Bite angle effect

In 2001, hybrid QM/MM strategies such as those in Section 3, provided a step forward in the modeling of real-world catalysts. However, the scope of these methods is also limited, because they only enable us to properly treat steric effects. Despite this drawback, some important aspects can be studied using these methods. Regioselectivity in diphosphine systems is explained by non-bonding interactions and bite angle effects. However, the role of ea complexes has not yet been determined. 

They constitute the first rhodium phosphine modified catalysts for such a selective linear hydroformylation of internal alkenes. The extraordinary high activity of 32 even places it among the most active diphosphines known. Since large steric differences in the catalyst complexes of these two ligands are not anticipated, the higher activity of 32 compared to 31 might be ascribed to very subtle bite angle effects or electronic characteristics of the phosphorus heterocycles. 

Bite angle effects in diphosphine metal catalysts Steric or electronic ... 

A. L. (2000) Origin of the bite angle effect on rhodium diphosphine catalyzed hydroformylation. Organometallics, 19, 872-883. 

Freixa, Z. and van Leeuwen, P.W.N.M. (2003) Bite angle effects in diphosphine metal catalysts Steric or electronic Dalton Trans., 1890. 

Ali and Alper later developed a method for y-lactone formation under neutral conditions from allylic alcohols according to Scheme 23, involving Pd(0) and dppb. The same protocol was also applied to synthesis of a,/3-butenolides from propargylic alcohols. Other bidentate or monodentate ligands give inferior results, and this correlates well with bite angle effects on the rate of the CO insertion reaction. Also, the allylic alcohol needs to be a-alkyl substituted to facilitate ring closure, in accordance with other studies.t t This process was postulated by the authors to be of the carbopalladative type. 

Van Leeuwen PWNM, Kamer P, Reek JNH, Dierkes P (2000) Ligand bite angle effects in metal-catalyzed C-C bond formation. Chem Rev 100 2741... 

Birkholz (nee Gensow) M-N, Freixa Z, Van Leeuwen PWNM (2009) Bite angle effects of diphosphines in C-C and C-X bond forming cross coupling reactions. Chem Soc Rev 38 1099... 

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