A hexacoordinate complex a) of formula MXY 2 (HCNN) b) of formula MX 2 c) of formula [M 2]W d) of formula (VIII): MXY 2 2 (VIII) e) of formula MX 2 wherein M = Ru or Os; X, Y are independently selected among halides, hydride, C1-C20 carboxylates and C1-C20 alkoxides; W is selected among halides, C1-C20 carboxylates and C1-C20 alkoxides; is a compound of formula Ia - Ic: (HCNN) is a compound of formula IIa - IIb: is a ligand of formula IIc - IId: wherein R 1 - R 13 are independently selected among H, C1-C20 aliphatic groups and C5-C20 aromatic groups; and HCP is a compound of formula (IVa) and CP is a ligand of formula (IVb) wherein R 21 - R 23 are independently selected among H, C1-C20 aliphatic groups and C5-C20 aromatic groups; provided that when M is Ru - and X = Y = Cl, R 23 is not hydrogen in the complex of formula MXY 2 2 (VIII); - and when M is Ru, X = Cl, HCP is not (2,6-dimethylphenyl) diphenylphosphine (Hdmpp) and CP is not the anion of (2,6-dimethylphenyl) diphenylphosphine (dmpp) in the complex of formula MX 2 a) of formula MXY 2 (HCNN) b) of formula MX 2 c) of formula [M 2]W d) of formula (VIII): MXY 2 2 (VIII) e) of formula MX 2 wherein M = Ru or Os; X, Y are independently selected among halides, hydride, C1-C20 carboxylates and C1-C20 alkoxides; W is selected among halides, C1-C20 carboxylates and C1-C20 alkoxides; is a compound of formula Ia - Ic: (HCNN) is a compound of formula IIa - IIb: is a ligand of formula IIc - IId: wherein R 1 - R 13 are independently selected among H, C1-C20 aliphatic groups and C5-C20 aromatic groups; and HCP is a compound of formula (IVa) and CP is a ligand of formula (IVb) wherein R 21 - R 23 are independently selected among H, C1-C20 aliphatic groups and C5-C20 aromatic groups; provided that when M is Ru - and X = Y = Cl, R 23 is not hydrogen in the complex of formula MXY 2 2 (VIII); - and when M is Ru, X = Cl, HCP is not (2,6-dimethylphenyl) diphenylphosphine (Hdmpp) and CP is not the anion of (2,6-dimethylphenyl) diphenylphosphine (dmpp) in the complex of formula MX 2 M = Ru or Os; X, Y are independently selected among halides, hydride, C1-C20 carboxylates and C1-C20 alkoxides; W is selected among halides, C1-C20 carboxylates and C1-C20 alkoxides; is a compound of formula Ia - Ic: (HCNN) is a compound of formula IIa - IIb: is a ligand of formula IIc - IId: wherein R 1 - R 13 are independently selected among H, C1-C20 aliphatic groups and C5-C20 aromatic groups; and HCP is a compound of formula (IVa) and CP is a ligand of formula (IVb) wherein R 21 - R 23 are independently selected among H, C1-C20 aliphatic groups and C5-C20 aromatic groups; provided that when M is Ru - and X = Y = Cl, R 23 is not hydrogen in the complex of formula MXY 2 2 (VIII); - and when M is Ru, X = Cl, HCP is not (2,6-dimethylphenyl) diphenylphosphine (Hdmpp) and CP is not the anion of (2,6-dimethylphenyl) diphenylphosphine (dmpp) in the complex of formula MX 2 is a compound of formula Ia - Ic: (HCNN) is a compound of formula IIa - IIb: is a ligand of formula IIc - IId: wherein R 1 - R 13 are independently selected among H, C1-C20 aliphatic groups and C5-C20 aromatic groups; and HCP is a compound of formula (IVa) and CP is a ligand of formula (IVb) wherein R 21 - R 23 are independently selected among H, C1-C20 aliphatic groups and C5-C20 aromatic groups; provided that when M is Ru - and X = Y = Cl, R 23 is not hydrogen in the complex of formula MXY 2 2 (VIII); - and when M is Ru, X = Cl, HCP is not (2,6-dimethylphenyl) diphenylphosphine (Hdmpp) and CP is not the anion of (2,6-dimethylphenyl) diphenylphosphine (dmpp) in the complex of formula MX 2 R 21 - R 23 are independently selected among H, C1-C20 aliphatic groups and C5-C20 aromatic groups; provided that when M is Ru - and X = Y = Cl, R 23 is not hydrogen in the complex of formula MXY 2 2 (VIII); - and when M is Ru, X = Cl, HCP is not (2,6-dimethylphenyl) diphenylphosphine (Hdmpp) and CP is not the anion of (2,6-dimethylphenyl) diphenylphosphine (dmpp) in the complex of formula MX 2 - and X = Y = Cl, R 23 is not hydrogen in the complex of formula MXY 2 2 (VIII); - and when M is Ru, X = Cl, HCP is not (2,6-dimethylphenyl) diphenylphosphine (Hdmpp) and CP is not the anion of (2,6-dimethylphenyl) diphenylphosphine (dmpp) in the complex of formula MX 2