Coordination of phosphinoboranes R2PB(C6F 5)2 to platinum: An alkene-type behavior

Article abstract of DOI:10.1021/ja301929n

The paucity of boron-containing heteroalkene complexes prompted us to explore the coordination of phosphinoboranes. The complexes {[R ₂PB(C₆F₅)₂]Pt(PPh₃) ₂} (R = Cy, t-Bu) were obtained by ethylene displacement. Spectroscopic and crystallographic data indicated symmetric side-on coordination of the phosphinoborane to Pt. Thorough analysis of the bonding situation by computational means revealed important similarities but also significant differences between the phosphinoborane and ethylene complexes.

Full text of DOI:10.1021/ja301929n

Communication
pubs.acs.org/JACS
Coordination of Phosphinoboranes R2PB(C6F5)2 to Platinum: An
Alkene-Type Behavior
Abderrahmane Amgoune,*,† Sonia Ladeira,‡ Karinne Miqueu,§ and Didier Bourissou*,†
†Universite
Toulouse, France
‡Universite
de Toulouse, UPS, Institut de Chimie de Toulouse, FR2599, 118 Route de Narbonne, F-31062 Toulouse, France
§Institut des Sciences Analytiques et de Physico-Chimie pour l’Environnement et les Mater
iaux (UMR 5254), Equipe Chimie
ident Angot, 64053 Pau cedex 09, France
́
de Toulouse, UPS, LHFA, 118 Route de Narbonne, F-31062 Toulouse, France; CNRS, LHFA UMR 5069, F-31062
́
́
́ ́ ́
Physique; Universite de Pau et des Pays de l’Adour, Helioparc, 2 Avenue du Pres
S
* Supporting Information
important role, and the o-phenylene moiety proved to be
particularly efficient in supporting the coordination of the
Lewis acid. At this stage, one may wonder about the actual
necessity of a linker. We thus became interested in evaluating
the coordination properties of phosphinoboranes (PBs)4
(Chart 1), and we report here our first results in this area.
Side-on coordination of the PBs R2PB(C6F5)2 (R = Cy, t-Bu)
to Pt has been crystallographically authenticated, and the
original bonding situation has been thoroughly analyzed by
computational methods.
Because of their ambiphilic character, PBs tend to form head-
to-tail dimers or higher oligomers via intermolecular P→B
interactions.4 However, sterically demanding substituents
enable the isolation of monomeric species, as first evidenced
by Power and co-workers.5 For this study, we chose PBs 1 and
2, which were recently shown by Stephan to activate H2
readily.6 The t-Bu/Cy substituents at phosphorus and the
C6F5 groups at boron not only prevent aggregation but also
amplify the double-bond character as a result of strong π
donation from P to B. Accordingly, some parallel may be drawn
between the coordination of PBs 1 and 2 and that of alkenes.
Coordination of 1 to Pt was readily achieved using the
[(C2H4)Pt(PPh3)2] precursor 3 (Scheme 1). The ensuing
complexes 4 and 5 are extremely air- and moisture-sensitive.
ABSTRACT: The paucity of boron-containing hetero-
alkene complexes prompted us to explore the coordination
of phosphinoboranes. The complexes {[R2PB(C6F5)2]Pt-
(PPh3)2} (R = Cy, t-Bu) were obtained by ethylene
displacement. Spectroscopic and crystallographic data
indicated symmetric side-on coordination of the phosphi-
noborane to Pt. Thorough analysis of the bonding
situation by computational means revealed important
similarities but also significant differences between the
phosphinoborane and ethylene complexes.
he ability of main-group Lewis acids to coordinate to
T
transition metals (TMs) as σ-acceptor ligands (so-called
Z-type ligands) has attracted growing interest over the past
decade.1 Thanks to the incorporation of Lewis acid moieties
into multidentate, ambiphilic ligands,2 more understanding has
been gained about the nature and influence of TM→Z
interactions. The scope of Lewis acids capable of behaving as
σ-acceptor ligands has also been significantly extended.
Typically, we have shown that group 13 or group 14 Lewis
acids appended with o-(C6H4)PR2 donor groups readily engage
in TM→Z interactions upon coordination (Chart 1).3 We
Chart 1. Schematic Representation of Different Ways of
Supporting M→B Interactions Using Phosphine Buttresses
Scheme 1. Coordination of the Phosphinoboranes 1 and 2 to
Pt
According to in situ NMR monitoring, the formation of
complex 4 was complete within 30 min at room temperature.
1
The release of ethylene was clearly apparent by H NMR
analysis (4.2 ppm), and the 31P and 11B NMR data argue in
varied the nature of the Lewis acid (B, Al, Ga, In, Si, Sn) and
the metal fragment as well as the number of phosphine side
arms to gain insight into the factors influencing the magnitude
of TM→Z interactions. The nature of the linker between the
Lewis acid and the donor buttresses was also shown to play an
favor of the coordination of both the phosphorus and boron
Received: February 27, 2012
Published: April 5, 2012
© 2012 American Chemical Society
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Communication
atoms of the PB. The 31P NMR resonance signal in complex 4
appears at 31 ppm (vs 121 ppm in 1) as a doublet of doublets
(JP−P = 230 and 13 Hz involving the two inequivalent PPh3
coligands) with 195Pt satellites (JP−Pt = 3750 Hz). The 11B
NMR signal is shifted upfield by ∼60 ppm upon coordination
and resonates in 4 at −19 ppm, in the typical range for
tetracoordinate boron centers enclosed in three-membered
rings.7 The change in the boron environment from tri- to
tetracoordinate is further supported by the chemical shift
difference between the para and meta fluorine atoms of the
C6F5 fragments [Δδ(19Fp,m) = 4 ppm in complex 4 vs 8 ppm in
ligand 1].8 Also noteworthy is the presence of a significant JP−B
coupling constant in complex 4 (42 Hz). This suggests that the
PB framework is retained but probably weakened upon
coordination to Pt (1 displays a much larger JP−B coupling of
150 Hz).
P and B and the PPh3 coligands induces a substantial shrinking
of the P2−Pt−P3 bond angle [from 111.6(1)° in 312 to
101.0(2)° in 4]. Notably, because of the unsymmetrical nature
of the PB ligand, the two PPh3 coligands are not equivalent in
complex 4, and the two Pt−PPh3 distances are slightly different.
The longer Pt−P distance is that to P3, which is trans to boron
[Pt−P3 = 2.3377(6) Å, Pt−P2 = 2.2961(6) Å)], which may be
attributed to the stronger trans effect of the borane relative to
the phosphine.1
The X-ray structures of complexes 4 and 5 revealed
symmetric side-on coordination of the PB to Pt. From the
ensuing geometrical data, the bonding situation can be formally
described as a Pt→borane interaction supported by adjacent
phosphine coordination (Chart 2, structure a). If the double-
Chart 2. Schematic Descriptions of the Coordination of 1
and 2 to Pt
PB 2 featuring t-Bu groups at phosphorus was also reacted
with 3. The higher steric demand of the ligand was found to
markedly disfavor the coordination (only 75% conversion could
be achieved even after 5 days at 35 °C), but according to 31P
and 11B NMR spectroscopy,9 the ensuing complex 5 adopts a
structure very similar to that of 4.
The coordination modes of complexes 4 and 5 were then
analyzed by X-ray diffraction studies (single crystals were grown
from dichloromethane or pentane/ether solutions at room
temperature).9 The two compounds adopt very similar
structures, and for sake of clarity, only that of 4 (Figure 1)
bond character of the PBs is taken into account, complexes 4
and 5 can also be considered as olefin-type complexes, with
participation of π(PB)→Pt donation and Pt→π*(PB) back-
donation (structure b). A thorough density functional theory
(DFT) study was carried out to gain more insight into the
coordination mode of the PB ligand and to draw an in depth
comparison with the corresponding ethylene complex.13
Calculations were carried out on complexes 3 and 4 (with
PPh3 coligands) and 3* and 4* (with PMe3 coligands). The
optimized geometries reproduced well the key features of the
structures determined crystallographically (Table S2).9 Re-
placement of PPh3 by PMe3 had only a small influence, and
thus, further analysis was focused on the model systems 3* and
4*. Displacement of ethylene by the PB on [Pt(PMe3)2] is
slightly favored energetically (ΔE = −8.2 kcal/mol, ΔG = −1.6
kcal/mol at 25 °C for the reaction outlined in Scheme 1), in
agreement with the experimental observations.
Figure 1. X-ray crystal structure of 4. Thermal ellipsoids have been
drawn at 50% probability, and H atoms and solvate molecules have
been omitted for clarity. Selected bond lengths (Å) and angles (deg):
P1−B, 1.917(3); P1−Pt, 2.2984(6); Pt−B, 2.234(3); P3−Pt,
2.3377(6); P2−Pt, 2.2961(6); P1−Pt−B, 50.02(7); P2−Pt−P3,
100.97(2).
The nature of the bonding interaction was then thoroughly
investigated starting with energy decomposition analysis
(EDA), as introduced by Morokuma and Ziegler14 (Table 1).
The bond dissociation energy predicted for 4* exceeds that for
3* by ∼5 kcal/mol (De = 24.3 vs 19.1 kcal/mol). Interestingly,
the interaction energy between the two fragments is much
higher for the PB than for ethylene (ΔEint = −82.1 vs −63.1
kcal/mol), but the respective preparation energies required to
will be discussed here. The Pt center is tetracoordinated and
adopts a distorted square-planar arrangement. The PB
coordinates in a side-on fashion and lies almost in the same
plane as the two PPh3 coligands (the P1−Pt−B plane deviates
by only 6.3° from the P2−Pt−P3 plane). The Pt−B distance is
short [2.234(3) Å] and falls in the same range as those
observed for supported Pt→borane interactions (2.12−2.43
Å).10 In fact, the Pt−B and Pt−P1 [2.298(6) Å] distances are
very close to the sum of their respective covalent radii,11
indicating the symmetric coordination of the PB ligand. Upon
coordination, the PB is slightly pyramidalized [∑αB = 349.6(6)
° and ΣαP1 = 351.2(3)°] and the P1−B bond length is
noticeably elongated [from 1.762(4) Å in the free ligand 16b to
1.917(3) Å in complex 4]. Replacement of ethylene with the
PB at Pt also affects the geometry of the [Pt(PPh3)2] fragment.
In particular, steric repulsion between the large substituents at
Table 1. EDA of Complexes [(C2H4)Pt(PMe3)2] (3*) and
{[Cy2PB(C6F5)2]Pt(PMe3)2} (4*) (Energies Reported in
kcal/mol)
3*
4*
ΔE=(-De)
ΔEint
ΔEprep
ΔEPauli
ΔEelstat
ΔEorb
−19.1
−63.1
44.0
−24.3
−82.1
57.9
207.6
262.0
a
a
a
a
−172.3 (63.7%)
−98.4 (36.3%)
−218.2 (63.5%)
−125.4 (36.5%)
a
Percentage contributions to the total attractive interaction energies
are given in parentheses.
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Communication
distort the two fragments to reach their actual geometries in the
complexes (ΔEprep = 57.9 vs 44.0 kcal/mol) compensates for
this difference. The three components of ΔEint (ΔEPauli, ΔEelstat
,
and ΔEorb) are all larger in magnitude in the PB complex 4*
than in the ethylene complex 3*, but their relative
contributions are about the same, with the electrostatic term
ΔEelstat representing ∼63% of the attractive interactions in both
complexes.
The nature of the covalent bonding was further assessed
using the charge decomposition analysis (CDA) method
developed by Frenking.14d,e,15 Donation and back-donation
contribute equally in the PB complex 4* (d = 0.623, b = 0.624),
whereas donation predominates over back-donation in the
ethylene complex 3* (d = 0.566, b = 0.430). Basically, the
bonding can be described within the Dewar−Chatt−
Duncanson (DCD) model,16 but the presence of a non-
negligible residual term in 4* (Δ = −0.15) suggests some
covalent bonding (associated with a metallacyclic structure) in
addition to the donor−acceptor interactions.
Figure 2. Molekel plots (cutoff: 0.04) of the NLMOs accounting for
the π→Pt and Pt→π* interactions in the model complexes 3*
(bottom) and 4* (top). Atomic contributions (%) are reported in
parentheses.
More insight into the relative contributions of P and B in the
PB complex 4* was then obtained from molecular orbital
(MO) analysis (Figure S2).9 The frontier MOs (FMOs) of the
PB 1 are essentially π(PB) and π*(PB) MOs, in line with the
strong π donation from P to B. The coordination of the PB
ligand to the [Pt(PMe3)2] fragment involves the same type of
orbital interactions as for ethylene: π(PB)→Pt donation and
Pt→π*(PB) back-donation. However, noticeable differences
between the PB complex 4* and the ethylene complex 3* were
found. Indeed, the electronic dissymmetry of the PB imparts
substantial polarization to the FMOs of the PB fragment
[π(PB) is centered on P while π*(PB) is centered on B], and
the ensuing MOs in 4* are similarly polarized. In addition,
π(PB) is higher in energy than π(ethylene) and π*(PB) is
lower in energy than π*(ethylene), and thus, the energy gap
between the FMOs is significantly lower for 1 than for ethylene
(3.3 vs 6.2 eV; Figures S2 and S3).9 As a result, the orbital
interactions are stronger in the PB complex 4*, in agreement
with the higher ΔEorb value found in the EDA. Overall, the
bonding situation in 4* can thus be described by the DCD
model, taking into account the fact that the donation and back-
donation interactions are polarized toward P and B,
respectively. Natural localized MO (NLMO) analyses further
corroborated these conclusions (Figure 2). The NLMO
associated with PB→Pt donation is mainly localized on the
ligand and strongly polarized toward P (55.4% contribution
from P but only 25.8% from B). As for the related ethylene
complex, slight delocalization tails are observed over Pt (14%).
Reciprocally, the NLMO associated with Pt→PB back-donation
is centered on Pt (75%), with the contribution from B
predominant over that from P (14.0 vs 7.6%).
Chart 3. Known Complexes of Boron-Containing
Heteroalkenes
Among E15E13 heteroalkenes (E15 = group 15 element, E13
=
group 13 element), only aminoboranes have been coordinated
to TMs. The mono and bis σ-(B−H) complexes C and D,
respectively, have recently been characterized,20 but side-on
coordination has not been authenticated experimentally to date,
although a few DFT studies have supported its possible
existence.20a,b,21 The PB complexes 4 and 5 reported here
provide unambiguous evidence for alkene-type coordination
with E15E13 heteroalkenes.22−24 Future work will seek to
explore the generality of such side-on coordination and
determine the influence of the metal fragment and the
substitution patterns at P and B.
In conclusion, this detailed bonding analysis has revealed
important similarities but also significant differences between
the coordination of PB 1 and ethylene to Pt(0). Side-on
coordination of the PB ligand is geometrically symmetric but
electronically dissymmetric, and the bonding situation in
complex 4 is best represented as a superposition of forms a
and b in Chart 2.
ASSOCIATED CONTENT
* Supporting Information
■
S
Detailed experimental conditions and procedures and computa-
tional data. This material is available free of charge via the
Internet at http://pubs.acs.org.
To date, the coordination chemistry of acyclic boron-
containing π ligands has been explored only scarcely.17
Typically, boron-containing alkene-type complexes are limited
to the B-amino-9-fluorenylideneborane Fe and Mn complexes
AUTHOR INFORMATION
Corresponding Author
amgoune@chimie.ups-tlse.fr; dbouriss@chimie.ups-tlse.fr
■
A reported by Noth18 on one hand and the Ta borataalkene
Notes
̈
complexes B reported by Piers19 on the other (Chart 3).
The authors declare no competing financial interest.
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(14) (a) Morokuma, K. J. Chem. Phys. 1971, 55, 1236. (b) Morokuma,
K. Acc. Chem. Res. 1977, 10, 294. (c) Ziegler, T.; Rauk, A. Theor. Chim.
ACKNOWLEDGMENTS
■
We dedicate this paper to Professor Guy Bertrand on the
occasion of his 60th birthday. This work was supported by the
Centre National de la Recherche Scientifique (CNRS), the
Acta 1977, 46, 1. (d) Frenking, G. J.; Frohlich, N. Chem. Rev. 2000,
̈
100, 717. (e) Boehme, C.; Uddin, J.; Frenking, G. Coord. Chem. Rev.
2000, 197, 249.
(15) Dapprich, S.; Frenking, G. J. Phys. Chem. 1995, 99, 9352.
(16) (a) Dewar, M. J. S. Bull. Soc. Chim. Fr. 1951, C79. (b) Chatt, J.;
Duncanson, L. A. J. Chem. Soc. 1953, 2929.
(17) Emslie, D. J. H.; Cowie, B. E.; Kolpin, K. B. Dalton Trans. 2012,
41, 1101.
́
Universite Paul Sabatier (UPS), and the Agence Nationale de la
Recherche (ANR-10-BLAN-070901). COST Action CM0802
(PhoSciNet) is also acknowledged. The theoretical work was
granted access to HPC resources of IDRIS under Allocation
2012 (i2012080045) made by Grand Equipement National de
Calcul Intensif (GENCI). We thank Prof. D. W. Stephan for
insightful discussions, S. J. Geier for providing samples of 1 and
2, Dr. C. J. Wallis for preliminary experimental studies, and Dr.
K. Costuas for assistance with ADF calculations.
(18) (a) Helm, S.; Noth, H. Angew. Chem., Int. Ed. Engl. 1988, 27,
̈
1331. (b) Channareddy, S.; Linti, G.; Noth, H. Angew. Chem., Int. Ed.
̈
Engl. 1990, 29, 199. (c) Helm, S. W.; Linti, G.; Noth, H.;
̈
Channareddy, S.; Hofmann, P. Chem. Ber. 1992, 125, 73.
(19) (a) Cook, K. S.; Piers, W. E.; McDonald, R. Organometallics
1999, 18, 1575. (b) Cook, K. S.; Piers, W. E.; McDonald, R.
Organometallics 2001, 20, 3927.
REFERENCES
■
(20) (a) Douglas, T. M.; Chaplin, A. B.; Weller, A. S.; Yang, X.; Hall,
M. B. J. Am. Chem. Soc. 2009, 131, 15440. (b) Alcaraz, G.; Vendier, L.;
Clot, E.; Sabo-Etienne, S. Angew. Chem., Int. Ed. 2010, 49, 918.
(c) Tang, C.; Thompson, A.; Aldridge, S. Angew. Chem., Int. Ed. 2010,
49, 921. (d) Tang, C. Y.; Thompson, A. L.; Aldridge, S. J. Am. Chem.
Soc. 2010, 132, 10578. (e) Stevens, C. J.; Dallanegra, R.; Chaplin, A.
B.; Weller, A. S.; Macgregor, S. A.; Ward, B.; Mckay, D.; Alcaraz, G.;
Sabo-Etienne, S. Chem.Eur. J. 2011, 17, 3011. (f) Vidovic, D.; Addy,
D. A.; Kramer, T.; McGrady, J.; Aldridge, S. J. Am. Chem. Soc. 2011,
133, 8494.
(1) Amgoune, A.; Bourissou, D. Chem. Commun. 2011, 47, 859.
(2) (a) Kuzu, I.; Krummenacher, I.; Meyer, J.; Armbruster, F.;
Breher, F. Dalton Trans. 2008, 5836. (b) Fontaine, F.-G.; Boudreau, J.;
Thibault, M.-H. Eur. J. Inorg. Chem. 2008, 5439. (c) Bouhadir, G.;
Amgoune, A.; Bourissou, D. Adv. Organomet. Chem. 2010, 58, 1.
(3) For selected references, see: (a) Bontemps, S.; Gornitzka, H.;
Bouhadir, G.; Miqueu, K.; Bourissou, D. Angew. Chem., Int. Ed. 2006,
45, 1611. (b) Bontemps, S.; Bouhadir, G.; Miqueu, K.; Bourissou, D. J.
Am. Chem. Soc. 2006, 128, 12056. (c) Sircoglou, M.; Bontemps, S.;
Mercy, M.; Saffon, N.; Takahashi, M.; Bouhadir, G.; Maron, L.;
Bourissou, D. Angew. Chem., Int. Ed. 2007, 46, 8583. (d) Sircoglou, M.;
Bontemps, S.; Bouhadir, G.; Saffon, N.; Miqueu, K.; Gu, W.; Mercy,
M.; Chen, C. H.; Foxman, B. M.; Maron, L.; Ozerov, O. V.; Bourissou,
D. J. Am. Chem. Soc. 2008, 130, 16729. (e) Sircoglou, M.; Mercy, M.;
Saffon, N.; Coppel, Y.; Bouhadir, G.; Maron, L.; Bourissou, D. Angew.
Chem., Int. Ed. 2009, 48, 3454. (f) Gualco, P.; Lin, T. P.; Sircoglou, M.;
Mercy, M.; Ladeira, S.; Bouhadir, G.; Perez, L. M.; Amgoune, A.;
Maron, L.; Gabbai, F. P.; Bourissou, D. Angew. Chem., Int. Ed. 2009,
48, 9892. (g) Derrah, E. J.; Sircoglou, M.; Mercy, M.; Ladeira, S.;
Bouhadir, G.; Miqueu, K.; Maron, L.; Bourissou, D. Organometallics
2011, 30, 657.
(21) (a) Zimmerman, P. M.; Paul, A.; Zhang, Z.; Musgrave, C. B.
Angew. Chem., Int. Ed. 2009, 48, 2201. (b) Zimmerman, P. M.; Paul,
A.; Musgrave, C. B. Inorg. Chem. 2009, 48, 5418. (c) Kawano, Y.;
Uruichi, M.; Shimoi, M.; Taki, S.; Kawaguchi, T.; Ogino, H. J. Am.
Chem. Soc. 2009, 131, 14946.
(22) η4 coordination of an aminovinylborane to Fe(CO)3 has been
suggested on the basis of IR and 11B NMR data. See: Schmid, G.;
Alraun, F.; Boese, R. Chem. Ber. 1991, 124, 2255.
(23) The ability of iminium cations (>CN<)+ to coordinate in a
side-on fashion was recognized early on. For selected examples, see:
(a) Abel, E. W.; Rowley, R. J.; Mason, R.; Thomas, K. M. J. Chem. Soc.,
Chem. Commun. 1974, 72. (b) Matsumoto, M.; Nakatsu, K.; Tani, K.;
Nakamura, A.; Otsuka, S. J. Am. Chem. Soc. 1974, 96, 6777.
(c) Sepelak, D. J.; Pierpont, C. G.; Barefield, E. K.; Budz, J. T.;
Poffenberger, C. A. J. Am. Chem. Soc. 1976, 98, 6178.
(4) For reviews, see: (a) Paine, R. T.; Noth, H. Chem. Rev. 1995, 95,
̈
343. (b) Power, P. P. Chem. Rev. 1999, 99, 3463. (c) Gaumont, A. C.;
Carboni, B. Sci. Synth. 2004, 6, 485. (d) Fischer, R. C.; Power, P. P.
Chem. Rev. 2010, 110, 3877.
(24) For a unique example of side-on coordination by a
methylenephosphonium cation (>CP<)+, see: Per
́
ez, J. M.;
(5) (a) Feng, X.; Olmstead, M. M.; Power, P. P. Inorg. Chem. 1986,
25, 4616. (b) Pestana, D. C.; Power, P. P. J. Am. Chem. Soc. 1991, 113,
8426.
Helten, H.; Donnadieu, B.; Reed, C. A.; Streubel, R. Angew. Chem.,
Int. Ed. 2010, 49, 2615.
(6) (a) Geier, S. J.; Gilbert, T. M.; Stephan, D. W. J. Am. Chem. Soc.
2008, 130, 12632. (b) Geier, S. J.; Gilbert, T. M.; Stephan, D. W. Inorg.
Chem. 2011, 50, 336.
(7) This high-field 11B NMR chemical shift is typically observed for
borate-containing three-membered rings. For example, see: Kropp, M.
A.; Schuster, G. B. J. Am. Chem. Soc. 1989, 111, 2316.
(8) Beringhelli, T.; Donghi, D.; Maggioni, D.; D’Alfonso, G. Coord.
Chem. Rev. 2008, 252, 2292.
(9) See the Supporting Information.
(10) (a) Crossley, I. R.; Hill, A. F.; Willis, A. C. Organometallics 2008,
27, 312. (b) Bontemps, S.; Sircoglou, M.; Bouhadir, G.; Puschmann,
H.; Howard, J. A. K.; Dyer, P. W.; Miqueu, K.; Bourissou, D. Chem.
Eur. J. 2008, 14, 731. (c) Bontemps, S.; Bouhadir, G.; Gu, W.; Mercy,
M.; Chen, C. H.; Foxman, B. M.; Maron, L.; Ozerov, O. V.; Bourissou,
D. Angew. Chem., Int. Ed. 2008, 47, 1481. (d) Owen, G. R.; Gould, P.
H.; Hamilton, A.; Tsoureas, N. Dalton Trans. 2010, 39, 49.
(11) Cordero, B.; Gomez, V.; Platero-Prats, A. E.; Reves, M.;
Echeverria, J.; Cremades, E.; Barragan, F.; Alvarez, S. Dalton Trans.
2008, 2832.
(12) Cheng, P. T.; Nyburg, S. C. Can. J. Chem. 1972, 50, 912.
(13) (a) Uddin, J.; Dapprich, S.; Frenking, G.; Yates, B. F.
Organometallics 1999, 18, 457. (b) Massera, C.; Frenking, G.
Organometallics 2003, 22, 2758.
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