The large size of amylopectin represents an experimental challenge for standard analytical techniques to characterize its structure at the molecular level in dilute solution. We introduce a methodology that combines pyrene excimer fluorescence (PEF), the fluorescence blob model (FBM), molecular mechanics optimizations (MMOs), and intrinsic viscosity ([η]) to probe the interior of complex macromolecules with a heterogeneous interior like amylopectin. The combination of PEF, FBM, and MMOs yields the density (ρ fluo ) of nanosized subvolumes of the macromolecule, called blobs within the framework of the FBM, while [η] yields the density (ρ) probed over the length scale of the entire macromolecule. Comparison of ρ and ρ fluo indicates whether matter is either homogeneously (ρ = ρ fluo ) or heterogeneously (ρ < ρ fluo ) distributed inside the macromolecule. The main advantage of the methodology is to shift the focus of the study from the entire polydisperse macromolecule to that of monodisperse blobs where a blob represents the volume probed by a given pyrene derivative. This methodology is thus ideally suited to probe polydisperse heterogeneous macromolecules in solution. It is applied to amylopectin. The finding that ρ was much smaller than ρ fluo for amylopectin in dilute solution led to the conclusion that the side chains of amylopectin are heterogeneously distributed inside the amylopectin interior. The ρ fluo value agreed with the notion that the helical side chains of amylopectin form clusters where the side chains are ∼2.7 nm apart. When ρ and ρ fluo were determined for nanosized amylopectin fragments (NAFs) produced through extrusion, ρ fluo took the same value as for amylopectin while ρ increased with decreasing NAF size, approaching ρ fluo for the smallest NAF. This observation led to the conclusion that the clusters of helical oligosaccharide side chains were loosely connected to each other via linear oligosaccharide segments. These features were captured by the solution-cluster (Sol-CL) model which seems to rationalize many of the experimental observations made about amylopectin.

A half-sandwich molybdenum(II) thiolate complex with a η 2 -MeCN ligand, Cp*Mo(1,2-Ph 2 PC 6 H 4 S)(η 2 -NCMe) (1(η 2 -NCMe)), was found to catalyze transfer hydrogenation of nitriles efficiently with ammonia borane (H 3 N•BH 3 ) at room temperature, producing primary amines. Through molybdenum-thiolate cooperation, the B−H bond of BH 3 is cleaved, affording a Mo(II)-H hydride (1H(BH 2 )) with the BH 2 moiety captured at the S−Mo unit. In the presence of NH 3 , 1H(BH 2 ) smoothly achieves the catalytic transfer hydrogenation of nitriles.

We report imine-and amine-based dinucleating ligands bearing a bisphenol backbone and explore their coordination chemistry with zinc to form zinc alkyl, alkoxide, acetate, and amide complexes. Full characterization of the complexes shows that this ligand framework can support dinuclear and trinuclear complexes. We explore the reactivity of the zinc alkyl and alkoxide complexes as catalysts for the ring opening polymerization of lactide and compared this reactivity to analogous mononuclear complexes. We show that 1) The amine-based complexes are more reactive than the imine-based analogues; 2) The trinuclear zinc alkyl species show unusual control and reproducibility for lactide polymerization; and 3) The extent of bimetallic cooperation is hampered by the ability of the ligand framework to form trinuclear clusters.

Diphosphinodithio ligated complexes of nickel(0), nickel(i) and nickel(ii)–alkyl with a reactivity relevant to the C–C bond formation were described.

We report a new method to synthesize cobalt arylborohydrides and incorporate the borane-amine unit into the coordination sphere of a half-sandwich cobalt system based on activation of primary amines. Insertion of BH3 into the Co­(II)–C­(aryl) bond of the phosphinoaryl cobalt compound Cp*Co­(2-C6H4PPh2) (1) provided the cobalt arylborohydride Cp*Co­(κ3-H,H,P-H3BC6H4PPh2) (2), which was oxidized to the cationic cobalt­(III) arylborohydride (2 + ). Complex 2 + can be synthesized alternatively by oxidation of the cobalt­(II) aryl compound (1), followed by BH3 insertion into the Co­(III)-C­(aryl) unit. This cationic borohydride enables alkyl amines activation. As exemplified by the reaction with cyclohexylamine, the phosphinoborohydride moiety in 2 + undergoes B–N bond coupling with the two amine molecules by release of 2 equiv of H2, leading to the borane-amino cobalt­(III) hydride (3) featuring a phosphinoborane-diamine ligand, 1,2-Ph2PC6H4B­(NHCy)2.