CC Insertion over NCO of Allyl Isocyanate into the GeSi Bond of a Germylene

Two isocyanates are reacted with the germylene, PhC(N t Bu) 2 Ge‐Si(SiMe 3 ) 3 ( 1 ). Phenyl isocyanate undergoes catalytic cyclotrimerization with 1 leading to 1,3,5‐triphenyl isocyanurate ( 2 ), while allyl isocyanate undergoes both cyclotrimerization and the CC bond insertion between the GeSi bond. The constitution of 3 is determined by single‐crystal X‐ray studies. The contrasting reactivity pattern is explained by comprehensive density functional theory studies.