Cooperative Bond Activation and Facile Intramolecular Aryl Transfer of Nickel-Aluminum Pincer-type Complexes

Pincer-type nickel-aluminum complexes were synthesized using two equivalents of the phosphinoamide, [(PhNCH2PPr2)-Pr-i](-). The Ni-0-Al-III complexes, {((PAlP)-P-Mes)Ni}(2)(mu-N-2) and {((PAlP)-P-Mes)Ni}(2)(mu-COD), where (PAlP)-P-Mes is (Mes)Al((NPhCH2PPr2)-Pr-i)(2), were structurally characterized. The (PAlP)Ni system exhibited cooperative bond cleavage mediated by the two-site Ni-Al unit, including oxidative addition of aryl halides, H-2 activation, and ortho-directed C-H bond activation of pyridine N-oxide. One intriguing reaction is the reversible intramolecular transfer of the mesityl ring from the Al to the Ni site, which is evocative of the transmetalation step during cross-coupling catalysis. The aryl-transfer product,(THF)Al((NPhCH2PPr2)-Pr-i)(2)Ni(Mes), is the first example of a first-row transition metal-aluminyl pincer complex. The addition of a judicious donor enables the Al metalloligand to convert reversibly between the alane and aluminyl forms via aryl group transfer to and from Ni, respectively. Theoretical calculations support a zwitterionic Ni delta--Al delta+ electronic structure in the nickel-aluminyl complex.

Automated summary

Complexes of pincer-type nickel-aluminum were synthesized and it was found that cooperative bond cleavage occurred mediated by the two-site Ni-Al unit. This included oxidative addition, H-2 activation, and adjacent C-H bond activation. The reversible intramolecular transfer of the mesityl ring from Al to Ni was noted, resembling a transmetalation step in catalysis. This research represents the first example of a first-row transition metal-aluminyl pincer complex.