Disproportionation of Bis(phosphaethenyl)pyridine Iron(I) Bromide Induced by tBuNC

Redox behavior of Fe­(I) complexes bearing a PNP-pincer-type phosphaalkene ligand, 2,6-bis­[1-phenyl-2-(2,4,6-tri-tert-butylphenyl)-2-phosphaethenyl]­pyridine (BPEP-Ph), is reported. The four-coordinate Fe­(I) complex [FeBr­(BPEP-Ph)] (1) readily reacts with 1 equiv of tBuNC in toluene at −35 °C to give [FeBr­(tBuNC)­(BPEP-Ph)] (2) with a 17e configuration. Complex 2 is fairly stable in neat benzene at room temperature, but smoothly undergoes disproportionation in the presence of added tBuNC to afford the Fe(0) complex [Fe­(tBuNC)2(BPEP-Ph)] (3) and the Fe­(II) complex [FeBr2(tBuNC)4] (4) along with free BPEP-Ph. The single-crystal X-ray diffraction studies of 3 and 4 reveal distorted trigonal bipyramidal and square pyramidal arrangements around Fe, respectively. The yield of 3 increases up to 50%/2 when 2 equiv of tBuNC is added to the system. A disproportionation process involving a 19e intermediate is proposed.