Pincer Ligand Precursors Research Articles

Synthesis, Reactivity and Coordination Chemistry of Group 9 PBP Boryl Pincer Complexes: [(PBP)M(PMe3)n] (M = Co, Rh, Ir; n = 1, 2).

The unsymmetrical diborane(4) derivative [(d(CH2P(iPr)2)abB)-Bpin] (1) proved to be a versatile PBP boryl pincer ligand precursor for Co(I) (2a, 4a), Rh(I) (2-3b) and Ir(I/III) (2-3c, 5-6c) complexes, in particular of the types [(d(CH2P(iPr)2)abB)M(PMe3)2] (2a-c) and [(d(CH2P(iPr)2)abB)M-PMe3] (2b-c). Whilst similar complexes have been obtained before, for the first time, the coordination chemistry of a homologous series of PBP pincer complexes, in particular the interconversion of the five- and four-coordinate complexes 2a-c/3a-c, was studied in detail. For Co, instead of the mono phosphine complex 2a, the dinitrogen complex [(d(CH2P(iPr)2)abB)Co(N2)(PMe3)] (4a) is formed spontaneously upon PMe3 abstraction from 2a in the presence of N2. All complexes were comprehensively characterised spectroscopically in solution via multinuclear (VT-)NMR spectroscopy and structurally in the solid state through single-crystal X-ray diffraction. The unique properties of the PBP ligand with respect to its coordination chemical properties are addressed.

Bisamidate-functionalized NHC ligands: Electronic and steric influences of N-substituents on the bisamidate moieties

Bis-anionic tethered NHC ligands have widely served as stable and useful catalysts. The properties of anionic donor sites make them useful for the tuning of metal complexes with the NHC ligands, and since amidate ligands can be functionalized on their nitrogen elements, they also have been applied as catalysts. There has been, however, a paucity of investigations into the influences of various N-substituents on bisamidate portions within bis-amidate functionalized NHCs. In this study, we used original NHCs, which we refer to as DHASIs, to synthesize various bisamide functionalized NHC pincer ligand precursors, and their Pd complexes also were successfully obtained. The structures of the synthesized complexes were unambiguously confirmed via XRD study, which showed that the N-substituents had a structural affect via the coordination modes of the resultant complexes. We applied the obtained pincer complexes to a Suzuki Miyaura coupling reaction and found that the strong Lewis basicity of the anionic N donors improved the catalytic performance of Pd–NCN pincer complexes.

Synthesis, Characterization of Rare‐Earth Metal Chlorides Bearing Indolyl‐Based NCN Pincer Ligand and Their Catalytic Activity toward 1,4‐cis Polymerization of Isoprene

Main observation and conclusionA novel indolyl‐based NCN pincer ligand precursor HL (HL = (1‐(2‐(CH2)4NCH2CH2)‐3‐(2,6‐iPr2C6H3N=CH)C8H5N)) was rationally and precisely designed, and successfully prepared in a high yield. Lithiation of HL with nBuLi in n‐hexane, followed by treatment with RECl3 in THF led to the isolation of rare‐earth metal chlorides in monomeric form (κ3‐L)RECl2(THF) (RE = Sc(2), Yb(3)), and dimeric form [(κ3‐L)RECl(THF)(μ‐Cl)]2 (RE = Er(4), Y(5)) bearing the novel indolyl‐based NCN pincer ligand in designed pincer ligation depending on different metal ionic radii; and the chloride bridged rare‐earth metal and lithium mixed complexes in form (κ2‐L)2RE(μ‐Cl)2Li(THF)2 (RE = Y(6), Dy(7). All complexes were fully characterized and their structures were determined. The diamagnetic complexes 2, 5 and 6 were furtherly characterized by the NMR spectroscopic method. The catalytic activity studies revealed that the central metal ions, borates, aluminum alkyls, and ligation of the central metal ions have influences on catalytic activity, and regio‐ and stereoselectivity for the polymerization of isoprene. With cooperation of the cocatalysts, the pincer‐type yttrium chloride 5 initiated the isoprene polymerization with a high activity producing polymers with high regio‐ and stereoselectivity (1,4‐cis polymers up to 99.6%), and the Mn as high as 8.76 × 105.

Preparation of SNS Cobalt(II) Pincer Model Complexes of Liver Alcohol Dehydrogenase.

Chemical model complexes are prepared to represent the active site of an enzyme. In this protocol, a family of tridentate pincer ligand precursors (each possessing two sulfur and one nitrogen donor atom functionalities (SNS) and based on bis-imidazole or bis-triazole compounds) are metallated with CoCl2·6H2O to afford tridentate SNS pincer cobalt(II) complexes. Preparation of the cobalt(II) model complexes for liver alcohol dehydrogenase is facile. Based on a quick color change upon adding the CoCl2·6H2O to acetonitrile solution that contains the ligand precursor, the complex forms rapidly. Formation of the metal complex is complete after allowing the solution to reflux overnight. These cobalt(II) complexes serve as models for the zinc active site in liver alcohol dehydrogenase (LADH). The complexes are characterized using single crystal X-ray diffraction, electrospray mass spectrometry, ultra-violet visible spectroscopy, and elemental analysis. To accurately determine the structure of the complex, its single crystal structure must be determined. Single crystals of the complexes that are suitable for X-ray diffraction are then grown via slow vapor diffusion of diethyl ether into an acetonitrile solution that contains the cobalt(II) complex. For high quality crystals, recrystallization typically takes place over a 1 week period, or longer. The method can be applied to the preparation of other model coordination complexes and can be used in undergraduate teaching laboratories. Finally, it is believed that others may find this recrystallization method to obtain single crystals beneficial to their research.

CNS and CNP Iron(II) Mono-Iron Hydrogenase (Hmd) Mimics: Role of Deprotonated Methylene(acyl) and the trans-Acyl Site in H2 Heterolysis.

We report syntheses and H2 activation involving model complexes of mono-iron hydrogenase (Hmd) derived from acyl-containing pincer ligand precursors bearing thioether (CNSPre) or phosphine (CNPPre) donor sets. Both complexes feature pseudo-octahedral iron(II) dicarbonyl units. While the CNS pincer adopts the expected mer-CNS (pincer) geometry, the CNP ligand unexpectedly adopts the fac-CNP coordination geometry. Both complexes exhibit surprisingly acidic methylene C-H bond (reversibly de/protonated by a bulky phenolate), which affords a putative dearomatized pyridinate-bound intermediate. Such base treatment of Fe-CNS also results in deligation of the thioether sulfur donor, generating an open coordination site trans from the acyl unit. In contrast, Fe-CNP maintains a CO ligand trans from the acyl site both in the parent and dearomatized complexes (the -PPh2 donor is cis to acyl). The dearomatized mer-Fe-CNS was competent for H2 activation (5 atm D2(g) plus phenolate as base), which is attributed to both the basic site on the ligand framework and the open coordination site trans to the acyl donor. In contrast, the dearomatized fac-Fe-CNP was not competent for H2 activation, which is ascribed to the blocked coordination site trans from acyl (occupied by CO ligand). These results highlight the importance of both (i) the open coordination site trans to the organometallic acyl donor and (ii) a pendant base in the enzyme active site.

Transfer hydrogenation of ketones catalyzed by nickel complexes bearing an NHC [CNN] pincer ligand

Four NHC [CNN] pincer nickel (II) complexes, [iPrCNN (CH2)4‐Ni‐Br] (5a), [nBuCNN (CH2)4‐Ni‐Br] (5b), [iPrCNN (Me)2‐Ni‐Br] (6a) and [nBuCNN (Me)2‐Ni‐Br] (6b), bearing unsymmetrical [C (carbene)N (amino)N (amine)] ligands were synthesized by the reactions of [CNN] pincer ligand precursors 4 with Ni (DME)Cl2 in the presence of Et3N. Complexes 5a and 5b are new and were completely characterized. The transfer hydrogenation of ketones catalyzed by the four pincer nickel complexes were explored. Complexes 5a and 6a have better catalytic activity than 5b and 6b. With a combination of NaOtBu/iPrOH/80 °C and 2% catalyst loading of 5a, 77–98% yields of aromatic alcohols could be obtained.

5,6-Membered CNN palladium pincer complexes of 3-benzyl-8-dimethylamino -3-azabicyclo[3.2.1]octane and 3-benzyl-9-dimethylamino-3-azabicyclo[3.3.1]nonane

The unsymmetrical CNN pincer ligand precursors 4 and 7b based on the structures of bicyclo[3.2.l]octane and bicyclo[3.3.l]nonane have been synthesized. The corresponding palladium pincer 5,6-membered complexes 5 and 9 were prepared by direct cyclopalladation of ligand precursors with Li2PdCl4 in MeOH. The molecular structure of the palladacycles was determined by 1H and 13C NMR and confirmed by X-ray diffraction analysis. The obtained complexes 5 and 9 exhibited good catalytic activity in the Suzuki reactions of aryl bromides with phenylboronic acid.

Nickel, Ruthenium, and Rhodium NCN-Pincer Complexes Featuring a Six-Membered N-Heterocyclic Carbene Central Moiety and Pyridyl Pendant Arms

NCN pincer ligand precursor 1·HX (X = Cl, PF6), having a six-membered N-heterocyclic carbene central moiety and pyridyl pendant arms, was prepared via N–C cross-coupling of 2-bromo-6-tert-butylpyridine with propane-1,3-diamine, followed by ring closure with triethylorthoformate. The free ligand 1 was not accessible via deprotonation, yet its copper(I) complex 2 was prepared by reacting 1·HCl with CuI and potassium hexamethyldisilazide. It was used further as a transmetalation agent to prepare nickel(II) and ruthenium(II) dihalide NCN-pincer complexes 3a, 4a, and 4b, featuring a distorted square-pyramidal geometry at the metal, with the carbene ligand in the axial position. The rhodium(III) NCN-pincer complex 6b was obtained from 2 and [Rh(cod)Cl]2 via transmetalation followed by oxidation with Cu(I) in THF. The rhodium(III) NCC-pincer complex 9b was prepared under similar conditions in acetonitrile, where a spontaneous rollover cyclometalation occurred. Complex 9b has a distorted octahedral geometry, with the acetonitrile ligand trans to the carbene. Very short Ru–CNHC and Rh–CNHC bonds were measured in complexes 4a, 4b, and 9b. Halogen exchange was observed by 1H and 13C NMR spectroscopy in both ruthenium and rhodium systems during the transmetalation stage, and the purification was accomplished by pushing the respective equilibrium with excess halide.

Ruthenium(II) pincer complexes featuring an anionic CNC bis(1,2,3-triazol-5-ylidene)carbazolide ligand coordinated in a meridional fashion

The preparation of a new neutral ruthenium(II) pincer complexes with formula [RuCl(CO)2(CTRZNCTRZ)] (CNC=bis(1,2,3-triazol-5-ylidene)carbazolide) is described. Access to the hydrido complex [RuH(CO)2(CTRZNCTRZ)] was attained by reaction of the pincer ligand precursor with base and with [RuCl(H)(AsPh3)3(CO)] in the presence of CO atmosphere. The meridional geometry pincer ligand in the complexes is confirmed by a single crystal X-ray diffraction study of [RuCl(CO)2(CTRZNCTRZ)]. Preliminary results of the use of [RuCl(CO)2(CTRZNCTRZ)] as catalyst in the transfer hydrogenation reaction of ketones, are reported.

Active O,Npy,N-Titanium(IV) Fluoride Precatalysts for Ethylene Polymerization: Exploring “Fluoride Effects” on Polymer Properties and Catalytic Performance

Three examples of discrete six-coordinate O,Npy,N-bearing titanium(IV) trifluoride complexes, [{2-(C5H4N)-6-(CMe2O)C5H3N}TiF3] (1), [{2-(C6H4-2′-O),6-(CMe═N(2,6-i-Pr2C6H3))C5H3N}TiF3] (2a), and [{2-(3-C12H8-2-O)-6-(CMe═N(2,6-i-Pr2C6H3))C5H3N}TiF3] (3a), were prepared using a one-step HF elimination protocol from cis-[(THF)2TiF4] and the corresponding pincer ligand precursor (HL1, HL2H, and HL2Ph). A mer configuration of the three fluoride ligands is adopted in their solid-state structures, which is mirrored in solution, as shown by mutual two-bond F–F coupling in their 19F{1H} NMR spectra. For purposes of comparison, the chloride counterparts of 2a and 3a, [{2-(C6H4-2′-O),6-(CMe═N(2,6-i-Pr2C6H3)C5H3N}TiCl3] (2b) and [{2-(3-C12H8-2-O)-6-(CMe═N(2,6-i-Pr2C6H3))C5H3N}TiCl3] (3b), are also reported. On treatment with excess MAO, 1 is scarcely active in ethylene polymerization, 2a is more active, and the most sterically protected system, 3a, represents the most active nonmetallocene metal-fluoride precatalyst r...

Optimised synthesis of monoanionic bis(NHC)-pincer ligand precursors and their Li-complexes

A straightforward preparation of bis(imidazol)carbazole 4 from carbazole, its transformation to various bis(imidazolium) salts and their deprotonation to Li carbene complexes is presented.

Synthesis, characterization, photophysical properties, and catalytic activity of an SCS bis(N-heterocyclic thione) (SCS-NHT) Pd pincer complex.

Treatment of 1,3-bis(3'-butylimidazolyl-1'-yl)benzene diiodide with elemental sulfur in the presence of a base produced a bis(N-heterocyclic thione) (NHT) pincer ligand precursor. Its reaction with PdCl2(CH3CN)2 produced chloro[1,3-bis(3'-butylimidazole-2'-thione-κ-S)benzene-κ-C]palladium(ii), a 6,6-fused ring SCS-NHT palladium pincer complex. This air stable compound is, to our knowledge, the first SCS pincer complex that utilizes N-heterocyclic thione (NHT) donor groups. The molecular structures of the ligand precursor and the palladium complex were determined by X-ray crystallography and computational studies provided insight into the interconversion between its rac and meso conformations. The photophysical properties of the complex were established, and its catalytic activity in Suzuki, Heck, and Sonogashira cross-coupling reactions was evaluated.

Syntheses and characterization of five-coordinate copper(II) complexes based on tridentate SNS pincer ligand precursors

A series of tridentate pincer ligands, each possessing two sulfur- and one nitrogen-donor functionalities (SNS), based on a bis-imidazolyl precursor were metallated with CuCl2 to give new tridentate SNS pincer copper(II) complexes [(SNS)CuCl2]. These purple complexes exhibit a five-coordinate pseudo-square pyramidal geometry at the copper center. The [(SNS)CuCl2] complexes were characterized with single crystal X-ray diffraction, electrospray mass spectrometry, EPR spectroscopy, attenuated total reflectance infrared spectroscopy, UV–Vis spectroscopy, cyclic voltammetry, and elemental analysis. The EPR spectra are consistent with typical anisotropic Cu(II) signals with four hyperfine splittings in the lower-field region (g||). Various electronic transitions are apparent in the UV–Vis spectra of the complexes and originate from d-to-d transitions or various charge transfer transitions. We preformed computational studies to understand the influence that structural constraints internal to our tridentate SNS ligand precursors have on the oxidation state of the resulting bound copper complex. We have determined that a d9 copper(II) metal center is better situated than a d10 copper(I) center to bind our tridentate SNS ligand set when it does not contain an internal CH2 group. Without this methylene linker, the SNS ligand forces the N and S atoms into a T-shaped arrangement about the metal center.

Synthesis and Characterization of a 1,3-Phenylene-Bridged N-Alkyl Bis(benzimidazole) CCC-NHC Pincer Ligand Precursor: Homobimetallic Silver and Rhodium Complexes and the Catalytic Hydrosilylation of Phenylacetylene

A new CCC-NHC pincer ligand precursor architecture based on 1,3-bis(N-alkylbenzimidazole)benzene has been synthesized and metalated using Ag2O, forming a homobimetallic Ag complex with a metal to ligand ratio of 1:1. The Ag complex was treated with either [Rh(COD)Cl]2 or Rh(COD)2OTf and NBu4I to yield a homobimetallic Rh complex by transmetalation. The Rh complexes were characterized, and an X-ray structure is reported. Their catalytic activity in the hydrosilylation of phenylacetylene is reported.

Syntheses, characterization, density functional theory calculations, and activity of tridentate SNS zinc pincer complexes based on bis-imidazole or bis-triazole precursors

A series of tridentate pincer ligands, each possessing two sulfur- and one nitrogen-donor functionalities (SNS), based on bis-imidazole or bis-triazole salts were metallated with ZnCl2 to give new tridentate SNS pincer zinc(II) complexes [(SNS)ZnCl]+. The zinc complexes serve as models for the zinc active site in liver alcohol dehydrogenase (LADH) and were characterized with single crystal X-ray diffraction, 1H, 13C, and HSQC NMR spectroscopies, electrospray mass spectrometry, and elemental analysis. The zinc complexes feature SNS donor atoms and pseudotetrahedral geometry about the zinc center, as is seen for liver alcohol dehydrogenase. The bond lengths and bond angles of the zinc complexes correlate well to those in horse LADH. The SNS ligand precursors were characterized with 1H, 13C, and HSQC NMR spectroscopies, elemental analysis, and cyclic voltammetry, and were found to be redox active. Gaussian calculations were performed and agree with the experimentally observed oxidation potentials for the pincer ligand precursors. The zinc complexes were screened for the reduction of electron-poor aldehydes in the presence of a hydrogen donor, 1-benzyl-1,4-dihydronicotinamide (BNAH), and it was determined that they enhance the reduction of electron-poor aldehydes. The SNS zinc pincer complexes with bis-triazole ligand precursors exhibit higher activity for the reduction of 4-nitrobenzaldehyde than do SNS zinc pincer complexes with bis-imidazole ligand precursors. Quantitative stoichiometric conversion was seen for the reduction of pyridine-2-carboxaldehyde via SNS zinc pincer complexes with either bis-imidazole or bis-triazole ligand precursors.

Trianionic NCN3– Pincer Complexes of Chromium in Four Oxidation States (CrII, CrIII, CrIV, CrV): Determination of the Active Catalyst in Selective 1-Alkene to 2-Alkene Isomerization

The synthesis and characterization of a series of four Cr complexes in the +2, +3, +4, and +5 oxidation states supported by an NCN trianionic pincer ligand are reported. Treating CrMeCl2(THF)3 with the dilithio salt pincer ligand precursor {[2,6-iPrNCHN]Li2}2 provides the CrIII complex [2,6-iPrNCN]CrIII(THF)3 (1), CrIV complex [2,6-iPrNCN]CrIVMe(THF) (2), and CrII complex [2,6-iPrNHCN]CrII(THF)2 (3). Complexes 2 and 3 are the result of disproportionation. Treating 1 with 1 equiv of styrene oxide in THF converts the CrIII complex to the CrV(O) species [2,6-iPrNCN]CrV(O)(THF) (4). Complex 2, characterized by single-crystal X-ray diffraction, is a rare CrIV methyl complex that is kinetically stable at 25 °C; at 85 °C, Cr–Me bond homolysis occurs. The homolytic cleavage results in CH4 formation and biphenyl via a radical mechanism. The metal-containing product from thermolysis is the same CrII species formed during metalation, except one of the protons is substituted for a deuterium from C6D6 (3-d). Complex 2 is a precatalyst for the selective isomerization of 1-hexene and 1-octene to the corresponding 2-alkenes. An induction period occurs during the catalytic isomerization, and the active catalyst was determined to be the CrII complex 3, not 2.

Synthesis and characterization of a trianionic pincer supported Mo-alkylidene anion and alkyne insertion into a Mo(IV)-C pincer bond to form metallocyclopropene( η2-vinyl) complexes

This report describes two approaches to form complexes featuring Mo–C multiple bonds and a trianionic pincer ligand. Treating the trianionic pincer ligand precursor [ t BuOCO]H 3 (1) with MeLi provides the corresponding dilithio salt [ t BuOCHO]Li 2(THF) 3 ( 6) in situ, which further reacts with Mo(NAr) (CHCMe 2Ph)(OTf) 2(DME) to provide the terphenyl diphenolate complex [ t BuOCHO]Mo(NAr)CHCMe 2Ph ( 5). Complex 5 is characterized by 1H, 13C{ 1H} NMR spectroscopy, combustion analysis, and single crystal X-ray diffraction. The solid state structure of 5 reveals a distorted trigonal pyramidal geometry for the Mo(VI) ion. Treating 5 with one equiv. of phosphorane in toluene converts the diphenolate ligand into a trianionic pincer ligand by deprotonation of the pincer C ipso -H proton to give the alkylidene salt {[ t BuOCHO]Mo(NAr)(CHCMe 2Ph)}{Ph 3PCH 3} ( 7). Treating [ t BuOCO]MoNMe 2(NHMe 2) 2 ( 2), containing a d 2 Mo(IV) ion, with terminal alkynes (H–C≡CR, R = Ph, 3,5-F 2C 6H 3, 3,5-(CF 3) 2C 6H 3 and SiMe 3) produces in excellent yield the corresponding metallocyclopropylidene complexes 10-R (R H, F, CF 3) and 11 (R = SiMe 3). X-ray diffraction studies on single crystals of 10-H and 11 reveal three important features: 1) a highly distorted hexacoordinate Mo(VI) center, 2) a metallocyclopropene( η 2-vinyl) fragment, and 3) a highly distorted CH group in the metallocyclopropene unit. A single point calculation and an NBO analysis performed on 10-H′ confirms the multiple bond between Mo1 and C28. The highest occupied Kohn–Sham molecular orbital (HOMO) represents a π-combination between d yz of Mo1 and the p y orbital of C28, and the corresponding π∗-combination of those orbitals constitutes the lowest unoccupied molecular orbital (LUMO).

A highly active and selective palladium pincer catalyst for the formation of α-aryl ketones via cross-coupling

Several air and moisture stable Pd(II) pincer complexes were synthesized via oxidative addition of Pd(0) to novel PheBox pincer ligand precursors. Low loadings (1 mol%) of the Pd complex [t-BuPhebox-Me(2)]PdBr are capable of efficiently promoting the selective α-monoarylation of a variety of ketones with numerous aryl bromides in only 1 h at 70 °C with 82-99% yields.

A Highly Stable Adamantyl-Substituted Pincer-Ligated Iridium Catalyst for Alkane Dehydrogenation

The adamantyl-substituted pincer-ligand precursor AdPCP-H [(AdPCP = κ3-C6H3-2,6-(CH2PAd2)2); Ad = 1-adamantyl] has been synthesized by the reaction of 1,3-dibromoxylene with di-1-adamantylphosphine in the presence of triethylamine. Treatment of AdPCP-H with [Ir(COD)Cl]2 (COD = 1,5-cyclooctadiene) affords the pincer-ligated complex (AdPCP)IrHCl, which was crystallographically characterized. Dehydrohalogenation of (AdPCP)IrHCl either with LiBEt3H or with KOtBu, under hydrogen atmosphere, yields the hydrides (AdPCP)IrH2 and (AdPCP)IrH4. (AdPCP)IrH2 catalyzes dehydrogenation of alkanes with a level of activity comparable to that of the previously reported (tBuPCP)IrH2, while it is thermally much more robust than the tBuPCP analogue, as well as iPrPCP or tBuPOCOP pincer complexes.

NCN Trianionic Pincer Ligand Precursors: Synthesis of Bimetallic, Chelating Diamide, and Pincer Group IV Complexes

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.