Ligand substitution reactions and catalytic hydroamination/cyclization of aminoalkenes have been studied with a new 3 oxazolinylborato yttrium compound, tris(4,4-dimethyl-2-oxazolinyl)phenylborato bis(trimethylsilylmethyl)yttrium ([Y-(kappa(3)-To(M))(CH2SiMe3)(2)(THF)], 1). THF exchange in 1 is rapid at room temperature, and activation parameters obtained by simulation of H-1 NMR spectra acquired from 190 to 280 K are consistent with a dissociative mechanism (Delta S double dagger = 30 +/- 1 e.u., Delta G double dagger = 11.9 kcal mol(-1) at 243 K). The related phosphine oxide adduct [Y(kappa(3)-To(M))(CH2SiMe3)(2)(OPPh3)] (2) also undergoes exchange via OPPh3 dissociation with a much (Delta G double dagger = 15.0 kcal mol(-1) at 320 K). Compound 1 reacts with the amines (BuNH2)-Bu-t, para-MeC6H4NH2, and 2,6-(Pr2C6H3NH2)-Pr-i to provide six-coordinate [Y(kappa(3)-To(M))-(NHR)(2)(THF)] (3: R = Bu-t; 4: R = para-MeC6H4) and five-coordinate [Y(kappa(3)-To(M))(NH-2,6-(Pr2C6H3)-Pr-i)(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.