Low-Coordinate Cobalt(I) Complexes Stabilized by an Extremely Bulky Amide Ligand

A series of low-coordinate, high-spin, mono- and dinuclear cobalt­(I) complexes bearing an extremely bulky amide (L″ = N­(Ar*)­(SiPh₃); Ar* = C₆H₂{C­(H)­Ph₂}₂Me-2,6,4) ligand have been synthesized and characterized. These include the first example of a neutral two-coordinate cobalt­(I) complex, [L″Co­(IPriMe)] (IPriMe = :C­{N­(Pr^<i>i</i>)­C­(Me)}₂), which has a near-linear cobalt coordination geometry

Extremely Bulky Amido First Row Transition Metal(II) Halide Complexes: Potential Precursors to Low Coordinate Metal–Metal Bonded Systems

Reactions of the extremely bulky potassium amide complexes, [KL′(η⁶-toluene)] or [KL″] (L′/L″ = N­(Ar*)­(SiR₃), Ar* = C₆H₂{C­(H)­Ph₂}₂Me-2,6,4; R = Me (L′) or Ph (L″)), with a series of first row transition metal­(II) halides have yielded 10 rare examples of monodentate amido first row transition metal­(II) halide complexes, all of which were crystallographically characterized. They encompass the dimeric, square-planar chromium complexes, [{CrL′(THF)­(μ-Cl)}₂] and [{CrL″(μ-Cl)}₂], the latter of which displays intramolecular η²-Ph···Cr interactions; the dimeric tetrahedral complexes, [{ML′(THF)­(μ-Br)}₂] (M = Mn or Fe), [{ML″(THF)­(μ-X)}₂] (M = Mn, Fe or Co; X = Cl or Br) and [{CoL″(μ-Cl)}₂] (which displays intramolecular η²-Ph···Co interactions); and the monomeric zinc amides, [L′ZnBr­(THF)] (three-coordinate) and [L″ZnBr] (two-coordinate). Solution state magnetic moment determinations on all but one of the paramagnetic compounds show them to be high-spin systems. Throughout, comparisons are made with related bulky terphenyl transition metal­(II) halide complexes, and the potential for the use of the prepared complexes as precursors to low-valent transition metal systems is discussed

Extremely Bulky Amido First Row Transition Metal(II) Halide Complexes: Potential Precursors to Low Coordinate Metal–Metal Bonded Systems

Reactions of the extremely bulky potassium amide complexes, [KL′(η⁶-toluene)] or [KL″] (L′/L″ = N­(Ar*)­(SiR₃), Ar* = C₆H₂{C­(H)­Ph₂}₂Me-2,6,4; R = Me (L′) or Ph (L″)), with a series of first row transition metal­(II) halides have yielded 10 rare examples of monodentate amido first row transition metal­(II) halide complexes, all of which were crystallographically characterized. They encompass the dimeric, square-planar chromium complexes, [{CrL′(THF)­(μ-Cl)}₂] and [{CrL″(μ-Cl)}₂], the latter of which displays intramolecular η²-Ph···Cr interactions; the dimeric tetrahedral complexes, [{ML′(THF)­(μ-Br)}₂] (M = Mn or Fe), [{ML″(THF)­(μ-X)}₂] (M = Mn, Fe or Co; X = Cl or Br) and [{CoL″(μ-Cl)}₂] (which displays intramolecular η²-Ph···Co interactions); and the monomeric zinc amides, [L′ZnBr­(THF)] (three-coordinate) and [L″ZnBr] (two-coordinate). Solution state magnetic moment determinations on all but one of the paramagnetic compounds show them to be high-spin systems. Throughout, comparisons are made with related bulky terphenyl transition metal­(II) halide complexes, and the potential for the use of the prepared complexes as precursors to low-valent transition metal systems is discussed

Reaction Pathways for Addition of H₂ to Amido-Ditetrylynes R₂N–EE–NR₂ (E = Si, Ge, Sn). A Theoretical Study

Quantum chemical calculations of the reaction profiles for addition of one and two H₂ molecules to amido-substituted ditetrylynes have been carried using density functional theory at the BP86/def2-TZVPP//BP86/def2-TZVPP level of theory for the model systems L′EEL′ and BP86/def2-TZVPP//BP86/def-SVP for the real compounds. The hydrogenation of the digermyne LGeGeL (L = N­(SiMe₃)­Ar*; Ar* = C₆H₂Me­{C­(H)­Ph₂}₂-4,2,6) follows a stepwise reaction course. The addition of the first H₂ gives the singly bridged species LGe­(μ-H)­GeHL, which rearranges with very low activation barriers to the symmetrically hydrogenated compound LHGeGeHL and to the most stable isomer LGeGe­(H)₂L, which is experimentally observed. The addition of the second H₂ proceeds with a higher activation energy under rupture of the Ge–Ge bond, yielding LGeH and LGeH₃ as reaction products. Energy calculations which consider dispersion interactions using Grimme’s D3 term suggest that the latter reaction is thermodynamically unfavorable. The second hydrogenation reaction LGeGe­(H)₂L → L­(H)₂GeGe­(H)₂L possesses an even higher activation barrier than the bond-breaking hydrogenation step. Further calculations which consider solvent effects change the theoretically predicted reaction profile very little. The calculations of the model system L′GeGeL′ (L′ = NMe₂) give a very similar reaction profile. Calculations of the model disilyne and distannyne homologues L′SiSiL′ and L′SnSnL′ suggest that the reactivity of the amido-substituted ditetrylynes always has the order Si > Ge > Sn. The most stable product of the addition of one H₂ to the distannyne L′SnSnL′ is the doubly bridged species L′Sn­(μ-H)₂SnL′, which has been experimentally observed when bulky groups are employed. Analysis of the H₂–L′EEL′ interactions in the transition state for the addition of the first H₂ with the EDA-NOCV method reveals that the HOMO–LUMO and LUMO–HOMO interactions have similar magnitudes

A Spatial Approach to Mereology

When do several objects compose a further object? The last twenty years have seen a great deal of discussion of this question. According to the most popular view on the market, there is a physical object composed of your brain and Jeremy Bentham’s body. According to the second-most popular view on the market, there are no such objects as human brains or human bodies, and there are also no atoms, rocks, tables, or stars. And according to the third-ranked view, there are human bodies, but still no brains, atoms, rocks, tables, or stars. Although it’s pleasant to have so many crazy-sounding views around, I think it would also be nice to have a commonsense option available. The aim of this paper is to offer such an option. The approach I offer begins by considering a mereological question other than the standard one that has been the focus of most discussions in the literature. I try to show that the road to mereological sanity begins with giving the most straightforward and commonsensical answer to this other question, and then extending that answer to further questions about the mereology of physical objects. On the approach I am recommending, it turns out that all of the mereological properties and relations of physical objects are determined by their spatial properties and relations

Efficient Reduction of Carbon Dioxide to Methanol Equivalents Catalyzed by Two-Coordinate Amido–Germanium(II) and −Tin(II) Hydride Complexes

The bulky amido–germanium­(II) and −tin­(II) hydride complexes, L^†EH [E = Ge or Sn; L^† = -N­(Ar^†) (SiPr^<i>i</i>₃); Ar^† = C₆H₂Pr^<i>i</i>{C­(H)­Ph₂}₂-4,2,6], which are two-coordinate in solution, are shown to be efficient and highly selective “single-site” catalysts for the reduction of CO₂ to methanol equivalents (MeOBR₂), using HBpin or HBcat as the hydrogen source. L^†SnH is the most active non-transition metal catalyst yet reported for such reductions, yielding turnover frequencies of up to 1188 h^–1 at room temperature. Computational studies have identified two thermodynamically and kinetically viable catalytic pathways by which these reductions may operate. Spectroscopic investigations have identified several reaction intermediates, which leads to the conclusion that one of these reaction pathways predominates in the experimental situation. Stoichiometric reactivity studies have shed further light on the reaction mechanisms in operation and indicate that the involvement of the second reaction pathway cannot be ruled out. This study highlights the potential of relatively cheap, main group complexes as viable alternatives to transition metal-based systems in the catalytic transformation of small molecules

Monomeric Group 13 Metal(I) Amides: Enforcing One-Coordination Through Extreme Ligand Steric Bulk

Reactions of the extremely bulky amido alkali metal complexes, [KL′(η⁶-toluene)], or in situ generated [LiL′] or [LiL″] {L′/ L″ = N­(Ar*)­(SiR₃), where Ar* = C₆H₂­{C­(H)­Ph₂}₂­Me-2,6,4 and R = Me (L′) or Ph (L″)} with group 13 metal­(I) halides have yielded a series of monomeric metal­(I) amide complexes, [ML′] (M = Ga, In, or Tl) and [ML″] (M = Ga or Tl), all but one of which have been crystallographically characterized. The results of the crystallographic studies, in combination with computational analyses, reveal that the metal centers in these compounds are one coordinate and do not exhibit any significant intra- or intermolecular interactions, other than their N-M linkages. One of the complexes, [InL′], represents the first example of a one-coordinate indium­(I) amide. Attempts to extend this study to the preparation of the analogous aluminum­(I) amide, [AlL′], were not successful. Despite this, a range of novel and potentially synthetically useful aluminum­(III) halide and hydride complexes were prepared en route to [AlL′], the majority of which were crystallographically characterized. These include the alkali metal aluminate complexes, [L′AlH₂­(μ-H)­Li­(OEt₂)₂­(THF)] and [{L′Al­(μ-H)₃K}₂], the neutral amido-aluminum hydride complex, [{L′AlH­(μ-H)}₂], and the aluminum halide complexes, [L′AlBr₂(THF)] and [L′AlI₂]. Reaction of the latter two systems with a variety of reducing agents led only to intractable product mixtures

Low Coordinate Germanium(II) and Tin(II) Hydride Complexes: Efficient Catalysts for the Hydroboration of Carbonyl Compounds

This study details the first use of well-defined low-valent p-block metal hydrides as catalysts in organic synthesis. That is, the bulky, two-coordinate germanium­(II) and tin­(II) hydride complexes, L^†(H)­M: (M = Ge or Sn, L^† = −N­(Ar^†)­(SiPrⁱ₃), Ar^† = C₆H₂{C­(H)­Ph₂}₂Pr^<i>i</i>-2,6,4), are shown to act as efficient catalysts for the hydroboration (with HBpin, pin = pinacolato) of a variety of unactivated, and sometimes very bulky, carbonyl compounds. Catalyst loadings as low as 0.05 mol % are required to achieve quantitative conversions, with turnover frequencies in excess of 13 300 h^–1 in some cases. This activity rivals that of currently available catalysts used for such reactions

Low Coordinate Germanium(II) and Tin(II) Hydride Complexes: Efficient Catalysts for the Hydroboration of Carbonyl Compounds

This study details the first use of well-defined low-valent p-block metal hydrides as catalysts in organic synthesis. That is, the bulky, two-coordinate germanium­(II) and tin­(II) hydride complexes, L^†(H)­M: (M = Ge or Sn, L^† = −N­(Ar^†)­(SiPrⁱ₃), Ar^† = C₆H₂{C­(H)­Ph₂}₂Pr^<i>i</i>-2,6,4), are shown to act as efficient catalysts for the hydroboration (with HBpin, pin = pinacolato) of a variety of unactivated, and sometimes very bulky, carbonyl compounds. Catalyst loadings as low as 0.05 mol % are required to achieve quantitative conversions, with turnover frequencies in excess of 13 300 h^–1 in some cases. This activity rivals that of currently available catalysts used for such reactions

Monomeric Group 13 Metal(I) Amides: Enforcing One-Coordination Through Extreme Ligand Steric Bulk

Reactions of the extremely bulky amido alkali metal complexes, [KL′(η⁶-toluene)], or in situ generated [LiL′] or [LiL″] {L′/ L″ = N­(Ar*)­(SiR₃), where Ar* = C₆H₂­{C­(H)­Ph₂}₂­Me-2,6,4 and R = Me (L′) or Ph (L″)} with group 13 metal­(I) halides have yielded a series of monomeric metal­(I) amide complexes, [ML′] (M = Ga, In, or Tl) and [ML″] (M = Ga or Tl), all but one of which have been crystallographically characterized. The results of the crystallographic studies, in combination with computational analyses, reveal that the metal centers in these compounds are one coordinate and do not exhibit any significant intra- or intermolecular interactions, other than their N-M linkages. One of the complexes, [InL′], represents the first example of a one-coordinate indium­(I) amide. Attempts to extend this study to the preparation of the analogous aluminum­(I) amide, [AlL′], were not successful. Despite this, a range of novel and potentially synthetically useful aluminum­(III) halide and hydride complexes were prepared en route to [AlL′], the majority of which were crystallographically characterized. These include the alkali metal aluminate complexes, [L′AlH₂­(μ-H)­Li­(OEt₂)₂­(THF)] and [{L′Al­(μ-H)₃K}₂], the neutral amido-aluminum hydride complex, [{L′AlH­(μ-H)}₂], and the aluminum halide complexes, [L′AlBr₂(THF)] and [L′AlI₂]. Reaction of the latter two systems with a variety of reducing agents led only to intractable product mixtures