Zinc‐Mediated C–H Borylation of Terminal Alkynes: Mechanistic Insights

A three‐coordinate amido zinc (II) complex, [L 1 ZnN(SiMe 3 ) 2 ] ( Zn‐1 ), supported by a bis‐guanidinate ligand {L 1 = (ArHN)(ArN)─C═N─C═(NAr)(NHAr); Ar = 2,6‐Et 2 C 6 H 3 }, has been synthesized and structurally characterized, via NMR, high‐resolution mass spectrometry, and single‐crystal x‐ray diffraction analyses. Zn‐1 acts as an efficient pre‐catalyst for the C–H borylation of terminal alkynes, affording the corresponding alkynyl boronates in excellent yields. Comparative studies with a β‐diketiminate‐supported analogue [L 2 ZnN(SiMe 3 ) 2 ] ( Zn‐1′ ; L 2 = [CH‐{(CMe)(NAr)} 2 ]; Ar = 2,6‐Et 2 ‐C 6 H 3 ) revealed comparable catalytic activity, with Zn‐1 showing slightly higher conversion. The catalytically relevant new bis‐guanidinate zinc acetylide intermediate [L 1 Zn–C≡C–(4‐OMe–C 6 H 4 )] 2 ( Zn‐2 ) was isolated and fully characterized. Stoichiometric investigations support a plausible catalytic cycle. This study highlights the key role of bis‐guanidinate ligation in enhancing zinc‐mediated alkyne borylation reactivity.