Synthesis and Reactivity of [Tp‘(CO)(PhC⋮CMe)WNPh]⁺ (Tp‘ = Hydridotris(3,5-dimethylpyrazolyl)borate)

Abstract

The tungsten(IV) nitrene complex [Tp‘(CO)(PhC⋮CMe)WNPh]+ (cation of 1; Tp‘ = hydridotris(3,5-dimethylpyrazolyl)borate) has been prepared by oxidation of the amido complex Tp‘(CO)(PhC⋮CMe)W(NHPh) (2) with elemental iodine in the presence of triethylamine. Oxidation in the absence of base also forms the aniline complex [Tp‘(CO)(PhC⋮CMe)W(NH2Ph)]+ (3), which has been independently synthesized. Reaction of 1 with 1 equiv of KBH4 adds hydride to the nitrene ligand to give the amido complex 2. Reaction of 1 with Li[HBEt3] forms the formyl adduct Tp‘(NPh)(PhC⋮CMe)W(η1-C(O)H) (4) as an intermediate, which ultimately yields the hydride complex Tp‘(NPh)(PhC⋮CMe)W(H) (5) with loss of CO. The hydride complex is also formed from reaction of 1 with 10 equiv of KBH4. Addition of acid to the hydride complex 5 protonates the nitrene nitrogen to form [Tp‘(H)(PhC⋮CMe)W(NHPh)][BAr‘4] (6). Both 5 and 6 exhibit surprisingly low-field hydride resonances in the 1H NMR (13.5 and 20.6 ppm, respectively). Addition of methylmagnesium bromide to the nitrene complex leads to the methyl acyl intermediate Tp‘(NPh)(PhC⋮CMe)W(η1-C(O)Me) (7), which readily adds a proton and cyclizes to [Tp‘(NHPh)W(C(Ph)C(Me)C(O)Me][BAr‘4] (8). Reaction of 1 with phenyllithium forms the phenyl acyl complex Tp‘(NPh)(PhC⋮CMe)W(η1-C(O)Ph) (9). X-ray crystal structures have been determined for 1 and 8. The ring in complex 8 exhibits a structure similar to a folded envelope, with the flap containing the Cα, W, and O atoms. The ring is bonded in an η4 fashion to the metal center.

Combined experimental and computational study of W(II), Ru(II), Pt(IV) and Cu(I) amine and amido complexes using 15N NMR spectroscopy

“…The previously reported six-coordinate W(II) (d 4 ) complex Tp * W(CO)(PhC"CMe)NHPh possesses an empty dp orbital and engages in W-amido multiple bonding, albeit in competition with alkyne p \ to W p-donation [16]. Previous studies are consistent with W-N amido multiple bonding as evidenced by spectroscopic data of the complexes [Tp * W(CO)(PhC"CMe)NH n Ph] m+ (n = 1, m = 0; n = 2, m = 1) [16]. For example, the 13 C NMR spectrum of Tp * W(CO)(PhC"CMe)NHPh reveals chemical shifts at 178.3 and 181.3 ppm for the alkyne carbons, consistent with p-donation from both the alkyne and amido ligands into a single vacant dp orbital.…”

“…As previously described by Templeton et al [16], for [Tp * W(CO)-(PhC"CMe)(NH n Ph)] m+ (n = 1, m = 0; n = 2, m = 1), in the absence of W-N p interactions, it is anticipated that the dp orbitals will split into: (1) a lowest energy molecular orbital that has d yz character and results from back-bonding with the CO and alkyne shift (ppm) and Anisotropy (Aniso, ppm) of the nucleus of interest calculated in THF solution, the Kohn-Sham HOMO and LUMO energies (a.u. ), the energy difference (gap, a.u.)…”

“…For example, amido ðNR À 2 Þ and imido ðNR 2À Þ moieties have been utilized as inert ancillary ligands as well as reactive ligands central to metalmediated catalysis [1][2][3][4][5][6][7][8][9][10][11][12][13]. When coordinated to transition metals with one or more vacant dp orbital(s), amido ligands can function as strong p-donors to produce metal-amido multiple bonding (Scheme 1) [14][15][16][17][18][19][20][21][22][23][24][25][26]. The amido-to-metal p-interaction reduces the electron density at the amido ligand and, hence, can decrease, in some cases substantially, the propensity of this ligand to react as a basic or nucleophilic center [18,19].…”

“…Along these lines, our groups have been pursuing the synthesis and reactivity of transition metal complexes with non-dative heteroatomic ligands. Collectively, we have studied the reactivity of W(II), Ru(II), Pt(IV), and Cu(I) systems with amido, alkoxo and related ligands [2,15,16,[30][31][32][33][34][35][36][37]41,43,[60][61][62][63]. The Ru(II), Pt(IV) and Cu(I) systems all exhibit reactivity that can be attributed, at least in part, to the disruption of ligand-to-metal p-donation.…”

Unusual activation pathways of amines in the reactions with molybdenum pentachloride

“…39 This synthetic strategy does not imply any change in the oxidation state of the metal centre, unless specific oxidative co-reactants are involved. 40 Imido ligands have been generated also by metathesis of metal oxide chlorides with isocyanates 41 and by addition of azides, RN 3 , to metal complexes.…”