Titanium and Zirconium Complexes Containing a Novel Dianionic Trifunctional Amido Ligand

Abstract

The novel tridentate diamidoamine ligands [RC(2-C5H4N)(CH2NSiMe,),l2~ (R = H, CH3) have been synthesized and coordinated to TiIV and ZrIV giving the pentacoordi- [~] have been studied in most detail. While they have enabled the stabilization of otherwise elusive molecular stuctures and offered the possiblity to investigate their reactivity, the scope of their use is limited. This warrants continuing efforts in the area of ligand design[9' and, given the results of the approach mentioned above, polyfunctional derivatives of amido systems are attractive candidates when early transition metals are involved.Our research has focussed on the metals of the titanium triad and the trianionic tripodal aniido ligands employed have generated nionofunctional MIv complexes, i.e. compounds in which one anionic ligand (such as a halide) may be substituted to yield derivatives. In order to study the chemistry of d<funcrionnZ compounds of the tetravalent metals, in which two anionic ligands may be displaced in subsequent conversions, it was necessary to develop dianionic amido ligands (Figure 1). This may be achieved in a trivial way by formal removal of an anionic "ligand arm" from the tripodal "claw" generating a simple chelate ligand of the type studied previously by Biirger~'"] and others. [111[121 If the tridentate nature of the ligand should, however, be retained, an anionic amido function may be formally replaced by a neutral tertiary amino group. This may be achieved most readily by incorporation of a pyridine ring into the ligand framework.We previously reported preliminary results related to the coordination of the type-A ligand [HC(2-C5H4N)(CH2NSiMe&I2-to titanium(IV), [13] however, the presence of the apical proton, which offers the possibilty of 1,2-eliminations in the ligand framework, renders the ligand precursors excedingly difficult to isolate and to handle. These difficulties were also encountered by Henrick and Tasker in their synthesis of late transition metal complexes containg the amine HC(2-C5H4N)(CH2NH2)2. [l41 In this paper we report the synthesis of a closely related ligand in which the apical position is occupied by a methyl group. The degradation pathway mentioned above therefore is avoided. Of particular intest was the degree to which the pyridyl-function participates in tlic coordination of the metal centre in amido complexes obtained with the potentially tridentate ligand. Results and Discussion A) Syntheses of the Amine Precursors for the Amido LigandsThe precursor material of a type-B ligand is the known 2-(2-pyridyl)propane-1,3-diamine which may be easily converted to the desired secondary amine 1 by silylation. However, as already indicated, the synthesis of this compound is complicated by its tendency (as well as its precursors) to undergo elimination.

Structural Patterns and Forms of Aggregation of Metallated Diamido Donor Ligands upon Going from Lithium to Thallium(I)

“…Ϫ The 1 H, 13 2 (1) were prepared as reported previously. [6] All other chemicals used as starting materials were obtained commercially and used without further purification.…”

“…After workup, two types of crystalline solid, 5 and 6, were obtained by cooling the pentane solution of the reaction product(s). Colourless crystals (5) were collected along with a deep orange crystalline solid (6) and were separated by hand. Whereas the orange product did not contain any lithium and was analyzed as the dithallium(I) diamide [(2-C 5 H 4 N)C(CH 3 ){CH 2 N(Tl)SiMe 3 } 2 ] 2 (6) the colourless product was found to be a mixed lithiumϪthallium amide and was formulated as [(2- (5).…”

“…[1,2] We recently reported the synthesis of a novel dianionic tripodal ligand in which two amido functions are combined with a neutral pyridyl unit. [5,6] This ligand system provides the key to stabilizing a whole range of early transition metal complexes, among these a series of imido complexes. [7,8] Whereas the role of this polydentate ligand in transition metal chemistry is clearly the protection of a large part of the coordination sphere around the metal centre and the masking of potentially accessible coordination sites by the displaceable neutral pyridyl function, the latter may play the part of a ''capping'' functionality in aggregates of its in two steps, yielding the mixed metal amide [(2-C 5 H 4 N)C(CH 3 ){CH 2 N(Li)SiMe 3 }{CH 2 N(Tl)SiMe 3 }] 2 (5) and the thallium(I) diamide [(2-C 5 H 4 N)C(CH 3 ){CH 2 N(Tl)-SiMe 3 } 2 ] 2 (6).…”

A Zirconium Hydrazide as a Synthon for a Metallanitrene Equivalent: Atom‐by‐Atom Assembly of [EN2]2− Units (E=S, Se) by Chalcogen‐Atom Transfer in the Coordination Sphere of a Transition Metal

“…We introduced a tridentate diamidopyridyl ligand [N 2 R N py ] 2À as a supporting ligand to stabilize early-transition-metal complexes containing reactive M=N bonds and their derivatives, [8] thus allowing, among other things, the isolation of key intermediates of the catalytic hydroamination of alkynes.…”

Iron(II) Complexes of Two Amine/Imine N5 Chelate Ligands Containing a 1,4‐Diazepane Core – To Crossover or Not To Crossover

“…[10] The generation of 3 from 1 requires the formal introduction of 1,2-ethylenediamine (en) by nucleophilic substitution. When this is attempted directly, the reaction is unspecific and proceeds, at least in part, with the intermolecular coupling of 1.…”