Enediynes via Sequential Acetylide Reductive Coupling and Alkyne Metathesis: Easy Access to Well-Defined Molybdenum Initiators for Alkyne Metathesis

Portability of the RNNMo(3+) core — Application to the synthesis of dinitrogen-derived trialkoxymolybdenum organodiazenido complexes

An alcoholysis strategy has been employed in the synthesis of new oligo- or polymeric trialkoxymolybdenum diazenido complexes [R1NNMo(O-1-Ad)3]x (R1 = Me or C(O)OMe) as well as their mononuclear THF solvates R1NNMo(O-1-Ad)3(THF). Dinitrogen-derived diazenido precursor complexes R1NNMo(N[R]Ar)3 (R = i-Pr, Ar = 3,5-C6H3Me2) react smoothly with 3 equiv. 1-adamantanol to liberate 3 equiv. HN(R)Ar without disruption of the diazenidomolybdenum(3+) core. X-ray structural investigations were carried out for diazenido complex MeNNMo(O-1-Ad)3(THF) and for the corresponding cationic dimethyldiazenido complex [Me2NNMo(O-1-Ad)3(THF)]+, obtained as its triflate salt. The latter cation was found upon cobaltocene reduction to undergo N—N bond cleavage, producing nitride NMo(O-1-Ad)3 (synthesized independently) and dimethylamine. Key words: molybdenum, dinitrogen, bond cleavage, hydrazido, diazenido.

A Fine-Tuned Molybdenum Hexacarbonyl/Phenol Initiator for Alkyne Metathesis

A new, highly potent activator for molybdenum hexacarbonyl and 2-fluorophenol is described. An "instant"catalyst formed in situ from molybdenum hexacarbonyl and 2-fluorophenol shows high activity for cross- and ring-closing alkyne metathesis reaction. The use of 2-fluorophenol can be combined with other activation methods to allow alkyne metathesis at relatively low temperature (80 degrees C).

Highly Active Trialkoxymolybdenum(VI) Alkylidyne Catalysts Synthesized by a Reductive Recycle Strategy

A systematic study of alkyne metathesis catalyzed by trialkoxymolybdenum(VI) alkylidyne complexes is reported, in which substrate functional groups, alkynyl substituents, and catalyst ligands are varied. Sterically hindered trisamidomolybdenum(VI) propylidyne complex 5 was prepared conveniently through a previously communicated reductive recycle strategy. Alcoholysis of 5 with various phenols/alcohols provides a set of active catalysts for alkyne metathesis at room temperature, among which the catalyst with p-nitrophenol as ligand shows the highest catalytic activity and is compatible with a variety of functional groups and solvents. A key finding that enabled the use of highly active molybdenum(VI) catalysts is replacement of the commonly used propynyl substituents on the starting alkyne substrates with butynyl groups. Under reduced pressure using 1,2,4-trichlorobenzene as an involatile solvent, the alkyne metathesis of butynyl substituted compounds proceeds well at 30 degrees C providing high yields (83%-97%) of dimers. Rationalization of the special role played by butynyl substrates is discussed.