Cleavage of unstrained C(sp2)-C(sp2) single bonds with Ni0 complexes using chelating assistance

Article abstract of DOI:10.1021/om800054m

The reaction of Ni(COD)₂ with a ligand containing a biphenyl subunit (P(ⁱPr)₂-O-Ph-Ph-O-P(ⁱPr)₂, L1) resulted in a mixture of compounds, the main product being [L1]Ni(COD), which could be quantitatively transferred to product 2 using bis(p-toluyl)acetylene. The possible activation products, cis-and trans-3 (3^c and 3^t, respectively), which would result from the cleavage of the bridging C-C single bond were synthesized independently. The mechanism of the cis/trans-isomerization was examined, activation parameters determined and trapping tests performed. Reaction of (PPh₃) ₂Ni(CO)₂ with L1 gave a novel complex 4 by a ligand exchange reaction. This compound, when heated to 95°C under a 5 bar atmosphere of CO for several days, slowly incorporated CO into the bridging C-C single bond. This behavior as well as isotopic labeling experiments with ¹³CO indicated that, following a dissociation of CO in complex 4, an interaction between the metal center and the biphenyl moiety is induced, leading to activation. The reaction of Ni(COD)₂ with P(ⁱPr) ₂-O-Ph-CO-Ph-O-(P(ⁱPr)₂ (L3), which contains a benzophenone moiety, resulted in the quantitative activation of the PhC-CO bond at 20°C, leading to complexes 3^c/t (trans/cis 80/20 at 20°C). The mechanism was examined and intermediates of it were identified as well as activation parameters for their further reaction determined. Reaction of (PPh₃)₂Ni(CO)₂ with L3 gave complex 5, which is stable at 20°C. Complexes 3^c/t were shown to react quantitatively to give compound 5 under an atmosphere of CO. Selective isotopic labeling with ¹³CO proved that an activation similar to that observed with Ni(COD)₂ occurs in complex 5 at 95°C but much more slowly and is accompanied by the formation of complex 4. Molecular structures of the novel complexes 2, 3^c, 4, and 5 have been determined by single crystal X-ray diffraction studies.

Full text of DOI:10.1021/om800054m

3482
Organometallics 2008, 27, 3482–3495
Cleavage of Unstrained C(sp2)sC(sp2) Single Bonds with Ni0
Complexes Using Chelating Assistance
Klaus Ruhland,* Andreas Obenhuber, and Stephan D. Hoffmann
TU Mu¨nchen, Department Chemie, Lehrstuhl fu¨r Anorganische Chemie, Lichtenbergstr. 4,
D-85748 Garching, BaVaria, D-85747, Germany
ReceiVed January 22, 2008
The reaction of Ni(COD)2 with a ligand containing a biphenyl subunit (P(iPr)2-O-Ph-Ph-O-P(iPr)2,
L1) resulted in a mixture of compounds, the main product being [L1]Ni(COD), which could be
quantitatively transferred to product 2 using bis(p-toluyl)acetylene. The possible activation products, cis-
and trans-3 (3c and 3t, respectively), which would result from the cleavage of the bridging CsC single
bond were synthesized independently. The mechanism of the cis/trans-isomerization was examined,
activation parameters determined and trapping tests performed. Reaction of (PPh3)2Ni(CO)2 with L1
gave a novel complex 4 by a ligand exchange reaction. This compound, when heated to 95 °C under a
5 bar atmosphere of CO for several days, slowly incorporated CO into the bridging CsC single bond.
This behavior as well as isotopic labeling experiments with 13CO indicated that, following a dissociation
of CO in complex 4, an interaction between the metal center and the biphenyl moiety is induced, leading
to activation. The reaction of Ni(COD)2 with P(iPr)2-O-Ph-CO-Ph-O-(P(iPr)2 (L3), which contains a
benzophenone moiety, resulted in the quantitative activation of the PhCsCO bond at 20 °C, leading to
complexes 3c/t (trans/cis 80/20 at 20 °C). The mechanism was examined and intermediates of it were
identified as well as activation parameters for their further reaction determined. Reaction of (PPh3)2Ni(CO)2
with L3 gave complex 5, which is stable at 20 °C. Complexes 3c/t were shown to react quantitatively to
give compound 5 under an atmosphere of CO. Selective isotopic labeling with 13CO proved that an
activation similar to that observed with Ni(COD)2 occurs in complex 5 at 95 °C but much more slowly
and is accompanied by the formation of complex 4. Molecular structures of the novel complexes 2, 3c,
4, and 5 have been determined by single crystal X-ray diffraction studies.
and co-workers (directed cleavage of a C(sp3)sC(sp2)dO bond
Introduction
and a C(sp3)sC(sp2)dN bond, respectively)3 and W. D. Jones
and co-workers (cleavage of a C(sp2)sC(sp) bond in precoor-
dinated diphenylacetylene;4a cleavage of a C(sp2)sC(sp)tN
bond in precoordinated aryl nitriles;4d–f cleavage of a
C(sp3)sC(sp)tN bond in allyl cyanide and acetonitrile4c,d (the
nitrile chemistry was done in cooperation with the group of J. J.
Garcia)). C(sp)sC(sp) single bonds have also been cleaved by
group-4 Cp2M complexes5 in the group of U. Rosenthal and
nonstrained C(sp3)sC(sp3) bonds have been successfully acti-
vated by early transition metals (ꢀ-alkyl elimination).6 No
unequivocal evidence exists for a cleavage of an unstrained
C(sp2)sC(sp2) single bond, although it has been proposed in
The activation and cleavage of CsC single bonds by
transition metal complexes is one of the most challenging
problems in molecular organometallic chemistry and reviews
about this reaction have been published.1 With regard to
nonstrained CsC single bonds, the principle of chelating (or at
least coordinating) assistance is still required for activation. The
most prominent examples of successful activation systems
include the work of D. Milstein and co-workers (cleavage of a
C(sp3)sC(sp2) bond in their successful PCP pincer-type
ligand),2 of J. W. Suggs and co-workers as well as C.-H. Jun
* To whom correspondence should be addressed. E-mail:
klaus.ruhland@ch.tum.de.
(1) (a) Jones, W. D.; Feher, F. J. Acc. Chem. Res. 1989, 22, 91–100.
(b) Arndtsen, B. A.; Bergman, R. G.; Mobley, T. A.; Peterson, T. Z. Acc.
Chem. Res. 1995, 28, 154–162. (c) Rybtchinski, B.; Milstein, D. Angew.
Chem., Int. Ed. 1999, 38, 870–883. (d) Chul-Ho, J. Chem. Soc. ReV. 2004,
33, 610–618.
(2) (a) Rybtchinski, B.; Oevers, S.; Montag, M.; Vigalok, A.; Rozenberg,
J. M. L.; Martin, H.; Milstein, D. J. Am. Chem. Soc. 2001, 123, 9064. (b)
Sundermann, A.; Uzan, O.; Milstein, D.; Martin, J. L. J. Am. Chem. Soc.
2000, 122, 7095. (c) Gozin, M.; Weisman, A.; Ben-David, Y.; Milstein, D.
Nature 1993, 364, 699. (d) Rytchinski, B.; Vigalok, A.; Ben-David, Y.;
Milstein, D. J. Am. Chem. Soc. 1996, 118, 12406. (e) Liou, S.-Y.; Gozin,
M.; Milstein, D. J. Am. Chem. Soc. 1995, 117, 9774. (f) Vigalok, A.;
Rybtchinski, B.; Shimon, L. J. W.; Ben-David, Y.; Milstein, D. Organo-
metallics 1999, 18, 895–905. (g) Vigalok, A.; Milstein, D. Organometallics
2000, 19, 2061. (h) Vigalok, A.; Milstein, D. Organometallics 2000, 19,
2341. (i) Salem, H.; Ben-David, Y.; Shimon, L. J. W.; Milstein, D.
Organometallics 2006, 25, 2292. (j) van der Boom, M. E.; Liou, S.-Y.;
Shimon, L. J. W.; Ben-David, Y.; Milstein, D. Inorg. Chim. Act. 2004,
357, 4015–4023.
(3) (a) Suggs, J. W.; Jun, C.-H. J. Am. Chem. Soc. 1984, 106, 3054–
3056. (b) Suggs, J. W.; Jun, C.-H. J. Am. Chem. Soc. 1986, 108, 4679–
4681. (c) Jun, C.-H.; Lee, H.; Lim, S.-G. J. Am. Chem. Soc. 2001, 123,
751–752. (d) Jun, C.-H.; Lee, H. J. Am. Chem. Soc. 1999, 121, 880–881.
(4) (a) Mu¨ller, C.; Iverson, C. N.; Lachicotte, R. J.; Jones, W. D. J. Am.
Chem. Soc. 2001, 123, 9718–9719. (b) Brunkan, N. M.; Brestensky, D. M.;
Jones, W. D. J. Am. Chem. Soc. 2004, 126, 3627–3641. (c) Acosta-Ramirez,
A.; Munoz-Hernandez, M.; Jones, W. D.; Garcia, J. J. Organometallics 2007,
26, 5766–5769. (d) Garcia, J. J.; Arevalo, A.; Brunkan, N. M.; Jones, W. D.
Organometallics 2004, 23, 3997–4002. (e) Garcia, J. J.; Jones, W. D.
Organometallics 2000, 19, 5544–5545. (f) Garcia, J. J.; Brunkan, N. M.;
Jones, W. D. J. Am. Chem. Soc. 2002, 124, 9547–9555.
(5) (a) Rosenthal, U.; Arndt, P.; Baumann, W.; Burlakov, V. V.;
Spannenberg, A. J. Organomet. Chem. 2003, 670, 84–96. (b) Rosenthal,
U.; Go¨rls, H. J. Organomet. Chem. 1992, 439, C36.
(6) (a) Resconi, L.; Piemontesi, F.; Franciscono, G.; Abis, L.; Fiorani,
T. J. Am. Chem. Soc. 1992, 114, 1025–1032. (b) Evans, W. J.; Perotti,
J. M.; Ziller, J. W. J. Am. Chem. Soc. 2005, 127, 1068–1069. (c) Etienne,
M.; Mathieu, R.; Donnadieu, B. J. Am. Chem. Soc. 1997, 119, 3218–3228.
(d) Watson, P. L.; Roe, D. C. J. Am. Chem. Soc. 1982, 104, 6471–6473.
10.1021/om800054m CCC: $40.75
2008 American Chemical Society
Publication on Web 06/05/2008

CleaVage of C(sp2)sC(sp2) Single Bonds
Organometallics, Vol. 27, No. 14, 2008 3483
Scheme 1
the context of decarbonylative cleavage in alkyl phenyl ketones
with Ru3(CO)12.7 The strained biphenylene has been successfully
transformed by several groups.8
Different Ni0 complexes have been employed in the activation
of CsC bonds for organic precursors such as biphenylene8a–f,l,n
and cyclobutenone.9 The CsCN single bond also exhibits
reactivity, and organo-nitriles have been successfully cleaved
by Ni0complexes.4b–f,10,11 Mechanistic studies in the groups of
J. J. Garcia and W. D. Jones, using [(dippe)NiH]2 as a source
for the reactive (dippe)Ni0 fragment, have shown that an η2-
nitrile complex is first formed that is subsequently followed by
the activation of the CsCN single bond. The choice of ligand
and geometry imposed by these ligands has an influence on the
reversibility of resultant aryl nitrile activation. The activation
reaction was shown to be reversible using the dippe ligand,
which forces a cis-geometry in the activated NiII complex.4b,c
In contrast, the irreversible cleavage of aryl nitriles with a Ni0
complex containing two N-heterocyclic carbene ligands is
observed, most likely because with this ligand NiII complexes
with trans-geometry are obtained.11d Milstein and co-workers
were successful in breaking the C(sp2)sC(sp3) bond in their
PCP pincer type ligand using NiII.2j
In our previous work, a biphenyl moiety containing -O-PR2
chelating anchors in the 2 and 2′ position was reacted with Pt0
complexes. Our experiments, as well as calculations, indicated
that the backbone of this ligand is too short for Pt0 to allow a
sterically unhindered approach of the bridging C(sp2)sC(sp2)
bond to the metal center.12 To reduce the impact of steric strain
and facilitate the approach of the bridge, we extended our study
to examine the smaller Ni0 metal center. We herein present our
most recent explorations in CsC activation, with Ni0 acting as
a transition metal center that serves to activate the nonstrained
C(sp2)sC(sp2) single bonds.
Results and Discussion
Ligand Choice and Complexation. The ligands L1-L3
shown in Scheme 1 were employed.
According to the work of D. Milstein and co-workers the
use of an oxo linker between the phenyl molecular moiety and
the coordinating phosphorus anchor is electronically
unfavorable.1c Nevertheless, we chose to explore this design
motif as it provides the shortest possible chelating anchor length
and forces the bridging CsC single bond in the biphenyl moiety
as close as possible to the metal, using Ni(COD)2 and
(PPh3)2Ni(CO)2 as metal precursors. Scheme 2 summarizes the
results observed with ligand L1.
Ligand L1 coordinates immediately to Ni(COD)2 at room
temperature. A mixture of five compounds was detected by 31
P
NMR spectroscopy for the reaction product. One main sharp
peak at 184 ppm is observed along with four smaller broadened
peaks between 181 and 186 ppm. The coordinated olefinic
C-atoms of the COD were observed in the 13C NMR spectrum
in the area of 60 ppm as multiplets. The main peak appears as
a doublet of doublets at 60.5 ppm. The ratio between free and
1
coordinated COD double bonds can be assigned by H NMR
spectroscopy to 4:1. This mixture is stable in solution for several
days and does not change in composition. The main peak at
184 ppm is assigned to compound 1a in Scheme 2 and the
smaller peaks to compound 1b, which can exist in chair/boat
configuration of the COD and in two diasteriomeric forms
concerning the axial chiral biphenyl ligand. This conclusion is
confirmed by the observation of the 31P NMR spectrum recorded
in 1,5-COD as solvent, where the intensity of the four smaller
peaks decreases decisively, leaving only the peak at 184 ppm
and indicating an equilibrium shift toward 1a. In addition, 1
reacts quantitatively with 1 equiv of bis(p-toluyl)acetylene at
room temperature in a slow ligand exchange reaction to form
compound 2 in Scheme 2. A perspective drawing of a molecular
moiety in the solid state of 2 is provided in Figure 1. Selected
structural data are given in Table 1.
When compound 1 is held at room temperature under an
atmosphere of CO for several hours, the quantitative formation
of compound 4, shown in Scheme 2, is observed. This reaction
offers the possibility to synthesize compound 4* with 13C-
labeled CO groups. Neither 1 nor 2 shows the anticipated
activation reaction to generate 3 (see Scheme 3 for 3) even if
heated to 95 °C in toluene. Instead, decomposition to an
unidentified product mixture occurs. In the course of the
decomposition of 1, 1,5-COD is partly isomerized to 1,4- and
1,3-COD. To prove that the activation products 3c and 3t are
stable and, thus, observable under the previously mentioned
conditions, these compounds were synthesized independently
using ligand L2 (Scheme 3).
(7) Chantani, N.; Ie, Y.; Kakiuchi, F.; Murai, S. J. Am. Chem. Soc. 1999,
121, 8645–8646.
(8) (a) Edelbach, B. L.; Lachicotte, R. J.; Jones, W. D. J. Am. Chem.
Soc. 1998, 120, 2843–2853. (b) Perthuisot, C.; Edelbach, B. J.; Zubirs, D. L.;
Simhai, N.; Iverson, C. N.; Mu¨ller, C.; Satoh, T.; Jones, W. D. J. Mol.
Catal. A: Chem. 2002, 189, 157–168. (c) Edelbach, B. L.; Lachicotte, R. J.;
Jones, W. D. Organometallics 1999, 18, 4040–4049. (d) Edelbach, B. L.;
Lachicotte, R. J.; Jones, W. D. Organometallics 1999, 18, 4660–4668. (e)
Mu¨ller, C.; Lachicotte, R. J; Jones, W. D. Organometallics 2002, 21, 1975–
1981. (f) Edelbach, B. L.; Vicic, D. A.; Lachicotte, R. J.; Jones, W. D.
Organometallics 1998, 17, 4784–4794. (g) Ujaque, G.; Maseras, F.;
Eisenstein, O.; Liable-Sands, L.; Rheingold, A. L.; Yao, W.; Crabtree, R. H.
New J. Chem. 1998, 1493–1498. (h) Lu, Z.; Jun, C. H.; de Gala, S. R.;
Sigalas, M. P.; Eisenstein, O.; Crabtree, R. H. Organometallics 1995, 14,
1168–1175. (i) Iverson, C. N.; Jones, W. D. Organometallics 2001, 20,
5745–5750. (j) Zhang, X.; Carpenter, G. B.; Sweigart, D. A. Organome-
tallics 1999, 18, 4887–4888. (k) Schwager, H.; Spyroudis, S.; Vollhardt,
K. P. C. J. Organomet. Chem. 1990, 382, 191–200. (l) Eisch, J. J.;
Piotrowski, A. M.; Han, K. I.; Kru¨ger, C.; Tsay, Y. H. Organometallics
1985, 4, 224–231. (m) Shaltout, R. M.; Sygula, R.; Sygula, A.; Fronczek,
F. R.; Stanley, G. G; Rabideau, P. W. J. Am. Chem. Soc. 1998, 120, 835–
836. (n) Schaub, T.; Radius, U. Chem.sEur. J. 2005, 11, 5024–5030.
(9) Huffman, M. A.; Liebeskind, L. S. J. Am.Chem. Soc. 1991, 113,
2771–2772.
(10) (a) Nakazawa, H.; Itazaki, M.; Kamata, K.; Ueda, K. Chem. Asian
J. 2007, 2, 882–888. (b) Taw, F. L.; Mueller, A. H.; Bergman, R. G.;
Brookhart, M. J. Am. Chem. Soc. 2003, 125, 9808–9813. (c) Taw, F. L.;
White, P. S.; Bergman, R. G.; Brookhart, M. J. Am. Chem. Soc. 2002, 124,
4192–4193. (d) Klei, S. R.; Tilley, T. D.; Bergman, R. G. Organometallics
2002, 21, 4648–4661. (e) Nakazawa, H.; Kawasaki, T.; Miyoshi, K.; Suresh,
C. H.; Koga, N. Organometallics 2004, 23, 117–126.
(11) (a) Morvillo, A.; Turco, A. J. Organomet. Chem. 1981, 208, 103–
113. (b) Favero, G.; Morvillo, A.; Turco, A. J. Organomet. Chem. 1983,
241, 251–257. (c) Abla, M.; Yamamoto, T. J. Organomet. Chem. 1997,
532, 267–270. (d) Schaub, T.; Do¨ring, C.; Radius, U. J. Chem. Soc., Dalton
Trans. 2007, 1993–2002.
Complex 3c can be synthesized in two steps either by
treatment of Ni(COD)2 with 2 equiv of ligand L2 followed by
the reaction of the resulting complex 6 with sec-BuLi or by the
addition of 2 equiv of ligand L2 to (DME)NiCl2 (DME: 1,2-
dimethoxyethane) and, again, treatment with sec-BuLi in the
second step. In both cases, exclusively the cis-isomer 3c is
(12) (a) Ruhland, K.; Bru¨ck, A.; Herdtweck, E. Eur. J. Inorg. Chem.
2007, 7, 944–964. (b) Ruhland, K.; Herdtweck, E. J. Organomet. Chem.
2005, 690, 5215–5236.

3484 Organometallics, Vol. 27, No. 14, 2008
Ruhland et al.
Scheme 2
generated. For this compound, single crystals suitable for X-ray
analysis could be grown from diethyl ether and a depiction of
a molecular moiety in the solid state is shown in Figure 2 and
selected structural data are listed in Table 2.
P-atoms, that show a coupling with one another in 31P NMR
spectroscopy at 183 and 150 ppm (2JPP ) 325 Hz), although
the formation of 7 does not go to completion within a few days.
We therefore assume that there is an equilibrium between 3t
2
The ligand environment about the Ni is distorted from the
ideal square planar structure toward a pseudotetrahedral geom-
etry. The angle between the two planes defined by (P2, Ni, C7)
and (P1, Ni, C6) is 33.5°, and the distance between the two
C-atoms connected to the Ni center is 2.8 Å.
and 7. The JPP coupling constant of 325 Hz is indicative of a
trans-configuration of the P atoms, and the dimeric structure 7
in Scheme 3 is proposed for this compound. A similar behavior
was observed for the analogous Pt complexes.12a J. J. Eisch
and co-workers found the formation of a peculiar dimer
containing a NisNi bond when they reacted Ni(PEt3)4 with
biphenylene.8l However, in that case, 2 equiv of the phosphine
ligand were lost during the reaction. The proposed dimer in
our case is, thus, certainly different from that of the Eisch group,
although Ni...Ni interactions could also be involved in our
system. Similar dimeric structures have appeared in recent
literature for Pd and Pt with acetate groups that bridge the two
metal centers and also possess ortho-metallated aryls as ad-
ditional ligands.13 Figure 3 shows the isomerization process of
3c to 3t at a concentration of 0.05 mol/L with time.
When 3c is heated to temperatures higher than 80 °C, a
quantitative isomerization to the trans-isomer 3t takes place.
At concentrations of 3t higher than 0.2 mol/L, a defined new
compound 7 can be observed containing two different types of
Figure 4 shows the percentage of 3c with respect to time at
85 °C, starting with three different concentrations of 3c.
Figure 4 demonstrates that there is no significant concentration
dependence observed for the cis/trans-isomerization in the
concentration range studied and that the consumption of 3c can
be described using a first order rate law at 85 °C. Three different
concentrations were examined at 105 °C and the same trend
was observed. Thus, it can be concluded that within the
temperature range of 80 to 109 °C and at concentrations of 25
mg/mL (0.05 mol/L), the rate determining step of isomerization
is a monomolecular process.
Three possible pathways for the course of the reaction are
suggested in Scheme 4.
One is along a spin-forbidden tetrahedral transition state
without any bond breaking (I). The second is by breaking one
NisP bond and switching from one T-shaped structure to the
second, followed by rebinding the phosphorus atom (II). The
third proposed pathway occurs via reductive elimination of the
two phenyl ligands, leading to a Ni0 intermediate, which
undergoes further oxidative addition of the bridging CsC single
Figure 1. ORTEP representation of a molecule in the solid state
of compound 2. Thermal ellipsoids are given at 50% probability
level. Hydrogen atoms are omitted for clarity.
Table 1. Selected Structural Data for Compound 2
d(C6-C6a) [Å]
1.470(16)
4.009(10)
122.30(11)
37.9(4)
d(C6-Ni) [Å]
(13) (a) Frech, C. M.; Leitus, G.; Milstein, D. Organometallics 2008,
27, 894–899. (b) Vicente, J.; Arcas, A.; Galvez-Lopez, M.-D. D.; Julia-
Hernandez, F.; Bautista, D.; Jones, P. G. Organometallics 2008, 27, 1582–
1590.
R(P-Ni-Pa) [°]
R(C20-Ni-C20a) [°]
γµ(C5-C6-C6a-C5a) [°]
105.2(13)

CleaVage of C(sp2)sC(sp2) Single Bonds
Organometallics, Vol. 27, No. 14, 2008 3485
Scheme 3
bond in the formed biphenyl subunit, as was anticipated in our
basic strategy (III).
The activation parameters for the isomerization were deter-
mined using an Eyring-plot, shown in Figure 5. The kinetic data
are summarized in Table 3.
The addition of iodobenzene does not change the isomeriza-
tion behavior. From this observation one can conclude that the
third pathway is not used for the isomerization, as a Ni0
intermediate should be trapped otherwise by oxidative addition
of the iodobenzene. The addition of strained olefins such as
COD or norbornene did not effect the isomerization reaction
nor did the presence of alkynes like t-butyl- or diphenylacety-
lene. The addition of PPh3 slowed the rate of isomerization.
The free PPh3 was observed in 31P NMR spectra, though it was
broadened. The reaction of compound 1 with PPh3 immediately
and quantitatively leads to [L1]Ni(PPh3) (31P NMR: 166.4 ppm
(d), 20.7 ppm (t), 2JPP ) 128.5 Hz), again supporting that a Ni0
complex, if present, would be trapped by PPh3. These findings
eliminate the possibility of pathway III, and they strongly
support pathway II. For pathway I, no influence of the PPh3
would have been expected because no coordinatively unsaturated
compound is formed in this route.
An activation enthalpy of 128 ( 8 kJ/mol and an activation
entropy of 34 ( 22 J/(mol K) were extracted from the data
(Figure 5). The major difference between pathway I and II is
that in II a coordinatively unsaturated intermediate is formed.
Pathway III differs from the other two in that the oxidation state
of nickel in the intermediate is zero. To test these pathways,
several reagents were added to the isomerization reaction to
trap intermediates or to influence the kinetics of the reaction.
Both 3c and 3t transform to compound 5 under an atmosphere
of CO at room temperature within hours (complex 4 is not
observed). This facilitates the synthesis of 5** with three 13C-
labeled carbonyl carbon atoms by using 13CO. Behavior
observed is similar to that found by J. J. Eisch and co-workers
as well as by W. D. Jones and co-workers with biphenylene as
substrate. They were able to observe the formation of fluorenone.
The dissociation enthalpy for a NisP bond is 149 kJ/mol.14
Taking into account the activation parameters (∆H# ) 128 kJ/
mol, ∆S# ) 34 J/(mol K)), a transition state is proposed that
contains a nearly cleaved NisP bond.
Reaction of (PPh3)2Ni(CO)2 with ligand L1 yields compound
4. A perspective drawing of a molecular moiety in the solid
state of 4 determined by X-ray analysis is shown in Figure 6,
with selected structural data presented in Table 4.
The bond length of the bridging CsC single bond in the
biphenyl subunit is 1.495(5) Å. Although typical bond lengths
of 1.48-1.49 Å are observed (1.470(16) for 2), an interaction
of this bond with the metal center can be excluded as a reason
for the slightly elongated bond. The two carbon centers of this
bond are 3.8 and 4.1 Å from the Ni atom (for comparison:
atomic radius of Ni, 1.25 Å; Van der Waals radius of C, 1.85
Å) and for an 18-electron metal center with strong ligand
environment, a coordination of additional electron pairs is
unfavorable. Two peaks at 2007 and 1937 cm-1 are found for
the carbonyl stretching vibrations by IR spectroscopy (KBr
pellet). The starting complex shows peaks at 1999 and 1934
cm-1. These values indicate a decrease in the electron density
at the Ni center during the reaction in accordance with a change
from a phosphine to a phosphinite, again supporting that an
interaction of the Ni center with the biphenyl moiety, which in
this case would increase the electron density at the metal center,
is not observed.
Figure 2. ORTEP representation of a molecule in the solid state
of compound 3c. Thermal ellipsoids are given at 50% probability
level. Hydrogen atoms are omitted for clarity.
Table 2. Selected Structural Data for Compound 3c
d(C6-Ni) [Å]
1.932(2)
1.930(2)
2.824(4)
82.97(7)
82.62(8)
108.89(3)
94.0(1)
d(C7-Ni) [Å]
d(C6-C7) [Å]
R(C6-Ni-P1) [°]
R(C7-Ni-P2) [°]
R(P2-Ni-P1) [°]
R(C6-Ni-C7) [°]
angle between the planes (P2,Ni,C7) and (P1,Ni,C6) [°]
33.48(12)
(14) Martinho, J. A.; Beauchamp, J. L. Chem. ReV. 1990, 90, 629–688.

3486 Organometallics, Vol. 27, No. 14, 2008
Ruhland et al.
Figure 3. Development of the cis/trans-isomerization of compound 3 followed by 31P NMR spectroscopy at 109 °C in toluene-d8. Spectra
were recorded in 2 min intervals, where the concentration of 3 was 25 mg/mL (0.05 mol/L).
as a possible pathway. The corresponding diphenyl ketones
failed to react, though.7
Chelating assistance is mandatory for our system. The reaction
of Ni(PEt3)4 with benzophenone leads to a stable π-complex
between the Ni center and the carbonyl double bond and has
been reported by J. K. Kochi and co-workers.15 An X-ray-
structure of the π-complex has been provided by this group,
and the kinetics of formation were followed. A melting point
of 70-78 °C was reported for this compound, underlining its
thermal stability. It is proposed that the chelating assistance in
our case prevents or at least disfavors an approach of the CdO
axis coplanar to the PsNisP plane. This type of approach
appears to be necessary for the formation of the π-complex.
Figure 7 shows the development of the reaction monitored by
Figure 4. Percentage of 3c as a function of time at 85 °C with
31P NMR spectroscopy.
three different starting concentrations of 3c (), 14.3 mg/mL; ∆,
31.3 mg/mL; 0, 55.0 mg/mL). In the upper right corner, the
evaluation assuming a first order rate law for the cis/trans-
isomerization is shown for the three concentrations.
At the onset of the reaction, two poorly defined peak groups
at 200 and 165 ppm are present, which are assigned to different
complexes containing ligand L3, Ni, and COD (compound 9
in Scheme 5 is one proposed structural representation). These
peaks disappear in favor of a sharp peak at 190 ppm for 3t and
two doublets at 165 ppm and 202 ppm (2JPP ) 29.5 Hz), which
are assigned to 8c (see Scheme 6 for 8c). The small 2JPP coupling
constant observed supports a NiII center4b,c and a cis-configu-
ration. The 31P NMR peaks of 8c are broadened at 20 °C and
can be sharpened by lowering the temperature. It can be
concluded from this finding that a dynamic exchange between
the two degenerate forms of 8c occurs at the spectral time scale
of 31P NMR spectroscopy. Later in the reaction, a small peak
at 192 ppm for 3c can be detected (3t/3c 80/20 at 20 °C after
complete conversion; if the complete reaction is performed at
higher temperatures, this ratio decreases in favor of 3c). Because
the examination of the cis/trans-isomerization of 3 showed that
3c is quantitatively converted to 3t only at temperatures g80
°C, it can be concluded that the formation of 3c and 3t during
the activation of ligand L3 occurs via parallel pathways. On
the other hand, the ratio between 3t and 3c in the course of the
reaction is not constant, which means that the two isomers
By heating a toluene solution of complex 4 to 95 °C under
an atmosphere of 5 bar of CO for 7 days, the formation of 5 in
low yield (20%) could be detected. After heating a solution of
complex 4 in toluene-d8 under an argon atmosphere for several
days, no significant amounts of 3 could be observed. Irradiation
of complex 4 with UV light for 3 h only led to the complete
reisolation of the starting material.
Ligand L3 and complexes containing L3 show very different
behaviors, which are summarized in Scheme 5. When ligand
L3 is reacted with Ni(COD)2 at 20 °C, a mixture of adducts is
formed (compound 9 in Scheme 5 as one proposed structural
representation), which slowly reacts further under activation of
the C(sp2)sC(sp2)dO single bond. J. W. Suggs and co-workers
could cleave a C(sp3)sC(sp2)dO single bond in a RhI complex
using chelating assistance.3
The unequivocal cleavage of a nonstrained C(sp2)sC(sp2)
single bond is unprecedented, but alkyl phenyl ketones with an
oxazoline anchor for chelating assistance were successfully
decarbonylated by Ru3(CO)12 at 160 °C in toluene at 5 atm of
CO and a C(sp2)sC(sp2)dO single bond cleavage was discussed
(15) Tsou, T. T.; Huffman, J. C.; Kochi, J. K. Inorg. Chem. 1979, 18,
2311–2317.

CleaVage of C(sp2)sC(sp2) Single Bonds
Organometallics, Vol. 27, No. 14, 2008 3487
Scheme 4
cannot be formed from the same intermediate, even with
different rates. This is indirect evidence for the existence of 8t
(see Scheme 6 for 8t) as the precursor for the formation of 3c,
although 8t cannot be observed. Compound 8t is most likely
formed by isomerization of 8c, which reacts further to yield 3c
in a fast, consecutive step. Scheme 6 summarizes the mecha-
nistic considerations mentioned so far.
By evaluating the integrals of the different compounds with
time (Figure 7), activation parameters for the consumption of
8c could be obtained, assuming a first order rate law for this
reaction (Table 6).
Using this information, an Eyring plot was made. The values
of ∆8cH# ) 120 ( 6 kJ/mol and ∆8cS# ) 75 ( 20 J/(mol K)
can be extracted from the Eyring plot (Figure 10, Table 6) in
an admittedly narrow temperature range. At temperatures higher
than 45 °C, the peaks for 8c are too broad to be evaluated
quantitatively. At temperatures lower than 15 °C, the reaction
becomes too slow.
On performing line shape analysis for the peaks of 8c, kred
can be extracted, assuming that kox is much larger than kred
,
which is justified as the Ni0 intermediate cannot be detected in
contrast to 8c (Figure 8, Table 5).
Further analysis of this data was done in the form of a Eyring
The activation process cannot be trapped by the addition of
bis(p-toluyl)acetylene, and the acetylene complex 10 can be
detected by 31P NMR spectroscopy at about 191 ppm but it
reacts further and quantitatively (consumption of 10: first order
kinetics, k20 °C ) 0.786 h-1) to give the same ratio of 3t to 3c,
plot (Figure 9). The values of ∆redH# ) 86 ( 8 kJ/mol and
∆
redS# ) 80 ( 26 J/(mol K) were extracted.
Figure 5. Eyring plot of the cis/trans-isomerization of compound
3.
Table 3. Rate Constants of the cis/trans-Isomerization of Compound
3 at Variable Temperatures
Figure 6. ORTEP representation of a molecule in the solid state
of compound 4. Thermal ellipsoids are given at 50% probability
level. Hydrogen atoms are omitted for clarity.
T [°C]
kct [1/min]
80
85
87.5
90
0.0028 ( 0.0002
0.0057 ( 0.0004
0.0076 ( 0.0006
0.0142 ( 0.0004
0.0207 ( 0.0005
0.020 ( 0.002
0.0267 ( 0.0007
0.034 ( 0.003
0.057 ( 0.001
0.119 ( 0.003
Table 4. Selected Structural Data for Compound 4
95
d(C6-C7) [Å]
1.495(5)
3.807(4)
4.063(4)
116.51(5)
111.1(2)
104.5(7)
97.5
100
102
105
109
d(C6-Ni) [Å]
d(C7-Ni) [Å]
R(P2-Ni-P1) [°]
R(C25-Ni-C26) [°]
γ(C5-C6-C7-C8) [°]

3488 Organometallics, Vol. 27, No. 14, 2008
Ruhland et al.
Scheme 5
which was found without the addition of the alkyne through
the same intermediate 8 (Figure 11).
is very similar to that of the free ligand (1655 cm-1, both
measured as KBr pellet). In (PEt3)2Ni(benzophenone), the peak
for this vibration disappeared.15 A nucleophilic interaction of
the Ni center (as a Lewis base) with the carbonyl carbon (as a
Lewis acid) is most likely the first step in the activation reaction
of ligand L3 with Ni(COD)2, as has been suggested earlier by
J. W. Suggs and co-workers in the case of their RhI complex.3b
The study of complex 5 provides remarkable spectroscopic
results. Only one resonance is observed for the two NisCO
carbon atoms in 13C NMR spectroscopy (sharp signal at 200
ppm, t, 2JCP ) 6.2 Hz), indicating that the two metal-carbonyls
are equivalent on the spectral 13C NMR time scale. The keto-
carbonyl carbon appears well-separated at 191 ppm as a sharp
The reaction of (PPh3)2Ni(CO)2 with ligand L3 resulted in
complex 5. This compound is stable at room temperature. A
perspective drawing of a molecular moiety in the solid state of
5 determined by X-ray analysis is shown in Figure 12.
Selected structural parameters are listed in Table 7. Although
the keto CO group is distorted slightly (O5 is bent away from
the Ni center slightly), the distance of the carbonyl carbon C27
as well as the CdO bond length and the two C(Ph)sCO bond
lengths provide no indication for an interaction between the
benzophenone subunit and the Ni center. Moreover, the IR
stretching frequency for the keto carbonyl group at 1657 cm-1
Figure 7. Development of the reaction of ligand L3 with 1 equiv of Ni(COD)2 at 20 °C in toluene-d8 with time. NMR spectra were taken
in 5 min intervals.

CleaVage of C(sp2)sC(sp2) Single Bonds
Organometallics, Vol. 27, No. 14, 2008 3489
Scheme 6
singlet with approximately half the intensity of the peak at 200
ppm. Spin saturation transfer between the two peaks at 200 and
191 ppm was not observed using mixing times up to 1 s. The
signals of the iPr-methine (one broad signal) and iPr-methyl
and 13C NMR spectroscopy, while still only one sharp triplet is
found for the two metal-carbonyls at 200 ppm in the 13C NMR
spectrum. In addition, the difference in the chemical shifts
between the metal-carbonyl and keto carbonyl peaks does not
change with the temperature.
1
groups (one broad signal in H NMR, 2 broad signals in 13C
1
NMR) are the only ones that show line broadening in the H
The signal in 31P NMR spectroscopy is not broadened
significantly, either at 20 °C or at -95 °C. In the IR spectrum,
recorded as a KBr pellet, three rather than two bands are found
for the NisCO groups (2012, 1965, 1948 cm-1). For complex
5*, with two 13C-labeled metal-carbonyls, the same splitting
pattern is observed though shifted by a factor of 0.976 to smaller
and 13C NMR spectra at room temperature, indicating a dynamic
processthatisslowerthantheequilibrationofthemetal-carbonyls.
At -95 °C, in toluene-d8, the iPr-signals are split (two broad
peaks for the methine signals, 4 broad peaks for the methyl
1
signals with two peaks being very close together) both in H
Figure 8. Line broadening of the 31P NMR signals of 8c at various temperatures.

3490 Organometallics, Vol. 27, No. 14, 2008
Ruhland et al.
Table 5. Rate Constants for the Intramolecular Degenerate
Exchange of Compound 8c at Different Temperatures
Table 6. Rate Constants for the Consumption of Compound 8c to 3
at Different Temperatures
temperature [°C]
kred [Hz]
temperature [°C]
k8c [h-1
]
52
42
35
27
17
1732 ( 71
1018 ( 58
259 ( 22
148 ( 12
38 ( 5
17
22
27
35
42
0.045 ( 0.003
0.131 ( 0.005
0.330 ( 0.004
0.851 ( 0.005
2.886 ( 0.006
wave numbers (1966, 1920, 1902 cm-1) in accordance with
theory. The splitting disappears if the IR spectrum is recorded
in CCl4 solution, and the expected two peaks for the carbonyl
stretching vibrations are observed at 2014 cm-1 and 1955 cm-1
(1967 cm-1 and 1911 cm-1 for 5*).
with the metal center is that ligand L1 is a nucleophile, while
ligand L3 can act as an electrophile. Compounds 1 in Scheme
2 and 9 in Scheme 6 are both 16-electron complexes, and thus,
by way of electron counting, an interaction in both cases (with
ligand L1 or ligand L3) is possible. However, the P2Ni(CdC)
unit contains an electron-rich metal center and as such an
interaction with the nucleophilic ligand L1 is disfavored. In
contrast, the electrophilic ligand L3 is activated even at low
temperature (20 °C) by the Ni center. This is in accordance
with the behavior of the corresponding acetylene complexes 2
and 10, which are considered to be 18-electron complexes. An
interaction of ligand L1 with a P2Ni(CtC) moiety is unexpected
on the basis of electron counting and is not found experimen-
tally, though the electrophilic interaction of ligand L3 with the
same P2Ni(CtC) unit is observed at 20 °C as expected.
For the equilibration of the metal-carbonyl groups, the
pathway shown in Figure 13 is proposed.
On the spectral NMR time scale, a fast flipping of the
benzophenone backbone followed by a slow reorganization of
the iPr groups at the two P atoms (which explains the observed
line-broadening only for them) leads to an averaged C2 or C2v
symmetry of the complex and would explain the spectroscopic
results. The simple fast rotation about several bonds (leading
to the fast equilibration of the benzophenone unit and the
metal-carbonyls) and a fast activation of the CsCO bond
(similar to that described in Scheme 6) are indistinguishable,
and it is not possible to decipher which occurs. This activation,
if present, must occur according to a σ-CAM-metathesis
mechanism,16 because in the case of a complete oxidative
addition, a 20-electron complex would be formed (although 20-
electron complexes of Ni are known, the strong ligand field in
our case suggests that such kind of electronic situation is highly
unfavorable). An exchange between the keto carbonyl and the
metal-carbonyls takes place, which was shown by selective
13CO isotopic labeling in compound 5, as will be discussed
below, however, the reaction is very slow (in the range of days
even at elevated temperatures) and, thus, cannot be included in
the equilibration of the NisCO groups on the spectral 13C NMR
time scale. If complex 5 is heated to 95 °C for 4 days in toluene,
the formation of compound 4 (∼20%) is observed. On irradia-
tion with UV light in toluene for 3 h, the complete reisolation
of 5 was found.
The main difference when altering the metal precursor from
Ni(COD)2 to (PPh3)2Ni(CO)2 is the electron density at the metal
center, especially when comparing the resulting subunits
P2Ni(CtC) and P2Ni(CO)2. Both of them have 18-electron
metal centers, but the former is electron-rich due to the electron-
donating triple bond, while the latter is electron-poor due to
the electron-withdrawing carbonyl groups. Scheme 7 shows the
interdependence between the two ligand systems concerning the
P2Ni(CO)2 moiety.
No interaction is expected and none is found between the
biphenyl unit in ligand L1 and the P2Ni(CO)2 unit (18-electron
complex). No reactivity is observed at 20 °C for complex 5 in
contrast to the behavior of complex 10 in Scheme 4. This
demonstrates the different nucleophilicities of the two metal
subunits. In complex 10, the Ni center is electron-rich and can
interact with the electrophilic keto carbonyl group of the ligand
L3 at 20 °C, whereas in complex 5 it is not. Still, complex 5 is
not completely inert against the activation of the C(Ph)sCO
single bond. This can be observed by selective 13C labeling of
the metal-carbonyl carbons in complex 5 (Scheme 8).
Comparison of L1 and L3 Ligand Systems, Including
Explanations of Behavior and Reactivity. The formation of
compound 4 from complex 5 at elevated temperatures not only
indicates that an activation of the C(Ph)sCO single bond in
ligand L3 must take place in 5 but also provides a connection
between the two ligand systems discussed in this paper. The
main difference with regards to an interaction of the two ligands
The scrambling of the 13C label between the metal-carbonyls
(13C NMR signal at 200 ppm) and the keto carbonyl (13C NMR
signal at 191 ppm) is slow. It can be detected after several days
and it requires more than a week for completion at 95 °C in
Figure 9. Eyring plot for the intramolecular degenerate exchange
of compound 8c.
Figure 10. Eyring plot for the reaction of compound 8c to 3.

CleaVage of C(sp2)sC(sp2) Single Bonds
Organometallics, Vol. 27, No. 14, 2008 3491
Figure 11. Development with time of the reaction of 10 (peak with decreasing intensity at 191 ppm) yielding 3 at 20 °C followed by 31P
NMR spectroscopy. Spectra were recorded in 16 min intervals.
Figure 12. ORTEP representation of a molecule in the solid state
of compound 5. Thermal ellipsoids are given at the 50% probability
level. Hydrogen atoms are omitted for clarity.
Figure 13. Proposed equilibrium of the two carbonyl groups in
compound 5.
Table 7. Selected Structural Data for Compound 5
d(C27-O5) [Å]
d(C6-C27) [Å]
d(C7-C27) [Å]
d(C27-Ni) [Å]
d(O5-Ni) [Å]
R(P2-Ni-P1) [°]
R(C25-Ni-C26) [°]
1.219(2)
1.499(2)
1.491(2)
3.5218(16)
3.8580(13)
120.36(2)
109.56(8)
Scheme 7
toluene. A dissociative and a nondissociative pathway can
explain the scrambling. Both possible pathways are shown in
Scheme 8. The dissociative pathway is most likely favored, as
it explains the elevated temperatures necessary to observe
scrambling and requires the temporary dissociation of one
carbonyl. Moreover, in the course of the scrambling at 95 °C,
the slow formation of complex 4 is observed. As a third point,
if 5* is heated to 95 °C in an atmosphere of nonlabeled CO,
the labeling completely vanishes. Among the observed chemical
shifts for complex 5 (200 ppm and 191 ppm) and complex 4
(200.5 ppm), additional signals at ∼195 ppm (singlets without
coupling to 31P) are observed in the 13C NMR spectrum during
scrambling (noncoordinated 13CO appears at 184 ppm). The
(16) Perutz, R. N.; Sabo-Etienne, S. Angew. Chem., Int Ed. 2007, 46,
2578–2592.

3492 Organometallics, Vol. 27, No. 14, 2008
Ruhland et al.
Scheme 8
formation of these peaks is accompanied by some small, broad
signals in the 31P NMR spectrum at about 185 ppm. Compound
3 is not observed in this process, and the presence of CO appears
to prevent formation. If 3t is examined in a CO atmosphere,
the immediate transformation of 3t to 5 is observed without the
detection of an intermediate, most notably the absence of 8c. In
the case of 3c, a new, very broad peak at ∼186 ppm appears in
the 31P NMR spectrum. The chemical shift and the degree of
broadness are dependent on the CO pressure. When the CO
pressure decreases, the chemical shift moves upfield and the
line-broadening increases, resulting in a nearly invisible peak
due to line-broadening. When 13CO is used in this experiment,
a broad singlet at 194 ppm in 13C NMR spectroscopy is
observed. The only peaks that remain at the end of the reaction
are, as observed for 3t, those of complex 5. The broadening of
the peaks is ascribed to a fast equilibrium among 3c, 8t, and
11c shown in Scheme 6. The extreme line-broadening at low
CO pressure is most likely the reason why no intermediates
are detected along the line 8tf11cf3c in the course of the
reaction of Ni(COD)2 with ligand L3.
Compound 12, shown in Scheme 7, is the equivalent of
compound 1a (Scheme 2), and though both are 16-electron
complexes, they represent two extremes with 1a being electron-
rich and 12 being electron-poor. For compound 1a, no interaction
of the biphenyl subunit with (or activation by) the Ni center is
observed, whereas indirect evidence for this interaction in 12
occurs. If 4 is kept under an atmosphere of 13CO overnight at
20 °C, the incorporation of 13CO into the metal complex is
observed. Complex 5 does not exchange CO under the same
conditions. This is taken as indirect evidence for the existence
of a temporary interaction of the biphenyl unit with the Ni center
acting as a hemilabile ligand, which serves to support the
temporary dissociation of CO. This interaction does not neces-
sarily occur through the bridging CsC single bond. It is
reasonable to suggest the coordination occurs by the delocalized
double bond of a phenyl ring. The π-complexes between a
(dippe)Ni0 fragment and aromatic heterocycles like quinoline
or acridine have been published with X-ray structure by J. J.
Garcia and W. D. Jones.4f Further evidence for 12 is that 4
under an atmosphere of 5 bar of CO and at 95 °C slowly
transforms into 5. Thus, the bridging CsC single bond must
be activated in 4. However, 4 is an 18-electron complex, and
the formation of 12 is necessary for an interaction of the
electron-poor metal center and the biphenyl moiety.
Concluding Remarks. We have shown that a nonstrained
C(sp2)sC(sp2) single bond could be cleaved using a Ni0 metal
complex when chelating assistance is employed. Activation takes
place at 20 °C for the CsCO single bond, and the mechanism
for this activation was confirmed to be nucleophilic with respect
to the metal center. The mechanism of several individual steps
within the activation pathway was explored by synthesis and
study of proposed organometallic intermediates to provide an
accurate description of the ongoing chemistry. In addition to
reactivity with a Ni metal center, the L3 ligand system has also
shown interesting reactivity with Rh and Ir metal centers and
studies in this area are currently ongoing in our laboratories.
We eventually hope to use knowledge in this area to facilitate
the activation of biphenyl, through the use of CO as a catalyst.
Experimental Section
General Procedures. Manipulations and experiments were
performed under an argon atmosphere using standard Schlenk
techniques and in an argon-filled glovebox if not otherwise stated.
Diethyl ether, pentane, acetonitrile, dichloromethane, and toluene
were dried and degassed using a two-column drying system
(MBraun) and stored under an argon atmosphere over molecular
sieves. Deuterated solvents used in NMR studies, including CDCl3,

CleaVage of C(sp2)sC(sp2) Single Bonds
Organometallics, Vol. 27, No. 14, 2008 3493
Table 8. Crystallographic Data for Compounds 2, 3c, 4 and 5
compound 2
compound 3c
C24H36NiO2P2
477.16
compound 4
compound 5
formula
Fw
C40H50NiO2P2
757.55
C26H36NiO4P2
533.18
C27H36NiO5P2
561.19
color/habit
pale yellow plate
0.40 × 0.30 × 0.05
orthorhombic
P21212
light orange fragment
0.15 × 0.20 × 0.45
monoclinic
P21/c
colorless plate
0.16 × 0.23 × 0.32
monoclinic
P21/c
yellow plate
0.15 × 0.21 × 0.46
monoclinic
P21/c
cryst dimensions (mm3)
cryst syst
space group
a, Å
b, Å
c, Å
13.922(1)
14.436(1)
10.417(2)
90
2093.5(2)
4
15.0464(5)
10.5122(2)
16.5700(5)
112.802(4)
2416.07(14)
4
11.1191(5)
16.6497(6)
14.3339(6)
90.172(3)
2653.62(19)
4
14.9964(1)
9.3798(1)
19.6238(2)
102.520(1)
2694.71(4)
4
ꢀ, deg
V, Å3
Z
T, K
150
1.202
0.576
812
150
1.312
0.953
1016
150
1.335
0.881
1128
150
1.383
0.874
1184
Dcalcd, g cm-3
µ, mm-1
F(000)
θ range, deg
2.82-21.04
(13, ( 14, ( 14
2216
2.67-25.34
(18, ( 12, ( 19
4395
1.83-25.35
(13, ( 20, ( 17
4850
2.74-27.75
(19, ( 12, ( 25
6389
index ranges (h, k, l)
no. of indep rflns
no. of obsd rflns (I > 2σ(I))
no. of data/restraints/params
2100
3298
4269
5611
2216/0/245
0.070/0.183
0.074/0.192
1.069
4395/0/406
0.030/0.062
0.052/0.078
1.182
4850/0/308
0.050/0.134
0.056/0.137
1.068
6389/0/460
0.031/0.071
0.039/0.078
1.139
a
R1/wR2 (I > 2σ(I))
a
R1/wR2 (all data)
GOF (on F2)a
largest diff peak and hole (e Å-3
)
0.89 and -0.37
0.38 and -0.34
0.56 and -0.50
0.41 and -0.40
a R1 ) Σ(|Fo| - |Fc|)/Σ|Fo|; wR2 ) {Σ[w(Fo - Fc ) ]/Σ[w(Fo2)2]}1/2; GOF ) {Σ[w(Fo - Fc ) ]/(n - p)}1/2
2
2 2
2
2 2
toluene-d8, and benzene-d6 were stored under argon over molecular
sieves. Carbon monoxide 2.5 was purchased from Messer Griessheim
and used without further purification. Metal precursors, Ni(D-
ME)Cl2, Ni(COD)2, and Ni(CO)2(PPh3)2 from Strem Chemicals
were used as received. Chlorodiisopropylphosphane, 13CO, 2-bro-
mophenol, 2,2′-dihydroxobiphenyl, 2,2′-dihydroxobenzophenone,
and sec-butyl lithium (1.3 M hexane/benzene) were purchased from
Aldrich and used without further purification. Ligands L1 and L2
were synthesized according to the previously reported literature
methods.12
The NMR measurement was performed on a Bruker AMX400.
1H NMR (400 MHz) and 13C NMR (100 MHz) chemical shifts
are given in ppm relative to the solvent signal for CDCl3 (7.24 and
77.0)/C6D6 (7.15 and 128.0)/C7D8 (2.09 and 20.4) and 31P NMR
(161 MHz) used 85% H3PO4 as an external standard. The FTIR
spectra were measured on a JASCO FI7IR-460plus spectrometer
using KBr pellets or in a KBr cell as CCl4 solution.
Crystal Structure Analysis. Preliminary examination and data
collection were carried out on a κ-CCD device (Oxford Diffraction
Xcalibur3) for compounds 2, 3c, and 5 and on an image plate device
(STOE, IPDS 2T) for compound 4 with an Oxford Instruments
cooling system with graphite monochromated Mo KR radiation (λ
) 0.71073 Å). Data collection was performed at 150 K within a Θ
range given in Table 8. Raw data were corrected for Lorentz,
polarization, and, arising from the scaling procedure, for latent decay
and absorption effects. After merging independent reflections
remained and all were used to refine the parameters given in Table
8. The structure was solved by a combination of direct methods
and difference Fourier syntheses.17 All nonhydrogen atoms were
refined with anisotropic displacement parameters. All hydrogen
atoms were placed in calculated positions and refined using a riding
model for compounds 2 and 4. All hydrogen atoms were located
from difference Fourier maps and refined independently for
compounds 3c and 5. Full-matrix least-squares refinements were
carried out by minimizing Σw(Fo2 - Fc2)2 and converged (R1, wR2,
and GOF values given in Table 8). The final difference Fourier
maps showed no striking features.
Ligand L3. This compound was synthesized in an analogous
method to ligand L1. A total of 1 g (4.67 mmol) of 2,2′-
dihydroxobenzophenone was dissolved in 10 mL of acetonitrile
together with 2.0 mL (14 mmol, 3 equiv) of triethylamine. To this
solution, 1.56 mL (9.8 mmol, 2.1 equiv) of di-iso-propylchloro-
phosphane was added with a syringe. This mixture was stirred for
12 h at ambient temperature and resulted in the formation of a white
precipitate. The color of the solution changed from green to maroon
over the course of the reaction. Pentane (40 mL) was added to the
reaction mixture and was allowed to stir for 1 h. The upper organic
phase was transferred in a new flask with a canula and the solvent
was removed in vacuo, leaving a dark purple viscous oil (1.52 g,
3.4 mmol, crude yield 73%). 1H NMR (CDCl3, ppm): 0.80 (12 H,
3
3
dd, JHH ) 7.36 Hz, JPH ) 11.0 Hz, CHCH3), 0.91 (12H, dd,
3JHH ) 7.36 Hz, 3JPH ) 15.93 Hz, CHCH3), 1.54 (4H, dhept, 3JHH
2
3
) 7.36 Hz, JPH ) 2.44 Hz, CHCH3), 6.97 (2H, pseudo t, JHH
)
7.32 Hz, Ar-H), 7.27-7.35 (4H, m, Ar-H). 13C{1H} NMR
2
2
(CDCl3, ppm): 17.0 (d, JCP ) 8.78 Hz, CHCH3), 17.4 (d, JCP
)
1
18.9 Hz, CHCH3), 27.8 (d, JCP ) 17.5 Hz, CHCH3), 117.6 (d,
3JCP ) 21.8 Hz, Ar-C), (121.1 (s, Ar-C), 130.1 (s, Ar-C), 132.2
4
4
2
(d, JCP ) 1.45 Hz), 132.4 (d, JCP ) 1.45 Hz), 157.5 (d, JCP
)
8.01 Hz), 196.6 (s). 31P {1H} NMR (CDCl3, ppm): 151.2. IR (KBr-
pellet) [cm-1]: 1655, 1597.
[L1]Ni(COD) (1a) and ([L1]Ni)2(COD) (1b). The ligand L1
(120 mg, 0.73 mmol) and Ni(COD)2 (80 mg, 0.73 mmol, 1 equiv)
were dissolved in 5 mL of toluene and the resulting orange solution
was stirred. After 30 min, the solvent was removed in vacuo and
the orange solid obtained was washed with 3 mL of pentane and
dried in vacuo to give 144 mg of a yellow solid. Whereas a toluene-
d8 solution of this material containing access COD is stable over
days, the yellow solid must be stored at low temperatures to avoid
1
3
decomposition. H NMR (C7D8, ppm): 0.71 (6H, dd, JHH ) 7.4
4
3
4
Hz, JPH ) 15.9 Hz, CHCH3), 0.82 (6H, dd, JHH ) 7.3 Hz, JPH
) 12.2 Hz, CHCH3), 1.30 (12H, br m, CHCH3), 1.65 (4H, br m,
CH2), 2.14 (4H, br m, CH2), 2.41 (1H, br m, CHCH3), 2.64 (1H,
br m, CHCH3), 2.81 (1H, br m, CHCH3), 3.00 (1H, br m, CHCH3),
4.29 (2H, br s, Ni-CHd), 5.56 (2H, s, CHd), 6.90 (2H, br pseudo
3
3
t, JHH ) 6.1 Hz, Ar-H), 7.00 (2H, br d, JHH ) 6.1 Hz, Ar-H),
7.07 (2H, br pseudo t, 3JHH ) 7.4 Hz, Ar-H), 7.08 (2H, br d, 3JHH
) 8.6 Hz, Ar-H). 13C{1H} NMR (C7D8, ppm): 17.7 (s, CHCH3),
18.0 (s, CHCH3), 19.3 (s, CHCH3), 19.4 (s, CHCH3), 30.8 (s), 31.2
(17) Sheldrick, G. M. SHELXS-97, Program for the Solution of Crystal
Structures; Universita¨t Go¨ttingen: Go¨ttingen, Germany, 1997; SHELXL-
97, Program for the Refinement of Crystal Structures; Universita¨t Go¨ttingen:
Go¨ttingen, Germany, 1997.

3494 Organometallics, Vol. 27, No. 14, 2008
Ruhland et al.
3
(s), 31.4 (s), 32.4 (s), 32.6 (s), 32.8 (s), 33.7 (d, JCP ) 8.0 Hz),
33.8 (d, JCP ) 8.0 Hz), 35.1 (d, JCP ) 20.7 Hz, CHCH3), 35.5 (d,
JCP ) 23.8 Hz, CHCH3), 61.2 (dd, JCPcis ) 14.4 Hz, JCPtrans ) 97.5
NMR (C6D6, ppm): 0.99 (6H, d, JHH ) 7.36 Hz, CHCH3), 1.02
3 3
(6H, d, JHH ) 7.36 Hz, CHCH3), 1.05 (6H, d, JHH ) 7.36 Hz,
CHCH3), 1.28 (6H, d, 3JHH ) 7.32 Hz, CHCH3), 1.42 (6H, d, 3JHH
3
) 6.12 Hz, CHCH3), 2.25 (4H, s, CHCH3), 6.92 (2H, d, JHH
)
Hz, Ni-CHd), 89.7 (s), 123.0 (d, JCP ) 4.8 Hz), 123.4 (d, JCP
)
3
7.36 Hz, Harom), 7.31 (2H, t, JHH ) 7.36 Hz, Harom), 7.49 (4H, d,
12.8 Hz), 132.0 (d, JCP ) 6.4 Hz), 134.3 (d JCP ) 8.0 Hz), 155.1
(s, C-O-P). 31P{1H} NMR (C7D8, ppm): 180.3 (br s), 182.3 (s),
182.9 (br s), 184.0 (br s), 185.8 (br s), ratio 1/2/0.5/0.5/0.05.
[L1]Ni(bis(p-toluyl)acetylene) (2). The Ni(COD)2 (20 mg, 0.73
mmol) and ligand L1 (30 mg, 0.73 mmol, 1 equiv) were dissolved
in 0.4 mL of toluene with 15 mg of bis(p-toluyl)acetylene (0.73
mmol, 1 equiv). The solution was stirred overnight. The solvent
was removed in vacuo and the brownish yellow residue was washed
with 2 mL of pentane. A yellow solid was produced (32 mg, 0.57
mmol, 79%). 1H NMR (C6D6, ppm): 0.99 (6H, dd, 3JHH ) 6.1 Hz,
3JHH ) 7.36 Hz, Harom). 13C{1H} NMR (C6D6, ppm): 17.5 (s,
2
2
CHCH3), 18.2 (pseudo t, JCP ) 3.66 Hz, CHCH3), 18.6 (d, JCP
2
) 3.66 Hz, CHCH3), 18.6 (d, JCP ) 2.19 Hz, CHCH3), 32.2
(pseudo t, 1JCP ) 7.31 Hz, CHCH3), 33.2 (pseudo t, 1JCP ) 10.61
3
Hz, CHCH3), 124.0 (s), 124.5 (s), 129.4 (d, JCP ) 10.98 Hz),
3
133.44 (s), 134.8 (d, JCP ) 19.03 Hz), 155.2 (s, COP), 201.5 (t,
2JCP ) 5.86 Hz, CO). 31P{1H} NMR (C6D6, ppm): 188.7 (s). IR
(KBr pellet) [cm-1]: 2007, 1937; (CCl4-solution) [cm-1]: 2007,
1949. EA calcd for C26H36NiO4P2: C, 58.57; H, 6.81. Found: C,
58.64; H, 6.72.
3
4
4JPH ) 19.6 Hz, CHCH3), 1.08 (6H, dd, JHH ) 7.4 Hz, JPH
)
3
4
11.0 Hz, CHCH3), 1.28 (6H, dd, JHH ) 7.4 Hz, JPH ) 7.4 Hz,
For the crystal structure analysis data of [L1]Ni(CO)2 see Table
8. Pseudomerohedral twinning of the crystal was refined using the
matrix -1 0 0 0 -1 0 0 0 1, yielding a batch scale factor BASF of
0.371.
3
4
CHCH3), 1.49 (6H, dd, JHH ) 7.4 Hz, JPH ) 17.2 Hz, CHCH3),
3
1.79 (4H, m, CHCH3), 2.28 (6H, s, tol-CH3), 6.94 (2H, t, JHH
)
3
7.3 Hz, Harom), 6.98 (2H, d, JHH ) 7.3 Hz, Harom), 7.11 (2H, t,
3JHH ) 7.3 Hz, Harom), 7.14 (2H, d, JHH ) 7.3 Hz), 7.20 (2H, d,
3
[L1]Ni(13CO)2 (4*). (a) A solution of 0.5 mL of CDCl3 and 30
mg of [L1]Ni(CO)2 was held under an atmosphere of 13CO for
24 h.
3JHH ) 7.3 Hz), 7.23 (2H, d, 3JHH ) 7.3 Hz). 13C {1H} NMR (C6D6,
ppm): 18.0 (s, tol-CH3), 20.7 (s, CHCH3), 20.8 (s, CHCH3), 21.2
1
(s, CHCH3), 21.7 (s, CHCH3), 32.7 (d, JCP ) 26.7 Hz, CHCH3),
(b) Ni(COD)2 (20 mg, 0.73 mmol) and ligand L1 (30 mg, 0.73
mmol, 1 equiv) were transferred in a Schlenk tube, which was set
under vacuum. The volume was refilled with 13CO and 0.5 mL of
toluene were added through a septum. The sample was stirred for
30 min. It was then filtered through celite and the solvent was
removed in vacuo from the light yellow solution. A colorless solid
was obtained.
1
33.6 (d, JCP ) 17.8 Hz, CHCH3), 123.3 (s), 123.5 (s), 126.9 (s),
132.2 (s), 132.8 (dd, 2JCPcis ) 11.9 Hz, 2JCPtrans ) 41.6 Hz, CtC),
133.7 (s), 134.2 (s), 136.7 (br t, C-O-P). 31P {1H} NMR (C6D6,
ppm): 192.2 (s). EA calcd for C40H50NiO2P2: C: 70.29, H: 7.37;
found: C: 70.04, H: 7.31.
For the crystal structure analysis data of [L1]Ni(bis(p-toluy-
l)acetylene) see Table 8. The data set was cut off, because
decomposition of the compound took place after several hours in
the diffractometer.
[L3]Ni(CO)2 (5). (a) cis- and trans-Ni(κ2-P,C-P(OC6H4)-(iPr)2)2
(15 mg, 0.03 mmol) were added in an NMR tube under argon.
The atmosphere was changed to carbon monoxide and 0.4 mL of
toluene-d8 were added. The reaction was finished after 30 min at
ambient conditions. Yield: quantitative.
cis-Ni(K2-P,C-P(OC6H4)-(iPr)2)2 (3c). A total of 143.0 mg of 6
(0.225 mmol) was dissolved in 20 mL of diethylether and cooled
to -78 °C for 20 min. To this cold solution, 0.189 mL (0.45 mmol,
2.1 equiv) sec-BuLi (1.3 M in hexane/benzene) was added. The
solution was allowed to warm to room temperature overnight. The
mixture was then filtered and the solvent was removed in vacuo.
The residue was washed 2 times with 4-5 mL of pentane to yield
(b) The metal precursor, 200 mg of bis(triphenylphosphane)Ni-
(CO)2 (0.31 mmol), was added to a solution of 140 mg of ligand
L3 (0.31 mmol, 1 equiv) in 10 mL of toluene and it was stirred for
3 d at room temperature. The color of the solution changed from
red to dark brown, and the solvent was removed in vacuo. The
residue was extracted with 4 mL of pentane, with the solvent
removed in vacuo, and the resulting solid was washed with 1 mL
of acetonitrile and dried in vacuo to yield a yellow solid, 32% (57
mg, 0.1 mmol).
1
103 mg (97%, 0.218 mmol) of an orange solid. H NMR (C7D8,
ppm): 1.07 (24H, dd, 3JHH ) 7.36 Hz, 3JPH ) 12.24 Hz, CHCH3),
1.97 (4H, m, 3JHH ) 7.32 Hz, 2JPH ) 2.44 Hz, CHCH3), 6.92 (2H,
3
pseudo t, JHH ) 7.32 Hz, Harom), 7.00-7.09 (4H, m, Harom), 7.68
3
4
(2H, dd, JHH ) 7.36 Hz, JHH ) 2.44 Hz, Harom). 13C{1H} NMR
1H NMR (C7D8, ppm): 0.85 (6H, m, CHCH3), 1.07-1.13 (12H,
m, CHCH3), 1.24-1.34 (6H, m, CHCH3), 1.49 (2H, s, CHCH3),
(C7D8, ppm): 17.2 (s, CHCH3), 18.2 (s, CHCH3), 29.9-30.2 (m,
3
3
CHCH3), 109.7 (pseudo t, JCP ) 7.32 Hz), 122.2 (s), 126.6 (s),
1.87 (2H, s, CHCH3), 6.75 (2H, t, JHH ) 7.36 Hz, Harom), 6.79
2
2
(2H, d, 3JHH ) 8.56 Hz, Harom), 6.98 (2H, t, 3JHH ) 6.12 Hz, Harom),
144.4 (s), 153.9 (dd, JCPcis ) 21.95 Hz, JCPtrans ) 71.72 Hz,
2
CaromNi), 168.3 (pseudo t, JCPcyc
)
3JPC ) 8.78 Hz, CaromOP).
7.46 (2H, d, JHH ) 7.36 Hz). 13C {1H} NMR (C7D8, ppm): 17.7
3
31P{1H} NMR (C7D8, ppm): 193.1 (s). MS (FAB m/z): 476.2
(br s, CHCH3), 18.3 (br s, CHCH3), 18.7 (br s, CHCH3), 32.9 (br
s, CHCH3), 123.6 (d, 3JCP ) 19.04 Hz), 129.8 (s), 131.7 (s), 132.2
(100%), [M], correct isotopic pattern for C24H36NiO2P2.
2
For the crystal structure analysis data of cis-Ni(κ2-P,C-P(OC6H4)-
(iPr)2)2 see Table 8. All hydrogen atoms were located from
difference Fourier maps and refined independently.
(s), 133.9 (s), 154.8 (s), 190.8 (s, C6H4COC6H4), 200.2 (t, JCP
)
6.22 Hz, CO). 31P {1H} NMR (C7D8, ppm): 191.9 (s). MS (FAB,
m/z): 504.1 [M - 2CO] (85%) with correct isotopic pattern for
C35H36NiO3P2, 476.1 [M - 3CO] (100%), with correct isotopic
pattern for C24H36NiO2P2. IR KBr pellet [cm-1]: 2012, 1965, 1948,
1657; CCl4 solution [cm-1]: 2014, 1955, 1659.
trans-Ni(K2-P,C-P(OC6H4)-(iPr)2)2 (3t). Compound 3c (5 mg,
0.01 mmol) was dissolved in 0.4 mL of toluene-d8 in a NMR tube
and heated for 25 min at 109 °C in an oil bath to give quantitative
conversion to the trans-isomer. 13C{1H} NMR (C7D8, ppm): 17.6
For the crystal structure analysis data of [L3]Ni(CO)2 see Table
8. All hydrogen atoms were located from difference Fourier maps
and refined independently.
1
(s, CHCH3), 19.9 (s, CHCH3), 29.7 (pseudo t, JCP ) 11.70 Hz,
CHCH3), 111.8 (s), 121.3 (s), 127.1 (s), 142.7 (s), 143.9 (t, 2JCPcis
) 6.59 Hz, CaromNi), 169.5 (s, CaromOP). 31P {1H} NMR (C7D8,
ppm): 189.2 (s).
[L3]Ni(13CO)2 (5*). The metal precursor, Ni(COD)2 (20 mg,
0.73 mmol) and ligand L3 (32.5 mg, 0.73 mmol, 1 equiv) were
added to a Schlenk flask and then set under vacuum. The volume
was refilled with 13CO, 0.5 mL of toluene was added through a
septum, and the solution was stirred for 30 min. The resultant dark
yellow solution was filtered through a celite pad and the solvent
was removed in vacuo to yield a brown solid. It was extracted two
times with 5 mL of pentane and the pentane was removed in vacuo
[L1]Ni(CO)2 (4). Bis(triphenylphosphane)Ni(CO)2 (186 mg, 0.29
mmol) was dissolved in 7 mL of toluene and added to a solution
of ligand L1 (120 mg, 0.29 mmol, 1 equiv) in 5 mL of toluene
through a canula. After 12 h, the solvent was removed in vacuo
and the residue was washed 3 times with 4-5 mL of pentane and
dried in vacuo. Yield: 35%, white powder. (54 mg, 0.1 mmol) 1H

CleaVage of C(sp2)sC(sp2) Single Bonds
Organometallics, Vol. 27, No. 14, 2008 3495
3
2
to obtain a bright yellow solid. IR KBr pellet [cm-1]: 1966, 1920,
1902, 1657; CCl4 solution [cm-1]: 1967, 1911, 1659.
Hz, COP), 156.6 (d, JPC ) 7.31 Hz), 168.7 (dd, JPC ) 4.21 Hz,
3JPC ) 16.10 Hz, CcycOP). 31P{1H} NMR (C6D6, ppm): 168.8 (d,
[L313CO]Ni(13CO)2 (5**). (a) A mixture of 3c and 3t was
transferred in a Schlenk tube and set under vacuum. The volume
was refilled with 13CO and 0.5 mL of toluene were added through
a septum. The sample was stirred for 30 min. The workup was
done as described above for the analogous partially labeled
compound 5*. IR [cm-1]: 1966, 1920, 1902, 1618.
2JPP ) 317.0 Hz), 198.4 (d, JPP ) 319.0 Hz, Pcyc). EA calcd for
2
C24H36Br2NiO2P2: C, 45.25; H, 5.70. Found: C, 45.42; H, 5.64.
Kinetics of the cis/trans-Isomerization. In a 5 mm NMR tube,
10 mg of 3c was dissolved in 0.4 mL of toluene-d8 under Argon.
The NMR tube was sealed with an adhesive tape and placed in an
oil bath at a defined temperature for a defined temperature-
dependent time interval (2 min at 109 °C, 1 h at 80 °C). The
temperature of the oil bath was controlled by a digital contact
thermometer and temperatures confirmed with a mercury thermom-
eter. The temperature was constant within (1 °C. After the defined
time interval, the sample was removed from the heating bath, cooled
with ice, and analyzed by 31P NMR spectroscopy at 20 °C. The
sample was then heated for a further time interval until complete
isomerization was observed. It was confirmed that at 20 °C no
isomerization is observed, even after 24 h.
(b) [L3]Ni(13CO)2 was heated in toluene at 95 °C under an
atmosphere of 13CO for 7 days.
trans-Ni[(K2-P,C-P(OC6H4)-(iC3H7)2)((iC3H7)2P(OC6H4-2-
Br))Br) (6). To a solution of 100 mg (0.36 mmol) of Ni(COD)2 in
3.5 mL of toluene, a solution of L2 (210 mg, 0.72 mmol, 2 equiv)
in 3.5 mL of toluene was added slowly via syringe. The color
changed from yellow to orange. After 12 h, the solvent was removed
in vacuo and the resulting residue was washed two times with 3
mL of pentane to yield 197 mg of a yellow-orange solid (85%,
0.31 mmol). 1H NMR (C6D6, ppm): 1.26-1.39 (15H, m, CHCH3),
1.42 (3H, d, 3JHH ) 6.12 Hz, CHCH3), 1.49 (6H, dd, 3JHH ) 6.74
Hz, 3JPH ) 15.94 Hz, CHCH3), 2.50 (2H, s, CHCH3), 2.79 (2H, s,
Acknowledgment. K. R. thanks the DFG for financial
support (Ru519/3-2), NANOCAT (International Graduate
School as part of the Bavarian Excellence Cluster) for
financial support, and Prof. W. A. Herrmann for the
opportunity to use the infrastructure of his group.
CHCH3), 6.23 (1H, t, 3JHH ) 7.32 Hz, Harom), 6.48 (1H, d, 3JHH
)
3
7.36 Hz, Harom), 6.63 (2H, t, JHH ) 7.32 Hz, Harom), 6,34 (1H, d,
3JHH ) 6.12 Hz, Harom), 6.93 (1H, d, 3JHH ) 6.12 Hz, Harom), 7.32
(1H, d, 3JHH ) 7.32 Hz, Harom), 7.84 (1H, d, 3JHH ) 7.36 Hz, Harom).
13C{1H} NMR (C6D6, ppm): 17.0 (s, CHCH3), 18.0 (s, CHCH3),
18.7 (d, 2JPC ) 3.66 Hz, CHCH3), 20.8 (d, 2JPC ) 4.40 Hz, CHCH3),
Supporting Information Available: Crystallographic data as a
CIF file. This material is available free of charge via the Internet
at http://pubs.acs.org.
1
1
28.8 (d, JPC ) 24.52 Hz, CHCH3), 30.7 (d, JPC ) 18.66 Hz,
3
3
CHCH3), 110.9 (d, JPC ) 13.90 Hz), 114.2 (d, JPC ) 3.66 Hz),
121.2 (s), 123.6 (s), 127.1 (s), 127.4 (s), 133.4 (s), 142.2 (dd, 2JPCcisA
2
2
) 13.17 Hz, JPCcisB ) 1.46 Hz, CaromNi), 151.9 (d, JPC ) 2.93
OM800054M