The reaction of (R2NCS2)Pt(PEt3)Cl (R = Me, Et), prepared from [Pt(PEt3)Cl2]2 and Na(R2NCS2), with alkyllithium or Grignard reagents yields (R2NCS2)Pt(PEt3) (alkyl) (alkyl = Me, n-Pr, i-Pr, n-Bu, sec-Bu, i-Bu, t-Bu) complexes. These new alkylplatinum complexes are very stable and can be heated in solution at 100 °C for extended periods without decomposition. The reaction of (R2NCS2)Pt(PEt3)Cl with NaBH4 yields the stable complexes (R2NCS2)Pt(PEt3)H, which decompose only slowly at 110 °C. This hydride (R = Me) does not react with ethylene or phenylacetylene but will react with MeO2CC≡CCO2Me to yield a mixture of the E and Z isomers of (Me2NCS2)Pt(PEt3)(η1-C(CO2Me)═C(H)CO2Me). The reaction of (R2NCS2)Pt(PEt3)Cl with AgBF4 and ethylene yields [(R2NCS2)Pt(PEt3)(C2H4)]BF4, but these complexes are very unstable, decomposing rapidly in the absence of ethylene. The complexes (Me2NCS2)PtLCl (L = CO, C2H4) are prepared by mixing the L ligand with [Pt(Me2NCS2)Cl]2. © 1990, American Chemical Society. All rights reserved.