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Novel amine bis(phenolate) zirconium dibenzyl complexes were synthesized in quantitative yields from a versatile family of chelating amine−bis((2-hydroxyaryl)methyl) ligand precursors, their X-ray structures solved, and their reactivity in the polymerization of 1-hexene in the presence of B(C6F5)3 studied. Several minor peripheral structural modifications were studied and found to have a major influence on the catalyst performance. Thus, a variety of reactivities, ranging from extremely high to negligible, were obtained, demonstrating a unique structure−reactivity relationship. This relationship is partially revealed from the crystal structures of the precatalysts, indicating similar [ONO] ligand cores in all structures solved. A correlation between the solid and the solution structures is obtained from 1H NMR spectra, which reveal a rigid binding of the ligand to the metal. The solid structures are therefore proposed to serve as reliable references when studying structure−reactivity relationships. The most significant structural parameter was found to be the existence of an extra donor located on a pendant arm. [ONO]-type pentacoordinate complexes lacking such an additional donor are rapidly deactivated and lead only to traces of oligomers. On the other hand, hexacoordinate complexes based on [ONNO]-type ligands, in which strong donation of a side donor to the metal is obtained through formation of a five-membered chelate, lead to extremely reactive polymerization catalysts. The nitrogen hybridization and aromatic ring substituents have a more subtle effect on reactivity. Increasing the chelate size results in either no binding of the side donor, yielding negligible reactivity, or strong binding yet moderate polymerization reactivity. Increasing the steric bulk on the donor results in weakening of the metal−donor bond, leading to a moderate oligomerization catalyst. The sidearm nitrogen is therefore proposed to play a crucial role in determining the propagation process rate, as well as the propagation/termination rate ratio.

The molecular weight‐viscosity relationships for polystyrene are reviewed and it is recommended that the Staudinger relationship be discarded in favor of the conventional modification of it, [η] = KMa. An emulsion‐prepared polystyrene was fractionated and the viscosities and osmotic molecular weight determined. The corresponding relationship between the viscosities in butanone and toluene is observed to follow the above equation. A table containing the molecular weight‐viscosity relationships for polymers is appended.

In this paper the authors used the term "metallocene" to refer to compounds containing at least one Cp-type ligand. This paper reports the first Cp-type free catalyst for living and isotactic polymerization of 1-hexene. Two other catalysts for living and isotactic 1-hexene polymerization were reported previously, which were cited in ref 10. Reference 10 also should have been cited after the last sentence of the first paragraph.

carbonyls to give the products of 1,4-addition after hydrolysis of the intermediate boron enolates, in 68-86% isolated yield (four examples). In addition, we discovered that diazomethane reacts with bis(pinacolato)diborane to insert methylene to give (pinacolato) 2 BCH 2 B in 83% yield. An alternative synthesis involved coupling of (pinacolato)BCH 2 I with various metals.Boronic acids have a variety of important uses and applications. They are highly valued synthetic intermediates 1 and also possess significant biological activity. 2 Hydroboration, 3 haloboration, 4 reactions with organometallics, 5 and homologation 6 are important protocols for their preparation. A more recent and very convenient method for the preparation of boronic acids involves diborane(4) derivatives. 7 In particular, tetraalkoxydiborane(4) compounds have been shown to add to alkenes, 8 alkynes, 9 1,3-butadienes, 10 allylic acetates, 11 methylenecyclopropanes, 12 substituted 4-arylbut-3-en-2-ones, 13 and various other substrates. 14 Mechanistic and theoretical studies of diboration have also been reported. 15 The latter reaction reported by Marder and Norman et al. is particularly interesting, in that it opens the way for addition of diborane(4) compounds to other R,β-unsaturated systems. Three-membered 16 and fivemembered 17 aminodiborane(4) derivatives undergo insertion reactions with CO and isonitrile to give inter- † Hebrew University in Jerusalem.