David R. Neithamer

(Silox)3Nb(η2-N,C-4-picoline) as a source of (silox)3Nb: structure of [(silox)3Nb]2(μ-η2,η2-C6H6) (silox=tBu3SiO)

Abstract Electrochemical and chemical reductions of (silox) 3 NbCl 2 ( 1 , −1.42 V versus Ag/Ag + ) and (silox) 3 TaCl 2 ( 2 , −2.18 V) generated [(silox) 3 NbCl 2 ] − ( 1 − ) and [(silox) 3 TaCl 2 ] − ( 2 − ). The anions were subject to Cl − loss, leading to (silox) 3 NbCl ( 3 ) and probable disproportionation (Ta). Complex 3 formed reversible solvent adducts (silox) 3 ClNbL ( 3 -L, L=THF, py). Na/Hg reduction of (silox) 3 NbCl 2 ( 1 ) in the presence of 4-picoline afforded (silox) 3 Nb(η 2 -N,C-4-NC 5 H 4 CH 3 ) ( 6 ), which can be considered a source of ‘(silox) 3 Nb’, analagous to (silox) 3 Ta ( 4 ). Adducts such as (silox) 3 Nb(η 2 -H 2 CCHR) (R=H, 7 ; Ph, 8 ) may be formed upon addition of olefins, and 6 abstracted an oxygen from N 2 O, NO or ethylene oxide to give (silox) 3 NbO ( 9 ) and N 2 or C 2 H 4 , respectively, which are reactions also observed for 4 . 4-Picoline may be abstracted from 6 by 4 to give {(silox) 3 Nb} 2 (μ:η 2 ,η 2 -C 6 H 6 ) ( 11 ) and (silox) 3 Ta(η 2 -N,C-4-NC 5 H 4 CH 3 ) ( 12 ). An X-ray structure determination of 11 revealed a disordered bridge that was modeled as a μ:η 2 ,η 2 -benzene. Extended Huckel molecular orbital (EHMO) calculations showed that the μ:η 2 ,η 2 -configuration was energetically better than a μ:η 6 ,η 6 -alternative, but about the same as a plausible μ:η 3 ,η 3 -arrangement.