Preparation of benzyne complexes of group 10 metals by intramolecular Suzuki coupling of ortho-metalated phenylboronic esters: Molecular structure of the first benzyne-palladium(0) complex

Article abstract of DOI:10.1021/ja0264091

A series of nickel(II) and palladium(II) aryl complexes substituted in the ortho position of the aromatic ring by a (pinacolato)boronic ester group, [MBr{o-C₆H₄B(pin)}L₂] (M = Ni, L₂ = 2PPh₃ (2a), 2PCy₃ (2b), 2PEt₃ (2c), dcpe (2d), dppe (2e), and dppb (2f); M = Pd, L₂ = 2PPh₃ (3a), 2PCy₃ (3b), and dcpe (3d)), has been prepared. Many of these complexes react readily with KO^tBu to form the corresponding benzyne complexes [M(η²-C₆H₄)L₂] (M = Ni, L₂ = 2PPh₃ (4a), 2PCY₃ (4b), 2PEt₃ (4c), dcpe (4d); M = Pd, L₂ = 2PCy₃ (5b)). This reaction can be regarded as an intramolecular version of a Suzuki cross-coupling reaction, the driving force for which may be the steric interaction between the boronic ester group and the phosphine ligands present in the precursors 2 and 3. Complex 3d also reacts with KO^tBu, but in this case disproportionation of the initially formed η²-C₆H₄ complex (5d) leads to a 1:1 mixture of a novel dinuclear palladium(I) complex, [(dcpe)Pd(μ₂-C₆H₄)Pd(dcpe)] (6), and a 2,2′-biphenyldiyl complex, [Pd(2,2′-C₆H₄C₆H₄)-(dcpe)] (7d). Complexes 2a, 3b, 3d, 4b, 5b, 6, and 7d have been structurally characterized by X-ray diffraction; complex 5b is the first example of an isolated benzyne-palladium(0) species.

Full text of DOI:10.1021/ja0264091

Published on Web 06/20/2002
Preparation of Benzyne Complexes of Group 10 Metals by
Intramolecular Suzuki Coupling of ortho-Metalated
Phenylboronic Esters: Molecular Structure of the First
Benzyne-Palladium(0) Complex
Mikael Retbøll, Alison J. Edwards,† A. David Rae,† Anthony C. Willis,†
Martin A. Bennett, and Eric Wenger*
Contribution from the Research School of Chemistry, Australian National UniVersity,
Building 35, Canberra ACT 0200, Australia
Received April 3, 2002
Abstract: A series of nickel(II) and palladium(II) aryl complexes substituted in the ortho position of the
aromatic ring by a (pinacolato)boronic ester group, [MBr{o-C6H4B(pin)}L2] (M ) Ni, L2 ) 2PPh3 (2a), 2PCy3
(2b), 2PEt3 (2c), dcpe (2d), dppe (2e), and dppb (2f); M ) Pd, L2 ) 2PPh3 (3a), 2PCy3 (3b), and dcpe
(3d)), has been prepared. Many of these complexes react readily with KOtBu to form the corresponding
benzyne complexes [M(η2-C6H4)L2] (M ) Ni, L2 ) 2PPh3 (4a), 2PCy3 (4b), 2PEt3 (4c), dcpe (4d); M ) Pd,
L2 ) 2PCy3 (5b)). This reaction can be regarded as an intramolecular version of a Suzuki cross-coupling
reaction, the driving force for which may be the steric interaction between the boronic ester group and the
phosphine ligands present in the precursors 2 and 3. Complex 3d also reacts with KOtBu, but in this case
disproportionation of the initially formed η2-C6H4 complex (5d) leads to a 1:1 mixture of a novel dinuclear
palladium(I) complex, [(dcpe)Pd(µ2-C6H4)Pd(dcpe)] (6), and a 2,2′-biphenyldiyl complex, [Pd(2,2′-C6H4C6H4)-
(dcpe)] (7d). Complexes 2a, 3b, 3d, 4b, 5b, 6, and 7d have been structurally characterized by X-ray
diffraction; complex 5b is the first example of an isolated benzyne-palladium(0) species.
benzyne, [Zr(η5-C5H5)2(η2-C6H4)], which is readily generated
Introduction
by elimination of methane or benzene, respectively, from [Zr-
Although benzyne and its substituted derivatives (arynes)
are highly reactive, transient molecules that cannot be isolated
under normal conditions, they are useful reagents in organic
synthesis because they readily undergo Diels-Alder reactions,
cycloadditions with 1,3-dipoles, and nucleophilic additions.1 The
benzyne fragment can also be stabilized by coordination to both
early and late transition metal centers,2-8 in the forms of both
mononuclear and cluster complexes. In particular, zirconocene
(η1-C6H5)(R)(η5-C5H5)2] (R ) Me, Ph), undergoes stoichio-
metric insertions with a wide range of unsaturated molecules,
thus providing a potentially useful synthetic methodology.2,4
Benzyne-nickel(0) complexes of the type [Ni(η2-4,5-R2C6H2)-
(PEt3)2] (R ) H, F) insert successively 2 equiv of alkynes to
give, after reductive elimination of the Ni(PEt3)2 moiety,
substituted naphthalenes with fair to good regioselectivity
(Scheme 1).9-14 It would obviously be desirable to make a
reaction of this type catalytic in nickel, but, unfortunately, the
reaction conditions, which require alkali metal reduction of the
nickel(II) precursors [NiBr(2-Br-4,5-R2C6H2)(PEt3)2], are in-
compatible with most common functional groups likely to be
used as aryl substituents and with the alkynes, which have to
be added after the reduction.
* To whom correspondence should be addressed. E-mail: wenger@
rsc.anu.edu.au.
† Single Crystal X-ray Diffaction Unit.
(1) For selected reviews, see: (a) Hoffmann, R. W. Dehydrobenzene and
Cycloalkynes; Academic Press: New York, 1967. (b) Hoffmann, R. W. In
Chemistry of Acetylenes; Viehe, H. G., Ed.; Marcel Dekker: New York,
1969; pp 1063-1149. (c) Schore, N. E. Chem. ReV. 1988, 88, 1081. (d)
Gilchrist, T. L. In The Chemistry of Triple-Bonded Functional Groups;
Patai, S., Rappoport, Z., Eds.; Wiley: New York, 1983; Vol. Suppl. C2,
pp 383-419. (e) Kessar, S. V. In ComprehensiVe Organic Synthesis; Trost,
B. M., Fleming, I., Semmelhack, M. F., Eds.; Pergamon: Oxford, 1991;
Vol. 4, pp 483-513. (f) Oppolzer, W. In ComprehensiVe Organic Synthesis;
Trost, B. M., Fleming, I., Paquette, L. A., Eds.; Pergamon: Oxford, 1991;
Vol. 5, p 379. (g) Schore, N. E. In ComprehensiVe Organic Synthesis; Trost,
B. M., Fleming, I., Paquette, L. A., Eds.; Pergamon: Oxford, 1991; Vol.
5, pp 1129-1162. (h) Hart, H. In The Chemistry of Triple-Bonded
Functional Groups; Patai, S., Ed.; Wiley: Chichester, 1994; Vol. Suppl.
C2.
Recently, it has been reported that arynes, generated in situ
by treatment of (2-trimethylsilyl)aryl triflates with CsF, cyclo-
(7) Majoral, J.-P.; Meunier, P.; Igau, A.; Pirio, N.; Zablocka, M.; Skowronska,
A.; Bredeau, S. Coord. Chem. ReV. 1998, 178-180, 145.
(8) Brait, S.; Deabate, S.; Knox, S. A. R.; Sappa, E. J. Cluster Sci. 2001, 12,
139.
(9) Bennett, M. A.; Wenger, E. Organometallics 1995, 14, 1267.
(10) Bennett, M. A.; Wenger, E. Organometallics 1996, 15, 5536.
(11) Bennett, M. A.; Cobley, C. J.; Wenger, E.; Willis, A. C. Chem. Commun.
1998, 1307.
(2) Buchwald, S. L.; Nielsen, R. B. Chem. ReV. 1988, 88, 1047.
(3) Bennett, M. A.; Schwemlein, H. P. Angew. Chem., Int. Ed. Engl. 1989,
28, 1296.
(4) Buchwald, S. L.; Broene, R. D. In ComprehensiVe Organometallic
Chemistry II; Abel, E. W., Stone, F. G. A., Wilkinson, G., Hegedus, L. S.,
Eds.; Pergamon: Oxford, 1995; Vol. 12, p 771.
(12) Bennett, M. A.; Cobley, C. J.; Rae, A. D.; Wenger, E.; Willis, A. C.
Organometallics 2000, 19, 1522.
(13) Bennett, M. A.; Macgregor, S. A.; Wenger, E. HelV. Chim. Acta 2001, 84,
(5) Bennett, M. A.; Wenger, E. Chem. Ber. 1997, 130, 1029.
(6) Jones, W. M.; Klosin, J. AdV. Organomet. Chem. 1998, 42, 147.
3084.
(14) Edwards, A. J.; Willis, A. C.; Wenger, E. Organometallics 2002, 21, 1654.
9
8348
J. AM. CHEM. SOC. 2002, 124, 8348-8360
10.1021/ja0264091 CCC: $22.00 © 2002 American Chemical Society

Benzyne Complexes of Group 10 Metals
A R T I C L E S
Scheme 1
Scheme 3
Scheme 2
Scheme 4
trimerize in the presence of catalytic amounts of a palladium-
(0) complex to yield triphenylenes.15,16 By addition of 1 or 2
equiv of alkyne, these reactions can be directed to yield
polyaromatic compounds such as phenanthrenes, naphthalenes,
and/or indene derivatives (Scheme 2).17-21 Most of these
products probably arise from cocyclotrimerization of the free
aryne with the alkynes catalyzed by the palladium complex or
by insertion of the alkynes into an aryl-palladium(II) bond
resulting from oxidative addition of the aryl triflate to palladium-
(0); although palladium(0)-benzyne complexes may have been
formed, none were detected. In contrast, the catalytic carbony-
lation of arynes, generated in the same way, to give either
anthraquinones (in the presence of cobalt carbonyls) or fluo-
renones (in the presence of [RhCl(cod)]2) is postulated to occur
via species derived by insertion of CO into a metal-benzyne
complex.22 Intermediates of this type have been observed in
the stoichiometric reaction of benzyne-nickel(0) complexes with
CO.23
wider range of aromatic substituents and hence potentially
applicable to catalytic conditions. Recently, nickel(0), assumed
to be formed from the combination of a nickel(II) halide-tertiary
phosphine complex and n-butyllithium, has been used to catalyze
cross-coupling reactions of boronic esters with aryl halides,
leading to the formation of biphenyls (Scheme 3).24,25
Mild bases such as K3PO4 initiate the cleavage of the boronic
ester, thus forming the second aryl-Ni bond necessary for the
coupling to occur. If both functionalities were present on the
same arene in the form of a bromoarene substituted in the ortho
position by a boronic ester, one could envisage that replacement
of the bromine by the metal center and subsequent intramo-
lecular Suzuki coupling could generate a benzyne complex
(Scheme 4). We show here that this methodology is indeed
feasible and can be used to form new benzyne complexes of
nickel(0) and palladium(0).
Results
We have chosen to investigate new ways of generating
benzyne-nickel(0) complexes that might be compatible with a
The nickel(II) complex [NiBr{o-C6H4B(pin)}(PPh3)2] (2a)26
was obtained by oxidative addition of o-bromophenyl (pinaco-
lato)boronic ester (1) to a nickel(0) species prepared in situ by
zinc reduction of [NiBr2(PPh3)2] (Scheme 5); the procedure was
the same as that developed for the o-bromo analogue [NiBr(2-
(15) Pen˜a, D.; Escudero, S.; Pe´rez, D.; Guitia´n, E.; Castedo, L. Angew. Chem.,
Int. Ed. 1998, 37, 2659.
(16) Pen˜a, D.; Pe´rez, D.; Guitia´n, E.; Castedo, L. Org. Lett. 1999, 1, 1555.
(17) Radhakrishnan, K. V.; Yoshikawa, E.; Yamamoto, Y. Tetrahedron Lett.
1999, 40, 7533.
(18) Pen˜a, D.; Pe´rez, D.; Guitia´n, E.; Castedo, L. J. Am. Chem. Soc. 1999, 121,
5827.
(19) Pen˜a, D.; Pe´rez, D.; Guitia´n, E.; Castedo, L. J. Org. Chem. 2000, 65, 6944.
(20) Yoshikawa, E.; Yamamoto, Y. Angew. Chem., Int. Ed. 2000, 39, 173.
(21) Yoshikawa, E.; Radhakrishnan, K. V.; Yamamoto, Y. J. Am. Chem. Soc.
2000, 122, 7280.
(22) Chatani, N.; Kamitani, A.; Oshita, M.; Fukumoto, Y.; Murai, S. J. Am.
Chem. Soc. 2001, 123, 12686.
(23) Bennett, M. A.; Hockless, D. C. R.; Humphrey, M. G.; Schultz, M.; Wenger,
E. Organometallics 1996, 15, 928.
(24) Selected reviews: (a) Miyaura, N.; Suzuki, A. Chem. ReV. 1995, 95, 2457.
(b) Suzuki, A. In Metal-Catalyzed Cross-Coupling Reactions; Diederich,
F., Stang, P. J., Eds.; Wiley-VCH: Weinheim, 1998; p 49.
(25) Saito, S.; Oh-tani, S.; Miyaura, N. J. Org. Chem. 1997, 62, 8024.
(26) Abbreviations: pin ) pinacolate, -OCMe2CMe2O-; dcpe ) 1,2-bis-
(dicyclohexylphosphino)ethane, Cy2PCH2CH2PCy2; dppe ) 1,2-bis(diphe-
nylphosphino)ethane, Ph2PCH2CH2PPh2; dppb ) 1,4-bis(diphenylphosphino)-
butane, Ph2P(CH2)4PPh2; depe ) 1,2-bis(diethylphosphino)ethane, Et2PCH2C-
H2PEt2; dppm ) bis(diphenylphosphino)methane, Ph2PCH2PPh2; dba )
dibenzylideneacetone, PhCHdCHC(O)CHdCHPh; bipy ) 2,2′-bipyridine.
9
J. AM. CHEM. SOC. VOL. 124, NO. 28, 2002 8349

A R T I C L E S
Retbøll et al.
Scheme 5
59.1 and 63.7 for the cis phosphorus atoms (JPP ) 21.0 Hz),
cf. δP 63.3 and 67.6 (JPP ) 19.4 Hz) for the hydrolysis product
[NiBr(Ph)(dcpe)], δP 61.3 and 65.4 (JPP ) 17.1 Hz) for [NiBr-
(o-C6H4Me)(dcpe)],29 and δP 66.8 and 69.0 (JPP ) 30.5 Hz)
for [NiBr(2-Br-4,5-F2C6H2)(dcpe)].9 The 13C NMR spectra of
the nickel(II) complexes show two characteristic signals for the
boronic ester substituent at δC ca. 84 ppm for the quaternary
carbons of the pinacolato fragment and in the region δC 24-26
ppm for the four CH3 groups; in some cases, the latter signal
shows a splitting attributable to hindered rotation around the
aryl-B bond. The quaternary carbon C1 bonded to nickel is
observed as a triplet in the region δC 160-170 ppm with JPC
values of ca. 30 Hz for 2a and 2c, indicating that the two
phosphorus atoms are mutually trans. The dppe adduct 2e shows
a doublet of doublets for C1 with respective trans and cis JPC
coupling values of 83.9 and 38.5 Hz. For the dppb species 2f,
the signal for C1 is also a triplet with JPC ) 33.8 Hz, but the
31P NMR spectrum shows two signals with very similar
chemical shifts (δP 11.4 and 12.0) with a coupling of 39.3 Hz
that is larger than that usually observed for a cis coupling,
perhaps as a consequence of distortion from planar coordination.
The palladium(II) precursors 3a and 3b are prepared similarly
by oxidative addition of 1 with [Pd(dba)2] in the presence of 2
mol equiv of PPh3 or PCy3, respectively, but heating to 100 °C
is required (Scheme 5). With the chelating diphosphines, direct
oxidative addition did not occur, and, in the case of dcpe, the
species [Pd(η2-dba)(dcpe)] was isolated.30,31 As in the case of
nickel, the dcpe and dppe species 3d and 3e were obtained by
ligand exchange from either 3a or 3b, the latter complex being
preferred because residual PPh3 from reaction of 3a proved more
difficult to remove than that with the nickel analogue.
The 31P NMR data for 3a, 3d, and 3e are similar to those of
their nickel counterparts, but the chemical shift of 3b (δP 16.2)
is very deshielded relative to that of 2b (δP 6.4). The 13C NMR
data are similar to those of the nickel(II) products, the main
difference for the cis complexes being the increased values of
the couplings of C1 with the phosphorus atom located trans to
the Pd-C bond (135.7 Hz for 3d and 129.3 Hz for 3e vs 83.9
Hz for 2e) and the decrease in both the cis and the trans
complexes of the cis JPC values (2.5 Hz for 3a, 3.1 Hz for 3b,
and 2.5 Hz for 3e vs 33.1 Hz for 2a, 34.1 Hz for 2c, and 38.5
Hz for 2e).
The reactions of the nickel and palladium precursors 2b-e
and 3a,b, respectively, with KOtBu give η2-benzyne complexes
(Scheme 6). Thus, on addition of KOtBu to the dcpe-nickel(II)
complex 2d in THF at room temperature, the 31P NMR peaks
to 2d were replaced instantaneously by a singlet at δP 78.4, the
chemical shift being identical to the value reported for the
benzyne complex [Ni(η2-C6H4)(dcpe)] (4d) prepared from
reduction of [NiCl(o-C6H4Br)(dcpe)] with 1% Na/Hg amal-
gam.29 The measured 1H and 13C NMR spectra were also
identical to those reported previously for 4d. The corresponding
reaction with the PEt3 precursor 2c was slower, but after 2 h at
room temperature the 31P NMR spectrum showed the charac-
teristic broad signal at δP 27.9 of the benzyne complex [Ni(η2-
Br-4,5-F2C6H2)(PPh3)2].9 The 31P NMR spectrum shows one
peak at δP 21.4, indicative of a relative trans geometry for the
two phosphine ligands. The structure of 2a has also been
confirmed by X-ray diffraction (see below).
Oxidative addition of 1 to other nickel(0) precursors, for
example, [Ni(η2-C2H4)(dcpe)], [NiBr2(PCy3)2]/Zn, or [Ni(cod)2]/
2PEt3, gave only poor yields of the corresponding nickel(II)
adducts. However, these complexes could be obtained by ligand
exchange reactions. Addition of various phosphines to 2a
allowed the preparation of the complexes [NiBr{o-C6H4B(pin)}-
(PR3)2] (2PR3 ) 2PCy3 (2b), 2PEt3 (2c), dcpe (2d), dppe (2e),
dppb (2f)) in excellent yields (Scheme 5), but exchange with
diphosphines having larger bite angles such as {Ph2P(C6H4)-
CH2}2 or large diphosphite ligands failed. In contrast to 2a,
complexes 2b and 2d proved to be extremely sensitive toward
hydrolysis of the aryl-B bond; thus, attempted crystallization
of 2d always gave [NiBr(C6H5)(dcpe)], identified by X-ray
crystallography.27 As a consequence, the exchange reactions
were generally carried out in a solvent such as ether or toluene
in which the resulting complexes were insoluble and could be
isolated by filtration. Although complete characterization of
these complexes (especially 13C NMR spectra) was not always
possible, the collected spectroscopic data support the formula-
tion.
The 31P NMR chemical shifts of complexes 2b-2f are
generally more shielded than those of their phenyl or o-haloaryl
analogues. For example, complex 2b shows a singlet at δP 6.4
for the two trans PCy3 groups, cf. δP 9.6 for [NiCl(o-C6H4Cl)-
(PCy3)2].28 This shielding is even more pronounced for the PEt3
species (δP 5.1 for 2c vs 10.7 for [NiBr(o-C6H4Br)(PEt3)2]9).
The same effect is observed for the complexes formed with the
chelating diphosphine ligands. The complex [NiBr{o-C6H4B-
(pin)}(dcpe)] (2d) shows the characteristic two doublets at δP
(29) Bennett, M. A.; Hambley, T. W.; Roberts, N. K.; Robertson, G. B.
Organometallics 1985, 4, 1992.
(27) The spectroscopic data of [NiBr(Ph)(dcpe)] are analogous to those reported
for the iodo complex [NiI(Ph)(dcpe)]; see ref 29. For the X-ray structure
of [NiBr(Ph)(dcpe)], see: Edwards, A. J.; Retboll, M.; Wenger, E. Acta
Crystallogr., Sect. C, submitted.
(28) Bennett, M. A.; Okano, T.; Roberts, N. K.; Schwemlein, H. P.; Welling,
L. L., unpublished work.
(30) (a) McGuinness, D. S.; Cavell, K. J.; Yates, B. F.; Skelton, B. W.; White,
A. H. J. Am. Chem. Soc. 2001, 123, 8317. (b) Reid, S. M.; Mague, J. T.;
Fink, M. J. J. Organomet. Chem. 2000, 616, 10.
(31) Retbøll, M.; Wenger, E.; Willis, A. C. Acta Crystallogr., Sect. E 2002, 58,
m275.
9
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Benzyne Complexes of Group 10 Metals
A R T I C L E S
Scheme 6
Scheme 7
C6H4)(PEt3)2] (4c), the yield as estimated from the 31P NMR
spectrum being >80%. All of the spectroscopic data were in
agreement with those previously reported for this species.9,32
Reaction of the PCy3 species 2b with KOtBu was instanta-
neous; the 31P NMR spectrum of the solution showed a singlet
at δP 46.7 assignable to the benzyne complex [Ni(η2-C6H4)-
(PCy3)2] (4b), cf. δP 49.0 for the cyclohexyne analogue [Ni-
1
(η2-C6H8)(PCy3)2].33 The H NMR spectrum of 4b, which can
together with free PPh3. The reaction of 2a with KOtBu was
investigated by low-temperature 31P NMR spectroscopy. At -70
°C, the broad peak moved to δP ca. -5 ppm while sharpening
significantly, the peak in the region δP 27-28 broadened, and
a new broad peak at ca. 40 ppm started to appear. At -90 °C,
there were three main resonances: a very broad peak at δP 27-
28, a fairly sharp peak at δP -7.0, presumably belonging to
free PPh3, and a broad peak at δP 40.7 ppm, the last two being
in an ca. 2.5:1 intensity ratio. The peak at δP 40.7 is tentatively
assigned to the benzyne complex [Ni(η2-C6H4)(PPh3)2] (4a), cf.
δP 43.1 for the cyclohexyne analogue [Ni(η2-C6H8)(PPh3)2]33
or δP in the range 38-42 for [Ni(η2-alkyne)(PPh3)2].36 Unfor-
tunately, the 13C NMR spectrum recorded at -90 °C was very
broad, and no conclusion could be drawn. The free PPh3 could
be removed by evaporating the mixture to dryness and washing
the residue thoroughly with hexane. The 31P NMR spectrum of
the residue at room temperature now showed only the signal at
δP 27-28, while its 13C NMR spectrum was similar in
appearance to that of the original reaction mixture except that
the resonance of Cipso-P was now a doublet (JPC ) 21.1 Hz);
moreover, the integration suggested that the PPh3 and C6H4
groups were now in a 1:1 ratio, whereas in the original reaction
mixture the relative amount of PPh3 was clearly much greater
than 1. The 31P NMR spectrum began broadening only at -90
°C; at -100 °C a very small, broad peak appeared at δP 40.2.
Attempts to isolate a pure solid from the solution by low-
temperature crystallization were unsuccessful, and both the mass
spectra of the original mixture or the solid obtained after removal
of free PPh3 showed no identifiable peaks.
be extracted from the potassium salts with benzene, showed
the expected AA′BB′ multiplet for the aromatic protons (δH 7.53
and 7.82). The 13C NMR spectrum showed the quaternary
carbons C1 and C2 of the coordinated triple bond as a doublet
of doublets at δC 141.6 with separations arising from P-C
coupling of 53.2 and 17.4 Hz. Crystals of 4b were obtained
from a solution in benzene, and the proposed structure was
confirmed by X-ray diffraction analysis (see below). This
complex has also been prepared by reduction of [NiCl(o-C6H4-
Cl)(PCy3)2] with 1% sodium amalgam.28
The corresponding reaction of the dppe analogue 2e was
slower and not clean. After 1.5 h at room temperature, only
20% of the desired benzyne complex [Ni(η2-C6H4)(dppe)] (4e)
had formed. It was identified tentatively from the appearance
of a singlet at δP 60.2 in the 31P NMR spectrum of the reaction
mixture, this chemical shift being identical to that of the
cyclohexyne analogue [Ni(η2-C6H8)(dppe)].33 The main product
gave rise to a singlet at δP 44.7 assigned to [Ni(dppe)2];34
unidentified resonances also appeared in the region δP 23-35.
A similar reaction with 2f, containing the larger dppb ligand,
gave only [Ni(dppb)2] (δP 17.8).34,35
The reaction of the PPh3 complex 2a with KOtBu was more
complicated. After 15 min, the 31P NMR spectrum of the
reaction mixture showed complete disappearance of the peak
at δP 23.2 belonging to 2a and appearance of a very broad,
intense signal at about δP 0 ppm accompanied by a small singlet
at δP 27.9. The 13C NMR spectrum was surprisingly well
resolved, showing peaks characteristic of symmetrically coor-
dinated C6H4 at δC 123.3, 128.3 for the aromatic CH and at δC
142.8 for the two quaternary carbon atoms C1,2 coordinated to
the metal. These signals and that for Cipso-P at δC 137.7 showed
no 31P-coupling, suggesting the possibility of fast intermolecular
exchange of coordinated PPh3. The presence of species contain-
ing coordinated benzyne was confirmed by addition of 1 equiv
of dcpe to the reaction mixture, which gave 4d quantitatively
We conclude tentatively that 4a is in dissociative equilibrium
on the NMR time scale (fast at room temperature, slow at -90
°C) with a species [Ni(C6H4)(PPh3)] (8), which is responsible
for the signal at δP 27-28 (Scheme 7). Complex 8 could be
dinuclear, containing a pair of C6H4 units bridging two 14e,
three-coordinate nickel(II) atoms, [Ni2(µ-o-C6H4)2(PPh3)2] (8′);
a similar dinuclear formulation was postulated on the basis of
molecular weight data for the product isolated from lithium
reduction of [NiCl(o-BrC6H4)(PEt3)2],37 although the spectro-
scopic data obtained subsequently for the product from similar
(32) Bennett, M. A.; Hockless, D. C. R.; Wenger, E. Organometallics 1995,
14, 2091.
(33) Bennett, M. A.; Johnson, J. A.; Willis, A. C. Organometallics 1996, 15,
68.
(34) Fisher, K. J.; Alyea, E. C. Polyhedron 1989, 8, 13.
(35) Edwards, A. J.; Retbøll, M.; Wenger, E. Acta Crystallogr., Sect. E 2002,
accepted.
(36) Bartik, T.; Happ, B.; Iglewsky, M.; Bandmann, H.; Boese, R.; Heimbach,
P.; Hoffmann, T.; Wenschuh, E. Organometallics 1992, 11, 1235.
9
J. AM. CHEM. SOC. VOL. 124, NO. 28, 2002 8351

A R T I C L E S
Retbøll et al.
Scheme 8
reductions were consistent with the mononuclear formulation
4c.9 Alternatively, one could consider a mononuclear 16e
structure 8′′ in which η2-benzyne acts as a four-electron donor;
this coordination mode is believed to occur in certain benzyne
complexes of early transition metals, for example, [Ta(η5-C5-
Me5)(η2-C6H4)Me2]38,39 and [Ta(η5-C5Me5)(η4-C4H6)(η2-C6H4)].40
However, the 13C NMR chemical shift of the quaternary carbons
bonded to nickel, observed at δP 142.8, is more consistent with
the dimeric structure 8′, the reported chemical shifts for η4-
benzyne complexes being considerably more deshielded (>200
ppm).40
The reactions of the palladium(II) complexes with KOtBu
were much slower than those of nickel and generally required
heating (Scheme 6).41 The PPh3 complex 3a gave initially a
31P NMR singlet at δP 41.5 that may belong to the benzyne
complex [Pd(η2-C6H4)(PPh3)2] (5a), because the 1H NMR
spectrum showed a characteristic [AA′BB′] multiplet in the
region δH 7.45, 8.45, but rapid decomposition hindered further
identification. However, the PCy3 complex 3b reacted with KOt-
Bu at room temperature overnight or at 80 °C for 2 h to give
exclusively a compound showing a 31P NMR singlet at δP 43.3
assigned to the benzyne-palladium(0) complex [Pd(η2-C6H4)-
(PCy3)2] (5b). The NMR data are analogous to those of 4b; the
quaternary carbon atoms of the coordinated triple bond appeared
as an apparent doublet of doublets at δC 138.1 with separations
arising from P-C coupling of 86.7 and 6.5 Hz. The FAB mass
spectrum did not show any molecular ion corresponding to 5b,
but the compound crystallized from C6D6, and its structure was
confirmed by X-ray diffraction analysis (see below).
Reaction of the dppe complex 3e with KOtBu led to
decomposition, and 31P NMR monitoring showed no peaks
assignable to a benzyne complex. On standing, however, crystals
deposited from the reaction mixture that were identified by X-ray
analysis as being the dppe-analogue of 7d, viz., the 2,2′-
biphenyldiyl species [Pd(2,2′-C6H4C6H4)(dppe)] (7e).
The reaction of the palladium(II)-dcpe precursor 3d with KOt-
Bu was not as clean as that of its nickel analogue. After 5 min
at room temperature, the 31P NMR spectrum showed a small
peak at δP 67.0 that may belong to the benzyne complex [Pd-
(η2-C6H4)(dcpe)] (5d), in addition to broad signals from 3d.
After heating at 50 °C for ca. 1 h, two new products, 6 and 7d,
had formed in approximately equal amount, characterized by
two very broad signals at δP 60 and 69 (6) and a singlet at δP
55.1 (7d). When the reaction was carried out at room temper-
ature, the same mixture was obtained after 16 h; a minor product
showing two doublets at δP 60.7 and 64.6 (JPP ) 17.3 Hz),
assigned to the hydrolysis product [PdBr(Ph)(dcpe)], was also
formed. Poorly soluble, X-ray quality crystals of 6 deposited
overnight, but they could not be redissolved in CD2Cl2 for
spectroscopic analysis without decomposition. Diffraction analy-
sis showed complex 6 to be a dinuclear palladium(I) species
[(dcpe)Pd(µ-o-C6H4)Pd(dcpe)] (see below), while the second
complex (7d) was identified as the (2,2′-biphenyldiyl)palladium-
Figure 1. Molecular structure of [NiBr{o-C6H4B(pin)}(PPh3)2] (2a) with
selected atom labeling. Displacement ellipsoids show 50% probability levels;
hydrogen atoms have been omitted for clarity.
1
(II) complex [Pd(2,2′-C6H4C6H4)(dcpe)] on the basis of its H
and 13C NMR spectra (see Experimental Section) (Scheme 8).
Attempts to generate the benzyne complex 5d by reduction of
[PdI(o-C6H4Br)(dcpe)] with 1% Na/Hg amalgam gave initially
a solution showing the 31P NMR singlet at δP 67.0 tentatively
assigned to 5d, but the mixture rapidly decomposed to metallic
palladium and unidentified products.
Molecular Structures of [NiBr{o-C6H4B(pin)}(PPh3)2]
(2a), [PdBr{o-C6H4B(pin)}(PCy3)2] (3b), [PdBr{o-C6H4B-
(pin)}(dcpe)] (3d), [Ni(η2-C6H4)(PCy3)2] (4b), [Pd(η2-C6H4)-
(PCy3)2] (5b), [(dcpe)Pd(µ-o-C6H4)Pd(dcpe)] (6), and [Pd-
(2,2′-C6H4C6H4)(dppe)] (7e). The molecular structures of the
boronic ester precursors 2a, 3b, and 3d are shown in Figures
1-3, respectively. Selected bond lengths and angles are given
in Table 1.42
(37) Dobson, J. E.; Miller, R. G.; Wiggen, J. P. J. Am. Chem. Soc. 1971, 93,
554.
(38) Churchill, M. R.; Youngs, W. J. Inorg. Chem. 1979, 18, 1697.
(39) McLain, S. J.; Schrock, R. R.; Sharp, P. R.; Churchill, M. R.; Youngs, W.
J. J. Am. Chem. Soc. 1979, 101, 263.
(40) Mashima, K.; Tanaka, Y.; Nakamura, A. Organometallics 1995, 14, 5642.
(41) These reactions have been studied with the same batch of commercial KOt-
Bu. The benzyne complexes are formed more rapidly if freshly sublimed
base is used.
(42) The numbering scheme for the arylboronic ester moiety used throughout
this paper (C1-M and C2-B) differs in some cases from that of the deposited
structures.
9
8352 J. AM. CHEM. SOC. VOL. 124, NO. 28, 2002

Benzyne Complexes of Group 10 Metals
A R T I C L E S
Table 1. Selected Bond Lengths (Å) and Angles (deg) for
[NiBr{o-C6H4B(pin)}(PPh3)2] (2a), [PdBr{o-C6H4B(pin)}(PCy3)2]
(3b), and [PdBr{o-C6H4B(pin)}(dcpe)] (3d)
2a [M(1) ) Ni]
3b [M(1) ) Pd]
3d [M(1) ) Pd]
M(1)-Br(1)
2.3680(4)
2.2348(7)
2.2372(7)
1.894(3)
1.546(4)
174.42(3)
170.57(8)
90.81(2)
87.35(7)
88.70(7)
125.16(19)
122.7(2)
2.5525(7)
2.3611(11)
2.3611(11)a
2.026(5)
2.490(1)
2.348(2)
2.258(2)
2.099(7)
1.561(11)
86.3(1)
M(1)-P(1)
M(1)-P(2)
M(1)-C(1)
C(2)-B(1)
1.567(8)
P(1)-M(1)-P(2)
C(1)-M(1)-Br(1)
P(2)-M(1)-Br(1)
P(1)-M(1)-C(1)
P(2)-M(1)-C(1)
M(1)-C(1)-C(2)
C(1)-C(2)-B(1)
167.73(4)
176.08(15)
90.03(3)
89.2(1)
174.7(1)
174.1(2)
90.9(1)
123.3(5)
127.8(4)
90.39(3)
90.39(3)a
124.0(4)
126.0(5)
a P(2) ) P(1′) (generated by symmetry relation).
Figure 2. Molecular structure of [PdBr{o-C6H4B(pin)}(PCy3)2] (3b) with
selected atom labeling; only one orientation of the disordered group is
shown. Displacement ellipsoids show 30% probability levels; hydrogen
atoms have been omitted for clarity. The asterisk indicates an atom generated
by crystallographic symmetry.
Figure 4. Molecular structure of [Pd(η2-C6H4)(PCy3)2] (5b) with selected
atom labeling. Displacement ellipsoids show 50% probability levels;
hydrogen atoms of the cyclohexyl rings have been omitted for clarity.
and C(1) lie 0.2310 and 0.1889 Å, respectively, from the plane
defined by Pd(1) and the two cis-phosphorus atoms. The
significantly different Pd-P distances in 3d [2.348(2) Å trans
to η1-aryl, 2.258(2) Å trans to Br] reflect the relative trans
influence of these ligands. There is no evidence for interaction
between the metal atoms and the pinacolato oxygen atoms, as
judged by the M-O separations: 2.9998(12) for 2a, 3.276(5)
Å for Pd(1)-O(1) in 3b, and 3.166(5) Å in 3d. The phosphine
ligands tend to bend away from the boronic ester substituent,
the effect being particularly noticeable in the structures of 3b
and 3d because of their bulky cyclohexylphosphine ligands.
Thus, in 3b, the P-M-P angle is 167.73(4)° (cf. 173.98(5)°
for [PdCl(Ph)(PCy3)2]45 and 174.42(3)° for 2a), while the C(1)-
C(2)-B(1) angles in the η1-aryl group are increased markedly
from the expected 120° [126.0(5)° for 3b, 127.8(4)° for 3d].
The benzyne complexes 4b and 5b are isomorphous. The
structure of 5b is shown in Figure 4;46 selected geometric
parameters are listed in Table 2. They show a symmetrical η2-
coordination of the benzyne triple bond, the metal atom being
Figure 3. Molecular structure of [PdBr{o-C6H4B(pin)}(dcpe)] (3d) with
selected atom labeling; only the major orientation of the disordered group
is shown. Displacement ellipsoids show 30% probability levels; hydrogen
atoms have been omitted for clarity.
The metal atoms in the boronic ester-substituted precursors
2a, 3b, and 3d are in the expected, approximately square-planar
coordination environment. The metrical data are unexceptional,
the M-C and M-P distances for 2a being similar to those
reported for the ortho-substituted arylnickel(II) complexes [NiCl-
(o-C6H4X)(PPh3)2] (X ) Me,43 CF344), those of 3b resembling
the data for [PdCl(Ph)(PCy3)2].45 In complex 3d, atoms Br(1)
(43) Spek, A. L.; Kooijman, H.; Smeets, W. J. J. Cambridge Crystallographic
Database Centre, refcode VEWRUK.
(44) Lutz, M.; Spek, A. L.; Brandsma, L.; Peters, T. A. Cambridge Crystal-
lographic Database Centre, refcode NAVSOS.
(45) Huser, M.; Youinou, M.-T.; Osborn, J. A. Angew. Chem., Int. Ed. Engl.
1989, 28, 1386.
(46) A figure showing 4b is available in the Supporting Information.
9
J. AM. CHEM. SOC. VOL. 124, NO. 28, 2002 8353

A R T I C L E S
Retbøll et al.
Table 2. Selected Bond Lengths (Å) and Angles (deg) for
[Ni(η2-C6H4)(PCy3)2] (4b) and [Pd(η2-C6H4)(PCy3)2] (5b)
4b [M(1) ) Ni]
5b [M(1) ) Pd]
M(1)-P(1)
2.2007(12)
2.2002(12)
1.888(4)
1.875(4)
1.320(6)
2.3276(14)
2.3415(14)
2.042(6)
2.032(6)
1.324(8)
M(1)-P(2)
M(1)-C(1)
M(1)-C(2)
C(1)-C(2)
P(1)-M(1)-P(2)
C(1)-M(1)-P(1)
C(2)-M(1)-P(2)
122.19(5)
141.63(15)
136.93(14)
119.56(5)
140.47(18)
137.78(17)
in an almost perfect trigonal planar arrangement, typical of
[M(η2-alkyne)L2] complexes of group 10 metals.47 The two
Ni-P bonds in 4b are slightly longer than those reported for
[Ni(η2-C6H4)(dcpe)] (4d) (ca. 2.20 Å vs 2.140(1) and 2.152(1)
Å),29 but the Ni-C bond lengths in the two complexes are
similar (average value ) 1.88 Å). As expected on the basis of
atomic radii, the M-C and M-P bonds in 5b are ca. 0.15 Å
longer than those in 4b; the Pd-C distances compare with those
reported for the 3,5-cycloheptadien-1-yne complex [Pd(η2-
C7H6)(PPh3)2] (2.031(4) and 2.039(4) Å).48 The P-M-P angles
are similar, 122.19(5)° for 4b and 119. 56(5)° for 5b, but they
are much larger than the value reported for 4d (91.8(1)°),29 as
expected from the presence in the latter of a C2H4 bridge
between the phosphorus atoms. The lengths of the coordinated
triple bond C(1)-C(2) in 4b, 4d, and 5b are identical within
experimental error (1.32-1.33 Å), as also are the lengths of
the uncoordinated aryl C-C bonds; the latter are in the range
1.37-1.40 Å, indicating that the fragment retains aromatic
character. Most other mononuclear η2-benzyne complexes show
similar trends,49 although [TaMe2(η2-C6H4)(η5-C5Me5)]38,39 and
[Ir(η2-C6F4)(η5-C5Me5)(PMe3)]50 are exceptional in having
alternating long-short C-C distances in the ring.
Figure 5. Molecular structure of [(dcpe)Pd(µ-o-C6H4)Pd(dcpe)] (6) with
selected atom labeling; only one of the two molecules present in the
asymmetric unit is shown. Displacement ellipsoids show 30% probability
levels; hydrogen atoms have been omitted for clarity.
Table 3. Selected Bond Lengths (Å) and Angles (deg) for
[(dcpe)Pd(µ-o-C6H4)Pd(dcpe)] (6)
Pd(1)-P(11)
2.296(1)
2.301(1)
2.061(3)
2.645(1)
164.2(1)
65.4(1)
159.2(1)
98.8(1)
94.7(2)
Pd(2)-P(21)
2.304(1)
2.303(1)
2.060(3)
1.368(7)
163.1(1)
64.7(1)
160.6(1)
98.5(1)
95.9(2)
Pd(1)-P(12)
Pd(2)-P(22)
Pd(1)-C(11)
Pd(1)-Pd(2)
Pd(2)-Pd(1)-P(11)
Pd(2)-Pd(1)-C(11)
C(11)-Pd(1)-P(12)
C(11)-Pd(1)-P(11)
Pd(1)-C(11)-C(12)
Pd(2)-C(12)
C(11)-C(12)
Pd(1)-Pd(2)-P(21)
Pd(1)-Pd(2)-C(12)
C(12)-Pd(2)-P(22)
C(12)-Pd(2)-P(21)
Pd(2)-C(12)-C(11)
The molecular structure of the dinuclear complex 6 is shown
in Figure 5, and selected values of bond lengths and angles are
given in Table 3. Each palladium atom is coordinated to a pair
of phosphorus atoms from bidentate dcpe and a σ-aryl carbon
atom of the bridging C6H4 unit. The second palladium atom
occupies a fourth coordination site, the resulting geometry being
highly distorted from planarity. The molecule possesses a
pseudorotation symmetry axis that bisects the midpoints of the
C(14)-C(15), C(11)-C(12), and Pd(1)-Pd(2) bonds. The four
Pd-P bonds are of similar lengths (ca. 2.30 Å), and one
phosphorus atom of each dcpe is located approximately trans
to the Pd-Pd bond, the Pd-Pd-P angles being 164.2(1) and
163.1(1)°. The second phosphorus atom of one dcpe is bent
away from the other, presumably because of steric repulsion
between the cyclohexyl substituents. As these phosphorus atoms
and the two Pd-C bonds of the o-phenylene bridge occupy
positions that are almost transoid, a pronounced tilt is induced
in the ortho-phenylene unit, the plane of the latter being rotated
by 46° relative to the Pd-Pd axis. The two Pd-C bond lengths
(ca. 2.06 Å) are in the normal range for aryl-Pd bonds, and
the C-C bonds of the phenyl ring are normal. The distance
between the metal atoms [2.645(1) Å] is within the range
normally found for palladium(I)-palladium(I) bonds; most of
the reported structures of this type show Pd-Pd bond lengths
between 2.53 and 2.70 Å,51 the shortest values being found in
nonbridged dipalladium(I) species of the type [Pd2(NCMe)4L2]
(L ) NCMe, Cl, I).52 Some examples of dinuclear complexes
bridged by aliphatic groups include [Pd2(µ-η3-2-MeC3H4)(µ-
C5H5)(PPh3)2] (Pd-Pd ) 2.679 Å),53 [Pd2(µ-η3-C3H5)2(PPh3)2]
(2.720 Å),54 and alkyne-bridged species [Pd2(µ-C2Ph2)(η5-C5-
(47) Ittel, S. D.; Ibers, J. A. AdV. Organomet. Chem. 1976, 14, 33.
(48) Klosin, J.; Abboud, K. A.; Jones, W. M. Organometallics 1996, 15, 2465.
(49) Selected examples of structurally characterized benzyne complexes or
analogues for various transition metals. For Zr: (a) Buchwald, S. L.; Watson,
B. T.; Huffman, J. C. J. Am. Chem. Soc. 1986, 108, 7411. (b) Erker, G.;
Albrecht, M.; Kru¨ger, C.; Werner, S.; Binger, P.; Langhauser, F. Orga-
nometallics 1992, 11, 3517. (c) Rosa, P.; Le Floch, P.; Ricard, L.; Mathey,
F. J. Am. Chem. Soc. 1997, 119, 9417. For V: (d) Buijink, J. K. F.; Kloetstra,
K. R.; Meetsma, A.; Teuben, J. H.; Smeets, W. J. J.; Spek, A. L.
Organometallics 1996, 15, 2523. For Nb, Ta: (e) Bartlett, R. A.; Power, P.
P.; Shoner, S. C. J. Am. Chem. Soc. 1988, 110, 1966. (f) Koschmieder, S.
U.; Hussain-Bates, B.; Hursthouse, M. B.; Wilkinson, G. J. Chem. Soc.,
Dalton Trans. 1991, 2785. (g) Cockcroft, J. K.; Gibson, V. C.; Howard, J.
A. K.; Poole, A. D.; Siemeling, U.; Wilson, C. J. Chem. Soc., Chem.
Commun. 1992, 1668. (h) Houseknecht, K. L.; Stockman, K. E.; Sabat,
M.; Finn, M. G.; Grimes, R. N. J. Am. Chem. Soc. 1995, 117, 1163; see
also refs 38-40. For Cr, Mo, W: (i) Koschmieder, S. U.; McGilligan, B.
S.; McDermott, G.; Arnold, J.; Wilkinson, G.; Hussain-Bates, B.; Hurst-
house, M. B. J. Chem. Soc., Dalton Trans. 1990, 3427. For Ru: (j) Hartwig,
J. F.; Bergman, R. G.; Andersen, R. A. J. Am. Chem. Soc. 1991, 113, 3404.
For Re: (k) Arnold, J.; Wilkinson, G.; Hussain, B.; Hursthouse, M. B. J.
Chem. Soc., Chem. Commun. 1988, 704. (l) Arnold, J.; Wilkinson, G.;
Hussain, B.; Hursthouse, M. B. Organometallics 1989, 8, 415. For Ir: see
ref 50. For Ni: see ref 29.
(51) Cambridge Crystallographic Database Centre, Vista analysis of 73 deposited
structures of four-coordinate dipalladium(I) complexes.
(52) (a) Goldberg, S. Z.; Eisenberg, R. Inorg. Chem. 1976, 15, 535. (b)
Yamamoto, Y.; Yamazaki, H. Bull. Chem. Soc. Jpn. 1985, 58, 1843. (c)
Rutherford, N. M.; Olmstead, M. M.; Balch, A. L. Inorg. Chem. 1984, 23,
2833.
(53) Werner, H.; Ku¨hn, A.; Tune, D. J.; Kru¨ger, C.; Brauer, D. J.; Sekutowski,
J. C.; Tsay, Y.-H. Chem. Ber. 1977, 110, 1763.
(54) Jolly, P. W.; Kru¨ger, C.; Schick, K.-P.; Wilke, G. Z. Naturforsch. 1980,
B35, 926.
(50) Hughes, R. P.; Williamson, A.; Sommer, R. D.; Rheingold, A. L. J. Am.
Chem. Soc. 2001, 123, 7443.
9
8354 J. AM. CHEM. SOC. VOL. 124, NO. 28, 2002

Benzyne Complexes of Group 10 Metals
A R T I C L E S
Table 4. Selected Bond Lengths (Å) and Angles (deg) for
[Pd(2,2′-C6H4C6H4)(dppe)] (7e)
Pd(1)-P(1)
2.321(2)
2.066(6)
1.397(8)
1.483(9)
84.52(5)
178.1(2)
Pd(1)-P(2)
Pd(1)-C(12)
C(1)-C(6)
2.320(2)
2.059(6)
1.389(8)
Pd(1)-C(1)
C(7)-C(12)
C(6)-C(7)
P(1)-Pd(1)-P(2)
P(2)-Pd(1)-C(1)
C(1)-Pd(1)-C(12)
P(1)-Pd(1)-C(12)
80.3(2)
177.1(1)
expected square planar coordination, the biphenyldiyl unit being
coplanar with the plane defined by Pd and the two phosphorus
atoms (the two carbon atoms C1 and C12 lie only -0.0057
and 0.0631 Å, respectively, from the latter plane). The Pd-C
and Pd-P distances are similar to those discussed above, and
this structure is analogous to those reported for other 2,2′-
biphenyldiyl complexes of group 10 metals, viz., [Ni(2,2′-
C6H4C6H4)(dcpe)],64 [Ni(2,2′-C6H4C6H4)(dippe)],65 [Pt(2,2′-
C6H4C6H4)(PPh3)2],66 and [Pd(2,2′-C6H4C6H4)(depe)].67
Figure 6. Molecular structure of [Pd(2,2′-C6H4C6H4)(dppe)] (7e) with
selected atom labeling. Displacement ellipsoids show 30% probability levels;
hydrogen atoms have been omitted for clarity.
Discussion
Ph5)(L)(L′)] (2.541-2.639 Å) [L,L′ ) η5-C5Ph5;55 L ) bipy,
L′ ) absent, MeCN, P(OPh)3].56
In this work, we have demonstrated that benzyne complexes
of nickel(0) and, for the first time, palladium(0)68 can be
generated by an intramolecular Suzuki coupling occurring within
an arylmetal(II) complex containing an ortho-substituted boronic
ester group. The required precursors are prepared by oxidative
addition of the o-bromophenyl(pinacolato) boronic ester 1 to
nickel(0) or palladium(0) complexes; the process occurs readily
only when the auxiliary ligands are monodentate tertiary
phosphines (PPh3 for Ni; PPh3, PCy3 for Pd) and is unsatisfac-
tory for bidentate tertiary diphosphines, probably because of
the steric bulk of the pinacolato substituent. Steric interactions
between this group and the phosphines are evident in the X-ray
structures of 2a, 3b, and 3d. In accord with the usual trend,69
the oxidative additions to nickel(0) are, qualitatively, much faster
than those to palladium(0). For the Pd-PCy3 system, which
reacts faster than the Pd-PPh3 one, oxidative addition probably
occurs to an intermediate containing only one bulky PR3 group
in the coordination sphere, as proposed for the rapid Suzuki
coupling reactions observed with palladium catalysts bearing
very bulky phosphine ligands.70,71 Fortunately, the precursors
containing bidentate tertiary diphosphine ligands can readily
obtained by ligand substitution from the complexes containing
monodentate phosphines 2a, 3a, and 3b.
The structure of 6 is exceptional in several respects. It is the
first example of an ortho-phenylene bridging two palladium(I)
centers. Some examples with palladium(II) are known in which
the two metal atoms are not bonded (Pd‚‚‚Pd separation > 3.5
Å), the complexes containing additional bridging ligands such
as dppm, dialkyl sulfide, OAc, or Ph2PCH2SCH2Ph.57-59
Examples of complexes having a metal-metal bond bridged
by an ortho-phenylene unit are known for iron, [Fe2(µ-o-C6F4)-
(CO)8],60 and iridium, [Ir2(µ-o-C6H4)(η5-C5H5)2(CO)2]61 and [Ir2-
(µ-o-C6H4)(µ-PPh2)(µ-H)(η5-C5H5)2],62 but in all of these cases
the aromatic bridge is coplanar with the two metal atoms.
Complex 6 is unique in the observed tilting of its ortho-
phenylene bridge. The closest analogy to such a tilted bridge
comes from a dinuclear iridium complex, [Ir2(µ-1-η1-1,2-η2-p-
C6H4OMe)(η5-C5Me5)2(CO)2], in which the aryl group is
coordinated simultaneously in a σ-fashion to one iridium atom
and π-bonded to the second metal center, the resulting bridge
being not symmetrical.63 Similar π-interactions in complex 6
between Pd(1)-C(12) and Pd(2)-C(11) [2.565(4) Å and 2.589-
(4) Å, respectively] cannot be ruled out, but these distances are
much longer than the Ir-phenyl π-bonds mentioned above [Ir-
C(π) ) 2.324(7) and 2.394(7) Å; Ir-C(σ) ) 2.054(7) Å] or
those observed in dipalladium(I) π-bridged complexes, cf. Pd-C
distances of 2.12-2.16 Å in the η3-allyl species [Pd2(µ-η3-
C3H5)2(PPh3)2].54
The reactivity of the palladium(II) and nickel(II) complexes
depends strongly on the steric bulk of the auxiliary phosphine
ligands. Hydrolytic cleavage of the aryl-B bond occurs most
readily with the nickel complexes containing the cyclohexyl-
substituted ligands PCy3 (2b) and dcpe (2d). The palladium
analogues are less prone to hydrolysis, whereas the PPh3
complexes of both Ni and Pd, 2a and 4a, and the PEt3 complex
The molecular structure of the 2,2′-biphenyldiyl complex 7e
is shown in Figure 6, and selected values of bond lengths and
angles are given in Table 4. The palladium atom has the
(55) Ban, E.; Cheng, P.-T.; Jack, T.; Nyburg, S. C.; Powell, J. J. Chem. Soc.,
Chem. Commun. 1973, 368.
(56) Connelly, N. G.; Geiger, W. E.; Orpen, A. G.; Orsini, J. J., Jr.; Richardson,
K. E. J. Chem. Soc., Dalton Trans. 1991, 2967.
(64) Bennett, M. A.; Kopp, M. R.; Wenger, E.; Willis, A. C. J. Organomet.
Chem., submitted.
(57) Balch, A. L.; Hunt, C. T.; Lee, C.-L.; Olmstead, M. M.; Farr, J. P. J. Am.
Chem. Soc. 1981, 103, 3764.
(65) Vicic, D. A.; Jones, W. D. J. Am. Chem. Soc. 1999, 121, 7606.
(66) Bennett, M. A.; Dirnberger, T.; Hockless, D. C. R.; Wenger, E.; Willis, A.
C. J. Chem. Soc., Dalton Trans. 1998, 271.
(58) Fuchita, Y.; Nakashita, S. Inorg. Chim. Acta 1993, 211, 61.
(59) Fuchita, Y.; Akiyama, M.; Arimoto, Y.; Matsumoto, N.; Okawa, H. Inorg.
Chim. Acta 1993, 205, 185.
(67) Edelbach, B. L.; Vicic, D. A.; Lachicotte, R. J.; Jones, W. D. Organome-
tallics 1998, 17, 4784.
(60) Bennett, M. J.; Graham, W. A. G.; Stewart, R. P., Jr.; Tuggle, R. M. Inorg.
Chem. 1973, 12, 2944.
(68) The existence of a benzyne complex of isoelectronic silver(I) has been
postulated, see: Friedman, L. J. Am. Chem. Soc. 1967, 89, 3071.
(69) Stille, J. K. In The Chemistry of the Metal-Carbon Bond; Hartley, F. R.,
Patai, S., Eds.; John Wiley: New York, 1985; Vol. 2, p 625.
(70) Littke, A. F.; Dai, C.; Fu, G. C. J. Am. Chem. Soc. 2000, 122, 4020 and
references therein.
(61) Rausch, M. D.; Gastinger, R. G.; Gardner, S. A.; Brown, R. K.; Wood, J.
S. J. Am. Chem. Soc. 1977, 99, 7870.
(62) Grushin, V. V.; Vymenits, A. B.; Yanovskii, A. I.; Struchkov, Y. T.;
Vol’pin, M. E. Organometallics 1991, 10, 48.
(63) Yan, X.; Batchelor, R. J.; Einstein, F. W. B.; Zhang, X.; Nagelkerke, R.;
Sutton, D. Inorg. Chem. 1997, 36, 1237.
(71) Zapf, A.; Ehrentraut, A.; Beller, M. Angew. Chem., Int. Ed. 2000, 39, 4153
and references therein.
9
J. AM. CHEM. SOC. VOL. 124, NO. 28, 2002 8355

A R T I C L E S
Retbøll et al.
with nickel than with palladium and more rapidly with sterically
demanding tertiary phosphines in the coordination sphere.
Because the formation of the arylmetal(II) precursors by
oxidative addition is faster with nickel than with palladium, the
former would appear to be more suitable for developing a
catalytic cycle based on benzyne complexes. Catalytic reactions
with alkynes and the extension of the methodology to other
transition metals are currently being investigated.
Figure 7. Schematic representation of the trinuclear nickel complexes
reported in ref 71, and illustration of the cleavage postulated for the
formation of 6 and 7d.
Experimental Section
General Procedures. All experiments were carried out under
nitrogen. All solvents were dried and degassed prior to use. NMR
spectra were recorded on a Varian XL-200E (1H at 200 MHz, 13C at
50.3 MHz, 31P at 81.0 MHz), a Varian Gemini 300BB or Varian
Mercury 300 (1H at 300 MHz, 13C at 75.4 MHz, 31P at 121.4 MHz), or
a Varian Inova-500 instrument (1H at 500 MHz, 13C at 125.7 MHz).
of Ni, 2c, seem to be inert to water. Qualitatively, a similar
trend is observed for the rates of the reactions of the boronic
ester complexes with KOtBu to give benzyne complexes, viz.,
dcpe > PCy3 > PPh3 > PEt3 and Ni > Pd, suggesting that the
reactions are sterically driven. Presumably, the mechanism of
this intramolecular Suzuki coupling reaction (postulated in
Scheme 4) is similar to that of the intermolecular version
(Scheme 3), in which the base is commonly assumed to attack
directly at boron to generate a carbanion, although initial
substitution of the halide at the metal center cannot be excluded.
At this stage it is not clear why, in the case of palladium, weaker
bases than KOtBu are ineffective, and further studies of a range
of bases with both nickel and palladium are required.
The new procedure has allowed the preparation of novel C6H4
complexes of palladium(0) and palladium(I) which do not
survive the strongly reducing alkali metal reagents that have
previously been required for forming benzyne complexes of
nickel(0). In contrast to [Pd(η2-C6H4)(PCy3)2] (5b), the dcpe
analogue 5d is unstable to disproportionation, giving the novel
metal-metal bonded dipalladium(I) species [(dcpe)Pd(µ2-C6H4)-
Pd(dcpe)] (6) and the 2,2′-biphenyldiyl complex [Pd(2,2′-
C6H4C6H4)(dcpe)] (7d). The mechanism of this process is
unknown, although the fact that these two species are always
formed in equimolar ratio suggests a common intermediate. One
possibility could be the fragmentation of a trinuclear cluster
similar to the compound [Ni3(µ3-C6H4)(µ3-2,2′-C6H4C6H4)(Pi-
Pr3)3] that was isolated as a minor product of the reduction of
[NiCl(o-C6H4Cl)(PiPr3)2] with 1% Na/Hg amalgam (Figure 7).72
Reaction of the dppe complex 3e with KOtBu also leads to
formation of a 2,2′-biphenyldiyl complex (7e), although in this
case neither the benzyne-palladium(0) complex [Pd(η2-C6H4)-
(dppe)] (5e) nor the corresponding µ-o-phenylenedipalladium-
(I) complex could be detected. 2,2′-Biphenyldiyl complexes
related to 7d and 7e have also been obtained from the insertion
of free benzyne into nickel(0)- and platinum(0)-benzyne
bonds64,66 and by oxidative cleavage of the C-C bond of
biphenylene with nickel(0).73 The first of these processes
provides an alternative route to 7e; partial decomposition of 5e
could liberate benzyne, which could react immediately with its
progenitor.
1
The chemical shifts (δ) for H and 13C are given in ppm relative to
residual signals of the solvent and to external 85% H3PO4 for 31P. The
spectra of all nuclei (except 1H) were 1H-decoupled. The coupling
constants (J) are given in Hz with an estimated error of (0.2 Hz.
Infrared spectra were measured on a Perkin-Elmer Spectrum One
instrument. Mass spectra of the complexes were obtained on a ZAB-
SEQ4F spectrometer by the fast-atom bombardment (FAB) technique
using matrixes of either dry tetraglyme or 3-nitrophenyl octyl ether
(NOPE), and those of the organic ligands on a Fisons VG Autospec
instrument by electron impact (EI). Unfortunately, the benzyne
complexes and several of the nickel(II) precursors were sensitive to
heat and sometimes moisture, and, generally, they were too difficult
to handle to obtain satisfactory analyses. When elemental analyses were
possible, they were carried out in-house.
Starting Materials. The complexes [NiBr2(PPh3)2],74 [Ni(cod)2],75
[Ni(η2-C2H4)(dcpe)],29 and [Pd2(dba)3‚dba]76 (also referred to as [Pd-
(dba)2] in the text) were prepared according to published procedures.
o-Bromophenylboronic acid was obtained commercially and used as
received.
o-C6H4BrB(pin) (1). Commercial o-C6H4BrB(OH)2 (1.8 g, 8.95
mmol) was suspended in pentane (20 mL), and pinacol (1.06 g, 8.95
mmol) was added. The slurry slowly solubilized while being stirred
for 2 h at room temperature. The solution was decanted, dried over
MgSO4, and evaporation of the solvent yielded 1 (2.1 g, 84%) as a
colorless liquid. Impurities that were present in the 1H NMR spectrum
of the starting boronic acid could not be removed, and the product
was used directly for the preparation of the complexes. 1H NMR (200
MHz, CDCl3): δ 1.36 (s, 12H, CH3), 7.18-7.27 (m, 2H, H4,5), 7.50-
7.54 (m, 1H, H6 or 3). 13C{1H} NMR (50.3 MHz, CDCl3): δ 24.5 (CH3),
83.9 (O-C), 125.9 (CH), 127.9 (C 1-Br), 131.5 (CH), 132.2 (CH),
136.1 (CH); C 2-B not observed. EI-MS (C12H16BBrO2): m/z 282 (27,
M+), 267 (25, M+ - Me), 203 (100, M+ - Br), 183 (67, C6H4BrBOH+),
161 (78).
(i) Preparation of Aryl-Ni(II) and Pd(II) Complexes. [NiBr{o-
C6H4B(pin)}(PPh3)2] (2a). A suspension of zinc powder (200 mg, 3.1
mmol) in THF (5 mL) was activated by ultrasound for 1 h. [NiBr2-
(PPh3)2] (2.02 g, 2.7 mmol) and o-C6H4BrB(pin) (2.0 g, 7.1 mmol)
were added, and the suspension was stirred for 2 h at room temperature
during which time the color changed from green to yellow/brown. The
solution was evaporated to dryness, and the residue was washed
successively with 30 mL and 70 mL portions of ether. The powder
was redissolved with CH2Cl2, and this filtrate was evaporated to dryness
leaving a yellow powder. Yield: 2.1 g (89%). Single crystals of 2a
Conclusion
Benzyne complexes of nickel(0) and, for the first time,
palladium(0) can be generated by a KOtBu-promoted, intramo-
lecular coupling of an arylmetal(II) complex ortho-substituted
with a boronic ester group. The reactions occur more rapidly
1
were obtained from a toluene solution layered with hexane. H NMR
(74) Venanzi, L. M. J. Chem. Soc. 1958, 719.
(72) Bennett, M. A.; Griffiths, K. D.; Okano, T.; Parthasarathi, V.; Robertson,
G. B. J. Am. Chem. Soc. 1990, 112, 7047.
(73) Eisch, J. J.; Piotrowski, A. M.; Han, K. I.; Kru¨ger, C.; Tsay, Y. H.
Organometallics 1985, 4, 224.
(75) Schunn, R. A. Inorg. Synth. 1974, 15, 5.
(76) Synthetic Methods of Organometallic and Inorganic Chemistry; Herrmann,
W. A., Salzer, A., Eds.; Georg Thieme Verlag: Stuttgart, 1996; Vol. 1, p
160 and references therein.
9
8356 J. AM. CHEM. SOC. VOL. 124, NO. 28, 2002

Benzyne Complexes of Group 10 Metals
A R T I C L E S
(300 MHz, C6D6): δ 1.29 (s, 12H, CHpin), 6.32 (t, 1H, J 7.4, H4 or 5),
[NiBr{o-C6H4B(pin)}(dppb)] (2f). This was obtained as above in
3
1
6.48 (t, 1H, J 7.0, H5 or 4), 7.05-7.15 (m, 18H, HPPh), 7.33 (d, 1H, J
7.1, H3 or 6), 7.78 (d, 1H, J 7.4, H6 or 3), 7.85-7.98 (m, 12H, HPPh). 13C-
{1H} NMR (75.4 MHz, CD2Cl2): δ 25.5 (CH3pin), 83.6 (C pin-O),
120.9 (t, JPC 2.4, CH), 126.7 (t, JPC 2.2, CH), 127.7 (t, JPC 4.8, CHm-PPh),
129.6 (s, CHp-PPh), 132.4 (t, JPC 21.2, Ci-PPh), 135.2 (t, JPC 5.3, CHo-PPh),
135.8 (t, JPC 4.6, C6-H), 138.7 (t, JPC 2.5, C3-H), 162.5 (t, JPC 33.1,
C1-Ni); C2-B not observed. 31P{1H} NMR (81.0 MHz, CD2Cl2): δ
21.4. FAB-MS (C48H46BBrNiO2P2, NOPE): m/z 866 (M+, very weak),
785 (M+ - Br). Anal. Calcd for C48H46BBrNiO2P2: C, 66.55; H, 5.35.
Found: C, 66.10; H, 5.71.
92% yield. H NMR (300 MHz, CD2Cl2): δ 0.5-1.5 (m, 8H, CH2),
1.3 (br s, 12H, CH3pin), 6.3-7.8 (m, 24H, Harom). 13C{1H} NMR (50.3
MHz, CD2Cl2): δ 24.8-26.3 (m, CH2), 25.5 (s, CHpin), 25.7 (s,
3
CHp3in), 84.0 (s, OCpin), 121.1 (s, CH), 127.5-130.0 (m, CH), 130.6-
131.3 (m, CPPh), 131.4-136.0 (m, CH), 163.2 (t, JPC 33.8, C1-Ni). 31
{1H} NMR (81.0 MHz, C6D6): δ 11.4 (d), 12.0 (d, JPP 39.3).
P
[PdBr{o-C6H4B(pin)}(PPh3)2] (3a). A mixture of [Pd(dba)2] (300
mg, 0.52 mmol), PPh3 (574 mg, 1.14 mmol), and 1 (382 mg, 0.7 mmol)
in toluene (20 mL) was stirred for 1 h at room temperature and then
heated for 100 °C for 5 h until 31P NMR monitoring showed the reaction
to be complete. The solvent was evaporated, and the pale yellow powder
was washed first with a mixture of toluene (2 mL) and hexane (5 mL)
and then with just hexane. Recrystallization from a CH2Cl2 solution
General Procedure for the Preparation of [NiBr{o-C6H4B(pin)}-
L2] (2b-2e). These complexes were prepared by replacement of the
PPh3 ligands in 2a using as solvent toluene (2d) or ether (2b, 2c, 2e)
from which the product precipitated. This procedure avoided hydrolysis
of the products, which decomposed on attempted purification. The
preparation of 2d is given as a characteristic example.
1
layered with hexane yielded 3a as an off-white solid. H NMR (300
MHz, CD2Cl2): δ 1.19 (s, 12H, CHpin), 6.50 (app [AA′BB′] m, 2H,
3
H4,5), 6.81-6.84 (m, 1H, H3 or 6), 7.19-7.24 (m, 1H, H6 or 3), 7.27 (br
tt, 12H, J 7.2, 1.2, HPPh), 7.38 (br t, 6H, J 7.3, HPPh), 7.49-7.55 (m,
12H, HPPh). 13C{1H} NMR (50.3 MHz, CD2Cl2): δ 25.2 (s, CH3pin),
83.5 (s, Cpin-O), 121.8 (s, CH), 127.9 (t, JPC 5.0, CHPPh), 128.6 (s,
CH), 129. 9 (s, CHPPh), 132.0 (t, JPC 22.2, CPPh), 135.1 (s, CH), 135.2
(t, JPC 6.3, CHPPh), 139.0 (s, C6-H), 165.5 (t, JPC 2.5, C1-Pd); C2-B
not located. 31P{1H} NMR (81.0 MHz, CD2Cl2): δ 23.2. FAB-MS
(C48H46BBrO2P2Pd): m/z 833 (MH+ - Br), 630 (Pd(PPh3)2+), 571
(MH+ - Br - PPh3). Anal. Calcd for C48H46BBrO2P2Pd‚1/2CH2Cl2:
C, 60.91; H, 4.95. Found: C, 61.26; H, 5.00.
[NiBr{o-C6H4B(pin)}(dcpe)] (2d). Solid [NiBr{o-C6H4B(pin)}-
(PPh3)2] (2a) (1.38 g, 1.59 mmol) and dcpe (700 mg, 1.65 mmol) were
dissolved in toluene (5 mL), and the mixture was stirred for 2 h at
room temperature. The pure product, 2d, precipitated as a yellow
powder, which was isolated by filtration. Yield: 1.16 g (95%). 1H NMR
(300 MHz, CD2Cl2): δ 0.90-2.02 (m, 48H), 1.27 (s, 12H, CH3pin),
6.79 (t, 1H, J 7.2, CH), 6.94 (t, 1H, J 7.4, CH), 7.55 (app d, 2H, J 7.8,
CH). 31P {1H} NMR (81.0 MHz, C6D6): δ 59.1 (d), 63.7 (d, JPP 21.0).
FAB-MS (C38H64BBrNiO2P2, NOPE): m/z 765 (MH+), 683 (M+
-
Br).
[PdBr{o-C6H4B(pin)}(PCy3)2] (3b). A mixture of [Pd(dba)2] (1 g,
1.74 mmol), PCy3 (1 g, 3.57 mmol), and 1 (500 mg, 1.77 mmol) in
toluene (30 mL) was stirred at room temperature for 10 min during
which time a yellow solution was formed. The reaction was complete
after heating at 100 °C for 15 min. The solvent was evaporated, the
residue was suspended in hexane, and the suspension was filtered
through Celite. The residual powder was washed several times with
ether until dba was no longer eluted, and then the solid was redissolved
with CH2Cl2 and eluted from the Celite plug. The solvent was removed
to yield pure 3b (970 mg, 59%) as a white powder. Single crystals
[NiBr{o-C6H4B(pin)}(PCy3)2] (2b). This was similarly prepared in
ether. Yield 94%. 1H NMR (300 MHz, CD2Cl2): δ 0.90-1.40 (m, 20H,
CH2), 1.39 (s, 6H, CHpin), 1.50-1.95 (m, 40H, CH2), 2.05-2.30 (m,
3
6H, PCH), 6.62 (br t, 1H, J 7.2, H4 or 5), 6.79 (br t, 1H, J 7.2, H5 or 4),
7.43 (br d, 1H, J 7.2, H3 or 6), 7.74 (br d, 1H, J 7.2, H6 or 3). 31P{1H}
NMR (81.0 MHz, CD2Cl2): δ 6.4. FAB-MS (C48H82BBrNiO2P2,
NOPE): m/z 902 (M+, very weak), 822 (MH+ - Br).
The 13C NMR spectra of 2b and 2d could not be recorded because
the solutions decomposed.
1
were obtained from a CH2Cl2 solution layered with hexane. H NMR
[NiBr{o-C6H4B(pin)}(PEt3)2] (2c). This was prepared as described
above using ether as solvent. The sensitive complex was isolated as a
brown oil containing traces of PPh3 after evaporation of the solvent in
vacuo and was not purified further. The yield was quantitative as
estimated by 31P NMR spectroscopy. This compound was best converted
immediately into the corresponding benzyne complex 4c by treatment
with KOtBu. 1H NMR (300 MHz, C6D6): δ 0.90-1.04 (m, 18H,
CH3PEt), 1.24 (s, 12H, CH3pin), 1.30-1.45 (m, 12H, CHP2Et), 6.70-6.90
(300 MHz, CD2Cl2): δ 1.2-2.4 (m, 66H, Cy), 1.55 (s, 12H, CHpin),
3
7.07 (t, 1H, J 7.2, Harom), 7.22 (t, 1H, J 7.5, Harom), 7.83 (app d, 2H, J
7.8 Hz, Harom). 13C{1H} NMR (75.4 MHz, CH2Cl2/C6D6): δ 25.2 (s,
CH3pin), 27.1 (s, CH2), 28.0-28.3 (m, CH2), 30.3 (s, CH2), 34.1 (t, JPC
9.2, PCH), 83.7 (s, Cpin-O), 121.3 (s, CH), 129.2 (s, CH), 137.0 (s,
CH), 138.8 (t, JPC 3.8, C6-H), 165.4 (t, JPC 3.1, C1-Pd); C2-B not
located. 31P {1H} NMR (81.0 MHz, CH2Cl2/C6D6): δ 16.2. FAB-MS
(C48H82BBrO2P2Pd, NOPE): m/z 870 (MH+ - Br), 589.
(m, 2H, H4,5), 7.56 (d, 1H, J 7.8, H3 or 6), 7.87 (d, 1H, J 7.1, H6 or 3). 13
C
{1H} NMR (75.4 MHz, C6D6): δ 8.7 (s, CHPEt), 15.5 (t, JPC 12.1,
[PdBr{o-C6H4B(pin)}(dcpe)] (3d). A mixture of [PdBr{o-C6H4B-
(pin)}(PCy3)2] (3b) (465 mg, 0.49 mmol) and dcpe (230 mg, 0.54 mmol)
in toluene (5 mL) was stirred for 1 h at 50 °C during which time a
white powder formed. The solid was filtered off and washed with
toluene. Drying in vacuo gave pure 3d (315 mg, 79%). Single crystals
suitable for X-ray analysis were obtained from a CH2Cl2 solution layered
3
CH2PEt), 25.5 (CH3pin), 83.7 (C pin-O), 120.9 (t, JPC 2.6, C4 or 5-H),
136.0 (t, JPC 2.8, C3-H), 136.3 (t, JPC 4.3, C6-H), 167.9 (t, JPC 34.2,
C1-Ni); one aromatic CH located underneath residual solvent peaks,
while C2-B was not located. 31P{1H} NMR (81.0 MHz, CD2Cl2): δ
5.1.
1
with hexane. H NMR (300 MHz, CD2Cl2): δ 0.95-2.20 (m, 48H,
[NiBr{o-C6H4B(pin)}(dppe)] (2e). This was prepared similarly to
dcpe), 1.36 (s, 6H, CH3pin), 1.38 (s, 6H, CHp3in), 6.71 (t, 1H, J 7.1,
H4 or 5), 6.91 (t, 1H, J 7.3, H5 or 4), 7.44 (app t, 1H, J 6.1, H6), 7.54 (d,
1H, J 7.4, H3). 13C{1H} NMR (50.3 MHz, CD2Cl2): δ 19.5 (dd, JPC
2b in 92% yield. 1H NMR (300 MHz, CD2Cl2): δ 1.36 (s, 6H, CHpin),
3
1.38 (s, 6H, CHp3in), 1.45-1.70 (m, 4H, PCH2), 6.35-6.41 (m, 1H,
H4 or 5), 6.60-6.70 (m, 1H, H5 or 4), 7.05-7.65 (m, 22H, HPPh + H3,6).
13C{1H} NMR (75.4 MHz, CD2Cl2): δ 22.8 (dd, JPC 26.8, 22.4, PCH2),
23.9 (CHp3in), 25.4 (CHp3in), 31.0 (dd, JPC 25.6, 12.7, PCH2), 83.4 (s,
OCpin), 121.1 (s, CH), 127.7 (d, JPC 9.9, CHPPh), 128.7 (d, JPC 9.4,
CHPPh), 128.8 (d, JPC 10.3, CHPPh), 128.9 (d, JPC 8.5, CHPPh), 128.9 (d,
19.2, 10.2, PCH2), 23.0-24.0 (m, PCH2), 23.6 (s, CHpin), 24.2 (s,
3
CHp3in), 25.9-30.3 (m, CH2), 31.5 (d, JPC 23.8, PCH), 34.0 (d, JPC
18.2, PCH), 35.3 (dd, JPC 14.7, 2.5, PCH), 36.4 (d, JPC 26.8, PCH),
83.2 (s, Cpin-O), 121.9 (s, CH), 128.3 (d, JPC 8.4, CH), 135.4 (d, JPC
5.2, CH), 136.2 (d, JPC 10.2, CH), 170.3 (d, JPC 135.7, C1-Pd); C2-B
not located. 31P{1H} NMR (81.0 MHz, CD2Cl2): δ 58.6 (d), 61.9 (d,
J
PC 6.4, CH), 129.8 (d, JPC 2.8, CHPPh), 130.3 (d, JPC 2.0, CHPPh), 130.7
(d, JPC 2.3, CHPPh), 131.4 (d, JPC 2.5, CHPPh), 132.5 (d, JPC 9.3, CHPPh),
132.6 (d, JPC 7.8, CHPPh), 134.3 (d, JPC 11.1, CHPPh), 134.9 (d, JPC 11.3,
CHPPh), 136.4 (dd, JPC 2.3, 2.9, CH), 137.1 (dd, JPC 7.0, 1.7, C6-H),
170.0 (dd, JPC 83.9, 38.5, C1-Ni); C-P and C2-B were not located.
31P {1H} NMR (81.0 MHz, C6D6): δ 30.9 (d), 54.8 (d, JPP17.9). FAB-
MS (C38H40BBrNiO2P2, NOPE): m/z 740 (M+), 659 (M+ - Br).
J
PP 20.5). FAB-MS (C38H64BBrO2P2Pd, NOPE): m/z 731 (M+ - Br),
609.
[PdBr{o-C6H4B(pin)}(dppe)] (3e). A mixture of [PdBr{o-C6H4B-
(pin)}(PCy3)2] (3b) (203 mg, 0.21 mmol) and dppe (85 mg, 0.21 mmol)
in toluene (10 mL) was heated for 30 min at 95 °C. Evaporation
9
J. AM. CHEM. SOC. VOL. 124, NO. 28, 2002 8357

A R T I C L E S
Retbøll et al.
followed by suspension in ether and filtration gave pure 3e (100 mg,
60%). 1H NMR (300 MHz, CD2Cl2): δ 1.24-1.38 (m, 2H, PCH), 1.60
(br s, 13H, CHp3in + PCH), 1.80-1.92 (m, 1H, PCH), 6.78 (br t, 1H, J
7.2, H4 or 5), 6.85 (br dd, 2H, J 8.4, 3.0, HPPh), 7.11 (td, 2H, J 7.5, 2.4,
HPPh), 7.28-7.34 (m, 2H, HPPh), 7.36-7.54 (m, 11H, Harom), 7.75 (ddd,
2H, J 11.7, 8.4, 1.5, HPPh), 7.89-7.96 (m, 2H, HPPh), 8.02-8.08 (m,
2H, HPPh). 13C{1H} NMR (75.4 MHz, CD2Cl2): δ 22.9 (dd, JPC 25.3,
[Ni(η2-C6H4)(dppe)] (4e). Monitoring by 31P NMR spectroscopy
of the reaction of 2e with KOtBu showed formation of 4e after 1.5 h
at room temperature (ca. 20%) together with [Ni(dppe)2] (δP 44.7)34 as
the major compound and other unidentified species giving signals in
the region δP 23-35.
4e. 31P{1H} NMR (81.0 MHz, C6D6): δ 60.2.
Attempted Preparation of [Ni(η2-C6H4)(dppb)] (4f). Very slow
reaction of 2f with KOtBu led to formation of [Ni(dppb)2] (δP 17.8),34
the structure of which was confirmed by X-ray analysis of crystals
deposited from the C6D6 extract used for NMR investigation.35
[Pd(η2-C6H4)(PPh3)2] (5a). Reaction of the palladium precursor 3a
in THF/C6D6 (0.5 mL, 0.1 mL) with KOtBu showed initially a peak in
the 31P NMR spectrum at δP 41.5 that may belong to the benzyne
complex 5a. Rapid decomposition hindered further characterization.
[Pd(η2-C6H4)(PCy3)2] (5b). Reaction of 3b (52 mg, 0.05 mmol) with
KOtBu (20 mg, 0.18 mmol) in toluene (3 mL) for 16 h at room
temperature gave 5b in >90% yield as shown by 31P NMR spectros-
copy. X-ray quality crystals were obtained from an NMR solution in
C6D6. 1H NMR (300 MHz, C6D6): δ 1.05-2.25 (m, 66H, Cy), 7.41-
7.49 (m, 2H, CHbenzyne), 7.71-7.77 (m, 2H, CHbenzyne). 13C {1H} NMR
(75.4 MHz, C6D6): δ 26.9 (s, CH2), 28.1 (d, JPC 8.9, CH2), 31.0 (d,
JPC 12.4, CH2), 37.0 (d, JPC 17.9, PCH), 122.7 (t, JPC 9.1, C3,6-H),
128.3 (s, C4,5-H), 138.1 (app dd, sepns 86.7, 6.5, C1,2-Pd). 31P{1H}
NMR (81.0 MHz, C6D6): δ 43.3.
Attempted Preparation of [Pd(η2-C6H4)(dcpe)] (5d). A suspension
of 3d (ca. 20 mg) and KOtBu (excess) in a mixture of THF (0.5 mL)
and C6D6 (0.2 mL) was prepared in a NMR tube, and the reaction was
monitored by 31P NMR spectroscopy (see text). Small amounts of
complex 5d were initially formed, but disproportionation gave two
major products (ratio ca. 1:1) that could be readily separated; single
crystals of the poorly soluble dimer [(dcpe)Pd(µ-o-C6H4)Pd(dcpe)] (6)
deposited from the mixture, while the 2,2′-biphenyldiyl species 7d
remained in solution.
12.0, PCH2), 23.9 (s, CHpin), 25.3 (s, CH3pin), 30.7 (dd, JPC 30.6, 21.9,
3
PCH2), 83.1 (s, Cpin-O), 122.1 (d, JPC 1.4, C4-H), 127.9 (d, JPC 10.4,
CHPPh), 128.4 (dd, JPC 8.7, 2.1, C3 or 5-H), 128.8 (d, JPC 9.9, CHPPh),
129.0 (d, JPC 10.9, CHPPh), 129.0 (d, JPC 9.0, CHPPh), 130.3 (d, JPC 2.8,
CHPPh), 130.5 (d, JPC 18.2, CPPh), 130.6 (d, JPC 2.2, CHPPh), 130.8 (d,
JPC 2.3, CHPPh), 131.6 (d, JPC 2.6, CHPPh), 131.9 (d, JPC 20.9, CPPh),
132.5 (d, JPC 9.0, CHPPh), 132.9 (d, JPC 11.0, CHPPh), 133.5 (d, JPC 33.3,
CPPh), 134.0 (d, JPC 12.3, CHPPh), 134.8 (d, JPC 12.9, CHPPh), 136.5
(dd, JPC 5.0, 2.7, C5 or 3-H), 137.1 (dd, JPC 10.1, 1.8, C6-H), 169.5
(dd, JPC 129.3, 2.5, C1-Pd); one C-P and C2-B were not located.
31P{1H} NMR (81.0 MHz, CD2Cl2): δ 30.1 (d), 49.5 (d, JPP 18.0).
FAB-MS (C38H40BBrO2P2Pd, NOPE): m/z 707 (M+ - Br).
(ii) Preparation of the Benzyne-Ni(0) and -Pd(0) Complexes.
General Procedure for the Preparation of Ni-Benzyne Complexes
[Ni(η2-C6H4)L2] (4a-f). The nickel(II) precursors 2a-f (ca. 150 mg)
were mixed with solid KOtBu (2-3 equiv), and THF (2 mL) was added.
The mixtures were stirred at room temperature and monitored by 31P
NMR spectroscopy. Once the reaction was complete, the solvent was
removed in vacuo, and the residue was washed with hexane to yield
creamy white powders that were reactive to air and moisture, especially
the complexes of monodentate phosphines. Further spectroscopic
measurements were run on C6D6 extracts, when possible.
[Ni(η2-C6H4)(PPh3)2] (4a). The reaction required 15 min at room
temperature. Product 4a shows complex exchange processes of the PPh3
ligands in solution (see text). 1H NMR (200 MHz, C6D6, room
temperature): δ 6.94-7.03 (br m, 11H, Harom), 7.36-7.46 (br m, 8H,
Harom). 13C {1H} NMR (75.4 MHz, C6D6, room temperature): δ 123.3
(s, CHC6H4), 128.3 (s, CHC6H4), 128.5 (s, CHPPh), 128.8 (d, JPC 11.0,
CHPPh), 134.2 (d, JPC 17.9, CHPPh), 137.7 (s, CPPh), 142.8 (s, C1,2-Ni).
31P{1H} NMR (81.0 MHz, C6D6, room temperature): δ 0 ( 2 (br),
26.9 (8, <10%). 31P{1H} NMR (81.0 MHz, C6D5CD3, -90 °C): δ
40.7.
5d. 31P {1H} NMR (81.0 MHz, C6D6): δ 67.0.
[(dcpe)Pd(µ-o-C6H4)Pd(dcpe)] (6). 31P{1H} NMR (81.0 MHz,
C6D6): δ 60 (br), 69 (br).
[Pd(2,2′-C6H4C6H4)(dcpe)] (7d). 1H NMR (500 MHz, C6D6): δ
1.0-2.4 (m, 48H, dcpe), 7.19-7.21 (m, 4H, Harom), 7.70 (d, 2H, J 7.0,
H3,3′), 7.76-7.81 (m, 2H, H6,6′). 13C{1H} NMR (75.4 MHz, C6D6): δ
The solvent was removed in vacuo, and the residue was washed
with hexane. This procedure removed free PPh3 leaving a solid which
may be the dinuclear species [(Ph3P)Ni(µ-o-C6H4)2Ni(PPh3)] (8′). 13C
{1H} NMR (75.4 MHz, C6D6, room temperature): δ 123.3 (s, CHC6H4),
128.3 (s, CHC6H4), 128.5 (d, JPC 12.9, CHPPh), 129.0 (br s, CHPPh), 134.2
(d, JPC 25.8, CHPPh), 137.3 (d, JPC 21.1, CPPh), 142.8 (s, C1,2-Ni). 31P-
{1H} NMR (81.0 MHz, C6D6, room temperature): δ 26.9.
[Ni(η2-C6H4)(PCy3)2] (4b). Addition of THF to a mixture of 2b and
KOtBu caused an immediate reaction, and 31P NMR monitoring
indicated the yield of 4b to be >80%. Single crystals suitable for X-ray
diffraction analysis were obtained from a solution in benzene that had
been used for NMR spectroscopy. 1H NMR (300 MHz, C6D6): δ 1.3-
2.3 (m, 66H), 7.52-7.54 (m, 2H, CHbenzyne), 7.80-7.83 (m, 2H,
CHbenzyne). 13C{1H} NMR (75.4 MHz, C6D6): δ 27.1 (s, CH2), 28.1 (d,
JPC 8.9, CH2), 31.8 (d, JPC 12.4, CH2), 36.9 (3 line m, sepn of outer
lines ) 17.9, PCH), 123.3 (t, JPC 4.0, C3,6-H), 128.3 (s, C4,5-H), 141.6
(app dd, sepns 53.2, 17.4, C1,2-Ni). 31P{1H} NMR (81.0 MHz, C6D6):
δ 46.7 (br). FAB-MS (C42H70NiP2, tetraglyme): m/z 695 [MH+]. Anal.
Calcd for C42H70NiP2: C, 72.52; H, 10.14. Found: C, 73.26; H, 10.18.
20.8 (t, JPC 36.1, PCH2), 26.6-34.7 (m, CHdcpe), 36.0 (t, JPC 7.2,
2
PCH), 120.2 (s, CH), 124.3 (s, CH), 125.2 (t, JPC 11.9, CH), 140.3 (t,
JPC 15.0, CH), 160.1 (s, C2,2′), 171.4 (dd, JPC 116.6, 10.5, C1,1′-Pd).
31P{1H} NMR (81.0 MHz, C6D6): δ 55.1.
Attempted Preparation of [Pd(η2-C6H4)(dppe)] (5e). Reaction of
[PdBr{o-C6H4B(pin)}(dppe)] (3e) with KOtBu, carried out as described
above, led to complete decomposition. The poorly soluble complex
[Pd(2,2′-C6H4C6H4)(dppe)] (7e) crystallized from the solution and was
identified only by X-ray diffraction analysis and FAB-MS. FAB-MS
(C38H32P2Pd, NOPE): m/z 757 (MH+).
X-ray Crystallography of 2a‚1.5C6H5Me, 3b, 3d, 4b‚C6H6, 5b‚
C6H6, 6‚C6H5Me, and 7e. Crystal data, details of data collection, data
processing, structure analyses, and structure refinements are given in
Table 5.
The crystals were mounted on a quartz fiber, and data were collected
at 200 K on a Nonius Kappa CCD diffractometer equipped with a 95
mm camera and graphite monochromated Mo KR radiation (λ )
0.71073 Å). The data were measured by use of COLLECT,77 while
the intensities of the reflections were processed and the data reduced
by use of the computer programs Denzo and Scalepak.78 The structures
[Ni(η2-C6H4)(PEt3)2] (4c). The reaction was complete after 2 h at
room temperature. The spectroscopic data (1H, 13C, and 31P NMR, FAB-
MS) were identical to those previously reported.9
[Ni(η2-C6H4)(dcpe)] (4d). The reaction was instantaneous and
quantitative as shown by 31P NMR spectroscopy. The spectroscopic
data (1H, 13C, and 31P NMR, FAB-MS) were identical to those
previously reported.29
(77) COLLECT Software, Nonius BV, 1997-2001.
(78) Otwinowski, Z.; Minor, W. In Methods in Enzymology; Carter, C. W., Jr.,
Sweet, R. M., Eds.; Academic Press: New York, 1997; Vol. 276, pp 307-
326.
9
8358 J. AM. CHEM. SOC. VOL. 124, NO. 28, 2002

Benzyne Complexes of Group 10 Metals
A R T I C L E S
Table 5. Crystal and Structure Refinement Data for Compounds 2a, 3b, 3d, 4b, 5b, 6, and 7e
2a
3b
3d
4b
5b
6
7e
(a) Crystal Data
C42H70Ni-
P2‚C6H6
773.79
chemical formula
C
48H46BBrNi-
C48H82BBr-
O2P2Pd
950.24
C38H64BBr-
O2P2Pd
811.98
C42H70P2-
Pd‚C6H6
821.48
C58H100P4Pd2
‚C6H5Me
1226.26
C38H32P2Pd
O2P2‚1.5C7H8
fw
1004.39
657.02
crystal system
space group
a (Å)
b (Å)
c (Å)
triclinic
orthorombic
Pnma (No. XX)
20.3184(3)
22.7581(4)
10.5870(1)
monoclinic
P21/n (No. 14)
8.7037(1)
12.4606(1)
36.1403(4)
monoclinic
P21/n (No. 14)
9.99820(10)
28.9827(3)
15.1034(5)
monoclinic
P21/n (No. 14)
10.1512(1)
29.5301(3)
15.0770(2)
triclinic
monoclinic
P21/n (No. 14)
11.7245(4)
18.1595(8)
14.7765(6)
P1h (No. 2)
9.92980(10)
12.95530 (10)
20.4921(3)
85.1981(4)
88.5163(4)
72.3410(4)
2503.14(5)
1.333
P1h (No. 2)
13.9055(2)
19.0192(2)
24.0778(3)
80.6763(5)
85.7074(4)
89.81279(6)
6265.9(1)
1.300
R (deg)
â (deg)
γ (deg)
V (Å3)
94.6632(5)
96.1217(5)
97.1577(6)
99.223(2)
4895.5
1.289
4
3906.56(6)
1.380
4
4351.63(9)
1.181
4
4484.35(9)
1.217
4
3105.4(2)
1.405
4
D
Z
calc (g cm-3
)
2
4
µ (mm-1
)
1.292 (Mo KR)
1.298 (Mo KR)
1.614 (Mo KR)
0.550 (Mo KR)
0.516 (Mo KR)
0.714 (Mo KR)
0.726 (Mo KR)
(b) Data Collection, Processing, and Refinement
50.08 54.98 51.28
2θ max (deg)
55.04
50.06
55.06
50.46
data collected (h,k,l) (-12,-16,-26) to (-24,-27,-12) to (-10,-14,-43) to (-12,-37,-19) to (-12,-35,-17) to (-18,-23,-31) to (-13,-21,-17) to
(12,16,26) (24,27,12) (10,14,43) (12,35,19) (12,35,17) (18,24,31) (14,21,17)
75 844 59 885 46 354 75 271 68 283 124 400 39 996
11 494 (5.1) 28 627 (5.9) 5561 (6.1)
total reflections
unique reflections
(Rint/%)
4440 (5.0)
3896 (4.5)
9960 (5.4)
8375 (6.5)
observed reflections 5981 [I > 3σ(I)]
4042 [I > 2σ(I)]
integration
(0.848 to 0.950)
290
5487 [I > 3σ(I)]
integration
(0.743 to 0.942)
120
3614 [I > 3σ(I)]
integration
(0.870 to 0.979)
449
4548 [I > 3σ(I)]
integration
(0.931 to 0.975)
460
17 995 [I > 3σ(I)] 3843 [I > 3σ(I)]
integration integration
(0.852 to 0.922) (0.921 to 0.966)
absorp. corr.
integration
(trans. factors)
(0.745 to 0.939)
no. of parameters
583
244
370
R
Rw
0.0286
0.0318
0.049
0.077
0.0631
0.1135
0.0403
0.0452
0.0630
0.0350
0.0667
0.1029
0.0531
0.0634
of 3b and 3d were solved by Patterson method (PATTY),79 while the
others were solved by direct methods by use of SIR9280 for 5b‚C6H6,
6‚C6H5Me, and 7e, and SIR9781 for 2a‚1.5C6H5Me and 4b‚C6H6.
axial systems83 allowed the local mirror-related boronic ester fragments
[B1, O1, O2, C7-C12] and [B1′, O1′, O2′, C7′-C12′] to have local
coordinates defined relative to C6 with B1 in the plane of C6, O1, and
O2. These fragments were constrained to have local 2-fold symmetry,
and C6-B1 and C6-B1′ were restrained to be collinear. The thermal
displacement parameters were obtained using rigid body parametriza-
tions.84 The H atoms were recalculated at chemically sensible positions
after each refinement cycle. The above modeling allowed 120 inde-
pendent variables to adequately refine the structure. The data fit suggests
that the final atomic parameters are reliably determined and the quoted
errors are meaningful. The maximum and minimum peaks in the final
difference Fourier map were 1.25 and -1.10 e/Å3.
In the crystal structure of 4b‚C6H6, each molecular species was
accompanied by one molecule of benzene that was perfectly defined.
The non-hydrogen atoms were refined anisotropically by full matrix
least squares. Hydrogen atoms were included at geometrically deter-
mined positions (C-H 1.00 Å) and periodically recalculated, but they
were not refined. The maximum and minimum peaks in the final
difference Fourier map were 0.88 and -0.35 e/Å3. The structure of
5b‚C6H6 was isomorphous to 4b‚C6H6, but the crystal was thin and
twinned, producing two sets of reflections. One set was indexed and
the intensities extracted from it, while the other set was ignored. The
maximum and minimum peaks in the final difference Fourier map were
2.10 and -1.66 e/Å3, respectively, the biggest ones being located near
the Pd atom.
The structure of 2a‚1.5C6H5Me consists of one molecule of complex
with one toluene molecule that is well ordered, while the second toluene
lies about a center of inversion in a well-resolved 50:50 disordered
fashion. Hydrogen atoms were included at geometrically determined
positions (C-H 1.00 Å) and periodically recalculated, but they were
not refined. The maximum and minimum peaks in the final difference
Fourier map were 0.38 and -0.38 e/Å3, respectively.
In the structure of 3b, the molecule is located on a crystallographic
mirror plane. The boronic ester unit, C6H12BO2, is not planar but is
disordered across this plane. The unit possesses approximate C2
symmetry, and restraints were added to the B-O distances. All non-H
atoms were refined anisotropically, apart from the B atom that lies too
close to the mirror plane. The hydrogen atoms were included in the
refinement at idealized positions (C-H 0.95 Å) and frequently
recalculated. The maximum and minimum peaks in the final difference
Fourier map were 0.54 and -0.65 e/Å3, respectively, the maximum
being located in the vicinity of the disordered boronic ester group.
The crystal of 3d showed a small amount of twinning, and the
boronic ester part, C6H12BO2, was disordered over two orientations in
a 0.706:0.294 ratio. The refinement was carried out with the help of
the constrained least squares refinement program RAELS2000.82 The
four cyclohexyl groups were defined relative to the phosphorus atom
to which they were attached and were constrained to be identical. Atoms
C1-C6 of the aromatic ring were constrained to be planar. Multiple
The structure of 6‚C6H5Me possesses a pseudo translational sym-
metry with the toluene molecule departing somewhat from it, and the
constrained least squares refinement program RAELS2000 was used.82
Atoms in each of the two molecules of 6 present in the asymmetric
unit are approximately related by a local 2-fold rotation axis, and this
is reflected in the atom labeling. The 16 cyclohexyl groups were defined
relative to the phosphorus atom to which they were attached and were
constrained to be identical. The toluene molecules were constrained to
be planar. The thermal displacement parameters were obtained using
rigid body parametrizations.84 The Pd and P atoms were effectively
(79) Beurskens, P. T.; Admiraal, G.; Beurskens, G.; Bosman, W. P.; Garcia-
Granda, S.; Gould, R. O.; Smits, J. M. M.; Smykalla, C. The PATTY and
DIRDIF Program System, Technical Report of the Crystallographic
Laboratory, University of Nijmegen, Nijmegen, The Netherlands, 1992.
(80) Altomare, A.; Cascarano, M.; Giacovazzo, C.; Guagliardi, A.; Burla, M.
C.; Polidori, G.; Camalli, M. J. Appl. Crystallogr. 1994, 27, 435.
(81) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G. L.; Giacovazzo,
C.; Guagliardi, A.; Moliterni, A. G. G.; Spagna, R. J. Appl. Crystallogr.
1999, 32, 115.
(82) Rae, A. D. RAELS2000: A ComprehensiVe Constrained Least-Square
Refinement Program, Australian National University, Canberra, ACT,
Australia, 2000.
(83) Haller, K. J.; Rae, A. D.; Heerdegen, A. P.; Hockless, D. C. R.; Welberry,
T. R. Acta Crystallogr. 1995, B51, 187.
(84) Rae, A. D. Acta Crystallogr. 1975, A31, 560 and 570.
9
J. AM. CHEM. SOC. VOL. 124, NO. 28, 2002 8359

A R T I C L E S
Retbøll et al.
refined as isolated anisotropic atoms by allowing extra parametrization,
but constrained so that pseudo translationally related atoms had identical
parameters.85 The H atoms were recalculated at chemically sensible
positions after each refinement cycle. The structure was adequately
refined using only 244 independent variables. The data fit suggests
that the final atomic parameters are reliably determined and the quoted
errors are meaningful for the average geometry. The maximum and
minimum peaks in the final difference Fourier map were 2.28 and -1.95
e/Å3.
The crystal of 7e was of poor quality with a high mosaic spread,
but the derived data were able to produce a final structure of reasonable
quality. The non-hydrogen atoms were refined anisotropically by full
matrix least squares. Hydrogen atoms were included in the refinement
at geometrically determined positions (C-H 0.95 Å) which were
periodically recalculated. The maximum and minimum peaks in the
final difference Fourier map were 1.44 and -0.86 e/Å3, respectively,
the biggest ones being located near the Pd atom.
Acknowledgment. E.W. is grateful to the Australian Research
Council for the award of a QEII Fellowship. The authors would
like to thank Professor N. Miyaura (Hokkaido University) for
helpful discussion.
Supporting Information Available: CIF files giving full
crystallographic data for 2a‚1.5C6H5Me, 3b, 3d, 4b‚C6H6, 5b‚
C6H6, 6‚C6H5Me, and 7e, and figure for 4b‚C6H6 (PDF). This
material is available free of charge via the Internet at
http://pubs.acs.org.
JA0264091
(86) TEXSAN: Single-Crystal Structure Analysis Software, Vers. 1.8; Molecular
Structure Corp., 3200 Research Forest Drive, The Woodlands, TX 77381,
1997.
(87) Mackay, S.; Gilmore, C. J.; Edwards, C.; Stewart, N.; Shankland, K. maXus
Computer Program for the Solution and Refinement of Crystal Structures;
Nonius, The Netherlands, MacScience, Japan & The University of Glasgow,
2000.
(88) Watkin, D. J.; Prout, C. K.; Carruthers, J. R.; Betteridge, P. W. CRYSTALS
Issue 10; Chemical Crystallography Laboratory, Oxford, U.K., 1996.
(89) International Tables for X-ray Crystallography; Kynoch Press: Birming-
ham, England, 1974; Vol. IV.
The calculations were performed with use of the crystallographic
software packages teXsan,86 maXus,87 RAELS2000,82 and CRYS-
TALS.88 The neutral atom scattering factors were taken from ref 89.
The mass attenuation coefficients used were those implemented in
maXus.87
(85) Rae, A. D. Acta Crystallogr. 1996, A52, C44.
9
8360 J. AM. CHEM. SOC. VOL. 124, NO. 28, 2002