Synthesis and Protonation Studies of Molybdenum(0) Bis(di­nitrogen) Complexes Supported by Diphosphine Ligands ­Containing Pendant Amines

A series of molybdenum bis(dinitrogen) complexes of the formula trans-[Mo(N2)2(PEtNRPEt)2] (PEtNRPEt = Et2PCH2N(R)CH2PEt2; R = phenyl (1), 2,6-difluorobenzyl (2), 3,5-difluorobenzyl (3), CH2CH2NMe2 (4), CH2-o-Py (5)] were synthesized and characterized by NMR and IR spectroscopy, and X-ray crystallography. Protonation studies with stoichiometric amounts of triflic acid (HOTf) were performed, and the protonated products were characterized by NMR and in situ IR spectroscopic methods. Products formed in the stepwise protonation reactions included, for example, a mixture of the seven-coordinate molybdenum bis(dinitrogen) hydride, trans-[Mo(H)(N2)2(PEtNPhPEt)2]+ [1H]+, and the Mo-hydrazido triflate complex, trans-[Mo(NNH2)(OTf)(PEtNPhPEt)2]+ [1(NNH2)]+. Complex 2, with more basic pendant amines, can be protonated up to three times, affording the highly-charged molecule, trans-[Mo(H)(N2)2(PEtN2,6-F2-Bn(H)PEt)2)]3+ [2H(PN(H)P)2]3+.