Synthesis and decomposition of alkyl complexes of tungsten(IV) that contain a [(Me3SiNCH2CH2)(3)N](3-) ligand

The synthesis of a variety of tungsten alkyl complexes of the type [N3N]WR ([N3N](3-) = [(Me3SiNCH2CH2)(3)N](3-); R = Me, Et, Bu, CH2Ph, CH2SiMe3, CH2CMe3, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cyclopentenyl) was attempted by alkylation of [N3N]WCl complexes. Only the methyl, phenyl, and cyclopentenyl complexes could be isolated. The susceptibility of the [N3N]WR complexes is similar to that of [N3N]WCl; the effective moment is depressed as a consequence of a combination of spin-orbit effects and low-symmetry ligand-field components that result in zero-field splitting of the d(2) ground-state spin triplet. No linear alkyl complexes could be observed as a consequence of alpha,a-dehydrogenation to give molecular hydrogen and alkylidyne complexes, [N3N]W=CR'. [N3N]W(cyclopropyl) evolves ethylene in a first-order process to give [N3N]W=CH, while [N3N]W(cyclobutyl) is converted into the 1-tungstacyclopentene complex, [N3N]W(CHCH2CH2CH2), as confirmed in an X-ray study. [N3N]W(CHCH2CH2CH2) decomposes readily in a first-order manner to give [N3N]W=CCH2CH2CH3. An attempt to prepare [N3N]W(cyclopentyl) led to formation of [N3N]W(cyclopentylidene)(H), as confirmed in an X-ray study. NMR studies suggest that [N3N]W(cyclopentylidene)(H) is in equilibrium with [N3N]W(cyclopentyl) where Delta H degrees = 11.8-(6) kcal mol(-1) and Delta S degrees = 33(2) eu or K-eq approximate to 0.1 at 46 degrees C. From these and other data it is concluded that the rate constant for ct elimination in [N3N]M(cyclopentyl) is approximately the same for Mo and W. The [N3N]W(cyclopentenyl) complex is unstable, decomposing to give a complex containing a ''bent imido'' ligand, [(Me3SiNCH2CH2)(2)(NCH2CH2)N]W(1-(trimethylsilyl)cyclopentene), as confirmed in an X-ray study.