Syntheses and Structures of Transition Metal Complexes with Phosphanylphosphinidene Chalcogenide Ligands

Expanding the Utility of β-Diketiminate Ligands in Heavy Group VI Chemistry of Molybdenum and Tungsten

We report the synthesis of 17 molybdenum and tungsten complexes supported by the ubiquitous BDI ligand framework (BDI = β-diketiminate). The focal entry point is the synthesis of four molybdenum and tungsten(V) BDI complexes of the general formula [MO(BDI^R)Cl₂] [M = Mo, R = Dipp (1); M = W, R = Dipp (2); M = Mo, R = Mes (3); M = W, R = Mes (4)] synthesized by the reaction between MoOCl₃(THF)₂ or WOCl₃(THF)₂ and LiBDI^R. Reactivity studies show that the BDI^Dipp complexes are excellent precursors toward adduct formation, reacting smoothly with dimethylaminopyridine (DMAP) and triethylphosphine oxide (OPEt₃). No reaction with small phosphines has been observed, strongly contrasting the chemistry of previously reported rhenium(V) complexes. Additionally, the complexes 1 and 2 are good precursors for salt metathesis reactions. While 1 can be chemically reduced to the first stable example of a Mo(IV) BDI complex 15, reduction of 2 resulted in degradation of the BDI ligand via a nitrene transfer reaction, leading to MAD (4-((2,6-diisopropylphenyl)imino)pent-2-enide) supported tungsten(V) and tungsten(VI) complexes 16 and 17. All reported complexes have been thoroughly studied by VT-NMR and (heteronuclear) NMR spectroscopy, as well as UV-vis and EPR spectroscopy, IR spectroscopy, and X-ray diffraction analysis.

Reactivity of the pentelidene complexes [Cp*E{W(CO)5}2] (E = P, As) towards dichalcogenides and chalcogenols - synthesis of novel chalcogenopentelidene complexes

Pentelidene complexes of the type [Cp*E{W(CO)₅}₂] (Cp* = C₅Me₅; 1a: E = P, 1b: E = As) were reacted with the dichalcogenides R₂Ch₂ (R = Ph, Mes, Tipp; Ch = S, Se, Te; Mes = 2,4,6-trimethylphenyl; Tipp = 2,4,6-triisopropylphenyl) and the chalcogenols PhChH (Ch = S, Se). It has been shown that the formation of new E-Ch bonds proceeds under elimination of the Cp* substituent. The resulting chalcogenopentelidene complexes, which have been isolated and fully characterised, represent a novel class of phosphinidene complexes which can be synthesised through this general synthetic route.

Experimental and theoretical investigation of the reactivity of [(BDI*)Ti(Cl){η2-P(SiMe3)-PiPr2}] towards selected ketones

In this work, we report a new type of reactivity of [(BDI*)Ti(Cl){η2-P(SiMe3)-PiPr2}] (1) towards ketones (BDI* = 2,6-diisopropylphenyl-β-methyldiketiminate ligand). In the reaction of 1 with acetone, cyclopentanone or cyclohexanone, a ketone moiety is inserted into Ti-Pphosphanyl or Ti-Pphosphido bonds to form complexes with a new C-P-P moiety, providing [(BDI*)Ti(Cl){η2-P(SiMe3)-PiPr2-C(Me)2O}] (2a), [(BDI*)Ti(Cl){η2-OC(Me)2P(SiMe3)-PiPr2}] (2b), [(BDI*)Ti(Cl){η2-P(SiMe3)-P(iPr)2-{C(CH2)4}O}] (3a), and [(BDI*)Ti(Cl){η2-P(SiMe3)-P(iPr)2-{C(CH2)5}O}] (4a). Starting complex 1 reacts with cyclohexanone, yielding a monocrystalline complex [{(ArN[double bond, length as m-dash]C(Me)CHC(Me)[double bond, length as m-dash]NAr)C(CH2)5O}Ti(Cl){PiPr2-P(SiMe3)C(CH2)5O}] (4d) with the insertion of two ketone molecules. Interestingly, we found that monoinserted complexes 2a and 3a may be oxidized via a reaction with AgCl, leading to elimination of the -SiMe3 group and oxidation of the titanium atom. This reaction led us to isolate the Ti(iv) complex [(BDI*)Ti(Cl){η2-P-P(iPr)2-{C(CH2)5}O}] (5) in crystalline form. To identify the kinds of products that may be formed and determine which products are the most energetically favoured ones, we conducted a thermodynamic DFT study of 1 towards acetone, cyclopentanone and cyclohexanone. Structures 2a, 2b, 3a, 3e, 4a, 4d, and 5 were characterized by X-ray crystallography, and complex 5 was also identified by NMR spectroscopy.