Seven-Coordinate Group 6 Metal Hydrides Obtained by H2 Activation at B(C6F5)3 Adducts of N2 Complexes: Frustrated Lewis Pair-Type Reactivity of The B-N Linkage.

Abstract

The adducts 2M,R of general formula trans-[(L)M{R2P(CH2)2PR2}2{N2B(C6F5)3}] (L=ø or N2, M=Mo or W, R=Et or Ph), formed from Lewis acid-base pairing of B(C6F5)3 to a dinitrogen ligand of zero-valent group 6 bis(phosphine) complexes trans-[M{R2P(CH2)2PR2}2(N2)2] are shown to react with dihydrogen to afford hepta-coordinated bis(hydride) complexes [M(H)2{R2P(CH2)2PR2}{N2B(C6F5)3}] 3M,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 3W,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 H2. Those oily compounds were found to have limited stability in solution or in their isolated states. Finally, treatment of 3W,Et with the Lewis base N,N-dimethylaminopyridine (DMAP) affords the simple but unknown bis(hydride)-dinitrogen species [W(H)2(depe)2(N2)] 11Et (depe=1,2-bis(diethylphosphino)ethane) which direct, selective formation from trans-[W(N2)2(depe)2] is not possible.