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Abstract Tethered tungsten‐alkylidenes bearing azoimido ligands (M≡N_γ‐N_β=N_αR) are synthesized, characterized, and tested as initiators for ring expansion metathesis polymerization (REMP). While these ligands are typically unstable and prone to dinitrogen loss, this work demonstrates that tethered alkylidene complexes bearing azoimido ligands are stable enough to be REMP initiators. Moreover, they are more efficient, long‐lived, and stereoselective than their corresponding imido derivatives (M≡NR). Density Functional Theory (DFT) analysis of the azoimido complexes provides insight into their unusual stability. 

Abstract Reported here is the synthesis and self‐assembly characterization of [n.n]paracyclophanes ([n.n]pCps,n=2, 3) equipped with anilide hydrogen bonding units. These molecules differ from previous self‐assembling [n.n]paracyclophanes ([n.n]pCps) in the connectivity of their amide hydrogen bonding units (C‐centered/carboxamide vs.N‐centered/anilide). This subtle change results in a ≈30‐fold increase in the elongation constant for the[2.2]pCp‐4,7,12,15‐tetraanilide ([2.2]pCpNTA) compared to previously reported[2.2]pCp‐4,7,12,15‐tetracarboxamide ([2.2]pCpTA), and a ≈300‐fold increase in the elongation constant for the[3.3]pCp‐5,8,14,17‐tetraanilide ([3.3]pCpNTA) compared to previously reported[3.3]pCp‐5,8,14,17‐tetracarboxamide ([3.3]pCpTA). The[n.n]pCpNTAmonomers also represent the reversal of a previously reported trend in solution‐phase assembly strength when comparing[2.2]pCpTAand[3.3]pCpTAmonomers. The origins of the assembly differences are geometric changes in the association between[n.n]pCpNTAmonomers—revealed by computations and X‐ray crystallography—resulting in a more favorable slipped stacking of the intermolecular π‐surfaces ([n.n]pCpNTAvs.[n.n]pCpTA), and a more complementary H‐bonding geometry ([3.3]pCpNTAvs.[2.2]pCpNTA).