Recent developments in multiple bonding between heavier main group atoms are the focus of this review. Emphasis is placed on compounds with homonuclear bonds. It is clear that the Group 15 derivatives REER (E = P, As, Sb or Bi; R = alkyl or aryl ligand) display double bonding throughout the group. For the Group 14 species R2EER2 (E = Si, Ge, Sn or Pb, R = organo or related group), it is argued that, at present, only the silicon and certain germanium derivatives merit designation as ‘dimetallenes’. Data for multiply bonded heavier Group 13 compounds are currently very scarce. Nonetheless, the available structures of compounds such as (MR)n (M = Al, Ga, In or Tl; R = alkyl or aryl group; n = 1—6) indicate weakness of the M—M interaction especially for the gallium, indium and thallium compounds where monomeric species are obtained readily. The M—M bond order in the dimers RMMR is apparently less than 1 but can be increased by reduction to give [RMMR]2– but it is probable that the overall M—M bond order remains less than 2.

Homonuclear multiple bonding in heavier main group elements

Organotitanium reagents in organic synthesis a simple means to adjust reactivity and selectivity of carbanions

Organometallic compounds display a wide variety of non-classical bonding interactions largely as a result of the ability of the π-electrons of organic groups to form covalent bonds with d-block transition metals. Photoelectron spectroscopy has proved an invaluable tool in confirming and extending ideas on the nature of these interactions. Studies reported are all on gas phase species for which detailed information on the valence electrons may be obtained. Relative intensity changes observed on varying the ionizing radiation between He (1) and He (11) are of considerable assistance in assigning photoelectron bands and in providing information on the localization of the molecular orbitals from which the associated electrons are ionized. Most assignments are discussed in relation to simple, qualitative molecular orbital schemes. Comparisons are made between bonding of different metals and different organic groups. Particular emphasis is placed, where information is available, on the differences between d- and f-block metals in this class of compounds. The detailed understanding which has resulted from a combination of photoelectron spectroscopy and theoretical studies in this area has led to reliable models which should prove useful to the experimental chemist.

Gas phase photoelectron spectra of d- and f-block organometallic compounds

The coordination chemistry of bivalent group IV donors

This paper reports significant dependence of ion-pair formation energetics and stereomutation rates upon the metal-bound alkyl substituent (R) and the solvent dielectric constant in the metallocenium series (1,2-Me2Cp)2MR+ MeB(C6F5)3- where R = Me, CH2tBu, CH2TMS, CH(TMS)2, and M = Zr and Hf, as determined by reaction titration calorimetry and dynamic NMR spectroscopy. For the ion-pair forming reaction, (1,2-Me2Cp)2M(R)Me + B(C6F5)3 → (1,2-Me2Cp)2MR+ MeB(C6F5)3-, enthalpies in toluene solution at 25 °C for M = Zr and R = Me, CH2TMS, and CH(TMS)2 are −24.6(0.8), −22.6(1.0), and −59.2(1.4) kcal/mol, respectively. Corresponding values for M = Hf and R = Me and CH2TMS are −20.8(0.5) and −31.1(1.6) kcal/mol, respectively. ΔH‡reorg values for the reorganization process that interchanges the ion-pair enantiotopic sites for M = Zr and R = Me, CH2tBu, CH2TMS, and CH(TMS)2 are 22(1), 18(1), 17(1), and 9(2) kcal/mol, respectively. Corresponding ΔH‡reorg values for M = Hf and R = Me, CH2tBu, and CH2TMS are >24, 12(3)...

Metal-Alkyl Group Effects on the Thermodynamic Stability and Stereochemical Mobility of B(C6F5)3-Derived Zr and Hf Metallocenium Ion-Pairs

Bonding studies of compounds of boron and the group IV element

Bonding studies of compounds of boron and the group IV elements : X. Photoelectron spectra of compounds Me4M (MC, Si, Ge, Sn, or Pb) and the lack of participation of M d-orbitals

J.B. Pedley

Papers

Bonding studies of compounds of boron and the group IV element

Bonding studies of compounds of boron and the group IV elements : X. Photoelectron spectra of compounds Me4M (MC, Si, Ge, Sn, or Pb) and the lack of participation of M d-orbitals

Bonding studies of transition metal complexes

Bonding studies of compounds of boron and the group IV elements

Photoelectron spectra and energy level trends in MenSiCl4-nand related series.