High reactivity of (P,N)Pd(methyl)+ derivatives toward mixtures of CO and norbornene

Article abstract of DOI:10.1021/om980368t

The reactivity of cationic (P,N)PdMe(CO)⁺ (P,N = Ph₂P-o-C₆H₄CH₂NMe₂, Me₂N-o-C₆H₄-CH₂PPh₂, 1-(dimethylamino)-8-(diphenylphosphino)naphthalene; anion, ^-B[3,5-Ph(CF₃)₂]₄) toward CO and norbornene is described. CO and norbornene insert slowly into the palladium-methyl bond to yield (P,N)Pd[C(O)Me]⁺ and [-3-methyl-2-norbornyl]⁺ derivatives. Compounds (P,N)PdMe(CO)⁺ react fast with mixtures of CO and norbornene under formation of (P,N)Pd[C₇H₁₀C(O)Me]⁺ and two isomers of (P,N)Pd[C₇H₁₀C(O)C₇H₁₀Me] ⁺. The dissimilarity in rates is explained in a kinetic model, wherein reactive intermediates are reversibly formed and trapped by norbornene in case of trans-P (P,N)Pd[C(O)Me]⁺ and CO in case of trans-P (P,N)Pd(C₇H₁₀Me)⁺ complexes. CO insertion into the Pd-alkyl bond takes place in the trans-N Pd-alkyl complexes, and norbornene inserts into the Pd-acyl bond from the trans-P Pd-acyl complexes. Isomerization from trans-P to trans-N in (P,N)Pd[C(O)Me]⁺ is slow with respect to CO deinsertion and subsequent norbornene insertion into the trans-P (P,N)Pd⁺-acyl bond. Fast and reversible trans-N-to-P isomerization is found in compounds (P,N)Pd[C(O)-3-Me-2-C₇H₁₀]⁺.

Full text of DOI:10.1021/om980368t

5160
Organometallics 1998, 17, 5160-5165
High Rea ctivity of (P ,N)P d (m eth yl)+ Der iva tives tow a r d
Mixtu r es of CO a n d Nor bor n en e
Gerrit A. Luinstra* and Peter H. P. Brinkmann
Department of Chemistry, University of Konstanz, Fach M738, D-78457 Konstanz, Germany
Received May 11, 1998
The reactivity of cationic (P,N)PdMe(CO)+ (P,N ) Ph2P-o-C6H4CH2NMe2, Me2N-o-C6H4-
-
CH2PPh2, 1-(dimethylamino)-8-(diphenylphosphino)naphthalene; anion, B[3,5-Ph(CF3)2]4)
toward CO and norbornene is described. CO and norbornene insert slowly into the
palladium-methyl bond to yield (P,N)Pd[C(O)Me]+ and [-3-methyl-2-norbornyl]+ derivatives.
Compounds (P,N)PdMe(CO)+ react fast with mixtures of CO and norbornene under formation
of (P,N)Pd[C7H10C(O)Me]+ and two isomers of (P,N)Pd[C7H10C(O)C7H10Me]+. The dissimilar-
ity in rates is explained in a kinetic model, wherein reactive intermediates are reversibly
formed and trapped by norbornene in case of trans-P (P,N)Pd[C(O)Me]+ and CO in case of
trans-P (P,N)Pd(C7H10Me)+ complexes. CO insertion into the Pd-alkyl bond takes place in
the trans-N Pd-alkyl complexes, and norbornene inserts into the Pd-acyl bond from the
trans-P Pd-acyl complexes. Isomerization from trans-P to trans-N in (P,N)Pd[C(O)Me]+ is
slow with respect to CO deinsertion and subsequent norbornene insertion into the trans-P
(P,N)Pd+-acyl bond. Fast and reversible trans-N-to-P isomerization is found in compounds
(P,N)Pd[C(O)-3-Me-2-C7H10]+.
In tr od u ction
ligands and with two different donor atoms in general
were found to be much less active in this regard.4 Vrieze
and co-workers,5 who studied the reaction between CO
and (P,N)Pd-Me complexes, attributed this fact among
other factors to an additional activation energy involved
with the generation of an unfavorable trans-P Pd-acyl
or Pd-alkyl complex (Scheme 1, size of L represents the
magnitude of the trans influence). The two possible
geometrical isomers of square planar complexes with
non-C2-symmetric cis-coordinating ligands and two
nonidentical groups X and Y, (L,L′)MXY, differ in
energy.6 Since acyl and methyl groups both exert a
relatively high trans influence, they tend to bind to the
same coordination site in the thermodynamic most-
stable configuration.7 This implies that, after migration
of an alkyl group in trans-N (P,N)PdR(CO) to coordi-
nated CO, the most stable isomer is not formed and a
driving force for a postinsertion isomerization exists.
The Pd-acyl compound may adversely be formed through
a preinsertion isomerization through an energetically
unfavorable trans-P Pd-alkyl derivative (Scheme 1). It
is an open question what role pre- or postinsertion
isomerizations in palladium acyl and alkyl compounds
play in the formation of polyketones with (L,L′)PdR(X)
complexes through consecutive CO and olefin insertion.5
The formation of polyketones through the alternating
insertion of CO and R-olefins into Pd-C bonds has
become a major subject of both fundamental and indus-
trial research.1-4 Palladium(II) complexes with sym-
metrical P,P2 and N,N3 ligands are productive catalysts
for the copolymerization.1 Group 8 complexes with P,N
(1) (a) Lai, T. W.; Sen, A. Organometallics 1984, 3, 866. (b) Drent,
E.; van Broekhoven, J . A. M.; Doyle, M. J . J . Organomet. Chem. 1991,
417, 235. (c) Brookhart, M.; Rix, F. C.; DeSimone, J . M. J . Am. Chem.
Soc. 1992, 114, 5894. (d) Sen, A. Acc. Chem. Res. 1993, 26, 303. (e)
Bronco, S.; Consiglio, G.; Batistini, A.; Suter, U. W. Macromolecules
1994, 27, 4436. (f) Busico, V.; Corradini, P.; Landriani, L.; Trifuoggi,
M. Makromol. Chem., Rapid Commun. 1993, 14, 261. (g) Drent, E.;
Budzelaar, P. H. M. Chem. Rev. 1996, 96, 663. (h) Drent, E.; van
Broekhoven, J . A. M.; Budzelaar, P. H. M. Recl. Trav. Chim. Pays-
Bas 1996, 115, 263. (i) Kacker, S.; Sen, A. J . Am. Chem. Soc. 1995,
117, 10591. (j) Amevor, E.; Bu¨rli, R.; Consiglio, G. J . Organomet. Chem.
1995, 497, 81. (k) Milani, B.; Vicentini, L.; Sommazzi, A.; Garbassi,
F.; Chiarparin, E.; Zangrando, E.; Mestroni, G. J . Chem. Soc., Dalton
Trans. 1996, 3139 and references therein. (l) Svensson, M.; Matsubara,
T.; Morokuma, K. Organometallics 1996, 15, 5568. (m) Borkowsky, S.;
Waymouth, R. M. Macromolecules 1996, 29, 6377. (n) Kim, J . S.;
Pawlow, J . H.; Wojcinski, L. M., II; Murtuza, S.; Kacker, S.; Sen, A. J .
Am. Chem. Soc. 1998, 120, 1932.
(2) (a) Abu-Surrah, A. S.; Wursche, R.; Rieger, B.; Eckert, G.;
Pechhold, W. Macromolecules 1996, 29, 4806. (b) Vavasori, A.; Toniolo,
L. J . Mol. Catal. 1996, 110, 13. (c) J iang, Z.; Sen, A. J . Am. Chem.
Soc. 1995, 117, 4455.
(3) (a) Sen, A.; J iang, Z. Macromolecules 1993, 26, 911. (b) Drent,
E. Eur. Pat. 229, 408, 1986. (c) Rix, F. C.; Brookhart, M.; White, P. S.
J . Am. Chem. Soc. 1996, 118, 8, 4746. (d) Bartolini, S.; Carfagna, C.;
Musco, A. Macromol. Rapid Commun. 1995, 16, 9.
(4) See e.g.: (a) Brookhart, M.; Wagner, M. J .; Balavoine, G. G. A.;
Haddou, H. A. J . Am. Chem. Soc. 1994, 116, 3641. (b) Brookhart, M.;
Wagner, M. I. J . Am. Chem. Soc. 1996, 118, 7219. (c) Britovsek, G. J .
P.; Mecking, K. W. S.; Sainz, D.; Wagner, T. J . Chem. Soc., Chem.
Commun. 1993, 1632. (d) J iang, Z.; Adams, S. E.; Sen, A. Macromol-
ecules 1994, 27, 2694. (e) Sperrle, M.; Aeby, A.; Consiglio, G.; Pfaltz,
A. Helv. Chim. Acta 1996, 79, 1387. (f) Nozaki, K.; Sato, N.; Takaya,
H. J . Am. Chem. Soc. 1995, 117, 9911. (g) Britovsek, G. J . P.; Cavell,
K. J .; Green, M. J .; Gerhards, F.; Skelton, B. W.; White, A. H. J .
Organomet. Chem. 1997, 533, 201. (h) Nozaki, K.; Sato, N.; Tonomura,
Y.; Yasutomi, M.; Takaya, H.; Hiyama, T.; Matsubara, T.; Koga, N. J .
Am. Chem. Soc. 1997, 119, 12779 and see also references cited there.
(5) Palladium methyl chloro and triflate complexes with ligand c
were studied before: Dekker, G. P. C. M.; Buijs, A.; Elsevier: C. J .;
Vrieze, K.; van Leeuwen, P. W. N. M.; Smeets, W. J . J .; Spek, A. L.;
Wang, Y. F.; Stam, C. H. Organometallics 1992, 11, 1937. For other
studies on carbonylation in Pd complexes with non-C2-symmetrical
ligands, see e.g.: (a) J in, H.; Cavell, K. J .; Skelton, B. W.; White, A.
H. J . Chem. Soc., Dalton Trans. 1995, 2159. (b) Ankersmit, H. A.;
Veldman, N.; Spek, A. L.; Eriksen, K.; Goubitz, K.; Vrieze, K.; van
Koten, G. Inorg. Chim. Acta 1996, 252, 203.
(6) In the most stable complex, the groups with the highest trans
influences are cis to each other: Hartley, F. R. Chem. Soc. Rev. 1973,
2, 163.
(7) Appleton, T. G.; Clark, H. C.; Manzer, L. E. Coord. Chem. Rev.
1973, 10, 335.
10.1021/om980368t CCC: $15.00 © 1998 American Chemical Society
Publication on Web 10/24/1998

(P,N)Pd(methyl)+ Derivatives
Sch em e 1
Organometallics, Vol. 17, No. 23, 1998 5161
F igu r e 1. P,N ligand systems.
Resu lts
The P,N frameworks in this study have a more or less
rigid C3-bridge (Figure 1). Ligand a is N,N-dimethyl-
(o-(diphenylphosphino)benzyl)amine, ligand b is N,N-
dimethyl(2-(diphenylphosphino)methyl)aniline
and,
Van Leeuwen has shown in two elegant and convinc-
ing studies on platinum phenyl and palladium methyl
compounds with P,P′ bidentates (P,P′: phosphine-
phosphine′ and/or phosphine-phosphite) that CO inser-
tion in cationic monoalkyl CO complexes, (L,L′)MR-
(CO)+, proceeds through migration of the methyl group
and is faster than cis-trans Pd-Me preinsertion isomer-
ization.8
ligand c is 1-(diphenylphosphino)-8-(N,N-dimethylami-
no)naphthalene.5 Complexes (P,N)PdMe(CO)+ (1a -c)
were obtained by reacting the parent (P,N)PdMeCl
(2a -c) with NaBAr′4 (BAr′4: B[3,5-Ph-(CF3)2]4) in a CO-
saturated solution. In a slow process, the corresponding
acetyl complexes, (P,N)Pd[C(O)Me](CO)+ (3a -c), were
formed.9 The carbonylation is easily monitored by 31P
NMR, and during reaction no other compounds than the
CO adducts of alkyl and acetyl complexes were observed.
The CO stretching frequency of compounds 1a -c and
3a -c is found at 2135 cm-1, indicative of a weak
interaction between (P,N)PdR+ and CO.5 Subsequent
reactions of compounds 3a -c with norbornene yield
(P,N)Pd[C7H10C(O)Me]+ (4a -c, eq 1). This process is
The cationic palladium methyl complex with the
(R,S)-BINAPHOS (R,S-2-(diphenylphosphino)-1,1′-bi-
naphthalen-2′-yl 1,1′-binaphthalen-2,2′-diyl phosphite)
ligandsphosphine and phosphite donorsswas shown to
be an active catalyst for the copolymerization of CO and
propene. Nozaki4f,h et al. obtained polyketones from this
catalyst with a high isotacticity and with a high enan-
tioselectivity. In contrast to the post-migratory-inser-
tion isomerization in the palladium acyl complexes
documented by van Leeuwen,8b it is proposed that CO
insertion proceeds in the high-energy trans-phosphite
(P,P′)Pd-alkyl(CO) complex (preinsertion isomeriza-
tion) and that the subsequent olefin insertion into the
Pd-acyl bond also starts from the high energy isomer.
Their arguments are based on observations also made
by Van Leeuwen,8 who found that entities bonded trans
to ligands with the higher trans-effect have an exceed-
ingly higher aptitude for migratory insertion than those
in their geometrical isomers. It was observed by Nozaki
et al.4h that cis-trans isomerizations of cationic acyl and
alkyl palladium species are fast with respect to olefin
and CO insertion, respectively, and hence are compat-
ible with a preinsertion isomerization.
also slow with half-lives of about 2-10 h. In these
(P,N)Pd complexes, both alkyl and acetyl groups are
coordinated trans to the N donor, the thermodynami-
cally most stable isomer.
Surprising observations were made when the com-
plexes 1a -c were reacted with mixtures of CO and
norbornene. A detailed study was carried for complex
1a , but similar behavior was found for the cationic Pd
methyl complexes of the other ligands. Instead of the
expected sluggish formation of 3a , followed by a slow
norbornene insertion into the Pd-acetyl bond to yield
4a , a fast decrease in the concentration of 1a was
observed (by 1H NMR spectroscopy). Dependent on the
molar ratio and the concentration of norbornene and 1a ,
three new species are formed in various ratios. These
were identified as 4a and two isomersstentatively
assigned to the exo,endo and exo,exo formssof (P,N)-
Pd[C7H10C(O)C7H10Me]+ (5a ) (see Experimental Sec-
tion). The formation of the latter compounds is the
result of the consecutive insertion of norbornene (exo),
CO, and insertion of a second norbornene molecule (exo
or endo) into the Pd-C bond.
This leaves an interesting ambiguity about the sig-
nificance of cis-trans isomerizations and the relative
insertion rates of the different monomers at different
coordination sites in the polyketone formation with
palladium complexes carrying nonsymmetrical ligands.
To address this matter, we recently started a study on
the reactivity of Pd-alkyl and -acyl compounds with
P,N bidentate ligands toward CO and norbornene.9 It
was found that CO insertion takes place in the trans-N
Pd-alkyl isomers and that norbornene insertion into
the Pd-acyl bond takes place in the trans-P Pd-acyl
complex. The chemoselectivity arises from the fact that
trans-N to trans-P isomerization is slow in Pd-alkyl
compounds and fast in Pd-acyl complexes, relative to
insertion of CO and norbornene, respectively.
(8) (a) van Leeuwen, P. W. N. M.; Roobeek, C. F.; van der Heijden,
H. J . Am. Chem. Soc. 1994, 116, 12117. (b) van Leeuwen, P. W. N. M.;
Roobeek, K. F. Recl. Trav. Chim. Pays-Bas 1995, 114, 73.
(9) (a) Brinkmann, P. H. P.; Luinstra, G. A. manuscript in prepara-
tion. (b) Brinkmann, P. H. P. Dissertation, University of Konstanz,
1998.
The identification is based on a combination of
multidimensional and multinuclear NMR, IR, and MS
analysis as well as independent synthesis. The reaction

5162 Organometallics, Vol. 17, No. 23, 1998
Luinstra and Brinkmann
Ta ble 1. 31P NMR Sh ifts a n d Sign a l Ra tios of th e
Rea ction Mixtu r es of 5 equ iv of Nor bor n en e w ith
1a -c u n d er CO Atm osp h er ea
(P,N)PdMeCl (2a ), NaBAr′4, and excess of norbornene
is subsequently treated with CO, fast formation of (P,N)-
Pd[C7H10C(O)C7H10Me]+ (5a ) takes place.
obsd M+
The acetonitrile adduct of the norbornene insertion
product (P,N)Pd(C7H10Me)(NCMe)+ (6a ) can be isolated
from the reaction of (P,N)PdMe+ with excess of nor-
bornene after addition of 1 equiv of acetonitrile.10 This
compound reactssin contrast to 1a swith CO in a fast
process to give the carbonylated compound (P,N)Pd-
[C(O)C7H10Me](NCMe)+ (7a): reaction is complete within
minutes at room temperature and 1 bar of CO pressure.
The consecutive norbornene insertion into the Pd-acyl
bond of (P,N)Pd[C(O)C7H10Me]+ (to yield 5a ) is also fast,
complete within 2 min under the latter conditions after
the addition of norbornene.
est
δ(31P) (ppm)
(M+ calc)
1x:
x
ratios half-life
5 (A) 5 (B) 4 (X) B/A/X
(h)
0.3
0.3 656 (657.1) 562 (563.0)
692 (693.2) c (599.0)
5
4
a
33.95 34.04 34.14 1/2/1
bb 44.26 44.45 44.75 1/6/2
ca 39.33 39.59b
c
5/1/c
≈5
a
(P,N)Pd[C(O)Me]+ (3c) complex is also formed. b More products
are formed. c Trace amount.
mixture of 1a and norbornene-13CO shows three CdO
resonances in the 13C NMR spectrum, at δ 236.96 ppm
(4a ) and δ 241.3/242.2 ppm (5a ). In the IR spectrum, 3
new bands of Pd-coordinated CdO entities arise around
1700 cm-1, confirming the expectation of the presence
of three carbonyl compounds.5 In the mass spectrum
(FAB) of the mixture, signals for 4a and 5a are found.
The 31P NMR spectrum shows three new signals at
chemical shifts that are characteristic for palladium
alkyl derivatives of ligand a .9 The acyl species 3a is
not detectable in the 31P NMR spectrum of the reaction
mixture. Compound 4a could be synthesized and
isolated from the reaction of 1 equiv of norbornene and
1a in the presence of CO. Other products were not
formed under those conditions. Adversely, 5a was
prepared by reacting 1a with a large excess of nor-
bornene in a CO atmosphere (>20 eq/Pd).
Discu ssion
A couple of remarkable observations were made
during the insertion reactions of the cationic (P,N)Pd
methyl and acyl complexes (Scheme 2). A high rate of
reaction of the methyl complexes 1a -c toward a mix-
ture of CO-norbornene is found relative to the consecu-
tive insertion of CO into the Pd-Me and norbornene
into the Pd-acyl bond, althoughsat least at low nor-
bornene concentrationsthe same products are formed.
The same is true for 5a : its formation from the parent
methyl cation is fast, but formation of 6a through
norbornene insertion into the Pd-Me bond of 1a is slow.
Second, norbornene coordination and subsequent inser-
tion into the Pd-Me+ bond is competitive with that of
CO.
Evidently, reactions of CO and norbornene and mix-
tures thereof with the (P,N)Pd compounds are not
simple processes. A possible rationalization for the
observations is given in Scheme 2. It contains the
reaction products and feasible intermediates together
with an assessment of relative rates. In the proposal,
CO and norbornene compete for the fourth coordination
site in the cationic palladium methyl complexes. The
exclusive formation of 5a at high norbornene concentra-
tion and 1 bar CO is explained through a higher
isomerization rate of the trans-P (P,N)PdC7H10Me+
intermediate relative to that of the analogous reaction
products of CO (assuming Curtin-Hammett conditions).
Carbon monoxide is not particularly strongly bonded to
(P,N)PdMe+, as is indicated by the CO stretching
frequency of 2135 cm-1 in the CO adducts 1a -c, and is
apparently readily displaced by norbornene. Facile
decoordination of CO was also observed in (BINAPHOS)-
PdMe+.4h CO adducts with the same stretching fre-
quency are known to be exceedingly more stable (K ≈
10-(5-6)) than ethene adducts, like the ones observed
for P,P and N,N systems reported by Drent1h and
Brookhart.3c Since the rate of the consecutive reactions
is here the determining factor for product formation,
olefin insertion is overall a faster process than CO
insertion.
The 31P NMR spectrum of the reaction mixtures of
1b,c and CO/norbornene (Table 1, 5-fold excess based
on Pd) are reminiscent of the one obtained for 1a , and
the MS (FAB) show that fragments with mass corre-
sponding to 5b,c and 4b,c are formed. Although it was
not possible to correlate the individual amounts of exo,-
endo- or exo,exo-inserted products with their signal
positions in the 31P NMR spectrum, the relative sig-
nal intensities show that the ratios are dependent on
of the type of ligand a -c (Table 1). In case of 1c, the
acetyl complex 3c is also formed in appreciable amounts
(˜30% of the total of Pd complexes). The increase in
reactivity of the palladium complex with ligand c toward
mixtures of CO and norbornene issin comparison to
carbonylation of the cationic methyl derivativessnot as
pronounced as was found for complexes with ligand a
or ligand b. The reactivity of the later two is generally
higher (vide infra).
The formation of (P,N)Pd[C7H10C(O)C7H10Me]+ (5a )
indicates that initial insertion of norbornene into the
Pd-Me bond has taken place. Norbornene insertion
was also observed in the absence of CO. Treatment of
complex (P,N)PdMeCl (2a ) with 1 equiv of NaBAr′4 in
the presence of an excess of norbornene gives evidence
for insertion into the palladium-methyl bond but at a
rate that is substantially lower than the consecutive
norbornene-CO-norbornene insertion. The 31P NMR
spectrum of the reaction mixture in early stages of the
reaction shows a broad resonance at about 41 ppm.
Broad signals are also present in the reaction mixture
of 1a -c and mixtures of norbornene and CO. The broad
resonances are tentatively assigned to a contact ion pair
(P,N)PdMe+(borate)- and/or CO and norbornene ad-
ducts of (P,N)PdMe+. The adducts may be in dynamic
equilibrium with the free cation and CO or norbornene;
its exact nature unknown. If the reaction mixture of
The key to understanding the increased reactivity of
the (P,N)PdMe+ compounds toward mixtures of CO and
norbornene is to assume that an intermediate is fast
and reversibly formed from the starting materials which
(10) The cationic complex (L1)Pd-C7H10Me+ decomposes slowly
without addition of acetonitrile.

(P,N)Pd(methyl)+ Derivatives
Organometallics, Vol. 17, No. 23, 1998 5163
Sch em e 2
is subsequently trapped if CO and norbornene are
present. This intermediate is trans-P Pd[C(O)Me] in
the formation of compounds 4 (Pd[C7H10C(O)Me]) or
trans-P Pd(3-methyl-2-norbornyl) for product 5 (Pd-
[C7H10C(O)C7H10Me]) formation. They derive from the
CO and the norbornene adduct of trans-N (P,N)PdMe+
through migratory insertion. In the absence of nor-
bornene, the trans-P Pd[C(O)Me] compounds isomerize
in a slow step to the more stable trans-N isomers. Since
the trans-P Pd[C(O)Me] complex is not observed in
detectable amounts during reaction of (P,N)PdMe+ with
CO, it follows that trans-P (P,N)Pd[C(O)Me]+ complexes
will undergo rapid decarbonylation to give back the
starting materials. This was also observed in (N,N)-
Pd(alkyl)+ compounds.3c Note that the formation of the
trans-P (P,N)Pd[C(O)Me]+ is fast. In the presence of
norbornene, the trans-P Pd[C(O)Me] is rapidly captured
to give compounds 4. This accounts for the high reac-
tion rates that are found if mixtures of CO and nor-
bornene are reacted with the palladium methyl com-
pounds.
tive with norbornene deinsertion and hence, formation
of 6a is slow. Apparently, trapping of the trans-P
isomer of 6a by norbornene is not effective and polynor-
bornene is not formed. Steric repulsions may prevent
the formation of the congested intermediate (P,N)Pd-
(C7H10Me)+(norbornene) adduct. This is different for
the smaller CO that can trap the trans-P isomer of 6a
to yield the thermodynamically stable trans-N deriva-
tive (P,N)Pd[C(O)C7H10Me]+ (7a ). It could be indepen-
dently shown that the latter reacts rapidly with nor-
bornene (<2 min) to compounds 5a . Thus addition of
CO to a mixture of the methyl compound and ex-
cess of norbornene leads to a rapid formation of com-
pounds 5a .
Such a kinetic scheme would account for all observa-
tions. Its feasibility is discussed below. One of the
assumptions made is that the primary insertion inter-
mediates of the methyl derivatives are formed from the
ground state in a single step and that their postinsertion
isomerization is relatively slow. The latter was ob-
served before: Van Leeuwen8b obtained the high-energy
forms of the CO insertion into the Pd-Me bond in
cations with nonsymmetric cis-coordinating bidentates
as reactive products (in contrast to the mechanistic
scheme proposed by Nozaki4h). A direct argument in
favor of the explanation given here is that if 3a (or 6a )
alternatively would have been formed via a preinsertion
isomerization in 1a and thus that the trans-P Pd[C(O)-
Me] (and Pd(C7H10Me)) is not an intermediate, then it
is hard to envision how the formation of the norbornyl
acyl complex 4a (and 5a ) through the action of nor-
bornene (or CO) could be so much faster than that of
3a (or 6a ; vide supra). Note that acyl compound 3a was
not found to undergo rapid decarbonylation (and 6a is
Similar arguments are put forward to describe the
process leading to 6a and subsequently to 5a . Under
CO free conditions and in the presence of excess
norbornene, migratory insertion of the methyl group in
the norbornene adduct gives a trans-P (P,N)Pd(C7H10
-
Me)+ complex. The preferred reaction mode of this
reactive intermediate is deinsertion to the starting
materials, a reaction that was also described by Catel-
lani.11 Isomerization to the thermodynamically more
stable trans-N Pd(C7H10Me) isomer is not very competi-
(11) (a) Catellani, M.; Fagnola, M. C. Angew. Chem. 1994, 106, 2559.
See also: (b) Gallezzi, M. C.; Porri, L.; Vitulli, G. J . Organomet. Chem.
1975, 97, 131.

5164 Organometallics, Vol. 17, No. 23, 1998
Luinstra and Brinkmann
stable toward norbornene deinsertion).9 Therefore a
isomerization is fast in both directions. Trans-P to
trans-N isomerization in (P,N)Pd(alkyl)+ complexes
appears to be slower than CO insertion in both the
methyl and 3-methyl-2-norbornyl compounds. Nor-
bornene insertion into the Pd-C bond in (P,N)Pd-
[C(O)R]+ (R ) Me, C7H10Me) takes only place from the
reactive trans-P isomer. In contrast, norbornene inser-
tion proceeds from the trans-N isomer of (P,N)PdMe+.
This leads to the following mechanistic scheme for the
consecutive insertion of CO and olefins into the Pd-C
bond in (P,N)PdR+ complexes: CO insertion takes place
from the ground-state configuration and olefin insertion
from the high-energy acyl intermediate. This leads to
alternating insertions of different monomers at different
sites: Migratory insertion of the olefinic monomer
occurs from the coordination site with the smallest trans
influence. The chemoselectivity arises from the fact
that norbornene does not insert into the Pd-acyl bond
of the thermodynamically more stable isomer, and
Pd-alkyl preinsertion isomerization is slow relative
to CO coordination and insertion. The underlying
grounds for a slow trans-N-trans-P isomerization in the
Pd-alkyls and a faster one for the Pd-acyl complexes
may lay in the higher reactivity in general (Hammond
postulate13,14) or in the fact that the acyl group may
become η2-coordinated, thereby lowering the activation
energy and/or thermodynamic differences between cis
and trans-P isomers. The rate-determining step in the
putative polyketone formation with these complexes is
CO insertion into the Pd-alkyl bond of the thermody-
namically most stable isomer. This kinetic scheme
contrast the one reported for (phen)PdMe+ cations,
where olefin insertion is the rate-determining factor.3c
different, i.e. the trans-P, Pd[C(O)Me] (and Pd(C7H10
Me)) complex is intermediately formed. Furthermore,
the trans-P (P,N)Pd[C(O)Me]+ and (P,N)Pd(C7H10Me)+
intermediates do not have the thermodynamic most
stable configuration. It has been know from calculations
and experiments that such compounds are significantly
more reactive than the cis-P isomers.8b,12
-
The carbonylation of 6a is fast, contrasting that of
1a . Since cis-trans isomerization in 6a is slowsimplied
by the fact that the product is stable and its formation
is slowsit is concluded that Pd[C(O)-3-Me-2-C7H10
]
formation proceeds through postinsertion isomerization,
the same pathway as for 1a . In contrast to the acyl
complex 3a, postinsertion isomerization is fast in trans-P
(P,N)Pd[C(O)-3-Me-2-C7H10] (6a ). This may be the
result of the higher steric congestion (vide infra) in
trans-P (P,N)Pd[C(O)-3-Me-2-C7H10] compared to trans-P
(P,N)Pd[C(O)Me] (3a ).
It is further concluded that norbornene insertion into
the Pd-C(O)R+ bond of compounds 3 and 7 occurs only
in the trans-P isomers. This is suggested by the
geometry of the trans-N configuration of the products
4 and 5: a preinsertion isomerization is very likely since
the alternative postisomerization in the products with
a chelating keto functionality is expected to be slow
enough to allow the observation of the trans-P geo-
metrical isomer. Trans-P-to-trans-N isomerization in
complexes (P,N)Pd(alkyl)+ (methyl or C7H10Me) is gen-
erally slow.8b The dissimilar ratios exo,endo- and ex-
o,exo-5a -c that are obtained with the various P,N
ligands also suggest that olefin insertion takes place cis
to the phosphine where the largest changes in the
sterics of the ligands are. The fact that we are not able
to assign the configuration of the exo,endo- or exo,exo-
5a-c products, however, thwarts further interpretation.4h
Another observation corroborates the assumption of
norbornene insertion from the high-energy acyl isomers.
Norbornene insertion into the Pd-acyl bond in 3a , a
compound with a slow cis-trans-P isomerization, is
slow, whereas in compound 7a a fast cis-trans isomer-
ization and a fast olefin insertion is found. The faster
preisomerization in 7a relative to 3a can be understood
from a steric point of view. The steric bulk of the P,N
ligand is the smallest cis to the amine, implying that,
for sterically more demanding groups bonded cis-P to
Pd, a driving force for isomerization to cis-N emanates
(and decreasing the Gibbs free energy difference be-
tween trans-N and trans-P isomers). A possible lower
aptitude for deinsertion of CO relative to isomerization
in cis-N 7a can likewise be expected on the basis of the
steric strain imposed by the P substituents in the
putative product (P,N)Pd(3-Me-2-C7H10)(CO)+.
Exp er im en ta l Section
Gen er a l Con sid er a tion s. All operations were performed
in an inert atmosphere with rigorous exclusion of oxygen and
moisture using Schlenk, vacuum-line, or glovebox techniques.
Solvents were thoroughly dried (ether and THF over Na/
benzophenone, pentane over Na/K alloy, toluene over Na,
CCl2H2 over CaH2) and distilled prior to use. CDCl3 was
vacuum transferred from CaH2. Pd compounds were prepared
as reported.5,9 NaBAr′4 was prepared as published.16 Nor-
bornene was distilled from CaH2. CO (5N) was obtained from
Messer-Griesheim and was dried over a column (2 ft, diameter
2 in.) of blue silica prior to use. IR spectra were recorded on
a Mattson Galaxy spectrometer as Nujol mulls between KBr
disks. NMR spectra were recorded on Bruker WM250, AC250,
DXR 600 Avance or J EOL FX-90Q, J NM GX400 spectrom-
eters. Chemical shifts are reported in ppm and referenced to
residual protons in deuterated solvents (CDCl3: δ ) 7.24 ppm)
for 1H NMR and to characteristic multiplets for 13C NMR
(CDCl3: δ ) 77.0 ppm). 31P NMR spectra were recorded in
the 1H-decoupled mode, and 31P NMR shifts are reported
against external H3PO4 at δ ) 0 ppm. Mass spectra were
obtained with Finnigan MAT312 or Finnigan MAT 312/
AMD5000 instruments. Elemental analyses were carried out
at the Micro Analytical Department of the University of
Konstanz.
Con clu d in g Rem a r k s
The reactions of the (P,N)Pd-alkyl and -acyl com-
plexes with CO and norbornene, and mixtures thereof,
form a complex system of competing and reversible
reactions. The rate of trans-P to trans-N isomerization
in (P,N)Pd[C(O)Me]+ is the rate-determining factor in
the carbonylation of (P,N)PdMe+ (1a -c). For (P,N)Pd-
[C(O)-3-Me-2-C7H10] derivatives, the trans-N trans-P
(13) (a) Hammond, G. S. J . Am. Chem. Soc. 1955, 77, 334. (b) Evans,
M. G.; Polanyi, M. Trans. Faraday Soc. 1938, 34, 11.
(14) From the upfield shift of 31P NMR resonances of 1a -c upon
carbonylation may be inferred that the electron density in (P,N)PdR+
is higher in the ac(et)yl complexes making them more reactive but
decreasing the equilibrium concentration of the high energy isomer.9
(15) Parshall, G. W.; Ittel, S. D. Homogeneous Catalysis; J . Wiley
& Sons: New York, 1992.
(16) Nishida, H.; Takada, N.; Yoshimura, M.; Sonoda, T.; Kobayashi,
H. Bull. Chem. Soc. J pn. 1984, 57, 2600.
(12) Koga, N.; Morokuma, K. J . Am. Chem. Soc. 1985, 107, 7231.

(P,N)Pd(methyl)+ Derivatives
Organometallics, Vol. 17, No. 23, 1998 5165
Ta ble 2. 1H NMR a n d 13C NMR Da ta for
Com p ou n d s 5a
major isomer
minor isomer
1H NMR
13C NMR
assgnt
CdO
Me
NMe
NMe
PCH
PCH
NB-CH
NB-CH
NB-CH
NB-CH
NB-CH
NB-CH
NB-CH
NB-CH
NB-CH2
13C NMR
1H NMR
242.2
18.51
50.11
46.44
65.56
241.3
17.33
50.11
46.31
65.56
0.93, d, 7 Hz
2.766
2.38
3.42, d, 12 Hz
2.98, d, 12 Hz
2.78
3.02, d, 8 Hz
2.53, d, 10 Hz
2.28
2.17, br m
1.95, br s
1.75, br s
1.67
1.75, br s
1.27, br s
1.75
0.81, d, 7 Hz
2.77
2.37
Com p ou n d 5a . Compound 2a (90 mg, 0.19 mmol), NaBAr′4
(180 mg, 0.19 mmol), and norbornene (1.2 g, 12.7 mmol) were
suspended in 5 mL of CCl2H2. The mixture was stirred for
1.5 h under a CO atmosphere. A black precipitate formed
during this time. The reaction mixture was subsequently
filtered, and the filtrate was evaporated to dryness. The oily
residue solidified after the addition of 10 mL of pentane. The
pentane was decanted off, and the remaining off-white solid
was washed with two other portions of pentane (10 mL). An
off-white solid was isolated after drying. Yield: 183 mg (0.12
mmol, 63%). The NMR (1H, 13C, 31P) spectra show that two
similar isomers are formed in a ratio A/B of about 2/1 (Table
2). Anal. Calcd for C69H57BF24NOPPd: C, 54.51; H, 3.78; N,
0.92; Found: C, 54.17; H, 3.84; N, 1.09. Decomposition was
achieved by adding Lawessons reagent to a solution of 5a in
CDCl3 after 24 h. The resulting solution was characterized
3.42, d, 12 Hz
2.98, d, 12 Hz
2.55
3.10, d, 8 Hz
2.55, br s
2.33, br s
2.17, br m
1.92, br s
1.77, m
1.67
74.56
55.03
41.56
43.67
43.78
43.23
43.71
55.54
37.58
73.62
55.33
43.34
41.3
42.94
43.76
43.43
54.6
37.47
1.87, m
1.3, s
1.67
34.8
NB-CH2
34.8
1.23
1.20
b
b
b
b
1.4-1.6
0.9-1.2
0.3, br s
28.75
29.33
29.64
29.87
NB-CH2
NB-CH2
NB-CH2
NB-CH2
28.66
29.20
29.38
29.91
1.4-1.6
0.9-1.2
0.3, br s
by H and 13C NMR.
1
a
Assignments on basis of 1H NMR, 13C{1H} NMR, APT, HMQC,
and/or HMBC NMR spectroscopic techniques. Phenylic resonances
7.25-7.66 ppm in 1H NMR, 117.49, 124.59 (q, J CF ) 271 Hz, CF3),
125.03, 127.21, 128.19, 128.79, 128.96, 129.07, 129.38, 130.12 (d,
Com p ou n d 6a (MeCN). Compound (P,N)PdMeCl (2a ) (98
mg, 0.21 mmol), NaBAr′4 (200 mg, 0.22 mmol), MeCN (11 µL,
0.20 mmol), and norbornene (200 mg, 2.1 mmol) were sus-
pended in 10 mL of CH2Cl2. The mixture was stirred for 24
h, after which it was filtered over a short column of Na2SO4.
The volatiles were removed in a vacuum, and the remaining
ochre solid was washed twice with 10 mL of pentane and dried.
Yield: 230 mg (0.16 mmol, 77%). 1H NMR (400 MHz,
CDCl3): δ ) 0.34 (m, br, 1H, NB), 0.8-1.9 (m, 7H, NB), 1.28
(d, 3H, J HH ) 6.9 Hz, NB-Me), 2.1 (m, 1H, NB), 2.20 (s, 3H,
NMe/NCMe), 2.27 (s, 3H, NMe/NCMe), 2.40 (s, 3H, NMe/
J CP ) 10.7 Hz), 131.9, 133.68 (d, J CP ) 10.8 Hz), 134.43 (d, J CP
)
13 Hz), 134.84, 135.21 (d, J CP ) 13 Hz), 138.71 (d, J CP ) 4.6 Hz)
ppm in 13C{1H} NMR. Correlation between 1H and 13C shift not
b
unambiguously established. HMBC spectrum of the 13CdO-labeled
compound shows cross signals of the major isomer to NB-CH
resonances at 3.02, 2.78, 2.28, 1.67 (Pd-CH) ppm and for the
minor isomer at 3.1, 2.55 ppm. After decomposition of the
complexes 5a through addition of Lawesson’s reagent (reaction
time 24 h), the resonances of the methyl groups show up as
doublets at 0.79 and 0.71 ppm in the 1H NMR spectrum, and in
the 13C NMR APT spectrum, again 28 signals show up for the four
different norbornene units, as well as two signals for the methyl
groups at 17.48 and 17.11 ppm (ratio ≈ 2/1).
NCMe), 3.18 (d, 1H, J HH ) 13 Hz, NCH), 3.36 (d, 1H, J HH
)
13 Hz, NCH), 6.9-7.7 ppm (m, 26H, aryl). 31P{1H} NMR (161
MHz, CDCl3): δ ) 35.74 ppm. Anal. Calcd for C63H50BF24N2-
PPd: C, 52.57; H, 3.50; N 1.94. Found: C 53.13, H 3.77, N,
1.48.
Rea ction of 1a -c w ith CO a n d Mixtu r es of Nor -
bor n en e a n d CO. A typical experiment is described. Com-
pound (P,N)PdMeCl (2a ) (6.35 mg, 0.0133 mmol), NaBAr′4
(11.8 mg, 0.0133 mmol), and norbornene (4.7 mg, 0.05 mmol)
were dissolved in 0.7 mL of CO-saturated CDCl3. The reaction
was monitored by both 31P and 1H NMR spectroscopy. After
conversion was detected, an aliquot was removed from the
sample, evaporated to dryness, and analyzed by FAB mass
spectroscopy. Reactions of the acyl complexes 3a -c with
norbornene were performed in a similar way, both starting
from (P,N)Pd(COMe)Cl (8a -c) and from the reaction products
of the above experiments.
Com p ou n d 7a . Compound 6a (MeCN) (65 mg, 0.045 mmol)
was dissolved in 5 mL of CO-saturated CHCl3. After the
solution was stirred for 15 min, the volatiles were removed in
a vacuum. A brown solid resulted that was isolated. Yield:
58 mg (0.039 mmol, 87%). The compound is unstable and
decomposes both in solution and the solid state. 1H NMR (400
MHz, CDCl3): δ ) 0.7-1.6 (m, 11H, NB, NB-Me), 1.66 (d,
1H, J HH ) 3.6 Hz, NB), 1.75 (m, 1H, NB), 2.14 (s, 3H, NMe/
NCMe), 2.26 (s, 3H, NMe/NCMe), 2.31 (s, 3H, NMe/NCMe),
2.61 (d, 1H, J HH ) 4.8 Hz, NB), 3.04 (m, 1H, NCH2), 3.14 (m,
1H, NCH2), 6.9-7.7 ppm (m, 26H, aryl). 31P{1H} NMR (161
MHz, CDCl3): δ ) 20.13 ppm. Anal. Calcd for C64H50BF24N2-
OPPd: C, 52.39; H, 3.43; N, 1.91. Found: C, 50.33; H, 3.48;
N, 1.11.
Com p ou n d 4a . (P,N)PdMeCl (2a ) (84 mg, 0.18 mmol),
norbornene (20 mg, 0.19 mmol), and NaBAr′4 (160 mg, 0.18
mmol) were suspended in 15 mL of CO-saturated CH2Cl2. The
mixture was stirred for 4 d, after which it was filtered over a
short column of Na2SO4. The volatiles were removed in a
Ack n ow led gm en t. Support from Degussa in the
form of a generous gift of PdCl2 is gratefully acknowl-
edged. This investigation was supported by the BMBF
(No. 03 N 1028 0).
1
vacuum to yield an ochre solid (203 mg, 0.14 mmol, 79%). H
NMR (600 MHz, CDCl3): δ ) -0.03 (m, 1H, H3-exo), 0.9 (m,
1H, H3-endo), 1.03 (m, 1H, H4-exo), 1.25 (d, 1H, J HH ≈ 10 Hz,
H7-endo), 1.39 (m, 1H, H4-endo), 1.63 (m, 1H, Pd-CH), 1.75
(m, 1H, H7-exo), 1.77 (m, 1H, H2), 2.30 (s, 3H, C(O)Me), 2.32
(s, 3H, NMe), 2.46 (m, 1H, H5), 2.69 (d, 1H, J HH ) 6.6 Hz,
H6), 2.70 (s, 3H, NMe), 2.96 (d, 1H, J HH ) 12 Hz, NCH), 3.39
(d, 1H, J HH ) 12 Hz, NCH), 7.1-7.8 (m, 26H, aryl) ppm. 31P-
{1H} NMR (101 MHz, CDCl3): δ ) 34.14 ppm. Anal. Calcd
for C62H47BF24NOPPd: C, 52.21; H, 3.32; N, 0.98. Found C,
51.73; H, 3.56; N, 0.87.
Su p p or tin g In for m a tion Ava ila ble: Text describing
spectroscopic data for and/or synthetic procedures of 4a -c,
6a (MeCN), 7a , 5a , 1a -c, and 3a -c (2 pages). Ordering
information is given on any current masthead page.
OM980368T