Spectroscopic and synthetic studies relating to a dirhodium hydroformylation catalyst
The main goal of this dissertation research was to further study and characterize our bimetallic hydroformylation catalyst, rac-[Rh2(nbd)2(et,ph-P4)](BF4)2, and to fully identify the catalytically inactive mono- and dirhodium complexes formed upon fragmentation of the catalyst under hydroformylation conditions. Various in situ NMR methods such as 1D 1H and 31P, and 2D COSY, HMBC, and HMQC were employed and indicated the formation of the key catalyst, [rac-Rh2H2(μ-CO)2(CO)4(et,ph-P4)]2+, 4, and a number of other Rh-phosphine species on and off the catalytic cycle. Detailed spectroscopic data was used to propose the structures of these catalytically inactive fragmentation complexes, namely [RhH2(η4-et,ph-P4)]+, 10, and [rac,rac-Rh(η4-et,ph-P4)2RhH2]2+, 11. Mono- and bimetallic rhodium tetraphosphine compounds, RhCl2(η4-et,ph-P4)BF4, 12, Rh(Cl)(CH2Cl)(η4-et,ph-P4)BF4, 13, and [Rh2(η4-et,ph-P4)2](BF4)2, 14 were synthesized, characterized, and their NMR spectroscopic data was obtained. The 31P analyses of these compounds were correlated with the spectroscopic data obtained from the in situ NMR studies of [Rh2(nbd)2(et,ph-P4)](BF4)2 catalyst precursor and indicated that none of these three complexes are present during hydroformylation catalysis. The above compounds were studied to help us expand our knowledge about the bimetallic catalyst and the possible mechanism of the fragmentation process occurring during hydroformylation. In addition, me,ph-P4 ligand, a variation of the et,ph-P4, and dirhodium me,ph-P4 catalyst were synthesized. Separation of meso and racemic diastereomers of this ligand was also achieved. Research in this area involved the synthesis of dimethylchlorophosphine, Me2PCl, and the halogenated methylene bridged bisphosphine, Cl2PCH2PCl2.
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