Chemistry and Biochemistry

Janet Braddock-Wilking

 

Janet Braddock-WilkingDr. Braddock-Wilking received her B.A. degree from the University of Missouri-St. Louis and her Ph.D. from Washington University. She joined the UM-St. Louis faculty in 1993 following postdoctoral fellowships at Harvard University and Mallinckrodt Medical, Inc. Between 1993 and 2004 she was Research assistant and then Research Associate Professor and Manager of the NMR Facility. In 2004 she was appointed to a tenure track position.

wilkingj@umsl.edu
Office: N306
Phone: (314) 516-6436
Fax: (314) 516-5342

Research Interests

Dr. Braddock-Wilking's research focuses on the synthesis, characterization, and reactivity of compounds containing heavier Group 14 elements (E = Si, Ge, Sn). A major area of interest involves the chemistry of heterocyclopentadienes containing Group 14 elements, also known as metalloles (Figure 1) and related metallafluorenes.

Figure 1. General metallole and metallafluorene structures (M = Si, Ge)

The heavy group 14 metalloles and metallafluorenes are known to exhibit unusual optoelectronic properties and high electron affinity and mobility and thus have potential application as components for electronic devices such as OLEDs and as chemical and biological sensors. We are currently investigating the preparation of metalloles and metallafluorenes that contain either H or organic groups at the Group 14 center and a variety of π-conjugated organic groups bound to the ring carbons that enable us to fine tune the optoelectronic properties of the metalloles. We are also investigating the synthesis of related systems that incorporate heteratoms that can potentially coordinate to transition-metal centers for applications in chemical sensing. Equation 1 shows a novel fluorescent diplatinum macrocycle recently synthesized in our research group produced from the coordination of two siloles with terminally-linked diphenylphosphine units that coordinate to the Pt centers.

Heavier Group 14 metalloles and metallafluorenes are known to exhibit enhanced photoluminescence as amorphous and crystalline solids or as thin films that has been attributed to aggregation induced emission (AIE) caused by restricted intramolecular rotation (RIR) of the peripheral substituents. Recently, we prepared a series of twelve 1,1-disubstituted-2,3,4,5-tetraphenylgermoles (Scheme 1) that exhibit strong emission in the solid state and have found to be potential chemosensors for volatile organic compounds (VOCs) such as acetone. Addition of increasing amounts of water to an acetone solution of a germole resulted in the formation of highly fluorescent aggregated nanoparticles in solution (Figure 2). The germoles exhibit fluorescence near 480 nm.

Figure 2. Vials of solutions of germole in pure acetone (far left) and acetone-water mixtures (40%, 50%, 60%, 70%, 80%, and 90% respectively).

The Braddock-Wilking research group also studies complexes containing bonds between heavier Group 14 elements and late transition-metals (E-M). There are a variety of synthetic methods known for the formation of complexes containing E-M bonds but the most common and versatile approach involves the formal insertion of the metal center into an E-H bond. This reaction may proceed to full addition of the E-H bond at M or may be arrested at an earlier stage to give a nonclassical (M…H…E) interaction. This reaction is known for nearly all of the transition metal elements with hydrosilanes containing a variety of substituents. However, the related chemistry involving Ge-H and Sn-H bonds is largely unexplored. The Si-H bond activation by a metal center has been extended to catalytic processes such as hydrosilylation and dehydrocoupling. Work is currently underway in the group on hydrosilylation reactions catalyzed by novel late transition metal complexes containing PTA ligands (PTA =1,3,5-triaza-7-phosphaadamantane).

Our previous results have shown that constrained cyclic secondary hydrosilanes (R2SiH2) such as silafluorene (C12H8SiH2) show enhanced reactivity compared to the acyclic analog (Ph2SiH2) upon reaction with (Ph3P)2Pt(η2-C2H4). The nature of the Group 14 element center also has an effect on the type of products that are generated. However, the type of platinum-phosphine precursor used has a dramatic influence on the structural motif formed. An array of different products have been produced the reactions of Pt(0) and Pt(II) phosphine precursors with secondary hydrosilanes, germanes, and stannanes. For example, a unique unsymmetrical dinuclear complex was produced from the reaction of (Ph3P)2Pt(η2-C2H4) with the 1,1-dihydridosilole, H2SiC4Ph4 (eq 2).

Selected Publications

"Synthesis of 2,5-substituted siloles and optical study of interactions with mercury(II), copper(II), and nickel(II) cations," J. B. Carroll and J. Braddock-Wilking, Organometallics 2013, 32, 1905. 

"Synthesis, characterization and Crystal Structures of 1,1-Disubstituted-2,3,4,5-tetraphenylgermoles that Exhibit Aggregation-Induced Emission", T. L. Bandrowsky, J. B. Carroll and J. Braddock-Wilking, Organometallics201130, 3559.

"Luminescent platinum complexes containing phosphorus-linked silole ligands", J. Braddock-Wilking, Li-B. Gao, and N. P. Rath, Dalton Trans. 201039, 9321.

"Reactions of (Et2CH2CH2NEt2).H2SiCl2 with Selected Diorganometallic Reagents of Magnesium and Lithium", J. Y. Corey, K. A. Trankler, J. Braddock-Wilking and N. P. Rath, Organometallics 201029, 5708

“Preparation and Photophysical Properties of Phosphino- and Phosphine Oxide-Linked Siloles”, J.  Braddock-Wilking, L.-B. Gao and N. P. Rath, Organometallics201029, 1612.

“Sila- and Germaplatinacycles produced from a Stepwise E-E Bond Forming Reaction”, J. Braddock-Wilking, T. Bandrowsky, N. Praingam, N. P. Rath, Organometallics 2009,28, 4098.

"Preparation of 1,1-disubstituted silacyclopentadienes " J. Braddock-Wilking, Y. Zhang, J. Y. Corey and N. P. Rath, J. Organomet. Chem. 2008, 693, 1233

"Activation of Group 14 El-H Bonds at Platinum(0)", C. P. White, J. Braddock-Wilking, J. Y. Corey, H. Xu, E. Redekop, S. Sedinkin, and N. P. Rath, Organometallics, 2007,26, 1996

"Si-H Bond Activation by (Ph3P)2Pt(η2-C2H4) in Dihydrosilicon Tricycles that also contain O and N Heteroatoms," J. Braddock-Wilking, J. Y. Corey, L. M. French, E. Choi, V. J. Speedie, M. F. Rutherford, S. Yao, H. Xu, and N. P. Rath,Organometallics2006,25, 3974.

"Spectroscopic and Reactivity Studies of Pt-Si Monomers and Dimers," J. Braddock-Wilking, J. Y. Corey, C. White, H. Xu, and N. P. Rath, Organometallics200625, 2859.

"Reaction of Diphenylgermane with (Ph3P)2Pt(h2-C2H4): Generation of Mono- and Dinuclear Complexes Containing Pt-Ge Bonds. X-ray Crystal Structure Determination of [(Ph3P)Pt(m-h2-H-GePh2)]2," J. Braddock-Wilking, J. Y. Corey, K. A. Trankler, H Xu, L. M. French, N. Praingam, C. White, and N. P. Rath Organometallics, 200524, 4113.

"Reaction of Silafluorenes with (Ph3P)2Pt(h2-C2H4): Generation and Characterization of Pt-Si Monomers, Dimers and Trimers," J. Braddock-Wilking, J. Y. Corey, K. A. Trankler, K. M. Dill, L. M. French, N. P. Rath, Organometallics200423, 4576.

" Formation and X-ray Crystal Structure Determination of a Novel Triplatinum Cluster, ([(Ph3P)Pt(m-SiC12H8)]3 from Reaction of Silafluorene with (Ph3P)2Pt(h2-C2H4)," J. Braddock-Wilking, J. Y. Corey, K. Dill, N. P. Rath, Organometallics200221, 5467.

"Reactivity of {(Ph3P)Pt[m-h2-H-SiH(Ar)]}(Ar = 2-isopropyl-6-methylphenyl) with Phosphines.  X-ray Crystal Structure of trans-{(dppe)Pt[m-SiH(Ar)]}2," J. Braddock-Wilking, Y. Levchinsky, N. P. Rath, Inorg. Chim. Acta2002330, 82.

"Synthesis, Characterization, and X-ray Structural Analysis of Diplatinum Complexes Containing Bridging m-SiHAr Ligands, {(PhnMe3-nP)2Pt[m-SiHAr]}2 [n = 0-2; Ar = 2-isopropyl-6-methyl(phenyl)]," J. Braddock-Wilking, Y. Levchinsky, N. P. Rath,Organometallics200120, 474.