Treatment of [η 5 :σ-Me 2 C(C 5 H 4 )(C 2 B 10 H 10 )]Ru(COD) (1) with phosphites, phosphines, amines or N-heterocyclic carbene in THF afforded the COD displacement complexes [η 5 :σ-Me 2 C(C 5 H 4 )(C 2 B 10 H 10 )]Ru[P(OEt) 3 ] 2 (2), [η 5 :σ-Me 2 C(C 5 H 4 )(C 2 B 10 H 10 )]Ru[PPh 2 (OEt)] 2 (3), [η 5 :σ-Me 2 C(C 5 H 4 )(C 2 B 10 H 10 )]Ru[NH 2 CH 2 CH 2 Pr i ] 2 (4), [η 5 :σ-Me 2 C(C 5 H 4 )(C 2 B 10 H 10 )]Ru(NH 2 Pr n ) 2 (5), [η 5 :σ-Me 2 C(C 5 H 4 )(C 2 B 10 H 10 )]Ru (η 2 -NH 2 CH 2 CH 2 NH 2 ) (6), [η 5 :σ-Me 2 C(C 5 H 4 )(C 2 B 10 H 10 )]Ru[η 2 -NH(CH 3 )CH 2 CH 2 NH(CH 3 )] (7) or [η 5 :σ-Me 2 C(C 5 H 4 )(C 2 B 10 H 10 )]Ru[NHC] 2 (8, NHC=1,3,4,5-tetramethylimidazol-2-yilidene), respectively. Ruthenium–amine complexes were much more labile than 1. Upon exposure to moisture, 5 was converted into [{η 5 :σ-Me 2 C(C 5 H 4 )(C 2 B 10 H 10 )}Ru(μ-H 2 O)] 2 (9). Reactions of 5 with PR 3 (R=PPh 3 , Cy), TMEDA (TMEDA=N,N,N′,N′-tetramethylethylenediamine) and CH 3 CN afforded the corresponding amine replacement products[η 5 :σ-Me 2 C(C 5 H 4 )(C 2 B 10 H 10 )]Ru(NH 2 Pr n )(PPh 3 ) (10), [η 5 :σ-Me 2 C(C 5 H 4 )(C 2 B 10 H 10 )]Ru(NH 2 Pr n )(PCy 3 ) (11), [η 5 :σ-Me 2 C(C 5 H 4 )(C 2 B 10 H 10 )]Ru(TMEDA) (12) and [η 5 :σ-Me 2 C(C 5 H 4 )(C 2 B 10 H 10 )]Ru(NCCH 3 ) 2 (13). These results indicated that the steric factor dominated these substitution reactions. The electrochemical studies showed that the electron richness of the Ru atom decreased in the order L 2 Ru(NHC) 2 >L 2 Ru(amine) 2 >L 2 Ru(NCMe) 2 >L 2 Ru(P) 2 . All of these complexes were fully characterized by various spectroscopic techniques and elemental analyses. The molecular structures of 2, 3, 5–10, 12 and 13 were further confirmed by single-crystal X-ray analyses.