: The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

This review is essentially an update of one entitled “πBonding and The Lone Pair Effect in Multiple Bonds Between Heavier Main Group Elements” which was published more than 10 years ago in this journal.1 The coverage of that survey was focused on the synthesis, structure, and bonding of stable compounds2 of heavier main group elements that correspond to the skeletal drawings reproduced in Tables 1 and 2. A row of numbers is listed at the bottom of each column in these tables. This refers to the number of stable complexes from each class that are currently known. The numbers in parentheses refer to the number of stable species that were known at the time of the previous review. Clearly, many of the compound classes listed have undergone considerable expansion although some remain stubbornly rare. The most significant developments for each class will be discussed in detail under the respective sections. As will be seen, there are also a limited number of multiple bonded heavier main group species that do not fit neatly in the classifications in Tables 1 and 2. However, to keep the review to a manageable length, the limits and exclusions, which parallel those used earlier, are summarized as follows: (i) discussion is mainly confined to compounds where experimental data on stable, isolated species have been obtained, (ii) stable compounds having multiple bonding between heavier main group elements and transition metals are not generally discussed, (iii) compounds in which a multiple bonded heavier main group element is incorporated within a ring are generally not covered, and (iv) hypervalent main group compounds that may incorporate faux multiple bonding are generally excluded. Such compounds are distinguished from those in Tables 1 and 2 in that they apparently require the use of more than four valence bonding orbitals at one or more of the bonded atoms. The remainder of this review is organized in a similar manner to that of the previous one wherein the compounds to be discussed are classified according to those summarized in Tables 1 and 2. The key unifying feature of almost all molecules discussed in this review is that they are generally stabilized by the use of bulky substituents which block associative or various decomposition pathways.3 Since the previous review was published in 1999, several review articles that cover parts of the subject matter have appeared.4

π-Bonding and the Lone Pair Effect in Multiple Bonds Involving Heavier Main Group Elements: Developments in the New Millennium

In recent decades, it has generally been recognized that carbenes play an important role as transient intermediates. As a result of a number of stable carbenes having been isolated and investigated in detail, it is not an exaggeration to say that the chemistry of carbenes has been thoroughly investigated and is now well-understood.1 In addition, much attention has also been paid to the heavier analogues of carbenes, i.e., silylenes (R2Si:), germylenes (R2Ge:), stannylenes (R2Sn:), and plumbylenes (R2Pb:). These so-called metallylenes are monomeric species of the polymetallanes. This is especially true of the silylenes, which are believed to be monomers of polysilane. The metallylenes could be expected to be of great importance in fundamental and applied chemistry as a result of their many differences and similarities to carbenes. The valency of the central atom of the heavier carbene analogues (R2M:, M ) Si, Ge, Sn, Pb) is two. That is, its oxidation state is MII and its stability increases as the principal quantum number (n) increases. In fact, dichloroplumbylene and dichlorostannylene, PbCl2 and SnCl2, respectively, are very stable ionic compounds. However, these dihalides exist as polymers or ion pairs both in solution and in the solid state. The dichlorogermylene complex GeCl2 · (dioxane)3 is also known to be stable and isolable, whereas the dihalosilylenes are barely isolable compounds.2 The early silylene research was concerned largely with comparing the chemistry of the dihalosilylenes with that of carbenes. Hence, the chemistry of the metallylenes has been considered mainly from the molecular chemistry point of view.4 In contrast to the carbon atom, the heavier group 14 atoms have a low ability to form hybrid orbitals. They therefore prefer the (ns)2(np)2 valence electron configurations in their divalent species.5 Since two electrons remain as a singlet pair in the ns orbital, the ground state of H2M: (M ) Si, Ge, Sn, Pb) is a singlet, unlike the case of H2C:, where the ground state is a triplet (Figure 1).1a On the basis of theoretical calculations, the singlet-triplet energy differences ∆EST for H2M, [∆EST ) E(triplet) E(singlet)], are found to be 16.7 (M ) Si), 21.8 (M ) Ge), 24.8 (M ) Sn), and 34.8 (M ) Pb) kcal/mol, respectively. That of H2C: is estimated as -14.0 kcal/mol.6 Furthermore, the relative stabilities of the singlet species of R2M: (M ) C, Si, Ge, Sn, Pb; R ) alkyl or aryl) compared to the corresponding dimer, R2MdMR2, are estimated to increase as the element row descends, C < Si < Ge < Sn < Pb. It follows, therefore, that one can expect that a divalent organolead compound such as plumbylene should be isolable as a stable compound. However, some plumbylenes, without any electronic or steric stabilization effects, are known to be thermally unstable and undergo facile disproportionation reactions, giving rise to elemental lead and the corresponding tetravalent organolead compounds.7 On this basis, it could be concluded that it might be difficult to isolate metallylenes as stable compounds under ambient conditions, since they generally exhibit extremely high reactivity toward other molecules as well as themselves. Metallylenes have a singlet ground state with a vacant p-orbital and a lone pair of valence orbitals. This extremely high reactivity must be due to their vacant p-orbitals, since 6 valence electrons is less than the 8 electrons of the “octet rule”. Their lone pair is expected to be inert due to its high s-character. In order to stabilize metallylenes enough to be isolated, either some thermodynamic and/or kinetic stabilization of the reactive vacant p-orbital is required (Figure 2). A range of “isolable” metallylenes have been synthesized through the thermodynamic stabilization of coordinating Cp* ligands, the inclusion of heteroatoms such as N, O, and P, * To whom correspondence should be addressed. Phone: +81-774-38-3200. Fax: +81-774-38-3209. E-mail: tokitoh@boc.kuicr.kyoto-u.ac.jp. Chem. Rev. 2009, 109, 3479–3511 3479

https://pubs.acs.org/doi/pdf/10.1021/cr900294f

Stable Heavier Carbene Analogues

Amine- and phosphine-borane adducts: new interest in old molecules.

Mononuclear complexes of certain lanthanide ions are known to have large magnetization reversal barriers caused by strong spin–orbit coupling. Now, careful tuning of the ligand field of a transition metal complex has engendered a comparable spin-reversal barrier — and in turn magnetic blocking at 4.5 K.

/pdf/magnetic-blocking-in-a-linear-iron-i-complex-1m5wvev7qj.pdf

Magnetic blocking in a linear iron( I ) complex

There is much current interest in the organometallic chemistry of the f-block elements. Considerable progress has been made in developing the chemistry of the +3[sub la] and 0[sub lb] oxidation states: work on the +2 oxidation state has been mainly concerned with polyhapto ligands, especially substituted cyclopentadienyls. We report the synthesis and crystal structure of bis[l brace]tris-(trimethylsilyl)methyl[r brace] ytterbium, Yb[l brace]C(SiMe[sub 3])[sub 3][r brace][sub 2], obtained in good yield as a highly air- and moisture-sensitive orange solid from the reaction between YbI[sub 2] and K[l brace]C(SiMe[sub 3])[sub 3][r brace][sup 5] in benzene, and the determination of its crystal structure. As far as we are aware this is the first solvent-free dialkyl lanthanide to be characterized. We also describe the preparation and structure of an Yb analogue of a Grignard reagent; these have been used in synthesis but have not previously been isolated. The most interesting and surprising feature of the solid-state structure is that the C-Yb-C angle is 137[degree]. 19 refs., 2 figs.

A Monomeric Solvent-Free Bent Lanthanide Dialkyl and a Lanthanide Analog of a Grignard Reagent. Crystal Structures of Yb{C(SiMe3)3}2 and [Yb{C(SiMe3)3}I.cntdot.OEt2]2

Alkyl Derivatives of Europium(+2) and Ytterbium(+2). Crystal Structures of Eu[C(SiMe3)3]2, Yb[C(SiMe3)2(SiMe2CHCH2)]I·OEt2 and Yb[C(SiMe3)2(SiMe2OMe)]I·OEt2

The reaction between 1.5 equiv of elemental iodine and rare earth metals in powder form in THF at room temperature gives the rare earth triiodides LnI3(THF)n in good yields. Purification by Soxhlet...

Keith Izod

Papers

A Monomeric Solvent-Free Bent Lanthanide Dialkyl and a Lanthanide Analog of a Grignard Reagent. Crystal Structures of Yb{C(SiMe3)3}2 and [Yb{C(SiMe3)3}I.cntdot.OEt2]2

Alkyl Derivatives of Europium(+2) and Ytterbium(+2). Crystal Structures of Eu[C(SiMe3)3]2, Yb[C(SiMe3)2(SiMe2CHCH2)]I·OEt2 and Yb[C(SiMe3)2(SiMe2OMe)]I·OEt2

A Convenient Route to Lanthanide Triiodide THF Solvates. Crystal Structures of Lnl3(THF)4 [Ln = Pr] and Lnl 3(THF)3.5 [Ln = Nd, Gd, Y]

The First Structurally Authenticated σ‐Bonded Organosamarium(II) Derivative and Its Reaction with Benzophenone

Crystal Structures of (Tris(trimethylsilyl)methyl)- and (Tris(dimethylphenylsilyl)methyl)potassium