Synthesis and reactivity of a conveniently prepared two-coordinate bis(amido) nickel(II) complex

A strictly two-coordinate nickel(II) bis(amido) complex has been prepared and its reactivity towards a variety of small molecules is described. Ni[N(SiMe(3))(DIPP)](2) reacts with DMAP and acetonitrile to form T-shaped three-coordinate complexes, and preliminary results show that Ni[N(SiMe(3))(DIPP)](2) is a catalyst for the hydrosilation of olefins with secondary silanes at ambient temperature.     

Synthesis, structure and reactivity of new yttrium bis(dimethylsilyl)amido and bis(trimethylsilyl)methyl complexes of a tetradentate bis(phenoxide) ligand

The reactions of a bulky amino-methoxy bis(phenolate) ligand H₂L with Y(CH₂SiMe₃)₃(THF)₂ and Y[N(SiHMe₂)₂]₃(THF)₂ under mild condition leads to the selective formation of the thermally stable complexes [L]Y(CH₂SiMe₃)(THF) (1) and [L]Y[N(SiHMe₂)₂](THF) (2). The X-ray structures revealed very similar binding of the [ONOO] ligand core to the metal for both complexes, which feature an octahedral geometry involving coordination of the methoxy side-arm of the ligand and of a remaining THF molecule. ¹H-NMR spectroscopy indicates that the solid state structure of 1 and 2 is retained in hydrocarbon solutions with THF coordinated to yttrium. Alkyl complex 1 showed no activity in ethylene polymerization, presumably due to the presence of coordinated THF. The amido complex 2 catalyzed sluggishly the polymerization of methyl methacrylate to give isotactic-rich PMMA but is very active for the ring-opening polymerization of ε-caprolactone.     

Synthesis,crystal structures,and properties of copper(II) dicarboxylate complexes with [bis(2-pyridylcarbonyl)amido]

Four new complexes, [Cu₂(Bpca)₂(L¹)(H₂O)₂] · 3H₂O (I), [Cu₂(Bpca)₂(L²)(H₂O)₂] (II), [Cu₂(Bpca)₂(L³)] · 2H₂O (III), [Cu₂(Bpca)₂(L¹)(H₂O)] · 2H₂O (IV) (Bpca = bis(2-pyridylcarbonyl)amido, H₂L¹ = glutaric acid, H₂L² = adipic acid, H₂L³ = suberic acid, H₂L⁴ = azelaic acid) have been synthesized and characterized by single-crystal X-ray diffraction methods (CIF files CCDC nos. 1432836 (I), 1432835 (II), 817411 (III), and 817412 (IV)), elemental analyses, IR spectra. Structural analyses reveal that compounds I, II, and IV have similar structures [Cu(Bpca)]⁺ units bridged by dicarboxylate forming dinuclear units, whereas the dinuclear of compound III are edge-shared through two carboxylate oxygen atoms of different suberate anions. Hydrogen bonds are response for the supramolecular assembly of compounds I to IV. The temperature-dependent magnetic property of III was also investigated in the temperature range of 2 to 300 K, and the magnetic behaviour suggests weak antiferromagnetic coupling exchange.     

The crystal and molecular structures of bis (pentafluorophenyl)disulphide and bis(pentafluorophenyl)diselenide

The structures of (C₆F₅)₂S₂ and (C₆F₅)₂Se₂ have been determined by single crystal, X-ray diffraction techniques. The compounds are isostructural although the molecules are packed differently in the crystal in comparison with their phenyl analogues. Important bond lengths and angles are: SS, 2.059(4)Å; SeSe, 2.319(4)Å; SC, 1.770Å; SeC, 1.910(15)Å; SSC, 101.3(3)°; SeSeC, 98.8(1)°.     

Reactions of bis[bis(trimethylsilyl)methyl]germylene and the corresponding stannylene with diazidosilanes

The reactions of bis[bis(trimethylsilyl)methyl]-germylene ( 1 ) and the corresponding stannylene ( 2 ) with di-tert-butyldiazidosilane gave N-(azidosilyl)germanimine ( 4 ) and the stannanimine ( 5 ) in quantitative yields. The structures have been confirmed by single-crystal X-ray diffraction. Crystal data for 4 : space group P1 , Z = 2, a = 9.236 (1), b = 12.066 (1), c = 17.068 (1) Å, α = 98.45 (1), β = 90.43, γ = 110.27 (1)°. V = 1761.3 ų, R = 0.051, and Rw = 0.069 based on 4218 reflections with |Fo²| ⩾ 3σ|Fo²|. For 5 : space group P1 , Z = 2, a = 9.183 (1), b = 12.193 (1), c = 17.292 (1) Å, α = 98.74 (1), β = 90.21, γ = 109.96 (1)°, V = 1795.5 ų, R = 0.040, and Rw = 0.051 based on 4795 reflections. The similar reactions of 1 and 2 with 1,3-diazidohexamethyltrisilane ( 16 ) provided azatrisilacyclobutanes quantitatively.     

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.     

1,1,1,3,3,3-Hexamethyltrisilanylene-bridged bis(cyclopentadienyl)tetracarbonyldiiron and its derivatives: Synthesis,properties and molecular structures

The title ring-bridged bis(cyclopentadienyl)diiron complexes [η⁵,η⁵-C₅H₄–Si(SiMe₃)₂–C₅H₄]Fe₂(CO)L(μ-CO)₂ [L = CO (1), P(OPh)₃ (2), P(OMe)₃ (3), PPh₃ (4), PMe₃ (5)] that contain exocyclic Si–Si bonds attached to the bridging silicon atom have been synthesized. The Si–Si bonds were found to be stable to the intramolecular iron centers under both thermal and photochemical conditions, in sharp contrast to the facile cleavage of the Si–Si bond in 1,1,2,2-tetramethyldisilanylene-bridged analogous complexes. The stability of the Si–Si bonds in the present cases may be attributed to the fact that these Si–Si bonds are spatially unapproachable by the intramolecular coordinatively unsaturated iron centers. Molecular structures of 1 and 2 have been determined by X-ray diffraction methods. An obvious conformational change due to substitution of CO for P(OPh)₃ was observed.     

Static and dynamic disorder in organotin compounds: A bis(amido)stannylene coordinated by N,N′-diisopropyl-1,8-diamidonaphthalene

The root-mean-square amplitude of vibration of the tin atom in the bis(amido)stannylene Sn[1,8-(NⁱPr)₂C₁₀H₆] has been determined from temperature-dependent ¹¹⁹Sn Mössbauer effect measurements over the range 98 < T < 225 K and compared with the U_i,j value extracted from a single crystal X-ray diffraction study. The large difference in these values (at 238 K) is associated with the flexibility in the bonding between the Sn center and chelating diamido ligand in this complex.     

Synthesis and structures of some diorganotin bis(hydroxamate)s

Analysis of literature data on the antitumor activity of organotin compounds reveals that R₂SnX₂ and their complexes containing Sn? O, Sn? N or Sn? S bonds often exhibit biological activity, especially if such bonds are formed by means of intramolecular coordination. Furthermore, a wide range of biological activities, from fungicidal, bactericidal and antiseptic to psychotropic and antitumor, is found to be characteristic for some organic hydroxamic acids (N-acylhydroxylamines). From this point of view the diorgantion bis-hydroxamates in this paper are of particular interest as potential biologically active antitumor drugs. Di-n-butyltin bis(N-methyl-N-p-bromobenzoylhydroxylamine) is being screened for antitumor activity.     

Elimination of bis(trimethylsilyl)stannylene from tris(trimethylsilyl)stannylated zirconocene and hafnocene chlorides

Reactions of (Me₃Si)₃SnK with Cp₂MCl₂ (M = Zr, Hf) give the respective stannylated metallocene chlorides. These complexes display a tendency to eliminate bis(trimethylsilyl)-stannylene under Cp₂M(Cl)SiMe₃ formation.     

Complexes of mono- and bis(2-carboxyethyl)-2-picolylamine: Synthesis and crystal and molecular structures

N-(2-Pyridylmethyl)iminodipropionic (I) and N-(2-pyridylmethyl)-3-aminopropionic acids (II) were obtained. A reaction of acid I with a Cu(II) salt gave a 2: 2 complex (III); a reaction of acid II with a Ni(II) salt yielded a 1 : 2 complex (IV). The crystal structures of these complexes were determined by X-ray diffraction. The abilities of compounds I and II to form complexes were compared with the literature data for other ligands containing the N-(2-pyridylmethyl)amino fragment. The structural features of the chelate complexes with 2-aminomethylpyridine derivatives were revealed, depending on the other substituents and the metal center.     

Synthesis and characterization of a chromium(V) cis-dioxo bis(1,10-phenanthroline) complex and crystal and molecular structures of its chromium(III) precursor

The first structurally characterized Cr(V) dioxo complex, cis-[CrV(O)2(phen)2](BF4) (2, phen=1,10-phenanthroline) has been synthesized by the oxidation of a related Cr(III) complex, cis-[Cr(III)(phen)2(OH2)2](NO3)3.2.5H2O (1, characterized by X-ray crystallography), with NaOCl in aqueous solutions in the presence of excess NaBF4, and its purity has been confirmed by electrospray mass spectrometry (ESMS), EPR spectroscopy, and analytical techniques. Previously reported methods for the generation of Cr(V)-phen complexes, such as the oxidation of 1 with PbO2 or PhIO, have been shown by ESMS to lead to mixtures of Cr(III), Cr(V), Cr(VI), and in some cases Cr(IV) species, 3. Species 3 was assigned as [CrIV(O)(OH)(phen)2]+, based on ESMS and X-ray absorption spectroscopy measurements. A distorted octahedral structure for 2 (CrO, 1.63 A; Cr-N, 2.04 and 2.16 A) was established by multiple-scattering (MS) modeling of XAFS spectra (solid, 10 K). The validity of the model was verified by a good agreement between the results of MS XAFS fitting and X-ray crystallography for 1 (distorted octahedron; Cr-O, 1.95 A; Cr-N, 2.06 A). Unlike for the well-studied Cr(V) 2-hydroxycarboxylato complexes, 2 was equally or more stable in aqueous media (hours at pH=1-13 and 25 degrees C) compared with polar aprotic solvents. A stable Cr(III)-Cr(VI) dimer, [Cr(III)(Cr(VI)O4)(phen)2]+ (detected by ESMS), is formed during the decomposition of 2 in nonaqueous media. Comparative studies of the oxidation of 1 by NaOCl or PbO2 have shown that [Cr(V)(O)2(phen)2]+ was the active species responsible for the previously reported oxidative DNA damage, bacterial mutagenicity, and increased incidence of micronuclei in mammalian cells, caused by the oxidation products of 1 with PbO2. Efficient oxidation of 1 to a genotoxic species, [Cr(V)(O)2(phen)2]+, in neutral aqueous media by a biological oxidant, hypochlorite, supports the hypothesis on a significant role of reoxidation of Cr(III) complexes, formed during the intracellular reduction of Cr(VI), in Cr(VI)-induced carcinogenicity. Similar oxidation reactions may contribute to the reported adverse effects of a popular nutritional supplement, Cr(III) picolinate.     

Tris(bis(trimethylsilyl)amido)samarium: X-ray structure and DFT study

The compound Sm[N(SiMe(3))(2)](3) has been investigated experimentally by X-ray crystallography and computationally by DFT methods. The structure is analogous to that of other tris[bis(trimethylsilyl)amido]lanthanides, featuring positional disorder of the metal atom above and below the plane defined by the three N donor atoms, resulting in a trigonal pyramidal configuration. One of the methyl groups of each amido ligand is placed above the apex of the pyramid at close distance to the metal center suggesting the presence of agostic interactions. The DFT calculations have been carried out on the real molecule and on a Si[N(SiH(3))(SiH(2)Me)](3) model where the unique Me group was placed above the apex of the pyramid to probe the agostic interaction. In both cases, the optimized geometry reproduces very well the experimental structure and indicates the presence of beta-Si-C agostic interactions. A comparison of the optimized geometries obtained in the presence/absence of the Sm d and the Si d orbitals serves to illustrate the relevance of these orbitals for (i). the establishment of the pyramidal configuration at Sm, (ii). the Sm-N bond length, and (iii). the Sm-(beta-Si-C) bond length. The bonding analysis, which was carried out by both Mulliken and NBO methods, not only confirms the importance of the metal d orbitals for the Sm-N and Sm-(beta-Si-C) chemical bonding but also illustrates the relevance of electrostatic terms in the agostic interaction. Sm-N and N-Si pi bonding is present according to the bonding analysis but is not important for enforcing the planar configuration at N, nor the pyramidal configuration at Sm.     

Synthesis and crystal structures of bis(cyclopentyl)gallium phenoxide dimer and bis (cyclopentyl) gallium naphthoxide dimer

Tricyclopentylgallium reacted with phenol, naphthol respectively to yield phenox-ide (or naphthoxide) of biscyclopentylgallium which have been characterized by elemental analysis, IR, 1H NMR and mass spectrometry. X-ray diffraction analysis of compound 1 indicated that it belongs to the monoclinic system, space groups P21/c, with cell constants 0=9.602(3), 6=14.365(7), c=11.256(4)A, and β=97.54(3)°, Z=2(dimers), R=0.0706. Compound 2 assigned to the triclinic system, space groups P1 with cell constants a=9.392(4), 6=9.928(7), c=11.263(7) A, a=112.48(5), β=104.74(4), γ=99.95(5)°, and Z=l(dimers), R=0.0526. The molecule of 1 or 2 contains an oxygen-bridged coplanar Ga2O2 four-membered ring respectively.     

Synthesis and structural characterization of two-coordinate low-valent 14-group metal complexes bearing bulky bis(amido)silane ligands

A series of germylene, stannylene and plumbylene complexes [η(2)(N,N)-Me(2)Si(DippN)(2)Ge:] (3a), [η(2)(N,N)-Ph(2)Si(DippN)(2)Ge:] (3b), [η(2)(N,N)-Me(2)Si(DippN)(2)Sn:] (4), [η(2)(N,N)-Me(2)Si(DippN)(2)Pb:](2) (5a), and [η(2)(N,N)-Ph(2)Si(DippN)(2)Pb:] (5b) (Dipp = 2,6-iPr(2)C(6)H(3)) bearing bulky bis(amido)silane ligands were readily prepared either by the transamination of M[N(SiMe(3))(2)](2) (M = Sn, Pb) and [Me(2)Si(DippNH)(2)] or by the metathesis reaction of bislithium bis(amido)silane [η(1)(N),η(1)(N)-R(2)Si(DippNLi)(2)] (R = Me, Ph) with the corresponding metal halides GeCl(2)(dioxane), SnCl(2), and PbCl(2), respectively. Preliminary atom-transfer chemistry involving [η(2)(N,N)-Me(2)Si(DippN)(2)Ge:] (3a) with oxygen yielded a dimeric oxo-bridged germanium complex [η(2)(N,N)-Me(2)Si(DippN)(2)Ge(μ-O)](2) (6). All complexes were characterized by (1)H, (13)C, (119)Sn NMR, IR, and elemental analysis. X-ray single crystal diffraction analysis revealed that the metal centres in 3b, 4, and 5b are sterically protected to prevent interaction between the metal centre and the nitrogen donors of adjacent molecules while complex 5a shows a dimeric feature with a strong intermolecular Pb···N interaction.     

Chromium(III) and chromium(IV) bis(trimethylsilyl)amido complexes as ethylene polymerisation catalysts

Oxidation of Cr[N(SiMe(3))(2)](2)(THF)(2) with iodine and dicumyl peroxide results in tetrahedral Cr(iv) Cr[N(SiMe(3))(2)](2)I(2) and trigonal planar Cr(iii) Cr[N(SiMe(3))(2)](OCMe(2)Ph)(2), respectively; both complexes have been characterised by single-crystal X-ray diffraction, and both are active for ethylene polymerisation with alkylaluminium co-catalysts.