The synthesis of palladacyclopentadienyl derivatives from rigid bis-alkynes and their use as precursors in the synthesis of fluoroanthene-like cycles under mild conditions. A reactivity investigation

Article abstract of DOI:10.1016/j.jorganchem.2007.01.046

The palladium(0) derivatives of the type [Pd(η²-ol)(LL′)] (2) (ol = dmfu: dimethylfumarate (a), fn: fumaronitrile (b), tmetc: tetramethylethylenetetracarboxylate (c), LL′ = HNSPh: 2-(phenylthiomethyl)-pyridine (A), BiPy: 2,2′-bipyridyl (B), DPPE: bis-diphenylphosphinoethane (C)) were reacted in CH₂Cl₂ with 1,8-bis(methylpropynoate)naphthalene (1) and 2,2′-bis(methylpropynoate)biphenyl (1′). At variance with the flexible 1′ derivative, the rigid bis-alkyne 1 reacts smoothly to give the corresponding cyclopalladate complexes [PdC₄(COOMe)₂(Ph)₂(LL′)] (3). The rates of reaction were determined and the X-ray diffraction structure of the complex [PdC₄(COOMe)₂(Ph)₂(HNSPh )] (3A) is reported. The reactivity of the complexes [PdC₄(COOMe)₂(Ph)₂(LL′)] (LL′ = HNSPh (3A), BiPy (3B), DPPE (3C)) was studied by reacting these complexes with fn and tetracyanoethylene (tcne), respectively. The ensuing fluoroanthene-like compounds were fully characterized.

Full text of DOI:10.1016/j.jorganchem.2007.01.046

Journal of Organometallic Chemistry 692 (2007) 2342–2345
www.elsevier.com/locate/jorganchem
Note
The synthesis of palladacyclopentadienyl derivatives from rigid
bis-alkynes and their use as precursors in the synthesis
of fluoroanthene-like cycles under mild conditions.
A reactivity investigation
a,
a
a
a
Luciano Canovese *, Fabiano Visentin , Gavino Chessa , Paolo Uguagliati ,
a
b
Claudio Santo , Lucia Maini
a
`
Dipartimento di Chimica, Universita Ca’ Foscari, Calle Larga S. Marta 2137, 30123 Venezia, Italy
b
Dipartimento di Chimica ‘‘G. Ciamician’’, via Selmi 2, 40126 Bologna, Italy
Received 28 November 2006; received in revised form 18 January 2007; accepted 18 January 2007
Available online 31 January 2007
Abstract
The palladium(0) derivatives of the type [Pd(g2-ol)(LL0)] (2) (ol = dmfu: dimethylfumarate (a), fn: fumaronitrile (b), tmetc: tetram-
ethylethylenetetracarboxylate (c), LL0 = HNSPh: 2-(phenylthiomethyl)-pyridine (A), BiPy: 2,20-bipyridyl (B), DPPE: bis-diphenylphos-
phinoethane (C)) were reacted in CH2Cl2 with 1,8-bis(methylpropynoate)naphthalene (1) and 2,20-bis(methylpropynoate)biphenyl (10).
At variance with the flexible 10 derivative, the rigid bis-alkyne 1 reacts smoothly to give the corresponding cyclopalladate complexes
[PdC4(COOMe)2(Ph)2(LL0)] (3). The rates of reaction were determined and the X-ray diffraction structure of the complex [PdC4(COO-
Me)2(Ph)2(HNSPh )] (3A) is reported. The reactivity of the complexes [PdC4(COOMe)2(Ph)2(LL0)] (LL0 = HNSPh (3A), BiPy (3B),
DPPE (3C)) was studied by reacting these complexes with fn and tetracyanoethylene (tcne), respectively. The ensuing fluoroanthene-like
compounds were fully characterized.
ꢀ 2007 Elsevier B.V. All rights reserved.
Keywords: Palladium complexes; Olefin insertion; Palladacyclopentadienyl complexes
The reactions of unsaturated molecules catalyzed by
palladium complexes represent an important topic in orga-
nometallic chemistry and consequently a wealth of papers
have been recently published in this interesting field [1].
Moreover, exhaustive investigations on the attack of some
dissymmetrically and symmetrically substituted alkynes on
palladium(0) olefin derivatives to give the corresponding
palladacyclopentadienyl complexes were recently carried
out by Elsevier’s group [2] and in our laboratory .In the lat-
ter case, the related mechanism was proposed on the basis
of structural and kinetic evidence [3].
reactivity was found to be strongly related to their steric
hindrance as can be expected in the case of an associative
alkyne attack. Thus, we decided to decrease the molecular
degrees of freedom by linking together two alkyne groups
in hopes that this approach could represent a further step
toward the synthesis of novel cyclopalladate compounds
which might eventually collapse into new condensed poly-
cyclic compounds. We have therefore synthesized the
diynes 1,8-bis(methylpropynoate)naphthalene 1 and 2,20-
bis(methylpropynoate)biphenyl 10 and studied their reac-
tivity toward olefin palladium(0) derivatives 2 to give
the corresponding palladacyclopentadienyl complexes 3
(Chart 1).
In particular, the alkynes used had the general struc-
ture ZC„CZ (Z@COOMe, COOEt, COOt–Bu) and their
The electron-deficiency of the alkyne – a prerequisite for
the quantitative oxidative coupling toward palladium(0)
olefin complexes – is obtained, in the case of the bis-alkyne
*
Corresponding author. Tel.: +39 041 2348571; fax: +39 041 2348517.
E-mail address: cano@unive.it (L. Canovese).
0022-328X/$ - see front matter ꢀ 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2007.01.046

L. Canovese et al. / Journal of Organometallic Chemistry 692 (2007) 2342–2345
2343
Table 1
COOMe
COOMe
Reaction time and conversion ratio for the reaction between the complexes
MeOOC
[Pd(g2-ol)(L–L0)] (2 · 10ꢀ2 mol dmꢀ3) and diyne 1 (3 · 10ꢀ2 mol dmꢀ3
followed by NMR technique at 25 ꢁC in CDCl3
)
COOMe
2Aa 2Ab 2Aca 2Ba 2Bb 2Bca 2Ca 2Cb
1
1'
Complex
L'
L
Conversion (%) 100
Reaction time
100
<50
100
24 h
100 100
<50 600
5
95
5
Pd ol
<50
48 h 48 h 48 h
2
a
Values determined from the second order rate constant (see text).
MeOOC
LL' = HNSPh; ol = dmfu 2Aa
ol = fn 2Ab
L'
ol = tmetc 2Ac
Pd
LL' = BiPy; ol = dmfu 2Ba
ol = fn 2Bb
L
to the palladium(0) centre [4] and the species HNSPh
belongs to the pyridylthioether ligand family which imparts
a remarkable reactivity to its complexes [3a,3c]. In this
respect, the HNSPh derivatives are unable to differentiate
among leaving olefins. At variance, the importance of the
olefin is well documented by complexes 2B in which the
strength of the Pd–olefin bond is clearly borne out by the
comparison between substrates 2Ba and 2Bb: the fn deriv-
ative is far less reactive, albeit sterically favoured, due to
the relative strength of the Pd–dmfu vs. Pd–fn bonds [4].
The tmetc derivatives are important since they belong to
the most widely studied Pd(0) substrates and in this respect
they provide a useful comparison test [4,5]. As a matter of
fact, the steric hindrance of tmetc makes achievable a vari-
ety of reaction rates that would otherwise be too high to be
conveniently studied by usual techniques. The 2Cc deriva-
tive is almost unreactive (only a partial decomposition is
noticed after several days) while complexes 2Ac and 2Bc
were studied in detail and the data in Table 1 are better
described by the k2 values which are (2.25 0.05) · 10ꢀ3
and (1.77 0.05) · 10ꢀ5 molꢀ1 dm3 sꢀ1, respectively [6].
In Fig. 1 plots of the concentration changes for the com-
plexes 2Aa and 3A determined by NMR technique and
the related non-linear fit are reported.
MeOOC
ol = tmetc 2Bc
LL' = DPPE; ol = dmfu 2Ca
ol = fn 2Cb
3
LL' = HNSPh3A
LL' = BiPy 3B
LL' = DPPE 3C
HNSPh(A)
BiPy (B)
DPPE(C)
N
P
P
S
Ph
PhPh Ph
N
N
dmfu = dimethylfumarate (a)
fn = fumaronitrile (b)
tmetc = tetramethy lethylenetetracarboxy late
(c)
Chart 1.
1, through the presence of two electron withdrawing ester
groups coupled with the extended delocalized naphthalene
p-system. On the other hand, the bis-alkyne 10 reacts only
with the most efficient palladium(0) complexes [Pd(g2-
dmfu)(BiPy)] (2Ba) and [Pd(g2-dmfu)(HNSPh)] (2Aa),
yielding however several uncharacterized by-products in
both the reaction mixtures. Apparently, the spatial disposi-
tion of the unsaturated triple bond is also important and
the two alkyne moieties forced in the same plane might give
further information on the mechanism of attack while
reducing the possibility of formation of bridged complexes
and other by-products.
We have therefore studied the reaction reported in
Scheme 1 and the results are summarized in Table 1.
As can be seen in Table 1 the reaction rate is heavily
influenced by the nature of the ancillary ligand and of
the olefin. As a matter of fact the complex 2Aa is the most
reactive substrate since dmfu is the olefin less firmly bound
The direct comparison of the ensuing k2 with the k2
value determined for the same complex 2Aa when reacting
with DMA[3a] (k2 = 0.137 molꢀ1 dm3 sꢀ1; DMA = dimeth-
ylacetylenedicarboxylate) shows that the diyne 1 is consid-
0.030
0.025
0.020
2Aa
3A
MeOOC
0.015
L'
L
L'
COOMe
COOMe
Pd
ol
+
Pd
0.010
0.005
L
MeOOC
3
2
1
0.000
1x104
2x104
3x104
s
4x104
5x104
6x104
0
2= 2Aa, 2Ab, 2Ac, 2Ba, 2Bb, 2Bc, 2Ca, 2Cb
Fig. 1. Concentration profiles determined by 1H NMR in CDCl3 at 298 K
and related best fit for the reaction between the complex 2Aa and 1 to give
complex 3A.
3 = 3A, 3B, 3C
Scheme 1.

2344
L. Canovese et al. / Journal of Organometallic Chemistry 692 (2007) 2342–2345
erably less reactive since it is disfavoured by both steric
(rigid system) and electronic factors (naphthalene is less
effective than the ester group in withdrawing electrons).
The structure of 3A substrate was determined by X-ray dif-
fraction and the ORTEP representation is reported in
Fig. 2.
An important feature of complexes 3 is represented by
their reactivity toward electron-poor olefins to give fluo-
ranthene-like macrocycles under very mild conditions. On
the contrary, it is well known that the synthesis of fluo-
ranthene-like compounds proceeds via a Diels–Alder con-
densation process between a diene and a dienophile
performed at high temperature and using the dienophile
itself as the solvent [7].
Catalyzed production of cycles and in general of poly-
substituted benzene derivatives has been recently reviewed
[8] and a number of compounds have been obtained by
condensation of alkynes under relatively mild conditions.
Itoh and co-workers were able to produce cycles in good
yield by taking advantage of the palladium catalyzed reac-
tions between flexible diynes and DMA [9] or of thermal
decomposition of the Pd(0) triyne complex or of the
Pd2(DBA)3 catalyzed reaction of dimethyl 4,9-dioxatri-
deca-2,7,12-triyne-1,13-dioate [10]. Rigid diynes were
instead used by Costa and co-workers [11] in cobalt cata-
lyzed reactions to give mixtures of well characterized poly-
condensed cycles. However, at the best of our knowledge
no other attempts at condensing similar rigid diynes with
palladium complexes were carried out. Therefore, we tried
to form the polycyclic species by reacting the substrates 3
with fumaronitrile and tetracyanoethylene, thereby obtain-
ing the fluoranthene derivatives 4 and 5 respectively,
according to Scheme 2.
The complex crystallizes with one water molecule which
does not interact with the organometallic molecule but
forms a hydrogen bond with another water molecule
. . .
˚
(O O 2.900(5) A). The palladium(0) has a planar geome-
try, two coordination sites being occupied by the bidentate
ligand 2-((phenylthio)methyl)pyridine, and the other two
by the carbons of the cyclopalladate moiety. The Pd1–
S1and Pd1–N1 bond lengths are very close to those deter-
mined in the case of related pyridylthioether and
quinolylthioether complexes [3a,c] while the Pd1–C2 and
Pd1–C15 distances lie within those of the pyridylthioether
˚
(2.013, 2.042 A) and those of the quinolylthioether deriva-
˚
tives (2.056, 2.064 A).
The mechanism of the reaction in Scheme 2 carried out
in chlorinated solvents at RT presumably involves a preli-
minary coordination of the electron-poor olefin on the flat
palladium(II) centre followed by a Diels–Alder type con-
densation between the olefin and the coordinate diene.
The subsequent displacement of the fluoranthene-like cycle
is promoted by the stabilization of the ensuing Pd(0) deriv-
ative by the olefin in excess. In this respect, the difference
among the rates of reaction (1) and (2) as reported in Table
2 reflects the efficiency of tcne when compared with fn as a
dienophile, the yields and the rates being independent of
the nature of the ancillary ligand, indicating that the elec-
tronic factors overwhelm the steric ones.
Fig. 2. The X-ray diffraction structure of the complex 3A. Selected bond
distances (A): Pd1–C2 2.027(8), Pd1–C15 2.060(7), Pd1–N1 2.134(7), Pd1–S1
2.364(2).
˚
MeOOC
COOMe
CN
NC
Pd
NC
CN
CN
L'
NC
2
NC
CN
CN
NC
NC
L'
L
(1)
Pd
+
+
L
CN
MeOOC
COOMe
3
5
MeOOC
L'
COOMe
CN
CN
L'
(2)
Pd
+
2
NC
Pd
+
+ HCN
L
L
NC
NC
MeOOC
COOMe
3
4
Scheme 2.

L. Canovese et al. / Journal of Organometallic Chemistry 692 (2007) 2342–2345
2345
Table 2
(d) M. Rubin, A.W. Sromek, V. Gevorgyan, Synlett. 15 (2003) 2265;
(e) R. van Belzen, H. Hoffman, C.J. Elsevier, Angew. Chem., Int. Ed.
Eng. 36 (1997) 1743;
(f) R. van Belzen, R.A. Klein, H. Kooijman, N. Veldman, A.L.
Spek, C.J. Elsevier, Organometallics 17 (1998) 1812;
(g) R. van Belzen, C.J. Elsevier, A. Dedieu, N. Veldman, A.L. Spek,
Organometallics 22 (2003) 722;
(h) B.M. Trost, G.J. Tanoury, J. Am. Chem. Soc. 109 (1987) 4753;
(i) B.M. Trost, G.J. Tanoury, J. Am. Chem. Soc. 110 (1988) 1636;
(j) B.M. Trost, M.K. Trost, J. Am. Chem. Soc. 113 (1991) 1850;
(k) B.M. Trost, S.K. Hashmi, J. Am. Chem. Soc. 116 (1994) 2183;
(l) H. Suzuki, K. Itoh, Y. Ishii, K. Simon, J.A. Ibers, J. Am. Chem.
Soc. 98 (1976) 8494;
Reaction time and conversion ratio for the reaction between the complexes
3 (2 · 10ꢀ2 mol dmꢀ3) and olefin (6 · 10ꢀ2 mol dmꢀ3) followed by NMR
at 25 ꢁC in CDCl3
Complex
3A
3B
3C
Reacting olefin
Conversion (%)
Reaction time (h)
a
fn
tcne
91
1
fn
82
60
tcne
93
1
fn
89
60
tcne
87
1
52a
60
The reaction between 3A and fumaronitrile yields the compound 4 and
a mixture of unidentified compounds.
Reaction (2) involves slow formation of a bis-nitrile die-
nyl intermediate which undergoes fast aromatization by de-
hydrocyanation to give dimethyl 8-cyanofluoranthene-
7,10-dicarboxylate 4. This fact deserves a further comment
since the formation of fluoranthene cycle proceeds in the
absence of a strong base, in contrast with other findings
[12]. Apparently, the driving force of the reaction arises
from the synergic interplay of the aromatization process
yielding the cycle and the stabilization of the palladium(0)
derivative induced by an efficient electron withdrawing
olefin.
(m) C.M. Crawforth, I.J.S. Fairlamb, A.R. Kapdi, J.L. Serrano,
R.J.K. Taylor, G. Sanchez, Adv. Synth. Cat. 348 (2006) 406;
(n) J.L. Serrano, I.J.S. Fairlamb, G. Sanchez, L. Garcia, J. Perez, J.
Vives, G. Lopez, C.M. Crawforth, R.J.K. Taylor, Eur. J. Inorg.
Chem. 13 (2004) 2706;
(o) K. Moseley, P.M. Maitlis, J. Chem. Soc., Dalton Trans. (1974)
109.
[2] A. Holuigue, C. Sirlin, M. Pfeffer, K. Goubitz, J. Fraanje, C.
Elsevier, J. Inorg. Chim. Acta 359 (2006) 1773.
[3] (a) L. Canovese, F. Visentin, G. Chessa, P. Uguagliati, C. Levi, A.
Dolmella, Organometallics 24 (2005) 5537;
(b) L. Canovese, F. Visentin, G. Chessa, C. Santo, C. Levi, P.
Uguagliati, Inorg. Chem. Com. 9 (2006) 388;
(c) L. Canovese, F. Visentin, G. Chessa, P. Uguagliati, C. Levi, A.
Dolmella, G. Bandoli, Organometallics 25 (2006) 5355.
[4] L. Canovese, F. Visentin, P. Uguagliati, B. Crociani, J. Chem. Soc.,
Dalton Trans. (1996) 1921.
We also endeavoured to investigate the possibility of the
catalytic production of the fluoranthene cycle, but we
obtained no significant results. The reaction of complex 3
with tcne leads to the formation of the dimethyl-8,8,9,9-tet-
[5] (a) L. Canovese, F. Visentin, G. Chessa, P. Uguagliati, A. Dolmella,
J. Organomet. Chem. 601 (2000) 1;
racyano-8,9-dihydrofluoranthene-7,10-dicarboxylate
5,
thereby confirming the proposed mechanism, but also to
the formation of the very stable [Pd(g2-tcne)(L-L0)] deriva-
tive which prevents any catalytic process.
The reaction under catalytic conditions of complexes
3A–3C with fn leads to a slight stoichiometric excess
of the dimethyl-8-cyanofluoranthene-7,10-dicarboxylate
(TON 6 3) but, in this case the presence in solution of
hydrocyanic acid could trigger the formation of inert cyano
species even in the presence of the base NEt3.
We are now involved in a supplementary study explor-
ing the temperatures, solvents and alkenes that will allow
an efficient catalytic process in the production of similar
fluoranthenyl derivatives.
(b) L. Canovese, F. Visentin, G. Chessa, G. Gardenal, P. Uguagliati,
J. Organomet. Chem. 62 (2001) 155;
(c) L. Canovese, F. Visentin, G. Chessa, C. Santo, P. Uguagliati, L.
Maini, M. Polito, J. Chem. Soc., Dalton Trans. (2002) 3696;
(d) L. Canovese, F. Visentin, P. Uguagliati, G. Chessa, Coord.
Chem. Rev. 248 (2004) 945.
[6] In the case of the complex 2Bc, k2 was determined by the method of
initial rates by taking advantage of the simple structure of the time
dependent complex concentration which can be expressed by the
equation –d[2Bc] = k2[2Bc] [1a] dt. From the slope of the straight line
obtained from the plot of [2Bc] vs time from NMR determinations at
early reaction times one can obtain the second order rate constant
k2 ꢁ slope/[2Bc]0[1a]0 ([2Bc]0 = 3.6 · 10ꢀ2, [1a]0 = 8.3 · 10ꢀ2 mol dmꢀ3).
[7] (a) K. Harano, M. Yasuda, K. Kanematsu, J. Org. Chem. 47 (1982)
3736;
(b) M. Eto, T. Aoki, K. Harano, Tetrahedron 50 (1994) 13395;
(c) M. Matsuda, H. Matsubara, M. Sato, S. Okamoto, K. Yamam-
oto, Chem. Lett. (1996) 157.
Appendix A. Supplementary material
[8] S. Saito, Y. Yamamoto, Chem. Rev. 100 (2000) 2901.
[9] Y. Yamamoto, A. Nagata, K. Itoh, Tetrahedron Lett. 40 (1999)
5035.
[10] Y. Yamamoto, A. Nagata, Y. Arikawa, K. Tatsumi, K. Itoh,
Organometallics 19 (2000) 2403.
[11] (a) Z. Zhou, L.P. Battaglia, G.P. Chiusoli, M. Costa, M. Nardelli,
C. Pelizzi, G. Predieri, J. Chem. Soc. Chem. Commun. (1990)
1632;
X-ray crystallographic data in CIF format, crystal data
and structure refinement. Details on the synthesis and char-
acterization of the novel chemical derivatives. Supplemen-
tary data associated with this article can be found, in the
online version, at doi:10.1016/j.jorganchem.2007.01.046.
References
(b) Z. Zhou, M. Costa, G.P. Chiusoli, J. Chem. Soc., Perkin Trans.
(1992) 1399;
[1] (a) N.E. Schore, Chem. Rev. 88 (1988) 1081;
(b) H. Tom Dieck, C. Munz, C. Mueller, J. Organomet. Chem. 19
(2000) 2403;
(c) Z. Zhou, M. Costa, G.P. Chiusoli, J. Chem. Soc., Perkin Trans.
(1992) 1407.
[12] K. Mizuno, K. Terasaka, N. Ikeda, Y. Otsuji, Tetrahedron Lett. 26
(1985) 5819.
(c) S. Cacchi, J. Organomet. Chem. 576 (1999) 42;