Rational synthesis of [Ge9{Si(SiMe3)3}3]- from its parent Zintl ion Ge9(4-)

Reported is the first rational synthesis of a trisubstituted deltahedral Zintl ion, [Ge(9){Si(SiMe(3))(3)}(3)](-) in this case, by the addition of the three substituents in a reaction of the parent naked deltahedral Zintl ion Ge(9)(4-) with {(Me(3)Si)(3)Si}Cl. The new species were crystallized and structurally characterized in [K(2,2,2-crypt)](2)[Ge(9){Si(SiMe(3))(3)}(3)] (monoclinic, P2(1)/c, a = 26.497(3) ?, b = 24.090(2) ?, c = 29.268(3) ?, β = 113.888(2)°, V = 17082(3) ?(3), Z = 8, R1/wR2 = 0.0436/0.0812 for the observed data and 0.1023/0.1010 for all data).     

A kinetic study of the silyl substitution in tantalum amide silyl complex (Me(2)N)(3)Ta[Si(SiMe(3))(3)](2)

Kinetic studies have been performed for the substitution of the first silyl ligand in (Me(2)N)(3)Ta[Si(SiMe(3))(3)](2) (1) by Li(THF)(3)SiButPh(2) at 233 K (THF = tetrahydrofuran). In the presence of excess Li(THF)(3)SiButPh(2), these studies reveal that the reaction likely follows a dissociative pathway. THF, a polar solvent, is found to promote the substitution, and the order of the reaction with respect to THF is 1.7(0.3).     

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.     

The formal combination of three singlet biradicaloid entities to a singlet hexaradicaloid metalloid Ge14[Si(SiMe3)3]5[Li(THF)2]3 cluster

The reaction of GeBr with LiSi(SiMe(3))(3) leads to the metalloid cluster compound [(THF)(2)Li](3)Ge(14)[Si(SiMe(3))(3)](5) (1). After the introduction of a first cluster of this type, in which 14 germanium atoms form an empty polyhedron, [(THF)(2)Li](3)Ge(14)[Ge(SiMe(3))(3)](5) (2), we present here further investigations on 1 to obtain preliminary insight into its chemical and bonding properties. The molecular structure of 1 is determined via X-ray crystal structure solution using synchrotron radiation. The electronic structure of the Ge(14) polyhedron is further examined by quantum chemical calculations, which indicate that three singlet biradicaloid entities formally combine to yield the singlet hexaradicaloid character of 1. Moreover, the initial reactions of 1 after elimination of the [Li(THF)(2)](+) groups by chelating ligands (e.g., TMEDA or 12-crown-4) are presented. Collision induced dissociation experiments in the gas phase, employing FT-ICR mass spectrometry, lead to the elimination of the singlet biradicaloid Ge(5)H(2)[Si(SiMe(3))(3)](2) cluster. The unique multiradicaloid bonding character of the metalloid cluster 1 might be used as a model for reactions and properties in the field of surface science and nanotechnology.     

N,N'-diisopropyl-N'-bis(trimethylsilyl)guanidinate ligand as a supporting coordination environment in yttrium chemistry. Synthesis, structure, and properties of complexes [(Me(3)Si)(2)NC(Ni-Pr)(2)]YCl(2)(THF)(2), [(Me(3)Si)(2)NC(Ni-Pr)(2)]Y(CH(2)SiMe(3))(2)(THF)(2), and [(Me(3)Si)(2)NC(Ni-Pr)(2)]Y[(mu-H)(mu-Et)(2)BEt](2)(THF)

The reaction of anhydrous YCl3 with an equimolar amount of lithium N,N'-diisopropyl-N' '-bis(trimethylsilyl)guanidinate, Li[(Me3Si)2NC(Ni-Pr)2], in tetrahydrofuran (THF) afforded the monomeric monoguanidinate dichloro complex {(Me3Si)2NC(Ni-Pr)2}YCl2(THF)2 (1). Alkylation of complex 1 with 2 equiv of LiCH2SiMe3 in hexane at 0 degrees C yielded the monomeric salt-free dialkyl complex {(Me3Si)2NC(Ni-Pr)2}Y(CH2SiMe3)2(THF)2 (2). The bis(triethylborohydride) complex [(Me3Si)2NC(Ni-Pr)2]Y[(mu-H)(mu-Et)2BEt]2(THF) (5) was prepared by the reaction of complex 1 with 2 equiv of LiBEt3H in a toluene-THF mixture at 0 degrees C. The complexes 1, 2, and 5 were structurally characterized. Complex 2 as well as the systems 2-Ph3B, 2-Ph3B-MAO, and 1-MAO (MAO = methylaluminoxanes) in toluene were inactive in ethylene polymerization, while the product obtained in situ from the reaction of complex 2 with a 2-fold molar excess of PhSiH3 in toluene polymerized ethylene with moderate activity.     

Synthesis of the (N2)3- radical from Y2+ and its protonolysis reactivity to form (N2H2)2- via the Y[N(SiMe3)2]3/KC8 reduction system

Examination of the Y[N(SiMe(3))(2)](3)/KC(8) reduction system that allowed isolation of the (N(2))(3-) radical has led to the first evidence of Y(2+) in solution. The deep-blue solutions obtained from Y[N(SiMe(3))(2)](3) and KC(8) in THF at -35 °C under argon have EPR spectra containing a doublet at g(iso) = 1.976 with a 110 G hyperfine coupling constant. The solutions react with N(2) to generate (N(2))(2-) and (N(2))(3-) complexes {[(Me(3)Si)(2)N](2)(THF)Y}(2)(μ-η(2):η(2)-N(2)) (1) and {[(Me(3)Si)(2)N](2)(THF)Y}(2)(μ-η(2):η(2)-N(2))[K(THF)(6)] (2), respectively, and demonstrate that the Y[N(SiMe(3))(2)](3)/KC(8) reaction can proceed through an Y(2+) intermediate. The reactivity of (N(2))(3-) radical with proton sources was probed for the first time for comparison with the (N(2))(2-) and (N(2))(4-) chemistry. Complex 2 reacts with [Et(3)NH][BPh(4)] to form {[(Me(3)Si)(2)N](2)(THF)Y}(2)(μ-N(2)H(2)), the first lanthanide (N(2)H(2))(2-) complex derived from dinitrogen, as well as 1 as a byproduct, consistent with radical disproportionation reactivity.     

Extremely bulky amido-group 14 element chloride complexes: potential synthons for low oxidation state main group chemistry

The preparation of a series of extremely bulky secondary amines, Ar*N(H)SiR(3) (Ar* = C(6)H(2){C(H)Ph(2)}(2)Me-2,6,4; R(3) = Me(3), MePh(2) or Ph(3)) is described. Their deprotonation with either LiBu(n), NaH or KH yields alkali metal amide complexes, several monomeric examples of which, [Li(L){N(SiMe(3))(Ar*)}] (L = OEt(2) or THF), [Na(THF)(3){N(SiMe(3))(Ar*)}] and [K(OEt(2)){N(SiPh(3))(Ar*)], have been crystallographically characterised. Reactions of the lithium amides with germanium, tin or lead dichloride have yielded the first structurally characterised two-coordinate, monomeric amido germanium(II) and tin(II) chloride complexes, [{(SiR(3))(Ar*)N}ECl] (E = Ge or Sn; R = Me or Ph), and a chloride bridged amido-lead(II) dimer, [{[(SiMe(3))(Ar*)N]Pb(μ-Cl)}(2)]. DFT calculations on [{(SiMe(3))(Ar*)N}GeCl] show its HOMO to exhibit Ge lone pair character and its LUMO to encompass its Ge based p-orbital. A series of bulky amido silicon(IV) chloride complexes have also been prepared and several examples, [{(SiR(3))(Ar*)N}SiCl(3)] (R(3) = Me(3), MePh(2)) and [{(SiMe(3))(Ar*)N}SiHCl(2)], were crystallographically characterised. The sterically hindered group 14 complexes reported in this study hold significant potential as precursors for kinetically stabilised low oxidation state and/or low coordination number group 14 complexes.     

Homolysis of the Ln-N (Ln = Yb, Eu) bond. Synthesis, structural characterization and catalytic activity of ytterbium(II) and europium(II) complexes with methoxyethyl functionalized indenyl ligands

The interaction of methoxyethyl functionalized indene compounds (C(9)H(6)-1-R-3-CH(2)CH(2)OMe, R =t-BuNHSiMe(2)(1), Me(3)Si (2), H (3)) with [(Me(3)Si)(2)N](3)Ln(mu-Cl)Li(THF)(3)(Ln=Yb (4), Eu (5)) produced a series of new ytterbium(II) and europium(II) complexes via tandem silylamine elimination/homolysis of the Ln-N (Ln=Yb, Eu) bond. Treatment of the lanthanide(III) amides [(Me(3)Si)(2)N](3)Ln(mu-Cl)Li(THF)(3)(Ln=Yb (4), Eu (5) with 2 equiv. of, 1,2 and 3, respectively, produced, after workup, the ytterbium(II) complexes [eta5:eta1-Me(2)Si(MeOCH(2)CH(2)C(9)H(5))(NHBu-t)](2)Yb(II) (6), (eta5:eta1-MeOCH(2)CH(2)C(9)H(5)SiMe(3))(2)Yb(II) (7), (eta5:eta1-MeOCH(2)CH(2)C(9)H(6))(2)Yb(II)(8) and the corresponding europium(II) complexes [eta5:eta1-Me(2)Si(MeOCH(2)CH(2)C(9)H(5))(NHBu-t)](2)Eu(II)(9), (eta5:eta1-MeOCH(2)CH(2)C(9)H(5)SiMe(3))(2)Eu(II)(10) and (eta5:eta1-MeOCH(2)CH(2)C(9)H(6))(2)Eu(II)(11) in moderate to good yield. In contrast, interaction of the corresponding indene compounds 1, 2 or 3 with the lanthanide amides [(Me(3)Si)(2)N](3)Ln (Ln = Yb, Eu) was not observed, while addition of 0.5 equiv. of anhydrous LiCl to the corresponding reaction mixture produced, after workup, the corresponding ytterbium(II) or europium(II) complexes. All the new compounds were fully characterized by spectroscopic and elemental analyses. The structures of complexes, and were determined by single-crystal X-ray analyses. The catalytic activity of all the ytterbium(II) and europium(II) complexes on MMA polymerization was examined. It was found that all the ytterbium(II) and europium(II) complexes can function as single-component MMA polymerization catalysts. The temperature, solvent and ligand effects on the catalytic activity were studied.     

Heteroleptic Lanthanide Complexes with Aryloxide Ligands. Synthesis and Structural Characterization of Divalent and Trivalent Samarium Aryloxide/Halide and Aryloxide/Cyclopentadienide Complexes

Synthesis of a new class of heteroleptic samarium aryloxide complexes has been achieved by the use of homoleptic samarium(II) bis(aryloxide) Sm(OAr)(2)(THF)(3) (1, Ar = C(6)H(2)Bu(t)(2)-2,6-Me-4) as a starting material, which is easily obtained by reaction of Sm(N(SiMe(3))(2))(2)(THF)(2) with 2 equiv of ArOH in THF. 1 reacts with 1 equiv of SmI(2) in THF to give Sm(II) mixed aryloxide/iodide [(ArO)Sm(&mgr;-I)(THF)(3)](2) (2), which adopts a dimeric structure via very weak Sm.I (3.534(2) ?) interactions. Reaction of 2 with C(5)Me(5)K in THF/HMPA affords the corresponding Sm(II) aryloxide/cyclopentadienide (C(5)Me(5))Sm(OAr)(HMPA)(2) (3). Oxidation of 1 with 0.5 equiv of I(2) in THF gives monomeric samarium(III) aryloxide/iodide (ArO)(2)SmI(THF)(2) (4), while the similar reaction of 1 with ClCH(2)CH(2)Cl or (t)BuCl in THF affords dimeric samarium(III) aryloxide/chloride [(ArO)(2)Sm(&mgr;-Cl)(THF)](2) (5). Crystal data for 1: monoclinic, space group P2(1), a = 9.903(3) ?, b = 16.718(5) ?, c = 13.267(2) ?, beta = 95.17(2) degrees, V = 2187(2) ?(3), Z = 2, D(c) = 1.223 g cm(-)(3), R = 0.0634. Crystal data for 2.2THF: monoclinic, space group P2(1)/a, a = 18.330(6) ?, b = 14.320(4) ?, c = 13.949(3) ?, beta = 103.16(2) degrees, V = 3563(2) ?(3), Z = 2, D(c) = 1.46 g cm(-)(3), R = 0.0606. Crystal data for 3: triclinic, space group P&onemacr;, a = 10.528(1) ?, b = 12.335(2) ?, c = 19.260(2) ?, alpha = 101.33(1) degrees, beta = 95.230(9) degrees, gamma = 108.54(1) degrees, V = 2293.1(5) ?(3), Z = 2, D(c) = 1.25 g cm(-)(3), R = 0.0358. Crystal data for 4: monoclinic, space group C2/c, a = 17.191(7) ?, b = 10.737(6) ?, c = 21.773(7) ?, beta = 98.80(3) degrees, V = 3971(3) ?(3), Z = 4, D(c) = 1.44 g cm(-)(3), R = 0.0467. Crystal data for 5: monoclinic, space group P2(1)/n, a = 13.750(3) ?, b = 17.231(3) ?, c = 14.973(6) ?, beta = 95.81(2) degrees, V = 3529(2) ?(3), Z = 2, D(c) = 1.31 g cm(-)(3), R = 0.0557.     

Synthesis and structural characterization of alkaline-earth-metal bis(amido)silane and lithium oxobis(aminolato)silane complexes

Several of alkaline-earth-metal complexes [(η(2):η(2):μ(N):μ(N)-Li)(+)](2)[{η(2)-Me(2)Si(DippN)(2)}(2)Mg](2-) (4), [η(2)(N,N)-Me(2)Si(DippN)(2)Ca·3THF] (5), [η(2)(N,N)-Me(2)Si(DippN)(2)Sr·THF] (6), and [η(2)(N,N)-Me(2)Si(DippN)(2)Ba·4THF] (7) of a bulky bis(amido)silane ligand were readily prepared by the metathesis reaction of alkali-metal bis(amido)silane [Me(2)Si(DippNLi)(2)] (Dipp = 2,6-i-Pr(2)C(6)H(3)) and alkaline-earth-metal halides MX(2) (M = Mg, X = Br; M = Ca, Sr, Ba, X = I). Alternatively, compounds 5-7 were synthesized either by transamination of M[N(SiMe(3))(2)](2)·2THF (M = Ca, Sr, Ba) and [Me(2)Si(DippNH)(2)] or by transmetalation of Sn[N(SiMe(3))(2)](2), [Me(2)Si(DippNH)(2)], and metallic calcium, strontium, and barium in situ. The metathesis reaction of dilithium bis(amido)silane [Me(2)Si(DippNLi)(2)] and magnesium bromide in the presence of oxygen afforded, however, an unusual lithium oxo polyhedral complex {[(DippN(Me(2)Si)(2))(μ-O)(Me(2)Si)](2)(μ-Br)(2)[(μ(3)-Li)·THF](4)(μ(4)-O)(4)(μ(3)-Li)(2)} (8) with a square-basket-shaped core Li(6)Br(2)O(4) bearing a bis(aminolato)silane ligand. All complexes were characterized using (1)H, (13)C, and (7)Li NMR and IR spectroscopy, in addition to X-ray crystallography.     

(N2)3- radical chemistry via trivalent lanthanide salt/alkali metal reduction of dinitrogen: new syntheses and examples of (N2)2- and (N2)3- complexes and density functional theory comparisons of closed shell Sc3+, Y3+, and Lu3+ versus 4f(9) Dy3+

New syntheses of complexes containing the recently discovered (N(2))(3-) radical trianion have been developed by examining variations on the LnA(3)/M reductive system that delivers "LnA(2)" reactivity when Ln = scandium, yttrium, or a lanthanide, M = an alkali metal, and A = N(SiMe(3))(2) and C(5)R(5). The first examples of LnA(3)/M reduction of dinitrogen with aryloxide ligands (A = OC(6)R(5)) are reported: the combination of Dy(OAr)(3) (OAr = OC(6)H(3)(t)Bu(2)-2,6) with KC(8) under dinitrogen was found to produce both (N(2))(2-) and (N(2))(3-) products, [(ArO)(2)Dy(THF)(2)](2)(μ-η(2):η(2)-N(2)), 1, and [(ArO)(2)Dy(THF)](2)(μ-η(2):η(2)-N(2))[K(THF)(6)], 2a, respectively. The range of metals that form (N(2))(3-) complexes with [N(SiMe(3))(2)](-) ancillary ligands has been expanded from Y to Lu, Er, and La. Ln[N(SiMe(3))(2)](3)/M reactions with M = Na as well as KC(8) are reported. Reduction of the isolated (N(2))(2-) complex {[(Me(3)Si)(2)N](2)Y(THF)}(2)(μ-η(2):η(2)-N(2)), 3, with KC(8) forms the (N(2))(3-) complex, {[(Me(3)Si)(2)N](2)Y(THF)}(2)(μ-η(2):η(2)-N(2))[K(THF)(6)], 4a, in high yield. The reverse transformation, the conversion of 4a to 3 can be accomplished cleanly with elemental Hg. The crown ether derivative {[(Me(3)Si)(2)N](2)Y(THF)}(2)(μ-η(2):η(2)-N(2))[K(18-crown-6)(THF)(2)] was isolated from reduction of 3 with KC(8) in the presence of 18-crown-6 and found to be much less soluble in tetrahydrofuran (THF) than the [K(THF)(6)](+) salt, which facilitates its separation from 3. Evidence for ligand metalation in the Y[N(SiMe(3))(2)](3)/KC(8) reaction was obtained through the crystal structure of the metallacyclic complex {[(Me(3)Si)(2)N](2)Y[CH(2)Si(Me(2))NSiMe(3)]}[K(18-crown-6)(THF)(toluene)]. Density functional theory previously used only with reduced dinitrogen complexes of closed shell Sc(3+) and Y(3+) was extended to Lu(3+) as well as to open shell 4f(9) Dy(3+) complexes to allow the first comparison of bonding between these four metals.     

Synthesis and Reactivity of Organosamarium Diarylpnictide Complexes: Cleavage Reactions of Group 15 E-E and E-C Bonds by Samarium(II)

(C(5)Me(5))(2)Sm (2 equiv) reacts with Ph(2)EEPh(2) to give (C(5)Me(5))(2)SmEPh(2) (E: P, 1; As, 2), while (C(5)Me(5))(2)Sm(THF)(2) (2 equiv) reacts with Ph(2)EEPh(2) to give (C(5)Me(5))(2)Sm(EPh(2))(THF) (E: P, 3; As, 4). 3 and 4 are also available from the reactions of 1 and 2 with THF. 3 and 4 undergo further reaction to produce the THF ring-opened products (C(5)Me(5))(2)Sm[O(CH(2))(4)EPh(2)](THF) (E: P, 5; As, 6).(C(5)Me(5))(2)Sm (4 equiv) reacts with Ph(2)EEPh(2) to give the mixed-valent (C(5)Me(5))(2)Sm(&mgr;-EPh(2))Sm(C(5)Me(5))(2) (E: P, 7; As, 8). These compounds are also available from the reaction of 1 and 2 with (C(5)Me(5))(2)Sm. The X-ray crystal structure of 2, crystallized from hexanes (P2(1)/n; a = 26.188(24) ?, b = 9.911(10) ?, c = 23.280(23) ?, beta = 97.150(12) degrees, V = 5995(2) ?(3), D(calcd) = 1.488 Mg/m(3); Z = 8; T = 156 K), revealed, in addition to a conventional seven-coordinate bent metallocene geometry with 2.698 ? Sm-C(C(5)Me(5)) and 2.970 ? Sm-As average distances, two very different Sm-As-C(Ph) angles, 74.2 and 118.7 degrees. As a result, one phenyl group is closer to the metal (2.901 ? minimum Sm-C distance). 4, crystallized from toluene (P2(1)/n; a = 10.713(9) ?, b = 14.143(11) ?, c = 21.620(16) ?, beta = 101.08(6) degrees, V = 3215(4) ?(3), D(calcd) = 1.492 Mg/m(3); Z = 4; T = 163 K), and 6, crystallized from hexanes (P2(1)/n; a = 9.3958(16) ?, b = 22.245(3) ?, c = 17.931(3) ?, beta = 96.497(11) degrees, V = 3724(1) ?(3), D(calcd) = 1.416 Mg/m(3); Z = 4; T = 163 K), have conventional eight-coordinate, bent metallocene structures.     

Structural Aspects of Lithium Arenethiolate Complexes with Intramolecular Coordinating Amine Donors

Reaction of aryllithium reagents LiR (R = C(6)H(4)((R)-CH(Me)NMe(2))-2 (1a), C(6)H(3)(CH(2)NMe(2))(2)-2,6 (1b), C(6)H(4)(CH(2)N(Me)CH(2)CH(2)OMe)-2 (1c)) with 1 equiv of sulfur (1/8 S(8)) results in the quantitative formation of the corresponding lithium arenethiolates [Li{SC(6)H(4)((R)-CH(Me)NMe(2))-2}](6) (3), [Li{SC(6)H(3)(CH(2)NMe(2))(2)-2,6}](6) (4), and [Li{SC(6)H(4)(CH(2)N(Me)CH(2)CH(2)OMe)-2}](2) (5). Alternatively, 3 can be prepared by reacting the corresponding arenethiol HSC(6)H(4)((R)-CH(Me)NMe(2))-2 (2) with (n)BuLi. X-ray crystal structures of lithium arenethiolates 3 and 4, reported in abbreviated form, show them to have hexanuclear prismatic and hexanuclear planar structures, respectively, that are unprecedented in lithium thiolate chemistry. The lithium arenethiolate [Li{SC(6)H(4)(CH(2)N(Me)CH(2)CH(2)OMe)-2}](2) (5) is dimeric in the solid state and in solution, and crystals of 5 are monoclinic, space group P2(1)/c, with a = 17.7963(9) ?, b = 8.1281(7) ?, c = 17.1340(10) ?, beta = 108.288(5) degrees, Z = 4, and final R = 0.047 for 4051 reflections with F > 4sigma(F). Hexameric 4 reacts with 1 equiv of lithium iodide and 2 equiv of tetrahydrofuran to form the dinuclear adduct [Li(2)(SAr)(I)(THF)(2)] (6). Crystals of 6 are monoclinic, space group P2(1)/c, with a = 13.0346(10) ?, b = 11.523(3) ?, c = 16.127(3) ?, beta = 94.682(10) degrees, Z = 4, and final R = 0.059 for 3190 reflections with F > 4sigma(F).     

Formation of Metal Clusters or Nitrogen-Bridged Adducts by Reaction of a Bis(amino)stannylene with Halides of Two-Valent Transition Metals

When the cyclic bis(amino)stannylene Me(2)Si(NtBu)(2)Sn is allowed to react with metal halides MX(2) (M = Cr, Fe, Co, Zn; X = Cl, Br [Zn]) adducts of the general formula [Me(2)Si(NtBu)(2)Sn.MX(2)](n) are obtained. The compounds are generally dimeric (n = 2) except the ZnBr(2) adduct, which is monomeric in benzene. The crystal structures of [Me(2)Si(NtBu)(2)Sn.CoCl(2)](2) (triclinic, space group &Pmacr;1; a = 8.620(9) ?, b = 9.160(9) ?, c = 12.280(9) ?, alpha = 101.2(1) degrees, beta = 97.6(1) degrees, gamma = 105.9(1) degrees, Z = 1) and of [Me(2)Si(NtBu)(2)Sn.ZnCl(2)](2) (monoclinic, space group P2(1)/c; a = 8.156(9) ?, b = 16.835(12) ?, c = 13.206(9) ?, beta = 94.27(6) degrees, Z = 2) were determined by X-ray diffraction techniques. The two compounds form similar polycyclic, centrosymmetrical assemblies of metal atoms bridged by chlorine or nitrogen atoms. While in the case of the cobalt compound Co is pentacoordinated by three chlorine and two nitrogen atoms, in the zinc derivative Zn is almost tetrahedrally coordinated by three chlorine atoms and one nitrogen atom. The iron derivative [Me(2)Si(NtBu)(2)Sn.FeCl(2)](2) seems to be isostructural with the cobalt compound as can be deduced from the crystal data (triclinic, a = 8.622(7) ?, b = 9.158(8) ?, c = 12.353(8) ?, alpha = 101.8(1) degrees, beta = 96.9(1) degrees, gamma = 105.9(1) degrees, Z = 1). If NiBr(2), PdCl(2), or PtCl(2) is combined with the stannylene, the reaction product is totally different: 4 equiv of the stannylene are coordinating per metal halide, forming the molecular compound [Me(2)Si(NtBu)(2)Sn](4)MX(2), which crystallizes with half a mole of benzene per molecular formula. The crystal structures of [Me(2)Si(NtBu)(2)Sn](4).NiBr(2).(1)/(2)C(6)H(6) (tetragonal, space group I4(1)/a, a = b = 43.86(4) ?, c = 14.32(2) ?, Z = 16) and [Me(2)Si(NtBu)(2)Sn](4).PdCl(2).(1)/(2)C(6)H(6) (tetragonal, space group I4(1)/a, a = b = 43.99(4) ?, c = 14.318(14) ?, Z = 16) reveal the two compounds to be isostructural. The molecules have an inner Sn(4)M pentametallic core (mean distances: Sn-Ni 2.463 ?, Sn-Pd 2.544 ?) with the transition metal in the center of a slightly distorted square formed by the four tin atoms, the distortion from planarity resulting in a weak paramagnetism of 0.2 &mgr;(B) for the nickel compound. The halogen atoms form bridges between two of the tin atoms and have no bonding interaction with the transition metal. The nickel compound has also been prepared by direct interaction of Br(2) or NR(4)Br(3) with [Me(2)Si(NtBu)(2)Sn](4)Ni as a minor product, the main products being Me(2)Si(NtBu)(2)Sn(NtBu)(2)SiMe(2,) Me(2)Si(NtBu)(2)SnBr(2), NiBr(2) and SnBr(2). Other metal clusters have been obtained by the reaction of Me(2)Si(NtBu)(2)Sn with tetrakis(triphenyphosphine)palladium or by the reaction of Me(2)Si(NtBu)(2)Ge with RhCl(PPh(3))(3). In the first case Ph(3)PPd[Sn(NtBu)(2)SiMe(2)](3)PdPPh(3) (rhombohedral, space group R3c, a = b = 21.397(12) ?, c = 57.01(5) ?, alpha = beta = 90 degrees, gamma = 120 degrees, Z = 12) is formed and is characterized by X-ray techniques to be composed of a central PdSn(3)Pd trigonal bipyramid with the tin atoms occupying the equatorial positions (Pd-Sn = 2.702(5) ?). In the second reaction all the triphenylphosphine ligands are replaced from rhodium and Rh[Ge(NtBu)(2)SiMe(2)](4)Cl is formed (monoclinic, space group P2(1)/n, a = 12.164(2) ?, b = 23.625(5) ?, c = 24.128(5) ?, beta = 102.74(3) degrees, Z = 4). The central core of this molecule is made up of a rhodium atom which is almost square planarly coordinated by the germanium atoms, two of which are bridged by chlorine (mean Ge-Rh = 2.355 ?).     

Synthesis, molecular and electronic structure of U(V)(O)[N(SiMe3)2]3

Addition of 1 equiv of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) to U(NR(2))(3) in hexanes affords U(O)(NR(2))(3) (2), which can be isolated in 73% yield. Complex 2 is a rare example of a terminal U(V) oxo complex. In contrast, addition of 1 equiv of Me(3)NO to U(NR(2))(3) (R = SiMe(3)) in pentane generates the U(IV) bridging oxo [(NR(2))(3)U](2)(μ-O) (3) in moderate yields. Also formed in this reaction, in low yield, is the U(IV) iodide complex U(I)(NR(2))(3) (4). The iodide ligand in 4 likely originates from residual NaI, present in the U(NR(2))(3) starting material. Complex 4 can be generated rationally by addition of 0.5 equiv of I(2) to a hexane solution of U(NR(2))(3), where it can be isolated in moderate yield as a tan crystalline solid. The solid-state molecular structures and magnetic susceptibilities of 2, 3, and 4 have been measured. In addition, the electronic structures of 2 and 3 have been investigated by density functional theory (DFT) methods.     

Synthesis and structures of the [benzamidinato]3- complexes Li3(tmeda)(L1)]2 and [Li(thf)4][Li5(L2)(OEt2)2] [L1 = N(SiMe3)C(Ph)N(SiMe3) and L2 = N(SiMe3)C(C6H4-4)NPh

Reduction at ambient temperature of each of the lithium benzamidinates [Li(L(1))(tmeda)] or [{Li(L(2))(OEt(2))(2)}(2)] with four equivalents of lithium metal in diethyl ether or thf furnished the brown crystalline [Li(3)(L(1))(tmeda)] (1) or [Li(thf)(4)][Li(5)(L(2))(2)(OEt(2))(2)] (2), respectively. Their structures show that in each the [N(R(1))C(R(3))NR(2)](3-) moiety has the three negative charges largely localised on each of N, N' and R = Aryl); a consequence is that the "aromatic" 2,3- and 5,6-CC bonds of R(3) approximate to being double bonds. Multinuclear NMR spectra in C(6)D(6) and C(7)D(8) show that 1 and 2 exhibit dynamic behaviour. [The following abbreviations are used: L(1) = N(SiMe(3))C(Ph)N(SiMe(3)); L(2) = N(SiMe(3))C(C(6)H(4)Me-4)N(Ph); tmeda = (Me(2)NCH(2)-)(2); thf = tetrahydrofuran.] This reduction is further supported by a DFT analysis.     

Syntheses and structures of the first terminal phosphanylphosphido complex of hafnium [Cp2Hf(Cl){η(1)-(Me3Si)P-P(NEt2)2}] and the first zirconocene-phosphanylphosphinidene dimer [Cp2Zr{μ(2)-P-P(NEt2)2}2ZrCp2

Reactions of (Et(2)N)(2)P-P(SiMe(3))Li with [Cp(2)MCl(2)] (M = Zr, Hf) in toluene or pentane yield the related terminal phosphanylphosphido complexes [Cp(2)M(Cl){η(1)-(Me(3)Si)P-P(NEt(2))(2)}]. The solid state structure of [Cp(2)Hf(Cl){η(1)-(Me(3)Si)P-P(NEt(2))(2)}] was established by single crystal X-ray diffraction. The reaction of (Et(2)N)(2)P-P(SiMe(3))Li with [Cp(2)ZrCl(2)] in THF or DME solutions leads to the formation of deep red crystals of the first neutral diamagnetic zirconocene-phosphanylphosphinidene dimer [Cp(2)Zr{μ(2)-P-P(NEt(2))(2)}(2)ZrCp(2)]. The molecular structure of this compound was confirmed by X-ray diffraction. The reactions of (R(2)N)(2)P-P(SiMe(3))Li with [CpZrCl(3)] yield the related tetraphosphetanes R(2)NP(μ(2)-PSiMe(3))(2)PNR(2), which apparently are formed as a result of a transfer of NR(2) groups from a P atom to the Zr atom.     

Double silyl migration converting ORe[N(SiMe(2)CH(2)PCy(2))(2)] to NRe[O(SiMe(2)CH(2)PCy(2))(2)] substructures

The reaction of (R(2)PCH(2)SiMe(2))(2)NM (PNP(R)M; R = Cy; M = Li, Na, MgHal, Ag) with L(2)ReOX(3) [L(2) = (Ph(3)P)(2) or (Ph(3)PO)(Me(2)S); X = Cl, Br] gives (PNP(Cy))ReOX(2) as two isomers, mer,trans and mer,cis. These compounds undergo a double Si migration from N to O at 90 degrees C to form (POP(Cy))ReNX(2) as a mixture of mer,trans and fac,cis isomers. Additional thermolysis effects migration of CH(3) from Si to Re, along with compensating migration of halide from Re to Si. DFT calculations on various structural isomers support the greater thermodynamic stability of the POP/ReN isomer vs PNP/ReO and highlight the influence of the template effect on the reactivities of these species.     

Reaction of the silylene Si[(NCH2But)2C6H4-1,2] with the alkali metal silylamides M[N(SiMe3)R](M = Li, Na or K; R = SiMe3 or SiMe2Ph)

The thermally stable silylene Si[(NCH(2)Bu(t))(2)C(6)H(4)-1,2] 1 undergoes oxidative addition reactions with the alkali metal silylamides MN(SiMe(3))(2)(M = Li, Na or K) to afford the new alkali metal amides MN(SiMe(3))[(1)SiMe(3)][M = Li (2), Na (3) or K (4)]. Reaction of two equivalents of 1 with LiN(R)(SiMe(3)) leads in a two-step process to the compound LiN[(1)R][(1)SiMe(3)][R = SiMe(2)Ph (5) or SiMe(3) (6)]. Alternatively, 1 reacts with 3 to afford NaN[(1)SiMe(3)](2) (7). The structures of 2-5 and are presented and the formation of 2-7 is discussed.     

Synthesis and reactivity of tris(imido)rhenium complexes containing rhenium-main group element bonds. silicon-carbon bond activations of PhSiH(3) by silyl complexes

The synthesis and reactivity of a series of complexes of the (DippN=)(3)Re (Dipp = 2,6-(i)Pr(2)C(6)H(3)) fragment are reported. The anionic, Re(V) complex (THF)(2)Li(micro,micro-NDipp)(2)Re(=NDipp) (1), prepared by the reaction of (DippN=)(3)ReCl with (THF)(3)LiSi(SiMe(3))(3) or (t)BuLi (2 equiv) in the presence of THF (4 equiv), served as an important starting material for the synthesis of rhenium-element-bonded complexes. For example, treatment of 1 with ClSiR(3) gave the corresponding silyl complexes (DippN=)(3)ReSiR(3) (SiR(3) = SiMe(3) (2a), SiHPh(2) (2b), SiH(2)Ph (2c)). Complexes 2a-c are thought to exist in equilibrium between the Re(VII) (DippN=)(3)ReSiR(3) and Re(V) (DippN=)(2)ReN(SiR(3))Dipp isomers. Complexes 2a,b reacted with PhSiH(3) to give reaction mixtures that included 2c, Ph(2)SiH(2), SiH(4), and C(6)H(6). The silane and organic products arise from Si-C bond formation and cleavage. Treatment of 2a with CO gave (DippN=)(2)Re[N(SiMe(3))Dipp](CO) (3), which appears to result from trapping of the reactive Re(V) isomer of 2a by CO. Complex 1 reacted with the main group halides MeI, Ph(3)GeCl, Me(3)SnCl, Ph(2)PCl, and PhSeCl to give the corresponding rhenium complexes (DippN=)(3)ReER(n) (ER(n)() = Me (4), GePh(3) (5), SnMe(3) (6), PPh(2) (7), SePh (8)) in high yields. X-ray diffraction data for 5 indicate that the germyl ligand is bonded to rhenium, but positional disorder of the phenyl and Dipp groups prevented refinement of accurate metric parameters.