ABSTRACT
The method of continuous variation in conjunction with (1)H and (19)F NMR spectroscopies was used to characterize lithium and sodium enolates solvated by N,N,N',N'-tetramethylethyldiamine (TMEDA) and tetrahydrofuran (THF). A strategy developed using lithium enolates was then applied to the more challenging sodium enolates. A number of sodium enolates solvated by TMEDA or THF afford exclusively tetramers. Evidence suggests that TMEDA chelates sodium on cubic tetramers.
Subject(s)
Fluorine/chemistry , Ketones/chemistry , Lithium/chemistry , Sodium/chemistry , Magnetic Resonance Spectroscopy , Molecular Structure , ProtonsABSTRACT
Applications of the method of continuous variations (MCV or the Method of Job) to problems of interest to organometallic chemists are described. MCV provides qualitative and quantitative insights into the stoichiometries underlying association of m molecules of A and n molecules of B to form A(m)B(n) . Applications to complex ensembles probe associations that form metal clusters and aggregates. Job plots in which reaction rates are monitored provide relative stoichiometries in rate-limiting transition structures. In a specialized variant, ligand- or solvent-dependent reaction rates are dissected into contributions in both the ground states and transition states, which affords insights into the full reaction coordinate from a single Job plot. Gaps in the literature are identified and critiqued.
Subject(s)
Organometallic Compounds/chemistry , Coordination Complexes/chemical synthesis , Coordination Complexes/chemistry , Kinetics , Ligands , Organometallic Compounds/chemical synthesis , Solvents/chemistry , Transition Elements/chemistryABSTRACT
The method of continuous variation (MCV) was used in conjunction with (6)Li NMR spectroscopy to characterize four lithium phenolates solvated by a range of solvents, including N,N,N',N'-tetramethylethylenediamine, Et2O, pyridine, protic amines, alcohols, and highly dipolar aprotic solvents. Dimers, trimers, and tetramers were observed, depending on the precise lithium phenolate-solvent combinations. Competition experiments (solvent swaps) provide insights into the relative propensities toward mixed solvation.
