Novel large platinacycloalkane compounds containing 19- and 21- membered rings of the type L2Pt(CH2)n (L2 = dppp and n = 18, 20) are synthesized through the ring closing metathesis (RCM) reaction of bis(1-alkenyl)platinum(II) complexes using Grubbs' catalysts. These compounds are characterized by various spectroscopic and analytical techniques. The cross metathesis reactions with different dienes and substituted alkynes yielded interesting inter- and intra- molecular metathesis reaction products. Various factors such as concentration, solvent, phosphine ligand and length of the alkenyl chains affect the RCM reaction significantly to yield different products such as monomeric, dimeric and polymeric species. The novel chemical reactivity aspects of these title compounds with elemental sulfur, carbon monoxide and methyl iodide are discussed. © 2010 Elsevier B.V.