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Cobalt complexes supported by a tetramethylated PNP pincer ligand (Me4iPrPNP = 2,6-(iPr2PCMe2)2(C5H3N)) have been synthesized and structurally characterized. Examples include cobalt(I)–choride, −me...

Enantioenriched N-alkyl-imidazole-substituted pyridine dicarbene iron dialkyl complexes have been synthesized and characterized by 1H NMR and zero-field 57Fe Mossbauer spectroscopies as well as sin...

Well-defined bis(silylene)pyridine cobalt(III) precatalysts for C(sp2)–H borylation have been synthesized and applied to the investigation of the mechanism of the catalytic borylation of furans and...

Cobalt complexes supported by a tetramethylated PNP pincer ligand (Me(4)(iPr)PNP = 2,6-((i)Pr(2)PCMe(2))(2)(C(5)H(3)N)) have been synthesized and structurally characterized. Examples include cobalt(I)–choride, –methyl, –aryl and –benzofuranyl derivatives. The performance of these compounds was evaluated in the catalytic borylation of fluorinated arenes using B(2)Pin(2) as the boron source. While P–C bond cleavage, a known deactivation pathway in [(PNP)Co]-catalyzed borylation was suppressed, the overall activity and selectivity of the borylation of fluoroarenes was reduced as compared to the previously reported [(PNP)Co] catalyst lacking isopropylene spacers. Stoichiometric reactions support an increased barrier for oxidative addition to cobalt(I), a result of the increased steric profile and decreased conformational flexibility of the pincer resulting from methylation distal to the active site. With a more activated substrate such as benzofuran, catalytic borylation with cobalt(I) precatalysts and HBPin was observed. Monitoring the progress of the reaction by NMR spectroscopy revealed the presence of cobalt(III) intermediates during the course of the borylation, supporting a cobalt(I)-(III) redox cycle.

Well-defined bis(silylene)pyridine cobalt(III) precatalysts for C(sp(2))–H borylation have been synthesized and applied to the investigation of the mechanism of the catalytic borylation of furans and pyridines. Specifically, [((Ar)SiNSi)CoH(3)]·NaHBEt(3) ((Ar)SiNSi = 2,6-[EtNSi(N(t)Bu)(2)CAr](2)C(5)H(3)N, Ar = C(6)H(5) (1-H(3)·NaHBEt(3)), 4-MeC(6)H(4) (2-H(3)·NaHBEt(3))) and trans-[((Ar)SiNSi)Co(H)(2)BPin] (Ar = C(6)H(5) (1-(H)(2)BPin), 4-MeC(6)H(4) (2-(H)(2)BPin), Pin = pinacolato) were prepared and employed as single component precatalysts for the C(sp(2))–H borylation of 2-methylfuran, benzofuran and 2,6-lutidine. The cobalt(III) precursors, 2-H(3)·NaHBEt(3) and 2-(H)(2)BPin also promoted C(sp(2))–H activation of benzofuran, yielding [((Ar)SiNSi)CoH(Bf)(2)] (Ar = 4-MeC(6)H(4), 2-H(Bf)(2), Bf = 2-benzofuranyl). Monitoring the catalytic borylation of 2-methylfuran and 2,6-lutidine by (1)H NMR spectroscopy established the trans-dihydride cobalt(III) boryl as the catalyst resting state at low substrate conversion. At higher conversion two distinct pincer modification pathways were identified, depending on the substrate and the boron source.