Catalyzes the attachment of leucine to tRNA(Leu) in the mitochondrion. ATP + L-leucine + tRNA(Leu) = AMP + diphosphate + L-leucyl-tRNA(Leu) Optimum pH is 8.0-9.5. Optimum temperature is 37 degrees Celsius. PubMed:3034607 authors identified this protein as the gene product of the NAM2 gene, which is capable of compensating for mutations in mRNA maturase encoded by the fourth intron of the mitochondrial cytochrome b gene. Present with 2120 molecules/cell in log phase SD medium. Belongs to the class-I aminoacyl-tRNA synthetase family.