Terminal alkyne coupling reactions promoted by rhodium(I) complexes of macrocyclic NHC-based pincerl igands-which feature dodecamethylene,t etradecamethylene or hexadecamethylene wingtip linkers viz. [Rh(CNCn)(C 2 H 4)][BAr F 4 ](n = 12, 14, 16;A r F = 3,5-(CF 3) 2 C 6 H 3)-have been investigated, using the bulky alkynes HCCtBu and HCCAr'(Ar' = 3,5-tBu 2 C 6 H 3)a ss ubstrates. These stoichiometric reactions proceed with formation of rhodium(III) alkynyl alkenyl derivatives andp roduce rhodium(I) complexes of conjugated 1,3-enynes by CÀCbond reductiveelimination through the annuluso ft he ancillary ligand. The intermediates are formed with orthogonal regioselectivity,w ith E-alkenyl complexes derived fromH C CtBu and gem-alkenyl complexes derived from HCCAr', and the reductive elimination step is appreciably affected by the ring size of the macrocycle. For the homocoupling of HCCtBu, E-tBuCCCH= CHtBu is produced via direct reductivee limination from the corresponding rhodium(III)a lkynyl E-alkenyl derivatives with increasing efficacy as the ring is expanded. In contrast, direct reductivee limination of Ar'CCC(= CH 2)Ar'i se ncumbered relative to head-to-head coupling of HCCAr'a nd it is only with the largest macrocyclic ligand studied that the two processesa re competitive.T hese results showcaseh ow macrocyclic ligands can be used to interrogate the mechanism and tune the outcomeo ft erminal alkyne coupling reactions, and are discussed with reference to catalytic reactions mediated by the acyclic homologue [Rh(CNC-Me)(C 2 H 4)][BAr F 4 ] and solventeffects. Scheme1.Metal catalysed reactionsoft erminal alkynes. Mes = 2,4,6-Me 3 C 6 H 2 .