Quadrupolar effects transferred to spin-12 magic-angle spinning spectra of solids

Ethylene's cycloadditions to unsaturated hydrocarbons occupy well-established ground in classical organic chemistry. In contrast, its reactivity toward alkene and alkyne analogs of carbon's heavier-element congeners silicon, germanium, tin, or lead has been little explored. We show here that treatment of the distannynes Ar(iPr4)SnSnAr(iPr4) [Ar(iPr4) = C6H3-2,6(C6H3-2,6-iPr2)2, 1] or Ar(iPr8)SnSnAr(iPr8) [Ar(iPr8) = C6H-2,6(C6H2-2,4,6-iPr3)2-3,5-iPr2, 2] with ethylene under ambient conditions affords the cycloadducts Ar(iPr4) Sn(mu2:nu1:n1-C2H4)2Sn Ar(iPr4 (3) or Ar(iPrs) Sn(mu2:nu1:nu1-C2H4)2Sn AriPrs (4) that were structurally and spectroscopically characterized. Ethylene incorporation in 3 and 4 involves tin-carbon sigma bonding and is shown to be fully reversible under ambient conditions; hydrocarbon solutions of 3 or 4 revert to the distannynes 1 or 2 with ethylene elimination under reduced pressure or upon standing at approximately 25 degrees C. Variable-temperature proton nuclear magnetic resonance studies showed that the enthalpies of reaction were near -48 (3) and -27 (4) kilojoules per mole.

https://science.sciencemag.org/content/sci/325/5948/1668.full.pdf

Reversible Reactions of Ethylene with Distannynes Under Ambient Conditions

Spin -spin coupling tensors as determined by experiment and computational chemistry

Recent theoretical studies are reviewed which show that the naked group 14 atoms E = C–Pb in the singlet 1D state behave as bidentate Lewis acids that strongly bind two σ donor ligands L in the donor–acceptor complexes L→E←L. Tetrylones EL2 are divalent E(0) compounds which possess two lone pairs at E. The unique electronic structure of tetrylones (carbones, silylones, germylones, stannylones, plumbylones) clearly distinguishes them from tetrylenes ER2 (carbenes, silylenes, germylenes, stannylenes, plumbylenes) which have electron-sharing bonds R–E–R and only one lone pair at atom E. The different electronic structures of tetrylones and tetrylenes are revealed by charge- and energy decomposition analyses and they become obvious experimentally by a distinctively different chemical reactivity. The unusual structures and chemical behaviour of tetrylones EL2 can be understood in terms of the donor–acceptor interactions L→E←L. Tetrylones are potential donor ligands in main group compounds and transition metal complexes which are experimentally not yet known. The review also introduces theoretical studies of transition metal complexes [TM]–E which carry naked tetrele atoms E = C–Sn as ligands. The bonding analyses suggest that the group-14 atoms bind in the 3P reference state to the transition metal in a combination of σ and π∥ electron-sharing bonds TM–E and π⊥ backdonation TM→E. The unique bonding situation of the tetrele complexes [TM]–E makes them suitable ligands in adducts with Lewis acids. Theoretical studies of [TM]–E→W(CO)5 predict that such species may becomes synthesized.

/pdf/new-bonding-modes-of-carbon-and-heavier-group-14-atoms-si-pb-pw8hfvaupq.pdf

New bonding modes of carbon and heavier group 14 atoms Si–Pb

The nuclear magnetic resonance properties of chromium, molybdenum and tungsten compounds

Bis[bis(trimethylsiiyl)methyl]tin, SnR2, has an extensive chemistry, behaving as (i) a Lewis base, (ii) a Lewis acid, or (iii) undergoing oxidative addition (insertion reactions). The following complexes have been isolated, many as well characterised crystals. For class (i), these include (M = Cr or Mo)[M(CO)5(SnR2)], trans-[M(CO)4-(SnR2)2], [Fe2(η-C5H5)2(CO)3(SnR2)], [RhCl(PPh3)2(SnR2)], and [PtCl(PEt3)(SnR2)(SnR2Cl)]: for class (ii), the readily thermally-dissociable 1 : 1 adducts with pyridine, 4-methylpyridine, or piperidine, and for class (iii), SnR2(A)B (AB = HCl,HF, MeI, RCl, Cl2, Br, O2, CH2:CMeCMe:CH2, [Mo(η-C5H5)(CO)3X](X = H or Me), [Fe(η-C5H5)(CO)2X](X = Cl or Me), [{Fe(CO)4}2]. and [PtCl2(PEt3)(SnR2)]). An interesting feature is the appearance in the 1H n.m.r. spectra of doublets characteristic of diastereotopicallv distinct SiMe3 groups in compounds of the form SnR2(A)B (A ≠ B). The complex [Mo(CO)5(PbR2)] has also been obtained.

Subvalent Group 4B metal alkyls and amides. Part II. The chemistry and properties of bis[bis(trimethylsilyl)methyl]tin(II) and its lead analogue

The reactions of acetonitrile solutions of copper(I) chloride, CuCl, and copper(I) bromide, CuBr, with the sterically hindered, highly basic tertiary phosphine ligand tris(2,4,6-trimethoxyphenyl)phosphine ({equivalent to}P(2,4,6){sub 3}) have been shown to form 1:1 monomeric adducts, (P(2,4,5){sub 3}CuX). The two compounds are isomorphous, crystallizing in the tetragonal space group P4{sub 3}. For the chloride, a = 15.237 (4) {angstrom}, c = 12.373 (3) {angstrom}, Z = 4, and R = 0.029 for 2339 observed (I {ge} 3{sigma}(I)) reflections, while for the bromide, a = 15.312 (8) {angstrom}, c = 12.457 (6) {angstrom}, Z = 4, and R = 0.052 for 2148 observed reflections. Cu-P is 2.177 (1) {angstrom} and Cu-Cl is 2.118 (2) {angstrom} in the chloro compound; for the bromide, Cu-P is 2.197 (3) {angstrom} and Cu-Br is 2.259 (2) {angstrom}. In both complexes, the copper atom is displaced toward the nearest o-methoxy oxygen with Cu{hor ellipsis}O = 2.629 (4) (Cl) and 2.628 (7) {angstrom} (Br); P-Cu-X angles are 172.97 (6) (Cl) and 172.00 (9){degree} (Br). Far-infrared spectra show expected strong {nu}(Cu-Cl) and {nu}(Cu-Br) bands at 355 and 262 cm{sup {minus}1}, respectively. Strong bands in the range 90-100 cm{sup {minus}1} are assigned to {delta}(P-Cu-X) bending modes. No bands assignable to {nu}(Cu-P)more » modes were observable. The solid-state {sup 31}P NMR spectrum of the ligand is characterized by a single line at -73 ppm (with respect to 85% H{sub 3}PO{sub 4}). The spectrum for each complex shows an asymmetric quartet centered at -65 ppm with highly asymmetric line spacings of 1.40, 2.21, and 2.50 kHz and 1.48, 2.17, and 2.43 kHz, respectively. These data have been used to estimate copper nuclear quadrupole coupling constants for the two compounds. 20 refs., 5 figs., 4 tabs.« less

Solid-state sup 31 P NMR, far-IR, and structural studies on two-coordinate (tris(2,4,6-trimethoxyphenyl)phosphine)copper(I) chloride and bromide

Mossbauer spectra of SnR2[R = CH(SiMe3)2] and of 16 of its derivatives have been recorded. The latter fall into two classes: (i) the dialkylstannylene complexes such as [Cr(CO)5(SnR2)] in which bivalent Sn is three-co-ordinate: and (ii) dialkylstannylene insertion products into C–X, M–H, M–Cl, M–Me, or M–M bonds (M = a transition metal, X = halogen) such as [Fe(η-C5H5)(CO)2(SnR2Cl)], in which quadrivalent tin is four-co-ordinate. The compound SnR2 and class (i) complexes are characterised by isomer shifts of 2.15 ± 0.1 mm s–1 relative to BaSnO3 and large quadrupole splittings [2.31 (for SnR2) or 4.25 ± 0.2 mm s–1 for class (i)]. Class (ii) complexes show lower isomer shifts (1.49 ± 0.25 mm s–1) and quadrupole splittings (<2.37 mm s–1). Magnetic Mossbauer measurements on SnR2 and [Cr(CO)5(SnR2)] show that for both complexes the sign of the quadrupole coupling constant eQVzz, is negative and hence Vzz the principal component of the field gradient tensor, is positive.

John D. Cotton

Papers

Subvalent Group 4B metal alkyls and amides. Part II. The chemistry and properties of bis[bis(trimethylsilyl)methyl]tin(II) and its lead analogue

Solid-state sup 31 P NMR, far-IR, and structural studies on two-coordinate (tris(2,4,6-trimethoxyphenyl)phosphine)copper(I) chloride and bromide

Subvalent Group 4B metal alkyls and amides. Part III Mössbauer spectroscopy studies of bis[bis(trimethylsilyl)methyl]tin(II) and its derivatives

Substituent effects in dimethylsulfoxide-promoted carbon monoxide insertion into iron-alkyl bonds

Alkyl substituent effects in ligand-induced carbon monoxide insertion reactions in [(η5-C5H5)(CO)3Mo(benzyl)] systems