Molecules were optimized in the gas phase using Gaussian16 with density functional theory (DFT) using the Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional. The 6-311G(d,p)basis set was used for all atoms. The optimization threshold was set to tight and an ultrafine integral grid was used. MOs are plotted at an isosurface value of 0.02 unless otherwise noted. For the metallacumulene, we used cc-pVTZ basis set for C, H and P atoms and SDD basis set and effective core potential for the Ru atom. To quantify how helical an MO is, we first need to define the component of the MO that we want to consider. A helical MO has two defining characteristics: Its nodal plane propagates helically through space and so will any choice of isovalue (a specific value of the wavefunction amplitude). While this allows for two different approaches for defining helicality, we choose the spatial propagation of the nodal plane along the molecular axis.