TERMINAL VS BRIDGING IMIDO LIGATION IN COMPLEXES OF ZIRCONIUM(IV) AND HAFNIUM(IV) - STRUCTURAL CHARACTERIZATION OF A MU-[ETA-1(N)-ETA-2(N,C)] IMIDO LIGAND

The reaction of 4 equiv of LiNHAr (Ar = 2,6-C6H3iPr2) with a solution of ZrCl4(THF)2 in THF/pyridine yields Zr(=NAr)(NHAr)2(py)2 (1) in high yield. Zr(=NAr)(NHAr)2(py)2 reacts with 1 and 2 equiv of Me3SiCl in THF/pyridine to provide Zr(=NAr)(NHAr)Cl(py)2 (2) and Zr(=NAr)Cl2(py)3 (3), respectively. ZrCl4(THF)2 reacts with 4 equiv of LiNHAr, followed by 2 equiv of Me3SiCl (in THF), to afford Zr(=NAr)Cl2(THF)2 (4) in a high-yield, one-pot synthesis. Hf(=NAr)Cl2(THF)2 (5) is prepared similarly. Zr(=NAr)(NHAr)Cl(py) 2 reacts with 1 equiv of K[N(SiMe3)2] in THF to provide Zr(=NAr)(NHAr)[N(SiMe3)2](py)2 (6), which could not be converted into-a bis(imido) species. Both Hf(=NAr)Cl2(THF)2 and Zr(=NAr)Cl2(THF)2 react with K2(C8H8) to provide [(eta-8-C8H8)Zr(=NAr)]2 (7) and [(eta-8-C8H8)Hf(=NAr)]2 (8) in high yield. Zr(=NAr)Cl2(THF)2 reacts with 1 equiv of Li(C5H4Me) in THF to provide [(eta-5-C5H4Me)Zr(=NAr)Cl]2 (9) in moderate yield. An X-ray structural determination of this compound reveals a dimeric structure with bridging imido ligands. [(eta-5-C5H4Me)Zr(=NAr))Cl]2 (9) crystallizes in the orthorhombic space group Pbca with a = 16.591 (1) angstrom, b = 20.173 (2) angstrom, c = 21.469 (2) angstrom, and V = 7185 (1) angstrom3 with Z = 8 and rho(calcd) = 1.41 g cm-3. This complex exhibits an unusual (mu-[eta-1(N):eta-2(N,C)]) imido ligand in which C(ipso) of the mu-NAr ligand is within bonding distance of one of the Zr atoms. (eta-5C5Me5)ZrCl3 reacts with 3 equiv of LiNHAr in THF to provide the imide-amide-amine complex (eta-5-C5Me5)Zr(=NAr)(NHAr)(NH2Ar)(THF)(10) in high yield. Complex 10 reacts with pyridine to form dimeric [(eta-5-C5Me5)Zr(=NAr)(NHAr)(py)]2 (11). When (eta-5-C5Me5)ZrCl3 reacts with 3 equiv of LiNHAr (in THF/pyridine), followed by the addition of 1 equiv of Me3SiCl, golden yellow crystals of (eta-5-C5Me5)Zr(=NAr)Cl(py)2 (12) are formed in high yield. Complex 12 crystallizes in the monoclinic space group P2(1)/n with a = 10.827 (5) angstrom, b = 16.687 (5) angstrom, c = 17.631 (9) agnstrom, beta = 101.04 (5)-degrees, and V = 3126.6 (2) angstrom3 with Z = 4 and rho(calcd) = 1.26 g cm-3. In the solid state, this compound is characterized by a Zr-N distance of 1.876 (4) angstrom and Zr-N-C(ipso) angle of 164.5 (3)-degrees.