Effect of Phosphine, B(C6F5)3 in Ring Opening Metathesis Polymerization (ROMP) of Cyclic Olefins by (arylimido)vanadium(v) Alkylidene Catalysts and the Chain Transfer ROMP of Cycloheptene

Effects of additives (t-phosphine, borane etc.) in ring-opening metathesis polymerization (ROMP) of nor-bornene (NBE) and cycloheptene (CHPE) were investigated using a series of (arylimido)vanadium(V)-alkylidene catalysts, V(CHSiMe3)(N-2,6-C12C(6)H(3))(OR)(PMe3)(2) [RC6F5 (1), C6Cl5 (3), OC(CF3)(3) (5)], V(CHSiMe3)(N-2,6-F2C6H3)(OC(6)C1(5))(PMe3)(2) (2), V(CHSiMe3)(NR')[OC(CF3)(3)](PMe3)(2) [R'C H-6(5) (4), C6F5 (6)]. Catalytic activities of 4 and 5 in the ROMP of NBE at 25 ? were affected by the additives. Addition of B(C6F5)(3) led to the deactivation in the ROMP of NBE accompanied by formation of Me3SiHCCHSiMe (3) as the major product, suggesting a dimeric catalyst decomposition by dissociation of PMe3. Addition of 3 equiv. of PMe3, PEt3 increased the activities in the ROMP of NBE, but addition of 3 equiv. of P "Bu-3, PBu3, PPh3, and P(OMe)(3) did not improve or decreased the activities. The high cis specificity (97 similar to > 99 %) was maintained regardless of these additives. Addition of PEt3 into a C6D6 solution of 3 monitored by P-31 VT-NMR spectra and F-19 VT-NMR spectra suggested the fast ligand exchange occurred to form another alkylidene species. ROMP of CHPE in the presence of allyltrimethylsilane (ATMS) as the chain transfer (cross metathesis) agent proceeded by 2 and the M-n values could be controlled by varying the ATMS concentration, whereas the ROMP by 1 and 6 with negligible activities by addition of ATMS. Synthesis of end functionalized linear ring-opened oligomers was thus achieved.