Tris bridging

Reactions leading to a series of remarkable dizirconium alkyls and hydrides are outlined in Scheme 213. In solution, the tetrahydride undergoes a rapid fluxional process (observed by NMR spectroscopy) that exchanges the four hydrides. At low temperature three distinct hydrides can be observed, which is consistent with either a dibridged structure, or a tri-bridged species undergoing... 

J. Baschnagel K. Binder P, Doruker A. A. Gusev O. Hahn K. Kremer W. L. Mattice E Miiller-Plathe M. Murat W. Paul S. Santos - U. W. Suter V. Tries Bridging the Gap Between Atomistic and Coarse-Grained Models of Polymers Status and Perspectives... 

The instability of [10] annulene is caused by steric factors, as demonstrated by E. Vogel when he synthesized bridged [10]- and [14]annulenes with naph-thalenic and anthracenic peripheries, respectively,34 and by V. Boekelheide with bis- or tris-bridged [14]-annulenes with a pyrenic periphery.35... 

M. Histome, N. Watanabe, T. Sakamoto, K. Yamakawa, Organometallic compounds. XXIII. Formation of novel di- and tri-bridged ferrocenophanes. J. Organomet. Chem. 1977, 125, 79-93. 

The first approach to the formation of a ditopic cavitand complex has been reported by Sorrell et al. [56]. They identified the tri-bridged resorcinarene as a... 

Direct arylation of methyl imidazole with 2,7-dichloronaphthyridine leads to a potentially tetradentate and practically tridentate bis-carbene ligand on a naphthyridine scaffold [363]. Reaction of the bis-imidazolium salt with silver(l) oxide in the usual way yields a linear trinuclear silver carbene complex with this tris-bridging hgand (see Figure 3.115). 

J. Baschnagel, K. Binder, P. Doruker, A. A. Gusev, O. Hahn, K. Kremer,W. L. Mattice, F. Muller-Plathe,M. Murat, W. Paul, S. Santos, U. W. Suter, andV. Tries, Bridging the gap between atomistic andcoarse-grainedmodelsofpolymers Status andperspectives,H[Pg.125]

Tri-bridged resorcinarene 5, prepared in 54% yield by reaction of the corresponding resorcinarene with CH2BrCl in DMSO, could be selectively debrominated at two of the four aromatic rings by treatment with 5 equiv of /z-BuLi at -70 °C for 15 seconds... 

Schmidbaur andSchier [3a] distinguish semi-supported, supported, and unsupported interactions. Figure 11.16. Supported interactions are not limited to two-coordinate gold, but tri-bridged cases with three-coordinate gold are rare. Recent activity in dinuclear gold chemistry is animated by potential applications in catalysis, film deposition, and luminescence. Selected developments of broad interest are considered here. 

The fission and formation of a variety of mono-, di, and tri-bridged di-cobalt(III) complexes will be discussed in this section, in this order. At the end comparison will be made with a cobalt(III)-iron(II) system, very closely related in that again both metal ions are low-spin centers. 

Silver nitrate potassium tert-butoxide Intramolecular C-alkylation of ketones Tris-bridged cyclophanes... 

First, we optimized the synthesis of tri-bridged diol 3 by variation of the reaction conditions, temperature (and the reaction time), solvent, and amount of CHaBrCl. These reactions were carried out with octols with different side chains (Ri). The results are summarized in Table IV. 

One of the first things that becomes clear from the data in Table IV is that reactions run at 70°C (entries 2, 6, 7, 10, 12 and 14-16) generally give higher overall yields than the corresponding reactions at room temperature (entries 1,5,8, 9,11 and 13). With respect to the formation of tri-bridged diol 3 there is a marked difference between the solvents DMF (entries 4, 11, 12, 15 and 16) and DMSO (entries 1-3,5-10,13 and 14). 

In DMSO the reaction temperature has hardly any influence. Both at room temperature and at 70°C the tri-bridged diol 3 is formed as the main product, regardless of the amount of excess CH2BrCl used. The introduction of the fourth bridge took place, to some extent, only in the case of octol la (entry 2). This result is quite surprising, because DMSO is one of the best solvents for S//2 reactions [36]. 

These results show that the optimum reaction conditions for the formation of tri-bridged diols 3 are (a) reaction at 70°C for 3 days in DMSO with excess CH2BrCl or (b) in DMF with 4 equiv. of CH2B1CI comparable results can be obtained by reaction at room temperature in DMF of DMSO with excess CH2B1CI for 8 days. 

When the lithiated product, obtained by reaction of 3d with n-BuLi, was quenched with B(OMe>3, we were able to isolate tri-bridged diol 8c functionalized at the 8- and 12-positions with hydroxyl groups in 47% yield. In the same way, starting from 3c, two thiomethyl (8d) or iodo (8e) groups could be intro-... 

The different aromatic rings in the tri-bridged diols (3) exhibit different reactivities. Bromo-lithium exchange of two bromo substituents with n-BuLi provides an easy way to selectively functionalized cavitands of type 8. After incorporation of the fourth bridge, the remaining two bromines can be substituted for a variety of functional groups, leading to selectively functionalized cavitands 9c-h. 

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