Research Plan:
Presented by Dr. B. Murugesapandian
Abstract:
First part of the research proposal aims with synthesis of Group VI metal (Cr, Mo and W) containing heterometallic
complexes by using Group VI metal tricarbonyl based organometallic ligand as metalloligand. The second metal
ions can be varied from alkaline earth metal to lanthanides. After the successful synthesis and characterization of
metal complexes, these complexes will be investigate for catalytic applications and photochemical reaction with
small molecules activation like H2 and N2 since these compounds contains photochemically active CO ligands.
Second part of the proposal aims with synthesis of 3f-4f Metal Organic Polyhedra (MOP) and their application in
catalysis, sensors and magnetic properties.
Introduction:
Heterometallic compounds play a major role in catalysis. Since, these complexes may activate the substrate
molecule cooperatively or simultaneously and the substrate can able to switch between the metal atoms which is not
possible in mononuclear complexes. There are several strategies are available to obtain hetero-metallic complexes.
One fascinating strategy is the metallo-ligand approach; in this approach ligand has already bound to metal ion, is
used for coordination to the other metals. This proposal aims to synthesis the novel group VI metal incorporated
heterometallic compounds using (ɳ6-aniline)M(CO)3 based metalloligand and to study their catalytic activities.
Arene Metal tricarbonyl complexes (ɳ6-arene-M(CO)3) M= Cr, W. Mo belongs to a class of polyene M(L3)
compounds with interesting and fascinating reactivity. Like many other classes of organometallic compounds, the
chemistry of Arene-M(CO)3 complexes has proven to be useful in asymmetric synthesis, in catalysis as chiral
ligands, as catalyst themselves, in supra-molecular chemistry, bio-organometallic chemistry and many
interdisciplinary research areas. The awareness of Arene-M(CO)3 based ligands in coordination chemistry are very
scarce. For example the derivative (benzoic acid)tricarbonylchromium was first reported in 1958 by Fischer et al,
and these compounds have been known for a long time, the number of structurally characterized derivatives is very
limited.
During my post-doc research with Prof. Roesky, we explored the coordination chemistry of (benzoic
acid)tricarbonylchromium. The coordination chemistry of (aniline)tricarbonylchromium based ligands was
completely unexplored. In this regard the aim of this proposal is attachment of group VI metal carbonyl [M(CO)3] to
N,N donor multi-dentate ligands and study their coordination chemistry. For example the coordination chemistry of
mono, bis(imino)pyrrolyl ligand,1,4-diaza-1,3-butadiene ligand, β-diketiminato ligand, bis(imino)pyridine ligand
etc.,(hart 1,1-6) is well known. Prof. Mazhima group has explored the reactivity of imino pyrole ligands (1) and 1,4diaza-1,3-butadiene ligand (3) with metal alkyl, metal amides. Prof Peter W. Roesky group showed the coordination
chemistry of tridentate 2,5-bis(imino)pyrrole ligands (2) towards the lanthanides and heavier alkaline-earth metal
ions. Some of the complexes act as efficient catalysts for intra-molecular hydroamination reactions. Tridentate
bis(imino)pyridine ligand (5) has been utilized extensively by coordination chemist. For example Budzelaar and coworkers, established the utility of bis(imino)pyridine cobalt dichloride (activated with excess AliBu3) and alkyl
complexes for the hydrogenation of 1- and 2-alkenes. Commonly speaking aryl-substituted bis(imino)pyridine iron
and cobalt compounds have used as an effective class of base-metal olefin hydrogenation catalysts. Several group’s
have paid extensive attention to the β-diketiminato ligands (6), since this ligand act as versatile supporting ligands in
organometallic chemistry for stabilizing low-coordinate and highly reactive main-group, transition-metal and
lanthanides, also in homogeneous catalysis.
Chart 1: Established N,N donor multi-dentate ligands
Methodology:
M(CO)3 moiety is consider as electron withdrawing group, it may induce the electronic communication between
the metal ion and substrate in catalysis. M(CO)3 (M = Cr, Mo, W) can also act as structure directing group for
incoming substrate in catalysis by occupying one face of the ligand and also by making hydrogen bonds. Here this
proposal interest is to first synthesis the well established ligands shown in chart 1 with electron withdrawing
M(CO)3 moiety (scheme 1) (M = Cr, Mo, W).
Scheme 1: Proposed ligands with M(CO)3 group.
Ligand Synthesis:
These ligands can be synthesized by two ways, first way is preparation of (ArNH2)M(CO)3 complex, followed
by condensation with corresponding aldehydes (scheme 2). Second way is to make the pro-ligand then treatment of
pro-ligand with excess of M(CO)6 in high boiling solvents (scheme 2).
Scheme 2: Proposed scheme for synthesis of Metallo-ligands
Metal Complexes:
In the above examples some ligand can act as neutral, redox active, some can act as mono anionic or dianionic.
The coordination chemistry of these ligands will study by salt elimination reaction. These ligands can easily
deprotonated by n-BuLi or M”[N(SiMe3)2] (M” = Li, Na, K) and it can treated with anhydrous metal salt to produce
metal complexes. In another way is the treatment of this ligand, with metal amides or metal alkyl complexes lead to
amido or alkyl containing complexes.
R
N
R
R
OC M CO
CO
N
M' R
Xn
R
R
OC M CO
CO
R
R
N
M'
Xn
N
R
OC M CO
CO
R
R
R
OC M CO
CO
R
N
N
N
N
M'
Xn
R
R
OC M CO
CO
M= Cr, Mo, W; M' = alkaline earth metal, transition metal ion, lanthanides; X= anion; n= 1,2.. depends on metal ion
Scheme 3: Schematic representation of Metal complexes of M(CO)3 appended ligands.
Application:
After the complete characterization of the ligands and metal complexes by x-ray and other studies, ligands will
be used as supramolecular synthons for study the supramolecular interaction with some protic acids, and sensors for
some anions.
Scheme 4: Photo-chemical study of metal complexes with N2 or H2.
The influence of M(CO)3 moiety in the structure and catalytic application can be studied in comparison to
their non-substituted derivatives. We will examine influence by phosphine ligands in the catalytic activities of these
complexes, since phosphine ligand can replace the CO group.
Finally these complexes will investigate for the activation of small molecule like H2 or N2 by photolysis. Since the
CO group present in (Ar)M(CO)3 can be replaced by small diatomic molecules in the presence of light (scheme 4).
Other than the proposed ligands, this proposal will also aims to introduce the M(CO)3 group to all the
possible ligands, like different multifunctional carboxylic acids, phosphonic acids and explore their coordination
chemistry with and without co-ligands and investigate the physical, chemical, catalytic properties.
Further this proposal look for the introduction M(CO)3 group to chiral multidetate ligands and study their complexes
as asymmetric catalyst.
-------------------------------------------------------------------------------------------------------------------------------------------Synthesis of heterometallic 3d-4f Metal Organic Polyhedra (MOP)
Introduction:
Metal-organic polyhedra are discrete molecular architectures constructed via the coordination of metal ions and
organic linkers. Because of their intriguing structures, relevance to biological self-assembled systems, and diverse
potential applications (such as in guest molecule inclusion, sensing and catalysis), MOPs have attracted great
attention in past decade. Recently synthetic strategy for constructing functional coordination cages with various
structures and novel inclusion properties have been well established. Here this proposal aims, to synthesis 3d-4f
metal-organic polyhedra by using proper choice of ligands and study the catalytic properties inside the voids, guest
molecule inclusion, sensing properties and guest dependent magnetic properties.
N
OH HN
OH
HO
O
O
N
N
N
N
O
O
OH HN
N
N
NH HO
OH
HO
NH HO
N
Chart 2: Example of proposed ligand for 3d-4f metal organic polyhedral:
Methodology:
In the proposed ligand (two examples) was shown (chart 2) to make 3d-4f metal-organic polyhedra. The
proposed ligand contain two different coordination sites one can able to bind transition metal ion (tetra dentate part;
O-, N, N, O-) and other can able to bind lanthanides (tridentate chelating group; O, N, O-) (scheme 5). Treatment of
this ligand with 3d and 4f metal ion’s may produce 3d-4f metal-organic polyhedral contains big voids. The 3d metal
ion will coordinate by two -imino nitrogen and two phenolic oxygen so other two more coordination sites are
occupied by solvent molecules. After removal of this solvent by vacuum leads to the vacant coordination sites so it
can be useful for catalysis and guest-host interaction. This MOP also contains voids inside the cage, combination of
voids with vacant coordination sites will improve the efficiency for catalysis, guest inclusion and sensing properties.
Due to the presence of lanthanide metal ion, interesting magnetic and luminescent property also expected. By tuning
the aldehyde part we can tune the properties of the metal complexes. Also by proper modification of amine part may
produce the different variety of metal organic polyhedra with different voids space.
Scheme 5: Metal coordination sites of proposed ligand
Application:
After the successful synthesis of 3d-4f MOP, with different 3d metal ion and series of lanthanides contains
different voids spaces. These MOP will be investigate for the catalytic application, guest-host interaction, sensor
properties and guest dependent magnetic studies.
Other than the above proposal, the research interest includes:
Synthesis of oxo, hydroxo lanthanide clusters for catalytic, magnetic and luminescent properties.
Synthesis of transition metal clusters and 3d-4f cluster for interesting magnetic properties.
Synthesis of novel multi-dentate ligands and their coordination chemistry.