MONOARSENIC, DIARSENIC AND MIXED PHOSPHORUS-ARSENIC SUBSTITUTED NIOBOCENES

Arsenic monobromides BrAsR2 (R = Me, Et) insert easily into the Nb-H b ond of [Cp2NbH3] affording the ionic complexes [Cp2NbH2(HAsR2)]Br (R = Et (la), Me (Ib)). Deprotonation of la produces the dihydridarsenido derivative [Cp2NbH2(AsEt2)] (2a) cleanly and in high yield (93%), wher eas deprotonation of Ib gives the expected [Cp2NbH2(AsMe2)] (2b) toget her with a considerable amount of [Cp2NbH3]. Reaction of (AsEt2)(2) wi th [Cp2NbBH4] in the presence of NEt3 results in the formation of comp lexes [Cp2Nb(HAsEt2)(BH3AsEt2)] (6) and [Cp2NbH2(BH3AsEt2)] (7). It wa s found that NEt3 is a catalyst of this reaction. The orange complex [ Cp2Nb(HAsEt2)(HPi-Pr2)]Br (9) was prepared by the reaction of BrAsEt2 with [Cp2NbH(HPi-Pr2)]. Deprotonation of 9 affords the phosphinoarseni do complex [Cp2Nb(AsEt2)(HPPr2-i)] (10). The molecular structure of 6 was found from an X-ray structure determination (C) 1997 Elsevier Scie nce S.A.