Open Collections

Group 10 complexes of an unsymmetrical electron-rich diphosphine ligand

University of British Columbia

Three unsymmetrical PPC pincer-type ligand precursors, containing a terminal aryl group, for the synthesis of nickel and palladium complexes were developed. The ligand precursors were based off the ButPCP (ButPCP = C₆H₃-2,6-(CH₂P(But)₂)₂) donor set with the intent of studying the effect of the new donor atom arrangement on the chemistry at metal center. However, what quickly emerged was the ability of the terminal aryl group to participate in reactivity rendering the ligand non-innocent. Only one ligand scaffold was successfully installed on both nickel and palladium in a tridentate fashion, requiring oxidative addition of a carbon–bromine bond to the metal to generate square planar nickel(II) and palladium(II) bromide complexes. Salt metathesis reactions of the nickel(II) bromide complex with hydride and alkyl sources (methyl, ethyl and propyl) typically resulted in isolation of nickel(0) complexes as a result of reductive elimination, preceded by beta-elimination in the case of longer-chain alkyl complexes. The nickel(II) methyl complex was isolated, however reductive elimination was induced thermally. Deuterium labelling studies were consistent with a reversible beta-elimination process prior to reductive elimination. Reaction of the nickel(II) bromide complex with heteroatom-containing species resulted in nickel(0) and/or nickel(II) complexes depending on the heteroatom. Corresponding hydride and alkyl palladium(II) complexes were also synthesized with the hydride complex showing a similar propensity for reductive elimination. The palladium(II) alkyl complexes were kinetically more stable than their nickel analogues and the palladium(II) alkyl complex was isolable in each case. Reductive elimination of the terminal aryl and alkyl moieties was induced thermally and the longer-chain alkyl complexes also underwent beta-elimination followed by reductive elimination. As with nickel, deuterium labelling studies supported a reversible beta-elimination process prior to reductive elimination. Carbonylation of the palladium(II) methyl complex also induced reductive elimination. Nickel(II) alkyl complexes lacking beta-hydrogens were synthesized in an attempt to examine the alpha-elimination process from these complexes. However, they proved to be poor model complexes as they underwent alkyl aryl reductive elimination at room temperature or when heated. A nickel(II) amido complex, lacking beta-hydrogens, was also synthesized, however, this complex was also susceptible to carbon–nitrogen reductive elimination upon heating.

Text

2019-05-22

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/70249

Chemistry

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/