Alkenes are ligands in transition metal alkene complexes. This complex further complexes with the ubiquitin ligase protein CUL4A and with PARP1. Numerous mixed ligand complexes of these metals with the hydroxide ion exist. Other chromium(I) complexes contain cyclopentadienyl ligands. They also occur in nested clusters in association with complex tuff ring and maar complexes. Ethylene is a fundamental ligand in transition metal alkene complexes. Ammonia can act as a ligand in transition metal complexes. Proteins are capable of forming very tight complexes. Acetonitrile is a ligand in many transition metal nitrile complexes. Metal carbonyls are important precursors for the synthesis of other organometalic complexes. Ruthenium forms a variety of coordination complexes. Tris also complexes with metal ions in solution. Azides can be used as precursors of the metal nitrido complexes. Homogeneous reactions with metal coordination complexes proceed somewhat faster. Kinetic resolution relies upon differences in reactivity between enantiomers or enantiomeric complexes.