N-phosphorylated azolylidenes: Novel ligands for dinuclear complexes of coinage metals

Article abstract of DOI:10.1021/om301051t

Dinuclear silver(I) complexes with bridging N-phosphorylated azolylidene ligands have been synthesized. Subsequent transfer of the ligands to other group 11 metal centers (Cu, Au) has been accomplished, highlighting the usefulness of the silver complexes

Full text of DOI:10.1021/om301051t

Note
pubs.acs.org/Organometallics
N‑Phosphorylated Azolylidenes: Novel Ligands for Dinuclear
Complexes of Coinage Metals
†
†
†
†
Anatoliy P. Marchenko, Heorgiy N. Koidan, Anastasiya N. Hurieva, Oleksii V. Gutov,
,
†
‡
‡
‡
§
Aleksandr N. Kostyuk,* Cristina Tubaro, Samira Lollo, Arianna Lanza, Fabrizio Nestola,
,
‡
and Andrea Biffis*
†Institute of Organic Chemistry, National Academy of Sciences of Ukraine, Murmanska Street 5, Kyiv-94, 02094, Ukraine
‡Dipartimento di Scienze Chimiche, Universita
di Padova, Via Marzolo 1, 35131 Padova, Italy
§Dipartimento di Geoscienze, Universita
di Padova, Via Gradenigo 6, 35131 Padova, Italy
S Supporting Information
̀
̀
*
ABSTRACT: Dinuclear silver(I) complexes with bridging N-
phosphorylated azolylidene ligands have been synthesized.
Subsequent transfer of the ligands to other group 11 metal
centers (Cu, Au) has been accomplished, highlighting the
usefulness of the silver complexes as an easy to handle, air- and
moisture-stable source of these ligands. Preliminary results
indicate that dinuclear copper(I) complexes with N-
phosphorylated imidazolylidene ligands display notable
catalytic efficiency in nitrene transfer reactions.
6
7
INTRODUCTION
us (with Ag) as well as by the group of Hofmann (with Cu).
■
1,2
In light of our continuing research interest on the synthesis and
application of NHC complexes of coinage metals, we wish
now to report on the development of a general strategy for the
mild and productive synthesis of complexes of such ligands with
group 11 metal centers, as well as on preliminary data
concerning the properties of such complexes.
N-Heterocyclic carbenes (NHC) represent a recent but
extremely valuable addition to the arsenal of supporting ligands
for metal complexes available to the organometallic chemist.
However, although a lot of different NHC ligand structures
have been proposed, modular NHC-based ligand systems, the
steric and electronic properties of which can be easily and
extensively tuned by substitution of one of the moieties making
8
1
,3
RESULTS AND DISCUSSION
4
■
out the ligand, are still underdeveloped. In this connection, a
Free N-phosphorylated azolylidenes can be distilled without
decomposition under high vacuum, but they are quite unstable
and tend to decompose with time even when kept under strict
exclusion of air and moisture. Therefore, in order to have more
practical, stable, and easy to handle reagents for the preparation
of metal complexes of such carbene ligands, we considered the
use of the corresponding Ag(I) complexes. Such complexes
should serve as stable transmetalating agents, easily transferring
the NHC ligand to other metal centers in analogy to Ag(I)
yet almost unexplored class of NHC-based ligands with these
characteristics is represented by phosphorylated azolylidenes
with a direct N−P bond (Scheme 1). In the past few years,
several original synthetic approaches to such free carbenes have5
been developed by some of us as well as by others.
Furthermore, very recently the first examples of dinuclear
complexes with these carbenes as ligands have been reported by
9
Scheme 1. N-Phosphorylated Azolylidene Ligands Employed
in This Work
complexes with more traditional NHC ligands.
The commonly employed route for the preparation of Ag(I)-
NHC complexes, upon direct reaction of the azolium NHC
9
precursor with Ag O, can be readily applied to our novel
2
phosphorylated ligands, and we have very recently reported on
the success of this synthetic strategy for the preparation o6f
stable Ag complexes with ligands 2 and 3 (Scheme 1).
Similarly, treatment of a solution of the imidazolium precursor
of 1 (Scheme 1) in dichloromethane with 0.5 equivalent of
Ag O at room temperature yielded cleanly the dinuclear
2
Received: November 5, 2012
©
XXXX American Chemical Society
A
dx.doi.org/10.1021/om301051t | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Note
complex 1-Ag as a crystalline, colorless, air-stable solid (Scheme
characteristic range for other silver(I) carbene and phosphine
1
0,11
2). The same complex was formed even when an excess of
complexes previously reported.
Finally, the very short
recorded intermetallic distance of 2.8221(3) Å in 1-Ag
Ag O was used.
2
(
compare the conventionally tabulated covalent radius of 1.45
1
0
10
±
0.05 Å for silver) makes it likely that closed shell d −d
Scheme 2. Synthesis of Complex 1-Ag
12
interactions are present in the complex.
We then started to investigate whether the Ag(I) complexes
could indeed act as transmetalating agents. Indeed, the
phosphorylated imidazolylidene ligand 1 could be cleanly
transferred under mild conditions from 1-Ag to either Cu(I) or
Au(I) centers (Scheme 3).
The identity of the Cu complex 1-Cu was confirmed by
comparison with its characterization data reported by
Hofmann, who prepared the same complex starting from the
7
free carbene ligand. Instead, the identity of the Au complex 1-
Au was confirmed by determination of its crystal structure
We were able to determine the crystal structure of complex
-Ag (Figure 1). The imidazolylidene rings and the silver atoms
(
Figure 2). The structure of complex 1-Au is as expected
1
Figure 2. ORTEP view of complex 1-Au (left) and view along the
Au−Au direction (right). Thermal ellipsoids are at the 50% probability
level. Hydrogen atoms and triflate anions are omitted for clarity.
Selected bond lengths [Å] and angles [deg]: C1−N1 1.347(8), C1−
N2 1.322(9), P1−Au1 2.299(2), C1−Au1 2.061(7), P1−N1 1.756(5),
Au1···Au1′ 2.8099(4); N1−C1−N2 106.8(5), C1−Au1−P1 177.5(2),
Au1−Au1′−C1 89.4(2), Au1−Au1′−P1 89.16(4), P1−N1−C1
Figure 1. ORTEP view of complex 1-Ag (left) and view along the Ag−
Ag direction (right). Thermal ellipsoids are at the 50% probability
level. Hydrogen atoms and triflate anions are omitted for clarity.
Selected bond lengths [Å] and angles [deg]: C10−N1 1.372(3), N2−
C10 1.343(4), P1−Ag1 2.3852(6), C10−Ag1 2.111(2), P1−N1
1
.739(2), Ag1··Ag1′ 2.8221(3), N2−C10−N1 104.5(2), C10−Ag1−
1
25.5(4).
P1 166.99(7), Ag1−Ag1′−C10 88.13(6), Ag1−Ag1′−P1 87.92(2),
P1−N1−C10 121.8(2).
similar to that of complex 1-Ag. Relevant bond lengths are
slightly shorter than in the Ag case; for example, the metal−C
and metal−P bond lengths are respectively 2.111(2) and
2.3852(6) Å in 1-Ag versus 2.061(7) and 2.299(2) Å in 1-Au.
Nevertheless, such bond lengths are in agreement with those of
other gold(I) carbene and phosphine complexes previously
connected to them are found almost in a plane (the sum of
N2−C10−N1, N1−C10−Ag1, and N2−C10−Ag1 angles is
359.7°). The phosphorus atoms connected to Ag protrude
instead above and below this plane as the angle C10−Ag1−P1
is 166.99(7)° (torsion angles C10−Ag1−Ag1′−P1 12.40(7)°;
P1−Ag1−C10′−N1′−87.3(4)°, N1′−P1′−Ag1′−C10
13
reported. The Au−Au distance of 2.8099(4) Å is very short,
as it lies below the Au−Au distance in elemental gold (2.88 Å),
10
10
85.2(3)°). The Ag−C and Ag−P bond lengths are in the
making it likely that closed-shell d −d interactions are
Scheme 3. Synthesis of Complexes 1-Au and 1-Cu
B
dx.doi.org/10.1021/om301051t | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Note
Scheme 4. Synthesis of Complexes 2-Au and 3-Au
12
present also in this case. The main difference between the
structures of the Ag and the Au complexes is the higher degree
of planarity of the latter (Figure 2, right side), in which the
coordination geometry around the two Au atoms is almost
perfectly linear (C1−Au1−P1 angle 177.5(2)°) and with the
coordination axes parallel to each other. Consequently, gold
atoms, phosphorus atoms, and imidazolylidene rings all lie in
the same plane.
The NMR spectrum of the 1-Au complex exhibits the
expected peaks, and it turns out to be very similar to that of 1-
1
3
Ag. The carbene carbon resonance in the C NMR spectrum
of 1-Au is found at 192.7 ppm, well below the value in the free
ligand (223.6 ppm) and similar to the value for the Ag complex
(195.1 ppm).
Transmetalation to Au was successful also with complexes 2-
Ag and 3-Ag (Scheme 4) and yielded the corresponding Au
complexes 2-Au and 3-Au, which once again displayed
spectroscopic features analogous to the corresponding Ag
complexes (see the Supporting Information) On the other
hand, transmetalation to Cu apparently yielded products that
were too unstable to be conveniently isolated in pure form and
characterized.
Figure 3. ORTEP view of complex 2-Au (left) and view along the
Au−Au direction (right). Thermal ellipsoids are at the 50% probability
level. Hydrogen atoms and triflate anions are omitted for clarity.
Selected bond lengths [Å] and angles [deg]: C1−N1 1.38(1), C1−N3
1
.35(2), P1−Au1 2.288(3), C1−Au1 2.03(1), P1−N1 1.75(1), Au1−
The molecular structure of 2-Au was determined by means
of single-crystal X-ray diffraction analysis (Figure 3). As
expected, the gold atoms are linearly coordinated (C1−Au1−
P1 angle 177.6(3)°), as in the case of 1-Au, and the Au−C and
Au−P bond lengths (Au1−C1 2.03(1) Å, Au1−P1 2.288(3) Å)
are also very close to those exhibited by 1-Au. The Au1−Au1′
distance (2.8554(7) Å) is slightly longer than in 1-Au; the same
trend for the metal−metal distance is observed in the
Au1′ 2.8554(7); N1−C1−N3 102.6(9), C1−Au1−P1 177.6(3), Au1−
Au1′−C1 88.5(3), Au1−Au1′−P1 89.45(8), P1−N1−C1 125.9(8).
Scheme 5. Nitrene Transfer Reactions Catalyzed by
Complex 1-Cu
6
corresponding silver complexes (2-Ag vs 1-Ag). The structure
of complex 2-Au is also very similar to that of the parent silver
6
complex 2-Ag, the main difference being, as in the case of
ligand 1, the Ccarbene−metal−P angle (177.6(3)° for Au and
166.99(7)° for Ag).
Finally, we have preliminarly investigated the properties of
the newly synthesized complexes 1-Cu and 1-Au. The
photophysical properties of the Au complex were evaluated in
the solid state under conditions previously employed by some
of us for investigating related dinuclear dicarbene complexes of
8
b
gold(I). Unfortunately, it was determined that despite the
very short Au−Au distance the complex displayed negligible
emission under these conditions (Φ < 0.01). On the other
hand, the catalytic efficiency of 1-Cu in nitrene transfer
reactions was also preliminarly evaluated (Scheme 5). Once
again reaction protocols previously developed by some of us for
which the new complex displayed higher catalytic efficiency
(94% yield) compared to more conventional dinuclear
8
a
dicarbene copper(I) complexes. Moderate yields were
recorded also in the more challenging C−H insertion of the
nitrene into the α-C−H bond of dioxane (41% yield).
8a
CONCLUSIONS
In conclusion, we have shown with the present work that N-
phosphorylated azolylidenes can act as bridging ligands in
related dinuclear dicarbene copper(I) catalysts were em-
ployed. Excellent results were obtained in the aziridination of
styrene with in situ formed N-tosyliminophenyliodinane, in
■
C
dx.doi.org/10.1021/om301051t | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Note
dinuclear metal complexes of group 11 metals. In particular, we
have demonstrated that disilver(I) complexes of such ligands
behave as convenient, air-stable reagents that transfer the
carbene ligand to other metal centers. Further studies on the
properties of such complexes as well as on the preparation and
characterization of complexes with other metals are currently
under way.
Graiff, C. J. Organomet. Chem. 2012, 714, 41−46. (d) Baron, M.;
Tubaro, C.; Basato, M.; Biffis, A.; Natile, M. M.; Graiff, C.
Organometallics 2011, 30, 4607−4615. (e) Biffis, A.; Tubaro, C.;
Scattolin, E.; Basato, M.; Santini, C.; Papini, G.; Alvarez, E.; Conejero,
S. Dalton Trans. 2009, 7223−7229. (f) Tubaro, C.; Biffis, A.; Scattolin,
E.; Basato, M. Tetrahedron 2008, 64, 4187−4195. (g) Biffis, A.; Gioia
Lobbia, G.; Papini, G.; Pellei, M.; Santini, C.; Scattolin, E.; Tubaro, C.
J. Organomet. Chem. 2008, 693, 3760−3766. (h) Baron, M.; Tubaro,
C.; Basato, M.; Natile, M. M.; Graiff, C. J. Organomet. Chem. 2013,
ASSOCIATED CONTENT
Supporting Information
7
23, 108−114.
9) (a) Wang, H. M. J.; Lin, I. J. B. Organometallics 1998, 17, 972−
75. (b) Lin, I. J. B.; Vasam, C. S. Coord. Chem. Rev. 2007, 251, 642−
70.
10) Ma, Y.; Wei, S.; Lan, J.; Wang, J.; Xie, R.; You, J. J. Org. Chem.
008, 73, 8256−8264.
11) Radloff, C.; Weigand, J. J.; Hahn, F. E. Dalton Trans. 2009,
9392−9394.
(12) Pyykko
■
S
(
9
6
(
2
*
Full experimental procedures and X-ray crystallographic data in
CIF format for 1-Ag, 1-Au, and 2-Au. This material is available
free of charge via the Internet at http://pubs.acs.org.
(
AUTHOR INFORMATION
Corresponding Author
E-mail: andrea.biffis@unipd.it; a.kostyuk@yahoo.com.
■
*
̈
, P. Chem. Rev. 1997, 97, 597−636.
(13) (a) Baker, M. V.; Barnard, P. J.; Berners-Price, S. J.; Brayshaw, S.
K.; Hickey, J. L.; Skelton, B. W.; White, A. H. J. Organomet. Chem.
Notes
2
005, 690, 5625−5635. (b) Gaillard, S.; Nun, P.; Slawin, A. M. Z.;
The authors declare no competing financial interest.
Nolan, S. P. Organometallics 2010, 29, 5402−5408.
ACKNOWLEDGMENTS
C.T. and A.B. thank the University of Padova for financial
support (CPDA085452 and HELIOS project).
■
REFERENCES
■
(
1) General references on NHC ligands: (a) Diez-Gonzalez, S., Ed.
N-Heterocyclic Carbenes: From Laboratory Curiosities to Efficient
Synthetic Tools; RSC Catalysis Series; RSC: Cambridge, 2010.
(
b) Cazin, C. S. J., Ed. N-Heterocyclic Carbenes in Transition Metal
Catalysis and Organocatalysis. Catalysis by Metal Complexes, Vol. 32;
Springer: Heidelberg, 2010. (c) Kuhl, O. Functionalised N-Heterocyclic
̈
Carbene Complexes; John Wiley and Sons: New York, 2010. (d) Nolan,
S. P., Ed. N-Heterocyclic Carbenes in Synthesis; Wiley-VCH: Weinheim,
2
(
006.
2) Selected reviews on NHCs: (a) Melaimi, M.; Soleilhavoup, M.;
ge,
Bertrand, G. Angew. Chem., Int. Ed. 2010, 49, 8810−8849. (b) Dro
̈
T.; Glorius, F. Angew. Chem., Int. Ed. 2010, 49, 6940−6952. (c) Hahn,
F. E.; Jahnke, M. C. Angew. Chem., Int. Ed. 2008, 47, 3122−3172.
(
3) Selected reviews on NHC metal complexes: (a) Corberan, R.;
Mas-Marza, E.; Peris, E. Eur. J. Org. Chem. 2009, 1700−1716.
(
b) Glorius, F., Ed. N-Heterocyclic Carbenes in Transition Metal
Catalysis. Topics in Organometallic Chemistry, Vol. 21; Springer:
Heidelberg, 2007. (c) Herrmann, W. A. Angew. Chem., Int. Ed. 2002,
4
(
1, 1290.
4) For a comprehensive account on efforts to overcome this
limitation, see: Benhamou, L.; Chardon, E.; Lavigne, G.; Bellemin-
Laponnaz, S.; Cesar, V. Chem. Rev. 2011, 111, 2705−2733.
(
5) (a) Marchenko, A. P.; Koidan, H. N.; Huryeva, A. N.;
Zarudnitskii, E. V.; Yurchenko, A. A.; Kostyuk, A. N. J. Org. Chem.
010, 75, 7141−7145. (b) Marchenko, A. P.; Koidan, H. N.; Pervak, I.
2
I.; Huryeva, A. N.; Zarudnitskii, E. V.; Tolmachev, A. A.; Kostyuk, A.
N. Tetrahedron Lett. 2012, 53, 494−496. (c) Marchenko, A. P.;
Koidan, H. N.; Hurieva, A. N.; Pervak, I. I.; Shishkina, S. V.; Shishkin,
O. V.; Kostyuk, A. N. Eur. J. Org. Chem. 2012, 4018−4033.
(
2
d) Herrlich (nee
007.
6) Marchenko, A. P.; Koidan, H. N.; Zarudnitskii, E. V.; Hurieva, A.
́
̈
Blumbach), U. Dissertation, Universitat Heidelberg,
(
N.; Kirilchuk, A. A.; Yurchenko, A. A.; Biffis, A.; Kostyuk, A. N.
Organometallics 2012, 31, 8257−8264.
(
̈
7) Kuhnel, E.; Shishkov, I. V.; Rominger, F.; Oeser, T.; Hofmann, P.
Organometallics 2012, 31, 8000−8011.
8) (a) Tubaro, C.; Biffis, A.; Gava, R.; Scattolin, E.; Volpe, A.;
Basato, M.; Diaz-Requejo, M. M.; Perez, P. J. Eur. J. Org. Chem. 2012,
367−1372. (b) Baron, M.; Tubaro, C.; Basato, M.; Biffis, A.; Graiff,
C.; Poater, A.; Cavallo, L.; Armaroli, N.; Accorsi, G. Inorg. Chem. 2012,
1, 1778−1784. (c) Baron, M.; Tubaro, C.; Basato, M.; Biffis, A.;
(
1
5
D
dx.doi.org/10.1021/om301051t | Organometallics XXXX, XXX, XXX−XXX