期刊
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
卷 135, 期 8, 页码 3224-3236出版社
AMER CHEMICAL SOC
DOI: 10.1021/ja311966h
关键词
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资金
- AFOSR [FA9550-11-1-0008]
- UCB Department of Chemistry for the Howard W. Crandall Fellowship
- Division of Chemical Sciences, Geosciences, and Biosciences, Office of Basic Energy Sciences, U.S. Department of Energy at LBNL [DE-AC02-05CH11231]
- Heavy Element Chemistry Program at LANL [DE-AC52-06NA25396]
- LANL by Glenn T. Seaborg Institute Postdoctoral Fellowships
- Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy [DE-AC02-05CH11231]
- Direct For Mathematical & Physical Scien
- Division Of Chemistry [840505] Funding Source: National Science Foundation
Monometallic niobium arene complexes [Nb(BDI)((NBu)-Bu-t)(R-C6H5)] (2a: R = H and 21): R = Me, BDI = N,N'-diisopropylbenzene-beta-diketiminate) were synthesized and found to undergo slow conversion into the diniobium inverted arene sandwich complexes [[(BDI)Nb((NBu)-Bu-t)](2)(mu-RC6H5)] (7a: R = H and 7b: R = Me) in solution. The kinetics of this reaction were followed by H-1 NMR spectroscopy and are in agreement with a dissociative mechanism. Compounds 7a-b showed a lack of reactivity toward small molecules, even at elevated temperatures, which is unusual in the chemistry of inverted sandwich complexes. However, protonation of the BDI ligands occurred readily on treatment with [H(OEt2)][B(C6F5)(4)], resulting in the monoprotonated cationic inverted sandwich complex 8 [[(BDI#)Nb((NBu)-Bu-t)][(BDI)Nb((NBu)-Bu-t)](mu-C6H5)][B(C6F5)(4)] and the dicationic complex 9 [[(BDI#)Nb((NBu)-Bu-t)](2)(mu-RC6H5)][B(C6F5)(4)](2) (BDI# = (ArNC(Me))(2)CH2). NMR, UV-vis, and X-ray absorption near-edge structure (XANES) spectroscopies were used to characterize this unique series of diamagnetic molecules as a means of determining how best to describe the Nb-arene interactions. The X-ray crystal structures, UV-vis spectra, arene H-1 NMR chemical shifts, and large J(CH) coupling constants provide evidence for donation of electron density from the Nb d-orbitals into the antibonding pi system of the arene ligands. However, Nb L-3,L-2-edge XANES spectra and the lack of sp(3) hybridization of the arene carbons indicate that the Nb -> arene donation is not accompanied by an increase in Nb formal oxidation state and suggests that 4d(2) electronic configurations are appropriate to describe the Nb atoms in all four complexes.
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