That Contain the Trimethylsilyl-Substituted - American Chemical Society

William M. Davis. Department of Chemistry 6-331. Massachusetts Institute of Technology. Cambridge, Massachusetts 02139. Received February 24, 1995...
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J. Am. Chem. SOC.1995,117, 6609-6610

6609

a-Elimination Can Be Faster than /?-Elimination in d’ Alkyl Complexes of Molybdenum and Tungsten That Contain the Trimethylsilyl-Substituted Triamidoamine Ligand Richard R. Schrock,* Keng-Yu Shih, Daniel A. Dobbs, and William M. Davis Department of Chemistry 6-331 Massachusetts Institute of Technology Cambridge, Massachusetts 02139 Received February 24, 1995 Reactivity characteristics of transition metal complexes that contain triamidoamine ligands’ are beginning to he We recently published some unusual reactions of Mo8 and w9 complexes containing the [(Me3SiNCH2CHhNI3- ([N3N13-) ligandI5 that included (inter alia) loss of molecular hydrogen from W alkyls to give alkylidyne complexes. We show here that when a.a-dehydrogenation is blocked (by employing a cyclopentyl ligand), a-elimination to give an alkylidene hydride complex of W (but not one of Mo) as well as eventual @-eliminationto give stable paramagnetic monohydride complexes of both Mo and W can be observed. Addition of cyclopentyllithium to [NxN]WCl9in diethyl ether yields lithium chloride and a pentane-soluble yellow crystalline complex quantitatively. An X-ray study16 (Figure 1) shows it to be the 18-electron’7 cyclopentylidene hydride complex, [N,N]W(C5Hn)(H). The cyclopentylidene ligand is oriented so that it lies (approximately) in a plane that passes through W, N(5). and N(8). spreading N(6) and N(7) apart slightly (125.7” versus 112.4” and 105.4’). Electron density ascribable to the hydride ligand also was found approximately in this plane 1.81 A from the metal, but it would not survive refinement. Since JHw= 89 Hz, C(9). *H = 2.43 A, N(5). *H = 1.68 A, and the p orbitals on C(9) and N(5) are oriented perpendicular to the C(9)-W-H-N(5) plane, there does not appear to he any significant interaction between H and either C(9) or N(5). The position and observed orientation of the cyclopentylidene ligand are consistent with the nature of the three available bonding orbitals, approximately d,, d!,: and a u hybrid pointing along the z (W-Nd,.,,)-axis.” Formation of two u-bonding hybrid f

( I ) Verkade. J. G. Acc. Chem. Res. 1993. 26. 483. (2) Naiini. A. A,: Menge. W. M. P. B.; Verkade. J. G. Inorp. Chem. 1991.30. 5009. (31 Cummins. C. C.: Lee. I.: Schrock. R. R. Anper. Chem., lnt. Ed. Engl. 1992.31, 1501. (4) Cummins, C. C.: Schmck, R. 8.:Davis. W. M. 0rpmometaffic.v1992. I ,

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