Transition Metal Complexes with Sterically Demanding Ligands. 2.¹ Meisenheimer Complex Formation and Deprotonation Reactions of a Sterically Demanding Aromatic Diimine

Abstract

The synthesis of the novel diimine 1 is described, and its low/absent propensity for the complexation of group 9 transition metals (Co, Rh, Ir) is rationalized by a potentially difficult C-H activation step required for terdentate coordination. To overcome this problem, deprotonation of this unique C-H bond in 1 with a variety of bases was attempted. The unexpected outcome of these reactions, including the formation of the Meisenheimer complex 3 by addition of butyllithium, is reported. In addition, the formation of the double-addition product 4 through reaction with t-BuLi is described. Deprotonation at the diimine methyl group with the hard base lithium dimethylamide gives the corresponding diketiminate 5. The structures of the novel compounds 1 and 3-5 were unambiguously confirmed by X-ray crystal structure analyses.

Metal–Ligand Electron Transfer in 4d and 5d Group 9 Transition Metal Complexes with Pyridine, Diimine Ligands

“…[9] Nevertheless, the electrochemistry of PhDI and its formation of stable Meisenheimer complexes upon (nucleophilic) addition of butyllithium to the phenyl ring in PhDI clearly established the electron-deficient character of the aromatic system. [10] For pyridine congeners of PhDI even more pronounced electron acceptor properties were therefore anticipated, that is, ideally suited for the accommodation of a metal oxo/nitrido unit. Nearly coincidental with our findings for the PhDI phenyl system, the pyridine, diimine ligand experienced a renaissance initiated by the independent discovery of cobalt-and iron-based olefin polymerization catalysts by the groups of Gibson [11] and Brookhart.…”

“…[31] Here n denotes the number contributed from the d electrons, an additional electron stems from the NO ligand. For the nitrosyl complexes with a neutral PDI ligand a {MNO} 10 The linear binding mode of the M-NO unit observed in the X-ray crystal structure of the nitrosyl ligand might be taken as a first hint for a positively charged NO + ligand, although this older criteria is clearly outdated. [28,31,33,34,35] Currently, charges of +1, -1, and -3 for the linear and -1 and -3 for the bent M-NO binding modes are considered.…”

Energetic Descriptors of Steric Hindrance in Real Space: An Improved IQA Picture**

“…Since then, steric congestion along with strain effects have been claimed to be the driving force of a wide variety of phenomena ranging from classic textbook examples of reactivity [8][9][10] to state-of-the-art developments in supra-molecular chemistry. [11][12][13] Some phenomena where SH has been invoked to play a major role include: the origin of the rotational barriers of alkanes and other derivatives, [14][15][16][17] the stability of conformers of cycloalkanes and macrocycles, [18,19] the ligand ability towards metal centers, [20,21] the trends in the reactivity of nucleophilic substitution and elimination reactions, [22,23] the torsional barriers of biphenyls and their optically active derivatives, [24] the reactions between tertiary amines and boron derivatives, [25] the geometrical features of methyl like radicals, [26] the stability of cis-trans isomers, [27] the competition between the basicity and nucleophilicity of nucleophiles and the stereopreference and the selectivity of the active site of enzymes or organic catalysts, [28] among others.…”

Synthesis, characterization of the dilithium bis-azaallyl complex [CH 2 C(NAr)C(NAr) CH 2 ]Li 2 (THF) 4 and its catalytic activity for the anionic polymerization of methyl methacrylate

“…The Li-N bond distances of 1.935 (7) and 1.913 (7) A indicate it to be an amidic structure. The structural character of the Li-N bond is similar to that in the analogue complexes Li{N(Ar)C(R)C[N(Ar)]@ C(H)Ph}(TMEN) [5], {1,3-[2,6-i Pr 2 C 6 H 3 NC(@CH 2 )] 2 -C 6 H 4 }Li 2 (DME) [6], and [{2,6-(SiMe 3 )NC(Bu t )CH} 2 -C 5 H 3 N][Li 2 (THF) 2 ] [7].…”