SYNTHESIS AND CHARACTERIZATION OF THE FIRST NIOBOCENE GERMYL COMPLEXES AND REACTIVITY OF TRIPHENYLSILYLNIOBOCENE, TRIPHENYLGERMYLNIOBOCENE,AND TRIPHENYLSTANNYLNIOBOCENE DERIVATIVES - X-RAY MOLECULAR-STRUCTURES OF D(0)NB(ETA(5)-C5H4SIME3)(2)(H)(2)(EPH3) (E=GE, SN)

Thermal treatment of Nb(eta(5)-C5H4SiMe3)2(H)3 (1) with the appropriat e organogermanium hydrides (HGeR3) and HSnPh3 gives the corresponding niobocene germyl hydrides Nb(eta(5)-C5H4SiMe3)(2)(H)(2)(GeR3), GeR3=Ge Ph3 (2), GePh2H (3), GeEt3 (4), Ge(C6H13)(3) (5), (GeAm3)-Am-i (Am-i = CH2CH2CH(CH3)(2)) (6), Ge(C6H13)(2)Cl (7), (GeAm2Cl)-Am-i (8), Ge(C6H 13)(2)H (9), (GeAm2H)-Am-i (10), and Nb(eta(5)-C5H4SiMe3)(2)(H)(2)(SnP h3) (11) in good yields. Spectroscopic data indicate the presence of o nly one of the two possible structural isomers in which the germyl or stannyl group is in the equatorial plane with a symmetrical structure. Reactivity studies on the series Nb(eta(5)-C5H4SiMe3)(2)(H)(2)(ER3), E = Si (12), Ge (2), Sn (11), were carried out. 12 reacts with H-2 to give 1, but 2 and 11 were unreactive toward this reagent. Furthermore, a similar behavior was observed with CO and CN(2,6-Me2C6H3). Thus, 12 reacts with these reagents to give rise, after elimination of HSiPh3, to Nb(eta(5)-C5H4SiMe3)(2)(H)(CO) and Nb(eta(5)-C5H4SiMe3)(2)(H)(CN(2 ,6-Me2C6H3)), respectively, while 2 and 11 do not react. Reactions of 12 with HGePh3 and HSnPh3 and of 2 with HSnPh3 gave sigma-bond metathe sis products, but no reactions were observed between 2 and HSiPh3 or b etween 11 and HSiPh3 or 11 and HGePh3. The kinetics of these processes have been studied by H-1 NMR spectroscopy and indicated the following reactivity trends Nb-SiPh3 > Nb-GePh3 > Nb-SnPh3 for the different pr ocesses considered. The X-ray molecular structures of 2 and 11 were es tablished by diffraction studies. The two isostructural complexes show a bent-sandwich coordination with the two hydrides flanking either si de of the Nb-Ge and Nb-Sn bonds (2.710(1), 2.830(1) Angstrom in 2 and 11, respectively).