The preparation and reaction chemistry of β-diketiminato aluminum complexes are described. (TTP)AlCl2 (1) (TTPH = 2-(p-tolylamino)-4-(p-tolylimino)-2-pentene) is formed by the treatment of AlCl3 with LiTTP. Sequential alkylation of 1 with CH3Li results in the formation of the mono- and dimethyl aluminum complexes (TTP)AlMeCl (2) and (TTP)AlMe2 (3), respectively. Only monoalkyl complexes are produced when more hindered alkyllithium reagents are used. Compounds 2 and 3 are more conveniently prepared by treating Al(CH3)3 with TTPH·HCl and TTPH, respectively. The more sterically hindered β-diketimine ligand 2-((2,6-diisopropylphenyl)amino)-4-((2,6-diisopropylphenyl)imino)-2-pentene (DDPH) also reacts smoothly with Al(CH3)3 to yield (DDP)Al(CH3)2 (4). Compound 3 undergoes methyl abstraction reactions upon addition of B(C6F5)3 or AgOTf. Cationic species formed from 3 and B(C6F5)3 are unstable and decompose to (TTP)Al(CH3)(C6F5) and MeB(C6F5)2. In contrast, (TTP)Al(CH3)(OTf) (6) is thermally stable, but the triflate group is surprisingly inert toward displacement by Lewis bases. Compounds 1, 3, 4, and 6 were crystallographically characterized. The structures all indicate that the β-diketiminato backbone is essentially planar. The pseudotetrahedral aluminum center is displaced from the plane formed by the ligand backbone in 4 by 0.72 Å.

The preparation and reaction chemistry of beta-diketiminate titanium and zirconium complexes is described. Amine elimination reactions work well for introducing Tolnacnac or Tolnacac to the metal centers (TolnacnacH = 2-(p-tolylamino)-4-(p-tolylimino)-2-pentene; TolnacacH = 4-p-toluidinopent-3-en-2-one). In certain cases, the iminium salt of the diketimine can be used to circumvent the unfavorable reaction kinetics. Salt elimination reactions starting from group 4 metal halides and beta-diketiminate lithium reagents are the most versatile method for introducing beta-diketiminate ligands to the metal. For (beta-diketiminate)MCl(3) compounds (M = Ti, Zr) eta(5)- and eta(2)-coordination modes can be controlled by modifying the diketiminate ligands. Several structures of five- and six-coordinate metal complexes were solved by X-ray diffraction methods. Five-coordinate metal complexes adopt both trigonal bipyramidal and square pyramidal geometries, and the six-coordinate metal complexes possess pseudooctahedral metal centers. For (Tolnacnac)(2)ZrX(2) (X = Cl, OR, NMe(2)) the activation parameters for Lambda/Delta conversion have been probed by dynamic NMR and are consistent with a Bailar-twist mechanism. At a common temperature, the isomerization rates follow the order Cl > OR > NMe(2).

An alkane elimination reaction generates the diketiminate compound (TTP)Zr(CH2Ph)3 (1) from Zr(CH2Ph)4 and TTPH (TTPH = 2-p-tolylamino-4-p-tolylimino-2-pentene). The molecular structure of 1 was solved, and it shows a five-coordinate zirconium with three η 1-coordinated benzyl groups and an η 2-bound TTP ligand. When 1 is heated to 45 °C in hydrocarbon solvents, toluene is eliminated and the orthometalated product 2 is formed. The molecular structure of 2 indicates η 1 and η 2 benzyl groups. The variable-temperature 1H NMR (−78 to 50 °C) spectra exhibit a single benzyl resonance. The magnitude of 1 J CH for the benzyl methylene resonance is consistent with a rapid exchange between η 1 and η 2 bonding modes in solution. Isotopic labeling experiments employing (PPP-d 10)Zr(CH2Ph)3(3-d 10, PPP = 2-phenylamino-4-phenylimino-2-pentenato) support direct C−H activation through a four-centered transition state. Based on kinetic experiments, C−H activation is unimolecular, and the rate-limiting step exhibits a large kinetic isotope effect:  k H/k D = 5.2(5) at 65 °C. The thermal stability of alkyl complexes is improved by replacing the ortho protons with isopropyl groups. (DDP)ZrMe3 (5) can be prepared from (DDP)ZrCl3 via halide metathesis using MeLi (DDP = 2-(2,6-diisopropyl)phenylamino-4-(2,6-diisopropyl)phenylimino-2-pentenato). The thermal stability of 5 is greatly enhanced compared to those of 1 and 3.

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This paper provides an entry point to the coordination chemistry of the group VIII chemistry of the bis(8-quinolinyl)amine (BQA) ligand. In this context, mono- and disubstituted BQA complexes of iron, ruthenium, and osmium are described. For example, the low-spin bis-ligated Fe(III) complex [Fe(BQA)(2)][BPh(4)] has been prepared via amine addition to FeCl(3) in the presence of a base and NaBPh(4). Complexes featuring a single BQA ligand are more readily prepared for Ru and Os. Auxiliary ligands featuring a single BQA ligand, along with two other L-type donor ligands, allow for a variety of ligand types to occupy a sixth coordination site. Representative examples include the halide and pseudohalide complexes trans-(BQA)MX(PPh(3))(2) (M = Ru, Os; X = Cl, Br, N(3), OTf), as well as the hydride and alkyl complexes trans-(BQA)RuH(PMe(3))(2) and trans-(BQA)RuMe(PMe(3))(2). Electrochemical studies are discussed that help to contextualize the BQA ligand with respect to its neutral counterpart 2,2',2''-terpyridine (terpy) in terms of electron-releasing character. Bidentate ligands have been explored in conjunction with the BQA ligand. Thus, the bidentate, monoanionic aryl(8-quinolinyl)amido ligand 3,5-(CF(3))(2)-(C(6)H(3))QA has been installed onto the (BQA)Ru platform to provide (BQA)Ru(3,5-(CF(3))(2)-(C(6)H(3))QA)(PPh(3)). A bis(phosphino)borate ligand stabilizes the five-coordinate complex [Ph(2)B(CH(2)PPh(2))(2)]Ru(BQA). Finally, access to dinitrogen complexes of the types [(BQA)Ru(N(2))(PPh(3))(2)][PF(6)], [(BQA)Ru(N(2))(PMe(3))(2)][PF(6)], and [(BQA)Os(N(2))(PPh(3))(2)][PF(6)] is provided by exposure of the sixth coordination site under a N(2) atmosphere.