Zirconium and hafnium polyhydrides. 2. Preparation and characterization of M{sub 3}H{sub 6}(BH{sub 4}){sub 6}(PMe{sub 3}){sub 4} and M{sub 2}H{sub 4}(BH{sub 4}){sub 4}(dmpe){sub 2}
- Univ. of Illinois, Urbana, IL (United States)
Prolonged treatment of the tetrakis (tetrahydroborate) complexes Zr(BH{sub 4}{sub 4}) or Hf(BH{sub 4}){sub 4} with trimethylphosphine has given the first trinuclear group 4 polyhydrides, M{sub 3}H{sub 6}(BH{sub 4}){sub 6}(PMe{sub 3}){sub 4}, where M is Zr or Hf. The {sup 1}H, {sup 31}P, and {sup 11}B NMR data suggest that these trinuclear compounds contain noncyclic M ({mu}-H){sub 3}M({mu}-H){sub 3}M backbones with the phosphine and tetrahydroborate ligands distributed in 2:2:0 and 2:1:3 ratios among the three metal centers. Interestingly, several of the {eta}{sup 3}-BH{sub 4} groups are bonded asymmetrically, so that of the three Zr-H bonds to each BH{sub 4} ligand, one Zr-H bond is longer than the other two. Addition of 1,2-bis(dimethylphosphino) ethane(dmpe) to the previously reported polyhydrides of stoichiometry M{sub 2}H{sub 3}(BH{sub 4}){sub 5}(PMe{sub 3}){sub 2} results in phosphine exchange and loss of one BH{sub 3} unit to yield the new dinuclear hydrides M{sub 2}H{sub 4}(BH{sub 4}){sub 4}(dmpe){sub 2}. The NMR and X-ray crystallographic data show that three of the hydrides bridge the Zr{hor_ellipsis}Zr axis; the fourth hydride, one {eta}{sup 2}-BH{sub 4} group, and the two dmpe ligands are coordinated variable-temperature NMR data show that the terminal and bridging hydrides on zirconium exchange with each other via a {open_quotes}windshield wiper{close_quotes} type of motion with an activation energy of 12.6 {plus_minus} 0.1 kcal mol{sup -1}. 35 refs., 9 figs., 6 tabs.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 269186
- Journal Information:
- Journal of the American Chemical Society, Journal Name: Journal of the American Chemical Society Journal Issue: 24 Vol. 114; ISSN JACSAT; ISSN 0002-7863
- Country of Publication:
- United States
- Language:
- English
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