Ligand‐Controlled Formation of a Low‐Valent Pincer Rhodium(I)–Dioxygen Adduct Bearing a Very Short OO Bond

Treatment of [{Me 2 C 6 H(CH 2 P t Bu 2 ) 2 }Rh( η 1 ‐N 2 )] ( 1a ) with molecular oxygen (O 2 ) resulted in almost quantitative formation of the dioxygen adduct [{Me 2 C 6 H(CH 2 P t Bu 2 ) 2 }Rh( η 2 ‐O 2 )] ( 2a ). An X‐ray diffraction study of 2a revealed the shortest OO bond reported for RhO 2 complexes, indicating the formation of a Rh I O 2 adduct, rather than a cyclic Rh III η 2 ‐peroxo complex. The coordination of the O 2 ligand in 2a was shown to be reversible. Treatment of 2a with CO gas yielded almost quantitatively the corresponding carbonyl complex [{Me 2 C 6 H(CH 2 P t Bu 2 ) 2 }Rh(CO)] ( 3a ). Surprisingly, treatment of the structurally very similar pincer complex [{C 6 H 3 (CH 2 P i Pr 2 ) 2 )}Rh( η 1 ‐N 2 )] ( 1b ) with O 2 led to partial decomposition, with no dioxygen adduct being observed.