Hydrogen Atom Transfer Reactions of the Unsaturated Hydroxycarbyne Complex [W₂Cp₂(μ-COH)(μ-PPh₂)₂]BF₄

Abstract

The hydroxycarbyne complex salt [W2Cp2(μ-COH)­(μ-PPh2)2]­BF4 (1) reacted rapidly with water in the presence of the oxidant [FeCp2]­BF4 to give the hydroxo complex salt [W2Cp2(OH)­(μ-PPh2)2(CO)]­BF4, a preparation that could be replicated using the neutral carbonyl complex [W2Cp2(μ-PPh2)2(μ-CO)] (2) instead. A similar reaction took place slowly with HSPh and rapidly in the presence of [FeCp2]­BF4, to yield the known 32-electron complex salt [W2Cp2(SPh)­(μ-PPh2)2(CO)]­BF4. In contrast, 1 did not react with PhOH or H2Np-tol even in the presence of [FeCp2]­BF4. However, a fast reaction between these molecules and 2 took place in the presence of [FeCp2]­BF4, to give the phenolato complex salt [W2Cp2(OPh)­(μ-PPh2)2(CO)]­BF4 and the imido-hydride [W2Cp2(μ-H)­(Np-tol)­(μ-PPh2)2(CO)]­BF4 (W–W = 2.9135(8) Å), respectively, after formal elimination of hydrogen. The hydroxycarbyne complex 1 reacted rapidly with PH2Cy to give the hydride derivative [W2Cp2(H)­(μ-PPh2)2(CO)­(PH2Cy)]­BF4, this requiring H-migration from O to W atoms. The M–H bonds in the latter hydride cations were deprotonated by strong bases to give the corresponding neutral complexes [W2Cp2(Np-tol)­(μ-PPh2)2(CO)] and [W2Cp2(μ-PPh2)2(CO)­(PH2Cy)]. Compound 1 also reacted easily with two-electron donors such as NCMe, CN t Bu, and CNp-tol, to give products derived from the addition of two molecules of reagent in each case, and some rearrangement of the COH ligand. The first reaction gave the new cationic complex [W2Cp2(μ-PPh2)2(μ-N:N,N′-N2HC2Me2)­(CO)]­BF4, derived from the C–C coupling of two nitrile molecules accompanied by an O to N shift of the hydroxycarbyne proton. In contrast, no C–C coupling processes were observed in the reactions with isocyanides, although proton migration occurred in all cases, either to the metal (reaction with CN t Bu), to give the hydride [W2Cp2(H)­(μ-PPh2)2(μ-CN t Bu)­(CN t Bu)]­BF4, or to the N atom of one of the incoming isocyanides (reaction with CNp-tol), to give the aminocarbyne derivative [W2Cp2{μ-CN­(H)p-tol}­(μ-PPh2)2(CNp-tol)­(CO)]­BF4.

Reactions of the Tetrafluoroborate Complex [Mo2Cp2(κ2-F2BF2)(μ-PPh2)2(CO)]BF4 with Mono- and Bidentate Ligands Having E–H bonds (E = O, S, Se, N, P)

“…The proposed structure for 10 is based on the corresponding spectroscopic data (Table 3 and Experimental Section) and crystallographic analysis of its ditungsten analogue. 26 In fact, the IR spectrum of 10 exhibits a C−O stretch at 1876 cm −1 , a position ca. 10 cm −1 above that of the ditungsten analogue (1865 cm −1 ), as expected when comparing isostructural molybdenum and ditungsten complexes, 27 while being lower than the frequencies of all cationic complexes discussed above, due to the increased electron density at the dimetal center in this neutral complex.…”

Metal-Mediated and Metal-Catalyzed Reactions of Isocyanides

“…Several other works report on the generation of aminocarbyne complexes from isocyanides that proceed by other routes (i.e., isocyanide insertion into M–H and/or M–M bonds, see section ), while in some cases formation of aminocarbyne species through deprotonation/protonation processes could not be excluded …”

Carbyne–Carbyne Coupling and H-Shifts in Reactions of the Unsaturated Methoxy- and Hydroxycarbyne Complexes [Mo2Cp2(μ-COR)(μ-CPh)(μ-PCy2)]+with CO and Isocyanides

“…Reactions with CN t Bu and CNXyl proceeded in both cases with consumption of 3 equiv of reagent and release of CO, and without any observable intermediates, to yield the corresponding aminoalkyne derivatives [Mo 2 Cp 2 {μ-η 2 :η 2 -C­(NHR)­CPh}­(μ-PCy 2 )­(CNR) 2 ]­BF 4 as unique products (R = t Bu ( 7a ), Xyl ( 7b ); Scheme ). The process likely involves an H-transfer from the hydroxycarbyne ligand to an isocyanide molecule to yield an aminocarbyne intermediate at some stage of the reaction (see below), a critical step which we have reported recently for the isoelectronic ditungsten hydroxycarbyne complex [W 2 Cp 2 (μ-COH)­(μ-PPh 2 ) 2 ]­BF 4 . Besides, we note that compounds 7a and 7b are generated as different stereoisomers, with the CN t Bu complex being obtained as the cis-syn isomer whereas the CNXyl derivative is formed selectively as the trans isomer, a matter also to be discussed later on.…”

“…The process likely involves an H-transfer from the hydroxycarbyne ligand to an isocyanide molecule to yield an aminocarbyne intermediate at some stage of the reaction (see below), a critical step which we have reported recently for the isoelectronic ditungsten hydroxycarbyne complex [W 2 Cp 2 (μ-COH)(μ-PPh 2 ) 2 ]BF 4 . 25 Besides, we note that compounds 7a and 7b are generated as different stereoisomers, with the CN t Bu complex being obtained as the cis-syn isomer whereas the CNXyl derivative is formed selectively as the trans isomer, a matter also to be discussed later on. We finally note that some aminoalkyne complexes have been previously generated through acid-induced coupling between carbyne and isocyanide ligands at mononuclear centers, 4a,26 although polynuclear species have been typically prepared previously upon reaction of the free ligands (ynamines) with suitable precursors.…”

“…Even when using just 1 equiv of isocyanide, only partial formation of the corresponding complex 7 was observed, along with unreacted 3. Yet, a sensible reaction pathway can be envisioned on the basis of previous studies on reactions of isocyanides with the related hydroxycarbyne complex [W 2 Cp 2 (μ-COH)(μ-PPh 2 ) 2 ]BF 4 , 25 and with the methoxycarbyne analogues [M 2 Cp 2 (μ-COMe)-(μ-PR 2 ) 2 ]BF 4 (M = Mo, R = Et; M = W, R = Ph). 31 Reaction should be initiated with the nucleophilic attack of an isocyanide molecule to the unsaturated substrate 3 via its less hindered position (between the COH and CPh ligands) and transient displacement of the hydroxycarbyne ligand to a terminal position (A in Scheme 5).…”