Most metal alkyl complexes contain other, non-alkyl ligands.  Great interest, mainly theoretical, has focused on the homoleptic complexes.  Indeed, the first reported example of a complex containing a metal-sp carbon bond was the homoleptic complex diethylzinc.  Other examples include hexamethyltungsten, tetramethyltitanium, and tetranorbornylcobalt.
Mixed ligand, or heteroleptic, complexes containing alkyls are numerous. In nature, vitamin B12 and its many derivatives contain reactive Co-alkyl bonds.