Coming full circle: Bis(alkenyl)-platinum(II) complexes cis-[L 2Pt-{(CH2)nCH=CH2}2] (L = PPh3 or L2 = Ph2P(CH2) 3PPh2; n = 3-6) have been prepared and fully characterized. Ring-closing metathesis leads to new platinacycloalkenes, which can be hydrogenated to platinacycloalkanes with 9-, 11-, 13-, and 15-membered rings (see picture for 15-membered ring; Pt green, P orange, C blue, H white). (Chemical Equation Presented). © 2007 Wiley-VCH Verlag GmbH & Co. KGaA.