The Co1-Co2 distance in the solid-state is 2.5172(6)Å, which is well within the sum of Van der Waals radii for cobalt and also within the range of M-M distances that have been observed before in PNNP complexes. It is, however, long compared with known complexes which feature a Co-Co bond, especially considering that the current consensus in the field is that, in Co 2 (CO) 8 (Co-Co 2.52 Å) such a bond is not present, despite what was long believed. In literature, conclusions on Co-Co bonding (or lack thereof) for similar complexes are based mainly on the metal-metal distance. However, in our experience with dicopper PNNP complexes, the metal-metal distance is not an ideal indication for metal-metal bonding in these complexes. An in-depth study on the Co-Co bonding in 3 using X-ray absorption spectroscopy is reported in a separate study, in which this question is addressed both experimentally and with TDDFT calculations. From that work we were able to conclude that there is a direct Co-Co bond present in complex 3 (and also in complex 4, see below) and also that cobalt is in its 2+ oxidation state in these complexes. The sum of angles around the silicon atoms with the two ethyl groups and a centroid in the middle of the two cobalt centers is on average 359.9°. Together with the chemical shift of these nuclei in Si NMR, this suggests that these silicon groups have significant silylene character (R1, Scheme 5). Although the position of H1M and H3M in the solid-state structure implies the presence of some silyl character as well (R2, Scheme 5). From electronic structure calculations, we conclude that this is likely best described as a base stabilized silylene structure in which H1M and H3M act as a base to stabilize the empty p-orbital on the silylene moieties. This is in essence a combination of R1 and R2 shown in Scheme 5.