Reactivity Study of Pyridyl‐Substituted 1‐Metalla‐2,5‐diaza‐cyclopenta‐2,4‐dienes of Group 4 Metallocenes

Abstract

In this work the reactivity of 1-metalla-2,5-diaza-cyclopenta-2,4-dienes of group 4 metallocenes, especially of the pyridyl-substituted examples, towards small molecules is investigated. The addition of H2 , CO2 , Ph-C≡N, 2-py-C≡N, 1,3-dicyanobenzene or 2,6-dicyanopyridine results in exchange reactions, which are accompanied by the elimination of a nitrile. For CO2 , a coordination to the five-membered cycle occurs in case of Cp*2 Zr(N=C(2-py)-C(2-py)=N). A 1,4-diaza-buta-1,3-diene complex is formed by H-transfer in the conversion of the analogous titanocene compound with CH3 -C≡N, PhCH2 -C≡N or acetone. For CH3 -C≡N a coupling product of three acetonitrile molecules is established additionally. In order to split off the metallocene from the coupled nitriles, we examined reactions with HCl, PhPCl2 , PhPSCl2 and SOCl2 . In the last case, the respective thiadiazole oxides and the metallocene dichlorides were obtained. A subsequent reaction produced thiadiazoles.

Recent Synthetic and Catalytic Applications of Group 4 Metallocene Bis(trimethylsilyl)acetylene Complexes

“…This type of coupling reaction was extended to 2,6‐dicyanopyridine, [108a] and very recently by Reiß, Beweries and co‐workers to other heteroatom containing aromatic nitriles such as 2‐cyanofuran as well as 2‐cyanothiophene in homo‐ and heterocoupling reactions by using Cp* 2 M(η 2 ‐btmsa) (M = Ti, Zr). [108b] With adiponitrile as an example for an alkyldinitrile and Cp* 2 Ti(η 2 ‐btmsa) by protonation a trinuclear diazadiene complex was formed …”

“…It is important to distinguish these complexes from afore described multinuclear group 4 metallocene complexes with N ‐containing bridged ligands which exist in different types. The first group contains bridging neutral ligands like 4,4′‐bipyridine or pyrazine and the second group possesses bridging units that are generated by C‐C coupling with or without C‐H bond activation (Scheme ) , , , . The third family consists of e.g.…”

A second polymorph of 3,4-bis(6-bromopyridin-3-yl)-1,2,5-thiadiazole

“…The title compound was formed by the reaction of SOCl 2 with [Ti(C 5 Me 5 ) 2 (N=C(R)-C(R)=N)] (R = 6-Br-3-py), as the coupling product of two molecules of 2-bromo-5cyanopyridine at [Ti(C 5 Me 5 ) 2 ] (Becker et al, 2016). Triclinic (P1) and monoclinic (C2/c) polymorphs of the title compound were observed, the triclinic one being presented here (Fig.…”

“…Molecular structure of the monoclinic polymorph of 3,4-bis(6-bromopyridin-3-yl)-1,2,5-thiadiazole with displacement ellipsoids drawn at the 50% probability level. [Symmetry code: added via syringe and the mixture was warmed to 60 C for 7 d. Upon cooling to ambient temperature, yellow crystals formed (Becker et al, 2016).…”

Activation of Molecular Hydrogen by Bis(η5 ,η1 -pentafulvene)-titanium Complexes - Efficient Formation of Titanium(III)hydrides

“…Generally, group 4 metal hydrides are compounds of great interest due to their application as reagents for the synthesis of various organic compounds, as intermediates in olefin hydrogenation or catalysts for asymmetric hydrogenation of imines . Common synthetic routes for such compounds are the hydrogenation of the corresponding precursor complexes, reaction of group 4 dihalide compounds with hydride sources like LiAlH 4 or exchange reactions of halide precursors with silanes . The most simple titanocene hydride complex was synthesized by Bercaw and Brintzinger via hydrogenolysis of Cp 2 TiMe 2 and elimination of methane.…”