Planar‐Chiral 1,1′‐Diiminoferrocenes [Fe{η⁵‐C₅H₃‐1‐(N=CHPh)‐2‐(C≡CAr)}{η⁵‐C₅H₄(N=CHPh)}] Containing a Bulky Ethynyl Substituent Adjacent to One of the Imino Groups

The planar‐chiral stannylated diaminoferrocene [Fe{η 5 ‐C 5 H 3 ‐1‐(Sn n Bu 3 )‐2‐(NH 2 )}{η 5 ‐C 5 H 4 (NH 2 )}] ( A ) and its diimine derivative [Fe{η 5 ‐C 5 H 3 ‐1‐(Sn n Bu 3 )‐2‐(N=CHPh)}{η 5 ‐C 5 H 4 (N=CHPh)}] ( B ) gave unsatisfactory results in attempts to achieve Stille cross‐coupling reactions with PhBr in the presence of [PdCl 2 (PPh 3 ) 2 ] or [Pd(PPh 3 ) 4 ]/CuO as catalysts. Analogous attempts aiming at the Stille cross‐coupling of the iodo derivative [Fe{η 5 ‐C 5 H 3 ‐1‐I‐2‐(N=CHPh)}{η 5 ‐C 5 H 4 (N=CHPh)}] ( C ) with PhSn n Bu 3 are equally fruitless, whereas Sonogashira cross‐coupling reactions of C are successfully performed with ethynylbenzene, ethynyl‐2,4,6‐trimethylbenzene, 4‐ethynyl‐1,1′‐biphenyl, 9‐ethynylphenanthrene, and 1‐ethynylpyrene, affording [Fe{η 5 ‐C 5 H 3 ‐1‐(N=CHPh)‐2‐(C≡CAr)}{η 5 ‐C 5 H 4 (N=CHPh)}] (Ar = phenyl, mesityl, 1,1′‐biphenyl‐4‐yl, 9‐phenanthryl, and 1‐pyrenyl for 1 , 2 , 3 , 4 , and 5 , respectively) in ≈60% yield under optimized conditions ( C /ArC≡CH/[Pd(P t Bu 3 ) 2 ]/CuI/N i Pr 2 Et = 1/4/0.5/3/40, toluene, 70 °C, 16 h). 4 (Ar = 9‐phenanthryl) is structurally characterized by single‐crystal X‐ray diffraction (XRD). The suitability of the diimines of this study for metal chelation is demonstrated by reactions with [PdCl 2 (MeCN) 2 ]. [PdCl 2 ( C )] and [PdCl 2 ( 5 )] are structurally characterized by XRD. The 1‐pyrenyl unit present in [PdCl 2 ( 5 )] effectively blocks one side of the N , N ‐chelated metal center by wall‐like steric shielding.