Data Centre as supplementary publication no.
CCDC-249089 (2a[Mo]), 249090 (2a[W]), 249091 (3a[Mo]), 249092
(4a[Cr2]), 249093 (4b[Cr2]). Copies of the data can be obtained free
of charge on application to The Director, CCDC, 12 Union Road,
[12] (a) G. M. Sheldrick, Acta Crystallogr. 1990, A46, 467Ϫ473;
(b) G. M. Sheldrick, Univ. Göttingen 1997.
54
© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim
zaac.wiley-vch.de
Z. Anorg. Allg. Chem. 2005, 631, 47Ϫ54