Stefano Stagni

The substituents in 2,6‐bis(2‐R‐2 H ‐tetrazol‐5‐yl)pyridyl neutral ligands R 2 btp (R=Me, t Bu) revealed a prominent effect when reacting with iron(II) salts, in combination with the nature of the anion. According to metal:ligand molar ratio, reaction of R 2 btp with FeCl 2 led to isolate [Fe II (R 2 btp‐κ 3 N,N’,N” ) 2 ](Fe III Cl 4 ) 2 , R=Me ( 1 a ) and t Bu ( 2 a ), where the octahedral iron(II) centres bring two tridentate ligands in mer coordination mode, but also [Fe II ( t Bu 2 btp‐κ 3 N,N’,N” )( t Bu 2 btp‐κ N ) 2 (H 2 O‐κ O )](Fe III Cl 4 ) 2 ( 2 b ), where one ligand is tridentate, while the other two coordinate the iron(II) through one tetrazolyl nitrogen atom, and the octahedral sphere is completed by one water molecule. In all cases, half of the iron ions are oxidised to iron(III) forming the paramagnetic tetrachloroferrato counterions. Reaction of t Bu 2 btp with Fe(ClO 4 ) 2 ⋅ 6H 2 O led to the octahedral [Fe II ( t Bu 2 btp‐κ 3 N,N’,N” ) 2 ](ClO 4 ) 2 ⋅ 4DCM ( 4 a ⋅ 4DCM), which shows solvent‐dependent spin crossover behaviour: while 4 a ⋅ 4DCM is blocked in the high spin state, its unsolvated form, 4 a , undergoes spin transition to low spin in two subsequent steps at 206 K, with opening of a 23‐K hysteresis ( T 1/2↓ =194 K, T 1/2↑ =217 K), and at 136 K ( T 1/2↓ =135 K, T 1/2↑ =137 K). The magnetic profile changes to an incomplete spin transition when the sample absorbs water molecules yielding 4 a ⋅ 1.5H 2 O.

A new family of ionic Ir(III) cyclometalated complexes with general formula [Ir(CN) 2 (NN)][Br], was designed and prepared to be assessed as photocalysts for the visible light assisted ATRP polymerization of MMA. To this purpose, our design strategy involved both: i) the decoration of the cyclometalating (CN) and the ancillary (NN) ligands with various electron withdrawing and/or electron donor substituents and, ii) the use of Br − as the counter anion for these cationic Ir(III) species. After an extensive screening in which the [Ir(CN) 2 (NN)][Br]‐type compounds were compared to the model neutral complex fac ‐[Ir(ppy) 3 ], the “fully” amino‐substituted ion pairs abbreviated as [10][Br] and [11][Br] , exhibited the best photocatalytic performances under irradiation with CFL lamps. It is worth noting that the outcomes of transient absorption spectroscopy (TAS) experiments combined with theoretical DFT calculations, enlightened the role played by the Ir(III) complexes in the mechanism of the photoATRP process, and suggested the rationalization of the different performances that were highlighted by our Ir(III) catalyst in the visible light assisted photopolymerization of MMA.