Generation of Organoniobium(II) Radicals and Synthesis of Heterometallic Niobium−Mercury Compounds

Abstract

Amalgam reduction of the Nb(III) compounds Cp‘2Nb(Cl)(L) (1, L = CO; 2, L = PMe3; 3, L = CNtBu) gives rise to the electron-rich Nb(II) radicals Cp‘2Nb(L). In one case (L = CO) the intermediate radical was observed using ESR spectroscopy. The radicals undergo a facile reaction with elemental mercury to give the heterometallic compounds [Cp‘2Nb(L)]2Hg, one of which (L = PMe3) was characterized crystallographically; since this process is reversible, the mercury adducts constitute convenient sources of the niobium(II) radicals.

Spin-flip luminescence

“…Complexes of the heavier homologues Nb II and Ta II are rare and no spin-flip emission has been reported to date [137,[174][175][176][177][178].…”

Niobium−Mercury Heterometallic Compounds as Sources of Niobium(II): Radical Paths to Organoniobium Species

“…Nonetheless, we have used reduction reactions in a variety of synthetic processes which may proceed through Nb(II) intermediates and chose to undertake a synthetic and voltammetric study of this process. This led to the production of the niobium−mercury compounds shown in eq 2, and the details of the syntheses have already been published . As such, we will devote this section to a description of the voltammetric experiments, the results of which are depicted in Figure .…”

“…Moreover, we see no evidence for production of this anion in the synthetic studies using sodium amalgam, which does not have sufficient reducing power to effect this second redox process. As a result, we have suggested that the production of the heterometallic compounds 4 − 6 is due to attack of the Nb(II) radicals on elemental mercury present in the amalgam . As a means of understanding the chemistry involved in the second reduction process (Figure ), we carried out reductions using sodium-naphthalene.…”

“…NbCl 5 , [Cp 2 Fe 2 (CO) 4 ], Co 2 (CO) 8 , and [CpNi(CO)] 2 (Aldrich) were commercial materials and used as supplied. Compounds 4 − 6 were prepared using literature methods …”

“…We have recently communicated our discovery of a series of heterometallic niobium−mercury compounds with a L n Nb−Hg−NbL n structure pattern The method involves synthesis of d 3 radicals, and if Nb−Hg bond formation is reversible, the heterometallic Nb−Hg product has the potential to serve as a convenient precursor for radical intermediates.…”