Bis(acetylacetonate) Tungsten(IV) Complexes Containing a π-Basic Diazoalkane or Oxo Ligand

Abstract

Tungsten(IV) bis(acetylacetonate) (acetylacetonate = acac) complexes were synthesized by incorporating either a diazoalkane or an oxo ligand into the coordination sphere of a tungsten(II) reagent. The reaction of free diazoalkane (N 2 CRR′) with W(CO) 3 (acac) 2 leads to loss of two carbon monoxide ligands and coordination of the diazoalkane reagent through the terminal nitrogen to produce W(CO)(acac) 2 (N 2 CRR′). This monomer is best formulated as a tungsten(IV) complex. A second example of converting a d 4 tungsten carbonyl complex to a d 2 product involves oxidation of W(CO)(acac) 2 (PhCN) with m-chloroperoxybenzoic acid (MCPBA) to replace the CO ligand with an oxygen atom. This increase in metal oxidation state causes rotation of the nitrile ligand by 90°relative to the two bidentate acac ligands. Electrophilic addition at the nitrogen of the π-bound nitrile ligand using methyl triflate (MeOTf) and subsequent nucleophilic addition at carbon with sodium trimethoxyborohydride, Na[HB(OMe) 3 ], reduces the CN bond stereoselectively and produces the neutral imine complex W(O)(acac) 2 (PhHCNMe) with a diastereomeric ratio of 11:1.

Thermally Stable Diazoalkane Derivatives of the Unsaturated Ditungsten Hydride [W2Cp2(H)(μ-PCy2)(CO)2]

“…The metric parameters of the coordinated diazoalkane are indicative of a strong imido-like (four-electron donor) coordination of this group ( SB1 in Chart ), this implying the presence of essentially triple W–N [1.759(6) Å], single N–N [1.337(9) Å], and double N–C [1.28(1) Å] bonds, a situation further supported by the proximity of the values of the angles W–N–N [160.0(5)°] and N–N–C [120.1(7)°] to the ideal figures of 180° and 120°, respectively. Similar bond lengths and angles have been observed for a number of mononuclear tungsten complexes bearing terminal N-bound diazoalkanes ,, and also in the binuclear compounds [W 2 Cp 2 (μ-PPh 2 ) 2 ­( N -N 2 CPh 2 )­(CO)] and [Mo 2 Cp 2 (μ-PCy 2 )­{μ-C­(CO)­Ph}­( N -N 2 CPh 2 )­(CO)] . A four-electron donation of the diazoalkane ligand in turn implies that compound 2a might be considered a 34-electron complex; therefore a single metal–metal bond should be formulated for this molecule according to the 18-electron rule, which is fully consistent with the intermetallic separation of 2.9907(5) Å, a figure comparable to those determined in the mentioned PCy 2 -bridged alkyl complexes (in the range 2.95–3.10 Å), which also are 34-electron species. , …”

Synthesis and reactivity of oxygen ligated molybdenum(II) carbonyl complexes

“…In this d 2 system the strongly p-donating oxo ligand can serve as up to a 6-electron donor, but is donating approximately 5-electrons in this case. In (acac) 2 W(O)(g 2 -alkyne) complexes the alkyne ligand rotates 90°and bind perpendicular to the W-O bond and their rotation is locked at room temperature [34]. Due to the locked configurations there are now two diastereomers present.…”

“…Moving to an oxygen based chelate will eliminate these undesirable side reactions and stabilize the metal with stronger field oxygen donor atoms. Despite the widespread use of chelating oxygen ligands, particularly acetylacetonate, across the periodic table [23][24][25][26][27][28], their substitution for dithiocarbamates on low valent group VI metals has only recently been reported for tungsten and is mostly unexplored for molybdenum [29][30][31][32][33][34], though a few mono ligand species are known [35]. The unusual ability of (acac) 2 W complexes to coordinate nitriles in a p-bound fashion and subsequently derivatize them in a stoichiometric fashion is a substantial difference from dtc chemistry and provides further motivation to explore the chemistry of low valent Mo complexes of acetylacetonate (acac) and tropolonate (trop) [30][31][32][33][34]36].…”

Multiple Mechanisms for the Thermal Decomposition of Metallaisoxazolin-5-ones from Computational Investigations

“…Such a structure was first reported in the 1980s with molybdenum as the metal center. Similar tungsten complexes , are also well-known, but complexes with a more electron-rich metal center like iridium or rhodium are less common. To account for the observed C–H functionalization products (see, for instance, IIa in Scheme ), it was proposed that the η 2 nitrile complex releases the nitrile, generating an active 16-electron species ( Ia ), which subsequently inserts into a C–H bond of the hydrocarbon solvent molecule .…”