Fryzuk, Michael D;
Giesbrecht, Garth R;
Rettig, Steven J
Synthesis, characterization, and reactivity of scandium chloro, alkyl, aryl, and borohydride complexes, Sc(η5-C5H5)R[N(SiMe2CH2PiPr2)2] (R = Cl, Me, Ph, and BH4)
Description:
<jats:p> Reaction of ScCl<jats:sub>2</jats:sub>(THF)[N(SiMe<jats:sub>2</jats:sub>CH<jats:sub>2</jats:sub>P<jats:sup>i</jats:sup>Pr<jats:sub>2</jats:sub>)<jats:sub>2</jats:sub>] with NaCp(DME) leads to Sc(η<jats:sup>5</jats:sup>-C<jats:sub>5</jats:sub>H<jats:sub>5</jats:sub>)Cl[N(SiMe<jats:sub>2</jats:sub>CH<jats:sub>2</jats:sub>P<jats:sup>i</jats:sup>Pr<jats:sub>2</jats:sub>)<jats:sub>2</jats:sub>] (1). The X-ray crystal structure shows the scandium centre to reside in a square pyramidal environment with the [N(SiMe<jats:sub>2</jats:sub>CH<jats:sub>2</jats:sub>P<jats:sup>i</jats:sup>Pr<jats:sub>2</jats:sub>)<jats:sub>2</jats:sub>] - ligand bound in a pseudo-meridional fashion. The <jats:sup>1</jats:sup>H NMR spectrum is consistent with a C<jats:sub>s</jats:sub> symmetric structure in solution. Metathesis of the chloride ligand with RLi (R = Me, Ph, BH<jats:sub>4</jats:sub>) yields the five-coordinate species Sc(η<jats:sup>5</jats:sup>-C<jats:sub>5</jats:sub>H<jats:sub>5</jats:sub>)R[N(SiMe<jats:sub>2</jats:sub>CH<jats:sub>2</jats:sub>P<jats:sup>i</jats:sup>Pr<jats:sub>2</jats:sub>)<jats:sub>2</jats:sub>]. Phenyl 3 and borohydride 4 are isolated as crystalline solids, while methyl 2 resisted crystallization. 2-4 exhibit <jats:sup>1</jats:sup>H NMR spectra consistent with C<jats:sub>s</jats:sub> symmetric solution structures. Sc(η<jats:sup>5</jats:sup>-C<jats:sub>5</jats:sub>H<jats:sub>5</jats:sub>)Ph[N(SiMe<jats:sub>2</jats:sub>CH<jats:sub>2</jats:sub>P<jats:sup>i</jats:sup>Pr<jats:sub>2</jats:sub>)<jats:sub>2</jats:sub>] (3) was characterized in the solid state and found to have a similar geometry to that of the parent chloride. Reaction of Sc(η<jats:sup>5</jats:sup>-C<jats:sub>5</jats:sub>H<jats:sub>5</jats:sub>)Me[N(SiMe<jats:sub>2</jats:sub>CH<jats:sub>2</jats:sub>P<jats:sup>i</jats:sup>Pr<jats:sub>2</jats:sub>)<jats:sub>2</jats:sub>] (2) with NH<jats:sub>2</jats:sub>R (R = Ph, <jats:sup>t</jats:sup>Bu) yields the amides Sc(η<jats:sup>5</jats:sup>-C<jats:sub>5</jats:sub>H<jats:sub>5</jats:sub>)NHPh[N(SiMe<jats:sub>2</jats:sub>CH<jats:sub>2</jats:sub>P<jats:sup>i</jats:sup>Pr<jats:sub>2</jats:sub>)<jats:sub>2</jats:sub>] (5) and Sc(η<jats:sup>5</jats:sup>-C<jats:sub>5</jats:sub>H<jats:sub>5</jats:sub>)NH<jats:sup>t</jats:sup>Bu [N(SiMe<jats:sub>2</jats:sub>CH<jats:sub>2</jats:sub>P<jats:sup>i</jats:sup>Pr<jats:sub>2</jats:sub>)<jats:sub>2</jats:sub>] (6) via σ-bond metathesis routes; these reactions are accompanied by a competing reaction at the scandium-amide bond to produce the protonated ligand, HN(SiMe<jats:sub>2</jats:sub>CH<jats:sub>2</jats:sub>P<jats:sup>i</jats:sup>Pr<jats:sub>2</jats:sub>)<jats:sub>2</jats:sub>. 5 and 6 are also produced by salt-elimination from the chloride 1 and LiNHR (R = Ph, <jats:sup>t</jats:sup>Bu). Sc(η<jats:sup>5</jats:sup>-C<jats:sub>5</jats:sub>H<jats:sub>5</jats:sub>)(BH<jats:sub>4</jats:sub>)[N(SiMe<jats:sub>2</jats:sub>CH<jats:sub>2</jats:sub>P<jats:sup>i</jats:sup>Pr<jats:sub>2</jats:sub>)<jats:sub>2</jats:sub>] (4) reacts with PMe<jats:sub>3</jats:sub> to produce the putative hydride, Sc(η<jats:sup>5</jats:sup>-C<jats:sub>5</jats:sub>H<jats:sub>5</jats:sub>)H[N(SiMe<jats:sub>2</jats:sub>CH<jats:sub>2</jats:sub>P<jats:sup>i</jats:sup>Pr<jats:sub>2</jats:sub>)<jats:sub>2</jats:sub>] (7); this species was identified in solution. An equilibrium between 4, PMe<jats:sub>3</jats:sub>, 7, and PMe<jats:sub>3</jats:sub>·BH<jats:sub>3</jats:sub> exists which greatly favors the starting scandium-borohydride. Crystals of Sc(η<jats:sup>5</jats:sup>-C<jats:sub>5</jats:sub>H<jats:sub>5</jats:sub>)Cl[N(SiMe<jats:sub>2</jats:sub>CH<jats:sub>2</jats:sub>P<jats:sup>i</jats:sup>Pr<jats:sub>2</jats:sub>)<jats:sub>2</jats:sub>] (1) are monoclinic, a = 17.409(2), b = 10.0803(7), c = 17.688(2) Å, β = 94.606(8)°, Z = 4, space group P2<jats:sub>1</jats:sub>/c; and those of Sc(η<jats:sup>5</jats:sup>-C<jats:sub>5</jats:sub>H<jats:sub>5</jats:sub>)Ph[N(SiMe<jats:sub>2</jats:sub>CH<jats:sub>2</jats:sub>P<jats:sup>i</jats:sup>Pr<jats:sub>2</jats:sub>)<jats:sub>2</jats:sub>] (3) are triclinic, a = 10.5129(15), b = 19.124(2), c = 9.114(2) Å, α = 95.582(13), β = 107.047(12), γ = 90.042(11)°, Z = 2, space group P. The structures were solved by Patterson (1) and direct (3) methods and refined by full-matrix least-squares procedures to R = 0.047 and 0.054 (R<jats:sub>w</jats:sub> = 0.042 and 0.049) for 2414 and 2844 reflections with I [Formula: see text] 3σ(I), respectively.Key words: scandium, σ-bond metathesis, borohydride. </jats:p>