Metal-mediated coupling of amino acid esters with isocyanides leading to new chiral acyclic aminocarbene complexes

Abstract

Metal-mediated coupling between equimolar amounts of cis-[PdCl₂(CNR¹)₂] (1–5) and the amino acid esters L-HTyrOMe (7) or L-HProOtBu (8) proceeds at 40 °C in chloroform over ca. 6 h. The subsequent workup affords the complexes cis-[PdCl₂(CNR¹){C(TyrOMe)NHR¹}] (R¹ = Xyl 9, 2-Cl-6-Me-C₆H₃10) or cis-[PdCl₂(CNR¹){C(ProOtBu)NHR¹}] (R¹ = Xyl 11, 2-Cl-6-Me-C₆H₃12, Cy 13, tBu 14, 2-naphthyl 15) in good to excellent isolated yields (75–94%). The corresponding reaction between trans-[PdI₂(CNR¹)₂] (6) and 8 brings about the formation of trans-[PdI₂(CNCy){C(ProOtBu)NHCy}] (16, 76% isolated yield). The reaction of 6 with 7 proceeds non-selectively giving a broad mixture of products. Complexes 9–16 were characterized by elemental analyses (C, H, N), ESI^+/−-MS, IR, 1D (¹H, ¹³C{H}) and 2D (¹H,¹H-COSY, ¹H,¹³C-HMQC/¹H,¹³C-HSQC, ¹H,¹³C-HMBC) NMR spectroscopic techniques, and by single-crystal X-ray diffraction (for 9, 11–13, and 16).