Halogen Bonding : An Odd Chemistry?

Halogen bonding is a flourishing field of research, but has for long been little recognized. The same goes for its scientific hero, Odd Hassel, who laid the foundations for all current developments. The crystallographic observation of halogen−oxygen interatomic distances shorter than the sum of the van der Waals radii of the involved atoms, and the interpretation of this phenomenon as a charge-transfer interaction, have been ground-breaking. Today, charge-transfer to a polarized halogen is not any longer seen as “odd”, but is commonly referred to as halogen bonding, and is widely exploited in chemistry. Despite the recognition of Hassel's work with a Nobel prize in 1969, surprisingly little appreciation is given to date to the devoted scientist, who established a world-leading laboratory during one of the darkest eras of history. Herein, we wish to revive the legacy and highlight the impact of Odd Hassel's ground-breaking discoveries

Cleave and capture chemistry illustrated through bimetallic-induced fragmentation of tetrahydrofuran

The cleavage of ethers is commonly encountered in organometallic chemistry though rarely studied in the context of newly emerging bimetallic reagents. Recently it was reported that a bimetallic sodium-zinc base can deprotonate cyclic tetrahydrofuran (THF) under mild conditions without opening its heterocyclic (OC4) ring. In marked contrast to this synergic sedation, herein we show that switching to more reactive sodium-magnesium or sodium-manganese bases promotes cleavage of at least six bonds in THF, but the ring fragments are uniquely captured in separate crystalline complexes. Oxide fragments occupy guest positions in bimetallic inverse crown ethers and C4 fragments ultimately appear in bimetallated butadiene molecules. These results demonstrate the special synergic reactivity that can be executed by bimetallic reagents, including the ability to capture and control and thereby study reactive fragments from sensitive substrates

Conformational analysis of 1,4-disilabutane and 1,5-disilapentane by combined application of gas-phase electron diffraction and ab initio calculations and the crystal structure of 1,5-disilapentane at low temperatures

Mitzel NW, Smart BA, Blake AJ, Robertson HE, Rankin DWH. Conformational analysis of 1,4-disilabutane and 1,5-disilapentane by combined application of gas-phase electron diffraction and ab initio calculations and the crystal structure of 1,5-disilapentane at low temperatures. JOURNAL OF PHYSICAL CHEMISTRY. 1996;100(22):9339-9347.The gas-phase structures of the conformers of 1,4-disilabutane and 1,5-disilapentane have been analyzed from electron-diffraction data augmented by flexible restraints derived from ab initio calculations. This allowed the simultaneous refinement of 22 and 29 parameters for 1,4-disilabutane and 1,5-disilapentane, respectively. 1,4-Disilabutane has been found to be present in the vapour predominantly in the anti (A) form (76(2)% from the experiment, 83% predicted by theory). Consistency in the geometries is found between theoretical predictions and experimental findings, except for the torsion angle angle(SiCCSi) of the gauche (G) conformer [exptl 78.5(21)degrees, theor 68.0 degrees]. The AA conformer of 1,5-disilapentane was always found to be the lowest energy structure, while some doubt still remains about the ordering of the AG and G(+)G(-) conformers. The AA conformer is found to be the sole form present in the crystal [C2/c, a = 15.585(8), b = 4.704(3), c = 9.895(6) Angstrom, beta = 95.77(4)degrees, Z = 4]. Good agreement is found for geometrical parameters determined experimentally in the gas phase and solid state and calculated by nb initio methods. The following values represent the most important distances (r(g)/Angstrom) and angles (angle(g)/deg) found for the gas phase and crystal structures. 1,4-Disilabutane GED (A/G, esd's correspond to 1 sigma): r(CSi) 1.882(1)/1.885(1), r(CC) 1.563(5)/1.563(5), r(SiH) both 1.499(3), angle(CCSi) 110.7(2)/114.4(5), angle(SiCCSi) 180.0/78.5(21). 1,5-Disilapentane GED [AA/G(+)G(-)]: r(CSi) 1.886(1)/1.888(1), r(CC) 1.537(2)/1.539(2), r(SiH) both 1.487(4), angle(CCC)114.8(7)/118.8(7), angle(CCSi)114.1(4)/116.8(7), angle(SiCCC) 180.0/60.9(10); X [%, AA/AG/G(+)G(-)] 28(4)/40(5)/26(6). 1,5-Disilapentane XRD: r(CSi) 1.868(2), r(CC) 1.527(2), angle(CCC) 113.8(2), angle(CCSi) 115.2(1), angle(siCCC) 180.0(1)