Borane-mediated silylation of a metal-oxo ligand

The addition of 1 equiv of HSiPh(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 the formation of U(OSiPh(3))(OB{C(6)F(5)}(3))((Ar)acnac)(2) (1), via silylation of an oxo ligand and reduction of the uranium center. The addition of 1 equiv of Cp(2)Co to 1 results in a reduction to uranium(IV) and the formation of [Cp(2)Co][U(OSiPh(3))(OB{C(6)F(5)}(3))((Ar)acnac)(2)] (2) in 78% yield. Complexes 1 and 2 have been characterized by X-ray crystallography, while the solution-phase redox properties of 1 have been measured with cyclic voltammetry.     

Facile reduction of a uranyl(VI) β-ketoiminate complex to U(IV) upon oxo silylation

Reaction of the uranyl β-ketoiminate complex UO(2)((tBu)acnac)(2) (1) ((tBu)acnac = (t)BuNC(Ph)CHC(Ph)O) with Me(3)SiI, in the presence of Ph(3)P, results in the reductive silylation of the uranyl moiety and formation of the U(V) bis-silyloxide complex [Ph(3)PI][U(OSiMe(3))(2)I(4)] (2). Subsequent reaction of 2 with Lewis bases, such as 2,2'-bipyridine (bipy), 1,10-phenanthroline (phen), and tetrahydrofuran (THF), results in a further reduction of the metal center and isolation of the U(IV) complexes U(OSiMe(3))(2)I(2)(bipy)(2) (3), U(OSiMe(3))(2)I(2)(phen)(2) (4), and [U(OSiMe(3))(2)I(THF)(4)][I(3)] (5), respectively.     

Novel micro3-oxo complexes prepared from Cp*Zr(B(3R)3 (R = H, CH3) and B(C6F5)3 in diethyl ether

From the reactions of Cp*ZrCl(3) with 3 equiv. of LiBH(3)R (R = CH(3), Ph), the organotrihydroborate complexes, Cp*Zr(BH(3)CH(3))(3), 1, and Cp*Zr(BH(3)Ph)(3), 2, were isolated. One of the Zr-H-B bonding interactions in 2 could be described as an intermediate case between the bidentate and tridentate modes. Reactions of and Cp*Zr(BH(4))(3), 3, with Lewis acid B(C(6)F(5))(3) in diethyl ether produced the novel 14-electron ionic compounds [(micro(3)-O)(micro(2)-OC(2)H(5))(3){(Cp*Zr(OC(2)H(5)))(2)(BCH(3))}][HB(C(6)F(5))(3)], 4, and [(micro(3)-O)(micro(2)-OC(2)H(5))(3){(Cp*Zr(OC(2)H(5)))(2)(BOC(2)H(5))}][HB(C(6)F(5))(3)], 5, respectively. These two unique compounds resulted from a sequential cleavage of Zr-H-B bonds of 1 and 3 and C-O bonds of ether followed by the formation of O-B bonds. The solid state single crystal X-ray analyses revealed that both compounds have similar structures. A micro(3)-oxygen bridges two zirconiums and a boron atom. The latter three atoms are further connected by three micro(2)-bridging ethoxy groups giving rise to three four-membered metallacycles within the structure of each cation.     

Differences in actinide metal-ligand orbital interactions: comparison of U(IV) and Pu(IV) β-ketoiminate N,O donor complexes

Syntheses and characterization of UCl(2)((Ar)acnac)(2), UI(2)((Ar)acnac)(2), and PuI(2)((Ar)acnac)(2) are reported ((Ar)acnac denotes a bis-phenyl β-ketoiminate ligand where Ar = 3,5-(t)Bu(2)C(6)H(3)). Structural analyses and computations show significant metal-ligand orbital interaction differences in U(IV) vs. Pu(IV) bonding.     

Bonding Trends Traversing the Tetravalent Actinide Series: Synthesis, Structural, and Computational Analysis of An(IV)((Ar)acnac)(4) Complexes (An = Th, U, Np, Pu; (Ar)acnac = ArNC(Ph)CHC(Ph)O; Ar = 3,5-(t)Bu(2)C(6)H(3))

A series of tetravalent An(IV) complexes with a bis-phenyl β-ketoiminate N,O donor ligand has been synthesized with the aim of identifying bonding trends and changes across the actinide series. The neutral molecules are homoleptic with the formula An((Ar)acnac)(4) (An = Th (1), U (2), Np (3), Pu (4); (Ar)acnac = ArNC(Ph)CHC(Ph)O; Ar = 3,5-(t)Bu(2)C(6)H(3)) and were synthesized through salt metathesis reactions with actinide chloride precursors. NMR and electronic absorption spectroscopy confirm the purity of all four new compounds and demonstrate stability in both solution and the solid state. The Th, U, and Pu complexes were structurally elucidated by single-crystal X-ray diffraction and shown to be isostructural in space group C2/c. Analysis of the bond lengths reveals shortening of the An-O and An-N distances arising from the actinide contraction upon moving from 1 to 2. The shortening is more pronounced upon moving from 2 to 4, and the steric constraints of the tetrakis complexes appear to prevent the enhanced U-O versus Pu-O orbital interactions previously observed in the comparison of UI(2)((Ar)acnac)(2) and PuI(2)((Ar)acnac)(2) bis-complexes. Computational analysis of models for 1, 2, and 4 (1a, 2a, and 4a, respectively) concludes that both the An-O and the An-N bonds are predominantly ionic for all three molecules, with the An-O bonds being slightly more covalent. Molecular orbital energy level diagrams indicate the largest 5f-ligand orbital mixing for 4a (Pu), but spatial overlap considerations do not lead to the conclusion that this implies significantly greater covalency in the Pu-ligand bonding. QTAIM bond critical point data suggest that both U-O/U-N and Pu-O/Pu-N are marginally more covalent than the Th analogues.     

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.     

Generation of cationic [Zr-[tert-butyl enolate]] reactive species: methyl abstraction versus hydride abstraction

Treatment of the neutral methyl-Zr-enolate [Cp(2)Zr(Me)[O(tBuO)C=CMe(2)]] (1) with one equivalent of B(C(6)F(5))(3) or [HNMe(2)Ph][B(C(6)F(5))(4)] as a methyl abstractor in THF at 0 degrees C leads to the selective formation of the free ion pair complex [Cp(2)Zr(THF)[O(tBuO)C=CMe(2)]](+) [anion](-) (2) (anion=MeB(C(6)F(5))(3) (-), B(C(6)F(5))(4) (-)), which is relevant to the controlled polymerization of methacrylates. Cation 2 rapidly decomposes at 20 degrees C in THF with release of one equivalent of isobutene to form the cationic Zr-carboxylate species [Cp(2)Zr(THF)(O(2)CiPr)](+) (3), through a proposed intramolecular proton transfer process from the tert-butoxy group to the enolate. The reaction of 1 with one equivalent of B(C(6)F(5))(3) or [HNMe(2)Ph][B(C(6)F(5))(4)] in CH(2)Cl(2) leads to the direct, rapid formation of the dimeric micro-isobutyrato-Zr dicationic species [[Cp(2)Zr[micro-(O(2)CiPr)]](2)](2+) (4), which gives 3 upon dissolution in THF. Contrastingly, when [Ph(3)C][B(C(6)F(5))(4)] is used to generate the cationic Zr-enolate species from 1 in CD(2)Cl(2), a 15:85 mixture of dicationic complexes 4 and [[Cp(2)Zr[micro-(O(2)C-C(Me)=CH(2))]](2)](2+)[B(C(6)F(5))(4)]]2-(5-[B(C(6)F(5))(4)](2)) is obtained quantitatively. The formation of 5 is proposed to arise from initial hydride abstraction from a methyl enolate group by Ph(3)C(+), as supported by the parallel production of Ph(3)CH, and subsequent elimination of methane and isobutene. In addition to standard spectroscopic and analytical characterizations for the isolated complexes 2-5, complexes 4 and 5 have also been structurally characterized by X-ray diffraction studies.     

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).     

Mixed-ligand uranyl(V) beta-diketiminate/beta-diketonate complexes: synthesis and characterization

The reaction of [UO 2(Ar 2nacnac)Cl] 2 [Ar 2nacnac = (2,6- (i)Pr 2C 6H 3)NC(Me)CHC(Me)N(2,6- (i)Pr 2C 6H 3)] with Na(RC(O)CHC(O)R) (R = Me, Ph, CF 3) in tetrahydrofuran results in the formation of UO 2(Ar 2nacnac)(RC(O)CHC(O)R) (R = Me, 1; Ph, 2; CF 3, 3), which can be isolated in moderate yields. The structures of 1 and 2 have been confirmed by X-ray crystallography, while the solution redox properties of 1- 3 have been measured by cyclic voltammetry. Complexes 1- 3 exhibit reduction features at -1.82, -1.59, and -1.39 V (vs Fc/Fc (+)), respectively, at a scan rate of 100 mV.s (-1). The decrease in the reduction potential follows the electron-withdrawing ability of each beta-diketonate ligand. Chemical reduction of 1 and 2 with Cp* 2Co in toluene yields [Cp* 2Co][UO 2(Ar 2nacnac)(RC(O)CHC(O)R)] (R = Me, 4; Ph, 5), while reduction of 3 with Cp 2Co provides [Cp 2Co][UO 2(Ar 2nacnac)(CF 3C(O)CHC(O)CF 3)] ( 6). Complexes 4- 6 have been fully characterized, while the solid-state molecular structure of 5 has also been determined. In contrast to the clean reduction that occurs with Cp* 2Co, reduction of 1 with sodium ribbon, followed by cation exchange with [NEt 4]Cl, produces [NEt 4][UO 2(Ar 2nacnac)(H 2CC(O)CH(O)CMe)] ( 7) in modest yield. This product results from the formal loss of H (*) from a methyl group of the acetylacetonate ligand. Alternately, complex 7 can be synthesized by deprotonation of 1 with NaNTMS 2 in good yield.     

New cationic and zwitterionic Cp*M(kappa2-P,S) complexes (M = Rh, Ir): divergent reactivity pathways arising from alternative modes of ancillary ligand participation in substrate activation

Treatment of 0.5 equiv of [Cp*IrCl(2)](2) with 1/3-P(i)Pr(2)-2-S(t)Bu-indene afforded Cp*Ir(Cl)(kappa(2)-3-P(i)Pr(2)-2-S-indene) (1) in 95% yield (Cp* = eta(5)-C(5)Me(5)). Addition of AgOTf or LiB(C(6)F(5))(4) x 2.5 OEt(2) to 1 gave [Cp*Ir(kappa(2)-3-P(i)Pr(2)-2-S-indene)](+)X(-) ([2](+)X(-); X = OTf, 78%; X = B(C(6)F(5))(4), 82%), which represent the first examples of isolable coordinatively unsaturated [Cp'Ir(kappa(2)-P,S)](+)X(-) complexes. Exposure of [2](+)OTf(-) to CO afforded [2 x CO](+)OTf(-) in 91% yield, while treatment of [2](+)B(C(6)F(5))(4)(-) with PMe(3) generated [2 x PMe(3)](+)B(C(6)F(5))(4)(-) in 94% yield. Treatment of 1 with K(2)CO(3) in CH(3)CN allowed for the isolation of the unusual adduct 3 x CH(3)CN (41% isolated yield), in which the CH(3)CN bridges the Lewis acidic Cp*Ir and Lewis basic indenide fragments of the targeted coordinatively unsaturated zwitterion Cp*Ir(kappa(2)-3-P(i)Pr(2)-2-S-indenide) (3). In contrast to the formation of [2 x CO](+)OTf(-), exposure of 3 x CH(3)CN to CO did not afford 3 x CO; instead, a clean 1:1 mixture of (kappa(2)-3-P(i)Pr(2)-2-S-indene)Ir(CO)(2) (4) and 1,2,3,4-tetramethylfulvene was generated. Treatment of [2](+)OTf(-) with Ph(2)SiH(2) resulted in the net loss of Ph(2)Si(OTf)H to give Cp*Ir(H)(kappa(2)-3-P(i)Pr(2)-2-S-indene) (5) in 44% yield. In contrast, treatment of [2](+)B(C(6)F(5))(4)(-) with Ph(2)SiH(2) or PhSiH(3) proceeded via H-Si addition across Ir-S to give the corresponding [Cp*Ir(H)(kappa(2)-3-P(i)Pr(2)-2-S(SiHPhX)-indene)](+)B(C(6)F(5))(4)(-) complexes 6a (X = Ph, 68%) or 6b (X = H, 77%), which feature a newly established S-Si linkage. Compound 6a was observed to effect net C-O bond cleavage in diethyl ether with net loss of Ph(2)Si(OEt)H, affording [Cp*Ir(H)(kappa(2)-3-P(i)Pr(2)-2-SEt-indene)](+)B(C(6)F(5))(4)(-) (7) in 77% yield. Furthermore, 6a proved capable of transferring Ph(2)SiH(2) to acetophenone, with concomitant regeneration of [2](+)B(C(6)F(5))(4)(-); however, [2](+)X(-) did not prove to be effective ketone hydrosilylation catalysts. Treatment of 1/3-P(i)Pr(2)-2-S(t)Bu-indene with 0.5 equiv of [Cp*RhCl(2)](2) gave Cp*Rh(Cl)(kappa(2)-3-P(i)Pr(2)-2-S-indene) (8) in 94% yield. Combination of 8 and LiB(C(6)F(5))(4) x 2.5 Et(2)O produced the coordinatively unsaturated cation [Cp*Rh(kappa(2)-3-P(i)Pr(2)-2-S-indene)](+)B(C(6)F(5))(4)(-) ([9](+)B(C(6)F(5))(4)(-)), which was transformed into [Cp*Rh(H)(kappa(2)-3-P(i)Pr(2)-2-S(SiHPh(2))-indene)](+)B(C(6)F(5))(4)(-) (10) via net H-Si addition of Ph(2)SiH(2) to Rh-S. Unlike [2](+)X(-), complex [9](+)B(C(6)F(5))(4)(-) was shown to be an effective catalyst for ketone hydrosilylation. Treatment of 3 x CH(3)CN with Ph(2)SiH(2) resulted in the loss of CH(3)CN, along with the formation of Cp*Ir(H)(kappa(2)-3-P(i)Pr(2)-2-S-(1-diphenylsilylindene)) (11) (64% isolated yield) as a mixture of diastereomers. The formation of 11 corresponds to heterolytic H-Si bond activation, involving net addition of H(-) and Ph(2)HSi(+) fragments to Ir and indenide in the unobserved zwitterion 3. Crystallographic data are provided for 1, [2 x CO](+)OTf(-), 3 x CH(3)CN, 7, and 11. Collectively, these results demonstrate the versatility of donor-functionalized indene ancillary ligands in allowing for the selection of divergent metal-ligand cooperativity pathways (simply by ancillary ligand deprotonation) in the activation of small molecule substrates.     

Dinuclear oxidative addition of N-H and S-H bonds at chromium. Reaction of (*)Cr(CO)(3)(C(5)Me(5)) with [o-(HA)C(6)H(4)S-Cr(CO)(3)(C(5)Me(5))] (A = S,NH) yielding [eta(2)-o-(mu-A)C(6)H(4)S-Cr(C(5)Me(5))](2) and H-Cr(CO)(3)(C(5)Me(5))

Reaction of the 17-electron radical (*)Cr(CO)(3)Cp* (Cp* = C(5)Me(5)) with 0.5 equiv of 2-aminophenyl disulfide [(o-H(2)NC(6)H(4))(2)S(2)] results in rapid oxidative addition to form the initial product (o-H(2)N)C(6)H(4)S-Cr(CO)(3)Cp*. Addition of a second equivalent of (*)Cr(CO)(3)Cp* to this solution results in the formation of H-Cr(CO)(3)Cp* as well as (1)/(2)[[eta(2)-o-(mu-NH)C(6)H(4)S]CrCp*](2). Spectroscopic data show that (o-H(2)N)C(6)H(4)S-Cr(CO)(3)Cp* loses CO to form [eta(2)-(o-H(2)N)C(6)H(4)S]Cr(CO)(2)Cp*. Attack on the N-H bond of the coordinated amine by (*)Cr(CO)(3)Cp* provides a reasonable mechanism consistent with the observation that both chelate formation and oxidative addition of the N-H bond are faster under argon than under CO atmosphere. The N-H bonds of uncoordinated aniline do not react with (*)Cr(CO)(3)Cp*. Reaction of the 2 mol of (*)Cr(CO)(3)Cp* with 1,2-benzene dithiol [1,2-C(6)H(4)(SH)(2)] yields the initial product (o-HS)C(6)H(4)S-Cr(CO)(3)Cp and 1 mol of H-Cr(CO)(3)Cp*. Addition of 1 equiv more of (*)Cr(CO)(3)Cp to this solution also results in the formation of 1 equiv of H-Cr(CO)(3)Cp*, as well as the dimeric product (1)/(2)[[eta(2)-o-(mu-S)C(6)H(4)S]CrCp*](2). This reaction also occurs more rapidly under Ar than under CO, consistent with intramolecular coordination of the second thiol group prior to oxidative addition. The crystal structures of [[eta(2)-o-(mu-NH)C(6)H(4)S]CrCp*](2) and [[eta(2)-o-(mu-S)C(6)H(4)S]CrCp*](2) are reported.     

Half-sandwich bis(tetramethylaluminate) complexes of the rare-earth metals: synthesis, structural chemistry, and performance in isoprene polymerization

The protonolysis reaction of [Ln(AlMe(4))(3)] with various substituted cyclopentadienyl derivatives HCp(R) gives access to a series of half-sandwich complexes [Ln(AlMe(4))(2)(Cp(R))]. Whereas bis(tetramethylaluminate) complexes with [1,3-(Me(3)Si)(2)C(5)H(3)] and [C(5)Me(4)SiMe(3)] ancillary ligands form easily at ambient temperature for the entire Ln(III) cation size range (Ln=Lu, Y, Sm, Nd, La), exchange with the less reactive [1,2,4-(Me(3)C)(3)C(5)H(3)] was only obtained at elevated temperatures and for the larger metal centers Sm, Nd, and La. X-ray structure analyses of seven representative complexes of the type [Ln(AlMe(4))(2)(Cp(R))] reveal a similar distinct [AlMe(4)] coordination (one eta(2), one bent eta(2)). Treatment with Me(2)AlCl leads to [AlMe(4)] --> [Cl] exchange and, depending on the Al/Ln ratio and the Cp(R) ligand, varying amounts of partially and fully exchanged products [{Ln(AlMe(4))(mu-Cl)(Cp(R))}(2)] and [{Ln(mu-Cl)(2)(Cp(R))}(n)], respectively, have been identified. Complexes [{Y(AlMe(4))(mu-Cl)(C(5)Me(4)SiMe(3))}(2)] and [{Nd(AlMe(4))(mu-Cl){1,2,4-(Me(3)C)(3)C(5)H(2)}}(2)] have been characterized by X-ray structure analysis. All of the chlorinated half-sandwich complexes are inactive in isoprene polymerization. However, activation of the complexes [Ln(AlMe(4))(2)(Cp(R))] with boron-containing cocatalysts, such as [Ph(3)C][B(C(6)F(5))(4)], [PhNMe(2)H][B(C(6)F(5))(4)], or B(C(6)F(5))(3), produces initiators for the fabrication of trans-1,4-polyisoprene. The choice of rare-earth metal cation size, Cp(R) ancillary ligand, and type of boron cocatalyst crucially affects the polymerization performance, including activity, catalyst efficiency, living character, and polymer stereoregularity. The highest stereoselectivities were observed for the precatalyst/cocatalyst systems [La(AlMe(4))(2)(C(5)Me(4)SiMe(3))]/B(C(6)F(5))(3) (trans-1,4 content: 95.6 %, M(w)/M(n)=1.26) and [La(AlMe(4))(2)(C(5)Me(5))]/B(C(6)F(5))(3) (trans-1,4 content: 99.5 %, M(w)/M(n)=1.18).     

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.     

Marked counteranion effects on single-site olefin polymerization processes. Correlations of ion pair structure and dynamics with polymerization activity, chain transfer, and syndioselectivity

Counteranion effects on the rate and stereochemistry of syndiotactic propylene enchainment by the archetypal C(s)-symmetric precatalyst [Me(2)C(Cp)(Flu)]ZrMe(2) (1; Cp = C(5)H(4); Flu = C(13)H(8), fluorenyl) are probed using the cocatalysts MAO (2), B(C(6)F(5))(3) (3)(,) B(2-C(6)F(5)C(6)F(4))(3) (4)(,) Ph(3)C(+)B(C(6)F(5))(4)(-) (5), and Ph(3)C(+)FAl(2-C(6)F(5)C(6)F(4))(3)(-) (6), offering greatly different structural and ion pairing characteristics. Reaction of 1 with 3 affords [Me(2)C(Cp)(Flu)]ZrMe(+) MeB(C(6)F(5))(3)(-) (7). In the case of 4, this reaction leads to formation the micro-methyl dinuclear diastereomers [([Me(2)C(Cp)(Flu)]ZrMe)(2)(micro-Me)](+) MeB(2-C(6)F(5)C(6)F(4))(3)(-) (8). A similar reaction with 6 results in diastereomeric [Me(2)C(Cp)(Flu)]ZrMe(+) FAl(2-C(6)F(5)C(6)F(4))(3)(-) (10) ion pairs. The molecular structures of 7 and 10 have been determined by single-crystal X-ray diffraction. Reorganization pathways available to these species have been examined using EXSY and dynamic NMR, revealing that the cation-MeB(C(6)F(5))(3)(-) interaction is considerably weaker/more mobile than in the FAl(2-C(6)F(5)C(6)F(4))(3)(-)-derived analogue. Polymerizations mediated by 1 in toluene over the temperature range of -10 degrees to +60 degrees C and at 1.0-5.0 atm propylene pressure (at 60 degrees C) reveal that activity, product syndiotacticity, m and mm stereodefect generation, and chain transfer processes are highly sensitive to the nature of the ion pairing. Thus, the complexes activated with 4 and 5, having the weakest ion pairing, yield the highest estimated propagation rates, while with 6, having the strongest pairing, yields the lowest. The strongly coordinating, immobile FAl(2-C(6)F(5)C(6)F(4))(3)(-) anion produces the highest/least temperature-dependent product syndiotacticity, lowest/least temperature-dependent m stereodefect abundance, and highest product molecular weight. These polypropylene microstructural parameters, and also M(w), are least sensitive to increased propylene pressure for FAl(2-C(6)F(5)C(6)F(4))(3)(-), but highest with MeB(C(6)F(5))(3)(-). In general, mm stereodefect production is only modestly anion-sensitive; [propylene] dependence studies reveal enantiofacial propylene misinsertion to be the prevailing mm-generating process in all systems at 60 degrees C, being most dominant with 6, where mm stereodefect abundance is lowest. For 1,3-dichlorobenzene as the polymerization solvent, product syndiotacticity, as well as m and mm stereodefects, become indistinguishable for all cocatalysts. These observations are consistent with a scenario in which ion pairing modulates the rates of stereodefect generating processes relative to monomer enchainment, hence net enchainment syndioselectivity, and also dictates the rate of termination relative to propagation and the preferred termination pathway. In comparison to 3-6, propylene polymerization mediated by MAO (2) + 1 in toluene reveals an estimated ordering in site epimerization rates as 5 > 4 > 2 > 3 > 6, while product syndiotacticities rank as 6 > 2 > 5 approximately 4 > 3.     

Synthesis, characterization, and reactivity of a uranyl beta-diketiminate complex

Addition of 1 equiv of Li(Ar2nacnac) (Ar2nacnac = (2,6-(i)Pr2C6H3)NC(Me)CHC(Me)N(2,6-(i)Pr2C6H3)) to an Et2O suspension of UO2Cl2(THF)3 generates the uranyl dimer [UO2(Ar2nacnac)Cl]2 (1) in good yield. A second species can be isolated in low yield from the reaction mixtures of 1, namely [Li(OEt2)2][UO2(Ar2nacnac)Cl2] (2). The structures of both 1 and 2 have been confirmed by X-ray crystallography. Complex 1 reacts with Ph3PO to generate UO2(Ar2nacnac)Cl(Ph3PO) (3). In addition, 1 reacts with AgOTf and either 1 equiv of DPPMO2 or 2 equiv of Ph2MePO to provide [UO2(Ar2nacnac)(DPPMO2)][OTf] (4) and [UO2(Ar2nacnac)(Ph2MePO)2][OTf] (5), respectively. Both 4 and 5 have been fully characterized, including analysis by X-ray crystallography and cyclic voltammetry. Reduction of 4 with Cp2Co provides UO2(Ar2nacnac)(CH{Ph2PO}2) (6), a uranyl(VI) complex that is generated by the formal loss of H* from the DPPMO2 ligand. Labeling studies have been performed in an attempt to elucidate the mechanism of hydrogen loss. In contrast, reduction of 5 with Cp2Co provides UO2(Ar2nacnac)(Ph2MePO)2 (7), a rare example of a uranyl(V) complex. As expected, the solid-state molecular structure of 7 reveals slightly longer U-O(oxo) bond lengths relative to 5. Furthermore, complex 7 can be converted back into 5 by oxidation with AgOTf in toluene.     

Synthesis and reactions of group 6 metal half-sandwich complexes of 2,2-dicyanoethylene-1,1-dichalcogenolates [(Cp*)M[E(2)C=C(CN)(2)](2)]-(M = Mo,W; E = S,Se)

A series of group 6 transition metal half-sandwich complexes with 1,1-dichalcogenide ligands have been prepared by the reactions of Cp*MCl(4)(Cp* = eta(5)-C(5)Me(5); M = Mo, W) with the potassium salt of 2,2-dicyanoethylene-1,1-dithiolate, (KS)(2)C=C(CN)(2) (K(2)-i-mnt), or the analogous seleno compound, (KSe)(2)C=C(CN)(2) (K(2)-i-mns). The reaction of Cp*MCl(4) with (KS)(2)C=C(CN)(2) in a 1:3 molar ratio in CH(3)CN gave rise to K[Cp*M(S(2)C=C(CN)(2))(2)] (M = Mo, 1a, 74%; M = W, 2a, 46%). Under the same conditions, the reaction of Cp*MoCl(4) with 3 equiv of (KSe)(2)C=C(CN)(2) afforded K[Cp*Mo(Se(2)C=C(CN)(2))(2)] (3a) and K[Cp*Mo(Se(2)C=C(CN)(2))(Se(Se(2))C=C(CN)(2))] (4) in respective yields of 45% and 25%. Cation exchange reactions of 1a, 2a, and 3a with Et(4)NBr resulted in isolation of (Et(4)N)[Cp*Mo(S(2)C=C(CN)(2))(2)] (1b), (Et(4)N)[Cp*W(S(2)C=C(CN)(2))(2)] (2b), and (Et(4)N)[Cp*Mo(Se(2)C=C(CN)(2))(2)] (3b), respectively. Complex 4 crystallized with one THF and one CH(3)CN molecule as a three-dimensional network structure. Inspection of the reaction of Cp*WCl(4) with (KSe)(2)C=C(CN)(2) by ESI-MS revealed the existence of three species in CH(3)CN, [Cp*W(Se(2)C=C(CN)(2))(2)]-, [Cp*W(Se(2)C=C(CN)(2))(Se(Se(2))C=C(CN)(2))]-, and [Cp*W(Se(Se(2))C=C(CN)(2))(2)]-, of which [Cp*W(Se(2)C=C(CN)(2))(Se(Se(2))C=C(CN)(2))]-(5) was isolated as the main product. Treatment of 2a with 1/4 equiv of S(8) in refluxing THF resulted in sulfur insertion and gave rise to K[Cp*W(S(2)C=C(CN)(2))(S(S(2))C=C(CN)(2))](6), which crystallized with two THF molecules forming a three-dimensional network structure. 6 can also be prepared by refluxing 2a with 1/4 equiv of S(8) in THF. 3a readily added one Se atom upon treatment with 1 mol of Se powder in THF to give 4 in high yield, while the treatment of 3a or 4 with 2 equiv of Na(2)Se in THF led to formation of a dinuclear complex [(Cp*Mo)(2)(mu-Se)(mu-Se(Se(3))C=C(CN)(2))] (7). The structure of 7 consists of two Cp*Mo units bridged by a Se(2-) and a [Se(Se(3))C=C(CN)(2)](2-) ligand in which the triselenido group is arranged in a nearly linear way (163 degrees). The reaction of 2a with 2 equiv of CuBr in CH(3)CN yielded a trinuclear complex [Cp*WCu(2)(mu-Br)(mu(3)-S(2)C=C(CN)(2))(2)] (8), which crystallized with one CH(3)CN and generated a one-dimensional chain polymer through bonding of Cu to the N of the cyano groups.     

Synthesis and structure of amido- and imido(pentafluorophenyl)borane zirconocene and hafnocene complexes: N-H and B-H activation

Treatment of Me(2)S·B(C(6)F(5))(n) H(3-n) (n=1 or 2) with ammonia yields the corresponding adducts. H(3)N·B(C(6)F(5))H(2) dimerises in the solid state through N-H···H-B dihydrogen interactions. The adducts can be deprotonated to give lithium amidoboranes Li[NH(2)B(C(6)F(5))(n)H(3-n)]. Reaction of the n=2 reagent with [Cp(2)ZrCl(2)] leads to disubstitution, but [Cp(2)Zr{NH(2)B(C(6)F(5))(2)H}(2)] is in equilibrium with the product of β-hydride elimination [Cp(2)Zr(H){NH(2)B(C(6)F(5))(2)H}], which proves to be the major isolated solid. The analogous reaction with [Cp(2)HfCl(2)] gives a mixture of [Cp(2)Hf{NH(2)B(C(6)F(5))(2)H}(2)] and the N-H activation product [Cp(2)Hf{NHB(C(6)F(5 )(2)H}]. [Cp(2)Zr{NH(2)B(C(6)F(5))(2)H}(2)]·PhMe and [Cp(2)Hf{NH(2)B(C(6)F(5))(2)H}(2)]·4(thf) exhibit β-B-agostic chelate bonding of one of the two amidoborane ligands in the solid state. The agostic hydride is invariably coordinated to the outside of the metallocene wedge. Exceptionally, [Cp(2)Hf{NH(2)B(C(6)F(5))(2)H}(2)]?PhMe has a structure in which the two amidoborane ligands adopt an intermediate coordination mode, in which neither is definitively agostic. [Cp(2)Hf{NHB(C(6)F(5))(2)H}] has a formally dianionic imidoborane ligand chelating through an agostic interaction, but the bond-length distribution suggests a contribution from a zwitterionic amidoborane resonance structure. Treatment of the zwitterions [Cp(2)MMe(μ-Me)B(C(6)F(5))(3)] (M=Zr, Hf) with Li[NH(2)B(C(6)F(5))(n)H(3-n)] (n=2) results in [Cp(2) MMe{NH(2)B(C(6)F(5))(2)H}] complexes, for which the spectroscopic data, particularly (1)J(B,H), again suggest β-B-agostic interactions. The reactions proceed similarly for the structurally encumbered [Cp'(2)ZrMe(μ-Me)B(C(6)F(5))(3)] precursor (Cp'=1,3-C(5)H(3)(SiMe(3))(2) , n=1 or 2) to give [Cp'(2)ZrMe{NH(2)B(C(6)F(5))(n)H(3-n)}], both of which have been structurally characterised and show chelating, agostic amidoborane coordination. In contrast, the analogous hafnium chemistry leads to the recovery of [Cp'(2)HfMe(2)] and the formation of Li[HB(C(6)F(5))(3)] through hydride abstraction.     

Cyclopropenylidene carbene ligands in palladium catalysed coupling reactions: carbene ligand rotation and application to the Stille reaction

Reaction of [Pd(PPh(3))(4)] with 1,1-dichloro-2,3-diarylcyclopropenes gives complexes of the type cis-[PdCl(2)(PPh(3))(C(3)(Ar)(2))] (Ar = Ph 5, Mes 6). Reaction of [Pd(dba)(2)] with 1,1-dichloro-2,3-diarylcyclopropenes in benzene gave the corresponding binuclear palladium complexes trans-[PdCl(2)(C(3)(Ar)(2))](2) (Ar = Ph 7, p-(OMe)C(6)H(4)8, p-(F)C(6)H(4)9). Alternatively, when the reactions were performed in acetonitrile, the complexes trans-[PdCl(2)(NCMe)(C(3)(Ar)(2))] (Ar = Ph 10, p-(OMe)C(6)H(4)11 and p-(F)C(6)H(4)) 12) were isolated. Addition of phosphine ligands to the binuclear palladium complex 7 or acetonitrile adducts 11 and 12 gave complexes of the type cis-[PdCl(2)(PR(3))(C(3)(Ar)(2))] (Ar = Ph, R = Cy 13, Ar = p-(OMe)C(6)H(4), R = Ph 14, Ar = p-(F)C(6)H(4), R = Ph 15). Crystal structures of complexes 6·3.25CHCl(3), 10, 11·H(2)O and 12-15 are reported. DFT calculations of complexes 10-12 indicate the barrier to rotation about the carbene-palladium bond is very low, suggesting limited double bond character in these species. Complexes 5-9 were tested for catalytic activity in C-C coupling (Mizoroki-Heck, Suzuki-Miyaura and, for the first time, Stille reactions) and C-N coupling (Buchwald-Hartwig amination) showing excellent conversion with moderate to high selectivity.     

Structural characterization of four members of the electron-transfer series [PdII(L)2)2]n (L = o-Iminophenolate derivative; n = 2-, 1-, 0, 1+, 2+). ligand mixed valency in the monocation and monoanion with S = (1)/(2) ground states

The reaction of the ligand 2-(2-trifluoromethyl)anilino-4,6-di-tert-butylphenol, H(2)((1)L(IP)), and PdCl(2) (2:1) in the presence of air and excess NEt(3) in CH(2)Cl(2) produced blue-green crystals of diamagnetic [Pd(II)((1)L(ISQ))(2)] (1), where ((1)L(ISQ))(*)(-) represents the o-iminobenzosemiquinonate(1-) pi radical anion of the aromatic ((1)L(IP))(2-) dianion. The diamagnetic complex 1 was chemically oxidized with 1 equiv of Ag(BF(4)), affording red-brown crystals of paramagnetic (S = (1)/(2)) [Pd(II)((1)L(ISQ))((1)L(IBQ))](BF(4)) (2), and one-electron reduction with cobaltocene yielded paramagnetic (S = (1)/(2)) green crystals of [Cp(2)Co][Pd(II)((1)L(ISQ))((1)L(IP))] (3); ((1)L(IBQ))(0) represents the neutral, diamagnetic quinone form. Complex 1 was oxidized with 2 equiv of [NO]BF(4), affording green crystals of diamagnetic [Pd(II)((1)L(IBQ))(2)](3)(BF(4))(4){(BF(4))(2)H}(2).4CH(2)Cl(2) (5). Oxidation of [Ni(II)((1)L(ISQ))(2)] (S = 0) in CH(2)Cl(2) solution with 2 equiv of Ag(ClO(4)) generated crystals of [Ni(II)((1)L(IBQ))(2)(ClO(4))(2)].2CH(2)Cl(2) (6) with an S = 1 ground state. Complexes 1-5 constitute a five-membered complete electron-transfer series, [Pd((1)L)(2)](n) (n = 2-, 1-, 0, 1+, 2+), where only species 4, namely, diamagnetic [Pd(II)((1)L(IP))(2)](2-), has not been isolated; they are interrelated by four reversible one-electron-transfer waves in the cyclic voltammogram. Complexes 1, 2, 3, 5, and 6 have been characterized by X-ray crystallography at 100 K, which establishes that the redox processes are ligand centered. Species 2 and 3 exhibit ligand mixed valency: [Pd(II)((1)L(ISQ))((1)L(IBQ))](+) has localized ((1)L(IBQ))(0) and ((1)L(ISQ))(*)(-) ligands in the solid state, whereas in [Pd(II)((1)L(ISQ))((1)L(IP))](-) the excess electron is delocalized over both ligands in the solid-state structure of 3. Electronic and electron spin resonance spectra are reported, and the electronic structures of all members of this electron-transfer series are established.     

Synthesis, structures, and reactivity of weakly coordinating anions with delocalized borate structure: the assessment of anion effects in metallocene polymerization catalysts.

The formation of adducts of tris(pentafluorophenyl)borane with strongly coordinating anions such as CN(-) and [M(CN)(4)](2)(-) (M = Ni, Pd) is a synthetically facile route to the bulky, very weakly coordinating anions [CN[B(C(6)F(5))(3)](2)](-) and [M[CNB(C(6)F(5))(3)](4)](2-) which are isolated as stable NHMe(2)Ph(+) and CPh(3)(+) salts. The crystal structures of [CPh(3)][CN[B(C(6)F(5))(3)](2)] (1), [CPh(3)][ClB(C(6)F(5))(3)] (2), [NHMe(2)Ph](2)[Ni[CNB(C(6)F(5))(3)](4)].2Me(2)CO (4b.2Me(2)CO), [CPh(3)](2)[Ni[CNB(C(6)F(5))(3)](4)].2CH(2)Cl(2) (4c.2CH(2)Cl(2)), and [CPh(3)](2)[Pd[CNB(C(6)F(5))(3)](4)].2CH(2)Cl(2) (5c.2CH(2)Cl(2)) are reported. The CN stretching frequencies in 4 and 5 are shifted by approximately 110 cm(-1) to higher wavenumbers compared to the parent tetracyano complexes in aqueous solution, although the M-C and C-N distances show no significant change on B(C(6)F(5))(3) coordination. Zirconocene dimethyl complexes L(2)ZrMe(2) [L(2) = Cp(2), SBI = rac-Me(2)Si(Ind)(2)] react with 1, 4c or 5c in benzene solution at 20 degrees C to give the salts of binuclear methyl-bridged cations, [(L(2)ZrMe)(2)(mu-Me)][CN[B(C(6)F(5))(3)](2)] and [(L(2)ZrMe)(2)(mu-Me)](2)[M[CNB(C(6)F(5))(3)](4)]. The reactivity of these species in solution was studied in comparison with the known [[(SBI)ZrMe](2)(mu-Me)][B(C(6)F(5))(4)]. While the latter reacts with excess [CPh(3)][B(C(6)F(5))(4)] in benzene to give the mononuclear ion pair [(SBI)ZrMe(+).B(C(6)F(5))(4)(-)] in a pseudo-first-order reaction, k = 3 x 10(-4) s(-1), [(L(2)ZrMe)(2)(mu-Me)][CN[B(C(6)F(5))(3)](2)] reacts to give a mixture of L(2)ZrMe(mu-Me)B(C(6)F(5))(3) and L(2)ZrMe(mu-NC)B(C(6)F(5))(3). Recrystallization of [Cp' '(2)Zr(mu-Me)(2)AlMe(2)][CN[B(C(6)F(5))(3)](2)] affords Cp' '(2)ZrMe(mu-NC)B(C(6)F(5))(3) 6, the X-ray structure of which is reported. The stability of [(L(2)ZrMe)(2)(mu-Me)](+)X(-) decreases in the order X = [B(C(6)F(5))(4)] > [M[CNB(C(6)F(5))(3)](4)] > [CN[B(C(6)F(5))(3)](2)] and increases strongly with the steric bulk of L(2) = Cp(2) < SBI. Activation of (SBI)ZrMe(2) by 1 in the presence of AlBu(i)(3) gives extremely active ethene polymerization catalysts. Polymerization studies at 1-7 bar monomer pressure suggest that these, and by implication most other highly active ethene polymerization catalysts, are strongly mass-transport limited. By contrast, monitoring propene polymerization activities with the systems (SBI)ZrMe(2)/1/AlBu(i)(3) and CGCTiMe(2)/1/AlBu(i)(3) at 20 degrees C as a function of catalyst concentration demonstrates that in these cases mass-transport limitation is absent up to [metal] approximately 2 x 10(-5) mol L(-1). Propene polymerization activities decrease in the order [CN[B(C(6)F(5))(3)](2)](-) > [B(C(6)F(5))(4)](-) > [M[CNB(C(6)F(5))(3)](4)](2-) > [MeB(C(6)F(5))(3)](-), with differences in activation barriers relative to [CN[B(C(6)F(5))(3)](2)](-) of DeltaDeltaG = 1.1 (B(C(6)F(5))(4)(-)), 4.1 (Ni[CNB(C(6)F(5))(3)](4)(2-)) and 10.7-12.8 kJ mol(-)(1) (MeB(C(6)F(5))(3)(-)). The data suggest that even in the case of very bulky anions with delocalized negative charge the displacement of the anion by the monomer must be involved in the rate-limiting step.