4th EucheMs chemistry congress

Poster Session 1
s968
chem. Listy 106, s587–s1425 (2012)
Poster session 1 - inorganic Chemistry
P - 0 2 1 4
A SuLfonyL SuBStituted diLithio
MethAndiide: froM itS eLeCtroniC
StruCture to trAnSition MetAL CArBene
CoMPLexeS
v. GeSSner 1 , f. SChMitt 1 , P. SChrÖter 1
1 Institut für Anorganische Chemie, Universität Würzburg,
Wuerzburg, Germany
Since the pioneering work by E. O. Fischer and R. R. Schrock,
transition metal carbene complexes have found wide-ranging
applications. These complexes are generally divided into two
classes, the Fischer-type carbene and the Schrock-type alkylidene
complexes. However in this context, carbene complexes formed
from geminal dianions, above all dilithiated bis(iminophosphorano)
and bis(thiophosphoryl)methanes, have gained special interest as
they seem to contradict this general classification pattern. [1] Here,
the metal carbon bond is formed by a four-electron donation from
the ligand to the metal, resulting in a highly nucleophilic carbon
atom. [2]
Investigations have so far concentrated on the readily
available bis(phosphonium) systems, thus leaving the impact of
the α-substituent on the nature of the metal carbon bond and thus
on the reactivity of the complex unknown. However, electronic
effects of substitutents at the carbene carbon have shown to
crucially influence the electronic properties and reactivity of
carbene complexes. Here we present a novel sulfonyl substituted
dilithio methandiide as precursor for transition metal carbene
complexes. [3] The methandiide features a distorted carbon
environment which differs from the ideal tetrahedral arrangement.
This is mainly due to geometrical restriction of the donor
functions and can be described by two different bonding modes
of the lithium atoms with the sp2hybridized carbon atom.
Transmetallation with metal salts gives way to early and late
transition metal carbene complexes in high yields.
references:
1. D.J. Mindiola, J. Scott, Nature Chem. 2011, 3, 15.
2. a) T. Cantat, N. Mézailles, A. Auffrant, P. Le Floch,
Dalton Trans. 2008, 1957.
b) S. Harder, Coord. Chem. Rev. 2011, 255, 1252.
4. V. H. Gessner, P. Schröter 2012, submitted.
Keywords: lithium; carbene; carbanions; transition metals;
4 th EucheMs chemistry congress
P - 0 2 1 5
SwitCh it! – PhotoChroMiC CArBene LiGAndS
u. MonKowiuS 1 , M. KAiSer 1 , S. Leitner 1 ,
C. hirtenLehner 1
1 Johannes Kepler University Linz, Institut für Anorganische
Chemie, Linz, Austria
N-Heterocyclic carbenes (NHC) are established ligands for
almost all transition metals and various highly active catalyst
systems bearing NHC ligands have been reported. Nevertheless,
the control of their catalytic performance by external stimuli is
still a challenging task. Various concepts for the regulation of the
activity including the variation of the pH-value, temperature or
solubility have been introduced, but besides the activation of
precatalysts by irreversible photolytic reactions the reversible
regulation of catalysts by light is still in its infancy [1] . Promising
candidates for this purpose are photochromic systems which can
be switched between two different states, e.g. diazobenzenes or
spiropyranes. Based on these moieties, ligands can be designed
which are capable of reversibly shielding an active center of a
metal complex catalyst by steric hindrance.
We will present our first results of NHC based ligands
bearing a diazobenzene group and demonstrate their ligand
properties by the synthesis of the corresponding Ag(I) and Au(I)
complexes. The Ag(I) complex is obtained by the reaction of the
functionalized imidazolium salt with Ag O, successive
2
transmetallation with (Me S)AuCl yields the Au(I) complex. The
2
E->Z isomerisation is induced by UV-light. The thermal back
reaction is very slow and account for minutes even at 80 °C
making an effective switching under catalytic conditions feasible.
references:
1. R. S. Stoll, S. Hecht, Angew. Chem. Int. Ed. 2010, 49,
5054-5075;
M. D. Segarra-Maset, P. W. N. M. van Leeuwen, Z. Freixa,
Eur. J. Inorg. Chem. 2010, 2075-2078.
Keywords: Photochromism; Carbene ligands; Gold; Silver;
AUGUst 26–30, 2012, PrAGUE, cZEcH rEPUbLIc