General considerations.All manipulations were carried out in an MBraun glovebox or using standard Schlenk techniques under an atmosphere of N 2 or Ar. Solvents were degassed and dried by thoroughly sparging with N 2 gas followed by passage through an activated alumina column. Unless otherwise noted, all reagents were purchased from commercial vendors and used without further purification. Deuterated solvents were purchased from Cambridge Isotope Laboratories, Inc., degassed, and stored over 3A molecular sieves prior to use. Milli-Q water was used in the preparation of all aqueous solutions, which were rigorously degassed (3 × freeze-pump-thaw cycles) or extensively sparged (≥ 30 min) with Ar prior to contact with catalyst. NMR spectra were recorded on a VarianMercury 300 MHz spectrometer and referenced according to the solvent residual peak. S1 Absorbance spectra were recorded on a Varian Cary Bio50 UV-Visible Spectrophotometer using degassed solutions in Teflon valve sealed quartz cells. Gas chromatograms for headspace analyses were recorded on an Agilent Technologies 7890A GC System, with peak areas calibrated for % H 2 by volume. Volumetric were dried by passage through a plug of neutral alumina and degassed (3 × freeze-pump-thaw cycles)prior to use and storage in the glovebox. Electrochemistry.Solutions for electrochemical analysis were prepared from 1(PF 6 ) 2 stored and weighed in the glovebox under an N 2 atmosphere. A CH Instruments 660D or 600B ElectrochemicalAnalyzer was used for aqueous and acetonitrile solutions, respectively. Aqueous measurements were obtained using a Bioanalytical Systems Controlled Growth Mercury Drop Electrode (BAS CGME) working electrode run in static mode with an average drop surface area of 0.013 ± 0.002 cm 2 (calculated by determining the average weight of a single drop collected in each buffer medium) S3 and a commercially available saturated calomel reference electrode (SCE). Data is reported as the average of three runs obtained at a given set of experimental parameters using a fresh Hg drop for each run. In acetonitrile, a glassy carbon disk served as the working electrode (area = 0.07 cm 2 ). A platinum wire was used as the auxiliary electrode in cyclic and linear sweep voltammograms, each performed in a single compartment cell in the glovebox (N 2 atmosphere) or in aqueous solutions on the benchtop (sparged ≥ 30 min with Ar prior to and between runs, and blanketed with Ar during runs). The nonaqueous reference electrode S-3was Ag + /Ag, exhibiting a reversible Fc + /Fc couple centered at +0.14 V in CH 3 CN when added as an internal standard. Bulk controlled potential electrolysis experiments were performed in an N 2 atmosphere using a mercury pool working electrode (area = 0.8 or 1.8 cm 2 ), aqueous AgCl/Ag reference electrode stored in a 3 M NaCl solution, and either a silver or platinum mesh auxiliary electrode in rapidly stirred solutions sealed in gastight dual compartment cells bearing Teflon valves and ground glass stopcocks amenable to GC analysis and/or volumet...
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(eta5-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' ' = eta5-Me4C5; Bn = CH2Ph, 4), Cp'2AnR2 (Cp' = eta5-Me5C5; R = CH2SiMe3; An = Th, 5, U, 6), and analogous organolanthanide complexes. Deuterium KIEs measured at 25 degrees 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 sigma-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.
A series of "constrained geometry" organoactinide complexes, (CGC)An(NMe)2 (CGC = Me2Si(eta5-Me4C5)(tBuN); An = Th, 1; U, 2), has been prepared via efficient in situ, two-step protodeamination routes in good yields and high purity. Both 1 and 2 are quantitatively converted to the neutrally charged, solvent-free dichlorides (1-Cl2, 2-Cl2) and slightly more soluble diiodides (1-I2, 2-I2) with excess Me3Si-X (X = Cl, I) in non-coordinating solvents. The new complexes were characterized by NMR spectroscopy, elemental analysis, and (for 1 and 2) single-crystal X-ray diffraction, revealing substantially increased metal coordinative unsaturation vs the corresponding Me2SiCp' '2AnR2 (Cp' ' = eta5-Me4C5; An = Th, R = CH2(SiMe3), 3; An = U, R = CH2Ph, 4) and Cp'2AnR2 (Cp' = eta5-Me5C5 ; An = Th, R = CH2(SiMe3), 5; An = U, R = CH2(SiMe3), 6) complexes. Complexes 1-6 exhibit broad applicability for the intramolecular hydroamination 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, along with moderate to high diastereoselectivities (up to 90% trans ring closures). 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/CC insertion into the An-N sigma-bond.
The synthesis, characterization, and reactivity of a series of organoactinide constrained-geometry complexes, (CGC)An (NRR′) are reported. These complexes are effective precatalysts for intramolecular catalytic hydroamination/cyclization of aminoalkenes and aminoalkynes. Comparisons of structure and reactivity are drawn with previously reported trivalent organolanthanide CGC catalytic systems.
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