The reaction of platinum(IV) complex trans- [PtCl4(EtCN)(2)] with pyrazoles 3,5- RR'pzH (R/R' = H/H, Me/H, Me/Me) leads to the formation of the trans- [PtCl4 {NH=C( Et)(3,5-RR' pz)}(2)] ( 1 - 3) species due to the metal-mediated nitrile pyrazole coupling. Pyrazolylimino complexes 1 - 3 ( i) completely convert to pyrazole complexes cis-[PtCl4(3,5-RR' pzH)(2)] by elimination of EtCN upon reflux in a CH2Cl2 solution or upon heating in the solid state; (ii) undergo exchange at the imino C atom with another pyrazole different from that contained in the pyrazolylimino ligand. The reaction of trans-[(PtCl2)-Cl-II(EtCN)(2)] and 3,5- RR' pzH, conducted under conditions similar to those for trans- [(PtCl4)-Cl-IV(EtCN)(2)], is much less selective, and the composition of the products strongly depends on the pyrazole employed: ( a) with pzH, the reaction gives a mixture of three products, i. e., [PtCl2 {NH=C(Et) pz-kappa(2) N, N}] ( 4), [PtCl(pzH) {NH=C(Et)pz-kappa(2) N, N}] Cl ( 5), and [Pt(pzH)(2) {NH=C(Et) pz-kappa(2) N, N}] Cl-2 ( 6) ( complexes 5 and 6 are rather unstable and gradually transform to trans- [PtCl2(pzH)(2)] and [Pt(pzH)(4)] Cl-2 and free EtCN); ( b) with 3,5- Me(2)pzH, the reaction leads to the formation of [PtCl2 {NH=C(Et)(3,5-Me(2)pz)-kappa(2) N, N}] (7) and [PtCl(3,5-Me(2)pzH)(3)] Cl ( 8); ( c) in the case of asymmetric pyrazole 3( 5)- MepzH, which can be added to EtCN and/or bind metal centers by any of the two nonequivalent nitrogen sites, a broad mixture of currently unidentified products is formed. The reduction of 1 - 3 with Ph3P=CHCO2Me in CHCl3 allows for the formation of corresponding platinum(II) compounds trans- [PtCl2 {NH=C(Et)(3,5- RR'pz)}(2)] (9 -11). Ligands NH=C(Et)(3,5- RR' pz) (12 - 14) were almost quantitatively liberated from 9 - 11 with 2 equiv of 1,2-bis-(diphenylphosphino) ethane in CDCl3, giving free imines 12 - 14 in solution and the precipitate of trans- [Pt( dppe)(2)]( Cl)(2). Pyrazolylimines 12 - 14 undergo splitting in CDCl3 solution at 20 - 25 degrees C for ca. 20 h to furnish the parent propiononitrile and the pyrazole 3,5- RR' pzH, but they can be synthetically utilized immediately after the liberation.