Monoazadiene Complexes of Early Transition Metals. 2.¹ Syntheses and Structures of Titanium 1-Aza-1,3-diene Complexes and Their Reactions with Ketones

Abstract

The novel dark green or violet and air-sensitive 1-aza-1,3-diene titanocene complexes Cp2Ti[N(R1)CHC(R2)CH(Ph)] [R1 = t-Bu, R2 = H (7a); R1 = C6H4-4-Me, R2 = H (7b); R1 = c-C6H11, R2 = Me (7c)] were prepared by the complexation of the 1-aza-1,3-dienes 1a−c to the titanocene “Cp2Ti” generated in situ by reduction of Cp2TiCl2 with magnesium. The solid-state structure of 7c shows a bent azatitanacyclic ring with a fold angle of 130.9(4)°. A series of electron-deficient 14e 1-aza-1,3-diene titanium complexes CpTi[N(R1)CHC(Me)CH(Ph)]Cl [R1 = c-C6H11 (8a), t-Bu (8b), C6H4-2-Me (8c), C6H4-4-Me (8d)] has also been prepared by reduction of CpTiCl3 with magnesium in the presence of the 1-aza-1,3-dienes R1NCHC(Me)CH(Ph) 1c−f. These new complexes were isolated as air-sensitive brown (8a,b) or dark red (8c,d) crystals in 50−65% yield. The X-ray crystal structure of 8c revealed that the coordination geometry for the 1-aza-1,3-diene ligands has substantial σ2,π-η4-metallacyclopent-4-ene character. The 1-aza-1,3-diene complexes 8a,c,d only exhibit supine geometry as confirmed by 1H NMR spectroscopy, while 8b exists in both the conventional supine geometry and the prone geometry, which is demonstrated by quite different 1H NMR chemical shift values. Addition of 8c to 1 equiv of acetophenone gives the seven-membered metallacyclic ring system CpTi[N(C6H4-4-Me)CHC(Me)CH(Ph)C(Me)PhO] (9), whose structure has also been characterized by NMR spectral data and by X-ray diffraction analysis. In contrast to 8c, the 1-aza-1,3-diene titanocene complex Cp2Ti[N(c-C6H11)CHC(Me)CH(Ph)] (7c) does not react with acetophenone even at high temperatures.

Diene complexes of early transition metals: ideas and progresses at Osaka University

“…In case of azadiene complexes, we found some interesting C-C bond formation reactions of the ligand [106]. Prof. J. Scholz concurrently reported some interesting aza-and diazadiene complexes of early transition metals and their unique transformations [107][108][109][110][111][112][113][114][115][116].…”

From Five to Seven: Ring Expansion of Monoazadiene Titanium Complexes by Insertion of Aldehydes, Ketones and Nitriles

“…In the case of six‐membered rings, the formation of azatitanacyclohexadiene VIb is found in reaction of titanium imido species with two equivalents of acetylenes . Until now, only a few examples of seven‐membered azatitanacycles VIIc* resulting from insertion reactions of carbonyl compounds into azadiene titanium complexes are reported ,. In the case of Cp 2 Ti–azadiene complexes, no insertion reactions to seven‐membered rings are found.…”

Titanocene derivatives containing titanium–carbon σ-bonds

“…Thus its reduction by magnesium in the presence of Schiff's bases prepared from a,bunsaturated aldehydes yields titanazacyclopentenes 111. 198 Reduction of bis(pentamethylcyclopentadienyl)titanium dichloride by magnesium in the presence of 1,4-bis(trimethylsilyl)buta-1,3-diyne (112) results in the Z 3 -enyne complex 113. 199 Reduction of bis(trimethylsilyltetramethylcyclopentadienyl)titanium dichloride by magnesium in THF in the presence of bis(trimethylsilyl)acetylene gives…”