Reactions of a platinum(II) agostic complex: Decyclometalation, dicyclometalation, and solvent-switchable formation of a rollover complex

Article abstract of DOI:10.1021/om200293e

Good donor ligands react with an sp² cyclometalated complex of platinum containing an agostic interaction, initially causing displacement of the agostic interaction and decyclometalation. Eventually, these complexes rearrange to give sterically

Full text of DOI:10.1021/om200293e

ARTICLE
pubs.acs.org/Organometallics
Reactions of a Platinum(II) Agostic Complex: Decyclometalation,
Dicyclometalation, and Solvent-Switchable Formation of a
Rollover Complex
Sarah H. Crosby, Guy J. Clarkson, and Jonathan P. Rourke*
Department of Chemistry, Warwick University, Coventry, CV4 7AL U.K.
S Supporting Information
b
ABSTRACT: Good donor ligands react with an sp2 cyclome-
talated complex of platinum containing an agostic interaction,
initially causing displacement of the agostic interaction and
decyclometalation. Eventually, these complexes rearrange to
give sterically less congested complexes containing an sp3
cyclometalated group. The same end products are observed
even with poor donor ligands that do not displace the agostic
interaction, and this, together with other results, suggests to us that the route to the end products goes via a different agostic species.
These sp3 cyclometalated complexes can be made to dicyclometalate via the simple expedient of adding water/base. Finally,
dissolution of the agostic complex in DMSO results in a reversible “rollover” reaction, giving a C∧C chelated ligand.
’ INTRODUCTION
once formed, the rollover complex was able to reversibly abstract
hydrogen from a coordinated dimethyl sulfide ligand.
In this paper we now present details of the reaction pathways,
X-ray structures of products, and additional reactivity of our
previously described agostic complex, including a reversible roll-
over reaction that takes place at the platinum center in solution,
one that is driven not by the release of a hydrocarbon but by the
relief of steric strain.
Agostic complexes are much sought after as part of the search
for the selective and general transformation of unreactive CꢀH
bonds to other functional groups1 and are widely invoked as
intermediates in such reactions.2 Many metals have been inves-
tigated in the quest for such transformations: of particular
relevance to this paper is the use of platinum.3 Agostic interac-
tions have been invoked in the stabilization of the formally
14e T-shaped Pt(II) complexes,4 and such electrophilic centers
ought to be ideally set up for subsequent CꢀH activation, where
it is generally recognized that a preference exists for the activation
of sp2 over sp3 CꢀH bonds.3 Our own contribution to this area
includes a recent communication in which we described the
synthesis and characterization of a platinum(II) complex that
contained a unique bifurcated agostic interaction.5
’ RESULTS AND DISCUSSION
Direct reaction of potassium tetrachloroplatinate with 2-tert-
butyl-6-(4-fluorophenyl)pyridine, in ethanoic acid, activates one
of the sp2 CꢀH bonds of the fluorinated phenyl ring to give a
cyclometalated product containing an agostic interaction, 1. We
can now report that the reaction of this agostic complex with 1
equiv of ligand to exchange the site of cyclometalation, activating
an sp3 CꢀH bond to give complexes 2, is general (Scheme 2).
Reactions take place in solvents such as acetone and chloro-
form, and new complexes containing triphenylphosphine and
pyridine ligands, 2b and 2c, respectively, have been synthesized.
Though complexes 2 might be thought to be rather sterically
crowded, they do have the formulation depicted: a definitive
confirmation of the structure of 2b in the form of an X-ray
structure can now be reported (Figure 1).
The platinum center of 2b in the X-ray structure is indeed
rather crowded, and this induces significant distortions away
from a perfect square-planar geometry. Thus, while the PꢀPtꢀ
Cl angle of 88.5° is close to 90°, all other angles at the Pt center
are between 6 and 12° away from ideal values of 90 or 180°. Bond
lengths to the platinum are all slightly longer than those for
“Rollover” complexes, where the normal N∧N chelation mode
of a ligand such as 2,20-bypridine is converted to a C∧N coordi-
nation mode can be thought of as the products of cyclometala-
tion or CꢀH activation reactions. Rollover complexes have
historical precedent, with the first platinum example being
reported in 19856 and considerable further work being done
by Zucca et al.7 In all these documented examples, the rollover is
accompanied by loss of hydrocarbon, which presumably goes a
long way toward providing the thermodynamic basis for the
reaction to proceed: e.g., Scheme 1.7b Certainly, the release of
hydrocarbons from these reactions makes the reverse rather
unlikely, and the reverse has yet to be observed.
More recently, some examples of rollover complexes detected
in the gas p∧hase have been reported.8 In that recent work, a
“normal” N N-bound 2,20-bipyridine complex was made to
undergo collision-induced decomposition, which resulted in loss
of methane and formation of a C∧N-bound rollover complex.
Computational studies and isotopic labeling demonstrated that,
Received: April 5, 2011
Published: June 13, 2011
r
2011 American Chemical Society
3603
dx.doi.org/10.1021/om200293e Organometallics 2011, 30, 3603–3609
|

Organometallics
ARTICLE
Scheme 1
Scheme 2
related undistorted complexes.9 The coordination plane of the
platinum is by no means flat: a plane defined by N1, Pt1, P17, and
either C16 or Cl1 is reasonably flat, but the other coordinating
atom (Cl1 or C16) is approximately 0.44 Å away from this plane.
The reaction of 1 with DMSO in chloroform or acetone
solution proceeds directly to 2a. In contrast, the reactions of 1
with pyridine or triphenylphosphine clearly initially form new
complexes. NMR spectra show that addition of 1 equiv of pyri-
dine to a solution of 1 results in the rapid formation of a complex
that is still cyclometalated via the fluorophenyl ring (as shown
by the coupling pattern of the protons there and by the presence
of platinum satellites on the 19F resonance) and contains a co-
ordinated pyridine but does not contain an agostic interaction.
NOE measurements suggest that the coordinated pyridine is
adjacent to the cyclometalated ring and distant from the tert-
butyl group, and we have assigned the structure 3c to this new
complex (Scheme 3). The new complex 3c is sufficiently long-
lived in solution for us to characterize it spectroscopically but, as
will become clear, we were unable to isolate pure samples.
Addition of another 1 equiv (or simply excess) of pyridine results
in the formation of a further new complex, one with two added
ligands coordinated per platinum (indicated by the integrals in
Figure 1. Molecular structure of 2b, with thermal ellipsoids at the 50%
probability level and chloroform solvent removed for clarity. Selected
bond lengths (Å) and angles (deg): Pt(1)ꢀC(16), 2.033(2); Pt(1)ꢀN-
(1), 2.1193(18); Pt(1)ꢀP(17), 2.2078(6); Pt(1)ꢀCl(1), 2.4337(5);
C(16)ꢀPt(1)ꢀN(1), 78.13(8); C(16)ꢀPt(1)ꢀP(17), 96.78(7); N-
(1)ꢀPt(1)ꢀP(17), 174.69(5); C(16)ꢀPt(1)ꢀCl(1), 169.27(6); N-
(1)ꢀPt(1)ꢀCl(1), 96.79(5); P(17)ꢀPt(1)ꢀCl(1), 88.48(2); C(6)ꢀ
N(1)ꢀC(2), 119.79(19); C(6)ꢀN(1)ꢀPt(1), 128.48(16); C(2)ꢀ
N(1)ꢀPt(1), 111.47(15); C(2)ꢀC(13)ꢀC(15), 111.37(19); C(2)ꢀC-
(13)ꢀC(16), 107.24(19); C(15)ꢀC(13)ꢀC(16), 110.31(17); C(2)ꢀ
C(13)ꢀC(14), 108.87(17); C(15)ꢀC(13)ꢀC(14), 108.91(19); C-
(16)ꢀC(13)ꢀC(14), 110.12(19).
1
the H NMR). The new complex maintains the sp2 carbon to
1
metal bond (the couplings in the H NMR on this ring retain
1, whereupon an equimolar mixture of 1 and 4b forms. Com-
plexes 4b,c appear to be indefinitely stable, and we were able to
fully characterize them.
their pattern, and satellites are still present on the 19F resonance)
and (from mass spectrometric data) appears to still contain a
chloride. The two added ligands appear to be chemically identical
(a single set of resonances in the 1H NMR for the coordinated
pyridine), and we therefore assign them as mutually trans, with
the complex having the formulation depicted as 4c (Scheme 3).
When 2 equiv of triphenylphosphine is added to 1, the
analogous complex 4b is formed very rapidly. Once again the
integrals in the 1H NMR indicate two added ligands coordinated
per platinum, and again the couplings in the 1H NMR on this ring
retain their pattern and satellites are still present on the 19F
resonance, indicating the complex maintains the sp2 carbonꢀ
metal bond. Again, the two added ligands appear to be chemically
identical (a single resonance in the 31P NMR), and we therefore
assign the formulation depicted as 4b (Scheme 3). In fact, 4b
forms even when only 1 equiv of triphenylphosphine is added to
The formation of complexes 4b,c requires the breaking of the
chelating pyridine nitrogen to platinum bond, compensated
by the formation of a new metal to ligand bond. In the reaction
of 3c to give 4c, it would seem that the replacement of one PtꢀN
bond by another PtꢀN bond would be energetically neutral, but
once we consider the relief of the steric strain from the five-
membered metallacycle and that caused by the proximity of the
tert-butyl group, we can see why such a reaction would actually be
favorable. With triphenylphosphine as the incoming ligand we
can easily rationalize the formation of 4b from the unseen 3b on
the basis of a stronger donor ligand (phosphine) replacing a
weaker one (pyridine). Presumably the formation of this stron-
ger bond, together with the relief of strain (further enhanced by
the bulky triphenylphosphine), is sufficient to stabilize 4b with
3604
dx.doi.org/10.1021/om200293e |Organometallics 2011, 30, 3603–3609

Organometallics
ARTICLE
Scheme 3
Scheme 4
Scheme 5
additionally we have established that there is an intramolecular
hydrogen transfer from the tert-butyl group of 1 to the phenyl
group of 2a.5 We have also recently proved the existence of an
agostic interaction from the phenyl ring in a platinum complex
containing a cyclometalated tert-butyl group of the same pyridine
ligand used in this paper.11a Thus, the experimental evidence indi-
cates that an isomeric form of 1 (shown as 5 in Scheme 4) ought to
be accessible as an intermediate, and indeed DFT calculations
suggest that 5 is only 25 kJ molꢀ1 higher in energy than 1.
We can therefore envisage two possible routes into the for-
mation of complexes 2 from the initial agostic complex 1: one
where complex 3 is an intermediate (route A, Scheme 4) or one
where 3 is simply an initial kinetic product (route B, Scheme 4).
That the actual reaction steps are all reversible equilibria is
demonstrated by the addition of an extra 1 equiv of triphenylpho-
sphine to pure 2b, whereupon complex 4b slowly forms.
Though we cannot definitively rule out the direct transforma-
tion of 3 into 2 and cannot definitively confirm the intermediacy
of 5, we do feel the experimental evidence is more strongly
in favor of the rate-determining formation of 5 from 1 followed
by rapid formation of 2. The crucial step of the transformations
will be the transfer of a hydrogen from the alkyl group, across
the platinum to the aryl group: it seems self-evident that such
a step ought to be easier from one agostic complex to another
(i.e., from 1 to 5), rather than between ones in which the metal
centers are congested with other ligands (i.e., from 3 to 2).
A process of H transfer across the metal is strongly remini-
scent of the σ-CAM mechanism proposed by Perutz and
Sabo-Etienne.12
respect to 3b by a greater amount than 3b is stabilized with
respect to 1, and thus the reaction of 1 with triphenylphosphine
gives 4b directly; certainly reactions of this type have been seen
before.10 We do not, however, see the decyclometalation reaction
with DMSO nor, to the best of our knowledge, has anyone else.
We do not even see the formation of complex 3a. Presumably a
DMSO ligand is an insufficiently good donor to displace the
agostic interaction and to give the sterically congested 3a,11 and
certainly we would not have expected DMSO to displace the
nitrogen of the pyridine to give complex 4a.
Over a time scale of tens of hours at room temperature,
complex 1 and 1 equiv of DMSO transforms into complex 2a, an
equimolar mixture of 1 and 4b transforms into 2b, and 3c
transforms into 2c. Though we have not performed an exhaustive
kinetic analysis, it is apparent that the rates of formation of 2aꢀc
are similar. It is worth noting, however, that the sp3 cyclometa-
lated products are visible in the NMR spectra as soon as any
spectra are run, making the isolation of pure 3c impossible. A
comparison of complexes 2 and 3 (they are simply isomers of
each other) shows that while complex 3 would be expected to
have the stronger PtꢀC bond, the complex will be very sterically
congested, with the chloride ligand adjacent to the bulky tert-
butyl group. By comparison, complex 2 might have the weaker
PtꢀC bond, but it will be significantly less sterically congested,
with the chloride ligand adjacent to the phenyl ring: thus,
complex 2 becomes the thermodynamically favored isomer. A
DFT calculation shows that, in the case of L = pyridine, 2c is
Addition of water to complexes 2 to induce a second cyclo-
metalation13 is also general (Scheme 5): two further derivatives
containing triphenylphosphine and pyridine ligands, 6b and
6c, respectively, have been synthesized and fully characterized.
The X-ray structure of 6a is reported here for the first time
(Figure 2).
favored over 3c by some 33 kJ molꢀ1
.
At this point, it is worth noting that we have already
established that complex 1 will exchange hydrogen for deuterium
in both the tert-butyl group and the position meta to the fluorine
at essentially identical rates (once normalized for the number of
available hydrogens) when dissolved in deuterated ethanoic acid;
Bond lengths and angles are remarkably similar to those in the
dicycloplatinated DMSO complex of 2,6-diphenylpyridine we
reported some years ago.13a The presence of two cyclometalated
rings results in some distortion around the central platinum, with
the NꢀPtꢀC bond angles both being close to 81°.
3605
dx.doi.org/10.1021/om200293e |Organometallics 2011, 30, 3603–3609

Organometallics
ARTICLE
The DMSO ligands in 6a can be replaced by either triphenyl-
phosphine or pyridine to directly give 6b and 6c, respectively,
with no observable impurities.
We therefore conclude that, in addition to the metalated fluoro-
phenyl ring, we have metalated the pyridine ring at one of the
carbons, to give two C∧C chelated complexes, and protonated
the pyridine nitrogen (which maintains the overall neutrality of
the molecules) (Scheme 6).
A new reaction was also observed: when complex 1 was
dissolved in DMSO and left to stand over several days, two
new complexes were formed in roughly equal yields with no
other byproduct. The new products can be isolated from the
DMSO solvent and characterized: they exhibit spectroscopic
features very similar to each other, with only slight changes in
chemical shifts in the NMR. The presence of platinum satellites
on the 19F NMR signals indicates both species maintain the
original PtꢀC bond, and two signals of integral 6 (relative to the
other signals) at 3.32 and 3.35 ppm in the 1H NMR, both with
platinum satellites, indicate the presence of sulfur-bound DMSO
We account for two sets of resonances in all the various NMR
spectra as arising from the presence of two isomers. While we
have not been able to fully separate the two isomers, and indeed it
is likely that the two isomers are in slow equilibrium with each
other (either via the starting material, or via ligand exchange), we
have synthesized mixtures where the clear preponderance of one
isomer over the other has allowed us to assign complete sets of
NMR resonances to each isomer. The use of NOE (in particular
finding which signals are affected by the DMSO signals) allows us
to assign resonances definitively to the cis and trans isomers.
Normally we would expect a strong preference for one iso-
meric form of organometallic complexes of platinum(II),10c,14
but the C∧C chelate in 7 means that both cis and trans isomers
have to have both chloride and DMSO ligands trans to very
similar carbon donors. There will be little steric preference
for one isomer over the other, as the molecule is not crowded
around the platinum. A DFT optimization of the both structures
1
ligands. Further study of the H NMR shows that the three
signals of the pyridine ring in 1 have been replaced by two sets of
only two (one of which exhibits platinum satellites) with two
further broad resonances (relative integral one) at ∼10 ppm.
predicts a favoring of the cis over the trans by only 6 kJ molꢀ1
,
barely significant given the inherent uncertainties in DFT
calculations.
The rollover of C∧N cyclometalated pyridines to give C∧C
complexes has never been observed before, implying that the
simple replacement of the pyridine NꢀPt bond by a pyridine
CꢀPt bond is unfavorable. Indeed, a DFT calculation on the
isomerism of 8 to 9 (neither complex was actually made)
depicted in Scheme 7 shows that 9 would be disfavored by some
47 kJ molꢀ1, relative to 8. This value of 47 kJ molꢀ1 is the value
calculated with the solvation effect that arises from a solvent of
dielectric constant 4.8 (i.e., CHCl3), and it drops to 36 kJ molꢀ1
when a solvent of dielectric constant 46.7 (i.e., DMSO) is used.
Simplistically, we can understand this effect of solvent on the
basis that the zwitterionic 9 will be more stabilized in more polar
solvents.14c,15
The sensible comparison we need to make in our new rollover
reaction is between 3a and 7, the analogues of 8 and 9 above.
Now, in addition to the (unfavorable) replacement of one PtꢀN
Scheme 7
Figure 2. Molecular structure of 6a, with thermal ellipsoids at the 50%
probability level. Selected bond lengths (Å) and angles (deg): Pt(1)ꢀ
N(1), 2.008(3); Pt(1)ꢀC(8), 2.077(3); Pt(1)ꢀC(16), 2.102(4); Pt(1)ꢀ
S(18), 2.1744(9); F(10)ꢀC(10), 1.367(4); O(18)ꢀS(18), 1.481(3);
N(1)ꢀPt(1)ꢀC(8), 80.54(13); N(1)ꢀPt(1)ꢀC(16), 81.05(14); C-
(8)ꢀPt(1)ꢀC(16), 161.20(15); N(1)ꢀPt(1)ꢀS(18), 178.06(9); C-
(8)ꢀPt(1)ꢀS(18), 101.20(10); C(16)ꢀPt(1)ꢀS(18), 97.16(11);
C(2)ꢀN(1)ꢀC(6), 123.3(3); C(2)ꢀN(1)ꢀPt(1), 118.9(2); C(6)ꢀ
N(1)ꢀPt(1), 117.8(2); O(18)ꢀS(18)ꢀPt(1), 120.76(12); C(17)ꢀ
S(18)ꢀPt(1), 108.50(15); C(19)ꢀS(18)ꢀPt(1), 111.46(14).
Scheme 6
3606
dx.doi.org/10.1021/om200293e |Organometallics 2011, 30, 3603–3609

Organometallics
ARTICLE
Scheme 8
bond by a PtꢀC bond in the formation of rollover 7, there is the
(favorable) release of the steric strain caused by the close
proximity of the tert-butyl group to the chloride, and this is
presumably enough to drive the reaction to give rollover 7.
In fact, as noted earlier, we never actually see 3a but instead
see 2a, where the steric strain is already somewhat relieved by
the exchange of sites of cyclometalation.
referenced to external Na2PtCl6. All accurate mass spectra were run
on a Bruker MaXis mass spectrometer, and X-ray crystal structures were
collected on an Oxford Diffraction Gemini four-circle system with Ruby
CCD area detector. The syntheses of 1, 2a, and 6a have been reported
previously,5 and the syntheses of 2b,c and 6b,c follow these procedures.
Compound 2b. Yield: 89%. δH: 8.00ꢀ8.04 (2H, m, phenyl), 7.76
(1H, t, 3J = 8 Hz, pyridine), 7.53ꢀ7.59 (6H, m, PPh3), 7.25ꢀ7.31 (10H,
m, pyridine and PPh3), 7.16 (1H, d, 3J = 7.6 Hz, pyridine), 7.10 (2H, t,
Solutions of 7 in chloroform revert slowly to the sp3 cyclo-
metalated complex 2a on a time scale of days (Scheme 8). This,
then, begs the question as to why we even see the rollover
complexes at all. Once again, DFT calculations are of assistance:
while the formation of cis-7 and trans-7 are predicted to be
favored over 2a by 12 and 6 kJ molꢀ1, respectively, in the polar
DMSO, they are predicted to be disfavored by 4 and 11 kJ molꢀ1
in the nonpolar chloroform. Thus we are at the cusp of the
relative stabilities of the isomeric complexes with the change of
the solvent sufficient to drive the reaction one way or another: a
polar solvent gives zwitterionic rollover complexes and a non-
polar solvent gives conventional N∧C chelates.
3
2
3JHꢀH,HꢀF = 8.8 Hz, phenyl), 1.57 (2H, d, JHꢀP = 2.5 Hz, JHꢀPt
=
52 Hz, CH2), 1.35 (6H, s, Me). δC: 175.2, 163.8 (d, 1JCꢀF = 248 Hz),
159.6, 138.0, 137.1 (d, 4JCꢀF = 2 Hz), 134.5 (d, 2JCꢀP = 11.5 Hz), 131.3
(d, 1JCꢀP = 63 Hz), 131.1 (d, 3JCꢀF = 9 Hz), 130.1, 127.8 (d, 3JCꢀP
=
10.7 Hz), 124.0, 119.6 (3JCꢀPt = 35 Hz), 114.6 (d, 2JCꢀF = 22 Hz), 49.9,
33.0 (3JCꢀPt = 40.6 Hz), 31.7 (d, 2JCꢀP = 4 Hz). δF: ꢀ112.4. δP: 16.0
(1JPꢀPt = 4665 Hz). δPt: ꢀ4161 (d). HR-MS (ESI): m/z 684.1715, calcd
for C33H30FNP194Pt ((M ꢀ Cl)þ) 684.1721. Anal. Found (calcd): C,
54.61 (54.96); H, 4.32 (4.19); N, 1.98 (1.94).
3
4
Compound 2c. Yield: 94%. δH: 8.78 (2H, dd, J = 6.8 Hz, J =
1.5 Hz, pyridine), 8.05ꢀ8.08 (2H, m, phenyl), 7.74 (1H, t, 3J = 7.8 Hz,
phenylpyridine), 7.63 (1H, tt, 3J = 7.5 Hz, 4J = 1.6 Hz, pyridine), 7.18
(1H, dd, 3J = 7.8 Hz, 4J = 1.4 Hz, phenylpyridine), 7.12ꢀ7.15 (2H, m,
Rollover reactions, whether reversible or not, have a hydrogen
transfer step as a key part of their mechanism; indeed, the
reaction depicted in Scheme 8 has two separate ones. Computa-
tional evidence8a suggests a mechanism along the lines of the
σ-CAM process,12 and there seems no reason not to invoke an
intramolecular mechanism. Thus, rollover reactions have the
potential to offer considerable insight into CꢀH activation
reactions such as those where competition results in differing
products according to reaction conditions.16
3
pyridine), 7.09 (2H, t, JHꢀH,HꢀF = 8.6 Hz, phenyl), 7.07 (1H, dd,
3J = 7.8 Hz, 4J = 1.5 Hz, pyridine), 2.09 (2H, s, 2JHꢀPt = 70 Hz, CH2),
1
1.54 (6H, s, Me). δC: 178.1, 163.5 (d, JCꢀF = 250 Hz), 161.1, 154.1
(2JHꢀPt = 34 Hz), 137.4 (d, JCꢀF = 3.6 Hz), 137.0, 136.4, 130.6
4
(d, 3JCꢀF = 9.2 Hz), 125.1 (3JCꢀPt = 51.6 Hz), 124.2, 119.8, 114.9 (d,
2JCꢀF = 21.5 Hz), 50.4, 32.3, 27.6. δF: ꢀ111.9. δPt: ꢀ3003. HR-MS
(ESI): m/z 501.1236, calcd for C20H20FN2194Pt ((M ꢀ Cl)þ) 501.1232.
Anal. Found (calcd): C, 44.19 (44.66); H, 3.86 (3.75); N, 5.25 (5.21).
Synthesis of 3c. Pyridine (0.0009 g, 1.090 ꢁ 10ꢀ5 mol, 1 equiv)
was added to a solution of complex 1 (0.005 g, 1.090 ꢁ 10ꢀ5 mol,
1 equiv) in CDCl3 at room temperature. Characteristic NMR data are as
follows. δH: 8.79ꢀ8.80 (2H, m, 3JHꢀPt = 48 Hz, pyridine), 7.28 (1H, dd,
3J = 8 Hz, 4J = 1 Hz, phenylpyridine), 7.27ꢀ7.41 (2H, m, pyridine), 6.73
(1H, td, 3JHꢀH,HꢀF = 8.6 Hz, 4J = 2.5 Hz, cyclomet ring), 5.91 (1H, dd,
’ CONCLUSIONS
The chemistry of the agostic compound 1 is complex. How-
ever, most of the interesting aspects of its reactivity can be traced
back to the presence of the large tert-butyl group responsible for
the agostic interaction. Relief of steric strain caused by this group
is sufficient to drive reactions in a number of different directions,
dependent upon conditions. Thus, where there is a choice of
reactions that relieve the steric strain we see the additional factor
of solvent polarity coming into play. This gives us a unique
reversible rollover reaction driven by a change of solvent.
4
3
3JHꢀF = 9.4 Hz, J = 2.5 Hz, JHꢀPt = 49 Hz, H adjacent to Pt), 1.77
(9H, s, tBu). δF: ꢀ111.3 (4JFꢀPt = 64 Hz). δPt: ꢀ2849.
Synthesis of 4b. Only details for 4b are given, as the synthesis of
4c followed a very similar procedure. Triphenylphosphine (0.011 g,
4.359 ꢁ 10ꢀ5 mol, 2 equiv) was added to a solution of complex 1
(0.010 g, 2.179 ꢁ 10ꢀ5 mol, 1 equiv) in CHCl3 at room temperature.
The mixture was stirred (96 h) and the solvent removed to give the
product in analytical purity. Yield: 96%. δH: 8.52 (1H, br d, 3J = 7.5 Hz,
’ EXPERIMENTAL SECTION
3
pyridine), 7.37ꢀ7.40 (13H, m, pyridine and PPh3), 7.25 (6H, t, J =
All chemicals were used as supplied, unless noted otherwise. All NMR
spectra were obtained on a Bruker Avance 300, 400, 500, or 600 MHz
spectrometer in CDCl3 or d6-acetone; 1H and 13C shifts are referenced
to external TMS, assignments being made with the use of decoupling,
NOE, and the HMBC, HMQC, DEPT, and COSY pulse sequences. 19F
chemical shifts are quoted from the directly observed signals and are
referenced to external CFCl3. 1Hꢀ195Pt correlation spectra were
recorded using a variant of the HMBC pulse sequence, with the 195Pt
chemical shifts quoted taken from the 2D HETCOR spectra and
7.4 Hz, PPh3), 7.14ꢀ7.16 (12H, m, PPh3), 7.01ꢀ7.03 (2H, m, pyridine
and phenyl), 6.31 (1H, dd, 3JHꢀF = 10 Hz, 4J = 2.6 Hz, 3JHꢀPt = 62 Hz,
phenyl), 6.04 (1H, td, JHꢀH,HꢀF = 8.5 Hz, 4J = 2.5 Hz, phenyl),
3
1.10 (9H, s, tBu). δC: 166.6, 160.8 (d, 1JCꢀF = 249 Hz), 159.4, 143.8 (d,
4JCꢀF = 8 Hz), 139.2 (d, 3JCꢀF = 5 Hz), 133.6 (t, 2JCꢀP = 6 Hz), 129.0,
128.6 (t, 1JCꢀP = 28.3 Hz), 126.8 (t, 3JCꢀP = 5 Hz), 123.6 (d, 2JCꢀF
=
2
17.5 Hz), 119.4, 114.8, 107.1 (d, JCꢀF = 21 Hz), 36.4, 29.1. δP:
21.6 (1JPꢀPt = 3127 Hz). δPt: ꢀ4188 (t, JPtꢀP = 3146 Hz). HR-MS
1
(ESI): m/z 982.2411, calcd for C51H4635ClFNP2194Pt ((M þ H)þ)
3607
dx.doi.org/10.1021/om200293e |Organometallics 2011, 30, 3603–3609

Organometallics
ARTICLE
982.2399. Anal. Found (calcd): C, 62.32 (62.29); H, 5.07 (4.61);
N, 1.83 (1.42).
7.07 (1H, dd, 3J = 8.2 Hz, 4J = 2.0 Hz, py ring), 6.75 (1H, td, 3JHꢀH,HꢀF
=
8.2 Hz, 4J = 2.6 Hz, Ph ring), 3.35 (6H, s, 3JHꢀPt = 11.5 Hz, DMSO),
1.43 (9H, s, tBu) ppm. δC: 150.7 (2JCꢀPt = 28.5 Hz, py ring), 125.3 (d,
3JCꢀF = 9.5 Hz, 3JCꢀPt = 76 Hz, Ph ring), 122.9 (d, 2JCꢀF = 20 Hz, Ph
ring), 118.5 (3JCꢀPt = 55 Hz, py ring), 110.5 (d, 2JCꢀF = 25 Hz, Ph ring),
44.6 (2JCꢀPt = 29 Hz, DMSO), 36.4 (C), 29.2 (tBu) ppm. δF: ꢀ108.1
(4JFꢀPt = 54 Hz) ppm. δPt: ꢀ4023 ppm.
Compound 4c. Yield: 92%. δH: 8.57 (4H, dd, 3J = 7 Hz, 4J = 1.5 Hz,
2JHꢀPt = 40 Hz, pyridine), 7.56 (2H, tt, 3J = 7.7 Hz, 4J = 1.5 Hz, pyridine),
7.31 (1H, t, 3J = 7.6 Hz, phenylpyridine), 7.27 (1H, dd, 3J = 7.7 Hz, 4J =
3
4
1 Hz, phenylpyridine), 7.11 (1H, dd, J = 8.5 Hz, JHꢀF = 6.2 Hz,
phenyl), 7.09 (1H, dd, 3J = 7.4 Hz, 4J = 1.2 Hz, phenylpyridine), 6.97
(4H, t, 3J = 7.1 Hz, pyridine), 6.90 (1H, dd, 3JHꢀF = 9.7 Hz, 4J = 2.7 Hz,
phenyl), 6.61 (1H, td, 3JHꢀH,HꢀF = 8.5 Hz, 4J = 2.7 Hz, phenyl), 1.34
(9H, s, tBu) ppm. δC: 167.1, 160.7, 157.7 (d, 1JCꢀF = 249 Hz), 152.9,
142.2, 141.6 (d, 3JCꢀF = 4 Hz), 135.8, 134.2, 128.7 (d, 3JCꢀF = 8.4 Hz),
123.7 (3JCꢀPt = 48 Hz), 121.6 (d, 2JCꢀF = 17 Hz), 119.2, 114.6, 109.0
(d, 2JCꢀF = 21 Hz), 36.8, 29.5. δF: ꢀ117.3 (4JFꢀPt = 40 Hz). δPt: ꢀ2741.
HR-MS (ESI): m/z 616.1413, calcd for C25H2635ClFN3194Pt ((M þ
H)þ) 616.1420; 501.1232, calcd for C20H20FN2194Pt ((M ꢀ Cl ꢀ
Py)þ) 501.1232. Anal. Found (calcd): C, 47.98 (48.66); H, 3.90 (4.08);
N, 6.86 (6.81).
Data on the mixture of cis-7 and trans-7: HR-MS (ESI): m/z
500.0952, calcd for C17H21FNO194PtS ((M ꢀ Cl)þ) 500.0949. Anal.
Found (calcd): C, 37.65 (38.03); H, 4.32 (3.94); N, 2.73 (2.61).
X-ray Crystallographic Studies of 2b and 6a. Crystal data for
2b: the asymmetric unit contains the complex and two molecules of
chloroform solvent, C35H32Cl7FNPPt, Mr = 959.83, monoclinic, space
group P21/c, a = 16.0210(3) Å, b = 16.4039(2) Å, c = 15.4546(3) Å,
β = 116.349(2)°; U = 3639.61(11) Å3 (by least-squares refinement on
11 844 reflection positions), T =100(2) K, λ = 0.710 73 Å, Z = 4,
D(calcd) = 1.752 Mg/m3, F(000) = 1880, μ(Mo KR) = 4.445 mmꢀ1
,
Compound 6b. Yield: 87%. δH: 7.66 (1H, t, 3J = 7.8 Hz, pyridine),
colorless block, crystal dimensions 0.20 ꢁ 0.10 ꢁ 0.10 mm, no crystal
decay, θmax = 29.39°; hkl ranges ꢀ21 to þ22, ꢀ16 to þ22, and ꢀ21 to
þ15; 18 996 reflections measured, 8628 unique reflections (R(int) =
0.0281), goodness-of-fit on F2 0.919, R1 (for 7067 reflections with I >
2σ(I)) = 0.0213, wR2 = 0.0372, 8628/2/423 data/restraints/para-
3
4
7.58ꢀ7.63 (6H, m, PPh3), 7.52 (1H, dd, J = 8.5 Hz, JHꢀF = 5.2 Hz,
phenyl), 7.40 (1H, br d, 3J = 8 Hz, pyridine), 7.29ꢀ7.31 (9H, m, PPh3),
6.93 (1H, br d, 3J = 8 Hz, pyridine), 6.58 (1H, td, 3JHꢀH,HꢀF = 8.7 Hz,
4J = 2.8 Hz, phenyl), 6.38 (1H, dd, 3JHꢀF = 10 Hz, 4J = 2.5 Hz, 3JHꢀPt
=
meters, largest difference Fourier peak and hole 0.660 and ꢀ0.912 e Åꢀ3
.
30 Hz, phenyl), 1.48 (2H, d, 3JHꢀP = 1 Hz, 2JHꢀPt = 40 Hz, CH2), 1.21
(6H, s, Me). δC: 179.1 (2JCꢀPt = 61 Hz), 175.7 (dd, 3JCꢀF = 6 Hz, 2JCꢀP
3 Hz), 164.7 (2JCꢀPt = 52 Hz), 164.6 (d, 1JCꢀF = 254 Hz), 145.8 (4JCꢀF
=
=
Crystal data for 6b: C17H20FNOPtS, Mr = 500.49; monoclinic, space
group Cc; a = 9.9679(2) Å, b = 18.6651(3) Å, c = 9.5993(2) Å, β =
111.176(3)°, U = 1665.37(6) Å3 (by least-squares refinement on 6729
reflection positions), T =100(2) K, λ = 0.710 73 Å, Z = 4, D(calcd) =
1.996 Mg/m3, F(000) = 960, μ(Mo KR) = 8.561 mmꢀ1, colorless block,
5.4 Hz), 138.2, 134.6 (d, 2JCꢀP = 12.3 Hz, 3JCꢀPt = 41 Hz), 132.2 (d, 1JCꢀP
= 58 Hz), 130.1 (d, 4JCꢀP = 2.3 Hz), 128.0 (d, 3JCꢀP = 10.7 Hz), 125.3
(d, 3JCꢀF = 7.7 Hz), 124.4 (d, 2JCꢀF = 14.6 Hz, 2JCꢀPt = 61 Hz), 118.6
(d, 4JCꢀP = 2.3 Hz, 3JCꢀPt = 33 Hz), 115.4 (d, 4JCꢀP = 2.3 Hz, 3JCꢀPt = 27
crystal dimensions 0.25 ꢁ 0.20 ꢁ 0.08 mm, no crystal decay, θmax
=
Hz), 109.1 (d, 2JCꢀF = 23 Hz), 52.6 (d, 3JCꢀP = 3.8 Hz), 41.4 (d, 2JCꢀP
5.4 Hz, 1JCꢀPt = 461 Hz) 34.0 (3JCꢀPt = 17.6 Hz). δF: ꢀ111.2 (4JFꢀPt
=
=
29.20°; hkl ranges ꢀ9 to þ13, ꢀ25 to þ25, and ꢀ13 to þ10, 6952
reflections measured, 2742 unique reflections (R(int) = 0.0210), good-
ness-of-fit on F2 1.073, R1 (for 2711 reflections with I > 2σ(I)) = 0.0142,
wR2 = 0.0344, 2742/4/209 data/restraints/parameters, largest differ-
26.3 Hz). δP: 26.7 (1JPꢀPt = 4117 Hz). δPt: ꢀ4110 (d). HR-MS (ESI): m/
z 684.1741, calcd for C33H30FNP194Pt ((M þ H)þ) 684.1721. Anal.
Found (calcd): C, 57.36 (57.89); H, 3.87 (4.27); N, 2.10 (2.05).
Compound 6c. Yield: 90%. δH: 8.93ꢀ8.94 (2H, m, pyridine), 7.73
ence Fourier peak and hole 0.624 and ꢀ1.097 e Åꢀ3
.
In both cases, the structures were solved by direct methods using
SHELXS,17 with additional light atoms found by Fourier methods.
Hydrogen atoms were added at calculated positions and refined using a
riding model, except the hydrogens on C16, which were located in a
difference map. Their position was refined but given a distance restraint.
Anisotropic displacement parameters were used for all non-H atoms; H
atoms were given isotropic displacement parameters equal to 1.2 (or 1.5
for methyl H atoms) times the equivalent isotropic displacement
parameter of the atom to which they are attached.
3
4
3
(1H, tt, J = 7.8 Hz, J = 1.5 Hz, pyridine), 7.60 (1H, t, J = 8.0 Hz,
3
4
phenylpyridine), 7.52 (1H, dd, J = 8.5 Hz, JHꢀF = 5.0 Hz, phenyl),
3
7.26ꢀ7.29 (3H, m, pyridine and phenylpyridine), 6.83 (1H, d, J =
3
4
7.9 Hz, phenylpyridine), 6.77 (1H, dd, JHꢀF = 8.5 Hz, J = 2.6 Hz,
3JHꢀPt = 28 Hz, phenyl), 6.68 (1H, td, 3JHꢀH,HꢀF = 8.8 Hz, 4J = 2.7 Hz,
phenyl), 1.97 (2H, s, 2JHꢀPt = 50 Hz, CH2), 1.36 (6H, s, Me). δC: 180.3,
178.1, 165.8 (d, 1JCꢀF = 253 Hz), 165.5, 153.6, 144.3, 136.9, 135.4, 126.0
(3JCꢀPt = 48 Hz), 125.5 (d, 3JCꢀF = 8.2 Hz), 118.6, 117.7 (d, 2JCꢀF
=
14.2 Hz), 115.2, 109.1 (d, 2JCꢀF = 24 Hz), 51.5, 42.2, 34.0. δF: ꢀ111.0
(4JFꢀPt = 20 Hz). δPt: ꢀ2949 ppm. HR-MS (ESI): m/z 501.1231, calcd
for C20H20FN2194Pt ((M þ H)þ) 501.1232. Anal. Found (calcd): C,
44.72 (44.66); H, 3.96 (3.75); N, 4.83 (5.21).
DFT Calculations. All DFT calculations used the Amsterdam
density functional (ADF) code, version 2008.01.18 The general features
available in ADF have been described.19 Here, we have used scalar zero-
order regular approximation (ZORA) relativistic corrections with the
OPBE functional20 and the supplied frozen-core, triple-ζ plus polariza-
tion ZORA basis sets. Solvation effects were included via the conductor-
like screening model (COSMO) as implemented in ADF. Default SCF
and geometry optimization convergence criteria were used.
Synthesis of 7. Complex 1 (0.010 g, 2.18 ꢁ 10ꢀ5 mol) was dis-
solved in DMSO (3 mL, excess) and left standing at room temperature
for 3 weeks. The solvent was removed under high vacuum to give a
yellow solid.
trans-7. δH: 10.14 (1H, br s, NꢀH), 9.23 (1H, d, 3J = 7.7 Hz, 3JHꢀPt
=
=
64 Hz, py ring), 8.02 (1H, dd, 3JHꢀF = 10.2 Hz, 4J = 2.5 Hz, 3JHꢀPt
’ ASSOCIATED CONTENT
61 Hz, Ph ring), 7.14 (1H, dd, 3J = 8.5 Hz, 4JHꢀF = 5.0 Hz, Ph ring), 6.98
(1H, dd, 3J = 8.0 Hz, 4J = 2.0 Hz, py ring), 6.74 (1H, td, 3JHꢀH,HꢀF
=
S
Supporting Information. Tables giving DFT optimized
b
8.5 Hz, 4J = 2.7 Hz, Ph ring), 3.32 (6H, s, 3JHꢀPt = 10 Hz, DMSO), 1.42
coordinates and energies for 1, 2a,c, 3c, 5, cis-7, trans-7, 8,
and 9 and CIF files giving crystallographic data for 2b and 6a.
This material is available free of charge via the Internet at http://
pubs.acs.org.
t
(9H, s, Bu) ppm. δC: 150.1 (2JCꢀPt = 33.5 Hz, py ring), 124.7 (d,
3JCꢀF = 8.5 Hz, 3JCꢀPt = 71 Hz, Ph ring), 122.5 (d, 2JCꢀF = 19 Hz, Ph
ring), 119.5 (3JCꢀPt = 60 Hz, py ring), 111.8 (d, 2JCꢀF = 24 Hz, Ph ring),
44.3 (2JCꢀPt = 25.5 Hz, DMSO), 36.3 (C), 29.1 (tBu) ppm. δF: ꢀ109.0
(4JFꢀPt = 43 Hz) ppm. δPt: ꢀ4032 ppm.
’ AUTHOR INFORMATION
cis-7. δH: 10.14 (1H, br s, NꢀH), 8.99 (1H, d, 3J = 7.7 Hz, 3JHꢀPt
=
=
3
4
3
Corresponding Author
*E-mail: j.rourke@warwick.ac.uk.
57 Hz, py ring), 8.34 (1H, dd, JHꢀF = 11 Hz, J = 2.5 Hz, JHꢀPt
70.5 Hz, Ph ring), 7.17 (1H, dd, 3J = 8.5 Hz, 4JHꢀF = 5.4 Hz, Ph ring),
3608
dx.doi.org/10.1021/om200293e |Organometallics 2011, 30, 3603–3609

Organometallics
ARTICLE
’ ACKNOWLEDGMENT
(15) Ashkenazi, N.; Vigalok, A.; Parthiban, S.; Ben-David, Y.;
Shimon, L. J. W.; Martin, J. M. L.; Milstein, D. J. Am. Chem. Soc. 2000,
122, 8797.
(16) Garner, A. W.; Harris, C. F.; Vezzu, D. A. K.; Pike, R. D.; Huo, S.
Chem. Commun. 2011, 47, 1902.
(17) Sheldrick, G. M. SHELXL-97, Program for Crystal Structure
Refinement; University of G€ottingen, G€ottingen, Germany, 1997.
(18) Baerends, E. J. B., A.; Bo, C.; Boerrigter, P. M.; Cavallo, L.;
Deng, L.; Dickson, R. M.; Ellis, D. E.; Fan, L.; Fischer, T. H.; Fonseca
Guerra, C.; van Gisbergen, S. J. A.; Groeneveld, J. A.; Gritsenko, O. V.;
Harris, F. E.; van den Hoek, P.; Jacobsen, H.; van Kessel, G.; Kootstra, F.;
van Lenthe, E.; Osinga, V. P.; Philipsen, P. H. T.; Post, D.; Pye, C. C.;
Ravenek, W.; Ros, P.; Schipper, P. R. T.; Schreckenbach, G.; Snijders,
J. G.; Sola, M.; Swerhone, D.; te Velde, G.; Vernooijs, P.; Versluis, L.;
Visser, O.; van Wezenbeek, E.; Wiesenekker, G.; Wolff, S. K.; Woo,
T. K.; Ziegler, T. ADF 2008.01; Scientific Computing and Modelling
NV, Free University, Amsterdam, 2008.
We thank Warwick University for a WPRS award to S.H.C.
and support from Advantage West Midlands (AWM) (partially
funded by the European Regional Development Fund) for the
purchase of a high-resolution mass spectrometer and the XRD
system that was used to solve the crystal structures of 2b and 6a.
’ REFERENCES
(1) (a) Labinger, J. A.; Bercaw, J. E. Nature 2002, 417, 507.
(b) Bergman, R. G. Nature 2007, 446, 391.
(2) (a) Brookhart, M.; Green, M. L. H.; Parkin, G. Proc. Natl. Acad.
Sci. U.S.A. 2007, 104, 6908. (b) Haller, L. J. L.; Page, M. J.; Macgregor,
S. A.; Mahon, M. F.; Whittlesey, M. K. J. Am. Chem. Soc. 2009, 131, 4604.
(3) Goldman, A. S.; Goldberg, K. I., In Activation and Functionaliza-
tion of C-H Bonds; Goldberg, K. I., Goldman, A. S., Eds.; American
Chemical Society: Washington, DC, 2004; ACS Symposium Series 885.
(4) (a) Carr, N.; Dunne, B. J.; Orpen, A. G.; Spencer, J. L. J. Chem.
Soc., Chem. Commun. 1988, 926. (b) Carr, N.; Mole, L.; Orpen, A. G.;
Spencer, J. L. J. Chem. Soc., Dalton Trans. 1992, 2653. (c) Ingleson, M. J.;
Mahon, M. F.; Weller, A. S. Chem. Commun. 2004, 2398.
(5) Crosby, S. H.; Clarkson, G. J.; Rourke, J. P. J. Am. Chem. Soc.
2009, 131, 14142.
(19) te Velde, G.; Baerends, E. J. J. Comput. Phys. 1992, 99, 84.
(20) (a) Perdew, J. P.; Burke, K.; Ernzerhof, M. Phys. Rev. Lett. 1996,
77, 3865. (b) Handy, N. C.; Cohen, A. J. Mol. Phys. 2001, 99, 403.
(6) Skapski, A. C.; Sutcliffe, V. F.; Young, G. B. J. Chem. Soc., Chem.
Commun. 1985, 609.
(7) (a) Zucca, A.; Doppiu, A.; Cinellu, M. A.; Stoccoro, S.; Minghetti,
G.; Manassero, M. Organometallics 2002, 21, 783. (b) Minghetti, G.;
Stoccoro, S.; Cinellu, M. A.; Soro, B.; Zucca, A. Organometallics 2003,
22, 4770. (c) Zucca, A.; Cinellu, M. A.; Minghetti, G.; Stoccoro, S.;
Manassero, M. Eur. J. Inorg. Chem. 2004, 4484. (d) Zucca, A.; Petretto,
G. L.; Stoccoro, S.; Cinellu, M. A.; Minghetti, G.; Manassero, M.;
Manassero, C.; Male, L.; Albinati, A. Organometallics 2006, 25, 2253.
(e) Minghetti, G.; Stoccoro, S.; Cinellu, M. A.; Petretto, G. L.; Zucca, A.
Organometallics 2008, 27, 3415. (f) Zucca, A.; Petretto, G. L.; Stoccoro, S.;
Cinellu, M. A.; Manassero, M.; Manassero, C.; Minghetti, G. Organometallics
2009, 28, 2150.
(8) (a) Butschke, B.; Schlangen, M.; Schr€oder, D.; Schwarz, H. Chem.
Eur. J. 2008, 14, 11050. (b) Butschke, B.; Schwarz, H. Organometallics
2010, 29, 6002.
(9) (a) Newman, C. P.; Casey-Green, K.; Clarkson, G. J.; Cave,
G. W. V.; Errington, W.; Rourke, J. P. Dalton Trans. 2007, 3170.
(b) Mamtora, J.; Crosby, S. H.; Newman, C. P.; Clarkson, G. J.; Rourke,
J. P. Organometallics 2008, 29, 5559.
(10) (a) Albrecht, M.; Dani, P.; Lutz, M.; Spek, A. L.; van Koten, G.
J. Am. Chem. Soc. 2000, 122, 11822. (b) Rodriguez, G.; Albrecht, M.;
Schoenmaker, J.; Ford, A.; Lutz, M.; Spek, A. L.; van Koten, G. J. Am.
Chem. Soc. 2002, 124, 5127. (c) Crespo, M.; Granell, J.; Solans, X.;
Font-Bardia, M. J. Organomet. Chem. 2003, 681, 143. (d) Crespo, M.;
Solans, X.; Font-Bardia, M. J. Organomet. Chem. 1996, 509, 29.
(11) (a) Crosby, S. H.; Clarkson, G. J.; Deeth, R. J.; Rourke, J. P.
Dalton Trans. 2011, 40, 1227. (b) Conley, B. L.; Williams, T. J. J. Am.
Chem. Soc. 2010, 132, 1764. (c) Crosby, S. H.; Clarkson, G. J.; Deeth,
R. J.; Rourke, J. P. Organometallics 2010, 29, 1966.
(12) Perutz, R. N.; Sabo-Etienne, S. Angew. Chem., Int. Ed. 2007,
46, 2578.
(13) (a) Cave, G. W. V.; Alcock, N. W.; Rourke, J. P. Organometallics
1999, 18, 1801. (b) Cave, G. W. V.; Fanizzi, F. P.; Deeth, R. J.; Errington,
W.; Rourke, J. P. Organometallics 2000, 19, 1355.
(14) (a) Vicente, J.; Arcas, A.; Bautista, D.; de Arellano, M. C. R.
J. Organomet. Chem. 2002, 663, 164. (b) Forniꢀes, J.; Sicilia, V.; Larraz, C.;
ꢀ
Camerano, J. A.; Martin, A.; Casas, J. M.; Tsipis, A. C. Organometallics
2010, 29, 1396. (c) Newman, C. P.; Clarkson, G. J.; Alcock, N. W.;
Rourke, J. P. Dalton Trans. 2006, 3321. (d) Newman, C. P.; Deeth, R. J.;
Clarkson, G. J.; Rourke, J. P. Organometallics 2007, 26, 6225.
(e) Petretto, G. L.; Wang, M.; Zucca, A.; Rourke, J. P. Dalton Trans.
2010, 39, 7822. (f) Rourke, J. P.; Fanizzi, F. P.; Bruce, D. W.; Dunmur,
D. A.; Maitlis, P. M. J. Chem. Soc., Dalton Trans. 1992, 3009.
3609
dx.doi.org/10.1021/om200293e |Organometallics 2011, 30, 3603–3609