Synthesis and Structures of TiIII and TiIV Complexes Supported by a Bulky Guanidinate Ligand

In this work, titanium complexes of the bidentate bulky guanidine ligand [{(Dip)N}2CNR2]H (where Dip = C6H3iPr2-2,6 and R = CH(CH3)2) (LH) were prepared. Reaction of LH with one equivalent of [(CH3)2NTiCl3] underwent amine elimination to afford the monomeric complex [LTiCl3] (1) in high yield. Attempts to reduce 1 with potassium graphite (KC8) in tetrahydrofuran (THF) were unsuccessful. However, reacting 1 with 3.3 equivalents of KC8 in hexane led to the first example of structurally characterized mono-guanidinate ligand stabilized dimeric TiIII complex [LTiCl(μ–Cl)]2 (2). The synthesized complexes were characterized by NMR spectroscopy and the structures were further confirmed by X-ray crystallography.

Probing the factors that influence the conformation of a guanidinato ligand in [(η5-C5Me5)M(NN)X] (NN = chelating N,N′,N′′-tri(o-substituted aryl)guanidinate(1−); X = chloro, azido and triazolato)

The conformational difference illustrated is ascribed to a subtle repulsive interaction between the o-Cl substituent of two proximal aryl rings in the guanidinate ligand.

Low-valent Iron Complexes Stabilised by a Bulky Guanidinate Ligand: Synthesis and Reactivity Studies

A toluene-capped guanidinato iron(i) complex [(Pipiso)Fe(η6-toluene)] (Pipiso = [(DipN)2C(cis-NC5H8Me2-2,6)]–) was prepared by magnesium metal reduction of {[(Pipiso)FeII(µ-Br)]2} in toluene. The reactivity of the closely related FeI–FeI multiply bonded species, {[Fe(μ-Pipiso)]2} towards a range of unsaturated small molecule substrates was investigated, and found to be broadly similar to that of low-valent β-diketiminato iron complexes. That is, its reaction with CO yielded the iron(i) carbonyl complex [(Pipiso)Fe(CO)3], whereas reaction with CO2 formed the same product via an apparent reductive disproportionation of the substrate. In contrast, reaction between {[Fe(μ-Pipiso)]2} and CS2 led to reductive C=S bond cleavage and the isolation of {[(Pipiso)Fe]2(μ-S)(μ-CS)}. Different reactivity was seen with AdN3 (Ad = 1-adamantyl), which was reductively coupled by the iron(i) dimer to give iron(ii) hexaazenyl complex {[(Pipiso)Fe]2(μ-AdN6Ad)}.