Chemistry of Unsaturated Group 6 Metal Complexes with Bridging Hydroxy and Methoxycarbyne Ligands. 1. Synthesis, Structure, and Bonding of 30-Electron Complexes

Abstract

The new cationic alkoxy and hydroxycarbyne complexes [M2Cp2(μ-COR)(μ-PR‘2)2]BF4 (Cp = η5-C5H5; M = W, R = Me, R‘ = Ph; M = Mo, R = Me and H, R‘ = Et) and [Mo2Cp2(μ-COR)(μ-COR‘)(μ-PCy2)]BF4 (R = Me; R‘ = H, Me, Et) are obtained in high yield by the reaction of the corresponding neutral monocarbonyl precursors with either [Me3O]BF4 or HBF4·OEt2 in dichloromethane. While the methoxycarbyne complexes are stable at room temperature, the analogous hydroxycarbyne species are thermally unstable, and above ca. 253 K they experience a hydrogen migration from oxygen to metal, to give the new hydride carbonyl complexes [Mo2Cp2(H)(μ-PEt2)2(CO)]BF4 and [Mo2Cp2(H)(μ-COMe)(μ-PCy2)(CO)]BF4 as major products. The electronic structure and bonding in some of these face-sharing bioctahedral complexes were studied by means of density functional theory. These calculations allow us to describe the intermetallic interaction present in the carbonyl-bridged 30-electron complexes by a configuration of type σ2δ4, with the δ orbitals being involved in π back-bonding to the carbonyl bridges. Upon methylation of the latter ligands, these δ-bonding orbitals become more delocalized over the Mo2C(carbyne) triangle and constitute the π-bonding component of the metal−carbyne bond. Therefore, a partial reduction of the direct metal−metal overlap occurs upon formation of these methoxycarbyne complexes, which still retain some multiplicity in the corresponding C−O bonds. The topological analysis of the electron density under the AIM scheme supports the above description of the Mo−Mo, Mo−C, and C−O bonds in these complexes.

Reactivity of the 30-electron dimolybdenum anion [Mo2(η5-C5H5)2(μ-PCy2)(μ-CO)2]− towards β,γ-unsaturated organic halides: Alkenyl, allenyl and alkoxycarbyne derivatives

“…Table 1 Selected IR a and NMR b spectroscopic data for new compounds. [12,9] 153.2 5.28 [12,3], 4.91 [9,3] 84.2 e [Mo 2 Cp 2 (l-g 1 :g 2 -CHCH 2 )(l-PCy 2 )(CO) 3 …”

“…These unsaturated molecules can be properly described as having a triple intermetallic bond, according to the EAN formalism and to DFT calculations on the methoxycarbyne complex [Mo 2 Cp 2 (l-COMe)(l-PCy 2 )(l-CO)] [12]. Therefore, a detailed structural discussion is not needed for compound 5.…”

C−C Bond Formation between the μ‐Alkylidyne Ligands in a Diruthenium Bis(μ‐alkylidyne) Complex; σ‐ and π‐Aromaticity of the Ru2C2 Core

“…Due to the delocalization of d‐electrons via the π‐bonding interaction with the μ‐alkyne and μ‐CO ligands (Figure S17), it is difficult to estimate the bond order of the Ru−Ru bond directly. Ruiz and co‐workers showed a correlation between the ρ b value at the intermetallic bond critical point and bond order for several prototypal dimolybdenum complexes, and established the presence of a Mo≡Mo triple bond in [Cp 2 Mo 2 (μ‐COMe)(μ‐CO)(μ‐PCy 2 )], where the ρ b value (0.606 eÅ −3 ) is comparable to that calculated for the triply bonded [Cp 2 Mo 2 (CO) 4 ] ( ρ b =0.576 eÅ −3 ) [38] . The ρ b value of 6 a (0.479 eÅ −3 ) is smaller than that reported for the Mo≡Mo triple bond, but is considerably larger than that calculated for a singly bonded dimolybdenum complex, [Cp 2 Mo 2 (CO) 6 ] ( ρ b =0.171 eÅ −3 ).…”

“…Ruiz and co-workers showed a correlation between the 1 b value at the intermetallic bond critical point and bond order for several prototypal dimolybdenum complexes, and established the presence of a Mo�Mo triple bond in [Cp 2 Mo 2 (μ-COMe)(μ-CO)(μ-PCy 2 )], where the 1 b value (0.606 eÅ À 3 ) is comparable to that calculated for the triply bonded [Cp 2 Mo 2 (CO) 4 ] (1 b = 0.576 eÅ À 3 ). [38] The 1 b value of 6 a (0.479 eÅ À 3 ) is smaller than that reported for the Mo�Mo triple bond, but is considerably larger than that calculated for a singly bonded dimolybdenum complex, [Cp 2 Mo 2 (CO) 6 ] (1 b = 0.171 eÅ À 3 ). The relatively large 1 b value suggests the presence of a Ru=Ru double bond in 6 a, which is consistent with the short RuÀ Ru distance.…”

Reactivity of the unsaturated dimolybdenum anion [Mo2(η5-C5H5)2(μ-PCy2)(μ-CO)2]− towards electrophiles based on p- and d-block elements

“…A few years ago we reported an efficient synthetic route to the dicyclohexylphosphide-bridged anion [Mo 2 Cp 2 (lPCy 2 )(l-CO) 2 ] À (1), for which a MoÀMo triple bond must be formulated under the Effective Atomic Number (EAN) formalism (Chart 1) [3]. Subsequent DFT calculations on this anion allowed us to describe more precisely this multiple bond as being composed of one r and two d components, with the latter ones also involving p-backbonding to the bridging carbonyls [4]. In our early report we found that this anion was reactive towards many different electrophiles, both based in p-block and in d-block elements, thus opening a new synthetic path to novel unsaturated derivatives that might be difficult or impossible to prepare from conventional (electron-precise) precursors [3].…”