Pcp Pincer Ligand Synthesis Essay

The 15e square-planar complexes [Co(PCPMe-iPr)Cl] (2a) and [Co(PCP-tBu)Cl] (2b), respectively, react readily with NaBH4 to afford complexes [Co(PCPMe-iPr)(η2-BH4)] (4a) and [Co(PCP-tBu)(η2-BH4)] (4b) in high yields, as confirmed by IR spectroscopy, X-ray crystallography, and elemental analysis. The borohydride ligand is symmetrically bound to the cobalt center in η2-fashion. These compounds are paramagnetic with effective magnetic moments of 2.0(1) and 2.1(1) μB consistent with a d7 low-spin system corresponding to one unpaired electron. None of these complexes reacted with CO2 to give formate complexes. For structural and reactivity comparisons, we prepared the analogous Ni(II) borohydride complex [Ni(PCPMe-iPr)(η2-BH4)] (5) via two different synthetic routes. One utilizes [Ni(PCPMe-iPr)Cl] (3) and NaBH4, the second one makes use of the hydride complex [Ni(PCPMe-iPr)H] (6) and BH3·THF. In both cases, 5 is obtained in high yields. In contrast to 4a and 4b, the borohydride ligand is asymmetrically bound to the nickel center but still in an η2-mode. [Ni(PCPMe-iPr)(η2-BH4)] (5) loses readily BH3 at elevated temperatures in the presence of NEt3 to form 6. Complexes 5 and 6 are both diamagnetic and were characterized by a combination of 1H, 13C{1H}, and 31P{1H} NMR, IR spectroscopy, and elemental analysis. Additionally, the structure of these compounds was established by X-ray crystallography. Complexes 5 and 6 react with CO2 to give the formate complex [Ni(PCPMe-iPr)(OC(C═O)H] (7). The extrusion of BH3 from [Co(PCPMe-iPr)(η2-BH4)] (4a) and [Ni(PCPMe-iPr)(η2-BH4)] (5) with the aid of NH3 to yield the respective hydride complexes [Co(PCPMe-iPr)H] and [Ni(PCPMe-iPr)H] (6) and BH3NH3 was investigated by DFT calculations showing that formation of the Ni hydride is thermodynamically favorable, whereas the formation of the Co(II) hydride, in agreement with the experiment, is unfavorable. The electronic structures and the bonding of the borohydride ligand in [Co(PCPMe-iPr)(η2-BH4)] (4a) and [Ni(PCPMe-iPr)(η2-BH4)] (5) were established by DFT computations.

Related Content:

  • A Bimetallic Nickel–Gallium Complex Catalyzes CO2 Hydrogenation via the Intermediacy of an Anionic d10 Nickel Hydride

    Journal of the American Chemical Society

    Cammarota, Vollmer, Xie, Ye, Linehan, Burgess, Appel, Gagliardi, and Lu

    2017139 (40), pp 14244–14250

    Abstract: Large-scale CO2 hydrogenation could offer a renewable stream of industrially important C1 chemicals while reducing CO2 emissions. Critical to this opportunity is the requirement for inexpensive catalysts based on earth-abundant metals instead of precious ...

    Abstract | Full Text HTML | PDF w/ Links | Hi-Res PDF

  • Selective ortho C–H Activation of Pyridines Directed by Lewis Acidic Boron of PBP Pincer Iridium Complexes

    Journal of the American Chemical Society

    Shih and Ozerov

    2017139 (48), pp 17297–17300

    Abstract: Transition-metal mediated C–H functionalization has emerged as a powerful method in the chemistry relevant to the synthesis of pharmaceuticals, agrochemicals, and advanced materials. Because organic molecules typically contain multiple types of C–H bonds, ...

    Abstract | Full Text HTML | PDF w/ Links | Hi-Res PDF

  • Nickel and Iron Pincer Complexes as Catalysts for the Reduction of Carbonyl Compounds

    Accounts of Chemical Research

    Chakraborty, Bhattacharya, Dai, and Guan

    201548 (7), pp 1995–2003

    Abstract: The reductions of aldehydes, ketones, and esters to alcohols are important processes for the synthesis of chemicals that are vital to our daily life, and the reduction of CO2 to methanol is expected to provide key technology for carbon ...

    Abstract | Full Text HTML | PDF w/ Links | Hi-Res PDF

  • Direct Synthesis of Benzimidazoles by Dehydrogenative Coupling of Aromatic Diamines and Alcohols Catalyzed by Cobalt

    ACS Catalysis

    Daw, Ben-David, and Milstein

    20177 (11), pp 7456–7460

    Abstract: Herein, we present the base-metal-catalyzed dehydrogenative coupling of primary alcohols and aromatic diamines to selectively form functionalized 2-substituted benzimidazoles, liberating water and hydrogen gas as the sole byproducts. The reaction is ...

    Abstract | Full Text HTML | PDF w/ Links | Hi-Res PDF

  • Catalytic Nitrogen-to-Ammonia Conversion by Osmium and Ruthenium Complexes

    Journal of the American Chemical Society

    Fajardo and Peters

    2017139 (45), pp 16105–16108

    Abstract: Despite the critical role Ru and Os complexes have played in the development of transition metal dinitrogen chemistry, they have not been shown to mediate catalytic N2-to-NH3 conversion (N2RR), nor have M-NxHy complexes been derived from protonation of ...

    Abstract | Full Text HTML | PDF w/ Links | Hi-Res PDF

  • Synthesis and Catalytic Activity of PNP-Supported Iron Complexes with Ancillary Isonitrile Ligands


    Smith, Bernskoetter, Hazari, and Mercado

    201736 (20), pp 3995–4004

    Abstract: Pincer-supported iron complexes of the form [(iPrPNHP)Fe(H)(HBH3)(CO)] (iPrPNHP = HN(CH2CH2PiPr2)2), [(iPrPNHP)Fe(H){OC(O)H}(CO)], [(iPrPNP)Fe(H)(CO)]; iPrPNP = N(CH2CH2PiPr2)2) have proven to be a privileged class of catalysts for hydrogenation and ...

    Abstract | Full Text HTML | PDF w/ Links | Hi-Res PDF

  • 0 Replies to “Pcp Pincer Ligand Synthesis Essay”

    Lascia un Commento

    L'indirizzo email non verrà pubblicato. I campi obbligatori sono contrassegnati *