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.

The adducts 2 M,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 }{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.