Heteroleptic Magnesium n -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 NN L as an ancillary support for magnesium organometallics with a special emphasis on hydrides. The proligand NN L H ( N -[2,6-bis(1-methylethyl)phenyl]-α,6-diphenyl-2-pyridinemethanamine) gives [( NN L)Mg( n Bu)(thf)] ( 1 ) by n butane elimination from Mg( n Bu) 2 (thf) n . A stronger donor such as DMAP replaces the THF from 1 to give [( NN L)Mg( n Bu)(dmap)] ( 2 ). Both are air-sensitive, and 1 is adventitiously oxidized into [( NN L)Mg(μ-O n Bu)] 2 ( 3 2 ). The homoleptic [( NN L) 2 Mg] ( 8 ) is made from 1 and a second equiv of NN L H . 1 's terminal n Bu group is selectively protonated by HN(SiMe 3 ) 2 to give [( NN L)MgHMDS] ( 4 ; HMDS = N(SiMe 3 ) 2 ), whereas Ph 3 SiOH partially protonates the backbone anilide as well to give a mixture of [( NN L)Mg(OSiPh 3 )(thf)] ( 5 ) and free NN L H . Like HN(SiMe 3 ) 2 , aprotic MeOTf also reacts by selectively abstracting the n Bu group from 1 to give [( NN L)Mg(μ:κ 2 - O , O' -OTf)(thf)] 2 ( 6 2 ). Interestingly, screening the common synthetic routes for magnesium hydrides leads to diverse outcomes upon varying the Mg precursors and hydride sources. 1 and PhSiH 3 give the hydride cluster [{( NN L) 2 Mg 2 (μ-H)} 2 (μ-H) 4 Mg] ( 7 ), whereas 2 and PhSiH 3 give the molecular complex [( NN L de )Mg(dmap) 2 ] ( 9 ) with a dearomatized pyridyl backbone. 1 and HBpin (pinacolborane) give a product mixture, from which a different hydride cluster [( NN L) 2 Mg 2 (μ-H)} 2 (μ:κ 2 - O , O' -O 2 C 2 Me 4 )] ( 10 ) is identified, showing a rare instance of complete deborylation of a HBpin molecule. 1 and HBcat (catecholborane) also give a product mixture, one of which is the borylated ligand [( NN L)Bcat] ( 11 ). HBpin with 4 as the Mg precursor takes the ligand borylation route more selectively to give [( NN L)Bpin] ( 12 ). Last, 1 reacts with i PrNH 2 BH 3 to give [( NN L)Mg{NH( i Pr)BH 3 }] ( 13 ), which shows a slow and fractional conversion into the dinuclear mixed hydrido amidoborane [( NN L) 2 Mg 2 (μ-H){(μ-NH( i Pr)BH 3 }] ( 14 ) by partial β-hydride elimination. In comparison, [( NN L)Mg( i PrNHBH 3 )(dmap)] ( 15 ) arising from the DMAP-bound 2 and i PrNH 2 BH 3 is stable toward such elimination.