Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2017 Nov;57(10-11):1032-1036.
doi: 10.1002/ijch.201700072. Epub 2017 Sep 25.

Insights into Activation of Cobalt Pre-Catalysts for C(sp2)-H Functionalization

Jennifer V Obligacion  1 , Hongyu Zhong  1 , Paul J Chirik  1
Affiliations

Insights into Activation of Cobalt Pre-Catalysts for C(sp2)-H Functionalization

Jennifer V Obligacion et al. Isr J Chem. 2017 Nov.

Abstract

The activation of readily prepared, air-stable cobalt (II) bis(carboxylate) pre-catalysts for the functionalization of C(sp2)-H bonds has been systematically studied. With the pyridine bis(phosphine) chelate, iPrPNP, treatment of 1-(O2CtBu)2 with either B2Pin2 or HBPin generated cobalt boryl products. With the former, reduction to (iPrPNP)CoIBPin was observed while with the latter, oxidation to the cobalt(III) dihydride boryl, trans-(iPrPNP)Co(H)2BPin occurred. The catalytically inactive cobalt complex, Co[PinB(O2CtBu)2]2, accompanied formation of the cobalt-boryl products in both cases. These results demonstrate that the pre-catalyst activation from cobalt(II) bis(carboxylates), although effective and utilizes an air-stable precursor, is less efficient than activation of cobalt(I) alkyl or cobalt(III) dihydride boryl complexes, which are quantitatively converted to the catalytically relevant cobalt(I) boryl. Related cobalt(III) dihydride silyl and cobalt(I) silyl complexes were also synthesized from treatment of trans-(iPrPNP)Co(H)2BPin and (iPrPNP)CoPh with HSi(OEt)3, respectively. No catalytic silylation of arenes was observed with either complex likely due to the kinetic preference for reversible C-H reductive elimination rather than product- forming C-Si bond formation from cobalt(III). Syntheses of the cobalt(II) bis(carboxylate) and cobalt(I) alkyl of iPrPONOP, a pincer where the methylene spacers have been replaced by oxygen atoms, were unsuccessful due to deleterious P-O bond cleavage of the pincer. Despite their structural similarity, the rich catalytic chemistry of iPrPNP was not translated to iPrPONOP due to the inability to access stable cobalt precursors as a result of ligand decomposition via P-O bond cleavage.

Keywords: C–H activation; PNP ligand; PONOP ligand; borylation; cobalt.

PubMed Disclaimer

Figures

Figure 1
Figure 1
Solid state structure of 2 at 30% probability ellipsoids. Hydrogen atoms were omitted for clarity.
Scheme 1
Scheme 1
(PNP)cobalt pre-catalysts employed for C–H borylation of arenes. The parent pincer ligand (X=H) is shown for the different catalysts for simplicity.
Scheme 2
Scheme 2
Different activation modes of pincer cobalt borylation catalysts.
Scheme 3
Scheme 3
Stoichiometric reactions of 1-(O2CtBu)2 with B2Pin2 and HBPin.
Scheme 4
Scheme 4
Stoichiometric reactions of 1-(H)2BPin and 1-Ph with HSi (OEt)3.
Scheme 5
Scheme 5
Synthesis of 2.
Scheme 6
Scheme 6
Evaluation of 2 for catalytic C–H borylation.
Scheme 7
Scheme 7
Attempted synthesis of a cobalt alkyl derived from iPrPONOP.
See this image and copyright information in PMC

References

    1. Godula K, Sames D. Science. 2006;312:67–72. - PubMed
    2. Rouquet G, Chatani N. Angew Chem Int Ed. 2013;52:11726–11743. - PubMed
    3. McMurray L, O’Hara F, Gaunt M. Chem Soc Rev. 2011;40:1885–1898. - PubMed
    4. Gutekunst WR, Baran PS. Chem Soc Rev. 2011;40:1976–1991. - PubMed
    5. Colby DA, Tsai AS, Bergman RG, Ellman JA. Acc Chem Res. 2012;45:814–825. - PMC - PubMed
    1. Iverson CN, Smith MR. J Am Chem Soc. 1999;121:7696–7697.
    2. Cho JY, Tse MK, Holmes D, Maleczka RE, Smith MR. Science. 2002;295:305–308. - PubMed
    3. Ishiyama T, Takagi J, Ishida K, Miyaura N, Anastasi NR, Hartwig JF. J Am Chem Soc. 2002;124:390–391. - PubMed
    4. Ishiyama T, Takagi J, Hartwig JF, Miyaura N. Angew Chem Int Ed. 2002;41:3056–3058. - PubMed
    1. Hall DG. Boronic Acids. Wiley-VCH; Weinheim: 2005.
    1. Mazzacano TJ, Mankad NP. J Am Chem Soc. 2013;135:17258–17261. - PubMed
    2. Hatanaka T, Ohki Y, Tatsumi K. Chem – Asian J. 2010;5:1657–1666. - PubMed
    3. Dombray T, Werncke CG, Jiang S, Grellier M, Vendier L, Bontemps S, Sortais JB, Sabo-Etienne S, Darcel C. J Am Chem Soc. 2015;137:4062–4065. - PubMed
    4. Yan G, Jiang Y, Kuang C, Wang S, Liu H, Zhang Y, Wang J. Chem Commun. 2010;46:3170–3172. - PubMed
    1. Obligacion JV, Semproni SP, Chirik PJ. J Am Chem Soc. 2014;136:4133–4136. - PubMed
    2. Schaefer BA, Margulieux GW, Small BL, Chirik PJ. Organometallics. 2015;34:1307–1320.
    3. Scheuermann ML, Johnson EJ, Chirik PJ. Org Lett. 2015;17:2716–2719. - PubMed
    4. Léonard NG, Bezdek MJ, Chirik PJ. Organometallics. 2017;36:142–150.

LinkOut - more resources