Effects of the η⁵-C₅H₄ⁱPr Ligand on the Properties Exhibited by Its Tungsten Nitrosyl Complexes

Abstract

Reaction of Na[η(5)-C5H4(i)Pr] with W(CO)6 in refluxing THF for 4 days generates a solution of Na[(η(5)-C5H4(i)Pr)W(CO)3] that when treated with N-methyl-N-nitroso-p-toluenesulfonamide at ambient temperatures affords (η(5)-C5H4(i)Pr)W(NO)(CO)2 (1) that is isolable in good yield as an analytically pure orange oil. Treatment of 1 with an equimolar amount of I2 in Et2O at ambient temperatures affords (η(5)-C5H4(i)Pr)W(NO)I2 (2) as a dark brown solid in excellent yield. Sequential treatment at low temperatures of 2 with 0.5 equiv of Mg(CH2CMe3)2 and Mg(CH2CH═CMe2)2 in Et2O produces the alkyl allyl complex, (η(5)-C5H4(i)Pr)W(NO)(CH2CMe3)(η(3)-CH2CHCMe2) (3), as a thermally sensitive yellow liquid. Complex 3 may also be synthesized, albeit in low yield, in one vessel at low temperatures by reacting 1 first with 1 equiv of PCl5 and then with the binary magnesium reagents specified above. Interestingly, similar treatment of 1 in Et2O with PCl5 and only 0.5 equiv of Mg(CH2CH═CMe2)2 results in the formation of the unusual complex (η(5)-C5H4(i)Pr)W(NO)(PCl2CMe2CH═CH2)Cl2 (4), which probably is formed via a metathesis reaction of the binary magnesium reagent with (η(5)-C5H4(i)Pr)W(NO)(PCl3)Cl2. The C-D activation of C6D6 by complex 3 has been investigated and compared to that exhibited by its η(5)-C5Me5, η(5)-C5Me4H, and η(5)-C5Me4(n)Pr analogues. Kinetic analyses of the various activations have established that the presence of the η(5)-C5H4(i)Pr ligand significantly increases the rate of the reaction, an outcome that can be attributed to a combination of steric and electronic factors. In addition, mechanistic studies have established that in solution 3 loses neopentane under ambient conditions to generate exclusively the 16e η(2)-diene intermediate complex (η(5)-C5H4(i)Pr)W(NO)(η(2)-CH2═CMeCH═CH2), which then effects the subsequent C-D activations. This behavior contrasts with that exhibited by the η(5)-C5Me5 analogue of 3 which forms both η(2)-diene and η(2)-allene intermediates upon thermolysis. Sixteen-electron (η(5)-C5H4(i)Pr)W(NO)(η(2)-CH2═CMeCH═CH2) has been isolated as its 18e PMe3 adduct. All new organometallic complexes have been characterized by conventional spectroscopic and analytical methods, and the solid-state molecular structures of two of them have been established by single-crystal X-ray crystallographic analyses.

Functionalization of Methane Initiated by Cp*W(NO)(CH2CMe3)(η3-CH2CHCMe2)

“…A kinetic analysis of the reaction of 1 with C 6 D 6 has been performed previously by monitoring the consumption of 1 at different temperatures by 1 H NMR spectroscopy . This monitoring afforded pseudo-first-order rate constants that have been used during the current study to determine the optimum reaction times for higher-temperature C–H activations by 1 .…”

“…A kinetic analysis of the reaction of 1 with C 6 D 6 has been performed previously by monitoring the consumption of 1 at different temperatures by 1 H NMR spectroscopy. 21 This monitoring afforded pseudo-first-order rate constants that have been used during the current study to determine the optimum reaction times for higher-temperature C−H activations by 1. This approach is valid, since the ratedetermining step in these activations is loss of neopentane from 1 to generate the reactive 16e η 2 -allene and η 2 -diene intermediates.…”

Thermal Chemistry of Cp*W(NO)(CH2CMe3)(H)(L) Complexes (L = Lewis Base)

“…The effect of replacing the Cp* ligand with the η 5 -C 5 H 4 i Pr group on the chemistry of the PPh 3 system has also been investigated because we have previously demonstrated that such a substitution in other Cp*W­(NO)-containing complexes causes them to initiate C–H activations at a markedly faster rate . In this system, however, this is not the case.…”

“…All binary magnesium reagents used were prepared from the corresponding Grignard reagents . Complexes Cp*W­(NO)­Cl 2 , Cp*W­(NO)­(CH 2 CMe 3 ) 2 , and (η 5 -C 5 H 4 i Pr)­W­(NO)­I 2 and the proligand P­(OCH 2 ) 3 ­CMe were prepared according to the published procedures. Pentamethylcyclopentadiene was obtained from the Boulder Scientific Co. All other chemicals and reagents were ordered from commercial suppliers and used as received.…”

Synthesis and structure of a pyridine-stabilized silanone molybdenum complex and its reactions with PMe3and acetone

“…26 In contrast, the signals representative of the internal H 2 C C carbons are observed at 134.1 (M = Mo) and 133.8 ppm (M = W). These chemical shifts shifted significantly downfield from those observed for the H 2 C C R 2 carbons in the η 2 -H 2 CCR 2 -coordinated complexes (39–84 ppm (M = Mo), 25 55–85 ppm (M = W)) 26 and are comparable to non-coordinated H 2 C C R 2 carbons including those in the molybdenum and tungsten complexes (112–138 ppm (M = Mo), 25 b ,30 101–149 ppm (M = W) 31 ), implying weak interactions between the C4 atoms and metal centers in C 6 D 6 solutions. CO ligand signals could not be detected, likely due to severe broadening and overlapping with the baselines.…”