Synthesis of ((t)Bu3SiNH)2ClW triple bond WCl(NHSi(t)Bu3)2 and its degradation via NH bond activation

Treatment of NaW2Cl7(THF)5 with 4 equiv of (t)Bu3SiNHLi afforded the C2 W(III) dimer [((t)Bu3SiNH)2WCl]2 (1, d(W triple bond W) = 2.337(2) A), which is a rare, primary amide M2X4Y2 species. Its degradation provided evidence of NH bond activation by the ditungsten bond. Addition of 2 equiv of (t)Bu3SiNHLi or TlOSi(t)Bu3 to 1 yielded H2 and hydride ((t)Bu3SiN)2((t)Bu3SiNH)WH (2, d(WH) = 1.67(3) A) or ((t)Bu3SiN)2((t)Bu3SiO)WH (3). Thermolysis (60 degrees C, 16 h) of 1 in py gave ((t)Bu3SiN)2WHCl(py) (4-py, 40-50%), ((t)Bu3SiN)2WCl2(py) (6-py, 10%), and ((t)Bu3SiN)2HW(mu-Cl)(mu-H)2W(NSi(t)Bu3)py2 (5-py2, 5%), whereas thermolysis in DME produced ((t)Bu3SiN)2WCl(OMe) (7, 30%), ((t)Bu3SiN)2WCl2 (6, 20%), and ((t)Bu3SiN)2HW(mu-Cl)(mu-H)2W(NSi(t)Bu3)DME (5-DME, 3%). Compound 7 was independently produced via thermolysis of 4-py and DME (-MeOEt, -py), and THF and ethylene oxide addition to hydride 2 gave ((t)Bu3SiN)2((t)Bu3SiNH)WO(n)Bu (8) and ((t)Bu3SiN)2((t)Bu3SiNH)WOEt (9), respectively. Dichloride 6 was isolated from SnCl4 treatment of 1 with the loss of H2. Sequential NH bond activations by the W2 core lead to "((t)Bu3SiN)2WHCl" (4) and subsequent thermal degradation products. Thermolysis of 1 in the presence of H2C=CH(t)Bu and PhC triple bond CPh trapped 4 and generated ((t)Bu3SiN)2W((neo)Hex)Cl (10) and a approximately 6:1 mixture of ((t)Bu3SiN)2WCl(cis-CPh=CPhH) (11-cis) and ((t)Bu(3)SiN)2WCl(trans-CPh=CPhH) (11-trans), respectively. Thermolysis of the latter mixture afforded ((t)Bu3SiNH)((t)Bu3SiN)WCl(eta2-PhCCPh) (12) as the major constituent. Alkylation of 1 with MeMgBr produced ((t)Bu3SiN)2W(CH3)2 (13), as did addition of 2 equiv of MeMgBr to 6. X-ray crystal structure determinations of 1, 2, 5-py2, 6-py, 11-trans, and 12 confirmed spectroscopic identifications. A general mechanism that features a sequence of NH activations to generate 4, followed by chloride metathesis, olefin insertion, etc., explains the formation of all products.

Single-site beta-diiminate zinc catalysts for the alternating copolymerization of CO2 and epoxides: catalyst synthesis and unprecedented polymerization activity

Synthetic routes to zinc beta-diiminate complexes are reported. The synthesis of 11 beta-diimine [(BDI)-H] ligands, with varying N-aryl substituents and bridging structures, is described. These ligands are converted to (BDI)ZnX complexes (X = OAc, Et, N(SiMe3)2, Br, Cl, OH, OMe, O(i)Pr). X-ray structural data revealed that all zinc complexes examined exist as micro-X-bridged dimers in the solid state, with the exception of the zinc ethyl and amido complexes which were monomeric. Complexes of the form (BDI)ZnOR (R = alkyl, acyl) and (BDI)ZnN(SiMe3)2 are highly active catalysts for the alternating copolymerization of epoxides and CO2. Copolymerizations of cyclohexene oxide (CHO) and CO2 with (BDI-1)ZnX [(BDI-1) = 2-((2,6-diisopropylphenyl)amido)-4-((2,6-diisopropylphenyl)imino)-2-pentene)] and (BDI-2)ZnX [(BDI-2) = 2-((2,6-diethylphenyl)amido)-4-((2,6-diethylphenyl)imino)-2-pentene)], where X = OAc, Et, N(SiMe3)2, Br, Cl, OH, OMe, O(i)Pr, were attempted at 50 degrees C and 100 psi CO2. Complexes with X = OAc, N(SiMe3)2, OMe, O(i)Pr all produced polycarbonate by the alternated insertion of CHO and CO2 with similar catalytic activities, comparable molecular weights, and narrow molecular weight distributions (MWD approximately 1.1), indicating the copolymerizations are living. Furthermore, ligand effects were shown to dramatically influence the polymerization activity as minor steric changes accelerated or terminated the polymerization activity.

Polymerization of lactide with zinc and magnesium beta-diiminate complexes: stereocontrol and mechanism

A series of zinc(II) and magnesium(II) alkoxides based upon a beta-diiminate ligand framework has been prepared. [(BDI-1)ZnO(i)Pr](2) [(BDI-1) = 2-((2,6-diisopropylphenyl)amido)-4-((2,6-diisopropylphenyl)imino)-2-pentene] exhibited the highest activity and stereoselectivity of the zinc complexes studied for the polymerization of rac- and meso-lactide to poly(lactic acid) (PLA). [(BDI-1)ZnO(i)()Pr](2) polymerized (S,S)-lactide to isotactic PLA without epimerization of the monomer, rac-lactide to heterotactic PLA (P(r) = 0.94 at 0 degrees C), and meso-lactide to syndiotactic PLA (P(r) = 0.76 at 0 degrees C). The polymerizations are living, as evidenced by the narrow polydispersities of the isolated polymers in addition to the linear nature of number average molecular weight versus conversion plots and monomer-to-catalyst ratios. The substituents on the beta-diiminate ligand exert a significant influence upon the course of the polymerizations, affecting both the degree of stereoselectivity and the rate of polymerization. Kinetic studies with [(BDI-1)ZnO(i)Pr](2) indicate that the polymerizations are first order with respect to monomer (rac-lactide) and 1.56 order in catalyst. Polymerization experiments with [(BDI-1)MgO(i)Pr](2) revealed that this complex is extremely fast for the polymerization of rac-lactide, polymerizing 500 equiv in 96% yield in less than 5 min at 20 degrees C.

Covalent metal-organic networks: pyridines induce 2-dimensional oligomerization of (mu-OC6H4O)2Mpy2 (M = Ti, V, Zr)

Treatment of M(OiPr)4 (M = Ti, V) and [Zr(OEt)4]4 with excess 1,4-HOC6H4OH in THF afforded [M(OC6H4O)a(OC6H4OH)3.34-1.83a(OiPr)0.66-0.17a(THF)0.2]n (M = Ti, 1-Ti; V, 1-V, 0.91 < or = a < or = 1.82) and [Zr(1,4-OC6H4O)2-x(OEt)2x]n (1-Zr, x = 0.9). The combination of of 1-M (M = Ti, V, Zr) or M(OiPr)4 (M = Ti, V), excess 1,4- or 1,3-HOC6H4OH, and pyridine or 4-phenylpyridine at 100 degrees C for 1 d to 2 weeks afforded various 2-dimensional covalent metal-organic networks: [cis-M(mu 1,4-OC6H4O)2py2] infinity (2-M, M = Ti, Zr), [trans-M(mu 1,4-OC6H4O)2py2.py] infinity (3-M, M = Ti, V), solid solutions [trans-TixV1-x(mu 1,4-OC6H4O)2py2.py] infinity (3-TixV1-x, x approximately 0.4, 0.6, 0.9), [trans-M(mu 1,4-OC6H4O)2(4-Ph-py)2] infinity (4-M, M = Ti, V), [trans-Ti(mu 1,3-OC6H4O)2py2] infinity (5-Ti), and [trans-Ti(mu 1,3-OC6H4O)2(4-Ph-py)2] infinity (6-Ti). Single-crystal X-ray diffraction experiments confirmed the pleated sheet structure of 2-Ti, the flat sheet structure of 3-Ti, and the rippled sheet structures of 4-Ti, 5-Ti, and 6-Ti. Through protolytic quenching studies and by correspondence of powder XRD patterns with known titanium species, the remaining complexes were structurally assigned. With py or 4-Ph-py present, aggregation of titanium centers is disrupted, relegating the building block to the cis- or trans-(ArO)4Tipy2 core. The sheet structure types are determined by the size of the metal and the interpenetration of the layers, which occurs primarily through the pyridine residues and inhibits intercalation chemistry.

Influence of Perfluoroarene-Arene Interactions on the Phase Behavior of Liquid Crystalline and Polymeric Materials

A stabilization of the liquid-crystalline mesophase and thus an enlarged temperature range of the mesogenic phase is achieved by adding perfluorotriphenylene to a chiral liquid-crystalline triphenylene. This mesophase is based on 1:1 perfluoroarene-arene interactions (see picture). In a polymer with triphenylenes as mesogens in the side chains, the addition of perfluorotriphenylene led to crystallization.