Hemilability of the 1,2-Bis(dimethylphosphino)ethane (dmpe) Ligand in Cp*Mo(NO)(κ2-dmpe).

Abstract

Reaction of Cp*Mo(NO)Cl2 with 1 equiv of 1,2-bis(dimethylphosphino)ethane (dmpe) in THF at ambient temperature forms [Cp*Mo(NO)(Cl)(κ2-dmpe)]Cl (1), which is isolable as an analytically pure yellow powder in 65% yield. Further addition of 2 equiv of Cp2Co to 1 in CH2Cl2 affords dark red Cp*Mo(NO)(κ2-dmpe) (2), which was isolated in 36% yield by recrystallization from Et2O at -30 °C. Reaction of a benzene solution of 2 with an equimolar amount of elemental sulfur results in the immediate production of dark blue (μ-S)[Cp*Mo(NO)(κ1-dmpeS)]2 (3), which is a rare example of a bimetallic transition-metal complex bridged by only a single sulfur atom and involving Mo═S═Mo bonding. In contrast, reaction of 2 with an excess of sulfur in benzene results in the formation of Cp*Mo(NO)(η2-S2)(κ1-dmpeS) (4). Complex 4 can also be formed by the addition of elemental sulfur to 3, thereby indicating that 3 is a precursor to 4. Cp*Mo(NO)(κ2-dmpe) (2) also undergoes interesting transformations when treated with organic bromides. For instance, reaction of 2 with 5 equiv benzyl bromide in THF produces the bimetallic complex (μ-dmpe)[Cp*Mo(NO)Br2]2 (5) and bibenzyl after 4 d at 70 °C probably via radical intermediates. In contrast to its reaction with benzyl bromide, complex 2 forms [Mo(NO)Br2(κ2-dmpe)]2 (6), olefin, alkane, and Cp*H when treated with 5 equiv of 1-bromopropane or 1-bromooctane in THF at 70 °C for 72 h. Interestingly, complex 2 does not display any reactivity with bromobenzene or 1-bromoadamantane even after being heated for several days at 70 °C. All new complexes were characterized by conventional spectroscopic and analytical methods, and the solid-state molecular structures of most of them were established by single-crystal X-ray crystallographic analyses.