Seven‐coordinate group 6 metal hydrides obtained by H$_2$ activation at B(C$_6$F$_5$)$_3$ adducts of N$_2$ complexes: Frustrated Lewis Pair‐type Reactivity of the B–N linkage
Résumé
The adducts 2M,R of general formula trans-[(L)M{R$_2$P(CH$_2$)$_2$PR$_2$}$_2${N$_2$B(C$_6$F$_5$)$_3$}] (L = ø or N$_2$, M = Mo or W, R = Et or Ph), formed from Lewis acid-base pairing of B(C$_6$F$_5$)$_3$ to a dinitrogen ligand of zero-valent group 6 bis(phosphine) complexes trans-[M{R$_2$P(CH$_2$)$_2$PR$_2$}$_2$(N$_2$)$_2$] are shown to react with dihydrogen to afford hepta-coordinated bis(hydride) complexes [M(H)$_2${R$_2$P(CH$_2$)$_2$PR$_2$}$_2${N$_2$B(C$_6$F$_5$)$_3$}] 3$^{M,R}$ which feature the rare ability to activate both dinitrogen and dihydrogen at a single metal center, except in the case where M = Mo and R = Ph for which fast precipitation of insoluble [Mo(H)$_4$(dppe)$_2$] (dppe = 1,2-bis(diphenylphosphino)ethane) occurs. The frustrated Lewis pair (FLP)-related reactivity of the B–N linkage in compounds 3$^{W,R}$ was explored and led to distal N functionalization without involvement of the hydride ligands. It is shown in one example that the resulting bis(hydride) diazenido compounds may also be obtained through a sequence involving first FLP-type N-functionalization followed by oxidative addition of H$_2$. Those oily compounds were found to have limited stability in solution or in their isolated states. Finally, treatment of 3$^{W,Et}$ with the Lewis base N,N-dimethylaminopyridine (DMAP) affords the simple but unknown bis(hydride)-dinitrogen species [W(H)$_2$(depe)$_2$(N$_2$)] 11$^{Et}$ (depe = 1,2-bis(diethylphosphino)ethane) which direct, selective formation from trans-[W(N$_2$)$_2$(depe)$_2$] is not possible.
Domaines
Chimie de coordination
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Boegli, Seven‐coordinate group 6 metal hydrides, 2024.pdf (1.09 Mo)
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