Stabilizing high-valent metal ions with a ketimide ligand set: synthesis of Mn(N=C(t)Bu2)4

Reaction of MnCl(2) with 4 equiv of Li(N=C(t)Bu(2)) generates [Li(THF)](2)[Mn(N=C(t)Bu(2))(4)] (1) in 80% yield. Oxidation of 1 with 0.5 equiv of I(2) produces [Li][Mn(N=C(t)Bu(2))(4)] (2) in 88% yield. Both complexes 1 and 2 exhibit tetrahedral structures about the Mn center in the solid-state, as determined by X-ray crystallography. Reaction of 2 with 12-crown-4 generates [Li(12-crown-4)(2)][Mn(N=C(t)Bu(2))(4)] (3) in 94% yield. Interestingly, in the solid-state, complex 3 exhibits a squashed tetrahedral structure about Mn. Addition of 1 equiv of I(2) to 1 generates the Mn(IV) ketimide, Mn(N=C(t)Bu(2))(4) (4), in 75% yield. Complex 4 was fully characterized, including analysis by X-ray crystallography and cyclic voltammetry. Like 3, complex 4 also exhibits a squashed tetrahedral structure in the solid-state. Interestingly, thermolysis of complex 4 at 50 °C for 6 h results in the formation of Mn(3)(N=C(t)Bu(2))(6) (6), which can be isolated in 49% yield. Also observed in the reaction mixture is pivalonitrile, isobutylene, and isobutene, the products of ketimide ligand oxidation. We have also synthesized the homoleptic Cr(IV) ketimide complex, Cr(N=C(t)Bu(2))(4) (5), and have analyzed its electrochemical properties with cyclic voltammetry.     

High-valent uranium alkyls: evidence for the formation of U(VI)(CH2SiMe3)6

Oxidation of [Li(DME)(3)][U(CH(2)SiMe(3))(5)] with 0.5 equiv of I(2), followed by immediate addition of LiCH(2)SiMe(3), affords the high-valent homoleptic U(V) alkyl complex [Li(THF)(4)][U(CH(2)SiMe(3))(6)] (1) in 82% yield. In the solid-state, 1 adopts an octahedral geometry as shown by X-ray crystallographic analysis. Addition of 2 equiv of tert-butanol to [Li(DME)(3)][U(CH(2)SiMe(3))(5)] generates the heteroleptic U(IV) complex [Li(DME)(3)][U(O(t)Bu)(2)(CH(2)SiMe(3))(3)] (2) in high yield. Treatment of 2 with AgOTf fails to produce a U(V) derivative, but instead affords the U(IV) complex (Me(3)SiCH(2))Ag(μ-CH(2)SiMe(3))U(CH(2)SiMe(3))(O(t)Bu)(2)(DME) (3) in 64% yield. Complex 3 has been characterized by X-ray crystallography and is marked by a uranium-silver bond. In contrast, oxidation of 2 can be achieved via reaction with 0.5 equiv of Me(3)NO, producing the heteroleptic U(V) complex [Li(DME)(3)][U(O(t)Bu)(2)(CH(2)SiMe(3))(4)] (4) in moderate yield. We have also attempted the one-electron oxidation of complex 1. Thus, oxidation of 1 with U(O(t)Bu)(6) results in formation of a rare U(VI) alkyl complex, U(CH(2)SiMe(3))(6) (6), which is only stable below -25 °C. Additionally, the electronic properties of 1-4 have been assessed by SQUID magnetometry, while a DFT analysis of complexes 1 and 6 is also provided.     

Halide, amide, cationic, manganese carbonylate, and oxide derivatives of triamidosilylamine uranium complexes

Treatment of the complex [U(Tren(TMS))(Cl)(THF)] [1, Tren(TMS) = N(CH(2)CH(2)NSiMe(3))(3)] with Me(3)SiI at room temperature afforded known crystalline [U(Tren(TMS))(I)(THF)] (2), which is reported as a new polymorph. Sublimation of 2 at 160 °C and 10(-6) mmHg afforded the solvent-free dimer complex [{U(Tren(TMS))(μ-I)}(2)] (3), which crystallizes in two polymorphic forms. During routine preparations of 1, an additional complex identified as [U(Cl)(5)(THF)][Li(THF)(4)] (4) was isolated in very low yield due to the presence of a slight excess of [U(Cl)(4)(THF)(3)] in one batch. Reaction of 1 with one equivalent of lithium dicyclohexylamide or bis(trimethylsilyl)amide gave the corresponding amide complexes [U(Tren(TMS))(NR(2))] (5, R = cyclohexyl; 6, R = trimethylsilyl), which both afforded the cationic, separated ion pair complex [U(Tren(TMS))(THF)(2)][BPh(4)] (7) following treatment of the respective amides with Et(3)NH·BPh(4). The analogous reaction of 5 with Et(3)NH·BAr(f)(4) [Ar(f) = C(6)H(3)-3,5-(CF(3))(2)] afforded, following addition of 1 to give a crystallizable compound, the cationic, separated ion pair complex [{U(Tren(TMS))(THF)}(2)(μ-Cl)][BAr(f)(4)] (8). Reaction of 7 with K[Mn(CO)(5)] or 5 or 6 with [HMn(CO)(5)] in THF afforded [U(Tren(TMS))(THF)(μ-OC)Mn(CO)(4)] (9); when these reactions were repeated in the presence of 1,2-dimethoxyethane (DME), the separated ion pair [U(Tren(TMS))(DME)][Mn(CO)(5)] (10) was isolated instead. Reaction of 5 with [HMn(CO)(5)] in toluene afforded [{U(Tren(TMS))(μ-OC)(2)Mn(CO)(3)}(2)] (11). Similarly, reaction of the cyclometalated complex [U{N(CH(2)CH(2)NSiMe(2)Bu(t))(2)(CH(2)CH(2)NSiMeBu(t)CH(2))}] with [HMn(CO)(5)] gave [{U(Tren(DMSB))(μ-OC)(2)Mn(CO)(3)}(2)] [12, Tren(DMSB) = N(CH(2)CH(2)NSiMe(2)Bu(t))(3)]. Attempts to prepare the manganocene derivative [U(Tren(TMS))MnCp(2)] from 7 and K[MnCp(2)] were unsuccessful and resulted in formation of [{U(Tren(TMS))}(2)(μ-O)] (13) and [MnCp(2)]. Complexes 3-13 have been characterized by X-ray crystallography, (1)H NMR spectroscopy, FTIR spectroscopy, Evans method magnetic moment, and CHN microanalyses.     

Actinide metals with multiple bonds to carbon: synthesis, characterization, and reactivity of U(IV) and Th(IV) bis(iminophosphorano)methandiide pincer carbene complexes

Treatment of ThCl(4)(DME)(2) or UCl(4) with 1 equiv of dilithiumbis(iminophosphorano) methandiide, [Li(2)C(Ph(2)P═NSiMe(3))(2)] (1), afforded the chloro actinide carbene complexes [Cl(2)M(C(Ph(2)P═NSiMe(3))(2))] (2 (M = Th) and 3 (M = U)) in situ. Stable PCP metal-carbene complexes [Cp(2)Th(C(Ph(2)P═NSiMe(3))(2))] (4), [Cp(2)U(C(Ph(2)P═NSiMe(3))(2))] (5), [TpTh(C(Ph(2)P═NSiMe(3))(2))Cl] (6), and [TpU(C(Ph(2)P═NSiMe(3))(2))Cl] (7) were generated from 2 or 3 by further reaction with 2 equiv of thallium(I) cyclopentadienide (CpTl) in THF to yield 4 or 5 or with 1 equiv of potassium hydrotris(pyrazol-1-yl) borate (TpK) also in THF to give 6 or 7, respectively. The derivative complexes were isolated, and their crystal structures were determined by X-ray diffraction. All of these U (or Th)-carbene complexes (4-7) possess a very short M (Th or U)═carbene bond with evidence for multiple bond character. Gaussian 03 DFT calculations indicate that the M═C double bond is constructed by interaction of the 5f and 6d orbitals of the actinide metal with carbene 2p orbitals of both π and σ character. Complex 3 reacted with acetonitrile or benzonitrile to cyclo-add C≡N to the U═carbon double bond, thereby forming a new C-C bond in a new chelated quadridentate ligand in the bridged dimetallic complexes (9 and 10). A single carbon-U bond is retained. The newly coordinated uranium complex dimerizes with one equivalent of unconverted 3 using two chlorides and the newly formed imine derived from the nitrile as three connecting bridges. In addition, a new crystal structure of [CpUCl(3)(THF)(2)] (8) was determined by X-ray diffraction.     

Synthesis and reactivity of cationic niobium and tantalum methyl complexes supported by imido and β-diketiminato ligands

The synthesis and reactivity of the cationic niobium and tantalum monomethyl complexes [(BDI)MeM(N(t)Bu)][X] (BDI = [Ar]NC(CH(3))CHC(CH(3))N[Ar], Ar = 2,6-(i)Pr(2)C(6)H(3); M = Nb, Ta; X = MeB(C(6)F(5))(3), B(C(6)F(5))(4)] was investigated. The cationic alkyl complexes failed to irreversibly bind CO but formed phosphine-trapped acyl complexes [(BDI)(R(3)PC(O)Me)M(N(t)Bu)][B(C(6)F(5))(4)] (R = Et, Cy) in the presence of a combination of trialkylphosphines and CO. Treatment of the monoalkyl cationic Nb complex with XylNC (Xyl = 2,6-Me(2)-C(6)H(3)) resulted in irreversible formation of the iminoacyl complex [(BDI)(XylN[double bond, length as m-dash]C(Me))Nb(N(t)Bu)][B(C(6)F(5))(4)], which did not bind phosphines but would add a methide group to the iminoacyl carbon to provide the known ketimine complex (BDI)(XylNCMe(2))Nb(N(t)Bu). Further stoichiometric chemistry explored i) migratory insertion reactions to form new alkoxide, amidinate, and ketimide complexes; ii) protonolysis reactions with Ph(3)SiOH to form thermally robust cationic siloxide complexes; and iii) catalytic high-density polyethylene formation mediated by the cationic Nb methyl complex.     

Synthetic and structural investigations of monomeric dilithium boraamidinates and bidentate NBNCN ligands with bulky N-bonded groups

The dilithiated boraamidinate complexes [Li(2)[PhB(NDipp)(2)](THF)(3)] (7a) (Dipp = 2,6-diisopropylphenyl) and [Li(2)[PhB(NDipp)(N(t)Bu)](OEt(2))(2)] (7b), prepared by reaction of PhB[N(H)Dipp][N(H)R'] (6a, R' = Dipp; 6b, R' = (t)Bu) with 2 equiv of (n)BuLi, are shown by X-ray crystallography to have monomeric structures with two terminal and one bridging THF ligands (7a) or two terminal OEt(2) ligands (7b). The derivative 7a is used to prepare the spirocyclic group 13 derivative [Li(OEt(2))(4)][In[PhB(NDipp)(2)](2)] (8a) that is shown by an X-ray structural analysis to be a solvent-separated ion pair. The monoamino derivative PhBCl[N(H)Dipp] (9a), obtained by the reaction of PhBCl(2) with 2 equiv of DippNH(2), serves as a precursor for the synthesis of the four-membered BNCN ring [[R'N(H)](Ph)B(mu-N(t)Bu)(2)C(n)Bu] (10a, R' = Dipp). The X-ray structures of 6a, 9a, and 10a have been determined. The related derivative 10b (R' = (t)Bu) was synthesized by the reaction of [Cl(Ph)B(mu-N(t)Bu)(2)C(n)Bu] with Li[N(H)(t)Bu] and characterized by (1)H, (11)B, and (13)C NMR spectra. In contrast to 10a and 10b, NMR spectroscopic data indicate that the derivatives [[DippN(H)](Ph)B(NR')(2)CR(NR')] (11a: R =( t)Bu, R' = Cy; 11b: R = (n)Bu, R' = Dipp) adopt acyclic structures with three-coordinate boron atoms. Monolithiation of 10a produces the novel hybrid boraamidinate/amidinate (bamam) ligand [Li[DippN]PhB(N(t)Bu)C(n)Bu(N(t)Bu)] (12a).     

Synthesis and reactivity of a uranyl-imidazolyl complex

Treatment of [UO(2)(Ar(2)nacnac)Cl](2) with 4 equiv. of Li(C(4)H(5)N(2)) results in the formation of a rare uranyl organometallic complex [Li(MeIm)][UO(μ-O)(Ar(2)nacnac)(μ-C,N-C(4)H(5)N(2))(2)] (2), in moderate yield. Reaction of 2 with 1 equiv. of MCl(2) (M = Fe, Co) yields the bimetallic complexes [MCl(MeIm)][UO(2)(Ar(2)nacnac)(μ-N,C-C(4)H(5)N(2))(2)] (M = Fe, 3; M = Co, 4).     

Syntheses, luminescence behavior, and assembly reaction of tetraalkynylplatinate(II) complexes: crystal structures of [Pt((t)Bu(3)trpy)(Ctbd1;CC(5)H(4)N)Pt((t)Bu(3)trpy)](PF(6))(3) and [Pt(2)Ag(4)(Ctbd1;CCtbd1;CC(6)H(4)CH(3)-4)(8)(THF)(4)

A series of tetraalkynylplatinate(II) complexes, (NBu(4))(2)[Pt(Ctbd1;CR)(4)] (R = C(6)H(4)N-4, C(6)H(4)N-3, and C(6)H(3)N(2)-5), and the diynyl analogues, (NBu(4))(2)[Pt(Ctbd1;CCtbd1;CR)(4)] (R = C(6)H(5) and C(6)H(4)CH(3)-4), have been synthesized. These complexes displayed intense photoluminescence, which was assigned as metal-to-ligand charge transfer (MLCT) transitions. Reaction of (Bu(4)N)(2)[Pt(Ctbd1;CC(5)H(4)N-4)(4)] with 4 equiv of [Pt((t)Bu(3)trpy)(MeCN)](OTf)(2) in methanol did not yield the expected pentanuclear platinum product, [Pt(Ctbd1;CC(5)H(4)N)(4)[Pt((t)Bu(3)trpy)](4)](OTf)(6), but instead afforded a strongly luminescent 4-ethynylpyridine-bridged dinuclear complex, [Pt((t)Bu(3)trpy)(Ctbd1;CC(5)H(4)N)Pt((t)Bu(3)trpy)](PF(6))(3,) which has been structurally characterized. The emission origin is assigned as derived from states of predominantly (3)MLCT [d(pi)(Pt) --> pi((t)Bu(3)trpy)] character, probably mixed with some intraligand (3)IL [pi --> pi(Ctbd1;C)], and ligand-to-ligand charge transfer (3)LLCT [pi(Ctbd1;C) --> pi((t)()Bu(3)trpy)] character. On the other hand, reaction of (Bu(4)N)(2)[Pt(Ctbd1;CCtbd1;CC(6)H(4)CH(3)-4)(4)] with [Ag(MeCN)(4)][BF(4)] gave a mixed-metal aggregate, [Pt(2)Ag(4)(Ctbd1;CCtbd1;CC(6)H(4)CH(3)-4)(8)(THF)(4)]. The crystal structure of [Pt(2)Ag(4)(Ctbd1;CCtbd1;CC(6)H(4)CH(3)-4)(8)(THF)(4)] has also been determined. A comparison study of the spectroscopic properties of the hexanuclear platinum-silver complex with its precursor complex has been made and their spectroscopic origins were suggested.     

Cationic Ti(IV) and neutral Ti(III) titanocene-phosphinoaryloxide frustrated Lewis pairs: hydrogen activation and catalytic amine-borane dehydrogenation

Titanium-phosphorus frustrated Lewis pairs (FLPs) based on titanocene-phosphinoaryloxide complexes have been synthesised. The cationic titanium(IV) complex [Cp(2)TiOC(6)H(4)P((t)Bu)(2)][B(C(6)F(5))(4)] 2 reacts with hydrogen to yield the reduced titanium(III) complex [Cp(2)TiOC(6)H(4)PH((t)Bu)(2)][B(C(6)F(5))(4)] 5. The titanium(III)-phosphorus FLP [Cp(2)TiOC(6)H(4)P((t)Bu)(2)] 6 has been synthesised either by chemical reduction of [Cp(2)Ti(Cl)OC(6)H(4)P((t)Bu)(2)] 1 with [CoCp*(2)] or by reaction of [Cp(2)Ti{N(SiMe(3))(2)}] with 2-C(6)H(4)(OH){P((t)Bu)(2)}. Both 2 and 6 catalyse the dehydrogenation of Me(2)HN·BH(3).     

Synthesis and characterization of three homoleptic alkoxides of uranium: [Li(THF)]2[UIV(OtBu)6], [Li(Et2O)][UV(OtBu)6], and UVI(OtBu)6

Addition of 6 equiv of LiOtBu to a THF/Et2O solution of UCl4 at -25 degrees C generates [Li(THF)]2[U(OtBu)6] (1) in 61% yield. 1 is soluble in polar organic solvents and is stable for several days in THF. However, 1 slowly decomposes in benzene or hexanes, forming the dinuclear uranium(IV) species [Li(THF)][U2(OtBu)9] (2) as one of the decomposition products. Alternatively, 2 can be directly prepared in moderate yield by the addition of 4.5 equiv LiOtBu to UCl4 in hexanes/THF at room temperature. The decomposition of 1 has been studied by 1H and 7Li{1H} NMR spectroscopies to elucidate the nature of this transformation. Oxidation of 1 occurs readily in the presence of 0.5 or 1 equiv of I2 to give [Li(Et2O)][U(OtBu)6] (3) and U(OtBu)6 (4), respectively, in good yields. Alternately, 3 can be generated by comproportionation of 1 and 4. 1-4 have been fully characterized, including analysis by X-ray crystallography. In the solid-state these complexes possess large U-O-Cq bond angles, suggestive of a significant U-O pi interaction. In addition, we have studied the redox properties of 4 by cyclic voltammetry.     

Aluminium complexes containing bidentate and symmetrical tridentate pincer type pyrrolyl ligands: synthesis, reactions and ring opening polymerization

A series of aluminium derivatives containing substituted bidentate and symmetrical tridentate pyrrolyl ligands, [C(4)H(3)NH(2-CH(2)NH(t)Bu)] and [C(4)H(2)NH(2,5-CH(2)NH(t)Bu)(2)], in toluene or diethyl ether were synthesized. Their reactivity and application for the ring opening polymerization of ε-caprolactone have been investigated. The reaction of AlMe(3) with one equiv. of [C(4)H(3)NH(2-CH(2)NH(t)Bu)] in toluene at room temperature affords [C(4)H(3)N(2-CH(2)NH(t)Bu)]AlMe(2) (1) in 70% yield by elimination of one equiv. of methane. Interestingly, while reacting AlMe(3) with one equiv. of [C(4)H(3)NH(2-CH(2)NH(t)Bu)] in toluene at 0 °C followed by refluxing at 100 °C, [{C(4)H(3)N(2-CH(2)N(t)Bu)}AlMe](2) (2) has been isolated via fractional recrystalliztion in 30% yield. Similarly, reacting AlMe(3) with two equiv. of C(4)H(3)NH(2-CH(2)NH(t)Bu) generates [C(4)H(3)N(2-CH(2)NH(t)Bu)](2)AlMe (3) in a moderate yield. Furthermore, complex 1 can be transformed to an aluminium alkoxide derivative, [C(4)H(3)N(2-CH(2)NH(t)Bu)][OC(6)H(2)(-2,6-(t)Bu(2)-4-Me)]AlMe (4) by reacting 1 with one equiv. of HOC(6)H(2)(-2,6-(t)Bu(2)-4-Me) in toluene via the elimination of one equiv. of methane. The reaction of AlR(3) with one equiv. of [C(4)H(2)NH(2,5-CH(2)NH(t)Bu)(2)] in toluene at room temperature affords [C(4)H(2)N(2,5-CH(2)NH(t)Bu)(2)]AlR(2) (5, R = Me; 6, R = Et) in moderate yield. Surprisingly, from the reaction of two equiv. of [C(4)H(2)NH(2,5-CH(2)NH(t)Bu)(2)] with LiAlH(4) in diethyl ether at 0 °C, a novel complex, [C(4)H(2)N(2-CH(2)N(t)Bu)(5-CH(2)NH(t)Bu)](2)AlLi (7) has been isolated after repeating re-crystallization. Furthermore, reacting one equiv. of C(4)H(2)NH(2,5-CH(2)NH(t)Bu)(2) with AlH(3)·NMe(3) in diethyl ether generates an aluminium dihydride complex, [C(4)H(2)N(2,5-CH(2)NH(t)Bu)(2)]AlH(2) (8), in high yield. Additionally, treating 8 with one equiv. of HOC(6)H(2)(-2,6-(t)Bu(2)-4-Me) in methylene chloride produces [C(4)H(2)N(2,5-CH(2)NH(t)Bu)(2)][OC(6)H(2)(-2,6-(t)Bu(2)-4-Me)]AlH (9) with the elimination of one equiv. of H(2). The aluminium alkoxide complex 4 shows moderate reactivity toward the ring opening polymerization of ε-caprolatone in toluene.     

Silylation of the uranyl ion using B(C6F5)3-activated Et3SiH

Addition of 2 equiv of HSiEt(3) to UO(2)((Ar)acnac)(2) ((Ar)acnac = ArNC(Ph)CHC(Ph)O, Ar = 3,5-(t)Bu(2)C(6)H(3)) in the presence of 1 equiv of B(C(6)F(5))(3) results in formation of the U(V) bis(silyloxide) complex [U(OSiEt(3))(2)((Ar)acnac)(2)][HB(C(6)F(5))(3)] (1) in 80% yield. Also produced in the reaction, as a minor product, is U(OSiEt(3))(OB{C(6)F(5)}(3))((Ar)acnac)(2) (2). Interestingly, thermolysis of 1 at 85 °C for 24 h also results in formation of 2, concomitant with production of Et(3)SiH. Addition of 1 equiv of Cp(2)Co to 1 results in formation of U(OSiEt(3))(2)((Ar)acnac)(2) (3) and [Cp(2)Co][HB(C(6)F(5))(3)] (4), which can be isolated in 61% and 71% yields, respectively. Complexes 1-3 have been characterized by X-ray crystallography, while the solution-phase redox properties of 1 have been measured with cyclic voltammetry.     

Investigations on the interaction of dichloroaluminum carboxylates with Lewis bases and water: an efficient road toward oxo- and hydroxoaluminum carboxylate complexes

A series of dichloroaluminum carboxylates [Cl(2)Al(O(2)CR)](2) (were R = Ph (1a), (t)Bu (1b), CHCH(2) (1c) and C(11)H(23) (1d)) were prepared and extended investigations on their structure and reactivity toward various Lewis bases and H(2)O performed. Compounds [Cl(2)Al(O(2)CR)](2) and their adducts with Lewis bases show a large structural variety, featuring both molecular and ionic forms with different coordination numbers of the metal center and various coordination modes of the carboxylate ligand. Upon addition of a Lewis base of moderate strength the molecular form [Cl(2)Al(O(2)CR)](2) equilibrates with new ionic forms. In the presences of 4-methylpyridine the six-coordinate Lewis acid-base adducts [Cl(2)Al(λ(2)-O(2)CR)(py-Me)(2)] [R = Ph (3a), (t)Bu (3b)] with a chelating carboxylate ligand were formed. The reactions of 1a, 1b, and 1d with 0.33 equiv of H(2)O in THF-toluene solution lead to oxo carboxylates [(Al(3)O)(O(2)CR)(6)(THF)(3)] [AlCl(4)] [where R = Ph (4a(THF)), (t)Bu (4b(THF)), and C(11)H(23) (4d(THF))] in high yield. The similar reaction of 1c in tetrahydrofuran (THF) afforded the chloro(hydroxo)aluminum acrylate [(ClAl)(2)(OH)(O(2)CC(2)H(3))(2) (THF)(4)][AlCl(4)] (5), while the hydrolysis of 1b in MeCN lead to the hydroxoaluminum carboxylate [Al(2)(OH)(O(2)C(t)Bu)(2)(MeCN)(6)][AlCl(4))(3)] (6). All compounds were characterized by elemental analysis, (1)H, (27)Al NMR, and IR spectroscopy, and the molecular structure of 1a, 3a, 3b, 4a(THF), 4b(THF), 4b(py-Me'), 5, and 6 were determined by single-crystal X-ray diffraction. The study provides a platform for testing transformations of secondary building units in Al-Metal-Organic Frameworks toward H(2)O and neutral donor ligands.     

Synthesis and structure of diamido ether uranium(IV) and thorium(IV) halide "ate" complexes and their conversion to salt-free bis(alkyl) complexes

The high-yield synthesis, spectroscopic and structural determination of three new uranium(IV) and thorium(IV)ate complexes supported by three different diamido ether ligands are reported. The reaction of Li2[2,6-iPr2PhN(CH2CH2)]2O (Li2[DIPPNCOCN]) with 1 equiv. of UCl4 in THF generates [DIPPNCOCN]UCl3Li(THF)2(1), while reaction in toluene/ether gives salt-free [DIPPNCOCN]UCl2.1/2C7H8(2), which was identified by paramagnetically shifted 1H NMR. Reaction of 0.5 equiv. of {[tBuNON]UCl2}2([tBuNON]=[(CH3)3CN(Si(CH3)2)]2O2-) with 3.5 equiv. LiI in toluene and a minimal amount of THF results in [tBuNON]UI3Li(THF)2(3) and is very similar in structure to 1. {[MesNON]ThCl3Li(THF)}2(4), a dimeric complex with a Th2Li2Cl6 core, is prepared by reaction of Li2[2,4,6-Me3PhN(Si(CH3)2)]2O (Li2[MesNON]) with ThCl4 in THF. The analogous reaction in toluene did not yield the salt-free complex but rather a sterically crowded diligated compound, [MesNON]2Th (5), which was also structurally characterized. Complex 5 was prepared rationally by reacting 2 equiv. Li2[MesNON] with ThCl4 in toluene. The reaction of 1 and 3 with 2 equiv. of LiCH2Si(CH3)3 generates the stable, salt-free organoactinides [DIPPNCOCN]U(CH2Si(CH3)3)2(6) and [tBuNON]U(CH2Si(CH3)3)2(7). Complex 6 was structurally characterized. These reactions illustrate the viability of ate complexes as useful synthetic precursors.     

Cationic aluminum alkyl complexes incorporating aminotroponiminate ligands

The synthesis, structures, and reactivity of cationic aluminum complexes containing the N,N'-diisopropylaminotroponiminate ligand ((i)Pr(2)-ATI(-)) are described. The reaction of ((i)Pr(2)-ATI)AlR(2) (1a-e,g,h; R = H (a), Me (b), Et (c), Pr (d), (i)Bu (e), Cy (g), CH(2)Ph (h)) with [Ph(3)C][B(C(6)F(5))(4)] yields ((i)()Pr(2)-ATI)AlR(+) species whose fate depends on the properties of the R ligand. 1a and 1b react with 0.5 equiv of [Ph(3)C][B(C(6)F(5))(4)] to produce dinuclear monocationic complexes [([(i)Pr(2)-ATI] AlR)(2)(mu-R)][(C(6)F(5))(4)] (2a,b). The cation of 2b contains two ((i)()Pr(2)-ATI)AlMe(+) units linked by an almost linear Al-Me-Al bridge; 2a is presumed to have an analogous structure. 2b does not react further with [Ph(3)C][B(C(6)F(5))(4)]. However, 1a reacts with 1 equiv of [Ph(3)C][B(C(6)F(5))(4)] to afford ((i Pr(2)-ATI)Al(C(6)F(5))(mu-H)(2)B(C(6)F(5))(2) (3) and other products, presumably via C(6)F(5)(-) transfer and ligand redistribution of a [((i)()Pr(2)-ATI)AlH][(C(6)F(5))(4)] intermediate. 1c-e react with 1 equiv of [Ph(3)C][B(C(6)F(5))(4)] to yield stable base-free [((i)Pr(2)-ATI)AlR][B(C(6)F(5))(4)] complexes (4c-e). 4c crystallizes from chlorobenzene as 4c(ClPh).0.5PhCl, which has been characterized by X-ray crystallography. In the solid state the PhCl ligand of 4c(ClPh) is coordinated by a dative PhCl-Al bond and an ATI/Ph pi-stacking interaction. 1g,h react with [Ph(3)C][B(C(6)F(5))(4)] to yield ((i)Pr(2)-ATI)Al(R)(C(6)F(5)) (5g,h) via C(6)F(5)(-) transfer of [((i)Pr(2)-ATI)AlR][(BC(6)F(5))(4)] intermediates. 1c,h react with B(C(6)F(5))(3) to yield ((i)Pr(2)-ATI)Al(R)(C(6)F(5)) (5c,h) via C(6)F(5)(-) transfer of [((i)Pr(2)-ATI)AlR][RB(C(6)F(5))(3)] intermediates. The reaction of 4c-e with MeCN or acetone yields [((i)Pr(2)-ATI)Al(R)(L)][B(C(6)F(5))(4)] adducts (L = MeCN (8c-e), acetone (9c-e)), which undergo associative intermolecular L exchange. 9c-e undergo slow beta-H transfer to afford the dinuclear dicationic alkoxide complex [(((i)Pr(2)-ATI)Al(mu-O(i)()Pr))(2)][B(C(6)F(5))(4)](2) (10) and the corresponding olefin. 4c-e catalyze the head-to-tail dimerization of tert-butyl acetylene by an insertion/sigma-bond metathesis mechanism involving [((i)Pr(2)-ATI)Al(C=C(t)Bu)][B(C(6)F(5))(4)] (13) and [((i)Pr(2)-ATI)Al(CH=C((t)()Bu)C=C(t)Bu)][B(C(6)F(5))(4)] (14) intermediates. 13 crystallizes as the dinuclear dicationic complex [([(i Pr(2)-ATI]Al(mu-C=C(t)Bu))(2)][B(C(6)F(5))(4)](2).5PhCl from chlorobenzene. 4e catalyzes the polymerization of propylene oxide and 2a catalyzes the polymerization of methyl methacrylate. 4c,e react with ethylene-d(4) by beta-H transfer to yield [((i)Pr(2)-ATI)AlCD(2)CD(2)H][B(C(6)F(5))(4)] initially. Polyethylene is also produced in these reactions by an unidentified active species.     

First complexes of scandium and yttrium with NNO and NNS heteroscorpionate ligands

The reaction of ScCl(3)(THF)(3) or YCl(3) in a 1:1 molar ratio under reflux for 8 h with [{Li(bdmpza)(H(2)O)}(4)] [bdmpza = bis(3,5-dimethylpyrazol-1-yl)acetate], [{Li(bdmpzdta)(H(2)O)}(4)] [bdmpzdta = bis(3,5-dimethylpyrazol-1-yl)dithioacetate], and (Hbdmpze) [bdmpze = 2,2-bis(3,5-dimethylpyrazol-1-yl)ethoxide] affords the corresponding complexes [MCl(2)(kappa(3)-bdmpzx)(THF)] (x = a, M = Sc (1), Y (2); x = dta, M = Sc (3), Y (4); x = e, M = Sc (5), Y (6)). However, when the reaction was carried out for 1 h under reflux between ScCl(3)(THF)(3) and [{Li(bdmpzdta)(H(2)O)}(4)], a new anionic complex [Li(THF)(4)][ScCl(3)(kappa(3)-bdmpzdta)] (7) was obtained. Reaction of [{Li(bdmpza)(H(2)O)}(4)] with YCl(3) in a 2:1 molar ratio under reflux for 8 h gave the complex [YCl(kappa(3)-bdmpza)(2)] (8). The same reaction, but with the lithium compound [{Li(bdmpzdta)(H(2)O)}(4)], led to the formation of an anionic complex [Li(THF)(4)][YCl(3)(kappa(3)-bdmpzdta)] (9). The X-ray crystal structures of 7 and 9 were established. Finally, the addition of 1 equiv of [{Li(bdmpza)(H(2)O)}(4)] or [{Li(bdmpzdta)(H(2)O)}(4)] to a solution of YCl(3) in THF under reflux, followed by the addition of 1 equiv of 1,10-phenanthroline, resulted in the formation of the corresponding complexes [YCl(2)(kappa(3)-bdmpzx)(phen)] (x = a (10), x = dta (11)). These complexes are the first examples of group 3 metals stabilized by heteroscorpionate ligands. In addition, we have explored the reactivity of some of these complexes with alcohols and amides. For example, the direct reaction of [YCl(2)(kappa(3)-bdmpza)(THF)] (2) with several alcohols gave the alkoxide complexes [YCl(kappa(3)-bdmpza)(OR)] (R = Et (12), iPr (13)). Finally, the reaction between [ScCl(2)(kappa(3)-bdmpzdta)(THF)] (3) or [Li(THF)(4)][ScCl(3)(kappa(3)-bdmpzdta)] (7) and LiN(SiMe(3))(2).Et(2)O in 1:1 and 1:2 molar ratios gave rise to the complexes [ScCl(kappa(3)-bdmpzdta){N(SiMe(3))(2)}] (14) and [Sc(kappa(3)-bdmpzdta){N(SiMe(3))(2)}(2)] (15), respectively.     

Synthesis of a uranium(VI)-carbene: reductive formation of uranyl(V)-methanides, oxidative preparation of a [R2C═U═O]2+ analogue of the [O═U═O]2+ uranyl ion (R = Ph2PNSiMe3), and comparison of the nature of U(IV)═C, U(V)═C, and U(VI)═C double bonds

We report attempts to prepare uranyl(VI)- and uranium(VI) carbenes utilizing deprotonation and oxidation strategies. Treatment of the uranyl(VI)-methanide complex [(BIPMH)UO(2)Cl(THF)] [1, BIPMH = HC(PPh(2)NSiMe(3))(2)] with benzyl-sodium did not afford a uranyl(VI)-carbene via deprotonation. Instead, one-electron reduction and isolation of di- and trinuclear [UO(2)(BIPMH)(μ-Cl)UO(μ-O){BIPMH}] (2) and [UO(μ-O)(BIPMH)(μ(3)-Cl){UO(μ-O)(BIPMH)}(2)] (3), respectively, with concomitant elimination of dibenzyl, was observed. Complexes 2 and 3 represent the first examples of organometallic uranyl(V), and 3 is notable for exhibiting rare cation-cation interactions between uranyl(VI) and uranyl(V) groups. In contrast, two-electron oxidation of the uranium(IV)-carbene [(BIPM)UCl(3)Li(THF)(2)] (4) by 4-morpholine N-oxide afforded the first uranium(VI)-carbene [(BIPM)UOCl(2)] (6). Complex 6 exhibits a trans-CUO linkage that represents a [R(2)C═U═O](2+) analogue of the uranyl ion. Notably, treatment of 4 with other oxidants such as Me(3)NO, C(5)H(5)NO, and TEMPO afforded 1 as the only isolable product. Computational studies of 4, the uranium(V)-carbene [(BIPM)UCl(2)I] (5), and 6 reveal polarized covalent U═C double bonds in each case whose nature is significantly affected by the oxidation state of uranium. Natural Bond Order analyses indicate that upon oxidation from uranium(IV) to (V) to (VI) the uranium contribution to the U═C σ-bond can increase from ca. 18 to 32% and within this component the orbital composition is dominated by 5f character. For the corresponding U═C π-components, the uranium contribution increases from ca. 18 to 26% but then decreases to ca. 24% and is again dominated by 5f contributions. The calculations suggest that as a function of increasing oxidation state of uranium the radial contraction of the valence 5f and 6d orbitals of uranium may outweigh the increased polarizing power of uranium in 6 compared to 5.     

1,4-dicyanobenzene as a scaffold for the preparation of bimetallic actinide complexes exhibiting metal-metal communication

Reaction of two equivalents of [(C(5)Me(4)Et)(2)U(CH(3))(Cl)] (6) or [(C(5)Me(5))(2)Th(CH(3))(Br)] (7) with 1,4-dicyanobenzene leads to the formation of the novel 1,4-phenylenediketimide-bridged bimetallic organoactinide complexes [{(C(5)Me(4)Et)(2)(Cl)U}(2)(mu-{N==C(CH(3))-C(6)H(4)-(CH(3))C==N})] (8) and [{(C(5)Me(5))(2)(Br)Th}(2)(mu-{N==C(CH(3))-C(6)H(4)- (CH(3))C==N})] (9), respectively. These complexes were structurally characterized by single-crystal X-ray diffraction and NMR spectroscopy. Metal-metal interactions in these isovalent bimetallic systems were assessed by means of cyclic voltammetry, UV-visible/NIR absorption spectroscopy, and variable-temperature magnetic susceptibility. Although evidence for magnetic coupling between metal centers in the bimetallic U(IV)/U(IV) (5f(2)-5f(2)) complex is ambiguous, the complex displays appreciable electronic communication between the metal centers through the pi system of the dianionic diketimide bridging ligand, as judged by voltammetry. The transition intensities of the f-f bands for the bimetallic U(IV)/U(IV) system decrease substantially compared to the related monometallic ketimide chloride complex, [(C(5)Me(5))(2)U(Cl){-N==C(CH(3))-(3,4,5-F(3)-C(6)H(2))}] (11). Also reported herein are new synthetic routes to the actinide starting materials [(C(5)Me(4)Et)(2)U(CH(3))(Cl)] (6) and [(C(5)Me(5))(2)Th(CH(3))(Br)] (7) in addition to the syntheses and structures of the monometallic uranium complexes [(C(5)Me(4)Et)(2)UCl(2)] (3), [(C(5)Me(4)Et)(2)U(CH(3))(2)] (4), [(C(5)Me(4)Et)(2)U{-N==C(CH(3))-C(6)H(4)-C==N}(2)] (10), and 11.     

Synthesis and group 4 complexes of tris(pyrrolyl-alpha-methyl)amine

The tetradentate, trianionic ligand tris(pyrrolyl-alpha-methyl)amine (H(3)tpa) is available in 84% yield in a single step by a triple Mannich reaction involving 3 equiv of pyrrole, 3 equiv of formaldehyde, and ammonium chloride. The new ligand is readily placed on titanium by transamination on Ti(NMe(2))(4), which generates Ti(NMe(2))(tpa) (1) in 73% yield. Treating 1 with 1 equiv of 1,3-dimethyl-2-iminoimidazolidine (H-imd) in toluene provided a rare example of a titanium 2-iminoimidazolidinide, which displays some interesting structural features. Of note is the Ti-N(imd) distance of 1.768(2) A, a typical Ti-N double to triple bond distance. Reaction of Zr(NMe(2))(4) with H(3)tpa gave a complex of variable composition, probably varying in the amount of labile dimethylamine retained. However, stable discreet compounds were available by addition of THF, pyridine, or 4,4'-di-tert-butyl-2,2'-bipyridine (Bu(t)bpy) to in situ generated Zr(NMe(2))(NHMe(2))(x)(tpa). Three chloro zirconium complexes were generated using three different strategies. Treating Zr(tpa)(NMe(2))(Bu(t)bpy) (5) with ClSiMe(3) afforded Zr(tpa)(Cl)(Bu(t)bpy) (6) in 92% yield. Reaction of Li(3)tpa with ZrCl(4)(THF)(2) in THF gave a 72% yield of ZrCl(tpa)(THF)(2) (7). In addition, treatment of ZrCl(NMe(2))(3) with H(3)tpa cleanly generated ZrCl(NHMe(2))(2)(tpa) (8) in 95% yield. An organometallic zirconium complex was generated on treatment of 6 with LiCtbd1;CPh; alkynyl Zr(Ctbd1;CPh)(tpa)(Bu(t)bpy) (9) was isolated in 62% yield. 1, Ti(imd)(tpa) (2), 6, and 9 were characterized by X-ray diffraction.     

Syntheses and X-ray structures of monocyclic,bicyclic, and spirocyclic gallium and indium boraamidinates

The reactions of [Li(2)[PhB(N(t)Bu)(2)]](2) with GaCl(3) in various stoichiometries yield [Li(thf)(4)][PhB(mu-N(t)Bu)(2)GaCl(2) x GaCl(3)] (1), [PhB(mu-N(t)Bu)(2)GaCl](2) (2), and [mu-Li(OEt(2))[PhB(N(t)Bu)(2)]Ga] (3a), a series of complexes in which the three chloride ligands are successively replaced by the dianion [PhB(N(t)Bu)(2)](2-). The X-ray structures of 1, 2, and 3a show that the boraamidinate ligand adopts an N,N'-chelating mode. In the ion-separated complex 1, one of the nitrogen atoms is coordinated to a GaCl(3) molecule. The related indium complexes [mu-LiCl(thf)(2)][PhB(mu-N(t)Bu)(2)InCl](2) (4) and [mu-Li(OEt(2))[PhB(mu-N(t)Bu)(2)]In] (3b) were obtained in a similar manner. Complex 4 is the indium analogue of 2 with the incorporation of a bissolvated LiCl molecule. In 3a and 3b the spirocyclic [[PhB(mu-N(t)Bu)(2)](2)M](-) (M = Ga, In) anions are N,N'-chelated to the [Li(OEt(2))](+) counterion. Prolonged reactions result in the formation of [PhB(mu-N(t)Bu)(2)GaCl][(t)BuN(H)GaCl(2)] (5) and [[PhB(mu-N(t)Bu)(2)InCl][(t)BuN(H)InCl(2)][mu-LiCl(OEt(2))(2)]] (6), respectively. The X-ray structures of 5 and 6 reveal bicyclic structures which formally involve the entrapment of the monomers (t)BuN(H)MCl(2) by a four-membered BN(2)M ring (M = Ga, In). The synthesis and X-ray structure of Cl(2)Ga[mu-N(H)(t)Bu](2)GaCl(2) are also reported.