Adducts of cyclotriphosphorus complexes: Synthesis, solid state structure and solution behaviour of the bis-adducts [{(triphos)Co}(P3){M(CO)5}2] [triphos=MeC(CH2PPh2)3; M=Cr, Mo, W]

Article abstract of DOI:10.1016/S0022-328X(99)00388-5

Treatment of [(triphos)CoP₃] (1) [triphos=1,1,1-tris(diphenylphosphinomethyl)ethane] which has a pseudotetrahedral core formed by three unsubstituted phosphorus atoms and one cobalt, with an excess of Group 6 pentacarbonyl moieties affords the compounds [{(triphos)Co}(μ₃,η^3:1:1-P₃){M(CO)₅}₂] [M=Cr (2), Mo (3), W (4)]. The notable features of the solid state structure of 4 are compared with those of the bischromium adduct 2. The variable temperature NMR data of the compounds are suggestive of three fluxional processes in solution which may be interpreted as {(triphos)Co} rotation about its C₃ axis, {M(CO)₅} scrambling over the P₃ cycle and a concerted motion of the two {M(CO)₅} fragments.

Full text of DOI:10.1016/S0022-328X(99)00388-5

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 593–594 (2000) 127–134
Adducts of cyclotriphosphorus complexes: synthesis, solid state
structure and solution behaviour of the bis-adducts
[{(triphos)Co}(P3){M(CO)5}2] [triphos=MeC(CH2PPh2)3; M=Cr,
Mo, W]
Massimo Di Vaira a, Markus P. Ehses a, Maurizio Peruzzini b, Piero Stoppioni a
a Dipartimento di Chimica, Uni6ersita` di Firenze, 6ia Maragliano 77, I-50144 Florence, Italy
b I.S.S.E.C.C., C.N.R., 6ia J. Nardi 39, I-50132 Florence, Italy
Received 26 May 1999; accepted 29 June 1999
Abstract
Treatment of [(triphos)CoP3] (1) [triphos=1,1,1-tris(diphenylphosphinomethyl)ethane] which has a pseudotetrahedral core
formed by three unsubstituted phosphorus atoms and one cobalt, with an excess of Group 6 pentacarbonyl moieties affords the
compounds [{(triphos)Co}(m3,h3:1:1-P3){M(CO)5}2] [M=Cr (2), Mo (3), W (4)]. The notable features of the solid state structure
of 4 are compared with those of the bischromium adduct 2. The variable temperature NMR data of the compounds are suggestive
of three fluxional processes in solution which may be interpreted as {(triphos)Co} rotation about its C3 axis, {M(CO)5}
scrambling over the P3 cycle and a concerted motion of the two {M(CO)5} fragments. © 2000 Elsevier Science S.A. All rights
reserved.
Keywords: Group 6 pentacarbonyl complexes; Unsubstituted phosphorus compounds; X-ray crystal structure; 31P-NMR spectroscopy
reagents having Lewis acidic properties. These reactions
yield compounds in which the added fragment is bound
in h3 [4], h2 [5] or h1 [2a,6] fashion to the P3 ring,
depending on its binding properties. The compounds
have been characterized in the solid state by X-ray
analysis while their behaviour in solution, which was
investigated by 31P-NMR, was considered to a lesser
extent. The scattered data have shown that the parent
compounds [(triphos)MP3] (M=Co (1), Rh, Ir) [2] and
[(triphos)MP3]BF4 (M=Ni, Pd, Pt) [3], as well as the
diamagnetic triple decker derivatives [{(triphos)-
M}(P3){M(triphos)}]+ (M=Ni, Rh, Pd) [4] are highly
fluxional at room temperature, which has been inter-
preted in terms of free rotation of the {(triphos)M}
moieties with respect to the cyclo-P3 unit. All com-
pounds formed by reaction of an unsaturated Lewis
acidic metal fragment over one edge of the P3 unit of
the mononuclear complexes also present equivalence of
the phosphorus atoms of the triphos ligand as well as of
those of the P3 unit at ambient temperature [5]. Al-
though a lower limit form in the NMR spectra of
1. Introduction
The field of coordinatively stabilized Pn fragments is
currently under intense investigation. In the last 25
years a large number of complexes containing a variety
of Pn ligands (n=1–14) have been synthesized and in
the main part have been characterized by X-ray struc-
ture analysis in the solid state as well as by 31P-NMR
spectroscopy in solution [1]. A series of neutral [2] and
cationic [3] compounds (1) have been described in
which the cyclic triatomic P3 ligand is bound to one
metal atom of the cobalt or of the nickel group which
in turn bears the tripodal tridentate 1,1,1-tris-
(diphenylphosphinomethyl)ethane (triphos) as coligand.
The unsubstituted phosphorus atoms are susceptible of
addition reactions of metal moieties or of organic
0022-328X/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(99)00388-5

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M. Di Vaira et al. / Journal of Organometallic Chemistry 593–594 (2000) 127–134
these compounds has never been reached, the results
point to the occurrence of a process(es) involving mi-
gration of the metal fragment(s) over the P3 unit which
may be accompanied by the above mentioned rotation
of the {(triphos)M} moiety. In contrast to the com-
plexes bearing metal fragments on the cyclo-P3 unit, the
compound [(triphos)Co(P3CH3)]BF4, which forms upon
interaction of 1 with Me3OBF4, does not exhibit flux-
ionality at the cyclo-P3 ligand [6c].
Although compounds presenting one organometallic
16 valence electron fragment bound per naked phos-
phorus atom have been described some time ago, their
behaviour in solution has not yet been considered
[2a,6a]. With the aim of obtaining information on the
dynamic process(es) we have synthesized compounds
which form upon the addition of two metal pentacar-
bonyls to 1 and investigated their behaviour in solution.
In this paper we report the synthesis and characteriza-
tion both in the solid state and in solution of the
adducts [{(triphos)Co}(P3){M(CO)5}2] [M=Cr (2), Mo
(3), W (4)]. The crystal structure of 4 has been deter-
mined by X-ray analysis and its features are compared
to those of the previously reported structure of the
dichromium adduct 2 [2a].
form tetranuclear complexes of formulae [{M%}(P3)-
{Cr(CO)5}3] (M%=Cp*(OC)2W [7], Cp*Ni [8]). It is
likely that the sterically demanding triphos ligand in 1
suppresses the formation of the tris-adducts; in fact,
only in the presence of the less sterically demanding 16
valence electron fragment {Mn(CO)2Cp} the tris-ad-
duct [{(triphos)Co}(P3){Mn(CO)2Cp}3] has been ob-
tained [6b].
The IR absorptions of the compounds in solution
(see Section 3.2) exhibit relative intensities and band
shapes that are similar to those of the phosphine com-
plexes [M(CO)5(PR3)] [e.g. M=W, R=Ph: 2072(m),
1980(w), 1938(vs), 1920(sh)]. Therefore the donor/ac-
ceptor properties of the naked phosphorus atoms in the
‘ligand’ {(triphos)CoP3} towards the present carbonyl
fragments may be regarded as comparable to those of a
variety of phosphines. The two pentacarbonyl groups
are non-independent as evidenced by the presence of
more bands than the four ones expected for the
[M(CO)5L] complexes. Especially for the A1 absorption
in the high wavenumber region (ca. 2070 cm−1) and for
the very intense E one (ca. 1950 cm−1) two separated
bands are well distinguishable, with the higher energy
one being slightly more intense.
2.2. X-ray crystal structure analysis of
[{(triphos)Co}(P3){W(CO)5}2] (4)
2. Results and discussion
2.1. Syntheses of compounds and infrared properties
The structure of the compound 4 consists of trimetal
molecules and interposed CH2Cl2 solvate molecules dis-
orderly arranged in proximity to inversion centres. The
overall arrangement within the molecule of the com-
pound (Table 1, Fig. 1) is substantially similar to that
reported for 2 [2a]. There are, however, differences
which may be traced to the different effects of steric
repulsion and should be ultimately due to the different
lengths of the WꢀP and the CrꢀP bonds. As far as the
Compounds 2, 3 and 4, which may be considered as
the bis-adducts of the Group 6 pentacarbonyl frag-
ments {M(CO)5} of the cyclo-P3 ligand in 1, are synthe-
sized by adding the solvent-stabilized 16 valence
electron fragment to the cobalt complex in THF. The
immediate colour change of the solution from yellow to
red upon addition of the metal pentacarbonyls indicates
that formation of adducts occurs immediately. By mon-
itoring the reaction (IR spectroscopy) it is observed
that the mono-adduct forms within minutes ending
subsequently in the final bis-adduct after ca. 4 h. After
chromatographic work-up the complexes are isolated in
moderate yields as orange to red crystalline solids,
which are moderately soluble in toluene and very solu-
ble in CH2Cl2 and THF. The solids, which may be
handled in the air for a short time, show decomposition
even under an inert atmosphere after a few weeks. With
a threefold excess of the parent compound 1 in THF
solution, the bis-adduct 2 commutates to the appropri-
ate mono-adduct within 7 h at r.t.; however, no detach-
ment reaction is observed with carbon monoxide. The
highest yield of the bis-adducts 2, 3 and 4 is obtained
by applying a large excess of the complexing reagent
[M(CO)5(THF)]. Remarkably, the organometallic P3
complexes [{Cp*(OC)2W}(P3)] and [{Cp*Ni}(P3)] under
similar conditions to those used in the present study
,
WꢀP bonds are concerned, their 2.554(7) A mean value
,
in 4 is slightly larger that the 2.516(2) A value found for
the WꢀP distance in the compound [W(CO)5(PMe3)] (5)
,
[9], but is much smaller than the 2.686(4) A value
Table 1
,
Selected
bond
lengths
(A)
and
angles
(°)
for
[{(triphos)Co}(P3){W(CO)5}2].0.5CH2Cl2 (4)
,
Bond lengths (A)
CoꢀP(1)
CoꢀP(2)
CoꢀP(3)
CoꢀP(4)
CoꢀP(5)
CoꢀP(6)
2.226(4)
2.199(4)
2.216(4)
2.280(4)
2.291(4)
2.350(4)
P(4)ꢀP(5)
P(4)ꢀP(6)
P(5)ꢀP(6)
W(1)ꢀP(4)
W(2)ꢀP(5)
2.137(5)
2.146(5)
2.152(5)
2.559(3)
2.549(4)
Bond angles (°)
CoꢀP(4)ꢀW(1)
P(5)ꢀP(4)ꢀW(1)
P(6)ꢀP(4)ꢀW(1)
161.1(2)
133.3(2)
130.1(2)
CoꢀP(5)ꢀW(2)
P(4)ꢀP(5)ꢀW(2)
P(6)ꢀP(5)ꢀW(2)
164.6(2)
130.9(2)
128.1(2)

M. Di Vaira et al. / Journal of Organometallic Chemistry 593–594 (2000) 127–134
129
Fig. 1. A view of the [{(triphos)Co}(P3){W(CO)5}2] molecule in the structure of 4, with 20% probability thermal ellipsoids. The phenyl rings are
identified by serial numbers for clarity.
exhibited by the more hindered [W(CO)5(PtBu3)] (6)
The attack of the two pentacarbonyl groups to two
phosphorus atoms of the CoP3 core has a small but
significant effect on its geometry. The CoꢀP bond
formed by the unsubstituted phosphorus atom of the P3
[10]. Compared to the CrꢀP distances in 2 the present
WꢀP distances are longer, in the mean, by 0.13 A. Such
,
a difference is within the (wide) range of those found
for distances formed by the two metals to phosphorus
in related compounds [11]. In both the compounds 4
and 2 the two pentacarbonyl groups are oriented about
their metal–phosphorus bonds in such a way as to
minimize their interactions (Fig. 1). The W···W 5.561(2)
,
ring in 4, CoꢀP(6)=2.350(4) A, is longer than the other
,
two CoꢀP(P3) bonds (2.285(8) A, mean) the former
value being definitely larger and the latter slightly
,
smaller than the unique 2.301(1) A value of the
CoꢀP(P3) bonds in the parent compound 1 [2a]. The
PꢀP distance between the two substituted phosphorus
,
,
A and Cr···Cr 5.588(7) A separations in the two com-
pounds are comparable and may correspond to the
closest possible approaches of the pentacarbonyl
groups in the present arrangement [e.g. there is an
,
atoms of the ring (P(4)ꢀP(5)=2.137(5) A) is slightly
shorter than the other two PꢀP distances, which aver-
,
age to 2.149(4) A. Although the significance of the last
comparison might be questioned, it should be noted
that similar trends in the geometry of the CoP3 core are
,
O(73)···O(83) 2.99(2) A contact in 4 and an O(8)···O(14)
,
3.09(2) A contact in 2]. However, in the case of the
,
found for 2, with (i) a 2.340(4) A CoꢀP distance formed
chromium derivative the double addition on the P3 unit
through shorter metal–phosphorus bonds is attained at
the expense of some strains, as revealed by a less
symmetrical mode of attack of the two pentacarbonyl
groups compared to 4. In particular, there is a larger
difference (8.2°) between the two CoꢀPꢀCr angles in 2
than between the CoꢀPꢀW angles (3.5°) in 4 and the
spread of the PꢀPꢀCr angles in 2 (14.8°) is larger than
that (5.2°) of the PꢀPꢀW angles in 4. Moreover, the
angles formed by the direction of the WꢀP bonds with
the normal to the plane of the P3 group are closer
together in 4, 47.3(1) and 50.4(1)°, than are the corre-
sponding angles, 46.3(1) and 53.7(1)°, formed by the
CrꢀP bonds in 2.
by the unsubstituted phosphorus atom, which is longer
than the other two CoꢀP(P3) distances (average 2.286
,
,
A) and (ii) with a 2.124(4) A bond length between the
,
substituted phosphorus atoms versus the 2.149(6) A
mean of the other two PꢀP bonds. The CoꢀP(triphos)
distances in 4 do not seem to be notably affected by the
addition to the P3 atoms, although the slightly shorter
bond formed by P(2), compared to the other two
CoꢀP(triphos) bonds (Table 1), might be caused by the
fact that the former lies almost trans to the longest
CoꢀP(P3) bond (P(2)ꢀCoꢀP(6)=156.1(1)°).
The geometry of the pentacarbonyl tungsten groups
is normal, with the WꢀC distances in the range 1.96–
,
2.04 A and all of the CꢀO distances in the range

130
M. Di Vaira et al. / Journal of Organometallic Chemistry 593–594 (2000) 127–134
,
,
1.13–1.16 A (except for C(72)ꢀO(72)= 1.22(2) A), in
agreement with the values found for the compounds 5
and 6. Neither in the structure of 4, nor in those of 5 or
6, is a clear effect of shortening of the WꢀC bond trans
to the phosphorus atom observed, whereas that type of
shortening is found in 2 as well as for the chromium
pentacarbonyl groups in some other compounds, where
it has been attributed to a trans influence between
groups competing for p bonding [12]. The largest
deviations from the idealized 180° angles at the W
and C atoms in the pentacarbonyl fragments [C(73)ꢀ
yielding slightly larger/smaller op values for the bonds
of the core which are found to be shorter/longer than
the other bonds of the same type. Such effects result
from a relatively complex balance of differences in both
bonding and antibonding interactions. However, it is
clear that donation of electron density from two P3
phosphorus atoms into the s-type LUMO’s of the
{W(CO)5} groups allows a small fraction of antibond-
ing interactions between those two P atoms to be
released. The PꢀW interaction appears to be essentially
of s type, with only a small p contribution.
W(1)ꢀC(74)=167.7(5)°,
O(73)ꢀC(73)ꢀW(1)=173.9-
(1.2)°, O(74)ꢀC(74)ꢀW(1)=173.6(1.3)°] are presented
by two carbonyls involved in short intramolecular con-
tacts, such as the above mentioned O(73)···O(83) con-
2.3. NMR properties
The 31P-NMR spectra of the three compounds under
investigation are very similar (Fig. 2, Table 2). At room
temperature they exhibit two well separated resonances,
one in the typical region for the triphos signals, the
second in the characteristic high field region for cyclo-
P3 atoms. The shift of the signal due to the triphos
coligand is substantially unchanged on going from the
chromium to the tungsten derivative, whereas the reso-
nances attributed to the P3 ligand show a significant
trend to higher field on moving down the periodic
table. The difference in the shifts is more pronounced
on going from chromium to molybdenum (Dl=43
,
tact and a O(74)···H(43) 2.52(2) A close approach. A
possible indication of the significance of the latter inter-
action, as well as of hindrances between bulky groups
in the molecule, may be provided by the fact that the
phenyl group (n. 4) carrying H(43) approaches copla-
narity with the plane through the triphos P atoms more
than any other phenyl group of the ligand.
Extended-Hu¨ckel (EH) calculations [13,14] on undis-
torted model systems have provided a pattern of over-
lap population (op) values in agreement with the
experimental geometries of the CoP3 core in 2 and 4,
Fig. 2. 31P{1H}-NMR spectra of [{(triphos)Co}(P3){W(CO)5}2] (4) at different temperatures (CD2Cl2, 81.02 MHz).

M. Di Vaira et al. / Journal of Organometallic Chemistry 593–594 (2000) 127–134
131
Table 2
31P-NMR data of the compounds [{(triphos)Co}(P3){M(CO)5}2] (M=Cr (2), Mo (3), W (4)) at different temperatures a
Temperature (K)
2
3
4
Triphos
31.0 (3P,s)
Cyclo-P3
Triphos
29.6 (3P,s)
Cyclo-P3
Triphos
Cyclo-P3
r.t.
−210 (3P,s,br)
−253.4 (3P,s)
29.6 (3P,s)
32 (1P,s,br)
−269.4 (3P,s)
201
33.3 (1P,s,br) −195.3 (2P,d,br,283)
29.8 (2P,s,br) −293.8 (1P,td,283,22)
34.0 (3P,m,br) −230.3 (2P,d,br,250)
−255.9 (2P,d,br,274)
−295.4 (1P,td,283,14) 28.4 (2P,s,br,) −300.2 (1P,td,277,19)
170
31.4 (br)
25.5 (br)
−193.7 (1P,tr,280)
−200.0 (1P,tr,283)
−297.2 (1P,tr,283)
31.4 (3P,m,br) −225.8 (1P,tr,290)
−238.0 (1P,tr,280)
32.1 (s,br)
30.5 (s,br)
26.1 (s,br)
−250.1 (1P,tr,265)
−261.8 (1P,tr,270)
−301.8 (1P,tr,275)
−298.0 (1P,tr,280)
a l (ppm); J (Hz); in CD2Cl2; br=broad, m=multiplet, s=singlet, d=doublet, tr=triplet, td=triplet of doublets.
ppm) than between the heavier congeners (Dl=16
ppm). The equivalence of the atoms within the two sets
of phosphorus donors is not in accord with the solid
state structures of 2 and 4, in which the atoms of both
sets fall into chemically different environments. These
findings point to a dynamic behaviour which equalizes
the different positions on the NMR time scale. Actu-
ally, on cooling the solutions down to ca. 200 K, the
singlet at higher field, after running through coales-
cence (Tc (K) 2, 265; 3, 220; 4, 250), transforms into a
broad doublet and a triplet with relatively narrow lines,
the latter additionally showing a doublet fine structure.
The relative chemical shifts and the integral ratios of
the A2B spin system allow the assignment of the lower
field doublet to the end-on coordinated P atoms. The
separation of the multiplets decreases drastically with
increasing atomic number (Dw (Hz) 2, 7980; 3, 5275; 4,
3590). On further cooling the solutions to ca. 170 K,
the doublet, after further coalescence (Tc (K) 2, 180; 3,
195; 4, 190), furnishes two triplets of similar chemical
shift; whereas the high field triplet remains substantially
unchanged (apart from line broadening due to the
increased viscosity of the solution). The three pseudo-
triplets of this ABC spin system have similar coupling
constants which are in the range of other unsymmetri-
cal cyclo-P3 ligands (e.g. [{M%}(P3){Mn(CO)2Cp}3]:
The 1H-NMR measurements qualitatively confirm
the trend observed in the phosphorus spectra (Table 3).
The three methylene groups of the triphos coligand at
room temperature give rise to one signal, which splits
into two broad peaks having an approximate integral
ratio of 1:2 at ca. 200 K; such splitting confirms the
existence of two different chemical environments for the
tripodal arms.
1
A full line shape analysis of the 31P-f and H-NMR
spectra could not be satisfactorily performed for the
high line broadening due to low homogenity, overlap of
signals and quadrupolar interactions (especially for the
phosphine 31P resonances).
The experimental data summarized above points to
the presence of several dynamic processes. The chemical
and magnetic equivalence of the P-triphos atoms may
be achieved by rotation of the {(triphos)Co} fragment
around its C3 symmetry axis. However, this process
cannot explain the equalization of the cyclo-P3 posi-
tions; hence, also the exchange of the two pentacar-
bonyl fragments between the three phosphorus
coordination sites has to be assumed. On lowering the
temperature to 200 K these two dynamic processes are
blocked as shown by the appearance of two signals
having a 1:2 integral ratio in both regions of the 31P
spectra. A fixed mutual arrangement of the triphos and
the P3 ligand at this temperature is confirmed by the
coupling (doublet fine structure) of the unsubstituted P
atom of cyclo-P3 with one of the phosphorus of
triphos-probably the trans configured one. The block-
ing of the rotation in the substituted triphosphorus
complexes in contrast to the free rotation in the parent
compound 1 may be due to sterical interactions of the
bulky (fixed) substituents at both ligands.
248Hz,
[{M%}(P3){Cr(CO)5}3]:
258Hz;
[M%=
Cp*(OC)2W] [7] and [(triphos)Co(P3CH3)]BF4: 362Hz
[6c]); such coupling constants are distinctly smaller than
those found in complexes containing the larger P5 cycle
bearing organometallic fragments (ca. 410–510 Hz)
[15]. In the low field region of the spectra, the single
resonance of the triphos P atoms at ca. 200 K splits
into two broad signals of 1:2 intensity ratio (Tc (K) 2,
230; 3, 200; 4, 230) which is in accord with two differ-
ent environments for the three phosphorus atoms of the
polyphosphine. Further variations in the shapes of the
signals appear below 200 K. Unfortunately, the line
widths do not allow detection of fine structure partly
because of the cobalt-quadrupolar broadening and
partly because of the low homogenity.
At 170 K the two h1 coordinated P atoms are no
longer equivalent. The small differences in the chemical
shifts may stem from different environments of the
{M(CO)5}-bearing P3 atoms. Orientations of the pen-
tacarbonyl fragments similar to those found in the solid
state structures of 2 and 4 (see Section 2.2) may be
responsible for their inequivalence at low temperature

132
M. Di Vaira et al. / Journal of Organometallic Chemistry 593–594 (2000) 127–134
in solution. A possible equalization process active be-
tween 170 and 200 K might consist in a concerted
rotation around the MꢀP axes (M=Cr, Mo, W).
In the present study a lower limit NMR spectrum has
been reached for the first time for addition products of
[(triphos)MP3]n+ complexes. Previously it has been ob-
served that all cationic compounds featuring one metal
fragment bound to two P atoms of the MP3 [5] core in
the solid state are fluxional at room temperature in
solution, exhibiting one 31P resonance for the triphos
and P3, respectively. The dynamic behaviour of these
compounds is not blocked even at the lowest tempera-
ture reached (ca. −90°C). Furthermore, such be-
haviour does not appear to be affected by the extent of
interaction between the metal fragment and the PꢀP
bond to which the addition occurs [5].
rocene derivatives [15]. Probably, the tetrahedral core
(MP3 or M2P2) allows this kind of fluxionality due to
the availability of appropriate sets of cluster orbitals.
To elucidate this mechanism, further studies are cur-
rently being carried out.
3. Experimental
3.1. General
All reactions and manipulations were performed un-
der an atmosphere of dry oxygen-free argon. THF was
freshly distilled from potassium; dichloromethane, hex-
ane and Al2O3 (neutral, act. I) for chromatography
were degassed and flushed with argon prior to use. The
IR spectra were recorded on a Perkin–Elmer Spectrum
BX spectrometer using a KBr cell. The 31P{1H}- and
1H-NMR spectra were measured on a Bruker AC 200
spectrometer at 81.02 MHz (200.13 MHz). 31P (1H)
positive chemical shifts are to high frequency relative to
85% H3PO4 as external standard (relative to TMS as
internal standard) at 0.0 ppm. Analytical data for car-
bon and hydrogen were obtained from the Microana-
lytical Laboratory of the Department of Chemistry.
The hexacarbonyl complexes were used as purchased
and [(triphos)CoP3] (1) was synthesized according to
the literature method [13].
Rotation of the cyclic three-membered ligand against
the metal-coligand moiety is well investigated and es-
tablished for substituted cyclo-propenyl complexes. Ex-
amples include the cobalt complex [{(OC)2(Me3P)-
Co}(cyclo-Ct3Bu3)] for which a rotation barrier of
DG"298=(56.791.0) kJ mol−1 has been found [16] and
[{(triphos)Pd}(cyclo-C3H3)]+ with a similar barrier of
5294 kJ mol−1 [17]. The blocking of the rotation of
cyclo-P3 in mononuclear complexes has never been
achieved pointing to a very low barrier which is ex-
pected in the range of those calculated for the hypothet-
ical [{(OC)3Fe}(cyclo-C3H3)]− [18] and [{(OC)3Co}-
(cyclo-C3H3)] [19] (24 kJ mol−1 and 28 kJ mol−1
,
respectively) complexes. Only when strongly sterically
demanding groups are introduced does it seem to in-
crease the barrier sufficiently as to allow freezing of the
process on the NMR time scale [7].
The exchange of coordinating metal fragments be-
tween different positions of end-on coordinated P
atoms has scarcely been documented. In the diphospho-
rus complex [{Cp*(OC)2W}2(m3,h2:2:1-P2){W(CO)5}]
(WꢀW) [1] a barrier of ca. 50 kJ mol−1 has been
estimated for the process which equilibrates the two P
atoms [20]. In contrast to the P3 and P2 complexes
mentioned here, no fluxional behaviour is reported
along the P5 perimeter of substituted pentaphosphafer-
3.2. Syntheses of [{(triphos)Co}(P3){M(CO)5}2]
(M=Cr (2), Mo (3), W (4))
To
[(triphos)CoP3] (1) in 30 ml THF is added at r.t. under
stirring the appropriate solvent stabilized
a yellow solution of 0.10 g (0.13 mmol)
[M(CO)5(THF)] complex in THF (freshly prepared via
r.t. photolysis in a pyrex Schlenk tube {[Cr(CO)6]: 25,
[Mo(CO)6]: 30, [W(CO)6]: 15 min.} of the hexacarbonyl
(ca. 0.50 mmol in ca. 50 ml of THF)). The colour of the
solution immediately changed to red. After about 4 h
the reaction is completed (IR monitoring). The solvent
is removed in a stream of inert gas and the residue
Table 3
1H-NMR data of the compounds [{(triphos)Co}(P3){M(CO)5}2] (M=Cr (2), Mo (3), W (4)) at different temperatures a
Temperature
(K)
2
3
4
Phenyl
CH2
CH3
Phenyl
CH2
CH3
Phenyl
CH2
CH3
r.t.
7.0–7.5
(30H,m,br)
2.36 (6H,br) 1.51 (3H,br) 6.9–7.8
(30H,m,br)
2.33 (6H,br) 1.45 (3H,br) 7.0–7.5
(30H,m,br)
2.37 (6H,br) 1.53 (3H,br)
201
6.6–7.6
(30H,m,br)
2.41 (4H,br) 1.43 (3H,br) 6.8–7.9
(30H,m,br)
2.10 (2H,br)
2.35 (4H,br) 1.45 (3H,br) 6.5–7.6
(30H,m,br)
2.21 (2H,br)
2.42 (4H,br) 1.46 (3H,br)
2.07 (2H,br)
a l (ppm); in CD2Cl2; br=broad.

M. Di Vaira et al. / Journal of Organometallic Chemistry 593–594 (2000) 127–134
133
Table 4
resolved in a small amount of CH2Cl2 (ca. 3 ml) and
transferred onto a column (water-cooled; 1×20 cm;
Al2O3, in n-hexane). The products were eluted with 2/1
hexane/CH2Cl2 as red bands, giving red crystalline
solids on evaporating the solvents. They may be recrys-
tallized from hexane/CH2Cl2 by reducing the volume of
the solution in a light stream of inert gas. Yields: 59%
(2); 31% (3); 49% (4). Anal. Calc.: for C51H39CoCr2-
O10P6 (2): C: 52.77; H: 3.39. Found: C: 53.83; H: 3.80.
Anal. Calc. for C51H39CoMo2O10P6 (3): C: 49.06; H:
3.15. Found: C: 49.22; H: 3.58. Anal. Calc. for
C51.5H40ClCoO10P6W2 (4) 0.5 CH2Cl2: C: 42.17; H:
2.75. Found: C: 42.25; H: 2.84.
Crystallographic data for [{(triphos)Co}(P3){W(CO)5}2]·0.5CH2Cl2
(4)
Formula
M
Crystal system
Space group
C51.5H40ClCoO10P6W2
1466.73
Triclinic
(
P1 (No. 2)
,
a(A)
11.185(3)
12.302(8)
22.008(5)
75.71(4)
81.59(2)
69.40(4)
2741(2)
2
,
b(A)
,
c(A)
h (°)
i (°)
k (°)
3
,
U(A )
Z
IR (w (cm−1); CH2Cl2): 2, 2065(m), 2056(m), 1988(w),
1950(vs), 1929(vs), 1915(sh); 3, 2074(m), 2068(m),
1995(w), 1955(vs), 1936(vs), 1917(sh); 4, 2073(m),
2066(m), 1986(w), 1948(vs), 1926(vs), 1911(sh).
Dcalc (g cm−3
)
1.777
0.03×0.17×0.70
4.76
Crystal size (mm)
v (mm−1
)
,
Radiation
Data collected
Scan type
2q range (°)
MoꢀKa (u=0.71069 A)
9h,9k,+l
ꢀ−2q
5–46
4. X-ray data collection, structure determination and
refinement
Reflections collected
Unique reflections
Unique observed reflections,
with I\2|(I)
7401
7120
4986
X-ray diffraction data were collected for the CH2Cl2
solvate of 4 at r.t. with an Enraf–Nonius CAD4 dif-
fractometer using MoꢀKa radiation. Crystal data and
details about data collection and structure refinement
are given in Table 4. Unit-cell parameters were ob-
tained from the settings of 25 reflections with 13BqB
15°. No crystal decay was observed during data
collection. An empirical correction for absorption was
applied („ scans, min/max transmission factors 0.554/
0.999). The main programs used in the crystallographic
calculations are listed in Refs. [21–24].
The structure was solved by direct and heavy-atom
methods, with SIR [21] and SHELXL 93 [22], and was
refined by full-matrix least-squares on F2o. In addition
to one molecule of the compound the asymmetric unit
contains half of a dichloromethane solvate molecule,
since there is one such molecule in the triclinic cell,
disorderly arranged about an inversion centre. In the
final refinement cycles all the non-hydrogen atoms,
including the fractional atoms of the solvent, were
assigned anisotropic temperature factors (with re-
straints for the solvent). Hydrogen atoms were in calcu-
Absorption correction
No. of parameters
R1 (observed reflections)
R1 (all unique reflections)
wR2
„ scan method
655
0.051
0.093
0.117
Goodness of fit
1.036
1.08, −0.87
Largest features (max, min)
−3
,
in final DF map (e A
)
free of charge from: The Director, CCDC, 12 Union
Road, Cambridge CB2 1EZ UK (Fax. +44(1223)
336033 or e-mail: deposit@ccdc.cam.ac.uk, www: http:/
/www.ccdc.cam.ac.uk).
Acknowledgements
We acknowledge financial support by the Italian
Ministero dell’Universita` e della Ricerca Scientifica e
Tecnologica. The work has been enabled by support
with a post-doctoral grant (M.P.E.) of the ‘Gemeinsa-
men Hochschulsonderprogramm III von Bund und
La¨ndern’ by the DAAD (German Academic Exchange
Service). This work was supported by the European
Commission (INCO ERB-IC15CT960746).
lated positions, riding on the carrier atoms, with
eq
C,
UH=1.2U (methyls were treated as rigid groups with
UH=1.5UeCq). Soft restraints were imposed on the CꢀC
distances of the phenyl groups as well as on the geome-
try of the solvent molecule.
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121764. Copies of this information may be obtained

134
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