UC Santa Barbara

Herein, I report the synthesis, characterization, and reactivity of the N-(isocyanoimine)triphenylphosphine (CNNPPh3) adduct of [Ce(NR2)3] (R = SiMe3): namely, [(NR2)3Ce(CNNPPh3)]. Photolysis of [(NR2)3Ce(CNNPPh3)] with a 380 nm LED source for 1 month results in clean formation of [(NR2)3Ce(NCNPPh3)], via reorganization of the nitrilimine ligand to its carbodiimide isomer. Reaction of U(N(SiMe2)3) (R = SiMe3) with 2 equiv tert-Butyl isocyanide proceeded to oxidize the uranium center and reduce the ligand to synthesize, [U(NR2)3(CN)(CNtBu)], in pentane, suggesting that the C-N triple bond in the tert-Butyl isocyanide ligand was not strong enough to withstand the reaction conditions. Utilizing the sp2 bond in 2,6-Dimethylphenyl isocyanide (CNXyl, Xyl = 2,6-Me2C6H3), reaction of U(NR2)3 with 2 equiv 2,6-Dimethylphenyl isocyanide resulted in the isolation of [U(NR2)3(CNXyl)2], as well as [U{N(R)SiC(=CH2)N(Xyl)}(NR2)2], formed by [U{N(R)(SiMe2)CH2}(NR2)2], a decomposition product of U(NR2)3, reacting with 1 equiv of 2,6-Dimethylphenyl isocyanide. Reduction reactivity of [U(NR2)3(CNXyl)2] was also explored and is discussed. Herein, I report the synthesis and characterization of three novel actinide imido complexes, [K(18-crown-6)][U(NTs)(NR2)3] (R = SiMe3), [Li(12-crown-4)2][Th(NCPh3)(NR2)3], and [K(18-crown-6)][Th(NTs)(NR2)3], where the corresponding amide salts, [Li(NHCPh3)(THF)] or KNHTs (Ts = MeC6H4SO2) were used to protonate the actinide metallacycle, [An(CH2SiMe2NSiMe3)(NR2)2] (An = U, Th), as well as two novel actinide amido borane complexes, [Na(2,2,2-cryptand)][U(NR2)3NHBPh3] and [K(dibenzo-18-crown-6)][Th(NR2)3NHBPh3], through the reaction of NH3BPh3 with the actinide bis(metallacycle), [An{N(R)(SiMe2CH2)}2(NR2)]- (An = U, Th). These imido and amido complexes are ideal for synthesizing actinide nitrido species through the method of reductive deprotection, in an effort to cleave the N-C, N-S, and N-B bond. Reaction of the thorium metallacycle, [Th{N(R)(SiMe2)CH2}(NR2)2] (R = SiMe3) with 1 equiv. of NaNH2 in THF, in the presence of 18-crown-6, results in formation of the bridged thorium nitride complex, [Na(18-crown-6)(Et2O)][(R2N)3Th(μ-N)(Th(NR2)3], which can be isolated in 66% yield after work-up. [Na(18-crown-6)(Et2O)][(R2N)3Th(μ-N)(Th(NR2)3] is the first isolable molecular thorium nitride complex. Mechanistic studies suggest that the first step of the reaction is deprotonation of [Th{N(R)(SiMe2)CH2}(NR2)2] by NaNH2, which results in formation of the thorium bis(metallacycle) complex, [Na(THF)x][Th{N(R)(SiMe2CH2)}2(NR2)], and NH3. NH3 then reacts with unreacted [Th{N(R)(SiMe2)CH2}(NR2)2], forming [Th(NR2)3(NH2)], which protonates [Na(THF)x][Th{N(R)(SiMe2CH2)}2(NR2)] to give [Na(18-crown-6)(Et2O)][(R2N)3Th(μ-N)(Th(NR2)3]. Consistent with hypothesis, addition of excess NH3 to a THF solution of [Th{N(R)(SiMe2)CH2}(NR2)2] results in formation of [Th(NR2)3(NH2)], which can be isolated in 51% yield after work-up. Furthermore, reaction of [K(DME)][Th{N(R)(SiMe2CH2)}2(NR2)] with [Th(NR2)3(NH2)], in THF-d8, results in clean formation of [K(18-crown-6)(THF)2][(R2N)3Th(μ-N)(Th(NR2)3], according to 1H NMR spectroscopy. The electronic structures of [(R2N)3Th(μ-N)(Th(NR2)3]− and [Th(NR2)3(NH2)] were investigated by 15N NMR spectroscopy and DFT calculations. This analysis reveals that the Th–Nnitride bond in [(R2N)3Th(μ-N)(Th(NR2)3]− features more covalency and a greater degree of bond multiplicity than the Th–NH2 bond in [Th(NR2)3(NH2)]. Similarly, this analysis indicates a greater degree of covalency in [(R2N)3Th(μ-N)(Th(NR2)3]− vs. comparable thorium imido and oxo complexes. Reaction of the thorium bis(metallacycle), [K(DME)][Th{N(R)(SiMe2CH2)}2(NR)2] (R = SiMe3) with 1 equiv of the newly synthesized uranium parent amide, [U(NR2)3(NH2)], in THF, in the presence of 18-crown-6, results in formation of a bridged uranium-thorium nitride complex, [K(18-crown-6)(THF)2][(NR2)3UIV(μ-N)ThIV(NR2)3], which can be isolated in 56% yield after work-up. [K(18-crown-6)(THF)2][(NR2)3UIV(μ-N)ThIV(NR2)3] is the first isolable molecular mixed actinide nitride complex. Additonally, a μ-CH2 bridging mixed actinide nitride complex, [(K(18-crown-6)0.5)(K(18-crown-6)0.5Et2O)][(NR2)2UIV(μ-N)(CH2SiMe2NR)ThIV(NR2)2], is also isolated in this reaction in 34% yield. Furthermore, [K(18-crown-6)(THF)2][(NR2)3UIV(μ-N)ThIV(NR2)3] is oxidized by 0.5 equiv of I2 to a mixed-valent UV/ThIV bridged nitride, [(NR2)3UV(μ-N)ThIV(NR2)3], which can be isolated in 42% yield after work-up. The structural assignments have been supported by means of 15N-isotopic labeling, electronic absorption spectroscopy, magnetometry, electronic structure calculations, and elemental analyses. Reaction of 3 equiv of NaNR2 (R = SiMe3) with NpCl4(DME)2 in THF afforded the Np(IV) silylamide complex, [Np(NR2)3Cl], in good yield. Reaction of [Np(NR2)3Cl] with 1.5 equiv of KC8 in THF, in the presence of 1 equiv of dibenzo-18-crown-6, resulted in formation of [{K(DB-18-C-6)(THF)}3(μ3-Cl)][Np(NR2)3Cl]2, also in good yield. Complex [{K(DB-18-C-6)(THF)}3(μ3-Cl)][Np(NR2)3Cl]2 represents the first structurally characterized Np(III) amide. Finally, reaction of NpCl4(DME)2 with 5 equiv of NaNR2 and 1 equiv of dibenzo-18-crown-6 afforded the Np(IV) bis(metallacycle), [{Na(DB-18-C-6)(Et2O)0.62(κ1-DME)0.38}2(μ-DME)][Np{N(R)(SiMe2CH2)}2(NR2)]2, in moderate yield. Complex [{Na(DB-18-C-6)(Et2O)0.62(κ1-DME)0.38}2(μ-DME)][Np{N(R)(SiMe2CH2)}2(NR2)]2 was characterized by 1H NMR spectroscopy and X-ray crystallography and represents a rare example of a structurally characterized neptunium–hydrocarbyl complex. To support these studies, I also synthesized the uranium analogues, namely, [K(2,2,2-cryptand)][U(NR2)3Cl], [K(DB-18-C-6)(THF)2][U(NR2)3Cl], [Na(DME)3][U{N(R)(SiMe2CH2)}2(NR2)], and [{Na(DB-18-C-6)(Et2O)0.5(κ1-DME)0.5}2(μ-DME)][U{N(R)(SiMe2CH2)}2(NR2)]2. Complexes were characterized by a number of techniques, including NMR spectroscopy and X-ray crystallography.