PREPARATION AND PROPERTIES OF THE D(O) (ETA(5)-C(5)ME(5))TA(=NR)(2) FUNCTIONAL-GROUP

The reaction of 2 equiv of LiNHAr (Ar = 2,6-(C6H3Pr2)-Pr-i) with Cp*TaCl4 (Cp* = eta(5)-C(5)Me(5)) in THF affords the imido compound Cp*Ta(=NAr)Cl-2 (1). Upon reaction of Cp*TaCl4 with 4 equiv of LiNHAr in Et(2)O, the bis(imido) complex [Li(OEt(2))][Cp*Ta(=NAr)Cl] (2) is isolated. The THF adduct [Li(THF)][Cp*Ta(=NAr)(2)Cl] (3) is formed when this reaction is carried out in THF or when 1 is reacted with 2 equiv of LiNHAr in THF. [Li(OEt(2))][Cp*Ta(=NAr)(2)Cl] (2) crystallizes in the monoclinic space group P2(1)/n (No. 14) with a = 13.108(3) Angstrom, b = 17.998(5) Angstrom, c = 16.919(4) Angstrom, beta = 96.69(1)degrees, and V = 3964 (3) Angstrom(3) With Z = 4 and rho(calcd) = 1.31 g cm(-3). The molecular structure of 2 is characterized as containing a mu-[Li(OEt(2))](+) moiety bridging the imide nitrogens. In solution the imido ligands are equivalent with restricted rotation about Ta-N-C-ipso, implying an intact [Li(OEt(2))](+) bridge. Cp*Ta(=NAr)(NEt(2))Cl (5; prepared from Ta(=NAr)(NEt(2))Cl-2(THF)2 (4) and Li[C(5)Me(5)]) reacts with LiNHAr (in refluxing THF) to afford [Li(THF)] [Cp*Ta(=NAr)(2)Cl] (3) only very slowly.