Copolymerization of Ethylene and Vinyl Fluoride by Self-Assembled Multinuclear Palladium Catalysts.

The self-assembled multinuclear Pd complexes {(Li-OPO)PdMe(4-5-nonyl-pyridine)}LiCl (, Li-OPO = PPh(2-SOLi-4,5-(OMe)-Ph)(2-SO-4,5-(OMe)-Me-Ph)), {(Zn-OP-P-SO)PdMe(L)} (, L = pyridine or 4-Bu-pyridine, [OP-P-SO] = P(4-Bu-Ph)(2-PO-5-Me-Ph)(2-SO-5-Me-Ph)), and {(Zn-OP-P-SO)PdMe(pyridine)} () copolymerize ethylene and vinyl fluoride (VF) to linear copolymers. VF is incorporated at levels of 0.1-2.

Template-Free Synthesis of a Macrocyclic Bis(pyridine-dienamine) Proligand and Metal Complexes of Its Bis(pyridine-diimine) and Bis(pyridine-dienamido) Forms.

We describe the template-free synthesis of the bis(pyridine-dienamine) proligand [4,5-(xylylenediamine)NH-C═(CH)(9-butyl-octahydroacridine)] (), a variant of Burrows's macrocyclic bis(pyridine-diimine) (bis-PDI) ligand [2,6-(xylylenediamine)N═C(py)] (), using octahydroacridine as the ligand backbone. The octahydroacridine backbone favors macrocyclization by constraining the PDI units in the (s-) conformation. The template-free synthesis of enables facile access to a wide array of bis-PDI and bis(pyridine-dienamido) (bis-PDE) metal complexes.

Sterically Controlled Self-Assembly of a Robust Multinuclear Palladium Catalyst for Ethylene Polymerization.

The self-assembly and reactivity of a robust multinuclear Pd catalyst based on the sterically expanded phosphine- bis-arenesulfonate ligand PPh(2-SO-4,5-(OMe)-Ph) (OPO, 2) are described. The reaction of Li[2] with (COD)PdMeCl and 4-(5-nonyl)-pyridine (py') generates the tetranuclear complex {(OPO-Li)PdMe(py')}LiCl (3) in which four (phosphine-sulfonate)PdMe(py') units are arranged around the periphery of a LiSO·LiCl cage. The Pd atoms in 3 are arranged in pairs with a Pd-Pd distance of 6.

Crystal structure of 3-[(2-acetamido-phen-yl)imino]-butan-2-one.

In the title compound, 3-[(2-acetamido-phen-yl)imino]-butan-2-one, CHNO, the imine C=N bond is essentially coplanar with the ketone C=O bond in an conformation. The benzene ring is twisted away from the plane of the C=N bond by 53.03 (14)°.

Transformation of Metal-Organic Framework Secondary Building Units into Hexanuclear Zr-Alkyl Catalysts for Ethylene Polymerization.

We report the stepwise and quantitative transformation of the Zr(μ-O)(μ-OH)(HCO) nodes in Zr-BTC (MOF-808) to the [Zr(μ-O)(μ-OH)Cl] nodes in ZrCl-BTC, and then to the organometallic [Zr(μ-O)(μ-OLi)R] nodes in ZrR-BTC (R = CHSiMe or Me). Activation of ZrCl-BTC with MMAO-12 generates ZrMe-BTC, which is an efficient catalyst for ethylene polymerization. ZrMe-BTC displays unusual electronic and steric properties compared to homogeneous Zr catalysts, possesses multimetallic active sites, and produces high-molecular-weight linear polyethylene.

Heterolytic H-H and H-B Bond Cleavage Reactions of {(IPr)Ni(μ-S)}.

Kinetic and DFT computational studies reveal that the reaction of {(IPr)Ni(μ-S)} (1, IPr = 1,3-bis(2,6-diisopropyl-phenyl)imidazolin-2-ylidene) with dihydrogen to produce {(IPr)Ni(μ-SH)} (2) proceeds by rate-limiting heterolytic addition of H across a Ni-S bond of intact dinuclear 1, followed by cis/trans isomerization at Ni and subsequent H migration from Ni to S, to produce the bis-hydrosulfide product 2. Complex 1 reacts in a similar manner with pinacolborane to produce {(IPr)Ni}(μ-SH)(μ-SBPin) (3), showing that heterolytic activation by this nickel μ-sulfide complex can be generalized to other H-E bonds.

Autoxidation of Heterocyclic Aminals.

The autoxidation reactions of 2-acyl-2,3-dihydroquinazolin-4(1)-ones and and 2,2'-bis(dihydroquinazolinone) are described. These reactions generate aminyl radicals that undergo β-C-C cleavage, and subsequent reactions of the resulting C-based radicals with O lead to diverse products with good selectivity, depending on the structure of the substrate. Oxidation of , in which the 2-acyl group is part of a cyclic acenaphthenone unit, yields a heterocyclic -hydroperoxylaminal via 1,2-acyl migration.

Controlling quantum-beating signals in 2D electronic spectra by packing synthetic heterodimers on single-walled carbon nanotubes.

In multidimensional spectroscopy, dynamics of coherences between excited states report on the interactions between electronic states and their environment. The prolonged coherence lifetimes revealed through beating signals in the spectra of some systems may result from vibronic coupling between nearly degenerate excited states, and recent observations confirm the existence of such coupling in both model systems and photosynthetic complexes. Understanding the origin of beating signals in the spectra of photosynthetic complexes has been given considerable attention; however, strategies to generate them in artificial systems that would allow us to test the hypotheses in detail are still lacking.

Olefin Insertion into a Pd-F Bond: Catalyst Reactivation Following β-F Elimination in Ethylene/Vinyl Fluoride Copolymerization.

The discrete (phosphinoarenesulfonate)Pd fluoride complex (PO )PdF(lutidine), where PO =(2-MeOC H )(2-{2,6-(MeO) C H }C H )(2-SO -5-MeC H )P, inserts vinyl fluoride (VF) to form (PO )PdCH CHF (lutidine) and inserts multiple ethylene (E) units to generate polyethylene that contains -CH F chain ends. These results provide strong evidence that the -CHF and -CH F chain ends in E/VF copolymer generated by (phosphinoarenesulfonate)PdR catalysts form by β-F elimination of Pd(β-F-alkyl) species, VF or E insertion of the resulting (PO)PdF species, and subsequent chain growth. These results also imply that β-F elimination is not an important catalyst deactivation reaction in this system.

Crystal structure of 1-phenyl-imido-1-{6-[1-(phenyl-imino)-eth-yl]pyridin-2-yl}ethan-1-yl-κ,','')iron(II).

The title iron complex, [Fe(CHN)], consists of an Fe atom chelated by two tridentate bis-(imino)-pyridine radical anions in a slightly distorted octa-hedral coordination environment. In the solid state, there are two independent half-mol-ecules in the asymmetric unit, and the complete mol-ecular structure is formed by applying twofold rotation symmetry with the twofold rotation axis passing through an Fe atom. In the crystal, the Fe-containing complexes are not involved in any particular direct inter-molecular inter-actions, with the shortest C-H contacts between neighboring phenyl groups being 3.

Crystal structure of zwitterionic 2-[bis-(2-meth-oxy-phen-yl)phosphanium-yl]-4-methyl-benzene-sulfonate monohydrate di-chloro-methane monosolvate.

In the title compound, C21H21O5PS·H2O·CH2Cl2, the phospho-nium-sulfonate zwitterion has the acidic H atom located on the P atom rather than the sulfonate group. The S-O bond lengths [1.4453 (15)-1.

Crystal structure of (n-but-yl)[2-(2,6-di-meth-oxy-phen-yl)-6-methyl-phen-yl](2-meth-oxy-phen-yl)phospho-nium chloride monohydrate.

The title hydrated salt, C26H32O3P(+)·Cl(-)·H2O, contains four different substit-uents (H, alkyl, aryl, and biar-yl) on the P atom. The P-H hydrogen atom of the phospho-nium ion was located in a difference Fourier map and refined without imposing additional restraints. In the crystal, the Cl(-) ions and water mol-ecules are linked by pairs of Owater-H⋯Cl(-) hydrogen bonds and further linked to the phospho-nium cation by P-H(+)⋯Cl(-) and CAr/OMe-H⋯Owater hydrogen bonds to form an infinite one-dimensional chain along the [010] direction.

Protonolysis and amide exchange reactions of a three-coordinate cobalt amide complex supported by an N-heterocyclic carbene ligand.

A three-coordinate cobalt species, IPrCoCl{N(SiMe3)2} [1; IPr = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene], was synthesized by the reaction of {IPrCoCl2}2 with NaN(SiMe3)2. Compound 1 is a useful starting material for low-coordinate (IPr)Co species. 1 reacts with 2,6-di-tert-butyl-4-methylphenol (BHT-H) via aminolysis of the Co-N bond to generate a three-coordinate phenoxide complex, IPrCoCl(O-2,6-(t)Bu2-4-MeC6H2) (2).

Synthesis and reactivity of NHC-supported Ni2(μ(2)-η(2),η(2)-S2)-bridging disulfide and Ni2(μ-S)2-bridging sulfide complexes.

The (IPr)Ni scaffold stabilizes low-coordinate, mononuclear and dinuclear complexes with a diverse range of sulfur ligands, including μ(2)-η(2),η(2)-S2, η(2)-S2, μ-S, and μ-SH motifs. The reaction of {(IPr)Ni}2(μ-Cl)2 (1, IPr = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene) with S8 yields the bridging disulfide species {(IPr)ClNi}2(μ(2)-η(2),η(2)-S2) (2). Complex 2 reacts with 2 equiv of AdNC (Ad = adamantyl) to yield a 1:1 mixture of the terminal disulfide compound (IPr)(AdNC)Ni(η(2)-S2) (3a) and trans-(IPr)(AdNC)NiCl2 (4a).

Ortho-phosphinobenzenesulfonate: a superb ligand for palladium-catalyzed coordination-insertion copolymerization of polar vinyl monomers.

Ligands, Lewis bases that coordinate to the metal center in a complex, can completely change the catalytic behavior of the metal center. In this Account, we summarize new reactions enabled by a single class of ligands, phosphine-sulfonates (ortho-phosphinobenzenesulfonates). Using their palladium complexes, we have developed four unusual reactions, and three of these have produced novel types of polymers.

Palladium-catalyzed dimerization of vinyl ethers to acetals.

(Alpha-diimine)PdCl(+) species catalytically dimerize alkyl and silyl vinyl ethers to beta,gamma-unsaturated CH(2)=CHCH(2)CH(OR)(2) acetals, and they cyclize divinyl ethers to analogous cyclic acetals. A plausible mechanism comprises in situ generation of an active PdOR alkoxide species, double vinyl ether insertion to generate Pd{CH(2)CH(OR)CH(2)CH(OR)(2)} species, and beta-OR elimination to generate the acetal product. In the presence of vinyl ethers, (alpha-diimine)PdCl(+) species can be used to initiate ethylene polymerization.

Cationic polymerization and insertion chemistry in the reactions of vinyl ethers with (alpha-diimine)PdMe(+) species.

The reactions of (alpha-diimine)PdMe(+) species (1, alpha-diimine = (2,6-(i)Pr(2)-C(6)H(3))N=CMeCMe=N(2,6-(i)Pr(2)-C(6)H(3))) with vinyl ethers CH(2)=CHOR (2a-g: R = (t)Bu (a), Et (b), SiMe(3) (c), SiMe(2)Ph (d), SiMePh(2) (e), SiPh(3) (f), Ph (g); 2a-g: R = (t)Bu (a), Et (b), SiMe(3) (c), SiMe(2)Ph (d), SiMePh(2) (e), SiPh(3) (f), Ph (g)) were investigated. Two pathways were observed. First, 1 initiates the cationic polymerization of 2a-c with concomitant decomposition of 1 to Pd(0).

Self-assembled tetranuclear palladium catalysts that produce high molecular weight linear polyethylene.

The phosphine-bis-arenesulfonate ligand PPh(2-SO(3)Li-4-Me-Ph)(2) (Li(2)[OPO]) coordinates as a kappa(2)-P,O chelator in Li[(Li-OPO)PdMe(Cl)] (2a) and (Li-OPO)PdMe(L) (L = pyridine (2b); MeOH (2d); 4-(5-nonyl)pyridine) (py', 3)). 2a reacts with AgPF(6) to form {(Li-OPO)PdMe}(n) (2c). Photolysis of 2d yields {(OPO)Pd}(2) (5) in which the [OPO](2-) ligand coordinates as a kappa(3)-O,P,O pincer.

Multiple insertion of a silyl vinyl ether by (alpha-diimine)PdMe+ species.

This paper reports that (alpha-diimine)PdMe+ species (1) (alpha-diimine = (2,6-iPr2 C6H3)N CMeCMe N(2,6-iPr2 C6H3)) undergo multiple insertions of CH2 CHOSiPh3 (2), ultimately forming Pd allyl products. The reaction of (alpha-diimine)PdMeCl, [Li(Et2O)2.8][B(C6F5)4] (1 equiv), and 2 (8 equiv) in CH2Cl2 yields [(alpha-diimine)Pd{eta3-CH2CHCHCH(OSiPh3)CH2CH(OSiPh3)Me}][B(C6F5)4] (7-B(C6F5)4) in 83% NMR yield.

Copolymerization of silyl vinyl ethers with olefins by (alpha-diimine)PdR+.

This paper reports that (alpha-diimine)PdMe+ catalyzes the copolymerization of olefins and silyl vinyl ethers. The reactions of (alpha-diimine)PdMe+ (alpha-diimine = (2,6-iPr2-C6H3)N=CMe-CMe=N(2,6-iPr2-C6H3)) with excess vinyl ethers CH2=CHOR (1a-d: R = tBu (a), SiMe3 (b), SiPh3 (c), Ph (d)) in CH2Cl2 at 20 degrees C afford polymers for 1a (rapidly) and 1b (slowly) but not for 1c or 1d. The structures of poly(1a,b) indicate a cationic polymerization mechanism.