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

Abstract

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.

Syntheses, structures, and1H,13C{1H} and119Sn{1H} NMR chemical shifts of a family of trimethyltin alkoxide, amide, halide and cyclopentadienyl compounds

“…6f The authors noted that the monostannylamine (Me 3 Sn)(NH-2,6-i Pr 2 C 6 H 3 ) is not thermodynamically stable; two equivalents of (Me 3 Sn)(NH-2,6-i Pr 2 C 6 H 3 ) similarly yielded a mixture of 3 and H 2 N-2,6-i Pr 2 C 6 H 3 . 13 Finally, preparation of the known compounds Me 3 SnN(SiMe 3 ) 2 (5) and Me 3 Sn(C 5 Me 5 ) (6) is straightforward by reaction of Me 3 SnCl with K[N(SiMe 3 ) 2 ] or K(C 5 Me 5 ), respectively, yielding the products in 66% and 90% isolated yields. reported.…”

“…The most relevant aspects of the structure are the Sn-N bond distance, Sn-N-C ipso bond angle, and the Sn-C bond distances (Sn-N = 2.050(2) Å, Sn-N-C ipso = 126.50( 14)°, Sn-C = 2.131(2)-2.144(3) Å), which compare favorably with those reported for the few structurally characterized four-coordinate trialkyltin arylamide complexes: 13) Å, Sn-N-C ipso = 127.98(12)°, Sn-C = 2.1318(23)-2.1584(18) Å). 13 Finally, preparation of the known compounds Me 3 SnN(SiMe 3 ) 2 (5) and Me 3 Sn(C 5 Me 5 ) ( 6) is straightforward by reaction of Me 3 SnCl with K[N(SiMe 3 ) 2 ] or K(C 5 Me 5 ), respectively, yielding the products in 66% and 90% isolated yields.…”

“…We show that transmetallation from a potassium amide, alkoxide or cyclopentadienyl reagent and Me 3 SnCl provides an improved route for accessing the corresponding trimethyltin derivatives and offers an alternative to existing literature procedures. For completeness, we have compiled 1 H and 13 C{ 1 H} NMR data of eleven Me 3 SnX compounds in six common deuterated solvents (benzene-d 6 , toluene-d 8 , dichloromethane-d 2 , chloroform-d 1 , acetonitrile-d 3 , and tetrahydrofuran-d 8 ). In addition, 119 Sn{ 1 H} NMR data is also presented (in benzene-d 6 or chloroform-d 1 ) for all compounds.…”

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

“…In this study we explore the use of a NCN 3À trianionic pincer ligand 54,55 to stabilize a Cr IV alkyl. Trianionic pincer ligands 54À65 are capable of supporting reactive metal species, since they occupy three coordination sites but can only contribute a maximum of 10À12 electrons.…”

“…However, precedent suggests that treating CrCl 2 with the dilithio salt {[2,6-i PrNCHN]Li 2 } 2 would provide a complex in which the pincer aryl CÀH bond would remain intact and the ligand would be bound instead via two amido linkages. 54 Insight into why the observed Cr II species exhibits the unexpected conformation comes from thermolysis of the Cr IV complex in C 6 D 6 . The products from thermolysis indicate the unstable Cr IV deuteride [2,6-i PrNCN]Cr IV (D)(THF) 2 forms as an intermediate; subsequent NÀD reductive elimination provides Cr II (3-d).…”