Cyanide complexes in Molecular Orbital Theory In molecular orbital theory, please explain why cyanide ion combines with metal from the carbon end and not from the nitrogen end?
In this answer of Martin’s, you can find a molecular orbital diagram of $\ce{CO}$. The corresponding diagram for cyanide, $\ce{CN-}$ is essentially identical, there will only be different orbital energies and very slightly different extends of the lobes.

When forming a coordinate bond to a metal centre, cyanide will primarily attack with its highest occupied molecular orbital, the HOMO, since it is a nucleophile (attacking a positively polarised metal centre). You can also see the HOMO depicted as the bottom image of the following set as taken from Wikipedia:



Note the large lobe extending outwards on carbon’s side. An attack with this lobe is greatly preferred, hence why isocyanides are comparatively rare.