We report a modular approach to synthesise zwitterionic phosphorus analogues of cyclobutadienyl ligands in the coordination sphere of 3d transition metals. Specifically, cationic manganese and cobalt complexes featuring η 4 ‐coordinated, onium‐substituted LL′C 2 P 2 ligands L, L′ = PPh 3, IPr (1, 3‐bis (2, 6‐diisopropyl‐phenyl) imidazolium−2‐ylidene) were accessed via reaction of halogenated phosphorus cycles RR’C 2 (PX) 2 (X = Cl, Br) with the corresponding carbonyl metalates. Here, the choice of the substituents L, L′ allows for precise control of the steric environment while retaining exceptional π‐donating properties exceeding those of C 5 H 5 −. Furthermore, the carbonyl ligands serve as versatile entry points for further derivatization, as demonstrated by the light‐driven formation of the 2, 3‐dimethylbutadiene (DMB) complex Co η 4 ‐DMB η 4 ‐ (PPh 3) 2 C 2 P 2 OTf and the acetonitrile complex Mn (CO) 2 (MeCN) η 4 ‐ (PPh 3) 2 C 2 P 2 OTf.
Frei et al. (Sun,) studied this question.