Reduction of a Coordinated Acetonitrile Ligand:  Synthesis of an Ethylimido Complex of Tungsten

Abstract

Treatment of the dinitrogen complex W(N2)2(dppe)2 (1; dppe = 1,2-bis(diphenylphosphino)ethane) with trifluoromethanesulfonic acid yields the novel hydrazido complex [W(N2H2)(OTf)(dppe)2]+[OTf]- (2; OTf = CF3SO3 -). The triflato ligand is readily displaced by other ligands and coordinating solvents. The triflato complex 2 yields the complex [W(N2H2)(NCCH3)(dppe)2]2+ (5), when it is dissolved in acetonitrile, and 5 is readily deprotonated by a variety of bases to give the acetonitrile−dinitrogen complex W(N2)(NCCH3)(dppe)2 (3). Complex 3 is protonated at the β-carbon by tetrafluoroboric acid, resulting in the reduction of the coordinated nitrile to give the novel imido complex [WF(NCH2CH3)(dppe)2]+[BF4]- (4). The X-ray crystal structure of the imido complex 4 reveals an effectively linear W−N−C bond (171.8°) in the imido ligand with a W−N bond length of 1.741(4) Å.

Chemistry of Highly Electrophilic Binuclear Cations. 1. Oxidation Reactions of [M2(η5-C5H5)2(CO)4(μ-Ph2PCH2PPh2)] (M = Mo, W) with [FeCp2]X (X = BF4, PF6)

“…For both compounds, the more shielded methylenic resonance exhibits a large coupling to the bridging fluoride ( 4 J FH = 10−13 Hz) and is significantly broader than the other one. For comparison, 4 J HF = 3.7 Hz for the trans ethylimido fluoro complex [W(F)(NEt)(dppe) 2 ]BF 4 . We interpret the unusual broadening effect as derived from the presence in solution of some H-bonding interaction between this proton and the tetrafluoroborate counterion, as found in the solid state.…”

Protonation Studies of a Tungsten Dinitrogen Complex Supported by a Diphosphine Ligand Containing a Pendant Amine

“…To confirm that [ 3 (N 2 ) 2 ]BF 4 was protonated only at the metal center, the reaction was performed with a 15 N-labeled amine in the PNP ligand, trans -[W(N 2 ) 2 (dppe)(P Et ( 15 N) Me P Et )][BF 4 ] ( 1 (N 2 ) 2 ( 15 N)). The corresponding 15 N{ 1 H} NMR spectrum of trans -[W(N 2 ) 2 (H)(dppe)(P Et ( 15 N) Me P Et )][BF 4 ] ([ 3 (N 2 ) 2 ( 15 N)]BF 4 ) contains a triplet at δ −362 ( J NP = 14 Hz) and does not exhibit 15 N–H coupling (typically ∼80 Hz) , in the proton-coupled 15 N NMR spectrum. Seven-coordinate transition-metal hydride bis(dinitrogen) complexes have been reported for Mo and W supported by traditional chelating phosphine ligands (such as dppe) upon reaction with mineral acids such as HCl in methanol or THF, , and additional details are described below.…”

Double deprotonation of coordinated ethylimide to CH3CN: molecular mechanism and relevance to the chemistry of Mo and W organoimides

“…The starting compounds [MCl(NEt)(dppe) 2 ]Cl (1; M = Mo/W) were prepared by reaction of the mixed acetonitrile-N 2 complexes [M(N 2 )(CH 3 CN)(dppe) 2 ] (M = Mo, W) with HCl in benzene (Scheme 1). 7 Under these conditions, the acetonitrile ligands are protonated to yield the corresponding M(IV) ethylimido complexes. 7, 9 Recently we investigated this reaction in more detail and found that in complexes of the type [M(N 2 )(CH 3 CN)(diphos) 2 ] (M = Mo, W; diphos = dppe, depe) the nitrile ligand is activated towards protonation at the sp carbon center after exchange of dinitrogen by a Lewis base X, in general the conjugated base of the acid HX employed for protonation.…”