RESUMO
Phenoxyimine (FI)-nickel(II)(2-tolyl)(DMAP) compounds were synthesized and evaluated as precatalysts for the C(sp2)-C(sp3) Suzuki-Miyaura cross coupling of (hetero)arylboronic acids with alkyl bromides. With 5 mol % of the optimal (MeOMeFI)Ni(Aryl)(DMAP) precatalyst, the scope of the cross-coupling reaction was established and included a variety of (hetero)arylboronic acids and alkyl bromides (>50 examples, 33-97% yield). A ß-hydride elimination-reductive elimination sequence from reaction with potassium isopropoxide base, yielding a potassium (FI)nickel(0)ate, was identified as a catalyst activation pathway that is responsible for halogen atom abstraction from the alkyl bromide. A combination of NMR and EPR spectroscopies identified (FI)nickel(II)-aryl complexes as the resting state during catalysis with no evidence for long-lived organic radical or odd-electron nickel intermediates. These data establish that the radical chain is short-lived and undergoes facile termination and also support a "recovering radical chain" process whereby the (FI)nickel(II)-aryl compound continually (re)initiates the radical chain. Kinetic studies established that the rate of C(sp2)-C(sp3) product formation was proportional to the concentration of the (FI)nickel(II)-aryl resting state that captures the alkyl radical for chain propagation. The proposed mechanism involves two key and concurrently operating catalytic cycles; the first involving a nickel(I/II/III) radical propagation cycle consisting of radical capture at (FI)nickel(II)-aryl, C(sp2)-C(sp3) reductive elimination, bromine atom abstraction from C(sp3)-Br, and transmetalation; and the second involving an off-cycle catalyst recovery process by slow (FI)nickel(II)-aryl â (FI)nickel(0)ate conversion for nickel(I) regeneration.
RESUMO
OBJECTIVE: Given the prevalence of illegal mobile phone use while driving and reliance upon messaging campaigns in deterring the behavior, there is a need to explore to what extent comparative judgements may influence desired outcomes of such campaigns. This exploratory study investigated (a) the perceived relevance and influence of different mobile phone road safety campaigns within a sample of Queensland motorists who reported using their mobile phone while driving and (b) if these varied depending on whether participants believed that their crash risk whilst using a phone was higher (comparative pessimism), lower (comparative optimism) or similar to the same-age and sex driver. METHODS: A total of 350 licensed drivers residing within Queensland (Australia) were included in this study, of which 200 reported using their hand-held phone on some occasion. Participation involved completing a 20-25 min online anonymous survey, which included viewing three mobile phone road safety campaigns (injury-based, sanction-based and humor) and responding to questions about the perceived relevance and impact of each campaign. RESULTS: A total of 64 (32%) participants displayed comparative optimism, 50 displayed similar judgements (25%) and 86 (43%) exhibited comparative pessimism. First, it was found that the injury-based campaign was perceived to be significantly more relevant than the humor campaign. Second, whilst the relevance of each campaign did not vary as a function of group membership, the campaigns were significantly less relevant to those displaying comparative optimism relative to those with similar judgements and comparative pessimism. Finally, the injury-based campaign was perceived to be significantly more influential than the other campaigns. However, overall, participants displaying comparative optimism believed that they would be less influenced by the campaigns compared to those with comparative pessimism. CONCLUSIONS: Although preliminary, these findings suggest that low perceptions of risk may dilute or extinguish the desired behavioral outcomes of mobile phone road safety campaigns. Nonetheless, experimental research is needed to examine these effects directly.