Tetraaza Macrocycles as Ancillary Ligands in Early Metal Alkyl Chemistry. Synthesis and Characterization of Out-of-Plane (Me4taen)ZrX2 (X = Alkyl, Benzyl, NMe2, Cl) and (Me4taen)ZrX2(NHMe2) (X = Cl, CCPh) Complexes

Abstract

The synthesis, properties, and structures of a series of out-of-plane (N4-macrocycle)ZrX2complexes incorporating the tetraaza macrocycle Me4taen2-are described ((Me4taen)H2 = 5,7,12,14-tetramethyl-1,4,8,11-tetraazacyclotetradeca-4,6,11,13-tetraene). Alkane elimination reactions of (Me4taen)H2(1) with ZrR4 yield (Me4taen)ZrR2 (2, R = CH2Ph; 3, R = CH2SiMe3). The amine elimination reaction of 1 with Zr(NMe2)4 yields (Me4taen)Zr(NMe2)2 (4). Protonolysis of 4 with [HNHMe2]Cl yields the seven-coordinate amine adduct (Me4taen)-ZrCl2(NHMe2) (5), which loses amine under vacuum (120 °C, 10 h) to afford base-free (Me4-taen)ZrCl2(6). The reaction of 4 with phenylacetylene yields the seven-coordinate bisacetylide complex (Me4taen)Zr(CCPh)2(NHMe2) (7). The reaction of 6 with RLi reagents in toluene yields (Me4taen)ZrR2 (8, R = CH2CMe3; 9, R = CH3). Halide displacement does not provide facile access to 6. Deprotonation of 1 yields [Li(THF)2[Me4taen] (10), which readily loses THF to yield Li2[Me4taen] (11); however, the reaction of 11 with ZrCl2(THF)2yields mixtures of 6 and (Me4taen)2Zr (12). Bismacrocycle complex 12 is formed in good yield via reaction of Zr(NMe2)4 with 2 equiv of 1. Dialkyls 2 and 9 rearrange thermally by migration of an alkyl group from Zr to a macrocycle imine carbon. The solid state structures of 1, 2, 4–6, and 10 have been determined. Compounds 1 and 10 exhibit rather planar Me4taen conformations. Dichloride 6 adopts a trigonal prismatic structure in which the chlorides occupy adjacent edge sites, and the Me4taen2- conformation is similar to that in 1 and 10. Dibenzyl complex 2 adopts a similar but more twisted trigonal prismatic structure. Bisamide complex 4 adopts a distorted octahedral structure in which the Me4taen2-ligand is significantly folded. These structural differences are rationalized in terms of the conformational preference of the Me4taen2-ligand, as deduced from the structures of 1 and 10, and the π-donating ability of the X group. Seven-coordinate complex 5 adopts a side-capped trigonal prismatic structure with a tripodal arrangement of chloride and amine ligands. The structures and properties of these new compounds are compared to those of CP2MX2 and other early metal analogues. © 1995, American Chemical Society. All rights reserved.