David H. McConville

Ligand variation in alkylidene complexes of the type Mo(CHR)(NR′)(OR″)2

A variety of complexes of the type Mo(NR)2Cl2L2 (R = 4-Br-2,6-iPr2-C6H2, 4-CN-2,6-iPr2-C6H2, 3,5-Me2- C6H3, 2-iPr-C6H4, 2-CF3-C6H4, 2-Ph-C6H4, and 1-adamantyl; L = 12 DME or pyridine) have been synthesized by treating [NH4]2[Mo2O7]with four equivalents of RNH2 in the presence of Me3SiCl and Et3N. They are readily alkylated by Grignard reagents to give complexes of the type Mo(NR)2(CH2R′)2 (R = 4-Br-2,6-iPr2-C6H2, 4-CN-2,6-i Pr2-C6H2, 2,6-Me2-C6H3, 3,5-Me2-C6H3, 2-tBu-C6H4, 2-iPr-C6H4, 2-CF3-C6H4, 2-Ph-C6H4, 1-adamantyl, R′  tBu or PhMe2C) from which alkylidene complexes of the type Mo(NR)(CHR′)(OTf)2(DME) are formed upon addition of triflic acid. Addition of various alkoxides to the triflate complexes yields four-coordinate complexes of the type Mo(NR)(CHR′)(OR″)2 (combinations include R = 2,6-iPr2-C6H3, 4-Br-2,6-iPr2-C6H2, 4-CN-2,6-iPr2- C6H2, 2,6-Me2-C6H3, 3,5-Me2-C6H3, 2-tBu-C6H4, 2-iPr-C6H4, 2-CF3-C6H4, 2-Ph- C6H4, and 1-adamantyl; OR″  OCMe3, OCEt3, O-1-adamantyl, OCHMe2, OCMe2(CF3), OCMe(CF3)2, OC(CF 3)3, and OC(CF3)2CF2CF2CF3).

13C NMR spectra of tactic and atactic hydrogenated ring-opened polymers of enantiomeric and racemic endo,exo-5,6-dimethylnorbornene

Polymers 1 of the title monomer, prepared using well-defined molybdenum carbene complexes as catalysts, have been hydrogenated and the structures of the resultant polymers 2 examined by 13 C NMR spectroscopy. The hydrogenated polymer made from the all-cis isotactic polymer of (+)-monomer showed a single set of 13 C NMR lines as expected for an NX sequence of endo (N) and exo (X) substituents. The hydrogenated polymer made from a cis isotactic polymer of (±)-monomer showed additional fine structure arising from the random incorporation of both enantiomers in the isotactic polymer chain: four equal lines for C-9 (orientational triad sensitivity), two equal lines for C-3, C-4, C-5, and C-1 (dyad sensitivity), but single lines for C-8, C-2, C-7 and C-6 (insensitive to the relative orientation of adjacent repeating units). The hydrogenated polymer made from a trans atactic polymer of (+)-monomer showed fine structure due to the presence of both m and r dyads. That made from a trans atactic polymer of (±)-monomer contains 16 possible triad sequences and gave a more complicated spectrum. A complete assignment was made for the first three polymers and a partial assignment for the fourth. Polymers made using non-carbene catalysts were also examined. Hydrogenation of an all-trans precursor made from (±)-monomer using RuCl 3 as catalyst gave an atactic polymer, confirming previous observations. Hydrogenation of a 61% cis, cis/trans blocky precursor, made from (+)-monomer using OsCl 3 /PhC≡CH as catalyst, gave a syndiotactic-biased stereoblocky polymer, indicating a c/r, t/m correlation in the precursor polymer.