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))

Abstract

Molecular orbital analysis depicts the CNC(nb) 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-κ(3),κ(3)-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-κ(4),κ(4)-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.

Disparate reactivity from isomeric {Me 2 C(CH 2 N CHpy) 2 } and {Me 2 C(CH NCH 2 py) 2 } chelates in iron complexation

“…Formation of the dimetallic products is consistent with deprotonation of the original imine by the metal amides, followed by an azaallyl radical coupling reaction (e.g. via (2-py)(C(Á)H-N(-)@C(Á)H(2-py)), or an alternative nucleophile/ electrophile coupling through an (2-py)(CH(-)-N@CH(2-py)) fragment [5].…”

“…After 37.5 h there was complete conversion to the title pyrrolidine product (TON = 11; TOF = 0.29 h À1 ). 1 H (C 6 D 6 ): d 0.89 (s, syn-CH 3 , 3H), 1.00 (s, anti-CH 3 , 3H), 2.85 (dd, J = 7.6 Hz, 9.5 Hz, syn-2 CH 2 , 1H), 3.08 (ddd, J = 7.6 Hz, 8 Hz, 9 Hz, 1 NH, 1H), 3.44 (dd,J = 7.6 Hz,9.5 Hz, anti-2 CH 2 , 1H), 3.58 (d,J = 5.5 Hz,4 CH,1H),4.89 (dd,J = 5.5 Hz,9 Hz,5 CH, 1H), 6.42 (dd,J = 4.5 Hz,7.5 Hz, Py 1 -5-py CH, 1H), 6.50 (dd, J = 4.5 Hz, 7.5 Hz, Py 2 -4-py CH, 1H), 6.92 (t, J = 7.5 Hz, Py 2 -5-py CH, 1H), 6.98 (t, J = 7.5 Hz, Py 1 -4-py CH, 1H), 7.21 (d, J = 7.5 Hz, Py 1 -3-py CH, 1H), 7.69 (dd, J = 7.5 Hz, Py 2 -3-py CH, 1H), 8.27 (s, im CH, 1H), 8.37 (d, J = 4.5 Hz, Py 1 -6-py CH, 1H), 8.39 (d, J = 4.5 Hz, Py 2 -6-py CH, 1H). See Fig.…”

“…The generation of 2-N(TMS) 2 , and the ensuing thermolysis, suggested the potential for carbon-carbon bond formation in the system [3][4][5]7], hence a hydrazine derivative, 1,2-diphenyl-1,2-dimethylhydrazine, was added to oxidatively release organic product from the metal. For example, 1 equiv dmp(PM) 2 and 1 equiv hydrazine were placed in C 6 D 6 with 10% Fe{N(TMS) 2 } 2 (THF), and a new organic product formed after 2 d at 23°C.…”

“…As part of an investigation involving 1,3-di-(2-pyridyl)-2-azaallyls [1][2][3][4][5][6][7][8] and related species as chelating agents, imines that can serve as azaallyl precursors were incorporated into tetradentate platforms. In Fig.…”

“…Selected interatomic distances (Å) and angles (°): Fe-N1,1.9574(11); Fe-N2,1.8812(12); Fe-N3,1.8862(11); Fe-N4,1.9438(12); N2-C7, 1.4607(18); N3-C9,1.4639(18); N2-C6,1.3293(17); N3-C10, 1.3299(17); C5-C6,1.3940(19); C10-C11, 1.393(2); N1-C5,1.3959(16); N4-C11, 1.3889(17); N1-C1, 1.3664(17); N4-C15,1.3692(19); Fe-P, 2.1952(4); N1-Fe-N2, 81.21(5); N1-Fe-N3, 155.80(5); N1-Fe-N4, 100.29(5); N2-Fe-N3, 92.72(5); N2-Fe-N4, 169.22(5); N3-Fe-N4, 81.56(5); N1-Fe-P, 99.86(3); N2-Fe-P, 94.65(4); N3-Fe-P, 103.99(4); N4-Fe-P, 95.59(3); C7-N2-Fe, 126.19(9); C9-N3-Fe, 128.20(9); C7-N2-C6, 116.53(12); C9-N3-C10, 115.09(11); N2-C6-C5, 115.09(12); N3-C10-C11, 115.32(12); C6-C5-N1, 112.75(11); C10-C11-N4, 112.83(12); C5-N1-C1, 115.06(11); C11-N4-C15, 115.01(12); Fe-N1-C5, 112.90(9); Fe-N4-C11, 113.52(9). the presence of PMe 3 , but a brown insoluble byproduct prevented use of this route.…”