Synthesis and Decomposition of Alkyl Complexes of Tungsten(IV) That Contain a [(Me₃SiNCH₂CH₂)₃N]^3- Ligand

Abstract

The synthesis of a variety of tungsten alkyl complexes of the type [N3N]WR ([N3N]3- = [(Me3SiNCH2CH2)3N]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 d2 ground-state spin triplet. No linear alkyl complexes could be observed as a consequence of α,α-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 ΔH° = 11.8(6) kcal mol-1 and ΔS° = 33(2) eu or K eq ≈ 0.1 at 46 °C. From these and other data it is concluded that the rate constant for α 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.

Antimony–Tungsten Triple Bond: A Stable Complex with a Terminal Antimony Ligand

“…[16] The synthesis and spectroscopic data of 7 have been reported previously, as it is obtained in the reaction of 5 with Li[CH 2 SiMe 3 ]. [17] Complex 6 is a diamagnetic, air-sensitive, brown crystalline compound, which is readily soluble in hydrocarbons. In the mass spectra the molecular ion peak was observed.…”

Highlights in the Renaissance of Amidometal Chemistry

“…The reaction of 64 with a-D-cyclopentyllithium at low temperatures gives the kinetically preferred intermediate 66 with ªdeuterido ligandº, which confirms that in this system a-cleavage occurs faster than b-elimination under the given conditions. [224] At temperatures above 0 8C the D atom wanders to the cyclopentylidene ligand, first to the b-position, then to the g-position. After cyclopentene cleavage and the formation of the thermodynamically stable final product 67, statistical deuteration of the cyclopentene is found.…”

Catalytic Reduction of Dinitrogen to Ammonia by Molybdenum

“…A variety of unusual species have been prepared that contain the [TMSN 3 N] 3 − ligand, among them a tantalum phosphinidene ([TMSN 3 N]Ta = PR) [38] , an alkylidene hydride ([TMSN 3 N]W(H)(cyclopentylidene)) [39] , and a [TMSN 3 N]W(L) species, where L is an arsenide [40,41] , phosphide [41,42] , or stibide [43] . Unusual reactions, such as elimination of H 2 from alkyls to give alkylidynes, suggest that the M ≡ C bond (M = Mo or W) is highly favorable in the triamidoamine setting [39,44,45] .…”

“…Unusual reactions, such as elimination of H 2 from alkyls to give alkylidynes, suggest that the M ≡ C bond (M = Mo or W) is highly favorable in the triamidoamine setting [39,44,45] . However, several problems with TMS substituents were also encountered.…”

“…However, several problems with TMS substituents were also encountered. Examples include migration reactions (e.g., 2.1 [39] ) or CH activation [29,45] …”