3 years ago

Heterobimetallic Complexes Comprised of Nb and Fe: Isolation of a Coordinatively Unsaturated NbIII/Fe0 Bimetallic Complex Featuring a NbFe Triple Bond

Heterobimetallic Complexes Comprised of Nb and Fe: Isolation of a Coordinatively Unsaturated NbIII/Fe0 Bimetallic Complex Featuring a NbFe Triple Bond
Mark W. Bezpalko, Matthew J. T. Wilding, Jeremy P. Krogman, Bruce M. Foxman, Gursu Culcu, Diana A. Iovan, Christine M. Thomas
Heterometallic multiple bonds between niobium and other transition metals have not been reported to date, likely owing to the highly reactive nature of low-valent niobium centers. Herein, a C3-symmetric tris(phosphinoamide) ligand framework is used to construct a Nb/Fe heterobimetallic complex Cl–Nb(iPrNPPh2)3Fe−Br (2), which features a Fe→Nb dative bond with a metal–metal distance of 2.4269(4) Å. Reduction of 2 in the presence of PMe3 affords Nb(iPrNPPh2)3Fe–PMe3 (6), a compound with an unusual trigonal pyramidal geometry at a NbIII center, a Nb≡Fe triple bond, and the shortest bond distance (2.1446(8) Å) ever reported between Nb and any other transition metal. Complex 6 is thermally unstable and degrades via P–N bond cleavage to form a NbV═NR imide complex, iPrN═Nb(iPrNPPh2)3Fe−PMe3 (9). The heterobimetallic complexes iPrN═Nb(iPrNPPh2)3Fe−Br (8) and 9 are independently synthesized, revealing that the strongly π-bonding imido functionality prevents significant metal–metal interactions. The 57Fe Mössbauer spectra of 2, 6, 8, and 9 show a clear trend in isomer shift (δ), with a decrease in δ as metal–metal interactions become stronger and the Fe center is reduced. The electronic structure and metal–metal bonding of 2, 6, 8, and 9 are explored through computational studies, and cyclic voltammetry is used to better understand the effect of metal–metal interaction in early/late heterobimetallic complexes on the redox properties of the two metals involved.

Publisher URL: http://dx.doi.org/10.1021/jacs.7b04151

DOI: 10.1021/jacs.7b04151

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