Heteroleptic Magnesium -Butyl on a Chemically Non-innocent 2-Anilidomethylpyridine Ligand Leading to Diverse Magnesium Hydrides.

Molecular magnesium hydrides and hydride-rich clusters are of significant interest for applications ranging from catalysis and small molecule activation to hydrogen storage. Here, we investigate the 2-anilidomethylpyridine framework L as an ancillary support for magnesium organometallics with a special emphasis on hydrides. The proligand L (-[2,6-bis(1-methylethyl)phenyl]-α,6-diphenyl-2-pyridinemethanamine) gives [(L)Mg(Bu)(thf)] () by butane elimination from Mg(Bu)(thf). A stronger donor such as DMAP replaces the THF from to give [(L)Mg(Bu)(dmap)] (). Both are air-sensitive, and is adventitiously oxidized into [(L)Mg(μ-OBu)] (). The homoleptic [(L)Mg] () is made from and a second equiv of L. 's terminal Bu group is selectively protonated by HN(SiMe) to give [(L)MgHMDS] (; HMDS = N(SiMe)), whereas PhSiOH partially protonates the backbone anilide as well to give a mixture of [(L)Mg(OSiPh)(thf)] () and free L. Like HN(SiMe), aprotic MeOTf also reacts by selectively abstracting the Bu group from to give [(L)Mg(μ:κ-,-OTf)(thf)] (). Interestingly, screening the common synthetic routes for magnesium hydrides leads to diverse outcomes upon varying the Mg precursors and hydride sources. and PhSiH give the hydride cluster [{(L)Mg(μ-H)}(μ-H)Mg] (), whereas and PhSiH give the molecular complex [(L)Mg(dmap)] () with a dearomatized pyridyl backbone. and HBpin (pinacolborane) give a product mixture, from which a different hydride cluster [(L)Mg(μ-H)}(μ:κ-,-OCMe)] () is identified, showing a rare instance of complete deborylation of a HBpin molecule. and HBcat (catecholborane) also give a product mixture, one of which is the borylated ligand [(L)Bcat] (). HBpin with as the Mg precursor takes the ligand borylation route more selectively to give [(L)Bpin] (). Last, reacts with PrNHBH to give [(L)Mg{NH(Pr)BH}] (), which shows a slow and fractional conversion into the dinuclear mixed hydrido amidoborane [(L)Mg(μ-H){(μ-NH(Pr)BH}] () by partial β-hydride elimination. In comparison, [(L)Mg(PrNHBH)(dmap)] () arising from the DMAP-bound and PrNHBH is stable toward such elimination.