The half-sandwhich ruthenium chloro complexes bearing chelated diphosphazane ligands, [(η 5-Cp)RuCl{κ 2-P,P-(RO) 2PN(Me)P(OR) 2}] [R = C 6H 3Me 2-2,6] ( 1) and [(η 5-Cp ∗)RuCl{κ 2-P,P-X 2PN(R)PYY′}] [R = Me, X = Y = Y′ = OC 6H 5 ( 2); R = CHMe 2, X 2 = C 20H 12O 2, Y = Y′ = OC 6H 5 ( 3) or OC 6H 4 t Bu-4 ( 4)] have been prepared by the reaction of CpRu(PPh 3) 2Cl with (RO) 2PN(Me)P(OR) 2 [R = C 6H 3Me 2-2,6 ( L 1)] or by the reaction of [Cp ∗RuCl 2] n with X 2PN(R)PYY′ in the presence of zinc dust. Among the four diastereomers (two enantiomeric pairs) possible for the “chiral at metal” complexes 3 and 4, only two diastereomers (one enantiomeric pair) are formed in these reactions. The complexes 1, 2, 4 and [(η 5-Cp)RuCl{κ 2-P,P-Ph 2PN(( S)- ∗CHMePh)PPhY}] [Y = Ph ( 5) or N 2C 3HMe 2-3,5 ( S C S P R Ru)-( 6)] react with NaOMe to give the corresponding hydride complexes [(η 5-Cp)RuH{κ 2-P,P-(RO) 2PN(Me)P(OR) 2}] ( 7), [(η 5-Cp ∗)RuH{κ 2-P,P′-X 2PN(R)PY 2}] [R = Me, X = Y = OC 6H 5 ( 8); R = CHMe 2, X 2 = C 20H 12O 2, Y = OC 6H 4 t Bu-4 ( 9)] and [(η 5-Cp)RuH{κ 2-P,P-Ph 2PN(( S)- ∗CHMePh)PPhY}][Y = Ph ( 10) or N 2C 3HMe 2-3,5 ( S C S P R Ru)-( 11a) and ( S C S P S Ru)-( 11b)]. Only one enantiomeric pair of the hydride 9 is obtained from the chloro precursor 4 that bears sterically bulky substituents at the phosphorus centers. On the other hand, the optically pure trichiral complex 6 that bears sterically less bulky substituents at the phosphorus gives a mixture of two diastereomers ( 11a and 11b). Protonation of complex 7 using different acids (HX) gives a mixture of [(η 5-Cp)Ru(η 2-H 2){κ 2-P,P-(RO) 2PN(Me)P(OR) 2}]X ( 12a) and [(η 5-Cp)Ru(H) 2{κ 2-P,P-(RO) 2PN(Me)P(OR) 2}]X ( 12b) of which 12a is the major product independent of the acid used; the dihydrogen nature of 12a is established by T 1 measurements and also by synthesizing the deuteride analogue 7-D followed by protonation to obtain the D–H isotopomer. Preliminary investigations on asymmetric transfer hydrogenation of 2-acetonaphthone in the presence of a series of chiral diphosphazane ligands show that diphosphazanes in which the phosphorus centers are strong π-acceptor in character and bear sterically bulky substituents impart moderate levels of enantioselectivity. Attempts to identify the hydride intermediate involved in the asymmetric transfer hydrogenation by a model reaction suggests that a complex of the type, [Ru(H)(Cl){κ 2-P,P-X 2PN(R)PY 2}(solvent) 2] could be the active species in this transformation.