Reaching Out to Zirconium

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Science  08 May 2009:
Vol. 324, Issue 5928, pp. 695
DOI: 10.1126/science.324_695c

When alkyl chains bind to transition metals, the metal center can sometimes loosely attract electrons from the hydrogen bonds two carbons away. This attraction, termed an agostic interaction, plays an influential role in stereoselective olefin polymerizations at zirconocene centers, but it is typically too fleeting to characterize in a persistently stable complex. Forster et al. prepared an analog to an agostically coordinated ethyl ligand by replacing the two carbons (CH2-CH3) with nitrogen and boron (NH2-BH3). On coordinating through nitrogen to a zirconocene derivative, the ligand's boron hydride binds more stably to the metal center than the corresponding ethyl C-H. The authors characterized several such complexes in the solid state and in solution, and observed interconversion of isomers (which differed in the positions of N and B-H relative to a third substituent) on a time scale of tens of seconds.

J. Am. Chem. Soc.131, 10.1021/ja901460y (2009).

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