Bulky bis-guanidine ligand-based neutral and cationic zinc alkyl, halide, and hydride complexes: synthesis, characterization, and catalytic application.

The tetra-aryl substituted bis-guanidine ligand L(3H) (L(3H) = {(ArHN)(ArNH)-CN-C=(NAr)(NHAr)}; Ar = 2,6-iPr2-C6H3) was used for the synthesis of mononuclear zinc(II) alkyl [L(2H)ZnR, R = Me (Zn-1), Et (Zn-2)], iodide [L(2H)ZnI, (Zn-3)], and hydride [L(2H)ZnH, (Zn-4)] complexes. Moreover, the reactions of Zn-1, Zn-2, and Zn-3 with [PhNMe2H]+ [B(C6F5)4]- yielded the biguanide zinc alkyl [L(3H)ZnR]+ [B(C6F5)4]- (R = Me (Zn-5), Et (Zn-6)) and iodide [L(3H)ZnI]+ [B(C6F5)4]- (Zn-7) cationic compounds in good yields. All newly isolated and thermally stable zinc complexes (Zn-1-Zn-7) were well characterized by multinuclear NMR (1H, 13C{1H}, with additional 11B and 19F{1H} for Zn-5-Zn-7), HRMS, and single crystal X-ray diffraction studies. Moreover, the well-defined zinc iodide cation (Zn-7) [L(3H)ZnI]+ [B(C6F5)4]- was further used as a catalyst for the synthesis of cyanohydrin enol ether products (RCR'CNOSiMe3) by TMSCN addition to carbonyl compounds (RCOR', R' = alkyl/aryl) under mild reaction conditions.