4-COORDINATE GROUP-14 ELEMENTS IN THE FORMAL OXIDATION-STATE OF ZERO - SYNTHESES, STRUCTURES, AND DYNAMICS OF [((CO)(5)CR)(2)SN(L-2)] AND RELATED SPECIES

The sodium salts Na-2[{(CO)(5)M}(2)EX2] (M = Cr, Mo, W; E = Ge, Sn, Pb ; X = Cl, I, OOCCH3) react with 2,2'-bipyridine (bipy) to form neutral compounds [{(CO)(5)M}(2)E(bipy)] (E = Sn: la-lc; E = Ge: 3a; E = Pb: 4). 1,10-Phenanthroline (phen) analogues of compounds la-le and 3a [{( CO)(5)M}(2)E(phen)] (E = Sn: Id-if, E = Ge: 3b) are as well accessible . The 2,2'-bipyridine ligand in 1 may be formally replaced by two pyri dine (py) ligands resulting in [{(CO)(5)M}(2)Sn(py)(2)] (Ig: M = Cr, I h: M = W). The bis-bidentate ligand 2,2'-bipyrimidine (bpmd) is found to coordinate just one [{(CO)(5)M}(2)Sn] entity in [{(CO)(5)M}(2)Sn(bp md)] (2b: M = Cr, 2c: M = W). The biimidazolato (biim) ligand binds tw o [{(CO)(5)Cr}(2)Sn] moieties in [{(CO)(5)Cr}(2)Sn(biim)Sn{Cr(CO)(5)}( 2)](2-), 2a. It is shown by H-1-NMR that the pyrimidine entities in th ese compounds (2b, 2c) are able to rotate by a full 180 degrees turn-a round with respect to one another. This process must involve complete de-coordination of at least one of the two nitrogen donors in again at least one of the chelate cycles, the activation energy for this proce ss being around 60 kJ/mol. By Sn-119-NMR spectroscopy of almost all of the tin compounds described it is shown that equilibria between [{(CO )5M}(2)Sn(L)] and [{(CO)(5)M}(2)Sn(L)] + L exist in all cases. From th e temperature dependence of the delta values ii: is concluded that the activation barriers for this association/dissociation process is belo w 10 kJ/mol. The structures of all new compounds are documented by X-r ay analyses and all compounds are characterized by the usual analytica l and spectroscopical techniques.