Nomenclature of Coordination compounds containing nitrogen
As per rules, double m is used when the ligand is just $\ce{NH3}$, ammonia:

Cite from IUPAC Nomenclature of Inorganic Chemistry, Recommendations 2005:


  IR-7.1.3 Representing ligands in additive names
  
  Additive names are constructed by placing (sometimes modified) ligand names as prefixes
  to the name of the central atom. For anionic ligands, the anion endings ‘ide’, ‘ate’ and ‘ite’
  (see Section IR-5.3.3) are changed to ‘ido’, ‘ato’ and ‘ito’, respectively,
  when generating
  these prefixes. Names of neutral and cationic ligands are used unchanged, except in a few
  special cases, most notably water (prefix ‘aqua’), ammonia (prefix ‘ammine’), carbon
  monoxide bound through carbon (prefix ‘carbonyl’), and nitrogen monoxide bound through
  nitrogen (prefix ‘nitrosyl’) (cf. Section IR-9.2.4.1).


E.g. in $\ce{[CoCl(NH3)5]^{2+}}$ pentaamminechloridocobalt(2+).

For amines, the ligand name is unchanged, e.g.
$\ce{[Co(en)3]^{3+}}$ tris(ethane-1,2-diamine)cobalt(3+).