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Issue 32, 2012
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Scandium and yttrium metallocene borohydride complexes: comparisons of (BH4)1−vs. (BPh4)1− coordination and reactivity

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Abstract

The synthetically accessible borohydride complexes (C5Me4H)2Ln(THF)(BH4) and (C5Me5)2Ln(THF)(BH4) (Ln = Sc, Y) were examined as precursors alternative to the heavily-used tetraphenylborate analogs, [(C5Me4H)2Ln][BPh4] and [(C5Me5)2Ln][BPh4], employed in LnA2A′/M reduction reactions (A = anion; M = alkali metal) that generate “LnA2” reactivity and form reduced dinitrogen complexes [(C5R5)2(THF)xLn]2(μ-η22-N2) (x = 0, 1). The crystal structures of the yttrium borohydrides, (C5Me4H)2Y(THF)(μ-H)3BH, 1, and (C5Me5)2Y(THF)(μ-H)2BH2, 2, were determined for comparison with those of the yttrium tetraphenylborates, [(C5Me4H)2Y][(μ-Ph)2BPh2], 3, and [(C5Me5)2Y][(μ-Ph)2BPh2], 4. The complex (C5Me4H)2Sc(μ-H)2BH2, 5, was synthesized and structurally characterized for comparison with (C5Me5)2Sc(μ-H)2BH2, 6, [(C5Me4H)2Sc][(μ-Ph)BPh3], 7, and [(C5Me5)2Sc][(μ-Ph)BPh3], 8. Structural information was also obtained on the borohydride derivatives, (C5Me4H)2Sc(μ-H)2BC8H14, 9, and (C5Me5)2Sc(μ-H)2BC8H14, 10, obtained from 9-borabicyclo(3.3.1)nonane (9-BBN) and (C5Me4R)2Sc(η3-C3H5), where R = H, 11; Me, 12. The preference of the metals for borohydride over tetraphenylborate binding was shown by the facile displacement of (BPh4)1− in 3, 4, 7, and 8 by (BH4)1− to make the respective borohydride complexes 1, 2, 5, and 6. These results are consistent with the fact that the borohydrides are not as useful as precursors in A2LnA′/M reductions of N2. An unusual structural isomer of [(C5Me4H)2Sc]2(μ-η22-N2), 13′, was isolated from this study that shows the variations in ligand orientation that can occur in the solid state.

Graphical abstract: Scandium and yttrium metallocene borohydride complexes: comparisons of (BH4)1−vs. (BPh4)1− coordination and reactivity

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Publication details

The article was received on 19 Apr 2012, accepted on 01 Jun 2012 and first published on 11 Jun 2012


Article type: Paper
DOI: 10.1039/C2DT30861D
Citation: Dalton Trans., 2012,41, 9659-9666
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    Scandium and yttrium metallocene borohydride complexes: comparisons of (BH4)1−vs. (BPh4)1− coordination and reactivity

    S. Demir, N. A. Siladke, J. W. Ziller and W. J. Evans, Dalton Trans., 2012, 41, 9659
    DOI: 10.1039/C2DT30861D

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