The hydride-supported [Mo Fe ] cluster complex {Cp*Mo(PMe )} {FeN(SiMe ) } (H) (2 a; Cp*=η -C Me ) and its [Mo Mn ] congener 2 b were synthesized from the reactions of Cp*Mo(PMe )(H) (1) with M{N(SiMe ) } (M=Fe, Mn). The amide-to-thiolate ligand-exchange reactions of complex 2 a with bulky thiol reagents (HSR; R=2,4,6-iPr C H (Tip), 2,6-(SiMe ) C H (Btp)) furnished the corresponding hydride-supported [Mo Fe ](SR) cluster complexes. The [Mo Fe ] clusters served as catalyst precursors for the reductive silylation of N and yielded ≈65-69 equivalents of N(SiMe ) relative to the [Mo Fe ] clusters. Treatment of complexes 2 a and b with an excess of CNtBu resulted in the formation of dinuclear Mo-Fe and Mo-Mn complexes, which indicated that the [Mo M ] cores (M=Fe, Mn) split into two dinuclear species upon accommodation of substrates.
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, CpRMo(PMe3)(H)(μ‐H)3FeCp* (2 a; CpR=Cp*=C5Me5, 2 b; CpR=C5Me4H), were synthesized via deprotonation of CpRMo(PMe3)H5 (1 a; CpR=Cp*, 1 b; CpR=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 [CpRMo(PMe3)(THF)(μ‐H)3FeCp*]+ (3 a; CpR=Cp*, 3 b; CpR=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.
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