Two pathways have been proposed in the formation of (ButCH2)3Ta=CHBut (1) from (ButCH2)4TaCl (2).1-3  In the first pathway, 2 reacts with ButCH2Li (3) to form pentaneopentyltantalum Ta(CH2But)5 (4), followed by a-H abstraction to give 1.  In the second pathway, 2 undergoes a-H abstraction first to give �(ButCH2)2Ta(=CHBut)Cl� (5), followed by substitution of the Cl- ligand by ButCH2Li (3) to give 1.  We have reported direct observation of Ta(CH2But)5 (4) and Ta(CD2But)5(4-d10) in the formation of 12 and 1-d7, respectively.3  In order to rule out the second pathway, we have studied the kinetics of the a-H abstraction of (ButCH2)4TaCl (2), and compared it with that of the formation of (ButCH2)3Ta=CHBut(1) from 2 and ButCH2Li (3).  In addition, variable-temperature NMR spectroscopy has been used to study potential axial-equatorial ligand exchanges in (ButCH2)4TaCl (2), (ButCD2)3TaCl2 (6-d6), and (ButCD2)5Ta (4-d10).  D-induced isotope shifts in 1H and13C NMR spectra of 1-d7 and 6-d6 have been investigated as well.  These studies will be discussed. 1. Schrock, R. R.; Fellmann, J. D. J. Am. Chem. Soc. 1978, 100, 3359.2. Li, L.; Huang, M. ; Xue, Z.-L. J. Am. Chem. Soc. 1995, 117, 12746.3. Abbott, J. K. C.; Xue, Z-L. J. Am. Chem. Soc. 2009, 131, 8246.

Formation of the archetypal tantalum alkylidene complex (ButCH2)3Ta=CHBut: Additional studies

239th National Meeting (2010)

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