C–C Bond Formation and Related Reactions at the CNC Backbone in (smif)FeX (smif = 1,3-Di-(2-pyridyl)-2-azaallyl): Dimerizations, 3 + 2 Cyclization, and Nucleophilic Attack; Transfer Hydrogenations and Alkyne Trimerization (X = N(TMS)2, dpma = (Di-(2-pyridyl-methyl)-amide))

Molecular orbital analysis depicts the CNCnb backbone of the smif (1,3-di-(2-pyridyl)-2-azaallyl) ligand as having singlet diradical and/or ionic character where electrophilic or nucleophilic attack is plausible. Reversible dimerization of (smif)­Fe{N­(SiMe3)2} (1) to [{(Me3Si)2­N}­Fe]2(μ-κ3,κ3-N,py2-smif,smif) (2) may be construed as diradical coupling. A proton transfer within the backbone-methylated, and o-pyridine-methylated smif of putative ( b Me2 o Me2­smif)­Fe­N(SiMe3)2 (8) provides a route to [{(Me3Si)2­N}­Fe]2(μ-κ4,κ4-N,py2,C-( b Me, b CH2, o Me2(smif)­H))2 (9). A 3 + 2 cyclization of ditolyl-acetylene occurs with 1, leading to the dimer [{2,5-di(pyridin-2-yl)-3,4-di-(p-tolyl-2,5-dihydro­pyrrol-1-ide)}­FeN­(SiMe3)2]2 (11), and the collateral discovery of alkyne cyclotrimerization led to a brief study that identified Fe(N­(SiMe3)2­(THF) as an effective catalyst. Nucleophilic attack by (smif)2­Fe (13) on t BuNCO and (2,6- i Pr2C6H3)­NCO afforded (RNHCO-smif)2­Fe (14a, R = t Bu; 14b, 2,6- i PrC6H3). Calculations suggested that (dpma)2­Fe (15) would favorably lose dihydrogen to afford (smif)2­Fe (13). H2-transfer to alkynes, olefins, imines, PhNNPh, and ketones was explored, but only stoichiometric reactions were affected. Some physical properties of the compounds were examined, and X-ray structural studies on several dinuclear species were conducted.