Catalytic C-C bond activation in biphenylene and cyclotrimerization of alkynes: Increased reactivity of P,N- versus P,P-substituted nickel complexes

Article abstract of DOI:10.1021/om0110989

Reaction of Ni(COD)₂ with the bidentate hybrid ligand (ⁱPr)₂CH₂CH₂NMe₂ (PN) and PhC≡CR (R = Ph, ^tBu, CF₃, C≡CPh) afforded the donor-stabilized mononuclear Ni(0) comple

Full text of DOI:10.1021/om0110989

Organometallics 2002, 21, 1975-1981
1975
Ca ta lytic C-C Bon d Activa tion in Bip h en ylen e a n d
Cyclotr im er iza tion of Alk yn es: In cr ea sed Rea ctivity of
P ,N- ver su s P ,P -Su bstitu ted Nick el Com p lexes
Christian Mu¨ller, Rene J . Lachicotte, and William D. J ones*
Department of Chemistry, University of Rochester, Rochester, New York 14627
Received December 28, 2001
Reaction of Ni(COD)2 with the bidentate hybrid ligand (iPr)2CH2CH2NMe2 (PN) and
t
PhCtCR (R ) Ph, Bu, CF3, CtCPh) afforded the donor-stabilized mononuclear Ni(0)
t
complexes (PN)Ni(η2-PhCtCR) (R ) Ph (1), Bu (4), CF3 (5)) and the dinuclear compound
(PN)Ni(η2;η2-PhCtC-CtCPh)Ni(PN) (3), respectively. In the presence of excess alkyne,
compounds 1, 3, and 4 turned out to be active species for the catalytic carbon-carbon bond
activation in biphenylene and formation of the corresponding 9,10-disubstituted phenan-
threnes. However, cyclotrimerization to benzene derivatives instead of C-C bond cleavage
occurred with complex 5 in the presence of excess CF3CtCPh and biphenylene. In contrast,
the corresponding bis-phosphino-substituted species (dippe)Ni(η2-PhCtCR) (R ) Ph (2), CF3
(9)) showed substantially reduced catalytic activity toward phenanthrene formation or
cyclotrimerization reactions.
In tr od u ction
phenylacetylene.4 A similar result was obtained by
reaction of diphenylacetylene with CpCo(PPh3)(2,2′-
biphenyl).5 Our group has demonstrated the catalytic
formation of 9,10-diphenylphenanthrene by heating a
mixture of diphenylacetylene and biphenylene in the
presence of the catalyst precursor (dippe)Ni(η2-
PhCtCPh). However, oxygen was required for the
catalytic process to remove the bis-phosphino ligand
from the metal center and to generate a reactive Ni(0)
species.6 We have also found that (dippe)RhCl(alkyne)
can be used to catalytically form phenanthrenes from
biphenylene plus acetylenes,7 but side reactions to
produce cyclotrimerized arenes and fluorenes8 were a
problem in this system.
The selective activation of carbon-carbon bonds and
their functionalization by transition metal complexes
has recently attracted much interest due to its potential
application in industrial petroleum refining and trans-
formation processes. Because the target bond is both
thermodynamically stable and kinetically inert, the
cleavage of C-C single bonds under mild homogeneous
conditions is still a fundamental challenge in organo-
metallic chemistry. To achieve stoichiometric oxidative
addition of C-C bonds to metal centers, a number of
strategies have been developed, such as relief of ring
strain or attainment of aromaticity. The activation of
unstrained C-C bonds has been observed in the pres-
ence of highly reactive species, by forcing the target
molecule into close proximity to the metal center or by
the formation of strong M-aryl bonds.1,2 Catalytic C-C
bond activation and functionalization is much less
common, but it has been shown in some cases that
biphenylene is an appropriate substrate for this proc-
ess.3 The insertion of a reactive LnM fragment into the
central C-C bond of biphenylene generates a LnM(2,2′-
biphenyl) complex with two strong M-aryl bonds, which
is thermodynamically favorable. Eisch et al. reported
on the formation of 9,10-diphenylphenanthrene by heat-
ing (PEt3)2Ni(2,2′-biphenyl) in the presence of di-
We now wish to report on the synthesis of various
Ni(η2-alkyne) complexes that are stabilized by the
bidentate chelating P,N-hybrid ligand (iPr)2CH2CH2-
NMe2 (PN).9 According to Pearson’s concept of “hard”
and “soft” Lewis acids and Lewis bases, the coordinated
metal-nitrogen bond in (PN)Ni(η2-alkyne) complexes is
considered to be labile.10 The nickel compounds are
expected to be more reactive toward C-C bond activa-
tion of biphenylene and functionalization reactions with
alkynes compared to corresponding (dippe)Ni(η2-alkyne)
complexes.
(4) Eisch, J . J .; Piotrowski, A. M.; Han, K. I.; Kru¨ger, C. Tsay, Y.
H. Organometallics 1985, 14, 224.
(5) Wakatsuki, Y.; Nomura, O.; Tone, H.; Yamazaki, H. J . Chem.
Soc., Perkin Trans. 2 1980, 1344.
(6) Edelbach, B. L.; Lachicotte, R. J .; J ones, W. D. Organometallics
1999, 18, 4040.
(7) Iverson, C. N.; J ones, W. D. Organometallics 2001, 20, 5745.
(8) Formation of fulvenes from acetylene + metallacyclopentadienes
is known: O’Conner, J . M.; Hiibner, K.; Merwin, R,; Gantzel, P. K.;
Fong, B. S. J . Am. Chem. Soc. 1997, 119, 3631.
(9) Werner, H.; Hampp, A.; Peters, K.; Peters, E. M.; Walz, L.; von
Schnering, H. G. Z. Naturforsch. 1990, 45b, 1548.
(10) Pearson, R. G.; Scott, A. In Survey of Progress in Chemistry;
Academic Press: New York, 1969; Chaper 1.
(1) For recent reviews on C-C bond activation see: (a) Rybtchinski,
B.; Milstein, D. Angew. Chem., Int. Ed. 1999, 38, 870. (b) Murakami,
M.; Ito, Y. In Topics in Organometallic Chemistry; Murai, S., Ed.;
Springer-Verlag: New York, 1999; Vol. 3, pp 96-129. (c) Rosenthal,
U.; Pellny, P.-M.; Kirchbauer, F. G.; Burlakov, V. V. Acc. Chem. Res.
2000, 33, 119.
(2) (a) Garcia, J . J .; J ones, W. D. Organometallics 2000, 19, 5544,
and references therein. (b) J ones, W. D. Nature 1993, 364, 676. (c)
Anderson, G. K.; Lumetta, G. J .; Siria, J . W. J . Organomet. Chem.
1992, 434, 253.
(3) Perthuisot, C.; Edelbach, B. L.; Zubris, D. L.; Simhai, N.; Iverson,
C. N.; Mu¨ller, C.; Satoh, T.; J ones, W. D. J . Mol. Catal., A 2002, in
press.
10.1021/om0110989 CCC: $22.00 © 2002 American Chemical Society
Publication on Web 04/05/2002

1976 Organometallics, Vol. 21, No. 9, 2002
Mu¨ller et al.
Ta ble 1. Selected Bon d Len gth s (Å) a n d Bon d
An gles (d eg) for 1
Bond Lengths
Ni(1)-N(1)
Ni(1)-P(1)
Ni(1)-C(11)
2.036(3)
2.1565(10)
1.845(3)
Ni(1)-C(12)
C(11)-C(12)
1.904(3)
1.291(5)
Bond Angles
C(11)-Ni(1)-C(12) 40.27(14) C(12)-Ni(1)-N(1) 111.97(13)
N(1)-Ni(1)-P(1)
89.44(8) C(12)-C(11)-C(13) 144.0(3)
C(11)-Ni(1)-P(1) 118.32(11) C(11)-C(12)-C(19) 145.0(3)
plexes (L2 ) CNtBu, dmpe, COD, bipy, dippe) show
similar C-C triple bond distances (1.276-1.300 Å) and
CtC-C bending angles (144.0-151.3°).6,15 Ni-C bond
distances in these compounds are slightly shorter when
trans to N (∼1.85 Å) than to π-acceptor ligands (∼1.88
Å), as observed in 1. In all of these complexes except
the bipy derivative, the phenyl rings lie approximately
in the square plane of the metal complex.
F igu r e 1. Molecular structure of (PN)Ni(η2-PhCtCPh) (1)
(ORTEP diagram; 30% probability ellipsoids).
Resu lts a n d Discu ssion
The nickel complex 1 turned out to be an effective
catalyst for the C-C bond activation in biphenylene. In
the presence of 1 (8.3 mol %), a mixture of biphenylene
and diphenylacetylene was quantitatively converted into
9,10-diphenylphenanthrene within 22.5 h at T ) 70 °C
(∼0.5 TO/h). No cyclotrimerization of PhCtCPh to
We recently described the synthesis of the zerovalent
Pt-alkyne complex (PN)Pt(η2-PhCtCPh), which is sta-
bilized by the chelating ligand (iPr)2PCH2CH2NMe2.
This compound turned out to undergo stoichiometric
C(sp)-C(sp2) bond activation in diphenylacetylene un-
der photochemical conditions to afford the Pt(II) species
(PN)Pt(Ph)(CtCPh).11 However, formation of a platina-
cyclopenta-2,5-diene complex and subsequent catalytic
generation of hexaphenylbenzene were observed with
excess diphenylacetylene under thermal conditions.12
The corresponding Ni(0) complex (PN)Ni(η2-PhCt
CPh) (1) was synthesized by reaction of Ni(COD)2 with
(iPr)2PCH2CH2NMe2 and diphenylacetylene in pentane
and was isolated as an orange, air- and moisture-
sensitive solid (eq 1). The 1H NMR spectrum of 1 showed
1
hexaphenylbenzene was observed by H NMR spectros-
copy or GC/MS. Furthermore, 1 is the only observed
species by NMR spectroscopy during the course of the
reaction. The corresponding bis-phosphino-substituted
complex (dippe)Ni(η2-PhCtCPh) (2), however, produced
only small amounts of 9,10-diphenylphenanthrene (∼0.2
turnovers) after 40 h at T ) 110 °C. To increase the
turnover rate, oxygen was required to render the process
catalytic (vide supra). We attribute the enhanced reac-
tivity of 1 compared to (dippe)Ni(η2-PhCtCPh) to the
properties of the mixed donor ligand system; although
the dimethylamino group is a good σ-donor, it also lacks
in π-acceptor capability. This situation can lead to a
certain lability of the coordinated Ni-NR2 bond. As a
result, an additional free coordination site can be
generated which is essential for a catalytic cycle. We
propose the mechanism shown in Scheme 1 for the
formation of 9,10-diphenylphenanthrene. We assume
that the first step in the production of the organic
product is fast dissociation of the NR2 group from the
nickel atom and formation of a vacant coordination site.
Subsequently the highly reactive metal center is able
to cleave the C-C bond in biphenylene to generate the
Ni(II) intermediate I. Insertion of the alkyne into the
Ni-C bond then leads to the Ni(II) species II. Reductive
two sets of o-, m-, and p-phenyl protons of the alkyne
moiety due to the asymmetric bidentate P,N ligand.
Crystals of 1 suitable for X-ray diffraction were obtained
by recrystallization from pentane at T ) -30 °C. The
molecular structure of 1 is illustrated in Figure 1, and
selected bond lengths and angles are listed in Table 1.
The structural analysis revealed the expected distorted
square-planar geometry at the metal center. The alkyne
ligand is positioned in the P-Ni-N plane and is bonded
slightly asymmetrically to the nickel atom. The Ni-C
distances are 1.845(3) and 1.904(3) Å, with the longer
bond trans to phosphorus. Major contribution of π* back-
donation13 is suggested by the elongated CtC bond
(1.291(5) Å) and the bending of the CtC-C angles
(145.0(3)°, 144.0(3)°) compared to free diphenylacet-
ylene.14 Other donor-stabilized L2Ni(η2-PhCtCPh) com-
(13) (a) Dewar, M. J . S. Bull. Soc. Chim. Fr. 1951, 18, C79. (b) Chatt,
J .; Duncanson, L. A. J . Chem. Soc. 1953, 2939. (c) Greaves, E. O.; Lock,
C. J . L.; Maitlis, P. M. Can. J . Chem. 1968, 46, 3879. (d) Otsuka, S.;
Nakamura, A. Adv. Organomet. Chem. 1976, 14, 245, and references
therein. (e) Rosenthal, U.; Schulz, W. J . Organomet. Chem. 1987, 321,
103. (f) Bartik, T.; Happ, B.; Iglewsky, M.; Bandmann, H.; Boese, R.;
Heimbach, P.; Hoffmann, T.; Wenschuh, E. Organometallics 1992, 11,
1235. (g) Edelbach, B. L.; Lachicotte, R. J .; J ones, W. D. Organo-
metallics 1999, 18, 4660. (h) Rosenthal, U.; Nauck, C.; Amdt, P.; Pulst,
S.; Baumann, W.; Burlakov, V. V.; Gorls, H. J . Organomet. Chem. 1994,
484, 81.
(14) The CtC bond length in free diphenylacetylene is 1.198(4) Å:
Mavriris, A.; Moustakali-Mavridis, I. Acta Crystallogr. 1977, B33, 3612.
(15) (a) Dickson, R. S.; Ibers, J . A. J . Organomet. Chem. 1972, 36,
191. (b) Goddard, R.; Apotecher, B.; Hoberg, H. Acta Crystallogr., Sect.
C 1987, C43, 1290. (c) Po¨rschke, K. R.; Mynott, R.; Angermund, K.;
Kru¨ger, C. Z. Naturforsch. 1995, 40b, 199. (d) Eisch, J . J .; Ma, X.; Han,
K. I. Eur. J . Inorg. Chem. 2001, 77.
(11) Mu¨ller, C.; Iverson, C. N.; Lachicotte, R. J .; J ones, W. D. J .
Am. Chem. Soc. 2001, 123, 9718.
(12) In the presence of biphenylene and diphenylacetylene no
catalytic formation of the corresponding 9,10-diphenylphenanthrene
was observed. Further details are reported in: Mu¨ller, C.; Lachicotte,
R. J .; J ones, W. D. Organometallics 2002, 21, 1118.

P,N- versus P,P-Substituted Nickel Complexes
Organometallics, Vol. 21, No. 9, 2002 1977
Sch em e 1
Sch em e 2
elimination of 9,10-diphenylphenanthrene and com-
plexation of a second alkyne regenerates the Ni(0)
complex 1.
same reaction conditions. Even at T ) 100 °C, no
cyclotrimerization reaction was observed. This observa-
tion supports the assumption that an additional free
coordination site at the metal center for alkyne com-
plexation is a prerequisite for this process. The hemi-
labile19 P,N ligand offers this possibility.
Catalytic C-C bond activation of biphenylene and
functionalization with diphenylacetylene were also
achieved by the dinuclear Ni(0) complex (PN)Ni(η2;η2-
PhCtC-CtCPh)Ni(PN) (3).20 This compound was syn-
thesized by reaction of Ni(COD)2 with (iPr)2PCH2CH2-
NMe2 and 1,4-diphenylbutadiyne in the ratio 2:2:1 in
pentane according to eq 2. A mixture of biphenylene and
We further observed that in the absence of bi-
phenylene, hexaphenylbenzene is formed catalytically
from diphenylacetylene in the presence of 1 (initial
rate: 0.4 TO/d). The lability of the M-NR2 bond might
facilitate the coordination of a second alkyne to generate
the Ni(0) intermediate Ia (Scheme 2).16 According to the
commonly accepted mechanism for the cyclotrimeriza-
tion of alkynes,13e,17 reductive coupling of the ligands
leads to the formation of the donor-stabilized Ni(II)
metallacyclopentadiene IIa .15e,18 Again, dissociation of
the NR2 group from the metal center provides a vacant
coordination site for the third alkyne (IIIa ), which
subsequently inserts into the Ni-C bond to form the
Ni(II) intermediate IVa . Reductive elimination of
hexaphenylbenzene and complexation of an incoming
alkyne regenerates the Ni(0) species 1. In contrast to
the results described above, no hexaphenylbenzene was
produced with (dippe)Ni(η2-PhCtCPh) (2) under the
(16) For a stable L-Ni(0)-bis(alkyne) complex see: Rosenthal, U.;
Pulst, S., Kempe, R.; Po¨rschke, K. R.; Goddard, R.; Proft, B. Tetra-
hedron 1998, 54, 1277. Po¨rschke, K.-R. J . Am. Chem. Soc. 1989, 111,
5691.
(17) For cyclotrimerization reactions of substituted acetylenes by
Ni-complexes see for example: (a) Reppe, W.; von Kutepow, N.; Magin,
A. Angew. Chem., Int. Ed. Engl. 1968, 8, 7. (b) J olly, P. W.; Wilke, G.
The Organic Chemistry of Nickel; Academic Press: New York, 1975;
Vol. 2. (c) Schore, N. E. Chem. Rev. 1988, 88, 1081. (d) Takahashi, T.;
Xi., Z.; Yamazaki, A.; Liu, Y.; Nakajima, K.; Kotora, M. J . Am. Chem.
Soc. 1998, 120, 1672. (e) Rosenthal, U.; Schulz, W. J . Prakt. Chem.
1986, 328, 335. (f) Sauer, J . C.; Cairns, T. L. J . Am. Chem. Soc. 1957,
79, 2659. (g) Meriwether, L. S.; Colthup, E. C.; Kennerly, G. W.; Reusch,
R. N. J . Org. Chem. 1961, 26, 5155. (h) Donda, A. F.; Moretti, G. J .
Org. Chem. 1966, 31, 985. (i) Whitesides, G. M.; Ehmann, W. J . J .
Am. Chem. Soc. 1969, 91, 3800. (j) Chalk, A. J .; J erussi, R. A.
Tetrahedron Lett. 1972, 61. (k) Kru¨erke, U.; Hu¨berl, W. Chem. Ber.
1961, 94, 2829. (l) Hopff, H.; Gat, A. Helv. Chim. Acta 1965, 48, 509.
(18) For the role of nickelole intermediates in the oligomerization
of alkynes see: (a) Eisch, J . J .; Galle, J . E. J . Organomet. Chem. 1975,
96, C23. (b) Eisch, J . J .; Damasevitz, G. A. J . Organomet. Chem. 1975,
96, C19. (c) Hoberg, H.; Richter, W. J . Organomet. Chem. 1980, 195,
355. (d) Eisch, J . J .; Aradi, A. A.; Han, K. I. Tetrahedron Lett. 1983,
24, 2073. (e) Eisch, J . J . Piotrowski, A. M.; Aradi, A. A.; Kru¨ger, C.;
Roma˜o, M. J . Z. Naturforsch. 1985, 40b, 624. (f) Eisch, J . J . Galle, J .
E.; Aradi, A. A.; Boleslawski, M. P. J . Organomet. Chem. 1986, 312,
399.
diphenylacetylene was quantitatively converted into
9,10-diphenylphenanthrene in the presence of 3 (8.3 mol
% Ni) within 22.5 h at T ) 70 °C (0.5 TO/h). No
(19) For the concept of hemilability see for example: (a) J effrey, J .
C.; Rauchfuss, T. B. Inorg. Chem. 1979, 18, 2658. (b) Okuda, J .
Comments Inorg. Chem. 1994, 16 185. (c) Slone, C. S.; Weinberger, D.
A.; Mirkin, C. A. Prog. Inorg. Chem. 1999, 48, 233. (d) Mu¨ller, C.; Vos,
D.; J utzi, P. J . Organomet. Chem. 2000, 600, 127. (e) Braunstein, P.;
Naud, F. Angew. Chem., Int. Ed. 2001, 40, 680.
(20) For Ni(0) complexes containing the 1,4-diphenylbutadiyne
ligand see for example: (a) Tillack, A.; Pulst, S.; Baumann, W.;
Baudisch, H.; Kortus, K.; Rosenthal, U. J . Organomet. Chem. 1997,
532, 117. (b) Pulst, S.; Arndt, P.; Heller, B.; Baumann, W.; Kempe, R.;
Rosenthal, U. Angew. Chem., Int. Ed. Engl. 1996, 35, 1112. (c)
Rosenthal, U.; Pulst, S.; Arndt, P.; Baumann, W.; Tillack, A.; Kempe,
R. Z. Naturforsch., B 1995, 50, 377. (d) Rosenthal, U.; Pulst, S.; Arndt,
P.; Baumann, W.; Tillack, A.; Kempe, R. Z. Naturforsch., B 1995, 50,
368. (e) Maekawa, M.; Munakata, M.; Kuroda-Sowa, T.; Hachiya, K.
Inorg. Chim. Acta 1995, 231, 213. (f) Maekawa, M.; Munakata, M.;
Kuroda-Sowa, T.; Hachiya, K. Polyhedron 1995, 14, 2879.

1978 Organometallics, Vol. 21, No. 9, 2002
Mu¨ller et al.
incorporation of 1,4-diphenylbutadiyne or cyclotrimer-
ization reactions were observed. On the basis of 31P{1H}
NMR spectroscopy, however, we assume that compound
3 acts as a catalyst precursor. In the presence of excess
diphenylacetylene, 3 was instantaneously converted into
the η2-diphenylacetylene complex 1 at T ) 70 °C. As
described above, this compound is most likely the active
species in the phenanthrene formation.
We were also interested in the catalytic C-C bond
activation of biphenylene and functionalization with
t
different alkynes, such as BuCtCPh and F3CCtCPh.
The corresponding Ni(η2-alkyne) complexes were syn-
thesized similar to the procedure described for com-
pound 1 by reaction of Ni(COD)2 with 1 equiv of
(iPr)2PCH2CH2NMe2 and 1 equiv of the alkyne. (PN)Ni-
(η2-tBuCtCPh) (4) and (PN)Ni(η2-F3CCtCPh) (5) were
obtained as orange, air- and moisture-sensitive solids
after recrystallization from petroleum ether/THF at T
) -30 °C. The 1H, 31P{1H}, and 19F{1H} NMR data
showed that 4 and 5 were formed as two isomers, with
the phenyl group either trans (4a , 5a ) or cis (4b, 5b) to
phosphorus (eq 3). We assume that the electron-donat-
F igu r e 2. Molecular structure of (PN)Ni(η2-F3CCtCPh)
(5b) (ORTEP diagram; 30% probability ellipsoids).
Ta ble 2. Selected Bon d Len gth s (Å) a n d Bon d
An gles (d eg) for 5b
Bond Lengths
Ni(1)-N(1)
Ni(1)-P(1)
Ni(1)-C(1)
2.039(4)
2.1674(13)
1.868(4)
Ni(1)-C(2)
C(1)-C(2)
C(2)-C(3)
1.864(4)
1.296(6)
1.452(6)
Bond Angles
C(1)-Ni(1)-C(2)
N(1)-Ni(1)-P(1)
40.63(18) C(1)-Ni(1)-P(1) 117.71(14)
89.36(11) C(1)-C(2)-C(3)
139.3(5)
142.4(4)
C(2)-Ni(1)-N(1) 112.06(17) C(2)-C(1)-C(4)
bond lengths Ni-C(1) and Ni-C(2) are 1.868(4) and
1.864(4) Å, respectively. Furthermore, the X-ray struc-
tural analysis confirmed the NMR data and showed that
the CF3 group is indeed positioned trans to phosphorus,
while the phenyl group is trans to nitrogen. Other
L2Ni(PhCtCR) complexes with asymmetrically substi-
tuted acetylenes are known (R ) aryl, SiMe3) and
display similar geometric features.13f-h,16
Similar to 1, (PN)Ni(η2-tBuCtCPh) turned out to be
a catalyst for the production of 9-phenyl-10-tert-butyl-
phenanthrene (6). Within 16 days at T ) 40 °C (0.4 TO/
d), a mixture of t-BuCtCPh and biphenylene was
quantitatively converted into the 9,10-disubstituted
phenanthrene in the presence of 4 (16.6 mol %) (eq 4).
We propose the same mechanism for the catalytic
production of 6 as for the formation of 9,10-diphenyl-
phenanthrene shown in Scheme 1.
t
ing Bu group prefers the position trans to the nitrogen
atom in 4 (4a :4b ) 93:7). The molecular structure of
the isoelectronic platinum complex (PN)Pt(η2-tBuCtCPh)
revealed this feature.21 The electron-withdrawing CF3
group, however, is preferentially oriented in the cis
position to the nitrogen in 5 (5a :5b ) 1:9). In particular,
a quartet at δ ) 59.8 (4J P-F(trans) ) 11.9 Hz) was
observed for 5b in the 31P{1H} NMR spectrum, while
complex 5a showed a singlet at δ ) 61.4. Complemen-
tary to this observation, a doublet at δ ) -54.4
(4J F-P(trans) ) 12.9 Hz) was detected for 5b in the 19F{1H}
NMR spectrum. Compound 5a , with the CF3 group cis
to phosphorus, showed a singlet at δ ) -57.2. This is
consistent with the fact that trans-coupling between two
nuclei is usually much stronger compared to cis-
coupling.
A crystal of the major compound 5b suitable for X-ray
diffraction was obtained by recrystallization from pe-
troleum ether/THF at T ) -30 °C. The molecular
structure is depicted in Figure 2, and selected bond
lengths and angles are listed in Table 2. Again, the
square-planar structure of 5b and the C(2)-C(1)-C(4)
angle of 142.4(4)° suggest a significant amount of π*-
back-bonding to generate d8 Ni(II) metallacyclopropene
character. The C(1)-C(2) distance is 1.296(6) Å, and the
In contrast, no catalytic C-C bond activation of
biphenylene was observed with complex (PN)Ni(η2-
F3CCtCPh) (8.3 mol %) and a mixture of F3CCtCPh
and biphenylene. Instead, quantitative cyclotrimeriza-
tion of the alkyne occurred, and the benzene derivatives
7 and 8 (ratio: 3:7) were generated within 4.5 h at T )
70 °C (∼0.9 TO/h) (eq 5). Obviously, complexation of a
second alkyne with subsequent reductive coupling to a
metallacyclopentadiene is much faster than oxidative
addition of biphenylene to the metal center (Scheme 2).
To test whether the activity of 5 toward cyclotrimer-
ization of F3CCtCPh is again due to the hemilabile
(21) Mu¨ller, C.; Lachicotte, R. J .; J ones, W. D. Unpublished results.

P,N- versus P,P-Substituted Nickel Complexes
Organometallics, Vol. 21, No. 9, 2002 1979
(alkyne)6 or (dippe)RhCl(alkyne)7 complexes, described
previously.
Exp er im en ta l Section
Gen er a l Con sid er a tion s. All manipulations were carried
out under a nitrogen atmosphere, either on a high-vacuum line
using modified Schlenk techniques or in a Vacuum Atmo-
spheres Corporation glovebox unless otherwise stated. The
solvents were commercially available and distilled from dark
purple solutions of benzophenone ketyl. A Siemens-SMART
3-Circle CCD diffractometer was used for the X-ray crystal
structure determinations. The elemental analyses were ob-
tained from Desert Analytics (Tuscon, AZ) and Complete
Analysis Laboratories, Inc. (Parsippany, NH). 1H, 13C{1H},
31P{1H}, and 19F{1H} NMR spectra were recorded on a Bruker
Avance-400 spectrometer, and all 1H chemical shifts are
reported relative to the residual proton resonance in the
deuterated solvents. 31P{1H} NMR data are referenced to
H3PO4 (85%), while CFCl3 was used as an external standard
for the 19F{1H} NMR data (δ (ppm) ) 0.0). (iPr)2PCH2CH2NMe2
(PN),9 (iPr)2PCH2CH2P(iPr)2 (dippe),22 tBuCtCPh,23 and
F3CCtCPh24 were synthesized according to published proce-
dures. Ni(COD)2, diphenylacetylene, and 1,4-diphenylbutadiyne
were obtained from Aldrich and were used without further
purification.
character of the P,N ligand, we synthesized the corre-
sponding Ni(0) complex (dippe)Ni(η2-F3CCtCPh) (9).
This compound was prepared according to eq 6 and was
(P N)Ni(η2-P h CtCP h ) (1). (iPr)2CH2CH2NMe2 (53.0 mg,
59.0 µL, 0.28 mmol) was added to a suspension of Ni(COD)2
in pentane (4.5 mL). An orange solution was formed, and
diphenylacetylene (50.0 mg, 0.28 mmol), dissolved in pentane
(2.0 mL), was added. An orange solid was formed within 20
min. Stirring was continued for 1 h, and the solid was filtered
and washed with cold pentane (2 × 1.0 mL). The product was
dried in vacuo. 1 was obtained as an orange, air- and moisture-
sensitive solid. Yield: 68.0 mg (0.16 mmol, 57%). 1H NMR
obtained as an orange, air- and moisture-sensitive solid
after recrystallization from petroleum ether/THF at T
) -30 °C. The 31P{1H} NMR spectrum of 9 (C6D6)
showed a doublet at δ ) 83.4 (2J P-P ) 29.7 Hz), as well
as a multiplet at δ ) 81.4 due to phosphorus-fluorine
trans-coupling. A solution of 9 (8.3 mol %) and F3CCt
CPh in C6D6 was heated to T ) 70 °C, and the reaction
was monitored by 1H, 31P{1H}, and 19F{1H} NMR
spectroscopy. Only traces of the cyclotrimerization
products were generated after 5.5 h. Even after pro-
longed heating at T ) 100 °C (78 h) the amounts of 7
and 8 were found to be less than 1%. Furthermore, no
reaction of F3CCtCPh with biphenylene in the presence
of 9 was observed either. Clearly, the mixed donor
system P,N enhanced the reactivity of the Ni(0) species
toward the catalytic cyclotrimerization reaction dra-
matically.
i
3
(C6D6): δ (ppm) 0.95 (m, 8 H, Pr, -CH-), 1.12 (dd, J H-P
)
3
i
16.0 Hz, J H-H ) 7.2 Hz, 6 H, Pr), 1.83 (m, 4 H, -CH2CH2-),
2.38 (s, 6 H, N-CH3), 7.06 (m, 2 H, p-C6H5), 7.20 (pseudo-t, 2
H, m-C6H5), 7.31 (pseudo-t, 2 H, m-C6H5), 7.60 (d, 3J H-H ) 7.5
Hz, 2 H, o-C6H5), 7.69 (d, 3J H-H ) 8.3 Hz, 2 H, o-C6H5). 13C{1H}
2
NMR (C6D6): δ (ppm) 18.4 (-CH-CH3), 20.1 (d, J C-P ) 9.5
1
Hz, -CH-CH3), 20.2 (d, J C-P ) 9.7 Hz, P-CH2-), 24.2 (d,
2
2J C-P ) 16.9 Hz, -CH-), 50.8 (N-CH3), 62.6 (d, J C-P ) 10.4
Hz, N-CH2-), 123.5 (Ph-C), 124.8 (Ph-C), 126.6 (ipso-Ph-
2
2
C), 126.8 (d, J C-P ) 2.7 Hz), 137.9 (d, J C-P(trans) ) 9.5 Hz,
tC-Ph), 139.2 (d, J C-P(cis) ) 5.3 Hz, tC-Ph). 31P{1H} NMR
2
(C6D6): δ (ppm) 58.3. Anal. Calcd for C24H34NNiP (426.23
g/mol): C, 67.63; H, 8.04; N, 3.29. Found: C, 67.56; H, 7.88;
N, 3.18.
[(P N)Ni]2(η2;η2-P h CtC-CtCP h ) (3). (iPr)2CH2CH2NMe2
(105.6 mg, 0.56 mmol, 117.8 µL) was added to a suspension of
Ni(COD)2 (153.5 mg, 0.56 mmol) in pentane (8 mL). An orange
solution was formed, which was stirred for 40 min at room
temperature. A solution of 1,4-diphenylbutadiyne (56.4 mg,
0.28 mmol) in pentane (2 mL) was slowly added, and the color
changed to dark red. A red solid was formed immediately,
which was filtered and washed with cold pentane (2 mL). The
product was dried in vacuo. 3 was obtained as a red, air- and
moisture-sensitive solid. Yield: 160.0 mg (0.23 mmol, 82%).
1H NMR (C6D6): δ (ppm) 1.02 (m, 16 H, iPr, -CH-), 1.27 (dd,
Con clu sion s
The Ni(0) complexes (PN)Ni(η2-PhCtCR) (R ) Ph,
tBu) are effective catalysts for the C-C bond activation
in biphenylene and functionalization with PhCtCPh or
tBuCtCPh to give 9,10-disubstituted phenanthrenes.
Hexaphenylbenzene can be catalytically generated in
the absence of biphenylene with (PN)Ni(η2-PhCtCPh)
and excess diphenylacetylene. In the presence of (PN)-
Ni(η2-F3CCtCPh), only cyclotrimerization of F3CCt
CPh rather than phenanthrene formation was observed.
In contrast, the bis-phosphino-substituted complexes
(dippe)Ni(η2-PhCtCR) (R ) Ph, CF3) produce only
traces of phenanthrene or cyclotrimerization products
under similar reaction conditions. We attribute the
enhanced reactivity of P,N- versus P,P-substituted Ni(0)
complexes to the hemilabile character of the P,N ligand.
Furthermore, these nickel systems turned out to be
more selective for phenanthrene formation from bi-
phenylene and acetylenes than any of the (dippe)Ni-
3
i
3J H-P ) 15.8 Hz, J H-H ) 7.0 Hz, 12 H, Pr), 1.85 (m, 4 H,
3
P-CH2-), 1.97 (q, J H-H ) 6.8 Hz, 4 H, N-CH2-), 2.55 (s, 12
H, N-CH3), 7.03 (t, 3J H-H ) 7.3 Hz, 2 H, p-C6H5), 7.27 (t, 4 H,
3
m-C6H5), 7.83 (d, J H-H ) 7.4 Hz, 4 H, o-C6H5). 13C{1H} NMR
2
(C6D6): δ (ppm) 18.6 (-CH-CH3), 20.4 (d, J C-P ) 10.4 Hz,
(22) (a) Fryzuk, M. D.; J ones, T.; Einstein, F. W. B. Organometallics
1984, 3, 185. (b) Burg, R. J .; Chatt, J .; Hussain, W.; Leigh, G. J . J .
Organomet. Chem. 1979, 182, 203.
(23) Bock, H.; Alt, H. Chem. Ber. 1970, 103, 1784.
(24) Kobayashi, Y.; Yamashita, T.; Takahashi, K.; Kuroda, H.;
Kumadaki, I. Chem. Pharm. Bull. 1984, 32, 4402.

1980 Organometallics, Vol. 21, No. 9, 2002
Mu¨ller et al.
1
2
-CH-CH3), 20.7 (d, J C-P ) 9.2 Hz, P-CH2-), 24.3 (d, J C-P
) 9.1 Hz). Anal. Calcd for C23H37F3NiP2 (491.25 g/mol): C,
54.58; H, 6.99. Found: C, 54.58; H, 7.68.
2
) 16.5 Hz, -CH-), 49.8 (N-CH3), 62.8 (d, J C-P ) 11.7 Hz,
N-CH2-), 122.5 (Ph-C), 123.3 (Ph-C), 129.2 (Ph-C), 132.6
Ca ta lytic F or m a tion of 9,10-Dip h en ylp h en a n th r en e.
A solution of 1 (8.5 mg, 0.02 mmol), diphenylacetylene (42.7
mg, 0.24 mmol), and biphenylene (36.4 mg, 0,24 mmol) in C6D6
(0.6 mL) was transferred to a resealable NMR tube. The
sample was heated to T ) 70 °C, and the reaction was
monitored by 1H and 31P{1H} NMR spectroscopy. Complete
conversion to the disubstituted phenanthrene was achieved
within 22.5 h. Subsequently, the solution was diluted in a
mixture of pentane and dichloromethane (5 mL) and filtered
to remove decomposition products. The solvents and all
volatiles were evaporated in vacuo to yield pure 9,10-di-
phenylphenanthrene (78.0 mg, 0.236 mmol, 98%). 1H NMR
2
(ipso-Ph-C), 133.0 (tC-Ph), 137.7 (d, J C-P(trans) ) 6.9 Hz,
tC-Ph). 31P{1H} NMR (C6D6): δ (ppm) 59.0. Anal. Calcd for
C
36H58N2Ni2P2 (698.27 g/mol): C, 61.92; H, 8.37; N, 4.01.
Found: C, 62.02; H, 8.29; N, 3.98.
(P N)Ni(η2-tBu CtCP h ) (4). (iPr)2CH2CH2NMe2 (12.0 mg,
13.3 µL, 0.063 mmol) was added to a suspension of Ni(COD)2
(17.4 mg, 0.063 mmol) in C6D6 (0.6 mL). The orange solution
was transferred to a vial containing tBuCtCPh (10.0 mg, 0.063
mmol). The quantitative formation of the η2-alkyne complex
was confirmed by H and 31P{1H} NMR spectroscopy. Subse-
1
quently, the solvent and all volatiles were evaporated in vacuo.
An orange oil remained, which slowly solidified. 4 (two isomers,
4a and 4b) was obtained as an air- and moisture-sensitive
orange solid after recrystallization from petroleum ether/THF
at T ) -30 °C. Yield: 9.0 mg (0.022 mmol, 35%). 1H NMR
3
(C6D6): δ (ppm) 6.95 (t, J H-H ) 7.2 Hz, 2 H, p-C6H5), 7.04
(pseudo-t, 4 H, m-C6H5), 7.10 (d, 3J H-H ) 7.6 Hz, 4 H, o-C6H5),
3
7.30, 7.44 (2×pseudo-t, 2 × 2 H, C6H4), 7.76, 8.60 (2×d, J H-H
) 8.0 Hz, 2 × 2 H, C6H4). The reaction was repeated with
complex 3 (7.0 mg, 0.01 mmol) instead of 1 at T ) 70 °C.
Quantitative formation of 9,10-diphenylphenanthrene from
diphenylacetylene (42.7 mg, 0.24 mmol) and biphenylene (36.4
mg, 0.24 mmol) was achieved within 22.5 h. The reaction was
worked up as described above to yield 76.0 mg (0.23 mmol,
96%) of 9,10-diphenylphenanthrene.
i
3
(C6D6): δ (ppm) 0.97 (m, 8 H, Pr, -CH-), 1.22 (dd, J H-P
)
3
i
t
15.6 Hz, J H-H ) 7.1 Hz, 6 H, Pr), 1.43, 1.58 (2×s, 9 H, Bu-
H), 1.78 (m, 4 H, -CH2CH2-), 2.30, 2.55 (2×s, 6 H, N-CH3),
3
7.06 (t, J H-H ) 7.1 Hz, 1 H, p-C6H5), 7.26 (pseudo-t, 2 H,
m-C6H5), 7.43 (d, J H-H ) 7.4 Hz, 2 H, o-C6H5). 31P{1H} NMR
3
(C6D6): δ (ppm) 55.8 (7%, 4b), 57.4 (93%, 4a ). Anal. Calcd for
Ca ta lytic F or m a tion of Hexa p h en ylben zen e. A solution
of 1 (4.7 mg, 0.01 mmol) and diphenylacetylene (20.2 mg, 0.113
mmol) in C6D6 (0.6 mL) was transferred to a resealable NMR
tube and heated to T ) 70 °C. The reaction was monitored by
1H and 31P NMR spectroscopy and went to completion within
60 days. To isolate the organic product, the solution was
diluted in dichloromethane (10 mL) and filtered to remove
decomposition products. The solvent and all volatiles were
evaporated in vacuo to afford pure hexaphenylbenzene (19.3
C
22H38NNiP (406.25 g/mol): C, 65.04; H, 9.43; N, 3.45.
Found: C, 64.82; H, 9.64; N, 3.46.
(P N)Ni(η2-CF 3CtCP h ) (5). Ni(COD)2 (27.2 mg, 0.099
mmol) was suspended in C6D6 (0.5 mL), and (iPr)2CH2CH2-
NMe2 (18.7 mg, 20.8 µL, 0.099 mmol) was added. The orange
solution was transferred to a vial containing CF3CtCPh (16.8
mg, 0.099 mmol). The color changed to yellow, and the
quantitative formation of the η2-alkyne complex was confirmed
by 1H and 31P{1H} NMR spectroscopy. The solvent and all
volatiles were evaporated in vacuo to afford an orange oil,
which slowly solidified. 5 was obtained as an orange, air- and
moisture-sensitive solid after recrystallization from petroleum
ether/THF at T ) -30 °C (two isomers, 5a and 5b in a ratio
1
3
mg, 96%). H NMR (C6D6): δ (ppm) 6.73 (t, J H-H ) 7.3 Hz, 6
3
H, p-C6H5), 6.83 (pseudo-t, 12 H, m-C6H5), 7.12 (d, J H-H
7.1 Hz, 12 H, o-C6H5).
)
Ca ta lytic F or m a tion of 9-P h en yl-10-ter t-bu tylp h en a n -
th r en e (6). A solution of 4 (20.3 mg, 0.05 mmol), biphenylene
1
of 1:9). Yield: 27.0 mg (0.065 mmol, 66%). H NMR (C6D6): δ
t
(ppm) 0.83 (dd, 3J H-P ) 12.6 Hz, 3J H-H ) 6.9 Hz, 6 H, iPr, 5b),
0.88 (m, 2 H + 2 H, -CH-, 5a , 5b), 0.96 (dd, 3J H-P ) 16.3 Hz,
3J H-H ) 7.1 Hz, 6 H + 6 H, iPr, 5a , 5b), 1.16 (dd, 3J H-P ), 16.2
(45.0 mg, 0.3 mmol), and BuCtCPh (46.8 mg, 0.3 mmol) was
transferred to a resealable NMR tube and heated to T ) 40
°C. The reaction was monitored by 1H NMR spectroscopy.
Within 16 days the organic product was quantitatively gener-
ated. The solution was diluted in a mixture of pentane and
chloroform (5 mL) and filtered to remove decomposition
products. The solvents and all volatiles were evaporated in
vacuo, and the residue was recrystallized from acetone at T )
-30 °C to afford colorless crystals. Yield: 77.3 mg (0.25 mmol,
83%). 1H NMR (C6D6): δ (ppm) 1.42 (s, 9 H, tBu), 7.23 (d, 3J H-H
) 8.5 Hz, 1 H), 7.33 (m, 3 H), 7.44 (m, 3 H), 7.55 (m, 3 H),
Hz, J H-H ) 7.6 Hz, 6 H, iPr, 5a ), 1.70 (m, 4 H + 4 H,
3
-CH2CH2-, 5a , 5b), 2.24 (s, 6 H, N-CH3, 5a ), 2.44 (s, 6 H,
N-CH3, 5b), 7.04 (m, 1 H + 1 H, p-C6H5, 5a , 5b), 7.16 (pseudo-
t, 2 H, m-C6H5, 5b), 7.23 (pseudo-t, 2 H, m-C6H5, 5a ), 7.56 (d,
3J H-H ) 7.8 Hz, 2 H, o-C6H5, 5a ), 7.65 (d, 3J H-H ) 7.1 Hz, 2 H,
o-C6H5, 5b). 31P{1H} NMR (C6D6): δ (ppm) 59.8 (q, J P-F
)
4
11.9 Hz, trans-P-CF3), 61.4 (cis-P-CF3). 19F{1H} NMR
4
(C6D6): δ (ppm) -57.2 (s, cis-P-CF3), -54.4 (d, J F-P ) 12.9
3
3
8.61 (d, J H-H ) 8.9 Hz, 1 H), 8.66 (d, J H-H ) 7.5 Hz, 1 H),
Hz, trans-P-CF3). Anal. Calcd for C19H29F3NNiP (418.15
g/mol): C, 54.58; H, 6.99; N, 3.35. Found: C, 54.29; H, 7.08;
N, 3.37.
3
8.76 (d, J H-H ) 8.0 Hz, 1 H). Anal. Calcd for C24H22 (310.44
g/mol): C, 92.86; H, 7.14. Found: C, 93.04; H, 7.36.
Ca ta lytic F or m a tion of Tr is(tr iflu or om eth yl)tr ip h en -
ylben zen e (7, 8). A solution of 5 (6.5 mg, 0.016 mmol) and
F3CCtCPh (31.7 mg, 0.187 mmol) in C6D6 (0.6 mL) was heated
to T ) 70 °C in a resealable NMR tube. The reaction was
(d ip p e)Ni(η2-F 3CCtCP h ) (9). A solution of bis(diisopro-
pylphosphino)ethane (22.6 mg, 0.086 mmol) in C6D6 (0.5 mL)
was added to Ni(COD)2 (23.7 mg, 0.086 mmol). An orange
solution was formed, which was transferred to a vial contain-
ing F3CCtCPh (14.7 mg, 0.086 mmol). The NMR tube was
heated to T ) 55 °C for 4 h. The formation of the η2-alkyne
complex was confirmed by 1H, 31P{1H}, and 19F{1H} NMR
spectroscopy. Subsequently the solvent and all volatiles were
evaporated in vacuo and the residue was recrystallized from
petroleum ether/THF at T ) -30 °C. 9 was obtained as an
orange, air- and moisture-sensitive solid. Yield: 14.0 mg (0.029
1
monitored by H and 19F{1H} NMR spectroscopy. Within 4.5
h the benzene derivatives 7 and 8 were generated quantita-
tively. The solution was diluted in pentane (5 mL), and
decomposition products were removed by filtration. The solu-
tion was concentrated to ∼2 mL and stored at T ) -30 °C. A
mixture of 7 and 8 (ratio 3:7) was obtained as a colorless solid
after decanting the mother liquor and drying the residue in
vacuo. Yield: 25.0 mg (0.049 mmol, 79%). 19F{1H} NMR
(C6D6): δ (ppm) -55.9 (q, J F-F ) 16.6 Hz, 3 F, 8), -54.6 (q,
J F-F ) 16.6 Hz, 3F, 8), -52.9 (s, 3 F, 8), -51.4 (s, 7). Anal.
Calcd for C27H15F9 (510.42 g/mol): C, 63.54; H, 2.96. Found:
C, 63.37; H, 3.28.
1
3
mmol, 33%). H NMR (C6D6): δ (ppm) 0.77 (dd, J H-P ) 12.4
Hz, 3J H-H ) 7.0 Hz, 6 H, iPr), 0.85 (dd, 3J H-P ) 12.6 Hz, 3J H-H
i
3
3
) 7.0 Hz, 6 H, Pr), 0.93 (dd, J H-P ) 16.0 Hz, J H-H ) 7.2 Hz,
i
i
6 H, Pr), 1.15 (m, 10 H, Pr, -CH-), 1.83, 1.95 (2×m, 2 × 2
3
H, -CH2-CH2-), 7.05 (t, J H-H ) 7.3 Hz, 1 H, p-C6H5), 7.21
(pseudo-t, 2 H, m-C6H5), 7.73 (d, 3J H-H ) 7.7 Hz, 2 H, o-C6H5).
31P{1H} NMR (C6D6): δ (ppm) 81.4 (m, trans-P-F), 83.4 (d,
2J P-P ) 29.7 Hz). 19F{1H} NMR (C6D6): δ (ppm) -55.8 (d, 4J F-P
Ack n ow led gm en t is made to the U.S. Department
of Energy, grant FG02-86ER13569, for their support of

P,N- versus P,P-Substituted Nickel Complexes
Organometallics, Vol. 21, No. 9, 2002 1981
atomic coordinates, and anisotropic thermal parameters for 1
and 5b. This material is available free of charge via the
Internet at http://pubs.acs.org.
this work. C.M. thanks the Deutsche Forschungsge-
meinschaft (DFG) for a postdoctoral fellowship. We also
thank Dr. Nicole Brunkan for assistance with compound
characterization.
Su p p or tin g In for m a tion Ava ila ble: Details of data
collection parameters, bond lengths, bond angles, fractional
OM0110989