Binuclear Carbyne and Ketenyl Derivatives of the Alkyl-Bridged Complexes [Mo₂(η⁵-C₅H₅)₂(μ-CH₂R)(μ-PCy₂)(CO)₂] (R = H, Ph)

Abstract

The 30-electron benzylidyne complex [Mo2Cp2(μ-CPh)(μ-PCy2)(μ-CO)] (Cp = η5-C5H5) could be conveniently prepared upon photolysis of the benzyl-bridged complex [Mo2Cp2(μ-CH2Ph)(μ-PCy2)(CO)2]. It reacted with CO to give the ketenyl complex [Mo2Cp2{μ-C(Ph)CO}(μ-PCy2)(CO)2] (2.6101(2) Å), which in turn could be selectively decarbonylated at 353 K to give the 32-electron benzylidyne derivative [Mo2Cp2(μ-CPh)(μ-PCy2)(CO)2] (Mo−Mo = 2.666(1) Å). Related methylidyne complexes could be obtained from the methyl-bridged complex [Mo2Cp2(μ-CH3)(μ-PCy2)(CO)2] via its trinuclear derivative [Mo3Cp2(μ3-CH)(μ-PCy2)(CO)7]. Thus, the carbonylation of the latter cluster gave the ketenyl complex [Mo2Cp2{μ-C(H)CO}(μ-PCy2)(CO)2], whereas its reaction with P(OMe)3 gave the substituted cluster [Mo3Cp2(μ3-CH)(μ-PCy2)(CO)6{P(OMe)3}], which in turn could be thermally degraded to give selectively the 30-electron methylidyne derivative [Mo2Cp2(μ-CH)(μ-PCy2)(μ-CO)] (Mo−Mo = 2.467(1) Å). DFT calculations on the phenylketenyl complex revealed that the metal−ligand interaction is intermediate between the extreme descriptions represented by the acylium (3-electron donor) and ketenyl (1-electron donor) canonical forms of this ligand.

Recent advances in ketene chemistry

“…Protonation of the ketene complex 371 ([Mo2Cp2{μ-C(Ph)CO)}(μ-PCy2)(CO)2]) gave the metal complex 372 in 88% yield as a red solid, and was interpreted as involving protonation on oxygen (Scheme 131). 179,180 The structure of 372 was confirmed by an X-ray determination. …”

Heterometallic clusters derived from the unsaturated carbyne-bridged dimolybdenum complexes [Mo 2 (η 5 -C 5 H 5 ) 2 (μ-CPh) (μ-PCy 2 ) (CO) x ] (x = 1, 2)

“…The 16-electron fragments MnL(CO) 2 (L = Cp,  5 -C 5 H 4 Me) can be generated in situ through photolysis of the corresponding precursors [MnL(CO) 3 ]. Unfortunately, the photolysis of compound 1 in presence of these complexes only rendered partial transformation of 1 into its ketenyl derivative [Mo 2 Cp 2 {-C(Ph)CO}(-PCy 2 )(CO) 2 ] [3].…”

“…Unfortunately, the photolysis of compound 1 in presence of these complexes only rendered partial transformation of 1 into its ketenyl derivative [Mo 2 Cp 2 {-C(Ph)CO}(-PCy 2 )(CO) 2 ] [3]. This is obviously due to reaction of 1 with the carbon monoxide generated by the photolytic process, and is in contrast with the behaviour of the related methoxycarbynebridged complex [Mo 2 Cp 2 (-COMe)(-PCy 2 )-CO)], which gave the trinuclear complexes [Mo 2 MnCp 2 L(-COMe)(-PCy 2 )CO) 4 ] under similar conditions [7].…”

“…The minor isomer displays a PCy 2 resonance at 223.8 ppm, a position almost identical to those of compounds 8b,c, and is thus assigned to the isomer syn. The major isomer of 8a, identified by a slightly more shielded 31 3 }]PF 6 a molecule proposed to be formed through initial attack of the gold electrophile to the Mo-P bond of the parent carbyne complex [8]. This exemplifies the great influence that subtle electronic and steric factors exert over the course of these cluster-building reactions.…”

“…The reactivity of these complexes mainly stems from the metalcarbon multiple bonds present in these molecules, of highest order (three) for terminal ligands. Carbyne-bridged complexes have reduced metalcarbon bond orders (between one and two) and hence reduced reactivity; however, such reactivity can be significantly increased by the presence of metalmetal multiple bonds in the same molecule [2,3]. In this line of work, we recently initiated studies on the reactivity of the unsaturated benzylidyne-bridged complexes [Mo 2 Cp 2 (-CPh)(-PCy 2 )-CO)] (1) [4] and [Mo 2 Cp 2 (-CPh)(-PCy 2 )CO) 2 ] (2) [5] (Cp =  5 -C 5 H 5 ) (Chart 1), which combine multiple Mo-Mo and Mo-C bonds and therefore provide a platform for the analysis of the synergic effect of these functionalities on their chemical behaviour.…”