Reactions of cationic palladium(II) methyl and vinyl complexes with alkynes

Article abstract of DOI:10.1021/om9710125

[(phen)Pd(CH₃)(OEt₂)]⁺[BAr′ ₄]- (phen = 1,10 phenanthroline, Ar′ = 3,5-(CF₃)₂C₆H₃) reacts with RC=CR′ to form the η²-alkyne complexes [(phen)Pd(CH₃)(η²-RC≡CR′] ⁺[BAr′₄]^- (5a, R = R′ = SiMe₃; 5b R=C₆H₅, R′ = H). In contrast, the reaction of the diimine complexes [(ArN=C(R)C(R)=NAr)Pd(CH₃)(NCCH₃)] ⁺[BAr′₄]^- (1-3) (Ar = 2,6-(CH₃)₂C₆H₃, 2,6-(i-Pr)₂C₆H₃; R = H, CH₃, 1/2BIAN) with HC=CR′ (R′ = H, f-Bu) yielded the alkyne insertion products [(ArN=C(R)C(R)=NAr)Pd(CH=C(R)CH₃)(NCCH₃)] ⁺[BAr(Equivalent to sign)₄]^- (3) while the reaction of 1-hexyne with 1a yielded a mixture of the 2,1- and 1,2-insertion products [(N-N)Pd-(C(C₄H₉)=CHCH₃)(NCCH ₃)]⁺[BAr′₄]^- and [(N-N)Pd(CH=C(C₄H₉)(CH₃)(NCCH ₃)]⁺[BAr′₄]^-, respectively The vinyl complexes [(N-N)Pd(CH=CRCH₃)(NCCH₃)]⁺[BAr′ ₄]- react with acetylene to form the η¹-dienyl complexes [(N-N)Pd(CH=CHCH=CRCH₃)(NCCH₃)] ⁺[BAr′₄]^-, which then react with acetylene and rearrange to form the novel 5-ethyhdene-2-cyclopenten-1-yl complexes [(N-N)Pd(η³-C(CH₃)(R)C₅H₅)] ⁺[X]^-. (R = H, t-Bu; X = BAr′₄, O₃SCF₃) (8).

Full text of DOI:10.1021/om9710125

1530
Organometallics 1998, 17, 1530-1537
Rea ction s of Ca tion ic P a lla d iu m (II) Meth yl a n d Vin yl
Com p lexes w ith Alk yn es
Anne M. LaPointe† and Maurice Brookhart*
Department of Chemistry, University of North Carolina at Chapel Hill,
Chapel Hill, North Carolina 27599-3290
Received November 17, 1997
[(phen)Pd(CH3)(OEt2)]+[BAr′4]- (phen ) 1,10 phenanthroline, Ar′ ) 3,5-(CF3)2C6H3) reacts
with RCtCR′ to form the η2-alkyne complexes [(phen)Pd(CH3)(η2-RCtCR′]+[BAr′4]- (5a , R
) R′ ) SiMe3; 5b, RdC6H5, R′ ) H). In contrast, the reaction of the diimine complexes
[(ArNdC(R)C(R)dNAr)Pd(CH3)(NCCH3)]+[BAr′4]- (1-3) (Ar ) 2,6-(CH3)2C6H3, 2,6-(i-
1
Pr)2C6H3; R ) H, CH3, /2BIAN) with HCtCR′ (R′ ) H, t-Bu) yielded the alkyne insertion
products [(ArNdC(R)C(R)dNAr)Pd(CHdC(R)CH3)(NCCH3)]+[BAr′4]- (3) while the reaction
of 1-hexyne with 1a yielded a mixture of the 2,1- and 1,2-insertion products [(N-N)Pd-
(C(C4H9)dCHCH3)(NCCH3)]+[BAr′4]- and [(N-N)Pd(CHdC(C4H9)(CH3)(NCCH3)]+[BAr′4]-,
respectively. The vinyl complexes [(N-N)Pd(CHdCRCH3)(NCCH3)]+[BAr′4]- react with
acetylene to form the η1-dienyl complexes [(N-N)Pd(CHdCHCHdCRCH3)(NCCH3)]+[BAr′4]-,
which then react with acetylene and rearrange to form the novel 5-ethylidene-2-cyclopenten-
1-yl complexes [(N-N)Pd(η3-C(CH3)(R)C5H5)]+[X]-. (R ) H, t-Bu; X ) BAr′4, O3SCF3) (8).
In tr od u ction
characterized σ-acetylide complex, Rh(CtC-Ph)(nor-
bornadiene)(PPh3)2, initiates a living polymerization of
phenylacetylene, which supports the operation of a
coordination/insertion mechanism for this family of
catalysts.
Recent studies in these and other laboratories have
focused on the use of cationic Pd(II) methyl complexes
as precatalysts for olefin dimerization,8 oligomerization,
and polymerization,9,10 olefin hydrosilation and dehy-
drogenative silation,11 and ethylene/CO copolymeri-
zation.12-15 In particular, the square-planar Pd(II)
diimine complexes (1-3) are versatile precatalysts for
the homo- and copolymerization of R-olefins.9,10
The reactions of alkynes with late transition metal
hydrido, alkyl, and aryl complexes have been the subject
of much research.1 In many cases, alkyne insertion into
the metal-hydrogen or metal-carbon σ-bond occurs,
yielding a vinyl complex. Although such a reaction
represents the first step in the polymerization of alkynes
via a coordination/insertion pathway,2 there is little
mechanistic information concerning the details of such
processes for late transition metal systems.3-5 Several
rhodium- and platinum-based catalysts for the polym-
erization of alkynes have been reported,6 but the nature
of the catalyst resting state and the specific details of
the chain growth for these systems have not been
investigated. Noyori7 has reported that the well-
The goal of this work was to examine the reactivity
of the cationic methyl complexes 1-4 with alkynes in
† Current Address: Symyx Technologies, 3100 Central Expressway,
Santa Clara, CA 95051.
(1) (a) Collman, J . P.; Hegedus, L. S.; Norton, J . R.; Finke, R. G.
Principles and Applications of Organotransition Metal Complexes;
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) In some cases, it has been shown that vinyl complexes are inert
toward further insertion of alkynes, see: (a) Etienne, M.; Mathieu,
R.; Donnadieu, B. J . Am. Chem. Soc. 1997, 119, 3218. (b) Samsel, E.
G.; Norton, J . R. J . Am. Chem. Soc. 1984, 106, 5505.
(3) For examples of alkyne dimerization catalysts, see refs 3a-d.
Mechanistic studies suggest that carbon-carbon bond formation occurs
via acetylide migration to a vinyl ligand. (a) Rappert, T.; Yamamoto,
A. Organometallics 1994, 13, 4984. (b) J un, C.-H.; Lu, Z.; Crabtree, R.
H. Tetrahedron Lett. 1992, 47, 7119 (c) Bianchini, C.; Frediani, P.;
Masi, D.; Peruzini, M.; Zanobini, F. Organometallics 1994, 13, 4616.
(d) Barbaro, P.; Bianchini, C.; Peruzini, M.; Polo, A.; Zanobini, F. Inorg.
Chim. Acta 1994, 220, 5. (e) Slugovc, C.; Merciter, K.; Zobertz, E.;
Schmid, R.; Kirchner, K Organometallics 1996, 15, 3998.
(5) For examples of niobium, tantalum, molybdenum, and tungsten
alkyne polymerization catalysts which operate via metal alkylidene
intermediates, see: (a) Schrock, R. R.; Luo, S.; Lee, J . C., J r.; Zanetti,
N. C.; Davis, W. M. J . Am. Chem. Soc. 1996, 118, 3883. (b) Schlund,
R.; Schrock, R. R.; Crowe, W. E. J . Am. Chem. Soc. 1989, 111, 8004.
(c) Katz, T. J .; Ho, T.-H.; Shih, N.-Y.; Ying, Y.-C., Stuart, V. I. W. J .
Am. Chem. Soc. 1984, 106, 2658. (d) Masuda, T.; Higashimura, T. Adv.
Polym. Sci. 1987, 81, 121.
(6) (a) Furlani, A.; Napoletano, C.; Russo, M. V. J . Polym. Sci.,
Polym. Chem. Ed. 1989, 27, 75. (b) Furlani, A.; Licoccia, S.; Russo, M.
V. J . Polym. Sci., Polym. Chem. Ed. 1986, 24, 991. (c) Goldberg, Y.;
Alper, H. J . Chem. Soc., Chem. Commun. 1994, 1209. (d) Tabata, M.;
Wang, Y.; Yokota, K J . Polym. Sci., Polym. Chem. Ed. 1994, 32, 1113.
(7) Kishimoto, Y.; Eckerle, P.; Miyatake, T.; Ikariya, T.; Noyori, R.
J . Am. Chem. Soc. 1994, 116, 12131.
(8) Rix, F. C.; Brookhart, M. J . Am. Chem. Soc. 1995, 117, 1137.
(9) J ohnson, L. K.; Killian, C. M.; Brookhart, M. J . Am. Chem. Soc.
1995, 117, 6414.
(10) J ohnson, L. K.; Mecking, S.; Brookhart, M. J . Am. Chem. Soc.
1995, 117, 11664.
(4) For references to numerous examples of alkyne polymerization
by d0 early transition metal catalysts, see: (a) Gibson, H. W.; Porchan,
J . M. In Encyclopedia of Polymer Science and Engineering 2nd ed.;
Kvoschwitz, J . I., Ed.; Wiley and Sons: New York, 1984; Vol. 1, p 87.
(b) Simionescu, C. I.; Percec, V. Prog. Polym. Sci. 1982, 8, 133. (c)
Shirakawa, H.; Masuda, T.; Takeda, K. In The Chemistry of Triple-
Bonded Functional Groups; Patai, S., Ed.; Wiley: Chichester, 1994;
Suppl. C2, Chapter 17.
(11) LaPointe, A. M.; Rix, F. C.; Brookhart, M. J . Am. Chem. Soc.
1997, 119, 906.
(12) Brookhart, M.; Rix, F. C.; DeSimone, J . M.; Barborak, J . C. J .
Am. Chem. Soc. 1992, 114, 5894.
(13) Rix, F. C.; Brookhart, M.; White, P. S. J . Am. Chem. Soc. 1996,
118, 4746.
(14) Drent, E.; Budzelaar, P. H. M. Chem. Rev. 1996, 96, 663.
(15) Sen, A. Acc. Chem. Res. 1993, 26, 303.
S0276-7333(97)01012-1 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 03/18/1998

Reactions of Cationic Palladium(II) Complexes
Organometallics, Vol. 17, No. 8, 1998 1531
pling constant between the vinylic protons (J HH ) 6 Hz)
suggests that the insertion occurs with cis geometry.16
No intermediate species were observed by 1H NMR
spectroscopy. Qualitatively, the insertion of acetylene
occurs faster than the analogous insertion reaction of
ethylene.
6a can be isolated as a thermally stable orange solid
if excess acetylene is removed from the reaction mixture
prior to warming. 6a shows no evidence of isomerizing
into an η3-allyl complex or an η2-vinyl complex. When
complexes containing less bulky supporting ligands
(1b,c, 2, 4) are reacted with acetylene in CD2Cl2 at -60
°C, vinyl complexes analogous to 6a are observed by 1H
NMR spectroscopy, but these complexes are difficult to
isolate in pure form due to their rapid reaction with a
second equivalent of acetylene (see below).
B. ter t-Bu t yla cet ylen e. Complexes 1b , 2, and 3
react with tert-butylacetylene in dichloromethane at 25
°C to form the η1-vinyl complexes [(N-N)PdCHdC(t-
Bu)(CH3)(NCCH3)]+[BAr′4]- (6b-d ). From the NMR
data, it cannot be determined whether alkyne insertion
has occurred in a cis or trans fashion; however, steric
arguments, and the observed preference for cis insertion
of acetylene suggest that cis addition is likely (eq 3).
an effort to generate Pd(II) methyl alkyne adducts and
study their migratory insertion reactions, as well as to
determine whether such complexes could function as
effective alkyne oligomerization or polymerization cata-
lysts. We report here the results of these studies.
Resu lts a n d Discu ssion
1. F or m a t ion of Alk yn e Ad d u ct s. [(phen)Pd-
(CH3)(OEt2)]+[BAr′4]- (4) reacts with bis(trimethylsilyl)-
acetylene to form the η2-alkyne adduct [(phen)-
Pd(CH3)(η2-Me3SiCtCSiMe3)]+[BAr′4]- (5a ) (eq 1). 5a
(1)
is a thermally stable, colorless crystalline solid and is
moderately air- and water-stable. No evidence for
migratory insertion of alkyne into the palladium-
methyl bond was observed.
The reaction of [(phen)Pd(CH3)(OEt2)]+[BAr′4]- with
phenylacetylene at -78 °C in CD2Cl2 yielded a complex
whose 1H NMR spectrum was consistent with the
formulation [(phen)Pd(CH3)(η2-C6H5CtCH)]+[BAr′4]-
(5b). In the presence of excess phenylacetylene, ex-
change between free and coordinated phenylacetylene
was observed at -60 °C, as evidenced by a broadening
of the coordinated PhCtCH peak (5.05 ppm). CD2Cl2
solutions of 5b were unstable above -40 °C, transform-
ing into an unidentifiable mixture of products.
The diimine complexes, [(N-N)Pd(CH3)(NCCH3)]+-
[BAr′4]- (1-3), did not react with bis(trimethylsilyl)-
acetylene or diphenylacetylene, perhaps for steric rea-
sons. Less hindered alkynes reacted rapidly with 1-3
to insert into the Pd-CH3 bond. This will be discussed
in the next section.
Complexes 6b-d are thermally stable solids and show
no evidence of converting into η3-allyl or η2-vinyl
complexes.
C. 1-Hexyn e. Complexes 1a -c, 2, and 3 were
allowed to react with 1-hexyne (0.8 equiv) in CDCl3 at
25 °C, eq 4. A mixture of the 1,2-insertion product [(N-
2. Migr a tor y In ser tion of Alk yn es. A. Acety-
len e. The reaction of 3a with acetylene in CD2Cl2 at
-60 °C yields the η1-vinyl complex [(Ar2BIAN)Pd-
(CHdCHCH3)(NCCH3)]+ (6a ), eq 2. The vincinal cou-
N)Pd(CHdC(C4H9) (CH3))(NCCH3)]+ and the 2,1-inser-
tion product [(N-N)Pd(C(C4H9)dCHCH3)(NCCH3)]+ was
(16) Friebolin, H. Basic One- and Two-Dimensional NMR Spectros-
copy, 2nd ed.; VCH: New York, 1993.
6a
(2)

1532 Organometallics, Vol. 17, No. 8, 1998
LaPointe and Brookhart
Ta ble 1. Liga n d In flu en ce on th e Regioch em istr y of th e Rea ction of 1-Hexyn e w ith
[(N-N)P d (CH3)(NCCH3)]+[BAr ′4]- (CDCl3, 25 °C)
formed.17 The relative amounts of the two insertion
products are shown in Table 1.
(entries 3-5) or there is a bulky substituent on the
alkyne (eq 3), 1,2-insertion is favored. If the alkyne
must lie approximately in the square plane formed by
the metal and the diimine ligand for migratory insertion
to occur (eq 5), then the observed preference for 1,2-
insertion when the alkyne substituents and/or the
diimine are bulky can be explained by steric repulsion
between the alkyne substituent R and the aryl substit-
uents of the diimine disfavoring the 2,1-insertion.
For a given ligand backbone (complexes 1a -c), the
percentage of 1,2-insertion increases as the steric
demands of the ligand aryl substituents increase (2,6-
(i-Pr)2C6H3 > 2,6-(CH3)2C6H3 > 4-CH3C6H4). Likewise,
for a given aryl substituent (2,6-(i-Pr)2C6H3), the per-
centage of 1,2-insertion increases as the steric demand
of the ligand backbone increases (1 > 3 . 2).
The results with 1-hexyne and tert-butylacetylene
suggest that the regiochemistry of alkyne insertion is
governed by the steric demands of both the metal center
and the alkyne. 2,1-Insertion is favored when there is
little steric hindrance (entries 1 and 2), but when there
is substantial steric congestion at the metal center
There have been several studies on the insertion of
alkynes into cyclometalated Ni(II) and Pd(II)
complexes.18-23 For these neutral complexes, alkyne
insertion occurs only at 10 °C. The alkyne insertion
(18) Sutter, J .-P.; Pfeffer, M.; De Cian, A.; Fischer, J . Organome-
tallics 1992, 11, 386.
(17) In the presence of excess 1-hexyne, the vinyl complexes react
to form the second insertion products as a mixture of regioisomers.
Qualitatively, the 1,2-insertion products reacted more rapidly than the
2,1-insertion products; the second insertion reactions were significantly
slower than the first insertion reactions. For this reason, a slight deficit
(0.8 equiv) of 1-hexyne was used.
(19) Ryabov, A. D.; van Eldik, R.; Le Borgne, G.; Pfeffer, M.
Organometallics 1993, 12, 1386.
(20) Martinez, M.; Muller, G.; Panyella, D.; Rocamora, M.; Solans,
X.; Font-Bardia, M. Organometallics 1995, 14, 5552.
(21) Dupont, J .; Pfeffer, M.; Daran, J .-C.; Gouteron, J . J . Chem. Soc.,
Dalton Trans. 1988, 2421.

Reactions of Cationic Palladium(II) Complexes
Organometallics, Vol. 17, No. 8, 1998 1533
revealed that a CH2 group was present in the fragment
resulting from the coupled alkyne, suggesting that
isomerization had occurred. However, the connectivity
of the incorporated alkynes was not readily determined
from the spectral data alone.
The connectivity of the coupled alkyne fragment in
8d was determined by X-ray crystallography; however,
the structure was disordered and accurate bond dis-
tances could not be determined. As shown in Scheme
1, the three alkyne fragments have coupled to form a
5-ethylidene-2-cyclopenten-1-yl fragment, which coor-
dinates to the metal in an allylic fashion. The exact
position of the double bond could not be determined from
the X-ray data.
(5)
reactions reported here occur at significantly lower
temperatures (-60 °C); this enhanced reactivity is
attributed to the higher electrophilicity of the cationic
Pd(II) complexes.
The structural information provides an explanation
for the unusual features observed in the 1H NMR
spectra. The two signals coupled to each other with J HH
) 24 Hz are the methylenic protons of the cyclopenta-
3. Rea ction s of [(N-N)P d (CHdCHR)(NCCH3)]+-
[BAr ′4]- (R ) H, t-Bu ) w ith Alk yn es. The reactions
of the η1-vinyl complexes with acetylene were investi-
gated by low-temperature 1H NMR spectroscopy. At
-20 °C, 6b reacts with acetylene to form a new product
2
dienyl ring; high J HH values have been observed for
hydrogens of an sp3-hybridized carbon adjacent to a
1
vinylic center.16 The H and COSY NMR spectra of 8a
1
whose H NMR spectrum is consistent with the formu-
reveal that the methylenic protons exhibit weak cou-
pling to only one proton on the noncoordinated double
bond. No coupling of the methylenic protons to the
allylic proton was observed, suggesting that the con-
nectivity is best represented by 8 rather than 8′.
One possible mechanism for the formation of 8 is
shown in Scheme 2. The first and second insertion of
acetylene have been directly observed. Following the
insertion of the third equivalent of acetylene, the next
step is intramolecular cyclization resulting from migra-
tory insertion of the pendant double bond into the Pd-C
bond. â-Hydride elimination would yield a fulvene
complex, which undergoes rapid rearrangement to form
8 (Scheme 2). The fact that the third insertion product
cannot be observed suggests that the intramolecular
cyclization and rearrangement are rapid relative to the
alkyne insertion reactions.
lation [(N-N)Pd(CHdCHCHdCH(t-Bu)(NCCH3)]+-
[BAr′4]- (7). Qualitatively, the insertion of acetylene
into the Pd-vinyl bond is slower than the insertion of
acetylene into the Pd-methyl bond. However, quanti-
tative measurements were not possible since the forma-
tion of 7 is competitive with the formation of another
product, 8 (eq 6).
A similar transformation has recently been reported
by Roper and co-workers.24 The hydride complexes
MHCl(CO)(PPh3)2 (M ) Ru, Os) react with 3 equiv of
acetylene to form the 5-methylene-2-cyclopenten-1-yl
complexes (eq 7). The connectivity of the coupled alkyne
In the presence of excess acetylene at -40 °C, 7 is
eventually converted into 8a . A variety of complexes
with the same connectivity as 8a can be more conve-
niently prepared by purging CH2Cl2, Et2O, or CH3CN
solutions of 1a -c, 2-4 , or 6a -d with acetylene at 25
°C. 8a -d are isolated as highly crystalline, air- and
water-stable solids whose colors range from deep green
to deep purple and red. 1H and 13C NMR spectroscopy
and elemental analyses revealed that CH3CN was not
present in 8a -d and that a total of 3 equiv of alkyne
was incorporated. Furthermore, the connectivity of the
coupled alkyne fragment was similar in all of the
complexes. In particular, one unusual feature was
fragment in the Ru and Os systems is similar to that
proposed for 8.
On the basis of the proposed mechanism for formation
of 8, we investigated whether the intramolecular cy-
clization was disfavored in the presence of more strongly
coordinating neutral ligands or counterions; such ligands
might bind strongly enough to the metal to inhibit
formation of the chelate or allyl complexes. All attempts
to prevent formation of 8 by changing to a coordinating
solvent (CH3CN, THF) or switching to a more coordi-
nating counterion (triflate) were unsuccessful. Like-
wise, lowering the reaction temperature (to increase the
1
noted in the H and 13C NMR spectra. Two signals (1H
each) were observed between 2.8 and 3.0 ppm, which
were coupled to each other with an extremely high
geminal coupling constant (J HH ) 24 Hz). 1H and COSY
spectra revealed that these protons exhibit a very weak
coupling with one vinylic proton. 13C NMR spectroscopy
(22) Albert, J .; Granell, J .; Sales, J .; Solans, X. J . Organomet. Chem.
1989, 379, 177.
(23) . Tao, W.; Silverberg, L. J .; Rheingold, A. L.; Heck, R. F.
Organometallics 1989, 8, 2550.
(24) Irvine, G. J .; Roper, W. R.; Wright, L. J . 213th National Meeting
of the American Chemical Society, San Franscisco, CA, April 1997.

1534 Organometallics, Vol. 17, No. 8, 1998
Sch em e 1. Rea ction of 1-3 or 6a -d w ith Excess Acetylen ea
LaPointe and Brookhart
a
[Pd] ) (N-N)Pd+.
Sch em e 2. P r op osed Mech a n ism for th e F or m a tion of 8a
a
[Pd] ) (N-N)Pd+; R ) H, t-Bu.
amount of acetylene in solution), changing the substit-
uents on the diimine ligand, or switching to the phenan-
throline complexes (4) resulted in the formation of
complexes analogous to 8a -d .
At 25 °C in CH2Cl2, the cyclic compounds 8a -d did
not react with excess acetylene, ethylene, H2, or CO.
Likewise, no reaction was observed between 8a -d and
HCl, pyridine, or HSiEt3. Since such substrates are
normally quite reactive toward cationic Pd(II) alkyl
complexes such as 1-4 or vinyl complexes such as 6a -
d , these results suggest that the equibrium between the
π-allyl structure 8 and a σ-alkyl structure 8σ lies
strongly in favor of the π-allyl, perhaps for steric reasons
(eq 8).
associated with the design of cationic, highly electro-
philic complexes for use as polymerization catalysts,
namely, that even if migratory insertion reactions with
unsaturated substrates occur readily, reactive function-
alities attached to the growing oligomer chain can
The results reported here illustrate one problem

Reactions of Cationic Palladium(II) Complexes
Organometallics, Vol. 17, No. 8, 1998 1535
2
135.2 (Co), 129.3 (q, J C-F ) 31 Hz, Cm), 125.0 (q, J C-F ) 272
compete with external substrate for the vacant coordi-
nation site at the metal. If there is an equilibrium
between chelation and coordination of monomer, then
polymerizations are still possible; this is the case in the
alternating copolymerization of C2H4/CO by 412 or the
copolymerization of methylacrylate and ethylene by
1-3.10 However, if the chelate does not open readily
or if an intramolecular reaction occurs between the
metal center and a site of unsaturation on the chelate,
then polymerization reactions are strongly disfavored.
This is the case in the formation of 8a -d , when
cyclization and rearrangement to an allylic structure
result in complexes that are inert toward further
insertion reactions with alkynes, alkenes, or carbon
monoxide. Thus, the rational design of late transition
metal catalysts for the polymerization of alkynes will
require a precise tuning of the steric and electronic
factors to develop systems in which migratory insertion
reactions of alkynes are facile but in which intramo-
lecular cyclization is disfavored.
Hz, CF3), 117.8 (Cp). 13C NMR chemical shifts and coupling
constants are consistent to within (1 ppm and (2 Hz,
respectively. Note: because of the large number of aromatic
peaks (100-160 ppm) from complexes containing the acenaph-
thene backbone, the 13C spectra for these complexes were
difficult to assign and full spectral data are usually not
included here.
[(p h en )P d (CH3)(Me3SiCtCSiMe3)]+[BAr ′4]- (5a ). Solid
(phen)Pd(CH3)2 (116 mg, 0.37 mmol) and [H(OEt2)2][BAr′4]
(365 mg, 0.37 mmol) were combined. The reaction flask was
cooled to -30 °C, and Et2O (10 mL) and CH2Cl2 (5 mL) were
added. The resulting slurry was allowed to warm to 25 °C to
dissolve solid (phen)Pd(CH3)2, and then the solution was cooled
to -30 °C. Bis(trimethylsilyl)acetylene was added, and color-
less microcrystals formed. The mixture was allowed to warm
to room temperature, and the solid dissolved. The mixture
was stirred for 1 h, and then the volume was reduced to 5 mL
in vacuo and cooled slowly to -78 °C. Colorless needles formed
and were washed with 10 mL of cold Et2O, collected, and dried
(yield ) 285 mg; 59%). 1H NMR (CD2Cl2, 20 °C): δ 8.95 (δ, 1,
phen Ha), 8.71 (d, 1, phen Ha′), 8.59 (dd, 1, phen Hc), 8.54 (dd,
1, phen Hc′), 8.05 (s, 2, phen Hd), 8.00 (dd, 1, phen Hb), 7.92
(dd, 1, phen Hb′), 1.06 (s, 3, PdCH3), 0.32 (s, 18, Si(CH3)3). 13C
NMR (CD2Cl2): δ 147.2, 145.2 (Ca, Ca′), 146.2, 143.2 (Ce, Ce′),
139.7, 138.4 (Cc, Cc′), 129.9, 129.3 (Cf, Cf ′), 126.8, 126.5 (Cd,
Cd′), 124.6, 124.4 (Cb, Cb′), 103.6 (Me3SiCtCSiMe3), 7.9 (PdCH3),
-1.7 (SiMe3). Anal. Calcd for C53H41N2BF24PdSi2: C, 47.67;
H, 3.09; N, 2.10. Found: C, 47.83; H, 3.04; N, 1.94.
[(p h en )P d (CH3)(C6H5tCH)]+[BAr ′4]- (5b). In a drybox,
solid 4 (45 mg, 0.036 mmol) was loaded into a 5-mm NMR tube.
CD2Cl2 (700 µL) was added at -78 °C, and the tube was
shaken briefly to dissolve the solid. Phenylacetylene (5 µL,
0.045 mmol) was added via syringe, and the sample was
inserted into a precooled (-78 °C) NMR probe. 1H NMR (CD2-
Cl2, -78 °C): δ 8.92 (d, 1, phen Ha), 8.68 (d, 1, phen Ha′), 8.58
(d, 1, phen Hb), 8.50 (d, 1, phen Hb′), 7.99 (s, 2, phen Hd, -d′),
7.84 (m, 2, phen Hb, -b′), 5.05 (s, 1, PhCtCH), 1.18 (s, 3, Pd-
CH3).
Exp er im en ta l Section
Gen er a l. Unless otherwise noted, all reactions were con-
ducted under an atmosphere of dry, deoxygenated argon using
standard Schlenk techniques or in a Vacuum Atmospheres
glovebox. Pentane, hexane, ether, toluene, and tetrahydrofu-
ran were distilled from sodium benzophenone ketyl under a
nitrogen atmosphere prior to use. Dichloromethane was
distilled from P4O10 under a nitrogen atmosphere. CD2Cl2
(CIL) was dried over CaH2 under argon and was degassed and
vacuum transferred. CDCl3 was used as received. (phen)P-
dMe2,12 H(OEt2)2BAr′4,25 and complexes 1a -c, 2-48,9 were
prepared according to reported procedures. Acetylene was
purchased from Matheson and used without further purifica-
tion. Alkynes were purchased from Aldrich and used without
further purification.
Routine NMR spectra were recorded on a Varian XL-400,
Varian Gemini 300 MHz, or Bruker AC-200 NMR spectrom-
eter. Low-temperature NMR spectra were recorded on a
Varian XL-400 spectrometer. 1H and 13C chemical shifts were
referenced to residual protio solvent peaks and solvent 13C
peaks, respectively. Elemental analyses were performed by
Oneida Laboratories.
[BIAN(Ar )2P d (CHdCHMe)(NCCH3)]+[BAr ′4]- (Ar ) 2,6-
C6H3(i-P r )2) (6a ). Solid 3 (270 mg, 0.18 mmol) was dissolved
in 15 mL of dichloromethane. The solution was cooled to -70
°C, and acetylene gas was bubbled through the solution for 5
min. The mixture was allowed to stir at -70 °C for 30 min
and then was placed under an active vacuum. After 5 min,
the cooling bath was removed and the mixture was allowed to
warm as dichloromethane was removed in vacuo. An orange-
brown solid was isolated and recrystallized from a mixture of
dichloromethane and pentane at 25 °C. Orange-brown crystals
were collected and dried (yield ) 159 mg, 58%). 1H NMR (CD2-
Cl2): δ 6.42-8.12 (m, 12 total, BIAN + Ar), 4.80 (m, 1,
PdCHdCHCH3), 4.61 (d, 1, J HH ) 6 Hz, PdCHdCHCH3), 3.22,
3.15 (sept, 2 each, CHMe2), 1.88 (CH3CN), 1.78 (d, 3, PdCH-
CHCH3), 1.40, 1.30, 1.02, 0.87 (d, 6 each, CHMe2). Anal. Calcd
for C73H60N3BF24Pd: C, 56.48; H, 3.89; N, 2.71. Found: C,
56.24; H, 3.92; N, 2.34.
The atom-labeling schemes for the phenanthroline and
((CF3)2C6H3)4B- counterion resonances are as follows:
[(Ar N dC (M e )sC (M e )dN Ar )P d (C H dC M e (t -B u ))-
(NCCH3)]+[BAr ′4]- (Ar ) 2,6-C6H 3(Me)2) (6b ). [(ArNd
C(Me)sC(Me)dNAr)Pd(CH3)(NCCH3)]+[BAr′4]- (282 mg, 0.21
mmol) was dissolved in 10 mL of dichloromethane, and tert-
butylacetylene (30µ L, 0.26 mmol) was added. The mixture
became orange and was allowed to stir for 30 min. Dichlo-
romethane was removed in vacuo, and the resulting yellow
glassy solid was washed with hexane and dried (yield ) 192
mg, 64%). 1H NMR (CD2Cl2): δ 7.21, 7.16 (m, 6 total, Ar),
4.27 (s, 1, PdCH), 2.25, 2.17, 2.15, 2.14 (s, 18 total, NdC(CH3)
+ ArCH3), 1.85, 1.75 (s, 3 each, CH3CN + PdCHdC(t-Bu)-
1
The H NMR resonances were assigned into groups of a, b, c,
f or a, a′, b, b′, c′ or according to their characteristic coupling
patterns. The 13C NMR resonances were assigned in pairs
such as Ca or Ca′ and Ca′ or Ca based on their chemical shifts
1
and J CH
.
The 1H and 13C NMR data attributed to the counterion
BAr′4- (Ar′ ) 3,5(CF3)2C6H3) follow. These are consistent for
all cationic complexes examined and are not included in each
compound characterized below. 1H NMR (CD2Cl2): δ 7.72 (8,
Ho), 7.56 (4, Hp). 1H chemical shifts are accurate to within
(0.02 ppm. 13C NMR (CD2Cl2): δ 162.1 (q, J C-B ) 50 Hz, Ci),
(CH3)), 0.61 (s, 9, t-Bu). 13C NMR (CDCl3): δ 146.4 (Ciso
,
note: the two Cipso peaks are apparently coincident), 142.6,
142.3 (Ar Cpara), 129.0, 128.8 (Ar Cmeta), 122.6, 122.2 (Ar Cortho),
120.8 (CH3CN), 37.3 (dC(CH3)), 28.8 (CMe3), 28.7 (CMe3), 19.7,
(25) Brookhart, M.; Grant, B.; Volpe, A. F. Organometallics 1992,
11, 3920.

1536 Organometallics, Vol. 17, No. 8, 1998
LaPointe and Brookhart
19.5, 18.7, 17.6, 17.5 (NdCCH3 and ArCH3), 1.7 (CH3CN).
Anal. Calcd for C61H52N3BF24Pd: C, 52.33; H, 3.74; N, 3.00.
Found: C, 52.41; H, 3.82; N, 2.19.
at 25 °C. CH2Cl2 and CH3CN were then removed in vacuo,
yielding a microcrystalline powder which was then recrystal-
lized from CH2Cl2/pentane. Triflate complexes were prepared
in a similar manner. The peaks associated with the coupled
tris(alkyne) fragment are labeled according to the following
assignments.
[(Ar NdC(H)sC(H)dNAr )P d(CHdCMe(t-Bu ))(NCCH3)]+-
[BAr ′4]- (Ar ) 2,6-C6H3(i-P r )2) (6c). Following the above
procedure, an orange powder was isolated in 79% yield. 1H
NMR (CD2Cl2): δ 8.26 (d, 2, Ar), 7.27-7.37 (m, 4, Ar), 4.48 (s,
1, PdCH), 3.16, 3.06 (sept, 2 each, CHMe2), 1.88, 1.80 (s, 3 each,
CH3CN + PdCHdC(t-Bu)(CH3)), 1.39, 1.37, 1.25, 1.17 (d, 6
each, CHMe2), 0.63 (t-Bu). 13C NMR (CD2Cl2): δ 167.5, 161.6
(CdN), 147.4, 142.8 (Ar Cipso), 139.4, 138.5 (Ar Cpara), 129.6,
129.4 (Ar Cmeta), 124.4, 124.3 (Ar Cortho), 123.4 (CH3CN), 37.6
(CMe3), 29.4 (CMe3), 29.5, 29.3 (CHMe2), 25.1, 23.9, 22.3, 19.7
(CHMe2), 2.6 (CH3CN). Anal. Calcd for C67H64N3BF24Pd: C,
54.21; H, 4.34; N, 2.83. Found: C, 53.87; H, 4.13; N, 2.42.
[(BIAN)(Ar )2P d (CHdCMe(t-Bu ))(NCCH3)]+[BAr ′4]- (Ar
) 2,6-C6H 3(i-P r )2) (6d ). [(BIAN)(Ar)2Pd(CH3)(NCCH3)]+-
[BAr′4]- (525 mg, 0.34 mmol) was dissolved in 20 mL of
dichloromethane, and tert-butylacetylene (45 µL, 0.40 mmol)
was added via syringe. The resulting orange solution was
allowed to stir for 30 min. Dichloromethane was removed in
vacuo, leaving an orange microcrystalline solid which was
[(Ar NdC(CH 3)C(CH 3)dNAr )P d (η3-CH (CH 3)C5H 5)]+-
[BAr ′4]- (Ar ) 2,6-(CH3)2C6H3) (8a ). Purple crystals were
prepared in the manner described above from 1b (103 mg,
0.078 mmol) and acetylene (yield ) 78 mg, 68%) 1H NMR (CD2-
Cl2, 25 °C): δ 7.2-7.4 (m, 6 total, Ar), 6.44 (br d, 1, J HH ) 6
Hz, H4), 4.92 (d, 1, J HH ) 6 Hz, H3), 4.64 (br s, 1, H5), 3.88 (q,
1, J HH ) 6 Hz, CHCH3), 2.93, 2.78 (d, 1 each, J HH ) 24 Hz, H1
and H2), 2.31, 2.27, 2.17, 2.14, 1.95, 1.77 (s, 3 each, diimine
CH3), 0.39 (d, 3, J HH ) 6 Hz, CHCH3). 13C NMR (coupled
alkyne fragment only) (CD2Cl2, 25 °C): δ 101.1 (d, J CH ) 179
Hz, cyclopentadienyl), 97.8 1 (d, J CH ) 178 Hz, cyclopentadi-
enyl), 83.4 1 (d, J CH ) 166 Hz, cyclopentadienyl), 70.1 (d, J CH
) 154 Hz, cyclopentadienyl), 40.2 (t, J CH ) 132 Hz, CH3H4).
Note: the peak corresponding to the internal allylic carbon
could not be located and may be hidden under diimine or BAr′4
peaks. Anal. Calcd for C59H45N2BF24Pd: C, 52.29; H, 3.34;
N, 2.07. Found: C, 52.28; H, 3.19; N, 1.96.
[(Ar NdC(CH3)C(CH3)dNAr )P d (η3-C(t-Bu )(CH3)C5H5)]+-
[BAr ′4]- (Ar ) 2,6-(CH3)2C6H3) (8b). Orange-brown crystals
were prepared from 6b (250 mg, 0.19 mmol) and acetylene in
the manner described above (yield ) 215 mg, 80%). 1H NMR
(CD2Cl2, 25 °C): δ 7.2-7.4 (m, 6 total, Ar), 6.43 (d, 1, J HH ) 6
Hz, H3), 4.76 (dd, 1, J HH )2 Hz, 6 Hz, H4), 4.10 (d, 1, J HH ) 2
Hz, H5), 3.04, 2.75 (d, 1 each, J HH ) 24 Hz, H1 and H2), 2.33,
2.20, 2.13, 2.12, 1.98, 1.73 (s, 3 each, Ar-CH3, NdCCH3), 0.87
(s, 9, t-Bu), 0.80 (s, 3, C(t-Bu)(CH3)). 13C NMR (coupled alkyne
fragment only) (CD2Cl2, 25 °C): δ 97.4, 85.5, 44.4, 41.1
(cyclopentadienyl). Note: the peaks corresponding to the
internal and quaternary terminal allylic carbons could not be
located. Anal. Calcd for C63H53N2BF24Pd: C, 53.62; H, 3.78;
N, 1.99. Found: C, 53.72; H, 3.61; N, 1.87.
recrystallized from
a CH2Cl2/hexane mixture at -30 °C.
Orange cubes were collected and dried (370 mg, 68%). 1H
NMR (CD2Cl2): δ 6.5-8 (m, 12, BIAN + Ar), 4.47 (s, 1, PdCH),
3.40, 3.35 (sept, 2 each, CHMe2), 1.87, 1.86 (s, 3 each,
PdCHdC(t-Bu)(CH3) + CH3), 1.46, 1.38, 1.08, 0.93 (d, 6 each,
CHMe2), 0.68 (s, 9, t-Bu). Anal. Calcd for C77H68N3BF24Pd:
C, 57.50; H, 4.26; N, 2.61. Found: C, 57.59; H, 4.04; N, 2.30.
Reaction s of [(Ar NdC(R)sC(R)dNAr )P d(CH3)(NCCH3)]-
+[BAr ′4]- w ith 1-Hexyn e: Regioch em istr y of In ser tion .
Solid 1-3 (0.03 mmol) was loaded into a 5-mm NMR tube and
dissolved in CDCl3 (0.7 mL). 1-Hexyne (2.5 µL, 0.022 mmol)
was then added via syringe; the sample was shaken 3 times
and inserted into a NMR probe. The relative amounts of 1,2-
insertion and 2,1-insertion were analyzed by the relative
integrals of the peaks attributed to PdCHdC(CH3)(C4H9) and
PdC(C4H9)dCH(CH3), respectively (Table 1). Note: a deficit
(0.7 equiv) of 1-hexyne was used in order to prevent the vinyl
complexes that are formed from reacting with excess alkyne.17
1H NMR data for the vinylic protons is given below. Due to
the large number of overlapping ligand peaks in the aromatic
and aliphatic regions, the remainder of the peaks are difficult
to assign and are not listed below.
1H NMR (CDCl3, 25 °C). 1a + 1-hexyne: δ 3.58 (s,
PdCH)C(CH3)(C4H9)), 3.96 (q, J HH ) 7 Hz, PdC(C4H9)d
CH(CH3)). 1b + 1-hexyne: δ 4.08 (s, PdCH)C(CH3)(C4H9)),
4.39 (q, J HH ) 7 Hz, PdC(C4H9)dCH(CH3)). 1c + 1-hexyne: δ
4.53 (s, PdCH)C(CH3)(C4H9)), 4.27 (q, J HH ) 8 Hz, PdC-
(C4H9)dCH(CH3)). 2 + 1-hexyne: δ 4.26 (s, PdCH)C(CH3)-
(C4H9)), 4.44 (q, J HH ) 7 Hz, PdC(C4H9)dCH(CH3)). 3 +
1-hexyne: δ 4.28 (s, PdCH)C(CH3)(C4H9)), 4.48 (q, J HH ) 7
Hz, PdC(C4H9)dCH(CH3)).
[(BIAN)(NAr )2)P d (η3-CH(CH3)C5H5)]+[BAr ′4]- (Ar ) 2,6-
(i-P r )2C6H3) (8c). In a modification of the above procedure,
acetylene was bubbled through
a CH3CN solution of
[(BIAN)(NAr)2Pd(CH3)(NCCH3)]+[BAr′4]- (370 mg, 0.24 mmol).
After acetylene addition had ceased, green crytals formed on
the sides of the flask and were collected, washed with CH3-
CN, and dried (yield ) 276 mg, 74%). 1H NMR (coupled alkyne
fragment only) (CD2Cl2, 25 °C): 6.55 (d, 1, J HH ) 6 Hz, H4),
5.34 (d, 1, J HH ) 6 Hz, H3), 4.96 (s, 1, H5), 4.15 (q, 1, J HH ) 6
Hz, CHCH3), 2.93, 2.80 (d, 1 each, J HH ) 24 Hz, H1 and H2),
0.61 (d, 3, J HH ) 6 Hz, CHCH3). 13C NMR (coupled alkyne
fragment only) (CD2Cl2, 25 °C): δ 104.6, 98.4, 83.9, 70.3
(cyclopentadienyl vinylic C), 40.0 (cyclopentadienyl CH2), 14.2
(CHCH3). Note: the peak corresponding to the internal allylic
carbon could not be located and may be hidden under diimine
or BAr′4 peaks. Anal. Calcd for C75H61N2BF24Pd: C, 57.62;
H, 3.90; N, 1.79. Found: C, 57.49; H, 3.85; N, 1.78.
Ob ser va t ion of [(Ar NdC(CH3)C(CH3)NAr )P d CHd
CHCHdCHC(t-Bu )(CH3)]+ (Ar ) 2,6-(CH3)2C6H3) (7). Solid
6b (25 mg, 0.018 mmol) was loaded into a 5-mm NMR tube
and dissolved in 0.7 mL of CD2Cl2. The solution was cooled
to -78 °C, and acetylene (1 mL, 0.044 mmol) was added via
gastight syringe. The sample was then inserted into a
precooled (-78 °C) NMR probe. 1H NMR (CD2Cl2, -60 °C): δ
6.37 (d, 1, J HH ) 11 Hz, PdCH)CH), 5.50 (dd, 1, J HH ) 11, 6
Hz, PdCHdCHCH), 4.75 (dd, 1, J HH ) 6 Hz, PdCHdCHCH ).
The terminal CH3 and t-Bu peaks could not be unambiguously
assigned due to the presence of substantial amounts of 6b and
8b.
[(BIAN)(NAr )2)P d (η3-CH(CH3)C5H5)]+[O3SCF 3]- (Ar )
2,6-(i-P r )2C6H3) (8d ). Green crystals were formed from 3b
(282 mg, 0.35 mmol) and acetylene according to the above
procedure (yield ) 225 mg, 76%). NMR data for the cationic
portion of the molecule matched that of 8c. Anal. Calcd for
C44H49N2F3O3PdS: C, 62.22; H, 5.81; N, 3.30. Found: C, 62.43;
H, 5.71; N, 3.02.
F or m a t ion of 8a -d . In
a typical procedure, solid
[(ArNdC(R)sC(R)dNAr)Pd(CH3)(NCCH3)]+[BAr′4]- or [(ArNd
C(R)-C(R)dNAr)Pd(CHdC(t-Bu)(CH3)(NCCH3)]+[BAr′4]- was
loaded into a Schlenk flask. The solid was dissolved in CH2-
Cl2, and acetylene was bubbled through the solution for 5 min

Reactions of Cationic Palladium(II) Complexes
Organometallics, Vol. 17, No. 8, 1998 1537
Ack n ow led gm en t. This research was supported by
the National Science Foundation (Grant No.
CHE9412095). A.M.L. thanks the National Science
Foundation for a postdoctoral fellowship. We thank Dr.
William Marshall of Dupont for the X-ray structural
determination of 8 and Prof. J . L. Templeton for helpful
discussions.
OM9710125