Group 13 elements Monochlorides

Similar to the reaction of zirconacyclopentadiene with main group dihalides EX2, the Cp2Ti unit in titanacyclopentadiene could also be replaced directly by main group elements to give five-membered heteroaromatic cycles. For example, titanacyclopentadiene 85, which was prepared by the homocoupling of 1,4-bis(trimethylsilyl)butadiyne, reacted with sulfur monochloride to give thiophene derivative 86 in a moderate yield, as shown in Scheme 11.33 [34]. 

A general strategy for the synthesis of 1,2-dithioles is the addition of two sulfur atoms to the CH = CH-CH- group also, non-ethylenic CH groups should be activated. Elemental sulfur is obviously the best reagent although sulfur monochloride is sometimes used. 

The reaction very likely proceeds through the disproportionation of 4-ethoxyphenyl tellurium monochloride to tellurium and the diaryl tellurium dichloride. Bis[trifluoromethyl] tellurium transferred its trifluoromethyl groups to iodine, sulfur, selenium, phosphorus, arsenic, and antimony on heating with the elements, sulfur dichloride, selenium tetrabromide, or the triiodides of phosphorus, arsenic, and antimony at 170 to 220° in sealed tubes3. 

Structure and bonding in the gaseous monochlorides, trichlorides and trimethyl derivatives of the Group 13 elements... 

Table 11.1. Gaseous, monomeric mono- and tri-chlorides of the Group 13 elements M-Cl bond distances, R (in pm), and bond energies, Dq or MBE (in kJ mol ). The Tl-Cl bond distance and the mean bond energy of TICI3 are unknown, presumably because of the low stability of the gaseous trichloride relative to the monochloride. Gaseous monomeric trimethyl derivatives M-C bond distances and mean bond energies. ...

The ground state valence electron configuration of the Group 13 elements is ns np. Formation of the first M-Cl bond may presumably take place without hybridization the M-Cl bonding orbital may be formed by combination of an unhybridized p orbital on M with a p orbital on the Cl atom. Such a description is in agreement with the observation that the M-Cl bond in the trichlorides of Al, Gaand In are shorter than in the monochlorides we have seen that sp-hybridization increases the electron density between the two bonded atoms. 

The electron-rich late transition elements are best suited for the formation of stable bonds to silicon. Therefore, most of the cyclosilanyl transition metal compounds described in the literature so far contain transition metals belonging to the groups 7-10. A few examples with early transition elements, however, are also known °. Cp2ZrCl2, for instance, reacts with KSieMen to give red crystals containing one cyclohexasilanyl and one chlorine substituent on the zirconium. The second chlorine atom can be easily replaced by treatment with MeLi. Addition of excess KSisMen to the monochloride, however, does not afford the dicyclosilanyl derivative (Scheme 27). 

The first four elements of Group 13 form trichlorides that are stable at normal temperatures and pressures. BCI3 is a volatile liquid at room temperature and monomeric in the gas phase. AICI3, GaCl3, and lnCl3 form solids at room temperature. Evaporation at moderate temperatures yields mixtures of monomeric and dimeric species. At higher temperatures aU the gaseous trichlorides suffer partial decomposition to form monochlorides and CI2 ... 

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