Synthesis of Dinuclear Mo−Fe Hydride Complexes and Catalytic Silylation of N2

Two transition-metal atoms bridged by hydrides may represent a useful structural motif for N₂ activation by molecular complexes and the enzyme active site. In this study, dinuclear Mo^IV-Fe^II complexes with bridging hydrides, Cp^RMo(PMe₃)(H)(μ-H)₃FeCp* ( 2 a ; Cp^R=Cp*=C₅Me₅, 2 b ; Cp^R=C₅Me₄H), were synthesized via deprotonation of Cp^RMo(PMe₃)H₅ ( 1 a ; Cp^R=Cp*, 1 b ; Cp^R=C₅Me₄H) by Cp*FeN(SiMe₃)₂, and they were characterized by spectroscopy and crystallography. These Mo−Fe complexes reveal the shortest Mo−Fe distances ever reported (2.4005(3) Å for 2 a and 2.3952(3) Å for 2 b ), and the Mo−Fe interactions were analyzed by computational studies. Removal of the terminal Mo−H hydride in 2 a – 2 b by Ph₃C]⁺ in THF led to the formation of cationic THF adducts Cp^RMo(PMe₃)(THF)(μ-H)₃FeCp*]⁺ ( 3 a ; Cp^R=Cp*, 3 b ; Cp^R=C₅Me₄H). Further reaction of 3 a with LiPPh₂ gave rise to a phosphido-bridged complex Cp*Mo(PMe₃)(μ-H)(μ-PPh₂)FeCp* ( 4 ). A series of Mo−Fe complexes were subjected to catalytic silylation of N₂ in the presence of Na and Me₃SiCl, furnishing up to 129±20 equiv of N(SiMe₃)₃ per molecule of 2 b . Mechanism of the catalytic cycle was analyzed by DFT calculations.