Preparation, via double oxidative addition, and characterization of bimetallic platinum and palladium complexes: Unique building blocks for supramolecular macrocycles. 13C NMR analysis of the nature of the palladium-carbon bond

Article abstract of DOI:10.1021/om961049+

The high-yield preparation, by double oxidative addition, of nine novel platinum and palladium bis(trans-M(PR₃)₂X)aryl (M = Pt or Pd; R = PPh₃ or PEt₃; X = Br or I; aryl = 1,4-benzene, 4,4′-biphenyl, 4,4″-ter-p-phenyl, 4,4′-tolane, or 4,4′-benzophenone) complexes from the reaction of Pt(PPh₃)₄, Pt(PEt₃)₄, or Pd(PPh₃)₄ with the respective dihalo aromatic in toluene is described. These complexes were fully characterized by elemental analysis, mass spectrometry, and NMR (¹H, ¹³C{¹H}, and ³¹P{¹H}) and vibrational (IR or Raman) spectroscopies. The single-crystal molecular structure of 4,4′-bis(trans-Pt(PEt₃)₂I)biphenyl (2a) was determined by X-ray crystallography. The key structural feature of this complex is the dihedral angle of 18.9° between the two planes defined by the phenyl groups of the biphenyl linkage. The nature of the palladium-carbon bond is investigated by ¹³C{¹H} NMR spectroscopy; Taft's σ_R parameter is found to correlate in a linear fashion with [δ(C_ipso) - δ(C_o)] for these palladium complexes. These data indicate the ¹³C chemical shift of C_ipso is linearly related to the amount of π-electron density of the carbon bound to the palladium center. The potential utility of these bimetallic platinum and palladium complexes as subunits in the generation of organometallic macrocycles is described.

Full text of DOI:10.1021/om961049+

Organometallics 1997, 16, 1897-1905
1897
P r ep a r a tion , via Dou ble Oxid a tive Ad d ition , a n d
Ch a r a cter iza tion of Bim eta llic P la tin u m a n d P a lla d iu m
Com p lexes: Un iqu e Bu ild in g Block s for Su p r a m olecu la r
Ma cr ocycles. 13C NMR An a lysis of th e Na tu r e of th e
P a lla d iu m -Ca r bon Bon d †
J oseph Manna,* Christopher J . Kuehl, J effery A. Whiteford, and Peter J . Stang*
Department of Chemistry, University of Utah, Salt Lake City, Utah 84112
Received December 12, 1996X
The high-yield preparation, by double oxidative addition, of nine novel platinum and
palladium bis(trans-M(PR3)2X)aryl (M ) Pt or Pd; R ) PPh3 or PEt3; X ) Br or I; aryl )
1,4-benzene, 4,4′-biphenyl, 4,4′′-ter-p-phenyl, 4,4′-tolane, or 4,4′-benzophenone) complexes
from the reaction of Pt(PPh3)4, Pt(PEt3)4, or Pd(PPh3)4 with the respective dihalo aromatic
in toluene is described. These complexes were fully characterized by elemental analysis,
mass spectrometry, and NMR (1H, 13C{1H}, and 31P{1H}) and vibrational (IR or Raman)
spectroscopies. The single-crystal molecular structure of 4,4′-bis(trans-Pt(PEt3)2I)biphenyl
(2a ) was determined by X-ray crystallography. The key structural feature of this complex
is the dihedral angle of 18.9° between the two planes defined by the phenyl groups of the
biphenyl linkage. The nature of the palladium-carbon bond is investigated by 13C{1H} NMR
spectroscopy; Taft’s σR parameter is found to correlate in a linear fashion with [δ(Cipso) -
δ(Co)] for these palladium complexes. These data indicate the 13C chemical shift of Cipso is
linearly related to the amount of π-electron density of the carbon bound to the palladium
center. The potential utility of these bimetallic platinum and palladium complexes as
subunits in the generation of organometallic macrocycles is described.
In tr od u ction
organometallic macrocyclic speciessaccessible in high
yield by employing a self-assembly5 methodologysare
among the newest class of supramolecular complexes
that display microenvironments with interesting chemi-
cal, electronic, and optical properties.6 By exploiting a
“double” oxidative-addition strategy, it should be pos-
sible to readily synthesize a diverse class of building
blocks with tunable electronic, geometric, steric, and
solubility properties for constructing supramolecular
architectures. Indeed, we recently demonstrated the
first example of the aforementioned group with the
implementation of 4,4′-bis(trans-Pt(PPh3)2I)biphenyl,
synthesized from Pt(PPh3)4 and 4,4′-diiodobiphenyl, as
a subunit of organoplatinum and iodonium macrocycles.4b
The considerable interest in the complexes of the Ni
triad stems in large part from their catalytic reactivity
and utility as C-C bond forming reagents.1 Of the
group 10 transition metal complexes, Pd organometallic
complexes are arguably the most versatile reagents in
organic chemistry, as exemplified by the numerous
palladium-catalyzed molecular rearrangements, oxida-
tion, substitution, elimination, carbonylation (and de-
carbonylation), and range of C-C coupling processes
that are observed.2 In many of the latter processes, the
oxidative-addition of Pd{P(aryl)3}4 with L-X (L )
alkenyl, acyl, or aryl; X ) halide), to generate trans-
Pd{P(aryl)3}2LX (or the dimer {Pd{P(aryl)3}LX}2),3 is
a critical step in the catalytic cycle.
In contrast to their importance as reagents in organic
chemistry, our interest in zero-valent platinum and
palladium complexes and, in particular, their ability to
afford trans-M(PPh3)2XL complexes grew out of our
current studies in the design and self-assembly of novel
cationic organometallic macrocycles.4 Inorganic and
(4) (a) Whiteford, J . A.; Rachlin, E. M.; Stang, P. J . Angew. Chem.,
Int. Ed. Engl. 1996, 35, 2524. (b) Manna, J .; Whiteford, J . A.; Stang,
P. J .; Muddiman, D. C.; Smith, R. D. J . Am. Chem. Soc. 1996, 118,
8731. (c) Olenyuk, B.; Whiteford, J . A.; Stang, P. J . J . Am. Chem. Soc.
1996, 118, 8221. (d) Stang, P. J .; Olenyuk, B. Angew. Chem., Int. Ed.
Engl. 1996, 35, 732. (e) Stang, P. J .; Olenyuk, B.; Fan, J .; Arif, A. M.
Organometallics 1996, 15, 904. (f) Stang, P. J .; Chen, K.; Arif, A. M.
J . Am. Chem. Soc. 1995, 117, 8793. (g) Stang, P. J .; Cao, D. H.; Saito,
S.; Arif, A. M. J . Am. Chem. Soc. 1995, 117, 6273. (h) Stang, P. J .;
Chen, K. J . Am. Chem. Soc. 1995, 117, 1667. (i) Stang, P. J .; Whiteford,
J . A. Organometallics 1994, 13, 3776. (j) Stang, P. J .; Cao, D. H. J .
Am. Chem. Soc. 1994, 116, 4981. (k) Stang, P. J .; Zhdankin, V. V. J .
Am. Chem. Soc. 1993, 115, 9808.
(5) (a) Philip, D.; Stoddart, J . F. Angew. Chem., Int. Ed. Engl. 1996,
35, 1155. (b) Lawrence, D. S.; J iang, T.; Levett, M. Chem. Rev. 1995,
95, 2229. (c) Fujita, M.; Sasaki, O.; Mitsuhashi, T.; Fujita, T.; Yazaki,
J .; Yamaguchi, K.; Ogura, K. Chem. Commun. 1996, 1535. (d) Slone,
R. V.; Hupp, J . T.; Stern, C. L.; Albrecht-Schmitt, T. E. Inorg. Chem.
1996, 35, 4096. (e) Fujita, M.; Ibukuro, F.; Seki, H.; Kamo, O.; Imanari,
M.; Ogura, K. J . Am. Chem. Soc. 1996, 118, 899. (f) Fujita, M.; Ibukuro,
F.; Yamaguchi, K.; Ogura, K. J . Am. Chem. Soc. 1995, 117, 4175. (g)
Slone, R. V.; Yoon, D. I.; Calhoun, R. M.; Hupp, J . T. J . Am. Chem.
Soc. 1995, 117, 11813. (h) Fujita, M.; Oguro, D.; Miyazawa, M.; Oka,
H.; Yamaguchi, K.; Ogura, K. Nature 1995, 378, 469-471. (i) Fujita,
M.; Kwon, Y. J .;Washizu, S.; Ogura, K. J . Am. Chem. Soc. 1994, 116,
1151. References 5a and b are detailed reviews of the self-assembly
process.
†Dedicated to Professor Roald Hoffmann on the occasion of his 60th
birthday.
X Abstract published in Advance ACS Abstracts, April 1, 1997.
(1) (a) Collman, J . P.; Hegedus, L. S.; Norton, J . R.; Finke, R. G.
Principles and Applications of Organotransition Metal Chemistry;
University Science Books: Mill Valley, CA, 1987. (b) Hegedus, L. S.
Transition Metals in the Synthesis of Complex Organic Molecules;
University Science Books: Mill Valley, CA, 1994.
(2) (a) Heck, R. F. Palladium Reagents in Organic Syntheses;
Academic Press: New York, 1985. (b) McQuillin, F. J .; Parker, D. G.;
Stephenson, G. R. Transition Metal Organometallics for Organic
Synthesis; Cambridge University Press: New York, 1991. (c) Trost, B.
M. Acc. Chem. Res. 1990, 23, 34. (d) Cabri, W; Candiani, I. Acc. Chem.
Res. 1995, 28, 2.
(3) Hartwig, J . F.; Paul, F. J . Am. Chem. Soc. 1995, 117, 5373.
S0276-7333(96)01049-7 CCC: $14.00 © 1997 American Chemical Society

1898 Organometallics, Vol. 16, No. 9, 1997
Manna et al.
Sch em e 1
Herein we report on the double oxidative-addition
chemistry of Pt(PPh3)4, Pt(PEt3)4, and Pd(PPh3)4 with
a range of dihaloaryl organics and the full characteriza-
tion of the bimetallic complexes prepared. From exten-
sive 13C NMR studies, a detailed examination of the
nature of the metal-aryl interaction is undertaken.
Furthermore, the properties of these complexes are
briefly discussed, particularly regarding their potential
utility in organometallic supramolecular synthesis and
chemistry.
Resu lts a n d Discu ssion
variable and generally diminished. These nine bimetal-
lic complexes were characterized by NMR (1H, 31P{1H},
13C{1H}), vibrational (IR or Raman), and mass spec-
trometry (FAB-MS), as well as elemental analysis and
physical means (vide infra). As expected, milder condi-
tions were required for the reactions of Pd(PPh3)4 and
Pt(PEt3)4.8a These bimetallic complexes range in color
from white to light yellow and are air- and moisture-
stable solids, in accord with Parshall’s findings for the
related monometallic trans-M(PEt3)2(p- or m-C6H4F)X
(X ) halide or cyanide) complexes.8a The complexes
with PPh3 as the ancillary ligands are soluble in
chloroform and methylene chloride; whereas, the PEt3
derivatives (1a and 2a ) are highly soluble in toluene,
chloroform, and methylene chloride, insoluble in hex-
anes, and partially soluble in diethyl ether.
Syn th esis of Bis(tr a n s-M(P R3)2X)a r yl (M ) P t or
P d ; R ) P P h 3 or P Et3; X ) Br or I; Ar yl ) 1,4-Ben -
zen e, 4,4′-Bip h en yl, 4,4′′-Ter -p-p h en yl, 4,4′-Tola n e,
or 4,4′-Ben zop h en on e) Com p lexes. The utility of
zero-valent M(PR3)4 in the preparation of trans-M(PR3)2-
XL complexes (X ) halide; L ) alkyl, aryl, alkenyl, or
acyl) is well documented.7 In fact, it has been demon-
strated that the order of relative reactivity for group
10 M(PR3)4 complexes toward the C(aryl)-halide bond
is Ni(0) > Pd(0) > Pt (0) and C-I > C-Br > C-Cl.8
Furthermore, Fitton and Rick have established that
electron-withdrawing groups (e.g., NO2, CF3) para to the
C-X bond of the phenyl derivatives activate the aryl-
halide bond, the metal system being Pd(PPh3)4 in their
study.8b Conversely, they showed para-substituted
electron-donating groups (e.g., OMe) suppress the re-
activity of aryl halides. We will exploit the former fact
in this study.
Parshall’s detailed studies manifested the enhanced
reactivity of the triethyphosphine (PEt3) derivatives
toward aryl halides over the corresponding nickel, pal-
ladium, and platinum triphenylphosphine (PPh3) ana-
logs, as evidenced by the milder reaction conditions
required.8a The increase in basicity of the phosphine,
P(alkyl)3 versus PPh3, and the corresponding increase
in nucleophilicity of the reactive species, “M(PR3)2”,
accounts for this trend.
The organic reagents, 4,4′-dibromotolane and 4,4′-
dihalobenzophenone, are ideal reagents for oxidative
addition because of the presence of strong electron-
withdrawing functionalities (CtC and CdO) para to the
C-X bond (vide supra).
Unless a concerted mechanism is envisioned during
the formation of these bimetallic complexes, two se-
quential oxidative-additions are a more probable path-
way to the product. Indeed, we have found that reaction
of Pt(PPh3)4 (1 equiv) and 4,4′-diiodobiphenyl (1.1 equiv)
at ∼70 °C yields a mixture of 4-iodo-4′-(trans-Pt(PPh3)2I)-
biphenyl (75 mol %) and complex 2b (25 mol %). The
excess 4,4′-diiodobiphenyl was removed during the
workup by washing the solid products with diethyl
ether. This product distribution suggests the -p-C6H4-
(trans-Pt(PPh3)2I) moiety is slightly electron-donating,
deactivating, toward the C-I bond of the -p-C6H4I
group (vide infra).
Reaction of 2.2 equiv of M(PPh3)4 or Pt(PEt3)4 with
the respective dihaloaryl organics (Schemes 1 and 2) in
toluene generates, via double oxidative addition of M(0),
the bis(trans-M(PPh3)2X)aryl complexes in good to ex-
cellent yield.9 These reactions can also be carried out
in a benzene media; however, the yields are quite
1H- a n d 31P {1H}-NMR Sp ectr oscop ic Ch a r a cter -
iza tion . Table 1 summarizes some of the key spectro-
(6) Recent key reviews pertaining to supramolecular chemistry: (a)
Templating, Self-Assembly and Self-Organization in Comprehensive
Supramolecular Chemistry; Sauvage, J . P.; Hosseini, M. W., Exec. Eds.,
Lehn, J .-M., Chair Ed.; Pergamon Press: Oxford, U.K., 1996; Vol. 9.
(b) Amabilino, D. B.; Stoddart, J . F. Chem. Rev. 1995, 95, 2725. (c)
Whitesides, G. M.; Simanek, E. E.; Mathias, J . P.; Seto, C. T.; Chin,
D. N.; Mammen, M.; Gordon, D. M. Acc. Chem. Res. 1995, 28, 37. (d)
Cram, D. J .; Cram, J . M. Container Molecules and Their Guests; The
Royal Society of Chemistry: Cambridge, England, 1994. (e) Lehn, J .-
M. Supramolecular Chemistry: Concepts and Perspectives; VCH Pub-
lishers: Weinheim, Germany, 1995. (f) Tour, J . M. Chem. Rev. 1996,
96, 537.
1
scopic data. The H-NMR spectra of the palladium and
platinum complexes 2b, 2c, 3a , 4b, 5a , 5b, and 5c
display the expected downfield resonances attributed to
the PPh3 hydrogens, in addition to two sets of doublets
attributable to the Ho and Hm nuclei magnetically
coupled to each other over three bonds (3J HH). These
(7) (a) Comprehensive Organometallic Chemistry II; Abel, E. W.,
Stone, F. G. A., Wilkenson, G., Eds.; Elsevier Science: Tarrytown, New
York, 1995; Vol. 9. (b) Stille, J . K. The Chemistry of the Metal-Carbon
Bond; Hartley, F. R., Patai, S., Eds.; Wiley: Chichester, England, 1985;
Vol. 2, Chapter 9. (c) Sen, A.; Chen, J .-T.; Vetter, W. M.; Whittle, R.
R. J . Am. Chem. Soc. 1987, 109, 148. (d) Crociani, B.; DiBianci, F.;
Giovenco, A.; Berton, A.; Bertani, R. J . Organomet. Chem. 1989, 361,
255.
(8) (a) Parshall, G. W. J . Am. Chem. Soc. 1974, 96, 2360. (b) Fitton,
P.; Rick, E. A. J . Organomet. Chem. 1971, 28, 287. (c) Mantovani, A.
J . Organomet. Chem. 1983, 255, 385. (c) Gerlach, D. H.; Kane, A. R.;
Parshall, G. W.; J esson, J . P.; Muetterties, E. L. J . Am. Chem. Soc.
1971, 93, 3543. (d) Hidai, M.; Kashiwagi, T.; Ikeuchi, T.; Uchida, Y. J .
Organomet. Chem. 1971, 30, 385.
latter resonances are shielded relative to the organic
(9) For the report of the only prior synthesis, to our knowledge, of
the platinum or palladium aryl-bridged bimetallics 1,4-bis(trans-Pt-
(PBu3)2Cl)benzene and 1,4-bis(trans-Pt(PBu3)2(C6H5))benzene, see:
Muller, W.-D.; Brune, H. A. Chem. Ber. 1986, 119, 759.

Bimetallic Platinum and Palladium Complexes
Organometallics, Vol. 16, No. 9, 1997 1899
Sch em e 2
Ta ble 1. Selected 1H- a n d 31P {1H}-NMRa a n d Ma ss
Sp ectr om etr y Da ta for P la tin u m a n d P a lla d iu m
Bim eta llic Com p lexes
Ta ble 2. Cr ysta l Da ta , Da ta Collection , a n d
Str u ctu r e Refin em en t P a r a m eter s for 2a
empirical formula
fw
C36H68I2P4Pt2
1268.76
Ho (3J HPt
)
Hm
31P (1J PPt
)
FAB-MSc
T, K
291(2)
orthorhombic
Fdd2
1a
2a
2b
2c
3a
4a
5a
5b
5c
6.86
10.3 (2787)
11.0 (2730)
24.3 (3095)
25.5
1192 (M+)
1268 (M+)
1845 (M+)
cryst syst
space group
cryst size, mm
F(000)
a, Å
b, Å
7.33 (66)
6.56 (55)
6.54
6.54 (56)
6.63
7.25
6.01
6.12
6.32
6.30
6.36
6.43
6.49b
0.38 × 0.38 × 0.36
4848
24.0 (3075)b
24.7
18.288(3)
21.962(5)
23.654(4)
90
9500(3)
8
1.774
7.34
0.710 73 (MoKR)
5-50
0 e h e 21, 0 e k e 26,
0 e l e 28
6.74 (55)
6.72
22.2 (3040)
23.8
1874 (M + H+)
1697 (M + H+)
1603 (M + H+)
c, Å
R ) â ) γ, deg
6.72b
25.0b
V, Å3
a
Chemical shifts in ppm are referenced to CD2Cl2 (1H NMR)
Z
F (calcd), Mg/m3
µ, mm-1
λ, Å
and external 85% H3PO4 (31P{1H}), unless otherwise noted. b NMR
obtained in CDCl3. All coupling constants are in Hertz. c Mass/
charge.
2θ range, deg
index ranges
precursors, as a consequence of the η1-M-C bond; in
all cases δH > δH
10
.
For the platinum complexes, the
no. reflns collected
abs corr
transm factors, range
refinement method
2133
o
m
semi-empirical, ψ-scans
0.709-0.999
full-matrix-block
least-squares, F2
2133/1/197
1.075
R1 ) 0.0287, wR2 ) 0.0761
R1 ) 0.1146, wR2 ) 0.1672
0.000206 (12)
0.780/-0.935
Ho resonance is accompanied by a pair of doublets
centered about the major peak due to additional three
bond (3J HPt) spin-spin coupling to platinum (195Pt; I )
1/2; 33.8% natural abundance) of 55-66 Hz.
The phosphorus methylene and methyl hydrogens of
the PEt3 derivatives 1a and 2a are observed as mul-
tiplets, due to coupling to each other and the phosphorus
data/restraints/param
goodness-of-fit on F2
final R indices [I > 2σ(I)]
R (all data)
extinction coefficient
1
larg diff. peak/hole, e Å-3
nuclei, upfield in the H-NMR spectra at 1.80 and 1.06
ppm, respectively.
The 31P{1H}-NMR spectra of the palladium complexes
display a downfield singlet, referenced to external 85%
phosphoric acid (δ ) 0.0). For the corresponding plati-
num bimetallic species, the 31P{1H} signal is observed
as a sharp singlet with concomitant platinum satellites.
Not surprisingly, the 31P resonances fall into two
groups: those with PPh3 (δ ) 22.2-26.5 ppm) and those
with the more basic PEt3 (δ ) 10.3 and 11.0) as the
ancillary ligands. We find no evidence for the possible
cis to trans isomerization at the metal center; a cis
geometry would display two sets of doublets in the 31P-
{1H}-NMR spectrum. Phosphorus-platinum single-
bond spin-spin couplings range from 2730 to 3095 Hz,
congruent with those reported for trans-PtP2 systems.11
X-r a y Cr ysta llogr a p h ic An a lysis of 2a . Crystals
of complex 2a were grown from a -20 °C solution of
toluene/ether. The crystal constants, data collection
details, refinement parameters, and residual values for
4,4′-bis(trans-Pt(PEt3)2I)biphenyl are given in Table 2.
Selected bond distances and angles are juxtaposed in
Table 3.
Because of the marginal precision of this crystal
structure, we will only discuss the undeniable features
that are apparent. As evidenced by the ORTEP dia-
gram (Figure 1), the platinum center displays the
(10) (a) Clark, H. C.; Ward, J . E. H. J . Am. Chem. Soc. 1974, 96,
1741. (b) Coulson, D. R. J . Am. Chem. Soc. 1976, 98, 3111.
(11) See refs 7d and 11a, b, and c for representative 31P NMR data
for trans-M(PR3)2(aryl)X complexes. (a) Anderson, G. K.; Clark, H. C.;
Davies, J . A. Organometallics 1982, 1, 64. (b) Crociani, B.; DiBianci,
F.; Giovenco, A.; Scrivanti, A. J . Organomet. Chem. 1984, 269, 295.
(c) Crociani, B.; DiBianci, F.; Giovenco, A.; Scrivanti, A. J . Organomet.
Chem. 1983, 251, 393.

1900 Organometallics, Vol. 16, No. 9, 1997
Manna et al.
phenyl is planar in the solid state.18 There would seem
to be no obvious trend in these data, signifying the
subtle factors that govern those ubiquitous “packing
forces”. One might expect that the π-π intermolecular
packing forces, so significant in the organic biphenyl
structures, are essentially nonexistent for 2a . If this
was the case, we could then infer from the 18.9° dihedral
angle that there is some degree of conjugation between
the phenyl groups. Unfortunately, the influence of other
packing forces, namely intramolecular interactions, on
the biphenyl dihedral angle cannot be fully assessed.
13C{1H}-NMR Ch a r a cter iza tion a n d Evid en ce for
π-Con ju ga tion betw een th e tr a n s-P d (P R3)2X a n d
Ar yl Lin k a ge. All PPh3-based derivatives display
similar resonances in the 13C{1H}-NMR spectra; the
Cipso (131.3-132.7 ppm), Co (134.9-135.5 ppm), Cm
(127.1-130.6 ppm), and Cp (128.8-130.5 ppm) chemical
shifts are akin to those previously reported for PPh3.19
Likewise, the upfield disposition of the methylene (15.7
ppm) and methyl (8.3 ppm) carbon chemical shifts for
complexes 1a and 2a are also as expected.19,11c Chemi-
cal shifts in the 13C{1H}-NMR spectra for the bridging
aryl fragments of platinum complexes 1a , 2a , 2b, and
5a are unexceptional; because a significant amount of
13C-NMR data for trans-Pt(PEt3)2X(aryl) complexes has
been published by others, these values will not be
discussed in detail.10
Ta ble 3. Selected Bon d d ista n ces (Å), An gles (d eg),
a n d Tor sion An gles (d eg) for 2a a
Pt-I
2.697(1)
2.305(14)
2.296(14)
2.026(10)
1.39(3)
C(3)-C(4)
C(4)-C(5)
C(5)-C(6)
C(6)-C(1)
C(4)-C(4′)
1.42(3)
1.37(3)
1.37(2)
1.42(3)
1.49(2)
Pt-P(1)
Pt-P(2)
Pt-C(1)
C(1)-C(2)
C(2)-C(3)
1.35(2)
C(1)-Pt-I
P(1)-Pt-P(2)
C(1)-Pt-P(1)
178.6(9)
179.1(4)
90.5(9)
C(1)-Pt-P(2)
P(1)-Pt-I
P(2)-Pt-I
89.0(9)
90.0(2)
90.6(2)
P(1)-Pt-C(1)-C(2) -82.07(2.62) P(2)-Pt-C(1)-C(2) 97.23(2.64)
P(1)-Pt-C(1)-C(6) 93.74(2.42) P(2)-Pt-C(1)-C(6) -86.96(2.39)
a
Estimated standard deviations are in parentheses.
F igu r e 1. ORTEP diagram of 2a .
Table 4 lists the 13C{1H}-NMR chemical shifts for the
aryl linkages of the bipalladium derivatives. Further-
more, the data for three para-substituted palladium
complexes, trans-Pd(PEt3)2(p-C6H4-X′)Br (X′ ) Me (6a ),
Cl (7a ), and NO2 (8a )), taken from the literature are
also included (Scheme 3).20 Assignments of the 13C{1H}
chemical shifts for the bridging carbons were made as
follows: Cipso is observed as a weak triplet (intensity ≈
1); Co is observed as a triplet (intensity ≈ 2), Cm is
observed as a singlet (intensity ≈ 2), and Cp is observed
expected square planar coordination geometry; the four
cis angles about platinum are essentially orthogonal
(89-90.5°). The molecule lies about a crystallographic
2-fold axissthe C2 symmetry axis bisects the C-C bond
between the two carbons (C4 and C4′) and is orthogonal
to a plane defined by the biphenyl linkage.
The Pt-P bond distances of 2.296(14) and 2.305(14)
Å are not unusual; the Pt-I and Pt-C(1) distances of
2.697(1) and 2.026 (10) Å, respectively, are also unre-
markable.12 Sizable estimated standard deviations (esd’s)
of the biphenyl Pt-C and C-C distances preclude their
use for any detailed discussion of the possible M-C(aryl)
π-bonding in this system. Fortunately, the 13C NMR
data will be a significant value in this regard (vide
infra).
The most noteworthy feature of this structure is the
dihedral angle of 18.9° between the two planes defined
by the phenyl groups of the biphenyl linkage, which can
be compared to the dihedral angles of biaryls. Evalu-
ation of the gas phase structure of biphenyl by electron
diffraction yielded a dihedral angle of ∼45°.13 In
contrast, biphenyl is planar in the solid state (with
significant thermal libration even at low temperature).14
Crystallographic dihedral angles for the para nitro,15
dinitro,16 and dimethylbiphenyl17 derivatives exhibit
values between 30 and 40°; whereas, p-dihydroxybi-
as a singlet (intensity ≈ 1). Interestingly, 3J C
>
m-P
2J C
for all of the palladium bimetallic complexes.
ipso-P
We will now briefly address a question of fundamental
importance to our understanding of the bonding of these
4,4′-bis(trans-Pd(PR3)2X)aryl complexes: How much
π-symmetry-directed electronic communication is there
between the metal center and the conjugated aryl
framework, or restated, to what extent does a “quinoi-
dal” resonance structure contribute to the ground-state
structure of these molecules?
The nature of the η1-M-C(aryl) π-bonding interaction
was initially examined more than 30 years ago.10,21
Although the conclusions from several detailed NMR
studies have not been entirely harmonious, the general
consensus indicates that the fragments trans-M(PEt3)2X
(M ) Pt or Pd; X ) halide) are π-donors that interact
with the π-framework of the phenyl substituent. The
reported Taft σR° values, largely determined by 19F
NMR studies, for trans platinum and palladium range
from -0.24 to -0.27.21 It should be noted that most of
the detailed studies were undertaken on trans-M(PEt3)2-
(m- or p-C6H4F)X or trans-M(PEt3)2(C6H5)X (X ) halide,
SCN, OCN, CN, Me, C6H5, CtCC6H5) complexes.
(12) See refs 12a and b for the X-ray structures of trans-Pt(PPh3)2-
(Ph)Cl and [trans-Pt(PEt3)2(p-chlorophenyl)(CO)][PF6], respectively. (a)
Conzelmann, W.; Koola, J . D.; Kunze, U.; Stra¨hle, J . Inorg. Chim. Acta
1984, 89, 147. (b) Field, J . S.; Wheatley, P. J . J . Chem. Soc., Dalton
Trans. 1974, 702.
(13) Batiasen, O. Acta Chem. Scand. 1949, 3, 408.
(14) (a) Charbonneau, G.-P.; Delugeard, Y. Acta Crystallogr. 1977,
B33, 1586. (b) Charbonneau, G.-P.; Delugeard, Y. Acta Crystallogr.
1976, B32, 1420.
(15) Casalone, G.; Gavezzotti, A.; Simonetta, M. J . Chem. Soc.,
Perkin Trans. 1973, 342.
(16) Boonstra, E. G. Acta Crystallogr. 1963, 16, 816.
(17) Casalone, G.; Mariana, C.; Mugnoli, A.; Simonetta, M. Acta
Crystallogr. 1969, B25, 1741.
(18) Farag, M. S.; Kader, N. A. J . Chem. U. A. R. 1960, 3, 1.
(19) Isobe, K.; Nanjo, K.; Nakamura, Y.; Kawaguchi, S. Bull. Chem.
Soc. J pn. 1986, 59, 2141.
(20) Granell, J .; Muller, G.; Rocamora, M.; Vilarrasa, J . Magn.
Reson. Chem. 1986, 24, 243.
(21) (a) Parshall, G. W. J . Am. Chem. Soc. 1966, 88, 704. (b) Stewart,
R. P.; Treichel, P. M. J . Am. Chem. Soc. 1970, 92, 2710.

Bimetallic Platinum and Palladium Complexes
Organometallics, Vol. 16, No. 9, 1997 1901
Ta ble 4. 13C{1H} Ch em ica l Sh ift Da ta a for tr a n s-M(P R3)2(a r yl)X Com p lexes a n d Ta ft σR P a r a m eter s
complex
Cipso
Co
Cm
Cp
other
Cipso-Co
σR, groupd
2c
4a
5b
156.5
158.2
169.6
167.0
149.0
152.3
170.1
136.0
136.5
135.6
135.5
136.0
137.2
136.6
127.2
130.6
129.3
128.9
128.6
127.5
121.1
136.8
117.6
n/o
131.8
131.4
130.4
144.5
20.5
21.7
34.0e
31.5e
13.0
15.1
33.5
-0.08, C6H5
0.01, CtCC6H5
0.16, OdC(C6H5)
0.16, OdC(C6H5)
-0.13, Me
88.5 (CtC)
196.0 (CdO)
196.2 (CdO)
20.8 (Me)
5cb
6a b,c
7a b,c
8a b,c
-0.16, Cl
0.16, NO2
NMR solvent was CD2Cl2, unless otherwise noted. NMR data collected in CDCl3. c Data taken from ref 20. Taft’s σR parameters
a
b
d
taken from ref 29. e The average of these two values (32.8) is employed in Figure 2.
Sch em e 3
In contrast, this study examines more directly the
tunability of the palladium-aryl bonding interaction by
varying the para substituent of the phenyl group with
several electronically distinct functional groups and
measuring the corresponding change in the 13C-NMR
parameters.
The structures of the bimetallic derivatives can be
expressed by several resonance canonicals. For ex-
ample, complex 2c has two possible resonance struc-
tures with the negative charge localized on the para
carbons; we have not shown the other possible reso-
nances with charge migration onto the meta carbon for
the sake of brevity. Unlike 2c, in the case of 4a we
expect only the two resonance forms, as shown in
Scheme 3, with the acceptor being the alkynyl â-car-
bons.25 (Alternatively, the alkynyl moiety could be the
donor; however, we find this scenario unlikely given the
metal fragment’s negative value of σR°.) Unlike the
other bimetallic complexes, we expect 4a to be a planar
structure, as observed for diphenylacetylene in the solid
state.26 Probably the most interesting bimetallic com-
pounds prepared are 5b and 5c; these two compounds
are organometallic analogs to organic cross-conjugated
compounds, as is 4a , and are expected to possess a high
level of ground-state charge-transfer character.27 The
possible resonance structures for 6a and 7a are not
Among the donor-acceptor aromatics studied, p-
nitroaniline is the quintessential example of an organic
substrate that displays a considerable amount of charge-
transfer character, via electron migration through the
conjugated phenyl unit from NH2 (donor) to NO2 (ac-
ceptor), in the ground-state structure, as manifested
crystallographically (Scheme 3).22 Complexes that pos-
sess donor-acceptor electronic functional groups that can
communicate through a conjugated framework are of
significant interest because of their unusual electronic
properties.23 We can likewise draw several resonance
structures for the monometallic and bimetallic palla-
dium complexes, as illustrated in Scheme 3. Complex
8a is an interesting organometallic analog to p-nitro-
aniline.24
(24) A brief discussion of resonance canonicals in organic systems
is given in March, J . Advanced Organic Chemistry: Reactions, Mech-
anisms, and Structure; J ohn Wiley & Sons: New York, 1992; p 30-
40.
(25) Shorter, J . The Chemistry of Triple Bonded Functional Groups,
Supplement C2; Patai, S., Eds.; J ohn Wiley & Sons: New York, 1994;
Chapter 5.
(26) Abramenko, A. V.; Almenningen, A.; Cyvin, B. N.; Cyvin, S. J .;
J onvik, T.; Khaikin, L. S.; Romming, C.; Vilkov, L. V. Acta Chem.
Scand. 1988, A42, 674.
(22) Colapietro, M.; Domenicano, A.; Marciante, C.; Portalone, G.
Z. Naturforsch. 1982, 37B, 1309.
(23) For an interesting study of the quinoidal contribution to the
ground-state and excited-state structures of p-NH2C6H5(CtC)nC6H5-
NO2 (n ) 0-3), see: Graham, E. M.; Miskowski, V. M.; Perry, J .
W.; Coulter, D. R.; Stiegman, A. E.; Schaefer, W. P.; Marsh, R. E.
J . Am. Chem. Soc. 1989, 111, 8771 and Stiegman, A. E.; Miskowski,
V. M.; Perry, J . W.; Coulter, D. R. J . Am. Chem. Soc. 1987, 109,
5884.

1902 Organometallics, Vol. 16, No. 9, 1997
Manna et al.
not examine the direct through phenyl ring resonance
contribution by systematically varying the para group.10
It should be noted that we find no correlation between
Taft’s σI parameter and Co (Cm as defined in the organic
study), in agreement with the finding for para-substi-
tuted phenyl derivatives.28 Attempts to correlate [δ-
+
(Cipso)-δ(Co)] with σR°, σp, or σp yielded poorer fits of
the data.
Admittedly, there are several crude approximations
that we make in this correlation. Firstly, the σR values
were determined in nonpolar solvents; whereas, our
NMR data were obtained in chloroform and methylene
chloride solvent media. However, it has been shown
that employing chloroform or methylene chloride leads
to only minor differences in the NMR chemical shifts.10a
Secondly, we presume the σR (or σR°) values of the PEt3
and PPh3 trans-M(PR3)2X derivatives to be essentially
identical. Electronic differences in the phosphine ligands
should largely influence the inductive electronic effects
(σI), which are presumably corrected for by subtracting
δ(Co) from δ(Cipso). Along this line, it has been shown
that σR° for trans-Pd(PEt3)2Br and Pt(PEt3)2I are identi-
cal (-0.27) while σI differs by 0.03.21b Obviously, the
assumption that subtracting Co corrects for inductive
effects is not entirely true since [δ(Cipso) - δ(Co)] differs
for 5b and 5c and represents the influence of the
bromide versus iodide ligand. Thirdly, the σR value for
CtCC6H5 is not available; therefore, we have utilized
the σR° parameter of this group. As previously noted,
in most cases σR° and σR are only marginally different.30
The last, and most significant, approximation made in
Figure 2 is due to our lack of knowledge for the σR values
of the para groups for the bimetallic complexes. For
example, it would be ideal to know the σR value for
p-C6H4-(trans-Pd(PPh3)2Br) for complex 2c rather than
using just the σR value for C6H5. However, these
parameters are not available. The extent of this ap-
proximation can be gauged by comparison of the σR
values for C(O)C6H5 (0.16), C(O)C6H5-p-Cl (0.16), and
C(O)C6H5-p-SMe (0.15).29 We might expect a small
decrease in σR for all of the p-aryl-(trans-Pd(PPh3)2X)
groups and, therefore, apply an appropriate correction;
however, we did not want to introduce yet another layer
of approximation to this correlation.
F igu r e 2. Linear plot of [δ(Cipso) - δ(Co)] versus σR.
shown; they would not be expected to contribute to any
measurable extent because of the negative σR values for
both para substituents.
It has been demonstrated that δ(Cp) for substituted
benzenes correlates nicely with Taft’s σR° or σR param-
eter, thus, indicating that changes in δ(Cp) are domi-
nated by the π-resonance effects.28 A slight improve-
ment on this correlation was obtained by linearly
plotting [δ(Cp) - δ(Cm)] versus Taft’s σR° or σR param-
eter. Apparently, this correction removes the inductive-
effect contribution to δ(Cp) and better represents the
substituent’s “pure” resonance interaction with the
phenyl ring. J uxtaposed in Table 4 are the [δ(Cipso) -
δ(Co)] values for the organopalladium complexes, σR, and
the remaining 13C NMR chemical shifts.29 The com-
parison of [δ(Cipso) - δ(Co)] versus σR is analogous to
the [δ(Cp) - δ(Cm)] versus σR correlation in the organic
study, only our labeling schemes differ.
Is the aforementioned correlation applicable to these
substituted phenyl organometallics? Figure 2 illus-
trates the linear plot between [δ(Cipso) - δ(Co)] and σR.
[δ(Cipso) - δ(Co)] ) 59.853σR - 23.157
Little evidence for significant charge transfer can be
gleaned from the 13C chemical shifts of the alkyne and
carbonyl carbon atoms of 4a , 5b, and 5c. The alkynyl
carbon resonance of 4a (88.5 ppm) is nearly identical
to the value of 89.6 ppm in diphenylacetylene.31 Fur-
thermore, the strongly deshielded carbonyl carbon reso-
nance at 196 ppm for 5b and 5c are akin to the in-
variant parameters, 193.1-195.5 ppm, for diverse groups
of organic 4,4′-substituted benzophenones.32 It would
appear that the carbonyl carbon chemical shift is largely
insensitive to the nature of the para group and subtle
changes in the π-bonding of the system. However, it is
noteworthy that the downfield Cipso chemical shifts for
5b, 5c, and 8a fall in the intermediate range between
η1-metal-phenyl and metal-carbene complexes. 13C-
chemical shifts for palladium- and platinum-carbene
complexes range from 175 to 321 ppm.33
The strong linear correlation (r ) 0.977) between the
two parameters is impressive, or alternatively, quite
fortuitous. It should also be noted that plotting δ(Cipso
)
versus σR results in r ) 0.971, indicating δ(Co) is only
of modest utility in correcting for inductive electronic
effects. We have utilized the average value of [δ(Cipso
)
- δ(Co)] for complexes 5b and 5c.29 Previous studies
have cast doubt as to the extension of this organic
relationship to organometallic systems; however, in
these prior studies, [δ(Cp) - δ(Cm)] spanned a range of
less than a third of that observed in this study and did
(27) An explanation of cross-conjugation is given in ref 24 and in
Phelan, N. F.; Orchin, M. J . Chem. Educ. 1968, 45, 633.
(28) Maciel, G. E.; Natterstad, J . J . Chem. Phys. 1965, 42, 2427.
For a detailed discussion of the numerous correlations, or lack there
of, between 13C NMR data for substituted aromatics and a variety of
Hammett structure-reactivity parameters, see: Ewing, D. F. Cor-
relation Analysis in Chemistry, Recent Advances; Chapman, N. B.,
Shorter, J ., Eds.; Plenum Press: New York, 1978; Chapter 8.
(29) Taft’s σR parameters are taken from Hansch, C.; Leo, A.; Taft,
R. W. Chem. Rev. 1991, 91, 165. The value of σR° for CtCC6H5 is taken
from ref 10b. There is no difference in the correlation coefficient if the
two values of 5b and 5c are not averaged, but utilized in the plot of
[δ(Cipso) - δ(Co)]versus σR.
(30) Ehrenson, S.; Brownlee, R. T. C.; Taft, R. W. Prog. Phys. Org.
Chem. 1973, 10, 1.
(31) Wrackmeyer, B.; Horchler, K. Prog. Nucl. Magn. Reson. Spect.
1990, 22, 209.
(32) Nyquist, R. A.; Hasha, D. L. Appl. Spectrosc. 1991, 45, 849.

Bimetallic Platinum and Palladium Complexes
Organometallics, Vol. 16, No. 9, 1997 1903
Examination of ν(CtC) for 4a shows little evidence
for the extreme resonance canonicals displayed in
Scheme 3; the solid-state triple-bond stretching fre-
quencies of 2215 and 2221 cm-1 for 4a and diphenyl-
acetyene,34 respectively, in the Raman spectra differ
only slightly. This fact is a likely consequence of the
modest π-electron-accepting ability of the CtCPh group.
Conversely, because of the strong π-electron-accepting
ability of the CdO group, the vibrational data for 5b
and 5c does manifest the resonance canonical’s contri-
bution to the ground-state structure. These complexes
display strong carbon-oxygen double-bond stretches of
1634 and 1636 cm-1, respectively, and are considerably
less than those reported for a broad class of substituted
organic benzophenones.32,35a For example, the lowest
ν(CdO) is observed at 1650 cm-1 for 4-(dimethyamino)-
benzophenone, measured in a carbon tetrachloride solu-
tion. However, we cannot completely exclude the pos-
sibility that structural distortions, regarding the
R-C(O)-R angle, are the root cause of the reduction in
ν(CdO) for 5b and 5c.35b
What implications does the aromatic 13C-NMR data
of these bimetallic complexes and the good correlation
with σR have in regard to our understanding of the
nature of the palladium-carbon bond? In analogy to
organic systems, these data indicate the 13C chemical
shift of Cipso is linearly related to the amount of
π-electron density of the carbon bound to the palladium
center. Indeed, the π contribution to the Pd-C(aryl)
bond is electronically tunable.
It is widely accepted that changes in the local para-
magnetic term dominate the observed 13C-NMR shift.33,36
Our data indicate the strong influence of the π-electron
density to changes in the local paramagnetic shielding
term for Cipso. Failure of this model in predicting Cipso
can likely be expected for studies where the para group
differs only slightly, for example, between 5b and 5c.
In this case, other subtle local and nonlocal paramag-
netic, diamagnetic, and anisotropic term contributions
would be expected to play an important role in deter-
mining the Cipso chemical shift. Given the true origin
of the local paramagnetic term, the electronic excitation
energies, it would be interesting to examine the elec-
tronic spectra of these palladium bimetallics and at-
tempt to correlate transition energies, for example the
metal-to-ligand charge-transfer bands, with the 13C-
NMR data.
π-acceptor groups. From this work, we conclude that
the linear bimetallic complexes 1a , 2a , 2b, 2b, 3a , and
4a should prove to be functional building blocks for a
new class of electronically tunable organometallic su-
pramolecular “squares”. We can also control the solu-
bility properties of the desired macrocycles by imple-
menting either the PPh3 or PEt3 derivatives. Fur-
thermore, the rich chemistry of alkynes opens the door
to the exploration of a plethora of possible reactions for
those macrocycles implementing unit 4a . Utilization of
the benzophenone derivatives 5a , 5b, and 5c, in contrast
to their linear cousins, are expected to be useful linkages
in the design and self-assembly of nanoscale supramo-
lecular hexagons. These latter species are currently the
focus of considerable study in our laboratory.
Exp er im en ta l Section
Gen er a l Meth od s. All experiments were performed under
an inert atmosphere of nitrogen utilizing standard Schlenk
and glovebox techniques. Solvents used in the reactions were
of reagent or HPLC grade and purified in the following
manner: benzene was distilled from sodium/potassium (2:1)
alloy after employing the recommended workup, toluene was
distilled from sodium metal, diethyl ether was distilled from
sodium/benzophenone, triethylamine was distilled from potas-
sium hydroxide, and hexanes and methylene chloride were
distilled from calcium hydride.37 All NMR solvents (CD2Cl2
and CDCl3) were stored over 4 Å molecular sieves in the dry
glovebox prior to use.
Palladium tetrakis(triphenylphosphine) was purchased from
Lancaster Chemical Co. and used as received. The solids
1-bromo-4-iodobenzene, 1,4-diiodobenzene, and 4,4′-dibro-
mobenzophenone were purchased from Aldrich Chemical Co.
and used as received. 4,4′-Diiodobiphenyl, technical grade,
was purchased from the Aldrich Chemical Co. and purified
by recrystallization from chloroform. Platinum tetrakis(tri-
phenylphosphine) (Pt(PPh3)4), platinum tetrakis(triethylphos-
phine) (Pt(PEt3)4),38 and 4,4′′-diiodo-p-terphenyl39 were pre-
pared by the standard literature procedures. The latter diiodo
compound was recrystallized twice at room temperature from
hot (∼140 °C) 1,1,2,2-tetrachloroethane and then sublimed
(∼0.1 mmHg, 190 °C) prior to use. Finally, 4,4′-diiodoben-
zophenone was prepared analogously to the literature proce-
dure employed in the synthesis of bis(4-pyridyl)ketone.40
All NMR spectra were obtained at room temperature with
a
Varian XL-300 or VXR-500 spectrometer employing a
deuterium sample as an internal lock unless noted otherwise.
The operating frequencies of the former spectrometer for the
1H, 13C{1H}, 31P{1H}, and 19F{1H} NMR spectra were 300.0,
75.4, 121.4, and 282.3 MHz, respectively. For the latter
1
spectrometer, the operating frequencies of the H and 13C{1H}
Con clu sion s
NMR spectra were 499.8 and 125.7 MHz, respectively. The
1H chemical shifts are reported relative to the residual
nondeuterated solvent of CD2Cl2 (5.32 ppm) or CDCl3 (7.27
ppm). The 13C{1H} chemical shifts are reported relative to
This study demonstrates that the reaction of several
4,4′-dibromo or 4,4′-diiodo aromatics with M(PR3)4 is an
effective methodology for the synthesis of several elec-
tronically unique bis(trans-M(PR3)2X)aryl units. The
degree of π-electron interaction between the metal and
aryl unit has been gauged by 13C NMR spectroscopy and
is found to be significant in the systems with good
1
CDCl3 (77.0 ppm) or CD2Cl2 (54.0 ppm). In contrast to the H
and 13C{1H} spectra, the 31P{1H} and 19F{1H} NMR spectra
were referenced to sealed external standards of 85% phospho-
ric acid and fluorotrichloromethane, respectively.
Mass spectra were obtained with a Finnigan MAT 95 mass
spectrometer with a Finnigan MAT ICIS II operating system
under positive ion fast atom bombardment (FAB) conditions
at 8 keV. 3-Nitrobenzyl alcohol was used as a matrix, in
(33) Mann, B. E.; Taylor, B. F. 13C NMR Data for Organometallic
Compounds; Academic Press: New York, 1981.
(34) Schrader, B. Raman/ Infrared Atlas of Organic Compounds;
VCH Publishers: New York, 1989.
(35) (a) Laurence, C.; Berthelot, M. J . Chem. Soc., Perkins Trans.
II 1979, 98. (b) Bellamy, L. J . The Infrared Spectra of Complex
Molecules; Chapman and Hall: New York, 1980; Vol. 2, Chapter 5.
(37) Perrin, D. D.; Armarego, W. L. F. Purification of Laboratory
Chemicals; Pergamon Press: Tarrytown, NY, 1988.
(38) Ugo, R.; Cariati, F.; La Monica, G. Inorg. Synth. 1990, 28, 123.
(39) Unroe, M. R.; Reinhardt, B. A. J . Synthesis 1987, 981.
(40) Minn, F. L.; Trichilo, C. L.; Hurt, C. R.; Filipescu, N. J . Am.
Chem. Soc. 1970, 92, 3600.
(36) Harris, R. K. Nuclear Magnetic Resonance Spectroscopy:
A
Physicochemical View; Longman Scientific & Technical: Essex, U.K.,
1986, Chapter 8.

1904 Organometallics, Vol. 16, No. 9, 1997
Manna et al.
CH2Cl2 or CHCl3 as the solvent; polypropylene glycol and
cesium iodide were used as a reference for peak matching.
FT-Raman spectra were recorded as crystalline solids in
capillary tubes using a Nicolet 950 spectrometer (Nd:YVO4
source λ ) 1064 nm, 2-6 mW) at 4 cm-1 resolution. The
Raman signal was detected with an Applied Detector Corp.
high-purity germanium-diode detector (model 203NR). Data
reduction was accomplished using Omnic software (version
1.1).
Elemental analysis were performed by Oneida Research
Service, Whitesboro, NY or Atlantic Microlab Inc., Norcross,
GA. IR spectra were obtained with a Mattson Polaris FT-IR
spectrometer at 2 cm-1 resolution. Reported melting points
were obtained with a Mel-Temp capillary apparatus and are
uncorrected.
the glovebox with 1.0 equiv of the dihalo aromatic and 2.2
equiv of M(PPh3)4. To the flask, now attached to a Schlenk
line, was added a measured volume of dry toluene. The
suspension was then heated in the dark at the prescribed
temperature for the noted period of time. The suspension
transformed to a clear yellow solution, then back to a white
or off-white suspensionsindicative of product formation. Fol-
lowing reaction completion, the suspension was cooled to room
temperature and 10-15 mL of diethyl ether were added with
stirring to complete precipitation of the product. The solvents
were then removed by cannula filtration, and the solid white
product was subsequently washed with ether (3 × 15 mL) to
remove PPh3 and dried in vacuo. Note: The reaction can also
be performed with benzene as the solvent, although this
generally results in lower, inconsistent yields.
4,4′-Dibr om otola n e. To a Schlenk flask containing freshly
distilled NEt3 (40 mL) were added 1-bromo-4-ethynylbenzene
(0.98 equiv, 0.674 g, 2.38 mmol)41 and 1-bromo-4-iodobenzene
(1.00 equiv, 0.440 g, 2.43 mmol). The catalysts Pd(PPh3)2Cl2
(0.034 g) and CuI (0.005 g) were then added, with stirring, to
the solution. The reaction was stirred for 24 h at room
temperature in the dark. Purification of the desired product
was successfully achieved by employing the standard workup.42
Yield: 0.190 g (26%); mp 182-184 °C (lit.42,43 182-184 °C);
4,4′-Bis(tr a n s-P t(P P h 3)2I)bip h en yl (2b). Reagent or sol-
vents (quantity): Pt(PPh3)4 (0.350 g, 0.281 mmol), 4,4′-di-
iodobiphenyl (0.053 g, 0.131 mmol), toluene (11 mL). Tem-
perature/time: 88-90 °C/24 h. Yield: 0.210 g (87%); mp 295-
297 °C (dec); IR (thin film, CD2Cl2, cm-1) 3055 (C-H), 1580,
1484, 1435 (Ar), 1097, 997; 1H NMR (CD2Cl2) δ 7.55 (m, 24H,
Ho-P), 7.33 (t, 12H, 3J HH ) 7.1 Hz, Hp-P), 7.24 (m, 24H, Hm-
3
3
P), 6.56 (d, 4H, J HH ) 8.1 Hz, J HPt ) 55 Hz, Ho-Pt), 6.01 (d,
4H, 3J HH ) 8.1 Hz, Hm-Pt); 13C{1H} NMR (CD2Cl2) δ 144.1 (t,
2J CP ) 8.4 Hz, Ci-Pt), 136.2 (br s, Co-Pt), 135.5 (t, J CP ) 6.0
1
Raman (solid, cm-1) 2215 (CtC); H NMR (CDCl3) δ 7.50 (d,
3
3
2
4H, J HH ) 8.8 Hz, Ho), 7.39 (d, 4H, J HH ) 8.8 Hz, Hm).
1,4-Bis(tr a n s-P t(P Et3)2I)ben zen e (1a ). A 25 mL round-
bottom Schlenk flask was loaded in the glovebox with 1,4-
diiodobenzene (47 mg, 0.143 mmol) and 2.1 equiv of Pt(PEt3)4
(200 mg, 0.300 mmol). To the flask, now attached to a Schlenk
line, was added 10 mL of dry toluene. The mixture was then
heated in the dark at 55 °C for 27-30 h to afford a clear yel-
low solution. The toluene was then removed in vacuo, and
the remaining off-white solid residue was washed with di-
ethyl ether and filtered under nitrogen. Yield: 0.155 g (91%);
mp 206-211 °C (dec); IR (thin film, CD2Cl2, cm-1) 2959, 2931
(C-H), 1448, 1456 (Ar); 1H NMR (CD2Cl2) δ 6.86 (m, 4H, 3J HH
) 7.3 Hz, Ho-Pt), 1.80 (m, 24H, PCH2), 1.06 (pseudo quin,
36H, PCH2CH3); 13C{1H} NMR (CD2Cl2) δ 144.1 (t, 1J CPt ) 933
Hz, Co-P), 131.9 (t, J CP ) 28.4 Hz, J CPt ) 29.0 Hz, Ci-P),
130.3 (s, Cp-P), 128.8 (s, Cp-Pt), 128.0 (t, J CP ) 5.2 Hz, Cm-
3
P), 126.6 (s, J CPt ) 70.4 Hz, Cm-Pt); 31P{1H} NMR (CD2Cl2)
1
δ 24.3 (s, J PPt ) 3095 Hz). FAB-MS m/z (ion, relative
intensity); 1845 (M+, 22), 1718 (M - I+, 68), 1456 (M - I -
PPh3+, 100). Anal. Calcd for C84H68I2P4Pt2: C, 54.67; H, 3.71.
Found: C, 55.17; H, 3.95.
4,4′-Bis(tr a n s-P d (P P h 3)2I)b ip h en yl (2c). Reagent or
solvents (quantity): Pd(PPh3)4 (0.500 g, 0.433 mmol), 4,4′-
diiodobiphenyl (0.0836 g, 0.206 mmol), toluene (10 mL). Tem-
perature/time: 50-55 °C/8 h. Yield: 0.316 g (92%); mp 178-
184 °C (dec); IR (thin film, CD2Cl2; cm-1) 3055 (C-H), 1580,
1484, 1435 (Ar), 1097, 997; 1H NMR (CD2Cl2) δ 7.52 (m, 24H,
Ho-P), 7.35 (t, 12H, 3J HH ) 7.2 Hz, Hp-P), 7.24 (m, 24H, Hm-
P), 6.54 (d, 4H, 3J HH ) 8.1 Hz, Ho-Pd), 6.12 (d, 4H, 3J HH ) 7.8
Hz, Hm-Pd); 13C{1H} NMR (CD2Cl2) δ 156.5 (t, 2J CP ) 4.7 Hz,
Ci-Pd), 136.8 (s, Cp-Pd), 136.0 (t, 3J CP ) 4.8 Hz, Co-Pd), 135.4
(t, J CP ) 6.1 Hz, Co-P), 132.7 (t, J CP ) 23 Hz, Ci-P), 130.2 (s,
Cp-P), 127.1 (t, J CP ) 5.0 Hz, Cm-P), 127.2 (s, Cm-Pd); 31P{1H}
NMR (CD2Cl2) δ 25.5 (s). Anal. Calcd for C84H68I2P4Pd2: C,
60.49; H, 4.11. Found: C, 60.59; H, 4.15.
2
Hz, J CP ) 7.1 Hz, Ci-Pt), 137.2 (m, Co-Pt), 15.73 (pseudo
quin, J CP ) 18 Hz, PCH2), 8.29 (pseudo t, J CP ) 13 Hz, PCH2-
CH3); 31P{1H} NMR (CD2Cl2) δ 10.3 (s, 1J PPt ) 2787 Hz). FAB-
MS m/z (ion): 1192 (M+). Anal. Calcd for C30H64I2P4Pt2: C,
30.21; H, 5.41. Found: C, 30.32; H, 5.37.
4,4′-Bis(tr a n s-P t(P Et3)2I)bip h en yl (2a ). A 25 mL round-
bottom Schlenk flask was loaded in the glovebox with 4,4′-
diiodobiphenyl (58 mg, 0.143 mmol) and 2.1 equiv of Pt(PEt3)4
(200 mg, 0.300 mmol). To the flask, now attached to a Schlenk
line, was added 10 mL of dry toluene. The mixture was then
heated in the dark at 55 °C for 27-30 h to afford a clear yellow
solution. The toluene was then removed in vacuo, and the
remaining off-white solid residue was washed with hexane and
filtered under nitrogen. Yield: 0.157 g (93%); mp 198-211
°C (dec); IR (thin film, CD2Cl2, cm-1) 3058, 3004 (C-H), 1581,
4,4′′-Bis(tr a n s-P t(P P h 3)2I)-p-ter p h en yl (3a ). Reagent or
solvents (quantity): Pt(PPh3)4 (0.400 g, 0.321 mmol), 4,4′′-di-
iodo-p-terphenyl (0.072 g, 0.149 mmol), toluene (12 mL). Tem-
perature/time: 92-93 °C/22 h. Yield: 0.263 g (92%); mp 334-
337 °C (dec); 1H NMR (CD2Cl2) δ 7.52 (m, 24H, Ho-P), 7.40 (t,
12H, 3J HH ) 7.2 Hz, Hp-P), 7.31 (m, 24H, Hm-P), 7.22 (s, γ-H),
6.54 (d, 4H, 3J HH ) 8.4 Hz, 3J HPt ) 56 Hz, Ho-Pt), 6.32 (d, 4H,
1
3J HH ) 8.4 Hz, Hm-Pt); 31P{1H} NMR (CDCl3) δ 24.0 (s, J PPt
1
3
1470, 1455 (Ar); H NMR (CD2Cl2) δ 7.33 (d, 4H, J HH ) 8.1
) 3075 Hz). Anal. Calcd for C90H72I2P4Pt2: C, 56.26; H, 3.78.
Found: C, 56.26; H, 3.38. Limited solubility of this complex
prevented a 13C{1H} NMR spectrum with good signal-to-noise
from being acquired.
3
3
Hz, J HPt ) 66 Hz, Ho-Pt), 7.25 (d, 4H, J HH ) 8.1 Hz, Hm-
Pt), 1.80 (m, 24H, CH2), 1.06 (pseudo quin, 36H, PCH2CH3);
13C{1H} NMR (CDCl3) δ 142.5 (t, J CP ) 8.9 Hz, J CPt ) 945
2
1
2
Hz, Ci-Pt), 136.9 (s, J CPt ) 40 Hz, Co-Pt), 134.8 (s, Cp-P),
4,4′-Bis(tr a n s-P d (P P h 3)2Br )tola n e (4a ). Reagent or sol-
vents (quantity): Pd(PPh3)4 (0.400 g, 0.346 mmol), 4,4′-
dibromotolane (0.054 g, 0.161 mmol), toluene (11 mL). Tem-
perature/time: 70 °C/24 h. Yield: 0.220 g (85%); mp 246-
250 °C (dec); Raman (solid, cm-1) 2215 (CtC); 1H NMR (CD2-
3
125.5 (s, J CPt ) 77 Hz, Cm-Pt), 15.73 (pseudo quin, J CP ) 17
Hz, PCH2), 8.29 (pseudo t, J CP ) 12 Hz, PCH2CH3); 31P{1H}
1
NMR (CD2Cl2) δ 11.0 (s, J PPt ) 2730 Hz). FAB-MS m/z (ion,
relative intensity): 1268 (M+, 40), 1142 (M - I+, 100). Anal.
Calcd for C36H68I2P4Pt2: C, 34.08; H, 5.40. Found: C, 34.34;
H, 5.30.
3
Cl2) δ 7.52 (m, 24H, Ho-P), 7.39 (t, 12H, J HH ) 7.2 Hz, Hp-
3
P), 7.29 (m, 24H, Hm-P), 6.63 (d, 4H, J HH ) 8.2 Hz, Ho-Pd),
Gen er a l P r oced u r e for th e Syn th esis of Bis(tr a n s-
M(P P h 3)2X)a r yl (M ) P t or P d ; X ) I or Br ) Com p lexes.
Typically, a 25 mL round-bottom Schlenk flask was loaded in
3
6.30 (d, 4H, J HH ) 8.2 Hz, Hm-Pd); 13C{1H} NMR (CD2Cl2) δ
2
158.2 (t, J CP ) 3.4 Hz, Ci-Pd), 136.5 (t, J CP ) 5.1 Hz, Co-
Pd), 135.2 (t, J CP ) 6.3 Hz, Co-P), 131.9 (t, J CP ) 22.9 Hz,
Ci-P), 130.6 (s, Cm-Pd), 130.4 (s, Cp-P), 128.4 (t, J CP ) 5.4
Hz, Cm-P), 117.6 (s, Cp-Pd), 88.5 (s, CtC); 31P{1H} NMR (CD2-
Cl2) δ 24.7 (s). Anal. Calcd for C86H68Br2P4Pd2: C, 64.64; H,
4.29. Found: C, 64.50; H, 4.34.
(41) Dawson, D. A.; Reynolds, W. F. Can. J . Chem. 1975, 53, 373.
(42) Misumi, S.; Kuwana, M.; Nakagawa, M. Bull. Chem. Soc. J pn.
1962, 35, 135.
(43) Barker, H. J .; Slack, R. J . Chem. Soc. 1944, 612.

Bimetallic Platinum and Palladium Complexes
Organometallics, Vol. 16, No. 9, 1997 1905
4,4′-Bis(tr a n s-P t(P P h 3)2I)ben zop h en on e (5a ). Reagent
or solvents (quantity): Pt(PPh3)4 (0.300 g, 0.241 mmol), 4,4′-
diiodobenzophenone (0.0498 g, 0.115 mmol), toluene (12 mL).
Temperature/time: 86 °C/16 h. Yield: 0.193 g (90%); mp 300-
304 °C (dec); IR (thin film, CD2Cl2, cm-1) 3057 (C-H), 1637
Calcd for C85H68Br2OP4Pd2: C, 64.37; H, 4.32. Found: C,
64.22; H, 4.36.
X-r a y An a lysis of 2a . Colorless, X-ray quality crystals of
2a were grown from a concentrated toluene/ether solution at
-20 °C. A crystal of dimensions 0.38 × 0.38 × 0.36 mm was
immersed in epoxy and glued onto a glass fiber prior to
mounting on a Enraf-Nonius CAD diffractometer. Unit-cell
parameters for 2a were determined from the accurate room
temperature least-square refinement of ∼25 centered reflec-
tions with 2θ values between 20° and 30°. The space group,
Fdd2 (No. 43), was unambiguously determined from the
systematic absences in the data. A variable scan speed,
employing the θ-2θ scan technique, was used for the data
collection of 2133 reflections with Mo KR radiation (0.710 73
Å). No decay in the data was observed for the standard
reflections. Raw data were corrected for Lorentz, polarization,
and absorption effects. The latter semiempirical correction
was applied after analyzing the intensity of several standard
reflections based on a series of ψ scans.
The structure was solved by the Patterson method utilizing
the SHELXTL software package. All non-hydrogen atoms
were refined anisotropically; whereas, hydrogen atoms were
placed in calculated positions with the isotropic thermal
parameter riding on that of the attached carbon. Scattering
factors, ∆f ′ and ∆f ′′′, were taken from the International Tables
for X-ray Crystallography. The structure was refined to values
of 2.87% (Rf) and 7.62 (Rwf) based full-matrix least-squares
refinement on F2 of 2133 reflections (I > 2σ(I)) and 197
parameters.
1
(CdO), 1963, 1897, 1575, 1480 (Ar); H NMR (CD2Cl2) δ 7.57
3
(m, 24H, Ho-P), 7.34 (t, 12H, J HH ) 7.3 Hz, Hp-P), 7.26 (m,
3
3
24H, Hm-P), 6.74 (d, 4H, J HH ) 8.4 Hz, J HPt ) 55 Hz, Ho-
Pt), 6.36 (d, 4H, J HH ) 8.4 Hz, Hm-Pt); 13C{1H} NMR (CD2-
3
Cl2) δ 196.1 (s, CdO), 156.2 (t, J CP ) 8.1 Hz, Ci-Pt), 136.0 (br
s, Co-Pt), 135.5 (t, J CP ) 5.9 Hz, Co-P), 131.7 (s, Cp-Pt), 131.5
3
(t, J CP ) 28.6 Hz, Ci-P), 130.5 (s, Cp-P), 129.3 (s, J CPt ) 71
Hz, Cm-Pt), 128.1 (t, J CP ) 5.3 Hz, Cm-P); 31P{1H} NMR (CD2-
1
Cl2) δ 22.3 (s, J PPt ) 3040 Hz). FAB-MS m/z (ion, relative
intensity): 1874 (M + H+, 25), 1746 (M + H - I+, 100), 1483
(M + H - I - PPh3+,100). Anal. Calcd for C85H68I2OP4Pt2:
C, 54.50; H, 3.66. Found: C, 54.89; H, 3.56.
4,4′-Bis(tr a n s-P d (P P h 3)2I)ben zop h en on e (5b). Reagent
or solvents (quantity): Pd(PPh3)4 (0.400 g, 0.346 mmol), 4,4′-
diiodobenzophenone (0.0715 g, 0.165 mmol), toluene (12 mL).
Temperature/time: 55-60 °C/20 h. Yield: 0.239 g (85%); mp
178-182 °C (dec); IR (thin film, CD2Cl2, cm-1) 3060 (C-H),
1
1634 (CdO), 1966, 1569, 1435 (Ar); H NMR (CD2Cl2) δ 7.52
3
(m, 24H, Ho-P), 7.33 (t, 12H, J HH ) 7.2 Hz, Hp-P), 7.26 (m,
3
24H, Hm-P), 6.72 (d, 4H, J HH ) 8.3 Hz, Ho-Pd), 6.43 (d, 4H,
3J HH ) 8.3 Hz, Hm-Pd); 13C{1H} NMR (CD2Cl2) δ 196.0 (s,
CdO), 169.6 (t, J CP ) 2.8 Hz, Ci-Pd), 135.6 (t, J CP ) 4.8 Hz,
Co-Pd), 135.3 (t, J CP ) 6.3 Hz, Co-P), 132.4 (t, J CP ) 23.7 Hz,
Ci-P), 130.4 (s, Cp-P), 129.3 (s, Cm-Pd), 128.3 (t, J CP ) 5.1
Hz, Cm-P), obscured (s, Cp-Pd); 31P{1H} NMR (CDCl3) δ 23.8
(s). FAB-MS m/z (ion, relative intensity): 1697 (M + H+, 7),
1434 (M + H - PPh3+, 13), 1308 (M + H - I - PPh3+,100).
Anal. Calcd for C85H68I2OP4Pd2: C, 60.20; H, 4.04. Found:
C, 60.20; H, 4.20.
Ack n ow led gm en t. Financial support from the NSF
(CHE-9529093) is gratefully acknowledged. We thank
J ohnson-Matthey for a generous loan of K2PtCl4 and
PtCl2. We are grateful to A. M. Arif (University of Utah)
for his assistance with the crystallographic analysis of
2a and K. D. J ohn and M. D. Hopkins (University of
Pittsburgh) for obtaining the Raman spectra. We thank
Dr. J . H. Ryan for helpful discussions.
4,4′-Bis(tr a n s-P d (P P h 3)2Br )b en zop h en on e (5c). Re-
agent or solvents (quantity): Pd(PPh3)4 (0.300 g, 0.260 mmol),
4,4′-dibromobenzophenone (0.0421 g, 0.124 mmol), toluene (10
mL). Temperature/time: 60-65 °C/24 h. Yield: 0.183 g
(92%); mp 194-197 °C (dec); IR (thin film, CD2Cl2, cm-1) 3078,
3049 (C-H), 1636 (CdO), 1566, 1480 (Ar); 1H NMR (CDCl3) δ
7.55 (m, 24H, Ho-P), 7.32 (t, 12H, 3J HH ) 7.5 Hz, Hp-P), 7.25
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal
structure data and structure refinement, calculated positional
parameters and U for the hydrogen atoms, non-hydrogen
positional parameters and anistropic thermal parameters,
complete bond lengths and angles, and torsional angles (8
pages). Ordering information is given on any current mast-
head page.
3
(m, 24H, Hm-P), 6.72 (d, 4H, J HH ) 8.1 Hz, Ho-Pd), 6.49 (d,
4H, 3J HH ) 8.2 Hz, Hm-Pd); 13C{1H} NMR (CDCl3) δ 196.2 (s,
2
CdO), 167.0 (t, J CP ) 3.6 Hz, Ci-Pd), 135.5 (t, J CP ) 4.7 Hz,
Co-Pd), 134.9 (t, J CP ) 6.2 Hz, Co-P), 131.8 (s, Cp-Pd), 131.3
(t, J CP ) 23.1 Hz, Ci-P), 130.1 (s, Cp-P), 128.9 (s, Cm-Pd),
128.1 (t, J CP ) 5.1 Hz, Cm-P); 31P{1H} NMR (CDCl3) δ 25.0
(s). FAB-MS m/z (ion, relative intensity): 1603 (M + H+, 100),
1523 (M + H - Br+, 25), 1444 (M + H - 2Br+, 33). Anal.
OM961049+