Neutral dimers

Fig. 11 a,b The neutral dimer formed by a two Cr(ri6-C6H5COO)2 molecules is compared with b the cationic chains formed by [CrI(rt6-C6H5COOH)2]+units in the [PF6]( ) salt... 

In general, two different kinds of iridium precursors are used. Isolated cationic [Ir(COD)2]A complexes and the in situ precursors formed from the neutral dimer [Ir(p-Cl)(COD)]2 by addition of the corresponding phosphorus ligand. 

Hydroxyl radicals were generated radiolytically in NaO-saturated aqueous solutions of thiourea and tetramethylthiourea. Conductometric detection showed that HO and a dimeric radical cation were produced. The dimeric radical cation is formed by addition of a primary radical to a molecule of thiourea. In basic solution, the dimeric radical cation decays rapidly to a dimeric radical anion, which is formed via neutralization of the cation and subsequent deprotonation of the neutral dimeric radical (Scheme 16). This was not observed in tetramethylurea. These dimeric radical cations of thiourea and tetramethylurea are strong oxidants and readily oxidize the superoxide radical, phenolate ion, and azide ion. 

Evidence for the existence of neutral dimers of oxygen on surfaces has been discussed earlier (Section II) and it is now appropriate to consider the corresponding anion, 04. Although a number of reports have been published on the existence of 04, very few present direct evidence for its identification. 

It is also practical to invoke a one-electron approximation in the FCD method [41] when one estimates donor and acceptor charges. Thus, one approximates the fragment charges of the radical cations [(G C),(AT)] and [(GC),(A+T)] via the corresponding Mulliken populations of the HOMO and HOMO-1 of the neutral dimer. Then, the charge on fragment / in [(G+C),(AT)] is... 

Only one paper has reported on catalytic asymmetric hydrogenation. In this study by Corma et al., the neutral dimeric duphos-gold(I)complex 332 was used to catalyze the asymmetric hydrogenation of alkenes and imines. The use of the gold complex increased the enantioselectivity achieved with other platinum or iridium catalysts and activity was very high in the reaction tested [195] (Figure 8.5). 

This is just what has been done with Ag2. A sputtering source followed by a phase-space compressor chamber provided a beam of cooled negative cluster ions of many sizes. From these, the dimers were selected, accumulated in a quadrupole trap, and photodetached with a femtosecond, titanium-sapphire laser. After photodetachment by a 60-fs pulse, the neutral dimers oscillate, causing corresponding oscillations in the ionization cross section, in turn generating the oscillations that dominate the intensity pattern in Fig. 11. This is a simple phenomenon, yielding in a simple way the... 

Lower yields of Na3[Mn(CO)4] were obtained from the direct reduction of Mn2(CO)10 in Na-HMPA, because the neutral dimer underwent slow disproportionation in this medium to form [Mn(HMPA)Jt][Mn(CO)5]2, in contrast to Re2(CO)10, which showed no tendency to react with HMPA at room temperature. Of all neutral binary carbonyl dimers known, Re2(CO)10 appears to be the most resistant toward Lewis base-promoted disproportionation reactions. The slightly lower yields of Na3[Re(CO)4], compared to those of Na3[Mn(CO)4], may have arisen from the fact that Re2(CO)10 does not cleanly reduce to [Re(CO)5] in HMPA or other solvents (22). It should... 

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