Synthesis of monoalkoxide monopyrrolyl complexes Mo(NR)(CHR')(OR'')(pyrrolyl): enyne metathesis with high oxidation state catalysts.

We recently reported the synthesis, characterization, and reactivities of molybdenum bispyrrolyl complexes of the type Mo(NR)(CHR′)(pyrrolyl)2 where pyrrolyl is either the parent pyrrolyl1 or 2,5-dimethylpyrrolyl (Me2Pyr). We are interested primarily in the use of bispyrrolyl species as precursors to bisalkoxide catalysts3 of the type Mo(NR)(CHR′)(OR)2 or Mo(NR)(CHR′)(diolate) through addition of an alcohol or a diol to Mo(NR)(CHR′)(pyrrolyl)2 complexes. Preliminary experiments suggest that bispyrrolyls are less reactive toward olefins than bisalkoxide species, but serve as effective precursors to Mo-based bisalkoxides or diolates.1,2 We were attracted to the possibility that monoalkoxide monopyrrolyl species might be intercepted and might prove to be of interest in their own right. This expectation partly arises from the high reactivities observed for supported catalysts prepared through addition of bispyrrolyl species to silica4 where the predominant surface species is Mo(NR)(CHR′)(pyrrolyl)(OSisurf). High catalytic activities have been observed (and also rationalized through theoretical studies5) for these and related pseudotetrahedral metal complexes that are asymmetric at the metal center. We report here the synthesis of species of the type Mo(NR)(CHR′)(OR′′)(pyrrolyl) and their use in catalytic enyne metathesis reactions.6 Addition of 1 equiv of ROH to Mo(NAr)(CHCMe2Ph)(Me2Pyr)2 (Ar ) 2,6-i-Pr2C6H3; Me2Pyr ) 2,5-Me2NC4H2) in diethyl ether or THF yields Mo(NAr)(CHCMe2Ph)(OR)(Me2Pyr) species where R ) (CH3)3C (1, 22% isolated yield), (CH3)2CH (2, 83%), Ar (3, 81%), (CF3)2CH (4, 45%), or (CF3)2(CH3)C (5, 80%) (eq 1). In