Warren Roper conducted important studies on organometallic and coordination chemistry, particularly of the group 8 metals. Warren did some very early work on oxidative addition reactions. Another important contribution has been the synthesis and determination of the structure of organometallic and coordination complexes containing very reactive ‘intermediates’, for example, NHO, NHOH, NH2OH, CS, CSe, CTe, CF2, CCl2, CH2O, CH2S, CH2Se, which were stabilised by coordination to metal centres. Warren has also synthesised compounds with metal to carbon triple and double bonds, and established the first example of a mononuclear zero-valent methylene complex, LnM–CH2. He has studied hydride transfer reactions to coordinated nitric oxide, isocyanide and thiocarbonyl groups — reactions that are model systems for catalytic studies. He has synthesised the first metallabenzene compound, some metallacyclobutadienes, and molecules containing multiple metal–phosphorus bonds. Many of Warren’s pioneering contributions to synthetic chemistry have been particularly elegant and place him in the forefront of preparative organometallic and coordination chemists.