Synthesis, characterization, and reactivity of scandium chloro, alkyl, aryl, and borohydride complexes, Sc(η5-C5H5)R[N(SiMe2CH2P(i)Pr2)2] (R = Cl, Me, Ph, and BH4)

Reaction of ScCl2(THF)[N((SiMe2CH2PPr2)-Pr-i)(2)] with NaCp(DME) leads to Sc(eta(5)-C5H5)Cl[N((SiMe2CH2PPr2)-Pr-i)(2)] (1). The X-ray crystal structure shows the scandium centre to reside in a square pyramidal environment with the [N((SiMe2CH2PPr2)-Pr-i)(2)] - ligand bound in a pseudo-meridional fashion. The H-1 NMR spectrum is consistent with a C-s symmetric structure in solution. Metathesis of the chloride ligand with RLi (R = Me, Ph, BH4) yields the five-coordinate species Sc(eta(5)-C5H5)R[N((SiMe2CH2PPr2)-Pr-i)(2)]. Phenyl 3 and borohydride 4 are isolated as crystalline solids, while methyl 2 resisted crystallization. 2-4 exhibit H-1 NMR spectra consistent with C-s symmetric solution structures. Sc(eta(5)-C5H5)Ph[N((SiMe2CH2PPr2)-Pr-i)(2)] (3) was characterized in the solid state and found to have a similar geometry to that of the parent chloride. Reaction of Sc(eta(5)-C5H5)Me[N((SiMe2CH2PPr2)-Pr-i)(2)] (2) with NH2R (R = Ph, Bu-t) yields the amides Sc(eta(5)-C5H5)NHPh[N((SiMe2CH2PPr2)-Pr-i)(2)] (5) and Sc(eta(5)-C5H5)(NHBu)-Bu-t- [N((SiMe2CH2PPr2)-Pr-i)(2)] (6) via sigma-bond metathesis routes; these reactions are accompanied by a competing reaction at the scandium-amide bond to produce the protonated ligand, HN((SiMe2CH2PPr2)-Pr-i)(2) 5 and 6 are also produced by salt-elimination from the chloride 1 and LiNHR (R = Ph, Bu-t). Sc(eta(5)-C5H5)(BH4)[N((SiMe2CH2PPr2)-Pr-i)(2)] (4) reacts with PMe3 to produce the putative hydride, Sc(eta(5)-C5H5)H[N((SiMe2CH2PPr2)-Pr-i)(2)] (7); this species was identified in solution. An equilibrium between 4, PMe3, 7, and PMe3,BH3 exists which greatly favors the starting scandium-borohydride. Crystals of Sc(eta(5)-C5H5)Cl[N((SiMe2CH2PPr2)-Pr-i)(2)] (1) are monoclinic, a = 17.409(2), b = 10.0803(7), c = 17.688(2) A, beta = 94.606(8) degrees, Z = 4, space group P2(1)/c; and those of Sc(eta(5)-C5H5)Ph[N((SiMe2CH2PPr2)-Pr-i)(2)] (3) are triclinic, a = 10.5129(15), b = 19.124(2), c = 9.114(2) A, alpha = 95.582(13), beta = 107.047(12), gamma = 90.042(11)degrees, 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-w = 0.042 and 0.049) for 2414 and 2844 reflections with I greater than or equal to 3 sigma(I), respectively.