5 For representative examples of non-covalent combinatorial
approaches for synthesis of bidentate ligands, see: B. Breit, Angew.
Chem., Int. Ed., 2005, 44, 6816; C. Waloch, J. Wieland, M. Keller
and B. Breit, Angew. Chem., Int. Ed., 2007, 46, 3037;
A. C. Laungani and B. Breit, Chem. Commun., 2008, 844;
V. F. Slagt, M. Roder, P. C. J. Kamer, P. W. N. M. van Leeuwen
and J. N. H. Reek, J. Am. Chem. Soc., 2004, 126, 4056;
P.-A. R. Breuil, F. W. Patureau and J. N. H. Reek, Angew. Chem.,
Int. Ed., 2009, 48, 2162; J. M. Takacs, D. S. Reddy, S. A. Moteki,
D. Wu and H. Palencia, J. Am. Chem. Soc., 2004, 126, 4494. For
solid phase-based approach, see: G. Y. Li, P. J. Fagan and
P. L. Watson, Angew. Chem., Int. Ed., 2001, 40, 1106.
6 G. S. Akimova, V. N. Chistokletov and A. A. Petrov, Zh. Org.
Khim., 1967, 3, 968; A. Krasinski, V. V. Fokin and K. B. Sharpless,
Org. Lett., 2004, 6, 1237.
7 S. W. Kwok, J. E. Hein, V. V. Fokin and K. B. Sharpless,
Heterocycles, 2008, 76, 1141; M. Yamauchi, T. Miura and
M. Murakami, Heterocycles, 2010, 80, 177.
Fig. 2 Perspective view of molecules (a) 17 and (b) 18.
zwitterionic bisphosphine complex based on a triazole frame.
Although examples of mesoionic or ‘‘truly zwitterionic’’ metal
complexes bearing chelating bidentate ligands with negatively
charged backbones are limited, they have found spectacular
applications in inorganic and organometallic chemistry.15,16
As such, complexes based on anionic ligand 14 represent an
attractive extension of this family of compounds.
8 Sole example of symmetrical 4,5-bis(diphenylphosphinoyl)-1,2,3-
triazole and its seleno-analog were previously prepared by thermal
Huisgen cycloaddition of the corresponding Ph2P(E)CꢁCP(E)Ph2
(E = O, Se) with NaN3 and studied as ligands for transition
metals. However, metal complexes based on the reduced bis-
(diphenylphosphanyl)-1,2,3-triazole are not reported. See:
A. L. Rheingold, L. M. Liable-Sands and S. Trofimenko, Angew.
Chem., Int. Ed., 2000, 39, 3321–3324; M. Moya-Cabrera,
V. Jancik, R. A. Castro, R. Herbst-Irmer and H. W. Roesky,
Inorg. Chem., 2006, 45, 5167; J. A. Balanta-Dıaz, M. Moya-
Cabrera, V. Jancik, L. W. Pineda-Cedeno, R. A. Toscano and
R. Cea-Olivares, Inorg. Chem., 2009, 48, 2518; J. Alcantara-
Garcia, V. Jancik, J. Barroso, S. Hidalgo-Bonilla, R. Cea-Olivares,
R. A. Toscano and M. Moya-Cabrera, Inorg. Chem., 2009, 48,
5874; S. Trofimenko, A. L. Rheingold and C. D. Incarvito, Angew.
Chem., Int. Ed., 2003, 42, 3506.
The prepared ligand set allows for direct access to both
neutral and zwitterionic metal complexes. Since ligands 14 and
16 are isostructural and isoelectronic, they open the door to
direct evaluation of the influence of ligand-charge on the
properties of the metal center. Moreover, our zwitterionic
system offers an interesting alternative to the known
bisphosphine boronate-based zwitterionic complexes, as the
charged triazolide backbone (possessing an Nꢀ unit) can be further
functionalized or can serve as an additional reaction center.16
In summary, we have discovered a new N–C rearrangement
of substituted triazoles which represents a valuable extension
of the chemistry of these increasingly useful compounds.
This allowed us to prepare novel diverse classes of
bisphosphine ligands and their metal complexes with highly
modifiable triazole backbones. These include the first zwitterionic
complex prepared based on a bisphosphine triazole frame.
Investigation of the properties of these systems, especially of
the potential for cooperative chemistry between the basic/
nucleophilic negatively charged triazolide ligand and the metal
center, is currently underway in our labs.
9 See ESIz for experimental details.
10 For some relevant examples of 31P NMR spectra of (Alk)2P(E)–N
(E = BH3 or O) pattern, see: C. G. Hartung, A. Fecher, B. Chapell
and V. Snieckus, Org. Lett., 2003, 5, 1899; R.K. Kanjolia,
D. K. Srivastava, C. L. Watkins and L. K. Krannich, Inorg.
Chem., 1989, 28, 3341; B. Wrackmeyer, Spectrochim. Acta, Part
A, 1984, 40, 963.
11 CCDC 767176 (6a), 767178 (17) and 767177 (18) contain
the supplementary crystallographic data for this paper
(ESIz).
12 Once intermediate 10 is formed, PQO in this species may act as a
Lewis base activator of the electrophilic iPr2P(BH3) group for
nucleophilic attack by a second molecule of 10. Activation of Lewis
acids with Lewis basic phosphine oxides is well documented; see:
S. E. Denmark and G. L. Beutner, Angew. Chem., Int. Ed., 2008,
47, 1560, and references therein; X. Pu, X. Qi and J. M. Ready,
J. Am. Chem. Soc., 2009, 131, 10364. Another possibility is
intramolecular transfer of the iPr2P(BH3) group by double nucleo-
Financial support from Israel Science Foundation (Grant
No. 1292/07) and The FIRST Program of the Israel Science
Foundation (Grant No. 1514/07) is acknowledged.
philic displacement, initiated by PQO, and involving
a
(Ph)2P+–O–P(iPr)2 species as an intermediate.
13 Calculated using Gaussian 03 (Revision D.01): M. J. Frisch, et al.,
see ESIz.
14 A. B. Charette, A. A. Boezio, A. Cote, E. Moreau, J. Pytkowicz,
J.-N. Desrosiers and C. Legault, Pure Appl. Chem., 2005, 77,
1259–1267; N. J. Farrer, R. McDonald, T. Piga and
J. S. McIndoe, Polyhedron, 2010, 29, 254.
Notes and references
1 E. M. Schuster, M. Botoshansky and M. Gandelman, Angew. Chem.,
Int. Ed., 2008, 47, 4555–4558; E. M. Schuster, G. Nisnevich,
M. Botoshansky and M. Gandelman, Organometallics, 2009, 28, 5025.
2 A. Meldal and C. W. Tornøe, Chem. Rev., 2008, 108, 2952; P. Wu
and V. V. Fokin, Aldrichimica Acta, 2007, 40, 7.
15 R. Chauvin, Eur. J. Inorg. Chem., 2000, 577; M. Stradiotto,
K. D. Hesp and R. J. Lundgren, Angew. Chem., Int. Ed., 2010,
49, 494.
3 V. Rostovtsev, L. G. Green, V. V. Fokin and K. B. Sharpless,
Angew. Chem., Int. Ed., 2002, 41, 2596; C. W. Tornøe,
C. Christensen and M. Meldal, J. Org. Chem., 2002, 67, 3057.
4 For review on use of the Cu(I)-catalyzed azide–alkyne cyclo-
addition for adaptable ligands construction, see: H. Struthers,
T. L. Mindt and R. Schibli, Dalton Trans., 2010, 39, 675.
16 For some related examples, see: J. C. Thomas and J. C. Peters,
J. Am. Chem. Soc., 2001, 123, 5100; C. C. Lu and J. C. Peters,
J. Am. Chem. Soc., 2004, 126, 15818; A. N. Vedernikov,
J. C. Fettinger and F. Mohr, J. Am. Chem. Soc., 2004, 126,
11160; E. Khaskin, P. Y. Zavalij and A. N. Vedernikov, Angew.
Chem., Int. Ed., 2007, 46, 6309.
c
This journal is The Royal Society of Chemistry 2011
Chem. Commun., 2011, 47, 319–321 321