Synthesis of Dinuclear Mo-Fe Hydride Complexes and Catalytic Silylation of N2.

Abstract

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 MoIV -FeII complexes with bridging hydrides, CpR Mo(PMe3 )(H)(μ-H)3 FeCp* (2 a; CpR =Cp*=C5 Me5 , 2 b; CpR =C5 Me4 H), were synthesized via deprotonation of CpR Mo(PMe3 )H5 (1 a; CpR =Cp*, 1 b; CpR =C5 Me4 H) 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 [Ph3 C]+ in THF led to the formation of cationic THF adducts [CpR Mo(PMe3 )(THF)(μ-H)3 FeCp*]+ (3 a; CpR =Cp*, 3 b; CpR =C5 Me4 H). 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 Me3 SiCl, 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.