Extremely Bulky Amido First Row Transition Metal(II) Halide Complexes: Potential Precursors to Low Coordinate Metal–Metal Bonded Systems

2-Anilidomethylpyridine-Derived Three-Coordinate Zinc Hydride: The Journey Unveils Anilide Backbone's Reactive Nature

Low-coordinate heteroleptic zinc hydrides are catalytically important but rare and synthetically challenging. We herein report three-coordinate monomeric zinc hydride on a 2-anilidomethylpyridine framework (NNL). The synthetic success comes through systematically screening a few different routes from different precursors. During the process, the ligand's anilide backbone interestingly appears to be more reactive than Zn's terminal site to electrophilic Lewis and Brønsted acids. The proligand NNLH reacts with [Zn{N(SiMe3)2}2] and ZnEt2 to give [(NNL)ZnA] (A = N(SiMe3)2 (1), Et(2)). Both are inert to PhSiH3 and H2 but react with HBpin only through the internal Zn-Nanilide bond to give the borylated ligand NNLBpin (3). The reactions of 1 and 2 with Ph3EOH (E = C, Si) afford a series of divergent compounds like [(NNLH)Zn(OSiPh3)2] (4), [Zn3(OSiPh3)4Et2] (5), and [EtZn(OCPh3)] (6). But in all cases, it is invariably the Zn-Nanilide bond protonated by the -OH with equal or higher preference than the terminal Zn-N or Zn-C bonds. A DFT analysis rationalizes the origin of such a reactivity pattern. Realizing that an acid-free route might be the key, reacting [(NNL)Li] with ZnBr2 gives [(NNL)Zn(μ-Br)]2 (7), which on successively treating with KOSiPh3 and PhSiH3 gives the desired [(NNL)ZnH] (8) as a three-coordinate monomer with a terminal Zn-H bond. Estimating the ligand steric in 8 shows the openness in Zn's coordination sphere, a desired criterion for efficient catalysis. This and a positive influence of the pyridyl sidearm is reflected in 8's superior activity in hydroborating PhC(O)Me by HBpin in comparison to Jones' two-coordinate anilido zinc hydride.

H2 and carbon-heteroatom bond activation mediated by polarized heterobimetallic complexes

The field of heterobimetallic chemistry has rapidly expanded over the last decade. In addition to their interesting structural features, heterobimetallic structures have been found to facilitate a range of stoichiometric bond activations and catalytic processes. The accompanying review summarizes advances in this area since January of 2010. The review encompasses well-characterized heterobimetallic complexes, with a particular focus on mechanistic details surrounding their reactivity applications.

Intramolecular Metal⋅⋅⋅π-Arene Interactions in Neutral and Cationic Main Group Compounds

The role of intramolecular metal⋅⋅⋅π-arene interactions has been investigated in the solid-state structures of a series of main group compounds supported by the bulky amide ligands, [N(^tBu Ar^≠ )(SiR₃ )]^- (^tBu Ar^≠ =2,6-(CHPh₂ )₂ -4-tBuC₆ H₂ , R=Me, Ph). The lithium and potassium amide salts showed different patterns of solvation and demonstrated that the SiPh₃ substituent is able to be involved in stabilizing the electrophilic metal. These group 1 metal compounds served as ligand transfer reagents to access a series of bismuth(III) halides. Chloride extraction from Bi(N{^tBu Ar^≠ }{SiPh₃ })Cl₂ using AlCl₃ afforded the 1:1 salt [Bi(N{^tBu Ar^≠ }{SiPh₃ })Cl][AlCl₄ ]. This was accompanied by a significant rearrangement of the stabilizing π-arene contacts in the solid-state. Attempted preparation of the corresponding tetraphenylborate salt resulted in phenyl-transfer and generation of the neutral Bi(N{^tBu Ar^≠ }{SiPh₃ })(Ph)Cl.

Cobalt(II) amido complexes derived from a monodentate arylamido ligand featuring a highly electron-withdrawing C6F5 substituent

A series of cobalt(ii) complexes of a highly electron-withdrawing amido ligand, [N(C6F5)(C6H3Pr(i)2-2,6)](-) (L), were synthesized and structurally characterized. Mononuclear [CoL(Cl)(TMEDA)] (3) and heterobimetallic [CoL2(μ-Cl)Li(THF)3] (4) were obtained by direct metathetical reactions of anhydrous CoCl2 with one molar equivalent of [LiL(TMEDA)] (1) (TMEDA = Me2NCH2CH2NMe2) and [LiL(THF)3] (2), respectively. Complex 3 underwent facile ligand substitution reactions with LiMe and NaN3, yielding the corresponding mixed-ligand complexes [CoL(X)(TMEDA)] (X = Me 5, N36). Treatment of 3 with NaOMe led to the heterobimetallic complex [CoL2(μ-OMe)Na(TMEDA)] (7). The solid-state structures of complexes 1-7 were established by X-ray diffraction analysis.

Synthesis and characterization of extremely bulky amido-germanium(II) halide complexes

The extremely bulky aryl/silyl secondary amines, HN(Ar)(SiMe3), Ar = C6H2-i-Pr2(CPh3)-2,6,4 (LDipH), C6H2{C(H)Ph2}2-i-Pr-2,6,4 (L†H), or C6H2{C(H)Ph2}2-t-Bu-2,6,4 (Lt-BuH), have been synthesized via salt metathesis reactions between the appropriate lithium anilide complex and ClSiMe3. The related diaryl secondary amines, HN(Ar*)(R), Ar* = C6H2{C(H)Ph2}2Me-2,6,4 and R = C6H3Me2-3,5 (LMeH), C6H3(CF3)2-3,5 (LCF3H), or C6H2-i-Pr3-2,4,6 (LTripH), were prepared via palladium catalyzed cross-coupling reactions. Three of the amines were crystallographically characterized. Treatment of GeCl2·dioxane with 1 equiv. of each of the deprotonated amines led to the isolation of the amido-germanium(II) chloride complexes, [LGeCl] (L = L†, Lt-Bu, LCF3, or LTrip). Similarly, reaction of the known amido-digermyne, [L*Ge–GeL*] (L* = –N(Ar*)(SiMe3)), with I2 resulted in the oxidative cleavage of the Ge–Ge bond of the digermyne, and the formation of the first two-coordinate amido-germanium(II) iodide complex, [L*GeI]. Crystallographic characterization of [Lt-BuGeCl] and [L*GeI] revealed both to have similar monomeric structures. The compounds described in this study should prove useful as synthons for synthetic chemists working in the field of low oxidation state main group chemistry.