Ligand Mediated Metal‐Metal and Metal‐Ligand Cooperativity in Cesium Coordination Polymers and its Beneficial Role in the ROP of Cyclic Esters

Designing a multimetallic catalyst based on the principle of metalloenzymes has emerged as a promising route to enhance catalytic performance owing to the combined action of different metal centers in a cooperative fashion. The cooperativity of metal centers with the surrounding ligand environment in metalloenzymes plays a crucial role in driving efficient catalysis. However, the replication of such cooperativity in a synthetic system is very challenging. In this work, we report the synthesis and characterization of diverse cesium coordination polymeric networks, a 2D sheet, [Cs{κ 2 ‐C 4 H 3 N‐2(CH = N(2,6‐ i Pr 2 C 6 H 3 ))}] ∞ ( 1 ), an infinite ladder chain, [Cs{κ 3 ‐C 4 H 3 N‐2(CH = N(CHPh 2 ))}] ∞ ( 2 ), and a 3D cage [Cs 2 {κ 3 ‐(C 4 H 3 N‐2(CH = NCH 2 CH 2 N(CH 2 CH 2 ) 2 O))}] ∞ ( 3 ). This was accomplished by a variation of the substituent on the iminopyrrolyl ligand. Moreover, we studied a breakdown of the 2D sheet coordination polymer ( 1 ) into contact pair monomeric cesium complex [(18‐Cr‐6)Cs(κ 2 ‐C 4 H 3 N‐2(CH = N(2,6‐ i Pr 2 C 6 H 3 )))] ( 4 ). In the coordination polymers, multiple Cs centers are held together within a proximal distance (3.5–6 Å) via an iminopyrrolyl ligand. The Cs coordination polymer 2 displays the highest catalytic efficiency in ring opening polymerization of rac ‐lactide (ROP), giving a turnover frequency (TOF) value of 49.5 h −1 compared to 15.7 h −1 and 24.0 h −1 for 1 and 3 . The higher reactivity of 2 in comparison to 1 and 3 is due to the metal‐metal cooperativity in cesium coordination polymeric networks.