New studies on the reactivity of hydride-containing niobocene complexes towards insertion and protonation processes

The trihydride complex [Nb(eta(5)-C5H4SiMe3)(2)(H)(3)] (1) reacts with diph enylphosphane to afford the monohydride [Nb(eta(5)-C5H4SiMe3)(2)(H)(PHPh2)] (3). The synthesis of complex 3 has also been achieved from the initial fo rmation of the phosphonium salt [Nb(eta(5)-C5H4SiMe3)(2)(H)(2)(PHPh2)]Cl (2 ) by reaction of the trihydride complex [Nb(eta(5)-C5H4SiMe3)(2)(H)(3)] (1) with chlorodiphenylphosphane, followed by deprotonation of this salt in aq ueous NaOH. Protonation of complex 3 at low temperature with a slight exces s of CF3COOH or CF3COOD leads to the eta(2)-dihydrogen complex [Nb(eta(5)-C 5H4SiMe3)(2)(eta(2)-H-2)(PHPh2)]CF3CO2 (4) or its monodeuterated isotopomer [Nb(eta(5)-C5H4SiMe3)(2)(eta(2)-HD)(PHPh2)]CF3CO2 (5). When the temperatur e is increased to room temperature, complexes 4 and 5 transform into the tr ansoid dihydrides [Nb(eta(5)-C5H4Si-Me-3)(2)(H)(2)(PHPh2)]CF3CO2 (6) and [N b(eta(5)-C5H4SiMe3)(2)(H)(2)-(PDPh2)]CF3CO2 (7), respectively. Complex 3 un dergoes an insertion of CS2 into the niobium-hydrogen bond to give the eta( 1)-dithioformato complex [Nb(eta(5)-C5H4SiMe3)(2)(PHPh2)(eta(1)-S-S(S)CH)] (8). This complex could be detected by NMR spectroscopy but could not be is olated due to rapid conversion into the eta(2)-dithioformato complex [Nb(et a(5)-C5H4SiMe3)(2)(eta(2)-S,S-SSCH)] (9) by loss of the phosphane molecule. Complex 3 also reacts with CO2 to give the eta(2)-formato complex [Nb(eta( 5)-C5H4SiMe3)(2)(eta(2)-O,O-OOCH)] (10); in this case the eta(1)-formato co mplex could not be detected. The reagent ClPPh2 very smoothly inserts into the Nb-H bond of the complexes [Nb(eta(5)-C5H4SiMe3)(2)(H)(L)] [L = PHPh2, CN(xylyl), CO; xylyl = 2,6-dimethylphenyl], yielding the new ionic complexe s [Nb(eta(5)-C5H4SiMe3)(2)(PHPh2) (L)]Cl [L = PHPh2 (11), CN(xylyl) (12), C O (13)]. All the complexes described have been characterized by analytical and spectroscopic methods.