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

Abstract

Reaction of Cp*Mo(NO)Cl with 1 equiv of 1,2-bis(dimethylphosphino)ethane (dmpe) in THF at ambient temperature forms [Cp*Mo(NO)(Cl)(κ-dmpe)]Cl (1), which is isolable as an analytically pure yellow powder in 65% yield. Further addition of 2 equiv of CpCo to 1 in CHCl affords dark red Cp*Mo(NO)(κ-dmpe) (2), which was isolated in 36% yield by recrystallization from EtO 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)(κ-dmpeS)] (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)(η-S)(κ-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)(κ-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)Br] (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)Br(κ-dmpe)] (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.

Effects of Coordinating a Hemilabile Ligand to 14e Cp*M(NO) Scaffolds (M = Mo, W)

“…The nitrosyl ligand in 7 is essentially linear with a Mo–N–O bond angle of 172.75(10)°. The N–O distance of 1.2338(15) Å is somewhat longer than that extant in the related complexes Cp*Mo­(NO)­(κ 2 -dppe) [N–O = 1.223(2) Å] or Cp*Mo­(NO)­(κ 2 -dmpe) [N–O = 1.2243(14) Å] and is consistent with the increased Mo → NO back-bonding suggested by the IR spectrum of 7 .…”

“…Subsequent workup of the final reaction mixture affords 7 as a dark-blue-green solid whose 1 H and 31 P­{ 1 H} NMR spectra are as expected for this formulation (Figures S27–S29). The IR spectrum of 7 as a C 6 H 6 solution shows a single absorption at 1479 cm –1 , a value significantly lower in energy than those exhibited by 3 or Cp*Mo­(NO)­(κ 2 -dmpe) [ν­(NO) = 1535 cm –1 ], and represents, to the best of our knowledge, the lowest ν­(NO) ever reported for a complex containing the Cp*M­(NO) fragment (M = Mo, W). The substantial Mo → NO back-bonding indicated by the IR spectrum of 7 evidently results from the unique electronic character of the i Pr 2 PN ligand.…”

“…Extension of the i Pr 2 PN chemistry outlined in the preceding sections to the analogous molybdenum system has revealed that the reaction of [Cp*Mo­(NO)­Cl 2 ] 2 with the hemilabile proligand proceeds in a slightly different manner than that discovered for its tungsten congener (Scheme ). In contrast, the reactivity of [Cp*Mo­(NO)­Cl 2 ] 2 with dmpe has previously been shown to be virtually identical with that of the analogous tungsten complex . As illustrated in Scheme , the addition of 2 equiv of i Pr 2 PN to an orange-brown suspension of [Cp*Mo­(NO)­Cl 2 ] 2 in C 6 H 6 immediately produces a clear, bright-red solution that persists for up to 10 min.…”

“…In contrast, the reactivity of [Cp*Mo-(NO)Cl 2 ] 2 with dmpe has previously been shown to be virtually identical with that of the analogous tungsten complex. 20 As illustrated in Scheme 4, the addition of 2 equiv of…”