With the aim of understanding the influence of donor solvents on the reactivity of the amine complexes [RuCI2(PPh3)(2)(piperidine)] (1) and [RuCI2(PPh3)(2)(imidazole)(2)] (2) in the presence of ethyldiazoacetate, and on the properties of the resulting polymer, a ring opening metathesis polymerization of norbornene was carried out in the presence of small amounts of common solvents such as additives (isopropanol, THF, N,N-dimethylformamide, 2,6-lutidine, isopropanethiol, acetonitrile, dimethyl sulfoxide, NEt3, NH2Me and pyridine). From observations, typical coordinating solvents like DMSO, NEt3, NH2Me and pyridine, hardly affected the yields when either complex was employed. With other additives, the major advantage was the decrease in the polydispersity indices. On using complex 1 with 2,6-lutidine, observed values of M-w/M-n were as low as 1.3, while the yield decreased from 99% to about 20-30% at RT for similar to 1 min in pure solution. In the case of complex 2, which is almost inactive to ROMP (19% at 50 degrees C for 5 min with M-w/M-n = 6.30), the yield was three-fold (60% at 50 degrees C for 5 min with M-w/M-n = 1.95) compared to that of without the Further, the M-w/M-n was observed to decrease to 1.34 with 200 eq. of THF. (c) 2005 Elsevier B.V. All rights reserved.