Constrained Geometry Organoactinide Complexes: Scope and Mechanism of Intramolecular Hydroamination/Cyclization of Primary and Secondary AminesPublic Deposited
In Chapter 1, a series of "constrained geometry" organoactinide complexes, (CGC)An(NMe)2 (CGC = Me2Si(h5-Me4C5)(tBuN); An = Th, 1; U, 2), prepared via efficient in situ, two-step protodeamination routes in good yields and high purity, is presented. Both 1 and 2 are quantitatively converted to the neutrally charged, solvent-free dihalides (1-Cl2, 2-Cl2 and 1-I2, 2-I2) with excess Me3Si-X (X = Cl, I) in non-coordinating solvents. Characterization of 1 and 2 by single crystal X-ray diffraction reveals substantially increased metal coordinative unsaturation vs. the corresponding Me2SiCp''2AnR2 (Cp'' = Me4C5; An = Th, R =CH2(SiMe3), 3; An = U, R = CH2Ph, 4) and Cp'2AnR2 (Cp' = Me5C5 ; An = Th, R =CH2(SiMe3), 5; An = U, R = CH2(SiMe3), 6) complexes. Complexes 1-6 exhibit broad applicability for the intramolecular hydroamination (HA) of diverse C-C unsaturations, including terminal and internal aminoalkenes (primary and secondary amines), aminoalkynes (primary and secondary amines), aminoallenes, and aminodienes. Large turnover frequencies (Nt up to 3000 h-1) and high regioselectivities (> 95%) are observed throughout. With several noteworthy exceptions, reactivity trends track relative 5f ionic radii and ancillary ligand coordinative unsaturation. Reactivity patterns and activation parameters are consistent with a reaction pathway proceeding via turnover-limiting C=C/C&#8801;C insertion into the An-N sigma-bond. In Chapter 2, a detailed mechanistic study of intramolecular HA/cyclization catalyzed by tetravalent organoactinide and organozirconium complexes is presented. A series of selectively substituted complexes, (CGC)M(NR2)Cl (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 are 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 (1-3), (Me2SiCp''2)UBn2 (4), Cp'2AnR2 (5-6) and analogous organolanthanide complexes. Deuterium KIE measured at 25 °C in C6D6 for aminoalkene D2NCH2C(CH3)2CH2CHCH2 (11-d2) with precatalysts 2 and 2-Cl indicate kH/kD = 3.3(5) and 2.6(4), respectively. This provides strong evidence in these systems for turnover limiting C-C insertion into an M-N(H)R sigma-bond in the transition state. Related complexes (Me2SiCp''2)U(CH2Ph)(Cl) (4-Cl) and Cp'2An(R)(Cl) (An = Th, 5-Cl; An = U, 6-Cl) are also found to be effective precatalysts for this transformation. Additional arguments in favor of M-N(H)R intermediates vs. M=NR intermediates are presented.