A general route to sandwich and half-sandwich titanium imido complexes: X-ray structure of [Ti(η⁴-Me₈taa)(NBu^t)](Me₄taa = tetramethyldibenzotetraaza[14]annulene)

Abstract

The readily available complex [Ti(NB~t)Cl~(Butpy)~] (Butpy = 4-tert-butylpyridine) is a useful precursor to a range of sandwich-and half-sandwich titanium imido derivatives including [Ti(q-C9H4Me3) (NBut)CI(Butpy)] (C9H4Me3 = trimethylindenyl), [Ti(q-C5H5)2(NBuf)(Butpy)], [Ti(dm bpz)(NBuf)CI(Butpy)] [dmbpz = tris(3,5-dimethylpyrazolyl) borate] and [Ti(r14-Me,taa)(NBut)l { n = 4 or 8; Met4 or 8)taa = (tetra-or octa-)methyl-dibenzotetraaza[l4]annulene respectively}. Much of the current interest in transition metal-ligand multiple bonds has focused on the early transition metals.1-5 Reactive group 4 imido transients such as Bergman's [Zr(q5-CSH5)2(NBut)] ,2 and Wolczanski's [zr(B~t~SiNH)~(NSiBut~)l and [Ti(B~t~SiO)~(NSiBut~)13 have demonstrated a rich chemistry including [2 + 21 cycloadditions and alkane and arene C-H bond activations. Group 4 metal-ligand multiply-bonded complexes which have reactive M=E functionalities yet are sufficiently kinetically stable to be isolated are rare. The few examples include the monomeric oxo-and sulfido-derivatives [Ti(q4-Me4taa)(E)] (Me4taa = tetramethyldibenzotetraaza[l4]annulene; E = 0, S), first reported by Goedken in 1982.4 The first fully characterised monomeric titanium imido complexes were first reported as late as 1990 by Roesky and Rothwell.5 We describe here the synthesis of monomeric h R = H 3 2bR=Me \. / 1 4

Di-μ-chlorido-bis[dichlorido(N,N-diethylacetamidinato)(N,N-diethylacetamidine)titanium(IV)] acetonitrile disolvate

“…This can be attributed to electrostatic repulsion caused by substantial pi-electron donation from the diethylacetamidino nitrogen to the empty 3 d orbitals on Ti 4+ . The approximately linear Ti-N1-C1 bond angle (165.7 (2)°) and the short Ti-N1 bond length (1.751 (2) Å) indicate significant Ti-N1 multiple-bond character analogous to those observed in titanium(IV) imides (Guiducci et al, 2001;Lewkebandara et al, 1994;Dunn et al, 1994).…”

“…For the structure, see: Dunn et al (1994); Guiducci et al (2001); Lewkebandara et al (1994); Nielson et al (2001). For the reaction mechanism, see: Bradley & Ganorkar (1968); Chandra et al (1970); Forsberg et al (1987); Maresca et al (1986); Rouschias & Wilkinson (1968).…”

The Progression of Synthetic Strategies to Assemble Titanium Complexes Bearing the Terminal Imide Group

“…The use of excess H 2 NtBu promotes dehydrohalogenation to form the Ti À NHtBu linkage and the ammonium salt [H 3 NtBu][Cl], while the donor ligands (e.g, pyridine, phosphine oxides) likely play several roles such as displacement of the metal-bound amine, a-hydrogen deprotonation, and formation of the titanium imide monomer. Winters seminal work has demonstrated that the presence of a Lewis base such as O=PPh 3 is critical in these reactions, since it prevented formation of the amide-amine oligomers [{TiCl 2 - [36] Mountford [5,[65][66][67] also applied an analogous strategy, generating the terminal imide group by using other donors such as pyridine, monoamines, N,N,N',N'-tetramethyl-ethylenediamine (TMEDA), among many others. Such an approach is practical given the availability of the starting materials, TiCl 4 and H 2 NtBu, and the ability to produce the corresponding titanium tert-butyl imide in multigram quantities for subsequent reactions.…”

“…Winter's seminal work has demonstrated that the presence of a Lewis base such as OPPh 3 is critical in these reactions, since it prevented formation of the amide–amine oligomers [{TiCl 2 (NH t Bu) 2 (NH 2 t Bu) 0–2 } n ] 36. Mountford5, 65–67 also applied an analogous strategy, generating the terminal imide group by using other donors such as pyridine, monoamines, N , N , N ′, N ′‐tetramethyl‐ethylenediamine (TMEDA), among many others. Such an approach is practical given the availability of the starting materials, TiCl 4 and H 2 N t Bu, and the ability to produce the corresponding titanium tert ‐butyl imide in multigram quantities for subsequent reactions.…”

Synthesis and structural characterization of a fully conjugated macrocyclic tetraaza(14)-membered Schiff base and its bivalent metal complexes

“…The chemistry of macrocyclic complexes has received much attention in recent years on account of its various applications in bioinorganic chemistry [2,3]. Transition metal complexes with macrocyclic ligands are well known for their enhanced kinetic and thermodynamic stability [4][5][6][7][8][9][10][11][12][13][14]. Many tetradentate Schiff bases are known to stabilize unusual oxidation states of the coordinated metal [15][16][17][18][19].…”