Group 7 carbonyl complexes of a PNN-heteroscorpionate ligand.

A series of rhenium and manganese carbonyl complexes of a heteroscorpionate ligand with an atypical NP-donor set has been prepared to better understand their electronic and CO releasing properties. Thus, the ligand, pzTTP, with an ,-bis(pyrazol-1-yl)tolyl group decorated with an -situated di(-tolyl)phosphanyl reacts with carbonyl group 17 reagents to give [-(κNP-pzTTP)Re(CO)Br], 1, and [-(κNP-pzTTP)M(CO)](OTf = OSCF), 2-M (M = Re, Mn), if care is taken during the preparation of the manganeses derivative. When heated in CHCN, 2-Mn slowly transforms to [,-(κNP-pzTTP)Mn(CO)(NCCH)](OTf), 3-Mn. In contrast, the corresponding 3-Re can only be prepared from 2-Re using MeNO; pure 3-Mn can also be prepared by this method. Experimental and density functional calculations at the M06L/Def2-TZVP/PCM(CHCN) level show that the replacement of a carbonyl with an acetonitrile solvent decreases the oxidation potential by around 0.8 V per carbonyl released, making decarbonylated species potent reductants. At the same time, the electronic spectrum broadens and undergoes a red-shift, making dicarbonyl complexes more susceptible to photo-initiated decarbonylation reactions than tricarbonyls. When 2-Mn or 3-Mn are irradiated in with 390 nm LED light in aerated solutions, [-Mn(pzTTP = O)](OTf), 4, along with insoluble manganese oxides are rapidly formed.