Reactions of a dimetallated N,NA?-dimethyl substituted porphyrinogen Sm(II) complex with a series of t-butyl substituted heteroalkynes affords a diverse range of reactivity. The phosphaalkyne t-BuCa? P gives a dinuclear Sm(III) Pa??P reductively coupled complex of (t-BuC=PP=C-t-Bu)2- featuring a new m-h2(1,2-C,P) binding mode. In contrast, the nitrile aza analogue t-BuCa? N forms Sm(II) adducts that undergo reductive Ca??C bond cleavage at elevated temperatures to afford a trimeric Sm(III) cyanide (m-Ca? N-) complex. The isomeric isonitrile t-BuNa? C undergoes the related reductive Ca??N bond cleavage reactivity at milder temperatures, allowing the trapping of the tert-butyl fragment as a Sm(III) h2-iminoacyl (t-BuC=N-t-Bu)- complex.