Ligand exchange reactions and hydroamination with tris(oxazolinyl)borato yttrium compounds.

Ligand substitution reactions and catalytic hydroamination/cyclization of aminoalkenes have been studied with a new oxazolinylborato yttrium compound, tris(4,4-dimethyl-2-oxazolinyl)phenylborato bis(trimethylsilylmethyl)yttrium ([Y(kappa(3)-To(M))(CH(2)SiMe(3))(2)(THF)], 1). THF exchange in 1 is rapid at room temperature, and activation parameters obtained by simulation of (1)H NMR spectra acquired from 190 to 280 K are consistent with a dissociative mechanism (DeltaS(++) = 30 +/- 1 e.u., DeltaG(++) = 11.9 kcal mol(-1) at 243 K). The related phosphine oxide adduct [Y(kappa(3)-To(M))(CH(2)SiMe(3))(2)(OPPh(3))] (2) also undergoes exchange via OPPh(3) dissociation with a much higher barrier (DeltaG(++) = 15.0 kcal mol(-1) at 320 K). Compound 1 reacts with the amines (t)BuNH(2), para-MeC(6)H(4)NH(2), and 2,6-(i)Pr(2)C(6)H(3)NH(2) to provide six-coordinate [Y(kappa(3)-To(M))(NHR)(2)(THF)] (3: R = (t)Bu; 4: R = para-MeC(6)H(4)) and five-coordinate [Y(kappa(3)-To(M))(NH-2,6-(i)Pr(2)C(6)H(3))(2)] (6). These oxazolinylborato yttrium compounds are precatalysts for the cyclization of aminoalkenes; the kinetics of catalytic conversion indicate zero-order substrate dependence and first-order catalyst dependence. Kinetic investigations of ligand exchange processes and hydroamination reactions indicate that the tris(oxazolinyl)borato-yttrium interaction is robust even in the presence of excess phosphine oxide and primary and secondary amines.