Synthesis, characterization and reactivity of soluble oxo-chalcogenoniobates.

Synthesis, characterization and reactivity of soluble oxo-chalcogenoniobates is reported. Base-assisted C-S bond cleavage as a synthetic tool is reported in the conversion of $\rm(PPh\sb4)\lbrack Nb(S)\sb2(S\sp{t}Bu)\sb2\rbrack,$ 1. to $\rm(PPh\sb4)\sb2\lbrack Nb(S)\sb3S\sp{t}Bu\rbrack,$ 2. Substitution reactions of $\rm\lbrack Nb(S)\sb3S\sp{t}Bu\rbrack\sp{2-}$ with MeOH or H$\sb2$O lead to the tetrahedral $\rm(PPh\sb4)\sb2\lbrack Nb(S)\sb3OMe\rbrack,$ 3, and the linear oxo-bridged dimer, with idealized $\rm D\sb{3d}$ symmetry, $\rm(Et\sb4N)\sb4\lbrack (S)\sb3Nb$-O-Nb(S)$\sb3\rbrack,$ 4 respectively. Protonation of 2 or reaction of 3 or 4 with $\rm(Me\sb3Si)\sb2S$ leads to an apparent thermodynamic sink, the known $\rm C\sb{5v}$ cage cluster, $\rm\lbrack Nb\sb6S\sb{17}\rbrack\sp{4-}.$ The pentagonal pyramidal anion, $\rm\lbrack Nb(O)(S\sb2)\sb2SH\rbrack\sp{2-}$ isolated as a $\rm(Et\sb4N)\sp+$ salt, 5 or 6, a PPh$\sb4\sp+$ salt is reported also. The metal is displaced by 0.70 A from the pentagonal plane of the two $(\eta\sp2$-S$\sb2)$ and the SH ligands towards the apical oxo ligand. Dimeric $\rm(Et\sb4N)\sb3\lbrack(S\sb2)Nb(S)(\mu$-SH)($\mu$-$\eta\sp1,\eta\sp2$-$\rm S\sb2)\sb2Nb(S)(S\sb2)\rbrack,$ 7, is obtained by sulfidation of 5. The metal centers are bridged by a $(\mu$-SH) and two $(\mu$-$\eta\sp2,\eta\sp1$-S$\sb2)$ ligands. Abstraction of oxygen and sulfur from 6 by PEt$\sb3$ gives the protonated tetrathioniobate derivative, $\rm(PPh\sb4)\sb2\lbrack Nb(S)\sb3SH\rbrack,$ 8. The anion in 8, has D$\sb2$d symmetry with two long Nb=S bonds associated with the proton at 2.312 (1) A. Use of (Et$\sb4$N)CN instead, resulted in the mixed valence, $\rm\lbrack(S)\sb2Nb(\mu$-S, $\mu$-$\rm SH)Nb(S)\sb2CN\rbrack\sp{4-}$ anion 9. In 9, the distorted tetrahedral anion in 8 is found chelating the proposed $\rm\lbrack Nb\sp{(III)}(S)\sb2CN\rbrack\sp{2-}$ fragment through the longer pair of bonds associated with the proton, to give a distorted pentagonal bipyramidal geometry at the latter center. Efforts to make molecules containing the (NbOS) $\sp+$ chromophore from $\rm\lbrack NbOCl\sb5\rbrack\sp{2-},$ 10, and $\rm\lbrack NbO(S\sp{t}Bu)\sb4\rbrack\sp-,$ 11 are also reported. The complex, 5 reacts with HCl to give 10 and the blue, $\rm\lbrack(S\sb2)Nb(O)(S\sb2)\rbrack\sp-$ anion. $\rm\lbrack(S\sb2)Nb(O)(S\sb2)\rbrack\sp-$ reacts with $\rm(Et\sb4N)\sb2MNT$ and NaS(S)C-N(Et)$\sb2\cdot$3H$\sb2$O, to give respectively the dimeric, $\rm(Et\sb4N)\sb4\{\lbrack(MNT)\sb2Nb\sp{(IV)}\rbrack\sb2(\mu$-$\rm\eta\sp2,\eta\sp2S\sb2)\sb2\},$ 12 and the pentagonal bipyramidal $\rm(Et\sb4N)\lbrack(dtc)\sb2Nb(O)(S\sb2)\rbrack,$ 13. In 13, which is obtained in better yield by the oxidation of 5 with tetraethylthiuram disulfide, one of the dtc ligands coordinates both an axial and an equatorial site. The exact selenoniobate analogs of 4, (17); 5, (14); 6, (15) and 8 are also reported. Reaction of 14 with Se in a 1:2 ratio gives the dimeric, $\{$ ((Se$\sb2)\sb2$Nb(O)) $\sb2(\mu$-Se$\sb4)\} \sp{4-},$ 16. In 16 the square pyramidal subunits, ((Se$\sb2)\sb2$Nb(O)) $\sp-$ are bridged by a $\mu$-Se$\sb4$ to give a pentagonal pyramidal geometry at each center.PhDInorganic chemistryPure SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/130775/2/9811139.pd