Square-planar palladium complexes with trans Di-and tribenzylphosphine ligands bearing O(CH2)4CH=CH2 substituents; Two-and three-fold intramolecular ring-closing metatheses

Article abstract of DOI:10.1021/om100536g

When trans-PdCl₂{PPh_n[CH₂C ₆H₄O(CH₂)₄CH=CH₂] _3-n}₂, with ortho or meta C₆H₄ linkages and n = 0, 1 (tribenzyl-or dibenzylphe

Full text of DOI:10.1021/om100536g

Organometallics 2010, 29, 3231–3234 3231
DOI: 10.1021/om100536g
Square-Planar Palladium Complexes with Trans Di- and
Tribenzylphosphine Ligands Bearing O(CH2)4CHdCH2 Substituents;
Two- and Three-Fold Intramolecular Ring-Closing Metatheses
Jun Han,† Chao Deng,† Ru Fang,† Deyang Zhao,† Leyong Wang,*,† and
John A. Gladysz*,‡
†Key Laboratory of Mesoscropic Chemistry of Ministry of Education, School of Chemistry and Chemical
Engineering, Nanjing University, Nanjing 210093, People’s Republic of China, and Department
‡
of Chemistry, Texas A&M University, P.O. Box 30012, College Station, Texas 77842-3012
Received May 31, 2010
Summary: When trans-PdCl2{PPhn[CH2C6H4O(CH2)4CHd
CH2]3-n}2, with ortho or meta C6H4 linkages and n = 0, 1
(tribenzyl- or dibenzylphenylphosphine cores), are treated with
Grubbs’ catalyst and then H2/PtO2, the macrocycles trans-
directed syntheses of numerous types of architecturally
sophisticated complexes.1-5 However, many of these break-
throughs were first reached by “trial and error”, and hence
further advances require ongoing empirical studies. In pre-
vious efforts, the principal authors reported that the square-
planar palladium and platinum bis(phosphine) dichloride
complexes trans-MCl2(P((CH2)nCHdCH2)3)2 (M/n = Pt/6,
Pt/8, Pd/6; see I in Scheme 1), as well as Rh(CO)(Cl)
analogues, underwent 3-fold intramolecular interligand al-
kene metatheses to yield, after hydrogenations, gyroscope-
like molecules with three-spoke di(trialkyl)phosphine cages
or “stators” (IV).5b,d It was also established that the para-
substituted triarylphosphine complexes trans-Rh(CO)(Cl)-
[P(p-C6H4O(CH2)nCHdCH2)3]2 (n = 5, 6) underwent simi-
lar conversions to “giant” gyroscope-like molecules with
di(triaryl)phosphine stators (V).5c In all of these efforts,
there was a surprising absence of products of the type III,
principally derived by intraligand metathesis.
PdCl2{P[CH2-o-C6H4O(CH2)10O-o-C6H4CH2][CH2-o-C6H4-
O(CH2)10O-o-C6H4)CH2]P[CH2-o-C6H4O(CH2)10O-o-C6H4C-
H2]}, trans-PdCl2{PPh[CH2C6H4O(CH2)10OC6H4 CH2]}2
(o- or m-C6H4), and trans-PdCl2{PPh[CH2-m-C6H4O(CH2)10-
O-m-C6H4CH2]2PhP} are isolated in high yields.
It is now well established that alkene metatheses can be
effected in a variety of metal coordination spheres, enabling
We wondered whether such macrocyclizations could be
extended to group 10 metals and tribenzylphosphine- and
dibenzylphenylphosphine-based ligands that feature O(CH2)4-
CHdCH2 substituents ortho or meta to the benzylic carbon
atoms. These would possess additional conformational degrees
of freedom, which could possibly lead to different selecti-
vities and/or higher fractions of oligomeric products. Also,
tribenzylphosphine is sterically and electronically intermediate
between PPh3 and PCy3.6 In this communication, we describe
intramolecular alkene metatheses of complexes of the formula
trans-PdCl2{PPhn[CH2C6H4O(CH2)4CHdCH2]3-n}2, in which
the CC6H4O linkages can be ortho or meta and n can be 0 or 1.
Interestingly, these systems exhibit a distinct preference for
macrocyclizations involving intraligand metathesis and give
little or no di- or polypalladium byproducts. They further-
more generate novel ditertiary diphosphines that would be
otherwise very difficult to prepare and for which the possibi-
lity of facile decomplexation has been demonstrated.5b
*To whom correspondence should be addressed. Tel/e-mail: þ86-
25-8359-7090/lywang@nju.edu.cn (L.W.); 979 845-1399/gladysz@mail.
chem.tamu.edu (J.A.G.).
(1) Bauer, E. B.; Gladysz, J. A. In Handbook of Metathesis; Grubbs,
R. H., Ed.; Wiley-VCH: Weinheim, Germany, 2003; Vol. 2, pp 403-431.
(2) (a) Chambron, J.-C.; Collin, J.-P.; Heitz, V.; Jouvenot, D.; Kern,
J.-M.; Mobian, P.; Pomeranc, D.; Sauvage, J.-P. Eur. J. Org. Chem.
2004, 1627 (review of work by this group). (b) Frey, J.; Kraus, T.; Heitz, V.;
Sauvage, J.-P. Chem. Eur. J. 2007, 13, 7585.
(3) Representative leading references: (a) Martinez, V.; Blais, J.-C.;
Bravic, G.; Astruc, D. Organometallics 2004, 23, 861. (b) Chase, P. A.;
Lutz, M.; Spek, A. L.; van Klink, G. P. M.; van Koten, G. J. Mol. Catal. A
2006, 254, 2. (c) Song, K. H.; Kang, S. O.; Ko, J. Chem. Eur. J. 2007, 13,
5129. (d) Zheng, X.; Jones, C. W.; Weck, M. J. Am. Chem. Soc. 2007, 129,
1105. (e) Fuller, A.-M. L.; Leigh, D. A.; Lusby, P. J. Angew. Chem., Int. Ed.
2007, 46, 5015; Angew. Chem. 2007, 119, 5103. (f) Chen, W.-Z.;
Protasiewicz, J. D.; Davis, S. A.; Updegraff, J. B.; Ma, L.-Q.; Fanwick,
P. E.; Ren, T. Inorg. Chem. 2007, 46, 3775. (g) Sivaramakrishna, A.; Su, H.;
Moss, J. R. Angew. Chem., Int. Ed. 2007, 46, 3541; Angew. Chem. 2007,
119, 3611. (h) Asada, Y.; Yasuda, Y.; Yorimitsu, H.; Oshima, K.
Organometallics 2008, 27, 6050. (i) Alhomaidan, O.; Bai, G.; Stephan,
D. W. Organometallics 2008, 27, 6343. (j) Youm, K.-T.; Nguyen, S. T.;
Hupp, J. T. Chem. Commun. 2008, 3375. (k) Buchowicz, W.; Szmajda, M.
Organometallics 2009, 28, 6838. (l) Hiraoka, S.; Yamauchi, Y.; Arakane, R.;
Shionoya, M. J. Am. Chem. Soc. 2009, 131, 11646.
(5) (a) Shima, T.; Hampel, F.; Gladysz, J. A. Angew. Chem., Int. Ed.
2004, 43, 5537; Angew. Chem. 2004, 116, 5653. (b) Nawara, A. J.; Shima,
T.; Hampel, F.; Gladysz, J. A. J. Am. Chem. Soc. 2006, 128, 4962. (c)
Wang, L.; Hampel, F.; Gladysz, J. A. Angew. Chem., Int. Ed. 2006, 45,
4372; Angew. Chem. 2006, 118, 4479. (d) Wang, L.; Shima, T.; Hampel,
F.; Gladysz, J. A. Chem. Commun. 2006, 4075. (e) Hess, G.; Hampel, F.;
Gladysz, J. A. Organometallics 2007, 26, 5129. (f) Skopek, K.; Gladysz,
J. A. J. Organomet. Chem. 2008, 693, 857.
(4) (a) Ruwwe, J.; Martın-Alvarez, J. M.; Horn, C. R.; Bauer, E. B.;
´
Szafert, S.; Lis, T.; Hampel, F.; Cagle, P. C.; Gladysz, J. A. Chem. Eur. J.
2001, 7, 3931. (b) Bauer, E. B.; Hampel, F.; Gladysz, J. A. Organometallics
2003, 22, 5567. (c) Shima, T.; Bauer, E. B.; Hampel, F.; Gladysz, J. A. Dalton
Trans. 2004, 1012. (d) Lewanzik, N.; Oeser, T.; Bl€umel, J.; Gladysz, J. A. J. Mol.
Catal. A 2006, 254, 20. (e) de Quadras, L.; Bauer, E. B.; Mohr, W.; Bohling, J. C.;
Peters, T. B.; Martin-Alvarez, J.; Hampel, F.; Gladysz, J. A. J. Am. Chem. Soc.
2007, 129, 8296. (f) de Quadras, L.; Bauer, E. B.; Stahl, J.; Zhuravlev, F.; Hampel,
F.; Gladysz, J. A. New J. Chem. 2007, 31, 1594. (g) Skopek, K.; Barbasiewicz,
M.; Hampel, F.; Gladysz, J. A. Inorg. Chem. 2008, 47, 3474.
(6) Landaeta, V. R.; Peruzzini, M.; Herrera, V.; Bianchini, C.;
ꢀ
Sanchez-Delgado, R. A.; Goeta, A. E.; Zanobini, F. J. Organomet.
Chem. 2006, 691, 1039.
r
2010 American Chemical Society
Published on Web 07/08/2010
pubs.acs.org/Organometallics

3232 Organometallics, Vol. 29, No. 15, 2010
Han et al.
Scheme 1. Possible Intramolecular Ring-Closing Metathesis
Products (II, III) derived from trans-Bis(phosphine) Complexes
with Vinyl-Terminating Phosphorus Substituents (I) and Some
Previously Synthesized Complexes (IV, V)
Scheme 2. Representative Phosphine Synthesis/Complexation
and Alkene Metathesis/Hydrogenation within a Palladium
Coordination Sphere To Give 5
In a Williamson ether recipe, 2-hydroxybenzaldehyde,
6-bromohex-1-ene, and the base K2CO3 (1:1:1) were com-
bined in DMF at 55 °C. Workup gave the corresponding
ether OdCH-o-C6H4O(CH2)4CHdCH2 (1a) in ∼98% yield.
AsshowninScheme2, subsequent reductionwith NaBH4 and
treatment with SOCl2 afforded the benzyl chloride ClCH2-o-
C6H4O(CH2)4CHdCH2 (2a; 79%). The corresponding
Grignard reagent was treated with PCl3 (3.1:1.0 mol ratio)
to give the phosphine P(CH2-o-C6H4O(CH2)4CHdCH2)3
(3a; 63%). The new compounds 1a-3a and all others below
were characterized by NMR (1H, 13C, and 31P) and micro-
analyses, as summarized in the Supporting Information.
The reaction of 3a and Pd(COD)Cl2 afforded the palla-
dium bis(phosphine) complex trans-PdCl2{P[CH2-o-C6H4-
O(CH2)4CHdCH2]3}2 (4; 60%) (Scheme 2). Next, 4 (ca.
0.001 M in CH2Cl2) and Grubbs’ catalyst (first generation;
∼half of 15 mol %) were combined with stirring at room
temperature under a nitrogen atmosphere. The remaining
catalyst was added after 24 h, and the solution was then
refluxed for 24 h. Following chromatography, the crude
mixture of CdC isomers was hydrogenated (1 atm H2,
15 mol % of PtO2) to give 5 as a yellow solid in 86%
overall yield. The 31P NMR spectrum exhibited a singlet at
10.8 ppm. However, the 13C NMR spectrum showed two
sets of PCH2-o-C6H4O- signals in a ca. 2:1 ratio, with the
PCH2 peaks being phosphorus-coupled virtual triplets.7
This would be inconsistent with a product with the sym-
metry of II (Scheme 1). Accordingly, the structure shown in
Scheme 2, corresponding to macrocyclization mode III,
was tentatively assigned.
Figure 1. Molecular structure of 5 with thermal ellipsoids at the
50% probability level.
The substituents on the trans phosphorus atoms were essen-
tially eclipsed, as reflected by CH2-P-P-CH2 torsion angles
of ca. 0° (0.9-11.6°) and 120° (105.9-134.6°). The trans
spanning linkage involved a CH2-P-P-CH2 moiety with a
ca. 120° torsion angle (see Figure s1, Supporting Information).
Alkene metatheses of the dibenzylphenylphosphine adducts
trans-PdCl2{PPh[CH2C6H4O(CH2)4CHdCH2]2}2 (7a,b, o-/m-
C6H4) were investigated next. These were accessed by first
generating Grignard reagents derived from 2a (Scheme 2) or
the meta isomer 2b (analogously prepared per the Supporting
Information) and condensing them with PhPCl2. As shown
in Schemes 3 and 4, the resulting crude phosphines PPh(CH2-
C6H4O(CH2)4CHdCH2)2 (6a,b, o-/m-C6H4) were directly
combined with (PhCN)2PdCl2 to give 7a,b (12-17%).
As shown in Figure 1, a crystal structure confirmed
the composition of 5. In this structure and all others below,
the bond lengths and angles about palladium were routine.
(7) Hersh, W. H. J. Chem. Educ. 1997, 74, 1485.

Communication
Scheme 3. Alkene Metathesis/Hydrogenation of 7a
Organometallics, Vol. 29, No. 15, 2010 3233
Figure 2. Molecular structure of (E,E)-8a with thermal ellip-
soids at the 50% probability level.
Scheme 4. Alkene Metathesis/Hydrogenation of 7b
Figure 3. Molecular structure of 9c with thermal ellipsoids at
the 50% probability level.
with mixtures of E/Z CdC linkages, only (E,E)-8a crystal-
lized. As is evident in Figure 2, the C-P-P-C units were
nearly staggered (torsion angles 52.8-63.6 and 180°), with the
phenyl groups anti. The 180° value results from an inversion
center at platinum, a feature also found in the other structure
below.
On the other hand, a similar sequence with 7b (Scheme 4)
afforded a mixture of two products, 9b,c, which could be
crystallized from CH2Cl2/hexane and then carefully separated
according to habit with tweezers (45% and 46%, respectively).
It was thought that one was likely derived from intraligand
metathesis and the other from interligand metathesis. How-
ever, there was no obvious NMR criterion for assigning the
structure. Fortunately, the crystal structure of 9c could be
determined, the results of which are shown in Figure 3. This
established that 9c was an interligand metathesis product, as
rendered in Scheme 4. In principle, two stereoisomers differing
in the relative orientation of the PPh moieties are possible.
Figure 3 shows that these are anti with respect to the “plane” of
the largest macrocycle. In this context, the C-P-P-C units
are staggered, with torsion angles of 56.3-59.1 and 180°.
Results from several other studies are relevant to the
preceding data. First, ring-closing metatheses of alipha-
tic analogues of the dibenzylphenyl systems 7a,b, trans-
PtCl(C6F5)(PPh((CH2)nCHdCH2)2)2, have been carried out
(n = 4-6, 8).4c In every case, the only monoplatinum
products detected were derived from interligand metatheses
In the case of 7a, a metathesis/hydrogenation sequence
followed by chromatography afforded 9a, derived from
intraligand metathesis, in 80% yield (Scheme 3). This struc-
ture, as opposed to one derived from interligand metathesis,
was assigned on the basis of a crystal structure of the bis(alkene)
intermediate 8a. Although 31P NMR spectra of all crude
metatheses products showed three or more signals, consistent

3234 Organometallics, Vol. 29, No. 15, 2010
Han et al.
(analogous to 9c). Second, Garcia-Garibay has reported the
metathesis of a p-diethynylbenzene capped with meta-sub-
stituted trityl groups, (H2CdCH(CH2)4O-m-C6H4)3CCtC-
p-C6H4CtCC(m-C6H4O(CH2)4CHdCH2)3.8 Interestingly,
the sole monomeric product after hydrogenation corres-
ponded to macrocyclization mode III (Scheme 1). Finally,
we have generated additional complexes of the type III via
metatheses of octahedral species with two trans aliphatic
phosphines P((CH2)nCHdCH2)3, but almost always as min-
or byproducts accompanying II.9
In summary, we have demonstrated that palladium com-
plexes of the formula trans-PdCl2{PPhn[CH2C6H4O(CH2)4-
CHdCH2]3-n}2 (o- or m-C6H4; n = 0, 1) undergo ready two-
and 3-fold intramolecular alkene metatheses in high yields.
There is generally a distinct preference for intraligand
metathesis, as opposed to the essentially exclusive forma-
tion of interligand metathesis products from square-planar
complexes with related trans-disposed trialkylphosphine
or para-substituted triphenylphosphine ligands. Perhaps
the benzylic and ortho or meta linkages in Schemes 2-4
facilitate the adoption of conformations more favorable
for intraligand metathesis, and studies to probe such possi-
bilities are in progress. These, and extensions of this chemis-
try to other substituted tribenzylphosphine complexes, will
be detailed in future reports.
Acknowledgment. We thank the Natural Science Foun-
dation of China (No. 20602017, No. 20932004), the National
Basic Research Program of China (No. 2007CB925103), the
Natural Science Foundation of Jiangsu (No. BK2008259),
and the Humboldt Foundation (L.W.) for support and the
reviewers for helpful comments.
Supporting Information Available: Text, figures, tables, and
CIF files giving experimental procedures and characterization
data for all new compounds and crystallographic data for 5, 8a,
and 9c. This material is available free of charge via the Internet
at http://pubs.acs.org.
~
(8) Nunez, J. E.; Natarajan, A.; Khan, S. I.; Garcia-Garibay, M. A.
Org. Lett. 2007, 9, 3559.
(9) Fiedler, T. Unpublished data, Universitat Erlangen-Nurnberg.
€
€