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Dr. Eric A. Maatta

 

Professor and Head

B.S., Carnegie Mellon University, (1974)
Ph.D., Indiana University, (1980)
Postdoctoral Associate, Northwestern University, (1981)

Email: eam@ksu.edu
Office Phone: 785-532-6687
Lab Phone: 785-532-6683
Fax: 785-532-6666

Maatta Group

 

Research Overview

Our program is broadly grounded in synthetic inorganic and organometallic chemistry, with a focus on transition-metal systems containing multiply-bonded ligands. Of particular interest to us are organoimido transition metal complexes, of the form [LnMºN-R]. Like their isoelectronic oxo counterparts, organoimido ligands are excellent pi-donors capable of stabilizing high oxidation state metals in a variety of coordination environments. Unlike the situation for oxo ligands, however, organoimido systems provide an appealing route for the introduction of desirable physical and chemical properties through manipulation of the imido substituent. A sampling of our current interests in organoimido chemistry is provided below.

 I. Imido derivatives of polyoxometalate clusters.

The truly large class of anionic polyoxometalate clusters [MxOyE]n- (where M is typically  high-valent Mo, W, V, Nb or Ta, and E can be a range of main group elements) presents an astonishing variety of unusual structural, catalytic, magnetic and biological properties. We are studying ways to replace the oxo ligands in several such systems with organoimido groups, in an effort to further extend the utility of this class of nano-scale clusters. For example, we have demonstrated that the superoctahedral "hexamolybdate" cluster [Mo6O19]2- can be functionalized sequentially to replace from one to six terminal oxo ligands with arylimido ligands – Figure 1 below shows the molecular structures of the [Mo6O19]2- parent system along with its hexakis(imido) derivative [Mo6(NAr)6O13H]-. Related highly functionalized systems are very attractive building blocks for the rational construction of tunable, redox-active, porous three-dimensional molecular materials. We have acquired a thorough understanding of this family of compounds by using a combination of X-ray crystallography, electronic and vibrational spectroscopy, cyclic voltammetry, and multinuclear (95Mo, 17O, 14N, 1H) NMR techniques.

Figure 1. Structures of [Mo6O19]2-(left) and its hexakis(NAr) derivative (right). 

II. Organoimido ligands incorporating remote functionality.

The flexibility inherent in an [N-R]2- ligand can be exploited through judicious choice of the imido substituent R. For example, if R includes a functionality capable of serving as a donor ligand, then specifically targeted multimetallic systems should be easily accessible. We've demonstrated the feasibility of this concept through the synthesis of a 4-pyridylimido complex of vanadium, [(N3N)VºN-py], shown in Figure 2. The exposed nitrogen atom of the pyridylimido ligand is a competent donor toward both low-valent (e.g., RhI) and high-valent (e.g., WVI) metal centers producing unprecedented types of conjugated heterobimetallic complexes. We also described the first example of an electroactive imido ligand in the form of a ferrocenylimido-hexamolybdate complex, [Mo6O18(NFc)]2-, whose structure is also shown in Fig. 2. This complex displays a prominent Fe(II)–[Mo6] charge transfer absorption at 536 nm, suggesting the possibility to create bi-stable materials in which magnetic and optical changes are triggered by absorption of visible light. There are many further opportunities for synthesizing useful and unusual molecular materials by varying the functionality present in an organoimido ligand..

Figure 2. Functional imido ligands. Structures of the metalloligand [(N3N)VºNpy] (left) and the covalent donor-acceptor ferrocenylimido system [Mo6O18(NFc)]2- (right).

III. Organic - Inorganic Hybrid Materials: Imido Complexes as Polymer Pendants.

We've begun a program to prepare new types of hybrid materials in which exploitable transition metal complexes are present within conventional organic polymers as covalently attached backbone substituents. Our method, which is both simple and general, consists of preparing an organoimido complex in which the imido ligand substituent incorporates a polymerizable functionality (such as a vinyl group), followed by co-polymerization into a particular organic matrix. An example which provides polyoxometalate substituents within a polystyrene matrix is illustrated in Figure 3: the styrylimido hexamolybdate (shown on the left) undergoes free radical-induced co-polymerizations with styrene derivatives to afford soluble hybrid materials ( a segment of one such species is shown on the right). We have made several such polymerizable imido complexes of various transition metals, and these systems offer many opportunities for incorporating useful properties such as luminescence, photo- and electrochromism, and electron and ion conduction into conventional polymeric environments.

Figure 3. Imido-metal complexes in hybrid polymeric materials. Structure of the styrylimido hexamolybdate [Mo6O18(NC6H4CH=CH2)]2– (left) and its methylstyrene copolymer (right).

 IV. Homogeneous modeling of ammoxidation catalysis.

Approximately 10 billion pounds of acrylonitrile are produced worldwide each year in the remarkable heterogeneous allylic oxidation of propylene in the presence of ammonia known as ammoxidation. Various molybdenum oxides catalyze this reaction, but the precise details are not known. Our interest in this chemistry stems from the proposed involvement of various multiply-bonded nitrogenous ligands at the Mo surface sites, many of which were unknown in solution chemistry. We have prepared a range of soluble complexes bearing such catalytically relevant ligands and have studied their reaction chemistry. We have been able to mimic certain aspects of the purported surface chemistry and are constantly refining our models to bring them into closer congruence with the structure and reactivity of the likely active site. Nitrogenous derivatives of the [Mo6O19]2- cluster are a current focus of our work in this area since the Mo coordination environment in this soluble anion provides a striking similarity to that of the MoO3 catalyst component. A particularly exciting recent result which suggests that we are getting very close to a functional ammoxidation mimic is our observation of the production of benzonitrile from the benzylimido complex [Mo6O18(NCH2Ph)]2-.

 

Selected Publications

1. Mohs, T. R.; Yap, G. P. A.; Rheingold, A. L.; Maatta, E. A. "An Organoimido Derivative of the Hexatungstate Cluster: Preparation and Structure of [W6O18(NAr)]2- (Ar = 2,6-(i-Pr)2C6H3)", Inorg. Chem. 1995, 34, 9.
 
2. Hill, P. L.; Yap, G. P. A.; Rheingold, A. L.; Maatta, E. A. "Organoimido Ligands with Remote Functionality: A p-Pyridylimido Complex of Vanadium(V) and Its Use as a Metalloligand", J. Chem. Soc., Chem. Commun. 1995, 737.
 
3. Stark, J. L.; Rheingold, A. L.; Maatta, E. A. "Polyoxometalate Clusters as Building Blocks: Preparation and Structure of Bis(hexamolybdate) Complexes Covalently Bridged by Organodi-imido Ligands", J. Chem. Soc., Chem. Commun. 1995, 1165.
 
4. Stark, J. L.; Young, V. G., Jr.; Maatta, E. A. "A Functionalized Polyoxometalate Bearing a Ferrocenylimido Ligand: Preparation and Structure of [(FcN)Mo6O18]2-", Angew. Chem. 1995, 107, 2751; Angew. Chem. Int. Ed. Engl. 1995, 38, 2547.
 
5. Strong, J. B.; Haggerty, B. S.; Rheingold, A. L.; Maatta, E. A. "A Superoctahedral Complex Derived From a Polyoxometalate: The Hexakis(arylimido)hexamolybdate Anion [Mo6(NAr)6O13H]–", J. Chem. Soc., Chem. Commun. 1997, 1137.
 
6. Mohs, T. R.; Plashko, B.; Du, Y.; Maatta, E. A. "Homogeneous Modeling of Ammoxidation Chemistry: Nitrile Formation From a Soluble Analogue of MoO3", J. Chem. Soc., Chem. Commun. 1997, 1707.
 
7. Wheeler, D. E.; Wu, J.-F.; Maatta, E. A. "Organoimido and Organodi-imido Vanadium Complexes", Polyhedron  1998, 17, 969 (honoring Prof. Donald C. Bradley).
 
8. Kwen, H.; Young, V. G., Jr.; Maatta, E. A. "A Diazoalkane Derivative of a Polyoxometalate: Preparation and Structure of [Mo6O18(NNC(C6H4OCH3)CH3)]2–", Angew. Chem. Int. Ed. Engl. 1999, 38, 1145.
 
9. Strong, J. B.; Yap, G. P. A.; Ostrander, R.; Liable-Sands, L. M.; Rheingold, A. L.; Thouvenot, R.; Gouzerh, P.; Maatta, E. A. "A New Class of Functionalized Polyoxometalates: Synthetic, Structural, Spectroscopic and Electrochemical Studies of Organoimido Derivatives of [Mo6O19]2–", J. Am. Chem. Soc. 2000, 122, 639.
 
10. Moore, A. R.; Kwen, H.; Beatty, A. M.; Maatta, E. A. "Organoimido-Polyoxometalates as Polymer Pendants", Chem. Commun. 2000, 1793.