The results presented here reveal that Co2(CO)4dppm is an excellent masking group for the synthesis of long polyynes, and particularly polyyne polyrotaxanes, because it is stable to Glaser-type oxidative coupling conditions and it can be removed efficiently by peracid oxidants, such as mCPBA and MMPP. When synthesizing conjugated polymers, it is often desirable to use a 'precursor route'. In this strategy, a non-conjugated precursor polymer is synthesized and then converted into the target conjugated polymer through an elimination step, so that the extended π-system is only revealed after construction of the covalent backbone . The precursor route presented here (Fig. ) is advantageous, even for the synthesis on polyynes with no threaded macrocycles, as illustrated by the synthesis of C48 from mC48, because it avoids the need for a long terminal polyyne intermediates and it allows the polymer backbone to be created before unmasking the whole polyyne chain. The use of Co2(CO)4dppm masking groups is particularly attractive for the synthesis of polyyne polyrotaxanes, because these organometallic complexes act as temporary stoppers, to prevent the macrocycles from unthreading. We have demonstrated this chemistry by All relevant data are available within the paper and its Supplementary Information files. The NMR data are presented in detail in the main Supplementary Information file and are available upon reasonable request from the authors.