The synthesis, isolation, and metalation of the trianionic PrNCNLi 3 ] 2 (2) is described. The terdentate coordination ability of 2 is demonstrated in the synthesis of the hafnium dichloride anion [2,6-i PrNCNHfCl 2 ]-[Li(DME) 3 ] (3-DME). Complex 3-DME is distorted square pyramidal in the solid state, but NMR eVidence indicates the complex is fluxional and trigonal bypyramidal in solution. Straightforward ligand modification proVides the additional trianionic pincer ligand [3,5-MeNCNLi 2 ] 2 [Li 2 (DME) 6 ] ( 5). This sterically smaller ligand leads to the hafnium pincerate dianion complex [(3, 2 Hf][Li 2 (DME) 2 ] ( 6), which contains two trianionic pincer ligands. The new compounds are characterized by elemental analysis, multinuclear NMR, and X-ray diffraction crystallography.

The synthesis, characterization, and unprecedented catalytic activity of cationic aluminum alkyl complexes toward hydrosilylation are described. X-ray crystallographic analysis of Tp*AlMe2 (1) and [Tp*AlMe][I3] (3) revealed the preference of Al for a tetrahedral coordination environment and the versatility of the Tp* ligand in stabilizing Al in bi- and tridentate coordination modes. [Tp*AlMe][MeB(C6F5)3] (2) is highly active toward the hydrosilylation of a wide variety of carbonyls and imines, thus providing an inexpensive and versatile alternative to late transition metal catalysts.

The catalytic activity of commercially available [Al(NMe2)3]2 (1) and a dimethyl aluminum guanidinate complex toward the hydro-amination/-hydrazination of carbodiimides was studied. The guanidinate-supported complex 2 was prepared via salt metathesis reactions of AlMe2Cl and an in situ generated lithium guanidinate reagent. X-ray crystallographic studies revealed the influence of the guanidinate ligand on the Al metal center. Hydroamination reactions were successfully carried out at room temperature with 2 as the catalyst, while 1 proved to be ineffective under these conditions. On the contrary, both 1 and 2 were active toward the hydro-hydrazination of carbodiimides, which were run at elevated temperatures (120 °C). Consequently, the reaction temperature had a significant influence on the choice of the catalyst since the catalytically active species can be generated from various precatalysts under different conditions. The formation of guanidines and aminoguanidines showed a high functional group tolerance and typically proceeded with excellent yields at low catalyst loadings. X-ray crystallographic studies of compound 4a revealed interesting structural features of the previously unknown aminoguanidine products. The independently isolated Al aminoguanidinate complex 5 showed catalytic activity toward hydro-hydrazination chemistry and provided valuable evidence in support of the proposed reaction mechanism.

This report details the synthesis of new NCN trianionic pincer ligand precursors and metalation reactions to form group (IV) complexes. N,N'-[1,3-phenylenebis(methylene)]bis-2,6-diisopropylaniline [2,6-(i)PrNCN]H(3) (8) was converted to the N,N'-substituted Si(IV), Sn(IV), Mg(II), and Zn(II) derivatives. [2,6-(i)PrNCHN](SiMe(3))(2) (9-Si) and [2,6-(i)PrNCHN](SnMe(3))(2) (9-Sn) form by first treating 8 with MeLi followed by Me(3)MCl, where M = Si or Sn. Single crystal X-ray experiments indicate 8, 9-Si, and 9-Sn have similar structural features in the solid state. [2,6-(i)PrNCHN](mu-MgCl.THF)(2) (12) forms by treating 8 with MeMgCl, and its solid state structure revealed a bis-mu-MgCl bridging unit. The (1)H NMR spectrum of 12 reveals a dynamic process occurs in solution. A variable temperature (1)H NMR experiment failed to quench the dynamic process. {[2,6-(i)PrNCHN]Zn}(2) (13) forms upon treating {[2,6-(i)PrNCHN]Li(2)}(2) (10) with anhydrous ZnCl(2) and is a dimer in the solid state. Again, dynamic (1)H NMR behavior is observed, and a mechanism is provided to explain the apparent low symmetry of 13 in solution. Extension of the aliphatic arm of the NCN ligand provides the new N(C)C(C)N pincer ligand precursors N,N'-(2,2'-(1,3-phenylene)bis(ethane-2,1-diyl))bis(3,5-bis(trifluoromethyl)aniline) [3,5-CF(3)N(C)C(C)N]H(3) (16) and [3,5-CF(3)N(C)CH(C)N](SiMe(3))(2) (17). A more rigid ligand architecture was accessed by synthesis of the anthracene derived pincer ligand anthracene-1,8-diylbis(N-3,5-bistrifluormethylaniline) [3,5-CF(3)N(C)C(anth)(C)N]H(3) (18). Treating {Zr(NMe(2))(4)}(2) with 2 equiv of 16 provides the dimer {(mu-3,5-CF(3)N(C)CH(C)N)Zr(NMe(2))(3)NHMe(2)}(2) (19). Treating Hf(NMe(2))(4) with 18 provides the bimetallic complex (mu-3,5-CF(3)N(C)CH(anth)(C)N){Hf(NMe(2))(3)NHMe(2)}(2) (20) in which one ligand bridges two Hf(IV) ions. Salt metathesis between 10 and ZrCl(2)(NMe(2))(2)(THF)(2) provides the mononuclear complex [2,6-(i)PrNCHN]Zr(NMe(2))(2) (21) in which the NCN ligand is bound as a chelating diamide. Thermoysis of 21 does not lead to formation of a trianionic pincer complex. Instead, treating HfCl(4) with {[2,6-(i)PrNCN]Li(3)}(2) (11) followed by MeLi provides the trianionic pincerate complex [2,6-(i)PrNCNHfMe(2)][Li(DME)(2)] (23). In the solid state the Hf ion has distorted trigonal bipyramidal geometry.

The synthesis and characterization of mixed alkyl/amide Al complexes supported by guanidinate and monoanionic OCO-pincer ligands are described. In situ generation of the lithium-guanidinate reagents via reaction of carbodiimides and lithium-amide reagents, followed by reaction with the corresponding AlMe x Cl 3-x reagents, resulted in the formation of compounds 1-3. Subsequent reaction with lithium arylamide reagents provided access to mixed alkyl/amide-and bis-amidesubstituted complexes 4-6, which were characterized by multinuclear NMR spectroscopy and elemental analysis. Single-crystal X-ray diffraction of compounds 5a and 6a confirmed the monomeric nature of these complexes and revealed the influence of the alkyl/amide functionalities on the bonding of the guanidinate ligands. A similar synthetic approach resulted in isolation of an OCO-pincer-supported Al dialkyl complex, which was also fully characterized. In contrast to the guanidinate compounds, complex 8 showed activity toward intramolecular hydroamination of 2,2diphenylpent-4-en-1-amine.