4th EucheMs chemistry congress

wednesday, 29-Aug 2012
s694
chem. Listy 106, s587–s1425 (2012)
inorganic Chemistry plus Young inorganic chemistry day
New trends in organometallic chemistry – iV
o - 3 1 6
AMMoniA ACtivAtion ProCeSSeS LeAdinG to
noveL AMido And iMido iridiuM And rhodiuM
CoMPLexeS
L. A. oro 1 , M. A. CASAdo 1 , i. MenA 1
1 University of Zaragoza, Inorganic Chemistry, Zaragoza, Spain
Amido-bridged polynuclear complexes [{M(µ -NH ) 2 2
(diolefine)}x] (M = Ir, Rh; diolefin = 1,5-cyclooctadiene (cod) or
tetrafluorobenzobarrelene (tfbb)) can be prepared by treatment of
the methoxo-bridged compounds [{M(µ-OMe)(diolefine)} ] with 2
gaseous ammonia in diethyl ether at atmospheric pressure. [1] The
nuclearity of these unprecedented parent amido complexes
depends on the olefin (trinuclear for tetrafluorobenzobarrelene
and dinuclear for 1,5-cyclooctadiene). They are active catalysts
in hydrogen transfer reactions from isopropanol to unsaturated
substrates. The studies performed on the diiridium(I) complex
[{Ir(µ -NH )(cod)} ] evidences the dinuclear nature of the species
2 2 2
involved and the participation of the two iridium centers in the
catalytic hydrogen transfer reactions. Interestingly, under the
absence of unsaturated substrates the concerted alcohol
dehydrogenation process gives rise to the formation of unusual
mixed amido/imido tetraiiridium and bis(imido) triiridium
clusters.
references:
1. I. Mena, M. A. Casado, P. García-Orduna, V. Polo,
F. J. Lahoz, A. Fazal and L. A. Oro, Angew. Chem. Int. Ed.,
2011, 50, 11735-11738.
Keywords: N ligands; Rhodium; Iridium; Cluster compounds;
Homogeneous catalysis;
New trends in organometallic chemistry – iV
4 th EucheMs chemistry congress
o - 3 1 7
SurPriSeS froM oLd friendS: nitron, the
ALder CArBene, And reLAtiveS
u. SieMeLinG 1 , C. färBer 1 , t. SChuLz 1 , C. Bruhn 1 ,
M. LeiBoLd 1 , t. PorSCh 2 , M. hoLthAuSen 2
1 University of Kassel, Institute of Chemistry, Kassel, Germany
2 University of Frankfurt, Institute of Inorganic and Analytical
Chemistry, Frankfurt am Main, Germany
The paradigm-shifting report of the first stable crystalline
N-heterocyclic carbene (NHC) 1,3-di-1-adamantylimidazol-2-
-ylidene (IAd) by Arduengo in 1991 showed that singlet carbenes
may be sufficiently stable for isolation. IAd is an iconic carbene,
which triggered the tremendous development of NHCs and related
diaminocarbenes from laboratory curiosities to powerful
workhorses in synthesis and catalysis. Conveniently, a limited
number of NHCs have become commercially available, with
1,3,4-triphenyl-1,2,4-triazol-5-ylidene (1) introduced by Enders
being the earliest such example. Unfortunately, prices exceed
several hundred US$ per gram. We found that the low-cost
analytical reagent Nitron, a relative of 1 that has been
commercially available for more than a century, exhibits a hitherto
unrecognised reactivity which is not compatible with its
conventional mesoionic Lewis structure 2, but rather is expected
for its NHC-type tautomer 2’ and closely resembles that of 1. In
fact, the properties of 1 and 2’ as ligands in coordination
chemistry turn out to be very similar. [1] We have investigated
several other mesoionic instant carbenes related to Nitron, which
are easily accessible from readily available starting materials.
Another iconic carbene is (iPr N) C, which was published by
2 2
Alder in 1996 as the first acyclic diaminocarbene to be isolated
and structurally characterised. The ‘Alder carbene’ is commonly
known as the simplest stable diaminocarbene. However, its
reactivity has been much underestimated. We found that (iPr N) C 2 2
is suitable for small-molecule activation [2] and even undergoes a
β-fragmentation in solution already at room temperature.
This is in stark contrast to the previous claims of inertness. The
β-fragmentation process which we uncovered very recently is not
limited to the ‘Alder carbene’.
references:
1. C. Färber, M. Leibold, C. Bruhn, M. Maurer,
U. Siemeling, Chem. Commun. 2012, 48, 227.
2. U. Siemeling, C. Färber, C. Bruhn, M. Leibold, D. Selent,
W. Baumann, M. von Hopffgarten, C. Goedecke,
G. Frenking, Chem. Sci. 2010, 1, 697.
Keywords: Carbenes; Nitrogen heterocycles; Carbene ligands;
C-H activation; Carbonylation;
AUGUst 26–30, 2012, PrAGUE, cZEcH rEPUbLIc