Repeating reactions of 1 with 13 CO, allowed the isolation of 13 C2-2, spectroscopic analysis of which show the two expected carbon-environments in the C NMR, now with a mutual 1 JC-C coupling of 78.3 Hz. JC-H ranging between 158.2 -174.4 Hz are also apparent in the 1 H NMR spectrum of 13 C2-2.