Synthesis of Dinuclear Mo−Fe Hydride Complexes and Catalytic Silylation of N 2

Two transition‐metal atoms bridged by hydrides may represent a useful structural motif for N 2 activation by molecular complexes and the enzyme active site. In this study, dinuclear Mo IV ‐Fe II complexes with bridging hydrides, Cp R Mo(PMe 3 )(H)(μ‐H) 3 FeCp* ( 2 a ; Cp R =Cp*=C 5 Me 5 , 2 b ; Cp R =C 5 Me 4 H), were synthesized via deprotonation of Cp R Mo(PMe 3 )H 5 ( 1 a ; Cp R =Cp*, 1 b ; Cp R =C 5 Me 4 H) by Cp*FeN(SiMe 3 ) 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 [Ph 3 C] + in THF led to the formation of cationic THF adducts [Cp R Mo(PMe 3 )(THF)(μ‐H) 3 FeCp*] + ( 3 a ; Cp R =Cp*, 3 b ; Cp R =C 5 Me 4 H). Further reaction of 3 a with LiPPh 2 gave rise to a phosphido‐bridged complex Cp*Mo(PMe 3 )(μ‐H)(μ‐PPh 2 )FeCp* ( 4 ). A series of Mo−Fe complexes were subjected to catalytic silylation of N 2 in the presence of Na and Me 3 SiCl, furnishing up to 129±20 equiv of N(SiMe 3 ) 3 per molecule of 2 b . Mechanism of the catalytic cycle was analyzed by DFT calculations.