Organometallics p. 2435 - 2446 (1995)
Update date:2022-08-03
Topics:
Morrison, Donald L.
Rodgers, Paula M.
Chao, Yuan-Wei
Bruck, Michael A.
Grittini, Carina
Tajima, Tracey L.
Alexander, Steven J.
Rheingold, Arnold L.
Wigley, David E.
The synthesis, reactivity, and structural characterization of the d0 tris(imido) complex [Li(THF)4][W(NAr)3Cl] (2, Ar = 2,6-C6H3-i-Pr2) are reported. When W(NAr)Cl4(THF) reacts with 2 equiv of Me3SiNHAr in THF, the bis(imido) compound W(NAr)2Cl2(THF)2 (1) is isolated. Reacting W(NAr)2Cl2(THF)2 with 2 equiv of LiNHAr in THF affords the yellow, crystalline tris(imido) complex [Li(THF)4][W(NAr3)Cl] (2). Complex 2 is shown to be the kinetic product of this reaction since it reacts with byproduct H2NAr to afford W(NAr)2-(NHAr)2 (3). Experiments are described that support the d0 W(=NR)2 functional group in W(NAr)2Cl2(THF)2 (1) arising by an intramolecular α-H abstraction in [W(NAr)(NHAr)2-Cl2(THF)n] (with loss of H2NAr), while the formation of [W(NAr)3Cl]- (2) from W(NAr)2Cl2-(THF)2 (1) most likely proceeds by an intermolecular deprotonation of nascent W(NAr)2-(NHAr)Cl by the second equivalent of [NHAr]-. These experiments include synthesis and reactivity studies of W(NAr)2Cl2(NH2Ar) (4), W(NAr)(NEt2)Cl3(THF) (5), and W(NAr)2-(NEt2)Cl (6). The d0 metal center in [W(NAr)3Cl]- (2) is susceptible to nucleophilic attack as seen in its reactions with PMePh2, PMe3, [n-Bu4N]Br, MeLi, and LiCH2SiMe3 to afford the substitution products W(NAr)3(PMePh2) (7), W(NAr)3(PMe3) (8), [n-Bu4N][W(NAr)3Br] (9), [Li(THF)4][W(NAr)3Me] (10), and [Li(THF)4][W(NAr)3(CH2SiMe3)] (11), respectively. Kinetic and mechanistic evidence is presented that suggests these reactions proceed by a bimolecular, SN2 attack at the d0 tungsten center. [Li(THF)4][W(NAr)3Cl] (2) crystallizes in the monoclinic space group P21/n (No. 14) with a = 13.787(4), A?, b = 17.348(5) A?, c = 22.781(8) A?, β = 90.426(28)°, and V = 5448.5(30) A?3, with Z = 4 and D(calc) = 1.268 g cm-3. W(NAr)3(PMe3) (8) crystallizes in the orthorhombic space group Pbca (No. 61) with a = 18.572(3) A?, b = 25.966(4) A?, c = 16.819(3) A?, and V = 8111(4) A?3, with Z = 8 and D(calc) = 1.29 g cm-3. The tungsten atom of [Li(THF)4][W(NAr)3Cl] (2) is tetrahedrally coordinated with three virtually identical imido ligands with an average W-N bond length of 1.78 A? and an average W-N-Cipso bond angle of 171°. W(NAr)3(PMe3) (8) is also tetrahedrally coordinated and displays an average imido W-N bond length of 1.79 A? and slightly bent W-N-Cipso bond angles (av 167°), though one imido ligand is more strongly bent than the other two. The electronic structure of the C3ν W(NAr)3L compounds suggests a ligand-based, nonbonding a2 HOMO comprised of a N(pπ) orbital combination oriented perpendicular to the molecule's C3 axis. Accordingly, an imido nitrogen is subject to electrophilic attack, as seen in the reactions of W(NAr)3(PMe3) (8) with HOAr′ (Ar′ = 2,6-C6H3Me2), Me3SiI, MeI, and PhNCO that afford W(NAr)2(NHAr)(OAr′) (12), W(NAr)2[N(SiMe3)Ar]I (13), W(NAr)2-(NMeAr)I (14), and W[NArC(O)NPh](NAr)2(PMe3) (15), respectively. Similarly, the reaction of [Li(THF)4][W(NAr)3Me] (10) with [HNMe3]BPh4 does not protonate the W-Me bond but rather attacks the imido nitrogen to afford W(NAr)2(NHAr)Me (16). W(NAr)2(NHAr)Me (16) does not eliminate CH4 upon thermolysis to afford base-free [W(NAr)3]; other attempts to generate this species are described.
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