Michael F. Lappert

Chemistry of thermally stable bis(amino)silylenes

Abstract This paper provides a comprehensive review of the chemistry of the thermally stable bis(amino)silylenes Si[(NCH 2 Bu t ) 2 C 6 H 4 -1,2] [abbreviated as Si(NN)] 1 and Si[N(Bu t )CH] 2 [abbreviated as Si(N′N′)] 2 and the somewhat less stable Si[N(Bu t )CH 2 ] 2 [abbreviated as Si(N″N″)] 3 . In a brief introduction, comments are made on the importance of transient silylenes in organosilicon chemistry and on thermally stable mononuclear silicon(II) compounds having a coordination number greater than two for silicon. The chemistry of 1 – 3 is discussed under the headings: synthesis, molecular and electronic structures, and reactions. The latter are classified into eight categories: (i) nucleophilic additions to an unsaturated organic substrate; (ii) insertions (oxidative addition reactions to the silylene) into a compound containing a OH, CCl, CBr, CI or BC bond; (iii) insertions into a main group element compound having a MN (M=Li, Na, K), LiC, LiSi, or M′(II)X (M′=Ge, Sn or Pb; X=C, N, O or Cl) bond; (iv) insertions into a transition metalX bond; (v) further (see ii) oxidative addition reactions of a chalcogen or Bu t NC; (vi) reduction reactions; (vii) silylenes as ligands in transition or 4f block metal chemistry, and (viii) silylenes as electrophiles.

Monomeric, volatile bivalent amides of group IVB elements, M(NR12)2 and M(NR1R2)2(MGe, Sn, or Pb; R1Me3Si, R2Me3C)

The reactions of SnCl2, PbCl2, or GeCl2, dioxan with LiNR12, OEt2 or LiNR1R2, OEt2 in Et2O at 0° yield the stable, monomeric, diamagnetic, coloured, volatile, hydrocarbon-soluble title compounds which are highly reactive.

Subvalent Group 4B metal alkyls and amides. Part 5. The synthesis and physical properties of thermally stable amides of germanium(II), tin(II), and lead(II)

A series of subvalent Group 4B metal amides of general formula M(NR1R2)2[(i) R1= SiMe3, R2= But; M = Ge, Sn, or Pb; (ii) R1= R2= SiMe3; M = Ge, Sn, or Pb; and (iii) R1= R2= GeMe3, SiEt3, or GePh3; M = Ge or Sn] has been prepared from the appropriate lithium amide and metal(II) halide. Under ambient conditions, the amides are pale yellow to red, thermochromic, diamagnetic, low-melting solids or liquids, and are soluble in hydrocarbons (C6H6 or C6H12) in which they are diamagnetic monomers. The lower homologues give parent molecular ions as the highest m/e species. Infrared spectra show a band at 380–430 cm–1[νasym(MN2)], and 1H or 13C n.m.r. spectra are consistent with the bent-singlet formulation. In the visible region the compounds exhibit a band (364–495 nm) of moderate intensity (Iµ= 600–2 050 dm3 mol–1 cm–1 in n-C6H14) indicative of an allowed electronic transition. Photolysis of each diamide in n-hexane in the cavity of an e.s.r. spectrometer affords (a) the persistent (t½ 5 min—3 months at 25° C) metal-centred radical Ṁ(NR1R2)3[(i) R1= SiMe3, R2= But, M = Ge or Sn; (ii) R1= R2= SiMe3 or GeMe3, M = Ge or Sn; or (iii) R1= R2= GeEt3, M = Sn], (b) a lead mirror (for the lead amides), or (c) no sign of reaction (for the more bulky diamides). E.s.r. parameters have been derived from the isotropic spectra.

Synthesis, structures and reactions of new thermally stable silylenes

Two representatives 1a and 1b of a new series of stable but reactive bis(amino)silylenes, derived from the N,N′-dineopentyl-1,2-phenylenediamido ligand RC6H3[(CH2But)]2, have been prepared by reductive elimination from RC6H3[[graphic omitted]SiCl2 and characterised by NMR spectroscopy and for 1a X-ray crystallography; the silyienes [graphic omitted](CH2But)]2C6H3-1,2-R (R = H 1a or 4-Me 1b) readily undergo oxidative addition with EtOH or Mel.

Homogeneous catalysis: VIII. Carbene-transition-metal complexes as hydrosilylation catalysts☆

Abstract Some carbene-transition-metal complexes, particularly those of rhodium(I) but also of ruthenium(II), have proved to be effective catalysts for the hydrosilylation (e.g., using SiHEt3 or SiH2Ph2) of ketones (to afford silyl ethers) or alkynes. The addition of triethylsilane to phenylacetylene or diphenylacetylene, catalysed by cis-[RhCl(COD)LMe] or trans-[RhCl(PPh3)2LMe] (COD=cycloocta-1,5-diene, LMe = : CN(Me)(CH 2 ) 2 N Me), proceeds stereoselectively via trans-addition; the stereochemistry of the hydrosilylation products and the catalytic enhancement observed in the presence of air or ultraviolet light suggests that the reaction proceeds via a radical intermediate. Diphenylsilane is catalytically converted into (SiHPh2)2, or O(SiHPh2)2 in presence of air, when for example cis-[RhCl(COD)LMe] is used.

Metal Amide Chemistry

Biographies. Preface. 1. Introduction. 1.1. Scope and Organisation of Subject Matter. 1.2. Developments and Perspectives. 2. Alkali Metal Amides. 2.1. Introduction. 2.2. Lithium Amides. 2.3. Sodium Amides. 2.4. Potassium Amides. 2.5. Rubidium Amides. 2.6. Caesium Amides. 3. Beryllium and the Alkaline Earth Metal Amides. 3.1. Introduction. 3.2. Beryllium Amides. 3.3. Magnesium Amides. 3.4. Calcium Amides. 3.5. Strontium Amides. 3.6. Barium Amides. 4. Amides of the Group 3 Lanthanide Metals. 4.1. Introduction. 4.2. The Pre-1996 Literature: Anwanders Review. 4.3. The Recent (Post-1995) Literature. 5. Amides of the Actinide Metals. 5.1. Introduction 5.2.Neutral Amidouranium (IV) and Thorium (IV) Complexes. 5.3. Neutral U III Amides. 5.4. Neutral Mixed Valence (U III/ U IV ), U II U V and U VI Amides. 5.5. Amidouranates. 5.6. Amidouranium Tetraphenylborates. 6. Amides of the Transition Metals. 6.1. Introduction. 6.2. Transition Metal Derivatives of Monodentate Amides. 6.3. Transition Metal Complexes of Polydentate Amido Ligands. 6.4. Other Chelating Amido Ligands. 7. Amides of Zinc, Cadmium and Mercury. 7.1. Introduction. 7.2. Neutral Homoleptic Zinc, Cadmium and Mercury Amides. 7.3. Ionic Metal Amides. 7.4. Lewis Base Complexes, Chelated Metal Amides and Heteroleptic Amido Complexes. 8. Amides of the Group 13 Metals. 8.1. Introduction. 8.2. Aluminum Amides. 8.3. Gallium Amides. 8.4. Indium Amides. 8.5. Thallium Amides. 9. Subvalent Amides of Silicon and the Group 14 Metals. 9.1. Introduction. 9.2. Subvalent Amidosilicon Compounds. 9.3. Amidometal(II) Chemistry [Ge(II), Sn(II), Pb(II)]. 9.4. Dimeric Metal(III) Imides: Biradicaloid Compounds. 9.5. Higher-Nuclearity Group 14 Metalloid Clusters having Amido Ligands. 10. Amides of the Group 15 Metals (As, Sb, Bi). 10.1. Introduction. 10.2. Mononuclear Group 15 Metal (III) Amides. 10.3. Oligomeric Group 15 Metal Imides. 10.4. Mononuclear Group 15 Metal (V) Amides. 10.5. Group 15 Metal (III) Macrocyclic Imides. 10.6. Miscellaneous Group 15 Metal-Nitrogen Compounds. Index.

Lanthanum Does Form Stable Molecular Compounds in the +2 Oxidation State

Getting down to business: Reduction of the LaIII tricyclopentadienide complex [LaCp′′3] (Cp′′=η5-1,3-(SiMe3)2C5H3) by K and [18]crown-6 or [2,2,2]cryptand produced thermally stable mononuclear crystalline lanthanate(II) salts. The La +2 oxidation state in these complexes was confirmed both in solution (EPR) and the solid state (EPR, SQUID, X-ray diffraction) and was supported by a computational study.

Recent studies on metal and metalloid bis(trimethylsilyl)methyls and the transformation of the bis(trimethylsilyl)methyl into the azaallyl and β-diketinimato ligands

Abstract Recent results (post-1990) on the synthesis and structures of bis(trimethylsilyl)methyls M(CHR2)m (R = SiMe3) of metals and metalloids M are described, including those of the crystalline lipophilic [Na(μ-CHR2)]∞, [Rb(μ-CHR2)(PMDETA)]2, K4(CHR2)4(PMDETA)2, [Mg(CHR2)(μ-CHR2)]∞, P(CHR2)2 (gaseous) and P2(CHR2)4, [Yb(CHR2)2(OEt2)2] and [{Yb(CR3)(μ-OEt)(OEt2)}2]; earlier information on other M(CHR2)m complexes and some of their adducts is tabulated. Treatment of M(CHR2) (M = Li or K) with four different nitriles gave the X-ray-characterized azaallyls or β-diketinimates , and (LL′ = N(R)C(tBu)CHR, L′L′ = N(R)C(Ph)C(H)C(Ph)NR, LL″ = N(R)C(Ph)NC(H)C(Ph)CHR, R = SiMe3 and Ar = C6H3Me2-2,5). The two lithium reagents were convenient sources of other metal azaallyls or β-diketinimates, including those of K, Co(II), Zr(IV), Sn(IV), Yb(II), Hf(IV) and U(VI)/U(III). Complexes having one or more of the bulky ligands [LL′]−, [L′L′]−, [LL]−, [LL″]−, [L″L‴]−, [LL‴]− and [{N(R)C(tBu)CH}2C6H4-2]2− are described and characterized (LL = N(H)C(Ph)C(H)C(Ph)NH, L″L‴ = N(R)C(tBu)C(H)C(Ph)NR, LL‴ = N(R)C(tBu)CHPh). Among the features of interest are (i) the contrasting tetrahedral or square-planar geometry for and , respectively, and (ii) olefin-polymerization catalytic activity of some of the zirconium(IV) chlorides.

“Dibutylmagnesium”, a convenient reagent for the synthesis of useful organic magnesium reagents MgA2 including cyclopentadienyls, aryloxides, and amides. Preparation of Zr(C5H5)Cl3. X-ray structure of [Mg{μ-N(SiMe)3C6H4N}(SiMe3)-o(OEt2)]2☆

Abstract n-Heptane-soluble “di-butylmagnesium” (I) (a commercially available material, prepared by addition of LiBus to MgBunCl, and subsequent addition of ca. 5% MgOct2n) has been found to be a useful starting material for obtaining numerous organic magnesium compounds. This is illustrated by its reaction with a number of protic compounds HA to give in good yields Mg(C5H5)2, Mg(C5H4Me)2, or the new compounds MgA2: IV (A = C5H4SiMe3), V [A = C5H3(SiMe3)2], VII (A = OC6H2Bu2t-2,6-Me-4), and X [A2 = N(SiMe3)C6H4N(SiMe3)-o(OEt2)]. The value of such compounds MgA2 as mild ligand transfer reagents is illustrated by the synthesis of Zr(C5H3X2)Cl3 (X = H or SiMe3). Compound X was isolated from OEt2 solution as the crystalline dimer with two o- N (SiMe3)C6H4 N (SiMe3) ligands bridging two magnesium atoms and a terminal OEt2 ligand completing a distorted tetrahedral environment around each Mg. Some key parameters are: MgNt 1.997(7), MgNb 2.083(8), MgO 2.041(7) A; OMgNt 112.1(3), OMgNb 119.7(3), and NtMgNb 118.5(3)°.

Lipophilic strontium and calcium alkyls, amides and phenoxides; X-ray structures of the crystalline square-planar [{trans-Sr(NR′2)2(µ-1,4-dioxane)}∞] and tetrahedral [CaR2(1,4-dioxane)2]; R′= SiMe3, R = CH(SiMe3)2]

Treatment of pyrophoric strontium powder in tetrahydrofuran with ArOH (Ar = C6H2But3-2,4,6) or HNR′2 at ambient temperature affords crystalline [Sr(OAr)2(THF)4] or [Sr(NR′2)2(THF)2]3, respectively, and 3 with 1,4-dioxane yields crystalline [{trans-Sr(NR′2)2(µ-1,4-dioxane)}∞]4; co-condensation of calcium vapour and RBr in THF at 77 K affords [CaR2(THF)3]5, which with 1,4-dioxane gives [CaR2(1,4-dioxane)2]6; X-ray structures reveal the alkaline earth metal environment to be square-planar for 4[Sr-N 2.449(7), Sr-O 2.533(9)A] but tetrahedral for 6[Ca-C 2.483(5), Ca-O 2.373(4)A] with dioxane as a bridging bidentate 4 or monodentate 6 ligand.