Mechanistic Investigation of Intramolecular Aminoalkene and Aminoalkyne Hydroamination/Cyclization Catalyzed by Highly Electrophilic, Tetravalent Constrained Geometry 4d and 5f Complexes. Evidence for an M−N σ-Bonded Insertive Pathway

A mechanistic study of intramolecular hydroamination/cyclization catalyzed by tetravalent
organoactinide and organozirconium complexes is presented. A series of selectively substituted constrained
geometry complexes, (CGC)M(NR2)Cl (CGC = [Me2Si(η5-Me4C5)(tBuN)]2-; M = Th, 1-Cl; U, 2-Cl; R =
SiMe3; M = Zr, R = Me, 3-Cl) and (CGC)An(NMe2)OAr (An = Th, 1-OAr; An = U, 2-OAr), has been
prepared via in situ protodeamination (complexes 1−2) or salt metathesis (3-Cl) in high purity and excellent
yield and is found to be active precatalysts for intramolecular primary and secondary aminoalkyne and
aminoalkene hydroamination/cyclization. Substrate reactivity trends, rate laws, and activation parameters
for cyclizations mediated by these complexes are virtually identical to those of more conventional (CGC)MR2 (M = Th, R = NMe2, 1; M = U, R = NMe2, 2; M = Zr, R = Me, 3), (Me2SiCp‘ ‘2)UBn2 (Cp‘ ‘ = η5-Me4C5;
Bn = CH2Ph, 4), Cp‘2AnR2 (Cp‘ = η5-Me5C5; R = CH2SiMe3; An = Th, 5, U, 6), and analogous
organolanthanide complexes. Deuterium KIEs measured at 25 °C in C6D6 for aminoalkene D2NCH2C(CH3)2CH2CHCH2 (11-d2) with precatalysts 2 and 2-Cl indicate that kH/kD = 3.3(5) and 2.6(4), respectively.
Together, the data provide strong evidence in these systems for turnover-limiting CC insertion into an
MN(H)R σ-bond in the transition state. Related complexes (Me2SiCp‘ ‘2)U(Bn)(Cl) (4-Cl) and Cp‘2An(R)(Cl) (R = CH2(SiMe3); An = Th, 5-Cl; An = U, 6-Cl) are also found to be effective precatalysts for this
transformation. Additional arguments supporting MN(H)R intermediates vs MNR intermediates are
presented.