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Abstract
The long-term research goal of the Shelby Group is to design
palladium compounds bonded to negatively charged dip...
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  1. 1. Abstract The long-term research goal of the Shelby Group is to design palladium compounds bonded to negatively charged diphosphorus compounds and to test them for catalysis. We have explored two ways to synthesize these compounds. In one route, we successfully deprotonated the diphosphine ligand, however, its coordination to palladium proved difficult. The other route, coordination of the neutral diphosphine to palladium followed by deprotonation seems more promising. We have narrowed our focus on unsymmetric diphosphine ligands that contain only aromatic substituents with different electronic and/or spatial character to further examine conditions that favor the diphosphine to become negatively charged. Currently, we are working to synthesize two unsymmetric ligands, (2-MeO-C6H4)2PCH2PPh2 and (3,5-dimethylphenyl)2PCH2PPh2. We have two general methods to make the Ar2PCH2PPh2 ligands. One method forms the unsymmetric phosphine sulfide percursor, Ph2PSCH2PAr2, which is then reduced with sodium. The (2-MeO-C6H4)2PCH2PPh2 ligand was made by this sulfide route. Although this method does not appear to be a good option for making the methoxy (2-MeO- C6H4)2PCH2PPh2 ligand because the oxygen might react with sodium, it may be a promising method for the (3,5- dimethylphenyl)2PCH2PPh2 ligand, which does not contain oxygen. Another method for making the Ar2PCH2PPh2 ligands is to treat Ar2PCH2Li with Ph2PCl to make the desired ligand directly. The direct method appears to be favorable for the synthesis of both target ligands, and we are at the stage of making minor changes to improve product yields. Background Symmetrical and unsymmetrical diphosphinomethane ligands (R2P – CH2 – PR2) have widespread use in transition metal chemistry and catalysis. The ligand can act as a bridging ligand (where the two phosphorus atoms bond to two different metals) or as a chelating ligand (where the two phosphorus atoms bond to the same metal). When the methylene ( – CH – ) backbone of the ligand is deprotonated to form , isolated complexes adopt bonding modes in which the ligand (that has become negatively-charged R2P – CH – PR2 ) is a mono-, bi-, or tri-dentate ligand by bonding to one, two, or three metal centers using its methanide carbon and phosphorus atoms. Our research focuses on the synthesis of palladium complexes containing unsymmetrical diphosphine ligands and the steric and/or electronic effects of the phosphorus substituents on the reactivity at the methylene carbon. Our results suggest that sterically bulky phosphorus substituents favor the formation of binuclear Pd Complexes in which the ligands bridge between the metal centers, and that the methylene proton is more acidic when the phosphine substituents are aromatic. Results Throughout reactions 1-5, two different substituents were used. These two aromatic substituents will be represented by Ar2. The following ligands are shown below : 3,5-dimethlyphenyl 2-MeO-C6H4 Reaction 1: • Methyl lithium reacted with Ar2PCl to give Ar2PCH3 . • The percent yield of Ar2PCH3 was not calculated due to its rapid need in reaction 2. Scheme 1: Synthesis of Ar2PCH3 Reaction 2:  LinBu reacted with Ar2PCH3 to give Ar2PCH2Li.  Reflux was done promptly after addition on LitBu.  The percent yield of Ar2PCH2Li was not calculated due to its rapid need in reaction 3. Scheme 2 : Synthesis of Ar2PCH2Li Reaction 3:  Ph2PCl reacted with Ar2PCH2Li to give rise to Ar2PCH2PPh2. Scheme 3 : Synthesis of Ar2PCH2PPh2 Phosphorus NMR Data Results: Future Research Reaction Four: -Similar to analogue in scheme 4, Ph2PCH2P(3,5-dimethylphenyl)2 and Ph2PCH2P(2-MeO- C6H4)2 will each be coordinated to Pd to give PdCl2[Ph2PCH2P(3,5-dimethylpheny)2] and PdCl2[Ph2PCH2P(2-MeO-C6H4)2], respectively. Scheme 4 : Synthesis of PdCl2[Ph2PCH2P(otolyl)2] Reaction Five: -Similar to analogue in scheme 5, PdCl2[Ph2PCH2P(3,5-dimethlyphenyl)2] and PdCl2[Ph2PCH2P(2-MeO-C6H4)2] will each be reduced by LinBu to give the zero valent palladium diphosphine dimer. Scheme 5 : Synthesis of the zero valent palladium diphosphine dimer Figure 4: Structure of the zero valent palladium diphosphine dimer Acknowledgements We thank the Chemistry Department of DePaul University and Louis Stokes Alliance for Minority Participation for the equipment and funding needed to supply our research project. References Badgett, A. H.; Gray, D. L.; Shelby, Q, D. Acta Cryst. 2009, E65, m1233. Eisentrager, F. et al. New J. Chem., 2003, 27, 540. Fernandez, E. J. et al. J. Chem. Soc. Dalton Trans. 1992, 3365. Fornies, J.; Navarro, R.; Urriolabeitia, E. P. J. Organomet. Chem. 1990, 390, 257. Gomez, M. et. al. J. Chem. Soc. Dalton Trans. 1993, 221. Hogarth, G.; Kilmartin, J. J. Organomet. Chem. 2007, 692, 5655. Issleib, K.; Abicht, H. P.; J. Prakt. Chem. 1970, 312, 456. Issleib, K.; Abicht, H. P.; Winkelmann, H. Z. Anorg. Allg. Chem. 1972, 388, 89. Lumbreras, E.; Sisler, E.; Shelby, Q. D. J. Organomet. Chem. 2010, 695, 201. Mosquera, M. E. G. et al. Organometallics, 2000, 19, 5533. Pitroda, P. P. et al. Acta Cryst. 2009, E65, o2307. Reid, S. M.; Fink, M. J. Organometallics 2001, 20, 2959. Studies of Steric and Electronic Behaviors of Palladium Compounds Bonded to Diphosphorus Darcy Velazquez, Khrystyna Hlukhenka, Stephanie Pacheco, & Dr. Quinetta Shelby Figure 1. (3,5-dimethylpheny)2PCH2PPh2 Figure 2. (2-MeO-C6H4)2PCH2PPh2 Figure 3. (3,5-dimethylpheny)2PCH2PPh2 via sulfur route

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