Donor-activated alkali metal dipyridylamides: co-complexation reactions with zinc alkyls and reactivity studies with benzophenone

Abstract

Previously it was reported that activation of (t)Bu2Zn by [(TMEDA)Na(μ-dpa)]2 led to tert-butylation of benzophenone at the challenging para-position, where the sodium amide functions as a metalloligand towards (t)Bu2Zn manifested in crystalline [{(TMEDA)Na(dpa)}2Zn(t)Bu2] (TMEDA is N,N,N',N'-tetramethylethylenediamine, dpa is 2,2'-dipyridylamide). Here we find altering the Lewis donor or alkali metal within the metalloligand dictates the reaction outcome, exhibiting a strong influence on alkylation yields and reaction selectivity. Varying the former led to the synthesis of three novel complexes, [(PMDETA)Na(dpa)]2, [(TMDAE)Na(dpa)]2, and [(H6-TREN)Na(dpa)], characterised through combined structural, spectroscopic and theoretical studies [where PMDETA is N,N,N',N'',N''-pentamethyldiethylenetriamine, TMDAE is N,N,N',N'-tetramethyldiaminoethylether and H6-TREN is N',N'-bis(2-aminoethyl)ethane-1,2-diamine]. Each new sodium amide can function as a metalloligand to generate a co-complex with (t)Bu2Zn. Reacting these new co-complexes with benzophenone proved solvent dependent with yields in THF much lower than those in hexane. Most interestingly, sub-stoichiometric amounts of the metalloligands [(TMEDA)Na(dpa)]2 and [(PMEDTA)Na(dpa)]2 with 1 : 1, (t)Bu2Zn-benzophenone mixtures produced good yields of the challenging 1,6-tert-butyl addition product in hexane (52% and 53% respectively). Although exchanging Na for Li gave similar reaction yields, the regioselectivity was significantly compromised; whereas the K system was completely unreactive. Replacing (t)Bu2Zn with (Me3SiCH2)2Zn shut down the alkylation of benzophenone; in contrast, (t)BuLi generates only the reduction product, benzhydrol. Zincation of the parent amine dpa(H) generated the crystalline product [Zn(dpa)2], as structurally elucidated through X-ray crystallography and theoretical calculations. Although the reaction mechanism for the alkylation of benzophenone remains unclear, incorporation of the radical scavenger TEMPO (2,2,6,6-tetramethylpiperidine-N-oxyl radical) into the reaction system completely inhibits benzophenone alkylation.

Formation of a hydride containing amido-zincate using pinacolborane

“…Complexes 1–4 were all fully characterised in solution (comparing well with the data previously reported for other dpa-zincates ( e.g. [(TMEDA) 2 Na 2 (μ-dpa) 2 Zn( t Bu) 2 ], A , and [Na(THF) 6 {Zn( t Bu) 2 (dpa)Zn( t Bu) 2 }], B ) 19 and L 2 ZnPh 2 systems, e.g. TMEDA·ZnPh 2 ) 20 and in the solid state by single crystal X-ray diffraction studies.…”

“…2a and b ), the anionic dpa ligand is also in an anti / anti conformation, but now bridges between a donor-capped Li + cation coordinated to the N amido with a ZnPh 2 unit chelated within the dipyridyl pocket, similar to that observed in zincates A and B . 19 Close comparison of 1 and 3 ( Table 2 ) reveal that the tetrahedral environment of Li in 3 is more distorted ( τ 4 = 0.7) from ideal than in 1 ( τ 4 = 0.9) but the average angles and Li–N amido bond lengths are identical within error. In both complexes Zn is in a distorted N 2 C 2 -tetrahedral environment, displaying essentially identical bond distances, average angles and the extent of distortion from an ideal tetrahedral environment ( τ 4 ).…”

“…aniline derived) incorporated into a chelating group could preclude Zn–N/H–BPin exchange. 2,2′-Dipyridylamide (dpa) was selected as it has three Lewis basic N-atoms incorporated within a flexible scaffold, favouring chelation to zinc, 19 and a significantly lower nucleophilicity amide (potentially disfavouring Zn–N/H–B exchange). Mixing Lidpa with ZnPh 2 and reacting this with one equivalent of HBPin afforded PhBPin as the major product (entry 7 and Fig.…”

Synthetic and Structural Studies of Mixed Sodium Bis(trimethylsilyl)amide/Sodium Halide Aggregates in the Presence of η2-N,N-, η3-N,N,N/N,O,N-, and η4-N,N,N,N-Donor Ligands

“…Displacement ellipsoids are displayed at 30% probability. Selected bond distances (Å) and angles (°) for 6: Na1-N1 2.425(5), Na2-N2 2.369(5), Na2-N1 2.377(5), Na3-N3 2.378(5), Na3-N2 2.382(5), Na4-N3 2.417(5), Na1-N4 2.479(7), Na1-N5 2.528(7), Na4-N7 2.496(6), Na4-N6 2.498(7), Na1-I1 3.128(2), Na2-I1 3.127(2), Na3-I1 3.139(2), Na4-I1 3.123(2); Na2-N1-Na1 94.75 (19), Na2-N2-Na3 91.29(17), Na3-N3-Na4 95.29(16), N2-Na2-N1 159.5(2), N3-Na3-N2 160.96 (18), Na2-I1-Na1 68.78(6), Na4-I1-Na3 68.94(5), Na2-I1-Na3 65.66(6), N1-Na1-N4 127.1(2), N1-Na1-N5 135.9(2), N4-Na1-N5 70.1(2), N1-Na1-I1 97.65(13), N4-Na1-I1 119.47 (18), N5-Na1-I1 106.90(17), N3-Na4-N7 128. 4(2), N3-Na4-N6 133.9(3), N7-Na4-N6 70.9(2), N3-Na4-I1 97.56(12), N7-Na4-I1 120.18(16), N6-Na4-I1 105.83 (19); for 7: Na3-N2 2.392(3), Na2-N1 2.383(3), Na2-N2 2.394(3), Na1-N3 2.369(3), Na1-N1 2.384(3), Na4-N3 2.374(3), Na3-N7 2.475(3), Na3-N6 2.491(3), Na4-N4 2.454(4), Na4-N5 2.518(3), Na1-I1 3.1049(15), Na2-I1 3.0964 (14), Na3-I1 3.1184(15), Na4-I1 3.1297 14; Na3-N2-Na2 91.45 (11), Na2-N1-Na1 93.64 (11), Na1-N3-Na4 92.75(12), N1-Na2-N2 159.41(12), N3-Na1-N1 160.47(12), Na2-I1-Na1 68.17(4), Na2-I1-Na3 66.92(4), Na1-I1-Na4 66.82(4), N2-Na3-N7 136.32(12), N2-Na3-N6 135.12(12), N7-Na3-N6 75.99 (11), N2-Na3-I1 100.53(8), N7-Na3-I1 96.01(9), N6-Na3-I1 106.09(9), N3-Na4-N4 138.38(12), N3-Na4-N5 133.18(12), N4-Na4-N5 75.78 (11), N3-Na4-I1 99.61(9), N4-Na4-I1 101.20 (9), N5-Na4-I1 102.59 (9).…”

Platinum(II)‐Mediated Double Coupling of 2,3‐Diphenylmaleimidine with Nitrile Functionalities To Give Annulated Pentaazanonatetraenate (PANT) Systems

“…[5] ). In addition to the good sequestering properties of triazapentadienes, the central N atom of the TAPD system can be deprotonated to afford, similarly to the 4,4′-dipyridylamine spacer, [6] a moiety for supramolecular assembly and for generating polymetallic systems. [7] Presynthesized stable triazapentadienes with electron-withdrawing substituents demonstrate interesting coordination modes; they are monodentate or bidentate chelate ligands in Cu I and Ag I complexes.…”