Extending the π-system: Modulation of arene and phosphine donor lability in polyarene diphosphine-supported molybdenum complexes and its application to small molecule reactivity

Previous work in our group has shown that low-valent molybdenum centers supported by a p-terphenyl diphosphine ligand are capable of activating and transforming a variety of small mols., including mediating the two- and four- electron reductive coupling of carbon monoxide. The hemilabile nature of the central arene and the phosphine arms has been postulated be important to their reactivities. To further probe the role of hemilabile arene binding, the use of polyarene-linked diphosphine ligands (1,4-naphthalenediyl, L^(naph), and 1,4-anthracenediyl, L^(anth)) is investigated. Previously, such polyarenes have shown greater propensity for η^4-arene binding to the non-fused carbons. Metalation with Mo(CO)_3(MeCN)_3 followed by oxidn. gives the complex [L^(naph)Mo(CO)_2][OTf]_2 with η^6- arene binding. Subsequent photolysis yields decarbonylated L^(naph)Mo(MeCN)_3, which exhibits η^4-arene binding, in contrast to the terphenyl system, which displays an η^6 metal-arene interaction with one less acetonitrile ligand. The impact of the differential binding on small mol. reactivity in these complexes will be discussed