[60]Fullerene displacement from fac-(dihapto-[60]fullerene)(dihapto-1,2- bis-(1,10-phenanthroline) tricarbonyl tungsten(0)

Article abstract of DOI:10.1016/S0020-1693(03)00494-8

The Lewis bases triphenyl phosphine and tricyclohexyl phosphine (L) displace [60]fullerene (C₆₀) from fac-(η²-C ₆₀)(η²-phen)W(CO)₃ (phen=1,10- phenanthroline) to produce fac-(η²-phen)(η

Full text of DOI:10.1016/S0020-1693(03)00494-8

Inorganica Chimica Acta 357 (2004) 881–887
www.elsevier.com/locate/ica
Note
[
60]Fullerene displacement from
fac-(dihapto-[60]fullerene)(dihapto-1,2-bis-(1,10-phenanthroline)
tricarbonyl tungsten(0)
1
1
Luis A. Rivera-Rivera, Gisela Crespo-Rom ꢀa n , D ꢀe bora Acevedo-Acevedo ,
Yessenia Ocasio-Delgado, Jos ꢀe E. Cort ꢀe s-Figueroa *
Organometallic Chemistry Research Laboratory, Department of Chemistry, University of Puerto Rico, P.O. Box 9019, Mayag €u ez,
Puerto Rico 00681-9019
Received 21 May 2003; accepted 2 August 2003
Abstract
2
2
The Lewis bases triphenyl phosphine and tricyclohexyl phosphine (L) displace [60]fullerene (C60) from fac-(g -C60)(g -
2
1
phen)W(CO)3 (phen ¼ 1,10-phenanthroline) to produce fac-(g -phen)(g -L)W(CO)3. Under flooding conditions, the reactions were
2
2
first order with respect to fac-(g -C60)(g -phen)W(CO)3. The order with respect to C60 and L depends on the reaction conditions
2
i.e., whether [C60]/[L] ꢀ 0 or 0 6 It [C60]/[L] ꢀ 1. Two limiting cases of an interchange displacement of [60]fullerene from fac-(g -
2
C60)(g -phen)W(CO)3, whose relative contributions to the overall mechanism depend on the nature of the solvent, are proposed
based on the rate law and on the activation parameters. The mechanism involves an initial [60]fullerene dissociation to produce (i)
2
the electronically unsaturated intermediate (g -phen)W(CO)3 for the dissociative displacement and (ii) the solvated intermediate
2
2
2
fac-(solvent)(g -phen)W(CO)3 for the solvent-assisted [60]fullerene dissociation. The W–C60 bond energy in fac-(g -C60)(g -
phen)W(CO)3 was estimated to be in the vicinity of 105 kJ/mol based on the enthalpy of activation of the step where presumably
2
2
2
[
60]fullerene dissociates from fac-(g -C60)(g -phen)W(CO)3 to produce (g -phen)W(CO)3.
Ó 2003 Elsevier B.V. All rights reserved.
Keywords: [60]Fullerene; Kinetics; Metal carbonyls; Transition metals
1
. Introduction
carbonyl complexes have been reported [19–21]. The
C60–metal bond dissociation energies, estimated by
density functional calculations, have been reported to be
The high electron affinity of [60]fullerene (C ) [1–7]
60
2
and its good p-acceptor capacity [8] make [60]fullerene a
strong ligand to bind transition metals. Its chemical and
physical properties are similar to those of electron-defi-
cient olefins [9,10]. The dihapto (g ¼ 2) mode of coor-
dination is preferred [11–15] due in part to its electronic
structure where the three-degenerated LUMOs are di-
rected away from each other on the spherical surface of
in the range of 63–108 kJ/mol for (g -C )M(L)
6
0
2
(M ¼ Ni, Pd, Pt; L ¼ PH , olefins) complexes [22]. For
3
2
W–C60 in (g -C60)W(CO)5, the estimated bond energy is
in the vicinity of 102 kJ/mol [23]. Interestingly, it seems
that [60]fullerene has the potential to labilize bidentate
2
2
ligands in fac- and mer-(g -C60)(g -dppe)M(CO)3 com-
plexes (M ¼ Cr, W, dppe ¼ 1,2-bis(diphenylphosph-
ino)ethane) [24]. For example, piperidine (pip) displaces
[60]fullerene [16–18]. The syntheses and molecular
structure of some fullerene-substituted transition metal
2
2
dppe from mer-(g -C )(g -dppe)W(CO) to produce
60 3
2
1
mer-(g -C )(g -pip) W(CO) . This observation is con-
6
0
2
3
trary to the reported cis labilizing capacity of dppe in
closely related complexes [25]. The large molecular size
of [60]fullerene and its unique electrochemical properties
may explain its labilizing property. The high electron
affinity and the large molecular size of [60]fullerene may
*
Corresponding author. Tel.: +7878324040x2028; fax: +7872653849.
E-mailaddress:jose.cortes.figueroa@usa.net(J.E. Cortes-Figueroa).
1
Participants of the University of Puerto Rico Undergraduate
Research Program and PR-AMP Summer Research Program.
0
020-1693/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved.
doi:10.1016/S0020-1693(03)00494-8

882
L.A. Rivera-Rivera et al. / Inorganica Chimica Acta 357 (2004) 881–887
2
2
ꢁ1
promote chelate labilization in mer-(g -C60)(g -
dppe)W(CO)3. It seems that the high electron affinity of
[
showed the four expected bands: (mCO, cm ): 2003 (w),
1889 (s), 1872 (sh, s), and 1835 (w).
2
2
60]fullerene and its ability to participate in p-backb-
The complex fac-(g -C60)(g -phen)W(CO)3 was pre-
pared thermally from [60]fullerene (Aldrich) and
(g -phen)W(CO)4. In a 25 ml round-bottomed flask
equipped with a magnetic stirring bar, a condenser, and
a nitrogen inlet, 0.0450 g (0.0945 mmol) of (g -
phen)W(CO) and 0.0652 g (0.0905 mmol) of C were
onding lower the electronic density on tungsten, with the
effect of decreasing the p-backbonding between phos-
phorus and tungsten. In addition, the bulkiness of
2
2
[
60]fullerene may promote elongation of the M–P bond
2
2
distances in mer-(g -dppe)(g -C )W(CO) and related
60
3
4
60
complexes [19]. As part of our ongoing investigation on
the reactivity of [60]fullerene-transition metal chelate
complexes, we report here the kinetics and the mecha-
nistic studies of the ligand exchange reactions of the
dissolved in 10 ml of nitrogen-purged and dried chlo-
robenzene. The resulting reddish solution was stirred
under nitrogen during one hour, and then refluxed for
30 min. During reflux the solution turned brown. The
progress of the reaction was monitored by observing
2
2
complex fac-(g -C60)(g -phen)W(CO)3 (phen ¼ 1, 10-
phenanthroline).
and recording the decrease of the m
at 2003, 1889, 1872 cm , and 1835 and the increase
band intensities
CO
ꢁ
1
of the band intensities at 1966, 1889, and 1822 cm 1,
ꢁ
2
2
corresponding to (g -phen)W(CO)4 and fac-(g -C60)
g -phen)W(CO)3 complexes, respectively. After the
2
. Experimental
2
(
reaction was complete, judging by the infrared spec-
trum, chlorobenzene was vacuum-distilled from the re-
action mixture (or by bubbling nitrogen directly into the
mixture). The reddish-brown solid was then dissolved in
approximately 10 ml of carbon disulfide. Thin layer
chromatography analysis showed three components.
The three fractions were separated by column chroma-
tography using a 15 cm long (1 cm diameter) column
2
.1. General
Infrared spectra were obtained on a Bruker Vector 22
Fourier transform infrared spectrophotometer and UV–
visible spectra on a Perkin–Elmer Lambda 25 UV/vis
spectrophotometer. All reactions were carried out under
an inert nitrogen atmosphere. A Julabo F 12-EC model
heating and refrigerating circulator and a K/J Fluke
digital thermometer equipped with a bead thermo-
couple were used as temperature control devices. Mid-
west Microlab, Indianapolis, IN, performed elemental
analyses.
ꢁ
packed with 62 grade, 60–2000 mesh, 150 A silica gel
(Aldrich). The first fraction was eluted using CS2 and
contained unreacted C60. The other two fractions were
eluted with chlorobenzene. The first of the two fractions
2
eluted with chlorobenzene was identified as fac-(g -C )
60
2
(
g -dppe)W(CO) . The second fraction was identified as
3
(g -phen)W(CO)4. The target complex was obtained in
a low yield of approximately 10%. The mCO of fac-(g -
C60)(g -dppe)W(CO)3 in dichloromethane showed three
bands: (mCO, cm ): 1966 (s), 1890 (w), and 1823 (s).
Anal. Calc. for C75H8O3N2W: C, 77.07; H, 0.69; Found:
C, 76.71; H, 1.06%.
2
2
.2. Preparation and purification of materials
2
2
Benzene (Fisher) and Toluene (Aldrich) were dried
ꢁ
1
over sodium. Chlorobenzene (Mallinckrodt) was dried
over phosphorous pentoxide. After drying the solvents
were fractionally distilled under nitrogen. Triphenyl
phosphine (Aldrich) and tricyclohexyl phosphine (Al-
drich) were recrystallized from absolute ethanol (Florida
Distillers Company) and the recovered crystals were
dried under a stream of nitrogen.
The complex (g -phen)W(CO)4 was prepared from
W(CO)6 (Aldrich) and 1,10-phenanthroline (Acros)
following a reported method, with a slight modification
2
.3. Kinetics experiments
Kinetics experiments were carried out under nitrogen.
2
The absorbance values at 440 nm of time infinity read-
ings (A1) for relatively slow reactions were determined
by the Kezdy–Swinbourne method [27–30]. For fast re-
[26]. In a 25 ml round-bottomed flask equipped with a
magnetic stirring bar, a condenser, and a nitrogen inlet,
actions the A values, determined experimentally as the
1
absorbance after ten half-lives, were the same within
experimental error as the values predicted by the Kezdy–
Swinbourne method.
a solution of 0.2069 g (0.5879 mmol) of W(CO) and
6
0
.1122 g (0.6226 mmol) of 1,10-phenanthroline was
dissolved in 15 ml of chlorobenzene. The mixture was
refluxed for 4 h. The volume of the resulting red solution
was reduced to approximately 5 ml by vacuum distilla-
tion and placed in a freezer to induce crystallization.
2.4. Data analysis
After filtration, 0.1418 g of a reddish-brown solid, later
2
Data of the kinetics experiments were analyzed using
a linear least-squares computer program. Error limits,
given in parentheses as the uncertainties of the last
identified as (g -phen)W(CO) was obtained in a 85%
4
2
yield. The mCO of (g -phen)W(CO) in chlorobenzene
4

L.A. Rivera-Rivera et al. / Inorganica Chimica Acta 357 (2004) 881–887
883
ꢁ
5
digit(s) of the cited value, are within one standard
deviation.
phen)W(CO) (ca. 10 M) and (ii) where the concen-
3
tration of L was at least 100 times the concentration of
the substrate and the concentration of C60 was negligible
(
[C60]/[L] ꢀ 0). Under either of these conditions plots of
3
. Results
lnðA
t
ꢁ A
1
Þ versus time (A ¼ absorbance at a given time
t
t, A ¼ absorbance at time infinity) were linear to more
1
2
2
3
phen)M(CO)3
.1. Displacement of C60 from fac-(g -C )(g -
than three half-lives. The pseudo-first order rate con-
stant (kobsd) values were determined for various [L] un-
der conditions where [C60]/[L] ꢀ 0, and also under
conditions where 0 6 [C60]/[L] ꢀ 1 (temperature con-
stant within ꢂ0.1 °C). For conditions where [C60]/
[L] ꢀ 0, the rate constant values were independent on the
chemical nature of L and of the concentration of L but
dependent of the nature of the solvent. The rate constant
values (kobsd) determined for various ligand concentra-
tions and temperatures in various solvents under con-
ditions that [C60]/[L] ꢀ 0 are presented in Table 1. The
corresponding activation parameters, also presented in
Table 1, were determined from the Eyring plots [31]. The
60
The Lewis bases (L) (L ¼ triphenyl phosphine (PPh3)
and tricyclohexyl phosphine (P(Cy)3)) displace [60]ful-
2
2
lerene (C60) from fac-(g -C60)(g -phen)W(CO)3 to
2
1
produce fac-(g -phen)(g -L)W(CO)3 (Eq. (1)).
2
2
fac-ðg -C Þðg -phenÞWðCOÞ þ L
!
60
3
2
1
fac-ðg -phenÞðg -ÞWðCOÞ þ C60
:
ð1Þ
3
2
1
The nature of the reaction product (fac-(g -phen)(g -
L)W(CO)
infrared spectrum in the CO stretching region (mCO, cm
in chlorobenzene for L ¼ PPh : 1909 (vs), 1817 (s), 1791
s)) with the mCO spectra of authentic samples. The rate
3
) was established by direct comparison of its
ꢁ
1
k
0
obsd values, determined under conditions where
6 [C60]/[L] ꢀ 1, are presented in Table 2. The kobsd
3
(
2
2
values under these conditions decrease as [C60]/[L] ratios
increase.
3
of disappearance of fac-(g -C60)(g -dppe)M(CO) was
monitored by observing the decrease of the absorbance
values at 440 nm using a Perkin–Elmer Lambda 25 UV/
visible spectrophotometer. The reactions were studied
under flooding conditions where (i) the concentrations
of L and C60 (0 6 [C60]/[L] ꢀ 1) were at least 50 times
4. Discussion
The activation parameter values in Table 1 suggest an
2
2
2
greater than the concentration of fac-(g -C60)(g -
interchange displacement of [60]fullerene from fac-(g -
Table 1
Values of rate constants and activation parameters for C60 displacement from fac-(g -C60)(g -phen)W(CO)3 by triphenylphosphine in various
2
2
2
2
solvents at various temperatures under flooding conditions such that [PPh3] ꢃ [fac-(g -C60)(g -phen)W(CO)3] and [C60] ꢀ 0
3
ꢁ1
z
z
Temperature (K)
(
Solvent
[PPh
3
] (M)
k
obsd (ꢄ 10 , s
)
DH
(kJ/mol)
DS
(J/K mol)
obsd
obsd
ꢂ 0.1)
3
3
3
47.2
37.2
27.2
chlorobenzene
0.0014
4.428(1)
4.851(9)
5.12(2)
105(4)
+15(11)
0
1
1
.6433
.0333
.5100
4.80(1)
0.1671
2.020(4)
1.9616(9)
1.7939(6)
1.571(4)
0.5074(7)
0.470(1)
0.4762(8)
1.359(6)
1.664(9)
0.454(2)
0.409(2)
0.134(1)
0.1766(5)
1.62(3)
0
0
1
.2576
.3588
.0088
0.0017
0
1
.6433
.0363
347.6
337.6
327.6
347.6
337.6
toluene
benzene
0.6998
.1394
0.6565
.0460
0.6298
.0200
0.0014
.6269
0.0015
105(6)
82(4)
+5(15)
1
1
1
)63(11)
0
1.745(7)
0.767(1)
0.741(3)
0.610(1)
0.261(3)
0.272(3)
0.312(2)
0
1
.5971
.0502
327.6
0.0014
0
0
.0021
.6620

884
L.A. Rivera-Rivera et al. / Inorganica Chimica Acta 357 (2004) 881–887
Table 2
Values of rate constants and competition ratios for C60 displacement from fac-(g -C60)(g -phen)W(CO)3 by L in chlorobenzene at various [C60]/[L]
under flooding conditions such that 0 6 [C60]/[L] ꢀ 1
2
2
3
3
3
ꢁ1
3
ꢁ1
)
L
Temperature
[L] ꢄ 10 (M)
[C60] ꢄ 10 (M)
[C60]/[L]
k
obsd (ꢄ 10 , s
)
*k
3
(ꢄ 10 , s
**kꢁ3=k
4
(K) (ꢂ 0.1)
PPh
3
347.2
1.4
43.3
0
0
4.428(1)
4.851(9)
5.12(2)
5(1)
9(3)
6
0
0
1
1
033.3
051.0
0
0
0
11
0
4.80(1)
3.089(4)
2.36(1)
1
2.4
0.089
0.22
0.29
0.39
0.52
0.65
0.84
0.91
0
1
2
0
1
1
2
1
.3
.6
.92
.5
.1
.6
.1
0.28
0.75
0.36
0.78
0.72
3.4
1.0
0
1.118(5)
1.417(6)
0.745(1)
0.891(5)
0.547(5)
0.587(5)
2.020(4)
1.9616(9)
1.7939(6)
1.571(4)
1.12(1)
PPh
3
337.2
167.1
1.8(1)
9.0(7)
2
3
57.6
58.8
0
0
0
0
1
008.8
0
0
1
1
1
1
5.9
5.0
0.1
9.1
0.97
2.0
1.9
5.23
0.50
0.58
0
0.061
0.13
0.19
0.274
0.36
0.41
0
0.880(3)
0.5972(9)
0.543(8)
0.4516(5)
0.3766(4)
3.87(2)
1
1
.4
.4
P(Cy)
3
347.2
1.5
3.5(9)
12(3)
4
3
2
2
0
1
2
.1
.1
.6
.8
.86
.6
.6
0
0
3.23(1)
0.33
0.97
1.1
0.53
1.3
3.03
0.11
0.37
0.39
0.62
0.81
1.2
1.480(3)
0.561(2)
0.713(3)
0.426(4)
0.350(3)
0.227(2)
Values estimated from the *intercept of the reciprocal plot and **(slope/intercept) of the reciprocal plot.
2
C60)(g -phen)W(CO)3. The proposed mechanism is de-
scribed in Scheme 1. Path A and path B of Scheme 1
describe two limiting mechanistic pathways. Path A
describes a solvent-assisted [60]fullerene associative
displacement and path B describes a dissociative dis-
placement. Assuming that the concentrations of the in-
termediate species are steady-state, both paths predict
mathematically equivalent rate laws (Eq. (2)).
mixture) the only source of C60 in the mixture comes
from substrate dissociation. The experimental rate
constant values, reported in Table 1, are independent of
the nature of L and of the concentration of L but de-
pendent on the nature of the solvent.
The reciprocal relations of Eqs. (3) and (4) are Eqs.
(5) and (6), respectively.
1
=kobsd;A ¼ ðk =k k Þð½C ꢅ=½LꢅÞ þ 1=k
ð5Þ
ð6Þ
ꢁ1
1
2
60
1
ꢁ
d½Sꢅ=dt ¼ kobsd½Sꢅ:
where
S ¼ substrate ¼ fac-(g -C60)(g -phen)W(CO)
For path A,
ð2Þ
2
2
1=kobsd;B ¼ ðk =k k Þð½C ꢅ=½LꢅÞ þ 1=k
ꢁ3
3
4
60
3
3
.
Eqs. (5) and (6) predict that under flooding conditions
such that ([C60] ꢀ [L]) ꢃ [S] plots of 1=kobsd versus [C60]/
k
obsd;A ¼ ðk
and for path B,
1
k
2
½Lꢅ=ðkꢁ1½C60ꢅ þ k
2
½LꢅÞÞ
ð3Þ
[L] should be linear. The intercept values of these plots
should be independent of the entering ligand because the
k
obsd;B ¼ ðk
3
k
4
½Lꢅ=ðkꢁ3½C60ꢅ þ k
4
½LꢅÞÞ:
ð4Þ
ligand is not involved in the step governed by k or k .
1
3
Under flooding conditions such that [C ]/[L] ꢀ 0, Eqs.
Flooding conditions are easily met since the concentra-
tions of L and C60 can be experimentally controlled. The
experimental reciprocal plots, constructed from data in
Table 2, for various ([C ]/[L]) ratios (L ¼ PPh and
6
0
(
3) and (4) are reduced to kobsd;A ꢀ k and k
ꢀ k
1
obsd;B
3
predicting that experimental kobsd values should be in-
dependent of the nature and concentration of L. Under
flooding the condition that [C60]/[L] ꢀ 0 is experimen-
tally met since (unless C60 is added to the reaction
6
0
3
P(Cy) ), presented in Fig. 1, support the mechanisms in
3
Scheme 1.

L.A. Rivera-Rivera et al. / Inorganica Chimica Acta 357 (2004) 881–887
885
support a concerted solvent–W bond making and a W–
C60 bond breaking in the transition state leading to the
2
species fac-(solvent)(g -phen)W(CO)3. The role of the
solvent in the ligand exchange reactions of metal car-
bonyl complexes has been reported extensively elsewhere
[
32–37]. For example, the mode of solvent interaction
with the substrate and intermediate species depends on
the nature of the solvent and the metal. The bonding with
aromatic solvents may take place via an olefinic linkage
or via a lone pair (in halogenated solvents) [34–36]. In
addition, once the solvent is coordinated to the metal it
may undergo a ‘‘chain walk’’ isomerization to attain the
most stable mode of coordination [34–36]. For alkanes a
metal–H–C agostic bond [38,39] has been proposed as
the mode of coordination [37].
The activation parameters for the reactions in chlo-
robenzene and in toluene suggest that path B might be a
better description for the reactions in those solvents. How
close is the enthalpy of activation value to the actual W–
C60 bond dissociation enthalpy depends on the degree of
solvent involvement in the step governed by k3 in Scheme
1. This subject has been addressed extensively elsewhere
[
37]. For example, comparison of the gas phase W–CO
bond dissociation enthalpy ( ¼ 192(12) kJ/mol) [40] with
the W–CO bond dissociation enthalpy in decalin
(
2
Scheme 1. Proposed mechanisms for C60 displacement from fac-(g -
¼ 167(7) kJ/mol) [26] suggests a transition state (TS)
2
C60)(g -phen)W(CO)3. Path A describes a solvent-assisted displace-
stabilization by decalin. It has been proposed that this TS
stabilization of approximately 25 kJ/mol comes from a C–
H–W agostic interaction [41]. Since this TS stabilization
ment of C60, whereas path B describes a dissociative displacement. IA
and IB are steady-state intermediates. TS1 and TS2 are plausible
transition states.
(ca. 25 kJ/mol) is smaller than the reported W–H–C ag-
4
.1. Mechanisms and competition ratios
ostic bond strength ( ¼ 56(12) kJ/mol) [42], the formation
of agostic bond in the TS must be partial. Thus, for non-
coordinating solvents or solvents that bind the metal via
an agostic bond the extent of L–W bond breaking should
6
The activation parameters (DH ¼ 82ð4Þ kJ/mol,
6¼
DS ¼ ꢁ63ð11Þ J/K mol) for the reactions in benzene
2
2
Fig. 1. Plots of 1=kobsd vs. [C60]/[L] for C60 displacement from fac-(g -C60)(g -phen)W(CO)3 by L in chlorobenzene at various [C60]/[L] under
flooding conditions such that 0 6 [C60]/[L] ꢀ 1. j L ¼ PPh3, T ¼ 337:2 K; N L ¼ P(Cy)3, T ¼ 347:2 K; r L ¼ PPh3, T ¼ 347:2 K. Ordinate ¼ 1=kobsd
(s), Abscissa ¼ [C60]/[L].

886
L.A. Rivera-Rivera et al. / Inorganica Chimica Acta 357 (2004) 881–887
be much larger than the extent of solvent–W bond making
in the TS. In such cases, the enthalpy of activation values
may be used as estimates of L–W bond enthalpies.
The enthalpies of activation of the system in chloro-
(L)W(CO)3 take place via an initial solvent-assisted
dissociation of [60]fullerene. The activation parameters
and competition ratios values support a dissociative
displacement of [60]fullerene as a better mechanistic
description for the reactions in chlorobenzene and in
toluene.
z
benzene and in toluene (DH ¼ 105ð4Þ and 105(6) kJ/
mol, respectively) are in the ballpark of the reported
values of 63–108 kJ/mol for C –M bond dissociation
60
2
enthalpies of (g -C )M(L) (M ¼ Ni, Pd, Pt; L ¼ PH ,
60
2
3
2
Acknowledgements
olefins) and in (g -C60)W(CO)5 complexes (vide supra).
2
2
In the complex fac-(g -C60)(g -phen)W(CO)3 it seems
that the rigidity of the phen chelate backbone inhibits the
ring-opening pathway. This behavior has been observed
Acknowledgment is made to the Donors of The Pe-
troleum Research Fund, administered by the American
Chemical Society, (ACS-PRF # 36623-B3) and to the
USA National Science Foundation (grant CHE-
0102167) for support of this work. Valuable comments
from Professor Deborah A. Moore are gratefully ac-
knowledged.
2
0
in cis-(g -dipy)W(CO)4 (dipy ¼ 2; 2 -dipyridyl) and cis-
2
(
g -phen)W(CO) complexes [43]. For example, reac-
4
2
tions of cis-(g -dipy)W(CO) with phosphites produce
fac-(g -dipy)(g -L)W(CO) and trans-(g -L) W(CO) ,
while the corresponding reactions of cis-(g -phen)W
CO)4 produce the complex fac-(g -phen)(L)W(CO)3
4
2
1
1
3
2
4
2
2
(
exclusively [43]. The term cis labilization has been coined
to describe the observation that ligands which are weaker
p-acceptors than CO may labilize a ligand-substituted
metal carbonyl complex toward dissociative ligand loss,
preferentially from a cis position relative to the labilizing
ligand [44].
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B
60
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5
ꢁ3
4
3
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[
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3 4
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[
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60
[
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[
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6
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