The preparation of trimethylsilyl and trimethylgermyl complexes of platinum(1i) of the type trans-(Et,P),Pt(MMe,(CI ( M = Si and Ge) from (Me,M),Hg and cis-(Et,P),PtCI, is described. Several reactions are reported involving both chloride ion replacement (Br-, I-, CN-, NCS-, Ph-, and GePh,-) and cleavage of the Pt-M bond [H,O, PhCiCH, (CH,CI),, and H,]. The hydrogenation a t 1 atmosphere has been studied in some detail, and both the Me,Ge and the Me,Si groups are cleaved in preference to the Ph,Ge group in the complexes trans-(Et,P),Pt(MMe,)(GePh,) Infrared and lH n.m.r. spectroscopy have been used to determine the stereochemistry of these complexes. Platinum-silicon, -phosphorus, and -chlorine stretching frequencies have been assigned. In cis-complexes, e.g., (Et,P),PtPh(GeMe,), a unique long-range coupling between the Me,Ge protons and the trans-,lP nucleus is observed. The mass spectrum of trans-(Et,P),Pt(GeMe,)CI is described.