Metallacyclopentadiene initiators for cyclic polymer synthesis from alkynes

A compound having a structure represented by formula (I) or formula (IV):

• wherein M is a transition metal;
• each R1 is independently H, C1-C20 alkyl, carboxyl, ester, amino, thiol, halo, C1-C22 haloalkyl, OH, or two adjacent R1, together with the carbon atoms to which they are attached, form a five- to eight-member cyclic group;
• R2 is selected from Ar1, C1-C22 alkyl, halo, C1-C22 haloalkyl, hydrogen, —NH2, —N—(C1-C22 alkyl)2, —NH(C1-C22 alkyl), —NHAr1, —NAr12, —O—Ar1, —O—(C1-C22 alkyl), and (R3)3—Si—;
• each R4 is independently C1-C22 alkyl or both R4 together with the carbon atom to which they are attached form a spiro five- to eight-member monocyclic group or a spiro eleven- to thirty-member polycyclic group;
• each R5 is independently H, C1-C22 alkyl, —NH2, —N—(C1-C22 alkyl)2, —NH(C1-C22 alkyl), —NHAr1, —NAr12, —O—Ar1, —OH, or —O—(C1-C22 alkyl);
• each n is independently 1, 2, 3, 4, or 5;
• each R6 is independently H, C1-C3 alkyl, halide, —NH2, —N—(C1-C3 alkyl)2, —NH(C1-C3 alkyl), —NHAr1, —NAr12, —O—Ar1, —O—(C1-C3 alkyl), —S—Ar1, —S—(C1-C3 alkyl);
• each R3 is independently selected from C1-C22 alkyl, Ar1, —O—(C1-C22 alkyl), —O—Ar1, —N(C1-C22 alkyl)2, —NH(C1-C22 alkyl), —NH2, or —NH—Ar1;
• A is selected from the group consisting of NH3, N(R7)3, Ar2, C1-C6 hydroxyalkyl, R7OR7, P(R7)3, R7CHO, R7COR7, R7COOR7, and S(R7)2;
• each Ar1 and Ar2 is independently an C6-C22 aryl or 5-12 membered heteroaryl comprising from 1 to 3 heteroatoms selected from O, N, and S;
• and
• each R7 is independently C1-C22 alkyl or Ar2, or two R7, together with the atoms to which they are attached, form a five- to eight-member heterocycle.